Contact-induced continuous electricity generation by ion-electron positive feedback coupled transport for self-powered ionic touch panel.

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Learn more: PMC Disclaimer | PMC Copyright Notice Microsyst Nanoeng . 2026 Jun 3;12:210. doi: 10.1038/s41378-026-01307-z Contact-induced continuous electricity generation by ion-electron positive feedback coupled transport for self-powered ionic touch panel Kedong Shang 1, 2 , Jiahao Fang 1 , Xiaobo Pu 3 , Peng Wang 3 , Yao Chen 1, 4 , Hai Liu 1 , Ning Zhang 1 , Junjie Hao 1 , Yong Zhang 1, 5 , Bingjun Yu 1, 6 , Linmao Qian 1, 6, ✉ , Tingting Yang 1, 6, 7, ✉ Author information Article notes Copyright and License information 1 Tribology Research Institute, School of Mechanical Engineering, Southwest Jiaotong University, Chengdu, PR China 2 School of Mechanical Engineering, Shandong University of Technology, Zibo, PR China 3 China Railway Academy Group. Ltd, Chengdu, PR China 4 Tangshan Institute, Southwest Jiaotong University, Tangshan, PR China 5 School of Mechanical and Electrical Engineering, Chengdu University of Technology, Chengdu, PR China 6 Institute of Smart City and Intelligent Transportation, Southwest Jiaotong University, Chengdu, PR China 7 Yanghua Chuangwei (Sichuan) Innovation Technologies Co. Ltd, Neijiang, PR China ✉ Corresponding author. Received 2026 Jan 15; Revised 2026 Mar 22; Accepted 2026 Mar 25; Collection date 2026. © The Author(s) 2026 Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/ . PMC Copyright notice PMCID: PMC13230852  PMID: 42230535 Abstract Ionic touch panels are regarded as a key platform for future human-computer interaction and meta-universe due to their stretchable, transparent and skin-fitting properties. Inspired by the fact that human skin relies on ionic current to sense contact position information, we have investigated an ionogel based closed-loop electrical system that also converts contact into ionic current to form a self-powered single-layer ionic touch panel. Benefiting from the slowed charge transfer dynamics, the positive feedback coupling of the electrical double layer, and the high-density charge characteristics, the device generates an approximately steady-state electrical signal when touched. It is clearly different from the pulsed electrical phenomenon of conventional contact electrification devices. When a finger touches the touch panel, the voltage/current signal amplitude at each corner electrode of the ionogel has been proven to express the touch position. The continuity of the electrical signal ensures high-resolution recognition of the touch trajectory without the need for further contact separation. With the advantages of good transparency, large stretchability, self-power, single-layer structure, fast response and high resolution, we expect this emerging ionic touch panel to be an ideal candidate for a variety of human-computer interaction applications. Subject terms: Electronic properties and materials, Physics Introduction Integrated touch panels have evolved into various types, including resistive 1 – 4 , capacitive 5 – 7 , triboelectric 8 – 11 , surface acoustic wave 12 – 14 , and infrared-based systems 15 – 17 . Among these, ionogels have emerged as key materials for next-generation flexible touch panels due to their stretchability, high transparency, and skin-friendliness. The rapid advancement of ionic touch panel technology is expected to enable a wide range of applications, such as human-computer interaction 11 , 18 – 20 , autonomous driving 20 – 22 , and metaverse interfaces 19 , 22 – 24 . An ideal touch panel for these applications should possess high transparency, excellent stretchability, and the ability to continuously detect touch positions with high precision. Moreover, it is desirable for the panel to operate without an external power supply, thereby enhancing the flexibility, durability, and lightweight nature of the sensing system. However, both ionic resistive and ionic capacitive touch panels are limited by issues arising from external power supply dependence 5 , 25 , 26 . Ion triboelectric touch panels, while capable of energy harvesting, generate only transient pulsed electrical signals during contact-separation events, making them suitable solely for point-contact sensing and unsuitable for accurately tracking continuous sliding motions 27 – 29 . Furthermore, most existing ionic touch panels feature complex, multi-layered structures with stacked layers and electrode arrays. These multilayer interfaces are susceptible to delamination and light diffraction, compromising deformability, optical transparency, and overall reliability 30 , 31 . And a comparison of the device characteristics based on the different mechanisms mentioned above is presented in Table S1 . To address these challenges, developing an ionic touch panel that outputs near-steady-state electrical signals upon touch and operates with a single-layer structure would significantly broaden its practical applicability. Contact charging is a common phenomenon on ionogel surfaces. When an ionogel comes into contact with another material, ions or electrons can be transferred across the interface 22 , 32 , 33 . If anions (or electrons) and cations (or holes) exhibit differing tendencies to transfer, this asymmetric carrier migration leads to a net charge transfer at the contact interface 34 – 38 . Although this phenomenon has been extensively studied, its underlying mechanism remains poorly understood due to the complex coupling between ionic and electronic processes. Nevertheless, it is widely accepted that the contact electrification response decays rapidly—within tens of milliseconds to seconds—owing to fast charge transfer kinetics and limited interfacial charge 37 , 39 – 42 . Therefore, achieving a touch-induced steady-state electrical signal remains a significant challenge. In this work, we present an ionic touch panel with a configuration comprising fixed metal corner electrodes, an ionogel layer, and a movable metal electrode, operating via a triboelectric-potentiometric hybrid sensing mechanism. Contact between the movable electrode and the ionogel surface closes the originally open circuit into a complete electrical loop, transforming the conventional interfacial effect of dynamic electrical double-layer modulation into a bulk effect. This bulk effect, combined with the slow ion migration dynamics of nano-confined ionogel, enables the output of steady-state electrical signals. Through a series of control experiments, we investigate the coupled transport behavior of electrons and ions underlying this bulk effect and elucidate design principles for the ionogel. The resulting touch panel features a simple single-layer structure and stable signal output, enabling reliable, continuous, and accurate recognition of various touch interactions, including short-term point contact, prolonged point contact, and continuous sliding contact. The design of ionic touch panel and performance impact factors Human skin is stimulated by touch and converts the different stimuli into a series of ionic currents that are transmitted via nerve fibers to the brain for analysis to recognize the touch location and pressure (Fig. 1a ). Inspired by the skin, researchers can also convert force signals into electrical signals and realize self-powered tactile perception through traditional triboelectric and piezoelectric principles. However, as shown in Fig. 1b, c , existing triboelectric and piezoelectric sensors can only respond to dynamic touch stimuli, i.e ., producing electrical output (especially current output) only at the moment of contact or separation, resulting in the inability to accurately recognize a stable touch over a long period of time. Sensors based on chemical-battery reactions enable detection of dynamic and static mechanical stimuli, but have not yet been utilized to develop touch-screen devices. The iontronic devices developed in recent years use ions as the main charge carriers and are closer to the response mode of the biological nervous system. The iontronic tactile sensors have the advantages of high sensitivity, low power consumption and biocompatibility. However, existing ion-triboelectric and ion-piezoelectric devices are also only suitable for dynamic measurements. Ion-piezocapacitive and ion-piezoresistive devices can be used for static measurements but still inevitably rely on an external power supply. So far, there is no self-powered ionic touch panel that can continuously detect the touch position with high precision. Fig. 1. Open in a new tab The conceptualization and electrical output of the ionic touch panel . a The sensing system of the human skin that senses external stimuli. b Contact response characteristics of triboelectric device, piezoelectric device and the device. c Schematic of the response mechanism of triboelectric and piezoelectric sensors. d Structural components of the device. e Voltage and current output of the device for long-term contact response Here, we developed an iontronic touch panel. In a closed loop, the aluminum sheet gently touches the touch panel (2 kPa), and the Cu corner electrode end can detect about 280 mV voltage and 27 nA current for up to 3 h, as shown in Fig. 1d, e . The main component of the touch panel is a piece of [EMIM][TFSI]/TPU composite ionogel film. The TPU polymer chain consists of hard segment and soft segment, where the hard segment ensures the strength of the material and the soft segment ensures the flexibility and stretchability of the material 43 , 44 . As shown in Fig. 1d, e , when the movable electrode (e.g., Al) contacts the ionogel surface, the originally open circuit is closed, forming a complete electrical loop comprising the movable electrode, ionogel, corner electrode, and external resistor. Prior to contact, a stable electric double layer (EDL C ) exists at the corner electrode/ionogel interface due to equilibrium ion redistribution. Upon contact, a new dynamic electric double layer (EDL M ) instantaneously forms at the movable electrode/gel interface as a result of contact electrification and asymmetric ion/electron transfer. Critically, the surface properties and work function of the movable electrode differ from those of the fixed corner electrode, creating an intrinsic asymmetry between EDL M and EDL C . This asymmetry generates a built-in potential difference that drives continuous charge migration through the closed external circuit. The sustained steady-state output arises from three synergistic factors. First, the positive feedback coupled ion-electron transport ensures that electron flow through the external circuit continuously reinforces ion redistribution at both EDL interfaces: the EDL C interface experiences cation inflow while the EDL M interface undergoes cation outflow, mutually sustaining the charge imbalance. Second, the nano-confined structure of the ionogel imparts exceptionally slow ion migration dynamics (ion diffusion coefficient of 2.94 × 10⁻¹⁵ m²/s, Fig. 2i ), which prolongs the charge redistribution process and prevents rapid signal decay. Third, the work function difference between the electrodes determines the driving force for electron transfer. As shown in Fig. 4d, e , the output amplitude follows the reverse order of work functions (Cu < Fe < Ti < Al < Zn), confirming that a larger work function mismatch enhances the built-in potential and signal amplitude. Thus, the stable electrical output is not a transient contact electrification pulse but rather a quasi-steady-state signal sustained by the positive feedback loop, retarded ion dynamics in the nano-confined ionogel, and asymmetric EDL stabilization. This mechanism distinguishes our device from conventional triboelectric or piezoelectric systems that produce only transient outputs. Fig. 2. Open in a new tab Effect of electrical circuit connections, material composition and electrode selection on the output performance of the iontronic devices . a – c Schematic of the iontronic devices with different electrical circuit connections: closed-loop and grounding ( a ), closed-loop ( b ), open-loop ( c ). d – f Response of the iontronic devices with different electrical circuit connections: closed-loop and grounding ( d ), closed-loop ( e ), open-loop ( f ). g Schematic representation of the transport mode of anions and cations in ionic liquid and ionogel. h Microstructural morphology of ionogel. i Electrochemical impedance spectra (Nyquist plot) of ionic liquid and ionogel. j – l , Effects of different corner electrode and movable electrode pairings on the voltage output of the ionic liquid (IL) device, including Cu-Al electrode pair ( j ), Au-Pt electrode pair ( k ), and Au-Au( l ) electrode pair Fig. 4. Open in a new tab Characterization and analysis of the ion-electron positive feedback coupled transport mechanism in the iontronic device . a Schematic diagram of the device output performance test using an Au-Au electrode pair. b , Voltage output performance of the device under Point touch mode under ( a ) test condition. c Current output performance of the device under Point touch mode under ( a ) test condition. d Comparison of the output performance of five different metals as movable electrodes, with the fixed corner electrode being copper. e Surface work function of these five different metals. f Schematic representation of the characterization of the anion ([TFSI - ]) and cation ([EMIM + ]) distribution states at locations of P1-P4 before and after the loop close using Raman mapping analysis. g Raman mappings of cation ([EMIM + ]: 2800–3050 cm −1 ) distribution at P4 (corner position of the zinc mesh aperture) before and after the loop close. h Raman mappings of cation ([EMIM + ]: 2800–3050 cm −1 ) distribution at P3 (center position of the zinc mesh aperture) before and after the loop close. i Raman mappings of cation ([EMIM + ]: 2800–3050 cm −1 ) distribution at P2 (corner position of the copper mesh aperture) and P1 (center position of the copper mesh aperture) before and after the loop close In order to explore the role of closed-loop electrical connection design, three electrical circuit connection modes including grounding & closed-loop, closed-loop, and open-loop, were designed and compared, respectively, as shown in Fig. 2a–c . In the experiments, the metals copper and aluminum were used as fixed corner electrode and movable electrode, respectively. And two contact modes were used during the experiment. Point contact mode 1: move the movable electrode from left to right to contact each of the 6 equally spaced points on the ionogel membrane for 2 s, then return and repeat the procedure in reverse. Prolonged contact mode 2: the movable electrode is in continuous contact with the gel membrane at a fixed position for more than 600 s. As shown in Fig. 2d, e and Fig. S1a, b , for the two electrical circuit connection modes, closed-loop & grounding and closed-loop, the voltage/current response value is highly consistent with the change pattern of the contact position. In contrast, When the loop is not closed (Fig. 2f and Fig. S1c ), the voltages and currents barely respond, indicating that closed-loop connection is necessary. When the loop is not closed, EDL C and EDL M can only transfer charge through the ionogel itself. Both EDL C and EDL M can also realize charge transfer via an external circuit when the loop is closed, i.e ., converting the traditional dynamic EDL modulation effect at the interface into a bulk effect. The related charge transfer process and intrinsic mechanism will be discussed and analyzed in depth later. Throughout the ion-electron coupled transport loop, we hypothesize that the ion transport kinetics within the ionogel is a key factor in whether the electrical signal exhibits a steady-state output. Therefore, an attempt was made to replace the ionogel (Fig. 2g ) with an ionic liquid (IL, [EMIM][TFSI]) for touch experiments. Unlike pure ionic liquids, ionogel exhibits a homogeneous nano-confined channel structure (Fig. 2h and inset) and extremely slow ion transport dynamics due to ion-polymer backbone interactions. As shown in Fig. 2i and Fig. S2 , through electrochemical impedance test and corresponding equivalent circuit analysis, the ion diffusion coefficient of ionogel was obtained to be 2.94 × 10 −15 , which is about 15.2% of that of the pure ionic liquid (1.94 × 10 −14 ). Interestingly, as the ion diffusion coefficient increases, the electrical signal output stability of the pure ionic liquid device with the application of a 600 s static touch stimulus (Fig. 2j and Fig. S3 ) decays dramatically within the first 200 s. The phenomenon of the electrical signal decay with time is originated from the ionic-triboelectric mechanism. Because after replacing the Cu-Al electrode pair with the inert metal Au-Pt (Fig. 2k ) or Au-Au electrode pair (Fig. 2l ), there is still a clear electrical signal and a similar decaying trend. In contrast, the Cu-IL-Al device shows steady state signal at 200–600 s, which is presumed to be caused by a slow and stable chemical reaction of galvanic cell. The electrical polarity of the ionic triboelectricity and the galvanic cell reaction is consistent. Since both ionic-triboelectric mechanism and potentiometric reaction are extremely charge-dense power generation phenomena, combined with slow charge transfer kinetics, it is understandable that the iontronic device could produce a small, persistent and stable current output at the nA level 33 , 43 , 45 . Furthermore, as can be seen from Fig. 2j–k , differences in pulse amplitude and decay time are observed when different electrode materials are used. This may be attributed to the combined effects of the electron transfer driving force, asymmetry in the interfacial electrostatic double layer, and the galvanic cell reaction. To be specific, the work function difference (analysis below) between the movable and corner electrodes determines the initial electron flow direction and magnitude upon contact. A larger work function mismatch drives stronger electron transfer through the external circuit, enhancing the built-in potential between EDL M and EDL C , thereby increasing the signal amplitude. For decay time, materials with lower work functions exhibit sustained signals due to continuous electron supply maintaining EDL asymmetry. In contrast, when using inert metals such as Au (Fig. 4b–c ), although pure ionic-triboelectric still generates an asymmetric EDL, the absence of additional driving force from galvanic reactions results in faster signal decay as the system relies solely on the limited interfacial charge and slower ion redistribution within the nano-confined ionogel. Thus, the material-dependent behavior is governed by the interplay between work function-induced electron transfer, EDL asymmetry stability, and electrochemical activity, which collectively modulate both the amplitude and persistence of the steady-state signal. And other detailed tests and structural characterizations of the ionogel are demonstrated in the Supplementary Material (Fig. S4 -Fig. S8 ). Varying the content of ionic liquid in the TPU/[EMIM][TFSI] membrane will also greatly affect the amplitude and stability of electrical output. Six ionogels with different doping concentrations (including 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt% and 30 wt%) were prepared, and the experiments were conducted using the same closed-loop electrical connection with a fixed contact position at 4 cm from the corner electrode, a fixed load resistance of 10 MΩ, and a fixed contact pressure of 3200 Pa. As shown in Fig. 3a and Fig. S9 , the electrical response gradually increases as the ionic liquid content increases from 5% to 20%, which may be due to the shortening of the Debye length and Debye time. By further increasing the ion content, the voltage and current response peaks tend to stabilize, indicating that the number of ions involved in EDL generation has reached saturation. On the other hand, the stability of the electrical signal output shows a decreasing trend with further increase of the ionic liquid content. In particular, when the doping concentration is further increased to 20–30%, a significant overshoot phenomenon has been observed, which could be attributed to the rapid formation of EDL. The increased free ions are rapidly and densely adsorbed on the electrode surface, followed by partial ion reflux or re-equilibration. For accurate sensing applications, low ionic liquid content is preferable. Fig. 3. Open in a new tab Factors affecting the output performance of iontronic devices . a Effect of ionic liquid doping concentration on voltage output. b Effect of contact pressure at the interface between the movable electrode and the ionogel on the voltage output performance. c Effect of contact pressure at the interface between the movable electrode and the ionogel on the current output performance. d Effect of external resistance on voltage output performance. e Effect of external resistance on current output performance. f Effect of contact area on voltage output performance. g Effect of ambient temperature on the voltage output The effect of contact pressure on the voltage and current response was also investigated and the results are shown in Fig. 3b, c . As the contact pressure gradually increases (0.5 kPa, 0.8 kPa, 1.6 kPa, 2.4 kPa, 3.2 kPa, 4.8 kPa, 6.4 kPa, 9.6 kPa, 16 kPa, 22.4 kPa, 32 kPa), the voltage and current output accordingly show a slowly increasing trend. The growth rate of output electrical signal is much slower than that of the pressure amplitude since the device responds to the contact behavior itself rather than the pressure. The slow increase in the electrical signal caused by pressure is attributed to the more effective contact and the decrease in ion transmission resistance due to gel deformation. Besides, the magnitude of the external load resistance also greatly affects the electrical output of the device. As shown in Fig. 3d, e , 0 Ω, 100 Ω, 1 kΩ, 10 kΩ, 100 kΩ, 1 MΩ, and 10 MΩ are selected as external resistors, respectively. In the 0–1 MΩ range, the current output of the device (7–8 nA) is essentially independent of the magnitude of the load resistance. As the resistance reaches 10 MΩ, the current output decays to approximately 6 nA. This is because in the entire closed-loop electrical system, although increasing the load resistance weakens the transmission of electrons, the charge transfer rate of the entire electrical system mainly depends on the slower moving ions. The voltage signal gradually increases from 0.05 mV to 206 mV as the load resistance changes. Consequently, in order to improve the sensitivity of the device, the load resistance was set to 1 MΩ and 10 MΩ respectively when testing the current and voltage in subsequent application demonstrations. In addition, the effect of the movable metal electrode size on the electrical output performance was investigated (Fig. 3f ). The movable electrode sizes were set to 0.5 cm 2 , 1 cm 2 , 2 cm 2 , 3 cm 2 , 5 cm 2 and other test conditions were identical. The results show that the electrical signal output increases with increasing contact area, which is attributed to the formation of more EDL at the interface. Moreover, the effect of ambient temperature was also investigated, as shown in Fig. 3g , which demonstrates the contact response performance of the device at 20 °C, 30 °C, 40 °C, 60 °C and 80 °C. The higher the temperature, the larger the electrical output amplitude, which is attributed to the high temperature promoting ion migration and rapid EDL formation. To investigate the effect of ambient humidity on output performance, the response of device to finger contact was tested under different ambient humidity conditions. As shown in Fig. S10 , the device’s response to finger contact exhibits a clear increasing trend with rising ambient humidity. This behavior can be attributed primarily to the hydration state of the fingertip skin. As humidity increases, the enhanced hydration promotes greater charge generation at the finger–ionogel interface, thereby amplifying the contact electrification effect. Moreover, elevated ambient humidity facilitates the formation of a thin moisture layer on the microscale surface structures of the fingertip, which increases the effective contact area and improves interfacial charge transfer efficiency during touch. This combined effect—enhanced interfacial charge density and improved conformal contact—leads to a higher electrical output. Relevant tests were also performed for contact response stability as well, as shown in Fig. S11a–c . At the same touch position, more than 200 contact-separation cycle operations were performed. The current output values do not show any obvious fluctuation or signal degradation. Besides, to verify that the device is not affected by water evaporation (i.e. its long-term storage stability), the ionogel was exposed to air for a period of time before undergoing contact response testing. As shown in Fig. S 12–13, the ionogel maintained its contact response output performance without degradation after exposure to air for 1, 3, and 7 days. This also demonstrates the good stability and durability of the device. Analysis of ion-electron positive feedback coupled transport mechanism In order to explore the intrinsic mechanism of the unique output characteristics of this iontronic device, the phenomena of solid-solid triboelectricity, chemical reaction and ionic piezoelectricity that may exist inside the device were firstly investigated. As shown in Fig. S14 , the ionogel film was replaced with a pure TPU polymer film, and other test conditions remained unchanged. No voltage or current response was observed from the test data, indicating that the electrical signal output cannot be obtained by relying solely on solid-solid friction. As mentioned earlier, when the electrodes involve active metals, we speculate that chemical reactions make partial contributions in the device. In order to investigate the contribution of pure ionic triboelectricity and exclude possible chemical reactions, both the corner electrode and the movable electrode were replaced with Au sheets, as shown in Fig. 4a . The voltage and current responses of point touch mode are shown in Fig. 4b, c . The trend is consistent with the previous test results: voltage and current amplitudes decrease or increase as the contact distance becomes farther or closer. This suggests that a purely ionic triboelectric phenomenon is still suitable for constructing an ionic touch panel, but the duration of the electric signal will be shortened. Despite the choice of gold for both the movable and corner electrodes, considering the relatively slow rate of ion diffusion in ionogel, the initial density of EDL M remains much lower than that of EDL C . Thus, the asymmetric EDL is still formed and provides power for charge transfer in closed-loop electrical system. In addition, ionic piezoelectricity may be introduced during contact process due to the presence of pressure. In order to investigate the role of ionic piezoelectricity, a typical sandwich-type device structure consisting of an upper electrode (Al), an ionogel film (middle layer), and a lower electrode (Cu) was used, as shown in Fig. S15 . In the 600 s long-term contact response test, ion piezoelectricity makes no contribution since there is no force gradient across the device structure. And both the contact electrical signal amplitude and stability do not match the typical transient response characteristics of ionic piezoelectricity. As shown in Fig. 4d , the fixed corner electrode is copper, while the metal type of the movable electrode is changed. These voltage and current output amplitudes are ranked in order: Cu <Fe <Ti <Al <Zn. This output performance ordering essentially agrees with the reverse ordering of the metal work function values. As shown in Fig. 4e , Zn with the smallest work function presents the largest electrical output. Based on these observations and the fact that the rate of electron transfer is much faster than the rate of ion migration, it is hypothesized that electron transfer occurs preferentially when the movable electrode touches the gel. Since the work function of the movable electrode is lower than that of the corner electrode, the electrons in the movable electrode are rapidly transferred to the corner electrode through the external circuit, which results in the loss of electrons at the movable electrode-polymer interface and leaves positively charged holes. Then, the interfacial electric field and nm-sized polymer pores will repel nearby cations [EMIM + ] and attract anions [TFSI - ]. In order to verify the above hypothesis, the migration behaviors of anions and cations when the closed-loop electrical circuit is in open state (Fig. 4f-i ) and closed state (Fig. 4f-ii )) are characterized by Raman mapping test. Relevant characterization techniques and analyses are described in detail in the Supplementary Material . In Raman mapping test, a copper mesh was used as the corner electrode and a zinc mesh was used as the movable electrode. Four representative positions were selected for testing, as shown in Fig. 4f-i ii and iv, including position P1: the center position of the copper mesh aperture; position P2: the corner position of the copper mesh aperture; position P3: the center position of the zinc mesh aperture; and position P4: the corner position of the zinc mesh aperture. As shown in Fig. S16 , since the concentration/content changes of cations and anions in the main region of the ionogel are not significantly different before and after circuit closure, test points P1 and P3 within the corner electrode grid were selected as positions distant from the corner electrodes. Several sets of in situ Raman mapping tests were performed at P4, i.e ., near the contact interface between the movable electrode and the ionogel. The distribution of anions and cations and their flow trends at this location were compared and analyzed under different electrical connection states, including open (original) (Fig. S17a ), closed for 20 min (Fig. S17b ), closed for 40 min (Fig. S17c ) and opened again for 10 min (Fig. S17d ). The migration of [EMIM + ] is usually dominant in the TPU ionogel due to the huge difference in the binding energy between [EMIM + ]/[TFSI - ] and the TPU skeleton 34 , 43 , 46 . The intensity changes of the corresponding Raman peaks of [TFSI - ] are very small, and therefore, the migration of anions will not be considered in the subsequent analysis. As shown in Fig. 4g , the Raman mapping intensity of the corresponding peaks of [EMIM + ] decreases significantly as the electrical circuit loop becomes closed, reflecting that the cation is moving away from the EDL M interface. Such [EMIM + ] moving away from the EDL M interface is also confirmed by the intensity enhancement of the corresponding Raman peak of [EMIM + ] at position P3, as shown in Fig. 4h and Fig. S18 . There is a difference in the intensity of the Raman scan corresponding to the closed loop for 20 min and 40 min, which confirms that ion migration is a very slow process and EDL cannot reach equilibrium in a short time. When the electrical circuit was opened again for 10 min, [EMIM + ] re-migrated back to the vicinity of EDL M as the direct connection between EDL C and EDL M was cut off. On the other hand, as shown in Fig. 4i and Fig. S19 , the corner electrode gets electrons and breaks the original EDL C equilibrium, which will attract [EMIM + ] near EDL C (P2) to gather. And the enhancement of the Raman mapping intensity at this location confirms the above speculation. The increased [EMIM + ] at P2 actually migrates from P1, so the Raman intensity at P1 is weakened. To summarize, during the contact electrification process of the device, since electrons can migrate from EDL M to EDL C through the external circuit load, the EDL C interface cations are always in an inflow state, while the EDL M interface cations are always in an outflow state. Since the above two processes are mutually reinforcing in positive feedback. The inflow of EDL C cations will cause the concentration of cations at the far end of EDL M to decrease, further accelerating the outflow of cations at EDL M . Similarly, the outflow of EDL M cations will lead to an increase in the concentration of cations at the far end of EDL C , further accelerating the inflow of cations at EDL C . In the above experiment, since the work function of the movable electrode is lower than that of the corner electrode, the electrons migrate from EDL M to EDL C , resulting in both positive voltage and current signals. A simplified schematic of the coupled ion-electron migration process in the whole closed-loop electrical system is shown in Fig. S20 . The positive feedback closed-loop electrical system design is critical, while the open-loop electrical system does not show a continuous electrical signal. This is mainly because the closed-loop feedback structure and working principle can effectively promote the continuous electron-ion coupling movement of EDL C and EDL M . Below are a few key factors: Optimization of electron transferring: In a closed-loop circuit, the ion-electron coupled inflow motion and the ion-electron coupled outflow motion are respectively carried out at two different electrode/gel interfaces. At the instant of loop closure, electrons flow from one electrode to the other through the external circuit due to the difference in the electrode materials work function. Such electron transfer process is more efficient than a single electrode directly interacting with the ions at the EDL interface. Charge separation: There is charge separation and opposite electronegativity between the movable and corner electrodes in the closed-loop circuit. This state of charge imbalance encourages more efficient migration of mobile ions. The role of ionic liquid: The ionic liquid within the polymer provides a conductive medium that allows ions to move between the electrodes and complete the circuit. This movement of ions helps to maintain the charge imbalance between the two electrodes, further contributing to the continued enhancement of EDL. Charge transfer kinetics: The design of the positive feedback closed-loop circuit reduces the potential energy of the EDL formation. Since the inflow and outflow of ions at the electrode/ionogel interfaces are located at two different electrodes, the possibility of random collisions between ions is reduced. This ordered ion transfer process improves the efficiency of charge transfer kinetics. Loop break: The ion-electron coupling positive feedback loop is interrupted, so the EDL C and EDL M are difficult to maintain. This leads to the return of the ions, i.e., the charge separation within the polymer gradually dissipates. In summary, it is reasonable to believe that the positive feedback coupled ion-electron transport inside the closed-loop circuit, the slow ion migration kinetics, and the high charge density qualities of the EDL are the essential reasons for the unique near-steady-state voltage and current output of the device. Application demonstration of ionic touch panel Another interesting phenomenon is that the iontronic device still has a nearly steady-state contact voltage/current response (−65 mV/−6.7 nA) and touch position recognition capability for a finger touch (400 Pa) with grounded electrostatic bracelet, as shown in Fig. 5a–c , Fig. S21 , and Supplementary Videos 1 – 3 . The negative voltage and current outputs observed during finger contact, in contrast to the positive signals obtained with metal electrodes, arise from the reversed electron transfer direction due to the grounded condition of the finger. As illustrated in Fig. 5a , the finger is connected to ground via an electrostatic bracelet, establishing a closed loop: grounded finger–ionogel–Au corner electrode–external resistor–ground. Upon contact, the grounded finger provides a lower potential reference compared to the Au corner electrode, driving electrons from the corner electrode through the external circuit toward the finger. This electron flow direction is opposite to that in the metal electrode case (e.g., Al–Cu), where electrons migrate from the movable electrode (lower work function) to the corner electrode. Consequently, the electrical double layer at the finger/ionogel interface becomes electron-rich (negative), while that at the corner electrode becomes electron-deficient, yielding negative voltage and current outputs. Despite the polarity reversal, the same positive-feedback ion-electron coupled transport mechanism governs the response, enabling stable, position-dependent signal output as demonstrated in Fig. 5b–c and Fig. S21 . This confirms the potential of the device for use in human-computer interfaces. Fig. 5. Open in a new tab Demonstration of the iontronic device as touch panel . a Schematic diagram of the ionic touch panel used for finger contact position recognition (corner electrode: Au, movable electrode: finger). b Voltage output response of a finger in prolonged (600 s) contact with the ionic touch panel. c Voltage output response of a finger briefly touching different positions of the ionic touch panel. d Square ionogel used as the touch screen for position recognition (corner electrode: Cu, movable electrode: Al). e Performance of the external voltage output at the four corner electrodes by touching five typical positions of the large touch screen. f Photograph of an S-trajectory written on the ionic touch panel (corner electrode: Cu, movable electrode: Al). g The real writing trajectory obtained by processing the output response of the four corner electrodes of the ion touch screen. h Positional resolution of the ionic touch panel (corner electrode: Cu, movable electrode: Al) In this case, the device only requires corner electrodes and a single layer of gel, further simplifying the device structure. In addition, despite the slow migration of ions, the iontronic device has a very fast response time of 60 ms in response to contact or separation (Fig. S22a, b ), which is consistent with the time required for ion migration to form the initial EDL. For example, ionic pressure capacitor devices that rely on EDL formation typically have response times of 60 ms to 70 ms 34 . Upon separation, the ion-electron coupling positive feedback loop is immediately interrupted and the electrical signal quickly disappears and returns to zero, rather than generating a negative pulse as in conventional triboelectric devices. The fast response capability means that the device can detect dynamic contact stimuli. The electrical response of the device can be effectively differentiated at finger touch frequencies of 1 Hz, 3 Hz, and 5 Hz, as shown in Fig. S22c, d . The ideal flexible touch panel should have high transparency, high stretchability, and the ability to continuously detect the touch position with high precision. It is also desirable to have no additional dependence on an external power source to increase the flexibility, longevity and light weight of the sensing system. The touch panel consists of only a single layer of gel and electrodes mounted on corner, thus the structure and manufacturing process are extremely simple. This fundamentally eliminates the weakening of the deformation, light transmittance and stability of gel materials by multi-layer interfaces. Good light transmission (Fig. S23a ) and flexibility (Fig. S23b, c ) of the devices can be observed from the photographs. And after 50% stretching and release, the device was able to recover its original shape (Fig. S23d ). When a grounded conductor ( e.g ., metal or a finger) touches the ionogel, the approximately steady-state potential difference and load current are generated between each corner electrode of the ionogel and the ground. The magnitude of the voltage/current is determined by the distance between the contact position and the corner electrode, as shown in Fig. 5d, e . The farther the contact position is from the corner electrode (meaning the longer the ion exchange diffusion path between EDL C and EDL M ), the lower the electrical signal output is. The touch panel’s simple structure and stable electrical signal output capability enable reliable and accurate recognition of multiple contact stimuli during soft interaction, including transient point contact, long-term point contact, and continuous slide contacts (Supplementary Video 4 ). In order to verify the feasibility of the touch panel for trajectory recognition, the letter “S” trajectory was written on the touch panel by contacting and continuously sliding the aluminum sheet. Specific test condition and photograph of the writing operation is shown in Fig. 5f , respectively. The four sets of voltage data obtained from the four fixed corner electrodes and the writing track position data were obtained by the relevant programs and algorithms as shown in Fig. 5g . As shown in Fig. 5h , the positional spatial resolution during a continuous sliding contact can be as high as 0.6 mV/100 μm. And the device still has an electrical signal output of 65 mV at the contact point 100 mm away from the corner electrode. Besides, the effect of different ionic gel panel sizes (6 × 6, 8 × 8, 10 × 10 and 12 × 12 cm 2 ) on voltage fluctuations and resolution in sliding contact responses was also conducted. As can be seen from Fig. S24 , as the panel size decreases, the contact voltage fluctuation/resolution tends to increase. The reason lies in the fact that, compared to smaller panels, larger panels provide a greater area for free diffusion of the same number of directionally migrating ions during the movement of the electrodes. This results in more ions undergoing free diffusion during their directional migration, rather than effectively reaching the corner electrodes to contribute to the electrical signal output of the external circuit, thereby weakening the current and voltage response generated across the external resistor. Conclusions This work demonstrates the contact-induced steady-state electrical signals generation in an ionogel closed-loop electrical system. When the movable electrode contacts the gel, contact-induced electron transfer occurs instantly, which in turn induces sustained ion-electron positive feedback coupling transmission inside the closed-loop system. The positive feedback coupled transport, combined with the slow ion migration kinetics and the high charge density properties of the EDL, results in a nearly steady-state voltage/current output. Furthermore, we have developed a self-powered, transparent, stretchable, single-layer structured ionic touch panel that demonstrates continuous trajectory detection with high spatial resolution. The touch panel demonstration conveys the wide applicability of our iontronic sensing technology and provides new opportunities for designing various iontronic devices that mimic biological neural systems. Methods Materials TPU granules (Type 75 A) were purchased from Taiwan Evermore Chemical Industry Co., Ltd. N, N-Dimethylformamide (DMF, AR, CAS: 68-12-2) was purchased from Chengdu Kelong Chemical Co., Ltd. The 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI], E101506, CAS: 174899-82-2) was purchased from Aladdin. All chemicals were used as received without further treatment. The copper (Cu), iron (Fe), titanium (Ti), aluminum (Al), zinc (Zn), Platinum (Pt) and other metals (thickness of 100 μm and custom sizes) used in the experiments are commercially available. The electrodes (copper and gold) and wires used in the experiments are also commercially available. The copper mesh and zinc mesh used in Raman test are commercially available in 100 mesh sizes. The copper mesh (100 mesh) and zinc mesh (100 mesh) used in the Raman test are commercially available. The external resistor box used in the test is a commercial simple resistor box with adjustable resistance. Synthesis of [EMIM][TFSI]/TPU composite ionogel Add 4 g of TPU pellets to 20 g of DMF liquid with magnetic stirring in a water bath (80 °C, 300 rpm/min) for 6 h to ensure that the TPU pellets are completely and uniformly dissolved into the DMF liquid. And a 20%wt TPU/DMF solution was obtained. Then, 0 g, 0.2 g, 0.4 g, 0.6 g, 0.8 g, 1 g and 1.2 g of [EMIM][TFSI] ionic liquids were weighed out and added to the above 24 g TPU/DMF solution, respectively. The ionic liquids were homogeneously and thoroughly mixed with the solution under 6 h of magnetic stirring in a water bath (80 °C, 300 rpm/min). Thus, seven [EMIM][TFSI]/TPU/DMF mixture solutions with [EMIM][TFSI] and TPU mass ratios of 0:4, 0.2:4, 0.4:4, 0.6:4, 0.8:4, 1:4 and 1.2:4 were prepared. Each of the above seven mixed solutions was weighed 12 g and poured into a PTFE fluted mold of size 120 mm × 120 mm. The above molds were placed on a heating plate at 80 °C, and after 4 h of heat curing, these [EMIM][TFSI]/TPU composite ionogels with ionic liquid content of 0 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt% and 30 wt% were obtained after the DMF solution had completely evaporated. Peel the above gel film from the mold and cut it to the desired size as needed. Assembly of iontronic devices The ionogel was cut into strips (20 mm × 120 mm) and used as the main body of the device. Copper or gold electrodes were connected at each of its ends as fixed corner electrodes of the device. Next, adjustable resistors were connected externally to the two fixed electrodes. And the other end of the external resistor was grounding or connected to the movable electrode with a wire to form a complete closed-loop electrical circuit. Metal sheets of different types and sizes were connected to two resistors or grounded through wires and used as movable electrodes to test the contact response electrical properties with the ionogel. When the finger was used as a movable electrode, it is necessary to wear a static bracelet on the wrist. And the bracelet was connected to the fixed corner electrode or grounded. Similarly, it is also necessary to connect the bracelet to the fixed corner electrode via a wire (or grounded) to ensure a complete closed electrical circuit between the movable electrode (finger) - ionogel - fixed corner electrode - external resistor. Characterizations of [EMIM][TFSI]/TPU composite ionogel The surface and cross section microstructures and elemental analysis of the composite ionogel were observed by scanning electron microscopy (ZEISS, Sigma 300) and energy dispersive spectrometer. The electrochemical impedance spectra of ionogels and ionic liquids were tested by means of an electrochemical analyzer (CH Instruments, CHI600F). The Raman spectra and Fourier transform infrared spectra of ionogels with different doping concentrations were analysed by laser confocal Raman spectrometer (Horiba, LabRAM HR Evolution) and Fourier transform infrared spectrometer (Thermo Scientific, Nicolet iS50), respectively. The mechanical response electrical output properties of the iontronic devices and the tensile properties of the ionogel were tested by an electronic universal testing machine (Shimadzu, AGS-X 50 N). The contact voltage and current responses of the device were monitored by high-precision, high-resolution digital multimeter (Keithley, DMM7510) and high resistance/low current electrostatic meter (Keithley, 6514). Supplementary information Download video file (129.4MB, mp4) Supplementary Video 1. Application demonstration 41378_2026_1307_MOESM2_ESM.docx (13.7MB, docx) Revised Supplementaty Material-clean version Download video file (151.7MB, mp4) Supplementary Video 2. Application demonstration Download video file (159KB, mp4) Supplementary Video 3. Application demonstration Download video file (80.8MB, mp4) Supplementary Video 4. Application demonstration Acknowledgements We acknowledge the financial supports from the National Natural Science Foundation of China (Grant Nos. 52575233), Science and Technology Research and Development Program Project of China Railway Group Limited (2025-Special-02), and Sichuan Provincial Natural Science Foundation Project (Grant Nos. 2026NSFSC0310), the Atomic-level Manufacturing Project of Southwest Jiaotong University (R110225H01077). The authors also thank the Research Center for Ultra-precision Surface Manufacturing, Analysis and Testing Center of Southwest Jiaotong University, and Shiyanjia Lab ( www.shiyanjia.com ) for their facility support. Author contributions K.D. Shang and T.T. Yang conceived the idea and designed the research. K.D. Shang, T.T. Yang and J.H. Fang designed, synthesized, and characterized the ionogel. Y. Zhang, Y. Chen and H. Liu tested the response performance of the iontronic device. R.X. Liu, C.H. Luo, and B.J. 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Application demonstration Download video file (159KB, mp4) Supplementary Video 3. Application demonstration Download video file (80.8MB, mp4) Supplementary Video 4. Application demonstration Data Availability Statement The data that support the findings of this study are available from the corresponding author upon reasonable request. Articles from Microsystems & Nanoengineering are provided here courtesy of Nature Publishing Group ACTIONS View on publisher site PDF (2.1 MB) Cite Collections Permalink RESOURCES Similar articles Cited by other articles Links to NCBI Databases Follow NCBI NCBI on X (formerly known as Twitter) NCBI on Facebook NCBI on LinkedIn NCBI on GitHub NCBI RSS feed Connect with NLM NLM on X (formerly known as Twitter) NLM on Facebook NLM on YouTube National Library of Medicine 8600 Rockville Pike Bethesda, MD 20894 Web Policies FOIA HHS Vulnerability Disclosure Help Accessibility Careers NLM NIH HHS USA.gov Back to Top

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