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 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/CGO10based electrolyte-supported cells. Commercial Ni/CGO10|CGO10|3YSZ|CGO10|Ni/CGO10 symmetrical cells were characterized between 550-975°C at pH 2 = 0.8 bar and pH 2 O = 0.2 bar, and for different H 2 /H 2 O gas mixtures at 550°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.

Performance and Limitations of Nickel‐Doped Chromite Anodes in Electrolyte‐Supported Solid Oxide Fuel Cells

“…Moreover, for Ni/CGO-based cells of the same type as used in the present study, we have reported the peak frequency of the anode charge transfer process to be between 1-10 Hz. [18,23] The impedance response at these frequencies is also increased in comparison with the cells with 25 μm thick L65SCrN and 19 μm thick L70SCrN anodes and responsible for the difference in polarization resistance between the cells. The increased polarization resistance of the cell with 8 μm thick L65SCrN electrode is mainly caused by an increased impedance response at frequencies of approximately 1 Hz.…”

Femtosecond Laser-Induced Surface Modification of the Electrolyte in Solid Oxide Electrolysis Cells

“…Before performing a quantitative analysis, the peak resistances need to be corrected. As shown in previous modeling studies [33][34][35] and experimental studies for symmetrical cells [36,37], the low frequency polarization resistance is increased by a gas diffusion and gas conversion resistance, even for open circuit measurements. The sum of both resistances is also named gas concentration resistance R gas [38].…”

“…The gas concentration resistance and its main origin (conversion or diffusion resistance in the gas channel) depend especially on the measurement setup and the gas supply. Unfortunately, R gas cannot be separated by a single peak in the DRT due to an overlapped electrode process for Ni/CGO electrodes [37]. A possible approach to approximate R gas would be the characterization of a cell with a Ni/YSZ fuel electrode, which has no characteristic overlapping process at the relevant relaxation frequency.…”

Effect of sintering temperature on electrochemical performance of porous SrTi1-xFexO3-δ (x = 0.35, 0.5, 0.7) oxygen electrodes for solid oxide cells

“…To further evaluate the influence of the sintering temperature on the electrode performances, distribution of relaxation times (DRT) analyses of their spectra were performed. DRT analysis is a powerful tool to investigate electrochemical processes [53][54][55][56]. The results of the DRT analysis of the spectra shown in Fig.…”