Study On The Preparation And Performances Of PEMs Based On Poly(2,6-dimethyl-1,4-phenylene Oxide) For Fuel Cells

Aromatic hydrocarbon polymers have always been considered as optimal alternative materials for proton exchange membrane(PEM).It has been widely developed in the application of direct methanol fuel cell(DM FC)and high temperature proton exchange membrane(HT-PEM FC)because of high mechanical properties,excellent thermal and chemical stability.Proton conductivity is the most important performance parameter of PEM.Generally,the sulfonic acids or phosphoric acids are introduced into the main chain or side chain,which serve as the active sites for proton transfer.Sulfonated and phosphonated polymers can be prepared by the condensation polymerization of monomer with-SO3 H or-P(O)(OH)2.It can also be obtained by the post-functionaliz ation of aromatic polymers.In general case,polymer containing high acid groups content will have high ion exchange capacity(IEC)and high proton conductivity.But,the high IEC will also lead to the poor dimensional stability for high water uptake,high methanol permeability and not enough electrochemical stability.To overcome the shortcoming,recently many novel PEM s based on aromatic polymers have been developed,and the performances can also be improved by the blending and organic–inorganic composite membrane.In this paper,sulfonic acid,phosphoric acid groups and alkaline quaternary ammonium groups are introduced into the benzene ring of poly(2,6-dimethyl-1,4-phenylene oxide)(PPO),which is chosen for the basic matrix.The performance of three types of PEM s are investigated where-SO3 H,-P(O)(OH)2 and H3PO4 provide the proton transfer sites.In addition,the performance of PEM is enhanced by the polymer blend and the incorporation of inorganic filler.In chapter two,sulfonated PPO(sPPO)with different degree of sulfonation are prepared firstly.The effect of the sulfonic acid content is investigated in detail on ion exchange capacity(IEC),water uptake,proton conductivity,methanol permeability,thermal and oxidative stability.To reduce the swelling and methanol crossover,sulfonated polydivinylbenzene(sPDVB)microspheres and sPPO composite membrane are prepared.sPDVB microspheres have a uniform particle size distribution at range of 1-2?m and are well dispersed in the sPPO matrix.The incorporation of sPDVB microspheres decreases the water uptake and methanol permeability of membranes.The conductivity of composite membranes has a little loss,but the thermostability and mechanical properties are improved.In chapter three,phosphonated PPO(pPPO)with different phosphonated level and a series of sPPO/pPPO blend membranes are prepared by solution casting.The performance of the blend membrane entirely depended on the weight ratio of sPPO/pPPO,which had markedly different properties in all aspects.Incorporation of sPPO could increase the water uptake and hydration number and improve the proton conductivity.While,blending with pPPO would enhance the methanol barrier property,mechanical properties,thermal and oxidative stability.The performance of blend membrane can be tailored with controlling the ratio of sulfonic acid and phosphoric acid as a suitable alternative membrane for the DM FC application.In chapter four,a series of poly(vinyl pyrrolidone(PVP)and pPPO blend membranes and PVP/pPPO/g-C3N4 nanocomposite membranes are prepared.The effect of PVP content on the water uptake,PA absorp tion ability and proton conductivity of the membranes are also studied.The PA uptake,volume swelling ratio and proton conductivity of the PVP/pPPO blend membrane increased with increasing PVP content.But PA molecules drastically reduced the mechanical strength of the PVP/pPPO blend membrane.The incorporation of g-C3N4 enhanced the dimensional stability and mechanical properties of the nanocomposite membrane,and the proton conduction also is improved due to the proton hopped sites provided by NH2 and the interaction of g-C3N4 and polymer chains.In chapter five,Brominated PPO(BPPO)react with trimethylamine(TMA)and trimethylamine(TEA),and the PA doped quaternary ammonium type membranes are prepared for the high temperature polymer electrolyte membrane.The BPPO-TEA have higher water uptake,PA uptake and swelling ratio than the BPPO-TMA,but the proton conductivity of BPPO-TEA-PA is lower than that of BPPO-TM A-PA.In addition,the water uptake,PA uptake,swelling ratio and proton conductivity of two type PA doped membranes increase with the increasing of the bromination.To the further study,graphite oxide(GO)modified by ethanediamine(EDA)is introduced into the BPPO-TM A-PA system.The –NH2 on the surface of GO-EDA form crosslinking bonds with the BPPO,which can improve the proton conduction performance of PA doped membranes.The incorporation of GO-EDA also enhances the dimensional,mechanical and thermal stability.