Probing the unusual anion mobility of LiBH4 confined in highly ordered nanoporous carbon frameworks via solid state NMR and quasielastic neutron scattering

Abstract

Particle size and particle-framework interactions have profound effects on the kinetics, reaction pathways, and even thermodynamics of complex hydrides incorporated in frameworks possessing nanoscale features. Tuning these properties may hold the key to the utilization of complex hydrides in practical applications for hydrogen storage. Using carefully synthesized, highly-ordered, nanoporous carbons (NPCs), we have previously shown quantitative differences in the kinetics and reaction pathways of LiBH 4 when incorporated into the frameworks. In this paper, we probe the anion mobility of LiBH 4 confined in NPC frameworks by a combination of solid state NMR and quasielastic neutron scattering (QENS) and present some new insights into the nanoconfinement effect. NMR and QENS spectra of

Confined LiBH4–LiAlH4 in nanopores of activated carbon nanofibers

“…7). The sharp resonance of LiBH 4 at À38.2 ppm could be attributed to highly mobile BH 4 À species due to nanoconfinement in nanoporous hosts as previous reports [47,48]. For the resonance of LiBH 4 at À42.7 ppm, with respect to the bulk LiBH 4 a small decrease in chemical shift of 1e2 ppm and an increase in line broadening are explained by large anisotropic magnetic susceptibility of carbon materials (ACNF in our studies), corresponding to other nanoconfined hydrides in carbon hosts [35,48,49].…”

Ultrasmall MgH2 Nanoparticles Embedded in an Ordered Microporous Carbon Exhibiting Rapid Hydrogen Sorption Kinetics

“…The latter assumption was recently proposed to explain the enhanced anion mobility of ∼4 nm LiBH 4 confined in a porous carbon scaffold. 35 However, it is yet to be further explored which hypothesis can better account for the two desorption peaks noticed in the TDS and HP-DSC curves from the 15MgH 2 @ CT composite. A similar description may be applied for the other composites.…”

Tuning LiBH4 for Hydrogen Storage: Destabilization, Additive, and Nanoconfinement Approaches

“…They attributed some effects to LiBH 4 remaining outside of the matrix, but DSC of their material might indicate some discrepancies (mostly the absence of melting peak from bulk). Later, they highlighted the gradient of ion mobility within the pore of small and controlled size [124]. More recently, this broadness of hydrogen release temperature was attributed to the core/shell structure of LiBH 4 nanoparticles [109,133].…”

“…Verkuijlen et al compared C versus Si matrices and varied the weight loading of hydrides. Liu et al combined NMR and QENS studies on LiBH 4 confined within 4 nm pores to demonstrate that the ions are more mobile next to the interface than in the core, even for such small pores [124]. These contributions are paralleled only by simulations studies when it comes to an understanding of the mechanism underlying the effects of nanoconfinement [110,115].…”