Hydrogen fuel cells offer a potential alternative to rechargeable cells…

The idea

A hydrogen fuel cell produces a voltage continuously while hydrogen and oxygen are supplied, because the reaction between them releases energy that is transferred electrically. Hydrogen enters the anode, where it is oxidised, and oxygen enters the cathode, where it is reduced; the only chemical product is water, so no carbon dioxide is released at the point of use. Unlike a rechargeable cell or battery, a fuel cell does not store its reactants internally and does not need recharging: it keeps working as long as fuel and oxygen flow. This makes it a potential alternative in vehicles and portable devices, but hydrogen must be made, stored and transported, which affects overall cost and environmental impact.

What earns the marks

• A hydrogen fuel cell generates electrical energy continuously while hydrogen and oxygen are supplied, rather than storing energy internally like a rechargeable cell.
• At the anode hydrogen is oxidised and at the cathode oxygen is reduced, so the overall reaction produces water as the only chemical product.
• Because the product is water, a hydrogen fuel cell releases no carbon dioxide at the point of use, unlike a cell or battery recharged using electricity from burning fossil fuels.
• A rechargeable cell or battery must be recharged from an external supply, whereas a fuel cell is refuelled by supplying more hydrogen.
• Evaluating the alternative requires comparing both benefits, such as continuous operation and only water as a product, and drawbacks, such as producing, storing and transporting hydrogen.
• Hydrogen is often made by processes that use fossil fuels, so the overall environmental benefit depends on how the hydrogen is produced.

Common mistakes and how to put them right

• Saying a fuel cell stores hydrogen and oxygen inside itself like a battery stores chemicals.

  Put it right by stating that reactants are supplied continuously from external stores.

• Claiming a hydrogen fuel cell produces carbon dioxide.

  Put it right by stating that the only chemical product is water.

• Describing a fuel cell as needing to be recharged.

  Put it right by explaining that it is refuelled with hydrogen and keeps producing electricity while reactants are supplied.

Exam tips

• When asked to compare, give at least one advantage and one disadvantage of hydrogen fuel cells relative to rechargeable cells or batteries.
• Link the absence of carbon dioxide at the point of use to the product water, and mention that hydrogen production may still involve fossil fuels.
• Use the terms anode, cathode, oxidation and reduction accurately when explaining how the fuel cell works.