Preparation And Conductivity Of Vanadium-Substituted Multiple Heteropoly Compounds And Their Hybrid Materials

Solid high-proton conductors are the core of many technological innovations, including hydrogen and humidity sensors, hydrogen permeation membranes, membranes for water electrolyzers, and most importantly high-efficiency electrochemical energy conversion in fuel cells working at low temperature (polymer electrolyte membrane or proton exchange membrane fuel cells, PEMFC) or intermediate temperature (proton-conducting ceramic fuel cells, PCFC). With the development of human civilization and science and technology, the exploitation of renewable energy has become an important subject of the international energy research. Thus, the exploration of new materials with high proton conductivity and investigation of their conductive mechanism had become a hot research point in materials science, being paid more attention all over the world.Heteropoly acids (HPAs), a large family of solid compounds with polynuclear and oxygen bridges, become a key research direction of solid electrolytes due to their excellent properties such as simple composition, structure determination, the structural features of both complex and metal-oxide, acidic oxidation-reduction, and good proton conductivity either in the pseudoliquid phase or in solid state.This thesis revolves around the preparation and conductivity of substituted heteropoly acids with Keggin structure and their composites, aiming to explore the relationship between conductivities of HPAs and their component elements, and provide more species for selection of proton conductors.First of all, three kinds of substituted heteropoly acids H5SiW11VO40·15H2O, H7SiW9V3O40·9H2O and H6AlW11VO40·8H2O have been synthesized by the stepwise acidification-stepwise addition of element solutions-ether extraction or the ion exchanging-cooling method. The products were characterized by chemical analysis, Infrared (IR) spectra, UV spectra, X-ray powder diffraction (XRD), thermogravimetry (TG) and differential thermal analysis (DTA). Electrochemical impedance spectroscopy (EIS) measurements show that their proton conductivities are up to 10-3-10-2 S·cm-1 in the temperature range 15-58℃, and the activation energies for proton conduction are 21.59 (H5SiW11VO40·15H2O),26.69 (H7SiW9V3O40·9H2O) and 30.32 KJ·mol-1 (H6AlW11VO40·8H2O), respectively, indicating that the proton conduction complies with Vehicle mechanism. The single crystal H5SiW11VO40·15H2O was obtained and the crystal structure was determined from single crystal X-ray diffraction. The data of crystal structure are following:in the space group Ⅰ -4, with a=12.716(3) A, b=19.881(5) A, c=19.099(5) A, α=90°,β= 90.796(5)°, γ=90°, V=4828(2) A3, Z=4.Secondly, proton conducting hybrid membranes, SPEEK/SiW11V, SPEEK/PW11V, PVA/SiW11V and PVA/PW11V, were synthesized from 70wt% of heteropolyacid (PW11V or SiW11V) and 30wt% of polymers (polyvinyl alcohol, PVA; or sulfonated polyether ether ketone, SPEEK). The membranes were characterized by IR, XRD and Scanning electron microscopy (SEM). EIS measurements show that the respective proton conductivities of SPEEK/PW11V and PVA/SiW11V membranes were in the order of 10-2 and 10-4 S·cm-1 at ambient temperature. The activation energy is 15.82 KJ·mol-1 for SPEEK/PW11V and 14.40 KJ·mol-1 for PVA/SiW11V. The proton conduction proceeds by Grotthuss mechanism.And then, some hybrid materials, PEG/SiW11V and PVP/SiW11V (20 wt% PEG or PVP,80 wt% SiW11V); PEG/SiO2/SiW11V and PVP/SiO2/SiW11V (12 wt% PEG or PVP,8 wt% SiO2 and 80 wt% SiW11V), were prepared from SiW11V, organic polymers (polyvinylpyrrolidone, PVP or polyethylene glycol, PEG) and tetraethyl orthosilicate (TEOS). The products were characterized by IR and XRD. The results of EIS measurements indicate that at 18℃ and 50%RH, the proton conductivity was 1.39×10-2 S·cm-1 (PVP/SiW11V)、5.82×10-3 S·cm-1 (PVP/SiO2/SiW11V) and 5.23×10-3 S·cm-1 (PEG/SiO2/SiW11V), respectively. The corresponding activation energy was 11.34=14.51 and 19.29 KJ·mol-1, indicating that the proton conduction proceeds by Grotthuss mechanism.Finally, a series of ionic liquid-based polyoxometalate compounds, [MIMPS]5GeW11VO40, [MIMPS]5GeW10MoVO40, [(C4H9)3N(C14H29)]5SiW11VO40, [(C4H9)3N(C10H21)]5SiW11V040 and [TOAMe]5SiW11VO40 have been synthesized from the corresponding substituted heteropoly acids (H5GeW11VO℉22H2O, H5GeW10MoVO40℉21H2O, H5GeMo11V04O℉24H2O and H5SiW11VO40℉15H2O), 1-(3-sulfonic group) propyl-3-methyl imidazolium (MIMPS) or quaternary ammonium ionic liquids ((C4H9)3N(C10H21)Br, (C4H9)3N(C,4H29)Br and (C8H17)3NCH3Cl (abbreviated as TOAMeCl)). The products were characterized by IR, UV, XRD and TG-DTA. The results indicate that they have an amorphous structure due to the influence of the cations, and exhibit the phase transformation process. The conductivity and activation energy were determined, and the conductive mechanism was clarified.This study provides theoretical and experimental data for the development of a new kind of polyoxometalate-based materials with high stability and proton conductivity.