2D Ti₃C₂T_x-MXene nanosheets and graphene oxide based highly sensitive humidity sensor for wearable and flexible electronics

To explore the potential of Ti₃C₂T_x-MXenes as an electrode over traditional metals, we designed a high-performance and cost-effective humidity sensor using 2D Ti₃C₂T_x MXene nanosheets (TMNSs) as electrodes and Graphene oxide (GO) as a sensing layer. The sensor was fabricated on a flexible and transparent Cyclic Olefin Copolymer (COC) substrate using UV-photolithography, spin coating, and spray coating techniques. Electrical impedance measurements demonstrated the sensor's remarkable sensitivity to humidity, with a response range of 6 % to 97 % at frequencies of 1 kHz and 10 kHz. The sensor exhibited fast response and recovery times of 0.8 s and 0.9 s, respectively, and maintained stable performance over 24 h. We further employed DFT simulations to establish the atomic level understanding of humidity sensing. The findings demonstrated the presence of a physical bond between the hydrogen (H) and oxygen (O) atoms, which are part of the water molecule and OH group, respectively, in the process of humidity sensing. Furthermore, the OH-configuration of graphene oxide (GO) acts as the main active site in humidity sensing, outperforming the O-configuration, due to its higher adsorption energy and charge transfer. Moreover, real-world applications for this 2D materials-based sensor were demonstrated, including non-contact proximity sensing and human breathing detection, demonstrating its potential. This study makes a substantial contribution to the development of low-cost humidity sensors based on 2D materials, with implications for a wide range of humidity sensing applications.