Chemical Cells and Fuel Cells

• Batteries and cells contain chemicals that react to produce electricity.
• A simple cell can be made by connecting 2 different electrodes and putting them into a liquid electrolyte.

  • The difference in reactivity of the metals produces a voltage
• A chemical cell produces a potential difference until the reactants are used up
• Changing the electrolyte changes the reactions that happen at the electrodes. This will result in the voltage output of the cell changing.
• A battery is a collection of more than one cell joined in series (ennd-to-end)
• The voltage of a battery is calculated as the sum of the voltages to its individual cell components.
• When the chemicals in a battery run out, the battery can not be used anymore
• In rechargeable cells and batteries, connection to an electric current reverses the reactions that happen at electrodes.
• This means that electricity can continue to be produced as long as there is access to an external electric current. (rechargeable batteries)
• Fuel cells produce electrical energy using a reaction between an external fuel source (often hydrogen) and oxygen. The fuel is added to the cell and then there is a constant supply of oxygen. The fuel is oxidised and this creates a voltage.
• Advantages of fuel cells include:

  • Compact and lightweight
  • High efficiency
  • Less pollution than traditional methods
  • The absence of moving parts means they are reliable
• In hydrogen fuel cells, the oxidation of hydrogen generates a voltage and the only waste product is water.
• ANODE HALF EQUATION:

  • Hydrogen is pumped at the anode.
  • Hydrogen ions are formed as hydrogen molecules are oxidised and lose electrons.
  • $2H_2 -> 4H^+$$+$$4e^-$
• CATHODE HALF EQUATION:

  • Oxygen is pumped at the cathode.
• CATHODE HALF EQUATION:

  • Oxygen is pumped at the cathode.
  • Water is formed as the oxygen reacts with the H+ ions that have moved to the electrolyte from the anode.
  • $O_2+$$4H^+$$+$$4e^-->2H_2O$
• Hydrogen fuel cells may be better than batteries because:

  • Batteries are made from toxic metal compounds and their disposal can cause pollution.
  • Hydrogen fuel cells use hydrogen and oxygen and the only waste product is water.
  • Batteries must be replaced after a certain amount of years.
  • Hydrogen fuel cells can be reused indefinitely
  • Batteries have a smaller capacity and have to be recharged more regularly.
  • Hydrogen fuel cells produce more energy per gram of hydrogen relative to petrol