Abstract
Black materials with low infrared absorption/emission are rare in nature but highly desired in numerous areas, such as solar-thermal energy harvesting, infrared camouflage, and anti-counterfeiting. Due to the lack of spectral selectivity in intrinsic materials, such counter-intuitive properties are generally realized by constructing complicated subwavelength artificial nanostructures with precise nanofabrication techniques. Here, we report that 2D Ti3C2Tx MXenes embrace both a low emissivity (down to 10%) and a high solar absorptance (up to 90%), yielding the best spectral selectivity (8.2) and the highest solar-thermal efficiency among the reported intrinsic solar absorbing materials. We demonstrate their appealing potentials in the aforementioned areas. Moreover, the spectral selectivity relies on both the nanoflake orientations and terminal groups, providing great tunability. First-principles calculations suggest more potential low-emissivity MXenes such as Ti2CTx, Nb2CTx, and V2CTx. This work opens the avenue to further exploration of a family of low-emissivity black materials with over 70 members.
Characterization of the reflectivity of various black materials