Temperature-dependent surface electrochemistry on Pt single crystals in alkaline electrolyte: Part 1: CO oxidation

In this work we studied the continuous electrooxidation of CO dissolved in 0.1 M KOH electrolyte (COb) on Pt(hkl) at 275 and 333 K, respectively. The results clearly demonstrate that Pt(hkl) electrodes in alkaline electrolyte represent a highly active system for COb oxidation. Significant reaction rates are observed even in the potential region for hydrogen underpotential deposition (H-upd). The COb oxidation on Pt(hkl) surfaces proceeds through a Langmuir-Hinshelwood type reaction between the adsorbed states of CO and OHad, the latter forming selectively at the defect/step sites. The coexistence of OHad in the Hupd potential region implies that the potential-dependent surface coverages by H-upd and OHad in alkaline solutions cannot be obtained by simple coulometry. The kinetics of CO oxidation on Pt(hkl) surfaces is found to vary with crystal face. The difference in activity is attributed to the structure-sensitive adsorption of OHad on the defect/step sites and mobility of adsorbed CO (COad).