The search of new materials having suitable characteristics to trap hydrogen for fuel applications is greatly challenging due to the stringent requirements that such materials must meet. In this sense, with the aid of computational chemistry, significant advances can be achieved. The present work explores the adsorption of hydrogen molecules by lithium clusters (Lin, where n = 1-6) coordinated to a graphitic carbon nitride (heptazine, gC3N4) cavity. The study was conducted using the density functional theory (M06-2X-D3) in combination with the def2-TZVP basis set. Our results suggest that lithium atoms in the gC3N4-cavity can coordinate up to 10 hydrogen molecules with bond energies in the range -0.10 to -0.19 eV. The [gC3N4Li5]+ and [gC3N4Li6] systems resulted to be the most promising in terms of lithium coordination. They feature the highest stabilization energies for hydrogen adsorption. According to the calculated Gibbs free energies for these systems, H2 adsorption remains a spontaneous process even at 400 K.
Keywords: Gibbs free energy; Graphitic carbon nitride; Hydrogen storage; Lithium cluster; NBO.
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