As inspired by natural photosynthesis, semiconductor-based photocatalytic water splitting into hydrogen and oxygen has attracted extensive attention, which provides a promising and clean method to convert solar energy into chemical fuel, for alleviating human's excessive reliance on fossil fuels. [1][2][3] For the water splitting process, the half-reaction of water oxidation to oxygen has been well recognized as the rate-limiting step for its four-electron oxidation process and high activation energy barrier (≈700 mV) for O-O bond formation, [4,5] which thus remains as the main challenge to achieve highly efficient overall water splitting. Although enormous efforts have been dedicated to develop photocatalysts for improved water oxidation performances in the past decades, by far only a few photocatalysts (e.g., WO 3 , BiVO 4 , and Ag 3 PO 4 , etc.) have been proven to be efficient for lightdriven oxygen evolution from water. [5][6][7][8] Worse still, several drawbacks always limit their practical application in oxygen-generating photocatalytic systems, including poor photostability, low charge carrier mobility, and high costs of raw materials. Since the pioneering work reported in 2009 by Wang et al., [9] metal-free graphitic carbon nitride (g-C 3 N 4 ) with a 2D conjugated structure has been intensively investigated for photocatalytic water redox reactions, owing to its earth-abundance, environmental friendliness, chemical stability, and suitable thermodynamical potentials for both hydrogen and oxygen evolution reactions. [10][11][12] In the past ten years, various strategies, including thermodynamic (such as doping with heteroatoms, [13][14][15][16] engineering defects with nitrogen vacancies or carbon vacancies, [17,18] etc.) and kinetic (such as compositing with other semiconductors, [7,[19][20][21][22] morphology design, [23][24][25][26][27] and loading cocatalysts, [28][29][30] etc.) modifications, have emerged to enhance the photocatalytic hydrogen evolution activity of g-C 3 N 4 and a high quantum yield of 34.4% at 400 nm has been achieved. [31] However, only very few results have been reported on g-C 3 N 4 based photocatalysts for water oxidation, and most of them were focused on surface modification by loading cocatalysts, such as cobalt (hydr)oxide and selenide, [32][33][34] etc., onto g-C 3 N 4 . Unfortunately, the photocatalytic oxygen evolution Electronic structure greatly determines the band structures and the charge carrier transport properties of semiconducting photocatalysts and consequently their photocatalytic activities. Here, by simply calcining the mixture of graphitic carbon nitride (g-C 3 N 4 ) and sodium borohydride in an inert atmosphere, boron dopants and nitrogen defects are simultaneously introduced into g-C 3 N 4 . The resultant boron-doped and nitrogen-deficient g-C 3 N 4 exhibits excellent activity for photocatalytic oxygen evolution, with highest oxygen evolution rate reaching 561.2 µmol h −1 g −1 , much higher than previously reported g-C 3 N 4 . It is well evidenced that with c...

CdS is a promising visible light response photoanode of photoelectrochemical (PEC) water splitting, but it remains a great challenge for practical application, due to the photohole‐induced self‐corrosion, and sulfide/sulfite ions as hole scavengers are always necessary for stable solar hydrogen generation. Herein, a CdS/SnSx nanorods/nanosheets hierarchical heterostructure with novel phase‐engineered band alignment is rationally designed via a two‐step solution reaction route for PEC water splitting. In the Na2SO4 aqueous electrolyte without any hole scavengers, compared with the pristine CdS, the CdS/SnSx photoanode achieves a remarkably enhanced photocurrent density of 1.59 mA cm−2 and a considerable stability at bias potential 1.23 V versus reversible hydrogen electrode (RHE) under simulated sunlight. It is proposed that the deposited SnSx nanosheets not only act as protective layers to restrain the photocorrosion of CdS, but also facilitate the charge separation in CdS by the virtue of the Type II heterojunction formed between CdS and SnSx.

The development of efficient noble-metal-free hydrogen evolution catalysts is quite appealing with the aim of providing cost-competitive hydrogen.Herein, nickel sulfides (NiS x ) with tunable NiS/Ni 3 S 4 molar ratios were synthesized via a simple hydrothermal method. Detailed electrochemical studies under neutral conditions indicated that the electrocatalytic property of NiS x catalysts was determined by the composition. Notably, the NiS x sample with the NiS/Ni 3 S 4 molar ratio of 1.0 exhibited the lowest overpotential and charge-transfer resistance. As analyzed from the Tafel plots, the rate determining step of NiS x catalysts for hydrogen generation was the Volmer step, in which the proton adsorption played a key role.Theoretical calculation revealed that NiS and Ni 3 S 4 exhibited the metallic behaviors with different work functions. Consequently, the NiS x sample with the NiS/Ni 3 S 4 molar ratio of 1.0 owned the most adsorbed protons, which led to the highest electrocatalytic property. Meanwhile, NiS x was demonstrated to be efficient cocatalysts to promote photocatalytic hydrogen generation. NiS x /CdS with the S 4 molar ratio of 1.0 showed the best photocatalytic activity with the apparent quantum efficiency of 56.5% at 420 nm. This result was in good agreement with the electrocatalytic activities of NiS x samples, indicating the intrinsic property for efficient hydrogen generation.

Developing active photocatalysts using wide-spectrum light is crucial to promote the application of photocatalytic water splitting. Elemental red phosphorus (RP) has attracted much attention as a potential nonmetal photocatalyst owing to its low cost, earth abundance, and narrow bandgap. Herein, RP nanosheets were synthesized and tightly combined with carbon nitride (CN) framework nanosheets to form RP/CN van der Waals (vdW) heterostructure. CN nanosheets could act as a substrate to generate RP nanosheets through a “confinement effect”. This hybrid photocatalyst could utilize the incident light with the wavelength longer than 620 nm for pure water splitting, with hydrogen production activity of 367.0 μmol h–1g–1 under full arc illustration and 239.8 μmol h–1g–1 under visible light irradiation. The improved photocatalytic property was ascribed to the wide light absorption and intimate electronic coupling between 2D RP and 2D CN for accelerated charge transfer. Instead of O2, water was oxidized into H2O2 via a two-electron pathway, which could avoid the potential explosion by producing H2 and O2 simultaneously. This work proved the great potential of RP-based vdW heterostructures for solar-driven water splitting.

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To gain high photocatalytic activity for hydrogen evolution, both charge separation efficiency and surface reaction kinetics must be improved, and together would be even better. In this study, the visible light photocatalytic hydrogen production activity of graphitic carbon nitride (g-C3N4) was greatly enhanced with MgFe2O4 modification. It was demonstrated that MgFe2O4 could not only extract photoinduced holes from g-C3N4, leading to efficient charge carrier separation at the g-C3N4/MgFe2O4 interface, but also act as an oxidative catalyst accelerating the oxidation reaction kinetics at g-C3N4 surface. This dual function of MgFe2O4 thus contributed to the great improvement (up to three-fold) in photocatalytic activity for hydrogen generation over g-C3N4/MgFe2O4 as compared to pristine g-C3N4, after loading Pt by photoreduction method. It was revealed that in the Pt/g-C3N4/MgFe2O4 system, the photoinduced electrons and holes were entrapped by Pt and MgFe2O4, respectively, giving rise to the promoted charge separation; moreover, as evidenced by electrochemical analysis, the electrocatalysis effect of MgFe2O4 benefited the oxidation reaction at g-C3N4 surface.

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The article describes a robust method for the facile polyol synthesis of high-quality CuS nanocrystals with a controlled hierarchical nanoplate structure.