Hydrogen adsorption and storage of Ca-decorated graphene with topological defects: A first-principles study

•Ca-decorated graphene with experimentally realizable vacancy defects was studied.•Ca atom can be stabilized on graphene with vacancy defects.•Up to six H2 molecules can stably bind to a Ca atom on defective graphene.•Double-side Ca-decorated defective graphene can absorb up to 5.2 wt% hydrogen.

As a candidate for hydrogen storage medium, geometric stability and hydrogen capacity of Ca-decorated graphene with topological defects are investigated using the first-principle based on density functional theory (DFT), specifically for the experimentally realizable single carbon vacancy (SV), 585 double carbon vacancy (585 DCV) and 555–777 double carbon vacancy (555–777 DCV) defects. It is found that Ca atom can be stabilized on above defective graphenes since Ca׳s binding energy on vacancy defect is much larger than its cohesive energy. Up to six H2 molecules can stably bind to a Ca atom on defective graphene with the average adsorption energies of 0.17–0.39 eV/H2. The hybridization of the Ca-3d orbitals with H2-σorbitals and the electrostatic interaction between the Ca cation and the induced H2 dipole both contribute to the H2 molecules binding. Double-side Ca-decorated graphene with 585 DCV and 555–777 DCV defects can theoretically reach a gravimetric capacity of 5.2 wt% hydrogen, indicating that Ca-decorated defective graphene can be used as a promising material for high density hydrogen storage.

Graphical abstractThe optimized atomic geometries for Ca-decorated pristine (a), SV (b), 585 DCV (c) and 555–777 DCV (d) defects graphene with their maximum H2 capacity; and Ca adsorbed on both sides of 585 DCV (e) and 555–777 DCV (f) defects graphene at their maximum H2 capacity. Green, blue and white balls represent the carbon, calcium and hydrogen atoms, respectively.Figure optionsDownload full-size imageDownload as PowerPoint slide