Hydrated Electrons Bypass the −1.9 V Activation Barrier in Electrochemical CO 2 Reduction

Electrochemical CO 2 reduction is traditionally thought to require catalytic surfaces to overcome the high activation barrier of inert CO 2 molecules. Here, we demonstrate that in bicarbonate solutions, hydrated electrons (e – aq ) generated at the CO 2 microbubble interfaces can activate CO 2 independently of catalysts or applied bias. Using spin-trapping mass spectrometry, we directly observe CO 2 •– radical intermediates (CO 2 + e – aq → CO 2 •– ), while inert Pt electrode experiments confirm subsequent solution-phase CO generation (CO 2 •– + H + / • H → CO + H 2 O). 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 CO 2 activation. The applied reduction potential (0–0.6 V RHE, above the onset of the H + /H 2 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 CO 2 activation.