NOVELTY - A bipolar plate (58) for a fuel cell (40), comprises two unipolar plates (70, 72) bonded together to define reactant gas flow channels (64) and cooling fluid flow channels (78); several pores (90) extending between the reactant gas flow channels and cooling fluid flow channels, and through the unipolar plates; and at least one pervaporation membrane (92) covering the pores, to selectively allow water contained in a cooling fluid (e.g. a water-glycol mixture) flowing through the cooling fluid flow channels, to pervaporate through the membrane and into the reactant gas flow channels.    USE - As a bipolar plate for a fuel cell (claimed) e.g. proton exchange membrane fuel cells (PEMFC) for vehicles.    ADVANTAGE - The pervaporation membrane selectively allows water in the cooling fluid (e.g. automotive cooling fluid) flowing through the cooling fluid flow channels, to pervaporate through the membrane and humidify a reactant gas flowing through the reactant gas flow channels. The pervaporation membrane operates such that greater quantity of water is evaporated in the reactant gas flow channels, at higher temperatures of the cooling fluid. Thus, as the temperature of the fuel cell stack increases, more humidification is provided by the pervaporation membrane, to maintain the wetness of a membrane in fuel cell stack. As a result, the selective pervaporation membrane provides internal humidification, improving the internal cooling of fuel cell stack.    DETAILED DESCRIPTION - A bipolar plate (58) for a fuel cell (40), comprises two unipolar plates (70, 72) bonded together to define reactant gas flow channels (64) and cooling fluid flow channels (78); several pores (90) extending between the reactant gas flow channels and cooling fluid flow channels, and through the unipolar plates; and at least one pervaporation membrane (92) covering the pores, to selectively allow water contained in a cooling fluid (e.g. a water-glycol mixture) flowing through the cooling fluid flow channels, to pervaporate through the membrane and pores and into the reactant gas flow channels. The pervaporation membrane preferably includes several membrane plugs (94) of pervaporation compound, positioned in the pores. The pervaporation membrane is deposited on the bipolar plate, preferably by dipping the bipolar plate in a solution of a pervaporation material, or by spraying/brushing a pervaporation material on the bipolar plate. An INDEPENDENT CLAIM is included for a fuel cell comprising a membrane electrode assembly (MEA); a first bipolar plate positioned on one side of the MEA; and additionally a second bipolar plate positioned on other side of the MEA; where each bipolar plate includes at least one pervaporation membrane covering the pores, for selectively allowing water in the cooling fluid flowing through the cooling fluid flow channels, to pervaporate through the membrane and pores, and enter into the reactant gas flow channels as water vapor.    DESCRIPTION OF DRAWING(S) - The figure shows a close-up, cross-sectional view of a portion of a fuel cell in a fuel cell stack, including flow holes or pores, and pervaporation membranes that selectively allow water in the cooling fluid flow channels to pervaporate the reactant gas flow channel.    Fuel cell (40)    Membrane in duel cell stack (46)    Diffusion media layers (50, 54)    Catalyst layers (52, 56)    Bipolar plates (58, 60)    Reactant gas flow channels (62, 64)    Unipolar plates (70, 72, 74, 76)    Cooling fluid flow channels (78, 82)    Pores (90)    Pervaporation membrane (92)    Membrane plugs. (94)