Tribochemically driven dehydrogenation of undoped sodium alanate under room temperature.

ABSTRACT

An application of mechanical energy was explored as a new non-thermal method to drive H2 emission from undoped sodium alanate at room temperature. It was found that mild rubbing of NaAlH4 pellets under vacuum led to intensive and almost instantaneous gas emission. The dominating species in the emitted gases was H2 (>99%). Traces of mono- and polyalanes, NaAlH4 vapours, CO2 and other non-identified gases were registered. H2 emission involved several first-order processes, whose characteristic time constants ranged widely from 0.6 to 465 s. None of the dehydrogenation reactions could be connected to either the thermal effect of friction or the direct coupling of mechanical forces to the energy landscape of chemical reactions. In turn, it was suggested that the tribochemical reactions can be triggered by plastic deformation and shearing. A linked diffusion-wear model of NaAlH4 triboinduced dehydrogenation, which consistently explains all empirical findings, was put forward.