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Achievements of NEDO durability projects on SOFC mode are summarized with a focus on the physicochemical mechanisms characterized by diffusion properties of cell components and chemical reactions of cell components with gaseous impurities. Ni sintering and depletion including impurity (P, B, S) effects have been examined in terms of the surface/interface energies of Ni/oxide cermet anodes. The conductivity degradation due to the transformation of the cubic YSZ electrolyte was found to be characterized in terms of two time constants for the reductive and the oxidative regions to be determined by the Y‐diffusivity and its enhancement on NiO internal reduction in YSZ, while observed gaps in conductivity degradation behavior between stacks and button cells were ascribed to differences in those physicochemical properties involved, namely cation diffusion and kinetics associated with NiO internal reduction. The cathode performance degradation due to sulfur poisoning exhibits a variety of dependences on the microstructure (dense or porous) of doped‐ceria interlayers, the thickness of YSZ electrolyte and the humidity in the anode atmosphere, suggesting effects of protons in the cathode vicinity and the SrO activity changes during fabrication the LSCF/GDC/YSZ multilayers. Some defect chemical considerations were made on how such defects are affected by fabrication processes.

Solid oxide fuel cell (SOFC) triple combined cycle system, integrated with gas turbine (GT) and steam turbine (ST), is an ultimate fossil fuel electric power generation system with very high efficiency. In 2008, Mitsubishi Heavy Industries, Ltd. (MHI) operated the 200 kW-class SOFC micro gas turbine (MGT) hybrid system under commission of New Energy and Industrial Technology Development Organization (NEDO) and we could demonstrate 52.1%-LHV net power generation efficiency. Based on the successful achievement, MHI developed a more compact 250 kW-class SOFC-MGT hybrid system for the purpose of utilization of a hybrid system in the NEDO project scheduled from fiscal 2011 to 2012. Furthermore, we have started a development of fundamental technologies of SOFC-GT-ST triple combined cycle system that aims to achieve more than 70% of power generation efficiency. In this paper, latest results on the development of SOFC and the systems are described.

Solid oxide fuel cell (SOFC) triple combined cycle system, integrated with gas turbine (GT) and steam turbine (ST), is an ultimate fossil fuel electric power generation system with very high efficiency. Mitsubishi Hitachi Power Systems, Ltd. (MHPS) has been developing for commercialization of an SOFC-micro gas turbine (MGT) system from several hundred kW to several MW class. Recently prototype of a 250 kW class SOFC-MGT hybrid system was operated at Tokyo Gas Senju Techno Station. This system was stable without voltage degradation under operating 4,100 hours. At the same time, we have started the development of fundamental technologies for realization of SOFC-Gas Turbine (GT)-Steam Turbine (ST) triple combined cycle system that aims to achieve more than 70% of power generation efficiency. In this paper, recent progress of the SOFC-micro gas turbine (MGT) hybrid system and development of triple combined cycle system are described.

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