Sulfonated poly(ether ether ketone)/zirconium tricarboxybutylphosphonate composite proton-exchange membranes for direct methanol fuel cells

摘要

Sulfonated poly(ether ether ketone)(SPEEK)is a very promising alternative membrane material for direct methanol fuel cells.However,with a fairly high degree of sulfonation(DS),SPEEK membranes can swell excessively and even dissolve at high temperature.This restricts mem-branes from working above a high tolerable temperature to get high proton conductivity.To deal with this contra-dictory situation,insolvable zirconium tricarboxybutyl-phosphonate(Zr(PBTC))powder was employed to make a composite with SPEEK polymer in an attempt to improve temperature tolerance of the membranes.SPEEK/Zr(PBTC)composite membranes were obtained by casting a homogeneous mixture of Zr(PBTC)and SPEEK in N,N-dimethylacetamide on a glass plate and then evaporating the solvent at 60℃.Many characteristics were investigated,including thermal stability,liquid uptake,methanol permeability and proton conductivity.Results showed significant improvement not only in tem-perature tolerance,but also in methanol resistance of the SPEEK/Zr(PBTC)composite membranes.The mem-branes containing 30 wt-%,40 wt-% of Zr(PBTC)had their methanol permeability around 10^(-7) cm^(2)·s^(-1) at room temperature to 80℃,which was one order of magnitude lower than that of Nafion H 115.High proton conductivity of the composite membranes,however,could also be achieved from higher temperature applied.At 100% rela-tive humidity,above 90℃ the conductivity of the compo-site membrane containing 40 wt-% of Zr(PBTC)exceeded that of the Nafion H 115 membrane and even reached a high value of 0.36 S·cm^(-1) at 160uC.Improved applicable tem-perature and high conductivity of the composite membrane indicatedits promisingapplication in DMFC operationsat high temperature.