Electrical conductivity of Ni-YSZ composites: Variants and redox cycling

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

    Research output: Contribution to journalArticleScientificpeer-review

    12 Citations (Scopus)

    Abstract

    Short-term changes in the electrical conductivity of different Ni–YSZ composites (cermets) were measured by an in-situ 4-point DC technique. The isothermal reduction was carried out in dry, humidified or wet hydrogen at temperatures from 600 to 850 °C. The cermets reduced at 600 °C showed a stable conductivity of about 1100 S/cm, which increased to an enhanced ~ 2000 S/cm upon re-oxidation and subsequent re-reduction cycling at the same temperature. At 850 °C, a rapid initial conductivity loss was observed; upon re-reduction after the re-oxidation both the conductivity and its loss rate were largely the same as in the initial reduction. The presence of steam had an accelerating effect on the conductivity loss at 850 °C. In addition to cermets with a typical microstructure, different modified microstructures and compositions were tested. In the modified cermets, Al, Mg, and Ce were used as Ni dopants alongside with undoped Ni. Scanning electron microscopy of cermets reduced in different conditions showed increasing particle size and loss of metal-to-metal percolation in the samples reduced at higher temperatures, and a very fine microstructure in the high conductivity sample re-oxidised at 600 °C. Short-term conductivity changes due to microstructural changes in both the standard and modified cermets with different Ni doping were compared by re-oxidation at 600 °C and subsequent thermal excursions up to 1000 °C by normalising the conductivity to a constant temperature. Modified cermets show reduced conductivity loss on both isothermal heating and high temperature ramping. Most stable cermets were the ones with undoped NiO and modified microstructure, as well as modified microstructures using Ti and Mg, or Ce secondary oxide coatings. Master sintering curve approach was successfully implemented to analyse the conductivity loss data. The MSC analysis yielded apparent activation energies for Ni sintering within the composite of 375 kJ/mol when heated in dry H2 and 440 kJ/mol when under wet H2.
    Original languageEnglish
    Pages (from-to)38-46
    Number of pages8
    JournalSolid State Ionics
    Volume222-223
    DOIs
    Publication statusPublished - 2012
    MoE publication typeA1 Journal article-refereed

    Fingerprint

    cermets
    Cermets
    yttria-stabilized zirconia
    conductivity
    cycles
    electrical resistivity
    composite materials
    Composite materials
    Microstructure
    microstructure
    Oxidation
    oxidation
    Sintering
    Temperature
    Metals
    Doping (additives)
    sintering
    Electric Conductivity
    Oxidation-Reduction
    Steam

    Keywords

    • SOFC
    • Ni-YSZ
    • electrical conductivity
    • redox stability
    • Ni particle growth
    • master sintering curve

    Cite this

    Pihlatie, Mikko ; Kaiser, A. ; Mogensen, M.B. / Electrical conductivity of Ni-YSZ composites : Variants and redox cycling. In: Solid State Ionics. 2012 ; Vol. 222-223. pp. 38-46.
    @article{4fea2794b7b34441930ffa3f2dbea862,
    title = "Electrical conductivity of Ni-YSZ composites: Variants and redox cycling",
    abstract = "Short-term changes in the electrical conductivity of different Ni–YSZ composites (cermets) were measured by an in-situ 4-point DC technique. The isothermal reduction was carried out in dry, humidified or wet hydrogen at temperatures from 600 to 850 °C. The cermets reduced at 600 °C showed a stable conductivity of about 1100 S/cm, which increased to an enhanced ~ 2000 S/cm upon re-oxidation and subsequent re-reduction cycling at the same temperature. At 850 °C, a rapid initial conductivity loss was observed; upon re-reduction after the re-oxidation both the conductivity and its loss rate were largely the same as in the initial reduction. The presence of steam had an accelerating effect on the conductivity loss at 850 °C. In addition to cermets with a typical microstructure, different modified microstructures and compositions were tested. In the modified cermets, Al, Mg, and Ce were used as Ni dopants alongside with undoped Ni. Scanning electron microscopy of cermets reduced in different conditions showed increasing particle size and loss of metal-to-metal percolation in the samples reduced at higher temperatures, and a very fine microstructure in the high conductivity sample re-oxidised at 600 °C. Short-term conductivity changes due to microstructural changes in both the standard and modified cermets with different Ni doping were compared by re-oxidation at 600 °C and subsequent thermal excursions up to 1000 °C by normalising the conductivity to a constant temperature. Modified cermets show reduced conductivity loss on both isothermal heating and high temperature ramping. Most stable cermets were the ones with undoped NiO and modified microstructure, as well as modified microstructures using Ti and Mg, or Ce secondary oxide coatings. Master sintering curve approach was successfully implemented to analyse the conductivity loss data. The MSC analysis yielded apparent activation energies for Ni sintering within the composite of 375 kJ/mol when heated in dry H2 and 440 kJ/mol when under wet H2.",
    keywords = "SOFC, Ni-YSZ, electrical conductivity, redox stability, Ni particle growth, master sintering curve",
    author = "Mikko Pihlatie and A. Kaiser and M.B. Mogensen",
    year = "2012",
    doi = "10.1016/j.ssi.2012.06.021",
    language = "English",
    volume = "222-223",
    pages = "38--46",
    journal = "Solid State Ionics",
    issn = "0167-2738",
    publisher = "Elsevier",

    }

    Electrical conductivity of Ni-YSZ composites : Variants and redox cycling. / Pihlatie, Mikko (Corresponding Author); Kaiser, A.; Mogensen, M.B.

    In: Solid State Ionics, Vol. 222-223, 2012, p. 38-46.

    Research output: Contribution to journalArticleScientificpeer-review

    TY - JOUR

    T1 - Electrical conductivity of Ni-YSZ composites

    T2 - Variants and redox cycling

    AU - Pihlatie, Mikko

    AU - Kaiser, A.

    AU - Mogensen, M.B.

    PY - 2012

    Y1 - 2012

    N2 - Short-term changes in the electrical conductivity of different Ni–YSZ composites (cermets) were measured by an in-situ 4-point DC technique. The isothermal reduction was carried out in dry, humidified or wet hydrogen at temperatures from 600 to 850 °C. The cermets reduced at 600 °C showed a stable conductivity of about 1100 S/cm, which increased to an enhanced ~ 2000 S/cm upon re-oxidation and subsequent re-reduction cycling at the same temperature. At 850 °C, a rapid initial conductivity loss was observed; upon re-reduction after the re-oxidation both the conductivity and its loss rate were largely the same as in the initial reduction. The presence of steam had an accelerating effect on the conductivity loss at 850 °C. In addition to cermets with a typical microstructure, different modified microstructures and compositions were tested. In the modified cermets, Al, Mg, and Ce were used as Ni dopants alongside with undoped Ni. Scanning electron microscopy of cermets reduced in different conditions showed increasing particle size and loss of metal-to-metal percolation in the samples reduced at higher temperatures, and a very fine microstructure in the high conductivity sample re-oxidised at 600 °C. Short-term conductivity changes due to microstructural changes in both the standard and modified cermets with different Ni doping were compared by re-oxidation at 600 °C and subsequent thermal excursions up to 1000 °C by normalising the conductivity to a constant temperature. Modified cermets show reduced conductivity loss on both isothermal heating and high temperature ramping. Most stable cermets were the ones with undoped NiO and modified microstructure, as well as modified microstructures using Ti and Mg, or Ce secondary oxide coatings. Master sintering curve approach was successfully implemented to analyse the conductivity loss data. The MSC analysis yielded apparent activation energies for Ni sintering within the composite of 375 kJ/mol when heated in dry H2 and 440 kJ/mol when under wet H2.

    AB - Short-term changes in the electrical conductivity of different Ni–YSZ composites (cermets) were measured by an in-situ 4-point DC technique. The isothermal reduction was carried out in dry, humidified or wet hydrogen at temperatures from 600 to 850 °C. The cermets reduced at 600 °C showed a stable conductivity of about 1100 S/cm, which increased to an enhanced ~ 2000 S/cm upon re-oxidation and subsequent re-reduction cycling at the same temperature. At 850 °C, a rapid initial conductivity loss was observed; upon re-reduction after the re-oxidation both the conductivity and its loss rate were largely the same as in the initial reduction. The presence of steam had an accelerating effect on the conductivity loss at 850 °C. In addition to cermets with a typical microstructure, different modified microstructures and compositions were tested. In the modified cermets, Al, Mg, and Ce were used as Ni dopants alongside with undoped Ni. Scanning electron microscopy of cermets reduced in different conditions showed increasing particle size and loss of metal-to-metal percolation in the samples reduced at higher temperatures, and a very fine microstructure in the high conductivity sample re-oxidised at 600 °C. Short-term conductivity changes due to microstructural changes in both the standard and modified cermets with different Ni doping were compared by re-oxidation at 600 °C and subsequent thermal excursions up to 1000 °C by normalising the conductivity to a constant temperature. Modified cermets show reduced conductivity loss on both isothermal heating and high temperature ramping. Most stable cermets were the ones with undoped NiO and modified microstructure, as well as modified microstructures using Ti and Mg, or Ce secondary oxide coatings. Master sintering curve approach was successfully implemented to analyse the conductivity loss data. The MSC analysis yielded apparent activation energies for Ni sintering within the composite of 375 kJ/mol when heated in dry H2 and 440 kJ/mol when under wet H2.

    KW - SOFC

    KW - Ni-YSZ

    KW - electrical conductivity

    KW - redox stability

    KW - Ni particle growth

    KW - master sintering curve

    U2 - 10.1016/j.ssi.2012.06.021

    DO - 10.1016/j.ssi.2012.06.021

    M3 - Article

    VL - 222-223

    SP - 38

    EP - 46

    JO - Solid State Ionics

    JF - Solid State Ionics

    SN - 0167-2738

    ER -