Computational Modeling for Cr and S Poisoning Pathways on La0.6Sr0.4Co0.2Fe0.8O3 Surfaces

Abstract

Perovskite oxygen electrode degradation caused by cation segregation sets the limit of performance and lifetime of solid oxide fuel cells (SOFC) [1][2]. For the state-of-art perovskite oxygen electrode, (La0.6Sr0.4)0.95Co0.2Fe0.8O3-δ (LSCF), the commonly known degradation mechanism is through Sr segregation, which can be further poisoned by Cr and as well as by S impurities to form insulating layers, limiting the oxygen evolution reaction (ORR) [3][4]. In order to advance our understanding of Cr and S poisoning pathways on LSCF surfaces, we will combine ab initio density functional theory (DFT) reaction energetics, defect chemistry, and microkinetic modeling to establish a quantitative model to find the deposition reaction on different termination slabs. To predict the reaction mechanism and kinetics of Cr and S poisoning reactions, we will study CrO3 and SO2 molecules deposition pathways on pristine LSCF, and surface-modified (eg. Hf, Zr, Pr, Nd, Ce surface-doped) LSCF slabs. I will correlate adsorption energies with LSCF surface characteristics to explain the origin of the deposition, and use these characteristics to evaluate the effectiveness of the surface infiltration. Ab initio molecular dynamics (AIMD) will be applied at different ensembles to investigate further steps of the reaction, and show how the surface modification will inhibit poisoning reactions. These findings will help to guide the design of better performance and more durable oxygen electrodes for SOFCs.[1] Neagu, D., Tsekouras, G., Miller, D. N., Ménard, H., & Irvine, J. T. (2013). In situ growth of nanoparticles through control of non-stoichiometry. Nature Chemistry, 5(11), 916–923.[2] Lee, K. T., & Wachsman, E. D. (2014). Role of nanostructures on SOFC performance at reduced temperatures. MRS Bulletin, 39(9), 783–791.[3] Jiang, S. P., & Chen, X. (2014). Chromium deposition and poisoning of cathodes of solid oxide fuel cells – a review. International Journal of Hydrogen Energy, 39(1), 505–531.[4] Chen, K., & Jiang, S. P. (2020). Surface segregation in solid oxide cell oxygen electrodes: Phenomena, mitigation strategies and electrochemical properties. Electrochemical Energy Reviews, 3(4), 730–765.