5.4 Chemical and fuel cells

Question 1

Chemical cells

Answer 1

Chemical cells are electrochemical cells that produce a voltage across the cell until one of the reactants has been used up. A fuel cell is a chemical cell that’s supplied with a fuel and oxygen (or air) and uses the reaction between them to efficiently release energy.

Question 2

Fuel cells

Answer 2

A fuel cell is an electrochemical cell in which a fuel donates electrons at one electrode and oxygen gains electrons at the other electrode.
These cells are becoming more common in the automotive industry to replace petrol or diesel engines.
As the fuel enters the cell it becomes oxidised which sets up a potential difference or voltage within the cell.
Different electrolytes and fuels can be used to set up different types of fuel cells.
An important cell is the hydrogen-oxygen fuel cell which combines both elements to release energy and water.

Question 3

Advantages of fuel cells

Answer 3

They do not produce any pollution: the only product is water.
They produce 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.
No batteries to dispose of which is better for the environment.
Continuous process and will keep producing energy as long as fuel is supplied.
Quieter so less noise pollution.

Question 4

Disadvantages of fuel cells

Answer 4

Materials used in producing fuel cells are expensive.
High pressure tanks are needed to store the oxygen and hydrogen in sufficient amounts which are dangerous and difficult to handle.
Fuel cells are affected by low temperatures, becoming less efficient.
Hydrogen is expensive to produce and store.
Quieter so potential danger to pedestrians if used in cars and lorries.

Question 5

Hydrogen - oxygen fuel cells

Answer 5

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 reaction between hydrogen (the fuel) and oxygen releases energy, which is used in hydrogen-oxygen fuel cells to produce a voltage. This voltage can be used to power an electrical device (e.g. an electric car) that the fuel cell is connected to. The reaction in the fuel cell doesn’t produce any harmful pollutants the only product is water. The overall reaction in a hydrogen-oxygen fuel cell is:
2H2 + O2 —– 2H2O