Nb2O5 Nanostructures as Precursors of Cycling Catalysts for Hydrogen Storage in MgH2

High operating temperatures and sluggish kinetics aremajor obstaclesfor practical applications of MgH2 as a solid hydrogencarrier. Introducing nanoscaled high-activity catalysts has been effectivein improving the hydrogen cycling of MgH2. However, itremains still unclear that between nanoparticle size and morphology,which one is the decisive factor of the catalytic activity of a givencatalyst. In this work, we studied this topic by taking nanostructuredniobium oxide (Nb2O5) as a representative sample.Five types of Nb2O5 catalytic additives withdifferent morphologies and nanosizes were synthesized, and their catalyticactivities were compared with commercial microparticles. Our resultsunambiguously demonstrate that the catalytic activity of Nb2O5 is determined by the primary particle size rather thanthe morphology and structure because the ultrasmall Nb2O5 nanoparticles that measured & SIM;5 nm in size enabledehydrogenation of MgH2 starting at 165 & DEG;C after one-cycleactivation. The smaller nanoparticle sizes not only enhance the reactivityof Nb2O5 but also lead to more uniform dispersionwhen ball-milled with MgH2, which enables in situ formationof more homogeneous and finer Nb-based active species and thereforemuch higher catalytic activity. This important insight will guidethe design and optimization of novel high-activity catalysts for hydrogencycling of MgH2 and other hydrogen storage materials.