Nanostructure and Hydrogen Spillover of Bridged Metal-Organic Frameworks

Abstract

The metal-organic frameworks (MOF) with low and medium specific surface areas (SSA) were shown to be able to adsorb hydrogen via bridged spillover at room temperature (RT) up to an amount of full coverage of hydrogen in the MOF. Anomalous small-angle X-ray scattering was employed to investigate the key relationship between the structures and storage properties of the involved materials. It was found that the tunable imperfect lattice defects and the 3D pore network in the MOF crystal are the most critical structures for RT hydrogen uptake rather than the known micropores in the crystal, SSA, and Pt catalyst structure.

Hydrogen storage measurement, synthesis and characterization of metal–organic frameworks via bridged spillover

“…Based on this ratio, Pt/AC/CB/IRMOF-8 prepared here has the same enhancement factors as that observed by Yang et al [6]. Our previous study showed that the adsorption kinetics via hydrogen spillover slowed with increasing pressure [19]. For the modified HPTGA measurement achieved by extending the measurement time to reach equilibrium, the slope of the isotherm (hydrogen uptake vs. pressure) increases, providing an additional margin of enhancement.…”

“…By comparison, the conventional measurement required several hours to over 1 day to complete. Additionally, it is important to point out that our bridged samples have very slow adsorption kinetics due to the diffusion limit of atomic hydrogen at RT [19]. In the present study, equilibrium of adsorption was achieved by extending the HPTGA measurement for up to 72 h at each pressure increment in the isotherm curve.…”

“…In our previous study [19], IRMOF-8 crystals having few lattice defects but enhanced RT hydrogen uptake via spillover were prepared using a much slower cooling rate (<0.5 • C/min) than that usually used (2 • C/min). The result suggested that thermal effects have a measurable influence on the crystallographic purity of MOFs formed during the heating and cooling periods of the reaction.…”

“…The mixture was then heated to 250 • C and held at this temperature for 12 h to convert molten D-glucose into carbon as a carbon bridge (CB). Bridged MOF-5 was prepared by the same procedure [19]. Bridged MOF-5 and IRMOF-8 samples are heretofore denoted Pt/AC/CB/MOF-5 and Pt/AC/CB/IRMOF-8, respectively.…”

Volumetric distribution of Pt nanoparticles supported on mesoporous carbon substrates studied by X-ray photoelectron spectroscopy depth profiling

“…Although a powerful tool for structural analysis [14,[21][22][23][24], SAXS has one inherent limitation, namely its inability to extract small particle location. This precludes obtaining a detailed understanding of the correlation between the particle geometry and the spatial distribution of impregnated Pt in the supporting material.…”