Effect of boron substitution on hydrogen storage in Ca/DCV graphene: A first-principle study

By using density functional calculations, the effects of boron are investigated in the new hydrogen storage systems, which are formed by substituting different numbers of boron atoms to the first (BDDCV-F) and the second (BDDCV-S) neighbor of double carbon-vacancy (DCV). The layered host systems of boron-substituted DCV graphene are decorated with Ca metal to increase the number of adsorbed H-2 molecules. Storing of H-2 applications are performed by using two coordinate algorithms as CLICH (Cap-Like Initial Conditions for Hydrogens) and RICH (Rotational Initial Conditions for Hydrogens). The adsorption properties of (1-14) H-2 molecules on the constructed systems are examined. The results for BDDCV-F and BDDCV-S boron-doped systems are compared with each other and those of the pure-DCV graphene. To compare the stabilities of BDDCV-systems, the formation energies are calculated. It is concluded from Mulliken charge analysis, the partial density of states and electron density differences that boron substitution process to different locations of the DCV graphene plays a crucial role on the charge transfer between Ca atom the layered host system, ionic nature and the binding properties of the systems. The herringbone-like anisotropic electron density is transformed to isotropic density with the substitution of the boron atoms. Then, the electric field, which is induced by ionic interactions and governs H-2 adsorption processes, is changed and intensified along with the sheet. In this way, it can be achieved more effective H-2 adsorption. It is seen from the adsorption energies of single- and double-side Ca-decorated systems that the processes of boron-substitution and Ca-decoration can considerably improve the hydrogen storage capability of pure-DCV graphene system, thus (8 and 10)H-2 can be adsorbed per Ca-atom in these-type systems. The high gravimetric density of 5.80% is calculated, although larger cell and empty surface states. Moreover, the average desorption temperatures are calculated by using van't Hoff equation, and it is seen that the DCV including boron-substituted systems have closer desorption temperatures to the room temperature than pure-DCV. To check the H-2 desorption of the systems, molecular dynamics simulations are performed at 200 K and 300 K temperatures. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.