Large Decrease in the Melting Point of Benzoquinones via High-n Eutectic Mixing Predicted by a Regular Solution...

Area of Science:

• Materials Science
• Physical Chemistry
• Electrochemistry

Background:

• Decreasing mixture melting points (Tm) is crucial for applications like cryopreservation and battery electrolytes.
• Current methods often rely on favorable enthalpic interactions (e.g., deep eutectic solvents).
• A complementary strategy utilizing increased entropy of mixing is explored.

Purpose of the Study:

• To demonstrate a novel method for decreasing melting points by increasing the number of components (n) and thus the entropy of mixing.
• To investigate the potential of this approach for creating high energy density flow battery electrolytes using redox-active molecules.
• To develop and apply thermodynamic models for predicting eutectic behavior in high-n mixtures.

Main Methods:

• Reformulation and application of fundamental thermodynamic equations for high-n eutectic mixtures.
• Differential scanning calorimetry (DSC) to measure melting points and enthalpies of mixing.
• Systematic investigation of binary mixtures and a multi-component system of benzoquinone derivatives.

Main Results:

• 1,4-benzoquinone derivatives exhibit eutectic mixing, decreasing Tm despite slightly positive enthalpies of mixing (0-5 kJ/mol).
• A mixture of seven benzoquinone derivatives achieved a significant Tm decrease to -6 °C.
• The regular solution model provided better predictions than the ideal solution model for these mixtures.

Conclusions:

• Mixing a high number of components is an effective strategy to lower melting points by maximizing entropy, complementing enthalpy-driven approaches.
• This entropy-tuning method is highly relevant for designing advanced energy storage materials.
• Thermodynamic modeling, particularly the regular solution model, is valuable for predicting eutectic properties in complex organic mixtures.