Spatially resolved electrical in-situ measurement techniques for fuel cells

In this work different measurement techniques are presented, which allow spatially resolved measurements of the reaction conditions inside a fuel cell. Those are two different temperature distribution measurement systems for low and high temperature polymer electrolyte fuel cells and two current distribution measurement systems, which also allow spatially resolved impedance spectroscopy. The measurement systems have been optimized for a simultaneous operation with neutron and synchrotron radiography. Together with a highly sensitive differential pressure sensor, this allows a simultaneous measurement of the water distribution and the current and temperature distribution and their impact on the flow resistance. The thesis closes with the presentation of a spatially resolved simulation model of a direct methanol fuel cell (DMFC), which can be used to calculate the current and concentration distribution in the cell. It is shown that the model can not only be used to model the normal fuel cell operation, but also some unusual operation modes. One of them is the „bifunctional regime“, in which parts of the cell operate in normal fuel cell mode, while other parts operate in electrolysis mode. The bifunctional regime can directly be detected with the spatially resolved current measurement systems, even though it is not directly measurable outside of the cell, as current is still delivered to the connected load like in normal mode of operation. The presented measurement techniques and results can contribute to a better understanding of the physical and chemical processes inside the fuel cell. This allows an optimization of the cell design in terms of power density, efficiency and durability.