Proton exchange membranes containing densely sulfonated quinquephenylene groups for high performance and durable fuel cells

For proton exchange membrane fuel cell applications, poly(arylene perfluoroalkylene)-based ionomers containing densely sulfonated quinquephenylene groups in the main chain (SPAF-QP) are synthesized. The combination of highly hydrophobic perfluoroalkylene and highly hydrophilic sulfonated quinquephenylene units is designed to achieve high proton conductivity with reasonable ion exchange capacity (IEC) values (1.83-1.97 meq g-1). Compared with our previous SPAF-MM membrane with fewer sulfonated hydrophilic groups, SPAF-QP membranes exhibit significant improvement in the proton conductivity, especially at low humidity (up to 6.9 mS cm-1 at 80 °C and 20% RH). The selected SPAF-QP (1 : 0.22) membrane exhibits much better fuel cell performance than the SPAF-MM membrane and comparable performance to the Nafion NRE 211 membrane even under low humidified conditions. The SPAF-QP cell also shows comparable mass activity of the Pt catalyst with that of the Nafion NRE 211 cell. During the open circuit voltage (OCV) hold test, the SPAF-QP cell retains high OCV over 0.95 V for 1000 h with a small average decay of 50 μV h-1. Post-test analyses reveal that the SPAF-QP cell retains its initial fuel cell performance with negligible changes of the molecular structure of the membrane. These properties of the SPAF-QP membrane seem highly promising for practical fuel cell applications. This journal is