| Vanadium redox flow battery (VRB) is a new battery for energy storage. The power and capacity of VRB are divided. It has the advantage of deep discharge capacity, long cycle life, and maintenance convenient. The VRB is an ideal large energy storage device for renewable energy sources such as solar energy, wind energy and smart grid for load shifting. Ion exchange membrane is key component for VRB. Nafion has been used as separator for its good chemical stability and high conductivity; however, it suffers from high cost and the crossover of vanadium ions. Therefore, study on alternative membranes and related membrane materials are necessary. Poly(phthalazinone ether ketone)(PPEK) and poly(phthalazinone ether ketone ketone)(PPEKK) are high performance polymers. They have high mechanical strength and good chemical stability. The poly(phthalazinone ether ketone)s membrane materials have lower cost than that of perfluorinated sulfonic acid materials.Chloromethyl poly(phthalazinone ether ketone ketone)(CMPPEKK) were prepared from PPEKK with sulfuric acid and nitrobenzene as solvents, respectively. The effects of reaction conditions on chloromethyl degree were studied. The resulting polymer were analysed by using FTIR and NMR. The resluts confirmed that chloromethyl groups were intrduced into polymer. The chloromethyl degree of CMPPEKK was in a range of0.9-1.9mmol/g. CMPPEKK membranes were aminated to prepare quaternized poly(phthalazinone ether ketone ketone)(QAPPEKK) anion exchange membranes. The ion exchange capacity (IEC) of QAPPEKK membranes was in a range of0.99-1.56mmol/g. Under the same current density (20-80mA/cm2), the current efficiency of VRB cell with QAPPEKK (IEC=1.56mmol/g) was higher than that of Nafion117, and the energy efficiency of both cells was comparable. QAPPEKK membranes showed good stability in VO2+solution and VRB.Poly(phthalazinone ether ketone ketone) anion exchange membranes with pyridinium groups (PyPPEKK) were prepared from CMPPEKK and pyridine. The amimation conditions were studied and optimized. The IEC of PyPPEKK was in a range of0.96-1.55mmol/g. FTIR confirmed that pyridinium groups were introduced into membranes. At80mA/cm2, the cell with PyPPEKK (IEC=1.55mmol/g) membrane showed a current efficiency of99.2%and energy efficiency of83.6%higher than that of cell with Nafionl17(current efficiency and energy efficiency were96.8%and80.7%, respectively). The stability test in VO2+solution (?)nd cell cycling test showed that PyPPEKK membranes had good stability. By designing the molecular structure of the polymer, the methyl groups were introduced into polymer to obtain poly(phthalazinone ether ketone) with methyl groups (DMPPEK). FTIR and NMR were used to characterize the structure of DMPPEK, the results indicated that DMPPEK were obtained. DMPPEK were brominated to prepare poly(phthalazinone ether ketone) with bromomethylated groups (BPPEK). The conversation ratio of bromomethyl groups was about50%. BPPEK was adequate to meet the requirement of preparation of anion exchange membrane. Quaternized poly(phthalazinone ether ketone)(QBPPEK) anion exchange membranes and poly(phthalazinone ether ketone) anion exchange membranes with pyridinium groups (PyBPPEK) were prepared from BPPEK with trimethylamine and pyridine, respectively. The IEC was in a range of0.82-1.53mmol/g for QBPPEK and0.85-1.50mmol/g for PyPPEK membranes, respectively. At the same current density (20-80mA/cm2), the current efficiency and energy efficiency of cells with QBPPEK (IEC=1.53mmol/g) and PyBPPEK (IEC=1.50mmol/g) were higher than those of cell with Nafionl17.Poly(phthalazinonc ether ketone ketone) with dimethyl groups (DMPPEKK) were prepared from polycondcnsation method. Poly(phthalazinone ether ketone ketone) with bromomethylated groups (BPPEKK) was prepared from bromination of DMPPEKK. Quaternized poly(phthalazinone ketone ketone)(QBPPEKK) anion exchange membranes and poly(phthalazinone ketone ketone) with pyridinium groups (PyBPPEKK) anion exchange membranes were prepared from BPPEKK with trimethylamine and pyridine as the amination reagents, respectively. At the same current density (20-80mA/cm2), the current efficiency of cells with QBPPEK (1.51mmol/g) and PyBPPEK (1.45mmol/g) was higher than that of cell with Nafionl17, and the energy efficiencies of cells were comparable.The relationships of structure-property of anion exchange membranes made from chloromethyl poly(phthalazinone ether ketone) and brominated poly(phthalazinone ether ketone) with dimethyl groups were investigated. The water content and swelling ratio of quaternizated poly(phthalazinone ether ketone) membranes and poly(phthalazinone ether ketone) anion exchange membranes with pyridinium groups were increased with the increasing IEC of membranes. The water content and swelling ratio of membranes with quaternary ammonium groups were higher than those of membranes with pyridinium groups. The voltage efficiency and energy efficiency of cells with poly(phthalazinone ether ketone)s membranes were mainly affected by the ion exchange capacity of membranes. |
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