Shouhai Zhang

Anion exchange membranes from brominated poly(aryl ether ketone) containing 3,5-dimethyl phthalazinone moieties for vanadium redox flow batteries

A series of heterocyclic poly(aryl ether ketone)s containing 3,5-dimethyl phthalazinone moieties were synthesized via the copolymerization of 4-(3,5-dimethyl-4-hydroxyphenyl)(2H)-phthalazin-1-one, 4-(4-hydroxyphenyl)(2H)-phthalazin-1-one and 4,4′-difluorobenzophenone. The resulting polymers were brominated with N-bromosuccinimide as the bromination reagent. Brominated poly(phthalazinone ether ketone) (BPPEK) with a degree of substitution in the range of 0.48–0.82 was obtained. Quaternized poly(phthalazinone ether ketone) anion exchange membranes (QBPPEK) were prepared from BPPEK membranes with trimethylamine as the amination reagent. Ion exchange capacity (IEC) values of the QBPPEK membranes were in the range of 0.82–1.53 mmol g−1. Compared with Nafion117 membrane, QBPPEK membranes showed much lower vanadium permeability. Coulombic efficiencies of the vanadium redox flow battery (VRB) with QBPPEK membranes were higher than that with the Nafion117 membrane. The energy efficiency of the VRB increased with an increase in the IEC of the QBPPEK membrane. The energy efficiency of the VRB cell with the QBPPEK membrane having an IEC of 1.53 mmol g−1 was 88%, which was higher than that of the cell with the Nafion117 membrane. During 100 charge–discharge cycles, the QBPPEK anion exchange membrane showed a stable performance.

Poly(phthalazinone ether ketone ketone) anion exchange membranes with pyridinium as ion exchange groups for vanadium redox flow battery applications

Poly(phthalazinone ether ketone ketone) anion exchange membranes with pyridinium as anion exchange groups (PyPPEKK) were prepared by reacting chloromethylated poly(phthalazinone ether ketone ketone) membranes with pyridine in solution. The reaction conditions including diluent solvents, pyridine concentration, reaction time and temperature were investigated. Under the optimized reaction condition, PyPPEKK anion exchange membranes with IEC values in the range of 0.96–1.55 mmol g−1 and water uptake in the range of 10.2–16.5% were obtained. The swelling ratio of PyPPEKK membranes in deionized water and VOSO4 solution were in the range of 3.2–10.6% and 2.5–7.8%, respectively. PyPPEKK membranes showed good chemical stability in VO2+ solution. Notably, PyPPEKK membranes had higher coulombic efficiencies of VRB and much lower vanadium permeability compared with Nafion117 membrane. The energy efficiency of VRB with PyPPEKK membrane reached 83.6% at 80 mA cm−2 while the energy efficiency of VRB with Nafion117 membrane was 80.7% at the same charge–discharge current density. Furthermore, PyPPEKK membrane exhibited good performance in the 100-cycle charge–discharge VRB test.

Effect of membrane-casting parameters on the microstructure and gas permeation of carbon membranes

In this work, membrane-casting parameters including solvents and drying methods were investigated to adjust the microstructure and gas permeation of poly(phthalazinone ether sulfone ketone) (PPESK) based carbon membranes. The structure and properties of the membrane samples were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, transmittance electron microscopy, single gas and mixed gas permeation. Results have shown that the membrane-casting parameters greatly influence the physico-chemical properties of the polymeric membranes, so as to affect the structure and gas permeation of their derived carbon membranes. Under the same drying conditions, the selection of a solvent with a high boiling point is beneficial to the thermal degradation of the polymeric membrane during pyrolysis. In addition, the adoption of a solvent with a close solubility parameter to PPESK is favorable to improving the permeability of carbon membranes. Compared to common warm air drying, cold drying is more favorable for the improvement of the thermal stability of the precursor membranes. With variation of the pyrolysis temperature from 650 °C to 850 °C, the best selectivities of carbon membranes are obtained at 850 °C for refrigerate-drying and at 750 °C for freeze-drying, respectively. All the gas separation data of the present carbon membranes made by cold drying surpass the Robesons upper bound.

Preparation and characterization of sulfonated poly(aryl ether ketone)s containing 3,5-diphenyl phthalazinone moieties for proton exchange membrane

A series of sulfonated poly(phthalazinone ether ketone)s containing 3,5-diphenyl phthalazinone moieties (SPPEK-dPs) were prepared by the sulfonation of poly(aryl ether ketone)s containing 3,5-diphenyl phthalazinone moieties (PPEK-dPs) which were synthesized via direct nucleophilic polycondensation from 4-(4-hydroxyphenyl)-2,3-phthalazin-1-ketone (DHPZ), 4-(3,5-diphenyl-4-hydroxyphenyl)-2,3-phthalazin-1-ketone (DHPZ-dP) and 4,4-difluorobenzophenone (DFB). The molecular structures were assessed by FTIR and 1H-NMR spectroscopy. The ion exchange capacity (IEC) of these sulfonated polymers were in the range of 0.99–1.81 mmol g−1. SPPEK-dP proton exchange membranes demonstrated good mechanical properties as well as dimensional, thermal, and oxidative stability. The proton conductivities of SPPEK-dP membranes increased with DHPZ-dP content and temperature. The proton conductivity of SPPEK-dP-55 was 13.18 × 10−2 S cm−1 at 95 °C. Furthermore, the methanol diffusion coefficients of SPPEK-dP membranes were 0.12 × 10−7 cm2 s−1 to 1.09 × 10−7 cm2 s−1 depending on the molar ratio of DHPZ-dP. Remarkably, the selectivity of SPPEK-dP membranes was 5–7 times higher than that of Nafion 117 membranes under the same conditions. All of the above properties indicate that SPPEK-dPs have potential applications in proton exchange membranes for direct methanol fuel cells.

Preparation of a new 2D MXene/PES composite membrane with excellent hydrophilicity and high flux

MXene, a new 2D transition metal carbide-based material, possesses excellent electrical conductivity and hydrophilicity. In this study, Ti3C2Tx (where T represents a functional group (O, OH, and/or F)) was produced by etching and ultrasonicating Ti3AlC2. Then, it was used to prepare the MXene composite membrane via a simple filtration method performed at 0.2 MPa on a polyethersulfone (PES) ultrafiltration membrane. The MXene composite membrane shows excellent flux (115 L m−2 h−1) and favorable rejection to Congo red dye (92.3% at 0.1 MPa). The membrane demonstrated rejection to inorganic salts below 23% with flux above 432 L m−2 h−1 at 0.1 MPa. Due to its loose lamellar structure, the composite membrane is able to demonstrate efficient permselectivity in the separation of dyes from salts. Furthermore, the composite membrane shows excellent hydrophilicity and flux because of the lamellar hydrophilic MXene.

Poly (phthalazinone ether ketone) anion exchange membranes with pyridinium groups as ion exchange groups for vanadium redox flow battery

Poly(phthalazinone ether ketone) anion exchange membranes with pyridinium groups (PyBPPEK) as ion exchange groups for vanadium redox flow battery were prepared from poly(phthalazinone ether ketone) containing bromomethyl groups and pyridine. FTIR were used to confirm the chemical structure of PyBPPEK. The thermal stability of PyBPPEK membranes were tested by using TGA analysis. PyBPPEK membranes exhibited tensile strength higher than 50 MPa and elongation at break higher than 25%. Columbic efficiencies of VRB with PyBPPEK membrane were higher than that of VRB with Nafion117 membrane. The energy efficiency of VRB with PyBPPEK membrane reached 89.7% at a charge-discharge current density of 40 mA·cm-2 while the energy efficiency of VRB with Nafion117 membrane was 86.0% at the same current density. When the ion exchange capacity of PyBPPEK membrane was 1.50 mmol·g-1, columbic efficiencies and energy efficiencies of VRB with the PyBPPEK membrane were higher than those of VRB with Nafion117 membrane at charge-discharge current densities ranging from 20 mA·cm-2 to 60 mA·cm-2. The results suggested that PyBPPEK membranes could be potential membranes for VRB applications.

Self-curing triphenol A-based phthalonitrile resin precursor acts as a flexibilizer and curing agent for phthalonitrile resin

Major problems currently limiting the widespread application of phthalonitrile resins are the high precursor melting point and volatility of the curing agent. Herein, a novel self-curing triphenol A-based phthalonitrile resin precursor (TPPA-Ph) was successfully synthesized by reacting α,α,α′-tris(4-hydroxyphenyl)-1-ethyl-4-isopropylbenzene (TPPA) with 4-nitrophthalonitrile (NPh) via nucleophilic substitution. The presence of residual phenolic hydroxyl groups in the TPPA-Ph precursor promoted the curing reaction of phthalonitrile resin in the absence of an additional curing reagent. Self-cured TPPA-Ph resins exhibited relatively low melting points (less than 100 °C), high thermal stability, and a wide processing window (116 °C). Furthermore, the TPPA-Ph precursors contained phenolic hydroxyl and cyano groups that can be used as flexibilizers and curing agents to optimize other phthalonitrile resins. Resorcinol-based phthalonitrile resin (DPPH) cured with various amounts of TPPA-Ph possessed excellent thermal and thermo-oxidative stability with a 5% weight loss temperature exceeding 530 °C, Tgs above 380 °C, and a wide processing window and time. Therefore, as a novel precursor and curing agent for phthalonitrile resins, the triphenol A-based phthalonitrile resin is an ideal resin matrix for high-performance composites with broad application prospects in aerospace, shipping, machinery, and other high-tech fields.

Effect of electric field intensity on the performance of poly(piperazine amide) nanofiltration membranes

Nanofiltration membrane has high flux and rejection to inorganic salts at relative low operation pressure, which is widely used in desalination and wastewater treatment. Negatively charged nanofilt...