An ionothermal electrochemical thin film, a preparation method thereof and an ionothermal electrochemical power generation device

Abstract

The application provides an ionic thermoelectric film, a preparation method thereof and an ionic thermoelectric power generation device, and belongs to the technical field of thermoelectric materials. The material of the ionic thermoelectric film is graphene oxide nanosheet or vermiculite nanosheet. The height of the ion transmission channel of the ionic thermoelectric film is sub-nanometer, so that the ionic thermoelectric film has nanometer ionic capillary condensation effect, and the thermoelectric potential and output power density of the ionic thermoelectric power generation film can be greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric materials technology, specifically relating to an ion thermoelectric thin film, its preparation method, and an ion thermoelectric power generation device. Background Technology

[0002] Existing ion thermoelectric (i-TE) power generation devices mainly rely on organic ion solutions or inorganic solutions with added organic reagents to generate voltage by driving ion diffusion through the establishment of a temperature gradient.

[0003] The main drawbacks of the existing technology include: (1) limited thermoelectric potential, which makes it impossible to achieve efficient energy conversion; (2) low output power density, which is limited by ionic conductivity; (3) reliance on organic additives, which leads to high material cost, environmental unfriendliness and poor stability; and (4) low thermal power in inorganic aqueous solutions (such as pure KCl), which makes it difficult to put into practical use. Summary of the Invention

[0004] The present invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of the present invention provide an ion thermoelectric thin film, a method for preparing the same, and an ion thermoelectric power generation device.

[0005] This invention provides an ion thermoelectric thin film, its preparation method, and an ion thermoelectric power generation device, which can solve the problems of low thermoelectric potential and insufficient output power density in existing ion thermoelectric power generation devices, making it difficult to efficiently utilize low-level heat (such as industrial waste heat, body heat, or environmental thermal differences) for energy conversion.

[0006] In a first aspect, embodiments of the present invention provide an ion thermoelectric thin film, wherein the material of the ion thermoelectric thin film is graphene oxide nanosheets.

[0007] The advantages and technical effects of the ion thermoelectric thin film of the present invention are as follows:

[0008] The ion thermoelectric thin film material of this invention is graphene oxide nanosheet. The height of the ion transport channel of the ion thermoelectric thin film is 0.43 nm. Nanoscale ion capillary condensation is achieved in the sub-nanometer ion transport channel of the ion thermoelectric thin film, that is, the ion concentration in the ion transport channel is higher than the ion concentration in the bulk solution, and the ion mobility in the ion transport channel is lower than the ion mobility in the bulk solution, resulting in entropy change. The thermal power and output power density of the ion thermoelectric power generation device are significantly improved by using inexpensive inorganic electrolyte solutions (such as KCl solution / NaBr solution / KBr solution / MgSO4 solution, etc.), and low-level heat (such as industrial waste heat, bulk heat or environmental thermal difference) can be efficiently utilized for energy conversion.

[0009] Secondly, embodiments of the present invention provide a method for preparing an ion thermoelectric thin film, the method comprising the following steps: a. Provide a dispersion of graphene oxide nanosheets; b. Disperse the graphene oxide nanosheet dispersion in water to obtain a diluted graphene oxide nanosheet solution; use a diaphragm to vacuum filter the diluted graphene oxide nanosheet solution to obtain an ion thermoelectric wet membrane. c. Remove the ion thermoelectric wet film from the diaphragm and dry the ion thermoelectric wet film to obtain the ion thermoelectric thin film described in the first aspect.

[0010] The advantages and technical effects of the preparation method of this invention are as follows: The preparation method of this invention can obtain an ion thermoelectric thin film with nano-ion capillary condensation effect, which greatly improves the thermal power and output power density of the ion thermoelectric power generation device.

[0011] In some embodiments, in step b, the concentration of the graphene oxide nanosheet diluent is 0.05-0.1 wt%, for example, 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, 0.1 wt%, etc. Meeting this condition is beneficial for improving the uniformity of the ion thermoelectric thin film.

[0012] In some embodiments, in step c, the product is dried for 1.5-3 hours at 50-80°C, such as 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, etc., for example, 1.5 hours, 2 hours, 2.5 hours, 3 hours, etc.

[0013] Thirdly, embodiments of the present invention provide an ion thermoelectric thin film, wherein the material of the ion thermoelectric thin film is vermiculite nanosheets.

[0014] The advantages and technical effects of the ion thermoelectric thin film of the present invention are as follows: The ion thermoelectric thin film material in this embodiment of the invention is vermiculite nanosheets. The height of the ion transport channel of the ion thermoelectric thin film is 0.3 nm. Nanoscale ion capillary condensation is achieved in the sub-nanometer ion transport channel of the ion thermoelectric thin film, that is, the ion concentration in the ion transport channel is higher than the ion concentration in the bulk solution, and the ion mobility in the ion transport channel is lower than the ion mobility in the bulk solution, resulting in entropy change. The thermal power and output power density of the ion thermoelectric power generation device are significantly improved by using inexpensive inorganic electrolyte solutions (such as KCl solution / NaBr solution / KBr solution / MgSO4 solution, etc.), and low-level heat (such as industrial waste heat, bulk heat or environmental thermal difference) can be efficiently utilized for energy conversion.

[0015] Fourthly, embodiments of the present invention provide a method for preparing an ion thermoelectric thin film, the method comprising the following steps: d. Preparation of vermiculite nanosheet dispersion; e. Disperse the vermiculite nanosheet dispersion in water to obtain a diluted vermiculite nanosheet solution; use a diaphragm to vacuum filter the diluted vermiculite nanosheet solution to obtain an ion-thermoelectric wet membrane; f. Remove the ion thermoelectric wet film from the diaphragm and dry the ion thermoelectric wet film to obtain an ion thermoelectric thin film.

[0016] The advantages and technical effects of the preparation method of this invention are as follows: The preparation method of this invention can obtain an ion thermoelectric thin film with nano-ion capillary condensation effect, which greatly improves the thermal power and output power density of the ion thermoelectric power generation device.

[0017] In some embodiments, in step d, the vermiculite nanosheet dispersion is prepared by the following method: expanded vermiculite is mixed with a saturated NaCl aqueous solution and heated at 100-120 °C for 20-30 hours; after cooling, a first vermiculite dispersion is obtained; the first vermiculite dispersion is centrifuged and washed until Ag is added to the supernatant. + Chloride ions were undetectable in the solution, and the first vermiculite was obtained as a precipitate. The first vermiculite was mixed with an aqueous LiCl solution (e.g., 1-3 mol / L) and heated at 100-120°C for 20-30 hours. After cooling, a second vermiculite dispersion was obtained. The second vermiculite dispersion was centrifuged and washed until Ag was added to the supernatant. + Chloride ions were not detected in the solution, and the second vermiculite was obtained in the form of a precipitate. The second vermiculite was mixed with an aqueous solution of hydrogen peroxide (e.g., 25-35 wt%) and heated at 100-120 °C for 20-30 hours. After cooling, a third vermiculite dispersion was obtained. The third vermiculite dispersion was subjected to ultrasonic treatment for 1-2 hours and then centrifuged to obtain the vermiculite nanosheet dispersion in the form of supernatant.

[0018] The purpose of treating the expanded vermiculite with NaCl aqueous solution and the first vermiculite with LiCl aqueous solution is to use Na / Li ions to exchange out the calcium, magnesium, and other impurity ions between the vermiculite layers, reducing the difficulty of peeling off the vermiculite nanosheets. The second vermiculite is treated with hydrogen peroxide aqueous solution because hydrogen peroxide readily generates a large amount of oxygen, thereby using the gas to further expand the vermiculite layers and assist in the peeling off of the vermiculite nanosheets.

[0019] In some embodiments, in step e, the concentration of the vermiculite nanosheet diluent is 0.15-0.3 mg / mL, for example, 0.15 mg / mL, 0.18 mg / mL, 0.2 mg / mL, 0.22 mg / mL, 0.25 mg / mL, 0.28 mg / mL, 0.3 mg / mL, etc. Meeting this condition is beneficial for improving the uniformity of the ion-thermoelectric thin film.

[0020] In some embodiments, in step f, the product is dried for 3-5 hours at 50-80°C, such as 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, etc., for example, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, etc.

[0021] Fifthly, embodiments of the present invention provide an ion thermoelectric power generation device, the ion thermoelectric power generation device comprising the ion thermoelectric material described in the first or third aspect, or comprising the ion thermoelectric material obtained by the preparation method described in the second or fourth aspect.

[0022] The advantages and technical effects of the ion thermoelectric power generation device of this invention are as follows: The ion thermoelectric power generation device of this invention has excellent thermal power and output power density, and can be applied to low-grade heat energy collection devices, wearable thermoelectric generators, IoT sensor self-powered systems, and nano-current energy conversion projects, such as achieving sustainable energy supply in smart wearable devices or industrial waste heat recovery systems. Attached Figure Description

[0023] Figure 1 This demonstrates that under confined conditions, an increase in ion concentration within the ion transport channel leads to a decrease in ion mobility.

[0024] Figure 2 The self-diffusion coefficients of sodium ions under confined conditions and in bulk solution are shown.

[0025] Figure 3 This demonstrates the validation of the capillary condensation effect of nano-ions controlled by temperature and confinement degree.

[0026] Figure 4 A simulation of the capillary condensation effect of nano-ions is shown.

[0027] Figure 5 The nano-ion capillary condensation effect in the ion transport channels of vermiculite films is shown.

[0028] Figure 6 This demonstrates the enhanced ion thermoelectric energy conversion due to the nano-ion capillary condensation effect. Detailed Implementation

[0029] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0030] The present invention will now be described in detail with reference to the embodiments and accompanying drawings.

[0031] Example 1 Preparation of graphene oxide (GO) films: 1.6 g of GO nanosheet dispersion (GO-V50 solution, 1 wt%, purchased from STANDARD GRAPHENE) was dispersed in 20 mL of deionized water to obtain a GO nanosheet dilution. The GO nanosheet dilution was vacuum filtered through a Celgard 2400 membrane to obtain a wet GO membrane, which was then removed from the Celgard 2400 membrane. Subsequently, the obtained wet GO membrane was placed in an oven and dried at 60 °C for 2 hours to obtain the GO film.

[0032] Example 1 prepared a uniform GO film that can be used as an ion thermoelectric film. The GO film is a two-dimensional layered GO nanosheet. The GO film has ion transport channels with a height of sub-nanometer (0.43 nm) and can provide negative surface charge to promote the capillary condensation effect of nano-ions.

[0033] Example 2 Preparation of vermiculite (VMT) nanosheet dispersion: 10 g of expanded vermiculite (purchased from Aladdin) was added to 100 mL of saturated NaCl aqueous solution and heated at 110 ℃ for 24 hours. After cooling, the first vermiculite dispersion was obtained. The first vermiculite dispersion was centrifuged at 6000 rpm, and the precipitate was washed with deionized water until Ag was added to the supernatant. + Chloride ions were undetectable in the solution, and the first vermiculite was obtained as a precipitate. Subsequently, the first vermiculite was transferred to 100 mL of a 2 mol / L LiCl aqueous solution and heated at 110 °C for 24 hours. After cooling, a second vermiculite dispersion was obtained. The second vermiculite dispersion was centrifuged at 6000 rpm, and the precipitate was washed with deionized water until Ag was added to the supernatant. + No chloride ions were detected in the solution, and the second vermiculite was obtained as a precipitate. Next, the second vermiculite was mixed with 100 mL of a 30 wt% hydrogen peroxide aqueous solution and heated at 110 °C for 24 hours. After cooling, a third vermiculite dispersion was obtained. The third vermiculite dispersion was ultrasonicated for 1.5 hours and then centrifuged at 6000 rpm for 10 minutes to obtain a VMT nanosheet dispersion as the supernatant.

[0034] Preparation of vermiculite (VMT) films: 12 mL of a 2 mg / mL VMT nanosheet dispersion was dispersed in 100 mL of deionized water to obtain a diluted VMT nanosheet solution. The diluted VMT nanosheet solution was vacuum filtered using a Celgard 2400 membrane to obtain a wet VMT membrane, which was then removed from the Celgard 2400 membrane. Subsequently, the obtained wet VMT membrane was placed in an oven and dried at 60 °C for 4 hours to obtain the VMT film.

[0035] Example 2 prepared a stable VMT film that can be used as an ion thermoelectric film, providing high charge density channels. This VMT film is a two-dimensional layered distribution of VMT nanosheets. The VMT film has ion transport channels with a height of sub-nanometer (0.3 nm), which can provide negative surface charge to promote the capillary condensation effect of nano-ions, and is used to verify the universality of the capillary condensation effect of nano-ions.

[0036] Performance testing 1. Material characterization: (1) The height of the nanosheets of the GO / VMT film was characterized using an atomic force microscope (AFM, model Bruker Multimode 8).

[0037] (2) The average interlayer spacing of the GO / VMT thin film was evaluated using an X-ray diffractometer (XRD, model Rigaku Mini Flex 600) to calculate the height of the ion transport channels in the GO / VMT thin film. Specifically, in the XRD test, characteristic peaks will appear, and the horizontal coordinate of the peak is the angle of the peak. The average interlayer spacing d can be calculated using the formula based on the angle of the peak. space d space Adding the thickness of a nanosheet to the height of an ion transport channel, d space The height of the ion transport channel can be calculated by subtracting the thickness of one nanosheet. The measured height of the ion transport channel in the GO film is 0.43 nm, and the height of the ion transport channel in the VMT film is 0.3 nm.

[0038] (3) The morphology and thickness of the GO film / VMT film were examined using a scanning electron microscope (SEM, model S-4800 Hitachi, Japan).

[0039] 2. Ionic conductivity, ion concentration, and ion mobility testing: First, pour about half the volume of liquid polydimethylsiloxane (PDMS, model SYLGARD 184, purchased from Dow Inc.) into a petri dish with a diameter of about 2.5 cm. Cure the PDMS in a 60 °C oven for 3 hours. Next, coat a thin layer of liquid PDMS onto the cured PDMS. Adhere a cut GO film (10 mm × 5 mm) onto the liquid PDMS layer. Finally, pour about half the volume of liquid PDMS into the petri dish for sealing. Cure the PDMS again at 60 °C for 3 hours, embedding the GO / VMT film within the PDMS. Using a scalpel, carve two reservoirs at both ends of the GO / VMT film onto the cured PDMS. Fill both reservoirs with a 0.1 mol / L electrolyte solution (KCl solution / NaBr solution / KBr solution / MgSO4 solution) and seal the reservoirs to obtain the test apparatus. The testing apparatus was then placed in a temperature and humidity controlled chamber (20 ℃ / 80 ℃, 90% relative humidity) to allow the solution to permeate for 24 hours to reach equilibrium. Afterward, the cured PDMS was cut away with a scalpel, and the permeated GO / VMT film was removed. XRD analysis was immediately performed to evaluate the average interlayer spacing of the permeated GO / VMT film, and the height of the ion transport channels in the permeated GO / VMT film was calculated.

[0040] The height of the ion transport channels in the GO film after permeation is approximately 0.99 nm, which is larger than that of the GO film itself. This is because the flexible nature of PDMS allows the GO film to hydrate and swell naturally, leading to an increase in the height of the ion transport channels after permeation. In contrast, the height of the ion transport channels in the VMT film remains essentially unchanged after permeation. This is because the VMT film hardly swells in this state.

[0041] In addition, liquid epoxy resin (model K-9741, purchased from Guangdong Hengda New Material Technology Co., Ltd.) was first coated onto aluminum foil and cured at room temperature for 2 hours to make the epoxy resin sheet about 2 mm high. Then, a thin layer of the aforementioned liquid epoxy resin was coated onto the epoxy resin sheet. The cut GO film (10 mm × 5 mm) was then adhered to the liquid epoxy resin. The aforementioned liquid epoxy resin was then used to encapsulate the GO film to a height of 2 mm, so that the GO film was sandwiched between two layers of epoxy resin, thus embedding the GO film into the epoxy resin. Using a scalpel, two liquid reservoirs were carved out at both ends of the GO film on the cured epoxy resin. Both liquid reservoirs were filled with an electrolyte solution (KCl solution) with a concentration of 0.1 mol / L and sealed to obtain the test device. The test device was then placed in a constant temperature and humidity chamber (20°C, 90% relative humidity) and allowed to permeate for 24 hours to reach equilibrium.

[0042] Because the epoxy resin is relatively hard, it can effectively suppress the expansion of the GO film. The GO film hardly swells in the epoxy resin, and the height of the ion transport channels remains almost unchanged.

[0043] (1) For electrical measurements, connect the Ag / AgCl electrodes to both ends of the permeated GO / VMT membrane in the test apparatus, and perform an IV scan test on the test apparatus using a source meter (model Keithley 2450). Following the reporting protocol: first calculate the thickness fraction h0 / d of the ion transport channels in the GO / VMT membrane, and then calculate the effective height h of the membrane channel. d = h×(h0 / d); where h d denoted as h, where h is the effective height of the membrane channel; h is the membrane thickness; d is the average interlayer spacing obtained from XRD measurements; and h0 is the effective height of a single ion transport channel (the average interlayer spacing obtained from XRD measurements minus the thickness of a single nanosheet). Combined with h... d Based on the IV test results, the ionic conductivity within the ion transport channel was derived.

[0044] To ensure the accuracy of temperature response testing, in IV testing, the ionic conductivity within the ion transport channel was measured by first gradually increasing the temperature and then gradually decreasing it, and the average ionic conductivity within the ion transport channel under both conditions was obtained. In all IV tests, the ionic conductivity within the ion transport channel when the temperature was increased was close to that when the temperature was decreased.

[0045] (2) The permeated GO film embedded in PDMS was digested using a microwave digestion system (model MARS 6, CEM Corporation), and the ion concentration in the ion transport channels was then measured using inductively coupled plasma mass spectrometry (ICP-MS, model Agilent 7850). However, the GO film embedded in epoxy resin was difficult to peel off for microwave digestion. In this case, the top epoxy resin was peeled off to expose part of the GO film, and the weight percentages of carbon, oxygen, and ions were measured using X-ray photoelectron spectroscopy (XPS, model ThermoScientific K-Alpha). After knowing the total weight of the GO film, the ion concentration in the ion transport channels was calculated.

[0046] (3) After deriving the ion concentration and average ion conductivity within the ion transport channel, calculate the apparent average mobility μ of the ions within the ion transport channel, simply referred to as ion mobility, μ = σ / (c × N). A ×e); where μ is the ion mobility; σ is the conductivity; c is the total cation and anion concentration; N A is Avogadro's constant; e is the charge constant.

[0047] (4) Place a 0.1 mol / L electrolyte solution (KCl solution / NaBr solution / KBr solution / MgSO4 solution) in a beaker as a bulk solution and test the ion concentration and ion mobility of the bulk solution.

[0048] 3. Construction of the Ion Thermoelectric Power Generation Device and Testing of Thermal Power and Output Power Density: The constructed ion thermoelectric power generation device includes a VMT thin film, two end reservoirs (containing 0.1 mol / L KCl solution, with different temperature gradients established, such as 57 ℃ at the low-temperature end and 57-67 ℃ at the high-temperature end), and Ag / AgCl electrodes. The open-circuit voltage of the ion thermoelectric power generation device was measured, the thermal power was derived, and the output power density was calculated by recording the current under different load resistances.

[0049] Test Result Analysis Previous literature has repeatedly reported that in two-dimensional nanochannels, the ionic conductivity of ion transport channels is significantly higher than that of the bulk phase due to surface charge-dominated transport behavior. These studies typically focus on the low to medium ion concentration region. In the experiments of this application ( Figure 1 a) When the ion concentration of the bulk solution is below 0.5 mol / L, the ionic conductivity of the ion transport channel is indeed much higher than that of the bulk solution. However, as the ion concentration of the bulk solution increases, the ionic conductivity of the ion transport channel gradually decreases below that of the bulk solution. For example, when the ion concentration of the bulk solution is 2 mol / L, the ionic conductivity of the ion transport channel is 40% of that of the bulk solution.

[0050] It is known that ions experience significant steric hindrance when entering certain narrow channels. This typically results in low ionic conductivity. In such cases, the ion concentration within the ion transport channel is much lower than the ion concentration in the bulk solution. However, in the ion transport channels of the GO film of Example 1 and the VMT film of Example 2, K... + and Cl - The concentrations were all measured to be much higher than those of K in the bulk solution. + and Cl - concentration( Figure 1 (b) indicates a relatively small confinement effect. Due to the negative surface charge of the GO nanosheets, the K0 within the ion transport channels... + Concentration greater than Cl - As a result, the ion mobility in the ion transport channels was 20% to 29% of the ion mobility in the bulk solution, such as... Figure 1 As shown in c. Similar phenomena have also been observed in solutions of other electrolytes (such as NaBr, KBr, and MgSO4).

[0051] Furthermore, this application used nuclear magnetic resonance spectroscopy to measure the content of GO thin films. 23The self-diffusion coefficient of Na ions (2 mol / L bulk NaBr solution) was observed to be lower than that in the bulk solution. 23 The self-diffusion coefficient of Na ions (2 mol / L bulk NaBr solution) Figure 2 These results consistently demonstrate that ions undergo a phase transition within the capillary nanofluidic channels. The ion concentration in the capillary nanofluidic channels increases, exceeding that in the bulk solution, while the ion mobility in the capillary nanofluidic channels significantly decreases, falling below that in the bulk solution. This phenomenon is termed the nano-ion capillary condensation effect. Previous theories have shown that, under strong confinement conditions, electrolytes completely dissociated from the bulk solution become weak electrolytes. Positively and negatively charged ions may form tightly bound Bjerrum pairs or polyelectrolytes, exhibiting lower ion mobility. Intuitively, this would also reduce the number of free ions in the bulk solution, lowering the entropy of ions in the ion transport channels. To restore the thermodynamic equilibrium between ions within the ion transport channels and those in the bulk solution, some ions must transport from the bulk solution into the ion transport channels, resulting in a higher ion concentration within the channels, thereby inducing the nano-ion capillary condensation effect.

[0052] To verify the mechanism of the aforementioned nano-ion capillary condensation effect, this application conducted several experiments and simulations. First, the nano-ion capillary condensation effect should be temperature-sensitive. By increasing the temperature, the ions should return to their free state. This application measured the ionic conductivity of the testing device at different temperatures. Figure 3 a and Figure 3 b shows that the phase transition occurs at approximately 60°C. The mechanism of the nano-ionic capillary effect described in this application further predicts that at higher temperatures, the ion concentration and ion mobility in the ion transport channels should gradually recover to those in the bulk solution. In fact, Figure 3 c and Figure 3 The results show that the ion concentration and ion mobility in the ion transport channel at 80 °C are closer to those in the bulk solution than those at 20 °C.

[0053] Finally, since the nano-ion capillary condensation effect is confined and induced, this application should expect the nano-ion capillary condensation effect to be more pronounced in narrower ion transport channels. To verify this, this application constructed a GO thin film with an ion transport channel height of 0.43 nm. Figure 3 e and Figure 3 The results showed that the ion concentration in the ion transport channels of the GO film was 5-7 times that in the bulk solution, while the ion mobility in the ion transport channels of the GO film was two orders of magnitude lower than that in the bulk solution.

[0054] To further verify the conclusions of this application, molecular dynamics (MD) simulations were used to visualize the capillary condensation effect of nano-ions. The simulation model consisted of two reservoirs connected by a long graphene nanochannel. Figure 4 a). Graphene was chosen because its inert surface allows this application to focus on confined effects, and its surface chemistry is similar to that of graphene regions of graphene oxide. The height of the graphene nanochannels was set to 1 nm to meet experimental conditions. Each reservoir contained 1 mol / L KCl. When the ion concentrations in the graphene nanochannels and reservoirs were set to be the same, ions spontaneously migrated from the reservoirs to the graphene nanochannels. However, this migration was too slow to be simulated within a reasonable time. This was expected, as ions would be congested at the inlet when migrating from large reservoirs to long, narrow graphene nanochannels. Conversely, ions migrated much faster from the graphene nanochannels to the reservoirs. Therefore, this application first set the ion concentration in the graphene nanochannels to a high value, allowing ions to diffuse within the graphene nanochannels and freely flow out to the reservoirs to reach equilibrium. This application observed spontaneous aggregation of ions in the graphene nanochannels, forming Bjerrum pairs or polyelectrolytes ( Figure 4 (b) This is consistent with the mechanism of this application. The radial distribution function of the confined ions shows sharper and more peaks, also indicating the formation of ion pairs. Furthermore, at equilibrium, the ion concentration in the graphene nanochannel with a height of 1 nm reaches 1.6 mol / L ( Figure 4 c). This qualitatively supports the experimental values, although, unlike the experiments, the cation and anion concentrations are the same, due to the absence of surface charge on the graphene. By applying an electric field, this application can further simulate ion mobility. Again, the ion mobility decreases, reaching 3.72 × 10⁻⁶ in 1 nm high-height graphene nanochannels. -8 m 2 ·s -1 ·V -1 ( Figure 4 d). These results provide clear evidence for the capillary condensation effect of nano-ions.

[0055] The nano-ion capillary condensation effect should occur in all narrow nanochannels, although the surface charge of the ion transport channels leads to different behaviors between cations and anions. Vermiculite has a higher surface charge density. This application tested VTM films with ion transport channels of 0.3 nm height using a 1 mol / L KBr solution. Cl was not used in this application. - Because a large amount of Cl was used in the preparation of vermiculite nanosheets - This will interfere with Cl - Concentration measurement. Within ion transport channels, such as... Figure 5As shown in Figure a, K in the ion transport channel of the VTM thin film + The concentration reached 12.4 mol / L, which is higher than that of K in the bulk solution. + The concentration is an order of magnitude higher. Br in the ion transport channels of the VTM thin film... - The concentration was 1.15 mol / L, which is also higher than the concentration of Br in the bulk solution. - Concentration. Note that Br in the ion transport channels of the VTM film... - The concentration may be underestimated because ICP-MS measurements require digestion of vermiculite with a strong acid. This strong acid inevitably causes some HBr evaporation during the test. The Br content within the ion transport channels of the VTM film is higher than that in the bulk phase. - The concentration exhibited phenomena different from conventional wisdom, but consistent with the mechanism of nano-ion capillary condensation. After measuring the ionic conductivity within the ion transport channels of the VTM film, the ion mobility within the ion transport channels was determined to be 1.04 × 10⁻⁴. -8 m 2 ·s -1 ·V -1 It is only 17.25% of the ion mobility in the bulk solution. Figure 5 b). Similar to GO films, the ionic conductivity within the ion transport channels of VTM films also exhibits a high temperature responsiveness. Figure 5 c, 5d), exhibiting typical phase transition behavior. A similar transition was observed by replacing KBr with KCl ( Figure 5 e, 5 f).

[0056] Ionic phase transitions have a significant impact on thermoelectric power generation. In recent decades, ionic thermoelectrics have attracted increasing interest due to their orders-of-magnitude higher thermal power and ability to harvest low-grade heat compared to conventional electronic thermoelectrics. For the scalability and practical application of ionic thermoelectrics, the use of inexpensive and environmentally friendly ionic solutions to enhance thermal power and power density is crucial. Therefore, inorganic aqueous solutions are the most promising if the thermal power of ionic thermoelectric power generation devices can be increased sufficiently. However, this remains challenging without the addition of organic agents. All of these challenges can be addressed using the nano-ionic capillary condensation effect.

[0057] For ion thermoelectric power generation devices, thermal power is related to entropy change. When nano-ion capillary condensation occurs in the ion transport channel, the entropy of the ions decreases significantly. Thus, when a temperature gradient is established across the GO / VMT thin film, the entropy change between the two ends increases substantially compared to the case without nano-ion capillary condensation, resulting in higher thermal power.

[0058] This application constructs as follows: Figure 6The ion thermoelectric power generation device shown in figure a. Two Ag / AgCl electrodes are connected to both ends of a VMT thin film to measure the performance of the ion thermoelectric power generation device. In this application, the lower temperature reservoir is set to 57 °C, and the higher temperature reservoir temperature is varied from 57 °C to 67 °C. The voltage response generated under different temperature differences is as follows: Figure 6 As shown in b. From these results, this application derives the thermal power of the ion thermoelectric power generation device to be 10 mV·K. -1 This is compared to a KCl solution in bulk water (0.17 mV·K). -1 Two orders of magnitude higher. Moreover, under constant temperature difference, the voltage in the confined ion transport channel exhibits relative stability, such as... Figure 6 As shown in c. Then, this application measures the output power density by recording the current on external loads with different resistances. The ion thermoelectric power generation device exhibits a maximum output power density of 492.6 mW·m. -2 ·K -2 This is the highest among all reported ion thermoelectric devices to date. Figure 6 d, 6 e).

[0059] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0060] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. An ion-thermoelectric thin film, characterized in that, The material of the ion thermoelectric thin film is graphene oxide nanosheets.

2. The method for preparing the ion thermoelectric thin film according to claim 1, characterized in that, The preparation method includes the following steps: a. Provide a dispersion of graphene oxide nanosheets; b. Disperse the graphene oxide nanosheet dispersion in water to obtain a diluted graphene oxide nanosheet solution; use a diaphragm to vacuum filter the diluted graphene oxide nanosheet solution to obtain an ion thermoelectric wet membrane. c. Remove the ion thermoelectric wet film from the diaphragm and dry the ion thermoelectric wet film to obtain an ion thermoelectric thin film.

3. The preparation method according to claim 2, characterized in that, In step b, the concentration of the graphene oxide nanosheet diluent is 0.05-0.1 wt%.

4. The preparation method according to claim 2, characterized in that, In step c, dry at 50-80 ℃ for 1.5-3 hours.

5. An ion-thermoelectric thin film, characterized in that, The material of the ion thermoelectric thin film is vermiculite nanosheets.

6. The method for preparing the ion thermoelectric thin film according to claim 5, characterized in that, The preparation method includes the following steps: d. Preparation of vermiculite nanosheet dispersion; e. Disperse the vermiculite nanosheet dispersion in water to obtain a diluted vermiculite nanosheet solution; use a diaphragm to vacuum filter the diluted vermiculite nanosheet solution to obtain an ion-thermoelectric wet membrane; f. Remove the ion thermoelectric wet film from the diaphragm and dry the ion thermoelectric wet film to obtain an ion thermoelectric thin film.

7. The preparation method according to claim 6, characterized in that, In step d, the vermiculite nanosheet dispersion is prepared by the following method: Expanded vermiculite was mixed with a saturated NaCl aqueous solution and heated at 100-120 °C for 20-30 hours. After cooling, a first vermiculite dispersion was obtained. The first vermiculite dispersion was centrifuged and washed until Ag was added to the supernatant. + Chloride ions were not detected in the solution, and the first vermiculite was obtained as a precipitate; The first vermiculite was mixed with an aqueous LiCl solution and heated at 100-120 °C for 20-30 hours. After cooling, a second vermiculite dispersion was obtained. The second vermiculite dispersion was centrifuged and washed until Ag was added to the supernatant. + Chloride ions were not detected in the solution, and the second vermiculite was obtained as a precipitate; The second vermiculite was mixed with an aqueous hydrogen peroxide solution and heated at 100-120 °C for 20-30 hours. After cooling, a third vermiculite dispersion was obtained. The third vermiculite dispersion was subjected to ultrasonic treatment for 1-2 hours and then centrifuged to obtain the vermiculite nanosheet dispersion in the form of supernatant.

8. The preparation method according to claim 6 or 7, characterized in that, In step e, the concentration of the vermiculite nanosheet diluent is 0.15-0.3 mg / mL.

9. The preparation method according to claim 6 or 7, characterized in that, In step f, dry at 50-80 ℃ for 3-5 hours.

10. An ion thermoelectric power generation device, characterized in that, Includes the ion thermoelectric thin film as described in claims 1 and / or 5, or includes the ion thermoelectric thin film obtained by the preparation method described in any one of claims 2-4, 6-9.

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