THE BEHAVIOR OF PLATINUM SINGLE-CRYSTAL ELECTRODES IN NEUTRAL PHOSPHATE BUFFERED SOLUTIONS

The voltammetric behaviour of the three basal Pt orientations (100), (110) and (111) in neutral phosphate buffered solutions are presented and discussed. The voltammograms corresponding to the hydrogen adsorption-desorption reaction and the influence of oxygen monolayer adsorption on these faces show some similarities with the corresponding results in acid media; in general they are intermediate between those observed in sulphuric and perchloric acids. The electric charges measured in the hydrogen adsorption-desorption potential range are higher than the corresponding theoretical values of the unreconstructed surfaces, particularly in the cases of Pt(100) and Pt(111). This is interpreted as being due to a reconstruction of the Pt(100) surface towards the (5x20) structure. For Pt(111) hydrogen is adsorbed in two separate potential ranges; however, the excess charge found for the state at higher potential suggests that oxygenated species are present on the surface in this range. The adsorption of bromide ions suppresses the adsorption of oxygenated species. In contrast, the Pt(110) orientation seems to experience a lower degree of initial reconstruction to a (1x2) structure in neutral phosphate buffer than in sulphuric acid, but it shows a progressive reconstruction of the type mentioned above upon cycling in a potential range including oxygen adsorption-desorption.