Fuel Cell Cathode Reaction

The cathode reaction involves the interaction of protons that have passed through the proton exchange membrane with oxygen from the oxidizer supplied at the cathode. The reaction is written as:
2H⁺ + 2e^_+½O₂ Þ H₂O
where the electrons needed to make a neutral water molecule have come from the external circuit to which the cell is connected.

As a result of this reaction, the overall reaction of the cell is just the recombination of hydrogen and oxygen to produce water. The energetics of this reaction are such that the voltage difference between the anode and the cathode is 1.229 volts.