An in situ infrared study on the effect of pH on anion adsorption at Pt(111) electrodes from acid sulfate solutions

From the in situ FTIR spectroscopy of the electrode/electrolyte solution interface at pH values of 1.2, 2.0, and 3.4, it can be confirmed that the adsorbate associated with the anomalous peaks in the cyclic voltammetry of Pt(111) in sulfate- and bisulfate-containing solutions is not the sulfate anion. The structure of the bisulfate-like adsorbate is tentatively postulated to be a sulfate ion/hydronium ion ion pair: SO42-. H3O+. Over the potentials in question, and only in solutions with appreciable HSO4- concentration, can IR bands be found that are associated with the adsorbed species.