1.9 Fuel Cells

Question 1

What is a fuel cell?

Answer 1

A type of electrochemical cell

Question 2

What does an electrochemical cell do?

Answer 2

It converts energy between electrical and chemical forms. They convert the chemical energy of a fuel and oxygen into electrical energy that we can then use to power things

Question 3

What do fuel cells produce across the cell, until all the reactants have been used up?

Answer 3

Potential difference

Question 4

What happens in a hydrogen-oxygen fuel cell?

Answer 4

The reaction between hydrogen and oxygen releases energy - you can produce a potential difference (i.e. you can transfer energy by electricity) by reacting hydrogen and oxygen, and it doesn’t produce any nasty pollutants - only nice, clean water. This makes it a good alternative to fossil fuels for powering cars

Question 5

What is the reaction of hydrogen-oxygen fuel cells equivalent to?

Answer 5

Combustion of hydrogen

Question 6

How is the reaction of hydrogen-oxygen fuel cells different to the combustion of hydrogen?

Answer 6

The reaction of hydrogen-oxygen fuel cells happen in a cell, so the energy is transferred by electricity to power an electrical motor, rather than by heating to power an internal combustion engine, which is what happens in a petrol or diesel car

Question 7

In a hydrogen-oxygen fuel cell, is the anode negative or positive?

Answer 7

Negative

Question 8

In a hydrogen-oxygen fuel cell, is the cathode positive or negative?

Answer 8

Positive

Question 9

In fuel cells, what are the electrodes made up of?

Answer 9

Porous carbon

Question 10

What does porous carbon mean?

Answer 10

They have lots of small holes

Question 11

What do the porous carbon found in the electrodes of fuel cells contain? (2)

Answer 11

Catalysts and tiny holes

Question 12

In fuel cells, what do each electrodes have in them at the top?

Answer 12

Inlets

Question 13

In hydrogen-oxygen fuel cells, what enters the inlet in the anode compartment?

Answer 13

Hydrogen

Question 14

In hydrogen-oxygen fuel cells, what enters through the inlet in the cathode compartment?

Answer 14

Oxygen

Question 15

What happens after the hydrogen-oxygen reaction in the fuel cell?

Answer 15

The water and heat leave via the outlet of the cathode compartment

Question 16

In hydrogen-oxygen fuel cells, what happens to the hydrogen once it is in the anode compartment?

Answer 16

It is oxidised by the anode which means that each hydrogen atom loses an electron to become a hydrogen ion

Question 17

In a hydrogen-oxygen fuel cell, what happens once the hydrogen atoms are oxidised?

Answer 17

The electrons pass through the wire to the cathode compartment while the hydrogen ions move through the electrolyte to the cathode. This means that the electrons and hydrogen ions can react with the oxygen that comes in from the right and together combine to form water

Question 18

What is meant by the ‘potential difference’ found in fuel cells?

Answer 18

The difference in charge between the two electrodes; this is what drives the electrons around the circuit so we can generate the electricity

Question 19

What are 7 advantages for hydrogen-oxygen fuel cells?

Answer 19

• They’re much more efficient than power stations or batteries at producing electricity. This is because:
• In a fuel cell, the electricity is generated directly from the reaction (so no turbines, generators, etc.)
• There aren’t a lot of stages to the process of generating electricity so there are fewer places for energy to be lost as heat
• Unlike a car engine or a power station that burns fossil fuels, there are no moving parts, so energy isn’t lost through friction.
• Also, fuel cell vehicles don’t produce any conventional pollutants - no greenhouse gases, no nitrogen oxides, no sulfur dioxide, no carbon monoxide. The only by-product is water. This would be a major advantage in cities, where air pollution from traffic is a major problem.
• Hydrogen and oxygen are both renewable
• Fuel cells last longer than batteries

Question 20

What are 3 disadvantages of fuel cells?

Answer 20

• Hydrogen is a gas, so it takes up loads ore space to store than liquid fuels like petroleum. This limits the practicality of using hydrogen as a fuel in cars unless other ways of storing it are developed
• It’s very explosive, so its difficult to store safely
• The hydrogen fuel is often made either from hydrocarbons (from fossil fuels) or by the electrolysis of water, which uses electricity (and that electricity’s got to be generated somehow - usually this involves fossil fuels), so pollutants may still be released to produce it

Question 21

Which direction do the electrons flow in a hydrogen-oxygen fuel cell?

Answer 21

From the anode to the cathode