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1.
Electrodeposition of aluminum from an AlCl3-EMIC ionic liquid with or without the addition of saturated LaCl3 was carried out by both direct- and pulse-current plating methods. The effects of various parameters, including current density, pulse frequency, current on/off duration (ton and toff), and temperature, on deposit morphology and crystal size were investigated. Deposits prepared by pulse-current plating gave a brighter and flatter surface than those prepared by direct-current plating at appropriate pulse current parameters. Temperature and pulse–current frequency (toff) were shown to significantly affect deposit morphology. Coalescence of grains during toff periods in the pulse current plating was observed, especially at temperatures above 60 °C. Increasing the temperature from 25 to 90 °C caused an increase in deposit grain size and resulted in a change of grain shapes from a small sphere-like form to a feather-like form. As a result, the adhesion of the deposited aluminum to the substrate was lowered. Smaller grain sizes and well-adhered deposits were achieved at lower temperatures. For example, deposition at 25 °C resulted in the smallest crystal size of about 0.3 μm under the conditions of ton = 80 ms, toff = 20 ms, and i = 8 mA/cm2. Furthermore, the addition of LaCl3 to the melt at 60 °C effectively reduced the porosity and improved compactness of deposits.  相似文献   

2.
In this study, Al was electrodeposited on a platinum substrate at room temperature from an ionic liquid bath of EMIC containing AlCl3 using potentiostatic polarization (PP), galvanostatic polarization (GP), monopolar current pulse polarization (MCP) and bipolar current pulse polarization (BCP). Transition of current or potential during galvanostatic or pulse polarization revealed that the initial stage of the deposition process was controlled by a nucleation process depending on the polarization condition. For example, the average size of Al deposits decreased with increasing current density in the case of GP. FE-SEM observation showed that dense and compact Al deposits with a smooth surface were obtained by the current pulse method. Roughness factor evaluated from electrochemical impedance measurement confirmed the smooth surface of these deposits. Adhesion strength of Al deposits was greatly improved using BCP in which an anodic pulse was combined with a cathodic pulse for electrodeposition. In this study, the optimal parameters for BCP were found to be IC = −16.0 mA cm−2, IA = 1.0 mA cm−2, rC (duty ratio) = 0.5, and f = 2 Hz. The mechanisms of electrodeposition by these three methods are discussed.  相似文献   

3.
Nano-γ-Al2O3 is dispersed onto the glass carbon electrode (GCE) by polishing. This nanostructured modified GCE exhibits a great enhancement to the redox responses of 3-nitrobenzaldehyde thiosemicarbazone (3-NBT). In comparison with bare GCE, 3-NBT gives a more sensitive voltammetric response because of the nanoparticle’s unique properties. The lowest detectable concentration (3σ) of 3-NBT is estimated to be 1.18 × 10−6 M (accumulation for 4 min). The linear relationship between peak current and concentration of 3-NBT holds in the range 1.0 × 10−5 M to 1.0 × 10−4 M (r = 0.9981). The electrochemical properties of 3-NBT on this modified electrode have been investigated with various electrochemical methods. The results indicate that the transference of one electron and one proton involves electrode radical reaction processes I and II, respectively. The coverage value (Γ) of 1.62 × 10−9 mol cm−2 was calculated and the electrochemical parameters, diffusion coefficient D (2.54 × 10−3 cm2 s−1, 2.03 × 10−3 cm2 s−1) and reaction rate constant ks (5.9573 s−1, 7.15 × 10−2 cm s−1) were obtained for quasi-reversible system I and irreversible system II, respectively.  相似文献   

4.
A Co3O4/graphene hybrid material was fabricated using a simple in situ reduction process and demonstrated as a highly reversible anode for lithium rechargeable batteries. The hybrid is composed of 5 nm size Co3O4 particles uniformly dispersed on graphene, as observed by transmission electron microscopy, atomic force microscopy, Raman spectroscopy and X-ray diffraction analysis. The Co3O4/graphene anode can deliver a capacity of more than 800 mA h g−1 reversibly at a 200 mA g−1 rate in the voltage range between 3.0 and 0.001 V. The high reversible capacity is retained at elevated current densities. At a current rate as high as 1000 mA g−1, the Co3O4/graphene anode can deliver more than 550 mA h g −1, which is significantly higher than the capacity of current commercial graphite anodes. The superior electrochemical performance of the Co3O4/graphene is attributed to its unique nanostructure, which intimately combines the conductive graphene network with uniformly dispersed nano Co3O4 particles.  相似文献   

5.
Non-spherical Li(Ni1/3Co1/3Mn1/3)O2 powders have been synthesized using a two-step drying method with 5% excess LiOH at 800 °C for 20 h. The tap-density of the powder obtained is 2.95 g cm−3. This value is remarkably higher than that of the Li(Ni1/3Co1/3Mn1/3)O2 powders obtained by other methods, which range from 1.50 g cm−3 to 2.40 g cm−3. The precursor and Li(Ni1/3Co1/3Mn1/3)O2 are characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscope (SEM). XPS studies show that the predominant oxidation states of Ni, Co and Mn in the precursor are 2+, 3+ and 4+, respectively. XRD results show that the Li(Ni1/3Co1/3Mn1/3)O2 material obtained by the two-step drying method has a well-layered structure with a small amount of cation mixing. SEM confirms that the Li(Ni1/3Co1/3Mn1/3)O2 particles obtained by this method are uniform. The initial discharge capacity of 167 mAh g−1 is obtained between 3 V and 4.3 V at a current of 0.2 C rate. The capacity of 159 mAh g−1 is retained at the end of 30 charge-discharge cycle with a capacity retention of 95%.  相似文献   

6.
Free standing PEDOT [poly(3,4-ethylenedioxythiophene)] films (with surface conductivities of 200-400 S cm−1) were generated in tetrabutylammonium trifluromethanesulfonate (TBACF3SO3) electrolytes by potentiostatic (EP 1.05 V vs. Ag wire) electropolymerisation in propylene carbonate (at −27 °C) and methyl benzoate (at −4 °C). Films obtained in the TBACF3SO3 electrolytes showed a length increase of 2-3% during scans to negative potentials under isotonic (constant load 1.35 MPa) and stress of 0.3 MPa under isometric (constant length) conditions. Cation movement occurred due to immobilisation of CF3SO3 anions during electropolymerisation. The system showed good stability and low creep during square wave electrochemical cycling in the potential range from 0.0 to 1.0 V. The surface morphology (SEM) of the PEDOT films showed that the polymer structure is dependent upon the solvent used during the polymerisation process.  相似文献   

7.
TiO2–Ni(OH)2 bilayer electrodes were prepared by the cathodic electrodeposition of Ni(OH)2 layer on a TiO2/ITO substrate. The porous Ni(OH)2 layers were obtained at relatively high current densities (≥1.0 mA cm−2), and the particle size increased with increasing the deposition current density. A porous nanostructured TiO2–Ni(OH)2 bilayer was obtained at a current density of 1.0 mA cm−2. The effects of OH concentration in the electrolyte and surface structure in the Ni(OH)2 layer on storage of the oxidative energy of TiO2 were investigated. In our experimental conditions the oxidative energy storage of an UV-irradiated TiO2 photocatalyst in Ni(OH)2 was obviously enhanced in the electrolyte with 1.0 M OH. The porous nanostructured TiO2–Ni(OH)2 bilayer electrode showed the notably improved oxidative energy storage performance, resulting from its porous structure and nanostructured Ni(OH)2 particles. The TiO2–Ni(OH)2 bilayer electrode during UV irradiation exhibited much higher potentials and larger photocurrent than the TiO2/ITO electrode. The transition from Ni(OH)2 to NiOOH under UV irradiation proceeded in the potential range of −0.5 to −0.2 V, much more negative than the Ni(OH)2/NiOOH redox potential. A possible mechanism on the oxidative energy storage of an UV-irradiated TiO2 photocatalyst in Ni(OH)2 was proposed, and the related experimental results were discussed in terms of the suggested model.  相似文献   

8.
Metal fluoride added carbon anodes treated by pre-electrolysis were investigated for electrolytic production of nitrogen trifluoride (NF3) in molten NH4F·KF·4HF at 100 °C. The conditions for pre-electrolysis were first optimized using a graphite sheet anode as a model anode. The formation of fluorine-graphite intercalation compounds (fluorine-GICs) with semi-covalent C–F bonds, (CxF)n, on the MgF2 and CaF2 added carbon anode surface was accelerated by pre-electrolysis at potentials less than 4.0 V. Critical current densities (CCD) on the MgF2 added carbon anodes pre-electrolyzed under various conditions were determined, and the highest CCD was 290 mA cm−2 obtained for that pre-electrolyzed at 3.5 V for 500 C cm−2. This anode was successfully used in the electrolysis at 100 mA cm−2 for 290 h and the maximum NF3 current efficiency was 55%. From these results, it was concluded that the metal fluoride added carbon anode treated by pre-electrolysis has a high potential for electrolytic production of NF3 at higher current density.  相似文献   

9.
The value of critical current density at 77 K in “zero” applied field (Jc) characterizing the superconducting state for YBa2Cu3O7−δ ceramics is closely related to the microstructure.The interrelationships between the microstructural factors such as pore volume fraction, oxygen content, average grain size, are complex. However, these factors also influence the normal state resistivity measured at room temperature (ρ300). We demonstrate how the current carrying cross section influences Jc and ρ300 in a similar way. Data, reported for two classes of YBa2Cu3O7−δ: small grain porous ceramics and larger-grain denser ceramics, reveal an approximate linear relation between ρ300 K and Jc. Extrapolation of this relation to a fully dense small grain YBa2Cu3O7−δ ceramic yields values of ρ300 = 0.4 mΩ cm and Jc = 103 A cm−2.  相似文献   

10.
Pure BiFeO3 (BFO) and Bi1−xTbxFeO3 (BTFO) thin films were successfully prepared on FTO (fluorine doped tin oxide) substrates by the sol–gel spin-coating method. The effects of Tb-doping on the structural transition, leakage current, and dielectric and multiferroic properties of the BTFO thin films have been investigated systematically. XRD, Rietveld refinement and Raman spectroscopy results clearly reveal that a structural transition occurs from the rhombohedral (R3c:H) to the biphasic structure (R3c:H+R-3m:R) with Tb-doping. The leakage current density of BTFOx=0.10 thin film is two orders lower than that of the pure BFO, i.e. 5.1×10−7 A/cm2 at 100 kV/cm. Furthermore, the electrical conduction mechanism of the BTFO thin films is dominated by space-charge-limited conduction. The two-phase coexistence of BTFOx=0.10 gives rise to the superior ferroelectric (2Pr=135.1 μC/cm2) and the enhanced ferromagnetic properties (Ms=6.3 emu/cm3). The optimal performance of the BTFO thin films is mainly attributed to the biphasic structure and the distorted deformation of FeO6 octahedra.  相似文献   

11.
We report on the use of the polyoxometalate acids of the series [PMo(12 − n)VnO40](3 + n)− (n = 0-3) as electrocatalysts in both the anode and the cathode of polymer-electrolyte membrane (PEM) fuel cells. The heteropolyacids were incorporated as catalysts in a commercial gas diffusion electrode based on Vulcan XC-72 carbon which strongly adsorbed a low loading of the catalyst, ca. 0.1 mg/cm2. The moderate activity observed was independent of the number of vanadium atoms in the polyoxometalate. In the anode the electrochemistry is dominated by the V3+/4+ couple. With a platinum reference wire in contact with the anode, polarization curves are obtained withVOC of 650 mV and current densities of 10 mA cm−2 at 100 mV at 80 °C. These catalysts showed an order of magnitude more activity on the cathode after moderate heat treatment than on the anode,VOC = 750 mV, current densities of 140 mA cm−2 at 100 mV. The temperature dependence of the catalysts was also investigated and showed increasing current densities could be achieved on the anode up to 139 °C and the cathode to 100 °C showing the potential for these materials to work at elevated temperatures.  相似文献   

12.
Solid polymer electrolytes are potentially useful electrolytes to be applied in high-energy batteries. In the present work, a novel polymer electrolyte, polyethylene oxide (PEO)-NaSCN-AlCl3, was prepared and investigated by FT-IR spectroscopic techniques. Based on the FT-IR data, the bands in the CN stretching envelope have been assigned and the effect of AlCl3 on ion-ion and ion-polymer interactions in the polymer electrolyte has been examined. It is shown that the Lewis acid-base interaction of AlCl3 with SCN1− leads to the formation of the complex anions AlCl3SCN and Al2Cl6SCN, depending on the content of AlCl3 and/or NaSCN in PEO; the preferential interactions of AlCl3 with crystal complex P(EO)3NaSCN occur in PEO-NaSCN-AlCl3 electrolytes; the AlCl3-NaSCN complex anions can play a plasticization role in PEO-NaSCN-AlCl3 electrolyte, and are expected to be a important factor to improve the conductivity and to enhance the cation transference number. In addition, the interactions between AlCl3 and ether oxygen of PEO were analyzed, and their effect on ionic association was also discussed.  相似文献   

13.
In this work, bare and Ta-substituted Nb2O5 nanofibers are prepared by electrospinning followed by sintering at temperatures in the 800–1100 °C range for 1 h in air. Obtained bare and Ta-substituted Nb2O5 polymorphs are characterized by X-ray diffraction, scanning electron microscopy, density measurement, and Brunauer, Emmett and Teller surface area. Electrochemical properties are evaluated by cyclic voltammetry and galvanostatic techniques. Cycling performance of Nb2O5 structures prepared at temperature 800 °C, 900 °C, and 1100 °C shows following discharge capacity at the end of 10th cycle: 123, 140, and 164 (±3) mAh g−1, respectively, in the voltage range 1.2–3.0 V and at current rate of 150 mA g−1 (1.5 C rate). Heat treated composite electrode based on M-Nb2O5 (1100 °C) in argon atmosphere at 220 °C, shows an improved discharge capacity of 192 (±3) mAh g−1 at the end of 10th cycle. The discharge capacity of Ta-substituted Nb2O5 prepared at 900 °C and 1100 °C showed a reversible capacity of 150, 202 (±3) mAh g−1, respectively, in the voltage range 1.2–3.0 V and at current rate of 150 mA g−1. Anodic electrochemical properties of M-Nb2O5 deliver a reversible capacity of 382 (±5) mAh g−1 at the end of 25th cycle and Ta-substituted Nb2O5 prepared at 900 °C, 1000 °C and 1100 °C shows a reversible capacity of 205, 130 and 200 (±3) mAh g−1 (at 25th cycle) in the range, 0.005–2.6 V, at current rate of 100 mA g−1.  相似文献   

14.
The electrochemical oxidation of Ibuprofen (Ibu) was performed using a Ti/Pt/PbO2 electrode as the anode, prepared according to literature, and a boron doped diamond (BDD) electrode, commercially available at Adamant Technologies. Tests were performed with model solutions of Ibu, with concentrations ranging from 0.22 to 1.75 mM for the Ti/Pt/PbO2 electrode and 1.75 mM for the BDD electrode, using 0.035 M Na2SO4 as the electrolyte, in a batch cell, at different current densities (10, 20 and 30 mA cm−2). Absorbance measurements, Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) tests were conducted for all samples. The results have shown a very good degradation of Ibu, with COD removals between 60 and 95% and TOC removals varying from 48 to 92%, in 6 h experiments, with higher values obtained with the BDD electrode. General Current Efficiency and Mineralization Current Efficiency, determined for both electrodes, show a similar behaviour for 20 mA cm−2 but a very different one at 30 mA cm−2. The combustion efficiency was also determined for both anodes, and found to be slightly higher with BDD at lower current density and equal to 100% for both anodes at 30 mA cm−2.  相似文献   

15.
The applicability of the 1-methyl-3-ethylimidazolium chloride — AlCl3 system for lithium battery application was investigated. Lithium chloride was found to dissolve up to 1.59 mole ratio of LiAlCl4/MeEtImAlCl4 upon reaction between LiCl and AlCl3 in the melt. Density, conductivity and viscosity of the melt upon addition of LiAlCl4 were determined. The density was found to increase monotonically from 1280 to 1480 kg m–3, while the conductivity decreased rapidly from the initial value of 5.6 mS to a steady plateau at 3.4 mS. The viscosity was varied from 1.46 Ns m–2 to a small but distinct initial fall prior to rising to 2.75 Ns m–2 when the mole ratio of LiAlCl4 increased from zero to 1.59. The chronopotentiometric studies indicate a satisfactory electrochemical behaviour with no apparent attack of the melt by the formation of the reactive lithium alloys. 350 cycles were achieved with cycling efficiency over 90% using an optimal c.d. of 6 mA cm–2 for lithium deposition on aluminium substrate in the melt. Prolonged cycling improved the nucleation rate but led to an increase in the internal resistance and a gradual reduction in the charge and discharge capacity.  相似文献   

16.
Layered metastable lithium manganese oxides, Li2/3[Ni1/3−xMn2/3−yMx+y]O2 (x = y = 1/36 for M = Al, Co, and Fe and x = 2/36, y = 0 for M = Mg) were prepared by the ion exchange of Li for Na in P2-Na2/3[Ni1/3−xMn2/3−yMx+y]O2 precursors. The Al and Co doping produced the T#2 structure with the space group Cmca. On the other hand, the Fe and Mg doped samples had the O6 structure with space group R-3m. Electron diffraction revealed the 1:2 type ordering within the Ni1/3−xMn2/3−yMx+yO2 slab. It was found that the stacking sequence and electrochemical performance of the Li cells containing T#2-Li2/3[Ni1/3Mn2/3]O2 were affected by the doping with small amounts of Al, Co, Fe, and Mg. The discharge capacity of the Al doped sample was around 200 mAh g−1 in the voltage range between 2.0 and 4.7 V at the current density of 14.4 mA g−1 along with a good capacity retention. Moreover, for the Al and Co doped and undoped oxides, the irreversible phase transition of the T#2 into the O2 structure was observed during the initial lithium deintercalation.  相似文献   

17.
Y.S Lee  K Adachi 《Electrochimica acta》2003,48(8):1031-1039
Well-defined orthorhombic LiMnO2 was synthesized using LiOH and γ-MnOOH starting materials at 1000 °C in an argon flow by quenching process. X-ray diffraction (XRD) revealed that the compound showed an orthorhombic phase of a space group with Pmnm (a=2.806 Å, b=5.750 Å, and c=4.593 Å). The prepared compound was composed of particles of about 5-15 μm diameter with a bar-shape and small spherical one of about 1-2 μm. It showed very small initial discharge capacity of about 34 mA h g−1 in the (3+4) V region at room temperature. However, after 12 h grinding, the LiMnO2 delivered 201 mA h g−1 in the first cycle and still delivered 200 mA h g−1 after 50 cycles at room temperature. We found that the initial discharge capacity of LiMnO2 agreed well with its specific surface area by Brunauer, Emmett and Teller (BET) analysis. Especially, the grinding treatment played an important role to activate the lithium insertion-extraction into the LiMnO2 layer in the 3 V region.  相似文献   

18.
The electrodeposition of tungsten in ZnCl2-NaCl-KCl-KF-WO3 melt at 250 °C was further studied to obtain a thicker deposit. In the ordinary electrolysis at 0.08 V vs. Zn(II)/Zn, the current density decreased from 1.2 mA cm−2 to 0.3 mA cm−2 in 6 h. A thickness of the obtained tungsten layer was 2.1 μm and the estimated current efficiency was 93%. A supernatant salt and a bottom salt were sampled after 6 h from the melting and were analyzed by ICP-AES and XRD. It was found that the soluble tungsten species slowly changes to insoluble ones in the melt. The soluble species was suggested to be WO3F anion. One of the insoluble species was confirmed to be ZnWO4 and the other one was suggested to be K2WO2F4. Electrodeposition was carried out under the same condition as above except for the intermittent addition of WO3 every 2 h. The current density was kept at the initial value and the thickness was 4.2 μm. The intermittent addition of WO3 was confirmed to be effective to obtain a thicker tungsten film.  相似文献   

19.
A cathode material, LiV3O8, for rechargeable lithium-based batteries has been prepared via a combined freeze-drying method and appropriately post-treated in argon atmosphere. It was found that the sample post-treated at 300 °C in Ar has the optimal performance. Electrochemical tests performed on this material demonstrated its very high insertion capacity of 347 mAh g−1 (3.7 Li+ per LiV3O8) at a current density of 50 mA g−1 (C/6). Most important is that it displayed an excellent cycling stability and after 60 cycles, a discharge capacity with 351 mAh g−1 was obtained. It was proposed that a short-range crystallographic order had a stronger influence on the electrochemical performance of an electrode material in this work, instead of the surface area, particle size and crystalline degree, etc.  相似文献   

20.
Anhydrous proton-conducting inorganic-organic hybrid membranes were prepared by sol-gel process with tetramethoxysilane/methyl-trimethoxysilane/trimethylphosphate and 1-ethyl-3-methylimidazolium-bis (trifluoromethanesulfonyl) imide [EMI][TFSI] ionic liquid as precursors. These hybrid membranes were studied with respect to their structural, thermal, proton conductivity, and hydrogen permeability properties. The Fourier transform infrared spectroscopy (FT-IR) and 31P, 1H, and 13C nuclear magnetic resonance (NMR) measurements have shown good chemical stability, and complexation of PO(OCH3)3 with [EMI][TFSI] ionic liquid in the studied hybrid membranes. Thermal analysis including TG and DTA confirmed that the membranes were thermally stable up to 330 °C. Thermal stability of the hybrid membranes was significantly enhanced by the presence of inorganic SiO2 framework and high stability of [TFSI] anion. The effect of [EMI][TFSI] ionic liquid addition on the microstructure of the membranes was studied by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) micrographs and no phase separation at the surfaces of the prepared membranes was observed and also homogeneous distribution of all elements was confirmed. Proton conductivity of all the prepared membranes was measured from −20 °C to 150 °C, and high conductivity of 5.4 × 10−3 S/cm was obtained for 40 wt% [EMI][TFSI] doped 40TMOS-50MTMOS-10PO(OCH3)3 (mol%) hybrid membrane, at 150 °C under anhydrous conditions. The hydrogen permeability was found to decrease from 1.61 × 10−11 to 1.39 × 10−12 mol/cm s Pa for 40 wt% [EMI][TFSI] doped hybrid membrane as the temperature increases from 20 °C to 150 °C. For 40 wt% [EMI][TFSI] doped hybrid membrane, membrane electrode assemblies were prepared and a maximum power density value of 0.22 mW/cm2 at 0.47 mA/cm2 as well as a current density of 0.76 mA/cm2 were obtained at 150 °C under non-humidified conditions when utilized in a H2/O2 fuel cell.  相似文献   

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