Photocatalytic Hydrogen Evolution Reaction Research Articles

Synergistic vacancy defects and the surface hydrophobic-to-superhydrophilic wetting engineering in W/S co-doped BiOI for enhanced photocatalytic hydrogen evolution

Bismuth oxyhalide (BiOI) has been used for photoelectrochemical catalysis in the field of catalytic hydrogen evolution, but it in a single-phase form has hardly been reported for photocatalytic hydrogen evolution reaction (PHER). Herein, we designed a W/S co-doped BiOI-based superhydrophilic catalyst with oxygen vacancy-rich defects and heterovalent valence states for efficient PHER under visible light. The W/S doping in BiOI not only adjusts the energy band structure and expands the visible light response range, but also transforms its hydrophobicity into superhydrophilicity, with which the gas bubble amount can be reduced and PHER activity enhanced. The introduction of sulfur regulates the content of oxygen vacancies which enhance the active surface sites for capturing water molecules and activating the H-O-H bond. The added tungsten exists in different valence states of W6+ and W5+ which is beneficial for electron hopping and PHER activity. The W/S-BiOI-3 with the suitable W/S doping content exhibits the highest visible-light PHER rate of 9.46 mmol·g−1·h−1, with an apparent quantum efficiency (AQE) of 9.7 % at 420 nm. W/S-BiOI-3 shows excellent PHER activity, stability, and durability, which provides a feasible scheme for other bismuth-based halogen oxides to be used in PHER.

TiO2-based heterojunctions for photocatalytic hydrogen evolution reaction

Solar-driven photocatalysis hydrogen evolution is a promising method to generate hydrogen from water, a green and clean energy source, using solar and semiconductors. Up to now, TiO2 still represents the most inexpensive and widely studied metal oxide semiconductors for photocatalysis. TiO2 coupling with other semiconductors to form heterojunctions is considered an efficient way to improve photocatalytic performances. In this review, TiO2-based heterojunctions are classified into conventional, p-n type, Z-scheme, S-scheme, and other heterojunctions based on their band structures. The photocatalytic mechanisms of various types of heterojunctions are described in detail. In order to rationally design and better synthesize heterojunctions with excellent performance, the contribution of theoretical calculations to the field of TiO2-based heterojunction photocatalysts and the key role of theoretical prediction are also discussed. Finally, the opportunities and current challenges to promote photocatalytic performance are provided to assist the design of TiO2-based heterojunction photocatalysts with superior performance.

Effect of Escherichia coli on the photocatalytic behavior of TiO2 nanoparticles for H2 evolution from water

Various microorganisms are present in natural waters, and understanding their impact on the photocatalytic behavior of photocatalysts is crucial, especially in large-scale hydrogen production. In line with this, we conducted a systematic investigation into the influence of Escherichia coli on the photocatalytic performance of TiO2 nanoparticles for H2 evolution. The findings revealed a significant reduction in the photocatalytic activity of TiO2 nanoparticles in the presence of Escherichia coli. Specifically, the H2 evolution rate was observed to be 57% lower (8.3 mmol g−1 h−1) compared to when Escherichia coli was absent (19.1 mmol g−1 h−1). The primary reason for this phenomenon appears to be the rupture of Escherichia coli cells during the photocatalytic process. As a result, intracellular proteins are released and subsequently adsorbed onto the surface of TiO2 nanoparticles, impeding the photocatalytic hydrogen evolution reaction. These results provide valuable insights that can inform the design of future photocatalytic hydrogen production processes.

Construction of Covalent organic frameworks with bex topology for efficient photocatalytic hydrogen production

Covalent organic frameworks (COFs) have become effective platforms for solar energy conversion and utilization. The rational design of the COF topology provides an effective strategy to expand the π-conjugation system and improve the photocatalytic activity. Herein, we have prepared two sub-stoichiometric pyrene-based 2D-COFs with the bex topology, HITMS-COF-10 and HITMS-COF-11, with high crystallinity and specific surface area. The HITMS-COF-11 exhibits an outstanding photocatalytic hydrogen evolution reaction (HER) rate of 25000 μmol g−1 h−1 in water under visible illumination (λ > 420 nm), demonstrating that the bex topological COFs could be one of the state-of-the-art photocatalyst candidates for hydrogen evolution and the importance of tuning the topological diversity at molecular levels for solar energy conversion and utilization.

Construction of 2D/2D ZnIn2S4/Nb2CTx (MXene) hybrid with hole transport highway and active facet exposure boost photocatalytic hydrogen evolution

In this study, leveraging the tunable surface groups of MXene, the two-dimensional (2D) Nb2CTx with OH terminal (NC) was synthesized. 2D ZnIn2S4 (ZIS) nanosheets were prepared with the aid of sodium citrate, enhancing the exposure ratio of active (110) facet. On this basis, 2D/2D ZnIn2S4/Nb2CTx heterojunctions were fabricated to improve photocatalytic hydrogen evolution reaction (HER) performance. The optimized 6 wt%Nb2CTx/ZnIn2S4-450 (6NC/ZIS-450) photocatalyt exhibits a remarkable HER rate of 3603 μmol g−1h−1, which is 10 times superior to that of the original ZnIn2S4. Its apparent quantum efficiency (AQE) at 380 nm reaches 14.9 %. Meanwhile, even after 5 rounds of HER, the activity of 2D/2D ZnIn2S4/Nb2CTx heterojunction remained at 90 %, far superior to that of pure ZnIn2S4 (34 % and 31 %). Energy band structure analysis and density functional theory (DFT) calculation indicate that Nb2CTx adsorbed with OH exhibit a low work function. By serving as a hole cocatalyst, it effectively boosts the photocatalytic HER rate of ZnIn2S4/Nb2CTx heterojunction and inhibits the photocorrosion of ZnIn2S4. This unique insight, via hole transport highways and increased exposure of active facets, effectively enhances the activity and stability of sulfides photocatalysts.

Application of Quantum Dots for Photocatalytic Hydrogen Evolution Reaction

There is increased interest in the conversion of solar energy into green chemical energy because of the depletion of fossil fuels and their unpleasant environmental effect. Photocatalytic hydrogen generation from water involves the direct conversion of solar energy into H2 fuels, which exhibits significant advantages and immense promise. Nevertheless, photocatalytic efficiency is considerably lower than the standard range of industrial applications. Low light absorption efficiency, the rapid recombination of photogenerated electrons and holes, slow surface redox reaction kinetics and low photostability are well known to be key factors negatively affecting photocatalytic hydrogen production. Therefore, to construct highly efficient and stable photocatalysts is important and necessary for the development of photocatalytic hydrogen generation technology. In this review, quantum dots (QDs)-based photocatalysts have emerged with representative achievements. Due to their excellent light-harvesting ability, low recombination efficiency of photogenerated electrons and holes, and abundant surface active sites, QDs have attracted remarkable interest as photocatalysts and/or cocatalyst for developing highly efficient photocatalysts. In this review, the application of QDs for photocatalytic H2 production is emphatically introduced. First, the special photophysical properties of QDs are briefly described. Then, recent progress into the research on QDs in photocatalytic H2 production is introduced, in three types: semiconductor QDs (e.g., CdS, CdMnS, and InP QDs), metal QDs (e.g., Au, Pt and Ag QDs), and MXene QDs and carbon QDs (CDQs). Finally, the challenges and prospects of photocatalytic H2 evolution with QDs in the future are discussed.

1 T′/2 H MoS2 nanoflowers integrated with bismuth halide perovskite for improved photocatalytic hydrogen evolution

Lead-free perovskites have attracted considerable attention in photocatalytic hydrogen evolution due to their better moisture stability and lower toxicity than those of their lead-based analogues. However, their activity remains low and needs to be improved for practical applications. Properly engineered heterojunction photocatalysts can provide more active sites and stimulate efficient charge transfer. In this study, 1 T′/2 H−MoS2 nanoflowers were synthesized and coupled with tri(dimethylammonium) hexaiodobismuthate (DMA3BiI6) to form heterojunctions using a simple heating−cooling process. The synthesized 1 T′/2 H−MoS2/DMA3BiI6 composites exhibit excellent photocatalytic hydrogen evolution activity of hydroiodic acid splitting under visible-light irradiation with up to a rate of 241.5 µmol g⁻1 h⁻1 and apparent quantum efficiency of 11.2 % at 420 nm. Furthermore, a retained long-term performance stability after 3 days (12 cycles) of repeated hydrogen evolution reaction (HER) measurements was observed. Experimental and DFT studies indicate that the improved photocatalytic HER performance after the introduction of 1 T′/2 H−MoS2 on DMA3BiI6 is due to the efficient charge transfer and separation at the heterojunction interfaces in the composite. Accordingly, our work highlights a new potentially viable strategy to construct lead-free halide perovskite-based heterostructures for efficient photocatalytic HER.

Hydrogel composites based on chitosan and CuAuTiO2 photocatalysts for hydrogen production under simulated sunlight irradiation

This study explored the photocatalytic hydrogen evolution reaction (HER) using novel biohydrogel composites comprising chitosan, and a photocatalyst consisting in TiO2 P25 decorated with Au and/or Cu mono- and bimetallic nanoparticles (NPs) to boost its optical and catalytic properties. Low loads of Cu and Au (1 mol%) were incorporated onto TiO2 via a green photodeposition methodology. Characterization techniques confirmed the incorporation of decoration metals as well as improvements in the light absorption properties in the visible light interval (λ > 390 nm) and electron transfer capability of the semiconductors. Thereafter, Au and/or Cu NP-supported TiO2 were incorporated into chitosan-based physically crosslinked hydrogels revealing significant interactions between chitosan functional groups (hydroxyls, amines and amides) with the NPs to ensure its encapsulation. These materials were evaluated as photocatalysts for the HER using water and methanol mixtures under simulated sunlight and visible light irradiation. Sample CuAuTiO2/ChTPP exhibited a maximum hydrogen generation of 1790 μmol g−1 h−1 under simulated sunlight irradiation, almost 12-folds higher compared with TiO2/ChTPP. Also, the nanocomposites revealed a similar tendency under visible light with a maximum hydrogen production of 590 μmol g−1 h−1. These results agree with the efficiency of photoinduced charge separation revealed by transient photocurrent and EIS.

Manipulating the morphology and charge accumulation driven- Schottky functionalized type II-scheme heterojunction for photocatalytic hydrogen evolution and SERS detection

Inspired by energy conversion and sensing strategies, the construction of a type-II heterojunction proves advantageous in enhancing interfacial charge transfer, redox capabilities, and sensitive detection. Herein, we have developed as-prepared a hierarchical heteronanostructure composed of 2D ultrathin g-C3N4 (g-CN) nanosheets, 3D SrTiO3 (STO) nanocubes, and Ag plasmonic nanoparticles (NPs) with a well-controlled configuration and intimate contact for improved practical applications. This multifunctional heterojunction not only exhibits outstanding hydrogen evolution reaction (HER) performance but also shows excellent SERS detection. The creation of hybrid morphologies and type II schemes contributes to expanding visible light absorption and shortening the path of charge carrier transition. The ternary sample also exhibits an efficient photocatalytic HER rate of 9378 μmol g−1 h−1, which is 13.3 and 26.3 times higher than that of STO (703 μmol g−1 h−1) and g-CN (356 μmol g−1 h−1), respectively. Photoluminescence spectroscopy and linear sweep voltammetry (LSV) measurements suggest that the synergistic effect among g-CN nanosheets, STO nanocubes and Ag contributes to enhanced charge separation, as indicated by the applied potential of −0.9 V vs. saturated Ag/AgCl to obtain a photocurrent density of −15 mA cm−2 for the HER. The obtained STO/g-CN/Ag sample exhibits significant capability in enriching small molecules, facilitating the determination of organic pollutants even at ultralow concentrations. Additionally, it exhibits impressive SERS sensitivity and photocatalytic performance. Crystal Violet (CV) at low concentrations can be distinguished and undergoes almost complete degradation under visible-light illumination. The detection platform exhibits ultralow detection capability down to 10−10 M for CV. The outstanding SERS detection may be assigned to the combined enrichment abilities of g-CN, STO and the localized surface plasmon resonance (LSPR) of Ag NPs. Furthermore, the type-II heterojunction of the ternary photocatalyst and the mechanisms governing charge carrier flow and transfer on the conductive Ag co-catalyst were also investigated. This work provides novel insights and techniques for effectively engineering 3D STO-like semiconductors, facilitating both green energy production and the detection of trace molecules.

A new Ni-based cocatalyst nickel thiocarbonate enhancing graphitic carbon nitride photocatalytic hydrogen production by constructing a built-in electric field

Despite the excellent photocatalytic activity under visible light, graphitic carbon nitride (g-C3N4) exhibits a high overpotential for hydrogen evolution. To address this issue, cocatalysts have been utilized to modify g-C3N4. However, the use of high-performance cocatalysts typically involves noble metals such as platinum and palladium, which are cost-prohibitive for practical applications. Therefore, the development of efficient and cost-effective cocatalysts is crucial for advancing photocatalysis. In this study, we synthesized a new Ni-based cocatalyst, nickel thiocarbonate (NiCS3), to enhance the photocatalytic hydrogen evolution reaction (HER) on g-C3N4. The NiCS3/g-C3N4 composite demonstrated a significantly increased hydrogen evolution rate of 951 μmol·h−1·g−1 under visible light, representing more than a 105-fold improvement compared to pure g-C3N4. Theoretical calculations suggested that the enhanced performance in photocatalytic hydrogen production can be attributed to the generation of a built-in electric field within the composite, facilitating efficient charge carrier separation and migration. Additionally, the C site in NiCS3 provides a favorable Gibbs free energy of adsorbed H* (ΔGH∗). This work underscores the potential of NiCS3 as a viable alternative to precious metals in photocatalytic hydrogen production using g-C3N4.

Metal–Organic Framework‐Based Hetero‐Phase Nanostructure Photocatalysts with Molecular‐Scale Tunable Energy Levels

AbstractAs 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.

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.

Leveraging electron spin driven photocatalytic hydrogen evolution ability of BiVO4 via crystal facet engineering and iron ion infiltration strategies

An electron spin regulated hydrogen evolution reaction (HER) for photocatalyst is significant to understand the underlying photocatalytic mechanism. Here, the iron with gradient distribution in BiVO4 can successfully activate HER of Fe-BiVO4. Mechanical performance calculations indicate that doped Fe3+ replacing V site can form stable chemical structure for BiVO4. Theoretical calculations suggest that the photo-generated electrons migrate from bulk to defect sites in surface layers of Fe-BiVO4. The doped Fe ions effectively improves the carrier transport ability and significantly reduces the carrier recombination probability. Electron spin state change of the 1Fe-BiVO4 (Mag) enhances evidently the current density in photocatalysis, and increases markedly the HER performance compared with that of 1Fe-BiVO4. More importantly, the magnetization further prolongs carrier lifetime and optimizes rate determining step free energy of water dissociation for Fe-BiVO4. Our work opens a new way to understand the effect of magnetic field controlling spin states on photocatalytic HER.

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.