A fuel cell is an electrochemical energy converter. Its operation is based on the following electrochemical reactions happening simultaneously on the anode and the cathode.
At the anode:
At the cathode:
More precisely, the reactions happen on an interface between the ionically conductive electrolyte and the electrically conductive electrode. Because there are gases involved in fuel cell electrochemical reactions, the electrodes must be porous, allowing the gases to arrive, ...