The present paper focuses on improving the water-holding ability of sulfonated poly(ether ether ketone) (SPEEK) (degree of sulfonation

DS = 55.1%) membranes.Functionalized silica (silica sol (SiO2) and silica powder with sulfonic acid groups (SiOx-S)) were chosen as the hygroscopic additive

respectively.SPEEK/SiO2、SPEEK/SiOx-S composite membranes were obtained by casting a homogeneous mixture of SiO2 (or SiOx-S) and SPEEK in N

N-dimethylacetamide onto glass plate and then evaporating the solvent at 60℃.The decrease in both the swelling degree and the methanol permeability and the improvement in the conductivity at a high temperature and a low humidity of the membranes were a dose-dependent result of addition of the SiO2 and SiOx-S powders.Pure SPEEK membranes swelled 52.6% at 80℃

whereas the SPEEK/SiO2 (15 wt%) and SPEEK/SiOx-S (15 wt%) membranes swelled only 26.2% and 27.3% at the same temperature

respectively.From room temperature to 80℃

SPEEK/SiO2 (20 wt%) and SPEEK/SiOx-S (20 wt%) membranes had methanol permeability of about two order of magnitude lower than that of Nafion 115.At 120℃ and 40% relative humidity (RH)

the conductivity of pure SPEEK membranes is only 2.610-4 Scm-1

and that of SPEEK/SiO2 (20 wt%) membranes is about 2.010-3 Scm-1

while that of SPEEK/SiOx-S (20 wt%) composite membranes reaches 1.010-2 Scm-1

which is close to that of Nafion 115.DMFCs single cell performance of SPEEK/SiO2 (20 wt%) and SPEEK/SiOx-S (20 wt%) membranes was better than that of pure SPEEK membranes because they had good dimensional stability and no separation of catalyzers and membranes in membrane electrode assembles.