Hydrogen for the future 192-193

Question 1

What is a reformer and what does it do?

Answer 1

Hydrogen-rich fuels include methanol, natural gas and petrol. Therese are mixed with water and converted into hydrogen gas by an onboard ‘reformer’.

Question 2

What temperatures does a reformer operate at?

Answer 2

The reformer operates at 250-300*C to generate the hydrogen gas.

Question 3

Give the reaction that converts methanol into hydrogen in a reformer.

Answer 3

CH₃OH + H₂O → 3H₂ + CO₂

Question 4

What are the advantages of methanol fuel cells compared with the use of hydrogen fuels cells?

Answer 4

• A liquid fuel is easier to store than hydrogen gas.
• Methanol can be generated from biomas.

Question 5

What is a disadvantage of a methanol fuel cell?

Answer 5

CO₂ is produced as a waste emission.

Question 6

What are the advantages of fuel cells over conventional petrol and diesel vehicles?

• compare both and give figures.

Answer 6

• Hydrogen-rich fuel produce only small amounts of CO₂ and air pollutants which petrol vehicles produce a lot of CO₂ and CO.
• A petrol engine is less than 20% efficient in converting chemical energy into mechanical energy. Hydrogen fuel cell vehicles are 40-60% efficient in converting the fuel’s energy.

Question 7

Give some methods that are being used to tackle the problem with storing hydrogen and explain the problems with these methods.

Answer 7

• Hydrogen can be stored as a liquid under pressure. This in istelf creates logistical problems. Even under pressure, a very low temperature is required and liquid hydrogen will need to be stored in a giant ‘thermos flask’ to prevent it from boiling.
• Hydrogen can be adsorbed onto the surface of a solid material in a similar way that a catalyst is able to hold gases to its surface.
• Hydrogen can be absorbed within some solid materials.

Question 8

Draw diagrams showing how hydrogen is adsorbed and absorbed onto the surface of a material.

Answer 8

Adsorption - H₂ molecules attach to the surface of a material.

Absorbtion - H₂ molecules dissociate into H atoms which are incorporated as ‘hydrides’ within a solid lattice.

Question 9

What are the limitations of hydrogen fuel cells?

Answer 9

• The large-scale storage and transportation of hydrogen poses problems.
• The feasibility of storing a pressurised liquid.
• Current ‘adsorbers’ and ‘absorbers’ of hydrogen have a limited lifetime.
• Current fuel cells have a limiteed lifetime, requiring regular replacement and disposal following high production costs.
• Fuel cells use toxic chemicals in their production.

Question 10

What are the limitations of the ‘hydrogen economy’ that need to be resolved?

• Explaine how some could be resolved.

Answer 10

• There are logistical problems in the handling and maintenance of hydrogen systems.
• Hydrogen is an ‘energy carrier’ not an ‘energy source’. Hydrogen must first be manufactured, either by electrolysis of water or by reacting methane(a finite fuel) with steam. The danger is that more energy may be used in making the hydrogen that is saved by its use. One strategy is to use renewable forms of energy, such as the wind or solar power, to generate the hydrogen.