Leo N.Y. Cao

As wearable devices in the fields of medical health, human–computer interaction, and motion detection continue to diversify in their materials and forms, they show vast application potential. Cellulose materials are emerging as prominent materials for fabricating flexible wearable electronic devices because of their favorable skin compatibility, cost-effectiveness, and abundance. However, there is little research on the use of kapok cellulose in wearable electronics. This study addresses this knowledge gap by exploring the high-yield production and waste recycling potential of kapok cellulose. To overcome the limitations of conventional cellulose films, such as poor flexibility, high haze, and limited light transmittance, a kapok cellulose nanofiber film (KCNF) with a transparency of > 90 % and a tensile strain of > 20 % is prepared. The use of of KCNF as a friction electric material in the triboelectric nanogenerator …

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 …

As one of the few self-powered instruments and devices, triboelectric nanogenerators (TENGs) have been developed for more than 10 years since its invention in 2012. With wide material selections and diverse design structures, and without having to use an external power supply, TENG has been applied in many key technologies. By the end of 2022, more than 16,000 researchers from 83 countries and regions around the world have authored scientific papers in TENG. In this review, we start from the theoretical principles and working mechanisms of TENG, and discuss its 5 major fields of application, namely, as self-powered sensors, high-voltage energy devices, blue energy devices, micro/nano-energy devices, and solid–liquid interface probes. Next, we review the breakthrough progress made using TENG as commercial products in the following fields: medical health, intelligent security, and marine energy …

The utilization of unmanned aerial vehicles (UAVs) is on the rise across various industries. In such a scenario, the issue of flight safety for these UAVs becomes increasingly paramount. Currently, UAVs exhibit shortcomings in flight attitude perception compared to more mature manned aircraft, especially concerning the position sensing of flight actuation, which poses significant safety risks. Mature position monitoring solutions for flight actuation used in manned aircraft cannot be directly integrated into systems of UAV due to compatibility issues. This necessitates the development of new position sensing technologies to address this challenge. Triboelectric nanogenerators, with their advantages of miniaturization, self‐powering capabilities, and the ability to generate voltage‐level electrical signals, are chosen to form a part of the position detection system for sensors in UAVs. In this study, a self‐powered …

Controlling the motion of charge carriers in semiconductor materials is a fundamental strategy for achieving many functional devices, which is typically achieved by applying an external voltage source. Herein, using the electrostatic potential generated by a triboelectric material taken as a sliding “gate”, a functional current is generated across a semiconductor channel when the gate is moving in parallel to the dielectric surface. Systematic studies verify that the motion of the electrified “gate” induces the regional and dynamical doping of the semiconductor channel, thereby driving the carrier transport without applying an external voltage. This sliding-gated generator achieves mechanoelectric energy conversion based on the coupled triboelectrification effect and electrostatic field effect and is therefore termed as a field effect nanogenerator (FENG). It can output electrical currents with a waveform that follows well with …

The anti‐glare panels along highways can block the dazzling lights of opposing vehicles at night, playing an important role in the highway safety. Inspired by the highway anti‐glare panels, wind energy harvesting triboelectric nanogenerator (AG‐TENG) arrays to properly capture energy from highway moving vehicles is developed. A single AG‐TENG installation module can achieve a high power density of 0.2 Wm−2 at a wind speed of 3 m s−1. This wind speed is too low to drive conventional wind energy harvesting equipment. The performance of the AG‐TENG shows no degradation after 80 h of continuous operation (1 440 000 times). Thus, with the rational consideration and features, the system can generate enough power to drive internet of things (IoT) devices and environmental sensors, as well as offer wireless alarming and radio frequency identification vehicle monitoring. This study provides a promising …

The monitoring of space debris assumes paramount significance to ensure the sustainability and security of space activities as well as underground bases in outer space. However, designing a wide range monitoring system with easy fabrication, low power, and high precision remains an urgent challenge under the scarcity of materials and extreme environment conditions of outer space. Here, we designed a one-piece, robust, but flexible, and repairable 3D metal-printed triboelectric nanogenerator (FR-TENG) by incorporating the advantages of standardization and customization of outer space 3D metal printing. Inspired by the structure of hexagonal and pangolin scales, a curved structure is ingeniously applied in the design of 3D printed metal to adapt different curved surfaces while maintaining superior compressive strength, providing excellent flexibility and shape adaptability. Benefiting from the unique …

The triboelectric nanogenerator (TENG) is regarded as an effective strategy for harvesting energy from raindrops, and is a complementary solution with solar cells to achieve all‐weather energy harvesting and sustainable energy supply. However, due to the irregularity of natural rainfalls in the volume, frequency, density, and location, designing high‐efficiency raindrop TENG (R‐TENG) arrays faces great challenges. In this work, a highly transparent, large‐area, and high‐efficiency R‐TENG array with rational material choice, electrode structure, and array distribution is developed for efficiently harvesting irregular raindrop energy. The problem of electrical signal cancellation among adjacent raindrops can be fully avoided, as viewed from the high‐resolution space–time analyses of high‐speed camera and electrical signal characteristics. With the rationally designed electrode instead of multiple complex electrodes …

Contact electrification (CE) in water has attracted much attention, owing to its potential impacts on the chemical reactions, such as the recent discovery of spontaneous generation of hydrogen peroxide (H2O2) in water microdroplets. However, current studies focus on the CE of bulk water, the measurement of CE between micrometer-size water droplets is a challenge and its mechanism still remains ambiguous. Here, a method for quantifying the amount of charge carried by the water microdroplets produced by ultrasonic atomization is proposed. In the method, the motions of water microdroplets in a uniform electric field are observed and the electrostatic forces on the microdroplets are calculated based on the moving speed of the microdroplets. It is revealed that the charge transfer between water microdroplets is size-dependent. The large microdroplets tend to be positively charged while the small microdroplets tend …

Artifacts are irreplaceable treasures of human culture, and transportation monitoring is critical for safeguarding valuable artifacts against damage during culture exchanges. However, current collision-monitoring technologies have limitations in regard to real-time monitoring, cushioning protection, and power supply requirements. Here, we present a method for constructing a smart artifact-monitoring system (SAMS) based on a porous carbon black (CB)/Ecoflex triboelectric nanogenerator (PCE-TENG) that can monitor collisions in real time and absorb vibrations during artifact transportation. The PCE-TENG is assembled using a flexible printed circuit board (FPCB) and a porous Ecoflex layer with CB powder. It exhibits cushioning protection, stretchability, pressure sensitivity, and durability. To enhance its electrical output, modifications were made to optimize the CB content and surface structure. The SAMS comprises six PCE-TENGs attached to the inner wall of the artifact transport package and enables collision monitoring and protection in different directions. Moreover, the SAMS has the capability to instantly transmit warning information to monitoring terminals in the event of improper operations, empowering carriers to promptly and efficiently safeguard artifacts by taking necessary measures. This paper presents a practical strategy for artifact transportation monitoring and package engineering that could have significant implications for the field.

Real-time monitoring of flow turbulence is very difficult but extremely important in fluid dynamics, which plays an important role in flight safety and control. Turbulence can cause airflow to detach at the end of the wings, potentially resulting in the aerodynamic stall of aircraft and causing flight accidents. Here, we developed a lightweight and conformable system on the wing surface of aircraft for stall sensing. Quantitative data about airflow turbulence and the degree of boundary layer separation are provided in situ using conjunct signals provided by both triboelectric and piezoelectric effects. Thus, the system can visualize and directly measure the airflow detaching process on the airfoil, and senses the degree of airflow separation during and after a stall for large aircraft and unmanned aerial vehicles.

Flexible electronic devices using natural biological protein materials have received extensive attention in recent years. However, it is rarely reported that biological protein materials are utilized in flexible display. Here we reported a novel epidermal e-ink display device in which the natural silk fibroin acts as an electrode layer. Through the mesoscopic doping of regenerated silk fibroin, the material overcomes the defects of high brittleness, poor water and temperature resistance, and poor chemical stability on the premise of retaining biocompatibility and biodegradability. This revolutionary technology of flexible display using bio-silk fibroin materials can be applied to the field of human electronic skin display since many parts of our human body can be used as display carriers, and the display technology on human body has made breakthroughs.

To facilitate the transition of triboelectric nanogenerators (TENG) from early stages to large-scale real-world applications, urgent mass production is imperative, necessitating standardized manufacturing processes. In this study, a novel “pause-and-insert” and “print-in-place” 3D printing approach has been devised, employing widely available fused deposition modeling (FDM) printers along with conductive (as electrodes) and nonconductive (for casing and support) filaments to make encapsulate microbeads triboelectric nanogenerator (MB-TENG). This innovation results in a fully enclosed freestanding-mode TENG pack, seamlessly integrated with a lightweight wind-induced oscillator featuring tuning systems, thus enabling efficient, safe, and noiseless omnidirectional wind energy harvesting. Through adept design and manufacturing techniques, systematic inner-structure optimization has been achieved, yielding …

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 …

The release and dissolution of an active pharmaceutical ingredient (API) from the solid oral formulation into the gastrointestinal (GI) tract is critical for the drug's absorption into systemic circulation. Extended-release (ER) solid oral dosage forms are normally subjected to physical shear and grinding forces as well as pressure exerted by peristaltic movements when passing through the GI tract. The complex physical contraction and sample friction exerted by the GI tract are not simulated well by compendial dissolution methods. These limitations render traditional in vitro dissolution testing unable to discriminate and predict a product's in vivo performance. The objective of this study was to develop a dissolution method that better simulates the GI environment that products are subject to when taken by patients. A newly designed Mechanical Apparatus under GI Conditions (MAGIC) was assembled with a dissolution …

Triboelectric nanogenerators (TENGs) are used to harvest high entropy energy. To optimize the energy harvesting, storage and effective utilization, a critical part is the power management system (PMS), which requires an ideal electrical switch as the key component. However, the current switch technologies cannot adapt and enhance the charging for the four operation modes of TENG simultaneously. Herein, a flexible film‐discharge‐switch (FDS), delivering an averaged charge‐enhance factor over 100 under four operation modes of TENG, compared to directly charging a capacitor with conventional rectifier is reported. More specifically, the charge‐enhancement factors of the FDS are 134.3, 64.7, 97.0, and 136.5 for the modes of contact‐separation, lateral sliding, single‐electrode, and freestanding triboelectric layer, respectively. Furthermore, the high flexibility, stability, simplicity, durability, and self‐driven …

Surface charge density (σSC) is essential to the output of the triboelectric nanogenerator (TENG). Massive efforts have been made to improve it, which can be totally categorized into four types. Two of them are utilized to optimize the basic electrification of the TENG, and the other two are for the device configuration and following circuits. However, the basic electrification of the 100 μm-thick film under ambient conditions still stays below 200 μC m–2. Herein, we proposed a brand-new technical route, by designing an asymmetric-internal-capacitance configuration, which forms a “hot surface” rich in free electrons at the electrification interface and finally promotes σSC to 550 μC m–2. Specifically, σSC of Cu is improved by 35 times, reaching 9.48 times that of nylon that is reported to be a strong positive triboelectric material. Furthermore, the hot surface improves the output of the TENG by 12.8 times and drives multiple …

Photoreduction of CO2 into value-added products offers a promising approach to overcome both climate change and energy crisis. However, low conversion efficiency, poor product selectivity, and unclear mechanism limit the further advancement of CO2 photoreduction. The development of two-dimensional (2D) materials and construction of single atom sites are two frontier research fields in catalysis. Combining the advantages of 2D materials and single atom sites is expected to make a breakthrough in CO2 photoreduction. In this review, we summarized the design and application, proposed challenges and opportunities, and laid a foundation for further research and application of 2D materials confining single atoms (SACs@2D) for CO2 photoreduction.

The triboelectric nanogenerator (TENG) developed by Z. L. Wang’s team to harvest random mechanical energy is a promising new energy source for distributed sensing systems in the new era of the internet of things (IoT) and artificial intelligence (AI) for a smart world. TENG has many advantages that make it suitable for a wide range of applications, including energy harvesting, environmental protection, wearable electronics, robotics, and self-powered sensors. Sensing as an important part of TENG applications is gradually expanding, with the in-depth study of TENG sensing in its working principle, material selection, processing technology, system integration, surface treatment, and back-end algorithms by researchers. In industry and academia, fluid dynamics sensing for liquid and air is urgently needed but lacking. In particular, local fluid sensing is difficult and limited to traditional sensors. Fortunately, with advantages for ordinary TENGs and TENGs as fluid dynamics sensors, fluid dynamics sensing can be better realized. Therefore, the paper summarizes the up-to-date work on TENGs as fluid dynamics sensors, discusses the advantages of TENGs as fluid dynamics sensors in-depth, and, most importantly, aims to explore possible new key areas to help guide the future direction of TENG in fluid dynamics sensing by addressing the key challenges.