The Ni-YSZ interface: Structure, composition and electrochemical properties at 1000°C

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    Abstract

    The anode/electrolyte interface in solid oxide fuel cells (SOFC) is known to cause electrical losses. Geometrically simple Ni/yttria-stabilised zirconia (YSZ) interfaces were examined to gain information on the structural and chemical changes occurring during experiments at 1000°C in an atmosphere of 97% H2/3% H2O. Electrochemical impedance spectroscopy at open circuit voltage (OCV) and at anodic and cathodic polarisations (100 mV) was performed. A correlation of the electrical data with the structure development and the chemical composition was attempted. Nickel wires with different impurity content (99.8% Ni and 99.995% Ni) were used to examine the impact of impurities on the polarisation resistance and contact area morphology. The electropolished nickel wires were pressed against a polished 8 mol% YSZ surface. Extensive structural changes from a flat interface to a hill and valley structure were found to occur in the contact area with the impure nickel wire, and a ridge of impurities was built along the rim of the contact area. Impurity particles in the interfacial region were also observed. The impurity phase was described as an alkali silicate glassy phase. No differences were found between polarised and non-polarised samples. With pure nickel wires, however, the microstructures depended on the polarisation/non-polarisation conditions. At non-polarised conditions a hill and valley type structure was found. Anodic polarisation produced an up to 1 μm thick interface layer consisting of nano-sized YSZ particles with some Ni present. At cathodic polarisation both a granulated structure and a hill and valley structure resembling the structure of non-polarised samples were found. Small impurity ridges were surrounding the contact areas on non-polarised and cathodically polarised samples. TOF-SIMS and XPS analyses showed the presence of impurities in both the impure and pure contact areas. The impedance spectroscopy revealed that depending on the impurity content of the nickel, different developments of the polarisation resistance with time took place. At open circuit voltage the samples with impure nickel electrodes showed an initial increase toward a high constant polarisation resistance, whereas the samples with pure nickel electrodes showed a considerable decrease to a low constant polarisation resistance with time. For both types of nickel the polarisation resistance dropped upon polarisation. The area specific polarisation resistances for the samples with pure electrodes were approximately 10 times lower than for samples with impure electrodes. This was mainly ascribed to the impurity content and distribution, both in the three phase boundary zone and as a more or less continuous film covering the interfacial region. The drop in the Rp upon polarisation may be ascribed to changes in the distribution of the impurity phase in the interfacial region.
    Original languageEnglish
    Place of PublicationRoskilde
    PublisherForskningscenter Risø
    Number of pages116
    ISBN (Print)87-550-3042-4
    Publication statusPublished - 2002
    SeriesDenmark. Forskningscenter Risoe. Risoe-R
    Number1335(EN)
    ISSN0106-2840

    Keywords

    • Risø-R-1335
    • Risø-R-1335(EN)

    Cite this

    Jensen, K. V. (2002). The Ni-YSZ interface: Structure, composition and electrochemical properties at 1000°C. Roskilde: Forskningscenter Risø. Denmark. Forskningscenter Risoe. Risoe-R, No. 1335(EN)
    Jensen, Karin Vels. / The Ni-YSZ interface : Structure, composition and electrochemical properties at 1000°C. Roskilde : Forskningscenter Risø, 2002. 116 p. (Denmark. Forskningscenter Risoe. Risoe-R; No. 1335(EN)).
    @phdthesis{c1a07bf6ede140fd95c867cf892441d2,
    title = "The Ni-YSZ interface: Structure, composition and electrochemical properties at 1000°C",
    abstract = "The anode/electrolyte interface in solid oxide fuel cells (SOFC) is known to cause electrical losses. Geometrically simple Ni/yttria-stabilised zirconia (YSZ) interfaces were examined to gain information on the structural and chemical changes occurring during experiments at 1000°C in an atmosphere of 97{\%} H2/3{\%} H2O. Electrochemical impedance spectroscopy at open circuit voltage (OCV) and at anodic and cathodic polarisations (100 mV) was performed. A correlation of the electrical data with the structure development and the chemical composition was attempted. Nickel wires with different impurity content (99.8{\%} Ni and 99.995{\%} Ni) were used to examine the impact of impurities on the polarisation resistance and contact area morphology. The electropolished nickel wires were pressed against a polished 8 mol{\%} YSZ surface. Extensive structural changes from a flat interface to a hill and valley structure were found to occur in the contact area with the impure nickel wire, and a ridge of impurities was built along the rim of the contact area. Impurity particles in the interfacial region were also observed. The impurity phase was described as an alkali silicate glassy phase. No differences were found between polarised and non-polarised samples. With pure nickel wires, however, the microstructures depended on the polarisation/non-polarisation conditions. At non-polarised conditions a hill and valley type structure was found. Anodic polarisation produced an up to 1 μm thick interface layer consisting of nano-sized YSZ particles with some Ni present. At cathodic polarisation both a granulated structure and a hill and valley structure resembling the structure of non-polarised samples were found. Small impurity ridges were surrounding the contact areas on non-polarised and cathodically polarised samples. TOF-SIMS and XPS analyses showed the presence of impurities in both the impure and pure contact areas. The impedance spectroscopy revealed that depending on the impurity content of the nickel, different developments of the polarisation resistance with time took place. At open circuit voltage the samples with impure nickel electrodes showed an initial increase toward a high constant polarisation resistance, whereas the samples with pure nickel electrodes showed a considerable decrease to a low constant polarisation resistance with time. For both types of nickel the polarisation resistance dropped upon polarisation. The area specific polarisation resistances for the samples with pure electrodes were approximately 10 times lower than for samples with impure electrodes. This was mainly ascribed to the impurity content and distribution, both in the three phase boundary zone and as a more or less continuous film covering the interfacial region. The drop in the Rp upon polarisation may be ascribed to changes in the distribution of the impurity phase in the interfacial region.",
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    Jensen, KV 2002, The Ni-YSZ interface: Structure, composition and electrochemical properties at 1000°C. Denmark. Forskningscenter Risoe. Risoe-R, no. 1335(EN), Forskningscenter Risø, Roskilde.

    The Ni-YSZ interface : Structure, composition and electrochemical properties at 1000°C. / Jensen, Karin Vels.

    Roskilde : Forskningscenter Risø, 2002. 116 p. (Denmark. Forskningscenter Risoe. Risoe-R; No. 1335(EN)).

    Research output: Book/ReportPh.D. thesisResearch

    TY - BOOK

    T1 - The Ni-YSZ interface

    T2 - Structure, composition and electrochemical properties at 1000°C

    AU - Jensen, Karin Vels

    PY - 2002

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    N2 - The anode/electrolyte interface in solid oxide fuel cells (SOFC) is known to cause electrical losses. Geometrically simple Ni/yttria-stabilised zirconia (YSZ) interfaces were examined to gain information on the structural and chemical changes occurring during experiments at 1000°C in an atmosphere of 97% H2/3% H2O. Electrochemical impedance spectroscopy at open circuit voltage (OCV) and at anodic and cathodic polarisations (100 mV) was performed. A correlation of the electrical data with the structure development and the chemical composition was attempted. Nickel wires with different impurity content (99.8% Ni and 99.995% Ni) were used to examine the impact of impurities on the polarisation resistance and contact area morphology. The electropolished nickel wires were pressed against a polished 8 mol% YSZ surface. Extensive structural changes from a flat interface to a hill and valley structure were found to occur in the contact area with the impure nickel wire, and a ridge of impurities was built along the rim of the contact area. Impurity particles in the interfacial region were also observed. The impurity phase was described as an alkali silicate glassy phase. No differences were found between polarised and non-polarised samples. With pure nickel wires, however, the microstructures depended on the polarisation/non-polarisation conditions. At non-polarised conditions a hill and valley type structure was found. Anodic polarisation produced an up to 1 μm thick interface layer consisting of nano-sized YSZ particles with some Ni present. At cathodic polarisation both a granulated structure and a hill and valley structure resembling the structure of non-polarised samples were found. Small impurity ridges were surrounding the contact areas on non-polarised and cathodically polarised samples. TOF-SIMS and XPS analyses showed the presence of impurities in both the impure and pure contact areas. The impedance spectroscopy revealed that depending on the impurity content of the nickel, different developments of the polarisation resistance with time took place. At open circuit voltage the samples with impure nickel electrodes showed an initial increase toward a high constant polarisation resistance, whereas the samples with pure nickel electrodes showed a considerable decrease to a low constant polarisation resistance with time. For both types of nickel the polarisation resistance dropped upon polarisation. The area specific polarisation resistances for the samples with pure electrodes were approximately 10 times lower than for samples with impure electrodes. This was mainly ascribed to the impurity content and distribution, both in the three phase boundary zone and as a more or less continuous film covering the interfacial region. The drop in the Rp upon polarisation may be ascribed to changes in the distribution of the impurity phase in the interfacial region.

    AB - The anode/electrolyte interface in solid oxide fuel cells (SOFC) is known to cause electrical losses. Geometrically simple Ni/yttria-stabilised zirconia (YSZ) interfaces were examined to gain information on the structural and chemical changes occurring during experiments at 1000°C in an atmosphere of 97% H2/3% H2O. Electrochemical impedance spectroscopy at open circuit voltage (OCV) and at anodic and cathodic polarisations (100 mV) was performed. A correlation of the electrical data with the structure development and the chemical composition was attempted. Nickel wires with different impurity content (99.8% Ni and 99.995% Ni) were used to examine the impact of impurities on the polarisation resistance and contact area morphology. The electropolished nickel wires were pressed against a polished 8 mol% YSZ surface. Extensive structural changes from a flat interface to a hill and valley structure were found to occur in the contact area with the impure nickel wire, and a ridge of impurities was built along the rim of the contact area. Impurity particles in the interfacial region were also observed. The impurity phase was described as an alkali silicate glassy phase. No differences were found between polarised and non-polarised samples. With pure nickel wires, however, the microstructures depended on the polarisation/non-polarisation conditions. At non-polarised conditions a hill and valley type structure was found. Anodic polarisation produced an up to 1 μm thick interface layer consisting of nano-sized YSZ particles with some Ni present. At cathodic polarisation both a granulated structure and a hill and valley structure resembling the structure of non-polarised samples were found. Small impurity ridges were surrounding the contact areas on non-polarised and cathodically polarised samples. TOF-SIMS and XPS analyses showed the presence of impurities in both the impure and pure contact areas. The impedance spectroscopy revealed that depending on the impurity content of the nickel, different developments of the polarisation resistance with time took place. At open circuit voltage the samples with impure nickel electrodes showed an initial increase toward a high constant polarisation resistance, whereas the samples with pure nickel electrodes showed a considerable decrease to a low constant polarisation resistance with time. For both types of nickel the polarisation resistance dropped upon polarisation. The area specific polarisation resistances for the samples with pure electrodes were approximately 10 times lower than for samples with impure electrodes. This was mainly ascribed to the impurity content and distribution, both in the three phase boundary zone and as a more or less continuous film covering the interfacial region. The drop in the Rp upon polarisation may be ascribed to changes in the distribution of the impurity phase in the interfacial region.

    KW - Risø-R-1335

    KW - Risø-R-1335(EN)

    M3 - Ph.D. thesis

    SN - 87-550-3042-4

    T3 - Denmark. Forskningscenter Risoe. Risoe-R

    BT - The Ni-YSZ interface

    PB - Forskningscenter Risø

    CY - Roskilde

    ER -

    Jensen KV. The Ni-YSZ interface: Structure, composition and electrochemical properties at 1000°C. Roskilde: Forskningscenter Risø, 2002. 116 p. (Denmark. Forskningscenter Risoe. Risoe-R; No. 1335(EN)).