Electrocatalytic oxygen evolution in acidic media is crucial for promoting water splitting. Herein, we report an Ag 1 /IrO x single atom catalyst (SAC) with Ag single atoms embedded in an IrO 2 matrix obtained through the oxidation of IrAg single atom alloy (SAA). The Ag 1 /IrO x SAC delivers a low overpotential of 224 mV at current density of 10 mA cm −2 and a long-term durability better than that of commercial Ir (C-Ir). DFT calculation indicates that six Ir atoms neighboring the single Ag atom exhibit a higher-valence Ir x+ (x > 4) and thus lower the adsorption free energy significantly to boost the oxygen evolution process. Furthermore, the strong Ir−O bonds and low overpotential prevent the loss of the lattice oxygen in the Ag 1 /IrO x SAC, resulting in high oxygen evolution reaction stability.

Developing highly efficient and low‐cost photocatalysts for overall water splitting has long been a pursuit for converting solar power into clean hydrogen energy. Herein, we demonstrate that a nonstoichiometric nickel–cobalt double hydroxide can achieve overall water splitting by itself upon solar light irradiation, avoiding the consumption of noble‐metal co‐catalysts. We employed an intensive laser to ablate a NiCo alloy target immersed in alkaline solution, and produced so‐called L‐NiCo nanosheets with a nonstoichiometric composition and O2−/Co3+ ions exposed on the surface. The nonstoichiometric composition broadens the band gap, while O2− and Co3+ ions boost hydrogen and oxygen evolution, respectively. As such, the photocatalyst achieves a H2 evolution rate of 1.7 μmol h−1 under AM 1.5G sunlight irradiation and an apparent quantum yield (AQE) of 1.38 % at 380 nm.

Engineering high‐performance electrocatalysts is of great importance for energy conversion and storage. As an efficient strategy, element doping has long been adopted to improve catalytic activity, however, it has not been clarified how the valence state of dopant affects the catalytic mechanism and properties. Herein, it is reported that the valence state of a doping element plays a crucial role in improving catalytic performance. Specifically, in the case of iridium doped nickel‐iron layer double hydroxide (NiFe‐LDH), trivalent iridium ions (Ir3+) can boost hydrogen evolution reaction (HER) more efficiently than tetravalent iridium (Ir4+) ions. Ir3+‐doped NiFe‐LDH delivers an ultralow overpotential (19 mV @ 10 mA cm−2) for HER, which is superior to Ir4+ doped NiFe‐LDH (44 mV@10 mA cm−2) and even commercial Pt/C catalyst (40 mV@ 10 mA cm−2), and reaches the highest level ever reported for NiFe‐LDH‐based catalysts. Theoretical and experimental analyses reveal that Ir3+ ions donate more electrons to their neighboring O atoms than Ir4+ ions, which facilitates the water dissociation and hydrogen desorption, eventually boosting HER. The same valence‐state effect is found for Ru and Pt dopants in NiFe‐LDH, implying that chemical valence state should be considered as a common factor in modulating catalytic performance.

Metallic materials with unique surface structure have attracted much attention due to their unique physical and chemical properties. However, it is hard to prepare bulk metallic materials with special crystal faces, especially at the nanoscale. Herein, we report an efficient method to adjust the surface structure of a Cu plate which combines ion implantation technology with the oxidation–etching process. The large number of vacancies generated by ion implantation induced the electrochemical oxidation of several atomic layers in depth; after chemical etching, the Cu(100) planes were exposed on the surface of the Cu plate. As a catalyst for acid hydrogen evolution reaction, the Cu plate with (100) planes merely needs 273 mV to deliver a current density of 10 mA/cm2 because the high-energy (100) surface has moderate hydrogen adsorption and desorption capability. This work provides an appealing strategy to engineer the surface structure of bulk metallic materials and improve their catalytic properties.

P-N depleted bulk BiOBr/α-FeO heterojunction (DBH) nanostructures with the growth of (001) BiOBr facets were prepared via a simple hydrothermal method. BiOBr possesses an average thickness of around 50 nm and shows preferential exposure of the (001) facets. α-FeO nanoparticles, with an average diameter of 5 nm, are attached on the surface of BiOBr as 20-50 nm clusters with an intimate contact interface. Such DBH nanostructures show high hydrogen evolution, and 193 mmol g of H is produced with DBH containing 1 wt% Pt, which is 6.3 times higher than that of α-FeO nanoparticles. The structural features of DBH are considered to be important to obtain attractive properties in photocatalytic water splitting.