共查询到20条相似文献,搜索用时 31 毫秒
1.
Guohong Qiu 《Electrochimica acta》2008,53(12):4074-4081
The direct electrochemical reduction process of Nb2O5 powder was investigated by cyclic voltammetry and constant potential electrolysis with a novel metallic cavity electrode in molten calcium chloride at 850 °C. The products of both constant potential and constant voltage electrolysis were characterized by XRD, SEM and EDX. CaNb2O6 was formed upon addition of solid Nb2O5 into molten CaCl2 when CaO was present. During the electrolysis solid Nb2O5 was reduced to various niobium oxides of lower oxidation states, including some composite oxides, and then was converted completely to metallic niobium near −0.35 V (vs. Ag/AgCl), which was more positive than the reduction potential of Ca2+. Constant potential electrolysis was applied at the potentials near the reduction current peaks derived from the cyclic voltammetry curves, and cell voltages were monitored. The voltage was near 2.4 V when the oxide was metallized at −0.35 V (vs. Ag/AgCl). Nb2O5 pellet could be used to prepared metallic niobium at cell voltage 2.4 V in a larger electrolysis bath filled with calcium chloride at 850 °C. The experiment results further demonstrated the direct electrochemical reduction mechanism of Nb2O5 powder in a molten system. 相似文献
2.
A simple solid state technique for electrochemical micromachining of metal substrates using a metal ion conductor (Na-β″-Al2O3) was proposed. The fundamental solid electrochemical cell consists of a (anode) metal substrate (M = Ag, Cu, Zn, and Pb)/pyramidal Na-β″-Al2O3/Ag (cathode) system, where the contact diameter between M/Na-β″-Al2O3 was extremely small, on the order of a few micrometer. Under an applied electric field, the metal substrate was electrochemically oxidized to metal ions (Mn+) at the M/Na-β″-Al2O3 microcontact. These Mn+ ions migrated into the Na-β″-Al2O3. As a result of continuous electrolysis, the metal substrate was locally consumed at the microcontact, and thus solid state electrochemical micromachining was accomplished. As expected, the machining size or depth depended on the electrolysis conditions (current, operating time) and the apex configuration of pyramidal Na-β″-Al2O3. Moreover, the scanning of the Na-β″-Al2O3 pyramid during electrolysis produced a fine patterned metal substrate. In the present paper, solid state electrochemical micromachining was performed for several metal substrates, and its advantages and disadvantages vis-a-vis the conventional electrochemical micromachining method are discussed in detail. 相似文献
3.
Metallic Cu electrode can electrochemically reduce CO2 to CH4, C2H4 and alcohols with high yields as revealed by the present authors. Many workers reported that formation of CH4 and C2H4 rapidly diminishes during electrolysis of CO2 reduction. This paper shows that such deactivation of Cu electrode is reproduced with electrolyte solutions prepared from reagents used by these workers. Deactivated Cu electrodes recovered the electrocatalytic activity for CO2 reduction by anodic polarization at −0.05 V versus she in agreement with the previous reports. Features of the deactivation depend greatly on the individual chemical reagents. Purification of the electrolyte solution by preelectrolysis with a Pt black electrode effectively prevents the deactivation of Cu electrode. Anode stripping voltammetry of Cu electrodes, which were deactivated during electrolysis of CO2 reduction, showed anodic oxidation peaks at ca. −0.1 or −0.56 V versus she. The severer the deactivation of the Cu electrode was, the higher electric charge of the anodic peak was observed. It is presumed that some impurity heavy metal, originally contained in the electrolyte, is deposited on the Cu electrode during the CO2 reduction, poisoning the electrocatalytic activity. On the basis of the potential of the anodic peaks, Fe2+ and Zn2+ are assumed to be the major contaminants, which cause the deactivation of the Cu electrode. Deliberate addition of Fe2+ or Zn2+ to the electrolyte solutions purified by preelectrolysis exactly reproduced the deactivation of a Cu electrode in CO2 reduction. The amount of the deposited Fe or Zn on the electrode was below the monolayer coverage. Electrothermal atomic absorption spectrometry (etaas) showed that Fe originally contained in the electrolyte solution is effectively removed by the preelectrolysis of the solution. Mechanistic difference is discussed between Fe and Zn in the deterioration of the electrocatalytic property of Cu electrode in the CO2 reduction. The concentration of the impurity substances originally contained in the chemical reagents as Fe or Zn is estimated to be far below the standard of the impurity levels guaranteed by the manufacturers. Presence of trimethylamine in the electrolyte solution also severely poisons a Cu electrode in the CO2 reduction. It was concluded that the deactivation of Cu electrode in CO2 reduction is not caused by adsorption of the products or the intermediates produced in CO2 reduction. 相似文献
4.
Takahisa Iida 《Electrochimica acta》2003,48(7):901-906
Electrochemical formation of Sm-Co alloy films at a Co cathode was studied in a molten LiCl-KCl-SmCl3 (0.5 mol.%) at 723 K. Very thin film (∼100 nm) of SmCo2 alloy was obtained by potentiostatic electrolysis at 0.20 V (vs. Li+/Li) for 24 h. Much thicker alloy film (∼5 μm) was formed by Li codeposition method (cathodic galvanostatic electrolysis at 50 mA cm−2) for 1 h. The formed alloy phase was suggested as LixSm4Co6 (x∼3). The formed alloy film was changed to various Sm-Co alloy phases by anodic potentiostatic electrolysis depending on the applied potentials. The formation potentials of Sm2Co17, SmCo3, SmCo2 and LixSm4Co6 were found to be 1.40, 0.80, 0.30 and 0.05 V, respectively. 相似文献
5.
In this work, Ni(OH)2 nanoplates grown on the Cu substrate were synthesized and characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Then a novel Cu-Ni(OH)2 modified glass carbon electrode (Cu-Ni(OH)2/GCE) was fabricated and evaluated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and typical amperometric response (i-t) method. Exhilaratingly, the Cu-Ni(OH)2/GCE shows significant electrocatalytic activity toward the reduction of H2O2. At an applied potential of −0.1 V, the sensor produces an ultrahigh sensitivity of 408.1 μA mM−1 with a low detection limit of 1.5 μM (S/N = 3). The response time of the proposed electrode was less than 5 s. What's more, the proposed sensor displays excellent selectivity, good stability, and satisfying repeatability. 相似文献
6.
Mohammed Dahbi Ismael Saadoune Torbjörn Gustafsson Kristina Edström 《Electrochimica acta》2009,54(11):3211-41
A crystalline LiNi0.65Co0.25Mn0.10O2 electrode material was synthesized by the combustion method at 900 °C for 1 h. Rietveld refinement shows less than 3% of Li/Ni disorder in the structure. Lithium extraction involves only the Ni2+/Ni4+ redox couple while Co3+ and Mn4+ remain electrochemically inactive. No structural transition was detected during cycling in the whole composition range 0 < x < 1.0. Furthermore, the hexagonal cell volume changes by only 3% when all lithium was removed indicating a good mechanical stability of the studied compound. LiNi0.65Co0.25Mn0.10O2 has a discharge capacity of 150 mAh/g in the voltage range 2.5-4.5 V, but the best electrochemical performance was obtained with an upper cut-off potential of 4.3 V. Magnetic measurements reveal competing antiferromagnetic and ferromagnetic interactions - varying in strength as a function of lithium content - yielding a low temperature magnetically frustrated state. The evolution of the magnetic properties with lithium content confirms the preferential oxidation of Ni ions compared to Co3+ and Mn4+ during the delithiation process. 相似文献
7.
Kaoru Dokko Jun-ichi Sugaya Hirokazu Munakata Kiyoshi Kanamura 《Electrochimica acta》2005,51(5):966-971
Fabrications of micro-dot electrodes of LiCoO2 and Li4Ti5O12 on Au substrates were demonstrated using a sol-gel process combined with a micro-injection technology. A typical size of prepared dots was about 100 μm in diameter, and the dot population on the substrate was 2400 dots cm−2. The prepared LiCoO2 and Li4Ti5O12 micro-dot electrodes were characterized with scanning electron microscopy, X-ray diffraction, micro-Raman spectroscopy, and cyclic voltammetry. The prepared LiCoO2 and Li4Ti5O12 micro-dot electrodes were evaluated in an organic electrolyte as cathode and anode for lithium micro-battery, respectively. The LiCoO2 micro-dot electrode exhibited reversible electrochemical behavior in a potential range from 3.8 to 4.2 V versus Li/Li+, and the Li4Ti5O12 micro-dot electrode showed sharp redox peaks at 1.5 V. 相似文献
8.
Satoshi Kaneco Nobu-hide HieiYue Xing Hideyuki KatsumataHisanori Ohnishi Tohru SuzukiKiyohisa Ohta 《Electrochimica acta》2002,48(1):51-55
The electrochemical reduction of CO2 on a Cu electrode was investigated in aqueous NaHCO3 solution, at low temperature. A divided H-type cell was employed, the catholyte was 0.65 mol dm−3 NaHCO3 aqueous solution and the anolyte was 1.1 mol dm−3 KHCO3 aqueous solution. The temperature during the electrolysis of CO2 was decreased stepwise to 271 K. Methane and formic acid were obtained as the main products. The maximum Faradaic efficiency of methane was 46% at −2.0 V and 271 K. The efficiency of hydrogen formation, a competing reaction of CO2 reduction, was significantly depressed with decreasing temperature. Based on the results of this work, the proposed electrochemical method appears to be a viable means for removing CO2 from the atmosphere and converting it into more valuable chemicals. The synthesis of methane by the electrochemical method might be of practical interest for fuel production and the storage of solar energy. 相似文献
9.
Titanium silicide (Ti5Si3) has been extracted directly from complex Ti-bearing compounds by electro-deoxidation. A pressed cylindrical pellet of the multi-component compounds acted as a cathode, and carbon-saturated liquid metal contained in a solid-oxide oxygen-ion-conducting membrane (SOM) tube served as an anode. This electrochemical process was carried out in a molten CaCl2 system at 950–1050 °C and 3.5–4.0 V. The parameters of electrolysis and the electrolytic characteristics were investigated, and the morphology and phase composition of the final products were examined. Ti5Si3 was directly extracted from Ti-bearing compounds. Electrolysis time, applied potential, and electrolysis temperature are the dominant factors that affect the characteristics of the final products. The mechanisms of the extraction of Ti5Si3 and the removal of metallic elements (Ca, Mg, and Al) are suggested based on our experimental results and theoretical analysis. The optimal conditions of the electrolysis are a temperature of ∼1050 °C and a potential of 3.5–4.0 V, which result in rapid reduction and good product morphology. The excellent oxidation resistance of the extracted Ti5Si3 is confirmed. 相似文献
10.
K.M. Shaju 《Electrochimica acta》2003,48(11):1505-1514
Layered Li(Ni1/2Mn1/2)O2 was prepared by the solution and mixed hydroxide methods, characterised by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) and studied by cyclic voltammetry (CV) and charge discharge cycling in CC and CCCV modes at room temperature (r.t.) and at 50 °C. The XPS studies show about 8% of Ni3+ and Mn3+ ions are present in Li(Ni2+1/2Mn1/24+)O2 due to valency-degeneracy. The compound prepared at 950 °C, 12 h, solution method gives a second cycle discharge capacity of 150 mA h g−1 (2.5-4.4 V) at a specific current of 30 mA g−1 and retains 137 mA h g−1 at the end of 40 cycles. CV shows that the redox process at 3.7-4.0 V corresponds to Ni2+↔Ni4+ and clear indication of Mn3+/4+ couple was noted at 4.2-4.5 V. The observed capacity-fading (2.5-4.4 V) is shown to be contributed by the polarisation at the end of charging. The cathodic capacity is stable up to 40 cycles in the voltage window, 2.5-4.2 V both at room temperature and 50 °C. 相似文献
11.
Yan-Hua Cui Ming-Zhe Xue Yong-Ning Zhou Shu-Ming Peng Xiao-Lin Wang Zheng-Wen Fu 《Electrochimica acta》2011,(5):2328
Crystalline CuF2 thin films were prepared by pulsed laser deposition under room temperature. The physical and electrochemical properties of the as-deposited thin films have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), galvanostatic cycling and cyclic voltammetry (CV). Reversible capacity of 544 mAh g−1 was achieved in the potential range of 1.0–4.0 V. A reversible couple of redox peaks at 3.0 V and 3.7 V was firstly observed. By using ex situ XRD and TEM techniques, an insertion process followed by a fully conversion reaction to Cu and LiF was revealed in the lithium electrochemical reaction of CuF2 thin film electrode. The reversible insertion reaction above 2.8 V could provide a capacity of about 125 mAh g−1, which makes CuF2 a potential cathode material for rechargeable lithium batteries. 相似文献
12.
Jung-Min Kim 《Electrochimica acta》2004,49(6):937-944
In this research, we studied the first cycle characteristics of Li[Ni1/3Co1/3Mn1/3]O2 charged up to 4.7 V. Properties, such as valence state of the transition metals and crystallographic features, were analyzed by X-ray absorption spectroscopy and X-ray and neutron diffractions. Especially, two plateaus observed around 3.75 and 4.54 V were investigated by ex situ X-ray absorption spectroscopy. XANES studies showed that the oxidation states of transition metals in Li[Ni1/3Co1/3Mn1/3]O2 are mostly Ni2+, Co3+ and Mn4+. Based on neutron diffraction Rietveld analysis, there is about 6% of all nickel divalent (Ni2+) ions mixed with lithium ions (cation mixing). Meanwhile, it was found that the oxidation reaction of Ni2+/Ni4+ is related to the lower plateau around 3.75 V, but that of Co3+/Co4+ seems to occur entire range of x in Li1−x[Ni1/3Co1/3Mn1/3]O2. Small volume change during cycling was attributed to the opposite variation of lattice parameter “c” and “a” with charging-discharging. 相似文献
13.
The subject of this paper is the effect of foreign cations on the reactivity of the CaO-SiO2-Al2O3-Fe2O3 system. One reference mixture and eighteen modified mixtures, prepared by mixing the reference sample with 1% w/w of chemical grade MnO2, CuO, V2O5, PbO, CdO, ZrO2, Li2O, MoO3, Co2O3, NiO, WO3, ZnO, Nb2O5, CrO3, Ta2O5, TiO2, BaO2 and H3BO3 were studied. The effect on the reactivity is evaluated on the basis of the free lime content in samples sintered at 1200 and 1450 °C. At 1200 °C, the reactivity of the mixture is greatly increased in the presence of Cu and Li oxides. Based on their effect at 1450 °C, the added elements can be divided into three groups. W, Ta, Cu, Ti and Mo show the most positive effect, decreasing the free CaO (fCaO) content by 30-60%, compared with the pure sample. Cr and B cause an increase of fCaO content, while the rest of the elements exhibit a marginal positive effect. According to their volatility at 1450 °C, the added compounds can be subdivided into three groups of low (Ti4+, Cu2+, Mo6+, W+6, V5+, Zn2+, Zr4+), moderate (Cr6+, Co3+, Ni2+, Mn4+) and high volatility (Cd2+, Pb2+). All burned samples, analyzed by means of X-ray diffraction, have a final mineralogical composition, which corresponds to the structure of a typical clinker. 相似文献
14.
Electrochemical and thermal properties of Co3(PO4)2- and AlPO4-coated LiNi0.8Co0.2O2 cathode materials were compared. AlPO4-coated LiNi0.8Co0.2O2 cathodes exhibited an original specific capacity of 170.8 mAh g−1 and had a capacity retention (89.1% of its initial capacity) between 4.35 and 3.0 V after 60 cycles at 150 mA g−1. Co3(PO4)2-coated LiNi0.8Co0.2O2 cathodes exhibited an original specific capacity of 177.6 mAh g−1 and excellent capacity retention (91.8% of its initial capacity), which was attributed to a lithium-reactive Co3(PO4)2 coating. The Co3(PO4)2 coating material could react with LiOH and Li2CO3 impurities during annealing to form an olivine LixCoPO4 phase on the bulk surface, which minimized any side reactions with electrolytes and the dissolution of Ni4+ ions compared to the AlPO4-coated cathode. Differential scanning calorimetry results showed Co3(PO4)2-coated LiNi0.8Co0.2O2 cathode material had a much improved onset temperature of the oxygen evolution of about 218 °C, and a much lower amount of exothermic-heat release compared to the AlPO4-coated sample. 相似文献
15.
This work provides kinetic and transport parameters of Li-ion during its extraction/insertion into thin film LiNi0.5Mn1.5O4 free of binder and conductive additive. Thin films of LiNi0.5Mn1.5O4 (0.2 μm thick) were prepared on electronically conductive gold substrate utilizing the electrostatic spray deposition technique. High purity LiNi0.5Mn1.5O4 thin film electrodes were observed with cyclic voltammetry, to exhibit very sharp peaks, high reversibility, and absence of the 4 V signal related to the Mn3+/Mn4+ redox couple. The electrode subjected to 100 CV cycles of charge/discharge delivered a capacity of 155 mAh g−1 on the first cycle and sustained a good cycling behavior while retaining 91% of the initial capacity after 50 cycles. Kinetics and mass-transport of Li-ion extraction at LiNi0.5Mn1.5O4 thin film electrode were investigated by means of electrochemical impedance spectroscopy. The apparent chemical diffusion coefficient (Dapp) value determined from EIS measurements changed depending on the electrode potential in the range of 10−10-10−12 cm2 s−1. The Dapp profile shows two minimums at the potential values close to the peak potentials of the corresponding cyclic voltammogram. 相似文献
16.
Electrochemical performance of the carbon coated Li3V2(PO4)3 cathode material synthesized by a sol-gel method 总被引:1,自引:0,他引:1
A carbon coated Li3V2(PO4)3 cathode material for lithium ion batteries was synthesized by a sol-gel method using V2O5, H2O2, NH4H2PO4, LiOH and citric acid as starting materials, and its physicochemical properties were investigated using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDAX), transmission electron microscope (TEM), and electrochemical methods. The sample prepared displays a monoclinic structure with a space group of P21/n, and its surface is covered with a rough and porous carbon layer. In the voltage range of 3.0-4.3 V, the Li3V2(PO4)3 electrode displays a large reversible capacity, good rate capability and excellent cyclic stability at both 25 and 55 °C. The largest reversible capacity of 130 mAh g−1 was obtained at 0.1C and 55 °C, nearly equivalent to the reversible cycling of two lithium ions per Li3V2(PO4)3 formula unit (133 mAh g−1). It was found that the increase in total carbon content can improve the discharge performance of the Li3V2(PO4)3 electrode. In the voltage range of 3.0-4.8 V, the extraction and reinsertion of the third lithium ion in the carbon coated Li3V2(PO4)3 host are almost reversible, exhibiting a reversible capacity of 177 mAh g−1 and good cyclic performance. The reasons for the excellent electrochemical performance of the carbon coated Li3V2(PO4)3 cathode material were also discussed. 相似文献
17.
Adsorption and antibacterial effect of copper-exchanged montmorillonite on Escherichia coli K88 总被引:1,自引:0,他引:1
Calcium montmorillonite (Ca-MMT), sodium montmorillonite (Na-MMT) and acid-activated montmorillonite (AAM), and their Cu2+-exchanged montmorillonites (Cu-MMT), Cu*Ca-MMT, Cu*Na-MMT and Cu*AAM, were used to study the antibacterial activity on Escherichia coli K88. AAM, Na-MMT and Ca-MMT showed some ability to reduce bacterial plate counts by 37.4%, 13.4% and 14.2%, respectively. Exchanging the montmorillonite with Cu2+ enhanced the antibacterial activity. The Cu*AAM, Cu*Na-MMT and Cu*Ca-MMT reduced the bacterial plate counts by 98.6%, 97.5% and 95.6%. Attempts were made to study the desorption of Cu2+ by washing with sterile physiological saline solution for 24 h. The washing solutions did not show a significant reduction of the bacterial counts, while the washed Cu-MMT retained their full antibacterial activity. Results from time-depending studies showed that the reduction of the bacterial counts by Cu-MMT increased during 24 h. The ranking of antibacterial activity of the three Cu-MMT was as Cu*AAM > Cu*Na-MMT > Cu*Ca-MMT. E. coli thrived optimally in a pH range from 5 to 7. Beyond this range, the bacterial counts decreased as the pH reduced the viability of the bacteria. The ranking of antibacterial activity of Cu-MMT was not affected by pH. The mechanism by which bacterial counts are reduced may involve the enhanced affinity of Cu-MMT for E. coli K88 and the antibacterial activity of Cu2+. 相似文献
18.
Uniform and spherical Li(Ni1/3Co1/3Mn1/3)O(2−δ)Fδ powders were synthesized via NH3 and F− coordination hydroxide co-precipitation. The effect of F− coordination agent on the morphology, structure and electrochemical properties of the Li(Ni1/3Co1/3Mn1/3)O(2−δ)Fδ were studied. The morphology, size, and distribution of (Ni1/3Co1/3Mn1/3)(OH)(2−δ)Fδ particle diameter were improved in a shorter reaction time through the addition of F−. The study suggested that the added F improves the layered characteristics of the lattice and the cyclic performance of Li(Ni1/3Co1/3Mn1/3)O2 in the voltage range of 2.8-4.6 V. The initial capacity of the Li(Ni1/3Co1/3Mn1/3)O1.96F0.04 was 178 mAh g−1, the maximum capacity was 186 mAh g−1 and the capacity after 50 cycles was 179 mAh g−1 in the voltage range of 2.8-4.6 V. 相似文献
19.
N Sharma 《Electrochimica acta》2004,49(7):1035-1043
The electrochemical performance of mixed oxides, Ca2Fe2O5 and Ca2Co2O5 for use in Li-ion batteries was studied with Li as the counter electrode. The compounds were prepared and characterized by X-ray diffraction and SEM. Ca2Fe2O5 showed a reversible capacity of 226 mAh/g at the 14th cycle and retained 183 mAh/g at the end of 50 cycles at 60 mA/g in the voltage window 0.005-2.5 V. A reversible capacity in the range, 365-380 mAh/g, which is stable up to 50 charge-discharge cycles is exhibited by Ca2Co2O5 in the voltage window, 0.005-3.0 V and at 60 mA/g. This corresponds to recycleable moles of Li of 3.9±0.1 (theoretical: 4.0). Significant improvement in the cycling performance and attainable reversible capacity were noted for Ca2Co2O5 on cycling to an upper cut-off voltage of 3.0 V as compared to 2.5 V. Coulombic efficiency for both compounds is >98%. Electrochemical impedance spectroscopy (EIS) data clearly indicate the reversible formation/decomposition of polymeric surface film on the electrode surface of Ca2Co2O5 in the voltage window, 0.005-3.0 V. Cyclic voltammetry results compliment the galvanostatic cycling data. 相似文献
20.
Arman Bonakdarpour Daniel Esau Hillary Cheng Andrew Wang Elöd Gyenge David P. Wilkinson 《Electrochimica acta》2011,56(25):9074
Numerous transition metal–carbon composite catalysts (M = V, Zn, Ni, Sn, Ce, Ba, Fe, Cu) have been synthesized and tested for electroreduction of O2 to H2O2, The activity and selectivity of all synthesized catalysts for electrosynthesis of H2O2 were determined by the rotating ring-disk electrode method in acidic and neutral electrolytes. The Co-based catalysts in general showed the highest activity towards H2O2 formation. Experiments with different loading contents of Co showed that the activation overpotential losses of oxygen reduction to H2O2 reduces as loading increases to about 4 wt% Co. Addition of Co beyond this level did not seem to impact the overpotential losses. The cobalt-based catalysts, were spray-coated onto 120 μm thick Toray® graphite substrates, and were studied in bulk electrolysis cells for up to 100 h at potentiostatic conditions (0.25 V vs. RHE) in pH 0, 3, and 7 electrolytes. At (25 °C and 1 bar) with a catalysts loading of about and using dissolved O2 in 0.5 M H2SO4, typical H2O2 electrosynthesis rates of about were reached with current efficiencies of about 85 ± 5% at 0.25 V (vs. RHE). 相似文献