The Former Main Result and Prospect for the Next 10 Years

　The main task is to act as the project leader for the following project:  “Basic study on rapid evaluation method of SOFC durability,” in “Technology development for SOFC commercialization promotion,” conducted by the New Energy and Industrial Technology Development (NEDO).  This is the cooperation project among industrial stack makers, public institutes and universities. The target is to achieve evaluation technique to ensure durability of 90,000 h and apply it to real stacks to help to improve their durability.  This includes investigations on materials properties and characteristics, electrochemical cell performance and stack behavior and particular focusses will be paid on materials compatibility (chemical and mechanical),   clarification of degradation mechanism, and simulation technology for predicting life time.  On the other hand, the stack performance is investigated in details to separate into several contributions to the voltage lowering.  The project leader has to make efforts in balancing between such experiments and simulations and in concentrating all efforts to improve durability of stacks and to predict their life time.
　
　High temperature thermodynamics is quite strong in evaluate the stability of interfaces between dissimilar materials.  This can be applied to interfaces issues in the low temperature electrochemical devices.  To do so, applications should be made for various cases to clarify common features and differences between high temperature chemistry and low temperature chemistry.

　In addition to deepen the understanding of solid oxide fuel cell materials, materials issues and particularly interface issues in other electrochemical devices or energy convertors are hoped to be investigated from the same point of view.

Recent 5 major papers

• H. Yokokawa, T. Horita, K. Yamaji, H. Kishimoto, T. Yamamoto, M. Yoshikawa, Y. Mugikura, K. Tomida, 　“Chromium Poisoning of LaMnO₃-Based Cathode within Generalized Approach,” Fuel Cells, 13(4), 526-535 (2013)　Chromium poisoning of the manganite-based cathodes in the Segment-in-series cells was investigated in details. Difference from other type of chromium poisoning in cathodes having other microstructure and materials has been clarified.  This cathodes also meet technological requirements as parts of hybrid systems. 　

• Jan Hayd, Harumi Yokokawa, Ellen Iverse-Tiffee, “Hetero-Interface at Nanoscaled (La,Sr)CoO_3-δ Thin-Film Cathode Enhancing Oxygen Surface Exchange, J. Electrochem. Soc. 160(4), F351-F359 (2013)　About LSC-based cathodes to be used at 600°C, thermodynamic calculations were made to clarify that the reducing atmosphere during fabrication process helps to prepare nano-scale interface between LSC and (LS)2CoO4 phases. 　
• H. Yokokawa, T. Horita, K. Yamaji, H. Kishimoto, M. E. Brito, 　“Degradation of SOFC Cell/Stack Performance in Relation to Materials Deterioration,” 　J. Korean Ceramic Society 49(1), 11-18 (2012)　Detailed description was made on results of NEDO durability/reliability projects with emphases on the clarification of degradation mechanism of real stacks. 　
• Harumi Yokokawa, Katsuhiko Yamaji, M. E. Brito, Haruo Kishimoto, and Teruhisa Horita,　 “General Considerations on Degradation of SOFC Anodes and Cathodes to Impurities in Gases,” J. Power Sources 196(17), 7070-7075 (2011)　Degradations of real cells/stacks due to gaseous impurities are generally considered to treat simple cases as well as complicated one.  In particular, emphasis was placed on secondary electrochemical reactions involved with impurities; it should be important to know how volatilization and condensation of impurities can occur as parts of electrochemical reactions. 　
• H. Yokokawa, H. Tu, B. Iwanschitz, A. Mai,　 “Fundamental Mechanisms Limiting Solid Oxide Fuel Cell Durability,”　 J. Power Sources 182(2), 400-412 (2008)　On the basis of the presentation and discussion in the international workshop on degradations, general review was made on experimental and theoretical investigations on what kind of factors are related to degradations.  Direction of the future investigations on degradation is presented.　

Current research topics (4~5 topics)

larification of degradation mechanism of solid oxide fuel cells stacks and
　　prediction of long term durability

Thermodynamic considerations on lithium batteries materials

Thermodynamic considerations on SOFC and SOEC

Thermodynamic database and its utilization in materials science