Destabilization of NH3BH3 by water during hydrothermolysis as a key factor in the high hydrogen evolution rates

• Published in: International journal of hydrogen energy 2016-10, Vol.41 (39), p.17484-17495
• Main Authors: Komova, O.V., Kayl, N.L., Odegova, G.V., Netskina, O.V., Simagina, V.I.
• Format: Article
• Language: English
• Subjects: Ammonia borane; ATR-FTIR; Dihydrogen bonds destabilization; Hydrolysis; Hydrothermolysis; NH3BH3; Thermolysis
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2016.07.163

The rates of non-catalytic hydrolysis, thermolysis and hydrothermolysis of ammonia borane (NH3BH3, AB) at 80 °C and 90 °C have been compared. It was found that by using water-wetted AB and carrying out the process of hydrothermolysis results in an order of magnitude increase in the rate of hydrogen generation. The highest rate of AB hydrothermolysis accompanied by a drastic heat-up of the reaction layer was observed at the optimal water content in AB. Carrying out this process in a polyethylene medium which is poor heat conductor resulted in even higher efficiency of the process. On the basis of spectroscopic ATR-FTIR data we conclude that the high reactivity of AB in hydrothermolysis was most likely caused by destabilization of dihydrogen BHδ−–δ+HN bonds in the NH3BH3 crystal lattice by polar water molecules leading to an increased dispersion of hydride. This increase in dispersion results in enhanced AB reactivity in dehydrogenation and leads to formation of polyaminoborane (PAB). It was shown that PAB which is formed after release of one equivalent of hydrogen is hydrolyzed more easily comparing with starting AB. On the other hand, the products of AB and PAB hydrolysis are believed to be also capable of accelerating AB hydrogenation. [Display omitted] •Hydrothermolysis of NH3BH3 has been compared with its hydrolysis and thermolysis.•Highest rate of H2 generation occurs at 90 °C from water-wetted granules of NH3BH3.•Polar H2O destabilizes the NH3BH3 lattice leading to increased hydride dispersion.•This probably results in enhanced NH3BH3 reactivity in dehydrogenation process.•(NH2BH2)x is hydrolyzed more easily comparing with starting NH3BH3.