Study On The Preparation And Conductivity Of Proton Exchange Membranes PVDF-Al₂O₃-CsHSO₄Operating At Medium Temperatures

In this thesis, the novel organic-inorganic composite electrolyte materials were synthesized by doping proton conductors Al2O3, CsHSO4and Al2O3-CSHSO4on the copolymer PVDF. The conductivity of membrane was improved by choosing different conductors and modifying the component of polymer and conductors. The novel PVDF-Al2O3-CSHSO4membrane with high conductivity in the wide range of temperature (30℃-200℃)and humidity(20%RH-90%RH) was prepared. By the characterization of structure and properties, the performance of PVDF-Al2O3-CSHSO4membrane was perfected and the mechanism of proton transport and methanol permeability was investigated. Research results were described as follows:Among the three kinds of organic-inorganic electrolyte materials, composite membrane PVDF-Al2O3-CSHSO4obtained the highest conductivity, above10-4S cm-1. The conductivity increased with increasing temperature in the wide temperature range (30℃-150℃). During the synthesis of PVDF-Al2O3-CsHSO4, CsAl(SO4)2-12H2O was formed and novel membrane PVDF-CsAl(SO4)2-12H2O was prepared. The conductivity of PVDF-CsAl(SO4)2-12H2O has a sharp increasing around the temperature of90℃. The release of the crystal water in the CsAl(SO4)2-12H2O around72℃was demonstrated by TG-DSC. For the sample PVDF-CsHSO4, the structure of CsHSO4was changed using the synthesis method in this paper and no typical crystal CsHSO4exists in the composite from XRD. As a result, phase supertransition was not happened and accordingly no steep increase of conductivity was observed between140-150℃.A system of composite membrane PVDF-CsAl(SO4)2-12H2O was prepared with change the composition of PVDF and proton conductors. The highest conductivity was obtained for the sample PVDF-CsAl(SO4)2-12H2O G:1). The methanol permeability of novel membrane was obviously lower than that of Nafion117. The methanol permeability coefficient was increased with increasing the amount of CsAl(SO4)2·12H2O. The conductivity of PVDF-CsAl(SO4)2·12H2O has a sharp increasing around the temperature of90℃and then keeps a steady increase trend up to200℃. The methanol permeability coefficient of PVDF-CsAl(SO4)2·12H2O was15times lower than that of Nafion. It can be deduced that the performance of novel membrane was better than that of Nafion117.The novel polymer composite membrane PVDF-CsAl(SO4)2·12H2O described here can be an attractive candidate as electrolvte in the low and medium fuel cell.