The adsorption of carbon dioxide on Pd-Pt alloy electrodes in acidic solution has been studied. The influence of both bulk and surface composition of the alloy on CO2 adsorption is presented. The results obtained suggest that only hydrogen interacting with platinum atoms is active in reaction with CO2. At the same time these platinum atoms are inactive in the hydrogen absorption/desorption process. The latter reaction probably proceeds only with participation of palladium atoms, unblocked by products of adsorption of CO2.