Lignin synergistically enhanced thermoelectric self-repairing hydrogel with high Seebeck coefficient as well as preparation method and application of lignin synergistically enhanced thermoelectric self-repairing hydrogel

Abstract

The invention provides a lignin synergistically enhanced thermoelectric self-repairing hydrogel with a high Seebeck coefficient as well as a preparation method and application of the lignin synergistically enhanced thermoelectric self-repairing hydrogel. The preparation method comprises the following steps: modifying alkali lignin through polyethylene glycol to obtain lignin-polyethylene glycol, then adding the lignin-polyethylene glycol into a polyethylene glycol aqueous solution containing acrylate, acrylamide monomers, metal salt and an inorganic micromolecule thermoelectric material, stirring and uniformly mixing, and finally adding an initiator, stirring and polymerizing to obtain the thermoelectric material. The lignin synergistically enhanced thermoelectric self-repairing hydrogel with the high Seebeck coefficient is successfully prepared. The thermoelectric self-repairing hydrogel has excellent mechanical performance, self-repairing performance and thermoelectric conversion efficiency. According to the thermoelectric self-repairing hydrogel, anion migration is limited through carboxyl, cation conduction is enhanced through a polyethylene glycol chain segment, the anion and cation migration rate difference is bidirectionally increased, then the Seebeck coefficient is increased, and the Seebeck coefficient obtained through fitting calculation reaches 21.8 mV / K; the problems that an existing thermoelectric self-repairing hydrogel is low in seebeck coefficient and low in thermoelectric conversion efficiency are solved.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric conversion technology. More specifically, it relates to a lignin-synergistically reinforced thermoelectric self-healing hydrogel with a high Seebeck coefficient, its preparation method, and its application. Background Technology

[0002] With the increasing demand for intelligent, portable, and comfortable wearable electronic devices, the application potential of flexible self-powered devices is constantly expanding. In self-powered devices, traditional thermoelectric materials (such as metal alloy conductors, semiconductors, and conductive polymers) typically possess high conductivity, but also suffer from low Seebeck coefficients and high costs. Novel ionic thermoelectric hydrogels, by introducing cross-linked networks, form a three-dimensional network structure within the matrix. This not only provides ion transport channels within the gel, solving the problem of liquid electrolyte leakage, but also optimizes the device's mechanical properties, ionic thermoelectric properties, and environmental adaptability by controlling the hydrogel composition to meet wearable requirements. These hydrogel-based self-powered materials can be attached to the surface of the human body or devices. When a temperature difference exists across the hydrogel, ions within the material migrate from the hot side to the cold side. Due to differences in ion size, activation energy, and Coulomb force, the migration rates of anions and cations are typically different, leading to an unbalanced ion concentration distribution. This, in turn, creates a potential difference between the hot and cold electrodes, thereby converting low-grade heat energy emitted from the surface of the human body or device into electrical energy.

[0003] In practical applications, traditional thermoelectric hydrogels often suffer from cracks or water loss due to long-term use, leading to a decline in properties such as thermoelectric conversion efficiency and electrical conductivity. Self-healing hydrogels, on the other hand, can self-heal damage through dynamic cross-linking and hydrogen bonding systems, thereby reducing performance loss. However, existing thermoelectric self-healing hydrogels still suffer from low Seebeck coefficients and relatively low thermoelectric conversion efficiency.

[0004] Therefore, it is particularly important to study a thermoelectric self-healing hydrogel with a high Seebeck coefficient. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of low Seebeck coefficient and low thermoelectric conversion efficiency of existing thermoelectric self-healing hydrogels, and to provide a method for preparing thermoelectric self-healing hydrogels.

[0006] Another object of the present invention is to provide a thermoelectric self-healing hydrogel.

[0007] Another object of the present invention is to provide a thermoelectric conversion device.

[0008] Another object of the present invention is to provide the application of the above-mentioned thermoelectric self-healing hydrogel or the above-mentioned thermoelectric conversion device in the fields of wearable self-powered devices, industrial waste heat and human body waste heat recovery, and temperature sensing and environmental monitoring.

[0009] To achieve the above objectives, the present invention provides the following technical solution: This invention protects a method for preparing a thermoelectric self-healing hydrogel, comprising the following steps: S1. Alkali lignin is modified by grafting polyethylene glycol to obtain lignin-polyethylene glycol; S2. Add lignin-polyethylene glycol, acrylate, acrylamide monomers, and metal salts to a polyethylene glycol aqueous solution containing inorganic small molecule thermoelectric materials and stir until homogeneous to obtain the reaction precursor. S3. Add an initiator to the reaction precursor, stir and polymerize to obtain the above thermoelectric self-healing hydrogel; The number-average molecular weight of the polyethylene glycol mentioned in step S1 is 600~1500; The number-average molecular weight of the polyethylene glycol mentioned in step S2 is below 400; The inorganic small molecule thermoelectric material is one or more of lithium chloride, sodium chloride, and potassium chloride.

[0010] This invention first modifies alkali lignin with polyethylene glycol to obtain lignin-polyethylene glycol. Then, it is added to an aqueous polyethylene glycol solution containing inorganic small-molecule thermoelectric materials, along with acrylates, acrylamide monomers, and metal salts, and stirred until homogeneous. Finally, an initiator is added and polymerization is stirred, successfully preparing a thermoelectric self-healing hydrogel. During the thermoelectric hydrogel reaction, the metal salts and lignin form a redox catalytic system, promoting the rapid polymerization of acrylates and acrylamide monomers. Simultaneously, metal ions complex with the hydroxyl groups of lignin or the carboxyl groups of acrylic acid, forming non-covalent bonds, endowing the thermoelectric hydrogel with excellent mechanical and self-healing properties. Furthermore, the carboxyl groups in polyacrylic acid effectively immobilize anions within the hydrogel, while the polyethylene glycol segments on the lignin accelerate the migration rate of cations within the hydrogel. By restricting anion migration and accelerating cation transfer, the difference in migration rates between anions and cations is widened, thereby increasing the output voltage of the hydrogel and resulting in a higher Seebeck coefficient. Additionally, using an aqueous polyethylene glycol solution as the reaction solvent further improves the long-term stability of the hydrogel.

[0011] The method for obtaining lignin-polyethylene glycol by modifying alkali lignin with polyethylene glycol can refer to existing technology. For example, alkali lignin and polyethylene glycol can be stirred and mixed, concentrated sulfuric acid catalyst can be added to react, the reaction product can be dropped into excess deionized water to obtain flocculent precipitate, washed and dried to obtain lignin-polyethylene glycol; preferably, the grafting rate of the lignin-polyethylene glycol is above 40%.

[0012] Preferably, the inorganic small molecule thermoelectric material is lithium chloride.

[0013] Preferably, the concentration of the inorganic small molecule thermoelectric material is 0.1~3 mol / L.

[0014] Preferably, the number-average molecular weight of the polyethylene glycol in step S2 is 200-400.

[0015] Preferably, in the polyethylene glycol aqueous solution, the mixing ratio of polyethylene glycol to water is V. 聚乙二醇 V 水 =1:1~5.

[0016] Preferably, the acrylate is one or more of lithium acrylate, sodium acrylate, and potassium acrylate.

[0017] More preferably, the acrylate is lithium acrylate.

[0018] Preferably, the acrylamide monomer is one or more of acrylamide, methacrylamide, and ethylacrylamide.

[0019] Preferably, the mass ratio of lignin-polyethylene glycol to acrylate to acrylamide monomer is 0.025:0.5~2:0.5~2.

[0020] Preferably, the metal salt is one or more of stannous chloride, ferric chloride, calcium chloride, barium chloride, aluminum chloride, nickel chloride, copper chloride, and silver chloride.

[0021] More preferably, the metal salt is stannous chloride.

[0022] Preferably, the stirring speed in step S2 is 600~900 rpm.

[0023] Preferably, the stirring temperature in step S2 is 20~25 ℃.

[0024] Preferably, the initiator is ammonium persulfate and / or potassium persulfate.

[0025] Preferably, the stirring speed in step S3 is 1200~1500 rpm.

[0026] Preferably, the stirring temperature in step S3 is 20~25 ℃.

[0027] This invention protects the thermoelectric self-healing hydrogel prepared by the above preparation method.

[0028] This invention protects a thermoelectric conversion device, which includes the aforementioned thermoelectric self-healing hydrogel and an electrode; the thermoelectric self-healing hydrogel is connected to the electrode as a thermoelectric conversion material.

[0029] This invention protects a method for preparing the above-mentioned thermoelectric conversion device, comprising the following steps: S1. Alkali lignin is modified by grafting polyethylene glycol to obtain lignin-polyethylene glycol; S2. Add lignin-polyethylene glycol, acrylate, acrylamide monomers, and metal salts to a polyethylene glycol aqueous solution containing inorganic small molecule thermoelectric materials and stir until homogeneous to obtain the reaction precursor. S3. Add an initiator to the reaction precursor and stir, then pour it into a mold containing electrodes for polymerization to obtain the above-mentioned thermoelectric conversion device; The number-average molecular weight of the polyethylene glycol mentioned in step S1 is 600~1500; The number-average molecular weight of the polyethylene glycol mentioned in step S2 is below 400; The inorganic small molecule thermoelectric material is one or more of lithium chloride, sodium chloride, and potassium chloride.

[0030] Preferably, the electrode is carbon cloth.

[0031] This invention protects the application of the above-mentioned thermoelectric self-healing hydrogel or thermoelectric conversion device in the fields of wearable self-powered devices, industrial waste heat and human body waste heat recovery, and temperature sensing and environmental monitoring.

[0032] Compared with the prior art, the beneficial effects of the present invention include: This invention first modifies alkali lignin to obtain lignin-polyethylene glycol (PEG). Then, PEG, along with acrylates, acrylamide monomers, and metal salts, is added to an aqueous PEG solution containing inorganic small-molecule thermoelectric materials and stirred until homogeneous. Finally, an initiator is added and polymerization is stirred, successfully preparing a thermoelectric self-healing hydrogel. During the thermoelectric hydrogel reaction, the metal salts and lignin form a redox catalytic system, promoting the rapid polymerization of acrylates and acrylamide monomers. Simultaneously, metal ions complex with the hydroxyl groups of lignin or the carboxyl groups of acrylic acid, forming non-covalent bonds, endowing the thermoelectric hydrogel with excellent mechanical and self-healing properties. Furthermore, the carboxyl groups in polyacrylic acid effectively immobilize anions within the hydrogel, while the PEG segments on the lignin accelerate the migration rate of cations within the hydrogel. By restricting anion migration and promoting cation transfer, the migration rate difference between anions and cations is widened, thereby increasing the output voltage of the hydrogel and resulting in a higher Seebeck coefficient. Additionally, using an aqueous PEG solution improves the long-term stability of the hydrogel. Through the combined action of these components, the hydrogel provided by this invention possesses excellent mechanical properties, self-healing properties, and thermoelectric conversion efficiency. Specifically, its tensile strength can reach 42 kPa, its elongation at break can reach 1802%, its self-healing efficiency after 2 hours can reach 88%, and its Seebeck coefficient, calculated through fitting, can reach 21.8 mV / K. This effectively solves the problems of low Seebeck coefficient and low thermoelectric conversion efficiency in existing thermoelectric self-healing hydrogels. Attached Figure Description

[0033] Figure 1 Fourier transform infrared spectra of alkali lignin, PEG-600, and lignin-polyethylene glycol obtained in Example 1 of this invention.

[0034] Figure 2 This is a tensile stress-strain diagram of the hydrogel provided in Embodiment 1 of the present invention.

[0035] Figure 3 The diagram shows the water retention performance of the hydrogel provided in Embodiment 1 of the present invention.

[0036] Figure 4 The image shows the self-healing effect of the hydrogel provided in Embodiment 1 of the present invention.

[0037] Figure 5 The tensile stress-strain diagram of the hydrogel after self-healing provided in Embodiment 1 of the present invention.

[0038] Figure 6 The image shows the electrochemical performance of the hydrogel after self-healing provided in Example 1 of this invention.

[0039] Figure 7 The diagram shows the saturated open-circuit voltage of the hydrogel provided in Embodiment 1 of the present invention under different temperature differences.

[0040] Figure 8 The Seebeck coefficient fitting diagram is shown for the hydrogel provided in Embodiment 1 of the present invention.

[0041] Figure 9 This is a schematic diagram of the thermoelectric conversion device provided in Embodiment 1 of the present invention.

[0042] Figure 10 This is a charge / discharge diagram of the thermoelectric conversion device provided in Embodiment 1 of the present invention.

[0043] Figure 11 This is a diagram illustrating the working effect of the thermoelectric conversion device provided in Embodiment 1 of the present invention.

[0044] Figure 12 The hydrogel impedance diagrams provided in Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0045] The present invention will be further described below with reference to embodiments and comparative examples. These embodiments are merely typical descriptions of the present invention, but the present invention is not limited thereto. Unless otherwise specified, the test methods used in the following embodiments and comparative examples are conventional methods, and the raw materials and reagents used are commercially available from conventional commercial sources.

[0046] Example 1 This embodiment provides a method for preparing a thermoelectric self-healing hydrogel, specifically including the following steps: S1. Weigh out 1 g of alkali lignin (AL) and 5 g of polyethylene glycol (PEG-600, M). n =600) was placed in a round-bottom flask and stirred until well mixed. The temperature was raised to 160 ℃ and 200 μL of concentrated sulfuric acid catalyst was added. The reaction was carried out for 4 hours. After the reaction was complete, the reaction product was dropped into excess deionized water to form a flocculent precipitate. After centrifugation, the precipitate was washed with deionized water. After washing 5 times, it was placed in a vacuum freeze dryer at -50 ℃ and dried for 48 h to obtain lignin-polyethylene glycol (LPEG). S2. Measure 1 mL of polyethylene glycol (PEG-200, M) n =200) and 5 mL of water were mixed evenly and 0.508 g of lithium chloride was added to prepare a 2 mol / L polyethylene glycol aqueous solution of lithium chloride. Then, 0.025 g of LPEG, 0.02 g of stannous chloride, 0.949 g of lithium acrylate and 0.865 g of acrylamide were added and stirred evenly to obtain the reaction precursor. S3. Add 0.012 g of ammonium persulfate to the reaction precursor and stir quickly until homogeneous. Pour the mixture into a cylindrical mold with carbon cloth as the electrode and polymerize in situ to obtain a thermoelectric conversion device containing thermoelectric self-healing hydrogel.

[0047] Fourier transform infrared characterization was performed on alkali lignin, polyethylene glycol-600, and the lignin-polyethylene glycol obtained in this example. The results are as follows: Figure 1 As shown.

[0048] Depend on Figure 1 It can be known that 2900 cm -1 and 1100 cm -1 The peak at 3400 cm⁻¹ corresponds to the characteristic absorption peak of the methylene and ether bonds in polyethylene glycol. -1 The peak at 3400 cm⁻¹ corresponds to the characteristic absorption peak of the hydroxyl groups in alkali lignin. The peak at 3400 cm⁻¹ corresponds to the characteristic absorption peak of lignin-polyethylene glycol. -1 The absorption peak weakens at 2900 cm⁻¹ and at 2900 cm⁻¹ -1 1100 cm -1 The increased absorption peak intensity at the point indicates that alkali lignin was successfully grafted onto polyethylene glycol.

[0049] Tensile properties were tested on the thermoelectric self-healing hydrogel obtained in this embodiment: Tensile tests were performed on the hydrogel at room temperature using a computer-controlled universal testing machine equipped with a 100 N load cell. The tensile strain of the hydrogel was determined by uniaxial tensile testing. The hydrogel was cut into rectangles approximately 2 mm thick, 16 mm long, and 4 mm wide, and stretched at a tensile speed of 50 mm / min. Four equilibrium samples were tested for each group of samples. The results are as follows: Figure 2 As shown.

[0050] Depend on Figure 2 It can be seen that the hydrogel provided in this embodiment has a tensile strength of 42 kPa and an elongation at break of 1820%. This indicates that the hydrogel provided in this embodiment has good tensile properties.

[0051] The water retention performance of the thermoelectric self-healing hydrogel obtained in this embodiment was tested: The hydrogel was placed in a constant temperature and humidity chamber, with the temperature set at 25 ℃ and the humidity at 65%. The original weight (W0) and the weight after water loss (W) of the hydrogel were measured. t Water retention rate = W t / W0, the result is as follows Figure 3 As shown.

[0052] Depend on Figure 3 As can be seen, the hydrogel provided in this embodiment still retains 77% of its water content after 7 days. This indicates that the hydrogel has good water retention properties, meets the requirements for long-term use, and has long-term stability.

[0053] The self-healing performance of the thermoelectric self-healing hydrogel obtained in this embodiment was tested: 1. Self-healing effect test: The hydrogel was cut, and the hydrogels were spliced ​​together along the cut without applying additional stress and left to stand for 1 hour. The recovery of the cut seam was observed, and the results were as follows: Figure 4 As shown.

[0054] Depend on Figure 4 It can be seen that the hydrogel provided in this embodiment undergoes self-healing after standing, and the self-healed hydrogel can withstand tension without breaking. This indicates that the hydrogel provided in this embodiment has excellent self-healing ability.

[0055] 2. Self-healing tensile property test: The hydrogel was cut, and the hydrogels were spliced ​​together along the cut without applying additional stress. The sections were then allowed to stand for 30 min, 1 h, and 2 h respectively. The tensile properties of the self-healing hydrogel were then tested. Results... Figure 5 As shown. The self-healing performance is calculated using the following formula:

[0056] Depend on Figure 5It can be seen that the tensile properties of the hydrogel after self-healing gradually increase with the increase of self-healing time. When the self-healing time is 30 minutes, the self-healing performance is 31%; when the self-healing time is 1 hour, the self-healing performance is 57%; and when the self-healing time is 2 hours, the self-healing performance reaches 88%. This indicates that the hydrogel provided in this embodiment has excellent self-healing ability.

[0057] 3. Resistance Change Test: The hydrogel is placed in a resistance change test device, and its resistance change is measured by repeatedly cutting the hydrogel. The results are as follows: Figure 6 As shown.

[0058] Depend on Figure 6 It can be seen that the resistance of the hydrogel did not change significantly after 8 cut-off-self-healing cycles. This indicates that the hydrogel provided in this embodiment has excellent self-healing ability.

[0059] Thermal effect tests were performed on the thermoelectric self-healing hydrogel obtained in this embodiment: The thermal effect was measured on an electrochemical workstation and an integrated instrument with a temperature controller. A temperature gradient was set, and thermal charging was performed. The changes in thermal voltage were recorded using the electrochemical workstation until the thermal voltage reached equilibrium. The open-circuit voltage at this point was then recorded. The results are as follows: Figure 7 As shown; after measuring the saturation voltage under different temperature gradients, the ionic Seebeck coefficient was obtained by the formula Si=ΔV / ΔT and through fitting calculation, and the results are as follows. Figure 8 As shown.

[0060] Depend on Figure 7 It can be seen that the hydrogel provided in this embodiment has excellent thermoelectric properties, specifically, the saturated open-circuit voltage is 371 mV at a temperature difference of 5 K, 431 mV at a temperature difference of 10 K, 594 mV at a temperature difference of 15 K, and 681 mV at a temperature difference of 20 K. Figure 8 As can be seen, the Seebeck coefficient obtained by fitting calculation is 21.8 mV / K, indicating that the hydrogel provided in this embodiment has excellent thermoelectric properties.

[0061] Performance characterization of thermoelectric conversion devices Six thermoelectric hydrogels are connected in series and placed on a temperature control platform to form a thermoelectric conversion device, such as... Figure 9 As shown in the figure. The temperature difference between the two ends of the hydrogel was set to 20 ℃ (25 ℃-45 ℃), and the voltage change was recorded using an electrochemical workstation. The results are as follows. Figure 10 As shown in the image. After the voltage stabilizes, connect the LED light bulb and observe its operation. The results are as follows. Figure 11 As shown.

[0062] Depend on Figure 10It can be seen that when connected in series with an LED bulb, when the thermoelectric conversion device generates a thermal voltage greater than 1.5 V, it can provide a stable current to the LED bulb, causing the LED bulb to light up. However, due to the resistance of the LED bulb, some voltage will be diverted, causing the thermal voltage of the thermoelectric conversion device to decrease.

[0063] Example 2 This embodiment provides a method for preparing a thermoelectric self-healing hydrogel, which differs from Example 1 only in the concentration of the polyethylene glycol aqueous solution of lithium chloride in step S2, specifically 1 mol / L. The Seebeck coefficient obtained by fitting calculation is similar to that of Example 1.

[0064] Example 3 This embodiment provides a method for preparing a thermoelectric self-healing hydrogel, which differs from Example 1 only in the concentration of the polyethylene glycol aqueous solution of lithium chloride in step S2, specifically 3 mol / L. The Seebeck coefficient obtained by fitting calculation is similar to that of Example 1.

[0065] Example 4 This embodiment provides a method for preparing a thermoelectric self-healing hydrogel. The only difference from Example 1 is the inorganic small molecule thermoelectric material in step S2, specifically replacing lithium chloride with sodium chloride. The Seebeck coefficient obtained by fitting calculation is similar to that of Example 1.

[0066] Example 5 This embodiment provides a method for preparing a thermoelectric self-healing hydrogel, which differs from Example 1 only in the metal salt used in step S2, specifically replacing stannous chloride with calcium chloride. The Seebeck coefficient obtained through fitting calculation is similar to that of Example 1.

[0067] Comparative Example 1 This comparative example provides a method for preparing a thermoelectric self-healing hydrogel, specifically including the following steps: S1. Measure 1 mL of polyethylene glycol (PEG-200, M) n =200) and 2 mL of water were mixed evenly and 0.254 g of lithium chloride was added to prepare a 2 mol / L polyethylene glycol aqueous solution of lithium chloride. Then, 0.025 g of alkali lignin, 0.02 g of stannous chloride, 0.949 g of lithium acrylate and 0.865 g of acrylamide were added and stirred evenly to obtain the reaction precursor. S2. Add 0.012 g of ammonium persulfate to the reaction precursor and stir rapidly until homogeneous. Pour the mixture into a cylindrical mold with carbon cloth as the electrode and polymerize in situ to obtain a thermoelectric conversion device containing thermoelectric self-healing hydrogel.

[0068] Comparative Example 2 This comparative example provides a method for preparing a thermoelectric self-healing hydrogel. The only difference from Example 1 is the number-average molecular weight of polyethylene glycol in step S1, which is 2000.

[0069] Comparative Example 3 This comparative example provides a method for preparing a thermoelectric self-healing hydrogel. The only difference from Example 1 is the number-average molecular weight of polyethylene glycol in step S1, which is 400.

[0070] Comparative Example 4 This comparative example provides a method for preparing a thermoelectric self-healing hydrogel. The only difference from Example 1 is that the number-average molecular weight of polyethylene glycol in step S2 is different, specifically 1000.

[0071] Comparative Example 5 This comparative example provides a method for preparing a thermoelectric self-healing hydrogel. The only difference from Example 1 is the solvent for lithium chloride in step S2. Specifically, the polyethylene glycol aqueous solution is replaced with a glycerol aqueous solution, wherein the mixing ratio of glycerol and water is as follows: V 甘油 V 水 =1:2.

[0072] Comparative Example 6 This comparative example provides a method for preparing a thermoelectric self-healing hydrogel, which differs from Example 1 only in that lithium chloride is not added in step S2.

[0073] The results of preparing hydrogels in Examples 1-5 and Comparative Examples 1-6 are shown in Table 1 below.

[0074] Table 1. Results of hydrogel preparation in Examples 1-5 and Comparative Examples 1-6

[0075] Hydrogel thermoelectric performance testing (1) Thermal effect test: The thermal effect was measured on an electrochemical workstation and an integrated instrument with a temperature controller. A temperature gradient was set, thermal charging was performed, and the changes in thermal voltage were recorded using the electrochemical workstation until the thermal voltage reached equilibrium, at which point the open-circuit voltage was recorded.

[0076] Under a temperature gradient of 20 K, the saturation open-circuit voltage of the thermoelectric self-healing hydrogels prepared in Examples 1-3 and Comparative Examples 1, 3, and 6 were tested respectively, and the results are shown in Table 2.

[0077] (2) Conductivity test: The conductivity of the hydrogel was determined by electrochemical impedance spectroscopy (EIS). Using an electrochemical workstation, the potential of the electrochemical system was controlled. The electrode system was subjected to voltage signal perturbations at different frequencies, generating corresponding response signals. The test potential was set to the stable thermal voltage value of the hydrogel, and the scanning frequency range was 0.1–100,000 Hz. The conductivity was calculated using the formula σ = S / (R·A), where σ is the conductivity, R is the resistance, S is the thickness of the sample between the two electrodes, and A is the cross-sectional area of ​​the hydrogel.

[0078] The conductivity of the thermoelectric self-healing hydrogels prepared in Examples 1-3 and Comparative Examples 1, 3, and 6 was tested respectively, and the results are shown in Table 2 below.

[0079] Table 2. Test results of saturation open-circuit voltage and conductivity of the thermoelectric self-healing hydrogels prepared in Examples 1-3 and Comparative Examples 1, 3, and 6.

[0080] A comparison of Example 1 and Comparative Example 1 shows that the saturated open-circuit voltage of the hydrogel prepared by unmodified lignin at a temperature difference of 20 K is 376 mV, while the saturated open-circuit voltage of the hydrogel prepared by LPEG is significantly improved, reaching 681 mV. This indicates that the continuous ether bonds on polyethylene glycol help to synergistically facilitate the rapid directional transport of lithium ions by lignin, thereby improving the thermoelectric properties of the hydrogel by increasing the migration rate difference between lithium ions and chloride ions.

[0081] A comparison of Examples 1-3 and Comparative Example 6 shows that when lithium chloride is not added as a thermoelectric material, the hydrogel exhibits certain thermoelectric properties even without the need for additional thermoelectric materials due to the presence of lithium acrylate in its framework. When lithium chloride is added as a thermoelectric material, the saturation open-circuit voltage of the hydrogel increases with increasing lithium chloride concentration. At a lithium chloride concentration of 2 mol / L, the conductivity is 2.77 S / m. With increasing lithium chloride concentration, the conductivity initially increases and then decreases. This is because excessively high electrolyte concentration leads to the formation of ion pairs, reducing the concentration of free ions capable of conducting electricity, thus decreasing the conductivity.

[0082] (3) Impedance test: The conductivity of the hydrogel was determined by electrochemical impedance spectroscopy (EIS). Using an electrochemical workstation, the potential of the electrochemical system was controlled, and the electrode system was subjected to voltage signal perturbations at different frequencies to generate corresponding response signals. The test potential was set to the stable thermal voltage value of the hydrogel, and the scanning frequency range was 0.1-100000 Hz. The impedance effects of Example 1 and Comparative Example 1 were compared. Figure 12As shown, compared with hydrogels prepared from unmodified lignin, hydrogels prepared from LPEG have lower impedance. This is because LPEG-prepared hydrogels contain polyethylene glycol segments, which can act as lithium-ion transport channels, significantly reducing the impedance of the hydrogel and thus improving its conductivity.

[0083] (4) Instantaneous power test: Using the linear voltammetry method, a linearly varying scanning potential was applied to the electrodes. The initial test potential was set to the stable thermal voltage value of the hydrogel, and the ending potential was 0 V. The scan rate was 100 mV / s. The instantaneous output power was obtained by multiplying the voltage and current. The current density and power density of the thermoelectric self-healing hydrogels prepared in Examples 1-3 and Comparative Example 6 were tested, and the results are shown in Table 3 below.

[0084] Table 3. Test results of current density and power density of the thermoelectric self-healing hydrogels prepared in Examples 1-3 and Comparative Example 6.

[0085] As shown in Table 3, the current density and power density of the hydrogel increase with increasing lithium chloride concentration. When the lithium chloride concentration is 3 mol / L, the current density and power density of the hydrogel reach 2.35 A / m². 2 and 350mW / m 2 .

[0086] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a thermoelectric self-healing hydrogel, characterized in that, Includes the following steps: S1. Alkali lignin is modified by grafting polyethylene glycol to obtain lignin-polyethylene glycol; S2. Add lignin-polyethylene glycol, acrylate, acrylamide monomers, and metal salts to a polyethylene glycol aqueous solution containing inorganic small molecule thermoelectric materials and stir until homogeneous to obtain the reaction precursor. S3. Add an initiator to the reaction precursor, stir and polymerize to obtain the thermoelectric self-healing hydrogel; The number-average molecular weight of the polyethylene glycol mentioned in step S1 is 600~1500; The number-average molecular weight of the polyethylene glycol mentioned in step S2 is below 400; The inorganic small molecule thermoelectric material is one or more of lithium chloride, sodium chloride, and potassium chloride.

2. The preparation method according to claim 1, characterized in that, The concentration of the inorganic small molecule thermoelectric material in the polyethylene glycol aqueous solution is 0.1~3 mol / L.

3. The preparation method according to claim 1, characterized in that, The mass ratio of lignin-polyethylene glycol to acrylate to acrylamide monomer is 0.025:0.5~2:0.5~2.

4. The preparation method according to claim 1, characterized in that, The acrylate is one or more of lithium acrylate, sodium acrylate, or potassium acrylate.

5. The preparation method according to claim 1, characterized in that, The acrylamide monomer is one or more of acrylamide, methacrylamide, or ethylacrylamide.

6. The preparation method according to claim 1, characterized in that, The metal salt is one or more of stannous chloride, ferric chloride, calcium chloride, barium chloride, aluminum chloride, nickel chloride, copper chloride, or silver chloride.

7. The thermoelectric self-healing hydrogel prepared by any of the preparation methods described in claims 1 to 6.

8. A thermoelectric conversion device, characterized in that, The thermoelectric conversion device includes the thermoelectric self-healing hydrogel of claim 7, and electrodes attached to its surface.

9. The method for preparing the thermoelectric conversion device according to claim 8, characterized in that, Includes the following steps: S1. Alkali lignin is modified by grafting polyethylene glycol to obtain lignin-polyethylene glycol; S2. Add lignin-polyethylene glycol, acrylate, acrylamide monomers, and metal salts to a polyethylene glycol aqueous solution containing inorganic small molecule thermoelectric materials and stir until homogeneous to obtain the reaction precursor. S3. Add an initiator to the reaction precursor and stir, then pour it into a mold containing electrodes for polymerization to obtain the thermoelectric conversion device; The number-average molecular weight of the polyethylene glycol mentioned in step S1 is 600~1500; The number-average molecular weight of the polyethylene glycol mentioned in step S2 is below 400; The inorganic small molecule thermoelectric material is one or more of lithium chloride, sodium chloride, and potassium chloride.

10. The application of the thermoelectric self-healing hydrogel of claim 7 or the thermoelectric conversion device of claim 8 in the fields of wearable self-powered devices, industrial waste heat and human body waste heat recovery, and temperature sensing and environmental monitoring.

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