Publications

Abstract Artificial electronic skin (e‐skin), a network of mechanically flexible sensors which can wrap irregular surfaces conformally and quantify various stimuli sensitively, is potentially useful in healthcare monitoring and human‐machine interaction (HMI). Although various approaches have mimicked the structures and functions of the human skin, challenges remain with high‐density integration, super sensitivity, and multi‐functionality. A multimodal and comfortable skin‐inspired active‐matrix circuitry is reported here with high pixel density (>100 cm –2 ) based on all 2D materials, which exhibits excellent performance to detect both mechanical interactions and humidity variations. The ultra‐high sensitivity (>400 and ≈ 10 4 for strain and humidity sensing, respectively), long‐term stability (>1000 cycles), and rapid response time for every pixel can fulfill simultaneous multi‐stimulus sensing. Accordingly, a respiratory monitor is constructed to realize healthcare monitoring through observing the human breath frequency, intensity, and humidity in real‐time. Moreover, the multimodal e‐skin breaks through shackles of the contact sensor medium for HMI. 3D strain and humidity spatial mapping can reflect object location information even without contact, avoiding cross‐infection of viruses effectively between users during the COVID‐19 pandemic. The reported e‐skin will broaden applications for future healthcare and human–machine interactive devices.

Enhancing the filtration efficiency of air filtering material without increasing its airflow resistance is a major challenge and of great significance. In this work, we report a type of active-poled nanofiber onto which in situ active poling is applied. It results in significantly enhanced filtration efficiency as well as dust holding capacity while keeping the airflow resistance constant. Owing to the in situ applied electric field, the nanofibers as well as the particulates are polarized. As a result, at a poling voltage of 2 kV, the removal efficiency and the quality factor for PM2.5 are enhanced by 17% and 130%, respectively. More importantly, the dust holding capacity represents a 3.5-fold enhancement over normal nanofibers. The approach reported in this work has the potential of being practically utilized in air purification purposes because it can bring about not only promoted filtration performance but also lowered noise and reduced power consumption.

Temperature effects on the contact electrification (CE) is of great interest. Here, different kinds of substoichiometric oxide films, such as TiO2-x, Al2O3-x, Ta2O5-x, and Cr2O3-x, are deposited and annealed at different temperatures, and the CE between the films and a Pt-coated tip is performed by using Kelvin probe force microscopy (KPFM). An intriguing finding is that the polarity on the TiO2-x surface changes from negative to positive with the increase of the sample annealing temperature in air atmosphere. Such a result is attributed to the fact that annealing under an oxidative atmosphere repairs oxygen vacancies and helps upgrade the low valency of Ti3+ to a stable high valency of Ti4+. On the contrary, after annealing occurs in an Ar/H2 atmosphere, the polarity on the TiO2-x surface reverses from positive to negative. This is mainly due to the increase of oxygen vacancies after annealing in reducing atmosphere. Through the KPFM results of Al2O3-x, Ta2O5-x, and Cr2O3-x films, the effect of oxygen vacancies is further confirmed, that is, the decrease of oxygen vacancies eases the films at capturing positive charges. Based on this, TiO2-x-based identical material triboelectric nanogenerators (IM-TENGs) are designed and prepared for the first time to control the current direction. Moreover, a surface state model for explaining the CE mechanism between the metal and annealed dielectric is proposed. This study is conducive to the development of the IM-TENGs which regulate the current direction or voltage output accurately in the future and also provides a further understanding of the dominant mechanism of electron transfer in the CE.

Abstract Triboelectric nanogenerators (TENGs) have been introduced as a new cost‐effective technology for harvesting renewable wave energy for their unmatchable performance in low frequency (<5 Hz). Here, bifilar‐pendulum‐assisted multilayer‐structured triboelectric nanogenerator (BM‐TENG) modules incorporated into a vessel for wave energy harvesting are reported, which have a high output performance and adaptive capacity in actual marine environment. Compared with previous research work on wave energy collection by TENG, the designed BM‐TENG, which is optimized by the structure and material, presents a milestone power density of 200 W m −3 and this performance is an improvement of 1–2 orders of magnitude. More importantly, by using a vessel as a platform, TENG can be integrated into it to eliminate the impact of the marine environment and enable convenient maintenance, easy connection, and long‐term stable operation of TENG. The findings provide not only a new design methodology for TENG but also a feasible method to harvest renewable energy efficiently.

Abstract Integrating power into fabrics offers exciting opportunities for wearable technologies, which has long remained challenging to make flexible, high temperature resistant textile‐based powers. Here, an all yarns‐based triboelectric nanogenerator (Y‐TENG) is proposed to harvest electrical energy and sense biological motion for temperatures between 25 and 400 °C, the upper limit of temperature is greatly improved. The Y‐TENG is capable of outputting a transferred charge density of 30 nC cm −2 , the external load resistance is 180 MΩ, and the peak power reaches 0.17 mW, and the average response time is lower than 15 ms. Based on a simple processing strategy, when introducing silica aerogel during electrospinning of polyimide nano‐covered layer to make multi‐ply and stabilized triboelectric yarns. Unlike ordinary fibers and yarns, the core‐shell structured design also shows a high sensitivity to all kinds of mechanical triggering sources. Furthermore, a self‐powered movement characteristic monitoring system by coordinating smart protective suit is further developed to provide real‐time sensing and rescuing assistance. This aerogel nano‐covered triboelectric yarn has great application prospects for energy generation and motion detection in high‐temperature and many other high‐risk environments.

Abstract The underlying mechanism on contact electrification (CE) has remained a topic of debate over centuries, and it is argued to be due to electron transfer, ion transfer, and/or even material species transfer. Recently, a previous study shows that CE is dominated by electrons, at least for solid–solid cases. Herein, by using a model detailing the charge transfer between triboelectric surfaces and thermionic emission of electrons via employing a sliding mode Ti–SiO 2 triboelectric nanogenerator (TENG), surface charge decay behavior is scrutinized in lateral‐sliding mode during operation at high temperature. The temperature dependence of TENG electric output contributes to characteristic metal–dielectric and dielectric–dielectric CEs, thereby providing further evidence that electrons are the dominating transferred charges in CE. The total surface charge output of the TENG is rationalized as a direct consequence of the coupling of the rate of electron thermionic emission, the charge transfer rate of CE, and the changing rate of the contacted area between the two materials. When the contacting area is larger than the displaced area, the CE between the two materials is the major contributor to measured surface charge. Conversely, the thermionic emission of the exposed surfaces dictates when the contacting area is smaller.

Three-dimensional (3D) tungsten oxide nanowire networks have been demonstrated as a high-surface area material for building ultrasensitive and highly selective gas sensors. Utilizing the 3D hierarchical structure of the networks, high sensitivity has been obtained towards NO2, revealing the capability of the material to detect concentration as low as 50ppb (parts per billion). The distinctive selectivity at different working temperatures is observed for various gases. The results highlight that the nanobelts (nanowires) technology can be adopted for the development of gas sensors with performances suitable for practical applications.

'Perfluorocarbon Nanoparticles' published in 'Encyclopedia of Nanotechnology'

Here we report an electrostatic-templated self-assembly (ETSA) method for arbitrarily patterning millimeter-sized polymer beads on a nanostructured surface without using an extra voltage source. A patterned electrode underneath an electrification layer generates "potential wells" of the corresponding pattern at predefined window sites, which capture and anchor the beads within the window sites by electrostatic force. Analytical calculation is combined with numerical modeling to derive the electrostatic force acting on the beads, which is in great agreement with experimentally measured values. The generated pattern is solely determined by the predefined underlying electrode, making it arbitrarily switchable by using different electrode patterns. By transferring the assembled beads into an elastomer matrix, possible applications of the ETSA in fabricating optical and flexible displays are demonstrated.

With the arrival of the Internet of Things (IoTs) era, there is a growing requirement for systems with many sensor nodes in a variety of fields of applications. The demands for wireless, sustainable and independent operation are becoming more and more important for large-scale sensor networks and systems. For these purposes, a self-powered sensory system that can utilize the self-harvested energy from its surroundings to drive the sensors and directly sense external stimuli has attracted great attention. The invention and rapid development of piezoelectric generators (PENGs), which take Maxwell's displacement current as the driving force, has been pushing forward research on self-powered active mechanical sensors, electronic skins, and human-robotic interaction. Here, this review starts with a brief introduction of piezoelectric materials, fabrication, and performance improvement. Then, the energy harvesters used for self-power systems based on recent progress are reviewed. After that, PENGs applications toward recent self-powered active sensors are divided into four aspects and highlighted, respectively. Moreover, some challenges and future directions for the self-powered multifunctional sensors are put forward. It is believed that through the continuous investigations into PENG-based self-powered active sensors, they will soon be used in touch screens, electronic skins, health care, environmental monitoring, and intelligence systems.