For the efficient and stable electrochemical reduction of carbon dioxide (CO2), we fabricated bimetallic catalysts composed of palladium (Pd) nanoparticles covered with copper (Cu) atomic layers. While a monometallic Pd nanoparticle catalyst has high activity toward the reduction of CO2 to formate, it has been reported to be readily subjected to self-poisoning by carbon monoxide (CO), which is produced as a minor byproduct of CO2 reduction. Cu layers prepared by underpotential deposition induced charge transfer from Pd to Cu and a downward shift of the average d-band center of the catalyst relative to the Fermi level. As a result, the Cu-modified Pd catalyst demonstrated improved CO tolerance and an increase in Faradaic efficiency for formate production without sacrificing CO2 reduction activity. (C) 2017 Elsevier Ltd. All rights reserved.