Designing Lithium-Decorated Aza-Triphenylene-Based Covalent Organic Frameworks for High-Capacity Hydrogen Storage: A Computational Study

In this study, we explore the potential of lithium-decorated aza-triphenylene-based covalent organic frameworks (AzaCOF) for efficient hydrogen storage applications. By decorating each unit cell of aza-triphenylene COF with six lithium (Li) atoms, a high hydrogen storage capacity of up to 9.49 wt % can be achieved, with each Li atom capable of adsorbing up to five H₂ molecules. The average adsorption energy of H₂ on the Li-decorated AzaCOF is approximately −0.30 eV/H₂, indicating an optimal interaction that balances hydrogen adsorption and desorption for practical storage and release, meeting the U.S. Department of Energy (DOE) guidelines for potential hydrogen storage mechanism. The strong interaction of Li with the AzaCOF arises from charge transfer from Li to the two-dimensional (2D) framework, while the enhanced adsorption energy is attributed to an electric field-induced polarization that facilitates assisted van der Waals interactions. The thermodynamic stability was confirmed by ab initio molecular dynamic simulation at 300 K and dynamic stability by computing phonon spectrum with all positive phonon frequencies. A high diffusion energy barrier of 4.09 eV may prevent Li atoms from migrating and clustering on the AzaCOF surface. Vapor pressure calculations suggest that the desorption temperature is above room temperature (330–360 K), making it a potential candidate for onboard, reversible hydrogen storage. This work provides a theoretical basis for experimental investigations into Li-decorated AzaCOF as advanced hydrogen storage materials.