Recent Advances of Metal-Oxide Photoanodes: Engineering of Charge Separation and Transportation toward Efficient Solar Water Splitting

Photoelectrochemical (PEC) water splitting has witnessed rapid development because of the potential of converting solar energy into renewable fuels. Photoelectrodes and electrolytes are two basic components for a PEC system. Metal-oxide photoanodes have been the most popular electrode candidates because of their excellent performance, good stability, abundance, and cost-effective features. However, metal-oxide photoanodes suffer from serious charge recombination due to the intrinsically poor electrochemical properties. Therefore, intensive research effort has been devoted to solving these challenges. A variety of effective strategies have been developed, including the construction of nanostructures, introduction of dopants, control of crystal facets, design of junctions, and modification of interfaces. Moreover, it is demonstrated that the combination of multiple strategies is much more efficient than a single one to suppress charge recombination. Herein, the recent advances in metal-oxide photoanodes for PEC water oxidation are summarized, mainly focusing on the engineering of charge separation and transportation process. At the end of this Review, some perspectives and outlooks for the development and design of metal-oxide photoanodes are also proposed, hoping to shed light on the rapid growth of this area in the future.