(635e) Hybrid Membranes for Proton Exchange Membrane Fuel Cell

Hybrid membranes prepared by incorporating inorganic fillers into the polymer matrix are promising candidates for proton exchange membranes (PEMs) and have spurred increasing attention. The work in our group mainly focuses on the regulation of membrane microstructure (e.g. free volume) and the intensification of membrane performances (e.g. methanol barrier property, proton conductivity). Inorganic fillers can regulate the free volume of the resultant hybrid membrane by interfering the mobility of polymer chains. It is found that the polymer-inorganic interfacial interaction governed the membrane microstructure: i) attractive force would generate strong interfacial stress, which inhibits the mobility of polymer chains and leads to dense chain packing, in turn reducing free volume cavity size; and ii) repulsive force enhances the mobility of polymer chains, which allows for a loosened chain packing and increased free volume cavity size. The methanol transport of through PEM can be described by solution-diffusion mechanism. Inorganic fillers can change the hydrophilic/hydrophobic nature of membrane surface, which in turn tunes the methanol dissolution. Meanwhile, inorganic fillers can tune the methanol diffusion by adjusting the free volume and methanol affinity properties of membrane bulk. Both the filler structure (e.g. shape, particle size, pore size) and filler composition (e.g. hydrophilic/hydrophobic nature, acid/base property) can affect methanol dissolution and diffusion properties of hybrid membranes. Accordingly, the methanol barrier property of hybrid membrane can be intensified. The less-conducting inorganic fillers generally dilute the concentration of proton conducting group and reduce water uptake, resulting in reduced proton conductivity of hybrid membranes. Therefore, the filler surface is modified to introduce proton-conducting groups, which render additional pathways for proton transfer. Furthermore, the proton transfer barrier can be reduced by optimizing proton donor/acceptor ability of the conducting groups. In addition to polymer-inorganic hybrid membrane, inspired by the water storage mechanisms in plant cells, polymeric microcapsules are synthesized and incorporated into polymer matrix to prepare polymer-organic ?hybrid membrane?. The microcapsules serve as water reservoirs and enhance water retention properties in particular under low humidity, endowing hybrid membranes with high proton conductivity.