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 (VO) 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 CoFeOx with abudant VO grown on nickle foam (denoted as F-CoFeOx-VO/NF) to induce partial electron localization. Due to highly active low valence metal sites and stable VO, the F-CoFeOx-VO/NF shows 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 aqueous solution and maintaining continuous operation of 600 h for overall water splitting. Density functional theory calculations reveal that hyper-electronegativity F atoms are capable of weakening the covalency 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 VO sites and yields a stabilized electron-rich VO, which gives rise to both enhanced OER activity and stability.