Paraelastic and Paraelectric Phenomena in Crystals

Record High Hydrogen Storage Capacity in the Metal–Organic Framework Ni2(m-dobdc) at Near-Ambient Temperatures

“…These first four adsorption sites were previously observed in neutron diffraction experiments carried out on Co 2 (m-dobdc) at 4 K and pressures below 1 bar. 39 Adsorption sites 5-7, which become occupied only at the higher D 2 pressures measured here, could likely have been located in the previous study if higher dosings were used. Sites 5 and 6 lie at the center of the hexagonal channels of the framework, while site 7 resides 3.10(3) Å from the D 2 located at site 5 and primarily relies on D 2 •••D 2 interactions for stabilization.…”

“…The compounds M 2 (m-dobdc) (M = Co, Ni) were synthesized and activated according to modified versions of the large-scale literature procedure. 39 Synthesis of H 4 (m-dobdc).…”

“…Structural characterization and low-pressure H 2 adsorption isotherms of Co 2 (m-dobdc), Ni 2 (m-dobdc), Co 2 (dobdc), Ni 2 (dobdc), and MOF-5 have been reported previously. 20,37,39,43 In this study, the high-pressure H 2 adsorption isotherms of these 5 materials were measured between 0 and 100 bar at temperatures of −75, −50, −40, −25, 0, 25, 50, 75, and 100 °C. Increments of 25 °C were chosen to provide a wide range of conditions for considering temperature swings when determining the volumetric usable capacity of these materials; −40 °C was also measured because it is the temperature at which hydrogen is stored at and dispensed from fueling stations.…”

“…Additionally, D 2 and H 2 have previously been shown to behave nearly identically in powder neutron diffraction experiments. 39 Samples were measured at 198 K at pressures of 36, 54, and 79 bar, as well as at 77 K at a pressure of 78 bar to most closely simulate the adsorption isotherm conditions while retaining the ability to crystallographically locate each D 2 binding site within the pores.…”

“…33 The most promising metal-organic framework identified to date for H 2 storage is Ni 2 (mdobdc) (m-dobdc 4− = 4,6-dioxido-1,3-benzenedicarboxylate), which was shown previously to display an H 2 binding enthalpy of −13.7 kJ/mol, as measured by variable-temperature infrared spectroscopy and representing the largest value yet observed in a MOF by this method. 39 Ni 2 (m-dobdc) is a structural isomer of Ni 2 (dobdc) (dobdc 4− = 2,5-dioxido-1,4benzenedicarboxylate; Ni-MOF-74), and its record binding enthalpy is largely a result of a higher charge density at its coordinatively unsaturated Ni 2+ centers. These sites strongly polarize H 2 , providing the primary binding sites for H 2 within the pores of the material and leading to a high gravimetric storage capacity of greater than 11 mmol/g (2.2 wt %) at 77 K and 1 bar.…”