Theoretical study of transition-metal decoration on carbon-based materials for enhancing hydrogen storage capacity

In this research, we investigated the adsorption properties of the hydrogen atom on newly designed materials using DFT calculations. We focused on the role of dopants in modulating the binding properties of the metal. We proposed Ti4 embellished on a pristine B- and N-doped graphene surface to enhance hydrogen storage capacity. The computational results indicate that the doping of B on graphene maximizes the interaction between the metal clusters and the graphene substrate, with a very high binding energy of -6.45 eV, the strongest among our proposed catalysts. This strong binding energy prevents the aggregation and formation of Ti-metal clusters. For hydrogen adsorption, we found a dissociative chemisorption of the first H2 molecule on all materials. The metal hydrides are optimally formed through strong overlap between the H-1s and Ti-3d orbitals. Furthermore, Ti4 embellished on B-graphene is the most effective material with a high level of hydrogen and reversible hydrogen adsorption. We confirmed that eight H2 molecules can be stably adsorbed on Ti4/BGr material with a hydrogen gravimetric density of 4.08 wt%, including six reversible hydrogen adsorptions. In comparison with various surfaces, our proposed new B-doped graphene of Ti4/BGr engenders not only high cluster stability on the substrate but increases hydrogen adsorption for hydrogen storage. Therefore, Ti4 embellished on B-graphene is a promising candidate for high capacity hydrogen storage, applicable to the design of a hydrogen storage medium.