Hydrogen storage based on physisorption.

Area of Science:

• Computational Chemistry
• Materials Science
• Physical Chemistry

Background:

• Hydrogen adsorption on molecular systems is crucial for energy storage.
• Aromatic molecules are investigated as potential adsorbents for hydrogen.
• Understanding physisorption mechanisms requires accurate binding energy estimations.

Purpose of the Study:

• To evaluate hydrogen physisorption on neutral and negatively charged aromatic systems.
• To compare ab initio calculated binding energies with experimental hydrogen adsorption data.
• To explore the impact of molecular structure and charge on adsorption capacity.

Main Methods:

• Ab initio calculations were employed to determine binding energies (DeltaH, DeltaG) at various temperatures and pressures.
• A range of neutral and charged aromatic molecular systems were studied, including corannulene, coronene, and phthalocyanine derivatives.
• Molecular dynamics (MD) simulations were used to validate experimental adsorption results.

Main Results:

• The thermal correction to Gibbs energy (TCGE) accurately approximates the adsorbent binding energy for thermodynamically favorable physisorption.
• Binding energy in neutral molecules correlates with curvature and functional groups.
• Charged phthalocyanine complexes ([LiPc](-)) exhibit doubled binding energy due to charge-induced dipole interactions.
• Tetrabutylammonium substitution in Li(2)Pc increased hydrogen uptake to 5.93 wt % at 77 K and 45 bar.
• Layered TMA-LiPc systems and sandwich structures show potential for enhanced hydrogen storage and reduced adsorption pressure.

Conclusions:

• Ab initio calculations provide reliable predictions for hydrogen adsorption on aromatic systems.
• Molecular design, particularly incorporating negative charges and layered structures, can significantly optimize hydrogen storage capacity.
• Phthalocyanine derivatives, especially when functionalized, represent promising materials for efficient hydrogen storage.