Efficient Photocatalytic Water Splitting Research Articles

Enhanced charge separation via ZnIn2S4@S-doped-C3N4 S-scheme heterojunction for efficient photocatalytic water splitting under visible light

Heterojunction photocatalysts possess high efficiency in photogenerated electron-hole separation, which give significant advantages in the field of solar hydrogen production. Herein, a novel ZnIn2S4@S doped g-C3N4 (ZIS@SCN) heterojunction with mesoporous structure was prepared for photocatalytic water splitting under visible light. Characterization showed that the element of S was successfully introduced into g-C3N4 (CN) by replacing N to form C–S–C bonds and significantly enhanced the visible light absorption ability. The constructed heterojunction exhibited excellent photocatalytic hydrogen evolution under visible light. The best performance belonged to the sample of ZIS@100SCN. The corresponding H2 production rate reached 9.3 mmol h−1 g−1, which was 1.87-fold higher than that of the undoped one. More importantly, the heterojunction realized overall water splitting of H2 and O2 evolution simultaneously with good stability. The mechanism analysis indicted that introducing the element of S could regulate the band structure of CN and induce the charge transfer switching of a ZnIn2S4@g-C3N4 (ZIS@CN) photocatalyst from Ⅰ-type to S-scheme, which promoted the efficient spatial charge separation and maintained the high redox ability of the ZIS and SCN. This work provides an insight in construction high performance S-scheme heterojunction for water splitting with a doping method.

Metal single atom-oxygen modification induced transformation of carbon nitride-based heterojunctions from type-II to S-scheme for efficient photocatalytic overall water splitting

Constructing semiconductor S-scheme hetero-(homo-)junctions (SSHs) is one of the most effective ways to enhance the photocatalytic overall water splitting (POWS) performance, but encumbered by deficiency of efficient water-oxidizing semiconductors. Herein, tungsten single atom-oxygen group (W-O) modified polymeric carbon nitride (WPCN, an example of metal single atom-oxygen group modified PCN) was used as a water-oxidizing semiconductor to construct a CdS/WPCN SSH, for which the W-O modification plays a key role that causes transformation from a PCN/CdS type-II heterojunction to the CdS/WPCN SSH which exhibits remarkably enhanced photoexcited charge separation than single CdS and WPCN. Pt-CdS/WPCN exhibits 2.6 and 7.2 times higher POWS activity than Pt-WPCN and Pt-CdS, respectively, further demonstrating the key role of the SSH, and lower activity than Pt@Cr2O3-CdS/WPCN that exhibits 5.4-fold higher activity than Pt@Cr2O3-PCN/CdS, and especially, higher photochemical stability by suppressing rapid photocorrosion of CdS. The solar-to-hydrogen conversion efficiency of Pt@Cr2O3-CdS/ WPCN reaches 0.014 %, with an external quantum yield of 0.093 % at 420 nm. This work reveals the role of metal single atom-oxygen modification of PCN in SSHs and provides a way to suppress rapid photocorrosion of CdS.

Efficient photocatalytic overall water splitting for hydrogen evolution and CO2 reduction with SiCP4 allotrope monolayers

Two-dimensional metal-free photocatalysts are catching the attention of researchers. Here, we present several allotrope SiCP4 monolayers with high stability, high carrier mobility, and excellent photocatalytic performance. Using a searching method based on the universal structure predictor evolutionary xtallography, together with assessing the energy and thermodynamic stabilities, and matching the potentials of band edges with the photocatalytic conditions for achieving overall water splitting, we successfully identify 5 highly favorable configurations (including the previously reported one) from a pool of 1056 allotrope SiCP4 monolayers. The results show that the largest solar-to-hydrogen efficiency of the considered monolayers can reach 21.89 %, while a high mobility of 2.7677 × 105 cm2 V−1 s−1 is observed, both are superior to those of the previously reported one. The Gibbs free energies for hydrogen or oxygen evolutions, and CO2 reduction reactions indicate they are thermodynamically feasible. Moreover, the hydrogen evolution reaction can proceed spontaneously with two allotrope SiCP4 monolayers. Therefore, the newfound allotrope SiCP4 monolayers are expected to have potential applications in the field of photocatalytic water splitting for hydrogen generation and carbon dioxide reduction.

Construction of NiS/MnCdS S-scheme heterojunction for efficient photocatalytic overall water splitting: Regulation of surface sulfur vacancy and energy band structure

The overall water splitting based on specific photocatalysts is one of the ultimate ways to solve the energy and environmental crisis facing humanity. Sulfide photocatalysts have greater potential in photocatalytic production of solar fuel. However, due to its easy photocorrosion phenomenon, it not effectively driving the water oxidation semi-reaction to produce oxygen, so how to use sulfide photocatalyst to decompose pure water to achieve stoichiometric reaction of H2/O2 production remains a quite challenging task. Herein, sulfur vacancies-rich MnCdS nanoparticles were modified with NiS nanosheets through the hydrothermal derivation method. Different concentration gradients of sulfur-vacancy in MnCdS nanoparticles (MnCdS-Vs-X) with tunable band structures were successful prepared by regulating the concentration of hydrazine hydrate, thus improves the efficiency of light energy utilization and charge separation and the existence of S defects was verified by transmission electron microscopy (TEM) and electron paramagnetic resonance (EPR). The density function theory (DFT) calculation bears out that the draw into of S vacancy adjusted the band structure of MnCdS. Moreover, the successful construction of an S-scheme heterojunction between NiS and MnCdS-Vs-3 has been strongly demonstrated by in-situ XPS and UPS, which promoted interfacial charge separation and further improved the photocatalytic hydrogen evolution efficiency. The as-obtained S-scheme 20 %NiS/MnCdS-Vs-3 heterojunction exhibit excellent visible-light H2 production activity of 4099.55 μmol g−1h−1, 6.75 times higher than pure MnCdS. Most importantly, the excellent and stable photocatalytic overall water splitting activity of H2-509.70 μmol g-1h−1/O2-254.90 μmol g-1h−1 were obtained over 20 % NiS/MnCdS-Vs-3, which further demonstrates the application value of NiS/MnCdS-Vs-3 photocatalysts. This work proposes new ideas for the application of S-vacancies and S-scheme heterojunction in addressing the stability issues associated with sulfide-based photocatalysts in photocatalytic water splitting.

Cu doping enhanced ZnIn2S4/TiO2(VO) Z-scheme heterojunction for efficient photocatalytic overall water splitting

The design and synthesis of efficient photocatalysts for overall water splitting is a promising research topic. By reasonable modification, the hydrogen evolution photocatalyst can have the ability for overall water splitting. Both ZnIn2S4 and TiO2 have shown great potential in the field of photocatalytic hydrogen evolution, but their use for efficient overall water splitting is challenging. In this work, a Z-scheme heterojunction material of Cu-doped ZnIn2S4 composite TiO2 with rich oxygen vacancies was synthesized. Cu doping enhanced the light absorption, reduced the bandgap, and improved photocatalytic activity. In addition, the oxygen vacancies in TiO2 were conducive to the separation and migration of electron-hole pairs, and the construction of a Z-scheme heterojunction between ZnIn2S4 and TiO2 can also effectively promote the separation and migration of carriers. Therefore, the photocatalytic activity of this material was significantly improved and exhibited excellent overall water splitting activity without any sacrificial agents and co-catalysts. The optimized hydrogen and oxygen evolution rates were 589.64 μmol/g/h and 292.75 μmol/g/h, respectively. This work provided favorable evidence for metal element doping to promote the photocatalytic activity of composite heterojunction materials and provided a new strategy for the development of heterojunction photocatalysts for overall water splitting.

Large electronegativity differences between adjacent atomic sites activate and stabilize ZnIn2S4 for efficient photocatalytic overall water splitting

Photocatalytic overall water splitting into hydrogen and oxygen is desirable for long-term renewable, sustainable and clean fuel production on earth. Metal sulfides are considered as ideal hydrogen-evolved photocatalysts, but their component homogeneity and typical sulfur instability cause an inert oxygen production, which remains a huge obstacle to overall water-splitting. Here, a distortion-evoked cation-site oxygen doping of ZnIn2S4 (D-O-ZIS) creates significant electronegativity differences between adjacent atomic sites, with S1 sites being electron-rich and S2 sites being electron-deficient in the local structure of S1–S2–O sites. The strong charge redistribution character activates stable oxygen reactions at S2 sites and avoids the common issue of sulfur instability in metal sulfide photocatalysis, while S1 sites favor the adsorption/desorption of hydrogen. Consequently, an overall water-splitting reaction has been realized in D-O-ZIS with a remarkable solar-to-hydrogen conversion efficiency of 0.57%, accompanying a ~ 91% retention rate after 120 h photocatalytic test. In this work, we inspire an universal design from electronegativity differences perspective to activate and stabilize metal sulfide photocatalysts for efficient overall water-splitting.

Amorphous W‐S‐P Modified ZnxCd1−xS with Tunable Band Structure for Efficient Photocatalytic Overall Water Splitting

The photocatalytic overall water splitting performance of the bandgap controllable ZnxCd1−xS solid solution is still restricted by its photo‐corrosion. In this study, amorphous tungsten phosphosulphide (W‐S‐P) modified ZnxCd1−xS solid solution is successfully prepared as a visible‐light‐driven photocatalyst and an efficient and stable ZnxCd1−xS/W‐S‐P heterojunction is constructed through intimate W‐S covalent bonds for efficient photocatalytic overall water splitting. The hydrogen evolution rate of the composite catalyst reached 18899.6 μmol g−1 h−1, which is 86 times and 5 times higher than that of W‐S‐P and Zn0.5Cd0.5S, respectively. At this time, the precipitation rates of H2 and O2 were 157.07 μmol g−1 h−1 and 78.05 μmol g−1 h−1 without any noble metal catalyst. In this work, the overall water splitting efficiency of the catalyst is greatly improved by constructing a ZnxCd1−xS/W‐S‐P Schottky heterojunction, which further inhibits the photo‐corrosion of the ZnxCd1−xS catalyst. At the same time, the strong internal electric field greatly improves the charge transfer efficiency. It provides a new idea for an in‐depth understanding of the chemical changes of elemental binding energy in ZnxCd1−xS solid solution and the design of new binary photocatalytic materials.

Full-Spectrum Responsive Naphthalimide/Perylene Diimide with a Giant Internal Electric Field for Photocatalytic Overall Water Splitting.

The co-assembly naphthalimide/perylene diimide (NDINH/PDINH) supramolecular photocatalysts were successfully synthesized via a rapid solution dispersion method. A giant internal electric field (IEF) in co-assembly structure was built by the larger local dipole. NDINH coated on PDINH could reduce the reflected electric field over PDINH to improve its responsive activity to ultraviolet light. Resultantly, an efficient full-spectrum photocatalytic overall water splitting activity with H2 and O2 evolution rate of 317.2 and 154.8 μmol g-1 h-1 for NDINH/PDINH together with optimized O2 evolution rate with 2.61 mmol g-1 h-1 using AgNO3 as a sacrificial reagent were achieved. Meanwhile, its solar-to-hydrogen efficiency was enhanced to 0.13 %. The enhanced photocatalytic activity was primarily attributed to the IEF between NDINH and PDINH, significantly accelerating transfer and separation of photogenerated carriers. Additionally, a direct Z-Scheme pathway of carriers contributed to a high redox potential. The strategy provided a new perspective for the design of supramolecular photocatalysts.

Revealing the Untapped Potential of Photocatalytic Overall Water Splitting in Metal Organic Frameworks

AbstractThe past decade witnessed substantial attention toward metal‐organic frameworks (MOFs) for photocatalytic water splitting owing to their versatile structural and optoelectronic characteristics. However, MOFs capable of efficient photocatalytic overall water splitting (OWS) remain notably scarce. Although MOF‐based photocatalysts with OWS potential are highly promising due to their diverse building blocks and topological configurations, the vast number of possible MOFs renders traditional trial‐and‐error materials discovery approaches impractical. Herein, a data‐driven methodology that integrates machine learning with high‐throughput first‐principles computations to identify MOFs with OWS capability is presented. By systematically assessing factors including water stability, band gap, band positions, charge carrier transport, and optical absorption properties, 14 MOFs from the Quantum‐MOF (QMOF) database containing over 20,000 MOFs as promising candidates for visible‐light‐driven OWS are identified. Notably, five of them exhibit exceptional electronic and optical properties, outperforming previously reported MOF OWS photocatalysts, such as UIO66(Zr)‐NH2, MIL125(Ti)‐NH2, and MIL53(Al)‐NH2 is established. This work represents a large‐scale, data‐driven exploration of MOF‐based photocatalysts for water splitting, shedding light on the untapped potential of photocatalysis in MOFs.

Synergistic Enhancement of Photocatalytic H2 Evolution over NH2-MIL-125 Modified with Dual Cocatalyst.

The construction of efficient photocatalysts for water splitting to enable H2 evolution is pivotal to alleviate energy issues and environmental concerns. In this work, carbon dots (CDs) were prepared by employing "green solvent" ionic liquids as carbon sources and then combined with Pt/NH2-MIL-125, resulting in the emergence of a high-efficiency photocatalyst termed CDs-Pt/NH2-MIL-125 for the first time. This composite photocatalyst exhibited outstanding photocatalytic activity in H2 production under visible light irradiation. Notably, the H2 production rate of CDs100-Pt/NH2-MIL-125 reaches up to 951.4 μmol/g/h, which was 3.1 times that of Pt/NH2-MIL-125. The characterization results indicate that CDs and Pt uniformly dispersed on the surface of NH2-MIL-125 and fabricated a synergistic compact structure, providing a high BET surface area (985 m2 g-1) and a suitable band gap. Furthermore, the distinctive embeddable-dispersed CDs and Pt, as dual cocatalyst, can harvest light and facilitate the transfer of photogenerated electrons, thereby significantly augmenting the exploitation of visible light. The plausible mechanism of photocatalytic H2 evolution over the CDs-Pt/NH2-MIL-125 catalyst was also discussed. This work introduces a promising strategy for designing high-performance CDs-MOFs-based photocatalysts, an innovative step toward achieving efficient photocatalytic water splitting for H2 production.

Hexagonal Janus Zn2XY (X=S, Se; Y[dbnd]Se, Te; X≠Y) monolayers: A high-performance photocatalyst for water splitting

Efficient photocatalytic water splitting is of holds paramount importance in addressing contemporary energy and environmental challenges. The emergence of symmetry-deficient Janus two-dimensional materials has opened new avenues for advancing the field of photocatalytic hydrogen production. Using first-principles calculations, we investigated a novel Janus Zn2XY (X = S, Se; YSe, Te; X≠Y) monolayer. The results demonstrate exceptional structural stability and favorable characteristics for water splitting, including direct band gaps and optimal band edge alignment. Spatially separating band edge states and the intrinsic vertical electric field effectively suppress the recombination rate of photogenerated electron-hole pairs. Strain engineering enhances the monolayer's capacity for visible light absorption. Furthermore, All Janus monolayers exhibit an impressive electron mobility of 103 cm2/V/s, with Janus Zn2STe and Zn2SeTe monolayers reaching 16.28% and 16.34% Solar-to-hydrogen (STH) efficiencies, respectively. These findings showcase the superior performance of Janus Zn2XY in water splitting and guide future experimental endeavors.

Criteria for Efficient Photocatalytic Water Splitting Revealed by Studying Carrier Dynamics in a Model Al‐doped SrTiO3 Photocatalyst

AbstractOverall water splitting (OWS) using semiconductor photocatalysts is a promising method for solar fuel production. Achieving a high quantum efficiency is one of the most important prerequisites for photocatalysts to realize high solar‐to‐fuel efficiency. In a recent study (Nature 2020, 58, 411–414), a quantum efficiency of almost 100 % has been achieved in an aluminum‐doped strontium titanate (SrTiO3 : Al) photocatalyst. Herein, using the SrTiO3 : Al as a model photocatalyst, we reveal the criteria for efficient photocatalytic water splitting by investigating the carrier dynamics through a comprehensive photoluminescence study. It is found that the Al doping suppresses the generation of Ti3+ recombination centers in SrTiO3, the surface band bending facilitates charge separation, and the in situ photo‐deposited Rh/Cr2O3 and CoOOH co‐catalysts render efficient charge extraction. By suppressing photocarrier recombination and establishing a facile charge separation and extraction mechanism, high quantum efficiency can be achieved even on photocatalysts with a very short (sub‐ns) intrinsic photocarrier lifetime, challenging the belief that a long carrier lifetime is a fundamental requirement. Our findings could provide guidance on the design of OWS photocatalysts toward more efficient solar‐to‐fuel conversion.

Criteria for Efficient Photocatalytic Water Splitting Revealed by Studying Carrier Dynamics in a Model Al-doped SrTiO3 Photocatalyst.

Overall water splitting (OWS) using semiconductor photocatalysts is a promising method for solar fuel production. Achieving a high quantum efficiency is one of the most important prerequisites for photocatalysts to realize high solar-to-fuel efficiency. In a recent study (Nature 2020, 58, 411-414), a quantum efficiency of almost 100 % has been achieved in an aluminum-doped strontium titanate (SrTiO3 : Al) photocatalyst. Herein, using the SrTiO3 : Al as a model photocatalyst, we reveal the criteria for efficient photocatalytic water splitting by investigating the carrier dynamics through a comprehensive photoluminescence study. It is found that the Al doping suppresses the generation of Ti3+ recombination centers in SrTiO3 , the surface band bending facilitates charge separation, and the in situ photo-deposited Rh/Cr2 O3 and CoOOH co-catalysts render efficient charge extraction. By suppressing photocarrier recombination and establishing a facile charge separation and extraction mechanism, high quantum efficiency can be achieved even on photocatalysts with a very short (sub-ns) intrinsic photocarrier lifetime, challenging the belief that a long carrier lifetime is a fundamental requirement. Our findings could provide guidance on the design of OWS photocatalysts toward more efficient solar-to-fuel conversion.

Surface-Degenerate Semiconductor Photocatalysis for Efficient Water Splitting without Sacrificial Agents via a Reticular Chemistry Approach.

The production of green hydrogen through photocatalytic water splitting is crucial for a sustainable hydrogen economy and chemical manufacturing. However, current approaches suffer from slow hydrogen production (<70 µmol·gcat-1·h-1) due to the sluggish four-electrons oxygen evolution reaction (OER) and limited catalyst activity. Herein, we achieve efficient photocatalytic water splitting by exploiting a multifunctional interface between a nano-photocatalyst and metal-organic framework (MOF) layer. The functional interface plays two critical roles: (1) enriching electron density directly on photocatalyst surface to promote catalytic activity, and (2) delocalizing photogenerated holes into MOF to enhance OER. Our photocatalytic ensemble boosts hydrogen evolution by ~100-fold over pristine photocatalyst and concurrently produces oxygen at ideal stoichiometric ratio, even without using sacrificial agents. Notably, this unique design attains superior hydrogen production (519 µmol·gcat-1·h-1) and apparent quantum efficiency up to 13-fold and 8-fold better than emerging photocatalytic designs utilizing hole scavengers. Comprehensive investigations underscore the vital role of the interfacial design in generating high-energy photoelectrons on surface-degenerate photocatalyst to thermodynamically drive hydrogen evolution, while leveraging the nanoporous MOF scaffold as an effective photohole sink to enhance OER. Our interfacial approach creates vast opportunities for designing next-generation, multifunctional photocatalytic ensembles using reticular chemistry with diverse energy and environmental applications.

Surface‐Degenerate Semiconductor Photocatalysis for Efficient Water Splitting without Sacrificial Agents via a Reticular Chemistry Approach

AbstractThe production of green hydrogen through photocatalytic water splitting is crucial for a sustainable hydrogen economy and chemical manufacturing. However, current approaches suffer from slow hydrogen production (&lt;70 μmol ⋅ gcat−1 ⋅ h−1) due to the sluggish four‐electrons oxygen evolution reaction (OER) and limited catalyst activity. Herein, we achieve efficient photocatalytic water splitting by exploiting a multifunctional interface between a nano‐photocatalyst and metal–organic framework (MOF) layer. The functional interface plays two critical roles: (1) enriching electron density directly on photocatalyst surface to promote catalytic activity, and (2) delocalizing photogenerated holes into MOF to enhance OER. Our photocatalytic ensemble boosts hydrogen evolution by ≈100‐fold over pristine photocatalyst and concurrently produces oxygen at ideal stoichiometric ratio, even without using sacrificial agents. Notably, this unique design attains superior hydrogen production (519 μmol ⋅ gcat−1 ⋅ h−1) and apparent quantum efficiency up to 13‐fold and 8‐fold better than emerging photocatalytic designs utilizing hole scavengers. Comprehensive investigations underscore the vital role of the interfacial design in generating high‐energy photoelectrons on surface‐degenerate photocatalyst to thermodynamically drive hydrogen evolution, while leveraging the nanoporous MOF scaffold as an effective photohole sink to enhance OER. Our interfacial approach creates vast opportunities for designing next‐generation, multifunctional photocatalytic ensembles using reticular chemistry with diverse energy and environmental applications.

Modulating impurity levels in two-dimensional polar materials for photocatalytic overall water splitting

Doping to induce suitable impurity levels is an effective strategy to achieve highly efficient photocatalytic overall water splitting (POWS). However, to predict the position of impurity levels, it is not enough to only depend on the projected density of states of the substituted atom in the traditional method. Herein, taking in phosphorus-doped g-C3N5 as a sample, we find that the impurity atom can change electrostatic potential gradient and polarity and then significantly affect the spatial electron density around the substituted atom, which further adjusts the impurity level position. Based on the redox potential requirement of POWS, we not only obtain suitable impurity levels but also expand the visible light absorption range. Simultaneously, the strengthened polarity induced by doping further improves the redox ability of photogenerated carriers. Moreover, the enhanced surface dipoles obviously promote the adsorption and subsequent splitting of water molecules. Our study provides a more comprehensive view to realize accurate regulation of impurity levels in doping engineering and gives reasonable strategies for designing an excellent catalyst of POWS.

Precisely loading Pt on Tb4O7/CN heterojunction for efficient photocatalytic overall water splitting: Design and mechanism

Constructing heterojunction is an effective strategy for fighting electron-hole pairs recombination. Loading of hydrogen evolution reaction (HER) cocatalysts on a heterojunction is crucial for efficient photocatalytic overall water splitting (POWS). However, how to achieve a synergy between the heterojunction and HER cocatalyst remains a challenge. Herein, we propose a novel design strategy: selectively loading HER cocatalyst Pt on Tb4O7/CN. We found that engineering Pt on the Tb4O7 section of Tb4O7/CN can synergistically promote the photogenerated charge separation and thus enhances the POWS activity. The H2 production rate is about 2.8 times higher than that of Tb4O7/CN. In contrast, engineering Pt on the CN section leads to increasing photogenerated electron-hole recombination and deactivating the POWS activity, about 2.6 times as low as that of Tb4O7/CN. These findings highlight the significance of synergism of Pt loading sites with the charge separation of heterojunctions, providing insights on developing efficient photocatalysts for POWS.

Plasmonic coupling-boosted photothermal nanoreactor for efficient solar light-driven photocatalytic water splitting

Photothermal nanoreactor with rapid charge transfer and improved spectral utilization is a key point in photocatalysis research. Herein, silver sulfide quantum dots (Ag2S QDs) were coating on the surface of porous graphitic carbon nitride nano vesicles (PCNNVs) to form Ag2S/PCNNVs nanoreactors by a simple calcination method for obtaining efficient photothermal-assisted photocatalytic hydrogen (H2) evolution under simulated/real sunlight irradiation. In particularly, the as-prepared optimal 3% Ag2S/PCNNVs sample exhibited the H2 production rate of 34.8 mmol h−1 g−1, which was 3.5 times higher than that of bare PCNNVs. The enhancement of photothermal-assisted activity over the Ag2S/PCNNVs composite system is mainly attributed to the coupling of the photothermal conversion performance of Ag2S QDs and the thermal insulation performance of PCNNVs based on the plasmonic coupling-boosted photothermal nanoreactor. This study presents a promising strategy for the development of high-efficient photothermal-assisted photocatalysts.

Two-dimensional anisotropic monolayers NbOX2 (X = Cl, Br, I): Promising candidates for photocatalytic water splitting with high solar-to-hydrogen efficiency

Motivated by the recent experimental synthesis of two-dimensional (2D) NbOI2 which possesses a moderate bandgap and outstanding absorption of sunlight, using the first-principles calculations, we conduct a thorough study of the geometric configuration, electronic structures, and photocatalytic properties for NbOX2 (X = Cl, Br, I) monolayers. These NbOX2 monolayers have been demonstrated to be dynamically, thermally, and mechanically stable. The significant anisotropic mechanical properties of NbOX2 monolayers are reflected by the calculated Young's modulus and Poisson's ratio. Our results indicate that these NbOX2 materials unfold semiconductor characters with indirect bandgaps of 1.886, 1.909, and 1.813 eV, respectively. Among these monolayers, it is found that the NbOBr2 system exhibits a favorable photocatalytic activity in an acidic condition (pH = 0), and the NbOI2 monolayer can act as a potential photocatalyst for spontaneous photocatalytic water splitting under a neutral environment (pH = 7). Furthermore, the response of bandgap and band edge positions of NbOX2 monolayers to the exerting in-plane strain (–6% to 6%) are investigated. These NbOX2 monolayers also show strong light absorption from the visible to ultraviolet region and anisotropic high carrier transport. Particularly, the high solar-to-hydrogen efficiency of the NbOCl2 (1% tensile strain), NbOBr2, and NbOI2 monolayers are predicted to be 14.11% (pH = 0), 16.34% (pH = 0), and 17.05% (pH = 7), respectively. Therefore, we expect the NbOX2 monolayers to be promising candidates for highly efficient photocatalytic water splitting.

Synergistic effect of internal electric field and ligand-to-metal charge transfer in Z-scheme CuPc/ZnIn2S4 for boosting photocatalytic hydrogen evolution

The construction of an efficient and stable photocatalytic water splitting system is the critical path and arduous challenge to convert solar energy into green hydrogen energy. Herein, a novel CuPc/ZnIn2S4 organic–inorganic hybrid photocatalyst was designed and used for photocatalytic hydrogen production from water. The separation of photogenerated electrons and holes was greatly enhanced due to the formation of the compact organic–inorganic heterointerface and the Z-scheme charge transport mechanism between CuPc and ZnIn2S4. Meanwhile, CuPc can broaden the light absorption of CuPc/ZnIn2S4 to the near infrared region, which enhances the utilization of sunlight. Moreover, the Cu metal center of CuPc could serve as the electron acceptor to accumulate photogenerated electrons via the ligand-to-metal charge transfer pathway, which further accelerates the separation of photogenerated charge carriers and enhances the photocatalytic hydrogen production efficiency. The optimal CuPc/ZnIn2S4 photocatalyst exhibited a hydrogen production rate of 151.2 μmol h−1, which was 8.1 times higher than that of pristine ZnIn2S4 under visible light irradiation. This work provides an idea for the construction of an organic–inorganic photocatalytic system for solar hydrogen production.