Electrochemical behaviour of irreversibly adsorbed bismuth on Pt (100) with different degrees of crystalline surface order

Abstract

Pt (100) oriented electrodes yield a variety of voltammogram profiles in the region of hydrogen adsorption-desorption in aqueous sulphuric acid which have been shown to correspond to different degress of bidimensional long range order. Two main profiles, S I and S II are reached, depending on the conditions of pretreatment of the (100) surface in the presence of either oxygen or hydrogen, respectively, interacting with the surfaces. From the S I or S II states, others with various degrees of surface perturbation, S n III, can be achieved after n voltammetric cycles involving full oxygen adsorption-desorption. A general view of the different ways of interchanging the various surface structures, S I, S II or S n III, is given. The aim of the present work is to investigate the behaviour of bismuth adsorbed irreversibly on the various surface structures of Pt (100). It is shown that surface defects deliberately created on the surface like randomly distributed steps are the preferential place for the dissolution of the adsorbed bismuth. The blocking of hydrogen adsorption sites as a function of the amount of electric charge exchanged at oxidation in the surface redox reaction of bismuth gives a linear relation in the whole range of bismuth coverage. Its slope indicates that one bismuth atom would block two hydrogen adsorption sites, independently of the type of structure, S I or S II. The recovery of these two structures after bismuth electrochemical desorption was completed, has been established.