Metal-Decorated C₈ Quantum Dots as Lightweight Hydrogen Storage Materials: A Comprehensive DFT Study

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• Lightweight, efficient, and reversible hydrogen storage materials are crucial for advancing hydrogen energy technologies.
• Carbon quantum dots (CQDs) are ultrasmall, highly curved nanomaterials with potential for hydrogen storage applications.

Purpose of the Study:

• To investigate hydrogen storage in pristine and metal-decorated C8 carbon quantum dots (CQDs) using density functional theory (DFT).
• To explore the effect of lithium, magnesium, and titanium decoration on hydrogen adsorption strength and reversibility.

Main Methods:

• Comprehensive DFT calculations were performed to study hydrogen adsorption on C8 CQDs.
• Metal decoration (Li, Mg, Ti) was investigated to tailor hydrogen binding energies.
• Grand canonical thermodynamic modeling was used to assess storage reversibility under practical conditions.

Main Results:

• Pristine C8 CQDs showed negligible hydrogen affinity.
• Metal decoration significantly enhanced hydrogen adsorption, with optimal single-molecule adsorption energies for Li-, Mg-, and Ti-CQDs (-0.172, -0.304, -0.451 eV).
• Mg-CQD achieved a reversible gravimetric hydrogen storage capacity of 21.7 wt%, outperforming other reported nanostructured materials.

Conclusions:

• Metal-decorated C8 CQDs represent a promising new class of high-performance nanomaterials for reversible hydrogen storage.
• Ultrasmall CQDs can overcome the trade-off between hydrogen uptake and reversibility in nanostructured storage media.
• The findings highlight the potential of CQDs for practical hydrogen energy applications.