Energy-efficient anodic reactions for sustainable hydrogen production via water electrolysis

Overall water splitting is considered as an effective technique for hydrogen (H2) production; however, it usually requires large operating voltage mainly due to the high equilibrium potential of the anodic oxygen evolution reaction (OER). Replacing OER with energy-saving anode reactions not only reduces the operating voltage for H2 production but also generates high-value-added chemicals or purifies wastewater. This review article provides an overview of the fundamental reaction principles of overall water splitting and typical energy-saving alternative anode reactions, including methanol oxidation, hydrazine oxidation, and urea oxidation reactions. Then, the preparation methods, regulation strategies, and composition/structure-performance relations of advanced catalysts for these energy-efficient H2 generation technologies are discussed. Finally, we propose the underlying challenges and perspectives for this promising field.