Intercalation/Deintercalation Dynamics in Ionic Liquid-Based Graphene Thermal Emissivity Modulators

Area of Science:

• Materials Science
• Electrochemistry
• Condensed Matter Physics

Background:

• Ionic liquids can intercalate into multilayer graphene (MLG).
• This intercalation modulates MLG's thermal emissivity and dielectric properties.
• Electrochemical control offers a pathway to tune these properties.

Purpose of the Study:

• To investigate the temperature-dependent behavior of electrochemically driven ionic liquid intercalation in MLG devices.
• To quantify the impact of temperature on intercalation extent and resulting thermal emissivity changes.
• To explore the operational temperature limits and influencing factors of such devices.

Main Methods:

• Fabrication of MLG devices with ionic liquid ([DEME+][TFSI-]) and copper electrodes.
• Electrochemical intercalation using voltages of 3.5-4 V.
• Raman spectroscopy to monitor intercalation from 10-100 °C.
• Thermal imaging to measure temperature changes (7.5-14 μm wavelength).

Main Results:

• Intercalation of [TFSI-] anions into MLG improves with increasing temperature (10-100 °C).
• Apparent temperature change due to intercalation increases with temperature, reaching a maximum of 25.5 °C.
• Intercalation causes a two-order-magnitude shift in free carrier concentration, altering complex dielectric function.
• Higher temperatures enhance intercalation but do not significantly affect cutoff frequencies.

Conclusions:

• Temperature significantly influences the electrochemical intercalation of ionic liquids in MLG devices.
• The observed changes in thermal emissivity are directly linked to carrier density modulation.
• Device performance, including intercalation degree and effective temperature range, is dependent on ambient temperature due to ion mobility and diffusion kinetics.