Charging System Optimization of Triboelectric Nanogenerator for Water Wave Energy Harvesting and Storage

Self-Powered Triboelectric Nanogenerator for Security Applications

Valuable jewels, documents, and files left in hotel rooms by guests can be stolen at any time by an unauthorized person. This could have a serious psychological and economic impact on the guests. The house/hotel owners should make efforts to prevent theft from occurring. In this study, a self-powered sliding-mode triboelectric nanogenerator (TENG) is used as a sensor on a drawer. It is fixed to the side of the drawer and works in the lateral sliding mode. The electricity generated by the device during the push-pull action of the draw is ~125 V and F~12.5 µA. An analysis of the electrical performance was carried out using PET, paper, and nitrile as sliding materials. The electrical output from the device is used to notify the guest or hotel owner of any theft by an unidentified individual via Arduino and node MCU devices. Finally, this device can be helpful at night and can be extended using different materials.

Anti-Overturning Fully Symmetrical Triboelectric Nanogenerator Based on an Elliptic Cylindrical Structure for All-Weather Blue Energy Harvesting

Triboelectric nanogenerators (TENGs) have shown promising potential for large-scale blue energy harvesting. However, the lack of reasonable designs has largely hindered TENG from harvesting energy from both rough and tranquil seas. Herein, a fully symmetrical triboelectric nanogenerator based on an elliptical cylindrical structure (EC-TENG) is proposed for all-weather blue energy harvesting. The novel elliptical cylindrical shell provides a unique self-stability, high sensitivity to wave triggering, and most importantly, an anti-overturning capability for the EC-TENG. Moreover, benefiting from its internal symmetrical design, the EC-TENG can produce energy normally, even if it was overturned under a rude oscillation in the rough seas, which distinguishes this work from previous reported TENGs. The working mechanism and output performance are systematically studied. The as-fabricated EC-TENG is capable of lighting 400 light-emitting diodes and driving small electronics. More than that, an automatic monitoring system powered by the EC-TENG can also monitor the water level in real-time and provide an alarm if necessary. This work presents an innovative and reliable approach toward all-weather wave energy harvesting in actual marine environments.

Micro Energy Storage Systems in Energy Harvesting Applications: Analytical Evaluation towards Future Research Improvement

During the last decade, countless advancements have been made in the field of micro-energy storage systems (MESS) and ambient energy harvesting (EH) shows great potential for research and future improvement. A detailed historical overview with analysis, in the research area of MESS as a form of ambient EH, is presented in this study. The top-cited articles in the field of MESS ambient EH were selected from the Scopus database, and based on articles published from 2010 to 2021, and the number of citations. The search for these top-cited articles was conducted in the third week of December 2021. Mostly the manuscripts were technical and contained an experimental setup with algorithm development (65%), whereas 27.23% of the articles were survey-based. One important observation was that the top 20 selected articles, which are the most-cited articles in the different journals, come from numerous countries of origin. This study revealed that the MESS integrated renewable energy sources (RESs) are an enhancement field of research for EH applications. On the basis of this survey, we hope to identify and solve research problems in the field of MESS and RESs integration, and provide suggestions for future developments for EH applications.

Coalescence-Induced Droplet Jumping

When two or more droplets coalesce on a superhydrophobic surface, the merged droplet can jump spontaneously from the surface without requiring any external energy. This phenomenon is defined as coalescence-induced droplet jumping and has received significant attention due to its potential applications in a variety of self-cleaning, anti-icing, antifrosting, and condensation heat-transfer enhancement uses. This article reviews the research and applications of coalescence-induced droplet jumping behavior in recent years, including the influence of droplet parameters on coalescence-induced droplet jumping, such as the droplet size, number, and initial velocity, to name a few. The main structure types and influence mechanism of the superhydrophobic substrates for coalescence-induced droplet jumping are described, and the potential application areas of coalescence-induced droplet jumping are summarized and forecasted.

A sliding mode contact electrification based triboelectric-electromagnetic hybrid generator for small-scale biomechanical energy harvesting

The present work describes the hybridization of two different energy harvesters works simultaneously in a single package. By applying simultaneous mechanical force, two components such as triboelectric nanogenerator (TENG) and electromagnetic generator (EMG) independently produce power. The hybrid device was made with a polymeric cylinder composed of Kapton in the inner wall; a copper coil wound outside the cylinder and neodymium magnet and small bits of paper housed inside it. The paper flakes having the dimension of 5 mm × 5 mm, which are triboelectric positive slides over the negative triboelectric layer Kapton. The potential difference between the two different triboelectric material leads to the generation of electric power. The triboelectric component generates the maximum output with the voltage of ≈ 20 V and the current of 300 nA. The magnet inside the cylinder moves simultaneously along with the paper made the production of electric flux in the coil. The alternating magnetic flux induces the current in the outer coil as per the Lenz’s law. The maximum output generated from the EMG component with the obtained voltage of 2 V and the maximum current of 10 mA. Further, to analyze the actual working behavior of the device, commercial capacitor charging behavior was analyzed. The TENG component runs the consistent charging behavior, whereas the EMG component offers a rapid charging behavior, under hybrid mode both the merits can be utilized. The device has had placed in a backpack, and the biomechanical energy from human motions such as walking, running and jumping had been demonstrated. This study confirms that the proposed hybrid generator is capable of powering small electronic devices such as global positioning system (GPS), flashlights and potentially be able to use as an active MEMS/NEMS-based self-powered sensor.

Triboelectric filtering for air purification

Air pollution becomes more and more serious with the rapid development of the society, and the haze caused by particulate matters (PMs) has become a global problem. Thus seeking an effective technology for removing the airborne PMs or other pollutants is much desirable for alleviating the air pollution. The newly invented triboelectric nanotechnology can realize efficient air filtering with obvious advantages over traditional fibrous filtering and electrostatic precipitation. Here, a review is provided for recent progress in air filter by utilizing the triboelectric nanotechnology, starting from the choices of triboelectric materials and main features of triboelectric nanotechnology. The mechanism of triboelectric air filtering technology was presented as the coupling of triboelectric filtering and mechanical filtering. Then the approaches of air filtering were summarized as the triboelectric nanogenerator (TENG)-driven air filtering, TENG-enhanced nanofiber air filtering, and self-powered triboelectric air filtering. The device structure, working principle and filtering performance were systematically discussed. Furthermore, the industry products which have been developed based on the triboelectric filtering technology were introduced.

Nanogenerators as a Sustainable Power Source: State of Art, Applications, and Challenges

A sustainable power source to meet the needs of energy requirement is very much essential in modern society as the conventional sources are depleting. Bioenergy, hydropower, solar, and wind are some of the well-established renewable energy sources that help to attain the need for energy at mega to gigawatts power scale. Nanogenerators based on nano energy are the growing technology that facilitate self-powered systems, sensors, and flexible and portable electronics in the booming era of IoT (Internet of Things). The nanogenerators can harvest small-scale energy from the ambient nature and surroundings for efficient utilization. The nanogenerators were based on piezo, tribo, and pyroelectric effect, and the first of its kind was developed in the year 2006 by Wang et al. The invention of nanogenerators is a breakthrough in the field of ambient energy-harvesting techniques as they are lightweight, easily fabricated, sustainable, and care-free systems. In this paper, a comprehensive review on fundamentals, performance, recent developments, and application of nanogenerators in self-powered sensors, wind energy harvesting, blue energy harvesting, and its integration with solar photovoltaics are discussed. Finally, the outlook and challenges in the growth of this technology are also outlined.

Self-propelled droplet-based electricity generation

Droplets are ubiquitous in nature and the preferential control of droplet transport offers limitless potential for efficient mass and momentum transfer as well as energy conversion. In this work, we show that even without the need for any external energy input, the self-propelled motion of droplets driven by a surface wetting gradient can lead to reliable electricity generation. Simple analytical analysis demonstrates that the output voltage results from the modulation of the surface charge distribution on the dynamically changing solid/liquid interfaces, which can be programmed by tailoring the wetting gradient and the size of the droplet. We demonstrate that a self-propelled 25 μL droplet can generate a peak current of 93.5 nA and a maximum output power of 2.4 nW. This work provides a new angle for optimizing energy harvesting devices based on liquid-solid interfaces.

Preparation of a New Type of Black TiO2 under a Vacuum Atmosphere for Sunlight Photocatalysis

Black TiO₂ as a solar-driven photocatalyst has attracted enormous attention from scientists and engineers in water and wastewater treatment field. Most of the methods used for the preparation of black TiO₂ are thermal treatment under a hydrogen atmosphere. Nevertheless, it is well known that working with hydrogen is not safe and needs special maintenance. Here, for the first time, we prepared black TiO₂ by sintering P25 pellets at different temperatures (500-800 °C) under a vacuum atmosphere that showed the same performance with the prepared black TiO₂ under a hydrogen atmosphere. The samples were characterized by X-ray diffraction, Raman spectra field emission scanning electron microscopy, transmission electron microscopy, electron paramagnetic resonance, X-ray photoelectron spectroscopy, and ultraviolet-visible deep resistivity sounding techniques. The differences between the formation of oxygen vacancy density and color turning in sintered powder and pellet were also studied. The results showed that the color of the P25 powder became darker after sintering but not completely turning to black, whereas the P25 pellets completely turned black after sintering. The resultant black TiO₂ was used for the photocatalytic degradation of the acetaminophen (ACE) in aqueous solution under AM 1.5G solar light illumination; it was found that the P25 pellet sintered in 500 °C had the highest photocatalytic performance for ACE degradation under AM 1.5G solar light illumination. The photocatalytic activity of prepared black TiO₂ under vacuum and hydrogen atmospheres was also compared together; the results showed that photocatalytic activities of both samples were so close together. The existence of the oxygen vacancy after 6 months and long and short-term stability (by application for photocatalytic degradation of ACE in an aqueous solution) of the black TiO₂ pellets was also studied; the results showed that the TiO₂ pellets in aqueous phase had acceptable stability.

Triboelectric-Electromagnetic Hybrid Generator for Harvesting Blue Energy

Progress has been developed in harvesting low-frequency and irregular blue energy using a triboelectric-electromagnetic hybrid generator in recent years. However, the design of the high-efficiency, mechanically durable hybrid structure is still challenging. In this study, we report a fully packaged triboelectric-electromagnetic hybrid generator (TEHG), in which magnets were utilized as the trigger to drive contact-separation-mode triboelectric nanogenerators (CS-TENGs) and coupled with copper coils to operate rotary freestanding-mode electromagnetic generators (RF-EMGs). The magnet pairs that produce attraction were used to transfer the external mechanical energy to the CS-TENGs, and packaging of the CS-TENG part was achieved to protect it from the ambient environment. Under a rotatory speed of 100 rpm, the CS-TENGs enabled the TEHG to deliver an output voltage, current, and average power of 315.8 V, 44.6 μA, and ~ 90.7 μW, and the output of the RF-EMGs was 0.59 V, 1.78 mA, and 79.6 μW, respectively. The cylinder-like structure made the TEHG more easily driven by water flow and demonstrated to work as a practical power source to charge commercial capacitors. It can charge a 33 μF capacitor from 0 to 2.1 V in 84 s, and the stored energy in the capacitor can drive an electronic thermometer and form a self-powered water-temperature sensing system.

Novel Deep-Eutectic-Solvent-Infused Carbon Nanofiber Networks as High Power Density Green Battery Cathodes

Redox flow batteries (RFBs) have emerged as a promising candidate for large-scale energy storage because of the flexible design for high energy, power, and safety. In this study, FeCl₃·6H₂O/urea composite deep eutectic catholyte (FeU-DEC)-infused self-standing carbon nanofiber (CNF) was synthesized for green and high power density RFB through industrially available processes. FeU-DEC-infused CNF displayed an extremely high power density (874 mW/g) as well as high capacity (27.28 mAh/g) derived from high theoretical capacity of FeU-DEC (89.24 mAh/g) in addition to the advantages of the FeU-DEC characteristics (e.g., nonflammable, biodegradable, facile preparation). This is because of the large electroactive area derived from the high surface area of CNF and superlyophilicity of FeU-DEC on CNFs. Furthermore, we compared the wettability of CNF with other electrodes, as well as the chemical stability and electrode performance, based on topological wetting analysis using parameters of fiber radius, fiber interval, the equilibrium contact angle of FeU-DEC on electrodes, and surface tension of FeU-DEC, giving wetting threshold for FeU-DEC on fibrous electrodes. The wetting analysis are applied not only for FeU-DEC, but also for a wide range of other DECs and deep eutectic anolyte. This work contributes to the further development of green and high-performance RFBs.

Silicone-Based Triboelectric Nanogenerator for Water Wave Energy Harvesting

Triboelectric nanogenerator (TENG) has been proven to be efficient for harvesting water wave energy, which is one of the most promising renewable energy sources. In this work, a TENG with a silicone rubber/carbon black composite electrode was designed for converting the water wave energy into electricity. The silicone-based electrode with a soft texture provides a better contact with the dielectric film. Furthermore, a spring structure is introduced to transform low-frequency water wave motions into high-frequency vibrations. They together improve the output performance and efficiency of TENG. The output performances of TENGs are further enhanced by optimizing the triboelectric material pair and tribo-surface area. A spring-assisted TENG device with the segmented silicone rubber-based electrode structure was sealed into a waterproof box, which delivers a maximum power density of 2.40 W m^-3, as triggered by the water waves. The present work provides a new strategy for fabricating high-performance TENG devices by coupling flexible electrodes and spring structure for harvesting water wave energy.

Simple and rapid fabrication of pencil-on-paper triboelectric nanogenerators with enhanced electrical performance

Paper and pencil have many advantages in triboelectric nanogenerators (TENGs) in terms of low-cost, light weight, and environment friendliness. In this work, a pencil-on-paper triboelectric nanogenerator (PP-TENG) with highly enhanced performance was introduced. In order to use paper as a friction layer and improve its triboelectric performance, a simple and rapid paper-coating process was utilized with polyvinylidene fluoride (PVDF), polyvinyledenedifluoride-trifluoroethylene (PVDF-TrFE), and poly(methyl methacrylate) (PMMA) solutions. The fabrication process of the PP-TENG was completed within 10 minutes via pencil drawing of an electrode followed by a solution coating. With an optimized electrode shape, the PP-TENG showed a maximum power density of 64 mW m^-2, which is more than 19 times higher than that of the uncoated paper TENG. The electrical performance of the PP-TENG was sufficient to drive a few hundred LEDs and charge various capacitors. It was maintained after the paper was folded or even crumpled. The proposed PP-TENG is expected to be utilized with other wearable electronic devices.

Fully Packaged Blue Energy Harvester by Hybridizing a Rolling Triboelectric Nanogenerator and an Electromagnetic Generator

Ocean energy, in theory, is an enormous clean and renewable energy resource that can generate electric power much more than that required to power the entire globe without adding any pollution to the atmosphere. However, owing to a lack of effective technology, such blue energy is almost unexplored to meet the energy requirement of human society. In this work, a fully packaged hybrid nanogenerator consisting of a rolling triboelectric nanogenerator (R-TENG) and an electromagnetic generator (EMG) is developed to harvest water motion energy. The outstanding output performance of the R-TENG (45 cm³ in volume and 28.3 g in weight) in the low-frequency range (<1.8 Hz) complements the ineffective output of EMG (337 cm³ in volume and 311.8 g in weight) in the same range and thus enables the hybrid nanogenerator to deliver valuable outputs in a broad range of operation frequencies. Therefore, the hybrid nanogenerator can maximize the energy conversion efficiency and broaden the operating frequency simultaneously. In terms of charging capacitors, this hybrid nanogenerator provides not only high voltage and consistent charging from the TENG component but also fast charging speed from the EMG component. The practical application of the hybrid nanogenerator is also demonstrated to power light-emitting diodes by harvesting energy from stimulated tidal flow. The high robustness of the R-TENG is also validated based on the stable electrical output after continuous rolling motion. Therefore, the hybrid R-TENG and EMG device renders an effective and sustainable approach toward large-scale blue energy harvesting in a broad frequency range.