Current Status of NEDO Project on Durability/Reliability of Solid Oxide Fuel Cell Stacks/Systems

Abstract

Fundamental investigations on the durability and reliability of SOFC modules/stacks have been started in one of the new NEDO SOFC projects from 2008 to 2013. The main target is to assure long term durability in the range of 40,000 h and reliability during 250 cycles of start and stop operation; for this purpose, we need to adopt accelerated methods for establishing durability and reliability. This project consists of industrial developers, public research institutes and universities. Investigations will be made using real stacks, real cells and single model cells to facilitate cooperation among the three parties. Industrial developers will focus on the test of durability and reliability using real stacks, whereas universities and research institutes will focus on the fundamental understanding of degradation using various kinds of cells from different approaches based on thermodynamic, chemical, and mechanical aspects. Since three phase boundaries are important in understanding of degradation in electrochemical performance, special emphasis will be paid on this research topic. Prediction of life is also an important topic in this project.

Achievements of NEDO Projects on SOFC Durability

“…Difference in Degradation Behavior Between Sulfur and Chromium Poisoning One interesting feature observed in cathode degradations is that the sulfur poisoning sensitively depends on stack details, whereas the chromium poisoning seems to be overcome by decreasing the Cr volatilization due to coating on metal interconnects / other components. Chemical reactions for two poisonings are written as follows: SrO(in LSCF) + SO 2 + 0.5O 2 (g) = SrSO 4 (s) [7] SrO(in LSCF) + CrO 2 (OH) 2 = SrCrO 4 (s) + H 2 O(g) [8] Differences can be seen in chemical forms of impurities; for chromium, CrO 2 (OH) 2 contains the water component, whereas oxygen is needed for sulfur. These differences can explain why SrSO 4 is formed at the TPB vicinity where O ad is available, whereas SrCrO 4 is formed on the surface layer of the cathode layer where the water vapor becomes smaller compared with that inside cathode layer.…”

“…The New Energy and Industrial Technology Development Organization (NEDO) is conducting the durability project for three stack groups having different histories within past NEDO durability/reliability projects (1)(2)(3)(4); the first stack group (Mitsubishi Hitachi Power System (MHPS) and Kyocera) has been already well investigated within cooperation among stack developers, research institutes (National Institute of Advanced Science and Technology (AIST), Central Research Institute of Electric Power Industry (CRIEPI)) and universities (Kyushu University, Kyoto University, The University of Tokyo, and Tohoku University) and successfully improved their degradation after 10-year cooperation; the second group (TOTO) spent two-year cooperation with success in clarifying the major degradation as Cr poisoning; and the third group consists of newcomers (NGK SPARK PLUG (NTK), NGK INSULATORS (NGK), Murata manufacturing and recently DENSO) with a focus on clarifying major degradation appearing in 3000-5000 h. Fundamental approaches with SIMS, FIB-SEM, STEM adopted previously are also applied for these stacks in the same manner (5)(6)(7)(8)(9)(10)(11)(12). In addition to the stack performance analyses by CRIEPI (13), Tokyo Gas contributes to thermal cycle tests from application viewpoint (14).…”

Comparative Study on Performance Stability of Ni–Oxide Cermet Anodes under Humidified Atmospheres in Solid Oxide Fuel Cells

“…For example, recently, we have reported the correlation between the performance and microstructural change of Ni-(Sc 2 O 3 ) 0.10 (CeO 2 ) 0.01 (ZrO 2 ) 0.89 anode in the cathodesupported tubular cells subjected to long term operation. 1,2 The nickel particles were excluded significantly from the anode/electrolyte interface to 4 μm-thick range after 6500 h of the operation, resulting in the significant reduction in performance and TPB length. It is thus of importance to evaluate the microstructural change in nickel particles during discharge.…”

Achievements of NEDO Durability Projects on SOFC Stacks in the Light of Physicochemical Mechanisms

“…The NEDO (New Energy and Industrial Technology Development Organization) projects on durability/reliability of SOFC stacks have been performed for 13 years as three successive projects initiated from 2005FY ; this has been made as cooperated investigations among stack developers, public institutes, namely, AIST (National Institute of Advanced Industrial Science and Technology) and CRIEPI (Central Research Institute for Electric Power Industries) and academic groups in UTokyo (The University of Tokyo), KyotoU (Kyoto University),KyushuU (Kyushu University) and TohokuU (Tohoku University). The stack degradation issues have been extracted from the stack performance tests made by CRIEPI on respective stacks with the same technique of separating measured voltage losses into several different contributions and their degradation rates and also by Tokyo Gas on thermal cycle characteristics .…”