Unraveling the Effect of Carbon Nanotube Oxidation on Solid-State Decomposition of Ammonia Borane/Carbon Nanotube Composites

Abstract

Among the routes to perform hydrogen release from ammonia in solid state, the nanoconfinement into a carbonaceous matrix or the use of carbon-supported catalysts for the thermal degradation of ammonia borane (AB) is the most interesting one. Oxidized carbon nanotubes (CNTs) represent a suitable choice for preparing AB mixtures or for anchoring catalysts for dehydrogenation. Nevertheless, literature lacks detailed study about the influence of CNT oxidation degree on the AB degradation/hydrogen release. In this study, we first described in a comprehensive way that the thermal degradation of AB mixed with CNTs by varying the CNT oxidation degree enlightens the degradative routes mainly active in each case. Using highly oxidized CNTs, we observed a decrement of activation energy of the degradative process up to around 53% and the activation/suppression of different pathways based on the amount of oxygen functionalities present in the mixtures. Furthermore, the presence of oxidized CNTs modulated the solid-state reactivity of AB reducing the release of nitrogen/boron species together with hydrogen. These findings lead the way for the design of new hydrogen storage materials.