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.