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

Abstract

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.