Cells, Batteries and Fuel Cells — AQA GCSE Chemistry (Separate)
Chemical reactions can be used to produce electricity in cells, batteries and fuel cells.
Simple cells
A cell produces a voltage (potential difference) when two different metals are connected and placed in an electrolyte. The greater the difference in reactivity between the two metals, the larger the voltage produced.
Batteries
A battery consists of two or more cells connected together in series, which adds up their voltages.
Rechargeable and non-rechargeable
- In non-rechargeable cells (e.g. alkaline batteries), the reaction stops once one of the reactants is used up.
- In rechargeable cells, the chemical reactions can be reversed by applying an external current.
Fuel cells
A fuel cell is supplied with a fuel (e.g. hydrogen) and oxygen (or air), and produces a voltage continuously as long as the fuel is supplied.
The hydrogen fuel cell
- Overall reaction: hydrogen + oxygen → water (the only product is water).
- Hydrogen is oxidised at one electrode; oxygen is reduced at the other.
Advantages over rechargeable batteries: no need to recharge, no polluting waste (only water), and they don't run down. Disadvantages: hydrogen is a gas that is difficult to store and is often made using energy from fossil fuels.
Exam tips
- Cell voltage depends on the difference in reactivity of the two metals.
- A battery = two or more cells.
- Rechargeable cells can have their reaction reversed.
- Hydrogen fuel cells produce only water — know their advantages and disadvantages.