Abstract
The durability of Pt-Co alloy cathode catalysts supported on high surface area carbon is investigated by subjecting them to accelerated stress tests (ASTs). The catalysts had different initial Co contents and nanoparticle morphologies: a "spongy" porous morphology for the high-Co (H) content catalyst, and a fully alloyed crystalline morphology for the medium-Co (M) and low-Co (L) content catalysts. The specific activity of the catalysts depends on their initial Co content, morphology and nanoparticle size, and remained higher than 1000 μA/cm2-Pt after 27-50% Co loss. The H-catalyst electrode showed the smallest kinetic overpotentials (ηcs ) due to higher initial Pt loading than the other two electrodes, but it had the fastest increase in ηcs with AST cycling due to lower Co retention; the L-catalyst electrode showed higher ηcs due to a lower initial Pt loading, but had a smaller increase in ηcs with aging due to higher Co retention; the M-catalyst electrode showed a similar increase in ηcs with aging, but this increase was due to the combined effects of Co dissolution and electrochemically active surface area (ECSA) loss. The modeled increase in mass transfer overpotentials with aging correlates with the initial Pt loading, ECSA loss and the initial catalyst morphology.
Original language | English |
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Pages (from-to) | F3166-F3177 |
Journal | Journal of the Electrochemical Society |
Volume | 165 |
Issue number | 6 |
DOIs | |
State | Published - 2018 |
Funding
Figure 3 shows STEM cross-section images of the CCL’s with catalyst H and L compared at BOT and EOT conditions, respectively. The EOT images show measurable thinning of both of the aged CCLs due to carbon corrosion combined with CCL compaction. CV studies in H2/N2 and potentiodynamic studies in H2/air confirm that the carbon support oxidizes, albeit slowly, to CO2 under normal fuel cell operating conditions over a potential range of 0.4 to 0.95 V.14,15 There is also evidence for dissolution of Pt from the CCL, which is supported by the significant amount of Pt precipitation in the membrane adjacent to the CCL. The authors wish to acknowledge the financial support of the U. S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, the Fuel Cell Performance and Durability (FC-PAD) Consortium, and Fuel Cell Component R&D Team Lead, Dr. Dimitrios Papageorgopoulos. The authors also wish to acknowledge General Motors, IRD (now EWii) Fuel Cells, and Umicore for supplying the SOA catalyst materials used in this study. This research used resources of the Advanced Photon Source (APS), a U. S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory. The authors thank Jan Ilavsky of APS 9-ID. The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U. S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. Microscopy performed as part of a user project at 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. The U. S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government. The views and opinions of the authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.