Improving PEM fuel cell catalyst activity and durability using nitrogen-doped carbon supports: observations from model Pt/HOPG systems

This study presents clear and compelling experimental evidence for the significant beneficial effects of nitrogen-doping on the activity of Pt/C catalyst systems for the methanol oxidation reaction. This evidence is obtained through the deployment of geometrically well-defined model catalytic systems consisting of tunable assemblies of Pt catalyst nanoparticles deposited onto undoped, Ar-doped, and N-doped highly oriented pyrolytic graphite (HOPG) substrates. Both Ar- and N-doping were achieved via ion beam implantation, and Pt was electrodeposited from solutions of H₂PtCl₆ in aqueous HClO₄. Morphology from scanning electron microscopy (SEM) and aqueous electrochemical analysis of catalytic activity was utilized to examine the effect of N-doping compared to the undoped and Ar-doped control samples. The results strongly support the theory that doping nitrogen into a graphite support significantly affects both the morphology and the behavior of the overlying Pt nanoparticles. In particular, nitrogen-doping was observed to cause a significant decrease in the average Pt nanoparticle size, an increase in the Pt nanoparticle dispersion, and a significant increase in catalytic activity and durability for methanol oxidation. The model catalytic systems demonstrated here represent a versatile platform to study catalyst-support interactions in electrocatalytically relevant nanoparticle systems.