STUDY OF THE CONDITIONS FOR IRREVERSIBLE ADSORPTION OF LEAD AT PT(H,K,L) ELECTRODES

In contrast to bismuth, lead can be observed in an irreversible adsorption state on platinum single crystal electrodes only by using more restrictive conditions. These may be determined by studying systematically the effect of the pH of the solution from which lead is adsorbed as well as the effect of the pH of the test electrolyte in which the adsorbed layer is characterized electrochemically. Thus acidic and neutral lead solutions were used to prepare the platinum modified electrodes with basal orientations, while acidic and alkaline solutions were used as test electrolytes to check the stability of the layer which was found to increase with pH. Evidence is presented for a surface redox reaction of the lead adlayer whose potential depends on the orientation of the Pt substrate and is independent of pH on a RHE scale. Thus lead undergoes a reversible valence change from zero to the divalent state, both in the adsorbed phase, the latter being in combination with oxygen. The stability with pH of this oxygenated compound determines the possibility or not to observe the irreversible adsorption of lead. © 1990.