Versatility of infrared properties of MXenes

Selective and ultrathin films and coatings capable of controlling infrared (IR) emission are crucial for highly integrated thermal management systems, but are challenging produce using conventional materials. Here, we report that the MXene family of two-dimensional carbides and carbonitrides offers a broad range of IR emissivity values (∼0.06–0.59) with diverse colors, varying with MXene composition and structure. Specifically, 200 nm thick purple Ti3C2Tx coating has an average IR emissivity of 0.06, while gold Nb2CTx coating is 0.59 at wavelengths from 3-25 μm. We demonstrate that the IR emissivity can be finely tuned by combining different metals in solid-solution MXenes. Furthermore, the IR identification capability at varying temperatures was validated using different MXene coatings and patterned MXene fabrics. The versatility of MXenes at optical and infrared wavelengths provides a platform for developing MXene-based smart, flexible devices and wearables capable of selective and localized thermal management, aiming at radiative heating/cooling, IR identification, photothermal conversion, and thermal imaging.