Electrochemical Oxygen Evolution Reaction on NixFe3-xO4 (0 ≤ x ≤ 1.0) in Alkaline Medium at 25ºC

Abstract

Spinel ferrites (NixFe3-xO4; x = 0.25, 0.5, 0.75 and 1.0) have been prepared at 550ºC by egg white auto-combustion route using egg white at 550ºC and characterized by physicochemical (TGA, IR, XRD, and SEM) and electrochemical (CV and Tafel polarization) techniques. The presence of characteristic vibration peaks in FT-IR and reflection planes in XRD spectra confirmed the formation of spinel ferrites. The prepared oxides were transformed into oxide film on glassy carbon electrodes by coating oxide powder ink using the nafion solution and investigated their electrocatalytic performance for OER in an alkaline solution. The cyclic voltammograms of the oxide electrode did not show any redox peaks in oxygen overpotential regions. The iR-free Tafel polarization curves exhibited two Tafel slopes (b1 = 59–90 mV decade−1 and b2 = 92–124 mV decade−1) in lower and higher over potential regions, respectively. Ni-substitution in oxide matrix significantly improved the electrocatalytic activity for oxygen evolution reaction. Based on the current density for OER, the 0.75 mol Ni-substituted oxide electrode was found to be the most active electrode among the prepared oxides and showed the highest value of apparent current density (~9 mA cm−2 at 0.85 V) and lowest Tafel slope (59 mV decade−1). The OER on oxide electrodes occurred via the formation of chemisorbed intermediate on the active sites of the oxide electrode and follow the second-order mechanism.