論文 / 著書情報
Article / Book Information
題目(和文)

吸着種領域モデル及び反応サイトイメージングによる固体酸化物型燃料電池多孔質電極における反応動力学に関する研究

Title(English)

Reaction Kinetics and Dynamics on Solid Oxide Fuel Cell Porous
Electrodes through Species Territory Adsorption Model and Active Sites
Imaging

著者(和文)

長澤剛

Author(English)

Tsuyoshi Nagasawa

出典(和文)

学位:博士(工学),学位授与機関:東京工業大学,
報告番号:甲第10789号,授与年月日:2018年3月26日,
学位の種別:課程博士,
審査員:花村 克悟,佐藤 勲,平井 秀一郎,山中 一郎,伏信 一慶

Citation(English)

Degree:Doctor (Engineering),
Conferring organization: Tokyo Institute of Technology,
Report number:甲第10789号,
Conferred date:2018/3/26,
Degree Type:Course doctor,
Examiner:,,,,

学位種別(和文)

博士論文

Category(English)

Doctoral Thesis

種別(和文)

論文要旨

Type(English)

Summary

Powered by T2R2 (Tokyo Institute Research Repository)

（博士課程）Doctoral Program論 文 要 旨ＴＨＥＳＩＳ ＳＵＭＭＡＲＹ

専攻：
Department of

機械制御システム

学生氏名：Student’s Name

長澤 剛

専攻

申請学位（専攻分野）： 博士
Academic Degree Requested

指導教員（主）：Academic Supervisor(main)

Doctor of（花村

工学克悟）
教授

指導教員（副）：Academic Supervisor(sub)要旨（英文 800 語程度）
Thesis Summary （approx.800 English Words ）The thesis entitled as “Reaction Kinetics and Dynamics on Solid Oxide Fuel Cell Porous Electrodes through Species
Territory Adsorption Model and Active Sites Imaging” consists of six chapters.
In Chapter 1 “Introduction”, background and current status of solid oxide fuel cell (SOFC), which is a promising energy
conversion technology with high efficiency, are reviewed and the main specific targets of the thesis are raised. For
state-of-the-art SOFCs, porous composite electrodes are widely used such as Ni/yttria-stabilized zirconia (YSZ) for anodes orstrontium-doped lanthanum manganite (LSM)/YSZ for cathodes. These electrodes have micro/nano-scale complex structuresconsisting of electron conductors, oxide ion conductors, and pore phases, where chemical species are transported andaccompanied by electrochemical reactions at the triple phase boundary (TPB). The accurate understanding and description of
the electrochemical reactions on porous electrodes are key issues for further development of materials and structural design
to enhance electrodes performance and stability. In this thesis, toward construction of the detailed kinetics and dynamics on
SOFC porous electrodes, analytical reaction model is constructed and imaging technique of active sites is developed.
In Chapter 2 “Species territory adsorption model for hydrogen oxidation in SOFC anode”, analytical model forhydrogen oxidation in the TPB of Ni/oxide ion conductor cermet anode, named as species territory adsorption model, isconstructed. It is assumed that the chemical species are adsorbed within a finite narrow area on Ni or oxide ion conductor
around the TPB. The reaction rate in the anode is controlled by the surface reaction between the adsorbed hydrogen andadsorbed oxygen; all other reactions take place under chemical equilibrium. Based on the reaction model, analyticalexpressions of the current density with respect to oxygen activity and the anode overpotential with respect to current density
can be obtained. The latter can combine the anode overpotential at low- and high-current-density regions, which areconventionally expressed independently. Moreover, it is clarified that the current density asymptotes the limiting value as theoxygen coverage around the TPB approaches unity. The theoretical limitation of current density given here is determined by
the rate constants of surface reactions and the coverage of adsorbed hydrogen on Ni.
In Chapter 3 “Comprehensive analysis of Ni/YSZ anode using species territory adsorption model”, the quantitative
validation of the species territory adsorption model for Ni/YSZ anode is discussed based on the comparison to measured andreported experimental results. By introducing referenced thermodynamic and kinetic parameters predicted by density
functional theory calculations, the model can predict anode overpotential using unknown values of quantities of state foroxygen migration process in YSZ near a TPB, frequency factor for hydrogen oxidation, and effective anode thickness. Theformer two are determined through careful fitting process between the model and experimental results of Ni/YSZ cermet andNi-patterned anodes. This makes it possible to estimate effective anode thickness based on the model, which shows a positive
correlation with temperature in six kinds of Ni/YSZ anodes used in this study and references. In addition, the comparison
between the model and published numerical simulation indicates that the model can predict more precise dependence ofanode overpotential on steam partial pressure than that by Butler-Volmer equation with empirical exchange current density.
In Chapter 4 “Imaging of microstructure-scaled active sites in porous composite cathode”, imaging technique of active
reaction sites in porous electrodes is developed in microstructure scale. A power generation equipment with a nozzle fordirect helium gas impinging jet to the cell is newly prepared to quench an SOFC reaction. The quench performance testshows that the temperature of YSZ electrolyte can be decreased from 830 to 150 ℃ within 1.5 sec, which is in good
agreement with analytical results based on the average Nusselt number of impinging jet heat transfer. Using constructed
quench system and oxygen isotope labeling, active sites for oxygen reduction reaction in LSM/ScSZ porous cathode arevisualized at 800 ℃. From the 18O concentration mappings of the quenched cathode obtained by secondary ion mass
spectroscopy (SIMS) with a spatial resolution of 50 nm, enhanced 18O diffusion into LSM, which is promoted byoverpotential, is observed only near the cathode/electrolyte interface. This result indicates that reaction sites near thecathode/electrolyte interface are more electrochemically active than those at other regions.
In Chapter 5 “Analysis method of oxide ion flux at cathode/electrolyte interface through oxygen isotope labeling”,
SOFC power generation in 18O2 and quench experiment is conducted at 700 ℃ using the methodology developed in Chapter
4. From the analysis of 18O diffusion profiles in YSZ electrolyte, quantitative oxide ion flux incorporated from thecathode/electrolyte interface is estimated. The results indicate that 22~31% of the overall electrochemical reaction occurs at
the cathode/electrolyte interface, while the remaining 69~78% of those proceeds inside the porous cathode.
In Chapter 6 “Conclusions”, the key findings and contributions are summarized and future perspective is presented.
備考 : 論文要旨は、和文 2000 字と英文 300 語を 1 部ずつ提出するか、もしくは英文 800 語を 1 部提出してください。
Note : Thesis Summary should be submitted in either a copy of 2000 Japanese Characters and 300 Words (Engｌish) or 1copy of 800
Words (English).
注意：論文要旨は、東工大リサーチリポジトリ（T2R2）にてインターネット公表されますので、公表可能な範囲の内容で作成してください。
Attention: Thesis Summary will be published on Tokyo Tech Research Repository Website (T2R2).