Spectrally selective solar energy phase change heat storage material and preparation method thereof

Abstract

The application discloses a kind of solar spectrum selective phase change heat storage materials and preparation method thereof, the material is composed of two layers of materials, bottom layer is porous silicon carbide material filled with phase change material, top layer is plasmonic nanomaterial foil;Preparation method is as follows: (1) porous silicon carbide material is filled with phase change material;(2) plasmonic nanomaterial foil is superimposed on the upper surface of porous silicon carbide material filled with phase change material.The application combines porous silicon carbide material filled with phase change material and plasmonic nanomaterial foil, improves the absorption efficiency in the solar spectrum range, while inhibiting the loss of infrared radiation.

Description

Technical Field

[0001] This invention relates to an energy storage material and its preparation method, and particularly to a spectrally selective solar phase change thermal storage material and its preparation method. Background Technology

[0002] With the continued growth of global energy demand and the increasing severity of environmental problems, the development of efficient and environmentally friendly energy storage technologies has become a key research focus. Solar energy, as a clean and renewable energy source, has broad application prospects. However, how to efficiently capture, store, and utilize solar energy remains a significant technological challenge that urgently needs to be addressed.

[0003] Solar phase change energy storage materials directly capture and store solar energy through a phase change process. However, the low spectral absorbance of phase change materials themselves leads to insufficient photothermal conversion efficiency. To address this issue, researchers have extensively explored methods of incorporating hyperspectral absorption nanoparticles into phase change materials to improve their spectral absorption characteristics. These nanoparticles mainly include carbon nanoparticles, metal nanoparticles, and ceramic nanoparticles, which enhance the full-spectrum absorbance of phase change materials, thereby improving solar energy storage efficiency.

[0004] Current research primarily focuses on enhancing the full-spectrum absorption of phase change materials (PCMs) by adding high-absorption-rate nanoparticles. However, research on suppressing the infrared emissivity of PCMs is relatively limited, especially in high-temperature applications. Infrared radiation loss is significant under high-temperature conditions, leading to substantial heat loss and severely impacting the overall efficiency of solar phase change thermal storage. Therefore, while improving the full-spectrum absorption of PCMs, suppressing infrared emissivity is crucial for enhancing solar thermal storage efficiency. Effectively addressing this issue will have a profound impact on the application of solar phase change thermal storage materials under high-temperature conditions. Summary of the Invention

[0005] Objectives of the invention: The first objective of this invention is to provide a solar phase change thermal storage material that can suppress the spectral selectivity of the infrared emissivity of the phase change material; the second objective of this invention is to provide a method for preparing the spectrally selective solar phase change thermal storage material.

[0006] Technical solution: The spectrally selective solar phase change thermal storage material of the present invention consists of two layers of materials. The bottom layer is a porous silicon carbide material (porous silicon carbide ceramic skeleton) filled with phase change material, and the top layer is a plasma nano metal foil.

[0007] Combining porous silicon carbide materials filled with phase change materials with plasma nano-metal foil improves absorption efficiency across the solar spectrum. At the same time, infrared emissivity was suppressed. This further improves the efficiency of solar phase change thermal storage.

[0008] Preferably, the porosity of the porous silicon carbide material is 74%–83%. Porosity plays a crucial role in the heat storage and release processes of porous silicon carbide-based composite phase change materials. Lower porosity helps promote heat conduction, thereby increasing the heat transfer rate, but leads to a decrease in energy storage density; higher porosity is beneficial for increasing the loading of the phase change material, thereby increasing the heat storage density, but it reduces the heat transfer rate. Experiments show that the heat storage performance is optimal when the porosity of the porous silicon carbide is 74%–83%.

[0009] Preferably, the plasma nano-metal foil is a zinc foil loaded with copper nanoparticles.

[0010] More preferably, the copper nanoparticles loaded on the zinc foil have a particle size of 60–70 nm. Variations in the size of the copper nanoparticles significantly affect the optical properties of the material, influencing its average spectral absorbance and infrared emissivity. Research results show that when the particle size of the copper nanoparticles is 60–70 nm, the highest spectral absorbance and lowest infrared emissivity can be obtained.

[0011] Preferably, the phase change material is bis(quaternary tetrapentacol). Other phase change materials can be used instead of bis(quaternary tetrapentacol), such as all organic phase change materials, but the final calculated efficiency will vary depending on the different phase change materials.

[0012] Preferably, the porous silicon carbide ceramic framework is generated by impregnating graphite carbon felt with phenolic resin, carbonizing it, and then reacting it with silicon. By using graphite carbon felt-phenolic resin as a precursor to prepare the silicon carbide framework, the porosity of the material can be flexibly controlled.

[0013] The method for preparing the spectrally selective solar phase change thermal storage material of the present invention includes the following steps:

[0014] (1) Filling porous silicon carbide material with phase change material;

[0015] (2) Plasma nano-metal foil is superimposed on the surface of porous silicon carbide material filled with phase change material.

[0016] Preferably, the method for preparing the porous silicon carbide material-filled phase change material is as follows:

[0017] Ⅰ. Clean and dry the graphite carbon felt, then impregnate it in a phenolic resin solution, and subsequently carbonize it;

[0018] II. Take a sufficient amount of silicon powder and react it with the graphite carbon felt carbonized in step I to generate silicon carbide; remove the excess silicon to obtain a porous silicon carbide ceramic skeleton derived from graphite carbon felt.

[0019] III. Using a vacuum impregnation method, bis(quaternary tetrapentayl alcohol) is filled into the pores of the porous silicon carbide ceramic skeleton obtained in step II, thus obtaining a graphite carbon felt-derived porous silicon carbide ceramic-based composite phase change material.

[0020] Preferably, the cleaning method for the graphite carbon felt is as follows: the graphite carbon felt is cleaned sequentially with ethanol and deionized water.

[0021] Preferably, the phenolic resin solution is obtained by dissolving phenolic resin in an ethanol solution and mechanically stirring until homogeneous.

[0022] Preferably, the solid content of the phenolic resin solution is 60-70 wt%. By adjusting the concentration of the phenolic resin in the impregnated graphite carbon felt, porous silicon carbide materials with different porosities can be obtained. Experiments show that when the solid content of the phenolic resin is controlled at 60% to 70%, the optimal porosity (74% to 83%) can be obtained.

[0023] Preferably, in step I, the carbonization process is carried out in a tube furnace, and the process parameters of the carbonization process are: argon atmosphere, heating rate of 1-3℃ / min, carbonization temperature of 900-1100℃, and holding time of 0.5-1 hour.

[0024] Preferably, in step II, the reaction of the carbonized graphite carbon felt to generate silicon carbide is as follows: take sufficient silicon powder and react it with the carbonized graphite carbon felt in a vacuum environment at a temperature of 1550-1600°C for 1.5-2 hours to generate silicon carbide; and sinter it at a temperature of 1800-1850°C for 2 hours. Repeat this process to remove excess silicon and obtain a porous silicon carbide skeleton derived from graphite carbon felt.

[0025] Preferably, in step III, the vacuum impregnation method is as follows: the porous ceramic skeleton and the diquaternary tetrapentacol phase change material are placed in a tube furnace, heated to 230°C to 250°C, and kept at this temperature for 1.5 to 2 hours under a vacuum atmosphere, so that the diquaternary tetrapentacol fills the pores of the porous silicon carbide ceramic skeleton.

[0026] Preferably, the plasma nano-metal foil is a zinc foil loaded with copper nanoparticles. The preparation method is as follows: after cleaning the zinc foil, it is immersed in a copper ion solution to undergo a displacement reaction, generating copper nanoparticles on the zinc foil surface. After the reaction is complete, the zinc foil is quickly placed in deionized water to terminate the chemical reaction. After drying, a solar-absorbing plasma nano-metal foil with spectral selectivity is obtained. In the displacement reaction, Cu... 2+ The concentration was 0.012M to 0.016M, the reaction temperature was 25℃ to 60℃, and the reaction time was 30 to 45 seconds.

[0027] Preferably, the zinc foil cleaning process involves ultrasonically cleaning the zinc foil sequentially in a sulfuric acid solution, deionized water, acetone solution, and deionized water. The process parameters are as follows: the zinc foil is ultrasonically cleaned in a 2-2.5 wt% sulfuric acid solution for 20-30 seconds, and then cleaned in acetone or ethanol for 5-10 minutes.

[0028] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) By combining porous silicon carbide material filled with phase change material and plasma nano metal foil, the absorption efficiency in the solar spectrum range is improved, while the infrared radiation loss is suppressed; (2) The graphite carbon felt-derived silicon carbide skeleton provides good thermal conductivity, ensuring effective heat transfer and storage; (3) Diquaternary tetrapentanol is filled in the porous silicon carbide ceramic skeleton as a phase change material, providing excellent phase change heat storage performance, and can efficiently store and release heat energy during temperature changes; (4) Copper nanoparticles loaded on zinc foil as plasma nano metal foil increase the spectral selective absorption characteristics of the material, especially the suppression performance in the infrared band, while having a high spectral absorption rate. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the preparation process of the spectrally selective solar phase change thermal storage material described in this invention;

[0030] Figure 2 This is a schematic diagram of the structure of the spectrally selective solar phase change thermal storage material in Example 2. The material includes a graphite carbon felt-derived silicon carbide framework, bis(quaternary tetrapentayl alcohol), and plasma nano-metal foil.

[0031] Figure 3 The diagram shows the structure of the spectrally selective solar phase change thermal storage material without plasma nano-metal foil in Comparative Example 1. The material includes a graphite carbon felt-derived silicon carbide framework and bis(quaternary tetrapentayl alcohol).

[0032] Figure 4 This is a schematic diagram of the preparation process of plasma nano-metal foil;

[0033] Figure 5 The images show the structural morphology of copper nanoparticles in Examples 2, 3, and 4.

[0034] Figure 6 Thermal conductivity diagrams for Examples 1 and 2;

[0035] Figure 7 The graph shows the enthalpy test results for Comparative Examples 1 and 2.

[0036] Figure 8 These are spectral comparison diagrams for Examples 2, 3, and 4;

[0037] Figure 9The spectral comparison diagrams are of Example 2, Comparative Example 1, and Comparative Example 2;

[0038] Figure 10 This is a comparison graph of the temperature rise curves of Example 2 and Comparative Example 1 under sunlight irradiation. Detailed Implementation

[0039] The technical solution of the present invention will be further described below with reference to the embodiments.

[0040] Example 1

[0041] The preparation of the spectrally selective solar phase change thermal storage material of the present invention includes the following steps:

[0042] 1. Preparation of porous silicon carbide ceramics derived from graphite carbon felt:

[0043] (1) The graphite carbon felt was washed with ethanol and deionized water in sequence and then dried;

[0044] (2) Dissolve the phenolic resin in an ethanol solution and stir mechanically until homogeneous to obtain a phenolic resin solution with a solid content of 60%.

[0045] (3) The graphite carbon felt is impregnated in a phenolic resin solution to fill the pores with phenolic resin, and then placed in a tube furnace for carbonization. The process parameters for carbonization are: argon atmosphere, heating rate of 1℃ / min, carbonization temperature of 900℃, and holding time of 0.5 hours.

[0046] (4) Take a sufficient amount of silicon powder and place it in a vacuum environment with the graphite carbon felt treated in step (3). React at 1600℃ for 1.5 hours to generate silicon carbide, and sinter at 1800℃ for 2 hours. Repeat this process 3 times to remove excess silicon and obtain a graphite carbon felt-derived porous silicon carbide skeleton.

[0047] 2. Preparation of graphite carbon felt-derived porous silicon carbide ceramic-based composite phase change materials:

[0048] (1) The graphite carbon felt-derived porous silicon carbide framework obtained in step 1 above and the diquaternary tetrapentayl alcohol phase change material are placed in a tube furnace.

[0049] (2) The bis(quaternary tetrapentanol) is filled into the pores of the porous silicon carbide ceramic skeleton by vacuum impregnation method to obtain the graphite carbon felt-derived porous silicon carbide ceramic-based composite phase change material; the process parameters are: the porous silicon carbide ceramic and the bis(quaternary tetrapentanol) are placed in a tube furnace, heated to 250°C, and kept at the temperature for 2 hours in a vacuum atmosphere.

[0050] 3. Preparation of plasma-enhanced nano-metal foil:

[0051] (1) The zinc foil was ultrasonically cleaned in sulfuric acid solution, deionized water, acetone solution and deionized water in sequence. The process parameters were: the zinc foil was ultrasonically cleaned in 2.5% sulfuric acid solution for 30 seconds and cleaned in acetone for 5 minutes.

[0052] (2) The cleaned zinc foil is immersed in a copper sulfate solution to undergo a displacement reaction, and copper nanoparticles are generated on the surface of the zinc foil. The concentration of the copper sulfate solution is 0.016M, the reaction temperature is 60℃, and the reaction time is 30 seconds.

[0053] (3) After the reaction is complete, the zinc foil is quickly placed into deionized water to terminate the chemical reaction. After drying, a solar energy absorbing material with spectral selectivity is obtained.

[0054] (4) Plasma nano metal foil is placed on the top surface of the graphite carbon felt-derived porous silicon carbide ceramic-based composite phase change material prepared in step 2 above to obtain the spectrally selective solar thermal storage material named SiC / PCMs / PNC.

[0055] Example 2

[0056] Based on Example 1, the solid content of phenolic resin in step 1 was changed to 70 wt%, while the other conditions remained unchanged.

[0057] Example 3

[0058] Based on Example 2, the reaction temperature of copper sulfate solution and zinc sheet in step 3 was changed to 20°C, while the other conditions remained unchanged.

[0059] Example 4

[0060] Based on Example 2, the reaction temperature of copper sulfate solution and zinc sheet in step 3 was changed to 40°C, while the other conditions remained unchanged.

[0061] Comparative Example 1

[0062] Based on Example 2, step 3 is omitted, and all other conditions remain unchanged. The resulting product is then named SiC / PCMs.

[0063] Comparative Example 2

[0064] The bis(quaternary tetrapentanol) phase change material PCMs were used without any other spectral or thermal conductivity enhancement treatments.

[0065] Comparative Example 3

[0066] Based on Example 2, steps 1 and 2 are omitted, and the pure phase change material bis(quaternary tetrapentapentol) is composited with the plasma nano-metal foil of step 3.

[0067] 1. Morphology characterization of copper nanoparticles

[0068] The morphology of the copper nanoparticles in Examples 2, 3, and 4 was characterized using a field emission scanning electron microscope (GeminiSEM 300) equipped with a backscattered electron detector. The results are as follows: Figure 5 As shown.

[0069] Depend on Figure 5 As can be seen from Comparative Examples 2, 3, and 4, when the reaction temperature increases from 20°C to 60°C, the average diameter of the copper nanoparticles increases from about 30 nanometers to about 70 nanometers.

[0070] 2. Thermal conductivity test

[0071] The thermal conductivity of Examples 1 and 2 was tested, and the thermal diffusivity of the samples was measured using the laser flash analysis method (Linseis, LFA500). The results are as follows: Figure 6 As shown.

[0072] The formula for calculating thermal diffusivity is α = ωL 2 / πt 1 / 2 Where α is the thermal diffusivity, L is the sample thickness, ω is a constant determined by the Clark and Taylor approximation, and t 1 / 2 This is the time required for the back side of the sample to reach half of its maximum temperature. Combining the density ρ(T) of the porous silicon carbide ceramic, the porosity of the sample can be determined by measuring the sample's weight and volume, calculated using the formula P(%) = (1 - ρ1 / ρ SiC )·100%, where ρ1 is the density of the prepared porous silicon carbide sample, ρ SiC The density of dense silicon carbide. Specific heat capacity C. p (T) can be obtained by differential scanning calorimetry (DSC). The thermal conductivity of the material can then be calculated.

[0073] k(T)=α(T)·C p (T)·ρ(T) (1)

[0074] The calculated porosities of the porous materials prepared in Examples 1 and 2 were 83% and 74%, respectively. When the porosity was 74%, the thermal conductivity was 14.0 W / m². -1 K -1 When the porosity is 83%, the thermal conductivity is 3.7 W / m. -1 K -1 .

[0075] 3. Phase transition enthalpy test:

[0076] The phase transition enthalpy values ​​of comparative examples 1 and 2 were tested. The specific heat capacity and phase transition enthalpy of the samples were measured using differential scanning calorimetry (TA, DSC 25).

[0077] Figure 7 The DSC enthalpy test results are shown for the PCMs of Comparative Example 2 and the SiC / PCMs composite material of Comparative Example 1. The test results show that the melting peak temperature of the PCMs is 224.28℃, corresponding to an enthalpy change of 374.00 kJ / kg. -1 Its solidification peak temperature is 200.99℃, corresponding to an enthalpy change of 370.94 kJ / kg. -1 After being combined with silicon carbide, the enthalpy values ​​of the melting and solidification processes of SiC / PCMs are 195.10 kJ kg, respectively. -1 and 176.60 kJ kg -1 The enthalpy values ​​of the SiC / PCMs composite materials in Examples 2-4 are the same as those of the SiC / PCMs composite material in Comparative Example 1, and the enthalpy values ​​are independent of the plasma metal foil.

[0078] 4. Spectral characteristics test:

[0079] The spectral properties of Examples 2-4, Comparative Example 1, and Comparative Example 2 were tested. The solar spectral absorption characteristics of the samples were measured using a UV-Vis-NIR spectrophotometer (LAMBDA1050+). Under normal incidence conditions, the spectral absorbance of the composite material in the wavelength range of 0.2 μm to 16 μm was measured, and the test results are as follows. Figure 8 and 9 As shown.

[0080] Depend on Figure 8 The average solar spectral absorptivity of Examples 2-4 were 90.57%, 62.27%, and 85.29%, respectively, and the average infrared spectral emissivity were 7.47%, 8.23%, and 8.02%, respectively. This shows that the solar spectral absorptivity gradually increases as the size of the copper nanoparticles increases from 30 nm to 70 nm. This indicates that the reaction temperature has a significant impact on the size of the copper nanoparticles and their corresponding optical properties.

[0081] from Figure 9It can be seen that the spectral characteristics of Example 2 differ significantly from those of Comparative Examples 1 and 2. For Comparative Example 2, the average solar spectral absorptivity of the pure phase change material is only 9.41%, and the infrared emissivity is 67.7%, indicating low absorptivity and difficulty in achieving effective solar energy capture. For Comparative Example 1, after the phase change material is combined with silicon carbide, the average solar spectral absorptivity of the SiC / PCMs composite material significantly increases to 91.22%. This significant increase in absorptivity is mainly attributed to the multiple light scattering effect within the porous structure of silicon carbide; however, the infrared emissivity of this composite material is high at 71.94%, leading to significant infrared radiation loss at high temperatures. In Example 2, the SiC / PCMs composite material is further combined with a plasmonic nanostructure to form a SiC / PCMs / PNC composite material, which has a solar spectral absorptivity of 90.57%, comparable to the SiC / PCMs composite material, but its infrared emissivity is significantly reduced to only 7.47%. By maintaining similar solar spectral absorptivity between SiC / PCMs / PNC and SiC / PCMs composites, the effect of significantly reducing infrared emissivity on improving thermal storage efficiency was verified.

[0082] 5. Thermal storage efficiency test

[0083] The temperature rise of Example 2 and Comparative Example 1 under direct sunlight was tested.

[0084] Test method: at a solar radiation intensity of 20 kW·m -2 The solar thermal storage efficiency of SiC / PCMs / PNC solar thermal storage materials containing plasma nano-metal foil and SiC / PCMs materials was tested after 240 seconds of solar radiation exposure. The formula for calculating solar thermal storage efficiency is:

[0085]

[0086] In the formula, η c For solar thermal conversion efficiency; η s The thermal energy storage efficiency depends on the thermal conductivity of the phase change thermal storage material; m is the mass of the phase change thermal storage material; ΔH is the latent heat of the phase change thermal storage material; P is the solar irradiance; and Δt is the duration of the phase change process. The test results are as follows: Figure 10 As shown.

[0087] Depend on Figure 10It can be seen that, under the same illumination conditions, the peak temperature of the SiC / PCMs / PNC material in Example 2 reached 251.68℃. In contrast, the highest temperature of the SiC / PCMs material in Comparative Example 1 under the same irradiation conditions was 228.42℃, with a temperature difference of 23.26℃. Furthermore, the experiment observed that the solar energy storage time of SiC / PCMs / PNC was only 48 seconds, significantly less than the 72 seconds of SiC / PCMs without infrared suppression, a reduction of approximately 1.5 times. Calculated using formula (2), the solar energy storage efficiency of the SiC / PCMs / PNC material in Example 2 was 81.65%, significantly better than the 54.56% of the SiC / PCMs material in Comparative Example 1. These results indicate that by suppressing infrared radiation loss, the solar energy storage efficiency of composite phase change materials can be significantly improved.

Claims

1. A spectrally selective solar phase change thermal storage material, characterized in that, The material consists of two layers: a bottom layer of porous silicon carbide filled with phase change material and a top layer of plasma nano-metal foil; the plasma nano-metal foil is a zinc foil loaded with copper nanoparticles; a layer of copper nanoparticles is loaded on the zinc foil, and the particle size of the copper nanoparticles is 60~70 nm.

2. The spectrally selective solar phase change thermal storage material according to claim 1, characterized in that, The porosity of the porous silicon carbide material is 74-83%.

3. The spectrally selective solar phase change thermal storage material according to claim 1, characterized in that, The phase change material is bisquaternary tetrapentacol.

4. A method for preparing a spectrally selective solar phase change thermal storage material according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Filling porous silicon carbide material with phase change material; (2) Plasma nano-metal foil is superimposed on the surface of porous silicon carbide material filled with phase change material.

5. The method for preparing the spectrally selective solar phase change thermal storage material according to claim 4, characterized in that, The method for preparing the porous silicon carbide-filled phase change material is as follows: Ⅰ. Clean and dry the graphite carbon felt, then immerse it in a phenolic resin solution, followed by carbonization; II. Take silicon powder and react it with the graphite carbon felt carbonized in step I in a vacuum environment at a temperature of 1550~1600℃ for 1.5~2h to generate silicon carbide, and sinter it at a temperature of 1800℃~1850℃ for 2 hours. Repeat this process to remove excess silicon and obtain a porous silicon carbide ceramic skeleton derived from graphite carbon felt. III. Using a vacuum impregnation method, bis(quaternary tetrapentayl alcohol) is filled into the pores of the porous silicon carbide ceramic skeleton obtained in step II, thus obtaining a graphite carbon felt-derived porous silicon carbide ceramic-based composite phase change material.

6. The method for preparing the spectrally selective solar phase change thermal storage material according to claim 5, characterized in that, The concentration of the phenolic resin solution is 60-70%.

7. The method for preparing the spectrally selective solar phase change thermal storage material according to claim 4, characterized in that, The plasma nano-metal foil is made by loading copper nanoparticles onto zinc foil. The preparation method is as follows: after cleaning the zinc foil, it is immersed in a copper ion solution, and copper nanoparticles are generated on the surface of the zinc foil through a displacement reaction, thus obtaining a plasma nano-metal foil with spectral selectivity for solar energy absorption.

8. The method for preparing the spectrally selective solar phase change thermal storage material according to claim 7, characterized in that, The displacement reaction conditions are: Cu 2+ The concentration was 0.012~0.016 M, the reaction temperature was 25~60℃, and the reaction time was 30~45 seconds.

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