Relation of the electrochemical interplay between H2PtCl6 and H2O/H3O+/H2+ and the hydrogen-evolution reaction

The electrodeposition of platinum from hexachloroplatinic acid solutions, on glassy carbon, was studied by developing multiple cyclic voltammetry transients. The development of an isopotential point, only observed under hydrogen-evolution conditions, is postulated to be associated with the reduction of [PtCl4](2-) to Pt-0 and the oxidation of the adsorbed molecular hydrogen ion (H-2(+)) ads species to (H3O+)ads. The adsorption of H-2(+) inhibits the continued reduction of [PtCl4](2-) and the 'cleansing' of the platinum surface, that is, the removal of H-2(+) through hydrogen evolution, results in the opening up of active sites to allow for the continued reduction of [PtCl4](2-) on the return sweep, which results in an isopotential point (IPP). This IPP is not observed in the absence of hydrogen evolution, due to saturation of the surface by (H-2(+))ads, and correlates with a model that explains the interplay between platinum chloride species, hydrogen containing species (H2O/H3O+/H-2(+)), and the hydrogenevolution reaction.