Tuning Electronic Structure and Composition of FeNi Nanoalloys for Enhanced Oxygen Evolution Electrocatalysis via a General Synthesis Strategy

Developing low-cost and efficient oxygen evolution electrocatalysts is key to decarbonization. A facile, surfactant-free, and gram-level biomass-assisted fast heating and cooling synthesis method is reported for synthesizing a series of carbon-encapsulated dense and uniform FeNi nanoalloys with a single-phase face-centered-cubic solid-solution crystalline structure and an average particle size of sub-5 nm. This method also enables precise control of both size and composition. Electrochemical measurements show that among Fe_xNi_(1−x) nanoalloys, Fe_0.5Ni_0.5 has the best performance. Density functional theory calculations support the experimental findings and reveal that the optimally positioned d-band center of O-covered Fe_0.5Ni_0.5 renders a half-filled antibonding state, resulting in moderate binding energies of key reaction intermediates. By increasing the total metal content from 25 to 60 wt%, the 60% Fe_0.5Ni_0.5/40% C shows an extraordinarily low overpotential of 219 mV at 10 mA cm⁻² with a small Tafel slope of 23.2 mV dec⁻¹ for the oxygen evolution reaction, which are much lower than most other FeNi-based electrocatalysts and even the state-of-the-art RuO₂. It also shows robust durability in an alkaline environment for at least 50 h. The gram-level fast heating and cooling synthesis method is extendable to a wide range of binary, ternary, quaternary nanoalloys, as well as quinary and denary high-entropy-alloy nanoparticles.