Study On Poly(Phthalazinone Ether Sulfone) Anion-exchange Membranes For Vanadium Redox Flow Batteries Applications

All-Vanadium redox flow battery (VRB) is one of the green environmental protection batteries and keeps on a good impetus of development. It has many advantages such as deep discharge capacity, fast response time, long cycle life and low cost and so on. However, the development of VRB has been limited owing to the research and development of separator membrane materials. Nowadays, VRB uses Nafion membranes as separator because Nafion membranes have good chemical stability and high conductivity. But Nafion membranes are cation-exchange membranes and expensive. It suffers from the crossover of vanadium ions when used in VRB, which results in decreases in energy efficiency. It is an effective method to investigate a novel anion-exchange membrane with low cost and good battery performance. Poly (phthalazinone ether sulfone)(PPES) and copoly(phthalazinone ether sulfone)(PPBES) are novel membrane materials with well membrane-forming, good chemical stability and low cost. It can be chemical modification by chloromethylation and quaternary ammoniation. The final anion-exchange membranes have good vanadium ions permselectivity and battery performance, thus possessing broad application foreground in VRB. Following is the main content:The study of preparation process on chloromethylated PPES and PPBES are investigated. The effect of reaction factors on degree of chloromethylation are investigated in detail. It is the first time to use organic solvent nitrobenzene as chloromethyaltion reaction solvent. Comparing with sulfuric acid method, organic solvent method has simple post treatment, no corrosion to equipment and low industrial pollution. The products are identified by1H-NMR and technology conditions are optimized and the degree of chloromethylation could be controllable. The solubility of CMPPES and CMPPBES are also examined. All of them have well solubility, which is soluble in CHCl3, NMP, DMAc and so on.The effects of membrane preparation process and amination condition on the properties of membranes are studied. A series of quaternized Poly (phthalazinone ether sulfone) (QAPPES) and quaternized Copoly (phthalazinone ether sulfone) (QAPPBES) with different ion-exchange capacity (IEC) are prepared. The solubility of QAPPES and QAPPBES membranes are also examined. It is found that QAPPES and QAPPBES are insoluble in NMP,DMAC,halohydrocarbon and benzene hydrocarbon et al. It proves that QAPPES and QAPPBES materials have excellent solvent-resistance. However, it is found that the introduction of chloromethyl groups and quaternary ammonium groups into the polymer chains led to a decrease in the decomposition temperature. The initial degradation temperature of CMPPES is 320℃and the QAPPES is 240℃. It is the degradation temperature of chloromethyl groups and quaternary ammonium groups, respectively.The effects of IEC, ion-exchange group species and membrane microstructure on the properties of QAPPES membranes are also investigated. It is found that the quaternary ammonium homogeneous membranes performed well in VRB. And comprehensive properties of membrane which the structure was uniform and dense were much better than the membrane which the structure is asymmetric. When the IEC of QAPPES membrane is 1.50 mmol/g, the current efficience of vanadium redox flow single battery could reach to 98.1%, voltage efficience reaches 87.0% and energy efficiency is 85.4%. The permeability coefficient of the QAPPES membrane is 3.58×10-5 cm-min-1. Under the same test condition, the current efficiency of QAPPES membrane is much higher than Nafion 117 membrane, and permeability coefficient is much smaller than Nafion 117.Chloromethylated/quaternized Poly sulfone (QAPSf) and Poly ether sulfone (QAPES) anion-exchange membranes with different IEC are prepared. The relationship between the structure and membrane propertie is investigated. It is the phthalazinone structure that made the QAPPES and QAPPBES have good ion permselectivity. Comparing with QAPPES, the structure of QAPSf has high electron density. And the chemical stability and permselectivity of the membranes became worse when IEC is high.