Synthesis of Sulfonium Based Polymers for Hydroxide Exchange Membrane Fuel Cell Applications

Membrane-Based Separations(02D)

02D04 Fuel Cell Membranes

Chair:

Winston Ho
Professor
Chemical and Biomolecular Engineering
The Ohio State University
140 WEST 19TH AVE
Columbus, OH 43210
Phone Number: 614-292-9970
Email: ho@chbmeng.ohio-state.edu 

Co-Chair:

Peter Pintauro
Professor of Chemical Engineering and Chair
Department of Chemical and Biomolecular Engineering
Vanderbilt University
Olin Hall 107
VU Station Box 351604 2301 Vanderbilt Place
Nashville, TN 37235
Phone Number: 615-343-3878
Email: peter.pintauro@Vanderbilt.Edu 

Synthesis of Sulfonium Based Polymers for Hydroxide Exchange Membrane Fuel Cell Applications

Bingzi Zhang, Shuang Gu, Yushan Yan*

Department of Chemical and Environmental Engineering

University of California, Riverside

Riverside, CA, 92521, USA

*yushan.yan@ucr.edu

Polymer electrolyte fuel cells, which convert chemical energy to electrical energy, are regarded as promising future power sources. So far, the most advanced polymer electrolyte fuel cells are based on proton exchange membranes (PEMs), in particular Nafion membranes. However, the high cost caused by the use of noble metals as catalysts hinders the widespread deployment of fuel cell technology. To solve this problem, there has been an increasing interest in developing hydroxide exchange membranes (HEMs) for fuel cell applications because it enables non-precious metals (e.g., nickel) as catalysts. In addition, HEM fuel cells also have the potential to offer fuel flexibility, reduce fuel crossover and prevent carbonate precipitation.

              The most commonly used HEMs today are quaternary ammonium based polymers. But currently available ammonium based HEMs were found to have low hydroxide conductivity and stability. In order to improve the performance, HEMs with novel functional groups have been explored. Recently, we have synthesized quaternary phosphonium based polymers and showed that they have higher hydroxide conductivity and stability than ammonium ones [1,2]. We have also implemented crosslinking for reducing water uptake and swelling [3]. Like phosphorus, sulfur is another neighbor of nitrogen in the periodic table and triarylsulfonium salts were reported to have high alkaline stability, which indicates that the corresponding form of sulfur°ªtertiary sulfonium based polymer is potentially a promising candidate for HEMs.

              In this study, we synthesized triarylsulfonium based polymers with functional groups either in the backbone or in the side chains. For the former, it was synthesized by reacting poly(arylenethioethersulfone) (PTES) with arylating agent, while the latter was synthesized by reacting brominated triarylsulfonium salt with polysulfone. The structures of these two polymers are characterized by NMR, infrared spectroscopy and elemental analysis. The alkaline stability and water uptake of the membranes were also tested. In addition, hydroxide conductivities were measured as a preliminary test for the application in alkaline fuel cells.

References

[1] S. Gu, R. Cai, T. Luo, Z. Chen, M. Sun, Y. Liu, G. He, Y. Yan, Angewandte Chemie International Edition 2009, 48, 6499.

[2] S. Gu, R. Cai, T. Luo, K. Jensen, C. Contreras, Y. S. Yan, ChemSusChem, 2010, 3, 555.

[3] S. Gu, R. Cai, Y. S. Yan, Chem. Commun., 2011, 47, 2856.

Key words: Sulfonium, Hydroxide exchange membrane, Fuel cells