Improvement in high temperature stability of Pd coating on Nb by Nb₂C intermediate layer

Niobium subcarbide (Nb₂C) was chosen as a material for non-porous intermediate layer to improve the high temperature durability of Pd-Nb composite membranes for hydrogen separation. A layer of Nb₂C was prepared between Nb substrate and thin Pd films (100 nm), and the stability of Pd coating at elevated temperatures (573-773 K) was examined by hydrogen absorption experiments. Hydrogen permeability through the Nb₂C layer appeared to be sufficiently high, and no noticeable deterioration was observed in hydrogen absorption rate under as-prepared conditions. The degradation in coating effect of Pd at elevated temperatures was substantially mitigated by Nb₂C layer. Such improved durability was ascribed to retardation of open porosity development by Nb₂C caused as a consequence of impeded interdiffusion between Pd and Nb.