Metal-Porphyrin Complexes: A DFT Study of Hydrogen Adsorption and Storage

It has been performed hydrogen adsorption on four metallo-porphyrin complexes by Density Functional Theory (DFT) calculations at room temperature. The WB97XD hybrid formalism method was used for hydrogen adsorption on metallo-porphyrin complexes formed with alkaline metal and alkaline earth metal (Na, K, Mg and Ca) atoms. It was determined that the adsorption energies for all complexes were negative, so that each of them could be a potential adsorbent for hydrogen storage. The adsorption enthalpy (ΔH) was calculated as -21.9 kJ/mol for the Na-Porphyrin (Na-P) complex structure. Moreover, the gravimetric hydrogen storage capacity for the Na-P complex was calculated to be ≈5.5 wt%. Thus, the DOE's target for 2025 has been achieved. In addition, van der Waals weak interactions were found to be effective in hydrogen adsorption and storage studies. Based on the electronic properties the metallo-porphyrin complexes could not be used as electronic sensors against the hydrogen molecule.