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A zero-dimensional and isothermal stationary model demonstrably predicting the current-voltage (C/V) characteristic of an anode supported SOFC single cell is for the first time verified for C/V characteristics measured in electrolysis mode. The accuracy of the presented model was increased by including the actual cell temperature under current load, determined by an impedance-based temperature measurement routine. C/V characteristics measured at 800°C in the range from 0.66 V to 1.6 V for H2O:H2 compositions 70:30 and 30:70 reveal a pronounced asymmetric operation of the fuel electrode supported cell in electrolysis mode. This experimentally observed behavior is accurately reproduced by the model and is explained by (i) increasing polarization losses related to Knudsen diffusion and (ii) decreasing reaction rate in dry conditions at the fuel electrode at high current densities in electrolysis mode.

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The impact of sulfur‐poisoning on reforming chemistry and electrochemistry of anode‐supported solid oxide fuel cells is analyzed via electrochemical impedance spectroscopy. Different types of anode supported cells are operated in hydrogen/steam – as well as simulated reformate – (H2 + H2O + CO + CO2 + N2) fuels containing 0.1–15 ppm of H2S. A detailed analysis of impedance spectra by the distribution of relaxation times (DRT) and a subsequent complex nonlinear least squares (CLNS) fit separates the impedance changes taking place at the anode and the cathode. Two main features were detected in the DRT, a decreased reaction rate of the electrochemical hydrogen oxidation and a deactivation of the catalytic conversion of CO via the water‐gas shift reaction. During the first exposure of the cell to a H2S‐containing fuel, an enhanced degradation is observed. The degradation rate increases several hours after H2S was added to the fuel and decreases after the poisoning is completed. The polarization resistance increased by a factor of 2–10, depending on H2S‐content, fuel composition and cell type. Comparing the temporal characteristics of the polarization resistance of two different anode supported cells, it could be shown that the accumulated H2S‐amount divided by the Ni‐surface area inside the anode substrate and anode functional layer determine the onset of the degradation.

The impact of sulfur-poisoning on the electrochemistry of anode-supported solid oxide fuel cells (SOFCs) has been analyzed via electrochemical impedance spectroscopy. Therefore, single cells manufactured by Forschungszentrum Jülich (FZJ) were operated with a reformate fuel. During operation, contents of H 2 S (0.1 and 0.5 ppm) were added to the fuel. A detailed analysis of the measured impedance spectra by the distribution of relaxation times (DRT) and a subsequent complex nonlinear least squares (CNLS) fit enabled a separated treatment of the resulting degradation of anodic and cathodic polarization processes. During the exposure to 0.5 ppm H 2 S, the polarization resistance increased by 200%, leveling off after 24 h. This strong increase has mainly been attributed to the decreased reaction rate of the electrochemical fuel oxidation. Additionally, a strongly decreased conversion rate of the water-gas shift reaction was determined from the impedance measurements. This decreased shift conversion rate results in a dramatically lowered utilization of the CO within the fuel.