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It is of essential importance to design an electrocatalyst with excellent performance for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in water splitting.

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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...

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With the intense interest in inorganic cesium lead halide perovskites and their nanostructures for optoelectronic applications, high-quality crystalline nanomaterials with controllable morphologies and growth directions are desirable. Here, we report a vapor-phase epitaxial growth of horizontal single-crystal CsPbX (X = Cl, Br, I) nanowires (NWs) and microwires (MWs) with controlled crystallographic orientations on the (001) plane of phlogopite and muscovite mica. Moreover, single NWs, Y-shaped branches, interconnected NW or MW networks with 6-fold symmetry, and, eventually, highly dense epitaxial network of CsPbBr with nearly continuous coverage were controllably obtained by varying the growth time. Detailed structural study revealed that the CsPbBr wires grow along the [001] directions and have the (100) facets exposed. The incommensurate heteroepitaxial lattice match between the CsPbBr and mica crystal structures and the growth mechanism of these horizontal wires due to asymmetric lattice mismatch were proposed. Furthermore, the photoluminescence waveguiding and good performance from the photodetector device fabricated with these CsPbBr networks demonstrated that these well-connected CsPbBr NWs could serve as straightforward platforms for fundamental studies and optoelectronic applications.

Different approaches to improving photoelectrochemical performance through α-Fe2O3 heterostructure design.

High-quality metal halide perovskite single crystals have low defect densities and excellent photophysical properties, yet thin films are the most sought after material geometry for optoelectronic devices. Perovskite single-crystal thin films (SCTFs) would be highly desirable for high-performance devices, but their growth remains challenging, particularly for inorganic metal halide perovskites. Herein, we report the facile vapor-phase epitaxial growth of cesium lead bromide perovskite (CsPbBr) continuous SCTFs with controllable micrometer thickness, as well as nanoplate arrays, on traditional oxide perovskite SrTiO(100) substrates. Heteroepitaxial single-crystal growth is enabled by the serendipitous incommensurate lattice match between these two perovskites, and overcoming the limitation of island-forming Volmer-Weber crystal growth is critical for growing large-area continuous thin films. Time-resolved photoluminescence, transient reflection spectroscopy, and electrical transport measurements show that the CsPbBr epitaxial thin film has a slow charge carrier recombination rate, low surface recombination velocity (10 cm s), and low defect density of 10 cm, which are comparable to those of CsPbBr single crystals. This work suggests a general approach using oxide perovskites as substrates for heteroepitaxial growth of halide perovskites. The high-quality halide perovskite SCTFs epitaxially integrated with multifunctional oxide perovskites could open up opportunities for a variety of high-performance optoelectronics devices.