First-Principles Investigation of CO2 Electrochemical Reduction on Space-Confined Sn Catalyst Surfaces

The formation of C3 species through electrochemical CO2 reduction is challenging because it requires multiple protonation steps and sequential C–C bond formation. In this study, Density Functional Theory calculations were performed to investigate the effect of spatial confinement on the reaction pathway and energetics of electrochemical CO2 conversion on Sn(100). A comparison of Sn(100) models with nominal intersurface spacings of 12 and 6 Å showed that direct coupling between two CO* intermediates did not result in the formation of a stable COCO* intermediate. Instead, COH*, formed through the protonation of CO*, was identified as a key intermediate in sequential C–C coupling. The resulting pathway involves an initial C–C coupling step, CO* + COH* → COCOH*, followed by a second coupling step, COH* + COCOH* → COH(CO)COH*, leading to the formation of a C3 intermediate. Decreasing the nominal intersurface spacing from 12 to 6 Å lowered the activation barriers and reaction energies for CO2 activation, COH* formation, and sequential C–C coupling. These results indicate that spatial confinement modifies the energetics of key intermediates, thereby facilitating C3 intermediate formation on Sn(100).