Preparation and performance of different amino acids functionalized titania-embedded sulfonated poly (ether ether ketone) hybrid membranes for direct methanol fuel cells

A series of amino acid functionalized titania submicrospheres were synthesized and incorporated into sulfonated poly (ether ether ketone) (SPEEK) to fabricate organic-inorganic hybrid proton exchange membranes. Pristine TiO2 with a uniform particle size of ~200nm were synthesized and functionalized with four kinds of amino acids including oxidized l-cysteine, O-phospho-l-serine, aspartic acid and histidine, designated as TiO2-Scys, TiO2-Pser, TiO2-Asp and TiO2-His, respectively. The effects of amino acid attribute on the membrane properties were investigated. At the filler content of 15wt%, the TiO2-Scys embedded membrane exhibited the highest proton conductivity of about 5.98×10-3Scm-1 (20°C, 100% RH), while the TiO2-His embedded membrane exhibited the lowest conductivity due to the strong acid-base interaction between the basic imidazole groups of histidine and the sulfuric acid groups of SPEEK. The TiO2-Pser embedded membrane exhibited the highest selectivity of 17.10×103Sscm-1. In addition, the methanol crossover of the hybrid membranes was reduced by two folds, and the anti-swelling property and thermal stability of the hybrid membranes were also enhanced. © 2014 Elsevier B.V.