Abstract: Specially prepared gas diffusion media improve the performance of PEM fuel cells. The media are made by first dipping an electrically conductive porous material such as carbon fiber paper into a suspension of hydrophobic polymer and drying the paper to create a desired deposition pattern of hydrophobic polymer on the substrate. Then a paste containing a fluorocarbon polymer and carbon particles is applied to a desired side of the substrate, and thereafter the paste and hydrophobic polymer are sintered together at high temperature on the paper. In particular, nonionic surfactants remain on the carbon fiber paper after the initial hydrophobic polymer is applied to the electrically conductive porous material. When the paste is coated on the dried paper, the paste is in contact with a hydrophilic surface.

Abstract: An electroconductive porous substrate such as carbon fiber paper with an electroconductive polymer deposited on the carbon fibers of the paper is used as a wicking material or diffusion medium in a fuel cell. The polymer may be deposited from a solution of monomers by electrochemical polymerization.

Abstract: A diffusion medium for use in a PEM fuel cell contains hydrophobic and hydrophilic areas for improved water management. A hydrophobic polymer such as a fluororesin is deposited on the paper to define the hydrophobic areas, and an electroconductive polymer such as polyaniline or polypyrrole is deposited on the papers defining the hydrophilic areas. In various embodiments, a matrix of hydrophobic and hydrophilic areas on the carbon fiber based diffusion media is created by electropolymerization of a hydrophilic polymer onto a diffusion medium which has been previously coated with a hydrophobic polymer such as a fluorocarbon polymer. When an aqueous solution containing monomers for electropolymerization is contacted with a fluorocarbon coated diffusion medium, the hydrophilic polymer will be preferentially deposited on areas of the carbon fiber based diffusion medium that are not covered by the fluorocarbons.

Abstract: Gas diffusion media for use in fuel cells are provided that contain a pattern of deposited hydrophobic polymer such that less than 100% of the surface of the diffusion media is covered with hydrophobic polymer. The media are made by first wetting a sheet of carbon fiber paper in an aqueous emulsion of the hydrophobic polymer. The wetted sheet is contacted with a pattern member containing one or more openings oriented to correspond to a predetermined or desired pattern of hydrophobic polymer deposition. While still in contact with the pattern member, the sheet is heated or otherwise treated to cause evaporation of the water from the sheet. Evaporation while in contact with the pattern member takes place in such a way that hydrophobic polymer is concentrated in the sheet at the openings of the pattern member by the process of evaporation.

Abstract: Favorable performance of diffusion media in fuel cells has found to be correlated to a parameter (the C/F ratio) that relates to a spatial and thickness distribution of the hydrophobic fluoropolymer on the carbon fiber substrate structure of the medium. Suitable diffusion media may be chosen from among commercially coated diffusion media by measuring the C/F ratio by means of energy dispersive spectroscopy, and choosing the diffusion media if the value of the C/F ratio is within the preferred range. Alternatively, the diffusion media may be manufactured with an improved process that consistently yields values of C/F ratio in the desired range.