Electrooxidation of adsorbed CO on Pt(1 1 1) and Pt(1 1 1)/Ru in alkaline media and comparison with results from acidic media

Oxidation of adsorbed CO on Pt(1 1 1) and Pt(1 1 1)/Ru electrodes was studied in 0.1 M NaOH by the use of cyclic voltammetry and chronoamperometry. The data obtained in alkali are compared to those in 0.1 M H₂SO ₄, and additional relevant information obtained with Pt(1 1 0) and Pt(1 0 0) surfaces is presented. We demonstrate, for the first time, that the voltammetric oxidation of CO on Pt(1 1 1)/Ru in alkali shows two clearly resolved CO stripping peaks, reminiscent of similar behavior in acids. On pure Pt(1 1 1), we confirm previous work that the voltammetric oxidation of a saturated CO adlayer in 0.1 M H₂SO₄ and in 0.1 M NaOH yields a single and a split peak, respectively. Notably, we have found that while the CO oxidation on the Pt(1 1 1) electrode in acid occurs via a Langmuir-Hinshelwood mechanism, the CO oxidation in alkali in the pre-peak region is controlled predominantly via an Eley-Rideal (E-R) mechanism. On Pt(1 1 1)/Ru, the low potential CO oxidation in alkali occurs simultaneously through the L-H mechanism and the E-R mechanism. The addition of Ru to clean Pt(1 1 1) further improves the CO tolerance by promoting the oxidation of a greater fraction of the CO adlayer at low potentials. Therefore, the use of Pt/Ru catalysts in acidic and alkaline media may substantially reduce the CO poisoning that has so far limited low temperature fuel cell electrocatalyst performance, thus contributing to the development of more efficient direct oxidation fuel cells.