(308h) Dynamic Modeling of the Synergistic Effects of Chemical and Thermo-Mechanical Degradation of Solid Oxide Cells

One notable barrier to successful commercialization of solid oxide cell (SOC) technologies is the relatively short lifespan of SOC materials due to the degradation of electrode microstructure by various chemical and electrochemical mechanisms. Another factor that significantly reduces the life of the cell is the presence of thermo-mechanical stresses that build up due to high spatial and temporal temperature gradients. Extended exposure of the cell to high temperature electrolysis operation can lead to severe changes in electrode composition and microstructure (McPhail et al., 2021; Wolf et al., 2022). Chemical degradation can result in an increase in local Ohmic resistances such that the overall efficiency of the cell decreases. The thermo-mechanical stress accumulation can lead to premature catastrophic failure of the cell components (Barelli et al., 2013). While there have been several studies in the open literature on modeling the effects of physical and chemical degradation (Clague et al., 2012; Khan et al., 2018; Nakajo et al., 2011; Parhizkar & Roshandel, 2017), they have been done separately without considering synergistic effects of these degradation mechanisms on each other. However, synergistic effects can rapidly accelerate the rate of degradation. This work seeks to model several synergistic effects of physical and chemical degradation and generates results by simulating a variety of operating scenarios.

In this work, a number of chemical degradation models are developed for the oxygen and the fuel electrodes. These models account for mechanisms such as chromium oxide and lanthanum zirconate scale growth, Ni agglomeration, etc. For modeling physical degradation, the cell components including electrodes and the electrolyte are assumed to be bonded together that allows for estimation of the uniform strain and the curvature of the cell components (Hsueh, 2002; Zhao et al., 2019). The Weibull distribution (Weibull, 1939) is applied to evaluate the failure probability (Bhattacharyya et al., 2009).

Multiple synergistic effects between physical and chemical degradation are modeled. For example, the cell temperature continues to rise due to chemical degradation because of the local rise in the Ohmic resistance even though current density is constant. The rise in temperature enhances physical degradation especially accelerating creep damage. In addition, chemical degradation affects the thermo-physical properties of the ceramic materials, which in turn, resulting in variation in the thermal profile in the cell thus affecting physical degradation. Furthermore, mechanical properties of the cell components such as Young’s modulus, Poisson’s ratio get affected due to chemical degradation and change in these properties has strong effect on the physical degradation. Models of thermo-physical and mechanical properties are developed as a function of ceramic composition and its operating conditions.

The degradation models are coupled with a first principles 2D non-isothermal dynamic model (Bhattacharyya et al., 2009) of a solid oxide cell enabling calculation of spatial-temporal variation of stresses, failure probability, and extent of chemical degradation as a function of operating conditions. Various operating scenarios are considered that differ in terms of current density, temperature as well as temperature transients. Our study shows that consideration of synergistic effects will be critical to obtain realistic estimate of the degradation of SOC and estimating remaining useful life of the cell before failure occurs.

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