Hydrogen fuel cells

HYDROGEN FUEL CELLS

Karen WangJoey Liu

Connections

1. Hydrogen Fuel Cells and Re-dox Reactions2. Alkaline Fuel Cells3. Hydrogen Fuel Cells and Electrochemistry &

thermodynamics1. Catalyst, anodes, cathodes

4. Temperature & efficiency of Hydrogen Fuel Cells

5. 5.4 Hydrogen Fuel Cells and the Environment6. 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

• 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 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

1. Hydrogen2. Electron flow3. Load4. Oxygen5. Cathode6. Electrolyte7. Anode8. Water9. 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%


& 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


& 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


& 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

http://www.youtube.com/watch?v=oy8dzOB-Ykg




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


& 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

Technology

Hydrogen fuel cells