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.

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.

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.

A tactile sensor should be able to detect both normal and tangential forces, which is mandatory for simulating human hands, but this fundamental function has been overlooked by most of the previous studies. Here, based on a triboelectric nanogenerator (TENG) with single-electrode mode, the fully elastic and metal-free tactile sensor that can detect both normal and tangential forces is proposed. With tiny burr arrays on the contact interface to facilitate the elastic deformation, the detected normal pressure by the device can reach to 1.5 MPa with a sensitivity of about 51.43 kPa V −1 , and a large range of tangential forces can be detected ranging from 0.5 to 40 N with rough sensitivity of 0.83 N V −1 (0.5-3 N) and 2.50 N V −1 (3-40 N). Meanwhile, the applied tangential forces from different directions can also be clearly distinguished by the four-partitioned electrode structure. Moreover, a shield film is coated on the top surface of the device, which can screen the electrostatic interference and enhance the repeatability of the device. The demonstrated concept of this self-powered tactile sensor has excellent applicability for industrial robotics, human-machine interactions, artificial intelligence, etc.

Wind is one of the most important sources of green energy, but the current technology for harvesting wind energy is only effective when the wind speed is beyond 3.5–4.0 m s−1. This is mainly due to the limitation that the electromagnetic generator works best at high frequency. This means that light breezes cannot reach the wind velocity threshold of current wind turbines. Here, a high‐performance triboelectric nanogenerator (TENG) for efficiently harvesting energy from an ambient gentle wind, especially for speeds below 3 m s−1 is reported, by taking advantage of the relative high efficiency of TENGs at low‐frequency. Attributed to the multiplied‐frequency vibration of ultra‐stretchable and perforated electrodes, an average output of 20 mW m−3 can be achieved with inlet wind speed of 0.7 m s−1, while an average energy conversion efficiency of 7.8% at wind speed of 2.5 m s−1 is reached. A self‐charging power package is developed and the applicability of the TENG in various light breezes is demonstrated. This work demonstrates the advantages of TENG technology for breeze energy exploitation and proposes an effective supplementary approach for current employed wind turbines and micro energy structure.

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.

meet big data transmission. [1][2][3] Intelligent transportation system based on IoTs includes wireless sensor, telecommunication network, safe driving warning. [4][5][6][7] For the overland traffic, the service is easy to be realized because of the strong power grid. However, the power supply of traffic warning system is limited on a vast sea area. Although some wireless warning devices like radio Aids-to-Navigation have been developed, they are generally powered by conventional batteries, which usually have limited lifetime and environmental issues. [8][9][10] Since ocean occupies 70% of the earth surface area and wave energy distributes vastly in these water bodies, it is promising to utilize the water wave energy as sustainable power supply. [11,12] Compared to other clean energy, water waves are also less affected by the alternating day and night as well as weather. [13,14] However, the capture of wave energy and the development of selfpowered navigation warning system is still difficult, due to the current technology limitation.Recently, the invention of triboelectric nanogenerator (TENG) has offered an unprecedented approach to collect environmental energy. [15][16][17] Based on coupling effect of triboelectrification and electrostatic induction, the TENG devices perform well in low-frequency resources harvesting. [18][19][20][21][22] Considering the massive amount on earth, the blue energy, which adopts TENG networks to collect wave energy, has been regarded as one of the major application fields of TENGs. [23,24] Accordingly, a series of TENG prototypes have been developed targeting wave energy harvesting. [25][26][27][28][29][30] Many kinds of novel materials and architectures are applied to these TENG prototypes, [28][29][30][31] and small electronics such as light-emitting diode indicators, thermometers have been driven by the harvested energy. [32,33] Although some wireless transmitters are also driven successfully by the TENG-based wave energy harvester, the transmission distance of which can only reach a few meters away. [34,35] Furthermore, the power supply circuits of these wireless transmission is not automatic but manual, which make these reported demonstrations hard to achieve really application value.In this work, a hybrid nanogenerator with TENG and electromagnetic generator (EMG) based on an optimized pendulum structure is reported to effectively harvest wave energy, used asThe internet of things in the context of the ocean is vitally important. For ships sailing on the wide ocean in adverse weather conditions, evasion of marine islands and reefs is crucial to ensure safe navigation. Here, a hybrid wave energy harvesting nanogenerator is proposed (HW-NG) as a power source for longdistance wireless transmission, and demonstrated a self-powered route avoidance warning system for ocean navigation. The HW-NG is developed based on a triboelectric nanogenerator (TENG) and an electromagnetic generator (EMG), integrated by a pendulum structure. The TENG based on a contact-separation mode is designe...

No abstract