The Modification Of Sulfonated Poly Ether Ether Keton Proton Exchange Membranes For Dmfc Applications

Proton exchange membrane is the heart of direct methanol fuel cells (DMFC), which plays the critical role of separating the anode and cathode side of DMFC and transferring the hydrated proton, etc. Although the commercialized Nafion membranes have been successfully applied in the hydrogen proton exchange membrane fuel cells (PEMFC), their high methanol penetrating coefficient and poor dimension stability make them difficult to be used in DMFC. In order to overcome the deficiencies of Nafion membranes, Poly ether ether keton (PEEK) was chosen as the base polymer and it was modified by chemical ways to prepare the sulfonated, hybrid, and crosslinked proton exchange membranes, respectively.1. PEEK was sulfonated by the concentrated sulfuric acid to synthesis the sulfonated PEEK (sPEEK) with hydrophilic surface. The affecting factors of sulfonation degree (SD) and the structure and properties of sPEEK membranes were investigated. The results showed that both the SD and the ion exchange content increased with the elongation of the reaction time. The amount of H2SO4affected the SD most seriously. The proton conductivity of sPEEK membranes increased with the accretion of SD. The membrane with the SD of83%possessed the higher proton conductivity than Nafion, which amounted to0.0755s·cm-1. The dimension stability of these membranes was poor, which could even dissolve in the methanol solution at high SD.2. TEOS was used as the inorganic precursor to prepare the sPEEK/SiO2hybrid membranes. The hydrolysis and polycondensation process of TEOS and the structure and properties of hybrid membranes were researched. The gelation time of TEOS abbreviated with the increase of temperature and decrease of ethanol amount. SiO2was dispersed evenly in sPEEK. The proton conductivity of all the hybrid membranes with different SiO2content was higher than Nafion115and the proton conductivity increased with elevating the temperature and decreasing the SiO2amount. The methanol penetrating coefficient was decreasing with the increase of SiO2content. The methanol penetrating coefficient of the hybrid membrane with8wt.%SiO2is of the order10-7cm2·s-1, compared with10-6cm2·s-1of Nafion115.3. NaBH4was used as the reducing agent to change the carbonyl group of sPEEK into the hydroxyl group. The new polymer was named sPEEA which was followed by a dehydration reaction using H2SO4as the dehydrating agent to prepare the crosslinked membranes. The factors which affected the hydroxyl value of sPEEA were discussed. The crosslinked degree, the swelling degree, the proton conductivity, the methanol penetrating coefficient as well as the dynamic mechanical thermal properties of crosslinked membranes were all tested. The results showed that all the membranes were totally crosslinked and the swelling degree reduced with the increase of H2SO4amount, which could even reduce to a lower level than Nafion115. The proton conductivity of crosslinked membranes decreased with the increase of H2SO4amount firstly at room temperature, and then increased. Proton conductivity at different temperature satisfied the Arrhenius equation. The methanol penetrating coefficient of crosslinked membranes had the same magnitude order but lower value than Nafion115when the H2SO4amount was higher, and the glass transition temperature was much higher after modification.