Materials for energy applications: hydrogen storage/production, solar cells, super capacitors, thermoelectric & carbon based materials

Resume : Based on novel organic semiconductors, organic solar cells are an interesting alternative to conventional silicon based solar cells as they feature new possibilities. Using wet chemical processing, they can be manufactured with large-scale production methods such as roll-to-roll printing. However, in terms of large-scale usability, one of the major challenges for organic solar cells is to overcome their relatively short lifetime, as compared to their inorganic counterparts. To gain a deeper understanding of organic solar cell degradation with respect to changes in the active layer morphology, we present operando studies during the first hours of operation. The studies reveal information on both, its evolving current-voltage characteristics and the changes of the active layer morphology in the organic solar cells. For that purpose, GISAXS / GIWAXS measurements and current-voltage (IV) tracking of the operating solar cell are performed simultaneously to gain fundamental understanding. Starting from an optimized morphology of the active layers in terms of highest device efficiencies, depending on the donor-acceptor organic semiconductor system, different morphological degradation pathways are identified. A mixing or demixing process can occur and cause changes of the active layer morphology. The altered morphology is less optimal for charge transport through the active layer due to poor percolation in a too fine morphology or a poor splitting of excitons in a too coarse morphology.

Resume : In recent years, solar interfacial evaporation has been one of the most promising techniques to alleviate freshwater scarcity. However, the salt deposition on the evaporation surface limits the long-term operation of evaporators. Herein, inspired by the salt dilution and secretion mechanisms in halophytes, a solar evaporator with a bundle-cross-layer structured absorber and salt secretion bundles is reported. The unique bundle-cross-layer structure realizes the salt dilution by enhancing the water storage and transport, which enables the absorber a high and stable evaporation efficiency of 90.2% over 60 h in brine. More importantly, the salt secretion bundles can completely separate salt crystallization from the absorber by a humidity-controlled salt creeping mechanism. The solar desalination prototype equipped with this evaporator exhibited a stable water collection rate over 600 h of continuous operation, realizing zero liquid discharge in desalination. The study provides new insights into the solar evaporator design and advances other applications such as sea-salt extract, wastewater treatment, and resource recovery.

Resume : Record-breaking organic solar cells (OSCs) based on blends of polymer donors and small molecule acceptors often show undesirable degradation, which severely precludes their practical use. Herein, we demonstrate a facile and cost-effective approach to construct thermally stable OSCs at 150 ºC by incorporating a small amount of a polymer insulator polyacenaphthylene (PAC) with high glass-transition temperature over 230 ºC into polymer:acceptor blends. The model PTB7-Th:EH-IDTBR blend with 10 wt% PAC maintained above 85% of its initial efficiency upon continuous heating at 150 ºC for over 800 hours, while the efficiency of the blend without PAC sharply dropped by 70% after ~300 hours. Owing to high miscibility with acceptors, PAC confines the motion of the acceptor molecules and suppresses the acceptor crystallization at elevated temperatures, leading to significantly improved stability. Importantly, the effectiveness of this blending approach was also validated in many other OSC systems, showing great potential for achieving high-performance thermally stable electronics.

Resume : stacks of intrinsic and doped hydrogenated amorphous silicon (a-Si:H) as passivating and carrier-selective layers. These stacks provide good surface passivation and selectivity thanks to the high hydrogen content and dopability of amorphous silicon, respectively. However, some drawbacks limit the cell efficiency, such as the lower conductivity of doped a-Si:H compared to crystalline silicon, low band offsets between these two crystalline phases, parasitic absorption below 500 nm due to the a-Si:H bandgap of about 1.7 eV. An interesting alternative to the doped Si:H layers is the transition metal oxide, owing to the high transparency in the ultraviolet-visible region, the high band gap and the high work function. In particular, substechiometric Molibdenum oxide, having work function higher than 6 eV and bandgap higher than 3 eV, and guaranteeing also a good passivation of silicon, represents a promising material as a hole-selective membrane, that simultaneously can limit the electrons diffusion and facilitate the holes conduction. The transparency and the conductivity of the layer are ruled in particular by presence of oxygen vacancies within the oxide lattice. Indeed, these vacancies generate defect levels in the energy gap which act as donor centers, thus increasing the free carriers. Moreover, the electron barrier is ruled by the MoO3-x work function that is strongly dependent on oxide stoichiometry. Therefore, the challenge is to find the right x value which balances the material properties to maximize its efficacy as hole selective contact. In this study, we synthesize substechiometric Molybdenum oxide, MoO3-x, thin films by UHV magnetron sputtering of an oxide target, and by controlling the film stoichiometry by the argon sputtering pressure. By increasing pressure, x value has been recorded to decrease from 0.25 to 0 by Rutherford Backscattering Spectrometry. Then, the optical characterization has been performed by spectrophotometer in the range 250-2500 nm and the electrical characterization by four point alignment probe and by current-tension curves. The correlation between stoichiometry, and thus oxygen vacancies, and the optical and electrical properties will be clearly showed. In particular, we will evidence the absorption of a peak corresponding to defect levels in the MoOx energy bandgap, related to oxygen vacancies, that decreases by decreasing x value. At the same time the electrical resistivity increases, due to the free carriers increase. The optimal stoichiometry for selective contact application will be discussed, by comparing the characteristics of different prototypes of solar cell having the deposited MoO3-x film as selective contact coupled with a thin Indium Tin Oxide layer.

Resume : Methane dry reforming (MDR) is a reaction utilizing two greenhouse gases, CH4 and CO2, and converting them into valuable synthesis gas. Big scale application of MDR is still hindered by the lack of a durable catalyst. The Ni and Co based catalysts used are often prone to coking and sintering [1]. A possibility to overcome these problems is the use of perovskite type oxide catalysts. Perovskite type oxides have the general formula ABO3. The A, as well as the B, site can be doped thus improving the properties of the catalyst. In our studies the A-site was made up from Nd and Ca. This mixture combines the good redox activity of Nd with the improvement of the defect chemistry brought into play by Ca. The B site was Fe, doped with different amounts of catalytically highly active Ni and Co. If the perovskite is exposed to reducing conditions these catalytically active metals can migrate to the surface, forming metallic nanoparticles [2]. These exsolved nanoparticles have shown to exhibit an increased resistance to sintering as well as coking [3]. We studied the behaviour of Ni and Co doped catalysts during the reaction with operando X-Ray Diffraction (XRD), in-situ near ambient pressure X-Ray Photoelectronspectroscopy (NAP-XPS) as well as catalytic tests. The aim was to assess if and when nanoparticles are formed during the reaction and how a reductive pretreatment is influencing the formation. The combination with Scanning Electron Microscopy (SEM) allowed us to characterize the exsolved nanoparticles regarding their size. The Ni doped variant of the catalyst was more active than the Co doped variant. The XRD experiments showed, the formation of a metallic phase during MDR at elevated temperatures. XPS results confirmed this behaviour and proved that the exsolution was indeed the dopants, Co and Ni, and not Fe. An analysis of the effect of an additional reductive pretreatment revealed an increase in catalytic activity by a huge margin. The main difference between in-situ exsolution and the reductive pretreatment was observed in the SEM images. The reductive pretreatment led to the formation of bigger nanoparticles. This bigger nanoparticles in turn led to an increase in catalytic activity, hinting to a correlation of nanoparticle size and catalytic activity. References: 1. Pakhare, D.; Spivey, J., Chemical Society Reviews 2014, 43 (22), 7813-7837. 2. Lindenthal, L.; Ruh, T.; Rameshan, R.; Summerer, H.; Nenning, A.; Herzig, C.; Loffler, S.; Limbeck, A.; Opitz, A. K.; Blaha, P.; Rameshan, C., Acta Crystallographica Section B-Structural Science Crystal Engineering and Materials 2020, 76, 1055-1070. 3. Neagu, D.; Oh, T. S.; Miller, D. N.; Menard, H.; Bukhari, S. M.; Gamble, S. R.; Gorte, R. J.; Vohs, J. M.; Irvine, J. T. S., Nature Communications 2015, 6. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement n° 755744 / ERC - Starting Grant TUCAS)

Resume : Today, most commercial crystalline silicon solar cells are double side contacted cells with conventional junctions and conversion efficiencies around 22 %, limited by recombination losses at the contacts. Passivation contacts have been applied to solar cells and proved to be able to overcome the efficiency bottleneck related to recombination. A big advantage is that they can passivate the entire surface of the wafer instead of localized regions. The current study shows the progress carried out in the development of SiO2/TiO2 passivating contacts for advanced silicon solar cells. To obtain a SiO2 layer in the order of 2 nm, to act as a tunnel effect barrier, dry thermal oxidation has been carried out in a tubular furnace. Several test oxidations were conducted and correlated with simulation predictions for equivalent conditions on silicon (100) [1], and then compared with ellipsometry measurements. As predicted, SiO2 thickness increases with oxidation time and temperature, through with an offset potentially justified by the pre-existing native oxide layer already measuring 1.4-2.5 nm. An e-beam evaporation system was used to stack 10 nm of TiO2 on top of the tunnel effect layer. With the aim of varying the TiO2 layer composition and interface properties, an equivalent group of samples was produced with a stack composed of an extra thin 1 nm layer of Ti over SiO2. The full stacks were finished with an ITO transparent contact for electrical probing. Raman spectroscopy analysis confirm the presence of ITO and its composition homogeneity though the contact, having the characteristic peak centered at 113 cm-1. Raman mapping was performed over the sample surface in areas of 5x5 µm2 and centered in the transition between ITO and TiO2. The two regions are clearly distinguishable from the composition point of view while presenting a sharp interface. Due to the high intensity of the Si/SiO2 peak, and reduced layer thicknesses, further dedicated experiments are being conducted to confirm the TiO2 phase after forming gas annealing. Minority carrier lifetimes were measured, and advanced electrical characterization of the samples is being performed to assess the impact of changes in the TiO2 properties and related interfaces. The authors would like to acknowledge the financial support of FCT through projects: UIDB/50019/2020 ? IDL and PTDC/CTM-CTM/28860/2017. [1] In Semiconductor materials and process technology handbook / edited by Gary .E. McGuire (pp. 48-57).

Resume : Owing to their remarkable characteristics, lead halide perovskites (LHP) offer new possibilities to outreach efficiency limits of photovoltaic devices. After a decade of optimizing LHP composition, researchers aim at improving their long-term stability. Methodic tests coupling different stress factors have enabled step-by-step improvement of the device stability, but in-depth knowledge of degradation mechanisms and resulting phases are still lacking. In the present work, we investigate the chemical and structural evolution of hybrid cation mixed halide perovskite at different scales through Photoluminescence (PL), Xray Diffraction Spectroscopy (XRD), Energy Dispersive X-ray Spectroscopy (EDS), and Cathodoluminescence (CL) analysis. We first study triple cation perovskite thin films (Cs0.05MA0.45FA0.5Pb(I0.95Br0.05)3) aged under controlled humidity. Structural (XRD) and chemical (EDS) analyses performed during aging reveal details on the degraded phase’s nature. We found a majority of PbI2, as expected, together with lead-rich inorganic phases CsPb2(Br,I)5. CL, as a highly localized optical measurement, yields responses from the different phases in the material separately. According to reference [1], perovskite emission is expected to redshift during aging due to halide segregation. However, we report here the opposite trend with a blue shift of the perovskite response with degradation. We discuss these results and draw a novel portrait of LHP’s evolution when subject to moisture. Second, we investigate powders of lead-rich inorganic compounds. These materials have raised interest as promising optoelectronic materials, but also as a dopant to enhance inorganic LHP thin film stability [2]. We report here their characterization by CL and PL measurements. Our results are in good agreement with the literature for CsPb2I5, but it remains unclear for CsPb2Br5 which demonstrates a high-energy response. A debate on the origin of its green emission is ongoing. Thus, this work comes to feed experimental studies on this controversial subject. Based on these results, we discuss the presence of lead-rich inorganic compounds in the degraded phases of perovskite films. Our results provide insight in the degradation mechanisms of perovskite thin-films and will help a better optimization of materials and device performances. [1] E. T. Hoke, D. J. Slotcavage, E. R. Dohner, A. R. Bowring, H. I. Karunadasa, and M. D. McGehee, ‘Reversible photo-induced trap formation in mixed-halide hybrid perovskites for photovoltaics’, Chem. Sci., vol. 6, no. 1, pp. 613–617, 2015, doi: 10.1039/C4SC03141E. [2] S. Caicedo-Dávila et al., ‘Effects of Postdeposition Annealing on the Luminescence of Mixed-Phase CsPb2Br5/CsPbBr3 Thin Films’, J. Phys. Chem. C, vol. 124, no. 36, pp. 19514–19521, Sep. 2020, doi: 10.1021/acs.jpcc.0c06955.

Resume : Halide perovskites offer impressively high solar conversion efficiencies and are being considered for applications as light emitters. These materials are often called “defect tolerant”, but we show that the impact of point defects on device efficiency has not been properly assessed to date. We have performed comprehensive studies for the prototypical hybrid perovskite MAPbI3 [MA=(CH3NH3)], as well as for other halide perovskites. To achieve accurate and reliable results, our first-principles calculations are based on hybrid density functional theory with spin-orbit coupling included [1]. Rigorous calculations of nonradiative recombination coefficients show the limitations of the widely adopted rule that only defects with charge-state transition levels deep in the band gap can be efficient nonradiative recombination centers. We demonstrate that the position of the level does not directly determine the capture rates, due to exceptionally strong lattice coupling and anharmonicity in the halide perovskites [2]. Our results clearly show that (1) point defects can indeed be present in relevant concentrations in the halide perovskites and (2) some of these point defects lead to nonradiative recombination rates that are just as high as in conventional semiconductors. We therefore conclude it is incorrect to call the halide perovskites “defect tolerant”. A more relevant distinction, compared to conventional semiconductors, is that halide perovskites with modest defect densities can be grown using low-cost deposition techniques. Finally, we show that point defects associated with the methylammonium molecule can act as strong nonradiative recombination centers, and we provide guidance for how this can be suppressed. Work performed in collaboration with X. Zhang, M. Turiansky, and J.-X. Shen. [1] X. Zhang, M. E. Turiansky, J.-X. Shen, and C. G. Van de Walle, Phys. Rev. B 101, 140101 (2020). [2] X. Zhang, M. E. Turiansky, and C. G. Van de Walle, J. Phys. Chem. C 124, 6022 (2020). [3] X. Zhang, J.-X. Shen, M. E. Turiansky, and C. G. Van de Walle, Nat. Mater. 20, 971 (2021). Work supported by DOE.

Resume : The ability to accurately model, understand and predict the behaviour of crystalline defects would constitute a significant step towards improving photovoltaic device efficiencies and semiconductor doping control, accelerating materials discovery and design.1 In this work, we apply hybrid Density Functional Theory (DFT) including spin-orbit coupling to accurately model the atomistic behaviour of the cadmium vacancy (VCd) in cadmium telluride (CdTe).1 In doing so, we resolve several longstanding discrepancies in the extensive literature on this species. CdTe is a champion thin-film absorber for which defects, through facilitation of non-radiative recombination, significantly impact photovoltaic (PV) performance, contributing to a reduction in efficiency from an ideal detailed-balance limit of 32% to a current record of 22.1%. Despite over 70 years of experimental and theoretical research, many of the relevant defects in CdTe are still not well understood, with the definitive identification of the atomistic origins of experimentally observed defect levels remaining elusive.2–4 In this work, through identification of a tellurium dimer ground-state structure for the neutral Cd vacancy, we obtain a single negative-U defect level for VCd at 0.35 eV above the VBM, finally reconciling theoretical predictions with experimental observations. Moreover, we reproduce the polaronic, optical and magnetic behaviour of VCd-1 in excellent agreement with previous Electron Paramagnetic Resonance (EPR) characterisation.5,6 We find the cadmium vacancy facilitates rapid charge-carrier recombination, reducing maximum power-conversion efficiency by over 5% for untreated CdTe—a consequence of tellurium dimerisation, metastable structural arrangements, and anharmonic potential energy surfaces for carrier capture. The origins of previous discrepancies between theory and experiment, namely incomplete mapping of the defect potential energy surface (PES) and approximation models, are highlighted and discussed. Importantly, these results demonstrate the necessity to include the effects of both metastability and anharmonicity for the accurate calculation of both charge-carrier recombination rates in emerging photovoltaic materials and the efficiency limits imposed by both native and extrinsic defect species. 1 Y.-T. Huang, S. R. Kavanagh, D. O. Scanlon, A. Walsh and R. L. Z. Hoye, Nanotechnology, 2021, 32, 132004. 2 S. R. Kavanagh, A. Walsh and D. O. Scanlon, ACS Energy Lett., 2021, 6, 1392–1398. 3 A. Lindström, S. Mirbt, B. Sanyal and M. Klintenberg, J. Phys. D: Appl. Phys., 2015, 49, 035101. 4 J.-H. Yang, W.-J. Yin, J.-S. Park, J. Ma and S.-H. Wei, Semicond. Sci. Technol., 2016, 31, 083002. 5 A. Shepidchenko, B. Sanyal, M. Klintenberg and S. Mirbt, Scientific Reports, 2015, 5, 1–6. 6 P. Emanuelsson, P. Omling, B. K. Meyer, M. Wienecke and M. Schenk, Phys. Rev. B, 1993, 47, 15578–15580.

Resume : AN ELLIPSOMETRIC ANALYSIS OF A SYNTHESIZED NANOSCALE LAYERED COMPOSITE WITH CONFORMAL COATING OF ALUMINIUM NITRIDE OVER THE DISTRIBUTION OF TITANIUM NITRIDE NANOPARTICLES, FOR CSP APPLICATIONS. Solar-thermal energy conversion is a promising technology that enables efficient energy harvesting from concentrated solar power (CSP). Recently, there is a lot of interest in metal- insulator based metamaterial absorbers due to the complete hold on the permittivity and permeability of these absorbers. The permittivity and permeability lean directly on the optical properties of the material that can be altered by controlling the morphology at the nanoscale. In our case, a part of the metamaterial absorber consists of near homogeneous distribution of nanoparticles (Titanium Nitride, TiN) in a matrix of (Aluminium Nitride, AlN), to form a composite. Electromagnetic wave absorbers have been investigated for many years with the aim of achieving high absorbance and tunability of both the absorption wavelength and the operation mode by geometrical control, small and thin absorber volume, and simple fabrication. The present work involves the synthesis of a composite dielectric of approximately 200 nm thickness where nanostructure control is a very challenging task. In this work, we choose a bottom-up approach of constructing a stack of, TiN nanoparticles distribution over a substrate and then a layer of AlN of 20 nm thickness, and so on. TiN particles are laid over Silicon wafer by wet chemical method and are then coated with a conformal coating of Aluminium Nitride, via Plasma- enhanced Atomic Layer deposition. These components together form the dielectric composite, where each component plays a different role in light absorption. The control of the morphology at the nanoscale is primordial to improve the material?s optical performance, thus in our case maximize the wave extinction inside the composite for the application as a solar absorber. Later, a straightforward and robust method is used to predict the optical properties of the prepared nanostructure, with high accuracy. The optical properties (n, k) of the composite are measured by Spectroscopic Ellipsometer. In order to have composite best suited for our requirement, two types of composites were prepared. One with TiN powder mixed in water as a solvent, and the other with commercially available TiN dispersions, both with a layer of AlN on top, covering the TiN particles. Both the composites were prepared in an identical way with alternate layers of TiN distribution and AlN film until a stack of approximately 200 nm was ready. In both cases, fewer clusters of 200nm to1µm of TiN particles were present however, enough steps were taken to minimize these clusters into smaller particles. In conclusion, the work presented here is the comparison of the two kinds of composites with their optical properties (n, k) measured by the ellipsometer.

Resume : Vanadium dioxide (VO2) is a promising material in the development of thermal and electrically sensitive devices due to its first order reversible metal-insulator transition (MIT) at 68 °C. Such high MIT temperature (TC) largely restricts its widespread application which could be enabled if a straightforward tuning mechanism were present. Here this need is addressed through a facile approach that uses the combined effects of temperature induced strain and oxygen vacancies in bulk VO2 colloidal particles. Simple thermal annealing process under varying vacuum is used to achieve phase transformation of metastable VO2 (A) into VO2 (M2), (M2+M3), (M1) and higher valence V6O13 phases. During this process, distinct multiple phase transition including increased as well as suppressed TC is observed with respect to the annealing temperature and varied amount of oxygen vacancies respectively. The latent heat of phase transition is also significantly improved upon thermal annealing by increasing the crystallinity of the samples. This work not only offers facile route for selective phase transformation of VO2 as well as to manipulate the phase transition temperature, but also contributes significantly to the understanding of the role played by oxygen vacancies and temperature induced stress on MIT which is essential for VO2 based applications.

Resume : The application of inexpensive and scalable materials in the industry for thermoelectric applications has received great interest, such as CuNi alloys in the last ears. Nanocrystalline CuNi alloys with different compositions were grown by pulsed electrodeposition reducing the crystallite size of the CuNi down to 30-40 nm by the incorporation of saccharine in the electrolyte1,2. The thermoelectric properties, such as electrical conductivity, Seebeck coefficient, and thermal conductivity of these nanocrystalline alloys, were studied. The maximum figure of merit at room temperature obtained was (6.4 ± 1.5) ·10-2 for nanocrystalline Cu0.65Ni0.35. The thermal conductivity of CuNi alloys was reduced by the nanostructuration to a value of 9.0 ± 0.9 W/m·K, making these nanocrystalline CuNi alloys more competitive than other more classical thermoelectric materials. This work opens a new field to be investigated, that can be described as the use of commercial alloys such as CuNi for thermoelectric applications, and shows the use of a new approach to enhance the thermoelectric properties of inexpensive and/or fewer pollutant materials. 1. C. V. Manzano*, O. Caballero-Calero, M. Tranchant, E. Bertero, P. Cervino-Solana, M. Martín González, and L. Philippe. Thermal Conductivity Reduction by Nanostructuration in Electrodeposited CuNi Alloys. J. Mater. Chem. C, 9(10), pp. 3447–3454, 2021. 2. High aspect-ratio nanocrystalline CuNi T-structures and micro-gears: Synthesis, numerical modeling and characterization. Manzano, C.V., Schürch, P., Pethö, L., Bürki, G., Michler, J., Philippe, L. Journal of the Electrochemical Society, 2019, 166(10), pp. E310–E316

Resume : Solar water splitting into hydrogen is one of the promising means for dealing with energy shortage and environmental problems. H-substituted graphdiyne (H-GDY), for the first time, is employed to fabricate a heterojunction with P25 to improve the photocatalytic activity. The obtained TiO2/H-GDY heterojunctions were characterized by XRD, EDX, TEM, XPS and UV-vis spectrums to ascertain the structure and electronic properties of the composites. Enhanced photocatalytic properties were demonstrated for the as-prepared samples. The influence of the H-GDY content on the photocatalytic activity was investigated and all the samples showed enhanced photocatalytic activity. The amount of hydrogen by the optimized heterojunctions was ~370 mmol after 6 hours test, much higher than that of pristine P25. Such enhancement was ascribed to the H-GDY/P25 heterojunction structure, which can simultaneously improve the absorption of visible light and facilitate the photo-excited electron?hole separation during the photocatalytic process. This work opens new perspectives for application of H-GDY in photocatalytic field.

Resume : Omnidirectional absorption is important to non-tracking systems designed for the harvesting of solar energy. Presently, we examine both experimentally and numerically the broadband absorption under oblique illumination driven by deep sidewall subwavelength structures (DSSS) in silicon nanopillar arrays (DSSS arrays). Specifically, we target DSSS geometries that are a built-in side effect of the top-down cyclic Bosch dry etch process employed to realize high aspect ratio silicon nanopillar (NP) arrays. We numerically compare the DSSS array with an optically-optimized straight-sidewall nanopillar array (SSNP array) under oblique illumination. We show how the presence of DSSS generates a higher absorptivity particularly for the spectral range >600 nm, induces the formation of absorptivity peaks at the near-infrared spectral range, and overall provides an enhanced omnidirectional broadband absorption. We experimentally show that the specular reflectivity and the total reflectivity of silicon DSSS arrays that were fabricated using a top-down Bosch dry etch process is significantly lower compared with that of the corresponding SSNP arrays. Specifically, we show a decrement in the broadband specular reflection of up to 30% for certain angles of illumination, and about 13% decrement in the total reflectivity.

Resume : Supercapacitors have become in one of the most promising energy storage and conversion devices with high power densities. Among the parts of a full supercapacitor device, the electrode is considered the key component which directly affects the electrochemical performance of a supercapacitor. In this context, transition metal oxides and hydroxides have been explored as a material for supercapacitor electrodes due to their high conductivity. Among them, the most commonly used electroactive materials are MnO2, Co3O4, NiO, Co(OH)2 or Ni(OH)2. By controlling the experimental conditions such as morphology, size or composition high-performance supercapacitors can be fabricated. In this work, Sn doped Ni(OH)2 nanostructures have been synthesized following a modified hydrothermal method which allows to control not only the Sn composition but also the formation of α- and β-Ni(OH)2 polymorphs. By controlling the experimental conditions such as Sn concentration, temperature, pH, or time reaction, different Ni(OH)2 polymorphs (α and β) have been obtained as has been confirmed by XRD and Raman spectroscopy. TEM analysis showed that undoped Ni(OH)2 is formed by nanoplatelets with dimensions around hundreds of nm, while Sn incorporation induces the formation of elongated structures in form of nanobars with lengths between 40 and 100 nm. Moreover, compositional mappings showed a homogeneous distribution of Sn for all the doped samples. Electrochemical measurements showed a maximum specific capacitance of 1870 F/g for the sample with lowest Sn content. The superior performance of this sample is attributed to the lower charge resistance confirmed by EID measurements. These results confirm that Sn doped Ni(OH)2 can be considered as alternative active materials with promising applicability as electrode in supercapacitors.

Resume : The rapidly depleting fossil resources and an ever-increasing demand for energy consumption around the world have resulted in the need for alternative sustainable and renewable energy resources. Among the developed electrochemical energy storage devices, supercapacitors (SCs) have been attracting a great deal of attention due to their unique features like high power output, rapid charging, and durability. However, the relatively low energy density of SCs still needs to be improved in view of their practical applications. Since active materials are crucial in achieving the high energy density of SCs, one should come up with a nice strategy to prepare them with high theoretical capacity, high redox-active, and good electrical conductive properties. Among the variable materials, bimetallic layered double hydroxides (LDHs) are most notable owing to their promising redox properties as well as facile preparation. In this presentation, we have synthesized the bimetallic LDH nanowires (NWs) directly on carbon cloth using a facile hydrothermal method. Furthermore, a metal sulfide nanolayer was wrapped over these NWs by a simple electrodeposition technique. The as-obtained composite material with redox properties of both bimetallic LDH and metal sulfide exhibited a noteworthy electrochemical response in a three-electrode system. Moreover, a pouch-type hybrid SC was fabricated with this composite material as a positive electrode and activated carbon as a negative electrode, which also demonstrated a superior energy storage performance along with notable energy density.

Resume : With the issues of global warming, energy crisis, and environmental pollution, there has attracted a lot of attention for developing clean and renewable energy storage/conversion systems, such as fuel cells, supercapacitors, and batteries. In this presentation, the nickel molybdenum phosphide (NMP) nanoparticles supported by graphene sheets directly grown on nickel foam were prepared by a facile hydrothermal method. Moreover, the structure and morphology of NMP-graphene oxide (GO) material were investigated by SEM, XRD, and TEM analyses. The optimized NMP-GO electrode material revealed enhanced specific capacity as compared to pristine NMP. Furthermore, the NMP-GO electrode material delivered an excellent specific capacity of 159 mAh g-1 at a current density of 1 A g-1. The fabricated pouch-like asymmetric supercapacitor (ASC) device exhibited improved rate capability, power density, and energy density as well as ultra-stable cycling performance. Also, various portable electronic devices were powered up using the ASC devices to test real-time applications. Distinctly, the obtained better results strongly suggest that the NMP-GO-based electrode materials are very promising for energy storage applications.

Resume : Fibre-shaped architectures/fibre assemblies have emerged as promising candidates as electrodes for energy storage devices, with improved rate capability and with the potential to out-perform traditional laminate/planar counterparts. Carbon nanotube (CNT) containing fibres have the potential to produce strong and highly electrically conducting devices and allow for a greater control over fibre properties through synthesis. In particular, solution spinning has been proven to be a versatile technique for producing tough, high performance CNT fibres. Fibre properties can be selectively tailored through altering the chemistry in the spinning dope and during the coagulation step in addition to varying the spinning conditions; to attain optimised fibres with maximal electrochemical and mechanical properties [1,2]. CNT-based fibres have been produced using surfactant-containing dispersions [3], by strong acid protonation [4], and via single-walled carbon nanotube (SWCNT) solutions prepared using reductive chemistry [5], producing strong and conductive fibres. In all methods of synthesis, CNT individualisation was critical to producing a high-performance fibre. In this research, neat SWCNT fibres are fabricated by means of solution spinning, serving as microelectrodes for proposed fibre-shaped supercapacitor devices. These fibres are both load bearing and display superior capacitive behaviour (40 F/g in aqueous electrolyte). [1] J. J. Vilatela, R. Marcilla, Tough Electrodes: Carbon Nanotube Fibers as the Ultimate Current Collectors/Active Material for Energy Management Devices, Chem. Mater., 2015, 27 (20), 6901-6917. [2] X. Zhang, et al., Understanding the Mechanical and Conductive Properties of Carbon Nanotube Fibers for Smart Electronics, Adv. Mater., 2020, 32, 1902928 (1-21). [3] B. Vigolo, et al., Macroscopic Fibers and Ribbons of Oriented Carbon Nanotubes, Science, 2000, 290, 1331-1334. [4] L. M. Ericson, et al., Macroscopic, Neat, Single-Walled Carbon Nanotube Fibers, Science, 2004, 305, 1447- 1450. [5] A.J. Clancy, et al., Reductive Dissolution of Supergrowth Carbon Nanotubes for Tougher Nanocomposites by Reactive Coagulation Spinning, Nano, 2017, 9, 8764-8773.

Resume : Energy-autonomous electronic devices (termed Internet of Things, IoT) call for novel integrated systems that are able to harvest, store and release energy. This can be achieved by coupling a photovoltaic energy harvester with a storage unit. The intermittency of the energy source and consumption requires the storage device to operate efficiently under fast charging and discharging conditions, which is a characteristic of a capacitive system but not a battery. In particular, electric double layer capacitors (EDLCs) deliver much faster power output as they do not suffer from slow solid-state diffusion reactions or redox process. An interesting approach to achieve energy autonomy is to combine the IoT device with a photovoltaic (PV) solar cell and a charge storage unit, such as an EDLC. The solar cell converts ambient light into an electric current to charge the storage unit, which then in turn supplies the IoT device. This allows for applications in a wide variety of environments, whether it be outdoors or indoors. Such a hybrid system is usually realised via modular coupling, where a PV cell is wired to an EDLC, using a total of four electrodes (two for the solar cell and two for the storage unit).1 The additional circuitry introduces energy loss, and further downsides include complex packaging and design. We approach this problem by developing a monolithic photorechargeable supercapacitor. It consists of a p-i-n halide perovskite solar cell integrated in a three-electrode configuration with an electrochemical double layer capacitor (EDLC) that has mesoporous N-doped carbon nanospheres (MPNC) as the active electrode material. Due to the large surface area, well-defined mesoporous structure and homogeneous particle size of the MPNC material, the EDLC shows both a high capacitance, resulting in large energy and power densities (3.3 Wh kg 1 and 2.6 kW kg 1 @ 5 mA cm 2) and high (95 %) coulombic efficiency.2,3 Using a sequence of layers that optimizes charge transport while minimising material degradation, we integrated the EDLC with a 12.5 % efficient, large-area (1 cm2) perovskite solar cell. The resulting photosupercapacitor exhibits fast (< 5 s) photocharging up to 1 V under 1 sun illumination and an outstanding overall energy conversion efficiency of 11.8 %. Our results show high potential for such integrated energy-harvesting and storage systems to help pave the way towards energy-autonomous devices. [1] Zeng, Q.; Lai, Y.; Jiang, L.; Liu, F.; Hao, X.; Wang, L.; Green, M. A. Adv. Energy Mater. 2020, 10 (14), 1. [2] Melke, J.; Schuster, R.; Möbus, S.; Jurzinsky, T.; Elsässer, P.; Heilemann, A.; Fischer, A. Carbon N. Y. 2019, 146, 44–59. [2] Melke, J.; Martin, J.; Bruns, M.; Hügenell, P.; Schökel, A.; Montoya Isaza, S.; Fink, F.; Elsässer, P.; Fischer, A. ACS Appl. Energy Mater. 2020, 3 (12), 11627–11640.

Resume : CeO2 is a promising material for many catalytic applications due to its ability to store and release oxygen at ease. The reactivity of ceria towards H2 dissociation can be altered by doping it with cationic species such as Ag, Au and Cu. Ceria doped with such metals reduces the activation energy for the dissociation of H2 and becomes a potential candidate for electrode material in fuel cells. In this work we investigate the reactivity of Cu-modified ultra-thin epitaxial CeO2 films on Pt (111) towards H2 dissociation in UHV conditions. The films are prepared by reactive MBE and XPS is used to study the changes in the oxidation state of Ce ions, O vacancy formation and hydroxyl group formation on the surface after thermal reduction cycles in H2. Cu-modified ceria films showed a higher concentration of Ce3+ after thermal treatments under H exposure and a lower activation temperature (470 K-570 K) than the Ag-modified and pure CeO2 films previously investigated [1]. The observed reactivity of the films is higher in presence of a pure CeO2 buffer layer, due to confinement of Cu atoms on the surface, in agreement with theoretical predictions [2]. A significant increase in OH concentration on the surface is observed with the increase in thermal reduction temperature in H atmosphere. STM results show no significant changes in the surface of Cu-modified ceria films after all reducing thermal treatments. [1] S. Benedetti et al., ACS Appl. Mater. Interfaces 12, 27682 (2020) [2] G. Righi et al. J. Phys. Chem. C 123, (2019) 9875

Resume : The triboelectric nanogenerator is one of the key technologies to efficiently harvest small-scale mechanical energy into electricity. Moreover, hybridizing triboelectric polymer with piezoelectric materials can enhance the electrical output of nanogenerators. In this regard, an efficient hybrid nanogenerator (HNG) was fabricated using the dopamine (DA) modified tin oxide (SnO2)/PVDF composite films. Initially, the SnO2 particles were synthesized using the hydrothermal synthesis method and their surface with a layer of DA was further modified. It is well known that the SnO2 and PVDF are piezoelectric materials that are efficiently used in nanogenerator fabrication. However, modifying the SnO2 particle surface with DA before loading into the PVDF polymer enhances the composite film properties, resulting in an enhanced electrical output. An HNG was fabricated using the DA modified SnO2/PVDF composite film and operated against PTFE. Furthermore, the effect of DA-SnO2 concentration in the PVDF was systemically studied. The maximum electrical output produced by the HNG is higher than the PVDF and SnO2/PVDF composite film-based HNGs. Additionally, the mechanical stability and durability of the HNG were investigated. To verify the practical applications of the HNG, the mechanical energy available in everyday human life was harvested to power various portable electronics.

Resume : The search for efficient materials for energy conversion and storage critically depends on novel protocols for materials discovery, simultaneously allowing for efficient property prediction, including static and dynamic properties. While crystal structure prediction of dense crystalline materials is reasonably straightforward, finding metastable and porous carbon materials remains a challenge; however, these material are of fundamental importance for energy storage and specifically for Li-ion batteries. Furthermore, better open-framework carbons can be considered for larger ions, simplifying the technology transfer from Li- to Na-based batteries. Here we demonstrate a novel strategy for crystalline and porous carbon framework prediction, which can facilitate the discovery and synthetic design of novel carbons. Therein, the concept of tiling of an underlying 2D, hyperbolic manifolds is used as a mathematical guidance to design frameworks ab initio, leveraging topological enumeration measured by the surface genus. Overall, a large number of carbons can be suggested, with important applications in transport and energy storage, including even nanoelectronics, due to distinguished, low-dimensional electronic properties. This large class of gaphenoid structures is demonstrated to perform well as Li or post-Li intercalation material by molecular dynamics simulations.

Resume : Overcharge of lithium-ion batteries (LIBs) not only causes irreversible battery degradation and failure but can also trigger disastrous thermal runaway. This paper presents a systematic investigation of the electrical and thermal behaviors of LIBs during overcharge up until thermal runaway, and reveals the underlying physical, structural, and chemical changes at each electrode at different stages of overcharge using microscopic and spectroscopy characterizations. The overcharge process for LIBs with Li(Ni0.6Mn0.2Co0.2)O2 cathode can be divided into four stages: Stage I involves the decomposition of LiMnO2 into MnO and LiNiO2 into NiO, accompanied by a slight collapse of the cathode. In stage II, the cathode forms a relatively stable hexagonal phase H3 while lithium plating occurs on the anode surface. NiO and Ni(OH)2 decompose into metallic Ni and release a lot of heat. In stage III, MnO2 is present on the cathode which is irreversibly damaged, and an unstable substance LiH is produced on the anode that accelerates the onset of thermal runaway. In stage IV, the battery ruptures at approximately 174 % state of charge (SOC), followed by thermal runaway in just 20 s. During overcharge, the crystallinity of the cathode is found to be linearly corelated with SOC.

Resume : The expansion of the field of applications of lithium-ion batteries as power sources and the future problem of limited lithium resources requires the development of new electrode materials with high capacity and energy density, but also replacement of lithium with cheaper and abundant sodium [1]. Simple substitution of lithium to sodium is impossible due to some problems. Also, standard graphitic anode materials for lithium-ion batteries are not suitable for use in sodium-ion batteries (SIBs) of the low capacity and absence of intercalation. However, different defects (vacancies, atom-dopants) in graphene planes and large interplanar distance promotes sodium intercalation. Among carbon materials, porous carbons (PCs) have a developed surface and the presence of pores, into which they can serve as additional pathways for sodium diffusion and adsorption. In our work, we propose to use brominated nitrogen-doped porous carbon as anode material for SIB. Nitrogen-doped carbon materials have proven themselves for lithium and sodium ion storage, and bromination can introduce the C-Br group affecting the capacity of PCs. At the first stage, porous nitrogen-doped carbon materials (N-PC) were synthesized by acetonitrile vapor deposition on the products of thermolysis of calcium tartrate, adipate, and glutarate at different synthesis temperature 650-850 °C to optimize the synthesis conditions and select the optimal material morphology for anodes SIB. Based on the results of testing and studying the composition and structure of the samples, a synthesis temperature of 750 °C was chosen. N-P?s were brominated using molecular bromine at room temperature. The study of the electronic state of the samples showed that in all porous carbons, bromine is contained in two main forms ? intercalated molecular bromine (Br2 and Brn) and covalent C-Br bonds. N-PC synthesized using calcium tartrate after bromination demonstrated the best performance in SIB of 245 mAhg-1 at 0.1 Ag-1, which is 40% more than the capacity of the original N-PC. Cyclic voltammetry and electrochemical impedance spectroscopy studies have shown that bromine is involved in the accumulation of sodium ions at different potentials 1.5 and 2.1 V for C-Br and Brn species, respectively. In conclusion, the bromination of nitrogen-doped porous carbons is an effective technique for improved sodium-ion storage performance. The work was conducted with financial support from the Russian Science Foundation (Grant 19-73-10068). References 1. A.A. Fedosova, S.G. Stolyarova, Y. V. Shubin, A.A. Makarova, A. V. Gusel?nikov, A. V. Okotrub, L.G. Bulusheva, Sodium storage properties of thin phosphorus-doped graphene layers developed on the surface of nanodiamonds under hot pressing conditions, Fullerenes Nanotub. Carbon Nanostructures. 28 (2020) 335?341.

Resume : The rapid technological development of electric vehicles and large-scale energy storage technologies requires electrochemical devices with a high energy and power metrics Such parameters can be delivered by hybrid metal-ion capacitors (MICs), which combine the advantages of metal-ion batteries (MIBs) and electrical double layer capacitor (EDLCs), by incorporating a highly porous EDL electrode (from activated carbon – AC) and a battery-type anode where alkali ions are reversibly inserted/deinserted. Nonetheless, one of the main issues existing in the development of MICs is the finding of an appropriate pre-metallation method of the anodic host. A recently suggested strategy is to incorporate sacrificial metal oxides or metal salts (from which metal ions can be irreversibly extracted and transferred to the negative electrode by electrochemical oxidation) in the positive electrode [1-4], leading to the realization of the MICs. However, the sacrificial materials should fulfill four important criteria: (i) exhibit a low extraction potential of the metallic ions to limit the risks of electrolyte oxidation; (ii) display a high irreversible capacity to reduce as much as possible the eventually remaining dead mass; (iii) should be stable in air for the easiness of electrodes manufacturing; and (iv) the residue should preferably be an inert gas or eventually a neutral liquid which remains dissolved in the electrolyte. Since squarates offer the essential advantage of stability in air - resulting in the simplification of the electrodes fabrication, as well as an oxidation potential ca. 4.0 V vs. Na/Na+ [4], our objective was to better identify the oxidation products of Na2C4O4 and further to incorporate it in AC-Na2C4O4//Sn4P3 cells for the presodiation of the Sn4P3 alloy anodic material, and thereof realize Na-ion capacitors (NICs). The irreversibility of sodium extraction was confirmed by cyclic voltammetry and galvanostatic charge/discharge, with a capacity of 342 mAh g-1, close to the theoretical one of 339 mAh g-1. Remarkably, the gaseous oxidation products of the C4O42- anion were identified as CO and CO2 by operando electrochemical mass spectrometry, whereas the presence of carbon blended in the electrode (produced by the disproportionation of CO) was proved by Raman spectroscopy and nitrogen adsorption/desorption at 77 K. The NICs resulting from the oxidative sodium transfer were then cycled at 0.18 A g-1 (per total mass of the electrodes) in the voltage range from 2.0 V to 3.8 V, demonstrating an excellent capacitance retention of 94% after 11,000 cycles. Such a remarkable life span of these NICs was ascribed to the CO2 oxidation product of the C4O42- anion, which allowed a Na2CO3 S.E.I. layer passivating very efficiently the anode surface to be formed. Hence, using Na2C4O4 shows great advantages over other sacrificial materials owing to the simultaneous simplification of the cell construction and improved properties of the NICs. Acknowledgment The authors acknowledge the financial support of the HYCAP project by the Foundation for Polish Science (research grant POIR.04.04.00-00-3D6F/16-00). References [1] X. Pan et al., Electrochim. Acta 318 (2019) 471-478. [2] P Jeżowski, et al., J. Mater. Chem. A 4, 32 (2016) 12609-12615. [3] D. Shanmukaraj et al., Electrochem. Commun. 12 (2010) 1344-1347. [4] M. S. Park et al., Adv. Energy Mater. 1 (2011) 1002-1006.

Resume : Cubic silicon carbide (3C-SiC) is a promising material for passivating contacts with low parasitic absorption as demonstrated in ref [1] for films deposited by hot wire chemical vapour deposition (HWCVD). In this contribution, we investigate the deposition with the more common plasma enhanced CVD using MMS as precursor gas on crystalline Si wafers covered with a passivating layer of SiO2. We studied the impact of the discharge parameters (e.g. plasma power, frequency, substrate temperature, gas flows) on the layer properties and we investigated the effect of thermal treatments similar to the ones in the current solar cell manufacturing. From ellipsometry and X-ray reflectivity we conclude that dense layers require discharge conditions with a high density of H radicals. These are obtained for a high H content in the plasma and for the combination of high discharge power and frequency. Based on the obtained results, we propose a model similar to the selective etching model used for poly-Si growth by PECVD. Annealing between 850 and 900 °C promotes the formation of nanocrystalline domains in the layer, X-Ray diffraction suggests a size of 1.5 to 2 nm. Preliminary results on surface passivation suggest the need of a buffer layer to protect the interfacial oxide against damage by the H-rich plasma. [1] Köhler, M., Pomaska, M., Procel, P. et al. A silicon carbide-based highly transparent passivating contact for crystalline silicon solar cells approaching efficiencies of 24%. Nat Energy 6, 529–537 (2021). https://doi.org/10.1038/s41560-021-00806-9

Resume : The search for optimal light absorbers based on halide perovskite materials expanded significantly since the synthesis of 2D-3D perovskites. Incorporating larger organic cations brings several advantages, such as introducing hydrophobic moieties, thus enhancing the chemical stability [1]. Also, increasing the size of the cations their mobility is reduced, which can be used to mitigate hysteretic effects in perovskite solar cells. Given a wide range of organic cations which can be incorporated, systematic studies are required for assessing both opto-electronic and stability properties. Here, we investigate the class of 2D halide perovskites of formula A'(2)A(n-1)B(n)X(3n 1), where A' and A are the alkyl-ammonium (e.g. up to penthyl- and hexylammonium) and methylammonium cations, respectively, and X = I, Br, Cl. Several compositions are investigated first by ab initio density functional theory calculations and the most promising candidates are synthesized, followed by optical and structural (XRD) characterizations. Using DFT simulations we perform an analysis regarding the optimal absorption and the stability properties based on the calculation of formation energies. In addition, we perform stability tests, by monitoring the structural changes following finite temperature treatments. [1] A.G. Tomulescu et al., Sol. Energy Mater. Sol. Cells 227, 111096 (2021) Acknowledgement: This work was supported by a grant of the Romanian Ministry of Education and Research, CCCDI - UEFISCDI, project number PN-III-P2-2.1-PED-2019-1567, within PNCDI III and has received funding from the EEA Grants 2014-2021, under Project contract no. 36/2021.

Resume : The Era of the IoT and the paradigm of Sustainable Energy boosted the search for self-powered devices that harvest and store energy to satisfy the electrical needs of the generation of autonomous wearable electronics.1,2 Thermally-chargeable supercapacitors are a clean energy technology that is able to convert the waste thermal energy into electrical energy (as a power source) and, simultaneously, store that energy (as an energy storage system). These hybrid devices allow converting the waste thermal energy provided from low-grade heat sources (e.g., human body) into electrical energy by a thermally-induced migration of electrolyte ions towards the device electrodes based on the Soret effect.1–3 Herein, we report on the fabrication of a thermally-chargeable textile supercapacitor (TCTSC) composed of two multiwalled carbon nanotube-coated cotton electrodes (MWCNT@cotton) and an all-solid-state ionic polyelectrolyte (PVA/H3PO4). The MWCNT@cotton electrodes were prepared by directly coating the cotton substrates with a MWCNTs dispersion through a scalable textile industry process. The ionic conductivity of PVA/H3PO4 electrolyte was tuned by doping the PVA matrix with different wt% of H3PO4, unveiling an ionic conductivity value of 39 mS/cm for a PVA/H3PO4 ratio of 1:1 (m/m). The TCTSC was fabricated by sandwiching the ionic electrolyte between the MWCNTs/cotton electrodes. The thermally-induced power generation of the TCTSC was evaluated, reaching a Soret coefficient of ~2 mV/K (up to 30 mV for an applied temperature gradient of 25 K). Concerning the energy storage features, the TCTSC presented an electric double-layer charge storage mechanism, affording a working voltage of 2.27 V and an energy density of 4.33 Wh/kg at a power density of 620 W/kg. The high flexibility and the efficient performance of the TCTSC, combined with the scalable and cost-effective fabrication process, make this device a feasible solution to satisfy the challenges of autonomous wearable electronics. Acknowledgements: This work was funded by FEDER – European Regional Development Fund through COMPETE 2020 – Operational Programme for Competitiveness and Internationalization (POCI) and by Portuguese funds through Fundação para a Ciência e a Tecnologia (FCT)/MCTES under Program PT2020 in the framework of the projects PTDC/CTM-TEX/31271/2017 and NORTE-01-0145-FEDER-022096. This work was also funded by projects UIDB/50006/2020 and UIDB/04968/2020 through FCT/MCTES. R.S.C. thanks the MSc. grant funding from FEDER through project POCI-01-0247-FEDER-039833. A.L.P. thanks the junior researcher contract funded by European Union’s Horizon 2020 Research and Innovation Programme under Grant Agreement No. 863307 (H2020-FETOPEN-2018-2019-2020-01). C.P. thanks FCT for FCT Investigator contract IF/01080/2015. 1X. Pu et al., Chem. Sci. 2021, 12 (1), 34–49. 2A.L. Pires et. al., ACS Appl. Electron. Mater. 2021, 3 (2), 696–703. 3M. Falk et al., Biosens. Bioelectron. 2019, 126 (July 2018), 275–291.

Resume : The amount of solar energy reaching the Earth exceeds the energy of all the world's reserves of non-renewable energy sources. The potential of solar energy is so great that the part of it that comes to Earth in one minute is enough to meet the current energy needs of mankind for a whole year [1]. The main barrier preventing widespread use of solar cells is the high cost of the generated electricity. A promising direction for reducing the cost of photovoltaic electricity is the development of technology for silicon solar cells having various antireflecting and passivation layers [2]. The production of solar cells based on mono- and polycrystalline silicon is 83% of the total cell production. Much of the work is currently devoted to reducing the reflection of incident light, which is almost 40% in traditional silicon wafers [2]. The creation of chemically textured Si pyramids makes it possible to additionally capture and absorb the energy of the solar spectrum due to diffuse scattering of light [3]. The proper selection of a material, along with a method of cost-effective fabrication of nanostructures, is the key to improving antireflection properties and the system performance at film integration on micro-structured Si surfaces [4]. However, to obtain a surface with improved self-cleaning properties and two-level roughness, the Si pyramids must be fine-tuned further by applying a suitable film of nano-sized thickness to their textured surfaces. ZnO films with suitable thickness on textured Si surfaces not only deliver self-cleaning properties, but also serve as an anti-reflective layer, which is significant for improving the efficiency of a solar cell by reducing reflection loss. The main objectives of the given study were the theoretical calculations and experimental investigation of thin ZnO films deposited using DC magnetron sputtering of Zn target, both on the flat surface of a single-crystal Si (100) substrate and Si pyramidal structures obtained by chemical etching. ZnO films of various thicknesses have been investigated using Lumerical Finite-Difference Time-Domain (FDTD) and synthesized by magnetron sputtering at a power of 100 W and an adjustable deposition time from 300 to 1200 s. The film thickness of 70-80 nm (namely 74 nm) was found to be most suitable both theoretically and experimentally. The use of ZnO films on arrays of pyramids ranging in size from 0.5 to 1.5 microns led to a decrease in reflection to 0.08-5.42% in the wavelengths region of 300-800 nm. The synthesized ZnO films on Si pyramidal structures were investigated using X-ray reflectometry, IR spectroscopy, spectrophotometry and atomic-force microscopy (AFM). 1 Gaewdang T., Wongchaoen N. IOP Conf. Ser.: Earth Environ. Sci. 463 2020. 012074. 2 Green M.A. Prog. Photovoltaics 17 (3) 2009. 183−189. 3 Sharma D., Bhowmick S., Das A., Kanjilal A., Saini C.P. Mater. Res. Express 6 2019. 095047. 4 Yan Y.Y., Gao N., Barthlott W. Adv. Colloid Interface Sci. 169(2) 2011. 80–105.

Resume : The cathode microporous layer (MPL), as one of the key components of the proton exchange membrane fuel cell (PEM-FC), requires specialized carbon materials to produce the two-phase flow and interfacial effects. In this respect, we designed a novel MPL based on super-hydrophobic nitrogen doped carbon nanowalls. Employing radio-frequency plasma deposition techniques directly on carbon paper we produced high quality microporous layers at competitive yield-to cost ratio with distinctive MPL properties: high porosity, good stability, considerably durability, super-hydrophobicity and substantial conductivity. Platinum-ink, serving as fuel cell (FC) catalyst, was directly sprayed on the MPLs and incorporated in the FC assembly by hot-pressing against a polymeric membrane. The integrated PEM-FCs were tested in a single cell PEM-FC on a BT-112 Single Cell Test System, showing power performance comparable to industrial quality membrane assemblies (0.33 W/cm2), with elevated working potential (0.95 V) and impeccable fuel crossover for a low-cost system resulting from a highly scalable, inexpensive, and rapid manufacturing method. Acknowledgements: This work was financially supported by UEFISCDI Romania, in the frame of the projects: PN-III-P1-1.1-PD-2019-0684 contract 106PD/2020, PN-III-P1-1.1-PD-2019-0540 contract 103PD/2020, PN-IIIP1-1.2-PCCDI-2017-0387 contract 80PCCDI/2018, PN-III-P1-1.2-PCCDI-2017-0619-contract 42PCCDI/2018, PED 271/2020, TE 205/2021 and Core Programs: PN 16N/2019 LAPLAS VII

Resume : Nanowires have exceptional promise for solar cell applications. Photovoltaic systems are the ideal method to harvest solar energy, but market-leading Silicon solar cells have limited potential for improvement in efficiency. The most promising class of materials is Cu(In,Ga)Se2 (CIGS): they are lighter, flexible, and significantly cheaper to produce, with a tunable direct bandgap and a high absorption coefficient in the visible spectrum. A record cell efficiency of 23.35% was demonstrated, but it is still more than 10% lower than the Shockley-Queisser theoretical performance limit (33.7%). Additionally, CIGS semiconductors contain indium, a relatively rare element. The use of nanowires (NW) as the PV absorber material can help in both these areas. In fact, they allow ~10x lower material consumption, thanks to high absorption-to-volume ratio through light-trapping, as well as an enhanced performance compared to planar layers1. It is well-known that the use of co-evaporation under vacuum is essential to obtain high-quality materials for CIGS solar cells2, thus we have focused on Molecular Beam Epitaxy deposition. By using an Al2O3 mask, we achieved position controlled growth of isolated CuInSe2 nanostructures. We are currently working on elongating the structures to obtain true 1D morphology, determining their crystalline structure by Transmission Electron Microscopy, and developing solar cell devices based on the nanostructures. 1 J.E.M. Haverkort, E.C. Garnett, and E.P.A.M. Bakkers, Applied Physics Reviews 5, 031106 (2018). 2 P. Jackson, R. Wuerz, D. Hariskos, E. Lotter, W. Witte, and M. Powalla, Physica Status Solidi (RRL) 10, 583 (2016).

Resume : New functional materials combining stability, resistance to degradation, and efficiency with reasonable cost and ease of synthesis are crucial for their use in renewable energy applications. In catalysis, active metal nanoparticles dispersed on oxide surfaces are of fundamental interest to overcome the use of bulk noble metals. However, these bear the substantial limitations of the conventionally employed “top-down” deposition techniques, resulting in loss of activity and performance during operation. Exsolution, i.e. metal atoms that, in a reducing environment, segregate to the surface from sites within a host oxide lattice to generate anchored nanoparticles, has proven a successful strategy to overcome such issues. However, many questions remain regarding their growth mechanism and the crystal structure evolution of the host during the reduction process. Here, the SrTiO3 perovskite has been doped with iridium (∼0.5 wt. %) at the B-site and subjected to reducing conditions required for exsolution. Ex situ characterization with a range of techniques including XRD, XPS, SEM, HR-TEM, and STEM–EDX showed that iridium metal nanoparticles are grown on the STO surface with the unique characteristic of “socketing” to the host lattice. In situ TEM studies allowed to monitor in real time nanoparticle exsolution, enabling us to deepen our understanding on the mechanistic steps involved, and to gain insights in the crystallographic behaviour of both the host lattice and the exsolved nanoparticles at the atomic scale, which is of fundamental importance in order to tailor materials design for better reactivity. The exsolved materials were tested for emission control (CO oxidation) catalysis, for which they approached 100% conversion at 450 °C. When benchmarked against a commercially available material (1% Ir/Al2O3), the exsolved samples showed a more gradual increase in activity with temperature as compared to the commercial reference sample, and also as compared to similar noble metal systems in the literature. Nevertheless, the exsolved samples showed high activity despite having nominally only half the noble metal loading (0.5% Ir-SrTiO3). Overall, this work provides a novel structure where the design of Ir-based perovskites with an extremely low noble metal amount (∼0.5% weight) is made possible by Ir incorporation in the lattice, subsequently exsolved as metallic NPs. These are reported to display catalytic activity for the CO oxidation reaction when compared to the unreduced 0.5% Ir-STO material, demonstrating that the emerged nanoparticles are responsible for the catalytic activity of this material. Overall, the distinctive socketing between the metal catalyst and the STO support, and the performance of the 0.5% Ir-doped STO reported here show promise for this material to be tested for other catalytic applications, such as water splitting, electro- catalysis for OER, and reforming reactions for syngas and/or hydrogen production.

Resume : Hybrid perovskite solar cells (with chemical formula ABX3) are of great interest due to the recently measured power conversion efficiency of greater than 25% (but theoretically, 33.7%). Perovskite structures are easily customisable, with a range of options for A, B and X. This enables us to both tune the electronic band gap and the stability by varying the composition. Two promising perovskites are the CH3NH3PbI3 (MAPI) and CH(NH2)2PbBr3 (FAPB) structures. By varying the ratio of FA and MA and doping with Br, we can potentially tune the band gap and effective masses (and hence electronic transport). In order to compromise for a more desirable bandgap for stand-alone PV and better structural stability, the hybrid perovskite constituents are then strategically layered into superlattice form. We explore the bulk properties and interfacial engineering to improve the material’s electronic transport. We present a theoretical investigation of the structural and electronic properties of MAPI(x)/FAPB(y) superlattice, performed using first–principles density functional theory and temperature dependent vibrational entropy correction. Our results show that dominating number of layers of FAPB over MAPI will decrease the band gap. We discuss why the formation energies of superlattice in hexagonal and cubic phases differ across temperature and contradicts from the ones of its ground-state constituents. The solutions will be suggested for experimental validation.

Resume : Given the wide capability of small positive ions (H+ and Li+) intercalation, WO3 represents a promising material for energy storage applications. In this scenario, nanostructured WO3 is extremely interesting due to its high surface-to-volume ratio allowing a high rate of charge transfer in supercapacitors with hexagonal crystal structure confirmed by XRD investigation and drop coated onto an appropriate substrate. Growth optimization against time, pH and temperature of synthesis allowed to get a stable morphology. A large electrochemical study (employing by cyclic voltammetry, electrochemical impedance spectrometry and galvanostatic charge discharge analysis) allowed to study firstly the mass dependence of electrochemical properties and then allowed to measure quantitative performances of WO3 nanorods in terms of specific capacitance (Cs). These data are presented and discussed.

Resume : Solar energy is a potential avenue to mitigate several planet crises, such energy supply and production. Global population is reaching ≈ 9 billion for 2050, with an expected electricity consumption of 28 TW. Therefore, harvesting and storing solar energy is regarded as a suitable solution for the energy crisis.1 Photocatalysis as a state-of-the-art technology has exhibited reasonable harvesting of solar energy, allowing chemical transformations to generate solar fuels, such as hydrogen (H2), a key vector for the foreseen low-carbon economy due to its high energetic density ca. 142 MJ/kg.2 A single catalyst exhibiting an efficient solar-to-photon conversion remains as the bottleneck for further technological development.3 Despite of using benchmark semiconductors (SCs), such as Titanium dioxide (TiO2) still do not surpass the needed efficient conversion. TiO2 limitations are described as water oxidation overpotential, large band gap i.e., 3.2 eV, and only UV light absorption. Thus, adding a metal (M) onto a SC, as TiO2, creates an interesting Schottky junction, regarded as one state-of-the-art approach in Materials Science to enhanced solar energy conversions. One relevant feature on the new interphase junction is the expected enhancement of SCs photoactivities in the order of 10-100 folds than the SC efficiency alone.4 Remarkably, the materials design aims at increasing the limited light absorption of TiO2 by plasmonic effects, to create an intimate M/SC interphase contact to promote new electronic paths and increase the amount of co-catalytic sites along the support surface.5 In this work, two scientific contributions are in evidence. The Schottky materials’ strategy and a new gas tight photochemical cell reactor. The latter was developed for acquiring accurate H2 photoproduction and to correlate the physico-chemical properties of the formed Schottky junctions with their activity. The as-synthesized composites (M/ TiO2, M: Pd. Pt, and Au) with varied M loading 0.5, 1, and 2 wt.% were characterized by X-ray scattering, Transmission electron microscopy, Infrared, UV-vis, Ultraviolet / X-ray photoelectron spectroscopies and Inductively coupled plasma. The ICP results confirm the expected M loadings, thanks to the controlled two-pot M reduction/deposition method. TEM results exhibited average M NPs sizes from 2 to 5 nm. Moreover, the photocatalytic H2 production was quantified over time, exhibiting rates of 13, 10, and 7 mmol h-1 gcat-1 for the highest loading, e.g., 2wt.% (Pd, Pt, Au)/TiO2, respectively, after 3h of irradiation. Correlations between structure, M loadings, distribution-size-coverage of M NPs, and the photocatalytic factors (quantum yield & H2 photoproduction) will be discussed. Also, a 2D photonic profile is provided for the new photoreactor. Acknowledgements The authors thank the French ANR agency for financial support (grant N° ANR-18-CE09-0001, C3PO) and CNRS through International Emerging Actions program (grant N° 08216). References 1. N. S. Lewis and D. G. Nocera, PNAS, 2006, 103, 15729-15735. 2. N. S. Lewis, Science, 2007, 315, 798-801. 3. M. Melchiona and P. Fornasiero, ACS Cat, 2020, 10, 10, 5493-5501. 4. Y. Dubi and Y. Sivan, Light Sci Appl, 2019, 8, 89. 5. P. Jiménez-Calvo et al., Nano Energy, 2020, 75, 104888.

Resume : Organic solar cells (OSCs) based on organic semiconducting molecules offer the possibility of low-cost solar power generation that can be deployed on light-weight and flexible substrates. Photogenerated charge carriers in OSCs manifest as strongly bound electron-hole pairs which must diffuse to an interface in the two-component active layers to be efficiently separated before they recombine. Given the current exciton diffusion lengths, this requires phase-separated domains on the order of ~100 Å to ensure efficient charge dissociation, with suboptimal morphology being a hindrance to commercialisation. Small Angle Neutron Scattering (SANS) can probe the microstructure at such length scales and has been used extensively to study the morphology of polymer OSCs [1], due to the natural scattering contrast between the hydrogen-rich polymers and the carbon-rich fullerenes. However, SANS has yet to be used to characterise the morphology of OSCs based on evaporated small molecule solar cells. In this work, we employ SANS at the ISIS Muon & Neutron Source to study the morphology/microstructure of active layers of evaporated OSCs for the first time. We investigate bulk heterojunctions manufactured under different fabrication conditions, such as different molecular ratios between the electron donor and acceptor moieties, evaporation rates, and varied substrate temperatures during deposition. Various donor molecules, such as alpha-sexithiophene, methylated DCV5T, zinc phthalocyanine, and rubrene, in conjunction with the fullerene C60 are investigated. Our results show how SANS can be used to qualitatively describe the phase mixing behaviour of different blends, such as whether the donor:acceptor system is fully mixed, weakly separating, or shows a distinct two-phase system [2], such as DCV5T spheres in a C60 matrix. These results are verified using Scanning Transmission Electron Microscopy with Energy Dispersive X-ray (STEM-EDX). In addition, we use SANS model fits to quantitatively describe changes in the morphology as growth conditions are varied and link these changes to OSC device performance, demonstrating how SANS can be used to develop key structure-property relationships of evaporated OSCs. [1] Y. Wen and M. Dadmun, "A new model for the morphology of P3HT/PCBM organic photovoltaics from small-angle neutron scattering: rivers and streams." ACS nano 5.6 (2011): 4756-4768. [2] A. Guinier and G. Fournet, ⤜Small-Angle Scattering of X-Rays⤝, John Wiley and Sons, New York, (1955)

Resume : Metal-organic frameworks (MOFs) are a class of crystalline porous materials constituted by metal ions or metal clusters coordinated to organic ligands.[1] Due to their high tunability and flexibility MOFs have found application in many areas. In particular, MOFs are envisioned as promising candidates for the solar-driven production of solar fuels.[2] In fact, many studies have reported the use of MOFs as photocatalysts for H2 generation from water using sacrificial agents. One of the most studied MOFs as photocatalysts is UiO-66(Zr) (Universitetet i Oslo). UiO-66(Zr) is constituted by Zr-oxo clusters coordinated to 1,4-benzenedicarboxylates having an ideal formula Zr6O4(OH)4(OOC-C6H4-COO)6. Theoretical and experimental evidences have demonstrated that the introduction of Ce4+ or Ti4+ ions in the metal cluster of UiO-66(Zr) facilitates the ligand-to-metal charge transfer (LMCT) mechanism from the organic ligand to the metal cluster and, therefore, its resulting photoactivity.[2,3] More recently, our group and others have reported the possibility of using MOFs as photocatalyst for the photocatalytic overall water splitting (OWS) into H2 and O2 in the absence of sacrificial agents.[4,5] In this work we report for the first time the preparation of a trimetallic UiO-66(Zr/Ce/Ti) with superior activity respect to their mono- or bimetallic MOFs for the photocatalytic OWS under UV-Vis or visible light irradiation.[6] In particular, the UiO-66(Zr/Ce/Ti) photocatalyst can achieve 210 μmol ∙ g−1 of H2 and 70 μ mol ∙ g−1 of O2, under visible light irradiation. Fluorescence and time-resolved absorption spectroscopies were employed to show favorable charge separation efficiency when using the trimetallic UiO-66(Zr/Ce/Ti) as photocatalyst.

Resume : Carbon-based materials and organic semiconductor nanoparticles are promising for use as low-cost and efficient photocatalyst materials, mainly due to the easy tunability of their properties through synthetic control, which allow the design of materials with tuned opto-electronic properties by incorporating different building blocks.1,2 The best performing systems are bulk heterojunctions nanoparticles prepared from a blend of polymers donor and non-fullerene small molecules acceptor, particularly due to their improved light absorption in the visible range.3 Despite the efficient performance of the donor/acceptor bulk heterojunction photocatalysts for hydrogen evolution, the fundamental understanding of the photophysical processes that determine their performance remain limited.2 In this presentation, I will introduce our recent spectroscopic studies of a series of donor/acceptor bulk heterojunction photocatalysts with different hydrogen evolution activity, including the highest performing donor/acceptor bulk heterojunction nanoparticles photocatalysts reported to date. Transient absorption spectroscopy, on timescales of femtoseconds to milliseconds after light absorption, was used to explore the charge carrier dynamics of bulk heterojunction nanoparticles and their correlation with photocatalytic performance. I will discuss the similarities and differences between the function of such donor/acceptor bulk heterojunction photocatalysts and single conjugated polymers photocatalyst. These results can provide insight into the design requirement for optimum function of organic semiconductors photocatalysts for solar-to-fuel conversion. References. 1. Wang, Y.; Vogel, A.; Sachs, M.; Sprick, R. S.; Wilbraham, L.; Moniz, S. J. A.; Godin, R.; Zwijnenburg, M. A.; Durrant, J. R.; Cooper, A. I.; Tang, J., Current understanding and challenges of solar-driven hydrogen generation using polymeric photocatalysts. Nature Energy 2019, 4 (9), 746-760. 2. Sachs, M.; Cha, H.; Kosco, J.; Aitchison, C. M.; Francàs, L.; Corby, S.; Chiang, C.-L.; Wilson, A. A.; Godin, R.; Fahey-Williams, A.; Cooper, A. I.; Sprick, R. S.; McCulloch, I.; Durrant, J. R., Tracking Charge Transfer to Residual Metal Clusters in Conjugated Polymers for Photocatalytic Hydrogen Evolution. Journal of the American Chemical Society 2020, 142 (34), 14574-14587. 3. Kosco, J.; Bidwell, M.; Cha, H.; Martin, T.; Howells, C. T.; Sachs, M.; Anjum, D. H.; Gonzalez Lopez, S.; Zou, L.; Wadsworth, A.; Zhang, W.; Zhang, L.; Tellam, J.; Sougrat, R.; Laquai, F.; DeLongchamp, D. M.; Durrant, J. R.; McCulloch, I., Enhanced photocatalytic hydrogen evolution from organic semiconductor heterojunction nanoparticles. Nature Materials 2020, 19 (5), 559-565.

Resume : In commercial polymer electrolyte fuel cells platinum(-alloys), supported on conductive carbon materials, catalyze the hydrogen oxidation (anodic process) and the oxygen reduction reaction (ORR) (cathodic process). Thereby, carbon materials play a crucial role, e.g. as catalyst support. The platinum/carbon catalyst system still can be optimized towards its activity for the ORR and, more importantly towards long-term stability. Indeed, electrochemically active surface area is lost during operation by Pt particle detachment and/or carbon corrosion [1]. To overcome these degradation processes, the carbon support can be modified by advantageous nanostructuring to achieve high Pt dispersion and/or by incorporation of nitrogen functionalities as anchoring groups for platinum [2]. Mesoporous N-doped carbon materials (N-HTC) obtained by hydrothermal carbonization from biomass derived precursors were developed and used as support for Pt nanoparticles [3]. By temperature treatments the N-content and graphitization of the N-HTC supports can be adjusted [4]. Platinum nanoparticle deposition on the various N-HTC supports was achieved by wetness impregnation and thermal reduction of a platinum salt precursor. The influence of the synthesis conditions and as such of the support and nanoparticle properties on the ORR activity and stability of the developed catalysts was investigated by electrochemical rotating disk electrode (RDE). The optimized Pt/N-HTC ORR catalyst showed higher stability (over 10000 AST cycles) when compared to a commercial Pt/C catalyst. [1] J.C. Meier, C. Galeano, I. Katsounaros, J. Witte, K.J.J. Mayrhofer, Beilstein J. Nanotech 5 (2014), 44–67. [2] J. Melke, R. Schuster, S. Möbus, T. Jurzinsky, P. Elsässer, A. Heilemann, A. Fischer, Carbon 146 (2019) 44–59. [3] J. Martin, J. Melke, C. Njel, A. Schökel, J. Büttner, A. Fischer, 2021, to be submitted. [4] J. Melke, J. Martin, M. Bruns, P. Hügenell, A. Schökel, S. M. Isaza, F. Fink, P. Elsässer, A. Fischer, ACS Appl. Energy Mater. 3, 12 (2020) 11627-11640.

Resume : With the recent growing interest in the environment and energy, the demands for green energy having a low carbon footprint are increasing. To make a breakthrough in these challenges, the development of material to control the gas molecules is crucial. Especially, understanding the gas adsorption behavior in porous materials is necessary for catalysis and gas storage applications. One of the best conventional analysis methods to characterize it is adsorption isotherm. However, if it is used alone, it is difficult to locate or identify the behavior of the adsorbate molecules. Herein we report CO2 behavior of early adsorption stages in MIL-101 (Cr, Fe, and V), by simultaneous analysis of their adsorption isotherms and X-ray diffraction patterns. Each adsorption isotherm shows unique characteristics; this was analyzed by the interaction between the adsorbate and the corresponding framework using the CO2 distribution map in the pores, electron paramagnetic resonance spectroscopy, and DFT simulation results. Notably, the CO2 isotherm shape for V-MIL-101 is convex at the very early stage and then becomes concave to the p/po axis, until the pore condensation starts. For Fe-MIL-101, the overall isotherm slope is relatively linear during the stage. Cr-MIL-101, which shows the highest CO2 uptake among the samples, has a concave-shaped isotherm. Meanwhile, Ar isotherms show similar profiles throughout the adsorption pressure range regardless of the metals. Their continuous adsorption processes before pore condensation are visualized as accumulated CO2 distribution maps based on in-situ X-ray diffraction. We can infer that Cr-MIL-101 has strong framework-adsorbate interaction and hence, high CO2 uptake in the initial adsorption stage, represented by the concave isotherm shape. The monolayer adsorption gradient changed greatly depending on the metal-CO2 attraction force. However, after CO2 adsorption and layer formation, the CO2-CO2 forces can promote the adsorption of more molecules thereby, making the isotherm of V-MIL-101 convex. Furthermore, under the CO2 atmosphere, the electron paramagnetic resonance intensity of MIL-101s, which is proportional to the number of unpaired electrons, decreased in all three materials significantly. These results indicate that though the three metals contain unpaired electrons, and their respective interactions with CO2 are explained with their d orbital configurations. Also, the adsorption energy values derived by the DFT calculation show that the trend of intermolecular interaction is in order of Cr >> Fe > V, consistent with the experimental results. Through this research, we can gain additional insights into the adsorbate distribution within pores during the gas adsorption process and the comprehensive adsorbate behaviors in the different pore environments. This approach can contribute to explaining adsorption mechanisms and construction guidelines for porous materials in gas-storage and catalysis industries.

Resume : Solar based hydrogen power is promising as a renewable fuel that can be generated anywhere there is sunshine and water. Many attempts have been made to integrate a water electrolyser and solar cell into one seamless package (a so-called artificial leaf) to take advantage of the cooling provided by the water to the solar cell, reduced losses from the lack of wiring and the increased portability afforded by an integrated unit 1. However, in literature, much less attention is payed to the need for a minimum current across the electrolyser under insufficient illumination to prevent excessive catalyst degradation and dissolution2. Attaching an appropriately sized, voltage matched battery to an artificial leaf could address this need and in theory could also increase efficiency of the setup across one diurnal cycle. We experimentally show that this can be achieved without any power electronics and, as is theorized, the presence of the battery also has a positive effect on the operation of the electrolyser and improves solar-to-hydrogen efficiency by reducing the current density across the electrolyser. A 7 cell silicon heterojunction module , two bifunctional NiFeMo electrolysers in series and a commercial Li-ion NMC battery were selected to provide the same amount of solar output power despite different working voltages and tested in a series of simulated diurnal cycles. The increased average solar to hydrogen efficiency per cycle (11.4% vs 10.5% without the battery) is analyzed and discussed with implications for future integrated artificial leaf design and implementation. 1. M. Lee, B. Turan, J.-P. Becker, K. Welter, B. Klingebiel, E. Neumann, Y. J. Sohn, T. Merdzhanova, T. Kirchartz, F. Finger, U. Rau and S. Haas, Advanced Sustainable Systems, 2020, 4, 2000070. 2. A. Weiß, A. Siebel, M. Bernt, T. H. Shen, V. Tileli and H. A. Gasteiger, Journal of The Electrochemical Society, 2019, 166, F487-F497.

Resume : Poly (3-hexylthiophene) (P3HT) has been considered as a promising commercial organic photovoltaic (OPV) material due to its low cost and large scalability. However, the power conversion efficiency (PCE) of current P3HT-based OPV cells is too low to meet the requirements of practical applications. In this work, we select the high-efficiency P3HT:ZY-4Cl blend as a model system to reveal the time-dependent evolution of crystallization, morphology and photovoltaic performance of the system during thermal annealing process. It was found that the amorphous acceptor crystallized/aggregated rapidly with the extension of annealing time, while the crystallinity of P3HT enhanced slightly but did not change visibly before and after annealing. Therefore, the phase separation of the device blends increases gradually with the annealing time prolonging, so that the device efficiency increases rapidly at first and then decreases slowly. We achieved an impressive PCE of more than 10% after only thermal annealing for 30 seconds at 130 ?, which is the highest efficiency of P3HT-based OPV. This is significantly higher than the efficiency of conventional annealing for 10 min (9.3%) and approximately 20 times that of as cast devices (0.5%). This work suggest that delicate control of both donor and acceptor crystallinity is crucial to the performance optimization of P3HT-based OPVs.

Resume : The evolution of smart electronics resulted in a movement towards real-time sensing and a web-connected society, leading to the rapid development of e-textiles. The extensive use of wearable technologies boosted the development of energy storage textiles that charge faster and store energy for longer time.[1,2] Additionally, the multifunctionality of textiles is also an important aspect to create high value-added products.[3] Herein, a novel dual-functional textile supercapacitor combining enhanced energy storage and optical properties was produced. A new redox-active solid-gel electrolyte based on fluorescent manganese(II)-doped zinc(II) sulfide was for the first time used to endow multifunctionality to the device when assembled with MWCNT-based textile electrodes. The fluorescent compound was composed of sphalerite and wurtzite ZnS phases doped with Mn2 and exhibited a rhombic structure. The MWCNT-coated textile electrodes (with high electrical conductivity, 704 Ω cm-2 of electrical resistance), were prepared through a simple eco-sustainable dip-pad-dry process using a natural cotton fabric as substrate. The fluorescent hybrid textile supercapacitor exhibited 20% higher working voltage (1.64 V), 48% higher energy density (1.63 W h kg-1) and 74% higher power density (641.6 W kg-1) than the textile supercapacitor based on the undoped electrolyte. These improvements arised from a synergistically-enhanced properties that lead to a hybrid energy storage mechanism. Additionally, it presented excellent cycling stability of 100% after 8000 charge/discharge cycles. The device exhibited an intense yellow-orange fluorescence under UV light, preserving at the same time the energy storage functionality. This work opens promising perspectives on multifunctional energy storage textiles for dark environment applications, such as in reflective/safety electronic clothing for nighttime users. Acknowledgments. Funded by FEDER through COMPETE 2020-POCI and by FCT/MCTES under Program PT2020 (project PTDC/CTM-TEX/31271/2017). Work also supported by UIDB/50006/2020 and UIDB/04968/2020 with funding from FCT/MCTES through national funds. JST and CP thank FCT for PhD scholarship (SFRH/BD/145513/2019) and FCT Investigator contract IF/01080/2015, respectively. References: [1] X. Zhang, C. Jiang, J. Liang, W. Wu, Electrode materials and device architecture strategies for flexible supercapacitors in wearable energy storage, J. Mater. Chem. A 9 (2021) 8099–8128. [2] R.S. Costa, A. Guedes, A.M. Pereira, C. Pereira, Fabrication of all-solid-state textile supercapacitors based on industrial-grade multi-walled carbon nanotubes for enhanced energy storage, J. Mater. Sci. 55 (2020) 10121–10141. [3] C. Pereira, A.M. Pereira, C. Freire, T. V Pinto, R.S. Costa, J.S. Teixeira, Chap. 21 - Nanoengineered textiles: from advanced functional nanomaterials to groundbreaking high-performance clothing, in: Handb. Funct. Nanomater. Ind. Appl., Elsevier, 2020, pp. 611-714.

Resume : During the last decades many effort has been devoted to understand the hematite-electrolyte interface due to its potential application in photoelectrochemical water splitting. It is well known that this interface can extend over lengths ranging from tens of nanometers to micrometers, therefore its realistic simulation via ab initio-calculations has been seen as an impossible task. However, recent experiments measured space charge layers smaller than ~10 Angstrom in highly doped nanostructured hematite photoanodes displaying high photocurrent densities in water splitting experiments [1]. Using a set of continuous equations based on the based on the Poisson-Boltzmann distribution and the Stern model [2], we investigated under which experimental conditions the space charge layer in hematite becomes ultrathin. In this regime a considerable fraction of the potential drop across the interface is located in the Helmholtz layer, therefore corrections to the Mott-Shottky equation should be taken into account in this regime. These equations also allowed us to examine the effect of the macroscopic properties provided by experiments on the microscopic properties of the interface: We got access to the width of the space charge layer; and the distribution of the electrostatic potential among the space charge layer in the solid, the Helmholtz layer and diffuse layer as a function of the experimental conditions. We then used density functional theory to get an atomistic insight of the space charge layer in the semiconductor in systems ranging from the pristine stoichiometric surface, a surface with adsorbed hydroxyls to Ti-doped slabs with doping densities of the order of ~1.0E21 cm^{-3}. According to our analysis with the continuous equations, space charge layers smaller than 10 Angstrom must have been present also in other experiments with some of highest photocurrent performances registered [3]. We found that at high doping densities the inverse of the square of the capacitance should have a quadratic behaviour near the flat-band potential and a sub-linear behaviour due to square-root-like corrections far from it. We computed the band bending of the proposed atomistic models using Density functional theory. The pristine stoichiometric and the hydroxylated undoped surfaces displayed band bendings of 0.14 eV and 0.49 eV, respectively, with space charge layers extending in the sub-nanometer regime. At high doping concentrations, we observed that space charge layers in hematite thin films can become comparable with interatomic distances. Contrary to the common picture of the electrochemical interface of a semiconductor and an electrolyte, the latter results give an insight of an unexpected regime of high photoelectrocatalytic efficiency in ultrathin space charge layers, which are accesible to quantum mechanical ab-initio calculations. [1] Z. Zhang, H. Nagashima, and T. Tachikawa, Angew. Chem. Int. Edit. 59, 9047 (2020). [2] Y. V. Pleskov and Y. Y. Gurevich, Semiconductor Photoelectrochemistry, 1st ed. (Consultants Bureau, New York, 1986) [3] F. L. Formal, N. Tétreault, M. Cornuz, T. Moehl, M. Grätzel, and K. Sivula, Chem. Sci. 2, 737 (2011).

Resume : Methylammonium Lead Iodide (MaPbI3) and Methylammonium Tin Iodide (MASnI3) thin absorber layers are potential candidates used as absorber layer in perovskite device. Herein, both compounds have been successfully prepared with one step spin coating technique. The prepared samples were characterized by different techniques like X-ray diffraction (XRD), atomic force microscopy (AFM), surface electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmittance electrons microscopy (TEM), UV–Visible spectroscopy and photoelectrochemical (PEC) analysis. The XRD analysis confirms the tetragonal structure of the prepared thin films. AFM analysis exposed that the MASnI3 displays better roughness (54 nm) and grain size (65 nm) than MAPbI3 which has of roughness of 30 nm and grain size of 21 nm. For both samples, SEM analysis revealed smooth and homogenous surface and large grain size and pinhole-free perovskite film. The optical absorption spectrum showed the direct bandgap of MASnI3 1.8 eV and 1.6 eV for MaPbI3 thin films. Based on the results the MASnI3 used as an absorber layer can be a good choice for an efficient photovoltaic device.

Resume : There is an increasing interest in developing energy vectors alternative to the use of fossil fuels.[1] One of the most interesting approaches to obtain sustainable energy is to convert solar energy into chemical energy. Heterogeneous photocatalysis is an important approach for this purpose. However, the development of efficient solar-driven heterogeneous photocatalysts still remains a challenge. In the last decades a relatively new class of crystalline and porous materials termed as metal-organic frameworks (MOFs) has emerged as potential heterogeneous photocatalysis for the production of hydrogen using UV-Vis or visible light irradiation.[2] Most of these studies, however, employ sacrificial agents such as triethanolamine or methanol and, therefore, hampering the real application of these systems. More recently, a series of studies have reported the possibility of using MOFs as heterogeneous photocatalysts for the overall water splitting (OWS). [3,4] In the present work we report the influence of the presence of Pt, RuOx and/or CoOx NPs as co-catalyst within the MOF named as MIL-125(Ti)-NH2 with ideal formula Ti8O8(OH)4-(O2CC6H5-CO2-NH2)6 for the photocatalytic OWS.[5] The simultaneous combination of Pt and RuOx NPs within the MIL-125(Ti)-NH2 network resulted in an active photocatalyst under UV-Vis light reaching a H2 and O2 production of 218 and 85 mol/g of photocatalyst at 24 h, respectively. With this photocatalyst a maximum apparent quantum efficiency at 400 nm of 0.32 % was obtained. More importantly, the Pt/RuOx@MIL-125(Ti)-NH2 photocatalyst is active under natural sunlight irradiation achieving a H2 and O2 productions of about 28 and 14 mol g-1 in 10 h. Refs.[1] N.S. Lewis, Introduction: Solar Energy Conversion, Chem. Rev, 115 (2015) 12631-12632. [2] A. Dhakshinamoorthy, Z. Li, H. Garcia, Catalysis and photocatalysis by metal organic frameworks Chem. Soc. Rev., 47 (2018) 8134-8172.[3] Y. An, Y. Liu, P. An, J. Dong, B. Xu, Y. Dai, X. Qin, X. Zhang, M.-H. Whangbo, B. Huang, NiII Coordination to Al-Based Metal–Organic Framework Made from 2-Aminoterephthalate for Photocatalytic Overall Water Splitting, Angew. Chem. Int. Ed., 56 (2017) 3036 –3040. [4] A. Melillo, M. Cabrero-Antonino, S. Navalón, B. Ferrer, H. García, Enhancing visible-light photocatalytic activity for overall water splitting in UiO-66 by controlling metal node composition. [5] S. Remiro-Buenamañana; M. Cabrero-Antonino; M. Martínez-Guanter; M. Álvaro; S. Navalón; H. García. Influence of co-catalysts on the photocatalytic activity of MIL-125(Ti)-NH2 in the H. water splitting. Clave A, Appl. Catal. B. Environ. 254, 677-684, 2019.

Resume : Materials that can change their optical properties as a response to an external electrical voltage are referred to as “electrochromic.” The materials’ coloration is denoted “cathodic” under ion insertion and “anodic” under ion extraction. Conventionally, electrochromic (EC) device structures have five superimposed layers: transparent conducting oxide (TCO) layer / cathodic EC layer / ion-conducting layer / anodic EC layer / TCO layer, either all on one substrate or positioned between two substrates in a laminated configuration. Ion conducting layers (electrolytes) play a vital role in the operation of EC systems. They should provide high ion conductivity and transparency, low electronic conductivity, and compatibility with both anode and cathode. In this work, we prepared W oxide thin films by reactive DC magnetron sputtering and investigated their electrochromic properties, durability, and potentiostatic rejuvenation in LiClO4-propylene carbonate electrolytes containing up to 3.0 wt% of SiO2 nanoparticles with a diameter of 7 nm. The effect of adding nanoparticles to the electrolyte on ionic conductivity, chemical state, and morphological structure of the thin films was examined. The addition of 1.0 wt% SiO2 in the electrolyte led to high charge capacity and optical modulation in the W oxide films. A significant improvement in durability during voltammetric cycling was observed in the commonly used potential range of 2.0–4.0 V as well as under harsh conditions, which correspond to the range 1.5–4.0 V.

Resume : Yttrium and other rare-earth (RE) metal oxy-hydrides (YHO, REHO – notations referred in the text hereinafter, in principle, is irrespective to the stoichiometry) are a new class of inorganic mixed-anion materials [1], which exhibit a photochromic effect and a light-induced resistivity change at room temperature and ambient pressure. These switchable optical and electrical properties enable their utilization in a multitude of technological applications, such as energy-saving smart windows, sensors, ophthalmic lenses, and medical devices. Recently reported studies show that the modification of the deposition parameters causes significant changes in the composition of REHO films, accompanied by a varying optical properties. In order to tune and fully exploit REHOs in applications, further progress requires: reaction conditions for film synthesis have to be investigated carefully, including the film oxidation kinetics and the characterization of the oxy-hydride phase. In this work, the films were fabricated on soda-lime glass using the vacuum PVD coater G500M (Sidrabe Vacuum, Ltd.) at various sputtering pressure (SP) from 3 mTorr up to 20 mTorr. Detailed characterisations by profilometer CART Veeco Dektak 150, X-ray diffractometer with Cu Kα radiation, Rigaku MiniFlex 600, high-resolution dual-beam scanning electron microscope Thermo Scientific Helios 5 UX, and spectroscopic ellipsometer WOOLLAM RC2 were performed. For the first time in-situ oxidation dynamics were observed by means of the transmittance measurements just after the deposition of the films by introducing the oxygen in the sputtering chamber. Transmittance increases and oxidation time constant rapidly decreases with increase of the film SP. XRD analysis show that the crystallographic structure of the film is just slightly affected by the SP: with increase of the SP the intensity of the peak around 29 degrees of 2-theta is decreasing thus films undergo compositional changes rather than structural. The SP of approximately 6.0-6.5 mTorr was found to be a critical pressure, where the refractive index n extinction coefficient k dispersion curves completely change the characteristic from metallic to semiconductor/dielectric behavior with Tauc optical band Eg around (2.5-2.8) eV. Moreover, all films fabricated at SP higher than this critical pressure exhibit optical gradient: n decreases in direction from the bottom to the top of the films, and the lower is the SP, the higher is the n difference within the depth of the films. For all films, the Eg and n increases and k decreases with increase of SP. ACKNOWLEDGMENTS This research is supported by the Horizon 2020 Project CAMART² under grant agreement No 739508 and national project “Thin films of rare-earth oxy-hydrides for photochromic applications” FLPP No LZP-2020/2-0291. [1] Kageyama, Hiroshi, et al., Nature communications 9.1 (2018): 1-15.