Rechargeable lithium–carbon dioxide (Li–CO₂) batteries have attracted significant attention as next-generation energy storage systems due to their high theoretical energy density and ability to utilize CO₂. However, their practical application is hindered by slow reaction kinetics, large charge–discharge voltage gap, poor reversibility, and short cycling lifetimes. The primary aim of this research was to enhance the electrochemical performance and stability of Li–CO₂ batteries through the rational design of efficient, durable, and low-cost cathode catalysts capable of accelerating the CO₂ reduction and evolution reactions (CRR/CER).

To achieve this, transition-metal-based phosphomolybdate catalysts were synthesized and systematically evaluated. Cesium phosphomolybdate (CsPM) was first introduced as a cathode catalyst, delivering a high discharge capacity of 15,440 mAh g^-1 at 50 mA g^-1, a low overpotential of 0.67 V, and stable cycling over 100 cycles under capacity-limited conditions. To further enhance catalytic performance through the introduction of additional active sites, a controlled thermal treatment strategy was developed to incorporate Ni, Co, and Fe into phosphomolybdic acid (PMA), producing two catalyst families: metal-substituted phosphomolybdates (MPMA) and novel mixed oxide composites (MoO₃/MPO_x).

Among the Ni- and Co-based derivatives, Ni-containing materials demonstrated superior catalytic activity, with NiMoO-500 achieving 22,320 mAh g⁻¹ compared to 16,150 mAh g⁻¹ for CoMoO-500. The Fe-based catalysts exhibited the most balanced and optimized performance overall. In particular, FeMoO-500 delivered the highest discharge capacity of 26,110 mAh g⁻¹ with a low overpotential of 0.8 V, enhancing reaction kinetics in Li–CO₂ batteries. Beyond electrochemical performance, iron offers advantages in abundance, cost, and environmental compatibility, making Fe-based catalysts the most sustainable option identified. Overall, this work demonstrates that transition-metal-incorporated phosphomolybdates, especially Fe- and Ni-based systems, effectively enhance reaction kinetics and electrochemical performance in Li‒CO₂ batteries, providing practical design strategies for sustainable CO₂-utilizing energy storage technologies.