Relationship between microstructure and deformation of porous Ni-based cermets under redox cycling

Abstract

This paper discusses the relationship between the elongation and compression behavior and microstructural changes under redox cycles of porous Ni(O)–YSZ cermets for solid oxide fuel cells (SOFC). Mechanical damage in SOFC and SOEC is one of the most important degradation factors governing the electrical performance of cells. Therefore, it is necessary to know the mechanical properties of each component material, such as elastic and deformation properties, in the operating environment. Particularly, of the Ni(O)–YSZ cermets which currently makes up 90% of the volume of the cell, with present mainstream anode supported SOFC and SOEC. Therefore, understanding the properties of the Ni(O)–YSZ cermets plays an important role in ensuring the performance of the entire SOFC and SOEC. In this study, the microstructural changes of Ni(O)–YSZ cermet by reduction, re-oxidation and re-reduction were observed in detail using microstructural observations and systematically compared with the dimensional change behavior. For the dimensional change behavior, a simple model considering the initial porosity and Ni content is proposed, which successfully predicts the dimensional change due to re-oxidation. Furthermore, Ni(O)–YSZ cermets with high Ni content show large initial dimensional changes, but the dimensional reversibility improves with increase of the number of redox cycles.

Recent Advances and Challenges in Thin-Film Fabrication Techniques for Low-Temperature Solid Oxide Fuel Cells

“…Although the initial reduction of the anode layer can be supported by the ceramic phase, any re-oxidation subsequent to the coarsening of nickel particles can result in severe physical damage to the cell (Figure 6) [119]. Such structural changes are of great importance in anode-supported systems, where they will result in the formation of cracks in the supported electrolyte membrane [120,121]. Despite the large research effort from the scientific community to stabilise this effect, this remains one major weakness of Ni-based anode-supported SOFCs, often adding complexity and cost to the operating system [122].…”