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The alkaline membrane fuel cell (AMFC) field continues to expand in interest. Membrane chemical stability is approaching the level required for commercial application (1), and membrane-electrode assembly (MEA) power output has reached and even surpassed 1 W/cm2 (2). In this presentation, work at NREL in the AMFC field regarding the synthesis of PFAEM and its implementation into MEAs will be summarized. For example, our ‘Generation 2’ PFAEM, based on sulfonamide-linked hexyl trimethyl ammonium, retains greater than 90% of its ion exchange capacity (IEC) after 14 days of exposure to 2 M KOH at 80°C. Well over 200g of this material has been synthesized and is readily processed into solutions (for membrane fabrication) and dispersions (for electrode ionomer use). MEAs employing PFAEM membranes and ionomers outperform commercial AEM materials from Tokuyama with equivalent catalyst loadings (see figure). Further improvements have been attained with MEAs comprising PFAEM membranes and advanced electrodes where ~1 W/cm2 peak power and >500 hr durability in H2/O2 at 60°C were demonstrated. Performance and durability across different electrode architectures and compositions were studied via impedance, RH dependence, and cyclic voltammetry. Comparisons will be presented along with insights gained into the relative contributions of electrodes and membranes to durability and performance of AMFCs. References 1. W.-H. Lee, Y. S. Kim and C. Bae, ACS Macro Lett., 4, 814 (2015). 2. L. Wang, E. Magliocca, E. L. Cunningham, W. E. Mustain, S. D. Poynton, R. Escudero-Cid, M. M. Nasef, J. Ponce-Gonzalez, R. Bance-Souahli, R. C. T. Slade, D. K. Whelligan and J. R. Varcoe, Green Chemistry, 19, 831 (2017). Figure 1. Comparison between all-PFAEM and all-Tokuyama AMFC MEAs. Cell conditions comprised H2/O2 gas flows at 0.2 slpm, 60°C, 121 kpa absolute, and 100RH. Catalysts were 46% Pt/HSC for each electrode and loadings for all were 0.4 mg/cm2. Figure 1 |
