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Poly(aryl piperidinium) membranes and ionomers for hydroxide exchange membrane fuel cells


One promising approach to reduce the cost of fuel cell systems is to develop hydroxide exchange membrane fuel cells (HEMFCs), which open up the possibility of platinum-group-metal-free catalysts and low-cost bipolar plates. However, scalable alkaline polyelectrolytes (hydroxide exchange membranes and hydroxide exchange ionomers), a key component of HEMFCs, with desired properties are currently unavailable, which presents a major barrier to the development of HEMFCs. Here we show hydroxide exchange membranes and hydroxide exchange ionomers based on poly(aryl piperidinium) (PAP) that simultaneously possess adequate ionic conductivity, chemical stability, mechanical robustness, gas separation and selective solubility. These properties originate from the combination of the piperidinium cation and the rigid ether-bond-free aryl backbone. A low-Pt membrane electrode assembly with a Ag-based cathode using PAP materials showed an excellent peak power density of 920 mW cm−2 and operated stably at a constant current density of 500 mA cm−2 for 300 h with H2/CO2-free air at 95 °C.

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The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

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This material is based upon work supported by the by the US Department of Energy, Advanced Research Projects Agency-Energy under Award No. DE-AR0000771. We thank Z. Green and H. Xu at Giner for performing the gas crossover measurement. We also thank R. Ma, J. Nash, J. A. Wittkopf and M. D. Woodroof for their assistance in the durability test of H2/O2 HEMFCs.

Author information

J.W. synthesized the polymers, fabricated the membranes, and performed the characterizations of polymers and membranes. Y.Z. prepared MEAs with Pt electrodes and tested their H2/O2 performance and durability. B.P.S. measured the electronic area specific resistance and stability of the membrane under RH cycling and pressure differential. S.R.-C. and L.S. developed the casting process for fabricating the large membranes. C.B.Y., A.A. and M.P. prepared MEAs with Ag cathodes and low-Pt anodes and tested their H2/CO2-free air performance and durability. L.W. performed the thermal analysis for the membranes. K.H. measured the polymer molecular weight. S.G. provided guidance in the development and testing of H2/CO2-free air MEAs. J.W., Y.Z., B.X. and Y.Y. conceived the ideas and wrote the manuscript with support from other coauthors.

Competing interests

C.B.Y, A.A. and M.P. are employed by Elbit Systems Ltd, which is a company specializing in fuel cells.

Correspondence to Bingjun Xu or Yushan Yan.

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Supplementary Figures 1–13, Supplementary Tables 1–2

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Fig. 1: Chemical structure of the PAP HEM family.
Fig. 2: Alkaline stability of PAP HEMs in 1 M KOH at 100 °C.
Fig. 3: Mechanical properties and durability of PAP-TP-85.
Fig. 4: Properties of PAP HEMs at different temperatures.
Fig. 5: The typical examples of membrane, ionomer, MEA and fuel cell performance based on PAP materials.