NOVELTY - The fuel cell stack for power requirement in automobile, comprises 20-500 proton exchange membrane fuel cells connected electrically in series in which the fuel cell has an anode, a cathode, a proton exchange membrane disposed between the anode and the cathode, and a diffusion medium adjacent to the anode and/or the cathode. The diffusion media in the fuel cells of the stack comprises a porous conductive substrate having a vapor-deposited fluorocarbon polymer on the substrate. The vapor-deposited fluorocarbon polymer covers less than 100% of the area of the diffusion medium.    USE - Useful for power requirement in automobile and other industrial uses to deliver electrical energy.    ADVANTAGE - The fuel stacks containing the diffusion media exhibit acceptable fuel cell performance to improve the vapor deposited diffusion media that retains hydrophobicity to a great extent upon aging.    DETAILED DESCRIPTION - The fuel cell stack for power requirement in automobile, comprises 20-500 proton exchange membrane fuel cells connected electrically in series in which the fuel cell has an anode, a cathode, a proton exchange membrane disposed between the anode and the cathode, and a diffusion medium adjacent to the anode and/or the cathode. The diffusion media in the fuel cells of the stack comprises a porous conductive substrate having a vapor-deposited fluorocarbon polymer on the substrate. The vapor-deposited fluorocarbon polymer covers less than 100% of the area of the diffusion medium. The areas of the diffusion medium are covered by a hydrophilic polymer. The fluorocarbon polymer is vapor-deposited by a process comprising exposing a monomer precursor gas to a heat source having a temperature sufficient to pyrolyze the monomer gas and produce a source of reactive fluorocarbon radicals in the vicinity of the substrate. The diffusion medium is covered with a microporous layer and the other side has the vapor deposited fluorocarbon polymer. An INDEPENDENT CLAIM is included for a proton exchange membrane fuel cell.    DESCRIPTION OF DRAWING(S) - The diagram shows vapor deposition through a mask:    Mask; (2)    Porous substrate; (4)    Solid portion; (6)    Open area; (10)    Contact area. (12)