MXene/Carboxylated Cellulose Nanofiber Inks for Direct Ink Writing Electromagnetic Interference Shielding, Humidity Sensing, and Joule Heating

Two-dimensional transition metal carbide/nitride (MXene)-based conductive inks are promising in the scalable production of printed electronics and wearable devices. Nevertheless, to realize desirable rheological properties of MXene-based inks and the multifunction of the resulting printed devices is still challenging. Herein, MXene inks with tunable rheological properties were developed by inducing carboxylated cellulose nanofibers (C–CNFs) modifier. The versatile rheological properties of MXene inks facilitate the preparation of MXene gratings by direct ink writing (DIW) and multifunctional devices integrated with electromagnetic interference (EMI) shielding, Joule heaters, and humidity sensors. The highest average EMI shielding effectiveness (SE) is 33.0 dB, with specific EMI SE up to 137481.5 dB cm2 g–1. Meanwhile, when functioning as a Joule heater, a low-voltage drive and excellent cyclic and long-term stability can be observed. In addition, the humidity-sensing function integrated with wireless transmission shows a maximum response value of 2768%. The MXene gratings fabricated by DIW are multifunctional and can be applied to the next generation of wearable devices.