Investigation of electrolyte materials and measurement techniques for nanocomposite fuel cells

Research output: ThesisLicenciate's thesis

Abstract

Solid oxide and molten carbonate fuel cells are considered promising for electricity production. Unfortunately, their high operating temperature and current stability issues prohibit their usage. Based on these fuel cell types, another kind of fuel cell has been developed allowing lower operating temperatures. This type of fuel cell has been called a low or intermediate temperature solid oxide fuel cell but due to its composite nature, we prefer to call it a composite fuel cell i.e. CFC. The electrolyte of the CFC is commonly a mixture of alkali carbonates and doped ceria. Its measured properties can be affected by different preparation and measurement methods. In this work we have conducted a literature review of conductivities of CFC electrolytes with the emphasis on a comparison between different measurement methods. In addition, we have also prepared CFC electrolytes and studied how freeze drying and spark plasma sintering affect the properties of the electrolyte and especially the conductivity. The most common measurement method has been an electrochemical impedance spectroscopy (EIS) producing also the highest measured conductivities. However, apparently the high conductivity is mainly due to the conductivity of the carbonate and the values acquired by EIS cannot be used to determine the goodness of the electrolyte in an operating fuel cell. On the other hand, lower conductivities have been acquired in constant current and product analysis measurements, but their results can be assumed to relate more to the effectiveness of the fuel cell. In case of the sample preparation, freeze drying has been noted to yield quite uniformly distributed nanoparticles and spark plasma sintering allowed more dense electrolytes to be prepared. These are both beneficial properties for the CFC cell and thus it is recommended in the future to produce samples using the freeze drying and, when applicable, spark plasma sintering methods. Similarly, the conductivity is recommended to be measured using either constant current or product analysis methods.
Original languageEnglish
QualificationLicentiate's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Lund, Peter, Supervising Professor
  • Lund, Peter, Thesis Advisor
Publisher
Publication statusPublished - 2014
MoE publication typeG3 Licentiate thesis

Keywords

  • LT-SOFC
  • CFC
  • Freeze drying
  • Spark plasma sintering
  • Ionic conductivity
  • Doped ceria/carbonate electrolyte
  • Electrochemical impedance spectroscopy
  • Constant current measurement
  • Product analysis

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