Papers by Keyword: Electrochemical Properties

Abstract: High energy density and rechargeable lithium ion batteries are attracting widely interest in renewable energy fields. The preparation of the high performance materials for electrodes has been regarded as the most challenging and innovative aspect. By utilizing a facile combustion synthesis method, pure nanostructure LiNi_0.5Mn_1.5O₄ cathode material for lithium ion batteries were successfully fabricated. The crystal phase of the samples were characterized by X-Ray Diffraction, and micro-morphology as well as electrochemistry properties were also evaluated using FE-SEM, electrochemical charge-discharge test. The result shows the fabricated LiNi_0.5Mn_1.5O₄ cathode materials had outstanding crystallinity and near-spherical morphologies. That obtained LiNi_0.5Mn_1.5O₄ samples delivered an initial discharge capacity of 137.2 mAhg^-1 at the 0.1 C together with excellent cycling stability and rate capability as positive electrodes in a lithium cell. The superior electrochemical performance of the as-prepared samples are owing to nanostructure particles possessing the shorter diffusion path for Li⁺ transport, and the nanostructure lead to large contact area to effectively improve the charge/discharge properties and the rate property. It is demonstrated that the as-prepared nanostructure LiNi_0.5Mn_1.5O₄ samples have potential as cathode materials of lithium-ion battery for future new energy vehicles.

Abstract: Ni foam with 3D porous structure has attracted attention in the field of catalysis. Expanding the specific surface area of Ni foam is an important method to enhance its chemical properties. In this study, the Cu-Ni/Ni foam were obtained by electroless plating copper on Ni foam and then heat treatment for homogenizing at 750°C. The dealloying of the Cu-Ni/Ni foam was carried out by electrochemical etching for obtaining the Ni foam with hierarchical pore structure. The microstructure, phase and electrochemical performance were characterized by SEM, XRD and electrochemical testing. The results showed that the optimized temperature of electroless plating Cu on Ni foam is 60oC. Ni-Cu alloy can be obtained by counter diffusion above 750°C. With prolonging time of etching, the content of Cu component decreased and the size of pores on the sturts of the Cu-Ni/Ni foam changed from nano to micro scale. The electrochemical properties of the alloywere significantly higher than that of the pure nickel foam.

Abstract: In this study, a new green approach has been developed for the recovery of tungsten by using tungsten carbide (WC) scrap material as consumable anode in LiCl-KCl molten salts at 773 K to produce metallic tungsten. The feasibility of the direct electrochemical dissolution of WC anode into metallic tungsten was evaluated based on the experimental verifications and electrochemical methods. The effects of the main technical parameters, including the cell voltage, electrolysis time and electrolysis temperature, on the dissolved condition of anode were studied and the optimal anode parameters were obtained. It was found that a large electrolytic voltage, high electrolytic temperature and long electrolysis time would be favorable for the dissolved state of the tungsten carbide anode under the same conditions. The cathode product was analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the tungsten particles with a diameter of 100 nm could be prepared by this process in a molten salt bath. Linear sweep voltammetry was applied to investigate the dissolution of WC anode, and showed that the WC scrap material could be used as consumable anode to produce tungsten powder. Other electrochemical techniques including cyclic voltammetry , square-wave voltammetry and chronopotentiometry were employed to explore the electrochemical properties of tungsten ion derived from WC anode in LiCl-KCl melts. These results confirmed that electroreduction of tungsten ion in the melts proceeded in one step with four exchanged electrons.

Abstract: LiNi_1/3Co_1/3Mn_1/3O₂ was prepared by high temperature solid-state method under different synthesis temperature. The structure and morphology of LiNi_1/3Co_1/3Mn_1/3O₂ were characterized by Scanning electron microscopy (SEM) and X-ray diffraction (XRD). Electrochemical performance of the cathode material was researched by Land 2001. XRD and SEM results show that the well-crystallized LiNi_1/3Co_1/3Mn_1/3O₂ composite with homogeneous small particles was obtained. And the optimum synthetic temperature was 500°C for 5 hour and 900°C for 20 hour. From charge/discharge test, it can be seen that at 0.1C, 0.2C and 0.5C rate, LiNi_1/3Co_1/3Mn_1/3O₂ has initial discharge capacities of 178.6mAh/g, 172.9mAh/g and 152.7mAh/g, respectively. The discharge capacities of optimum sample remain above 85% after 43 cycles. This study provides the selection of synthetic temperature via solid state methods.

Abstract: The inorganic-organic hybrid composite membranes have played a rocking role for separation, concentration, purification and clarification of food industry wastewater. The separation of wastewater produced from post-treatment part of food industry processing using PVC based magnesium molybdate (MM) composite membrane was studied in this paper. The physicochemical and electrochemical studies of composite membrane shows better results from previously reported membranes. In this study, the transport number, mobility ratio and surface charge density of composite membrane play a dominant role for understanding the membrane mechanism and these parameters depend on the concentration of various univalent electrolytes.

Abstract: Sacrificial anode protection of stainless steel is required in severe application environment. In this paper, two kinds of Fe-based sacrificial anodes (20CrMo and 20CrMn) were used to protect 310S stainless steel. Protective effects were evaluated through constant current test and self-discharge test. Scanning electron microscope (SEM) and Energy Dispersive Spectrometer (EDS) were used to analyze the surface morphology and element composition of 310S cathodes after the tests. Experimental result indicates that both Fe-based sacrificial anodes have a driving voltage over 500mV, which enables a longer life than those of the Al-based or Zn-based anodes. The 20CrMo sacrificial anode presented more stable working potential, better state of activation and more uniform corrosion behavior than 20CrMn sacrificial anode did. The 310S cathode protected by 20CrMo had smoother surface and less oxide formation on the substrate.

Abstract: 7072Al is widely used as cladding layer for heat-transfer components. In this paper, the microstructure, mechanical properties and electrochemical properties of simulated-brazing 7072Al alloy with Zn addition were investigated. Transmission electron microscopy (TEM) observations revealed that, in the simulated-brazing state, Zn-addition could promote the precipitation in the 7072Al alloy. Tensile testing results indicated that, in comparison with 7072Al alloy, the mechanical properties were improved after Zn-addition. Electrochemical testing results revealed that the simulated-brazing alloy showed a negative shift of the corrosion potential with the addition of Zn element.

Abstract: The precursor Ni (OH)₂ was synthesized by a simple hydrothermal method with NiSO₄•6H₂O and (CH₂)₆N₄ as reactants. Both concentrations of reactants are 0.02 M, 0.04 M, 0.06 M, 0.08 M for experiment contrast, and then NiO was gained after calcination at 400°C. The phase and morphology of the synthesized product were characterized by X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). The electrochemical capacitive characterization was performed using cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) and electrical impedance spectroscopy (EIS) measurements in a 6mol/L KOH aqueous solution electrolyte. The result shows that with the increase of concentrations of reactants, nanosheets stack together and turn into thick slices. CV curves have obvious redox peak, the GCD curves are nonlinear and EIS curves of high frequency area are semicircle. From electrochemical analysis, the capacitance type is pseudocapacitance. And a maximal specific capacitance value when two reactants concentration both are 0.08 M which the specific capacitance decreases from 97 F/g (at a current density of 0.3A/g) to 56 F/g (at a current density of 1 A/g).

Abstract: In this paper, a series of xLiFePO₄·yLi₃V₂(PO₄)₃/C (x/y = 1:0, 7:1, 5:1, 3:1, 1:1, 1:3 and 0:1, ratio in mol) nano-sized composite cathode materials were successfully prepared via the solid reaction method. Influence of x/y ratio, calcination temperatures and the content of citric acid on the composition, microstructure and electrochemical properties of the materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and electrochemical measurements, et al. results showed that the xLFP·yLVP/C (x and y ≠ 0) composites were composed of olivine LiFePO₄ and monoclinic Li₃V₂(PO₄)₃, both of which featured slight structural distortions as the formation of V-doped LFP/C and Fe-doped LVP/C, respectively; With the increase of calcination temperatures, the crystallinity and particles size of the 7LFP·LVP/C composites increased, when calcined at 700°C, the initial charge/discharge specific capacity of the composites reached a maximum value of 145.6 mAh/g, and the voltage drop values between charge/discharge platform possessed the minimum value(0.04 V), suggesting the minimum polarization of the composites in charge/discharge process. Content of citric acid did not affect the compositions of the composites, with the increase of the molar ratio of citric acid to V³⁺, the discharge specific capacities of 7LFP·LVP/C increased first and then decreased, when it equaled to 1.0:1.0, the discharge specific capacity of the relative composites was 119.18 mAh/g, with a capacity retention rate of 93.9 % after 50 cycles, owning the excellent electrochemical stability.

Abstract: Green monoliths (GMs) with different composition, labelled as GM1, GM2 and GM3, were prepared from self-adhesive carbon grains (SACG) produced from fibers of oil palm empty fruit bunches, SACG treated with 0.4 M H₂SO₄ and mixtures of SACG and carbon nanotubes (5 wt.%) treated with 0.4 M H₂SO₄, respectively. Each GMs was carbonized and then activated with holding time of 1 h and 2 h, respectively, to produce their respective activated carbon monoliths (ACMs). These ACMs were used as electrodes to fabricate supercapacitor cells using H₂SO₄ electrolytes, Teflon separator and stainless steel 316L current collector. The porosity of the ACMs, examined by nitrogen adsorption-desorption isotherm method were found affected after prolonging the activation time. From the electrochemical characterization of the ACMs electrodes using galvanic charge-discharge methods, it was found that supercapacitor cells fabricated using the ACMs produced by longer activation time (2 h) showed better performance, which had higher specific capacitance (113 F/g), specific power (159 W/kg) and specific energy (3.35 W h/kg), compared to the cells using ACMs produced by shorter activation time (1 h).