Ionized Water Facilitates the Sustainable Radical‐Mediated Reduction of CO ₂ to Multi‐Carbon Hydrocarbons and Oxygenates

Abstract The abiotic synthesis of organic compounds from CO 2 and water under prebiotic conditions is a fundamental yet unresolved challenge in understanding the origins of life. Here we demonstrate a radical‐mediated pathway for reducing CO 2 to C 1 ‒C 6 hydrocarbons and oxygenates driven solely by ultraviolet (UV) irradiation of water, mimicking early Earth environments. Using electron paramagnetic resonance (EPR), 17 O/ 13 C isotope labeling, and femtosecond transient absorption, we identify ionized water‐derived radicals (H 2 O •+ , • OH, e⁻ aq , • H) as the key redox mediators. e⁻ aq acts as a super‐reductant (−2.9 V) to activate CO 2 into CO 2 • ⁻, while • H enables sequential hydrogenation. Critically, oxidative radicals (H 2 O •+ and • OH) recycle recalcitrant oxygenates (formate and oxalate) back into active CO 2 • ⁻, sustaining a dynamic radical network. This process generates a diverse library of organic compounds, including methane, ethylene, and C 6 dimethyl succinate, via radical assembly mechanisms spanning hydrogen‐atom transfer (HAT), self‐coupling, and cross‐coupling. By integrating experimental validation with prebiotic simulations (formate‐mediated redox modulation), we resolve the paradox of inert CO 2 /H 2 activation in primordial environments and establish water not merely as a solvent but as a reactive matrix directing abiotic organic synthesis.