Fundamental Research On Polymer Membrane Preparation For Energy And Environmental Applications

Along with the deveolpmemt in technology and economy,energy and environmental problems,such as environmental pollution,global warming,and depletion of fossil fuels,have been holding back the sustainble development in human society.To cope with this situation,many solutions have been proposed.Membrane technology,due to its simplicity,high efficiency,low energy consumption,and environmental benignity,attracts increasing attention from the academia and industry.For cleaning production and alternative energy supply,bipolar membrane electrodialysis and fuel cells are two promising membrane techniques.Accordingly, the focus of this dissertaion falls on the preparation of multi-layer bipolar membranes and proton exchange membranes for application in the two processes mentioned above.With regard to bipolar membrane fabrication,since the intermediate layer plays a crucial role in bipolar membrane performance,AgCl-glutin,hyperbranched polyester and its derivatives were chosen as catalysts,and their catalytic effect on water splitting was investigated extensively.As for proton exchange membranes,two concepts - acid-base polymer blending and organic-inorganic hybridizaton - were incorporated into membrane preparation,and a series of high-performance proton exchange membranes for direct methanol fuel cells(DMFCs) were obtained.The main experimental results are listed below.(1) The introduction of AgCl/Glutin into bipolar membrane intermediate layer can catalyze water splitting effectively and thus makes the bipolar membrane suitable for industiral applications.When silver ions are introduced alone into the intermediate layer,they exist in the form of AgCl and act as a catalyst for water splitting.The amount of absorbed AgCl affects water splitting significantly.If glutin is introduced alone into the intermediate layer,the catalytic effect on water splitting depends on the competition between hydrophilicity and steric effect.However,when silver ions and glutin are introduced into the intermediate layer together,they can have a synergic effect and catalyze water splitting better than silver ions alone or glutin alone; moreover,the bipolar membrane's performance is more stable due the immobilizaton of silver ions by glutin.(2) Hyperbranched Boltorn(?) polyesters possess plentiful hydroxyl end groups and also can catalyze water splitting.Both the amount of absorbed hyperbranched polyester and the generation of the polyester play an important role in bipolar memnbrane performance,which is a result of the competition between hydrophilicity and steric effect.Furthermore,the end group of hyperbranched polymer is another important factor affecting water splitting,and the hyperbranched polymer with highlier hydrophilic end groups is the better catalyst,which is due to the formation of hydrogen bonding between hyperbranchend polyester and water moleculars.(3) A series of SPEEK/chitosan composite membrane were prepared by acid-base blending.Compared to pure SPEEK membrane,the composite membrane exhibited reduced water uptake and membrane swelling,and excellent thermal stability.The performance of the composite membrane prepared at the molar ratio of SPEEK(71.4%of sulphonation degree) to chitosan 5:1 is even comparable to commercial Nafion 117.(4) Novel proton-conducting membranes were prepared from sulfonated poly(ether ether ketone)(SPEEK) and 3-aminopropyltriethoxysilane(APTES) by acid-base blending and organic-inorganic hybridization.These acid-base hybrid membranes exhibited high proton condunctivity,low methanol permeability,and excellent thermal,dimensional,and mechanical stabilities.Upon successful preparation of bipolar membranes and proton exchange membranes with good and stable performance,there will be more large-scale applications for bipolar membrane electrodialysis and fuel cells,which will make more contribution to industrial sustainable development.