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

Abstract

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 H 2 PtCl 6 in aqueous HClO 4 . 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. Experimental HOPG substrate preparation, doping, and surface characterizationHighly oriented pyrolytic graphite (HOPG, 10 mm  10 mm  1 mm, grade 2, SPI Inc.) was used as a model graphitic carbon

Nitrogen Doping Effects on Carbon Nanotubes and the Origin of the Enhanced Electrocatalytic Activity of Supported Pt for Proton-Exchange Membrane Fuel Cells

“…Third, nitrogen doping results in an improvement in hydrophilicity and wettability of CNx. 52 The enhanced access of solvated and charged PtCl 6 2-ions to the CNx surface can be associated with the superior dispersion of Pt nanoparticles and the avoidance of agglomeration. It is found that CNx is easier to disperse in the solution during experiments.…”

CNx-modified Fe3O4 as Pt nanoparticle support for the oxygen reduction reaction

“…Nitrogen-doped carbon (CN x ) with noble metallic nanoparticles deposited on its surface exhibited an enhanced catalytic activity toward ORR as the CN x had greater electron mobility and showed n-type or metallic behavior [17][18][19][20][21]. Doping nitrogen into graphite has significant effects on both the morphology and electrocatalytic behavior of Pt nanoparticles [22]. If CN x can form on the surface of Fe 3 O 4 , this new material could be a new desirable catalyst support for electrocatalysts, since Pt will exhibit a good durability on the support surface due to anchoring from nitrogen incorporation [23,24].…”

Graphitic Carbon Nitride Materials for Energy Applications

“…The introduction of nitrogen into carbon supports has showed to improve durability, as well as enhancing the intrinsic catalytic activity for both oxygen reduction (ORR) and methanol oxidation (MOR) reactions (41)(42)(43)(44)(45)(46)(47)(48). The N-dopant has been reported to alter the catalyst electronic structure, resulting in a higher binding energy, which may decrease the specific interaction between the Pt nanoparticles and potential poisoning intermediates (49).…”