Role of crystalline defects in electrocatalysis: CO adsorption and oxidation on stepped platinum electrodes as studied by in situ infrared spectroscopy

The adsorption of CO and the electrochemical oxidation of a CO adlayer on stepped Pt electrodes, Pt(443), Pt(332), and Pt(322), has been studied using in situ infrared reflection-absorption spectroscopy (IRAS). Coverage-dependent and potential-dependent spectra of CO adlayers on stepped Pt surfaces are reported. Infrared spectra acquired during oxidation of the CO adlayer provide information on the mechanism of the reaction and the structure of the operational catalytic active site. CO adsorbed on the (111) terraces is found to be more reactive compared to that adsorbed on either (110) or (100) steps. The step trough of either (110) or (100) step is concluded to be the active site for the electrocatalytic oxidation of the CO adlayer, the most reactive combination involving CO from the terrace and an oxygen-containing species in the step trough.