Metal-free rapid dehydrogenation kinetics and better regeneration yield of ammonia borane

Abstract

Ammonia borane (AB), one of the promising hydrogen storage materials, is receiving more attention because of its high hydrogen content. However, to act as a sustainable material for hydrogen storage, regeneration from products obtained on dehydrogenation is essential. Regeneration of AB reported in literature involves the use of expensive reagents with high toxicity and environmental impact. In this work, we attempted to aid the dehydrogenation/regeneration process of pure ammonia borane as well as products obtained on thermolysis of AB, using acetone as the dehydrogenation/digestion reagent. During dehydrogenation, a total of 1.7 equivalent of hydrogen was obtained through a thermal and chemical reaction with the resultant formation of tri and tetrasubstituted borate ester. In the current work, a simple method for regeneration of AB is being demonstrated from the dehydrogenated products, which are borate esters, in this case. Using this method, an overall regeneration yield, i.e., from starting material AB→ dehydrogenated products→ regenerated material AB is observed to be 68%. The conversion yield of regenerated AB, starting from dehydrogenated products, was found to be 83%, and that into hydrazine borane (HzB) to be 15% (which can also act as hydrogen source).