Porous Palladium Nanoparticles-Modified Copper Foam Enhances the Adsorption Energy of Key Intermediate *LiCO ₃ to Aid Li-CO ₂ Batteries with Ultralow Overpotential and Resistance to 0 °C

Rechargeable Li-CO₂ batteries are attractive for next-generation energy storage owing to their high theoretical energy density and capability for CO₂ utilization. However, their practical application is hindered by sluggish reaction kinetics, large polarization, and poor cycling stability associated with the reversible formation and decomposition of Li₂CO₃. Herein, we report a free-standing cathode consisting of palladium nanoparticles uniformly anchored on copper (Pd NPs@Cu) foam, fabricated via a facile one-step galvanic displacement-assisted deposition strategy. The three-dimensional porous architecture combined with highly dispersed Pd nanocatalysts enables enhanced catalytic activity and mass transport, thereby effectively accelerating both CO₂ reduction and evolution reactions. The Pd NPs@Cu foam composite delivers a high discharge capacity exceeding 15,000 mAh g^-1, excellent rate capability (up to 2000 mA g^-1), and outstanding cycling stability with an ultralow overpotential of ∼0.36 V over 160 cycles (1600 h) at 25 °C and 200 mA g^-1. Even at the high current density of 1000 mA g^-1, stable cycling over 141 cycles is achieved with a low overpotential of ∼0.6 V. Notably, the system demonstrates robust low-temperature performance, sustaining 64 cycles at 0 °C (250 mA g^-1) with charge potentials below 4.0 V in the conventional ether-based electrolyte without any additives. Mechanistic investigations combining in situ electrochemical impedance spectroscopy coupled with distribution of relaxation times (in situ EIS-DRT) analysis and ex situ structural characterizations (SEM, XRD, FTIR, and XPS) confirm the highly reversible formation and decomposition of Li₂CO₃ and reveal that charge-transfer processes dominate the reaction kinetics. Density functional theory (DFT) calculations further demonstrate that Pd incorporation significantly strengthens the adsorption of key intermediate *LiCO₃, thereby lowering the reaction energy barriers and overall polarization along the four-electron pathway. These findings highlight the synergistic effect of Pd nanocatalysts and conductive porous Cu foam framework in promoting efficient and reversible CO₂/Li₂CO₃ conversion.