A flexible MXene–carbon nanotube-based triboelectric nanogenerator for self-powered pH sensors

Two-dimensional materials with semiconducting nature exhibit triboelectric responses, which is an important factor for the development of nanogenerators, tribotronics, and various electronic devices. Here, the manuscript describes the synthesis of MXene from the Ti₃AlC₂ MAX phase using the etching method, followed by the development of a flexible self-powered triboelectric nanogenerator (FTENG) based on Ti₃C₂T_<i>x</i> MXene-carbon nanotubes (CNTs), which produces an output voltage of 47.6 V, which is greater than that of the pure carbon nanotube-based TENG. For the synthesized MXene, electron microscopy and X-ray diffraction results show that Ti₃C₂T_<i>x</i> MXene has a layered morphology and forms a hexagonal structure. The band gap of Ti₃C₂T_<i>x</i> MXene is 2.1 eV, according to UV-Vis-NIR spectroscopy, indicating that it is semi-conducting. The FTENG results also reveal that the Ti₃C₂T_<i>x</i> MXene-carbon nanotube-based triboelectric nanogenerator is sensitive to varying pH. When the solution of varying pH interacts with an active triboelectric layer, its electron affinity, dielectric constant, and dielectric loss vary, causing a drastic change in the triboelectric output voltage. The dielectric constant of the MXene-multiwalled carbon nanotube is 66.54, and that of pristine carbon nanotubes is 18.06. Due to the large surface area, energy storage capacity, and dielectric enhancement of MXene, the Ti₃C₂T_<i>x</i> MXene-carbon nanotube-based triboelectric nanogenerator shows a higher output voltage than the pure carbon nanotube TENG. The current manuscript reveals a novel approach for harvesting mechanical energy to fabricate a self-powered pH sensor using Ti₃C₂T_<i>x</i> MXene and carbon nanotubes.