Fuel Cells

• Fuel cells use fuel and oxygen to produce electrical energy
• A fuel cell is an electrical cell that's supplied with a fuel and oxygen (or air) and uses energy from the reaction between them to produce electrical energy efficiently
• In fuel cells when the fuel enters the cell it becomes oxidised and sets up a potential difference within the cell
• There are a few different types of fuel cells, using different fuels and different electrolytes. One important example is the hydrogen-oxygen fuel cell
• The hydrogen-oxygen fuel cell combines hydrogen and oxygen to produce clean water and release energy
• Hydro-oxygen fuel cells involve a redox reaction
• The electrolyte is often an acid, such as phosphoric acid. The electrodes are often porous carbon with a catalyst

  
• Hydrogen goes into the anode compartment and oxygen goes into the cathode compartment - in electrolysis the anode is the positive electrode and the cathode is the negative one. When dealing with fuel cells, they're the other way round

  
• At the -ve electrode (the anode), H loses electrons to produce H+ ions. This is oxidation. H+ ions in the electrolyte move to the cathode (+ve)$H_2 → 2H^+$$+$$2e^-$

  
• At the +ve electrode (the cathode), O2 gains e- from the cathode and reacts with H+ ions (from the acidic electrolyte) to make H2O. This is reduction$O_2 +$$4H^+$$+$$4e^- → 2H_2O$

  
• The electrons flow through an external circuit from the anode to the cathode - this is the electric current

  
• The overall reaction is hydrogen plus oxygen, which gives water. $2H_2 +$$O_2 → 2H_2O$

  
• Hydrogen fuels for vehicles (such as petrol) have a finite supply - they won't last forever and they're very polluting. So vehicles that use electrical energy are becoming more and more popular
• Batteries are one way of getting cleaner energy but hydrogen-oxygen fuel cells might be even better:

  • Fuel cell vehicles don't produce as many pollutants as other fuels - no greenhouse gases, nitrogen oxides, sulfur dioxide or carbon monoxide. The only by-products are water and heat. Electric vehicles don't produce many pollutants either - but their batteries are more polluting to dispose of than fuel cells because they're made from highly toxic metal compounds
• Batteries are only one way of getting cleaner energy but hydrogen-oxygen fuel cells might be even better:

  • Batteries in electric vehicles are rechargeable but there's a limit to how many times they can be recharged. And batteries are more expensive to make than fuel cells
  • Batteries also store less energy than fuel cells and so would need to be recharged more often - which can take a long time
• There are still some disadvantages of using hydrogen fuel cells:

  • Hydrogen is a gas, so it takes up loads more space to store than a rechargeable battery
  • Hydrogen is explosive when mixed with air so it's hard to store safely
  • The hydrogen fuel is often made either from hydrocarbons (from fossil fuels), or by electrolysis of water which uses electricity (and that electricity has got to be generated somehow - usually from fossil fuels)