Power generation element, power generation device, and power generation method

Abstract

The present disclosure provides a novel power generation element that is advantageous in terms of being maintenance-free. A power generation element (1a) according to the present disclosure is provided with a first electrode (11), a second electrode (12), and an inorganic solid electrolyte (15). The first electrode (11) decomposes water. The inorganic solid electrolyte (15) is disposed between the first electrode (11) and the second electrode (12). The inorganic solid electrolyte (15) causes the ions generated by the decomposition of water at the first electrode (11) to be conducted toward the second electrode (12). The inorganic solid electrolyte (15) contains at least one selected from the group consisting of water molecules and hydroxide ions.

Description

Power generation element, power generation device, and power generation method

[0001] The present disclosure relates to a power generating element, a power generating device, and a power generating method.

[0002] 2. Description of the Related Art Thermochemical cells are known as a type of power generation device that utilizes electrochemical reactions.

[0003] For example, Patent Document 1 describes a thermochemical battery that can generate electricity when there is a temperature difference between a pair of electrodes. In this thermochemical battery, a pair of electrodes is bonded to both ends of an electrolyte. At least one of the pair of electrodes is a thin-film electrode made of a conductive polymer material. This thermochemical battery can generate electricity when there is a temperature difference between the pair of electrodes by a redox reaction occurring near the bonded surfaces of the electrolyte and the pair of electrodes. For example, a mixed aqueous solution of K3[Fe(CN)6] and K4[Fe(CN)6].3H2O is used as the electrolyte.

[0004] Patent Document 2 describes a thermoelectric conversion material having a redox pair and a capture compound. The capture compound selectively captures only one member of the redox pair at low temperatures and releases it at high temperatures. The capture compound is at least one compound selected from the group consisting of cyclic compounds and helical compounds. This thermoelectric conversion material is prepared, for example, as an aqueous solution.

[0005] Non-Patent Document 1 describes an electrochemical thermocell involving a redox reaction between acetone and isopropanol. When the temperature of the hot electrode of this electrochemical thermocell exceeds the boiling point of acetone, the acetone vaporizes and flows to the cold electrode. This reaction achieves a high Seebeck coefficient of -9.9 mV / K.

[0006] International Publication No. WO 2018 / 079325 International Publication No. WO 2017 / 155046

[0007] Hongyao Zhou and Ping Liu, “High Seebeck Coefficient Electrochemical Thermocells for Efficient Waste Heat Recovery”, ACS Appl. Energy Mater. 1 (2018) 1424-1428

[0008] The technology described in the above document uses a liquid, and therefore problems associated with leakage, loss, and drying of the liquid during use can occur, which can lead to limitations on use, such as reduced efficiency due to a decrease in power generation performance, the need for maintenance such as replacement of the thermochemical battery, and the risk of liquid leakage.

[0009] Therefore, the present disclosure provides a novel power generating element that has few restrictions on use and is advantageous from the viewpoint of being maintenance-free.

[0010] The power generation element of the present disclosure comprises: a first electrode that splits water; a second electrode; and an inorganic solid electrolyte that is disposed between the first electrode and the second electrode and that conducts ions generated by the splitting of water at the first electrode toward the second electrode, wherein the inorganic solid electrolyte contains at least one selected from the group consisting of water molecules and hydroxide ions.

[0011] According to the present disclosure, a novel power generating element can be provided that has few restrictions on use and is advantageous from the viewpoint of being maintenance-free.

[0012] FIG. 1 is a diagram schematically illustrating an example of a power generation element and its power generation principle according to the present disclosure. FIG. 2 is a diagram schematically illustrating an example of a thermochemical battery. FIG. 3 is an exploded perspective view schematically illustrating an example of a power generation device according to the present disclosure. FIG. 4 is an exploded perspective view schematically illustrating another example of a power generation device according to the present disclosure. FIG. 5 is a diagram schematically illustrating a measurement device used in the examples. FIG. 6 is a graph showing measurement results of the proton conductivity of saponite. FIG. 7 is a graph showing the relationship between the electromotive force and temperature of the power generation element according to Sample A-1. FIG. 8 is a diagram schematically illustrating another measurement device used in the examples. FIG. 9 is a graph showing the IV characteristics of the power generation element according to Sample A-1. FIG. 10 is a graph showing the continuous discharge characteristics of the power generation element according to Sample A-1. FIG. 11 is a graph showing the IV characteristics of the power generation element according to Sample B-3. FIG. 12 is a graph showing the continuous discharge characteristics of the power generation element according to Sample B-3.

[0013] (Knowledge forming the basis of the present disclosure) Effective energy utilization is required from the viewpoints of reducing CO2 emissions, zero carbon, and carbon neutrality. It is conceivable to effectively utilize unused heat generated from factories, automobiles, and living environments. Technologies for utilizing such unused heat are being tackled as national projects and could become important technologies for future society. For example, the widespread use of devices in the field known as energy harvesting is expected to enable the effective utilization of unused heat by converting it into electrical energy.

[0014] Thermoelectric conversion elements or thermochemical batteries that utilize physical phenomena such as the Seebeck effect are considered as devices that convert heat into electrical energy. Some thermoelectric conversion elements have already been commercialized. However, to convert heat into electrical energy using a thermoelectric conversion element, a predetermined temperature difference must be generated between both ends of the thermoelectric conversion element. Meanwhile, thermochemical batteries are limited to specific applications, such as rocket exhaust heat recovery and sodium-sulfur batteries, and further technological development is needed to utilize unused heat. Furthermore, when an electrolyte is used in a thermochemical battery, the amount of electrolyte may decrease and leak as heat is supplied to the thermochemical battery, requiring specific maintenance. On the other hand, providing a heat-to-electrical energy conversion device that can be installed in difficult-to-maintain locations, such as enclosed spaces, factory chimneys, and plant facilities, could potentially promote the utilization of unused heat.

[0015] Therefore, the present inventors conducted extensive research to find a new power generation element that is maintenance-free and has fewer usage restrictions. The present inventors newly discovered that an element capable of generating electricity using water widely available in the environment can be constructed. A solid ionic conductor is important for constructing a maintenance-free element capable of generating electricity using environmental water. Various types of solid proton conductors have been reported in recent years. However, the ionic conductivity of most inorganic solid proton conductors decreases with decreasing temperature, and few materials are known to exhibit high ionic conductivity below 200°C. On the other hand, the present inventors noticed that inorganic materials such as smectite, although not widely known as ionic conductors, can sometimes exhibit ionic conductivity even at low temperatures. The present inventors conducted extensive trial and error to construct a maintenance-free element capable of generating electricity using environmental water using a specific inorganic material, such as a mineral, which is widely distributed on Earth, harmless to the human body, and inexpensive. As a result, the present inventors newly discovered that such an element can be obtained by using a specific inorganic solid electrolyte. Based on this new finding, the present inventors have completed the power generation element according to the present disclosure.

[0016] (Embodiments of the Present Disclosure) Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0017] FIG. 1 is a diagram illustrating an example of a power generation element and its power generation principle according to the present disclosure. As shown in FIG. 1 , the power generation element 1a includes a first electrode 11, a second electrode 12, and an inorganic solid electrolyte 15. The power generation element 1a is an all-solid power generation element. The first electrode 11 splits water. Water may exist in a liquid or gas phase in an environment in contact with the first electrode 11. When water comes into contact with the first electrode 11, the water splits to generate specific ions. The inorganic solid electrolyte 15 is disposed between the first electrode 11 and the second electrode 12. The inorganic solid electrolyte 15 may be in direct contact with the first electrode 11, or a catalyst may be disposed between the inorganic solid electrolyte 15 and the first electrode 11. The inorganic solid electrolyte 15 may be in direct contact with the second electrode 12, or a catalyst may be disposed between the inorganic solid electrolyte 15 and the second electrode 12. The inorganic solid electrolyte 15 conducts ions generated by the splitting of water at the first electrode 11 toward the second electrode 12. The inorganic solid electrolyte 15 contains at least one selected from the group consisting of water molecules and hydroxide ions. A potential difference is generated between the first electrode 11 and the second electrode 12 due to the decomposition of water at the first electrode 11 and the generation of ions at the inorganic solid electrolyte 15, and a current is generated due to the conduction of the ions. As a result, the power generating element 1a supplies electrical energy to the outside of the power generating element 1a.

[0018] FIG. 2 is a schematic diagram illustrating an example of a thermochemical battery. As shown in FIG. 2, the thermochemical battery 9 includes an electrode 91, an electrode 92, and an electrolyte 95. The electrode 91 oxidizes the electrolyte at high temperatures, and the electrode 92 reduces the electrolyte at low temperatures. The electrolyte 95 contains first ions 95a and second ions 95b, which have different valences. For example, the first ions 95a are oxidized at the electrode 91 and converted into second ions 95b. The second ions 95b are reduced at the electrode 92 and converted into the first ions 95a. When a predetermined amount of heat is supplied to the thermochemical battery 9, for example, when the electrode 91 reaches a high temperature, the electrode 91 oxidizes the first ions 95a contained in the electrolyte 95 to generate second ions 95b, and electrons are donated to the electrode 91. Meanwhile, the electrode 92 receives electrons that have passed through the external circuit connected to the thermochemical cell 9 and reduces second ions 95b contained in the electrolyte 95 to produce first ions 95a. In the electrolyte 95, the first ions 95a move toward the electrode 91, and the second ions 95b move toward the electrode 92 due to convection and diffusion. As a result, a redox reaction involving the first ions 95a and the second ions 95b occurs continuously, generating a current in the external circuit. An electromotive force corresponding to the difference in redox potential between the electrodes 91 and 92 at a specific temperature is generated, generating a current from the electrode 91 with a higher redox potential to the electrode 92 with a lower redox potential. In this case, the thermal energy supplied to the thermochemical cell 9 is consumed in the redox reaction and the diffusion of each ion, and the surplus is extracted as electrical energy.

[0019] The thermochemical battery 9 uses an electrolyte 95. When heat is supplied to the thermochemical battery 9, the solvent in the electrolyte 95 may evaporate, potentially reducing the amount of the electrolyte 95. Additionally, the electrolyte 95 may leak from the thermochemical battery 9. For this reason, the thermochemical battery 9 requires predetermined maintenance. Meanwhile, the power generation element 1a can generate electricity when the first electrode 11 comes into contact with a fluid containing water present outside the power generation element 1a. Therefore, power generation is possible as long as water is present in the environment in contact with the first electrode 11. For example, a certain amount of moisture is always present in the air, and the power generation element 1a can generate power using such moisture. Additionally, the power generation element 1a uses a solid electrolyte to conduct ions generated by the decomposition of water, preventing reduction or leakage of the electrolyte. Therefore, the power generation element 1a is advantageous in terms of fewer usage restrictions and maintenance-free operation.

[0020] As described above, the inorganic solid electrolyte 15 exhibits ionic conductivity with respect to ions generated by the decomposition of water. The inorganic solid electrolyte 15 has ionic conductivity with respect to one ion selected from the group consisting of protons, oxide ions, hydronium ions, and hydroxide ions. In the example shown in FIG. 1 , the inorganic solid electrolyte 15 has proton conductivity. By containing at least one selected from the group consisting of water molecules and hydroxide ions in the inorganic solid electrolyte 15, the ionic conductivity of the inorganic solid electrolyte 15 tends to be high during power generation by the power generation element 1a.

[0021] The power generating element 1a will be described in more detail using an example in which protons are conducted through the inorganic solid electrolyte 15. For example, the catalytic activity of the first electrode 11 for water splitting at a predetermined temperature is higher than the catalytic activity of the second electrode 12 for water splitting at a predetermined temperature. In this case, the material of the first electrode 11 is different from the material of the second electrode 12. For example, heat can be supplied to the entire power generating element 1a so that no temperature difference occurs between the first electrode 11 and the second electrode 12. In this case, due to the difference in catalytic activity for water splitting between the first electrode 11 and the second electrode 12, the concentration of protons generated at the first electrode 11 is higher than the concentration of protons generated at the second electrode 12. Heat may be supplied to the power generating element 1a so that the temperature of the first electrode 11 is higher than the temperature of the second electrode 12. In this case, due to the difference in catalytic activity for water splitting between the first electrode 11 and the second electrode 12, the concentration of protons generated at the first electrode 11 is higher than the concentration of protons generated at the second electrode 12.

[0022] The material of the first electrode 11 may be the same as the material of the second electrode 12. In this case, heat can be supplied to the power generating element 1a so that the temperature of the first electrode 11 is higher than the temperature of the second electrode 12. Alternatively, heat may be supplied to the entire power generating element 1a so that no temperature difference occurs between the first electrode 11 and the second electrode 12, and the power generating element 1a may be placed in an environment in which the concentration of water supplied to the first electrode 11 is higher than the concentration of water supplied to the second electrode 12. In these cases as well, the concentration of protons generated at the first electrode 11 will be higher than the concentration of protons generated at the second electrode 12.

[0023] Due to this difference in proton concentration between the first electrode 11 and the second electrode 12, an electromotive force E is generated according to the following Nernst equation (3). Furthermore, protons diffuse in the inorganic solid electrolyte 15 due to the heat and concentration difference, and protons react with oxygen at the second electrode 12 to generate water vapor. This water vapor diffuses to the outside of the power generating element 1a. An electromotive force is generated between the first electrode 11 and the second electrode 12 due to the difference in ion activity, and electrons move through an external circuit of the power generating element 1a. The heat supplied to the power generating element 1a is consumed in the decomposition of water at the first electrode 11 and the diffusion of protons in the inorganic solid electrolyte 15. Excess chemical energy associated with the generation of water at the second electrode 12 is extracted as electrical energy.

[0024] According to the first law of thermodynamics, the extracted free energy G is defined as shown in equation (1) using enthalpy H, thermodynamic temperature T, and entropy S.

[0025] G = H - TS Equation (1) The relationship between the extracted free energy G and the electromotive force accompanying the battery reaction is expressed by Equation (2). In Equation (2), n is the number of reacting moles, E0 is the standard electromotive force, and F is the Faraday constant 96485 Cmol -1 is.

[0026] ΔG0 = -nE0F Equation (2) The ion activity in the oxidized state and the ion activity in the reduced state in the redox reaction are respectively a Ox and a Red In equation (3), the Nernst equation is obtained. 0 is the standard electrode potential, and R is the gas constant 8.31 JK -1 mol -1 where T is the absolute temperature, z is the number of transferred electrons, and F is Faraday's constant.

[0027] E=E 0 +(RT / zF)ln(a Ox / a Red The power generating element 1a can generate electricity by utilizing water present in the environment in contact with the first electrode 11, even when the inorganic solid electrolyte 15 conducts ions other than protons generated by decomposition of water.

[0028] Thus, the power generating element 1a is a novel power generating element that combines thermodynamic phenomena and electrochemical principles, using water present in the environment in which the power generating element 1a is placed as an electrolyte source. The power generating element 1a can generate electrical energy, for example, without the temperature difference required by the Seebeck effect or the like. As described above, the power generating element 1a can have the configuration A in which the catalytic activity of the first electrode 11 for water splitting at a predetermined temperature is higher than the catalytic activity of the second electrode 12 for water splitting at a predetermined temperature. The power generating element 1a may also have the configuration B in which the first electrode 11 and the second electrode 12 are made of the same material. When the power generating element 1a has the configuration A, the power generating element 1a can generate electricity even when the water vapor concentration around the power generating element 1a is uniform. When the power generating element 1a has the configuration B, the power generating element 1a can generate electricity by, for example, supplying heat to the power generating element 1a so that the temperature of the first electrode 11 is higher than the temperature of the second electrode 12. In addition, when the power generating element 1a has the configuration B, the concentration of water supplied to the first electrode 11 is higher than the concentration of water supplied to the second electrode 12, which also enables the power generating element 1a to generate electricity.

[0029] The water used for water decomposition at the first electrode 11 of the power generating element 1a may be water contained in the atmosphere, water present in an enclosed space, or water derived from humidified air supplied from the outside.

[0030] Using the power generating element 1a, for example, a power generation method can be provided that includes the following (I), (II), (III), and (IV): (I) placing the power generating element 1a in an environment where water is present and generating ions by decomposing water using the first electrode 11; (II) conducting the ions generated by (I) in the inorganic solid electrolyte 15 toward the second electrode 12; (III) generating water by oxidizing or reducing the ions generated by (I) at the second electrode 12; and (IV) generating a current outside the power generating element 1a.

[0031] In the above power generation method, for example, heat of 300°C or less is supplied to the power generation element 1a. The temperature of the heat supplied to the power generation element 1a may be 250°C or less, 200°C or less, or 150°C or less. The temperature of the heat supplied to the power generation element 1a is, for example, 20°C or more.

[0032] The material of the first electrode 11 is not limited to a specific material as long as it can decompose water. The first electrode 11 includes, for example, a predetermined metal or alloy. The predetermined metal or alloy includes, for example, at least one selected from the group consisting of Pt, Ag, Pd, Ru, Au, Cu, Ni, Ti, Fe, Cr, Al, W, and Zn. In this case, the first electrode 11 can exhibit high catalytic activity for water decomposition.

[0033] The first electrode 11 may contain an Au—Al alloy, a Pt—Ru alloy, or an Ag—Pd alloy. The shape, material, and method of forming the first electrode 11 are not limited to any particular shape, material, or method. The first electrode 11 can be obtained, for example, by forming a film of a paste containing a metal or alloy by printing or coating, and then baking the film. The first electrode 11 may also be formed by sputtering, thermal spraying, plating, or pressure bonding.

[0034] The first electrode 11 may contain a carbon material. In this case, the first electrode 11 may exhibit high catalytic activity for water decomposition. Examples of the carbon material include three-dimensional crystalline carbon such as graphite, glassy carbon, nanocarbon such as carbon nanotubes, amorphous carbon such as carbon black, activated carbon, and carbon fiber, and composite materials containing these carbon materials.

[0035] The material of the second electrode 12 is not limited to a specific material. As described above, the material of the second electrode 12 may be the same as or different from the material of the first electrode 11. The material of the second electrode 12 may include, for example, a predetermined metal or alloy. The predetermined metal or alloy includes, for example, at least one selected from the group consisting of Pt, Ag, Pd, Ru, Au, Cu, Ni, Ti, Fe, Cr, Al, W, and Zn.

[0036] The second electrode 12 may contain an Au—Al alloy, a Pt—Ru alloy, or an Ag—Pd alloy. The shape, material, and method of forming the second electrode 12 are not limited to any particular shape, material, or method. The second electrode 12 can be obtained, for example, by forming a film of a paste containing a metal or alloy by printing or coating, and then baking the film. The second electrode 12 may also be formed by sputtering, thermal spraying, plating, or pressure bonding.

[0037] The second electrode 12 may contain a carbon material. Examples of the carbon material include three-dimensional crystalline carbon such as graphite, glassy carbon, nanocarbon such as carbon nanotubes, amorphous carbon such as carbon black, activated carbon, and carbon fiber, and composite materials containing these carbon materials.

[0038] The ionic conductivity σ of the inorganic solid electrolyte 15 is not limited to a specific value. For example, the ionic conductivity σ is σ≧10 at 500° C. or less. -5 SCM -1 The ionic conductivity σ is the ionic conductivity of ions generated by the decomposition of water and conducting through the inorganic solid electrolyte 15. When this condition is satisfied, the amount of power generated in the power generating element 1a tends to be large. For example, the inorganic solid electrolyte 15 satisfies the condition σ≧10 at 20° C. or higher. -5 SCM -1 The inorganic solid electrolyte 15 satisfies the condition of σ≧10 at 400° C. or less, for example. -5 SCM -1 and σ≧10 at 300° C. or less. -5 SCM -1 and σ≧10 at 200° C. or less. -5 SCM -1 The conditions may be met.

[0039] The material of the inorganic solid electrolyte 15 is not limited to a specific material as long as it conducts ions generated by decomposition of water and contains at least one selected from the group consisting of water molecules and hydroxide ions. The inorganic solid electrolyte 15 may be, for example, a mineral. The mineral may be a natural mineral or an artificial mineral. The inorganic solid electrolyte 15 contains, for example, at least one selected from the group consisting of an oxide mineral, a carbonate mineral, a phosphate mineral, and a silicate mineral. In this case, the ion conductivity of the inorganic solid electrolyte 15 is likely to be higher. In addition, the power generating element 1a is likely to have high durability even when heat is supplied to the power generating element 1a, and there are fewer restrictions on the use of the power generating element 1a.

[0040] Each of the oxide minerals, carbonate minerals, phosphate minerals, and silicate minerals contained in the inorganic solid electrolyte 15 is not limited to a specific mineral. An example of an oxide mineral is silica gel. In this specification, artificially synthesized solids having a silicon oxide composition, such as silica gel, are classified as oxide minerals. The basic composition of silica gel is SiO2·H2O. An example of a carbonate mineral is hydrotalcite. The basic composition of hydrotalcite is Mg6Al2(OH) 16 CO3·4H2O. An example of a phosphate mineral is apatite. The basic composition of apatite is Ca 10The basic crystal structure of smectite is (PO4)6(OH)2. Examples of silicate minerals include smectite, kaolinite, zeolite F-9, and zeolite A-4. Smectite is a swelling silicate mineral. The basic crystal structure of smectite is a tetrahedral sheet, where (Si,Al)O4 tetrahedra are two-dimensionally bonded, and an octahedral sheet, where M(O,OH)6 hexahedrons are two-dimensionally connected in a network, sharing oxide ions. (Si,Al) means that at least one element selected from the group consisting of Si and Al is contained, and (O,OH) means that at least one element selected from the group consisting of O and OH is contained. Examples of M in the octahedral sheet are Al, Mg, Fe, and Ti. Smectite has a layered crystal structure composed of a combination of these two types of sheets. Smectite may be saponite, herculite, stevensite, or montmorillonite. The basic composition of saponite is (Ca 0.5 , Na) 0.33 Mg(Si 3.67 Al 0.33 ) O 10 (OH)2. The basic composition of Stevensite is (Ca 0.5 , Na) 0.3 (Mg,Fe)3Si4O 10 (OH)2. The basic composition of montmorillonite is (Ca 0.5 , Na) 0.33 (Al 1.67 Mg 0.33 ) SiO 10 (OH)2. The basic composition of kaolinite is Al4Si4O 10 (OH)8. The basic composition of zeolite F-9 is Na 86 [(AlO) 86 (SiO2) 106 ]·xH2O. The basic composition of zeolite A-4 is Na 12 [(AlO) 12 (SiO2) 12 ]·yH2O.

[0041] The inorganic solid electrolyte 15 may be a material having a layered crystal structure. In this case, hydration is likely to occur in the inorganic solid electrolyte 15, and the ionic conductivity of the inorganic solid electrolyte 15 is likely to be higher. For example, in smectite, cations exist between layers, and these cations exhibit very high moisture adsorption. This can increase the ionic conductivity of the inorganic solid electrolyte 15.

[0042] 1, the power generating element 1a has a terminal 17. The terminal 17 is a terminal for supplying electrical energy to the outside of the power generating element 1a. For example, by electrically connecting an external circuit to the terminal 17, the power generating element 1a can supply electrical energy to the external circuit.

[0043] Fig. 3 is an exploded perspective view schematically showing an example of a power generation device according to the present disclosure. As shown in Fig. 3, the power generation device 2a includes a power generation element 1a and an adsorbent / desorbent 21. The adsorbent / desorbent 21 is in communication with the space surrounding the first electrode 11 and adsorbs or desorbs water vapor depending on the temperature. With the power generation device 2a, even if the power generation element 1a is placed in an enclosed space, for example, the power generation element 1a can generate electricity by supplying moisture from the adsorbent / desorbent 21. In the power generation device 2a, for example, the adsorbent / desorbent 21 contains a predetermined amount of moisture.

[0044] The adsorbent / desorbent 21 is disposed, for example, in contact with the first electrode 11. The first electrode 11 is disposed, for example, between the inorganic solid electrolyte 15 and the adsorbent / desorbent 21. The adsorbent / desorbent 21 may be disposed apart from the first electrode 11, or another member may be disposed between the adsorbent / desorbent 21 and the first electrode 11.

[0045] The material of the adsorbent / desorbent 21 is not limited to a specific material as long as it can adsorb or desorb water vapor depending on the temperature. The adsorbent / desorbent 21 includes, for example, at least one selected from the group consisting of silica gel, layered double hydroxide, phosphate hydrate, zeolite, metal felt, and porous metal. This allows the adsorbent / desorbent 21 to exhibit desired adsorption / desorption characteristics for water vapor. Metal felt is felt formed from metal fibers. An example of a metal felt is nickel felt. An example of a porous metal is foamed nickel.

[0046] 3 , the power generation device 2a further includes, for example, a cap 22. The cap 22 can accommodate the power generation element 1a and the adsorbent / desorber 21. The cap 22 is made of a metal such as stainless steel, and is electrically connected to the first electrode 11. For example, by electrically connecting the cap 22 and the second electrode 12 to a predetermined measuring device 23, the electromotive force and current generated in the power generation device 2a can be measured.

[0047] 3, the power generation device 2a is supplied with heat from the heat source 25. This makes it easy for a high electromotive force to be generated in the power generation device 2a.

[0048] Fig. 4 is an exploded perspective view schematically illustrating another example of a power generation device according to the present disclosure. As shown in Fig. 4, the power generation device 2b includes a power generation element 1a and a first supply path 31a. The first supply path 31a is a flow path that guides a first fluid containing water to the first electrode 11. The first electrode 11 decomposes the water contained in the first fluid. With this configuration, the power generation element 1a generates electrical energy by decomposing the water contained in the first fluid at the first electrode 11. The first supply path 31a is formed, for example, so as to be in contact with the first electrode 11. The first fluid does not contain a gas used as a fuel gas in a fuel cell, such as hydrogen gas.

[0049] The power generation device 2b further includes, for example, a second supply path 31b. The second supply path 31b guides a second fluid containing, for example, water to the second electrode 12. Even with this configuration, electrical energy can be generated in the power generation element 1a. The second supply path 31b is formed, for example, so as to be in contact with the second electrode 12.

[0050] In the power generation device 2b, the first fluid has, for example, a first water vapor pressure. The second fluid has, for example, a second water vapor pressure. The first water vapor pressure is different from the second water vapor pressure. For example, the first water vapor pressure is higher than the second water vapor pressure. In other words, the concentration of water vapor in the first fluid is higher than the concentration of water vapor in the second fluid. Therefore, the concentration of protons generated at the first electrode 11 is higher than the concentration of protons generated at the second electrode 12, and electrical energy can be generated in the power generation element 1a.

[0051] As shown in FIG. 4 , the power generation device 2b includes a flow path member 32a, a flow path member 32b, and a heat-resistant insulating sheet 33. A first supply path 31a is formed inside the flow path member 32a, and a second supply path 31b is formed inside the flow path member 32b. The heat-resistant insulating sheet 33 and the power generation element 1a are disposed between the flow path member 32a and the flow path member 32b. An opening is formed on the surface of the flow path member 32a close to the power generation element 1a, allowing the first fluid flowing through the first supply path 31a to contact the first electrode 11 of the power generation element 1a. An opening is formed on the surface of the flow path member 32b close to the power generation element 1a, allowing the second fluid flowing through the second supply path 31b to contact the second electrode 12 of the power generation element 1a. The heat-resistant insulating sheet 33 has heat resistance and electrical insulation properties. An opening is formed in the center of the heat-resistant insulating sheet 33 that contacts the power generation element 1a.

[0052] The power generation device 2b includes, for example, a lead 35a and a lead 35b. The lead 35a is connected to the first electrode 11, and the lead 35b is connected to the second electrode 12. As a result, the electrical energy generated in the power generation element 1a is supplied to an external circuit.

[0053] The power generation device 2b further includes, for example, a drain pipe 36. The drain pipe 36 is attached to, for example, the flow path member 32a. Water generated by condensation of water vapor in the flow path member 32a passes through the drain pipe 36 and is discharged to the outside of the power generation device 2b.

[0054] 4, a heater 40 is disposed near the power generation device 2b. The flow path members 32a and 32b are maintained at a predetermined temperature by heat supplied from the heater 40. A heat insulating material 45 is disposed around the heater 40.

[0055] In the power generation device 2b, the second electrode 12 may be in contact with the atmosphere. Heat may be supplied from the heater 40 from the first electrode 11 side of the power generation element 1a, or the entire power generation element 1a may be heated uniformly.

[0056] (Additional Note) From the above description, the following techniques are disclosed.

[0057] (Technology 1) A power generating element comprising: a first electrode that splits water; a second electrode; and an inorganic solid electrolyte disposed between the first electrode and the second electrode, the inorganic solid electrolyte conducting ions generated by the splitting of water at the first electrode toward the second electrode, wherein the inorganic solid electrolyte contains at least one selected from the group consisting of water molecules and hydroxide ions.

[0058] (Technology 2) The power generating element according to Technology 1, wherein the inorganic solid electrolyte contains at least one selected from the group consisting of an oxide mineral, a carbonate mineral, a phosphate mineral, and a silicate mineral.

[0059] (Technology 3) The power generating element according to Technology 1 or 2, wherein the inorganic solid electrolyte has a layered crystal structure.

[0060] (Technology 4) The power generating element according to any one of Technologies 1 to 3, wherein the inorganic solid electrolyte has ion conductivity with respect to one ion selected from the group consisting of protons, oxide ions, hydronium ions, and hydroxide ions.

[0061] (Technology 5) The inorganic solid electrolyte has a thermal conductivity of σ≧10 at 500° C. or less. -5 SCM -1 5. The power generating element according to claim 1, wherein the condition σ is an ionic conductivity of the ions in the inorganic solid electrolyte.

[0062] (Technology 6) The power generating element according to any one of Technologies 1 to 5, wherein the material of the second electrode is different from the material of the first electrode.

[0063] (Technology 7) The power generating element according to any one of Techniques 1 to 6, wherein the first electrode includes a metal or an alloy including at least one selected from the group consisting of Pt, Ag, Pd, Ru, Au, Cu, Ni, Ti, Fe, Cr, Al, and Zn.

[0064] (Technology 8) The power generating element according to any one of Technologies 1 to 6, wherein the first electrode contains a carbon material.

[0065] (Technology 9) The power generating element according to any one of Technologies 1 to 8, wherein the first electrode is in contact with a fluid containing water present outside the power generating element.

[0066] (Technology 10) The power generating element according to any one of Technologies 1 to 9, further comprising a terminal for supplying electrical energy to an outside of the power generating element.

[0067] (Technology 11) A power generating device comprising: the power generating element according to any one of technologies 1 to 10; and a first supply path that introduces a first fluid containing water to the first electrode, wherein the first electrode decomposes water contained in the first fluid.

[0068] (Technology 12) The power generating device according to Technology 11, further comprising a second supply path that introduces a second fluid containing water to the second electrode, wherein the second electrode is in contact with the second fluid.

[0069] (Technology 13) The power generating apparatus according to Technology 12, wherein the first fluid has a first water vapor pressure, and the second fluid has a second water vapor pressure, and the first water vapor pressure is different from the second water vapor pressure.

[0070] (Technology 14) A power generating device comprising: the power generating element according to any one of technologies 1 to 13; and an adsorption / desorption body communicating with a space around the first electrode and adsorbing or desorbing water vapor depending on temperature.

[0071] (Technology 15) The power generating device according to Technology 14, wherein the adsorbent / desorbent includes at least one selected from the group consisting of silica gel, layered double hydroxide, phosphate hydrate, zeolite, metal felt, and porous metal.

[0072] (Technology 16) A power generation method comprising: placing a power generation element including a first electrode, a second electrode, and an inorganic solid electrolyte disposed between the first electrode and the second electrode and containing at least one selected from the group consisting of water molecules and hydroxide ions, in an environment where water is present, and generating ions by decomposing water using the first electrode; conducting the ions in the solid electrolyte toward the second electrode; oxidizing or reducing the ions at the second electrode to generate water; and generating a current outside the power generation element.

[0073] The present disclosure will be described in detail below with reference to examples, but the power generating element and power generating method of the present disclosure are not limited to the specific embodiments shown below.

[0074] (Measurement of Ionic Conductivity of Solid Electrolyte) Saponite Smecton-SA (manufactured by Kunimine Industries Co., Ltd.) was placed in a die with an inner diameter of 10 mm and pressed using a hydraulic press. During this pressing, a pair of Ag electrodes with a diameter of 10 mm was placed so that the saponite was positioned between them, and Ag electrodes were attached to both sides of the saponite to obtain an electrode-attached pellet. Saponite is a type of smectite. The obtained electrode-attached pellet was placed inside a cell 51 shown in Figure 5. The cell 51 had an inlet 52a and an outlet 52b. The inlet 52a was connected to a bubbler (not shown) set at 80°C, and air Gm containing water vapor was supplied from this bubbler to the inside of the cell 51. The gas flowed along both sides of the electrode-attached pellet inside the cell 51 and was discharged to the outside of the cell 51 through the outlet 52b. A heater 53 was placed inside the cell 51, and the temperature inside the cell 51 was adjusted so that the temperatures in the spaces in contact with both electrodes of the sample Sa were equal. While the temperature inside the cell 51 was changed from 25°C to 300°C, impedance measurements were performed on the electrode-attached pellets in the frequency range of 4 to 8 MHz to determine the proton conductivity of the saponite. An LCR meter IH 3536 manufactured by Hioki E.E. Corporation was used for the impedance measurements. The results are shown in Figure 6. As shown in Figure 6, saponite exhibited a proton conductivity of 10 -5 SCM -1The proton conductivity was as high as or higher than that of the conventional catalyst.

[0075] <Samples A-1 to A-5> Power generating elements according to Samples A-1 to A-5 were produced in the same manner as in the production of the above-mentioned pellets with electrodes, except that the electrodes attached to both sides of the saponite were changed to the combinations shown in Table 1. The Pt electrodes were obtained by applying a Pt-containing paste onto a Cu or Ti substrate, forming a coating, and then drying the resulting coating.

[0076]

[0077] <Reference Examples> Samples according to Reference Examples 1 and 2 were obtained in the same manner as in the preparation of the above-described pellets with electrodes, except that Cu electrodes and Ag electrodes were used as electrodes attached to both sides of the saponite.

[0078] (Evaluation of Electromotive Force) Samples A-1 to A-5 and sample Sa according to Reference Examples 1 and 2 were each placed inside a cell 51, and the temperature inside the cell 51 was changed from room temperature to 300°C while air Gm containing water vapor was supplied into the cell 51. The temperature inside the cell 51 was adjusted so that the temperature of the space in contact with both electrodes of each sample Sa was equal. Under these conditions, the electromotive force generated between the two electrodes of each sample was measured. The results are shown in Table 1. Additionally, FIG. 7 shows the relationship between the electromotive force and temperature of the power generation element according to sample A-1.

[0079] The generation of electromotive force was confirmed in Samples A-1 to A-5, which had different types of electrodes attached to both sides of the saponite. On the other hand, the generation of electromotive force was not confirmed in the samples according to Reference Examples 1 and 2, which had the same types of electrodes attached to both sides of the saponite.

[0080] <Samples A-6 to A-13> Power generation elements for Samples A-6 to A-13 were produced in the same manner as in the production of the above-mentioned electrode-attached pellets, except for the following points. The inorganic substances shown in Table 2 were used instead of saponite. A Pt electrode was used as one electrode attached to both sides of the saponite, and a Cu electrode was used as the other electrode. The electromotive force generated between the two electrodes of each sample was measured in the same manner as for Sample A-1. The results are shown in Table 2. Table 2 confirms that an electromotive force can be generated in a power generation element using an inorganic substance other than saponite.

[0081]

[0082] <Samples A-14 to A-30> Power generation elements for Samples A-14 to A-30 were prepared in the same manner as the preparation of the electrode-attached pellets described above, except for the following points. Montmorillonite was used instead of saponite. The electrodes attached to both sides of the montmorillonite were adjusted to the combinations shown in Table 3. In Table 3, Cu-Pt refers to an electrode in which Pt is supported on Cu, and was obtained by applying a Pt nano-dispersion liquid to Cu and drying it at 120°C. Carbon refers to glassy carbon, and Carbon-Pt refers to an electrode in which Pt is supported on carbon, and was obtained, similar to Cu-Pt, by applying a Pt nano-dispersion liquid to carbon and drying it at 120°C. Cu-Zn refers to an alloy of Cu and Zn (brass). The electromotive force generated between the electrodes of each sample at 30°C was measured in the same manner as for Sample A-1. The results are shown in Table 3.

[0083]

[0084] <Sample B-1> A power generating element according to Sample B-1 was obtained in the same manner as in the preparation of the above-described pellet with electrodes, except that Cu electrodes were used as the electrodes attached to both sides of the saponite.

[0085] <Sample B-2> Saponite alone was pressed using a hydraulic press to produce a pellet. Both sides of this pellet were coated with a Pt-containing paste manufactured by Tanaka Kikinzoku Co., Ltd., and the coated film of the Pt-containing paste was dried at 130°C to obtain a power generation element according to Sample B-2.

[0086] <Sample B-3> A pair of electrodes was obtained by applying a Pt-containing paste to a stainless steel mesh and heating the stainless steel mesh to 900° C. The pair of electrodes thus obtained was arranged so that the saponite was located between them, and pressure was applied using a hydraulic press to obtain a power generation element according to Sample B-3.

[0087] (Evaluation of Electromotive Force) The electromotive forces of the power generation elements of Samples B-1 to B-3 were evaluated as follows. The power generation elements of Samples B-1 to B-3 were placed inside a cell 61 shown in FIG. 8. A partition 65 was placed inside the cell 61, dividing the interior of the cell 61 into spaces 61a and 61b. An opening for placing each sample was formed in the center of the partition 65. Each sample Sa was fixed so as to cover this opening. The cell 61 had a first inlet 62a, a first outlet 62b, a second inlet 62c, and a second outlet 62d. The first inlet 62a and the first outlet 62b were in contact with the space 61a, and the second inlet 62c and the second outlet 62d were in contact with the space 61b. The first inlet 62a was connected to a bubbler (not shown) adjusted to 80°C, and air Gm containing water vapor was supplied to the space 61a through the first inlet 62a. The air Gm passed through the space 61a and was then discharged from the first outlet 62b. Dry air Gd was supplied to the space 61b through the second inlet 62c. The dry gas Gd passed through the space 61b and was then discharged from the second outlet 62d. A heater 63 was disposed inside the cell 61, and the temperature inside the cell 61 was adjusted to 70°C. Under these conditions, the electromotive force generated between the electrodes of each power generation element was measured. As a result, the generation of electromotive force was confirmed in the power generation elements of samples B-1 to B-3.

[0088] (Power Generation Characteristics) Figure 9 shows the IV characteristics of the power generation element of sample A-1. In Figure 9, the vertical axis represents voltage, and the horizontal axis represents current density. Figure 10 is a graph showing the continuous discharge characteristics of the power generation element of sample A-1. In Figure 10, the vertical axis represents voltage or current density, and the horizontal axis represents time. Figure 10 shows the change in voltage when a current load of 0.05 μA is continuously applied. As shown in Figure 10, it was possible to apply a current load when electromotive force was generated, and it was shown that electricity could be extracted from the power generation element as long as heat was continuously applied to the power generation element. Furthermore, current could be continuously extracted using the power generation elements of samples A-2 to A-30.

[0089] FIG. 11 is a graph showing the IV characteristics of the power generation element of sample B-3. FIG. 11 was measured under conditions where the cell temperature was maintained at 70°C and a gas Gm containing water vapor flowed along the anode. In FIG. 11, the vertical axis represents voltage and the horizontal axis represents current density. FIG. 12 is a graph showing the continuous discharge characteristics of the power generation element of sample B-3. In FIG. 12, the vertical axis represents voltage or current density and the horizontal axis represents time. FIG. 12 shows the continuous discharge characteristics of the power generation element of sample B-3. -3 This shows the change in voltage when a current load of 1 μA is continuously applied. As shown in Figure 12, it was demonstrated that electricity can be extracted from the power generating element as long as there is a difference in water concentration between the two electrodes of the power generating element. Furthermore, current could be continuously extracted using the power generating elements of samples B-1 and B-2.

[0090] The power generating element of the present disclosure can be used in a variety of applications, including applications for conventional power generating elements.

[0091] REFERENCE SIGNS 1a Power generating element 2a, 2b Power generating device 11 First electrode 12 Second electrode 15 Inorganic solid electrolyte 17 Terminal 21 Adsorption / desorption body 31a First supply path 31b Second supply path

Claims

1. A power generating element, a first electrode that splits water; A second electrode; an inorganic solid electrolyte disposed between the first electrode and the second electrode, for conducting ions generated by the decomposition of water at the first electrode toward the second electrode; the catalytic activity of the first electrode for water splitting at a predetermined temperature is higher than the catalytic activity of the second electrode for water splitting at the predetermined temperature; The inorganic solid electrolyte contains at least one selected from the group consisting of water molecules and hydroxide ions. Power generating element.

2. the inorganic solid electrolyte contains at least one mineral selected from the group consisting of an oxide mineral, a carbonate mineral, a phosphate mineral, and a silicate mineral; The power generating element according to claim 1 .

3. The inorganic solid electrolyte has a layered crystal structure. The power generating element according to claim 1 .

4. the inorganic solid electrolyte has ionic conductivity with respect to one ion selected from the group consisting of protons, oxide ions, hydronium ions, and hydroxide ions; The power generating element according to claim 1 .

5. The inorganic solid electrolyte has a σ≧10 at 500° C. or less. -5 SCM -1 Meet the conditions of In the above condition, σ is the ionic conductivity of the ion in the inorganic solid electrolyte. The power generating element according to claim 1 .

6. the first electrode contains a metal or an alloy including at least one selected from the group consisting of Pt, Ag, Pd, Ru, Au, Cu, Ni, Ti, Fe, Cr, Al, W, and Zn; The power generating element according to claim 1 .

7. The first electrode comprises a carbon material. The power generating element according to claim 1 .

8. the first electrode is in contact with a fluid containing water present outside the power generating element; The power generating element according to claim 1 .

9. Further provided with a terminal for supplying electrical energy to the outside of the power generating element, The power generating element according to claim 1 .

10. The power generating element according to any one of claims 1 to 3; a first supply path for introducing a first fluid containing water to the first electrode; The first electrode decomposes water contained in the first fluid. Power generation equipment.

11. a second supply path for introducing a second fluid containing water to the second electrode; the second electrode contacts the second fluid; The power generating device according to claim 10.

12. the first fluid has a first water vapor pressure; the second fluid has a second water vapor pressure; the first water vapor pressure is different from the second water vapor pressure; The power generating device according to claim 11.

13. The power generating element according to any one of claims 1 to 3; An adsorption / desorption body that is in communication with the space around the first electrode and adsorbs or desorbs water vapor depending on temperature. Power generation equipment.

14. the adsorbent / desorbent comprises at least one selected from the group consisting of silica gel, layered double hydroxide, phosphate hydrate, zeolite, metal felt, and a metal porous body; The power generating device according to claim 13.

15. placing a power generating element including a first electrode, a second electrode, and an inorganic solid electrolyte disposed between the first electrode and the second electrode and containing at least one selected from the group consisting of water molecules and hydroxide ions in an environment where water is present, and generating ions by decomposing water using the first electrode; conducting the ions in the inorganic solid electrolyte toward the second electrode; oxidizing or reducing the ions at the second electrode to produce water; and generating a current outside the power generating element. Power generation method.