Heat storage material and method for producing same, and method for utilizing thermal energy

Abstract

A heat storage material according to the present invention is characterized in that: said heat storage material contains a layered manganese oxide (100) which is represented by formulae (1) and (2) and which has a delta-type crystal structure; and the thickness of the layered manganese oxide (100) in the C-axis direction is 15 nm or less.　(1): AxMnO2 ⋅ H2O [In formulae (1) and (2): A is a symbol collectively representing elements A1, A2, ..., Am for maintaining a delta-type crystal structure; m is an integer greater than or equal to 1; X1, X2, ..., Xm respectively represent the composition ratios of the elements A1, A2, ..., Am, are numbers 0.00-0.50, and satisfy 0.00 < X1 + X2 + ... + Xm ≦0.50; and n is a number 0.00-2.50.]

Description

Heat storage material, method for manufacturing the same, and method for utilizing thermal energy

[0001] This invention relates to a heat storage material, a method for manufacturing the same, and a method for utilizing thermal energy. This application claims priority based on Japanese Patent Application No. 2024-159422, filed in Japan on September 13, 2024, the contents of which are incorporated herein by reference.

[0002] In recent years, efforts to effectively utilize sustainable energy sources have attracted attention from the perspective of protecting the global environment. For example, heat recovery systems such as chemical heat pumps, which effectively utilize surplus waste heat as a heat source, are well known.

[0003] A chemical heat pump is a system that uses the exothermic and endothermic phenomena associated with reversible chemical reactions (hydration and dehydration reactions) between a reaction medium and a heat storage material to supply (dissipate) and store heat. As a heat storage material to be used in a chemical heat pump, for example, Patent Document 1 proposes one containing magnesium sulfate. Magnesium sulfate can absorb a large amount of water, so it has a high energy density and can increase the amount of heat stored.

[0004] However, when magnesium sulfate absorbs water, its surface deliquesces and its crystal structure changes significantly, causing a decrease in the reaction rate and making it difficult for the reversible reaction to proceed. In this case, the heat dissipation rate decreases, which makes it difficult to reuse the material. To address this problem, for example, Patent Document 2 proposes a heat storage material containing lanthanum sulfate hydrate. According to Patent Document 2, lanthanum sulfate hydrate undergoes little change in its crystal structure when it absorbs water, thus maintaining a high reaction rate and promoting the reversible reaction. However, since lanthanum sulfate hydrate cannot absorb a large amount of water, it is difficult to increase the heat storage energy density of the heat storage material.

[0005] Japanese Patent Publication No. 2014-177619, International Publication No. 2017 / 099197

[0006] This invention has been made in view of the above circumstances, and aims to provide a heat storage material with increased heat storage capacity, a method for manufacturing the same, and a method for utilizing thermal energy using the heat storage material.

[0007] In order to solve the above problems, the present invention employs the following means.

[0008] 〔1〕The heat storage material according to one aspect of the present invention includes a layered manganese oxide represented by the following formulas (1) and (2) and having a delta-type crystal structure, and the thickness of the layered manganese oxide in the C-axis direction is 15 nm or less.

[0009] A Ｘ MnO ２ ・nH ２ O・・・(1)

[0010]

[0011] In the above formulas (1) and (2), A is a symbol collectively representing interlayer elements A １ , A ２ ,..., A ｍ ; m is a natural number; X1, X2,..., Xm each represent the composition ratio of the interlayer elements A １ , A ２ ,..., A ｍ ; they are numbers greater than or equal to 0 and less than or equal to 0.50, and satisfy 0 < X1 + X2 +... + Xm ≤ 0.50; n is a number greater than or equal to 0 and less than or equal to 2.50.

[0012] 〔2〕In the heat storage material according to the above [1], at least one of K, Na, Mg, Ca, Ni, Cu, and Zn may be included in the interlayer elements A １ , A ２ ,..., A ｍ .

[0013] 〔3〕In the heat storage material according to any one of the above [1] or [2], the width in the direction orthogonal to the C-axis may be 1 to 100 times the thickness in the C-axis direction.

[0014] 〔4〕The method for producing a heat storage material according to one aspect of the present invention is the method for producing a heat storage material according to any one of the above [1] to [3], and the preparation and heating of the raw materials of the heat storage material are carried out in an environment of 200 °C or lower.

[0015] [5] The method for utilizing thermal energy according to one aspect of the present invention is a method for utilizing thermal energy by the heat storage material described in any one of [1] to [4] above, and has a heat storage step of heating the heat storage material, desorbing water from the heat storage material, and storing heat.

[0016] [6] In the method for utilizing thermal energy described in [5] above, it may further have a heat release step of adsorbing water to the heat storage material that has stored heat and releasing heat.

[0017] According to the present invention, it is possible to provide a heat storage material with an increased heat storage amount, a method for manufacturing the same, and a method for utilizing thermal energy by the heat storage material.

[0018] This is a schematic diagram showing the crystal structure of layered manganese oxide contained in a heat storage material according to one embodiment of the present invention. This is an enlarged view of a part of the heat storage material in Figure 1A. This is a graph showing the relationship between the layered structure and the amount of water adsorbed in the layered manganese oxide of the same embodiment. This is a graph showing the results of X-ray diffraction measurements for the heat storage materials of Examples 1 and 2 and Comparative Example 1. This is a TEM image of the heat storage material of Example 1. This is a TEM image of the heat storage material of Example 2. This is a TEM image of the heat storage material of Comparative Example 1. This is a graph showing the TG / DTA results for the heat storage materials of Examples 1 and 2 and Comparative Example 1. This is a graph showing the results of water vapor adsorption isotherm measurements at 25°C for the heat storage materials of Examples 1 and 2 and Comparative Example 1. This is a graph showing the TG / DSC results for measuring the amount of heat generated and the amount of water adsorbed in the heat storage materials of Examples 1 and 2 and Comparative Example 1. This is a graph showing the TG / DSC results for measuring the amount of heat absorbed and the amount of water desorbed in the heat storage materials of Examples 1 and 2 and Comparative Example 1. This graph shows the TG / DTA cycle characteristics of the heat storage material of Example 1. This graph shows the TG / DTA results of the heat storage material of Example 3. This graph shows the TG / DTA results of the heat storage material of Example 4. This graph shows the TG / DTA results of the heat storage material of Example 5. This graph shows the TG / DTA results of the heat storage material of Example 6. This graph shows the TG / DTA results of the heat storage material of Example 7. This graph shows the TG / DTA results of the heat storage material of Example 8. This graph shows the TG / DSC results for measuring the heat generation amount and water molecule adsorption amount of the heat storage material of Example 6. This graph shows the results of nitrogen adsorption isotherm measurement at -196°C for specific surface area identification of the heat storage material of Example 6. This graph shows the volume energy density measurement results of the heat storage materials of Examples 1, 2, 6 and Comparative Example 1.

[0019] The following describes in detail, with reference to the drawings, a heat storage material, a method for manufacturing the same, and a method for utilizing thermal energy according to an embodiment of the present invention. Note that, for the sake of clarity, the drawings used in the following description may show enlarged versions of key features, and the dimensional ratios of each component may not be the same as those in reality. Furthermore, the materials, dimensions, etc., exemplified in the following description are merely examples, and the present invention is not limited to these; it can be modified as appropriate without altering its essence.

[0020] [Heat Storage Material] Figure 1A is a schematic diagram showing the crystal structure of layered manganese oxide 100 contained in a heat storage material according to one embodiment of the present invention. The layered manganese oxide 100 is represented by the following equations (1) and (2), and has a delta-type crystal structure (crystallite). Examples of layered manganese oxide 100 include delta-type manganese dioxide, δ-type manganese dioxide, and δ-type MnO ２ δ-MnO ２ Layered manganese dioxide or the like may also be used.

[0021] A Ｘ MnO ２ nH ２ O... (1)

[0022]

[0023] The definitions of each symbol in equations (1) and (2) above are as follows: A in equation (1) is element A, which is necessary to maintain the delta-type crystal structure. １ A ２ , ..., A ｍ This is a symbol that represents all of them together. Below, element A １ A ２ , ..., A ｍ This is sometimes simply called element A. (2) The symbol m represents a natural number. (2) X1, X2, ..., Xm are each element A １ A ２ , ..., A ｍThe symbol represents the composition ratio, which is between 0.00 and 0.50, and satisfies the condition 0.00 < X1 + X2 + ... + Xm ≤ 0.50. The X in equation (1) is a symbol representing the sum of X1, X2, ..., Xm in equation (2). The n in equation (1) is a symbol representing a number between 0.00 and 2.50. In this embodiment, "0.00 or more" can be considered as substantially equivalent to "0 or more".

[0024] As shown in Figure 1A, the layered manganese oxide 100 is, for example, MnO ６ The material has a hexagonal crystal structure in which layers 101 of manganese oxide are arranged (stacked) in the C-axis direction, and these layers 101 are based on a crystalline structure in which oxygen octahedra are connected by sharing vertices. Here, the case in which the layered manganese oxide 100 is composed of three layers 101 of manganese oxide is illustrated. The interlayer region S sandwiched between two adjacent layers 101 contains interlayer atoms (element A) 102 to maintain the delta-type crystalline structure.

[0025] Figure 1B is an enlarged view of a part P of the layered manganese oxide 100 in Figure 1A. Further water molecules (water, water vapor) 103 can be inserted and adsorbed (absorbed) in the interlayer region S. Also, water molecules 103 can be adsorbed (absorbed) on the outermost surface (outermost surface) 101a of the outermost layer, located at the end in the stacking direction L (C axis direction). The layered manganese oxide 100 generates heat by adsorbing water molecules 103 in the interlayer region S and absorbs heat by desorbing water molecules 103 from the interlayer region S. Furthermore, the layered manganese oxide 100 generates heat by adsorbing water molecules on the surface 101a of the outermost layer and absorbs heat by desorbing water molecules from the surface 101a of the outermost layer.

[0026] The layered manganese oxide 100 can repeatedly undergo exothermic (heat dissipation) and endothermic (heat storage) reactions as a reversible reaction through the insertion of water molecules 103 into the interlayer regions S and the desorption of water molecules 103 from the interlayer regions S. This reversible reaction is also called the water intercalation reaction. In this reversible reaction, the manganese oxide constituting each layer plays the role of a host, and the water molecules play the role of a guest. Because the layered manganese oxide 100 can intercalate and adsorb / desorb many water molecules 103 into the interlayer regions S and the surface 101a of the outermost layer through slight structural changes, it can achieve a high reaction rate and a high heat storage capacity.

[0027] The layered manganese oxide 100 consists of nanometer-sized crystallites. By reducing the size of the crystallites along the C-axis, the ratio of surface area to volume (specific surface area) increases, thereby improving the surface adsorption rate of water molecules 103. If adsorption to the crystal sides is possible, the amount of adsorption can be similarly improved.

[0028] Figure 2 is a graph showing the relationship between the layered structure and the amount of water molecules 103 adsorbed in layered manganese oxide 100. The lower horizontal axis of the graph shows the number of layers of manganese oxide stacked in the C-axis direction. The upper horizontal axis of the graph shows the thickness T [nm] of the manganese oxide in the C-axis direction. The vertical axis of the graph shows the molar ratio of water molecules to manganese oxide. ｉｎｔ , lol ａｄｓ These are the molar ratios (adsorption rates) of water molecules adsorbed at the interlayer and outermost layer surfaces, respectively, and w ｔｏｔａｌ This is the molar ratio of their total.

[0029] In this embodiment, the thickness T in the C-axis direction of the crystallite is about 15 nm or less, preferably 10 nm or less, and more preferably 7 nm or less. From the viewpoint of actual manufacturing, the lower limit of the thickness T is about 0.5 nm (i.e., manganese oxide (MnO ２(It is assumed that layer 101 is a single monosheet.) In the thickness T range of 15 nm or less, the number of manganese oxide layers stacked in the C-axis direction is generally between 1 and 20. As shown in Figure 2, in the range where the number of manganese oxide layers is 20 or less, the effect of the number of layers on the water molecule adsorption rate differs between the interlayers and the surface of the outermost layer. Interlayer adsorption rate w ｉｎｔ Even if the number of layers is reduced, it doesn't change much, but the adsorption rate on the surface of the outermost layer lol ａｄｓ The adsorption rate of the entire layered manganese oxide 100 increases sharply with decreasing number of layers. ｔｏｔａｌ This will also increase. Furthermore, as the number of manganese oxide layers decreases, the bonding force due to van der Waals forces in each layer weakens, so the distance R between adjacent layers tends to increase slightly.

[0030] From the viewpoint of improving the amount of water molecules adsorbed, it is preferable that the crystallites are thinner in the C-axis direction and that the number of manganese oxide layers be small. From the same viewpoint, it is preferable that the width W in the direction perpendicular to the C-axis of the crystallites be small, but when crystallites are prepared so that the thickness is about 15 nm or less, this width W tends to be in the range of about 1 to 100 times the thickness T. By adjusting the crystallite preparation conditions, it is also possible to obtain layered manganese oxide 100 having a width W outside this range.

[0031] Examples of interlayer atoms 102 (element A) for maintaining the delta-type crystal structure include metalloid elements and metallic elements, but metallic elements are particularly preferred. From the viewpoint of ease of insertion into the interlayer region S of the layered manganese oxide 100 and stability, metallic elements capable of forming cations are more preferred as interlayer atoms 102 (element A), and metallic elements capable of forming monovalent or divalent cations are even more preferred. Examples of metallic elements capable of forming cations include alkali metal elements, alkaline earth metal elements, base metal elements, and transition metal elements.

[0032] Examples of alkali metal elements include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).

[0033] Examples of alkaline earth metal elements include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).

[0034] Examples of base metal elements include aluminum (Al), gallium (Ga), indium (In), thallium (Tl), tin (Sn), lead (Pb), and bismuth (Bi).

[0035] Examples of transition metal elements include scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), zirconium (Zr), molybdenum (Mo), palladium (Pd), silver (Ag), cadmium (Cd), tungsten (W), platinum (Pt), and gold (Au).

[0036] Among the metal elements that can form the aforementioned cations, potassium, sodium, lithium, cesium, calcium, zinc, copper, aluminum, magnesium, and nickel are particularly preferred. That is, interlayer atom 102 (element A) (A １ A ２ , ..., A ｍ Preferably, the interlayer contains at least one of K, Na, Mg, Ca, Ni, Cu, and Zn. The interlayer atoms 102 contained in the interlayer region S may be of one type or multiple types. When the crystallite thickness T (number of layers) is within the above range, the adsorption rate of water molecules can be increased by using multiple types of interlayer atoms 102, including nickel, and can be further increased by using only one type, Ni.

[0037] In equation (1) above, X represents the ratio of moles of interlayer atoms 102 to moles of manganese atoms. By setting this ratio to be greater than 0 and less than or equal to 0.5, the crystal structure of the layered manganese oxide 100 can be stabilized, increasing the amount of water molecules adsorbed, and consequently increasing the energy density and heat storage capacity. By setting X to be greater than 0, the layered manganese oxide 100 can be made more resistant to repeated use as a heat storage material. Furthermore, by setting X to less than or equal to 0.5, the interlayers of the layered manganese oxide 100 can be secured, increasing the amount of water molecules 103 absorbed in the interlayer region S.

[0038] X can be determined, for example, by X-ray structural analysis, energy-dispersive X-ray spectroscopy (EDS), inductively coupled plasma spectroscopy (ICP), etc. X can be prepared by chemical treatment using an acid such as hydrochloric acid, electrochemical treatment, or a combination of these treatments.

[0039] [Method for Manufacturing Heat Storage Material] The heat storage material of this embodiment can be manufactured by synthesizing layered manganese oxide by preparing and heating raw materials in an oxygen-containing environment, and then performing predetermined post-treatments such as centrifugation, washing, and drying the required number of times. Heating during synthesis is carried out in a temperature range of room temperature (20±5℃) to about 200℃. Specific synthesis methods include, for example, synthesis methods utilizing oxidation-reduction reactions and hydrothermal synthesis methods.

[0040] In synthesis methods utilizing redox reactions, potassium permanganate (KMnO) is produced at room temperature. ４ Mix the solution with a sodium hydroxide (NaOH) solution, and then add manganese chloride (MnCl) to the resulting mixture. ２ By adding and mixing the solution and allowing it to react, layered manganese oxide can be synthesized.

[0041] In the hydrothermal synthesis method, potassium permanganate and manganese sulfate (MnSO4) are synthesized in hot water at approximately 120°C. ４Layered manganese oxide can be synthesized by mixing and reacting these substances. In this case, the size of the layered manganese oxide is larger than that of the layered manganese oxide produced using a redox reaction.

[0042] Furthermore, the thermal decomposition synthesis method requires high-temperature heating of approximately 700°C, and it is not possible to achieve a thickness of 15 nm or less in the resulting layered manganese oxide, making it difficult to use in this embodiment.

[0043] In the manufactured layered manganese oxide, the interlayer atoms (element A) are potassium. By performing an elemental substitution treatment on this layered manganese oxide, some or all of the elements in the interlayer atoms can be replaced with other elements. The elemental substitution treatment is a process in which the layered manganese oxide is reacted with an acidic aqueous solution containing ions of the element to be substituted. For example, when the elements to be substituted are Na, Ca, Mg, Ni, Zn, and Cu, the solutions are NaCl, Ca(NO), and so on. ３ ) ２ MgSO ４ NiCl ２ ZnSO ４ , CdSO ４ It is reacted with an aqueous solution.

[0044] [Method of Utilizing Thermal Energy] The method of utilizing thermal energy using the heat storage material of this embodiment includes a heat storage step. In the heat storage step, the heat storage material is heated, water is removed from the heat storage material, and heat is stored. The method of heating the heat storage material is not particularly limited and includes, for example, exposing it to direct sunlight, utilizing waste heat from a factory, utilizing waste heat from an engine of an automobile, heating it with an oven or heater, etc. From the viewpoint of effectively utilizing energy, the methods of heating the heat storage material are preferably exposing it to direct sunlight, utilizing waste heat from a factory, or utilizing waste heat from an engine of an automobile, etc.

[0045] The temperature range for heating the heat storage material (hereinafter also referred to as the "heating temperature") is preferably 50°C to 350°C (50°C or higher and 350°C or lower), more preferably 80°C to 250°C, and even more preferably 100°C to 200°C. When the heating temperature is 50°C or higher, water molecules can be sufficiently removed from the heat storage material. When the heating temperature is 350°C or lower, structural changes in the heat storage material can be suppressed.

[0046] The heating time for heating the heat storage material is preferably between 10 minutes and 6 hours, more preferably between 30 minutes and 4 hours, and even more preferably between 1 hour and 3 hours. A heating time of 10 minutes or more ensures sufficient heat storage. A heating time of 6 hours or less further improves the ease of use (usability) of the heat storage material.

[0047] The amount of heat stored in the heat storage process, when converted to a volumetric energy density, is 1000 MJ / m³. ３ Preferably, the above is 1100 MJ / m ３ More preferably, the above is 1200 MJ / m ３ The above is even more preferable. The amount of heat stored in the heat storage process is 1000 MJ / m³. ３ If the above is achieved, a sufficient amount of thermal energy can be released. The upper limit of the amount of heat stored in the interlayer during the heat storage process is 2000 MJ / m, which is the limit value for the water molecule intercalation reaction at 100-200°C. ３ This is considered to be the case. Furthermore, it is expected that an even greater amount of heat storage can be achieved by utilizing the surface adsorption of layered manganese oxide. The amount of heat stored in the heat storage process can be determined, for example, by differential scanning calorimetry (DSC).

[0048] The method for utilizing thermal energy using the heat storage material of this embodiment may further include a heat dissipation step. In the heat dissipation step, water molecules are adsorbed onto the heat storage material by exposure to air of a predetermined humidity, cooling, etc., and the heat is released. The relative humidity range of the air in the heat dissipation step is preferably, for example, 5% or more and 99% RH or less, more preferably 20 to 99% RH, and even more preferably 40 to 99% RH. When the relative humidity of the air is 40% RH or higher, the contact efficiency between the heat storage material and water is increased, and more water molecules can be adsorbed.

[0049] The ambient temperature range during the heat dissipation process is preferably 0 to 40°C, more preferably 5 to 35°C, and even more preferably 10 to 30°C. When the ambient temperature is 0°C or higher, more water molecules can be adsorbed onto the heat storage material. When the ambient temperature is 40°C or lower, the heat dissipation effect can be further enhanced.

[0050] The amount of heat dissipated in the heat dissipation process is preferably 50 J / g or more per unit mass of the heat storage material, more preferably 100 J / g or more, and even more preferably 150 J / g or more. If the amount of heat dissipated in the heat dissipation process is 50 J / g or more, a sufficient amount of thermal energy can be dissipated. The upper limit of the amount of heat dissipated in the heat dissipation process is not particularly limited, but for example, it is 1400 J / g. The amount of heat dissipated in the heat dissipation process can be determined, for example, by DSC.

[0051] In this embodiment, the method of utilizing thermal energy preferably involves alternating between a heat storage process and a heat release process. That is, in this embodiment, the method of utilizing thermal energy preferably involves two or more cycles, with the heat storage process and the heat release process forming one cycle. By repeating the heat storage process and the heat release process, thermal energy can be reused, contributing to the effective and sustainable use of energy. The number of cycles between the heat storage process and the heat release process (hereinafter also referred to as the "number of cycles") is two or more, preferably five or more, more preferably ten or more, and even more preferably fifteen or more. When the number of cycles is two or more, thermal energy can be effectively utilized. There is no particular upper limit to the number of cycles, but for example, it can be 50. The order in which the heat storage process and the heat release process are performed does not matter.

[0052] As described above, the layered manganese oxide 100 constituting the heat storage material of this embodiment is nanometer-sized, and the thickness T in the C-axis direction where each layer 101 of the manganese oxide overlaps is 15 nm or less. Layered manganese oxide 100 of this size can be obtained by preparing and heating the raw materials in an environment of 200°C or less.

[0053] Each layered manganese oxide 100 is reduced to approximately one-third or less in size compared to conventional layered manganese oxides intended for adsorption and desorption of water molecules in the interlayer region S, resulting in a larger specific surface area. In particular, the specific surface area of ​​layered manganese oxides synthesized by oxidation-reduction reactions is more than 10 times that of conventional layered manganese oxides. Therefore, the amount of water molecules 103 adsorbed in each layered manganese oxide 100 can be significantly increased. In particular, the ratio of the amount of water molecules adsorbed to the surface 101a of the outermost layer of each layered manganese oxide 100 can be increased. Consequently, the heat storage capacity of each layered manganese oxide 100 can be increased, and overall, a heat storage material with increased heat storage energy can be realized.

[0054] By using the heat storage material of this embodiment, large-capacity heat storage and release can be achieved, enabling the utilization of high thermal energy. By repeatedly storing and releasing heat using the heat storage material of this embodiment, reversible and sustainable high-energy effective utilization can be realized.

[0055] The effects of the present invention will be made clearer by the following examples. However, the present invention is not limited to the following examples and can be modified as appropriate without altering its essence.

[0056] (Example 1) Layered manganese oxide was synthesized using a redox reaction in an oxygen-containing environment at room temperature (20±5℃), and a sample of heat storage material was produced by post-processing such as centrifugation and washing. In the synthesis of layered manganese oxide, a potassium permanganate solution (pure water: 256 mL, KMnO) was added to a sodium hydroxide solution (pure water: 288 mL, NaOH: 5.6 g). ４ Add 8g of (mn) and mix (stir) to the resulting mixture, and then add manganese chloride solution (pure water: 256mL, Mn ２ Cl ２ 4H ２ O: 15g) was added and mixed.

[0057] (Example 2) Layered manganese oxide was synthesized by hydrothermal synthesis in a high-temperature environment with oxygen present, and a sample of heat storage material was produced by post-processing such as washing and drying. In the synthesis of layered manganese oxide, potassium permanganate powder (20.5 g) and manganese sulfate powder (6.0 g) were mixed in hot water (100 mL) at approximately 120°C.

[0058] (Comparative Example 1) Layered manganese oxide was synthesized by thermal decomposition in air, and a sample of heat storage material was produced by post-processing such as washing and drying. In the synthesis of layered manganese oxide, potassium permanganate (30 g) powder was heat-treated at approximately 700°C for approximately 5 hours under normal atmospheric pressure (1 atm) in the presence of air.

[0059] <Confirmation of Crystal Structure> X-ray diffraction measurements were performed on samples of the heat storage materials from Examples 1 and 2 and Comparative Example 1. Figure 3 is a graph showing the results. The X-ray diffraction patterns of all samples have peaks at the same positions as the ideal X-ray diffraction pattern obtained from simulations. From these results, it can be seen that all samples contain correctly synthesized layered manganese oxide. Furthermore, when comparing the peaks corresponding to the stacking direction of manganese oxide 101 in the X-ray diffraction patterns of each sample, the peak width widens in the order of Comparative Example 1, Example 2, and Example 1. From these results, it can be considered that the number of manganese oxide layers in the synthesized layered manganese oxide decreases and the specific surface area of ​​the layered manganese oxide increases in the order of Comparative Example 1, Example 2, and Example 1.

[0060] <Comparison of Crystallite Sizes> TEM observations were performed on samples of the heat storage materials from Examples 1 and 2 and Comparative Example 1. Figures 4A, 4B, and 4C are TEM images of the layered manganese oxide contained in the samples from Example 1, Example 2, and Comparative Example 1, respectively. The crystal size of the synthesized layered manganese oxide decreases in the order of Comparative Example 1, Example 2, and Example 1. The thickness in the C-axis direction of the layered manganese oxide synthesized in Example 1, Example 2, and Comparative Example 1 is 7-35 nm, 26-42 nm, and 100-200 nm, respectively. From these results, it can be seen that the number of manganese oxide layers is actually reduced in the samples from Examples 1 and 2, and it is considered that the specific surface area of ​​the layered manganese oxide is increased.

[0061] Table 1 shows the average thickness in the C-axis direction and specific surface area of ​​the layered manganese oxide contained in each sample. The layered manganese oxide obtained by the oxidation-reduction reaction synthesis method (Example 1) and the hydrothermal synthesis method (Example 2) have less than half the thickness and more than twice the specific surface area compared to the layered manganese oxide obtained by thermal decomposition (Comparative Example 1).

[0062]

[0063] <Confirmation of the amount of adsorbable and desorbable water molecules> Thermal analysis was performed on the samples of Examples 1 and 2 and Comparative Example 1 using a thermogravimetric differential thermal analyzer (TG / DTA, high-concentration water vapor atmosphere differential thermal balance (manufactured by Rigaku Corporation)) in an environment of nitrogen gas (nitrogen gas with a water content of 2.2 mass%) at a relative humidity of 70% RH at 25°C and 1 atm. Specifically, each sample was heated to 320°C at a heating rate of 20°C / min, and then cooled to 25°C at a cooling rate of 5°C / min, during which the differential heat and thermogravimetric analysis were measured. Figure 5 is a graph showing the results. The upper graph shows the measurement results of the temperature change of differential heat (DTA), and the lower graph shows the measurement results of the temperature change of weight (TG).

[0064] From the graphs of weight change with temperature, the thermogravimetric (mass) of the samples in Example 1 (shown with downward-pointing triangular markers (white indicates cooling, filled in indicates overheating)), Example 2 (shown with upward-pointing triangular markers (white indicates cooling, filled in indicates overheating)), and Comparative Example 1 (shown with circular markers (white indicates cooling, filled in indicates overheating)) all decreased with increasing temperature due to heating and increased with decreasing temperature due to cooling. The change in thermogravimetric is equivalent to the change in the number of water molecules contained in the sample. The decrease in thermogravimetric is significantly different for each sample during heating from 25°C to 320°C. In this case, the decrease in thermogravimetric is equivalent to the maximum amount of water absorbed, which is 0.74 molL for the sample in Example 1, 0.62 molL for the sample in Example 2, and 0.50 molL for the sample in Comparative Example 1, per 1 molL of layered manganese oxide. These results show that the number of water molecules that can be absorbed by the sample in Example 1 is approximately 1.5 times that of the sample in Comparative Example 1, and the number of water molecules that can be absorbed by the sample in Example 2 is approximately 1.2 times that of the sample in Example 2. Therefore, it can be seen that the samples in Examples 1 and 2 are heat storage materials that have increased heat storage capacity through the adsorption and desorption of water molecules.

[0065] During heating, the thermogravimetric values ​​of the samples in Examples 1 and 2 decreased gradually across the entire temperature range from 25°C to 320°C. Furthermore, during cooling, the thermogravimetric values ​​of the samples in Examples 1 and 2 increased gradually across the entire temperature range from 320°C to 25°C.

[0066] During heating, the thermogravimetric weight of the sample in Comparative Example 1 decreased gradually in the temperature range of 25°C to 100°C, decreased sharply in the temperature range of 100°C to 160°C, and decreased gradually in the temperature range of 160°C to 320°C. Furthermore, during cooling, the thermogravimetric weight of the sample in Comparative Example 1 increased gradually in the temperature range of 320°C to 130°C, increased sharply in the temperature range of 130°C to 80°C, and increased gradually in the temperature range of 80°C to 25°C.

[0067] From the temperature change graph of differential heat, it can be seen that in all samples of Examples 1, 2, and Comparative Example 1, there are endothermic peaks due to the desorption of water molecules and exothermic peaks due to the adsorption of water molecules. The temperatures of the endothermic and exothermic peaks differ for each sample. In the sample of Comparative Example 1, endothermic peaks were observed at temperatures of approximately 70°C and 150°C during heating, and an exothermic peak was observed at a temperature of approximately 100°C during cooling. In the sample of Example 1, an endothermic peak was observed at a temperature of approximately 70°C during heating, and a broad exothermic peak was observed when the temperature was between approximately 80 and 130°C during cooling. In the sample of Example 2, endothermic peaks were observed at temperatures of approximately 70°C and 160°C during heating, and an exothermic peak was observed at a temperature of approximately 120°C during cooling. The endothermic peaks indicate that water molecules were desorbed from the interlayer and the surface of the outermost layer, and the temperature of the endothermic peak is considered to be the water molecule desorption temperature. The exothermic peak indicates that water molecules have been adsorbed between the layers, and the temperature at the exothermic peak is considered to be the adsorption temperature of the water molecules.

[0068] <Comparison of Water Molecule Adsorption Amount> The water vapor adsorption isotherms of the samples from Examples 1 and 2 and Comparative Example 1 were measured. The measurement temperature was set to 25 [°C]. Figure 6 is a graph showing the results. It can be seen that the amount of water molecules absorbed by the samples from Examples 1 and 2 is greater than that of the sample from Comparative Example 1. Furthermore, in Comparative Example 1, the adsorption (desorption) isotherms during adsorption and desorption are almost identical, whereas in Examples 1 and 2, the adsorption (desorption) isotherm is larger during desorption than during adsorption.

[0069] <Confirmation of Heat Generation> Thermal analysis was performed on the samples of Examples 1 and 2 and Comparative Example 1 using a thermogravimetric / suggestive scanning calorimetry (TG / DSC) system. Specifically, each sample was heated to 300°C in a dry argon atmosphere to a dry state, and then cooled in a dry argon atmosphere while remaining dry. The cooling temperature was set to 28°C. After cooling, the samples were exposed to a gas containing water and argon at 28°C, and the heat generation characteristics of each sample due to water absorption in this state were measured. Figure 7 is a graph showing the results for Example 1 (indicated by a circular marker (white indicates cooling, and filled in indicates overheating)), Example 2 (indicated by a downward-pointing triangle marker (white indicates cooling, and filled in indicates overheating)), and Comparative Example 1 (indicated by an upward-pointing triangle marker (white indicates cooling, and filled in indicates overheating)). The marked solid line shows DSC (W / g), the solid line shows the calorific value (J / g), and the dashed line shows the weight change (mol ratio).

[0070] Exothermic reaction begins immediately after exposure (0 [s]), reaching a peak after approximately 200 seconds. Afterward, the amount of heat released decreases, and the exothermic reaction ends when it reaches almost zero. The exothermic amounts for the samples in Examples 1 and 2 and Comparative Example 1 are 298.8 [J / g], 286.3 [J / g], and 249.2 [J / g], respectively. Higher exothermic amounts were obtained in the samples of Examples 1 and 2 compared to the sample of Comparative Example 1. Furthermore, the amount of water molecules adsorbed by the samples in Examples 1 and 2 and Comparative Example 1, per 1 mol of layered manganese oxide, is 0.59 mol, 0.54 mol, and 0.45 mol, respectively. Higher water molecule adsorption was obtained in the samples of Examples 1 and 2 compared to the sample of Comparative Example 1.

[0071] <Confirmation of Endothermic Amount> Thermal analysis was performed on the samples of Examples 1 and 2 and Comparative Example 1 using a thermogravimetric / suggestive scanning calorimetry (TG / DSC) apparatus. Specifically, each sample was exposed to a gas containing water and argon at 28°C to induce a hydrated state, and then heated under a dry argon atmosphere. The heating temperature was set to 350°C and the heating rate to 10°C / min. The endothermic characteristics of each sample were measured by releasing water under these conditions (1st heat). Subsequently, the samples were cooled to 28°C at 20°C / min under a dry argon atmosphere. Then, while still in a dry state, they were heated again under a dry argon atmosphere. The heating temperature was set to 350°C and the heating rate to 10°C / min (2nd heat).

[0072] Figure 8 is a graph showing the measurement results for Example 1 (shown with a circular marker (white indicates cooling, filled in indicates overheating)), Example 2 (shown with a downward-pointing triangular marker (white indicates cooling, filled in indicates overheating)), and Comparative Example 1 (shown with an upward-pointing triangular marker (white indicates cooling, filled in indicates overheating)). The dashed line shows the weight change (molar ratio), the solid line with a filled marker shows the DSC (W / g) of the 1st heat, and the solid line with a white marker shows the DSC (W / g) of the 2nd heat. In the 1st heat, MnO ２ The specific heat (sensible heat) and the endothermic heat, including the latent heat associated with water desorption, are observed. On the other hand, in the 2nd heat, MnO ２ Only endothermic heating due to the specific heat of the substance is observed. This is because the dry sample is being heated, so no water desorption occurs.

[0073] The latent heat (endothermic) associated with water molecule desorption was evaluated by integrating the differences between these DSC plots. The endothermic amounts for the samples in Examples 1 and 2 and Comparative Example 1 were 281.8 [J / g], 270.0 [J / g], and 237.0 [J / g], respectively. Higher endothermic amounts were obtained in the samples of Examples 1 and 2 compared to the sample of Comparative Example 1. Furthermore, the amounts of water molecules desorbed in the samples of Examples 1 and 2 and Comparative Example 1 were 0.56 mol, 0.53 mol, and 0.44 mol, respectively, per 1 mol of layered manganese oxide. Higher amounts of water molecule desorption were obtained in the samples of Examples 1 and 2 compared to the sample of Comparative Example 1.

[0074] These results are thought to be due to the fact that in the samples of Examples 1 and 2, the size of each individual layered manganese oxide molecule was small, resulting in a large specific surface area. Layered manganese oxide molecules with a large specific surface area can adsorb more water molecules when the temperature is lowered, and can release more heat in proportion to the amount of water molecules adsorbed. Conversely, layered manganese oxide molecules with a large specific surface area can release more water molecules when the temperature is raised, and can absorb more heat in proportion to the amount of water molecules released.

[0075] <Evaluation of the cycle characteristics of the adsorption / desorption reaction> For the sample from Example 1, thermal analysis was repeated multiple times using a thermogravimetric differential thermal analyzer (TG / DTA, high-concentration water vapor atmosphere differential thermal balance (manufactured by Rigaku Corporation)) in an environment of nitrogen gas (nitrogen gas with a water content of 2.2 mass%) at a relative humidity of 70% RH. Sixteen cycles were performed. Specifically, in the first 1 to 6 cycles, each sample was heated to 320°C while changing the heating rate according to the cycle, and then cooled to 30°C at a cooling rate of 5°C / min. This process constituted one cycle, and the differential heat and thermogravimetric data were measured for each cycle. The heating rates were 10, 20, 40, 60, 80, and 100°C / min, respectively, from the first cycle onward. Next, in cycles 7 to 16, each sample was heated to 320°C at a heating rate of 20°C / min, and then cooled to 30°C at a cooling rate of 5°C / min. This process constituted one cycle, and the differential heat and thermogravimetricity were measured for each cycle. Figure 9 shows the results in graph form. The upper graph shows the measurement results of the temperature change of differential heat (DTA), and the lower graph shows the measurement results of the temperature change of thermogravimetricity (TG). Here, the temperature changes of thermogravimetricity and differential heat for cycles 7 to 16 are shown.

[0076] Since the temperature changes of thermogravimetric and differential heat in each cycle are almost identical, it can be seen that the sample in Example 1 maintains similar properties even after multiple repetitions of the adsorption-desorption reaction.

[0077] (Example 3) Layered manganese oxide prepared using the same procedure as in Example 1 was subjected to elemental substitution treatment with an aqueous NaCl solution to replace potassium contained as interlayer atoms with sodium.

[0078] (Example 4) Ca(NO) was added to the layered manganese oxide produced by the same procedure as in Example 1. ３ ) ２ By performing elemental substitution treatment using an aqueous solution, potassium contained as interlayer atoms was replaced with calcium.

[0079] (Example 5) MgSO4 was added to the layered manganese oxide produced using the same procedure as in Example 1. ４ By performing an elemental substitution treatment using an aqueous solution, potassium contained as interlayer atoms was replaced with magnesium.

[0080] (Example 6) NiCl was added to the layered manganese oxide prepared using the same procedure as in Example 1. ２ By performing an elemental substitution treatment using an aqueous solution, potassium contained as interlayer atoms was replaced with nickel.

[0081] (Example 7) Layered manganese oxide prepared using the same procedure as in Example 1 was treated with ZnSO ４ By performing elemental substitution treatment using an aqueous solution, potassium contained as interlayer atoms was replaced with zinc.

[0082] (Example 8) CuSO4 was added to the layered manganese oxide produced by the same procedure as in Example 1. ４ By performing an elemental substitution treatment using an aqueous solution, potassium contained as interlayer atoms was replaced with copper.

[0083] <Confirmation of the effect of substitution elements> Thermal analysis was performed on the samples of Examples 3 to 8 using a thermogravimetric differential thermal analyzer (TG / DTA, high-concentration water vapor atmosphere differential thermal balance (manufactured by Rigaku Corporation)) in an environment of nitrogen gas (nitrogen gas with a water content of 2.2 mass%) at a relative humidity of 70% RH. Specifically, each sample was heated to 320°C at a heating rate of 20°C / min, and then cooled to 30°C at a cooling rate of 5°C / min. This process constituted one cycle, and the differential heat and thermogravimetric data were measured during this time. Three cycles of measurements were performed, and after cooling, the samples were held at 30°C for 3 hours. Figures 10A to 10C and 11A to 11C are graphs showing the results for the samples of Examples 3 to 8, respectively. The upper graph shows the measurement results of the temperature change of differential heat (DTA), and the lower graph shows the measurement results of the temperature change of thermogravimetric data (TG).

[0084] As shown in Figures 10A-10C and 11A-11C, all samples exhibited a thermogravimetric temperature change equivalent to or greater than that of the sample from Example 1 (Figure 5), indicating that they are heat storage materials with increased heat storage capacity. The decrease in thermogravimetric temperature corresponds to the maximum amount of water molecules absorbed, and per 1 mol of layered manganese oxide, the values ​​were 1.60 mol for the sample from Example 3, 1.70 mol for the sample from Example 4, 2.20 mol for the sample from Example 5, 2.40 mol for the sample from Example 6, 1.90 mol for the sample from Example 7, and 1.90 mol for the sample from Example 8. In particular, the thermogravimetric temperatures of the samples from Examples 5 and 6, which used magnesium and nickel as substitution elements, showed a temperature change more than three times that of the sample from Example 1, indicating that they are superior heat storage materials.

[0085] Thermal analysis was performed on the samples of Example 6 using a thermogravimetric / suggestive scanning calorimetry (TG / DSC) system. Specifically, each sample was heated to 300°C in a dry argon atmosphere to a dry state, and then cooled in a dry argon atmosphere while remaining dry. The cooling temperature was set to 28°C. After cooling, the samples were exposed to a gas containing water and argon at 28°C, and the exothermic characteristics of each sample due to water absorption were measured. Figure 12 is a graph showing the results.

[0086] The heat generated by the sample of Example 6, in which the interlayer element is nickel, is 388.9 [J / g]. This is a higher heat generation than any of the samples mentioned above. Furthermore, the amount of water molecules adsorbed by the sample of Example 6 is 0.76 mol. This is a higher water molecule adsorption than any of the samples mentioned above. This is thought to be because, in the sample of Example 6, the thickness in the C-axis direction changes by substituting the interlayer element with nickel, resulting in a larger specific surface area. Layered manganese oxides with a large specific surface area can adsorb more water molecules when the temperature is lowered, and can release more heat in proportion to the amount of water molecules adsorbed.

[0087] Nitrogen gas adsorption isotherm measurements were performed on the samples of Examples 1 and 6. The measurement temperature was set to -196°C. Figure 13 is a graph showing the results. It can be seen that the amount of nitrogen gas adsorbed, i.e., the specific surface area, of the sample of Example 6 is larger than that of the sample of Example 1. From these results, it can be seen that by substituting the interlayer element with nickel, a heat storage material can be obtained that has an increased specific surface area and can adsorb more water molecules.

[0088] The volumetric energy density obtained during heat dissipation and heat absorption was calculated for the samples of Examples 1, 2, and 6, and Comparative Example 1. Figure 14 is a graph showing the results. The horizontal axis of the graph shows the ratio of water absorption to 1 mol of layered manganese oxide, and the vertical axis of the graph shows the volumetric energy density [MJ / m³]. ３ This shows that the nanometer-sized heat storage materials represented by Examples 1, 2, and 6 have a higher volumetric energy density compared to the heat storage material of Comparative Example 1, due to the increased adsorption capacity of water molecules, and thus significantly improve the heat storage function. In particular, the heat storage function when nickel is used as the interlayer element is outstanding compared to the other examples.

[0089] 100...Layered manganese oxide 101...Layer of manganese oxide 101a...Surface of the outermost layer 102...Interlayer atoms 103...Water molecules L...Layering direction of layered manganese oxide R...Distance between layers of layered manganese oxide S...Interlayer region of layered manganese oxide T...Thickness of layered manganese oxide W...Width of layered manganese oxide

Claims

1. A heat storage material comprising a layered manganese oxide represented by the following formulas (1) and (2) and having a delta-type crystal structure, wherein the thickness of the layered manganese oxide in the C-axis direction is 15 nm or less. A Ｘ MnO ２ ·nH ２ O···(1) [In the above formulas (1) and (2), A is a symbol collectively representing elements A １ , A ２ , ···, A ｍ . m is a natural number, and X1, X2, ···, Xm each represent the composition ratio of the above elements A １ , A ２ , ···, A ｍ , which are numbers of 0 or more and 0.50 or less, and satisfy 0 < X1 + X2 + ··· + Xm ≤ 0.

50. n is a number of from 0 to 2.50.] 2. Element A １ A ２ , ..., A ｍ The heat storage material according to claim 1, characterized in that it contains at least one of K, Na, Mg, Ca, Ni, Cu, and Zn.

3. The heat storage material according to either claim 1 or 2, characterized in that the width in the direction perpendicular to the C axis is 1 or more and 100 times or less the thickness in the C axis direction.

4. A method for producing a heat storage material according to claim 1 or 2, characterized in that the preparation and heating of the raw materials for the heat storage material are carried out in an environment of 200°C or lower.

5. A method for utilizing thermal energy using a heat storage material according to claim 1 or 2, characterized by comprising a heat storage step of heating the heat storage material, removing water from the heat storage material, and storing heat.

6. The method for utilizing thermal energy according to claim 5, further comprising a heat dissipation step of adsorbing water onto the heat-storing material that has stored heat and releasing the heat.

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