Shape and Hydriding Effects of Palladium Nanocatalyst Toward Oxygen Electroreduction Reaction

摘要

Proton exchange membrane fuel cells(PEMFCs) have received increasing considerations owing to the high energy conversion efficiency and carbon-free emission to meet the demands for environmental-friendly energy systems.Oxygen reduction reaction(ORR) occurring at the cathode of PEMFCs has been recognized as a major bottleneck due to the sluggish electron-transfer kinetics that limits the cell performance.While platinum(Pt) is the most active catalyst toward the ORR,palladium(Pd) has also received considerable attention as one of potential electrocatalysts for ORR in acidic and alkaline media.The ORR activity of Pd is surface facet-dependent,and the trend is in the order of(110) <(111) <(100) in HClO4 solutions,indicating that cubic shape of Pd nanocrystals is the most active among the other shapes.Xia and coworkers revealed that Pd cubes exhibited 10 times of specific activity than Pd octahedra.The activity trend of the ORR catalyst follows Sabatier's principle,which predicts that the ideal catalyst should not bind too strongly or too weakly to the reaction intermediates.Since Pd binds too strongly with oxygenated intermediates,Pd hydride(PdH) with reduced electron density weakens the Pd-O bond strength and therefore can be utilized for O44.In a previous work,we have demonstrated that PdH enables enhancement of catalytic activity toward liquid fuel oxidation due to the hydriding effect.