Fuel cells

• Fuel cells uses electrochemical oxidation of a fuel (e.g. hydrogen) to produce a potential difference
• In a fuel cell, the electrons flow from the anode to the cathode. The anode is negative and cathode is positive (this is the opposite for electrolysis).
• Oxidation at the anode (for a hydrogen fuel cell):

  H2 → 2 H+ + 2 e-
• Reduction at the cathode (for a hydrogen fuel cell):

  O2 + 4 H+ + 4 e- → 2 H2O
• Overall equation in a hydrogen fuel cell:

  2 H2 + O2 → 2 H2O
• How a hydrogen fuel cell works:

  1. Hydrogen enters the anode compartment.
  2. Then, the hydrogen is oxidised (H2 → 2 H+ + 2 e-) to become an ion.
  3. The electrons pass through the wire into the cathode, while the hydrogen ions pass through the electrolyte to the cathode.
  4. Oxygen enters the cathode compartment.
  5. This means that the electrons and hydrogen ions can react with oxygen.
  6. Together this combines to make water (O2 + 4 H+ + 4 e- → 2 H2O)
  7. Finally, the water leaves by the outlet
• Fuel cells convert energy between chemical and electrical
• Structure of hydrogen fuel cell:

  A) Anode

  B) Cathode

  C) Electrolyte

  D) Fuel in (hydrogen)

  E) Oxygen in

  F) Excess fuel out

  G) Outlet (water out)'

  H) Wire

  
• In fuel cells, the electrodes are made of porous carbon. This means that have lots of tiny holes and contain a catalyst which speed up the reaction.
• Advantages of hydrogen fuel cells compared to batteries:

  • Only require hydrogen and oxygen, which are both abundant
  • Don't produce any pollutants
  • Less polluting to dispose off
  • Don't need recharging/replacing as often
  • Cheaper to make
• Disadvantages of hydrogen fuel cells compared to batteries:

  • Storage of hydrogen gas takes up a lot of space
  • Can be explosive when mixed with air, making storage dangerous
  • Hydrogen requires energy to make, which usually comes from fossil fuels