Improving solid oxide cell performance and durability by optimizing ionic and electronic transport in electrolyte

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Title Improving solid oxide cell performance and durability by optimizing ionic and electronic transport in electrolyte
Publication Type dissertation
School or College College of Engineering
Department Materials Science & Engineering
Author Zhang, Lei
Date 2015
Description The current status of solid oxide fuel cell (SOFC) development is reviewed. A parametric model based on real cell materials and components was developed. Current cathode material and structure are sufficient, and the limiting factors are gas diffusion through the supporting layer and ohmic loss through the whole cell. Once the latter two losses can be minimized, SOFC can offer the best performance. Most of the ohmic loss can be attributed to ionic resistance in the electrolyte, of which more than 50% is due to grain boundary resistance. A quantitative space charge theory is developed for YSZ by considering all the possible defect species and defect complex. Both oxygen vacancy depletion and yttrium segregation near the grain boundary contribute to the very high grain boundary resistivity. A nonequilibrium analysis suggests that quenching at higher temperature can improve both grain bulk and grain boundary conductivity. Nowadays, reversible solid oxide cells (SOC) can be used in both fuel cell mode to generate energy and in electrolyser mode (SOEC) to store energy. However, a SOC degrades much faster when working in the SOEC mode. Oxygen chemical potential in the solid electrolyte near the oxygen electrode could be very high and leads to crack growth. Introducing finite electronic conductivity by doping can prohibit such crack growth. A novel oxygen permeation technique has been developed to measure electronic partial conductivities in solid electrolyte materials. Oxygen can be pumped into the sample by applying DC bias. As excess oxygen is stored in the cavity, the generated Nernst potential drives permeation current. At steady state, oxygen pumped into the cavity equals that which permeates out. When DC bias is turn off, Nernst potential follows a slow decay with time. Analysis of both steady state data and transient process data gives electronic resistance. Proton exchange membrane fuel cell (PEMFC) is now used in electrical cars. The wide application of PEMFC is currently limited by its cost and degradation. Even with a trace amount of carbon monoxide, Pt catalyst will be poisoned. A novel technique is developed to study CO adsorption and desorption kinetics by monitoring the resistance variation.
Type Text
Publisher University of Utah
Subject Electrocatalyst; Electrochemical Impedance Spectroscopy; Embedded Probe; Fuel Cell; Permeation Cell; Space Charge
Dissertation Name Doctor of Philosophy
Language eng
Rights Management ©Lei Zhang
Format application/pdf
Format Medium application/pdf
Format Extent 27,725 bytes
Identifier etd3/id/3982
ARK ark:/87278/s6kq19fz
Setname ir_etd
ID 197532
Reference URL https://collections.lib.utah.edu/ark:/87278/s6kq19fz
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