Understanding the Percolation Effect in Triboelectric Nanogenerator with Conductive Intermediate Layer

Spring Design of Triboelectric Nanogenerator with MXene-Modified Interface for Fluid Energy Harvesting and Water Level Monitoring

The introduction of two-dimensional materials with high capacitance that are dielectric into the triboelectric interface is critical for the development of a highly efficient triboelectric nanogenerator (TENG) due to its excellent electrical conductivity and versatile surface chemistry. This paper reports a spring-structured multilayer TENG (S-TENG), where a Nb2CTx MXene-PVDF composite was chosen as the triboelectric electrode for increasing the dielectric and surface charge density. The intense electrostatic interaction of the strong hydrogen bonds between anions on the MXene surface and hydrogen atoms of PVDF chains not only creates a dipole in responding to the applied electric field but also promotes the formation of a piezoelectric phase and induces a strong interface coupling effect. Consequently, an output power enhancement of 300% was shown in comparison with pure PVDF, and a spring-like design with a multilayer structure further increases the space utilization and contact area and presents an output voltage of 420 V, a current density of 1.47 mA/m2, and a maximal output power density of 619 mW/m2. In addition, the as-prepared S-TENG can serve as both a fluid energy harvester on an urban river and a real-time monitor to realize the automatic alarm of water level warning.

Structural design and preparation of Ti3C2Tx MXene/polymer composites for absorption-dominated electromagnetic interference shielding

Electromagnetic interference (EMI) is a pervasive and harmful phenomenon in modern society that affects the functionality and reliability of electronic devices and poses a threat to human health. To address this issue, EMI-shielding materials with high absorption performance have attracted considerable attention. Among various candidates, two-dimensional MXenes are promising materials for EMI shielding due to their high conductivity and tunable surface chemistry. Moreover, by incorporating magnetic and conductive fillers into MXene/polymer composites, the EMI shielding performance can be further improved through structural design and impedance matching. Herein, we provide a comprehensive review of the recent progress in MXene/polymer composites for absorption-dominated EMI shielding applications. We summarize the fabrication methods and EMI shielding mechanisms of different composite structures, such as homogeneous, multilayer, segregated, porous, and hybrid structures. We also analyze the advantages and disadvantages of these structures in terms of EMI shielding effectiveness and the absorption ratio. Furthermore, we discuss the roles of magnetic and conductive fillers in modulating the electrical properties and EMI shielding performance of the composites. We also introduce the methods for evaluating the EMI shielding performance of the materials and emphasize the electromagnetic parameters and challenges. Finally, we provide insights and suggestions for the future development of MXene/polymer composites for EMI shielding applications.

High-Output Lotus-Leaf-Bionic Triboelectric Nanogenerators Based on 2D MXene for Health Monitoring of Human Feet

As versatile energy harvesters, triboelectric nanogenerators (TENGs) have attracted considerable attention in developing portable and self-powered energy suppliers. The question of how to improve the output power of TENGs using cost-effective means is still under vigorous investigation. In this paper, high-output TENGs were successfully produced by using a simple and low-cost lotus-leaf-bionic (LLB) method. Well-distributed microstructures were fabricated via the LLB method on the surface of a polydimethylsiloxane (PDMS) negative triboelectric layer. 2D MXene (Ti₃C₂T_x) and graphene were doped into the structured PDMS to evaluate their effects on the performance of TENG. Owing to merits of the MXene doping and microstructures on the PDMS surface, the output power of MXene-doped LLB TENGs reached as high as 104.87 W/m², which was about 10 times higher than that of graphene-doped devices. The MXene-doped LLB TENGs can be used as humidity sensors, with a sensitivity of 4.4 V per RH%. In addition, the MXene-doped LLB TENGs were also sensitive to human body motions; hence, a foot health monitoring system constructed by the MXene-doped LLB TENGs was successfully demonstrated. The results in this work introduce a way to produce cost-effective TENGs using bionic means and suggest the promising applications of TENGs in the smart monitoring system of human health.

Effect of Ag nanoparticle size on triboelectric nanogenerator for mechanical energy harvesting

Triboelectric nanogenerators (TENG) are generally utilized on the grounds that they can catch low-recurrence mechanical energy from various types of movement and convert it into electricity. It has been proved that the adulteration of conductive particles in the triboelectric layer can improve its output performance, but metal nanomaterials have different properties at different scales. In this paper, the triboelectric layer of TENG is a composite film made of silver nanoparticles (AgNPs) with different particle sizes (20 nm, 50 nm, 200 nm and 500 nm) that were dispersed and mixed with two-component liquid silica gel step by step. The open circuit voltage (Voc) and short circuit current (Isc) of the 20 nm component of the AgNPs-dispersed/two-component liquid silica gel TENG(At-TENG) are 102.8 V and 4.42μA, which are higher than the result execution of the other components. Smaller size nanoparticles have more number of nanoparticles when the mass fraction is the same. AgNPs form micro-capacitance structures in the insulating polymer layer and enhance the dielectric properties of the composite films through an interfacial polarization mechanism. At-TENG can light up 53 commercial LEDs and power calculators or wristband electronic watches, proving its utility as a self-powered power source. An extensive experiment proves the advantage of small size using comparison and theoretical analysis and provides suggestions for the selection of TENG dopants.

3D Porous MXene Aerogel through Gas Foaming for Multifunctional Pressure Sensor

The development of smart wearable electronic devices puts forward higher requirements for future flexible electronics. The design of highly sensitive and high-performance flexible pressure sensors plays an important role in promoting the development of flexible electronic devices. Recently, MXenes with excellent properties have shown great potential in the field of flexible electronics. However, the easy-stacking inclination of nanomaterials limits the development of their excellent properties and the performance improvement of related pressure sensors. Traditional methods for constructing 3D porous structures have the disadvantages of complexity, long period, and difficulty of scalability. Here, the gas foaming strategy is adopted to rapidly construct 3D porous MXene aerogels. Combining the excellent surface properties of MXenes with the porous structure of aerogel, the prepared MXene aerogels are successfully used in high-performance multifunctional flexible pressure sensors with high sensitivity (306 kPa-1), wide detection range (2.3 Pa to 87.3 kPa), fast response time (35 ms), and ultrastability (>20,000 cycles), as well as self-healing, waterproof, cold-resistant, and heat-resistant capabilities. MXene aerogel pressure sensors show great potential in harsh environment detection, behavior monitoring, equipment recovery, pressure array identification, remote monitoring, and human-computer interaction applications.

A review of the advances in composites/nanocomposites for triboelectric nanogenerators

Material development is essential when studying triboelectric nanogenerators (TENGs). This importance is because the performance of TENGs is highly dependent on the properties of the utilized triboelectric materials. To obtain more specific properties, composites have been developed that combine the features of their components. According to Google Scholar, 55% of published papers related to triboelectric nanogenerators have utilized or mentioned composites. This number is 34.5% if one searches with the keyword nanocomposites instead of composites. The importance of composites is because they can exhibit new dielectric properties, better mechanical strength, enhanced charge affinities, etc. Therefore, the development of new composites has great importance in TENG studies. In this paper, we review the production of nanocomposites, the types of nanocomposites, and their application in TENG studies. This review gives an overview of how nanocomposites boost the performance of TENGs and provides guidance for future studies.

Advances in Inorganic Nanomaterials for Triboelectric Nanogenerators

Triboelectric nanogenerators (TENGs) that utilize triboelectrification and electrostatic induction to convert mechanical energy to electricity have attracted increasing interest in the last 10 years. As a universal physical phenomenon, triboelectrification can occur between any two surfaces that experience physical contact and separation regardless of the type of material. For this reason, many materials, including both organic and inorganic materials, have been studied in TENGs with different purposes. Although organic polymers are mainly used as triboelectric materials in TENGs, the application of inorganic nanomaterials has also been intensively studied because of their unique dielectric, electric, piezoelectric, and optical properties, which can improve the performance of TENGs. A review of how inorganic nanomaterials are used in TENGs would help researchers gain an overview of the progress in this area. Here, we present a review to summarize how inorganic nanomaterials are utilized in TENGs based on the roles, types, and characteristics of the nanomaterials.

Enhancement of triboelectricity based on fully organic composite films with a conducting polymer

Triboelectric nanogenerators (TENGs) based on ferroelectric organic materials have advantages of high flexibility, biocompatibility, controllable ferroelectric properties, etc. However, this has limited the electrical output performance due to their lower ferroelectric characteristics than those of inorganic ferroelectric materials. A lot of effort has been made to improve the organic ferroelectric characteristics through composites, surface modifications, structures, etc. Herein, we report TENGs made of ferroelectric composite materials consisting of poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The composite was prepared by simply blending PVDF-TrFE and PEDOT:PSS with a weight ratio from 0% to 60%. When the ratio was 20%, the ferroelectric-crystalline phase was enhanced and the highest dielectric constant was observed. Accordingly, the TENGs consisting of 20% composite film and polyimide exhibited the best output performance: the maximum open circuit voltage and short circuit current were ∼15 V and ∼2.3 μA at 1 Hz oscillation, respectively. These results indicate that the ferroelectric characteristics of PVDF-TrFE can be enhanced by adding PEDOT:PSS as a nanofiller.

Suppressing Thermal Negative Effect and Maintaining High-Temperature Steady Electrical Performance of Triboelectric Nanogenerators by Employing Phase Change Material

Triboelectric nanogenerators (TENGs) are newly developed energy-harvesting mechanisms, which can efficiently transmute irregular mechanical energy into scarce electrical energy. However, the electrical performance of TENGs shows a decreasing tendency with the increase in temperature, and the negative effect caused by friction heat and operating environmental thermal stresses for the output performance, durability, and reliability are still a bottleneck, restricting the practical application of TENG electronic devices. Especially for wearable TENG devices, the heat-induced temperature rise evokes extreme discomfort and even hazards to human health. To effectively suppress the thermal negative effect and maintain the high-temperature steady electrical performance of TENGs, a novel thermo-regulating TENG (Tr-TENG) based on phase change materials (PCMs) is designed. The results state clearly that the Tr-TENG can maintain steady output performance without deterioration by the introduction of PCMs, during continuous heating and natural cooling, while the output performance of conventional TENG is decayed by 18.33%. More importantly, the Tr-TENG possesses high-efficiency thermal management ability, resulting in its improved durability, reliability, and thermal comfort. This study creates new possibilities for the development of advanced multifunctional TENGs with attractive characteristics and desirable performances and promotes the application of TENG electronic devices in harsh environments.

Self-Powered Intelligent Human-Machine Interaction for Handwriting Recognition

Handwritten signatures widely exist in our daily lives. The main challenge of signal recognition on handwriting is in the development of approaches to obtain information effectively. External mechanical signals can be easily detected by triboelectric nanogenerators which can provide immediate opportunities for building new types of active sensors capable of recording handwritten signals. In this work, we report an intelligent human-machine interaction interface based on a triboelectric nanogenerator. Using the horizontal-vertical symmetrical electrode array, the handwritten triboelectric signal can be recorded without external energy supply. Combined with supervised machine learning methods, it can successfully recognize handwritten English letters, Chinese characters, and Arabic numerals. The principal component analysis algorithm preprocesses the triboelectric signal data to reduce the complexity of the neural network in the machine learning process. Further, it can realize the anticounterfeiting recognition of writing habits by controlling the samples input to the neural network. The results show that the intelligent human-computer interaction interface has broad application prospects in signature security and human-computer interaction.