NOVELTY - Operating a fuel cell stack to prevent mechanical failure of fuel cell membranes due to hygroexpansive ratcheting comprises providing fuel cells comprising a membrane (100), an anode electrode catalyst layer (16), and a cathode electrode catalyst layer (18), the membrane and electrodes interposed between bipolar plates having a face including a reactant flow field defined by lands and channels; humidifying; cycling the humidity from a condition below 100% relative humidity to a condition at 100% relative humidity or where there is condensation of water.    USE - For operating a fuel cell stack for vehicle or automotive applications, to prevent mechanical failure of fuel cell membranes due to hygroexpansive ratcheting.    ADVANTAGE - Reduces or eliminates pinhole development in the ionic membrane, and provides an extruded membrane that exhibits superior durability.    DETAILED DESCRIPTION - Operating a fuel cell stack to prevent mechanical failure of fuel cell membranes due to hygroexpansive ratcheting comprises providing fuel cells comprising a membrane and an anode electrode catalyst layer and a cathode electrode catalyst layer, the membrane and electrodes interposed between bipolar plates, each bipolar plate have a face including a reactant flow field defined, at least in part, by lands and channels; humidifying the fuel cell stack; cycling the humidity in the fuel cell stack from a condition below 100% relative humidity to a condition at 100% relative humidity or where there is condensation of water, and where at least two of the following conditions are met, where the cycling of the humidity comprises drying the fuel cell stack at a rate less than 0.2 lambda/second; the membrane comprises an extruded membrane; the planar expansion of the membrane during the cycling of the humidity is less than or equal to25%; the magnitude if the humidity cycle is less than 50% relative humidity; where each of the anode electrode catalyst layer and the cathode electrode catalyst layer are substantial free of cracks; operating the fuel cell stack at potentials below 700 mV; where the lowest compression between the gas diffusion media and the membrane electrode assembly over each channel is greater than or equal to0.2 MPa; or where a conductive restrictive layer underlies or overlies the anode electrode catalyst layer or the cathode electrode catalyst layer to restrict the planar expansion of the membrane, to prevent the membrane from being pinched in a crack formed in the anode electrode catalyst layer or the cathode electrode catalyst, or to arrest the propagation of an incipient crack in the electrode catalyst layers. The membrane comprises an extruded membrane comprising a perfluorosulfonic acid. The membrane comprises a fluoropolymer, a hydrocarbon polymer, or partially fluorinated hydrocarbon polymer. An INDEPENDENT CLAIM is included for a fuel cell.    DESCRIPTION OF DRAWING(S) - The figure shows a portion of the fuel cell.    Anode electrode catalyst layer (16)    Cathode electrode catalyst layer (18)    Membrane (100)    Conductive restrictive layers (200,202)