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A hybrid triboelectric nanogenerator for enhancing corrosion prevention of metallic in marine surroundings


Development of S-TENG

The spherical triboelectric nanogenerator (S-TENG) as schematically proven in Fig. 1a is principally composed of two elements: the internal solid-solid TENG and the outer strong–liquid TENG. For the strong–strong TENG, some sponge balls are positioned contained in the hole plastic sphere and sway periodically with the motion of waves. The outer strong–liquid TENG is a single electrode mode TENG, which is pushed by contact-separation of water and polytetrafluoroethylene (PTFE). The detailed fabrication means of the S-TENG gadget may be discovered within the Strategies and the photographs of the true gadgets is illustrated in Supplementary Fig. 1. It’s price mentioning {that a} pendulum is positioned contained in the sphere and swings periodically with the fluctuation of sea water, in order that drives the sponge balls for periodical contact and separation motion with the internal floor of the spherical. This built-in design is ready to successfully make full use of the outer and internal friction floor of the spherical, enhance the area utilization of the spherical construction and clearly improve the output efficiency of TENG.

Fig. 1: Schematic illustration of the design and precept of S-TENG.
figure 1

a Schematic illustration of the S-TENG. b Schematic construction of S-TENG within the internal. c Detailed construction of sponge balls. d Overhead view of the S-TENG. Operation precept of the internal strong–strong TENG (e) underneath contact–separation mode. Operation precept of the outer solid-liquid TENG (f) underneath single electrode mode.

The operation mechanism of the S-TENG is principally based mostly on the conjugation of triboelectrification and electrostatic induction. Determine 1e describes the operation precept of the internal strong–strong TENG. Accompanying the forwards and backwards motion of the sponge ball, the Al foils on the internal floor of the plastic sphere is involved–separation with the PTFE–Cu movies on the floor of sponge ball. Because of the totally different talents of attracting electrons between Al and PTFE, the Al foils are related because the constructive output finish and all of the Cu electrodes underneath PTFE movies are related collectively because the unfavorable output finish. In the beginning, there isn’t a cost between the PTFE movie and the Al electrode. When the gadget was pushed by water waves, the gap between the Al foil and the PTFE movie begins to lower and the potential distinction between the 2 surfaces is established, driving electrons from the Al foil to the Cu electrode underneath the PTFE movie and generate an instantaneous present. When the PTFE movie is in full contact with the Al electrode, the cost is neutralized. Because the S-TENG continued to oscillate with the ocean waves, the Al foil is separated from the PTFE movie and the potential distinction is established once more, the electron on the PTFE movie had been transferred to the Al foil till new stability is achieved. Correspondingly, a present with reverse route can be generated.

The operation precept of the strong–liquid TENG underneath single electrode mode for harvesting water wave vitality is depicted in Fig. 1f. Equally, as a result of totally different talents of attracting electrons between PTFE and water, they develop into negatively charged and positively charged after contacting with one another. Electrical potential distinction is produced when the PTFE movie is rotating throughout the water air interface. Electrons pushed by {the electrical} potential distinction are compelled to movement between the Cu electrode and floor, producing output present movement.

Floor remedy of PTFE movie

For solid-liquid TENG, you will need to have good hydrophobicity on the friction materials floor, as a result of the residual water on the fabric floor would scale back the facility technology capability37. Setting up microstructures on the electrode floor cannot solely enhance the friction space, but in addition enhance the hydrophobicity. Right here, the floor of PTFE movies had been handled with emery papers and their scanning electron microscope (SEM) photos are displayed in Fig. 2a, b. It’s clear that the floor roughness of PTFE movie is elevated after roughening with emery papers. The floor hydrophobicity of PTFE movie was evaluated by water contact angle measurements, from Fig. 2c and d, it may be seen that the contact angle between the PTFE movie and deionized water will increase from 108° to 132° after be handled with emery papers, and never residual water adsorbed on the floor. This consequence may be defined by the Wenzel’s equation (Eq. 1)38,39.

$$cos theta _1 = rcos theta _2$$

(1)

the place θ1 is Wenzel obvious contact angle, θ2 corresponds to actual contact angle on a easy floor, and r represents ratio of the particular floor to the geometric floor, that known as floor roughness issue. Based on the equation, it may be discovered that when θ2 is lower than 90°, the floor is hydrophilic, enhance of the floor roughness will result in a decrease θ1. Quite the opposite, when θ2 is greater than 90°, the floor is hydrophobic, the rise of the floor roughness will induce the next θ1. The results of PTFE movie floor roughness and get in touch with angle, as proven in Fig. 2, are in line with this conclusion. As well as, the linear motor was used to simulate the movement of ocean waves, on the frequency of 1 Hz, the comparability of output efficiency for the TENG with roughened and easy PTFE movie is proven in Fig. 2e, f. Each short-circuit currents (ISC) and open-circuit voltages (VOC) of the PTFE movie handled with emery papers are larger than that with out remedy, indicating that the output efficiency of PTFE movie will increase after roughening.

Fig. 2: The efficiency of PTFE movie after floor remedy.
figure 2

SEM picture of the PTFE movie earlier than (a) and after (b) being polished with emery papers. The hydrophobicity photos of deionized water drop on a PTFE movie earlier than (c) and after (d) being polished with emery papers. Brief-circuit present (e) and open-circuit voltage (f) between the 2 dielectric supplies of PTFE movie and Al foil.

Electrical characterizations of S-TENG

To comply with the working conduct of S-TENG, the gadget was examined in a tank that simulates the movement of ocean waves. Determine 3 presents the output efficiency of the S-TENG with totally different numbers of sponge balls within the hole plastic spherical. Each short-circuit currents (ISC) and open-circuit voltages (VOC) of solid-solid TENG as proven in Fig. 3c, d, respectively, enhance because the variety of sponge balls enhance, i.e., the best worth of ISC and VOC elevated from 95.8 μA to 174 μA and 9.6 V to 14.6 V, respectively, when the variety of the sponge balls elevated from 4 to six. This phenomenon is because of the truth that growing contact space between PTFE movie on the sponge balls and Al electrodes would enhance the quantity of cost by separated contact. Constrained by the restricted area, the optimum variety of the sponge balls with a diameter of 40 mm within the S-TENG, which with a diameter of 16 cm, is roughly six. Determine 3e, f reveals the output efficiency of the solid-liquid TENG with ISC and VOC of roughly 150 μA and 60 V, respectively. The output efficiency of S-TENG as proven in Fig. 3g, h, when the variety of the sponge balls will increase from 4 to six, the height worth of ISC and VOC additionally enhance from 237 μA to 399 μA and 73.6 V to 88.9 V, respectively. As the present outputs of the S-TENG reveals alternating present (AC) attribute, it’s required to be rectified. Determine 3i is a rectifier circuit diagram for TENG, and the present output of the S-TENG after rectified is about 220 μA as proven in Fig. 3j. What’s extra, from Fig. 3k, it’s apparent that the S-TENG stays secure after steady operation of 400,000 cycles and its output in enhanced after working for a very long time. The consequence is because of cost accumulation impact on the floor of PTFE triboelectrode and in addition signifies that the S-TENG gadget possesses good stability in simulated marine. The harvested wave vitality may be saved within the totally different capacitors as proven in Fig. 3l. The capacitors with capacities starting from 1 μF to 47 μF are charged to fifteen V, and the required time size is elevated from 2 s to 7 min.

Fig. 3: {The electrical} characterizations of S-TENG.
figure 3

a and b Schematic diagram of sponge balls with totally different numbers. Brief-circuit present (c) and open-circuit voltage (d) of the solid-solid TENG with totally different numbers of sponge balls. Brief-circuit present (e) and open-circuit voltage (f) of the solid-liquid TENG. Brief-circuit present (g) and open-circuit voltage (h) of the S-TENG with totally different numbers of sponge balls. i Schematic diagram of rectifier circuit of TENG. j The rectified present of the S-TENG. ok Stability take a look at of the S-TENG. l The charging curves of various capacitors charged by the S-TENG within the wave tank tools.

Cathodic safety system based mostly on the S-TENG

Determine 4a present schematic association of the wave-powered cathodic safety system based mostly on the S-TENG. When the water wave drives the S-TENG to start out working, the electrons generated by triboelectrification is transferred to the metals in sea water, leading to cathodic polarization to a sure extent. On this wave-powered cathodic safety system, potential shift is a key parameter to worth the efficiency of cathodic safety5. In brief, extra electrons transferred leads extra unfavorable shift of the potential of the metals and more practical cathodic safety. A 3-electrode system is used to check the potential variation of the 304 chrome steel (304SS) coupled with and with out TENG. From Fig. 4b, with out TENG, the potential of the 304SS in 3.5 wt% NaCl resolution is about −0.21 V (vs. SCE) and it dropped quickly to −0.47 V (vs. SCE) and −0.52 V (vs. SCE) when the 304SS was related to solid-solid TENG and solid-liquid TENG, respectively, then slowly restored to their unique potential when TENGs disconnected. As anticipated, whereas the 304SS is related with the S-TENG, the safety potential shifted to −0.62 V, presenting extra environment friendly cathodic safety than any single working-mode TENG. The periodic variation of the potential signifies that the excessive repeatability of the self-powered cathodic safety system pushed by totally different mode of TENGs. Furthermore, in Fig. 4c, after two hours of steady safety with S-TENG within the wave tank, the safety potential of the 304SS maintains at −0.62 V and additional signifies the steadiness of the cathodic safety system. The immersion checks of 304SS in 3.5 wt% NaCl resolution as proven in Fig. 4d, e had been carried out to additional examine the cathodic safety efficiency. In the beginning of immersion, the safety potential of 304SS shifted negatively by 0.34 V. It’s apparent that the safety potential shift of 304SS elevated from 0.34 V to 0.49 V as growing the immersion time, and it remained secure after 7 days. The constructive shift of safety potential may be attributed to the self-repair and development of passive movie on 304SS when immersed for the primary 0–4 days, that’s, with the rise of immersion time, the safety present required by 304SS step by step decreases. When the immersion time exceeds 4 days, the impact of cathodic safety reaches the height and tends to be secure, that’s, the safety present required additionally tends to be secure. Moreover, the metallic electrode with totally different space coupled with and with out S-TENG was examined to review the connection between safety potential adjustments and the realm of protected metallic. As proven in Fig. 4g, with the publicity space of 304SS enhance from 0.79 cm2 to five.31 cm2, the unfavorable shift of safety potential lower from 0.38 V to 0.11 V when related with the S-TENG. From the becoming curve in Fig. 4h, it may be clearly seen that the shift of safety potential of 304SS reveals a great unfavorable linear relationship with its space. The equation (Eq. 2) similar to the becoming curve is as comply with:

$$y = 0.41 – 0.057x$$

(2)

the place y is the shift of safety potential of 304SS when related with S-TENG, x is the publicity space of 304SS electrode. Based on the reported of Solar et al.40, the safety potential of 304SS ranged from −0.47 V to −0.8 V, that’s, the safety supplied by S-TENG is efficient solely when the shift of potential of 304SS reaches at the least 260 mV. Subsequently, our gadget (the amount is about 2144.66 cm3) can present successfully cathodic safety for 1.77 cm2 of 304SS in simulated marine. When the realm of 304SS larger than 1.77 cm2, it’s required to responsively enlarge S-TENG scale.

Fig. 4: The cathodic safety efficiency of S-TENG.
figure 4

a Schematic association of the S-TENG cathodic safety of metallic in 3.5 wt% NaCl resolution. b Potential adjustments of a 304SS electrode coupled with and with out solid-solid TENG, solid-liquid TENG and S-TENG respectively. c Stability take a look at of the S-TENG. d Potential adjustments of a 304SS electrode coupled with and with out S-TENG at totally different immersion time. e Potential drop worth of 304SS at totally different immersion time. f Tafel curves of 304SS with and with out S-TENG. g Potential adjustments of 304SS electrodes with totally different areas coupled with and with out S-TENG. h Potential drop worth of 304SS with totally different areas and its becoming curve. i Potential change of a Q235CS electrode coupled with and with out S-TENG at totally different the coating thickness. j Potential adjustments of Q235CS electrodes with totally different areas coupled with and with out S-TENG. ok Potential drop worth of Q235 with totally different areas and its becoming curve.

For Q235 carbon metal (Q235CS), the mixture of cathodic safety and natural coating is usually used to guard it from corrosion in marine surroundings41. The barrier impact of the coating can largely scale back the present density required for cathodic safety, and cathodic safety can keep efficient safety even when the coating regionally broken42. The cathodic safety potential of carbon metal is normally required from −0.77 V to −1.1V43. From Fig. 5i, it may be seen that when the thickness of waterborne acrylic coating is r = 25 μm, the safety potential of Q235CS related with S-TENG is throughout the efficient safety vary. As proven in Fig. 4j, the S-TENG is ready to present successfully cathodic safety for 7.07 cm2 of Q235CS in simulated marine, and the shift of safety potential of Q235CS additionally reveals a great unfavorable linear relationship with its publicity space. The equation (Eq. 3) similar to the becoming curve is as comply with:

$$y = 0.97 – 0.057x$$

(3)

the place y is the shift of safety potential of Q235CS when related with S-TENG, x is the realm of Q235CS electrode.

Fig. 5: The EIS of 304SS.
figure 5

a Nyquist curves of 304SS with and with out cathodic safety powered by the S-TENG. b The equal circuit of 304SS related with out the S-TENG and (c) the equal circuit of 304SS related with the S-TENG. d Impedance-frequency Bode plots and (e) Part-frequency Bode plots of 304SS with and with out cathodic safety powered by the S-TENG.

Tafel polarization curves are normally adopted to review the corrosion fee by measuring the corrosion potential and corrosion present density. Determine 4f reveals the Tafel plots of the 304SS related with and with out the S-TENG and its corresponding electrochemical parameters together with corrosion potential, corrosion present density, anodic Tafel slope (ba) and cathodic Tafel slope (bc) listed in Desk 1. Within the cathodic safety system, the bigger unfavorable shift of corrosion potential signifies that extra electrons movement to 304SS and thus, the stronger cathodic safety impact may be achieved. The corrosion potential of the 304SS is about −0.23 V and −0.64 V (vs. SCE) with out and with S-TENG. The outcomes point out that the corrosion resistance of 304SS could possibly be successfully improved by cathodic safety system pushed by S-TENG. What’s extra, as proven in Desk 1, in contrast with the 304SS with out S-TENG, the corrosion present density of 304SS with S-TENG elevated by ~40 instances. It may be concluded that the electrochemical response is accelerated by injecting electrons produced by S-TENG into the floor of 304SS. The above outcomes are in good settlement with the potential as proven in Fig. 4b. In conclusion, the Tafel plot reveals that the cathodic safety system pushed by S-TENG can enhance corrosion resistant efficiency by injecting a considerable amount of electrons into the floor of 304SS.

Desk 1 Electrochemical parameters obtained from Tafel curves of 304SS related with and with out the S-TENG.

The arc of Nyquist plot similar to the 304SS with S-TENG as proven in Fig. 5a is far smaller than that with out S-TENG. Apart from, in accordance with Fig. 5d, it’s apparent that the low frequency impedance modulus of the 304SS with S-TENG is sort of two orders of magnitudes decrease than that with out S-TENG. In Fig. 5e, the utmost part angle of 304SS with S-TENG turns into smaller and narrower than that of with out S-TENG, which may be attributed to the impact of injection of exterior electrons. Right here, the equal circuit of the S-TENG safety system and the worth of every part are obtained by curve becoming, and the electrochemical response mechanism and kinetic course of are described qualitatively and quantitatively. The CPE (fixed part aspect) is generally used to investigate the impedance spectrum of the particular electrode course of underneath non-ideal situations. There are two vital parameters of CPE in equal circuit: admittance Y and energy index quantity n, the method is Y = Y0()n. When n is the same as 0, CPE is flip into pure resistance, and when n is the same as 1, CPE is flip into pure capacitance. Normally, the worth of n is between 0 and 1. Determine 5b displays the equal circuit of 304SS with out the S-TENG described as Rs(QlRct). Extra particularly, Q corresponds to CPE, Rs represents electrolyte resistance and Rct represents cost switch resistance. Determine 5c reveals the equal circuit of 304SS with the S-TENG described as Rs(QlRct)(CdlRf). Particularly, Rf corresponds to the 304 chrome steel/resolution interface layer resistance and Cdl corresponds to the double-layer capacitance. The element electrochemical parameters of the equal circuit are displayed in Desk 2, through which Rct worth of the 304SS with S-TENG is far decrease than that of the 304SS with out S-TENG. Because of the Rct is the same as the cost switch resistance, a smaller Rct represents quicker electron switch to the metals, ensuing from the reciprocating oscillation of the S-TENG.

Desk 2 Electrochemical impedance parameters for 304SS with and with out impressed present cathodic safety powered by the S-TENG in 3.5 wt% NaCl resolution.

The immersion checks of Q235CS was carried out in simulated seawater to research the sensible impact of corrosion safety. Determine 6 reveals the digital images of the floor morphology of the Q235CS with and with out S-TENG after immersing in 3.5 wt% NaCl resolution at totally different instances. It’s apparent by bare eye that rather more rust appeared on the Q235CS with out S-TENG than that with S-TENG at totally different immersion time. Usually talking, as soon as corrosion occurred on Q235CS floor the corrosion fee will increase quickly and increasingly more rust expands on the floor. When the immersion time was prolonged to six h within the 3.5 wt% NaCl resolution, the Q235CS with out S-TENG is corroded in a big space, whereas just some corrosion spots appeared on the Q235CS with S-TENG. The outcomes show that the self-powered system based mostly on the S-TENG can successfully scale back the corrosion fee, that’s, the cathodic safety system powered by the S-TENG is an efficient anti-corrosion methodology.

Fig. 6: The digital images of Q235 carbon steels.
figure 6

The floor morphology of Q235 carbon steels immersed in 3.5 wt% NaCl resolution for two h, 4 h and 6 h, individually, related with out and with the S-TENG.

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