Structural architectures of polymer proton exchange membranes suitable for high-temperature fuel cell applications

High-temperature proton exchange membrane (HT-PEM) fuel cells offer more advantages than low-temperature PEM fuel cells. The ideal characteristics of HT-PEMs are high conductivities, low-humidity operation conditions, adequate mechanical properties, and competitive costs. Various molecular moieties, such as benzimidazole, benzo-thiazole, imide, and ether ether ketone, have been introduced to polymer chain backbones to satisfy the application requirements for HT-PEMs. The most common sulfonated polymers based on the main chain backbones have been employed to improve the rties. Side group/chain engineering, includ crosslinking, has been widely applied to HT-PEMs to further improve their proton conductivity, thermal stability, and mechanical properties. Currently, phosphoric acid-doped polybenzimidazole is the most successful polymer material for application in HT-PEMs. The compositing/blending modification methods of polymers are effective in obtaining high PA-doping levels and superior mechanical properties. In this review, the current progress of various membrane materials used for HT-PEMs is summarized. The synthesis and performance characteristics of polymers containing specific moieties in the chain backbones applied to HT-PEMs are discussed systemically. Various modification approaches and their deficiencies associated with HT-PEMs are analyzed and clarified. Prospects and future challenges are also presented

Oxidative evolution of Z/E-diaminotetraphenylethylene

We report that Z/E-diaminotetraphenylethylene (Z/E-2NH(2)-TPE) molecules suffer primarily from oxidative evolution rather than recognized isomerization. The oxide is separated and its structure is deciphered by single crystal X-ray diffraction. The oxidative evolution accompanying the rearrangement is explained through quantum theoretical calculation

Polyimides containing aliphatic/alicyclic segments in the main chains

Aliphatic/alicyclic (Al)-containing polyimides (PIs), including fully-Al-PIs and partially-Al-PIs, are widely employed in electric, electronics, optical materials, and other advanced material fields. Examples include high speed multiplayer printed wiring boards, alignment films for liquid-crystal displays, fuel cells, batteries, gas separation membranes, pervaporation membranes, biomedical applications, and composites/hybrid materials. In the past decades, research has focused on the synthesis and molecular design of fully-Al-PIs and partially-Al-PIs. However, the effects of aliphatic/alicyclic segments on the performance of fully-Al-PIs and partially-Al-PIs and their potential applications are not clear. Therefore, an overall clarification of aliphatic/alicyclic-containing monomers, the effects of aliphatic/alicyclic segments on PI performance, as well as recent applications for advanced technology are important topics for further study. This review systematically summarizes the available aliphatic/alicyclic monomers and clarifies the influence of aliphatic/alicyclic-containing segments in chain backbones on the morphology and properties of the resulting PIs. Further, the use of PIs in applications for advanced materials is discussed, along with the outlook for the future of aliphatic/alicyclic-containing polyimides and their advanced applications. (C) 2019 The Authors. Published by Elsevier B.V.</p

Colorless Partially Alicyclic Polyimides Based on Troger's Base Exhibiting Good Solubility and Dual Fluorescence/Phosphorescence Emission

This study proposes a molecular design and synthetic route to novel colorless, transparent polyimides that exhibit dual fluorescence/phosphorescence emission at long wavelengths applicable to solar energy conversion. Partially alicyclic polyimides (Ac-PI-TBs) based on Trager's base (TB) and denoted as Ac-PI-TB-1, Ac-PI-TB-2, and Ac-PI-TB-3 were synthesized by in situ TB formation. The resulting Ac-PI-TBs are readily soluble in common organic solvents and have good mechanical properties with tensile strengths of 72.5-102.3 MPa, elongations at breaks of 12.5-75.0%, low dielectric constants (similar to 2.66) and low thermal diffusivities (D-perpendicular to <= 7.7 X 10(-8) m(2)/s), and good thermal stability. The films are totally colorless and transparent with transmittances above 77% at 400 nm. The films also show dual fluorescence and phosphorescence emissions with Stokes shifts as large as 11 421 cm(-1) at low temperatures. The results highlight the possible application of these films in the spectral conversion of unused UV solar radiation to useful visible light

Ultrafast selective adsorption of pretreatment inhibitors from lignocellulosic hydrolysate with metal-organic frameworks: Performance and adsorption mechanisms

In this work, four metal-organic frameworks materials (MOFs, MIL-140A, MIL-140C, MIL-101(Fe) and NH2-MIL-101(Fe) were prepared, characterized and compared for the adsorptive removal of furfural and four phenolic inhibitors. MIL-140C demonstrated the best adsorption capability among the tested MOFs. Effects of pH, ionic strength, contact time, adsorbent dosage, temperature and sugars on adsorption of inhibitors on MIL-140C were systematically investigated. Inhibitors adsorption was ultrafast within minutes and kinetic data fitted pseudosecond-order model well. The Langmuir isotherm described the adsorption process satisfactorily with maximum adsorption capacities of 222.72, 240.38, 231.48, 207.04 and 60.79 mg/g for vanillin, syringaldehyde, ferulic acid, p-coumaric acid and furfural, respectively. Thermodynamic parameters disclosed that nature of the adsorption was exothermic and spontaneous under the experimental conditions. MIL-140C demonstrated exceptional adsorption selectivity towards inhibitors even with excessive amount of xylose and glucose, as well as excellent regeneration performance after five adsorption/desorption cycles. MIL-140C also exhibited satisfactory detoxification performance after treatment of real corn stover dilute acid hydrolysate. Furthermore, analysis of underlying adsorption mechanism showed that pi-pi interaction, hydrophobic interaction and hydrogen bonding/metal-coordination (depending on solution pH) were involved in the adsorption of tested phenolic inhibitors, while the pi-pi and hydrophobic interactions contributed to the furfural adsorption. The overall results revealed that MIL-140C could hold great promise in removing phenolic and furan inhibitors from lignocellulosic hydrolysate

Effect of Additives on Tribological Performance of Magnetorheological Fluids

In this study, nano-diamond (ND) and MoS2 powder are used as additives in a carbonyl iron-based magnetorheological fluid (MRF) to improve its tribological performance. MRFs are prepared by dispersing 35 wt.% of CI particles in silicone oil and adding different proportions (0, 1, 3, or 5 wt.%) of ND and MoS2 additives. Seven kinds of MRFs are made and tested using reciprocating friction and wear tester under different normal loads, and then the friction characteristics are evaluated by analyzing the experimental results. The morphological properties of MRFs and contacting surfaces before and after the tests are also observed using a scanning electron microscope and analyzed via energy-dispersive X-ray spectroscopy. The results show that the appropriate weight percentage of MoS2 additives may decrease the friction coefficient and wear zone. It is also demonstrated from detailed analyses of worn surfaces that the wear mechanism is influenced not only by additives, but also by the applied normal load and magnetic field strength

Highly Stable Silver-Loaded Membrane Prepared by Interfacial Polymerization for Olefin Separation

The separation of light olefins from paraffins by a silver-loaded facilitated transport membrane has received wide attention in recent years. However, the undesirable instability of carriers Ag+ has consistently restricted its further application. In this work, a silver-loaded facilitated transport membrane is developed by interfacial polymerization on PDMS/PSF support. A part of Ag+ in the prepared membrane is presented as silver(I)-polyetheramine (Ag(I)-PEA) complexes that can effectively enhance the stability of Ag+. To eliminate nonselective voids and bring more carriers (Ag+), secondary aqueous phase treatment was conducted. And the effect of PEA and TMC concentrations, ratio of PEA to AgNO3, as well as secondary aqueous phase treatment on the gas transport is systematically investigated. The results show that the facilitated transport of Ag+ to C3H6 can offset the increase in diffusion resistance induced by the incremental membrane thickness and cross-linking degree as well as the additional AgCl particles on the membrane. Finally, the optimum C3H6/C3H8 selectivity of the silver-loaded membrane is trebled over the membrane without silver. Remarkably, the TMC0.6%-PEA(10%)(AgNO3)(10:9)-2/PDMS/PSF membranes show great long-term stability of about 29 days. In this work, both monomer synthesis and preparation methods are facile and versatile, presenting a promising strategy for the preparation of silver-loaded membranes with a long-term separation property