Hydrogen transport properties of several vanadium-based binary alloys

Vanadium-based alloys are an emerging alternative to palladium alloys for use in hydrogen-selective alloy membranes. The tendency of vanadium to embrittle, due to its high hydrogen absorption, means it lacks the robustness required for industrial hydrogen separation applications. Alloying vanadium with certain elements reduces hydrogen absorption, but also influences the diffusivity of hydrogen through the bulk material. Consequently, diffusivity and absorption data must be decoupled in order to fully evaluate the influence of various alloying additions on the hydrogen transport properties of vanadium alloys. To address this need, the hydrogen transport properties of V–Al (V95Al5, V90Al10, V85Al15, V80Al20, V75Al25, expressed as atom%) and V–Cr (V95Cr5, V90Cr10, V85Cr15) alloys have been compared through a series of absorption and flux measurements. Pd-coated alloy disks were formed from arc melted and sectioned ingots, and each alloy was subjected to a microstructural analyses and a detailed examination of hydrogen absorption and permeation properties. Additions of Al and Cr reduce the hydrogen absorption and diffusivity of vanadium, with V–Cr alloys exhibiting the greatest hydrogen diffusivity for a given hydrogen feed pressure. The diffusivity of each alloy showed strong concentration dependence. Diffusivity-concentration results have been overlayed with an isoflux curve corresponding to a target flux of 1.0 mol m−2 s−1, enabling prediction of the thickness and pressure required to achieve this target flux target for a given alloy.