Ti 3 C 2 T x MXene with an organ-like structure was synthesized from Ti 3 AlC 2 (MAX phase) through the typical hydrofluoric (HF) acid etching method. Ti 3 C 2 T x MXene was further alkaline-treated with a sodium hydroxide solution to obtain alkalized Ti 3 C 2 T x . Room-temperature planar-type gas-and humidity-sensing devices were also fabricated by utilizing Ti 3 C 2 T x MXene and alkalized Ti 3 C 2 T x sensing material based on the dip coating method, respectively. The intercalation of the alkali metal ion (Na + ) and the increase of the surface terminal oxygen−fluorine ratio ([O]/[F]) in Ti 3 C 2 T x can effectively improve humidity-and gas-sensing properties at room temperature. The developed alkalized Ti 3 C 2 T x sensor exhibited excellent humidity-sensing characteristics (approximately 60 times response signal change) in the relative humidity (RH) with a range of 11−95% and considerable NH 3 sensing performance (28.87% response value to 100 ppm of NH 3 ) at room temperature. The improvement of NH 3 and humidity-sensing properties indicated that alkalized Ti 3 C 2 T x has great potential in chemical sensors, especially in NH 3 and humidity sensors. KEYWORDS: MXene, organ-like structure, alkalized Ti 3 C 2 T x , NH 3 and humidity sensing, room temperature

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Human skin is a self-healing mechanosensory system that detects various mechanical contact forces efficiently through three-dimensional innervations. Here, we propose a biomimetic artificially innervated foam by embedding three-dimensional electrodes within a new low-modulus self-healing foam material. The foam material is synthesized from a one-step self-foaming process. By tuning the concentration of conductive metal particles in the foam at near-percolation, we demonstrate that it can operate as a piezo-impedance sensor in both piezoresistive and piezocapacitive sensing modes without the need for an encapsulation layer. The sensor is sensitive to an object’s contact force directions as well as to human proximity. Moreover, the foam material self-heals autonomously with immediate function restoration despite mechanical damage. It further recovers from mechanical bifurcations with gentle heating (70 °C). We anticipate that this material will be useful as damage robust human-machine interfaces.