Recognizing the reactive sites of SnFeO for the oxygen evolution reaction: the synergistic effect of Sn and Fe in stabilizing reaction intermediates.

Among the reported spinel ferrites, the p-block metal containing SnFeO is scarcely explored, but it is a promising water-splitting electrocatalyst. This study focuses on the reaction kinetics and atomic scale insight of the reaction mechanism of the oxygen evolution reaction (OER) catalyzed by SnFeO and analogous FeO. The replacement of FeIIOh sites with SnIIOh in SnFeO improves the catalytic efficiency and various intrinsic parameters affecting the reaction kinetics. The variable temperature OER depicts a low activation energy () of 28.71 kJ mol on SnFeO. Experimentally determined second-order dependence on [OH] and the prominent kinetic isotope effect observed during the deuterium labelling study implies the role of hydroxide ions in the rate-determining step (RDS). Using density functional theory, the reaction mechanism on the (001) surface of SnFeO and FeO is modelled. The DFT simulated free energy diagram for the reaction intermediates shows an adsorbate evolution mechanism (AEM) on both the ferrites' surfaces where the formation of *OOH is the RDS on SnFeO while *O formation is the RDS on FeO. In contrast to other spinel ferrites, where individual metal sites act independently, in case of SnFeO, a synergy between FeIIIOh and the neighbouring SnIIOh atoms is responsible for stabilizing the OER intermediates, enhancing the catalytic OER activity of SnFeO as compared to isostructural FeO.