Exploring Anion Exchange Membrane Fuel Cell (AEMFC) Performance with Different Classes of Cathode Electrocatalysts
Authors: He Cheng , Yang-Neyerlin Ami C. , Pivovar Bryan S. 
Published: December 2020

AEMFCs as an alternative to acidic polymer electrolyte fuel cells have the potential to reduce cost and precious metal requirements of fuel cell systems.1 In the past decade, several highly conductive polymers have been developed and a number of these have demonstrated more than 1W∙cm-2 peak power density with hundreds of hours stability; however, most of these studies have focused on Pt containing cathodes with high loadings.2,3 While the promise of Pt and Pt group metal (PGM) free electrocatalysis has been a major selling point of AEMFCs, more work exploring the potential of PGM-free cathode electrocatalysis is needed. In this study we explore and compare the performance of three leading cathode electrocatalysts: Pt/C, Ag/C, and Fe-N-C. These electrocatalysts are tested in AEMFCs cathodes using both powder- and dispersion-based PF AEM Gen 2 ionomers.4 The ability to test the different catalyst and ionomer combinations leads to additional insight into performance and catalyst-ionomer interactions.

The performance trends of the tested MEAs will be presented. Pt/C has been found to be slightly superior to the performance of the non-Pt electrocatalysts. The performance of both metal nanoparticle catalysts, Pt/C and Ag/C, exhibit strong differences in performance depending on whether or not a powder or dispersion-based ionomer is used, with the powder-based approach showing much higher performance. Unlike the metal electrocatalysts, Fe-N-C catalysts show almost no change of performance between powder and dispersion-based ionomers.

These performance metrics are also reflected in high frequency resistance measurements (Figure 1) investigated as a function of relative humidity at 300 mA·cm-
2. This data clearly shows the expected trend of increasing HFR with decreasing humidification of reactant gasses. The Fe-N-C data shows the lowest HFR values and very small changes between powder and dispersion-based ionomers. Both, Pt/C and Ag/C show dramatic increases in HFR for the dispersion-based polymer compared to the powder-based ionomer. These large changes in HFR are unexpected and cannot be fully explained just by changes happening within the electrodes. They suggest that not only do the electrodes undergo variable electrochemical properties due to this processing, but water management within the cell is also impacted by the type of catalyst and ionomer used in processing the electrodes. These features and the impact they have on the performance of different AEMFC cathodes will be presented and discussed.

References:

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A. M. Park, Z. R. Owczarczyk, L. E. Garner, A. C. Yang-Neyerlin, H. Long, C. M. Antunes, M. R. Sturgeon, M. J. Lindell, S. J. Hamrock, M. Yandrasits and B. S. Pivovar, ECS Transactions, 80, 957 (2017).

Figure 1