Thermochemical energy storage composite material with bionic ordered structure and preparation method therefor

Abstract

The present invention relates to the interdisciplinary fields of new energy materials and thermochemical energy storage technology. Disclosed are a thermochemical energy storage composite material with a bionic ordered structure and a preparation method therefor. By means of an optimization strategy of the coordination of a "geometry-internal channel-surface effect", efficient adsorption / desorption kinetics and solar energy direct drive heat storage are realized. The thermochemical energy storage composite material comprises a matrix with a bionic multi-scale mass transfer structure and a hygroscopic inorganic salt, which is uniformly loaded inside the matrix, wherein the matrix is activated by KOH and is then loaded with the hygroscopic inorganic salt. The appearance of the matrix imitates that of a red blood cell, and the matrix has the shape of a single concave disc; and the inside of the matrix has a layered directional vein network imitating the shape of leaf veins. The present invention solves the problems of moisture absorption and caking, slow mass transfer and the low photothermal conversion efficiency of a traditional hydrated salt material, and provides a new solution for the efficient storage of renewable energy sources.

Description

A biomimetic ordered thermochemical energy storage composite material and its preparation method Technical Field

[0001] This invention relates to the interdisciplinary field of new energy materials and thermochemical energy storage technology, specifically to a biomimetic multi-scale mass transfer structure solar-driven thermochemical thermal storage composite material and its preparation method. Background Technology

[0002] With the development of the times, limited fossil energy resources cannot meet the ever-increasing energy demand, leading to energy and environmental crises. Promoting the development and utilization of renewable energy is an important means of increasing supply and can effectively solve the above problems. Renewable energy sources such as solar, wind, and biomass energy are inexhaustible. Promoting their utilization will facilitate the green and low-carbon transformation and sustainable development of the economy and society, and make a positive contribution to achieving the important strategic goals of "carbon peaking" and "carbon neutrality" in the country. However, renewable energy sources such as solar energy are intermittent and unstable, requiring efficient energy storage technologies to transfer energy in time or space to match supply and demand. Among various energy storage technologies, hydrated salt thermochemical energy storage has attracted much attention due to its high energy density, low heat loss, safety, and environmental friendliness. However, traditional hydrated salt materials suffer from bottlenecks such as moisture absorption and agglomeration, high mass transfer resistance, and low photothermal conversion efficiency. Existing research has achieved rich results by loading salts onto porous matrices such as silica gel, zeolite, and natural minerals to improve performance. However, the matrices are spherical or irregular in shape, and the internal channels are mostly disordered, resulting in long mass transfer paths, high mass transfer resistance, and a lack of photothermal synergistic design.

[0003] Currently, no technology can provide a device or method that simultaneously considers external shape, internal channels, and photothermal synergy. To overcome the problems faced by traditional designs, many scholars have drawn inspiration from nature. For example, the biconcave disc-shaped morphology of red blood cells and the hierarchical channels of leaf veins are naturally selected, highly efficient gas exchange and nutrient transport systems with unique advantages in material transport and energy transfer, providing inspiration for structural optimization. However, existing technologies have not yet effectively incorporated such biomimetic designs. Summary of the Invention

[0004] To address the above problems, this invention proposes a biomimetic ordered thermochemical energy storage composite material and its preparation method. Through a synergistic optimization strategy of "geometry-internal channels-surface effects", it achieves efficient adsorption / desorption kinetics and direct solar-driven thermal storage.

[0005] The material's structural design has the following characteristics:

[0006] In terms of geometry, the shape of this design is biomimetic to that of a red blood cell, with a single concave disc shape, a diameter of about 1.5 mm, a thickness of about 0.7 mm, a large surface area to body volume ratio, and a short mass transfer path.

[0007] From the perspective of internal channels, the biomimetic leaf vein-like layered directional vein network of this case includes: a main vein that divides the matrix into upper and lower halves along the thickness direction, and several branch veins distributed on the upper and lower sides of the main vein. Mass transfer channels are formed between adjacent branch veins. The mass transfer channels located in the center of the main vein are perpendicular to it, while the mass transfer channels in other positions have an angle of 0-90° with the main vein, and the angle gradually increases from the edge of the matrix.

[0008] Furthermore, after activation with KOH, several nanopores are generated in the main and branch pulse paths, giving it a large specific surface area and low mass transfer resistance.

[0009] From a surface effect perspective, this design introduces oxygen-containing functional groups such as hydroxyl groups after KOH activation, making the inherently hydrophobic carbon material hydrophilic, which is beneficial for salt loading. Furthermore, the material is black and exhibits good photothermal conversion properties.

[0010] In terms of functional composite, this invention uniformly distributes calcium chloride in the matrix, with a salt content of 20-50%, and the spectral absorbance after loading is still greater than 95%, exhibiting good adsorption capacity and photothermal desorption performance.

[0011] To achieve the above characteristics, the technical solution of the present invention is as follows:

[0012] The thermochemical energy storage composite material includes a biomimetic multi-scale mass transfer structure matrix and hygroscopic inorganic salt uniformly loaded in the matrix. The matrix is ​​activated by KOH and then loaded with hygroscopic inorganic salt.

[0013] The shape of the substrate is biomimetic to that of a red blood cell, and is in the shape of a single concave disc. The interior of the substrate has a layered directional vein network that resembles leaf veins. The layered directional vein network includes a main vein that divides the substrate into upper and lower halves along the thickness direction, and several branch veins distributed on the upper and lower sides of the main vein, forming mass transfer channels between adjacent branch veins.

[0014] Furthermore, the mass transfer channels located in the center of the main vein are perpendicular to it, while the mass transfer channels at other locations have an angle of 0-90° with the main vein, and this angle gradually increases from the edge of the matrix.

[0015] The matrix also contains several nanopores generated after KOH activation along its main and branch veins. This results in an average spectral absorbance >95%, good hydrophilicity, and a specific surface area >900 m² / g.

[0016] The matrix is ​​a carbon material formed by dropping a DMF solution of polyacrylonitrile into particles, followed by pre-oxidation, carbonization, and KOH activation.

[0017] The hygroscopic inorganic salts include, but are not limited to, CaCl2, LiCl, SrCl2, LiOH, and MgSO4.

[0018] The above-mentioned thermochemical energy storage composite material is prepared according to the following steps:

[0019] Step 1: Preparation of porous carbon materials mimicking the structure of erythrocytes and leaf veins;

[0020] Solution preparation: Polyacrylonitrile (PAN) with a molecular weight of 85,000 was dissolved in N,N-dimethylformamide (DMF), heated at 80 °C on a magnetic stirrer and stirred to prepare a solution with a concentration of 8 wt.%, and the solution was transferred to a 20 ml syringe equipped with a 21 G needle;

[0021] Dropping into granules: Control the injection speed of the syringe to 5 mm / min using an injection pump, and drop the above PAN solution into a water-ethanol coagulation bath with a mass ratio of 7:3, with a drop height of 15 cm, ensuring that the volume ratio of the dropped PAN droplet to the mass ratio of the coagulation bath is less than 1:5;

[0022] Washing, drying, pre-oxidation and carbonization: The dripped particles were left to stand in the coagulation bath for 24 hours. After 24 hours, the particles were sieved out, soaked in deionized water and washed multiple times. The washed gel particles were dried in an oven at 80 °C for 24 hours. The dried particles were pre-oxidized in a muffle furnace at 280 °C with a heating rate of 0.5 °C / min for 2 hours. The pre-oxidized particles were carbonized in a tube furnace under an inert gas atmosphere at 900 °C with a heating rate of 5 °C / min for 2 hours.

[0023] KOH activation: Weigh KOH and carbonized particles at a mass ratio of 2:1, transfer to a beaker, and add 17 times the weight of the particles in deionized water to prepare a solution. Stir at room temperature for 3 hours on a magnetic stirrer, then transfer to an alumina crucible and dry in an oven at 120 °C for 2 hours. Activate the dried crucible containing the above material in a tube furnace under an inert gas atmosphere at a temperature of 700 °C, 800 °C, or 900 °C, a heating rate of 5 °C / min, and hold for 1 hour. Then wash repeatedly with deionized water until the pH test paper is neutral.

[0024] Step 2: Preparation of composite thermochemical heat storage materials with a mimicking red blood cell-leaf vein structure;

[0025] Salt loading: The activated particles were first dried in an oven at 120 °C for 2 hours to ensure the removal of all moisture, and then immersed in an inorganic salt solution with a concentration of 10~40 wt.% and allowed to stand for 24 hours. After 24 hours, the particles were filtered and dried in an oven at 200 °C for 1 hour to obtain the composite thermochemical heat storage material.

[0026] This invention solves the problems of moisture absorption and clumping, slow mass transfer, and low photothermal conversion efficiency of traditional hydrated salt materials, providing a new solution for the efficient storage of renewable energy. Compared with existing technologies, this invention has the following advantages:

[0027] I. For the first time, the morphology of red blood cells was combined with the structure of leaf veins to construct a multi-scale hierarchical mass transfer structure. The morphology of red blood cells helps to increase the body surface area ratio and shorten the mass transfer distance, while the hierarchical directional vein network that mimics leaf veins helps to reduce diffusion resistance.

[0028] Second, KOH activation was used to transform carbon materials from hydrophobic to hydrophilic, and etching of carbon materials increased micropores and improved specific surface area.

[0029] Third, the integrated design of solar thermal energy storage reduces intermediate heat transfer links. The carbon material itself has good solar thermal conversion performance, realizing efficient solar direct-driven desorption thermal energy storage.

[0030] Fourth, the material itself is in the form of millimeter-sized particles and can be used directly in a packed bed.

[0031] In terms of practical effects, this project, inspired by the morphology of red blood cells and the structure of leaf veins, prepared a millimeter-scale porous carbon matrix using solvent-induced phase separation technology. After activation with KOH, it was loaded with calcium chloride hygroscopic salt to form a composite thermochemical heat storage material. The porous carbon matrix has a single concave disc-shaped shape and a leaf vein-like layered oriented network, possessing high specific surface area, short mass transfer path, low mass transfer resistance, excellent hydrophilicity, and high photothermal conversion efficiency. The composite material achieved an adsorption capacity of 885 mg / g and a heat storage density of 974 J / g at 20℃ and 60% relative humidity. Under 1000 W / m² illumination, the surface temperature rose to 79℃ in 30 minutes, the desorption efficiency reached 84%, and there was no performance degradation after 100 cycles. Attached Figure Description

[0032] Figure 1 is a flowchart of the material preparation process and a photograph of the actual product;

[0033] Figure 2 shows the SEM image and CT 3D reconstruction image of the RL800.

[0034] Figure 3 shows the hole structure test of RL800;

[0035] Figure 4 shows the FTIR and contact angle tests for RL and RL800;

[0036] Figure 5 shows the adsorption kinetics curves of RL800@25%CaCl2;

[0037] Figure 6 is the spectral absorption diagram of RL800@25%CaCl2;

[0038] Figure 7 shows the mass and temperature changes during the photothermal desorption process of RL800@25%CaCl2.

[0039] Figure 8 shows the cycle performance test results of RL800@25%CaCl2. Detailed Implementation

[0040] To clearly illustrate the technical features of this patent, the following detailed description is provided through specific embodiments and in conjunction with the accompanying drawings.

[0041] The specific embodiments of this case are described below through the preparation process route.

[0042] Step 1: Preparation of porous carbon materials mimicking the structure of erythrocytes and leaf veins:

[0043] Droplet formation: Weigh 8g of polyacrylonitrile (PAN) with a molecular weight of 85000 and 92g of N,N-dimethylformamide (DMF) into a beaker and seal it. Place the beaker on a magnetic stirrer and heat and stir at 80 °C until homogeneous to prepare a solution with a concentration of 8 wt.%. Transfer the above solution into a 20ml syringe equipped with a 21G needle.

[0044] Dropping into granules: The injection speed of the syringe is controlled by the injection pump to be 5 mm / min, the drop height is 15 cm, and the PAN solution is dropped into a coagulation bath composed of water and ethanol with a mass ratio of 7:3. The volume ratio of PAN solution to coagulation bath is less than 1:5, that is, a maximum of 20 mL of PAN solution is dropped into 100 g of coagulation bath.

[0045] Washing, drying, pre-oxidation and carbonization: The dripped particles were left to stand in the coagulation bath for 24 hours. After 24 hours, the particles were sieved out, soaked in deionized water and washed multiple times. The washed gel particles were dried in an oven at 80 °C for 24 hours. The dried particles were pre-oxidized in a muffle furnace at 280 °C with a heating rate of 0.5 °C / min for 2 hours. The pre-oxidized particles were carbonized in a tube furnace under an inert gas atmosphere at 900 °C with a heating rate of 5 °C / min for 2 hours. The carbonized particles were named RL.

[0046] KOH activation: Weigh 2g KOH and 1g RL, transfer to a beaker and add 17g deionized water to prepare a solution. Stir at room temperature for 3h on a magnetic stirrer, then transfer to an alumina crucible and dry in an oven at 120 ℃ for 2h. Activate the dried crucible containing the above materials in a tube furnace under an inert gas atmosphere at 800 ℃, a heating rate of 5 ℃ / min, and hold for 1h. Then wash repeatedly with deionized water until the pH test paper is neutral.

[0047] The particles activated at 800 °C were named RL800. The preparation process and physical sample are shown in Figure 1.

[0048] The SEM images and CT reconstructions of RL800 are shown in Figure 2. Figures 2(a) and (c) clearly show that the particles are uniconcave discs, resembling red blood cells in appearance. Figures 2(b) and (d) show that the internal mass transfer channels have a directional structure. The mass transfer channels in the middle are arranged vertically, while those on the sides are arranged at an angle, similar to the arrangement of the midrib and lateral veins in a leaf. Red blood cells and leaf veins are highly efficient gas exchange and nutrient transport systems selected by natural selection, possessing unique advantages in mass transport and energy transfer. This material combines the characteristics of these two highly efficient mass transfer structures. Due to the structural similarity, this material also exhibits highly efficient heat and mass transfer characteristics.

[0049] The pore structure of RL800 is shown in Figure 3. The nanoscale and microscale pores of the material were tested using N2 adsorption and mercury intrusion porosimetry, respectively. Figure 3(a) shows that the pore size distribution of the activated particles is mostly in the range of 0–2 nm, and the measured specific surface area is 901 m². 2 Since N2 adsorption can only measure nanoscale pore sizes, mercury intrusion porosimetry was used to test the micrometer-scale pore size of the material. As shown in Figure 3(b), the pore size distribution of the activated particles is between 100~4800 nm and 4800~60000 nm. Therefore, RL800 contains both nanoscale and micrometer-scale pores, and appears as millimeter-scale particles, exhibiting a multi-scale, hierarchically ordered, high specific surface area porous structure.

[0050] The FTIR and contact angle test results for RL and RL800 are shown in Figures 4(a) and (b). It can be seen that after activation at 800 °C, the particles reach a contact angle of approximately 3450 cm⁻¹. -1 A distinct peak appeared at the [specific location], which is the absorption peak of hydroxyl groups. Contact angle tests showed that the contact angle of RL was greater than 90°, while the contact angle of RL800 was 46.9°, indicating that the particles changed from hydrophobic to hydrophilic.

[0051] Step 2: Preparation of composite thermochemical heat storage materials with a mimicking red blood cell-leaf vein structure;

[0052] Salt loading: Weigh 0.5g of RL800 and immerse it in a 25wt.% CaCl2 solution consisting of 5g CaCl2 and 15g water. Let it stand for 24h, then filter it and dry it at 200℃ for 2h. The resulting material is named RL800@25%CaCl2.

[0053] The adsorption of RL800@25%CaCl2 was carried out at 20℃ and 60% relative humidity. No solution leakage was found after adsorption. The adsorption kinetic curve is shown in Figure 5. The equilibrium adsorption capacity is 885 mg / g.

[0054] Figure 6 shows the spectral absorption spectra of CaCl2 and RL800@25%CaCl2. Their average spectral absorbances are 5.17% and 96.88%, respectively. It can be seen that the average spectral absorbance of the composite material is significantly improved. RL800@25%CaCl2 was saturated with adsorption at 20℃ and 60% relative humidity, and then placed under a xenon lamp to simulate sunlight irradiation, with the light intensity controlled at 1000 W / m². 2 Meanwhile, the surface temperature was recorded using an infrared thermal imager, as shown in Figure 7. It can be seen that after 30 minutes of irradiation, the surface temperature of the material reached 79 ℃, and the desorption rate reached 84%. After 1 hour of irradiation, the surface temperature of the material reached 86 ℃, and the desorption rate reached 93%.

[0055] RL800@25%CaCl2 was subjected to cyclic testing in an adsorbent apparatus. The cyclic conditions were desorption at 300 °C for 2 h, adsorption at 20 °C and 60% relative humidity for 4 h, and this cycle was repeated 100 times, as shown in Figure 8. It can be seen that after 100 cycles, the material's performance is very stable with almost no degradation, indicating that it has excellent cyclic stability.

[0056] There are many specific ways to implement this invention. The above description is only a preferred embodiment of this invention. It should be noted that for those skilled in the art, several improvements can be made without departing from the principle of this invention, and these improvements should also be considered within the scope of protection of this invention.

Claims

1. A thermo-chemical energy storage composite material of biomimetic ordered structure, characterized in that, The thermo-chemical energy storage composite material comprises a matrix of biomimetic multi-scale mass transfer structure and hygroscopic inorganic salt uniformly loaded in the matrix, and the matrix is loaded with hygroscopic inorganic salt after KOH activation; The matrix has a shape of single-concave disc, which is similar to the shape of red blood cell; the matrix has a layered directional vein network in the shape of leaf vein in the inside, which comprises a main vein dividing the matrix into upper and lower halves along the thickness direction and a plurality of branch veins distributed on the upper and lower sides of the main vein, and a mass transfer channel is formed between adjacent branch veins.

2. A thermally chemically energy storing composite material of biomimetic order according to claim 1, characterized by The mass transfer channel located in the central part of the main vein is perpendicular to the main vein, and the mass transfer channels at other positions have an angle of 0-90° with the main vein, and the angle gradually increases from the edge of the matrix.

3. A bio-inspired ordered structured thermo-chemical energy storage composite material according to claim 1, characterized in that, The main vein and the branch veins in the inside of the matrix are further provided with a plurality of nanopores generated after KOH activation.

4. A bio-inspired ordered structured thermo-chemical energy storage composite material according to claim 1, characterized in that, The matrix is a carbon material after pre-oxidation, carbonization and KOH activation of polyacrylonitrile (PAN) DMF solution droplets into particles.

5. A bio-inspired ordered structured thermo-chemical energy storage composite material according to claim 1, characterized in that, The hygroscopic inorganic salt includes but is not limited to CaCl2, LiCl, SrCl2, LiOH and MgSO4.

6. A method for the preparation of a thermally-chemically energy storing composite material of biomimetic order according to claim 1, characterized in that, The following steps are used for preparation: Step 1, preparation of porous carbon material with red blood cell-leaf vein structure; Solution preparation: polyacrylonitrile (PAN) with a molecular weight of 85000 is dissolved in N,N-dimethylformamide (DMF) to prepare a solution with a concentration of 8wt.% by heating on a magnetic stirrer at 80 ℃ and stirring, and the solution is transferred to a 20 ml syringe provided with a 21G needle; Droplet into particles: the injection speed of the syringe is controlled by a syringe pump to be 5 mm / min, and the above PAN solution is dripped into a water-ethanol coagulation bath with a mass ratio of 7:3, the dripping height is 15 cm, and the mass ratio of the volume of the dripped PAN droplets to the coagulation bath is less than 1:5; Washing, drying, pre-oxidation and carbonization: the particles after dripping are placed in the coagulation bath for 24 h, and then the particles are screened out, soaked in deionized water and washed repeatedly; the washed gel particles are dried in an oven at 80 ℃ for 24 h; the dried particles are pre-oxidized in a muffle furnace at a temperature of 280 ℃ and a heating rate of 0.5 ℃ / min for 2 h; the pre-oxidized particles are carbonized in a tube furnace under an inert gas atmosphere at a temperature of 900 ℃ and a heating rate of 5 ℃ / min for 2 h; KOH activation: KOH and the carbonized particles are weighed according to a mass ratio of 2:1, transferred to a beaker, and deionized water is added to prepare a solution with a weight of 17 times that of the particles, stirred on a magnetic stirrer at room temperature for 3 h, then transferred to a corundum crucible and dried in an oven at 120 ℃ for 2 h; the crucible containing the above material after drying is activated in a tube furnace under an inert gas atmosphere at a temperature of 700 ℃, 800 ℃ or 900 ℃ and a heating rate of 5 ℃ / min for 1 h; then repeatedly washed with deionized water until the pH test paper is neutral; Step 2, preparation of composite thermo-chemical heat storage material with red blood cell-leaf vein structure; Salt loading: After activation, the particles were first dried in an oven at 120 °C for 2 h to ensure removal of all moisture, and then immersed in a solution of inorganic salt with a concentration of 10-40 wt.%, and left to stand for 24 h. After 24 h, the particles were filtered and dried in an oven at 200 °C for 1 h to obtain the composite thermo-chemical heat storage material.

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