Hydrogen–Oxygen Fuel Cells

A hydrogen–oxygen fuel cell uses hydrogen and oxygen to produce electricity, with water as the only chemical product.

What is a fuel cell?

A fuel cell is like a battery that does not run down while fuel is supplied. It converts the chemical energy of hydrogen and oxygen directly into electrical energy.

How it works (simple view)

• Anode (−): Hydrogen gas enters and loses electrons. These electrons travel through the external circuit to power a motor or light.
• Cathode (+): Oxygen gas enters and gains electrons. It reacts with hydrogen ions to form water.
• Electrolyte: Allows ions to move inside the cell but keeps gases and electrons separate.

In an acidic fuel cell, the half‑equations are:

$$\text{Anode: } \mathrm{H_2} \rightarrow 2\mathrm{H^+} + 2\mathrm{e^-}$$

$$\text{Cathode: } \tfrac{1}{2}\mathrm{O_2} + 2\mathrm{H^+} + 2\mathrm{e^-} \rightarrow \mathrm{H_2O}$$

Overall reaction:

$$2\mathrm{H_2} + \mathrm{O_2} \rightarrow 2\mathrm{H_2O}$$

Why it matters (uses)

• Vehicles: cars, buses, and forklifts.
• Spacecraft: electricity and drinking water on board.
• Backup power for hospitals and data centres.

Advantages compared with petrol engines

• Only water is produced at the point of use (no carbon dioxide or nitrogen oxides from the cell itself).
• Higher efficiency: more of the fuel’s energy becomes electricity.
• Quiet operation and fewer moving parts.
• Fast refuelling (minutes), good range.

Disadvantages and challenges

• Hydrogen storage is difficult (needs high pressure or very low temperature).
• Hydrogen refuelling stations are limited.
• Hydrogen production may release carbon dioxide if made from fossil fuels; “green” hydrogen needs renewable electricity.
• Fuel cells and catalysts (often platinum) are expensive.

Common misconceptions

• A fuel cell is not a battery: it generates electricity while fuel is supplied; it does not store much energy by itself.
• The reaction is not a flame; it is an electrochemical process that directly makes electricity.