Engineering the Near-Surface Structure of WO3 by an Amorphous Layer with Trivalent Ni and Self-Adapting Oxygen Vacancies for Efficient Photocatalytic and Photoelectrochemical Acidic Oxygen Evolution Reaction.

Exploiting an effective strategy to tailor the construction, composition, and local electronic structure of the photocatalyst surface is pivotal to photocatalytic activity, but remains challenging. Transition metal elements can boost the oxygen evolution reaction activity especially one like Ni in high oxidation states, whereas it is uneasy to prepare Ni3+ under mild conditions or play to their strengths in acidic conditions. In this article, we report a facile "etch and dope" synthesis of Ni3+-doped WO3 nanosheets with oxygen vacancies. Through detailed experimental and theoretical studies, it is established that the abundant oxygen vacancies and the doped Ni3+ ions in the near-surface amorphous layer can synergistically optimize the surface electronic structure of WO3 and the adsorption and desorption of intermediates. Impressively, the etched WO3 nanosheets coupled with Ni3+ offer a greatly promoted photocatalytic performance of 1.78 mmol g-1 h-1, and the photoanode achieves a photocurrent density of 2.11 mA cm-2 at 1.23 V versus reversible hydrogen electrode (VRHE). This work provides a new inspiration for rational manufacture of defects and high-valence metal ions in catalysts for photocatalytic and photoelectrochemical reactions.

Noble-metal-free Cd0.3Zn0.7S-Ni(OH)2 for high efficiency visible light photocatalytic hydrogen production.

Heterogeneously structured materials with supported precious metals, such as Pd, Pt, and Ru, as co-catalysts are important catalysts for efficient photocatalytic water splitting. However, the high costs and low reserves of precious metals have been an obstacle to their application in hydrogen production. In this work, the noble-metal-free Cd0.3Zn0.7S solid solution was designed and synthesized with an optimized molar ratio of Cd/Zn for the best visible light photocatalytic performance. In addition, a heterojunction hybrid material formed between the Cd0.3Zn0.7S and Ni(OH)2 nanosheet was engineered to improve the utilization of light and to inhibit the recombination of holes and electrons. Ni(OH)2 nanosheets assisted the transfer of the photoexcited electrons to participate in the reduction reactions which is critical for efficient and rapid catalytic hydrogen production. The photoelectrochemical property of the hybrid material was investigated with UV-vis absorption, photoluminance (PL) and electrochemical impedance spectroscopy measurements. The mechanism of the high-efficiency and low-cost photocatalytic hydrogen production was established by analyzing the hydrogen evolution kinetics. With the success of replacing precious metal with nickel-based surface heterostructure, this work is expected to provide a new type of photocatalyst for the application of photocatalytic hydrogen production.