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TECH 57210 Sustainable Energy I

TECH 57210 Sustainable Energy I. Energy Sources and Systems 8 Dr. Darwin L. Boyd Fall 2011. Storage Cell. _. Fuel Cell. +. _. +. H 2. Air (O 2 ). H 2 SO 4. Pb. Pb. H 2 O . Storage cell: reactants self contained and electrodes consumed Lead-Acid Battery Reaction

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TECH 57210 Sustainable Energy I

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  1. TECH 57210 Sustainable Energy I Energy Sources and Systems 8 Dr. Darwin L. Boyd Fall 2011

  2. Storage Cell _ Fuel Cell + _ + H2 Air (O2) H2SO4 Pb Pb H2O Storage cell: reactants self contained and electrodes consumed Lead-Acid Battery Reaction Pb + PbO2 + H2SO4  2 PbSO4 + 2 H2O Fuel cell: reactants supplied continuously and electrodes invariant Overall Fuel Cell Reactions: H2 + O2 H2O + heat + electrons Fuel Cells • Fuel Cell – Electrochemical energy conversion device in which fuel and oxidant react to generate electricity without any consumption, physically or chemically, of its electrodes or electrolyte.

  3. Fuel Cells

  4. US Army MCFC, 1966 William Jacques' carbon battery, 1896 Allis-Chambers PAFC engine, 1965 Photographs from FC History William Grove's drawing of an experimental “gas battery“, 1843

  5. OXYGEN (O2) HYDROGEN (H2) e - e - e - e - e - e - O- H+ H+ O- H+ Bipolar Plate O- H+ Cathode + Anode - Electrolyte Bipolar Plate WATER (H2O) + HEAT PEMFC: Protons formed at the anode diffuse through the electrolyte and react with electrons and oxygen at the cathode to form water and heat. ½O2 + 2H+ + 2e- H2O H2 2H+ + 2e-

  6. Single cells are arranged into “stacks” to increase total voltage and power output Ballard PEFC Stack Cathode: O2+ 4H+ + 4e- 2H2O 1.2 V Anode: 2H2 4H+ + 4e- - 0 V Total Cell: 2H2+ O2  2H2O 1.2 V per cell Power = Volts X Amps

  7. Electric Power Conditioner Air Fuel Exhaust Spent-Gas Burner Fuel Processor Fuel Cell Stack H2 Air Thermal & Water Management Fuel Cell System

  8. OXYGEN OXYGEN HYDROGEN HYDROGEN e e e - - - e e e - - - e e e - - - O O O 2 2 2 H+ H+ H+ O O O 2 2 2 H+ H+ H+ O O O 2 2 2 H+ H+ H+ - - Bipolar Plate Bipolar Plate Bipolar Plate Bipolar Plate Bipolar Plate Bipolar Plate Cathode + Cathode + Electrolyte Electrolyte Anode Anode Fuel Processor BARRIERS • Fuel processor start-up/transient operation • Durability • Cost • Emissions and environmentalissues • H2 purification/CO cleanup • Fuel processor systemintegration and efficiency On-Board Fuel Processing Fuel Processor Power

  9. Five major types of fuel cells

  10. AFCs from Apollo & Spaceshuttle Spacecrafts-- NASA Alkaline Fuel Cell (AFC) Applications • Space • Transportation Features • High performance • Very sensitive to CO2 • Expensive Pt electrodes Status • “Commercially” available Equations Cathode:½O2 + H2O + 2e¯ →2OH¯ Anode: H2 + 2OH¯ → 2H2O + 2e¯

  11. Applications Distributed power plants Combined heat and power Some buses UTC Fuel Cells 200-kW Phosphoric Acid Fuel Cell Features • Some fuel flexibility • High efficiency in cogeneration (85%) • Established service record • Platinum catalyst Status • Commercially available but expensive • Excellent reliability and availability • Millions of hours logged Equations Cathode:½O2 + 2H+ + 2e¯ → H2O Anode: H2→2H+ + 2e¯

  12. Applications Distributed power plants Combined heat and power Fuel Cell Energy MCFC stack Molten Carbonate Fuel Cells Features • Fuel flexibility (internal reforming) • High efficiency • High temperature good for cogeneration • Base materials (nickel electrodes) • Corrosive electrolyte Status • Pre-Commercially available but expensive Equations Cathode:½O2 + CO2 + 2e¯ →CO3= Anode: H2 + CO3= → 2H2O + CO2 + 2e¯

  13. Applications Truck APUs Distributed power plants Combined heat and power Features Slow start – subject to thermal shock High temperature High power density (watts/liter) Can use CO and light hydrocarbons directly “Cheap” components, solid electrolyte Low-yield manufacture Status Vehicle APUs Solid Oxide Fuel Cells Equations Cathode:O2 + 2e¯ →2O= Anode: H2 + O=→ H2O + 2e¯

  14. Applications Transportation, Forklifts, etc. Power backup systems Consumer electronics with methanol fuel Features Quick start Low temperature Expensive Pt electrodes Easy manufacture Operating window limits 53-67% thermal efficiency Status Vehicle demonstrations underway Stationary/backup power “commercially” available Toyota Fuel Cell Forklift Polymer Electrolyte Fuel Cells Equations Cathode:½O2 + 2H+ + 2e¯ → H2O Anode: H2→2H+ + 2e¯

  15. O2 out O2 in CH3OH in CH3OH out Cathode Anode Endplate Bipolar plate Direct Methanol Polymer Electrolyte FC (DMFC) Applications • Miniature applications • Consumer electronics • Battlefield Features • A subset of Polymer Electrolyte • Modified polymer electrolyte fuel cell components • Methanol crossover lowers efficiency Status • Pre-Alpha to Beta testing Equations Cathode:1.5 O2 + 6H+ + 6e¯ → 3H2O Anode: CH3OH + H2O → CO2 + 6H+ + 6e¯

  16. Fuel Cells • Advantages • Emissions • Efficiency • Some have fuel flexibility • Disadvantages • Cost – (Pt catalyst) • Some are high temp – may be slow to start • Some sensitive to fuel impurities (need pure H2)

  17. Fuel Cells

  18. Hydrogen • Hydrogen is a secondary energy source • Very clean energy both in ICE and fuel cells • Poor energy density by volume • Hydrogen Storage

  19. Hydrogen Storage Overview • Physical storage of H2 • Chemical storage of hydrogen • New emerging methods • Compressed • Cryogenically liquified • Metal Hydride (“sponge”) • Carbon nanofibers • Sodium borohydride • Ammonia • Methanol • Alkali metal hydrides • Solar Zinc production • Alkali metal hydride slurry • Amminex tablets • DADB (predicted)

  20. Compressed • Volumetrically and Gravimetrically inefficient, but • the technology is simple, so by far the most common in • small to medium sized applications. • 3500, 5000, 10,000 psi variants.

  21. Liquid (Cryogenic) • Compressed, chilled, filtered, condensed • Boils at 22K (-251 C). • Slow “waste” evaporation • Kept at 1 atm or just slightly over. • Gravimetrically and volumetrically efficient • but very costly to compress

  22. Metal Hydrides (sponge) • Sold by “Interpower” in Germany • Filled with “HYDRALLOY” E60/0 (TiFeH2) • Technically a chemical reaction, but acts like a physical storage method • Hydrogen is absorbed like in a sponge. • Operates at 3-30 atm, much lower than 200-700 for compressed gas tanks • Comparatively very heavy, but with good volumetric efficiency, good for small storage, or where weight doesn’t matter

  23. Carbon Nanofibers • Complex structure presents a large surface area for hydrogen to “dissolve” into • Early claim set the standard of 65 kgH2/m2 and 6.5 % by weight as a “goal to beat” • The claim turned out not to be repeatable • Research continues…

  24. Methanol • CH3OH • Broken down by reformer, yields CO, CO2, and H2 gas. • Very common hydrogen transport method • Distribution infrastructure exists – same as gasoline

  25. Ammonia • Slightly higher volumetric efficiency than methanol • Must be catalyzed at 800-900 deg. C for hydrogen release • Toxic • Usually transported as a liquid, at 8 atm. • Some Ammonia remains in the catalyzed hydrogen stream, forming salts in PEM cells that destroy the cells • Many drawbacks, thus Methanol considered to be a better solution

  26. Alkali Metal Hydrides • “Powerball” company, makes small (3 mm) coated NaH spheres. • “Spheres cut and exposed to water as needed” • H2 gas released • Produces hydroxide solution waste

  27. Sodium Borohydrate • Sodium Borohydrate is the most popular of many hydrate solutions • Solution passed through a catalyst to release H2 • Commonly a one-way process (sodium metaborate must be returned if recycling is desired.) • Some alternative hydrates are too expensive or toxic • The “Millennium Cell” company uses Sodium Borohydrate technology

  28. Amminex • Essentially an Ammonia storage method • Ammonia stored in a salt matrix, very stable • Ammonia separated & catalyzed for use • Likely to have non-catalyzed ammonia in hydrogen stream • Ammonia poisoning contraindicates use with PEM fuel cells, • but compatible with alkaline fuel cells.

  29. Amminex • High density, but relies on ammonia production for fuel. • Represents an improvement on ammonia storage, • which still must be catalyzed. • Ammonia process still problematic.

  30. Diammoniate of Diborane (DADB) • So far, just a computer simulation. • Compound discovered via exploration of Nitrogen/Boron/Hydrogen compounds (i.e. similar to Ammonia Borane) • Thermodynamic properties point towards spontaneous hydrogen re-uptake – would make DADB reusable (vs. other borohydrates)

  31. Solar Zinc production • Isreli research effort utilizes solar furnace to produce pure Zinc • Zinc powder can be easily transported • Zinc can be combined with water to produce H2 • Alternatively could be made into Zinc-Air batteries (at higher energy efficiency)

  32. Alkaline metal hydride slurry • SafeHydrogen, LLC • Concept proven with Lithium Hydride, now working on magnesium hydride slurry • Like a “PowerBall” slurry • Hydroxide slurry to be re-collected to be “recycled” • Competitive efficiency to Liquid H2

  33. Storage Method Comparison

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