Tuning CoFe and NiFe spinel oxide compositions by a fast glycine-nitrate autocombustion for oxygen evolution electrocatalysts and implications from their cyclic voltammograms on the role of Fe

Abstract

The last decade has witnessed a strong research interest toward CoFe and NiFe-based electrocatalysts for oxygen evolution reaction in alkaline solution. Herein, CoFe and NiFe spinel oxide solid solutions with different Fe/M (M: Co or Ni) ratios are produced by a fast autocombustion reaction between glycine and the metal nitrates. The CoFe and NiFe spinel oxide powders are characterized by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM), and Energy-Dispersive X-ray Spectroscopy(EDS); then the catalysts are studied by Cyclic Voltammetry (CV) in 1 M KOH solution. The CV curves reveal that the CV signatures and the corresponding OER activities for both systems are crucially affected by the Fe content. The OER overpotential versus Fe at.% curves show minima at around 17 at.% and 20 at.% Fe for NiFe oxide and CoFe oxide, respectively. Furthermore, it is found that for NiFe oxide the minimum overpotential coincides with the maximum CV mid-peak potential, while for the CoFe oxide the mid-peak potentials monotonically increase without a maximum. The CV studies of the underlying synergistic intermetallic effects imply that the Co2+ and Ni2+ centers act as the active OER centers, and the Fe ions modify their redox and OER activities.