Coupled sulfur vacancies enhance oxygen evolution reaction in monolayer FeNiP2S6-x

Abstract

High-efficiency and low-cost oxygen evolution reaction (OER) catalysts are essential for advancing water electrolysis technologies. Transition metal thiophosphates (TMPSs) have garnered considerable interest in the OER field due to their ability to modulate the electronic states of active atoms through surface defect engineering. In this study, monolayer theoretical calculations reveal that the interaction between adjacent single-double sulfur vacancies (S-DSVs) significantly alters the electronic structure of phosphorus atoms, thereby tuning the binding strength with reaction intermediates and effectively lowering the energy barrier of the rate-determining step. As a result, S-DSVs outperform isolated single sulfur vacancies (SSVs) and double sulfur vacancies (DSVs). Single-layer FeNiP₂S_6-x (SL-FeNiP₂S_6-x) catalysts with uniformly distributed S-DSVs were successfully synthesized via a mild and selective etching process using B(OH)₃. Electrochemical measurements demonstrate that SL-FeNiP₂S_6-x with an optimized S-DSV concentration delivers excellent OER performance, achieving a low overpotential of 171 mV at 10 mA cm^-2 and a Tafel slope of 38 mV dec^‑1 in 1 M KOH—surpassing most reported iron/nickel-based OER catalysts. This work introduces a novel strategy for enhancing electrocatalytic activity by precisely controlling the position and distribution of sulfur vacancies through controllable etching.