Fuel cells

• Applying a strong electrical force pushes the electrons back towards the negative terminal, which allows us to recharge a cell
• Discharging a cell means using up its electrical power.
• Why should batteries be recycled separately from other waste materials?

  • Batteries contain toxic and dangerous chemicals, which can harm the environment if not disposed of properly
  • Rechargeable batteries are advantageous in this regard as they can be used hundreds of times before being disposed of
• 3 main types of cells

  • primary
  • secondary
  • fuel
• What are primary cells?

  • Non-rechargable
  • Designed to only be used once
• When in use, electrical energy is produced by oxidation and reduction at the electrodes. However, the reactions cannot be reversed.

  Eventually the chemicals will be used up, voltage will fall, the battery will go flat, and the cell will be discarded or recycled.
• Most modern primary cells are alkaline based on zinc and manganese dioxide, Zn / MnO2 and a potassium hydroxide alkaline electrolyte.
• A fuel cell uses the energy from the reaction of a fuel with oxygen to create a voltage

  • The fuel and oxygen flow into the fuel cell and the products flow out. The electrolyte remains in the cell.
  • Fuel cells can operate continuously provided that the fuel and oxygen are supplied into the cell
  • Fuel cells do not have to be recharged
• Many different fuels can be used, but hydrogen is the most common fuel used in fuel cells.
• Hydrogen fuel cells produce no carbon dioxide during combustion, with water being the only combustion product. Fuel cells using many other hydrogen-rich fuels, such as methanol, are also being developed.
• A hydrogen cell can have either an alkali or acid electrolyte
• The cell voltages of a hydrogen fuel cell are both 1.23 V, despite the alkali and acid cells having different redox systems
• Hydrogen fuel cell overall equation in an acid and alkali cell is the same


  H2 (g) + 1/2 O2 (g) -> H2O (l)
• Secondary cells are rechargeable. Unlike primary cells, the cell reaction producing electrical energy can be reversed during recharging. The chemicals in the cell are then regenerated and the cell can be used again.
• Common examples of secondary cells include:

  • lead-acid batteries used in car batteries
  • nickel-cadmium, NiCd, cells and nickel-metal hydride, NiMH - the cylindrical batteries used in radios, torches
  • lithium-ion and lithium-ion polymer cells used in our modern appliances - laptops, tablets, cameras, mobile phones - and also being developed for cars
• In a fully-charged lithium ion battery, the lithium starts at the negative electrode, which is powdered graphite
• In a lithium ion battery as the lithium gives up electrons, it migrates through the electrolyte to the positive electrode, which is cobalt (IV) oxide
• Both the positive and negative electrodes act as support structures for lithium, allowing it to move freely
• The reaction which occurs when the Li ion battery is discharging is

  Li + CoO2 -> LiCoO2
• In lithium ion cell

  • lithum oxidised
  • cobalt reduced
• Suggest three reasons why lithium ion batteries are efficient in terms of the weight needed to supply a given amount of electricity

  • Lithium is the lightest metal
  • Lithium is one of the strongest reducing agents (meaning that it can create a relatively high voltage)
  • Lithium ion batteries can be constructed without any moisture whatsoever (saving weight and avoiding water-related damage over time)