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Next Generation Micro-fuel Cells: Fuel Storage, Control, and Power Generation
| Content Provider | Semantic Scholar |
|---|---|
| Author | Shannon, Mark A. |
| Copyright Year | 2009 |
| Abstract | The quest is on for high power and energy density power sources at ever smaller sizes for applications ranging from on-chip sensors to insertable pharma-delivery to flying microrobots. Fuel cells have often been touted as a next generation power source that can deliver both high power and energy density (in part because they do not have to carry the oxidizer on-board, using the oxygen in air). However, shrinking fuels to the microscale is fraught with problems. Unlike batteries that carry both redox reactants whose products remained within the battery, and which do not need ancillary devices (save for the container and electrodes), fuel cells additionally need a means to supply the fuel, oxygen, exhaust the products, and control the hydration level throughout the device. Moreover, fuel cells need a means to control the fuel and oxygen delivery with changes in electrical load, which often use elaborate mechanical and electrical control systems. Therefore, it is difficult for many fuel cells to handle huge changes in load. The main problems for microscale fuel cells, therefore, are how to supply fuel with high energy density, without using large ancillary systems that consume significant amounts of power, and for the fuel cell to respond to large changes in electrical load, in varying ambient temperatures and humidities. In spite of these challenges, proton exchange membrane (PEM) micro-fuel cells have now reached less than 10 microliters in total volume, 1 as shown in Figure 1, including the fuel, PEM, and ancillary systems, with instantaneous peak power density of 360 W/l and an energy density over 250 W·hr/l, and are headed to instantaneous power density higher than 1000 W/l and an energy density above 500 W·hr/l. These fuel cells also have a dynamic range of over three orders of magnitude of operation from micro-Watts (steady-state) to milli-Watts (steady-state), with 10 mW instantaneous peak power. However, to achieve this dynamic range, energy, and power densities, the membrane electrode assembly, control system, and fuel storage all have to be designed and optimized to maximize fuel storage, without having large fuel and power control systems, and without using parasitic power. The fuel that is used in these micro-fuel cells are metal hydrides (such CaH2, LiAlH4, NaBH4, etc.) with water supplied either through a separate chamber or through the air to generate hydrogen on contact with the hydride, with total possible energy densities near or over 700 W·hr/l accounting for stored water as shown in Table 1, and over a 1000 W·hr/l with scavenging water from the air. 2,3,4 However, the hydrides will react nearly instantaneously with water in any form to produce hydrogen gas, regardless of its pressure, which can cause the fuel cell to over pressurize and burst. Therefore the amount of water brought into contact |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://cap.ee.ic.ac.uk/~pdm97/powermems/2009/pdfs/papers/001_9001.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
