Irreversible adsorption of palladium on Pt(100) and Pt(111) is used to form electrocatalysts combining two catalytic elements. Their electrocatalytic activity towards formic acid oxidation is examined. A dramatic effect of the presence of adsorbed palladium on Pt(100) on this reaction is observed with a considerable lowering of the oxidation potential and the absence of self-poisoning on open circuit. In contrast, the activity of the Pt(111) substrate is not greatly changed by adsorbed Pd. A deactivation of the Pd-ad + Pt(100) electrocatalyst is observed when the oxidation of formic acid takes place, suggesting a slow step in the formation of an adsorbed species which blocks the adsorption of formic acid as a first step of the overall reaction. At all palladium coverages of Pt(100), even with a multilayer of palladium, the activity of the modified electrode towards the electro-oxidation of formic acid was found to be higher than that of bulk palladium.