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4.2Electrolysis

Hydrogen-oxygen fuel cells — Combined Science 0653 - Chemistry Revision Notes & Topical Questions

5 min read 8 parts Lesson 6 of 6 1 quiz

📚 Combined Science 0653 - Chemistry Hub / Topical Revision
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Lesson summary

4.2 Hydrogen-oxygen fuel cells — COMBINED SCIENCE (CHEMISTRY) notes: Describe how a hydrogen-oxygen fuel cell produces electricity and compare it with a petrol engine.Fuel — a substance that releases energy when it reacts, such as hydrogen.Fuel cell — = electrochemical cell in wh…

  • No pollutants
  • High efficiency
  • Renewable fuel
  • Hydrogen production
  • Storage and safety
  • Cost and infrastructure

Part 1 of 6What a fuel cell is

Fuel
  • Fuel a substance that releases energy when it reacts, such as hydrogen.
Fuel cell
  • = electrochemical cell in which a fuel gives up electrons at one electrode and oxygen gains electrons at the other.
Use
  • Use hydrogen fuel cells power some cars and hydrogen is used as a rocket fuel.

Part 2 of 6How the hydrogen-oxygen fuel cell works

Inputs
  • Inputs hydrogen is the fuel and oxygen comes from the air.
Output
  • Output electricity is produced and water is the only chemical product.
Supply
  • Supply the cell produces electricity for as long as hydrogen and oxygen are supplied.

Part 3 of 6Reactions in the cell

PartEquation
Hydrogen is oxidisedH2 → 2H+ + 2e-
Oxygen is reducedO2 + 4H+ + 4e- → 2H2O
Overall2H2 + O2 → 2H2O
  • Electrons
    • flow through the external circuit and produce the electric current.

Part 4 of 6Advantages over petrol engines (supplement)

No pollutants
  • No pollutants the only product is water, whereas petrol engines make carbon dioxide, oxides of nitrogen and carbon monoxide.
  • Carbon dioxide is a greenhouse gas.
  • Nitrogen oxides cause acid rain.
High efficiency
  • High efficiency fuel cells release more energy per kilogram than petrol or diesel.
Renewable fuel
  • Renewable fuel hydrogen can be made by the electrolysis of water.

Part 5 of 6Disadvantages (supplement)

Disadvantages (supplement)
Hydrogen production
  • Hydrogen production most hydrogen is made from fossil fuels such as methane, which releases carbon dioxide.
  • Electrolysis of water uses large amounts of electricity that may come from burning fossil fuels.
Storage and safety
  • Storage and safety hydrogen is highly flammable and hard and expensive to store, often needing high-pressure tanks.
Cost and infrastructure
  • Cost and infrastructure fuel cell materials are expensive and there are few hydrogen filling stations.

Part 6 of 6More from the specification

1
Hydrogen fuel cell
  • Hydrogen is oxidised at the anode and oxygen reduced at the cathode, producing water and electrical energy with no carbon emissions.
2
Electrode reactions
  • Anode
    • H2 → 2H+ + 2e-;
      • cathode: O2 + 4H+ + 4e- → 2H2O in acidic cells.
3
Electroplating
  • An object is made the cathode in a solution of metal ions, and the metal atoms are deposited as a thin coating layer.
4
Electroplating process
  • The anode is the plating metal, which dissolves to replace ions in solution.
5
Uses
  • Electroplating protects metals from corrosion and improves appearance.
6
Advantage
  • The only chemical product is water.
7
Disadvantage
  • Hydrogen is hard to store and often made from fossil fuels.
8
Electroplating
  • Coating one metal with a thin layer of another using electrolysis.
9
Cathode
  • The negative electrode, where reduction occurs.
10
Metal
  • An element with a lattice of positive ions in a sea of delocalised electrons, usually shiny, conductive and malleable.

Key terms

TermMeaning
Fuel cellCell that uses a fuel and oxygen to produce electricity.
FuelSubstance that releases energy when it reacts.
OxidationLoss of electrons.
ReductionGain of electrons.
ElectrolysisDecomposition of a compound by electric current.
Greenhouse gasGas that traps heat in the atmosphere.

Avoid these mistakes

1
Saying fuel cells produce carbon dioxide — the only product is water.
2
Saying hydrogen is reduced at the fuel electrode — it is oxidised.
3
Saying hydrogen is always a renewable fuel — it is often made from fossil fuels.
4
Writing the overall equation unbalanced.

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