Explaining the mechanism of formic acid oxidation on single crystal Pd sites by platinum-palladium alloy single-crystal surfaces

The oxidation of formic acid (FAOR) is a critical reaction for direct formic acid fuel cells (DFAFCs), offering high theoretical efficiency and potential for sustainable energy conversion. This study investigates the FAOR mechanism on well-defined Pt-Pd alloy single-crystal surfaces, focusing on the role of Pd incorporation in modifying the electrocatalytic behavior of Pt(111) and Pt(100) electrodes. Through cyclic voltammetry, high-scan-rate voltammetry, and chronoamperometric analysis, the effect of Pd in the reaction mechanism is explored. Results reveal that Pd incorporation significantly alters the adsorption behavior, reaction kinetics, and poisoning rates by shifting onset potentials, increasing current densities, and reducing CO formation rates at low potentials. On (111) surfaces, the presence of Pd enhances the direct oxidation pathway, while on (100) surfaces, it significantly reduces the indirect CO-mediated pathway, while accelerating the reaction through the active path, leading to improved catalytic performance. Furthermore, formate adsorption and its role in the oxidation mechanism are discussed, with implications for the reaction efficiency at various Pd compositions.