Preparation And Performance Of Crosslinked And Composite Crosslinked Vinyl-addition Polynorbornene Anion Exchange Membranes

As a new type of energy conversion device,fuel cell can directly convert the chemical energy of fuel and oxidant into electric energy.Anion exchange membranes(AEMs),as the core component of fuel cells,largely determine the service life and overall performance of the fuel cells.At present,the preparation of AEMs for high-performance fuel cells still faces severe challenges.On the one hand,it is necessary to solve the contradiction between the ion conductivity and alkaline stability of AEMs,so as to improve the electrochemical performance of AEMs.On the other hand,the swelling degree of AEMs needs to be reduced while increasing the ion exchange capacity to improve the dimensional stability.Aiming at these problems,vinyl-addition norbornene-based block copolymers were synthesized,and crosslinked and composite AEMs were prepared by the strategies of bis-imidazole ionic liquid crosslinking,in-situ sol-gel and the introduction of PTFE microporous membrane.The specific work is as follows:(1)5-norbornene-2-methylene hexyl ether(NB-MHE)and 5-norbornene-2-methylene-(6-bromohexyl)ether(NB-O-Br)were synthesized,and the vinyl-addition norbornene block copolymer aP(NB-O-Br-b-NB-MHE)was obtained by using(?³-allyl)Pd(PPh₃)Cl/Li[B(C₆F₅)₄]·2.5Et₂O(Li[FABA])catalytic system.A series of crosslinked AEMs CL-aP(NB-O-Br-b-NB-MHE)with different crosslinking degrees were prepared by adjusting the content of Bis-Me Im.The obtained addition polynorbornene-based AEMs exhibited good thermal stability,and the initial thermal decomposition temperature was about 250 ^oC.The crosslinked membranes showed moderate water uptake and low swelling ratio.The formation of the cross-linked network structure in the membrane can effectively inhibit excessive water absorption,making it more suitable for practical applications of electrolyte membranes.A distinct microphase separation structure was observed from the AFM phase images.Through the design of the light cross-linked structure,the dimensional stability of AEMs was improved,while maintaining high ion conductivity(85.07 m S cm^-1,80 ^oC)and alkaline stability.In the H₂/O₂ fuel cell test,the peak power density of the single cell assembled by CL5-aP(NB-O-Br-b-NB-MHE)was 177 m W cm^-2.(2)In order to improve electrochemical property of AEMs and processing performance of vinyl-additon polynorbornene material,the strategies of in-situ sol-gel technology and composite membrane technology were adopted.Epoxy functionalized norbornene block copolymer aP(NB-MGE-b-NB-MHE)was obtained by catalyzing the addition copolymerization of 5-norbornene-2-methylene epoxypropyl ether(NB-MGE)and NB-MHE using the late-transition metal catalyst system(?³-allyl)Pd(PPh₃)Cl/(Li[FABA]).A novel siloxane imidazole ionic liquid B(Im PS)was synthesized as the precursor,and a series of microporous PTFE/bis(siloxane imidazole)functionalized polynorbornene composite anion exchange membranes PTFE/CL-aP(NB-MGE-b-NB-MHE)with different sol-gel degree were prepared.The SEM result showed that the functionalized norbornene-based copolymer CL-aP(NB-MGE-b-NB-MHE)was completely filled into the PTFE micropores,and the two had a good composite effect.The obtained composite membranes exhibited excellent thermal performance and the initial thermal decomposition temperature was higher than 260 ^oC.In addition,the formation of the Si-O-Si three-dimensional cross-linked network structure and the effect of PTFE composite synergistically adjusted the water content in the AEMs,inhibited excessive swelling,and significantly improved the mechanical property.The use of PTFE reinforcement material greatly reduced the thickness of the membranes,so that the internal resistance was effectively decreased,and the material cost was reduced.PTFE/CL40-aP(NB-MGE-b-NB-MHE)showed high ionic conductivity(74.40 m S cm^-1,80 ^oC)and alkaline stability.It can retain 91%of the initial OH^-conductivity after immersed in 1 M Na OH solution for more than 500 h.The peak power density of the H₂/O₂ fuel cell assembled by PTFE/CL40-aP(NB-MGE-b-NB-MHE)was 182m W cm^-2,showing that it has potential application value as electrolyte membrane.