  Identifying a nanostructure suitable for hydrogen storage presents a
promising avenue for the secure and cost-effective utilization of hydrogen as a
green energy source. This study introduces a systematic approach for selecting
optimal doping on porous materials, emphasizing the intricate interplay between
doping with the material's structure and the interaction between doping and
hydrogen. Our proposed approach serves as a framework for evaluating and
predicting the performance of doped materials. To validate the efficacy of our
strategy, we conduct a comprehensive investigation in carbon nanotubes (CNTs).
Applying our criteria, we systematically screen several dopants in CNTs. The
results highlight Cu-doped CNTs as promising candidates for hydrogen storage
applications. Focusing on Cu-doped CNTs, we analyze binding energy, charge
transfer, partial density of states (PDOS), and desorption temperature to
assess the performance of modified CNTs. Additionally, we explore the
feasibility of doped CNTs featuring various sizes of copper clusters and the
effect on the release temperature, i.e., complete regeneration. The findings
indicate that incorporating 5 to 6% copper impurity onto CNT surfaces renders
these nanostructures highly applicable for reversible hydrogen storage near
ambient conditions.
