NOVELTY - Preparing a gold-palladium alloy gas separation membrane, involves providing a palladium layer having a mean surface roughness (Sa) of less than 0.8 micron; abrading the palladium layer with an abrasion media to increase the surface roughness to a mean surface roughness (Sa) above 0.8 micron; contacting the abraded palladium surface with a solution comprising chloroauric acid or its salt and hydrogen peroxide for a period of time to deposit layer of gold on the layer of palladium; and annealing the palladium and gold layers to produce the palladium-gold alloy gas separation membrane.    USE - For preparing a gold-palladium alloy gas separation membrane system (claimed) used in the production of energy in fuel cell power system; and in a wide variety of applications, especially those involving the separation of hydrogen from gas streams that comprise other gases, including gases containing concentrations of sulfur compounds, e.g. those selected from gases consisting of carbon dioxide, water, and/or methane.    ADVANTAGE - The method provides an inexpensive, highly efficient, and environmentally friendly method for preparing sulfur-resistant, thermally stable, gold-palladium alloy gas separation membrane system. This method does not involve galvanic displacement, does not require the use of palladium crystallites, and does not require any expensive activation, cleaning or functionalization techniques. The methods are capable of inexpensively and efficiently producing gas separation membrane systems which are resistant to poisoning by sulfur.    DETAILED DESCRIPTION - A method for preparing a gold-palladium alloy gas separation membrane, involves providing a palladium layer having a mean surface roughness (Sa) of less than 0.8 micron; abrading the palladium layer with an abrasion media to increase the surface roughness to a mean surface roughness (Sa) above 0.8 micron; contacting the abraded palladium surface with a solution comprising chloroauric acid or its salt and hydrogen peroxide for a period of time to deposit a layer of gold on the layer of palladium; and annealing the palladium and gold layers to produce the palladium-gold alloy gas separation membrane; or applying an intermetallic diffusion barrier to a porous substrate; depositing a palladium layer on the intermetallic diffusion barrier; heat treating the palladium layer to provide a heat treated palladium layer; abrading the heat treated palladium layer to a mean surface roughness (Sa) of above 0.8 microns up to 2.5 microns; and depositing on the heat treated, abraded palladium layer a gold layer by contacting the heat treated abraded palladium layer with a solution comprising chloroauric acid or its salt and hydrogen peroxide. An INDEPENDENT CLAIM is included for a palladium-gold alloy gas separation membrane system prepared by the methods.