Field Of Water Splitting Research Articles

Utilization of Cobalt and its Oxide/Hydroxide Mediated by Ionic Liquids/Deep Eutectic Solvents as Catalysts in Water Splitting.

With the ever-growing global demand for sustainable energy solutions, hydrogen has garnered significant attention as a clean, efficient, and renewable energy source. In the field of hydrogen production, catalyst research stands out as one of the foremost areas of focus. In recent years, the preparation of electrocatalysts using ionic liquids (ILs) and deep eutectic solvents (DESs) has attracted widespread attention. ILs and DESs possess unique physicochemical properties and are recognized as green media as well as functional materials. Cobalt-based catalysts have proven to be efficient electrocatalysts for water splitting. Incorporating ILs or DESs into the preparation of cobalt-based catalysts offers a remarkable advantage by allowing precise control over their structural design and composition. This control directly influences the adsorption properties of the catalyst's surface and the stability of reaction intermediates, thereby enabling enhanced control over reaction pathways and product selectivity. Consequently, the catalytic activity and stability of cobalt-based catalysts can be effectively improved. In the process of preparing cobalt-based catalysts, ILs and DESs can serve as solvents and templates. Owing to the good solubility of ILs and DESs, they can efficiently dissolve raw materials and provide a special nucleation and growth environment, obtaining catalysts with novel-structures. The main focus of this review is to provide a detailed introduction to metal cobalt and its oxide/hydroxide derivatives in the field of water splitting, with a particular emphasis on the research progress achieved through the utilization of IL and DES. The aim is to assist readers in designing and synthesizing novel and high-performance electrochemical catalysts.

Advances in Functional Ceramics for Water Splitting: A Comprehensive Review

The global demand for sustainable energy sources has led to extensive research regarding (green) hydrogen production technologies, with water splitting emerging as a promising avenue. In the near future the calculated hydrogen demand is expected to be 2.3 Gt per year. For green hydrogen production, 1.5 ppm of Earth’s freshwater, or 30 ppb of saltwater, is required each year, which is less than that currently consumed by fossil fuel-based energy. Functional ceramics, known for their stability and tunable properties, have garnered attention in the field of water splitting. This review provides an in-depth analysis of recent advancements in functional ceramics for water splitting, addressing key mechanisms, challenges, and prospects. Theoretical aspects, including electronic structure and crystallography, are explored to understand the catalytic behavior of these materials. Hematite photoanodes, vital for solar-driven water splitting, are discussed alongside strategies to enhance their performance, such as heterojunction structures and cocatalyst integration. Compositionally complex perovskite oxides and high-entropy alloys/ceramics are investigated for their potential for use in solar thermochemical water splitting, highlighting innovative approaches and challenges. Further exploration encompasses inorganic materials like metal oxides, molybdates, and rare earth compounds, revealing their catalytic activity and potential for water-splitting applications. Despite progress, challenges persist, indicating the need for continued research in the fields of material design and synthesis to advance sustainable hydrogen production.

Simultaneous enhancement of charge transfer and surface catalysis through a polymetallic oxide cocatalyst on BiVO4 photoanodes for highly efficient and stable water oxidation

The rate-determining oxygen evolution reaction (OER) always limits the high-efficient conversion of solar energy to green hydrogen fuels through photoelectrocatalytic or photocatalytic water splitting. The high catalytic overpotential and the instability of catalytic center are commonly regarded as the primary factors contributing to the low rate of OER, remaining to be a challenge in the field of water splitting. Herein, a polymetallic oxide cocatalyst (Mo-MnOy/FeCoNiOx) with well-defined electronic and catalytic properties is designed on BiVO4 photoelectrode for highly efficient and stable photoelectrocatalytic water oxidation. The experimental characterization demonstrates that the dual-layer design of Mo-MnOy/FeCoNiOx can significantly optimizes the electronic property of MnOy and FeCoNiOx components, boosting the photogenerated charge transfer between Mo-MnOy/FeCoNiOx cocatalyst and BiVO4 photoelectrode. The density functional theory (DFT) simulation reveals that the Mo sites in Mo-MnOy layer can activate the neighboring surface Mn sites instead of directly serving as the catalytic center, thereby establishing these Mn sites as primary active centers for achieving stable OER. The developed Mo-MnOy/FeCoNiOx/BiVO4 photoelectrode exhibits a current density of 6.18 mA cm−2 with an excellent stability for 30 h at 1.23 VRHE under 1 sun irradiation, exhibiting the excellent activity and durability. This work sheds light on design of high-performance multiple-component water-oxidation cocatalyst on photoanode.

Integrated Catalyst-Substrate Electrodes for Electrochemical Water Splitting: A Review on Dimensional Engineering Strategy.

Water splitting (or, water electrolysis) is considered as a promising approach to produce green hydrogen and relieve the ever-increasing energy consumption as well as the accompanied environmental impact. Development of high-efficiency, low-cost practical water-splitting systems demands elegant design and fabrication of catalyst-loaded electrodes with both high activity and long-life time. To this end, dimensional engineering strategies, which effectively tune the microstructure and activity of electrodes as well as the electrochemical kinetics, play an important role and have been extensively reported over the past years. Here, a type of most investigated electrode configurations is reviewed, combining particulate catalysts with 3Dporous substrates (aerogels, metal foams, hydrogels, etc.), which offer special advantages in the field of water splitting. It is analyzed the design principles, structural and interfacial characteristics, and performance of particle-3D substrate electrode systems including overpotential, cycle life, and the underlying mechanism toward improved catalytic properties. In particular, it is also categorized the catalysts as different dimensional particles, and show the importance of building hybrid composite electrodes by dimensional control and engineering. Finally, present challenges and possible research directions toward low-cost high-efficiency water splitting and hydrogen production is discussed.

Hollow CoVOx/Ag nanoprism with tailored electronic structure for high efficiency oxygen evolution reaction

Developing high-active and inexpensive electrocatalysts for oxygen evolution reaction (OER) is very important in the field of water splitting. The catalytic performance of electrocatalysts can be significantly improved by optimizing the electronic structure and designing suitable nanostructure. In this work, we represent the synthesis of hollow CoVOx/Ag-5 for OER. Due to the interaction of CoVOx and Ag nanoparticles, the electronic structure is optimized to improve the intrinsic catalytic activity. Additionally, the extrinsic catalytic activity of CoVOx/Ag is enhanced by the abundant active sites from the hollow structure. As a result, the CoVOx/Ag-5 demonstrates significantly enhanced OER catalytic activity with a low overpotential of 247 mV at 10 mA cm−2. In addition, it also exhibits excellent durability, without obvious attenuation in performance after continuous operation for 60 h. Furthermore, the catalyst can enable full water splitting with appropriate 100 % Faraday efficiency, demonstrating its practical application.

Ultrafine Ru nanoparticles stabilized by V8C7/C for enhanced hydrogen evolution reaction at all pH

The development of cost-effective electrocatalysts with high efficiency and long durability for hydrogen evolution reaction (HER) remains a great challenge in the field of water splitting. Herein, we design an ultrafine and highly dispersed Ru nanoparticles stabilized on porous V8C7/C matrix via pyrolysis of the metal–organic frameworks V-BDC (BDC: 1,4-benzenedicarboxylate). The obtained Ru-V8C7/C composite exhibits excellent HER performance in all pH ranges. At the overpotential of 40 mV, its mass activity is about 1.9, 4.1 and 9.4 times higher than that of commercial Pt/C in acidic, neutral and alkaline media, respectively. Meanwhile, Ru-V8C7/C shows the remarkably high stability in all pH ranges which, in particular, can maintain the current density of 10 mA cm−2 for over 150 h in 1.0 mol L−1 phosphate buffer saline (PBS). This outstanding HER performance can be attributed to the high intrinsic activity of Ru species and their strong interface interactions to the V8C7/C substrate. The synergistic effect of abundant active sites on the surface and the formed Ru–C–V units at the interface promotes the adsorption of reaction intermediates and the release of active sites, contributing the fast HER kinetics. This work provides a reference for developing versatile and robust HER catalysts by surface and interface regulation for pH tolerance.

Electrochemical water splitting enhancement by introducing mesoporous NiCoFe-trimetallic phosphide nanosheets as catalysts for the oxygen evolution reaction.

Transition metal-based catalysts are widely used in electrocatalysis, especially in the field of water splitting, due to their excellent electrochemical performance, which focuses on improving the efficiency of the complex oxygen evolution reaction (OER) that occurs at the anode. Transition metal-based catalysts will undergo electrochemical surface reconstruction and form (oxy)hydroxide-based hybrids, which consider the actual active sites for OER. So many efforts have been made to know the origin of the effect of electrochemical surface reconstruction on the performance of the OER. Herein, NiCoFe-phosphide catalyst nanosheets were constructed by a simple one-step hydrothermal reaction by adding oleylamine and ethanol to water solvent during the preparation of the catalyst precursor and high-temperature gas-phase phosphating and significantly showed high effectiveness catalytic activity and conductivity in comparison to normal and traditional preparation methods. Electrochemical analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) demonstrate that the surface was constructed during the electrochemical reaction and formed an amorphous layer of MOx(OH)y active sites, which increased the electrochemical surface area and promoted charge transfer. As well, the synthesized NiCoFePx-PNSs catalyst nanosheets exhibit excellent catalytic activity with a low overpotential equal to 259 mV to achieve the OER at a current density of 10 mA cm-2 and a low Tafel slope of 50.47 mV dec-1 which is better than for most reported transition metal-based electrocatalysts. This work provides a new design for a transition metal-based catalyst for OER as well as further insights into the effect of electrochemical surface reconstruction on intrinsic activity and OER performance.

One-step engineering Co8FeS8 electrocatalyst based on Co–Fe bimetal foam for a highly-efficient oxygen evolution reaction

The sluggish oxygen evolution reaction (OER) is still the bottleneck problem for a highly efficient hydrogen generation by water splitting. Herein, the CoFe bimetallic foam (CFF) is used for the one-step hydrothermal-vulcanization to engineer the special crystal structure of CoFe sulfide (Co8FeS8/CFF), and the resulting electrocatalyst of Co8FeS8/CFF demonstrates a remarkable OER performance in 1 M KOH electrolyte, which only requires 73 mV to drive a current density of 10 mA cm−2 (j10). Meanwhile, the chronoamperometry curve further demonstrates the good electrocatalytic stability of Co8FeS8/CFF, and the I-t curve maintains for 20 h at a current density of j15. Furthermore, the theoretical calculations reveal that the (311) facet of Co8FeS8 serves a crucial role in the OER process, and the Fe site is more conducive to transfer electrons, facilitating the OER process. Noticeably, the reported one-step hydrothermal-vulcanization method successfully synthesized the Co8FeS8/CFF electrocatalyst at a low cost. The significance of Fe sites on the Co8FeS8/CFF (311) plane for the OER process was confirmed through DFT calculations, further enhancing the application potential of transition-metal-based sulfides in the field of water splitting.

Compositional engineering of HKUST‐1/sulfidized NiMn‐LDH on functionalized MWCNTs as remarkable bifunctional electrocatalysts for water splitting

AbstractWater‐splitting reactions such as the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) typically require expensive noble metal‐based electrocatalysts. This has motivated researchers to develop novel, cost‐effective electrocatalytic systems. In this study, a new multicomponent nanocomposite was assembled by combining functionalized multiwalled carbon nanotubes, a Cu‐based metal–organic framework (MOF) (HKUST‐1 or HK), and a sulfidized NiMn‐layered double hydroxide (NiMn‐S). The resulting nanocomposite, abbreviated as MW/HK/NiMn‐S, features a unique architecture, high porosity, numerous electroactive Cu/Ni/Mn sites, fast charge transfer, excellent structural stability, and conductivity. At a current density of 10 mA cm−2, this dual‐function electrocatalyst shows remarkable performance, with ultralow overpotential values of 163 mV (OER) or 73 mV (HER), as well as low Tafel slopes (57 and 75 mV dec−1, respectively). Additionally, its high turnover frequency values (4.43 s−1 for OER; 3.96 s−1 for HER) are significantly superior to those of standard noble metal‐based Pt/C and IrO2 systems. The synergistic effect of the nanocomposite's different components is responsible for its enhanced electrocatalytic performance. A density functional theory study revealed that the multi‐interface and multicomponent heterostructure contribute to increased electrical conductivity and decreased energy barrier, resulting in superior electrocatalytic HER/OER activity. This study presents a novel vision for designing advanced electrocatalysts with superior performance in water splitting. Various composites have been utilized in water‐splitting applications. This study investigates the use of the MW/HK/NiMn‐S electrocatalyst for water splitting for the first time to indicate the synergistic effect between carbon‐based materials along with layered double hydroxide compounds and porous compounds of MOF. The unique features of each component in this composite can be an interesting topic in the field of water splitting.

Cobalt di-selenide embedded polymerised melamine paraformaldehyde resin: A robust and efficient electrocatalyst for OER with operando investigations

In past research metal selenides have reported versatile results in the field of water splitting. Cobalt di-selenide has received much attention in the oxygen evolution reaction (OER) due to its excellent results towards OER. To excel the reaction capability, herein we have reported CoSe2, pMF-R and CoSe2@pMF-R nanostructures in which the freshly prepared CoSe2 nanostructures were decorated on the surface of pMF-R (polymerised melamine paraformaldehyde resin). The study showed that the bonds between cobalt and nitrogen were well formed, which is maintaining the improved charge transfer channels to annihilate the barriers between the GC (glassy carbon) electrode surface and active sites of CoSe2. Because of the coaction of CoSe2 and pMF-R, the OER calibration of the CoSe2@pMF-R catalyst has shown a low onset potential 1.56 V and its electrochemical activity towards OER was found to be much higher as 10 mAcm−2 at 1.608 V Vs. RHE. Operando spectroelectrochemical investigations revealed that active sites of selenium, Co2+, Co3+ and pMF-R available for generation of intermediate oxygen species and responsible for exponential increase in rate of OER. The order of reaction is found to one. The compositional and structural characteristics of CoSe2@pMF-R composite over other electrocatalysts is responsible for outstanding electrochemical performance.

Revealing the effect of crystallinity and oxygen vacancies of Fe-Co phosphate on oxygen evolution for high-current water splitting

Strategically tuning the composition and structure of transition metal phosphates (TMPs) holds immense promise in the development of efficient oxygen evolution reaction (OER) electrocatalysts. However, the effect of crystalline phase transformation for TMPs on the catalytic OER activity remains relatively uncharted. In this study, we have deftly orchestrated the reaction process of anion-etched precursor to induce the amorphization process of FeCo-POx from crystalline to amorphous states. The as-obtained amorphous FeCo-POx (A-FeCo-POx) exhibited an optimized OER performance with a low overpotential of 270 mV at a current density of 10 mA cm−2, which could be attributed to the flexibility of its amorphous structure and the synergistic effect of oxygen vacancies. Moreover, when incorporated into an overall water splitting (OWS) device configured as A-FeCo-POx(+)||Pt/C(–), it displayed long-term solid stability, sustaining operation for 300 h at a current density of 200 mA cm−2. This work not only provides valuable insights into understanding the transformation from crystalline to amorphous states, but also establishes the groundwork for the practical utilization of amorphous nanomaterials in the field of water splitting.

In-depth investigation on the self-catalyzed growth of W2N/In2O3 composite nanowires synthesized via nitrogen plasma assisted in-situ thermal annealing for boosting photoelectrochemical performance

Enhancing the charge separation efficiency through interface engineering of In2O3-based photoanodes represents a critical and complex research endeavor in the field of water splitting. Herein, we report a self-catalyzed growth of intrinsic Indium oxide (In2O3) Nanowires (NWs) and Tungsten nitride/Indium oxide (W2N/In2O3) composite nanowires (CNWs) on c-Si substrates by plasma assisted reactive thermal evaporation (PARTE) and nitrogen plasma assisted in-situ thermal annealing, respectively. The nitrogen plasma assisted in-situ thermal annealing effectively transforms the intrinsic In2O3 NWs to W2N/In2O3 CNWs. The optical energy gap, Eg gradually decreases from 2.49 to 2.40 eV when combine with W2N nanostructures. Decrease in the Eg simultaneously increases the photocurrent density of W2N/In2O3 CNWs at V = 0.4 V from 1.9 to 3.8 mA/cm2. This could attribute to the effective electron−hole separations at the interfaces of the heterojunction CNWs. The correlation between the substantially prolonged lifetime of charge carriers and narrowing the bandgap of the composite NWs could be feasible as a good electrochemical electrode. Moreover, the self-catalyzed and secondary growth mechanisms of hierarchically branched In2O3 NWs and W2N/In2O3 CNWs are discussed.

Optimized electroless deposition of NiCoP electrocalysts for enhanced water splitting

Great scientific effort has strived to develop a low-cost and sustainable electrocatalyst with high electrocatalytic activity and long-term stability in the field of water splitting. In this work non-noble metal based NiCoP alloys are burgeoned from catalytic Ni substrates via a facile and eco-friendly electroless deposition method under mild conditions. By appropriately tuning the cobalt content in the chemical bath, we realize NiCoP coatings with tailored Co concentration. The electrochemical investigations of coatings deposited on flat Ni indicate an optimal Co content of 17 at % (Ni0.83Co0.17P) to maximize OER performance. Impressively, the Ni0.83Co0.17P coating deposited on nickel foam exhibits remarkable OER catalytic activity (η = 295 mV at 10 mA cm−2), noteworthy catalytic kinetics (Tafel slope as small as 45 mV dec−1) and high rate of oxygen production for each active site (turnover frequency of 0.16 s−1 at 300 mV) in 1 M KOH. Importantly, the Ni0.83Co0.17P/NF demonstrates excellent long-term stability as inferred by continuous test for 25 h. Furthermore, a full alkaline electrolyzer is designed using Ni0.83Co0.17P/NF as the anode and Pt decorated Ni−P/NF as the cathode, which can drive overall water splitting with a potential as low as 1.60 V at 10 mA cm−2, and also shows outstanding long-term durability.The cheapness of the present preparation method as well as its suitability for large-scale production without the need of expensive raw materials and energy-consuming processes paves the way towards commercial production of transition metal phosphide-based electrocatalysts.

SrZrO3 Cube-Decorated PbS Nanoflowers as Robust Electrocatalysts for the Oxygen Evolution Reaction

Shrinkage of reservoirs of fossil fuels has already created an alarming situation in the energy sector, and the side products produced during their burning affect the environment adversely. Therefore, it is a need of time to replace fossil fuels with any other source with huge reservoirs. Herein, we fabricated a PbS/SrZrO3 nanocomposite, exhibiting promising oxygen evolution reaction activity. The synthesized samples were characterized by various techniques to confirm the material phase, morphology, surface area, composition, and oxidation states. As a result, it displays a very promising overpotential of 228 mV at a current density of 10 mA/cm2, a lower Tafel slope of 64 mV/dec, a higher turnover frequency of 1.45 s–1, an electrochemically active surface area of 280 cm2/g, and high stability up to 24 h, in contrast to the most advanced noble metal electrocatalysts Pt, oxides of Ir and Ru, and their constituents. High activity and low cost make this material one of the best to endeavor in the field of water splitting.

Ni(OH)2 microspheres in situ self-grown on ultra-thin layered g-C3N4 as a heterojunction electrocatalyst for oxygen evolution reaction

Oxygen evolution reaction (OER), as a part reaction of the overall water splitting, is deemed as a prospective technology for large-scale energy storage. However, the sluggish kinetics (large overpotential) and the expensive cost of noble metal-based electrocatalysts (RuO2 and IrO2) restrain the widespread usage of OER. Hence, the discovery of non-precious metal-based electrocatalysts with tiny overpotential, satisfactory current density and outstanding stability has become urgent. In this work, we have prepared ultra-thin layered g-C3N4 by a two-step thermal peeling method and synthesized Ni(OH)2/g-C3N4 composite by a simple one-step solvothermal method. Benefiting from the layered g-C3N4 as substrate, the overpotential of Ni(OH)2/g-C3N4 composite was just 240 mV at 10 mA cm−2, which gives an unexpected improvement in the electrochemical performance of the composite samples compared to pure Ni(OH)2 (η = 460 mV). Additionally, the formation of heterojunction effectively reduces the resistance to electron transport in OER, the resistance of Ni(OH)2/g-C3N4 (Rct = 38.8 Ω) is far smaller than those of bare Ni(OH)2 (Rct = 41.6 Ω) and layered g-C3N4 (Rct = 43.6 Ω) at the open circuit potential. Ni(OH)2/g-C3N4 composite samples display outstanding electrochemical stability, maintaining 85% of initial current density for 12 h. Moreover, density functional theory (DFT) demonstrates that ΔG3 of Ni(OH)2/g-C3N4 composite (η = 0.46 V) is much lower than that of bare Ni(OH)2 (η = 0.64 V). These undeniable results demonstrate that Ni(OH)2/g-C3N4 composite materials is promising alternative materials to replace precious metal-based OER electrocatalysts in the field of water splitting.

A Review of Recent Developments in Molecular Dynamics Simulations of the Photoelectrochemical Water Splitting Process

In this review, we provide a short overview of the Molecular Dynamics (MD) method and how it can be used to model the water splitting process in photoelectrochemical hydrogen production. We cover classical non-reactive and reactive MD techniques as well as multiscale extensions combining classical MD with quantum chemical and continuum methods. Selected examples of MD investigations of various aqueous semiconductor interfaces with a special focus on TiO2 are discussed. Finally, we identify gaps in the current state-of-the-art where further developments will be needed for better utilization of MD techniques in the field of water splitting.

Toward practical solar-driven photocatalytic water splitting on two-dimensional MoS2 based solid-state Z-scheme and S-scheme heterostructure

Solar-driven splitting of water to hydrogen production is one of the utmost auspicious and cost-effective technologies providing sustainable fuel as it necessitates only sunlight and water. This substantial technology can be achieved in a two step-photoexcitation system using an artificial Z-scheme process. The key to comprehend this reaction is to discover an effective and robust photocatalyst which preferably makes sufficient use of solar energy. Benefiting from the ultrahigh surface area, appropriate band potentials and unique physiochemical properties of 2D layered structure, MoS2 has attained intensive research attention for hydrogen evolution reaction. The comprehensive review summarizes the recent progression in solid mediator Z-scheme based MoS2 particularly in the field of water splitting. The review initiates with the important bases of Z-scheme water splitting mechanism in addition to structural and optoelectronic properties of MoS2. In addition, detailed discussion on the solid-mediator Z-schemes to further improve the photocatalytic efficacy and limit the back (water-forming) reactions. The review mainly focuses on the solid-mediator based Z-schematic systems involving new tandem structures with an efficient synergistic effect to achieve both wide-range light absorptivity and charge pairs transference. In addition, a new S-scheme heterostructing is briefly introduced to understand the charge-transport route clearly and vividly. The aim of wide-spreading water splitting devices from lab-scale to wide-range potential applications has been considered as ‘artificial photosynthetic leaf-to-tree challenge’. Finally, a summary and outlook on the challenges and future research topics on MoS2 based Z-scheme heterostructure photocatalysts are presented.

Ab-initio insights into electronic structures, optical and photocatalytic properties of Janus WXY (X/Y = O, S, Se and Te)

Two-dimensional materials attracted widespread attention due to their striking performances compared with bulk materials. In this presentation, we theoretically investigate the electronic structures, optical and photocatalytic properties of Janus WXY (X/Y is O, S, Se and Te) through first-principles calculations. Our results indicate the recombination rate of photogenerated electron-hole pairs could be distinctly reduced because of the internal electric field of Janus WXY (X/Y is O, S, Se and Te) nanostructures. Moreover, Janus WXY (X/Y is S, Se and Te) own the decent band gaps and band-edge positions with water redox potential, i.e. the reduction and oxidation potentials are both contained by the corresponding band gap regions, demonstrating the significent potential as efficient photocatalysts for water splitting. The acid environment (pH = 0) can be used as the most suitable condition to forecast the significant potentical applcation for Janus WXY (X/Y is S, Se and Te) materials as distinguished photocatalysts for water splitting reactions. Addtionally, the response of the band gaps (EG) of Janus WXY (X/Y is S, Se and Te) systems to tensile strain strains is more sensitive than compressive strain. These findings are intended to provide appealing significance for the fascinating applications of Janus WXY (X/Y is S, Se and Te) in the field of water splitting and offer a reliable guidelines for experiments.

Theoretical calculation of a TiO2-based photocatalyst in the field of water splitting: A review

AbstractCurrently, energy and environmental problems are becoming more serious. The use of solar energy to split water and produce clean, renewable hydrogen as an energy source is a feasible and effective approach to solve these problems. As the most promising semiconductor material for photocatalytic water splitting, TiO2-based nanomaterials have received increasing attention from researchers in academia and industry in recent years. This review describes the research progress in the theoretical calculations of TiO2-based photocatalysts in water splitting. First, it briefly introduces some commonly used theoretical calculation methods, the crystal structure of TiO2and its photocatalytic mechanism, and the principle of doping and heterojunction modification to improve the photocatalytic performance of TiO2. Subsequently, the adsorption state of water molecules with different coverages on the surface of TiO2, the rate-limiting steps of the splitting of water molecules on the surface of TiO2, and the transfer process of photogenerated current carriers at the interface between water molecules and TiO2are analyzed. In addition, a brief review of research into the theoretical calculations of TiO2-based commercial photocatalysts in the field of water splitting is also provided. Finally, the calculation of TiO2-based photocatalytic water-splitting simulations is summarized, and possible future research and development directions are discussed.

2D Thin Sheet Heterostructures of MoS2 on MoSe2 as Efficient Electrocatalyst for Hydrogen Evolution Reaction in Wide pH Range.

Two-dimensional layered transition metal dichalcogenides, MoSe2 and MoS2, have drawn potential attention in the field of water splitting. Coupling of MoS2 and MoSe2 provides a sustainable route to improve the electrocatalytic activity for the hydrogen evolution reaction (HER). Here, the heterostructures of thin sheets (ts) of MoSe2 and MoS2 are combined to develop the MoSe2-ts@MoS2-ts heterostructure via multiple-step methodology. First, thin sheets of MoSe2 are synthesized following the stepwise hydrothermal method. After the successful synthesis of MoSe2-ts, MoS2-ts is synthesized on it to develop the heterostructure: MoSe2-ts@MoS2-ts. By tuning the amount of MoS2-ts and MoSe2-ts in the heterostructure separately, the optimum condition is obtained for HER. The unique heterostructure is efficient for HER under wide pH conditions like 1 M KOH, pH-7 phosphate buffer, 3.5% saline water, and finally 0.5 M H2SO4. MoSe2-ts@MoS2-ts can generate 10 mA/cm2 current density under the application of -0.186 V vs RHE with a low Tafel value of 71 mV/decade. The formation of the heterojunction plays an essential role in facilitating charge transportation. Furthermore, the heterostructure provides the more active sites for the adsorption of hydrogen to generate H2. An excess amount of any of the bare counter parts in the heterostructure leads to a decrease in electrocatalytic efficiency because of the lowered heterojuction formation. MoSe2-ts@MoS2-ts has very high stability during the electrocatalytic reaction, which is determined from 1000 consecutive cycles and a 24 h prolonged scan. MoSe2-ts@MoS2-ts can generate 147 μmol of H2 in ∼50 min of reaction time with 100% Faradaic efficiency.