Recent advances in non-noble metal-based electrocatalysts for hybrid water electrolysis systems

The electrocatalytic water-splitting process is widely acknowledged as the most sustainable and environmentally friendly technology for hydrogen (H2) production. However, its energy efficiency is significantly constrained by the kinetically slow oxygen evolution reaction (OER) at the anode, which accounts for about 90% of the electrical energy consumption in the water-splitting process. A new strategy is urgently needed to reduce its energy consumption. In recent years, electrochemical oxidation of small molecules has been considered for replacement of OER for efficient H2 production, due to its benign operational conditions, low theoretical thermodynamic potential, high conversion efficiency and selectivity, and environmental sustainability. Hybrid electrolysis systems, by integrating cathodic hydrogen evolution reaction with anodic oxidation of small molecules, have been introduced, which can generate high-purity H2 and produce value-added products or pollutant degradation. In this review, we highlight the recent advancements and significant milestones achieved in hybrid water electrolysis systems. The focus is on non-noble metal electrocatalysts, reaction mechanisms, and the construction of electrolyzers. Additionally, we present the prevailing challenges and future perspectives pertinent to the evolution of this burgeoning technology.