Studies On Proton Conductors Working At High Temperatures And Low Humidity

Proton exchange membrane (PEM) is the key factor of proton exchange membrane fuel cell (PEMFC), and the performance of PEMFC depends on PEM. At the present time, the perfluorosulfonic PEM is used in PEMFC extensively, such as Nafion. Because of water dependence proton conductivity, its working temperature is usually lower than 80℃, which brings some problems such as low conductivity, critical water and thermal managements and catalyst poisoning by fuel impurities. Developing high temperature PEM can solve the problems mentioned above. So researching high temperature PEM is one of the important issues in PEMFC.In this work, imidazole and pyridine were doped in pure phosphoric acid to obtain the proton conducting system with high proton conductivity at high temperature and low humidity. The conductivity of imidazole or pyridine doped pure phosphoric acid was lower than that of pure phosphoric acid. SnP2O7 and SnInP2O7 were synthesized from tin oxide, indium oxide and 85% phosphoric acid. SnP2O7 was employed to prepare anhydrous conducting membranes based on sulfonated polyetheretherketone (SPEEK) and polyvinylidenefluoride (PVDF), respectively. The conductivities of SnP2O7 and its composite membranes as well as the mechanical strength of the composite membranes were investigated at room temperature and at 130℃under anhydrous conditions. The conductivity of SnP2O7 was 0.058 S/cm at 200℃. At the same temperature and with the same content of SnP2O7, the mechanical strength of SnP2O7/PVDF was better than SnP2O7/SPEEK. For example, the content of SnP2O7 was 40% in both composite membranes, the stress of SnP2O7/PVDF was 14.95MPa, comparing to 6.36MPa of the SnP2O7/SPEEK with the sulfonation degree of 51% at 130℃. The influences of SnP2O7 content and temperature on the mechanical properties were also investigated.