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Half-equations in the hydrogen fuel cell

Energy changes • Chemical and fuel cells

Key concepts

What you'll likely be quizzed about

  • A half-equation details either the oxidation or reduction component of a redox reaction.
  • It lists species, electrons, and charges while balancing mass and charge through the use of electrons and hydrogen or hydroxide ions as necessary.
  • When combined, half-equations yield the complete redox equation by ensuring the electrons lost in oxidation equal those gained in reduction.

Flashcards

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What does oxygen do at the cathode?

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Oxygen accepts electrons and combines with protons or water to form water or hydroxide ions, depending on the electrolyte.

Key notes

Important points to keep in mind

Half-equations depict either oxidation or reduction separately and must balance atoms and charge.

In acidic electrolyte, anode: H2 -> 2H+ + 2e-; cathode: 1/2 O2 + 2H+ + 2e- -> H2O.

In alkaline electrolyte, anode: H2 + 2OH- -> 2H2O + 2e-; cathode: 1/2 O2 + H2O + 2e- -> 2OH-.

Electrons lost at the anode equal electrons gained at the cathode before combining half-equations.

Overall reaction simplifies to 2H2 + O2 -> 2H2O regardless of electrolyte.

Catalyst, fuel purity, temperature, and membrane condition affect reaction rates without changing half-equations.

Balance oxygen and hydrogen atoms using H2O, H+, or OH- according to the electrolyte.

Membrane type determines whether H+ or OH- facilitate transport between electrodes.

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