Cobalt/Nickel Double Oxides Prepared by Two Methods Exhibiting Supercapacitive Performances
Dongxia An,
Yu Zhang,
Meigui Feng,
Hong Zhang,
Gang Ma,
Cuimiao Zhang,
Zhiguang Ma
Issue:
Volume 4, Issue 1, June 2018
Pages:
1-8
Received:
10 May 2018
Accepted:
9 July 2018
Published:
7 August 2018
Abstract: Two different three-dimensional nanostructured cobalt/nickel layered double oxides grown on Ni foam (NF) were synthesized through one-step (NF/NiCo2O4) and two-step (NF/Co3O4/NiO) solvothermal method for flexible and high performance supercapacitor applications. The as-prepared composites have been systematically characterized by powder X-ray diffraction, scanning electron microscopy, and Brunauer-Emmett-Teller analysis. The pseudocapacitive performances of composite electrode materials were investigated by the electrochemical tests. Cyclic voltammetry (CV), Galvanostatic charge–discharge (GCD) and Electrochemical impedance spectra (EIS) were performed using workstation. When the current density is 1 A/g, the capacitance of NF/Co3O4/NiO electrode material is 992 F/g; the capacitance of NF/NiCo2O4 is 239 F/g. And the retention of NF/NiCo2O4 electrode is 93.8% after 2000 cycles. From this comparison, it could see that the NF/Co3O4/NiO electrode exhibits more than four times higher specific capacitance at a current density of 1 A/g, good capacitance retention and excellent cycling stability than NF/NiC2O4 electrode. Furthermore that the specific capacitance of NF/Co3O4/NiO electrode increases after testing for 2000 cycles. And it can see the comparison between the interfacial charge transfer resistance (Rct) (occurring at the electrode/electrolyte interface and double layer capacitance caused by Faradaic reactions) and Warburg resistance (W), (corresponding to the ion diffusion in the host material diffusive resistance of the electrolyte in the electrode surface). The Nyquist plots are characteristic of being able to separate the charge transfer resistance and series resistance directly. However it is evident that the Nyquist plot of NF/Co3O4/NiO electrode is higher than that of NF/NiCo2O4 and NF/Co3O4 electrodes, demonstrating the Rct and Warburg resistance (W) of NF/Co3O4/NiO electrode is higher. The comprehensive test results show that the NF/Co3O4/NiO coreshell nanostructure arrays with remarkable electrochemical properties could be considered as potential electrode materials for next generation supercapacitors in high energy density storage systems.
Abstract: Two different three-dimensional nanostructured cobalt/nickel layered double oxides grown on Ni foam (NF) were synthesized through one-step (NF/NiCo2O4) and two-step (NF/Co3O4/NiO) solvothermal method for flexible and high performance supercapacitor applications. The as-prepared composites have been systematically characterized by powder X-ray diffr...
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Analysis of Hybrid Parameters of a Single Stage Small Signal Transistor Amplifier Using Two-Port Network
Henry Erialuode Amhenrior
Issue:
Volume 4, Issue 1, June 2018
Pages:
9-15
Received:
19 July 2018
Accepted:
3 August 2018
Published:
31 August 2018
Abstract: This paper presents the analysis of the h-parameter of a single stage small signal transistor amplifier using two-port network. This is motivated by the need to have the rudimentary knowledge of the h-parameter transistor analysis model and to demonstrate its equivalence in the three configuration of the transistor. In this analysis, it was borne in mind the characteristics of a small signal operating conditions of the transistor. Among these characteristics is the assumption that Small – signal operations applies when variations are restricted to such a small amplitude that the partial differential derivatives can be applied. In the methodology, the transistor two-port network was used in deriving the hybrid parameter performance quantities from the first principle by applying partial derivative mathematical tool. The four variables of the input and output of the two-port network namely the currents and voltages which could be combined in six different ways were identified. These were described and analyzed by mathematical functions which relates one of the four variables to two other variables at a time, and by this, six various functions were generated. The partial derivatives of these functions were obtained and these gave the performance quantities which are the key components of the h parameter equations. The initial conditions of each of the component parameters where properly observed and substituted appropriately. This was then transformed into the equivalent circuits of the three transistor configurations. Since the transistor is frequently used for the amplification of sinusoidal currents, the changes in instantaneous total voltage and current were then replaced by root mean square ac quantities, which are considered to be impressed on the direct value. The results obtained are the basic h-parameter equations and the key components of the h parameter transistor model namely the Input Resistance, the Reverse Voltage Gain, the Forward Current Gain and the Output Admittance.
Abstract: This paper presents the analysis of the h-parameter of a single stage small signal transistor amplifier using two-port network. This is motivated by the need to have the rudimentary knowledge of the h-parameter transistor analysis model and to demonstrate its equivalence in the three configuration of the transistor. In this analysis, it was borne i...
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Oxidation Behavior of YAG-Al2O3 Coatings Toughened by Pt Nano-Particles
Peng Wang,
Yu Xinmin,
Liu Junpeng,
Zuo Hongjun,
Huo Pengfei
Issue:
Volume 4, Issue 1, June 2018
Pages:
16-22
Received:
20 July 2018
Accepted:
3 August 2018
Published:
1 September 2018
Abstract: YAG (Y3Al5O12)-Al2O3-Pt composite TBCs have been prepared on Ni-based superalloy (0.1% C, 12% Co, 6.5% Cr, 6.2% Al, 5% W, 1% Mo, 1.5% Hf, 6.5% Ta, 0.01% B, balance Ni, wt.%) by cathode plasma electrolytic deposition (CPED). As polyethylene glycol (PEG) is added in solution, the spark ignition current density is reduced significantly, and CPED would be a promising technique to deposit the uniform coatings on large-sized cathode. The cyclic oxidation tests at 1100°C reveal that the high temperature oxidation resistance of such TBCs are significantly improved by dispersing Pt particles. These excellent performances can be attributed to the effects: the low porosity of coating can inhibit further oxidation of alloy substrate, the toughening role of Pt particles and the stress relaxation caused by the deformation in the porous structure can improve the mechanical properties remarkably. The spallation resistance of YAG-Al2O3-Pt composite coating can be significant improved by using the following two method: one is adding PEG 20000 to the solution during the CPED process; the other is using Pt particle to toughness the coating. In addition, such YAG-Al2O3-Pt composite coatings possess quite well thermal insulation owing to the thermal insulation capability of YAG and the structure of vertical block micropores.
Abstract: YAG (Y3Al5O12)-Al2O3-Pt composite TBCs have been prepared on Ni-based superalloy (0.1% C, 12% Co, 6.5% Cr, 6.2% Al, 5% W, 1% Mo, 1.5% Hf, 6.5% Ta, 0.01% B, balance Ni, wt.%) by cathode plasma electrolytic deposition (CPED). As polyethylene glycol (PEG) is added in solution, the spark ignition current density is reduced significantly, and CPED would...
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