Hydride-Induced Amplification of Performance and Binding Enthalpies in Chromium Hydrazide Gels for Kubas-Type Hydrogen Storage

Abstract

Hydrogen is the ideal fuel because it contains the most energy per gram of any chemical substance and forms water as the only byproduct of consumption. However, storage still remains a formidable challenge because of the thermodynamic and kinetic issues encountered when binding hydrogen to a carrier. In this study, we demonstrate how the principal binding sites in a new class of hydrogen storage materials based on the Kubas interaction can be tuned by variation of the coordination sphere about the metal to dramatically increase the binding enthalpies and performance, while also avoiding the shortcomings of hydrides and physisorpion materials, which have dominated most research to date. This was accomplished through hydrogenation of chromium alkyl hydrazide gels, synthesized from bis(trimethylsilylmethyl) chromium and hydrazine, to form materials with low-coordinate Cr hydride centers as the principal H(2) binding sites, thus exploiting the fact that metal hydrides form stronger Kubas interactions than the corresponding metal alkyls. This led to up to a 6-fold increase in storage capacity at room temperature. The material with the highest capacity has an excess reversible storage of 3.23 wt % at 298 K and 170 bar without saturation, corresponding to 40.8 kg H(2)/m(3), comparable to the 2015 DOE system goal for volumetric density (40 kg/m(3)) at a safe operating pressure. These materials possess linear isotherms and enthalpies that rise on coverage, retain up to 100% of their adsorption capacities on warming from 77 to 298 K, and have no kinetic barrier to adsorption or desorption. In a practical system, these materials would use pressure instead of temperature as a toggle and can thus be used in compressed gas tanks, currently employed in the majority of hydrogen test vehicles, to dramatically increase the amount of hydrogen stored, and therefore range of any vehicle.

Comprehensive review on synthesis and adsorption behaviors of graphene-based materials

“…Thus, by use gen molecules are basically non-polar, but the strong interaction of the metal particles leads to the dipole inducing effects of the hydrogen molecules. The third group and any remaining hydrogen molecules are adsorbed by the same mechanism of high gas pressure, but this equilibrium can be broken when the interaction of oxidized graphite surfaces and dipole-induced hydrogen molecules is stronger than metal-hydrogen interactions [98][99][100][101][102]. This mechanism can be applied only under higher pressure, and when graphite supports are charged strong electron acceptors.…”

Room Temperature Hydrogen Physisorption on Exposed Metals in A Highly Cross‐Linked Organo‐Iron Complex

“…[6][7][8] Considerably high hydrogen uptake at room temperature was reported in several materials of this class. [6][7][8] Classthree compounds invoke electrostatic interactions stronger than the van der Waals force to induce polarization of adsorbed hydrogen molecules at room temperature. [ 9 ] The adsorption relies on strong cations [ 10 ] or anions [ 11 ] as the active sites in the host compounds.…”

“…[ 13 ] We note here that the surface area of class two materials is in general substantially smaller than that of class-one and class-three compounds with metal hydrazide gel materials as a typical example. [ 7,8 ] The highest hydrogen capacity of the class-three materials reported to date is 1.01 wt% at room temperature and 90 atm, in spite of the large surface area up to 5109 m 2 g −1 , likely attributed to the limited access of the active metal sites available to H 2 molecules. [ 14 ] Clearly, an appropriate porosity and abundant adsorption sites are two essential attributes required to induce strong physisorption at a near ambient temperature.…”

“…[ 3,5 ] Class-two materials contain active sites for hydrogen adsorption in the form of under-coordinated metal elements in organometallic complexes. [6][7][8] In these materials, the Kubas type bonding dictates the host-H 2 interaction through the overlapping between the H 2 -σ orbital and an empty orbital of the metal (forward donation), and/or between the H 2 -σ* orbital and an occupied orbital of the metal (back donation). [6][7][8] Considerably high hydrogen uptake at room temperature was reported in several materials of this class.…”

“…[6][7][8] In these materials, the Kubas type bonding dictates the host-H 2 interaction through the overlapping between the H 2 -σ orbital and an empty orbital of the metal (forward donation), and/or between the H 2 -σ* orbital and an occupied orbital of the metal (back donation). [6][7][8] Considerably high hydrogen uptake at room temperature was reported in several materials of this class. [6][7][8] Classthree compounds invoke electrostatic interactions stronger than the van der Waals force to induce polarization of adsorbed hydrogen molecules at room temperature.…”