Enhanced electrocatalytic OER activity following electrochemical pre-cathodic treatment of Mn-substituted nickel ferrite

In this study, the electronic engineering of a high-valent active site for enhanced oxygen evolution reaction (OER) was achieved through the electrochemical pre-cathodic treatment method (EPCTM). This method involves applying a cathodic potential to the drop-cast working electrode of Mn-substituted nickel ferrite (Ni1−xMnxFe2O4; where x = 0.0, 0.2, and 0.4) electrocatalysts. X-ray photoelectron spectroscopy analysis revealed an increase in the ratios of Ni3+/Ni2+ and Mn3+/Mn2+ in Ni1−xMnxFe2O4 after EPCTM followed by OER, leading to an enhancement in electrochemical OER current density at 600 mV overpotential by 3.65 times for x = 0.0, 5.56 times for x = 0.20, and 4.72 times for x = 0.40. This enhancement was further supported by a decrease in the slope of the anodic Tafel equation after EPCTM, indicating improved efficiency of the interaction between the working electrode and electrolyte, as a lower Tafel slope suggests better charge exchange at the electrode–electrolyte interface. The positive slope in the Mott–Schottky (MS) plot for all Ni1−xMnxFe2O4 samples confirmed the p-type nature of the electrocatalysts. Additionally, the significant decrease in the slope of the linear portion of the MS plot indicated an increase in carrier concentration after electrochemical pre-cathodic treatment in all Ni1−xMnxFe2O4 samples. This increase in p-type carrier concentration supports the observed increase in the Ni3+/Ni2+ ratio for OER after EPCTM.