The Synthesis and Design of Metal-Organic Framework as Hydrogen Storage Material

Abstract

As hydrogen has 3 times higher energy density than gasoline, storing hydrogen is important in vehicles these days. Although the hydrogen storage system car has already been commercialized, the capability of storing hydrogen under safe and cost-efficient temperatures and pressures is still challenging. Those conditions mean creating ambient temperature and low pressure with a gravimetric capacity of over 5.5 wt% and a volumetric capacity of over 40 g/L. Metal-organic framework (MOF) is known as a good candidate for efficient hydrogen storage material because of its high surface area and reversible hydrogen recharging kinetics. Among the MOFs, the Zn-MOF-5 has been computationally and experimentally proven as a good hydrogen storage material and was synthesized by a new method for hydrogen storage. The first synthetic strategy is the cation-exchange Zn atom of Zn-MOF-5 to light metal Mg and V, which leads to high gravimetric capacity. Especially, V is well known Kubas-type hydrogen storage metal that exerts high uptake in ambient temperature. Also, in order to improve the volumetric capacity, the last synthetic strategy is gel-like synthesis. This synthesis method makes less void per unit volume than crystalline analog MOF, then makes high packing density and high volumetric capacity. The synthesized Zn-MOF-5 store hydrogen under the swing conditions of 77 K and 50 bar as adsorption to 160 K and 5 bar as desorption, the gravimetric capacity of 6.00 wt% and volumetric capacity of 39.1 g/L. Reducing the adsorption pressure from 100 bar to 50 bar is a cost-benefit performance in a practical hydrogen storage tank system. In addition, the synthesized Mg-MOF-5 a new MOF never been reported, under 77 K and 48 bar as adsorption to 160 K and 5 bar as desorption shows a high-performance gravimetric capacity of 5.41 wt%. Especially, the V-MOF-5 shows the second ranking among ambient targets MOFs in gravimetric uptake compared to surface area. Therefore, the gel-like synthesis method shows early hydrogen saturation uptake at lower pressure, and lowering pressure is cost-efficient for an industrial hydrogen tank. Also, the cation-exchange method shows great enhancement of gravimetric capacity uptake. These synthetic strategies allow for designing cost-efficient and safe hydrogen storage material.