Development of Methanol Fueled Micro-SOFC System for Mobile Electronic Devices

Abstract

Recently, mobile electronic devices such as mobile phones and laptop computers have been dramatically developed. This development strongly requires high power and long usable power sources. Current Li ion secondary batteries are already insufficient for the requirement, as a result, small mobile electronic devices such as mobile phones and tablets are volumetrically occupied by Li ion battery packs. Micro-SOFCs, which miniaturized by adoption of MEMS fabrication technics, could show high energy density with liquid fuels because liquid fuels such as methanol, ethanol, and compressed butane show significantly high energy density that of Li ion batteries. Liquid fuels can also be fed easily than electronic charging. In addition, generally, power density of SOFCs are higher than other secondary batteries. Therefore, micro-SOFC systems fueled by liquid fuels could be a promising candidate for new power sources. However, for practical application of micro-SOFC systems, some problems mainly due to high temperature operation of SOFCs are still remained. Considering small size and place in mobile electronic devices, outer temperature of micro-SOFC systems should be lower than maximum operating temperature of other electronic circuits: thermal consistency. However, mobile-SOFCs also achieve heat self-supporting for high energy efficiency. Furthermore, micro-SOFC systems have self-start-up function, which heats micro-SOFCs to operating temperature. In other words, thermal design for thermal management is important factor. However, considerations for micro-SOFC systems based on thermal design are not performed well although much effort have been spent for the improvement of cell performances. Therefore, we focused on the development of whole systems based on micro-SOFCs for mobile electronic devices. In previous study, we fabricated a micro-SOFC system consisted of a package with vacuum space for thermal insulation and a gas-liquid heat exchanger as shown in image. A micro-SOFC with micro-heater for self-start-up stored in the package. Wasted heat during operation was led to the gas-heat exchange, and liquid alcohols in the exchanger were boiled to be vapor. Thermal consistency was achieved because the temperature of the exchanger was limited to boiling temperature during vaporization, and boiling temperature of some liquid alcohols were lower than maximum operating temperature of electronic elements in electronic devices. In addition, wasted heat was recycled utilizing vaporized alcohols as the fuel of micro-SOFCs. In our previous study, thermal self-supporting was numerically confirmed to be achieved by recycling of wasted heat. By using this micro-SOFC system, we performed power generation test. At that time, micro-SOFCs were fueled by humidified hydrogen fed from elsewhere, but the gas-liquid heat exchanger was fulfilled with ethanol and methanol solutions. In the test at the operating temperature of 300oC, outer surface temperature of the thermal insulation package, and the exchanger were limited to be 85oC. The result confirmed that thermal consistency was achieved by this system. Hence, we tried to generate utilizing methanol solutions as liquid fuel by equipment package in this system to improve of thermal self-supporting. In this presentation, we report results of the generation utilizing methanol solutions. Figure 1