Abstract: The development of cost-effective bifunctional electrocatalysts is crucial for advancing water electrolysis technologies toward sustainable hydrogen production. In this study, we present a rational dealloying strategy to simultaneously tailor the morphology, structure, and composition of transition metal-nonmetal multicomponent alloys, achieving exceptional catalytic performance for overall water splitting. By dealloying Fe₂₅Ni_50-xCo_xP₁₀C₁₀B₅ (x = 5-45, in at.%) amorphous ribbons, sandwich-like nanoporous CoNiFePCBO (np-CoNiFePCBO) with a unique heterostructure was formed, where (Co, Ni)P₂ nanocrystals are embedded within an oxygen-incorporated CoNiFePCB amorphous matrix. Tuning the composition of precursors enables precise control of the nanoporous morphology and significantly enhances catalytic activity. Specifically, at x = 25, the np-CoNiFePCBO with a uniform bicontinuous nanoporous/ligament structure exhibits outstanding bifunctional electrocatalytic activity in alkaline media, requiring overpotentials of only 231 mV for oxygen evolution reaction (OER) and 101 mV for hydrogen evolution reaction (HER) at a current density of 10 mA cm^-2. The electrolyzer assembled with np-CoNiFePCBO as both cathode and anode achieves efficient overall water splitting with a low cell voltage of 1.57 V at 10 mA cm^-2 and maintains excellent long-term stability even at a high current density of 500 mA cm^-2. Comparative experiments and density functional theory calculations reveal that the enhanced OER and HER activity arises from the synergistic effects of multicomponent incorporation, nanocrystalline/amorphous heterointerfaces, nanoporous architecture, and the generation of (Co, Ni)OOH active species during the OER process. Furthermore, the dealloying mechanism and the evolution of the nanoporous structure are discussed.

Key words: Nanoporous alloy, CoNiFePCB multicomponent alloy, Water splitting electrocatalyst, Dealloying, Nanocrystalline/amorphous heterointerface