Patrick Metzger

Investigation of Locally Resolved SOFC Characteristics along the Flow Path

Solid oxide fuel cells (SOFCs) are characterized locally in a segmented cell arrangement. The tests were performed in counter flow operation for hydrogen concentrations from 2% to 100% to identify concentration limitations and to optimize fuel utilization. Cell characterisations were obtained for different cell concepts by voltage/current density U(i) and temperature measurements as well as gas chromatography measurements at 16 distinct points across the cell. The results show a substantial variation of current density and voltage distribution along the flow path with varying hydrogen content and fuel utilization. Especially at high fuel utilizations approaching 100% a dramatic dependence of power density along the flow path occurs which is associated with increasing degradation. The observation of inhomogeneous temperature distribution emphasizes the importance of thermal management adapted to the cell operation characteristics, particularly when the stack itself only has a low thermal mass.

Diagnostic Tools for in-situ and ex-situ investigations of fuel cells and components at the German Aerospace Center

The analysis of the processes in fuel cells like the degradation and the alteration during start-up processes and the analysis of fuel cell components especially of the electrodes and their components is a main topic at the DLR. For this purpose physical and electroche¬mical methods are used individually and combined. In this paper different example of applications of studies performed at DLR using different methods in combination will be presented. The examples in the field of low temperature fuel cells - alkaline fuel cells, polymer electrolyte fuel cells and direct methanol fuel cells – are mainly focused on the alteration of the electrodes due to electrochemical loading; for SOFC an example for the investi¬ga¬tion of the local operating conditions is given.