Co doping induced structural evolution of FeNi-based amorphous alloy for enhanced electrocatalytic water oxidation

The sluggish kinetics of the oxygen evolution reaction (OER) remain a major bottleneck for large-scale hydrogen production via water electrolysis. Herein, we propose a micro-alloying strategy to induce structural evolution in FeNi-based amorphous alloys by introducing a trace amount of Co. Benefiting from the similar atomic size and near-zero mixing enthalpy between Co and Fe/Ni, Co doping weakens the glass-forming ability of Fe₄₀Ni₄₀B₂₀ (Fe₄₀) and triggers the in-situ formation of Fe₂B nanocrystals within the amorphous matrix, yielding a nanocrystal/amorphous (N/A) heterostructure. The resulting Fe₄₀Ni₃₈Co₄B₁₈ (Co₄) N/A alloy fibers exhibit abundant high-energy N/A interfaces, residual strain, and optimized electronic structure, which markedly boosts OER activity. Therefore, Co₄ N/A alloy exhibits an overpotential of 238 mV at a current density of 10 mA cm⁻², which is 25% lower than that of Fe₄₀ amorphous alloy, and delivers excellent industrial-level performance with stable operation at 1000 mA cm⁻² for over 500 h.