Preparation And Properties Of Proton Exchange Membrane Doped With Heteropolyacids

Perfluorinated sulfonic acid proton exchange membrane is the key component of polymer proton exchange membrane fuel cell, through which allows protons to pass but not water and gas. Properties of the PEM, like mechanical strength, elevated temperature resistance and chemical resistance, have great impact on life time of the membrane. Modification of the PEM doped with inorganic hydrophilic particles, inorganic proton conductors can largely enhance thermal stability and high temperature water retention of it, is of great significance.Using the method of sol-gel and crosslinking, the domestic perfluorinated sulfonic acid ionic membrane provided by Dongyue Group, were doped with Phosphomolybdic acid(PMoA), Silicotungstic acid(SiWA), TiO2and SiO2particles. And then PMoA/SiWA-PEM, SiWA-PEM, TiO2/SiO2-PEM can be obtained. Then, impedance spectrum at the temperature of20℃,30℃～90℃and low-temperature of0℃～-30℃of the PEM were measured, respectively. Therefore, proton conductivity of the composite membrane can be obtained. It can be found that proton conductivity of the film is significantly higher than the original membrane. For as in90℃example, proton conductivity of the PMoA/SiWA-PEM and the original film are27.5×10-6S·cm-1and2.70×10-6S·cm-1. With the temperature increasing, proton conductivity of both original and composite membrane shows a tendency to increase. When it raises from20℃to90℃, proton conductivity of TiO2/SiO2-PEM rises about3times compared to20℃. The influence of perturbation amplitude(5mV,10mV,20mV,100mV, respectively) on the impedance spectrum were also measured. But little influence can be found on the high frequency semicircles with the perturbation amplitude changs.Use thermo-gravimetric method to investigate thermal stability of the composite membrane. For PMoA/SiWA-PEM, using Kissinger and Flynn-wall-Ozawa method to study its thermal degradation kinetics and we can get kinetic parameters such as apparent activation energy E, correlation coefficient r, and so on. Make a comparison of the original and composite membrane, when the temperature is below363.3℃, thermal stability of the composite membrane is not good as the original film; however, when the temperature is above363.3℃, composite membrane shows better stability. For SiWA-PEM and TiO2/SiO2-PEM, using Kissinger, Flynn-Wall-Ozawa, Starink and Friedman method to study their thermal degradation kinetics, Achar-Brindley-Sharp and Coats-Redfern and a-Z(a) mothod were employed to deduce their possible thermal degradation mechanisms. Mechanism of SiWA-PEM in first thermal degradation stage is controlled by the R1function is:f(a)=1, g(a)=a; in second thermal degradation stage is controlled by F2mechanism. Thermal decomposition mechanism is also controlled by F2mechanism.