Publications

Abstract A general theoretical analysis of a 3D generic TENG structure is presented. Using a dimensionless formulation, it is demonstrated that the optimal TENG geometry does not depend on the frequency of the moving dielectric but the external ohmic impedance for maximum power output is inversely proportional to the frequency. It is also found that the energy is proportional to the cube of the size of the TENG, the square of the triboelectric charge density σ T , and the angular frequency ω of the moving dielectric. In the case of a spherical TENG where the moving dielectric is a sphere and the electrodes are spherical caps on a larger sphere three dimensionless parameters that determine the harvested energy are identified: the ratio between the radii of the two spheres = r/R, the polar angle θ of the two spherical caps formed by the electrodes, and = ZεRω, where Z is the external impedance, R is the radius of the large sphere, ε is the permittivity of the system, and ω is the angular frequency of the moving sphere. Under the crude assumption of constant charge density on the electrodes, the optimal parameters can be easily calculated. It is found that θ = 1.1 rad, = 0.67, and = 0.18.

The triboelectric nanogenerator (TENG) is a newly invented technology that is effective for harvesting ambient mechanical energy for portable electronics, self‐powered sensor networks, etc. Here, by introducing segmentation and multilayer integration into the cylindrical TENG, the generator's output is enhanced significantly. With a four‐layer and thirty‐segment configuration, the TENG produces a short‐circuit current of 86 μA (13.5 μA m −2 ) and power of 4.3 mW (676 mW m −2 ) at a rotating speed of 600 rpm, which are respectively over 70 and 15 times higher than those of the one‐layer and one‐segment structure. This makes the TENG a sufficient power supply for conventional electronics, such as light bulbs and temperature sensors. Furthermore, it is demonstrated that the segmentation design is a perfect self‐power management technique to automatically lower the TENG's output voltage and increase its output current without scarifying the output power. The fractal geometry is an effective way to maximize the TENG's contact surface area and thereby the output performance.

Abstract Shelter forests (or shelter‐belts), while crucial for climate regulation, lack monitoring systems, e.g., Internet of Things (IoT) devices, but their abundant wind energy can potentially power these devices using the trees as mounting points. To harness wind energy, an omnidirectional fluid‐induced vibration triboelectric nanogenerator (OFIV‐TENG) has been developed. The device is installed on shelter forest trees to harvest wind energy from all directions, employing a fluid‐induced vibration (FIV) mechanism (fluid‐responding structure) that can capture and use wind energy, ranging from low wind speeds (vortex vibration) to high wind speeds (galloping). The rolling‐bead triboelectric nanogenerator (TENG) can efficiently harvest energy while minimizing wear and tear. Additionally, the usage of double electrodes results in an effective surface charge density of 21.4 µC m −2 , which is the highest among all reported rolling‐bead TENGs. The collected energy is utilized for temperature and humidity monitoring, providing feedback on the effect of climate regulation in shelter forests, alarming forest fires, and wireless wind speed warning. In general, this work provides a promising and rational strategy, using natural resources like trees as the supporting structures, and shows broad application prospects in efficient energy collection, wind speed warning, and environmentally friendliness.

Effective piezoelectric semiconductor based hybrid photocatalysts are successfully developed by assembling TiO2 nanoparticles on ZnO monocrystalline nanoplatelets. The piezopotential can be introduced and tuned by thermal stress on the piezoelectric material of ZnO monocrystalline nanoplatelets through cooling hybrid photocatalysts from high temperature to room temperature with different rates based on the mismatched thermal expansion coefficient of the two materials, which can be used to engineer the heterojunction band structure and significantly enhance the photocatalytic performance in a wide range by improving charge separation. It is proposed that the piezotronic effect enhanced photocatalyst will provide a strategy for high-performance photocatalysis applications.

Abstract As the dominant component for precise motion measurement, angle sensors play a vital role in robotics, machine control, and personalized rehabilitation. Various forms of angle sensors have been developed and optimized over the past decades, but none of them would function without an electric power. Here, a highly sensitive triboelectric self‐powered angle sensor (SPAS) exhibiting the highest resolution (2.03 nano‐radian) after a comprehensive optimization is reported. In addition, the SPAS holds merits of light weight and thin thickness, which enables its extensive integrated applications with minimized energy consumption: a palletizing robotic arm equipped with the SPAS can precisely reproduce traditional Chinese calligraphy via angular data it collects. In addition, the SPAS can be assembled in a medicare brace to record the flexion/extension of joints, which may benefit personalized orthopedic recuperation. The SPAS paves a new approach for applications in the emerging fields of robotics, sensing, personalized medicare, and artificial intelligence.

Due to the fragility and the poor optoelectronic performances of Si, it is challenging and exciting to fabricate the Si-based flexible light-emitting diode (LED) array devices. Here, a flexible LED array device made of Si microwires-ZnO nanofilm, with the advantages of flexibility, stability, lightweight, and energy savings, is fabricated and can be used as a strain sensor to demonstrate the two-dimensional pressure distribution. Based on piezo-phototronic effect, the intensity of the flexible LED array can be increased more than 3 times (under 60 MPa compressive strains). Additionally, the device is stable and energy saving. The flexible device can still work well after 1000 bending cycles or 6 months placed in the atmosphere, and the power supplied to the flexible LED array is only 8% of the power of the surface-contact LED. The promising Si-based flexible device has wide range application and may revolutionize the technologies of flexible screens, touchpad technology, and smart skin.

Abstract Osmotic energy from the ocean has been thoroughly studied, but that from saline‐alkali lakes is constrained by the ion‐exchange membranes due to the trade‐off between permeability and selectivity, stemming from the unfavorable structure of nanoconfined channels, pH tolerance, and chemical stability of the membranes. Inspired by the rapid water transport in xylem conduit structures, we propose a horizontal transport MXene (H‐MXene) with ionic sequential transport nanochannels, designed to endure extreme saline‐alkali conditions while enhancing ion selectivity and permeability. The H‐MXene demonstrates superior ion conductivity of 20.67 S m −1 in 1 M NaCl solution and a diffusion current density of 308 A m −2 at a 10‐fold salinity gradient of NaCl solution, significantly outperforming the conventional vertical transport MXene (V‐MXene). Both experimental and simulation studies have confirmed that H‐MXene represents a novel approach to circumventing the permeability‐selectivity trade‐off. Moreover, it exhibits efficient ion transport capabilities, addressing the gap in saline‐alkali osmotic power generation.

The trends in miniaturization of electronic devices give rise to the attention of energy harvesting technologies that gathers tiny wattages of power. Here this study demonstrates an ultrathin flexible single electrode triboelectric nanogenerator (S‐TENG) which not only could harvest mechanical energy from human movements and ambient sources, but also could sense instantaneous force without extra energy. The S‐TENG, which features an extremely simple structure, has an average output current of 78 μA, lightening up at least 70 LEDs (light‐emitting diode). Even tapped by bare finger, it exhibits an output current of 1 μA. The detection sensitivity for instantaneous force sensing is about 0.947 μA MPa −1 . Performances of the device are also systematically investigated under various motion types, press force, and triboelectric materials. The S‐TENG has great application prospects in sustainable wearable devices, sustainable medical devices, and smart wireless sensor networks owning to its thinness, light weight, energy harvesting, and sensing capacities.

We studied the bending phenomenon of ZnO nanowires (NWs) by using three kinds of sideways physical deposition processes: laser deposition (PLD), sputtering, and evaporation. Room temperature PLD is the most efficient method to bend NWs. The bending is probably caused by the ion implantation into the surface layers. Temperature can influence the bending angle at low temperatures (below 120 °C). The shape-modified NWs may have applications in nanoelectronics, optics, and surface wettability tuning.

Abstract Traditional topical ointment applied on the skin surface has poor drug penetration due to the thickening of the stratum corneum for psoriasis. Microneedles (MNs) provide a desirable opportunity to promote drug penetration. However, the common MNs are difficult to meet the requirement of on‐demand drug delivery. In this study, a smart electrical responsive MNs is fabricated by introducing conductive material of polypyrrole (PPy). Further, a self‐powered controllable transdermal drug delivery system (sc‐TDDS) based on piezoelectric nanogenerator (PENG) is developed. The sc‐TDDS can control drug release by collecting and converting mechanical energy into electrical energy. The sc‐TDDS can release 8.5 ng dexamethasone (Dex) subcutaneously per electrical stimulation. When treating psoriasis‐like skin disease with sc‐TDDS, the inflammatory skin returned to normal after 5 days, which is obviously better than treating with traditional Dex solution coating. This work provides a promising approach of on‐demand transdermal drug release for various disease treatment scenarios.

Abstract Using an Al‐foil of thickness ≈18 μm as a substrate and electrode, a piezoelectric nanogenerator (NG) that is super‐flexible in responding to the wavy motion of a very light wind is fabricated using ZnO nanowire arrays. The NG is used to harvest the energy from a waving flag, demonstrating its high flexibility and excellent conformability to be integrated into fabric. The NG is applied to detect the wrinkling of a human face, showing its capability to serve as an active deformation sensor that needs no extra power supply. This strategy may provide a highly promising platform as energy harvesting devices and self‐powered sensors for practical use wherever movement is available.

Abstract The accuracy and efficiency of shooting reports constitute indispensable cornerstones in modern military training and shooting fields. However, traditional shooting report systems struggle to offer precise and sensitive instant feedback, especially in rare scenarios, such as multiple piercing and shots on the ring boundaries. Simultaneously, ballistic analysis as a pivotal approach in criminal investigations, confronts similar challenges including high costs, complex data processing, and strong professional dependency. Thus, a flexible, high‐temperature resistant, and high‐accuracy recognition intelligent target reporting and ballistic analysis (ITBA) system is designed based on the mechanism of triboelectric nanogenerator (TENG), which recognizes multiple bullet piercings and delivers bullet velocity through a time‐difference algorithm combined with shooting angle to accurately determine the shooting position. Thanks to the novel structural design and preparation method, the ITBA system achieves remarkable integration, lightweight, and industrialization, ensuring exceptional stability even in harsh environments. Furthermore, the ITBA system integrates machine learning techniques to achieve 100% accuracy in bullet material recognition and 97% accuracy in determining shooting angles, providing a solid foundation for enhancing the precision of military training and the scientific rigor of forensic investigations.

Abstract Triboelectric nanogenerator (TENG), as an emerging technology for distributed energy harvesting, provides a promising energy solution for self‐powered environmental monitoring. However, the abrasion of triboelectric materials lowers the output performance of TENGs, severely limiting their practical applications. Herein, a novel travel‐controlled approach, by combining a gear train and cam switch, is proposed to reduce the mechanical wear. The automatic switching between the contact and non‐contact modes can be achieved in a tunable frequency, showing excellent electrical stability by maintaining 90% of electric outputs after continuous operation for 80 h (1 920 000 cycles). Meanwhile, based on the structural optimization, the power density per unit wind speed of the travel‐controlled TENG (TC‐TENG) is doubled as compared with that of previous related works. Moreover, by integrating the triboelectric‐electromagnetic hybrid device with an energy management circuit, a self‐powered close‐looped environmental monitoring and alarming system are demonstrated. Under breezy conditions (below 3 m s −1 ), the system can detect the environmental information continuously and steadily, and transmit it wirelessly to a mobile device. This work renders a novel approach to reducing the wear in TENGs toward self‐powered wireless sensing systems, showing broad application prospects in distributed unmanned environmental monitoring, smart farming, and Internet of Things.