The first use of cobalt coated carbon felt (Co-CF) as high performance negative electrode in sodium polysullfide/bromine battery (PSB) is presented. The Co-CF was prepared by electroless plating and evaluated by polarization tests and cycling experiment in a PSB single cell at room temperature. At current density of 40 mA cm⁻², the cathodic overpotential of the Co-CF for polysulfide/sulfide couple was −22 mV. When using Co-CF as negative electrode and CF as positive electrode, an energy efficiency up to 82.4% was achieved.

View full abstract

Fabrication of fine circuits on the printed circuit board (PCB) is one of the key process to realize the downsizing of electronic devices. Fine line circuits were created without roughening the surface of PCB and no extraneous deposition was observed between lines by introducing a surface modification by photocatalyst. Modified layer in depth of 20∼30 nm was produced on the PCB surface by the irradiation of UV light under the presence of TiO₂ as a photocatalyst. Adhesion was derived from the nano-level anchor effect by the formation of co-existed layer between modified PCB surface and deposited copper. This new surface modification method has an intrinsic advantage for the formation of fine patterned PCBs.

View full abstract

For the purpose of obtaining the most trustworthy value of the diffusion coefficient D of Li in Ag foil by avoiding the influence of Li–Ag alloy formation, we attempted to use a Li⁺ sensor electrode mounted in a bipolar cell, in which an Ag foil was sandwiched by two facing cylindrical cell compartments. A tungsten oxide electrode doped with Li was prepared for the purpose of sensing the ion concentration of Li⁺ in the electrolyte. The sensor electrode was mounted in the Li extraction compartment, and the potential of the Li⁺ sensor electrode (the Li⁺ concentration)-time curve in the extraction compartment was measured by stepping the potential of the bipolar electrode in the Li insertion compartment. The Li⁺ concentration in the extraction compartment was found to increase within one second after the potential step, and the break through time was found to be independent of the polarization potential in the insertion compartment.
The apparent diffusion coefficient, D_app, was calculated from the break through time. The obtained value was approximately constant at 10⁻⁶ cm² s⁻¹ throughout the range of polarization potential examined for foils of 10- and 20-µm in thickness.

View full abstract

Electrocrystallization of cobalt on a glassy carbon electrode (GEC) from aqueous sulfate solutions was investigated through the electrochemical techniques coupled with scanning electron microscopy (SEM) studies. The nucleation mechanism was examined as a function of deposition potential. By fitting the chronoamperometry experimental data into the Scharifker-Hills nucleation models, it was found that instantaneous nucleation following with the three-dimensional growth occurred for all deposition potentials, which was in accordance with the SEM observations. The nucleation kinetic parameters, using experimental current transients and theoretical formalism, were determined. The calculated diffusion coefficient was smaller than those presented in the literatures, which might result from solution without the supporting electrolyte. An increase of deposition overpotential produced higher nuclei population density.

View full abstract

Response test methods for a hydrogen gas sensor were inspected for application methods in diffusion-type hydrogen sensors. As important elements of the standard test, the internal volume of a test chamber, conditions of a circulation fan, the location of the sensor in the chamber and the method of humidity control were examined from the viewpoints of the operationality and precision of obtained sensing properties. We suggest a basic test method for the response of a hydrogen gas sensor and a precise test method for the response time.

View full abstract

Olivine structured LiFePO₄ cathode is the promising cathode active material for lithium secondary batteries due to its low cost and quite excellent reversibility. On the other hand, lithium polymer secondary batteries (LPBs) have been studied for the purpose of large-scaled batteries (for example, electric power load leveling). In this study, we prepared LPBs using the LiFePO₄ cathode. By measuring the charge-discharge properties and electrochemical impedance spectroscopy, basic properties were investigated compared with the LPBs using the 4V-class LiCoO₂ cathode.

View full abstract

This paper describes characteristics of passive direct methanol fuel cell (DMFC), especially the effect of the thickness of electrolyte membrane. Cell performances were compared for membrane electrode assemblies (MEAs) made with Nafion 112, 115, and 117, whose typical thicknesses were 51 µm, 127 µm, and 183 µm, respectively. The MEA made with Nafion 112 showed performance inferior to the other MEAs with thicker membranes. It appears that the mass of methanol permeated to the cathode through Nafion 112 was large, resulting in the loss of a large quantity of fuel, because its thickness was the smallest among the membranes used in this experiment. The observation of fuel level in the reservoir during open circuit stand indicated that most of the fuel was lost by methanol crossover and evaporation due to the rise in cell temperature. Also, the relationship between the concentration of methanol and the electrode potential at open circuit was investigated with a pseudo dynamic hydrogen electrode calibrated against an Ag/AgCl reference electrode. We found that it is essential to overcome the loss of fuel by methanol crossover and evaporation, which decreases the performance of the anode significantly even when the cell is in the stand-by mode.

View full abstract