(578c) Phosphoric Acid Doped Ion-Pair Coordinated Proton Exchange Membrane with Improved Water Tolerance

It is well-known that sulfonic acid-based proton exchange membrane (PEM), such as Nafion^®, highly relies on water molecules to achieve efficient proton transport, thus limiting its operating conditions to low temperature (<100 ˚C) and high relative humidity (>80% RH). By contrast, phosphoric acid-doped polybenzimidazole PEMs only work at high temperatures (typically >140 ˚C) and anhydrous environments. Otherwise, their performance would severely decline due to the phosphoric acid leaching. Therefore, a new type of PEM that is capable of working effectively within a wide operating window is highly desirable for the sake of further commercialization of PEM fuel cells. This presentation will report a phosphoric acid-doped ion-pair coordinated PEM which exhibits high proton conductivity and improved water tolerance. The material was prepared from a biphenyl backbone-based quaternary ammonium polymer, and the existence of quaternary ammonium cation-biphosphate anion ion pair interaction enables to maintain stable proton conductivity across a broad relative humidity range. The effect of the size and structure of three different cation head groups on the ion-pair interaction and PEM performance will also be discussed. Our ion-pair PEM outperforms Nafion^® in terms of proton conductivity at low-to-intermediate RHs, and a good conductivity stability test indicates it could tolerate up to 70% RH at 80 ˚C. These results, as well as its excellent chemical stability and mechanical properties, impart great potential for this type of PEM to be employed among multiple electrochemical applications.