Electrochemistry, Vol. 72. No.4, 2004

p232

Gas Diffusion Electrodes for Polymer Electrolyte Fuel Cells
Using Novel Organic^Inorganic Hybrid Electrolytes

Osamu NISHIKAWA,a,c Kazuo DOYAMA,a
Kenji MIYATAKE,b Hiroyuki UCHIDA,c and Masahiro WATANABE@b,

aNBO Development Center, Sekisui Chemical Co. Ltd. (32 Wadai, Tsukuba 300]4292, Japan)
bClean Energy Research Center, University of Yamanashi (4 Takeda, Kofu 400]8510, Japan)
cGraduate School of Engineering, University of Yamanashi (4 Takeda, Kofu 400]8511, Japan)

Received October 27, 2003 ; Accepted February 3, 2004

We have prepared gas diffusion electrodes for polymer electrolyte fuel cells (PEFC) using new organic^inorganic hybrid electrolytes. The catalyst layers were prepared by mixing 3](trihydroxysilyl)]1]propanesulfonic acid m(THS)Pro]SO3Hn, 1,8]bis(triethoxysilyl) octane (TES]Oct), Pt loaded carbon black (Pt]CB) and water, followed by a sol]gel reaction. The polarization properties and the microstructure of the catalyst layer were investigated as a function of the composition. The catalyst layer exhibited higher catalyst utilization than that with conventional Nafion® ionomer. The maximum cathode performance was obtained at (THS)Pro]SO3H^CB1 (by weight). It was found by a mercury porosimetry that the volume of both primary and secondary pores decreased with increasing the acidic ionomer content. The high catalyst utilization with increasing the acid content is ascribed to an enhanced proton conduction, because the hybrid ionomer could penetrate both in the primary and secondary pores. However, an excess ionomer loading showed a detrimental effect due to disturbance of the gas diffusion. The novel organic^inorganic hybrid materials have proved to be a potential material as the ionomer in the electrodes for high temperature PEFCs.


p238

Silicon Chemical Oxide Growth by a Novel Wet Treatment in
Aqueous Chlorine Solutions

Marius CHEMLA,a Didier LEVY,c Sébastien PETITDIDIER,c
François ROUELLE,a and Sandrine ZANNA@b

aLaboratoire d'Electrochimie, LI2C, Universite P. M. Curie (Paris, France)
bLaboratoire Physico]Chimie des Surfaces. ENSCP (Paris, France)
cSTMicroelectronics R D Center (38920 Crolles, France)

Received October 27, 2003 ; Accepted February 5, 2004

For the wet cleaning of silicon surfaces, a few new reactants, such as ozone dissolved in UPW, have been proposed to replace the original RCA process using H2O2 solutions. In the present work we describe, for the first time, the mechanism of silicon surface oxidation by dilute solutions of elemental chlorine. Upon reaction with this highly oxidizing agent, the open circuit potential shifted immediately to positive values, the effect being identical for both n] and p]type Si substrates. The surface transformation was firstly investigated by electrochemical impedance spectroscopy which showed successive semicircles representing RC equivalent circuits, revealing a gradual growth of an insulating layer. XPS recordings demonstrated unequivocally the formation of a pure and uniform chemical oxide layer, the possible contamination by Cl element being negligible. The analysis of the charge transfer reaction by voltammetry led to the conclusion that the exchange between the semiconductor and the solution involved positive holes. The reduction current, at a negative bias potential, was extremely small with p]type Si as a consequence of a depletion layer appearance. On the contrary, in n]type substrates, an accumulation region was formed, so that the electric field, as high as 107 V cm|1, will promote a conduction mode through the insulating oxide layer. This novel technique of surface treatment seems promising with respects to the economy and environmental requirements, and also for the possible subsequent growth of multi]layer high]k dielectric structures.


p246

Electrochemical Reaction in a High Gravity Field Vertical to Electrode
Surface\Analysis of Electron Transfer Process by Gravity Electrode

Yoshinobu OSHIKIRI,a,c Makoto SATO,b Akifumi YAMADA,c and Ryoichi AOGAKI@d

aDepartment of Environmental Engineering Yamagata College of Industry Technology (2]2]1, Matsuei, Yamagata]shi, Yamagata 990]2487, Japan)
bAizu Polytechnic Center (292, Fukagawa]Nishi, Minami]Shigo, Kouzashi, Aizu]Wakamatu, Fukushima 965]0858, Japan)
cDepartment of Chemistry, Nagaoka University of Technology (1603]1, Kamitomioka, Nagaoka, Niigata 940]2188, Japan)
dDepartment of Product Design, Polytechnic University (4]1]1, Hashimoto]dai, Sagamihara 229]1196, Japan)

Received November 10, 2003 ; Accepted January 6, 2004

For quantifying the vertical gravity effect on electron]transfer processes in an electrochemical reaction, a theoretical equation was derived, which depicted the reaction in the mixed]rate]controlling state of diffusion and reaction in a gravity field vertical to an electrode surface. Then, the vertical gravity effect on electron]transfer processes in a ferrocyanide]ferricyanaide system up to 650g was studied. The Tafel lines obtained were compared with the results from the conventional chronopotentiometry in the natural gravity field. Consequently, it was concluded that there is no change in the reaction process in the gravity fields up to 650g, and the validity of the equation was experimentally certified.


p252

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Electrochemical Noise Analysis for the Under]Film Corrosion
of Polymer Coated Iron

Yasuhiko ITOI, Seisyo TAKE, and Masaru OKUYAMA

Department of Materials Chemistry and Bioengineering, Oyama National College of Technology (771 Nakakuki, Oyama 323]0806, Japan)

Received September 11, 2003 ; Accepted December 26, 2003

Efficient and selective N]arylation of pyridine derivatives was demonstrated as nucleophilic substitution reaction of electrochemically generated ΁]radical cations such as pyrene and perylene. 1]Methylimidazole also worked as a nucleophile toward pyrene ΁]radical cation to give the imidazorium. This reaction provides a widely applicable and powerful method for pyridinium]conjugated assembly in which redox]active pyridinium moieties can be integrated through ΁]conjugated system. Preparative scale synthesis was demonstrated successfully by using perylene ΁]radical cation prepared by chemical oxidation with I2^AgClO4. The resulting pyridinium]conjugated assembly shows both one]electron reduction assigned to the pyridium moiety and one]electron oxidation of the pyrene and perylene moieties. UV]visible absorption and fluorescence spectra indicated intramolecular charge transfer character from the pyrenyl and perylenyl moieties to the pyridinium ones of the pyridinium]conjugated assembly.


p261

Characterization of R.F. Magnetron Sputtered Vanadium Oxide
Thin Films and Intercalation of Lithium in the Oxide Films

Naoaki KUMAGAI,a Shinichi KOMABA,a Osamu NAKANO,a Mamoru BABA,a
Henri GROULT,b and Didier DEVILLIERS@b

aFaculty of Engineering, Iwate University (4]3]5, Ueda, Morioka 020]8551, Japan)
bUniversite Pierre et Marie Curie, Laboratory LI2C]Electrochimie]CNRS UMR]7612 (4 Place Jussieu, 75252, Paris, France)

Received August 1, 2003 ; Accepted January 28, 2004

Vanadium oxide films were deposited by r.f. magnetron sputtering technique on SUS 304 stainless steel substrates in Ar{O2 atmosphere using V2O5 target. The films obtained were characterized by X]ray diffractometry and scanning electron microscopy. The XRD and SEM observations show that the crystallographic orientation and surface morphology of the vanadium oxide films are changed with film thickness. For the thin film with thickness of 450nm the V205 phase with the ab plane parallel to the substrate is formed, resulting in a highly smooth surface, while for thicker films with thickness of 1.0`4.0m the V2O5 phase with the ab plane perpendicular to the substrate is formed, giving a considerably rugged surface. The vanadium oxide films undergo a reversible lithium intercalation and deintercalation process, and the thicker film (4.0m) showed more distinct stepwise discharge profile than the thin film (0.45m). The kinetics of intercalation process of lithium into the V2O5 film was studied using an electrochemical transient technique, deducing kinetic parameters such as chemical and lithium component diffusion coefficients and activation energy for lithium diffusion.


p266

New Electrochemical Process for CO2 Reduction to from Formic Acid
from Combustion Flue Gases

Yumi AKAHORI,a Nahoko IWANAGA,a Yumi KATO,b Osamu HAMAMOTO,c
and Mikita ISHII@a,b

aDepertment of Industrial Chemistry, Meiji University, School of Science and Technology (Higashi]mita 1]1]1, Tama]ku, Kawasaki, Kanagawa 214]8571, Japan) bJapan Analysis Evaluation Center (Kitanodai 1]41]8, Hachioji]shi, Tokyo 192]0011, Japan) cSteel structure Logistic Systems Hq., Mitsui Engineering Shipbuilding Co., Ltd. (Tskiji 5]6]4, chuo]ku, Tokyo 104]8439, Japan)

Received August 22, 2003 ; Accepted January 10, 2004

Flow cell technologies for electrochemical reactors were applied to the system for carbon dioxide absorption and its electrochemical reduction. Small flow]by type reactors with two chambers separated by a sheet of ion]exchange membrane were employed for both CO2 absorbtion and reduction. Absorbtion of CO2 into phosphate buffer solutions through the ion exchange membrane and succeeding electrochemical reduction of the absorbed CO2were studied; and the opimum conditions to form formic acid with high current efficiency were discussed. Formic acid is expected to be available to chemiluminescent reagents for oxidant detections and chemical lamps. Almost 100 in current efficiency of CO2 reduction to form formic acid was realized by using In impregnated lead wire cathode. The applied cell voltage was reduced to under 1.5V due to sulfur dioxide absorption into counter electrode solution.


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