Promotion of hydrogen release from ammonia borane with magnesium nitride.

Hydrogen release from ammonia borane (NH(3)BH(3), AB) can be greatly promoted by mechanical milling with magnesium nitride (Mg(3)N(2)). For example, a post-milled 6AB/Mg(3)N(2) sample started to release hydrogen from ∼65 °C and gave a material-based hydrogen capacity of ∼11 wt% upon heating to 300 °C. In addition to the improved dehydrogenation kinetics, the 6AB/Mg(3)N(2) sample also showed satisfactory performance in suppressing the volatile byproducts. X-ray diffraction, Fourier transform infrared spectroscopy and solid-state (11)B MAS NMR, as well as a series of designed experiments, were carried out to gain mechanistic understanding of the property improvements that arise from addition of Mg(3)N(2). Our study found that the formation of 3Mg(NH(2)BH(3))(2)·2NH(3), which is in single or mixed amidoborane ammoniate phases in nature, is an important mechanistic step in the dehydrogenation process of the 6AB/Mg(3)N(2) sample.

Facile solid-phase synthesis of the diammoniate of diborane and its thermal decomposition behavior.

The recent mechanistic finding of the hydrogen release pathways from ammonia borane (AB) has sparked new interest in the chemistry and properties of the diammoniate of diborane (DADB), an ionic isomer of AB. We herein report a facile one-step solid-phase synthesis route of DADB using inexpensive starting materials. Our study found that mechanically milling a 1 : 1 NaBH(4)/NH(4)F powder mixture causes the formation of crystalline DADB via a NH(4)BH(4) intermediate. The produced DADB can be readily separated from the sodium fluoride (NaF) by-product by a purification procedure using liquid ammonia at -78 °C. The thermal decomposition behavior of DADB was studied using synchronous thermal analyses, particularly in comparison with AB. It was found that the decomposition steps and products of DADB are similar to those of AB. But meanwhile, DADB exhibits a series of advantages over AB that merit its potential hydrogen storage application, such as lower dehydrogenation temperature, free of foaming and lack of an induction period in the thermal decomposition process. Our study further found that the volatile non-hydrogen products from DADB can be effectively suppressed by milling with MgH(2).

Promoted hydrogen release from ammonia borane by mechanically milling with magnesium hydride: a new destabilizing approach.

Ammonia borane (NH(3)BH(3), AB) is an intriguing molecular crystal with an extremely high hydrogen capacity and moderate thermal stability. In the present study, we show a simple but effective approach for destabilizing AB for promoted hydrogen release at moderate temperatures. It is found that mechanically milling with magnesium hydride (MgH(2)) can dramatically improve the dehydrogenation properties of AB, on both the kinetic and thermochemical aspects. For the mechanically milled AB/0.5MgH(2) material, over 8 wt% hydrogen can be released from AB within 4 h at around 100 degrees C without undesired volatile by-products. Moreover, the dehydrogenation reaction of the AB/0.5MgH(2) sample becomes significantly less exothermic than that of neat AB. In situ X-ray diffraction results demonstrate that the MgH(2) additive well maintains its phase stability during the ball-milling and the subsequent heating processes. Meanwhile, Raman spectroscopy and in situ(11)B NMR studies show that the MgH(2) additive exerts considerable influence on the chemical bonding state and decomposition process/products of AB. Combined phase/structure analyses results suggest that MgH(2) exerts effect via developing solid phase interaction with AB.

Ammonia borane destabilized by lithium hydride: an advanced on-board hydrogen storage material.

An advanced hydrogen storage material, with potential for on-board application, is readily prepared by mechanically milling a 1:1 ammonia borane/lithium hydride (AB/LiH) mixture. The material possesses a H capacity of around 10 wt %, higher than the 2015 DOE gravimetric H capacity target, and can rapidly release over 7 wt % pure H2 at around 100 °C.