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Strontium Titanate-based Anodes for Solid Oxide Fuel Cells

Blennow Tullmar, Peter LU (2007)
Abstract (Swedish)
Popular Abstract in Swedish

Syftet med detta arbete har varit att utveckla nya, stabila bränsleelektroder till bränsleceller baserade på fasta oxider, SOFC (solid oxide fuel cells). Vi har undersökt olika keramiska material eller kompositer med lovande egenskaper för att användas på anodsidan av bränslecellerna. För att förbättra redox-stabiliteten så ska bränsleelektroden företrädesvis inte innehålla någon metall, eller åtminstone inte vara en huvudbeståndsdel.



Vi har också försökt att uppnå en bättre förståelse för de elektrokatalytiska egenskaperna för oxidation av vätgas hos några intressanta keramiska material, däribland material baserade på strontiumtitanat i kombination med dopad ceriumdioxid... (More)
Popular Abstract in Swedish

Syftet med detta arbete har varit att utveckla nya, stabila bränsleelektroder till bränsleceller baserade på fasta oxider, SOFC (solid oxide fuel cells). Vi har undersökt olika keramiska material eller kompositer med lovande egenskaper för att användas på anodsidan av bränslecellerna. För att förbättra redox-stabiliteten så ska bränsleelektroden företrädesvis inte innehålla någon metall, eller åtminstone inte vara en huvudbeståndsdel.



Vi har också försökt att uppnå en bättre förståelse för de elektrokatalytiska egenskaperna för oxidation av vätgas hos några intressanta keramiska material, däribland material baserade på strontiumtitanat i kombination med dopad ceriumdioxid (ceria). Materialen har undersökts med olika experimentella metoder för att bestämma vilka fysikaliska och kemiska egenskaper som styr de elektrokemiska egenskaperna och redox-stabiliteten.



Vi har undersökt de elektrokemiska egenskaperna hos odopad strontiumtitanat (Sr1-xTiO3) som är understökiometrisk med avseende på strontium. Det visade sig att odopad strontiumtitanat är en dålig elektrokatalysator för oxidation av vätgas, och vi påbörjade sökandet efter ett material med högre elektrokemisk aktivitet och bättre ledningsförmåga. Konformade elektroder har använts med fördel som en relativ mätmetod för att jämföra den elektrokemiska aktiviteten mellan olika material.



En ny våtkemibaserad syntes har utvecklats för att framställa kemiskt homogen Nb-dopad SrTiO3. De framställda partiklarna har partikelstorlekar i submikrometerområdet. Defektstrukturegenskaperna och de elektriska transportegenskaperna för materialet, har studerats där den generella teorin om defektkemin för n-dopade titanater har kunnat verifieras med experimentella mättekniker. Vi har funnit att Nb-dopad SrTiO3 är ett keramiskt material med hög elektrisk ledningsförmåga (sigma > 120 S/cm vid 1000 ºC i reducerande atmosfär). Vidare har vi använt XANES (X-ray Absorption Near Edge Structure) för att klarlägga oxidationstillståndet för Ti i titanat-materialet. De elektrokemiska egenskaperna hos Nb-dopad SrTiO3 undersöktes, och materialet hade lovande redox-stabilitet, även om det visade sig att den elektrokatalytiska aktiviteten behövde förbättras minst 100 gånger för att materialet ska kunna utgöra ett alternativ som bränsleelektrod.



För att kombinera effekter av olika material i en komposit, undersöktes impregnering av aktiva material in i en porös struktur av elektriskt ledande Nb-dopad SrTiO3. Resultaten visade att impregnering med en ceria-lösning innehållande tensider bidrog till bildandet av nanometerstora ceria-partiklar (i detta fall Gd-dopad ceria, CGO) på titanatpartiklarnas exponerade ytor. Den elektrokatalytiska aktiviteten hos den nya keramiska anodkompositstrukturen visade sig vara jämförbar eller till och med bättre i jämförelse med den nuvarande mest använda Ni/YSZ-baserade bränsleelektroden. Den keramiska kompositelektroden visade sig tillika vara redox-stabil. Elektroden aktiverades dessutom under en redox-cykel vid 650 ºC. Resultaten tyder på att CGO fungerar som den blandat ledande och elektrokatalytiskt aktiva fasen medan den porösa strukturen, bestående av Nb-dopad SrTiO3, huvudsakligen fungerar som elektronisk ledare. (Less)
Abstract
The purpose for this work has been to develop new robust fuel electrodes for solid oxide fuel cells (SOFC). The aim was to find suitable ceramic materials or composites with promising properties for the use as SOFC anodes. Preferably, the electrode should not contain any metal (or at least a metal should not be a major component) in order to improve the redox properties. The present work focuses on trying to understand the electrocatalytical properties for hydrogen oxidation of a few interesting ceramic materials, such as strontium titanate-based materials in combination with doped ceria. The materials have been characterized with different experimental methods in order to determine which physical and chemical properties that govern the... (More)
The purpose for this work has been to develop new robust fuel electrodes for solid oxide fuel cells (SOFC). The aim was to find suitable ceramic materials or composites with promising properties for the use as SOFC anodes. Preferably, the electrode should not contain any metal (or at least a metal should not be a major component) in order to improve the redox properties. The present work focuses on trying to understand the electrocatalytical properties for hydrogen oxidation of a few interesting ceramic materials, such as strontium titanate-based materials in combination with doped ceria. The materials have been characterized with different experimental methods in order to determine which physical and chemical properties that govern the electrochemical performance and redox behavior.



In the first section, the electrochemical properties for hydrogen oxidation of undoped Sr-deficient strontium titanate (Sr1-xTiO3) were investigated. In general, it was found that the undoped titanate materials were poor electrocatalysts for hydrogen oxidation and materials with higher electrochemical activity and higher electronic conductivity were needed. The benefits of using cone-shaped electrodes, as a relative method of comparing the electrochemical activity of different materials, were discussed.



In the next section, a new wet chemistry based synthesis route was developed for fabricating homogeneous Nb-doped SrTiO3 particles with submicron particle sizes. The defect and electronic transport properties of Nb-doped SrTiO3 were investigated, where the theory about the general defect chemistry for n-doped titanates were discussed and confirmed with various experimental techniques. It was found that Nb-doped SrTiO3 is a ceramic material with high electrical conductivity (sigma > 120 S/cm at 1000 ºC in reducing atmosphere). The use of XANES (X-ray Absorption Near Edge Structure), for determining the oxidation state of Ti in the titanate, was also discussed. The electrochemical properties of Nb-doped SrTiO3 were subsequently investigated and it was concluded that Nb-doped SrTiO3 had promising redox stability properties. However, the electrocatalytic performance needed to be improved at least 100 times.



In the last section, infiltration of active materials into a backbone structure of electronically conductive Nb-doped SrTiO3 was studied. It was found that a surfactant-assisted infiltration route promoted the formation of nano-sized ceria particles (in this case Gd-doped ceria, CGO) on the surfaces of the backbone material. The performance of the novel ceramic composite anode structure was similar or even improved in comparison with the current state-of-the-art Ni/YSZ anodes, when investigated on symmetrical cells. The ceramic composite fuel electrode was also found to be redox stable, the electrodes actually activated upon redox cycling at 650 ºC. CGO was suggested to act as the mixed conducting electrocatalytically active phase whereas the backbone structure, consisting of Nb-doped SrTiO3, mainly functioned as the electronic conductor. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Irvine, John T. S., School of Chemistry, University of St Andrews, St Andrews, Scotland
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Kondenserade materiens egenskaper:elektronstruktur, spectroscopy, relaxation, magnetic resonance, supraconductors, magnetic and optical properties, electrical, Condensed matter:electronic structure, fasjämvikt, egenskaper (termiska och mekaniska), kristallografi, phase equilibria, Kondenserade materiens egenskaper:struktur, Condensed matter:stucture, thermal and mechanical properties, crystallography, infiltration, surfactant, ceria, Gd-doped ceria, redox stability, SOFC, ceramic anode, XRD, XANES, electrochemical impedance spectroscopy, defect chemistry, Nb-doped SrTiO3, electron microscopy, egenskaper (elektriska, magnetiska och optiska), supraledare, magnetisk resonans, spektroskopi, Inorganic chemistry, Oorganisk kemi, Electrochemistry, Elektrokemi, Energy research, Energiforskning, Composite materials, Kompositmaterial, Ceramic materials and powders, Keramiska material och pulver
pages
209 pages
publisher
Polymer and Materials Chemistry (LTH)
defense location
Kemicentrum (Lecture hall K:B) Getingevägen 60 221 00 Lund
defense date
2007-11-02 13:15
ISBN
978-91-7422-172-5
language
English
LU publication?
yes
id
7db2e709-9c67-4b3e-b377-f94d9a54e922 (old id 599001)
date added to LUP
2007-11-13 07:15:29
date last changed
2016-09-19 08:45:11
@phdthesis{7db2e709-9c67-4b3e-b377-f94d9a54e922,
  abstract     = {The purpose for this work has been to develop new robust fuel electrodes for solid oxide fuel cells (SOFC). The aim was to find suitable ceramic materials or composites with promising properties for the use as SOFC anodes. Preferably, the electrode should not contain any metal (or at least a metal should not be a major component) in order to improve the redox properties. The present work focuses on trying to understand the electrocatalytical properties for hydrogen oxidation of a few interesting ceramic materials, such as strontium titanate-based materials in combination with doped ceria. The materials have been characterized with different experimental methods in order to determine which physical and chemical properties that govern the electrochemical performance and redox behavior.<br/><br>
<br/><br>
In the first section, the electrochemical properties for hydrogen oxidation of undoped Sr-deficient strontium titanate (Sr1-xTiO3) were investigated. In general, it was found that the undoped titanate materials were poor electrocatalysts for hydrogen oxidation and materials with higher electrochemical activity and higher electronic conductivity were needed. The benefits of using cone-shaped electrodes, as a relative method of comparing the electrochemical activity of different materials, were discussed.<br/><br>
<br/><br>
In the next section, a new wet chemistry based synthesis route was developed for fabricating homogeneous Nb-doped SrTiO3 particles with submicron particle sizes. The defect and electronic transport properties of Nb-doped SrTiO3 were investigated, where the theory about the general defect chemistry for n-doped titanates were discussed and confirmed with various experimental techniques. It was found that Nb-doped SrTiO3 is a ceramic material with high electrical conductivity (sigma &gt; 120 S/cm at 1000 ºC in reducing atmosphere). The use of XANES (X-ray Absorption Near Edge Structure), for determining the oxidation state of Ti in the titanate, was also discussed. The electrochemical properties of Nb-doped SrTiO3 were subsequently investigated and it was concluded that Nb-doped SrTiO3 had promising redox stability properties. However, the electrocatalytic performance needed to be improved at least 100 times.<br/><br>
<br/><br>
In the last section, infiltration of active materials into a backbone structure of electronically conductive Nb-doped SrTiO3 was studied. It was found that a surfactant-assisted infiltration route promoted the formation of nano-sized ceria particles (in this case Gd-doped ceria, CGO) on the surfaces of the backbone material. The performance of the novel ceramic composite anode structure was similar or even improved in comparison with the current state-of-the-art Ni/YSZ anodes, when investigated on symmetrical cells. The ceramic composite fuel electrode was also found to be redox stable, the electrodes actually activated upon redox cycling at 650 ºC. CGO was suggested to act as the mixed conducting electrocatalytically active phase whereas the backbone structure, consisting of Nb-doped SrTiO3, mainly functioned as the electronic conductor.},
  author       = {Blennow Tullmar, Peter},
  isbn         = {978-91-7422-172-5},
  keyword      = {Kondenserade materiens egenskaper:elektronstruktur,spectroscopy,relaxation,magnetic resonance,supraconductors,magnetic and optical properties,electrical,Condensed matter:electronic structure,fasjämvikt,egenskaper (termiska och mekaniska),kristallografi,phase equilibria,Kondenserade materiens egenskaper:struktur,Condensed matter:stucture,thermal and mechanical properties,crystallography,infiltration,surfactant,ceria,Gd-doped ceria,redox stability,SOFC,ceramic anode,XRD,XANES,electrochemical impedance spectroscopy,defect chemistry,Nb-doped SrTiO3,electron microscopy,egenskaper (elektriska,magnetiska och optiska),supraledare,magnetisk resonans,spektroskopi,Inorganic chemistry,Oorganisk kemi,Electrochemistry,Elektrokemi,Energy research,Energiforskning,Composite materials,Kompositmaterial,Ceramic materials and powders,Keramiska material och pulver},
  language     = {eng},
  pages        = {209},
  publisher    = {Polymer and Materials Chemistry (LTH)},
  school       = {Lund University},
  title        = {Strontium Titanate-based Anodes for Solid Oxide Fuel Cells},
  year         = {2007},
}