Redox stability of SOFC: Thermal analysis of Ni-YSZ composites

Mikko Pihlatie (Corresponding Author), A. Kaiser, M. Mogensen

    Research output: Contribution to journalArticleScientificpeer-review

    82 Citations (Scopus)

    Abstract

    A re-oxidation of a Ni-based SOFC can seriously damage the cells. Important aspects of this thermomechanical instability are reduction–oxidation kinetics and the dimensional behaviour of the Ni–YSZ composites. These were investigated in the temperature range of 600–1000 °C and different combinations of reduction and oxidation temperatures. Automated temperature and gas change programmes were implemented in thermogravimetry and identically repeated using a high precision dilatometer to show the dimensional behaviour of the cermets simultaneously with the Degree of Oxidation (DoO) as a function of time during redox cycling. The activation energy for reduction was 84.4 kJ/mol and the kinetics was largely linear. Different kinetic models were fitted to the reduction data; the best agreement was found using the Avrami equation. On the re-oxidation, initially linear kinetics was observed, followed by a period of parabolic kinetics slowing down to logarithmic towards full DoO. The shifts in the kinetic shape with time depended on the temperature and DoO. The rate constants for oxidation were fitted to the data. The BET surface area of the cermets after different reduction and oxidation treatments was measured and show decrease of surface area with increasing reduction temperature and no significant differences in the surface area depending on the re-oxidation temperature in the range of 600–1000 °C.
    Original languageEnglish
    Pages (from-to)1100 - 1112
    Number of pages13
    JournalSolid State Ionics
    Volume180
    Issue number17-19
    DOIs
    Publication statusPublished - 2009
    MoE publication typeA1 Journal article-refereed

    Keywords

    • BET
    • dilatometry
    • kinetics
    • Ni oxidation
    • Ni-YSZ
    • NiO reduction
    • rate constant
    • redox stability
    • SOFC
    • TGA

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