The possibility of Solid Oxide fuel cells (SOFCs) to not only operate on hydrogen but hydrocarbon based fuels is certainly beneficial compared to other fuel cell technologies. Yet, the use of carbon-containing fuels can lead to electrochemical deactivation of the cell if carbon deposition occurs 1.Various studies were dedicated to understand the influence of different operation conditions to prevent this detrimental failure to occur. However, even though the thermodynamic limit offers a good guideline for SOFC operation, studies on specific operation conditions are still controversial 2 , 3. Therefore, recent research activities are focusing on the development of online-monitoring tools to prevent destructive failure and maintain fault free conditions 4. Our recent study investigates the evolvement of carbon deposition in an anode-supported single cell under operation with a steam/methane fuel. Cell voltage monitoring, temperature monitoring and additionally employing in situ electrochemical impedance spectroscopy (EIS) in combination with the distribution of relaxation time (DRT) method allowed state-of-health assessment of the cell. The electrochemical examination is furthermore complemented by post-mortem investigations. ‘Failure’ was simulated by operating the cell on methane without steam. Via time-dependent EIS and DRT measurements, it was possible to correlate the onset of carbon deposition for the individual layers within the SOFC anode with different frequency ranges which will be presented at the meeting. Furthermore, a recovery possibility via the set back to nominal operating conditions (to simulate a close-to-real approach) is evaluated with the same methodology. The cell voltage measurement during the performed experiment is shown in Figure 1. Figure 1 Cell voltage for the cell operated under steam reforming conditions and methane. Our findings have the potential to utilize EIS characteristics for recognizing carbon deposition in anode-supported cells in due course to counteract fatal failure of the SOFC and are a promising method to ensure safe operation of SOFC under steam-reforming conditions for industrial purposes. Boldrin, P. et al., Chem. Rev. 2016, 116, 13633-13684. Kuhn, J. & Kesler, O., J. Power Sources 2015, 277, 443-454. Kuhn, J. & Kesler, O., J. Power Sources 2015, 277, 455-463. Sinha, V. & Mondal, S., Int. J. Dynam. Control 2017. Figure 1