Study Of Proton Exchange Membranes Based On Poly (aryl Ether Ketone) Modified By POSS

Fuel cell is a kind of high efficient and clean electric device.It is able to convert chemical energy into electric energy directly.The rate of energy conversion is very high,up to 60%-80%.Since the process of operation was not undergo combustion arising from that it is not subject to Carnot cycle.Besides of the high rate of energy conversion,fuel cell does not release pollution and noise,which can effectively avoid the environment pollution from common energy source.Proton exchange membrane fuel cell(PEMFC)is one kind of fuel cell.Proton exchange membrane(PEM)is the core of PEMFC which plays an important role in PEMFC such as transport protons,isolates electron and fuel.Poly(arly ether ketone)(PAEK)possesses many advantages,such as high thermal stability,excellent mechanical performance and low cost.It can be easily functionalized with different groups.Thus,as one kind of proton exchange membranes,poly(arly ether ketone)has been widely investigated.Silicone materials have been widely used in the investigation of modification thanks to its high solubility and easy functionalization,as well as high thermal stability and chemical stability.In the chapter three,Octaphenylsilsesquioxane(OPS)was prepared by phenyltrichlorosilane firstly.Then octa(nitrophenyl)silsesquioxane(ONPS)and octa(aminophenyl)silsesquioxane(OAPS)were prepared by nitration reaction and reduction reaction respectively.The products were confirmed by the nuclear magnetic resonance and infrared spectroscopy.Next,OAPS was used to modify PAEK.Cross-linking membranes was prepared based on bromomethylated poly(ether ether ketone)and OAPS.Then the quaternized cross-linking membranes were immersed in trimethylamine solution.OAPS plays a role in membrane as cross-linker.For cross-linking membranes,various factors can influence the proton conductivity.One of factors has been mentioned above.Meanwhile,it was relative to cross-linking degree,that is,high cross-linking degree can confine the transmission of phosphoric acid.Furthermore,three-dimensional nanostructure of OAPS provides space between polymer chains.The structure of(Si—O—Si)on the surface of OAPS can perform hydrophilic phosphoric acid exchange channel.Thus,the channel can promote the proton conductivity.When the content of OAPS is limited,the phosphoric acid uptake plays a critical role on the proton conductivity.Thus the proton conductivity of membranes has the same trend with the phosphoric acid uptake.Compared with pure membrane,higher proton conductivity was measured.The oxidation stability,tensile strength and proton conductivity can be improved with the addition of OAPS.In the chapter four,Sulfonated poly(aryl ether ketone)(SPAEK)was modified respectively by OPS,ONPS and OAPS which possess different functional group.Then,the properties of sulfonated poly(aryl ether ketone)were studied at low temperature.The thermal stability,mechanical properties,water absorption,proton conductivity,swelling ratio and methanol permeability were tested.Due to the thermal stability of phenyl groups,the introduction of OPS can improve the thermal stability obviously,and maybe the hydrophobic groups and hydrophilic groups can preferably form a phase separation structure,so it performs highest proton conductivity in a series of composite membranes.