The component-activity interrelationship of cobalt-based bifunctional electrocatalysts for overall water splitting: strategies and performance

Cobalt-based electrocatalysts take advantage of potentially harmonizable microstructure and flexible coupling effects compared to commercial noble metal-based catalytic materials. However, conventional water electrolysis systems based on cobalt-based monofunctional hydrogen evolution reaction (HER) or oxygen evolution reaction (OER) catalysts have certain shortcomings in terms of resource utilization and universality. In contrast, cobalt-based bifunctional catalysts (CBCs) have attracted much attention in recent years for overall water splitting systems because of their practicality and reduced preparation cost of electrolyzer. This review aims to address the latest development in CBCs for total hydrolysis. The main modification strategies of CBCs are systematically classified in water electrolysis to provide an overview of how to regulate their morphology and electronic configuration. Then, the catalytic performance of CBCs in total-hydrolysis is summarized according to the types of cobalt-based phosphides, sulfides and oxides, and the mechanism of strengthened electrocatalytic ability is emphasized through combining experiments and theoretical calculations. Future efforts are finally suggested to focus on exploring the dynamic conversion of reaction intermediates and building near-industrial CBCs, designing advanced CBC materials through micro-modulation, and addressing commercial applications.