Synthesis and hydrogen permeation properties of ultrathin palladium-silver alloy membranes

The present work focuses on the synthesis and gas permeation properties of ceramic supported ultrathin palladium-silver alloy membranes. PdAg films with a thickness ranging from 250 to 500 nm are coated on the surface of 3 nm pore sol-gel derived γ-alumina support using an RF magnetron sputtering equipment. The coated PdAg membranes exhibit the same composition and phase structure as those of the PdAg foil used as the target in sputter deposition. The hydrogen to nitrogen separation factor of the ultrathin PdAg membrane is 5.7 at 250°C and increases with increasing temperature. Under proper preparation conditions, use of a pinhole-free γ-alumina support is the key to ensure the gas-tightness and high-selectivity of the coated PdAg membranes. A method is demonstrated for studying hydrogen permeation through ultrathin metallic films. Hydrogen permeation data at different hydrogen pressures and temperatures (100-250°C) are reported to examine the mechanism of hydrogen permeation through the ultrathin metallic membranes. The experimental results clearly indicate the dominant role of surface reactions for hydrogen permeation through ultrathin metallic films at low temperatures.