MXene Nanoclusters as High-Performance Hydrogen Storage Media: First-Principles Insights into Hf₂C, Ta₂C, and W₂C.

This study investigates the hydrogen storage capabilities of MXene-based nanoclusters (Hf₂C, Ta₂C, and W₂C) using first-principles density functional theory calculations. All nanoclusters exhibit outstanding structural stability, reflected by strong binding energies (- 6.54 to - 7.38 eV) and the absence of vibrational instabilities. Electronic structure analysis identifies transition-metal sites with moderate positive electrostatic potentials as the most favorable centers for hydrogen adsorption. With increasing hydrogen loading, the adsorption mechanism evolves from chemisorption to a synergistic chemisorption-physisorption process. Non-covalent interaction analysis further confirms that progressive hydrogenation in M₂C-nH₂ complexes (M = Hf, Ta, W) strengthens both attractive hydrogen-bond-like interactions and van der Waals forces. Notably, Ta₂C and W₂C nanoclusters achieve exceptional storage capacities (~ 6.41 wt%), surpassing the DOE targets, while maintaining optimal adsorption energies ( ~ - 0.24 to - 0.28 eV/H₂) and practical desorption temperatures (222-364 K). These results position Ta₂C and W₂C MXene nanoclusters as highly promising materials for reversible hydrogen storage, offering a compelling balance of high capacity and favorable thermodynamic performance.