Modulation of the electronic structure of NiS₂/NiS <i>via</i> Fe and Mn dual-doping to boost the oxygen evolution reaction

Doping in transition metal sulfides can effectively induce lattice distortion and introduce asymmetry, thereby lowering the energy required to overcome the rate-controlling step in the oxygen evolution reaction (OER). This work presents a simple hydrothermal synthesis strategy combined with vapor-phase vulcanization to prepare iron and manganese dual-doped NiS₂/NiS nanoflowers with a heterogeneous interface, directly supported on nickel foam (NF). In this approach, NF was adopted not only as a self-supporting conductive substrate but also as the nickel source for the composite. The as-prepared FeMn-NiS₂/NiS/NF (FM-NiS₂/NiS/NF) exhibits superior OER performance, requiring an ultra-low overpotential of 107 mV at a current density of 10 mA cm^-2 and demonstrating a low Tafel slope of 87.4 mV dec^-1 in an alkaline medium. Additionally, the catalyst shows a robust durability, maintaining stable activity after 48 hours of continuous operation, illustrating its high value as a highly efficient OER electrocatalyst. These vigorous OER kinetics primarily originate from the synergistic effects of the NiS₂/NiS heterojunction, which provides abundant electroactive sites, and the optimized electronic structure induced by Fe and Mn dual-doping. X-ray photoelectron spectroscopy analysis further reveals an increase in high-valence metal states Mn⁴⁺ and an oxidation of Ni²⁺ to Ni³⁺ during the OER process, contributing significantly to the acceleration of the electrochemistry kinetics. Moreover, density functional theory simulations revealed that the cooperative interaction between bimetallic doping and sulfide matrix efficiently tuned the electronic structure and adjusted the d-band center to a more favorable position. This work demonstrates a promising strategy to design high-performance water-splitting catalysts <i>via</i> dual-metal doping and heterointerface engineering.