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Inversely polarised ferroelectric polymer contact electrodes for triboelectric-like generators from identical materials
Abstract
Although it is known that triboelectric nanogenerators (TENG) based on ferroelectric polymer films show better performance, the origin of this enhancement remains poorly understood. To date, it has been accepted that enhancement is observed to due shift of the “effective work function” of ferroelectric polymer insulator which in turn enhance electron transfer between TENG electrodes. The present study reveals that this view is incorrect and, in reality, the enhancement is observed due to induction driven by piezoelectric charges. Furthermore a novel piezoelectric-electrostatic generator (PEEG) has been constructed from inversely polarised polyvinylidene films, which exhibit higher performance than TENG for mechanical energy conversion to electricity.
... [10][11][12][13][14][15] The performance can be also enhanced by using ferroelectric polymer or composite films as the contacting surfaces. [16][17][18][19][20][21][22][23][24][25][26] State-of-the-art performance of ferroelectric materials based TENG devices can be expected when the ferroelectric material layers on contacting sides of the device are inversely polarised. 23,24 The contacted inversely polarized layers then act similarly to a series of connected capacitors. ...
... [16][17][18][19][20][21][22][23][24][25][26] State-of-the-art performance of ferroelectric materials based TENG devices can be expected when the ferroelectric material layers on contacting sides of the device are inversely polarised. 23,24 The contacted inversely polarized layers then act similarly to a series of connected capacitors. 24 The total capacitance of the system decreases dramatically while the potential difference increases as the air gap is created during separation. ...
... The polymer films were spin-coated on indium-tin oxide (ITO) conductive electrode and contacted against another ITO (see Supplemental Information (SI) Figure S1 for schematic TENG device representation). The polymer films were given ferroelectric properties by adding 7.5 vol% BaTiO 3 nanoparticles <100 nm in size (see SI Figure S2 than the other is widely reported before, 16,18,[22][23][24][25][26] however, the explanation provided for that has been inaccurate. We argue that the observed difference can be explained by elementary match and mismatch between the directions of the electric field from the ferroelectric dipole moment and the dipole moment created by triboelectric charges. ...
Embedding additional ferroelectric dipoles in contacting polymer layers is known to enhance the performance of triboelectric nanogenerator (TENG) devices. However, the influence of dipoles formed between the triboelectric surface charges on two contacting ferroelectric films has been ignored in all relevant studies. We demonstrate that proper attention to the alignment of the distinct dipoles present between two contacting surfaces and in composite polymer/BaTiO3 ferroelectric films can lead to up to four times higher energy and power density output compared to cases when dipole arrangement is mismatched. For example, TENG device based on PVAc/BaTiO3 shows energy density increase from 32.4 μJ m⁻² to 132.9 μJ m⁻² when comparing devices with matched and mismatched dipoles. The presented strategy and understanding of resulting stronger electrostatic induction in the contacting layers enable the development of TENG devices with greatly enhanced properties.
... Hence, the P(VDF-TrFE) polymer dissolved in the DMSO had a relatively high charge-accepting ability, leading to the output enhancement of triboelectric energy harvesters. More notably, the shift of effective work function and the corresponding electron transport which had been insisted in the previous reports about ferroelectric (highly dielectric)-induced triboelectric enhancement [111,118] has been denied in reality [57,122]. According to the very recent study, the performance enhancement is almost due to the induction driven by piezoelectric charges [122]. ...
... More notably, the shift of effective work function and the corresponding electron transport which had been insisted in the previous reports about ferroelectric (highly dielectric)-induced triboelectric enhancement [111,118] has been denied in reality [57,122]. According to the very recent study, the performance enhancement is almost due to the induction driven by piezoelectric charges [122]. In fact, the correlation between dielectric properties and triboelectric energy harvesting signals is not clearly unveiled, yet. ...
Mechanical energy harvesting technology converting mechanical energy wasted in our surroundings to electrical energy has been regarded as one of the critical technologies for self-powered sensor network and Internet of Things (IoT). Although triboelectric energy harvesters based on contact electrification have attracted considerable attention due to their various advantages compared to other technologies, a further improvement of the output performance is still required for practical applications in next-generation IoT devices. In recent years, numerous studies have been carried out to enhance the output power of triboelectric energy harvesters. The previous research approaches for enhancing the triboelectric charges can be classified into three categories: i) materials type, ii) device structure, and iii) surface modification. In this review article, we focus on various mechanisms and methods through the surface modification beyond the limitations of structural parameters and materials, such as surficial texturing/patterning, functionalization, dielectric engineering, surface charge doping and 2D material processing. This perspective study is a cornerstone for establishing next-generation energy applications consisting of triboelectric energy harvesters from portable devices to power industries.
... As mechanical energy is widely obtainable in our living environment, conversion of mechanical energy to electricity using micro/nano-scale generators [1,2] has become a promising approach. Based on the coupling of the contact electrification and electrostatic induction effects, triboelectric nanogenerator [3] (TENG) has become a popular energy harvesting approach in recent years and has shown advantages of low cost, simple fabrication, diverse structures [4][5][6][7][8] and flexible materials selection [9][10][11], which can be applied to harvest almost all forms of mechanical energies [12][13][14][15][16]. Hybrid effect mechanical energy harvesting generators have rapidly attracted researchers' interests for their flexible capabilities in harvesting different frequencies [17][18][19] of mechanical energies. ...
... Finally, the theoretical J sc-TPEG can be addressed by summing J sc-TEG and J sc-PEG (Fig. 3g, cyan dash line). The theoretical V oc-PEG and J sc-PEG presented a linear relationship with contact frequency according to Eqs. (10) and (11) as demonstrated in Fig. 3f and g, purple dash line, which shows consistent trends with the experimental results. Experimental and theoretical transfer charge Q sc are also demonstrated in Fig. 3h using the same analytical approach as in gap distance. ...
... The approaches to enhance the contact-electrification within TENGs and therefore increase the electrical output typically involve three basic methods: modifying surface morphology, modifying surface chemistry, and utilising ferroelectric materials [24]. There are various mechanisms by which the use or addition of ferroelectric materials can improve triboelectrification. Early theories based upon the change in work function of the ferroelectric polymer which enhances electron transfer [25] have been superseded by research that demonstrates it is due to the piezoelectric effect whereby charge is generated within the material during contact that increase electrostatic induction [26]. Polyvinylidene fluoride (PVDF) is one such ferroelectric polymer commonly used in TENGs [27][28][29][30]. ...
This work presents an investigation into the energy harvesting performance of a combination of PTFE and PVDF materials prepared using a one-step electrospinning technique. Before electrospinning, different percentages of the 1-micron PTFE powder were added to a PVDF precursor. The surface morphology of the electrospun PTFE/PVDF fibre was investigated using a scanning electron microscope (SEM) and tunnelling electron microscope (TEM). The structure was investigated using Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction analysis (XRD). A highly porous structure was observed with a mix of the α- and β-phase PVDF. The amount of β-phase was found to reduce when increasing the percentage of PTFE. The maximum amount of PTFE that could be added and still be successfully electrospun was 20%. This percentage showed the highest energy harvesting performance of the different PTFE/PVDF combinations. Electrospun fibres with different percentages of PTFE were deployed in a triboelectric energy harvester operating in the contact separation mode and the open circuit voltage and short circuit current were obtained at frequencies of 4 to 9 Hz. The 20% PTFE fibre showed 4 (51 to 202 V) and 7 times (1.3 to 9.04 µA) the voltage and current output respectively when compared with the 100% PVDF fibre. The Voc and Isc were measured for different load resistances from 1kΩ to 6GΩ and achieved a maximum power density of 348.5 mW/m2 with a 10 MΩ resistance. The energy stored in capacitors 0.1, 0.47, 1, and 10 µF from a book shaped PTFE/PVDF energy harvester were 1.0, 16.7, 41.2 and 136.8 µJ, respectively. The electrospun fibre is compatible with wearable and e-textile applications as it is breathable and flexible. The electrospun PTFE/PVDF was assembled into shoe insoles to demonstrate energy harvesting performance in a practical application.
... This model is supported by the variation of charge-flow direction depending on the work function of the metal electrode. The other scenario is the increase of electrostatic induction via the piezoelectric charge of the FE polymer, which results in the enhanced charge flow between two FE polymers [20][21][22]. The piezoelectric charge represents the surface charge originating from the piezoelectricity of FE polymer during applied pressure. ...
While ferroelectric polymer-based triboelectric nanogenerators (FE-TENGs) have been regarded as one of the most efficient mechanical energy harvesting devices, their fundamental mechanism is still debated. Here, we propose a dipole charge-shifted work function as the main origin of enhanced performance rather than a piezoelectric charge-increased electrostatic induction. P(VDF-TrFE) FE polymers were contacted with and separated from an ITO metal electrode and another P(VDF-TrFE) FE polymer under the variation of poling voltage, pressure, and temperature. The power outputs of the ITO-P(VDF-TrFE) and P(VDF-TrFE)-P(VDF-TrFE) FE-TENGs increased with poling voltage and pressure, but decreased with temperature; these behaviors are consistent with that of dipole charge rather than piezoelectric charge. Surface-sensitive spectroscopy and microscopy investigations suggested that electrons should be transferred, depending on the dipole direction, in the ITO-P(VDF-TrFE), whereas electrons and material should be transferred, depending on Young’s modulus, in the P(VDF-TrFE)-P(VDF-TrFE). The dipole- and piezoelectric charge-induced electric field plays a crucial role in the overlapped electron cloud model for the triboelectrification of FE-TENGs.
Millions of tonnes of polystyrene (PS) are produced annually, with only an estimated 12% being recycled. Herein, the upcycling of expanded or foamed PS waste into electromechanically responsive triboelectric laminates (TLs) is described. These TLs possess internal triboelectric dipoles offering an alternative to ferroelectric fluoropolymers, and, when manufactured into triboelectric nanogenerators (TENGs), are able to generate over 200 V and 12 μA from motion. This energy harvesting is enabled by electrospinning alternating layers of small and large diameter PS fibers, which upon friction establish an effective dipole moment within the TL. The PS‐TENG shows remarkable stability and is able to charge a 0.47 μF capacitor to 15 V in 200 s of vibration from same material contact electrification, with piezoelectric contact‐mode testing showing that a single PS laminate is comparable to state‐of‐the‐art piezoelectric fluoropolymers for overall electromechanical conversion.
Extensive efforts have been made to improve the output performance of triboelectricity-based mechanical-to-electrical energy generators (TBMEGs). However, the existing improvement strategies roughly treat various dielectrics as ideal capacitor models in charge storage and release, restricting the output enhancement of TBMEGs owing to neglecting the electric displacement response characteristics of dielectrics. Herein, an electric displacement–internal field modulation strategy is proposed for dielectrics that are actually non-ideal capacitors, which fully exploits their gain-of-function effects by synergistically boosting their surface electrostatic polarization change and discharge energy. As proof-of-concept demonstration, an elaborate dielectric consisting of polydimethylsiloxane-filled submicron interconnected lead zirconate titanate skeletons shows good modulation results. The corresponding TBMEG delivers high outputs of 203.3 μC m−2 and 27.6 mJ m−2, realizing a 330% improvement compared to the classical ideal capacitor model strategy. These findings provide more practical insights into output enhancement strategies for TBMEGs composed of non-ideal capacitive dielectrics.
Triboelectric nanogenerators (TENGs) utilize the synergetic effect of triboelectrification and electrostatic induction to guide electrons through an external circuit, enabling low‐frequency mechanical and biomechanical energy harvesting and self‐powered sensing. Integrating 2D material with a high specific surface area into flexible ferroelectric polymers such as polyvinylidene difluoride (PVDF) has proven to be an efficient strategy to improve the performance of TENG devices. Scalable fabrication of graphene‐integrated PVDF nanocomposite fiber using thermal drawing process is demonstrated for the first time in this study. The open‐circuit voltage and short‐circuit current show 1.41 times and 1.48 times improvement with the integration of 5% graphene in the PVDF fibers, respectively. The TENG fabric shows a maximum power output of 32.14 µW at a matching load of 7 MΩ and a power density of 53.57 mW m ⁻² . The fibers exhibit excellent stability in harsh environmental conditions such as alkaline medium, high/low temperature, multi‐washing cycle, and long‐time usage.
Triboelectric nanogenerator (TENG) devices are exemplar systems for mechanical‐to‐electrical energy conversion due to their simplicity and promising performance. However, little attention has been paid to recycling or reusing TENG devices. Indeed, most TENG devices are based on non‐biodegradable polymers, and thus end up in a landfill. Developing biodegradable triboelectric materials is crucial to mitigate negative environmental impacts from their growing use, however, it is challenging to identify such a materials that generate an applicable charge. Herein, such a biodegradable polymer triboelectric pair is demonstrated, by combining poly(butylene succinate) (PBS) films with microcrystalline cellulose (MCC) filler. A power density of 143 mW m⁻² and a charge density of 1.36 nC cm⁻² is measured when contacting pristine PBS with 70 wt% MCC/PBS composite film, which is comparable to polydimethylsiloxane‐based TENGs under identical testing conditions. These devices are shown to degrade via composting at 58 °C over 70 days, enabling long‐term (>10 000 cycle) performance and degradation upon disposal. It is suggested that this approach can be extended to control triboelectric properties for other biodegradable polymers. The technology and concepts developed herein directly address the United Nations Sustainable Development Goals for Responsible Consumption & Production and Affordable and Clean Energy.
Contact electrification and triboelectric charging are areas of intense research. Despite their low ability to accept or donate electrons, polymer insulator based triboelectric nanogenerators have emerged as highly efficient mechanical‐to‐electrical conversion devices. Here, it is reviewed the structure–property–performance of polymer insulators in triboelectric nanogenerators and focus on tools that can be used to directly enhance charge generation, via altering a polymer's mechanical, thermal, chemical, and topographical properties. In addition to the discussion of these fundamental properties, the use of additives to locally manipulate the polymer surface structure is discussed. The link between each property and the underlying charging mechanism is discussed, in the context of both increasing surface charge and predicting the polarity of surface charge, and pathways to engineer triboelectric charging are highlighted. Key questions facing the field surrounding data reporting, the role of water, and synergy between mass, electron, and ion transfer mechanisms are highlighted with aspirational goals of a holistic model for triboelectric charging proposed.
Triboelectric polymer materials are the essential element for triboelectric nanogenerator (TENG). Designing and synthesizing strategy of triboelectric polymers is the foundation for improving the performance of TENG and the related...
In addition to traditional piezoelectric polymers, mono-crystals and ceramics, piezoelectrets or charged voided polymers have shown an interesting piezoelectric response by converting the mechanical energy into electrical and vice versa, therefore being incorporated in a number of advanced electromechanical transducers. This article is a review on the different phases for the elaboration of pseudo piezoelectric films based on passive polymers. First, several methods for the elaboration of the cellular structure of these materials are explained in the main text, with the morphological representation of the reached porosity. The porosity represents a cell to embed the positive and negative electrical charges created by the most common electrical charging processes, which are subsequently mentioned. Different theoretical models are emphasized as well to predict the piezoelectric behavior of this porous polymers. Finally, some of the latest harvesting energy applications based on porous polymers are collected. All the considerations cited above make Piezoelectric porous polymers open access materials that can be developed and optimized by the control of the porosity then used in energy harvesting applications.
Triboelectric nanogenerator (TENG) has attracted much interest due to its efficiency, flexibility and cost-effectiveness to harvest wasted mechanical energy. However, the relationship between the chemical composition and output performance of triboelectric materials is still not completely revealed. As an attempt to understand the structure-performance relationship at the molecular level, representative fluorinated poly (arylene ether)s with varying content of electron-donating groups (fluorene groups) in the backbone are synthesized and compared in the performance of TENGs. The structure-dependent performance of triboelectric materials in TENGs is closely related to the potential energy difference (∆E) between the HOMO energy level of the positive material and the LUMO energy level of the negative material. With an introduction of 50 mol% fluorene groups and the smaller ∆E, the fluorinated poly (arylene ether) (DFAFW50) contacting with PEEK provides the best output performance of the TENG, and remains stable output performance in 120 000 cycles. For fluorinated poly (arylene ether)s, the introduction of electron-donating groups makes materials tend to lose electrons. Within this effort, a potential molecular design protocol is proposed to develop high-performance positive and negative triboelectric materials applicable in TENGs.
In operando techniques have emerged to elucidate the fundamental mechanism of triboelectrification via relevant physical quantity measurement during the physical contact of two materials. Here, a correlation between frictional heat and triboelectric charge is reported in a metal-polymer triboelectric nanogenerator through the in operando temperature measurement. Fluorine-doped tin oxide (FTO) metal is slid back-and-forth under different contact pressures across polydimethylsiloxane (PDMS) polymers having different degrees of crosslinking, i.e., mixing ratio. Both the triboelectric charge and temperature variation increase and become saturated with different time-constants. Notably, the saturated triboelectric charge increases, while the saturated temperature decreases, with increasing mixing ratio. In contrast, both saturated triboelectric charge and temperature increase with increasing contact pressure. X-ray photoemission spectroscopy reveals that chemical bonds are modified inhomogeneously at the surface, and that charged materials are transferred from PDMS to FTO in accordance with the mixing ratio- and sliding time-dependent triboelectric charges. Frictional heat plays a distributive role in bond rupture and temperature variation, depending on the activation energy and frictional coefficient of PDMS. In operando temperature variation measurement provides important information on the specific bonds for triboelectrification and detailed charge-transfer process during physical contact.
The annual energy consumption to supply traditional power for cooling or heating applications is tremendous. Refrigeration or heating technology that does not rely on traditional energy sources is of great interest for modern society to achieve energy conservation and emission reductions. In this work, we demonstrated a self-powered cooling and heating system, consisting of a triboelectric nanogenerator (TENG), a power and charging management module, and an electrocaloric (EC) material. Ferroelectric ceramics of 0.1 PbTiO3–0.9 PbSc0.5Ta0.5O3 (PSTT) with high EC at room temperature were successfully prepared. By converting the TENG-harvested kinetic energy of the mechanical motion into electrical energy and applying or releasing a polarized electric field to 12 PSTT sheets through circuit management, we achieved excellent dual self-powered cooling/heating functions in the room-temperature range. When the operating frequency of the TENG was 3 Hz, in a space with a specific surface area ratio of only 3.328% and a volume ratio of 0.433%, a temperature change of 0.5 K was achieved within 5.5 min, and the energy conversion efficiency reached 10.926%. Because the TENG can effectively harvest the kinetic energy of various motions, including body motions and widely distributed wind, water wave, and raindrop energy in nature, it can be used to develop compact, miniaturized, and self-powered solid-state cooling/heating devices based on the EC effect. With the advantages of a high coefficient of performance, ease of use, zero emissions and lack of pollution production, our proposed approach is expected to achieve widespread application in various fields.
From fundamental research to the development of next-generation technologies, considerable progress has been achieved in the field of ultrathin 2DMs research during the previous decade. With the rapid rise of smart devices, wearable electronicsWearable electronics, and the Internet of Things, a lot of work has lately gone into developing practical, portable, and distributed energy sources for a new era of energy. Mechanical, thermal, solar, and chemical energy are just a few examples of environmentally friendly energy sources.
Ferroelectric and piezoelectric polymers have attracted great attention from many research and engineering fields due to its mechanical robustness and flexibility as well as cost‐effectiveness and easy processibility. Nevertheless, the electrical performance of piezoelectric polymers is very hard to reach that of piezoelectric ceramics basically and physically, even in the case of the representative ferroelectric polymer, poly(vinylidene fluoride‐co‐trifluoroethylene) (P(VDF‐TrFE)). Very recently, the concept for the morphotropic phase boundary (MPB), which has been exclusive in the field of high‐performance piezoelectric ceramics, has been surprisingly confirmed in P(VDF‐TrFE) piezoelectric copolymers by the groups. This study demonstrates the exceptional behaviors reminiscent of MPB and relaxor ferroelectrics in the feature of widely utilized electrospun P(VDF‐TrFE) nanofibers. Consequently, an energy harvesting device that exceeds the performance limitation of the existing P(VDF‐TrFE) materials is developed. Even the unpoled MPB‐based P(VDF‐TrFE) nanofibers show higher output than the electrically poled normal P(VDF‐TrFE) nanofibers. This study is the first step toward the manufacture of a new generation of piezoelectric polymers with practical applications.
The contact electrification of ferroelectric polymer can be more complicated due to its ordered permanent molecular dipoles and dipole–dipole interactions. Herein, the polyvinylidene fluoride (PVDF)-Cu is taken as an example to investigate the mechanism of ferroelectric polymer-metal contact electrification via first-principles calculations. It is revealed that different from non-ferroelectric polymers, when ferroelectric polymers are in contact with metals, the charge transfer occurs not only at the interface but also inside the polymer due to the existence of polar phases. Specifically, the polar phases in the crystallization region can effectively enhance the charge transfer between the ferroelectric polymer and metal because the polar molecules in PVDF possess the stronger electrostatic potential, more delocalized lowest unoccupied molecular orbital, and additional dipole–dipole interactions compared with nonpolar molecules. In addition, the coupling mechanism of piezoelectricity and triboelectricity in ferroelectric polymer-metal contact electrification under compression is also investigated. It is demonstrated that the deformation increases the degree of noncoincidence between positive and negative charge centers in polar phases and causes charge transfer between the polar molecular chains of PVDF, thus producing the extra charge transfer between the ferroelectric polymer and metal. This study provides a theoretical basis for the material design of triboelectric nanogenerators based on ferroelectric polymers.
As an efficient power technology, a triboelectric nanogenerator (TENG) has made a huge impact on many research fields and exhibits exciting prospects in the future world. There are two output modes of the TENG, the alternating current (AC) mode based on the coupling of triboelectrification and electrostatic induction, and the direct current (DC) mode based on the coupling of triboelectrification and air-breakdown. AC can be converted into DC by rectification. However, from the symmetry argument, there should be an inverting mode to convert the DC into AC. Herein, an inverting TENG to realize the AC mode based on the coupling of triboelectrification and air-breakdown is proposed for the first time by setting alternating polarity distribution areas. Different from the fixed waveforms of a traditional AC-TENG, the inverting TENG exhibits such unique characteristics that both the width ratio and amplitude ratio of AC signals can be changed by tuning the distributed width and electronegativity difference of two opposite materials. This work paves the way for the development of a symmetry output mechanism for the TENG, from AC to DC, and from DC to AC, or even hybrid DC and AC in one TENG, and these powerful functions endow the inverting TENG with more advantages for future self-powered intelligent systems.
Triboelectric nanogenerator (TENG) is a kind of capacitive conduction to convert mechanical triggering into electricity, which is the realized applications of Maxwell's equations in the field of nano energy and self-powered systems. As a conductor to participate electrostatic induction, the induction electrode has received little cognition. According to the unified theory of electromagnetics, the investigation of magnetic medium in TENG should not be ignored. Here we fabricate flexible single-electrode triboelectric nanogenerator (S-TENG) by the Micro Electromechanical System (MEMS) compatible technology, including non-destructive peeling technology and in-situ electrodeposition. Specifically, the S-TENG is composed of polydimethylsiloxane (PDMS) as the negative triboelectric layer and electrodeposited nickel as the induction electrode. Theoretically and experimentally, we demonstrate that ferromagnetic Ni electrode could substantially enhance the electrical output of TENG, which is attributed to the generated magnetizing current. The enhancement mechanism proposed in this work follows the law of energy conservation, which utilizes the natural magnetostatic energy inside the ferromagnetic medium and couples the working principle of TENG, thus making great contributions to the output of TENG. Furthermore, the relationship between the magnetic structure and performance is surveyed, and the stability of Ni and Ni-based S-TENG is also investigated. Finally, the proposed strategy for fabricating enhanced and stable Ni electrode is utilized in flexible energy harvester, and shows great prospects in flexible electronics.
The performance of triboelectric nanogenerator is limited by interfacial charge losses due to alternate charge transfer. This is usually suppressed by addition of electron blocking, electron transporting layers or through external excitation. However, these approaches screen only electrons from the interface while the unstable positive charges remain. Herein, we report a stable tribopositive layer with an overall positive surface and embedded magnetic active negative centers for stabilizing positive charges to prevent cation recombination with anion of counterpart. Besides, a counterpart with high electron delocalization density is used for screening interfacial negative charges, leading to enhanced charge accumulation of 11 nC with short circuit current of 0.8 µA, increasing to 54 nC and 17.4 µA by staking 4 units of 2.25 cm² device in alternate layered structure, with an enhancement rate of 15.1 nC and 5.6 µA per unit. Further, the embedded negative centers in response to magnetic field form skewed charge transporting channels, causing homogeneous distribution of potential on the tribopositive layer, effectively transporting charges to electrode via hindering bulk losses. The single unit shows 15900% enhancement reaching 4.8 µA, 208 µCm⁻² and 1.66 Wm⁻² and demonstrating the highest enhancement capacity compared to previously reported strategies and thus a promising potential for wearable electronics with high power demand.
Layered double hydroxides (LDHs) have been extensively investigated for various applications such as drug delivery, energy storage, catalysis, and luminescence. In this study, an eco-friendly ZnAl-CO3-LDH-poly(vinylidene fluoride) (ZnAl-LDH-PVDF) composite acting as a triboelectric dielectric material is described. The composite material can realize a high-performance, flexible, and transparent triboelectric nanogenerator (TENG). The strong interactions between ZnAl-LDH and PVDF facilitate the formation of a spontaneous polar β-PVDF phase and enhance the dielectric properties of composite films considerably. The output performance of ZnAl-LDH-PVDF composite-based TENGs with various amounts of ZnAl-LDH was investigated. 20 wt% ZnAl-LDH-PVDF TENG demonstrated an output voltage of ∼230.6 V, current density of ∼5.6 μA cm⁻², and power density of 0.43 mW cm⁻². The pressure- and humidity-dependent outputs of the device enable it to be an effective self-powered pressure and humidity sensor. As a pressure sensor, the device revealed an excellent pressure sensitivity of 13.07 V kPa⁻¹. As a humidity sensor, it exhibited a response of 259.4% in the voltage detection mode. The improved polar β-PVDF phase and dielectric properties of the ZnAl-LDH-PVDF composite make it suitable for high-performance mechanical energy harvesters in self-powered sensor applications.
In this study, we investigate triboelectrification in polymer-based nanocomposites using identical polymer matrixes containing different concentrations of nanoparticles (NPs). The triboelectric surface charge density on polymer layers increased as the difference in nanoparticle filler concentration between the two triboelectric layers escalated, despite the fact that the polymer matrix was the same in both layers. This effect was observed in tests of various polymer types and filler NPs. Our mechanical experiments and finite element analysis simulations confirmed that polymeric triboelectrification is related to the surface viscoelastic deformation that occurs during mechanical contact and separation, and is not dependent on electronic or chemical properties, but rather physicochemical and mechanical properties. This supports the heterolytic scission of covalent bonds in polymer chains as an explanation for the triboelectricity. Accordingly, this study marks a significant contribution to the fundamental understanding of the mechanism of polymeric triboelectrification and will be relevant to the development of triboelectric sensors and energy harvesters.
Soft ferroelectrics based on organic and organic–inorganic hybrid materials have gained much interest among researchers owing to their electrically programmable and remnant polarization. This allows for the development of numerous flexible, foldable, and stretchable nonvolatile memories, when combined with various crystal engineering approaches to optimize their performance. Soft ferroelectrics have been recently considered to have an important role in the emerging human‐connected electronics that involve diverse photoelectronic elements, particularly those requiring precise programmable electric fields, such as tactile sensors, synaptic devices, displays, photodetectors, and solar cells for facile human–machine interaction, human safety, and sustainability. This paper provides a comprehensive review of the recent developments in soft ferroelectric materials with an emphasis on their ferroelectric switching principles and their potential application in human‐connected intelligent electronics. Based on the origins of ferroelectric atomic and/or molecular switching, the soft ferroelectrics are categorized into seven subgroups. In this review, the efficiency of soft ferroelectrics with their distinct ferroelectric characteristics utilized in various human‐connected electronic devices with programmable electric field is demonstrated. This review inspires further research to utilize the remarkable functionality of soft electronics.
Huge demand for portable electronics and wearable devices in the era of the Internet of Things (IoT) has driven the demand for sources of clean energy harvested from ambient environments. Here, all-organic piezo-assisted triboelectric nanogenerators (P-TENGs) were fabricated by subsequently pairing polarized poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) with polyvinyl alcohol (PVA), which is a tribopositive polymer, and silicone rubber, which is a tribonegative polymer. This work aims to investigate the effect of piezoelectric polarization in P(VDF-TrFE) on the contact electrification (CE) of P-TENGs. By tuning the direction of piezoelectric polarization in P(VDF-TrFE), the electrical outputs (open circuit voltage, short circuit current density, and short circuit charge density) of the P-TENGs can be enhanced by an average of 135%. These observations were explained using a modified overlapped electron cloud (OEC) model. It is proposed that the CE was affected by the shift in energy levels of electrons which is induced by the piezoelectric polarization of P(VDF-TrFE). A maximum power density of 450 μW cm⁻² was achieved by applying a constant force of 100 N on the P-TENG reverse-polarized P(VDF-TrFE) with silicone rubber. The experimental results in this work show a reliable method of electrical power enhancement in a P-TENG by tuning the piezoelectric polarization into a favored state. Moreover, the modified OEC helps to elucidate the enhancement effect of the polymer–polymer CE by providing a fundamental understanding of the effect of piezoelectric polarization on CE.
As a promising sustainable power source for intelligent electronics, triboelectric nanogenerator (TENG) has attracted remarkable attention and various strategies have been sought to improve its output performance. However, most of these approaches for triboelectric materials optimization only focus on either chemical composition modulation or surface microstructure fabrication. In this work, both aspects are considered and an effective strategy is proposed to construct high performance TENGs based on polyvinylidene fluoride (PVDF) via graphene nanosheets incorporation in conjunction with electrospinning technology. Hence, a 20 × 20 mm² TENG comprising of PVDF/G nanofibers and polyamide-6 (PA6) films demonstrates superior triboelectric performance with an output voltage of ~1511 V, a short-circuit current density of ~189 mA m⁻², and a maximum peak power density of ~130.2 W m⁻², nearly eight times higher than that of the PVDF-PA6 TENG. Additionally, under impedance matching condition, the PVDF/G-PA6 TENG can harvest ~74.13 μJ energy per cycle, with a time-averaged output power density of 926.65 mW m⁻². Detail investigation reveals that both composition modulation with graphene and nanofiber structure fabricated through electrospinning contribute to the triboelectric performance enhancement of PVDF/G NF films. This work provides an effective strategy of simultaneously optimizing the chemical composition and surface microstructure of triboelectric materials to significantly improve the output performance of TENGs, and to further promote the widespread application of TENGs.
The hexagonal boron nitride nanosheets (BNNSs) are one of the 2-dimensional(2D) materials, and have been explored for their applications in nanoelectronics etc, owing to their unique properties. Here, BNNSs are utilized to develop a high-performance hybrid piezo/triboelectric nanogenerator (PTEG). BNNSs of a few percentages in weight are incorporated into polydimethylsiloxane (PDMS) to form composites that are able to produce piezo-electric voltages up to ~ 5.4 V with d 33 ~ 12 pC/N. A PTEG composed of BNNS-PDMS and polyamide-6 (PA6) membranes (20 × 20 mm 2) demonstrates a current density of ~ 230 mA m − 2 , an output voltage of ~ 1870 V and a maximum power density of ~ 103.7 Wm − 2 , more than three times higher than those of the control PDMS/PA6 nanogenerator. Electric polarization of the BNNS-PDMS membranes can further enhance the output of PTEGs. Detailed investigation reveals that the dramatically enhanced performance originates from the synergy of piezoelectric effect of BNNSs and increased electron affinity of BNNS-PDMS membranes, demonstrates the excellent potential of BNNS-based PTEGs.
To meet the future need for clean and sustainable energies, there has been considerable interest in the development of triboelectric nanogenerators (TENGs) that scavenge waste mechanical energies. The performance of a TENG at the macroscale is determined by the multifaceted role of surface and interface properties at the nanoscale, whose understanding is critical for the future development of TENGs. Therefore, various protocols from the atomic to the macrolevel for fabrication and tuning of surfaces and interfaces are required to obtain the desired TENG performance. These protocols branch out into three categories: chemical engineering, physical engineering, and structural engineering. Chemical engineering is an affordable and optimal strategy for introducing more surface polarities and higher work functions for the improvement of charge transfer. Physical engineering includes the utilization of surface morphology control, and interlayer interactions, which can enhance the active interfacial area and electron transfer capacity. Structural engineering at the macroscale, which includes device and electrode design/modifications has a considerable effect on the performance of TENGs. Future challenges and promising research directions related to the construction of next‐generation TENG devices, taking into consideration “interfaces” are also presented.
The effective conversion of vibrational energy from the motion of human body into electricity has been considered as one of the most promising technologies for charging portable electronic devices. Here, we report an electric polarization-controlled PVDF-based hybrid triboelectric-piezoelectric nanogenerator (TP-NG) as for an effective energy harvesting of various mechanical vibrations from human foot. The hybrid TP-NG simply consists of PVDF, Al, and acrylic, and the triboelectric NG component is vertically stacked on the piezoelectric NG component. We observed the strong electric-polarization-dependent electric power due to the modulated surface potential and negative piezoelectricity of PVDF. We also observed the in-phase power generation due to the vertical stacking of two flat NGs, irrespective of various loading rate, contact time, force, and frequency. Three hybrid TP-NGs were embedded at the forefoot, arch, and heel positions in a shoe insole. During normal walking, the shoe insole generated sufficient power to operate light-emitting diodes, which could be used in lightning at night. In addition, the insole operated a wireless pressure network, which could be used in monitoring and transmitting the pressure distribution on the foot to a cellular phone. This work provides an important step in the harvesting of random and irregular vibrational energy from the human foot, and in the realization of self-powered lightning for safety and self-powered wireless pressure monitoring system for diagnostic healthcare.
With the rapid advances in wearable electronics and photonics, self-sustainable wearable systems are desired to increase service life and reduce maintenance frequency. Triboelectric technology stands out as a promising versatile technology due to its flexibility, self-sustainability, broad material availability, low-cost, and good scalability. Various triboelectric-human-machine-interfaces (THMIs) have been developed including interactive gloves, eye blinking/body motion triggered interfaces, voice/breath monitors, and self-induced wireless interfaces. Nonetheless, THMIs conventionally use electrical readout and produce pulse-like signals due to the transient charge flows, leading to unstable and lossy transfer of interaction information. To address this issue, we propose a strategy by equipping THMIs with robust nanophotonic aluminum nitride (AlN) modulators for readout. The electrically capacitive nature of AlN modulators enable THMIs to work in the open-circuit condition with negligible charge flows. Meanwhile, the interaction information is transduced from THMIs’ voltage to AlN modulators’ optical output via the electro-optic Pockels effect. Thanks to the negligible charge flow and the high-speed optical information carrier, stable, information-lossless, and real-time THMIs are achieved. Leveraging the design flexibility of THMIs and nanophotonic readout circuits, various linear sensitivities independent of force speeds are achieved in different interaction force ranges. Toward practical applications, we develop a smart glove to realize continuous real-time robotics control and virtual/augmented reality interaction. Our work demonstrates a generic approach for developing self-sustainable HMIs with stable, information-lossless, and real-time features for wearable systems.
Ocean wave energy is a promising energy source for large-scale exploitation owing to its abundant reserve and renewability. An effort is underway to develop a generator that can adapt to the ultra-low frequency of ocean wave vibration. Here, we designed a cylindrical triboelectric nanogenerator with an internal swing structure for effective water wave energy harvesting. Based on the supporting effect of the bearing component, the rotary dielectric films can be suspended over the stator electrodes, rather than coming into direct contact with them. Benefiting from the largely reduced resistance and continuous swing of an internal rotary component, the fabricated triboelectric nanogenerator can operate for about 85 s and produce over one thousand current pulses after one water wave excitation. Being agitated by a 0.033 Hz water wave (during a period of 30 s), the optimized cylindrical triboelectric nanogenerator can produce a peak power density of 231.6 mW·m⁻³ and an average one of 39.8 mW·m⁻³. Successful demonstrations of powering portable electronic devices and iron material corrosion inhibition under such simulated excitation indicate the robust capability for ultra-low-frequency water wave energy conversion. This triboelectric nanogenerator offers a new vision for efficient ultra-low-frequency wave energy harvesting with the possibility of large-scale blue energy.
Self-powered multlifunctional sensors have been receiving great attention for their potential use in sustainable wearable electronics. In this work, we demonstrate a facile approach for the development of self-powered multimodal pressure-temperature sensors based on an identical ferroelectric copolymer, poly (vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) for the contact pair materials by switching the triboelectric polarity via ferroelectric polarization. This approach enables the identical material-based triboelectric devices with remarkably enhanced triboelectric and pyroelectric output performances. The inversely-polarized P(VDF-TrFE) device exhibits ∼106 and ∼12 times higher triboelectric and pyroelectric currents, respectively, compared to those of non-polarized devices. Consequently, our triboelectric device provides the highest pressure sensitivity of 40 nA kPa⁻¹ and 1.4 V kPa⁻¹ with a broad pressure detection range (98 Pa to 98 kPa) as well as competitive temperature sensitivity of 0.38 nA °C⁻¹ and 0.27 nA °C⁻¹ in cooling and heating states, respectively, compared to previous PVDF-based self-powered sensors. Furthermore, our self-powered sensor can discriminate multiple stimuli including pressure as well as temperature without signal interference. Our sensor can be utilized for the monitoring of weak pulse pressure as well as multimodal finger touch. This work provides a facile fabrication approach to realize triboelectric and pyroelectric multimodal devices with outstanding output performances.
In the present work, the contact electrification of polymers that differ in adhesion strength is studied. Electrical current is measured along with adhesion in macroscale contacting‐separation experiments. Additionally, local adhesion and roughness are studied with atomic force microscopy to get deeper insight into relations between surface properties and electrification. Measurements reveal that higher surface charge is formed on more adhesive surfaces, thus confirming covalent bond cleavage as a mechanism for contact electrification of polymers. Investigated materials possess enhanced contact electrification making them attractive candidates for the conversion of mechanical energy to electrical in triboelectric nanogenerator devices. Heterolysis and mass transfer are confirmed by XPS and AFM as the primary mechanism for contact electrification of polymers as suggested by an evident correlation between adhesion and charge density. A new look is proposed on the calculation of TENG efficiency—one that takes into account separation forces.
Triboelectric nanogenerators (TENGs) are considered as one of the most important renewable power sources for mobile electronic devices and various sensors in the Internet of Things era. However, their performance should inherently be degraded by the wearing of contact surfaces after long‐term use. Here, a ferroelectric polymer is shown to enable TENGs to generate considerable electricity without contact. Ferroelectric‐polymer‐embedded TENG (FE‐TENG) consists of indium tin oxide (ITO) electrodes, a polydimethylsiloxane (PDMS) elastomer, and a poly(vinylidene fluoride) (PVDF) polymer. In contrast to down‐ and non‐polarization, up‐polarized PVDF causes significantly large triboelectric charge, rapidly saturated voltage/current, and considerable remaining charge due to the modulated surface potential and increased capacitance. The remained triboelectric charges flow by just approaching/receding the ITO electrode to/from the PDMS without contact, which is sufficient to power light‐emitting diodes and liquid crystal displays. Additionally, the FE‐TENG can charge an Li‐battery with a significantly reduced number of contact cycles. Furthermore, an arch‐shaped FE‐TENG is demonstrated to operate a wireless temperature sensor network by scavenging the irregular and random vibrations of water waves. This work provides an innovative and simple method to increase conversion efficiency and lifetime of TENGs; which widens the applications of TENG to inaccessible areas like the ocean.
Paper‐based electronics has attracted growing interest owing to many advantages of papers including low‐cost, abundance, flexibility, biocompatibility, and environmental friendliness. Despite recent progress in paper electronics, however, development of a high‐performance paper‐based triboelectric nanogenerator (TENG), which is a power‐generating device that converts mechanical energy into electric energy by coupling triboelectrification and electrostatic induction, remains a challenge mainly due to weak electron‐donating tendency of cellulose‐based papers. In this work, highly conductive ferroelectric cellulose composite papers containing silver nanowires and BaTiO3 nanoparticles are fabricated, and their successful application for realizing a large‐area TENG with enhanced electrical output performance is demonstrated. It is found that triboelectric charge generation on the ferroelectric cellulose composite paper can be promoted by simple poling treatment, which significantly enhances TENG performance. The ferroelectric cellulose composite paper–based TENG exhibits an electrical output performance that surpasses those of aluminum‐based and pristine cellulose–based TENGs by more than two times, as well as outstanding output stability without a noticeable degradation in performance during 10 000 cycles of a repeated pushing test. The work demonstrates the great potential of multifunctional cellulose‐based papers for TENG and other self‐powered electronic applications. Highly conductive ferroelectric cellulose composite papers containing silver nanowires and BaTiO3 nanoparticles are prepared to fabricate high‐performance paper‐based triboelectric nanogenerators. Poling treatment of this ferroelectric paper leads to dipole alignment, which promotes triboelectric charge generation on the paper and thus enables to achieve enhanced electrical output performance.
It was recently reported that more efficient triboelectric nanogenerator (TENG) like devices can be prepared using inversely polarized ferroelectric films made of same material as the contacting layers. In the present work, a clear correlation between the piezoelectric response of inversely polarized ferroelectric PVDF/BaTiO3 nanocomposite films and the performance of TENG-like device based on these films is demonstrated. This observation is explained by magnified electrostatic induction that is driven by piezoelectric charges and ferroelectric properties of these films. Double capacitor model is proposed that effectively portrays the interactions between ferroelectric layers during contact-separation and subsequent charge redistributions in the external circuit. The new understanding has allowed reaching three-fold higher open circuit voltages (2.7 kV from 5 cm²) than state of the art TENG. Furthermore, findings uncover the potential for vast improvement in the field of nanogenerators for mechanical energy harvesting as a significantly better piezoelectric performance of flexible nanogenerators has been reported elsewhere.
In the present study, a feather rotating-TENG (FTR-TENG) was developed by analyzing the properties of nanostructure and changes in friction areas by the aerodynamic motion of naturally evolved feathers. The motion and area of surface of the feathers vary according to the interlocking effect of the aerodynamic nanostructure that was found appropriate for the FTR-TENG in the present study. Owl feather, employed in the present study, demonstrated peak output performance of FTR-TENG of 51.4 V, 4.47 μA at 1.6 cm ² of friction area and 7 m/s of wind speed. In addition, the positive surface charge potential of all feathers has increased by the electrostatic adsorption of hematoxylin, the natural dye, used to maximize the electricity generation efficiency of FTR-TENG by raising the positive triboelectric series of the β-keratin structure of feather. As a consequence, the performance of triboelectric generation was increased, despite the small area and low wind power, compared to the previous results of the rotational wind power generator. The owl feather demonstrated generation of 64.3 V and 6.55 μA with 1.6 cm ² of frictional area at wind speed of 7 m/s, which represented an approximately 25% increase in voltage, and 47% increase in current, compared with that before adsorption.
As a promising nanoenergy technology to harvest mechanical energy from environment, triboelectric nanogenerator (TENG) has attracted much attention and various strategies focused on optimization of triboelectric materials have been proposed to further improve its output power density. This work focuses on the electrode material for improvement of TENGs. A commercial double-sided conductive carbon tape composed of carbon powder is proposed as the electrodes for TENGs, based on which a superior performance TENG comprised of spin-coated flat polydimethylsiloxane (PDMS) and polyamide-6 (PA6) films is fabricated. Owing to the strong additional interaction between carbon electrode and tribo-layer, a 20 × 20 mm² carbon-PDMS/PA6 TENG demonstrates a peak output voltage of ~ 1760 V, a short-circuit current density of ~ 240 mA m⁻², and a maximum power density of ~ 120 W m⁻², much higher than those of aluminum electrode-based Al-PDMS/PA6 TENGs. Detailed investigations reveal that the dramatically enhanced performance originates from the additional interaction in the pores between coarse carbon electrode and PDMS film, and from the enhanced electric negative polarity of PDMS films with the peeling and transferring treatment. This study provides a promising simple and low-cost strategy of selecting and preparing electrode materials with special micro/nanostructures to interact with triboelectric layers to generate additional triboelectric charges for high performance TENGs.
Harvesting mechanical energy and effectively converting it into electrical power by triboelectric nanogenerators (TENGs) have been demonstrated as a burgeoning field of research, that can be essential for the energy of the new era, which is the era of internet of things, big data, and artificial intelligence. Here the structural figure-of-merits (FOMS) for quantitatively evaluating and comparing the output performance of TENGs under different load resistances are studied. Firstly, we introduce the triboelectric process and transient process to analyze the charges transfer in each half cycle. Because each process corresponds to a first-order differential equation, four basic governing equations in a whole cycle are built up. After solving these equations, the real-time output characteristics of TENG are demonstrated, which comprehensively reveal the output behavior of TENG devices. Then, same method is utilized to investigate the maximum harvested energy and structural FOMRS with different load resistances at various maximum displacements. These theoretical results especially about the derived FOMRS provide an improved capability of comparing different configurations of TENGs. This work can not only completely explain the working principles of TENGs, but also enhance the applicability of structural FOMRS, enabling more efficient design and optimization of various TENG structures in practical applications.
Energy scavenging techniques based on the piezoelectric and triboelectric effects have become increasingly attractive in last few years due to their efficient working process as well as promising output potential. Here, we fabricate hybrid generators based on PDMS composite films embedded with a range of functional materials combining both piezoelectric and triboelectric properties. Meanwhile, generators of single effect are also fabricated in order to analyze the output contribution of each effect in contrast to the combined effect and to understand the impact of each material on the piezoelectricity or triboelectricity during the power generation process. An average open-circuit voltage of 48.46V with an energy conversion efficiency of 31.62% are achieved by a device based on PDMS composite with PVDF/MWCNT/BaTiO3. The ratio between triboelectric and piezoelectric effects in composite generators is also introduced and analyzed in this work. Our findings not only indicate that individual materials in a composite can synergistically enhance their intrinsic properties, but also validate that the capacity of composites in converting mechanical energy is far beyond individual material.
Piezoelectric and triboelectric nanogenerators have been developed as rising energy harvesting devices in the past few years to effectively convert mechanical energy into electricity. Here, a novel hybrid piezo/triboelectric nanogenerator based on BaTiO3 NPs/PDMS composite film was developed in a simple and low cost way. The effect of BTO content and polarization degree on the output performance was systematically studied. The device with 20 wt% BTO in PDMS and 100 µm thickness film shows the highest output power. We also designed three measurement modes to record hybrid, tribo, piezo output separately with simple structure, which has only two electrodes. The hybrid output performance is higher than that of tribo and piezo. This work will provide not only a new way to enhance output power of nanogenerators, but also new opportunities for developing built-in power source in self-powered electronics.
All-textile triboelectric generators (TEGs) allow for seamless integration of TEGs into garments, while maintaining the intrinsic flexibility, breathability, durability, and aesthetic value of normal textiles. However, practical approaches to construct fabric TEGs using traditional textile processes, such as sewing, weaving, and knitting, are underreported. In this work, two approaches to create an all-textile TEG using straight-forward textile manufacturing methods are presented. The first approach is to assemble two different cloths of opposite surface charge characteristics in a face-to-face configuration. A cotton fabric functionalized with fluoroalkylated polymeric siloxanes is necessary to generate usable triboelectric power output, when coupled with a pristine nylon cloth. The increased surface charge density by introducing fluoroalkyl groups is confirmed by Kelvin probe force microscopy measurements. The second approach is to weave or knit together two different conductive threads of opposite surface charge characteristics to create a monolithic triboelectric textile. The weave or knit pattern used to assemble this textile directly controls the density of contact points between the two types of threads, which, ultimately, determines the areal triboelectric power output of the textile. Overall, two feasible methods for constructing unprecedented textile-based triboelectric generators with notable power output are presented.
For existing triboelectric nanogenerators (TENGs), it is important to explore unique methods to further enhance the output power under realistic environments to speed up their commercialization. We report here a practical TENG composed of three layers, in which the key layer, an electric double layer, is inserted between a top layer, made of Al/polydimethylsiloxane, and a bottom layer, made of Al. The efficient charge separation in the middle layer, based on Volta's electrophorus, results from sequential contact configuration of the TENG and direct electrical connection of the middle layer to the earth. A sustainable and enhanced output performance of 1.22 mA and 46.8 mW cm 2 under low frequency of 3 Hz is produced, giving over 16-fold enhancement in output power and corresponding to energy conversion efficiency of 22.4%. Finally, a portable power-supplying system, which provides enough d.c. power for charging a smart watch or phone battery, is also successfully developed.
A theoretical model for contact-mode TENGs was constructed in this paper. Based on the theoretical model, its real-time output characteristics and the relationship between the optimum resistance and TENG parameters were derived. The theory presented here is the first in-depth interpretation of the contact-mode TENG, which can serve as important guidance for rational design of the TENG structure in specific applications.
A new kind of triboelectric nanogenerator (TENG) is developed based on electrospun PVDF and nylon nanowires. This nanogenerator exhibits the remarkable characteristics of easy fabrication, low cost and high output. Its open-circuit voltage and short-circuit current density respectively reach up to 1163 V and 11.5 μA cm(-2) driven by the vibration with a triggering frequency of 5 Hz and an amplitude of 20 mm. The peak power density is 26.6 W m(-2). It directly powered a DC motor without an energy storage system for the first time. By harvesting energy from the environment using this TENG, a fully self-powered UVR detection device is developed to show the level of UVR directly without additional components.
A stretchable-rubber-based (SR-based) triboelectric nanogenerator (TENG) is developed that can not only harvest energy but also serve as self-powered multifunctional sensors. It consists of a layer of elastic rubber and a layer of aluminum film that acts as the electrode. By stretching and releasing the rubber, the changes of triboelectric charge distribution/density on the rubber surface relative to the aluminum surface induce alterations to the electrical potential of the aluminum electrode, leading to an alternating charge flow between the aluminum electrode and the ground. The unique working principle of the SR-based TENG is verified by the coupling of numerical calculations and experimental measurements. A comprehensive study is carried out to investigate the factors that may influence the output performance of the SR-based TENG. By integrating the devices into a sensor system, it is capable of detecting movements in different directions. Moreover, the SR-based TENG can be attached to a human body to detect diaphragm breathing and joint motion. This work largely expands the applications of TENG not only as effective power sources but also as active sensors; and opens up a new prospect in future electronics.
Motivated by a desire to resolve the needs of sustainable energy resources, remote sensing electronics, wireless autonomous devices, mobile internet of things (IoT) and portable self-power generators, triboelectric nanogenerators have recently been suggested. However, more specialized target applications to biomedical and wearable devices will require biocompatible and eco-friendly triboelectric materials in power generators. Herein, we report for the first time a bio-triboelectric nanogenerator based on an eco-friendly and naturally abundant biomaterial, bacterial nanocellulose. Initially, bacterial cellulose pellicles were produced in a gel state by Acetobacter xylinum KJ1 in the Glu-Fruc medium and then a bacterial nanocellulose film having transparent and flexible functionalities was regenerated on a current collector via a solubilization process. The bacterial nanocellulose triboelectric nanogenerator was investigated with various input conditions and structural aspects. The working mechanism was also considered by measuring the contact angle and the surface potential of the friction materials. We believe that this study provides new insights to advancing the biocompatible and eco-friendly triboelectric power generator and optimization strategies to achieve high performance of triboelectric nanogenerators.
Vertical contact-separation mode triboelectric generator (TEG) based on lead-free perovskite, zinc stannate (ZnSnO3)-polyvinylidene fluoride (PVDF) composite and polyamide-6 (PA6) membrane is demonstrated. For the 5wt% PVDF-ZnSnO3 nanocomposites, the facile phaseinversion method provides a simple route to achieve high crystallinity and β-phase with a piezoelectric coefficient d33 of -65 pmV-1, as compared to -44 pmV-1 for pristine PVDF membranes. Consequently, at a cyclic excitation impact of 490 N/3 Hz, the PVDFZnSnO3/
PA6 based TEGs provide a significantly higher voltage of 520 V and a current density of 2.7 mAm-2 (corresponding charge density of 62.0 μCm-2), as compared to the pristine PVDF-PA6 TEG which provides up to 300 V with a current density of 0.91 mAm-2 (corresponding to a charge density of 55.0 μCm-2). This increase in the electrical output can be attributed to not only the enhanced polarisation of PVDF by ZnSnO3 leading to an increase in the β-phase content, but also to the surface charge density increase by stress induced polarisation of ZnSnO3, leading to the generation of stronger piezoelectric potential. The work thus introduces a novel method of enhancing the surface charge density via the addition of suitable high polarization piezoelectric materials thus eliminating the need for prior charge injection for fluoropolymer membranes.
Triboelectric nanogenerators (TENGs) have been invented as a new technology for harvesting mechanical energy, with enormous advantages. One of the major themes in its development is the improvement of the power output, which is fundamentally determined by the triboelectric charge density. Besides the demonstrated physical surface engineering methods to enhance this density, the chemical surface functionalization to modify the surface potential could be a more effective and direct approach. In this paper, we introduced the method of using self-assembled monolayers (SAMs) to functionalize surfaces for the enhancement of TENG’s output. By using thiol molecules with different head groups to functionalize Au surfaces, the influence of head groups on both the surface potential and the triboelectric charge density were systematically studied, which reveals their direct correlation. With amine as the head group, the TENG’s output power is enhanced by ~4 times. By using silane-SAM with amine head group to modify silica surface, this approach is also demonstrated for insulating triboelectric layers in TENG. This research provides an important route for the future research on improving TENGs’ output through materials optimization.
Triboelectric nanogenerators have been invented as a highly efficient, cost-effective and easy scalable energy-harvesting technology for converting ambient mechanical energy into electricity. Four basic working modes have been demonstrated, each of which has different designs to accommodate the corresponding mechanical triggering conditions. A common standard is thus required to quantify the performance of the triboelectric nanogenerators so that their outputs can be compared and evaluated. Here we report figure-of-merits for defining the performance of a triboelectric nanogenerator, which is composed of a structural figure-of-merit related to the structure and a material figure of merit that is the square of the surface charge density. The structural figure-of-merit is derived and simulated to compare the triboelectric nanogenerators with different configurations. A standard method is introduced to quantify the material figure-of-merit for a general surface. This study is likely to establish the standards for developing TENGs towards practical applications and industrialization.
Negatively polarized ferroelectric polymer β-P(VDF-TrFE) shows higher positive triboelectric properties than skin, which could lead to new medical applications. Kelvin force microscope measurements and triboelectric nanogenerator characterizations are performed to demonstrate this new property. In addition, how many negative charges are exchanged by contact electrification between the negatively polarized β-P(VDF-TrFE) and the skin is estimated.
© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
A facile and scalable synthesis of mesoporous films impregnated with Au nanoparticles (NPs) as effective dielectrics is demonstrated for enhancing the nanogenerator performance based on vertical contact-separation mode. This technique is so simple and scalable, providing a promising solution for developing large-scale and practical self-powered devices. The spatial distribution of the Au NPs made it possible to fabricate the Au NPs-embedded mesoporous triboelectric nanogenerator (AMTENG) with high output power of 13 mW under cycled compressive force, giving over 5-fold power enhancement, compared with the flat film-based TENG under the same mechanical force. It is proposed that the presence of aligned dipoles produced due to the charges created by the contact between Au NPs and PDMS inside the pores can influence the surface potential energy of mesoporous films. With such an enhanced power output and unique device design, we demonstrate various applications such as self-powered shape mapping sensor, foot-step driven large-scale AMTENG, and an integrated circuit with a capacitor for powering a commercial cell phone for realizing self-powered systems from footsteps, wind power, and ocean waves.
Due to its flexibility, transparency, easy fabrication, and high negative polarity, polydimethylsiloxane (PDMS) has been considered as one of the most appropriate materials for the use in triboelectric nanogenerator (TENG) applications. Here, we report the significantly enhanced triboelectric surface charge of PDMS simply by sprinkling of NaOH solution. Fresh PDMS-based TENGs generated an open-circuit voltage of 3.8 V and a closed-circuit current of 65 nA after the contact/separation from an indium tin oxide (ITO) electrode. After sprinkling the PDMS surface with 1 M NaOH, in contrast, the resulting TENG generated voltage of 10.4 V and current of 179 nA. Exposing the PDMS to ultraviolet-ozone prior to sprinkling with NaOH solution resulted in a triboelectric voltage and current of 49.3 V and 1.16 μA, respectively, which are almost 15-fold larger than those of fresh PDMS. The origin of the enhanced triboelectric charge is related with an increase of polar SiO bonds at the expense of non-polar SiCH3 bonds in PDMS. This work demonstrates a cost-effective method for producing large-area and high-efficiency PDMS-based TENGs and helps clarify the triboelectric mechanism of PDMS.
Hydropower is the most important and wildly-used renewable energy source in the environment. In this paper, we demonstrate a multi-layered triboelectric nanogenerator (TENG) to effectively harvest the water wave energy. For a single-layered TENG, interdigitive electrodes are incorporated in order to generate multiple electric outputs under water wave or water drop impact. For the collection of water wave energy, a polyurethane (PU) coated copper rod is used to roll back and forth and contact with the polytetrafluoroethylene (PTFE) film covered interdigitative electrodes. The surfaces of the PU and PTFE films are fabricated as porous structures and nanowire arrays, which provide an advantages of large contact area and efficient separation. Under one wave impact, the single-layered TENG composed of 9 pairs of interdigitative electrodes can provide 9 pulses of electric outputs (each pulsed output voltage is 52 V and output current density is 13.8 mA m‒2). The instantaneous output power density of a five-layered TENG is 1.1 W m‒2. In addition, the PTFE film covered interdigitative electrodes has been successfully used to harvest water drop energy, whcih can also generate 9 pulses of electric outputs upon one water drop falling. All these results show the developed TENG has a potential to harvest the hydropower of ocean wave and raindrop in the near future.
Two different materials, apart from each other in a triboelectric series, are required to fabricate high performance triboelectric generators (TEGs). Thus, it often limits the choices of materials and causes related processing issues for TEGs. To address this issue, we report a simple surface functionalization method that can effectively change the triboelectric charging sequence of the materials, broadening material choices and enhancing the performance of TEGs. Specifically, we functionalized the surfaces of the polyethylene terephthalate (PET) films either with poly-L-lysine solution or trichloro(1H,1H,2H,2H-perfluorooctyl) silane (FOTS). Consequently, the PET surfaces were modified to have different triboelectric polarities in a triboelectric series. The TEGs, fabricated using this approach, demonstrated the maximum Vopen-circuit (Voc) of ~330 V and Jshort-circuit (Jsc) of ~270 mA/m2, respectively, at an applied force of 0.5 MPa. Furthermore, the functionalized surfaces of TEGs demonstrated superior stability during cyclic measurement over 7200 cycles, maintaining the performance even after a month. The approach introduced here is simple, effective, and cost-competitive way to fabricate TEGs, which can also be easily adopted for various surface patterns and device structures.
A 125 μm thickness, rollable, paper-based acoustic energy harvester triboelectric nanogenerator (TENG) has been developed for harvesting sound wave energy, which is capable of delivering a maximum power density of 121 mW/m2 and 968 W/m3 under a sound pressure of 117 dBSPL. The TENG is designed in the contact-separation mode using membranes that have rationally designed holes at one side. The TENG can be implemented onto a commercial cell phone for acoustic energy harvesting from human talking; the electricity generated can be used to charge a capacitor at a rate of 0.144 V/s. Additionally, owing to the superior advantages of a broad working bandwidth, thin structure and flexibility, a self-powered microphone for sound recording with rolled structure is demonstrated for all-sounding recording without an angular dependence. The concept and design presented in this work can be extensively applied to a variety of other circumstances for either energy-harvesting or sensing purposes, e.g. wearable and flexible electronics, military surveillance, jet engine noise reduction, low-cost implantable human ear and wireless technology applications.
A simple-to-fabricate, high-performance, wearable all-fiber triboelectric nanogenerator (TENG)-based insole composed of electrospun piezoelectric polyvinylidene fluoride (PVDF) nanofibers sandwiched between a pair of conducting fabric electrodes that effectively harvests energy during human walking is reported. The surface of the nanofibers is roughened with secondary nanostructure to enhance insole performance. The maximum output voltage, instantaneous power and output current from the insole reach 210 V, 2.1 mW and 45 μA, respectively. The role of the piezoelectric effect in the electrospun PVDF nanofibers in this TENG-based insole is then systematically investigated. This device is shown to be a reliable power source that can be used to light up 214 serially connected light-emitting diodes directly. The soft fiber-based electric power generator demonstrated in this paper is capable of meeting the requirements of wearable devices because of its efficient energy-conversion performance, high durability, user comfort, and low cost.
Triboelectric nanogenerators (TENGs) have been demonstrated as an effective way to harvest mechanical energy to drive small electronics. The density of triboelectric charges generated on contact surfaces between two distinct materials is a critical factor for dictating the output power. We demonstrate an approach to effectively tune the triboelectric properties of materials by taking advantage of the dipole moment in polarized polyvinylidene fluoride (PVDF), leading to substantial enhancement of the output power density of the TENG. The output voltage ranged from 72 V to 215 V under a constant contact force of 50 N. This work not only provides a new method of enhancing output power of TENGs, but also offers an insight into charge transfer in contact electrification by investigating dipole-moment-induced effects on the electrical output of TENGs.
The open-circuit voltage of a triboelectric nanogenerator (TENG) increases with the tribo-charge density and the separated distance between two tribo-surfaces, which can reach several thousand volts and is much higher than the working voltage required by most electrical devices and energy storage units. Therefore, improving the effective efficiency of TENGs requires reducing the output voltage and enhancing the transferred charges. Here, a multilayered-electrode-based TENG (ME-TENG) is developed in which the output voltage can be managed by controlling the charge flow in a process of multiple (N) steps, which results in N times lower voltage but N times higher total charge transport. The ME-TENG is demonstrated to work in various modes, including multichannel, single-channel, and double-tribo-surface structures. The effects of insulator layer thickness and total layer number on the output voltage are simulated by the finite element method. The output voltage can be modulated from 14 to 102 V by changing the insulator layer number between two adjacent working electrodes, based on which the 8-bit logic representations of the characters in the ACSII code table are demonstrated. The ME-TENG provides a novel method to manage the output power and has potential applications in self-powered sensors array and human–machine interfacing with logic communications.
Charges induced in triboelectric process are usually referred as a negative effect either in scientific research or technological applications, and they are wasted energy in many cases. Here, we demonstrate a simple, low cost and effective approach of using the charging process in friction to convert mechanical energy into electric power for driving small electronics. The triboelectric generator (TEG) is fabricated by stacking two polymer sheets made of materials having distinctly different triboelectric characteristics, with metal films deposited on the top and bottom of the assembled structure. Once subjected to mechanical deformation, a friction between the two films, owing to the nano-scale surface roughness, generates equal amount but opposite signs of charges at two sides. Thus, a triboelectric potential layer is formed at the interface region, which serves as a charge “pump” for driving the flow of electrons in the external load if there is a variation in the capacitance of the system. Such a flexible polymer TEG gives an output voltage of up to 3.3 V at a power density of ∼10.4 mW/cm3. TEGs have the potential of harvesting energy from human activities, rotating tires, ocean waves, mechanical vibration and more, with great applications in self-powered systems for personal electronics, environmental monitoring, medical science and even large-scale power.
Triboelectrification is an effect that is known to each and every one probably ever since the ancient Greek time, but it is usually taken as a negative effect and is avoided in many technologies. We have recently invented a triboelectric nanogenerator (TENG) that is used to convert mechanical energy into electricity by a conjunction of triboelectrification and electrostatic induction. As for this power generation unit, in the inner circuit, a potential is created by the triboelectric effect due to the charge transfer between two thin organic/inorganic films that exhibit opposite tribo-polarity; in the outer circuit, electrons are driven to flow between two electrodes attached on the back sides of the films in order to balance the potential. Since the most useful materials for TENG are organic, it is also named organic nanogenerator, which is the first of using organic materials for harvesting mechanical energy. In this paper, we review the fundamentals of the TENG in the three basic operation modes: vertical contact-separation mode, in-plane sliding mode, and single-electrode mode. Ever since the first report of the TENG in January 2012, the output power density of TENG has been improved for five orders of magnitude within 12 months. The area power density reaches 313 W/m2, volume density reaches 490 kW/m3, and a conversion efficiency of ~60% has been demonstrated. The TENG can be applied to harvest all kind mechanical energy that is available but wasted in our daily life, such as human motion, walking, vibration, mechanical triggering, rotating tire, wind, flowing water and more. Alternatively, TENG can also be used as a self-powered sensor for actively detecting the static and dynamic processes arising from mechanical agitation using the voltage and current output signals of the TENG, respectively, with potential applications for touch pad and smart skin technologies. To enhance the performance of the TENG, besides the vast choices of materials in the triboelectric series, from polymer to metal and to fabric, the morphologies of their surfaces can be modified by physical techniques with the creation of pyramids-, square- or hemisphere-based micro- or nano-patterns, which are effective for enhancing the contact area and possibly the triboelectrification. The surfaces of the materials can be functionalized chemically using various molecules, nanotubes, nanowires or nanoparticles, in order to enhance the triboelectrific effect. The contact materials can be composites, such as embedding nanoparticles in polymer matrix, which may change not only the surface electrification, but also the permittivity of the materials so that they can be effective for electrostatic induction. Therefore, there are numerous ways for enhancing the performance of the TENG from the materials point of view. This gives an excellent opportunity for chemists and materials scientists to do extensive study both in the basic science and in practical applications. We anticipate that a much more enhancement of the output power density will be achieved in the next few years. The TENG is possible not only for self-powered portable electronics, but also as a new energy technology with a potential of contributing to the world energy in the near future.
Piezoelectric and triboelectric nanogenerators (NGs) have been proposed in the past few years to effectively harvest mechanical energy from the environment. Here, a polydimethylsiloxane (PDMS) layer is placed under the aluminum electrode of polyvinylidene fluoride (PVDF), thus forming an r-shape hybrid NG. Micro/nanostructures have been fabricated on the PDMS surface and the aluminum electrodes of PVDF to enhance the output performance. Power densities of the piezoelectric part and the triboelectric part are 10.95 mW/cm(3) and 2.04 mW/cm(3), respectively. Moreover, influence of the triboelectric charges on the piezoelectric output voltage is investigated. Both finite element method (FEM) simulations and experimental measurements are conducted to verify this phenomenon. The novel hybrid NG is also demonstrated as a power source for consumer electronics. Through one cycle of electric generation, ten light emitting diodes (LEDs) are lighted up instantaneously, and a 4-bit liquid crystal display (LCD) can display continuously for more than 15 s. Besides, the device is integrated into a keyboard to harvest energy in the typing process.
We aimed for permanently supplying the electrical energy to an apparatus for in vivo use such as a cardiac pacemaker and proposed and developed an electrostatic (ES) generator that harnesses the motion of the living body. The generating system consists of a battery as an initial charge supply (ICS), a variable capacitor (VC) in which mechanical energy is converted to electrical energy, a capacitor for energy storage and two rectifiers. In this study, an ES generator which does not consume electrical energy of the ICS was used. Since high frequency driving of the VC leads to large power generation, it is effective to introduce a resonant phenomenon. A honey-comb-type variable capacitor whose capacitance varies from approximately 32 to 200 [nF] was used as the VC. The resonator (resonant frequency 4.76 [Hz]) which consists of a honeycomb-type VC, tension coil springs and mass was made. It was possible to generate electrical power of 58 [μW] in case of the ICS with constant voltage of 24 [V] and a load with resistance of 1.0 [MΩ]. We found that use of resonant phenomenon was effective to increase generated power.
A semi-quantitative tribo-charging series that includes a wide range of synthetic and natural polymers was constructed by combining four qualitative triboelectric series from literature reports plus quantitative charging results with metal contacts. This not only connects the results from different laboratories but it also provides a series with a wide variety of polymeric materials which can be used to estimate their relative charging capacity. The ordering of the polymers in the series suggests that the charging develops from the transfer of protons between the contacting surfaces.
If two materials are brought into contact and then separated they are found to be charged; this is the phenomenon of `contact electrification'. The subject falls naturally into three divisions---electrification of metals by metals; of insulators by metals; and of insulators by insulators. The first of these is well understood; charge transfer between metals is such as to bring the two Fermi levels into coincidence. The second division, electrification of insulators by metals, has been much studied recently and takes up the main part of our review; our understanding remains imperfect, chiefly because of lack of knowledge about the relevant electron states in insulators. Electrification of insulators by insulators has not been studied so extensively, but there is evidence that an understanding of the metal/insulator case will lead to an understanding of the insulator/insulator case as well.
This article describes a simple, cost-effective, and scalable approach to fabricate a triboelectric nanogenerator (NG) with ultrahigh electric output. Triggered by commonly available ambient mechanical energy such as human footfalls, a NG with size smaller than a human palm can generate maximum short-circuit current of 2 mA, delivering instantaneous power output of 1.2 W to external load. The power output corresponds to an area power density of 313 W/m2 and a volume power density of 54,268 W/m3 at an open-circuit voltage of ~1200 V. The power was capable of instantaneously lighting up as many as 600 multi-color commercial LED bulbs. The record high power output for the NG is attributed to optimized structure, proper materials selection, and nano-scale surface modification. This work demonstrated the practicability of using NG to harvest large-scale mechanical energy, such as footsteps, rolling wheels, wind power, and ocean waves.
Harvesting energy from our living environment is an effective approach for sustainable, maintenance-free and green power source for wireless, portable or implanted electronics. Mechanical energy scavenging based on triboelectric effect has been proven simple, cost-effective and robust. However, its output is still insufficient for sustainably driving electronic devices/systems. Here, we demonstrated a rationally designed arch-shaped triboelectric nanogenerator (TENG) by utilizing the contact electrification between a polymer thin film and a metal thin foil. The working mechanism of the TENG was studied by finite element simulation. The output voltage, current density and energy volume density reached 230 V, 15.5 µA/cm2 and 128 mW/cm3, respectively, and an energy conversion efficiency as high as 10~39% has been demonstrated. The TENG was systematically studied and demonstrated as a sustainable power source that can not only drive instantaneous operation of light-emitting diodes (LEDs), but also charge a lithium ion battery as a regulated power module for powering a wireless sensor system and a commercial cell phone, which is the first demonstration of the nanogenerator for driving personal mobile electronics, opening the chapter of impacting general people's life by nanogenerators.
In this paper, we propose a passive gap-spacing control method in order to avoid stiction between top and bottom structures in in-plane sensor/actuator/generator applications. A patterned electret using a high-performance perfluoro polymer material is employed to induce a repulsive electrostatic force. An out-of-plane repulsive force is successfully demonstrated with our early prototype, in both air and liquid. By using the present electret-based levitation method to keep the air gap, a MEMS electret generator has been developed for energy-harvesting applications. A dual-phase electrode arrangement is adopted in order to reduce the horizontal electrostatic damping force. With the present prototype, about 0.5 µW is obtained for both phases of the generator, resulting in a total power output of 1.0 µW at an acceleration of 2 g with 63 Hz. With our electromechanical model of the generator, we have confirmed that the model can mimic the response of the generator prototype.
By converting ambient energy into electricity, energy harvesting is capable of at least offsetting, or even replacing, the reliance of small portable electronics on traditional power supplies, such as batteries. Here we demonstrate a novel and simple generator with extremely low cost for efficiently harvesting mechanical energy that is typically present in the form of vibrations and random displacements/deformation. Owing to the coupling of contact charging and electrostatic induction, electric generation was achieved with a cycled process of contact and separation between two polymer films. A detailed theory is developed for understanding the proposed mechanism. The instantaneous electric power density reached as high as 31.2 mW/cm(3) at a maximum open circuit voltage of 110 V. Furthermore, the generator was successfully used without electric storage as a direct power source for pulse electrodeposition (PED) of micro/nanocrystalline silver structure. The cathodic current efficiency reached up to 86.6%. Not only does this work present a new type of generator that is featured by simple fabrication, large electric output, excellent robustness, and extremely low cost, but also extends the application of energy-harvesting technology to the field of electrochemistry with further utilizations including, but not limited to, pollutant degradation, corrosion protection, and water splitting.
This paper describes the analysis, simulation and testing of a microengineered motion-driven power generator, suitable for application in sensors within or worn on the human body. Micro-generators capable of powering sensors have previously been reported, but these have required high frequency mechanical vibrations to excite a resonant structure. However, body-driven movements are slow and ir-regular, with large displacements, and hence do not effectively couple energy into such generators. The device presented here uses an alternative, non-resonant operating mode. Analysis of this generator shows its potential for the application considered, and shows the possibility to optimise the design for particular conditions. An experimental prototype based on a variable parallel-plate capacitor operat-ing in constant charge mode is described which confirms the analysis and simulation models. This prototype, when precharged to 30 V, develops an output voltage of 250 V, corresponding to 0.3 J per cycle. The experimental test procedure and the instrumentation are also described.
Transparent, flexible and high efficient power sources are important components of organic electronic and optoelectronic devices. In this work, based on the principle of the previously demonstrated triboelectric generator, we demonstrate a new high-output, flexible and transparent nanogenerator by using transparent polymer materials. We have fabricated three types of regular and uniform polymer patterned arrays (line, cube, and pyramid) to improve the efficiency of the nanogenerator. The power generation of the pyramid-featured device far surpassed that exhibited by the unstructured films and gave an output voltage of up to 18 V at a current density of ∼0.13 μA/cm(2). Furthermore, the as-prepared nanogenerator can be applied as a self-powered pressure sensor for sensing a water droplet (8 mg, ∼3.6 Pa in contact pressure) and a falling feather (20 mg, ∼0.4 Pa in contact pressure) with a low-end detection limit of ∼13 mPa.
This review covers new experimental and theoretical physical research related to the formation of polymeric membranes by phase separation of a polymer solution, and to the morphology of these membranes. Two main phase separation processes for polymeric membrane formation are discussed: thermally induced phase separation and immersion precipitation. Special attention is paid to phase transitions like liquid-liquid demixing, crystallization, gelation, and vitrification, and their relation to membrane morphology. In addition, the mass transfer processes involved in immersion precipitation, and their influence on membrane morphology are discussed.
When dielectric materials are brought into contact and then separated, they develop static electricity. For centuries, it
has been assumed that such contact charging derives from the spatially homogeneous material properties (along the material’s
surface) and that within a given pair of materials, one charges uniformly positively and the other negatively. We demonstrate
that this picture of contact charging is incorrect. Whereas each contact-electrified piece develops a net charge of either
positive or negative polarity, each surface supports a random “mosaic” of oppositely charged regions of nanoscopic dimensions.
These mosaics of surface charge have the same topological characteristics for different types of electrified dielectrics and
accommodate significantly more charge per unit area than previously thought.
Was Thales right about water? Contrary to previous reports, contact charging can occur in the absence of water. At the same time, water helps stabilize the developed charges. Water-free conditions are realized by performing all experiments and charge measurements under oil-immersion.
Nanogenerators capable of converting energy from mechanical sources to electricity with high effective efficiency using low-cost, nonsemiconducting, organic nanomaterials are attractive for many applications, including energy harvesters. In this work, near-field electrospinning is used to direct-write poly(vinylidene fluoride) (PVDF) nanofibers with in situ mechanical stretch and electrical poling characteristics to produce piezoelectric properties. Under mechanical stretching, nanogenerators have shown repeatable and consistent electrical outputs with energy conversion efficiency an order of magnitude higher than those made of PVDF thin films. The early onset of the nonlinear domain wall motions behavior has been identified as one mechanism responsible for the apparent high piezoelectricity in nanofibers, rendering them potentially advantageous for sensing and actuation applications.
Ch-ch-ch-charges: Pieces of identical, atomically flat insulators separate a charge Q when brought into contact and then parted. Repeated contacts cause the magnitudes of the separated charges to increase monotonically (see picture). A theoretical model is presented that explains these phenomena by the inherent, molecular-scale fluctuations in the composition of the seemingly identical contacting surfaces. Figure Presented
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