Silver composites as highly stable cathode current collectors for solid oxide fuel cells
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Silver composites as highly stable cathode current collectors for solid oxide fuel cells Ayhan Sarikaya, Vladimir Petrovsky, and Fatih Dogana) Department of Materials Science and Engineering, Missouri University of Science and Technology, Rolla, Missouri 65409 (Received 13 January 2012; accepted 4 May 2012)
Time stability of the solid oxide fuel cells (SOFCs) has been a significant concern toward realization of their practical applications. Its operation at elevated temperatures and in oxidizing atmospheres makes the cathode current collector one of the most vulnerable components of the SOFCs. Silver and silver-based metal oxide [lanthanum–strontium manganite (LSM) and yttria-stabilized zirconia] composites were investigated for the development of low-cost current collectors with long-term stability. While densification of pure silver limited its use as current collector, incorporation of oxide particles to the silver matrix led to formation of porous composites. However, addition of YSZ particles did not result in a stable porosity. Analysis of the impedance spectra allowed further investigations on the obtained microstructures and the formed contacts. No microstructural degradation has been observed in the porous Ag–LSM composite current collector and its electrical properties remained stable for over 5000 h of measurements at 800 °C in air.
I. INTRODUCTION
Ohmic losses, which arise due to the high resistance of the contact materials, have been a vital concern for the development of solid oxide fuel cells (SOFCs).1–3 Stability and efficiency of the current collection on the cathode side of the SOFCs is a relatively more challenging issue than the anode side especially for the intermediate temperature (600–800 °C) SOFCs due to high temperature oxidation.4–6 Common current collectors include ceramics (e.g., LaCoO3 and LaCrO3) and noble metals (e.g., Pt, Pd, Au, and Ag).7 Although ceramic materials have high stability in oxidizing conditions, their lower electrical conductivities limit their use. Noble metals such as Pt, Au, or Pd are used as common current collectors stable at high temperatures, while their relatively high cost makes them less desirable for use in SOFC applications.7–10 Its relatively low-cost and advantageous attributes such as high conductivity, high ductility, and self-healing at operating temperatures make Ag a good candidate for the current collection.8,11 However, operational conditions deteriorate its structural stability and limit its use in SOFCs.8,11–13 Operational temperatures of SOFCs (e.g., 800 °C) allow sintering of Ag particles and result in nearly full density of initially porous microstructure within a relatively short time (,170 h) with respect to the target lifetime of 40,000 h14 due to relatively low melting temperature of pure Ag (962 °C), as shown in Figs. 1(a) and 1(b).15
Development of a porous and structurally stable Ag-based current collector was aimed by this study. Since the degradation of the cathode and anode layers limits the detailed analysis of the degradation mech
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