Electrocatalysis by foreign metal monolayers: Oxidation of formic acid on palladium

Catalytic effects of foreign metal monolayers deposited at underpotentials have been found for the oxidation of formic acid on palladium electrode. Palladium is known to form no poisoning species in oxidation of HCOOH. However, the auto-inhibition of the reaction is found, caused most probably by a species _xC_x(OH)₂. Submonolayer amounts of Pb, Bi, Cd, Tl, Ag and Cu electrosorbed at underpotentials exhibited significant catalytic effects which could be explained by the so-called “third-body” effect in terms of a previously published semiquattitative model. The results have bearing on the understanding of the catalytic effects observed under comparable conditions on platinum and rhodium. Since these effects are orders of magnitude larger than those on palladium, the “third-body” effect probably plays only a minor role at the other two noble metals.