Hyper-electronegativity fluorine induced electron localization enables highly efficient and stable oxygen evolution electrocatalysis on VO-rich cobalt–iron oxides

Abstract

While abundant oxygen vacancies (V_O) in CoFe oxides can significantly enhance oxygen evolution reaction (OER) activity, they often suffer from instability under high-current electrolysis. To address this issue, we use a stepwise method to introduce F into CoFeO_x with abundant V_O grown on nickel foam (denoted as F-CoFeO_x-V_O/NF) to induce partial electron localization. Due to highly active, low-valence metal sites and stable V_O, F-CoFeO_x-V_O/NF exhibits robust structural and compositional stability toward highly efficient and durable OER electrocatalysis, showing a low overpotential of 201 mV at 10 mA cm⁻² in 1.0 M KOH solution and exhibiting continuous operation for 600 h for overall water splitting. Density functional theory calculations reveal that hyper-electronegativity F atoms are capable of weakening the covalency of Co–O and Fe–O bonds, thereby inducing the partial localization of Co and Fe 3d electrons nearby. This electronic modulation facilitates directional charge transfer toward V_O sites and yields a stabilized electron-rich V_O, which gives rise to both enhanced OER activity and stability.