nanostructured materials for solid oxide fuel cells...
TRANSCRIPT
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Nanostructured materials for
Solid Oxide Fuel Cells (SOFC)
Adriana Serquis
Departamento Caracterización de Materiales
Centro Atómico Bariloche - ARGENTINA
INN-CONICET-CNEA
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Centro Atómico BarilocheInstituto Balseiro
UNCuyo
cuenta con...
Profesores
Estudiantes
Laboratorios
CONICET - CNEA
Investigadores
Apoyo técnico
Actividades en
Iinvestigación
Laboratorios
aportan...
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Departamento Caracterización de Materiales
A. Serquis
L. Mogni
M. Arce
L. Baque
H. Triani
A. Soldati *
C. Chanquía
C. González Oliver
A. Montenegro
M. Esquivel
F. Napolitano
J. Basbús
M. Esquivel
A. Caneiro*
Becarios:
J. Ascolani
Y. Mansilla
M. Melone
M. Santaya
H. Saraceni
S. Obregón
A. Fernadez Zuvich *
P. Dager *
Técnicos
W. Fürst
M. Corte
P. Troyon
J. Perez
D. Salas
*Ex- integrantes
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➢ D. Lamas, UNSan Martin, Argentina
➢ Susana Larrondo, CITEDEF, Buenos Aires, Argentina.
➢ Martín E. Saleta, Instituto de Física “GlebWataghin”, Campinas, Brasil (ahora en CAB)
➢ G. Leyva, CAC-CNEA, Argentina
➢ J. Yoon, R. Araujo and H. Wang, Texas A & M University EEUU
➢ Santiago Figueroa (XAFS2), Cristiane Rodella (XPD), LNLS – Campinas, Brasil
➢ Scott Barnett , Northwestern University, USA
➢ José Antonio Alonso , Instituto de Ciencia de Materiales de Madrid, CSIC, Spain
➢ L. Suescum, Universidad de la República, Uruguay
➢ Elisabeth Djurado, Samuel Georges, Laboratoire d’Electrochimie et de Physico-chimie des Matériaux et des Interfaces, LEPMI, France
➢ Aldo Craievich, USP, Brazil
➢ Anja Schreiber, Richard Wirth, Helmholtz-Zentrum Potsdam, Chemie Physik der Geomat., Germany
➢ L. Civale, B. Maiorov, M. Jaime, Y. Zhu, J. Yates Coulter, F. Mueller, D. PetersonSuperconductivity Technology Center (STC), Los Alamos, EEUU
➢ G. Cuello, ILL Grenoble Francia
➢ Jochen Geck (IFW-Dresden), A. Schreiber y R. Wirth (GFZ, Postdam) Alemania
Colaboraciones del grupo
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Futuras:
• Estudio de textura por EBSD (Ej: aleaciones de zirconio, cables superconductores)
• Estudio de nanoestructuraspor SAXS
• Técnicas asociadas con TOF-SIMS (PME 2015)
Líneas de trabajoActuales:• Celdas SOC (SOEC-SOFC)
• Óxidos nanoestructurados para electrodos de celdas de combustible
• Películas de óxidos de zirconiasobre zircalloy (para aplicaciones nucleares)
• Desarrollo de cables superconductores basados en MgB2
• Membranas de intercambio y purifcación de gases (conductores iónicos y protónicos)
Colaboraciones con CAC, CAE y con el exterior (Brasil, Colombia, Mexico, Alemania, Francia)
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• Difractómetro de Rayos X
Panalytical Empyrean
• Difractómetro Philips 1700
Servicios actuales
• SEM-FEG FEI Nova Nano
Sem 230
• Inspect S50 NUEVO
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OutlineIntroduction ➢ Fuel cells and materials
➢ Crystalline structures and defects in solids
➢ Materials in SOC: solid oxides ionic or mixed conductors. ➢ Requirements and strategies
Characterization techniques:➢ Electrochemical characterization: EIS
➢ Microstructural characterization: microscopy and FIB
➢ Thermogravimetry and pO2 control (defect models)
➢ Structural and electronic characterization (XRD, XANES, EXAFS, etc)
Synthesis Methods of nanostructured powders:➢ Cathode LSCF➢ Electrolyte➢ Anode: cermet CGO/NiO
Summary
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½ O2 + H2 2 H2O
INTRODUCCIÓN Celdas o pilas de combustible
e-
O2 H2
ELECTROLITO
ÁNODOCÁTODO
Principio de funcionamiento
Cristian Schönbein, Suiza
Philos. Mag. 86, Dec. (1838).
William R. Grove,
Philos Mag 86,
127 (1839).
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INTRODUCCIÓN Tipos de celdas de combustible
Tipos de celda
Alcalina (AFC)Alkaline Fuel Cell
Ácido polimérico (PEFC)Polymer Electrolyte Fuel Cell
PEM (Proton Exchange Membrane)
Ácido fosfórico (PAFC)Phosphoric Acid Fuel Cell
Carbonato fundido (MCFC)Molten Carbonate Fuel Cell
Óxido sólido (SOFC)Solid Oxide Fuel Cell
O2 (aire) H2H2O
OH-
O2 (aire)
CO2
O2 (aire)
O2 (aire)
O2 (aire)
reformado
externo
H2, CO2
reformado
Interno
CO,
H2, CH4
H2O
CO2
H2O
H2O
O2-
CO32-
H+
H+
H2O
CO2
Metanol Directo (DMFC)*
* Metanol,
etanol, etc
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Al enfriarse un líquido o un gas algunos materiales solidifican …
… como monocristales(todos ordenados en la
misma dirección)
… y otros como amorfos o VIDRIOS
… otros forman policristales
Bariloche Sábado 4 de Junio 2011 Partícula de vidrio volcánico
http://www.doitpoms.ac.uk/tlplib/atomic-scale-structure/intro.php
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Ciencia de materiales
microestructura
estructura cristalina
composición
parámetros de fabricación
Propiedadesfisicoquímicas
tipos de enlacesdefectos
Eficiencia de losmateriales para
aplicaciones
parámetros de operación
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Ciencia de materiales y técnicas de
caracterización
Caracterizacióncristalográfica
Óxidos
Propiedadeselectroquímicas
Conversión de energíaeficiente
Microscopía electrónica(SEM, TEM)Difracción de Rayos-X y NeutronesMétodos de radiación sincrotrón
(XANES, EXAFS, etc)
- perovskitas- fluoritas
- Ruddlesden-Popper
SOC: celdasde óxidosólido
técnicasin-situ/in-operando
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Reversible solid oxide cells (Fuel or Electrolyzer)
Development, synthesis and characterization of oxides➢ Several synthesis route to tailor morphology➢ Resolution of the high temperature phase diagram through the determination of the oxygen chemical potential➢ High temperature defect structure through thermogravimetric and electrochemical measurements
Fuel Cell Mode
COMBINED
CYCLE
OTHER
PRIMARY
SOURCE
Electrolyzer Mode
Electricity +
HEAT
H2, CO,
CH4
H2, CO,
CH4
Electricity +
Heat
L. Mogni courtesy
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Tipos de defectos
• 0-D Defectos puntuales o cero-dimensionales tienen el volúmen de dimensiones atómicas. – Defectos en las posiciones atómicas: sustituciones, sitios vacantes,
átomos extra.
– Defectos electrónicos: fonones, polarones, centro de color, etc.
• 1-D Defectos Lineales (ej. dislocaciones)
• 2-D Defectos superficiales-borde entre dos regions ordenadas del cristal (ej. Bordes de grano, interfases, superficies)
• 3-D Defectos en volúmen-inhomogeneidades en la forma o estructura del sólido (ej.: precipitados, poros, fisuras, inclusiones)
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Defectos puntuales (0-D)
a) Substitución de átomos, (impurezas usualmente másgrande)
b) Intersticiales, ocupan sitios de red (impurezasusualmente más chicas)
c) Vacancias (átomos faltantes)
Substitución
Intersticial
Vacancia
http://www.fisk.edu/~aburger/Publi
shed03_06/Structure/3-D/3-d.html
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Defectos en equilibrio
Physical Ceramics, Principles for Ceramic Science and Engineering. Y. M.
Chiang, D. Birnie III, and W. D. Kingery
DG = DGo + n Dg - T DS (1)
DS es proporcional al número de configuraciones W,
DS = k lnW = k ln[N!/(N-n)!n!] (2)
donde k es la constant de Boltzman.
La concentración de defectos diluidos (n<<N), minimizando DG
c = exp (- Dg /kT) (3)
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Defectos en sólidos iónicos
• Tienen en cuenta la
neutralidad de cargas
Defectos Frenkel Defectos Schottky
Vacancia o Schottky
Iones positivos y negativos se mueven a
la superficie dejando un par de vacancias
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1-D Defectos lineales: dislocacionesLas dislocaciones fueron originalmente pensadas para explicar la discrepancia
entre los valores teóricos determinados para el modulo de deformación y los valores determinados experimentalment, mucho antes que pudieran ser
directamente observadas. Se caracterizan por su vector de Burger (diferenciaen el circuito imperfecto (arriba) y en el cristal perfecto (abajo).
Borde (Edge) Hélice (Screw)
Vectors describing dislocation line and Burger's vector are
Perpendicular Parallel
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2-D Defectos bidimensionalesa) Superficie libre de un cristal (sólido/vapor)
b) Bordes de grano (sólido/sólido: interfaces a/a)
• Separan dos regiones del cristal con diferente orientación en
el espacio pero con la misma composición y estructura
c) Interfaces de Interfases (sólido/sólido: interfaces a/b)
• Separan dos regiones del cristal con diferente structura y/o
composición
Phase Transformations in Metals and
Alloys. D. A. Porter and K. E. Easterling
Cálculo de la energía libre de una
superficie g
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3-D Defectos tridimensionales o
de volumen
➢ Inclusiones o precipitados
➢Porosidad (gas atrapado)
➢ Grietas
Ejemplos de precipitados b en una matriz a
coherente
parcialmente coherente
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Introducción: SOFC
Principio de funcionamiento de una celda de combustible de óxido sólido
(Solid Oxide Fuel Cell - SOFC)
• Ánodo: Ni-YSZ
• Electrolito: YSZ
• Cátodo: LSM
SOFC convencionales:
(700 – 1000 °C)
Larminie, J. y Dicks, A.,
“Fuel cell systems
explained”, John Wiley &
Sons, 2a ed. (2003).
Electrolito
CH4 + 4 O2- CO2+ 2 H2O + 8 e-e-
e-
e-
e-
Combustible
Ej: H2,
metano
O2-
2 O2 + 8 e- 4 O2-
Oxígeno
del aire
O2-
Ánodo
Cátodo
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Introducción: SOFC
Principio de funcionamiento de una celda de combustible de óxido sólido
(Solid Oxide Fuel Cell - SOFC)
Electrolito
CH4 + 4 O2- CO2+ 2 H2O + 8 e-e-
e-
e-
e-
Combustible
Ej: H2,
metano
O2-
2 O2 + 8 e- 4 O2-
Oxígeno
del aire
O2-
Ánodo
Cátodo
Cátodo:
•Estructura Porosa
•Reacción Catódica (ORR)
• Compatibilidad estructural
con el electrolito
•Conductor eléctrico o mixto
(MIEC)
•Ej: LSM o LSCF
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Introducción: SOFC
Principio de funcionamiento de una celda de combustible de óxido sólido
(Solid Oxide Fuel Cell - SOFC)
Electrolito
CH4 + 4 O2- CO2+ 2 H2O + 8 e-e-
e-
e-
e-
Combustible
Ej: H2,
metano
O2-
2 O2 + 8 e- 4 O2-
Oxígeno
del aire
O2-
Ánodo
Cátodo
Ánodo:
•Estructura Porosa
•Reacción Anódica
• Compatibilidad
estructural con el
electrolito
•Conductor eléctrico
•Cermet de Ni soportado
en YZO o CGO
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Introducción: SOFC
Principio de funcionamiento de una celda de combustible de óxido sólido
(Solid Oxide Fuel Cell - SOFC)
Electrolito
CH4 + 4 O2- CO2+ 2 H2O + 8 e-e-
e-
e-
e-
Combustible
Ej: H2,
metano
O2-
2 O2 + 8 e- 4 O2-
Oxígeno
del aire
O2-
Ánodo
Cátodo
Electrolito:
•Conductor IónicoSOFC→O2-→Top ≈ 600-1000 ºC
•Conductividad Electrónica ≈0
•Denso
•Estabilidad Química y
estructural en atmósfera
reductora y oxidante.
•Ej. (Y,Zr)O2-x (YZO), (Ce,Gd)O2-x
(CGO)
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EFICIENCIA TERMODINÁMICA
Celda de
Combustible
Hidrógeno(u otro
combustible)
Oxígeno
Energía
eléctrica = VIt
Calor
Agua
Energía por unidad de mol:
Dgf = D g f (H2O) – Dg f (H2) – ½ Dg f (O2)
Energía Libre de Gibbs:
DGf = DGf (productos) - DGf (reactivos)
Esta energía depende de temperatura y
del estado final del agua:
Dgf(200 °C) = – 220 kJ mol-1
ProductoH2O
Temp
(°C)
Dgf
(kJ mol-1)
Líquido 25 -237.2
Líquido 80 -228.2
Gas 80 -226.1
Gas 200 -220.4
Gas 400 -210.3
Gas 800 -188.6
Reacción básica:
H2 + ½ O2 H2O
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Voltaje a circuito abierto
Por cada mol de H2:
Energía eléctrica = carga x voltaje
-2Ne x E = -2 F x E (*)
e: carga de un electrón
N : número de Avogadro
F : constante de Faraday
E : voltaje a circuito abierto (EMF)
Dgf = - 2F x E E = - D gf / 2F
Ánodo
Electrolito
CátodoC
arga H+
H2 2 H+ + 2 e-e-
e-
e-
e-
Combustible Hidrógeno
H+
½ O2 + 2 e- + 2 H+ H2O
Oxígeno del aire
Reacciones en una
PEM
(*) Unidades: J (Joule) = C (coulomb) x V (volt)
Ejemplo operando a 200°C
E = -220 kJ
= 1.14 V2 x 96.485 C
Reacción básica:
H2 + ½ O2 H2O
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950 900 850 800 750 700 650
0.0
0.2
0.4
0.6
0.8
1.0
1.2
DUCátodo
DUÁnodo
Volta
je (
V)
T (°C)
DUElectrolito
E = E0 - (DU
Electrolito + DU
Ánodo + DU
Cátodo ) E
0
Voltaje de salida y sobrepotenciales de una SOFC convencional
Ni-(ZrO2)1-x (Y2O3)x
(ZrO2)1-x (Y2O3)x
La1-xSrxMnO3-
Ánodo
Electrolito
Cátodo
I = 100 mA/cm2
Ivers-Tiffée et al, JECS 21 (2001) 1805
A bajas temperaturas
DUcátodo limita el
rendimiento de la celda
Introducción: SOFC a IT-SOFC
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Cómo funciona una SOFC
CátodoÁnodo
2e-H2
H+
2-
Electrolito
O2-
Electrodo del combustible Electrodo de aire
2H2+2O2-2H2O+4e- O2 + 4e- 2O2-
(Conductor iónico)
2-
4e-
½ O2 +H2 H2O
DHr = DG + TDS
DG = -Welec (reversible)
O2
Tesis doctoral Alejandra Montenegro
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CátodoÁnodo
H2+CO
2-
Electrolito(Conductor iónico)
2-
O2
4e-
H2O+CO2
ELECTRICIDAD
+
CALOR
SOLID OXIDE FUEL CELL
Membrane Electrode Assembly (MEA)
SOFCGas Natural
Reformador
CH4
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SOLID OXIDE FUEL CELL
• Completamente sólida
Materiales cerámicos que no presentan problemas de corrosión.
• Símil batería pero sin tiempos muertos de recarga.
Alto rendimiento energético
Calor de calidad como subproducto aprovechable
• Tecnología Modular
Fácilmente escalable para otras aplicaciones
• Flexible
Funciona con diferentes combustibles
(GNC, Biocombustibles, etc)
Combustible
H2O + CO2
Aire
SOFC
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Technología planar
Electrolito: 200 µm
Ánodo y cátodo sostenidos
Fotografía del módulo
Características :
48 celdas, 1.7 kW
1 W/cm2
2000 h sin deterioro
52% eficiencia
Technología nueva: 750 °C
Electrolito: 30 µm
sostenido en el ánodo (serigrafía)
Material de interconexión: Acero
0.65 W/cm2
Tokyo Gas (Japón)
Celdas SOFC comerciales
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Anode– Fuel oxidation
reaction Catalyst
– Good electronic
conductor
– Good ionic
conductor
CERMET
Cathode– O2 Reduction
Reaction Catalyst
– Good electronic
conductor
– Good ionic
conductor
MIEC
2
2 4 2O e O 2
2 2
4 2 2
2 2 2 4
3
H O H O e
CH H O H CO
SOFC electrodes
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Ele
ctro
lyte
O-2
10 nm
1 μm
10 μm 1 μm 10 nm
Nanomaterials for IT-SOFC E
lec
tro
ch
em
istr
yC
om
m.
10 (
2008)
1905
EC
S T
ran
s.
25 (
2009)
2473
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SOC materials
➢ Market requirements :
➢ Lower Cost
➢ Reliability
➢ Durability
➢ Material requirements :
➢ Better efficiencies
➢ Structural stability
➢ Chemical and mechanical
compatibility
❖ IT-SOFC
❖ Nanomaterials?
➢ ¿ ?
❖ Strategies:
❖ Search for new compositions
❖ Improve morphology
❖ Improve interfaces
Goal: To understand the correlation between structural and physicochemical properties
Operation at high temperature isa critical issue
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1-Cátodo (electrodo aire)
La1-xSrxMnO3- La1-xSrxCoO3-
Conductor mixto (MIEC)
▪ La corriente es transportada tanto por
iones como por electrons
▪La reacción puede ocurrir en toda la
interfase cátodo/gas.
Triple Phase Boundary: la reacción sólo
ocurre donde hay contacto entre gas, cátodo
y electrolito
Conductor electrónico
S. Adler,
Chem.Rev.
104(2004)
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Disminución de DUcatódico: composición
Conductor mixto
•La corriente es transportada por iones
oxígeno y electrones
• La reacción también puede ocurrir en las
zonas donde están en contacto el gas y el
cátodo.
La,Sr
Fe,Co
OLas fases perovskitas de
(La,Sr)(Fe,Co)O3 son buenas
candidatas para ser usadas como
material de cátodo con CGO
•CONTACTO TRIPLE: la reacción sólo
ocurre en la zona donde están en contacto
el gas, el conductor electrónico y el
electrolito
Conductor electrónico
S. Adler,
Chem.Rev.
104(2004)
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Reacción de reducción de oxígeno (ORR)
Conductor electrónico puro (ej. La1-xSrxMnO3)
1. Difusión en fase gaseosa
2a. Adsorción-desorción no disociativa de O2
2b. Disociación
2a-b. Adsorción disociativa
3’’. Difusión superficial de Oad
4’’. Transferencia iónica en el punto triple
O2
O2ad
Oad
e-
O2-
e-
1
2a
2b
3’’
4’’
Electrodo
Electrolito
Gas
DUCátodo
• Composites (ej. La1-xSrxMnO3/YZS)
• Nano/microestructura
N° puntos triples
Cátodos: reacción de electrodo
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Reacción de reducción de oxígeno (ORR)
Conductor mixto (ej. La1-xSrxCo1-yFeyO3-)
1. Difusión en fase gaseosa
2a. Adsorción-desorción no disociativa de O2
2b. Disociación
2a-b. Adsorción disociativa
3’a. Transferencia de carga e incorporación iónica
al electrodo
3’b. Difusión de O2- en el interior del electrodo
4’. Transferencia iónica en la interfase
electrodo/electrolito
O2
O2ad
Oad
e-
O2-
O2-
O2-
1
2a
2b
3’a
3’b
4’Electrolito
Gas
DUCátodo
• Composición
• Nano/microestructura
Electrodo
e-
O2-
3’’
4’’
Cátodos: reacción de electrodo
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Espectroscopia de Impedancia
Electroquímica (EIS)
Esquema del
equipo de medida
Menor frecuencia
Resistencia de
polarización ASR
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1
2
24
2
2
O
iffd pOeff
D
L
F
TR=R
1- Difusión de O2 en fase gaseosa
2/1
2
1
2
2ads pOkF
TR=R2- Adsorción disociativa
3- Incorporación del O ads en el
electrodo (transf. carga) 4
11
0 2
Ogas piR
4- Difusión en el conductor mixto
vV
WD
l
CSF
TRR
1
4 2
Diagrama de Nyquist
Espectroscopia de Impedancia Electroquímica (EIS)
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Mejorar la ASR de los cátodos variando la micro/nanoestructuray entender los mecanismos de reacción electrodos porosos de la misma composición, (LSCFO), preparados por diferentes métodos.
➢Spray
Pyrolisis
➢ Acetatos
➢ HMTA
➢ PLD
➢ Nanotubos
-spray
-dip-coating
-Spin-coating
LSCF
CGO Mediciones electroquímicas EIS
(impedancia compleja) en celdas
simétricas en función de T y p(O2)
controlada
Disminución de DUcatódico: microestructura
Los materiales nanoestructurados con alta relación área/volumen, aumentarían la extensión de la zona de reacción y disminuirían el sobrepontencial catódico
Tesis doctoral
Laura Baqué
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Método de Acetatos
La2O3 (secado a 1100°C); SrCO3;
Co(CH3COO)2; Fe(CH3COO)2
Mezcla con ácido acético
Reflujo a 80°C
Formación de solución
Evaporación y formación del gel
Calcinado del gel (400°C – 2 hs)
Tratamiento térmico
Molienda
Molienda
H2O + H2O2
Entrada
H2O
Salida
H2O
Columna de
refrigeración
Balón Camisa
térmica
Plato caliente
y agitador
Cátodos: métodos de síntesis
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Método de Acetatos
La2O3 (secado a 1100°C); SrCO3;
Co(CH3COO)2; Fe(CH3COO)2
Mezcla con ácido acético
Reflujo a 80°C
Formación de solución
Evaporación y formación del gel
Calcinado del gel (400°C – 2 hs)
Tratamiento térmico
Molienda
Molienda
H2O + H2O2
Método de HMTA
La2O3 (secado a 1100°C); SrCO3;
Co(CH3COO)2; Fe(CH3COO)2
Mezcla con ácido acético, acac y HMTA
Reflujo a 80°C
Formación de solución
Evaporación y formación del gel
Calcinado del gel (400°C – 2 hs)
Tratamiento térmico
Molienda
Molienda
H2O + H2O2
Cátodos: métodos de síntesis
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Métodos químicos
Ts= 900 C Ts= 800 C
Acetatos HMTA
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Spray pyrolisis
(b)(b)
(c)
• Acetate: 8.3 ± 0.1 m2/gr• HMTA: 12.35 ± 0.02 m2/gr• Spray pyrolysis: 11.71 ± 0.04 m2/gr
Surface area (BET) from as prepared powders:
Collaboration ECOS-SUD (Djurado-Caneiro) L. Baque
Laboratoire d’Electrochimie et de Physico-chimie des Matériaux et des Interfaces,
LEPMI
Baque et al, ECS 25 (2009) 2473
100 nm
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PLD for Vertical aligned
nanocomposites (VAN)
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Vertically-aligned nanopores (VANP)
and nanocomposite (VAN)
Cell voltages and Power densities ofanode-supported single cells increasealmost three times with the VAN interlayer
S. M. Cho, J. S. Yoon, J. H. Kim, Z. X. Bi, A. Serquis, A. Manthiram, H. Y. Wang,
Advanced Functional Materials 19 (2009) 3868
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La0.4Sr0.6Co0.8Fe0.2O3-
Acetate - Spray – Particle size: 600 nmPhD Thesis – IB - 2006
La0.4Sr0.6Co0.8Fe0.2O3- (Acetate)
Spin coating – Particle size: 180 ± 40 nm
La0.4Sr0.6Co0.8Fe0.2O3- (HMTA)
Spin coating – Particle size: 130 ± 30 nmBaqué et al, Electrochem. Comm. 10 (2008) 1905
La0.4Sr0.6Co0.8Fe0.2O3- / Ce0.9Gd0.1O2-
PLDAPS 254 (2007)266
0.9 1.0 1.1 1.2 1.3 1.4 1.5
-2
-1
0
1
2800 700 600 500 400
Murray et al
Dusastre et al
Deganello et al
Beckel et al
Yoon et al
Haile et al
Lo
g (
AS
R(
cm
2))
1000/T (K-1)
T (ºC)
La0.6Sr0.4Co0.2Fe0.8O3- / YSZ
Spin coating – Particle size 100-200 nmSSI 148 (2002) 27
La0.6Sr0.4Co0.2Fe0.8O3- / Ce0.9Gd0.1O2-
SlurrySSI 126 (1999) 163
La0.6Sr0.4Co0.95Fe0.05O3- / Ce0.8Sm0.2O2-
Screen printing – Particle size 150 nmJES 154 (2007) A89
Ba0.25 La0.25Sr0.5Co0.8Fe0.2O3- / Ce0.8Gd0.2O2-
Spray pyrolysis - Partícula 35 nmSSI 178 (2007) 407
Ba0.5 Sr0.5Co0.8Fe0.2O3- / Ce0.85Sm0.15O2-
SprayNature 431 (2004) 170
Microstructure allows decrease ASR in more than two order of magnitud!!!
ASR: LSCF cathodes
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: A
: O: B
: Vacancia
de O
ABO3-(A = La,Sr – B = Co,Fe)
Ordenamiento
de vacancias
de oxígeno
Deterioro de
propiedades de
transporte
Para la composición La0.4Sr0.6Co0.8Fe0.2O3- otros autores* no
observaron la formación de fases con ordenamiento de
vacancias para 20°C T 900°C y -5 Log pO2 0
* Prado et al SSI 167 (2004) 147
Tesis doctoral Laura Baqué
Ejemplo cátodo: LSCF
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9.0 9.5 10.0 10.5 11.0
Inte
nsid
ad
(u
.a.)
2 (°) ( = 1.37699 Å)
40.0 40.5 41.0 41.5 42.0 42.5 43.0
Inte
nsid
ad
(u
.a.)
2 (°) ( = 1.37699 Å)
— La0.4Sr0.6Co0.8Fe0.2O3- - R-3c
— La0.4Sr0.6Co0.8Fe0.2O2.875 - I4/mmm
(A8B8O23)
— La0.4Sr0.6Co0.8Fe0.2O2.75 – Cmmm (A4B4O11)
— La0.4Sr0.6Co0.8Fe0.2O2.5 – Icmm
(A2B2O5)
Posibles fases con ordenamiento de vacancias de oxígeno
(Simulación XRD)
(0 2 4)
29/46
Estabilidad estructural
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9.0 9.5 10.0 10.5 11.0
Ca
len
tam
ien
to
95°C
200°C290°C
400°C
500°C
20°C
2 ( = 1.37699 Å)
100°C
190°C
300°C
400°C
490°C
600°C
En
fria
mie
nto
Calentamiento:
150°C T 300°C: ABO3- + ABO2.875
300°C T 600°C: ABO3- + ABO2.75 + ABO2.5
Enfriamiento:
600°C T 20°C: ABO3- + ABO2.5
He puro
43.042.5
42.041.5
41.040.5
40.0
Enfr
iam
iento
Cale
nta
mie
nto 20°C
200°C
310°C
500°C
600°C
450°C
310°C
70°C
70°C
310°C450°C
310°C
600°C500°C E
nfria
mie
nto
2 ( = 1.37699 Å)
200°C
Cale
nta
mie
nto
20°C
HMTA
Datos adquiridos en XPD LNLS - Brasil
Estabilidad estructural y electroquímica de los
cátodos de La0.4Sr0.6Co0.8Fe0.2O3-
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Cátodos: La0.4Sr0.6Co0.8Fe0.2O3-
Técnica de FIB/lift-out*
* Muestras cortadas por A. Schreiber y R. Wirth – GFZ, Postdam, Alemania
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Técnica de FIB/lift-out*
* Samples prepared by A. Schreiber y R. Wirth – GFZ, Postdam, Germany
Cátodos: La0.4Sr0.6Co0.8Fe0.2O3-
HR-TEM interfase coherente
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Envejecimiento acelerado
Evolución de las propiedades microestructurales y electroquímicas
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2- Ejemplo electrodos: celda simétrica
S
S
O
F
C
-
Tesis doctoral Federico Nappolitano
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Electrodos: SOC
Ánodo– Catalizador de
reacción de
oxidación del
combustible
– Buen conductor
electrónico
– Buen conductor
iónico
Cátodo– Catalizador de
reacción de
reducción de O2
– Buen conductor
electrónico
– Buen conductor
iónico
2
2 4 2O e O 2
2 2
4 2 2
2 2 2 4
3
H O H O e
CH H O H CO
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LSTC: candidato para SFC
Preparación por método de baja temperaura
F. Napolitano et al, Int. J. Hyd Energ. 37 (2012)
18302
Ts = 750 °C Ts = 1100 °C
Caracterización morfológica (TEM)1100 °C
[Co] Ts = 750°C (nm) Ts = 1100°C (nm)
0.1 27 (18) 152 (204)
0.3 27 (12) 340 (144)
0.5 41 (28) 357 (210)
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Estructura LSTC
¨Transición de fase: R-3c --› Pm-3m a T ~ 350, 600,
300°C para y = 0.1, 0.3 y 0.5, respectivamente.
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Usando difracción de RX y
neutrones
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Espectroscopía de absorción2
( ) | |E i f H
Metal transición 3d
1s 4p (D)
∆l = +1∆l = +2
1s 3d (Q)
Región EXAFS
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EXAFS
2 22 2 / ( )
2
( )( ) sin 2 ( )
j jk R k
j j
j j
j j
N e e f kk kR k
kR
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Resultados EXAFS
Transición de fase de R-3c a Pm-3m a T ~ 350, 600, 300°C
para y = 0.1, 0.3 and 0.5, respectivamente.
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Espectroscopía de Absorción
(XANES)
Región
XANES
Depende del entorno
local del átomo
absorbente
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XRD y XANES in-situ
XRD
XANES
La0.6Sr0.4Ti0.5Co0.5O3±
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Correlación resultados XRD –
XANES – TPR
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XRD in-situ – Efecto de tamaño
de grano
Transformación de
fase de 1er orden
3R c
3Pm m
3Pm m
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E hXRD
Temperature
Atmosphere
• XRD: average crystalline structure
WE-CE-RE → EIS
• EIS: electrochemical characterization
2W/4W conductividad
• Electrical Conductivity: transport
properties
( ) ( )E ht tXAS
• XAS: local electronic structure
In-operando cell design
GOAL From in-situ measurements toin-operando measurements
Federico Napolitano
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In-operando cell design
Federico Napolitano
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In-operando cell design
Federico Napolitano
Design conceived with several constrains:
- Versatile, several experimental techniquesmust be used without changes in the cellconfiguration: in-house or synchrotron XRD, X-ray absorption spectroscopy (XANES/EXAFS),electrical conductivity, and electrochemicalimpedance spectroscopy.
- Easily adapted to several high temperaturechambers existing at LNLS and at CAB (AntonPaar HTK1200 and XRK900, Canario furnace).
- Portable in order to be carried to synchrotronbeamlines.
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0.8 1.0 1.2 1.4 1.6 1.8 2.0
-4
-3
-2
-1
0900800 700 600 500 400 300
Lo
g (
(
S/c
m))
1000/T (K-1)
YSZ
GDC
T (°C)
Y o Gd
Vacanciade oxígeno
•• OOCe VOGdOGd 3 2 '
32
Zr o Ce
Brandon, N. P. et al
Annu. Rev. Mater. Res.
33 (2003) 183
3 - Electrolitos: de SOFC a IT-SOFC
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- Model: microcrystalline solid electrolytes: bulk ionic transport(characteristic of the material) through grains and GBtransport, which depends on microstructure.
- Proposed increased conductivity in nanostructuredelectrolytes.
Ionic transport mechanisms in solid ceramic electrolytes O2-ion
M. G. Bellino, D. G. Lamas and N. E. Walsöe de Reca,
Advanced Materials 18 (2006) 3005-3009
3-Electrolyte: ionic conductor
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Cerium Gadolinium Oxide (CGO) desirable properties:• High density
• Stability: both in the oxidizing atmosphere (cathode)and reducing (anode)
• Chemical compatibility and coefficient of expansion:with those of the electrodes to avoid degradation
• High Ion Conductivity (negligible electronicconductivity)
5µm5µm5µm
1250ºC 1350ºC 1450ºC
3-Electrolyte: ionic conductor
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0 5 10 15 20 25 30 35 40 45 500
10
20
30
40
Cou
nt
Crystal Size / nm
CGO_MetA_250C_r=2C/min_1ml/cm
n=126
6.8 ± 2.5
CGO (electrolyte) new synthesis method
Crystallite size:
dependence on ramp
speed
T
250 °C
Ramp
2 °C/min
Modified Sol-gel
method
(patent in
progress)
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Cermet: CGO/NiO (anodes) SEM/TEM
ECS Transactions 64 (2014) 233-240
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Cermet: CGO/NiO (anodes) XRD
All samples have two separated phases NiO and GDC with cubic crystal
phase (Fm3m space group) and initially present crystallite sizes in the
nanometric range, depending on the sintering temperature.
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New Sol Gel
A1350
C1350
commercial
Cermet: CGO/NiO (anodes) EIS
Symmetric cell
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DXAS (Dispersive X-ray
Absoption Spectroscopy)
Cermet: CGO/NiO (anodes) DXAS
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DXAS (Dispersive X-ray
Absoption Spectroscopy)
5%
H2/He
20%
O2/He
20%
CH4/ He
Cermet: CGO/NiO (anodes) DXAS
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Cermet: CGO/NiO (anodes) XPD
New Sol Gel
A1350
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DXAS (Dispersive X-ray
Absoption Spectroscopy)
Cermet: CGO/NiO (anodes) DXAS
0
25
50
75
100
1 2 3 4 5 6 7
0
25
50
75
100
Ni0
20%
CH4/He
20%
O2/He
5%
H2/He
C1350
A1350
A 900
Ce+3
Time (h)
Com
ponents
(%
)
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TG of CeO2
Cermet: CGO/NiO (anodes) DXAS
0
25
50
75
100
1 2 3 4 5 6 7
0
25
50
75
100
Ni0
20%
CH4/He
20%
O2/He
5%
H2/He
C1350
A1350
A 900
Ce+3
Time (h)
Com
ponents
(%
)
100% ≡ 3,45
0
200
400
600
800
1000
0 1 2 3 4 5 6 7
0,525
0,530
0,535
0,540
Ce+3.45
T (
C)
time (h)
Ce+4Ar/H2 5%
ma
ss (
mg
)
+ 3,45
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In-operando: proton conductivity
Conductor-O vs Conductor-HSOFC: O-2 ion/VO PC-SOFC H+ ion /H2O
J. Basbus, PhD Thesis 2017 BaCe0.8Pr0.2O3-δ
BaCe0.4Zr0.4Y0.2O3-δ
J. Basbus et al J. Electrochem Soc. 161 (2014) F969
J. Basbus et al, J. Power Sources 329 (2016) 262
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Proton conductivity
BaCe0.4Zr0.4Y0.2O3-δ
J. Basbus et al J. Electrochem Soc. 161 (2014) F969
J. Basbus et al, J. Power Sources 329 (2016) 262
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In-operando: proton conductivity
200 400 600 800 100010
-5
10-4
10-3
10-2
10-1
Aire Sintetico
2 % vapor de H2O
2 % vapor de D2O
b
ulk (
S/c
m)
T (oC)
XRD-EIS in-
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In-operando: proton conductivity
20 40 60 80 100
b) Yobs
Ycalc
Yobs-Ycalc
Bragg_position
I (u
. a
.)
2 (o)
0 1 2 3 4 5 60
1
2
3
4
5
6
-Z´´
(k
.cm
)
Z´(k.cm)
a)
10-3
10-2
300 400 500 600 7004.310
4.315
4.320
4.325
4.330
bu
lk (S
/cm
)
c)
a (Å
)
T (oC)
BCZY XPD (8 keV) cubic (P m -3 m)
Bulk protonic
conductivity
asociated to
high frecuency
BCZY.
Cell parameter by Rietveld
correlates with proton
conductivity
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Perovskites
La0.6Sr0.4Fe0.8Cu0.2O3-d (S. Vázquez et al Journal of Solid State Chemistry 228 (2015) 208–213)
Double perovskites
LnBaCo2O6-d (Ln = La, Nd, Pr) Garcés et al. Journal of Applied Crystallography 47 (2014) 325
La0.75Sr0.25Cr0.5Mn0.5O3-δ (STF) Montenegro et al. Journal of Power Sources 245 (2014) 377-388
Sr2MgMoO6
Ruddlesden-Popper
Ln2NiO4+d (Ln = La, Nd, Pr) Montenegro et al. International Journal of Hydrogen Energy 37 (2012)
YBCO and REBCO
Ln2NiO4+d (Ln = La, Nd, Pr)
(Poster 812)
Other studied compounds
A
B
X
MgMo
Sr
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Algunas conclusiones
➢ Las celdas de combustible son dispositivos que permiten
transformar energía química en eléctrica de manera muy eficiente,
mientras que los superconductores permiten almacenar energía
➢El desarrollo de materiales deberá permitir resolver los desafíos
planteados para su comercialización masiva:
➢Costo
➢Confiabilidad
➢Durabilidad
➢ Para comprender los efectos es necesario una variedad de
técnicas de caracterización tanto estructural (XRD, microscopías)
como su correlación con propiedades electrónicas y de transporte
(EIS, XANES, etc)
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1- Cátodo (air electrode)➢ Eficiente reacción de reducción de O2 y
estabilidad a largo plazo para el nuevo método de preparación de LSCF
➢ Estudio de nuevos compuestos (experimentos in situ de XRD)
3- Electrolitos➢ Reactividad con electrodos
➢ Estudio de tamaño de grano enconductors iónicos
➢ Conductor protónico (in-operando)
2- Electrodos para SSOC➢ Nuevo LSTC propuesto: correlación
de propiedades con varios experimentos in situ
Prototipo
propuesto
con los
mejores
materiales
Resumen: materialesSOFC