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

Abstract

The invention discloses a thermochemical energy storage composite material with a bionic ordered structure and a preparation method of the thermochemical energy storage composite material, and relates to the crossing field of new energy materials and thermochemical energy storage technologies. Through an optimization strategy of coordination of geometrical shape, internal channel and 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 hygroscopic inorganic salt uniformly loaded in the matrix, wherein the matrix is activated by KOH and then is loaded with the hygroscopic inorganic salt; the appearance of the base body imitates that of red blood cells, and the base body is in a single concave disc shape; and a vein-like layered directional vein network is arranged in the base body. The problems of moisture absorption and caking, slow mass transfer and low photothermal conversion efficiency of a traditional hydrated salt material are solved, and a new scheme is provided for efficient storage of renewable energy sources.

Description

Technical Field

[0001] The present invention relates to the intersection of new energy materials and thermochemical energy storage technology, and specifically to a solar-driven thermochemical heat storage composite material with a bionic multi-scale mass transfer structure and a preparation method thereof. Background Art

[0002] With the development of the times, limited fossil energy cannot cope with the growing energy demand, leading to energy and environmental crises. Promoting the development and utilization of renewable energy is an important means of opening up new sources of energy, which can effectively solve the above problems. Renewable energy such as solar energy, wind energy, and biomass energy are inexhaustible. If their utilization can be promoted, it will promote the green and low-carbon transformation and sustainable development of the economy and society, and make positive contributions to the realization of the important strategic goals of "carbon peak" and "carbon neutrality" in the country. However, renewable energy such as solar energy is intermittent and unstable, and efficient energy storage technology is needed to realize the transfer of 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 protection, but traditional hydrated salt materials have bottlenecks such as moisture absorption and agglomeration, large mass transfer resistance and low photothermal conversion efficiency. Existing research has achieved rich results by improving performance by loading salts on porous matrices, such as silica gel, zeolite, and natural minerals. However, the matrix is ​​spherical or irregular in appearance, and the internal channels are mostly disordered, resulting in long mass transfer paths, large 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 challenges faced by traditional designs, many researchers 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 systems for efficient gas exchange and nutrient transport. These unique advantages in material transport and energy transfer provide insights for structural optimization, but existing technologies have yet to effectively incorporate such biomimetic designs. Summary of the Invention

[0004] In response to the above problems, the present invention proposes a thermochemical energy storage composite material with a biomimetic ordered structure and a preparation method thereof. Through the synergistic optimization strategy of "geometry-internal channel-surface effect", efficient adsorption / desorption kinetics and direct solar-driven heat storage are achieved.

[0005] The structural design of the material has the following characteristics: In terms of geometry, the appearance of this case mimics red blood cells, with a single concave disc shape, a diameter of about 1.5 mm, a thickness of about 0.7 mm, a large surface-to-body ratio and a short mass transfer path.

[0006] In terms of internal channels, the bionic leaf-vein-like layered directional vein network in this case includes: a main vein that divides the substrate into two 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 channel located in the center of the main vein is perpendicular to it, 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 substrate.

[0007] In addition, after KOH activation, several nanopores are generated in the main veins and branch veins, so that they have a larger specific surface area and smaller mass transfer resistance.

[0008] In terms of surface effects, this case introduces oxygen-containing functional groups such as hydroxyl groups after KOH activation, rendering the inherently hydrophobic carbon material hydrophilic, facilitating salt loading. Furthermore, the material is black, demonstrating excellent light-to-heat conversion performance.

[0009] In terms of functional compounding, this case evenly distributes calcium chloride in the matrix, with a salt content of 20~50%, and the spectral absorption rate after loading is still greater than 95%, with good adsorption capacity and photothermal desorption performance.

[0010] In order to achieve the above features, the technical solution of the present invention is: The thermochemical energy storage composite material comprises a matrix of a biomimetic multi-scale mass transfer structure and a hygroscopic inorganic salt uniformly loaded in the matrix, wherein the matrix is ​​activated by KOH and then loaded with the hygroscopic inorganic salt; The outer shape of the matrix is ​​similar to that of red blood cells and is in the shape of a single concave disc. The interior of the matrix has a layered directional vein network that imitates leaf veins. The layered directional vein network includes a main vein that divides the matrix into two halves along the thickness direction and a number of branch veins distributed on both sides of the main vein, forming mass transfer channels between adjacent branch veins.

[0011] Furthermore, the mass transfer channel located in the center of the main vein is perpendicular to it, 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 substrate.

[0012] The matrix also has several nanopores on its main and branch veins after KOH activation, resulting in an average spectral absorptivity greater than 95%, excellent hydrophilicity, and a specific surface area greater than 900 m² / g.

[0013] The matrix is ​​a carbon material obtained by dripping a DMF solution of polyacrylonitrile into particles and then pre-oxidizing, carbonizing and KOH-activating the solution.

[0014] The hygroscopic inorganic salts include but are not limited to CaCl2, LiCl, SrCl2, LiOH, and MgSO4.

[0015] The above-mentioned thermochemical energy storage composite material is prepared according to the following steps: Step 1, preparation of porous carbon material imitating red blood cell-vein structure; Solution preparation: Dissolve polyacrylonitrile (PAN) with a molecular weight of 85,000 in N,N-dimethylformamide (DMF). Heat at 80°C on a magnetic stirrer and stir to prepare an 8 wt.% solution. Transfer the solution to a 20 ml syringe equipped with a 21G needle. Dropping into particles: Using a syringe pump to control the injection speed of the syringe at 5 mm / min, the PAN solution was dripped into a water-ethanol coagulation bath with a mass ratio of 7:3. The dripping height was 15 cm, ensuring that the mass ratio of the dripped PAN droplet volume to the coagulation bath was less than 1:5. Washing, drying, pre-oxidation and carbonization: The dripped particles were placed in the above-mentioned 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 placed in an 80°C oven to dry for 24 hours; the dried particles were pre-oxidized in a muffle furnace at a temperature of 280°C, a heating rate of 0.5°C / min, and kept warm for 2 hours; the pre-oxidized particles were carbonized in a tube furnace under an inert gas atmosphere at a temperature of 900°C, a heating rate of 5°C / min, and kept warm for 2 hours; KOH activation: Weigh KOH and carbonized particles in a mass ratio of 2:1, transfer them to a beaker, and add deionized water 17 times the weight of the particles to prepare a solution. Stir on a magnetic stirrer at room temperature for 3 hours, then transfer them to a corundum crucible and dry them in an oven at 120°C for 2 hours. Activate the crucible containing the dried materials in a tube furnace under an inert gas atmosphere at 700°C, 800°C, or 900°C at a heating rate of 5°C / min for 1 hour. Then wash repeatedly with deionized water until the pH paper is neutral. Step 2: Preparation of composite thermochemical heat storage material imitating red blood cell-vein structure; Salt loading: The activated particles were first dried in an oven at 120°C for 2 hours to remove all moisture. They were 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 a composite thermochemical heat storage material.

[0016] This invention solves the problems of traditional hydrated salt materials, such as moisture absorption and agglomeration, slow mass transfer, and low light-to-heat conversion efficiency, and provides a new solution for the efficient storage of renewable energy. Compared with existing technologies, this invention has the following advantages: First, the team combined red blood cell morphology with leaf vein structure for the first time, constructing a cross-scale hierarchical mass transfer structure. The red blood cell-like shape helps improve the surface-to-body ratio and shorten the mass transfer distance, while the layered and directional vein network mimicking leaf veins helps reduce diffusion resistance. Second, KOH activation was used to achieve the transformation of carbon materials from hydrophobic to hydrophilic, and the carbon materials were etched to increase micropores and improve the specific surface area; 3. The integrated design of photothermal heat storage reduces the intermediate heat transfer link. The carbon material itself has good photothermal conversion performance, realizing efficient solar-directly driven desorption heat storage. 4. The material itself is in millimeter-sized granular form and can be used directly in the packing bed.

[0017] In terms of practical effects, this case is inspired by the morphology of red blood cells and the structure of leaf veins. A millimeter-scale porous carbon matrix is ​​prepared through solvent-induced phase separation technology, and calcium chloride hygroscopic salt is loaded after KOH activation to form a composite thermochemical heat storage material. The porous carbon matrix has a single concave disc shape and a layered directional vein network in the shape of leaf veins. It has high specific surface area, short mass transfer path, small mass transfer resistance, excellent hydrophilicity and high photothermal conversion efficiency. The composite material reaches an adsorption capacity of 885 mg / g at 20°C and 60% relative humidity, and a heat storage density of 974 J / g. Under 1000 W / m² light, the surface temperature rises to 79°C in 30 minutes, the desorption efficiency reaches 84%, and there is no performance degradation after 100 cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the material preparation process flow chart and actual photos; Figure 2 This is the SEM photo and CT 3D reconstruction of RL800; Figure 3 It is the hole structure test of RL800; Figure 4 It is FTIR and contact angle test of RL and RL800; Figure 5 This is the adsorption kinetic curve of RL800@25%CaCl2; Figure 6 This is the absorption spectrum of RL800@25%CaCl2; Figure 7 This is the mass and temperature change diagram of the photothermal desorption process of RL800@25%CaCl2; Figure 8 This is the cycle performance test chart of RL800@25%CaCl2. DETAILED DESCRIPTION

[0019] In order to clearly illustrate the technical features of this patent, this patent is described in detail below through specific implementation methods and in combination with its accompanying drawings.

[0020] The specific embodiments of this case are described below through the preparation process route.

[0021] Step 1: Preparation of porous carbon material imitating red blood cell-vein structure: Dropwise pelletization: Weigh 8 g of 85,000 molecular weight polyacrylonitrile (PAN) and 92 g of N,N-dimethylformamide (DMF) into a sealed beaker. Place the beaker on a magnetic stirrer and heat at 80°C while stirring until homogeneous, creating an 8 wt.% solution. Transfer the solution to a 20 ml syringe equipped with a 21G needle.

[0022] Dripping into particles: The syringe pump is used to control the injection speed of the syringe to 5 mm / min and the dripping height to 15 cm. The solution is dripped into a coagulation bath composed of water and ethanol in a mass ratio of 7:3. The volume ratio of the PAN solution to the mass ratio of the coagulation bath is less than 1:5, that is, a maximum of 20 mL of PAN solution can be dripped into 100 g of the coagulation bath.

[0023] Washing, drying, pre-oxidation and carbonization: The dripped particles were placed in the above-mentioned 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 placed in an 80°C oven and dried for 24 hours; the dried particles were pre-oxidized in a muffle furnace at a temperature of 280°C, a heating rate of 0.5°C / min, and kept warm for 2 hours; the pre-oxidized particles were carbonized in a tube furnace under an inert gas atmosphere at a temperature of 900°C, a heating rate of 5°C / min, and kept warm for 2 hours. The carbonized particles were named RL.

[0024] KOH activation: Weigh 2 g of KOH and 1 g of RL, transfer them to a beaker, and add them to 17 g of deionized water to prepare a solution. Stir on a magnetic stirrer at room temperature for 3 h, then transfer them to a corundum crucible and dry them in an oven at 120°C for 2 h. Activate the crucible containing the dried materials in a tube furnace under an inert gas atmosphere at 800°C at a heating rate of 5°C / min for 1 h. Then wash the crucible repeatedly with deionized water until the pH paper is neutral.

[0025] The particles activated at 800℃ are named RL800. Figure 1 shown.

[0026] The SEM photos and CT reconstruction images of RL800 are as follows: Figure 2 As shown. Figure 2 (a) and (c) clearly show that the particles are in the shape of single concave disks, and their appearance is very similar to that of red blood cells. Figure 2As can be seen in (b) and (d), the internal mass transfer channels have a directional structure, with those in the center arranged vertically and those on the sides arranged at an angle, similar to the arrangement of the main and lateral veins in a leaf. Red blood cells and leaf veins are naturally selected efficient gas exchange and nutrient transport systems, respectively, offering unique advantages in material transport and energy transfer. This material combines the characteristics of these two efficient mass transfer structures. Given these structural similarities, it also exhibits efficient heat and mass transfer properties.

[0027] The pore structure of RL800 is as follows Figure 3 The nano-scale and micro-scale pores of the material were tested by N2 adsorption method and mercury intrusion method respectively. Figure 3 (a) It can be seen that the pore size distribution of the activated particles is mostly between 0 and 2 nm, and the measured specific surface area is 901 m 2 / g, since the N2 adsorption method can only measure the nanometer-level pore size, the mercury intrusion method is used to test the micrometer-level pore size of the material. Figure 3 (b) shows that the pore size distribution of the activated particles ranges from 100 to 4800 nm and from 4800 to 60000 nm. Therefore, RL800 possesses both nanoscale and microscale pores internally, yet appears as millimeter-scale particles, exhibiting a hierarchically ordered, high-specific-surface-area porous structure across scales.

[0028] The FTIR test results and contact angle test results of RL and RL800 are as follows Figure 4 (a) and (b). It can be seen that after the particles are activated at 800 ℃, the -1 A clear peak appears at the bottom, which is the absorption peak of hydroxyl. The contact angle test shows that the contact angle of RL is greater than 90°, and the contact angle of RL800 is 46.9°, indicating that the particles change from hydrophobic to hydrophilic.

[0029] Step 2: Preparation of composite thermochemical heat storage material imitating red blood cell-vein structure; Salt loading: 0.5 g of RL800 was immersed in a 25 wt.% CaCl2 solution consisting of 5 g of CaCl2 and 15 g of water. The solution was allowed to stand for 24 h, filtered, and dried at 200 °C for 2 h. The resulting material was named RL800@25%CaCl2.

[0030] The adsorption of RL800@25%CaCl2 was carried out at 20℃ and 60% relative humidity. No solution leakage was found after adsorption. The adsorption kinetics curve is shown in Figure 2. Figure 5 As shown, the equilibrium adsorption capacity is 885 mg / g.

[0031] The absorption spectra of CaCl2 and RL800@25%CaCl2 are shown in the figure below. Figure 6 As shown in the figure, the average spectral absorption rates of the two materials are 5.17% and 96.88% respectively. It can be seen that the average spectral absorption rate of the composite material has been greatly 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 a controlled light intensity of 1000 W / m 2 , and use an infrared thermal imager to record its surface temperature, such as Figure 7 It can be seen that after 30 minutes of irradiation, the surface temperature of the material reached 79 °C and the desorption rate reached 84%. After 1 hour of irradiation, the surface temperature of the material reached 86 °C and the desorption rate reached 93%.

[0032] RL800@25%CaCl2 was tested in a cycle in an adsorption instrument. The cycle conditions were desorption at 300℃ for 2h, adsorption at 20℃ and 60% relative humidity for 4h, and this cycle was repeated 100 times. Figure 8 As shown in the figure, it can be seen that after 100 cycles, the performance of the material is very stable with almost no attenuation, indicating that it has excellent cycle stability.

[0033] There are many specific implementation ways of the present invention. The above is only the preferred implementation method of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements can be made without departing from the principles of the present invention. These improvements should also be considered as the scope of protection of the present invention.

Claims

1. A thermochemical energy storage composite material with a biomimetic ordered structure, characterized in that: The thermochemical energy storage composite material comprises a matrix of a biomimetic multi-scale mass transfer structure and a hygroscopic inorganic salt uniformly loaded in the matrix, wherein the matrix is ​​activated by KOH and then loaded with the hygroscopic inorganic salt; The outer shape of the matrix is ​​similar to that of red blood cells and is in the shape of a single concave disc. The interior of the matrix has a layered directional vein network that imitates leaf veins. The layered directional vein network includes a main vein that divides the matrix into two halves along the thickness direction and a number of branch veins distributed on both sides of the main vein, forming mass transfer channels between adjacent branch veins.

2. The biomimetic ordered structure thermochemical energy storage composite material according to claim 1, characterized in that: The mass transfer channel located in the center of the main vein is perpendicular to it, and the mass transfer channels at other positions have an angle of 0-90 degrees with the main vein, and the angle gradually increases from the edge of the substrate.

3. The thermochemical energy storage composite material with a biomimetic ordered structure according to claim 1, characterized in that: The main veins and branch veins inside the matrix are also provided with a number of nanopores generated after KOH activation.

4. The thermochemical energy storage composite material with a biomimetic ordered structure according to claim 1, characterized in that: The matrix is ​​a carbon material obtained by dripping a DMF solution of polyacrylonitrile into particles and then pre-oxidizing, carbonizing and KOH-activating the solution.

5. The thermochemical energy storage composite material with a biomimetic ordered structure according to claim 1, characterized in that: The hygroscopic inorganic salts include but are not limited to CaCl2, LiCl, SrCl2, LiOH, and MgSO4.

6. A method for preparing the thermochemical energy storage composite material with a biomimetic ordered structure according to claim 1, characterized in that: Prepare as follows: Step 1, preparation of porous carbon material imitating red blood cell-vein structure; Solution preparation: Dissolve polyacrylonitrile (PAN) with a molecular weight of 85,000 in N,N-dimethylformamide (DMF). Heat at 80°C on a magnetic stirrer and stir to prepare an 8 wt.% solution. Transfer the solution to a 20 ml syringe equipped with a 21G needle. Dropping into particles: Using a syringe pump to control the injection speed of the syringe at 5 mm / min, the PAN solution was dripped into a water-ethanol coagulation bath with a mass ratio of 7:

3. The dripping height was 15 cm, ensuring that the mass ratio of the dripped PAN droplet volume to the coagulation bath was less than 1:

5. Washing, drying, pre-oxidation and carbonization: The dripped particles were placed in the above-mentioned 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 placed in an 80°C oven to dry for 24 hours; the dried particles were pre-oxidized in a muffle furnace at a temperature of 280°C, a heating rate of 0.5°C / min, and kept warm for 2 hours; the pre-oxidized particles were carbonized in a tube furnace under an inert gas atmosphere at a temperature of 900°C, a heating rate of 5°C / min, and kept warm for 2 hours; KOH activation: Weigh KOH and carbonized particles in a mass ratio of 2:1, transfer them to a beaker, and add deionized water 17 times the weight of the particles to prepare a solution. Stir on a magnetic stirrer at room temperature for 3 hours, then transfer them to a corundum crucible and dry them in an oven at 120°C for 2 hours. Activate the crucible containing the dried materials in a tube furnace under an inert gas atmosphere at 700°C, 800°C, or 900°C at a heating rate of 5°C / min for 1 hour. Then wash repeatedly with deionized water until the pH paper is neutral. Step 2: Preparation of composite thermochemical heat storage material imitating red blood cell-vein structure; Salt loading: The activated particles were first dried in an oven at 120°C for 2 hours to remove all moisture. They were 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 a composite thermochemical heat storage material.

Images