Sc-Decorated Porous Graphene for High-Capacity Hydrogen Storage: First-Principles Calculations

Abstract

The generalized gradient approximation (GGA) function based on density functional theory is adopted to investigate the optimized geometrical structure, electron structure and hydrogen storage performance of Sc modified porous graphene (PG). It is found that the carbon ring center is the most stable adsorbed position for a single Sc atom on PG, and the maximum number of adsorbed H2 molecules is four with the average adsorption energy of −0.429 eV/H2. By adding a second Sc atom on the other side of the system, the hydrogen storage capacity of the system can be improved effectively. Two Sc atoms located on opposite sides of the PG carbon ring center hole is the most suitable hydrogen storage structure, and the hydrogen storage capacity reach a maximum 9.09 wt % at the average adsorption energy of −0.296 eV/H2. The adsorption of H2 molecules in the PG system is mainly attributed to orbital hybridization among H, Sc, and C atoms, and Coulomb attraction between negatively charged H2 molecules and positively charged Sc atoms.

Scandium Decoration of Boron Doped Porous Graphene for High-Capacity Hydrogen Storage

“…As shown in Table 1 on 1B/PG, adsorption sites were named 1, 2, 3, 4, 5, and 6, which represented the hole position of the C ring, C-C bridge, half C ring hole position, large hexagon hole position, C top position and B top position. Results indicated that position 1 was the most easily adsorbed position of a single Sc atom on B-PG, which was similar to the situation of the undoped-PG adsorbing Sc atom [42]. The optimized geometry is shown in Figure 2a.…”

“…Simultaneously, the B-PG plane was slightly deformed, and the adsorption energy of the Sc atom on the B-PG was −4.004 eV. In our previous study, the adsorption energy of a single Sc atom on clean PG was −2.143 eV [42], which was much smaller than that of single Sc on B-PG of −4.004 eV. It can be seen that B doping can enhance the adsorption activity of the system; compared with pure porous graphene, the Sc atom was closer to the substrate and therefore had greater binding energy on the B-doped PG.…”

“…Due to the limited space around the Sc atom and the repulsion between the adsorbed H 2 molecules, the fifth H 2 molecule moved to the upper layer after relaxation in Figure 4e. Therefore, the fifth H 2 molecule had a H-H bond length of 0.762 Å, and it had a minimum adsorption energy of −0.187 eV, which was still bigger than −0.093 eV of the Sc-PG system without B doped [42]. The bond length of the adsorbed H 2 molecule was in the range of 0.762~ 0.831 Å, and no dissociation of the H 2 molecule was found.…”

“…The positive charge of Sc in the hydrogen storage process had been increasing. After the first H 2 molecule was adsorbed by the Sc-B/PG structure, the Sc atom was charged to 1.72 e, which is greater than that of 1.56 e in the undoped B atom system [42]. It was shown that after doping the B atom, the catalytic effect of Sc atoms in hydrogen storage was more obvious.…”

Li-Decorated β12-Borophene as Potential Candidates for Hydrogen Storage: A First-Principle Study

“…The average adsorption energy of Li atom on β 12 -borophenec [ 32 ] is defined as: where , and are the total energy of the n Li- β 12 -borophene with i , i − 1 H 2 molecules and β 12 -borophene with n Li atoms, respectively. , and are the total energy of the β 12 -borophene, free Li atom and an isolated H 2 , respectively.…”