A quest to high-capacity hydrogen storage in zirconium decorated pentagraphene: DFT perspectives

Abstract

The main crisis that impedes the way to successful hydrogen generation for energy purposes is the paucity of efficient hydrogen storage materials. Using First Principles calculations, we predict that zirconium atom adorned on the surface of an advanced carbon allotrope; penta graphene can attach 11 molecular hydrogens as a maximum, having average adsorption energy of −0.42 eV. This gives gravimetric hydrogen uptake of 14.8 wt%, far more than the Department of Energy's requirement of 5.5 wt%. Due to electron transfer from the 3d orbitals of zirconium to 2p orbital of carbon atom of pentagraphene, Zr is tightly linked to it, with a strong adsorption energy of −3.41 eV. The adsorption of hydrogen molecules on Zr is because of Kubas type of interactions involving electron transfer from Zr 3d orbital to hydrogen 1s orbital and subsequently, back donation from H 1s to Zr 3d orbital providing suitable adsorption energy for fuel cell applications which is higher than physisorption but lower than chemisorption energy. The stability of the structure (Zr-decorated pentagraphene) has been verified through Molecular Dynamics Simulations at 300 K and metal-metal clustering is prevented by the substantial energy barrier for the movement of Zr atom on pentagraphene. As the system is stable, adsorption energy of H2 molecules is in the desired range (0.2–0.7 certified by DoE), wt% of H2 is more than DoE's prescription, we infer from our DFT results that Zr-decorated pentagraphene may be a promising reversible high-capacity hydrogen storage material.