Sulfonated poly(ether ether ketone)(SPEEK) is a very promising alternative membrane material for direct methanol fuel cells (DMFC).The demand of high proton conductivity calls for the membranes to have a high degree of sulfonation (DS) and work at elevated temperatures.However

with a fairly high DS

SPEEK membrane can swell excessively and even dissolve at high temperatures.To deal with this contradictory situation

phenolphthalein poly(ether sulfone)(PES-C) and sulfonated phenolphthalein poly(ether sulfone)(SPES-C

DS=53.7%) were respectively blended into SPEEK polymer to prepare SPEEK/PES-C and SPEEK/SPES-C blend membranes.DSC results revealed that the two blended polymers showed good miscibility.The effect

that both PES-C and SPES-C can decrease effectively the swelling degree and methanol permeability of blend membranes

became evident with the increment of PES-C and SPES-C contents.Pure SPEEK membrane dissolved completely at 75℃

however

the swelling degree of SPEEK/PES-C（30%）and SPEEK/SPES-C（30%）were 22.5％ and 26.32% at 80℃

respectively.From room temperature to 80℃

the blend membranes presented methanol permeability of around 10-7cm2·s-1

which was about one order of magnitude lower than that of Nafion115.Under 100% relative humidity

the proton conductivity of blend membranes with 20 wt% PES-C exceeded that of Nafion115 above 90℃

the proton conductivity of blend membranes with 30 wt% SPES-C reached 0.11 S·cm-1 of Nafion115 at 110℃.The blend membranes are promising for DMFC application because of their improved applicable temperature

high conductivity and low methanol permeability.