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TECH 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 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. Fuel cell: reactants supplied continuously and electrodes invariant Overall Fuel Cell Reactions: H2 + O2  H2O + heat + electrons Fuel Cell _ + Air (O2) H2 H2O Storage cell: reactants self contained and electrodes consumed Lead-Acid Battery Reaction Pb + PbO2 + H2SO4  2 PbSO4 + 2 H2O + _ H2SO4 Pb Storage Cell Fuel-Cells-by-Argonne-2007

3 Fuel Cells Fuel-Cells-by-Argonne-2007

4 Photographs from FC History
William Jacques' carbon battery, 1896 William Grove's drawing of an experimental “gas battery“, 1843 US Army MCFC, 1966 Allis-Chambers PAFC engine, 1965 Fuel-Cells-by-Argonne-2007

5 Bipolar Plate Cathode + Electrolyte Anode - FUEL CELL PRIMER
HYDROGEN (H2) OXYGEN (O2) O- e - 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. Fuel-Cells-by-Argonne-2007 H+ ½O2 + 2H+ + 2e H2O H H+ + 2e-

6 Single cells are arranged into “stacks” to increase total voltage and power output
Ballard PEFC Stack Cathode: O2 + 4H+ + 4e-  2H2O V Anode: H2  4H+ + 4e V Total Cell: H2 + O2  2H2O V per cell Power = Volts X Amps Fuel-Cells-by-Argonne-2007

7 Thermal & Water Management Electric Power Conditioner
Fuel Cell System Fuel Processor Fuel Cell Stack Spent-Gas Burner Thermal & Water Management Air H2 Exhaust Electric Power Conditioner Fuel-Cells-by-Argonne-2007

8 On-Board Fuel Processing
Fuel Processor BARRIERS Fuel processor start-up/ transient operation Durability Cost Emissions and environmental issues H2 purification/CO cleanup Fuel processor system integration and efficiency Fuel Processor Power Bipolar Plate Cathode + Anode - Electrolyte H+ HYDROGEN OXYGEN e O 2 Fuel-Cells-by-Argonne-2007

9 Five major types of fuel cells
COMPARISON OF 5 TYPES OF FUEL CELLS Fuel Cell Type Temperature Applications Electrolyte / Ion Polymer Electrolyte Membrane (PEM) ° C Electric utility Portable power Transportation Perfluorosulfonic acid / H+ Alkaline (AFC) 90 – 100° C Military Space KOH / OH- Phosphoric Acid (PAFC) 175 – 200° C Distributed power H3PO4 / H+ Molten Carbonate (MCFC) 600 – 1000° C (Li,K,Na)2CO3 / CO2- Solid Oxide (SOFC) APUs (Zr,Y) O2 / O- Fuel-Cells-by-Argonne-2007 PEM – Low temperature allows for quick start-up, transient response – good for transportation

10 Alkaline Fuel Cell (AFC)
Applications Space Transportation Features High performance Very sensitive to CO2 Expensive Pt electrodes Status “Commercially” available AFCs from Apollo & Spaceshuttle Spacecrafts-- NASA Fuel-Cells-by-Argonne-2007 Equations Cathode: ½O2 + H2O + 2e¯ → 2OH¯ Anode: H2 + 2OH¯ → 2H2O + 2e¯

11 Phosphoric Acid Fuel Cell
Applications Distributed power plants Combined heat and power Some buses 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 UTC Fuel Cells 200-kW Fuel-Cells-by-Argonne-2007 Equations Cathode: ½O2 + 2H+ + 2e¯ → H2O Anode: H2 → 2H+ + 2e¯

12 Molten Carbonate Fuel Cells
Applications Distributed power plants Combined heat and power Features Fuel flexibility (internal reforming) High efficiency High temperature good for cogeneration Base materials (nickel electrodes) Corrosive electrolyte Status Pre-Commercially available but expensive Fuel Cell Energy MCFC stack Fuel-Cells-by-Argonne-2007 Equations Cathode: ½O2 + CO2 + 2e¯ → CO3= Anode: H2 + CO3= → 2H2O + CO2 + 2e¯

13 Solid Oxide Fuel Cells Applications Features Status
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 Fuel-Cells-by-Argonne-2007 Equations Cathode: O2 + 2e¯ → 2O= Anode: H2 + O= → H2O + 2e¯

14 Polymer Electrolyte Fuel Cells
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 Fuel-Cells-by-Argonne-2007 Equations Cathode: ½O2 + 2H+ + 2e¯ → H2O Anode: H2 → 2H+ + 2e¯

15 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 Endplate O2 in CH3OH out Cathode Anode Bipolar plate O2 out CH3OH in Fuel-Cells-by-Argonne-2007 Equations Cathode: O2 + 6H+ + 6e¯ → 3H2O Anode: CH3OH + H2O → CO2 + 6H+ + 6e¯

16 Fuel Cells Advantages Disadvantages 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 Hydrogen Storage Amminex tablets DADB (predicted) Solar Zinc production Alkali metal hydride slurry

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. Hydrogen Storage

21 Liquid (Cryogenic) Compressed, chilled, filtered, condensed
Hydrogen Storage 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 for compressed gas tanks Comparatively very heavy, but with good volumetric efficiency, good for small storage, or where weight doesn’t matter Hydrogen Storage

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… Hydrogen Storage

24 Methanol CH3OH Broken down by reformer, yields CO, CO2, and H2 gas.
Very common hydrogen transport method Distribution infrastructure exists – same as gasoline Hydrogen Storage frequently used as a denaturant additive for ethanol

25 Ammonia Slightly higher volumetric efficiency than methanol
Must be catalyzed at 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 Hydrogen Storage

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 Hydrogen Storage

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 Hydrogen Storage

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. Hydrogen Storage

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. Hydrogen Storage

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) Hydrogen Storage Performing quantum calculations on a supercomputer, scientists at Pacific Northwest National Laboratory have characterized a material that might allow on-board refueling of hydrogen powered vehicles. Researchers, led by Maciej Gutowski, looked at different crystalline structures of a compound made up of nitrogen, boron and hydrogen - NBH6 - and found one that might be more stable compared to ammonia borane, a molecular crystal built of NH3BH3 molecules. Ammonia borane can hold a lot of hydrogen but isn't easily reversible - or able to be refilled with hydrogen. Ammonia borane, as a storage material, would likely have to be removed from the vehicle and be sent to some sort of processing plant and undergo a reaction to be refilled. The more stable compound, diammoniate of diborane or DADB, holds more promise for reversibility. Initial thermodynamic properties for the compound indicate that it might spontaneously uptake hydrogen fuel. This work is performed under the Grand Challenge Project "Computational studies of materials to hydrogen storage" in the Molecular Sciences Computing Facility at PNNL. Researchers plan to perform additional calculations, synthesize the diammoniate of diborane compound and test their theories on the material in the coming year.

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) Hydrogen Storage Breaking the water molecules by simply heating them is not practical, since it requires achieving temperature above 2,500°C (4,530F). Many years ago it was discovered that it is possible to use pure zinc to extract the oxygen from water, therefore releasing hydrogen. This process can be done in the much lower temperature of 350°C (662F). Since zinc is a relatively abundant metal, and is the fourth among all metals in world production – being exceeded only by iron, aluminum and copper – it can be considered a natural choice for producing hydrogen. The problem is that the current industrial production of pure zinc (Zn) from zinc oxide (ZnO) by either electrolysis or smelting furnaces is characterized by its high-energy consumption and concomitant pollution, derived mostly from the combustion of fossil fuels for heat and electricity. To address the issue solar energy can be used as the main energetic source in the production of Zn from ZnO. In 2004 the European Union and the Swiss Federal Office of Science and Education decided to fund a joint research to explore this possibility using a 45 kW solar furnace in Villigen, Switzerland, a 75kW solar simulator in Zurich and the largest solar research facility in the world with 1MW output located at the Weitzman Institute in Israel. The need for such a large amount of power is due to the need for very high temperatures required for the production of Zn from ZnO (normally around 1750°C / 3182F). Adding small amounts of carbon in the form of coal enabled the Weitzman team to reduce the Zn production temperature to a more manageable 1200°C (2192F). For the future, the team sees the possibility of replacing the coal completely with biomass thus making the entire process completely pollution free. The real achievement of the Weitzman team is the scale of production of Zn which reached an average of about 50kg/h during tests using the existing Solzinc solar reactor located at the center of the Institute. On a full scale industrial facility much larger amounts could be extracted using a similar process. The energy cycle developed by the researchers is very efficient and relatively self-sustaining. ZnO is mined and transported to the Solzinc solar facility where it is mixed with small amounts of coal and put inside the solar furnace located on top of a high tower. A large array of heliostats (computer guided highly reflective mirrors) follows the sun around the sky and reflects the light to a hyperbolic mirror located inside the solar tower producing highly concentrated heat inside the solar furnace. At a heat of above 1200°C (2192F) the ZnO breaks down into Zn and oxygen which in turn recombines with the carbon to create CO as a minor by-product. The Zn is then cooled down to create a fine powder which can be safely handled and transported. In order to produce hydrogen from the Zn powder a much simpler process is performed where the Zn is mixed with water at a temperature of 350°C (662F). The oxygen inside the water recombines with the Zn to produce ZnO once again and the by-product is pure hydrogen. This process has many advantages over existing ways of producing hydrogen. First and foremost it uses a renewable form of energy - the sun. Furthermore the main material required for the process is the relatively inexpensive zinc oxide which is almost completely recycled back by the end of the process. Another important advantage is that the hydrogen could be produced where it is needed, i.e., at the local fuel station instead of transporting large amounts of explosive hydrogen across the country. Trucks loaded with safe Zn powder would transport it to the fuel station where it would undergo the relatively simple treatment of extracting the hydrogen using steam. Last but not least, the entire process is relatively clean and when biomass will replace the coal as an additive to the ZnO mix, the process will be completely nonpolluting. And now for the 10 million dollar question: if the process is so simple and efficient why can't you buy zinc-based hydrogen fuel at your local fuel station right now? First of all, there is the lack of infrastructure. Currently there are almost no hydrogen fuel stations, let alone hydrogen-based cars. This could change within 5-10 years but it will require great investments by both countries and the industry. It will also require large amounts of inexpensive accessible hydrogen, and here enters the Solzinc process developed at the Weitzman Institute. As Michael Epstein, head of the Solar Research Facilities Unit in the Weitzman Institute explained in an interview to IsraCast, it is now up to the industry to push the project forward into full commercialization. His assessment is that with the backing of the industry, full-scale production of hydrogen from Zn using the industrial Solzinc facility could begin within 8-10 years. In the meantime, Epstein is considering more immediate uses for Zn such as Zinc-Air batteries which are similar to existing batteries but get one of their main reactants-oxygen-from the outside air. These batteries are nontoxic and are neither highly reactive nor flammable. Several companies across the world are currently developing Zinc-Air batteries; among the leading ones is the Israeli company Electric Fuel which develops Zinc-Air battery technology for automobiles. Pictures courtesy of the Weitzman Institute

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 Hydrogen Storage The superior storage density of chemical hydride slurry is indicated in the chart below. One unit of slurry carries the potential of generating twice as much volume of hydrogen (at about the same weight ) as one unit of cryogenically cooled liquid hydrogen. Liquid hydrogen is a proven method of storing hydrogen, but it takes substantial energy to liquefy the hydrogen and there is continual "boil off" of hydrogen during storage. Slurry, on the other hand, is stored at normal temperature and normal pressure. The Safe Hydrogen patented and proprietary chemical hydride slurry releases hydrogen as needed by the addition of water. Because hydrogen is also contributed by the water in the reaction, the Safe Hydrogen fuel carries an impressive hydrogen generation potential. The reaction, besides producing hydrogen, generates some heat and a hydroxide byproduct. Cost and Energy Efficiencies No material waste The recycling process converts the hydroxide byproduct back to the original hydride. All other materials, constituting the slurry are also reclaimed and may be used over and over again. Recycling is achieved in very large-scale, centralized manufacturing processes. The recycling process is designed to use any energy source to generate the hydrogen carried by the slurry. Core Materials are safe to use and widely available The initial development and demonstration of the concept utilized lithium hydride. Safe Hydrogen is developing the technology using magnesium hydride. Magnesium hydride offers superior cost, efficiency and safety benefits. No Need for a New Distribution Infrastructure While slurry must be transported to the market and returned from the market, the slurry's exceptional hydrogen storage efficiency makes it a cost efficient hydrogen fuel that - unlike other options- can meet near term DOE hydrogen cost targets. A major cost advantage of this technology is based on the characteristics of the slurry. Slurry is a nonexplosive, noncorrosive, environmentally safe, pumpable "hydrogen fuel". Slurry can be stored, transported and pumped with existing tanks, pumps and pipelines and can therefore distribute hydrogen to the market utilizing the existing fossil fuel infrastructure. The only difference from existing fuel delivery systems is that the delivery devices such as trucks or rail tankers don't return empty. They are fully loaded in both directions. They return from delivery runs, loaded with depleted slurry that needs to be recycled.

33 Storage Method Comparison
Hydrogen Storage These numbers should be in the same ranges, but the slurry data doesn’t agree completely. Sodium Hydride slurry .9 1.0 Must reclaim used slurry DADB .09-.1 (numbers for plain “diborane”and sodium borohydride, should be similar) Amminex 9.1 .081 Zinc powder unsure US DOE goal 9.0

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