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

Abstract

Solid oxide cells (SOCs) offer the possibility to operate on hydrogen/steam (H₂/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-δ) 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 H₂/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.