High surface area niobium oxides as catalysts for improved hydrogen sorption properties of ball milled MgH2

We report, high surface area (up to 200 m(2)/g) nanocrystalline niobium oxide (so called p-Nb2O5) synthesized by 'chimie douce' route and its importance in enhancing the hydrogen sorption properties of MgH2. p-Nb2O5 induces faster kinetics than commonly used commercial Nb2O5 (c-Nb2O5) when ball milled with MgH2 (named (MgH2)(catalyst)) by reducing the time of desorption from 35 min in (MgH2)c-Nb2O5 to 12 min in (MgH2)p-Nb2O5 at 300 degrees C. The BET surface area of as-prepared Nb2O5 was tuned by heat treatment and its effect on sorption properties was studied. Among them, both p-Nb2O5 and Nb2O5:350 (p-Nb2O5 heated to 350 degrees C with a BET specific surface area of 46 m(2)/g) desorb 5 wt.% within 12 min, exhibiting the best catalytic activity. Furthermore, thanks to the addition of high surface area Nb2O5, the desorption temperature was successfully lowered down to 200 degrees C, with a significant amount of desorbed hydrogen (4.5 wt.%). In contrast, the composite (MgH2)c-Nb2O5 shows no desorption at this "low" temperature. (C) 2007 Elsevier B.V. All rights reserved.