Palladium-Gold Coated Vanadium Alloy Membranes for Hydrogen Separation

Vanadium alloy membranes have high hydrogen permeabilities and are less expensive than palladium alloys. However, the surface of vanadium is easily contaminated and must be protected by a thin palladium or palladium alloy layer. Fossil fuel derived hydrogen may contain traces of sulfur that will quickly reduce hydrogen flux through the membrane. Alloys of palladium such as palladium-copper and palladium-gold have been reported to be somewhat sulfur tolerant. The goal of this work was to develop a method for depositing a palladium-gold alloy coating onto a vanadium alloy membrane.

Vanadium alloy foils (0.25 mm thick) were coated with a palladium-gold alloy by sequential deposition. First, palladium was deposited to a thickness of 750 nm using physical vapor deposition (PVD), and then gold was deposited using electroless deposition. Pd-Au/V-alloy composite membranes were characterized for hydrogen permeability at 673 and 723 K as the gold and palladium diffused together, changing the permeability over time. As-coated and tested membranes were characterized using Rutherford backscattering-spectrometry (RBS) and X-ray photoelectron spectroscopy (XPS) depth profiles to analyze the deposition process and to study the effects of metallic interdiffusion on the coating during hydrogen permeation testing.