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4.3.6Additional lessons

Fuel Cells — IB Chemistry HL Revision Notes & Topical Questions

5 min read 5 parts Lesson 84 of 172

📚 IB Chemistry HL Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Part 1 of 5Parts of a Hydrogen Fuel Cell

A fuel cell converts the chemical energy of a continuously supplied fuel directly into electrical energy.

Anode
  • Anode Hydrogen is oxidised at the anode: H₂(g) → 2H⁺(aq) + 2e⁻ in an acidic proton-exchange membrane cell.
Cathode
  • Cathode Oxygen is reduced at the cathode: O₂(g) + 4H⁺(aq) + 4e⁻ → 2H₂O(l).
Membrane
  • Membrane A proton-exchange membrane lets H⁺ ions pass through but blocks electrons, forcing them through the external circuit.
Overall
  • Overall 2H₂(g) + O₂(g) → 2H₂O(l), with a standard cell potential of about 1.23 V.

Part 2 of 5How Current Is Produced

1
Hydrogen gas is supplied continuously to the anode, where a catalyst such as platinum helps it split into protons and electrons.
2
Electrons travel through the external circuit and do electrical work, such as powering a motor.
3
Protons move through the membrane to the cathode side.
4
Oxygen from air reacts with the arriving protons and electrons at the cathode to form water.
5
The only product is water, so no CO₂ is produced at the point of use.

Part 3 of 5Fuel Cells Versus Combustion

Fuel Cells Versus Combustion
Efficiency
  • Efficiency Fuel cells convert a greater proportion of chemical energy to electrical energy than a heat engine.
Emissions
  • Emissions Hydrogen fuel cells emit only water, though producing the hydrogen may release CO₂.
Storage
  • Storage Hydrogen is a low-density gas and needs compression or special materials to store it safely.
Running
  • Running The cell works as long as fuel is supplied, unlike a battery, which runs down.
FeatureFuel cell vs battery
ReactantsSupplied continuously from outside
LifetimeContinues while fuel is provided
RechargingNot needed; refuel instead

Part 4 of 5Worked Example

Question

  • Calculate the charge passed when 1.00 g of hydrogen is oxidised in a fuel cell (M(H₂) = 2.02 g mol⁻¹;
    • F = 96 500 C mol⁻¹).

  1. Moles of H₂ = 1.00 ÷ 2.02 = 0.495 mol.
  2. Each H₂ releases 2 electrons, so moles of electrons = 0.990 mol.
  3. Charge = 0.990 mol × 96 500 C mol⁻¹ = 9.55 × 10⁴ C.

Answer Charge = 9.55 × 10⁴ C

Part 5 of 5Exam Checklist & Tips

4.3.6 – Key Points for the Exam

  • Fuel cell A cell in which a fuel is oxidised continuously to generate electrical energy.
  • Anode The electrode where oxidation occurs.
  • Proton-exchange membrane A membrane that allows only H⁺ ions to move between the electrodes.
  • Cell potential The voltage produced by a cell under standard conditions.

Common Mistakes

  • Writing the reactions the wrong way round so that hydrogen is reduced at the anode.
  • Letting electrons flow through the membrane instead of the external circuit.
  • Saying a fuel cell stores charge like a rechargeable battery.
  • Claiming hydrogen is always a zero-emission fuel regardless of how it is produced.

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Cambridge 9700 AS Biology Core Formula

Magnification Triangle & Unit Conversion

Formula: M = I / A  ⇔  A = I / M  ⇔  I = M × A

Units: 1 mm = 1,000 μm = 1,000,000 nm.
Rule: Convert Image size (ruler mm) to μm by ×1,000 before dividing by Actual size.

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