Electrocatalysis by Pb adatoms of HCOOH oxidation at Pt(111) in acidic solution

Abstract

Pt(111) possesses lower catalytic activity for the HCOOH oxidation in acidic solution than do Pt(100) and Pt(110), but in the presence of Pb adatoms, it shows strong catalytic action. Such a catalytic effect of Pb adatoms on Pt(111) has been investigated using cyclic voltammetry ( cv), differential electrochemical mass spectrometry (DEMS) and the modulated potential-time waveform ( mptw) technique, also with the “solution substitution” experiments. It was found that: 1. (1) the adsorbed Pb(0)/Pb(II) redox couple remains on the surface during at least several potential cycles in 0.1 M HClO 4 and Pb(0) shows strong catalytic action; 2. (2) less than one third of Pb monolayer is enough to develop the catalytic action and retards the formation of poisonous CO; 3. (3) an abrupt change in the oxidation current occurs corresponding to the change in the Pb oxidation state at the ‘transient region’ potential; and 4. (4) the catalytic effect cannot easily be explained by a simple model, such as the “third-body” effect or “bifunctional theory”. The cooperation of the molecular orientation on the surface with the surface state as modified by Pb adatoms should be taken into account.