Empowering metal oxide photoanodes via zeolitic imidazolate frameworks for efficient photoelectrochemical water splitting: Current advances and future perspectives

In the global pursuit of sustainable energy, solar-powered resources have received significant attention due to their potential to provide clean and renewable energy. Among these, PEC water splitting stands out as the most effective and environmentally benign technology, with tremendous potential to meet future global demands. However, identifying high-performance, economically viable materials for photoelectrodes which are building blocks of water splitting process, remains a significant challenge. In this regard, transition metal oxide photoanodes such as TiO2, WO3, BiVO4, ZnO, α-Fe2O3, etc. are potential candidates for efficient water splitting. Nonetheless, intrinsic barriers including limited light harvesting, poor charge separation/transport, and sluggish OER kinetics limit their practical application. To address these issues, zeolitic imidazolate frameworks, a class of unique materials belonging to the metal-organic frameworks family are emerging as a potential catalyst for the development of photoelectrodes owing to their large surface area, extensive redox-active sites, excellent thermal and chemical stability, and hierarchical porosity. This review highlights advancements in employing ZIF-8 and ZIF-67 catalysts to improve the PEC efficiency of established metal oxide semiconducting photoanodes, addressing a gap in the existing literature. For broader context, this review covers PEC water splitting fundamentals and advanced metal oxide/ZIF-based photoelectrode mechanisms, aiding next-generation PEC device design. The conversation about current challenges and future directions will provide new avenues for improving the ZIF-based PEC water splitting landscape.