Spatially Resolved Measuring Technique for SOFC

In order to optimize SOFC cells for operation in highly efficient systems a new measuring system with segmented cells has been developed that allows to determine local effects and to identify critical operating parameters during operation. The setup of the measuring system and experimental results for two examples – influence of hydrogen content and fuel utilization on performance and influence of load on power density and fuel utilization at operation with gasoline reformate as fuel – are presented to demonstrate the potential of the spatiallyresolved measuring technique. INTRODUCTION Solid oxide fuel cells exhibit the advantage of using hydrocarbons as a fuel without needing an extensive cleaning step. This favors the application of an SOFC as an ‘Auxiliary Power Unit’ (APU) for vehicles and aircraft where conventional fuels such as gasoline, diesel or kerosene are used. Although large progress has been achieved in the past years in SOFC development the behavior of SOFC cells under technical relevant operating conditions needs to be investigated for a more detailed understanding of the reaction processes, in particular during operation with high power densities and using reformate of hydrocarbons as fuel. In order to optimize cells for operation in highly efficient systems a measuring technique has been developed at DLR that allows to determine local effects and to identify critical operating parameters. By means of this measuring system with segmented cells current density/voltage characteristics, impedance spectroscopy data and operating temperature can be determined individually at 16 distinct segments. EXPERIMENTAL DETAILS Square-shaped cells with an area of 100 cm2 which are divided into 16 segments are integrated in a metallic cell housing and sealed with glass seal. The metallic housing is also subdivided into 16 galvanically isolated segments resulting in an active area of 73.96 cm2. In order to determine the temperature at each segment thermocouples are introduced. Additionally, 16 capillaries are integrated to collect samples of the anode gas to be analyzed by gas chromatography. More details on the measuring system are given in [1, 2]. The method is quite flexible with regard to the integration of different cell designs: metal-supported cells (MSC) as they are developed and fabricated at DLR according to its spray concept as well as electrolyte(ESC) and anode-supported cells (ASC) can be characterized. ESCand ASC-type cells used were supplied by InDEC, Netherlands (ESC2 and ASC2, resp.). With MSC and ASC cells only the cathode is segmented, whereas ESC cells are segmented on both the anode and the cathode side. The ESC2 cell consists of a 45 μm thick NiO/GDC anode, a 90 μm thick YSZ (3 mol% TZ3Y) electrolyte and a 40 μm thick LSM cathode. The ASC2 cell contains a 540 μm thick NiO/YSZ anode with a thin anode functional layer, a 7 μm thick 8YSZ electrolyte, a 7 μm thick YDC interlayer and a 30 μm thick LSCF cathode. RESULTS AND DISCUSSION The measuring system described has been applied to locally characterize SOFCs with the segmented cell arrangement. Two examples are given to demonstrate the potential of this spatially-resolved measuring technique: (i) investigation of electrolyte-supported cells (ESC2) under variation of hydrogen content and fuel utilization, and (ii) investigation of anode-supported cells (ASC2) during operation with reformate of gasoline as the fuel. As a first example for the capability of this new analytical tool the influence of the variation of the hydrogen content and hence of the fuel utilization on the performance of an electrolyte-supported cell (ESC2) was studied. The content of