Advanced catalytic materials for (photo)electrochemical energy conversion

Resume : Understanding the mode of operation of heterogeneous catalysts is of great scientific and economic interest. Such a knowledge based approach strongly relies on the development and application of spectroscopic methods that allow for monitoring the relevant (sub)surface processes under working conditions (operando approach). In this presentation, the potential of combined in situ and operando spectroscopies (IR, Raman, UV-Vis) for direct characterization of adsorbates and the (defect) structure of working heterogeneous catalysts will be illustrated by examples from current research relevant to electrochemical energy conversion. It is shown that the spectroscopic assignment and interpretation of the results is largely facilitated by the use of DFT calculations. Focus will be put on oxide-based materials, including ceria and noble metal doped ceria as a case study; however, approaches for the in situ and operando spectroscopic characterization of carbon-containing materials will also be outlined. Our studies underline that detailed spectroscopic analysis under working conditions of heterogeneous catalysts using combined operando spectroscopies is essential to unravel their mode of operation.

Resume : Pt-alloy nanoparticles (NPs) with octahedral shapes are attractive as fuel cell catalysts for the oxygen reduction reaction (ORR). A deep understanding of their atomic-scale structure, formation and degradation is a prerequisite for their use as rationally-designed NP catalysts. Here, we present results from a comprehensive microstructural study of the growth and degradation of various octahedral Pt-alloy NPs performed using ex situ, in situ and identical location high-resolution (S)TEM combined with EEL and EDX spectroscopy. We show that the NPs often show compositional anisotropy and form Ni-rich {111} facets, leading to complex structural degradation during ORR electrocatalysis. We also reveal element-specific anisotropic growth as the reason for their compositional anisotropy and limited stability. In situ thermal annealing of phase-segregated octahedral Pt-Ni alloy NPs was performed to study their morphological stability and surface compositional evolution. On being annealed, the Pt-rich surface atoms at the corners/edges diffuse onto and subsequently cover the concave Ni-rich {111} surfaces, leading to the formation of favorable flat Pt-rich {111} surfaces with Ni-rich subsurface layers. Finally, we present results from a systematic comparison of Rh-doped and undoped Pt-Ni NPs and demonstrate that surface doping of octahedral Pt-Ni NPs is found to be an effective method for stabilization of the octahedral shapes of the NPs thereby improving their long-term stability during electrochemical cycling.

Resume : I will present an overview of density functional theory (DFT) based molecular modelling of hydrogen and oxygen evolution reactions (HER and OER). The emphasis is on the fast screening type modelling (ΔG) of various catalyst. We have studied HER on several different catalyst, including carbon nanotube (CNT) based materials [1], MoS2 [2], Ni2P [3] and Ni-oxo-hydride. In addition, the OER can be studied with ΔG-type models [4]. In all these studies the role of catalyst doping has been addressed. On MoS2 and Ni2P, the metal doping has been considered and in CNT the N doping has been studied in detailed [1,4]. Some remarks of the limitations of the ΔG models and models with explicit water molecules will be discussed. Overall, the molecular modelling of electrochemical reactions in under intense development and many new methods have been introduced recently. One of them is the use of contrained-DFT for studying coupled electron-proton transfer reaction [5]. References [1] N. Holmberg, and K. Laasonen, J. Phys. Chem. C. 119, 16166 (2015). [2] M. Hakala et al., Sci. Rep. 7, 15243 (2018), R. Kronberg et al., Phys. Chem. Chem. Phys. 19, 16231 (2017) [3] L. Partanen, and K. Laasonen, Phys. Chem. Chem. Phys., 21, 184-191, (2019). [4] G. Murdachaew and K. Laasonen, J. Phys.Chem. C, 122, 25882, (2018). [5] N. Holmberg and K. Laasonen, J. Chem. Phys. 149, 104702, (2018).

Resume : Titanium oxide is used in a myriad of applications such as in capacitors, insulation paints among others. It is a prime candidate for water splitting due to its photocatalytic properties. In this work, undoped TiO2thin films were prepared by anodizing titanium followed by electrodepositing dopants of copper ions on anodized titanium. Spectrophotometric data was analyzed to obtain absorption coefficient and using the same to determinethe bandgap of the films. It was noted that the films exhibited reduced integrated reflectance with increasing anodizing voltagehence affecting absorption. Further, annealing and copper doping of the films lead to increased absorption. Key words: TiO2, Doping, Bandgap, anodization, photocatalysis, optical properties, electrodeposition

Resume : Converting water and CO2 to renewable fuels using (photo)catalysis is an area of significant interest and high potential for producing renewable fuels to meet the increase in world energy demand and the climate emergency. Converting water to hydrogen will enable long distance transportation. Capturing and converting CO2 produced in industrial processes will allow useful chemicals to be produced. We have been working on combined experiment and first principles modelling of modified TiO2 to find catalysts that can promote hydrogen evolution and CO2 reduction. In this presentation we present DFT simulations of modifications to TiO2 rutile and anatase by nanoclusters of metal oxides and chalcogenides. We show that modifying TiO2 with metal chalcogenides (sulfide, selenide) or bimetallics based on Cu can promote hydrogen adsorption to make these heterostructures viable for hydrogen evolution. For CO2 conversion we identify a number of modifiers to TiO2 that can activate or dissociate CO2 to CO. This includes bismuth oxide, ceria and very low loadings of copper. Key aspects appear to be the presence of active sites as a result of oxide reduction, the presence of reduced cations and the electronic structure of the modifiers. Comparison with experimental results on modified TiO2 will also be presented.

Resume : Among the several approaches, the gas phase photocatalytic conversion of CO2 to useful fuels with the help of renewable energy source and water vapor has attracted widespread attention and is considered to be the best alternative to tackle both energy and global environmental challenges. In this report, a chemical vapor transport (CVT) grown 2D SnS2 thin film is prepared and used as a semiconductor photocatalyst for CO2 reduction. The as-grown SnS2 sample is doped with a controlled amount of carbon using ion implantation operated at 5 keV energy. The adsorbate-catalyst surface interactions are studied using in-situ Raman spectroscopy and electronic studies on dark current and photocurrent responses when the samples are exposed to different adsorbate gases. SnS2 based devices are prepared to in-situ study the adsorbate and catalyst surface interactions in the dark and during light illumination while the devices are exposed to Ar, CO2, H2O vapor and CO2+H2O vapor in sequence. Similarly, Raman spectroscopy is used to in-situ study the structural changes of SnS2 and the interaction of the abovementioned adsorbates on the surface of catalysts. Additional information on the mechanism of interfacial charge transfer was obtained using X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) analysis. The photocatalytic activity and product selectivity towards the gas-phase photocatalytic conversion of CO2 under simulated solar light is analyzed using gas chromatography and the 1 wt % carbon implanted SnS2 (C-SnS2) film has demonstrated very high product selectivity and activity. The C-SnS2 has exhibited more than 26 times enhancement in the total quantum efficiency and more than 90% product selectivity for CH3CHO formation as compared to the as-grown SnS2 sample. The improved photocatalytic activity and selectivity can be ascribed due to pronounced charge-transfer taking place between SnS2 and carbon and improved carrier lifetime with the availability of highly reactive carbon sites that serve as favorable CO2 adsorption sites during the photocatalytic reaction. The detail characterization and experimental results with the future perspective of this study will be presented.

Resume : Considering the excessive emission of atmospheric carbon dioxide (CO2) caused by the combustion of fossil fuels, the sunlight-driven CO2 reduction into higher energy chemicals, such as carbon monoxide, formic acid, methanol or methane, offers a more promising approach to alleviate both global warming and energy crisis. Designing new photocatalytic materials for improving the photoconversion efficiency is a promising route to achieve this goal. Despite the invention of a large number of catalytic materials with well-defined structures, their overall efficiency in photocatalysis is still quite limited as the three key steps ? light harvesting, charge generation and separation, and charge transfer to surface for redox reactions ? have not been substantially improved. To improve each step in the complex process, there is a major trend to develop materials based on inorganic hybrid structures, in which surface and interface engineering holds the promise for boosting the overall efficiency. In this talk, I will demonstrate several different approaches to designing inorganic hybrid structures with improved photocatalytic performance via surface and interface engineering. It is anticipated that this series of works open a new window to rationally designing inorganic hybrid materials for photo-induced applications.

Resume : Semiconductor photocatalysts for overall water splitting into H2 and O2 require metal cocatalyst, such as Pt, to catalyze H2 evolution efficiently. However, these metal cocatalysts can also catalyze hydrogen and oxygen recombination to form water. In this work, we found that the pre-adsorbed halogen atom catalyst could inhibit the reverse reaction of water formation from H2 and O2 due to the decrease of adsorption energies of H2 and O2 on Pt. This inhibition was achieved via the occupation of halogen atom on the Pt surface sites, and thereby the adsorption and activation of hydrogen and oxygen molecules were decreased. The occupation difference of halogen atoms leads the different activity for H2 and O2 recombination. By inhibition of water formation reverse reaction, the over-all water splitting over various TiO2 photocatalysts has been achieved. Isotope experiments with D2O and H218O confirmed the over-all water splitting to H2 and O2. This study may help scientist to develop high-efficient photocatalyst for overall water splitting.

Resume : CdS has been researched on photocatalysis for decades by virtue of the favorable band structure for technologically important reactions such as hydrogen evolution. Further performance enhancement can be achieved by introducing Au nanoparticles, which improves both charge carrier separation and light harvesting capability. Moreover, nanocrystals exposing different facets may exhibit distinct catalytic activities due to the variation of surface energy. Approaches by employing nanocrystals with specific exposed facets have been proven effective in optimizing the photocatalytic efficiency. In this work, we have precisely synthesized Au@CdS yolk@shell nanocrystals with various shell morphology, including cube ({100}-bound), octahedron ({111}-bound), rhombic dodecahedron ({110}-bound) and sphere (isotropic facets). The samples were prepared by using Au@Cu2O core@shell nanocrystals as the template, followed by the sulfidation treatment and cation exchange reaction. Due to the nanosized Kirkendall effect, abundant voids were generated and coalesced during the sulfidation process, producing yolk@shell nanocrystals that possessed hollow shells. For yolk@shell nanocrystals, the cavity enclosed by the nanosized shells provided a confined space to facilitate molecular diffusion, promoting homogeneous reaction to enhance the overall catalytic activities. The effect of the exposed facet on the photocatalytic hydrogen evolution for Au@CdS nanocrystals were systematically studied and interpreted in terms of the surface energy of the facet.

Resume : Ammonia borane (NH3BH3) storing 19.6 wt.% of hydrogen has been considered as a practical hydrogen carrier for producing hydrogen by pyrolysis or hydrolysis method. In this work, we demonstrated the use of Au@Cu2O core@shell nanocrystals as a hydrolysis catalyst to produce hydrogen from ammonia borane. Compared to pure Au and pure Cu2O, a significant enhancement in hydrogen production was achieved for Au@Cu2O, illustrating the synergy of Au and Cu2O in enhancing the catalytic activity toward ammonia borane dehydrogenation. The hydrogen production efficiency can be further improved by applying visible light irradiation during the hydrolysis process. This performance improvement was attributed to the superior photocatalytic activity of Au@Cu2O rendered by the significant charge separation at Au/Cu2O interface as well as the plasmonic effect of Au.

Resume : The discovery of graphene has opened up new horizons in material science research with its unique and spectacular physical, mechanical, electrical and optical properties.1 Graphene research has sparked great interest in a wide range of 2-dimensional layered materials with varying electronic properties. Atomically thin layered transition metal dichalcogenides (TMDs) such as MoS2, WS2, MoSe2 and WSe2 have been emerging as the cutting edge in materials science and engineering, due to their interesting electronic properties.2 These materials open up new opportunities for a variety of applications, including optoelectronics, energy conversion, and catalysis. To realize their potential device applications, it is highly desirable to achieve controllable growth of these layered nanomaterials, with tuneable structure and morphology.3,-6 In this talk, I will first introduce the controlled synthesis technique that we have recently developed for the growth of luminescent quantum dots of TMDs.6 The method could be extended for other layered materials and such tailored materials show exceptional electrocatalytic properties toward hydrogen evolution reaction (HER)7 and oxygen evolution reaction (OER).8 The talk will also present some of our recent efforts on morphological and electrocatalytic studies of chemical vapour deposition (CVD) grown spiral and pyramid-like few-layer TMDs. References 1. A. K. Geim, K. S. Novoselov, Nat. Mater. 2007, 6, 183-191. 2. H. R. Gutiérrez, N. Perea-López, A. L. Elías, A. Berkdemir, B. Wang, R . Lv, F. López-Urías, V. H. Crespi, H. Terrones, M. Terrones, Nano Lett. 2013, 13 (8), 3447-3454. 3. Y. Gong, P. M. Ajayan et al., Nat. Mater., 2014, 13, 1135–1142 4. D. Gopalakrishnan, D. Damien and M. M. Shaijumon, ACS Nano, 2014, 8, 5297-5303. 5. D. Damien, A. Anil, D. Chatterjee and M. M. Shaijumon, J. Mater. Chem. A 2017, 5, 13364-13372. 6. D. Gopalakrishnan, D. Damien, B. Li, H. Gullappalli, V. K. Pillai, P. M. Ajayan, and M. M. Shaijumon, Chem. Commun. 2015, 51, 6293-6296. 7. Prasad, Shaijumon et al., Nanoscale , 2018, 10, 9516-9524 8. R. Prasannachandran, T.V. Vineesh, A. Anil, B. M. Krishna and M. M. Shaijumon, ACS Nano, 2018, 12, 11511-11519

Resume : Photocatalytic water splitting, which can directly convert sunlight to molecular hydrogen (H2) and oxygen (O2) from water, represents a promising route towards producing clean and renewable energy. Current photocatalysts for overall water splitting, however, still suffer from insufficient stability, low quantum efficiency, and limited tunability in optical and electronic properties. The search for efficient photocatalysts that can directly split pure water under visible light irradiation remains one of the most challenging tasks for solar energy utilization. On the basis of first-principles calculations and topological modelling method, we designed two-dimensional (2D) nanomaterials, i.e. 2D phosphorous allotropes and conjugated microporous polymers, of which the electronic band structure can be tuned by the basic units assembled in the 2D networks.Our results firstly demonstrate that nine 2D phosphorous allotropes and two conjugated microporous polymers have appropriate valence band and covalent band edge, meeting the requirement for the overall water splitting.

Resume : Semiconducting conjugated polymers have emerged as a novel class of photocatalyst for solar-driven water splitting. Compared to their inorganic counterparts, these synthetic conjugated polymers offer great versatility to develop highly efficient photocatalyts with tunable electronic structures for photocatalytic applications. However, conjugated polymers that are able to efficiently split pure water under visible light (>400 nm) still remain to be explored. We show that 1,3-diyne-linked 2D conjugated polymer nanosheets obtained by oxidative coupling of terminal alkynes such as 1,3,5-tris-(4-ethynylphenyl)-benzene (TEPB) and 1,3,5-triethynylbenzene (TEB) are possessing suitable band structures for photocatalytic overall water splitting and can act as highly efficient photocatalysts for splitting pure water (pH~7) into stoichiometric amounts of H2 and O2 under visible light irradiation. Using in situ techniques, we could further elucidate the reaction pathways during the photocatalytic process, providing strong evidence that the water splitting reaction could occur on the surface of polymer photocatalysts. Meanwhile, inspired by natural photosynthesis, Z-scheme photocatalytic systems are very appealing for achieving efficient overall water splitting. We also show the construction of polymer-based van der Waals heterostructures as metal-free Z-scheme photocatalytic systems for overall water splitting using aza-CMP and C2N ultrathin nanosheets as O2-evolving and H2-evolving catalysts, respectively. We believe that our study could provide new insights in design and synthesis of semiconductors that are able to catalyze overall water splitting at neutral pH with sunlight as the only energy input.

Resume : Artificial photosynthesis is a promising breakthrough to convert CO2 into hydrocarbons under solar energy. Among the various semiconductors, metal sulfide semiconductors have been shown as a promising visible-light photocatalyst due to their interesting optoelectronic properties [1-4]. However, these semiconductors faced great challenge for practical application due to high charge recombination process. Recently, the heterostructure photocatalysts have triggered interface engineering displayed superior efficiency because the proper heterojuction formation between two semiconductors can effectively improve the recombination due to the proper charge separation. Therefore, design a heterostructure composite between two semiconductors is profound significance in photcatalyst research. The semiconductor heterojuction or homojunction by type II mechanism is a promising approach to enhance the photocatalytic performance. Cu2S is one of the p-type narrow band gap semiconductor materials and among various CuxS composites, Cu1.8S band structures are relatively similar energy level as compared with the n-type SnS2. We developed Cu2S decorated SnS2 nanoflowers heterostructure as a visible-light photocatalyst for CO2 reduction. The two-step solvothermal reactions, integrates two distinct metal sulfides into hierarchical hybrids with homogeneous interfacial contacts between two semiconductors. Accordingly, the Cu1.8/SnS2 heterostructure facilitate separation and migration of photoinduced charge carriers, enhance surface redox reactions. The hierarchical Cu1.8S/SnS2 hybrid with an optimal composition ratio possesses around 36 times enhanced performance than SnS2. In the continuation of interface engineering approach most recently, we developed another ZnS-In2S3 hybrid photocatalyst system, which exhibits remarkable high performance (QE: ~0.8%) for CO2 reduction. The detail's catalyst preparation, photocatalytic performance, quantum yield and C-2 product selectivity will be discussed in the presentation. References: [1] I. Shown et al. Nano Letters, 14, 6097, (2014). [2] I. Shown et al. US Patent US 2018 / 0280942 A1 [3] I. Shown et al. Nature Communications, 9, 169, (2018). [4] T. Billo, I. Shown et al. Small, 1702928 (1-11), (2018).

Resume : With the advent of increasing renewable energy, energy storage is a critical issue which is being addressed in various ways. The challenge of our era is to change from fossil driven chemical processes to electrical ones while dealing with the intermittency of renewable sources. One promising way is to store electrical energy into chemical bonds. This requires the development of new approaches for converting electrical energy and base molecules (i.e. H2O, N2, CO2) into high energy ones. In the transition from low to high energy molecules (e.g. H2, NO, NH3, CO) the activation of chemical bonds is the major issue that it should be tackled. Among the three base molecules, N2 is by far the less reactive since its triple bond is very strong and difficult to activate due to the absence of a permanent dipole. Consequently, even with the best catalysts known to date a substantial energy input is required for its activation. Up to now solutions were sought on materials, however recent theoretical studies have revealed that there are intrinsic limitations (i.e. scaling relationships) of catalysis which keep the processes far from the optimum performance. In this work, we will present a unique solution to the aforementioned limitations. We employ electrochemical cells with ionic conducting membranes that allow us to provide reacting species on catalysts with a controllable manner while a radiofrequency plasma is used to increase the reactivity of N2. The spatial separation of nitrogen dissociation and catalytic formation of the target molecules provides true independent parameters to optimise the electrocatalytic reactions. The advantages of our approach compared to conventional plasma catalysis, catalysis or pure plasma processes will be discussed.

Resume : Photoelectrochemical (PEC) water-splitting has been regarded as a completely renewable method to convert the intermittent solar energy into storable chemical energy, hydrogen. However, the most studied semiconductors have either too large bandgap or undesired energy band positions for the PEC water splitting. In this respect, cubic silicon carbide (3C-SiC) can be a good candidate. With a relatively small bandgap of 2.36 eV, 3C-SiC can absorb visible sunlight. Moreover, the conduction and valence band positions of 3C-SiC ideally straddle the water redox potentials. In this work, we demonstrate the great potential of 3C-SiC for the PEC water oxidation [1]. Furthermore, by introducing electrocatalytic and p-type NiO nanoclusters on an n-type 3C-SiC photoanode, we show a significant enhancement of photovoltage and photocurrent together with a substantial decrease of onset potential under AM1.5G 100 mW cm−2 illumination. The photovoltage can reach ~1 V versus reversible hydrogen electrode. The faradaic efficiency measurements demonstrate that NiO also protects the 3C-SiC surface against photo-corrosion. The mechanism of the efficiency enhancement will be also discussed in detail. References: [1] Jingxin Jian, Yuchen Shi, Sebastian Ekeroth, Julien Keraudy, Mikael Syväjärvi,Rositsa Yakimova, Ulf Helmersson and Jianwu Sun*, “A nanostructured NiO/cubic SiC p–n heterojunction photoanode for enhanced solar water splitting”, Journal of Materials Chemistry A, 7, 4721-4728, (2019).

Resume : Graphitic carbon nitride (C3N4) holds an individual 2D structure and tunable electronic structure, which could serve as an excellent candidate for environmental remediation and solar fuel generation. Herein, self-supported oxygen-doped carbon nitride aerogel (OCNA) was successfully fabricated through a facile self-assembly method combined with hydrothermal process, without adopting any harmful solvents or cross-linking agents. The fabrication mechanism of OCNA was discussed. OCNA exhibited much faster charge separation efficiency, longer carriers’ lifetime than bulk carbon nitride (BCN). More importantly, oxygen-doping led to a more negative conduction band (CB) position and narrower band gap (Eg). Hence, the spectral response range of OCNA was extended dramatically and the hydrogen evolution rate (HER) of OCNA (λ > 510 nm) was about 26 times as high as that of BCN prepared herein. OCNA exhibited a remarkable apparent quantum yield (AQY) of 20.42% at 380 nm, 7.43% at 420 nm and 1.71% at 500 nm, superior to most of the reported C3N4-based materials. This work paves a facile colloid chemistry strategy to assemble self-supported 3D CNA that could be widely adopted in the sustainability field.

Resume : In general, a heterogeneous photocatalyst shows low activity due to the rapid recombination of the photoexcited electron-hole pairs and long diffusion path from the bulk to surface to react with reactants. Herein, to the best of our knowledge, it is the first time to report the new concept of quasi homogeneous photocatalysis in bulk, and to construct the corresponding reaction system: low polymeric carbon nitride (PCN) with suitable reactants such as formic acid and oxalic acid. In this system, the PCN with low polymeric degree can allow the reactants to effectively enter its bulk, which greatly decreases the diffusion path of the photoinduced holes to the reactants. Thus, the reactants efficiently scavenge the holes to improve the photocatalytic hydrogen evolution originated from the photoinduced electrons. The highest apparent quantum yield for hydrogen generation at 420 nm reaches 39.1% in formic acid reaction system, much higher than the most reported data. These findings provide new insights for understanding the photocatalytic nature of PCNs, and pave a way to fabricate new efficient photocatalyts and construct new reaction systems for hydrogen production.

Resume : Global warming, caused by green house gases, has been emerging as one of the biggest environmental issue. The raising temperature could be very harmful to us and our earth. To prevent the global warming, many researches has been conducted to lower the concentration of CO2 in the air. For the reason, the interest for conversion of CO2 into energy-rich fuels using solar energy has been increased as a promising approach to address the environmental pollution. p-type Si is considered to be one of the most promising candidates for photocathode because of its narrow band gap, earth abundance, and well-established production technology with relatively low costs. It also has the appropriate band energies to transport the photogenerated electrons to the CO2 reduction potential for various products, such as CO, HCOOH. But there are some issues about Si photocathodes for CO2 reduction. The high reflectance of Si lowers the light absorption. And Si is not stable in the electrolyte due to photocorrosion, and has a disadvantage that the hydrogen reduction reaction as unwanted competitive reaction is dominant. Herein, We demonstrate the fabrication of Si photocathode with Ag nanoparticles decorated TiO2 nanorods using hydrothermal method and electrodeposition method. TiO2 is known to be thermodynamically stable in aqueous electrolytes. Also the nanostructured TiO2 can enhance the light absorption by reduce the light reflection. Furthermore, Ag is well known material to selectively reduce CO2 to CO. Therefore we report the selective CO2 reduction to CO on p-Si photocathode using solar light.

Resume : Development of sustainable energy sources is an urgent issue to meet growing demand in world energy consumption. Among the various types of sustainable energy, hydrogen and ammonia are one of the most promising renewable energy sources with a high energy density. The discovery of efficient catalysts represents one of the most important and challenging issues for the implementation of photoelectrochemical (PEC) or electrochemical fuel production. A critical requirement for outstanding catalysts is not only an ability to boost the kinetics of a chemical reaction but also a durability against electrochemical and photo-induced degradation. Generally, precious metals, such as platinum, exhibit superior performance in these requirements; however, high cost of the precious metal is the biggest barrier to widespread commercial use. To address this critical and long-standing technical barrier, I have focused on an intense search for efficient, durable, and inexpensive alternative catalysts. M y research have been concentrated on two subjects; (1) new possibilities of an atomic-scale catalyst as the efficient water splitting catalysts, (2) the electrochemical production of ammonia using metal nitride-based catalysts. (1) Carbon-based nanomaterials have emerged as promising candidate catalyst for HER. The design of carbon-based catalysts represent an important research direction in the search for non-precious, environmentally benign, and corrosion resistant catalysts. Especially, graphene possesses excellent transmittance and superior intrinsic carrier mobility, thus there have been several attempts to use graphene as a catalyst. It has been reported that reduced graphene oxide containing catalytic active materials exhibited improved activity in HER, oxygen evolution reactions, and oxygen reduction reactions. In most cases, the role of carbon materials is limited to an electrical conducting substrate or a supporter that enhances the performance of other decorated active catalysts. There is no report of the application of monolayer graphene to hydrogen production. For the first time, I investigated new possibilities for monolayer graphene as an electrocatalyst for efficient HER and found that atom ic defect engineering such as nitrogen doping through treatment with N2 plasma improved the catalytic activity. This study has also attracted particular interest to the materials and chemical society in that it has demonstrated the role of carbon-based catalysts with comprehensive electrochemical analysis as well as the first demonstration of monolayer graphene as the HER catalyst. (2) The reduction of nitrogen to produce ammonia has been attracting much attention as a renewable energy technology. Ammonia is the basis for many fertilizers and is also considered an energy carrier that can power internal combustion engines, diesel engines, gas turbines, and fuel cells. Traditionally, ammonia has been produced through the Haber-Bosch process, in which atmospheric nitrogen combines with hydrogen at high temperature (350-550?) and high pressure (150-300 bar). This process consumes 1-2% of current global energy production and relies on fossil fuels as an energy source. Reducing the energy input required for this process will reduce CO2 emissions and the corresponding environmental impact. For this reason, developing electrochemical ammonia-production methods under ambient temperature and pressure conditions should significantly reduce the energy input required to produce ammonia. Metal nitrides are an interesting class of materials for electrochemical ammonia synthesis because they may be able to form ammonia through Mars-van Krevelen mechanism. In the mechanism, a surface N atom is reduced to ammonia, leaving behind a vacancy in the metal nitride surface. This vacancy can then be filled by dissolved N2, which can be further hydrogenated releasing ammonia and regenerating the metal nitride surface. Thus, the suggested might also cause a dynamic Faradaic redox reaction to occur at the surface of the electrode. Here, we report on the experimental electrochemical production of ammonia using metal nitride-based catalysts. Upon applying a reducing potential in N2 purge electrolyte, ammonia was detected using a colorimetry assay test and FTIR spectroscopy. VN, ZrN, Mo2N are interesting materials going forward to study for nitrogen reduction to ammonia due to its significant Faradaic efficiency in an aqueous system under ambient conditions.

Resume : In this work, we report on a facile and novel method for decorating titanium dioxide (TiO2) nanotubes with Rh nanonetworks for photocatalytic applications. In a first step, a metallic Ti-Rh (0.2 at%) alloy is etched in kroll’s solution leading to dealloying surface which results in the formation of Rh nanoparticle-networks on the alloy surface. By subsequent anodization of the surface samples, Rh:TiO2 nanotubes can be grown where the tubes mouth are strongly decorated with Rh nanoparticles network (RhNs) as evident from X-ray photoelectron spectroscopy (XPS) analysis. These Rh oxide Ns are converted to metallic Rh under UV irradiation. Here a time dependence increasing H2 evolution from the RhN decorated TiO2 nanotubes is observed under steady state conditions. These nanotubes Rh-decorated by pre-dealloying yield a stable structure providing 5-times higher H2 evolution activity in comparison to nanotubes decorated by conventional sputtering (same loading), and 228 times higher activity than pristine TiO2 nanotubes.

Resume : Template-Free Synthesis of Hollow Iron Phosphide?Phosphate Composite Nanotubes for Use as Active and Stable Oxygen Evolution Electrocatalysts Junyuan Xu, Ana Aráujo, Lifeng Liu* International Iberian Nanotechnology Laboratory (INL), 4715-330 Braga, Portugal * lifeng.liu@inl.int Keywords: oxygen evolution reaction, iron phosphide?phosphate, hollow nanotube The oxygen evolution reaction (OER) is a half-cell reaction that is of importance to many electrochemical processes, especially for electrochemical and photoelectrochemical water splitting. Developing efficient, durable, and low-cost OER electrocatalysts comprising Earth-abundant elements has been the focus of electrocatalysis research. We report a cost-effective, scalable, and template-free approach to the fabrication of hollow iron phosphide?phosphate (FeP?FePxOy) composite nanotubes (NTs), which is realized by hydrothermal growth of iron oxy-hydroxide nanorods and a subsequent post phosphorization treatment. [1] When used to catalyze the OER in basic medium, the as-synthesized FeP?FePxOy composite NTs exhibit excellent catalytic activity, delivering the benchmark current density of 10 mA cm?2 at a low overpotential of 280 mV and showing a small Tafel slope of 48 mV dec?1 and a high turnover frequency of 0.10 s?1 at the overpotential of 350 mV. Moreover, the composite NTs demonstrate outstanding long-term stability, capable of catalyzing the OER at 10 mA cm?2 for 42 h without increasing the overpotential, holding substantial potential for use as active and inexpensive anode catalysts in water electrolyzers. References [1] J. Y. Xu, D. H. Xiong, I. Amorim, L. F. Liu ACS Appl. Nano Mater. 2018, 1, 617-624.

Resume : The precise identification toward active sites of catalysts and the monitoring of product information are highly desirable to understand how the materials catalyze a specific electrocatalytic reaction. With recent developments of in situ and operando characterization techniques, it has been extensively observed that most of the catalysts would undergo structural self-reconstruction as a result of electro-derived oxidation or reduction process of the catalysts at a given potential, often accompanied by the increase or decrease of catalytic activity as well as the change of catalytic selectivity. Here, we will present couple of works regarding structural self-reconstruction of electrocatalysts in several typical electrochemical reactions [1-3]. With this, we hope to provide deep insight into electrocatalysis during dynamitic working process, as well as to offer guidelines for rational design of advanced electrocatalysts. Ref: [1] Zhang Y.K., Wu C.Q., Jiang H.L., Lin Y.X., Liu H.J., He Q., Chen S.M., Duan T., Song L. Atomic Iridium Incorporated in Cobalt Hydroxide for Efficient Oxygen Evolution Catalysis in Neutral Electrolyte. Advanced Materials, 1707522 (2018). [2] Jiang H.L., He Q., Li X.Y., Su X.Z., Zhang Y.K., Chen S.M., Zhang S., Zhang G.B., Jiang J., Luo Y., Ajayan P.M., Song L. Tracking Structural Self-Reconstruction and Identifying True Active Sites toward Cobalt Oxychloride Precatalyst of Oxygen Evolution Reaction. Advanced Materials, 1805127 (2019). [3] Jiang H.L., He Q., Zhang Y.K., Song L. Structural self-reconstruction of catalysts in electrocatalysis. Accounts of Chemical Research, 51, 2968-2977 (2018).

Resume : p-Silicon has been widely used as a photocathode in solar-driven hydrogen production. However, due to the poor electrochemical stability and sluggish catalytic behavior, a passivation layer and hydrogen evolution reaction (HER) catalysts are usually needed to couple with Si photocathodes, to achieve satisfactory photoelectrochemical (PEC) performance. As opposed to the commonly used Si/passivation layer/catalyst sandwich configuration, we herein report conformal and continuous deposition of a bifunctional cobalt phosphide (Co2P) layer directly on lithography-patterned highly-ordered SiNW arrays and inverted pyramid textured Si wafers [1, 2]. The deposition was realized by drop-casting of Co-containing precursor solutions on Si photocathodes, followed by a low-temperature phosphorization treatment. The conformal and continuous Co2P layer endows dual functions: on the one hand, it serves as a highly-efficient catalyst capable of substantially improving the photoelectrocatalytic activity towards the HER; on the other hand, it can effectively passivate Si protecting it from photo-oxidation, thus prolonging the lifetime of the electrodes. As a consequence, both photocurrent density and operational stability have been substantially improved. The combination of passivation and catalytic functions in a single continuous layer represents a promising strategy for designing high-performance semiconductor photoelectrodes for use in solar-driven water splitting, which may simplify the fabrication procedures and potentially reduce the production cost. References: [1] S.M. Thalluri, J. Borme, K. Yu, et al. Nano Res. 2018, 11, 4823. [2] S.M. Thalluri, B. Wei, R. Thomas, et al. ACS Energy Letters, in revision

Resume : The development of materials to monitor and minimize negative impacts on the environment and human health has been widely studied. In this sense, the aim of this work was the development of a high performance device for the , built by electrospinning the BiVO4/GO, obtaining through the technique, nanofibers with high surface area when compared with other techniques of deposition. The BiVO4 band gap value (2.4 eV) and its absorption in the visible region (520 nm), together with the high conductivity of the GO, a p-n heterojunction was formed, thus increasing the efficiency of the device, provided optimum results [1]. Optical and Scanning Electron Microscopes (SEM) were able to morphologically confirm the efficiency of the electrospinning technique in the preparation of the BiVO4/GO nanofibers, showing excellent fiber uniformity, no coalescence and obtaining fibers with diameters between 60 and 96 nm. The photoelectrovoltaics measurements showed a significant improvement in the photogenerated current, using the nanofibers, confirmed by the increase of the peak current and the decrease in the value of the peak potential when compared to other methods of preparation already described in literature [2]. In this way, the data corroborate that the union of the photoelectrocatalytic effect of BiVO4/GO and electro-spinning process have a high potential for applications in the field of renewable energy generation. Acknowledgement: CDMF (CEPID/FAPESP) 2013/07296-2, CNPq 159615/2018-6. References: [1] LIU, M., SUZUKI, Y., Current Nanoscience 11 (2015) 499-503 [2] SILVA, M. R., et. al., J Solid State Electrochem 16 (2012) 3267–3274

Resume : Fossil fuels are a finite resource that produce emissions which are polluting and warming the planet. However, the sun can be used for water splitting to generate hydrogen and oxygen, which can be used as clean fuels. Towards this end, it has been established that plasmonic metal/ semiconductor heterostructures are promising candidates for visible light driven photocatalysis [1]. Herein we present the colloidal growth of titania, a semiconductor which absorbs in the ultraviolet, in nanoporous gold, a spongelike nanostructured gold network that displays broadband plasmonic absorbance and can catalyze the oxygen evolution reaction [2]. The thickness and homogeneity of the titania grown can be controlled by changing reaction parameters such as pH, surfactant chain length and concentration, and reaction time. Controlled titania growth within the nanoporous gold provides photocatalytic water splitting in the visible spectrum, and a range of structural colors can be produced by the growth of a titania film atop the surface. The purported mechanism for hydrogen evolution in the visible spectrum is plasmon resonance-enhanced injection of hot electrons into titania [3]. References: [1] Ma, Liang, et al. Catalysts 2018, 8(12), 634 [2] Graf, Matthias, et al. Nanoscale 2017, 9(45), 17839-17848 [3] Si, Yuelei, et al. Appl. Cat. B: Env. 2018, 220, 471-476

Resume : Photo-electro-catalytic (PEC) water splitting is a promising approach to produce fuels, such as hydrogen,from water using solar energy. An integrated PEC cell consists of a photovoltaic cell (PV) directly combined with an electrolysis cell (EC), where the chemical reactions take place. The efficiency of an integrated PEC device is defined by the solar-to-fuel efficiency, describing the amount of fuel produced by the incident power of the illumination spectrum. In the case of multi-junction Si based solar cells [1], used as photoelectrodes in the present work, annual variations in the solar spectral quality influence the amounts of photogenerated charge carriers in each sub cell. This influences long-term energy conversion, and thus both the photoelectrode and PEC device performance under varied spectral conditions differfrom the performance obtained under standard AM1.5G illumination. Our model accounts for spectral effects in terms of annual variations in illumination for a range of average photon energies of the spectrum. The electrical output of the photoelectrode is combined with the current voltage behavior of the electrolysis, enabling the long-term (annual) performance of the PEC device to be evaluated. We report on the long-term evaluation of the hydrogen production by an integrated PEC device employing various types [1] of multi-junction silicon thin film (STF) solar cells in respect of the influencing parameters.The long-term outputof PEC devices based onthese multi-junction cells is compared and discussed for different catalyst systems based on earth-abundant [2] and precious metal catalysts. [1] F. Urbain, V. Smirnov, J.P. Becker et al, Energy Env. Sci. 2016, 9, 145–154 [2] K. Welter, N.Hamzelui, V. Smirnov et al, J. Mater.Chem. A 2019, 6, 15968-15976

Resume : Despite the recent promise of transition metal carbides as non-precious catalysts for hydrogen evolution reaction (HER), their extension to oxygen evolution reaction (OER) in order to achieve the goal of overall water splitting remains a significant challenge. Herein, a new Ni/MoxC (MoC, Mo2C) nanoparticles supported N-doped graphene/CNT hybrid (NC) catalyst is developed via a facile, one-step integrated strategy which can catalyze both the HER and OER in an efficient and robust manner. The catalyst affords low overpotentials of 162 and 328 mV to achieve a current density of 10 mA/cm2 for HER and OER, respectively, in an alkaline medium which either compares favourably or exceeds most of the Mo-based catalysts documented in the literature. The electronic synergistic effect between MoxC, Ni and NC are responsible for the higher electrocatalytic activity wherein, a tandem electron transfer process yields both excellent HER and OER activity. [1] Unfortunately, however, the synergy among the components was curtailed on account of large spatial separation. To mitigate this problem, we pyrolyzed a PANI/NiMoO4 nanowire@rGO hybrid which brought the individual components closer as compared to the previously adopted method resulting in improved catalytic activity. To further enhance the intimacy in these multi-component catalysts, a MOF-confined synthesis method was developed which resulted in the best activity among all the catalysts developed in the series.

Resume : Utilization of carbon dioxide conversion to chemical fuels using an artificial photocatalyst under solar irradiation is an ideal goal in renewable energy studies. To date, a variety of strategies have been demonstrated to boost the quantum efficiency of CO2 photoreduction. Coupling of semiconductors considered one of the key challenges to designing a good photocatalyst that can activate the CO2 molecule with smallest possible activation energy and produce selective fuels. Since the activity and selectivity are mainly determined by the suitable band structures and surface states of photocatalysts as well as the photoreaction conditions. In this study, we fabricate ZnS/ZnIn2S4 composite for CO2 reduction under visible light irradiation. When the mass ratio between Zinc and Indium is varied, the composite catalyst shows dramatically increasing of acetaldehyde and methanol formation as major products of CO2 conversion. The optimum ratio exhibits a 200 times enhancement over a single phase of ZnS. The as synthesized samples were characterized by XRD, SEM, TEM, Photoluminescence, UV-Visible diffuse reflectance spectroscopy, XPS, UPS, surface area and CO2 adsorption measurements. Based on the experimental evidence, the interface between both phases is the crucial role of interfacial charge transfer and subsequent enhancing of catalytic activity. In-situ FTIR study has been done to get a deeper insight into the product formation and gain a detailed comprehension of the fundamental reaction steps during the photocatalysis. In conclusion, my presentation will focus on how to efficiently manage the photo-generated charge carriers and surface reactions of semiconductor photocatalysts to boost the photoreduction activity.

Resume : Photovoltaic (PV) driven electrochemical (EC) cells can be used for the generation of clean chemical fuels, such as hydrogen. We added a storage battery to this system to investigate how far one could reduce the volatility of PV output by “shaving” peaks of energy production and thereby approach stability requirements e. g. for the electricity distribution grid. A properly matched battery will back up idle periods in PV generation and reduce required peak power of the costly EC part of the system. We have investigated a small scale system that includes a storage battery and an EC cell, together with a multijunction solar cell made of amorphous (a-Si:H) and microcrystalline (μc-Si:H) silicon. In the case of PV-driven water splitting devices, solar-to-hydrogen (STH) efficiencies around 10 % have been achieved with thin-film silicon multijunction solar cells [1]. In the set-up used in the present study, an additional battery is placed in parallel to the EC cell such that the current from the PV device is split between the EC cell and the battery. The energy balance in the system under AM1.5 standard illumination conditions has been investigated with particular focus on how this affects the solar-to-hydrogen (STH), solar-to-battery (STB) and battery-to-hydrogen (BTH) conversion efficiencies. It was observed that the overall system efficiency is strongly dependent on the STH efficiency. The catalysts systems [2] (Ni/Ni and NiFeOX/NiMo) used in the EC cell are found to play a significant role in the power distribution within the entire system. For the Ni/Ni catalyst system the proof-of-concept is demonstrated and the storage battery can be used to power the EC cell in the dark. [1] F. Urbain et al, Energy & Environmental Science 9, 145-154 (2016). [2] K. Welter et al, J. Mater. Chem. A, 6,15968 (2018).

Resume : Titanium dioxide Ti02 exists in three phases; Rutile with a band gap of 3.0 eV (413 nm), Anatase with 3.2 eV (387 nm), and Brookite with 3.3 eV (376 nm). TiO2 reveals a photocatalytic effect starting with wavelengths below the range of the band gaps. Many applications exists by exploiting the UVA range of sun light. With the advent of UVC LEDs new applications were promised; they are smaller and less delicate than traditional mercury vapor lamps which, in addition, need a high voltage as a source. We investigate the quantum efficiency of the photo catalytic effect of TiO2 with UVC LEDs in water. The wavelength were 265 nm, 285 nm, and 365 nm. The samples of Rutile were prepared under pressure and/or sintered. For Anatase samples doctor blade - method and sintering was employed. The photocatalytic effect of titanium dioxide has been evaluated by the oxidative effect of the hydroxyl radicals produced by the photocatalytic effect. The hydroxyl radicals conversed methylene blue accompanied with a change of the color. A photometer signal determined the decay of the methylene blue in function of time. The resulting properties of the quantum efficiency in function of the wavelengths below 400 nm is still under investigation.

Resume : Global warming and exhaustion of resources, resulting mainly from expansive demand of fossil fuels by continuously increasing population and industrialization of recently emerging developing countries, became an important issue in the world. Among representative CO2 treatment processes (storage in waster coal layer, storage in aquifer, thermochemical catalysis, photochemical catalysis, photo-electrochemical reaction in a system etc.) reported until now, the sun light assisted conversion of CO2 into small organic molecules is emerging and seriously considered, over the world, as a valuable eco-friendly route for CO2 treatment. TiO2 is recognized for its highly economical advantage, its chemical stability and its photo-active properties. It is a photocatalytic materials which, under certain conditions, like a coupling with a conductive graphene sheet, may produce highly valuable chemical products such as formic acid, methanol and methane by redox photo-conversion of CO2. Among various CO2 reduction products, methanol can be an alternative of gasoline. It can be also used as a cheap chemical reagent for the production of ethylene, propylene or more complex molecules in chemical industry. Finally, it can be used in fuel cells instead of hydrogen, reducing the dependency of this energy technology to liquefied fossil natural gas. It is expected that solar light-assisted CO2 conversion in methanol will be increasingly significant as a solution for environmental problems, allowing the development of green economies and opening business opportunities.

Resume : Global energy consumption is one of the biggest problem of the last decades and there are a lot of studies in the direction of solving this problem. Approximately 90% of global energy is produced by burning fossil fuels leading to high emission of greenhouse gases, including numerous carbon and nitrogen oxides. A renewable technology capable to generate high energy yield, avoinding the production of secundary products, is photocatalytic water splitting using sunlight. Multiferroic materials such as BiFeO3 (BFO) are of great interest in this application field. The ferroelectric properties can improve the separation of photogenerated charged carriers leading to an increase of the photogenerated current. In this work, we have studied the functional properties of BFO thin films on different semiconducting or conducting substrates, the deposition method of the films being the pulsed laser deposition (PLD). The optical properties were analysed by spectroscopic ellipsometry (SE) and the band gap value was calculated by using Tauc plot. The structural properties were studied by X-Ray diffraction (XRD), while the topography was analysed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The water splitting efficiency through photocatalytic reaction was performed in a photoelectrochemical cell using a three electrodes system. We have obtained high values of generated photocurrents (up to 0.8 mA/cm2), small leakage currents and high stabilities in time.

Resume : TiO2 nanotube arrays (TNTAs) are self-organized nanomaterials whose vertical orientation and ~10 nm wall-thickness enables the orthogonalization of light absorption and charge separation [1]. TNTAs also provide directed percolation paths for fast electron transport [2]. TNTAs have been shown to be effective photoanodes for water-splitting [3]. The key limitation of TNTAs is the wide bandgap of titania due to which visible photons are not absorbed. We report the successful sensitization of TNTAs by narrow bandgap 1D and 2D nanomaterials such as doped nano-needles of the double helical inorganic semiconductor SnIP [4], nano-sized phosphorus allotropes [5] and quantum dots of doped carbon nitride [6, 7]. The sensitized TNTAs were shown to harvest a significant fraction of visible light and perform photoelectrochemical water-splitting at Faradaic efficiencies higher than 90 %. Photocurrent densities as high as 2.5 mA/cm2 and H2 generation rates as high as 22 micromoles/hour were achieved under AM1.5 one sun illumination using sensitized TNTAs. REFERENCES 1. P. Kar et al. Chem. Commun. 51, pp 7816-7819 (2015) 2. A. Mohammadpour et al. Curr. Nanosci. 11, pp 593-614 (2015) 3. P. Kar et al. Nanotechnology 29, Art. No. 014002 (2017) 4. E. Uzer et al. Nanoscale Adv. DOI: 10.1039/C9NA00084D (2019) 5. E. Uzer et al. ACS Appl. Nano Mater. DOI: 10.1021/acsanm.9b00221 (2019) 6. P. Kumar et al. Carbon 137, pp 174-187 (2018) 7. P. Kumar et al. J. Mater. Chem A 6, pp 12876-12931 (2018)

Resume : Water splitting is regarded as a promising step towards environmentally sustainable energy schemes because electrolysis produces only hydrogen and oxygen, without any by-products. The oxygen evolution reaction (OER), an anodic half-cell reaction, requires extremely high overpotential due to its slow reaction kinetics. In nature, there exists a water oxidation complex (WOC) in photosystem II (PSII) comprised of the Mn and Ca elements. The WOC in PSII, in the form of a cubical Mn4CaO5 cluster, efficiently catalyzes water oxidation with extremely low overpotential value (~160 mV) and a high turnover frequency (TOF) number (~25,000 mmolO2 mol-1Mn s-1). We first identified a new crystal structure, Mn3(PO4)2-3H2O[1], and demonstrated its superior catalytic performance at neutral pH. We revealed that structural flexibility can stabilize Jahn-Teller distorted Mn(III), and thus facilitate Mn redox during catalysis. Additionally, a new pyrophosphate based Mn compound, Li2MnP2O7[2] was studied. We verified the influence of Mn valency and asymmetric geometry on water oxidation catalysis using Li2MnP2O7 and its derivatives. Specific questions that our group intensively focus for the further applications include 1) how we can translate the underlying principles in Mn4CaO5 cluster into the synthetic heterogeneous catalysts and 2) how we can mimic the redox molecule involved biological dark reaction for the CO2 reduction. Toward this vision, we have been developing a new catalytic platform based on sub-10 nm uniform nanoparticles to bridge the gap between atomically defined biological catalysts or their metalloenzyme counterparts and the scalable, electrode depositable heterogeneous catalysts. In this approach, the local atomic geometry is controlled by the nitrogen containing graphitic carbon and the heterogeneous atom doping, that enhance the catalytic activity and selectivity. Additional surface modification by the specific ligand allows for the atomic scale tunability to realize the unique electronic hybridization. References [1] Kyoungsuk Jin, Jimin Park, Joohee Lee, Ki Dong Yang, Gajendra Kumar Pradhan, Uk Sim, Donghyuk Jeong, Hae Lin Jang, Sangbaek Park, Donghun Kim, Nark-Eon Sung, Sun Hee Kim, Seungwu Han, and Ki Tae Nam, J. Am. Chem. Soc. 136, 7435–7443, 2014 [2] Jimin Park, Hyunah Kim, Kyoungsuk Jin, Byung Ju Lee, Yong-Sun Park, Hyungsub Kim, Inchul Park, Ki Dong Yang, Hui-Yun Jeong, Jongsoon Kim, Koo Tak Hong, Ho Won Jang, Kisuk Kang, and Ki Tae Nam, J. Am. Chem. Soc. 136, 4201-4211, 2014

Resume : The electrochemical reduction of CO2 to CO is a promising strategy to convert CO2 into value-added chemicals and to foster the introduction of renewable electricity in the chemical industry. Gold is the most active electrocatalysts capable to produce CO at low overpotentials and with excellent selectivity [1]. Many nanostructuring strategies have been proposed to further enhance its performance. However, the fundamental knowledge of how the atomistic structure of the catalyst surface influences reaction rates and selectivity remains a very important missing fundamental insight. In this work, we experimentally established – for the first time – that atomic steps and undercoordinated sites control the activity of Au for CO2 reduction [2]. We performed a thorough experimental investigation of gold single crystals having well-defined surface orientations. Low-index single crystals, such as (111), (100) and (110), were compared to a steps-rich (211) surface. The electrochemical reduction of CO2 to CO was found to exhibit a pronounced structure sensitivity: the CO partial current density registered with the most active catalysts (i.e., (110) and (211)) is ca. 20-fold higher than the one measured with Au (100). We further established the dominance of steps by selective poisoning experiments. The findings obtained with these model electrodes provide important targets for the development of more efficient nanostructured catalysts. Furthermore, they offer elements to optimize the theoretical description of the electrochemical interface and reaction kinetics.

Resume : Defect engineering is widely adopted technique to increase the density of exposed active sites.[1] Plasma technique is proved as an effective technique to tune the surface properties and edge reactive sites for greatly improving the electrochemical activities.[2] In this report, controlled oxygen (O) and nitrogen (N) plasma used to generate defects and introduce dopants N and O in MoS2 nanosheets to form defect-induced nanocomposite material MoS2-xXx (X= N, O) with sulphur vacancies. Defects in the MoS2 nanosheets help to improve the number of active sites but extra defects deteriorate electron mobility. [3] So here mild plasma technique is used to (1) increase the hydrogen evolution reaction (HER) catalytic activity of MoS2 S-edge and (2) electron mobility of MoS2 nanosheets for fast electron transfer which are one of the responsible factors to increase the electrochemical activities. Electrochemical measurements prove that with the combination of both HER active sites along with the incorporation of O & N dopants enhance HER activities. The superior activity and stability for the hydrogen evolution reaction with low overpotential and fast electron transfer is derived from the coexistence of both doping effect and sulphur vacancies. References: [1] J Xie, Y Xie (2015) ChemCatChem 7: 2568. [2] L Tao, X Duan, C Wang, X Duan, S Wang (2015) Chemical Communications 51: 7470. [3] W Xiao, P Liu, J Zhang, et al. (2017) Advanced Energy Materials 7: 1602086.

Resume : Electrodes based on electro-conductive micro- / nanofiber networks have been widely used as gas diffusion electrodes in many applications, such as environmental sensing, wearable and flexible electronics, and electrochemical energy conversion. We present a versatile method for producing three-dimensional electro-conductive networks by conformally coating an ultrathin Cu layer (~ 50 nm) on electrospun polymer nanofiber membranes. Cu coated nanofibers main-tain the initial topography of polymer nanofibers. The root mean square roughness of the Cu layer remains as low as ~ 5.3 nm. Scanning electron microscopy and elemental mapping via en-ergy dispersive X-ray spectroscopy are used to visualize the cross-section of a Cu coated nano-fiber membrane, confirming the conformal Cu coating on all nanofibers both in the outermost layers and in the bulk of the membrane. An 8-µm-thick Cu coated electrospun membrane has a sheet resistivity < 2.41 Ω□, and a permeability > 1.65 × 10-14 m2 for air. The morphology of nan-ofibers on micro- and nanometer scale and the gas permeability of the electro-conductive net-work are adjustable in the demonstrated process. This innovative design has been proposed for a wide range of potential applications in conjoining solid-liquid-gas three-phase interfaces.

Resume : Chemical treatment of transition metal dichalcogenides (TMDs) is an important process for various energy and electronic device applications. In particular, phase engineering and fabricating nanometer-scale flakes of MoS2 by chemical intercalation has been used as a critical step for electrochemical catalysis, such as active hydrogen evolution1, competing with high performances by platinum-based catalysts. However, the critical chemical process suffers from local and non-uniform phase transition that significantly limits the catalytic efficiency and stability2 moreover, it has been a long-standing challenge to tune phase of tellurium based TMDs, MoTe2, a widely-investigated TMD that possesses intriguing semiconducting, topological and catalytic properties. Considering the small energy difference between polymorphs of MoTe2, compared with that of MoS2, it remains a puzzling issue the tailoring of MoTe2 by chemical ways. Here, we introduce convection-induced chemical intercalation to realize dual-face vertical heterophase TMDs enabling uniform phase transition and novel catalysis. As the intercalation mainly occurs in the vicinity of the top and bottom surfaces, a unique vertical heterophase MoTe2 could be achieved; the resulting dual-face heterophase TMD significantly improves charge transfer resistance (top surface proximity) and electrical contact resistances (bottom surface proximity) for active hydrogen evolution. Moreover, the weak adhesion of flakes by the chemical intercalation allows surface tension-driven automatic exfoliation of large flakes down to monolayer. The bulk heterophase engineering suggests a new platform for hybrid catalysts and next-generation electronic devices based on TMDs. The key novelty and findings of our work can be summarized below. 1. Synthesis of dual-face vertical heterophase TMDs. The induced convectional flow of Li ions provides sufficient energy to overcome the intercalation energy barrier and assure enough charge transfer to manifest uniform phase transition in semiconducting TMDs. The effective intercalation of Li ions near the vicinity of top and bottom surfaces realizes dual-face phase transition (for the first time with tellurides) enabling vertical heterophase MoTe2 single-crystals. 2. Highly-efficient and stable electrochemical catalyst based on the vertical heterophase TMDs. The dual-face phase engineering substantially, 1) lowers the charge transfer resistances on the top surface and improves the hydrogen adsorption, 2) enhance charge carrier conduction through metallic contact on the bottom surface, and 3) The underneath 2H phase keep structural integrity and stability of the active surface and subsurface region that enhance the overall electrochemical catalytic activity. 3. Surface-tension driven automatic exfoliation of TMDs. The surface tension from water droplets cleaves top-most layers of the strained heterophase MoTe2 to producing large lateral-size and high-quality monolayer flakes. The flakes could be used for various energy and device applications studies. 1. Voiry et al. Nat.Materials. 2013,12, 850–855. 2. Wang et al. Chem. Soc. Rev. 2015,44, 2664-2680.

Resume : The electrocatalytic conversion of CO2 and H2O into fuels and valuable chemicals has gained significant interest as a promising route for the storage of renewable energy and the utilization of the captured CO2. An essential step for achieving commercial-scale applications of this technology is to reduce CO2 selectively at high reaction rates. Here, we present the selective electrocatalytic conversion of CO2 into C2H4 on thin Cu surface in a flow-cell configuration. Cu catalysts were synthesized on a gas diffusion layer by magnetron sputtering, showing an improved catalytic selectivity for C2H4 formation while inhibiting H2 evolution and CH4 formation with increasing current densities in neutral electrolytes. Notably, this thin Cu layer is able to achieve about 44% catalytic selectivity in the electroreduction of CO2 to C2H4 at a current density of 200 mA/cm2 in neutral electrolytes. The elevated current densities are likely able to create a high pH near the catalyst surface, which can reduce the activation energy barrier for the C-C coupling step that is linked to C2H4 formation, accompanying with suppressed catalytic selectivity for H2 and CH4.

Resume : Photoelectrochemical solar water splitting offers a clean solution to the world energy requirements of a sustainable future. Achieving its full potential depends on developing inexpensive photoanodes that can efficiently evolve oxygen from aqueous electrolytes, the most kinetically demanding step in water splitting. Here I present recent developments we have achieved in the preparation of inexpensive photoanodes: a nanostructured TiO2 with exposed {0 1 0} facets [1], an α-Fe2O3 self-coated with FeOx electrocatalyst [2] and with an electrodeposited CoFeOx [3], and a novel all-inorganic halide perovskite CsPbBr3 [4]. The nanostructured TiO2 photoanodes are prepared using Ti7O4(OEt)20 clusters as a precursor and resulting photoanodes show a unique morphology resembling desert roses, pure anatase phase and high exposure of the very active {0 1 0} facet, achieving remarkable ⁓100% IPCE efficiency at 350 nm wavelength [1]. α-Fe2O3 photoanodes simultaneously coated with FeOx electrocatalyst are prepared using precursors whose morphology and crystallinity is tuned with lactic acid additive, boosting photoanode photocurrents from 0.32 to 1.39 mA cm-2 at 1.23 V (vs. RHE) [2]. An extended electrochemical characterisation also shows that the charge transfer to electrolyte at α-Fe2O3 interfaces can be boosted by an extremely thin layer of CoFeOx, unlike less thin CoFeOx layers that just reduces surface recombination due to self-oxidation [3]. Finally, all-inorganic halide perovskite CsPbBr3 photoanodes are prepared using carbon as a hole transport layer [4]. This type of semiconductor is revolutionising the field of solar cells due to their high efficiencies and inexpensive preparation but remain practically unexplored in applications using aqueous electrolytes. However, our developed inexpensive carbon layers effectively protect the halide perovskite for more than 30 h directly immersed in water, evolving oxygen with a Faradaic efficiency of 82% and achieving photocurrents above 2 mA cm−2 at 1.23 V (vs. RHE). [1] M. Regue, S. Sibby, I. Y. Ahmet, D. Friedrich, F.F. Abdi, A. L. Johnson, S. Eslava, submitted, 2019 [2] D. Walsh, J. Zhang, M. Regue, R. Dassanayake, S. Eslava, ACS Appl. Energy Mater. 2019, 2, 2043–2052 [3] J. Zhang, R. García-Rodríguez, P. Cameron, S. Eslava, Energy Environ. Sci. 2018,11, 2972-2984 [4] I. Poli, U. Hintermair, M. Regue, S. Kumar, E.V. Sackville, J. Baker, T.M. Watson, S. Eslava, P.J. Cameron, Nature Communications 2019, 10, 2097

Resume : Nanostructured semiconductor metal oxides has recently gained considerable attention due to their intrinsic properties such as a high surface area, short solid state diffusion path, high aspect ratio (1D materials), fast electron separation and transport. They are commonly considered as materials for clean energy generation and storage using photovoltaic, photoelectrochemical water splitting, photocatalytic, fuel cell devices, batteries and supercapacitors. Recently, anodization of metals has been adapted for formation of nanostructured oxide semiconductors such as TiO2, WO3, Fe2O3, SnO2 and others. By controlling parameters of the electrochemical oxidation, especially the applied anodizing potential, temperature, electrolyte composition and the process duration, a great variety of unique oxide structures with different morphologies and characteristic parameters can be obtained. Here, we presented some data on the photoelectrochemical properties of nanostructured anodic metal oxides. Semiconducting properties of those oxides, especially band gap energy values, were studied by using UV-Vis reflectance spectroscopy and electrochemical techniques. Photoelectrochemical measurements were carried out using a potentiostat in a three-electrode cell where anodic oxide photoanodes were used as working electrodes. A correlation of the semiconducting behavior with the morphology, structure and composition of anodic oxides was performed. Acknowledgements This work was partially supported by National Science Centre, Poland (Project No. 2016/23/B/ST5/00790).

Resume : An efficient conversion of solar energy to hydrogen via photo-electrochemical water splitting is one of the strategic goals of sustainable energy research. This approach smartly overcomes the problems on energy storage from the solar flux, by transforming solar light into compounds, which can be stored, transported and later used on demand. Among various semiconductor photocatalytic materials, tantalum nitride (Ta3N5) is one of the promising candidates due to its low energy band gap (2.1 eV), suitable band position and theoretical STH of ~15.9%. However, Ta3N5 has a poor charge transport which can be partially illuminated by controlling materials crystallinity, and by integration of a co-catalyst to prevent materials corrosion from self-oxidation by the photogenerated holes. An alternative approach to compensate the poor charge transport in the Ta3N5 material, a (1-D) nanostructure, such as nanorods, was proposed. Here we report on the fabrication of vertically oriented and well-separated single crystalline Ta3N5 nanorods (NRs) on a Ta substrate. The fabrication of TaOx-NRs is performed by combining the Glancing Angle Deposition technique with the nitridation process in ammonia, followed by co-catalyst modification. The fabricated photoanodes Ta/Ta3N5-NRs/NiFeOx show the highest photocurrent in the range of 9.9 mA cm-2 at 1.23VRHE, which is 80 % of the possible theoretical maximum. Additionally, the onset potential was detected at 0.45VRHE and the photocurrent value was completely saturated at 1.05 VRHE.

Resume : Quaternary chalcopyrite semiconductors draw great attention in solar cell applications due to their proper bandgap energy for sunlight harvesting and high optical absorption coefficient. Recently, many world-wide research groups have been focused on the fabrication of copper-based chalcopyrite semiconductor thin films via low-cost and rapid, solution-based techniques. In this study, we have reported the deposition of copper-indium-gallium-sulfide (CIGS) and indium sulfide (InS) heterojunctions via spray pyrolysis, a facile and cost-effective method to built functional thin films. After successful deposition of the CIGS-InS thin films on the nanostructured ZnO, deposited by chemical bath deposition technique, they have been utilized into the photoelectrochemical solar cell (PEC-SC) for water splitting. It has been observed that the inverted configuration of ZnO-CIGS-InS resulted in the higher photoconversion efficiency compared to the other device structures. More specifically, the incident photon to charge carrier efficiency (IPCE) of 42% has been calculated at 367 nm. Besides, we have been demonstrated that the structure and the morphology of the ZnO electrodes have a drastic impact on PEC-SC performance. In other words, various morphologies, such as nanowire, nanoflower, and nanosheet, having a different crystal structure and stochiometry resulted in a change in optical absorption, photo-generated current density, and efficiency. Bare ZnO electrodes with the morphology of nanowire, nanosheet, and nanoflower had the maximum IPCE of 2, 12 and 39 %, respectively. Hence, we have also been demonstrated here the enhancement of the PEC-SC performance of CIGS-InS based photoelectrodes having various ZnO morphologies.

Resume : The most suitable way to solve the global energy and environmental issues is to use clean and renewable energy production methods. Sunlight can be used as energy source in different photocatalytic reaction, such as water splitting with hydrogen H2 and O2 generation and/or photodecomposition of different organic pollutants from the waste waters. The materials having perovskite-type structure, such as BiFeO3 (BFO) and LaFeO3 (LFO) can be successfully used as photocatalyst in the previously mentioned reactions. The high ferroelectric properties of BFO combined with the great chemical stability and the small band gap value (~ 2.1 eV) of LFO can lead to a new class of heterostructure materials with enhanced photocatalytic properties. In the reported work, heterostructures BFO/LFO and LFO/BFO thin films having different thickness values were produced by pulsed laser deposition (PLD) and their functional properties were studied. The X-ray diffaction (XRD) technique was used as structural characterisation technique, the spectroscopic ellipsometry (SE) for the optical properties study and atomic force microscopy (AFM) and scanning electron microscpoy (SEM) were chosen to study the thin films morphological properties. The PLD obtained thin films were tested in photocatalytic water splitting reaction in the dark and light irradiation conditions. Moreover, the influence of the order of layer depositon (BFO/LFO or LFO/BFO) on the photocatalytic efficiency and stability with the time were investigated.

Resume : Semiconductor photocatalysis technology, which uses solar energy and semiconductor materials to obtain green and clean energy, has become an important way to solve energy and environmental problems. Light absorption efficiency, separation and collection efficiency of photogenerated carriers and redox reaction rate are the three key factors that determine the photocatalytic performance. However, in the actual photocatalytic reaction process, the bandgap of semiconductor materials must satisfy certain conditions to meet the thermodynamic conditions required for specific chemical reactions. Taking photocatalytic water splitting as an example, the minimum Gibbs free energy required is 237.18 kJ mol-1 and the conversion potential is about 1.23 V. Additionally, due to the existence of overpotential, the minimum bias voltage required for water splitting is actually higher than 1.23 V and the minimum is about 1.6 to 1.7 V, which requires the bandgap of semiconductor to be more than 1.6 eV to 1.7 eV. Accordingly, Solar light below 750 nm can only be absorbed, while near infrared light (700-1100 nm), which accounts for about 54% of the solar spectrum, cannot be absorbed and utilized. Different semiconductors combine to form heterostructures can effectively break the trade-off of light absorption and target reaction. Firstly, different semiconductors have different band gaps, which can absorb light in different wavelength ranges. After forming heterostructure, the absorption range of a single semiconductor will increase. Secondly, band bending will occur when they combine because of their different Fermi levels and form a space charge region. The photogenerated carriers can be effectively separated and the recombination rate can be reduced by the internal field in the space charge region. Thirdly, the photoetching of narrow bandgap semiconductors is prevented. Based on this, we designed and constructed heterostructure using semiconductors with different band structure. By regulating the electronic and band structure, light absorption efficiency and carrier separation and collection efficiency enhanced simultaneously, which thereby promoted the photocatalytic performance effectively. Hematite (α-Fe2O3), an n-type semiconductor with band gap of 2.1 eV, is one of few semiconductors meeting these requirements. In addition to up to 40% of the solar light absorptance, the valence band maximum (VBM) of α-Fe2O3 is at 2.3 V vs. reversible hydrogen electrode (RHE), providing enough extra potential for oxygen evolution reaction (OER). Theoretically, α-Fe2O3 photoanode can provide the photocurrent density of 12.6 mA cm-2 under AM 1.5G solar illumination, holding a maximum solar-to-hydrogen (STH) conversion efficiency of 15.5%. However, the actual maximum STH efficiency achieved at present for α-Fe2O3 photoanode is only 3.4%. The low practical STH efficiency of α-Fe2O3 stems from several problems. Firstly, there is a conflict between generation and collection of photogenerated carriers. The hole diffusion length of α-Fe2O3 is only 2-4 nm,[7] and far less than the light penetration depth.[8] So, it is difficult to maintain light absorption and carrier transport performance simultaneously. Secondly, based on thermodynamic requirements, bare α-Fe2O3 with the conduction band edge lower than H+/H2 redox potential is not conducive to hydrogen evolution reaction (HER). Thirdly, surface reaction kinetics is slow and recombination of photogenerated carriers is aggressive, causing a large overpotential for the OER reaction. In this work, we designed and prepared planar n-Si/α-Fe2O3 heterostructure to overcome the drawbacks of α-Fe2O3 mentioned above. One curial consideration is the band alignment. Z-scheme heterostructure is a desirable charge transfer mode because it maintains the strongest redox capacity. It requires the Fermi level of Si be more negative than that of α-Fe2O3 to avoid Schottky barrier so that both the photogenerated electrons of α-Fe2O3 and the photogenerated holes of Si move towards the interface under irradiation. Nevertheless, Fermi level of the most commonly used p-type Si in Si/α-Fe2O3 heterostructure is too positive, which may form a Schottky barrier at the interface and hinder the Z-scheme conduction. Moreover, too positive Fermi level is not conducive to improving photovoltage and decreasing onset potential. Compared with p-type Si, n-type Si has more negative Fermi level that can overcome the above-mentioned shortcomings. Band structures of n-Si and α-Fe2O3 were studied to help design the structure of photoelectrodes. By the process of optimizing the resistivity of n-Si substrate, the depletion layer width of n-Si with a resistivity of 1 Ωcm is the closest to this photo penetration depth, so the photogenerated electron-hole pairs in the depletion region (or the photo penetration depth) can be separated efficiently by the internal electric field, leading to the highest photocatalytic performance. An ohmic contact layer, indium tin oxide (ITO), was introduced as an electron transport mediate at the Si/α-Fe2O3 interface to reduce the trapping of carriers by interface states and hence improve the carrier separation. In addition, the VBM of ITO is more positive than that of α-Fe2O3, so it acts as a hole transport barrier to prevent the reversed movement of photogenerated holes of α-Fe2O3 to the VBM of Si. The cocatalysts were introduced to improve the surface reaction kinetics. After these optimizations, The absorptance of the n-Si/α-Fe2O3 film increases over the measured wavelength range, especially in the visible light region. The introduction of the ITO intermediate layer further promotes the light absorption of electrode by ~30% compared with n-Si/α-Fe2O3 electrode in the range of 600 nm to 800 nm. Simultaneously, the PEC performance of α-Fe2O3 was improved significantly. The photocurrent density at 1.23 V vs. RHE reached as high as 1.987 mA cm-2, which is 99.35 times that of the pure α-Fe2O3 and is the best value for the planar super thin (the thickness is lower than 50 nm) α-Fe2O3 and its heterostructures. Besides, the onset potential was enhanced by 0.57 V compared with unmodified α-Fe2O3. This work may provide inspiration for optimizing the performance of other heterostructure photocatalysts.

Resume : Water electrolysis is an appealing solution to energy sustainability, being able to convert surplus electrical energy to chemical energy by producing hydrogen for end-use and as an energy storage medium. Among the various approaches, alkaline electrolysis is the only commercialized technology, since it relies on low-cost electrocatalysts. However, its market penetration is still low due to limited efficiency and insufficient compatibility with the intermittency of renewables. On the other hand, PEM electrolysers utilize a H conducting polymer electrolyte and have a zero-gap design which offers high currents and responsiveness to variable power input. PEM electrolysis has not yet reached commercialization because platinum-group metal (PGM) electrocatalysts are required due to the acidic nature of the membrane. To address this, research is directed towards the development of acid-stable low-cost electrocatalysts (i.e. transition metal sulfides/phosphides). An alternative approach is the replacement of the H exchange membrane with an Anion Exchange Membrane. This technology, known as AEM electrolysis, combines the merits of PEM (zero-gap design) and alkaline electrolysis (non-PGM electrocatalysts), but alkaline membranes suffer from low ionic conductivity and poor stability. In this presentation the current status, challenges and perspectives of PEM and AEM water electrolysis will be discussed in terms of the applicability of emerging materials into realistic conditions.

Resume : Hydrogen plays an important role in clean energy technology, complementing intermittent solar/wind power. Remarkably, lightweight hydrogen has the highest specific energy of any known non-nuclear fuel, and it can be used for both energy generation and storage purposes. More importantly, hydrogen is an environmentally friendly fuel, since only energy and water are the end products of the reaction between hydrogen and oxygen, giving rise to the emerging fuel cell technologies and devices. An interesting way to generate hydrogen is offered by water electrolysis, wherein water is simply decomposed to hydrogen and oxygen by applying a voltage bias. Notably, the water electrolysis is a kinetically controlled process characterized by slow charge transfer and insufficient chemical reaction rates, and in reality, a significantly higher overpotential than the standard potential of the water electrolysis (−1.23 V at 25 °C) needs to be applied to drive the reaction. Therefore, electrocatalysts are used to facilitate water electrolysis by reducing the value of the applied overpotential to conduct cathodic water reduction, known as hydrogen evolution reaction, and anodic water oxidation, known as oxygen evolution reaction, which are the key half reactions of electrochemical water splitting. Whereas the best electrocatalysts for water electrolysis are platinum group metals (PGMs), their main drawback is obvious: they are critical and expensive, thus limiting the viability of PGMs for widespread applications. Hence, the current research trend is aiming at searching for alternatives to PGMs. In this talk, I will first introduce transition metal phosphides and borides as an emerging earth-abundant class of electrocatalysts for water electrolysis, followed by our approaches in interface engineering, synthesis, and electrocatalytic understanding. I will then showcase our recent progress in using these electrocatalysts for water reduction and oxidation.

Resume : Appropriate electrode materials and electrolytes need to be developed for the implementation of solar water splitting with tandem devices, which help to relax requirements for the materials and to increase the solar-to-hydrogen conversion efficiency. Electrode materials based on earth-abundant elements are particularly interesting. Binary oxides have been investigated for more than four decades, while ternary (and more complex) oxides and oxynitrides only recently are starting to draw significant attention. Among the oxides that have been demonstrated to yield significant efficiencies we find CuO as a photocathode and Fe2O3 as a photoanode. Ternary oxides and oxynitrides may offer new opportunities with an adequate trade-off between band gap value and stability. The consortium of the FotoH2 project is working along these lines to identify on theoretical grounds novel electrode materials and to modify classical ones with the aim of developing a practical, cost-effective water splitting device. Strategies for electrode preparation, modification and characterization will be presented. We are also exploring the prospects of using polymer electrolyte membranes as a way to develop a scalable quasi-solid state photoelectrolyzer design. Some results on this approach will be presented together with the challenges of this type of device. This work has been financed by European Commission, in the framework of the Horizon2020 Programme, Project FotoH2, Grant No. 760930.

Resume : Water electrolysis (WE) and fuel cells (FC) are becoming highly attractive technologies in coupling the sectors electricity supply, mobility and transport, heating, energy storage and industry in a future sustainable energy and economic system. Two different polymer electrolyte membrane technologies are currently under enhanced investigation ? the more mature proton exchange membrane (PEM - acidic environment) which requires PGM catalysts and which is already used in commercial available products and the recently developed anion exchange membrane (AEM - alkaline environment) which enables non-PGM catalysts application but up to now is suffering from poor stability. Oxygen reduction reaction (ORR) in FC and oxygen evolution reaction (OER) in WE are still one of the most challenging reactions in catalysis. Although studies on new Pt and Ir alloys and Pt-free systems are promising, Pt (PEMFC) and Ir (PEMWE) are still considered as benchmark catalysts. Recently developed catalysts and catalyst layers show extremely high activity, performance and durability for both reactions in lab scale but in industrial scale devices their high potential is not yet utilized. The entire process from a lab scale synthesis and tests of active materials (membranes, ionomers, catalysts, catalyst layers, porous structures) to membrane electrode assemblies (MEA) for the use in industrial applications is highly challenging in terms of cost, duration and capital risk. ZBT has the experience and know-how to identify promising active materials for FC and WE via self-developed stepwise testing algorithms and protocols using commercial as well as self-developed test systems and can demonstrate their performance in fully functional close-to-industry operating systems with an active area of up to 400 cm^2.

Resume : Metal-organic frameworks (MOFs) are a class of porous hybrid solids consisting of metal-containing nodes coordinated with multitopic organic linkers. Recently there has been tremendous interest in the exploration of MOFs and their derivatives for electrocatalysis, however slow charge-transport kinetics often limit the performance. Therefore, making suitable carbon composites would greatly improve their electronic conductivity and subsequently the electrocatalytic activity. Herein, we have developed two different routes using cobalt imidazolate frameworks (ZIF-67) to design cobalt selenide (CoSe) hybridized with nitrogen-doped carbon. The solid-state strategy involves the direct conversion of ZIF-67 into CoSe nanoparticles with an average size of ~20 nm encapsulated within N-doped graphitic carbon shells with an average size of 300 nm. Interestingly, this method can easily be extended to similarly synthesize CoTe encapsulated N-doped graphitic carbon cages by simply changing the precursor. The other method involved the self-templated conversion of ZIF-67 into Co nanoparticles encapsulated N-doped carbon polyhedral and their subsequent transformation into vertically aligned CoSe grafted N-doped carbon sheets via a hydrothermal selenization method. Both, these class of materials so synthesized were found to exhibit excellent electrocatalytic activity towards HER and OER in alkaline medium. It is believed that the methods being developed here may be extended to other transition metal chalcogenides for various applications

Resume : Graphene has emerged as a likely candidate for a wide range of electrochemical energy-storage applications, driving research into novel synthetic techniques to produce graphene with appealing properties. Bottom-up synthesis is a scalable route to produce graphene foam with high quality, high purity, high yield and low cost. The mechanism of sodium ethoxide decomposition, as one of the critical synthetic steps, has been studied thoroughly in this study to produce graphenic foam with controlled properties. Both the decomposition temperature and heating rate have a strong influence on the final product. Optimization of the decomposition process yields products with an extremely high surface area approaching theoretical calculation. This optimized material is capable of more than 4 wt% H2 storage at 77K and 10 bar, ranking as the highest hydrogen uptake capacity ever reported for graphitic carbons as hydrogen storage material. Graphenic foam with the large surface area was further decorated with different metal oxide nanoparticles for electrochemical conversion applications. We prepared CeOx islands uniformly dispersed on the graphenic foam using a hydrothermal approach. Due to its 3D structure, these CeOx decorated foam play a significant role as catalyst support in heterogeneous catalysis. Graphenic foam decorated with TiO2 nanoparticles was also studied as photocatalysts for hydrogen evolution from water using a methanol sacrificial reagent, under UV-vis irradiation. Use of the graphenic foam support significantly enhanced the photocatalytic activity compared with pure TiO2 nanoparticles, carbon black support, or reduced graphene oxide supports reported in the literature. The enhanced activity is attributed to the large surface area, and intimate contact between the carbon support and the metal oxide particles, suppressing charge recombination and therefore increasing photocatalytic performance.

Resume : Cu2ZnSnSxSe4-x (CZTSSe) has been developed to be promising platinum (Pt)-free counter electrode (CE) for dye-sensitized solar cells (DSSCs) with porous or crystalline structures. However, it's still challenge to develop CZTSSe electrode with high surface area and low temperature synthesize process. Herein, we develop a low temperature and solution-processable approach to prepare CZTSSe nanosheets as a CE in DSSCs. The synthesized CZTSSe nanosheets on FTO substrate as DSSCs cathode demonstrated a satisfied power conversion efficiency of (5.55%) that is comparable to a Pt-based CE (5.88%). The impressive performance was ascribed from the CZTSSe nanosheets morphology, excellent electrocatalytic activity and the fast reduction reaction kinetics for the electrolyte. Cyclic voltammogram and electrochemical impedance spectroscopy measurements confirmed a low charge transfer resistance at the interface of the CZTSSe nanosheets and electrolyte. The low temperature process, high surface area as well as high reproducibility help the CZTSSe nanosheets stand out as an alternative CE electrocatalyst in DSSC.

Resume : We report the investigation of nanoporous gold-palladium binary alloy catalyst for electro-oxidation of ethanol. We made a ternary alloy of gold, palladium, magnesium and dissolved it in dilute acetic acid for making a nanoporous structure. The microstructure of this catalyst has been characterized using scanning electron microscopy. The results show the as-prepared nanoporous gold-palladium(NPGP) has open pores and ligaments with a size of ~30 nm. Electrochemical measurements demonstrate that this NPGP catalyst has a remarkable electrocatalytic activity and stability towards ethanol oxidation in alkaline media. This method could be extended to easily prepare binary nanoporous structures with designed composition and desired catalytic activity.

Resume : With falling prices for electricity from renewable sources, electrification of important processes in the chemical industry has become relevant. [1] Propene can be oxidized either in the allylic position or at the double bond, allowing for insights into the reaction mechanism, while also yielding important commodity chemicals such as acrolein, acrylic acid and propylene oxide. We showed previously that product selectivity on Pd is steered by in-situ formation of a layer of surface adsorbates.[2] We propose that changing the adsorption geometry by providing different surface sites can influence the formation of such a layer and therefore the product distribution. High surface area catalysts of with different Pd:Au ratios were prepared electrochemically using the hydrogen bubble template method, and characterized with XRD, XPS and SEM. We explore how changing surface sites by alloying impacts adsorption of propene and product distribution by combining electrochemistry-mass spectrometry with bulk oxidation experiments. [1] M. T. M. Koper, in Catalysis in Chemistry and Biology, World Scientifc, 2018, pp. 229–232. [2] A. Winiwarter, L. Silvioli, S. B. Scott, K. Enemark-Rasmussen, M. Sariç, D. B. Trimarco, P. C. K. Vesborg, P. G. Moses, I. E. L. Stephens, B. Seger and I. Chorkendorff, Energy Environ. Sci., 2019, 1055–1067.

Resume : Decoration of atomic scaled Pt clusters in surface defects of highly disordered oxide core (O) – metal shell (M) nanoparticles (NP) is synthesized by using self-aligned nanocrystal growth followed by atomic quench with strong reduction agent. Those clusters localize electrons from neighboring atoms and boost activity of O-M NP in oxygen reduction reaction. With a proper reaction time and loading control, the Pt cluster decorated O - M nanoparticles hold its durability in an accelerated degradation test for more than 0.3M potential sweeping cycles.

Resume : Although the polymer electrolyte membrane fuel cells are close to commercialization, lifetime issues of membrane-electrode assembly (MEA) are still unsolved. The lifetime issues of MEA can be categorized to two reasons, membrane degradation and Pt catalyst degradation. In terms of membrane degradation, CeO2 is the most widely used materials as a radical scavenger to improve chemical stability of membrane. Despite of high chemical stability of CeO2 introduced membrane, however, the negative effect of Ce ions, in particular Ce4+, on fuel cell catalyst has not been studied yet. In this research, we reported the oxidation phenomenon of Pt/C by CeO2 and its mitigation strategy, coating carbon nitride (C3N4) protective layer on CeO2. By using electrochemical analysis, UV-vis and XPS, it is observed that the Ce4+, which is easily dissolved from CeO2 in acidic condition, induces carbon corrosion and accelerates Pt dissolution leading to significant ECSA loss. The negative effect of CeO2 can be mitigated by restricting Ce4+ dissolution from CeO2 particles. In this reason, we introduced C3N4 protective layer, which is highly stable against the strong oxidation power of Ce4+, on CeO2 and observed significantly reduced Ce4+ dissolution rate. Whereas the performance of MEA containing pristine CeO2 was severely decayed with ECSA loss after OCV holding test, the MEA containing C3N4 coated CeO2 showed stable performance and ECSA retention with high OCV durability.

Resume : Over the past few years, graphitic carbon nitride (g-CN) has attracted widespread attention due to its outstanding electronic properties, which have been exploited in applications including in photo- and electro-catalysis, CO2 reduction, water splitting, LEDs and solar cells. g-CN comprises only carbon and nitrogen, and its synthesis entails the polymerization of C and N rich monomers, such like dicyanamide or melamine.[1] However, the traditional solid-state reaction usually yields unordered materials with grain boundaries and low photo-catalytic activity. We recently showed that the supramolecular preorganization of g-CN monomers by using non-covalent interactions prior their calcination at high temperatures results in highly active materials for photocatalytic applications.[2] In this work I will show that the rational design of supramolecular assemblies allow the control of chemical, photophysical and catalytic properties of g-CN toward its utilization as photocatalyst for various reactions.[3] Furthermore, the supramolecular interactions between different starting monomers in different conditions (i.e. solvents),[4] and their role on the materials growth and chemical, photophysical and catalytic properties will be thoroughly discussed. References [1] J. Zhu, P. Xiao, H. Li, S. A. C. Carabineiro, ACS. Appl. Mater. Interfaces 2014, 6, 16449-16465. [2] J. Barrio, M. Shalom, ChemCatChem 2018, 10, 5573-5586. [3] J. Barrio, L. Lin, P. Amo-Ochoa, J. Tzadikov, G. Peng, J. Sun, F. Zamora, X. Wang, M. Shalom, Small 2018, 14, 1800633. [4] S. Dolai, J. Barrio, G. Peng, A. Grafmüller, M. Shalom, Nanoscale 2019, 11, 5564-5570.

Resume : In this work, we developed a hierarchically nanostructured photoanode composed of electrodeposited nanoporous BiVO4 as light absorber and SILAR deposited iron phosphate (FePi) nano-branches as oxygen evolution cocatalyst. It was found that immersion time plays a pivotal role in tuning the morphologies of the formed hierarchical iron phosphate structures. By applying such a hierarchical nanostructure as a photoanode for water splitting reaction, the hybrid photoanode shows a much improved PEC performance compared with bare BiVO4, with a photocurrent density enhancement of 250% and a huge negative shift (~500 mV) in onset potential compared with the reported BiVO4 based nanostructures. Additionally, the maximum photoconversion efficiency of the hybrid electrode also gives 6-fold enhancement compared to that in the absence of iron phosphate. Moreover, the composite photoanode demonstrates a stable photostability at 1.23 V for 6h without observably declining. It is concluded that the giant enhancement of the properties benefits from the improved charge transfer efficiency caused by the coupling with ferrite phosphate, which provides an alternative pathway for the transfer of holes. This, in turn, suppress unproductive and energy-waste surface recombination, reduce surface kinetics barriers and enhance photostability. Therefore, our work demonstrates a facile solution for constructing hierarchical nanostructures for efficient solar water splitting, which is possibly scaled up and extended to other oxide-based electrodes and photoelectrochemical reactions.

Resume : Among other metal oxides, monoclinic BiVO4 is one of the most promising photoanode materials for photoelectrochemical (PEC) water splitting, considering its relatively low band gap value. However, this semiconductor displays intrinsic limitations such as excessive surface recombination and poor charge transfer, which tend to limit its overall performance. In order to alleviate these limitations, several co-catalysts have been commonly used aiming to improve the oxygen evolution kinetics. In this work, we have studied and optimized Ni-Mo layers electrodeposited on BiVO4 and BiVO4/WO3 heterojunctions, which have a significant influence on the PEC behavior improvement, especially at low polarization values. Moreover, a more in-deep analysis through Electrochemical Impedance Spectroscopy has been carried out, for understanding the charge transfer processes in dark and under illumination conditions. Finally, we have combined this approach with the growth of passivation layers by ALD and photoelectrodeposition. A significant interplay between the layers is observed.

Resume : Photoelectrochemical (PEC) water splitting using solar energy to form hydrogen as a storable and eco-friendly chemical fuel provides a potential solution for future energy requirements in a sustainable manner. In a PEC system, semiconductor-based photoelectrodes play a crucial role in light absorption and electron-hole pair generation. Metal oxide semiconductors are the most commonly used photoelectrode materials in PEC process. However, they suffer from low photocurrent density generation owing to their wide band gap. On the other hand, lead halide perovskite (LHP) derivatives are well-known solar cell materials as they can absorb sunlight in the whole visible region. Additionally, the LHP based photoelectrodes exhibit relatively good performance and can be improved via structure optimization and bandgap engineering. This work presents the investigation of LHPs-3D ZnO based photoelectrodes for the feasible use in PEC hydrogen generation. It is observed that the absorptivity of the photoelectrodes increased four times in the visible region when compared to common perovskite thin film structure of LHP-TiO2. Resultingly, the prepared photoelectrode achieved the highest photocurrent of about 11 mA cm2 at 0 V (vs Ag/AgCl) in Na2S/Na2SO3 electrolyte solution under AM 1.5 simulated sunlight conditions. The applied bias photon to current efficiency (ABPE %) has been calculated as 2.5% which is higher than reported literature results. Additionally, the incident photon to charge carrier efficiency (IPCE%) value reached up to 38% at 500 nm under 0V (vs Ag/AgCl). In this work, the effect of the encapsulation metal has also been investigated.

Resume : Solar-driven photoelectrochemical (PEC) hydrogen (H2) generation is a promising approach to harvest solar energy for clean chemical fuels, to address future global energy needs [1, 2]. In the past few years, the performance of PEC devices based on wide bandgap semiconductors sensitized with colloidal quantum dots (QDs) has significantly improved [3]. However, the low photon-to-fuel conversion efficiency and long-term stability of PEC devices based on QDs sensitized wide bandgap semiconductors, are major challenges for its large-scale potential commercialization. Herein, for the first time, we report a simple, fast and cost-effective approach to fabricate high efficiency and stable PEC devices for H2 generation, by fabricating a hybrid photoanode obtained by incorporating small amounts of multiwall carbon nanotubes (MWCNTs) into a TiO2 mesoporous film and sensitized with colloidal heterostructured CdSe/(CdSexS1-x)5/(CdS)2 quantum dots (QDs). We will discuss the role of band engineering of heterostructured QDs to accelerate the exciton separation as well as the incorporation of MWCNTs to enhance the carrier transport within TiO2-MWCNTs mesoporous hybrid film. Resulting PEC devices based on TiO2/QDs-MWCNTs (T/Q-M) hybrid photoanode with optimized amount of MWCNTs (0.015 wt%), yield a saturated photocurrent density of 15.90 mA.cm-2 (at 1.0 V RHE) under one sun illumination (AM 1.5 G, 100 mWcm-2), which is 40% higher than the reference device based on TiO2/QDs (T/Q) photoanodes. Furthermore, the effect of MWCNTs to enhance the long-term stability of PEC device based on T/Q-M hybrid photoanodes under continuous one sun illumination will be highlighted. These results provide fundamental insights and a different approach to improve the efficiency and long-term stability of PEC devices and an essential step towards the commercialization of this emerging solar-to-fuel conversion technology. References [1] Y. Tachibana, L. Vayssieres, and J. R. Durrant, Nat. Photonics, 2012, 6, 511–518. [2] S. C. Warren, K. Voitchovsky, H. Dotan, C. M. Leroy, M. Cornuz, F. Stellacci, C. Hebert, A. Rothschild and M. Graetzel, Nat. Mater, 2013, 12, 842–849. [3] H.-J. Ahn, M.-J. Kim, K. Kim, M.-J. Kwak and J.-H. Jang, Small, 2014, 10, 2325–2330.

Resume : Recycling of carbon dioxide to renewable fuels using green energy sources in is an urgent but challenging task. Up to date, Ni supported by CeO2 remains the most widely used material for CO2 methanation due to its high activity and ease of availability. Nevertheless, the working temperature for CO2 hydrogenation in presence of this catalyst is still relatively high. Another uprising field for CO2 reduction is LSPR (local surface plasmon resonance)-enhanced catalysis. Owing to the fact that Ni exhibits a plasmon resonance under visible light illumination, it may result in increasing of its catalytic activity towards CO2 reduction. In this work, we used a photothermal approach to study the effect of temperature and light on the carbon dioxide hydrogenation over Ni-CeO2 catalyst. The hybrid catalysts were tested in a flow-type reactor, which allowed simultaneous heating and illumination of the catalyst. We detected conversion of CO2 to methane starting from 250°C, which significantly increased under light illumination. The improved CO2 yield is attributed to two contributions from light: absorption of light by ceria and the LSPR enhancement induced by the Ni-nanoparticles. Based on these results, it appears that the reaction temperature can be reduced when the LSPR approach is applied therefore leading to savings in the required thermal energy input. We expect the LSPR approach to pave way to more ecological CO2 methanation using sunlight as the alternative energy source.

Resume : Surface plasmon in metals which has an excellent light-trapping and electromagnetic field concentrating properties can achieve a higher solar light harvesting rate. Surface plasmon can induce hot charge carriers which have been primarily used for photochemistry applications. Hot charge carriers transfer from a plasmonic excited material to an adjacent adsorbate and electron-accepting semiconductor in either direct or indirect styles. However, most of the hot charge carriers decay rapidly before these transferring, thus resulting in a low efficiency of photochemical reactions. In this study, we show that two-dimensional hydrogen doped molybdenum oxide exhibits excellent plasmon resonance effect across the whole visible light and part of the near-infrared light region, depending on the level of hydrogen dopants. At the same time, the plasmonic molybdenum oxide induces significantly prolonged lifetimes of hot charger carriers. The photochemical production of H2 and photo-oxidation of organic dyes using two-dimensional plasmonic molybdenum oxide will be shown in this presentation.