One of the critical techniques for developing hydrogen storage applications is the advanced research to build novel two-dimensional materials with significant capacity and effective reversibility. In this work, we perform first-principles unbiased structure search simulations to find a novel AsC 5 monolayer with a variety of functionally advantageous characteristics. Based on theoretical simulations, the proposed AsC 5 has been found to be energetically, dynamically, and thermally stable, supporting the viability of experiment. Since the coupling between H 2 molecules and the AsC 5 monolayer is quite weak due to physisorption, it is crucial to be enhanced by thoughtful material design. Hydrogen storage capacity can be greatly enhanced by decorating the AsC 5 monolayer with Li atoms. Each Li atom on the AsC 5 substrate is shown to be capable of adsorbing up to four H 2 molecules with an advantageous average adsorption energy (E a d ) of 0.19 eV/H 2 . The gravimetric density for hydrogen storage adsorption with 16Li and 64 H 2 of a Li-decorated AsC 5 monolayer is about 9.7 wt%, which is helpful for the possible application in hydrogen storage. It is discovered that the desorption temperature (T D ) is much greater than the hydrogen critical point. Therefore, such crucial characteristics make AsC 5 -Li be a promising candidate for the experimental setup of hydrogen storage. [ABSTRACT FROM AUTHOR]