MOLTEN CARBONATE FUEL CELLS ANSALDO FUEL CELLS: Experience & Experimental results

1. MOLTEN CARBONATE FUEL CELLSANSALDO FUEL CELLS: Experience & Experimental results Filippo Parodi /Paolo Capobianco (Ansaldo Fuel Cells S.p.A.) Roma, 14th & 29th March 2007

2. MOLTEN CARBONATE FUEL CELLSANSALDO FUEL CELLS EXPERIENCE General Content • Working principles of Fuel Cells • MCFC technology • Key components and materials • Technological development • LAB level tests Paolo Capobianco (Ansaldo Fuel Cells S.p.A.) Roma, 29th March 2007

3. 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.

4. Fuel Cells • 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

5. Fuel Cells • How a Battery works Zn + Cu++  Zn++ + Cu + Heat e 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++.) e Zn + Cu++  Zn++ + Cu + Heat

6. Fuel Cells • 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 DG=0 => I=0 (you have to recharge Battery with an external generator)

7. Fuel Cells • Daniell Battery e Ea Ec Anode - Zn Cathode + Cu Porous Septum Electrolyte Electrolyte e e Zn  Zn++ Cu++  Cu Zn++SO4--- Cu++SO4--- Anodic Semireaction Zn  Zn++ + 2e Cathodic Semireaction Cu  Cu++ + 2e Total reaction Zn+ Cu++  Zn++ + Cu

8. Fuel Cells • How a Fuel Cell works H2 + 1/2O2  H2O + Heat The reaction transfers directly 2 electrons from H2 to O2. e 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. H2 + 1/2O2  H2O + Heat e H2 O2

9. Fuel Cells • Key feature of Fuel Cell is its suitability to provide the spontaneous oxidation-reduction reaction, but by maintaining separate the two reagents ( usually H2 and O2). • Electrons current (I) flows from H2 to O2 through an external circuit • In Fuel Cell you can continuously fed gases (DG  0 => I  0)

10. 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

11. Molten Carbonate Fuel Cell (MCFC) H2+ ½ O2 H2O + heat + electrical current ELECTROCHEMICAL REACTION Anodic H2+ CO3-- CO2+ H2O + 2e- Cathodic CO2 + ½ O2 + 2e- CO3-- Operation Temperature T=650 °C

12. Key components and materials (MCFC) (Electrolyte) ACTIVE POROUS COMPONENTS

13. 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

14. Key materials and components (MCFC) • 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

15. 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

16. 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 Anode section SEM analysis. Pores size is suitable for gas diffusion and electrolyte storage

17. 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

18. 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)

19. Key materials and components (MCFC) METALLIC COMPONENTS

20. Key materials and components (MCFC) • 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

21. 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

22. Key materials and components (MCFC) NO ACTIVE AREA ACTIVE AREA (cells current flow through)

23. 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 Ni AISI310S Ni ACC section OM analysis. It is possible to see AISI310S layer between Ni layers

24. Key materials and components (MCFC) • 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 AISI310S Sep.plate section OM analysis (active area). It is possible to see very thin corrosion layers

25. 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) AISI310S AI Sep.plate section OM analysis.(no active area) It is possible Al coating layer

26. Key materials and components (MCFC) • End first session