Materials for Energy Applications: Li-ion, Na-ion Batteries, supercapacitors and beyond, perovskite-type Solar cells and beyond

Resume : Understanding the origin of the high solar conversion efficiency of hybrid perovskites is of key importance to the field. We perform first-principles calculations to explicitly compute the radiative and nonradiative recombination coefficients in the prototypical hybrid perovskite, (CH3NH3)PbI3, as well as in other halide perovskites. Some research groups attributed the high efficiency to low radiative recombination due to strong Rashba spin-orbit coupling. We demonstrate that the radiative recombination in hybrid perovskites is actually strong, and that spin-orbit coupling has only a minor impact on radiative recombination [1,2]. The computed radiative recombination coefficient is as high as in typical direct-gap semiconductors used in optoelectronics. The demonstrated high radiative recombination coefficient thus enables promising applications in light-emitting diodes. However, our first-principles calculations of nonradiative rates show that strong Auger recombination will suppress efficiency [3]. Fortunately, our insights into the origins of the strong Auger recombination indicates potential avenues for engineering the Auger coefficient. Finally, I will discuss defect-assisted recombination, which is a limiting factor for both light emitters and solar cells, and is closely coupled to the issue of degradation. This work was performed in collaboration with Xie Zhang, Jimmy-Xuan Shen, and Wennie Wang, and supported by DOE. [1] X. Zhang, J.-X. Shen, and C. G. Van de Walle, J. Phys. Chem. Lett. 9, 2903 (2018). [2] X. Zhang, J.-X. Shen, W. Wang, and C. G. Van de Walle, ACS Energy Lett. 3, 2329 (2018). [3] J.-X. Shen, X. Zhang, S. Das, and E. Kioupakis, C. G. Van de Walle, Adv. Energy Mater. 10, 1801027 (2018).

Resume : Li-ion batteries have been successfully utilized as a power source for hybrid electric vehicles and mobile electronic devices because of their excellent electrochemical performance, such as high energy density and stable capacity retention. However, the price of lithium resources has been stiffly increased, leading to an increase in the production cost of Li-ion batteries. As a result, Na-ion batteries are attracting attention as a promising candidate to replace Li-ion batteries because sodium resources are abundant and inexpensive. However, the current Na-ion batteries have slightly lower energy densities than Li-ion batteries, indicating that the energy density limitations offset the cost savings due to the use of sodium instead of lithium. Therefore, it is necessary to develop high capacity electrode materials to improve the energy density of Na-ion batteries. In this presentation, we will focus on our recent works involving the development of new promising cathode materials to improve the energy density of Na-ion batteries. We have examined various layered Na1-xMO2 (M = Fe, Mn, Ni, and their solid solution analogues) materials. We also discuss the reaction and failure mechanisms of those cathode materials and suggest a strategy for improving electrochemical performance.

Resume : Global climate change increasingly demands technologies to harness and store clean energy. Particularly, efforts to reduce vehicular emission, which accounts for large portion of greenhouse gas, have drawn attentions to electric vehicles (EVs) and fuel cell vehicles (FCVs) technologies. EVs and FCVs have discrepancies such that batteries for EVs store and convert chemical energies into electrical energies, while hydrogen storage materials for FCVs store chemical energies and require fuel cells to generate electrical energies. However, these technologies, especially metal-air batteries and metal hydrides for solid-state hydrogen storage, share much in common in underlying mechanisms, for example, mass transport, charge transfer, gas evolution, and phase nucleation and growth. For broad adoption of EVs and FCVs, key thermodynamic and kinetic limitations associated with insufficient cyclability, poor kinetics, and low efficiency of rechargeable batteries and hydrogen storage materials should be overcome. In this talk, I’ll present the role of first-principles calculations to account for non-ideal factors in reaction thermodynamics of materials for batteries and hydrogen storage. Along with thermodynamic impacts, I’ll also discuss computational strategies to address structural and compositional discontinuities at interfaces, and phase nucleation and evolution kinetics, combining with mesoscale modeling and findings from experiments. Acknowledgement: This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Resume : Rechargeable sodium-ion batteries (SIBs) are now attracting special attention with a great cost advantage over rechargeable lithium-ion batteries (LIBs) especially in the field of large-scale applications. For the successful development of the SIBs, it is imperative to find new cathode and anode materials with high capacity, high power, and long cycle life. With this perspective, we have examined the electrochemical properties of O3-layer structured oxides, Na3M(II)2M(V)O6, with a honeycomb ordering of M(II) and M(V) in the metal layer for the cathode material in SIBs.[1] One of this class materials, Na3Ni2BiO6, can reversibly deliver specific discharge capacities of up to 109 mAh/g with very flat voltage plateaus ~3.5V vs. Na/Na+. Structural changes occurring during charging/discharging investigated by using in situ X-ray diffraction (XRD) are correlated with its long cycle life. Long and short-range structure changes at various state of (dis)charge have been also probed ex-situ using combined synchrotron-based high-resolution X-ray powder diffraction (HRPD) and extended X-ray absorption fine structure (EXAFS). Some of its derivatives with increased redox voltages will also be presented. For the anode materials, various compositions of transition metal oxides including Ti and Fe elements having tunnel based structures (single- and double- tunnels) are explored as rechargeable SIBs.[2] Detailed electrochemical results combined with structural characterization will be presented in the seminar. References: [1] D.S. Bhange, G. Ali, D.-H. Kim, D.A. Anang, T.J. Shin, M.G. Kim, Y.-M. Kang, K.Y. Chung, K.-W. Nam, J. Mat. Chem. A 5 (2017) 1300-1310. [2] D.S. Bhange, G. Ali, J.-Y. Kim, K. Y. Chung, K.-W. Nam, J. Power Sources 366 (2017) 115-122.

Resume : With the gradual consumption of fossil fuels and rigorously increasing pressures from environment pollution, it is important and necessary to develop and harvest clean renewable energy in large scales to fulfill the global sustainable development in economy and society. Hydrogen generated from electrochemical water splitting can not only replace fossil fuels as clean and efficient energy carrier, but also realize the large-scale decentralized conversion and storage of sustainable energy-produced electricity. Generally, electrocatalytic water splitting consists two half reactions of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), and extra additional potential is required because of the limitation in slow cathodic and anodic kinetics. Non-noble metal-based electrocatalysts (such as manganese, iron, cobalt, and nickel) are of huge advantages in low cost and rich abundance as compared with noble metals, but their activity and stability are still not satisfactory for practical application. In this regard, rational design of the structures and composites of electrocatalysts using various strategies are widely explored to aim for reducing the overpotentials for efficient water splitting. Methods including controlling the morphology, employing conductive substrates as supports, regulating the ratios of various components, engineering defects, doping foreign elements, as well as surface coating and decoration are applied to enhance the catalytic activity and stability. Recently, more attentions are paid on regulating the electrocatalytic activity of electrocatalysts by incorporating hierarchical nanostructures with rare earth elements. Because of the stable chemical property and unique electronic structure of rare earth elements, their collaboration with hierarchical transition metal-based electrocatalysts is developed as a novel method to modify electronic structures and electrochemical properties of electrocatalysts. In this presentation, cerium as a typical rare earth element, is selected and introduced into transition metal-based electrocatalysts to improve their HER and OER property. The role of cerium-based species and their influences on the structures and properties of electrocatalysts are also investigated.

Resume : Electrochemical energy storage is needed to enable energy to be stored for use when it is needed later. Diminishing fossil fuels and increasing oil prices have created the need to derive energy from sustainable sources. The energy storage device from alternative and inexpensive sources, such as bio-waste chicken eggshells, has a niche in storing and releasing the energy. The research is the first of its kind in the world and tested whether eggshells can provide an alternative to the traditional reliance on fossil fuels in assist to power lithium-ion batteries used in households. Mapping new materials for renewable energy storage is critical to our planet?s future. Chicken eggs are used worldwide in large quantities in the food, pharmaceutical, and household purposes. However, after using the egg, the shells are discarded as solid waste. The shell is a composite made of CaCO3 and a protein-rich fibrous membrane. This bio-waste is commonly disposed of in landfills, which attracts a cost. In order to achieve sustainable development, reusing waste streams can provide both economic and environmental returns. The fine eggshell powders are used as an electrode against a metallic lithium anode in a non-aqueous electrolyte. The initial discharge capacitance of the eggshell system was found to be 232 F g-1, while the reversible capacitance was 120 F g-1. From thereon, the cell maintained an excellent capacitance retention of 92% over 1000 cycles. The electrochemical performance obtained is comparable to that of commercially available classical activated carbon (AC) material. The CaCO3 showed a non-faradaic behaviour and the shape of the electrochemical curves resemble that of the AC electrode. The preliminary findings suggest that CaCO3 from eggshells can be used as the electrode in lithium supercapacitors to store and release charges effectively over a wide electrochemical stability window of 4 V.

Resume : Research on Li-ion batteries (LIBs) focused so far on the improvement of intercalation cathode materials of transition metals while relying on graphitic anodes. However, novel anode materials promise the next big leap in LIBs performance. Silicon offers an 11 times higher theoretical storage capacity than graphite, while being comparably cheap and earth abundant. Si incorporates lithium through conversion, which is accompanied by volume expansion of up to 400%, leading to cracking and a rapid capacity fading. Reducing the Si to thin films is a promising strategy to accommodate the volume changes. Furthermore, as for the graphite counterpart, the solid electrolyte interface (SEI) is crucial for the electrochemical performance. The volatile nature of the SEI and relaxation processes in the conversion zone requires operando experiments to fully understand and advance Si thin films as LIBs anodes. Hence, we have developed an electrochemical cell for operando X-ray absorption (XA) spectroscopy of Si thin film anodes. Recording a transmission signal in the soft X-ray regime allows us to investigate the Si conversion, the formation of the SEI, and changes in both the electrolyte (LiPF6 in EC:DMC) and the SEI during battery operation. We will present our operando cell setup and first evidence of the SEI formation within the first charging cycles based on changes in the F, C, and O K-edge as well as P and Si L-edge XA spectra obtained at the BESSY II synchrotron radiation facility.

Resume : Among the next-generation energy storage system, all-solid-state battery (ASSB) is attracting great attention due to its high energy density and better safety. As the most promising candidate for solid electrolyte materials, lithium-ion-conductive oxides have received much attention over the past few decades [1]. The oxide-based solid electrolytes are more advantageous than sulfides- or polymer-based electrolytes because they are non-toxic and electrochemically stable [2]. However, since the ionic conductivity is about 1/10 of the sulfides, it is necessary to develop oxides exhibiting high ionic conductivity even at room temperature [3]. In addition, it is essential to develop low-temperature sintered solid electrolyte with high ion conduction characteristics in order to co-sinter with a cathode active material without inter-diffusion, and consequently to form a complete ASSB. Herein, we synthesized Li-hafnates solid electrolyte with conventional solid state reaction. Various compositions were synthesized to investigate the influence of Li concentration on the changes in ionic conductivity at room temperature. It was also observed the activation energy for the Li ion migration changes according to various experimental conditions such as sintering temperature and time. Finally, Li stability was also evaluated to confirm whether it is applicable to actual ASSB. Therefore, this study is expected to provide an inspiration to determine the lithium hafnates as a solid electrolyte for ASSB. [1] Z. Gao, H. Sun, L. Fu, F. Ye, Y. Zhang, W. Luo and Y. Huang, Adv. Mater. 30 (2018) 1705702 [2] A. Manthiram, X. Yu and S. Wang, Nat. Rev. (Mater.) 2 (2017) 16103 [3] Z. Zhang, Y. Shao, B. Lotsch, Y. Hu, H. Li, J. Janek, L. F. Nazar, C. Nan, J. Maier, M. Armand and L. Chen, Energy Environ. Sci., 11 (2018) 1945 [4] K. H. Lim, Y. Iriyama, K. Yamamoto, S. Kumazaki, T. Asaka, K. Tanabe, C. A.J. Fisher, T. Hirayama, R. Murugan and Z. Ogumi, J. Power Sources 196 (2011) 764.

Resume : Storing energy from the grid requires the development of cost-effective, high-energy-density batteries. In this respect, sodium metal batteries seem to be promising as Na is abundant and cheap, which may offset energy densities lower than those of Li counterparts. The identification of new electrolytes that are compatible with sodium metal, enabling a non-dendritic deposition of sodium, is critical. They should also possess high sodium concentration, high conductivity and low cost. Recently, (Energy Environ, Sci,, 10 (2017) 1936) we have demonstrated that some liquid ammoniates of sodium inorganic salts give rise to a reversible behavior for the sodium redox couple while maintaining sodium shiny for weeks. The formulas for these ammoniates are NaI·3.3NH3, NaBH4·1.5NH3 and NaBF4·2.5NH3, demonstrating a very high concentration of Na+ (over 7 M) and a very high specific conductivity (0.1 S/cm). They are also characterized by a low flammability in comparison with organic solvents. These intriguing liquids could be considered as a special ionic liquids with only moderate viscosities. They present though some drawbacks such as a high volatility (bp around room temperature) and a relatively narrow potential window (< 3.5 V). In this contribution, we will give an account of the last results obtained in our laboratory, focusing on cathode materials that are compatible with these liquids together with an analysis of the prospects that they give rise to a new family of devices.

Resume : The exfoliated 2D nanosheets of layered metal compounds (layered metal oxides, layered double hydroxides, transition metal dichalcogenides, and layered metal carbides) attract intense research interest because of their unique physicochemical properties and useful functionalities. The 2D inorganic nanosheets can be synthesized by soft-chemical exfoliation reaction and used as efficient 2D building blocks for superlattice nanohybrids, porous nanocomposites, freestanding hybrid films, etc. The wide 2D surface area, very thin thickness, and high electrochemical and catalytic activities render these inorganic nanosheets promising materials for energy conversion and storage. In this talk, versatile roles of monolayered 2D inorganic nanosheets in energy-functional nanohybrids will be presented together with in-depth analysis for the relationship between chemical bonding nature and energy functionality. References (1) Lee, J. M.; Mok, E. K.; Lee, S.; Lee, N.-S.; Debbichi, L.; Kim, H.; Hwang, S.-J.* Angew. Chem. Int. Ed. 2016, 55, 8546. (2) Lim, J.; Jin, X.; Jo, Y. K.; Lee, S.; Hwang, S.-J.* Angew. Chem. Int. Ed. 2017, 56, 7093. (3) Gu, T. H.; Agyeman, D. A.; Shin, S.; Jin, X.; Lee, J. M.; Kim, H.; Kang, Y. -M.; Hwang, S.-J.* Angew. Chem. Int. Ed. 2018, 57, 15984. (4) Patil, S. B.; Kim, H. J.; Oh, S. M.; Kim, J.; Shin, J.; Choi, J. W.; Hwang, S.-J.* ACS Energy Lett. 2018, 3, 412. (5) Islam, M. S.; Kim, M.; Jin, X.; Oh, S. M.; Lee, N.-S.; Kim, H.; Hwang, S.-J.* ACS Energy Lett. 2018, 3, 952. (6) Adpakpang, K.; Oh, S. M.; Agyeman, D. A.; Jin, X.; Jarulertwathana, N.; Kim, I. Y.; Sarakonsri, T.; Kang, Y.-M.; Hwang, S.-J.* Adv. Funct. Mater. 2018, 28, 1707106. (7) Jin, X.; Shin, S.-J.; Kim, N.; Kang, B.; Piao, H.; Choy, J.-H.; Kim, H.; Hwang, S.-J.* Nano Energy 2018, 53, 841.

Resume : Considering the fact that 1/3 of the energy consumption is related to the transportation sector, underlines the importance to find suitable energy storage solutions that enable a CO2 free or neutral supply of automotive propulsion. Batteries, fuel cells and the use of synthetic fuels for heavy trucks and aircrafts contribute to the solution. Iron and nitrogen doped carbon catalysts reveal excellent activities for the oxygen reduction reaction. Based on this, they can be used for proton exchange fuel cells, alkaline fuels and metal air batteries. While their activity is high and already competes with low platinum content catalysts, their structural constitution remains under debate. In this work, I will present our recent results from operando Mössbauer spectroscopy and nuclear inelastic scattering on the active site identification. It is the first time that a new iron environment, only present under operando conditions, can be identified by Mössbauer spectroscopy that also correlates with the oxygen reduction reaction current. The new insights deduced from these experiments help in a fundamental understanding of these catalysts as well as for future materials optimization.

Resume : High-efficiency thermoelectric (TE) materials are important for power-generation devices designed to convert waste heat into electrical energy or to use in solid-state refrigeration. These applications require innovative materials which not only possess high conversion efficiency but should also be non-toxic and have high chemical stability in air over a wide range of temperature. The TE efficiency is related to high dimensionless number called figure of merit ZT, which is a combination of three material properties: Seebeck coefficient, electrical conductivity and thermal conductivity. The advent of nanotechnology has led to a dramatic effect on the development of TE materials and has resulted in the synthesis of nanostructured materials with better thermoelectric properties (as compared to conventional materials) mainly because of the reduction of the lattice thermal conductivity. As part of our ongoing project ?Othello? to develop metal oxide-based thermoelectric materials, we are currently studying TiO2-based materials, which are cheap, chemically stable and non- toxic in nature, although the poor electronical conduction of TiO2 remains a technological limitation to meet the requirements for thermoelectric applications. This talk will present sol-gel synthesis of Nb5 -doped TiO2 and TiO2-SnO2 nanoparticles, their conversion to dense ceramic pellets using spark plasma sintering (SPS) technique and their thermoelectric properties. Impact of the temperature of SPS process on the densification, nanostructuration and the dopant distribution will be discussed.

Resume : In the past, market demands for high performance and appearance were the pacemaker in the development of polymers for coatings. In consequence, solvent-borne systems were mainly in use. A change has been introduced by the trend to be more environmentally conscious. As a result, coatings regulations have been implemented to restrict solvent emissions, especially when coatings are being applied. This trend was led by government regulations like the Clean Air Act in the United States and the German TA-Luft. Consequently, there have been tremendous research efforts to make water-borne colloids with desirable properties that have been often obtained with solvent-based polymers. Nowadays, in most of polymer industries, water-borne polymer techniques have replaced the traditional role of solvent-based polymer techniques. These industrial fields include non-woven fabrics, paper coating, synthetic rubbers, adhesives, toughened plastics, catalytic supports and medical diagnostic areas. Nonetheless, there have been no successful report on fabricating water-borne colloid of semiconductor, although there have been a very successful water-borne colloid of electrode material, PEDOT:PSS. Because most organic electronics are assembled by combinations of semiconductor and electrode, a development of highly performing water-borne ink of semiconductor can be a breakthrough, milestone discovery to realize environmentally benign organic electronics. Especially, considering rapid growth of organic semiconductor in terms of charge carrier mobility which is now exceeding minimal industrial requirement, the development of environmentally benign process is very urgent assignment. The reason why the research results so far could not lead to the development of the water-borne colloid of semiconductors is that there was no strategic consideration of the polarity of the surfactant, the molecular size of the surfactant, and the concentration of the surfactant when the semiconductor nanoparticles were synthesized by the miniemulsion synthesis. In this work, we set four key criteria that should be satisfied for a universal colloid technique and find the surfactant and its miniemulsion synthesis method which satisfy all these key criteria. 1) The first criterion is to induce efficient emulsification to make the size of the nanoparticles small and uniform. The coalescence of colloid particles during thin film formation is induced by osmotic pressure of trapped solvent between particle-particle boundary and the osmotic pressure is inversely proportional to the particle size. Therefore, thin film quality fabricated from colloid solution is entirely related to the size and its distribution of colloidal particles. 2) The second criterion is to prevent depletion interaction of colloid particles for realizing homogeneous coalescence. Especially, at the last stage of thin film fabrication from colloidal solution, surfactant micelles concentration becomes very high which can accelerate the depletion interaction between colloid particles of polymer semiconductors. 3) The third criterion is minimizing the amount of excess surfactant molecules remaining in the polymer film cast from colloid solution. This is particularly important to recover electronic communication between polymer backbone and realize high charge carrier mobility. 4) The fourth criterion is realizing highly ordered crystalline structure of polymer semiconductors within the nanoparticles for efficient charge transport. Systematic experiments and analyses were carefully conducted for various surfactants considering all those key-criteria. We demonstrate that the selected surfactant and its optimized miniemulsion method can be applied to various high performance polymer semiconductor materials regardless of their polarity and backbone planarity. Based on this, we demonstrate high performance polymer electronic, opto-electronic, energy harvesting devices and solar water splitting application using water as a processing solvent for the first time.

Resume : Inorganic metal halide perovskite nanocrystals are one of the most promising candidates for light-emitting applications due to their high photoluminescence (PL) quantum yield, color tunability, and thermal stability. However, due to the bulky ligands these nanocrystals show poor conduction properties, which results in low external quantum efficiency of LEDs. To overcome this issue, a perovskite material, which has less bulky ligands, moderate binding energy, high PL quantum yield at lower excitation, and relatively higher stability is needed. A quasi-2D perovskite with higher number of planes could be an alternate solution. Here we demonstrate the synthesis of CsPb(Br/Cl)3 quasi 2D perovskite with butylammonium as a separating ligand. The number of layers are controlled by changing the butylammonium concentration in the precursor solution. We fabricate a stable perovskite phase with thin emission line widths, which is further used for the fabrication of highly efficient perovskite LEDs. We are able to report record efficiencies for blue emitting perovskite nanocrystal LEDs with a maximum external quantum efficiency (EQE) of 2.4% and 6.2% at 465 and 487 nm and a maximum luminance of 3340 cd/m2. We also demonstrate efficient green LEDs with a maximum efficiency of 10.1% EQE, 23.3 cd/A and 9.8 lm/W at 16.3 mA/cm2.

Resume : Environmentally friendly Li4Ti5O12 (LTO) is considered the anode material of choice for low-cost, high-power lithium-ion batteries. However, to ensure that not only the active material, but moreover the final electrode is sustainable and cost-efficient, also the electrode preparation needs to be considered. In this regard, the aqueous processing of LIB electrodes is a very attractive approach, as it offers significantly reduced cost when using, e.g., biodegradable carboxymethyl cellulose (CMC) to replace rather expensive poly(vinylidene difluoride) (PVdF) and water instead of toxic N-methylpyrrolidone (NMP).[1][2] Herein, we present an in-depth investigation of the impact of aqueous processing routes for LTO electrodes with elevated mass loadings. In fact, the high sensitivity of LTO towards water leads to severe corrosion issues for the Al current collector, while the simple use of CMC does not allow for obtaining mechanically stable electrodes at such loading levels. To overcome these challenges, we developed an optimized combination of processing additives to prevent Al corrosion, and (crosslinked) binder formulations to ensure mechanical stability, while simultaneously targeting high-performance lithium storage. Interestingly, certain compositions reveal the growth of new particles upon electrode processing, for which the electron transport appears to play a decisive role. [1] D. Bresser et al., Energy Environ. Sci. 2018, 11, 3096. [2] V.D. Carvalho et al., Polymers 2016, 8.

Resume : Nickel-Zinc (NiZn) batteries are considered as promising candidates for hybrid/electric vehicles and portable electronic devices due to high specific energy (up to 300 Whkg-1), high power density (40-100 kWkg-1) and environmental and safety concerns. However, NiZn batteries have not reached their full potential due to major issues such as shape change of Zn electrode with increasing charge/discharge cycle count, Zn electrode passivation, and dendritic Zn growth leading to short-circuiting of the battery. In this work, the effect of ZnO morphology on performance of Zn electrodes in NiZn batteries was investigated. ZnO powders with different morphologies were synthesized using ZnCl2 and Zn(NO3)2.6H2O precursors Synthesized ZnO powders and conventional ZnO powder which had a wide range of particle size distribution with needle shape as well as tripod and nanorod shapes, were used to prepare Zn electrodes. It was observed that initial morphology of Zn electrode changes drastically after a few charge/discharge cycles. However, Zn electrodes with different starting merohologies led to varying capacities between 92 Whkg-1 and 118 Whkg-1. The average discharge capacities of Zn electrodes were found to vary between 270 mAhg-1 and 345 mAhg-1.

Resume : Lithium-ion batteries (LIBs) became an integral part of human life because of excellent combination of their properties. Today the most used commercial anode is graphite, but, its low reversible capacity of 372 mAh g-1 results in batteries with low energy density. Therefore, there is a need to find an alternative active material with high reversible capacity, safety, and low cost. Transition metal oxides with relatively high capacity and cycle stability are potential candidates to replace conventional anodes. Tungsten oxide (WO3) with a theoretical capacity of 693 mAh g-1 stands out against other transition metal oxides due to combination of low cost and very large volumetric capacity but struggles from capasity losses at high charging rates. To address this issue we created array of aligned vertically standing WO3 nanorods (NRs) directly onto current collector using glancing angle deposition technique. Such anode configuration enables directional electronic/ionic transportation, leading to high electron collection efficiency. Controlled geometry of NRs also enables us to minimize effect of volumetric expansion on the mechanical stability of electrode, and significantly increase rate characteristics of the LIB. As a result, WO3 NRs exhibit stable cycle performance up to 3C rates, without mechanical degradation of electrode.

Resume : Concentrated solar thermal power is a quickly emerging technology [1,2]. However, the search for a more efficient and cost effective energy storage media as a successor for molten salts is highly relevant. Metal carbonates have great potential as thermochemical energy storage materials through the endo- and exothermic release and uptake of CO2 with low cost and high energy density [3]. However, the major challenge is the loss of CO2 capacity, which drastically decreases over multiple cycles [4,5]. Recently, it was established that dolomite, CaMg(CO3)2, dug straight out of the ground, is a candidate for thermochemical energy storage – even better than laboratory synthesized dolomite due to the positive effect of chemically inert impurities present in the sample [3]. However, its relatively low 550 °C operational temperature leaves room for improvement. Thus, both CaCO3 and BaCO3 have been investigated, which have operational temperatures at 900 and 850 °C, respectively. Preliminary results suggest that a suitable additive drastically enhances the cyclic stability and reaction kinetics. This presentation will give an overview of present research and an outline of future perspectives. References [1] M. Fellet, et al., MRS Bull, 2013, 38, 1012. [2] https://www.solarpaces.org/csp-technologies/csp-projects-around-the-world/ [3] T. Humphries, K. T. Møller, et al., J. Mater. Chem. A, 2019, 7, 1206. [4] G. S. Grasa, J. C. Abanades, Ind. Eng. Chem. Res. 2006, 45, 26, 8846. [5] J. Abanades, D. Alvarez, Energy Fuels 2003, 17, 2, 308.

Resume : Surface Nanoparticles modication has been observed on alumina coated LMO cathodes. During discharging (lithiation) the SEM has revealed the presence of holes formation in the electrode while similar effects were not visible in other phases of the Voltammogram. We put in relation this observation with the coating characteristics of the nanoparticles used for electrode. Such a surface modication cannot be preserved by the specic Al2O3 coating, that results to be much more effective for stopping the strong reduction processes occurring during charging at high voltage of the battery, when Mn bonds with organic species, making Mn capture and electrolyte reaction with the oxide nanoparticles possible. Nevertheless similar modication at low voltages cannot be seen in absence of the coating. This is pointing to the peculiar role of the Al2O3 coating in shaping the LMO surface of the active nanoparticles during lithiation. As in recent works [1,2] we followed the transition by XAS spectroscopy to detect the signatures of the transformation, observing a reversible modification of the surface character of the nanoparticle from a spinel to a layered structure. In particular by studying the Mn L2,3, F and O K-edge we could have direct access at the structural physical mechanisms. Soft X-ray spectroscopy is particularly suitable to detect modication of the active material at the frontier of the nanoparticle, where the interphase between electrolyte and active nanoparticle is formed, after still unclear modications of the surface of nanoparticles by means of the electrolyte during phases of oxidation/reduction. References [1] Andrea Di Cicco, Angelo Giglia, Roberto Gunnella, Stephan L. Koch, Franziska Mueller, Francesco Nobili, Marta Pasqualini, Stefano Passerini, Roberto Tossici, and Agnieszka Witkowska. Sei growth and depth proling on ZFO electrodes by soft x-ray absorption spectroscopy. ADVANCED ENERGY MATERIALS, 5(18), SEP 23 2015. [2] S. J. Rezvani, R. Gunnella, A. Witkowska, F. Mueller, M. Pasqualini, F. Nobili, S. Passerini, and A. Di Cicco. Is the solid electrolyte interphase an extra-charge reservoir in li-ion batteries? ACS Appl. Mater. Interfaces, 9:4570, 2017.

Resume : The cost-effective approaches to improve the solar cells efficiency, the quantum cutting is one of the interesting ways proposed. Placed on top of a solar cell, a special layer should absorb high energy photons and re- emits photons absorbed by the classical Si solar cell below. We propose to use CdTe/CdS for this idea. Nanocrystals in colloidal solution were prepared according to a method based on the interaction between cadmium thioglycolate and Te2− anions in an aqueous medium. To prepare the initial precursor aliquots of 0.01 M of solution of 3CdSO4•8H2O and 98 % thioglycolic acid from Sigma-Aldrich were mixed and the solution was titrated by 1 M sodium hydroxide until the pH became 11. As a Te2− source we used electrolytically generated hydrogen telluride which was bubbled through the preceding solution deaerated by argon flow. The final step of the synthesis was the formation of CdS shell by refluxing the colloid for several hours. Photoluminescence measurements were carried out at room temperature in the 400–800 nm wavelength range using a Perkin-Elmer LS55 PL spectrometer. A source of excitation was light with wavelength of 300 nm and emittance of 5 μW/cm2. The spectral dependencies of the optical density were measured at 300 K with a spectrophotometer Specord 210 in the 350–1100 nm of wavelength range. The PL spectra corresponding with CdTe/CdS nanocrystals obtained under different values of the time etching consist of one band with the position in the range within 500-800 nm. Its depends on diameter of nanocrystal. So, re- emission in the range close to band gap of silicon will create additional excitation and support to improve the solar cells efficiency. The stability in time is the most problem of obtained re-emission and required further optimization

Resume : Stretchable piezoelectric nanogenerators (SPENGs) for biomechanical energy harvesting face various restrictions owing to their lower mechanical robustness under stretching motion and multi-directional straining. Selection of appropriate type and form of piezoelectric materials, as well as the choice of superior structural design for omnidirectional stretchability, plays a vital role in this. Herein, we report a high performance and multi-directionally stretchable SPENG comprises of a carbon-based electrode on a 3D micro-patterned stretchable substrate and electrospun piezoelectric nanofibers. The stacked mat of electrospun nanofibers is alternatively contained nanocomposite nanofibers of polyurethane loaded with barium titanate nanoparticles and poly(vinylidene fluoride-trifluoroethylene) nanofibers. The nanofiber SPENG (nf-SPENG) reveals an extraordinary stretchability of 40% and high stability up to 9000 stretching cycles at 30% strain, which are ascribed to the stress-releasing nature of the 3D micro-pattern on the substrate and the free-standing stacked nanofibers. The nf-SPENG produced a peak open circuit voltage (Voc) and short circuit current (Isc) of 9.3 V and 189 nA, respectively, and a peak power density of 1.76 µW/cm2 at the 40% stretching mode. The nf-SPENG also has the ability to respond in various multi-modal straining modes such as twisting, pressing, crinkling and stretching. The nf-SPENG was validated to harvest the energy from human kinematics while walking when placed over the knee cap of a subject, generating a maximum Voc of 10.1 V. The energy harvested by biomechanical motions was effectively and repeatedly stored in a capacitor The multi-directional stretchability, efficiency, simplistic fabrication process, mechanical endurance, environmentally friendly lead-free components and response to multi-modal straining make this device suitable for self-powered wearable sensing systems. Keywords: Piezoelectric Nanogenerators, Nanofibers, Stretchable Electronics

Resume : In the past decades, most of the attention was focused on electrochemical energy conversion applications based on perfluorosulfonic acid based Nafion membranes, which possesses a suitable combination of high ionic conductivity and excellent chemical stability. Despite of the great success, there are still many challenges to be addressed. Among these challenges, the dependence on the use of noble metal catalyst is critical. Polymers based on anion exchange property have begun to attract a lot of attention recently because of the significant advantages in terms of moving from highly acidic environment to alkaline conditions, high kinetic for oxygen reduction and fuel oxidation in alkaline environment and lower cost by using non-precious metal catalysts. Many researchers have developed different routes to develop anion exchange functional groups in the polymer matrix. However, most of the newly developed materials have issues with chemical stability, low ion exchange capacity, and low ion conductivity. Among the poly-aromatic material candidates, we focused here on new anion exchange membranes (AEM) based on tetra aryl-phosphonium ionomers (TAP) for energy conversion/storage applications. In this particular study, we successfully developed a novel class of AEM based on TAPs. Our obtained results show that our membranes have demonstrated a high ionic conductivity along with an improved alkaline chemical stability, in addition to enhanced mechanical properties. Results will be presented and discussed emphasizing on chemical and electrochemical characterization of such AEM.

Resume : Supercapacitive performance of material either in the form of a thin film or of a pallet, used as an electrode can be assayed by cyclic voltammetry (CV) and galvanostatic charge-discharge measurement. In this work, we focus on magnesioferrite- carbon black nanocomposites synthesized by the green method using Moringa Olefeira natural extract as an efficient electrode material for supercapacitors. Green chemistry routes are on the rise due to their various advantages including cost-effectiveness, no requirement of additional chemicals, reliability and the fact that is a very easy, environmentally friendly method with a minimum of waste generation. The natural plant extracts hide some phytochemicals that act as both agent capping or stabilization and reducing agent in the synthetic process of nanocomposites. The electrodes material will be prepared by drop coating process the bismuth ferrite- carbon black nanocomposites slurry on the surface area of the glassy/platinum electrode. Their electrochemical performance will be studied using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). Their crystalline structure, morphology, isothermal behavior and optical properties will be studied using various characterization techniques such as X-ray diffraction (XRD) and Energy Dispersive X-ray Spectroscopy (EDS), Fourier transform infrared (FTIR), High Resolution Transmission Electron Microscopy (HRTEM), Differential scanning calorimetry/thermogravimetric analysis (DSC/TGA) Ultra-violet visible (UV-vis) and Photoluminescence (PL).

Resume : One-dimensional fiber-shaped supercapacitors have recently attracted lots of attention as a potential energy storage solution for emerging wearable devices. However, fiber supercapacitors often exhibit low energy storage capacity and poor rate capability due to their small volume, low specific volumetric capacitance, and poor electrode electrical conductivity. Here we demonstrate a novel hydrothermally assembled core-sheath fiber comprised of a graphite fiber core and a MoS2 nanosheet intercalated holey graphene oxide (HGO) sheath as electrodes for fiber supercapacitors. HGO and MoS2 nanosheets self-assemble around the graphite fiber core in a space-confined reactor during the hydrothermal synthesis. HGO nanosheets supply abundance channels for electrolyte ion transfer, MoS2 nanosheets provide large pseudocapacitance, and graphite fibers serve as faster electron transfer highways. The mass loading of MoS2 is easily tunable. The optimized composite fiber with 34.9 wt.% MoS2 delivers a high volumetric capacitance 421 F cm−3 at the CV scan rate of 5 mV s–1 and the capacitance retention of 51.0% when the scan rate increases from 2 to 100 mV s–1. The core-sheath fiber enables fast reversible redox kinetics, and its surface capacitive energy storage contributes ~75-80% of its total energy storage. The assembled solid-state fiber supercapacitor delivers a high device volumetric capacitance of 94 F cm−3 at 0.1 A cm−3 and an energy density of 8.2 mWh cm−3 at the power density of 40 mW cm−3, outperforming many recently reported fiber supercapacitors. The core-sheath fiber electrode design based on HGO, MoS2 and graphite fiber cores provides an efficient platform for designing various novel fiber electrodes for potential electrochemical applications.

Resume : Fiber-shaped micro supercapacitors (FMSCs) are promising energy storage blocks for building wearable and durable electronic devices, yet their wide application is hindered by their unsatisfactory energy density. Here, we demonstrate a new-type Zn-ion hybrid FMSC using a novel N, N′-methylenebisacrylamide (MBAA) cross-linked polyacrylic acid (PAA) hydrogel electrolyte. This device can deliver a landmark energy density of 48.5 mWh cm–3, an ultrahigh volumetric capacitance of 104.5 F cm–3, as well as superior durability with ~98% capacity retention after 10000 charge/discharge cycles. We attribute the excellent electrochemical performance to: (1) the fast ion adsorption/desorption at the capacitor-type carbon nanotube/reduced graphene oxide based fiber cathode, (2) the reversible battery-type stripping/plating of Zn electrodeposited on the carbon fiber anode, as well as (3) the high ionic conductivity of the PAA gel electrolyte. This work will inspire the research effort on the fabrication and development of novel high-performance micro-energy storage devices for practical applications.

Resume : Nitrogen-doped porous carbons with uniformed pore structure and large surface area are promising materials as sorbents for acidic gases and electrocatalysts for oxygen-related reactions. Herein, we report the synthesis of nitrogendoped porous carbon (NPC) materials through carbonization of imidazolefunctionalized polyhedral oligomeric silsesquioxane (POSS) at 900 C followed by removal of POSS blocks. The imidazole moieties act as both nitrogen and carbon sources and the POSS blocks are nano-sized hard templates. The resulting NPC has a surface area of 980 m2g-1 with average pore size of 4.7 nm and the pyridinic nitrogen in the formed NPC contribute to about 33% of overall nitrogen species. The carbon dioxide adsorption property and the electrocatalytic performance toward oxygen reduction reaction of the formed NPC are further evaluated. The formed NPC materials exhibit a total carbon dioxide adsorption capacity of 0.30 mmolg-1 at 30 C under the partial pressure of carbon dioxide of 0.2 bar. Although the formed NPC is less active than commercial Pt/C catalyst for oxygen reduction reaction, the half-wave potential shifts to the negative side by only about 10 mV after 10000 cycling tests, demonstrating the great stability of the formed NPC materials

Resume : The engineering of photovoltaic (PV) properties in ferroic perovskite oxide superlattices (SLs) can be considered as promising alternative routes for better understanding the origins of the anomalous PV effect and improving the PV activity in such materials. This way is motivated by the possibility of tuning the functional properties of these materials since we can vary many parameters such as the nature of materials, modulation period and layer thickness. Here, we report the study of the PV activity in epitaxial multiferroic (BiFeO3)(1-x)?/(LaFeO3)x? ((BFO)(1-x)?/(LFO)x?) SLs grown by PLD technique on (111) oriented SrTiO3 substrate. We focus on the effect of the variation of BFO and LFO layer thickness for a fixed period of about ?=10nm. Room temperature X-ray diffraction and Raman spectroscopy investigations have evidenced a structural change at about x=0.5 from a rhombohedral/monoclinic structure for rich BiFeO3 to an orthorhombic symmetry for rich LaFeO3. The PV response in BFO/LFO SLs were investigated by illuminating the sample by 1mW power laser in vertical geometry of measurements using SRO as bottom electrode and ITO as semi-transparent top electrode. By changing x between 0.1 and 0.4 we have evidenced a change of PV characteristics from a positive Voc and a negative Jsc for SLs with x?0.2 to an inverse effect for x?0.3. These results indicate different origin of the mechanisms of photo-carries separation in PV devices. The origin of PV effect for x< 0.2 (Voc=0.62 V and Jsc=-0.11 mA/cm2 for x=0.1) can be attributed to the presence the spontaneous polarization since the PV effect in these rich BFO SLs can be switched by applying negative pulse voltages higher than the coercive electric field of ferroelectric P-E loops (Pr=80µC/cm2 for x=0.1). However, for the SLs with x?0.3, the P-E loops showed a paraelectric like character with low ferroelectricity and in this case the PV is rather dominated by the interfaces since the Voc and Jsc increases to reach -0.6V and 0.06 mA/cm2 for x=0.4 when the ratio (x) of LFO layer in the period increases. These results are promising and indicate the possibility to employing the vertical geometry of measurements for tuning the PV effect in multiferroic SLs.

Resume : Abstract Sodium-ion batteries (NIBs) are growing exceptionally popular as a replacement for lithium-ion batteries, particularly for grid level electricity storage applications [1]. Using density functional theory (DFT) calculations [2], we investigate molybdenum sulfo-selenides alloy as a negative electrode for rechargeable NIBs. Electrochemical properties of the electrode material in terms of voltage profile, theoretical capacity and sodium diffusion. Our results show that the electrode possess maximum storage capacity of 375 mA h g-1 and a low average electrode potential of 0.73 V, shown in Fig. 1. The inset depicts the adsorption of Na atoms to its full capacity. The calculated low energy barrier of 0.15 eV suggests fast mobility of Na, indicating fast charging/discharging rate. Our results suggest MoSSe alloy as promising anode for NIBs. References 1. M. Mortazavi, C. Wang, J. Deng, V. B. Shenoy, N. V. Medhekar, Ab initio characterization of layered MoS2 as anode for sodium-ion batteries, J. Power Sources 268 (2014) 279-286. 2. G. Kresse, J. Furthmuller, Efficient iterative schemes for ab initio total energy calculations using a plane-wave basis set, Phys. Rev. B 54 (1996) 11169.

Resume : Over the last years, rechargeable sodium metal batteries have received great attention as promising power sources because they are a lower cost option than lithium counterparts for energy storage from the electric grid. Considerable research work has been undertaken to develop a sodium metal battery at room temperature. We report here on a highly concentrated sodium electrolyte based on liquid ammonia which can be formulated as NaI·3.3NH3. However, the development of sodium-based batteries is also limited by the requirement of finding active materials compatible with the electrolyte. Organic compounds show several advantages, they present high theoretical capacity and their synthesis do not imply elevated energy consumption, and even they may come from natural sources. Here we show the electrochemical behavior of two organic compounds based on an organic antraquinonyl structure: polyanthraquinonylsulfide, commonly known as PAQS, and Indanthrone Blue. The second one is an organic dye extensively used in the textile industry. Both materials can exchange several electron per molecule during the charge-discharge processes and they show a theoretical capacity beyond 200 mAh/g. The system PAQS or IB using NaI·3.3NH3 as an electrolyte can achieve hundreds of cycles using C rates as high as 10 C, with a coulombic efficiency close to 100%. The aforementioned batteries can lead to high-energy-density and high-power-density devices at low temperature using sodium metal as an anode.

Resume : To examine basically the interactions occurred among the components of the gel polymer electrolyte consisting of two polymers (poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) and hydroxypropylcellulose (HPC), 7:3 w/w), solvent (N-methyl-2-pyrrolidone (NMP)), and liquid electrolyte (LE) solution (1.0 M LiPF6 dissolved in a ternary mixture of ethylene carbonate (EC)/propylene carbonate (PC)/ethylmethyl carbonate (EMC), 1.0:1.5:1.0 w/w/w), thermal properties measured from the thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) are systematically investigated for PVdF-HFP-based, HPC-based, and their 7:3 blend-based samples in terms of NMP-added, LE-added, and NMP LE-added cases. The thermal properties are also measured for sol and gel samples in the gel polymer electrolytes with the LE content over 500% to analyze how sol-gel transition or thixotropicity by shearing with a time interval. In the PVdF-HFP/HPC (7:3) system, LE-added and NMP LE-added samples show similar trends of melting temperatures in the range of 125-165oC. The interaction between PVdF-HFP/HPC and LE molecules appears to be dominant compared to the case between PVdF-HFP/HPC and NMP. The reversible process between sol and gel states of the thixotropic gel polymer electrolytes can also be approved by the flexible PVdF-HFP chain to recover the nematic phase (gel) of rigid rod HPC molecules from the isotropic phase (sol).

Resume : The graphene based supercapacitor electrodes are an intelligent choice. Graphene’s fascinating electrical, mechanical and physical properties have triggered a prolific work on this material [1] Likewise transition metal dichalcogenides such as MoS2 , due to their layered geometry and high electrical conductivity as well as good electrochemical performance [2], form another wise choice as electrode material. Here we present fabrication of MoS2/rGO nanocomposite based electrodes and their comparison with pristine rGO based electrodes. The MoS2 has been obtained via hydrothermal process [3] where as graphene has been synthesised using Hummer’s method [4]. The PVA/H2SO4 has been used as the gel polymer electrolyte to add flexibility to the Supercapacitor. It has been found that the specific capacitance in case of MoS2/rGO nanocomposites significantly increased vis a vis rGO based electrodes from 156 F g-1 to 210 F g-1. Reason for this being synergistic similarity between rGO and MoS2 as both have a layered structure. References 1. Q. Ke, J. Wang, J Materiomics 2 ,2016 37-54 2. D. Duphil, S. Bastide and C. Le. Cle´ment, J. Mater. Chem., 12, 2002, 2430–2432 3. L. J. Ye, H. Y. Xu, D. K. Zhang and S. J. Chen, Mater. Res. Bull., 55, 2014, 221–228 4. S. Khan , J. Ali , Harsh , M.Husain , M. Zulfequar Physica E 81, 2016, 320–325

Resume : Recently, the stability against moisture has received a considerable amount of attention in order to ensure the commercial viability in the field of perovskite photovoltaics. Many efforts have been devoted to modifying the stability of either the perovskite material itself or the electron and hole transport layers but the fundamental solutions have not been found to date. Therefore, the encapsulation technologies are essential for the long-term stability of perovskite solar cells (PSCs). Among the various encapsulation technologies, in this study, we investigated the inorganic multi-layered barrier thin films deposited by the plasma-enhanced atomic layer deposition (PEALD). The multi-layered films consist of Al2O3 and SiO2 layer which have high moisture barrier properties. We optimized the deposition temperature, ALD process sequences and the thickness of each layers to secure the low water vapor transmission rate (WVTR). And we explored the effect of substrate types on the encapsulation performances of barrier films; we used three different types of substrates such as PEN, PET and PI. Through the MOCON test, it was demonstrated that the WVTR of Al2O3/SiO2 multi-layered barrier film deposited on PEN is lower than that deposited on PET and PI substrates. And, in the case of multi-layered encapsulation, it was indicated that the number of Al2O3/SiO2 interfaces, substrate types and the density of each layers strongly affect the values of WVTR. As a results, we achieved a very low WVTR value of 4.63*10-5 with 50 nm-thick Al2O3/SiO2 multi-layered barrier film on PEN substrate. Based on above results, we applied the Al2O3/SiO2 multi-layered barrier films (on PEN substrate) to PSCs and investigated the moisture stability. We attached the barrier films on the top of n-i-p type perovskite solar cells using the UV and thermal curing resins and we explored the effect of curing conditions on the moisture stability of the encapsulated PSCs. Furthermore, we will discuss the performance degradation of large-scale PSC modules with the Al2O3/SiO2 multi-layered encapsulation under damp heat conditions consisting in 85 °C and 85 % relative humidity. We believe that this work would pave the way for the commercialization of the practical PSC modules in the near future.

Resume : Water-soluble binders have many advantages for slurry and electrode preparation for various battery materials, such as low cost and environmental friendliness. Nowadays, the linear chain nature of the poly (acrylic acid) (PAA) binder in Si-anodes makes it susceptible to slide during the continuous volume variation of the Si particles during lithiation and delithiation. Therefore, modified or three-dimensional, interconnected network polymer binders are required to provide robust mechanical adhesion with Si particles for excellent cycle life and high Columbic efficiency. Here, Pentaerythritol (PER) is used as a crosslinking agent to connect the linear PAA polymer to enhance its adhesion strength for Si anode. Crosslinked Si-PAA-PER electrode has achieved a more robust electrode integrity compared to linear Si-PAA electrode, which can better buffer the volume changes of Si particles during the long-term cycling. The crosslinking of PAA with PER was confirmed using Fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) measurements. Si-PAA-PER electrodes maintained a higher discharge capacity of 514.3 mAh g-1 after the first ten cycles than that of Si-PAA (257.6 mAh g-1), indicating its enhanced electrode integrity due to the interconnected PAA-PER binder.

Resume : Organic solar cells (OSCs) have become the area of interest in organic photoelectronic technology. Studies have been conducted to produce organic based solar cells with high power conversion efficiencies. One of the most widely used method to obtain low band gap polymers and high conversion efficiency for organic solar cells is the donor -acceptor (D-A) approach. In this approach, two different type of units are used in the polymer backbone named as electron deficient and electron rich moieties. In this study, quinoxaline derivatives are served as acceptor moiety due to their imine nitrogen in pyrazole ring and benzodithiophenes are served as donor moiety due to planar conjugated structure and π bridge properties. A series of quinoxaline monomers and selenophene based benzodithiophene monomer were coupled via Stille cross coupling reactions to obtain desired polymers. Structure of the substances were examined by mean of Nuclear Magnetic Resonance Spectroscopy (1H-NMR and 13C-NMR). HOMO LUMO energy levels and electronic band gap of the polymers were estimated by using cyclic voltammetry and optical studies were performed by using UV Spectrophotometry and Fluorescence Spectroscopy to investigate absorption behaviour of polymers. Bulk heterojunction solar cell with following configuration ITO/PEDOT:PSS/Polymer: PC71BM/LiF /Al was used to obtain power conversion efficiency of the devices.

Resume : Piezoelectric PVDF fibers were prepared by electrospinning. During the electrospinning process, the travelling fiber is subjected to an electric field and shear stress simultaneously. This condition favors formation of polar Beta phase. XRD investigation indicated that the amount of Beta phase increases versus applied voltage up to 14 kV at 15 cm traveling distance. Further increasing in voltage results in formation of beads instead of fibers. FE-SEM studies showed that the average diameter of the prepared fibers is 325 nm. The fibers were aligned on a rotating drum and the output piezoelectric voltage was measured about 1.26 mV upon applying 8 kPa at 4 Hz frequency.

Resume : In this work, effect of synthetic method on the photovoltaic performance of an oxadiazole bearing conjugated polymer was investigated. Polymer was synthesized via both Stille cross coupling and direct heteroarylation reactions. Cells were constructed by spin coating of PEDOT:PSS on ITO as the hole transport layer, spin coating of the active layer including polymer:PC71BM blend inside glove box, and LiF/Al deposition as the cathode layer by vacuum evaporation at 1x10-6 mbar. For polymer synthesized by Stille cross coupling reaction, PSt, maximum power conversion efficiency was found as 2.46% with 1:3 polymer:PC71BM ratio. Same blend yielded open circuit voltage value of 0.65 V, short circuit current of 7.03 mA/cm2 and fill factor of 53.8%. For polymer synthesized via direct heteroarylation, PDA, open circuit voltage, short circuit current, fill factor and power conversion efficiency values were achieved as 0.72 V, 6.70 mA/cm2, 34.4% and 1.66%, respectively with 1:3 polymer:PC71BM ratio. Additive treatments via diiodooctane and diphenyl ether with different concentrations were also performed for both polymers, however, no improvement was observed. Further optimizations will be carried out.

Resume : A detailed understanding on the instability of PbTe quantum dots (QDs) is presented and a combinatorial passivation protocol is developed to yield air stable thin films. Stability of PbTe QDs is very subjective to the synthetic conditions. Parameters like size, shape, stabilizing ligand and catalyst concentration play crucial roles. Defects, the origin of both poor stability and low photo conversion efficiency (PCE), are mainly introduced during post-synthesis processes and application of a passivation technique during growth phase is the most effective strategy for achieving octahedral shape QDs with a superior shelf-life and improved endurance at the ligand exchange process. In situ growth phase passivation not only control the shape by dictating the {111} / {200} facet ratio but also controls the packing direction and mid gap state formation. The combinatorial passivation strategy produces solar cells with a 100% increase in PCE and up to fivefold increase in short circuit current.

Resume : Developing efficient energy production and storage technologies from renewable energy sources is a highly attractive area for researchers to supply energy for small scale applications. In this regard, electricity storage through redox flow batteries and solar energy storage as a form of H2 from photoelectrochemical (PEC) water splitting process are the most investigated alternative technologies in recent years. Therefore, this work aims to investigate the direct conversion of sunlight into electrochemical energy stored in a redox flow battery. In other words, the proposed study presents the direct conversion of sunlight into the electrochemical energy stored in a PEC cell integrated into a vanadium redox battery (PEC-VRB). As a typical PEC cell, our system contains a semiconductor-based photoelectrode which can absorb sunlight to form photocurrents to charge a vanadium redox flow cell (VO2 /V3 ). TiO2 and CdS semiconductors are in common photoelectrode materials for PEC and solar redox flow battery applications. However, the limited photocurrent density generated through TiO2 owing to its wide band gap (3.2 eV) and the toxicity of CdS are drawbacks for their usage as green energy applications. On the other hand, indium sulfide (In2S3) as an eco-friendly material exhibits competitive photocurrents, when compared to other photoelectrochemical devices and yields enough photovoltage to charge the vanadium battery containing 0.01 M VO2 /V3 / 2 M H2SO4. More specifically, TiO2 and In2S3 photoelectrodes utilized PEC-VRB generated 40 and 150 uA.cm-2 photocurrent densities, respectively. As a result, it has been demonstrated here that the In2S3 electrodes show superior performance compared to the state-of-art TiO2 electrodes.

Resume : Phosphonic acids (PA) form stable and ambient-atmosphere-resistive self-assembled monolayers on Indium tin oxide (ITO) surfaces1. They can serve to passivate the ITO surface and by using different functional groups we can tune the work function of the ITO surface. SAMs have been used to alter the properties at the semiconductor interface in electronic devices. Herein, we intend to use PA SAM with an electron withdrawing, electron donating and neutral functional group and examine their effect when used in an inverted type perovskite solar cell. We used (4-cyanophenyl) phosphonic acid (electron withdrawing), (4-methoxyphenyl) phosphonic acid (electron donating) and Phenylphosphonic acid (neutral) to form a SAM on the ITO surface. In addition to imparting a change in work function to the ITO, the SAM also changes the surface energy of the surface and in most of the cases lowers it. The SAM bonding was confirmed by X-ray photoemission spectroscopy, change in the work function and contact angle of the surface. The complete device was formed by spin coating a CH3NH3PbI3 perovskite layer on the substrate, followed by an electron transporting PCBM layer and finally a silver electrode on the top via a shadow mask. The substrates used in the device were SAM modified ITO and a reference blank ITO substrate. The SAM modified device shows an improvement of 12.77% as compared to the reference cell. Current and voltage values for the SAM modified device also showed an improved value. Apart from the above mentioned, SAM modification of ITO can additionally aid in the field hole transporting material-free devices.

Resume : It?s not a breaking news that Perovskite solar cells (PSC?s) have taken the PV community by storm. The commercialization of these solar cells is stalled at present thanks to their poor environmental and light stability. The main goal of this work is to improve the stability of perovskite solar cells in terms of structure and device operation. One way to achieve this is to reduce the dimensionality of the photoactive perovskite layer. A transition from the conventional 3D structure to 2D occurs spontaneously when a large insulating organic cation tries to fit in the cubo-octahedral space of the perovskite structure. In our case Phenyl Ethyl Ammonium Iodide (PEAI) owing to its large ionic radius was chosen to the large cation, while Methyl ammonium iodide (MAI) and Lead Iodide (PbI2) form the standard perovskite layer. The perovskite layer is synthesized by spin coating and subsequent annealing inside a N2 filled glovebox. In order to obtain perovskite layers with high crystallinity and vertical orientation certain coordinating additives are used in small amounts. With our optimized process flow we have fabricated working devices in the range of 8 ? 10% efficiency with an open circuit voltage between 1.05V ? 1.15V. The fabricated perovskite layers have excellent optical properties (intense PL signal even for low carrier injection) and long lifetimes (> 200 ns) compared to their 3D counterparts (MAPI) that have a higher efficiency (>14%) prepared in our lab. Detailed XRD analysis reveal that the perovskite layers of the best devices exhibit a preferred orientation along the (111) axis of the cubic lattice. When the perovskite layers show random orientation of crystallites no working devices were obtained indicating that the performance of these 2D perovskites strongly depends on the crystalline orientation. Electrically speaking the 2D perovskite solar cells exhibit an IV crossover of the illuminated and dark curves, similar to CZTS and CIGS devices. The crossover acts like a barrier to carrier transport in the cell reducing the short circuit current (Jsc) and the fill factor (FF) of our best devices. Despite a high lifetime the carrier collection is very poor in these devices leading to very low short circuit currents (10 -11 mA/cm2). From theoretical one diode analysis of the light and dark IV curves of these devices a large diode saturation current of the order 10-7 A/cm2 and an ideality factor > 2 could be calculated. These numbers indicate a complex recombination (affecting the Voc and FF) in the device structure resulting in lower efficiencies. Our best devices retain about 95% of the original efficiency after 1400 hours of storage inside a N2 filled glovebox. The stabilized power output of these devices shows exceptional stability under AM1.5G illumination wherein the efficiency of the solar cell at the maximum power point remains constant or increases slightly with the exposed time.

Resume : Organic photovoltaics (OPV) have recently made great strides in terms of efficiency with reports of increased PCEs of over 15 %. Such high efficiencies in combination with other attractive properties, for example the possibility for flexible substrates, semi-transparent devices or solution processability, make OPV increasingly attractive for larger scale industrial production, especially when considering specialized applications like building-integrated photovoltaics. However, in order to efficiently produce OPV cells or modules on a larger scale, quick and reliable quality control measures are crucial. One of the most widely used means for quality control is imaging of the radiative or non-radiative recombination of solar cells, namely (lock in) thermography (LIT) and luminescence imaging. These methods are limited in some respects. For example a determination of the lateral position of a defect is easily possible, while the exact resolution of the nature of a defect, e.g. in which layer of a thin film stack a defect is located, is challenging. Our approach to overcome this difficulty is the introduction of well-defined artificial defects into certain layers of an OPV stack and subsequent imaging analysis of the defected cells. The unique response gained from cells with artificial defects can then be transferred to the imaging of cells or modules with naturally occurring manufacturing defects.

Resume : ?Improved Colloidal stability of Precursor solution by a novel Hydroiodic acid free synthesis route of Methylammonium Iodide for efficacious solar cells? Shyantan Dasguptaa,b, Kasjan Misztalc, Rosinda Fuentes Pinedac, Barbara Wilka,d, Sylvester Sahayaraja, Alina Dudkowiak b and Konrad Wojciechowski a,c a,Saule Research Institute(SRI),division of Saule Technologies,11 Dunska,54-130,Wroclaw,Poland b,Faculty of technical physics,Poznan University of Technology,Piotrowo 3 street,60-965 Poznan,Poland c,Saule Tehnologies,11 Dunska,54-130,Wroclaw,Poland d,Department of Physics, Polytechnic Wroclawska, Wroclaw,Poland Perovskite semiconductor research is being one of the most widely investigated technologies in the contemporary world for its numerous distinguished optoelectronic and structural properties like defect tolerance, sharp band edge and a highly tunable band gap covering the visible and near infrared region. The ?wonder material? can be processed from solution processing to thermal evaporation techniques with the former technique being broadly explored. However the chemical purity problem is a concern for the Methlyammonium iodide(MAI) in the precursor solution which can have an impact on the morphology of fabricated perovskite films which in turn affect carrier dynamics and other electrical properties of the solar cell. The use of hydrohalic acids like Hydroiodic acid (HI) for the synthesis of MAI for MAPbI3 precursor has been well reported in literature and is a conventional route for MAI formation. This conventional route also involves the presence of hypophosphorous acid which acts as a stabilizer HI[1,2].This presence of stabiliser H2PO2 leads to impurities in the MAI materialsuch as different phosphate salts.These impurities have been shown to have significant effect on the crystallization of perovskite material.This effect likely originates from the impact of these impurities which have effect on the colloidal chemistry of the precursor solution(growing colloids of different sizes which evolve over time). In this work we demonsrate the synthesis of ultra-pure MAI without the conventional HI based route and without the presence of phosphorus-containing impurities. This allows to have much better control on the colloidal chemistry in the precursor solution and in turn much better control over perovskite crystallization process. We investigate the colloid formation and its evolution with dynamic light scaterring (DLS) technique. We show that perovskite thin-films grown with such optimized ink composition results in films with fewer defects, leading to solar cells with superior performance and stability. The optimized MAPbI3-based perovskite solar cells in p-i-n architecture reached 16% power conversion efficiencies. References [1] Ievgen Levchuk,Yi Hoh,Marco Gruber,Marco Brandl,Patrick Herre,Xiaofeng Tang,Florian Hoegl,Miroslaw Batentschuk,Andres Osvet,Rainer Hock,Wolfgang Peukert,Rik R.Tywinski,and Christoph J.Brabec- Deciphering the Role of Impurities in Methylammonium Iodide and Their Impact on the performance of Perovskite Solar Cells.Adv Mater.Interfaces 2016, 1600593 [2] Zhengguo Xiao,DongWang,Qingfeng Dong,Qi Wang,Wei Wei,Jun Dai,Xiaocheng Zeng and Jinsong Huang-Unraveling the Hidden Function of Stabiliser in Precursor in Improving Hybrid Perovskite Film Morphology for High Efficiency Solar Cells.RSC Energy Environ ,Sci,2016,00183A [3] David P McMeekin,Zhipin Wang,Waqaas Rehman,Federico Pulvirenti,Jay B.Patel,Nakita K.Noel,Michael B.Johnston,Seth R.Marder,Laura M.Herz, and Henry J.Snaith-Crystallization Kinetics and Morphology Control of Formaamidinium-Cesium MixedCation Lead Mixed-Halide Perovskite via tunability of the Colloidal Precursor Solution,Adv. Mater. 2017,1607039

Resume : We have studied surface modification of rutile TiO2 with metal chalcogenide nanoclusters for promotion of the hydrogen evolution reaction (HER) using density functional theory corrected for on-site Coulomb interactions (DFT+U). Recently, metal chalcogenides have emerged as potential catalysts for the HER due to the favourable interaction of H at chalcogen sites, particularly those that are undercoordinated. Analogous to noble metal loading, surface modification of TiO2 with nanoclusters of HER co-catalysts, based on earth-abundant materials, is an emerging strategy. This approach combines the desirable properties of the titania photocatalyst with active sites provided by the low-coordinated chalcogen ions of the supported clusters. Our models consist of M4X4 (M = Sn, Zn; X = S, Se) nanoclusters at the rutile (110) surface and we examine the Gibb’s free energy of H adsorption at the modified surface which is a useful material descriptor in assessing the performance of a HER catalyst. These calculations take into account changes in the entropy and the zero-point energies (ZPEs) of the reactants and products, which our results show are material specific. As expected, the interaction of H is more favourable at the titania surface and forms stable hydroxyls. However, after subsequent adsorption events the surface sites become saturated and H adsorption at chalcogen sites exhibit Gibb’s free energies in the active range, particularly for MS modifiers relative to MSe.

Resume : The promising cathode structure for tomorrows Li-ion batteries, are nickel-rich LiNixMnyCozO2 (NMC, x+y+z=1) materials. They outperform other contenders for the application of Li-ion batteries due to their high specific energy. However, unwanted side reactions at high potentials (> 4.2 V vs. Li+/Li) remain a challenge, leading to structural degradation and hence lower cyclic stability [1]. Surface coating has been proven in several materials fields to solve the problems related to the material degradation caused by side reactions. Hence, the present study was carried to prepare carbon-coated LiNi0.6Mn0.2Co0.2O2((NMC622/C) materials since carbon has high conductivity and is stable against the electrolyte. In order to achieve a homogenous carbon coating, this study has taken the approach of polymerization of furfuryl alcohol followed by a calcination for the first time. Especially the effect of monomer dilution in ethanol on their polymerisation process which lead to different thickness and homogeneity of carbon coating were systematically studied. Thermogravimetric analysis (TGA) was performed to understand the polymerisation kinetics, in-situ High-Temperature X-Ray Diffraction (HT-XRD) was done to monitor the phase changes and Scanning and Transmission Electron Microscopy (SEM & TEM) were used to observe the morphology. Electrochemical investigations of the carbon coated NMC622 were performed to evaluate the performance and cyclic stability improvements. References 1. Liu et. al., Angew. Chem. Int. Ed. 2015, 54, 4440 – 4458.

Resume : Flexible polymer-based electrolytes providing good electrode-electrolyte interfaces offer the most promising solution to address the all solid-state battery requirements. However, substantially higher temperatures are required to achieve the optimal conductivity for a polymer electrolyte for electrochemical application, which is still an important bottleneck in lithium polymer batteries. To improve the performance of polymer electrolytes, ionic liquids (ILs) have been combined as a reinforcing agent with suitable polymer matrices. ILs add numerous advantages to the electrolyte such as high thermal stabilities, higher operating temperature range, moderate ion conductivity and safety. Moreover, due to non-reactivity with lithium, IL-based polymer electrolytes may also be used in secondary lithium-metal batteries, outperforming the conventional IL-free polymer electrolytes. In this study, in order to improve the functionality and ion conductivity of polymer electrolyte further, a highly conducting ionic liquid based nanofluid is used as the plasticizer. The ionanofluid is prepared and optimized by dispersing 5.0 w t% of surface functionalized Al2O3 nanoparticles in 1-Decyl-3-methylimidazole bis(tri?uoromethanesulfonyl) imide, [Deim][NTf2] IL to achieve the highest conductivity. In order to analyze the thermophysical and electrical properties, the as-prepared lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt doped poly (ethylene oxide) based ionanofluid reinforced nanocomposite gel polymer electrolytes are subjected to different characterization techniques viz. XRD, DSC, FT-IR, SEM, HR-TEM and impedance spectroscopy. The highest conductivity for freestanding electrolyte w ith 30 w t% ionanofluid is obtained as ~2.5×10-3 S/ cm at 30 °C. The electrochemical properties of the optimized highest conducting electrolyte demonstrate its brilliant application potentiality as an electrolyte in secondary energy storage devices.

Resume : Ni-rich layered cathode materials Li[NixMnyCoz]O2 (NMC; x=0.6, 0.8, x+y+z=1) are considered as the most promising cathode materials in Lithium-ion batteries due to high discharge capacity and working voltage. However, the application of NMCs is limited by strong capacity decay after long-term cycles mainly caused by surface degradation [1]. As a low-cost material, SiO2 can protect the surface from direct physical contact with electrolyte, reduce surface degradation significantly by acting as a HF scavenger [2]. SiO2 has been coated on cathode particles, i.e. Cho et al. coated NMC622 particles via a wet process by using SiO2 nanopowders to improve their high-temperature cycle performance [3]. In this research, a homogenous amorphous SiO2 layer was applied on commercial NMC through hydrolyzation and polymerization of tetraethyl orthosilicate. Their composition and morphologies were analyzed by ICP, SEM, and TEM. Electrochemical tests, i.e. CV, cycling, and rate capability were carried out to compare the performance of the non-coated and coated NMC materials. It is shown that the initial discharge capacity of the electrodes and rate performance are not affected by the coating layer. After 700 cycles between 3.0 - 4.3 V at 2C, the cells with coated materials retained 80% of initial capacity, higher than uncoated ones which were 74%. Post mortem analysis was performed to reveal the stabilizing mechanism of the SiO2 coated electrodes. It is confirmed that SiO2 coating is a facile surface protection method for enhancing the cyclic stability of Ni-rich NMC materials. References: 1. H.-H. Ryu, et al., Chem. Mater., 2018, 30, 1155-1163. 2. T. Yim, et al., RSC Adv., 2013, 3, 25657-25661. 3. W. Cho, et al., J. Power Sources, 2015, 282, 45-50.

Resume : Conjugated polymers attract more and more attention from researchers due to their promise as materials for light-emitting diodes and photovoltaic cells. Polymers containing both electron-donor and electron-acceptor moieties in the monomer unit are promising as photoconductive materials. This work presents the results of studies of optical and photoelectric properties of a new polymeric material, a polyphenylquinoline (PPQ) class polymer containing a phenylamine bridging group and 2,1,3-benzothiadiazole (DBT) fragment as an aromatic radical in the polymer backbone. The photoconductivity and absorption spectral dependences measurements showed that band gap of the pristine PPQ-DBT is 1.85 eV and can be increased up to 2.1 eV after annealing of the polymer at 150 °C. The measurements showed that the annealing does not affect the value of dark conductivity. In the temperature range 294-380 K, the dark conductivity temperature dependences of both pristine and annealed PPQ can be satisfactorily described by an exponential law with an activation energy E ≈ 0.8 eV. An absence of the effect of annealing on the dark conductivity value and its temperature dependence seems to be contradictory while the optical band gap of the studied polymer irreversible changes in result of the annealing. The analysis of the absorption spectra allowed to model the polymer energy structure and showed that this optical band gap change is strongly correlated to energy distance between HOMO and LUMO of each molecular fragment. The results of the effect of annealing on the spectral dependences of the photoconductivity and absorption coefficient are analyzed. Mechanism leading to an increase in the optical band gap of the polymer as a result of its annealing is proposed. The reported study was funded by RFBR according to the research project № 18-29-23005.

Resume : Incorporation of ionic liquid functionalized TiO2 nanoparticles in low conducting, 0.6 M lithium salt doped N-methyl-N-butylpyrrolidinium bis(tri?uoromethylsulfonyl)imide (Pyr14 TFSI) ionic liquid electrolyte is found to not only suppress crystallinity but also signi?cantly improve both ionic conductivity and lithium transference number in the electrolyte. The Li/LiMn2 O4 cell w ith the best conducting ionano?uid electrolyte delivers a discharge capacity of about 131 mAh g?1 at 25 °C at a current density of 24 mAg?1 , much higher than that obtained in conventional 0.2 M Li salt dissociated Pyr14 TFSI electrolyte (87 mAh g?1 ). Excellent rate performance with outstanding capacity retention of the cell as compared to the conventional one indicate superior electrode-electrolyte interfacial compatibility, which further establishes great application potentiality of this optimized newly developed electrolyte for safer lithium metal batteries.

Resume : A flexible binder free electrode made of VxOy nanoparticles (NPs) on carbon nanotubes coated graphitic felt (VxOy/CNTs/felt) offers the opportunity to greatly enhance operation performances as recently proposed for applications of vanadium redoc flow batteries [1,2]. The advantage of this approach is the resulting composite VxOy/CNT/felt as an electrode ready to use with scale-up capability, which can be processed by thermal and chemical treatments. They are robust electrodes with possible use under  high pressure and high temperature conditions. The VxOy/CNTs/felt were prepared by chemical vapor deposition and electrochemical route, resulting in a binder free electrode with excellent performance for Li+ ion transfer. The VxOy/felt and VxOy/CNTs/felt surfaces were characterized by Raman Scattering (RS), Scanning Electron Microscopy (SEM), X-ray Energy Dispersive Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS) and electrochemical techniques. From RS, two major phases were detected such as ?-V2O5 and ?-V2O5 at room temperature measurement. The VxOy NPs are in a mixed phase of ?-V2O5 and ?- V2O5 with plane and wrinkle like array surface morphology, which depends on electrodeposition conditions. Morphology can vary from regular flat to more wrinkled ones especially with the increase of deposition time. CNTs modified the surface morphology of VxOy on felt as detected by SEM. The oxidation states were mostly in V+5 (V 2p B.E. ~517 eV) valence state along with very less amount of V+4/V+3 (B.E. ~ 515/514 eV). The specific capacity with 600 mAhg-1 was obtained for VxOy/CNTs/felt electrodes. The mixed phase (?+?)-V2O5 was observed for low electro-deposition time 30 min. at both 2 and 4 mA current. References [1] A. Bhattarai et al J. Power Sources 341 83 (2017) [2]X. Ke, J. M. Prahl, J. I. D. Alexander, R. F. Savinell , J. Power Sources 384 295 (2018)

Resume : Mixing high dielectric constant ceramic nanoparticles with high breakdown polymers is considered to be one of the most promising methods to achieve high energy density in dielectric material. However, the interface between these materials provides a region for charge concentration. Due to the large difference in dielectric constant, the local electric field is also large at the interface. This makes the interface region vulnerable to dielectric breakdown even at low external electric field. Proper surface functionalization of nanoparticles can improve the energy density of these nanocomposite materials by decreasing the charge concentration and introducing traps at the interface. In this study, we have functionalized the surface of the barium titanate nanoparticles with silane coupling agents and included these functionalized nanoparticles in a polymer matrix. The polymer matrix is prepared by UV curing of thiol and alkene monomers: Pentaerythritol tetrakis mercaptopropionate (PEMP), Diisopropenylbenzene (DPB) and 2,4,6 Triallyoxy 1,3,5 Triazine (TOTZ). The resulting polymer matrix is highly cross-linked and homogeneous. By optimizing the surface chemistry of the ceramic nanoparticles (BaTiO3, ?99%, < 100 nm) and the processing parameters during the polymerization process, we have prepared nanocomposites with energy density greater than 20 J/cm3. These nanocomposites have high efficiency due to the inherent low loss of the thiol-ene polymer matrix. The process used to make these nanocomposites uses a xenon flash lamp to produce short pulses of UV-Visible light to cure the polymer in inexpensive and low temperature flexible substrates. The process is roll to roll amenable and thus provides a route to cost effective, large scale production of polymer ceramic nanocomposite materials.

Resume : To enhance the safety of conventional lithium-ion batteries (LIBs), there have been many studies trying to replace flammable liquid electrolytes with non-flammable solid electrolytes. Although diverse inorganic solid electrolytes have been developed, downsides from their intrinsic properties still restrict the practical application. One promising candidate is solid polymer electrolyte not only allowing the battery to have more enhanced safety but also providing the intimate contact between electrode and electrolyte. However, solid polymer electrolyte have suffered from lower ionic conductivity. Several studies have shown the addition of inorganic filler such as Al2O3, SiO2, or TiO2 is effective to improve mechanical, thermal and electrochemical performance. Moreover, the electrochemical performances of hybrid electrolytes consisting of Li salt and polymer filled with Li+ conductive inorganic fillers have been remarkably increased, which then has received much attention. In this study, the hybridization of Poly(vinylidene fluoride) (PVdF) as polymer matrix and garnet-type cubic phase LLZO as Li+ conductive active inorganic filler showed superior mechanical, thermal stability and electrochemical performances than pure PVdF polymer electrolyte. Furthermore, the surface modification of LLZO brought about better electrochemical performance. The morphological property and crystal structure of the hybrid solid electrolyte were evaluated by conducting SEM, EDS, XRD, raman and XPS analysis. The electrochemical properties of hybrid solid electrolyte were further investigated through impedance, LSV and galvanostatic cycling test.

Resume : Perovskite solar cells represent one of the most promising photovoltaic technologies. Over the past few years, the performance of perovskite solar cells was gradually improved up to >23%, which is close to the characteristics of crystalline silicon photovoltaics. However, high toxicity and low stability of complex lead halides used as absorber materials hamper commercialization of this technology. Compositional engineering of lead perovskites was actively pursued in order to improve their stability and/or performance. In particular, a partial or full replacement of Pb2+ in MAPbI3 is highly desirable in terms of developing more environmentally friendly materials. Here we present a systematic study of lead substitution in MAPbI3 with >20 different cations introduced in atomic concentrations ranging from 10-5 to 20-30%. It was shown that replacing even minor fraction of lead could change significantly the perovskite film crystallinity and morphology. Importantly, the efficiency and stability of p-i-n and n-i-p perovskite solar cells were improved considerably by appropriate modification of MAPbI3 films. Moreover, important relationships were established between the nature of the substituting ions (e.g. ionic radius or charge) and their effects on electronic properties and photovoltaic performance of the resulting hybrid perovskites. The obtained results should facilitate the rational design of more stable and less toxic absorber materials for advanced perovskite solar cells.

Resume : Maximizing activity of Pt catalysts towards methanol oxidation reaction (MOR) together with minimized poisoning of adsorbed CO during MOR still remains as a big challenge. A promising approach is to reduce the adsorption energy of CO on the Pt catalysts and meanwhile to increase the amount of adsorbed OH species. Herein, we anchor uniform and well-distributed Pt nanoparticles (NPs) on an atomic carbon layer that is in-situ formed by means of dry-etching of SiC NPs with CCl4 gas. In comparison to the commercial Pt/C catalysts, as-synthesized catalysts exhibit remarkably higher MOR catalytic activity (e.g., 647.63 mA mg-1 at a peak potential of 0.85 V vs. NEH) and much improved anti-CO poisoning ability. As confirmed from density functional theory (DFT) calculations and X-ray absorption fine structure (XAFS) measurements, such high performance is due to reduced adsorption energy of CO on the Pt NPs and meanwhile an increased amount of adsorbed energy OH species that remove fast and efficiently adsorbed CO. The used amount of expensive Pt is also few times lower than that on the commercial and reported catalyst systems. Therefore, these catalysts can be utilized for the development of large-scale and industry-orientated direct methanol fuel cells.

Resume : Ammonia has potential as a sustainable transportation fuel (1). But, to achieve this potential, ammonia must be split into Hydrogen and Nitrogen by means of catalytical processes that are not yet viable for sustainable applications (2) . The solid solutions of lithium amide (LiNH2) and lithium imide (Li2NH) play a key role in improving these processes. The atomic structure of the LiNH2-Li2NH solid solution is still under debate (3, 4). Recently, Makepeace et. al.(5) proposed a model for the LiNH2-Li2NH solid solution, which revealed the presence of both imide (NH) and amide (NH2) groups whose Raman stretching frequencies indicated a variety of different atomic environments for NH and NH2. In this work, we performed DFT calculations to elucidate the atomic structure of the LiNH2-Li2NH solution, study the stability of the observed non-stoichiometric phases and model their Raman scattering results. ----------------- 1) Mukherjee S., Devaguptapu S. V., Sviripa A., Lund C. R. F. and Wu G., Low-Temperature Ammonia Decomposition Catalysts for Hydrogen Generation, Appl. Catal., B, 226, 162–181 (2018). 2) Thomas G. and Parks G., Potential Roles of Ammonia in a Hydrogen Economy, U.S. Department of Energy, (2006). 3) Ludueña G. A., Wegner M., Bjålie L. and Sebastiani D., Local Disorder in Hydrogen Storage Compounds: The Case of Lithium Amide/Imide, Chem. Phys. Chem, 11, 2353 – 2360, (2010). 4) Balogh M. P., Jones C. Y., Herbst .F., Hector L. G. and Kundrat M., Crystal structures and phase transformation of deuterated lithium imide, Li2ND, Journal of Alloys and Compounds, 420, 326–336, (2006). 5) Makepeace J. W and David W. I. F., Structural Insights into the Lithium Amide-Imide Solid Solution, J. Phys. Chem. C, 121, 12010−12017, (2017)

Resume : For the commercialization of the PSCs, halogen free solvent based processability of the photoactive layers at room temperature is among the highly desirable properties along with thickness tolerance and reproducible PCEs, for the fabrication of large area PSC modules. However, high efficiency polymers (typically PNTz4T) need high temperature processing conditions where solution and substrate need ?100 oC to produce PCEs >10% due to the polymer?s intrinsic high aggregation tendency, which is incompatible with the current industrial roll-to-roll manufacturing techniques. To address this issue, we have synthesized random terpolymers and high temperature processability issue is alleviated by introducing methyl thiophene-3-carboxylate (MTC) in the polymer backbone of PNTz4T. The resulting terpolymers (PNTz4T-MTC) showed reduced crystallinity and aggregation, and weaker intermolecular interaction thus resulting in fully RT processable PNTz4T-MTC polymers from halogen-free solvent. The new polymer (especially PNTz4T-5MTC) based RT processed PSCs have shown comparable PCE (9.66%) with the reference PNTz4T based high temperature processed (solution/substrate?100oC) PSCs (9.76%), from an eco-friendly halogen-free solvent. A top PCE of 9.66% is among the highest reported PCE from fully RT processed PSCs based on fullerene acceptors and halogen-free solvent system. Large area module fabricated with PNTz4T-5MTC:PC71BM have shown PCE of 6.61% in comparison to 4.29% with PNTz4T:PC71BM at 54.45 cm2 area in air which is highest reported PCE at fully RT processed conditions.

Resume : Pero-photovoltaics that recently have created a fastest growing solar cell efficiency in the history, needs efficiency improving. In-series tandem generates the minimal current of the subcell with lowest Isc. A parallel connection allows to obtain Isc which is sum of two currents, and two organic photovoltaic (OPV) have created tandems with semitransparent carbon nanotubes (CNT) interlayers. The pero-photovoltaics with laminated AgNW/CNT have been simulated and after it compared with experimental results. Tandem device scheme was made as connection off perovskite sub-cell which was installed directly on the top of GaAs sub-cell (shading area). The aim of this work is to find trends for different tandem configurations using high ? current sub-cells, based on GaAs p-i-n detector structure and CH3NH3PbI3 perovskite. Analyzing the results of this work, it should be noted that GaAs and perovskite technologies are the most effective and promising at the moment for applications in their areas ?substrate and solid-state technology, thin-film technology of organometallic semiconductors. The main advantage of this device is the high photocurrent production, which allows to obtain high power. Therefore, in this paper we have developed a tandem in-parallel, nonmonolithic connection showing a high short-circuit current 41 mA from a square centimeter and obtained an efficiency of about 22 %. The approach presented in this paper clearly shows the advantages of parallel tandems over in-serious ones with appropriate balancing the output characteristics: the filling factor and the idling voltage.

Resume : High electrochemical performance energy storage devices coupled with low cost and high safety operation are in urgent need due to the increasing demand for flexible and wearable electronics. For these applications lithium-ion and sodium-ion batteries are vastly limited due to their relatively low power density and security risks. On the other hand, conventional supercapacitors are suitable for flexible and wearable electronics due to their high power density while their low energy density has hindered their wide applications. Lithium or sodium ion hybrid supercapacitors are promising energy storage devices that benefit from the combined high energy density of batteries and high power density of supercapacitors. However, the use of organic electrolytes and shortage of lithium resources are expected to limit their widespread commercialization for flexible and wearable electronics. Here, for the first time, we introduce a safe and flexible solid-state zinc ion hybrid supercapacitor (ZHS) based on Co-polymer derived hollow carbon spheres (HCS) as cathode, polyacrylamide (PAM) hydrogel as electrolyte and deposited-Zn on carbon cloth as anode. Owing to the high surface area of the HCS and the hollow structure which improve the ions adsorption and desorption kinetics of the cathode, the flexible solid-state ZHS delivers a highest capacity of 86.8 mAh g-1 and a maximum energy density of 59.7 Wh kg-1 with the power density of 447.8 W Kg-1. Besides, it displays excellent cycling stability with 98% capacity retention over 15,000 cycles at a current density of 1.0 A/g. Moreover, the solid-state ZHS is flexible enough to sustain various deformations including squeezing, twisting and folding due to the use of flexible electrodes and electrolyte. Our study unveils a pioneering flexible solid-state ZHS with high safety, which is a promising candidate for flexible and wearable energy storage devices. Reference: S. M. Chen, L. T. Ma, K. Zhang, M. Kamruzzaman, C. Y. Zhi and J. A. Zapien, J. Mater. Chem. A, 2019,7, 7784-7790.

Resume : This study analyzes cooling and anti-pollution characteristics of functional coating films on glass substrates for PV modules with different processes of annealing. The substrates were coated two times with silicon-based anti-pollution solution via brushing coating method. After self-drying for 10 minutes, the substrates were annealed using hot air fan and torch, respectively. Then they were analyzed along with an uncoated glass substrate for their cooling function, anti-pollution properties, contact angle, optical characteristics and other mechanical properties. All three specimens were exposed to sun simulator at the power of 250W for 2 hours, with their back side covered by matte black body and then let cool naturally under room temperature of 25oC for another 30 minutes. Cooling process was recorded by heat-radiation camera in order to examine effects of coating layers on cooling function. Afterwards, their mechanical properties such as hardness and adhesion were again inspected. Based on the result of this study, the most suitable annealing method to enhance cooling and anti-pollution functions for PV modules was found. If the coating process proposed in this study is applied to PV modules production, improvement in cooling and anti-pollution characteristics as well as energy generation efficiency can be expected.

Resume : Perovskite quantum dots (QDs) constitute a novel and rapidly developing field of nanotechnology with promising potential for optoelectronic applications. However, few perovskite materials for QDs and other nanostructures have been theoretically explored. In this study, we present a wide spectrum of different hybrid halide perovskite cuboid-like QDs with the general formula of ABX3 with varying sizes well below the Bohr exciton radius. Density functional theory (DFT) and time-dependent DFT calculations were employed to determine their structural, electronic, and optical properties. Our calculations include both stoichiometric and nonstoichiometric QDs, and our results reveal several materials with high optical absorption and application-suitable electronic and optical gaps. Our study highlights the potential as well as the challenges and issues regarding nanostructured halide perovskite materials, laying the background for future theoretical and experimental work.

Resume : Cation dissolution from the aluminum current collector as well as cathode materials presents a great challenge for achieving long-term stable cycling behavior of lithium-ion batteries ? particularly for elevated anodic cut-off potentials exceeding 4 V. In fact, the anodic dissolution of the aluminum current collector takes place at ~3.6 V vs. Li+/Li.[1] Similarly, high-voltage cathodes like, e.g., LiNi0.5Mn1.5O4 (LNMO) suffer cation dissolution and structural degradation at the surface when being continuously charged to high voltages. [2,3] Herein, we will report on the facile and economic, but highly efficient approach to apply a protective coating to both the aluminum current collector and the cathode active material prior or after the electrode preparation, thus, rendering it easily applicable to essentially every active material. In fact, this coating effectively stabilizes the interface of the cathode material and the current collector with the electrolyte and allows for excellent cycling stability of high-voltage LNMO cathodes ? substantially improved when compared to the non-coated reference electrodes. As such, this work contributes to the smart design of interfaces in lithium-ion batteries and the facile implementation in common electrode preparation process in combination with the commercial availability of the required precursors renders it easily applicable also on large-scale. 1 S. S. Zhang and T. R. Jow, J. Power Sources, 2002, 109, 458?464. 2 J. B. Goodenough and Y. Kim, Chem. Mater., 2010, 22, 587?603. 3 J. H. Kim, N. P. W. Pieczonka, Z. Li, Y. Wu, S. Harris and B. R. Powell, Electrochim. Acta, 2013, 90, 556?562.

Resume : Complex metal halides are intensively explored primarily in the context of their potential applications as absorber materials for perovskite photovoltaics. Despite a significant progress achieved with perovskite solar cells based on complex lead halides, it is still unclear if they can be practically useful because of the unresolved so far severe operational stability issues. At the same time, the success and challenges faced with lead-based perovskites stimulate active screening of other complex metal halides in order to develop more stable and, probably, even more efficient absorber materials. In this work we explored for the first time a family of Te(IV) polyhalides A2TeX6I2, where A represents organic cation and X denotes Br or I. The crystal structures of these compounds feature [TeX6] octahedra interconnected by I2 bridge molecules. These compounds can be synthesized using a simple single-step procedure, which makes them available on a large scale. The tellurium complex bromides and, particularly, iodides exhibited interesting optical properties favoring their photovoltaic applications (e.g. band gaps below 1.5 eV). Thin films of the tellurium halides showed semiconductor behavior and revealed strong photoconductivity effects enabling their application as active materials in efficient photodetectors.

Resume : Cu2SnS3 (CTS) polycrystalline single crystal was grown by a melt growth method. Stoichiometric ratios of Cu (5N), Zn (6N), Sn (6N), S (6N), and Se (5N) were charged into a quartz ampoule. The ampoule, charged with the elements, was sealed off after evacuation to a pressure about 10-6Torr. The ampoule was inserted into a vertical furnace, heated up to 1100 °C in three steps with different rates, and kept at this temperature for 24 h. After, the ampoule was cooled to 300 °C with different rates and in the last phase in the atmosphere. The XRD patterns of CTS powder exhibit major peaks corresponding to diffraction lines of the monoclinic structure of CTS and no distinct peaks of secondary phases were observed in the XRD pattern. This result is confirmed by Raman measurements. Electrical parameters were carried out by Hall effect measurements. The p-type material was observed. The carrier concentration, the resistivity and the mobility were 4.76x1015 cm-3, 2.8 Ωcm and 19.3 cm2V-1s-1, respectively. Measurements at low and high temperatures (from 80 K to 350 K), the Cu on Sn antisite defect (CuSn) and the Cu vacancy (VCu) were detected and are the dominant acceptor defects in CTS, which leads to p-type conductivity. The activation energies of 33 and 75 meV at low and high temperatures were determined, respectively from Arrhenius plot of ln(σ) versus1/T. The study of variation of mobility with temperature result in the acoustic and impurity scattering mechanisms at high and low temperatures, respectively.

Resume : Aluminum doped hydrogenated amorphous silicon carbide (a-SiC:H:Al) thin films are a promising photoactive material to be used as electrodes for several applications. This is due to its good chemical stability, the abundance of raw materials and low cost of processing. This material has been investigated as photocathode for hydrogen production photo-assisted electrolysis, exhibiting solar to hydrogen conversion efficiencies up to 7.5%. In particular, it opens up the possibility to tailor its relatively wide bandgap from 2.4 eV to 3.3 eV to harvest a wider range of the solar spectrum. In this work, Al-doped amorphous SiC:H thin films were grown on silicon and fused silica substrates by radio frequency magnetron sputtering. In order to evaluate the potential use of this material for photocathodes in photo-electrochemical devices, surface treatments with HF etching (20 vol%) and rapid thermal annealing were performed to improve the system photocurrent efficiency. The semiconductor-electrolyte interface properties were assessed via Mott-Schottky measurements from which charge carrier concentration and flat band potential values are estimated. The absorption coefficient in the fundamental absorption spectral region was determined by means of UV VIS spectrophotometry. Subsequently, optical bandgap and Urbach energy were calculated from the fundamental absorption via a band-fluctuations model and contrasted for each annealing temperature. Hydrogen concentration, Si-C, and Si-CH bond densities were determined by means of FTIR absorbance measurements for each annealing temperature in order to evaluate the evolution of the thermal induced depletion of hydrogen in the host and its impact on the optical and electrical properties.

Resume : Organic-inorganic hybrid perovskites are a novel class of semiconducting materials showing great potential as solar cell absorbers. This is due to their high device efficiencies, high absorption, tunable direct bandgap and disruptively low manufacturing costs. However, they are currently limited by their tendency to degrade under high illuminations and temperatures. While these issues have been widely reported in their electrical behavior, there is relatively little information on the effects of degradation on their optical properties, namely their refractive indices and absorption coefficients. Therefore, in this work we investigate the changes in optical properties of a variety of scientifically relevant multi-cation perovskite compositions under the effects of UV light soaking and high temperatures. This is done using Variable Angle Spectroscopic Ellipsometry in the range of 190 nm ? 25 ?m, thus covering the UV/VIS/NIR/MIR regions. Changes are observed in the absorption edge and high energy transitions, as well as in the IR absorption bands which are sensitive to chemical composition. A variety of behaviors are observed with increasing degradation time, with the most recurring being rapid decomposition of methylammonium ions, highly visible in the MIR region, coupled with a loss of film thickness. At the same time, large changes in the film surface quality and phase segregation become noticeable in the UV/VIS/NIR region.

Resume : The effect of local surface plasmon resonance (LSPR) of a metal nano-composites in polymer solar absorber was investigated with the view to improve the performance of thin film organic solar cell (TFOSC). The nano-particles are expected to improve photons harvesting by way of enhanced solar absorption and improved exciton dissociations. In this study, we are reporting the incorporation of two types bimetallic nanocomposites such as silver:zinc (Ag:Zn) and silver:magnesium (Ag:Mg) in conductive polymers blend composed of poly [[4,8-bis [(2-ethyhexyl)oxy] benzo(1,2-b:4,5-b?)dithiophene-2,6-diyl][3-uoro-2-[(2 ethylhexyl)carbonyl] thieno [3,4-b]thiophenediyl]] (PTB7) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The solar cells were fabricated in inverted device architecture to enhance device stability and power conversion efficiency (PCE). The LSPR effect of Ag nanoparticles (NPs) coupled with the remarkable electrical and optical properties of naturally abundant Zn and Mg NPs led to about 11 % - 41 % increment in power conversion efficiency (PCE) of the fabricated devices. The results are discussed based on the optical, electrical and morphological properties of the synthesized NPs and the fabricated devices. 1) M. Tang, B. Sun, D. Zhou, Z. Gu, K. Chen, J. Guo, L. Feng, Y. Zhou, Broad-band plasmonic Cu-Au bimetallic nanoparticles for organic bulk heterojunction solar cells, Organic Electronics, 38 (2016) 213-221. 2) G.T. Mola, E.A.A. Arbab, Bimetallic nanocomposite as hole transport co-buffer layer in organic solar cell, Applied Physics A, 123 (2017) 772. 3) S.O. Oseni, K. Kaviyarasu, M. Maaza, G. Sharma, G. Pellicane, G.T. Mola, ZnO:CNT assisted charge transport in PTB7:PCBM blend organic solar cell, Journal of Alloys and Compounds, 748 (2018) 216-222.

Resume : In order to produce pv-capable silicon on glass, crystalline silicon is grown from tin solution. A silicon source is dissolved and crystalline silicon is continuously grown from an amorphous seed layer on glass. Inspired by the float glass process, this novel method promises scalability to substrates of 10 m2 or more. Layers can be grown to the desired thickness and without kerf-loss. Since the temperatures can be kept below 500 °C during growth, these substrates can contain functionalizations and backside contacts. We show our progress in the development of these layers, how they influence growth and how they withstand growth conditions.

Resume : Piezoelectric devices have been fabricated from Pb-added piezoelectric materials (PZT), because of their exceptional properties. Lead free materials are being intended to synthesize with comparable properties to those of PZT to decrease the use of Lead because of its hazardous effects on environment. Therefore lead free ceramics play an important role in environmental friendly materials. In this study, the electromechanical properties of (1-x) Bi0.5Na0.5TiO3–xSrTiO3 (x=0.26, Hereafter ST26) / (1-y) Bi0.5Na0.5TiO3–ySrTiO3 (y=0.10, and 0.20, Hereafter ST10 and ST20) (matrix/seed) composites were studied. The degradation of polarization and strain, ferroelectric, dielectric, and strain characteristics with frequency and temperature were investigated in detail. In this report, (1-x) Bi0.5Na0.5TiO3-xSrTiO3 (x = 0.26) as a matrix material weas selected to fabricate the ceramic/ceramics composites, because of low triggering electric field for the electric field induced phase transition in S-E curve. Solid state method was implied for the synthesis of ceramic and sintered at 1150°C for 4 hr. It is revealed that ST26 composite with seed (ST10 and ST20) is a relaxor ferroelectric as shown by the temperature and frequency-dependent dielectric properties with an incipient piezoelectricity featured by the presence of a reversible electric-field-induced phase transformation at room temperature. This effect is also observed by a large strain that is associated with matrix and seed effect originating by inhomogeneous composition. However, ST26/ST10 composite makes a prominent Pb-free material as it shows a d33* of ~980 pm/V at a low ‘E’ of 2.5 kV/mm for frequency of 0.1Hz. The properties of ST26 composite with the ST10 seed exhibit a prominent decay with frequency dependence of polarization and strain due to the low relaxation time and domain wall velocity determined by KAI model. References [1] C. H. Hong, H. P. Kim, B. Y. Choi, H. S. Han, J. S. Son, C. W. Ahn, W. Jo, J. Materiomics, 2, 1, (2016) [2] W. Jo, R. Dittmer, M. Acosta, J. Zang, C. Groh, E. Sapper, K. Wang, J. Rodel (2012), J. Electroceram, 29, 1 (2012) [3] M. Saleem, I.S. Kim, M. S. Kim, S. A. Pervez, U. Farooq, M. Z. Khan, A. Yaqoob, S. J. Jeong, RSC Adv, 6, 89210 (2016)

Resume : While organic batteries have some advantages over their inorganic counterparts, they have a number of drawbacks, chief among which as conventionally accepted is the dissolution of the active material leading to the shuttle effect. Using N,N’-dimethylphenazine (DMPZ) as a highly soluble cathode material, together with its hexafluorophosphate and triflimide salts as compounds modelling its first oxidation state, we found a poor correlation between solubility and battery operability. Furthermore, measurements of diffusivity and shuttle currents suggest that the shuttle effect is unlikely to be mediated by molecular diffusion as commonly accepted, but rather by electron hopping as part of the electron self-exchange reaction based on electron paramagnetic resonance results. These findings led to two counter-strategies: 1) pre-treatment of the anode to promote the formation of a surface-electrolyte-interface to limit electron hopping to the anode, and 2) using DMPZ salt rather than neutral DMPZ as the active material to restrict electron self-exchange of DMPZ/DMPZ•+ in the electrolyte. Despite some deficiencies, these strategies led to cells with high coulombic efficiency and stable capacity retention, demonstrating that solubility of organic materials does not necessarily exclude their applications in batteries.

Resume : Organic photovoltaics (OPVs) have quickly become one of the most promising families of photovoltaic devices. OPV devices comprise a complex sandwich-like architecture; in which, each of the layers needs to be carefully optimized in order to yield a high-performance device. Traditionally, these devices have been optimized through highly time-intensive and expensive single parameter optimization. A methodology1 devised by my colleagues, utilizes design of experiment and machine learning to dramatically reduce the amount of time and effort required to optimize these devices by investigating parameters simultaneously. Design of experiment (DoE) allows us to factorially reduce the number of devices required to explore effect of processing parameters like annealing and solvent additives on performance. Once the series of devices prescribed by (DoE) have been manufactured, the resulting data set is fed into a machine learning algorithm. The algorithm produces “maps” that outline the areas of power conversion efficiency (PCE) that would otherwise likely be missed with serial optimization. The devices in this work contained bulk heterojunctions (BHJs) consisting of the small molecule donor, DRCN5T2 and non-fullerene acceptor, ITIC3. Donor acceptor ratio, annealing temperature, annealing time and BHJ solution concentration were all optimized to produce devices exhibiting a power conversion efficiency (PCE) of above 4.0 %. References [1] Cao, B. et al. How To Optimize Materials and Devices via Design of Experiments and Machine Learning: Demonstration Using Organic Photovoltaics. ACS Nano 12, 7434–7444 (2018). [2] Kan, B. et al. A Series of Simple Oligomer-like Small Molecules Based on Oligothiophenes for Solution-Processed Solar Cells with High Efficiency. J. Am. Chem. Soc. 137, 3886–3893 (2015). [3] Lin, Y. et al. An electron acceptor challenging fullerenes for efficient polymer solar cells. Adv. Mater. 27, 1170–1174 (2015).

Resume : Titanium oxide (TiO2) is one of the mostly studied photocatalysts for the environmental remediation because of its low cost and stability. On the other hand, the photocatalytic performance of TiO2 is limited due to its wide band gap (3.2 eV), low quantum efficiency and high electron-hole pairs recombination rate. Various approaches such as tailoring its morphology (thin films etc.), doping with noble metals (gold, silver etc.) and coupling with metal oxides have been suggested to improve photocatalytic activity of TiO2. Recent studies have been shown that particle size of TiO2 plays a significant role in the photocatalytic performance of it. Decreasing the particle size to the nanoscale (increasing active surface area) leads to a higher photocatalytic activity. However, the use of nanoparticles for photocatalytic applications in continuous flow systems (such as water treatment) has some practical limitations. In such systems, it is difficult to separate and recycle nano-scaled photocatalysts from the water. Therefore, the use of photocatalysts as a robust and stable thin film is more suitable for functional applications However, thin films have a limited surface area in comparison to nanoparticles and they show limited photocatalytic activity. Here we present some case studies on preparation of phocatalytic TiO2 based thin films with high activity. Main attention will be given to plasmon enhanced photocatalysis and as well as mixed oxides and their catalytic performance. In addition, a novel approach for nanostructuring of surfaces by photocatalytic reduction will be presented.

Resume : Using organic redox-active molecules provides a new paradigm for future development of metal-ion batteries. Organic materials are based on light elements and hence can enable much higher specific capacities compared to the salts and oxides of heavy transition metals. Most of organic materials are non-toxic and environment friendly, which makes easy their recycling as a common household waste. In contrast to crystalline inorganic cathodes and anodes, organic materials are soft and, therefore, can operate at high rates thus delivering ultrafast batteries. In this talk, we will highlight our recent results on the design of organic and metal-organic cathode and anode materials for lithium, sodium and potassium batteries. In particular, we will present ultrafast K-ion batteries delivering specific capacities of 169 mA h g?1 at an impressive current density of 10 A g?1 (charge in ca. one minute) and 245 mA h g?1A at a lower current density of 50 mA g?1. Specific energy of ~550-600 W h kg-1 is reached for the best organic cathodes in K-ion batteries. The polymer-based devices also demonstrated record-high cycling stability with no capacity decay after 4600 cycles. The obtained results suggest that organic electrode materials, while still being at the infancy of their development, start to show commercially interesting performances thus paving a way to implementation of a new generation of post-lithium metal-ion batteries.

Resume : Among various SEs, the inorganic?type include oxides (LLZO, pervoskites, LISICONs, NASICONs), sulfides (LGPS, Li2S-P2S5) and argyrodites (Li6PS5X (X= Cl, Br, I)). When compared with their polymer counterparts, inorganic SEs offer higher ionic conductivities, better thermal stabilities, and Li transference number of unity (tLi+ = 0.2-0.5 for polymers). However despite the aforementioned advantages, the issue of high electrode-electrolyte interfacial resistance hampers the progress of solid-state batteries. While it is difficult to prove experimentally the exact mechanism for interface resistance, current studies indicate that chemical incompatibility, electrochemical instability and mechanical issues between electrodes and SEs may be the possible reasons for the interfacial instability. In this regards, LLZO is a preferred choice over other types of SEs, due to its better compatibility with Li anode and electrochemical stability in a wider potential range (0-6V vs. Li). However, the main limitation with LLZO is its brittle nature which prevents proper physical contact with Li metal and other electrodes, resulting in high interfacial resistance. This presentation outlines our strategies to address the issue of high interfacial resistance in LLZO based solid-state systems. We show that by proper interfacial modifications, the interface resistance can be significantly reduced resulting in improved Li cyclability and suppression of Li-dendrites.

Resume : The functionality of many energy materials is critically dependent on details of their chemical composition. In particular light elements as either constituents or unwanted contaminations can have huge impact on device performance. At the same time, species like hydrogen, lithium or oxygen are hard to detect directly despite their ultimate relevance in materials for hydrogen storage, electro- and photochromic applications or solar cells. In this contribution, we present our recent efforts to employ advanced characterization tools for overcoming these issues. Specifically, we have performed advanced ex- and in-situ investigations of photochromic materials based on rare-earth oxyhydrides. Non-destructive ion-beam based depth profiling of the materials was conducted in combination with material growth, modification and during illumination and relaxation. The obtained information on sample composition was subsequently correlated with optical properties, enabling an effective search for optimum performance and manufacturing conditions. Furthermore, we also have studied a series of electrochromic materials and thin film solar cells focusing on light elements, in particular H and Li. The focus has been on materials based on WO3 as well as CZTS-solar cells and their capability for rejuvenation and thermal stability respectively.

Resume : Recently, Si has emerged as a potential candidate for high-capacity Li ion batteries. However, the practical implementation of Si is challenging as it suffers a large volumetric change upon lithiation/delithiation. This results in cracks, pulverization of active Si and the continuous formation of the solid electrolyte interphase (SEI), that eventually lead to rapid capacity fading and hence the mechanical failure of the electrode. To circumvent these drawbacks, composite materials such as Si/FeSi2 alloy/graphite are considered. Here, we have investigated the aging mechanism of a-Si/c-FeSi2 alloy/graphite composite at different stages (1, 100, 300 and 700 cycles) upon lithiation/delithiation. The composite electrode is very complex considering features of different length scales (µm to nm) e.g., graphite, a-Si/c-FeSi2 alloy, carbon black and binder. Therefore, a multiscale correlative approach has been utilized by combining FIB-SEM tomography and STEM-EDX methods. We have been able to characterize in-depth the morphology and chemical changes at length scales ranging from µm down to sub-nm. The morphology and chemical evolution of the a-Si/c-FeSi2 alloy particles has changed markedly at 300 cycles, yielding a core (mainly a-Si/c-FeSi2) and a porous complex oxide SEI shell that was typically a few 100 nm thick. Chemical analysis revealed that the percolation network of the active a-Si is still intact, leading to a capacity retention of 70% after 700 cycles at C/20 cycling rate.

Resume : The insertion of heteroatoms with different electronegativity into a carbon network can greatly tune its electronic, optical, and electrochemical properties along with its chemical reactivity. The introduction of nitrogen and sulfur that serve as electron donors or boron as an electron withdrawing group, into a carbon structure will alter its electronic states, (electro)catalytic properties, and chemical stability to oxidation and to high temperatures. The traditional methods of synthesizing heteroatom-modified carbon matrices is carried out by solid state reactions, chemical vapor deposition (CVD), and functionalization of the carbon materials. Although an impressive wide range of materials were synthesized by these methods, there are still some drawbacks that limit the progress in this field. CVD offers very low scalability while the solid state offers low control over the composition and position of the heteroatoms within the carbon network. Herein we show a new, scalable, and easy way to synthesize heteroatom-incorporated carbon materials by means of molten-state intermediate. This method enables the synthesis of BNCO, and CS materials. The elemental composition is easily controlled within these materials (up to 30 wt.% boron, 20 wt.% sulfur, and 30 wt.% nitrogen) resulting in fine tuning of the materials properties. In addition, BNCO, and CS materials show state-of-the-art reversible capacity values as anodes in Li-ion, and Na-ion batteries, respectively. Refrences: J. Tzadikov, M. Auinat, J. Barrio, M. Volokh, G. Peng, C. Gervais, Y. Ein-Eli, M. Shalom, ChemSusChem 2018, 11, 2912–2920

Resume : In 21st century electron waste or e-waste is the toxic legacy of our digital age. E-waste is created when an electronic product is discarded or expired. Therefore, with the rapid expansion of technology, there is a tremendous increment of e-wastes, which are polluting drinking water and harming ecosystems around the world. On this context, using paper as an alternative substrate for digital electronics has obvious advantages such as low cost, flexibility biodegradability, compostability and ease of disposal through fiber recycling or incineration. Here in, we have presented an innovative conception for a non-destructive self-powered energy harvesting paper base on mechano-responsive charge transfer mechanism at the polymer/metal interface layer that could be integrated safely into everyday paper-based objects from packing box materials to sticker to improve quality of life. The core idea behind this is to initiation of mechanoresponsive charge-transfer and energy-transfer process in ?-conjugated polymer at the organic-metal interface layer. The ?-conjugated polymers are fascinating materials with a unique combination of hard (metal like) and soft (organic like) matter which can be exerted to convert mechanical-stimuli to electrical potential energy. Work has been demonstrated through an understanding and specific investigation on the dynamics of localized electronic transport mechanism at metal-polymer interface layer using atomic force microscopy integrated with electrical mode. A localized forced deformation of the interface has been enacted by pressing the atomic force microscopic probe against the polymer surface, allowing charge transfer between material interfaces. Results explored that during contacting force, polyaniline film shows electrical output through the charge transfer mechanism within materials interfaces. Our proposed research approach and manufacturing product concept will address both technical performance and cost-effectiveness of energy harvesting based on paper platform.

Resume : We attempt to demonstrate the experimentally supercapacitive performance of polyaniline (PANI) - cobalt hydroxide (Co(OH)2)-nickel hydroxide (Ni(OH)2) nanocomposites (NCs), prepared potentiostically via electrochemical deposition, compared to phase pure individual nanostructures. Amorphous PANI, Co(OH)2 – Ni(OH)2 and NCs are entirely different from one another from the surface appearance point of view, PANI exhibits nanofiber morphology, NCs exhibits nanofiber partially covered with Co(OH)2 - Ni(OH)2 materials and Co(OH)2 - Ni(OH)2 shows platelet morphology. The electrochemical properties of the PANI, Co(OH)2 - Ni(OH)2 and HNs electrodes have been investigated by cyclic voltammograms and galvanostatic charge-discharge. The specific capacitances of PANI, NCs, and Co(OH)2 – Ni(OH)2 are found to be 0.59, 50, 46.4, 85.7, 74.1 and 312.5 F/g, respectively, at a sweep rate of 10 mV/s in 1.0 M NaOH electrolyte. The same nature of retention values in area of CV curves and power densities of PANI, NCs and Co(OH)2 – Ni(OH)2 with increased in scan rates are 25.8, 70.5, 75.5, 76.6, 57 and 42.4%, respectively and the same nature of retention in charge density, specific capacitance, and energy density values are 38.7, 33.8, 40.7, 42.6, 23.1 and 17.3% respectively for PANI, NCs and Co(OH)2 - Ni(OH)2 electrodes with increase in scan rate.

Resume : Rechargeable sodium metal batteries have attracted attention as promising power sources over the last several years because they are a lower cost option than Li ones for large scale energy storage. However, the Na-metal anode is characterized by poor reversibility at room temperature due to the formation of nonuniform solid electrolyte interfaces as well as to the dendritic growth of sodium metal. Here, we report on a highly-concentrated sodium electrolyte based on liquid ammonia, which can be formulated as NaI·3.3NH3. It has excellent properties such as high ionic conductivity and non-flammability. Nevertheless, the search of effective and economic materials to be used in sodium batteries remain a priority for the scientific community. Titanium dioxide shows several advantages as ecological, cost-effective and non-toxic. Here we present an electrochemical study of electrodes based on amorphous nanotubes of TiO2 prepared by a simple anodization process. The electrochemical behavior of TiO2 nanotube electrodes in the NaI·3.3NH3 electrolyte is characterized by a highly reversible insertion/deinsertion process of sodium with a gravimetric capacity around to 150 mAh/g(TiO2), even when employing a C rate as high as 3000 mA/g(TiO2). The development of inorganic electrolytes based on liquid ammonia along with suitable electrodic materials may pave the way for engineering new high power density devices based on sodium at room temperature.

Resume : I present an overview of our experimental and theoretical investigations of CrN-, ScN-, and Ca3Co4O9-based thin films for thermoelectric energy harvesting. We have introduced a two-step sputtering/annealing method for the formation of highly textured Ca3Co4O9 thin films. These can be deposited on flexible mica substrates, enabling flexible inorganic thermoelectric thin films that withstand repeated bending without deterioration. They can also be made as free-standing and/or nanoporous films. ScN thin films exhibit a high power factor (S2/) of 2.5-3.3×10-3 W/mK2 at 800 K. We have explained this result, from first-principles calculations, by nitrogen vacancies generating an asymmetric sharp feature in the density of states which allows low electrical resistivity with relatively large S. To reduce lattice thermal conductivity, potential strategies are nanostructuring, alloying or nanoinclusion formation. We have modeled the thermal conductivity in pure ScN as a function of grain size using time-dependent effective potentials (TDEP), correlating the ideal thermal conductivity of an infinite ideal crystal with the thermal conductivity reduction of grain-size effects. Pure CrN exhibits n-type conduction with a high power-factor enabled by a high electron concentration thermally activated from N vacancies, and alloys can be made of rocksalt-Cr1-xScxN. We have demonstrated that it can be rendered p-type by Al alloying in combination with N superstoichiometry.

Resume : Recently, a new type of metal porphyrin complex with promising redox behavior at an average voltage of around 3 V was developed in our group.1,2 Introducing of terminal alkyne functionality and copper metal were found to significantly improve the degradation of [5,15‐bis‐(ethynyl)‐10,20‐diphenylporphinato]copper(II) (CuDEPP) upon cycling as above 60% of the capacity was retained after 8,000 cycles at a current density of 4 A g−1. A rapid redox conversion involving up to four electron transfers was lead to the gravimetric energy and power densities of as high as 345 Wh kg−1 and 29 kW kg−1, respectively. To further explore the potential of such materials, new generation of porphyrin complexes of various metal atoms as well as different substitution on the porphyrin structure have been developed and are under evaluations. This presentation will address the comparative study on various conductive carbon additives for CuDEPP cathode, where carbon nanotube, carbon black, graphene nanoplatelets and their mixtures have been used to fabricate the cathode. Diverse chemical and structural analysis as well as electrochemical techniques have been utilized to establish structure-performance correlation. It will be shown that there is a remarkable potential to extract greater performance from such materials through optimization of type and content of conductive carbon additives. References: 1. Gao, P. et al. A Porphyrin Complex as a Self-Conditioned Electrode Material for High-Performance Energy Storage. Angew. Chemie Int. Ed. 56, 10341–10346 (2017). 2. Zhao-Karger, Z. et al. New Organic Electrode Materials for Ultrafast Electrochemical Energy Storage. Adv. Mater. 1806599 (2019).

Resume : 2D carbides of transition metals known as MXenes have already attracted much attention and about 20 of them have been reported, leading to breakthroughs in the fields from energy storage to electromagnetic shielding and recently, as (photo)-catalysts for clean energy conversions such as hydrogen evolution and CO2 reduction. To this end, by mixing of two or more elements, alloying offers an avenue to simultaneously tune catalytic performances and photo-adsorption characteristics. First-principles electronic structure calculations has proven to be a reliable tool for catalyst and photocatalyst design by providing fundamental insights into the reaction mechanisms and band structure. However, for alloy design, the prediction will only be accurate provided the correct material structure is given as the input for the first-principles calculations. To this end, we couple first-principles calculations with the cluster expansion method to realize a cost-effective way to identify stable MXene alloys, using which, reliable property predictions, e.g., band alignments, can be made from DFT. After a brief introduction to the methodology [1], I will showcase some of our recent applications (e.g., photocatalysis [2], CO2 reduction [3]). [1] Teck L. Tan, H. Jin, M. Sullivan, Y. Gogotsi et al., ACS Nano 11, 4407 [2] Teck L. Tan, S. W. Yang, G. Q. Xu et al., ACS Appl. Mater. Interfaces 10, 39879 [3] Teck L. Tan, H. Jin, Z. W. Seh et al., J. Mater. Chem. A 6, 21885

Resume : In luminescent solar concentrator (LSC) systems, broadband solar energy is absorbed, down-converted and waveguided to the panel edges where peripheral photovoltaic cells convert the concentrated light to electricity. Achieving a low-loss LSC requires reducing the reabsorption of emitted light within the absorbing medium while maintaining high photoluminescence quantum yield (PLQY). Here we employ layered hybrid metal halide perovskites—ensembles of two-dimensional perovskite domains—to fabricate low-loss large-area LSCs that fulfil this requirement. We devised a facile synthetic route to obtain layered perovskite nanoplatelets (PNPLs) that possess a tunable number of layers within each platelet. Efficient ultrafast non-radiative exciton routing within each PNPL (0.1 ps−1) produces a large Stokes shift and a high PLQY simultaneously. Using this approach, we achieve an optical quantum efficiency of 26% and an internal concentration factor of 3.3 for LSCs with an area of 10 × 10 cm2, which represents a fourfold enhancement over the best previously reported perovskite LSCs.

Resume : Silicon as a negative electrode material attracts significant research and development attention for next-generation lithium-ion batteries (LIBs). However, the enormous volume change (300%) during lithiation and delithiation is the primary reason why silicon is not widely adopted in LIBs. To counteract the high-volume expansion associated with lithiation, silicon nanoparticles emerged as materials engineered to extend cycle life. However, correlating particle morphology, size and structure with performance in and lifetime of battery is still needed to make use of the diverse approaches toward predictable tunability of nanoparticle properties. Within this presentation we will provide an overview of the advantages and disadvantages of amorphous silicon prepared through the pyrolysis of silane and compare its performance to its crystalline competitors. We will also demonstrate that temperature and silane concentration during synthesis influence the size and morphology of the silicon nanoparticles ultimately controlling the battery behavior. Furthermore, we will illustrate how post-processing of amorphous silicon may increase or decrease its lifetime as an active material in LIB.

Resume : Metal halide perovskites have emerged as a promising photo-active material in solar cells and LEDs, reaching efficiencies up to 24.2 %[1]and 20.3%[2] respectively. An intriguing feature is that the bandgap can easily be tuned by varying the halide ratio.[3] To achieve high device performance, the quality of the semiconductor material is key. Therefore, in–depth understanding of film formation is crucial to control phase evolution, increase film quality and opto-electronic properties. In this work, we will elucidate the formation processes of mixed halide perovskites with different bandgaps employing in-situ UV/vis (Absorption and Reflection) and Photoluminescence measurements during spin-coating and annealing. Extracting spectra on a sub-second time scale, we are able to detect crystallization onsets and kinetics of the formation process and distinguish intermediate stages during film formation. The influence of halide and cation compositions, as well as the solvent and additives, on the formation mechanism will be discussed. These parameters critically determine the structural, morphological and therefore optical and electronic properties of the resulting thin films. Based on this knowledge, synthesis parameter can be adjusted to obtain optimized perovskite layers for devices to further increase their performance. [1] https://www.nrel.gov/pv/cell-efficiency.html, checked: 2019/04/14 [2] Nature (2018), 562, 245–248. [3] Journal of Materials Chemistry A (2017), 5 (23), 11401-11409.

Resume : Hydroborates are a promising alternative class of solid electrolytes that combine liquid-like ionic conductivity with high electrochemical stability, high thermal stability and favorable mechanical properties [1-3]. Using the mixed-anion compound Na4(B12H12)(B10H10) as electrolyte, we realized stable cycling of 3 V all-solid-state battery using sodium metal as anode and NaCrO2 as cathode. We achieved a capacity of 85 mAh/g at C/20 and 80 mAh/g at C/5 with more than 90% capacity retention after 20 cycles at C/20 and 85% after 250 cycles at C/5 [1,2]. Here, we elucidate the conduction mechanism of this electrolyte and related compounds. We show that the fast sodium ion diffusion is correlated to the rotational and librational motions of the anions, resulting in a complex temperature dependence of the conductivity [4,5]. Based on this observation we discuss design rules to achieve high ionic conductivities in this class of materials. Acknowledgement: Financial support by the Swiss National Science Foundation and by InnoSuisse is gratefully acknowledged. References [1] L. Duchêne et al., Chem. Commun., 53, 4195 (2017). [2] L. Duchêne et al., Energy Environ. Sci., 10, 2609 (2017). [3] R. Moury et al., Acta Cryst. B, in press [4] L. Duchêne et al., Chem. Mat., 31, 3449, (2019). [5] T. Burankova et al., J. Phys. Chem. Lett. 9, 6450 (2018).

Resume : The interest in iron pyrite (cubic FeS2) as a PV material has picked up recently because of its earth-abundance, nontoxicity and suitable band gap for efficient visible light absorption (~0.95 eV).[1] On the other hand, the low open-circuit voltage (VOC) of 200 mV limits its solar energy conversion efficiency (PV cell or PEC cell) to ~3 %. The presence of orthorhombic marcasite FeS2 is generally believed to be detrimental to photochemical performance because of its much smaller band gap (0.34 eV). Nevertheless, recently published theoretical calculations predict that marcasite should have a band gap of 0.8-1.0 eV, which is quite similar to that of pyrite.[2] In this report, we present FeS2 films with mixed pyrite-marcasite phase (p/m-FeS2) junctions obtained via sulfurization of iron thin films on highly doped Si wafers. The p/m-FeS2 films show tremendously improved photocurrent compared with phase-pure pyrite films. We propose that the enhanced photocatalytic performance is due to efficient charge separation across the pyrite-marcasite phase junction. Consistently, we demonstrate, through state-of-the-art materials simulation technique based on the Density Functional Theory, that a staggered band alignment exists between marcasite and pyrite with both the valence and conduction bands of marcasite positioned higher than those of pyrite, indicating that photo-generated conduction band electrons will flow from marcasite to pyrite and vice versa for photo-generated valence band holes in mixed-phase FeS2 thin films. These findings point to efficient charge separation in the mixed systems as the primary origin of the observed high photo-activity (photocurrent) of the mixed marcasite–pyrite thin films over the individual pyrite counterpart.

Resume : Zn/Co3O4 battery is one of the few aqueous electrolyte batteries with a potential >2 V voltage. Unfortunately, so far, all reported Zn/cobalt oxides batteries are using alkaline electrolyte, resulting in poor cycling stability and environmental problems. Here, we report a Co(III) rich- Co3O4 nanorod material with vastly improved electrochemical kinetics. The Zn/Co(III) rich-Co3O4 batteries can work well in ZnSO4/CoSO4 aqueous solution as a mild electrolyte, delivering a high voltage of 2.2 V, a capacity of 205 mAh∙g-1 (Co3O4), and an extreme cycling stability of 92% capacity retention even after 5000 cycles. Further mechanism study reveals a conversion reaction between in-situ formed CoO and Co3O4, which has never been observed in an alkaline Zn/Co3O4 battery. Subsequently, a flexible solid-state battery is constructed and reveals high flexibility and high energy density of 360.8 Wh∙Kg-1 at current density of 0.5 A∙g-1. Our research initiates the first Zn/Co3O4 battery working in a mild electrolyte, resulting in excellent electrochemical performance. It also indicates that the electrochemical kinetics can be effectively enhanced by fine tuning atomic structure of electrode materials, opening a new door to improve performances of aqueous electrolyte batteries. Publication: 1. L. Ma, S. Chen, C Zhi*, et al. Initiating A Mild Aqueous Electrolyte Co3O4/Zn Battery with 2.2 V-High Voltage and 5000-Cycle Lifespan by a Co (III) Rich-electrode, Energy & Environmental Science, 11(2018), 2521-2530. (Highly cited paper); 2. L. Ma, S. Chen, C Zhi*, et al. Flexible Waterproof Rechargeable Hybrid Zinc Batteries Initiated by Multifunctional Oxygen Vacancies-Rich Cobalt Oxide, ACS Nano, 12 (2018) 8597-8606.

Resume : Recently, lead halide perovskite solar cells have demonstrated impressive efficiencies exceeding 24%, but their practical application is still hampered by stability issues. Besides the intensively investigated photochemical and thermal degradation effects, a particular attention should be paid to the electrochemical stability of absorber materials and completed photovoltaic devices. Here we report a systematic comparative study of the electrochemical stability of lead halide based perovskite solar cells assembled in p-i-n architecture using different hole-selective layer materials such as PEDOT:PSS, NiOx, PTAA, CuI, Cu2O, CuSCN and their combinations. Devices were exposed to a stepwise potentiostatic polarization under anoxic conditions in dark. The evolution of the solar cell performance was analyzed using ToF-SIMS profiling to unravel ion migration and possible redox processes occurring at the cathode and anode. The obtained results showed that the electrochemical stability of perovskite solar cells is largely affected by the used HTL materials. We also explored the effect of polarization conditions on the kinetics of the electrochemical degradation of perovskite solar cells assembled using PTAA as a hole-transport material. The revealed degradation pathways featured a crucial importance of controlling interfacial electrochemistry while designing highly efficient and stable perovskite solar cells. This work was supported by Russian Science Foundation (project 19-73-30020).

Resume : Photon recycling, the iterative process of re-absorption and re-emission, has previously been claimed to occur in thin films of GaAs to explain the observed long apparent carrier diffusion lengths. Recently, several reports on lead halide perovskites have used novel experimental setups to claim the occurrence of exactly this same process of photon recycling. However, there exists some controversy on whether the observed results should be explained by carrier diffusion or photon recycling. In this work we present clear evidence of photon recycling in inorganic lead halide nanocrystals in colloidal solution. The comparison of experimental PL data, the Beer-Lambert law and a model that includes re-emission conclusively shows long distance diffusion of photons. In addition, we elucidate the photon recycling process by performing time-resolved photoluminescence experiments on samples with varying dilutions where we show clear differences in decay times between samples and note the emergence of a rise-component in the more concentrated samples evidencing an additional indirect excitation mechanism. Together with photoluminescence quantum yield determinations we establish the photon recycling process in three independent measurements while excluding the possibility of carrier diffusion, thus providing the clearest evidence of photon recycling in CsPbBr3 nanocrystals to date. Since photon recycling has been shown to increase open-circuit voltages and power conversion efficiencies, our results will support development of more efficient perovskite photovoltaic devices.

Resume : Rechargeable energy storage devices have been extensively investigated over the past decade owing to the increasing popularity in portable electronics and electric vehicles (EVs). Currently, lithium-ion batteries (LIBs) are widely used for energy storage applications due to its excellent cyclability and low maintenance. However, LIBs are not perfect and their relatively low energy density as well as limited supply restrict their scope of application.(1) Zinc-air batteries are attractive LIB alternatives because of their high energy density, low cost, and the abundance of the raw materials.(2) Despite their obvious advantages, the oxygen evolution (OER) and oxygen reduction (ORR) reactions at the air cathode are kinetically unfavoured, resulting in sluggish reaction rate.(3) If this apparent limitation is to be overcome and widespread commercialization is to be realized, appropriate ORR and OER catalysts must be developed. Transition metal oxides supported by carbon nanomaterials have shown promising catalytic reactivity for both reactions.(4) In this work, nitrogen-doped hollow carbon spheres decorated with Mn3O4 nanoparticles were synthesized. The hybrid material exhibits comparable ORR performance to platinum, which is the bench mark catalyst. References: (1) Goodenough, J. B.; Park, K. The Li-Ion Rechargeable Battery : A Perspective. 2013. (2) Fu, J.; Cano, Z. P.; Park, M. G.; Yu, A.; Fowler, M.; Chen, Z. Electrically Rechargeable Zinc–Air Batteries: Progress, Challenges, and Perspectives. Adv. Mater. 2017, 29 (7). (3) Zhang, J.; Zhao, Z.; Xia, Z.; Dai, L. A Metal-Free Bifunctional Electrocatalyst for Oxygen Reduction and Oxygen Evolution Reactions. Nat. Nanotechnol. 2015, 10 (5), 444–452. (4) Qu, L.; Liu, Y.; Baek, J.-B.; Dai, L. Nitrogen-Doped Graphene as Efficient Metal-Free Electrocatalyst for Oxygen Reduction in Fuel Cells. ACS Nano 2010, 4 (3), 1321–1326.

Resume : Due to its theoretical capacity of 959 mAh/g, which is significantly larger than that of carbon (372 mAh/g), as well as its natural abundance, Sn is considered an interesting anode active material for lithium ion batteries. However, as a result of the prohibitively large volume expansion during lithiation (>185 % for full reaction to Li17Sn4), pure Sn electrodes suffer from extensive crack formation, continuous pulverization, lithium trapping, loss of electrical contact, and unstable SEI growth during cycling. One way to still utilize the high capacity of Sn and simultaneously overcome the detrimental effects associated with its volume expansion may be to use Sn-based chalcogenides such as SnS, Sn2S3 and SnS2 as active anode materials. During lithiation of these compounds, a rigid Li2S matrix phase, which forms at potentials between 1.6 and 1.3 V, can restrict the volume expansion of Sn during subsequent alloying reactions, thereby yielding reversible capacities of ~ 600mAh/g. Although heterogeneous, mixed-phase tin sulfides are easily produced via the thermal reaction of tin and sulphur, the mass-scale synthesis of phase pure materials is both challenging and expensive. To lower battery material costs, heterogeneous tin sulfides should then be considered as active anode materials. Therefore, in this work, galvanostatic cycling, cyclic-voltammetry, and the galvanostatic intermittent titration techniques were used to investigate the lithiation of mixed-phase tin sulfides. Furthermore, a thermodynamic description of the Li-Sn-S system was developed for the first time and used to predict the Li-Sn-S phase diagrams, simulate phase formation reactions, and calculate the open circuit voltages of the tin sulfides during lithiation.

Resume : The development of renewable energy resources and novel energy storage techniques is needed to realize sustainable development. Among all of the energy storage approaches, dielectric capacitors with fast charge-discharge speed (~100 ns to 1 ms) and ultrahigh power density (up to 100 MW/kg) are indispensable in electric power systems, including advanced electronic devices, medical apparatus and electrical vehicles. Compared with traditional inorganic-based bulk materials and thin films, flexible polymer-based dielectric materials have drawn considerable attention from both academia and industry owing to their high breakdown strength, superior mechanical properties and low cost. However, the current commercially available material, biaxially oriented polypropylene (BOPP), only exhibits a low discharged energy density of 1-2 J/cm3 at 600-700 kV/mm, prohibiting it from fulfilling the requirement for the modern energy storage system. Poly(vinylidene fluoride) (PVDF) with different polymorphs (non-polar α, polar β, γ and δ phase) has been widely studied for dielectric capacitor applications because of its high polarizability and high dielectric breakdown strength. However, the ferroelectric nature of the polar β phase results in high remnant polarization and low charge-discharge efficiency. The current technology for solving this problem involves complex and expensive synthesis of relaxor ferroelectric terpolymers poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene/chlorotrifluoroethylene) (PVDF-TrFE-CTFE/CFE) or high-energy electron-beam irradiation copolymer poly(vinylidenefluoride-trifluoroethylene) (PVDF-TrFE), which break the ferroelectric domains into polar nanodomains but severely reduce the mechanical properties and breakdown strength of PVDF. Therefore, obtaining PVDF with polar nanostructure and high breakdown strength is still a tough challenge. Herein, a facile process of pressing-and-folding (P&F) is proposed to produce free-standing PVDF films with ultrahigh β-phase content (~98%) regardless the molecular weight, as a result of a pressure induced phase transformation, and importantly, more effective stress transfer during P&F. More interestingly, for the first time, the relaxor-like ferroelectric behaviour under high field (>800 kV/mm) was observed in PVDF homopolymer with high molecular weights (Mw>534 kg mol-1), which is attributed to highly-mobile dipoles in small-sized polar structures, suggested by the decreasing crystallite size (down to~ 4 nm) after P&F. Therefore, an ultra-high discharged energy density (35 J cm-3) with high efficiency (74%) was achieved in a 7-fold P&F PVDF (Mw: 670-700 kg mol-1), which is the highest value ever reported for a polymer-based dielectric capacitor. This simple and scalable processing technique, as well as the unprecedentedly properties, will not only make P&F PVDF a promising candidate for high power energy storage applications but also provide a new direction for designing the next generation materials with high energy density.

Resume : Energy storage performances of Ni-based electrodes rely mainly on the peculiar nanomaterial design. In this work, a novel and low-cost approach to fabricate a promising core-shell battery- like electrode is presented [1]. Ni(OH)2@Ni core-shell nanochains were obtained by an electrochemical oxidation of a 3D nanoporous Ni film grown by chemical bath deposition and thermal annealing. This innovative nanostructure demonstrated remarkable charge storage ability in terms of capacity (237 mAh g-1 at 1 A g-1) and rate capability (76% at 16 A g-1, 32% at 64 A g-1). The relationships between electrochemical properties and core-shell architecture were investigated and modelled. The high-conductivity Ni core provides low electrode resistance and excellent electron transport from Ni(OH)2 shell to the current collector, resulting in improved capacity and rate capability. The reported preparation method and unique electrochemical behaviour of Ni(OH)2@Ni core-shell nanochains show potential in many field, including hybrid supercapacitors, batteries, electrochemical (bio)sensing, gas sensing and photocatalysis. [1] M. Urso et al. Scientific reports 9 (1), 7736 (2019).

Resume : Sodium-ion batteries (SIBs) face with several challenges, including low capacity, short cycle life, and poor low-temperature performance. In this work, TiO2–B/anatase dual-phase nanowires are synthesized and applied as SIB anode to address above challenges. For the first time, we find the excellent Na-storage performance of the nanowire anode like rate-independent capacities and ultra-stable cycling stability at low temperature. Operando Raman spectroscopy shows that the nanowires are completely amorphized after cycling at 303 K; however, the TiO2–B phase of the dual-phase nanowires remains crystalline after cycling at 273 K. The different sodiation mechanism at different temperatures results in a lower capacity but a more stable structure during cycling at 273 K than at 303 K. Kinetic analysis shows that the nanowire anode possesses ultralow charge-transfer energy barrier and resistance with higher apparent Na diffusion coefficient at 273 K than at 303 K during desodiation, which significantly enhances the Na+ intercalation pseudocapacitive process at low temperature. The synergy between structural transition and diffusion kinetics leads to rate-independent and ultra-stable Na-storage performance at low temperature. This work provides new perspectives for the understanding and design of low-temperature SIBs with high rate capability and long cycle life.