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

Abstract

One of the most powerful tools in solid oxide cell (SOC) characterization is electrochemical impedance spectroscopy, which can
\nunfold important insights into SOC performance characteristics and degradation behavior. To obtain a better understanding of the
\nelectrochemical behavior of Ni/CGO fuel electrodes, this work presents a comprehensive investigation of state-of-the-art Ni/CGO10-
\nbased electrolyte-supported cells. Commercial Ni/CGO10|CGO10|3YSZ|CGO10|Ni/CGO10 symmetrical cells were characterized
\nbetween 550–975°C at pH2 = 0.8 bar and pH2O = 0.2 bar, and for different H2/H2O gas mixtures at 550°C. (i) Small electrode area,
\n(ii) thin electrodes and (iii) large gas flow rates were used to minimize mass transport contributions. Based on distribution of relaxation
\ntimes (DRT) analysis an equivalent circuit model was derived. Electrode process contributions on Ni/CGO were determined by means
\nof 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
\nand one middle frequency process at 10–100 Hz were identified and correlated to a surface and a bulk process, respectively. Values
\nfor the apparent activation energy barriers and reaction orders with respect to steam and hydrogen content were determined