Fuel cells: hydrogen + oxygen (HT)
A fuel cell generates electricity from a continuous supply of fuel and oxygen, with water as the only product for the H₂/O₂ cell. Unlike batteries, the cell doesn't run down as long as fuel keeps flowing.
How a hydrogen-oxygen fuel cell works
Inside the cell:
- At the anode (−): H₂ → 2H⁺ + 2e⁻. (Hydrogen is oxidised.)
- At the cathode (+): O₂ + 4H⁺ + 4e⁻ → 2H₂O. (Oxygen is reduced.)
- Overall: 2H₂ + O₂ → 2H₂O.
The H⁺ ions move through an electrolyte; electrons travel through the external circuit, doing work.
Why it's an alternative to rechargeable batteries
- Continuously fuelled — refill hydrogen and the cell keeps going (vs recharging a battery for hours).
- No charging time other than refuelling.
- Light for the energy delivered (good for vehicles).
- Only product is water — no greenhouse gases at point of use.
Advantages of H₂/O₂ fuel cells
- Zero CO₂ emissions (only water at point of use).
- High efficiency (chemical energy → electrical, fewer steps than combustion).
- Quiet (no moving parts).
- No toxic waste like used batteries.
Disadvantages
- Hydrogen is hard to store safely — needs high pressure or low temperature.
- Hydrogen production often requires electrolysis (energy-intensive) or methane reforming (releases CO₂).
- Infrastructure cost for fuelling stations is huge.
- Hydrogen is flammable — safety risk.
Comparison with rechargeable batteries
| Property | Fuel cell | Battery |
|---|---|---|
| Energy source | Continuous fuel supply | Stored chemicals |
| Recharging | Refill fuel | Plug in to mains |
| Lifespan | Fuel-limited | Fixed cycles |
| Emissions | Water only (Hydrogen) | Manufacturing + disposal |
| Power density | Lower per kg | Higher per kg |
⚠Common mistakes
- Saying "fuel cells produce H₂" — they consume it.
- "Zero emissions" oversimplified — only at the point of use; producing H₂ may release CO₂.
- Confusing fuel cell with combustion engine — fuel cell is electrochemical, no flame.
- Forgetting the electrolyte conducts H⁺ — it's not just any liquid.
Links
Builds on C5.4 (cells and batteries). Connects to C9.5 (atmospheric pollutants — fuel cells avoid them) and C10.1 (sustainable energy).
AI-generated · claude-opus-4-7 · v3-deep-chemistry