A cyclic open circuit voltage (COCV) accelerated stress test (AST) is designed to screen the simultaneous effect of chemical and mechanical membrane degradation in polymer electrolyte fuel cells. The ...AST consists of a steady state OCV phase to accelerate chemical degradation and periodic wet/dry cycles to provide mechanical degradation. The membrane degradation process induced by COCV AST operation is analyzed using a standard MEA with PFSA ionomer membrane. The OCV shows an initially mild decay rate followed by a higher decay rate in the later stages of the experiment. Membrane failure, defined by a threshold convective hydrogen leak rate, is obtained after 160 h of operation. Uniform membrane thinning is observed with pinhole formation being the primary cause of failure. Mechanical tensile tests reveal that the membrane becomes stiffer and more brittle during AST operation, which contributes to mechanical failure upon cyclic humidity induced stress. Solid state 19F NMR spectroscopy and fluoride emission measurements demonstrate fluorine loss from both side chain and main chain upon membrane exposure to high temperature and low humidity OCV condition.
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•A combined chemical/mechanical membrane accelerated stress test is applied.•Membrane failure via pinhole formation is generated in 160 h.•NMR and fluoride emission data show both side chain and main chain degradation.•Membrane degradation is intensified by periodic chemical and mechanical stressors.•Insight is provided into the conjoint chemical/mechanical degradation mechanism.
A N‐heterocyclic olefin (NHO), a terminal alkene selectively activates aromatic C−F bonds without the need of any additional catalyst. As a result, a straightforward methodology was developed for the ...formation of different fluoroaryl‐substituted alkenes in which the central carbon–carbon double bond is in a twisted geometry.
NHO activation: The activation of aromatic C−F bonds by N‐heterocyclic olefin (NHO) occurs without the need of any additional catalyst. As a result, a straightforward methodology was developed for the formation of different fluoroaryl‐substituted alkenes.
Fabrication of advanced electrocatalysts with high activity and durability is urgently needed to achieve energy conversion and pollution treatment at the same time. Herein, we highlight a ...fluorine-doped nickel-based heterostructure, in which fluorine doping displays a dual effect in Ni(OH)2 nanosheets/Ni3S2 heteronanorods. On the one hand, fluorine doping can facilitate the formation of Ni(OH)2 nanosheets/Ni3S2 heteronanorods through one-step in situ growth on nickel foams. The unique heterostructure enables good exposure of abundant active sites and highly active heterointerfaces. On the other hand, the uniform incorporation of fluorine can effectively modulate the electron density at the Fermi level of Ni3S2, contributing to the improved electrical conductivity and charge transfer efficiency, further improving the electrocatalytic activity in the oxygen evolution reaction (OER) and urea oxidation reaction (UOR). The optimal heterostructure presents a low overpotential of 360 mV to reach the OER current density of 100 mA cm-2. Finally, this heterostructure also displays a superior UOR anodic peak current of about 322.9 mA cm-2, almost the highest value at the anodic peak compared to the literature.
Over the years, in order to enhance the thermal efficiency, coal-fired power plants have witnessed great improvements in water and waste heat recovery. This paper aims to investigate the water vapor ...and latent heat recovery from the low temperature flue gases exiting a limestone-gypsum wet desulfurization system. A pilot-scale testing system mainly composed of a two-stage fluorine plastic heat exchanger (FHE) was built in a 660 MW lignite-fired power plant in northern China. The additional FHE configuration was first developed and used for water and latent heat recovery based on the condensation mechanism of water vapor. Results showed that the FHE can overcome the shortcomings of the conventional metal heat exchanger, especially when flue gas temperature is below the acid dew point. The recovered latent heat accounted for more than 80% of the total heat recovered from low temperature flue gases, and the heat supply of 92 MWth was achieved. The overall heat transfer coefficient of the FHE reached up to 275 W/(m2•K). The water recovery efficiency increased with an increase in cooling water velocity and a decrease in flue gas velocity. The water recovery efficiency higher than 70% was reached when the flue gas velocity was less than 5 m/s and the cooling water velocity was greater than 0.24 m/s. The highest water recovery efficiency of the two-stage FHE was 85%, suggesting that this technology has a greater application potential in all industrial processes. The recovered water mass from the flue gas by condensation was nearly equal to, or even exceeded, the equivalent mass of supplemental water for the desulfurization system. The good water recovery performance of the FHE device implied that zero water consumption of the desulfurization system could be achieved, which is of great significance for power plants, especially in water scarce regions. This technology will offer an innovative and feasible solution to resolve the issue of water and heat recovery in the highly corrosive conditions.
•Fluorine plastic heat exchanger was developed for water and latent heat recovery.•Optimized operational parameters result with higher water and heat recovery rate.•Zero water consumption for wet desulfurization system could be realized.•The water recovery efficiency of fluorine plastic heat exchanger reached up to 85%.
Convergent routes to a variety of indolines, indoles, oxindoles, and their aza analogues involving radical additions of xanthates are described. Three approaches are summarized. The first is the ...least general and relies on the generation of aryl or heteroaryl radicals starting from diazonium salts. The second involves radical addition to N‐allylanilines followed by ring‐closure onto the aromatic core. A large variety of indolines and azaindolines can thus be obtained and, in many cases, converted into the corresponding indoles and azaindoles by various methods. The synthesis of novel fluoroazaindolines and fluoroazaindoles by a rare homolytic ipso‐substitution of fluorine atoms is particularly noteworthy. The last approach hinges on the direct modification of indoles by radical addition to the pyrrole subunit of the indole nucleus. Application of this methodology to the total synthesis of melatonin and the alkaloids mersicarpine, caulerpine, and the pentacyclic skeleton of tronocarpine is briefly discussed. Most of the compounds described herein would be difficult to obtain by more traditional routes.
Indoles and friends: Xanthates provide multiple convergent radical‐based routes to indoles, indolines, oxindoles, and their aza analogues including fluorinated derivatives. Numerous otherwise inaccessible structures can now be obtained quickly using inexpensive, metal‐free reagents.
Newly designed fluorine-doped magnetic carbon (F-MC) was synthesized in situ though a facile one-step pyrolysis-carbonization method. Poly(vinylidene fluoride) (PVDF) served as the precursor for both ...carbon and fluorine. 2.5% F content with core-shell structure was obtained over F-MC, which was used as a adsorbent for the Cr(VI) removal. To our best knowledge, this is the first time to report that the fluorine doped material was applied for the Cr(VI) removal, demonstrating very high removal capacity (1423.4 mg g−1), higher than most reported adsorbents. The unexpected performance of F-MC can be attributed to the configuration of F dopants on the surface. The observed pseudo-second-order kinetic study indicated the dominance of chemical adsorption for this process. High stability of F-MC after 5 recycling test for the Cr(VI) removal was also observed, indicating that F-MC could be used as an excellent adsorbent for the toxic heavy metal removal from the wastewater.
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Dark current density (Jdark) is the most important factors determining signal‐to‐noise ratio, linear dynamic range and detectivity (D*) of organic photodetectors (OPDs). However, the ...solution‐processed OPDs generally suffer from high Jdark under bias because the origin of Jdark still remains unclear and related to complicate factors. In this work, the effect of fluorinated alkyl side chain (FAC) of conjugated polymers (CPs) on the OPD performance is systematically investigated according to the number of fluorine atom. The OPDs, comprising the CPs with a FAC (CP‐FAC), exhibit at least two orders lower Jdark (≈3.73 × 10‐10 A cm‐2 at ‐2 V) compared to that without FAC while significantly maintaining high external quantum efficiency (≈78%). This is because the side chain fluorination leads to the formation of a more ordered molecular structure of the CPs, which reduces the trap density and energetic disorder, thus resulting in the effective suppression of Jdark and in the enhancement of charge carrier mobility. The CP‐FAC based OPD exhibits an exceptionally high D* (≈3.39 × 1013 cm Hz1/2 W‐1 at ‐2 V) and a reasonable response speed (f‐3db = ≈56.31 kHz). Furthermore, a photoplethysmography sensor comprising the CP‐FAC based OPD in a transmission mode is demonstrated.
The suppression of dark current density directly affects the detectivity of organic photodetectors. This study demonstrates that the fluorination of the alkyl side chains of conjugated polymers can lead to the formation of closely and evenly stacked molecular structures that decreases the number of trap states and degree of energetic disorder, thereby effectively suppressing the dark current density.
Herein, we report a copper salt-controlled divergent reactivity toward alpha-diazocarbonyl compounds. By a simple change of the copper counteranion under identical reaction conditions, the reported ...method allowed an easy access to either (Z)-alpha-fluorovinylphosphonate or alkyl-SCF2PO(OEt)2 derivatives in good yields. Mechanistic studies were performed and suggested two different pathways to explain the formation of these products.
The straightforward introduction of the trifluoromethylseleno group into aromatic and heteroaromatic compounds is accomplished by the utilization of readily available aryldiazonium ...tetrafluoroborates, potassium selenocyanate, and Ruppert–Prakash reagent. The reaction tolerates a wide range of aromatic and heteroaromatic diazonium salts and is also amenable to the synthesis of pentafluoroethyl selenoethers. Furthermore, the methodology can be applied directly starting from anilines.
Easily scalable! A mild procedure for the trifluoromethylselenolation of aromatic compounds has been developed. Various readily available aryl diazonium tetrafluoroborates smoothly underwent reactions to give products in good to high yields (see scheme; TMS=trimethylsilyl). Both electron‐rich and ‐poor substrates are suitable for the process.
We report on a novel, simple, and environmentally benign synthesis route for a free-standing reduced graphene oxide (r-GO) aerogel and its application as supporting electrode for the electrochemical ...redox reaction of sulphur in a catholyte-based lithium-sulphur battery. A mesoporous matrix is formed by a layers of r-GO, providing sites for electrochemical reactions and a highly conducting pathway for electrons. The highly porous structure is easily infiltrated by a catholyte solution providing a homogeneous distribution of the sulphur active material in the conductive graphene matrix and ensuring efficient electrochemical reactions. This is demonstrated by a high capacity, 3.4 mAh cm−2, at high mass loading, 3.2 mg cm−2 of sulphur in the cathode and in total the sulphur loading in the Li-S cell is even double (6.4 mg cm−2). Additionally, the presence of oxygen groups in the r-GO aerogel structure stabilizes the cycling performance and the Li-S cell with the fluorine free catholyte shows a capacity retention of 85% after 350 cycles.
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•New synthetic route for free-standing reduced graphene oxide aerogel.•Semi-liquid Li-S cells designed through fluorine-free electrolyte medium.•Reduced graphene oxide aerogel stabilizing Li-S cells cyclability and capacity retention.
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