Study On Applation Of Novel Two-dimensional Material MXene In Triboelectric/Tribovoltaic Nanogenerators

With the rapid development of artificial intelligence,big data,and the Internet of Things,human‘s demands for miniaturized and distributed power sources have increased dramatically.Compared with traditional electromagnetic generators（EMGs）and solar cells,piezoelectric nanogenerators（PENGs）and triboelectric nanogenerators（TENGs）demonstrate better efficiency to convert random,low-frequency mechanical energy and other forms of high-entropy energy,promising to form distributed power supplies.Tribovoltaic nanogenerators（TVNGs）are an emerging high-entropy energy harvesting technology with the advantages of low matching resistance,high current density,and continuous output performance,which are not available in traditional piezoelectric and triboelectric nanogenerators.It has great potential for development in the field of energy harvesting and self-driven sensing.Two-dimensional（2D）carbides and nitrides（MXene）has been developed to produce dozens of different chemical species since it was first reported.MXene exhibiting many properties such as tunable electronic,optical,mechanical and electrochemical properties or other chemical properties.Therefore,it has a wide range of applications in optoelectronics,electromagnetic interference shielding and wireless antennas,as well as in energy storage,catalysis,sensing and medicine.Here,an MXene/polyvinyl alcohol（PVA）hydrogel TENG（MH-TENG）is presented with simple fabrication,high output performance,and versatile applications.The doping of MXene nanosheets promotes the crosslinking of the PVA hydrogel and improves the stretchability of the composite hydrogel.The MXene nanosheets also form microchannels on surfaces,which not only enhances the conductivity of the hydrogel by improving the transport of ions but also generates an extra triboelectric output via a streaming vibration potential mechanism.The measured open-circuit voltage of the MH-TENG reaches up to230 V even in a single-electrode mode.The MH-TENG can be stretched up to200%of the original length and demonstrates a monotonical increasing relationship between the stretchable length and the short-circuit voltage.By utilizing the MH-TENG‘s outstanding stretchable property and ultrahigh sensitivity to mechanical stimuli,applications in wearable movement monitoring,high-precision written stroke recognition,and low-frequency mechanical energy harvesting are demonstrated.Besides,an MXene layer and a semiconducting silicon wafer are assembled into a tribovoltaic nanogenerator（named MS-TVNG）.The output peak current of the MS-TVNG reaches up to 22μA for a P-type（0.1–0.5Ω·cm）silicon wafer under a normal force of 4.56 N and a sliding speed of 2m·s^-1.Owing to the unique metal characteristics of the MXene layer,the performance is superior to those previously reported TVNGs using traditional metals.The layered structure of MXene endows the real-time MS-TVNG with outstanding wear-resistance and stable output properties.The performance of the MS-TVNG can be tuned by the doping type and concentration of the silicon wafer,as well as by the pressure and the relative sliding speed between two friction surfaces.The MSTVNG has proven to be a solid foundation for high-performance self-powered speed sensors and has excellent potentials for application.