Energy-saving cathodic H₂ production enabled by non-oxygen evolution anodic reactions: A critical review on fundamental principles and applications

The energy efficiency of water electrolysis is constrained by the kinetic limitation of the anodic oxygen evolution reaction (OER). Replacing the OER with thermodynamically more favorable reactions has the potential to significantly reduce electricity consumption and boost cathodic hydrogen generation. In this review, we first summarized the recent advancement of hydrogen production assisted by various alternative anodic reactions, with a special focus on the current status of coal and biomass, which are especially rich in resources. Other auxiliary chemicals such as sulfite, organic contaminants, urea, and carbon are also reviewed. Key indicators such as current densities and corresponding cell voltages are compared. Following this, other cathodic reactions that are of interest are assisted by non-oxygen evolution anodic reactions, such as CO₂ reduction reaction (CO₂RR), O₂ reduction reaction (ORR), and N₂ reduction reaction (NRR), are also discussed. Finally, the challenges and future directions in this fascinating and emerging field are outlined.