Energy-saving and value-added anodic electro-oxidation reactions toward green hydrogen production

Water electrolysis is an important technology for renewable hydrogen production, yet its overall energy efficiency and economic viability are severely limited due to the intrinsically sluggish reaction dynamics, high thermodynamic overpotential, and low-value products of the anodic oxygen evolution reaction (OER) process. Replacing OER with alternative oxidation reactions to construct coupled electrolysis systems therefore serves as a viable strategy to simultaneously decrease the consumption of electrical energy and improve the economic worth of the whole system. Within this framework, representative anodic oxidation reactions mainly include sacrificial agent oxidation reactions (SAOR) and electrochemical synthesis reactions (ESR). SAOR employs thermodynamically favorable substrates such as urea, hydrazine, and sulfides to lower cell voltage and suppress oxygen evolution, enabling energy-efficient hydrogen production and, in some cases, pollutant remediation. ESR is an anodic electrochemical synthesis strategy that converts organic molecules, including alcohols, aldehydes, and biomass-derived compounds, into high-value chemicals via selective electro-oxidation. Coupling ESR with the cathodic hydrogen evolution reaction can further enhance the economic appeal of the entire process. This paper offers a comprehensive overview of recent advances in alternative anodic reactions, highlighting critical catalyst design approaches such as defect and interface engineering, heterostructure construction, and active-site regulation. Mechanistic insights into representative reactions, including urea, hydrazine, sulfide, alcohol, and aldehyde oxidation, are discussed in terms of activity, selectivity, and stability. Finally, critical challenges and future directions are outlined, with emphasis on reaction mechanism elucidation, catalyst durability under practical conditions, and system-level integration, aiming to guide the development of low-energy-consumption and economically viable electrolysis-based hydrogen production technologies.