Graphene-Based Soft Actuator with Dynamic Spectrum Modulation for a Smart Thermal Surface

Two-dimensional structures enable ion activation and actuation. These structures also enable ions to intercalate, shifting the energy level and altering the optical absorption. In this study, a dual-function, graphene-based smart surface with actuation and spectrum regulation was developed. This surface was composed of a graphene working electrode, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide electrolyte, and a Au counter electrode. The smart surface could vary its thickness by 17.4% and regulate multiple wavelengths, including ultraviolet, visible, near-, and mid-infrared. Within a 2.2-3.3 V electric field, linear emissivity regulation was established, and the highest emissivity modulation depth approached 0.41. By investigating electromechanical, electrochemical, in situ structural, and electrical features, three stages of ion movement under electrical voltage, including dispersion, intercalation into graphene layers, and double layer capacitance, were observed. The ion intercalation process was associated with Fermi level shifting and dynamic spectrum turning of graphene, whereas the production of double layer capacitance was associated with the maximum modulation depth. Such soft actuators with dynamic spectrum tunability may render smart thermal surfaces feasible for other application scenarios, for example, thermal camouflage robotics, optical communication, and radiative cooling.