Ethanol vapor-driven multicarbon chemistry enables high-performance Mg-CO₂ battery

Recent advancements in metal-CO₂ batteries with enhanced energy efficiency in a sustainable manner largely rely on catalytic improvements to accelerate the sluggish kinetics of the CO₂ reduction and evolution reactions (CO₂RR/CO₂ER) occurring at the multiphase interface. However, conventional solid and liquid catalysts often increase the adsorption of both reactant gas and solid-phase discharge products, lowering discharge overpotentials but impeding product decomposition during charging. This trade-off complicates efforts to simultaneously reduce charge-discharge overpotentials and improve overall battery efficiency. Here, we introduce an ethanol vapor-driven strategy for Mg-CO₂ batteries-distinct from traditional solid and liquid catalysis-that selectively enhances CO₂ adsorption while limiting the adsorption of discharge products. This approach enables high energy efficiency through the formation and decomposition of the first conductive organic multicarbon (C₂₊) product in metal-CO₂ batteries, specifically Mg(CH₃COO)₂·4H₂O. The Mg-CO₂ battery delivers outstanding discharge and charge capacities beyond 50 000 mAh g^-1, coupled with stable cycling over 600 h, ranking it the best Mg-CO₂ system reported to date. This catalyst-free strategy for multicarbon production holds potential for applications in CO₂ reduction and carbon fixation.