Chemical cells and fuel cells

• Electrochemical cell


  A simple cell that is a source of electrical energy
• Simple cell

  • Two electrodes made from metals of different reactivity immersed in an electrolyte
  • Connected to an external voltmeter by wire, creating a complete circuit
• Common example

  • Zinc and copper
• Zinc

  More reactive metal, forms ions more easily, readily releasing electrons
• Electrons


  Give the more reactive electrode a negative charge and set up a charge difference between the electrodes
• Voltage produced


  Difference in the ability of the electrodes to release electrons
• Greater difference in the metals' reactivity

  Greater the voltage produced
• Electrolyte


  Affects the voltage as different ions react with the electrodes in different ways
• Cells produce a voltage until one of the reactants is used up
• Simple cell made with Cu and Mg

  • Produces a greater voltage than Cu and Zn because the metals are further apart on the reactivity series
• Fuel cell


  An electrochemical cell in which a fuel donates electrons at one electrode and oxygen gains electrons at the other electrode
• Fuel cells are becoming more common in the automotive industry to replace petrol or diesel engines
• Fuel entering the cell

  Becomes oxidised which sets up a potential difference or voltage within the cell
• Fuel cells


  • Different electrolytes and fuels can be used to set up different types
• Hydrogen-oxygen fuel cell


  Combines both elements to release energy and water
• In fuel cells the polarity on the electrodes are the other way around: the anode is the negative electrode and the cathode is the positive electrode
• Advantages of fuel cells

  • Do not produce any pollution: the only product is water
  • Produce more energy per kilogram than either petrol or diesel
  • No power is lost in transmission as there are no moving parts, unlike an internal combustion engine
  • No batteries to dispose of which is better for the environment
  • Continuous process and will keep producing energy as long as fuel is supplied
  • Quieter so less noise pollution
• Disadvantages of fuel cells

  • Materials used in producing fuel cells are expensive
  • High pressure tanks are needed to store the oxygen and hydrogen in sufficient amounts which are dangerous and difficult to handle
  • Fuel cells are affected by low temperatures, becoming less efficient
  • Hydrogen is expensive to produce and store
  • Quieter so potential danger to pedestrians if used in cars and lorries