📖 In-Depth Theory
How Hydrogen Fuel Cells Work
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.