A combination of in situ XANES, temperature programmed oxidation, kinetic and density functional theory results demonstrate that the d-band centers (εd) of Au and Pt metals are upshifted when 39.9 V m-1 of electric field is applied. This leads to the enhancement of the adsorption strength of CO on both metals, and, thus, results in the promotion (+15%) and the depression (-23%) of CO conversions on Au and Pt, respectively, in the CO oxidation.