Takuya Tsujiguchi

Catalytic activity of baker's yeast in a mediatorless microbial fuel cell

The catalytic activity of bakers yeast, Saccharomyces cerevisiae, as a biocatalyst was investigated in a mediatorless microbial fuel cell. The yeast cells that adhered on the anode surface were the active biocatalyst for glucose oxidation in a mediatorless biofuel cell, suggesting that the electron transfer took place through the surface confined species. The species in the anolyte solution including the dispersed yeast cells did not take a part in the electron transfer and thus in the power generation.

Catalytic activity of yeast extract in biofuel cell.

It was revealed that the dry powder yeast extract (YE) has the ability to act as a biocatalyst as well as a mediator in a biofuel cell. The yeast extract, from Nihon Pharmaceutical Co., Ltd., was used as a biocatalyst in an open air cathode biofuel cell containing phosphate buffer for glucose oxidation. The anode medium with only the YE showed an immediate activity by producing a current and delivering power depending on its concentration. By adding glucose to the anode medium, the anode potential decreased with time to -0.2 V vs. normal hydrogen electrode (NHE), and produced a higher power compared to that without glucose. The biofuel cell produced an open circuit voltage (OCV) as high as 1 V.

Effect of Metal Modification to Carbon Paper Anodes on the Performance of Yeast-Based Microbial Fuel Cells Part Ι: In the Case without Exogenous Mediator

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.

Effect of Metal Modification to Carbon Paper Anodes on the Performance of Yeast-Based Microbial Fuel Cells Part ΙΙ: In the Case with Exogenous Mediator, Methylene Blue

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.

Coproduction of acetic acid and electricity by application of microbial fuel cell technology to vinegar fermentation

The coproduction of a useful material and electricity via a novel application of microbial fuel cell (MFC) technology to oxidative fermentation was investigated. We focused on vinegar production, i.e., acetic acid fermentation, as an initial and model useful material that can be produced by oxidative fermentation in combination with MFC technology. The coproduction of acetic acid and electricity by applying MFC technology was successfully demonstrated by the simultaneous progress of acetic acid fermentation and electricity generation through a series of repeated batch fermentations. Although the production rate of acetic acid was very small, it increased with the number of repeated batch fermentations that were conducted. We obtained nearly identical (73.1%) or larger (89.9%) acetic acid yields than that typically achieved by aerated fermentation (75.8%). The open-cycle voltages measured before and after fermentation increased with the total fermentation time and reached a maximum value of 0.521 V prior to the third batch fermentation. The maximum current and power densities measured in this study (19.1 μA/cm² and 2.47 μW/cm², respectively) were obtained after the second batch fermentation.

PAN Based Carbon Nanofibers as an Active ORR Catalyst for DMFC

Polyacrylonitrile (PAN) based carbon nanofibers containing different proportions of transition metals in the form of metal phthalocyanine, MPc, where, M is Co and Fe, have been prepared by electrospinning and their activities for oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) in acidic media were 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. The ORR activity significantly increased with the addition of the transition metals, and also increased the pyridine N content. The highest ORR activity was obtained for CoPc PAN nanofibers at 900 oC, this would be related to the balance between electrical conductivity and pyridine N content. FePc PAN based carbon nanofibers at 900 oC showed a high stability and ORR activity comparable to that of the commercial Pt/C catalyst while FePc PAN nanofibers has no MOR activity.

Tungsten Carbide Nanofiber Prepared by Electrospinning for Methanol Oxidation Reaction

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.

PAN Based Carbon Nanofibers as an Active ORR Catalyst

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.

Control of Methanol Crossover Using a Perforated Metal Sheet for DMFC Application

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%.

Carbon-Supported PtRuRh Nanoparticles as a Catalyst for Direct Ethanol Fuel Cells

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.