Optimizing the adsorption strength of oxygen intermediates on NiCo2O4 by Fe doping to improve the oxygen evolution reaction performance

Abstract

Spinel oxide ($\mathrm{NiC}{\mathrm{o}}_2{\mathrm{O}}_4$) is an attractive catalyst for oxygen evolution reaction (OER) due to its rich redox reactions and unique electronic structure. However, the electrocatalytic OER performance of $\mathrm{NiC}{\mathrm{o}}_2{\mathrm{O}}_4$ has always been limited by the low specific surface area and poor intrinsic conductivity of $\mathrm{NiC}{\mathrm{o}}_2{\mathrm{O}}_4$. Cationic doping is an effective method in modulating the electrocatalytic activity at the atomic level to improve the conductivity and activity. Herein, a series of Fe-doped $\mathrm{NiC}{\mathrm{o}}_2{\mathrm{O}}_4$ electrocatalysts were successfully prepared using a simple solvothermal method. Impressively, Fe-doped $\mathrm{NiC}{\mathrm{o}}_2{\mathrm{O}}_4$ delivers an attractive small overpotential of 341 mV at $10\mathrm{mA}\mathrm{c}{\mathrm{m}}^{-2}$ and a Tafel slope of $74\mathrm{mV}\mathrm{de}{\mathrm{c}}^{-1}$ compared to $\mathrm{NiC}{\mathrm{o}}_2{\mathrm{O}}_4$. The x-ray photoelectron spectroscopy and the density functional theory calculations reveal that Fe dopants can regulate the electronic structure of Ni sites by donating electrons to Co atoms, which leads to an increased $\mathrm{N}{\mathrm{i}}^{3+}$ ratio and a reduced adsorption strength of oxygen intermediates at Ni sites, thus facilitating the conversion of *OH to *O. This work provides an effective approach to enhancing the electrocatalytic activities of non-noble-metal-based catalysts.