Electrolytic ions are known to impact the rates of electrocatalytic reactions, though a molecular understanding of the mechanism of such impact is not well understood. We employ density functional theory to investigate the specific adsorption of potassium and iodine ions on Cu (111), Cu (100) and Cu (211) electrode surfaces under CO2 electroreduction (CO2 ER) conditions and explore their effect on the reaction energetics and binding strength of reaction intermediates. The calculated equilibrium potentials for K* and I* adsorption (* denotes surface-adsorbed species) suggest that a low coverage of adsorbed K* and/or I* is thermodynamically favorable, at different pH, at CO2 ER overpotentials. Co-adsorbed I* serves to primarily weaken CO* binding and may promote CO* desorption or subsequent formation of C-H bonds, phenomena that are typically obstructed by a high surface coverage of CO*. Co-adsorbed K* preferentially increases the binding strength of O-terminated species, including CO* and CHO* relative to COH*. The presence of K* will shift the selectivity and kinetics of CO* reduction towards the CHO* pathway by destabilizing the COH* formation transition state. The impact of solvation in conjunction with the effects of ion specific adsorption on the energetics of CO* reduction are also discussed. (C) 2016 The Electrochemical Society.