Self‐Etching Synthesis of Superhydrophilic Iron‐Rich Defect Heterostructure‐Integrated Catalyst with Fast Oxygen Evolution Kinetics for Large‐Current Water Splitting

Developing catalysts with rich metal defects, strong hydrophilicit, and extensive grain boundaries is crucial for enhancing the kinetics of electrocatalytic water oxidation and facilitating large‐current water splitting. In this study, we utilized pH‐controlled etching and gas‐phase phosphating to synthesize a flower‐like Ni2P‐FeP4‐Cu3P modified nickel foam heterostructure catalyst. This catalyst features pronounced hydrophilicity and a high concentration of Fe defects. It exhibits low overpotentials of 156 mV and 210 mV at current densities of 10 and 100 mA cm−2 respectively, and maintains stability for up to 200 h at 100 mA cm−2 with only 7.3% degradation, showcasing outstanding electrocatalytic water oxidation performance. Furthermore, when integrated into a Ni2P‐FeP4‐Cu3P/NF||Pt‐C/NF electrolyzer, it achieves excellent overall water splitting performance, reaching current densities of 10 and 400 mA cm−2 at just 1.47 V and 1.73 V, respectively, and operates stably for 60 h at 500 mA cm−2 with minimal degradation. Analysis indicates that high‐valence oxyhydroxides/phosphides of Ni, Fe, and Cu act as the primary active species. The presence of abundant Fe defects enhances electron transfer, strong hydrophilicity improves electrolyte contact, and numerous grain boundaries synergistically modulate the activation energy between active sites and oxygen‐containing intermediates, significantly improving the kinetics of water oxidation.