New trend of miniature fuel cells

This chapter introduces general overviews of miniature fuel cells and discusses theirfascinating application potentiality. In the modern world, development of power sourcesis necessary for fulfilling our demands such as for the realization and improvement ofcellular phones and electric vehicles. The development is unfortunately slower than thatof devices needing them, and such slowness has been one of the critical issues for thepractical application of the devices [1]. This scenario holds true for "micro-devices", e.g.,micro-sensors and lab-on-a-chip, whose widespread application is going to change ourworld in various aspects of life. For example, micro-thermometers and pH sensors are ofgreat use for health monitoring of human beings and animals. Lab-on-a-chip is a kind oflaboratories or plants integrated on a small chip, and, for example, can synthesize andanalyze at any place on demand. Such micro-devices inevitably require micro-powersources, e.g., micro-batteries, micro-solar cells and micro-fuel cells. Of these powersources, micro-fuel cells are attractive in terms of their possible operation as long as fueland oxidant are supplied.Such a tiny fuel cell was for the first time fabricated using microfabricationtechniques for downsizing conventional polymer electrolyte fuel cells in 2000, then,numerous research works have been reported. Since optimum size and design of microfuelcells are considered to be dependent on the application of choice, our research grouphas focused on a monolithic design consisting of microchannels of submilimeter size,which is suitable for on-chip application, and named the innovative fuel cells as "on-chipfuel cells". The fuel cells were first fabricated on Si wafers, and later, on flexiblepolymeric films, whose bendable feature overcame the most troubling aspect ofminiaturized devices, i.e., brittleness and expensiveness. The cell operates on alcohol solutions, such as ethanol and methanol, which are supplied just by dropping on the end of the microchannel without using pumps. Since their power was more than a few μW, this device can probably be used as power sources for micro-sensors as illustrated in Figure 1. On the basis of simulation results, the performance may potentially be improved to over 100 μW by increasing the effective surface areas of catalysts to a level comparable with general methanol fuel cells.If successful, such performance enhancements would position the on-chip fuel cell as a viable candidate for future micro-devices, and point to promising directions for fuel cell development efforts.