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MOLTEN CARBONATE FUEL CELLSANSALDO FUEL CELLS: Experience &
Experimental results
Filippo Parodi /Paolo Capobianco
(Ansaldo Fuel Cells S.p.A.)
Roma, 14th & 29th March 2007
MOLTEN CARBONATE FUEL CELLSANSALDO FUEL CELLS EXPERIENCE
General Content
Working principles of Fuel CellsWorking principles of Fuel Cells MCFC technologyMCFC technology Key components and materialsKey components and materials Technological developmentTechnological development LAB level testsLAB level tests
Paolo Capobianco (Ansaldo Fuel Cells S.p.A.)Paolo Capobianco (Ansaldo Fuel Cells S.p.A.)
Roma, 29Roma, 29thth March 2007 March 2007
Fuel Cells
What is a Fuel Cell? It is an electrochemical device that converts
energy of a chemical reaction into electricity without any kind of combustion and with high conversion capability.
How a Fuel Cell work? It operates like a Battery but it can
continuously generate electricity as long as fuel (typically H2) and oxidant (Air) are fed to its electrodes.
Battery A generic Battery operation is based on spontaneous Oxidation-Reduction chemical reaction (G 0), between two materials (f. e. Zn and Cu++)
Fuel Cell Fuel cell is a specific kind of Battery based on spontaneous Oxidation-Reduction chemical reaction between two gases
Fuel Cells
Zn + Cu++ Zn++ + Cu + Heat
How a Battery works
Fuel Cells
e
e
Zn + Cu++ Zn++ + Cu + Heat
The reaction transfers directly 2 electrons
from the Zn atom to the Cu ++ ion.
To exploit the “natural tendency” of the Zn atom to deliver
2 electrons to the Cu++ ion so to produce electrical energy,
it is necessary to force the 2 electrons to reach the Cu++
through the external circuit (no direct contact of Zn and Cu++.)
Key feature of any electrochemical generator is its suitability to provide the spontaneous oxidation-reduction reaction, but by maintaining separate the two reagents ( Zn and Cu++ in this example).
Electrons current (I) flows from Zn to Cu++ through an external circuit
When G=0 => I=0 (you have to recharge Battery with an external generator)
Fuel Cells
Zn Cu
Zn++SO4--- Cu++SO4---
Porous Septum
Zn Zn++
e
Anode - Cathode +
Cu++ Cu
e
Ea Ece
Fuel Cells
Daniell Battery
Anodic Semireaction
Zn Zn++ + 2e
Cathodic Semireaction
Cu Cu++ + 2e
Total reaction
Zn + Cu++ Zn++ + Cu
Electrolyte Electrolyte
How a Fuel Cell works
Fuel Cells
e
e
H2 + 1/2O2 H2O + Heat
H2 + 1/2O2 H2O + Heat
H2 O2
The reaction transfers directly 2 electrons from H2 to O2.
To exploit the “natural tendency” of the H2 atom to deliver
2 electrons to the O2 atom so to produce electrical energy, it is necessary to force the 2 electrons to reach O2 through the external circuit.
Key feature of Fuel Cell is its suitability to provide the spontaneous oxidation-reduction reaction, but by maintaining separate the two reagents ( usually H 2 and O2).
Electrons current (I) flows from H2 to O2 through an external circuit
In Fuel Cell you can continuously fed gases (G 0 => I 0)
Fuel Cells
The direct conversion of the chemical energy of the Fuel (H2) into electrical energy permits conversion efficiencies significantly higher than by using the conventional processes combustion based
Moreover, no combustion means low environmental emissions
Fuel Cells
Molten Carbonate Fuel Cell (MCFC)
ELECTROCHEMICAL REACTIONELECTROCHEMICAL REACTION
Anodic H2+ CO3
-- CO2+ H2O + 2e
-
Cathodic CO2 + ½ O2 + 2e- CO3
--
H2+ ½ O2 H2O + heat + electrical current
Operation Temperature T=650
°C
ACTIVE POROUS COMPONENTS
(Electrolyte)
Key components and materials (MCFC)
Key materials and components (MCFC)
Anode Anode material is not directly involved in gas
reaction: It is the catalyst of H2 oxidation reaction
Other requirements for Anode material are chemical (gas and electrolyte) and morphological (high surface area) stability and high electrical conductivity
Cathode Cathode material is not directly involved in gas
reaction: It is the catalyst of O2 reduction reaction
Other requirements for Cathode material are chemical (gas and electrolyte) and morphological (high surface area) stability and high electrical conductivity
Key materials and components (MCFC)
Electrolyte Electrolyte material is directly involved in gas
reaction Other requirements for Electrolyte material is low
ionic resistance and high electronic resistance MCFC electrolyte material is liquid A porous layer (Matrix) is filled by Electrolyte Matrix material must have high chemical stability
(gas and Electrolyte) Matrix filled by Electrolyte must avoid direct
reaction between H2 and O2
Key materials and components (MCFC)
Anode: Nickel (Ni-Cr/Al) Nickel is catalyst for H2
oxidation (no Platinum request: low cost, CO use)
Nickel has high chemical stability in MCFC Anode working condition
Nickel has high electrical conductivity
Nickel is suitable to produce high porosity/high surface area anode
Key materials and components (MCFC)
Anode section SEM analysis. Pores size is suitable for gas diffusion and electrolyte storage
Key materials and components (MCFC)
Cathode: LixNi(1-x)O Nickel Oxide is catalyst for
O2 reduction Nickel Oxide has good (no
total) chemical stability in MCFC working condition
Litiated Nickel Oxide has “high” electrical conductivity
Nickel Oxide is suitable to produce high porosity/high surface area cathode (typical catalyst bimodal structure) Cathode section SEM analysis. It is
possible to see the bimodal structure: larger size pores for gas diffusion , lower size pores for electrolyte storage
Key materials and components (MCFC) Electrolyte:Li2CO3/K2CO3
Liquid Li/K-Na carbonate is an electrolyte solution of Li+, K+ (or Na+), CO3
-- Liquid Li/K-Na carbonate has low
ionic resistance Liquid Li/K-Na carbonate has high
electronic resistance Matrix layer is made by LiAlO2
Chemical stability of LiAlO2 is very high
Electronic resistance of LiAlO2 is very high
Matrix section OM analysis. It is possible to see very low size pores (sub-micron size) for electrolyte storage. Matrix must be totally filled by electrolyte to avoid direct reaction between H2 and O2)
Key materials and components (MCFC)
METALLIC COMPONENTS
Current collector Current collectors have to permit a good gas
distribution in the electrodes (anode, cathode)
Main requirements for current collector material are chemical stability (gas and electrolyte), good electrical conductivity, good mechanical properties
Key materials and components (MCFC)
Separator plate Separator plate have to separate each single
cells of a stack
Main requirements for separator plate material are chemical stability (gas and electrolyte), good electrical conductivity in active area, good mechanical properties
Key materials and components (MCFC)
ACTIVE AREA
(cells current flow through)
NO ACTIVE AREA
Key materials and components (MCFC)
Anode current collector: Ni/AISI310S/Ni
Nickel has high chemical stability in MCFC anodic working condition
Nickel has low electrical resistivity
Mechanical properties of Nickel in MCFC working condition (650 °C) are very poor
Trilayer Ni/AISI310S/Ni is used to have good chemical stability and adeguate mechanical properties
Key materials and components (MCFC)
ACC section OM analysis. It is possible to see AISI310S layer between Ni layers
Ni
Ni
AISI310S
Separator plate AISI310S (Active area)
AISI310S has good chemical stability in MCFC anodic and cathodic working condition (no direct contact with electrolyte)
AISI310S has low electrical resistivity
AISI310S corrosion layer has low electrical resistivity
Key materials and components (MCFC)
Sep.plate section OM analysis (active area). It is possible to see very thin corrosion layers
AISI310S
Key materials and components (MCFC)
Separator plate AISI310S (No active area)
AISI310S is protected by Al coating (direct contact with electrolyte)
In stack operation Al coating forms Allumina layers very stable in working conditions (gas and electrolyte)
Sep.plate section OM analysis.(no active area) It is possible Al coating layer
AISI310S
AI
End first session
Key materials and components (MCFC)