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.