Full-liquid friction nano-generator for collecting distributed energy

Abstract

The invention relates to comprehensive research on main mechanisms of contact electrification in various liquid-liquid systems, and provides a total liquid friction nano generator (TENG) with optimized materials and structures, which is used for collecting energy from rainwater. Embodiments of the provided all-liquid TENG are capable of producing high charge density (e.g., 3.63 [mu] C / L) and have high output stability (e.g., crest factor approximately equal to 1.1) and longer effective contact electrification time. In some embodiments, based on direct current characteristics, energy collected from rainwater may be directly supplied to electronics, and a self-powered rainfall sensor may also be implemented. Embodiments of the present invention provide full liquid systems suitable for use in distributed green energy sources, passive sensors, and other self-powered devices.

Description

[0001] CROSS REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Application Serial No. 63 / 376,915, filed on September 23, 2022, the entire contents of which, including any figures, tables, or drawings, are incorporated herein by reference. Background of the Invention

[0004] As one of the most widely distributed water resources, rainwater contains huge energy, but it has not been effectively utilized so far. Triboelectric nanogenerator (TENG) is a distributed method based on contact electrification, which can convert tiny mechanical energy into electrical energy. Benefiting from the large and renewable contact interface in liquid-liquid system, all-liquid TENG is further expected to achieve efficient charge transfer. However, the limited understanding of the liquid-liquid contact electrification mechanism restricts its development. Summary of the invention

[0005] Embodiments of the present invention provide a means for comprehensively studying the dominant mechanism of contact electrification in various liquid-liquid systems, and provide an all-liquid TENG with optimized materials and structures for collecting energy from purified water (including but not limited to rainwater). The all-liquid TENG embodiment provided by the present invention is capable of producing a high charge density (e.g., 3.63 μC / L) and has high output stability (e.g., crest factor ≈ 1.1) and a long effective contact electrification time. In some embodiments, based on the characteristics of direct current, the energy collected from rainwater can be directly supplied to electronic devices, and self-powered rainfall sensors can also be realized. Embodiments of the present invention provide an all-liquid system suitable for distributed green energy, passive sensors, and other self-powered devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 A schematic diagram of a rainwater-based all-liquid TENG system for energy harvesting according to an embodiment of the present invention is shown. a) Schematic diagram of the use of the provided all-liquid TENG system. i) The generated raindrops can rise spontaneously, promoting electron transfer, thereby generating positively charged water droplets in the HFE. ii) The electrostatic induction of the positively charged water droplets can generate a displacement current between the electrode ring and the ground. b) Three states of water droplets in the all-liquid TENG, including: i) generation, ii) approach, and iii) distance. c) Periodic short-circuit current generated in the three states of water droplets. d) An embodiment of the present invention is compared with the all-liquid TENG system of the prior art [23,26] in terms of charge density, effective contact electrification time, and output stability.

[0007] Figure 2The study of the liquid-liquid contact electrification mechanism in different liquid-liquid systems according to various embodiments of the present invention is shown. a) Schematic diagram showing three existing theories of liquid-liquid contact electrification, including group dissociation, preferential ion adsorption and electron transfer. Before liquid-liquid contact electrification, the original dissociable groups, free ions and electrically neutral molecules will form dissociated groups and dissociated ions, adsorbed anions, and transferred electrons and adsorbed cations after contact electrification. b) Graph of the change in charge of the oil / water layer during liquid-liquid contact electrification, revealing the transfer of positive and negative charges at the liquid-liquid interface caused by liquid-liquid contact electrification. For each liquid-liquid system, at least three bottles of oil-water mixture were prepared, such as Fig. 6A As shown, at least twenty samples were extracted from each bottle for charge measurement at the same time to obtain the average value for each bottle, which is shown as a point in (b). The average and standard deviation of all samples in different bottles are shown as a bar graph and error bars in (b). c) Graph of pH changes after the formation of oil / water emulsions, revealing the changes in free OH- and H+ in the water phase. For each liquid-liquid system, at least four oil / water emulsion samples were prepared and each sample was measured at least twenty times to obtain the average value of each sample, which is shown as a point in (c). The average and standard deviation of all test results for different samples are shown as a bar graph and error bars in (c). d) Graph showing the increase in H+ concentration in the emulsion and the charge transferred between the oil and water layers. e) Graph showing the relationship between the zeta potential of Hex, HFE and OA emulsions and the HCl / NaCl concentration, revealing the coexistence mechanism of liquid-liquid contact charging. f) Schematic summary of the dominant mechanism and coexistence mechanism in HFE-water, Hex-water and OA-water systems. g) Graph showing the effect of H+ ions on the zeta potential of Hex, HFE and OA emulsions, expressed as the difference in zeta potential between an emulsion containing HCl and an emulsion containing the same amount of NaCl.

[0008] Figure 3 According to an embodiment of the present invention, the key design parameters of the rainwater-based all-liquid TENG are evaluated. a) Schematic model of the all-liquid TENG system, used to calculate the induced charge on the electrode ring and the corresponding short-circuit current. b) The electric field of a water droplet moving in the all-liquid TENG is simulated using COMSOL to calculate the short-circuit current. c) A comparison chart showing the short-circuit current during the movement of a water droplet obtained by the schematic model and the simulation calculation. d) A rainwater simulation liquid (5×10 -6Figure 2. Graph showing the ratio of transferred charge in liquid-liquid contact electrification (L-LCE) between HFE, Hex and OA in MHCl solution. e) Graph showing the ratio of transferred charge in liquid-liquid contact electrification at different contact distances. f) Graph showing the ratio of transferred charge in liquid-liquid contact electrification at different salt concentrations in water. g) Graph showing the short-circuit current output when using the optimized setting parameters. h) Graph showing the generated charge in the all-liquid TENG calculated by the short-circuit current.

[0009] Figure 4 According to an embodiment of the present invention, a DC all-liquid TENG for energy storage and load driving is presented. a) Alternating current generated in a conventional prior art TENG. b) A typical prior art circuit utilizing alternating current generated by a TENG, in which a rectifier is required. c) According to an exemplary and non-limiting embodiment of the present invention, a DC power generated by an all-liquid TENG with a low crest factor is presented. d) A circuit utilizing direct current in this exemplary and non-limiting embodiment is presented, in which no rectifier is required, showing the advantages of reducing switching energy losses and miniaturization of the device. e) Schematic diagram of a capacitor model of an all-liquid TENG embodiment. f) A graph showing the open circuit voltage output as the energy generation process progresses. g) A graph showing the voltage change of a capacitor (1 μF) during the energy storage process, including a fast charging process and a linear charging process. h) A graph showing the use of energy stored in a capacitor to light up an LED and related images.

[0010] Figure 5 Demonstration of the application of rain-based all-liquid TENG and self-powered sensor according to an embodiment of the present invention. a) Graph showing the variation of open circuit voltage over time at different flow rates. The inset is the linear relationship between open circuit voltage and total rainfall. b) Graph showing the variation of short circuit current over time at different flow rates. The inset is the linear relationship between open circuit voltage and real-time flow rate. c) Image showing an all-liquid TENG-based passive rainfall sensor and alarm system according to an embodiment of the present invention, showing an outdoor setting (scale: 30 mm). d) Demonstration of an automated rainfall alarm system based on an all-liquid TENG, which can monitor the total rainfall based on the generated open circuit voltage, display the total rainfall on an LCD screen when the rainfall is below the warning line, and issue an excessive rainfall warning when the rainfall exceeds the warning line.

[0011] Figures 6A-6DThe process of quantifying the charge change in liquid-liquid contact electrification (L-LCE) according to an embodiment of the present invention is shown. (6A) Liquid samples are prepared by rotating emulsions of HFE-water, Hex-water and OA-water to separate the two liquids under centrifugal force. (6B) Photos of the oil layer and water layer after separation, including: i) oil layer in HFE-water system, ii) water layer in HFE-water system, iii) oil layer in Hex-water system, iv) water layer in Hex-water system, v) oil layer in OA-water system, vi) water layer in OA-water system (scale: 100 μm). (6C) A graph showing the average charge of the water layer and HFE layer before and after liquid-liquid contact electrification (0.8 ml sample). For each liquid-liquid system, at least three bottles of oil-water mixture were prepared, and at least twenty samples were extracted from each bottle for charge measurement. Fig.6D Shown Figures 6A-6C The relationship between.

[0012] Figure 7 The process of measuring the charge density near the liquid-liquid interface according to an embodiment of the present invention is demonstrated. (a) The liquid sample is pumped out dropwise to measure the cumulative charge of all falling droplets, and measurements are performed in (b) HFE and water system, (c) hexadecane and water system, and (d) oleic acid and water system, respectively. The charge values ​​measured within 30 seconds before and after the liquid-liquid interface are differentiated (or variable step differentiation is performed when the data is step-type) and smoothed to obtain the "charge density-time" result. By defining the starting point and end point of the valid data as -50% and 50%, respectively, (e) the charge distribution near the oil-water interface is obtained, which is represented by the changing trend of the charge density near the interface (x=0%). The positive trend approaching the interface indicates that the liquid becomes more positively charged near the liquid-liquid interface, and vice versa.

[0013] Figure 8 A comparison chart showing the structural influence of contact distance on short-circuit current and the influence of contact distance on charge transfer during liquid-liquid contact electrification according to an embodiment of the present invention is shown, showing the positive correlation between contact distance and liquid-liquid contact electrification, and the negative correlation between contact distance and short-circuit current.

[0014] Fig. 9 The equivalent circuit model according to an embodiment of the present invention is shown. The output voltage is given by formula [57,59]: where Q is the charge transferred from the main electrode to the reference electrode. Since the output voltage V is equal to 0 under short-circuit conditions, the short-circuit charge Q SC It can be expressed as: Q SC =V OC ·C, where C is approximately a constant (C0) during operation because the electrodes of the all-liquid TENG are fixed

[56] . Therefore, the short-circuit current can be expressed as:

[0015] Fig.10 Graph showing the average charge of deionized water (DI water) samples added by different pipettes / pipettes according to embodiments of the present invention.

[0016] Fig.11 Demonstrate that according to an embodiment of the present invention, through data processing Get the graph of k values ​​in formula (4). First, from To obtain a uniform current, k is equal to the uniform current peak value. The approaching value of .

[0017] Fig.12 Continuous photographs of the generation and rising process of water droplets taken from side and top perspectives according to an embodiment of the present invention are shown (the water droplets are dyed with methylene blue), indicating that there is no direct contact between the water droplets and the electrode ring.

[0018] Fig.13 Two different all-liquid TENG systems for water-based energy harvesting according to embodiments of the present invention are shown. In panel (a), when the density of oil is greater than that of water, the generated raindrops can spontaneously rise under the action of gravity. In panel (b), when the density of oil is less than that of water, the generated raindrops can spontaneously fall under the action of gravity. This can be used in experimental settings to measure the ratio of transferred charges in liquid-liquid contact electrification (L-LCE) between rainwater and (a) HFE, (b) Hex, and OA. For some HFE-water-based L-LTENG embodiments, water droplets are generated from the outlet at the bottom of the HFE and rise through the electrodes by buoyancy. For some Hex-water and OA-water-based L-LTENG embodiments, since the density of Hex and OA is lower than that of water, water droplets are generated from the outlet at the top of Hex or OA and fall under the action of gravity. By controlling the relative distance between the outlet and the electrode ring to be the same, the contact electrification process and electrostatic induction process occurring in these two settings are the same.

[0019] Fig.14 The current (I SC ) and the speed at which friction occurs, including the speed at which the droplet expands during its generation (V g ) and the velocity of the water droplet rising (V r ). a) The short-circuit current I generated SC It consists of two parts: I SC_g Produced by the droplet generation process, I SC_r Produced by the rising process of water droplets, respectively affected by V g and V r b) The experimental results show that SC and V gThe correlation between the measured I SC Overall, V g There is a positive correlation, which is consistent with the relationship between speed and energy generation in most other TENG devices. SC_g With V g c) At different V r Next Generation I SC_r Theoretical data show that the generated current amplitude varies with V r increases, but the generated current has no effect on V g The change of V r more sensitive to changes.

[0020] Fig.15 Schematic diagram of pA-level current measurement using a Keithley 6514 electrometer according to an embodiment of the present invention is shown. a) Schematic diagram of the experimental setup. The L-LTENG is covered by a Faraday cage for electrostatic shielding, and the electrometer is set to pA-level current measurement. b) The actual measured current noise is about fA-level, which meets the requirements of pA-level current measurement. DETAILED DESCRIPTION

[0021] Green energy and sustainable development can be achieved by converting ambient energy into electrical energy [1-3]. The traditional method is to collect large-scale energy through electromagnetic generators and then transmit it through centralized power grids, such as wind power plants or hydroelectric power plants [4,5]. However, the large-scale energy required to drive bulky electromagnetic generators, the losses in long-distance power transmission, and the fixed location of power grid facilities limit their flexibility and the types of energy that can be efficiently utilized [6]. In contrast, direct-to-consumer nanogenerators use widely distributed energy sources, such as rainwater or slight vibrations in nature, to provide new perspectives for flexible self-powered devices and areas beyond the coverage of the power grid [7,8]. Among them, the triboelectric nanogenerator (TENG) based on contact electrification (CE) provides one of the most flexible, cost-effective and clean options [9]. By establishing an interfacial electrostatic field through contact electrification, the tiny mechanical movement of the friction layer can generate Maxwell displacement current in the TENG [10-12].

[0022] The advantage of all-liquid TENG lies in the compact and reproducible contact interface between liquid and liquid, which can easily achieve a large effective contact area and eliminate surface defects by inducing liquid flow, thereby achieving efficient charge transfer during contact electrification [13,14]. Various hypotheses have been proposed to explain the contact electrification mechanism in liquid-liquid (LL) systems. For example, hydroxide ions are believed to be preferentially adsorbed on the liquid-liquid interface, resulting in the pH-dependent zeta potential of oil-in-water (O / W) emulsions [15-19]. For oils containing dissociable groups, the dissociation of functional groups is regarded as a controllable way to self-charge and stabilize the oil-water interface [20,21]. Recently, simulations and experiments have also shown that electrons can be transferred across hydrophobic liquid-liquid interfaces, resulting in negative zeta potentials for O / W emulsions [22-25]. However, these theories were proposed after studying specific phenomena or single liquid-liquid systems. The lack of comprehensive studies on various systems has limited the understanding of their respective necessary conditions and compatibility in different systems. Therefore, in the few existing all-liquid TENG studies, the selection of materials and structures has not been systematically guided, which limits the control over the generated charge density, effective contact electrification time, and output stability [23,26].

[0023] The embodiments of the present invention allow the systematic study of liquid-liquid contact electrification in different all-liquid systems by studying the changes in charge, pH value and zeta potential, and revealing their respective dominant mechanisms and coexistence mechanisms. The embodiments of the present invention provide a novel all-liquid TENG that uses preferred materials and structures to harvest energy from rainwater ( Figure 1 a, where the density of oil is higher than that of water). HFE was chosen as the friction oil material to make the collected raindrops positively charged by electron transfer ( Figure 1 ai), and designed a ring electrode to generate displacement current ( Figure 1 aii). Due to the fluidity of the liquid friction layer, the contact surface can be continuously refreshed. Therefore, each water droplet gradually becomes positively charged due to the loss of electrons, thus periodically generating displacement current. Figure 1 bi), the short-circuit current basically behaves as a normal number ( Figure 1 c). During the movement of the water droplet, when the positively charged water droplet approaches the electrode ring ( Figure 1 bii), electrons are attracted from the ground to the electrode ring, producing a positive current peak. Similarly, when a positively charged water drop leaves the electrode, electrons move in the opposite direction ( Figure 1 bii), thus generating a reverse peak.

[0024] Through reasonable friction material selection and structural design, the all-liquid TENG embodiment provided by the present invention has advantages in the following aspects: high charge density (3.63 μC / L), long effective contact electrification time (1200 seconds) and high output stability (1 / crest factor ≈ 0.9, defined as the ratio of the root mean square value to the peak value) ( Figure 1 d)[23,26]. Due to the DC characteristics of the generated current, the all-liquid TENG embodiment provided by the present invention can also drive the load without a rectifier, avoiding additional energy loss in the switching device and promoting the miniaturization of the device[9,27]. In addition, its electrical output is linearly related to the rainfall, thus demonstrating the function of passive sensing. With the ability of energy harvesting and self-powered sensing, the all-liquid TENG embodiment provided by the present invention has important applications in building distributed green energy networks and promoting the miniaturization and flexibility of self-powered devices.

[0025] Embodiments of the present invention identify contact electrification mechanisms in different all-liquid systems. In prior art studies of liquid-liquid contact electrification, a variety of phenomena have been found at the oil-water interface ( Figure 2 a): The dissociable functional groups in the oil can dissociate into two parts with opposite charge polarities [20, 21]; the free OH- ions in the water phase can be preferentially adsorbed on the hydrophobic interface [15-19]; electrons can also be transferred from the electrically neutral water molecules to the oil, forming cations in the water phase and transferred electrons in the oil phase [22-25]. However, the necessary conditions for each of these mechanisms in various systems have not yet been clarified, and it is difficult to determine whether multiple mechanisms can coexist, which limits the design and optimization of all-liquid TENGs [23, 24]. To solve this problem, the embodiments of the present invention provide hydrofluoroether fluid HFE7500 (HFE)-water, hexadecane (Hex)-water and oleic acid (OA)-water systems as typical examples, and systematically study the existing mechanisms of liquid-liquid contact electrification by comparing their charge, pH value and zeta potential.

[0026] First, the charge change of the oil / water phase caused by liquid-liquid contact electrification is measured to indicate the amount of charge transferred through the liquid-liquid interface. By measuring the electrostatic charge of pure oil / water before and after liquid-liquid contact electrification (Figure 6), the charge change caused by liquid-liquid contact electrification can be calculated ( Figure 2 b) In the HFE-water and OA-water systems, the water phase was positively charged and the oil phase was negatively charged after contact charging. In the Hex-water system, no obvious charge change was observed in the two phases.

[0027] The Examples also measured the change in pH when a 10% oil-in-water (O / W) emulsion was formed to reveal the free H + / OH-Changes( Figure 2c). In HFE and Hex emulsions, the pH value was only reduced by about 0.04 compared with deionized water (DI water); while in OA emulsion, the pH value was reduced by 2.3, which is much higher than the other two systems. Figure 2 c Calculated free H in the emulsion + The increase in concentration and Figure 2 b The average charge transferred between the oil and water layers calculated, the embodiment can directly explain the reason for the charge change ( Figure 2 d) In the Hex-water system, H + The concentration was slightly increased by 0.01 mM. Since no significant charge transfer was observed between the oil / water phases, this free H + The change in can be explained by the preferential adsorption of OH- at the liquid-liquid interface ( Figure 2 a) [15-18,28]: The formation of an emulsion increases the area of ​​the liquid-liquid interface, and the adsorbed OH- on the interface also increases accordingly. Therefore, the increase in adsorbed OH- will slightly release additional free H in the aqueous phase. + This inference is further supported by the charge distribution near the liquid-liquid interface, where the charge density of the water layer becomes less positive as it approaches the liquid-liquid interface, while no change in charge density is observed in the Hex layer ( Figure 7 ). For the OA-water system, after the OA emulsion is formed, H + concentration increases sharply, and obvious charge transfer is also observed between the two phases. 17 H 33 COOH) contains a dissociable hydrophilic carboxyl group, and these results are consistent with the group dissociation theory, such as Figure 2 As shown in a: COOH will dissociate with water to form dissociated H + , forming COO in the oil phase - [21,29,30], thereby increasing the H + For the HFE-water system, although significant charge transfer between the two phases was also observed, the H + The change in concentration is very small. This means that the charge transfer is not caused by H + / OH- ion transfer is dominant, but electron transfer is dominant ( Figure 2 a). Due to HFE(C9H5F 15 O) due to the strong electronegativity of fluorine, electrons tend to transfer from water to HFE [13,31-33], generating a positively charged water layer and a negatively charged HFE layer after the liquid-liquid contact is charged. The charge distribution near the OA-water and HFE-water interfaces also supports the above inference ( Figure 7). When approaching the interface, the charge density of both the oil and water layers increases because their dominant mechanisms both generate positive and negative charges on both sides of the interface, and the Coulomb attraction accumulates the charge at the interface.

[0028] Based on the dominant mechanisms in the above Hex-water, OA-water, and HFE-water systems, most of the phenomena related to charge and pH can be well explained. However, the “electron transfer” mechanism alone still cannot explain the H transfer during the formation of HFE / water emulsions. + To further investigate the mechanism of liquid-liquid contact electrification, the zeta potentials of three 1% water-in-oil emulsions (Hex, OA, and HFE) at different NaCl or HCl concentrations were measured. Figure 2 e). The characteristic trends of zeta potential vary with different mechanisms, so embodiments can identify dominant mechanisms or coexisting mechanisms in different systems.

[0029] For Hex emulsions without additives, the preferential adsorption of OH- at the interface leads to a negative zeta potential [15,16,28]. With the addition of NaCl, the magnitude of the negative zeta potential decreases because the increased ionic strength compresses the double layer [17,34,35]. However, with increasing HCl concentration, the negative zeta potential turns positive. This is because the H + The ions will neutralize the OH adsorbed on the liquid-liquid interface. -

[36] . When H + When the concentration exceeds the threshold, OH - Depleted, H + The isoelectric point is between pH 3.3 and 3, indicating that OH - The adsorption ratio of H on the Hex-water interface + At least 10 7.4 times

[15] . In addition, spectral shifts and molecular dynamics simulations in other studies have also demonstrated electron transfer through C─H┄O hydrogen bonds in the Hex-water system. Considering that electron transfer can only produce about -0.015e / nm at the interface 2 The surface charge density of

[22] , which may be too small to be observed in the above experiments, suggests that a coexistence mechanism may exist in the Hex-water system.

[0030] In the OA-water system, the dissociation of carboxyl groups generates a negative zeta potential. As the NaCl concentration increases, the magnitude of the negative zeta potential first increases and then decreases due to the competition between the salt effect and the double layer compression

[39] . When HCl is added to the OA emulsion, the magnitude of the negative zeta potential decreases because the H introduced into the solution + will inhibit the dissociation of the carboxyl group[40,41]. +When the concentration exceeds 1 mM, the zeta potential becomes positive. Since carboxyl dissociation can only produce negative zeta potential, this change indicates that hydroxyl ions are also preferentially adsorbed on the OA-water interface [42,43]. Since the contribution of preferential ion adsorption is small compared with group dissociation, in some embodiments, preferential ion adsorption can be ignored in the previous charge / pH measurement (see, for example, Example S1). Therefore, in addition to the dominant group dissociation mechanism, there may be a coexistence mechanism of preferential ion adsorption in the OA-water system.

[0031] For the HFE-water system, electron transfer causes the oil-in-water (O / W) emulsion to exhibit a negative zeta potential. The magnitude of the negative zeta potential is reduced by the addition of NaCl, because the increased salt concentration hinders electron transfer, similar to the changes in solid-liquid contact electrification [44-46]. When HCl is added to the HFE emulsion, the negative zeta potential increases in the H + When the concentration exceeds 1 mM, it turns positive. This trend is similar to that in OA emulsion, indicating that there is also a coexistence mechanism of preferential ion adsorption on the interface. This analysis is also consistent with the previous results that H + The concentration increased slightly ( Figure 2 d).

[0032] The embodiments of the present invention are Figure 2 f. In the Hex-water system, the dominant liquid-liquid contact electrification mechanism is preferential ion adsorption, while the electron transfer mechanism is also in effect. For the OA-water system, functional group dissociation is dominant, while preferential ion adsorption also coexists. Similarly, in the HFE-water system, in addition to the dominant electron transfer mechanism, preferential ion adsorption also exists. This conclusion can be quantified by ζ HCl -ζ NaCl Further support, larger HCl -ζ NaCl The value indicates H + The influence on liquid-liquid contact electrification is greater ( Figure 2 g) Among the three liquid-liquid systems, the OA-water system is affected by H + The biggest impact is due to H + It affects both the dissociation of the groups and the preferential adsorption of OH-. + The effect of H is minimal because + Affects OH only - The preferential adsorption of , while the dominant electron transfer will not be affected. Figure 2 The results of g are consistent with the above conclusions.

[0033] Based on the above understanding, favorable mechanisms can be selected for application scenarios by optimizing materials. Considering that rainwater is usually weakly acidic[47,48], the liquid-liquid contact electrification in rainwater-based TENG is affected by H + The effect of the increase is minimal. Therefore, HFE can be used as a suitable friction material to effectively charge the collected rainwater, and electron transfer will dominate in the all-liquid TENG, while preferential ion adsorption also coexists. Since the additional adsorbed hydroxyl ions at the interface will hinder the charge conduction through direct contact, the structure of the all-liquid TENG is designed in a non-contact mode with a ring electrode. In this way, water droplets can rise through the electrode ring without contact ( Fig.12 ), and generates displacement current through long-range electrostatic induction, such as Figure 1 As shown in aii.

[0034] The embodiments of the present invention provide an optimized design of an all-liquid TENG based on rainwater. Based on the above research on the liquid-liquid contact electrification mechanism, HFE and non-contact structure are selected as the preferred materials and structures of the all-liquid TENG embodiment based on rainwater, respectively. In order to further optimize the system, the effects of different design parameters (including friction material, contact distance and salt concentration) on liquid-liquid contact electrification during the operation of the all-liquid TENG can be quantified, as follows.

[0035] First, a theoretical model is established to describe the relationship between short-circuit current and raindrop charge. Based on this model, we can calculate the amount of additional charge obtained by each water droplet in the TENG and quantitatively compare the performance of different parameters in charging rainwater. Figure 3 In a), the water droplet is assumed to be a point charge moving along the central axis of the electrode ring. When the electrostatic charge or relative position of the water droplet changes, the induced charge on the electrode ring will also change accordingly. Therefore, the short-circuit current generated by the directional movement of the induced charge can be expressed as:

[0036]

[0037] Among them, q c is the induced charge on the electrode ring

[49] , q d is the charge carried by the water drop, z and z1is are the position of the water drop and the edge position of the electrode ring, h is the height of the electrode ring, and R c is the radius of the electrode ring. To prove the applicability of formula (1), we can use COMSOL to simulate the electric field in the all-liquid TENG ( Figure 3 b) and short-circuit current I SC By comparison Figure 3c The short-circuit current obtained by theoretical calculation and simulation during the movement of the water droplet. Formula (1) is proven to be applicable to certain all-liquid TENG embodiments (see, for example, Example S2).

[0038] Based on formula (1), we can measure I SC The ratio of the transferred charge to the original charge of the water droplet in the liquid-liquid contact electrification (L-LCE) is calculated (e.g., as described in the Materials and Methods section below). Considering that the function of the friction material in the all-liquid TENG is to charge the raindrops, the ratio of the transferred charge of each water droplet can quantitatively demonstrate the performance of the friction material. HFE and other oils with different dominant mechanisms (including OA and Hex) can be used as friction materials in the all-liquid TENG ( Fig.13 ). Under the condition of weakly acidic rainwater, the I SC , to calculate the ratio of transferred charges during the operation of the all-liquid TENG, such as Figure 3 d. The transferred charge in HFE is much larger than that in OA and Hex, indicating that HFE can charge rainwater the most among the three materials. Therefore, HFE performs best in the all-liquid TENG based on rainwater harvesting, and the material selection is proven to be effective in this embodiment.

[0039] In addition to the selection of friction materials, the effects of other parameters on liquid-liquid contact electrification also need to be characterized in this way. By setting the electrode ring at different distances from the outlet, an all-liquid TENG with different liquid-liquid contact distances was designed. By measuring I SC The ratio of the transferred charge in the liquid-liquid contact electrification is obtained ( Figure 3 e). Before triboelectric saturation (about 1200 seconds), the transferred charge increases with the increase of contact distance, indicating that the water droplet can obtain more additional charges from HFE at a longer contact distance. At the same time, the contact distance also structurally affects the generated current I SC , but in the opposite way ( Figure 8 In this embodiment, the contact distance can be preferably set to 2.7 cm to balance the positive correlation with liquid-liquid contact electrification and the positive correlation with I SC Similarly, by adding different salt concentrations into water, all-liquid TENGs with different ionic strengths were designed, and the ratio of transferred charge in liquid-liquid contact electrification was obtained ( Figure 3 f). The results show that higher ionic strength leads to reduced charge transfer in liquid-liquid contact charging, which is consistent with previous zeta potential results ( Figure 2e). Therefore, in the designed rainwater-based all-liquid TENG, no additional salt needs to be added to the collected rainwater. Through the optimized design parameters, the rainwater-based all-liquid TENG can continuously generate displacement current ( Figure 3 g). The generated charge density is about 3.63μC / L ( Figure 3 h), which is higher than that of previously reported all-liquid TENGs [23,26] due to the optimized design of materials and structures.

[0040] The embodiment provides a DC all-liquid TENG for energy storage and load driving. Based on optimized materials, structures and other parameters, the provided rainwater-based all-liquid TENG shows great potential in energy harvesting, and the harvested energy can then be stored or used to drive a load. Considering that most electronic devices require DC power drive, conventional TENGs usually generate AC power ( Figure 4 a), so a rectifier is needed to utilize the generated power to drive the electronic load ( Figure 4 b)[9,50], such as full-wave rectifier, rotary rectifier bridge

[51] or multi-phase rotary structure

[52] . These additional complex circuits not only increase the energy loss of the switching device, but also reduce the integration and portability of the device[53,54]. In contrast, the embodiments of the present invention provide an all-liquid TENG capable of generating direct current with a relatively low crest factor ( Figure 4 c). Therefore, the embodiment provides a DC all-liquid TENG that can be directly connected to one or more energy storage units, DC devices or other electronic loads without the need for additional devices ( Figure 4 d). Low crest factor further reduces the impact on electronic equipment, which helps to extend the service life of the equipment [26,55].

[0041] In order to better explain why the designed all-liquid TENG can generate DC power, the system of the all-liquid TENG is simplified into a capacitor model[56,57]. Figure 4 e. Capacitors C1, C2...C6 are formed between the water droplets, the electrode ring (main electrode), the accumulated water layer and the ground. The open circuit voltage V OC It can be expressed as:

[0042]

[0043] Among them, Q droplet (t) is a function of time, which indicates the total charge carried by the water droplet. During the water droplet generation process, Q droplet (t) increases, while C1 and C2 remain essentially unchanged (see, e.g., Example S3), resulting in V OCWhen the water droplet starts to move, C2 first increases and then decreases, while C1 remains almost unchanged (see, e.g., Example S3). OC A positive peak is produced in the waveform.

[0044] Although in some embodiments, the water droplets appear to be a discrete system where water droplets are added one by one, in some embodiments of the all-liquid TENG system, the water droplet generation process is actually continuous because the outlet is located at the bottom of the HFE. In the continuous water droplet generation process, V OC At the same time, the V OC The peaks are distributed on the voltage curve.

[0045] When the first water droplet rises and merges into the accumulated water layer, the charge of the water droplet accumulates in the upper water layer, suppressing V OC Then, the second droplet will repeat the process, and V OC In general, it will continue to increase with discrete fluctuations ( Figure 4 f).

[0046] according to Fig. 9 In the equivalent circuit model, the short-circuit current I SC It can be described as:

[0047]

[0048] Based on the previous V OC Analysis of I SC During the process of water droplet rising, it will fluctuate into positive and negative values ​​in turn, forming the time variation part of the current curve. SC Since V OC The increase of is maintained as a positive direct current, thereby generating a continuous DC bias. In certain embodiments of the present invention, through appropriate design parameters, the combination of these two parts of current can form a time-varying current that is generally greater than zero, thereby forming a DC TENG according to an embodiment of the present invention.

[0049] To achieve energy storage and load driving, the DC all-liquid TENG, capacitor and load (such as LED in some embodiments) are arranged in a Figure 4 d. Initially, S1 is closed and charges are accumulated in the all-liquid TENG due to the continuous generation of water droplets. OC When it reaches 2.1V, S1 opens and the all-liquid TENG starts to charge the capacitor. The charging process includes fast charging and linear charging ( Figure 4g). In the first stage, the charging speed is fast and time-nonlinear because the charge accumulates in the all-liquid TENG for a period of time. In the second stage, the charging process becomes time-linear, and its slope is positively correlated with the flow rate. The stored energy can also be released in a programmed manner (e.g., Figure 4 h). After the capacitor is charged, the LED can be turned on by opening S2. When S2 is closed again, the capacitor charging process repeats until the capacitor voltage is high enough to turn on the LED again. In some embodiments, the energy storage speed can be further increased exponentially by connecting in parallel.

[0050] The embodiments of the present invention provide a rain-based all-liquid TENG for a self-powered sensor. In addition to energy harvesting, the provided all-liquid TENG also has the potential to be used as a rainfall self-powered sensor. According to formula (2), during the water droplet generation process, the open circuit voltage V OC Approximation and Q droplet (t). Since Q droplet will increase faster as the outlet flow rate increases, so V OC The rate of increase of V is positively correlated with the flow rate. OC It has also been shown to be positively linearly correlated with total rainfall, e.g. Figure 5 a. Similarly, according to formula (3), the overall short-circuit current I SC will also increase with the increase of flow rate, and I SC The average value of the flow rate has a clear linear relationship ( Figure 5 b). Therefore, based on the generated open circuit voltage or short circuit current, the all-liquid TENG embodiment provided by the present invention can be used as a passive sensor of rainfall.

[0051] The embodiment provides a rainfall alarm system based on all-liquid TENG, which can monitor the total rainfall or rainfall rate ( Figure 5 c). By using a water reservoir to collect rainwater, raindrops can be passively pumped out from the bottom of the TENG under the action of hydrostatic pressure (see, for example, Example S4). Based on the linear relationship between the open circuit voltage and the total rainfall, the value of the total rainfall can be calculated and compared with the set warning line. When the total rainfall is still below the warning line, the LCD screen can display the rainfall value and light up the green LED light. When the total rainfall exceeds the warning line, the LCD can display "overflow" to warn of excessive rainfall and automatically light up the red LED. This demonstration can typically show the potential of the proposed all-liquid TENG as a self-powered sensor.

[0052] The embodiments of the present invention provide a rainwater-based all-liquid TENG by studying, recording and optimizing the design variables of liquid-liquid contact electrification (L-LCE) in various liquid-liquid systems. By exploring the mechanism of liquid-liquid contact electrification, the embodiments are able to solve the key issues of designing all-liquid TENGs for different application scenarios, including material selection and structural design. For example, if a rainwater-based all-liquid TENG is designed, as shown in certain embodiments, HFE may be preferred as one of the best materials. If seawater is collected, oleic acid (OA) may be preferred as one of the feasible materials because its dominant mechanism - functional group dissociation - is least affected by high salt concentrations ( Figure 2 e). In both cases, water will acquire a positive charge and the electrode structure is preferably designed to be non-contact. Therefore, the current can be generated by electromagnetic induction and the adsorption effect of negatively charged OH- on the liquid-liquid interface can be avoided. On the contrary, if the preferential adsorption of OH- is dominant, or water is negatively charged by dissociation of functional groups, it is preferred to select an electrode that transfers the charge by direct contact.

[0053] Through optimized materials and structures, the rainwater-based all-liquid TENG embodiment provided by the present invention is capable of generating direct current with high charge density (3.63μC / L) and high output stability (crest factor ≈ 1.1). The embodiment provides a paradigm for collecting energy from nature through liquid-liquid contact electrification, which provides the possibility of improving the development of all-liquid systems in green energy. The embodiment can also be dispersed in areas with frequent rainfall to realize distributed energy networks and supply energy directly to consumers. Based on the demonstration of the proposed all-liquid TENG as a rainfall alarm system, the sensitive response of the electrical output to various parameters can further expand its application in passive sensors, which has significant advantages over traditional electronic devices based on solid materials.

[0054] Materials and Methods

[0055] In the following examples and examples, oleic acid (Sigma-Aldrich), hexadecane (Macklin) and HFE7500 (Fluorochem) were selected as experimental subjects for studying liquid-liquid contact electrification (L-LCE). In the zeta potential experiment, NaCl (Sigma-Aldrich) and HCl (Aladdin) were added to the oil-in-water (O / W) emulsion. Deionized water (resistivity of 18.3 MΩcm) was obtained by a water purification system (Direct-Q5UV-R, Merck).

[0056] To prepare the oil and water layer samples for charge measurement, deionized water was first mixed with HFE / oleic acid / hexadecane in a volume ratio of 1:1 and vertically shaken 25 times. The mixture was then fixed on a spin coater (650 series, Laurell) and spun at 700 rpm (accelerated from 0 rpm at 100 rpm / s) for 70 seconds to separate the two immiscible liquids and generate friction between them (Figure 6a). During the emulsion formation and spin centrifugation process, the relative motion between the two liquids resulted in liquid-liquid contact charging. Microscopic photographs of the separated oil and water layers showed that the separation was thorough and few water (oil) droplets remained in the oil (water) layer (Figure 6b). The same procedure was repeated for the control groups of pure deionized water and pure HFE / oleic acid / hexadecane to eliminate the effect of contact charging between the sample and the glass bottle.

[0057] During the charge measurement of the oil / water layer, an aluminum foil (18 μm thick, Diamond) was used to make a Faraday cup and connected to a programmable electrometer (model 6514, Keithley Instruments) in charge measurement mode

[58] . To measure the charge of a liquid sample, the sample was placed in the inner cup and the induced charge flowed into the electrometer while shielding any atmospheric or stray electric fields. By measuring the charge of a deionized water sample using droppers made of different materials, it was found that the glass dropper caused the least and most stable solid-liquid contact charge ( Fig.10 ). Therefore, a liquid sample is extracted using a glass dropper and added to the Faraday cup for charge measurement. To quantify the amount of charge transferred, the charge of the control group needs to be measured first and then subtracted from the charge of the corresponding oil / water layer sample (Figure 6c). In this way, the original charge and additional charge brought by the contact electrification between the sample and the dropper can be eliminated.

[0058] To provide an example of outdoor demonstration, the rainwater-based all-liquid TENG system consists of a reservoir for collecting rainwater and an all-liquid TENG body for generating current, e.g. Figure 5 c. The two parts are made of 3D-printed transparent resin and connected by microtubes (LDPE, Scientific Commodities) with an inner diameter of 0.034 inches and an outer diameter of 0.052 inches. The electrodes are made of aluminum foil (18 μm thick, Diamond), placed inside the main body, and connected to the electrometer. For all experiments requiring quantitative analysis, a commercial pump (LSP01-3A, Longer Pump) was used instead of the water reservoir for better control, and the main body of the all-liquid TENG was covered by a grounded Faraday cage to eliminate the influence of the external environment [23,49]. In the quantitative experiments, the electrode was 2.2 cm in diameter and 2 cm in height, and according to previous analysis and optimization, it was placed on the axis of the water outlet in most experiments, and the distance was kept at 2.7 cm.

[0059] The simulation of the water droplet passing through the electrode ring was performed using a finite element analysis tool (COMSOL). Several simplifications were made during the modeling process. The shape of the system was abstracted as a combination of perfect geometric primitives, and the dimensions were based on experimental measurements. The water droplet was set to be uniformly positively charged. The surface of the electrode ring was set to a floating potential boundary. The oil environment was modeled as a cube with a size much larger than the electrode ring and the wire, and all surface boundaries were set to ground. The electrostatic interaction in the system was considered to be the dominant factor, so other physical phenomena were ignored in the simulation. By studying the electric field and surface charge density on the electrode ring at different water drop positions, the short-circuit current can be calculated by the derivative of the electrode surface charge over a certain time.

[0060] In order to calculate the ratio of transferred charges in liquid-liquid contact electrification (L-LCE), the short-circuit current I SC It consists of two parts: I0 (generated by the water droplet generation process) and ΔI (generated by the water droplet movement process). Based on the analysis in Example S5, we can set I0 = k0q0 (where q0 is the charge of the water droplet at the end of its generation process) and ΔI PEAK =k1(q0+δq)(where ΔI peak is the peak value of ΔI, and δq is the additional charge obtained from the liquid-liquid contact electrification). The peak value of the uniform current can be described as:

[0061]

[0062] Since a bottle of oil will eventually reach triboelectric saturation, it is possible to satisfy δq→0 and Therefore, we can obtain k from the uniform current ( Fig.11 ).

[0063] After obtaining k:

[0064]

[0065] therefore, From the original experimental data I SC The ratio of the transferred charge to the original charge of the water droplet in liquid-liquid contact electrification is obtained.

[0066] Considering that the charge transfer process between the refreshing water droplet and the constant volume oil can be compared to the discharge process of a capacitor, the exponential decay fitting (ExpDecayfitting) can be used to describe the change law of the transferred charge in the liquid-liquid contact electrification:

[0067]

[0068] In the experimental measurements, a programmable electrometer (6514, Keithley Instruments model) was used to measure the charge of the sample, the short-circuit current and the open-circuit voltage of the all-liquid TENG. In order to reduce the electromagnetic interference of the external environment, a copper Faraday cage was grounded and placed outside the experimental device. By applying electrostatic shielding and setting the current measurement range to pA level, the 6514 electrometer can achieve a reading accuracy of ±1% according to its user manual, while the actual measured current noise of the electrometer 6514 is about fA level, which meets the requirements of pA level current measurement ( Fig.15 The pH value of the emulsion was measured using a pH meter (pH550, Oakton). The zeta potential of the emulsion was measured using a Zetasizer (Zetasizer pro, Malvern Panalytical) with a folded capillary cell (DTS1070, Malvern Panalytical).

[0069] In the statistical analysis, the raw data were analyzed as recorded without preprocessing. In order to measure the charge changes of different all-liquid TENG systems, e.g. Figure 2 As shown in (b), at least three bottles of oil-water mixture were prepared for each all-liquid TENG system ( Fig. 6A ), and at least twenty samples were taken from each bottle for charge measurement to obtain the average value of each bottle. Figure 2 (b) is shown as a point. The average and standard deviation of all samples from different bottles in each all-liquid TENG system are shown in Figure 2 (b) is shown as a bar graph and error bars. In order to measure the pH changes of different all-liquid TENG systems, Figure 2 As shown in c, at least four oil-in-water (O / W) emulsion samples were prepared for each all-liquid TENG system, and each sample was measured at least twenty times to obtain the average value of each sample. Figure 2 (c) is shown as a point. The mean and standard deviation of all test results for different samples are shown in Figure 2 (c) is shown as a bar graph with error bars. The measured pH changes are presented as mean ± standard deviation. All statistical data were analyzed using Microsoft Excel.

[0070] All patents, patent applications, provisional applications, and publications mentioned or cited herein are hereby incorporated by reference in their entirety, including all figures, to the extent they are not inconsistent with the explicit teachings of this specification.

[0071] The following are examples of procedures for implementing the present invention. These examples should not be construed as limiting. Unless otherwise indicated, all percentages are by weight and all solvent mixing ratios are by volume.

[0072] Example S1:

[0073] In order to compare the contribution of OH- preferential adsorption and carboxyl dissociation to the charge / pH measurements, we used the experimental results of the hexadecane-water system and the oleic acid-water system as benchmarks. When the preferential adsorption of OH- dominates the system (hexadecane-water system), there is almost no charge transfer between the two liquid phases ( Figure 2 b), and the pH difference between deionized water and water-in-oil emulsion is about 0.03 ( Figure 2 c). When carboxyl dissociation is dominant in the system (oleic acid-water system), the charge transfer between the two liquid phases is about 25 pC per 0.8 ml sample ( Figure 2 b), and the pH difference between deionized water and water-in-oil emulsion is about 2.3 ( Figure 2 c), which is much larger than the result of hexadecane-water system. Therefore, even if the preferential adsorption of OH- and the dissociation of carboxyl groups exist simultaneously in the oleic acid-water system, the small contribution of OH- adsorption can be ignored and its presence may not be detected in the previous charge / pH measurement.

[0074] Example S2:

[0075] COMSOL simulation is performed to verify the correctness of formula (1). In order to make the model closer to the actual situation, Figure 3 The point charge in a is replaced by a perfect sphere with uniform positive charge in the simulation model ( Figure 3 b) The I caused by the movement of water droplets is obtained through simulation results SC , and compare it with the result calculated by formula (1) ( Figure 3 c) Both results consist of a positive peak followed by a negative peak with different half-height widths, which may be caused by the volume effect of the water drop model. However, the ΔI peak (Forward peak I SC The peak value of ) is the same, indicating that a reliable ΔI can be obtained through formula (1) peak , and is used to calculate the ratio of the transferred charge to the original charge of the water droplet in the liquid-liquid contact electrification (L-LCE) during the operation of the all-liquid TENG.

[0076] Example S3:

[0077] The capacitors C1 and C2 formed between the reference electrode, the water droplet and the main electrode ( Figure 4 e) can be expressed as:

[0078] C=εAd(S1)

[0079] in ε is the electrical constant of the dielectric, A is the effective area of ​​the plates, and d is the distance between the two plates.

[0080] During the droplet generation process, the changes in all the above parameters can be ignored. Therefore, C1 and C2 are approximately constant. During the movement of the droplet, the distance between the rising droplet and the electrode ring first decreases and then increases, resulting in the opposite change trend of C2. The change of C1 can be ignored because the reference electrode is grounded and can be regarded as being at infinity.

[0081] Example S4:

[0082] In some designed all-liquid TENG embodiments, rainwater is collected in a water reservoir, and water droplets are formed at the bottom of the oil phase due to the hydrostatic pressure difference. In order to continuously generate water droplets, h1 (the height difference between the water level in the water reservoir and the water outlet in the oil phase) and h2 (the height difference between the oil level in the all-liquid TENG and the water outlet in the oil phase) need to meet the following conditions:

[0083] ρ oil h2≤ρ water h1 (S2)

[0084] When the equation in formula (S2) holds true, no water droplets are formed in the all-liquid TENG and the system is in equilibrium.

[0085] Example S5:

[0086] The current generated during the water droplet generation process is referred to as I0 in the following discussion. In formula (1), the position of the water droplet z = z0 + r, so z1-z = (z1-z0)-r, where z1-z0 is the distance between the water outlet and the electrode ring, and r is the radius of the water droplet during its generation process. According to the actual parameters, we have z1-z0>>r. Therefore, r can be ignored in the calculation of formula (1). When r is ignored in formula (1), we have where q d is the real-time charge of the water droplet. When the flow rate is constant, can be approximated as a constant, so we have where q0 is the charge of the water droplet at the end of its generation process.

[0087] The current caused by the movement of the water droplet is referred to as ΔI in the following discussion. The real-time charge of the water droplet can be expressed as q d =q0+δq(t), where q0 is the charge of the water droplet at the end of its generation process, and δq(t) is the real-time additional charge obtained from liquid-liquid contact electrification (L-LCE). The position of the water droplet can be expressed as where z g is the position of the droplet's center at the end of its generation process, and After substituting these actual parameters into formula (1), ΔI can be expressed as in Therefore, ΔI peak It can be approximated as ΔI peak ∝q d =q0+δq, where q0 is the charge of the water droplet at the end of its generation process and δq is the additional charge gained from the liquid-liquid contact electrification.

[0088] Exemplary Embodiments

[0089] The present invention may be better understood by reference to the following illustrative examples, including but not limited to the following:

[0090] Embodiment 1: A liquid-liquid (LL) contact electrification (CE) triboelectric nanogenerator (TENG) system for generating electrical energy in a self-powered sensor, the system comprising:

[0091] a first fluid volume comprising purified water or an aqueous solution;

[0092] The purified water or aqueous solution can be water from nature for green power generation, including rainwater, seawater, moisture captured from the air or other natural water sources. The purified water or aqueous solution can also be water or aqueous solution used for other applications (such as microfluidic platforms) to achieve the recycling or secondary use of water resources and provide energy for the original equipment;

[0093] Among them, in some embodiments, lower ion concentration in aqueous solution has been shown to improve the performance of TENG;

[0094] a second fluid volume comprising an oil having a density different from that of the purified water or aqueous solution;

[0095] wherein the oil may be selected from suitable oils known in the art, or any suitable liquid that is immiscible with the first fluid volume, and the first fluid volume may be electrically insulated from the second fluid volume;

[0096] In one embodiment, an oil having a lower density than the first fluid volume may be used for the water outlet or a droplet generator is located on top of the second fluid volume, configured to generate water droplets from the top of the oil phase and allow them to sink due to gravity (e.g., see Fig.13 (b) in the embodiment);

[0097] In one embodiment, oil having a higher density than the first fluid volume may be used for the water outlet or the droplet generator is located at the bottom of the second fluid volume, configured to generate water droplets from the bottom of the oil phase and cause them to rise due to buoyancy (e.g., see Fig.13 (a) in the embodiment);

[0098] a droplet generator fluidly connecting the first fluid volume and the second fluid volume;

[0099] an electrode having a positive terminal and a ground terminal, the ground terminal being connected to the ground or a bulk conductive material;

[0100] Wherein, the mass of the bulk conductive material may be equal to or approximately equal to 1 / 2 of the mass of the TENG, or equal to or approximately equal to the mass of the TENG, 1.5 times the mass of the TENG, twice the mass of the TENG, five times the mass of the TENG, ten times the mass of the TENG, or greater, including combinations, increments, and fractions thereof;

[0101] The positive terminal and the ground terminal are directly connected to an electronic circuit containing a capacitor in parallel with a load;

[0102] The electrode is located within the second fluid volume;

[0103] The electrode is aligned with, above or below, an outlet of the first fluid volume in the droplet generator;

[0104] The first fluid volume has a first height (h1) above the droplet generator;

[0105] The second fluid volume has a second height (h2) above the droplet generator;

[0106] The first fluid volume has a first density (ρ1);

[0107] The second fluid volume has a second density (ρ2);

[0108] The first fluid volume, the second fluid volume and the droplet generator are respectively configured and adapted so that when the following equation is satisfied:

[0109] ρ2h2<ρ1h1

[0110] a plurality of aqueous solution droplets are formed and released, each droplet ascending or descending, respectively, through the second fluid volume, approaching the electrode, driven by gravity acting on the first density and the second density, respectively; and

[0111] When multiple droplets pass near the electrode, a displacement current is generated between the positive terminal and the ground terminal.

[0112] Embodiment 2: The system of embodiment 1, wherein the direct connection comprises a first switch (S1) between the electrode and the electronic circuit and a second switch (S2) between S1 and the load.

[0113] Embodiment 3: The system of embodiment 1, characterized in that there is no rectifier between the electrodes and the electronic circuit.

[0114] Example 4: The system of Example 1 exhibits a charge density greater than or equal to about 1 μC / L, a contact electrification time greater than or equal to about 500 seconds, and an output stability greater than or equal to about 0.7.

[0115] Example 5: The system of Example 4 exhibits at least one of the following: (i) a charge density greater than or equal to about 3.63 μC / L, or (ii) a contact electrification time greater than or equal to about 1200 seconds, or (iii) an output stability greater than or equal to about 0.9.

[0116] Example 6: The system of Example 1 exhibits (i) a charge density greater than or equal to about 3.63 μC / L, (ii) a contact electrification time greater than or equal to about 1200 seconds, and (iii) an output stability greater than or equal to about 0.9. The contact electrification time is defined as the effective time for the oil friction material to transfer electrons to water and make it positively charged. The method for measuring the contact electrification time is as follows: Figure 3 (d) When the ratio of transferred charge approaches zero, it means that the specific volume of oil has reached triboelectric saturation and cannot provide more electrons to charge the water droplets. The time required for the ratio of transferred charge to become zero (measured by Figure 3 The upper limit curve fitting slope of each data series in (d) is projected to the x-axis intercept point, which is the effective contact electrification time.

[0117] Embodiment 7: The system of embodiment 1, wherein the first fluid volume comprises collected rainwater, and the oil (optionally comprising a friction oil material) is configured to positively charge the collected raindrops by electron transfer and preferential ion adsorption. Wherein, the friction oil material used in certain embodiments is an oil capable of charging water droplets by contact electrification (also known as triboelectric charging) and has desired (optionally: improved, enhanced, or functionally sufficient) properties.

[0118] Embodiment 8: The system of embodiment 7, wherein the electrode is a ring electrode configured to generate a displacement current by electrostatic induction.

[0119] Example 9: In the system of Example 8, the contact distance is about 2.7 cm, the diameter of the annular electrode is about 2.2 cm, and the height is about 2 cm.

[0120] Embodiment 10: The system of embodiment 9, wherein the friction oil material comprises hydrofluoroether (HFE). Although not limited by theory, in certain embodiments, HFE can be replaced by other oil materials that can positively charge a sufficient number of water droplets through electron transfer (for example, oil liquids containing fluorine elements, such as perfluoropolyether (PFPE), are expected to achieve similar functions).

[0121] Embodiment 11: The system of embodiment 1, wherein the first fluid volume comprises collected seawater, and the oil comprises a friction oil material configured to positively charge the collected seawater droplets by functional group dissociation and preferential ion adsorption.

[0122] Embodiment 12: The system of embodiment 11, wherein the electrode is a ring electrode configured to generate a displacement current by electrostatic induction.

[0123] Embodiment 13: The system of embodiment 12, wherein the friction oil material comprises oleic acid (OA). In certain embodiments, OA can be replaced by any oil material that can dissociate into a sufficient number of water droplets with positive charge through functional groups. Although not limited by theory, in certain embodiments, oil liquids containing dissociated functional groups (e.g., -COOH) are expected to achieve similar functions.

[0124] Embodiment 14: The system of embodiment 1, wherein the oil comprises a friction oil material configured to make the corresponding droplets negatively charged by functional group dissociation, electron transfer, or selective adsorption of negative ions at the oil-water interface.

[0125] Embodiment 15: The system of embodiment 14, wherein the electrode is configured to generate a displacement current by direct contact with the droplet.

[0126] Embodiment 16: The system of embodiment 15, wherein the friction oil material comprises hexadecane (Hex). Wherein, in certain embodiments, Hex can be replaced by an oil material capable of generating sufficient amount of negative ion adsorption at the oil-water interface. Although not limited by theory, the inventors assume that many common oils will show good performance in certain embodiments (e.g., dodecane).

[0127] Embodiment 17: A method for generating electrical energy in a self-powered sensor using a liquid-liquid (LL) contact electrification (CE) triboelectric nanogenerator (TENG) system, the method comprising:

[0128] providing a first fluid volume comprising purified water or an aqueous solution, the first fluid volume having a first density;

[0129] providing a second fluid volume comprising an oil, the second fluid volume having a second density different from the first density;

[0130] providing an electrode having a positive terminal and a ground terminal,

[0131] The positive terminal and the ground terminal are directly connected to the electronic circuit containing the capacitor in parallel with the load,

[0132] The electrode is located in the second fluid volume,

[0133] The electrodes are vertically aligned above or below the droplet generator;

[0134] providing a droplet generator fluidly connected to the first fluid volume and the second fluid volume;

[0135] The first fluid volume has a first height (h1) above the droplet generator;

[0136] The second fluid volume has a second height (h2) above the droplet generator;

[0137] The first density has a value (ρ1);

[0138] The second density has a value (ρ2);

[0139] The first fluid volume, the second fluid volume and the droplet generator are respectively configured and adapted so that when the following equation is satisfied:

[0140] ρ2h2<ρ1h1

[0141] forming and releasing a plurality of aqueous solution droplets, each droplet ascending or descending through the second fluid volume, respectively, approaching the electrode, driven by gravity acting on the first density and the second density, respectively;

[0142] Among them, when multiple droplets pass near the electrode, a displacement current is generated between the positive terminal and the ground terminal;

[0143] Wherein, the direct connection includes a first switch (S1) between the electrode and the electronic circuit and a second switch (S2) between S1 and the load;

[0144] The circuit is characterized in that no rectifier is present.

[0145] Embodiment 18: The method of Embodiment 17, wherein the TENG exhibits (i) a charge density greater than or equal to about 3.63 μC / L, (ii) a contact electrification time greater than or equal to about 1200 seconds, and (iii) an output stability greater than or equal to about 0.9;

[0146] wherein the first fluid volume comprises collected rainwater, and the oil comprises a hydrofluoroether (HFE) configured to positively charge the collected raindrops by electron transfer and preferential ion adsorption;

[0147] The electrode is a ring electrode configured to generate a displacement current through electrostatic induction.

[0148] Embodiment 19: A liquid-liquid (LL) contact electrification (CE) triboelectric nanogenerator (TENG) system for generating electrical energy in a self-powered sensor, the system comprising:

[0149] a first fluid volume comprising purified water or an aqueous solution;

[0150] a second fluid volume comprising an oil having a density different from or greater than that of the purified water or aqueous solution;

[0151] a droplet generator fluidly connecting the first fluid volume and the second fluid volume;

[0152] an electrode having a positive terminal and a ground terminal,

[0153] The positive terminal and the ground terminal are directly connected to the electronic circuit containing the capacitor in parallel with the load,

[0154] The electrode is located in the second fluid volume,

[0155] The electrode is aligned above the droplet generator;

[0156] The first fluid volume has a first height (h1) above the droplet generator;

[0157] The second fluid volume has a second height (h2) above the droplet generator;

[0158] The first fluid volume has a first density (ρ1);

[0159] The second fluid volume has a second density (ρ2);

[0160] The first fluid volume, the second fluid volume and the droplet generator are respectively configured and adapted so that when the following equation is satisfied:

[0161] ρ2h2<ρ1h1

[0162] A plurality of aqueous solution droplets are formed and released, each droplet rising through the second fluid volume and approaching the electrode;

[0163] Among them, when multiple droplets pass near the electrode, a displacement current is generated between the positive terminal and the ground terminal;

[0164] Wherein, the direct connection includes a first switch (S1) between the electrode and the electronic circuit and a second switch (S2) between S1 and the load;

[0165] Among them, the system is characterized by the absence of any rectifier between the electrodes and the electronic circuit;

[0166] wherein the system exhibits (i) a charge density greater than or equal to about 3.63 μC / L, (ii) a contact electrification time greater than or equal to about 1200 seconds, and (iii) an output stability greater than or equal to about 0.9;

[0167] wherein the first fluid volume comprises rainwater, and the oil comprises a hydrofluoroether (HFE) configured to positively charge corresponding raindrops by electron transfer and preferential ion adsorption;

[0168] wherein the electrode is a ring electrode configured to generate a displacement current by electrostatic induction; and

[0169] The load includes a rainfall alarm system configured to monitor total rainfall based on a voltage between a positive terminal and a ground terminal, display total rainfall on an LCD screen when the voltage is below a warning line, and issue an excessive rainfall warning when the voltage exceeds the warning line.

[0170] Example 20: The system of Example 19, wherein the ring electrode has a contact distance, ring diameter, and ring height above the droplet generator, the contact distance is about 2.7 cm, the ring diameter is about 2.2 cm, and the ring height is about 2 cm.

[0171] Embodiment 21: A liquid-liquid (LL) contact electrification (CE) triboelectric nanogenerator (TENG) system for generating electrical energy in a self-powered sensor, the system comprising:

[0172] a first fluid volume comprising purified water or an aqueous solution;

[0173] a second fluid volume comprising an oil having a density different from that of the purified water or aqueous solution;

[0174] a droplet generator fluidly connecting the first fluid volume and the second fluid volume;

[0175] An electrode having a positive terminal and a ground terminal, wherein the ground terminal is connected to the ground or a conductive material having a mass greater than that of the TENG;

[0176] The positive terminal and the ground terminal are directly connected to an electronic circuit containing a capacitor in parallel with a load;

[0177] The electrode is located within the second fluid volume;

[0178] The electrodes are aligned above or below the droplet generator;

[0179] The first fluid volume has a first height (h1) above the droplet generator;

[0180] The second fluid volume has a second height (h2) above the droplet generator;

[0181] The first fluid volume has a first density (ρ1);

[0182] The second fluid volume has a second density (ρ2);

[0183] The first fluid volume, the second fluid volume and the droplet generator are respectively configured and adapted so that when the following equation is satisfied:

[0184] ρ2h2<ρ1h1

[0185] A plurality of aqueous solution droplets are formed and released, each droplet passing through the second fluid volume and approaching the electrode under the action of gravity, the gravity acting on the first density and the second density respectively; and

[0186] When multiple droplets pass near the electrode, a displacement current is generated between the positive terminal and the ground terminal.

[0187] Embodiment 22: The system of Embodiment 21, wherein the direct connection comprises a first switch (S1) between the electrode and the electronic circuit and a second switch (S2) between S1 and the load.

[0188] Embodiment 23: The system of embodiment 21, characterized in that there is no rectifier between the electrodes and the electronic circuit.

[0189] Example 24: The system of Example 21 exhibits a charge density greater than or equal to about 1 μC / L, a contact electrification time greater than or equal to about 500 seconds, and an output stability greater than or equal to about 0.7.

[0190] Example 25: The system of Example 24, exhibiting at least one of the following: (i) a charge density greater than or equal to about 3.63 μC / L, or (ii) a contact electrification time greater than or equal to about 1200 seconds, or (iii) an output stability greater than or equal to about 0.9.

[0191] Example 26: The system of any of Examples 21 to 23, exhibiting (i) a charge density greater than or equal to about 3.63 μC / L, (ii) a contact electrification time greater than or equal to about 1200 seconds, and (iii) an output stability greater than or equal to about 0.9.

[0192] Embodiment 27: The system of any of Embodiments 21 to 25, wherein the first fluid volume comprises rainwater, and the oil comprises a friction oil material configured to positively charge corresponding raindrops via electron transfer and preferential ion adsorption.

[0193] Embodiment 28: The system of embodiment 27, wherein the electrode is a ring electrode configured to generate a displacement current by electrostatic induction.

[0194] Example 29: The system of Example 28, wherein the contact distance is approximately 2.7 cm, the ring diameter is approximately 2.2 cm, and the ring height is approximately 2 cm.

[0195] Embodiment 30: The system of Embodiment 29, wherein the friction oil material comprises a hydrofluoroether (HFE).

[0196] Embodiment 31: The system of any of Embodiments 21 to 25, wherein the first fluid volume comprises seawater, and the oil comprises a friction oil material configured to positively charge corresponding seawater droplets by functional group dissociation and preferential ion adsorption.

[0197] Embodiment 32: The system of embodiment 31, wherein the electrode is a ring electrode configured to generate a displacement current by electrostatic induction.

[0198] Embodiment 33: The system of Embodiment 32, wherein the friction oil material comprises oleic acid (OA).

[0199] Embodiment 34: The system of any one of Embodiments 21 to 25, wherein the oil comprises a friction oil material configured to make the corresponding droplets negatively charged by functional group dissociation, electron transfer, or selective adsorption of negative ions at the oil-water interface; and wherein the electrodes are configured to generate a displacement current by direct contact with the droplets.

[0200] Embodiment 35: The system of Embodiment 34, wherein the friction oil material comprises hexadecane (Hex).

[0201] Embodiment 36: A method for generating electrical energy in a self-powered sensor using a liquid-liquid (LL) contact electrification (CE) triboelectric nanogenerator (TENG) system, the method comprising:

[0202] providing a first fluid volume comprising purified water or an aqueous solution, the first fluid volume having a first density;

[0203] providing a second fluid volume comprising an oil, the second fluid volume having a second density different from the first density;

[0204] providing an electrode having a positive terminal and a ground terminal,

[0205] The positive terminal and the ground terminal are directly connected to the electronic circuit containing the capacitor in parallel with the load,

[0206] The electrode is located in the second fluid volume,

[0207] The electrodes are vertically aligned above or below the droplet generator;

[0208] providing a droplet generator fluidly connected to the first fluid volume and the second fluid volume;

[0209] The first fluid volume has a first height (h1) above the droplet generator;

[0210] The second fluid volume has a second height (h2) above the droplet generator;

[0211] The first density has a value (ρ1);

[0212] The second density has a value (ρ2);

[0213] The first fluid volume, the second fluid volume and the droplet generator are respectively configured and adapted so that when the following equation is satisfied:

[0214] ρ2h2<ρ1h1

[0215] A plurality of aqueous solution droplets are formed and released, each droplet passing through a second fluid volume and approaching an electrode under the action of gravity, the gravity acting on the first density and the second density, respectively;

[0216] Among them, when multiple droplets pass near the electrode, a displacement current is generated between the positive terminal and the ground terminal;

[0217] Wherein, the direct connection includes a first switch (S1) between the electrode and the electronic circuit and a second switch (S2) between S1 and the load;

[0218] The circuit is characterized in that no rectifier is present.

[0219] Embodiment 37: The method of Embodiment 36, wherein the TENG exhibits (i) a charge density greater than or equal to about 3.63 μC / L, (ii) a contact electrification time greater than or equal to about 1200 seconds, and (iii) an output stability greater than or equal to about 0.9;

[0220] wherein the first fluid volume comprises rainwater, and the oil comprises a hydrofluoroether (HFE) configured to positively charge corresponding raindrops by electron transfer and preferential ion adsorption;

[0221] The electrode is a ring electrode configured to generate a displacement current through electrostatic induction.

[0222] Embodiment 38: A liquid-liquid (LL) contact electrification (CE) triboelectric nanogenerator (TENG) system for generating electrical energy in a self-powered sensor, the system comprising:

[0223] a first fluid volume comprising purified water or an aqueous solution;

[0224] a second fluid volume comprising an oil having a density different from that of the purified water or aqueous solution;

[0225] a droplet generator fluidly connecting the first fluid volume and the second fluid volume;

[0226] An electrode having a positive terminal and a ground terminal, wherein the ground terminal is connected to the ground or a conductive material having a mass greater than that of the TENG;

[0227] The positive terminal and the ground terminal are directly connected to an electronic circuit containing a capacitor in parallel with a load;

[0228] The electrode is located within the second fluid volume;

[0229] The electrodes are aligned above or below the droplet generator;

[0230] The first fluid volume has a first height (h1) above the droplet generator;

[0231] The second fluid volume has a second height (h2) above the droplet generator;

[0232] The first fluid volume has a first density (ρ1);

[0233] The second fluid volume has a second density (ρ2);

[0234] The first fluid volume, the second fluid volume and the droplet generator are respectively configured and adapted so that when the following equation is satisfied:

[0235] ρ2h2<ρ1h1

[0236] A plurality of aqueous solution droplets are formed and released, each droplet passing through the second fluid volume and approaching the electrode;

[0237] Among them, when multiple droplets pass near the electrode, a displacement current is generated between the positive terminal and the ground terminal;

[0238] Wherein, the direct connection includes a first switch (S1) between the electrode and the electronic circuit and a second switch (S2) between S1 and the load;

[0239] Among them, the system is characterized by the absence of any rectifier between the electrodes and the electronic circuit;

[0240] The system exhibits (i) a charge density greater than or equal to about 3.63 μC / L, (ii) a contact electrification time greater than or equal to about 1200 seconds, and (iii) an output stability greater than or equal to about 0.9.

[0241] Embodiment 39: The system of embodiment 38, wherein:

[0242] The first fluid volume comprises rainwater, and the oil comprises a hydrofluoroether (HFE) configured to positively charge corresponding raindrops by electron transfer and preferential ion adsorption;

[0243] The first fluid volume, the second fluid volume and the droplet generator are respectively configured and adapted so that when the following equation is satisfied:

[0244] ρ2h2<ρ1h1

[0245] A plurality of aqueous solution droplets are formed and released, each droplet rising through the second fluid volume and approaching the electrode;

[0246] wherein the electrode is a ring electrode, aligned above the droplet generator, and configured to generate a displacement current by electrostatic induction; and

[0247] The load includes a rainfall monitoring system configured to monitor a corresponding rainfall amount based on a voltage between a positive terminal and a ground terminal.

[0248] Embodiment 40: The system of embodiment 38, wherein:

[0249] The first fluid volume comprises rainwater, and the oil comprises oleic acid (OA) or hexadecane (Hex) or both, configured to charge corresponding raindrops by functional group dissociation and / or preferential ion adsorption;

[0250] The first fluid volume, the second fluid volume and the droplet generator are respectively configured and adapted so that when the following equation is satisfied:

[0251] ρ2h2<ρ1h1

[0252] A plurality of aqueous solution droplets are formed and released, each droplet descending through the second fluid volume and approaching the electrode;

[0253] wherein the electrode is a ring electrode, aligned below the droplet generator, and configured to generate a displacement current by electrostatic induction; and

[0254] The load includes a rainfall monitoring system configured to monitor a corresponding rainfall amount based on a voltage between a positive terminal and a ground terminal.

[0255] Although the present invention has been illustrated and described herein by way of preferred embodiments and specific examples, it will be apparent to one of ordinary skill in the art that other embodiments and examples may perform similar functions and / or achieve similar results.

[0256] When the term "about" is used herein, when used in conjunction with a numerical value, it means that the value may be within 95% to 105% of the value, that is, the value may be ±5% of the value. For example, "about 1 kilogram" means from 0.95 kilograms to 1.05 kilograms.

[0257] When ranges are used herein, combinations and sub-combinations of ranges (eg, sub-ranges within the disclosed range) and specific examples therein are expressly included.

[0258] The transitional terms "comprising," "including," or "containing" are open ended and do not exclude additional, unrecited elements or method steps. In contrast, the transitional phrase "consisting of excludes any element, step, or ingredient not specified in the claim. The phrase "consisting essentially of indicates that the claim includes embodiments that include the specified materials or steps, as well as those that do not materially affect the basic and novel characteristics of the claim. Other embodiments that "consist of" or "consist essentially of" the recited components are also contemplated when the term "comprising" is used.

[0259] It should be understood that the examples and embodiments described herein are for illustrative purposes only, and those skilled in the art may propose various modifications or changes based on their inspiration, and these modifications or changes should be included in the spirit and scope of this application and the scope of the appended claims. In addition, any element or limitation of any invention or its embodiment disclosed herein may be combined with any and / or all other elements or limitations (alone or in any combination) or any other invention or its embodiment disclosed herein, and all these combinations are within the scope of the present invention without limitation.

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Claims

1. A liquid-liquid (LL) contact electrification (CE) triboelectric nanogenerator (TENG) system for generating electrical energy in a self-powered sensor, the system comprising: a first fluid volume comprising purified water or an aqueous solution; a second fluid volume comprising an oil having a density different from that of the purified water or aqueous solution; a droplet generator fluidly connecting the first fluid volume and the second fluid volume; An electrode having a positive terminal and a ground terminal, wherein the ground terminal is connected to the ground or a conductive material having a mass greater than that of the TENG; The positive terminal and the ground terminal are directly connected to an electronic circuit containing a capacitor in parallel with a load; The electrode is located within the second fluid volume; The electrodes are aligned above or below the droplet generator; The first fluid volume has a first height (h1) above the droplet generator; The second fluid volume has a second height (h2) above the droplet generator; The first fluid volume has a first density (ρ1); The second fluid volume has a second density (ρ2); The first fluid volume, the second fluid volume and the droplet generator are respectively configured and adapted so that when the following equation is satisfied: ρ2h2<ρ1h1 A plurality of aqueous solution droplets are formed and released, each droplet passing through the second fluid volume and approaching the electrode under the action of gravity, the gravity acting on the first density and the second density respectively; and When multiple droplets pass near the electrode, a displacement current is generated between the positive terminal and the ground terminal.

2. The system of claim 1, wherein the direct connection comprises a first switch (S1) between the electrode and the electronic circuit and a second switch (S2) between S1 and the load.

3. The system according to claim 1, characterized in that There is no rectifier between the electrodes and the electronic circuit.

4. The system of claim 1, exhibiting a charge density greater than or equal to about 1 μC / L, a contact electrification time greater than or equal to about 500 seconds, and an output stability greater than or equal to about 0.

7.

5. The system of claim 4, exhibiting at least one of the following: (i) a charge density greater than or equal to about 3.63 μC / L, or (ii) a contact electrification time greater than or equal to about 1200 seconds, or (iii) an output stability greater than or equal to about 0.

9.

6. The system of any one of claims 1 to 3, exhibiting (i) a charge density greater than or equal to about 3.63 μC / L, (ii) a contact electrification time greater than or equal to about 1200 seconds, and (iii) an output stability greater than or equal to about 0.

9.

7. The system of any one of claims 1 to 5, wherein the first fluid volume comprises rainwater and the oil comprises a friction oil material configured to positively charge corresponding raindrops by electron transfer and preferential ion adsorption.

8. The system of claim 7, wherein the electrode is a ring electrode configured to generate a displacement current by electrostatic induction.

9. The system of claim 8, wherein the contact distance is approximately 2.7 cm, the diameter of the ring electrode is approximately 2.2 cm, and the height is approximately 2 cm.

10. The system of claim 9, wherein the friction oil material comprises a hydrofluoroether (HFE).

11. The system of any one of claims 1 to 5, wherein the first fluid volume comprises seawater, and the oil comprises a friction oil material configured to positively charge corresponding seawater droplets by functional group dissociation and preferential ion adsorption.

12. The system of claim 11, wherein the electrode is a ring electrode configured to generate a displacement current by electrostatic induction.

13. The system of claim 12, wherein the friction oil material comprises oleic acid (OA).

14. The system according to any one of claims 1 to 5, wherein the oil comprises a friction oil material configured to make the corresponding droplets negatively charged by functional group dissociation, electron transfer or selective adsorption of negative ions at the oil-water interface; and wherein the electrode is configured to generate a displacement current by directly contacting the droplets.

15. The system of claim 14, wherein the friction oil material comprises hexadecane (Hex).

16. A method for generating electrical energy in a self-powered sensor using a liquid-liquid (LL) contact electrification (CE) triboelectric nanogenerator (TENG) system, the method comprising: providing a first fluid volume comprising purified water or an aqueous solution, the first fluid volume having a first density; providing a second fluid volume comprising an oil, the second fluid volume having a second density different from the first density; providing an electrode having a positive terminal and a ground terminal, The positive terminal and the ground terminal are directly connected to the electronic circuit containing the capacitor in parallel with the load, The electrode is located in the second fluid volume, The electrodes are vertically aligned above or below the droplet generator; providing a droplet generator fluidly connected to the first fluid volume and the second fluid volume; The first fluid volume has a first height (h1) above the droplet generator; The second fluid volume has a second height (h2) above the droplet generator; The first density has a value (ρ1); The second density has a value (ρ2); The first fluid volume, the second fluid volume and the droplet generator are respectively configured and adapted so that when the following equation is satisfied: ρ2h2<ρ1h1 A plurality of aqueous solution droplets are formed and released, each droplet passing through a second fluid volume and approaching an electrode under the action of gravity, the gravity acting on the first density and the second density, respectively; Among them, when multiple droplets pass near the electrode, a displacement current is generated between the positive terminal and the ground terminal; Wherein, the direct connection includes a first switch (S1) between the electrode and the electronic circuit and a second switch (S2) between S1 and the load; The circuit is characterized in that no rectifier is present.

17. The method of claim 16, wherein the TENG exhibits (i) a charge density greater than or equal to about 3.63 μC / L, (ii) a contact electrification time greater than or equal to about 1200 seconds, and (iii) an output stability greater than or equal to about 0.9; in, The first fluid volume comprises rainwater, and the oil comprises a hydrofluoroether (HFE) configured to positively charge corresponding raindrops by electron transfer and preferential ion adsorption; The electrode is a ring electrode configured to generate a displacement current through electrostatic induction.

18. A liquid-liquid (LL) contact electrification (CE) triboelectric nanogenerator (TENG) system for generating electrical energy in a self-powered sensor, the system comprising: a first fluid volume comprising purified water or an aqueous solution; a second fluid volume comprising an oil having a density different from that of the purified water or aqueous solution; a droplet generator fluidly connecting the first fluid volume and the second fluid volume; An electrode having a positive terminal and a ground terminal, wherein the ground terminal is connected to the ground or a conductive material having a mass greater than that of the TENG; The positive terminal and the ground terminal are directly connected to an electronic circuit containing a capacitor in parallel with a load; The electrode is located within the second fluid volume; The electrodes are aligned above or below the droplet generator; The first fluid volume has a first height (h1) above the droplet generator; The second fluid volume has a second height (h2) above the droplet generator; The first fluid volume has a first density (ρ1); The second fluid volume has a second density (ρ2); The first fluid volume, the second fluid volume and the droplet generator are respectively configured and adapted so that when the following equation is satisfied: ρ2h2<ρ1h1 A plurality of aqueous solution droplets are formed and released, each droplet passing through the second fluid volume and approaching the electrode; Among them, when multiple droplets pass near the electrode, a displacement current is generated between the positive terminal and the ground terminal; Wherein, the direct connection includes a first switch (S1) between the electrode and the electronic circuit and a second switch (S2) between S1 and the load; Among them, the system is characterized by the absence of any rectifier between the electrodes and the electronic circuit; The system exhibits (i) a charge density greater than or equal to about 3.63 μC / L, (ii) a contact electrification time greater than or equal to about 1200 seconds, and (iii) an output stability greater than or equal to about 0.

9.

19. The system of claim 18, wherein: The first fluid volume comprises rainwater, and the oil comprises a hydrofluoroether (HFE) configured to positively charge corresponding raindrops by electron transfer and preferential ion adsorption; The first fluid volume, the second fluid volume and the droplet generator are respectively configured and adapted so that when the following equation is satisfied: ρ2h2<ρ1h1 A plurality of aqueous solution droplets are formed and released, each droplet rising through the second fluid volume and approaching the electrode; wherein the electrode is a ring electrode, aligned above the droplet generator, and configured to generate a displacement current by electrostatic induction; and The load includes a rainfall monitoring system configured to monitor a corresponding rainfall amount based on a voltage between a positive terminal and a ground terminal.

20. The system of claim 18, wherein: The first fluid volume comprises rainwater, and the oil comprises oleic acid (OA) or hexadecane (Hex) or both, configured to charge corresponding raindrops by functional group dissociation and / or preferential ion adsorption; The first fluid volume, the second fluid volume and the droplet generator are respectively configured and adapted so that when the following equation is satisfied: ρ2h2<ρ1h1 A plurality of aqueous solution droplets are formed and released, each droplet descending through the second fluid volume and approaching the electrode; wherein the electrode is a ring electrode, aligned below the droplet generator, and configured to generate a displacement current by electrostatic induction; and The load includes a rainfall monitoring system configured to monitor a corresponding rainfall amount based on a voltage between a positive terminal and a ground terminal.

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