Atomic-Level Design of a Multifunctional MnC30:H Nanocage: A Promising Platform for Hydrogen Storage and Next-Generation Energy Technologies.

The development of multifunctional materials capable of combining hydrogen storage with energy-conversion properties is important for sustainable energy technologies. Herein, first-principles density functional theory (DFT) calculations are employed to systematically investigate the structural, electronic, magnetic, optical, thermodynamic, thermoelectric, vibrational, and hydrogen adsorption properties of the MnC₃₀:H nanocage. Structural optimization indicates that the system is energetically stable, while phonon calculations reveal the absence of imaginary frequencies, confirming its dynamical stability. The nanocage possesses a magnetic moment of approximately 4.0 µB, primarily originating from Mn-3d states, with pronounced Mn-3d/C-2p hybridization near the Fermi level contributing to spin-polarized electronic characteristics. Strong visible-light absorption and an enhanced dielectric response further indicate its potential for optoelectronic applications. Thermodynamic analysis suggests good thermal stability over the investigated temperature range. Hydrogen adsorption calculations demonstrate favorable molecular H₂ binding at the Mn active site, with a gravimetric hydrogen-storage capacity of 5.1 wt%. Dispersion-corrected calculations show that van der Waals interactions significantly influence the adsorption strength, with PBE-D3(BJ) yielding a moderate adsorption energy of - 0.42 eV, supporting potentially reversible hydrogen storage. Zero-point-energy corrections further reveal site-dependent adsorption energetics and structural responses. Thermoelectric calculations predict positive Seebeck coefficients and a maximum figure of merit (ZT) of 1.0 at 800 K, indicating promising high-temperature energy-conversion performance. Overall, the combined stability, magnetic, optical, thermoelectric, and tunable hydrogen-adsorption characteristics highlight MnC₃₀:H as a promising multifunctional nanomaterial for future sustainable energy and hydrogen-storage applications.