Pb-Induced Electronic Structure Modification Enhances Formic Acid Electrooxidation on Pd₃Pb

The efficiency of formic acid electrooxidation (FAEO) is often hindered by CO poisoning via the indirect pathway, underscoring the need for catalysts that promote the direct (CO-free) oxidation route. Pd-based catalysts are promising, but a limited understanding of surface interactions and catalytic behavior restricts further development. Density functional theory (DFT) combined with Crystal Orbital Hamilton Population (COHP) analysis was employed to investigate the FAEO on Pd₃Pb(111) and Pd(111) surfaces, revealing a key insight into their electronic and catalytic behavior. Incorporation of Pb into the Pd lattice enhances the catalytic performance by modifying the electronic structure and introducing new active sites. This study revealed the role of the subsurface Pb atom, which enhances HCOO binding at Pd–Pd bridge sites and strengthens CO and H adsorption at hexagonal closest packed (hcp) hollow sites over face-centered cubic (fcc) sites. The FAEO process proceeds more efficiently on Pd₃Pb via O–H bond cleavage, forming an HCOO intermediate with a lower activation energy (0.29 eV) than on Pd (0.35 eV). Pd₃Pb favors the HCOO-mediated pathway, while Pd prefers the COOH-mediated route. Additionally, Pb significantly lowers the energy barrier for HCOO rotation (0.51 vs 0.84 eV), enhancing CO-free oxidation.