Bentonite-regulated solar-driven light-heat-electricity conversion composite phase change material, and preparation method and application thereof

Abstract

The application discloses bentonite-regulated solar-driven light-heat-electricity conversion composite phase change material and a preparation method and application thereof, and relates to the technical field of phase change energy storage materials and solar energy utilization. The material is prepared by using bacterial cellulose aerogel as a porous framework, fixing MXene and TiN nanoparticles on the framework through cross-linking and gradient assembly to construct a light-heat-heat conduction network, dispersing bentonite intercalation in a polyethylene glycol matrix to form a composite phase change material, and then encapsulating the composite phase change material in the multistage pores of the aerogel. The surface of the framework has a hydrophobic modification layer. The preparation method comprises the steps of etching, aerogel framework construction, vacuum impregnation encapsulation and hydrophobic modification. The material has high light-heat conversion efficiency, high heat conduction promotion rate, excellent leakage prevention performance, fast crystallization characteristics and super-hydrophobic self-cleaning ability. When the material is combined with a thermoelectric power sheet, a solar light-heat-electricity conversion system can be constructed, and the material has a wide application prospect in the field of renewable energy.

Description

Technical Field

[0001] This invention relates to the field of phase change energy storage materials and solar energy utilization technology, specifically to a bentonite-regulated solar-driven photo-thermal-electric conversion composite phase change material, its preparation method, and its application. Background Technology

[0002] The continued consumption of fossil fuels makes the development of clean and renewable energy technologies such as solar energy crucial. However, the intermittent and unstable nature of solar energy limits its direct and continuous utilization. Phase change materials (PCMs), capable of reversibly storing and releasing heat energy in the form of latent heat, are one of the key media for realizing the temporal and spatial redistribution of solar energy. Among them, the organic phase change material polyethylene glycol (PEG) has been extensively studied due to its suitable phase change temperature, high phase change enthalpy, and good chemical stability.

[0003] However, PEG faces multiple challenges in practical applications: First, leakage during the solid-liquid phase transition is a serious problem; second, its low thermal conductivity results in a slow rate of heat storage / release; third, its weak light absorption capacity makes it unable to effectively drive photothermal conversion; and fourth, the existence of supercooling affects the controllable release of latent heat.

[0004] To address these issues, existing research has sought breakthroughs in three main directions, but all have limitations: (1) Encapsulation using porous matrices (such as bacterial cellulose aerogels). While these materials can physically confine PEG to prevent leakage, their framework is usually chemically inert, making it impossible to actively regulate the crystallization behavior of PEG to suppress overcooling. Furthermore, their poor thermal conductivity and photothermal performance become a bottleneck for system thermal management. (2) Incorporation of photothermal nanomaterials (such as MXene and TiN). These materials can effectively improve light absorption and photothermal conversion efficiency, but if only simple physical mixing is performed, it is difficult to construct a continuous and efficient thermal conduction path within the composite. The large amount of heat generated by photothermal conversion cannot be quickly transferred to the PEG body, limiting the improvement of overall energy storage efficiency. (3) Introduction of nucleating agents (such as bentonite). Bentonite (BT), with its layered structure and abundant surface functional groups, is expected to serve as a heterogeneous nucleation site to promote PEG crystallization. However, existing studies mostly utilize its physical adsorption capacity as the main body of the encapsulation matrix, and the exploration of how BT actively regulates the crystallization kinetics of PEG and how it synergistically enhances the anti-leakage mechanism in the aerogel pore structure after being combined with PEG is still insufficient.

[0005] In summary, existing technologies mostly employ single or limited improvement strategies, making it difficult to systematically and simultaneously address the interconnected bottlenecks such as leakage prevention under high loads, efficient photothermal conversion, rapid heat conduction, and active control of the crystallization process. Therefore, developing a synergistic strategy that integrates multiple functions such as porous confinement, photothermal conversion, enhanced thermal conductivity, and nucleation control, and subsequently preparing high-performance composite phase change materials, is of urgent need and significant importance for achieving efficient solar energy storage and gradient utilization (photothermal-electricity). Summary of the Invention

[0006] The main objective of this invention is to overcome the above-mentioned defects of the prior art and provide a bentonite-regulated solar-driven photo-thermal-electric conversion composite phase change material, its preparation method and application, while solving the problems of easy leakage, poor thermal conductivity, low photo-thermal conversion efficiency and severe overcooling of polyethylene glycol (PEG) phase change materials, and ultimately achieving efficient, stable and continuous conversion of solar energy into thermal and electrical energy.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution.

[0008] A bentonite-regulated solar-driven photo-thermal-electric conversion composite phase change material includes: a bacterial cellulose aerogel framework; MXene and TiN nanoparticles fixed on the aerogel framework through cross-linking and stepwise assembly; a composite phase change material with polyethylene glycol as the matrix and bentonite intercalation adsorption dispersed thereon; the composite phase change material is encapsulated in the multi-level channels of the aerogel; and the surface of the aerogel framework has a hydrophobic modification layer.

[0009] In this invention, the MXene is V2C MXene, and the TiN is nanoparticles with a particle size of 20 nm.

[0010] In this invention, further, based on the mass of the polyethylene glycol, the mass percentage of bentonite is 0.2-1.9%.

[0011] Furthermore, in this invention, the aerogel framework has a multi-level pore structure consisting of macropores, mesopores, and micropores, with a pore size distribution of 1.5-2 nm micropores, 2-50 nm mesopores, and 70 μm macropores.

[0012] The present invention also proposes a method for preparing the above-described composite phase change material, comprising the following steps.

[0013] (1) Preparation of V2C MXene powder: V2AlC precursor powder was added to hydrofluoric acid solution and etched under stirring conditions. After the reaction was completed, it was washed until neutral and dried under vacuum to obtain V2C MXene powder.

[0014] (2) Preparation of BC / MXene / TiN composite wet gel: V2C MXene powder obtained in step (1) is mixed with bacterial cellulose (BC) dispersion, and then methyltrimethoxysilane (MTMS) is added to carry out cross-linking reaction to obtain BC / MXene pre-cross-linked gel; then titanium nitride (TiN) nanoparticles are added to the BC / MXene pre-cross-linked gel and dispersed evenly to obtain BC / MXene / TiN composite sol; the composite sol is pre-frozen to obtain BC / MXene / TiN composite wet gel.

[0015] (3) Preparation of BC / MXene / TiN aerogel framework: The BC / MXene / TiN composite wet gel obtained in step (2) is pre-frozen and then freeze-dried to obtain the BC / MXene / TiN aerogel framework.

[0016] (4) Preparation of BT / PEG composite phase change precursor liquid: Bentonite (BT) powder is dispersed in molten polyethylene glycol (PEG) to form a uniform BT / PEG composite phase change precursor liquid.

[0017] (5) Vacuum impregnation and encapsulation: The BC / MXene / TiN aerogel skeleton obtained in step (3) is immersed in the BT / PEG composite phase change precursor liquid obtained in step (4) and impregnated under vacuum and heating conditions to allow the precursor liquid to penetrate into the multi-level channels of the aerogel. Then, excess PEG on the surface is removed to obtain the encapsulated composite phase change material precursor.

[0018] (6) Hydrophobic modification: The encapsulated composite phase change material precursor obtained in step (5) is immersed in an organic solution of trichlorooctadecylsilane (OTS), taken out and dried to form a hydrophobic layer on the surface of the material, thus obtaining the composite phase change material.

[0019] In this invention, further, the vacuum impregnation temperature in step (5) is 65°C and the time is 3 hours.

[0020] In this invention, the concentration of the trichlorooctadecylsilane solution used in step (6) for hydrophobic modification is 1%, and the solvent is n-hexane.

[0021] This invention also proposes an application of the composite phase change material described above in a solar-thermal-electric conversion system. The material serves as a photothermal conversion and thermal storage unit, which is combined with a thermoelectric generator to construct a photo-thermal-electric conversion system.

[0022] Furthermore, in this invention, a thermally conductive interface material is provided between the thermoelectric generator and the composite phase change material, as well as between the thermoelectric generator and the heat dissipation device, and the heat dissipation device is an active water circulation heat dissipation system.

[0023] In this invention, the system is further configured to continue driving the thermoelectric generator to output electrical energy using the latent heat of phase change released by the composite phase change material after the light exposure is stopped.

[0024] In summary, due to the adoption of the above technical solutions, the present invention has at least the following beneficial effects.

[0025] 1. This invention achieves multi-dimensional synergistic design of material structure and function, enhancing the overall performance of composite phase change materials. It innovatively integrates a three-dimensional hierarchical porous confined framework of bacterial cellulose (BC) aerogel, a gradient photothermal-thermal conductive network of MXene / TiN, heterogeneous nucleation regulation of bentonite (BT), and intercalation-based leak prevention and surface hydrophobic modification layers. This synergistic design, addressing multiple dimensions such as physical encapsulation, thermal management, crystallization kinetics, and environmental stability, simultaneously overcomes the intertwined technical challenges of traditional phase change materials, including leakage, poor thermal conductivity, low photothermal conversion efficiency, severe supercooling, and weak environmental tolerance, breaking through the limitations of single improvement strategies.

[0026] 2. Significantly enhanced thermal and photothermal energy management efficiency was achieved. Due to the complementary size and continuous distribution of thermal conductivity and photothermal conversion networks formed by V2C MXene and TiN nanoparticles within the BC framework, the thermal conductivity of the final composite material (BTV-BP) was increased by 433% compared to pure PEG, reaching 1.5 kW / m². 2 Under illumination, the surface temperature rapidly rises to 95.3℃. Meanwhile, the introduction of BT provides abundant heterogeneous nucleation sites through hydrogen bonding, increasing the crystallization rate of PEG by approximately 5 times and effectively reducing supercooling, thereby achieving rapid absorption, efficient storage (latent heat), and controlled release of solar energy.

[0027] 3. Demonstrates long-term reliability and environmental adaptability. The strong capillary constraint of the BC framework, the microscopic "fish scale" intercalation structure and "pore-blocking" effect of the BT / PEG composite, synergistically work with the surface hydrophobic layer to achieve a leakage rate of only 1.81% at 80°C. In addition, the modified surface of the material exhibits stable superhydrophobicity (contact angle of 151° at room temperature and still 142° at 65°C) and self-cleaning function, ensuring its long-term structural integrity and performance stability under complex outdoor conditions such as humidity, rain, and dust.

[0028] 4. A continuous conversion path from solar energy to electrical energy has been established, validating its application value. The thermoelectric power generation system constructed based on the material of this invention can achieve an electrical output of 156.5 mV and 18.6 mA under simulated sunlight. Furthermore, even after sunlight exposure ceases, it can continue to output electrical energy using the latent heat of phase change stored in the material, driving the load to operate continuously. This directly demonstrates the feasibility and practical potential of this material in achieving spatiotemporal control of solar energy distribution and serving as a continuous and stable power source. Attached Figure Description

[0029] Figure 1 The images show scanning electron microscope (SEM) images of the pure bacterial cellulose (BC) aerogel (BA) prepared in Example 1 of this invention. In the image (a), the three-dimensional porous network structure of the aerogel as a whole is shown, and a large number of macropores are visible between the framework. In the image (b), a partial magnification of the image (a) shows that the framework is composed of a finer micro-nanoporous secondary network of interwoven BC nanofibers.

[0030] Figure 2 The images show SEM images of the photothermal material used in this invention. (a) shows the morphology of titanium nitride (TiN) nanoparticles, and (b) shows the layered structure of V2C MXene.

[0031] Figure 3 SEM images of the BC / MXene / TiN (BTV) composite aerogel (BTVA) prepared in Example 1 of this invention are shown. (a) shows the aerogel maintaining a three-dimensional porous structure after loading nanomaterials; (b) is a magnified view of (a); and (c) is a magnified view of (b), showing that large-sized V2C MXene sheets (indicated by arrows) and small-sized TiN nanoparticles are uniformly immobilized on the BC fiber framework, exhibiting a gradient distribution assembly characteristic.

[0032] Figure 4 This is a diagram showing the pore structure of BTVA aerogel.

[0033] Figure 5 SEM images of aerogels encapsulated with different phase change materials. (a) The surface of a BTV-P sample impregnated with pure polyethylene glycol (PEG) is covered by a PEG layer, the pore structure is not visible, and the surface has a smooth water ripple pattern; (b) The surface of a BTV-BP sample impregnated with BT / PEG composite material is visible, with a large number of BT sheets scattered and the surface is rough; (c) A magnified view of (b) shows the irregular "fish scale" composite structure formed by the tight bonding of BT sheets and PEG; (d) A further magnified view of the BT / PEG composite structure in the internal pores of the BTV-BP sample.

[0034] Figure 6Differential scanning calorimetry (DSC) curves of composite phase change materials with different components are shown in the figure. The melting peak temperature (Tm) and the initial crystallization temperature (Tf) of each sample are marked in the figure, and the supercooling (ΔT = Tm - Tf) is calculated.

[0035] Figure 7 A bar chart comparing the thermal conductivity test results of composite phase change materials with different components.

[0036] Figure 8 This is a comparison of optical photographs of the crystallization process of pure PEG and BT / PEG suspension under the same conditions. The changes in crystal morphology over time from the molten state are recorded at timestamps of 0s, 15s, 45s, 90s, and 120s.

[0037] Figure 9 Optical photographs showing the leakage of composite phase change materials of various components after heating at 80°C for different times (0 min, 30 min, 40 min, 50 min, 60 min).

[0038] Figure 10 A bar chart showing the leakage rate and retention rate of each sample calculated for the experiment.

[0039] Figure 11 This is a SEM image of PEG in a molten state attached to the surface of the aerogel skeleton in the BTV-P sample, showing a relatively smooth interface.

[0040] Figure 12 SEM images of the internal microstructure of the BTV-BP sample. (a) shows the "fish scale" composite structure formed by BT and PEG on the skeleton; (b) shows the "pore-blocking" effect formed by BT / PEG aggregates in the pores; (c) and (d) are magnified views of the "fish scale" structure and "pore-blocking" effect inside the BTV-BP sample from different perspectives or regions.

[0041] Figure 13 The following are the photothermal performance characterization diagrams for each component material. (a) shows the UV-Vis-NIR absorption spectrum; (b) shows the absorption spectrum at 1.5 kW / m². 2 The surface temperature change curve over time under simulated illumination (temperature rise and fall curve).

[0042] Figure 14 BTV-BP samples with different BT addition amounts were tested at 1.5 kW / m³. 2 Comparison of temperature rise and fall curves under simulated illumination.

[0043] Figure 15The curves show the output voltage and current changes over time in a solar photothermal-electric conversion (STEG) system for a blank control group (without phase change material) and a BTV-BP sample during illumination and cessation of illumination; where (a) is the voltage curve and (b) is the current curve.

[0044] Figure 16 The images show the surface wettability of the composite phase change material. (a) is a photograph of the surface of the untreated sample (BTV-BPO) where water droplets rapidly wet the surface; (b) shows the water contact angle (WCA) of BTV-BPO at 0°; (c) shows a photograph of the superhydrophobic surface of the hydrophobic treated sample (BTV-BP) at room temperature, along with its WCA (151°) and the silver mirror effect when immersed in water; (d) shows a photograph of water droplets on the surface of BTV-BP under heating conditions, a thermal infrared image, and its WCA (142°); and (e) shows photographs of the dynamic water contact angle test process of BTV-BP (0s, 3s, 5s, 7s).

[0045] Figure 17 These are real-world comparison photos of the self-cleaning performance test of the materials. (a) After the BTV-BPO surface was contaminated with dust, it was rinsed with water, leaving dust residue and the surface wet; (b) After the BTV-BP surface was similarly contaminated, water droplets rolled off and carried away all the dust, achieving self-cleaning. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are specific implementations of a part of this invention, but not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0047] Example 1: Preparation of composite phase change material BTV-BP.

[0048] 1. Raw materials.

[0049] Methyltrimethoxysilane (MTMS, 98%), vanadium aluminum carbide (V2AlC, 400 mesh), nano-titanium nitride (TiN, 99.99%, 20nm), polyethylene glycol (PEG, Mn=6000), and hydrofluoric acid (HF, 40wt%) were purchased from Shanghai Maclean Chemical Co., Ltd. Bacterial cellulose dispersion (BC, 0.8wt%) was purchased from Guilin Qihong Technology Co., Ltd. Sodium bentonite (BT) was purchased from Guangxi Ningming Mining Co., Ltd. Trichlorooctadecylsilane (OTS) was purchased from Shanghai Aladdin Reagent Co., Ltd. Ultrapure water was used in the experiments.

[0050] 2. Preparation of V2C MXene powder.

[0051] 150 mL of 40 wt% HF solution was placed in a polytetrafluoroethylene beaker. 2.5 g of V₂AlC precursor powder was slowly added in approximately 10 portions, with 30-second intervals between each addition, while stirring at 200 rpm. After the addition was complete, the beaker was sealed, and the mixture was continuously magnetically stirred at 450 rpm for 48 hours at room temperature to carry out the etching reaction. After the reaction, the resulting suspension was centrifuged at 9000 rpm and repeatedly washed with ultrapure water until the pH of the supernatant stabilized at 6-7, ultimately yielding a multilayered V₂C MXene precipitate. This precipitate was then dried in a vacuum oven at 65 ℃ for 24 h to obtain V₂C MXene powder for later use.

[0052] 3. Preparation of BC / MXene / TiN (BTVA) aerogel framework.

[0053] In a 25 mL glass beaker, measure 0.5 mL of MTMS and add it to 9.5 mL of dilute hydrochloric acid solution with pH=3.0. Stir at 600 rpm for 30 minutes at room temperature to obtain an acidic MTMS crosslinking agent solution.

[0054] In another 25 mL beaker, 10 g of BC dispersion (containing approximately 0.08 g of solid BC) was measured, and 0.1 g of the V2C MXene powder prepared in step 2 (based on solids) was added. The mixture was placed in a 40°C water bath and stirred at 800 rpm for 30 minutes to ensure uniform dispersion of V2C. Subsequently, all of the above-mentioned acidic MTMS solution was added, and the mixture was stirred at 800 rpm for 1 hour in a 40°C water bath to carry out the hydrolysis-condensation crosslinking reaction, forming a BC / MXene pre-crosslinked gel.

[0055] 0.1 g of TiN nanoparticles were added to the pre-crosslinked gel, and the mixture was stirred for 30 minutes to allow it to disperse initially. The mixture was then subjected to ultrasonic treatment at 60% power at room temperature for 15 minutes to ensure it was fully homogenized and to remove air bubbles, resulting in a BC / MXene / TiN composite sol.

[0056] The composite sol was quickly transferred to an ultra-low temperature freezer at -50°C and pre-frozen for 1 hour to form a composite wet gel. Finally, the wet gel was placed in a freeze dryer and freeze-dried at -70°C and <10 Pa for 48 hours to obtain a lightweight and porous BC / MXene / TiN composite aerogel, denoted as BTVA.

[0057] 4. Preparation of BT / PEG composite phase change precursor solution.

[0058] Weigh 21 g of PEG6000 solid into a beaker and melt it in a 65°C water bath. Add 9 mL of ultrapure water and stir at 800 rpm to prepare a PEG aqueous solution with a mass fraction of approximately 70% (to reduce viscosity for easier impregnation). Weigh 0.1 g of BT powder and add it to 30 mL of the above 70% PEG solution. Stir at 800 rpm for 1 hour in a 65°C water bath, followed by ultrasonic treatment at 60% power for 15 minutes to ensure that BT is fully dispersed in the molten PEG, forming a homogeneous BT / PEG composite phase change precursor solution. In this precursor solution, the mass ratio of BT to pure PEG is 0.1:21, that is, the mass percentage of BT is approximately 0.43%.

[0059] 5. Vacuum impregnation packaging.

[0060] The BTVA aerogel framework prepared in step 3 was completely immersed in the BT / PEG composite phase change precursor solution prepared in step 4. The entire system was transferred to a vacuum oven and maintained at 65°C and -0.095 MPa for 3 hours, allowing the low-viscosity precursor solution to fully penetrate the pores of the aerogel under capillary force and pressure difference. After impregnation, the sample was removed and placed in a 65°C forced-air oven with filter paper at the bottom, and allowed to stand for 3 hours to remove excess PEG adsorbed on the surface and evaporate moisture, obtaining the encapsulated composite phase change material precursor.

[0061] 6. Hydrophobic modification.

[0062] Prepare a 1% (v / v) OTS solution: Add 1 mL of OTS to 99 mL of n-hexane and stir at room temperature for 15 minutes to mix thoroughly. Immerse the encapsulation precursor obtained in step 5 into the OTS solution and let it stand for 1 hour. After removal, rinse three times with fresh n-hexane to remove physically adsorbed OTS. Finally, place the sample in a 65℃ vacuum oven to dry for 2 hours, allowing OTS to condense on the material surface to form a strong hydrophobic monolayer, thus obtaining the final bentonite-regulated composite phase change material, denoted as BTV-BP.

[0063] Comparative Example 1: Composite Phase Change Materials with Different Components

[0064] To systematically verify the gradient synergistic effect of MXene and TiN, the crystallization regulation and leakage prevention enhancement function of bentonite, and the necessity of surface hydrophobic modification in this invention, the following comparative sample was prepared. Unless otherwise specified, the preparation steps are the same as in Example 1:

[0065] BTA-BP: Using only TiN as the photothermal component, BTA aerogel (without MXene) was prepared according to step 3 of Example 1, and then encapsulated with 0.1g of BT PEG solution and hydrophobically treated.

[0066] BVA-BP: Using only MXene as the photothermal component, BVA aerogel (without TiN) was prepared according to step 3 of Example 1, and then encapsulated with 0.1g of BT PEG solution and hydrophobically treated.

[0067] BTV-P: Uses BTVA aerogel, but encapsulates a pure 70% PEG solution (without BT) and is hydrophobically treated.

[0068] BTV-BPO: 0.1g of BT in a PEG solution is encapsulated using BTVA aerogel, but without hydrophobic treatment.

[0069] Pure PEG: used as a blank control.

[0070] Comparative Example 2: BTV-BP materials with different BT contents.

[0071] To investigate the optimal BT content, in step 4 of Example 1, precursor solutions were prepared using 0.05 g, 0.2 g, and 0.4 g of BT (calculated based on the mass of pure PEG contained in 30 mL of 70% PEG solution, corresponding to a BT mass percentage of approximately 0.24%, 0.87%, and 1.73%, respectively). The other steps were exactly the same as in Example 1, and a series of samples were obtained for performance testing.

[0072] Performance testing and results analysis.

[0073] 1. Structural and morphological characterization.

[0074] The microstructure of materials can be observed using SEM. For example... Figure 1 As shown in (a), pure BC aerogel (BA) has a typical three-dimensional nanofiber network with numerous micron-sized macropores between the framework; Figure 1 As shown in (b), its framework consists of an interwoven network of BC nanofibers forming a finer micro-nanoporous secondary network. This hierarchical porous structure provides ideal space for encapsulating PEG. Figure 2 As shown in (a) and (b), the TiN used in this invention exhibits a clustered nanoparticle morphology, while V2C MXene displays a typical accordion-like multilayer structure. Figure 3 As shown in (a), the BTVA composite aerogel obtained after the introduction of MXene and TiN still maintains a well-preserved three-dimensional porous structure. Figure 3 As shown in (b) and (c), which are progressively magnified images, it is evident that large-sized V2C MXene sheets (indicated by the arrows) and small-sized TiN nanoparticles exhibit a gradient-distributed assembly characteristic, uniformly immobilized on the BC fiber framework. Figure 4As shown, the main plot is the pore size distribution curve obtained by mercury intrusion porosimetry, with a main peak at approximately 70 μm, indicating that the material has a highly uniform macroporous structure; the inset plot is the pore size distribution obtained by BET method, showing that the pore size is mainly concentrated in the mesoporous range of 2-50 nm. Figure 4 The pore size distribution curve confirms that BTVA has a multi-level pore structure of "macropore-mesopore-micropore", which generates strong capillary force, which is the basis for achieving high load and leakage prevention.

[0075] After encapsulation with PEG, the morphology changed significantly. For example... Figure 5 As shown in (a), the surface of the BTV-P sample is completely covered by a relatively smooth molten PEG layer, and the aerogel pores are filled. However, after the addition of BT, a large number of BT sheets appear on the surface of the BTV-BP sample, and the roughness increases, as shown in (a). Figure 5 As shown in (b). Under high magnification SEM, as... Figure 5 As shown in (c), BT sheets and PEG molecules are tightly bonded together through hydrogen bonds and other interactions, forming a unique "fish-scale" intercalation structure on the fiber surface. Figure 5 (d) Further, the composite structure formed by BT and PEG is tightly attached to the skeleton and forms an effective seal in the pores.

[0076] 2. Thermal performance analysis.

[0077] (1) Phase transition behavior and undercooling suppression: The melting and crystallization temperatures of the material were tested by DSC, and the results are as follows: Figure 6 As shown, the peak melting temperature (Tm) of pure PEG is 64.1 °C, the initial crystallization temperature (Tf) is 44.0 °C, and the supercooling (ΔT) is as high as 20.1 °C. The Tm of all composite materials decreased slightly, which is attributed to the accelerated heat transfer caused by the high thermal conductivity nanonetwork constructed from V2C MXene and TiN immobilized on the aerogel framework. Notably, the supercooling (ΔT) of the BT-added sample (BTV-BP) decreased to 18.0 °C, which is significantly lower than that of the BT-free BTV-P sample (supercooling 19.8 °C) and pure PEG (supercooling 20.1 °C). This indicates that the BT sheets dispersed in PEG provide abundant heterogeneous nucleation sites, effectively reducing the nucleation energy barrier of PEG, promoting the crystallization process, and facilitating the rapid and controllable release of latent heat.

[0078] (2) Thermal conductivity: The thermal conductivity test results are as follows Figure 7 As shown, pure PEG has extremely low thermal conductivity, only 0.06 W·m. -1 ·K -1 After introducing TiN (BTA-BP) or MXene (BVA-BP), the thermal conductivity increased to 0.16 and 0.24 W·m, respectively. -1 ·K -1When MXene and TiN are used together to construct a gradient thermal conductivity network (BTV-P), the thermal conductivity is further improved to 0.29 W·m. -1 ·K -1 This is thanks to the large-size MXene providing a two-dimensional thermally conductive surface, while the small-size TiN particles fill the gaps, creating "thermal bridges" that allow for rapid, long-distance heat transfer, significantly reducing thermal resistance. The addition of BT (BTV-BP) resulted in a slight increase in thermal conductivity (0.32 W·m). -1 ·K -1 It is speculated that the BT sheets also form auxiliary heat conduction paths within the PEG matrix. The final thermal conductivity of BTV-BP is 433% higher than that of pure PEG, greatly improving thermal management efficiency.

[0079] 3. Leakage prevention and crystallization rate test

[0080] (1) Leakage prevention performance: To evaluate the leakage prevention performance of the composite phase change material, pure PEG, BT-BP, BV-BP, BTV-P, BTV-BP, and BTV-BPO samples were weighed (initial mass recorded as m0) and placed in an 80℃ forced-air oven for 1 hour. The samples were observed periodically during heating. After heating, the samples were removed, allowed to cool naturally, and then weighed again (mass recorded as m1). The leakage loss rate (LLr) was calculated to quantitatively evaluate the leakage situation. The calculation formula is as follows.

[0081] .

[0082] Leakage of composite materials of different components after heating for different times, as follows Figure 9 As shown. Further testing of leakage rate and retention rate yielded the following results: Figure 10 As shown, pure PEG completely melted and leaked within 30 minutes, with a leakage rate of 100%. After aerogel encapsulation and hydrophobic treatment (BTV-P), the leakage rate was significantly reduced to 4.83%. Figure 11 As shown, in the BTV-P sample, PEG is attached to the surface of the aerogel framework in a molten state, and its interface is relatively smooth. This indicates that relying solely on physical encapsulation and hydrophobic treatment is insufficient to confine the molten PEG. However, in the BTV-BP sample, which simultaneously introduces BT and a hydrophobic layer, the leakage rate is further reduced to 1.81%. This is attributed to a triple synergistic mechanism: capillary confinement of the multi-level pores of the aerogel, the robust fish-scale structure formed by the intercalation of BT / PEG and the physical "pore-blocking" effect formed by microencapsulated aggregates scattered in the pores, and the enhanced capillary effect due to the repulsive effect of the OTS hydrophobic layer on the molten PEG.

[0083] like Figure 12 As shown, a more complex confined structure forms inside the BTV-BP sample: such as Figure 12As shown in (a), BT and PEG form a "fish scale" composite structure on the fiber surface; as Figure 12 As shown in (b), the pores exhibit a "pore-blocking" effect caused by BT / PEG aggregates; as Figure 12 As shown in (c) and (d), the tight adhesion morphology of the composite structure under different perspectives is further demonstrated. These microscopic features together constitute the basis for the excellent leak-proof performance of the BTV-BP sample.

[0084] (2) Crystallization rate: To visually evaluate the effect of BT on the crystallization rate of PEG, the following test was conducted: Two 30 mL aliquots of pure PEG solution were heated in a 65°C water bath, and 0.1 g of BT was added to one of them. Both were stirred at 800 rpm and sonicated to ensure complete melting and uniformity of the samples. Subsequently, both samples were simultaneously and rapidly poured into petri dishes, cooled under the same environmental conditions, and their crystallization process was recorded using a camera.

[0085] The results are as follows Figure 8 As shown, under the same cooling conditions, the BT / PEG suspension began to crystallize at the edges after 15 seconds, while pure PEG did not show obvious crystal nuclei until 90 seconds. The addition of BT increased the crystallization rate by about 5 times, which is consistent with the conclusion of increased Tf in the DSC test, proving the role of BT as a highly efficient heterogeneous nucleating agent.

[0086] 4. Analysis of photothermal conversion and thermal storage performance.

[0087] (1) Light absorption capacity: such as Figure 13 (a) shows that pure PEG hardly absorbs light. After the introduction of photothermal components, the absorption rate is greatly improved. The sample containing both TiN and MXene shows strong absorption across the entire solar spectrum, laying the foundation for efficient photothermal conversion.

[0088] (2) Photothermal-storage behavior: A solar simulator (CME-X300F) was used at 1.5 kW / m². 2 The sample was irradiated at a specific intensity, and the surface temperature change was recorded every 5 seconds using a thermocouple (YET-620L). Irradiation continued for 1 hour until the temperature stabilized, after which the irradiation was stopped, and the natural cooling process was recorded. The test results are as follows: Figure 13As shown in (b), the temperature of pure PEG only rose to 35.3℃, not reaching the phase transition point, and rapidly decreased to room temperature after the light exposure was stopped. In contrast, the surface temperature of BTV-BP rapidly rose above the melting point of PEG within 5 minutes, reaching a maximum of 95.3℃. Its heating curve exhibited a typical phase transition plateau, indicating that the absorbed solar energy was efficiently converted into latent heat storage. After the light exposure was stopped, the cooling curve of BTV-BP showed a clear plateau around 45℃, corresponding to the exothermic solidification process of PEG. Even after 30 minutes, the temperature remained above 41℃, demonstrating excellent heat storage and insulation capabilities. Figure 14 As shown, the sample with 0.1g BT (approximately 0.43% by mass) added exhibited the fastest heating rate and the earliest phase change exothermic plateau during cooling. Both excessively high and low BT content led to performance degradation, thus determining the optimal range for BT addition.

[0089] 5. Verification of solar photovoltaic-thermal-electric conversion applications.

[0090] A solar thermal-electric conversion (STEG) system was built for testing. The BTV-BP sample was placed at the hot end of the thermoelectric generator (TEG), and the cold end was connected to an active water-cooled radiator.

[0091] At 1.5 kW / m 2 Under sunlight, the system's power generation performance is as follows: Figure 15 As shown. Among them, as Figure 15 (a) and Figure 15 (b) shows the output voltage and current curves over time for the blank control group and the BTV-BP system, respectively. It can be seen that the blank control group (TEG hot end without heat storage material) rapidly reached its peak voltage and current (94.1 mV, 10.6 mA) and then stabilized, dropping sharply upon cessation of illumination. In contrast, the BTV-BP system, after an initial rapid increase in voltage and current, exhibited a change in the upward slope due to the emergence of a phase change endothermic plateau, but continued to increase until reaching an even higher peak (156.5 mV, 18.6 mA), with output increases of 66.4% and 75.5%, respectively. More importantly, after cessation of illumination, the voltage and current curves of the BTV-BP system did not immediately drop, but rather exhibited a slow downward plateau as the latent heat of the material's phase change was released, achieving continuous power output under no-illumination conditions.

[0092] To visually demonstrate its continuous power supply capability, the system was connected to an LED light panel for demonstration. Under illumination, the light panel was successfully lit and gradually reached its maximum brightness. After the illumination was stopped, the light panel continued to emit light for up to 95 seconds, relying on the stored heat energy released by the BTV-BP. This fully demonstrates the application potential of this composite material in achieving solar energy peak shaving and valley filling, and continuous and stable power supply.

[0093] 6. Surface wettability and environmental adaptability.

[0094] like Figure 16 As shown in (a), water droplets rapidly wet the unhydrophobic BTV-BPO surface. Figure 16 As shown in (b), its water contact angle (WCA) measurement is 0°, indicating complete hydrophilicity. After OTS modification, as... Figure 16 As shown in (c), BTV-BP exhibits superhydrophobicity at room temperature, with a WCA of 151°, and displays a silver mirror effect in water. Figure 16 As shown in (d), even under heating conditions at 65°C (above the phase transition temperature), the surface water droplet morphology, thermal infrared image, and WCA measurement (142°) of BTV-BP all demonstrate its excellent thermally stable hydrophobic properties. Figure 16 As shown in (e), the dynamic behavior of water droplets on the material surface indicates that their adhesion is extremely low. This property is key to achieving self-cleaning.

[0095] This superhydrophobicity endows the material with excellent self-cleaning properties. For example... Figure 17 (a) and Figure 17 As shown in the comparison in (b), when the surface is contaminated with dust, water droplets can easily roll off and carry away all contaminants, keeping the surface clean. Combined with its excellent leak-proof and heat-resistant properties, this demonstrates that the BTV-BP composite material can adapt well to complex outdoor environments such as humidity, rain, and dust, and possesses the reliability for practical applications.

[0096] In summary, this invention successfully prepared a multifunctional, synergistic, high-performance composite phase change material by carefully designing and integrating a porous bacterial cellulose aerogel framework, an MXene / TiN gradient photothermal network, bentonite for promoting crystallization and preventing leakage, and a hydrophobic surface layer. This material effectively solves the problems of severe leakage, poor thermal conductivity, low photothermal conversion efficiency, and high supercooling associated with traditional PEG materials. It has been successfully applied to solar photovoltaic (PVP) systems, achieving efficient energy capture, storage, and gradient utilization, and has broad application prospects in the renewable energy field.

[0097] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A bentonite-regulated solar-driven light-heat-electricity conversion composite phase change material, characterized in that, include: Bacterial cellulose aerogel framework; V2C MXene and TiN nanoparticles were fixed on the aerogel framework through cross-linking and stepwise assembly. A composite phase change material with polyethylene glycol as the matrix and bentonite intercalation adsorption dispersed therein; specifically, based on the mass of the polyethylene glycol, the mass percentage of the bentonite is 0.2-1.9%; The composite phase change material is encapsulated within the multi-level pores of the aerogel; The surface of the aerogel framework has a hydrophobic modification layer; The preparation method of the above-mentioned composite phase change material includes the following steps: (1) Preparation of V2C MXene powder: V2AlC precursor powder was added to hydrofluoric acid solution and etched under stirring conditions. After the reaction was completed, it was washed until neutral and dried to obtain V2C MXene powder. (2) Preparation of BC / MXene / TiN composite wet gel: V2C MXene powder obtained in step (1) is mixed with bacterial cellulose BC dispersion, and then methyltrimethoxysilane (MTMS) is added to carry out cross-linking reaction to obtain BC / MXene pre-cross-linked gel; then titanium nitride (TiN) nanoparticles are added to the BC / MXene pre-cross-linked gel and dispersed evenly to obtain BC / MXene / TiN composite sol; the composite sol is pre-frozen to obtain BC / MXene / TiN composite wet gel; (3) Preparation of BC / MXene / TiN aerogel framework: The BC / MXene / TiN composite wet gel obtained in step (2) is pre-frozen and then freeze-dried to obtain the BC / MXene / TiN aerogel framework. (4) Preparation of BT / PEG composite phase change precursor liquid: Bentonite BT powder is dispersed in molten polyethylene glycol (PEG) to form a uniform BT / PEG composite phase change precursor liquid; (5) Vacuum impregnation and encapsulation: The BC / MXene / TiN aerogel skeleton obtained in step (3) is immersed in the BT / PEG composite phase change precursor liquid obtained in step (4) and impregnated under vacuum and heating conditions, so that the precursor liquid penetrates into the multi-level channels of the aerogel. Then, excess PEG on the surface is removed to obtain the encapsulated composite phase change material precursor. (6) Hydrophobic modification: The encapsulated composite phase change material precursor obtained in step (5) is immersed in an organic solution of trichlorooctadecylsilane (OTS), taken out and dried to form a hydrophobic layer on the surface of the material, thus obtaining the composite phase change material.

2. The composite phase change material of claim 1, wherein, The TiN nanoparticles have a particle size of 20 nm.

3. The composite phase change material of claim 1, wherein, The aerogel framework has a multi-level pore structure consisting of macropores, mesopores, and micropores, with a pore size distribution of 1.5-2 nm micropores, 2-50 nm mesopores, and 70 μm macropores.

4. A method of producing a composite phase change material as claimed in any one of claims 1 to 3, characterised in that, Includes the following steps: (1) Preparation of V2C MXene powder: V2AlC precursor powder was added to hydrofluoric acid solution and etched under stirring conditions. After the reaction was completed, it was washed until neutral and dried to obtain V2C MXene powder. (2) Preparation of BC / MXene / TiN composite wet gel: V2C MXene powder obtained in step (1) is mixed with bacterial cellulose BC dispersion, and then methyltrimethoxysilane (MTMS) is added to carry out cross-linking reaction to obtain BC / MXene pre-cross-linked gel; then titanium nitride (TiN) nanoparticles are added to the BC / MXene pre-cross-linked gel and dispersed evenly to obtain BC / MXene / TiN composite sol; the composite sol is pre-frozen to obtain BC / MXene / TiN composite wet gel; (3) Preparation of BC / MXene / TiN aerogel framework: The BC / MXene / TiN composite wet gel obtained in step (2) is pre-frozen and then freeze-dried to obtain the BC / MXene / TiN aerogel framework. (4) Preparation of BT / PEG composite phase change precursor liquid: Bentonite BT powder is dispersed in molten polyethylene glycol (PEG) to form a uniform BT / PEG composite phase change precursor liquid; (5) Vacuum impregnation and encapsulation: The BC / MXene / TiN aerogel skeleton obtained in step (3) is immersed in the BT / PEG composite phase change precursor liquid obtained in step (4) and impregnated under vacuum and heating conditions, so that the precursor liquid penetrates into the multi-level channels of the aerogel. Then, excess PEG on the surface is removed to obtain the encapsulated composite phase change material precursor. (6) Hydrophobic modification: The encapsulated composite phase change material precursor obtained in step (5) is immersed in an organic solution of trichlorooctadecylsilane (OTS), taken out and dried to form a hydrophobic layer on the surface of the material, thus obtaining the composite phase change material.

5. The preparation method according to claim 4, characterized in that, In step (5), the vacuum impregnation temperature is 65°C and the time is 3 hours.

6. The production method according to claim 4, wherein The concentration of the trichlorooctadecylsilane solution used in step (6) for hydrophobic modification is 1%, and the solvent is n-hexane.

7. Use of a composite phase change material according to any one of claims 1 to 3 in a solar-thermal-electric energy conversion system, characterized in that, The material, as a photothermal conversion and heat storage unit, is combined with a thermoelectric generator to construct a photo-thermal-electric conversion system.

8. Use according to claim 7, wherein the compound is ###0002### Thermally conductive interface materials are provided between the thermoelectric generator and the composite phase change material, as well as between the thermoelectric generator and the heat dissipation device, and the heat dissipation device is an active water circulation heat dissipation system.

9. The use according to claim 7, wherein the compound is ###00006### The system is configured to continue driving the thermoelectric generator to output electrical energy after the light source is turned off, using the latent heat of phase change released by the composite phase change material.

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