New polymer electrolyte membranes for fuel cell applications were synthesized via covalent bonding of phosphonic acid (PA) onto poly(benzimidazole) (PBI). PBI was functionalized via N‐alkylation with an appropriate phosphonate, followed by hydrolysis of the grafted groups to the desired PA functions. Alternatively, polymer networks based on PBI and vinyl phosphonic acid (VPA) were successfully synthesized. In this second approach, PBI was first functionalized in a polymer analogous modification with polymerizable or radical‐forming groups. Thermally induced ‘grafting‐through’ or ‘grafting‐from’ polymerization of VPA led to the corresponding PBI/PVPA networks. The structure‐property relationships with respect to proton conducting properties of the membrane materials are discussed.magnified image
Recently, piezoelectric nanogenerators have received great interest as they can convert waste mechanical and radiative energy to electricity and can be used in self‐energy generating systems and sensor technologies. In this study, electrospun poly(vinylidene fluoride) (PVDF) nanofiber‐based piezoelectric nanogenerators with reduced graphene oxide (rGO), polyaniline (PANI), and PANI‐functionalized rGO (rGOPANI) have been developed. Two different types of nanofiber mats were produced: First, rGO‐ and rGOPANI‐doped PVDF nanofiber mats and second, rGO, PANI and rGOPANI‐spray‐coated PVDF nanofiber mats that have worked as nanogenerators' electrodes. Then, characterizations of samples were performed in terms of piezoelectricity, Fourier transform infrared (FTIR) spectrophotometric, X‐ray diffractions (XRD), and scanning electron microscopy analyses. FTIR and XRD results confirmed that piezoelectric β‐crystalline phase of PVDF occurred after the electrospinning process. Besides, maximum output voltages were obtained as 7.84 and 10.60 V for rGO‐doped PVDF and rGOPANI‐coated PVDF nanofiber mats, respectively. As a result, the doped nanofibers were found to be more successful due to the higher device accuracy in sensor technologies compared with spray‐coated samples. However, spray‐coating method proved to be more suitable technique for the production of nanogenerators on an industrial scale in terms of fast and large‐scale applicability. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48517.
Celtec-V is a proton exchange membrane based on polybenzimidazole ͑PBI͒ comprising an interpenetrating network of polyvinylphosphonic acid designed for application in the direct methanol fuel cell. The properties and fuel cell performance of Celtec-V are investigated and compared against a Nafion 117 standard. It is shown that with the PBI-based membrane, fuel cell performance can be sustained to higher methanol feed concentration at around half the methanol crossover rate. Above 1.0 M methanol, Celtec-V outperforms Nafion 117. Furthermore, lower water permeation is observed, with Celtec-V having an electro-osmotic drag coefficient of around 1 compared to a value of 4-5 for Nafion 117. Room for improvement is identified in the ohmic resistance of the membrane and the cathode-membrane interface, where higher losses are observed at increasing current density.
Pick your Pd partners: A number of catalytic systems have been developed for palladium‐catalyzed CH activation/CC bond formation. Recent studies concerning the palladium(II)‐catalyzed coupling of CH bonds with organometallic reagents through a PdII/Pd0 catalytic cycle are discussed (see scheme), and the versatility and practicality of this new mode of catalysis are presented. Unaddressed questions and the potential for development in the field are also addressed. In the past decade, palladium‐catalyzed CH activation/CC bond‐forming reactions have emerged as promising new catalytic transformations; however, development in this field is still at an early stage compared to the state of the art in cross‐coupling reactions using aryl and alkyl halides. This Review begins with a brief introduction of four extensively investigated modes of catalysis for forming CC bonds from CH bonds: PdII/Pd0, PdII/PdIV, Pd0/PdII/PdIV, and Pd0/PdII catalysis. A more detailed discussion is then directed towards the recent development of palladium(II)‐catalyzed coupling of CH bonds with organometallic reagents through a PdII/Pd0 catalytic cycle. Despite the progress made to date, improving the versatility and practicality of this new reaction remains a tremendous challenge.
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