Topic 5 - Fuel Cells
What is a fuel cell?
Hydrogen-oxygen fuel cells
Hydrogen fuel cells and batteries
Electrical cell that's supplied with a fuel and oxygen (or air) and efficiently transfers the energy releases by the reaction between them as electricity
The fuel enters the cell at one side, where it becomes oxidised and sets up a potential difference within the cell
This potential difference is what powers the device
The oxygen enters the cell at the other side, where it reacts to form water
Electrolyte is often a solution of potassium hydroxide
Electrodes often a porous carbon with a catalyst
Hydrogen goes into the anode compartment and oxygen goes into the cathode compartment
At the negative electrode (anode), hydrogen is oxidised to produce H+ ions which move to the cathode
At the positive electrode (cathode), oxygen is reduced and reacts with H+ ions (from the electrolyte) and makes water
The electrons flow through an external circuit from the anode to the cathode - this is the electric current
Half equations of a hydrogen-oxygen fuel cell
At the anode, hydrogen is oxidised to form H+ ions
H2 = 2H+ + 2e-
At the cathode, oxygen is reduced and reacts with H+ ions to form water
O2 + 4H+ + 4e- = 2(H2O)
Conventional fuels for vehicles have a finite supply - so vehicles that use electrical energy are becoming more popular. Batteries are one way of doing this but hydrogen-oxygen fuel cells might be better
Advantages
Fuel cell vehicles don't produce as many pollutants as other fuels - only by-products are water and heat - electric vehicles don't produce many pollutants either but their batteries are much more polluting to dispose of
Disadvantages
Batteries in electrical vehicles are rechargeable but they can only be recharged so many times and they are more expensive than fuel cells
Batteries need to be recharged more often - which can take more time
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
Hydrogen fuel is often made from hydrocarbons (from fossil fuels), or by electrolysis of water, which uses electricity (and that has to be generated)