An asymmetric double electric layer frictional ion electron sensor and a preparation method thereof

Abstract

The application discloses an asymmetric double electric layer rubbing ion electron sensor and a preparation method thereof, and relates to the technical field of rubbing ion electron and self-powered sensing. The sensor comprises an ionic hydrogel layer, a first electrode and a second electrode; a spacing layer is arranged between the ionic hydrogel layer and the second electrode; wherein the first electrode and the second electrode are made of different materials, and the first electrode and the second electrode have different affinities to ions.

Description

Technical Field

[0001] This invention relates to the fields of triboelectric ion electronics and self-powered sensing technology, specifically to an asymmetric double-layer triboelectric ion sensor and its fabrication method. Background Technology

[0002] In 2012, Wang et al. proposed a triboiontronic nanogenerator (TENG) based on electrostatic induction, providing an important approach for the development of flexible self-powered sensors. However, traditional TENGs rely on electron conduction, which is fundamentally different from the signal transduction mechanism carried by ions in biological organisms, limiting their direct application in biomimetic sensing and biointerfaces. In recent years, ion sensors based on ion migration and redistribution mechanisms have attracted widespread attention; these devices respond to external stimuli through the movement of ions in ion hydrogels, and their working mechanism is highly similar to the biological sensing process, opening up new pathways for realizing soft, biomimetic, and self-powered sensing. Ion hydrogels, composed of polymer networks and ion-rich solutions, possess flexibility, high transparency, stretchability, and tunable ionic conductivity. Replacing traditional electrodes or friction layers with ion hydrogels can construct a new type of triboiontronic device.

[0003] Among various interfacial double-layer modulation methods, triboiontronic devices with direct electrode-hydrogel contact have attracted significant attention due to their extremely high transferred charge density. By forming a high-density nano-confined double layer at the solid-liquid interface, these devices achieve strong ion-electron coupling and can output currents in the hundreds of microamps, overcoming the common limitation of low output current (microamps or even nanoamps) in traditional solid-solid triboiontronic devices. They have been explored for efficient harvesting of extremely low-frequency mechanical energy. However, in practical applications for biomimetic sensing, these devices still face a key bottleneck: under cyclic loading, the asymmetry of the double layer at the upper and lower electrode interfaces is difficult to maintain long-term due to the self-wetting of the liquid, leading to a rapid decay of the output current with each cycle. For example, the Triboiontronic device proposed by Ouyang et al., which dynamically modulates the ion-electron coupling effect at the electrode-hydrogel interface, experiences a rapid current decay from approximately 400 μA to approximately 6 μA within 60 s cycles. This stability issue introduces unacceptable measurement errors, limiting the device's ability to achieve highly reliable sensing applications.

[0004] The most similar prior art solution to this invention is as follows: Figure 1As shown, this is a triboelectric ionoelectronic device that generates ion current by controlling the formation and relaxation of the interfacial electric double layer through a dynamic contact-separation process between a mechanically driven hydrogel and a metal electrode. Specifically, in the initial separation state, the hydrogel and back electrode interface form a relatively stable and saturated electric double layer due to prolonged static contact; however, the hydrogel and counter electrode interface, being in a separated state, do not form an effective electric double layer. At this time, the electric double layers of the upper and lower electrode interfaces are in a highly asymmetric state, but there is no net charge flow in the system as a whole. When the counter electrode moves upward under mechanical drive and separates from the hydrogel, due to the strong adsorption force of Stern layer ions in the electric double layer, some cations are "captured" and retained on the counter electrode surface; at the moment of separation, these captured charges generate a reverse pulse current. Through continuous and periodic contact-separation mechanical motion, the dynamic and periodic construction and destruction of the double layer at the hydrogel-metal interface can be achieved. This dynamic control leads to periodic changes in the capacitance of the double layer, thereby generating an alternating induced current in the external circuit. The amplitude and direction of the induced current are directly controlled by the dynamic formation and relaxation process of the double layer.

[0005] The aforementioned prior art has the following two main drawbacks: First, refer to Figure 2 As shown, the sensor working mechanism of this device relies on the dynamic periodic construction and destruction of the double layer at the hydrogel-electrode interface. Under cyclic loading, the asymmetry of the double layer at the upper and lower electrode-hydrogel interface is difficult to maintain for a long time, resulting in a rapid decay of the output current with the number of cycles and extremely poor sensing performance stability.

[0006] Secondly, refer to Figure 3 As shown, although the sensing performance of this device can achieve a certain voltage / current output through dynamic mechanical mechanism, the device output power is low and unstable, making it difficult to meet actual energy requirements. Summary of the Invention

[0007] The purpose of this invention is to provide an asymmetric double-layer triboelectric ion electron sensor and its preparation method. By setting a first electrode and a second electrode made of different materials and having different ion affinities, and setting a spacer layer between the ion hydrogel layer and the second electrode, the double layer at the interface between the ion hydrogel layer and the two electrodes is asymmetrically distributed, thereby solving the technical problem of maintaining the asymmetry of the double layer at the electrode-hydrogel interface in triboelectric ion electron sensors.

[0008] To address the aforementioned technical problems, in a first aspect, embodiments of the present invention provide an asymmetric double-layer triboelectric ion electron sensor, comprising: Ionized hydrogel layer; The first electrode is embedded in one side of the ion hydrogel layer and cured. The second electrode is located on the other side of the ion hydrogel layer and is disposed opposite to the first electrode; A spacer layer is disposed between the ion hydrogel layer and the second electrode; The first electrode and the second electrode are made of different materials and have different affinities for ions, which makes the double layer formed at the interface between the ion hydrogel layer and the first electrode and at the interface between the ion hydrogel layer and the second electrode asymmetric.

[0009] As an optional implementation, the surface of the ionic hydrogel layer is provided with a conical structure.

[0010] As an optional implementation, the first electrode comprises a carbon cloth electrode, the second electrode comprises a gold Au-polyethylene terephthalate (PET) composite electrode, and the spacer layer comprises polyurethane (PU) foam.

[0011] As an optional implementation, the ion hydrogel layer contains salt ions, which are configured to regulate the micropore structure of the ion hydrogel layer based on the Hofmeister effect, forming a micron-scale pore network.

[0012] As an alternative embodiment, the salt ion includes lithium chloride (LiCl), and the ion hydrogel layer is formed by curing a prepolymer solution containing acrylamide (AAM), N,N'-methylenebisacrylamide (MBAA), ammonium persulfate (APS), and the lithium chloride (LiCl).

[0013] As an optional embodiment, the mass fraction of acrylamide (AAM) in the prepolymer solution is 10–20 wt%. The mass of N,N'-methylenebisacrylamide (MBAA) is 0.5-1% of the mass of acrylamide (AAM), the mass of ammonium persulfate (APS) is 3-6% of the mass of acrylamide (AAM), and the concentration of lithium chloride (LiCl) is 0.5-1.0 M.

[0014] In polyacrylamide (PAM) ionic hydrogel systems constructed from acrylamide (AAM), ammonium persulfate (APS), as a classic thermal initiator, directly determines the rate of free radical polymerization and the final network structure. Limiting the mass of ammonium persulfate (APS) to 3–6% of the mass of acrylamide (AAM) aims to find the optimal balance between reaction kinetics, crosslinking network density, and the overall physical properties of the gel.

[0015] Specifically, ammonium persulfate (APS) decomposes upon heating in aqueous solution to generate highly reactive sulfate radicals. These radicals can initiate the copolymerization reaction of acrylamide (AAM) monomer and crosslinking agent (MBAA). When the APS content is in the range of 3–6%, the rate of radical generation and monomer consumption are ideally matched. At this point, the monomer can undergo sufficient and uniform linear polymerization and crosslinking, resulting in a uniform and dense three-dimensional network structure of polyacrylamide. This ensures that the hydrogel not only possesses excellent tensile strength, elasticity, and water retention, but also maintains stable ion conduction channels, giving the gel excellent overall electrochemical performance.

[0016] If the amount of APS added is less than 3%, the initial free radical concentration generated in the system is too low, resulting in an excessively slow polymerization initiation rate. In some cases, the reaction may even fail to start due to the inhibitory effect of dissolved oxygen. Macroscopically, this manifests as an excessively long curing time, or even incomplete gelation and a semi-fluid, viscous consistency. This leads to a significant and precipitous drop in mechanical properties such as tensile strength and elastic modulus, rendering it unsuitable as a stable ion-conducting medium.

[0017] When the amount of APS added exceeds 6%, the system will generate a large number of free radicals in a short period of time, leading to an excessively vigorous polymerization reaction. The excessively rapid reaction rate causes the monomers to be consumed disorderly in a very short time. Overly dense initiation sites result in excessive local cross-linking, leading to a highly brittle and inflexible hydrogel network that is prone to brittle fracture under stress. Furthermore, excessive APS leaves behind a large number of inorganic byproduct ions after the reaction, which not only compromises the long-term chemical stability of the hydrogel but may also interfere with the original ion migration behavior of lithium chloride (LiCl), thus negatively impacting the electrosensing performance of the hydrogel.

[0018] In polyacrylamide (PAM) ionic hydrogel systems, N,N'-methylenebisacrylamide (MBAA), as a bifunctional crosslinking agent, plays a crucial role in "welding" linear polyacrylamide chains into a three-dimensional network structure. Limiting the mass of MBAA to 0.5–1% of the mass of acrylamide (AAM) is to achieve a precise balance between the hydrogel's elasticity (mechanical response) and flexibility (stretchability and water retention).

[0019] Specifically, the molecular structure of MBAA contains conjugated double bonds at both ends that can participate in polymerization. During free radical polymerization initiated by ammonium persulfate (APS), it can simultaneously bind to different acrylamide growth chains, thereby forming a stable three-dimensional network framework. When the amount of MBAA added is within the optimal range of 0.5% to 1%, a chemically cross-linked network with moderate pore size, uniform distribution, and both toughness and elasticity is formed inside the hydrogel. This structure provides just the right amount of spatial porosity, allowing the lithium chloride (LiCl) salt ions and water molecules locked within to migrate freely, thus ensuring excellent ionic conductivity and water retention.

[0020] If the amount of MBAA added is less than 0.5%, the density of crosslinking sites in the system will be too low, resulting in an overly sparse polymer network backbone. Macroscopically, this manifests as extremely poor mechanical strength of the hydrogel, with the gel becoming too soft and collapsing, even approaching the state of a fluid or viscous gel, causing the long-term stability of the sensor to completely fail.

[0021] When the addition of MBAA exceeds 1%, the macroscopic brittleness of the hydrogel increases significantly, resulting in a loss of its original high tensile strength and flexibility. An overly dense mesh can cause severe steric hindrance to the dissolved lithium chloride (LiCl) salt ions, greatly limiting the free migration rate of the ions. This leads to a significant decrease in the ionic conductivity of the hydrogel, directly weakening its high sensitivity advantage as a sensing layer.

[0022] Meanwhile, in the polyacrylamide (PAM) hydrogel system, lithium chloride (LiCl) was chosen as the electrolyte salt based on a precise match considering multiple dimensions, including the Hofmannst salting-out effect of lithium ions and their tolerance to extreme environments. LiCl not only imparts conductivity to the gel as a charge carrier, but also exhibits deep intermolecular interactions with water molecules and the PAM framework.

[0023] Specifically, LiCl plays a dual synergistic role in the hydrogel system, imparting ionic conductivity and regulating the state of water molecules. Lithium ions, due to their extremely small ionic radius, possess extremely high charge density and strong hydrophilicity (hydration) ability. After solidification of the prepolymer solution, they can be uniformly distributed within the three-dimensional network pores of polyacrylamide, providing excellent ionic conductivity. More importantly, the Hofmannst salting-out effect of lithium ions modulates the hydrogel network structure, thereby enhancing the sensor's sensitivity performance.

[0024] Compared to other salts, LiCl imparts unparalleled antifreeze properties and long-lasting dehydration resistance to hydrogels. Due to its extremely strong chemical hydration energy, it can form a stable hydration layer with high coordination numbers with water molecules, thereby strongly disrupting the original hydrogen bond network in the bulk water and making it difficult for excess water molecules to crystallize. This allows LiCl hydrogels to maintain high flexibility and high conductivity even in extreme cold conditions far below 0°C. Simultaneously, LiCl's extremely high saturation solubility and strong hygroscopicity allow it to absorb trace amounts of moisture from the environment when the surrounding air is dry, slowing down the evaporation rate of water within the gel and enabling the sensor to maintain stable sensing performance even in long-term open operating environments.

[0025] Replacing Li with Na significantly degrades the overall performance of the system. The macroscopic defects are primarily manifested in a precipitous drop in freeze-thaw resistance and water retention. The eutectic point of the NaCl system is much higher than that of LiCl, making the hydrogel highly susceptible to freezing and cracking at low temperatures. Furthermore, it is prone to severe salting out due to water loss in dry air, leading to device failure. In addition, sodium ions are far less effective than lithium ions in regulating the hydrogel network structure.

[0026] Secondly, embodiments of the present invention provide a method for fabricating an asymmetric double-layer triboelectric ion electron sensor, comprising the following steps: Mold preparation; The monomer, crosslinking agent, initiator and salt ions are dissolved in deionized water to prepare a prepolymer solution; The prepolymer solution is poured into the mold, and the first electrode is covered on one side of the prepolymer solution. After heating and curing, the mold is removed to obtain an ion hydrogel layer with the first electrode embedded on one side. A spacer layer is placed around the ion hydrogel layer, and a second electrode is attached to the spacer layer, wherein the second electrode is made of a different material from the first electrode, and the first electrode and the second electrode have different affinities for ions; The asymmetric double-layer triboelectric ion sensor is obtained by encapsulation.

[0027] As an optional implementation, the mold is a polydimethylsiloxane (PDMS) mold, and the PDMS mold is provided with a conical structure; For example, the tapered structure is configured as a tapered shape with dimensions of 4mm×4mm×3mm and a 7×7 interval of 1mm.

[0028] The polydimethylsiloxane PDMS mold is obtained by mixing polydimethylsiloxane PDMS prepolymer and curing agent (Dow Corning 184PDMS curing agent) at a weight ratio of 8 to 12:1, pouring the mixture into a conical mold, heating and curing at 70 to 90°C for 2 to 4 hours, and then peeling it off.

[0029] In one optional embodiment, the second electrode includes a polyethylene terephthalate (PET) film and a gold (Au) layer deposited on the PET film, wherein the thickness of the PET film is 40–60 μm and the thickness of the gold (Au) layer is 20–40 nm.

[0030] As an optional implementation, the heating and curing temperature is 70-90°C, and the curing time is 20-40 minutes.

[0031] Compared with the prior art, the embodiments of the present invention have the following advantages and beneficial effects: 1. In this embodiment of the invention, a first electrode is embedded on one side of an ion-hydrogel layer, and a second electrode is provided on the other side opposite to the first electrode and separated by a spacer layer. Different materials with different ion affinities are selected as the first electrode and the second electrode, respectively, so that the double electric layer formed at the interface between the ion-hydrogel layer and the first electrode and the interface between the ion-hydrogel layer and the second electrode is asymmetrically distributed. This asymmetrical distribution is based on the intrinsic difference in ion affinity of the electrode materials on both sides, so that the sensor maintains the asymmetrical state of the interface double electric layer under cyclic loading, stabilizes the ion and electron coupling effect, and achieves long-period stability of the output signal.

[0032] 2. In this embodiment of the invention, a carbon cloth electrode is selected as the first electrode, a gold Au / polyethylene terephthalate (PET) composite electrode is selected as the second electrode, and polyurethane foam is used as a spacer layer. By utilizing the inherent difference in ion affinity between the carbon cloth and the gold Au / PET, the double layer formed at the interface between the ion hydrogel layer and the carbon cloth electrode, and at the interface between the ion hydrogel layer and the gold Au / PET electrode, are asymmetrically distributed. This asymmetrical distribution causes differences in the ion adsorption and desorption behavior of the two interfaces under cyclic loading, thereby maintaining the asymmetrical state of the charge distribution of the double layer and ensuring stable electrical signal output of the device during periodic contact and separation processes.

[0033] 3. In this embodiment of the invention, the ion hydrogel layer contains salt ions, and the salt ions are used to regulate the micro-pore structure of the ion hydrogel layer based on the Hofmeister effect to form a micron-scale pore network. This micron-scale pore network increases the effective contact area and the concentration of mobile ions in the ion hydrogel layer, and reduces the interfacial impedance during the ion-electron conversion process, thereby synergistically enhancing the density of the interfacial double layer and improving the current output level and signal quality of the device.

[0034] 4. In this embodiment of the invention, a prepolymer solution is poured into a polydimethylsiloxane (PDMS) mold with a conical structure and then cured by heating to obtain an ionized hydrogel layer with a conical structure. Under mechanical excitation, the conical structure produces local deformation concentration, which increases the effective contact area change rate between the ionized hydrogel layer and the electrode, thereby improving the device's response sensitivity to mechanical stimulation and widening its pressure detection range. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 Schematic diagram of existing sensor structure and power generation principle; Figure 2 A diagram demonstrating the cyclic response capability achievable by existing sensor technologies; Figure 3 The values ​​represent the sensor current and voltage output magnitudes achievable by ion hydrogels under mechanical excitation in existing technologies, among which... Figure 3 In this context, 'a' corresponds to the current. Figure 3 In this context, 'b' corresponds to the voltage. Figure 4 This is a sensor fabrication process diagram provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the working mechanism of the double electric layer of the sensor prepared according to an embodiment of the present invention; Figure 6 This is a schematic diagram of the ion regulation mechanism of the ion hydrogel layer; Figure 7 This is a schematic diagram illustrating the performance regulation of the sensor prepared according to an embodiment of the present invention; Figure 8 The signal stability detection diagram is achieved by using asymmetric electrodes composed of Au / PET and carbon cloth as the second and first electrodes, respectively, to regulate the double layer effect. Figure 9 The signal stability detection diagram is achieved by using Au / PET, the same material for both the first and second electrodes, to regulate the double-layer effect. Figure 10 The signal stability detection diagram is achieved by using carbon cloth of the same material for both the first and second electrodes to regulate the double-layer effect. Figure 11 This is a comparison of the effect of initial prepolymer solutions with different salt ion concentrations on the pore size regulation of the sensor's functional layer. Figure 11In this context, 'a' corresponds to 0.2 M LiCl. Figure 11 In this context, b corresponds to 0.5M LiCl. Figure 11 c in the text corresponds to 0.8 MLiCl; Figure 12 The effect of an initial prepolymer solution of 0.2M LiCl on the sensor output signal is shown in the test graph. Figure 13 The effect of an initial prepolymer solution of 0.5M LiCl on the sensor output signal is shown in the test graph. Figure 14 The effect of an initial prepolymer solution of 0.8M LiCl on the sensor output signal is shown in the test graph. Figure 15 The test graph shows the effect of different initial prepolymer solution monomer concentrations on the sensor output current response. Figure 16 Sensor-strain curves showing the effect of different initial prepolymer solution monomer concentrations on the sensor-strain curves; Figure 17 The images show SEM images of samples with different monomer contents, where a in Figure 17 corresponds to 30% AAM. Figure 17 The 'b' in the text corresponds to 50% AAM; Figure 18 To optimize the signal output stability test of the sensor after the ion functional layer, among which Figure 18 In this context, 'a' corresponds to the current signal. Figure 18 In this context, 'b' corresponds to the voltage signal. Figure 19 The signal output power diagram of the sensor after optimizing the ion functional layer. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0037] Therefore, the detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0038] The purpose of this invention is to achieve long-term high stability of the output signal by synergistically designing the intrinsic asymmetry of the electrode and the microstructure regulation of the hydrogel to stably maintain the asymmetric double layer at the electrode-hydrogel interface under cyclic loading.

[0039] To address this, at the electrode level, an asymmetric electrode combination of gold (Au) / polyethylene terephthalate (PET) and carbon cloth was selected. The carbon cloth's abundant oxygen-containing functional groups and porous structure strongly adsorb specific ions, creating a natural difference in ion affinity with the gold (Au) / PET electrode. This constructs an electrode-hydrogel interface with inherent asymmetry, fundamentally solving the problems of maintaining double-layer asymmetry and rapid signal decay during cycling.

[0040] At the hydrogel level, salt ions are introduced to regulate its microstructure, forming a smaller and denser pore network. This increases the concentration of mobile ions and the interfacial contact area while reducing the interfacial impedance during the ion-electron conversion process, thus synergistically enhancing the density of the double layer and the quality of the output signal.

[0041] Therefore, the device can not only maintain a stable high current output during continuous cyclic excitation, but also improve the output power level.

[0042] Specifically, embodiments of the present invention provide a method for fabricating an asymmetric double-layer triboelectric ion electron sensor, comprising the following: First, a polydimethylsiloxane (PDMS) mold is prepared. The PDMS prepolymer Sylgard 184 and the curing agent (Dow Corning 184 PDMS curing agent) are mixed evenly at a weight ratio of 8 to 12:1. Then, the mixture is poured into a 3D-printed conical master mold and heated and cured at 70 to 90°C for 2 to 4 hours. Subsequently, the PDMS mold with a conical structure is obtained by peeling.

[0043] Subsequently, an ion-hydrogel layer was prepared, referring to... Figure 4 As shown, acrylamide (AAM), N,N'-methylenebisacrylamide (MBAA), ammonium persulfate (APS), and lithium chloride (LiCl) were dissolved in deionized water to prepare a homogeneous prepolymer solution. For example, 3 g of acrylamide (AAM), 20 mg of N,N'-methylenebisacrylamide (MBAA), 120 mg of ammonium persulfate (APS), and 0.8 M lithium chloride (LiCl) were prepared into a 20 ml solution. The mass fraction of acrylamide (AAM) was 10–20 wt%, the mass fraction of N,N'-methylenebisacrylamide (MBAA) was 0.5–1% of the mass of acrylamide (AAM), the mass fraction of ammonium persulfate (APS) was 3–6% of the mass of acrylamide (AAM), and the concentration of lithium chloride (LiCl) was 0.5–1.0 M. The mixture was stirred for 0.5–2 h to ensure complete dissolution and mixing. Subsequently, the prepared prepolymer solution was poured into the polydimethylsiloxane (PDMS) mold, and the first electrode was placed on top of the prepolymer solution. The mixture was then heated and cured at 70–90 °C for 20–40 minutes. After demolding, a cone-shaped ion hydrogel layer with the first electrode embedded on one side is obtained.

[0044] Continue to refer to Figure 4 As shown, the second electrode is then prepared and the device is assembled. The polyethylene terephthalate (PET) film is cleaned and subjected to oxygen plasma treatment. Then, a layer of gold (Au) is deposited on the surface of the PET film using a vacuum coating machine. The thickness of the PET film is 40–60 μm, for example, 50 μm, and the thickness of the gold (Au) layer is 20–40 nm, for example, 30 nm, to obtain a flexible gold (Au) / PET composite electrode. The first electrode is a commercially available carbon cloth electrode (200–300 μm thick, such as Cetech W0S1011SH).

[0045] Finally, the device is assembled. A 4-6 mm thick polyurethane (PU) foam is placed around the ion hydrogel layer with the first electrode embedded at the bottom as a spacer layer. Then, the second electrode is attached to the spacer layer and encapsulated with PI tape. Finally, an asymmetric double-layer triboelectric ion electron sensor with a sandwich structure is obtained.

[0046] This invention, through adjusting the proportions of each component in the prepolymer solution, modulates the micropore size of the ion hydrogel based on the Hofmeister effect, forming a micron-scale pore network with adjustable pore size on a macroscopic scale. This pore network increases the interfacial contact area and the concentration of mobile ions, improves the ion transport rate, and reduces the interfacial impedance during the ion-electron conversion process, thereby synergistically enhancing the density and stability of the interfacial electric double layer.

[0047] In this embodiment of the invention, the ion-hydrogel and the bottom carbon electrode are embedded and cured in the initial state, which improves the reliability and functional stability of the sensor. The abundant oxygen-containing functional groups and high specific surface area of ​​the carbon cloth surface are used to form an asymmetric electrode combination with the gold Au / polyethylene terephthalate PET electrode, so that the device forms an asymmetric electric double layer with inherent differences in ion affinity under mechanical excitation, which improves the reversible change capability and cycle stability of the ion double layer. At the same time, the introduction of the hydrogel microstructure further improves the sensitivity and range of the sensor.

[0048] To better demonstrate the significant effects of the embodiments of the present invention, specific experimental examples will be set up below to verify the effects.

[0049] Example 1: This embodiment of the invention provides a method for fabricating an asymmetric double-layer triboelectric ion electron sensor, comprising the following: First, a polydimethylsiloxane (PDMS) mold is prepared. The PDMS prepolymer Sylgard 184 and the curing agent (Dow Corning 184 PDMS curing agent) are mixed evenly at a weight ratio of 10:1. Then, the mixture is poured into a 3D-printed conical master mold and heated and cured at 80°C for 3 hours. Subsequently, the PDMS mold with a conical structure is obtained by peeling.

[0050] Subsequently, an ion-polymer layer was prepared by dissolving acrylamide (AAM), N,N'-methylenebisacrylamide (MBAA), ammonium persulfate (APS), and lithium chloride (LiCl) in deionized water to form a homogeneous prepolymer solution. The mass fraction of acrylamide (AAM) was 15 wt%, the mass fraction of N,N'-methylenebisacrylamide (MBAA) was 0.66% of the mass of acrylamide (AAM), the mass fraction of ammonium persulfate (APS) was 3.96% of the mass of acrylamide (AAM), and the concentration of lithium chloride (LiCl) was 0.8 M. The mixture was stirred for 1 h to ensure complete dissolution and mixing. The prepared prepolymer solution was then poured into the polydimethylsiloxane (PDMS) mold, and the first electrode was placed on top of the prepolymer solution. The mixture was then heated and cured at 80 °C for 30 min. After demolding, a cone-shaped ion-polymer layer with the first electrode embedded on one side was obtained.

[0051] Next, the second electrode was prepared and the device was assembled. The polyethylene terephthalate (PET) film was cleaned and treated with oxygen plasma. Then, a layer of gold (Au) was deposited on the surface of the PET film using a vacuum coating machine. The thickness of the PET film was 50 μm and the thickness of the gold (Au) layer was 30 nm, resulting in a flexible gold (Au) / PET composite electrode. The first electrode was a carbon cloth electrode purchased directly, with a thickness of 260 μm.

[0052] Finally, the device was assembled. A 5 mm thick polyurethane (PU) foam was placed around the ion hydrogel layer with the first electrode embedded at the bottom as a spacer layer. Then, the second electrode was attached to the spacer layer and encapsulated with PI tape, resulting in an asymmetric double-layer triboelectric ion sensor with a sandwich structure.

[0053] In Example 1 of this invention, the carbon cloth electrode at the bottom of the sensor maintains constant contact with the ion hydrogel. Benefiting from the abundant functional groups on the carbon cloth surface and the large contact area, it exhibits excellent ion adsorption performance. Figure 5 As shown, a large amount of Li +The ions are adsorbed onto the surface of the carbon cloth electrode, thus forming a dense ion adsorption layer on the first electrode. Simultaneously, when external pressure is applied to bring the second electrode (Au / PET) into contact with the ion hydrogel, the charge in the ion hydrogel is transferred to the Au / PET surface through a contact electrification effect, thereby inducing Li⁺ to migrate to the electrode-ion hydrogel interface and form an electrical bilayer. The second electrode then reacts with Li⁺... + The adsorption capacity of the electrode is significantly lower than that of the first electrode, thereby achieving long-term asymmetry of the electrical bilayer at the interface between the second and first electrodes of the device.

[0054] In addition, refer to Figure 6 As shown, the addition of Li salt induces the Hofmeister salting-out effect, leading to a large and dense aggregation of polymer chains in the ionogel. This process not only increases the number of migratable ions but also increases the interfacial contact area. These two factors synergistically amplify the density of the electric bilayer, ultimately resulting in an increase in current output. Experimental results show that, referring to… Figure 7 As shown, under periodic external stimulation of 13 kPa, this device can generate a stable output current of about 60 μA, while devices in other similar studies can only generate currents of a few microamps or even a few nanoamps, or the output current drops rapidly with the increase of the number of cycles.

[0055] The surface structure gel formed by optimizing monomer concentration and crosslinking agent content in Embodiment 1 of this invention exhibits excellent mechanical properties. Furthermore, the asymmetric combination of the second and first electrodes, as described in Example 1, demonstrates superior mechanical properties. Figure 18 As shown, high and stable signal output of current and voltage can be achieved. This is due to the formation of a stable and highly asymmetric electric double layer at the interface between the second electrode and the first electrode-hydrogel, and the Hofmeister effect, which enables precise control of the pore structure, specific surface area, and ionic conductivity of the ion hydrogel. The sensor achieves no decay in response time after 5000s of cycling. Figure 19 As shown, it also has high signal power output.

[0056] Example 2: This embodiment of the invention provides a method for fabricating an asymmetric double-layer triboelectric ion electron sensor, comprising the following: First, a polydimethylsiloxane (PDMS) mold is prepared. The PDMS prepolymer Sylgard 184 and the curing agent (Dow Corning 184 PDMS curing agent) are mixed evenly at a weight ratio of 8:1. Then, the mixture is poured into a 3D-printed conical master mold and heated and cured at 70°C for 4 hours. Subsequently, the PDMS mold with a conical structure is obtained by peeling.

[0057] Subsequently, an ion-hydrogel layer was prepared by dissolving acrylamide (AAM), N,N'-methylenebisacrylamide (MBAA), ammonium persulfate (APS), and lithium chloride (LiCl) in deionized water to form a homogeneous prepolymer solution. The mass fraction of acrylamide (AAM) was 10 wt%, the mass fraction of N,N'-methylenebisacrylamide (MBAA) was 0.5% of the mass of acrylamide (AAM), the mass fraction of ammonium persulfate (APS) was 3% of the mass of acrylamide (AAM), and the concentration of lithium chloride (LiCl) was 0.5 M. The mixture was stirred for 0.5 h to ensure complete dissolution and mixing. The prepared prepolymer solution was then poured into the polydimethylsiloxane (PDMS) mold, and the first electrode was placed on top of the prepolymer solution. The mixture was then heated and cured at 70 °C for 40 min. After demolding, a cone-shaped ion-hydrogel layer with the first electrode embedded on one side was obtained.

[0058] Next, a second electrode was prepared and the device was assembled. The polyethylene terephthalate (PET) film was cleaned and treated with oxygen plasma. Then, a layer of gold (Au) was deposited on the surface of the PET film using a vacuum coating machine. The thickness of the PET film was 40 μm and the thickness of the gold (Au) layer was 20 nm, resulting in a flexible gold (Au) / PET composite electrode. The first electrode was a carbon cloth electrode purchased directly, with a thickness of 260 μm.

[0059] Finally, the device was assembled. A 5 mm thick polyurethane (PU) foam was placed around the ion hydrogel layer with the first electrode embedded at the bottom as a spacer layer. Then, the second electrode was attached to the spacer layer and encapsulated with PI tape, resulting in an asymmetric double-layer triboelectric ion sensor with a sandwich structure.

[0060] Example 3: This embodiment of the invention provides a method for fabricating an asymmetric double-layer triboelectric ion electron sensor, comprising the following: First, a polydimethylsiloxane (PDMS) mold is prepared. The PDMS prepolymer Sylgard 184 and the curing agent (Dow Corning 184 PDMS curing agent) are mixed evenly at a weight ratio of 12:1. Then, the mixture is poured into a 3D-printed conical master mold and heated and cured at 90°C for 2 hours. Subsequently, the PDMS mold with a conical structure is obtained by peeling.

[0061] Subsequently, an ion-hydrogel layer was prepared by dissolving acrylamide (AAM), N,N'-methylenebisacrylamide (MBAA), ammonium persulfate (APS), and lithium chloride (LiCl) in deionized water to form a homogeneous prepolymer solution. The mass fraction of acrylamide (AAM) was 20 wt%, the mass fraction of N,N'-methylenebisacrylamide (MBAA) was 1% of the mass of acrylamide (AAM), the mass fraction of ammonium persulfate (APS) was 6% of the mass of acrylamide (AAM), and the concentration of lithium chloride (LiCl) was 1.0 M. The mixture was stirred for 2 hours to ensure complete dissolution and mixing. The prepared prepolymer solution was then poured into the polydimethylsiloxane (PDMS) mold, and the first electrode was placed on top of the prepolymer solution. The mixture was then heated and cured at 90°C for 20 minutes. After demolding, a cone-shaped ion-hydrogel layer with the first electrode embedded on one side was obtained.

[0062] Next, a second electrode was prepared and the device was assembled. The polyethylene terephthalate (PET) film was cleaned and treated with oxygen plasma. Then, a layer of gold (Au) was deposited on the surface of the PET film using a vacuum coating machine. The thickness of the PET film was 60 μm and the thickness of the gold (Au) layer was 40 nm, resulting in a flexible gold (Au) / PET composite electrode. The first electrode was a commercially available carbon cloth electrode with a thickness of 260 μm.

[0063] Finally, the device was assembled. A 5 mm thick polyurethane (PU) foam was placed around the ion hydrogel layer with the first electrode embedded at the bottom as a spacer layer. Then, the second electrode was attached to the spacer layer and encapsulated with PI tape, resulting in an asymmetric double-layer triboelectric ion sensor with a sandwich structure.

[0064] Example 4: This embodiment of the invention provides a method for preparing an asymmetric double-layer triboelectric ion electron sensor. The difference from Example 1 is that the concentration of lithium chloride (LiCl) is 0.2 M, while the other steps remain unchanged.

[0065] Example 5: This embodiment of the invention provides a method for preparing an asymmetric double-layer triboelectric ion electron sensor. The difference from Example 1 is that the concentration of lithium chloride (LiCl) is 1.2 M, while the other steps remain unchanged.

[0066] Example 6: This embodiment of the invention provides a method for preparing an asymmetric double-layer triboelectric ion electron sensor. The difference from Example 1 is that the mass fraction of acrylamide (AAM) is 8 wt%, while the other steps remain unchanged.

[0067] Example 7: This embodiment of the invention provides a method for preparing an asymmetric double-layer triboelectric ion electron sensor. The difference from Example 1 is that the mass fraction of acrylamide (AAM) is 30 wt%, while the other steps remain unchanged.

[0068] Example 8: This embodiment of the invention provides a method for preparing an asymmetric double-layer triboelectric ion electron sensor. The difference from Example 1 is that the mass fraction of acrylamide (AAM) is 50 wt%, while the other steps remain unchanged.

[0069] Example 9: This embodiment of the invention provides a method for preparing an asymmetric double-layer triboelectric ion electron sensor. The difference from Example 1 is that the polydimethylsiloxane (PDMS) mold does not have a conical structure, while the other steps remain unchanged.

[0070] Example 10: This embodiment of the invention provides a method for preparing an asymmetric double-layer triboelectric ion electron sensor. The difference from Example 1 is that lithium chloride is replaced with sodium chloride, while the other steps remain unchanged.

[0071] Comparative Example 1: A method for preparing a symmetrical electric double-layer triboelectric ion electron sensor is provided. The difference from Example 1 is that both the second electrode and the first electrode are made of Au / PET, while the other steps remain unchanged.

[0072] Comparative Example 2: A method for fabricating a symmetrical electric double-layer triboelectric ion electron sensor is provided, wherein the first electrode and the second electrode are both made of carbon cloth, and the remaining steps remain unchanged.

[0073] Comparative Example 3: A method for preparing a triboelectric ion electron sensor is provided. The difference from Example 1 is that polyurethane (PU) foam is not used as a spacer layer, while the other steps remain unchanged.

[0074] The sensors prepared in Examples 1-10 and Comparative Examples 1-3 were subjected to performance tests, and the specific test results are as follows: (1) The short-circuit current (Isc) and open-circuit voltage (Voc) generated by the sensor were measured using a programmable electrometer (Keithley 6514) and a digital multimeter (Keithley DMM7510); (2) Cyclic stability test: The sensor was installed on the tensile tester (AGS-S), and a fixed cyclic pressure (13 kAa, 5000 cycles) was applied through the computer control console. The electrical signal generated by the sensor was measured by a programmable electrometer (Keithley 6514) and a digital multimeter (Keithley DMM7510). (3) Sensitivity: The sensor was mounted on the stretching machine (AGS-S), gradient pressure was applied through the computer console, and then the electrical signal generated by the sensor at each pressure was measured using a programmable electrometer (Keithley 6514) and a digital multimeter (Keithley DMM7510).

[0075] The test results are shown in Tables 1, 2, and 3 below: Table 1

[0076] Table 2

[0077] Table 3

[0078] Please refer to Figure 11 As shown, by controlling the initial polymer concentration with different salt ion concentrations, the pore size of the hydrogel can be adjusted based on the Hofmeister effect of ions. The higher the ion salt concentration in the initial prepolymer, the more significant the pore-regulating effect; that is, the pore density of the polymer network increases with increasing ion concentration. Please refer to the reference. Figure 12 , Figure 13 , Figure 14 As shown, the sensor output signal increases accordingly with the increase of ion content (approximately 32 μA, 42 μA, and 58 μA, respectively).

[0079] Changing the monomer concentration in the initial prepolymer solution can also affect the signal output, such as... Figure 15 As shown, with the increase of monomer content in the ion-hydrogel, the sensor's output signal exhibits a significant attenuation trend, decreasing from 57.96 μA to 20 μA, and finally as low as 8.18 μA. This phenomenon arises because the increased monomer content leads to a thicker ion-hydrogel framework, a smaller specific surface area, and impaired ion migration. Figure 16 As shown, the stress-strain curve of the ionized hydrogel increases with increasing monomer content, which indirectly proves the significant thickening of the ionized hydrogel skeleton. This was confirmed by SEM (Sequencing). Figure 17 Morphological characterization of samples with different monomer contents showed that as the monomer content increased, the hydrogel skeleton thickened significantly and the porosity decreased accordingly.

[0080] As can be seen from the comparison between Comparative Examples 1 and 2 and Example 1, the signal stability of the ion hydrogel in Example 1 of this invention is regulated by controlling and changing the second electrode and the first electrode. By changing different combinations of the second and first electrodes, the adsorption strength of the second and first electrodes for ions can be changed, thereby achieving continuous high current and cycling stability. Please refer to... Figure 8 As shown, when the second and first electrodes of the device are asymmetric electrodes composed of Au / PET and carbon cloth, respectively, the sensor can generate a stable current of approximately 58 μA under external cyclic pressure stimulation. When both the second and first electrodes of the device are made of the same material (Au / PET-Au / PET or carbon cloth-carbon cloth), the output current of the device not only decreases significantly, but also shows a continuous decay trend with increasing cycle number, decreasing from 2 μA to 0.67 μA (refer to...). Figure 9 (as shown) and decay from 20 μA to 5.6 μA (refer to) Figure 10 (As shown).

[0081] Referring to Tables 1-3, a comparison of Examples 4 and 5 with Example 1 shows that when the lithium chloride concentration is less than 0.5M, the device output current decreases to 32 μA due to insufficient migrating ions. Figure 12 When the lithium chloride concentration is greater than 1 M, the number of mobile ions increases continuously, and the double layer formed at the electrode-hydrogel interface reaches saturation, so the output current of the device no longer increases (remaining at around 60 μA); therefore, the effect is better when the lithium chloride concentration is set in the range of 0.5 to 1 M.

[0082] A comparison of Examples 6, 7, and 8 with Example 1 shows that when the mass fraction of acrylamide (AAM) is less than 10 wt%, the resulting hydrogel has extremely poor mechanical strength due to the insufficient monomer content. The gel is too soft and collapses, even approaching the state of a fluid or viscous gel, leading to poor device cycling stability (decaying from 57 μA to 18 μA after 1800 s cycling). When the mass fraction of acrylamide (AAM) is greater than 20 wt%, the skeleton of the ion hydrogel becomes thicker, the specific surface area decreases, and ion migration is hindered, resulting in a decrease in output current (minimum 8.18 μA). Therefore, setting the mass fraction of acrylamide (AAM) in the range of 10–20 wt% yields better results.

[0083] As can be seen from the comparison between Example 9 and Example 1, when the polydimethylsiloxane PDMS mold does not have a conical structure, the contact area between the upper electrode and the hydrogel does not change with the force when under pressure, and the magnitude of the device output current does not change with the force. Therefore, the sensitivity of the device is almost 0.

[0084] A comparison of Example 10 and Example 1 shows that when lithium chloride is replaced with sodium chloride, the Hoffmanster salting-out effect, where Na ions cannot replace Li ions, leads to a sparse hydrogel network structure, causing the device output current to decrease to 30 μA. Furthermore, sodium chloride's water retention is far inferior to that of lithium chloride, causing dehydration of the device during long-term testing, resulting in a decrease in device stability (from 30 μA to 10 μA after 1800 s cycling).

[0085] As can be seen from the comparison between Comparative Example 3 and Example 1, when polyurethane (PU) foam is not set as a spacer layer, the output current of the device decreases with the increase of the number of cycles because the upper electrode cannot fully recover during the pressing / releasing process (it decreases from 59 μA to 20 μA after 1800s cycles).

[0086] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An asymmetric double-layer triboelectric ion-electron sensor, characterized in that, include: Ionized hydrogel layer; The first electrode is embedded in one side of the ion hydrogel layer and cured. The second electrode is located on the other side of the ion hydrogel layer and is disposed opposite to the first electrode; A spacer layer is disposed between the ion hydrogel layer and the second electrode; The first electrode and the second electrode are made of different materials and have different affinities for ions, which makes the double layer formed at the interface between the ion hydrogel layer and the first electrode and at the interface between the ion hydrogel layer and the second electrode asymmetric.

2. The asymmetric double-layer triboelectric ion electron sensor according to claim 1, characterized in that, The surface of the ion hydrogel layer is provided with a cone-shaped structure.

3. The asymmetric double-layer triboelectric ion electron sensor according to claim 2, characterized in that, The first electrode comprises a carbon cloth electrode, the second electrode comprises a gold-polyethylene terephthalate composite electrode, and the spacer layer comprises polyurethane foam.

4. An asymmetric double-layer triboelectric ion electron sensor according to claim 3, characterized in that, The ion hydrogel layer contains salt ions, which are configured to regulate the micropore structure of the ion hydrogel layer based on the Hofmeister effect, forming a micron-scale pore network.

5. An asymmetric double-layer triboelectric ion electron sensor according to claim 4, characterized in that, The salt ions include lithium chloride, and the ion hydrogel layer is formed by curing a prepolymer solution containing acrylamide, N,N'-methylenebisacrylamide, ammonium persulfate and the lithium chloride.

6. An asymmetric double-layer triboelectric ion electron sensor according to claim 5, characterized in that, In the prepolymer solution, the mass fraction of acrylamide is 10–20 wt%. The mass of the N,N'-methylenebisacrylamide is 0.5-1% of the mass of the acrylamide, the mass of the ammonium persulfate is 3-6% of the mass of the acrylamide, and the concentration of the lithium chloride is 0.5-1.0 M.

7. A method for fabricating an asymmetric double-layer triboelectric ion-electron sensor as described in any one of claims 1 to 6, characterized in that, Includes the following steps: Mold preparation; The monomer, crosslinking agent, initiator and salt ions are dissolved in deionized water to prepare a prepolymer solution; The prepolymer solution is poured into the mold, and the first electrode is covered on one side of the prepolymer solution. After heating and curing, the mold is removed to obtain an ion hydrogel layer with the first electrode embedded on one side. A spacer layer is placed around the ion hydrogel layer, and a second electrode is attached to the spacer layer, wherein the second electrode is made of a different material from the first electrode, and the first electrode and the second electrode have different affinities for ions; The asymmetric double-layer triboelectric ion sensor is obtained by encapsulation.

8. The method for fabricating an asymmetric double-layer triboelectric ion electron sensor according to claim 7, characterized in that, The mold includes a polydimethylsiloxane mold, which has a conical structure. The polydimethylsiloxane mold is prepared by mixing polydimethylsiloxane prepolymer and curing agent at a weight ratio of 8-12:1, pouring the mixture into a conical mold, heating and curing at 70-90°C for 2-4 hours, and then peeling it off.

9. The method for fabricating an asymmetric double-layer triboelectric ion electron sensor according to claim 7, characterized in that, The second electrode comprises a polyethylene terephthalate film and a gold layer deposited on the polyethylene terephthalate film, wherein the thickness of the polyethylene terephthalate film is 40–60 μm and the thickness of the gold layer is 20–40 nm.

10. The method for fabricating an asymmetric double-layer triboelectric ion electron sensor according to claim 7, characterized in that, The heating and curing temperature is 70–90°C, and the curing time is 20–40 min.

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