Tunable Electrochemical Entropy through Solvent Ordering by a Supramolecular Host

Area of Science:

• Supramolecular Chemistry
• Electrochemistry
• Materials Science

Background:

• Thermally regenerative electrochemical cycles (TRECs) are crucial for waste-heat harvesting and electrochemical cooling.
• Existing aqueous TREC electrolytes, like potassium ferricyanide, have limitations in their molar entropy change.
• Maximizing redox entropy change is key to improving TREC efficiency.

Purpose of the Study:

• To develop an aqueous electrochemically controlled host-guest encapsulation system with a large and tunable redox entropy change.
• To investigate a novel strategy for increasing entropy by displacing structured solvent molecules.
• To demonstrate the potential for rational design of high-entropy electrolytes.

Main Methods:

• Design and synthesis of a supramolecular host-guest system.
• Electrochemical characterization to measure redox entropy change (ΔS).
• Systematic modification of host ligands and metal vertices to tune performance.

Main Results:

• The host-guest system achieved a molar entropy change approximately four times greater than potassium ferricyanide.
• Encapsulation displaced ordered water molecules, contributing significantly to the entropy increase.
• Synthetic tunability allowed for a wide range of ΔS values, from -51 to -101 cal mol⁻¹ K⁻¹.

Conclusions:

• The developed host-guest system offers a promising new avenue for high-entropy electrolytes.
• This approach provides a strategy to overcome theoretical limits in ion solvation reorganization entropy.
• The findings pave the way for more efficient thermogalvanic waste-heat harvesting and electrochemical cooling technologies.