Preparation And Performance Of Anion Exchange Membrane Based On Quaternized Branched Polyethyleneimine

With the continuous consumption of fossil fuels and the increasingly prominent ecological and environmental problems,more and more countries have begun to study clean new energy power systems,such as wind energy,solar energy,and hydrogen energy.Fuel cell is a green and environmentally friendly device that can directly convert chemical energy into electrical energy.In today’s clean energy power systems,fuel cells play an indispensable role due to its high energy conversion rate,noiselessness,and pollution-free characteristics.Among the various fuel cells classified by electrolytes,polyelectrolyte fuel cells have attracted attention due to their low operating temperature and no electrolyte leakage.According to their working environment,polyelectrolyte fuel cells can be divided into proton exchange membrane fuel cells（PEMFC）and anion exchange membrane fuel cells（AEMFC）.Compared with PEMFC,AEMFC has many advantages,such as using non-noble metals（Ag,Ni,Fe）as catalysts and having higher electrode reactivity in alkaline media.Anion exchange membrane fuel cells（AEMFC）are currently the most widely studied energy conversion device.AEM is one of the core components of alkaline anion exchange membrane fuel cells.It is responsible for the important function of transporting anions（usually OH^-）and isolating fuel and oxidant.However,AEM is still one of the key technical barriers restricting the development of alkaline anion exchange membrane fuel cells.The working efficiency of the fuel cell is low,which is caused by the low ion conductivity of OH-in the AEM.Earlier research found that rationally designing the polymer structure to induce the formation of ion-conducting nanochannels can improve the ion conductivity of AEM.Generally,increasing the ion exchange capacity（IEC）of the AEM can make the membrane obtain a higher ion conductivity,but too high IEC makes the anion exchange membrane has high water swelling rate and low strength.In order to improve the ion exchange capacity and strength of AEM,the anion exchange membrane matrix material can be cross-linked.In response to this problem,quaternized branched polyethyleneimine（QBPEI）was introduced into the anion exchange membrane to construct a self-assembled ion transport channel,and a series of ion exchange membranes containing QBPEI were successfully prepared.The main research contents and results of this paper are summarized as follows:Preparation and performance of anion exchange membrane based on styrene-ethylene-butene-styrene tetra polymer（SEBS）and quaternary ammonium branched polyethyleneimine（QBPEI）.For the first time,BPEI was added to chloromethylated SEBS（CSEBS）as a cross-linking agent and OH^-conducting functional polymer,and a series of cross-linked CSEBS/QBPEI anion exchange membranes were prepared by simple casting method（CPx,x represents the mass ratio of CSEBS and QBPEI）.The introduction of QBPEI further promotes the formation of a good hydrophilic/hydrophobic microphase separation structure inside the system,and helps to improve and expand the ion transport channel of the CPx anion exchange membrane.Through chemical structure analysis（FT-IR and XRD）,morphology characterization（SEM,TEM,AFM）,TGA and other analytical tests about mechanical properties,water swelling degree,ion exchange capacity（IEC）,ion conductivity and chemical stability,the comprehensive performance of the anion exchange membrane was analyzed and evaluated.The research results show that the cross-linked CPx anion exchange membrane combines the advantages of QBPEI containing a large number of quaternary ammonium cationic groups and the excellent mechanical properties of SEBS,and the overall performance is improved within the range of optimized ratio.In particular,the IEC value of CP3 membrane is 2.47 meq./g,and its maximum ion conductivity at 80℃can reach 66.63 m S/cm.And,when the water absorption rate reaches 25.35 wt.%,the swelling degree of CP3 membrane is 4.5%.After the alkali resistance test,the CP3 membrane can maintain 81.2%of the initial ion conductivity,proving that the CP3 membrane has good alkali resistance and dimensional stability.The microscopic morphology results show that the CPx membranes has a compact internal structure,QBPEI is evenly distributed in the membrane,and a continuous ion transport channel is constructed in the AEM.Then,the CP3 membrane was assembled into a single cell,and its maximum power density was measured to be 60.07 m W/cm².Preparation and performance of anion exchange membrane based on quaternized polysulfone（QPSU）/quaternized branched polyethyleneimine（QBPEI）.Considering that SEBS is a strong hydrophobic polymer,it limits the water absorption of the ion exchange membrane,which is not conducive to the ion conductivity of the CPx anion exchange membrane.Furthermore,QPSU with moderate hydrophilicity is used as the matrix material to be mixed and cross-linked with QBPEI,and a series of cross-linked QPSU/QBPEI anion exchange membranes are prepared by casting method（QQx,x represents the mass ratio of QPSU to QBPEI）.The effects of different types of quaternization reagents on the ion conductivity and alkali resistance of pure QPSU anion exchange membranes,as well as the effects on the ion conductivity of QQx membranes have been systematically studied.The research results show that when trimethylamine and bromopropane are used as quaternization reagents of chloromethyl polysulfone and BPEI respectively,and the molar ratio of the functional groups of BPEI to bromopropane is 0.5:1,the performance of the prepared anion exchange membrane is the best.Through basic tests of QQx membranes about ion exchange capacity（IEC）,water absorption swelling rate,ion conductivity and chemical stability,it is found that the QQ3 membrane has good alkali resistance and the highest ion conductivity（66.14 m S at 80℃/cm,while its IEC value is 1.88meq./g）.In addition,the swelling degree of QQ3 is 33.5%when the water absorption rate reaches 104.8 wt.%,indicating that QQ3 membrane has good dimensional stability.Moreover,the single cell performance of the QQ3 membranes is improved compared with CP3 membranes,and the maximum power density can reach 75.34m W/cm².Preparation and performance of anion exchange membrane based on nanoparticle-modified QBPEI.In order to further improve the ion conductivity and alkali resistance of the QQ3 membrane,a more obvious hydrophilic-hydrophobic phase separation structure was constructed,and then nanoparticles of different dimensions were added to the anion exchange membrane.In addition,in order to improve the compatibility of nanoparticles and anion exchange membranes,QBPEI modified with nanoparticles of different dimensions was first prepared,and then added to the QPSU solution,and three types of cross-linked QQ-n-N-GQDs membranes,QQ-n-MWCNTs membranes and QQ-n-GO membranes were prepared by casting method（n represents the mass ratio of QPSU/QBPEI to nanoparticles）.The molecular structure and morphology characteristics of QBPEI modified with nanoparticles of different dimensions were characterized by FT-IR,XPS,SEM,DLS,TEM and AFM.In addition,the comprehensive performance of the modified QQ3membrane based on three kinds of nanoparticles was systematically tested.Compared with the QQ3 membrane,the ion conductivity and mechanical properties of the anion exchange membrane with nanoparticles have been improved.By systematically comparing the effects of N-GQDs,MWCNTs and GO nanoparticles with different dimensions（quasi-zero,one-dimensional and two-dimensional）on the performance of QQ3 membrane,it is found that the QQ3 membranes with MWCNTs have the best performance.Especially,the research results show that the QQ-0.7%-MWCNTs membrane has the highest ion conductivity,which can reach 83.19 m S/cm at 80℃,and its IEC value is 2.60 meq./g.This may be because the tubular structure of carbon nanotubes helps to build a more continuous ion transport channel in the membrane,and the jumping path of ions along the surface of the carbon nanotube is also consistent with the ion transport channel,which is conducive to the rapid transport of ions in the membrane.And,the QQ-0.7%-MWCNTs membrane has the best single cell performance,and the maximum power density is 102.44 m W/cm².Preparation and performance of anion exchange membrane based on in-situ polymerization filled QBPEI/Cellulose aerogel.Inspired by the above-mentioned nanoparticles of different dimensions,a three-dimensional ion-conducting structure was further constructed inside the anion exchange membrane,and the influence of the three-dimensional structure on the ion conduction performance of the membrane was explored.For the first time,a new idea of preparing anion exchange membranes based on in-situ polymerization filled aerogel three-dimensional network is proposed.First,the QBPEI containing a large number of ion exchange groups is chemically cross-linked with cellulose to construct a three-dimensional network structure of aerogels containing ion exchange groups.Subsequently,the three-dimensional network ion transmission channel is filled with polychloromethyl vinylbenzene（PVBC）by in-situ polymerization to construct a continuous and efficient three-dimensional ion conduction channel in the polymer matrix.Finally,the PVBC/QBPEI anion exchange membrane is prepared by the hot-pressing method（PQx membranes,x represents the mass ratio of PVBC to QBPEI）.The comprehensive performance of the anion exchange membrane with a three-dimensional ion conduction structure was tested systematically.The research results show that the PQ3 membrane has the highest ion conductivity,reaching 38.88 m S/cm at 80℃,and its IEC value is 1.58 meq./g.In addition,the swelling degree of PQ3 membrane is 18.91%,when its water absorption is 40.17 wt.%.The single cell performance test results of the PQ3 membrane show that its maximum power density is 46.32 m W·cm^-2.The matrix polymer of this type of AEM is introduced by in-situ polymerization,which can compensate for the limitations of the existing solution casting method for preparing anion exchange membranes（usually consider the good solvent of the polymer matrix）,and provide a new non-solvent method to prepare anion exchange membrane.