In situ photo-assisted deposition of MoS₂ electrocatalyst onto zinc cadmium sulphide nanoparticle surfaces to construct an efficient photocatalyst for hydrogen generation

Nanocomposite Marvels: Unveiling Breakthroughs in Photocatalytic Water Splitting for Enhanced Hydrogen Evolution

An overview of the significant innovations in photocatalysts for H2 development, photocatalyst selection criteria, and photocatalytic modifications to improve the photocatalytic activity was examined in this Review, as well as mechanisms and thermodynamics. A variety of semiconductors have been examined in a structured fashion, such as TiO2-, g-C3N4-, graphene-, sulfide-, oxide-, nitride-, oxysulfide-, oxynitrides, and cocatalyst-based photocatalysts. The techniques for enhancing the compatibility of metals and nonmetals is discussed in order to boost photoactivity within visible light irradiation. In particular, further deliberation has been carried out on the development of heterojunctions, such as type I, type II, and type III, along with Z-systems, and S-scheme systems. It is important to thoroughly investigate these issues in the sense of visible light irradiations to enhance the efficacy of photocatalytic action. In fact, another advancement in this area may include hiring mediators including grapheme oxide and metals to establish indirect Z-scheme montages with a correct band adjustment. The potential consideration of reaction chemology, mass transfer, kinetics of reactions, restriction of light diffusion, and the process and selection of suitable light and photoreactor also will optimize sustainable hydrogen output efficiency and selectivity.

Coupling Long-Range Facet Junction and Interfacial Heterojunction via Edge-Selective Deposition for High-Performance Z-Scheme Photocatalyst

The construction of photocatalytic systems that have strong redox capability, effective charge separation, and large reactive surfaces is of great scientific and practical interest. Herein, an edge-connected 2D/2D Z-scheme system that combines the facet junction and the interfacial heterojunction to achieve effective long-range charge separation and large reactive surface exposure is designed and fabricated. The heterostructure is realized by the selective growth of 2D-layered MoS₂ nanoflakes on the edge-sites of thin TiO₂ nanosheets via an Au-promoted photodeposition method. Attributed to the synergetic coupling of the facet junction and the interfacial heterojunction that assures the effective charge separation, and the tremendous but physically separated reactive sites offered by layered MoS₂ and highly-exposed (001) facets of TiO₂ , respectively, the artificial Z-scheme exhibits excellent photocatalytic performance in photodegradation tests. Moreover, the junctional plasmonic Au nanoclusters not only act as electron traps to promote the edge-selective synthesis but also generate "hot electrons" to further boost photocatalytic performance. The Z-scheme charge-flow direction in the heterostructure and the roles of electrons and holes are comprehensively studied using in situ irradiated X-ray photoelectron spectroscopy and photodegradation tests. This work offers a new insight into designing high-performance Z-scheme photocatalytic systems.

Transition Metal Dichalcogenides [MX2] in Photocatalytic Water Splitting

The quest for a clean, renewable and sustainable energy future has been highly sought for by the scientific community over the last four decades. Photocatalytic water splitting is a very promising technology to proffer a solution to present day environmental pollution and energy crises by generating hydrogen fuel through a “green route” without environmental pollution. Transition metal dichalcogenides (TMDCs) have outstanding properties which make them show great potential as effective co-catalysts with photocatalytic materials such as TiO2, ZnO and CdS for photocatalytic water splitting. Integration of TMDCs with a photocatalyst such as TiO2 provides novel nanohybrid composite materials with outstanding characteristics. In this review, we present the current state of research in the application of TMDCs in photocatalytic water splitting. Three main aspects which consider their properties, advances in the synthesis routes of layered TMDCs and their composites as well as their photocatalytic performances in the water splitting reaction are discussed. Finally, we raise some challenges and perspectives in their future application as materials for water-splitting photocatalysts.

Improving Wastewater Treatment by Triboelectric-Photo/Electric Coupling Effect

The ability to meet higher effluent quality requirements and the reduction of energy consumption are the biggest challenges in wastewater treatment worldwide. A large proportion of the energy generated during wastewater treatment processes is neglected and lost in traditional wastewater treatment plants. As a type of energy harvesting system, triboelectric nanogenerators (TENGs) can extensively harvest the microscale energies generated from wastewater treatment procedures and auxiliary devices. This harvested energy can be utilized to improve the removal efficiency of pollutants through photo/electric catalysis, which has considerable potential application value in wastewater treatment plants. This paper gives an overall review of the generated potential energies (e.g., water wave energy, wind energy, and acoustic energy) that can be harvested at various stages of the wastewater treatment process and introduces the application of TENG devices for the collection of these neglected energies during wastewater treatment. Furthermore, the mechanisms and catalytic performances of TENGs coupled with photo/electric catalysis (e.g., electrocatalysis, photoelectric catalysis) are discussed to realize higher pollutant removal efficiencies and lower energy consumption. Then, a thorough, detailed investigation of TENG devices, electrode materials, and their coupled applications is summarized. Finally, the intimate coupling of self-powered photoelectric catalysis and biodegradation is proposed to further improve removal efficiencies in wastewater treatment. This concept is conducive to improving knowledge about the underlying mechanisms and extending applications of TENGs in wastewater treatment to better solve the problems of energy demand in the future.

A metal-organic framework-derived Zn1-xCdxS/CdS heterojunction for efficient visible light-driven photocatalytic hydrogen production

ZCS-C (ZnCdS/CdS) QDs were synthesized via low-temperature vulcanization using zeolitic imidazolate framework-8 (ZIF-8) nanoparticles as a precursor, cation exchange, and heterojunction construction. Without any precious metal as a cocatalyst, the photocatalytic hydrogen production rate of ZCS-C-3 QDs reached 2.7 mmol g-1 h-1 under visible light irradiation. The optimized sample exhibited an outstanding chemical stability and recyclability, which is superior to most of the reported Zn1-xCdxS-based photocatalysts.

Metal Sulfide Nanoparticles: Precursor Chemistry

Fascination with and the need for evermore increasing efficiency, power, or strength have been the cornerstones for developing new materials and methods for their creation. Higher solar cell conversion efficiencies, increased battery storage power, and lightweight strong materials are some that have been at the forefront of attention for these efforts. Materials created for most applications start as simple chemical compounds. A study of how these chemicals have been used in the past can be used to create new materials and new methods of production. Herein, a class of materials that are valuable in a multitude of applications, metal sulfide nanoparticles, are examined, along with how they are being produced and how new methods can be established that will help to standardize and increase production capabilities. Precursor–solvent combinations that can be used to create metal sulfide nanoparticles in the gas phase are also explored.

Investigation on the Growth Mechanism of Cu2 MoS4 Nanotube, Nanoplate and its use as a Catalyst for Hydrogen Evolution in Water

Cu₂ MoS₄ is a ternary transition-metal sulfide that shows great potential in the field of energy conversion and storage, namely catalytic H₂ evolution in water and Li-, Na- or Mg-ion battery. In this work, we report on a growth mechanism of the single-crystalline Cu₂ MoS₄ nanotube from (NH₄ )₂ MoS₄ salt and Cu₂ O nanoparticle. By probing the nature and morphology of solid products generated in function of reaction conditions we find that the crystalline Cu(NH₄ )MoS₄ nanorod is first generated at ambient conditions. The nanorod is then converted into Cu₂ MoS₄ nanotube under hydrothermal treatment due to the Kirkendall effect or a selective etching of the Cu₂ MoS₄ core. Extending the hydrothermal treatment causes a collapse of nanotube generating Cu₂ MoS₄ nanoplate. The catalytic activities of these sulfides are investigated. The Cu₂ MoS₄ shows superior catalytic activity to that of Cu(NH₄ )MoS₄ . Catalytic performance of the former largely depends on its morphology. The nanoplate shows superior catalytic activity to the nanotube, thanks to its higher specific electrochemical surface area.

Gold nanorod/molybdenum sulfide core-shell nanostructures synthesized by a photo-induced reduction process

Coupling of plasmonic nanostructures and semiconductors gives promising hybrid nanostructures that can be used in different applications such as photosensing and energy conversion. In this report, we describe an approach for fabricating a new hybrid material by coupling a gold nanorod (Au NR) core and amorphous molybdenum sulfide (MoS_x) shell. The Au NR/MoS_x core-shell structure is achieved by exploiting the hot electrons generated in the plasmonic excitation of Au NRs to drive the reduction of [MoS₄]^2-, which is pre-adsorbed on the Au NR surface, producing a thin MoS_x layer. This approach allows us to control the thickness of the MoS_x coating layer on the Au NR surface. The resultant Au NR/MoS_x hybrid is characterized by absorption spectroscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive x-ray spectroscopy elemental mapping, x-ray diffraction and x-ray photoelectron spectroscopy.

Earth-Abundant MoS2 and Cobalt Phosphate Dual Cocatalysts on 1D CdS Nanowires for Boosting Photocatalytic Hydrogen Production

Cocatalysts play a significant role in accelerating the catalytic reactions of semiconductor photocatalyst. In particular, a semiconductor assembled with dual cocatalysts, i.e., reduction and oxidation cocatalysts, can obviously enhance the photocatalytic performance because of the synergistic effect of fast consumption of photogenerated electrons and holes simultaneously. However, in most cases, noble metal cocatalysts are employed, which tremendously increases the cost of the photocatalysts and restricts their large-scale applications. Herein, on the platform of one-dimensional (1D) CdS nanowires, we have utilized the earth-abundant dual cocatalysts, MoS₂ and cobalt phosphate (Co-Pi), to construct the CdS@MoS₂@Co-Pi (CMC) core-shell hybrid photocatalysts. In this dual-cocatalyst system, Co-Pi is in a position to expedite the migration of holes from CdS, while MoS₂ acts as an electron transporter as well as active sites to accelerate the surface water reduction reaction. Taking the advantages of the dual-cocatalyst system, the prepared CMC hybrid shows an obvious enhancement of both the photoactivity and photostability toward hydrogen production compared with bare 1D CdS nanowires and binary hybrids (CdS@MoS₂ and CdS@Co-Pi). This work highlights the promising prospects for rational utilization of earth-abundant dual cocatalysts to design low-cost and efficient hybrids toward boosting photoredox catalysis.

Influence of MoS2 on Activity and Stability of Carbon Nitride in Photocatalytic Hydrogen Production

MoS2/C3N4 (MS-CN) composite photocatalysts have been synthesized by three different methods, i.e., in situ-photodeposition, sonochemical, and thermal decomposition. The crystal structure, optical properties, chemical composition, microstructure, and electron transfer properties were investigated by X-ray diffraction, UV-vis diffuse reflectance spectroyscopy, X-ray photoelectron spectroscopy, electron microscopy, photoluminescence, and in situ electron paramagnetic resonance spectroscopy. During photodeposition, the 2H MoS2 phase was formed upon reduction of [MoS4]2− by photogenerated conduction band electrons and then deposited on the surface of CN. A thin crystalline layer of 2H MoS2 formed an intimate interfacial contact with CN that favors charge separation and enhances the photocatalytic activity. The 2H MS-CN phase showed the highest photocatalytic H2 evolution rate (2342 μmol h−1 g−1, 25 mg catalyst/reaction) under UV-vis light irradiation in the presence of lactic acid as sacrificial reagent and Pt as cocatalyst.

One-Step Synthesis of MoS2/TiSi2 via an In Situ Photo-Assisted Reduction Method for Enhanced Photocatalytic H2 Evolution under Simulated Sunlight Illumination

A new MoS2/TiSi2 complex catalyst was designed and synthesized by a simple one-step in situ photo-assisted reduction procedure. The structural and morphological properties of the composites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and ultraviolet-visible diffused reflectance spectroscopy (UV-vis DRS), which proved the formation of MoS2/TiSi2. MoS2/TiSi2 with optimized composition showed obviously enhanced photocatalytic activity and superior durability for water reduction to produce H2. The H2 generation rate over the MoS2/TiSi2 photocatalyst containing 3 wt % MoS2 reached 214.1 μmol·h−1·g−1 under visible light irradiation, which was ca. 5.6 times that of the pristine TiSi2. The improved photocatalytic activity of MoS2/TiSi2 could be related to the broad response spectrum, large visible light absorption, and synergies among MoS2 and TiSi2 that enhance photoexcited charge transfer and separation.

Enhanced photoelectrochemical activity of Co-doped β-In2S3nanoflakes as photoanodes for water splitting

This work is primarily focused on indium sulfide (β-In₂S₃) and cobalt (Co)-doped β-In₂S₃ nanoflakes as photoanodes for water oxidation. The incorporation of cobalt introduces new dopant energy levels increasing visible light absorption and leading to improved photo-activity. In addition, cobalt ion centers in β-In₂S₃ act as potential catalytic sites to promote electro-activity. 5 mol% Co-doped β-In₂S₃ nanoflakes when tested for photoelectrochemical water splitting exhibited a photocurrent density of 0.69 mA cm⁻² at 1.23 V, much higher than that of pure β-In₂S₃.

Doped indium sulfide as an efficient photocatalyst for water oxidation.

Recent advances in metal sulfides: from controlled fabrication to electrocatalytic, photocatalytic and photoelectrochemical water splitting and beyond

This review describes an in-depth overview and knowledge on the variety of synthetic strategies for forming metal sulfides and their potential use to achieve effective hydrogen generation and beyond.

In situ growth and activation of an amorphous MoSx catalyst on Co-containing metal–organic framework nanosheets for highly efficient dye-sensitized H2 evolution

In situ grown amorphous MoS_x on Co-containing MOF nanosheets could efficiently catalyze visible light H₂ evolution in an ErB-sensitized system.

MoS2 Quantum Dots-Modified Covalent Triazine-Based Frameworks for Enhanced Photocatalytic Hydrogen Evolution

MoS₂ quantum dots (QDs)-modified covalent triazine-based framework (MoS₂ /CTF) composites are synthesized through an in situ photodeposition method. MoS₂ QDs are well distributed and stabilized on the layers of CTFs by coordination of the frameworks to MoS₂ . The QDs-sheet interactions between MoS₂ and CTFs facilitate interfacial charge transfer and separation. As a consequence, the composites exhibit outstanding photocatalytic activity and stability for hydrogen evolution under visible light irradiation (λ≥420 nm), that exceed those over pristine CTFs and MoS₂ -modified g-C₃ N₄ (MoS₂ /g-C₃ N₄ ) composite, making them promising materials for solar energy conversion.

Hierarchical CdMoO4 nanowire–graphene composite for photocatalytic hydrogen generation under natural sunlight

Herein, a facile in situ solvothermal technique for the synthesis of a CdMoO₄/graphene composite photocatalyst for hydrogen generation under natural solar light.

One-pot Synthesis of CdS Irregular Nanospheres Hybridized with Oxygen-Incorporated Defect-Rich MoS2 Ultrathin Nanosheets for Efficient Photocatalytic Hydrogen Evolution

Robust and highly active photocatalysts, CdS@MoS₂, for hydrogen evolution were successfully fabricated by one-step growth of oxygen-incorporated defect-rich MoS₂ ultrathin nanosheets on the surfaces of CdS with irregular fissures. Under optimized experimental conditions, the CdS@MoS₂ displayed a quantum yield of ∼24.2% at 420 nm and the maximum H₂ generation rate of ∼17203.7 umol/g/h using Na₂S-Na₂SO₃ as sacrificial agents (λ ≥ 420 nm), which is ∼47.3 and 14.7 times higher than CdS (∼363.8 μmol/g/h) and 3 wt % Pt/CdS (∼1173.2 μmol/g/h), respectively, and far exceeds all previous hydrogen evolution reaction photocatalysts with MoS₂ as co-catalysts using Na₂S-Na₂SO₃ as sacrificial agents. Large volumes of hydrogen bubbles were generated within only 2 s as the photocatalysis started, as demonstrated by the photocatalytic video. The high hydrogen evolution activity is attributed to several merits: (1) the intimate heterojunctions formed between the MoS₂ and CdS can effectively enhance the charge transfer ability and retard the recombination of electron-hole pairs; and (2) the defects in the MoS₂ provide additional active S atoms on the exposed edge sites, and the incorporation of O reduces the energy barrier for H₂ evolution and increases the electric conductivity of the MoS₂. Considering its low cost and high efficiency, this highly efficient hybrid photocatalysts would have great potential in energy-generation and environment-restoration fields.

Hexagonal Zn1−xCdxS (0.2 ≤ x ≤ 1) solid solution photocatalysts for H2 generation from water

A series of hexagonal Zn_1−xCd_xS photocatalysts with variable composition (0.2 ≤ x ≤ 1) is synthesized by a solvothermal method.

MoS2/CdS Nanosheets-on-Nanorod Heterostructure for Highly Efficient Photocatalytic H2 Generation under Visible Light Irradiation

Semiconductor-based photocatalytic H2 generation as a direct approach of converting solar energy to fuel is attractive for tackling the global energy and environmental issues but still suffers from low efficiency. Here, we report a MoS2/CdS nanohybrid as a noble-metal-free efficient visible-light driven photocatalyst, which has the unique nanosheets-on-nanorod heterostructure with partially crystalline MoS2 nanosheets intimately but discretely growing on single-crystalline CdS nanorod. This heterostructure not only facilitates the charge separation and transfer owing to the formed heterojunction, shorter radial transfer path, and fewer defects in single-crystalline nanorod, thus effectively reducing the charge recombination, but also provides plenty of active sites for hydrogen evolution reaction due to partially crystalline structure of MoS2 as well as enough room for hole extraction. As a result, the MoS2/CdS nanosheets-on-nanorod exhibits a state-of-the-art H2 evolution rate of 49.80 mmol g(-1) h(-1) and an apparent quantum yield of 41.37% at 420 nm, which is the advanced performance among all MoS2/CdS composites and CdS/noble metal photocatalysts. These findings will open opportunities for developing low-cost efficient photocatalysts for water splitting.

2D Transition-Metal-Dichalcogenide-Nanosheet-Based Composites for Photocatalytic and Electrocatalytic Hydrogen Evolution Reactions

Hydrogen (H2) is one of the most important clean and renewable energy sources for future energy sustainability. Nowadays, photocatalytic and electrocatalytic hydrogen evolution reactions (HERs) from water splitting are considered as two of the most efficient methods to convert sustainable energy to the clean energy carrier, H2. Catalysts based on transition metal dichalcogenides (TMDs) are recognized as greatly promising substitutes for noble-metal-based catalysts for HER. The photocatalytic and electrocatalytic activities of TMD nanosheets for the HER can be further improved after hybridization with many kinds of nanomaterials, such as metals, oxides, sulfides, and carbon materials, through different methods including the in situ reduction method, the hot-injection method, the heating-up method, the hydro(solvo)thermal method, chemical vapor deposition (CVD), and thermal annealing. Here, recent progress in photocatalytic and electrocatalytic HERs using 2D TMD-based composites as catalysts is discussed.

Metallic 1T-LixMoS2 Cocatalyst Significantly Enhanced the Photocatalytic H2 Evolution over Cd0.5Zn0.5S Nanocrystals under Visible Light Irradiation

In the present work, metallic 1T-LixMoS2 is utilized as a novel cocatalyst for Cd0.5Zn0.5S photocatalyst. The obtained LixMoS2/Cd0.5Zn0.5S hybrids show excellent photocatalytic performance for H2 generation from aqueous solution containing Na2S and Na2SO3 under splitting visible light illumination (λ ≥ 420 nm) without precious metal cocatalysts. It turns out that a certain amount of intercalating Li(+) ions ultimately drives the transition of MoS2 crystal from semiconductor triagonal phase (2H phase) to metallic phase (1T phase). The distinct properties of 1T-LixMoS2 promote the efficient separation of photoexcited electrons and holes when used as cocatalyst for Cd0.5Zn0.5S photocatalyst. As compared to 2H-MoS2 nanosheets only having edge active sites, photoinduced electrons not only transfer to the edge sites of 1T-LixMoS2, but also to the plane active sites of 1T-LixMoS2 nanosheets. The content of LixMoS2 in hybrid photocatalysts influences the photocatalytic activity. The optimal 1T-LixMoS2 (1.0 wt %)/Cd0.5Zn0.5S nanojunctions display the best activity for hydrogen production, achieving a hydrogen evolution rate of 769.9 μmol h(-1), with no use of noble metal loading, which is about 3.5 times higher than that of sole Cd0.5Zn0.5S, and 2 times higher than that of 2H-MoS2 (1.0 wt %)/Cd0.5Zn0.5S samples. Our results demonstrate that Li(+)-intercalated MoS2 nanosheets with high conductivity, high densities of active sites, low cost, and environmental friendliness are a prominent H2 evolution cocatalyst that might substitute for noble metal for potential hydrogen energy applications.

Stabilizing and Improving Solar H2 Generation from Zn(0.5)Cd(0.5)S Nanorods@MoS2/RGO Hybrids via Dual Charge Transfer Pathway

The incorporated Zn(0.5)Cd(0.5)S (ZCS) nanorods with MoS2/RGO cocatalysts by a simultaneous reduction reaction was reported. The preparation of RGO and formation of MoS2 with intimate interfacial contact with ZCS were achieved. Through the optimizing of each component proportion, the ZCS@MoS2/RGO hybrid with 1.5 wt % MoS2 and 3 wt % RGO showed the highest photocatalytic H2 production activity (2.31 mmol/h) with long time stability (50 h). The relative mechanism has been investigated. It is believed that the stabilizing and improving solar H2 generation is originating from dual charge transfer pathway from excited ZCS to RGO, then to MoS2 due to intimate interfacial structure.

Fast preparation of MoS2 nanoflowers decorated with platinum nanoparticles for electrochemical detection of hydrogen peroxide

MoS₂ nanoflowers decorated with Pt nanoparticles show enhanced performances for electrochemical H₂O₂ sensing.

Rational design of semiconductor-based photocatalysts for advanced photocatalytic hydrogen production: the case of cadmium chalcogenides

This review summarizes the recent advances in developing CdX (X = S, Se, Te)-based photocatalyst systems for photocatalytic hydrogen production from water.

Driving electrocatalytic activity by interface electronic structure control in a metalloprotein hybrid catalyst for efficient hydrogen evolution

Schematic presentation of a silver incorporated lysine-216 (LYS-216) active site bonded with the retinal chromophore (RC) of bacteriorhodopsin (bR) bacteria for the hydrogen evolution reaction.

Recent advances in transition-metal dichalcogenide based nanomaterials for water splitting

The desire for sustainable and clean energy future continues to be the concern of the scientific community. Researchers are incessantly targeting the development of scalable and abundant electro- or photo-catalysts for water splitting. Owing to their suitable band-gap and excellent stability, an enormous amount of transition-metal dichalcogenides (TMDs) with hierarchical nanostructures have been extensively explored. Herein, we present an overview of the recent research progresses in the design, characterization and applications of the TMD-based electro- or photo-catalysts for hydrogen and oxygen evolution. Emphasis is given to the layered and pyrite-phase structured TMDs encompassing semiconducting and metallic nanomaterials. Illustrative results and the future prospects are pointed out. This review will provide the readers with insight into the state-of-the-art research progresses in TMD based nanomaterials for water splitting.

Noble-Metal-Free Molybdenum Disulfide Cocatalyst for Photocatalytic Hydrogen Production

Photocatalytic water splitting using powered semiconductors as photocatalysts represents a promising strategy for clean, low-cost, and environmentally friendly production of H2 utilizing solar energy. The loading of noble-metal cocatalysts on semiconductors can significantly enhance the solar-to-H2 conversion efficiency. However, the high cost and scarcity of noble metals counter their extensive utilization. Therefore, the use of alternative cocatalysts based on non-precious metal materials is pursued. Nanosized MoS2 cocatalysts have attracted considerable attention in the last decade as a viable alternative to improve solar-to-H2 conversion efficiency because of its superb catalytic activity, excellent stability, low cost, availability, environmental friendliness, and chemical inertness. In this perspective, the design, structures, synthesis, and application of MoS2 -based composite photocatalysts for solar H2 generation are summarized, compared, and discussed. Finally, this Review concludes with a summary and remarks on some challenges and opportunities for the future development of MoS2 -based photocatalysts.

Surface Activation of Faceted Photocatalyst: When Metal Cocatalyst Determines the Nature of the Facets

Pt nanoparticles with tunable size are prepared on the entire surface of facet-engineered Cu2WS4 decahedral photocatalyst via a kinetic-controlled chemical reduction process. The {101} facets of the photocatalyst which featured photo-oxidation, are successfully activated for photoreduction by Pt. The resulting photocatalyst shows an activity nine times higher compared to that of the only {001}-facets activated catalyst obtained by a conventional in situ photodeposition route.

Silicon decorated with amorphous cobalt molybdenum sulfide catalyst as an efficient photocathode for solar hydrogen generation

The construction of viable photoelectrochemical (PEC) devices for solar-driven water splitting can be achieved by first identifying an efficient independent photoanode for water oxidation and a photocathode for hydrogen generation. These two photoelectrodes then must be assembled with a proton exchange membrane within a complete coupled system. Here we report the preparation of a Si/a-CoMoSx hybrid photocathode which shows impressive performance (onset potential of 0.25 V vs RHE and photocurrent jsc of 17.5 mA cm(-2) at 0 V vs RHE) in pH 4.25 phosphate solution and under simulated AM 1.5 solar illumination. This performance is among the best reported for Si photocathodes decorated with noble-metal-free catalysts. The electrode preparation is scalable because it relies on a photoassisted electrodeposition process employing an available p-type Si electrode and [Co(MoS4)2](2-) precursor. Investigation of the mechanism of the Si/a-CoMoSx electrode revealed that under conditions of H2 photogeneration this bimetallic sulfide catalyst is highly efficient in extracting electrons from illuminated Si and subsequently in reducing protons into H2. The Si/a-CoMoSx photocathode is functional over a wide range of pH values, thus making it a promising candidate for the construction of a complete solar-driven water splitting PEC device.

Metallic MoO₂ cocatalyst significantly enhances visible-light photocatalytic hydrogen production over Mo₂/Zn₀.₅Cd₀.₅S heterojunction

As semiconductor-based nanoheterostructures play a decisive role in current electronics and optoelectronics, the introduction of active heterojunctions can afford new and improved capabilities that will enhance the conversion of solar energy into chemical energy. In this work, a novel metal/semiconductor MoO₂/Zn₀.₅Cd₀.₅S heterojunction has been designed and prepared to significantly enhance photocatalytic H₂ production efficiency. The photocatalytic activity of the as-prepared MoO₂/Zn₀.₅Cd₀.₅S for H₂ generation from water under visible-light irradiation (λ ≥ 420 nm) is measured. MoO₂/Zn₀.₅Cd₀.₅S hybrid nanoparticles have a higher photocatalytic activity than Zn₀.₅Cd₀.₅S even without the noble metal cocatalyst. The results show that the rate of H₂ evolution over annealed MoO₂/Zn₀.₅Cd₀.₅S is about 13 times higher than that of Zn₀.₅Cd₀.₅S alone, and 10 times higher than that of simply mixed MoO₂/Zn₀.₅Cd₀.₅S. Implying that the strong coupling at the interface of MoO₂ and Zn₀.₅Cd₀.₅S facilitates electron transfer from the conduction band of Zn₀.₅Cd₀.₅S to metallic MoO₂, thus promoting the separation of photogenerated electrons and holes. MoO₂ (2 wt%)/Zn₀.₅Cd₀.₅S heterostructured photocatalyst calcined at 673 K achieves the optimal overall activity for H₂ evolution. The introduction of metallic MoO₂ cocatalyst leads to a remarkable improvement in the photo current and photocatalytic H₂ production activity of Zn₀.₅Cd₀.₅S, and the content of MoO₂ in this catalyst has an important influence on the photocatalytic activity. It is shown that 2 wt% metallic MoO₂ loaded on Zn₀.₅Cd₀.₅S sample produces a maximum photocatalytic H₂ production rate of 252.4 μmol h(-1). The junctions formed between metallic MoO₂ and semiconductor Zn₀.₅Cd₀.₅S by calcination play a key role in high photocatalytic water splitting to produce H₂. Our study demonstrates that metallic MoO₂ is an excellent H₂ evolution cocatalyst, and could be used as a cocatalyst for other semiconductors to improve performances.