Kinetic characteristics and optimization of hydrogen absorption in carbon-based materials

With the development of hydrogen energy, hydrogen adsorption technology has been continuously innovated and optimized. However, hydrogen adsorption kinetics remains a critical factor limiting hydrogen storage performance. This study conducts a detailed molecular dynamics investigation into the hydrogen adsorption behavior of graphene structures, revealing key findings crucial for advancing the development of room-temperature hydrogen storage technology. The primary findings focus on the adsorption competition mechanism and adsorption equilibrium state between the inner and outer surfaces of a bilayer graphene (BG) structure. Molecular migration trajectories indicate that hydrogen preferentially adsorbs to the outer surface of pores, with a higher adsorption rate. The adsorption rate on the outer surface is 50.5 % higher than that on the inner surface in the initial stage of adsorption, clearly demonstrating the adsorption priority of the outer surface in the bilayer structure. Due to the saturation of adsorption sites, both the inner and outer surfaces of the pores will reach adsorption equilibrium under different conditions, at which point the hydrogen adsorption capacity reaches its maximum. It is noteworthy that, in the bilayer structure, when the pore size is 1.5 nm, the hydrogen adsorption layers begin to overlap and interact, achieving the maximum hydrogen storage capacity of 3.237 wt%. Smaller or larger pore sizes result in unoverlapped adsorption layers or excessive free states, respectively, leading to a decrease in hydrogen storage capacity. To enhance hydrogen storage capacity, this study also innovatively constructs a truncated bilayer graphene (TBG) structure. With the aim of creating adsorption edges, a hydrogen storage capacity of up to 3.321 wt% is achieved at a truncation width of 7.27 Å at room temperature. Throughout the hydrogen adsorption process, the stability of hydrogen adsorption is negatively correlated with the hydrogen diffusion coefficient. This study holds significant implications for the design of efficient hydrogen storage carbon materials and the promotion of room-temperature hydrogen energy utilization.