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

insolvable functionalized silica powder with sulfonic acid groups(SiO

x

-S) was added into the SPEEK matrix(DS=55.1%) to prepare SPEEK/SiO

x

-S composite membranes.The decrease in both the swelling degree and the methanol permeability of the membranes was a dose-dependent result of addition of the SiO

x

-S powder.Pure SPEEK membrane swelled 52.6% at 80℃

whereas the SPEEK/SiO

x

-S(15%

by mass) membrane swelled only 27.3% at the same temperature.From room temperature to 80℃

all SPEEK/SPEEK/SiO

x

-S composite membranes had methanol permeability of about o ne order of magnitude lower than that of Nafion 115.Compared with pure SPEEK membranes

the addition of the SiO

x

-S powder not only leads to higher proton conductivity

but also increases the dimensional stability at higher temperatures

and greater proton conductivity can be achieved at higher temperature.The SPEEK/SiO

x

-S(20%

by mass) membrane could withstand temperature up to 145℃

at which in 100% relative humidity(RH) its proton conductivity exceeded slightly that of Nafion 115 membrane and reached 0.17 S·cm

-1

while pure SPEEK membrane dissolved at 90℃.The SPEEK/SiO

x

-S composite membranes are promising for use in direct methanol fuel cells bec

ause of their good dimensional stability

high proton conductivity

and low methanol permeability.