Ultrathin niobium carbide nanosheets for humidity sensing

MXene, as a group of prominent two-dimensional (2D) materials, has attracted the attention in the field of sensors due to its large specific surface area, good electronic conductivity and abundant functional groups. In addition to the widely reported titanium carbide (Ti₃C₂T_x), other MXene nanomaterials are gradually developed in recent years. Herein, niobium carbide (Nb₂CT_x) MXene with ultrathin nanosheets is synthesized through the typical liquid-phase exfoliation (hydrofluoric acid) and special delamination (tetrapropylammonium hydroxide) method. The resistive-type humidity sensor prepared by simple dropping coating is tested at room temperature (25 °C). The results show that the resistance variation of the Nb₂CT_x humidity sensor is more than three orders of magnitude within the humidity range from 0 to 91.5 % relative humidity (RH) and the response (recovery) time of the sensor is only 1 s (8 s). Moreover, the Nb₂CT_x humidity sensor exhibits small humidity hysteresis (∼2.5 %RH) and good linearity. Ultrathin Nb2CTx nanosheets provide copious adsorption sites for water molecules, the ionization of physical adsorbed water molecules leads to a rapid decline in resistance. The ultrafast response of Nb₂CT_x sensor is expected to be applied in the field of industry, agriculture and human-respiration humidity monitoring.