Hydrogenated metal oxide semiconductors for photoelectrochemical water splitting: Recent advances and future prospects

Hydrogenated metal oxide semiconductors (HMOS) are witnessed tunable and superior structural, electrical, optical and catalytic properties, have emerged as a novel class of semiconductors in various applications, especially as photoanodes in photoelectrochemical (PEC) water splitting technology towards sustainable green hydrogen production, effectively overcoming the constraints associated with traditional metal oxides semiconductors which suffer limited visible light absorption and elevated electron-hole recombination rates. Herein, we offer a comprehensive overview of recent advances in fabrication, compositions and understanding of HMOS nanomaterials, as well as its crucial function in improving PEC activity, focusing on the potential hydrogenation techniques for practical applications and further surface and interface engineering strategies to boost PEC properties. We showcase a theoretical framework for understanding hydrogenation mechanisms and the impact on PEC activity. We also emphasize combining advanced and in-situ characterization techniques with theoretical simulations to unravel the mechanisms underlying the enhanced PEC activity to establish the structure-property-function relationships from both macroscopic and microscopic perspectives. Finally, we discuss the remaining challenges in HMOS design and provide a perspective on further research directions of HMOS nanomaterials for PEC water splitting that realize PEC technology to contribute to produce green hydrogen efficiently.