Hydrogen fuel cell opportunities Flashcards
Question; Fuel cells using Hydrogen are being developed as an energy source. Give two reasons why hydrogen is used in fuel cells. {2}
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.
Hydrogen Fuel Cells require a source of Hydrogen as a fuel.
List two methods of bulk Hydrogen production currently used. {2}
Any two from;
Steam reforming of fossil fuels.
Electrolysis of water using high pressure and temperature.
Photocatalytic splitting of water.
Outline the bulk production by electrolysis of water. Your answer must include a relevant equation. {5}
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)
State one other method used for the bulk production of hydrogen. {1}
Photocatalytic water splitting or steam reforming of fossil fuel gases.
Name two of the most common forms of Hydrogen fuel cell. {2}
Answer;
Any two from;
Polymer Electrolyte Membrane (PEM).
Alkaline.
Phosphoric acid.
Molten carbonate.
Solid oxide
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;
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
What are the two input gases used within a hydrogen fuel cell.
Hydrogen and Oxygen
With reference to the Anode and Cathode, explain the operation of a typical hydrogen fuel cell.
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}.
State two possible applications of hydrogen fuel cells. {2}
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; Discuss two challenges of using Hydrogen as an energy source.
{4}
Answer;
Any two from;
Production costs – expensive to produce.
Transport issues – lack of infrastructure.
Safe storage – highly explosive.
All relevant responses will be given credit.
Question; Discuss two challenges presented by using hydrogen as an energy source.
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.
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 ?
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
What are the two stages of steam reforming and the chemical equations for each step ?
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)