Optimization of the Pore Structures of MOFs for Record High Hydrogen Volumetric Working Capacity

Abstract

Metal–organic frameworks (MOFs) are promising materials for onboard hydrogen storage thanks to the tunable pore size, pore volume, and pore geometry. In consideration of pore structures, the correlation between the pore volume and hydrogen storage capacity is examined and two empirical equations are rationalized to predict the hydrogen storage capacity of MOFs with different pore geometries. The total hydrogen adsorption under 100 bar and 77 K is predicted as ntot= 0.085× Vp − 0.013× Vp2 for cage‐type MOFs and ntot= 0.076× Vp − 0.011× Vp2 for channel‐type MOFs, where Vp is the pore volume of corresponding MOFs. The predictions by these empirical equations are validated by several MOFs with an average deviation of 5.4%. Compared with a previous equation for activated carbon materials, the empirical equations demonstrate superior accuracy especially for MOFs with high surface area (i.e., SBET over ≈3000 m2 g−1). Guided by these empirical equations, a highly porous Zr‐MOF NPF‐200 (NPF: Nebraska Porous Framework) is examined to possess outstanding hydrogen total adsorption capacity (65.7 mmol g−1) at 77 K and record high volumetric working capacity of 37.2 g L−1 between 100 and 5 bar at 77 K.

Recent advances in process engineering and upcoming applications of metal–organic frameworks

“…The DOE targets are 4.5 wt% (gravimetric working capacity) and 30 g L −1 (volumetric working capacity) by 2020. Some MOFs satisfy the DOE gravimetric target so far [60] .…”

Hydrogen technologies for energy storage: A perspective

“…45 To increase adsorbed hydrogen density, efforts have focused on optimizing pore dimensions and total pore volume of porous materials, aided by computational efforts that can screen databases of model MOF structures. [46][47][48] Research has also been carried out on more efficient packing of adsorbent materials within the storage vessel to minimize free space. These efforts have included engineering crystal geometrics, investigating compaction methods, and developing nearcrystal-density monoliths.…”

Recent advancement in consolidation of MOFs as absorbents for hydrogen storage

“…However, high compression pressure of MOFs resulted in pellet with narrow pore apertures which yielded low volumetric and gravimetric H 2 useable capacities. 141,142 Recently, Chen et al 143 reported BET surface area of 7310 m 2 g −1 and volumetric BET surface area of 2060 m 2 cm −3 for NU-1501-Al. High gravimetric and volumetric storage capacities of 14.0 wt% and 46.2 g/L respectively were obtained under temperature and pressure swing of 77K/100 bar to 160K/5 bar.…”