Iron-nanoparticle-catalyzed hydrolytic dehydrogenation of ammonia borane for chemical hydrogen storage.

Iron, the most ubiquitous of the transition metals and the fourth most plentiful element in the Earth s crust, has been studied intensively because of its very potent magnetic and catalytic properties. However, its reactivity with respect to water and oxygen, especially on a nanoscale, generally limits its applications to a non-oxidizing environment where water and oxygen are not present. Recent studies involving coating Fe nanoparticles with an outer shell have succeeded in minimizing their oxidation and agglomeration. However, the presence of protective shell around the Fe particles is unfavorable for catalytic applications, where surface Fe active sites are needed. It is therefore understandable that, to date, there has been no report on the catalytic application of Fe nanoparticles without any protective shell other than the solvent components in aqueous solution in air. Fe nanoparticles that exert their powerful catalytic ability in aqueous solution or even in air will therefore significantly benefit both academic research and practical applications of iron-based materials. The search for effective hydrogen-storage materials is one of the most difficult challenges as we move towards a hydrogen-powered society as a long-term solution to current energy problems. Ammonia borane (AB; NH3BH3) has a hydrogen content of 19.6 wt%, which exceeds that of gasoline and therefore makes it an attractive candidate for chemical hydrogen-storage applications. The development of efficient and economical catalysts to further improve the kinetic properties under moderate conditions is therefore important for the practical application of this system. Herein we report the excellent catalytic activity of Fe nanoparticles with no protective shell for the hydrolytic dehydrogenation of aqueous AB under argon and even in air at room temperature. The Fe nanoparticles were pre-synthesized by reduction of FeSO4 with NaBH4 and then AB was immediately added to the solution to be catalytically hydrolyzed (AB/FeSO4/NaBH4 1.0:0.12:0.16). The gas generated was identified by mass spectrometry and its amount was measured volumetrically. Although black Fe nanoparticles were obtained rapidly, the evolution of 134 mL of hydrogen took more than 160 min (Figure 1a). The molar ratio of hydrolytically generated H2 to