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.

No abstract

Reduction of global carbon dioxide emissions is one of the most critical challenges for realizing sustainable society. In order to reduce carbon dioxide emissions, energy efficiency must be improved. Waste heat recovery with external combustion engine is expected to be one of the promising technologies for efficient energy utilization. However, the temperature of waste heat is getting lower with the progress of energy technologies. For example, in Japan which is known as one of the most energy-efficient countries in the world with advanced technologies such as cogeneration and hybrid automobiles, total amount of disposed heat below 300 °C is as much as 10% of the total amount of primary energy supply. Conventional external combustion engines, such as Stirling, thermoacoustic 1 and steam engines 2 show significant decrease in their efficiency at low temperatures below 300 °C. Utilization of high-temperature heat sources, however, requires relatively expensive materials and advanced processing technologies to achieve high reliability. In order to overcome these issues, a novel liquid-piston steam engine is developed, which achieves high efficiency as well as high reliability and low cost using low temperature heat below 300 °C. Present liquid-piston steam engine demonstrated a thermal efficiency of 12.7% at a heating temperature of 270 °C and a cooling temperature of 80 °C, which was about 40% of the Carnot efficiency operating at same temperatures. The liquid-piston steam engine operated even with wet steam, without requiring steam to be superheated. This low temperature operation yielded relatively little deformation of components, which leads to high reliability of the engine. In addition, present liquid piston engine can achieve both high efficiency and low cost compared to conventional external combustion engines, because it has only one moving part whereas both Stirling and Rankin engines have at least two moving parts.. The developed liquid piston engine is thus expected to possess large possibility of recovering energy from waste heat.

No abstract

A novel liquid-piston steam engine which can achieve high efficiency at low temperature region of T < 300 °C as well as high reliability and low cost is developed. In this study unsteady-local inner wall temperature is measured to clarify the phase change phenomena in the heating section of the liquid piston steam engine to improve the accuracy of the design method. Thin Platinum film temperature sensor with 1 kHz response has been deposited by sputtering on the heating surface of the hollow plane type liquid piston steam engine. Nucleate boiling begins when the liquid piston enters the heating section, and it terminates when the vapor pressure approaches saturation pressure. The evaporation of the liquid film continues after the liquid piston leaves out from the heating section. Vaporization model using both the mechanism of liquid film evaporation and nucleate boiling is valid. On the other hand, fluctuations of pressure and heat flux are observed in the experiment when liquid piston enters the heating section. In order to predict these fluctuations, it is necessary to consider the effect of steam bubbles mixed inside the liquid piston.