Reversible Hydrogen Uptake/Release over a Sodium Phenoxide-Cyclohexanolate Pair.

Area of Science:

• Materials Science
• Chemical Engineering
• Sustainable Energy

Background:

• Arene-cycloalkane pairs offer potential for hydrogen storage but face thermodynamic limitations for efficient release.
• Current methods for hydrogen release from these pairs are often energy-intensive and inefficient.

Purpose of the Study:

• To optimize the thermodynamics of hydrogen release from arene-cycloalkane systems.
• To investigate the effect of metal substitution on hydrogen storage and release properties.

Main Methods:

• Theoretical calculations (e.g., DFT) to analyze electronic structure changes and bonding.
• Experimental synthesis and characterization of metal-substituted phenoxides and cyclohexanolates.
• Thermodynamic analysis of hydrogen desorption and hydrogenation reactions.

Main Results:

• Replacing hydrogen with alkali or alkaline earth metals in cyclohexanol and phenol derivatives substantially decreases dehydrogenation enthalpy.
• Metal substitution leads to reduced HOMO-LUMO energy gaps and elongated alpha C-H bonds in cyclohexanolates, indicating activation.
• The sodium phenoxide-cyclohexanolate pair demonstrated efficient hydrogen desorption at 413 K (solid) and 373 K (aqueous solution), with hydrogenation at 303 K.

Conclusions:

• Metal substitution is a viable strategy to overcome thermodynamic barriers in arene-cycloalkane hydrogen storage systems.
• The developed sodium phenoxide-cyclohexanolate system shows promise as a stable and efficient material for on-demand hydrogen release and uptake.
• This research paves the way for improved hydrogen storage solutions for various applications.