The role of non-covalent interaction between both non-specifically adsorbed hydrated K+, Li+ and Ba2+ cations (M+) and hydroxyl species (M+-OHad) as well as underpotentially deposited Cu adatoms and OHad (Cu-upd-OHad) on bulk CO oxidation (COb) is investigated on Pt(111) and Pt(100) in alkaline solutions. The effect of Cu-upd-OHad on COb oxidation is observed almost at the reversible potential for CO oxidation, signaling that Cu-upd-induced adsorption of OHad activates COb oxidation at very low overpotentials. In contrast, the effect of M+-OHad was found to be strongly dependent on the surface coverage of OHad on Pt; e.g., while no effect is found when the surface is pre-covered by adsorbed CO (COad), a discernable effect is observed on OHad pre-covered Pt surface. (C) 2014 Elsevier Ltd. All rights reserved.