▎ 摘　　要

There is plenty of graphene based Hydrogen storage technologies and studies still few questions like 'what kind of interaction present between Metal-Metal, Metal-Graphene, Metal-Hydrogen and Graphene-Metal and a possible way of controlling it to enhance H-2 adsorption' are not revealed properly. Similarly, the chosen metal atoms Pd, Pt and Ni are widely reported as a promising catalyst yet there is no conclusive evidence to show the best among three atoms. Thus, in this present work 5-8-5 and 55-77 defected graphene is decorated with the Pd, Pt and Ni metal atoms to adsorb Hydrogen molecules. The obtained results have shown that the better adsorption of H-2 molecule depends on Metal-Metal and Metal-Graphene interaction. Similarly, the adhesive force between Pt and 5-8-5/55-77 sheets are slightly higher than the Pd and Ni atoms. Pd-Pd (-0.47 eV) and Pt-Pt (-1.99 eV) interaction values on the surface of 5-8-5 sheets are slightly lesser in magnitude than the Pd-C (-1.14 eV, -1.19 eV) and Pt-C (-2.42 eV, -2.55 eV) interactions. The topological analysis results exhibit the partially covalent nature of interaction and it confirms that the adhesive force between Metal-Graphene is higher than the cohesive force between Metal Metal on 5-8-5 and 55-77 sheets. The electrophilicity results of Pd, Pt and Ni decorated sheets show that the two Pt decorated 5-8-5 sheet has higher electrophilicity value of 16.782 eV which is considerably higher than other sheets and this particular 5-8-5-Pt-2 system has higher H-2 adsorption energy value of -1.696 eV. The overall pattern of H-2 adsorption on chosen three metals are Pt > Ni > Pd and our results show that both strong Metal-Metal and Metal-Graphene interactions lead to poor adsorption activity. The metals are strongly polarizing the H-2 molecules which lead to good adsorption. Further, the results confirm that the pi orbitals of Metal and Graphene play a major role in the adsorption of excessive H-2 molecules. In order to enhance and control the H-2 adsorption energy, a positive electric field is applied to the system. This applied electric field enhances the polarization which leads to H-H bond elongation and strong adsorption. From the obtained results, it is conclusive that the 5-8-5-Pt system has shown good response for the supplied electric field with the maximum adsorption energy value of -5.23 eV. Comparatively, the 5-8-5 systems are responding well for the applied electric field by increasing the adsorption energy than 55-77 systems. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.