Double layer charging driven carbon dioxide adsorption limits the rate of electrochemical carbon dioxide reduction on Gold

Electrochemical CO₂ reduction is a potential route to the sustainable production of valuable fuels and chemicals. Here, we perform CO₂ reduction experiments on Gold at neutral to acidic pH values to elucidate the long-standing controversy surrounding the rate-limiting step. We find the CO production rate to be invariant with pH on a Standard Hydrogen Electrode scale and conclude that it is limited by the CO₂ adsorption step. We present a new multi-scale modeling scheme that integrates ab initio reaction kinetics with mass transport simulations, explicitly considering the charged electric double layer. The model reproduces the experimental CO polarization curve and reveals the rate-limiting step to be *COOH to *CO at low, CO₂ adsorption at intermediate, and CO₂ mass transport at high overpotentials. Finally, we show the Tafel slope to arise from the *CO₂-dipole-field interaction. In sum, this work highlights the importance of surface charging for electrochemical kinetics and mass transport.