Mechanistic Insights into Hydrogen Storage Performance from the Substitution Doping Method: A Case Study on Alkali Metal-Doped Carbon Nanotubes

The development of suitable nanostructures for hydrogen
storage
applications is crucial to advancing clean and efficient energy technologies.
This study explores the potential of substituted carbon nanotubes
(CNTs) for hydrogen storage with a focus on the substitutional doping
strategy. A four-step screening approach identifies alkali metals
(Li, Na, and K) as highly effective dopants. All dopant atoms bind
strongly to the CNT surface, with binding energies (EB ≥ |−1| eV), ensuring structural stability
for long-term applications. Binding energy analysis indicates that
hydrogen adsorption occurs within the range defined by the U.S. Department
of Energy (|−0.15| ≤ EB ≤
|−0.6| eV). The best-performing structure, K-doped single-walled
CNT, achieves a gravimetric capacity of 5.79 wt % and a desorption
temperature of approximately 218 K. Moreover, mechanistic insights
are provided through analyses of the density of states, PDOS, charge
transfer, and band structure. These results highlight the promise
of substitutionally doped CNTs for hydrogen storage and establish
a broadly applicable strategy for dopant selection in low-dimensional
nanomaterials.