ePTFE reinforced, sulfonated aromatic polymer membranes enable durable, high-temperature operable PEMFCs

Abstract

Summary Sulfonated polyphenylene (SPP)-based ionomers have been developed for electrochemical applications in recent years due to their inherent thermal and chemical stability. However, the difficult synthesis, limited solubility, and rigid backbone obstructs their progress. Herein, a new monomer, 3,3″-dichloro-2′,3′,5′,6′-tetrafluoro-1,1':4′,1″-terphenyl (TP-f) with high polymerization reactivity was designed and polymerized with sulfonated phenylene monomer to prepare SPP-based ionomers (SPP-TP-f) with high ion exchange capacity up to 4.5 mequiv g −1 . The resulting flexible membranes were more proton conductive than Nafion (state-of-the-art proton exchange membrane) even at 120°C and 20% RH. Unlike typical SPP ionomers, SPP-TP-f 5.1 was soluble in ethanol and thus, could be reinforced with double expanded polytetrafluorethylene thin layers to obtain SPP-TP-f 5.1/DPTFE membrane. SPP-TP-f 5.1/DPTFE showed superior fuel cell performance to that of Nafion, in particular, at low humidity (30% RH, > 100°C) and reasonable durability under the severe accelerated conditions combining OCV hold and humidity cycling tests.

Protocol for synthesis and characterization of ePTFE reinforced, sulfonated polyphenylene in the application to proton exchange membrane fuel cells

“… After equilibrating under the test conditions for > 2 h, measure the stress-strain curves at a stretching rate of 10 mm min −1 . The detailed results are shown in our previous report ( Long and Miyatake, 2021a ). …”

“…Calculate the proton conductivity (δ (S cm −1 )) from the following equation: δ = l/(A × R), where l (cm) is the distance between the two reference electrodes, A (cm 2 ) is the cross-sectional area, and R (Ω) is the ohmic resistance. For the detailed results, refer to our previous report ( Long and Miyatake, 2021a ).

Figure 3 Evaluation of bulk membrane properties (A) Solid electrolyte analyzer system to measure the temperature/humidity dependence of the proton conductivity and water uptake.

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“…Calculate the proton conductivity (δ (S cm −1 )) from the following equation: δ = l/(A × R), where l (cm) is the distance between the two reference electrodes, A (cm 2 ) is the cross-sectional area, and R (Ω) is the ohmic resistance. For the detailed results, refer to our previous report ( Long and Miyatake, 2021a ).…”

“…The protocol also includes performance and durability evaluation of fuel cells using the reinforced membranes. For complete details on the use and execution of this protocol, please refer to Long and Miyatake (2021a ).…”

“…For complete details on the use and execution of this protocol, please refer to Long and Miyatake (2021a ).…”