A sulfonated poly(ether ether ketone)(SPEEK) membrane with fairly high degree of sulfonation(DS) swells excessively and even dissolves at high temperature.To solve these problems

sulfonated phenolphthalein poly(ether sulfone)(SPES-C

DS=53.7%) is blended with the SPEEK matrix(DS=55.1%

61.7%) to prepare SPEEK/SPES-C blend membrane.The decrease in swelling degree and methanol permeability of the membrane is dose-dependent.Pure SPEEK(DS=61.7%) membrane dissolves completely in water at 70℃

whereas the swelling degree of the SPEEK(DS=61.7%)/SPES-C(40%

by mass) membrane is 29.7% at 80℃.From room temperature to 80oC

the methanol permeability of all SPEEK(DS=55.1%)/SPES-C blend membranes is about one order of magnitude lower than that of Nafion115.At higher temperature

the addition of SPES-C polymer increases the dimensional stability and greater proton conductivity can be achieved.The SPEEK(DS=55.1%)/SPES-C(40%

by mass) membrane can withstand temperatures up to 150℃.The proton conductivity of SPEEK(DS=55.1%)/SPES-C(30%

by mass) membrane approaches 0.16 S·cm

-1

matching that of Nafion 115 at 140℃ and 100% RH

while pure SPEEK(DS=55.1%) membrane dissolves at 90℃.The SPEEK/SPES-C blend membranes are promising for use in direct methanol fuel cells because of their good dimensional stability

high proton conductivity

and low methanol permeability.