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/β″-
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/β′′-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 α value change would cause at
most a few percent change in the electrode performance parameter B.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1053 |
| Date | 15 May 2009 |
| Creators | Guo, Yuyan |
| Contributors | Hughbanks, Timothy R, Schuller, Michael |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
Page generated in 0.0016 seconds