Energy storage properties of a two-dimensional TiB₄ monolayer

Herein, the energy storage properties of TiB₄ monolayers were studied within the density functional theory framework. Both CH₄ and H₂ were chosen as adsorption molecules, and their interactions with a TiB₄ sheet were investigated. TiB₄ attracted gas molecules via open Ti sites, and each Ti atom could adsorb a maximum of two molecules. Via the electronic density of the states and atomic charge analysis, we found that the mechanism for gas adsorption was mainly electrostatic. For H₂ adsorption cases, orbital interactions also made contributions. As the combustion energy of one CH₄ molecule is three times that of one H₂, the TiB₄-2CH₄ compound can achieve the best equivalent gravimetric hydrogen density of 10.14 wt% with the average adsorption energy of 0.38 eV. Ab initio molecular dynamics calculations on this compound showed that there was no kinetic barrier during CH₄ desorption. Moreover, the stacking of the TiB₄ monolayers could weaken the energy storage capacity. Therefore, it should be avoided in practial usage. Based on the abovementioned results, the TiB₄ monolayer was suggested to be a promising candidate for onboard energy storage.