Comparative studies of adsorption capacities for graphene based sorbents with different potential functions in molecular simulations

• An exp-8 form CH2 potential function is proposed by the DFT-vdW calculations.
• New function takes adsorption sites and hydrogen molecule orientations into account.
• The simulated results are in good agreement with experiments.
• Accurate computation of hydrogen storage capacity is feasible once such modified CH2 potential function is employed.

The reliabilities of CH2 interaction potential functions are of great importance in the molecular simulation for accurate predictions of carbon-based hydrogen storage materials. In this work, by implementing the DFT–vdW calculations, we propose an exp-8 form CH2 potential function and compared with three widely used functions for the hydrogen molecules adsorbed onto graphene. Studies show that the simulated results by using the exp-8 potential function are in good agreement with experiments at 298 K, while other three potential functions are not enough to describe the CH2 interactions due to the mismatch of the stable adsorption distance and the interaction strength. At 77 K, all four potentials give overestimated predictions compared with experimental investigations. We suggest that the adsorption sites and hydrogen molecule orientations should be considered when constructing the CH2 potential function since they have large influences on the interactions between hydrogen molecules and graphene sorbents. With such modified potential functions, the computation precisions are expected to be improved and a relatively accurate prediction for the storage capability of carbon-based hydrogen storage materials is becoming feasible.