Theoretical study on porphyrin based covalent organic polyhedra as a hydrogen storage

We introduce a new covalent organic polyhedron (COP) containing porphyrinyl groups. The porphyrin based COP (PCOP) is designed by modeling and simulation using 6 tetraaldehyde molecules and 8 triamine molecules combined by 24 imine bonds. Probable molecular crystal structures of the modeled PCOP are suggested by the simulated annealing Monte Carlo simulation method. We found that the predicted crystal structures show large surface areas up to over 6000 m2/g and the surface area depends on how to pack PCOP molecules and the resulting pore structure. Grand canonical Monte Carlo simulations predict the hydrogen uptakes of these polymorphs of PCOP and the values are from 98 to 262 mg/g for gravimetric uptake and from 45 to 50 kg/m3 for volumetric uptake at 77 K. Hydrogen uptakes of PCOP crystals are comparable to the best records of metal-organic frameworks (164.1 mg/g for NU-100 and 176 mg/g for MOF-210 at 77 K). Hence, PCOP is expected to be applicable to hydrogen storage.