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Institute for Reliability and Microintegration IZM in Germany have developed a micro PEM fuel cell system, which is only a few cm 3 in volume and achieves a significantly higher power density than batteries. The work was recognized by the presentation of the Bronze Award at the recent f-cell 2005 conference in Stuttgart.
The technology developed at IZM is based on wafer-level and foil technologies, and is protected by several patent applications. Although a silicon wafer is used as the carrier substrate during production, the micro fuel cell consists of polymer and metal foils. Using proven industrial processes offers a route to economical production, such as roll-to-roll processing.
'The planar micro fuel cell developed by us is composed of three components,' explains Dr-Ing Robert Hahn, group leader at IZM, who coordinated the micro fuel cell development. 'A microstructured flow-field, i.e. the lower foil on the anode side, serves to feed and distribute the fuel. At the same time it generates an electric current. A perforated and similarly microstructured current collector foil regulates the gas exchange on the cathode side as well as the current collection.'
A commercial MEA is used between the two foils. This is divided into isolated regions for cells lying next to each other. The microstructuring of the current collectors means that further gas diffusion layers are not required. Sealing and contacting are achieved using screen printing and dispensing techniques.
Demonstration units of the planar, airbreathing PEM fuel cell are about 1 cm 2 in size and, in continuous operation with hydrogen, produce a stable power density of 80 mW/cm 2 , and up to twice that in ideal conditions. Three single cells are connected into series, to produce a total voltage of 1.5 V. This is sufficient to replace button-type batteries, for example. The use of foil technologies means that these fuel cells can be easily integrated into the surface of electronic devices.
IZM is investigating two options for supplying fuel. The first is hydrogen generation using inorganic materials such as zinc and potassium hydroxide, present in normal alkaline batteries. IZM is working with such a button cell from Varta Microbattery GmbH, optimized for combination with the micro fuel cell. This approach achieves more than twice the energy output of an equivalent-size AAA battery, and almost double that of Li-ion batteries. It also means
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