Low temperature proton exchange membrane (PEM) fuel cells that use perfluorinated sulfonic acid are at present being commercialized in fuel cell vehicles, but these cells can operate only at relatively low temperatures, ca. < 100°C, and high hydration levels. High temperature PEM fuel cells that use phosphoric acid-doped polybenzimidazole can operate effectively up to 180°C; however, these are difficult to operate below 140°C without suffering loss of phosphoric acid when exposed to water.¹ In this presentation, we discuss a new class of fuel cells based on ion pair-coordinated proton exchange membranes.²

In the ion pair-coordinated proton exchange membranes, quaternary ammonium functionalized membranes, also known as anion exchange membranes, are doped with phosphoric acid. Due to the high basicity of the quaternary ammonium hydroxide, the acidic proton of phosphoric acid is completely deprotonated to form a strong ionic interaction between quaternary ammonium and biphosphate. Our density functional theory calculation indicated that the ion-pair interaction is 8.5 times greater than the conventional acid base interaction in the phosphoric acid doped polybenzimidazole. The strong interaction between the ion pair enables fuel cell operation at lower temperatures with substantially higher water partial pressure than are possible for high-temperature phosphoric acid doped polybenimidazole fuel cells. In this presentation, the chemical structural difference between this new system and the conventional phosphoric acid-doped polybenzimidazole system will be compared. The benefits and challenges of the new system in fuel cell operations will be further discussed.

Acknowledgment

This work was supported by the US Department of energy, Energy Efficiency and Renewable Energy, Fuel Cell Technology Office (Program Manager: Dimitrios Papageorgopoulos).

References

1. G. Bendlamudi Systematic Characterization of HT PEMFCs Containing PBI/H₃PO₄ Systems: Thermodynamic analysis and Experimental Investigations 104 (Logos Verlag Berlin GmbH, 2011).
2. Kwan-Soo Lee, Jacob S. Spendelow, Yoong-Kee Choe, Cy Fujimoto, and Yu Seung Kim Nature Energy, 1, 16120 (2016).