Energy Harvesting Devices Research Articles

A first-principles study of MgSnN2 films using a DFT-1/2 approach

The thin films of a newly discovered MgSnN2 Pnma phase were computationally investigated using a recently developed DFT-1/2 functional. It was showing that the properties of the investigated films closely relate to the thickness. For those films with odd number of layers, the band gaps are accordingly 2.040 eV, 2.102 eV and 2.107 eV for three, five and seven layers, showing an increasing order along with depth. As for those with even number of layers, the band gaps show a reduction from 2.488 eV for double layer to 2.210 eV for four-layer and then to 2.136 eV for six-layer. The change of the band gap mainly comes from the intralayer and interlayer bonding relation. The valence and conduction band edges increase monotonically along with the number of layers of thin films, except for the conduction band edge of double layer. Moreover, the absorption spectra shows promising absorption peaks within visible range. Therefore, fabrication of films with thickness control can potentially be used to expand the applications of MgSnN2 for energy harvest, photocatalysis, electronic and optoelectronic devices.

Superior piezoelectric performance of chemically synthesized transition metal dichalcogenide heterostructures for self-powered flexible piezoelectric nanogenerator

In addition to the superior electrical and optoelectronic attributes, ultrathin two-dimensional transition metal dichalcogenides (TMDCs) have evoked appreciable attention for their piezoelectric properties. In this study, we report, the piezoelectric characteristics of large area, chemically exfoliated TMDCs and their heterostructures for the first time, as verified by piezoelectric force microscopy measurements. Piezoelectric output voltage response of the MoS2-WSe2 heterostructure piezoelectric nanogenerator (PENG) is enhanced by ∼47.5% if compared with WSe2 and ∼29% if compared to MoS2 PENG, attributed to large band offset induced by heterojunction formation. This allows the scalable fabrication of self-powered energy harvesting PENGs, which can overcome the various shortcomings of complicated synthesis processes, complex fabrication steps, low yield, and poor stability. The fabricated flexible, self-powered MoS2-WSe2 heterostructure nanogenerator exhibits piezoelectric output ∼46 mV under a strain of ∼0.66% yielding a power output ∼12.3 nW, which offers better performance than other two-dimensional material based piezoelectric devices and also reveals the ability of bio-mechanical energy harvesting. This cost effective approach to fabricate eco-friendly MoS 2 -WSe 2 based fatigue free, superior performance piezoelectric-nanogenerators can be utilized to evolve flexible energy harvesting devices and may also be attractive as a self-powered, smart wearable sensor devices.

Investigation of Submergence Depth and Wave-Induced Effects on the Performance of a Fully Passive Energy Harvesting Flapping Foil Operating Beneath the Free Surface

This paper investigates the performance of a fully passive flapping foil device for energy harvesting in a free surface flow. The study uses numerical simulations to examine the effects of varying submergence depths and the impact of monochromatic waves on the foil’s performance. For the numerical simulations, a in-house artificial compressibility two-phase solver is employed and coupled with a rigid body dynamic solver. The results show that the fully passive flapping foil device can achieve high efficiency for submergence depths between 4 and 9 chords, with an “optimum” submergence depth where the flapping foil performance is maximised. The effects of regular waves on the foil’s performance were also investigated, showing that waves with a frequency close to that of the natural frequency of the flapping foil-aided energy harvesting. Overall, this study provides insights that could be useful for future design improvements for fully passive flapping foil devices for energy harvesting operating near the free surface.

Interlayer Polymerization of 2D Chiral Perovskite Single‐Crystal Films toward High‐Performance Flexible Circularly Polarized Light Detection

Abstract2D chiral perovskite has greatly boosted the development of optoelectronic devices, ranging from nonlinear optics, spintronics, and ferroelectrics to energy harvesting devices. Despite circularly polarized light (CPL) detection based on chiral perovskite has been achieved, the environmental humidity‐, ultraviolet (UV), and temperature‐induced structural degradation and its large electro‐phonon coupling restrict its commercial application. Here, this study first realizes polymerized chiral perovskite single‐crystal films by combining in situ cross‐linking polymerization with the space‐confined crystallization method. Compared with uncross‐linked chiral perovskites, cross‐linked chiral perovskites exhibit enhanced crystallinity and lattice rigidity, yielding high‐performance circularly polarized photodetectors with a maximum anisotropy factor of 0.22, the responsivity of 1.6 A W−1, and detectivity of 2.17 × 1013 Jones. In addition, flexible circularly polarized photodetectors with extremely high mechanical stability are also realized originating from the polymer‐like behavior of cross‐linked chiral perovskite single‐crystal films. This study opens up new avenues to further enhance the performance and stability of portable and wearable devices based on chiral perovskites.

Hierarchically 3D Fibrous Electrode for High‐Performance Flexible AC‐Line Filtering in Fluctuating Energy Harvesters

AbstractIn light of the rapid development of intelligence and miniaturization in electronics, the growing demand for sustainable energy sources gives rise to a plethora of environmental/mechanical energy harvesters. However, the fluctuating nature of these generated energies frequently presents a challenge to their immediate usability. Although electrolytic capacitors can smooth fluctuating energy, lacking miniaturization and flexibility constrain their potential applications. Conversely, electrochemical capacitors (ECs), particularly fiber‐shaped electrochemical capacitors (FSECs), can offer superior flexibility. Nevertheless, the inherent trade‐off between ion transport and charge storage in fibrous electrodes poses a significant obstacle to their filtering capability. Here, a hierarchically 3D fibrous electrode that effectively balances ion transport and charge storage through its unhindered primary framework and intertwined secondary frameworks is presented. The resulting FSEC exhibits an exceptional specific areal capacitance of 1.37 mF cm−2 with a phase angle of −82° at 120 Hz, surpassing that of fiber‐shaped filter capacitors and most non‐fibrous filter ECs previously reported. Additionally, the FSEC displays excellent flexibility and high‐frequency response, rendering it well‐suited for filtering arbitrary ripple voltage and compatible with environmental/mechanical energy harvesters. These results demonstrate a promising approach for designing fibrous high‐frequency response electrodes and a foundation for portable environmental energy harvesting devices.

Stretchable Energy Harvesting Device based on Thermoelectric Composite Films

Thermoelectric energy harvesting has attracted a lot of attention for powering self-powered devices because of the potential to generate energy anywhere with a temperature difference. In particular, a stretchable thermoelectric generator (S-TEG) can be applied to the repetitively moving parts of a machine and even a human body. Herein, we suggested a S-TEG using thermoelectric composite films made by dispersing n-type Bi2Te2.7Se0.3 powders into the polyvinylidene fluoride elastomer. The prepared n-type thermoelectric composite film with 75 wt% of Bi2Te2.7Se0.3 powders showed a power factor of 1.81 mW m−1 K−2 at room temperature. Next, we fabricated S-TEG by encapsulating thermoelectric powders-based composite films, and Ag-coated textile electrodes with an Eco-flex matrix. The fabricated stretchable energy harvester generated a maximum output power of 2.35 nW at a temperature difference (ΔT) of 25 K. By repeatedly introducing ΔT=5K, our S-TEG converted the output voltage of 3.4 mV and current signals of 0.25 mA. Moreover, a finite element analysis with multiphysics COMSOL simulation software was conducted to compare the experimental and theoretical thermoelectric output performance of the fabricated S-TEG. Finally, we demonstrated energy harvesting by converting human body heat into electrical energy for potential utilization of our energy harvester. This study led to the development of a S-TEG design using thermoelectric film with a simple and low-cost fabrication procedure, providing a potential approach for use as a next-generation wearable device power source.

Numerical study of the effect of central platform motion on the wave energy converter array

Placing multiple wave energy converters (WECs) on a central floating platform has become a popular approach of ocean energy conversion in recent years. The strong interaction between the WECs and the platform brings a number of technical challenges for the design of such devices. The present study investigates the effect of the platform motion on the WEC array of a typical ocean energy harvesting device, consisting of a central support platform and eight point-absorber WECs arranged in a circular array. The numerical studies are performed in four stages based on the potential flow solver ANSYS-AQWA. The power absorption of each WEC in isolation and of eight WECs operating simultaneously is evaluated and compared in the first and second stages respectively, revealing the interaction among the WECs. The effect of a fixed and a floating platform on the power absorption of the WEC array is investigated in the next two stages. The systematic studies demonstrates that the heave motion of the platform improves the power absorption of the WEC array for most wave frequencies tested, due to the increase in the wave-surface elevations around the WECs and the phase differences of the heave motion between the WECs and the platform. The opposite is true for the pitch motion of the platform. Furthermore, the WEC dimension, the platform dimension, and the distance between the WECs and the platform should be optimized based on the actual operating sea conditions to increase the wave-surface elevations and the phase differences. Otherwise, the motion of the platform should be restricted as much as possible.

Effects of stretching on phase transformation of PVDF and its copolymers: A review

Abstract Poly(vinylidene fluoride) (PVDF) and its copolymers are promising candidates for energy-harvesting devices because of their flexibility, environmental friendliness, lightweight, and high halogen and acid resistance. However, the relatively low piezoelectricity limits their applications. The piezoelectricity of PVDF and its copolymers highly depends on the polar β-phase, while the non-polar α-phase is the most common one. As a result, the β-phase formation and α- to β-phase transformation have attracted much attention in recent years. Stretching is a widely used method to induce the α- to β-phase transformation for the improvement of piezoelectricity. In this work, the influences of the parameters during stretching on phase evolution and piezoelectricity are discussed and summarized. Besides, nontraditional stretching methods are also introduced and discussed. This work will provide important information for preparing high-performance piezoelectric polymer films.

Suppressing the self-discharge of MXene-based supercapacitors by liquid crystal additive

MXenes are widely used as electrodes for supercapacitors (SCs) due to their excellent conductivity and abundant redox active sites. However, the severe self-discharge of MXene-based SCs results in significant energy loss, limiting their integration with various energy-harvesting devices. Here we introduced the nematic liquid crystal 4-n-pentyl-4′-cyanobiphenyl (5CB) molecules into Ti3C2Tx films and LiCl aqueous electrolytes to suppress the self-discharge rate. The nematic liquid crystal molecules would arrange parallel to each other when the Ti3C2Tx films were charged, while the electrolyte viscosity would increase due to the electrorheological effect, causing the slow cross-diffusion of active ions and reducing the self-discharge. As a result, the MXene-based SCs had a low voltage drop of 35% after 4600 s and a low leakage current of 3.0 µA, respectively. The MXene-based SCs could store energy more effectively, improving their practical application potential in integrated energy harvesting devices, for example, storing the electrical energy harvested by the triboelectric nanogenerators. This work proposed a simple strategy to suppress the self-discharge of Ti3C2Tx-based SCs by liquid crystal additive, which can be extended to other MXenes, promoting the applications of MXenes in energy storage devices and integrated electronics.

Comparative study and multi-parameter analysis to optimize device structure of triboelectric nanogenerators

Triboelectric nanogenerator is becoming one of the most efficient energy harvesting device among all mechanical energy harvesters. This device consists of dielectric friction layers and metal electrode which generates electrical charges using electrostatic induction effect. There are several factors influencing the performance of this generator which needs to be evaluated prior to experiment. The absence of a universal technique for TENG simulation makes the device design and optimization hard before practical fabrication, which also lengthens the exploration and advancement cycle and hinders the arrival of practical applications. In order to deepen the understanding the core physic behind the working process of this device, this work will provide comparative analysis on different modes of TENG. Systematic investigation on different material combination, effect of material thickness, dielectric constant and impact of surface patterning is evaluated to shortlist the best material combination. COMSOL Multiphysics simulating environment is used to design, model and analyze factor affecting the overall output performance of TENG. The stationary study in this simulator is performed using 2D geometry structure with higher mesh density. During this study short circuit and open circuit condition were applied to observe the behavior of charge and electric potential produced. This observation is analyzed by plotting charge transfer/electric potential against various displacement distances of dielectric friction layers. The ouput is then provided to load ciruitary to measure the maximum output power of the models. Overall, this study provides an excellent understanding and multi-parameter analysis on basic theoretical and simulation modeling of TENG device.

Design of energy harvesting magneto-rheological fluid damper for vehicle

Modern vehicles must include dampers in the suspension system in order to absorb vibration energy while driving. Passive dampers have dominated the market for many years. To increase the passenger comfort levels, suspension systems with controlled dampers that can adjust to uneven road profiles are needed. Semi-active suspensions have emerged as one of the most popular modern damping solution types due to their ability to manage damping force. The semi-active suspension system of the car uses magneto-rheological (MR) dampers for vibration control. The MR damper consumes low energy, has quick response, and better controllability of the damping force. A part of the energy lost in vehicle dampers can be recovered due to developments in energy-harvesting devices. This regenerated energy can be used in vehicles to power a number of extra systems, such as lighting, heating and air conditioning, and other things. This research attempts to develop an MR fluid damper with energy-harvesting rack and pinion system. The purpose of this study is to design a suspension system that combines an MR fluid damper and an energy-harvesting rack and pinion system. The design calculation involves setting the design parameters for the system that harvests energy and the MR fluid damper. Also, static structural analysis is carried out for both systems using finite element analysis software.

Polyvinylidene Fluoride as an advanced polymer for multifunctional applications- a review

With the advancement of technological development, polymers are grabbing huge consideration in developing Energy Harvesting and Electromechanical devices. Polyvinylidene Fluoride, commonly referred to as PVDF, a semicrystalline polymer from the fluoropolymer family, has received tremendous interest among the research community. This polymer is astonishing to researchers with its excellent piezoelectric and dielectric properties. Apart from this, properties like outstanding thermal stability, flexible processing, anticorrosive, and mechanical strength make them more appropriate for applications such as wearable sensors, nanogenerators, spin valve ultrafiltration membranes, and separators in lithium-ion batteries. Furthermore, while exploring deep through its electrical properties, PVDF is a ferroelectric non-polar insulating matrix and is majorly adopted in insulating materials. But few researchers have resulted that incorporating certain fillers into PVDF can improve their electroactive crystalline phase without an external poling process. This enhancement enhances their piezoelectric properties and makes them an advanced polymer for multifunctional applications such as shielding material for Electromagnetic Interference (EMI), Acoustic sensors, energy storage and smart scaffolds. Hence this review discusses PVDF as an advanced polymer for Multifunctional applications.

3-DOF X-structured piezoelectric harvesters for multidirectional low-frequency vibration energy harvesting

Nonlinear energy harvesters with specially-designed nonlinear characteristics (e.g., quasi-zero stiffness, multi-stability, and internal resonance) have been extensively studied to develop broadband harvested energy at low and ultra-low frequencies. Nevertheless, most developed energy harvesting devices were restricted to unidirectional energy harvesting, which is a limitation in many applications. This paper proposes a novel 3-degrees-of-freedom (3-DOF) X-structured piezoelectric harvesting system, enabling simultaneous & enhanced multidirectional low-frequency energy harvesting. It is shown that the developed 3-DOF X-harvester can produce useful & powerful motion coupling effect and unique band-pass-like property of two peaks and large frequency range due to nonlinear dynamics incurred by the specially designed X-mechanism, and can thus offer greater flexibility in tuning structural parameters to achieve broadband and higher low- and ultralow-frequency energy harvesting in multi-directions, compared to many other literature results. In experiments, with 300 kΩ and two piezoelectric beams connected in-series, the prototyped 3-DOF X-harvester achieved peak power outputs of 2.5 mW in the z-DOF at 9 Hz and 2 mm, 41.2μW in the x-DOF at 13.5 Hz and 2 mm, and 86.2μW in the ψ-DOF at 13.5 Hz and 1.7 mm, much better than many other literature results. In real-world applications with multidirectional vibrations, the harvested power will definitely have a wider bandwidth and higher peak outputs due to the motion coupling effect, allowing for enhanced ultralow-frequency energy harvesting.

Experimental study on power generation performances of a novel piezoelectric energy harvester

In this article, a new type of piezoelectric energy harvester device is proposed, which has good output performance and can scavenge a large amount of vibration energy at low frequency. By setting up the experimental platform and testing, the results show that the external resistance, the mass of the cantilever end, the excitation acceleration and the magnet distance have an impact on the device. When the mass of the end of the cantilever beam is 15 g and the acceleration is 0.5 g, the output power of the device is 5.2 mW, and the output performance is good.

Study of spin control on half metallic ferromagnetism and thermoelectric properties of MgEu2(S/Se)4 for spintronic and energy harvesting devices

Spintronic is the emerging technology for next generation electronic devices that can improve memory and computing capability by use of electrons spin degree of freedom. The electronic, magnetic, and transport properties of MgEu2(S/Se)4 spinels are explored systematically. These spinels are stable in ferromagnetic state (FM) confirmed by energy release in optimization, phonons band structures, and enthalpy of formation (ΔHf). The Curie temperature and spin polarization signify spin polarization at high temperature. The hybridization of p-S/Se and f-Eu states have been discussed from Band structure, and density of states which explain the nature of ferromagnetism. The crystal field and exchange energies are also reported for the verification of control of electrons spin. Furthermore, the exchange constants, and double exchange mechanism also premeditated. The double exchange model is satisfied by the negative Δx (pf) and constant Noβ. Moreover, the Seebeck coefficient, conductivities, and power factor (PF) for spin (↑) and spin (↓) are investigated separately and collectively by BoltzTraP code. The high values of PF and ultralow values of thermal conductivity make the potential materials for thermoelectric generators.

Multi-functional zeolitic imidazolate framework-67 (ZIF-67) for solid-state fiber energy harvesting and storage devices

Wearable electronic devices using energy device-based smart fibers have brought changes in Internet of Things (IoT) technology paradigms. Since electric power is essential to drive all current electronic devices, a flexible energy device is essential to construct a wearable energy systems. Herein, two different types of the fiber-based energy devices were manufactured using ZIF-67, which can improve catalytic properties. First of all, it was confirmed that ZIF-67 was adsorbed on the electrodes of the solid-state fiber-shaped supercapacitor (SS-FSC) and the catalytic property was enhanced, thereby improving the specific capacitance. Second, it was verified that ZIF-67 was adsorbed on the surface of Pt wire, which is the counter electrode (CE) of the solid-state fiber dye-sensitized solar cell (SS-FDSSC), to improve the catalytic properties, resulting in the improvement of the power conversion efficiency (PCE) of the SS-FDSSCs. The optimized SS-FDSSC demonstrated enhanced electrocatalytic activity, with a PCE of up to 7.03%, which is about 40% greater than that of the pristine Pt wire electrode (5.02%). Therefore, the fiber-based energy devices functionalized with ZIF-67 with excellent catalytic properties and high surface area have been identified as having great potential for producing novel and efficient power sources for wearable electronic devices to be utilized in IoT applications.

One Material-Opposite Triboelectrification: Molecular Engineering Regulated Triboelectrification on Silica Surface to Enhance TENG Efficiency.

Molecular engineering is a unique methodology to take advantage of the electrochemical characteristics of materials that are used in energy-harvesting devices. Particularly in triboelectric nanogenerator (TENG) studies, molecular grafting on dielectric metal oxide surfaces can be regarded as a feasible way to alter the surface charge density that directly affects the charge potential of triboelectric layers. Herein, we develop a feasible methodology to synthesize organic-inorganic hybrid structures with tunable triboelectric features. Different types of self-assembled monolayers (SAMs) with electron-donating and withdrawing groups have been used to modify metal oxide (MO) surfaces and to modify their charge density on the surface. All the synthetic routes for hybrid material production have been clearly shown and the formation of covalent bonds on the MO's surface has been confirmed by XPS. The obtained hybrid structures were applied as dopants to distinct polymer matrices with various ratios and fiberization processes were carried out to the prepare opposite triboelectric layers. The formation of the fibers was analyzed by SEM, while their surface morphology and physicochemical features have been measured by AFM and a drop shape analyzer. The triboelectric charge potential of each layer after doping and their contribution to the TENG device's parameters have been investigated. For each triboelectric layer, the best-performing tribopositive and tribonegative material combination was separately determined and then these opposite layers were used to fabricate TENG with the highest efficiency. A comparison of the device parameters with the reference indicated that the best tribopositive material gave rise to a 40% increase in the output voltage and produced 231 V, whereas the best tribonegative one led to a 33.3% rise in voltage and generated 220 V. In addition, the best device collected ~83% more charge than the reference device and came up with 250 V that corresponds to 51.5% performance enhancement. This approach paved the way by addressing the issue of how molecular engineering can be used to manipulate the triboelectric features of the same materials.

Bioelectronic Applications of Intrinsically Conductive Polymers

AbstractSince the discovery of conducting polyacetylene in the 1970s, intrinsically conducting polymers (ICPs) have attracted great attention because of their interesting structure, properties, and applications. Notably different from conventional conductors such as metals and doped semiconductors, ICPs have high mechanical flexibility and are light weight. In addition, their properties can be easily tuned by controlling the doping level, modifying the chemical structure, or forming composites with organic or inorganic materials. Their application in bioelectronics is particularly interesting because they have good biocompatibility and good mechanical matching with biological tissues. In this article, the methods to increase the mechanical stretchability of ICPs are first reviewed because high stretchability is often required for bioelectronic applications while pristine ICPs generally have limited stretchability. The application of ICPs as stretchable electrodes for epidermal biopotential detection and neural interfaces is discussed. Then, the employment of ICPs as the electrodes or sensing material of mechanical sensors is reviewed. They also have important application in controllable drug delivery. Last, their applications in the wearable energy harvesting and storage devices including thermoelectric generators and supercapacitors are also covered.

Cellulose-based fabrics triboelectric nanogenerator: Effect of fabric microstructure on its electrical output

At present, fabric-based triboelectric nanogenerator (TENG) has been paid attention and developed for self-power generation systems with wearability for E-textiles, especially cotton. However, there are many commercial cellulose-based fabrics with different fiber characteristics and fabric structures that gain possibility to effect on TENG performance and has been underreported. This work presents the fabrication of the textile TENG by using four types of commercial cellulose-based fabrics as friction layer and compare the electrical output efficiency relating their molecular structure, fabric structure and surface morphology characteristics. As shown by the electrical output, though all fabrics can generate electricity for TENG device, nevertheless, the output signal is different because of their different total surface area of the fabric, affecting by different microstructure. The rayon fabric contains the smallest size fiber with highest surface area at the same woven structure. The obtained output voltage (VOC) and current (ISC) of ⁓23 V and ⁓13 µA are ⁓1.8 times higher than most studied cotton fabric. This research demonstrated the importance of the microstructure and surface area of the fabrics that significantly affect TENG properties. The investigation in this work will useful and knowledgeable to select fabric materials before improving and using them for energy harvesting devices.

Nanowires based solid-state asymmetric self-charging supercapacitor driven by PVA–ZnO–KOH flexible piezoelectric matrix

The development of an efficient mechanical to electric energy conversion system and its functional integration with an energy storage device for self-powered portable devices are advanced research fields. In the traditionalconfiguration, an additional energy harvesting device is connected with an energy storage device for developing a self-charging unit. As a result, large amount of energy is lost because of the external rectifiers. Moreover, this type of external circuit makes the system bulky and thus, limits the practical applications of such devices. In this work, nanoparticles of Zinc oxide (ZnO) are employed as a piezoelectric material, and are combined with an asymmetric device for developing a self-charging asymmetric piezo-supercapacitor. The developed asymmetric piezo-supercapacitor comprises of Ni and Mg-Co nanowires-based binder-free electrodes that were employed as the anode and cathode, respectively, as well as a ZnO-based separator as energy harvester along with KOH as electrolyte. The electrochemical results reveal tremendous cyclic stability with capacitive retention of 100% and 96.5% for Mg-Co and Ni nanowires array based electrodes even after 10,000 repeated GCD cycles, respectively. In addition, the device attained a maximum voltage of ∼99 mV as a result of the compressive force via thumb press. The proposed facile as well as cost-effective approach for smart self-chargeable power package supercapacitor provides new insights for developing next generation all-in-one energy harvesting and storage devices.