Cross-linked zwitterionic polyelectrolytes based on sulfonated poly(ether sulfone) with high proton conductivity for direct methanol fuel cells

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 SO 3 -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 Nafion ® 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   ×   10 −2   S   cm −1 , methanol permeability value of 2.46   ×   10 −7   cm 2   s −1 , ion-exchange capacity value of 1.37   mequiv   g −1 and a comparable selectivity parameter of 2.63   ×   10 5   S   cm −3   s.