Boosting oxygen evolution kinetics via sulfur/phosphorus dynamic migration induced surface enrichment in an anion-regulated iron selenide

Abstract

Optimizing the energetics of the elementary steps of Oxygen Evolution Reaction (OER) by tuning the electrode-intermediate/product interaction through d-band center energy tailoring is an essential yet under-explored concept in oxygen electrocatalysis. Herein, the interplay between sulfur/phosphorus and selenium toward improved OER kinetics is investigated and the synergistic interaction between these task-specific anions along with additional metal–anion interaction provides suitable tailoring of the d-band center for facilitating efficient electrocatalysis. S/P regulation of FeSe₂ resulted in a transition from high-spin Fe^2+/3+ to intermediate-spin Fe^2+/3+ affording simultaneous adsorption/desorption optimization leading to ultralow overpotentials of <300 mV at a current density of 600 mA cm⁻² [376 A g⁻¹] with highly stable performance for 50 h. These improvements stem from the strong electronic modulation arising from anion regulation-induced electron transfer and anion vacancies due to the dynamic migration of P/S to the outermost electrode surface during OER. This dynamic migration brings forth surface enrichment of S/P anions, endowing a hydrophilic surface for accelerating OH⁻ adsorption while the Se-rich core facilitates the desorption of oxygen via reinforced electron repulsion between metal/Se d-band and oxygen p-band electrons. This work paves the way for optimizing oxygen electrocatalysis through descriptor-guided tuning from an experimental standpoint by introducing functional task-specific elements.