Chemical Cells & Fuel CellsEdexcel GCSE Chemistry: Revision notes
Section 1
What is a chemical cell?
A chemical cell (battery) produces a voltage as a result of chemical reactions occurring inside it between two different electrodes and an electrolyte. A chemical cell continues to produce a voltage until one of the reactants is used up, at which point the cell goes flat and stops working.
Non-rechargeable cells go flat permanently because a reactant is fully used up; rechargeable cells can have the original reactants restored by passing a current the other way.
Section 2
What is a hydrogen-oxygen fuel cell?
A fuel cell produces a voltage continuously as long as it is supplied with fuel and oxygen — unlike a simple chemical cell, it does not go flat as long as fuel keeps being supplied.
In a hydrogen-oxygen fuel cell:
- Hydrogen and oxygen are supplied continuously
- The fuel cell produces a voltage
- The only product is water
overall reaction: hydrogen + oxygen → water
Don't confuse a fuel cell with combustion — no flame or burning is involved; the reaction happens electrochemically to generate electrical energy directly.
Section 3
What are the strengths and weaknesses of fuel cells?
Strengths:
- Produce water as the only waste product — no carbon dioxide or other pollutants at the point of use
- Can run continuously as long as fuel is supplied, unlike a battery which goes flat
- Often more efficient than burning fuel in an engine
Weaknesses:
- Hydrogen is difficult and expensive to store and transport safely (it is highly flammable and needs to be compressed or liquefied)
- Producing hydrogen fuel often requires energy from fossil fuels or electrolysis (which itself needs electricity), so the overall process may not be fully 'clean' depending on how the hydrogen was made
- Limited refuelling infrastructure currently exists
- Fuel cells can be expensive to manufacture compared with conventional engines
For 'evaluate the strengths and weaknesses' questions, always weigh a clean-emissions strength against a storage or production weakness for a balanced, high-mark answer.
Must Know
- A chemical cell produces a voltage until a reactant is used up
- A hydrogen-oxygen fuel cell is continuously supplied with hydrogen and oxygen, producing a voltage, with water as the only product
- Strength of fuel cells: clean at point of use (only water produced), can run continuously
- Weakness of fuel cells: hydrogen is hard/costly to store and transport, and producing it may still rely on fossil fuels
- Fuel cells are a genuine alternative to batteries and to burning fuel directly in engines
That's the notes covered.
Carry on to the next subtopic.