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)