Interfacial Pd-O-Ce Linkage Enhancement Boosting Formic Acid Electrooxidation

Metal-support interaction enhancement is critical in the fuel cell catalyst design and fabrication. Herein, taking the Pd@CeO₂ system as an example, we revealed the substrate morphology coupling effect and the thermal annealing-induced Pd-O-Ce linkage enhancement in the improved catalytic capability for formic acid electrooxidation. Three well-defined CeO₂ nanocrystals were employed to support Pd nanoparticles, and the best catalytic performance for formic acid oxidation and anti-CO poisoning ability was found on CeO₂ plates because of the high oxygen vacancy, Ce³⁺, and more Pd-O-Ce linkages resulting from the more edge/corner defects. This interaction of Pd-O-Ce linkages could be largely enhanced by thermal annealing in the N₂ atmosphere, as confirmed by a series of crystal structures, surface chemical state, and Raman analysis because the oxygen vacancies and lattice oxygen resulting from the oxygen atoms leaching from the CeO₂ lattice would trap the mobile Pd nanocrystals by forming strengthened Pd-O-Ce linkages. Due to the high oxygen vacancy and strong Pd-O-Ce linkages, largely increased catalytic activity and stability, catalytic kinetics, and rapid charge transfer were found for all the thermal annealed Pd@CeO₂ catalysts. A nearly 1.93-fold enhancement in the mass activity was achieved on the Pd@CeO₂-plate catalysts demonstrating the significance of Pd-O-Ce linkage enhancement. The formation mechanism of Pd-O-Ce linkage was also probed, and a valid Pd-O-Ce linkage can only be formed in the inert atmosphere because of the reaction between metallic Pd and CeO₂. This finding sheds some light on the more efficient catalyst interface construction and understanding for the fuel cell catalysis via metal-support interaction enhancement.