Lanthanum and nickel co-doped strontium titanates for solid oxide fuel cell anodes
File(s)
Author(s)
Stevenson, Graham Robert
Type
Thesis
Abstract
Fuel cells are a technology that can potentially revolutionise the means by which we store and
convert energy. High-temperature solid oxide fuel cells can do so at higher efficiencies than
conventional fuel cells and can utilise the waste heat to further boost overall efficiency, while
acting on a variety of fuels that could ease the transition to a clean energy infrastructure.
Solid oxide fuel cell materials are currently limited by anode degradation and overall lifetime.
In order to make the technology viable, these issues need addressing. One means of doing so
is investigating alternative anode materials. Perovskite materials, in particular lanthanum doped strontium titanates, have been of interest recently due to their respectable electronic
conductivity and stability in sulfur- and carbon-containing fuel sources. Furthermore, doping
of this material has led to further functionalisation through use of exsolution: the growth of
socketed catalytic nanoparticles to enhance material performance.
This thesis aims to investigate the technology, literature and answer the following questions on
the lanthanum-doped strontium titanate materials:
1) Is it possible to synthesise the materials by a non-solid-state route?
2) Can the number of processing steps in electrode formation be reduced?
3) Can an understanding of the exsolution process be further developed?
4) Can these materials be further improved through our understanding?
The material is shown to be able to form the required phase at temperatures as low as 1000 °C
through a modified synthesis route, still exhibiting the exsolution phenomenon that makes this
class of materials of interest, and is also shown to produce structures with inherent porosity.
This leads to the formation of one-step processed microstructures which perform slightly worse
than conventionally manufactured samples of the same material. Through RC-circuit fitting
and Gerischer element fitting of electrochemical impedance spectroscopy data, this change in
performance is attributed to be due to the difference in porosity between the two
microstructures. The formation of nanoparticles on the surface is also shown to improve
performance compared to similar materials in similar conditions, thus a sensitivity study into
the exsolution behaviour is undertaken. The factors that control exsolution are briefly
investigated and an understanding of how these may improve the exsolution profile is
developed, leading to the creation of a new composition of doped-titanate. This composition
shows a considerably more nanoparticle-dense exsolution profile than the predecessors treated
in the same conditions and also shows an approximately 22% improvement in electrochemical
performance measured through electrochemical impedance spectroscopy. Thus, this body of
work shows that the titanates can indeed be synthesised at lower temperatures, the inherent
microstructures formed this way may be functionalised for use as electrodes – where our
understanding of the interpretation of electrochemical impedance spectroscopy data is greatly
improved – and the conditions that produce consistent, nanoparticle-dense, exsolution arrays
are elucidated on, leading to demonstration of our understanding by improvement of the
material.
convert energy. High-temperature solid oxide fuel cells can do so at higher efficiencies than
conventional fuel cells and can utilise the waste heat to further boost overall efficiency, while
acting on a variety of fuels that could ease the transition to a clean energy infrastructure.
Solid oxide fuel cell materials are currently limited by anode degradation and overall lifetime.
In order to make the technology viable, these issues need addressing. One means of doing so
is investigating alternative anode materials. Perovskite materials, in particular lanthanum doped strontium titanates, have been of interest recently due to their respectable electronic
conductivity and stability in sulfur- and carbon-containing fuel sources. Furthermore, doping
of this material has led to further functionalisation through use of exsolution: the growth of
socketed catalytic nanoparticles to enhance material performance.
This thesis aims to investigate the technology, literature and answer the following questions on
the lanthanum-doped strontium titanate materials:
1) Is it possible to synthesise the materials by a non-solid-state route?
2) Can the number of processing steps in electrode formation be reduced?
3) Can an understanding of the exsolution process be further developed?
4) Can these materials be further improved through our understanding?
The material is shown to be able to form the required phase at temperatures as low as 1000 °C
through a modified synthesis route, still exhibiting the exsolution phenomenon that makes this
class of materials of interest, and is also shown to produce structures with inherent porosity.
This leads to the formation of one-step processed microstructures which perform slightly worse
than conventionally manufactured samples of the same material. Through RC-circuit fitting
and Gerischer element fitting of electrochemical impedance spectroscopy data, this change in
performance is attributed to be due to the difference in porosity between the two
microstructures. The formation of nanoparticles on the surface is also shown to improve
performance compared to similar materials in similar conditions, thus a sensitivity study into
the exsolution behaviour is undertaken. The factors that control exsolution are briefly
investigated and an understanding of how these may improve the exsolution profile is
developed, leading to the creation of a new composition of doped-titanate. This composition
shows a considerably more nanoparticle-dense exsolution profile than the predecessors treated
in the same conditions and also shows an approximately 22% improvement in electrochemical
performance measured through electrochemical impedance spectroscopy. Thus, this body of
work shows that the titanates can indeed be synthesised at lower temperatures, the inherent
microstructures formed this way may be functionalised for use as electrodes – where our
understanding of the interpretation of electrochemical impedance spectroscopy data is greatly
improved – and the conditions that produce consistent, nanoparticle-dense, exsolution arrays
are elucidated on, leading to demonstration of our understanding by improvement of the
material.
Version
Open Access
Date Issued
2020-07
Date Awarded
2021-01
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Brandon, Nigel
Boldrin, Paul
Publisher Department
Earth Science and Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)