Predicting hydrogen storage performances in porous aromatic frameworks containing carboxylate functional groups with divalent metallic cations

Abstract

We report force field predictions for the hydrogen uptakes of porous aromatic framework (PAF) materials containing carboxylate functional groups with divalent metallic cations. The ab initio calculations were performed on our proposed functional groups and hydrogen molecules using the MP2 method with the TZVPP basis set and basis set superposition error (BSSE) correction. A force field was developed based on the ab initio energetic data. The resulting force field was applied to predict hydrogen adsorption isotherms at different temperatures and pressures using the grand canonical Monte Carlo (GCMC) method. Each functional group of divalent metallic cations and two carboxylic acid groups provided 13 (Mg) or 14 (Ca) binding sites for hydrogen molecules with an average binding energy of 8 kJ·mol -1 per hydrogen molecule. The predicted hydrogen adsorption results were improved remarkably by the functional groups at normal ambient conditions, exceeding the 2015 target set by the department of energy (DOE) of USA. This work reveals the complex relationship between hydrogen uptake and surface area, and the free volumes and binding energies of different materials. © Editorial office of Acta Physico-Chimica Sinica.