Mechanistic insights into CO2 capture and electrochemical conversion in nonaqueous Na–CO2 batteries

Abstract

Developing efficient energy storage systems that capture and convert CO₂ is critical for mitigating carbon emissions. Here, we report a Na–CO₂ battery with ruthenium dioxide (RuO₂) cathode catalysts and propane-1,3-diamine (PDA) as an electrolyte additive to enhance CO₂ capture and conversion efficiency. The integration of CO₂ adsorption and electrochemical reduction facilitates activation of the inert CO₂ molecule and circumvents gas–solid–liquid ternary-phase reactions at the interface. We employed density functional theory (DFT) calculations to systematically unravel the reaction mechanisms and energetics governing CO₂ reduction, both with and without PDA. Our results reveal an energetically favorable pathway toward the formation of Na₂CO₃ and C as final discharge products, rather than sodium oxalate (Na₂C₂O₄). The CO₂–amine adduct facilitates charge transfer from PDA to CO_2, which results in activation of CO₂. The kinetics of CO₂ conversion and regeneration of PDA were found to be significantly enhanced on the RuO₂ surface compared to the bulk electrolyte. More importantly, pre-activation of CO₂via the amine–CO₂ adduct lowers the total overpotential to 2.44 V, compared to 3.13 V without PDA. This study provides fundamental insights into CO₂ electroreduction in Na–CO₂ batteries and underscores the promise of electrolyte engineering for sustainable CO₂ utilization and high-performance energy storage.