Hydrogen adsorption and storage on palladium-decorated graphene with boron dopants and vacancy defects: A first-principles study

• Pd atom can be stabilized on graphene with SV and 585 DCV defects.
• Pd-decorated B-doped, SV and 555-777 DCV defect graphene can bind three H2 molecules.
• Pd-decorated 585 DCV defect graphene can bind two H2 molecules.
• Pd-decorated SV defect graphene is the best for hydrogen storage.

The geometric stability and hydrogen capacity of Pd-decorated graphene with experimentally realizable boron dopants and various vacancy defects including single carbon vacancy (SV), “585”-type double carbon vacancy (585 DCV) and “555-777”-type double carbon vacancy (555-777 DCV) are investigated using the first-principles calculations based on density functional theory (DFT). It is found that among the four types of defective structures, Pd′s binding energies on SV and 585 DCV defect graphene sheets exceed the cohesive energy of the Pd metal bulk, thus Pd atoms are well dispersed above defective graphene sheets and effectively prevent Pd clustering. Up to three H2 molecules can bind to Pd atom on graphene with B dopants, SV and 555-777 DCV defects. For the cases of Pd-decorated graphene with B dopants and 555-777 DCV defect, a single H2 or two H2 are molecularly chemisorbed to Pd atom in the form of Pd–H2 Kubas complex, where the stretched H–H bond is relaxed but not dissociated. Out of two adsorbed H2, the third H2 binds to Pd atom by small van der Waals (vdW) forces and the nature of bonding is very weak physisorption. Different from above two cases, three H2 are all molecularly chemisorbed to Pd atom with stretched H–H bond for Pd-decorated SV defect graphene, the hybridization of the Pd-4d orbitals with the H2-σ orbitals and the electrostatic interaction between the Pd cation and the induced H2 dipole both contribute to the H2 molecules binding, and the binding energies of 0.25–0.41 eV/H2 is in the range that can permit H2 molecules recycling at ambient conditions.

Optimized atomic geometries for Pd-decorated B-doped, SV, 585 DCV and 555-777 DCV defective graphenes with one to three H2 molecules. Green, pink, blue and white balls represent C, B, Pd and H atoms, respectively.Figure optionsDownload as PowerPoint slide