Electrocatalytic Activity of Bimetallic Transition Metal Oxides for O₂ Evolution Reactions

O2 evolution reaction at the anodic half-cell forms the bottleneck for the electrochemical water-splitting reaction. Efficient electrocatalysts composed of earth-abundant materials are needed to improve the overall efficiency of the water-splitting reaction. In this study, we have explored the catalytic efficiency of a class of acid-stable bimetallic oxides with the molecular formula M1M2O3. We have considered four oxides, CoNiO3, FeNiO3, MnCoO3, and MnNiO3. Among the different surface terminations, 001 surfaces are found to be the most stable. Using the Bader charge partitioning scheme and comparison with monometallic oxides at +2, +3, and +4 oxidation states, we have characterized that the metal ions M1 and M2 at M1M2O3 are at +2 and +4 oxidation states, respectively. The density functional theory calculations are performed to understand the favored reaction pathways. We find that most of the surfaces with an adsorbate evolution mechanism (AEM) show lower overpotential in comparison to the lattice oxygen mechanism (LOM). The interaction of the surface lattice O with the reaction intermediates reduces the binding affinity of the intermediates. The crystal orbital Hamiltonian population and projected density of states analysis have been done to understand the orbital interactions and bonding picture of adsorbed O* intermediate, essentially determining the preference for the AEM vs LOM pathway. The potential dependent kinetic descriptor Gmax(η) is used to identify the rate-determining steps on the different surface active sites. We have found four surfaces with the reaction overpotential varying between 0.5 to 1 V at the acidic pH. The 001 surface of CoNiO3 shows the lowest overpotential of 0.53 V with Co as the active site.