Ambient-Temperature Hydrogen Storage via Vanadium(II)-Dihydrogen Complexation in a Metal–Organic Framework

Abstract

The widespread implementation of H2 as a fuel is currently hindered by the high pressures or cryogenic temperatures required to achieve reasonable storage densities. In contrast, the realization of materials that strongly and reversibly adsorb hydrogen at ambient temperatures and moderate pressures could transform the transportation sector and expand adoption of fuel cells in other applications. To date, however, no adsorbent has been identified that exhibits a binding enthalpy within the optimal range of −15 to −25 kJ/mol for ambient-temperature hydrogen storage. Here, we report the hydrogen adsorption properties of the metal-organic framework (MOF) V2Cl2.8(btdd) (H2btdd, bis(1H-1,2,3-triazolo[4,5b],[4′,5′-i])dibenzo [1,4]dioxin), which features exposed vanadium(II) sites capable of backbonding with weak π acids. Significantly, gas adsorption data reveal that this material binds H2 with an enthalpy of −21 kJ/mol. This binding energy enables usable hydrogen capacities that exceed that of compressed storage under the same operating conditions. The Kubas-type vanadium(II)-dihydrogen complexation is characterized by a combination of techniques. From powder neutron diffraction data, a V-D2(centroid) distance of 1.966(8) Å is obtained, the shortest yet reported for a MOF. Using in situ infrared spectroscopy, the vibration of the vanadium-bound H2 is identified, and it displays a red shift of 242 cm −1 relative to free H2. Electronic structure calculations show that a main contribution to bonding stems from the interaction between the vanadium dπ and H2 σ* orbital. Ultimately, the pursuit of MOFs containing high densities of weakly π-basic metal sites may enable storage capacities under ambient conditions that far surpass those accessible with compressed gas storage.

Densified HKUST-1 Monoliths as a Route to High Volumetric and Gravimetric Hydrogen Storage Capacity

“…This usable capacity represents the highest H2 volumetric usable capacity achieved to date for a densified adsorbent operating in this temperature range. Although these values are comparable to the current theoretical benchmarks (Ni2(dobdc), MOF-5 and V2Cl2.8(btdd)) (10,49) under these conditions (Table S21), it is important to highlight that these previous values are based on theoretical crystal densities and not experimental envelope densities, as reported here for monoHKUST-1. A natural assumption is to expect a ca.…”

Recent Progress Using Solid-State Materials for Hydrogen Storage: A Short Review

“…Metal-organic frameworks (MOFs), which have a microporous crystalline structure comprising metal ions or clusters, are connected via molecular bridges [66][67][68]. MOFs have good stability, high void volumes, well-defined tailorable cavities of uniform size, high surface areas, and adjustable pore sizes [69][70][71]. In particular, the design flexibility for tuning the porosity of MOFs has attracted attention for their usage as hydrogen adsorbents [72].…”

Support effects of metal–organic frameworks in heterogeneous catalysis

“…Metal–organic frameworks (MOFs) have emerged as a new class of crystalline porous materials; because of their unique features such as high materials variety and designable pores, they are considered for use in various applications such as separation, 1,2 storage, 3,4 delivery, 5,6 and electrolytes. 7–9 MOFs are organic–inorganic hybrid materials and thus have both organic and inorganic characters.…”