First principles investigation of the redox behavior of the VCo₂O₄ (001) surface

Due to the increased interest in vanadium cobaltite (VCo2O4) as a significant component of various catalysts, we have decided to investigate how its primary surfaces respond to oxidation and reduction processes. Our study employed computational modelling based on density functional theory to assess various surface types of geometries and surface free energies. This includes the stoichiometric plane and those containing either insufficient or excessive amounts of oxygen atoms. The most stable surface in the crystal is the (001) orientation. The crystal has an equilibrium morphology that resembles a cube with rounded corners. In our analysis, we identified the surface free energies of the most stable VCo2O4 (001) surface when oxygen atoms are adsorbed and reduced. The adsorption of oxygen atoms ensures the stability of the system, while their reduction causes it to become unstable. We analysed the oxygen adsorption (Γ= +1, +2) and vacancy formation energies (Γ= −1, −2); however, upon adsorption, we noticed the exothermic behaviour with decreasing adsorption energies. Conversely, the vacancy formation demonstrates an endothermic behaviour with increasing energies as oxygen atoms are reduced. The Bader charge provides insights into the interactions between atoms within a system. The reduction and adsorption of oxygen atoms result in minimal changes in the charge of the V and Co atoms, whether they are oxidized or reduced, compared to their original state. The interplanar distances indicate that the introduction of an oxygen atom leads to an expansion of the system, while its removal causes the system to contract. Understanding the work function aids in determining the system's level of reactivity. The presence of oxygen atoms reduces the system's reactivity, while their absence enhances it. We investigated and described the changes in the magnetic moment as the surface coverage increased. The findings will assist us in identifying a catalyst that can enhance the performance of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), ultimately improving the efficiency of Zn-air batteries.