Advanced insights into gas conversion and diffusion impedance of solid oxide cells by 2D multi-physics modelling
Julian Taubmann, Xiufu Sun, Omid Babaie Rizvandi, Henrik Lund Frandsen
Abstract
Two-dimensional (2D) multi-physics models of solid oxide cells (SOC) reproduce distributions inside the cell during operation, and allow to implement interdependencies of heat transfer, mass transport, charge transfer, and electrochemistry. So far, this approach has mostly been utilised for transient and steady-state problems, preventing widespread application to electrochemical impedance spectroscopy, one of the main methods in experimentally analysing SOCs. In the present work, a computationally efficient alternative is outlined, surpassing these shortcomings by transforming the set of equations from the transient into the frequency form. The coupled multi-physics implemented by partial differential equations are solved numerically over a 2D domain by the finite element method, reproducing the cross section of the SOC. The model is validated with experimentally obtained polarisation curves and impedance spectra. The 2D model reproduces the experimental results and further visualises frequency-dependent oscillations of gas phase and potentials. These insights separate between impedance features from electrochemistry, gas diffusion, and gas conversion. In addition, overlapping gas conversion and diffusion impedance features at low frequencies are deconvoluted and transition frequency regions are discussed.