High-entropy fluorite oxide modified calcium-based thermochemical heat storage material and preparation method thereof

Abstract

The application provides a high-entropy fluorite oxide modified calcium-based thermochemical heat storage material and a preparation method thereof, the material comprising a calcium-based material and a high-entropy fluorite oxide, the mass percentage of the calcium-based material being 70-85%, the calcium-based material being calcium oxide, and the high-entropy fluorite oxide being a fluorite structure oxide formed by zirconium, cerium, lanthanum, neodymium and ytterbium, the molar ratio of the zirconium, cerium, lanthanum, neodymium and ytterbium oxides being 1:1:1:1:1, the high-entropy fluorite oxide being used as an anti-sintering component to disperse the calcium oxide and hinder the sintering of the calcium oxide, and at the same time, the high-entropy fluorite oxide promotes the adsorption, dissociation and migration of CO2 on the surface of the material, so that the cycle stability and energy density of the heat storage material are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thermochemical energy storage, in particular to a high-entropy fluorite oxide modified calcium-based thermochemical heat storage material and a preparation method thereof. BACKGROUND

[0002] Solar energy is widely distributed in China and is considered to be one of the most promising new energy sources. However, the use of solar energy has problems such as intermittency and seasonality, which causes a mismatch between demand and supply.

[0003] The existing heat storage system matched with the solar energy concentrating heat collection power station can store excess energy during the peak period of energy utilization and release the stored energy during the energy valley period. The current heat storage methods mainly include sensible heat storage, latent heat storage and thermochemical heat storage, among which the energy density of thermochemical heat storage is much higher than that of sensible heat storage and latent heat storage, and it is a promising heat storage method.

[0004] Among many thermochemical heat storage systems, the calcium oxide-based carbon dioxide adsorption / desorption system has the advantages of high theoretical energy density (about 1.78 GJ / t), low preparation cost, long heat storage period, good safety, etc., and the temperature of heat release is about 650℃, which can meet the working temperature requirement of the third generation sCO2 (supercritical carbon dioxide) power cycle CSP power station.

[0005] However, the calcium-based heat storage medium used in the existing solar heat collection power station has the problem of cycle stability degradation caused by high-temperature sintering, and the energy density is significantly attenuated within 5 cycles. Due to the thermal stress caused by the temperature difference between the solar calcination furnace and the carbonation reaction furnace and the mechanical stress caused by the collision of the medium and the pipeline, the medium is broken and worn out during fluidization, and the active medium fragments are easily carried out of the system by the airflow, causing the loss of effective mass, and also causing pipeline wear and blockage. Therefore, it is necessary to design a calcium-based thermochemical heat storage material with high cycle stability and high energy density to overcome the above problems. SUMMARY

[0006] The present application aims to overcome the defects of the prior art and provides a high-entropy fluorite oxide modified calcium-based thermochemical heat storage material and a preparation method thereof. The high-entropy fluorite oxide is used as an anti-sintering component to disperse calcium oxide and hinder the sintering of calcium oxide, and the fluorite structure can promote the adsorption, dissociation and migration of CO2 on the surface of the material, thereby improving the cycle stability and energy density of the heat storage material.

[0007] The present application provides the following technical solutions:

[0008] The application provides a high-entropy fluorite oxide modified calcium-based thermochemical heat storage material, which comprises a calcium-based material and a high-entropy fluorite oxide, and the mass percentage of the calcium-based material is 70-85%, the calcium-based material is calcium oxide, and the high-entropy fluorite oxide is a fluorite structure oxide formed by zirconium, cerium, lanthanum, neodymium and ytterbium, and the molar ratio of the zirconium, cerium, lanthanum, neodymium and ytterbium oxides is 1:1:1:1:1.

[0009] In the application, the high-entropy fluorite oxide is a single fluorite structure oxide composed of tetravalent oxides of zirconium, cerium, lanthanum, neodymium and ytterbium, and the XO2 type fluorite oxide formed by zirconium and the oxides of the four rare earth elements acts as a physical barrier to prevent CaO crystal growth and aggregation. The material has a porous foam structure, a large number of pores provide a large adsorption area for active CaO, slow down the sintering of CaO crystals, and the XO2 type fluorite structure can provide oxygen vacancies to promote the adsorption, dissociation and migration of carbon dioxide in the adsorption / desorption reaction, thereby maintaining good cycle stability.

[0010] In the application, the sum of the mass ratios of the components of the material is 100%, the mass percentage of the calcium-based material is 70-85%, and the mass percentage of the high-entropy fluorite oxide is 15-30%. If the percentage of the high-entropy fluorite oxide is less than 15%, the dispersion degree of the high-entropy fluorite oxide in the calcium oxide is not enough to stabilize the calcium oxide; if the percentage of the high-entropy fluorite oxide is more than 30%, the insufficient content of the calcium oxide will lead to insufficient energy density of the material, and the material does not have cost performance in application. The high-entropy fluorite oxide modified calcium-based thermochemical heat storage material provided by the application has energy density and cycle stability that meet large-scale heat storage / release.

[0011] Further, the calcium-based thermochemical heat storage medium has a porous structure. The calcium oxide acts as a large particle carrier and is the heat storage active component of the application, and the high-entropy fluorite oxide is a single fluorite structure composed of tetravalent oxides of five metals of zirconium, cerium, lanthanum, neodymium and ytterbium, and the particles of the high-entropy fluorite oxide are much smaller than those of the calcium oxide and are uniformly distributed on the carrier, thereby playing a role in relieving medium sintering and improving carbon dioxide adsorption capacity.

[0012] The application also provides a preparation method of the high-entropy fluorite oxide modified calcium-based thermochemical heat storage material.

[0013] S1, raw materials are weighed according to the proportion, a solvent is added to dissolve to prepare a mixed solution;

[0014] S2, the mixed solution is obtained by immersing the acetate fiber in the mixed solution;

[0015] S3, the wet fiber is calcined at high temperature to obtain a powder, which is the calcium-based thermochemical heat storage material.

[0016] Further, the raw materials include calcium nitrate, nitrate of zirconium, cerium, lanthanum, neodymium and ytterbium; the ratio of the raw materials is calculated according to the mass ratio after calcination, and the ratio of calcium oxide to high-entropy fluorite oxide is 7:3-17:3; and the molar ratio of zirconium, cerium, lanthanum, neodymium and ytterbium oxides in the high-entropy fluorite oxide is 1:1:1:1:1.

[0017] Further, the solvent is water and an alcohol solvent, and the dissolving condition is water bath heating at 40-80 DEG C.

[0018] The volume ratio of water to the alcohol solvent is preferably 4:1, and the alcohol solvent is preferably methanol or ethanol.

[0019] Further, in order to ensure sufficient absorption of the mixed solution, in step S2, the solid-liquid ratio of the cellulose acetate and the mixed solution is preferably 1g:(6-7)mL.

[0020] Further, in step S3, the calcination temperature is 600-900 DEG C, the calcination time is 60-120 min, and the heating rate of calcination is 5-10 DEG C / min.

[0021] Further, in order to reduce the problems of medium attrition and elutriation and pipe wear and blockage of the calcium-based heat storage medium in large-scale fluidization application, the powder obtained in step S3 is granulated into spherical medium.

[0022] The method further includes granulating the powder into spherical medium, and the steps are as follows:

[0023] The powder is added into deionized water, and stirred to form a slurry;

[0024] The graphite powder is flattened in a petri dish to form a graphite layer, and then the petri dish is placed obliquely;

[0025] The slurry is sucked up by a capillary tube and dropped on the graphite layer, and then slides to form small balls;

[0026] After drying the small balls and the graphite layer together, the small balls are sieved to obtain the spherical medium.

[0027] Further, the mass ratio of the powder to the deionized water is 1:(3-4), and after mixing, the slurry is stirred at a speed of 300-400 rpm.

[0028] Further, the angle at which the petri dish is placed obliquely is 10-30 DEG.

[0029] Further, the drying temperature is 80-110 DEG C, and the drying time is 6-12 h.

[0030] The present application has the following beneficial effects:

[0031] 1. In the application, the oxides of zirconium and four rare earth elements form XO2 type fluorite oxides, which act as a physical barrier to prevent CaO crystal growth and aggregation, and the calcium-based material and high-entropy fluorite oxide in the calcium-based thermochemical heat storage material are well dispersed, forming a porous foam structure, and a large number of pores provide a large adsorption area for active CaO, slowing down CaO crystal sintering, and solving the sintering disability problem commonly existing in existing calcium-based heat storage materials.

[0032] 2. The XO2 type fluorite structure of the high-entropy fluorite oxide of the application can provide oxygen vacancies, promote the adsorption, dissociation and migration of carbon dioxide in the reaction, and maintain good cycle stability. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the application or the prior art, the drawings needed in the embodiment or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0034] Figure 1 Scanning electron microscope image and EDS element distribution map of the calcium-based thermochemical heat storage material powder prepared in Example 1 of the application;

[0035] Figure 2 XRD pattern of the material prepared in Example 1, Comparative Example 1 and Comparative Example 3 of the application;

[0036] Figure 3 Thermogravimetric curve of the material prepared in Example 2-3 and Comparative Example 1-2 of the application;

[0037] Figure 4 Cycle energy density graph of the material prepared in Example 2-3 and Comparative Example 1-2 of the application;

[0038] Figure 5 First and twentieth cycle reaction rate curve of the material prepared in Comparative Example 1 of the application;

[0039] Figure 6 First and twentieth cycle reaction rate curve of the material prepared in Example 2 of the application;

[0040] Figure 7 Temperature programmed desorption curve of the material prepared in Example 2 and Comparative Example 1 of the application;

[0041] Figure 8 N2 adsorption amount of the precursor of Example 1, Example 3 and Comparative Example 1-2 changes with relative pressure;

[0042] Figure 9S of the precursors of Example 1 and Example 3, Comparative Example 1-2 BET Adsorption area and V of unit mass sample BJH Adsorption volume of unit mass sample

[0043] Figure 10 Pore size distribution curve of the precursors of Example 1 and Example 3, Comparative Example 1-2

[0044] Figure 11 Cycle energy density graph of the precursors of Example 1-2, Comparative Example 1 and energy density of Comparative Example 1. DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0046] The embodiment of the present application provides a high-entropy fluorite oxide modified calcium-based thermochemical heat storage material, which comprises a calcium-based material and a high-entropy fluorite oxide, the mass ratio of the calcium-based material is 70-85%, the calcium-based material is calcium oxide, and the high-entropy fluorite oxide is a fluorite structure oxide formed by zirconium, cerium, lanthanum, neodymium and ytterbium, and the molar ratio of the zirconium, cerium, lanthanum, neodymium and ytterbium oxides is 1:1:1:1:1.

[0047] The high-entropy fluorite oxide refers to a single structure oxide formed by five or more metal elements, and the advantage is good stability, which is because the entropy of the high-entropy fluorite oxide dominates the free energy, and in the process of temperature cycle change, the phase structure is relatively stable and is not easy to sinter; meanwhile, the components in the high-entropy fluorite oxide are coupled with each other, which improves the adsorption, dissociation and migration of carbon dioxide, and is beneficial to maintaining a high energy density.

[0048] The material is a porous structure, in which the calcium oxide serves as a large particle carrier, and the high-entropy fluorite oxide is a single fluorite structure oxide composed of tetravalent oxides of zirconium, cerium, lanthanum, neodymium and ytterbium, and the particles are much smaller than the calcium oxide and are uniformly distributed on the carrier.

[0049] The embodiment of the present application further provides a preparation method of the high-entropy fluorite oxide modified calcium-based thermochemical heat storage material, which comprises the following steps:

[0050] The raw materials are weighed according to the proportion, a solvent is added to dissolve and prepare a mixed solution;

[0051] The acetate fiber is immersed in the mixed solution to sufficiently absorb the mixed solution, and a wet fiber is obtained;

[0052] The wet fiber is high-temperature calcined to obtain powder, that is, the calcium-based thermochemical heat storage material.

[0053] The calcium salt and the corresponding salt of each element component of the high-entropy fluorite oxide are dissolved in a solvent, poured into acetic acid fiber for soaking, and the wet fiber is high-temperature calcined to obtain the calcium-based thermochemical heat storage material in powder form, wherein the calcium oxide is an active medium for heat storage and release, and the other elements form a high-entropy fluorite oxide to modify the material.

[0054] As a preferred embodiment, the calcium salt and the corresponding salt of each element component of the high-entropy fluorite oxide are all nitrate salts, and the mass ratio of the calcium oxide to the high-entropy fluorite oxide after calcination is 7:3-17:3, and the molar ratio of the zirconium, cerium, lanthanum, neodymium and ytterbium oxides in the high-entropy fluorite oxide is 1:1:1:1:1.

[0055] As a preferred embodiment, the solvent is water and an alcohol solvent, and the dissolution condition is water bath heating at 40-80 DEG C.

[0056] The volume ratio of the water to the alcohol solvent is preferably 4:1, and the alcohol solvent is preferably methanol or ethanol.

[0057] As a preferred embodiment, in order to ensure sufficient absorption of the mixed solution, the solid-liquid ratio of the acetic acid fiber to the mixed solution is preferably 1g:(6-7)mL.

[0058] As a preferred embodiment, the calcination temperature is 600-900 DEG C, the calcination time is 60-120 min, and the heating rate of the calcination is 5-10 DEG C / min.

[0059] The calcium-based thermochemical heat storage medium powder is difficult to meet the industrial needs, and large-scale storage and release of energy needs to use fluidized circulation technology, and the powder material will cause serious elutriation and loss of a large amount of active medium, and secondly, the powder material will cause pipeline wear and blockage. Therefore, in order to better apply, the powder needs to be granulated into spherical medium, and in the specific embodiment of the present application, the graphite casting method can be used to granulate the spherical medium, and the specific steps are as follows:

[0060] The powder is added to deionized water and stirred to form a slurry;

[0061] The graphite powder is flattened in a petri dish to form a graphite layer, and then the petri dish is placed obliquely;

[0062] The slurry is sucked up by a capillary tube and dropped on the graphite layer to form small balls (a plurality of small balls are obtained by multiple dropping);

[0063] The small balls and the graphite layer are dried together, and the small balls obtained by screening are the spherical medium.

[0064] In specific embodiments, the mass ratio of the powder and deionized water is 1:(3-4), and the slurry is formed after mixing and stirring at a speed of 300-400 rpm.

[0065] In specific embodiments, the culture dish is placed at an angle of 10-30°.

[0066] In specific embodiments, the drying temperature is 80-110°C, and the drying time is 6-12 h.

[0067] The application is described below through specific embodiments:

[0068] Embodiment 1

[0069] This embodiment provides a high-entropy fluorite oxide modified calcium-based thermochemical energy storage material, and the specific preparation process is as follows:

[0070] (1) Take calcium nitrate tetrahydrate sample 17.91 g and Zr-containing sample (zirconium nitrate): 0.3801 g, Nd-containing sample (cerium nitrate): 0.3882 g, La-containing sample (lanthanum nitrate): 0.2877 g, Yb-containing sample (neodymium nitrate): 0.3738 g, Ce-containing sample (ytterbium nitrate): 0.3438 g, 80 ml deionized water, and 20 ml ethanol; mix the solution in a water bath and stir until the sample is completely dissolved.

[0071] (2) Take 14.3 g of acetic acid fiber and immerse it in the above mixed solution, and set the solid-liquid ratio to 1 g:7 mL to ensure that the acetic acid fiber completely absorbs the mixed solution, and obtain wet fiber;

[0072] (3) Place the wet fiber in a muffle furnace and calcine it at a heating rate of 5°C / min, heat to 750°C, and keep the temperature constant for 2 h, then naturally cool to room temperature and take out, to obtain calcium-based thermochemical energy storage material powder.

[0073] Embodiment 2

[0074] For large-scale application, the powder material is granulated into spherical media on the basis of Embodiment 1, and the specific steps further include:

[0075] (4) Mix the powder and deionized water according to a mass ratio of 1:3, and continuously stir until a stable slurry is formed;

[0076] (5) Pour the graphite powder into a glass culture dish and evenly spread it to form a smooth and wrinkle-free graphite layer, then place the glass culture dish at a small angle (an angle of 10-30° can be used);

[0077] (6) Use a capillary pipette to suck the slurry and drop it above the culture dish, and use the hydrophobic property of graphite to make the slurry roll down and form small balls with a graphite layer on the surface;

[0078] (7) The obtained graphite layer and small balls are placed in a 105°C oven for drying for 8 hours;

[0079] (8) The graphite layer and small balls are separated by using a screen to obtain spherical medium.

[0080] Example 3

[0081] The procedure is the same as that in Example 2, and the raw material ratio is such that the mass of the sample after calcination is 5 g, the mass ratio of calcium oxide: high-entropy fluorite oxide is 7:3, and the molar ratio of zirconium, cerium, lanthanum, neodymium and ytterbium oxides in the high-entropy fluorite oxide is 1:1:1:1:1.

[0082] Comparative Example 1

[0083] The procedure is the same as that in Example 2, and the sample after calcination is pure calcium oxide, and a pure calcium oxide-based adsorbent material is prepared using a pure calcium nitrate tetrahydrate sample.

[0084] Comparative Example 2

[0085] The procedure is the same as that in Example 2, and the raw material ratio is such that the mass of the sample after calcination is 5 g, the mass ratio of calcium oxide: high-entropy fluorite oxide is 19:1, and the molar ratio of zirconium, cerium, lanthanum, neodymium and ytterbium oxides in the high-entropy fluorite oxide is 1:1:1:1:1.

[0086] Comparative Example 3

[0087] The procedure is the same as that in Example 2, and the raw material ratio is such that the mass of the sample after calcination is 5 g, the mass ratio of calcium oxide: high-entropy fluorite oxide is 0:10, and the molar ratio of zirconium, cerium, lanthanum, neodymium and ytterbium oxides in the high-entropy fluorite oxide is 1:1:1:1:1.

[0088] The sample materials prepared in Examples 1-3 and Comparative Examples 1-3 are named according to the mass percentage of calcium oxide, and Example 1 is 85% sample (powder), Example 2 is 85% sample (small balls), Example 3 is 70% sample (small balls), Comparative Example 1 is 100% sample (small balls), Comparative Example 2 is 95% sample (small balls), and Comparative Example 3 is 0% sample (small balls).

[0089] Test Example

[0090] The 85% sample (powder) of Example 1 is subjected to scanning electron microscope analysis and EDS element analysis, as shown in Figure 1 It can be seen that the calcium-based heat storage material obtained by the application has uniform element distribution, forms a single-phase crystal structure, has a large number of pores, increases the adsorption area of active CaO, and slows down the growth of CaO crystals.

[0091] The sample materials prepared in Example 1, Comparative Example 1 and Comparative Example 3 are subjected to XRD analysis, as shown in Figure 2It can be seen that the diffraction peaks of calcium oxide and high-entropy fluorite oxide in the 85% sample (powder) in Example 1 are not shifted.

[0092] Test 1: The samples of Examples 2-3 and Comparative Examples 1-2 were subjected to a cyclic CO2 adsorption test using a constant HT-4 thermogravimetric analyzer: about 20 mg of the pellets were placed in an alumina crucible and subjected to a cyclic CO2 adsorption test under a specific gas atmosphere, with the temperature set to start at 50°C and increase at a rate of 20°C / min to 850°C, and then start the cycle of carbonation and decarbonation: under a gas atmosphere of nitrogen at a flow rate of 27 ml / min, the sample was held at 850°C for 5 min to complete the decarbonation process, and then decreased at a rate of 20°C / min to 650°C. The gas atmosphere was switched to air at a flow rate of 38 ml / min, and held at 30 min to complete the carbonation process. The gas atmosphere was switched to nitrogen at a flow rate of 27 ml / min, and increased at a rate of 20°C / min to 850°C.

[0093] This is one cycle, and the above process is repeated 20 times to analyze the actual cyclic CO2 adsorption process of the sample.

[0094] Test 2: The samples of Examples 2 and Comparative Examples 1 and 3 were subjected to a CO2 temperature programmed desorption experiment using a TCD analyzer: 100 mg of the sample was weighed into a reaction tube and subjected to a temperature programmed drying pretreatment at a rate of 10°C / min from room temperature to 300°C. He gas was purged at a flow rate of 30 mL / min for 1 h, cooled to 30°C, and then 7% CO2 / He mixed gas was introduced at a flow rate of 30 mL / min for 30 min to saturation, and then He gas was purged at a flow rate of 30 mL / min for 60 min to remove the weakly physically adsorbed CO2 on the surface, and finally the temperature was increased at a rate of 10°C / min to 800°C under He atmosphere to desorb CO2, and the desorbed gas was detected using a TCD analyzer.

[0095] Test 3: The powder precursors of Examples 1 and 3 and Comparative Examples 1 and 2 were subjected to a BET specific surface area and pore size test (BET test) using a specific surface area and pore size analyzer, and the mesopore analysis was performed: the sample was subjected to adsorption and desorption testing at a pre-designed different nitrogen partial pressure at -198.5°C, and the specific surface area of the sample was calculated. Based on the BJH model, the pore area distribution under unit pore size was calculated.

[0096] The patent believes that the cyclic heat storage capacity characterization data of the material has the following: the energy density in a single cycle, the CO2 adsorption amount per unit mass of the material, and the reaction rate, i.e. the derivative of the CO2 adsorption amount with respect to time. The CO2 adsorption, dissociation and migration ability of the material is characterized by the desorption peak and the corresponding temperature of the CO2 temperature programmed desorption curve. The specific calculation formula is as follows:

[0097]

[0098]

[0099]

[0100] C n : CO2 adsorption capacity per unit mass of medium

[0101] V n : reaction rate per unit mass of medium

[0102] D m,n : energy density per unit mass of medium

[0103] As can be seen from Figure 3 , 4 , the energy density of the 100% and 95% samples decreases significantly with the increase of the cycle number, and the cycle stability of the 85% and 70% samples is similar, and the energy density is almost unchanged after 17 cycles. At the same time, due to the high carbonation reaction rate of calcium-based material, the energy density of the 85% sample is greater than that of the 70% sample, and the first cycle adsorption capacity is 1770 and 1520 (kJ / kg), respectively, and the energy density of the twentieth cycle is 1500 and 1370 (kJ / kg), respectively, and the energy density of the 85% sample is higher than that of the 95% sample in the twentieth cycle, which is due to the sintering problem of calcium oxide. When high-entropy fluorite oxide is not added or the amount is small (the dispersion degree of calcium oxide is not enough), calcium oxide is the active substance of the heat storage medium, and when the content of calcium oxide decreases, the energy density of the material decreases, and too much high-entropy fluorite oxide is added. Therefore, when the content of calcium oxide is 70-85%, the prepared calcium-based thermochemical energy storage material has high cycle stability and high energy density.

[0104] As can be seen from Figure 5 , although the maximum reaction rate of the comparative example 1 in the first cycle is 1.58 g CO2 / g heat storage medium / min, the rate significantly decreases to 0.59 g CO2 / g heat storage medium / min after 20 cycles, and the significant decrease in rate is due to the sintering of calcium oxide inside the small ball, and carbon dioxide cannot enter the inside of the spherical medium. As can be seen from Figure 6As shown, in Example 2, the maximum carbonation reaction rates in the first and twentieth cycles were 0.86 and 0.80 (g CO2 / g thermal storage medium / min), respectively, with the rapid reaction phase exceeding 10 min. This is because the high-entropy fluorite oxide has a single-phase structure formed by multiple components, exhibiting ion diffusion retardation. The calcium oxide component is affected by this, resulting in a decrease in the migration rate of calcium ions during the reaction and a reduction in sintering. Simultaneously, the coupling of various components in the high-entropy fluorite oxide collectively promotes the generation of oxygen vacancies, facilitating the adsorption, dissociation, and migration of CO2 on the material surface. This reduces the resistance to CO2 diffusion into the medium and increases the activity of the medium. Therefore, after 20 cycles, Example 1 maintained a good rate during the rapid reaction phase.

[0105] Depend on Figure 7 As shown, the calcium-based thermal storage material obtained in this invention exhibits two desorption peaks in the programmed temperature-ramp desorption test of CO2, located near 415°C and 655°C, respectively. The low-temperature desorption peak of the high-entropy fluorite oxide-modified calcium oxide sample is higher than the high-temperature desorption peak, while the low-temperature desorption peak of the pure calcium oxide sample is one-third of the high-temperature desorption peak. This indicates that the oxygen vacancies present in the high-entropy fluorite oxide partially transform the high-temperature alkaline sites of the calcium-based material into low-temperature alkaline sites, thereby enhancing the material's CO2 adsorption capacity, promoting CO2 migration and dissociation on the surface of the calcium-based material, and ultimately improving the energy density and cycle stability of the calcium-based material after multiple cycles.

[0106] Depend on Figure 8 As shown, the N2 adsorption capacity curves of the precursors in Examples 1 and 3, and Comparative Examples 1-2, as a function of relative pressure indicate that the N2 adsorption capacity of the precursors in Examples 1 and 3 is similar, and both are better than those of the precursors in Comparative Examples 1-2. Figure 9 As shown, the BET specific surface area test results and single-point total pore volume results for the precursors of Examples 1 and 3, and Comparative Examples 1-2 show that the adsorption area per unit mass of the sample continuously increases with the increase of the proportion of high-entropy oxides, with Example 1 reaching 10.97 m. 2 / g, compared to 6.92m of the precursor powder in Comparative Example 1. 2 / g, an increase of about 60%; the sample adsorption volume per unit mass was highest in Example 1, reaching 0.0207 cm³. 3 / g. For example... Figure 10 As shown, the adsorption-desorption pore size distribution data obtained by the BJH method shows that, within the mesoporous range, Example 1 has the best effect, verifying the rationality of the present invention by adding high-entropy fluorite oxide for modification.

[0107] Depend on Figure 11As shown, the energy density of Example 1 and Example 2 in the first cycle is 1.23 GJ / t. Due to the decrease of specific surface area by the granulation process, the energy density of Example 2 slightly attenuates to 1.09 GJ / t after experiencing twenty cycles, which only attenuates 7% compared with Example 1. The energy density of Comparative Example 1 precursor and Comparative Example 1 in the first cycle is 1.59 GJ / t and 1.55 GJ / t, respectively, and is 1.03 GJ / t and 0.51 GJ / t, respectively, after experiencing twenty cycles, which is more than 50% relative to before granulation. Therefore, it is concluded that the cycle stability and energy density of Example 2 after granulation verification are basically the same as those of Example 1 before granulation, which meets the demand of large-scale application, and proves the modification effect of the present application.

[0108] The present application adds high-entropy fluorite oxide for modification, and the oxides of zirconium and four kinds of rare earth elements form XO2 type fluorite oxide, which acts as a physical barrier to prevent CaO crystal growth and aggregation. The prepared material is a porous foam structure, and a large number of pores provide a large adsorption area for active CaO, slow down the sintering of CaO crystal, and the XO2 type fluorite structure can provide oxygen vacancies to promote the adsorption / desorption of carbon dioxide in the adsorption / desorption reaction, and maintain good cycle stability.

[0109] The high-entropy fluorite oxide modified calcium-based thermochemical heat storage material provided by the present application improves the cycle stability, increases the energy density after multiple cycles, and further increases the medium cycle number, has high cycle stability and high energy density, and is a thermochemical heat storage material which can be used in solar thermal power plants, has good cycle capacity, low preparation energy consumption, and the like.

[0110] The above only describes the preferred embodiments of the present application and should not be used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A high-entropy fluorite oxide-modified calcium-based thermochemical heat storage material, characterized in that, The calcium-based thermo-chemical heat storage material has a porous structure and comprises a calcium-based material and a high-entropy fluorite oxide, the calcium-based material accounts for 70-85% in mass percentage, the calcium-based material is calcium oxide, which is used as a large-particle carrier and a heat storage active component; the high-entropy fluorite oxide is a fluorite structure oxide composed of tetravalent oxides of zirconium, cerium, lanthanum, neodymium and ytterbium, which are uniformly distributed on the calcium-based material, and the molar ratio of the oxides of zirconium, cerium, lanthanum, neodymium and ytterbium is 1:1:1:1:

1.

2. The method of producing high-entropy fluorite oxide-modified calcium-based thermochemical heat storage material according to claim 1, characterized in that: The method comprises the following steps: S1, raw materials are weighed according to a proportioning ratio, and a solvent is added to dissolve and prepare a mixed solution; the raw materials comprise calcium nitrate, nitrate salts of zirconium, cerium, lanthanum, neodymium and ytterbium; the proportioning ratio is calculated according to the mass ratio after calcination, and the mass ratio of calcium oxide to high-entropy fluorite oxide is 7:3-17:3, and the molar ratio of the oxides of zirconium, cerium, lanthanum, neodymium and ytterbium in the high-entropy fluorite oxide is 1:1:1:1:1; S2, acetic acid fibers are immersed in the mixed solution to obtain wet fibers; S3, the wet fibers are calcined at a high temperature to obtain a powder, which is a calcium-based thermo-chemical heat storage material modified by a high-entropy fluorite oxide.

3. The preparation method of the calcium-based thermochemical thermal storage material modified with high-entropy fluorite oxide as described in claim 2, characterized in that: The solvent is water and an alcohol solvent, and the dissolving condition is water bath heating at 40-80 ℃.

4. The method of claim 2, wherein the high-entropy fluorite oxide-modified calcium-based thermochemical heat storage material is prepared by the steps of: a) mixing a calcium-based precursor with a fluorite oxide precursor; b) heating the mixture to a temperature of 800-1200 °C; and c) maintaining the temperature for 1-10 hours. In step S2, the solid-liquid ratio of the acetic acid fibers to the mixed solution is 1 g:(6-7) mL.

5. The preparation method of the calcium-based thermochemical thermal storage material modified with high-entropy fluorite oxide as described in claim 2, characterized in that: In step S3, the calcination temperature is 600-900 ℃, the calcination time is 60 min-120 min, and the heating rate of calcination is 5-10 ℃ / min.

6. The preparation method of the calcium-based thermochemical thermal storage material modified with high-entropy fluorite oxide as described in claim 2, characterized in that: The method further comprises granulating the powder to prepare a spherical medium, and the steps are as follows: The powder is added to deionized water, and stirring is performed to form a slurry; Graphite powder is flattened in a petri dish to form a graphite layer, and then the petri dish is placed at an angle; The slurry is sucked up by a capillary tube and dropped on the graphite layer to form small balls by sliding; After drying, the small balls and the graphite layer are sieved to obtain the spherical medium.

7. The preparation method of the calcium-based thermochemical thermal storage material modified with high-entropy fluorite oxide as described in claim 6, characterized in that: The mass ratio of the powder to deionized water is 1:(3-4), and after mixing, the slurry is formed by stirring at a rate of 300-400 rpm.

8. The preparation method of the calcium-based thermochemical thermal storage material modified with high-entropy fluorite oxide as described in claim 6, characterized in that: The petri dish is placed at an angle of 10-30°, the drying temperature is 80-110 ℃, and the drying time is 6-12 h.

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