Photocatalytic Hydrogen Evolution Reaction Research Articles

Construction of 3D MoSx/Zn2In2S5 nanoflower heterojunction for boosted photothermal-assisted photocatalytic hydrogen evolution in biomass solution

Hydrogen production from solar energy conversion method is an attractive strategy to alleviate the energy crisis. The use of non-noble metal cocatalysts instead of noble metal monomers to improve the performance of photocatalytic hydrogen evolution reactions has been pursued by researchers. In this work, we develop a single-photon excited electron transport pathway system for photocatalytic hydrogen production performance studies by coupling 0D MoSx nanodots and 3D Zn2In2S5 nanoflowers. Experimental results combined with DFT calculations show that MoSx not only imparts photothermal properties to the composite material, but also acts as a conduit for electron transport, which can accelerate the rapid separation and transfer of photocatalytic charges. Among them, 3-MoSx/Zn2In2S5 selectively promoted photocatalyzed conversion of benzyl alcohol (BA, 100% conversion) into benzaldehyde (BAD, 96.82% selectivity) by simultaneous co-production of hydrogen (8.74 mmol•g−1•h−1) within 1 h, which is about 7.80 and 2.69 times higher than pure Zn2In2S5, respectively. Further, 3-MoSx/Zn2In2S5 can realize the hydrogen production reaction with glycerol as the substrate with a remarkable effect (up to 5.47 mmol•g−1•h−1). Additionally, 3-MoSx/Zn2In2S5 also showed some hydrogen production performance when other biomasses (glucose, xylose, and cellulose) were used as substrates. This work provides a feasible strategy for the design of photothermal photocatalysts for synergistic hydrogen production from biomass.

An intermediary route to CdS/Bi2S3 architectures with high-activity and stability in photocatalytic water splitting and dye degradation

The binary CdS/Bi2S3 heterostructures were fabricated by employing ZnO/Bi2S3 as active intermediates for the first time, which consisted of 0D CdS nanoparticles with sizes of 10–20 nm decorated on 3D Bi2S3 mircoflowers assembled by 1D nanorods. The whole formation mechanism of CdS/Bi2S3 heterostructure was systematically investigated. Specifically, the optimal CdS/Bi2S3 sample (CB-3) achieved the highest photocatalytic hydrogen evolution reaction rate of 3.85 mmol·g−1·h−1, about 16.74 and 25.67 times greater than that of single Bi2S3 and CdS. Besides, the apparent reaction rate constant of CB-3 for photodegradation of Congo red reached up to 0.0412 min−1, being 41.2 and 4.08 folds higher than that of solo Bi2S3 and CdS. The recycled tests over CB-3 were ready to take on the superb photostability. Furthermore, the S-scheme mechanism of photoinduced charges was rationally proposed. This work provides a new insight for the construction of composite photocatalysts for boosted solar-light-driven photocatalytic performance.

Strategically designing and fabricating nitrogen and sulfur Co-doped g-C3N4 for accelerating photocatalytic H2 evolution

Doping engineering is an effective strategy for graphitic carbon nitride (g-C3N4) to improve its photocatalytic hydrogen evolution reaction (HER) performance. In this work, a novel nitrogen and sulfur co-doped g-C3N4 (N, S-g-C3N4) is elaborately designed on the basis of theoretical predictions of first-principle density functional theory (DFT). The calculated Gibbs free energy of adsorbed hydrogen (ΔGH*) for N, S-g-C3N4 at the N-doping active sites is extremely close to zero (0.01 eV). Inspired by the theoretical predictions, the N, S-g-C3N4 is successfully fabricated through ammonia-rich pyrolysis synthesis strategy, in which ammonia is in-situ obtained by pyrolyzing melamine. Subsequent characterizations indicate that the N, S-g-C3N4 possesses high specific surface area, outstanding light utilization, good hydrophilicity, and efficient carrier transfer efficiency. Consequently, the N, S-g-C3N4 displays an extremely high H2 evolution rate of 8269.9 µmol g−1 h−1, achieves an apparent quantum efficiency (AQE) of 3.24%, and also possesses outsatnding durability. Theoretical calculations further demonstrate that N and S dopants can not only introduce doping energy level to reduce the band gap, but also induce charge redistribution to facilitate hydrogen adsorption, thus promoting the photocatalytic HER process. Moreover, femtosecond transient absorption (fs-TA) spectroscopy further corroborates the efficient photogenerated carrier transport of N, S-g-C3N4. This research highlights a promising and reliable strategy to achieve superior photocatalytic activity, and exhibits significant guidance for precise designing high-efficiency photocatalysts.

Visible-light harvesting SrTiO3 solid solutions for photocatalytic hydrogen evolution from water.

The fabrication of solid solutions represents a compelling approach to modulating the physicochemical properties of materials. In this study, we achieved the successful synthesis of solid solutions comprising SrTiO3 and SrTaO2N (denoted as (SrTiO3)1-x-(SrTaO2N)x, 0 ≤ x ≤ 1) using the magnesium powder-assisted nitridation method. The absorption edge of (SrTiO3)1-x-(SrTaO2N)x is tunable from 500 to 600 nm. The conduction band minimum (CBM) of (SrTiO3)1-x-(SrTaO2N)x comprises the Ti 3d orbitals and the Ta 5d orbitals, while the valence band maximum (VBM) consists of the O 2p and N 2p orbitals. The microstructure of the (SrTiO3)1-x‑(SrTaO2N)x consists of small nanoparticles, exhibiting a larger specific surface area than the parent compounds of SrTiO3 and SrTaO2N. In the photocatalytic hydrogen evolution reaction (HER) with sacrificial reagents, the activity of solid solutions is notably superior to that of nitrogen-doped SrTiO3 and SrTaO2N. This superiority is mainly attributed to its broad light absorption range and high charge separation efficiency, which indicates its potential as a promising photocatalytic material. Moreover, the magnesium powder-assisted nitridation method exhibits obvious advantages for the synthesis of oxynitrides and bears instructional significance for the synthesis of other nitrogen-containing compounds and even sulfur-containing compounds.

Charge separation control in organic photosensitizers for photocatalytic water splitting without sacrificial electron donors

Photocatalytic hydrogen evolution reaction (photoHER) is one of the most promising approaches towards production of “green” hydrogen. Currently, the state-of-the-art photoHER systems require the use of sacrificial electron donors (SED), because of inefficient charge separation in photosensitizers and thermodynamically challenging water oxidation by the same catalyst. Here, we present a molecular design approach for all-organic photosensitizers with effective intramolecular charge separation, microsecond lifetime of excited states, controllable direction of electron transfer, and ability to oxidize water for recovery of the photocatalytic system to its initial state. Such photosensitizers comprise weakly conjugated strong electron donor and acceptor what enables charge transfer during the light absorption. The excitation energy is stored in long-living triplet states, whose lifetime can be monitored by the thermally activated delayed fluorescence. Additionally, application of heavy-atom effect helps not only to increase the population of triplet state but also to increase its stability and lifetime. When such photosensitizers are attached to the platinized TiO2, efficient photoHER catalysts are obtained which produce H2 under irradiation with sunlight. In the presence of SED, the highest turnover number after 24 h (TON24h) of such systems exceed 3500, whilst in pure water without any SED, TON24h reaches 2000. Our best system performs photocatalytic SED-free water-splitting for 48 h keeping 100 % of its activity and constant turnover frequency of 26 h−1. The described here investigations reveal that water splitting can be performed by a simple three component system “photosensitizer|TiO2|Pt” under specific control of 1) the charge separation and its direction, 2) intersystem crossing rate and triplet state lifetime, and 3) favorable water oxidation thermodynamics within a photosensitizer together with 4) appropriate alignment of energy levels to the catalyst.

Zr dopant acting shallow donor and active site in CdS lattice for co-catalyst free photocatalytic H2 evolution

Hydrogen evolution by photocatalysis shows great potential in solar energy conversion process and thus has become an active field of research. Separation efficiency of photogenerated carriers, light absorption and surface reaction are the dominant aspects that affect the photocatalytic hydrogen evolution. Creating traps to prolong the lifetime of photogenerated charge carriers has been widely used but may be considered detrimental if they lead to recombination process of the photogenerated charge carriers. Herein, we design a kind of efficient atomic substitution strategy to create shallow donor for highly efficient hydrogen evolution reaction. The photocatalytic hydrogen evolution reaction rate reaches 3766.9 μmol h−1 g−1, which is about 2.98 times higher of pure CdS. The injected foreign atoms (Zr) not only reduce bandgap to extend light absorption but also generate shallow trap level to reduce recombination of photogenerated carriers. Moreover, the introduced atoms could downshift Fermi level to supply more carriers and act the role as active center to reduce Gibbs free energy, leading to the enhanced hydrogen generation rate and superior stability. This report offers new enlightenment into designing noble-metal free photocatalysts with extraordinary catalytic performance and excellent stability.

Boosted photocatalytic hydrogen evolution of S-scheme N-doped CeO2-δ@ZnIn2S4 heterostructure photocatalyst

The advancement of highly effective heterojunction photocatalysts with improved charge separation and transfer has become a crucial scientific perspective for utilizing solar energy. In this study, we developed the S-scheme heterostructure by depositing N-doped CeO2-δ (NC) nanoparticles onto two-dimensional ZnIn2S4 (ZIS) nanosheets via hydrolysis strategy for significantly enhanced photocatalytic hydrogen evolution reaction. The optimal H2 generation rate of ∼ 798 μmol g–1 h–1 was achieved for NC-3@ZIS under solar light irradiation, which is about 18 and 2 times higher than those of pristine CeO2 (∼44 μmol g–1 h–1) and ZIS (∼358 μmol g–1 h–1), respectively. The photogenerated electrons from NC interact with the photogenerated holes of ZIS driven by an internal electric field, confirmed by In-situ KPFM, DFT calculation, and XPS results. According to EPR and photoelectrochemical measurements, NC-3@ZIS composite shows dramatically high separation efficiency of photogenerated charge carriers. This study provides a new approach for developing non-noble metal S-scheme heterojunctions with enhanced photocatalytic hydrogen evolution.

Theory-Guided Experimental Design of Covalent Triazine Frameworks for Efficient Photocatalytic Hydrogen Production.

The high crystalline covalent triazine framework-1 (CTF-1), composed of alternating triazine and phenylene, has emerged as an efficient photocatalyst for solar-driven hydrogen evolution reaction (HER). However, it is of great challenge to further improve photocatalytic HER performance via increasing crystallinity due to its near-perfect crystallization. Herein, an alternative strategy of scaffold functionalization is employed to optimize the energy band structure of crystalline CTF-1 for boosting hydrogen-evolving activity. Guided by the computational predictions, versatile CTF-based polymer photocatalysts are prepared with different functional groups (OH, NH2, COOH) using binary polymerization for practical hydrogen production. Experiment evidence verifies that the introduction of a limited number of electron-donating groups is sufficient to maintain high crystallinity in CTF, modulate the band structure, broaden visible light absorption, and consequently enhance its photophysical properties. Notably, the functionalization with OH exhibits the most positive effect on CTF-1, delivering a photocatalytic activity with a hydrogen-producing rate exceeding 100µmol h-1.

Research progress of dual-atom site catalysts for photocatalysis.

Dual-atom site catalysts (DASCs) have sparked considerable interest in heterogeneous photocatalysis as they possess the advantages of excellent photoelectronic activity, photostability, and high carrier separation efficiency and mobility. The DASCs involved in these important photocatalytic processes, especially in the photocatalytic hydrogen evolution reaction (HER), CO2 reduction reaction (CO2RR), N2/nitrate reduction, etc., have been extensively investigated in the past few years. In this review, we highlight the recent progress in DASCs that provides fundamental insights into the photocatalytic conversion of small molecules. The controllable preparation and characterization methods of various DASCs are discussed. Subsequently, the reaction mechanisms of the formation of several important molecules (hydrogen, hydrocarbons and ammonia) on DASCs are introduced in detail, in order to probe the relationship between DASCs's structure and photocatalytic activity. Finally, some challenges and outlooks of DASCs in the photocatalytic conversion of small molecules are summarized and prospected. We hope that this review can provide guidance for in-depth understanding and aid in the design of efficient DASCs for photocatalysis.

Effect of nitro-substituted ending group on the photovoltaic and photocatalytic performance of non-fullerene acceptors

The Y-series non-fullerene acceptors (NFAs) significantly enhance organic photovoltaic device efficiency, approaching 20%. Recent studies demonstrate their commendable photocatalytic performance in bulk heterojunction photocatalysis. Chemical modification of end groups emerges as a pivotal way to modulate molecular electrical and optical characteristics, thereby improving the organic solar cells (OSCs) performance. Among Y-series NFAs, 2-(2,3-dihydro-3-oxo-1H-inden-1-ylidene)propanedinitrile (INCN) and its derivatives stand out as the most successful end groups. However, a restricted range of modifying groups, such as the fluorine atom (–F) and the hydroxyl group (–OH), are currently employed to explore both the photovoltaic and photocatalytic properties of Y-series NFAs, research on other substituents for INCN remains largely unexplored to date. In this study, nitro-substituted end groups were incorporated into the Y6 skeleton, resulting in a new NFA, named Y6-NO. Simultaneously, INCN is incorporated into the Y6 skeleton to create Y6-IN as a reference molecule for simultaneously investigating the photovoltaic and photocatalytic properties of the two NFAs. In organic photovoltaics, Y6-NO, featuring nitro groups, exhibits a red-shifted absorption, lower molecular energy levels, and enhanced electron transport, leading to a superior power conversion efficiency (PCE) of 17.03 % for OSCs, as opposed to 10.45 % for Y6-IN. Conversely, in the photocatalytic hydrogen evolution reaction (HER) for water splitting, the nitro groups in Y6-NO lowers the energy level of the lowest unoccupied molecular orbital (LUMO), resulting in a reduced overpotential when combined with the co-catalyst Pt. Consequently, the HER rate of PM6:Y6-NO nanoparticles (72.2 mmol h−1 g−1) is lower than that of PM6:Y6-IN nanoparticles (108.5 mmol h−1 g−1). This study highlights that through judicious end-group chemical modification, the photovoltaic and photocatalytic properties of the acceptors can be effectively modulated.

Water-Stable High-Entropy Metal-Organic Framework Nanosheets for Photocatalytic Hydrogen Production.

Metal-organic frameworks (MOFs) have emerged as promising platforms for photocatalytic hydrogen evolution reaction (HER) due to their fascinating physiochemical properties. Rationally engineering the compositions and structures of MOFs can provide abundant opportunities for their optimization. In recent years, high-entropy materials (HEMs) have demonstrated great potential in the energy and environment fields. However, there is still no report on the development of high-entropy MOFs (HE-MOFs) for photocatalytic HER in aqueous solution. Herein, the authors report the synthesis of a novel p-type HE-MOFssingle crystal (HE-MOF-SC) and the corresponding HE-MOFsnanosheets (HE-MOF-NS) capable of realizing visible-light-driven photocatalytic HER. Both HE-MOF-SC and HE-MOF-NS exhibit higher photocatalytic HER activity than all the single-metal MOFs, which are supposed to be ascribed to the interplay between the different metal nodes in the HE-MOFsthat enables more efficient charge transfer. Moreover, impressively, the HE-MOF-NS demonstrates much higher photocatalytic activity than the HE-MOF-SC due to its thin thickness and enhanced surface area. At optimum conditions, the rate of H2 evolution on the HE-MOF-NS is ≈13.24 mmol h-1 g-1, which is among the highest values reported for water-stable MOF photocatalysts. This work highlights the importance of developing advanced high-entropy materials toward enhanced photocatalysis.

Metal‐Organic Framework‐Based Hetero‐Phase Nanostructure via a Secondary Building Unit (SBU) Regulating Strategy for Efficient Photocatalysis

As an effective method to modulate the physicochemical properties of materials, crystal phase engineering, especially hetero‐phase, plays an important role in developing high‐performance photocatalysts. However, it is still a huge challenge but significant to construct porous hetero‐phase nanostructures with adjustable band structures. As a kind of unique porous crystalline materials, metal‐organic frameworks (MOFs) might be the appropriate candidate, but the MOF‐based hetero‐phase is rarely reported. Herein, we developed a secondary building unit (SBU) regulating strategy to prepare two crystal phases of Ti‐MOFs constructed by titanium and 1,4‐dicarboxybenzene, i.e., COK and MIL‐125. Besides, COK/MIL‐125 hetero‐phase was further constructed. In the photocatalytic hydrogen evolution reaction, COK/MIL‐125 possessed the highest H2 yield compared to COK and MIL‐125, ascribing to the Z‐scheme homojunction at hetero‐phase interface. Furthermore, by decorating with amino groups (i.e., NH2‐COK/NH2‐MIL‐125), the light absorbing capacity was broadened to visible‐light region, and the visible‐light‐driven H2 yield was greatly improved. Briefly, the MOF‐based hetero‐phase possesses periodic channel structures and molecularly adjustable band structures, which is scarce in traditional organic or inorganic materials. As a proof of concept, our work not only highlights the development of MOF‐based hetero‐phase nanostructures, but also paves a novel avenue for designing high‐performance photocatalysts.

Metal-Organic Framework-Based Hetero-Phase Nanostructure Photocatalysts with Molecular-Scale Tunable Energy Levels.

As an effective method to modulate the physicochemical properties of materials, crystal phase engineering, especially hetero-phase, plays an important role in developing high-performance photocatalysts. However, it is still a huge challenge but significant to construct porous hetero-phase nanostructures with adjustable band structures. As a kind of unique porous crystalline materials, metal-organic frameworks (MOFs) might be the appropriate candidate, but the MOF-based hetero-phase is rarely reported. Herein, we developed a secondary building unit (SBU) regulating strategy to prepare two crystal phases of Ti-MOFs constructed by titanium and 1,4-dicarboxybenzene, i.e., COK and MIL-125. Besides, COK/MIL-125 hetero-phase was further constructed. In the photocatalytic hydrogen evolution reaction, COK/MIL-125 possessed the highest H2 yield compared to COK and MIL-125, ascribing to the Z-Scheme homojunction at hetero-phase interface. Furthermore, by decorating with amino groups (i.e., NH2-COK/NH2-MIL-125), the light absorbing capacity was broadened to visible-light region, and the visible-light-driven H2 yield was greatly improved. Briefly, the MOF-based hetero-phase possesses periodic channel structures and molecularly adjustable band structures, which is scarce in traditional organic or inorganic materials. As a proof of concept, our work not only highlights the development of MOF-based hetero-phase nanostructures, but also paves a novel avenue for designing high-performance photocatalysts.

Solar‐Driven Hydrogen Evolution with Superior Efficiency by a Low‐Cost, Large‐Scale Synergetic Hybrid of 1D‐Si Nanowires/0D‐Au Nanoparticles/2D‐MoS2 Nanofilms

The technology of semiconductor photocatalystshas become an important research area. 2D molybdenum disulfide (MoS2) is recognized as a promising catalyst for photoelectrocatalytic and photocatalytic (PC) hydrogen evolution reaction (HER). However, owing to its 2D nature of low optical cross‐section, the effective light absorption needs to be further boosted. Herein, we dramatically amplify the light‐matter interaction by hybridizing these photocatalysts with plasmonic materials that present strong electromagnetic field confinement and with nanowires that offer efficient light management. Such a system is designed in the heterostructure of silicon nanowires (SiNW)/ gold nanoparticles (AuNP)/ MoS2 nanofilms (SiNW/AuNP/MoS2), which demonstrates excellent PC HER. The absorption frequency of 2D‐MoS2, the resonance frequency of the 0D‐AuNP, and the antireflection frequency of 1D‐SiNW match with the visible range, enabling this heterostructure to effectively utilize solar energy. Additionally, an optimal MoS2 nanofilm that is a mixture of 1 T and 2 H phases was prepared with high reproducibility using facile pyrolysis. Moreover, the SiNW substrate validates high antireflection properties, achieving 95% visible light absorption. In addition, SiNW forms a p–n junction with the MoS2 to facilitate charge separation. The synergetic hybrid of 1D‐SiNW/0D‐AuNP/2D‐MoS2 nanofilms exhibits the highest hydrogen generation rate of 246 mmol g−1 h−1.

Coupling amorphous WO3 with WP as a cocatalyst for efficient dye-sensitizated photocatalytic hydrogen evolution

Tungsten phosphide (WP) as an excellent hydrogen evolution reactions (HER) catalyst has attracted widespread attention, but its HER activity is low in alkaline media due to high water dissociation barrier. Herein, noble-metal-free cocatalyst WP/WO3 composite was synthesized by adjusting the P/W molar ratio in the raw material using a simple solid phosphidation reaction. The structure, morphology, composition, and optoelectronic properties of the as-synthesized samples were characterized by XRD, SEM, TEM, XPS, UV–vis DRS, PL techniques, and electrochemical methods. Under visible light irradiation (λ ≥ 420 nm), the photocatalytic HER activities of the as-prepared samples using Eosin-Y (EY) dye as a sensitizer and trimethylamine (TMA) as an electron donor were investigated. The result shows that WP/WO3 composite as a cocatalyst exhibits excellent photocatalytic HER activity and good stability. The highest apparent quantum yield (AQY) reaches 32.8 %. The presence of amorphous WO3 in crystalline WP can improve the separation efficiency of photogenerated electrons and holes, reduce HER overpotential, and promote the dissociation of H2O in alkaline media. Therefore, the photocatalytic HER activity of WP/WO3 composite is higher than that of single crystalline WP.

Metal-organic framework-templated ZnIn2S4 nanomaterials for high-performance photocatalytic H2‐evolution

ZIF-8-templated ZnIn2S4 (ZIS) crystals with different morphologies have been synthesized solvothermally by varying the organic solvents, while thioacetamide (TAA) and L-cysteine (L‐cyst) were used as sulfur precursors. It is found that solvothermal properties, including ions coordination, dielectric constant, and atomic chain length, influence the nucleation and growth of ZIS composites. The differences in morphology and composition of the prepared ZIS crystals strongly affect their photophysical properties and photocatalytic hydrogen evolution reactions (PHER). The hydrogen evolution rates for ZIS composites decrease in the following order: Leaf‐like (EG, TAA) > nanorods (EtOH, TAA) > nanoflowers (EG, L‐cyst) > nanosheets (Gly, TAA) > irregular particles (EDA, TAA) > plate‐like (DETA, TAA). The leaf‐like ZIS‐EG composite prepared using TAA as a sulfur precursor and ethylene glycol (EG) as a solvent shows an excellent PHER performance of 5208 μmol g−1 h−1 (44.91 μmol) with an apparent quantum yield (AQY) of 4.80% at 420 nm. The ZIS‐EG composites with different ZIF‐8 contents (50, 100, 150, and 200 mg) were also investigated for the PHER activity with mixed Na2S/Na2SO3 sacrificial agent at λ ≥ 420 nm. It shows that the nature of solvents and sulfur precursors had a significant influence on the morphology, photoabsorption, electrochemical properties, and PHER performance of ZIF‐8‐templated ZIS composites, which complements the knowledge of designing efficient and perspective photocatalysts with enhanced visible‐light‐driven PHER performance.

The Effect of Platinum Single Atoms in Titania for Photocatalytic Applications

The photocatalytic effect of titania has long been studied with respect to water oxidation and hydrogen evolution. At present, the modification of this semiconducting material by platinum single atoms (Pt-SAs) represents an interesting approach that has been developed in the past decade and has given good results in the photocatalytic hydrogen evolution reaction (HER). Experimental studies have shown that the deposition of Pt-SAs on the titania surface, in aqueous systems, is a spontaneous process and can also be promoted by different reducing processes. Theoretical studies suggest that this deposition is a site-specific reaction, which occurs in oxygen vacancies on the titania surface. Under such conditions, the Pt-SAs are not in a metallic state, due to the interaction with neighbouring atoms of the substrate. This complex system can be probed using different advanced characterisation techniques, which provide a deeper understanding about the modified surface and how this modification improves the photocatalytic performance of titania.

Surface-engineering of CaTiO3 for photocatalytic hydrogen evolution reaction through enhanced oxygen vacancy

Surface engineering has been an important strategy in attaining a higher catalytic activity in comparison with pristine samples. CaTiO3 is a well-known photoactive material but lacks photo-to-electron conversion efficiency. Herein, we demonstrate a simple path-way that could achieve a higher surface area, active site exposure, and oxygen vacancies. The experimental results using different concentrations of HNO3 illustrated the selective leaching of Ca(II) ions, which leads to the partial conversion of Ti4+ to Ti3+ and the formation of oxygen vacancy. This eventually resulted in an engineered electronic state that modifies the band alignment and improves the charge transfer and migration rate. The optimized photocatalyst (CTO-5) exhibits approximately six times enhanced hydrogen evolution rate of 58.1 μmol∙g−1 h−1 than the pristine CaTiO3 (8.7 μmol∙g−1 h−1). Our work offers new intuitions into the rational design of photocatalysts with surface-engineering methodology without using any noble metal.

Defective Cd0.3Zn0.7S / 1 T-2 H MoS2 Z-scheme heterojunctions: Rational design with efficient charge transfer for enhanced photocatalytic H2 generation

CdxZn1-xS photocatalysts have received increasing attention due to their better Photocatalytic hydrogen evolution. In this paper, Cd0.3Zn0.7S nanoparticles decorated by a small amount of 1 T-2 H mixed-phase MoS2 nanosheets ((X%) MoS2/Cd0.3Zn0.7S) were prepared by a secondary hydrothermal-hydrothermal precipitation method. The Z-scheme heterojunction between 2 H-MoS2 and Cd0.3Zn0.7S can effectively inhibit the recombination of photogenerated carriers in the photocatalysts, and 1 T-MoS2 with metallic properties in the mixed phase mainly acts as a bridge for the transfer of photoexcited electrons. Therefore, under UV–visible irradiation, when Na2S/Na2SO3 is used as the sacrificial agent, the photocatalytic hydrogen evolution reaction (HER) activity of 0.75% MoS2/Cd0.3Zn0.7S reaches 11172 umol.g−1.h−1, which is 1.8 fold higher than that of Cd0.3Zn0.7S. The apparent quantum yields of 0.75% MoS2/C3Z7S at 370 nm and 420 nm wavelength are 50.6% and 7.2%, respectively. There are no significant changes in the hydrogen production after three cycles, indicating that the 0.75% MoS2/C3Z7S sample has excellent stability. This study provides a facile and low-cost strategy for constructing composite photocatalysts with highly efficient steady hydrogen production activity.

Photocatalytic Hydrogen Production with A Molecular Cobalt Complex in Alkaline Aqueous Solutions.

The thermodynamic favorability of an alkaline solution for the oxidation of water suggests the need for developing hydrogen evolution reaction (HER) catalysts that can function in basic aqueous solutions so that both of the half reactions in overall water splitting can occur in mutually compatible solutions. Although photocatalytic HERs have been reported mostly in acidic solutions and a few at basic pHs in mixed organic aqueous solutions, visible-light driven HER catalyzed by molecular metal complexes in purely alkaline aqueous solutions remains largely unexplored. Here, we report a new cobalt complex with a tetrapyridylamine ligand that catalyzes photolytic HER with turnover number up to 218 000 in purely aqueous solutions at pH 9.0. Density functional theory (DFT) calculations suggested a modified electron transfer (E)-proton transfer (C)-electron transfer (E)-proton transfer (C) (mod-ECEC) pathway for hydrogen production from the protonation of CoII-H species. The remarkable catalytic activity resulting from subtle structural changes of the ligand scaffold highlights the importance of studying structure-function relationships in molecular catalyst design. Our present work significantly advances the development of a molecular metal catalyst for visible-light driven HER in more challenging alkaline aqueous solutions that holds substantial promise in solar-driven water-splitting systems.