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The development of efficient earth-abundant catalysts through scalable synthesis routes remains a critical challenge for advancing rechargeable lithium-CO2 (Li‒CO2) batteries. Herein, a facile synthesis strategy was developed by directly introducing Fe atoms into phosphomolybdic acid (PMA), followed by calcination at temperatures between 300 and 600 °C to optimize catalyst structure and performance. This approach produced two distinct catalyst families: Fe phosphomolybdate (FePMA), which preserves the Keggin ion structure, and FeMoO, a molybdenum trioxide-iron phosphate (MoO3/FePOx) composite formed at higher temperatures. Benefiting from abundant redox-active centers, the FeMoO-500 catalyst exhibited a high discharge capacity of 26,110 mAh g−1, with a coulombic efficiency of 93% and high stability of 92 cycles at a current density of 50 mA g−1. It also effectively facilitated the CO2 reduction/evolution reactions, displaying a very low overpotential of 0.8 V. Meanwhile, FePMA-300 also demonstrated good catalytic activity, achieving a high discharge capacity of 20,300 mAh g−1 and an overpotential of 0.9 V, thanks to its intact Keggin structure that hosts a rich network of Fe and Mo redox sites. This study introduces FePMA and FeMoO as cathode catalysts in Li‒CO2 batteries for the first time and sheds light on their potential applications in other CO2 conversion technologies.

Rechargeable lithium-CO2 batteries are emerging as attractive energy storage devices due to their potential for high capacity and efficient CO2 reduction, making them promising candidates for post-lithium-ion batteries with high energy densities. However, their practical applications have been restricted by low reversibility, poor cycle life, and sluggish redox kinetics induced by the high potential required for decomposing the discharge product Li2CO3. Despite the various cathode catalysts explored, their application is often limited by availability, high cost, and complexity of synthesis. Herein, caesium phosphomolybdate (CPM) is synthesized through a facile and low-cost method. The Li‒CO2 battery based on the CPM cathode demonstrates a high discharge capacity of 15,440 mAh g-1 at 50 mA g-1 with 97.3% coulombic efficiency. It further exhibits robust stability, operating effectively over 100 cycles at 50 mA g-1 with a capacity limitation of 500 mAh g-1. Remarkably, the CPM catalyst yields a low overpotential of 0.67 V, surpassing most catalysts reported in prior research. This study reports, for the first time, the application of a Keggin-type polyoxometalate as a bifunctional redox catalyst, significantly improving the reversible cycling of rechargeable Li–CO2 batteries.