Hybrid cross-linked membranes of SPES/TEOS/TPABS for direct methanol fuel cells (DMFCs) are synthesized by sulfonated poly(ether sulfone) (SPES), tetraethoxysilane (TEOS) and a zwitterionic silica containing sulfonic acid and ammonium groups, 3-[[3-(triethoxysilyl)-propyl]amino]butane-1-sulfonic acid (TPABS) using a sol-gel process with the goal of obtaining high proton conductivity, low methanol permeability and good stability. Increasing the amount of inorganic zwitterionic TPABS produces membranes that become denser and more uniform. The increasingly SO3-rich cross-linked networks consequently lead to higher proton conductivity and lower methanol permeability. It should be noted that the proton conductivity reaches as high as that of Nafio (R) n 117, whereas the methanol permeability is greatly reduced by the formation of the cross-linked structures. Among these membranes, SPES/TEOS/TPABS-70 (70 wt % of TPABS to SPES in the membrane matrix), shows the best performance with a proton conductivity value of 7.24 x 10(-2) S cm(-1), methanol permeability value of 2.46 x 10(-7) cm(2) s(-1), ion-exchange capacity value of 1.37 mequivg(-1) and a comparable selectivity parameter of 2.63 x 10(5) S cm(-3) s. (C) 2012 Elsevier B.V. All rights reserved.