Study of SOFC Operational Behavior by Applying In-Situ Diagnostic Methods

High electrical performance and long lifetime are key requirements that must be fulfilled for a successful introduction of fuel cells into the market. For achieving a high efficiency, a high fuel utilization is required. This requirement, on the other hand, results in strong concentration gradients at the anode where the fuel is successively diluted by reaction products during the reaction process and, hence, in an inhomogeneous distribution of electrochemical performance and temperature. Inhomogeneous distributions of electrochemical and thermal properties such as local power density and local temperature might detrimentally affect both efficiency and long-term durability through thermo-mechanical stress and degradation phenomena. In order to optimize the operational behavior of fuel cells and minimize cell degradation the application of advanced diagnostic methods by monitoring cell characteristics under real operating conditions can provide detailed information about the spatial distribution of the electrical, chemical and thermal cell properties. DLR has developed spatially resolved diagnostic techniques with a segmented cell arrangement where different techniques such as IV characteristics, impedance spectroscopy, gas chromatography and temperature measurement are involved [1, 2]. The segmented cell setup allows a largely extended insight into fuel cell processes both for increasing the fundamental understanding and for optimizing cell and flow field design. The obtained data can be used for mathematical modeling and model validation and for predicting physical, electrochemical and fluid mechanical properties [3, 4]. Recently, imaging techniques such as optical microscopy and Raman spectroscopy have been additionally adopted for in-situ observation of fuel cells. The paper gives an overview of in-situ diagnostic methods applied at DLR Stuttgart for the determination of local effects and the identification of critical operating conditions during technically relevant SOFC operation. Exemplary results from experimental investigations are presented