(Invited) Next Generation Designer Carbon Supports for Durable Polymer Electrolyte Fuel Cell Cathode Catalysts

Abstract

The implementation of polymer electrolyte membrane fuel cells (PEMFC) in medium- and heavy-duty vehicles is a promising strategy to eliminate greenhouse gas emissions as the only byproduct is water. However, the durability of PEMFC catalysts, especially for the kinetically sluggish oxygen reduction reaction (ORR) that occurs at the cathode, remains a significant obstacle. Current state-of-the-art electrocatalysts are comprised of platinum-based nanoparticles anchored on high surface area carbon black supports (Pt/C). While these catalysts meet the U.S. Department of Energy’s near-term activity benchmarks [2], they suffer heavily from degradation mechanisms that can lead to catastrophic failure of PEMFCs. Hence, carbon support materials that promote durability are crucial to further development of ORR catalysts. Here, we report on the physical and electrochemical characterization of next-generation commercial FCX carbon supports that aim to mitigate these degradation mechanisms.We synthesized Pt/C electrocatalysts by decorating FCX carbons with spherical Pt nanoparticles approximately 2-3 nanometers in diameter. The surface and pore structure of the supports were extensively probed to determine their effects on anchoring of Pt nanoparticles and ultimately catalytic activity. After physical and electrochemical characterization of the catalysts, structure-to-property relationships were established, leading to a schematic for an “ideal” Pt/C electrocatalyst as shown in Figure 1. The hierarchical pore structure is crucial for mass transport, and Pt nanoparticles are housed on the edges of stable graphitic carbon domains. Lastly, a promising alternative to the traditional Pt/C synthesis pathway is shown. As degradation is more pronounced on the catalyst’s exterior surfaces, this novel electrocatalyst contains Pt nanoparticles inside the support’s mesopores to mitigate the loss of electrochemically active surface area [3]. The insights gained from this work can be applied to optimizing carbon support morphology and chemistry for durable and highly active ORR electrocatalysts.[1] M. Rezaei Talarposhti, T. Asset, S. T. Garcia, Y. Chen, S. Herrera, S. Dai, E. J. Peterson, K. Artyushkova, I. Zenyuk, P. Atanassov, ChemPhysChem, 21 (2020) 1331-1339.[2] D.A. Cullen, K.C. Neyerlin, R.K. Ahluwalia, R. Mukundan, K.L. More, R.L Borup, A.Z. Weber, D.J. Myers, A. Kusoglu, Nature Energy, 6 (2021) 462–474.[3] G.S. Harzer, A. Orfanidi, H. El-Sayed, P. Madkikar, H.A. Gasteiger, J. Electrochem. Soc. 165 (2018) F770-F779. Figure 1