Simulation and Prediction of 3-D Microstructural Evolution and Long Term Performance of Ni-YSZ Anode

Abstract

The electrochemical performance of SOFCs degrades over the operation time due to a number of factors. The electrochemical activity of the anode is one of these changing parameters due to microstructure coarsening. The change in microstructure of a Ni cermet anode is mainly due to the mobile Ni phase at high temperatures and can be accelerated by the presence of water vapour. The reduced triple phase boundary (TPB) density caused by coarsening leads to degradation of electrochemical performance of the anode. In order to manufacture SOFCs with long- lasting high performance and predict their useful lifetime, it is necessary to understand and predict the microstructural evolution of the anode under different operation conditions. In this contribution, we will demonstrate that the evolution of a 3D real microstructure of a Ni-YSZ anode can be simulated and predicted using our newly developed cellular automaton approach. For this simulation, the YSZ is assumed to be immobile while the mobility of Ni is by the route of evaporation-condensation. In the model the surface energy of Ni and the YSZ/Ni interface energy are simulated based on a new concept of material structural imbalance. The 3D microstructures of anodes subjected to different aging conditions are reconstructed experimentally using focus ion beam (FIB) slice and view. It is shown that the simulation results fit the experimental results very well. Using these short time experimental observations as a calibration of the model, we demonstrate that it is feasible to predict the long time microstructure evolution of the Ni-YSZ anode and hence its long term performance and lifetime.