Interface-Engineered Construction of Amorphous FeNi(OH) and Crystalline NiS Heterojunction Catalysts for Achieving Efficient Bifunctional Electrocatalysts in Overall Water Splitting.

The advancement of inexpensive and productive bifunctional electrocatalysts for overall water splitting is essential for achieving hydrogen energy production. Herein, a hierarchical heterostructure catalyst composed of amorphous FeNi(OH) nanosheets supported on a crystalline NiS scaffold, which is anchored to nickel foam through a combined hydrothermal-electrodeposition strategy, is reported. The crystalline NiS framework exhibits metal-like electrical conductivity and optimized hydrogen adsorption kinetics, while the amorphous FeNi(OH) overlayer offers abundant adaptive active sites that enhance oxygen evolution reaction (OER) activity. The interfacial charge redistribution decreases the activation energy required for water splitting and accelerates the proton-coupled electron transfer process. Electrochemical tests demonstrate that the catalyst achieves performance at a current density of 10 mA cm, with hydrogen evolution reaction (HER) and OER overpotentials as low as 78 and 183 mV, respectively. In addition, an alkaline electrolyzer assembled with this catalyst serving as both cathode and anode can sustain a current density of 10 mA cm with only 1.51 V and keep a long-term stability exceeding 100 h, surpassing the performance of commercial Pt/C||IrO systems. This study provides a design paradigm that integrates conductive crystalline frameworks with amorphous layers, addressing the tradeoff between conductivity and catalytic multifunctionality in nonprecious metal electrocatalysts.