Structure of triboelectric nano generator for collecting low-frequency omnidirectional sea wave energy by using volume effect

Abstract

The floatable instantaneous generator comprises an outer layer in the form of a hemispherical floatable supporting bowl and an inner layer in the form of a liquid-solid triboelectric nano generator (ls TENG); the inner layer includes a fluorinated ethylene propylene (FEP) layer on an inner side of the bowl, a ring electrode on an upper surface of the FEP layer around a periphery thereof, a circular electrode on a bottom surface at a central portion of the FEP layer, and a droplet slidable on the upper surface of the FEP layer. When subjected to open sea waves, the bowl floats and tilts the ls TENG so as to slide droplets on the upper surface of the FEP, thereby creating and disconnecting contact between the ring electrode and the circular electrode and providing power to an electrical circuit connected between the ring electrode and the circular electrode.

Description

TECHNICAL FIELD

[0001] The present invention relates to harvesting of ocean wave energy, and more particularly, to power generation using floating triboelectric nanogenerators. BACKGROUND

[0002] With the increasing severity of energy demand and environmental problems, finding renewable and sustainable energy has become a hot spot of modern research. Among a series of new energies that can replace fossil fuels, ocean wave energy is known for its abundant and relatively stable renewable properties. The ocean covers more than 70% of the earth's surface, and the global ocean wave energy is estimated to be about 10 TW [1]. Therefore, successfully utilizing ocean energy will not only overcome the energy insecurity of conventional fuels, but also provide the possibility of driving economic and technological growth. However, due to the lack of mature technology for open ocean harvesting, ocean energy is only harvested around the coastline, which accounts for 20-30% of the global ocean energy [2].

[0003] There is an urgent need to develop energy harvesting technology for open ocean waves at an affordable cost. However, due to the low frequency and irregular characteristics of ocean wave energy, it is problematic to collect ocean wave energy. Electromagnetic generators are considered the most mainstream means of converting motion into renewable new energy, but when targeting ocean wave energy, they face problems such as price, low frequency harvesting effect, etc. However, triboelectric nanogenerators (TENGs) show excellent low frequency energy harvesting capability and are one of the best candidates for harvesting ocean energy. Triboelectric nanogenerators (TENGs) utilize low frequency mechanical stimuli with energy conversion efficiency up to 70.6% [3], making them excellent candidates for economic energy harvesting in open ocean environments. So far, many architectures, including but not limited to ball-embedded [4-12], liquid-activated [13-16], pendulum [17-20] and spring-assisted [21-24] types, have successfully converted open ocean energy into electricity, but all of these devices suffer from low output voltage of <300 V and output current of <100 μΑ.

[0004] In the research of TENG-based ocean wave energy harvesting, traditional solid-solid frictional electric nanogenerators (ss-TENGs) have been able to achieve excellent performance; however, they also face many inevitable problems, such as the problem of lost friction material when the two friction materials are in complete contact. For example, one study

[17] introduced a triboelectric nanogenerator that can harvest ocean wave energy in all directions. Its central symmetric structure ensures stable energy harvesting in disordered waves. However, due to its solid-solid contact electrostatic transfer mode (ss-TENG), the contact effect between the two friction materials reduces its effectiveness. At the same time, due to the mass pendulum with the lower end fixed and the balancer, the overall structure is complex and cumbersome, greatly hindering its ability to be commercialized.

[0005] Chinese patent CN202310684948A relates to a triboelectric nanogenerator for harvesting wave energy and its power generation system, which includes a substrate, a first cylinder, a slip ring, a transmission device, a second cylinder, a power generation component, and a floating ball. The generator can increase the relative rotation speed and relative rotation process of the two cylinders, convert low-frequency ocean energy into high-frequency mechanical energy, and thus more effectively output electrical energy. However, its structure is very complex, and due to the direct contact between solids and solids, material wear is easily caused. This significantly increases the cost of the invention. Similarly, US Patent Application No. US11545915B2 discloses a solid contact triboelectric nanogenerator in a closed spherical shell. The electrical signal is generated by a plurality of small balls rolling back and forth between the inner and outer shells. It has the advantage of good air tightness, so it is easy to float in water and does not require other supporting equipment. However, due to the design of the electrode position, it does not have the ability to collect ocean wave energy in all directions. At the same time, when nested in multiple layers, the manufacturing cost is high and the manufacturing cost is large.

[0006] To solve the problem of solid-solid contact, researchers have developed contact-separated ss-TENGs with complex mechanical structures, as well as ss-TENGs that utilize non-contact modes, etc. Although the results are optimized, one performance is usually sacrificed to obtain another performance improvement. This does not fundamentally solve the problem.

[0007] Recently, with the help of droplets in direct contact with electrodes, some studies have achieved instantaneous output voltage and current of up to about 460 V and 880 μA, respectively [25, 26]. In one study [8], a liquid-solid triboelectric nanogenerator for harvesting ocean wave energy takes full advantage of the ability of close contact between liquid and solid. Due to its structural design, it can collect energy at low frequencies. However, it does not have the ability to collect energy efficiently, nor does it have the ability to collect energy omnidirectionally. In another study

[13] , a liquid-solid triboelectric nanogenerator is based on a tubular container. It has high energy output efficiency and can produce a large amount of transferred charge at lower frequencies. It uses commercially available FEP tubes, which greatly reduces its production cost. But its shortcomings are also very obvious. Since it is actually a tubular container, it only has a single energy collection direction. At the same time, it has no platform to support, which means it has to be used with some stable equipment, which makes it very difficult to use. SUMMARY

[0008] According to the present invention, open ocean energy harvesting independent of wave direction is achieved with a floatable generator featuring asymmetric capacitance on the electrodes. Instead of using conventional solid-solid electrostatic induction, the present invention uses a small amount of droplets to form a liquid-solid triboelectric nanogenerator (ls-TENG) to solve the problem of frictional contact. The liquid has good fluidity and amorphous, so it can be in full contact with the solid surface, without wearing the frictional material surface of the solid. By utilizing ocean wave energy, the liquid can slide on the surface of the frictional material and generate current through electrostatic induction. Although liquid-solid electrostatic induction can collect ocean wave energy in an excellent and stable manner, due to the soft contact between the liquid and the solid, they generate little energy, and it often takes a long time to collect. The energy that the ss-TENG can collect in a short time. Therefore, in order to overcome this problem, a ring-shaped electrode is provided on the top of the device. This generates a volume effect mechanism that greatly increases the performance of the ls-TENG.

[0009] The device of the present invention has a hemispherical float-shaped structure for liquid-solid triboelectric nanogenerator. By adding a copper ring electrode at the edge, a volume effect is introduced to this hemispherical float-shaped droplet-based triboelectric nanogenerator (HFD-TENG), which enables 2.4 ml deionized water to generate voltage and current signals close to 110 V and 25 μΑ from simple reciprocation. Due to the unique ring design, the HFD-TENG can collect energy again in the cycle compared to the conventional ls-TENG, which greatly increases the energy efficiency of the HFD-TENG. By changing the salinity or pH of the liquid, the performance of the device can be further improved to more than 240 V and 90 μΑ. This central symmetric hemispherical structure ensures that the HFD-TENG has stable energy collection performance in all directions. At the same time, this hemispherical float structure ensures that the HFD-TENG does not need additional gravity devices to maintain its stable performance in the waves. In summary, the HFD-TENG is easy to manufacture, can collect energy indiscriminately at 360°, and is extremely energy efficient. Therefore, it is very suitable for providing a strategy for large-scale all-weather collection of blue energy.

[0010] By using the instantaneous switching of the closed-loop circuit and the asymmetric capacitor, it is possible to significantly enhance the amplitude of the output voltage and current while the amount of charge generated remains similar. From the point of view of omnidirectionality, cost, performance and scalability, the floatable generator shows a practical advantage for open ocean energy harvesting. BRIEF DESCRIPTION OF DRAWINGS

[0011] The foregoing and other objects and advantages of the present invention will become more apparent from the following detailed description and accompanying drawings, in which like reference numerals refer to like elements in the several views, and in which:

[0012] Figure 1A is a schematic of an open ocean with a hemispherical float-shaped droplet-based triboelectric nanogenerator (HFD-TENG) near a ship, Figure 1B is a series of illustrations showing the movement of the droplet in the hemispherical structure, and Figure 1C shows the change of output voltage over time;

[0013] Figure 2A is a schematic of a floatable instantaneous generator, where the insets represent the thickness (bottom left) and hydrophobicity (bottom center) of the contact electrification layer (FEP), and the optical image of the device (bottom right), Figure 2B shows the output current measured from the FEG at the same wave frequency of 0.28 Hz and droplet volume of 2.4 ml, with three different configurations for electrical connection, (left) open loop configuration to circular electrodes; (center) open loop configuration to ring electrodes; (right) closed loop configuration; Figure 2Cis a schematic of the working principle of the FEG, and Figure 2D is an equivalent circuit model of the FEG;

[0014] Figure 3A is a schematic of the reciprocating swing motor, and Figure 3B is a schematic of the device oscillation in the reciprocating swing motor;

[0015] Figure 4A is a schematic of the reciprocating swing motor relative to the output current, Figure 4B is a schematic of the device oscillation in the reciprocating swing motor relative to the output current;

[0016] Figure 5 is a plot of the transferred charge amount of the FEG with three different configurations (left, open loop configuration to a circular electrode; center, open loop configuration to a ring electrode; right, closed loop configuration);

[0017] Figure 6 is a plot of the characteristic instantaneous current peak and the fitted curve of the model, where the values in the plot indicate the parameters taken from the fit;

[0018] Figure 7A is a plot showing the instantaneous output current as a function of the droplet volume employed in the FEG, Figure 7B is a schematic of the behavior of droplets of different volumes moving on the device surface and the related parameters in the equivalent circuit, Figure 7C shows the output current, Figure 7D shows the generated charge measured from a control device comprising symmetric capacitances on the electrodes for comparison, demonstrating the importance of the asymmetry of the capacitances, and Figure 7E shows the output current from a device characterized by continuous switching "on" during the oscillation process, highlighting that the process of instantaneous switching "on" and "off" is a key factor in generating a huge instantaneous output current;

[0019] Figure 8 shows the output current of the FEG containing different amounts of droplets;

[0020] Figure 9A is a series of photos with droplets of different volumes on the FEG, and Figure 9B is a plot of the droplet width, height, and area as a function of the droplet volume;

[0021] Figure 10 is a plot of the current output as a function of the length ratio of the gap to the electrode diameter;

[0022] Figure 11A is a plot of the charge generated from a circular electrode, and Figure 11B is a schematic of a ring electrode;

[0023] Figure 12A is a bar graph showing the instantaneous current peaks from FEGs in contact with tap, pond, river, DI, and seawater, Figure 12B shows current output in the presence of different concentrations of salts containing the same anion but different cations, where cation mobility determines the strength of the current output, Figure 12C shows current output in the presence of different concentrations of salts containing the same cation but different anions, where an increase in anion mobility causes a decrease in current output, Figure 12D shows the addition of salt to a weak Bronsted acid, resulting in FEGs producing instantaneous current peaks, Figure 12E shows current output, voltage, and power from FEGs in contact with 0.5 mM Na2S04solution as a function of load resistance, where power is normalized to the volume of droplet used, Figure 12F shows the normalized charge and power density of FEGs compared to literature data of prior art droplet-based TENGs (from Figure 12E Data), including unidirectional and omnidirectional modes;

[0024] Figure 13 shows current output from FEGs under fluctuation at different frequencies from 0.28 to 0.75 Hz;

[0025] Figure 14 is a plot of charge generated from FEGs in contact with aqueous droplets with different concentrations of Na2S04;

[0026] Figure 15 is a plot of the capacitance of the double layer in contact with aqueous droplets as a function of Na2S04concentration;

[0027] Figure 16A shows the omnidirectionality of FEGs, Figure 16B is a plot of capacitive charging with FEGs, where the inset indicates the equivalent circuit, Figure 16C shows a snapshot of 80 LED lights with FEGs, Figure 16D shows the stability of FEGs over 400 cycles, Figure 16E is a plot of current and charge enhancement as a function of the number of devices, from one to twelve devices, with parallel connection, Figure 16F is a schematic of a “wave” box that simulates real random waves in the ocean, and Figure 16G is a photo of 4 FEGs being driven in the “wave” box, along with the power management circuit, where the power output from the 4 FEGs powers an electronic clock;

[0028] Figure 17A is a schematic of device rotation during oscillation,Figure 17B Device rotation as a function of time is shown when exposed to waves with a frequency and amplitude of 0.25 Hz and 0.1 m, respectively;

[0029] Figure 18 is a plot of the voltage on a 1 μF capacitor when charged by a FEG, subsequently discharged by an electronic calculator, along with simultaneous charging with a pair of devices (0, 4, 8, and 12 devices), where the inset in the upper left depicts the equivalent circuit, the plot in the upper right shows the amplified voltage discharge curve, showing the potential of the FEG continuously powering the calculator; and

[0030] Figure 19 Current output from a single FEG is shown when random waves are applied to the device. DETAILED DESCRIPTION

[0031] The floatable transient electric generator (FEG) according to the present invention is composed of two layers, Figure 1A and Figure 2A ). The inner layer is a thin electric generator or triboelectric nanogenerator (TENG) that includes a circular fluorinated ethylene propylene (FEP) layer or film 10 and a ring 11 and a circle 13 that form Cu electrodes at the circumference and center, respectively. The ring is adhesively attached to the top of the FEP layer 16, while the adhesive circular electrode is located underneath the FEP layer. The FEG is positioned on the inner surface of a hemispherical floatable support acrylic bowl 14, allowing the electric generator to float and be subjected to open sea waves. Liquid droplets that slide across the top of the FEP layer act as a counter-contact electrification material that creates a liquid-solid TENG. The FEP layer 16 has an inherent hydrophobicity that helps the liquid droplets to slide on its surface during sea waves Figure 2A , bottom center). The ring-shaped electrode 11 positioned on top of the FEP layer allows direct contact with the liquid droplets 16, while the circular electrode 13 located underneath the FEP layer 16 is fixed to avoid movement due to waves. In addition, the thin electric generator is tightly bonded to the acrylic bowl surface to seal it completely, protecting the circular electrode 13 from exposure to water Figure 2A , bottom right). The asymmetrical exposure of the electrodes to water (i.e., the ring-shaped electrode is exposed to water while the circular electrode is not) is a key factor in providing transient voltage and current output.

[0032] During construction, all FEGs were washed with ethanol three times to remove pre-charge, followed by a gentle annealing overnight at 80 °C.

[0033] Figure 1Bis a series of illustrations showing the movement of a droplet in a hemispherical structure from a resting position (in which the droplet is only above the central electrode), to a left tilt (in which the ring electrode and the central electrode are connected), to a right tilt (in which the ring electrode and the central electrode are again connected), and finally back to the resting electrode (where only the central electrode is contacted). Figure 1C is a plot of the output voltage as a function of time as the waves cause the droplet to slide from one side of the hemisphere to the other, thus making and breaking contact between the central electrode and the ring electrode.

[0034] Figure 2B shows the current output of the FEG with open loops when the droplet is only above the central electrode, open loops when the droplet is only in contact with the ring electrode, and closed loop configurations in which the liquid droplet bridges the ring electrode and the circular electrode, thus allowing charge to flow through the FEG internal circuitry. For this illustration, a reciprocating swing motor with a frequency of 0.28 Hz was used to oscillate a 2.4 ml droplet of deionized water on the FEP surface Figure 3A and Figure 3B ), thus simulating the droplet motion when the device is subjected to open sea waves. Notably, the FEG produced a high transient current output of 22.80 ± 1.68 μΑ, which is approximately 760 mA or 20 times higher than the values obtained for open loop configurations with only the circular or ring electrode, respectively. The FEG did not show a significant current output when the droplet was rolling on the FEP surface. Once the droplet contacted the ring electrode, the current rapidly rose to 25.3 A Figure 4A within 0.16 ms as the droplet opened the switch in the internal closed loop circuit in the FEG. The current then rapidly decreased with a full width at half maximum of 0.16 ms, indicating a rapid charge redistribution throughout the closed loop. In contrast, the current was found to gradually increase to 0.102 μΑ and then steadily decrease Figure 4B ) once the droplet started to reduce the contact area with the ring electrode. Note that the transient rise in current was also achieved in the open loop configuration with the ring electrode, implying that the direct contact between the electrode and the droplet plays an important role in the transient output. As Figure 5 shown, the amount of charge transferred sharply increased to 16.56 ± 0.39 nC upon contact and then decreased to zero after separation, indicating no charge accumulation on the two electrodes in the cycle.

[0035] Working mechanism of the FEG

[0036] The power generation process of the FEG is divided into four stages, as Figure 2Care shown. Upon contact of the FEP layer or the ring electrode with the water droplet, their surfaces accept a negative charge from the droplet according to the triboelectric series

[27] ; that is, when not in contact with the droplet, the surfaces of all device components are negatively charged. At stage I, the droplet starts to bridge the FEP layer on top of the ring electrode and the circular electrode, thus momentarily closing the looped circuit. At the moment of separation from the circular electrode, the circuit is opened. At stage II, the droplet slides towards the center of the FEP layer and reduces the contact area with the ring electrode, while inducing an overlap with the circular electrode, thus stably closing the circuit. When the droplet is completely separated from the ring electrode, the circuit is opened again. At stages III, IV, the process of switching "on", "off" repeats. During the "on" state, the charge is transferred between the two electrodes to balance the potential built therein. The equivalent circuit is shown. Figure 2D From the circuit point of view, the FEP layer on top of the circular electrode is considered as a capacitor C FEP , where the surface charge generated after electrification with the droplet acts as the top plate, while the circular electrode acts as the bottom plate. The double layer formed at the interface between the droplet and the ring electrode can be considered as a variable capacitor C d , whose value differs with the contact area. The droplet is a resistor and a switch.

[0037] After the switch "on" in the equivalent circuit and the charge transfer is completed, the potential V eq generated in the two capacitors can be given as:

[0038]

[0039] where C d and C FEP are the capacitances of the double layer and the FEP layer, respectively. Q FEP and Q d represent the initial charges stored in C FEP and C d , respectively. Then, the balanced charges can be calculated as:

[0040]

[0041] Then, the amount of transferred charge is calculated as:

[0042]

[0043]

[0044] The charges transferred from each electrode at stages 1 and 3 can be given as:

[0045]

[0046] where Q FEPand Q d are the charges stored in C FEP and C d respectively. According to equations (1) and (2), negative charges migrate from the ring electrode to the circular electrode at stages I and III, and travel back to the ring electrode at stages II and IV, thus delivering power to the external load.

[0047] We can solve such a circuit as a capacitor discharge model with two capacitors and resistors, and the time-dependent discharge current profile can be expressed as:

[0048]

[0049] where R water , R surface and R external denote the resistances of the water droplet, FEP surface and external load, respectively. Assuming that the droplet makes a point contact with the electrode at the moment when the switch is "closed", the capacitance of C d is several orders of magnitude smaller than that of C FEP , such that the magnitude of the current and the discharge time can be simplified as Q d / (C d (R water + R surface + R external )) and C d (R water + R surface + R external ), respectively. Considering the high surface charge on the ring electrode and small C d , a high transient current peak and fast discharge occur when the droplet is in contact with the ring electrode. In contrast, the capacitance of C d becomes negligible compared to that of C FEP while maintaining contact with the ring electrode, as the double layer is much thinner than the FEP layer. Therefore, the magnitude of the current discharge time can be approximated as Q FEP / (C FEP (R water + R surface + R external )) and C FEP (R water + R surface + R external ), respectively, resulting in a low current output and slow discharge. It is worth noting that the gradual decrease in contact area relative to the ring electrode results in a slow increase in the current peak at detachment. It has been found that this equation fits the transient peak data very well, as shown in Figure 6 C d was determined to be 1.79 ± 0.5 pF, which is in good agreement with C FEPCompared to two orders of magnitude lower, and consistent with the prediction of the circuit model. Furthermore, the amount of charge transfer can be estimated using Equations 1 and 2, and the measured charge for the open loop configuration, where the measured charge is set to half of the charge stored in each capacitor

[28] . ring | = |DQ circle The value of |DQ| was determined to be 14.1 nC, comparable to the amount of charge measured for the FEG.

[0050] Device design for transient output maximization in FEGs

[0051] The transient output of the FEG of the present invention can be tuned by different parameters, such as the resistances, capacitances, their charges, and the closing of the looped circuit. One can first examine the variation of the transient current peak as a function of the droplet volume ( Figure 7A and Figure 8 ). As the droplet volume is increased from 0.1 ml to 2.4 ml, the amplitude of the transient peak first increases from 0.4 μΑ to 22.8 μΑ, and then a further increase in the droplet volume leads to a decrease in the current peak. It should be noted that the maximum transient peak occurs when the droplet size approximately matches the size of the gap between the center electrode and the ring electrode. The transient peak in response to different droplet volumes indicates that, in addition to the capacitances and their charges, the output peak can also be manipulated by the resistances in the looped circuit. As shown in Figure 7B , a small droplet relative to the gap leads to a larger surface resistance, while a decrease in the water resistance leads to a decrease in the charge generated in the ring electrode surface. As the droplet size is further increased, the water bridge completely covers the gap ( Figure 9A and Figure 9B ), and then the output peak starts to depend only on the water resistance. The above model can be modified with variable resistances and charges, and this model fits the experimental data very well, as shown in Figure 7A . Furthermore, to gain further insight into the scaling factors of the device, one can vary the length ratio of the gap to the electrode diameter, while matching the droplet size to the gap length ( Figure 10 ), excluding the effect of the surface resistance. It is found that when the length ratio reaches about 0.7, the transient current peak exhibits a maximum of 22.80 μΑ, which can be attributed to the trade-off trend between the water resistance, R water , and Q d . This characteristic indicates that there is a specific length ratio of the gap to the circular electrode when scaling up the device.

[0052] To further investigate the importance of the asymmetry of the capacitances in the closed circuit on the transient current output, a controlled closed-loop device featuring a ring electrode developed underneath the FEP layer was utilized, seeking to increase the capacitance of the ring electrode to a value comparable to that of the circular electrode. Notably, no significant transient peaks were observed when a 2.4 ml droplet was repeatedly rolled over the device Figure 7C ). Using Equation 3 and the charge measured for the open-loop configuration Figure 11A and Figure 11B ), the capacitance of the ring electrode was approximated to be 0.216 nF, which is two orders of magnitude larger than that of the ring electrode in the FEG. Notably, the amplitude of the current peak was 456 times smaller than that of the FEG, while the amount of charge transferred was only 2.4 times smaller than that of the FEG Figure 7D ), implying that the symmetric capacitance of the two electrodes significantly reduced the current output. Moreover, it can be assumed that the process of switching "on" and "off" plays an important role in generating the huge transient current peak, as the charge accumulated in the ring electrode can be instantaneously discharged during the switching process.

[0053] A device was prepared in which the switch of the circuit was always "on" while the droplet was in contact with the ring electrode as a proof of concept by completely covering the bottom surface of the FEP layer with the circular electrode. Although transient current peaks in the range of ~0.3 μΑ to ~1 μΑ had already occurred at the moment of contact with the ring electrode, the amplitude of the peak was substantially low and independent of the difference in droplet volume Figure 7E ). The reduction in the amplitude of the peak can occur due to the continuous balancing of the charge generated in the two electrodes upon switching "on". Interestingly, the fast switching "on" and "off" of the circuit, evidenced by the rapid oscillations, contributed to the enhancement of the current output Figure 13 ), confirming the importance of the switching in generating high transient current output.

[0054] Salt dependence of the transient peak in the FEG

[0055] In addition to deionized water, transient current peaks can also be generated by other water droplets, including but not limited to tap water, pond water, river water, and sea water. Figure 12A It was shown that transient peaks of up to 67.10 ± 13.78 μΑ can be achieved in the case of engaging tap water, and this value was observed to decrease by approximately four times when sea water was used. It is important to note that each aqueous droplet exhibited different salt types and concentrations, resulting in variations in d and d Q Figure 12B and Figure 12Cpeaks are reached at concentrations of 1 mM and 0.5 mM, respectively, and then these values decrease with higher concentrations. Interestingly, it should be noted that the amount of cations influences the amplitude of the transient current peaks before the maximum current value is reached, as well as the concentration at which the maximum current value occurs. In addition, the ionic mobility is responsible for determining the transient current peaks beyond the critical concentration. This transient peak behavior can be attributed to the nature of the double layer formation

[29] . At low concentrations, increasing the concentration allows more cations to approach the negatively charged Cu surface to form the compact layer, thus allowing the double layer to store more charge. After the establishment of the compact Stern layer, both anions and cations compete to migrate to the fixed cations in the diffuse layer. As the ionic concentration increases, the charge remaining within the double layer is mainly neutralized by anions, which is attributed to their fast mobility compared to cations

[30] . Indeed, the charge generated by Na2S04droplets exhibits a consistent pattern related to the transient current response ( Figure 14 ), while the capacitance of the double layer remains almost similar ( Figure 15 ), contributing to rationalizing the observed transient peak behavior. It was also found that the addition of salts to weak Bronsted acids such as acetone, isopropanol, and ethanol helps to impart the ability of the generator to produce transient current peaks ( Figure 12D ), supporting the proposal that the supply of cations to the solvent helps to store more charge in the double layer.

[0056] To investigate the output power from the FEG with salt droplets, a variable resistor and a 0.5 mM Na2S04water droplet were used. Due to Ohmic losses, the current amplitude gradually decreases from 107.6 ± 12.2 μΑ as the external load increases, while the output voltage exhibits the opposite trend, reaching up to 310.8 ± 14.9 V at a load of 5 GΩ ( Figure 12E ). At an external resistance of 1 MΩ, the corresponding output power reaches a maximum of ~1.2 mW / ml. This volumetric power density (1190.6 W / m 3 ) is higher than any value reported so far for a floatable triboelectric nanogenerator (TENG) for harvesting omnidirectional blue energy (osmotic power) ( Figure 12F )[31, 32]. More importantly, it has been shown that the FEG of the present invention outperforms other floatable TENGs in terms of volumetric charge density (31.2 mC / m 3 ), which is particularly advantageous for practical applications [8, 13, 14, 26, 33, 34]. When the FEG is repeatedly swung, the potential energy of the device is converted into electrical energy, corresponding to E potential = mgh and E electric= Pt, where m is the mass of the device, g is the acceleration due to gravity, h is the height difference. P and t represent the maximum power output and duration of each cycle, respectively. The relationship η = E electric / E potential The estimated energy conversion efficiency η = 52.2%, which is comparable to the values reported for TENGs [16, 35].

[0057] Practical applications of FEG

[0058] The symmetric device architecture of the FEG of the present invention results in stable energy harvesting from omnidirectional wave motion Figure 16A , which potentially benefits blue energy harvesting as the FEG is shown to have experienced rotation while oscillating on the ocean even in the absence of wind Figure 17A and Figure 17B ). Capacitor charging was evaluated with the FEG and rectifier unit, where 0.22 μF, 0.47 μF, 0.68 μF, 1 μF, and 4.7 μF capacitors were stably charged to 1 V in 7.7 s, 16.8 s, 24.5 s, 44.3 s, and 213.2 s, respectively Figure 16B . The rectified electrical output of the FEG provided successful powering of 80 light emitting diodes (LEDs) Figure 16C , and the electrical output over 400 cycles demonstrated its long-term stability in contact with tap water Figure 16D . The output current and generated charge can be linearly improved by the parallel connection of multiple FEGs, achieving up to 1.2 ± 0.1 mA and 0.4 μC, respectively, with 12 FEGs Figure 16E . With the significant charge generated from the FEG of the present invention with a power management circuit composed of a rectifier and a capacitor, the discharge time of the capacitor at 1 V was successfully delayed up to eight times compared to the discharge time without the FEG device, and the capacitor maintained a constant voltage of 0.5 V even during continuous discharge Figure 18 . This result demonstrated the potential of the FEG to continuously power a calculator. Finally, the practical performance of the FEG was investigated for random fluctuations of water in a plastic container to simulate realistic fluctuation conditions in the ocean Figure 16F . Although the current output exhibited large variations in the range of 10-120 μA, significant instantaneous current peaks were observed Figure 19 , allowing successful powering of LEDs and an electronic clock Figure 16G .

[0059] Accordingly, the present application provides a floatable generator consisting of asymmetric electrodes and droplets on a charged layer. It outperforms conventional floatable generators in both power and charge density. The asymmetric capacitance of each electrode, and the transient switching of the closed loop circuit caused by the rolling of the droplets on the surface, significantly enhances the magnitude of the output current while the amount of charge produced remains similar. Moreover, the ion injection into the droplets improves the amount of charge generated, resulting in a high output power density of 1190.6 W / m 3 and a significant charge density of 31.2 mC / m 3 , far exceeding the previous records for floatable TENGs. Experimental exploration under realistic environmental conditions has demonstrated the potential of the floatable generator for blue energy harvesting. These demonstrations of omnidirectionality, stability, and scalability open a new avenue for continuous powering of electrical devices using floatable generators, even under low-frequency mechanical stimulation.

[0060] The above merely provides a specific implementation of the present application, and is not intended to limit the protection scope of the present application. Any modification or substitution apparent to those skilled in the art shall fall within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

[0061] References

[0062] The references cited in this application are incorporated herein by reference in their entirety and as follows:

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[0098] While the application has been explained in relation to certain embodiments, it will be apparent to those skilled in the art that various modifications can be made to the application once this teachings are fully appreciated. It is, therefore, to be understood that the presently disclosed application is intended to cover all such modifications that are within the scope of the application as set out in the following claims.

Claims

1. A floatable transient generator comprising: an outer layer in the form of a hemispherical floatable support bowl; and an inner layer comprising a layer of fluorinated ethylene propylene (FEP) on the inner side of the bowl, an annular electrode on the upper surface of the FEP layer around its circular perimeter, a circular electrode on the bottom surface at the central portion of the FEP layer, and a droplet that is slidable on the upper surface of the FEP layer, together forming a liquid-solid triboelectric nanogenerator (ls TENG); wherein, when subjected to open sea waves, the bowl causes the ls TENG to float and tilt so as to cause the droplet to slide on the upper surface of the FEP, thereby forming and breaking contact between the annular electrode and the circular electrode, and providing electrical power to a circuit connected between the annular electrode and the circular electrode.

2. The floatable transient generator of claim 1, wherein, The annular electrode and the circular electrode are made of copper.

3. The floatable transient generator of claim 1, wherein, The annular electrode and the circular electrode are adhered to the FEG layer.

4. The floatable transient generator of claim 1, wherein, The FEP layer has an inherent hydrophobicity that facilitates sliding of the droplet on its surface.

5. The floatable transient generator of claim 1, wherein, The bowl is made of an acrylic material.

6. The floatable transient generator of claim 1, wherein, The ls TENG is tightly bound to the acrylic bowl surface to completely seal it, thereby protecting the circular electrode from exposure to water.

7. The floatable transient generator of claim 1, wherein, During construction, the transient generator is washed with ethanol three times to remove pre-charge, and then annealed gently overnight at 80°C.

8. A circuit for powering electrical devices, the circuit comprising at least two floatable transient generators connected in parallel.

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