A chemical cell produces a voltage until one of the reactants is used up. In a hydrogen-oxygen fuel cell, hydrogen and oxygen are used to produce a voltage, and water is the only product.
Fuel cells have different strengths and weaknesses, depending on the intended use. For example, fuel cells are used in spacecraft and vehicles.
Hydrogen-oxygen fuel cells are used in spacecraft. Their strengths include:
Hydrogen-oxygen fuel cells must be supplied with hydrogen fuel and oxygen. This could be a problem once a spacecraft leaves the Earth. However, spacecraft in orbit have solar cells. These convert light into electricity, so the hydrogen and oxygen can be replaced by the electrolysis of water.
Solar cells only work when they are in the light, so the fuel cells allow electricity to be produced even when the spacecraft is in the dark.
Some cars and buses contain hydrogen-oxygen fuel cells. These power an electric motor, which turns the wheels. Other vehicles use engines fuelled by petrol or diesel.
The table shows some strengths and weaknesses of each type of vehicle.
| Fuel cell vehicle | Petrol or diesel vehicle | |
|---|---|---|
| Strengths | Quiet in use, only waste product is water, fewer moving parts | Petrol and diesel are easier to store, thousands of filling stations |
| Weaknesses | Hydrogen is more difficult to store, few filling stations | Noisy in use, carbon dioxide is a waste product, many moving parts |
Hydrogen, diesel and petrol are all highly flammable fuels, but hydrogen is more difficult to store. As there are far fewer hydrogen filling stations, it may be more difficult to travel long distances in a fuel cell vehicle. However, fuel cell vehicles have fewer moving parts, so they are often more reliable and easier to maintain.
Suggest a reason why the quietness of fuel cell vehicles may be a weakness.
Pedestrians may not hear the vehicle coming, and so they may be more likely to be run over when crossing the road.