Zirconium nitride intermetallic diffusion barriers enable stable hydrogen permeation in palladium–vanadium composite membranes

Abstract

Zirconium nitride (ZrN) is explored as a hydrogen permeable, intermetallic diffusion barrier for stable, high temperature operation of composite palladium-vanadium membranes for hydrogen purification. ZrN was deposited by reactive sputtering, and the properties and performance of films deposited in the metallic and compound mode were compared. Screening experiments using Pd-based sandwich structures showed that ZrN does not significantly impede H permeation until its thickness is increased above 40 nm. Stable hydrogen permeabilities up to >6 × 10−8 mol H2 m−1 s−1 Pa−0.5 were obtained in Pd|ZrN|V|ZrN|Pd composite membranes at operating temperatures of T = 400–450 °C, with superior performance obtained from ZrN deposited in the metallic mode. Long term stability (>200 h) was obtained and the structural integrity post-testing was confirmed by XRD and TEM imaging. Compositional profiling showed that oxygen originating in the V foil segregates to the ZrN–V interface but does not impede flux, and the transient behavior observed is attributed to this. Zirconium nitride decomposes at T > 450 °C, leading to rapid Pd–V interdiffusion and loss of permeability. However, with perfect selectivity and permeabilities up to 4X greater than Pd, these membranes are a promising cost effective alternative for hydrogen purification operations at 350–450 °C.