High-Performance Humidity Sensor Based on Urchin-Like Composite of Ti3C2 MXene-Derived TiO2 Nanowires.  Humidity sensors have broad applications in health monitoring, environmental protection and human-machine interface, and robotics. Here, we developed a humidity sensor using alkali oxidation method to grow in situ TiO2 nanowires on two-dimensional Ti3C2 MXene. With an order of magnitude larger surface area compared to pure Ti3C2 or TiO2 materials, the urchin-like Ti3C2/TiO2 composite demonstrates a record high sensitivity in a low relative humidity (RH) environment (∼280 pF/% RH from 7% RH to 33% RH). Complex impedance spectroscopy and Schottky junction theory were employed to understand the underlying sensing mechanisms of the Ti3C2/TiO2 composite under various humidity conditions. We demonstrate the application of humidity sensors made with the Ti3C2/TiO2 composite for noncontact detection of the presence of various liquids as well as human fingers.