Mechanistic Understanding of OER Degradation of SOEC through Computational Modeling

Abstract

One of the major barriers to the commercialization of solid oxide electrolysis cells (SOECs) for hydrogen production through electrochemical water splitting is the short cell/stack life caused by chemical-expansion-mismatch induced mechanical delamination of oxygen electrode. To address SOEC’s degradation problem, we have been developing an isostructural bilayer oxygen evolution reaction (OER) electrode that is electrocatalytically active and Cr-tolerant. The bilayer OER electrode structure consists of a commercial LSCF (La0.6Sr0.4Co0.4Fe0.6O3- d)-GDC (Ce0.8Gd0.2O1.9 porous backbone on a thin SrCo0.9Ta0.1O3- d (SCT10) film. The new oxygen electrode has an inherently fast OER electrokinetics (or high oxygen evolution rate) to mitigate the delamination problem by minimizing the accumulation of oxygen in OER electrode lattice and thus chemical stresses. To understand the fundamental Electro-Chemical-Mechanical coupling mechanism and its contribution to SOEC degradation, we propose a rigorous Multiphysics model to explore the interplays between reaction rates and transport properties in delamination probability of the pristine and bilayer OER electrodes.Figure 1 shows a schematic of model domain to be constructed with details at the interface. The model will address how the dimensional change of oxygen lattice incurred in the electrode during OER-operation affects its bonding strength with the electrolyte and how electronic/ionic conductivity in the oxygen electrode as well as electrolyte will alter the change. We will apply classical charge transport conservation, Ohm’s law and multi-species Maxwell-Stefan’s equation to simulate electronic/ionic transport and gas diffusion in the porous electrode. The distribution of oxygen vacancy concentrations in the electrode and across the electrode/electrolyte interface will be considered a key descriptor for the chemically-induced lattice dimensional change. The displacement associated with the lattice dimensional change is governed by Navier’s equation. Different criteria will be used to evaluate the failure modes at the O2-electrode/electrolyte interface, such as elastic energy and Weibull approach. The research work will lead to a better understanding of the delamination mechanisms and effective mitigation plan, and provide guidelines to the experimental optimization of bilayer OER electrode processing with improved electrochemical and mechanical performance.Figure 1 (a) Illustration of a SOEC cell; (b) Microscale electrode/electrolyte Interface Model; (c) Elastic energy in the particles and interfaces under chemical expansion. Figure 1