Hybrid Water Electrolysis toward Energy-Efficient Hydrogen Production Coupled with Value-Added Chemical Synthesis

Abstract

Water electrolysis powered by renewable energy is a green and efficient strategy to obtain high-purity H2. However, the conventional oxygen evolution reaction (OER) at the anode suffers from sluggish kinetics and limited economic value, thereby constraining the overall efficiency. To address these challenges, hybrid water electrolysis, in which OER is replaced by the electrooxidation of thermodynamically more favorable small molecules, has recently emerged as a promising alternative. This strategy not only significantly lowers the cell voltage and reduces energy consumption but also enables simultaneous production of high-value chemicals or pollutant degradation. Representative anodic reactions, such as the oxidation of alcohols, aldehydes, amines, urea, and hydrazine, have been extensively investigated and demonstrated remarkable potential in coupling energy-efficient H2 production with sustainable chemical synthesis. In this review, we systematically summarize recent progress in hybrid water electrolysis, focusing on the fundamental thermodynamic and kinetic advantages of alternative anodic reactions, the design of advanced catalysts, and mechanistic insights into small-molecule oxidation. Finally, we discuss the key challenges and future directions toward achieving efficient, selective, and industrially viable hybrid electrolysis systems, aiming to inspire further breakthroughs in this emerging field.