Abstract
Portable fuel cell systems consist of three essential parts: the fuel cell stack, the fuel storage and the balance of plant (BOP) which contains all required peripheral components. Scaling down fuel cell systems to smaller dimensions in the power range of 1 mW to 1 W currently leads to an increased volume fraction of the peripheral components. Consequently it is necessary to forego peripheral components in small systems and develop passive systems. Furthermore fuel storage is a challenging issue for portable micro fuel cell systems. Common approaches for hydrogen storage, e.g. pressure cartridges or reversible metal hydrides yield a low energy density for the entire system. In our approach a gas evolving cell (GEC) is used to generate hydrogen “on demand”. This allows to develop small micro fuel cell systems with a high energy density. The GEC is electrically connected in series to the fuel cell. Hydrogen is generated through the electro catalytic Zn-H 2O reaction and proportional to the cell current according to Faraday's law, which leads to a simple and passive system. The dynamic and long-term behavior of the GEC is studied experimentally in this work. The electrical and chemical behavior of the GEC plays an important role in the design and operation of the micro fuel cell system. Portable applications generally imply dynamic load profiles. Therefore the study focuses on the dynamic response of the GEC. The electric response of the GEC is examined for load pulses in the range of milliseconds with an amplitude of up to 150 mA for the lifecycle of a cell. The results are compared to the behavior of the GECs under an equivalent static load in order to draw conclusions on the effect of the dynamic load. Furthermore the electrical and chemical capacity of the GECs is examined for different loads. The obtained results provide an insight into the dynamic behavior of the GEC and provide the basis for the design and operation of the micro fuel cell system.
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