| All-vanadium flow battery(VRB)has become the fastest growing and most promising energy storage technology because of its flexible design,no phase change and high energy efficiency.Ion exchange membrane is the key component of VRB.Nafion membrane is the widely used perfluorinated sulfonic acid membrane,but its high cost,high vanadium ion permeability and other shortcomings constrain the commercial prospects of VRB.Therefore,in recent years,research and develop ment of a new low-cost,high selectivity,high cell performance ion exchange membrane has become the key issues to promote the further large-scale application for vanadium flow battery.Compared to the high vanadium permeability of the cation exchange membrane and the low conductivity of the anion exchange membrane,the amphoteric membrane(AIEM)has become a kind of membrane material which is expected to replace Nafion membrane to promote large-scale application of vanadium flow battery due to it has high conductivity of the cation exchange membrane and the selectivity of the anion exchange membrane.In this thesis,the composite amphoteric membranes were prepared by blending and pore-making methods with low cost polyether ether ketone(PEEK)and polysulfone(PS)as the main materials,and the performance of the composite membranes was evaluated by various test methods.The performance of the amphoteric membranes prepared by the two methods were tested and discussed.(1)Sulfonated poly(ether ether ketone)(SPEEK)and chloro methylated polysulfone(CMPSf)were blended with different proportions.Amphoteric membranes were prepared by using 1-methylimidazole as quaternizing agent.The effects of different chloromethylated polysulfone ratio on membrane properties were studied firstly.The results of the cell performance showed that the amphoteric membrane had the best cell performance when the chloromethylated polysulfone content was 15%.Based on it,the percentage of chloromethylated polysulfone for 15% was used as the basic membrane.Then different proportions of 1-methyl imidazole(MIm)to 1,3-propylamine imidazole(APIm)were usd as the quaternizing agent;their effect on cell performance,chemical and physical property were explored.The results show that the amphoteric membrane has the best selectivity and cell performance when MIm: APIm = 4: 1.The CE and EE of the cells were 97.1% and 81.0%,respectively,higher than 90.3% and 74.8% of Nafion212.(2)The SPEEK membranes with different porosity(or p-SPEEK)were prepared by using polyethylene glycol(PEG)as the pore-forming material.The p-SPEEK membrane was immersed in a CMPSf solution and finally made into amphoteric membranes.Artificial channels can be formed and used as the ion transport pathways;since the filling of the channels is the imidazolium functionalized polysulfone,it will improve the vanadium blocking ability of the membrane.At the same time,due to the effect of ionic cross-linging between imidazolium functionalized polysulfone and SPEEK,the filling is not easy to fall off from the channel.The effects of different methods on the properties of membranes were investigated.The experimental results show that the amphoteric membrane has the best cell performance when the degree of porosity is 10%.Compared with the method in(1),the amphoteric membrane prepared by this method gave better voltage efficiency of the battery,but its selectivity is poorer,leading to its coulombic efficiency and energy efficiency lower than membrane prepared by the(1).In summary,two different kinds of amphoteric membranes can effectively improve the performance of the membrane.And their low-cost and simple preparation methods are promising for VRB applications. |
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