Hydrogen Fuel Cells

• what is a fuel

  a substance which releases energy when burned. Hydrogen is used as a fuel in rocket engines and in fuel cells to power some cars
• fuel cell

  an electrochemical cell in which a fuel donates electrons at one electrode and oxygen gains electrons at the other electrode
• anode

  H2 ---> 2H+ + 2e-

  hydrogen is oxidized
• cathode

  O2 + 4e- ---> 2O2

  oxygen is reduced

  
  

  we're left with a spare oxygen atom, meaning you need two sets of hydrogen atoms and electrons to react with each oxygen molecule

  • O2 + 4H+ + 4e- ---> 2H2O.
• the hydrogen-oxygen fuel cell produces electricity by combining both elements, releasing energy and water. The overall equation for the reaction within a hydrogen fuel cell is:

  • hydrogen + oxygen ---> water: O2 + 2H2 ---> 2H2O
  • the air entering provides the oxygen
  • the fuel entering is hydrogen
  • the only chemical product made is water
• what are advantages of hydrogen-oxygen fuel cells

  • They do not produce any pollution: the only product is water whereas petrol engines produce carbon dioxide, and oxides of nitrogen
  • They release 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
  • Quieter so less noise pollution compared to a petrol engine
• disadvantages of hydrogen-oxygen fuel cells

  • Materials used in producing fuel cells are expensive
  • Hydrogen is more difficult and expensive to store compared to petrol as it is very flammable and easily explodes when under pressure 
  • Fuel cells are affected by low temperatures, becoming less efficient
  • There are only a small number of hydrogen filling stations across the country
  • Hydrogen is often obtained by methods that involve the combustion of fossil fuels, therefore releasing carbon dioxide and other pollutants into the atmosphere
• the electrical energy of this reaction comes from the movement through the wires at the top. Effectively, it would be powered by the chemical reaction

  If asked how fuel cells work in exams, make sure to mention:

  • as fuel enters the cell, it becomes oxidized, which sets up a potential difference across the cell. This means there is a difference in charge between the two electrodes, which drives the electrons around the circuit to generate electricity.