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In the EU-funded project "Solid oxide cell and stack testing and quality assurance" (SOCTESQA), standardized and industry wide test modules and programs for high temperature solid oxide cells and stacks are being developed. These test procedures can be applied for the fuel cell (SOFC), the electrolysis (SOEC) and in the combined SOFC/SOEC mode. In order to optimize the test modules the project partners have tested identical SOC stacks with the same test programs in several testing campaigns. Altogether 10 pre-normative test modules were developed: Start-up, currentvoltage characteristics, electrochemical impedance spectroscopy, reactant utilization, reactant gas composition, temperature sensitivity, operation at constant current, operation at varying current, thermal cycling and shut-down. The test modules were validated by comparing the results in terms of repeatability of the different testing campaigns and in terms of reproducibility among the different partners. Moreover, the results are discussed in context to the test input parameters.

A planar solid oxide fuel cell (SOFC) operated with hydrogen at T=1123 K was equipped with an optically transparent anode flow field to apply species concentration measurements by 1D laser Raman scattering. The flow channels had a cross section of 3 mm × 4 mm and a length of 40 mm. The beam from a pulsed high-power frequency-doubled Nd:YAG laser (λ=532 nm) was directed through one channel and the Raman scattered light from different molecular species was imaged onto an intensified CCD camera. The main goal of the study was an assessment of the potential of this experimental configuration for a quantitative determination of local gas concentrations. The paper describes the configuration of the optically accessible SOFC, the laser system and optical setup for 1D Raman spectroscopy as well as the challenges associated with the measurements. Important aspects like laser pulse shaping, signal background and signal quality are addressed. Examples of measured species concentration profiles are presented.

In the past much effort was spent for the detailed understanding of the electrochemical behavior of SOFC single cells. However, these results cannot be transferred to the entire SOFC stack technology because of huge differences in fuel utilization, temperature distribution, gas flow design and electrical current load. Therefore, proper and detailed understanding of the electrochemical behavior of the SOFC stacks is necessary for the successful introduction and acceptance of the SOFC technology into the global energy market. The paper presents the electrochemical behavior of SOFC stacks with anode supported cells (ASC) in the cassette design at different operating conditions. The focus lies on the investigation of the resistances of the stack repeat units as a function of operating temperature and fuel gas flow rate. The stacks were investigated by current-voltage curves, electrochemical impedance spectroscopy (EIS) and gas analysis.

The paper concentrates on the investigation of SOFC short stacks and stacks for mobile applications. A lightweight stack design was used, which is based on stamped metal sheet bipolar plates with anode supported cells (ASC). The stacks were electrochemically characterized mainly by long-term measurements, by current-voltage measurements and by impedance spectroscopy. The stacks were operated at different temperatures, varying fuel gas compositions, different flow rates and under dynamical electrical loading cycles. Their influence on the electrochemical performance of the short stacks is outlined. The fuel utilizations and the different power densities, i.e. area specific, gravimetric and volumetric ones, are presented. The nature of losses, e.g. ohmic and polarization resistances, were examined by combining the results of the current-voltage curves and the impedance spectra. Moreover, the degradation rates were determined from the long-term measurements. After operation, the stacks were examined by light microscopy and SEM in order to analyze possible degradation mechanisms.