Hydrogen sorption enhancement by Nb2O5 and Nb catalysts combined with MgH2

Three Nb materials, synthesized oxide (s-Nb2O5), commercial oxide (c-Nb2O5) and metallic Nb, were applied as catalysts to promote the enhancement of hydrogen sorption in MgH2. A high specific surface area, around 100 m2 g−1, was obtained for both oxides used as catalysts, s-Nb2O5 and c-Nb2O5 after being heat treated at 350 °C. X-ray diffraction (XRD) tests, performed prior to milling, revealed the amorphous structure of both oxides. All the catalysts were mixed for only 20 min with MgH2 by mechanical milling forming composites. Differential Scanning Calorimetric curves of the s-Nb2O5 and c-Nb2O5 showed the presence of exothermic crystallization peaks. A total capacity of 5.8 wt.% was attained when the hydrogen absorption kinetic tests were conducted at 350 °C, with the MgH2 + 5 wt.% s-Nb2O5 sample.

► The samples, MgH2 + Nb catalysts, were obtained by mechanical milling.
► The synthesized, high surface area, Nb2O5 showed to be a promising material.
► A hydrogen capacity of 5.2 wt.% was attained in 1.3 min with MgH2 + 5 wt.% s-Nb2O5.