Guo, Yuyan (2006-12). Mixed ionic and electronic conducting electrode studies for an alkali metal thermal to electric converter. Doctoral Dissertation. Thesis uri icon

abstract

  • This research focuses on preparation, kinetics, and performance studies of mixed ionic and electronic conducting electrodes (MIEE) applied in an alkali metal thermal to electric converter (AMTEC). Two types of MIEE, metal/sodium titanate and metal/??- alumina were investigated, using Ni, Cu, Co and W as the metal components. Pure metal electrodes (PME) were also studied, including Ta, Ni, Nb, Ir, W and MoRe electrodes. The stability of MIEE/???-alumina solid electrolyte (BASE) interface was studied in terms of the chemical potential of Na-Al-Ti-O system at 1100K (typical AMTEC operating temperature). Ni metal was compatible with sodium titanate and BASE and displayed the best initial performance among all tested PMEs. Ni/sodium titanate electrodes with 4/1 mass ratios of metal/ceramic performed best among all tested electrodes. Scanning Electron Microscope (SEM) observations showed that grain agglomeration, which is the main mechanism for electrode degradation, occurred in all tested electrodes. Ceramic components were able to effectively limit the growth of metal grains and resulted in a long lifetime for MIEEs. Ni particles in the MIEE formed a network microstructure that was close to the theoretical morphology of the ideal electrode. A model based on percolation theory was constructed to interpret and predict the performance of MIEEs. The electrode kinetics was studied and a theoretical expression for the interface impedance was derived for both PME and MIEE, using electrochemical impedance spectroscopy (EIS). The conductivity of the Na2Ti3O7 and Na2Ti6O13 mixture was measured. The average activation energy for the bulk conductivity was 0.87ev. Finally, theoretical analysis clarified that the transfer coefficient ? value change would cause at most a few percent change in the electrode performance parameter B.
  • This research focuses on preparation, kinetics, and performance studies of mixed
    ionic and electronic conducting electrodes (MIEE) applied in an alkali metal thermal to
    electric converter (AMTEC). Two types of MIEE, metal/sodium titanate and metal/??-
    alumina were investigated, using Ni, Cu, Co and W as the metal components. Pure metal
    electrodes (PME) were also studied, including Ta, Ni, Nb, Ir, W and MoRe electrodes.
    The stability of MIEE/???-alumina solid electrolyte (BASE) interface was studied in
    terms of the chemical potential of Na-Al-Ti-O system at 1100K (typical AMTEC
    operating temperature). Ni metal was compatible with sodium titanate and BASE and
    displayed the best initial performance among all tested PMEs. Ni/sodium titanate
    electrodes with 4/1 mass ratios of metal/ceramic performed best among all tested
    electrodes. Scanning Electron Microscope (SEM) observations showed that grain
    agglomeration, which is the main mechanism for electrode degradation, occurred in all
    tested electrodes. Ceramic components were able to effectively limit the growth of
    metal grains and resulted in a long lifetime for MIEEs. Ni particles in the MIEE formed a network microstructure that was close to the theoretical morphology of the ideal
    electrode. A model based on percolation theory was constructed to interpret and predict
    the performance of MIEEs.
    The electrode kinetics was studied and a theoretical expression for the interface
    impedance was derived for both PME and MIEE, using electrochemical impedance
    spectroscopy (EIS). The conductivity of the Na2Ti3O7 and Na2Ti6O13 mixture was
    measured. The average activation energy for the bulk conductivity was 0.87ev. Finally,
    theoretical analysis clarified that the transfer coefficient ? value change would cause at
    most a few percent change in the electrode performance parameter B.

publication date

  • December 2006