Special Issue [Development of New Batteries and Fuel Cells and Related Technologies]
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Takeo Yamaguchi, Seiji Kasahara, Shin-Ichi Nakao
2003 Volume 29 Issue 2 Pages
159-164
Published: March 20, 2003
Released on J-STAGE: May 30, 2009
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For direct methanol fuel cell (DMFC) application, a new type of electrolyte membrane was developed. We are proposing a pore-filling type electrolyte membrane for the application. Pores of porous substrate are filled with polyelectrolyte polymer. The filling polymer exhibits proton conductance and porous matrix suppress the filling polymer swelling to reduce methanol crossover and also provide mechanical strength at high temperature. The pore-filling electrolyte membrane was made by plasma graft-filling polymerization. Poly(tetrafluoroethylene) (PTFE) was employed as the substrate and poly(acrylic acid) or poly(acrylic acid co-allylsulfonate) was used as the filling grafted polymer. Using plasma power 30 W, pores of PTFE substrate was homogeneously filled with the grafted polymer, and the pore-filling type polyelectrolyte membrane was developed. For poly(acrylic acid-co-allylsulfonate) grafted polymer cases, grafting rate and allylsulfonate content were enhanced by adding salt to the monomer solution. This may be due to reduction of double charge layer thickness of sulfonic group, and the effect can enhance the reactivity of allylsulfonate. The membranes contains sulfonic group of 0.48 mmol/g-membrane.
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Tatsuya Watari, Jianhua Fang, Kazuhiro Tanaka, Hidetoshi Kita, Ken-Ich ...
2003 Volume 29 Issue 2 Pages
165-169
Published: March 20, 2003
Released on J-STAGE: May 30, 2009
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A novel sulfonated diamine monomer, 4,4′-bis(4-amino-phenoxy)biphenyl-3,3′-disulfonic acid (BAPBDS), was synthesized by direct sulfonation of the corresponding parent diamine. Sulfonated polyimides were prepared from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), BAPBDS and 2,2'-bis(trifluoromethyl)benzidine (TFMBz). BAPBDS-based polyimides exhibited the best water durability among the sulfonated polyimide membranes investigated so far. This is attributed to the flexible structure and the high basicity of BAPBDS. Proton conductivity of the sulfonated polyimides investigated was similar to that of Nafion117 at 100% relative humidity. With decreasing relative humidity, the proton conductivity decreased. The rate of decrease was in the order BAPFDS > ODADS > BAPBDS-based polyimides. NTDA-BAPBDS/TFMBz (4/1) copolyimide membrane displayed good water durability and reasonably high conductivity and showed potential for fuel cell applications.
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Keiichi Okajima, Kazuyoshi Furukawa, Fuminori Kaga, Masao Sudoh
2003 Volume 29 Issue 2 Pages
170-173
Published: March 20, 2003
Released on J-STAGE: May 30, 2009
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Cell performance and electrochemical properties of a DMFC system were investigated using asreceived Nafion117 (DuPont) and Nafion membrane modified with a counter-ion. The short circuit current of 392 mA/cm
2 and the open circuit voltage of 0.658 V were obtained at 363 K with Nafion117 membrane. For the modified Nafion membrane with the counter ion of (CH
3)
4N
+, the cell performance decreased in comparison with as-received Nafion117 membrane. The short circuit current density was 156 mA/cm
2 for the modified membrane at 353 K because of low proton conductivity of the membrane. However, the open circuit voltage was improved to 0.635 V and 0.732 V at 343 K and 383 K, respectively. Since the reduction of the methanol permeate flux raised the open circuit voltage, it was confirmed that the methanol crossover was suppressed by using the modified Nafion membrane.
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Yikun Xiu, Nobuyoshi Nakagawa
2003 Volume 29 Issue 2 Pages
174-178
Published: March 20, 2003
Released on J-STAGE: May 30, 2009
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The performance of a Direct Methanol Fuel Cell (DMFC) was investigated under different feeding conditions of methanol solution to the anode and oxidant gas to the cathode, by changing volume flow rate and concentration, to anode and cathode, respectively. The effects of feeding conditions on the open circuit voltage, current-voltage curve and electrode impedance measured at 353 K under atmospheric pressure were assessed. The impedance plot obtained comprised two semicircles, of which that on the high-frequency side decreased with the increase of methanol concentration, while that on the low-frequency side decreased with increasing oxygen partial pressure in the cathode gas. It was suggested that the mass transport processes at the anode and cathode each significantly influence the polarization of the cell.
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Hiroshi Fukunaga, Nozomu Teranishi, Koichi Yamada
2003 Volume 29 Issue 2 Pages
179-183
Published: March 20, 2003
Released on J-STAGE: May 30, 2009
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Anodic reaction mechanisms of a direct methanol fuel cell (DMFC) with vapor feed were studied. Membrane electrode assemblies with different catalysis loads were fabricated and AC impedance spectroscopy was measured. The spectrum was deconvolved into three elementary processes, which showed different polarization dependences. The medium-frequency process was considered to be the process related to methanol electrode oxidation and was dominant at a low polarization condition. The low-frequency process was observed only when the methanol concentration was low. This indicates that the removal of reaction product gas does not hinder the anodic reaction of the DMFC with vapor feed.
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Hiroshi Nonaka, Kunihiko Kasuya, Yukihiko Matsumura
2003 Volume 29 Issue 2 Pages
184-187
Published: March 20, 2003
Released on J-STAGE: May 30, 2009
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Using a pressure cell equipped with an Ag | AgCl | 0.1 M KCl external pressure-balanced reference electrode, electrochemical oxidation of methanol was potentiostatically studied on a Pt electrode under hot aqueous conditions (343–523 K), and the apparent activation energy for methanol was calculated. Below 0.4 V vs. RHE, the activation energies were 60 and 30 kJ mol
−1 for 0.1 and 1 mol kg
−1 methanol, respectively. Above 0.5 V vs. RHE, the activation energy was 60 kJ mol
−1 for every experimental methanol concentration and the reaction order was calculated as 0.4 with respect to methanol concentration.
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Hiroshi Nonaka, Kosuke Katayama, Yukihiko Matsumura
2003 Volume 29 Issue 2 Pages
188-190
Published: March 20, 2003
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Using a pressure cell equipped with an Ag | AgCl | 0.1 M KCl external pressure-balanced reference electrode (EPBRE), glucose was potentiostatically electro-oxidized on a Pt electrode at 0.8 V vs. RHE at 523 K. The products and the decomposition efficiency of glucose were compared with those without electrolysis. It was estimated that the electrochemical oxidation of glucose at 523 K involves 2–13 electrons. However, it was difficult to control the decomposition efficiency of glucose with our experimental cell. The construction of a cell with short residence time may be required for the further quantitative study on the electrochemical oxidation of glucose at high temperature.
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Gen Inoue, Yousei Shimomura, Yosuke Matsukuma, Masaki Minemoto
2003 Volume 29 Issue 2 Pages
191-196
Published: March 20, 2003
Released on J-STAGE: May 30, 2009
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The effect of changing operation temperature and H
2 and O
2 concentration in supply gas on the iV characteristic of a small PEFC was examined experimentally. Cell performance was found to decrease with decrease in H
2 and O
2 concentrations and the influence of O
2 concentration was larger than that of H
2. When the relative humidity of the supply gas at both anode and cathode was 100%, no influence of operation temperature could be found. Furthermore, a model was created that can express these influences on PEFC reaction characteristics. Combination of these model equations with gas flow analysis allows the reaction characteristics to be examined in an actual scale PEFC.
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Gen Inoue, Yousei Shimomura, Yosuke Matsukuma, Masaki Minemoto
2003 Volume 29 Issue 2 Pages
197-203
Published: March 20, 2003
Released on J-STAGE: May 30, 2009
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In order to estimate current density distribution, which is difficult to measure experimentally, a PEFC reaction and flow analysis model was constructed based on a reaction model obtained from PEFC power generation experiments. Analysis using the model revealed the presence of a gas flow rate distribution in the separator, which was larger on the cathode side than the anode side, and that this gave rise to concentration and current density distribution. When the supply gas to the anode contained 99% hydrogen and that to the cathode 21% oxygen, the oxygen concentration overvoltage had the greatest influence on the current density distribution, and the direction of a gas flow had almost no influence on the output performance. With the model constructed in this study, it became possible to examine in detail the optimal operation conditions and the optimal form of the separator.
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Takehisa Fukui, Hajime Okawa, Satoshi Ohara, Makio Naito, Kiyoshi Nogi
2003 Volume 29 Issue 2 Pages
204-207
Published: March 20, 2003
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The morphology and conductivity of a CoO-NiO composite cathode for use in a molten carbonate fuel cell (MCFC) were studied. A composite powder consisting of Ni particles covered with fine COO particles, was used as the starting material. Conductivity of the CoO-NiO composite cathode was improved by addition of MgCO
3 and reached the same level as that of a conventional NiO cathode. Moreover, the CoO-NiO composite cathode sintered at 950°C had better porous morphology with porosity of 66% and average pore size of 6 µm, and its cathodic polarization was almost same as that of the conventional cathode. Therefore, we conclude the CoO-NiO composite cathode is a candidate for use in new MCFC cathodes.
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Manabu Ihara, Keisuke Matsuda, Chiaki Yokoyama
2003 Volume 29 Issue 2 Pages
208-213
Published: March 20, 2003
Released on J-STAGE: May 30, 2009
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Stable power generation from a solid oxide fuel cell (SOFC) with a Ni/Gd-doped CeO
2 Cermet (GDC) anode in 100% dry-methane (CH
4) fuel was achieved at a maximum power density of 170 mW/cm
2 at 900° C. The SOFC did not degrade even after 120 h of operation. The DC polarization of the Ni/GDC anode in hydrogen (H
2) fuel and in 4.5% dry-methane fuel was measured by the current interruption method and then compared with those of Ni/YSZ, Pt/YSZ and Pt anodes. The apparent reaction orders of the oxygen activity for Ni/GDC anodes in both hydrogen fuel and 4.5% dry-methane fuel were smaller than those for Ni/YSZ, Pt/YSZ, and Pt anodes. Based on the previously proposed anode reaction mechanism for Ni/YSZ and Pt/YSZ anodes in hydrogen fuel and 4.5% dry-methane fuel, the stable power generation of the SOFC with the Ni/GDC anode in 100% dry-methane fuel was probably due to the high equilibrium constant between the oxygen in YSZ and the oxygen on the three-phase boundary on the anodes.
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Michihisa Koyama, Ching-Ju Wen, Junichiro Otomo, Noboru Taniguchi, Koi ...
2003 Volume 29 Issue 2 Pages
214-220
Published: March 20, 2003
Released on J-STAGE: May 30, 2009
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BaCeO
3, one of the candidate materials for solid oxide fuel cell electrolyte, is a H
+/O
2− mixed ionic conductor. In this study, we measured AC impedance of the anode with the O
2− , H
+ and O
2− , or H
+ as ionic charge carrier in the electrolyte. The measured impedance was analyzed by using the equivalent circuit, and the anodic reaction mechanism was analyzed by comparing the results and abstracted information in each system, in order to clarify the elementary reaction processes dominating the anodic reaction. The anodic reaction for H
+/O
2− mixed ionic conductor electrolyte is more complex than that for electrolytes with a single ionic charge carrier. Therefore, designing an electrode with lower overpotential requires the several elementary processes involved to be accelerated at the same time. A guideline for design of a lower overpotential electrode was proposed based on the knowledge acquired so far.
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Shin Robert Mukai, Yu Yamamoto, Takao Masuda, Hajime Tamon
2003 Volume 29 Issue 2 Pages
221-225
Published: March 20, 2003
Released on J-STAGE: May 30, 2009
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Si/C composites were synthesized by the co-carbonization of 3,5-xylenol-derived novolac resin with various polysilane polymers. A significant increase in the Li
+ reversible capacity due to the inclusion of Si in the C matrix was observed. However, the Li
+ irreversible capacities of the materials were also fairly large. The irreversible Li
+ capacities were fand to be explainable by two factors: the consumption of Li
+ due to the formation of solid electrolyte interface layers within the materials, the amount of which depends on the pore structure of the material, and the trapping of Li
+ by the O included in the material. It was also found that the Si in the materials synthesized using polydiphenylsilane as the Si source could store up to an average of 2.4 Li
+ per atom. These results indicate that by selecting a proper C source for the co-carbonization with polysilane polymers, an anode material for Li
+ batteries with a large reversible capacity and small irreversible capacity can be obtained.
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Izumi Taniguchi, Taro Nishino
2003 Volume 29 Issue 2 Pages
226-231
Published: March 20, 2003
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The deposition of LiCoO
2 thin films on a nickel substrate by Electrostatic Spray Deposition (EDS) method was studied. The precursor solution was prepared by dissolving the correct amount of lithium acetate and cobalt acetate into a mixture of 50 mol% ethanol and 50 mol% 2-(2-butoxyethoxy)ethanol. The effect of applied voltage on the jets formed at the tip of nozzle was investigated. The homogeneous deposition of sprayed droplets on the substrate was achieved by spraying in the cone-jet mode. The effect of process parameters such as deposition temperature and nozzle-to-substrate distance on the surface morphology and microstructure of the deposited thin films was examined by scanning electron microscopy (SEM). The deposited LiCoO
2 thin films were amorphous or nanocrystalline at the deposition temperature of 523 K. Subsequently, the samples were calcined at 973 K for 2 h in air and were studied using X-ray diffraction (XRD). As the result, the crystal structure of the samples transformed to the desired layered structure. The as-calcined thin films were then used as a cathode active material for lithium-ion battery and their electrochemical properties were investigated. The cyclic performance were found to be affected by the surface morphology of as-prepared thin films.
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Keigo Matsuda, Izumi Taniguchi
2003 Volume 29 Issue 2 Pages
232-237
Published: March 20, 2003
Released on J-STAGE: May 30, 2009
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Spinel lithium manganese oxide powders were prepared directly by a continuous droplet-to-particle conversion process using an ultrasonic spray pyrolysis method. Nine kinds of precursor solutions were used to synthesize LiMn
2O
4 powders. The aqueous precursor solutions were made from various combinations of Li-salt, such as Li(HCOO)· H
2O, Li(CH
3COO)· 2H
2O, Li(NO
3), were Mn(HCOO)
2. 2H
2O, Mn(CH
3COO)
2· 4H
2O or Mn(NO
3)· 6H
2O. The total concentration of metal ion is 0.54 mol/dm
3. The particle properties of as-prepared LiMn
2O
4 powders were examined by X-ray diffraction (XRD), the Brunauer-Emmet-Teller (BET) method, transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM). The chemical composition of the powders was determined by inductively coupled plasma spectroscopy (ICP). As the results, the powders were identified as singlephase spinel LiMn
2O
4, and the observed chemical compositions showed, good agreement with the stoichiometry one of LiMn
2O
4 for all samples. However, the particle morphology could be classified into four patterns depending on the original salts. The as-prepared particles were then used as cathode active materials for lithium-ion batteies and their charge/discharge properties were investigated. Their electrochemical properties in terms of cycle performance were also examined.
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Manabu Ihara, Koju Ito, Chiaki Yokoyama
2003 Volume 29 Issue 2 Pages
238-241
Published: March 20, 2003
Released on J-STAGE: May 30, 2009
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Dye sensitized solar cells have a relatively high conversion efficiency of about 10% and can be fabricated using an inexpensive wet method. If the conversion efficiency can be improved, it should be possible to produce a high-efficient solar cell at low cost. In the dye-sensitized solar cell, incident sunlight is absorbed by the dye on a porous TiO
2 film and produces electrons as carrier. Accordingly, the range of the wavelength of light utilized as the energy source is narrower than that in semiconductor solar cells. In this study, we expanded the range of the light producing photocurrent by using a mixture of Ru(bipy)
2(SCN)
2 and Pheophorbide a dyes in dye-sensitized solar cell. The single-dye-sensitized solar cell with Ru(bipy)
2(SCN)
2 has a high energy conversion efficiency of about 10%, and Pheophorbide a was expected to enhance the photocurrent and not to obstruct the light absorption by Ru(bipy)
2(SCN)
2. However, the energy conversion efficiency of the mixed dye sensitized solar cell was smaller than that of the single-dye-sensitized solar cell with Ru(bipy)
2(SCN)
2. Furthermore, we investigated the effect of the fabrication method of the counter electrode and of the mixing ratio of the dyes on the incident photon to current efficiency (IPCE) and on the evaluation parameters of solar cells such as open circuit voltage, short circuit current, fill factor and energy conversion efficiency.
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Shuhei Yokoyama, Manabu Ihara, Hiroaki Hashizume, Hiroshi Komiyama, Ch ...
2003 Volume 29 Issue 2 Pages
242-247
Published: March 20, 2003
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We previously reported that crystalline silicon films for solar cells with high crystal uniformity (Si (100) texture) and very low defect density could be fabricated by zone melting crystallization (ZMC). The defects of the ZMC films were concentrated at the interface between the Si film and the top SiO
2 film. The top SiO
2 film was needed to fabricate smooth and uniform Si films. In this study, we attempted to fabricate smooth and uniform Si films without concentrating defects at the surface by using a new method of gas-flow zone melting crystallization (gas-flow ZMC). Instead of the top SiO
2 film, the gas-flow ZMC used a flow of N
2 gas to the melting zone as a meams to prevent the formation of the rough surface. When the width of the melting zone was narrowed to 2.2–5.2 mm by the cooling effect of the gas flow, the gas-flow ZMC films had a smooth surface, uniform thickness and low defect density at the surface. However, the gas-flow ZMC films had several different crystal faces and the interior of the films had at least 60 times higher defect density than did that of the ZMC films. This result indicated that the top SiO
2 film functioned to orient the (100) crystal face and that the crystal orientation of the (100) crystal face prevented the defect formation inside the ZMC films. If the stability of the interface between the Si film and the bottom SiO
2 film can control the crystal orientation of the gas-flow ZMC films by thinning the Si film, the defect density of the gas-flow ZMC films is expected to be lower than that of the ZMC films.
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Koji Kita, Ching-Ju Wen, Junichiro Otomo, Hiroshi Komiyama, Koichi Yam ...
2003 Volume 29 Issue 2 Pages
248-254
Published: March 20, 2003
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A new process to produce multicrystalline silicon (Si) thin film by a solution growth method using copper-Si solution was designed and its manufacturing cost was evaluated. In order to reduce the cost, it is necessary to grow the Si crystal on a low-cost substrate. The feasibility of this was experimentally demonstrated by applying a new nucleation method of silica reduction by aluminum on the substrate. A process with a high production rate could be designed by the film growth model constructed using the experimental result of the Si diffusion coefficient in the solution. In the process, continuous Si film growth on alumina substrate from a supersaturated solution occurs when the solution is cooled down from 1,000°C to 800°C. The substrate is transferred at 20 mm/s through the temperature gradient of 25°C/m. The production cost of the Si thin film was evaluated for the case of solar cell production with an annual rate of 1 G
WP, by using the costs of raw materials, electricity, equipments, buildings, and labor. The estimated cost was ¥ 6.3/
WP, which was much lower than the substrate production cost by the conventional cast process of multicrystalline Si.
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Keiichi Okajima, Takashi Toya, Masao Sudoh
2003 Volume 29 Issue 2 Pages
255-260
Published: March 20, 2003
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An energy storage system consisting of electric double-layer capacitors was designed for hybrid electric vehicles (HEV). The input energy and the CO
2 emission for the capacitor system were compared with those for a lithium ion battery system. A vehicle of 2,000 cc class was assumed to run in the 10· 15 mode defined by Japanese Industrial Standard (JIS). From the result of calculations, the CO
2 emission in the life-cycle model for HEV decreased by 35.7% with increasing system capacity from 666 Wh to 903 Wh, even though the CO
2 emission increased with system capacity at the time of energy storage system manufacture. The superiority of the capacitor energy storage system was clarified by evaluation over the whole of the life cycle model.
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Eri Murakami, Akira Kimura, Nobuyoshi Nakagawa
2003 Volume 29 Issue 2 Pages
261-266
Published: March 20, 2003
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Calculations to evaluate the economic benefit of introducing fuel cell systems for residential use were conducted based on domestic energy demand. The energy demand, i.e., demand for electricity, city gas and hot-water, was measured in houses in Kiryu, Gunma. Energy cost reduction was obtained as a function of the power generation capacity of the fuel cells and the unit costs of electricity and city gas. In most houses, the optimum generating capacity of fuel cells was in the range between 0.5 kW and 1.0 kW. The effect of the parameters on cost reduction and the optimum power generating capacity was quantitatively demonstrated.
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