Integrated 3D Ionic Electrets Electronic Skin (e-Skin) For Harvesting of TENG Energy Through Push-Pull 3D Ionic Electrets and Ion-ion Hopping Mechanism

The development of highly durable, stretchable, and steady triboelectric nanogenerators (TENGs) is highly desirable to satisfy the tight requirement of energy demand. Here, we presented a novel integrated polymeric membrane that is designed by PEDOT:PSSa-naphthalene sulfonated polyimide (PPNSP)-EMI. BF 4 Electronic skin (e-skin) for potential TENG applications. The proposed TENG e-skin is fabricated by an interconnected architecture with push-pull 3D ionic electrets that can threshold the transfer of charges through an ion-hopping mechanism for the generation of a higher output voltage (Voc) and currents (Jsc) against an electronegative PTFE lm. PPNSP was synthesized from the condensation of naphthalene-tetracarboxylic dianhydride, 2, 2’-benzidine sulfonic acid, and 4,4’diaminodiphenyl ether through an addition copolymerization protocol, and PEDOT:PSSa was subsequently deposited using the dip-coating method. Porous networked PPNSP e-skin with continuous ion transport nano-channels is synthesized by introducing simple and strong molecular push-pull 3D interactions via intrinsic ions. In addition, EMI. BF 4 ionic liquid (IL) is doped inside the PPNSP skin to interexchange ions to enhance the potential window for higher output Voc and Iscs. In this article, we investigated the push-pull dynamic interactions between PPNSP-EMI.BF 4 e-skin and PTFE and tolerable output performance. The novel PPNSP- EMI.BF 4 e-skin TENG produced upto 49.1 V and 1.03 µA at 1 Hz, 74 V and 1.45 µA at 2 Hz, 122.3 V and 2.21 µA at 3 Hz and 171 V and 3.6 µA at 4 Hz, and 195 V and 4.43 µA at 5 Hz, respectively. The proposed novel TENG device was shown to be highly exible, highly durable, commercially viable, and a prospective candidate to produce higher electrical charge outputs at various applied frequencies. Signicant in both after with BF 4 into the PPNSP lm by dip The homogeneous BF into PPNSP, quantum jump enhancement was observed, and the quantitative output performance of PPNSP-EMI was determined. BF 4 due to active mobility of EMI. BF 4 ions within the host PPNSP polymer lm as well as the surface. In specic, it can be seen that the PPNSP-EMI. The BF 4 -PTFE TENG showed higher electrical output than the other two systems (i.e., NSP. H + -PTFE, and PPNSP-PTFE TENG) owing to the availability of abundant mobile BF 4− ions from EMI. BF 4 IL. Next, Performance Characteristics of PPNSP.EMI.BF 4 -PTFE TENG showed the load resistance analysis, power density calculations, and device stability at 5 Hz applied frequency, and load resistance was increased from 100 ohm Ω to 570 MΩ. The areal power density of the device was 33.2 mW, and the load resistance was 570 MΩ. Additionally, the unidirectional output was stored in energy storage systems such as capacitors and batteries and the rectied Voc of PPNSP.EMI.BF 4 -PTFE e-skin TENG device. The performance stability of Voc and Jsc of PPNSP.EMI. The BF 4 -PTFE TENG system was checked at a 5 Hz applied frequency, and it was stable for ~10000 cycles without any uctuations. The durability and stability of the proposed system showed excellent harvesting performance and superior mechanical strength without any surface damage. The present results have suggested that the controlled self-assembly process for strong ion-ion connections and ion transport nanochannels can be used for tailoring superior TENG applications, which are potentially required for next-generation electronic products such as wearable soft electronics, exible displays, and smart mobile phones.


Introduction
For two decades, a drastic increase in global warming, pollution, and carbon emissions has been increasing due to the enormous consumption of fossil fuels and deforestation of plants for energy generation. To overcome the above mentioned challenging issues, clean and renewable energy is an alternative conventional option, such as solar, wind, and tidal energies [1][2][3][4][5]. However, the reduction of paired materials and their coherent design can upsurge the rate of energy collection and conversion e ciency [11], [12]. At regular intermissions of TENG resources with oppositely charged electrets, ions or electrons can be driven to movement through the external load and produce a continuous current [13].
In recent times, the use of a sulfonated block copolymer that contains interpenetrating nano-channels and a well-ordered nano-morphology has been proposed to enhance the TENG performance [14].
Inappropriately, these sulfonated block copolymer lms are economically not viable due to their complex chemical synthesis and long manufacturing process [15][16][17][18]. Therefore, an alternative simple synthetic approach is needed for developing high-performance TENGs using modi ed sulfonated block copolymers. Sulfonated polyimide block copolymers (SPIs) contain regular porous nanochannels and present numerous manufacturing qualities, such as lm forming ability with resilience, elasticity, bendability, stretching ability, long shelf life, and electrochemomechanical properties. SPIs are expected to provide a special physical and chemical morphology, having additional mechanical integrity and limited solvent swelling, owing to the presence of sulfonic acid groups within the ionic network [19].
Although several groups have used a series of SPIs as ionomers for high-performance fuel cell applications and actuators but not applied for TENG applications [20].
A decade ago, Whitesides G. M. et.al. have bring into limelight the ion-transfer system by incorporating ionic clusters into a solid matrix (i.e. styrene polymer, and silica glass,) to produce ionic electrets on the external surface [21][22][23]. Contact electri cation is a process to generate charges through ion transfer by selective transfer of ions that harvests net electrostatic charges. Recently, Watanabe et al. have been developed an SPI for printable polymer actuators integrated from a combination of co-block polyimide, ionic liquid, and carbon materials for high actuation at low input voltage [24]. On the other hand, we have reported a soft actuator based on a 3D ionic network skin made by ultra-fast solution process using sulfonated polyimide block copolymers [20].
Recently, Jang Y. H. have designed conductivity enhancement experiments by mixing of ionic liquids into PEDOT:PSSa conducting polymer for a noteworthy conductivity improvement has been attained by adding ionic liquid (IL) [23]. The ion exchange between PEDOT: PSSa and IL mechanisms can assist PEDOT to decouple from PSSa and harvest bulk-scale conducting domains [25]. Also, they have reported free energy calculations using a density functional system on a simple energy harvesting model using IL pairs and they were loosely bound individuals with the lowest binding energies, which led to the most e cient ion exchange with PEDOT: PSSa conducting polymer [26]. The spontaneous ion exchange followed by nano channeled phase ghettoization between PEDOT and PSSa chains, with formation of a regular π-π stacked PEDOT cations were intercalated by IL anions, is further sustained by molecular dynamics performed on bulk PEDOT:PSSa models in solution [27][28][29][30][31].
PEDOT:PSSa is a combination of polymer mixture of two conductive ionomers. One of the components in this mixture is made up of sodium polystyrene sulfonate and some of the sulfonyl groups are deprotonated and carry a negative charge [32, 33,]. The other component PEDOT is a conjugated polymer that carries positive charges and is based on polythiophene. Together, they exist as charged macromolecules from a macromolecular sodium salt. PEDOT: PSSa displays the highest e cacy over other conductive organic thermoelectric materials (ZT ~0.42) and thus can be used in exible and biodegradable thermoelectric generators [34,35]. The PEDOT chain itself has a PEDOT conjugated polymer with quite a low energy gap and low oxidation potential. For example, world famous AGFA lm coats upto 200 million photographic lms per year with a thin, extensively stretched layer of virtually translucent and monochrome PEDOT:PSSa as an antistatic mediator to prevent electrostatic discharges through production [36]. Recently, Li et al. developed a strong and highly exible aramid nano ber/PEDOT:PSSa lm through the vacuum ltration method. A exible all-solid-state symmetric supercapacitor from an ANF/PEDOT:PSSa lm with an operating potential window of 0-1.6 V displays an energy density of 4.54 Wh.kg −1 and excellent capacitance retention of 84.5% upto 10000 cycles at room temperature. Extraordinarily, the device was displayed an energy density of 3.83 W h kg −1 with a capacitance retention of 89.5% beyond 5000 cycles, even at -20°C. Moreover, the IL can act as a bridge electrolite between the core SPI polymer and PEDOT:PSSa electrodes, it can provide a further signi cant intensi cation of charge distribution performance and extended durability. Recently, Deligoz et al., and Ye et al. were studied the interaction of SPI lms with imidazolium cations in various ionic liquids, but they focused on fuel cell applications [37,38]. From their motivation, we inspired to use a EMI.BF 4 ionic liquid for emerging high performance TENG by producing fast ion-hopping rate between cations and hydrophilic NSP.H + , and PEDOT:PSSa conduction layers by ion-ion interactions through porous nano channels. The nano channels can enhance the charge density through the charge transfer complex (CTC), and IL interactions can permit ions to transport easily within the proposed e-skin [39].
To develop an economically viable, highly endurable, and exchange of interionic 3D ionic electrets between electropositive and electronegative membranes when they contact each other, we designed an ionic networked lm with continuous and interconnected ion transport nano-channels by using simple and strong atom-level region-speci c interactions of hydrophilic and ionic SPI co-blocks with protons (H + ions) and anions in the ionic liquid. Additionally, we presented a simple but ultrafast two-step synthesis including dry casting and drop casting for a high-performance TENG. The 3D ionic electrets networked, hydrogen ion(H + ) rich naphthalene sulfonated polyimimide (NSP.H + ) ionic membrane, polyethylenedioxythiophene (PEDOT): polystyrenesulfonate (PSSa) as a conducting electrode layer, and 1-ethyl-3-methylimidazolium tetra uoroborate [EMI. BF 4 ] ionic liquid (IL) as the mobile electrolyte [20].
Molecular-level region-speci c interaction of cations and anions in IL with hydrophilic-hydrophobic coblocks of NSP mediocre is utilized for building a self-assembled ionic networked polymer with uninterrupted and intersected ion transport nano channels for high-performance TENG [28]. The developed TENG has signi cant bene ts, including hydrophilicity, good solvent exchange, stability in air without further oxidation, high ion exchange capacity, high thermal stability, strong ionic interactions between hydrophilic SPI coblocks and the ionic liquid, ion hopping mechanism, organic PEDOT: PSSa that maintains exibility and excels a higher TENG voltage and current. Additionally, the IL can act as a strong connection electrolytic solvent between the core NSP ionic membrane and PEDOT: PSSa electrodes through EMI.BF 4 can provide a surplus increment of long shelf life without any oxidative degradation [30][31].
Besides, the determination of the present work is to fabricate an ultrafast solvent drop-casting method to produce a combined networked electropositive ionic layer of PEDOT:PSSa-EMI.BF 4 -NSP (PPNSP) e-Skin strongly follows an ion-ion hopping mechanism (stages 1 and 2) using 3D ionic electrets. The ionic conductivity and ion exchange capacity of PPNSP are increased up to 3.3 times and 3.5 times through ionic electrets by an ion hopping mechanism that established that the higher density of excess protons (H + ions) on the active surface can activate polarized charges to produce a higher TENG output voltage (Voc) and output currents (Isc) when interacting with the electronegative PTFE surface by contact separation mode (stages 3 and 4). The developed PPNSP-PTFE-TENG system is a virtuous candidate for the generation of higher Voc and Isc through a 3D ion-ion hopping mechanism due to its signi cant bene ts, such as a π-π stacked layer that helps to push and pull quick response to travel the ions via interconnected neural networked knots when undergoing contact-separation time.  with a test speed rate of 10 mm/min. The gauge length among the grips was 10 mm. All samples were cut into a regular rectangular shape. TGA measurements of the composite lm membranes were completed on a thermogravimetric analyzer (TG209F3) from NETZSCH (Germany) nished temperatures ranging among 40°C and 800°C in N 2 gas at a heating rate of 10°C/min. All polymeric lms were air dried, and SEM interpretations were carried out on an FEI Sirion FE-SEM, 30 kV microscope. The lms were carefully dried before capturing the images, and the super cial morphology, and cross-sectional images were studied. The output signals of the all NSP.H + , PPNSP, PPNSP-EMI.BF 4 e-skin, and PTFE were achieved by intermittently forced and free by income of an oscillator, and the power output was measured using Keithley Digital Multi Meter (KDMM). Consequently, all experiments were determined the impact force via load cell of YC33-5K (SETECH) at numerous frequencies of 1 Hz, to 5 Hz, correspondingly.

Fabrication of the contact-separation PPNSP-EMI. BF 4 -TENG
The fabrication and working principle of the contact-separation PPNSP e-skin TENGs are discussed. A methodical understanding of PPNSP TENGs has been designated in wide-ranging studies [18,28]. At this juncture, the assembly of the characteristic model was depicted in Figure. 6a. First, NSP.H + electrode was cut into sizes of 4 cm × 4 cm = 16 cm 2 , and attached on Al electrode layer. Then, the fabricated NSP.H + -Al conductor was closed to viable exible foam to decrease the re ecting impact force while contact and separation is progressed. Then, a load cell was linked to the upper part of the Al conductor. A similar protocol was followed for the other two PPNSP-Al and PPNSP-EMI. BF 4 -Al electrodes [40].
Second, the Al electrode was positioned glued on the PTFE lm at 4.0 cm × 4.0 cm along with polyurethane exible foam. In the meantime, a linear oscillator is composed of a DC motor with eccentric arrangement steadily oscillated with a linear slider, as shown in Figure. 6a. The maximum oscillation amplitude was 40 mm. The upper portion of the PPNSP-EMI. BF 4 e-skin was adjourned using a cantileverstyle beam that was linked to the linear slider. The careful setup of the overall system give rise to in slight contact between the PPNSP-EMI. BF 4 e-skin, and PTFE lm, though the slider oscillation was steady, as shown in Figure. (2). The unstable radicals were rearranged into a stable dimer (3) by reaction steps that involved combination and deprotonation, as shown in Stage 2. In addition, a neutral PEDOT chain itself has a conjugated network with alternate double bonds with a low energy band gap and low oxidation potential.
Ionic interactions were occurred with NSP. H + , and PEDOT: PSSa to generate the PPNSP e-skin, Stage 3. Next, the PPNSP was soaked in 20% EMI. BF 4 in DMSO to generate the PPNSP: EMI. BF 4 composite eskin, Stage 4. Continuous recurrence of those steps resulted in the formation of well-dispersed, and doped PEDOT: PSSa solution showed the chemical structures of 3, 4-ethylenedioxythiophene (EDOT), and poly(3,4-ethylenedioxythiophene) (PEDOT). The structure of the as-prepared PEDOT is made up of benzoid, and quinoid forms. The benzoid structure possesses a π-electron localized, conjugated structure that remains largely unaffected by external sources. In contrast, the quinoid form of PEDOT owns a delocalized state of π-electrons, which can be strongly exaggerated by solvent treatment [42]. In the electrically active, oxidized state, there remains a positive charge on every PEDOT polymer chain. The charges on the backbone were balanced with an anions are from small molecules or a macromolecular anions such as poly(4-styrene sulfonic acid) (PSS). This higher charge transfer performance of the newly developed PPNSP: EMI. BF 4 e-skin TENG through an ion-hopping mechanism that induces high ionic conductivity and tuned the mechanical properties, resulting from strong ionic interactions among the NSP.H + , EMI. BF 4 , and PEDOT:PSSa, and interconnected 3D networked polymer matrix [43][44][45][46] [19] The strong stretching signals of the BF 4 group appear at 1191 cm −1 with a shoulder at 1230 cm −1 , and the deformation signals at 738 cm −1 and at 658 cm −1 strongly support the presence of an imidazolium ring. Additionally, additional strong peaks appearing at 1121 cm −1 for SO 2 and 1344 cm −1 with a left shoulder at 1329 cm −1 corresponding to the C=N of the imidazolium cation strongly support the presence of EMI. BF 4 in the PPNSP-EMI. BF 4 e-skin. As suggested in Figure 2, ionic clusters are formed by an ultraionic exchange reaction between the PPNSP membranes with EMI. BF 4 is well-supported by the FT-IR studies [21].In addition, 3D ionic electrets were developed during slow evaporation of DMSO from hydrophilic PPNSP and EMI. BF 4  show any phase separation due to the formation of strong intercalation through hydrophilicity by ionicionic interactions [19,20] distinct crystalline peaks were at 12.5 and 26.5, 2θ°, showing strong evidence of stretchy crystallinity due to exible ion-ion interactions within the membrane as a free-owing network. In addition, the EMI. BF 4 is strongly aggregated on the surface of the PPNSP due to the formation of ionic clusters. The broad peaks that were observed in the NSP.H + and PPNSP membranes transformed into sharp peaks at 12.5 and 26.5 2θ°, and the degree of crystallinity is increased due to the establishment of ionic 3D electrets, bridges between NSP.H + , and PPNSP through EMI.BF 4 .

Stress-strain (SS) Curves
With the good deposition of PEDOT:PSSa on top of NSP.H + base polymer through strong ionic bonding and reinforcement that can be expected. To demonstrate this reinforcement, tensile tests were performed for 3D ionic electrets, networked PPNSP, and PPNSP-EMI.BF 4 e-skin [20]. Typical stress-strain curves are shown in Figure 4c, and their mechanical properties are compared in Table 1 Figure 5 and reveal the surface morphologies. In particular, Figures 5a, and 5b show the wrinkle-free plain surface with no obvious changes. However, the inbuilt hydrophilic -SO 3 H groups were attached to the host polyimide co-blocks that could intercalate and generate nano level distances between the oligomeric networked chains. Signi cant submicron-sized porous grooves and micron-sized crests with tightly packed networks were found on the surface, as shown in Figure. 5c. The hollow groves and crests were created due to a signi cant 3D ionic network on the surface morphology. In the cross-sectional view, hydrophilic and hydrophilic interactions take place between NSP.H + , and PEDOT:PSSa through hydrogen bonding that created a loosely bound network between them, Figure 5d [21]. The hydrophilic-hydrophilic ionic system can establish a exible interpenetration complex between NSP --H + and PEDOT:PSSa to improve the charge densities on the polymeric surface. The 3D ionic networked morphology can exchange ions through strong ionic knots, which can travel through hydrophilic ionic channels and strongly support the ion hopping mechanism. After impregnation of EMI.BF 4 IL, the thickness of PPNSP e-Skin was increased due to swelling of ionic liquid. Figure 5e shows the strong spherical aggregations on the surface by 3D ionic clusters. In addition, the inset image clearly indicates the 3D ionic clusters at nanoscale levels. In the cross-sectional view, a loosely bounded net-like channeled network appears due to the strong intercalation between PEPDOT:PSSa and EMI.BF 4 IL. Additionally, the high-resolution surface and crosssectional images display the formation of zigzag net-like channels. In particular, EMI + cations were deposited on the hydrophilic regions as bright spots, which clearly indicate the formation of PPNSP-EMI + by an ion hopping mechanism, as shown in Figure 5f. The homogeneity of the blend membrane con rmed the strong ionic interactions, which included ionic cross-linking and hydrogen bonding between EMI.BF 4 and the PPNSP composite membrane, resulting in the enhanced interfacial compatibility and mechanical stiffness of the composite membrane. In addition, ionic cross-linking and hydrogen bonding can generate higher charges on the surface. These charges can enhance the open circuit voltage and short circuit currents. The overall morphologies were strongly justi ed to accelerate the charges within the charge transfer complexes when a contact-separation mode TENG was performed [25,39]. The BF 4 e-skin TENG was explained by the PPNSP surface, and the aluminum (Al) electrodes were initially free of charges (Figure 6c). When the oscillation was underway by the linear slider by the DC motor, the triboelectrically negative PTFE was in super cial contact on the surface of PPNSP-EMI.BF 4 .

Set-up Of Ppnsp-emi. Bf4 E-skin Teng For Generation Of Voltages And Currents
The PTFE surface was converted to temporarily negatively charged and, in contrast, PPNSP-EMI.BF 4 turned positive owing to the contact electri cation process (Figure 6d). During the contact electri cation process, the generated electrical charges are retained on the surface for a longer time due to the insulating properties of the surface. The PTFE surface showed superior charge separation when it was separated from PPNSP-EMI.BF 4 e-skin. At this time, the Al electrodes were strongly persuaded to collect charges by PPNSP-EMI. The BF 4 e-Skin and PTFE surfaces remained neutral, the top electrode was positively charged, and the bottom electrode was negatively charged. During the separation process, the generated charges were transformed through an external load, and current ow occurred (Figure 6e). When the two electrodes were completely separated, the current was clogged and reached the equilibrium state ( Figure 6f). When both the surfaces of PPNSP-EMI.BF 4 e-Skin and PTFE were locked together, and the electrostatic induction was high and broke the equilibrium state, resulting in charge redistribution of Al electrodes via acceptance and release of ions, as shown in Figure 6g. As a result, the current ows in the reverse direction. Till the two polymeric layers were fully contacted, the charge-transfer process disappeared, and no charges were generated at all [41].  It was noted that the peak Voc decreased with increasing resistance, whereas Jsc increased.
Consequently, the device output increased when the load resistance was increased from 100 ohm Ω to 570 MΩ. The areal power density of the proposed device at a 5 Hz applied load was evaluated using the following equation.
Where V is the generated output voltage from PPNSP.EMI.BF 4 -PTFE TENG device, R is the load resistance, and A is the device area (A= 4cm x 4 cm=8 cm 2 ). The areal power density of the device was 33.2 mW, and the load resistance was 570 MΩ. This indicated that 570 MΩ was the load-matching resistance for achieving the maximum output power required for real-time applications, as shown in Figure 8a. The unidirectional output can be stored in energy storage systems such as capacitors, and batteries and the recti ed Voc of PPNSP.EMI.BF 4 -PTFE TENG device is shown in Figures 8b, and 8c. The performance stability of Voc and Jsc of PPNSP.EMI. BF 4 -PTFE TENG system was checked at a 5 Hz applied frequency, and it was stable for ~10000 cycles without any uctuations (Figures 8d, and 8e). The durability and stability of the proposed system showed exceptional harvesting properties and superior mechanical strength.
The performance of Voc and Jsc of NSP.H + -PTFE-TENG>PPNSP-PTFE-TENG >PPNSP-EMI.BF 4 e-skin-PTFE-TENGs. The e-skin-TENG gradually increased with increasing ionic density both inside the network and outside the surface. Next, when the impact force was increased by the oscilloscope, surface charges were generated through the 3D ion hopping induction mechanism and surged the higher Voc and Jsc values. The output Voc, and Jsc of PPNSP.EMI.BF 4 -TENGs produced 316% and 300% at 5 Hz, respectively, as shown in Figures 9a, and 9b. The load cell YC33-5K (SETECH) was utilized to measure the contact force, and the results are shown in Figure 9c. Based on the obtained research data, the impact force was gradually increased with respect to the applied contact frequencies. When the impact force is high, an additional effective area is induced, and subsequently, higher output voltage and currents are generated. was stable for ~10000 cycles without any uctuations. The durability and stability of the proposed system showed excellent harvesting performance and superior mechanical strength without any surface damage. The present results have suggested that the controlled self-assembly process for strong ion-ion connections and ion transport nanochannels can be used for tailoring superior TENG applications, which are potentially required for next-generation electronic products such as wearable soft electronics, exible displays, and smart mobile phones.