NOVELTY - A gas diffusion layer (104) having electron conductivity and gas diffusibility, comprises: a first major surface (140) and a second major surface (150) positioned opposite to the first major surface and an interior between the first and second major surfaces, where the layer comprises a porous carbon substrate (160, 170) directly fluorinated in the interior and is free of fluorination on at least one of the first or second major surface.    USE - As gas diffusion layer having electron conductivity and gas diffusibility used for making a gas diffusion device including a fuel cell (all claimed) such as a proton exchange membrane fuel cell.    ADVANTAGE - The gas diffusion layer comprises a porous carbon substrate which is directly fluorinated in the interior and is free of fluorination on at least one of the first or second major surface. Thus, the conductivity of the gas diffusion layer is maintained. Moreover, the gas diffusion layer material is made more hydrophobic by direct fluorination, thus the gas diffusion layer is prevented from becoming flooded with liquid water.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) a fuel cell, comprising: a membrane-electrode assembly including a hydrogen ion conductive polymer electrolyte membrane; a pair of catalyst layers sandwiching the polymer electrolyte membrane; and a pair of the gas diffusion layers disposed on the outer surfaces of the catalyst layers; and    (2) making a gas diffusion device either involving: providing a porous carbon substrate having a first major surface and a second major surface positioned opposite to the first major surface and an interior between the first and second major surfaces; protecting at least one of the first or second major surface by contacting at least one surface with a protective layer; directly fluorinating the porous carbon substrate with fluorine gas; and removing the contact between the protective layer and at least one surface; where the interior of the gas diffusion device is fluorinated and at least one surface is not fluorinated; or involving: providing a porous carbon substrate having a first major surface and a second major surface positioned opposite to the first major surface and an interior between the first and second major surfaces, where the porous substrate is comprised carbon fibers having thousands of carbon atomic layers; directly fluorinating the porous carbon substrate with fluorine gas such that an outer carbon atomic layer of the fibers is fluorinated; and removing the outer carbon atomic layers of the carbon fibers forming at least one of the first and second major surfaces such that the interior of the gas diffusion device is fluorinated and at least one major surface is not fluorinated.    DESCRIPTION OF DRAWING(S) - The figure shows a view of the three-layer sandwich and one-layer setup for making the gas diffusion layer.    Gas diffusion layer (104)    First major surface (140)    Second major surface (150)    Porous protective gas diffusion layers (160, 170)