Electrochemical Hydrogen Generation by Oxygen Evolution Reaction‐Alternative Anodic Oxidation Reactions

Hydrogen (H2) as an environmentally friendly and sustainable energy carrier has been regarded as one of the most promising alternatives to carbon‐based fossil fuels. Electrochemical water splitting powered by renewable electricity provides a promising strategy for H2 production, but its energy efficiency is strongly limited by the kinetically sluggish anodic oxygen evolution reaction (OER), which consumes ≈90% electricity in the water‐splitting process. A new strategy is urgently needed to reduce its energy consumption. Small‐molecule electro‐oxidation reactions that replace OER have attracted increasing attention due to the advantages of low theoretical thermodynamic potential and the benefit of producing value‐added chemicals compared with OER. Hybrid electrolysis systems, by coupling cathodic hydrogen evolution reaction (HER) with anodic small‐molecule oxidation reactions, have been proposed, which can produce high‐purity H2 and value‐added products. This review aims to systematically summarize the recent research on OER‐alternative reactions at the anode for energy‐efficient water splitting. The state‐of‐the art electrocatalysts for OER‐alternative reactions are first presented. The electrolysis performance in hybrid electrolysis regarding the conversion rate, selectivity, yield, and corresponding Faraday efficiency of anodic value‐added products is then evaluated. Finally, the challenges and perspectives are discussed and it is suggested to develop energy‐efficient and economically viable hybrid electrolysis systems.