Predictions on conductivity and mechanical property evolutions of yttria-stabilized zirconia in solid oxide fuel cells based on phase-field modeling of cubic-tetragonal phase transformation

Abstract

Solid oxide fuel cell (SOFC) recently emerges as a promising power production technology with high efficiency. However, the degradation of yttria-stabilized zirconia (YSZ) electrolyte, brought by the cubic-tetragonal (c-t) phase transformation, remains a critical issue. Here, the c-t phase transformation of YSZ and its influences on the SOFC are quantitively investigated. First, micro-Raman spectroscopy characterization validates the occurrence of the c-t phase transformation during long-term operation. A microelasticity phase-field model is then built to simulate the phase transformation. The effects of variant nuclei and the misorientation angle between adjacent grains are investigated first based on both single-crystal and double-crystal systems. Subsequently, the phase-field model is applied on the 3D reconstructed real microstructure of polycrystalline YSZ. The results indicate that larger misorientation angles between adjacent grains suppress the development of the variants, and thus benefit in maintaining the ionic conductivity of the electrolyte and the mechanical strength of SOFCs.