Li-doped 2D aza-fused covalent organic framework: a promising avenue for hydrogen storage†

Designing an efficient high-capacity hydrogen storage material is a critical challenge for advancing clean energy storage. Through detailed density functional theory calculations and ab initio molecular dynamics simulations, we found that the recently synthesized two-dimensional (2D) aza-fused covalent organic framework (aza-COF) doped with Li exhibits considerable promise for hydrogen storage applications. Despite a H₂ storage capacity of 10.3 wt%, pristine aza-COF adsorbs H₂ molecules via weak van der Waals interactions, limiting its viability under ambient conditions. The strategy relies on increasing more active sites for H₂ adsorption, thereby improving the interactions between H₂ and positively charged Li atoms. Li-doped aza-COF adsorbs H₂ molecules with a combined effect of electrostatic and van der Waals interactions, resulting in enhanced H₂ adsorption energy, ranging from −0.22 to −0.33 eV. The H₂ storage capacity reaches 13.9 wt%, higher than that of the pristine aza-COF and the 5.5 wt% target of the U. S. Department of Energy. With appropriate structural stability, H₂ adsorption energy, desorption temperature, hydrogen occupation number and high H₂ storage ability, Li-doped 2D aza-COF exhibits great potential as a hydrogen storage material.