Naoya Miyajima

Electrochemical Behavior of Halogen-Doped Carbon Materials as Capacitor Electrodes

Electric double-layered capacitor (EDLC) usually uses high-surface area carbon materials as the electrodes, and the authors have reported that single-walled carbon nanotube (SWCNT) is a promising material for the electrode of EDLC [1-3]. For the further improvement of capacitance, modification of the electrode carbon materials is important. Doping is one of the methods to modify the carbons, and lithium doping is a recent hot topic to modify the negative carbon electrode which is the core technique of so-called lithium-ion capacitor. On the other hand, some of halogen is known to react with carbon strongly with p-doping. In particular, p-doping of SWCNT by bromine and iodine vapor has been investigated widely from the viewpoints of increase the carrier of SWCNT. We focus the p-doping by halogens to challenge the modification of positive carbon electrodes for capacitor system. In the present work, bromine and iodine vapors were reacted with various carbon materials such as SWCNT, graphite, and activated carbon to modify their electronic states, and their electrochemical behaviors in 1M Et4NBF4/PC were investigated, paying attentions to their capacitance, initial potential, and cyclic reversibility.

Piezoelectric Properties of Porous Potassium Niobate System Ceramics

Porous potassium niobate (KNbO3, KN) system ceramics were prepared by a conventional sintering method using carbon black (CB) nanoparticles. First, KN nanoparticles with a size of 100 nm was mixed with CB nanoparticles and binder using ball milling with ethanol. The mixture was dried, and pressed into pellets using uniaxial pressing. After binder burnout, these ceramics was sintered in air. Their piezoelectric properties were measured and discussed a relationship between porosity and piezoelectric properties. As the results, with increasing porosity, piezoelectric g33 constant increased significantly, which suggested that porous ceramics were effective for stress sensor application.

Preparation and Dielectric Properties of Dense Barium Titanate Nanoparticle Accumulations by Electrophoresis Deposition Method

Dense barium titanate (BaTiO3, BT) nanoparticle accumulations were prepared by an electrophoresis deposition (EPD) method using three kinds of BT nanoparticles with different particles sizes and tetragonality. First, the BT particles were dispersed into ethanol using ball-milling technique, and an optimum milling condition was investigated. As the results, it was confirmed that ball-milling led to a formation of mixture between single-dispersed nanoparticles and aggregated particles. Thus, the aggregated particles in the slurry were removed by a centrifuge in order to obtain narrow the size distribution. Using well-dispersed slurry, BT nanoparticle accumulations were deposited on paradigm electrode by the EPD method. Despite various BT nanoparticles, the dense BT nanoparticle accumulations were obtained at relative densities of around 60 %. After gold electrode deposition on the both surfaces of the accumulations by spattering method, dielectric properties were measured at 20 °C, the highest dielectric constants of around 160 was measured at 10 MHz.

Porosity Dependence of Piezoelectric Properties for Porous Potassium Niobate System Ceramics

Porous potassium niobate (KNbO3, KN) system ceramics were prepared by a conventional sintering method using carbon black (CB) nanoparticles. First, KN nanoparticles with a size of 100 nm was mixed with CB nanoparticles and binder using ball milling with ethanol. The mixture was dried, and pressed into pellets using uniaxial pressing. After binder burnout, these ceramics was sintered in air. Their piezoelectric properties were measured and discussed a relationship between porosity and piezoelectric properties. As the results, with increasing porosity, piezoelectric g33 constant increased significantly, which suggested that porous ceramics were effective for stress sensor application.

Adsorption Properties of Surface Modified Carbons with Metal Nanoparticles

The effect of surface modification by nanoparticles of metal compounds was investigated by means of gas and vapor adsorption analysis. The surface of activated carbon fiber cloths was modified by loading of Li2CO3 and MgO nanoparticles. The particles on the carbon surface played as initial adsorption site of water molecules, leading to the promotion of micropore filling without diminishing the micropore volume of the porous carbon supports. The increasing characteristic adsorption energy suggested some interaction between methane molecules and the particles.