Nanotube-mediated storage of methane and hydrogen: Insights from molecular simulation

We investigate the storage of methane (CH4) and hydrogen (H2) within single-walled nanotubes carbon, boron nitride (BN), and molybdenum disulfide (MoS2) nanotubes using Grand Canonical Monte Carlo (GCMC) algorithm. We observed that BN nanotubes exhibit the highest weight adsorption capacity for CH4 at 298 K, reaching up to 0.441 g/g at 8 MPa, closely aligning with the Department of Energy (DOE) target of 0.5 g/g. In contrast, MoS2 nanotubes, despite their larger radius, demonstrated the lowest weight adsorption capacity due to their higher atomic mass, with a value of 0.096 g/g at the same pressure. Volumetric adsorption capacity for CH4 was notably highest in (10,10) BN nanotubes, achieving 244 cm3/cm3 at 8 MPa, although this was still below the DOE target of 330 cm3/cm3. For hydrogen storage at 77 K, (30,30) BN nanotubes outperformed the 2025 DOE benchmarks of 5.5 wt% and 0.04 kg/L, with a weight adsorption of 12.19 wt% and a volumetric adsorption of 0.051 kg/L at 8 MPa, respectively. The adsorption heat within nanotubes showed a complex relationship with adsorption quantity, highlighting the interplay between fluid-wall and fluid-fluid interactions. The study also examines the impact of material structure on gas release, revealing a linear relationship between gas release and porosity or pore volume. The Ideal Adsorbed Solution Theory (IAST) was validated for predicting CH4/H2 mixture separations on amorphous carbon materials, and further reveals that the (30,30) BN nanotubes identified as the most suitable candidate for CH4/H2 separation, offering a balance of high CH4 adsorption capacity (20.2 mmol/g) and selectivity of 15 at 8 MPa.