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

Matthias Riegraf,Rémi Costa,K Andreas Friedrich,André Weber,Sebastian Dierickx,Günter Schiller

doi:10.1149/2.0051913jes

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/CGO10-based electrolyte-supported cells. Commercial Ni/CGO10|CGO10|3YSZ|CGO10|Ni/CGO10 symmetrical cells were characterized between 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, (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.

Highlights

The transition to energy systems based on the use of more renewable energy is accompanied by an increasing mismatch between production and demand, which leads to a growing demand for electric energy storage systems
Important insights into the kinetics of the Ni/YSZ electrode have been achieved via the use of electrochemical impedance spectroscopy (EIS) in symmetrical and full cell configurations.[5,6,7,8,9]
Based on EIS measurements and the calculation of the distribution of relaxation times (DRT), the process resistances can be determined by means of a complex non-linear least square (CNLS) fit of experimental data to a physically meaningful equivalent circuit model (ECM)

Summary

Introduction

The transition to energy systems based on the use of more renewable energy is accompanied by an increasing mismatch between production and demand, which leads to a growing demand for electric energy storage systems. In addition to a low frequency process, a middle frequency process at 102 Hz has been observed in impedance spectra as well which was suggested to originate from the oxide ion transport from bulk to surface or across the electrolyte/electrode interface.[21,22] a systematic study investigating state-of-the-art Ni/CGO10 symmetrical cells has not been carried out yet.

Results

Conclusion