Title page for ETD etd-08242011-134533


Type of Document Dissertation
Author Jin, Tongan
Author's Email Address tajin@vt.edu
URN etd-08242011-134533
Title Interactions of the Air Electrode with Electrolyte and Interconnect in Solid Oxide Cells
Degree PhD
Department Materials Science and Engineering
Advisory Committee
Advisor Name Title
Lu, P. Kathy Committee Chair
Lu, Guo-Quan Committee Member
Reynolds, William T. Jr. Committee Member
von Spakovsky, Michael R. Committee Member
Keywords
  • Sr-doped Lanthanum Manganite
  • Chromium Poisoning
  • Interconnect
  • Air Electrode
  • Solid Oxide Cells
Date of Defense 2011-08-08
Availability restricted
Abstract
The interactions between different components of solid oxide cells (SOCs) are critical issues for achieving the tens of thousands of hour’s goal for long-term performance stability and lifetime. The interactions between the ceramic electrolyte, porous ceramic air electrode, and metallic interconnect materials — including solid state interfacial reactions and vaporization/deposition of some volatile elements — have been investigated in the simulated SOC operating environment. The interactions demonstrate the material degradation mechanisms of the cell components and the effects of different factors such as chemical composition and microstructure of the materials, as well as atmosphere and current load on the air electrode side. In the aspect of materials, this work contributes to the degradation mechanism on the air electrode side and provides practical material design criteria for long-term SOC operation.

In this research, an yttria-stabilized zirconia electrolyte (YSZ)/strontium-doped lanthanum manganite electrode (LSM)/AISI 441 stainless steel interconnect tri-layer structure has been fabricated in order to simulate the air electrode working environment of a real cell. The tri-layer samples have been treated in dry/moist air atmospheres at 800°C for up to 500 h. The LSM air electrode shows slight grain growth, but the growth is less in moist atmospheres. The amount of Cr deposition on the LSM surface is slightly more for the samples thermally treated in the moist atmospheres. At the YSZ/LSM interface, La enrichment is significant while Mn depletion occurs. The Cr deposition at the YSZ/LSM interface is observed.

The stoichiometry of the air electrode is an important factor for the interactions. The air electrode composition has been varied by changing the x value in (La0.8Sr0.2)xMnO3 from 0.95 to 1.05 (LSM95, LSM100, and LSM105). The enrichment of La at the YSZ/LSM interface inhibits the Cr deposition. The mechanisms of Cr poisoning and LSM elemental surface segregation are discussed.

A 200 mA·cm-2 current load have been applied on the simulated cells. Mn is a key element for Cr deposition under polarization. Excessive Mn in the LSM lessens the formation of La-containing phases at the YSZ/LSM interface and accelerates Cr deposition. Deficient Mn in LSM leads to extensive interfacial reaction with YSZ forming more La-containing phase and inhibiting Cr deposition.

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