Elisa Gil Bardaji

Altered reaction pathways of eutectic LiBH4–Mg(BH4)2 by nanoconfinement

The effects of nanoconfinement on the dehydrogenation rate and reaction pathways of the eutectic LiBH4–Mg(BH4)2 have been comprehensively investigated. By means of thermal analysis, mass spectroscopy and solid state 11B MAS NMR, it has been revealed that the multistep thermal decomposition pattern of the binary LiBH4–Mg(BH4)2 has been altered in a two-step reaction and the desorption kinetics has also been significantly improved after infiltration. The formation of diborane and stable MnB12H12 intermediates of the bulk LiBH4–Mg(BH4)2 has been found to be inhibited by nanoconfinement.

High Resolution Raman and Neutron Investigation of Mg(BH4)2 in an Extensive Temperature Range

Raman spectra of Mg(BH(4))(2) have been measured in an extensive temperature range, from 15 to 473 K. Taking into account the high temperature conversion from the alpha to the beta phase, we have observed evident signatures of this phase transition and determined the Raman vibrational spectrum of each phase. The neutron scattering spectra of the beta phase sample were also recorded. The present experimental results have been compared to the density functional theory calculations available in the literature, and a substantial agreement has been found.

The crystal structure of the first borohydride borate, Ca3(BD4)(3)(BO3)

The previously observed intermediate from thermal decomposition of Ca(BH4)2 has been identified as a calcium borohydride borate with composition Ca3(11BD4)3(11BO3), synthesized from a double-isotope substituted sample Ca(11BD4)2. The crystal structure was determined on the basis of Synchrotron Radiation Powder X-ray Diffraction, supported by infrared spectroscopy measurements. The stability of the structure at ambient conditions is confirmed by Density Functional Theory calculations. Ca3(11BH4)3(11BO3) is the first example of a product from a borohydride oxidation containing both B–H(D) and B–O bonds and represents a novel category of compounds, being completely different from the hydroxoborate products upon borohydride hydrolysis. The result represents hence an important contribution to fundamental boron chemistry.

Influence of nanoconfinement on morphology and dehydrogenation of the Li11BD4–Mg(11BD4)2 system

The decomposition of a nanoconfined mixture of lithium-magnesium borohydride, Li(11)BD(4)-Mg((11)BD(4))(2), has been investigated and compared to the corresponding mixture in the bulk form. The systems were investigated by thermal analysis, small-angle neutron scattering, (11)B nuclear magnetic resonance and transmission electron microscopy. The dehydrogenation temperatures decreased by up to 60 °C in the nanoconfined system, with gas evolution following different steps, compared to the behaviour of the bulk material under the same conditions. Most importantly, desorption from the nanoconfined hydride proceeds without formation of diborane, B(2)D(6), which evolves from the bulk mixture. From small-angle neutron scattering, differences in morphology between the bulk and the nanoconfined systems are also demonstrated. Evidence of a complete decomposition has been found in the nanoconfined system, after heating up to 460 °C. Furthermore, (11)B NMR data show that nanoconfinement inhibits the formation of dodecaborane, [B(12)D(12)](2-), during decomposition, a result which is important for practical applications of borohydrides.