Polymer Blending-and Imidazole Filled-covalent Organic Framework Composite Membranes For Proton Transport

Energy shortage has become an important problem restricting economic and social development.The non renewable nature of fossil energy forces people to develop alternative energy.Proton exchange membrane fuel cell（PEMFC）,as a new type of green energy,has the advantages of environmental friendliness and high energy density.Proton exchange membrane is one of its core components,which directly affects the conversion efficiency of chemical energy to electrical energy.The development of proton exchange membrane with high proton conductivity and stability is the key of the development of PEMFC.Covalent Organic Frameworks（COFs）is a kind of porous crystal material,which has the characteristics of regular structure,high stability and modifiability.In this study,based on COFs,proton exchange membranes were prepared by mixing with polyelectrolytes and filling with proton conductors to improve proton transfer properties.The main research contents are as follows:TpPa-SO₃H,a sulfonic covalent organic framework material,was synthesized and blended with SPEEK as a filler to form composite membranes.The introduction of TpPa-SO₃H provides additional proton transfer sites,improves the ion exchange capacity of the membrane,forms an interface proton transfer channel and improves the proton conductivity.The proton conductivity of SPEEK/TpPa-SO₃H-5 composite membrane is 252 m S cm^-1 at 100%RH and 70℃,which is 2.2 times higher than that of pure SPEEK membrane.The peak power density and current density of the composite membrane are 92.8 m W cm^-2 and 377.6 m A cm^-2,respectively.Compared with SPEEK pure membranes,the peak power density and current density of the single cell of the fuel cell are increased by 52%and 72%,respectively.Three dimensional COF membrane was prepared by interfacial polymerization with COF-300 as building units,and propylimidazole（PI）was filled between COFs framework by"breathing effect"of COF-300.The respiratory effect of COFs is characterized by the change of geometry and molecular configuration of the solvent response.The pore size of COFs is 9.6（?） in ethanol solvent and 3.3（?） in aqueous solution.In the ethanol environment,the filling amount of propylimidazole can be increased by filling the hole of COF-300 in the stretch state;in the application situation of water environment,the hole of COF-300 is in the contraction state,which can avoid the loss of propylimidazole.In the membrane,propylimidazole increased the proton transfer sites,reduced the proton transfer resistance in the membrane,increased the proton conductivity,and then reduced the activation energy of the ion membrane.In addition,the nano channel structure formed by the regular channel of COF-300 can enhance the water retention performance based on the capillary effect,and improve the proton conductivity at low humidity.It was found that the proton conductivity of the COF/PI-7 membrane reached 186 m S cm^-1 at 100%RH and 80℃,which was four orders of magnitude higher than that of the pure COFs membrane.At40%RH and 80℃,the proton conductivity was 80 m S cm^-1.