Synthesis of Frameworks with Optimal Hydrogen Binding Enthalpy
Lawrence Berkeley National Laboratory (LBNL)
The realization of materials that strongly and reversibly adsorb hydrogen at ambient temperatures and moderate pressures could transform the transportation sector and vastly expand the adoption of fuel cells in other applications. It has been recognized that to maximize the deliverable H2 capacity under ambient working conditions, the enthalpy of H2 adsorption should fall within the optimal range of −15 to −25 kJ/mol.1,2 However, the majority of adsorbents studied for H2 storage exhibit binding enthalpies outside of this range, resulting in low hydrogen densities or prohibitively high regeneration energies. We recently reported the synthesis of the first metal–organic framework featuring exposed vanadium(II) sites, V2Cl2.8(btdd) (H2btdd, bis(1H-1,2,3-triazolo[4,5-b],[4′,5′-i])dibenzo[1,4]dioxin).3 These metal sites are capable of backbonding with weak π acids. Significantly, hydrogen adsorption data reveal that this material binds H2 at ambient temperatures with an enthalpy of −21 kJ/mol.4 This work demonstrates that engineering a high-density of Kubas-type vanadium(II)–dihydrogen complexation in frameworks is a suitable strategy to obtain ambient temperature adsorbents. The synthetic approach for V2Cl2.8(btdd) is being adapted to yield other vanadium(II) frameworks with an even higher density of open sites.
Online and available for use in collaboration with HyMARC.
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