Exploring the Role of Transition Metal Doping in Enhancing Hydrogen Storage Performance of Carbon Nanoribbon

Rational design of nanostructures is essential for safe, efficient, and reversible hydrogen (H₂) storage. In this study, we employ density functional theory to investigate transition-metal-doped carbon nanoribbons (CNRs) as high-performance H₂ storage materials. Using a four-stage screening, Sc-, Ti-, and V-doped CNRs are evaluated for their distinct adsorption behaviors, governed by metal–H₂ interactions. Sc- and Ti-doped CNRs show exceptional storage, adsorbing up to 29 and 26H₂ molecules, respectively, with optimal binding energies of –0.28 and –0.29 eV, within the DOE-recommended range for reversible storage. In contrast, V-doped CNRs adsorb 25H₂ molecules but bind them too strongly (–0.89 eV), limiting their practical application. Electronic structure analyses (DOS, PDOS, and charge transfer) reveal the underlying mechanisms of the adsorption process. The calculated gravimetric capacities and desorption temperatures, 6.10 wt% at 358 K for 5Sc@CNRs and 5.49 wt% at 371 K for 5Ti@CNRs, indicate strong potential for practical applications. Thermodynamic properties based on the Langmuir adsorption model show that 5Sc@CNR retains 15H₂ molecules up to 100 °C at 1 bar and approximately 200 °C at 100 bar, enabling practical pressure- and temperature-swing release. These findings highlight Sc- and Ti-doped CNRs as promising candidates for next-generation H₂ storage technologies.