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

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.

Automated summary

This study used first-principles density functional theory (DFT) calculations to understand the mechanisms governing the electrocatalytic conversion of reaction intermediates in nonaqueous Mg-CO2 batteries with molybdenum carbide (Mo2C) as a cathode catalyst. It was found that MgC2O4 is a favorable discharge product, but is expected to decompose into MgCO3, MgO, and C. The higher charge transfer in the case of MgC2O4 suggests its lower nucleation overpotential. The electrochemical free energy profiles of the most favorable reaction pathways were calculated, showing discharge and charge overpotentials of 1.15 V and 0.38 V, respectively. The study highlights the importance of catalyst design for overcoming performance bottlenecks in rechargeable nonaqueous Mg-CO2 batteries.