Electrochemical hydrogen production coupled with oxygen evolution, organic synthesis, and waste reforming

H2 gas is considered to be an ideal green energy carrier that can replace fossil fuels to ameliorate the rapidly increasing global issues of energy crisis and environmental pollution. Water splitting driven by electricity generated from renewable energy sources has attracted immense attention for H2 production. The conventional mode of water electrolysis involves two coupled half-reactions: the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). Numerous high-performance OER electrocatalysts have been developed to increase the efficiency of the cathodic HER. However, the OER exhibits slow kinetics and high overpotential values, generating the low-economic-value O2 gas which forms the highly damaging reactive oxygen species (ROS) and hazardous H2/O2 mixtures. Therefore, to improve the utility of the anodic reaction and reduce the cost and power implementation of hydrogen production, numerous kinetically and economically favorable oxidation reactions have been proposed to replace the OER as electron donors for integration with the HER. In such hybrid systems, the oxidative potential is used to synthesize valuable chemicals and decompose harmful pollutants. In this review, recent developments in the anodes of conventional and hybrid water splitting technologies have been systematically summarized. Additionally, various alternative anodic reactions and the corresponding 3D integrated electrocatalysts in alkaline media have been highlighted. The technical features, potential challenges, and future perspectives have been thoroughly discussed. This review could promote research on low-voltage hydrogen generation by the electrolysis of renewable organics and harmful wastes.