Multi-scale simulation of the fracture behavior of non-stoichiometric gadolinia-doped ceria solid electrolytes under the coupled mechanical and electrochemical field

Abstract

Solid oxide fuel cell (SOFC) works in a complex working environment, which is affected by many factors such as temperature, load and electrochemical reaction. When there are cracks in the material, the multi-field coupling effect will cause the electrolyte performance degradation, even failure and damage. In this paper, the coupling effects of mechanical and electrochemical field on mechanical behavior of gadolinia-doped ceria (GDC) electrolyte are investigated by using the Atom-to-Continuum (AtC) multi-scale method combining molecular dynamics (MD) and finite element method (FEM). Based on the electrochemomechanical coupling theory, we derive the defect diffusion equation of the finite element form. The non-stoichiometry of the cracked GDC electrolyte is calculated, and it is found that the stress concentration at the crack tip will induce non-stoichiometric effects, causing further concentration of oxygen vacancy defects at the crack tip. Subsequently, the effect of electrochemomechanical coupling effect on the fracture toughness of GDC electrolyte is studied by using the AtC multi-scale method. At 800°C under oxygen partial pressure logPO2=−22, this multi-field coupling effect reduces the fracture toughness of 10GDC and 20GDC by 16.13% and 23.33%, and this effect is more apparent with the increase of oxygen partial pressure gradient and external load.