Energy-Saving Hydrogen Production via Small Molecules Electrooxidation-Assisted Hybrid Systems.

To alleviate overdependence on traditional fossil resources, green hydrogen (H2) production from an electrochemical water splitting (EWS) system powered by renewable energy resources (i.e., tidal, wind, and solar energy) has garnered considerable attention for its environmental sustainability. Nevertheless, the H2 production efficiency of the EWS system is restricted by the sluggish four-electron transfer process of the anodic oxygen evolution reaction (OER), which inhibits its further large-scale applications. Herein, recent advances in the hybrid EWS systems that substitutes OER with the thermodynamically favorable small molecules electrooxidation reaction (SMEOR) to integrate with the hydrogen evolution reaction are reviewed. First, the catalytic mechanisms of electrocatalysts toward SMEOR, reactor configurations, and evaluation parameters are briefly summarized. Next, the advantages and characteristics of the hybrid systems of SMEOR integrated with hydrogen evolution reaction/oxygen reduction reaction are highlighted and discussed in detail, including pollutant degradation, waste plastic upgrading, production of value-added chemicals, bipolar H2 production, and electricity output. Subsequently, the optimization strategies for rationally engineering the catalysts of SMEOR are proposed. Last, the current obstacles and future expectations of the hybrid EWS systems are outlined. This review aims to stimulate the further evolution of green H2 production.