Combined Nitrogen Precursor Approach to Develop Cobalt-Based Non-Precious Catalysts for Polymer Electrolyte Fuel Cell Cathodes
The two most promising M-N-C catalyst technologies are based on either iron or cobalt, with the former conventionally providing enhanced ORR performance, approaching that of commercial platinum catalysts. From a system perspective, however, the presence of iron species in the catalyst layer is highly undesirable. This is owing to the well-known Fenton chemistry, resulting in the formation of highly reactive free-radical species that in turn leads to membrane and/or ionomer decomposition. To address this challenge, we prepared cobalt-based catalysts using the combined-precursor approach recently developed at Los Alamos National Laboratory . This approach utilizes both polyacrylonitrile (PANI) and cyanamide (CM) as nitrogen/carbon precursors that are combined and pyrolyzed with a carbon support and cobalt salt. Individually, both PANI and CM precursors have been previously demonstrated capable of forming highly ORR-active catalysts. Through this approach, we found that the relatively low decomposition temperature (ca. 260°C) of CM allows it to synergistically act as a pore-forming agent and yield high surface-area catalysts. This in turn leads to excellent H2-air fuel cell performance due to the reduced mass transport limitations in the cathode.
In this work, Co-CM-PANI-C was formed and found to provide promising activity towards the ORR in acidic electrolyte. Particularly, it was determined that 8.0 wt.% cobalt in the precursor mixture provided optimal ORR activity through half-cell investigation (Figure 1). A half-wave potential of ca. 0.74 V vs.RHE was achieved, with current investigations underway to understand and optimize the structure-performance-durability relationships. These results, along with performance and durability data from both half-cell and MEA evaluation, will be presented at the meeting.
Financial support for this was has been provided by the DOE-EERE through the Fuel Cells Technologies Office and by the Natural Sciences and Engineering Research Council of Canada (NSERC).
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