Solid-State Hydriding Mechanism in the LiBH₄ + MgH₂ System

Abstract

The LiBH4 + MgH2 system has great potential in reversible hydrogen storage for fuel cell vehicles. However, it has always been dehydrogenated and rehydrogenated in the liquid state until recently. The solid-state hydriding and dehydriding are necessary in order to achieve hydrogen uptake and release near ambient temperature. In this study, the solid-state hydriding mechanism of 2LiH + MgB2 mixtures has been investigated. It is found that the solid-state hydriding proceeds in two elementary steps. The first step is the ion exchange between the Mg2+ and Li+ ions in the MgB2 crystal to form an intermediate compound (Mg1−x Li2x )B2. The second step is the continuous ion exchange and simultaneous hydrogenation of (Mg1−x Li2x )B2 to form LiBH4 and MgH2. This finding is consistent with the observed diffusion-controlled hydriding kinetics.

Coupling Solid-State NMR with GIPAW ab Initio Calculations in Metal Hydrides and Borohydrides

“…From a comparison of calculated values with 6 Li experimental results 49 on LiH and LiBH 4 , it turned out that accurate results can be obtained with Quantum-ESPRESSO, by using both our PAW PP and the GIPAW standard ones. However, while our PP tend to underestimate the 6 Li chemical shift of LiBH 4 of 0.3 ppm, the GIPAW standards provided a value which is higher than the experimental one of the same quantity.…”

Ab Initio Computational Studies of Mg Vacancy Diffusion in Doped MgB2 Aimed at Hydriding Kinetics Enhancement of the LiBH4 + MgH2 System

“…27 The phenomenological analysis of the hydriding kinetics unveils that both reduction in the particle and crystallite sizes and increase in the structural defects contribute to the enhancement in the diffusion-controlled hydriding reaction. 27 The detailed nuclear magnetic resonance (NMR) analysis [28][29][30] indicates that the diffusion-controlled hydrogenation is related to the formation of a ternary compound, (Mg 1-x Li 2x )B 2 where x is a variable changing from 0 (for MgB 2 ) to less than 1, during hydrogenation. Diffusion arises because of the Li-Mg ion exchange to form the ternary diboride, (Mg 1-x Li 2x )B 2 , which facilitates the subsequent formation of LiBH 4 as hydrogenation proceeds.…”

“…The studies mentioned above [27][28][29][30] unequivocally show that further reduction in the hydriding temperature of the LiBH 4 + MgH 2 system can be achieved by (i) reducing particle sizes to minimize the diffusion distance, (ii) increasing diffusion coefficients via doping in MgB 2 , and (iii) enhancing diffusion * To whom correspondence should be addressed. E-mail: leon.shaw@ uconn.edu.…”

Improved reversible dehydrogenation of 2LiBH4+MgH2 system by introducing Ni nanoparticles

“…Clearly, the typical features of the [BH 4 ] group can be observed in the spectrum for the as-prepared sample, where the B-H bending vibration (;1125 cm À1 ) and B-H stretching vibration (2221, 2296, and 2380 cm À1 ) were detected. 37,41 After dehydrogenation, the peaks corresponding to B-H bond have almost disappeared, in addition, a characterized vibration signal corresponding to boron can be detected in the infrared spectrum. 34 It indicates that the addition of 0.5Ni to the MgH 2 + 2LiBH 4 material is still not enough to fully transmit the B element to Mg-Ni-B ternary alloy.…”