Rapid release of 1.5 equivalents of hydrogen from CO2-treated ammonia borane

This work addresses the accelerated dehydrogenation of ammonia borane (AB, NH3BH3) in two separate processes of CO2 pre-treatment of AB and dehydrogenation of the treated AB. Decoupling these two processes can still keep the dehydrogenation activity of CO2-treated AB and eliminate the purification step of H2 from gas phase. When AB is exposed to 1.38 MPa of carbon dioxide (CO2) at 70 °C, it shows the most favorable and controllable operating condition for the CO2 pre-treatment. The pre-treatment enhances not only the rate but also the amount of hydrogen release at the dehydrogenation step; 1.5 mol H2 per mol of AB rapidly desorbs at 85 °C in 1 h, corresponding to 10.1 wt.% of hydrogen with regard to pristine AB. Also, our observations show that the fast dehydrogenation resulted from the CO2 pre-treatment is preserved for more than four days of storage. The degree of dehydrogenation is further confirmed by ATR-FTIR spectroscopic and elemental analyses of the solid product. The spectra display the N–H stretching mode involving π-bonded nitrogen (sp2 N) at ca. 3434 cm−1,while the atom ratio of H:B is found to be 2.84:1. Based on the hydrogen release measurements, spectroscopic observations and elemental analyses, we deduce that the predominant solid product of dehydrogenation of CO2-treated AB at 85 °C is a polymer with an empirical formula of (NBH3)n. It corresponds to the solid product after 1.5 equivalent hydrogen release of AB.