Fuel cells produce electricity from the chemical reactions of a fuel with oxygen in the air. Fuel cells use the energy from the reactions of a fuel to create a voltage, whilst electrochemical cells are used to measure the voltage created in a redox reaction.
In these fuel cells, hydrogen combines with oxygen to form water, producing electricity as it does so.
At the anode:
H2 (g) ➔ 2H+ + 2e-(aq)
At the cathode:
½ O2 (g) + 2H+(aq) + 2e- ➔ H2O(l)
Combined they give:
H2O(l) ➔ ½ O2 (g) + H2(aq)
the advantages of hydrogen fuel cell:
- There is less pollution – in a pure hydrogen fuel cell there is no CO2, CO, nitrogen oxides etc produced and in methanol fuel cells (another fuel cell in A-Level Chemistry) only a small amount of CO2 is produced.
- They are more efficient – in conventional internal combustion engines, there is a lot of energy wasted as heat, but by using fuel cells the electrical energy is produced without wasting any as heat. A fuel cell driven car thus uses less fuel to go the same amount of distance as a conventional one.
the disadvantages of hydrogen fuel cell:
- Hydrogen is difficult to store as it has a very low boiling point and is explosive; solutions could be:
- Storage as a liquid under pressure.
- Adsorption onto the surface of a solid material
- Absorption within a solid.
- Adsorption & absorption allow a lot of hydrogen to be stored at room temperature, but current absorbers and absorbers have limited lifetimes.
- Hydrogen has to be manufactured; e.g. by electrolysis of water but this requires energy.
- Fuel cells have limited lifetimes and need to be replaced regularly whilst having high disposal costs.
- Toxic chemicals are used in the manufacture of fuel cells.
Hydrogen is a popular alternative to petroleum as:
- Fossil fuels are non-renewable
- so as resources dwindle, fuel prices rise.
- Using solely hydrogen as a fuel produces only water.
- Fuel cells are more efficient at converting energy.
- Hydrogen rich fuels (e.g. methanol) only produce small amounts of pollutants and CO2.
However it has limitations, in the future there may be a shift towards hydrogen for energy, but there would need to be:
1.Political & public acceptable of hydrogen as a fuel - hydrogen is explosive which may be a concern.
2.Infrastructure for large-scale storage, handling and distribution – this is needed and is not in place at the moment. It is feasible that existing infrastructure could be converted, or that cars could be fitted with a reformer that converts petrol to hydrogen for fuel cell use.
3.Viable methods of hydrogen production – pure hydrogen and oxygen can be made by the electrolysis of water, however this requires energy. It is possible that more energy will be used to produce hydrogen than will be saved. Other methods exist, however they also require energy. The energy needed will need to come from renewable sources.
Drafted by Eunice Wong (Chemistry)