Functionalized 2D Hexaazatriphenylene as Hydrogen Storage Platform: A DFT-Guided Design Approach

Abstract

Introduction: The development of sustainable energy systems critically depends on efficient hydrogen storage materials. Conventional physisorption frameworks, such as MOFs and COFs, are constrained by weak binding energies and limited tunability, necessitating new molecular platforms with superior adsorption characteristics. Methods: We employed density functional theory (DFT) calculations with dispersion corrections to investigate the strategic functionalization of 2D hexaazatriphenylene (HAT), a nitrogen-rich, π- conjugated macrocycle, as a next-generation hydrogen storage platform. Various substituents, including electron-donating (−Bpin, −OH), electron-withdrawing (−NO2, −COH), and ambiphilic (−SF5, −SO3H) groups, were systematically incorporated to modulate adsorption properties. Results: Our findings reveal that functionalized HAT derivatives synergize van der Waals interactions, quadrupole coupling, and substituent-induced polarization, achieving hydrogen binding energies of up to −8.6 kJ·mol?¹, approaching the U.S. DOE target of 15 kJ·mol?¹ for physisorption-based materials. The HAT-PB (−Bpin) derivative exhibited optimal non-dissociative physisorption, maintaining an H–H bond length of 0.74 Å, minimal charge transfer (−0.041 e), and tunable HOMOLUMO gaps (6.4–7.2 eV). Discussion: This work closes a significant research gap by presenting the first systematic study of HAT derivatives for hydrogen storage. The nitrogen-enriched core of HAT enhances charge localization, while substituent engineering provides precise control over adsorption energy and reversibility. Conclusion: Our computational insights establish functionalized HAT frameworks as promising candidates for reversible hydrogen storage, offering a design blueprint that could accelerate the development of lightweight, high-capacity energy materials.