Tribochemically driven dehydrogenation of undoped sodium alanate under room temperature.

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.

Optoelectronic generation of bio-aqueous femto-droplets based on the bulk photovoltaic effect.

The generation and manipulation of small aqueous droplets is an important issue for nano- and biotechnology, particularly, when using microfluidic devices. The production of very small droplets has been frequently carried out by applying intense local electric fields to the fluid, which requires power supplies and metallic electrodes. This procedure complicates the device and reduces its versatility. In this work, we present a novel and flexible, to the best of our knowledge, electrodeless optoelectronic method for the production of tiny droplets of biologically friendly aqueous fluids. Our method takes advantage of the photoinduced electric fields generated by the bulk photovoltaic effect in iron-doped lithium niobate crystals. Two substrate configurations, presenting the polar ferroelectric axis either parallel or perpendicular to the active surface, have been successfully tested. In both crystal geometries, small droplets on the femtoliter scale have been obtained, although with a different spatial distributions correlated with the symmetry of the photovoltaic fields. The overall results demonstrate the effectiveness of the optoelectronic method to produce femtoliter droplets, both with pure water and with aqueous solutions containing biological material.

Unconventional Approaches to Hydrogen Sorption Reactions: Non-Thermal and Non-Straightforward Thermally Driven Methods.

In the last decades, a broad family of hydrides have attracted attention as prospective hydrogen storage materials of very high gravimetric and volumetric capacity, fast H2 -sorption kinetics, environmental friendliness and economical affordability. However, constraints due to their high activation energies of the different H2 -sorption steps and the Gibbs energy of their reaction with H2 has led to the need of high thermal energy to drive H2 uptake and release. High heat leads to significant degradation effects (recrystallization, phase segregation, nanoparticles agglomeration…) of the hydrides. In this context, this short review aims to summarize alternative non-thermal methods and non-straightforward thermally driven methods to overcome the previous constraints. The phenomenology lying behind these methods, i. e. tribological activation, sonication, and electromagnetic radiation, and the effect of these processes on hydrogen sorption properties of hydrides are described. These non-usual approaches could boost the capability of the next generation of solid-hydride materials for hydrogen conversion in energy sector, in mobile devices and as hydrogen reservoirs.