Interfacial Hydrogen Spillover on Pd-TiO₂ with Oxygen Vacancies Promotes Formate Electrooxidation

Abstract

Pd-based catalysts are crucial in direct formate fuel cells owing to their high stability and selectivity for the formate oxidation reaction (FOR) to CO 2, avoiding carbonaceous poisoning species (e.g., CO ad, CH x ) in alkaline media. However, the kinetics of Pd-based electrocatalysts are considerably impeded by the unfavorable adsorption of hydrogen species (H ad ), which serve as the primary intermediators and occlude the active sites. Herein, we crafted electron-rich Pd nanoparticles on a TiO 2 support with oxygen vacancies (Pd/O v -TiO 2 ) to improve H ad desorption. The as-prepared Pd/O v -TiO 2 exhibited a high mass activity of 4.16 A mg Pd –1, outperforming Pd/TiO 2 without oxygen vacancies and commercial Pd/C by 1.41 and 2.72 times, respectively. Experimental characterizations and density functional theory calculations revealed that the oxygen-vacant TiO 2 can concurrently downshift the d-band center of Pd and facilitate hydrogen spillover, thereby accelerating H ad desorption and FOR kinetics. Our findings provide a strategy to refine Pd-based catalysts for broader electrochemical uses.