Tuning infrared emissivity of multilayer graphene using ionic liquid gel electrolytes†

Abstract

Actively controlling the infrared (IR) emissivity of materials is critical for numerous applications, such as radiative cooling and thermal camouflage. Multilayer graphene (MLG) has shown significant potential as a functional material with tunable IR emissivity. However, the poor long-term stability of currently reported MLG-based IR modulators greatly limits their practical applications. Herein, ionic liquid gel electrolytes (ILGPEs) are prepared and used as doping sources to assemble MLG-based IR modulators with a sandwich-like structure. The modulator lifetime is dramatically improved, while the modulation depth and dynamic response are retained at levels comparable to those using pure ionic liquids. Microscopic structural analyses, including Raman spectroscopy and X-ray diffraction, are correlated with the ionic conductivity of the ILGPE and the IR radiation of the MLG. The results indicate that the improvement in device performance is likely due to an improved interface between the ILGPE and MLG, as well as limited ion diffusion within the ILGPE, which preserves the structural integrity of the MLG. These findings shed light on the optimization of IR modulators based on ion intercalation.