Abstract
Understanding the mechanisms associated with Pt/C electrocatalyst degradation in proton exchange membrane fuel cell (PEMFC) cathodes is critical for the future development of higher-performing materials; however, there is a lack of information regarding Pt coarsening under PEMFC operating conditions within the cathode catalyst layer. We report a direct and quantitative 3D study of Pt dispersions on carbon supports (high surface area carbon (HSAC), Vulcan XC-72, and graphitized carbon) with varied surface areas, graphitic character, and Pt loadings ranging from 5 to 40 wt %. This is accomplished both before and after catalyst-cycling accelerated stress tests (ASTs) through observations of the cathode catalyst layer of membrane electrode assemblies. Electron tomography results show Pt nanoparticle agglomeration occurs predominantly at junctions and edges of aggregated graphitized carbon particles, leading to poor Pt dispersion in the as-prepared catalysts and increased coalescence during ASTs. Tomographic reconstructions of Pt/HSAC show much better initial Pt dispersions, less agglomeration, and less coarsening during ASTs in the cathode. However, a large loss of the electrochemically active surface area (ECSA) is still observed and is attributed to accelerated Pt dissolution and nanoparticle coalescence. Furthermore, a strong correlation between Pt particle/agglomerate size and measured ECSA is established and is proposed as a more useful metric than average crystallite size in predicting degradation behavior across different catalyst systems.
Original language | English |
---|---|
Pages (from-to) | 29839-29848 |
Number of pages | 10 |
Journal | ACS Applied Materials and Interfaces |
Volume | 9 |
Issue number | 35 |
DOIs | |
State | Published - Sep 6 2017 |
Funding
The research was supported by the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy (DOE). A portion of the research was performed as part of a user project through Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences, which is a U.S. DOE Office of Science User Facility, and by instrumentation provided by the U.S. DOE Office of Nuclear Energy, Fuel Cycle R&D Program, and the Nuclear Science User Facilities. We would like to thank S. Venkatakrishnan, M. Lei, E. Padgett, and M. Holtz for valuable discussions.
Keywords
- 3D
- PEM fuel cells
- electrochemically active surface area
- electron tomography
- graphitized carbon