Composition-Driven Structural Regulation of Fe-Co Aerogels for High-Current-Density Hydrogen Evolution

Cost-effective alkaline water electrolysis requires non-precious-metal electrocatalysts that sustain the hydrogen evolution reaction (HER) at high current densities while maintaining favorable interfacial kinetics and an accessible electrode structure. Here, Co incorporation was used to suppress the long-range crystalline order of Fe and generate poorly crystalline Fe-Co aerogels through one-pot NaBH₄ reduction, gelation, and freeze-drying. A Fe_100-xCo_x series (x = 0, 60, 80, and 100; nominal feed compositions) was examined to determine how composition-induced structural changes affect network morphology, interfacial accessibility, and high-current HER behavior. Among the series, FeCo60-A formed the finest interconnected particle network and exhibited the largest BET surface area (34.1 m² g^-1), a high double-layer capacitance (1.04 mF cm^-2), and the smallest apparent Nyquist arc. After iR correction, it required overpotentials of 345, 520, and 685 mV to reach 100, 500, and 1000 mA cm^-2, respectively, and maintained a nearly constant potential during 24 h operation at -1000 mA cm^-2 while largely retaining its interconnected porous morphology. These results demonstrate that Co incorporation into the Fe-based aerogel framework effectively tunes structural order and interfacial characteristics, enabling improved HER performance under high-current alkaline conditions.