Interaction between neighboring sulfur vacancies facilitates highly efficient nitrogen fixation in single-layer FeNiP2S6-x

Abstract

Iron-based transition metals, particularly iron-based thiophosphates, have attracted significant interest due to their ability to regulate iron electronic states through surface defect engineering. In this work, we fabricated and subsequently exfoliated single-layer FeNiP₂S_6-x (SL-FeNiP₂S_6-x), where mild and selective B(OH)₃ etching generated a disordered distribution of surface sulfur vacancies (SVs) for efficient nitrogen reduction reactions (NRR). Single-layer theoretical calculations suggest that interactions between neighboring SVs significantly enhance nitrogen fixation, with single-double sulfur vacancy (S-DSV) interactions causing the most pronounced shift in the d-band center of iron atoms towards the Fermi level. The improved alignment between the production rates of *NN and *H indicates that S-DSV enhances the catalytic activity of FeNiP₂S_6-x more effectively than single-single sulfur vacancy (S-SSV) or double-double sulfur vacancy (D-DSV), and far outperforms isolated SSV or DSV. Electrochemical tests demonstrated that in a 0.1 M KOH solution at −0.1 V, SL-FeNiP₂S_6-x with a sufficient concentration (>50 %) of S-DSV achieved a Faraday efficiency (FE) of 51.30 % and an NH₃ yield of 96.52 μg h⁻¹ mg⁻¹, surpassing the performance of previously reported NRR catalysts. This work introduces a useful strategy for enhancing electrocatalytic activity by strategically manipulating the position and distribution of adjacent non-metal atom vacancies on the surface.