How does a hydrogen fuel cell make electricity without burning fuel?

A hydrogen fuel cell converts chemical energy into electrical energy through coupled reactions. In a polymer electrolyte membrane, or PEM, cell, hydrogen reaches the anode and oxygen from air reaches the cathode. A membrane separates the two electrodes.

At the anode, a catalyst helps split hydrogen molecules into protons and electrons. Protons can pass through the membrane. Electrons instead travel through an external circuit, where their movement can supply a motor or another load. Keeping these routes separate is central to obtaining useful electrical output.

At the cathode, oxygen reacts with arriving protons and electrons to form water. The net reaction is 2 H₂ + O₂ → 2 H₂O. A catalyst changes reaction rates without supplying the net energy or being consumed in that overall reaction.

The cell also releases heat, and pumps and controls may consume part of the output. Unlike a rechargeable battery operating from a stored internal inventory, a fuel-cell system can continue while reactants are supplied and products are managed. Its water output alone does not establish the environmental impact: that also depends on how the hydrogen and other inputs were produced.