Nanoconfinement of Molecular Magnesium Borohydride Captured in a Bipyridine-Functionalized Metal–Organic Framework

Abstract

A new form of hydride nanoconfinement is demonstrated through the creation of a molecular hydride species coordinated to binding sites inside the pores of a metal-organic framework (MOF). Magnesium borohydride, which has a high hydrogen capacity, is incorporated into the pores of UiO-67bpy (Zr 6 O 4 (OH) 4 (bpydc) 6 with bpydc 2-= 2,2'-bipyridine-5,5'-dicarboxylate) by solvent impregnation. The MOF retained its long-range order, and transmission electron microscopy and elemental mapping confirmed the retention of the crystal morphology and revealed a homogeneous distribution of the hydride within the MOF host. Notably, the B, N and Mg-edge XAS data confirm the coordination of Mg(II) to the N atoms of the chelating bipyridine groups. In situ 11 B MAS-NMR studies helped elucidate the reaction mechanism and revealed that complete hydrogen release from Mg(BH 4 ) 2 occurs as low as 200 °C. Sieverts and thermogravimetric measurements indicate an increase in the rate of hydrogen release, with the onset of hydrogen desorption as low as 120 °C, which is approximately 150 °C lower than that of the bulk material. Furthermore, density functional theory calculations support the improved dehydrogenation properties and confirm the drastically lower activation energy for B-H bond dissociation.

Quantifying Species Populations in Multivalent Borohydride Electrolytes

“…Moreover, understanding the links between borohydride solvation environments and properties has high potential impact for both solid-state electrolytes and reversible hydrogen storage, areas in which borohydrides are under active investigation. [10][11][12][13] While several investigations into the liquid solvation environment of Mg(BH4)2 electrolytes have been conducted, [7][8][14][15][16][17] understanding of Ca(BH4)2 electrolyte solvation is relatively nascent. [18][19] Our recent findings underscored the importance of BH4coordination in determining speciation and delivery of the metal cation to the interface.…”

Reversing the Irreversible: Thermodynamic Stabilization of Lithium Aluminum Hydride Nanoconfined Within a Nitrogen-Doped Carbon Host

“…16 Most efforts to date have been focused on nanocon nement within nanoporous hosts to limit the hydride particle size. 16,17,[18][19][20][21][22] Carbons and carbon-based materials are by far the most common host materials, as they are lightweight and display remarkable chemical and thermal stability under conditions required to achieve reversible H 2 release. 16,17,23 Apart from utilizing the pores for maintaining nanoparticle size, recent studies by Carr et al show that the incorporation of heteroatoms in carbon affects the kinetics and desorption pathway of the hydride, making the host material an active participant in the reaction process.…”

Simulation of nanosizing effects in the decomposition of Ca(BH4)2 through atomistic thin film models

“…Analogously, it is expected that nanoconfiment through permeation into scaffolds would lead to a similar decrease of ∆H. [39][40][41] Size reduction from bulk to nanoscale is then a valuable method to tune the thermodynamics of hydrogen release from metal borohydrides 24,25 .…”