Water Splitting Process Research Articles

Robust Sandwiched B/TM/B Structures by Metal Intercalating into Bilayer Borophene Leading to Excellent Hydrogen Evolution Reaction

AbstractBilayer borophene, very recently synthesized on Ag and Cu, possesses an extremely flat large surface and excellent conductivity. The van der Waals gap of bilayer borophene can be intercalated by metal atoms, tailoring the properties of bilayer borophene. Herein, sandwiched B/TM/B (transition metal, TM = Co, Ni, Cu, Pd) is proposed as a new 2D formation with both energetic, structural, and thermal stability by TM atoms intercalated into bilayer borophene. In addition, it is a novel platform for the electrocatalytic hydrogen evolution reaction (HER). The intercalation metal atom serves as a single‐atomic catalyst. The TM is protected by outside boron layers from being corroded by acidic/alkaline solutions. B/Cux/B, B/Pdx/B, and B/Alx/B with different metal coverage exhibit defect‐independent extremely low HER free energy in the range of approximately −0.162 to 0.179, −0.134 to 0.183, and −0.082 to 0.086 eV which are comparable to the noble metal Pt. Combining excellent conduction, high structural and thermal stability, low resistance to intercalated behavior, an effortless water splitting process, excellent defect‐independent catalytic performance, cheapness and abundance of raw materials, and corrosion resistance, 2D sandwiched B/TM/B (TM = Co, Ni, Cu, Pd) is believed to be promising for electrocatalysis applications.

Metal-Organic Framework-Derived FeCo2S4/Co3O4 Heterostructure with Enhanced Electrocatalytic Performance for Oxygen Evolution and Hydrogen Evolution Reactions.

Herein, a versatile FeCo2S4/Co3O4 heterostructure consisting of zeolitic imidazolate framework ZIF-derived Co3O4 and FeCo-layered double hydroxide-derived Fe-doped Co sulfide is employed for the all-important alkaline full water splitting process. The heterostructure is prepared by combining pyrolysis and hydrothermal/solvothermal processes. The synthesized heterostructure possesses an electrocatalytically rich interface and renders excellent bifunctional catalytic performance. An overpotential of 139 mV for a standard cathodic current of 10 mA cm-2 with a low Tafel slope of 81 mV dec-1 is recorded for the hydrogen evolution reaction. An overpotential of 210 mV is observed for an anodic current of 20 mA cm-2 with a low Tafel slope of 75 mV dec-1 recorded for the oxygen evolution reaction. The full-symmetric two-electrode cell was capable of generating a current density of 10 mA cm-2 at a cell potential of 1.53 V and a low onset potential of 1.49 V. The symmetric cell architecture exhibits remarkable stability, as a negligible potential increase is observed for continuous water splitting over a 10 h period. With the reported performance, the heterostructure compares well with most of the excellent reported catalysts for alkaline bifunctional catalysts.

CeO2 decorated bimetallic phosphide nanosheet as efficient catalyst towards water splitting reaction

Developing low-cost and high-performance electrocatalysts for water splitting is crucial for hydrogen production. In this study, a high-performance hydrogen and oxygen evolution reaction (HER/OER) bifunctional electrocatalyst is developed by introducing oxygen-deficient CeO2 nanoparticles on (Ni, Co)2P nanosheets. The introduction of defective CeO2 modulates the electronic structure of the CeO2@(Ni, Co)2P/NF interface, which offers a synergistic effect promoting the HER/OER reaction in the alkaline water splitting process. Specifically, the CeO2@(Ni, Co)2P/NF electrode exhibits an overpotential of 151 mV for HER and 257 mV for OER at current density of 100 mA·cm−2. In the overall water electrolysis test, it exhibits excellent stability performance at a cell voltage of 1.70 V around 100 mA·cm−2. This work shows an alternative strategy for the development of active bifunctional water splitting electrocatalysts.

Na‐Sm Bimetallic Regulation and Band Structure Engineering in CaBi2Nb2O9 to Enhance Piezo‐photo‐catalytic Performance

AbstractThe piezoelectric enhancement of photo‐catalytic activity for water splitting and pollutant degradation is a novel approach to developing renewable energy and environmental protection applications. Herein, a new form of defect engineered Na‐Sm bimetallic‐regulated CaBi2Nb2O9 platelet is synthesized via a molten salt process for water splitting and pollutant degradation applications. An intermediate band structure is introduced by Sm‐doping, and empty orbitals in the conductive band are introduced by Na‐doping. These factors, combined with the increased local charge density around the Sm and Na atoms, result in an increased electrical conductivity, improved electron mobility, and provide additional electrons for enhancing catalytic reactions. As a consequence, the judicious co‐doping of CaBi2Nb2O9 with Sm and Na leads to a unique synergetic piezo‐photo‐electric effect to provide a superior piezo‐photo‐catalytic performance for H2 production (158.53 µmol g−1 h−1) and pollutant degradation (rate constant, k = 0.257 min−1). This new approach provides important insights into the application of defect engineering to exploit the cooperative doping of alkaline earth metals and rare metals to create high‐performance catalysts.

The role of aluminium in metal–organic frameworks derived carbon doped with cobalt in electrocatalytic oxygen evolution reaction

Water electrolysis is one of the most crucial processes in the development of new energy sources, where ultra-clean fuel is produced - hydrogen. Oxygen evolution reaction (OER) is the sluggish process of overall water splitting. Therefore, this study presents the design, characterization and electrochemical study of cobalt-based electrocatalysts embedded into porous carbons derived from an Al-metal–organic framework (MOF). The key aspects to be revealed were carbonization temperature and aluminium impact on the composite electrochemical performance. It was found that aluminium presence boosts the OER performance of the anode via lowering electrolyte resistance, reaching an overpotential of 380 mV at the current density of 10 mA/cm−2, which is improved by 80 mV compared to the composite without aluminium. Similar effect was present in EIS measurement, where the electrocatalyst functionalized with cobalt in the presence of aluminium showed the lowest resistances, 0.89 Ω and 2.82 Ω for R1 and R2. This is due to the formation of additional electrocatalytically active species in the form of Al-Co alloy what was clearly proved by the XPS study. It shows that cobalt favoured aluminium to act simultaneously as active sites accelerating the efficiency of the OER process. Additionally, carbon played the role of a booster of the OER activity of cobalt with sustained high durability during cycling. Therefore, a facile procedure to tune the structure of carbon-based structures derived from Al-based metal–organic frameworks is proposed and the resulting cobalt/aluminium modification serves as a robust electrocatalyst for OER.

Single Ni atom-anchored BN-yne for enhanced water splitting

Developing economical and highly active electrocatalysts for water splitting is generally critical for improvement of next-generation green energy technologies. Several single atomic non-noble metal catalysts provide satisfactory water splitting catalytic proficiency due to their natural electronic structures. Herein, by employing density functional theory (DFT) computation, a Ni-doping strategy is done to straight tune catalyst activity and electronic structure for hydrogen and oxygen evolution reactions (HER and OER). Electronic attributes, persistence and HER in addition to OER catalytic operations of Ni@BN-yne catalyst are investigated by carefully manipulating nickel-doping in graphyne-like BN-yne (BN-yne) nanosheets. It has been found that HER and OER efficiency depends on nickel-induced charge redistribution on the Ni@BN-yne catalyst area. Nickel-induced charge density weakens chemicad adsorption of oxygenated species and considerably reductions OER overpotential as well as grows active sites number on Ni@BN-yne and boosts its activity of catalyst in HER and makes Ni@BN-yne a hopeful bifunctional electrocatalyst to employ in water splitting process. Present research provides a practical approach for researchers to fine-tune electronic structures of catalysts and meliorate catalytic activity.

CdS@Ni3S2/Cu2S electrode for electrocatalysis and boosted photo-assisted electrocatalysis hydrogen production

Photo-assisted electrocatalysis (PA-EC) water splitting technology, which combines photocatalysis and electrocatalysis, has gradually become a research hotspot in the production of green hydrogen energy. Herein, for the first time, novel Cu/Ni alloy foam self-supporting CdS@Ni3S2/Cu2S core–shell nanorod arrays are prepared by a simple one-pot hydrothermal process. The CdS@Ni3S2/Cu2S exhibits both excellent electrocatalytic and photo-assisted electrocatalytic water splitting performance. During the long-time PA-EC water splitting test, the average H2 production rate reaches 568.1 μmol cm-2h−1, which is about 1.8 times higher than that of 284.1 μmol cm-2h−1 under dark condition. In addition, the electrical-to-hydrogen (ηETH) and solar-to-hydrogen (ηSTH) conversion efficiency reaches to be 97% and 8.9%, respectively. Mechanism investigation results show that during EC water splitting process, CdS nanorods mainly play as support material for the electroactive Ni3S2 and Cu2S. While, in the PA-EC process, CdS, Cu2S and Ni3S2 were photoexcited by light irradiation, and just as the presence of additional photogenerated electrons and holes, CdS@Ni3S2/Cu2S exhibits boosted photo-assisted water splitting properties. This work provides a new strategy for the construction of bifunctional photocatalysts combined with electrocatalysts in photo-assisted electrocatalysis overall water splitting.

The Fe2P/NiCoP phosphating compound supported by nickel foam functions as a superior bi-functional catalyst to speed up the overall water splitting

In this work, we designed a bifunctional Fe2P/NiCoP/NF catalyst with a self supporting structure based on nickel foam (NF) as a conducting matrix. For both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), this catalyst showed improved bifunctional catalytic function. CoFe precursor are co-phosphated with NF, and this causes the NF surface to take part in the reaction, forming a spherical composite material composed of NiCoP particles and Fe2P particles. In addition, it was found that NF provides good conductivity and stability in the electrocatalytic test, and NiCoP and Fe2P have an apparent synergistic impact, which has a superior catalytic function on both HER and OER. OER overpotential of 261 mV and HER overpotential of 125 mV, respectively, are displayed by the Fe2P/NiCoP/NF catalyst with current densities of 50 mA cm−2 and 10 mA cm−2 separately. Fe2P/NiCoP/NF further performed exceptionally well throughout the overall water splitting process. With just 1.43 V, it can attain 10 mA cm−2 and maintain stability for 50 h. The H2 production in the total water splitting process can reach 4.35 μmol min−1. As a result, the self-supporting bifunctional electrocatalyst composed of Fe2P/NiCoP/NF can be effective and long-lasting for overall water splitting.

Novel route of NiCr-layered double hydroxide nanosheets synthesis on nickel foam as a bifunctional electrocatalyst for water splitting process

In this study, we present a novel direct synthetic route for producing NiCr-layered double hydroxide (LDH) nanosheets on a nickel foam surface using the Successive Ionic Layer Deposition (SILD) method. The morphology of the nanolayers was characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Additionally, the electrocatalytic properties of the nanolayers were examined using electrochemical techniques. The NiCr-layered double hydroxide nanolayers produced through SILD using sodium hexahydroxochromate (III) anion precursor were found to be ultrathin “nanosheets” with a hydrotalcite-like structure and low crystallinity. The efficacy of electrodes based on these nanolayers as cathode and anode materials in electrocatalytic cells for hydrogen production through electrolytic water splitting in alkaline media were investigated. Our results showed that the electrode based on NiCr-LDH nanolayers exhibited good kinetics in both the cathode and anode areas.

Density functional theory modeling of critical properties of perovskite oxides for water splitting applications

AbstractWater splitting (WS) driven by solar energy is considered as a promising strategy to produce renewable hydrogen from water with minimal environmental impact. Realization of large‐scale hydrogen production by this approach requires cost‐effective, efficient and stable materials to drive the WS reaction. Perovskite oxides have recently attracted widespread attention in WS applications due to their unique structural features, such as compositional and structural flexibility allowing them to achieve desired sunlight absorption capability, precise control of electrocatalytic and redox activity to drive the chemical reaction, tuneable bandgaps and band edges, and earth‐abundance. However, perovskite oxides contain a large family of metal oxides and experimental exploration of novel perovskites without a priori knowledge of their properties could be costly and time‐consuming. First‐principles approaches such as density functional theory (DFT) are a useful and cost‐effective alternative towards this end. In this review, DFT‐based calculations for accurate prediction of the critical properties of ABO3 perovskite oxides relevant to WS processes are surveyed. Structural, electronic, optical, surface, and thermal properties are grouped according to their relevance to photocatalytic (PC), electrochemical (EC), photo‐electrochemical (PEC), and solar thermal water splitting (STWS) processes. The challenges associated with the choice of exchange‐correlation (XC) functional in DFT methods for precise prediction of these properties are discussed and specific XC functionals have been recommended where experimental comparisons are possible.This article is categorized under: Sustainable Energy > Solar Energy Emerging Technologies > Hydrogen and Fuel Cells Emerging Technologies > Materials

Effect of mixed-valence of manganese on water oxidation activity of La1-xCaxMnO3 (0 ≤ x ≤ 1) solid solutions

The water oxidation reaction is one of the crucial process involves 4e- and 4H+ transfer, which causes a high energy barrier and makes the water-splitting process a slow kinetic reaction. Herein, we have systematically observed the water oxidation activity of La1-xCaxMnO3 (0≤ x ≤ 1) solid solutions by tuning the valence of Mn ion through selective substitution of La3+ with Ca2+. With increasing Ca concentration in La1-xCaxMnO3 solid solutions, the water oxidation activity increases up to x = 0.5 and then decreases. Mixed-valence of Mn generated due to substitution of La3+ with Ca2+, which leads to the double exchange mechanism. This could results in high electrical conduction and a faster electron transfer rate because of the rapid charge exchange between Mn3+ and Mn4+ ions, which pinpoints the reason behind the enhanced oxygen evolution activity. Our findings will be a promising way to relate the Mn mixed-valence with its catalytic activity to design and development of efficient water oxidation catalysts.

Multifunctional electrocatalyst based on MoCoFe LDH nanoarrays for the coupling of high efficiency Electro-Fenton and water splitting process

Novel MoCoFe layered double hydroxide (LDH) nanoarray catalysts were prepared by a one-step solvothermal method. These catalysts served as multifunctional catalysts for the coupling of overall water splitting with the Electro-Fenton process. MoCoFe LDH displayed different array structures evolving with Mo content, which results in different catalytic activities in the Oxygen Reduction Reaction (ORR), Oxygen Evolution Reaction (OER), and Hydrogen Evolution Reaction (HER) processes. Among them, Mo2CoFe LDH exhibited about 90% H2O2 selectivity over a wide voltage range and almost 100% degradation efficiency of sulfonamide antibiotics within 45 min. This was due to more open nanowire array structures and bond expansion resulting from the Mo introduction. Density Functional Theory (DFT) calculations showed that the addition of Mo atoms significantly reduced the energy barrier of H2O2 generation at the active site of Co. Meanwhile, Mo0.5CoFe LDH displayed competitive OER performance with an overpotential of 190 mV (vs. RHE) and HER activity with an overpotential of 78 mV@10 mA cm−2. The water splitting cell consisting of Mo0.5CoFe LDH electrodes only required a voltage of 1.53 V to achieve a current density of 10 mA cm−2. This was due to the generation of the crystal-amorphous interface structure via the substitution of Mo for the metal sites in LDH, which contributed to the internal active site exposure. The crystallization-amorphous structure promotes an increase in the number of active sites in terms of unit area by accelerating the M−OH to M−OOH reconfiguration, in addition to that, corrosion resistance and self-healing properties of this structure also helps to improve the stability and durability of the material during the OER process. Noteworthy, the Electro-Fenton/water-splitting coupling device was constructed, benefiting from the excellent Electro-Fenton and water electrolysis performance in alkaline solutions. The complete decolorization of 20 mg L-1 methyl blue could be achieved within 80 min at pH = 14 (Iwater-splitting = 37 mA cm−2, IEF = 8 mA cm−2), and Faraday efficiency of water splitting still remains above 95% after coupling EF. This novel coupling device may help to improve the energy utilization in the electrocatalytic process.

Theoretical insight into water splitting mechanism of B doped tri-s-triazine-based g-C3N4/m-BiVO4(001) heterojunction photocatalyst

We evaluated the geometrical, electrical, optical properties and charge transfer of pristine g-C3N4 (tri-s-triazine-based graphitic phase carbon nitride) B-doped g-C3N4 (doping of boron atoms into graphitic phase carbon nitride), m-BiVO4(001) surface (monoclinic bismuth vanadate (001) surface), g-C3N4/m-BiVO4(001) heterojunction and B-doped g-C3N4/m-BiVO4(001) heterojunction using density functional theory (DFT) simulations. Based on the findings, the synergistic impact of doping and heterojunctions on g-C3N4’s electronic properties as well as the photocatalytic mechanism of heterojunctions were analyzed. The doping of B atoms gives g-C3N4 a unique structure and reduces the effective mass of carriers, proving to be an effective way to increase electron transport capacity. The interfacial adhesion energy, binding energy, and interfacial distance all point to a van der Waals (vdW) interaction between g-C3N4 and m-BiVO4(001) surface. The findings demonstrate that the g-C3N4/m-BiVO4(001) heterojunction, in comparison to pristine g-C3N4 and m-BiVO4(001) surface, has a narrow bandgap, absorbs more photons and has a build-in electric field, all of which are advantageous for visible light-driven activity, the separation and transfer of charge carriers, and maintaining a strong redox ability. Additionally, the B-doped g-C3N4/m-BiVO4(001) heterojunction outperformed the g-C3N4/m-BiVO4(001) heterojunction in terms of visible light absorption efficiency, hydrogen production capacity, and interfacial charge density. The Z-scheme mechanism over the heterojunction has been proposed based on semiconductor theory to disclose the separation and transfer pathway of photogenerated charge during the photocatalytic water splitting process. The theoretical design provided here provides a theoretical reference for the efficient of g-C3N4-based photocatalysts for the efficient use of solar energy and the protection of the environment.

Properties and Structure of Thermoplastic Polyvinyl Alcohol/Polyamide Sea-Island Fibers.

Ultra-fine fibers derived from sea-island fibers have attracted great attention due to their excellent overall performance. However, green and efficient splitting of sea-island fibers is still a challenging task. In this work, thermoplastic polyvinyl alcohol (TPVA) was prepared by the physical blending of plasticizer. The modified TPVA showed a high decomposition temperature (285 °C) and a wide thermoplastic processing window. This made TPVA match well with polyamide 6 (PA6) to form conjugated melts at 250 °C. Corresponding PVA/PA6 sea-island fibers were first reported to realize water-splitting instead of alkali-extraction of "sea" polymers. The effects of sea/island mass ratios and different spinning speeds on the properties of PVA/PA6 sea-island pre-oriented yarn (POY) were investigated. A higher spinning speed enhanced the orientation-induced crystalline behavior of fiber, therefore increasing the tensile strength of fibers. As the increase of spinning speed from 1000 to 1500 m/min, the crystalline degree of corresponding POYs increased from 9.9 to 14.3%. The plasticizer in PVA did not diffuse to the PA matrix during spinning. However, PVA could induce the crystallization of PA6 via interfacial hydrogen bonding. When the spinning speed was 1500 m/min, and PVA/PA6 was 7:3, the tensile strength reached the highest value of 1.67 cN/dtex. The uniform diameters of ultra-fine PA6 fibers (2-5 μm) were obtained by an environment-friendly water-splitting process. The "sea" phase (TPVA) in sea-island fiber could be removed quickly by boiling water treatment in 3 min. This green and energy-saving sea-island fiber splitting technique is of great significance in reducing CO2 emissions during the preparation of super-fine fibers.

Exergoeconomic performance evaluation of three, four, and five-step thermochemical copper-chlorine cycles for hydrogen production

Thermochemical water-splitting processes are among the most promising options for producing sustainable and green hydrogen due to being extremely environmentally benign. Being extensively investigated in the literature, the thermochemical copper-chlorine cycle has demonstrated much promise in this regard as one of the most efficient options for thermochemically obtaining hydrogen. Thus, this study focuses on investigating the exergoeconomic performances of the different variants of the copper-chlorine cycle including the three-, four-, and five-step versions. All cycles are modeled and simulated in Aspen-plus software by considering a recovery of thermal energy from industrial waste flue gases in addition to internal heat recovery. Moreover, a hydrogen production capacity of 668 kg/h is considered for all cycles. The Specific Exergy Costing methodology is employed to study the exergoeconomic performance of each cycle. All cycles are initially examined in terms of the cost rates of energy transfer and hourly levelized cost rates for each step. The cycle variants are further examined through a comparative assessment of several performance parameters including hydrogen cost rates, overall cost rates of energy transfer, and overall hourly levelized cost rates. According to the performed analyses, the three-step variant of the cycle that constitutes a high-temperature electrolysis process produces hydrogen at the lowest cost rate (0.83 $/kg) while the four-step cycle produces hydrogen at the highest cost rate (1.82 $/kg). Furthermore, the hydrolysis step is found to have the highest hourly levelized cost rates for all variants of the cycle. Several factors that impact the hydrogen cost rate are also examined comprehensively. In addition, the extent to which the hydrogen cost rate is sensitive to those factors is discussed.

Mild and Fast Construction of Ni-Based Electrodes for Industrial-Grade Water Splitting

Achieving high−efficiency and stable hydrogen evolution from water splitting is a great challenge. Herein, a facilely prepared two−dimenssional self−supported catalytic electrode with excellent stability is constructed for large−scale hydrogen production from alkaline simulated seawater. The bifunctional catalytic electrode is prepared by a fast and mild one−step of sodium borohydride etching on a nickel foam (NF) substrate without adding other additives (NF@NiBx−3h). The overpotential of the hydrogen/oxygen evolution reaction (HER/OER) in alkaline−simulated seawater at 10 mA cm−2 is 96 mV and 261 mV. At 200 mA cm−2, the NF@NiBx−3h electrode shows good stability over 7 days throughout the water splitting process due to the corrosion resistance of the NF substrate, and strong adhesion between the Ni−B active material and the substrate. This work demonstrates a novel strategy for fabricating catalytic electrodes with high−performance, low cost and excellent stability.

Non-Noble Nanoparticles Cocatalysts in TiO<sub>2</sub> for Photocatalytic Hydrogen Production from Water. A review

Among the many methods, the use of solar photocatalytic water splitting to produce hydrogen is the most promising one. The water splitting process mainly includes the following three steps: solar energy capture, transfer and separation of photogenerated charges, and catalytic protons to generate hydrogen. At present, a high number of studies mainly focus on the first and second steps, and there are relatively few studies garding the third step. The introduction of a co-catalyst can effectively improve the photocatalytic activity and increase the hydrogen production rate. Co-catalysts mainly include noble metal catalysts and non-noble metal catalysts. Although noble metal catalysts provide a better performance, their high price limits their wide application. Therefore, it is particularly important to develop efficient and inexpensive non-precious metal catalysts. This paper briefly summarizes the use of non-noble metal catalysts based on TiO2 photocatalytic hydrogen evolution. The action mechanism and related synthesis methods of the co-catalysts are discussed, and the development direction of non-noble metal cocatalysts is briefly described.

Construction of flower-like nanoassembly P-doped MOF-derived MoS2/Co9S8 grown on hexagonal microporous alumino-silicate framework for overall water splitting in alkaline media

Water splitting is a noteworthy process in the field of hydrogen and oxygen gas production. MoS2 has emerged as an effective material for catalyzing water splitting; however, its low electronic conductivity and oxidative corrosion in environmental conditions suppress its practical applications in electrolyzers. Herein, we constructed a new hetero-nanostructure composed of MoS2 and Co9S8 phases, which is assembled onto the hexagonal microporous alumino-silicate (HMS) structure. Different combinations ratios of Mo and Co elements in hetero-nanostructures offered tremendous opportunities for morphology control and, further, modification of chemical and physical properties to enhance the overall water splitting process. HMS/MoS2/Co9S8-31 (with the mole ratio of 3:1 for Mo:Co) showed synergistically enhanced electrocatalytic performance for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with overpotentials of −127 and 280 mV at 10 mA cm−2, respectively. In the next step, phosphorization of HMS/MoS2/Co9S8-31 was performed via a simple one-step route (HMS/MoS2/Co9S8/P-31), so the overpotentials were reduced to −85 and 200 mV, which shows dramatic improvement in the overall water splitting performance of electrocatalyst. In addition, for a symmetrical electrolyzer, a current density of 10 mA cm−2 was obtained at a quite low cell voltage of 1.56 V. Systematic studies on HMS/MoS2/Co9S8/P-31 and a set of finely designed control catalysts suggest that the enhanced electrocatalytic behavior should be related to electronic coupling effect and modulation between MoS2 and Co9S8 and the advantage of the ordered HMS architecture. In addition, phosphorus doping can modify the electronic properties of hetero-nanostructure and facilitates electron transfer between MoS2 and Co9S8 hetero-phases.

Formation of Ba3Nb0.75Mn2.25O9-6H during thermo-chemical reduction of Ba4NbMn3O12-12R.

The resurgence of inter-est in hydrogen-related technologies has stimulated new studies aimed at advancing lesser-developed water-splitting processes, such as solar thermochemical hydrogen production (STCH). Progress in STCH has been largely hindered by a lack of new materials able to efficiently split water at a rate comparable to ceria under identical experimental conditions. BaCe0.25Mn0.75O3 (BCM) recently demonstrated enhanced hydrogen production over ceria and has the potential to further our understanding of two-step thermochemical cycles. A significant feature of the 12R hexa-gonal perovskite structure of BCM is the tendency to, in part, form a 6H polytype at high temperatures and reducing environments (i.e., during the first step of the thermochemical cycle), which may serve to mitigate degradation of the complex oxide. An analogous compound, namely BaNb0.25Mn0.75O3 (BNM) with a 12R structure was synthesized and displays nearly complete conversion to the 6H structure under identical reaction conditions as BCM. The structure of the BNM-6H polytype was determined from Rietveld refinement of synchrotron powder X-ray diffraction data and is presented within the context of the previously established BCM-6H structure.

Water splitting over an ultrasonically synthesized NiFe/MoO3@CFP electrocatalyst

The development of non-precious metal catalysts exhibiting high performance towards both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) has been recognized as one of the ultimate goals in water electrolysis research. Herein, we report on the synthesis of an efficient OER and HER catalyst, NiFe/MoO3@CFP, using a unique synthetic technique that combines ultrasonic synthesis and electrochemical deposition. The Mo-based compound, used as a template for the NiFe structure, was formed during the ultrasonication, and cavitation bubbles generated via ultrasonication were found to play a key role for improving the catalyst performance. NiFe/MoO3@CFP achieved a current density of 20 mA cm−2 for the OER and HER at low overpotentials of 251 and 204 mV, respectively. It was found that a cell potential of 1.589 V was required to achieve 10 mA cm−2 in the overall water splitting process. This study presents the effective preparation of a catalyst using ultrasound technology, which has rarely been used, suggesting its potential for future applications.