Study On The Preparation And Performace Of Polysiloxane Phosphonic Acid Graft Polybenzimidazole High-temperature Proton Exchange Membrane

Proton exchange membrane fuel cell(PEMFC)is a kind of highly efficient and environmentally friendly power conversion device,which can convert chemical energy from hydrogen and oxidants directly inton electrical energy.Proton exchange membrane(PEM)is one of the core components of proton exchange membrane fuel cell and it is the focus of the research of fuel cells.Currently,Nafion membrane is the most widely used proton exchange membrane in PEMFC.Nevertheless,this kind of membranes is very expensive and can only operate under relatively lower operated temperature,generally lower than 80°C.Lower operating temperature brings many problems such as necessity of humidification,heat management and CO catalyst poisoning.Therefore,PEM which can be operated at high temperature(above 100°C)arouse more attention in recent years.In this paper,two kinds of proton exchange membranes were prepared by using aminotrimethylenephosphonic acid(ATMP)as proton conductor,as follows:(1)ATMP doped crosslinked polybenzimidazole(PBI)membranes were synthesized from 3-glycidoxypropyltrimethoxysilane(GPTMS),polybenzimidazole(PBI)and ATMP by sol-gel process.The structure of the membranes is characterized by Fourier transform infrared spectroscopy(FT-IR)and X-ray diffraction spectroscopy(XRD).The results show that GPTMS was grafted onto the PBI successfully and the PBI crosslinked with each other.The results also show that apart of ATMP was ionic bonded with PBI.Scanning electron microscopy(SEM)images indicate that the surface of the membranes is compact and homogeneous.The thermal stability,oxidation resistance,water resistance,water absorption and proton conductivity of the membranes were also investigated.The results show that the membranes have excellent thermal stability at 200?,good oxidation resistance,good water absorption and low swelling ratio.The proton conductivity of the membranes increase with the contant of the phosphonic and temperature.The proton conductivity of the membrane can reach 7.32×10~-22 S/cm at 160?under the anhydrous condition,which can meet the requirements of high temperature proton exchange fuel cell.(2)Polysiloxane phosphonic acid graft polybenzimidazole high temperature proton exchange membranes were prepared from aminotrimethylenephosphonic acid(ATMP),3-glycidoxypropyltrimethoxysilane(GPTMS)and polybenzimidazole(PBI)by sol-gel process.The ATMP was chemically bonded with GPTMS and fixed in the membranes,so the phosphonic acid can't easily leak out from the membrane.The FT-IR and XRD tests show that Polysiloxane phosphonic acid grafted onto molecular chain of the PBI,and the membrane is crosslinking structure.The thermal stability,mechanical property,chemical stability,ion-exchange capacity(IEC),and proton conductivity of the membranes were investigated.The results show that polysiloxane phosphonic acid grafted PBI high temperature proton exchange membrane has high thermal stability,good oxidation resistance and good mechanical properties.The results of the IEC of membranes show that the ATMP chemically bonded in the membrane,and can not easily leak out from the membrane.The proton conductivity tests show that the membranes have good proton conductivity under high temperature and low humidity conditions,and the proton conductivity increases with the increase of temperature.The proton conductivity of the membrane can reach 3.15×10~-22 S/cm at160?under anhydrous condition.