2.5 Hydrogen fuel cell opportunities

Question 1

Question; Fuel cells using Hydrogen are being developed as an energy source. Give two reasons why hydrogen is used in fuel cells. {2}

Answer 1

Answer;
Any two from;

 Hydrogen has a high energy density (per unit mass).

 The only by product from hydrogen is water.

 Hydrogen fuel cells are more energy efficient than internal combustion engines / electricity generators.

Question 2

Hydrogen Fuel Cells require a source of Hydrogen as a fuel.

List two methods of bulk Hydrogen production currently used. {2}

Answer 2

Any two from;

 Steam reforming of fossil fuels.

 Electrolysis of water using high pressure and temperature.

 Photocatalytic splitting of water.

Question 3

Outline the bulk production by electrolysis of water. Your answer must include a relevant equation. {5}

Answer 3

Electrodes are placed in water. {1}

An electric current is passed through the electrodes. {1}

The water is split into hydrogen and oxygen. {1}

2H2O + 2e- = H2 + 2OH-
OR
2H2O = 2H2 + O2 (2)

Question 4

State one other method used for the bulk production of hydrogen. {1}

Answer 4

Photocatalytic water splitting or steam reforming of fossil fuel gases.

Question 5

Name two of the most common forms of Hydrogen fuel cell. {2}

Answer 5

Answer;
Any two from;

 Polymer Electrolyte Membrane (PEM).

 Alkaline.

 Phosphoric acid.

 Molten carbonate.

 Solid oxide

Question 6

Explain the operating principles of a PEM (Polymer Electrolyte Membrane) Hydrogen Fuel Cell. Your answer should include equations for the reactions occurring at the anode and cathode. {6}

Answer 6

Answer;

 Hydrogen is introduced which is then oxidised / chemically split into H+ ions and electrons (at the anode). {1}

 Protons migrate through the PEM. {1}

 Electrons follow a conductive path between electrodes / follow a circuit / between electrodes either side of the PEM. {1}

 Protons and electrons then re-combine at the cathode to form water and heat. {1}

Equations:

H2 = 2H + 2e- at anode
and
4H+ + 4e- + O2 = 2H2O

Question 7

What are the two input gases used within a hydrogen fuel cell.

Answer 7

Hydrogen and Oxygen

Question 8

With reference to the Anode and Cathode, explain the operation of a typical hydrogen fuel cell.

Answer 8

Answer;

Anode;

Hydrogen atoms (H2) are split into protons (H+) and electrons (e-) at the anode {1}. The protons pass through the electrolyte layer and the electrons leave the cell and follow a circuit / conductive path on their way to the cathode {1}.

Cathode:

The protons (H+) and electrons (e-) recombine at the cathode {1}. These combine with the introduced oxygen (O2) to form water (2H2O) and heat {1}.

Question 9

State two possible applications of hydrogen fuel cells. {2}

Answer 9

Answer;
Any two from;

 Stationary generation as backup or in remote locations.

 Stand-alone power supplies for telecommunications installations.

 Transport, including cars, buses, trains, boats, or portable generators.
All relevant, valid responses will be given credit.

Question 10

Question; Discuss two challenges of using Hydrogen as an energy source.
{4}

Answer 10

Answer;
Any two from;

 Production costs – expensive to produce.

 Transport issues – lack of infrastructure.

 Safe storage – highly explosive.

Question 11

Question; Discuss two challenges presented by using hydrogen as an energy source.

Answer 11

Answer;
Any two points from;

 The cost of producing hydrogen gas is high due to the electricity requirement (for electrolysis).

 If the cost of hydrogen as a fuel is more than the cost of petrol or diesel the consumer will not switch to it (which will discourage investment in the technology).

 Methane can be used to produce hydrogen. There are concerns over using a fossil fuel as the raw material as it is non-renewable.

 Hydrogen gas must be liquefied in order to make storage feasible. This adds to the production costs as compression equipment must be used and low storage temperatures must be maintained.

 The low storage temperatures required for hydrogen mean that specialist delivery vessels and pipelines that can withstand these temperatures are required.

 Hydrogen is explosive so great care must be taken to ensure that it is stored safely. It must be stored in thick-walled leak proof tanks which add to the production costs.

Question 12

within the US, 95% of the of hydrogen produced utilises fossil fuel steam reforming. This process known as “Natural gas methane reforming” requires what features ?

Answer 12

The process requires:

Supply of methane
Temperatures of 700 to 1000 degrees Celsius
Steam generated
Pressures of between 3 and 25 bar
A catalyst such as nickel

Question 13

What are the two stages of steam reforming and the chemical equations for each step ?

Answer 13

Step 1: Steam methane reforming reactions:

CH4 + H2O (+heat) = CO + 3H2

Step 2: Water gas shift reaction:

CO + H2 = CO2 + H2O (+ a small amount of heat)