Sustainable photoanodes for water oxidation reactions: from metal-based to metal-free materials

Sunlight affords an inexhaustible and primary energy for Earth. A photoelectrochemical system can efficiently harvest solar energy and convert it into chemicals. However, sophisticated processes and expensive raw materials are critical to restrict its further development. In recent years, the research focus of the PEC system has gradually shifted from traditional metal-based materials to earth-abundant metal-free materials. In this feature article, the photoanode materials for water oxidation reactions have been focused upon. The discussions on metal-based materials mainly include TiO₂, BiVO₄, and Ta₃N₅, and the examples for metal-free photoanodes are mainly polymeric carbon nitride and carbon doped boron nitride. This review offers opportunities for the further development of sustainable and cost-effective materials for the rational design of photoanodes for water oxidation reactions.