Towards highly efficient photoanodes: boosting sunlight-driven semiconductor nanomaterials for water oxidation.

Harvesting energy directly from sunlight is a very attractive and desirable way to solve the rising energy demand. In the past few decades, considerable efforts have been focused on identifying appropriate materials and devices that can utilize solar energy to produce chemical fuels. Among these, one of the most promising options is the construction of a photoelectrochemical (PEC) cell that can produce hydrogen fuel or oxygen from water. Significant advancement in the understanding and construction of efficient photoanodes to improve performance has been accomplished within a short period of time owing to various newly developed ideas and approaches, including facilitating charge transportation in narrow band gap semiconductors or doping in wide band gap semiconductors for enhancing visible-light absorption; electrocatalysts for decreasing overpotentials; controlling the morphology of the materials for enhancing light absorption and shortening the transfer distance of minority carriers; and other methods such as using heterojunction structures for band-structure engineering, sensitization, and passivating layers. In this review, we focus on the recent developments of some promising visible-light active photoanode materials with high PEC performance, such as BiVO4, α-Fe2O3, WO3, TaON, and Ta3N5.