Devices For Energy Harvesting Applications Research Articles

Investigating the novel thermoelectric properties of magnesium, calcium, and barium divanadate oxides (XV2O6 where X = Mg, Ca, and Ba) for waste heat recovery applications in energy harvesting devices

Investigating the novel thermoelectric properties of magnesium, calcium, and barium divanadate oxides (XV2O6 where X = Mg, Ca, and Ba) for waste heat recovery applications in energy harvesting devices

Porosity effect on the functional properties and energy harvesting performance of Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramics

AbstractIn this study, the effect of porosity on the structural and functional (dielectric, ferroelectric, nonlinear, and piezoelectric) properties in Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramics was investigated. Various levels of microporosity in the range of 3% to 31 vol.% have been produced using poly(methyl methacrylate) microspheres as sacrificial templates. The structural investigation indicates a phase coexistence, as expected for this composition at room temperature. The maximum permittivity decreases with increasing porosity, from around 7000 (ceramic with 3 vol.% porosity) down to 3500 (ceramic with 31 vol.% porosity), and the Curie temperature shifts from 47 to 67°C when increasing porosity, related to the possible porosity‐induced structural and internal stress modifications. An enhanced piezoelectric response was found in the Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramic with intermediate porosity around 18 vol.%, with the highest value of piezoelectric response of 470 pC/N and a figure of merit of 7.3 pm2/N. The optimum piezoelectric properties at the intermediate porosity level are related to the microstructural changes (pore shape and connectivity) and possible field‐induced structural modifications. The piezoelectric energy harvesting measurement results have shown the possibility of using Pb‐free porous ferroelectric materials in devices for energy harvesting applications.

PMMA brush-modified graphene for flexible energy storage PVDF dielectric films

Flexible dielectric materials are highly desirable in many electric/electronic devices for energy harvesting applications, but they usually suffer from the paradox of high dielectric constant and large breakdown strength, thereby reducing the overall energy storage capacity and mechanical strength with large filler loadings. In this work, poly(methyl methacrylate) (PMMA) brush-modified graphene (rGO-g-PMMA) was successfully introduced into poly(vinylidene fluoride) (PVDF) matrix via solution casting method. The PMMA brush-modified graphene for one thing promoted graphene distribution in the PVDF matrix, for another, it effectively limited carrier leakage of conductive graphene by forming a thin insulating PMMA layer. Therefore, the dielectric constant of rGO-g-PMMA/PVDF films was obviously increased, while the dielectric loss was distinctly suppressed with a small addition of the “core-shell” like rGO-g-PMMA. What's more, the breakdown strength of composites increased with rGO-g-PMMA loadings up to 0.2 wt%, accompanied by a 157% increase in energy density of FGM-0.2 composite to that of neat PVDF. In addition, the obtained rGO-g-PMMA/PVDF dielectric films possessed improved thermal stability and mechanical strength due to the homogeneous dispersion and good interfacial adhesion of rGO-g-PMMA within PVDF matrix. Such study provided a new strategy in obtaining flexible, high strength and large energy storage dielectric films.

Dislocation singularities in layered magneto-electro-elastic plates

A general and unified theory is formulated to investigate static and time-harmonic field solutions induced by dislocation loops and dislocation arrays in three-dimensional multilayered structures. Each homogeneous plate consists of an orthotropic magneto-electro-elastic material including nonlocal effects. While the nonlocal constitutive relations with multi-phase coupling are treated by means of the original Eringen model using a Helmholtz-type operator, the field expressions are based on the mathematically elegant and computationally powerful Stroh formalism in matrix form, consistently combined with double Fourier series expansions and the dual variable and position technique to propagate the extended solutions among the different layers of the multilayered systems. The time-harmonic dislocation loops are represented by a discontinuity in the prescribed elastic displacement, electric potential, and magnetic potential on arbitrarily-located rectangular and elliptical surfaces in the multilayered structures, while the dislocation arrays are composed of infinitely long, straight and uniformly spaced parallel dislocations with the same local Burgers vectors. The new field solutions are first validated against existing frameworks limited to static and local elasticity theory of these two types of extrinsic and intrinsic dislocations, and subsequently applied to analyze several unexplored effects on the dislocation-induced magneto-electro-elastic fields, namely the material anisotropy, interaction with internal heterophase interfaces, multi-phase coupling, nonlocal core-spreading parameter, finite-valued driving forces, vibration frequency, and stacking sequences. The numerical outcomes indicate that each effect is significant and neglecting any one of them leads to an erroneous prediction on the extrinsic and intrinsic dislocation-induced response, thus providing a suitable route for the design of advanced magneto-electro-elastic fabrication devices for energy harvesting applications.

Electronic-ionic polymer composite for high output voltage generation

The ionic polymer transducers (IPT) have been widely proposed for actuators, energy harvesting, pressure sensing, and robotics applications owing to their exceptional flexibility and actuation performance. However, IPT sensors have a limitation of low output voltage (<1 V) with bending strain that hampers their application in energy harvesting devices and robotics. To address the issue of low output voltage in IPT sensors, we propose a strategy including the introduction of poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) into a poly(vinylidene-fluoride-trifluoroethylene-chlorotrifluoroethylene) (P(VDF-TRFE-CTFE)/polyvinylpyrrolidone blend to develop the electronic-ionic polymer composite (EIPC) that exhibits a high output voltage of up to 27 V in ionic liquid (IL) condition. The PVP aids in the formation of 89 nm (nm) PEDOT:PSS crystals, a low contact angle of 53.75°, and pores on the surface of the P(VDF-TRFE-CTFE)/PVP/PEDOT:PSS-based EIPC with a ratio of 10/05/85, resulting in high water uptake (WUP) (0.92), high DC conductivity (σdc) (0.02 S/cm) and high electrical current 0.02 A/cm2, which improve the high output voltage (27 V) and output power density (4.05 W/cm2) compared to previous existing PEDOT based composites sensors and IPTs based on P(VDF-TRFE-CTFE)/PVP/ionic liquid, P(VDF-TRFE-CTFE)/PVP/PSSA and Nafion membranes. For wearable sensor application, the EIPC was attached to the index finger of humans and generated 25 V with bending of the finger with an angle of 180°. With high ductile nature (tensile strain 223%) and high output voltage of 27 V with bending strain, the EIPC sensors will find practical applications in strain sensors, wearable devices, and energy harvesting devices.

Flexoelectricity of Multifunctional Polymer Electrolyte Membranes: Effect of Polymer Network Functionality

The phenomenon of flexoelectricity generation in flexible, thermally cross-linked, ionic multifunctional polymer electrolyte membranes (PEMs) was investigated subjected to mechanical deformation by bending. The effect of copolymer ratios of functional branched poly(ethylene imine) (PEI) and poly(ethylene glycol) diglycidyl ether (PEGDGE) on the mechanoelectrical transduction in their PEMs was demonstrated at a fixed lithium bis(trifluoromethane sulfonyl) imide (LiTFSI) content. By changing the PEI and PEGDGE copolymer ratios, the constructed co-networks comprised of various amines (primary, secondary, and tertiary) to ethylene oxide ratios, revealed distinctively different flexoelectric responses. With increasing the amount of PEGDGE, the multifunctional PEM exhibited not only lower glass transition temperature but also higher ionic conductivities. This finding may be attributed to the higher content of the linear ethylene oxide chain, which promotes both higher segmental motion and lithium ion complexation with ether oxygen. The examination of the flexoelectric response of the various multifunctional PEMs as a function of composition was performed under intermittent square-waves and sinusoidal bending modes along with flexoelectric responses as a function of relaxation time or frequency. A remarkable flexoelectric coefficient (μ = 210.1 μC/m) was obtained without requiring plasticization or network modification. The energy conversion efficiency of various PEMs was determined in order to evaluate potential applications in energy harvesting devices and sensors. The developed process of PEM fabrication involving thermal curing is compatible and scalable to current commercial processes such as tire vulcanization and shape conformable 3D printing for soft sensors and energy harvesters.

Recent advances in flexible PVDF based piezoelectric polymer devices for energy harvesting applications

Energy harvesting is one of the most promising research areas to produce sustainable power sources from the ambient environment. Which found applications to attain the extensive lifetime self-powered operations of various devices such as MEMS wireless sensors, medical implants and wearable electronic devices. Piezoelectric nanogenerators can efficiently convert the vastly available mechanical energy into electrical energy to meet the requirements of low-powered electronic devices. Among the piezoelectric materials, poly (vinylidene fluoride) (PVDF) and its copolymers are extensively studied for the development of energy harvesting devices. Due to the outstanding properties such as high flexibility, ease of processing, long-term stability, biocompatibility makes them a promising candidate for piezoelectric generators. Nevertheless, compared to piezoceramic materials, PVDF based generators produce lower piezoresponse. Over the last decades, tremendous research activities have been reported to endorse the performance of PVDF based energy harvesters. This review article mainly focused on the recent progress in the performance improvement with processing methods, piezoelectric materials, different filler loading. The new developments and design structures will lead to an increase in piezoelectricity, alignment of dipoles, dielectric properties and subsequently enhance the output performance of the device. Electronic circuits play a vital role in energy harvesting to efficiently collect the developed charge from the device. Here, we have proposed a detailed description of the electronic circuits. Also, in the application part deals with the recent progress in flexible, biomedical and hybrid generators based on PVDF polymers.

Cellulose-Based Fully Green Triboelectric Nanogenerators with Output Power Density of 300 W m-2.

Triboelectric nanogenerators (TENGs) have attracted increasing attention because of their excellent energy conversion efficiency, the diverse choice of materials, and their broad applications in energy harvesting devices and self-powered sensors. New materials have been explored, including green materials, but their performances have not yet reached the level of that for fluoropolymers. Here, a high-performance, fully green TENG (FG-TENG) using cellulose-based tribolayers is reported. It is shown that the FG-TENG has an output power density of above 300 W m-2 , which is a new record for green-material-based TENGs. The high performance of the FG-TENG is due to the high positive charge density of the regenerated cellulose. The FG-TENG is stable after more than 30 000 cycles of operations in humidity of 30%-84%. This work demonstrates that high-performance TENGs can be made using natural green materials for a broad range of applications.

In-Plane Second-Order Topologically Protected States in Elastic Kagome Lattices

Second-order topological insulators, which exhibit capability of hosting topologically protected zero-dimensional corner states distinct from the well-studied topological edge states, unveil a horizon beyond the conventional bulk-edge correspondence. Motivated by recent experimental observation of Wannier-type second-order corner states in acoustic structures, we investigate numerically and demonstrate experimentally the in-plane edge and corner states in a mechanical kagome lattice. By manipulating simply lattice geometry and quantized characterization, we exploit that the emerging corner states are topologically robust against disorders. We further present a second-order topological insulator with multi-interfaces such that the mechanical energy can be localized in multiple locations, which provides the possibility of practical application in energy harvesting devices. The present study is the physical observation to extend the second-order topological insulator to in-plane elastic dynamics, and modal coupling of in-plane elasticity makes it more challenging to be measured experimentally.

Printing –Based Manufacturing of Flexible Ferroelectric Devices for Energy Harvesting Applications

Flexible ferroelectric devices have attracted enormous interest in recent years due to their excellent energy harvesting performance.[1, 2] Most of the existing ferroelectric devices have rigid nature and therefore are incompetent for flexible/ wearable electronic applications.[3] Here, we report a flexible ferroelectric device developed by printing the ferroelectric device components on flexible substrates. The 3- D structures of graphene oxide (GO) and poly(vinylidene fluoride- trifluroethylene) [PVDF- TFE] were printed with different designs and configurations to develop an optimum device. The thickness of the printing layers and size of the components were optimized to achieve better device performance. This device exhibits excellent energy harvesting performance with outstanding device flexibility. The better performance of the hybrid material may be due to the high mechanical strength, excellent Young’s modulus, and high dielectric constant of GO. This study suggests the new manufacturing methods and better device design for further development of piezoelectric energy harvesting devices.

Flexoelectricity in Flexoionic Polymer Electrolyte Membranes: Effect of Thiosiloxane Modification on Poly(ethylene glycol) Diacrylate and Ionic Liquid Electrolyte Composites.

The present article entails the generation of flexoelectricity during cantilever bending of a solid polymer electrolyte membrane (PEM), composed of poly(ethylene glycol) diacrylate (PEGDA) precursor and ionic liquid (hexylmethylimidazolium hexafluorophosphate). The effects of thiosiloxane modification of PEGDA precursor on glass transition, ionic conductivity, and flexoelectric performance have been explored as a function of PEM composition. The glass transition temperature (Tg) of the PEM declines with increasing thiosiloxane amount in the PEGDA co-network, while the ionic conductivity improves. The PEM/compliant carbonaceous electrodes assemblies were assembled to determine the flexoelectric coefficients by monitoring electrical voltage/current outputs for various PEM compositions under the intermittent square-wave and dynamic oscillatory sine-wave deformation modes. Of particular interest is that the room temperature flexoelectric coefficient exhibits strong frequency dependence in the vicinity of 0.01-10 Hz, suggesting that ion polarization and ion transport through the ion-dipole complexed networks can still be affected by the mobile side chain branches even in the elastic regime of the covalently bonded PEGDA network. The in-depth understanding of the effect of thiosiloxane side chain on flexoelectricity generation is anticipated to have impact on the development of mechanoelectrical energy conversion devices for energy harvesting applications from natural and dynamical environment.

Ferroelectret materials and devices for energy harvesting applications

This paper provides an overview of ferroelectret materials for energy harvesting applications. These materials take the form of a cellular compliant polymer with polarised pores that provide a piezoelectric response to generate electrical energy as a result of an applied strain or surrounding vibration. The manufacturing processes used to create ferroelectret polymer structures for energy harvesting are discussed, along with the range of microstructural features and pore sizes that are formed. Their important mechanical, electrical and harvesting performance are then described and compared. Modelling approaches for microstructural design or for predicting the vibrational and frequency dependent response are examined. Finally, conclusions and future perspectives for ferroelectret materials for energy harvesting applications are provided.

Engineering the electronic band structures of novel cubic structured germanium monochalcogenides for thermoelectric applications

Germanium mono-chalcogenides have received considerable attention for being a promising replacement for the relatively toxic and expensive chalcogenides in renewable and sustainable energy applications. In this paper, we explore the potential of the recently discovered novel cubic structured (π-phase) GeS and GeSe for thermoelectric applications in the framework of density functional theory coupled with Boltzmann transport theory. To examine the modifications in their physical properties, the across composition alloying of π-GeS and π-GeSe (such as π-GeS1-xSex for x =0, 0.25, 0.50, 0.75, and 1) has been performed that has shown important effects on the electronic band structures and effective masses of charge carriers. An increase in Se composition in π-GeS1-xSex has induced a downward shift in their conduction bands, resulting in the narrowing of their energy band gaps. The thermoelectric coefficients of π-GeS1-xSex have been accordingly influenced by the evolution of the electronic band structures and effective masses of charge carriers. π-GeS1-xSex features sufficiently larger values of Seebeck coefficients, power factors and figures of merit (ZTs), which experience further improvement with an increase in temperature, revealing their potential for high-temperature applications. The calculated results show that ZT values equivalent to unity can be achieved for π-GeS1-xSex at appropriate n-type doping levels. Our calculations for the formation enthalpies indicate that a π-GeS1-xSex alloying system is energetically stable and could be synthesized experimentally. These intriguing characteristics make π-GeS1-xSex a promising candidate for futuristic thermoelectric applications in energy harvesting devices.

(Invited) Solution Processing and Structural Control of 2D Materials of Bi2Te3, MoS2 and V2O5 and Their Applications

Embedding 2D layered materials into polymers can form a paint with many useful applications. In bulk form the thermoelectric material bismuth telluride (Bi2Te3) has a high figure of merit (ZT) at room temperature. When bulk Bi2Te3 is exfoliated to smaller dimensions, such as its 2D form (nanosheets), its thermoelectric effects are improved by reduction in thermal conductivity due to phonon confinement and scattering, thus increasing the ZT. The difficulty involved in incorporating nanosheets into energy harvesting systems motivated the search for a form of Bi2Te3 that retains the high ZT apparent at the nanoscale with the capability of being deposited or painted onto device infrastructures. This work highlights a method whereby solvent exfoliation of Bi2Te3 into solution-dispersible 2D nanosheets can form a practical thin film that can be distributed across a surface. Optical transmission measurements quantify the relationship between efficient and stable exfoliation and the reduction in optical density. Optimized exfoliated suspension are also shown to form smooth, uniform blends when mixed with poly ethylene glycol and other polymers to produce a paintable Bi2Te3film that can be applied to surfaces using an innovative painting technique. Atomic force microscopy, transmission electron spectroscopy, Raman spectroscopy and scanning electron spectroscopy are used to examine the structure of the 2D nanosheets and the highly reproducible Bi2Te3thin films. Electrical transport studies show that the films have conductive pathways over a range of surfaces and various structural formations, linking the conductivity to the percolating conduction through the nanosheet ensemble. The combination of the facile preparation method and the scope for diverse surface coating as a cohesive and conductive thin film offers methods for integration with heat producing devices for energy harvesting applications. Direct Seebeck coefficient and thermal diffusivity measurements examine the role of the pain conductivity on its thermoelectric response. Separately, MoS2 nanosheets are also demonstrated by solvent exfoliation of uniquely formed hexagonal single crystals. These crystals are formed under high pressure from layered MoS2 and this talk demonstrates how multi-micron scale dimension flakes of 2D and few-layer hexagonal MoS2can be formed from compressed soluble solutions of the 2D and layered material. Finally, we demonstrate a method whereby 2D layers of V2O5 can be turbostratically assembled using organic-inorganic interactions with alkylamines under hydrothermal conditions, to scroll into very high quality V2O5 nanotubes. V2O5 layered materials intercalated with 1D Pt-Pt metal complexes exhibit high directional conductivity. We also show that the method can be used to make nanotubes of 2D and layered materials, and how MoS2 sheets can also be rolled into nanotubular form.

Active elements on a basis of ZnO nanorods for energy harvesting devices

It is represented the research of piezoelectric properties of nanorods and their application in energy harvesting devices. According to the simulation results with method of finite elements the value of electromechanic coupling coefficient of monolayer from ZnO nanorods is greater than one in compare to uniform film application. The sample manufacturing method consists of application of traditional microelectronic technique for shaping of top and bottom electrodes and also application of two-steps low-temperature chemical synthesis for ZnO nanorods. To provide acoustic perturbation of the sample the piezoceramic element is used in multilayer structure fixed on the glassceramic substrate. The results are obtained for two measurement modes, providing oscillations perturbation by rectangular pulses source and by harmonic generator. Obtained results demonstrate high efficiency of piezoelectric transformation for monolayer, which consists of ZnO nanorods that is possible to be used in different self-powered devices.

Nanostructural evolution of one-dimensional BaTiO₃ structures by hydrothermal conversion of vertically aligned TiO₂ nanotubes.

The use of TiO2 nanotube (NT) arrays as templates for hydrothermal conversion of one-dimensional barium titanate (BaTiO3) structures is considered a promising synthesis approach, even though the formation mechanisms are not yet fully understood. Herein we report a nanostructural study by means of XRD and (HR)TEM of high aspect ratio TiO2-NTs hydrothermally converted into BaTiO3. The nanostructure shows two different and well-defined regions: at the top the conversion involves complete dissolution of NTs and subsequent precipitation of BaTiO3 crystals by homogeneous nucleation, followed by the growth of dendritic structures by aggregation and oriented attachment mechanisms. Instead, at the bottom, the low liquid/solid ratio, due to the limited amount of Ba solution that infiltrates the NTs, leads to the rapid crystallization of such a solution into BaTiO3, thus allowing the NTs to act as a template for the formation of highly oriented one-dimensional nanostructures. The in-depth analysis of the structural transformations that take place during the formation of the rod-like arrays of BaTiO3 could help elucidate the conversion mechanism, thus paving the way for the optimization of the synthesis process in view of new applications in energy harvesting devices, where easy and low temperature processing, controlled composition, morphology and functional properties are required.

Atomic species identification at the (101) anatase surface by simultaneous scanning tunnelling and atomic force microscopy

Anatase is a pivotal material in devices for energy-harvesting applications and catalysis. Methods for the accurate characterization of this reducible oxide at the atomic scale are critical in the exploration of outstanding properties for technological developments. Here we combine atomic force microscopy (AFM) and scanning tunnelling microscopy (STM), supported by first-principles calculations, for the simultaneous imaging and unambiguous identification of atomic species at the (101) anatase surface. We demonstrate that dynamic AFM-STM operation allows atomic resolution imaging within the material's band gap. Based on key distinguishing features extracted from calculations and experiments, we identify candidates for the most common surface defects. Our results pave the way for the understanding of surface processes, like adsorption of metal dopants and photoactive molecules, that are fundamental for the catalytic and photovoltaic applications of anatase, and demonstrate the potential of dynamic AFM-STM for the characterization of wide band gap materials.

Well-aligned ZnO nanoneedle arrays grown on polycarbonate substrates via electric field-assisted chemical method

Well-aligned ZnO nanoneedle arrays were prepared for the first time on polycarbonate (PC) substrates via an electric field-assisted chemical method. The surface morphologies of ZnO nanoneedles at different current densities were studied using field emission scanning electron microscopy. The X-ray diffraction pattern of the ZnO nanoneedle arrays showed strong c-axis oriented crystal structure with preferred (002) orientation. Room-temperature photoluminescence measurement of the ZnO nanoneedles revealed an ultraviolet peak at 380nm, which is comparable with those found in high-quality ZnO films. UV–visible spectroscopy was also conducted to study further the optical properties of ZnO nanoneedles. The growth of ZnO nanoneedles on PC substrate exhibited the greatest absorption enhancement and the best antireflective property, which indicated that this product has great potential for the applications in energy-harvesting devices and flexible solar cell applications.

Correction: Pyroelectric materials and devices for energy harvesting applications

Correction for ‘Pyroelectric materials and devices for energy harvesting applications’ by C. R. Bowen et al., Energy Environ. Sci., 2014, 7, 3836–3856.

Effects of Fe2O3 addition on the piezoelectric and the dielectric properties of 0.99Pb(Zr0.53Ti0.47)O3-0.01Bi(Y1−x Fe x )O3 ceramics for energy-harvesting devices

The 0.99Pb(Zr0.53Ti0.47)O3-0.01Bi(Y1−x Fe x )O3 [PZT-BYF(x)] (x = 0.0 − 0.6) piezoelectric ceramics have been synthesized by using a modified conventional solid-state method. Initially, the perovskite Pb(Zr0.53Ti0.47)O3 (PZT) and the cubic-phase Bi(Y1−x Fe x )O3 [BYF(x)] were presynthesized and mixed to prepare PZT-BYF(x) ceramic composites. The effects of BYF(x) addition on the phase formation, microstructure, and piezoelectric/dielectric properties were measured as functions of sintering temperature. In addition to these measurements, the piezoelectric voltage constant (g 33) and the piezoelectric transduction coefficient (d 33 × g 33) were measured in order to evaluate the essential criteria for an energy-harvesting material. For all the specimens, X-ray diffraction analyses showed a complete solid solution with co-existing tetragonal and rhombohedral perovskite phases. All the ceramics exhibited denser and finer microstructures, which produced a high relative density of ≥ 98%. Scanning electron microscopy (SEM) observations revealed that BYF(x) addition enhanced the sintering density through the formation of a liquid phase. The doping with BYF(x) in the PZT system was found to be effective for maintaining a high Curie temperature of around 377–390 °C. With increasing content of Fe2O3 in the BYF(x) system, the piezoelectric and the dielectric properties were significantly improved. At a sintering temperature of 1170 °C, the piezoelectric and the dielectric properties of PZT-BYF(x) ceramics showed desirable values; this resulted in a significantly higher transduction coefficient. The compositions of PZTBYF(0.1), PZT-BYF(0.2), and PZT-BYF(0.3) showed a considerably lower e 33 T value, but higher d 33 and k p values. Therefore, within the concentration limit of x = 0.1 to 0.3 moles of Fe2O3, the g 33 and the d 33 × g 33 values were improved significantly (g 33 > 53 × 10−3 Vm/N and d 33 × g 33 > 20000 m2/N). The maximum transduction coefficient of 20167 × 10−15 m2/N was obtained from the composition of PZT-BYF(0.3). The high values of g 33 and d 33 × g 33 make these piezoelectric ceramics potential candidates for applications in energy-harvesting devices.