A solid oxide fuel cell (SOFC) is a fuel cell that can operate at high temperature. By applying its high-temperature exhaust heat to gas turbine (GT) combined-cycle power generation, an extremely high-efficiency thermal power system can be constructed, with a power generation efficiency of up to 70%. Mitsubishi Heavy Industries, Ltd. (MHI) is one of the first companies to focus on the potential of the SOFC as a component of large-scale power generation systems and has promoted both element and system development since the 1980s. New 250kW-class SOFC-MGT Hybrid System has been under trial operation since November 2012.

Mitsubishi Heavy Industries (MHI) has developed SOFC with tubular type cell stack since 1984. In this study, we report the current status toward commercialization of SOFC-GTCC power generation system at MHI. To Redox robustness of a cell stack, the sintering characteristics of interconnect was improved. To improve durability of cell stack, long-term change of the electrochemical characteristics had been measured, and analyzed the interface of cathode and electrolyte by SIMS. For compact module, the packing density of the cell stack was increased from 400 to 700 stack/m2, and confirmed I-V characteristics and the temperature distribution of improved module. The generation performance of improved module is roughly comparable to that of conventional type module, and the temperature distribution is also roughly agreement of simulation result.

For large-scale SOFC power generation systems, a shorter start-up time of SOFC cell stacks with relatively large heat capacity is one of the most important technological issues to determine the flexibility in SOFC system operation. In this study, start-up procedures have been examined to shorten the start-up time period. The conventional heating procedure using pre-heated hot air and self-heating by SOFC operation at low temperatures had a difficulty to shorten the start-up time period because of the limitation in power generation at lower temperatures. In this study, as an alternative start-up procedure, catalytic combustion at the SOFC cathodes is, for the first time, demonstrated to be useful on the system level. The applicability of the catalytic combustion to shorten the start-up time period has been verified numerically as well as experimentally by using a large-scale cell stack cartridge. This unique start-up procedure enables to operate SOFCbased large-scale power generation systems.

Mitsubishi Heavy Industries, Ltd. (MHI) and Electric Power Development Co.,Ltd. (JPOWER) started SOFC module development in collaboration in 1991. Since 2001 we have focused on improvement on SOFC module aiming for high reliability and lower cost. The 5kW-class Cartridge test with 104 cell-tubes was successfully accomplished in 2003. We also executed a dynamic simulation and thermal fluid analysis of improved SOFC module and control system development under atmospheric pressure. In 2006, we have succeeded in the operation of 25kW-class sub- module that will be a unit of highly scalable SOFC system. This module dose not need heating support to maintain the operating temperature, because the fuel exhaust gas from the SOFC module is burned in the combustor and used for heating supply air to SOFC module.

Pressurized solid oxide fuel cells (SOFCs) using a gas turbine for the bottoming cycle convert energy very efficiently. The performance of a tubular SOFC made by a plasma spray coating method was measured at levels of pressure between 0.1 and 0.59 MPa. The cell voltage increased with the operating pressure. Moreover, it was determined that polarization decreased under pressurization, using the current interruption. Anode performance was also measured with a reference electrode. The estimated concentration overvoltage from the measurement of permeability was used to estimate the activation overvoltage of the anode. The anode activation overvoltage was affected by the partial pressure of H 2 O instead than that of H 2 .

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