P-N Conversion in a Water-Ionic Liquid Binary System for Nonredox Thermocapacitive Converters.

Area of Science:

• Materials Science
• Electrochemistry
• Physical Chemistry

Background:

• Thermoelectric materials convert heat into electrical energy.
• Ionic liquids offer tunable properties for advanced applications.
• Controlling material properties is key to optimizing energy harvesting.

Purpose of the Study:

• To investigate the p-n conversion of thermoelectric properties in a water-ionic liquid binary system.
• To optimize the Seebeck coefficient by precisely controlling water content.
• To explore the integration of p-n thermocapacitive converters for enhanced energy harvesting.

Main Methods:

• Fabrication and characterization of water-ionic liquid ([EMIm][Ac]) binary systems.
• Optimization of water-[EMIm][Ac] molar ratios for p-type and n-type Seebeck coefficients.
• Density Functional Theory (DFT) calculations to understand the underlying mechanisms.
• Integration of p-n thermocapacitive converters.

Main Results:

• Observed an intriguing p-n conversion of thermoelectric property with controlled water content.
• Optimized highest p-type Seebeck coefficient at a water-[EMIm][Ac] molar ratio of 2:1.
• Optimized highest n-type Seebeck coefficient at a water-[EMIm][Ac] molar ratio of 4:1.
• DFT revealed solvent separation ion pairs at a 4:1 ratio, weakening electrode interactions and enabling p-n conversion.
• Integrated p-n thermocapacitive converters successfully enhanced output Seebeck voltages.

Conclusions:

• Precise control over water content in water-ionic liquid systems enables tunable thermoelectric properties, including p-n conversion.
• The observed p-n conversion is attributed to changes in ion pair configurations and electrode interactions.
• This research presents a promising approach for harvesting low-grade heat using fluidic thermoelectric materials.