Low-Temperature Operating Micro Solid Oxide Fuel Cells with Perovskite-type Proton Conductors
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Low-Temperature Operating Micro Solid Oxide Fuel Cells with Perovskite-type Proton Conductors Hiroo Yugami, Kensuke Kubota, Yu Inagaki, Fumitada Iguchi, Shuji Tanaka, Noriko Sata, and Masayoshi Esashi Graduate School of Engineering, Tohoku University, Aoba 6-6-01, Aramaki, Aoba-ku, 980-8579, Sendai, Japan. ABSTRACT Micro-solid oxide fuel cells (Micro-SOFCs) with yttrium-doped barium zirconate (BZY) and strontium and cobalt-doped lanthanum scandate (LSScCo) electrolytes were fabricated for low-temperature operation at 300 °C. The micro-SOFC with a BZY electrolyte could operate at 300 °C with an open circuit voltage (OCV) of 1.08 V and a maximum power density of 2.8 mW/cm2. The micro-SOFC with a LSScCo electrolyte could operate at 370 °C; its OCV was about 0.8 V, and its maximum power density was 0.6 mW/cm2. Electrochemical impedance spectroscopy revealed that the electrolyte resistance in both the micro-SOFCs was lower than 0.1 Ωcm2, and almost all of the resistance was due to anode and cathode reactions. Although the obtained maximum power density was not sufficient for practical applications, improvement of electrodes will make these micro-SOFCs promising candidates for power sources of mobile electronic devices. INTRODUCTION Mobile electronic devices such as laptop personal computers and smart-phones have been developed and widely popularized in the past decade. In accordance with this development, our lifestyle has been rapidly changing, and in the future, ubiquitous computing will be realized. Ubiquitous computing strongly requires new power sources that provide high power density and long life for mobile electronic devices. Micro-solid oxide fuel cells (micro-SOFCs) are promising candidates for such power sources and have attracted many researchers [1-6]. MicroSOFCs are based on the concept of minimization of the volume of SOFCs and maximization of the volume of liquid fuels such as methanol and liquid butane. Because the energy density of liquid fuels is much higher than that of Li-ion batteries, micro-SOFCs provide longer life and higher power density than Li-ion batteries. To achieve the smallest size, fabrication techniques have been appropriated from the realm of micro-engineering and mechanical systems (MEMS). Recently, power densities of more than 100 mW/cm2 at temperatures above 400 °C have been achieved for micro-SOFCs [1,6]. This value is quite promising for the power sources. However, packaging as power sources, which operate independently, requires reducing operating temperatures to below 300 °C for assembly and thermal management. At 300 °C, yttriumstabilized zirconia (YSZ), which is the most common electrolyte material in micro-SOFCs, does not exhibit sufficient conductivity. Therefore, micro-SOFCs with YSZ electrolytes lose their design flexibility. To use YSZ at such low temperatures, it is necessary to reduce the thickness of the electrolyte to less than 100 nm, which is too thin to ensure mechanical stability. Hence, other electrolyte materials that exhibit high conductivity at 300 °C should b
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