Tracking solid oxide cell electrode microstructural evolution during annealing by scanning 3D X-ray diffraction microscopy

TL;DR

This study employs high-resolution scanning 3D X-ray diffraction microscopy to monitor and analyze the microstructural evolution of Ni particles in solid oxide cells during annealing, revealing mechanisms of coarsening and degradation.

Contribution

It introduces the use of S3DXRD with 100 nm resolution to directly observe Ni microstructural changes during heat treatment in solid oxide cells.

Findings

Ni microstructure undergoes significant grain growth during annealing.

Disappearance of small grains occurs near pores, especially at Ni-pore interfaces.

Local curvature decreases as grains coalesce and grow.

Abstract

Ni particle coarsening is a primary degradation mechanism in Ni/YSZ solid oxide cells, limiting the lifespan of these devices. In this study, we demonstrate the use of Scanning 3D X-ray diffraction (S3DXRD) with an unprecedented spatial resolution of 100 nm, to monitor the microstructural evolution within the 3D volume of a solid oxide cell subjected to ex situ heat treatment. Unlike conventional tomography, S3DXRD combines crystallographic information with spatial maps, enabling precise identification of grain boundaries and the determination of local curvature changes in the Ni microstructure. Our study reveals that the Ni phase undergoes significant structural changes during annealing, driven by grain growth. This transformation is characterized by a reduction in local curvature, particularly in regions where grains disappear. We observe that the disappearing grains are the smallest grains in the size distribution and are often located near pores. As a result, the most notable reduction in local curvature occurs at the Ni-pore interface. The quantitative characterization of polycrystalline microstructural evolution in Ni/YSZ system provides new insights into the mechanisms of Ni particle coarsening in SOC devices, potentially guiding strategies to enhance the long-term stability of SOC devices.