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Internet-of-Everything (IoE) is defined as networked connections of things, people, data, and processes. IoE nodes, preferably shaped as printed flexible systems, serve as the frontier outpost of the Internet and comprise devices to record and regulate states and functions. To power distributed IoE nodes in an ecofriendly manner, a technology to scavenge energy from ambience and self-powered devices is developed. For this, piezoelectricity is regarded as a key property; however, the current technology typically based on polyvinylidene difluoride (PVDF) copolymers is expensive and produced via toxic protocols. We report piezoelectric characteristics of electrochemically poled cellulose nanofiber (CNF) thin films processed from water dispersions. Poling these films under humid conditions causes breaking and reorientation of CNF segments, which results in enhanced crystal alignment rendering the resulting material piezoelectric. Generators based on poled CNF show similar piezoelectric voltage and coefficient, here measured as d(33) = 46 pm V-1, to devices including PVDF copolymer layers of similar thickness. Our findings promise low-cost and printable ecofriendly piezoelectric-powered IoE nodes. Funding Agencies|Knut and Alice Wallenberg Foundation; Swedish Research Council [2016-06146, 2018- 04037, 2009-00971]; NCD- SWEET beamline of ALBA synchrotron in Barcelona, Spain; [VR 2016-05990]

Cellulose opens for sustainable materials suitable for radiative cooling thanks to inherent high thermal emissivity combined with low solar absorptance. When desired, solar absorptance can be introduced by additives such as carbon black. However, such materials still shows high thermal emissivity and therefore performs radiative cooling that counteracts the heating process if exposed to the sky. Here, this is addressed by a cellulose-carbon black composite with low mid-infrared (MIR) emissivity and corresponding suppressed radiative cooling thanks to a transparent IR-reflecting indium tin oxide coating. The resulting solar heater provides opposite optical properties in both the solar and thermal ranges compared to the cooler material in the form of solar-reflecting electrospun cellulose. Owing to these differences, exposing the two materials to the sky generated spontaneous temperature differences, as used to power an ionic thermoelectric device in both daytime and nighttime. The study characterizes these effects in detail using solar and sky simulators and through outdoor measurements. Using the concept to power ionic thermoelectric devices shows thermovoltages of >60 mV and 10 degrees C temperature differences already at moderate solar irradiance of approximate to 400 W m(-2). Funding Agencies|Wallenberg Wood Science Center; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Swedish Research Council [2018-04037, 2020-00287]; Knut and Alice Wallenberg Foundation; Linkoeping University

Radiative cooling passively removes heat from objects via emission of thermal radiation to cold space. Suitable radiative cooling materials absorb infrared light while they avoid solar heating by either reflecting or transmitting solar radiation, depending on the application. Here, we demonstrate a reflective radiative cooler and a transparent radiative cooler solely based on cellulose derivatives manufactured via electrospinning and casting, respectively. By modifying the microstructure of cellulose materials, we control the solar light interaction from highly reflective (> 90%, porous structure) to highly transparent (approximate to 90%, homogenous structure). Both cellulose materials show high thermal emissivity and minimal solar absorption, making them suitable for daytime radiative cooling. Used as coatings on silicon samples exposed to sun light at daytime, the reflective and transparent cellulose coolers could passively reduce sample temperatures by up to 15 degrees C and 5 degrees C, respectively. Funding Agencies|Linkoping University

Porous cellulose can be tuned dynamically between reflecting and transparent states through reversible wetting with liquids like water while remaining non-absorptive in both states. By combining porous cellulose with an underlying cellulose-carbon nanotube layer, we here report a Janus cellulose that instead switches between reflect-ing and absorptive states. While the material is reflective and low absorbing in its dry state, exposure to water increases the optical transparency of the top layer and enables the bottom layer to absorb solar light and generate heat. In turn, this initiates a self -adaptive process that drives water evaporation and dries the struc-ture, making it reflective again. In situ measurements of scattering intensity, temperature, and water evaporation reveal an intriguing dynamic relationship between the optical and thermal properties of the Janus cellulose. This study highlights the use of cellulose sys-tems for solar and thermal management, demonstrating solar -induced self-adaptive heating, evaporative drying, and thermal regulation. Funding Agencies|Knut and Alice Wallenberg Foundation; Linkoping University; Wallenberg Wood Science Center; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Swedish Research Council

Internet-of-everything (IoE) is defined as networked connections of things, people, data and processes. IoE nodes, preferably shaped as printed flexible systems, serves as the frontier outpost of the Internet and comprises devices to record and regulate states and functions. To power distributed IoE nodes in an ecofriendly manner, technology to scavenge energy from ambience and self-powered devices are developed. For this, piezoelectricity is regarded as a key-property, however current technology typically based on polyvinylidene difluoride (PVDF) co-polymers, are expensive and produced via toxic protocols. We report piezoelectric characteristics of electrochemically poled cellulose nanofiber (CNFs) thin films processed from water dispersions. Poling these films at humid conditions cause breaking and reorientation of CNF segments, which results in enhanced crystal alignment rendering the resulting material piezoelectric. Generators based on poled CNF show similar piezoelectric voltage and coefficient, here measured to d33 = 46 pm/V, as for devices including PVDF copolymer layers of similar thickness. Our findings promise for low cost and printable ecofriendly piezoelectric-powered IoE nodes.

Performance enhancement of triboelectric nanogenerators (TENGs) has been largely limited by the relatively low output current density. Thus, extensive research efforts have been made to increase the output current density. In this respect, this work presents a method to effectively increase output current density of TENGs by adopting polarized ferroelectric polymers and MoS2 composite. Specifically, by compositing bulk MoS2 flakes with both Nylon-11 and PVDF-TrFE, respectively, charge density of each triboelectric charging surface was significantly increased. In addition, proper polarization of both ferroelectric composite layers has also led to an additional increase in the charge density. A combination of them synergistically increases the surface charge density, generating huge output current and the power output density. By optimizing the fabrication process, the output voltage and current density up to ∼145 V and ∼350 μA/cm2 are achieved, respectively. Consequently, the TENG exhibits a recordable output power density of ∼50 mW/cm2, which is one of the highest output power densities reported to date. The method introduced in this work can greatly increase the output current density of TENGs, facilitating the development of high-performance triboelectric energy harvesting devices.

Radiative cooling passively removes heat from objects via emission of thermal radiation to cold space. Suitable radiative cooling materials absorb infrared light while they avoid solar heating by either reflecting or transmitting solar radiation, depending on the application. Here, we demonstrate a reflective radiative cooler and a transparent radiative cooler solely based on cellulose derivatives manufactured via electrospinning and casting, respectively. By modifying the microstructure of cellulose materials, we can control the solar light interaction from highly reflective (>90%, porous structure) to highly transparent (≈90%, homogenous structure). Both cellulose materials show strong thermal emissivity and minimal solar absorption, making them suitable for daytime radiative cooling. Used as coatings on silicon samples exposed to sun light at daytime, the reflective and transparent cellulose coolers could passively reduce sample temperatures by up to 32 °C and 15 °C, respectively.

The limited ionic conductivity is the main issue for the application of solid-state ionic conductors. In this work, we have shown that increasing the ferroelectric phase content in a polymer matrix could enhance the molar ionic conductivity of the incorporated ionic liquid by two orders of magnitude compared to the original films with the same composition. The ferroelectric polymer fiber mats were prepared through electrospinning to induce the ferroelectric phase that ensure the polarization of the dipoles. After analyzing the ferroelectric phase content and polarization of the fiber mats and films containing different ion concentration with FTIR spectroscopy and piezoelectric characterization, a detailed mechanism explaining the improved conductivity in the ferroelectric fiber mats was proposed. Benefiting from the good flexibility, improved ionic conductivity and high temperature coefficient of the fiber mats, we fabricated an organic ionic thermistor. The temperature tracking and mapping function of the ionic thermistor was demonstrated by using two devices with 4 and 16 pixels. Funding Agencies|Swedish Research Council VRSwedish Research Council [2016-05990, 2018-04037]; Wallenberg Wood Science Center; Advanced Functional Materials Center at Linkoping University [2009-00971]; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation

Piezoelectric nanogenerators are forthcoming alternative choices for scavenging different types of wasted mechanical energies. An inorganic-organic hybrid piezoelectric nanogenerator (HPNG) has been realized by incorporating zinc sulphide nanorods (ZnS-NRs) into electrospun poly(vinylidene fluoride) (PVDF) nanofibers for self-powered multifunctional sensing. As an acoustic energy harvester, the HPNG possesses a resonance frequency of 86 ± 3 Hz and an acoustic sensitivity of ∼3 V Pa−1. It can distinguish sound waves from low to mid frequency region that makes it suitable for noise detection. In addition, HPNG demonstrates the very high wind energy conversion efficiency of ∼58% that make it capable of detecting human exhalation. Apart from its noise detection and power generation capabilities, HPNG is possible to use as a self-powered microphone. This electromechanical coupling, integrated with their flexibility, makes it usable as a flexible electro-acoustic sensor for security purpose as well. These results establish the potential of hybrid piezoelectric structure, with their multi functionalities for several promising applications such as noise detection, wind energy harvesting, security monitoring and most promisingly to develop the self-powered system.

Methylammonium lead bromide (CH3NH3PbBr3) (MAPbBr) has been synthesized and then introduced in the poly(vinylidene fluoride) (PVDF) nanofiber made by the process of electrospinning. The β-phase composition, degree of crystallinity as well as mechanical, optical and energy harvesting properties of this composition has been investigated. Increased electroactive phase composition (91%) and dramatic improvement in tensile strength of the PVDF nanofiber mats is found by the addition of MAPbBr. This increase in electroactive phase composition can play a significant role in the enhancement of output power which is a premiere observation. The acoustic nanogenerator (ANG) made from MAPbBr doped PVDF nanofibers (NFs) can also be utilized in energy scavenging from acoustic vibration with a higher degree of acoustic sensitivity (~ 13.8 V Pa−1) and efficiency (58.5%). This suggests that ANG could be a potential tool for power generation in portable electronics. This fact may open up the prospect of using the MAPbBr doped PVDF electrospun nanofibers, with their multifunctional properties such as vibration sensitivity, piezoelectric energy harvesting, green light emission capability (quantum yield ~ 32.6%), for various promising applications in portable electronics, noise detection and security monitoring.

Conversion of temperature fluctuations to useable electrical energy is rendered by the pyroelectric effect. Waste of heat in our day to day environment and in industrial sector constitutes an abundant source of energy. Herein, we report a pyroelectric generator (PyG) that produces pyroelectric output up to 1.5 V and 1.5 µA. Its power density is 0.034 µW/cm2 upon exposure to heat-cool condition for a temperature variation from 310 K to 340 K. Due to the fast response time (121 ms) of the PyG, it is expected to be use as a self-powered temperature sensor. The generated electricity could also be stored in a capacitor up to 0.8 V in three heating–cooling cycles. It has been also demonstrated that PyG is possible to drive by water vapour where energy-consuming alternating devices is not necessary. The temperature oscillation achieved by spontaneous water condensation and evaporation from the surface of the PyG that produces open-circuit voltage of 1.6 V for a temperature variation from 303 K to 333 K. Thus the PyG driven by water vapour supports an efficient retrieval of energy from hot water vapour, which is wasted mostly. The linear increment of voltage as a function of temperature indicates PyG is also suitable to use a temperature sensor that may also work in self-powered mode. In addition, the PyG can also harvest the waste body heat, i.e., heat dissipation from human body surface and from the process of respiration. That promises an effective self-powered temperature sensor that might be useful in healthcare monitoring, safety and security sectors.

An integrated platform made with a piezoelectric nanogenerator (NG) is designed to convert daily human activities and acoustic vibration into useable electrical energy. The titanium dioxide (TiO2) nanoparticles (NPs) are playing a significant role as external fillers in poly(vinylidene fluoride) (PVDF) electrospun nanofiber that improves the overall performance of the NG. It effectively enhanced the piezoelectric β-phase content (16% higher F (β)) and mechanical (148% increment of tensile strength) properties of composite PVDF nanofiber. The superior integration of NG has been demonstrated to generate electricity from a human gait. The acoustic sensitivity and energy conversion efficiency are found to be 26 V Pa–1 and 61%, respectively, which are superior in comparison to the reported results. By scavenging the mechanical energy, NG is capable of charging up a 1 μF capacitor; for example, ∼20 V is within 50 s that ensures its ability to power up commercial LED tape and a LCD screen. Thus, in this work, a ...

Organic-inorganic nanocomposite film composed of poly(vinylidene fluoride) (PVDF) and zinc sulphide nanoparticles (ZnS-NPs) has been prepared. It is observed that composite film can stabilize the γ-phase. The PVDF-ZnS composite film exhibits superior dielectric property (ɛr∼14 at 1 kHz) than those of pure PVDF. Enhanced saturated polarization (Psat ∼0.38 µC cm-2) and remnant polarization values (Pr∼ 0.21 µC cm-2) are obtained in nanocomposite film that indicates to have potential to use as energy storage applications. In addition, ZnS-NPs incorporation also improves dielectric breakdown strength.

In this paper, we report an innovative technique for the rapid and simple synthesis of ZnO-containing paper ash (ZPA) within 30 min. It is demonstrated that as-synthesized ZPA can be an alternative for conventional semiconducting filler that is used to improve the electroactive β-phase content in the electrospun PVDF nanofiber (NF). Furthermore, the PVDF nanofiber-based nanogenerator (NFNG) that enables a high output voltage of 4.8 V under an exerted wind pressure of 145 Pa is fabricated. In addition, the detection capability of minute wind pressure, even from human mouth blowing, makes the NFNG an active sensor that might be utilized for charging a mobile phone during conversation. Thus, this strategy is expected to be a promising platform for harvesting wind energy that is beneficial for the design of integrated self-powered wearable electronic devices.

This work introduces a piezoelectric–pyroelectric nanogenerator (P-PNG) based on methylammonium lead iodide (CH3NH3PbI3) incorporated electrospun poly(vinylidene fluoride) (PVDF) nanofibers that are able to harvest mechanical and thermal energies. During the application of a periodic compressive contact force at a frequency of 4 Hz, an output voltage of ∼220 mV is generated. The P-PNG has a piezoelectric coefficient (d33) of ∼19.7 pC/N coupled with a high durability (60 000 cycles) and quick response time (∼1 ms). The maximum generated output power density (∼0.8 mW/m2) is sufficient to charge up a variety of capacitors, with the potential to replace an external power supply to drive portable devices. In addition, upon exposure to cyclic heating and cooling at a temperature of 38 K, a pyroelectric output current of 18.2 pA and a voltage of 41.78 mV were achieved. The fast response time of 1.14 s, reset time of 1.25 s, and pyroelectric coefficient of ∼44 pC/m2 K demonstrate a self-powered temperature sensin...

Performance enhancement of triboelectric nanogenerators (TENGs) has been largely limited by the relatively low output current density. Thus, extensive research efforts have been made to increase the output current density. In this respect, this work presents a method to effectively increase output current density of TENGs by adopting polarized ferroelectric polymers and MoS

Recently, human motion and respiration monitoring sensors have attracted significant research attention in the field of wearable electronics and healthcare applications. Fiber-based electronic sensors demonstrate significant potential for such applications due to their flexibility. However, the superior flexibility of fiber-based sensors is generally limited due to the partial use of rigid elements such as metal electrode layers. In this paper, a simple method is presented for the fabrication of all-nanofiber multifunctional sensors, which consist of triboelectric (TE), piezoresistive (PR), and thermoresistive (TR) sensing elements and demonstrate superior flexibility, excellent wearability, and multifunctionality. The TE sensing unit was fabricated by integrating two triboelectrically dissimilar nanofiber surfaces using a polymer mesh separator, for the formation of internal macro-scale air gaps; followed by the electrical polarization of nanofibers. The TR and PR sensing elements were realized using vapor-phase polymerized fiber electrode layers. Using the sensor developed in this study, different motions and breathing frequencies can be individually or simultaneously detected using the TE, PR, and TR sensing elements. This work therefore presents a novel scheme for human motion sensors and breathing sensors, which are widely applicable to wearable electronics, healthcare monitoring, and human-machine interfaces.

We demonstrate the requirement of electrical poling can be avoided in flexible piezoelectric nanogenerators (FPNGs) made of low-temperature hydrothermally grown wurtzite zinc sulfide nanorods (ZnS-NRs) blended with polydimethylsiloxane (PDMS). It has been found that conductive fillers, such as polyaniline (PANI) and multiwall carbon nanotubes (MWCNTs), can subsequently improve the overall performance of FPNG. A large electrical throughput (open circuit voltage ∼35 V with power density ∼2.43 μW/cm(3)) from PANI supplement added nanogenerator (PZP-FPNG) indicates that it is an effective means to replace the MWCNTs filler. The time constant (τ) estimated from the transient response of the capacitor charging curves signifying that the FPNGs are very much capable to charge the capacitors in very short time span (e.g., 3 V is accomplished in 50 s) and thus expected to be perfectly suitable in portable, wearable and flexible electronics devices. We demonstrate that FPNG can instantly lit up several commercial Light Emitting Diodes (LEDs) (15 red, 25 green, and 55 blue, individually) and power up several portable electronic gadgets, for example, wrist watch, calculator, and LCD screen. Thus, a realization of potential use of PANI in low-temperature-synthesized ZnS-NRs comprising piezoelectric based nanogenerator fabrication is experimentally verified so as to acquire a potential impact in sustainable energy applications. Beside this, wireless piezoelectric signal detection possibility is also worked out where a concept of self-powered smart sensor is introduced.

A flexible nanogenerator (NG) is fabricated with a poly(vinylidene fluoride) (PVDF) film, where deoxyribonucleic acid (DNA) is the agent for the electroactive β-phase nucleation. Denatured DNA is co-operating to align the molecular -CH2/-CF2 dipoles of PVDF causing piezoelectricity without electrical poling. The NG is capable of harvesting energy from a variety of easily accessible mechanical stress such as human touch, machine vibration, football juggling, and walking. The NG exhibits high piezoelectric energy conversion efficiency facilitating the instant turn-on of several green or blue light-emitting diodes. The generated energy can be used to charge capacitors providing a wide scope for the design of self-powered portable devices.

Methylammonium lead iodide (CH3NH3PbI3) (MAPI)-embedded β-phase comprising porous poly(vinylidene fluoride) (PVDF) composite (MPC) films turns to an excellent material for energy harvester and photodetector (PD). MAPI enables to nucleate up to ∼91% of electroactive phase in PVDF to make it suitable for piezoelectric-based mechanical energy harvesters (PEHs), sensors, and actuators. The piezoelectric energy generation from PEH made with MPC film has been demonstrated under a simple human finger touch motion. In addition, the feasibility of photosensitive properties of MPC films are manifested under the illumination of nonmonochromatic light, which also promises the application as organic photodetectors. Furthermore, fast rising time and instant increase in the current under light illumination have been observed in an MPC-based photodetector (PD), which indicates of its potential utility in efficient photoactive device. Owing to the photoresponsive and electroactive nature of MPC films, a new class of stand-alone self-powered flexible photoactive piezoelectric energy harvester (PPEH) has been fabricated. The simultaneous mechanical energy-harvesting and visible light detection capability of the PPEH is promising in piezo-phototronics technology.

Low content (0.5 wt. %) of dihydrate tin chloride (Sn2+) salt leads to inclusion of 98 % electroactive phase in poly(vinylidene fluoride) (PVDF), out of this a high yield of piezoelectric β-phase (∼ 49%) is found, which is most desirable for mechanical energy harvesting application. It is also found that Sn2+ salt can significantly enhanced the dielectric property of resulting Sn2+ incorporated PVDF composite film. Thus, the enhancement of β-phase in the PVDF/Sn2+ composite film owns to be a potential material for mechanical energy harvesting application. We have also demonstrated the mechanical energy harvesting capability of the nanogenerator (NG) made with PVDF/Sn2+ composite film under repeated human finger touch.

The electroactive β-phase is most desirable due to its highest piezo-, pyro- and ferroelectric properties in poly(vinylidene fluoride) (PVDF). Induction of the β-phase is successfully accomplished in titanium dioxide (TiO

To date, several attempts have been made to improve the performance of triboelectric nanogenerators (TENGs). Although notable advancements have been made in the output power density, it is still relatively low and further improvement in the output power density has been limited by air breakdown issue. In this work, we proposed preferable composite structures and an electrical activation method to maximize the output performance of TENGs by adopting ferroelectric composite interfacial layer. Specifically, by doping Nylon 11 with Poly (methyl methacrylate) - PMMA, we intensified the positive triboelectricity of Nylon 11 and simultaneously improved its physical durability. The negative triboelectricity of PVDF-TrFE was also enhanced by compositing with ZrO2 nanoparticles (NPs). Triboelectricity of both polymer composites was further boosted by polarizing them in favorable direction. Therefore, high frictional surface charge density of 220 μC/m2 was achieved in short-circuit condition, effectively promoting charge outputs. Consequently, the open circuit voltage and short circuit current density of ~500 V and ~500 μA cm−2 were achieved, respectively, exhibiting a remarkable output power density of ~42 mW cm−2.

A simple route for in situ platinum nanoparticles (Pt-NPs) synthesis is described. A trace amount (0.048 mM) of platinum precursor promotes the electroactive phase transformations (α → β and γ-phase) in poly(vinylidene fluoride) (PVDF) implying a new catalytic role of Pt-NPs. Furthermore, a complete conversion (∼99%) to the electroactive phase is achieved by simply controlling the platinum precursor amount. The PVDF film doped with Pt-NPs exhibits various functionalities, i.e., human touch response, enhanced ferroelectric remnant polarization and intense photoluminance in the UV-region. Apart from conventional piezoelectric sensors and actuators, it naturally lends itself to futuristic applications as a vibration based energy harvester, a ferroelectric non-volatile memory element and a large area coverage lightweight foldable optoelectronic device.

Lead free and flexible energy harvester made of polyvinylidene fluoride and zinc stannate (PVDF/ZnSnO3) hybrid nanofibers (HNFs) are fabricated by electrospinning technique for designing the mechanical energy harvester (MEH). It generates an output voltage of 10 V upon repetitive mechanical stress of hand punching and releasing. Furthermore, it is integrated with acoustic vibration and utilized to charge up capacitors unto 4 V that promises as an acoustic energy harvester and effective power source for tiny portable electronic.

Titanium dioxide (TiO

A flexible hybrid piezoelectric generator (HPG) based on native cellulose microfiber (NCMF) and polydimethylsiloxane (PDMS) with multi wall carbon nanotubes (MWCNTs) as conducting filler is presented where the further chemical treatment of the cellulose and traditional electrical poling steps for piezoelectric voltage generation is avoided. It delivers a high electrical throughput that is an open circuit voltage of ∼30 V and power density ∼9.0 μW/cm(3) under repeated hand punching. We demonstrate to power up various portable electronic units by HPG. Because cellulose is a biocompatible material, suggesting that HPG may have greater potential in biomedical applications such as implantable power source in human body.

We report the fabrication of flexible, low cost, and wearable piezoelectric nanogenerators (NG) composed of a poly(vinyl alcohol) (PVA) nanofiber web and oriented zinc sulfide (ZnS) nanorods (NRs) by a facile and scalable electrospinning technique. The piezoelectric performance of the NG is found to be increased by simply stacking the nanofiber web mats, where the ZnS NRs are incorporated in the PVA fiber matrix. Furthermore, we also designed a large area wearable nanogenerator (WNG) to harvest mechanical energy from acoustic random vibrations and convert it into electrical energy, and an improved acoustic sensitivity of 2 V Pa−1 is observed. This indicates that the WNG is ultrasensitive to random mechanical vibration, and possesses potential utility as a sustainable power source and sensitive pressure sensor particularly suited for portable electronics and wearable technology.