Current Status of Rapid Evaluation of Durability of Six SOFC Stacks within Nedo Project

Abstract

Six solid oxide fuel cell stacks manufactured by Kyocera, Mitsubishi Hitachi Power Systems (MHPS), TOTO, NGK SPARK PLUG, NGK INSULATORS, and Murata Manufacturing have been investigated to identify their performance degradation behavior, extract major sources of degradations, clarify the degradation mechanism, and predict the time dependent contributions of such degradations to life time. Stack performance was analyzed into several contributions, and in addition to identification of respective degradation rates, an interesting correlation between the overpotential values and the ohmic losses has been extracted. Respective degradation issues have been examined experimentally with SIMS, FIB-SEM, STEM and described as key simulation matters to predict the long life up to 90,000 h. Emphases have been placed on degradation of cathodes with Cr or S; to ensure the appropriateness for overcoming such poisoning effects, care was exercised to measure the impurity level after long term operations in various environments. For simulation, focus was made to overcome some gaps between knowledge on stacks and on single (or buttons) cells appearing in several degradations.

Recent Achievements of NEDO Durability Project with an Emphasis on Correlation Between Cathode Overpotential and Ohmic Loss

“…The present, third project started in 2013FY and spent already three years to extract further degradation issues from stack behaviors. In the first half of period, new features appear ; a remarkable feature is that rather significant degradations have been observed in some stacks and curiously enough these degradations appear in cathode overpotential, η (CA), as well as in ohmic loss, Δ V = R 0 I . To understand such behaviors, new insights have been made on stack behaviors.…”

Materials selection and R&D for commercial fuel cells

“…Further improvements from the experience of over 6.5 million operating hours were in the pipeline. Extrapolations of degradation rates for residential SOFC systems in the Japanese Enefarm Market Introduction Project indicate stack lives of >60 000 h …”

Accelerated Stress Tests for Solid Oxide Cells via Artificial Aging of the Fuel Electrode

“…On the cell and stack levels, there are numerous studies on the degradation of cell components with emphasis on electrodes, electrolytes, and interconnects [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. However, the picture is more complicated, since the degradation processes are related to the cell/stack design, operating conditions, geometrical and technological factors, quality of the raw materials, precision of the instrumentation, preconditioning, testing protocols, and predictable and unpredictable failures [25][26][27][28][29]. The "domino effect," in which one degradation factor activates other degradation mechanisms, cannot be avoided [30].…”