Controllable Phase Separation Engineering of Iron–Cobalt Alloy Heterojunction for Efficient Water Oxidation

The tailor-made transition metal alloy-based heterojunctions hold a promising prospect for the electrocatalytic oxygen evolution reaction (OER). Herein, a series of iron–cobalt bimetallic alloy heterojunctions are purposely designed and constructed via a newly developed controllable phase separation engineering strategy. The results show that the phase separation process and alloy component distribution rely on the metal molar ratio (Fe/Co), indicative of the metal content dependent behavior. Theoretical calculations demonstrate that the electronic structure and charge distribution of iron–cobalt bimetallic alloy can be modulated and optimized, thus leading to the formation of an electron-rich interface layer, which likely tunes the d-band center and reduces the adsorption energy barrier toward electrocatalytic intermediates. As a result, the Fe0.25Co0.75/Co heterojunction exhibits superior OER activity with a low overpotential of 185 mV at 10 mA cm–2. Moreover, it can reach industrial-level current densities and excellent durability in high-temperature and high-concentration electrolyte (30 wt % KOH), exhibiting enormous potential for industrial applications.