Micro Power Generation from Micro Fuel Cell Combined with Micro Methanol Reformer

Abstract

1.1 Background Thanks to the breakthroughs in microfabrication technologies, numerous concepts of microsystems including micro aerial vehicles, microbots, and nanosatellites have been proposed. Contrary to ordinary electronic devices, these microsystems perform mechanical work and require the extended operation. As their functions are getting complex and advanced, their energy consumption is also increasing exponentially. In order to activate these microsystems, a high density power source in a small scale is required. However, present portable devices still extract power from existing batteries. The energy density of the current batteries is too low to support these microsystems (Holladay et al., 2004). Therefore, a new micro power source is essential for the successful development of new microsystems. Various concepts for micro power generations have been introduced such as micro engines, micro gas turbines, thermoelectric generators combined with a micro combustor, and micro fuel cells. All of these concepts extract energy from a chemical fuel that have energy density much greater than that of the existing batteries. The first challenge to micro power source was the miniaturization of conventional heat engines. However, the development of micro heat engine reached a deadlock due to the difficulties of microfabrication and realization of miniaturized fast moving components and kinematics‘ mechanism to generate power in micro scale. Micro fuel cells have drawn attention as a primary candidate for a micro power source due to its distinctive merits that are absence of moving parts and high efficiencies. The fuel cell is an electrochemical device that directly converts chemical energy to electric energy. Due to its different energy conversion path, the fuel cell has high thermal efficiency compared to the heat engines. The energy density of the fuel cell is higher than that of the existing batteries because it uses a chemical fuel such as hydrogen (Nguyen & Chan, 2006). There are several types of fuel cell as summarized in Table 1 (O’Hayre et al., 2006), such as polymer electrolyte membrane fuel cell (PEMFC), phosphoric acid fuel cell (PAFC), alkaline fuel cell (AFC), molten carbon fuel cell (MCFC), and solid oxide fuel cell (SOFC). Of these fuel cells, PEMFC is suitable to a micro power device due to its low operating temperature and solid phase of electrolyte. Direct methanol fuel cell (DMFC) is a kind of PEMFC except that it directly uses methanol instead of hydrogen as a fuel. Formic acid, chemical hydrides, and other alcohols can be used as a direct fuel.