CO2 electrosorption: electric field effect on the metal–CO2 dipole

Electrosorption of CO2 at metal electrodes is a critical elementary step controlling the electrochemical CO2 reduction, yet its physical origin remains debated. Field-induced stabilization of adsorbed CO2 is commonly attributed to interaction between the applied electric field and the intrinsic molecular dipole of CO2. Here, using density functional theory (DFT) with an explicit external electric field, we re-examine this paradigm by systematically studying CO2 electrosorption on FCC(111) surfaces of Ag, Au, Cu, Ir, Pb, and Pt. We identify a clear electric-field-driven transition between physisorbed and chemisorbed CO2. Physisorption preserves a near-linear geometry with negligible charge transfer and weak field dependence, whereas chemisorption involves pronounced bending, substantial electron transfer from the metal, and strong stabilization at increasing negative fields. We show that this switching cannot be explained by the molecular CO2 dipole alone. Instead, it is governed by interaction of the electric field with an interfacial metal–CO2 dipole formed upon charge transfer. This interpretation provides a physically grounded reinterpretation of CO2 electrosorption and clarifies how strong interfacial fields drive the transition from physisorption to chemisorption.