Research On Sulfonated SBS Proton Exchange Membranes

Fuel cell is an instrument which converts the chemical energy of fuel and oxidant to electricity directly. Proton exchange memebrane fuel cell (PEMFC) is the fifth generation of fuel cell after the alkaline fuel cell, phosphorous fuel cell, molten carbonate fuel cell and solid oxide fuel cell. Proton exchange membranes are key materials for PEMFC. It is necessary to develop substitude membranes for perfluorosulfonic membranes because of high cost. A research of block copolymers as proton exchange materials was proposed in this thesis basing on the analysis of the relationship between the structure and performance of the perfluorosulfonic membranes and the status of research for substitude membranes home and abroad.A novel proton exchange material was fabricated through sulfonating the PolyStyrene-PolyButadiene-PolyStyrene copolymer(SBS) by the acetyl sulphate. The properties of the membranes such as proton conductivity, water uptake , swelling degree and thermal stability were measured. Results show that the sulfonated SBS membranes had good proton conductivity , at the same time, the water uptake and the swelling degree could meet the need of fuel cell. But the strength of sulfonated SBS membranes was poor and the dry membranes was brittle. The sulfonating reaction was found on the unsaturation bonds of polybutadiene basing on the research of dynamics of the sulfonating action and FTIR analysis of reacted products. It was supposed to be the reason for the brittleness of dry membranes. Resulting from the instability of bond of the [-SO3H] and C=C , the thermal stability of SBS decreased after sulfonation was found in our research. Despite of this, it had some potential value in the low temperature fuel cell. The power density of single cell achieved 0.138 W/cm2 under 40C.Fiber/sulfonated SBS composite membranes were made by way of integrating S-SBS with the glass fiber felts, just in connection with the problems of the brittleness and poor strength of S-SBS membranes. Comparing with the S-SBS membranes, the strength of composite membranes increased over 200% without increasing the resistance, meanwhile the swelling degree was decreased that resulted in the increase of dimention stability. The results of scan electron microscope indicated the close connection between the fibers and resin that meant the fibers could strengthen the membranes. The experiments of generating electricity showed that the power density of the single cell made from composite membranes could reach 0.14W/cm2 under 40C.The microphase seperation of S-SBS was also studied by transmission electron microscope. The difference of microphase seperation of SBS and S-SBS was compared by the way of staining the C=C by OsO4. The form of ion cluster was observed by transforming the [-SO3H] to [-SO3Ag] and the theory of the forming of cluster was discussed in this thesis. It was concluded that both the ion cluster and multiplet coexist in the membranes.