Manganese dioxides were obtained from heating manganese (II) salts (nitrate, carbonate and acetate) and ammonium nitrate at 250°C for 1 h. The formation of γ-MnO2 phase was confirmed by X-ray diffraction. The particle sizes and specific surface areas of the products were 0.2-1 µm and 170-190 m2 g−1, respectively. When the products were used as the cathode materials of lithium/manganese oxide cells, the discharge capacities of these cells were 240-255 mAh g−1, which were higher than that of the cell using electrolytic manganese dioxide (207 mAh g−1). It was found that the products by the simple process are hopeful as a cathode material.
A measurement without the influence of protein adsorption on the sensor surface has been developed using transient current of an enzyme-immobilized electrode. Response current decreases due to protein adsorption on the sensor surface and the enzyme-immobilized membrane causing glucose concentration gradient. By measuring glucose concentration in the transient state while controlling GOD activity, it is possible to prevent the influence of protein adsorption. A needle-type electrode glucose sensor on which enzyme is immobilized with a polyurethane membrane, with electrochemical on-off control of enzyme activity, is capable of accurate measurement of glucose concentration in bovine serum at least for 24 hrs.
Effects of organic additives on the surface morphology of electrodeposited Sn-Ag alloy for use as Pb-free soldering were investigated. Pyrophosphate-iodide bath was used as a basic Sn-Ag alloy electroplating bath. Polyethyleneglycol (mean molecular weight = 600 : PEG600) and formaldehyde were used as additives. Fine-grained and smooth electrodeposit was obtained from the bath containing both PEG600 and formaldehyde. Electrochemical behavior of tin pyrophosphate complex ion, silver iodide complex ion, PEG600, formaldehyde, and the combinations of them was examined by polarography. Formaldehyde decomposed reductively at about −1.5 V vs. saturated calomel electrode (SCE) on the mercury electrode and had no inhibitory effect on the reduction of tin pyrophosphate complex ion and silver iodide complex ion. PEG600 had a strong inhibitory effect on the reduction of tin pyrophosphate complex ion. As a result, the tin deposition (or tin-silver alloy codeposition) potential was shifted from −0.9 V to −1.6 V vs. SCE which is more negative than the potential of reductive decomposition of formaldehyde. It is suggested that the process of the reductive decomposition of formaldehyde on the cathode surface on which Sn-Ag alloy are being electrodeposited related to the smoothing of Sn-Ag alloy films.
Two specific phenomena were observed during electrochemical charging and discharging processes for Mg2Ni alloy electrode at the first cycle, i.e., the decrease of the absorbed hydrogen content (difference between the charged quantity of electricity and the hydrogen gas volume converted to the quantity of electricity) in an alloy during charging process and the discharge capacity larger than the absorbed hydrogen content. In order to investigate these phenomena, the electrochemical behavior of Mg2Ni alloy powders prepared by casting and bulk mechanical alloying (BMA) was studied in 6M KOH solution and water. It was consequently found that Mg(OH)2 was formed and at the same time atomic hydrogen was also formed in the solution so that the hydrogen was absorbed into Mg2Ni alloy. Hydrogen gas was also generated from the alloy surface after hydrogen absorbed was almost saturated in the alloy. Consequently, it was clearly concluded that the specific phenomenon of the former is due to the generation of gaseous hydrogen when Mg2Ni alloy reacted with H2O. The latter is also because of the discharge of the hydrogen absorbed into Mg2Ni by forming Mg(OH)2, except for discharge of the hydrogen absorbed electrochemically.
An electrode penetrated by cylindrical holes to inhibit the diffusion of heavy metal ions was proposed. Heavy metal ions diffusing into the holes are reduced to metal and are trapped on the inner surface of the holes. The inhibitory effect was examined using a model electrode made of gold with a cylindrical hole and a solution containing zinc cations. The diffusion of zinc cations was effectively inhibited. Calculations and an EPMA measurement of the elemental zinc on the inner surface of the hole showed that the zinc concentration along the hole decreased rapidly as the distance from the hole inlet increased.
Formal rate constants for electrode reactions of n-alkyl-ferrocene derivatives in propylene carbonate solution were determined by Fast Scan Cyclic Voltammetry. Simple correction for voltammograms was done by the subtraction of blank voltammogram from the original voltammogram to reduce the effect of the double layer charging current. The formal rate constant decreased from 7.29 ± 0.86 (ferrocene) to 0.0261 ± 0.0062 cm s−1 (n-tetradecylferrocene) with increasing alkyl chain length of ferrocene derivatives.
Amperometric sensing properties to H2O2 of the carbon electrodes loaded with various perovskite-type oxides have been investigated. It was found that the carbon electrodes loaded with perovskite-type oxides showed high activity to anodic reaction including H2O2. A limiting current was observed at the electrode potential between 0.7 and 1.0 V vs. SCE, and the current at a fixed potential increased with increasing H2O2 concentration between 10 and 1000 µM (M = mol dm−3). H2O2 responses of the elements loaded with La0.6Ca0.4BO3 (B = Fe and Cr) were hardly affected by dissolved oxygen. All solid-state H2O2 sensor element based on solid polymer electrolyte and La0.6Ca0.4FeO3-based electrodes also responded well to H2O2 at the concentration between 50 and 200 µM, with the 90% response time of as short as 20 s.