HYDROGEN FUEL CELLS

Presented by Amit sen

Connections

1. Hydrogen Fuel Cells and Re-dox Reactions

2. Alkaline Fuel Cells

3. Hydrogen Fuel Cells and Electrochemistry & thermodynamics

1. Catalyst, anodes, cathodes

4. Temperature & efficiency of Hydrogen Fuel Cells

5. 5.4 Hydrogen Fuel Cells and the Environment

6. Applications of Hydrogen Fuel Cells– nuclear energy

INTRODUCTIONFuel 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

2H2(g) + O2(g) 2H2O(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 H2 2H+ + 2e-

reduction Cathode (positive electrode): e- enter the cell 4H+ + 4e- + O2 2H2O

Connection 2: FUEL CELLS

& CATALYSTS (rate of reaction) the splitting of H2 into p+ and e- at the anode 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 CELLSALKALINE & 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

1. Hydrogen

2. Electron flow

3. Load

4. Oxygen

5. Cathode

6. Electrolyte

7. Anode

8. Water

9. 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:

H2 + 2OH- 2H2O + 2e- H2 2H+ + 2e-

Electrons flow through an external circuit and return to the cathode, reducing oxygen:

O2 + 2H2O + 4e- 4OH- 4H+ + 4e- + O2 2H2O

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

CO2, Nox, 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