Electrochemical performance of surface-treated natural graphite with Al has been investigated using CR 2032 coin type test cell. Aluminum tri-ethoxide was used as Al source. The solution of aluminum tri-ethoxide was mixed with natural graphite under ultrasonic wave. Calcination temperature of Al-treated graphite has critical influence on local structure of alumina. The local structure of alumina on the surface of the Al-treated graphite was investigated by curve fitting analysis of Al K-edge XANES study. The peak ratio of AlO4 tetrahedra to AlO6 octahedra was increased with the calcination temperature. The difference of chemical diffusion coefficient of lithium in the Al-treated and pristine graphite was measured by current pulse relaxation (CPR) method.
A novel fluorosilicate salt, 1-ethyl-3-methylimidazolium hexafluorosilicate ((EMI)2SiF6), was prepared by the reaction of EMICl and hexafluorosilicate acid aqueous solution. A transparent thin film containing silicon was deposited on a silver electrode by potentiostatic electrolysis in molten (EMI)2SiF6 at 90°C. The film was reactive against water to form silicon dioxide. (EMI)2SiF6 was found to dissolve in 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfone)imide (EMITFSI) room temperature molten salt. The same thin film was also obtained on a silver electrode by potentiostatic electrolysis in EMITFSI containing (EMI)2SiF6 at room temperature.
A coal tar based isotropic pitch was spun into fibers by using melt spinner and stabilized under air condition. The stabilized fibers was chopped and densified at 5-15 MPa and 400°C with no addition of binder to be bulk densities of 0.3∼1.2 g/cc. The component fibers were effectively densified sustaining the original fiber shape. The densified disc was carbonized and followed by steam activation. The activated carbon disc (DACF) showed high enough electrical conductivity of 2.3 × 10 S/cm to be used as an electrode. The pore size distribution and BET surface area of the DACFs prepared at various activation conditions were 15-19 Å and 2,023 m2/g at 82% burn-off, respectively. The BET surface area of the coal tar based ACF is normally higher than that of the ACF from petroleum based one. A unit cell of electric double layer capacitor (EDLC) was prepared with the DACFs in 7.5 mol dm−3 KOH aqueous solution. The charge/discharge capacitances of the unit cell showed relatively high specific capacitances of 45∼75 F/g and 22∼29 F/cm3. The AC impedance measurements of the unit cells showed a decrease in internal/interfacial resistance with an increase in burn-off and a decrease in thickness, indicating the enhanced ionic conductivity caused by both widening of pore size and an increase in surface area.
When sulfuric acid is added in an etching solution of 1 M hydrochloric acid, the effect of the sulfate ions on the aluminum etch pit formation and tunnel growth was investigated with the morphology study and current interruptions in applied etching current. Initial potential transient supports that sulfate ion works as a film forming agent and inhibits the pit initiation during the anodic current etching. Observation of ruptured oxide films suggests that cathodic hydrogen evolution can take place inside the pits. Current step reduction and cathodic pulse superimposition experiments indicate that the actively dissolving tunnel tip surface is covered with aluminum chloride salts and sulfate ion moves far behind inside tunnels during the tunnel growth.
Fine cobalt oxide xerogel powder was prepared by a unique solution chemistry associated with a sol-gel process. Investigation of effect of thermal treatment on the crystalinity, particle structure, and corresponding electrochemical properties of the resulting xerogel revealed that amorphous structure of Co(OH)2 remained up to 160°C. With an increase in the temperature above 200°C, both the surface area and pore volume decreased sharply, because the amorphous Co(OH)2 was converted to form CoO and was subsequently oxidized to crystalline Co3O4. In addition, the changes in the crystallinity, and particle structure were accompanied to the chemical reaction. All things were found to influence the electrochemical properties of the resulting xerogels. A maximum capacitance of 192 F/g was obtained for the CoOx Xerogel calcined at 150°C, which possessed highest values in both surface area and pore volume. To increase capacitance, we added PVA as a dispenser. It is better in terms of capacitance, and then it was carried out capacitance changes of CoOx to acquire stability in cycle tester during 1000 cycle, it shows 450 F/g in average.
Activated carbon (AC) powder as an active electrode material and open-pore nickel foam as a current collector material were used for an electric double layer capacitor (EDLC) with an aqueous electrolyte of KOH mixture. The electrochemical characteristics of the EDLC being made of 3 cm by 3 cm electrode size were investigated by charge-discharge cycle tests, impedance analyzer and cyclic voltametry measurements. As a current collector, nickel foam with concave surface and many open-pore showed larger specific capacitance and lower impedance than that of nickel foil with a flat surface. As results from experiments, much improved specific capacitance of about 300 F/g at 40 mA/cm2 of discharge current density and fairly low specific ESR of 0.63 Ωcm2 at 1 kHz were obtained from the EDLC with the nickel foam current collector. The specific leakage current was measured as 0.18 mA/cm2 with respect to the apparent electrode area of the EDLC with nickel foam current collector.
In order to improve the active material utilization of non-sintered type Ni(OH)2 positive electrode for alkaline storage batteries, we studied the effect of an oxidation treatment of β-Co(OH)2 by using air of various temperatures and NaOH aqueous solution spray on the conductivity, and examined its application to surface modification of Ni(OH)2 particles. Cobalt oxide after the oxidation treatment over 60°C showed higher specific conductivity than β-CoOOH. The chemical composition and formation process of the cobalt oxide were investigated with X-ray diffraction (XRD), atomic absorption spectrometry, iodometry and a transmission electron microscope (TEM), and the origin of the high conductivity was clarified. Surface modification of β-Ni(OH)2 particle with the cobalt oxide was examined and then the effect on the active material utilization was evaluated by the aid of the single electrode method.
The detection of the ammonia gas is an important task in many technological fields such as industrial processes, clinical diagnosis and environmental monitoring. Here, we report on a composite optical waveguide (COWG) ammonia sensor, which is based on evanescent field adsorption. The highly sensitive element of this sensor is a polytungstic acid (PTA) film/K+ ion exchanged glass COWG, fabricated by coating the PTA film over the potassium ion exchanged glass OWG. The sensing film of indicator dye of the bromothymol blue (BTB) was coated onto the optical waveguide surface by the spin coating method. The experimental arrangement and response characteristics are reported in detail. The sensor has a short response time, highly sensitivity, and detection limit is 1 ppb.