Hisayoshi Matsushima

Water Electrolysis under a Magnetic Field

The energy efficiency of water electrolysis was considerably improved under a high magnetic field. This was proved by measuring the cell voltage, the IR-drop, and the electrode potentials for the electrolysis which was galvanostatically operated in alkaline (4.46 and 0.36 M KOH) and acidic (0.05 M H 2 SO 4 ) solutions. A large reduction in the cell voltage was achieved in a magnetic field, especially at a high current density. The decrease of the IR-drop, which was measured by the current interrupter method, depended on the concentration of electrolyte solutions. In a magnetic field, the oxygen overpotential was reduced more than the hydrogen overpotential.

Ohmic Resistance Measurement of Bubble Froth Layer in Water Electrolysis under Microgravity

Galvanostatic water electrolysis was conducted in 2 wt % KOH and 0.1 N H 2 SO 4 solutions under microgravity. The corresponding terrestrial experiments employed two kinds of electrode configurations: a vertical cathode and downward-facing horizontal cathode-over-anode (C/A) arrangement. The latter configuration was designed to simulate the microgravity (μ-G) condition. The ohmic resistance of the gas bubble dispersion zone near Pt electrodes was measured by the current interrupter method and compared for these three different cases. The transient variation of resistance for C/A configuration behaved similarly to that under μ-G in H 2 SO 4 , but the resistance varied more slowly in KOH. When water electrolysis was conducted with a vertical plane cathode under 1-G, the resistance reached an essentially constant value within a few 100 ms in KOH, whereas the resistance increased linearly for a few seconds, followed by a zig-zag variation in H 2 SO 4 . Water electrolysis under μ-G resulted in stable froth layer formation, and the accompanying ohmic resistance increased in linear proportion to the froth layer thickness. The contributions of electrode surface coverage by bubbles and electrolyte-phase bubble void fraction to the ohmic drop were also assessed. These parameters were compared with corresponding values in terrestrial experiments analyzed by Balzer and Vogt.

Observation of bubble layer formed on hydrogen and oxygen gas-evolving electrode in a magnetic field

The evolution of hydrogen and oxygen gasses in a 0.36-M KOH electrolyte was observed in a magnetic field, and the void fraction was calculated by a hydrodynamic model. Both gasses evolving on a platinum working electrode formed a bubble layer which increased the ohmic resistance. In addition to natural convection, magnetohydrodynamic (MHD) convection in a magnetic field improved the electrolytic conductivity by supplying a fresh solution (pumping effect) and removing gas bubbles. The MHD convection reduced the void fraction of hydrogen gas more than that of oxygen, which can be explained by the poor wettability of the oxygen evolving electrode.

Novel PEFC Application for Deuterium Isotope Separation

The use of a polymer electrolyte fuel cell (PEFC) with a Nafion membrane for isotopic separation of deuterium (D) was investigated. Mass analysis at the cathode side indicated that D diffused through the membrane and participated in an isotope exchange reaction. The exchange of D with protium (H) in H2O was facilitated by a Pt catalyst. The anodic data showed that the separation efficiency was dependent on the D concentration in the source gas, whereby the water produced during the operation of the PEFC was more enriched in D as the D concentration of the source gas was increased.

Electrodeposition of NiFe Alloys in a Magnetic Field

The effects induced by a static magnetic field that was superimposed during the electrodeposition of NiFe alloy were investigated. It was found that the iron content of the alloy, the partial current due to hydrogen evolution reaction, the morphology and the texture of the alloys change when the magnetic field is applied perpendicular to the electric field lines. Beside changes in the morphology on a microscopic scale, no other significant effects were obtained when the magnetic field lines and the electric field lines were parallel to each other. The effects observed were considered to be induced by the additional convection generated by the interaction between the MHD convection and the natural convection.

Formation of Gloss Al Electroplating in 1-ethyl-3-methylimidazolium chloride-AlCl 3 Ionic Liquid Containing 1,10-Phenanthroline

To form glossy plating of Al on a Cu substrate, electroplating of Al was conducted in an ionic liquid mixture of 1-ethyl-3-methylimidazolium chloride and aluminum chloride (EMIC-AlCl3) containing 1,10-phenanthroline (Phen). The electroplated surface smoothness obtained using an Al-plate counter electrode was improved by stirring of the electrolyte. The reflectivity at the center of the specimen surface formed by a stirring rate of 400 rpm was the highest at 74.7% with stirring rates from 0 to 400 rpm and the reflectivity of the specimen was higher at the edge than at the center. The results suggest that the glossy surface of the substrate was enhanced by uniformity of the electrolyte in contact with the substrate. When the counter electrode was replaced with the Al mesh, the electroplated surface was glossy throughout the surface without stirring. Diffusion of the electrolyte through the Al mesh might have produced an effect similar to stirring of the electrolyte.