Hydrogen-passivated amorphous carbon nanosheets as high-capacity reversible hydrogen storage media: Density functional theory study

The development of lightweight, metal-free materials capable of reversible hydrogen (H 2 ) storage remains a central challenge for next-generation clean energy technologies. In this work, density functional theory (DFT) calculations were employed to systematically investigate the structural, electronic, thermodynamic, kinetic, and optical properties of pristine and H 2 -passivated monolayer amorphous carbon (MAC) nanosheets as potential H 2 storage media. Structural analysis confirms that H-passivation effectively stabilizes the amorphous framework by saturating dangling bonds and reducing local strain without compromising planarity. Electronic calculations reveal that H-passivation significantly widens the HOMO–LUMO gap and suppresses defect-induced mid-gap states, leading to enhanced electronic stability. Hydrogen adsorption studies demonstrate that pristine MAC₁ exhibits excessively strong chemisorption, whereas pristine MAC₂ shows weak physisorption. In contrast, H-passivated MAC₁–H achieves adsorption energies within the optimal range for reversible storage, accompanied by moderate desorption temperatures and ultrafast recovery times. Multi-H₂ adsorption simulations (up to 70H₂ molecules) confirm structural robustness and coverage-dependent physisorption behaviour. Notably, MAC₁–H delivers an exceptional gravimetric hydrogen storage capacity of 14.24 wt%, surpassing current DOE targets and outperforming many reported carbon-based systems. Optical analysis further indicates that H 2 uptake does not significantly disrupt the electronic backbone, preserving material stability at high loading. Overall, H-passivated MAC nanosheets emerge as highly promising, metal-free candidates for efficient and reversible H 2 storage applications.