SolidOxideFuel CellsSandeep.BSai Ravi Kiran.L.T.S
Outline• What is a Fuel Cell? 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
What is a Fuel Cell? Fuel Chemical Electrical Fuel Cell Energy Energy Water
Mechanism in a Fuel Cell Reactions: At Anode: At Cathode: Overall Reaction:
Solid Oxide Fuel Cells(SOFC’s) Fuel Cells High Temperature Low Temperature Fuel Fuel Cells cells (500-800 C) (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: • Cermet of Ni and type of electrolyte. • Thickest and strongest • Oxidize the H2 Fuel(b) Cathode: • Lanthanum Strontium Magnetite(LSM) • Similar thermal coefficient as of electrolyte. • Reaction occurs at triple phase boundary.
(a) Electrolyte:The electrolyte is a dense layer of ceramic thatconducts oxygen ions.Most Popular Electrolytes are :• Yttria Stabilized Zirconia (YSZ)• Gadolinium Doped Ceria (GDC)(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.
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 No corrosion problems.electrolyte, corrosion problem may arise.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 They work at high temperatures andfrom the fuel. hence don’t need a reformer for H2 collection.
Major Application(a) Chemical Industries and Power Plants:
Other Applications(a) Stationary energy resources:•Power for municipalities, rural areas and industries.•Heat and electricity for homes.•Long-lasting mobile power for computers, cell phonesand other electronics(b) Transportation:•Non polluting automobiles•Inexpensive fuels(c) Military applications:• Fuel cells could significantly reduce deployment costs
Research• Research is going now in the direction of lower-temperature SOFC (400°C) in order to decrease thematerials cost, which will enable the use of metallicmaterials with better thermal conductivity.• Research is also going on in reducing start-up time to beable to implement SOFCs in mobile applications.• Research is currently underway to improve the fuelflexibility of SOFCs.
Conclusion The Challenge Develop Commercially viable and efficient solid oxide fuel cells for large scale power generation. The Solution Pin point and minimize factors leading tolong term degradation of this type of Fuel cells
Concentration polarization:The concentration polarization is the result of practical limitations onmass transport within the cell, and represents the voltage loss due tospatial variations in reactant concentration at the chemically activesites.Activation polarization:The activation polarization is the result of the kinetics involved withthe electrochemical reactions. Each reaction hasa certain activation barrier that must be overcome in order to proceedand this barrier leads to the polarization. Theactivation barrier is the result of many complex electrochemicalreaction steps where typically the rate limiting stepis responsible for the polarization.
Target• DOE target requirements are 40,000 hours of service forstationary fuel cell applications and greater than 5,000 hoursfor transportation systems (fuel cell vehicles) at a factorycost of $400/kW for a 10 kW coal-based system withoutadditional requirements.•Lifetime effects (phase stability, thermal expansioncompatibility, 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%.