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

In a previous work from this laboratory, it was shown that it is possible t o electrochemically modify a polycrystalline surface of gold so that it beh aves towards O-2 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 i n deaerated and in O-2-saturated solutions. The observed cyclic voltammogra ms (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 o f 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 a nd by underpotential deposited Pb adatoms. Adsorbed Pb(ll) do not change th e reduction mechanism, it only altars the rate constant for HO2- disproport ionation, whereas the surface becomes able to reduce O-2 to OH- without des orption of HO2- to the solution bulk when modified by Pb adatoms. The detai ls of the electroreduction of O-2 and of HO2- are thoroughly discussed in r elation to the surface processes underneath. Together with the CV data, the y 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. (C) 1998 Elsevier Science Ltd. All rights reserved.