TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Components: The hydrophobic areas are predominantly on one side of the substrate, and the hydrophilic areas are predominantly on the other side. The diffusion medium has different content of hydrophobic polymer in an area adjacent the entrance side than in an area adjacent the exit side. The diffusion medium has higher content of hydrophobic polymer in area adjacent the exit side than in area adjacent the entrance side.    TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Method: Deposition of hydrophobic polymer includes wetting a sheet of carbon fiber paper with solvent in an aqueous emulsion containing the hydrophobic polymer, contacting the wet sheet with a pattern member (2), e.g. screen, having opening(s) (8) oriented to correspond to a predetermined pattern, and evaporating the solvent from the sheet while the sheet is in contact with the pattern member. The hydrophobic polymer is concentrated on the sheet at the openings. The contacting step includes holding the sheet between two mold surfaces, with one of the mold surfaces comprising openings through which solvent can evaporate and the other mold surface is solid. Both mold surfaces may comprise, and a pattern of hydrophobic polymer is deposited on both sides of the sheet. The evaporating step is accomplished by heating the sheet to remove solvent. At least one side of the sheet is coated with fluorocarbon polymer over 10-90% (preferably 10-60%) of its area. The electroconductive polymer is deposited by electrochemical polymerization from an aqueous monomer solution comprising an electrolyte and a monomer such as thiophene, furan, azulene, carbazole, derivative of these monomers, or preferably aniline or pyrrole.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The hydrophobic polymer is fluorocarbon polymer, preferably PTFE. The electroconductive polymer is polyaniline or polypyrrole.    TECHNOLOGY FOCUS - TEXTILES AND PAPER - Preferred Materials: The substrate is carbon fiber paper.