Comparison of a solid oxide cell with nickel/gadolinium-doped ceria fuel electrode during operation with hydrogen/steam and carbon monoxide/carbon dioxide

Solid oxide cells (SOCs) offer the possibility to operate on hydrogen/steam (H-2/H2O), carbon monoxide/carbon dioxide (CO/CO2), and mixtures thereof in the fuel cell as well as in the electrolyzer mode. In this study, the electrochemical processes in an electrolyte-supported SOC exhibiting a La-w Sr-x Co-y Fe-z O(3-delta) air electrode and a nickel/gadolinium-doped ceria (Ni/CGO) fuel electrode (FE) were analyzed by electrochemical impedance spectroscopy, and the subsequent impedance data analysis by the distribution of relaxation times for CO/CO2 fuel mixtures. A physicochemical equivalent circuit model was fitted to the measured spectra. With the help of the extracted parameters, a zero-dimensional direct current cell model was parametrized to simulate the current-voltage behavior of the cell. This approach, previously implemented for H-2/H2O fuel mixtures, is extended toward CO/CO2 fuels. It will be shown that the same model - with adapted parameters for the FE - can be applied. A comparison of measured and simulated current-voltage curves showed an excellent agreement for both fuels and operating modes (solid oxide fuel cell/solid oxide electrolyzer cell). Simulations reveal that there is nearly no performance difference between H2O and CO2 electrolysis for the electrolyte-supported cell with Ni/CGO FE in comparison to an anode-supported cell with Ni/yttria-stabilized zirconia FE.