What are hydrogen fuel cells?

Fuel cells are like chemical batteries, in that they produce a voltage that we can use to power devices. Hydrogen fuel cells use hydrogen and oxygen to make that voltage and have the overall equation:

2H₂(g) + O₂(g) → 2H₂O(l)

We can get this overall equation by looking at the equations happening at the electrodes in the fuel cell. At the negative electrode we have this:

2H₂ + 4OH^- → 4H₂O + 4e^-

And at the positive electrode we have:

O₂ + 2H₂O + 4e^- → 4OH^-

Which, if you combine them by placing all the reactants together on one side and all the products together on the other side, cancels down to the overall equation above.

Hope this helps!