Papers by Author: Takuya Tsujiguchi

Abstract: Tungsten carbide nanofibers for the anode catalyst of direct methanol fuel cells (DMFCs) were prepared from the precursor nanofibers with the diameter around 250 nm using an electrospinning technique. The electrospun nanofibers from the mixture of ammonium metatungstate and polyvinylpyrrolidone were dried and calcined in air at 700 °C to form tungsten oxide nanofibers, and reduced in 20 vol.% CH₄/H₂ atmosphere at 700 °C for 2 h. Surface morphology and crystalline structure of the prepared nanofibers were investigated using FE-SEM and XRD. The methanol oxidation reaction (MOR) activity of the prepared samples was evaluated by cyclic voltammetry (CV). The FE-SEM and XRD analyses showed that beaded nanofibers of tungsten carbide were successfully obtained. The WC nanofiber electrocatalyst exhibited a MOR activity suggesting it can be a candidate of the catalyst for DMFC. The presence of impurities, carbon and tungsten oxide, which may affect the activity, were detected at the surface.

Abstract: Effect of metal modification to carbon paper as the anode of mediator-aided yeast-based microbial fuel cell on the cell performance was investigated using methylene blue as an exogenous mediator. The modification was conducted using a sputtering technique by depositing Co or Au thin layer, 30 nm. The electrode performance was evaluated by measuring the electrode potentials and the fuel cell power output. The metal modification significantly increased the mediator-aided MFC performance.

Abstract: Effect of modification of carbon paper with a thin layer of cobalt or gold on the performance of yeast-based microbial fuel cells was investigated. The modification was conducted by depositing Co or Au thin layer with different thickness, 5 nm and 30 nm, using a sputtering technique. The electrode performance was evaluated by measuring the electrode potentials and the fuel cell power output. The Co modification significantly increased the performance of the fuel cell, while the Au modification inhibited the performance. SEM observation indicated that the adhesion density of the yeast cells on the electrode surface was affected by the metals. It was confirmed that the electron transfer took place through the surface confined species at the mediatorless anode.

Abstract: Polyacrylonitrile (PAN) based carbon nanofibers were prepared by electrospinning and their activity for oxygen reduction reaction (ORR) in acidic media was investigated. Field emission electron microscope (FE-SEM), transition electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV) were carried out to investigate the surface morphology, composition, and catalytic activity. Thin carbon nanofibers of a 150 nm diameter were successfully produced by electrospinning using 8 wt% PAN in dimethylformamide, 15 cm pin to plate distance, and applying voltage of 18 kV at different carbonization temperatures of 700, 900, 1000, 1100, and 1200 °C. The ORR activity of the prepared carbon nanofibers was evaluated. The PAN based carbon nanofibers showed a considerable ORR activity and this activity was increased by increasing the carbonization temperature. The high ORR onset potentials over 700 mV vs. RHE (milli-volt versus reversible hydrogen electrode) were obtained at temperatures over 1000 °C. The activity of PAN based carbon nanofibers increased with increasing carbonization temperature from 700 to 1100 °C, this would be related to the increasing in the electrical conductivity at low carbonization temperatures, and the high Pyridine N content at the high carbonization temperatures.

Abstract: Carbon-supported PtRuRh nanoparticles, PtRuRh/C, were prepared by an impregnation method as a new anode catalyst with a high activity for ethanol oxidation in a direct ethanol fuel cell (DEFC). PtRuRh (2:1:1)/C, of which the metal loading and the metal particle diameter was 40 wt% and 6.7 nm, respectively, with the metal composition of 2:1:1 for Pt:Ru:Rh, showed a higher oxidation current at a certain electrode potential compared to that of PtRu (1:1)/C and Pt/C prepared in a similar manner. The DEFC with PtRuRh (2:1:1)/C as the anode catalyst generated about a 1.5 times and 3 times higher electric power compared to that of PtRu (1:1)/C and Pt/C, respectively, with 2M ethanol.

Abstract: In this study, to control the methanol crossover occurring in a direct methanol fuel cell, DMFC, a perforated metal sheet of which the pore diameter and the porosity (open ratio) were regularly controlled was used in a passive DMFC, and the influence of the open ratio and the pore diameter on the power generation characteristics, and also on the methanol crossover of the passive DMFC were investigated on the basis of the power generation experiment at several different methanol concentrations. It was found that the pore diameter of the metal sheet did not affect the power generation characteristics and the methanol crossover in this experiment. On the other hand, the open ratio of the metal sheet significantly influenced the power generation characteristics, and the methanol transport was increased by decreasing open ratio of the metal sheets. It was found that a high concentration of methanol can be used at low open ratios below 3%. However, when the open ratio was higher than 3%, it hardly affected the current density and the mass transport. This means that the open ratio is not an important factor for the methanol transport or the electrode reaction in the range over 3%.