Unraveling Reaction Mechanisms of Mo2C as Cathode Catalyst in a Li-CO2 Battery

First-principles density functional theory calculations are first used to study possible reaction mechanisms of molybdenum carbide (Mo₂C) as cathode catalysts in Li-CO₂ batteries. By systematically investigating the Gibbs free energy changes of different intermediates during lithium oxalate (Li₂C₂O₄) and lithium carbonate (Li₂CO₃) nucleations, it is theoretically demonstrated that Li₂C₂O₄ could be stabilized as the final discharge product, preventing the further formation of Li₂CO₃. The surface charge distributions of Li₂C₂O₄ adsorbing onto catalytic surfaces are studied by using Bader charge analysis, given that electron transfers are found between Li₂C₂O₄ and Mo₂C surfaces. The catalytic activities of catalysts are intensively evaluated toward the discharge and charge processes by calculating the electrochemical free energy diagrams to identify the overpotentials. Our studies promote the understanding of electrochemical processes and shed more light on the design and optimization of cathode catalysts for Li-CO₂ batteries.