Enhancing the Surface-Active Sites of Bimetallic 2D Hydroxide Materials by Introducing Fe2+ Ions toward Effective Hydroxide Adsorption for the Water Oxidation Reaction

Here, in this work, via a simple wet chemical method, we have modified the CoFe layered double hydroxide (LDH) surface by doping active Fe2+ ions which function as an excellent electrocatalyst for the oxygen evolution reaction (OER) in 1 M KOH. Variations in the amount of Fe2+ ions show a noteworthy concentration dependency on the electrochemical performance of the catalyst. The catalyst shows an interesting Fe2+ ion dependency toward the OER, and a volcanic relationship between accumulated electronic charge and thermoneutral current densities is observed. This volcanic relation shows that with an optimum concentration of Fe2+ ions, the catalyst could effectively catalyze the OER by following the Sabatier principle of ion adsorption. The LDH having an intermediate amount of Fe2+ loading {FeII-LDH (0.04 M)} shows the highest OER activity, and it demands just a 268 mV overpotential to drive a 10 mA/cm2 current density, whereas the pristine CoFe-LDH displays an overpotential of 345 mV. Also, as a result of introducing Fe2+ ions, a 4-fold increase in the turnover frequency (TOF) value was noticed. Operando in situ impedance analysis reveals that the introduction of Fe2+ ions in the pristine CoFe-LDH lattice largely improvises the charge transfer kinetics at the interface by providing a greater number of surface-active sites toward OH– adsorption. Overall, this study shows an interesting Fe2+ ion loading dependency over the LDH surface toward the water oxidation reaction.