Intelligent hydrogel skin capable of harvesting energy from the outside world and preparation method thereof

Abstract

The application belongs to the technical field of intelligent energy, and particularly relates to an intelligent hydrogel skin capable of obtaining energy from the outside world and a preparation method thereof.The intelligent hydrogel skin comprises an air positive electrode, a hydrogel and a sensing electrode, the hydrogel is a simulated skin film, the sensing electrode is embedded in the film, one side of the hydrogel is attached to the air positive electrode, and the other side is in contact with a material acting as a negative electrode in the outside world, the air positive electrode is connected to the positive electrode of a power supply device, and the material acting as the negative electrode is connected to the negative electrode of the power supply device, when the hydrogel skin is in contact with the material acting as the negative electrode, a battery circuit is formed, and the function of obtaining energy from the outside world for power supply is realized, and the sensing electrode realizes the identification of the contacted object by the sensing voltage generated by the contact between the hydrogel skin and the surface of the material.The hydrogel skin of the application can obtain energy from any material acting as a negative electrode in the outside world at any time without charging, and the hydrogel skin also has the functions of adhesion and intelligent identification, so that the multi-function of the battery is realized while the endurance time is improved.

Description

Technical Field

[0001] This invention belongs to the field of smart energy technology, specifically relating to a smart hydrogel skin that obtains energy from the outside world and its preparation method. Background Technology

[0002] With the current trend of intelligent and miniaturized wireless devices, the development of batteries that power these devices faces new challenges. As device size decreases, battery size also needs to shrink. However, as battery size decreases, energy density declines exponentially, significantly shortening device lifespan. Furthermore, the fixed form factor of batteries necessitates additional space design for their placement. This is particularly problematic in the field of intelligent robotics, where robots have diverse task requirements, such as intelligent recognition, walking, and climbing. These tasks not only require ample energy supply but also necessitate the integration of more components to realize the robot's functions, creating a conflict with the robot's endurance requirements. Currently, to meet energy demands, some researchers are using higher energy density batteries to power robots, such as metal-air batteries. In metal-air batteries, the negative electrode active material is an active metal (aluminum, zinc, etc.), and the positive electrode active material is oxygen. During discharge, oxygen at the positive electrode undergoes an oxygen reduction reaction under the action of a catalyst, gaining electrons, while the metal at the negative electrode loses electrons. Because the positive electrode active material of metal-air batteries can be derived from air, and the theoretical capacity depends on the metal negative electrode, metal-air batteries have a much higher theoretical energy density than ordinary batteries, providing longer-lasting energy support. However, metal-air batteries also have their limitations. Discharge byproducts tend to accumulate on the surface of the metal and electrolyte, causing capacity decay and battery damage. Furthermore, the non-enclosed system of air batteries can lead to electrolyte loss. These factors result in the actual energy density of metal-air batteries being far lower than their theoretical value.

[0003] Some researchers have proposed a strategy, as described in the journal article (ACS Energy Letter, 2020, 5(3), 758–765.) and patent WO2020167965), to use hydrogels to immobilize the electrolyte, separating the active metal at the negative electrode from the electrolyte. The surface can be replaced at any time during use, effectively preventing the accumulation of metal byproducts in the battery. Furthermore, the active material at the negative electrode is derived from the environment and readily available, further improving the battery's energy density. However, this strategy still requires a separate battery for power, still occupies additional space in the robot, and the oxygen reduction reaction at the air positive electrode requires water; the loss of water from the exposed gel will severely affect the battery's discharge. Researchers in a journal article (Nature, 2019, 571(7763), 51–57.) employed a multi-functional battery strategy, organically combining flow batteries with a robotic fish. The pressure of the fluid flowing within the flow battery controls the movement of the fish's fins, allowing the battery to directly participate in the motion. This strategy endows the battery with multiple functions, not only providing power but also assisting the robot in performing tasks. It allows the battery to undertake some of the robot's functions, alleviating the contradiction of the battery occupying a large volume in the device and squeezing the space of other equipment. This integration strategy is also reflected in structural batteries, where the battery is structurally designed as part of the robot to provide support or flexibility. However, the irregular shape of the battery can also affect its charge-discharge cycle process, resulting in poor cycle performance. Therefore, batteries that can meet the robot's endurance requirements while integrating other functions to assist the robot in performing tasks have become a challenge in the design of robot power supply systems. Summary of the Invention

[0004] The purpose of this invention is to provide a smart hydrogel skin that can obtain energy from the outside world and a method for preparing the same.

[0005] This invention provides a smart hydrogel skin capable of acquiring energy from the outside environment, comprising an air positive electrode, a sensing electrode, and a hydrogel. The hydrogel is formed into a thin film to simulate skin. The sensing electrode is embedded within the hydrogel film, encased both above and below by the hydrogel. The air positive electrode is attached to one side of the hydrogel, with no obstruction above it. The other side of the hydrogel can contact a material from the outside, acting as a negative electrode. In use, the air positive electrode is connected to the positive electrode of the desired power supply device, and the negative electrode material is connected to the negative electrode. When the hydrogel skin contacts the surface of the negative electrode material, a battery circuit is formed, enabling power supply. The adhesiveness of the hydrogel skin provides adhesion to the surface of the negative electrode material. The water retention and absorbency of the hydrogel skin prevent the evaporation of the electrolyte and allow for the absorption of moisture from the air to replenish the electrolyte. The sensing electrode generates an induced voltage through contact between the hydrogel skin and the surface of the contact object, enabling the hydrogel skin to recognize the contact object surface.

[0006] The hydrogel includes a hydrogel matrix and an electrolyte portion; the hydrogel, as a gel electrolyte, provides channels for conducting ions to the positive and negative electrodes; the hydrogel is a three-dimensional cross-linked polymer with polar or charged groups, which is flexible, can be bent, folded, compressed and stretched, and can adhere to the surface of negative electrode materials of various shapes in the outside world.

[0007] The aforementioned air positive electrode is a porous positive electrode with oxygen reduction catalysis function. Its modulus can be rigid or flexible. The air positive electrode is attached to one side of the hydrogel and does not come into contact with the negative electrode.

[0008] The aforementioned sensing electrode does not undergo an electrochemical reaction with oxygen in an electrolyte environment. The sensing electrode can be two or more electrode sheets, or an array of two or more electrode points; the leads of the two sensing electrodes are respectively connected to the positive and negative terminals of the voltage detection device for detecting the device voltage; the sensing electrodes do not contact each other. Further:

[0009] The air positive electrode consists of three parts: a catalyst, a current collector, and a binder. The catalyst includes platinum, gold, silver, cobalt, manganese, lanthanum, palladium, nickel, iron, vanadium-titanium, nitrogen-doped graphene, and nitrogen-doped carbon nanotubes, all possessing oxygen reduction catalysis capabilities. The current collector includes porous conductive materials such as carbon paper, carbon cloth, and metal foam. The binder includes polytetrafluoroethylene, polyvinylidene fluoride and its copolymers, carboxymethyl cellulose nanoparticles, polyimide, and polydimethylsiloxane polymer binders. The catalyst, current collector, and binder are combined and molded into a thin film.

[0010] The hydrogel comprises a hydrogel matrix and an electrolyte portion. The hydrogel matrix comprises a three-dimensional cross-linked polymer hydrogel material with polar or charged groups, including cross-linked materials such as polyacrylic acid, polystyrene sulfonic acid, polyvinyl sulfonic acid, polymethacrylic acid, polyacrylamide, polyvinylamine, polymethacryloylpropyltrimethylammonium chloride, polyacryloyloxyethyltrimethylammonium chloride, and polydiallyl dimethylammonium chloride. The electrolyte is an aqueous solution of an electrolyte, which includes an aqueous solution of any one or more of the following: alkali metal hydroxide, inorganic acid, organic acid, metal halide salt, and ionic liquid. The alkali metal hydroxide is one or more of lithium hydroxide, sodium hydroxide, and potassium hydroxide; the inorganic acid is one or more of hydrochloric acid, perchloric acid, sulfuric acid, nitric acid, and phosphoric acid; the organic acid is one or more of formic acid, acetic acid, and propionic acid; and the metal halide salt... It is one or a combination of more than one of sodium chloride, sodium bromide, sodium fluoride, sodium iodide, potassium bromide, potassium chloride, lithium chloride, potassium fluoride, potassium iodide, lithium chloride, lithium bromide, lithium fluoride, and lithium iodide, and the ionic liquid is one or a combination of more than one of 1-butyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-butyl-1-methylpyrrolidine trifluoromethanesulfonate, 1-ethyl-3-methylimidazolium tetrafluoroborate, and 1-butyl-3-methylimidazolium tetrafluoroborate.

[0011] The sensing electrode includes gold, platinum, silver, nickel, carbon, or conductive glass, or an inert conductive material containing a gold, platinum, silver, nickel, or carbon coating.

[0012] The negative electrode includes aluminum, zinc, iron, copper, magnesium, calcium, gallium, indium, tin, lead, chromium, vanadium or their alloys, or non-metallic arsenic-doped silicon, boron-doped silicon or phosphorus-doped silicon, originating from the outside world. The specific form includes planar, curved, and powdered materials. The specific external environment in which the material is located can be metal parts such as aluminum cans, aircraft skins, automobile shells, window frames, fences, and roof drainage boards.

[0013] The present invention provides a method for preparing intelligent hydrogel skin:

[0014] (1) Weigh a certain amount of monomer, then add appropriate amounts of deionized water, crosslinking agent and electrolyte and stir thoroughly;

[0015] (2) Add an appropriate amount of initiator to the stirred solution, stir evenly, place any number of robot parts or sensing electrodes in the mold, and then pour the stirred solution into the mold.

[0016] (3) After sealing the mold, wait for the gel to solidify;

[0017] (4) After curing, remove the hydrogel, determine the positive and negative electrode interfaces, and attach the air positive electrode to the positive electrode interface.

[0018] The aforementioned mold is a smooth mold that is easy to demold, and the materials include polypropylene, polyethylene, polytetrafluoroethylene, polystyrene, polyvinyl carbonate, polymethyl methacrylate, and glass.

[0019] In the preparation method, the monomer in step (1) is selected from the precursor molecules of the hydrogel matrix, such as acrylic acid, styrene sulfonic acid, methacryloxypropyltrimethylammonium chloride, etc. The amount of electrolyte added in step (1) can be any value between 1 and 2.5 times the molar amount of the monomer. The crosslinking agent can be a molecule with two or more polymerizable double bonds, including N,N-methylenebisacrylamide, trivinylbenzene, divinylbenzene, trivinylamine, etc., and the amount added can be any value between 0.1% and 1% molar amount of the monomer. The amount of deionized water added can be any value between 13.5 and 27 times the molar amount of the monomer. The initiator in step (2) can be potassium persulfate, sodium persulfate, ammonium persulfate, bis(2-chloroisopropyl)ammonium persulfate, bis(2-ethylhexyl)potassium persulfate, 2,2'-bis(tert-butylperoxide)propane aqueous solution free radical polymerization initiator, and the amount added can be any value between 0.03% and 3% molar amount of the monomer. The curing process in step (3) can be carried out in a temperature range of 10 degrees Celsius to 70 degrees Celsius.

[0020] The beneficial effects of the intelligent hydrogel skin of this invention are as follows: the hydrogel skin can obtain energy from any external material (aluminum, zinc, tin, iron, etc.) that can serve as a negative electrode to power robotic devices without the need for charging; the charge carried by the groups of the hydrogel in the hydrogel skin can generate an electrostatic shielding effect on discharge byproducts, preventing byproducts from penetrating into the gel and maintaining the stability of the internal chemical environment of the gel; moreover, the hydrophilic groups carried by the hydrogel in the hydrogel skin have good water retention and water absorption properties, which can effectively prevent the evaporation of electrolyte and absorb moisture from the air to replenish the electrolyte, solving the problem of capacity decay caused by water loss when the hydrogel is exposed to the outside world; the polar or charged groups carried in the hydrogel can provide adhesion to the surface of the negative electrode material, providing assistance for the robot to climb, walk, or adhere on inclined surfaces; the sensing electrode in the hydrogel skin can identify the voltage signal of the sensing electrode and combine it with the current signal when the hydrogel skin obtains energy on the contact surface to determine the unevenness and material condition of the contact surface, which can collect and identify more information than ordinary electronic skin. The above integrates three major functions—energy harvesting, adhesion, and intelligent recognition—into the hydrogel skin. This not only improves the battery life of robotic devices but also enables functions that traditional batteries cannot achieve. It greatly improves the space utilization efficiency of batteries in robotic devices and provides a solution for the energy system design of miniaturized and intelligent robots. Attached Figure Description

[0021] Figure 1-1 This is a side view schematic diagram of the structure of the hydrogel skin in Embodiment 4 of the present invention.

[0022] Figure 1-2 This is a top view schematic diagram of the structure of the hydrogel skin in Embodiment 4 of the present invention.

[0023] Figure 2-1 This is a discharge curve diagram of hydrogel skin on the surface of aluminum metal and its alloys in Embodiment 1 of the present invention.

[0024] Figure 2-2 This is a discharge curve diagram of the hydrogel skin in Embodiment 1 of the present invention on the surface of zinc, tin, lead and arsenic-doped silicon.

[0025] Figure 3 This is a graph showing the water retention and absorption capacity of the hydrogel skin under different humidity conditions in Embodiment 1 of the present invention.

[0026] Figure 4 This is a graph showing the adhesion force of the robot crawler on the aluminum metal surface in Embodiment 2 of the present invention.

[0027] Figure 5 This is a simulated walking data diagram of the robot crawler in Example 2 of the present invention.

[0028] Figure 6 This is the discharge curve of the hydrogel skin in Example 3 of the present invention under a 180-degree bending state.

[0029] Figure 7-1 This is a contact test diagram of hydrogel skin on a material surface that cannot be used as a negative electrode, as shown in Example 4 of this invention.

[0030] Figure 7-2 This is a contact test diagram of the hydrogel skin on the surface of a material that can be used as a negative electrode in Example 4 of the present invention.

[0031] Figure 8 This is a schematic diagram of the contact recognition test of hydrogel skin under complex surface conditions in Example 5 of the present invention.

[0032] The diagram is labeled as follows: 1 is the positive air electrode, 2 is the hydrogel, 3 is the sensing electrode, 4 is the aluminum metal surface, 5 is the schematic part of the robot's crawler, 6 is the aluminum metal surface, 7 is the protrusion on the aluminum metal surface, 8 is the plastic protrusion on the aluminum metal surface, 9 is the nickel metal surface, 10 is the highly oxidized aluminum oxide surface, 11 is the polypropylene plastic surface, 12 is the protrusion on the polypropylene plastic surface, and 13 is the open area. Detailed Implementation

[0033] Example 1

[0034] Take 2.96g of acrylic acid and add it to 10g of water. Then, while stirring, add 0.022g of N,N-methylenebisacrylamide, followed by 5.92g of potassium hydroxide, and stir until completely dissolved. Add 0.0035g of potassium persulfate and stir for another minute. Pour the resulting solution into a polytetrafluoroethylene mold and seal it. After waiting at room temperature for 2 hours, remove the gel and cover the hydrogel with an air positive electrode of equal area.

[0035] Electrochemical performance testing:

[0036] The hydrogel skin obtained by the above method was applied to aluminum (1099Al), aluminum alloys (6061Al, 1060Al, 3004Al), zinc, lead, and tin, and then subjected to a 2mA cm... -2 Discharge tests were conducted using a current density of [value missing]. The hydrogel skin obtained using the above method was then applied to an arsenic-doped silicon wafer and discharged using a 0.1 mA cm⁻¹ [value missing]. -2 Discharge tests were performed using the current density, and the resulting curves are shown below. Figure 2-1 and Figure 2-2 As shown. The results show that, Figure 2-1 In this study, hydrogel skin exhibited a high and stable discharge plateau (>1.3V) on aluminum and its various alloys. Figure 2-2 In the study, the hydrogel skin exhibited highly stable discharge plateaus on zinc, lead, tin, and silicon, with voltage plateaus of approximately 1.3V, 0.65V, 0.95V, and 1.1V, respectively. This demonstrates that the hydrogel skin can be compatible with several different types of metals and their alloys, allowing energy to be harvested from their surfaces.

[0037] Water retention and water absorption tests:

[0038] The hydrogel skin obtained using the above method was placed under 60% and 80% relative humidity, respectively, and its weight change was observed. Figure 3 As shown, the skin at 60% relative humidity remained almost unchanged in weight after 72 hours, demonstrating the skin's water retention at 60% relative humidity. At 80% relative humidity, the skin absorbed up to 36% of the gel's own weight in water, maintaining a relatively stable range after 36 hours. This test demonstrates the excellent water retention and absorption properties of hydrogel skin, not only preventing evaporation from within the skin but also absorbing water at higher humidity levels to replenish moisture, thus solving the water loss problem of non-closed systems.

[0039] Example 2

[0040] Take 2.96g of acrylic acid and add it to 10g of water. Then, while stirring, add 0.022g of N,N-methylenebisacrylamide and 5.92g of potassium hydroxide. After stirring for 20 minutes, add 0.0035g of potassium persulfate and stir for another minute. Pour the mixture into a polystyrene mold containing the 3D-printed robot crawler skeleton. Seal the mold and let it stand at room temperature for 2 hours. Then, remove the gel. At this point, the hydrogel skin tightly wraps around the robot crawler. Cover the gel with an air electrode of equal area.

[0041] Adhesion test:

[0042] like Figure 4 As shown in the figure below, the adhesive force exhibited by the hydrogel-skin-wrapped robotic claw when detaching from the aluminum metal surface at an angle perpendicular to it and when moving parallel to the metal surface are both 0.065 N / cm. -2 and 0.4 Ncm -2 The difference is about 6 times, indicating that hydrogel skin can easily detach from the surface in a direction perpendicular to the surface, and can also adhere well to the surface on a plane with an inclined angle due to lateral shear adhesion. Figure 4 As shown in the image above, the robotic claw, wrapped in hydrogel skin, remained almost constant in adhesion to aluminum after being repeatedly attached 100 times, with no loss of adhesion.

[0043] Simulated robot walking test:

[0044] Connect the negative wire of the 612 DC geared motor to the surface of the aluminum plate, and connect the positive wire to the positive air terminal of the hydrogel skin. Simulate the crawling behavior of a single crawling robot on a metal surface by controlling the contact and detachment of the robot's claw, which is wrapped in hydrogel skin, from the aluminum plate. Figure 5 As shown, the robotic claw wrapped in hydrogel skin can walk more than 10,000 steps on the surface of a metal plate for more than 10 hours, with a discharge voltage plateau of about 1.2V to 1.4V and an average current of about 8mA.

[0045] Example 3

[0046] Take 2.96g of acrylic acid and add it to 10g of water. Then, while stirring, add 0.022g of N,N-methylenebisacrylamide, followed by 5.92g of potassium hydroxide. After stirring for 20 minutes, add 0.0035g of potassium persulfate and stir for another minute. Pour the resulting solution into a 500-micrometer-deep polypropylene mold. Allow the gel to set at room temperature for 2 hours before removing it.

[0047] The tensile properties of the skin were tested, and the elongation at break of the gel was measured to be 884% on a universal testing machine. After covering the gel surface with a flexible air positive electrode, the hydrogel skin was attached to an aluminum plate in a 180-degree bending state for 2mA cm. -2 Discharge test, such as Figure 6 As shown, the discharge platform is stable at around 1.3V, indicating that the prepared hydrogel skin is soft and has good toughness and bending properties, making it suitable for integration on complex robot surfaces and for harvesting energy on complex metal surfaces.

[0048] Example 4

[0049] Take 2.96g of acrylic acid and add it to 10g of water. Then, while stirring, add 0.022g of N,N-methylenebisacrylamide and 5.92g of potassium hydroxide. After stirring for 20 minutes, add 0.0035g of potassium persulfate and stir for another minute. Next, arrange two gold-plated induction electrodes spaced a certain distance apart and suspend them in the mold. Then, pour the stirred solution into the polystyrene mold, seal the mold, and cure it at room temperature for 2 hours. Remove the cured gel, cover it with an air positive electrode, and then connect the positive and negative wires of the geared motor to the positive electrode of the hydrogel skin and the surface to be tested, respectively. Lead the induction electrode out of the hydrogel skin, and then connect the positive and negative terminals of the voltage detection device to the two induction electrodes, with the relative positions as shown. Figure 1-1 As shown and Figure 1-2 As shown.

[0050] Intelligent recognition test for hydrogel skin:

[0051] First, press the hydrogel skin onto the raised polypropylene material surface at each of the different sensing electrode locations, and repeat the process once. For example... Figure 7-1 As shown, when the sensing electrode connected to the positive terminal of the voltage detection device senses pressure, the voltage signal will drop suddenly until the pressure disappears, and then the signal will slowly rise back to the baseline. Conversely, when the sensing electrode connected to the negative terminal of the voltage detection device senses pressure, the voltage signal will jump suddenly until the pressure disappears, and then the signal will slowly fall back to the baseline. Figure 7-1 The two signals were repeated once, proving that the relative unevenness of a material surface that cannot be used as a negative electrode can be identified through the signal peak response.

[0052] The hydrogel skin is then brought into contact with the surface of the material (aluminum metal) that has protrusions at different locations of the sensing electrodes, serving as the negative electrode, and the operation is repeated once. For example... Figure 7-2As shown, when the hydrogel skin at the positive terminal of the voltage detection device contacts the aluminum metal, the voltage signal jumps and remains at a certain value until the hydrogel skin separates from the aluminum metal surface, at which point the signal returns to the baseline. Conversely, when the hydrogel skin at the negative terminal of the voltage detection device contacts the aluminum metal, the voltage signal drops and remains at a certain value until the hydrogel skin separates from the aluminum metal surface, at which point the signal returns to the baseline. Because the relative unevenness of the aluminum metal determines that a portion of the hydrogel will first contact the aluminum metal and generate an induced voltage signal, this allows the hydrogel skin to identify the relative unevenness of the surface of a material that can serve as a negative electrode.

[0053] Because the above phenomena are distinguishable, hydrogel skin does not have a current response on material surfaces that cannot be used as negative electrodes, and the voltage signal is opposite. Therefore, hydrogel skin can not only identify the unevenness of the contact surface, but also distinguish the material of the contact surface.

[0054] Example 5

[0055] Take 2.96g of acrylic acid and add it to 10g of water. Then, while stirring, add 0.022g of N,N-methylenebisacrylamide and 5.92g of potassium hydroxide. After stirring for 20 minutes, add 0.0035g of potassium persulfate and stir for another minute. Next, place two gold-plated sensing electrodes at a certain distance and at the same height, suspending them in the mold. Pour the stirred solution into a polystyrene mold, seal the mold, and cure at room temperature for 2 hours. These gold-plated sensing electrodes have a high modulus and can simultaneously serve as the basic framework of a robot crawler. They also have a non-insulated rigid connection to each other, ensuring that the relative positions of the electrodes and the electrodes and hydrogel are maintained when the basic framework (sensing electrodes) moves the gel to and from the surface. Remove the cured gel and place an air positive electrode on top. Connect the geared motor to the positive electrode of the hydrogel skin and the surface to be tested, respectively. Then, connect the positive and negative terminals of the voltage detection device to the two sensing electrodes, referred to as the positive and negative sensing electrodes, respectively.

[0056] Intelligent recognition test of hydrogel skin on complex surfaces:

[0057] like Figure 8As shown, the robotic claw schematic 5 has two "toes," each containing a sensing electrode. The positive and negative markings represent the positive and negative terminals of the connected voltage detection device. The robotic claw schematic 5 crawls along the surface shown on the right, which has multiple uneven areas and different materials (divided into materials that can be used as negative electrodes to obtain energy and materials that cannot be used as negative electrodes to obtain energy). After conducting simulated crawling tests at the locations indicated by the arrows in the figure, the results were obtained... Figure 8The two data graphs are a voltage curve and a current curve. Starting from the first arrow from the left, the gel corresponding to the hydrogel skin sensing electrode simultaneously contacts the aluminum metal surface 6. The voltage graph shows a broad signal with a relatively localized roughness but an overall flat surface, while the current graph shows current output. Moving to the second arrow from the left, because the gel area of ​​the raised hydrogel skin near the positive sensing electrode first contacts the protrusion 7 on the aluminum metal surface, there is a voltage jump in the voltage graph. Subsequently, as the crawler continues to fall, the gel area near the negative sensing electrode also contacts the aluminum metal surface 6. At this point, the gel areas corresponding to both sensing electrodes are in contact with the aluminum metal, causing the voltage to drop. Because the gel is always in contact with the aluminum metal, the current graph shows continuous current output. Moving to the third arrow from the left, the gel corresponding to the hydrogel skin sensing electrode simultaneously contacts the aluminum metal surface 6. The voltage graph shows a broad signal with a localized roughness but an overall flat surface, while the current graph shows current output. Moving to the fourth arrow from the left, because the gel area of ​​the raised hydrogel skin near the negative sensing electrode first contacts the plastic protrusion 8 on the aluminum metal surface, there will be a voltage jump in the voltage graph. Subsequently, the hydrogel skin near the positive sensing electrode contacts the aluminum metal surface 6, showing a superposition peak of the signals from the energy-harvesting surface and the energy-extracting surface. The signal maintains a certain value until the hydrogel skin leaves the surface. In the current graph, because the hydrogel skin's first contact is with the plastic protrusion 8 on the aluminum metal surface, there is no current output initially, but there is a continuous current output after contacting the aluminum metal surface 6. Moving to the fifth arrow from the left, the gel corresponding to the sensing electrode of the hydrogel skin simultaneously contacts the aluminum metal surface 6. The voltage graph shows a wide signal that is locally rugged but generally flat, and the current graph shows a current output. Moving to the sixth arrow from the left, the gel in the hydrogel skin near the positive sensing electrode contacts the aluminum metal surface 6, and the gel near the negative sensing electrode contacts the nickel metal surface 9. Since no energy can be obtained from the nickel metal surface 9, there will be a voltage jump in the voltage graph, which will remain at a certain value until the hydrogel skin leaves the surface. The seventh arrow from the left indicates that the hydrogel skin sensing electrode is in contact with the aluminum metal surface 6. The voltage graph shows a broad signal that is locally rugged but generally flat, while the current graph shows a current output. The eighth arrow from the left indicates that the gel in the hydrogel skin near the positive sensing electrode is in contact with the highly oxidized aluminum oxide surface 10, while the gel near the negative sensing electrode is in contact with the aluminum metal surface 6. Because the highly oxidized aluminum oxide surface 10 blocks the electrochemical reaction, the energy acquisition efficiency is limited. Therefore, the voltage graph shows a slowly decreasing peak, and the current graph shows a slowly rising current output, with the trend corresponding to the voltage signal in the voltage graph.From the ninth arrow on the left, the hydrogel skin's sensing electrode simultaneously contacts a polypropylene plastic surface that cannot be used as a negative electrode to obtain energy. The voltage graph shows a broad signal that is flatter than that of the aluminum metal surface 6, while the current graph shows no current output. From the tenth arrow on the left, the gel in the hydrogel skin near the positive sensing electrode contacts a protrusion 12 on the polypropylene plastic surface, showing a voltage drop peak. The drop stops until the hydrogel skin leaves the surface, and the voltage signal slowly rises back to near the baseline. Since no energy can be obtained from the surface, no output current is shown in the current graph. From the eleventh arrow on the left, the robot's crawler arrives at an open area 13. The hydrogel skin does not contact any surface material, and the voltage signal in the voltage graph remains relatively stable for a considerable period. There is also no current response in the current graph, indicating a state of "stepping into empty space."

[0058] In summary, when hydrogel skin comes into contact with a material surface that can serve as a negative electrode and a material surface that cannot serve as a negative electrode, the material distribution and approximate morphology of the surface contacted by the hydrogel skin can be determined based on the voltage signal of the sensing electrode and the output current signal of the hydrogel skin powering the robot. This proves that hydrogel skin can effectively and accurately identify complex contact surfaces.

Claims

1. A smart hydrogel skin, characterized in that, The device includes an air positive electrode, a sensing electrode, and a hydrogel. The hydrogel is formed into a thin film to simulate skin. The sensing electrode is embedded within the hydrogel film, encased both above and below by the hydrogel. The air positive electrode is attached to one side of the hydrogel, with no obstruction above it. The other side of the hydrogel can contact an external material serving as the negative electrode. In use, the air positive electrode is connected to the positive terminal of the power supply device, and the negative electrode material is connected to the negative terminal. When the hydrogel skin contacts the negative electrode material, the internal circuit is activated, forming a battery circuit to power the robot. The hydrogel skin is adhesive, providing adhesion to the surface of the negative electrode material. The sensing electrode generates an induced voltage through the contact between the hydrogel skin and the negative electrode material surface, enabling the hydrogel skin to recognize the surface of the contact object. The hydrogel includes a hydrogel matrix and an electrolyte portion; the hydrogel, as a gel electrolyte, provides channels for conducting ions to the positive and negative electrodes; the hydrogel is a polymer with a three-dimensional cross-linked network, which is flexible, can be bent, folded, compressed and stretched, and can adhere to the surface of negative electrode materials of various shapes in the outside world. The air cathode is a porous cathode with oxygen reduction catalysis function, and its modulus can be rigid or flexible. The sensing electrode does not undergo an electrochemical reaction with oxygen in the electrolyte environment; the sensing electrode is an array of two or more electrode sheets or two or more electrode points; the leads of the two sensing electrodes are respectively connected to the positive and negative terminals of the voltage detection device for detecting the device voltage.

2. The intelligent hydrogel skin according to claim 1, characterized in that, The air positive electrode consists of three parts: a catalyst, a current collector, and a binder. The catalyst is selected from platinum catalysts, gold catalysts, silver catalysts, cobalt catalysts, manganese catalysts, lanthanum catalysts, palladium catalysts, nickel catalysts, iron catalysts, vanadium-titanium catalysts, nitrogen-doped graphene, and nitrogen-doped carbon nanotubes. The current collector is selected from carbon paper, carbon cloth, and metal foam mesh. The binder is selected from polytetrafluoroethylene, polyvinylidene fluoride and its copolymers, carboxymethyl cellulose nanoparticles, polyimide, and polydimethylsiloxane. The catalyst, current collector, and binder are combined together to form the air positive electrode.

3. The intelligent hydrogel skin according to claim 1, characterized in that, The hydrogel comprises a hydrogel matrix and an electrolyte; the hydrogel matrix is ​​selected from polyacrylic acid, polystyrene sulfonic acid, polyvinyl sulfonic acid, polymethacrylic acid, polyacrylamide, polyvinylamine, polymethacryloylpropyltrimethylammonium chloride, polyacryloyloxyethyltrimethylammonium chloride, and polydiallyldimethylammonium chloride; the electrolyte is selected from any one or more combinations of alkali metal hydroxides, inorganic acids, organic acids, metal halide salts, and ionic liquids in an aqueous electrolyte solution; wherein the alkali metal hydroxide is one or more combinations of lithium hydroxide, sodium hydroxide, and potassium hydroxide, and the inorganic acid is hydrochloric acid, perchloric acid, sulfuric acid, or nitrate. One or more combinations of acids and phosphoric acids; one or more combinations of organic acids, formic acid, acetic acid, and propionic acid; one or more combinations of metal halide salts, sodium chloride, sodium bromide, sodium fluoride, sodium iodide, potassium bromide, potassium chloride, lithium chloride, potassium fluoride, potassium iodide, lithium bromide, lithium fluoride, and lithium iodide; and one or more combinations of ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-butyl-1-methylpyrrolidine trifluoromethanesulfonate, 1-ethyl-3-methylimidazolium tetrafluoroborate, and 1-butyl-3-methylimidazolium tetrafluoroborate.

4. The intelligent hydrogel skin according to claim 1, characterized in that, The sensing electrode is made of gold, platinum, silver, nickel, carbon, or conductive glass, or a conductive material containing a gold, platinum, silver, nickel, or carbon coating.

5. The intelligent hydrogel skin according to claim 1, characterized in that, The negative electrode is derived from external sources such as aluminum, zinc, iron, copper, magnesium, calcium, gallium, indium, tin, lead, chromium, vanadium or their alloys, arsenic-doped silicon, boron-doped silicon or phosphorus-doped silicon; the specific form includes planar and curved surfaces.

6. The intelligent hydrogel skin according to claim 1, characterized in that, The sensing electrodes also include components of the original robotic equipment.

7. A method for preparing intelligent hydrogel skin as described in any one of claims 1-6, characterized in that: (1) Weigh the monomer, add appropriate amounts of deionized water, crosslinking agent and electrolyte and stir thoroughly; (2) Add an appropriate amount of initiator to the stirred solution and stir evenly. Any number of induction electrodes or robot parts can be placed in the mold. Then pour the stirred solution into the mold with a certain depth. (3) After sealing the mold, wait for the gel to solidify; (4) After curing, remove the hydrogel, determine the positive and negative electrode interfaces, and attach the air positive electrode to the positive electrode interface.

8. The method for preparing intelligent hydrogel skin according to claim 7, characterized in that, The mold is a smooth mold that is easy to demold, and the material is selected from polypropylene, polyethylene, polytetrafluoroethylene, polystyrene, polyvinyl carbonate, polymethyl methacrylate, and glass.

9. The method for preparing intelligent hydrogel skin according to claim 7, characterized in that: The monomers mentioned in step (1) are selected from the precursor molecules of the hydrogel matrix; the amount of electrolyte added is any value between 1 and 2.5 times the molar amount of the monomer; the crosslinking agent is a molecule with two or more polymerizable double bonds, and the amount added is between 0.1% and 1% of the molar amount of the monomer; the amount of deionized water is between 13.5 and 27 times the molar amount of the monomer. The initiator in step (2) is potassium persulfate, sodium persulfate, ammonium persulfate, bis(2-chloroisopropyl)ammonium persulfate, bis(2-ethylhexyl)potassium persulfate, and 2,2'-bis(tert-butylperoxide)propane, and the amount added is between 0.03% and 3% of the monomer molar amount; The curing process in step (3) is carried out in a temperature range of 10 degrees Celsius to 70 degrees Celsius.

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