Tailoring hydrogen storage performance of heteroatoms-doped polycrystalline carbon nanotubes via Ti functionalization: A molecular dynamics study

Abstract

In this study, molecular dynamics (MD) simulations have been employed to investigate the hydrogen adsorption behavior of heteroatom-doped polycrystalline carbon nanotubes (N/B-PCNTs). A potential energy distribution (PED)-based approach, integrated with hybrid grand canonical Monte Carlo (GCMC) simulations, was applied to estimate adsorbed hydrogen molecules. To mitigate Ti clustering observed in undoped PCNTs, local heteroatom doping at grain boundary (GB) sites was explored for its effect on Ti stability. The simulations revealed that N and B dopants effectively suppressed Ti clustering by providing strong and stable anchoring sites. Hydrogen uptake calculations indicated that 10 at% B-PCNTs achieved a maximum gravimetric density of 1.58 wt%, outperforming 10 at% N-PCNTs (1.34 wt%) at 300 K and 100 bar. By contrast, Ti-functionalized N/B-PCNTs (Ti/N/B-PCNTs) exhibited markedly higher storage capacities. At 200 K and 100 bar, Ti/N-PCNTs reached 7.53 wt%, while Ti/B-PCNTs attained 7.78 wt%

at 300 K, these values decreased to 5.25 wt% and 5.57 wt%, respectively. The average hydrogen adsorption energy increased substantially, reaching ∼0.214 eV/H<inf>2</inf> for Ti/N-PCNTs and ∼0.20 eV/H<inf>2</inf> for Ti/B-PCNTs at 300 K, corresponding to enhancements of 67 % and 56 % compared to Ti-PCNTs. Moreover, hydrogen diffusivity in Ti/N/B-PCNTs decreased by 10–24 %, reflecting stronger interactions between hydrogen molecules and doped frameworks. Overall, these results highlight the synergistic role of heteroatom doping and Ti-functionalization at GB sites in enhancing hydrogen adsorption capacity and energetics in PCNTs, demonstrating their strong potential as next-generation carbon-based materials for hydrogen storage applications. © 2026 Hydrogen Energy Publications LLC