TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Substrate: The substrate is made from a fine powder using a nickel-based superalloy containing chromium and iron, in particular Inconel 600. The intermediate layer is made from an ultrafine powder and of nickel or a superalloy similar to that of the substrate.    TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Composite Structure: The filtration layer is fixed by micro-welds at the peaks of the surface grains on the intermediate layer. The substrate contains veins to improve its permeability and is a cylindrical baton with a collar at one end for hydrogen evacuation and, if appropriate, a collar at the other for a vector gas feed. The cylinder is relatively long and has a rigid axial metallic armature to give it a good mechanical resistance.The membrane is in the form of a square grille using a large number of batons as described above placed close to each other and fixed to two hollow transverse beams which handle respectively the hydrogen collection and the vector gas feed.The substrate, including the porous body and the intermediate layer are in the form of a plate enclosed in a metallic border connected to the hydrogen extraction and vector gas feed.Fuel gas processor with a cold plasma reaction chamber containing these membranes and electrodes providing a high dielectric coefficient to produce the cold plasma in the gaps between the cylinders in response to an appropriate electrical supply.The material forming the intermediate layer has a satisfactory chemical stability relative to the substrate and the membrane in the operating conditions.The thermal dilation coefficient of the substrate and intermediate membrane is less than or at least not much greater than that of the filtration layer.The ultra-thin filtration layer is made of a palladium-based alloy containing silver and/or nickel.Hydrogen purification unit with a filtration chamber containing membranes as described above and means of heating, temperature control and compression so the membranes operate at their optimum conditions.