Preparation And Research Of IPTES Chemically Bonded HEDPA High Temperature And Low Humidity Proton Exchange Membrane

Proton exchange membrane fuel cells (PEMFC) show many advantages, such ashigh energy conversion efficiency, high energy density, low pollution levels, rapidstart-up, modular design and flexibility of scale (a few watts to hundreds of kilowatts).So PEMFC is considered to be a promising energy conversion systems technology forapplications ranging from transport, distributed power station, combined heat andpower (CHP) and portable electronic devices. The proton exchange membrane (PEM)is a key component of PEMFC, which directly determine the performance of PEMFC.Currently, the most commonly used perflurosulfonic acid membrane is not cheapat all and its performance is still not satisfactory; this becomes one of the obstacles tohinder the commercialization of fuel cells. Inorganic-organic hybrid membrane is oneof promising matrices for the proton-conducting materials because blending oforganic and inorganic components properties. Especially the organosiloxane-basedInorganic-organic hybrid membranes have attracted much attention for thedevelopment of high temperature PEM due to the simple of preparation conditions,good thermal stability, low cost and high proton conductivity.Proton conductive inorganic-organic hybrid membranes were synthesized from3-Isocyanatopropyltriethoxysilane (IPTES),1-hydroxyethane-1,1-diphosphonic acid(HEDPA) and Tetraethoxy-silicone(TEOS) by the sol-gel method. The hybridmembranes with different amounts of phosphonic acid were studied with respect totheir structural, thermal properties, water uptake and swelling property, protonconductivity and proton conduction mechanism.The results of FT-IR and13C NMR revealed that phosphonic anid groups ofHEDPA were chemcially bound to organosiloxane network as a results of reactionbetwee HEDPA and IPTES. The leach out of phosphonic acid groups from hybridmembranes were reduced. XRD patterns of the hybrid membranes showed diffractionpeaks assigned to Si-O backbones, and the membranes are amorphous. In addition,the formation of silicon-oxygen network is inhibited by increase the content ofphosphonic acid. Thermal analysis including TG and DSC confirmed that the hybridmembranes were thermally stability up to225℃and may be suitable for the use in thehigh temperature range of100~200℃for PEMFC. All membranes samples possess better water absorption and dimensional stability. The higher the content ofphosphonic acid is, the more water absorption and swelling degree is.Proton conductivity of the hybrid membranes increased with phosphonic acidcontent, In addition, the proton conductivity depended on the temperature and relativehumidity. The conductivities of the membranes IHM-3with a molar ratio ofIPTES/TEOS/HEDPA=1/0.5/0.8were4.6×10-2S cm-1and2.36×10-2S cm-1at100％relative humidity and non-humidified conditions, respectively, at160℃.1H and31PMAS NMR studies demonstrated that strong hydrogen bonds formed betweenphosphonic acid with carbamate groups, or just between phosphonic acid groups. Theproton conductive sites (P-OH) are likely to be partially immobilized by strongprotonic receptors (carbanyl group in carbamate), which reduces the free P-OHgroups. But the synergistic effect of N and P enhanced the continuous of hydrogenbond network. Variable-temperature FT-IR analysis revealed that the dynamicalhydrogen bond networks provide a continuous proton conduction pathway,accomplishing protons transport between phosphoric acid molecules through thehydrogen bond breaking and forming possesses. So the Vehicle mechanism dominatesthe proton conduction at high humidity, whereas the conductivity at low humidity islikely a consequence of the Grotthuss mechanism.