Nanostructured Fe-Doped Ni₃S₂ Electrocatalyst for the Oxygen Evolution Reaction with High Stability at an Industrially-Relevant Current Density

A novel oxygen evolution reaction (OER) electrocatalyst was prepared by a synthesis strategy consisting of the solvothermal growth of Ni₃S₂ nanostructures on Ni foam, followed by hydrothermal incorporation of Fe species (Fe-Ni₃S₂/Ni foam). This electrocatalyst displayed a low OER overpotential of 230 mV at 100 mA·cm^-2, a low Tafel slope of 43 mV·dec^-1, and constant performance at an industrially relevant current density (500 mA·cm^-2) over 100 h in a 1.0 M KOH electrolyte, despite a minor loss of Fe in the process. Based on a detailed characterization by (in situ) Raman spectroscopy, (quasi-in situ) XPS, SEM, TEM, XRD, ICP-AES, EIS, and C_dl analysis, the high OER activity and stability of Fe-Ni₃S₂/Ni foam were attributed to the nanostructuring of the surface in the form of stable nanosheets and to the combination of Ni₃S₂ granting suitable electrical conductivity with newly formed NiFe-based (oxy)hydroxides at the surface of the material providing the active sites for OER.