Enhanced proton conductivity of the proton exchange membranes by the phosphorylated silica submicrospheres

Two kinds of phosphorylated silica submicrospheres were synthesized and incorporated into the sulfonated poly(ether ether ketone) (SPEEK) matrices to fabricate the hybrid membranes. Phosphorylation was carried out by the reaction of phosphorus oxychloride and the epoxy groups on the silica surface introduced by glycidyl-silane (Sip-I) or poly(glycidyl methacrylate) (Sip-II). The length of the chains and the amount of phosphoric acid groups (-PO3H2) grafted on the silica surface were tuned by the above two different phosphorylation methods. The dispersion of SiP-II, anti-swelling and methanol resistant property of the SPEEK/SiP-II hybrid membranes were all enhanced. And the proton conductivity was increased by doping with both kinds of phosphorylated silica particles. While the SPEEK/SiP-I hybrid membranes with less amounts of -PO3H2 groups showed unexpectedly much higher proton conductivities than the SPEEK/SiP-II hybrid ones at the same loadings ranging from 5 wt% to 20 wt%, and the highest reached 0.335 S cm(-1) at 60 degrees C and 100% RH. The result was tentatively discussed in terms of effective proton-conducting groups/sites instead of the absolute amount of acidic groups. (C) 2012 Elsevier B.V. All rights reserved.