Advancing next-generation nonaqueous Mg–CO2 batteries: insights into reaction mechanisms and catalyst design

Abstract

Mg–CO₂ batteries are an attractive candidate for next-generation energy storage systems; however, a lack of in-depth understanding of the intricate electrochemical reaction mechanisms during charging and discharging processes poses a significant obstacle to their progress. We aim to bridge the knowledge gap and accelerate the development of nonaqueous Mg–CO₂ batteries. We employed first-principles density functional theory (DFT) calculations to gain a detailed understanding of the mechanisms governing the electrocatalytic conversion of reaction intermediates, considering molybdenum carbide (Mo₂C) as an archetypical cathode catalyst. MgC₂O₄ is expected to nucleate as the discharge product due to its lower overpotential relative to MgCO₃. The Gibbs free energy changes associated with the splitting reactions of MgC₂O₄ were investigated and it was found that while it is thermodynamically favorable as a discharge product, it is anticipated to decompose into MgCO₃, MgO, and C. The higher charge transfer found in the case of MgC₂O₄ suggests its lower nucleation overpotential. We investigated the electrochemical free energy profiles of the most favorable reaction pathways and calculated discharge and charge overpotentials of 1.15 V and 0.38 V, respectively. Our findings emphasize the critical role of catalyst design for the cathode material to overcome performance bottlenecks in rechargeable nonaqueous Mg–CO₂ batteries.