Electroreduction of oxygen on a (100)-like polycrystalline gold surface in an alkaline solution containing Pb(II)

Abstract

In a previous work from this laboratory, it was shown that it is possible to electrochemically modify a polycrystalline surface of gold so that it behaves towards O2 reduction like the (100) gold plane. To check whether this similarity in behavior is due to the presence on the (100)-like surface of sufficiently large (100) spots, the process of the upd of Pb(II) was used in this work as a probe of the surface crystallographic orientations both in deaerated and in O2-saturated solutions. The observed cyclic voltammograms (CV) and polarization curves were entirely different from those reported in the literature for a typical polycrystalline gold surface. The CV data were analyzed in an attempt to gain insight on the crystallography of the (100)-like surface. The influence of adsorbed lead on the electroreduction of oxygen in 1 M NaOH on the (100)-like surface was also scrutinised. It was found that the reduction is differently affected by adsorbed Pb(II) ions and by underpotential deposited Pb adatoms. Adsorbed Pb(II) do not change the reduction mechanism, it only alters the rate constant for HO2- disproportionation, whereas the surface becomes able to reduce O2 to OH- without desorption of HO2- to the solution bulk when modified by Pb adatoms. The details of the electroreduction of O2 and of HO2- are thoroughly discussed in relation to the surface processes underneath. Together with the CV data, they show that there are no significant (100) spots on the (100)-like surface and that this surface is structurally different from the gold (100) plane.