Computational insights into the energy storage of ultraporous MOFs NU-1501-M (M = Al or Fe): Protonization revealing and performance improving by decoration of superalkali clusters

In 2020, Chen et al. reported the synthesis of a series of promising metal–organic frameworks (MOFs) based on Al/Fe trinuclear clusters, known as NU-1501-M (M = Al or Fe). Both the gravimetric and volumetric Brunauer-Emmett-Teller (BET) areas of this novel structure are in an ideal range, making it highly promising for hydrogen storage. However, the physical chemistry of its adsorption processes has not been investigated. In this work, we applied grand canonical Monte Carlo (GCMC), density functional theory (DFT), and ab initio molecular dynamics (AIMD) to study their adsorption behaviours in details. These simulations suggest that the balance between the chemical porosity and the electronic structure is critical in determining the quality of the designed MOFs materials in deliverable energy storage. Moreover, theoretical predictions reveal the possible protonization of oxygen atoms from M trinuclear nodes by hydrogen molecules. To protect MOFs from being protonized, we proposed to employ NAl₃ clusters to decorate the MOFs. Simulations reveal that this novel strategy can not only stablize the oxygen atoms, but also significantly improve the hydrogen storage performance by almost one order of magnitude. Our work proposes an important and promising way to improve the energy storage performance of these MOFs.