How Do Hydrogen Fuel Cells Actually Generate Electricity?

A hydrogen fuel cell looks nothing like a battery, but people often lump the two together. A battery stores a fixed amount of chemical energy and runs down as it discharges. A fuel cell, by contrast, keeps generating electricity for as long as hydrogen and oxygen keep flowing in.

The basic reaction

Inside a fuel cell, hydrogen gas enters on one side and splits into protons and electrons at a catalyst-coated electrode. The protons pass through a membrane to the other electrode, while the electrons are forced through an external circuit, generating usable electric current along the way. On the far side, the protons, electrons and incoming oxygen recombine to form water. The only byproducts are water and heat, with no combustion and no carbon emissions from the reaction itself.

Why platinum matters

That reaction happens far too slowly on its own to be useful, so fuel cells rely on a catalyst, almost always platinum, to speed it up. Platinum is rare and expensive, so engineers try to spread it as thinly as possible, usually as nanoparticles a few nanometers wide, to maximize the exposed surface area per gram used. The trouble is that these tiny particles are unstable: over time they can dissolve, clump together or migrate, which is why so much fuel-cell research focuses on catalyst durability rather than the basic chemistry, which has been understood for more than a century.

Where fuel cells are used

Fuel cells already power some buses, forklifts, backup-power systems and a small number of passenger vehicles. Their appeal for larger users, such as data centers or factories, is the ability to generate electricity on-site from hydrogen rather than drawing entirely from the electrical grid, provided the hydrogen itself is produced cleanly.