Although pyridine bridged oxypolybenzimidazole (PyOPBI) membranes are considered to be promising hightemperature proton exchange membrane (HT-PEM) materials that have the potential to overcome many obstacles such as solubility, membrane processability, cost, etc., of the mainstream conventional polybenzimidazole (PBI)-based HT-PEM, the weak structural stability of PyOPBI in concentrated phosphoric acid (PA) and poor dimensional and mechanical stability have been the crucial issues restraining the performance. To mitigate these bottlenecks, in this work, we successfully synthesized three types of PyOPBIs with flexible aryl ether backbones and bulky substituents by polycondensation reaction of various aryl diacids and pyridine-bridged tetraamine 2,6-bis(3′,4′-diaminophenyl)-4-phenylpyridine (PyTAB) in Eaton's reagent followed by casting as HT-PEMs. Three designed bulky substitute containing PyOPBI membranes showed considerably high PA loading capacity (16−22 mol of PA/repeat unit) and proton conductivity (0.04−0.078 S/cm) at 180 °C as compared to earlier reported unsubstituted PyOPBI membranes (14 mol of PA/repeat unit and 0.007 S/cm at 180 °C). In addition, the obtained membranes showcased good chemical, mechanical, thermal, and long-term conductivity stabilities and outstanding stability in concentrated PA. The pendent groups and the bulkiness of the backbone are believed to be the cause behind better stability and facilitating proton transport that results in higher proton conductivity. The single cell made from the membrane electrode assembly of these bulky substituted PyOPBI membranes displayed a peak power density in the range of 144−240 mW cm −2 under H 2 /O 2 at 160 °C, which is considerably higher than that for unsubstituted PyOPBI membrane (90.4 mW cm −2 ). Overall, the current results provide an effective strategy to explore the benefits of structural modulation of PyOPBI using various structurally divergent diacids to enhance HT-PEM properties and suggest a scalable route for the advancement of PBI-based HT-PEM fuel cells.
Despite several unique advantages, high-temperature proton-exchange membrane fuel cells (HT-PEMFCs) based on polybenzimidazole (PBI) membranes suffer from various drawbacks like weak chemical resistance, poor mechanical strength, acid leaching, etc., which eventually reduces the performance of the cell. In order to minimize these drawbacks and to improve the cell performance, in this work we have developed proton-exchange membranes (PEMs) in which pyridine-bridged-oxypolybenzimidazole (PyOPBI) and brominated polyphenylene oxide (BrPPO) were chemically cross-linked by an ex situ methodology. Three cross-linked membranes P1, P2, and P3 consisting of 12.5, 25.0, and 37.5 wt % BrPPO, respectively, with respect to PyOBI were successfully fabricated and PEM properties were studied. These membranes showed much improved acid stability, oxidative stability, mechanical strength, and strong resistance to swelling in concentrated phosphoric acid (PA) solution. They were found to be completely stable in 85% PA whereas uncross-linked PyOPBI membranes readily dissolved in 60% PA. The reason for such stability has been ascribed to the cross-linked network structure of the membrane. The P1 membrane exhibited remarkably high proton conductivity (0.123 S cm −1 ) whereas the pristine PyOPBI membrane showed a conductivity of 0.008 S cm −1 at 180 o C. The single cell measurement under anhydrous conditions at 160 °C of membrane electrode assembly (MEA) obtained from the P1 membrane displayed good fuel cell efficiencies with power density 290 mW cm −2 and current density 848.7 mA cm −2 at 0.3 V whereas under the identical measurement conditions, MEA of the pristine PyOPBI membrane showed 96.4 mW cm −2 power density and 321.5 mA cm −2 current density at 0.3 V. All these results indicated that cross-linked membranes have great potential to be used in the HT-PEMFC.
The preparation of polymeric anhydrous proton conducting membrane is critical to the development of high-temperature proton-exchange membrane (HT-PEM) for the use in fuel cell and remains a significant scientific challenge...
The chemistry of the CT complex between donor 2-methyl-8-quinolinol (2 MQ) and acceptor chloranilic acid (CHLA) has been studied by using electronic absorption spectroscopy in acetonitrile, methanol, and ethanol at room temperature.
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