Conventionally, nickel oxyhydroxide as a cathode active material for the primary batteries has been prepared by a chemical synthetic method using a hypochlorite salt as an oxidant. However, a large amount of waste effluent generates because chemical oxidation process is operated using a batch container, therefore a new synthetic method is requested. We developed a new electrolytic synthetic method eliminating the waste problem. When a KCl solution suspended with Ni(OH)2 powders is electrolyzed under the alkaline region, chlorine gas is generated at the anode and immediately changed into ClO-. The suspended Ni(OH)2 powders in the KCl solution are oxidized into β-NiOOH by the produced hypochlorite ions. The discharge capacity of obtained nickel oxyhydroxide is 189 mAh/g and the value is 20-30% greater than that of the NiOOH obtained by the conventional chemical oxidation method. Moreover, electrolyte containing KCl can be repeatedly utilized as an oxidizing media since only trace amounts of nickel ions are remained in the electrolytic bath.
The basic electrical properties of Ta2O5 thin films, anodically oxidized in H3PO4 solution, were investigated with the aim of analyzing the electronic behavior of metal/Ta2O5/Ta capacitors. The investigation was done from the perspective of the work functions of the devices. The current-voltage (I-V) characteristics of Au, Cu and Ag/Ta2O5/Ta capacitors demonstrated that a Schottky-barrier might be formed at the Au, Cu or Ag/Ta2O5 interface. The capacitance at low frequency (1 kHz) increased with increasing forward bias, corresponding to the I-V behavior. This could be correlated with the lifetime of carriers (electrons or holes, or both) injected into the Ta2O5 film. When A1 was used as a counter electrode, the I-V and C-V characteristics (1 kHz) were nearly symmetrical for both bias polarities, although the work function is almost the same as that of Ag. This is because the barrier height for Al/Ta2O5 is lower than that of Ag/Ta2O5 due to the difference in the reactivity of the metals with oxygen at metal/Ta2O5 interfaces. An energy band diagram is proposed to explain the experimental results.
Reticular silver metal tree was successfully fabricated in silver nitrate aqueous solution from fine copper particles. The morphology of the silver metal tree depended on the size of former copper particles. Netted silver wires were formed from copper fine particles, which were electro-deposited on a transparent conducting glass plate. The dendrite silver metal was formed from copper particles embedded on an acrylic plastic plate with the particle size of larger than 40 μm, while a string-shaped silver metal was formed when the size of copper particles was 17 μm and smaller.
Chemiluminescence (CL) of luminol with hydrogen peroxide is useful for the highly sensitive determination of biochemicals by conjugation with oxidase. However, the method has stability problems because reactant-mixing conditions influence the results. However, electrochemiluminescence (ECL) of luminol can be performed on well-mixed solutions of luminol and hydrogen peroxide. ECL has not yet been applied to the quantitative analysis of biochemical due to low quantum yields at physiological pH. In this work, we evaluated the effect of modifying the electrode with cationic polymer on the ECL intensity of luminol. Transparent indium-tin oxide (ITO) electrode was treated with 1 wt% aqueous solution of polyethyleneimine (MW:70,000) buffered by 0.1 M borate at pH 8.0. ECL intensity at the ITO electrode was measured in a mixed solution of 1.0 mM luminol and 10-30 μM hydrogen peroxide buffered by phosphate or Tris-HCl (pH 7.4). The electrode potential was applied in alternate pulses of 0.00 V versus Ag/AgCl for 3 s and 1.00 V for 3 s. The sensitivity of ECL to hydrogen peroxide concentration at the treated ITO increased remarkably. Results indicate that the cationic polymer adsorbed on the electrode enhances ECL by increasing pH in the vicinity of the electrode surface. However, the cationic polymer also enhanced inhibition of ECL by ascorbic acid, an anionic reducing reagent.
An electrolyte-concentration cell was fabricated and its power generating characteristics were evaluated for the first time using salt-tolerant plant Bruguiera Gymnorrhiza. This plant is known to grow in sea water and the chloride concentration in sap is lower than that in the saline surrounding the root.1,2) Plant tissue that separated the saline and the sap usually contains several ions like potassium and calcium, and was thought to show ionic conductivity. An electrolyte-concentration cell was, therefore, thought to be able to fabricate using the chloride ion concentration difference and the ionic conductivity. One of the two Ag/AgCl electrodes was inserted into the petiole of the plant, and the other among the vermiculites that supported the plant root. The vermiculites were soaked in a 400 mM NaCl solution. Two electrodes were connected to a galvanostat and the voltage was measured under a fixed current (20 nA) mode. The voltage gradually decreased with time from 260 mV to ca. 175 mV in two weeks. A periodical change in the voltage was observed. The internal resistance of the system was estimated to be 1.78 GΩ.
We investigated the crystal structure, electronic structure and nuclear state of chemical delithiated spinel LixMn2-yMyO4 (M = Mg, Al, Cr, Mn, Co, Zn, Ni) dependence Li content, x. We obtained the electronic and nuclear density distributions of the samples from XRD and neutron diffraction data using the maximum entropy method. Li content of LixMn2-yMyO4 was controlled by changing concentration of H2SO4-H2O aqueous solution. Mn valence increased and lattice parameter, a, decreased with decreasing Li content. The electron of Li0.095Mn2O4 was delcolization from the results of electronic density distribution. The amount of change of covalent bonding of (Mn, M)-O for LixMn2-yMyO4 (M = Mg, Al, Cr, Co, Zn, Ni) decreased in comparison with that of LixMn2O4 when Li content changed. From the results, the host structure is stable with the substitution of M for LixMn2-yMyO4.
Activated carbon (AC) has high power dennsity, but has limited specific capacitance. In order to increase its capacitance, Cu(II)-picolinic acid (2-pyridine carboxylic acid) complex was adsorbed on AC by the immersion in an aqueous solution containing copper sulfate and picolinic acid. Electrochemical behavior of activated carbon electrode adsorbed with Cu(II) complex was characterized by cyclic voltammetry and constant current electrolysis in 0.2 mol dm-3 H2SO4. An increase in the cathodic and anodic current was observed at the potential of -0.15 V vs. SCE and the voltammograms were stable at least for 50 cycles. This indicates that the reduction of Cu(II) complex and the oxidation of copper occur stably on the surface of activated carbon. The capacitance of AC increased by the redox reaction of Cu/Cu(II) redox couple and enhancement of approximately 480% in capacitance was obtained with the adsorption of 0.48 mmol g-1 of Cu(II). This adsorption method is to be expected for increase the capacitance by the addition of pseudo capacitance on activated carbon.