Cells, fuel cells and batteries

What are electrochemical cells?

Cells which use chemical reactions to produce electricity

How is a cell made?

Connect two different electrodes with a wire and place them in contact with an electrolyte. Use a voltmeter to measure the voltage of the cell

What is an electrolyte?

A liquid through which charged ions can flow

How does a battery differ from a cell?

It consists of two or more cells connected together in series to provide a greater voltage

What factors affect the voltage of a cell?

1. The metals used for the two electrodes. The greater the difference in reactivity, the greater the voltage

2. The type and concentration of electrolyte

3. The conditions such as temperature

What are rechargeable cells and batteries?

Ones that can be recharged because the chemical reactions are reversed when an external electrical current is supplied. They are used in laptops and mobile phones

What are alkaline batteries?

Non-rechargeable batteries which have their chemical reactions stop when one of the reactants has been used up. Used in smoke alarms and tv remotes.

What is a fuel cell?

A type of electrochemical cell which converts the chemical energy of a fuel and oxygen into electrical energy used to power things.

What is a hydrogen-oxygen fuel cell?

A fuel that converts hydrogen and oxygen into water while generating large amounts of electrical energy

How is a hydrogen fuel cell different to electrolysis?

The cathode is positive and the anode is negative

What are the electrodes made of in a hydrogen fuel cell and what do they contain?

Made of carbon and contain a catalyst

How does a hydrogen fuel cell work?

1. Hydrogen enters and is oxidised by the anode to form hydrogen ions

2. The electrons move through the wire to the cathode and the hydrogen ions move through the electrolyte to the cathode

3. These react with the entering oxygen to produce water

4. Two sets of hydrogen ions and electrons are needed to react with each oxygen molecule

What is the half equation at the anode?

H2 → 2H+ + 2e-

Oxidation

What is the half equation at the cathode?

O2 + 4H+ + 4e- → 2H2O

Reduction

How is electrical energy released from a fuel cell?

From the movement of the electrons through the wire

Exam answer for how fuel cells work

As fuel enters the cell, it becomes oxidised producing a potential difference across the cell which drives the electrons around the circuit to generate electricity

Advantages of a hydrogen oxygen fuel cell?

• Only require hydrogen and oxygen which are abundant

• Don’t produce any other pollutants as waste

• Simple devices so last long and less polluting to dispose of

Disadvantages of a hydrogen oxygen fuel cell?

• Hydrogen requires lots of space to store as it is a gas

• Hydrogen is highly flammable

• Energy is required to produce the hydrogen fuel which is often made from fossil fuels