Electrochemical and Electrocatalytic Behavior of Platinum–Palladium Bulk Alloy Single Crystal Electrodes in Alkaline Media

The electrochemical and electrocatalytic behavior of platinum–palladium bulk alloy single-crystal electrodes with (111) and (100) orientations in alkaline media was systematically investigated. Using cyclic voltammetry and CO displacement experiments, the adsorption properties, potential of zero total charge (pztc), and electrocatalytic activity of Pt_100–xPd_x(111) and Pt_100–xPd_x(100) surfaces toward the oxidation of CO, sodium formate and methanol were analyzed as a function of Pd content. The incorporation of Pd altered the adsorption characteristics, shifting the onset of OH adsorption to lower potentials and influencing the electrode’s interfacial properties. CO stripping experiments revealed that the oxidation of CO adlayers remained largely unaffected by Pd incorporation, indicating that the structure of the CO adlayer and OH adsorption strength primarily govern CO oxidation. The small changes in the peak position should be assigned to the different initial defects present on the CO adlayers. The introduction of Pd significantly enhanced the oxidation of formate in alkaline media, a reaction that is otherwise inhibited on pure Pt surfaces at this pH. The observed catalytic activity was more pronounced for Pt_100–xPd_x(100) electrodes than for the (111) series. The observation of activity at these pH values indicates that the presence of Pd modifies the reaction mechanism, likely by altering the rate-determining step. Methanol oxidation was also catalyzed by Pd, with increased oxidation currents suggesting a facilitation of the dehydrogenation steps in the reaction mechanism. These findings provide fundamental insights into the electrochemical behavior of PtPd alloy electrodes and the role of Pd in modifying adsorption properties and oxidation pathways.