Circumventing Challenges: Design of Anodic Electrocatalysts for Hybrid Water Electrolysis Systems

Water electrolysis, driven by renewable energy resources, is a promising energy conversion technology that has gained intensive interest in recent years. However, conventional water electrolysis faces a number of challenges, including large thermodynamic potential gaps, valueless anodic products, explosive hydrogen/oxygen mixtures, reactive oxygen species, and limited pure water. Hybrid water electrolysis, appending different electrolytes in the anode compartment to circumvent the above-mentioned challenges in conventional water electrolysis, is a particularly attractive alternative. In this review, for the first time, a holistic and subtle description of hybrid water electrolysis is provided, focusing on the design of high-activity/selectivity/stability anodic electrocatalysts for the electrochemical oxidation of various chemicals, such as alcohol, aldehyde, amine, urea and hydrazine, or the oxygen evolution reaction in seawater electrolytes. Comprehensive judging criteria for anodic oxidation reactions, electrocatalysts, and reaction parameters in hybrid water electrolysis are discussed. Some technoeconomic assessments, feasibility analyses, mechanism explorations, and correlation comparisons are involved. Finally, perspectives on and opportunities for future research directions in hybrid water electrolysis systems are outlined.