This paper presents a solution to the control of the third harmonic of the neutral point in a VIENNA rectifier. A hybrid method combining a dynamic adjustment factor with a voltage deviation control ...of the split dc link is proposed. The fluctuation of the neutral point has been analyzed and the reason for the third harmonic fluctuation has been described with a mathematic model. In addition to minimizing the third-harmonic component in the neutral-point voltage, the proposed control method also provides immunity to the influence of changes in the capacitor voltage. Furthermore, the significant fluctuation in the neutral-point voltage caused by asymmetric capacitor parameters or unbalanced load can be effectively reduced by using a hybrid control method combining additional adjustment coefficients. The feasibility and effectiveness of the proposed strategy have been verified using both simulation and experimental results.
The excellent microporous layers (MPLs) in the gas diffusion layer requires superior mass transfer capacity, which is essential to high-performance proton exchange membrane fuel cells. However, the ...correspondence between MPL structure and mass transfer performance is ambiguous. Here, we design efficient mass transfer channels in MPLs with evolutionary structures by adjusting the content of whisker-like carbon nanotubes (WCNTs). The cell power density exhibits a bimodal shape with the increase of WCNTs in MPLs, which verifies that the perforated cracks of 5–10 μm in the MPL provide the separated channels for water and gas transport, and the optimal hydrophobic mesopores (34.87%) promote the mass transfer efficiency by elevating the capillary force of water transport. At 100% relative humidity (RH), the peak power densities of cells with the two MPLs are increased to 2.321 W cm−2 and 2.117 W cm−2, respectively. The electrochemical impedance spectroscopy confirms that the impedance of both MPLs are 109.35 mΩ cm2 and 63.55 mΩ cm2 at 100% RH and 3 A cm−2. The simple and scalable strategy provides a novel idea to relieve the mass transport loss of fuel cells.
•Mass transfer channels in MPLs with evolutionary structures are designed.•The mass transport performance of PEMFC exhibits a bimodal shape.•Crack morphology of MPLs are controlled by adjusting content of whisker-like CNTs.•Two mechanisms to improve the mass transfer capacity of GDL are proposed.•A novel strategy provides ideas to relieve the mass transport loss of fuel cells.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Microporous layer (MPL) is commonly applied to gas diffusion layer to improve water management performance of a proton exchange membrane fuel cell (PEMFC). In this work, we introduce a new type of ...MPL comprising whisker-like carbon nanotubes (WCNTs) and Ketjen Blacks (KBs) onto the macroporous substrate to optimize the pore structures. Scanning electron microscopy images show that KBs populate overlapping networks formed by WCNTs, leading to an increased proportion of mesopores (about 34.87%) of crack-free MPL. This optimal structure of MPL with a superhydrophobic surface ensures the maximum power density up to 2.046 W cm−2 at 100% relative humidity. The electrochemical impedance spectroscopy verifies that the mass transfer resistance is significantly lower, which means rapid drain of excess water and supply of reactant gas, and it is further confirmed by theoretical analysis of pore characteristics. A mechanism of gas-water transport balance promoted by the network structures of MPL constructed by WCNTs/KBs is proposed, which allows enhancing PEMFC performance at high humidity conditions.
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•A rational design of carbon network structure in microporous layer was proposed.•Optimal MPL was realized by synergy of Whisker-like CNTs and Ketjen Blacks.•Enhanced performance of PEMFC was achieved through alleviating flooding.•The reformative properties of MPL ensure ultra-low mass transport resistance.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
15.
Girl With Abdominal Pain Song, Zhang-Wei; Lin, Ling-Ling; Huang, Jun
Annals of emergency medicine,
August 2020, 2020-08-00, 20200801, Volume:
76, Issue:
2
Journal Article
Peer reviewed
Open access
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A systematic study shows that carbon nanotubes (CNTs) with tunable lengths can be obtained by a simple two-step electrochemical approach via oxygen defect engineering. The preoxidation of CNTs in the ...H2SO4 electrolyte controllably introduces oxygen defects onto the sp2-hybrid carbon skeleton. This is the key to high-efficiency tailoring of the CNTs with different length distributions (i.e., ∼640, ∼308, and ∼130 nm) by the following oxidation in NaOH electrolyte. In addition, the short-cut CNTs are free of metal impurities and destructive damage to their tubular structures, displaying excellent dispersibility in various solvents. This nondestructive cutting and purification strategy is a low-cost robust pathway to the scalable manufacturing of length-selective CNTs for various practical applications.
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IJS, KILJ, NUK, PNG, UL, UM
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•Long CNTs can be homogeneously coated on CF surface to form porous networks.•The epoxy serves as a local “welder” by the laser heating.•The networks were favourable for ...high-viscosity resin infiltration.•CNT/CF hybrids could afford a significantly higher interfacial bonding strength.•This method can be developed as a facile, scalable and cost-effective approach.
A facile method to prepare carbon nanotube/carbon fiber hybrid fiber was explored by an intermittent ultrasonic-directed electrophoretic deposition, and a following laser transient heating was used for welding the deposited carbon nanotubes on carbon fibers at joints. The formed porous networks were favourable for resin infiltration, leading a significant increase in interfacial bonding strength of carbon fiber reinforced polycarbonate composites.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Depending on the reactant property and reaction mechanism, one major regioisomer can be favored in a reaction that involves multiple active sites. Herein, an orthogonal regulation of nucleophilic and ...electrophilic sites in the regiodivergent hydroamination of isoprene with indazoles is demonstrated. Under Pd‐hydride catalysis, the 1,2‐ or 4,3‐insertion pathway with respect to the electrophilic sites on isoprene could be controlled by the choice of ligands. In terms of the nucleophilic sites on indazoles, the reaction occurs at either the N1‐ or N2‐position of indazoles is governed by the acid co‐catalysts. Preliminary experimental studies have been performed to rationalize the mechanism and regioselectivity. This study not only contributes a practical tool for selective functionalization of isoprene, but also provides a guide to manipulate the regioselectivity for the N‐functionalization of indazoles.
The Pd‐catalyzed regiodivergent coupling reactions between indazoles and isoprene have been developed through the orthogonal regulation of nucleophilic and electrophilic sites.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Through the formation of the thermodynamically favored Cr(III)–O bond, the Nozaki–Hiyama–Kishi reaction has been widely applied in the functionalization of carbonyl compounds with the help of Ni ...catalysis. Herein, a divergent regio- and stereoselective diarylation of dienes has been developed under Ni/Cr cocatalysis without the inherent driving force for the formation of polar metal alkoxides. Preliminary experimental studies have been conducted to elucidate the key roles of Ni, Cr, and redox-active bis(imino)pyridine (PDI) ligands. The proposed mechanism suggests that the newly formed C–C bond of this diarylation was created by organonickel species instead of organochromium species.
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IJS, KILJ, NUK, PNG, UL, UM
The surface modification of multiwall carbon nanotubes (MWCTNs) was achieved by electrochemical anodic oxidation in NaOH and H2SO4 electrolytes. Their defect structures, functional groups, morphology ...and dispersibility in aqueous solutions were characterized by SEM, TEM, XPS, FTIR, Raman spectroscopy, zeta potential analysis and a stability test of their suspensions. Results indicate that anodic oxidation with the NaOH electrolyte removes more amorphous carbon, introduces fewer defects and more oxygen-containing functional groups (mainly -OH), and produces shorter nanotubes, as a result of which the resulting nanotubes are more stable when dispersed in aqueous solutions compared with those oxidized by the H2SO4 electrolyte. MWCTNs are more easily oxidized in the NaOH electrolyte, and the numbers of oxygen-containing functional groups and hydroxyl groups increase continuously with the oxidation degree. In the H2SO4 electrolyte, however, the numbers of oxygen-containing functional groups and hydroxyl groups increase and level off with the oxidation degree.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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