Topic 5

• Voltage of a cell


  Depends on many factors
• Voltage of a simple cell


  • Depends on the reactivity of the electrodes
• Fuel cells use fuel and oxygen to produce electrical energy
• How a fuel cell works


  1. Fuel enters the cell and becomes oxidised

  2. Sets up a potential difference within the cell
• Hydrogen-oxygen fuel cells


  • Combine hydrogen and oxygen to produce water and energy
  • Don't produce pollutants like greenhouse gases, nitrogen oxides, sulfur dioxide or carbon monoxide
  • Only produce water and heat as by-products
• Fuel cell vehicles vs electric vehicles


  • Fuel cell vehicles don't produce many pollutants, but producing hydrogen can be polluting
  • Electric vehicles don't produce many pollutants when running, but their batteries are more polluting to dispose of
• Batteries vs fuel cells

  Batteries are more expensive to make, store less energy, and need to be recharged more often than fuel cells
• How hydrogen-oxygen fuel cells work

  1. Hydrogen goes into the anode compartment

  2. Oxygen goes into the cathode compartment

  3. At the anode, hydrogen loses electrons to produce H+ ions (oxidation)

  4. At the cathode, oxygen gains electrons from the H+ ions to make water (reduction)

  5. Electrons flow through an external circuit from the anode to the cathode, producing an electric current

  6. The overall reaction is the combustion of hydrogen, producing water
• Hydrogen-oxygen fuel cells involve a redox reaction
• Redox reactions are important in chemistry
• Different metals will react differently with the same electrolyte. This causes the charge difference/voltage of the cell.
• The bigger the difference in reactivity of the electrodes, the bigger the voltage of the cell
• The electrolyte used in a cell will also affect the size of the voltage since different ions in solution will react differently with the metal electrodes used
• A battery is formed by connecting to more cells together in series. The voltage of the cells in the battery are combined so there is a bigger overall voltage.
• In non-rechargeable batteries, the reactions get used up
• In some cells, the chemical reactions that happen at electrodes are irreversible
• Overtime the reacting particles – the ions in the electrolyte and metal ions on the electro get used up and turned into the products of the reaction. Once anyone of the reactions is used up the reaction can't happen and so no electricity is produced.
• The products cannot be turned back into the reactions so they still cannot be recharged. This happens in non-rechargeable batteries in rechargeable batteries. The reaction can be reversed by connecting it to an external electric current
• fuel cells use fuel and oxygen to produce electrical current
• Fuels contain hydrogen or carbon monoxide which combines with oxygen from air to form water vapour and carbon dioxide
• A few cell is an electrical cell that supplied with a fuel and an oxygen and uses energy from the reaction between them to produce electrical energy efficiently
• When the fuel enters the fuel cell, it becomes oxidised and sets up a potential difference in
• There are a few different different types of fuel cells using different fuels and different electrolytes. One of the types is a hydrogen-oxygen fuel cell.
• Hydrogen oxygen fuel cells involve a redox reaction
• The electrolyte in an hydrogen oxygen fuel cell is often an acid and the electrodes are often porous carbon with a catalyst
• Hydrogen goes into the anode compartment and oxygen goes into the cathode compartment
• at the negative electrode in the hydrogen oxygen fuel cell (anode) hydrogen loses electrons to produce H+ ions. this is oxidation
• The H+ ions in the electrolyte move to the cathode, at the positive cathode oxygen gains electrons from the cathode and reacts with H+ ions to make water. This is reduction.
• The electrons flow through the external circuit from the anode to the cathode in the hydrogen-oxygen fuel cell this is an electric current
• The overall reaction for a hydrogen oxygen fuel cell is

  hydrogen plus oxygen gives water