The Effect of Size on the Oxygen Electroreduction Activity of Mass-Selected Platinum Nanoparticles

摘要

The use of proton exchange membrane fuel cells (PEMFCs) could become widespread by improving the kinetics of the oxygen reduction reaction (ORR), where Pt is the typical electrocatalyst. Improvements to the reaction kinetics, however, require understanding of the fundamental factors that control the ORR activity of Pt, in particular the dependence of the ORR rate as a function of the particle size. This has been the topic of numerous studies in the last few decades. Most articles report an increase in the specific activity with increasing particle size. Norskov, Rossmeisl, and co-workers rationalized this phenomenon using density functional calculations. They proposed that the active sites for the ORR are located on the terrace sites of Pt. Undercoordinated sites at terrace edges or steps should provide a negligible contribution to the activity, because they bind strongly to the O-containing intermediates of the ORR. The increased population of undercoordinated sites on small nanoparticles (especially below 5 nm) explains their lower activity. Moreover, they predicted that the activity of nanoparticles with diameters greater than around 10 nm should be equal to that of extended surfaces.