Intermediate temperature solid oxide fuel cell under internal reforming: Critical operating conditions, associated problems and their impact on the performance

To simulate realistic operating conditions and analyze their effect on the performance of planar intermediate temperature solid oxide fuel cell systems, a large-area (11 × 11 cm2) anode-supported single cell was tested for ∼500 h, at 650 °C and 245 mA/cm2, corresponding to 43% of fuel utilization, running on a simulated pre-reformate natural gas composition. To correlate the evolution in the cell performance (i.e. voltage loss; total resistance) with specific thermo-fluid-physicochemical processes, localized gas analyses and temperature measurements through the anode surface, using a very particular spot-sampling set-up, as well as electrochemical impedance spectra and polarization curves, were frequently carried out. The impedance spectra have been analyzed through the distribution of relaxation times method and the cell study complemented with a post-mortem analysis. During its operation, the cell sequentially experienced several events to which thermal-cycling and intrinsic degradation have been correlated. Experimental results revealed that cathode humidification was the dominant contribution to the performance degradation, where strontium segregation has been observed and the formation of some insulating phases is suspected. This work is one of the first attempts to carry out an endurance test with real-time diagnosis by in-situ and in-operando gas and temperature analysis, thus monitoring in real conditions the electrochemical, chemical and thermal activity of the anode side in a commercial single solid oxide fuel cell.