A method for optimizing fuel feed of a fuel cell stack catalytic electrode, the fuel cell stack containing a cell comprising a proton exchange membrane located between said catalytic electrode and another electrode, operating in superstoichiometric mode, said fuel comprising a carbonyl-containing polluting agent compound reacting on said catalytic electrode, comprises: defining a reference voltage for said cell when fed with a fuel exempt from polluting agent; defining a threshold voltage corresponding to a preset operating voltage of said cell as a percentage of reference voltage; defining a calibration curve for given operating conditions, relating threshold voltage to flow rate of polluting agent and allowing a first parameter of flow rate of polluting agent to be defined; detecting polluting agent to define a second parameter corresponding to content of polluting agent present in said fuel; and determining a maximum stoichiometry coefficient for said fuel stream, depending on said two parameters.