Development of new ionomeric binding materials for the fabrication of fuel cell electrode is important to enhance performance and durability of alkaline membrane fuel cells.¹ Recently we reported that adsorption of benzene groups in the polymer electrolytes on Pt-based electrocatalyst may cause an adversary impact on the activity of the hydrogen oxidation reaction under alkaline condition.² In order to mitigate such adverse impact and further improve the fuel cell durability, here we report a new design of polyaromatic ionomers with dimethyl substituted aromatic backbone from acid-catalyzed Friedel-Crafts polycondensation³ using 2,2’-dimethylbiphenyl as a monomer. The backbone of the ionomer does not contain alkaline-labile aryl-ether linkage for chemical durability in high temperature alkaline condition.⁴

The hydroxide form of the ionomers with ion exchange capacity of 2.5 meq./g showed good solubility in a wide range of solvents including methanol, ethanol, isopropanol and polar aprotic solvents, which eases the fabrication of materials as electrode binders. The performance of the dimethylated ionomeric binders was tested in membrane electrode assembly using Pt-based catalysts under H₂/O₂ conditions and compared to that of poly(biphenyl alkylene) without methyl substituents. The membrane electrode assembly using the dimethylated ionomers showed good performance (peak power density up to 600 mW/cm²) with stable short-term stability. In this presentation, further structural effect of the polyaromatic ionomers will be discussed with other critical fuel cell operation factors that link with fuel cell performance.

Acknowledgments

This work is supported by the US Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technology Office (Program Manager: David Peterson).

References

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