Hydrogen Chemisorption and Physisorption on the Two-Dimensional TiC Sheet Surface

The TiC monolayer sheet, a new two-dimensional structure, is proposed as a promising hydrogen storage material because of its high specific surface area and the large number of exposed Ti ions on the surface. First principles calculations showed that both chemisorption and physisorption of H-2 can take place on the TiC sheet surface, with adsorption energies of 0.36 and 0.09 eV per H-2, respectively. For 1 and 1/4 monolayer (ML) coverages, the dissociation barriers of H-2 on the TiC sheet surface were calculated to be 1.12 and 0.33 eV, respectively. Thus, as well as physisorption and chemisorption, there were dissociated H atoms on the TiC sheet surface. The maximum H-2 storage capacity was calculated to be up to 7.69% (mass fraction). The capacities were 1.54%, 3.07%, and 3.07% for dissociated H atoms, and chemisorption and physisorption of H-2, respectively. Considering only Kubas adsorption, the hydrogen storage capacity was 3.07%. The adsorption energy for H-2 chemisorption on the TiC sheet surface only slightly changed at different coverages, which benefits the storage and release of H-2.