Preparation And Research Of Polysiloxane Phosphonic Acid-doped Polybenzimidazole High Temperature Proton Exchange Membrane

Fuel cell is a new energy conversion instrument,which converts the chemical energy stored in the oxide and fuel to the electrical energy.Proton exchange membrane fuel cell?PEMFC?is the fifth generation of fuel cell after the alkaline fuel cell,phosphorous fuel cell,molten carbonate fuel cell and solid oxide fuel cell.Compared to the other fuel cells,PEMFC has a lot of advantages,such as efficient energy transformation and fast initiation.It is considered that PEMFC is one of the most promising electrochemical energy conversion devices.PEM?Proton Exchange Membrane?is one of the key components for PEMFC.Currently,the most commonly used PEM for PEMFC is Nafion membrane.The proton conductivity of Nafion is considerable when the operation temperature under 80?.In fact,proton conductivity of Nafion is very dependent on water content of membrane.As we all know,proton conductivity of Nafion falls sharply when the operation temperature above 100?,which is due to the evaporation of moisture.Thus,the development of new type of PEM becomes an important project in the field of high temperature and low humidity PEMs.A series of high temperature and low humidity PEMs based on amino trimethylene phosphonic acid?ATMP?were studied.Particulaly,the arious performance of membranes,as follows:?1?The ATMP doped PBI high temperature membranes were prepared from amino trimethylene phosphonic acid?ATMP?and polybenzimidazole?PBI?by sol-gel process.The samples with different amounts of ATMP were characterized using FT-IR,and the results suggested that hydrogen bond form between PBI and ATMP.The structure of membranes with different ATMP content were extensively characterized by FT-IR,XRD and SEM,the results suggested that partly of ATMP is chemically bonded to PBI,and the other part of the ATMP is free in the membrane.The properties of membranes such as thermostability,chemical durability,water absorption,swelling ratio,proton conductivity,and proton conductive activation energy were measured.Results suggested that the ATMP doped PBI membranes show good thermostability and chemical durability;the water absorption,swelling ratio can meet the need of fuel cell;the proton conductivity of the samples depends on temperature up to a maximum of 0.081 S/cm^–1 at 140°C under nominally anhydrous conditions.But the membranes are too fragile and no practical application.?2?Polysiloxane phosphonic acid-doped Polybenzimidazole high temperature membrane is fabricated from amino trimethylene phosphonic acid?ATMP?,polybenzimidazole?PBI?and epoxycyclohexylethyltrimethoxysilane?EHTMS?by sol-gel process.Polysiloxane phosphonic acid instead of phosphoric acid is used as proton conductor to prevent acid leaks.The samples with different amounts of ATMP were characterized using FT-IR,XRD and SEM.The results suggested thatall of the ATMP is chemically bonded to EHTMS and polysiloxane phosphonic acid is successfully prepared;hydrogen bond form between PBI and polysiloxane phosphonic acid.The properties of membranes such as thermostability,chemical durability,water absorption,swelling ratio,proton conductivity,and proton conductive activation energy were measured.Results revealed that polysiloxane phosphonic acid doped PBI membranes show good thermostability and chemical durability;the water absorption,swelling ratio can meet the need of fuel cell;the proton conductivity of the samples depends on temperature up to a maximum of0.034 S/cm^–1 at 140°C under nominally anhydrous conditions.Furthermore,the tensile strength of the membrane with 10% PBI is 18.3MPa.