NOVELTY - Deposition of catalytic layer on surface of substrate comprises providing particulates comprising catalytic material in upstream region of fluid stream; providing spray comprising polymeric material to mix particulates with polymeric material in downstream region of fluid stream; and impinging fluid stream on substrate surface to co-deposit particulates and polymer on substrate surface.    USE - For depositing a catalytic layer on a surface of a substrate, useful in the cathodes and anodes of fuel cells.    ADVANTAGE - The porous catalytic layers have high levels of catalyst and high effective catalytic surface area of the catalyst. The method provides for efficient, large scale deposition of catalytic material to form catalytic layers. By depositing the material in a dry state, there is low moisture content in the deposited material. The as-deposited material has a low density due to its very porous nature. The low moisture content and porous routes eliminate or minimize mud cracking or desiccation cracking.    DETAILED DESCRIPTION - Deposition of catalytic layer on a surface of a substrate, comprises providing particulates comprising a catalytic material in an upstream region of a fluid stream; providing a spray (46) comprising polymeric material to mix the particulates with the polymeric material in a downstream region of the fluid stream; and impinging the fluid stream on the substrate surface to co-deposit the particulates and the polymer on the substrate surface.    INDEPENDENT CLAIMS are also included for:    (1) an apparatus for depositing a catalytic material on a substrate (14), comprising gas flow mechanism for directing a stream of gas through upstream-, downstream- and deposition regions (20); mechanism for locating a substrate in the deposition region such that the stream of gas impinges on a surface (12) of the substrate; introducing mechanism at the upstream region for introducing particulates comprising a catalytic material; and introducing mechanism for introducing a fluid comprising a polymer in finely divided form such that the particulates mix with the polymer, where the gas stream carries a mixture of particulates and polymer to the substrate surface;    (2) an electrocatalytic layer comprising in combination a gas permeable substrate having regions of greater and lesser permeability, and material comprising a catalyst deposited on the substrate such that the combination has higher catalyst loadings in regions of higher gas permeability than in regions of lower catalytic loading; and    (3) a proton-conducting membrane for a fuel cell comprising proton-transfer material intimately mixed with a water-binding material to allow continued operation of a fuel cell at above 100 degrees C.    DESCRIPTION OF DRAWING(S) - The figure is a diagrammatic illustration of deposition apparatus.    Surface (12)    Substrate (14)    Deposition housing (19)    Deposition regions (20)    Spray (46)