Creep behaviour of porous SOFC electrodes: Measurement and application to Ni-8YSZ cermets

• Published in: Journal of the European Ceramic Society 2011-01, Vol.31 (9), p.1741-1752
• Main Authors: Laurencin, J., Delette, G., Usseglio-Viretta, F., Di Iorio, S.
• Format: Article
• Language: English
• Subjects: Cermet; Cermets; Creep; Creep (materials); Four-point bending test; Ni-8YSZ; Nickel; Operating temperature; Phases; Solid oxide fuel cell (SOFC); Solid oxide fuel cells; Strain; Stresses
• ISSN: 0955-2219; 1873-619X
• DOI: 10.1016/j.jeurceramsoc.2011.02.036

A methodology is proposed in this study to investigate the creep properties of porous Ni-8YSZ cermet. Creep experiments have been conducted under reducing atmosphere at the typical SOFC operating temperatures. Specimens have been loaded in a four-point bending test bench. A special attention has been paid in this work to the analytical and numerical modelling of the mechanical test. It has been highlighted that Ni-8YSZ exhibits substantial creep strain rates even at relative low temperatures (700 °C < T < 850 °C). The creep exponent has been found to be just slightly higher than unity (1 < n < 2) while the activation energy has been determined equal to Q = 115 kJ mol −1. High-temperature plastic strains of both Ni and 8YSZ phases have been estimated through the local stress acting on the cermet particles. This analysis indicates that creep behaviour of the Ni-8YSZ composite is not influenced by the metallic phase, but is controlled by the deformation of the 8YSZ matrix. It is also proposed that cermet creep mechanism involves Zr 4+cations diffusion at the surface rather than in the bulk of the 8YSZ material. Impact of the Ni-8YSZ cermet creep on the internal stresses distribution in SOFC is discussed considering the anode supported cell (ASC) design. It is shown that cermet creep strain can induce a substantial stress decrease in the thin electrolyte.