Exceptional hydrogen storage achieved by screening nearly half a million metal-organic frameworks

Abstract

Few hydrogen adsorbents balance high usable volumetric and gravimetric capacities. Although metal-organic frameworks (MOFs) have recently demonstrated progress in closing this gap, the large number of MOFs has hindered the identification of optimal materials. Here, a systematic assessment of published databases of real and hypothetical MOFs is presented. Nearly 500,000 compounds were screened computationally, and the most promising were assessed experimentally. Three MOFs with capacities surpassing that of IRMOF-20, the record-holder for balanced hydrogen capacity, are demonstrated: SNU-70, UMCM-9, and PCN-610/NU-100. Analysis of trends reveals the existence of a volumetric ceiling at ∼40 g H₂ L^-1. Surpassing this ceiling is proposed as a new capacity target for hydrogen adsorbents. Counter to earlier studies of total hydrogen uptake in MOFs, usable capacities in the highest-capacity materials are negatively correlated with density and volumetric surface area. Instead, capacity is maximized by increasing gravimetric surface area and porosity. This suggests that property/performance trends for total capacities may not translate to usable capacities.

Fig. 1

High-throughput screening of MOFs. a Calculated usable hydrogen capacities of 43,777 MOFs compared to the measured capacity of IRMOF-20 (5.7 wt.%, 33.4 g-H₂ L⁻¹) and MOF-5 (4.5 wt.% and 31.1 g-H₂ L⁻¹). b Relative number of MOFs as a function of usable volumetric capacity and their originating database

Fig. 2

Crystal structures of MOFs whose hydrogen uptake was assessed experimentally following their identification by computational screening. a PCN-610/NU-100, b SNU-70, c ZELROZ, and d UMCM-9 (C: gray, H: white, O: red, Cu: orange and Zn: blue)

Fig. 3

H₂ adsorption isotherms. Measured total (a) volumetric and (b) gravimetric H₂ adsorption isotherms of NU-100, SNU-70, and UMCM-9 at 77 K. For comparison, isotherms (ref. ) for the two benchmark MOFs, MOF-5 and IRMOF-20, are also shown. Inset plots illustrate capacities at low pressure

Fig. 4

Measured usable H₂ storage capacities of MOFs. a Volumetric basis and b gravimetric basis. Capacities are reported for an isothermal pressure swing at 77 K between 5 and 100 bar. Data for MOF-5 and IRMOF-20 are taken from ref. . Percentages listed at the top of each bar correspond to improvements over MOF-5

Fig. 5

Relationship between five crystallographic properties and the usable capacities of the highest-capacity MOFs examined in the present study. Capacities are evaluated assuming an isothermal pressure swing between 5 and 100 bar at 77 K. (a, c, e, g, i) usable gravimetric capacities, (b, d, f, h, j) usable volumetric capacities

Fig. 6

Usable capacities of 43,777 MOFs as a function of five crystallographic properties, assuming pressure-swing operation between 100 and 5 bar at 77 K. (a, c, e, g, i) gravimetric capacities, (b, d, f, h, j) volumetric capacities

Fig. 7

Comparison of measured usable H₂ storage capacities of MOFs assuming temperature + pressure-swing operation between 100 bar-77 K and 5 bar-160 K. a Volumetric capacity, and b gravimetric capacity. Grey bars depict the performance of compounds reported in the present study or in the authors’ earlier report. Black bars depict the performance of two high-capacity MOFs reported in ref. . Percentages on top of each bar depict performance relative to MOF-5