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4.2Electrochemistry

Hydrogen-oxygen fuel cells — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 8 parts Lesson 2 of 2 1 quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Lesson summary

4.2 Hydrogen-oxygen fuel cells — IGCSE CHEMISTRY notes: Describe how a hydrogen-oxygen fuel cell works and compare it with a petrol engine.Fuel — a substance that releases energy when burned.Fuel cell — an electrochemical cell in which a fuel donates electrons at one electrode an…

  • Overall equation
  • No pollutants
  • High efficiency
  • Renewable fuel
  • Hydrogen production
  • Storage and safety

Part 1 of 6What a fuel cell is

Fuel
  • Fuel a substance that releases energy when burned.
Fuel cell
  • Fuel cell an electrochemical cell in which a fuel donates electrons at one electrode and oxygen gains electrons at the other.
Operation
  • Operation a fuel cell produces electricity as long as fuel is supplied.
Uses
  • Uses hydrogen fuels rocket engines and fuel cells that power some cars.

Part 2 of 6Reactions in the cell

1
Hydrogen enters at one electrode (the fuel).
2
Hydrogen is oxidised: H2 → 2H+ + 2e-.
3
Electrons flow through the external circuit and provide the electric current.
4
Oxygen from the air is reduced at the other electrode: O2 + 4H+ + 4e- → 2H2O.
5
Water leaves the cell as the only chemical product.
  • Overall equation
    • 2H2 + O2 → 2H2O.

Part 3 of 6Advantages over petrol engines

No pollutants
  • No pollutants the only product is water, so there is no carbon dioxide, carbon monoxide or oxides of nitrogen.
High efficiency
  • High efficiency they release more energy per kilogram than petrol or diesel.
Renewable fuel
  • Renewable fuel hydrogen can be made by the electrolysis of water.

Part 4 of 6Disadvantages

Disadvantages
Hydrogen production
  • Hydrogen production most hydrogen is made from fossil fuels such as methane, which releases carbon dioxide.
  • Electrolysis of water needs large amounts of electricity that may come from burning fossil fuels.
Storage and safety
  • Storage and safety hydrogen is a highly flammable gas that is difficult 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 5 of 6Comparison with petrol engines

FeatureHydrogen fuel cellPetrol engine
ProductsWater onlyCO2, CO and NOx
EfficiencyHigherLower
Fuel storageDifficult (flammable gas)Easy (liquid)
Fuel sourceNatural gas or electrolysisCrude oil
Filling stationsFewMany

Part 6 of 6More from the specification

1Catalytic dissociation of gaseous molecules
  • Catalytic dissociation of gaseous molecules porous transition metals catalyze separation of fuel molecules into individual reactive atoms on anode surfaces.
2Alkaline electrolyte solution ion transfer
  • Alkaline electrolyte solution ion transfer aqueous potassium hydroxide solution conducts hydroxide ions between electrodes without corrosive consumption of electrode metals.
3Operating Principle of Hydrogen-Oxygen Fuel Cells
  • A hydrogen-oxygen fuel cell generates an electric current through the controlled electrochemical reaction: 2H2 + O2 → 2H2O,
  • producing electrical energy and water with zero greenhouse emissions.
4Electrode Half-Equations in Alkaline Fuel Cells
  • At the anode, hydrogen gas is oxidised (2H2 + 4OH- → 4H2O + 4e-), while at the cathode, oxygen is reduced (O2 + 2H2O + 4e- → 4OH-).
5Principles of Electroplating Metal Objects
  • Electroplating uses electrolysis to deposit a thin, protective layer of metal onto a cathode object to prevent corrosion and improve appearance.
    • (such as nickel, silver, or chromium)
6Advantage
  • The only chemical product is water.
7Disadvantage
  • Hydrogen is hard to store and often made from fossil fuels.
8Electroplating
  • Coating one metal with a thin layer of another using electrolysis.
9Cathode
  • The negative electrode, where reduction occurs.
10Metal
  • An element with a lattice of positive ions in a sea of delocalised electrons, usually shiny, conductive and malleable.

Key terms

TermMeaning
Fuel cellConverts chemical energy directly into electrical energy.
Hydrogen-oxygen fuel cellCell in which H2 and O2 react to give water and electricity.
Anode (fuel cell)The electrode where H2 is oxidised.
Cathode (fuel cell)The electrode where O2 is reduced.
AdvantageThe only chemical product is water.
DisadvantageHydrogen is hard to store and often made from fossil fuels.

Avoid these mistakes

Avoid these mistakes
Saying a fuel cell burns hydrogen in a flame — hydrogen reacts electrochemically to give electricity.
Saying hydrogen fuel is completely pollution-free — making it can still release carbon dioxide.
Saying oxygen is oxidised in the cell — hydrogen is oxidised and oxygen is reduced.

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