Analyzing the Total Attractive Force and Hydrogen Storage on Two-Dimensional MoP2 at Different Temperatures Using a First-Principles Molecular Dynamics Approach

We performed first-principle molecular dynamics (FPMD) calculations to test the total attraction force on a physisorbed molecule at a given temperature and ambient pressure and applied it to the hydrogen storage on the 2D material MoP2. We considered a pristine material and one with 12.5% of Mo vacancies. By optimization, we calculated a gravimetric capacity for pristine MoP2 of 5.72%, with an adsorption energy of -0.13 eV/molecule. We found 6.02% and -0.14 eV/molecule for the defective surface. Next, we applied our approach to determine if the molecular hydrogen physisorption obtained by simple energy optimization exists for a given temperature and ambient pressure. We used this approach to determine the number of molecules adsorbed on the surface at a given temperature. Thus, we conducted a FPMD calculation at temperature T₁, using optimization as the initial system configuration. Subsequently, we performed a second FPMD calculation at a temperature T₂ (with T₂ << T₁), using the steady configuration of the first FPMD calculation as the initial configuration. We identified as adsorbed molecules at temperature T_1, only those forced back toward the surface at temperature T₂ due to kinetic energy loss at the lower temperature. The defective surface gave the best gravimetric capacity, ranging from 5.27% at 300 K to 6.02% at 77 K. The latter met the requirement from the US-DOE, indicating the potential practical application of our research in hydrogen storage.