Fabrication of sulfonated poly(ether ether ketone)-based hybrid proton-conducting membranes containing carboxyl or amino acid-functionalized titania by in situ sol–gel process

• Carboxylic acid or amino acid functionalized titania sol are prepared.
• Functionalized titania is incorporated into SPEEK through in situ sol–gel method.
• The proton conductivity of hybrid membrane is 3.5 times higher than pure SPEEK.
• The methanol permeability of hybrid membranes is effectively suppressed.

Functionalized titania are used as fillers to modify the sulfonated poly(ether ether ketone) (SPEEK) membrane for improved proton conductivity and methanol barrier property. The functionalized titania sol which contains proton conductive carboxylic acid groups or amino acid groups are derived from a facile chelation method using different functional additives. Then the novel SPEEK/carboxylic acid-functionalized titania (SPEEK/TC) and SPEEK/amino acid-functionalized titania (SPEEK/TNC) hybrid membranes are fabricated via in situ sol–gel method. The anti-swelling property and thermal stability of hybrid membranes are enhanced owing to the formation of electrostatic force between SPEEK and titania nanoparticles. The hybrid membranes exhibit higher proton conductivity than plain SPEEK membrane because more proton transfer sites are provided by the functionalized titania nanoparticles. Particularly, the proton conductivity of SPEEK/TNC membrane with 15% filler content reaches up to 6.24 × 10−2 S cm−1, which is 3.5 times higher than that of the pure SPEEK membrane. For methanol permeability, the SPEEK/TNC membranes possess the lowest values because the acid-base interaction between sulfonic acid groups in SPEEK and amino groups in functionalized titania leads to a more compact membrane structure.