Meanwhile, on the cathode side of the fuel cell, oxygen gas (O2) is being forced through the catalyst, where it forms two oxygen atoms.
Each of these atoms has a strong negative charge.
This negative charge attracts the two H+ ions through the membrane, where they combine with an oxygen atom and two of the electrons from the external circuit to form a water molecule (H2O).
This reaction in a single fuel cell produces only about 0.7 volts.
To get this voltage up to a reasonable level, many separate fuel cells must be combined to form a fuel-cell stack .