Miniaturized and High Volumetric Energy Density Power Supply Device Based on a Broad-Frequency Vibration Driven Triboelectric Nanogenerator.

The widespread vibration is one of the most promising energy sources for IoT and small sensors, and broad-frequency vibration energy harvesting is important. Triboelectric nanogenerators (TENGs) can convert vibration energy into electrical energy through triboelectricity and electrostatic induction, providing an effective solution to the collection of broad-frequency vibration energy. Also, the power supply in constrained and compact spaces has been a long-standing challenge. Here, a miniaturized power supply (MPS) based on a broad-frequency vibration-driven triboelectric nanogenerator (TENG) is developed. The size of the MPS is 38 mm × 26 mm × 20 mm, which can adapt to most space-limited environments. The TENG device is optimized through theoretical mechanical modeling for the external stimuli, it can efficiently harvest vibrational energy in the frequency range of 1-100 Hz and has a high output power density of 134.11 W/cm3. The developed device demonstrates its practical application potential in powering small electronics like LEDs, watches, and timers.

Hierarchical Wrinkles with Piezopotential Enhanced Surface Tribopolarity for High-Performance Self-Powered Pressure Sensor.

Achieving both high sensitivity and wide detecting range is significant for the applications of triboelectric nanogenerator-based self-powered pressure sensors (TPSs). However, most of the previous designs with high sensitivity usually struggle in a narrow pressure detection range (<30 kPa) while expanding the detection range normally sacrifices the sensitivity. To overcome this well-known obstacle, herein, piezopotential enhanced triboelectric effect realized by a rationally designed PDMS/ZnO NWs hierarchical wrinkle structure was exploited to develop a TPS (PETPS) with both high sensitivity and wide detecting range. In this PETPS design, the piezopotential derived from the deformation of ZnO NWs enhances its tribo-charge transferring ability; meanwhile, the hierarchical structure helps to establish a dynamically self-adjustable contact area. Benefiting from these advantages, the PETPS simultaneously achieves high sensitivity (0.26 nC cm-2 kPa-1 from 1 to 25 kPa, and 0.02 nC cm-2 kPa-1 from 25 to 476 kPa), fast response (46 ms), wide sensing range (1 to 476 kPa), and good stability (over 4000 cycles). In addition, the output charge density that is independent of the speed rate of driven force was adopted as the sensing signal of PETPS to replace the commonly used peak voltage/current values, enabling it more adaptive to accurately detect pressure variation in real applications.

Constructing Heterogeneous Photocatalysts Based on Carbon Nitride Nanosheets and Graphene Quantum Dots for Highly Efficient Photocatalytic Hydrogen Generation.

Although graphitic carbon nitride nanosheets (CNs) with atomic thickness are considered as promising materials for hydrogen production, the wide band gap (3.06 eV) and rapid recombination of the photogenerated electron-hole pairs impede their applications. To address the above challenges, we synergized atomically thin CNs and graphene quantum dots (GQDs), which were fabricated as 2D/0D Van der Waals heterojunctions, for H2 generation in this study. The experimental characterizations indicated that the addition of GQDs to the π-conjugated system of CNs can expand the visible light absorption band. Additionally, the surface photovoltage spectroscopy (SPV) confirmed that introducing GQDs into CNs can facilitate the transport of photoinduced carriers in the melon chain, thus suppressing the recombination of charge carriers in body. As a result, the H2 production activity of the Van der Waals heterojunctions was 9.62 times higher than CNs. This study provides an effective strategy for designing metal-free Van der Waals hetero-structured photocatalysts with high photocatalytic activity.

Trapezoidal Cantilever-Structure Triboelectric Nanogenerator Integrated with a Power Management Module for Low-Frequency Vibration Energy Harvesting.

Wide-band vibration is abundant in various industrial equipment, but extracting low frequency energy is challenging. Here, we demonstrated a trapezoidal cantilever-structure triboelectric nanogenerator (C-TENG) that can efficiently harvest energy from vibration in the range of 1-22 Hz. The C-TENG is fabricated with a flexible film electrode, and its mechanical model is analyzed with structural mechanics for the optimal performance of the device. The C-TENG can harvest the vibration source with a frequency as low as 1 Hz, and its output power density reaches 62.2 W/m3 at a vibration frequency of 5 Hz. Furthermore, a power management module is developed, and its integration with TENG arrays enables the self-powered timing and wireless transmitting systems. This work proposes an effective strategy to harvest ubiquitously distributed but usually neglected vibration sources, which would contribute to the development of self-powered electronic systems and Internet of Things.

Stimulation of ambient energy generated electric field on crop plant growth.

Eco-friendly technologies are of great significance to agricultural sustainability due to the environmental damage caused by agricultural activities. Here, we report a wind and rain energy-driven electrical stimulation system for enhancing crop production. The system is based on an all-weather triboelectric nanogenerator (AW-TENG), which is composed of a bearing-and-hair structured triboelectric nanogenerator (TENG) and a raindrop-driven TENG. Treated by the self-generated high-voltage electric field, the system can increase pea seeds germination speed by ~26.3% and pea yield by ~17.9%. By harvesting environmental wind and raindrop energy, the AW-TENG can be used to drive various agricultural sensors for optimizing plant growth. This work provides a fresh direction for self-powered systems in safe, efficient and eco-friendly agricultural production improvement and may profoundly contribute to the construction of a sustainable economy.

Probing Contact-Electrification-Induced Electron and Ion Transfers at a Liquid-Solid Interface.

As a well-known phenomenon, contact electrification (CE) has been studied for decades. Although recent studies have proven that CE between two solids is primarily due to electron transfer, the mechanism for CE between liquid and solid remains controversial. The CE process between different liquids and polytetrafluoroethylene (PTFE) film is systematically studied to clarify the electrification mechanism of the solid-liquid interface. The CE between deionized water and PTFE can produce a surface charges density in the scale of 1 nC cm-2 , which is ten times higher than the calculation based on the pure ion-transfer model. Hence, electron transfer is likely the dominating effect for this liquid-solid electrification process. Meanwhile, as ion concentration increases, the ion adsorption on the PTFE hinders electron transfer and results in the suppression of the transferred charge amount. Furthermore, there is an obvious charge transfer between oil and PTFE, which further confirms the presence of electron transfer between liquid and solid, simply because there are no ions in oil droplets. It is demonstrated that electron transfer plays the dominant role during CE between liquids and solids, which directly impacts the traditional understanding of the formation of an electric double layer (EDL) at a liquid-solid interface in physical chemistry.

Dual-Stimulus Smart Actuator and Robot Hand Based on a Vapor-Responsive PDMS Film and Triboelectric Nanogenerator.

Intelligent actuating materials with vapor-stimulated mechanical response usually require complicated synthesizing processes or have a high cost. Here, we found that the UV/O3-modified poly(dimethylsiloxane) PDMS) film can show spontaneous curling deformation when it encounters small alcohol molecules such as ethanol vapor. Based on the coupling of the vapor-responsive PDMS film and triboelectric nanogenerator (TENG), a flexible actuator for object transport and a double-finger gripper for loading small objects are designed. The deformation and size change induced by vapor stimulation help these devices to adapt to the target objects of different sizes, while the electrostatic force provided by TENG can move or control the target object, for instance, the double-finger gripper can clamp an object of a weight of 6 g.

Power generation from the interaction of a liquid droplet and a liquid membrane.

Triboelectric nanogenerators are an energy harvesting technology that relies on the coupling effects of contact electrification and electrostatic induction between two solids or a liquid and a solid. Here, we present a triboelectric nanogenerator that can work based on the interaction between two pure liquids. A liquid-liquid triboelectric nanogenerator is achieved by passing a liquid droplet through a freely suspended liquid membrane. We investigate two kinds of liquid membranes: a grounded membrane and a pre-charged membrane. The falling of a droplet (about 40 µL) can generate a peak power of 137.4 nW by passing through a pre-charged membrane. Moreover, this membrane electrode can also remove and collect electrostatic charges from solid objects, indicating a permeable sensor or charge filter for electronic applications. The liquid-liquid triboelectric nanogenerator can harvest mechanical energy without changing the object motion and it can work for many targets, including raindrops, irrigation currents, microfluidics, and tiny particles.

Environmental Energy Harvesting Adapting to Different Weather Conditions and Self-Powered Vapor Sensor Based on Humidity-Responsive Triboelectric Nanogenerators.

Triboelectric nanogenerators (TENGs) have been widely applied for energy harvesting and self-powered sensing, whereas smart deformable materials can be combined with the TENG to acquire a more intelligent and self-adaptive system. Here, based on the vapor-driven actuation material of a perfluorosulfonic acid ionomer (PFSA), we propose a type of humidity-responsive TENG. The integrated TENG array can automatically bend to the desired angles in response to different humidity conditions, and thus, it can effectively collect energy from both wind and rain drops, where the power density can reach 1.6 W m-2 at a wind speed of 25 m s-1 and 230 mW m-2 under rainy conditions. Meanwhile, this TENG array can fully lay down in dry weather, using the reflective surface to reflect sunlight and heat radiation. The vapor absorption process of the PSFA film can also result in the charge accumulation process. Accordingly, relying on the strong absorption capability of PFSA, a TENG-based vapor sensor with high sensitivity has been developed for monitoring chemical vapor leakage and humidity change. This work opens up a promising approach for the application of the humidity-responsive materials in the field of energy harvesting and self-powered sensors. It can also promote the development of TENG toward a more intelligent direction.

Piezo-phototronic Effect Enhanced Photodetector Based on CH3NH3PbI3 Single Crystals.

Piezoelectric organic-inorganic lead halide perovskites have recently attracted much attention in the field of optoelectronic devices. However, their piezoelectric properties as a possible way to modulate device performances have rarely been reported. Here, we study experimentally a photodetector based on CH3NH3PbI3(MAPbI3) single crystals, whose performance is effectively modulated via an emerging effect-the piezo-phototronic effect, which is to use the piezoelectric polarization charges to tune the optoelectronic processes at the interface. A piezoelectric coefficient of 10.81 pm/V of the CH3NH3PbI3 single crystal is obtained. Under 680 nm laser illumination with a power density of 3.641 mW/cm2 and at an external bias of 2 V, compared to the case without straining, the light current of the photodetector is enhanced by ∼120% when a 43.48 kPa compressive pressure is applied. The response speed of the photocurrent is 3 and 2 times faster than the cases without applying pressure for the light-on and light-off states, respectively. This work proves that the performance of the photodetector based on MAPbI3 single crystals can be effectively enhanced by the piezo-phototronic effect, providing a good method for optimizing the performance of future perovskite-based optoelectronic devices.

Characterization of NlHox3, an essential gene for embryonic development in Nilaparvata lugens.

Hox genes encode transcriptional regulatory proteins that control axial patterning in all bilaterians. The brown planthopper (BPH), Nilaparvata lugens (Hemiptera: Delphacidae), is a destructive insect pest of rice plants in Asian countries. During analysis of the N. lugens transcriptome, we identified a Hox3-like gene (NlHox3) that was highly and specifically expressed in the embryonic stage. We performed functional analysis on the gene to identify its roles in embryonic development and its potential use as a target in RNA interference (RNAi) based pest control. The sequence analysis showed that NlHox3 was homologous to the Hox3 gene and was most closely related with zen of Drosophila. There were no significant differences in oviposition between the treated and control females after injecting double-stranded RNA of NlHox3 (dsNlHox3) into newly emerged female adult BPHs; however, there was a significant difference in the hatchability of those eggs laid, which no egg from the treated group hatched normally. Injecting female adult BPHs with dsNlHox3 led to necrosis of these offspring embryos, with eye reversal and undeveloped organs, suggesting that NlHox3 was an essential gene for embryonic development and might be a potential target for RNAi-based control of this insect pest.

Self-Powered Microfluidic Transport System Based on Triboelectric Nanogenerator and Electrowetting Technique.

Electrowetting technique is an actuation method for manipulating position and velocity of fluids in the microchannels. By combining electrowetting technique and a freestanding mode triboelectric nanogenerator (TENG), we have designed a self-powered microfluidic transport system. In this system, a mini vehicle is fabricated by using four droplets to carry a pallet (6 mm × 8 mm), and it can transport some tiny object on the track electrodes under the drive of TENG. The motion of TENG can provide both driving power and control signal for the mini vehicle. The maximum load for this mini vehicle is 500 mg, and its highest controllable velocity can reach 1 m/s. Freestanding TENG has shown excellent capability to manipulate microfluid. Under the drive of TENG, the minimum volume of the droplet can reach 70-80 nL, while the tiny droplet can freely move on both horizontal and vertical planes. Finally, another strategy for delivering nanoparticles to the designated position has also been demonstrated. This proposed self-powered transport technique may have great applications in the field of microsolid/liquid manipulators, drug delivery systems, microrobotics, and human-machine interactions.

Tra-2 Mediates Cross-Talk Between Sex Determination and Wing Polyphenism in Female Nilaparvata lugens.

Sexual dimorphism and wing polyphenism are important and evolutionarily conserved features of many insect species. In this article, we found a cross-talk linking sexual differentiation with wing polyphenism in the brown planthopper (BPH) Nilaparvata lugens (order: Hemiptera). Knockdown of the sex determination gene Transformer-2 in N. lugens (NlTra-2) in nymph caused females to develop into infertile pseudomales containing undeveloped ovaries. Whereas males treated with dsNlTra-2 exhibited normal morphology, but lost fertility. Knockdown of NlTra-2 in adult females (maternal RNAi) resulted in long-winged female offspring, indicating that maternal RNAi changed the wing morphs in female offspring. In addition, silencing of NlTra-2 down-regulated the expression of the forkhead transcription factor FoxO (NlFoxO), and simultaneously up-regulated the expression of phosphatidylinositol-3-OH kinase (PI(3)K)-protein kinase B (NlAkt), the two critical genes in the insulin signaling pathway. Furthermore, the long-winged effect caused by maternal dsNlTra-2 RNAi could be reversed by silencing of NlInR1 and NlAkt, leading to short-winged morphs. We propose that there is a cross-talk between the sexual differentiation and wing polyphenism pathways mediated by NlTra-2 during embryonic stages.