(699a) Composite Vanadium Membranes for the Production of Ultrahigh Purity Hydrogen

Vanadium (V) membranes have great potential for hydrogen purification due to their perfect selectivity, high permeability, and relatively low cost. Ultrahigh purity hydrogen is required for many applications such as fuel cells and high end semiconductor processing. Vanadium is especially attractive for nuclear applications as it is a low neutron activation material. With appropriate surface cleaning, V foils efficiently permeates hydrogen at elevated temperature, but performance declines due to its affinity to absorb impurities. The application of palladium thin films maintains a clean surface that catalyzes hydrogen dissociation and recombination. Hydrogen permeation in Pd|V|Pd membranes initially reach theoretical permeability, but decline rapidly due to Pd-V interdiffusion. Transition metal nitrides (ZrN, TiN) are explored as hydrogen permeable, intermetallic diffusion barriers for stable, high temperature operation of composite palladium-vanadium membranes for hydrogen purification. The layers are produced by reactive sputtering, and screening experiments using Pd sandwich structures showed that sufficiently thin films (< 40 nm) do not significantly impede H permeation. Composite membranes with high temperature permeability exceeding palladium are described. Long term stability (>200 hours) was obtained and the structural integrity post-testing was confirmed by XRD and TEM imaging. We report permeabilities up to 4X greater than Pd, demonstrating that these membranes are a promising cost effective alternative for hydrogen purification operations at 350 – 450 °C.