Zhanzhao Fang

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.

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.

Improved hydrogen storage property of Li–Mg–B–H system by milling with titanium trifluoride

The Li–Mg–B–H system that is prepared from 2LiH + MgB2 or 2LiBH4 + MgH2 possesses high hydrogen capacity and relatively favorable thermodynamics, but it is greatly restricted in practical hydrogen storage applications by problematic H-exchange kinetics. In the present study, TiF3 was mechanically milled with a 2LiH + MgB2 mixture and examined with respect to its effect on reversible dehydrogenation of the Li–Mg–B–H system. Experimental study showed that TiF3 is highly effective for promoting the two-step dehydrogenation reaction in the Li–Mg–B–H system. Compared to the neat 2LiH + MgB2 sample, the 2LiH + MgB2 + 0.01TiF3 sample exhibits significantly reduced dehydrogenation temperature and markedly enhanced dehydriding rate at both steps. Furthermore, the catalytic enhancement arising upon adding TiF3 additive was observed to persist well in the hydrogenation/dehydrogenation cycles. Based on the results of phase analysis and a series of designed experiments, the mechanism underlying the observed property improvement is discussed.

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).