Constructing Anhydrous Hydrogen-Bonding Network in a Sulfonated Polymer Based Membrane for High Temperature Fuel Cell Applications

Proton exchange membrane fuel cells (PEMFCs) are most promising clean powers for vehicles.¹ Current PEMFCs relying on Nafion with water necessary for proton conduction can only work below 363 K owing to that Nafion loses its conductivity quickly in response to the inevitable evaporation of water at elevated temperatures. However, PEMFCs operating at temperatures higher than 423 K are highly desired to overcome many obstacles of present PEMFCs, such as slow reaction kinetics, CO poisoning of the electrode catalysts, and the complexity of water and heat managements.^2-4 Great efforts have been paid to develop anhydrous PEMs for these high-temperature FCs, particularly, those based on inorganic acids possessing intrinsic high proton conductivities at above 423K have been extensively studied.^3,4 Intermingling sulfonated polymers (SPs, such as Nafion) with non-volatile, thermally stable (up to 573 K) ionic liquids (ILs) for anhydrous PEMs has also attracted numerous attention, and ionic conductivities exceeding 10^-2 S cm^-1 have been reached. However, these PEMs often suffer from low proton transfer numbers (0.5~0.6), poor mechanical performanc, and the assembed H₂-O₂ FCs with these ILs based PEMs were often poor in performance at intermediate temperatures.^5,6

Here we report an anhydrous hydrogen-bond fusing strategy for high-performance PEMs by introducing hydroxyl functionalized IL (IL-OH) into the SPs. The IL-OHs selected as both proton donators and acceptors, that are evidenced to be strongly hydrogen-bonded with both Nafion and some nano-inorganic matters. Consequently, an effective interconnected hydrogen-bond network forms in a HFIL/SP based hybrid membrane, endowing the PEM with robust mechanical and thermal stability. At temperatures >430K , the anhydrous ionic conductivity of this kind of PEM can reach higher than 50 mS cm^-1 with a large proton transfer number close to 1. And the initial high performance of the assembled intermediate-temperature H₂-O₂ FCs showed promising applications of this new generation HFIL/SP PEMs.

 

References

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[2] Q. F. Li, C. Pan, J. O. Jensen, P. Noyé, N. J. Bjerrum, Chem Mater, 2007, 19, 350.

[3] J. A. Asensio, E. M. Sanchez, P. Gomez-Romero, Chem. Soc. Rev. 2010, 39, 3210.

[4] D. A. Boysen, T. Uda, C. R. I. Chisholm, S. M. Haile, Science 2003, 303, 68.

[5] M. Martinez, Y. Molmeret, L. Cointeaux, C. Iojoiu, J.-C. Leprêtre, N. El Kissi, P. Judeinstein, J.-Y. Sanchez, J. Power Sources 2010,195, 5829-5839;

[6] S. Y. Lee, A. Ogawa, M. Kanno, H. Nakamoto, T. Yasuda, M. Watanabe, J. Am. Chem. Soc. 2010, 132, 9764-9773