Charge-transfer Mechanism And Self-powered Sensing Applications Of Triboelectric Nanogenerator

With the development of the Internet of Things,wearable electronics,and big data,there has been an explosive growth of the monitoring devices,which has presented miniaturization,wireless portability,and multi-functionality.Traditional power supply units such as batteries cannot meet the requirement of their energy consumption.Therefore,the self-powered technology harvesting energy from the environment is highly demanded for the development of sensor networks.Among the most energy harvesting methods,more attention is paid to the triboelectric nanogenerator(TENG)that shows great ability in the low-frequency energy harvesting from the environment and human motion and possesses merits of high efficiency,simple structure,low cost,and to name a few.At the progressive development of TENG,the charge transfer mechanism of which is stilled unsettled.Moreover,the performance and sensing applications of the TENG need to be constantly promoted.In this paper,we systematically studied the charge transfer mechanism of the contact electrification,prepared the novel triboelectric materials,and optimized the structure design and performance of the TENG.In addition,the self-powered traffic volume sensor,acceleration sensor,and tactile sensor based on triboelectric effect were proposed.Details are as follows:(1)Debate on the contact electrification(CE)between two chemically identical materials has persisted for many decades.In this paper,by preparing the contact-separation mode TENG using identical materials that working at room temperature and high temperature.The distribution,polarity,and diffusion of the tribo-charges are studied regarding its dependence on curvatures of the sample surfaces.It is found that the positive curvature surfaces are net negatively charged,while the negative curvature surfaces tend to be net positively charged.Further verification on the electron transform dominant mechanism is conducted under vacuum and higher temperature conditions.Based on the received data,we propose a curvature-dependent charge transfer model by introducing the curvature-induced energy shifts of the surface states.(2)The inner charge transfer mechanism of the triboelectric materials is unclear.In this paper,the MXene embedded polyvinylidene fluoride(PVDF)membrane is fabricated as the contact layer of TENG,and the charge transfer regulation of which is studied.A charge transfer percolation model is proposed,in which the surface charge density of TENG maximizes when the content of the conductive filler reaches near the percolation limit,which is proved by the experiment results and theoretical analysis.At the optimal content of MXene,the surface charge density of the TENG is enhanced by 350%.This model provides the guidelines for the preparation of high-performance tribo-materials.(3)As the output current of TENG is relatively low,here,we present a hybridized nanogenerator of TENG and an electromagnetic generator.The output performance of the hybridized nanogenerator is significantly enhanced by introducing nanostructured materials and designing a power management circuit,showing an output power density of 55.7 W/m3.Moreover,the device is demonstrated as a self-powered traffic volume sensor for long-term and stable traffic volume monitoring in the remote tunnel by harvesting energy from the vehicle moving.(4)Poor durability and low effective contact area of the solid-solid contact triboelectric nanogenerator overshadow the real applications and industrialization of which.In this paper,the durability and the performance of the TENG are highly enhanced by introducing the liquid metal in the device and establishing a solid-liquid contact interface.Besides,we fabricated a self-powered acceleration sensor based on liquid metal triboelectric nanogenerator that presents the sensitivity of 0.26 V·s/m2 with the detection range of 0-60 m/s2.The output of the self-powered acceleration sensor shows a negligible decrease over 200,000 cycles.Finally,the acceleration sensor is demonstrated in mechanical vibration monitoring and human gait analysis.(5)The 3D acceleration sensor is an essential component in vehicle restraint systems.Traditional acceleration sensor needs an external power supply and suffers from low sensitivity as well as high cost.In this paper,we design a self-powered,high sensitive,high durable,low cost,and highly integrated 3D acceleration sensor because of the liquid metal and coded strategy of the electrodes.The device volume and weight of the sensor are 4.5 cm3 and 3.63g.The acceleration sensor possesses the sensitivity of 800 mV/g with the detection range of 0-100 m/s2 in the horizontal direction and 0-50 m/s2 in the vertical direction.Furthermore,the 3D acceleration sensor is demonstrated as a part of the airbag system to spot the collision position and force of the car simultaneously.(6)Electronic skin(E-skin)shows wide applications in human physiological signal monitoring and robotic tactile perception,a low-cost and scalable fabrication method is highly desired for its industrialization.In this paper,we proposed a low-cost and scalable method to engineer wrinkled polydimethylsiloxane(PDMS)membrane by introducing capillary force caused by water evaporation into the polymerization process,and the growth dynamics are systematically investigated.The wavelength of the wrinkles can be manipulated from 250 nm to 10.5 ?m.A flexible tactile sensor with nano-wrinkled PDMS based on contact electrification was fabricated and the sensitivity of which was enhanced by 327%.Moreover,it demonstrated great potentials in tactile perception and human physiological signal monitoring.