Hydrated Electrons Bypass the -1.9 V Activation Barrier in Electrochemical CO₂ Reduction

Electrochemical CO₂ reduction is traditionally thought to require catalytic surfaces to overcome the high activation barrier of inert CO₂ molecules. Here, we demonstrate that in bicarbonate solutions, hydrated electrons (e^-_aq) generated at the CO₂ microbubble interfaces can activate CO₂ independently of catalysts or applied bias. Using spin-trapping mass spectrometry, we directly observe CO₂^•- radical intermediates (CO₂ + e^-_aq → CO₂^•-), while inert Pt electrode experiments confirm subsequent solution-phase CO generation (CO₂^•- + H⁺/^•H → CO + H₂O). Unexpectedly, in situ Raman spectroscopy reveals CO adsorption and C-H bond formation on Cu even at 0.6 V_RHE, approximately 2.0 V above the reported potential for CO₂ activation. The applied reduction potential (0-0.6 V_RHE, above the onset of the H⁺/H₂ reduction potential) modulates the interfacial e^-_aq/^•H concentration through oxidative radical scavenging, enabling solution-mediated hydrogenation. These findings establish an unprecedented model in which electrolyte-driven processes operate in parallel with conventional surface electrocatalysis, challenging long-standing assumptions about the necessity of catalytic surfaces for CO₂ activation.