Pressurized well-inspired triboelectric nanogenerators for harvesting water wave energy toward marine environmental applications†

Yan Wu^abc, Xiutong Wang*^acd, Lihui Yang^a, Youqiang Wang^c, Youbo Nan^abd, Hui Xu^a, Hui Zhou^a and Weilong Liu^a
aState Key Laboratory of Advanced Marine Materials, Key Laboratory of Marine Environmental Corrosion and Bio-fouling, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, China. E-mail: wangxiutong@qdio.ac.cn
^bInstitute of Marine Corrosion Protection, Guangxi Key Laboratory of Marine Environmental Science, Guangxi Academy of Sciences, Nanning, 530007, China
^cQingdao University of Technology, Qingdao, 266525, China
^dUniversity of Chinese Academy of Sciences, Beijing, 100049, China

First published on 29th May 2025

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1. Introduction

Energy shortage and environmental pollution have raised widespread concerns around the world. The creation and application of sustainable energy are of crucial significance to the realization of sustainable global economic development.^1,2 Among the most abundant sources of renewable energy in the world, water wave energy has received extensive attention from different countries.^3,4 For wave energy harvesting, traditional electromagnetic generators (EMGs) are still mostly used, which have limitations such as heavy weight, large volume, high cost, and low efficiency for low-frequency energy harvesting. There is an urgent need for a small, efficient, easy-to-maintain, and low-cost technology for marine environments to efficiently harvest the high-entropy energy of the ocean.^5,6

Researchers from all around the world have been increasingly interested in triboelectric nanogenerators (TENGs) since their introduction in 2012. TENGs are based on the coupling effects of triboelectrification and electrostatic induction.^7–9 Vertical contact separation, contact sliding, single electrode, and freestanding triboelectric layers are the four fundamental operating modes of TENGs, which can harvest many sources of energy, including vibration,^10,11 wind energy,^12–14 water wave energy,^15–20 and human motion.^21–23 A TENG has the characteristics of light weight, low cost, diverse structure, wide selection of materials,²⁴ and extremely high efficiency even at low frequencies, making it unique in water wave energy harvesting. So far, many researchers have used the principle of triboelectric nanogenerators to develop and design suitable devices for harvesting water wave energy. Numerous structural devices have been developed to harvest energy from water waves. These devices include the following: a collectively exhaustive hybrid triboelectric nanogenerator based on a flow-induced impacting-sliding cylinder,²⁵ a segmented swing-structured fur-based triboelectric nanogenerator,²⁶ an anti-overturning fully symmetrical triboelectric nanogenerator based on an elliptic cylindrical structure²⁷ and a pulsed triboelectric nanogenerator.²⁸ The captured energy was used for power supply, sensing system, cathodic protection and signal transmission, etc.

To achieve high-performance wave energy harvesting, we are inspired by an ancient technique to lifting water. Several techniques were employed by early humans to transport potable water from near-surface rock formations. They created plunger pumps with bamboo pipes and stone-carved valves, and they used wooden poles to run the pumps from the surface.²⁹ Such devices were named pressure wells, as shown in Fig. S1(a).† The pressure well device uses the mechanical lever principle, the fulcrum and the resistance point, and the force points are all on the handle. The handle is a labor-saving lever that drives the piston up and down when the end of the handle is lifted. This technology has some applications in other fields such as the beam pumping unit, as shown in Fig. S1(b),† which has been used in more than 900000 oil wells worldwide for more than 150 years.³⁰ Herein, we propose a novel pressurized well structure-inspired triboelectric nanogenerator (IPW-TENG) for water wave energy harvesting in marine environmental applications. Based on the lever principle, irregular water wave energy is converted by the connecting rod system into vertical motion of the nylon brush, which is ultimately transformed into electricity. The core innovation of this study lies in the novel proposal and optimization of a cooperative working mechanism for multi-level linkage-independent friction units driven by wave energy under an innovative structural framework. The device exhibits low material requirements and features a simple architecture. Through unique mechanical decoupling design and parameter configuration optimization, the system achieves an open-circuit voltage of 960 V using commercial nylon/PTFE friction materials. An array of power generation units is integrated and driven by the IPW-TENG to collect simulated wave energy. At a driving frequency of 1 Hz, the IPW-TENG successfully powers LED lights, calculators, digital thermometers, and alarms. Compared with wave energy harvesters based on analogous principles, the IPW-TENG demonstrates superior electrical output performance. This device holds significant potential for offshore self-powered systems due to its innovative approach to large-scale water wave energy collection.

2. Results and discussion

2.1 Structure and principle

In this study, we optimized the IPW-TENG device, tested and discussed the performance from the aspects of charging and power supply. We demonstrated the possibility of the device to harvest water wave energy in the marine environment and applied it to a self-powered service system. Finally, the IPW-TENG device was applied to corrosion protection.

Ten key pieces make up the structure components of the IPW-TENG, which are displayed in Fig. 1(a): (1) central gravity cone; (2) foam swimming ring; (3) floating ball; (4) connecting rod system; (5) bracket; (6) friction cylinder; (7) nylon brush; (8) polytetrafluoroethylene (PTFE) film; (9) copper electrode; and (10) polyethylene terephthalate (PET) film. The part distribution position and different views of the IPW-TENG are shown in Fig. S2.† The digital photographs of structure components are shown in Fig. S3–S7.† Among these, the energy from irregular water waves is harvested using the floating ball, and the connecting rod system is equipped with a chain link, which is used as a motion transmission structure, wherein nylon brush, PTFE film, copper electrode and PET film constitute a tribological power generation unit, which is installed in the friction cylinder marked in Fig. 1(a) and arranged around the center of gravity cone. The IPW-TENG produced in this experiment uses 6 power generation units.

Upon positioning the IPW-TENG in the maritime setting, the floating ball used the irregular wave energy to generate a reciprocating vertical motion of the nylon brush via the connecting rod system. The foam swimming ring and the floating ball played the role of floating. The central gravity cone played the role of stabilizing the apparatus. The central gravity cone is a hollow structure with sand or other ballast filling in. In the state of no water waves, they guaranteed that IPW-TENG floated vertically on the water without tilting. At this moment, the nylon brush was in the same position as the middle copper electrode and remained stationary. As shown in Fig. 1(b), when the floating ball floated with the water wave, the connecting rod system and the floating ball formed different angles to drive the nylon brush to reciprocate to acquire voltage signals. When the wave crests came, the floating ball floated upward. Since the floating ball was fixed to the connecting rod, it drove the end of the connecting rod to move upward. According to the lever principle, the other end of the connecting rod drove the nylon brush vertically to move downward. When the wave trough came, the floating ball floated downward, and the connecting rod tilted again and drove the nylon brush straight up. Taking this as a cycle, the nylon brush moved vertically and reciprocated friction with the PTFE film. The IPW-TENG continuously converted kinetic energy under the surge of water waves and ultimately transformed it into electrical energy by means of the PTFE film's reciprocating friction with the nylon brush, realizing the harvest of water wave energy.

2.2 Finite element method simulations

The tribological power generation unit of the IPW-TENG converted the reciprocating friction motion of the nylon brush and the PTFE film into electrical energy. Its working principle is shown in Fig. 2(a).^26,31,32 The nylon brush acted as an independent layer, and the PTFE film acted as an intermediate isolation layer and completely covered the three fixed copper electrodes. The two contact surfaces of the nylon brush and the PTFE film produced triboelectric charges through the coupling effects of triboelectrification and electrostatic induction. As various materials have varying capacities for electron loss, the surface of the nylon brush was prone to losing electrons and being positively charged, while the polytetrafluoroethylene film was the opposite. When the nylon brush and PTFE film were at rest, the potential induced between the electrodes was constant.^33,34 When the floating ball drove the connecting rod to drive the relative motion of the nylon brush and PTFE film, electrons were forced to migrate between the electrodes in order to balance the electrostatic system since it created a potential difference between them, thus generating alternating current.^16,27,28,35 The electric field distribution and potential of the IPW-TENG of single power generation unit were analyzed through the finite element method in simulation. The TENG was designed as a “two-dimensional model” with the electrostatic module of COMSOL multiphysics 5.5, where the nylon brush was equivalent to a rectangle with a width of 60 mm and a height of 63.2 mm, and the PTFE film was equivalent to a rectangle with a width of 200 mm and a height of 0.1 mm, whose geometry was surrounded by air. The surface charge density of the nylon brush and PTFE film were calculated based on the output voltage, and the fundamental material properties of PTFE, nylon, and copper were incorporated accordingly. The boundary conditions for the electrostatic field were defined as follows: charge conservation was enforced across all domains, the air field boundary was set to zero charge, the initial potential of all domains was initialized to zero, the surface charge density of the nylon brush and PTFE film were specified, and the air field boundary was grounded. A refined mesh was subsequently constructed for the entire model to ensure computational accuracy, and parametric scanning was performed. The PTFE film was fixed in position, while the nylon brush was configured to be vertically movable within a predefined displacement range. Finally, the surface potential of the model was calculated, as displayed in Fig. 2(b). With the upward movement of the nylon brush, the progressive increase in the voltage differential between the copper electrode and the nylon brush, when the nylon brush moves to the top, the potential difference reaches the maximum. When the nylon brush gradually moves down, the potential difference changes in the same way, and the simulation results are shown in Fig. S8.†

2.3 Electrical performance of TENGs

To evaluate the output performance, the IPW-TENG of single power generation unit was fixed on the linear motor driven at a frequency of 3 Hz. Firstly, the influence of friction materials on the electrical output performance was systematically investigated. The height of the brush was set to be equal to that of the copper electrode to achieve a complete contact-separation state. The device performance was optimized through diameter variation in the bristles of positive friction materials (nylon brushes) and negative friction materials. When the bristle diameter of the nylon brush was 0.1 mm, the friction materials, respectively, were polyimide film (PI), polyethylene terephthalate film (PET), polytetrafluoroethylene film (PTFE), and polyvinyl chloride (PVC), and IPW-TENG electrical output performance is shown in Fig. 3(a) and (b). The test findings demonstrated that the IPW-TENG's open-circuit voltage and transmitted charge were only 160 V and 0.05 μA, respectively, when the PI film was utilized. The greatest values of 960 V for the open-circuit voltage and 0.4 μC for the transferred charge were achieved when the PTFE film was utilized. PTFE exhibited high electrical output performance mainly due to its strong electronegativity and self-lubricity. The strong electronegativity of PTFE was attributed to the high electronegativity of fluorine atoms in its molecular structure and the strong polarity of the C–F bond, which enabled electrons to be efficiently captured during friction. At the same time, the low friction properties of PTFE as a solid lubricant further optimized the charge transfer efficiency. The materials used for the triboelectric layers in triboelectric nanogenerators must not only exhibit excellent electrical output performance but also possess a low coefficient of friction, high wear resistance, thermal stability, and self-lubricating properties. In addition to the above-mentioned materials, some other candidate friction layer materials are provided in Table S1.† The test results of the short-circuit current of IPW-TENG under four different materials are shown in Fig. S9.† According to the triboelectric sequence, PTFE has a negative polarity and nylon has a positive polarity. The two materials are far apart in the sequence, and the corresponding transfer charge is larger, thereby achieving a better electrical output effect.³⁶ When the PTFE film was selected as the negative friction material, the electrical output test results of the IPW-TENG when the bristle diameter of the nylon brush were 0.08 mm to 0.3 mm are shown in Fig. 3(c) and S10.† It was found that the smaller diameter resulted in larger contact area and higher electrical output performance. When the diameter was 0.3 mm, the open-circuit voltage reached only 280 V and the short-circuit current only reached 2.83 μA. When the diameter was 0.08 mm, the bristle was relatively soft, the force between the friction materials was reduced, and the electrical output performance was slightly decreased. The test results of transferred charges of IPW-TENG under different bristle diameters of the nylon brush are shown in Fig. S11.† In summary, using a nylon brush with a diameter of 0.1 mm and a PTFE film, the electrical output performance was optimal, and the charge transfer amount reached 0.4 μC. The test result is shown in Fig. 3(d).^37–39

The influence of the mechanical driving frequency on the electrical output performance was studied, and Fig. 4(a) and (b) displays the test outcome. The results showed that the open-circuit voltage reached 84 V and the short-circuit current reached 0.57 μA at a low frequency of 0.5 Hz, and with the increase in frequency, both the voltage and the current displayed an increasing tendency. Ohm's law states that as the short-circuit current is mostly influenced by the speed at which the two surfaces separate, the voltage increases with the current.^40,41 When the frequency reached 4 Hz, the open-circuit voltage reached 1380 V, and the short-circuit current reached 13.87 μA. The transferred charge was observed to increase with the driving frequency, as demonstrated in Fig. S12.† Based on the relationship Q = I∫dt, where charge was defined as the time integral of current, the enhancement in charge transfer was attributed to the elevated short-circuit current under higher driving frequencies. When the driving frequency was raised from 0.5 Hz to 4 Hz, the transferred charge was measured to increase from 0.13 μC to 0.42 μC. To evaluate the power supply capacity, the charging performance of the IPW-TENG of single power generation unit was tested, and the results are shown in Fig. 4(c) and S13.† The 1 μF, 10 μF, and 100 μF capacitors could be charged to 91.84 V, 24.19 V, and 2.9 V, respectively, within 60 s. IPW-TENG has proven good power supply performance and has a wide application promise in the energy supply of electronic equipment.⁴² Considering the durability of the marine environment, the IPW-TENG device adopted a waterproof packaging design and a non-metallic PVC shell resistant to salt fog, thus establishing a primary protection system. The durability test results of IPW-TENG are displayed in Fig. 4(d). During the 11400 cycles, the electrical output of IPW-TENG was basically unchanged, which indicated that it has output stability.^23,41 In addition, after connecting the circuit to a range of resistors ranging from 0 MΩ to 100 MΩ, the power generation unit voltage and current were tested, and the peak power was calculated, and the test results are shown in Fig. 4(e) and (f). As the resistance increases, the current showed a decreasing trend, and the voltage showed an increasing trend. According to the measured peak voltage and peak current, the peak power of the IPW-TENG under external load was calculated using the formula P = U²/R. Due to the inherent capacitance characteristics of the triboelectric nanogenerator, when the external resistance was equal to the internal impedance with a value of 80 MΩ, the power reached the maximum value of 31.24 × 10⁻⁴ W.^28,43 It was worth noting that the output power of IPW-TENG was much higher than that of other TENGs reported previously, as shown in Table S2.†

Wave in the marine environment has the characteristics of low frequency, disorder and wide distribution.^44–46 The six-degree-of-freedom swing platform can reproduce the wave spectrum and simulate water waves. We integrated the six power generation units into the IPW-TENG to obtain multi-directional wave energy, as shown in Fig. 1(a), and the circuit connection is shown in Fig. 5(a). In order to prove the electrical output performance of the IPW-TENG in harvesting wave energy, the IPW-TENG was driven by a six-degree-of-freedom swing platform to harvest the energy of simulated water waves,^47–51 as shown in Fig. 5(b). The video is shown in ESI Video S1.† When the frequency of the simulated water wave was 0.33 Hz, the open circuit voltage of IPW-TENG reached 192 V and the short-circuit current reached 1.4 μA after rectification. As the frequency of the simulated water wave increased, the open-circuit voltage and short-circuit current showed an increasing trend. When the frequency of the simulated water wave was 2 Hz, the current reached 15.6 μA and the voltage reached 900 V, as shown in Fig. 5(c) and (d). In the actual ocean, each power generation unit will have a different motion state due to the disorder of the water wave, and since they are independent of each other, they will not affect each other. Not only that, more units will give the whole device better stability and greater friction area, resulting in better power output. The charging and power supply characteristics of the IPW-TENG driven by external low frequency were further studied. When the frequency of simulated water wave was 1 Hz, the IPW-TENG charged capacitors with different capacities, as shown in Fig. 5(e). Within 180 s, the capacitors of 10 μF, 100 μF and 470 μF were charged to 27.44 V, 5.3 V and 1.22 V, respectively. With the increase in capacitance, the charging voltage decreased with the decrease in charging speed.

In addition, the IPW-TENG device combination capacitor could drive electronic devices, and the circuit diagram is shown in Fig. 5(a). First, the electrical energy generated by the IPW-TENG was rectified separately and then connected in parallel to eliminate the interference caused by phase differences. The rectified pulse electrical energy was stored in the capacitor, and the capacitor's filtering and voltage-stabilizing effects were utilized to eliminate the influence of the pulse signal on the electronic device and achieve energy accumulation. Subsequently, the electronic device was connected to drive its operation. As shown in Fig. 6(a), the 470 μF capacitor was charged to 1.5 V by the IPW-TENG after 230 s, and the calculator could work normally after being connected, and the video is shown in ESI Video S2.† After 500 s, the 470 μF capacitor was charged to 3.5 V by the IPW-TENG, as shown in Fig. 6(b), and the thermometer could work normally after being connected, and the video is shown in ESI Video S3.† The IPW-TENG could light up to 260 commercial LED lights, as displayed in Fig. 6(c). The IPW-TENG could successfully charge the alarm, as shown in Fig. 6(d), the charging curve is shown in Fig. S14,† and the video is shown in ESI Video S4.† The above-mentioned test results demonstrate the possibility of the IPW-TENG for capturing water wave energy in marine environments and its great potential for application in self-powered service systems.

2.4 Application in cathodic protection

For the metal structures in the marine environment, corrosion can cause great economic loss and bring high safety risk.^52,53 TENG technology with efficient wave energy harvesting can provide protection for the steel. In many investigations, energy harvesting and self-utilization have been accomplished by combining TENGs and impressed current cathodic protection. Herein, we applied the IPW-TENG single power generation unit to cathodic protection in the marine environment, and the schematic diagram is shown in Fig. 7(a). To replicate a marine environment, a 3.5 wt% NaCl solution was prepared, and testing was conducted using a three-electrode system, with a platinum electrode serving as the counter electrode, a calomel electrode serving as the reference electrode, and a working electrode made of 304 stainless steel (304SS) with 10 mm diameter. By using a rectifier bridge, the alternating current produced by the IPW-TENG was changed into direct current, and then the positive electrode of the current was connected to the platinum electrode and the negative electrode was connected to the working electrode. Ultimately, the 304SS surface received electron transfer to prevent corrosion.

A crucial metric for assessing the effectiveness of cathodic protection is the metal's open circuit potential (OCP), the test results of which are displayed in Fig. 7(b). After submerging 304SS in a 3.5 wt% NaCl solution, its potential leveled off at −0.2 V. Upon connecting the IPW-TENG, the electrons were moved to the 304SS surface, causing a sharp decline in potential to −0.4 V by −0.2 V, and after disconnecting again, the potential quickly returned to the self-corrosion potential. After 4000 s of testing, it is strongly proved that the protection of 304SS by the IPW-TENG is effective and stable.^54–56 To make the change in electrode potential with current intensity clearer, we tested the polarization curve, and the result is shown in Fig. 7(c). Electrochemical parameters are shown in Table 1. In the corrosion process of steel, the oxidation of iron atoms was observed in the anode region, while the reduction of dissolved oxygen was conducted in the cathode region. With the introduction of the IPW-TENG, the generated electrons were delivered to the metal surface, leading to the induction of cathodic polarization. The continuous supply of electrons by the IPW-TENG resulted in the suppression of Fe atom oxidation, thereby causing a reduction in the corrosion rate of 304SS. This phenomenon was consistent with the negative shift in corrosion potential depicted in Fig. 7(b). Compared to the scenario where IPW-TENG was not connected, a significant increase in the current density of 304SS was observed upon IPW-TENG connection, which was attributed to the acceleration of the dissolved oxygen reduction reaction by electrons produced from the IPW-TENG. β_c represents the cathodic slope and β_a denotes the anodic slope, both of which reflect the magnitude of resistance in the electrochemical process. Following the application of cathodic protection, the alteration in the activation energy of the electrochemical reactions on the surface of 304SS resulted in a change in the reaction resistance, leading to a variation in the slopes. These findings further confirm that the corrosion of 304SS can be effectively prevented by the IPW-TENG-based cathodic protection system.³²

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The surface state of 304SS was further monitored through electrochemical impedance spectroscopy (EIS) testing, and the impedance curves were fitted to an equivalent circuit model. The complex electrochemical processes were simplified into intuitive circuit elements, and the electrochemical behavior of the cathodic protection system was simulated to further evaluate the system performance.^57,58 In the cathodic protection system, the electrochemical impedance spectroscopy was tested under working conditions with the application of cathodic protection current to reflect the impedance under actual operating conditions. The testing conditions and results of the electrochemical impedance are presented in Table S3† and Fig. 7(d), respectively. The arc diameter of the Nyquist plot was significantly lower with the IPW-TENG connected than it was without it. When the electrode was measured by electrochemical impedance, the electrode surface was subjected to the periodic charging and discharging process of double electric layers and the periodic changing process of the electrode reaction speed. At this time, the impedance of the electrode surface was equivalent to the circuit formed by the impedance of the two processes in parallel, and included the resistance caused by the reference electrode and the solution. After fitting the Nyquist curve using the ZSimpWin impedance spectrum fitting software, the equivalent circuit without the IPW-TENG could be described as R_s(Q₁R_ct), as shown in Fig. 7(e), and the equivalent circuit connected to IPW-TENG could be described as R_s(Q₁R_f) (C_dlR_ct), as shown in Fig. 7(f). The electrochemical parameters are shown in Table 2. The constant phase element (CPE) of Q₁ maintained a capacitive state on the interface. R_s is the electrolyte resistance, R_ct is the charge transfer resistance, R_f is the oxide film resistance, and C_dl is the double-layer capacitance.^59,60 Compared to the non-powered state, the charge transfer resistance (R_ct) of 304SS was significantly reduced, and the arc radius of the corresponding Nyquist curve was also observed to decrease. The reduction in R_ct was indicative of a lower charge transfer resistance, an increased electron transfer amount, and an accelerated transfer rate. This phenomenon was attributed to the triboelectric energy generated by the IPW-TENG, which was found to accelerate the charge transfer process, leading to a reduction in the R_ct value. This further demonstrated the effective corrosion protection provided by the coupled IPW-TENG.^55,61,62 The findings show that the IPW-TENG has a wide range of possible applications in the field of corrosion prevention in marine environments, including cathodic protection technology.

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3. Conclusion

In conclusion, an IPW-TENG device with kinetic energy conversion capacity was proposed, achieving high-entropy and low-frequency water wave energy harvesting based on TENG theory. Using the mechanical lever principle, the floating ball could effectively gather the energy from the erratic ocean waves, convert it into vertical motion of nylon brush through a connecting rod system, and finally, convert it into electrical energy. After a series of optimization experiments, the IPW-TENG of single power generation unit achieved an open-circuit voltage of 960 V and a short-circuit current of 9.8 μA under a mechanical driving frequency of 3 Hz and showed output stability. Through the array integration of a series of power generation units and the simulation of wave-driven IPW-TENG devices, the feasibility of harvesting water wave energy in marine environments was demonstrated. Additionally, electronic devices such as thermometers and alarm systems were successfully powered by the IPW-TENG device, illustrating its significant potential for application in self-powered service systems. More importantly, when the device was applied for the cathodic protection of metals, a potential drop exceeding 200 mV was observed for 304SS, demonstrating excellent anti-corrosion performance and enabling a self-driven electrochemical process without the need for external power sources. This study provides a viable solution for large-scale blue energy harvesting and offers support for achieving self-powered corrosion protection in marine environmental systems.

4. Experimental section

4.1 Manufacture of IPW-TENG device

A PVC pipe measuring 495 mm in length, 200 mm in diameter, and 2.5 mm in thickness was used to construct a central gravity cone and a conical cylinder with a height of 310 mm, which were glued together. The friction cylinder was a PVC pipe with a length of 200 mm, an inner diameter of 63.6 mm and a thickness of 5 mm, but its lower port was sealed with an acrylic sheet of the same diameter and fixed on a central gravity cone with glue. The friction cylinder was adhered to the bracket, which was 10 mm in width and 2 mm in thickness. The tribological power generation unit consisted of a PET film of dimensions 200 mm × 200 mm × 0.15 mm, three pieces of 200 mm × 60 mm × 0.1 mm copper tape, a 200 mm × 200 mm × 0.1 mm PTFE film and a nylon brush. Three pieces of copper tape were spaced 10 mm apart and connected to the wires. The PET film played a supporting role, copper tape as the electrode material, and the PTFE film as the friction material. They were assembled into a three-layer structure and fixed in the friction cylinder. According to the lever principle, the connecting rod system was divided into three points, the same principle as the mechanical lever used in ancient water pressure wells. It was fixed at the middle end of the bracket for the fulcrum. One end of the plastic float with a diameter of 150 mm was fixed as the force point. The other end of the nylon brush was fixed as the resistance point. The outer diameter of the nylon brush was 63.2 mm with a height of 60 mm, the bristle length was 20 mm with a diameter of 0.1 mm, and the diameter of the intermediate shaft was 22 mm. A foam swimming ring with a diameter of 500 mm, an inner diameter of 300 mm and a thickness of 85 mm was placed under the friction cylinder and fixed to the central gravity cone by ropes.

4.2 Characterization and measurements

A motor (PS01-37SX120F-HP-N, The LinMot. Inc., USA) was used to drive the IPW-TENG of single power generation unit. The IPW-TENG device of the integrated array power generation unit was driven by the six-degree-of-freedom swing platform (RX/YBT-6-5000(H), Ruixin Technology, China) to simulate water waves floating up and down. The wave height was fixed at 12 cm in the parameter analysis to determine the optimum wave characteristics for the best output performance. An electrometer was used to measure the short-circuit current, voltage while charging, and transferred charge of the IPW-TENG of single power generation unit (Keithley 6514, Tectronix, USA). The charging voltage of IPW-TENG was measured using a data collector (LR8431-30, HIOKI, Japan). Oscilloscope measurements (ROGOL DS12022-E, RIGOL (SUZHOU)TECHNOLOGIES INC, China) of the open-circuit voltage were carried out. An electrochemical workstation (CHI760E, Shanghai Chenhua, China) was used to assess the cathodic protection effect.

Data availability

The data that support the findings of this study are available in the ESI† of this article.

Author contributions

Yan Wu: conceptualization, data curation, writing – original draft, writing – review & editing. Xiutong Wang: supervision, funding acquisition, methodology, writing – review & editing. Lihui Yang: resources, funding acquisition. Youqiang Wang: resources, formal analysis. Youbo Nan: project administration, writing – original draft. Hui Xu: writing – original draft, software. Hui Zhou: investigation, software. Weilong Liu: visualization.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was supported by the fund of the National Natural Science Foundation of China (No. 42476207), the Innovation Platform for Academicians of Hainan Province, National Key Research and Development Plan of China (No. 2022YFB2603000), Key R&D Program of Shandong Province, China (No. 2022CXPT027), and Shandong Key Laboratory of Corrosion Science, Guangxi Science and Technology Program Foundation (No. AA23026007). The authors thank the Marine Instrument Center of Qingdao National Laboratory for Marine Science and Technology for the equipment support. The authors also thank Zunwei Li and Xiliang Cui for providing technical guidance.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4ta09110h

This journal is © The Royal Society of Chemistry 2025