Ni Coarsening in Ni-Yttria Stabilized Zirconia Electrodes: Three-Dimensional Quantitative Phase-Field Simulations Supported by Ex-Situ Ptychographic Nano-Tomography

Solid oxide cells (SOCs) are electrochemical devices for efficiently converting chemical energy to electrical energy when operated as solid oxide fuel cells (SOFCs), or vice versa when operated as solid oxide electrolysis cells (SOECs). The durability of SOCs during long-term operation is essential for a cost-effective and efficient energy storage [1]. The porous cermet of nickel (Ni) and yttria-stabilized zirconia (YSZ) composite electrode is the current state-of-the-art SOC fuel electrode [2, 3]. However, during the long-term operation at high temperature (600-1000 oC), the Ni particles in the active Ni-YSZ electrode coarsen, resulting in both a reduction of the active three-phase-boundary (TPB) density and loss of Ni percolation [4, 5]. Therefore, in-depth understanding of nickel (Ni) coarsening is helpful for improving the service life of Ni-yttria stabilized zirconia (YSZ) electrodes in solid oxide cells. Unfortunately, very few quantitative experimental/theoretical descriptions of Ni coarsening in Ni-YSZ electrodes during long-term operation exist. In this work, quantitative modelling of Ni coarsening in Ni-YSZ electrodes was achieved through three-dimensional (3D) phase-field simulation supported by ex-situ ptychographic nano-tomography and input of reliable thermophysical parameters. A pragmatic procedure was proposed to refine and verify the materials parameters for the simulations. Moreover, the microstructures of the Ni-YSZ electrode in the pristine and annealed states obtained via the ex-situ ptychographic nano-tomography were used as the initial input and experimental validation for the phase-field simulations. After that, comprehensive comparison between the simulated and the experimental 3D microstructures was conducted, indicating the successful quantitative phase-field simulation of Ni coarsening in Ni-YSZ electrodes presented here. The success of this work is expected to pave the way for accurate prediction of the service life and even design of high-performance Ni-YSZ electrodes.