Flexible non-contact printed humidity sensor: Realization of the ultra-high performance humidity monitoring based on the MXene composite material

MXene is regarded as a promising material in the research of humidity monitoring due to the unique chemical properties (presence of hydrophilic active sites) and physical properties (high specific surface area). In this study, we present a flexible non-contact printed humidity sensor prepared from the copper electrode and MXene composite material modified by the sodium lignin sulfonate (SL) and bacterial cellulose nanofibers (BCNF). Hydroxyl groups and carboxyl groups introduced by the SL effectively improved the bondability of the modified MXene composite material with water molecules. Meanwhile, the insertion of the BCNF optimized the interlaminar structure of the MXene, which is beneficial for the diffusion of water molecules. The humidity sensor possesses an excellent capacitance variation (770.74 % in 97 % RH) with satisfactory sensitivity (0.664 s/0.747 s for response time and recovery time), which is the highest performance among conventional low-dimensional carbon materials. Additionally, the humidity sensor exhibits exceptional structural stability (less than 2.5 % attenuation of the capacitance response after reversal and bending tests), storage stability, and performance repeatability. Eventually, the printed humidity sensor has realized non-contact monitoring of skin moisture, respiratory status, exercise states, and voice detection, revealing significant potential in health care, intelligent actuator, and human-machine interaction.