Electrochemical Impedance Analysis of Symmetrical Ni/Gadolinium-Doped Ceria (CGO10) Electrodes in Electrolyte-Supported Solid Oxide Cells

One of the most powerful tools in solid oxide cell (SOC) characterization is electrochemical impedance spectroscopy, which can unfold important insights into SOC performance characteristics and degradation behavior. To obtain a better understanding of the electrochemical behavior of Ni/CGO fuel electrodes, this work presents a comprehensive investigation of state-of-the-art Ni/CGO10-based electrolyte-supported cells. Commercial Ni/CGO10 vertical bar CGO10 vertical bar 3YSZ vertical bar CGO10 vertical bar Ni/CGO10 symmetrical cells were characterized between 550-975 degrees C at pH(2) = 0.8 bar and pH(2)O = 0.2 bar, and for different H-2/H2O gas mixtures at 550 degrees C. (i) Small electrode area, (ii) thin electrodes and (iii) large gas flow rates were used to minimize mass transport contributions. Based on distribution of relaxation times (DRT) analysis an equivalent circuit model was derived. Electrode process contributions on Ni/CGO were determined by means of a complex non-linear least square fit of the equivalent circuit model to the experimental data. One low frequency process at 0.1-1 Hz and one middle frequency process at 10-100 Hz were identified and correlated to a surface and a bulk process, respectively. Values for the apparent activation energy barriers and reaction orders with respect to steam and hydrogen content were determined. (c) The Author(s) 2019. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/),which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org.