Power generation system

Abstract

The present invention provides a power generation system comprising: a ceramic element including a ferroelectric ceramic having a Curie temperature of 90°C or less; and an electricity extraction device for extracting electricity from the ceramic element, wherein the ferroelectric ceramic has space charge polarization and generates electricity by applying a time-dependent temperature change across the Curie temperature to the ferroelectric ceramic.

Description

Technical Field

[0001] This disclosure relates to power generation systems and methods that utilize ceramics. Background Technology

[0002] In recent years, with the popularization of IoT technology, there has been a demand for various environmental power generation technologies from the perspective of providing continuous power to devices. Among these environmental power generation technologies, those that generate electricity through temperature changes over time are being researched. For example, Non-Patent Document 1 discloses a system for generating electricity using a ferroelectric material to operate a thermodynamic cycle, which includes temperature changes of the ferroelectric material, the application of an external electric field, and its removal. Furthermore, Patent Document 1 discloses that the power generation efficiency is improved by re-examining the electric field application curve in the power generation system of Non-Patent Document 1.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2014-113029

[0006] Non-patent literature

[0007] Non-patent literature 1: Randall B. Olsen, et al., Ferroelectrics, 38:1, 975-978 (1981) Summary of the Invention

[0008] The problem the invention aims to solve

[0009] In order to generate electricity, the power generation system described in Non-Patent Document 1 and Patent Document 1 requires an external electric field to be applied in conjunction with the timing of temperature changes. Therefore, an external circuit for applying the electric field and a control circuit for obtaining the timing are required.

[0010] The purpose of this disclosure is to provide a power generation system and method that utilizes ferroelectric materials and does not require external circuits and control circuits as described above.

[0011] means for solving problems

[0012] This disclosure includes the following methods.

[0013] [1] A power generation system, comprising:

[0014] Ceramic components, including ferroelectric ceramics with a Curie temperature below 90°C; and

[0015] A power extraction device for extracting power from the ceramic element.

[0016] in,

[0017] The ferroelectric ceramic has space charge polarization.

[0018] Electricity is generated by applying a temperature change over time across the Curie temperature to the ferroelectric ceramic.

[0019] [2] In the power generation system described in [1] above, the Curie temperature of the ferroelectric ceramic is below 60°C.

[0020] [3] In the power generation system described in [1] or [2] above, the ferroelectric ceramic is a perovskite ferroelectric.

[0021] [4] In the power generation system described in [3] above, the perovskite ferroelectric is selected from composite oxides and transition metal-doped composite oxides obtained by adding Cu, Mn, Fe, Cr, Mg or V to the composite oxides. The composite oxides are selected from BaTiO3, (Ba,Sr)TiO3, (Ba,Ca)TiO3, Ba(Zr,Ti)O3, Ba(Sn,Ti)O3, Ba(Hf,Ti)O3, (Ba,Ca)(Zr,Ti)O3, (Ba,Ca)(Hf,Ti)O3, (Ba,Ca)(Sn,Ti)O3, Pb(Mg 1 / 3 Nb 2 / 3 It is selected from (Pb,Sr)TiO3, (Pb,Ba)ZrO3, and (Pb,Ba)ZrO3.

[0022] [5] In any of the above [1] to [4] power generation systems, the power generation system further has a heat source, and the ceramic element is disposed under the thermal influence of the heat source.

[0023] [6] A power generation method is a method of generating electricity using ferroelectric ceramics with a Curie temperature below 90°C, wherein,

[0024] The power generation method includes:

[0025] A DC electric field is applied to the ferroelectric ceramic at a temperature higher than the Curie temperature, causing space charge polarization to occur inside the ferroelectric ceramic.

[0026] Next, a pyroelectric current is generated by applying a temperature change over time across the Curie temperature to the ferroelectric ceramic.

[0027] [7] In the power generation method described in [6] above, the Curie temperature of the ferroelectric ceramic is below 60°C.

[0028] [8] In the power generation method described in [6] or [7] above, the ferroelectric ceramic is a perovskite ferroelectric.

[0029] [9] In the power generation method described in [8] above, the perovskite ferroelectric is selected from composite oxides and transition metal-doped composite oxides obtained by adding Cu, Mn, Fe, Cr, Mg or V to the composite oxides. The composite oxides are selected from BaTiO3, (Ba,Sr)TiO3, (Ba,Ca)TiO3, Ba(Zr,Ti)O3, Ba(Sn,Ti)O3, Ba(Hf,Ti)O3, (Ba,Ca)(Zr,Ti)O3, (Ba,Ca)(Hf,Ti)O3, (Ba,Ca)(Sn,Ti)O3, Pb(Mg 1 / 3 Nb 2 / 3 It is selected from (Pb,Sr)TiO3, (Pb,Ba)ZrO3, and (Pb,Ba)ZrO3.

[0030] Invention Effects

[0031] According to this disclosure, a power generation system and method can be provided that do not require an external circuit for applying an electric field and a control circuit for obtaining timing by using a ferroelectric ceramic having space charge polarization internally and a Curie temperature of 90°C or less. Attached Figure Description

[0032] Figure 1 This is a schematic diagram illustrating an example of how the power generation system disclosed herein is used.

[0033] Figure 2 The PE hysteresis curve for sample number 7 is shown.

[0034] Figure 3 The behavior of the pyroelectric current generated when a temperature change is applied to sample number 7 is shown.

[0035] Figure 4 This is a schematic diagram showing the measurement system used in the calculation of power generation.

[0036] Figure 5 This is a graph showing the power generation under various load resistors used for sample number 7.

[0037] Figure 6 This is a coordinate graph showing the results of the TSDC measurement for sample number 7. Detailed Implementation

[0038] The power generation system disclosed herein will now be described.

[0039] The power generation system disclosed herein comprises: a ceramic element including a ferroelectric ceramic having internal space charge polarization and a Curie temperature below 90°C; and a power extraction device for extracting electricity from the ceramic element. The power generation system of this disclosure generates electricity by applying a time-dependent temperature change across the Curie temperature to the ferroelectric ceramic to produce a pyroelectric current.

[0040] Here, "space charge polarization" refers to the state in which charged monomers such as ions and oxygen vacancies move in the dielectric and accumulate at grain boundaries or electrode interfaces, thus generating dipoles.

[0041] The ferroelectric ceramic used in the power generation system disclosed herein has space charge polarization. Therefore, even if the ferroelectric polarization disappears at a temperature higher than the Curie temperature, it can be repolarized at a temperature lower than the Curie temperature by the internal electric field generated by the space charge polarization without the application of an external electric field. Therefore, it is not necessary to apply an electric field to polarize the ferroelectric ceramic at low temperatures, as is done in the power generation systems described in Non-Patent Document 1 and Patent Document 1.

[0042] The power generation system disclosed herein is, for example, as follows: Figure 1 As shown, the ceramic element 2 is placed under the thermal influence of a heat source 1 whose temperature changes over time. A power extraction device 3, used to extract power from the ceramic element, is connected to electrical equipment 4 such as a battery or capacitor.

[0043] The aforementioned ferroelectric ceramic is a ferroelectric ceramic with a Curie temperature of 90°C or below, preferably 60°C or below. By setting the Curie temperature to 90°C or below, power generation can be performed at a temperature sufficiently low than the temperature at which space charge polarization disappears, thus avoiding the disappearance of space charge polarization due to the temperature during power generation. The Curie temperature of the aforementioned ferroelectric ceramic is preferably -50°C or above, more preferably -30°C or above.

[0044] The Curie temperature mentioned above can be determined, for example, as the point where the relative permittivity is at its maximum in the temperature dependence of the relative permittivity measured using an LCR meter and a temperature-adjustable stage.

[0045] In a preferred embodiment, the ferroelectric ceramic is a perovskite-type ferroelectric.

[0046] Examples of perovskite-type ferroelectrics include BaTiO3, (Ba,Sr)TiO3, (Ba,Ca)TiO3, Ba(Zr,Ti)O3, Ba(Sn,Ti)O3, Ba(Hf,Ti)O3, (Ba,Ca)(Zr,Ti)O3, (Ba,Ca)(Hf,Ti)O3, (Ba,Ca)(Sn,Ti)O3, and Pb(Mg 1 / 3 Nb 2 / 3Composite oxides such as (Pb,Sr)TiO3, (Pb,Ba)ZrO3, etc., as well as transition metal-doped composite oxides obtained by adding Cu, Mn, Fe, Cr, Mg, or V to the above composite oxides. These can be used alone or in combination of two or more.

[0047] In a preferred embodiment, the ferroelectric ceramic can be a transition metal-doped composite oxide. By adding the transition metal, stronger space charge polarization can be formed during the pretreatment described later.

[0048] The amount of the added transition metal relative to the composite oxide is preferably 0.01 mol% or more and 1.0 mol% or less, more preferably 0.1 mol% or more and 1.0 mol% or less, more preferably 0.2 mol% or more and 1.0% or less, for example 0.2 mol% or more and 0.6 mol% or less. By adding this amount of transition metal, the decay of the pyroelectric current during power generation can be suppressed.

[0049] In one embodiment, the perovskite ferroelectric material may be one or more selected from composite oxides and transition metal doped composite oxides with Cu, Mn or Fe added, wherein the composite oxide is selected from (Ba,Sr)TiO3, (Ba,Ca)TiO3, Ba(Zr,Ti)O3 and (Pb,Sr)TiO3.

[0050] The aforementioned composite oxides and transition metal-doped composite oxides can be synthesized via solid-state reaction, co-precipitation, hydrothermal methods, oxalic acid methods, etc. Preferably, the aforementioned composite oxides and transition metal-doped composite oxides are synthesized using oxides and carbonates of each element as raw materials via solid-state reaction.

[0051] The ferroelectric ceramics used in the power generation system disclosed herein have space charge polarization.

[0052] The aforementioned space charge polarization is generated by applying a DC electric field to the ferroelectric ceramic at a temperature higher than its Curie temperature. This process will also be referred to as "pretreatment" below.

[0053] The temperature during the application of the aforementioned DC electric field is preferably 80°C or higher and 200°C or lower, more preferably 100°C or higher and 180°C or lower, and even more preferably 130°C or higher and 160°C or lower.

[0054] The aforementioned DC electric field is preferably above 1kV / mm and below 10kV / mm, and more preferably above 1.5kV / mm and below 5kV / mm.

[0055] The duration for which the aforementioned DC electric field is applied is preferably 30 minutes or more, and more preferably 1 hour or more.

[0056] In a preferred embodiment, after applying a DC electric field at a high temperature, the ferroelectric ceramic is cooled to room temperature, for example, 20°C, while maintaining the applied DC electric field. By cooling the ferroelectric ceramic while maintaining the applied DC electric field in this manner, greater space charge polarization can be obtained.

[0057] The aforementioned space charge polarization can be confirmed by measuring the hysteresis curve (PE hysteresis curve) of the electric field-electric polarization at room temperature. When the PE hysteresis curve becomes non-objective relative to the origin, it is determined that the ferroelectric ceramic exhibits space charge polarization. Alternatively, it can also be confirmed by measuring the thermally stimulated depolarization current (TSDC).

[0058] The aforementioned space charge polarization can disappear at high temperatures. Therefore, the pretreated ferroelectric ceramics can be used at temperatures lower than the space charge polarization disappearance temperature. The space charge polarization disappearance temperature can, for example, be in the range of 200°C or higher and 600°C or lower. It should be noted that even when space charge polarization disappears, it is possible to regenerate it through further pretreatment.

[0059] The shape of the ferroelectric ceramic is not particularly limited, but it can be, for example, sheet-like, block-like, or a shape obtained by solidifying powdered ferroelectric ceramic.

[0060] In a preferred embodiment, the ceramic element has an electrode electrically connected to the ferroelectric ceramic. The electrode is not particularly limited, but examples include Pt, Cu, Ag, Au, Pd, Ni, and Sn.

[0061] In a preferred embodiment, electrodes may be formed on both sides of a sheet of ferroelectric ceramic.

[0062] In one approach, the ceramic element can also be a stack of multiple ferroelectric ceramic sheets separated by internal electrodes.

[0063] The power extraction device used to extract power from the ceramic element is not particularly limited as long as it can extract power from the ceramic element. For example, it can use a common full-wave rectifier circuit, half-wave rectifier circuit, wire, smoothing circuit, diode, thyristor, etc.

[0064] As a heat source, any heat source whose temperature changes over time is acceptable; there are no particular limitations. Examples of such heat sources include internal combustion engines, factory exhaust gases, and exhaled breath.

[0065] The aforementioned electrical equipment is any device that stores or utilizes the electricity generated by the aforementioned ceramic components; there are no particular limitations. Typical examples include storage batteries and capacitors.

[0066] Next, the power generation method disclosed herein will be described.

[0067] The power generation method disclosed herein utilizes ferroelectric ceramics with a Curie temperature below 90°C, and includes:

[0068] Applying a DC electric field to the ferroelectric ceramic at a temperature higher than the Curie temperature causes space charge polarization to occur inside.

[0069] Next, a pyroelectric current is generated by applying a temperature change over time across the Curie temperature to the ferroelectric ceramic.

[0070] The ferroelectric ceramics with a Curie temperature of 90°C or below described above are the same as the ferroelectric ceramics described in relation to the aforementioned power generation system.

[0071] First, as a pretreatment, a DC electric field is applied to the ferroelectric ceramic at a temperature higher than the Curie temperature to induce space charge polarization within it. This pretreatment is the same as that described for the aforementioned power generation system.

[0072] Next, a pyroelectric current is generated by applying a temperature change over time across the Curie temperature of the pretreated ferroelectric ceramic.

[0073] The aforementioned temperature change is caused by a heat source. This heat source is the same as the one described in relation to the aforementioned power generation system.

[0074] The aforementioned temperature changes occur over time across the Curie temperature of the aforementioned ferroelectric ceramic. In other words, the temperature changes in this disclosure are temperature changes that occur over time from a temperature below the Curie temperature to a temperature above the Curie temperature, and temperature changes that occur over time from a temperature above the Curie temperature to a temperature below the Curie temperature.

[0075] The upper limit of the aforementioned temperature change is a temperature lower than the temperature at which the space charge polarization of the ferroelectric ceramic disappears. It is preferably a temperature 30°C or lower, more preferably a temperature 100°C or lower, and even more preferably a temperature 150°C or lower.

[0076] In a preferred embodiment, the temperature change described above is a periodic repetition of heating and cooling.

[0077] The aforementioned temperature change is preferably 1°C or more but less than 30°C, more preferably 5°C or more but less than 20°C, compared to the Curie temperature of the ferroelectric ceramic. By setting a larger temperature change, a sufficient pyroelectric effect can be obtained. Furthermore, by setting a smaller temperature change, which is far from the space charge polarization disappearance temperature, the disappearance of space charge polarization can be prevented.

[0078] When the aforementioned temperature changes repeat periodically, the period is preferably 1 to 500 cycles / second, more preferably 10 to 300 cycles / second, and even more preferably 50 to 200 cycles / second. By increasing the period, the hourly power generation can be further increased. Conversely, by slowing down the period, the pyroelectric effect can be obtained more reliably.

[0079] The electricity generated by the above-described power generation method is extracted from the ferroelectric ceramic by an electricity extraction device, which is used to extract electricity from the ferroelectric ceramic. This electricity extraction device is the same as the electricity extraction device described with respect to the above-described power generation system.

[0080] The electricity extracted as described above is stored in electrical equipment, typically batteries or capacitors.

[0081] The power generation system and method disclosed herein can be used to generate electricity using heat generated from internal combustion engines, factory exhaust gases, etc. Furthermore, the power generation system of this disclosure can be integrated into a mask to generate electricity using the heat from exhaled breath, serving as a power source for an IoT device used for examination, combined with sensors for reading vital signs.

[0082] The following describes the power generation system and power generation method of this disclosure in the embodiments, but this disclosure is not limited to such embodiments.

[0083] Example

[0084] (Manufacturing of ceramic components)

[0085] As ferroelectric ceramics, single plates (5mm × 5mm × 0.3mm in size) of composite oxides and transition metal-doped composite oxides, as shown in Table 1, were prepared. Each ferroelectric ceramic was synthesized from oxides and carbonates of the respective elements via a solid-state reaction method. The Curie temperature was estimated based on the point where the relative permittivity reaches its maximum in the temperature dependence of the relative permittivity measured using an LCR meter (E4980A: Keysight) and a temperature-controlled variable stage.

[0086] [Table 1]

[0087]

[0088] Pt electrodes were formed on both sides of the obtained ferroelectric ceramic plate by sputtering. Next, as a pretreatment, a 2 kV / mm DC electric field was applied at 150°C for 1 hour, followed by cooling to 20°C while maintaining the applied electric field. This yields a ceramic element for the power generation system and method disclosed herein.

[0089] (Determination of the decay rate of pyroelectric current)

[0090] A double-sided Pt electrode of a pretreated ceramic element is connected to an electrometer via a wire. The ceramic element, with the wire connected, is subjected to temperature changes on a temperature-controlled stage, and the pyroelectric current during these temperature changes is measured. The temperature changes are periodically varied within ±30°C of the Curie temperature of the ferroelectric ceramic in each ceramic element. For each sample, the current density of the pyroelectric current is measured. After applying temperature changes for 10 and 100 cycles, the peak value of the pyroelectric current is compared with the peak value of the first cycle, and the decay rate of the pyroelectric current is calculated. The decay rate is calculated based on the following formula.

[0091] [Formula 1]

[0092]

[0093] (where I) 1st and I Nth These are the peak values ​​of the pyroelectric current density in the first and Nth cycles, respectively.

[0094] The results are shown in Table 2 below. In the determination, a case where the decay rate is less than 5% after applying 10 cycles of temperature change is designated as G; furthermore, a case where the decay rate is less than 10% after applying 100 cycles of temperature change is designated as G※. A case where the decay rate is 5% or more after applying 10 cycles of temperature change is designated as NG.

[0095] [Table 2]

[0096]

[0097] Based on the above results, it was confirmed that the pyroelectric current decay rate after power generation was small for samples with a Curie temperature below 90°C. In particular, it was confirmed that the pyroelectric current decay rate was also small for samples with a Curie temperature below 60°C after 100 cycles.

[0098] (Determination of PE hysteresis curve)

[0099] For sample number 7, the PE hysteresis curves before and after pretreatment were measured. Figure 2The results are shown. When comparing the PE hysteresis curves of the ceramic element before and after pretreatment, it was confirmed that the PE hysteresis curve of the pretreated ceramic element shifted to the right (positive direction of electric field), resulting in space charge polarization.

[0100] (Determination of pyroelectric current value)

[0101] Using ceramic element (pretreated) with sample number 7, the pyroelectric current value was measured when the element's temperature changed across the Curie temperature range. Figure 3 The results are shown. It is confirmed that the pyroelectric current continues to flow relative to the temperature change over time, which spans 45°C above the Curie temperature. Based on these results, it is shown that when the temperature drops below the Curie temperature, the ferroelectric polarization spontaneously polarizes again in one direction without the application of an external electric field.

[0102] (Measurement of power generation)

[0103] For sample number 7, the power generation was estimated. Regarding the power generation, such as... Figure 4 As shown, a load resistor 5 is connected to the surface and back of the ceramic element 2 via wires. A voltmeter 7 is used to measure the electromotive force (EMF) across the load resistor when the ceramic element is subjected to a temperature change spanning the Curie temperature over time on a temperature-controlled platform. The power generation is then estimated. For multiple load resistor values, the EMF is measured when the ceramic element is subjected to a temperature change over time, and the result is obtained using P = V. 2 The instantaneous power consumption P is calculated using the formula / R (where P: power (W), V: electromotive force (V), R: load resistance (Ω)). This power consumption P is then integrated over time to calculate the energy U (J) consumed by the load resistance relative to the temperature change. A temperature change from the low-temperature side to the high-temperature side and back to the low-temperature side is defined as one cycle. The average energy consumption for seven temperature cycles is calculated. This average energy consumption is divided by the time required for one temperature change cycle to calculate the power generation for each cycle. Figure 5 The results are shown. Based on the results, it is confirmed that the starting charge is maximized within a load resistance of 1 GΩ.

[0104] (TSDC measurement)

[0105] TSDC was measured for sample number 7. Figure 6 The results are shown. The current peak on the negative side that can be confirmed near 40°C is the pyroelectric current corresponding to the Curie temperature at which ferroelectric polarization disappears (see reference). Figure 6 (Illustration). A large current peak flowing to the positive side was confirmed when the temperature was increased from around 250°C. This current peak is the temperature at which the space charge accumulated through pretreatment is released, thus confirming the presence of space charge polarization within the ferroelectric ceramic.

[0106] Industrial availability

[0107] The power generation system and method disclosed herein can be applied to equipment that requires a continuous supply of electricity.

[0108] Explanation of reference numerals in the attached figures

[0109] 1…heat source;

[0110] 2… Ceramic components;

[0111] 3…Power extraction equipment;

[0112] 4…Electrical equipment;

[0113] 5…load resistance;

[0114] 6…Temperature control table;

[0115] 7…Voltmeter.

Claims

1. A power generation system, comprising: Ceramic components, including ferroelectric ceramics with a Curie temperature below 90°C; and A power extraction device for extracting power from the ceramic element. in, The ferroelectric ceramic exhibits space charge polarization, which is generated by applying a DC electric field to the ferroelectric ceramic at a temperature higher than its Curie temperature. In the process of generating electricity by applying a temperature change over time across the Curie temperature to the ferroelectric ceramic, when the temperature becomes lower than the Curie temperature, the ferroelectric polarization is repolarized by the internal electric field generated by the space charge polarization without the application of an external electric field.

2. The power generation system according to claim 1, wherein, The Curie temperature of the ferroelectric ceramic is below 60°C.

3. The power generation system according to claim 1 or 2, wherein, The ferroelectric ceramic is a perovskite-type ferroelectric.

4. The power generation system according to claim 3, wherein, The perovskite ferroelectric is selected from composite oxides and transition metal-doped composite oxides obtained by adding Cu, Mn, Fe, Cr, Mg, or V to the composite oxides. The composite oxides are selected from BaTiO3, (Ba,Sr)TiO3, (Ba,Ca)TiO3, Ba(Zr,Ti)O3, Ba(Sn,Ti)O3, Ba(Hf,Ti)O3, (Ba,Ca)(Zr,Ti)O3, (Ba,Ca)(Hf,Ti)O3, (Ba,Ca)(Sn,Ti)O3, Pb(Mg)O3, and Pb(Mg)O3. 1 / 3 Nb 2 / 3 It is selected from (Pb,Sr)TiO3, (Pb,Ba)ZrO3.

5. The power generation system according to claim 1 or 2, wherein, The power generation system also has a heat source, and the ceramic element is configured under the thermal influence of the heat source.

6. A power generation method utilizing ferroelectric ceramics with a Curie temperature below 90°C, wherein, The power generation method includes: A DC electric field is applied to the ferroelectric ceramic at a temperature higher than the Curie temperature, causing space charge polarization to occur inside the ferroelectric ceramic. Next, a pyroelectric current is generated by applying a temperature change over time across the Curie temperature to the ferroelectric ceramic. In the process of generating electricity by applying a temperature change over time across the Curie temperature to the ferroelectric ceramic, when the temperature becomes lower than the Curie temperature, the ferroelectric polarization is repolarized by the internal electric field generated by the space charge polarization without the application of an external electric field.

7. The power generation method according to claim 6, wherein, The Curie temperature of the ferroelectric ceramic is below 60°C.

8. The power generation method according to claim 6 or 7, wherein, The ferroelectric ceramic is a perovskite-type ferroelectric.

9. The power generation method according to claim 8, wherein, The perovskite ferroelectric is selected from composite oxides and transition metal-doped composite oxides obtained by adding Cu, Mn, Fe, Cr, Mg, or V to the composite oxides. The composite oxides are selected from BaTiO3, (Ba,Sr)TiO3, (Ba,Ca)TiO3, Ba(Zr,Ti)O3, Ba(Sn,Ti)O3, Ba(Hf,Ti)O3, (Ba,Ca)(Zr,Ti)O3, (Ba,Ca)(Hf,Ti)O3, (Ba,Ca)(Sn,Ti)O3, Pb(Mg)O3, and Pb(Mg)O3. 1 / 3 Nb 2 / 3 It is selected from (Pb,Sr)TiO3, (Pb,Ba)ZrO3.

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