Solid oxide fuel cells (SOFCs) have been regarded as efficient generation, combined heat and power (CHP), and hybrid systems. SOFC CHP systems for household application with an output of 700 W have been recently commercialized in Japan. The development of small household SOFC systems and generation units with a few 100 kW are also close to commercialization in the United States and Europe. An SOFC-gas turbine combined system has been successfully operated with high generation efficiency in Japan. For variety of commercial applications of SOFC in the future, durability and reliability of the SOFC stacks should be further assured. Development of SOFC units for mobile and portable applications has been carried out based on their excellent fuel flexibility and efficiency. In this overview, current status and future prospect of SOFC have been summarized.

Development of solid oxide fuel cells (SOFCs) using LaGaO₃ based oxide thin film was introduced. Preparation of LaGaO₃ electrolyte film was studied by using two methods; one is conventional screen printing method followed by sintering, and the other is pulsed laser deposition (PLD) method. In case of conventional wet process, by using Ti sintering agent for La doped Ce0₂ as a buffer layer between LaGaO₂ and NiO, sintering of La doped Ce0₂ was achieved at 1300℃.The cell prepared by wet process shows reasonable power density of ca. 1.0W/cm² at 700℃. On the other hand, porous Ni-Fe bimetal substrate was successfully obtained by PLD method. Introduction of Sm_0.5Sr_0.5Co0₃/Ce_0.8Sm_0.20₂ double columnar is effective for high power density of SOFC and the maximum power density of 2.2 and 0.15 W/cm² were achieved at 700 and 400℃, respectively.

Mechanical reliabilities of solid oxide fuel cells (SOFCs) have been evaluated on the basis of physicochemical and mechanical properties of the constituent materials at elevated temper

atures. Mechanical properties at elevated temperatures under controlled atmospheres were measured by a resonance method and small-punch or four point bending tests. Oxygen potential profile and mechanical stress distribution in a cell were evaluated by a finite element method considering the microstructures of the electrode layers using a homogenization technique. Ionic/electronic mixed conductivity of the materials as well as oxygen nonstoichiometry were included in the calculation so that the oxygen potential profile inside the solid phases and then stress distribution were evaluated under steady state and transient conditions. Experimental techniques to verify the results of the simulations, e.g. in-situ Raman microscopy, cell deformation analysis, or acoustic emission measurements were developed depending on the design of the cell stack.

Abstract: The degradation and durability of SOFC stacks have been a major concern for commercialization. Many degradation factors should be taken into account for assuring the stability and the durability of cells, stacks and systems. To solve the degradation issues in cell and stack, the national project, “Development of system and elemental technology for SOFCs/ Fundamental research for improvement of durability” has been started in 2008 FY. In this project, the degradation factors were investigated in several cell-stacks and durability was improved after modification of the stacks. The degradation rates so far are about 0.3%/1000h or even better by the modification of materials, cell structures, and stack designs. Here we show a recent progress of stack durability and degradation mechanism. In addition, analyses of the degradation mechanism are shown in relation to the impurity condensation at active sites of electrode. Secondary ion mass spectrometry (SIMS) technique has been applied to detect the concentration levels of several elements (in the order of ppm level) at active components. Possible degradation mechanisms were suggested based on the observed impurity data.

Chemical degradation of SOFCs has been systematically analyzed for extrinsic cases caused by various impurities and for intrinsic cases caused by interdiffusion associated with transport phenomena as well as by thermal cycling. Degradation phenomena are classified, which can be used to minimize performance degradation of SOFC systems. Future perspectives including academia-industry collaborations are discussed.

Abstract: We have been developing varied types of fuel cell systems using the petroleum as the fuel since 1980’s. In October 2011, we launched residential SOFC cogeneration system powered by LPG and LNG based natural gas (category 13A).

Abstract: Since 2002, TOTO Ltd. has been developing anode support type microtubular cell stack modules that work at lower temperatures as power generating systems with capacities ranging from tens to hundreds of watts. Using lanthanum gallate thin film electrolyte, we have successfully developed a cell stack that is capable of generating power at temperatures of 500°C-700°C. This cell stack has been confirmed to have high tolerance against rapid thermal shock. TOTO Ltd. and Noritz Corp. have been jointly developing 700W residential SOFC cogeneration system. Since 2008, we have taken part in the “Demonstrative Research on Solid Oxide Fuel Cells Project” conducted by New Energy Foundation(NEF) and New Energy and Industrial Technology Development Organization(NEDO). We had installed 2 units in 2008 and 6 units in 2009. In this paper, the development statuses of SOFC system and demonstration result are reported.

Abstract: SOFC (Solid Oxide Fuel Cell) Tripe Combined Cycle System, combined with Gas turbine (GT) and Steam turbine (ST), is an ultimate fossil power generation system with extremely high efficiency. Mitsubishi Heavy Industries, Ltd. (MHI) has been developing SOFC from fundamental to system integration technologies during decades. In 2008, MHI operated the 200kW-class SOFC-Micro Gas Turbine (MGT) combined cycle system, under commission of New Energy and Industrial Technology Development Organization (NEDO), with the successful result of 52.1%- LHV net power generation efficiency. Now MHI is fabricating improved SOFC-MGT combined cycle system for demonstration, with 250kW-class power output and 55%-LHV power generation efficiency under NEDO project. MHI continues to develop SOFC for practical power systems. Now MHI is ready to proceed torward SOFC-GT-ST Triple Combined Cycle System as a practical fossil power generation system. In this article, MHI’s recent development results on development of SOFC and power systems are described.

Abstract: A current status is surveyed of research and development of solid oxide fuel cells (SOFCs) in overseas countries. Several cases are presented concerning national subsidies for SOFCs in America and Europe, as well as R&D or deployment activities of SOFC manufacturers. These examples lead us to the idea that an activity towards SOFC deployment is glowing not only in Japan but also in the world.

In order to establish the design methodology of the hydrogen pipeline network, the design concept of the pipeline diameter was examined. Firstly, the flow experiments of hydrogen were conducted to verify the applicability of the general equation to calculate the relationship between flow rate and pressure loss in a pipe. By using the equation, the diameter of the hydrogen pipelines was determined under some virtual target conditions of flow rate or calorific value and was compared with that of typical city gas in Japan. As a result, it was suggested that the diameter of the hydrogen pipelines is equivalent to that of city gas in case of transporting the same calorific value

This paper describes an analysis of a consumer survey on environmentally friendly vehicles including hybrid vehicles, electric vehicles and fuel cell vehicles. The survey was conducted for those who had already purchased or considered purchasing these vehicles in order to clarify the reasons why they had chosen environmentally friendly vehicles. The images for the vehicles were also investigated and compared with the reasons. The results of the survey suggest that, even if the consumers are sharing good images for environmentally friendly vehicle, it is not easy for the vehicles to become popular in the future unless consumers feel safe to use them. Especially the number of refueling station is important for users, and it is necessary to introduce at least 1/10 of that of the existing gas stations.