Surface charge and interfacial acid-base properties: pKa,2 of carbon dioxide at Pt(110)/perchloric acid solution interfaces

Abstract

In this work, we investigate the in-situ spectro-electrochemical behavior of Pt(110) electrodes in contact with acid solutions saturated with CO2. Similar to previous observations reported for Pt(111) electrodes, potential-dependent signals associated to adsorbed bicarbonate and carbonate anions are observed in the FT-IRRA spectra collected for Pt(110), even when the concentration of these anions are near to zero in the bulk solution. The relative intensities of the infrared bands at different pH and applied potential values can be used to determine the interfacial pKa,2 of CO2. The surface pKa,2 value found for Pt(110) electrodes is lower than that for Pt(111) electrodes. This result can be interpreted by assuming that the more open (110) surface leads to a more alkaline interphase than the close packed (111), in the sense that it reacts with acids in a higher extent. We attribute this difference to the lower potential of zero free charge and work function values for Pt(110) electrodes compared to Pt(111) electrodes.