Abstract: A fuel cell system including a mechanism supplying hydrogen to the anode of the cell, a mechanism supplying oxygen to the cathode of the cell, and a control unit. A first control controls the hydrogen supply to the anode of the cell and a second control controls the oxygen supply to the cathode of the cell. A further mechanism determines hydrogen over-stoichiometry in an anodic oxidation half-reaction and a further mechanism determines oxygen over-stoichiometry in a cathodic reduction half-reaction. The first and second controls can adapt hydrogen and oxygen over-stoichiometry of the cell respectively as a function of the required cell power.