Tuning Carbon-Based Fuel Cell Catalyst Support Structures via Nitrogen Functionalization. II. Investigation of Durability of Pt–Ru Nanoparticles Supported on Highly Oriented Pyrolytic Graphite Model Catalyst Supports As a Function of Nitrogen Implantation Dose

Abstract

Nitrogen functionalization of carbon-based support materials for lowtemperature fuel cell catalysts has been shown to improve catalystÀsupport interactions and therefore enhance both the performance and durability of the supported electrocatalyst. While previous work has focused on pure Pt electrocatalysts, this work focuses on understanding the role of nitrogen functionalization on the durability of PtÀRu alloy nanoparticle catalysts. A well-defined model catalyst system approach is used by employing highly oriented pyrolytic graphite (HOPG) as a model graphitic carbon support, nitrogen ion beam implantation as the doping route, and magnetron sputtering from a single alloyed PtÀRu target for nanoparticle catalyst deposition. A series of PtRu/HOPG substrates with different levels of doped nitrogen but very similar initial PtRu nanoparticle coverage, size, and composition were evaluated using TEM and XPS before and after potential cycling. As compared to an undoped support, supports doped with low nitrogen dosage levels (both oxygen and nitrogen sites are present, oxygen sites are predominant, and nitrogen concentration is relatively low) appear to have a negative effect on PtRu nanoparticle stability. However, higher nitrogen doses (both oxygen and nitrogen sites are present, nitrogen concentration is relatively high) have a positive effect on durability, reaching an optimum with an implantation dosage of 4.7 Â 10 16 ions cm À2 . The improvement in durability can be directly related to nitrogen levels and specifically to the amount of pyridinic nitrogen. It is shown that strong positive tethering effects are related to formation of clustered multinitrogen defects, i.e., pyridinic rings in which more than one carbon is replaced with nitrogen, a condition that is met only when the nitrogen dosage is sufficiently high.

Nitrogen Post Modification of PtRu/Carbon Catalysts for Improved Methanol Oxidation Reaction Performance in Alkaline Media

“…It was suggested that that these defects limit nanoparticle agglomeration, likely serving as trapping sites. 16,28 There is some debate as to the actual functional groups present in these types of systems and some recent studies have suggested these nitrogen clusters may be the start of a structures observed in carbon nitride films. 25 TEM images acquired from the post-modified catalyst sample are shown in Figure 2.…”

High‐Performance Alkaline Direct Methanol Fuel Cell using a Nitrogen‐Postdoped Anode

“…These results suggest that the main difference between the two catalysts is metal surface area, a conclusion that is substantiated by the TEM comparison of the two samples (Figure 2). In addition, XPS19 also indicates a change in the surface content. The total amount of Pt and Ru determined from XPS of the N‐doped PtRu/C is 8.2 vs. 7.2 at % for the undoped PtRu/C.…”

Nitrogen‐Doped Porous Carbon Matrix Derived from Metal‐Organic Framework‐Supported Pt Nanoparticles with Enhanced Oxygen Reduction Activity

“…have exhibited improved electrochemical ability ,. Heteroatom doped the carbon support matrix always led to the enhanced charge density and catalytic activity .Meanwhile, the altered electronic properties also facilitate the interaction between metal atom (such as Pt) and carbon support matrix which acts as a “cross‐linking agent” to prevent Pt nanoparticles agglomeration by the formation covalent bond ,. Recently, Sahu et al have prepared the nitrogen and fluorine co‐doped graphite nanofibers (NF‐GNFs) and applied as a highly corrosion resistant support matrix to disperse Pt nanoparticles .…”