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Hydrogen fuel cells
 

Hydrogen fuel cells

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  • Fuel cells have been discovered for about 150 years, in the 19 th century, there was a rapid increase of its knowledge, but it is only recently that they have become prominent technology. Fuel cells are increasingly relevant in today’s technological world, as can be seen in electric cars and NASA technology.
  • Components: 2 electrodes – pos&neg – cathode & anode, electrolyte
  • Same as combustion of hydrogen (exothermic) Fuel cell: produces energy in the form of electricity H2 is led to the anode, tow which it may lose e- and thereby form H+ Ions capable of diffusing through the electrolyte, while e- flow through the external circuit. Gaseous oxygen is similarly led to the cathode, combines with returning e- from the circuit and H+ from the electrolyte
  • Converts 25% of the chemical energy of the fuel into the kinetic energy of the car. Rechargeable batteries – run down quickly.
  • Even better, since fuel cells create electricity chemically, rather than by combustion, they are not subject to the thermodynamic laws that limit a conventional power plant
  • The automobile internal combustion engines use gasoline as fuel, produce CO2, NOx, & volatile organic compounds.

Hydrogen fuel cells Hydrogen fuel cells Presentation Transcript

  • HYDROGEN FUEL CELLS Karen Wang Joey Liu
  • Connections
    • Hydrogen Fuel Cells and Re - dox Reactions
    • Alkaline Fuel Cells
    • Hydrogen Fuel Cells and Electrochemistry & thermodynamics
      • Catalyst, anodes, cathodes
    • Temperature & efficiency of Hydrogen Fuel Cells
    • 5.4 Hydrogen Fuel Cells and the Environment
    • Applications of Hydrogen Fuel Cells– nuclear energy
  • INTRODUCTION Fuel Cell Overview
  • Historical Overview
    • 1838: discovered by German scientist Christian Friedrich Schöenbein
    • 1839: Demonstrated by Welsh scientist Sir William Robert Grove
  • What are Fuel Cells?
    • Battery that produces electricity
    • overall reaction: oxidation of a fuel by oxygen
    • 2H 2(g) + O 2(g)  2H 2 O (l)
    • (Hydrogen) Fuel + oxygen  water
    • Unlimited fuel supply: reactants continuously supplied from an external source (open system)
      • Also known as flow battery
    • Used as a stack
  • Types of Fuel Cells
    • Molten carbonate cells
    • Solid oxide cells
    • Direct methanol and other non-hydrogen cells
    • Biofuel cells
    • Phosphoric Acid
    • Proton Exchange Membrane
    • Acid and alkaline cells
  • How Do Fuel Cells Work? HYDROGEN FUEL CELLS & ELECTROCHEMISTRY
  • Connection 1: FUEL CELLS & REDOX REACTION
    • oxidation
      • Anode (negative electrode): e- leave the cell
      • H 2  2H + + 2e -
    • reduction
      • Cathode (positive electrode): e- enter the cell
      • 4H + + 4e - + O 2  2H 2 O
  • Connection 2: FUEL CELLS & CATALYSTS (rate of reaction)
    • the splitting of H2 into p+ and e- at the a node is typically speeded up by the presence of a catalyst (typically metal placed on the anode, or the electrode itself)
    • Platinum film is often used
    • Electrolyte – permit only appropriate ions to pass between anode and cathode; otherwise the chemical reaction may be disrupted
    • End product: water = drained
  • Types of Fuel Cells Connection 3 HYDROGEN FUEL CELLS ALKALINE & PEM FUEL CELLS
  • TYPES OF HYDROGEN FUEL CELLS
    • Alkaline Fuel Cells
    • Aka: Bacon fuel cell
    • Used in NASA since mid-1960s (Appollo)
    • Efficiency – 70%
    • hydrogen + oxygen  water, heat, electricity
    • PEM Fuel Cells
    • Proton Exchange Membrane (or Proton Electrolyte Membrane)
    • Transport applications and stationary fuel cell applications
    • Lower temp./pressure ranges (50-100℃)
  • Alkaline Fuel Cells
    • Hydrogen
    • Electron flow
    • Load
    • Oxygen
    • Cathode
    • Electrolyte
    • Anode
    • Water
    • Hydroxyl ions
  • How Hydrogen Fuel Cells Work – PEM
    • Proton exchange membrane cells
    • A fuel cell produced electricity by combining Hydrogen and Oxygen atoms electrochemically rather than through combustion
    • Hydrogen = fuel  electrolysis – stored as a compressed gas/liquid/metal compound
    • A single fuel cell consists of an anode and a cathode with an electrolyte in between
    • Hydrogen molecules enter the anode  react with catalysts (1)  split into H+ & e-  H+ pass through electrolyte, e- directed through an external circuit = electrical current
    • Oxygen molecules enter at the cathode + H + + e-  water & heat
    • Individual fuel cells placed in a series = fuel cell stack  power vehicle
  •  
  •  
  • HYDROGEN FUEL CELLS & REDOX REACTION
    • Alkaline Fuel Cells
    • @ Anode, H2 is oxidized:
    • H 2 + 2OH -  2H 2 O + 2e - H 2  2H + + 2e -
    • Electrons flow through an external circuit and return to the cathode, reducing oxygen:
    • O 2 + 2H 2 O + 4e -  4OH - 4H + + 4e - + O 2  2H 2 O
    • PEM Fuel Cells
  • HYDROGEN FUEL CELLS AS AN ENERGY SOURCE
  • Connection 4 : HYDROGEN FUEL CELLS & EFFICIENCY and THERMODYNAMICS
    • Automobile internal combustion engines
      • inefficient – 25%
    • Rechargeable batteries (modified lead-acid, nickel-cadmium batteries)
      • Run down quickly – 250 Km
      • Recharged from external electrical source
      • Takes hours
    • Fuel cells
      • Efficient – 80%
  • Connection 4 : HYDROGEN FUEL CELLS & EFFICIENCY and THERMODYNAMICS
    • Fuel cells create electricity chemically; unlike combustion, are not subject to thermodynamic laws
    • ∴ fuel cells are more efficient
      • Some waste heat can also be harnessed
  • Connection 5: HYDROGEN FUEL CELLS & THE ENVIRONMENT
    • Automobile engines: gasoline = pollutants
      • CO 2 , No x , VOCs
      • health & environmental problems: smog, greenhouse effect
    • Electric cars: hydrogen fuel cells = pollution free
      • Cleaner, quieter, more efficient
      • Product: water vapour
  • Connection 5: HYDROGEN FUEL CELLS & THE ENVIRONMENT
    • Production of hydrogen fuel – unnatural resource
      • Hydrocarbon fuels (petroleum, methane) = pollution
      • Electrolysis of water powered by solar energy or hydroelectricity = low pollution
    • Renewable energy source
  • systems
    • Fuel cell powered cars
      • http:// www.youtube.com/watch?v =oy8dzOB-Ykg
      • Efficiency, pollution-free
  • Connection 6: HYDROGEN FUEL CELLS AS AN ENERGY SOURCE
    • Production of hydrogen fuel – unnatural resource
      • Hydrocarbon fuels (petroleum, methane) = pollution
      • Electrolysis of water powered by solar energy or hydroelectricity = low pollution
  • Connection 6: HYDROGEN FUEL CELLS & NUCLEAR ENERGY
    • Implementation scenarios
      • Fossil
      • nuclear
  • References
    • (Sørensen), B. S. (2005). Hydrogen and Fuel Cells: Emerging Technologies and Applications (Sustainable World) . Toronto: Academic Press.
    • Harkin, T., & Hoffmann, P. (2001).  Tomorrow's Energy: Hydrogen, Fuel Cells, and the Prospects for a Cleaner Planet . London: The Mit Press.
    • Holland, G., & Provenzano, J. (2007).  Hydrogen Age, The . Layton: Gibbs Smith, Publisher.
    • ollecting the History of Proton Exchange Membrane Fuel Cells. (n.d.).  National Museum of American History . Retrieved April 20, 2010, from http://americanhistory.si.edu/fuelcells/basics.htm