Entwicklung einer innovativen Methode für die Untersuchung der Stromdichteverteilung sowie der relativen Feuchtigkeit an Brennstoffzellen

Kurzfassung

The performance of fuel cells is strongly dependent on design as well as operational conditions. Individual parameters are interdependent and thus influence each other, making it hard to observe the effect of a certain parameter on its one. Therefore, for research in fuel cells, it would be helpful to know the effect of different parameters on the spatial resolution of the current density and humidity distribution. The aim of this thesis was to develop and design a novel research fuel cell in which simultaneous measurement of current density and humidity distribution can be performed. For the measurement of the current density distribution a segmented board containing one hundred individual segments, developed by the “Deutsches Zentrum für Luft- und Raumfahrt” was used. A sensor plate with one hundred capacitive humidity sensors was installed to measure the humidity distribution. Firstly, a concept was developed to integrate the segmented board and the sensor plate into a research fuel cell. The segmented board with integrated flow field acts as the anode of the cell. For the cathode a novel plate with a flow field was developed and designed. The special feature of this plate is that the flow field is connected to the humidity sensors by drilled holes. Between this plate and the senor plate a teflon plate was integrated to seal the fuel cell. End plates were added to both the anode and the cathode side. The gas supply can be connected to this plate and the gases can be transferred into the flow fields. After the design phase the parts were manufactured and the fuel cell was assembled. Experiments were conducted to measure the local humidity distribution in the cell as well as to test the installed sensors under operational conditions. In the first few experiments the additional humidity of the gas as well as the mass flow were varied. The reaction of the sensors were as expected. The function of the developed method could also be confirmed by drying experiments. Lastly, the reaction time of the system was investigated and yielded to practically useable values. In conclusion all results confirmed that the designed fuel cell is well functioning. This demonstrates that a combination of sensors to simultaneously measure current density and humidity distribution is possible. The current state of this successful method is a good foundation for further research.