Synthesis of ammonia borane for hydrogen storage applications

Abstract

A new synthetic procedure to make the condensed phase hydrogen storage material, ammonia borane (NH 3 BH 3 , abbreviated as AB), is described and compared with previous literature procedures. Ammonia borane with a gravimetric density ca. 194 gm H 2 kg À1 and a volumetric density ca. 146 H 2 litre À1 , is a promising chemical hydrogen storage material for fuel cell powered applications. The work shows that ammonium borohydride, NH 4 BH 4 , formed in situ by the metathesis of NH 4 X and MBH 4 salts (M ¼ Na, Li; X ¼ Cl, F) in liquid NH 3 , can be induced to decompose in an organic ether to yield AB in near quantitative yield. The purity of the AB prepared by this one-pot synthetic strategy is sufficient to meet the thermal stability requirements for on-board hydrogen storage.

Novel hydrogen storage materials: A review of lightweight complex hydrides

“…Recently Ramachandran and Gagare [321] obtained high yield ∼96% of ammonia borane and suggested that a low concentration of the reaction medium is necessary for the purity and yield of the product. More recently, Heldebrant et al [322] proposed that ammonium borohydride, NH 4 BH 4 can be induced to decompose in an organic ether to yield AB in near quantitative yield. They found the purity of this AB is sufficient to meet the thermal stability requirements for on board hydrogen storage.…”

Ammonia as a Potential Substance

“…Regarding pipeline transportation, following Bartles (2008), the distribution energy efficiency is 93% with respect to HHV at an energy density of 14 GJ/m 3 . Ammonia can be stored onboard a vehicle in pressurized cylinders in an anhydrous form or in some chemical form such as metal amines or ammonia boranes, which are produced using recently developed physical-chemical reversible methods; see Heldebrant et al (2008) and Christensen et al (2005). In this technology, ammonia is adsorbed on a porous metal-amine complex, for example, hexaaminemagnesium chloride, Mg(NH 3 ) 6 Cl 2 ; to do this, NH 3 is passed over an anhydrous magnesium chloride (MgCl 2 ) powder at room temperature.…”

Hydrogen-storage materials dispersed into nanoporous substrates studied through incoherent inelastic neutron scattering

“…Thus at the end of the synthesis procedure the following melt-infiltrated NaAlH 4 + ACF25 sample were available: NaAlH 4 :ACF25 = 1:1 by weight, m = 2.5 g. (2) MCM-41 silica was obtained from Mobil Corporation, while ammonia borane was synthesized according to the procedure reported in Ref. [20] and purified by sublimation in vacuum. In order to disperse NH 3 BH 3 into the porous substrate, a solution of ammonia borane (m = 5.6 g, containing isotopically enriched 11 B to reduce neutron absorption) in tetrahydrofuran (about 100 cm 3 ) was slowly added to a sample of MCM-41 (11.2 g).…”