A FUEL CELL is an electrochemical cell that continuously converts the chemical energy of a fuel directly into electrical energy, as long as fuel and oxygen are supplied.
HYDROGEN FUEL CELL:
Fuel: hydrogen gas (H₂) supplied continuously.
Oxidant: oxygen (O₂) from air.
Product: water (H₂O) — the only chemical product.
OVERALL REACTION:
H₂ + ½O₂ → H₂O (or: 2H₂ + O₂ → 2H₂O)
Hydrogen is OXIDISED at the negative electrode (anode).
Oxygen is REDUCED at the positive electrode (cathode).
Electrons flow through external circuit → electrical energy.
KEY DIFFERENCE from batteries:
A battery stores a fixed amount of reactants — it 'runs out'.
A fuel cell is supplied continuously — it works as long as fuel is provided.
Advantages of Hydrogen Fuel Cells
ENVIRONMENTAL ADVANTAGES:
Only product is water — no CO₂, no NOₓ, no particulates emitted during operation.
Zero direct emissions — appealing for transport in cities.
EFFICIENCY ADVANTAGES:
Converts chemical energy directly to electrical energy — more efficient than combustion engines.
No moving parts in the cell itself — less mechanical energy lost to friction.
PRACTICAL ADVANTAGES:
Refuel quickly — fill hydrogen tank in minutes (vs hours to recharge batteries).
Long range — hydrogen has very high energy density per kg.
Continuous operation — unlike batteries which discharge over time.
APPLICATIONS:
Fuel cell vehicles (FCEVs): Toyota Mirai, Hyundai Nexo.
Buses and HGVs where range and refuelling speed matter.
Portable power generators.
Space exploration (used on Apollo missions — water produced was also used by crew).
Disadvantages and Challenges
HYDROGEN PRODUCTION:
Most hydrogen is currently made from NATURAL GAS (steam reforming) — releases CO₂.
'Green hydrogen' made by electrolysis of water using renewable energy — still expensive.
Until green hydrogen is widespread, fuel cells are not truly zero-carbon overall.
STORAGE AND DISTRIBUTION:
Hydrogen is highly flammable and must be stored under pressure or as a liquid.
Requires new infrastructure — hydrogen refuelling stations are rare.
Storage tanks take up significant space and add weight.
COST:
Fuel cells use platinum as a catalyst — platinum is rare and very expensive.
Fuel cell vehicles are more expensive than petrol or battery-electric vehicles currently.
SAFETY:
Highly flammable — requires careful handling and leak detection.
High pressure storage adds engineering complexity.
COMPARISON WITH RECHARGEABLE BATTERIES:
Fuel cells: faster refuelling, longer range, but expensive hydrogen infrastructure.
Battery-electric: established infrastructure (electricity grid), lower cost, but slower charging.
Both are zero direct emission — choice depends on application.
⚠️ Common Mistake
Fuel cells are NOT the same as batteries. A battery stores fixed reactants and runs out. A fuel cell is continuously supplied with fuel — it runs as long as hydrogen and oxygen are provided. The ONLY product of a hydrogen fuel cell is water — no CO₂ is produced during operation.
📐 Key Equations
2H₂ + O₂ → 2H₂O (overall fuel cell reaction)
📌 Key Note
Hydrogen fuel cell: H₂ + O₂ → H₂O. Only product = water. Continuous supply of fuel. More efficient than combustion. Advantages: zero direct emissions, fast refuelling, high energy density. Disadvantages: hydrogen production (usually from natural gas), storage challenges, platinum catalyst (expensive), limited infrastructure.
🎯 Matching Activity — Fuel Cell Pros and Cons
Sort each statement into advantage or disadvantage of hydrogen fuel cells. — drag the symbols on the right to match the component names on the left.
Advantage
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Advantage
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Disadvantage
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Disadvantage
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Disadvantage
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Platinum catalyst is rare and expensive — increases fuel cell cost
Most hydrogen is made from natural gas — produces CO₂ in production
Hydrogen is highly flammable and requires high-pressure storage
Refuels quickly — hydrogen tank filled in minutes unlike battery charging
Only product is water — zero direct emissions during operation
⭐ Higher Tier Only
Write half equations for the hydrogen fuel cell: negative electrode (anode): H₂ − 2e⁻ → 2H⁺; positive electrode (cathode): O₂ + 4H⁺ + 4e⁻ → 2H₂O. Evaluate hydrogen fuel cells vs rechargeable batteries for transport applications using data.
🔬 Triple Science Only
Fuel cells (4.5.2.2) is chemistry-only — not in Combined Science. Students must describe how hydrogen fuel cells work and evaluate their advantages and disadvantages compared to rechargeable batteries.
🎯 Test Yourself
Question 1 of 2
1. What is the only chemical product of a hydrogen fuel cell during operation?
2. Why are hydrogen fuel cells not yet truly 'zero carbon' in most current applications?
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