Understanding Catalytic Mechanisms and Cathode Interface Kinetics in Non-Aqueous Mg-CO2 Batteries

We leverage first-principles density functional theory (DFT) calculations to understand the electrocatalytic processes in Mg-CO2 batteries, considering ruthenium oxide (RuO2) as an archetypical cathode catalyst. Our goal is to establish a mechanistic framework for understanding the charging and discharging reaction pathways and their influence on overpotentials. Interestingly, we discover that Mg adsorption energies are enhanced, leading to the activation of CO2. On the RuO2 (211) surface, we predict that MgC2O4 will form as the discharge product due to its lower overpotential compared to MgCO3. However, MgC2O4 is thermodynamically unstable and expected to decompose into MgCO3, MgO, and carbon (C) as final discharge products. Through Bader charge analysis, we investigate the covalent interactions between intermediates and catalyst sites. We find that CO2 is inactivated due to negligible electron transfer, making the formation of carbonate (CO32-) and oxalate (C2O42-) intermediates thermodynamically unfavorable. Moreover, we study the electrochemical free energy profiles of the most favorable reaction pathways and determine discharge and charge overpotentials of 1.30 V and 1.35 V, respectively. Our results underscore the importance of catalyst design for the cathode material to overcome performance limitations in non-aqueous Mg-CO2 batteries.