Ionized Water Facilitates the Sustainable Radical‐Mediated Reduction of CO2 to Multi‐Carbon Hydrocarbons and Oxygenates

The abiotic synthesis of organic compounds from CO2 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 CO2 to C1‒C6 hydrocarbons and oxygenates driven solely by ultraviolet irradiation of water, mimicking early Earth environments. Using electron paramagnetic resonance (EPR), 17O/13C isotope labelling, and femtosecond transient absorption, we identify ionized water‐derived radicals (H2O•+, •OH, e⁻aq, •H) as the key redox mediators. e⁻aq acts as a super‐reductant (‐2.9 V) to activate CO2 into CO2•⁻, while •H enables sequential hydrogenation. Critically, oxidative radicals (H2O•+ and •OH) recycle recalcitrant oxygenates (formate and oxalate) back into active CO2•⁻, sustaining a dynamic radical network. This process generates a diverse library of organic compounds, including methane, ethylene, and C6 dimethyl succinate, via radical assembly mechanisms spanning hydrogen‐atom transfer, self‐coupling, and cross‐coupling. By integrating experimental validation with prebiotic simulations (formate‐mediated redox modulation), we resolve the paradox of inert CO2/H2 activation in primordial environments and establish water not merely as a solvent, but as a reactive matrix directing abiotic organic synthesis.