Solid Oxide Fuel CellsSandeep.BSai Ravi Kiran.L.T.S

Outline• What is a Fuel Cell?• Mechanism in Fuel Cells• What is Solid Oxide Fuel Cell? ???• Mechanism in Solid Oxide Fuel cells• Advantages of Solid Oxide Fuel cells• Applications• Research

Fuel Cell

What is a Fuel Cell?

Fuel CellChemical Energy

Electrical Energy

Fuel

Water

Mechanism in a Fuel CellReactions:

At Anode:

At Cathode:

Overall Reaction:

Solid Oxide Fuel Cells(SOFC’s)Fuel Cells

High Temperature Fuel Cells

(500-800 C)

Low Temperature Fuel cells

(10-60C)

Solid Oxide Electrolytes Used: • Yttria-stabilized zirconia (YSZ)• Gadolinium Doped Ceria (GDC)

Mechanism of SOFC’s

Reactions:

At Anode:2H2 + 2O–2 → 2H2O + 4e–

At Cathode:O2 + 4e– → 2O–2

Overall Reaction: 2H2 + O2 → 2H2O

(a) Anode:

(b) Cathode:

• Cermet of Ni and type of electrolyte.• Thickest and strongest• Oxidize the H2 Fuel

• Lanthanum Strontium Magnetite(LSM)• Similar thermal coefficient as of electrolyte.• Reaction occurs at triple phase boundary.

(a) Electrolyte:

(d) Inter Connect :

• The interconnect can be either a metallic or ceramic layer that connects each individual cell.• Chromium and steel-based alloys are mostly used.• 95Cr-5Fe alloy.

The electrolyte is a dense layer of ceramic that conducts oxygen ions.Most Popular Electrolytes are :• Yttria Stabilized Zirconia (YSZ)• Gadolinium Doped Ceria (GDC)

Fuel’sAir

Tubular Design of SOFC’s

Configuration Of SOFC’s

Configuration for planar SOFC

Configuration for Tubular SOFC

Power Output

MCFC

Tubular SOFC

Planar SOFC

PEMFC

0 20 40 60 80 100 120

Power (MW)

Power (MW)

Theoretical Vs Practical Efficiency

Planar SOFC Tubular SOFC DMFC PEMFC0

10

20

30

40

50

60

70

80

90

TheroticalPractical

Advantages of SOFC’s over other FC’s: FUEL CELLS SOFC’sThey generally have a liquid electrolyte. They have a solid electrolyte.

The off gases produced may be harmful. The by product produced is water.

Due to presence of liquid electrolyte, corrosion problem may arise.

No corrosion problems.

There may be a leakage of electrolyte. No leakage occurs as it is a solid electrolyte.

They don’t have much fuel flexibility. They can use any type of fuel.

They are of high cost. They are quite inexpensive.

They need a reformer to collect H2 gas from the fuel.

They work at high temperatures and hence don’t need a reformer for H2 collection.

Major Application(a) Chemical Industries and Power Plants:

(a) Stationary energy resources:•Power for municipalities, rural areas and industries.•Heat and electricity for homes.•Long-lasting mobile power for computers, cell phones and other electronics(b) Transportation:•Non polluting automobiles•Inexpensive fuels (c) Military applications:• Fuel cells could significantly reduce deployment costs

Other Applications

Research • Research is going now in the direction of lower-temperature SOFC (400°C) in order to decrease the materials cost, which will enable the use of metallic materials with better thermal conductivity.

• Research is also going on in reducing start-up time to be able to implement SOFCs in mobile applications.

• Research is currently underway to improve the fuel flexibility of SOFCs.

Conclusion The Challenge

Develop Commercially viable and efficient solid oxide fuel cells for large

scale power generation.

The SolutionPin point and minimize factors leading to long term degradation of this type of Fuel

cells

Any Quires?

Back Up Slides Electrodes Equations

Anode Oxidation

Cathode Reduction

Overall reaction Red ox reaction

Methanol as fuel

External Steam Reformer

Proton Exchange Membrane Fuel Cell

Concentration polarization:The concentration polarization is the result of practical limitations on mass transport within the cell, and represents the voltage loss due to spatial variations in reactant concentration at the chemically active sites.

Activation polarization: The activation polarization is the result of the kinetics involved with the electrochemical reactions. Each reaction hasa certain activation barrier that must be overcome in order to proceed and this barrier leads to the polarization. Theactivation barrier is the result of many complex electrochemical reaction steps where typically the rate limiting stepis responsible for the polarization.

Target• DOE target requirements are 40,000 hours of service for stationary fuel cell applications and greater than 5,000 hours for transportation systems (fuel cell vehicles) at a factory cost of $400/kW for a 10 kW coal-based system without additional requirements. •Lifetime effects (phase stability, thermal expansion compatibility, element migration, conductivity and aging) must be addressed. •The Solid State Energy Conversion Alliance 2008 (interim) target for overall degradation per 1,000 hours is 4.0%.