Blue Energy Harvesting Research Articles

Spherical triboelectric nanogenerator based on spring-assisted swing structure for effective water wave energy harvesting

Abstract Ocean wave energy is one of the most promising clean and renewable energy sources, so developing effective methods to collect such ‘random’ and ultra-low frequency energy is indispensable. The invention of triboelectric nanogenerators (TENGs) provides new prospects for large-scale blue energy harvesting. In this work, a new spherical TENG based on the coupling of spring-assisted structure and swing structure, integrated with a charge excitation circuit (CEC), was constructed to scavenge water wave energy. The particular structure can transform low-frequency water wave vibrations to high-frequency motions, elevating the frequencies of electrical outputs. Moreover, a TENG array consisting of four TENGs with CECs was fabricated, exhibiting a maximum output power of 16.6 mW and a 205 times enhanced output current of 23.3 mA. The charge excitation TENG array was demonstrated to successfully power a digital thermometer and a wireless signal transmission and reception system without any external power supply. Our study not only provides a new type of TENG with improved performance, but also offers a strategy for constructing maritime internet of things (IoTs) system.

Shadow enhanced self-charging power system for wave and solar energy harvesting from the ocean

Hybrid energy-harvesting systems that capture both wave and solar energy from the oceans using triboelectric nanogenerators and photovoltaic cells are promising renewable energy solutions. However, ubiquitous shadows cast from moving objects in these systems are undesirable as they degrade the performance of the photovoltaic cells. Here we report a shadow-tribo-effect nanogenerator that hybrids tribo-effect and shadow-effect together to overcome this issue. Several fiber-supercapacitors are integrated with the shadow-tribo-effect nanogenerator to form a self-charging power system. To capture and store wave/solar energy from oceans, an energy ball based on the self-charging power system is demonstrated. By harnessing the shadow-effect, i.e. the shadow of the moving object in the energy ball, the charging time shortens to 253.3 s to charge the fiber-supercapacitors to the same voltage (0.3 V) as using pure tribo-effect. This cost-effective method to harvest and store the wave/solar energy from the oceans in this work is expected to inspire next-generation large-scale blue energy harvesting.

Harvesting blue energy with carbon electrodes of asymmetric nanopore distributions

Extracting the Gibbs free energy from natural water salination, a.k.a. the blue energy, has attracted a long-standing, global interest. While pressure-retarded osmosis (PRO) and reverse electrodialysis (RED) are by far the most studied methods for such a purpose, the concept of using the capacitive electrode response for blue energy harvesting has been shown to offer unique advantages. Despite that porous electrodes are predominately used in capacitive methods, the role of pore properties in energy extraction remains unclear. Here we show that the distribution of the nano-sized pores in an electrode imposes a profound impact on the electrode capacitive response under a salinity gradient. Such a pore-size effect can be sufficiently strong that leads to structural changes of the electric double layer, resulting in highly efficient extraction of the Gibbs free energy. We demonstrate that a device fabricated with carbon electrodes with significantly different nanopore distributions can generate a high power density without membranes or an external charge source. • Nano-confinement induces significant structural changes of EDLs. • Electrodes with different nanopores create dissimilar responses to salinity gradients. • Gibbs free energy from mixing can be harvested with asymmetric nanopore distributions.

Nanofluidic osmotic power generators - advanced nanoporous membranes and nanochannels for blue energy harvesting.

The increase of energy demand added to the concern for environmental pollution linked to energy generation based on the combustion of fossil fuels has motivated the study and development of new sustainable ways for energy harvesting. Among the different alternatives, the opportunity to generate energy by exploiting the osmotic pressure difference between water sources of different salinities has attracted considerable attention. It is well-known that this objective can be accomplished by employing ion-selective dense membranes. However, so far, the current state of this technology has shown limited performance which hinders its real application. In this context, advanced nanostructured membranes (nanoporous membranes) with high ion flux and selectivity enabling the enhancement of the output power are perceived as a promising strategy to overcome the existing barriers in this technology. While the utilization of nanoporous membranes for osmotic power generation is a relatively new field and therefore, its application for large-scale production is still uncertain, there have been major developments at the laboratory scale in recent years that demonstrate its huge potential. In this review, we introduce a comprehensive analysis of the main fundamental concepts behind osmotic energy generation and how the utilization of nanoporous membranes with tailored ion transport can be a key to the development of high-efficiency blue energy harvesting systems. Also, the document discusses experimental issues related to the different ways to fabricate this new generation of membranes and the different experimental set-ups for the energy-conversion measurements. We highlight the importance of optimizing the experimental variables through the detailed analysis of the influence on the energy capability of geometrical features related to the nanoporous membranes, surface charge density, concentration gradient, temperature, building block integration, and others. Finally, we summarize some representative studies in up-scaled membranes and discuss the main challenges and perspectives of this emerging field.

Soft-contact cylindrical triboelectric-electromagnetic hybrid nanogenerator based on swing structure for ultra-low frequency water wave energy harvesting

Abstract Ocean waves are promising green sources for energy exploitation, but harvesting such energy is quite challenging due to the apparent drawbacks of ultra-low vibration frequency and low efficiency. Here, a hybrid nanogenerator containing soft-contact cylindrical triboelectric nanogenerator and electromagnetic generator with swing structure was designed for ultra-low frequency wave energy converting. Brushes made of flexible rabbit hairs were introduced to separate stator-rotor pairs, with the function of charge pumping onto dielectric surface, which can reduce the operation resistance and improve the device durability. Based on the swing motion of rotor, over 60 current pulses can be generated within 15 s from either module by one external triggering, implying the output frequency multiplication and operation time extension. The optimized hybrid nanogenerator exhibits the best output response at 0.1 Hz of water wave agitation, delivering a peak power density of 10.16 W·m−3 and an average power density of 0.23 W·m−3. Furthermore, self-powered temperature mapping and wireless transmitting were successfully realized by a hybrid nanogenerator array to demonstrate its capability in collecting ultra-low frequency water wave energy. The distinctive structure and operation mechanism prompt the proposed hybrid nanogenerator to be a good candidate for large-scale blue energy harvesting.

Recent Progress in Hybridized Nanogenerators for Energy Scavenging.

SummaryAs the world's demand for alternative energy increases, the development of green energy harvesters becomes ever more important. As a result, the creation of triboelectric (TENG), piezoelectric (PENG), and pyroelectric nanogenerators, electromagnetic generators (EMG), solar cells, and electrochemical cells is attracting interest in an effort to convert mechanical, thermal, magnetic, solar, and chemical energy into electricity. In order to take advantage of the ambient energies from our surrounding environment, the design of hybridized generator units that can simultaneously scavenge energy in a variety of forms continues to develop. These systems are being considered to satisfy the energy needs of a range of electronic devices and adapt to a variety of working environments. This review demonstrates the latest progress in hybridized nanogenerators in accordance with their structure, operating principle, and applications. These studies demonstrate new approaches to developing hybrid techniques and novel assemblies for efficiently harvesting environmental energy from a number of sources.

Encapsulated Triboelectric–Electromagnetic Hybrid Generator for a Sustainable Blue Energy Harvesting and Self-Powered Oil Spill Detection

Hybridizing the triboelectric and electromagnetic generator shows a great potential in harvesting the water wave energy in a wide frequency range from low to high upon water wave motions. The tribo...

Liquid-Solid Slip on Charged Walls: The Dramatic Impact of Charge Distribution.

Nanofluidic systems show great promise for applications in energy conversion, where their performance can be enhanced by nanoscale liquid-solid slip. However, efficiency is also controlled by surface charge, which is known to reduce slip. Combining molecular dynamics simulations and analytical developments, we show the dramatic impact of surface charge distribution on the slip-charge coupling. Homogeneously charged graphene exhibits a very favorable slip-charge relation (rationalized with a new theoretical model correcting some weaknesses of the existing ones), leading to giant electrokinetic energy conversion. In contrast, slip is strongly affected on heterogeneously charged surfaces, due to the viscous drag induced by counterions trapped on the surface. In that case slip should depend on the detailed physical chemistry of the interface controlling the fraction of bound ions. Our numerical results and theoretical models provide new fundamental insight into the molecular mechanisms of liquid-solid slip, and practical guidelines for searching new functional interfaces with optimal energy conversion properties, e.g., for blue energy or waste heat harvesting.

Power cables for triboelectric nanogenerator networks for large-scale blue energy harvesting

Abstract Triboelectric nanogenerators (TENGs), a prospective technology for large-scale harvesting of blue energy from the ocean, have been extensively investigated recently. However, little attention has been paid to the cables linking the individual TENG units to form an energy harvesting network. Herein, several basic requirements for power cables suitable for effective TENG networks are outlined. The cables should avoid tangling among the TENG units, protect the transmission wires, and output electric power. Here, a TENG network based on plane-like power cables consisting of spring steel tapes and three polymer films is described. The steel tape inside the power cables has a dual role as both structural skeleton and an electrode. The tape guarantees the stability of the TENG network and eliminates the electrostatic induction from ions in seawater. The porous PTFE film on the outside is highly hydrophobic and generates electricity by liquid-solid interface contact while collaborating with the steel tapes. The working mechanism and output performance of the power cable were systematically studied. A maximum open-circuit voltage of 34 V and a transferred charge quantity of 25 nC were achieved using a single cable in a single period. An over-water test was also carried out to experimentally demonstrate the feasibility of the TENG networks. This work provides a possible strategy for network construction for large-scale blue energy harvesting.

Polyaniline for Improved Blue Energy Harvesting: Highly Rectifying Nanofluidic Diodes Operating in Hypersaline Conditions via One-Step Functionalization

Solid-state nanochannels have attracted substantial attention of the scientific community due to their remarkable control of ionic transport and the feasibility to regulate the iontronic output by different stimuli. Most of the developed nanodevices are subjected to complex modification methods or show functional responsiveness only in moderate-ionic-strength solutions. Within this project, we present a nanofluidic device with enhanced ionic current rectification properties attained by a simple one-step functionalization of single bullet-shaped polyethylene terephthalate (PET) nanochannels with polyaniline (PANI) that can work in high-ionic-strength solutions. The integration of PANI also introduces a broad pH sensitivity, which makes it possible to modulate the ionic transport behavior between anion-selective and cation-selective regimes depending on the pH range. Since PANI is an electrochemically active polymer, ionic transport also becomes dependent on the presence of redox stimuli in solution. We demonstrate that PANI-functionalized single-nanochannel membranes function as an efficient salinity gradient-based energy conversion device even in acidic concentrated salt solutions, opening the door to applications under a variety of novel operating conditions.

Ion transport through graphene oxide fibers as promising candidate for blue energy harvesting

Nanostructured graphene based membranes demonstrated excellent capabilities in various applications in nanofiltration and energy conversion due to unique atomically smooth surfaces and adjustable pore size or interlayers spacing at Angstrom scales. There are some reports on the osmotic power generation using physical confinements and electrostatic interactions between ions and GO membranes. However, the results indicated insufficient power densities (˂1 W/m2) can be achieved because of swelling of interlayer spacing of the GO membranes upon exposure to aqueous solutions which results in reducing the influence of confinement on ionic motilities. Here, the GO fibers is presented as one dimensional macrostructures including abundant aligned 2D nanochannels to produce electricity from salt concentration gradient. We used the GO fibers intercalated via cations to control the interlayer’s spacing depending on the cation’s hydrated size and consequently enhancing a stable confinement on ionic transport. Remarkable surface charge on nanochannel walls as well as cation pining of interlayer distances, provide a high mobility discrimination and the osmotic power density can reach to a value of 38 W/m2. This study introduces the GO fibers as new scalable structures for nanofluidics systems which could find range of applications in energy harvesting and molecular sieving.

A self-powered and self-functional tracking system based on triboelectric-electromagnetic hybridized blue energy harvesting module

Abstract The position tracking and attitude monitoring are essential for marine equipment's survival in the boundless ocean. The power solution for aforementioned monitoring system became the bottleneck once its own equipped traditional battery pack run out of the power. Hence, a self-powered and self-functional tracking system has been proposed to meet the technique gap, which consists of a triboelectric-functioned inertial module and an electromagnetic powered global position system (GPS) module. A sophisticated-designed rotating gyro structure, together with triboelectric-electromagnetic working principal, established a battery-less tracking system successfully. Specially, the remarkable gyro rolling mode solution of triboelectric nanogenerator (TENG) features its sensitivity, multiple directions and robustness. Finally, the triboelectric-electromagnetic hybridized module was well validated in an autonomous underwater vehicle (AUV) in the Huanghai Sea. This work not only provides an effective and sustainable way toward large-scale blue energy scavenging, but also reveals TENG′ promising potential on inertial sensing capability for marine equipment.

Thin Films in Triboelectric Nanogenerators for Blue Energy Harvesting: Fabrication, Characterization, and Modeling

Renewable energy attracts many researchers as the non-renewable one has negative environmental impacts and limited availability. One of the main types of renewable energy is the blue energy where electricity is generated by water waves using triboelectric nanogenerators (TENGs). Thin films play an important role in the performance and therefore the efficiency of TENGs as they represent the electrodes between which electrons move producing electricity. In order to increase the generated electricity from TENGs, the properties of these electrodes should be modified. Therefore, in this paper, nano- and micro-size thin films are fabricated and characterized by measuring the geometrical parameters and electrical properties. Thin films are fabricated using aluminum with thicknesses 0.5 μm and 1.5 μm on acrylic substrate and 0.5 μm copper film on different types of dielectric materials including PVC and polystyrene. Atomic force microscopy is used to measure the geometrical parameters of the fabricated films including thickness and surface roughness. Also, Gwyddion software is used for the grain size evaluation. On the other hand, Keithley is used for measuring the electrical properties including electrical conductivity and sheet resistance. It is found that the electrical conductivity of aluminum films is inversely proportional to the thickness. The corresponding measured values of the electrical conductivity of the fabricated thinner and thicker aluminum films equal 1.7 x 107 (Ω.m)-1 and 1.4×107 (Ω.m)-1, respectively. Whereas, the electrical conductivity of the fabricated copper film equals 8.8×107 (Ω.m)-1. In addition, the temperature effects on the electrical conductivity are studied. Finally, simulation of a TENG using COMSOL software is accomplished in order to evaluate the electrical outputs of potential, charge, and energy.

Monocharged electret based liquid-solid interacting triboelectric nanogenerator for its boosted electrical output performance

Among various energy harvesters to effectively use the renewable clean energy sources, the triboelectric nanogenerator (TENG) is in the spotlight due to its advantages of material and processing diversity. Especially, the novel TENG utilizing an interaction of moving liquid on the hydrophobic solid surface instead of a solid-solid interaction, called liquid-solid interacting TENG (L-S TENG), is regarded as a promising platform for harvesting ubiquitous liquid-solid contact and separation such as an ocean wave or a falling rainwater. However, the electrical output performance from the L-S TENG is too low to be practically utilized as a power source in our daily lives and further, the L-S TENG has demonstrated an issue in its output degradation with ions containing aqueous solutions. In this study, instead of introducing microscale or nanoscale surface topography on the L-S TENG to enhance the triboelectricity, the strategy to improve induction of electrical charges during its operation is proposed to amazingly enhance its output performance. More than 1000 times increase of peak power with high flexibility and high light transmittance (~92%) can be easily achieved by artificially injecting the electrical charges on amorphous fluoropolymer. The proposed strategy shows the possibility to generate more than 80 V with seawater-like electrolyte solution without application of cumbersome and complicated processes. In this regard, this study would broaden the applicability of the L-S TENG by effectively overcoming one of the fatal drawbacks of the L-S TENG and eventually, it would enable practical use of the L-S TENG such as blue energy harvesting.

Active control of salinity-based power generation in nanopores using thermal and pH effects.

Harvesting blue energy from saline solutions has attracted much attention recently. Salinity-based power generation in nanopores is governed by both passive factors (e.g., the nanopore diameter, nanopore length, nanopore material, and pore density) and active factors (e.g., the concentration gradient, temperature, and pH environment). The present study performs COMSOL multiphysics numerical simulations based on the Poisson–Nernst–Planck equations, Navier–Stokes equations and heat transfer equation to examine the combined effects of the temperature gradient and pH level on the diffusion voltage and maximum power generation in single silica nanopores with lengths of 100 nm and 500 nm, respectively. In performing the simulations, the pH value is adjusted in the range of pH 5–11, the salinity concentration gradient is 100-fold and 1000-fold, respectively. Three different thermal conditions are considered, namely (1) isothermal-room temperature (298 K); (2) asymmetric thermal (temperature of low-concentration reservoir and high-concentration reservoir are 323 K and 298 K, respectively); and (3) isothermal-high temperature (323 K). The results show that the generated power varies significantly with both the pH level and the temperature conditions. In particular, the asymmetric thermal condition yields an effective improvement in the power generation performance since it reduces the surface charge density on the surface of the nanopore near the low-concentration end and therefore suppresses the ion concentration polarization (ICP) effect. The improvement in the energy harvesting performance is particularly apparent at pH levels in the range of 9–10 (about 100% higher than that of pH 7). Overall, the results confirm the feasibility of using active factors to enhance the power generation performance of salinity gradient-based nanopore systems.

Triboelectric nanogenerators for a macro-scale blue energy harvesting and self-powered marine environmental monitoring system

TENG is not only a promising candidate for harvesting blue energy, but also an indispensable picture puzzle in intelligent ocean.

A teeterboard-like hybrid nanogenerator for efficient harvesting of low-frequency ocean wave energy

Recently, a large number of triboelectric nanogenerators (TENGs) have been explored to harvest blue energy from the ocean. In this work, a teeterboard-like hybrid nanogenerator (named as THNG) is fabricated for harvesting the widely distributed low-frequency ocean wave energy. The unique design includes a multi-layered TENG at one end of the teeterboard and an electromagnetic generator (EMG) at the other end. Benefiting from the novel design, the TENG unit can realize a full-packaged and light-weight structure that can be easily triggered by ocean waves with a low-frequency and it demonstrates desirable performance without environmental impact. The motion amplitude of EMG unit can be easily adjusted by changing the fulcrum position between the TENG and EMG. Even in a slight wave state, the EMG can still move with a reasonable amplitude to generate an ideal electrical output, which overcomes the problem of low efficiency of EMG when working at low frequency. Moreover, because of the innovative design, the THNG can automatically adjust the direction to match the incident wave and consequently capture wave energy from any directions. The impact of wave frequency, pitch angle and fulcrum position to the performance of THNG have been systematically investigated, and the maximum voltage of TENG and maximum current of EMG reach 760 V and 10 mA respectively at the optimum working condition. Moreover, the as-fabricated THNG is capable of charging commercial capacitors, lighting more than 200 LEDs and driving a rain-drop senor directly under simulated tide flow. This work presents an innovative and reliable approach towards large-scale low-frequency (<0.8 Hz) blue energy harvesting and applications.

Origami-inspired electret-based triboelectric generator for biomechanical and ocean wave energy harvesting

One of the critical issues for the conventional TENGs for applications in biomechanical and blue energy harvesting is to develop adaptive, simple-structured, high performance but low-cost TENGs for the complex excitation conditions. To solve this problem, we propose an origami-inspired TENG integrated with folded thin film electret, which can be facilely formed from two pieces of liquid crystal polymer (LCP) strips through high degrees of paper folding. It has been proved efficient for harvesting energy from both sinusoidal vibrations and impulse excitations which are universally existed in the ambient environment. Double-side corona discharging process is employed to maximize the charge density generated by the electret thin films. Attributing to the excellent elastic property of self-rebounding spring structures based on the origami design, the flexible TENGs can be readily integrated into smart shoes, floors, watches and clothes for wearable and energy harvesting applications. Triggered by impulse excitation of gentle finger tapping, instantaneous open-circuit voltage and short-circuit current of 1000 V and 110 μA, respectively, have been obtained with a remarkable peak power density of 0.67 mW/cm3 (or 1.2 mW/g). A spherical floating buoy generator integrating multiple origami TENGs is further developed to harvest ocean wave energy at various frequencies and amplitudes as well as in arbitrary directions. The outcomes of this work offer new insights of realizing single structured TENG designs for multifunctional applications.

Matryoshka-inspired hierarchically structured triboelectric nanogenerators for wave energy harvesting

There is a tremendous interest to harvest ocean wave energy due to its promising advantages of high-power density, wide distribution, independence of time of day, weather or seasons, and sustainability. However, most of the current energy harvesters or converters based on electromagnetic generators are suffering from unsatisfactory efficiency at low ocean wave triggering frequency and have the drawbacks of complex design, high cost and ease of corrosion in seawater. In this work, we report a matryoshka-inspired hierarchically structured triboelectric nanogenerator (HS-TENG) by nest-assembling multiple shells with decreasing sizes for effectively harvesting low-frequency wave energies with low-cost, high power density and high efficiency. As a proof-of-concept, we have fabricated a three-hierarchical-level HS-TENG by nesting three spherical acrylic shells filled with polytetrafluoroethylene (PTFE) balls into the gap spaces between the neighboring shells. The important factors that may affect the energy harvesting performance of the HS-TENG are studied, including the size and number of moving balls, the diameter of the holding shell, the amplitude and frequency of wave actuation, as well as the orientation angle between wave motion direction and electrode gap. It is demonstrated that the HS-TENG has superior output performance over the traditional single ball TENG (SB-TENG), with a maximum output peak power of 544 μW at a low frequency of 2 Hz, more than 6.5 times of that obtained by a SB-TENG with the same size, capable of driving different wearable electronics. Based on the optimized design, we further demonstrate that a HS-TENG network formed by a 3 × 3 device array can directly lighten dozens of light-emitting diodes and power an electronic thermometer for monitoring water condition, indicating its capability in effectively harvesting water wave energy for potential large-scale deployment in the ocean. This study provides an innovative hierarchical structure that can effectively improve the output performance of TENGs and paves the way for developing next-generation high-performance TENGs for blue energy harvesting.

A High-Power Density Triboelectric Nanogenerator for Harvesting Wave Energy

The global power by waves breaking around the coastlines worldwide has been estimated to be 2-3TW, and if wave energy is collected on open oceans, the global wave power is estimated to be one order of magnitude larger[1]. The water wave energy could turn out to be an even more benign source of power than wind, due to its abundance in the ocean [2]. Although it is a promising prospect for harvesting wave energy, most technologies for capturing wave power still remain in the testing phase. Currently, traditional devices usually harvest wave energy with complex hydraulic or mechanical structures and they drive an electromagnetic generator by transforming the energy from the water waves into rotary motion or linear reciprocal motion. However, these current oceans wave energy apparatuses exhibit unsatisfactory energy harvesting efficiency, high cost, and other methods of harvesting energy would have to be implemented [3-4]. In this work, a high-power density triboelectric nanogenerator (HPD-TENG) is designed and systematically investigated.This HPD-TENG is designed to be built by multiple units made of PTFE balls and 3D printed arc surface coated with melt adhesive reticulation nylon film. The integration of power generation model together with the kinetic model for the HPD-TENG is proposed and studied. The HPD-TENG can effectively transform arbitrary directional wave energy into electrical energy by utilizing charged balls rolling on optimized arc surface induced by ocean wave excitation. Furthermore, with the power generation units increases from 1 to 10 in one block, the power density increases linearly from 1.03 W/m3 to 10.6 W/m3. This indicates that the power density of the HPD-TENG increases proportionally with the number of units connected in parallel without rectifiers due to its distinctive mechanism and structure. Hence the design of HPD-TENG can be regarded as an innovative and effective approach for large-scale blue energy harvesting through integrating more units to form HPD-TENG networks.