S–N Co-doped Carbon-Inducing Electronic Rearrangement in NiFe ₂ O ₄ for Enhanced Oxygen Evolution Reaction Kinetics

To address the challenges of conductivity and stability faced by inverse spinel NiFe₂O₄ in the oxygen evolution reaction (OER), this study developed a porous NiFe₂O₄/SNC composite material supported on S-N co-doped carbon. The material, prepared via a simple one-step pyrolysis method, exhibits an overpotential of only 212 mV at a current density (<i>j</i>) of 10 mA cm^-2. Furthermore, after 175 h of chronopotentiometry testing at a high <i>j</i> of 100 mA cm^-2, the potential decay is only 2.3%, outperforming most reported values in the literature. The excellent performance of the NiFe₂O₄/SNC composite is attributed to the fact that its porous structure provides a fast channel for mass transfer and exposes more reaction sites; the N-doped carbon substrate enhances its electrical conductivity and stability, while S doping synergistically regulates its electronic structure. In addition, electron-rich Ni²⁺ accelerates the formation of Ni(Fe)OOH, which can be confirmed by <i>in situ</i> Raman/Bode analysis, while electron-deficient Fe³⁺ significantly reduces the kinetic barrier of the rate-limiting step (* → *OOH) by stabilizing the *O/*OOH intermediate, which can be validated by density functional theory calculations. This work provides insights for the design of high-performance OER catalysts.