NPRENPRE--470470 FuelFuel CellCell TypesTypes Chapter 8 of Fuel Cell Fundamentals Dr. Kyu-Jung Kim Department of Nuclear, Plasma and Radiology Engineering University of Illinois BasicBasic FuelFuel CellCell OperationOperation PEM FC + - • Anode : 2H2 4H + 4e + - • Cathode : O2 + 4H + 4e 2H2O • Cell : 2H2 + O2 2H2O • Eo = 1.23 V 2 OxidationOxidation vs.vs. ReductionReduction . Oxidation • Electrons removed from species • Electrons liberated by reaction • Anode half reaction (Hydrogen Oxidation Reaction: HOR) + - • 2H2 4H + 4e . Reduction • Electrons added to species • Electrons consumed by reaction • Cathode half reaction (Oxygen Reduction Reaction: ORR) + - • O2 + 4H + 4e 2H2O 3 LowLow TempTemp FuelFuel CellsCells 180 ~ 210 oC 60 ~ 250 oC 90 oC 90 oC 4 HighHigh TempTemp FuelFuel CellsCells 600 ~ 1,000 oC 650 oC 5 PEMFCPEMFC – Polymer Electrolyte Membrane Fuel Cell 90 oC Porous Pt/C PEM Pt/C Porous Carbon Carbon • PEM – 20~200 μm • Advantages Highest power density as 500 ~ 2500 mW/cm2 Fast start-stop, Low temperature operation • Disadvantages Platinum catalyst, active water management, poor CO and S tolerance 6 Pt/CPt/C catalystcatalyst * * Transmission Electron Microscopy 7 PEMFCPEMFC – Typical PEMFC MEA fabrication process 8 PEMFCPEMFC – Polymer Electrolyte Membrane Fuel Cell 15% 37.8% = 1.36 million Btu/hr 47.2% = 498 kW 9 PEMFCPEMFC – Polymer Electrolyte Membrane Fuel Cell Backup Water Heater Ene-Farm Home Fuel Cell TM • 700 W maximum • Combined Heat and Power generation (CHP) • Tokyo Gas and Panasonic Fuel Cell Unit Hot Water Unit 10 PEMFCPEMFC – Polymer Electrolyte Membrane Fuel Cell • System Schematics 11 PEMFCPEMFC – Polymer Electrolyte Membrane Fuel Cell 95 % co-gen = 6.8 years Price 12 DMFCDMFC – Direct Methanol Fuel Cell 90 oC Porous Pt/C PEM Pt/C Porous Carbon Ru, Sn, W, Re Carbon • Advantages Direct use of liquid fuel Suitable for potable application • Disadvantages Low power density as 30 ~ 100 mW/cm2 Undesirable intermediates formation such as CO Methanol cross-over through PEM 13 DMFCDMFC – Direct Methanol Fuel Cell 14 DMFCDMFC – Direct Methanol Fuel Cell 1 month of operation with 650 Whr/ℓ of power density and 1,200 Whr of energy storage 1 month = 8 hrs/day and 5 days/week 30 W of average power Methanol DMFC Extended Tank (100cc) Methanol 1.1 Whr/cc Tank (1,000cc) 15 DirectDirect MethanolMethanol FuelFuel CellCell Specification Type DMFC` For use in Lap-top computer Power 25 W Nominal Voltage 8 ~ 10 Volt Typical capacity 250 Whr 1.25 Whr/cc Fuel capacity 200 cc Fuel type 100 % Methanol Nominal weight 1.7 kg (3.75 lbs) Size 232 x 106 x 54 mm Lifetime 4,000 hr 16 DirectDirect MethanolMethanol FuelFuel CellCell Control circuit board Display Switch Battery & power converter Stack Fuel manifold Methanol fuel canister 17 DirectDirect MethanolMethanol FuelFuel CellCell 18 AFCAFC – Alkaline Fuel Cell 60 ~ 250 oC Porous Pt/C KOH Pt/C Porous Carbon or Ni aqueous or Ni Carbon solution • Advantages Non-precious catalyst due to higher cathode performance Low-cost electrolyte • Disadvantages - 2- Pure H2 and O2 only due to 2OH + CO2 → CO3 + H2 O and K2CO 3 precipitation Occasional replenishment of KOH electrolyte Water removal from anode is critical 19 AFCAFC – Alkaline Fuel Cell 20 PAFCPAFC – Phosphoric Acid Fuel Cell o 180~210 C Porous Pt/C H3 PO4 in Pt/C Porous Graphite SiC matrix Graphite • Phosphoric acid under 42 oC solidifies, over 210 oC phase transition loosing ability as an electrolyte. • Advantages – Reliability, long-term performance, low-cost electrolyte. • Disadvantages – Platinum catalyst, CO and S poisoning, replenishment of corrosive electrolyte. 21 PAFCPAFC – Phosphoric Acid Fuel Cell 22 MCFCMCFC – Molten Carbonate Fuel Cell 650 oC Porous Porous Li2CO 3 Nickel / Chrome Nickel Oxide K2CO 3 In LiOAlO2 23 MCFCMCFC – Molten Carbonate Fuel Cell • Suitable for stationary continuous power application • Advantages Fuel flexibility – H2, CO, CnH m (Methane, alcohols) Non-precious metal catalyst High quality of waste heat for cogeneration application • Disadvantages CO2 recycling complexity Corrosive molten carbonate electrolyte Degradation / Life-time issues 24 MCFCMCFC – Molten Carbonate Fuel Cell (a) (b) 25 MCFCMCFC – Molten Carbonate Fuel Cell 26 MCFCMCFC – Molten Carbonate Fuel Cell 84 % co-gen 27 MCFCMCFC – Molten Carbonate Fuel Cell 21 units 28 SOFCSOFC – Solid Oxide Fuel Cell YSZ 600 ~ 1000 oC Porous Solid Porous Nickel / YSZ* cermet ceramic Conducting oxide * Yttria-Stabilized Zirconia 29 SOFCSOFC – Solid Oxide Fuel Cell • High temperature environment of operation • Anode – durable against highly reducing environment Nickel : catalytic activity, conductivity YSZ cermet : ion conductivity, thermal expansion compatibility, mechanical stability, maintain high porosity & surface area • Cathode – durable against highly oxidizing environment MIEC : Mixed Ion-Electron Conducting ceramic material LSM : Strontium-doped Lanthanum Manganite LSF : Lanthanum Strontium Ferrite LSC : Lanthanum Strontium Cobaltite LSCF : Lanthanum Strontium Cobaltite Ferrite 30 SOFCSOFC – Solid Oxide Fuel Cell • Advantages Fuel flexibility – H2, CO, CnH m Non-precious metal catalyst High quality of waste heat for cogeneration application Solid electrolyte • Disadvantages High temperature materials issues Sealing issues Expensive components and fabrication Fuel dilution problem because H2O generation from anode 31 SOFCSOFC – Solid Oxide Fuel Cell 32 SOFCSOFC – Solid Oxide Fuel Cell 33 SOFCSOFC – Solid Oxide Fuel Cell 34 SOFCSOFC – Solid Oxide Fuel Cell . SOFC and Gas Turbine Combined Cycle for 1 MW Power Plant 35 SOFCSOFC – Solid Oxide Fuel Cell . Triple Combined Cycle ( SOFC + Gas Turbine + Steam Turbine ) 55% 45% 1200 oC Turbocharger Mitsubishi Heavy Industries 36 SOFCSOFC – Solid Oxide Fuel Cell . Energy Balance of Triple Combined Cycle for 400 MW Plant Mitsubishi Heavy Industries 37 SingleSingle--ChamberChamber SOFCSOFC Ni–GDC (Gadolinium-Doped Ceria) cermets Sm0.5Sr 0.5CoO 3-x (SSC) 38 SingleSingle--ChamberChamber SOFCSOFC Advantages • Simple design structure • Require no high-temperature seals • The electrolyte no longer needs to be gastight, significantly relaxing electrolyte fabrication requirements. • Size reduction/miniaturization is facilitated by the intrinsic simplicity of single-chamber design and reduced gas manifolding requirements. Disadvantages • The risk of fuel–air mixture explosions. • Operation on very dilute (typically < 4%*) fuel mixtures, decreasing performance. • Electrode materials are never 100% selective, and parasitic non- electrochemical reactions result reducing of fuel utilization and decrease efficiency. * Flammability of H2 = 4.1~72.5 vol. % 39 DirectDirect FlameFlame SOFCSOFC 40 DirectDirect FlameFlame SOFCSOFC Advantages • The fuel flexible system - intermediate flame species are similar for all kinds of hydrocarbons, the cell can be operated on virtually any carbon- based fuel. • Remarkably simple structure - The anode is simply held in the exhaust gases close to a fuel-rich flame, while the cathode breathes ambient air. • The system is thermally self-sustained and there are no sealing requirements. • System start-up is rapid - typically within seconds depending on the thermal mass of the fuel cell. Disadvantages • Low-efficiency, low-power density • Issues with coking depending on the flame chemistry and thermal shock due to rapid thermal cycles. 41 LiquidLiquid--TinTin AnodeAnode SOFCSOFC 42 LiquidLiquid--TinTin AnodeAnode SOFCSOFC Advantages • Uses conventional SOFC electrolytes and cathodes but employs an anode based on liquid tin. • The liquid-tin anode allows direct oxidation of almost any carbon- containing fuel (including biomass, JP8 - a sulfur-rich military logistics fuel, coal, woodchips, even plastic bags) without reforming or other fuel processing. • The liquid-tin anode is surprisingly durable, it is not harmed by coking, and it is not poisoned by sulfur but can be used as a fuel. Disadvantages • The required operation temperature is quite high (> 900∘C). • Power densities remain low. • Lifetime/durability issues must be investigated further. 43 MembranelessMembraneless FuelFuel CellsCells 44 MetalMetal--AirAir CellsCells - - • Anode Reaction: Zn + 2OH ZnO + H2O + 2e - - • Cathode Reaction: ½ O2 + H2O + 2e 2OH • Overall Reaction: ½ O2 + Zn ZnO 45 ProtonicProtonic CeramicCeramic FuelFuel CellsCells ((PCFCsPCFCs)) • PCFCs are based on proton-conducting capable of solid-state oxide electrolytes include acceptor-doped perovskite (CaTiO3) compositions based on o BaZrO3 and BaCeO3 with operation temp 350 ~ 500 C • Advantages - PCFCs share many characteristics in common with SOFCs. - Enable operation on non-hydrogen fuels - Relatively inexpensive oxide materials requiring little or no precious metal catalysts - Like PEMFCs produce water at the cathode. Therefore the anode fuel is not diluted by product water gas, enabling potential gains in cell operating voltage and efficiency. • Disadvantage - Poor performance unless the new electrode materials (especially new cathode materials) that work at lower temperatures and are compatible with PCFC electrolytes are developed 46 SolidSolid--AcidAcid FuelFuel CellsCells • SAFCs use a solid proton-conducting electrolyte based on an inorganic acid salt (“a solid acid”) which is thought to be of as in-between normal salts and normal acids. • For example, if sulfuric acid (H2SO 4 ) is reacted with cesium sulfate (Cs2SO 4 ) salt, the solid acid CsHSO4 is produced: ½ H2 SO4 + ½ Cs2SO 4 → CsHSO4 • The structure of most solid acids like CsHSO4