NOVELTY - A fuel cell includes: first and second reactant inputs; humidified reactant output; diffusion media comprising diffusion media substrate and mesoporous layer; and controller for operating the device at high relative humidity and configured such that a relative humidity of the humidified reactant output exceeds 150%. The diffusion media substrate comprises a carbonaceous porous fibrous matrix.    USE - The device, i.e. fuel cell used in vehicle (claimed), is for converting hydrogenous fuel source to electrical energy.    ADVANTAGE - The fuel cell optimizes water management properties of the diffusion media.    DETAILED DESCRIPTION - A fuel cell (10) includes: first and second reactant inputs, humidified reactant output, diffusion media (20) for passing multiphase reactants within the device, and controller for operating the device at high relative humidity. The controller is configured such that a relative humidity of the humidified reactant output exceeds 150%. The diffusion media comprises a diffusion media substrate and a mesoporous layer. The diffusion media substrate comprises a carbonaceous porous fibrous matrix defining first and second major faces. The mesoporous layer is carried on a portion of first or second major face of the substrate and comprises a hydrophilic carbonaceous component and a hydrophobic component. The hydrophilic carbonaceous component comprises a low surface area carbon having a surface area of below 85 m2/g and a mean particle size of 35-70 nm.    An INDEPENDENT CLAIM is also included for fabricating a diffusion media for a device by identifying the operational humidity as a low, moderate, or high operational humidity; configuring a diffusion media; and configuring the mesoporous layer such that the hydrophilic carbonaceous component comprises a high surface area carbon.    DESCRIPTION OF DRAWING(S) - The figure is a schematic view of the fuel cell incorporating a porous diffusion media.    Fuel cell (10)    Diffusion media (20)    Membrane electrode assembly (30)    Catalytic electrode layer (32)    Ion exchange membrane (34)    Anode flow field (40)    Cathode flow field (50)