Tracking degradation in solid oxide cells by a coupled time and frequency domain multi-physics model: A case study on nickel migration in electrolysis mode

The microscopic and heterogeneous degradation processes in a solid oxide cell (SOC) complicate their analysis by only macroscopic measurements. Multi-physics models can complement the experimental analysis, while generating additional in-depth insights. In this study, a new approach is proposed based on the combination of transient and frequency domain simulations. In such a way, the state-of-the-art experimental impedance characterisation of SOC durability can be reproduced. This approach provides insights into the processes that contribute to the degradation of SOCs, which are otherwise unattainable from only transient simulations. The multifaceted degradation of the nickel (Ni)/yttria stabilised zirconia (YSZ) fuel electrode in electrolysis mode is a prime example of entangled microscopic processes varying locally according to the operation conditions. It therefore presents a well-suited case study to showcase the introduced modelling framework with an improved understanding of degradation mechanisms by comparing impedance and microscopic descriptors to experiments. A degradation mechanism based on surface and interfacial energies of Ni and YSZ and surface diffusion of Ni is implemented. The mechanism can reproduce the electrochemical measurements and microstructural changes observed after testing. Both can ultimately improve the understanding of Ni/YSZ degradation by explaining phenomena related to observed changes in ohmic resistance and gas conversion impedance. • A 2D multi-physics model for solid oxide electrolysis degradation is presented. • A time–frequency domain model is introduced for improved validation and insights. • A degradation mechanism for the Ni/YSZ fuel electrode is implemented. • The model reproduces experimental trends for voltage, impedance and microstructure. • The cause of the increase in gas conversion impedance is holistically explained.