Date

2016

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Chemical Engineering

First Adviser

McIntosh, Steven

Other advisers/committee members

Caram, Hugo; Gilchrist, James; Baltrusaitis, Jonas; Strandwitz, Nicholas; McIntosh, Steven

Abstract

Solid oxide fuel cells (SOFCs) possess the potential for efficient conversion of chemical energy to electrical energy with minimal production of pollutants. Development of intermediate temperature solid oxide fuel cells (IT-SOFCs) requires the development of more active electrode materials due to the high activation energies associated with oxygen dissociation and incorporation. Both the surface activities and bulk conductivities for oxygen dissociation and transport have been measured for a wide variety of cathode materials utilizing isotopic depth profiling and thermogravimetric analysis techniques, with a correlation found between these values. As discussed within however, these techniques can be misleading for a variety of reasons. Consequently, a combination of bulk and surface measurement techniques including neutron powder diffraction, isotopic oxygen pulsing, as well as surface composition measurements were performed for a range of perovskite-related materials to define the nature of this relationship between surface and bulk properties.It was found that the link between surface reaction rates and bulk conductivity is caused by a difficulty in measuring the actual “surface” reaction rate, as several materials with notably similar surface compositions exhibited significantly different reaction rates. Similarly, these surface reaction rates were directly linked to the bulk structure through an oxygen vacancy hopping mechanism. As such, we conclude that the measurement of surface reaction rates is limited by an incorporation step which has oxygen on the surface of the material migrate into the bulk structure rather than any actual limitation of oxygen dissociation on the surface or bulk oxygen transport.

Share

COinS