SULFONATED POLY(ETHER ETHER KETONE)/ZIRCONIUM TRICARBOXYBUTYL-PHOSPHONATE COMPOSITE PROTON-EXCHANGE MEMBRANES FOR DIRECT METHANOL FUEL CELLS

Abstract

Sulfonated poly(ether ether ketone) (SPEEK) is a very promising alternative membrane material for direct methanol fuel cells.However,with fairly high degree of sulfonation (DS) SPEEK membranes can excessively swell or even dissolve at high temperatures.This restricts the membranes from working above a high tolerable temperature to get the high proton conductivity.To deal with this contradictory,insolvable zirconium tricarboxybutylphosphonate (Zr(PBTC))powder was employed to make composite with SPEEK polymerwith the attempt to improve the temperature tolerance of membranes.SPEEK/Zr(PBTC) composite membranes were obtained by casting homogeneous mixtures of Zr(PBTC)and SPEEK in N,N-dimethylacetamide on glass plates and then evaporating solvent at 60℃.Many characteristics of composite membranes were investigated,including thermal stability,liquid uptake,methanol permeability and proton conductivity.Results show that not only the temperature tolerance but also the methanol resistance of the SPEEK/Zr(PBTC) composite membranes was improved.The composite membranes with 30 wt%～40 wt% of Zr(PBTC) have their methanol permeability around 10~ -7 cm~25s~-1 ,which is one order of magnitude lower than that of Nafion~115.High proton conductivity of the composite membranes can be also achieved because of the increased high tolerable temperature.Under 100% relative humidity the conductivity of the composite membrane with 40 wt% of Zr(PBTC) exceeded that of the Nafion~ 115 membrane at 90℃ and reached a high value of 0.36 S5cm~ -1 at 160℃.Improved applicable temperature and high conductivity of the composite membrane indicate its promising application in DMFC operating at high temperature.