Power generation element and power generation method

Abstract

This power generation element 1a comprises a first electrode 11, a second electrode 12, and an electrolyte 15. The first electrode 11 decomposes water. The electrolyte 15 is disposed between the first electrode 11 and the second electrode 12. The 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 electrolyte 15 is in a semi-solid or plastic state. The electrolyte 15 contains, for example, at least one selected from the group consisting of water molecules and hydroxide ions.

Description

Power generation element and power generation method

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

[0002] 2. Description of the Related Art Power generating elements that utilize electrochemical reactions are known.

[0003] For example, Patent Document 1 describes a power generating element that includes a solid electrolyte that conducts ions generated by the decomposition of water at a first electrode toward a second electrode.

[0004] Patent Document 2 describes a microbial fuel cell that can extract electrical energy from a field or upland where plants grow and from a plant cultivation container in which the plants are cultivated. This microbial fuel cell includes an electrolyte, an anode electrode, and a cathode electrode. The electrolyte includes water, organic matter or sugar, and current-generating bacteria that decompose the organic matter or sugar to generate protons and electrons. The anode electrode uses a metal with a negative ionization tendency, and the cathode electrode uses carbon or a metal with a positive ionization tendency.

[0005] Patent Document 3 describes a power generation element for a fuel cell. This power generation element for a fuel cell includes a positive electrode, a negative electrode, and a solid electrolyte. The positive electrode reduces oxygen. The negative electrode oxidizes fuel. The solid electrolyte is disposed between the positive electrode and the negative electrode. Each of the positive electrode and the negative electrode includes a catalyst layer having pores. The positive electrode diffusion layer and the positive electrode catalyst layer are integrated to form the positive electrode. The negative electrode catalyst layer and the negative electrode diffusion layer are integrated to form the negative electrode.

[0006] International Publication No. 2023 / 157402 Japanese Patent Application Laid-Open No. 2021-61178 Japanese Patent Application Laid-Open No. 2006-278022

[0007] Clay Science, (Sun), 2019, Volume 23, Issue 2, p.19-24

[0008] The techniques described in the above documents have room for reexamination from the viewpoint of power generation efficiency. Therefore, the present disclosure provides a novel power generation element that is advantageous from the viewpoint of power generation efficiency.

[0009] The power generation element disclosed herein comprises: a first electrode containing a first conductive material and splitting water; a second electrode containing a second conductive material having a different composition from the first conductive material; and an inorganic solid electrolyte disposed between the first electrode and the second electrode, for conducting ions generated by the splitting of water at the first electrode toward the second electrode, wherein the power generation element satisfies the following condition (ia) or (ib): the electrolyte contains at least one selected from the group consisting of water molecules and hydroxide ions, and is in a semi-solid or plastic state: (ia) the ionization tendency of the first element contained in the first conductive material is greater than the ionization tendency of the second element contained in the second conductive material. (ib) the ionization tendency of the first element is greater than the ionization tendency of Au, and the second element is C.

[0010] According to the present disclosure, a novel power generating element that is advantageous in terms of power generation efficiency can be provided.

[0011] 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 graph schematically illustrating the relationship between the volume of the electrolyte and the water content. FIG. 3 is a diagram schematically illustrating an example of a thermochemical battery. FIG. 4 is an exploded perspective view schematically illustrating an example of a power generation device according to the present disclosure. FIG. 5 is an exploded perspective view schematically illustrating another example of a power generation device according to the present disclosure. FIG. 6 is a graph showing the relationship between the ratio of the power density of the samples according to Examples 1-1 and 1-2 to the power density of the sample according to Comparative Example 1-1 and the elapsed time from the start of measurement.

[0012] (Knowledge forming the basis of the present disclosure) A power generation element capable of generating electricity using water, which is widely present in the environment, is thought to be able to be placed in places where maintenance is difficult, such as enclosed spaces, factory chimneys, and plant equipment. It is important that such a power generation element has few usage constraints and high power generation efficiency. Patent Document 1 does not specifically consider the power generation efficiency of the power generation element. Furthermore, in the microbial fuel cell described in Patent Document 2, the electrolyte must contain current-generating bacteria, and the current-generating bacteria are Shewanella bacteria present in soil. For this reason, the microbial fuel cell described in Patent Document 2 is thought to have significant usage constraints. The fuel cell power generation element described in Patent Document 3 requires a supply of fuel such as hydrogen. For this reason, the fuel cell power generation element described in Patent Document 3 is thought to have significant usage constraints.

[0013] Therefore, the present inventors conducted extensive research to determine whether it would be possible to construct a power generation element that can generate electricity using water, which is widely available in the environment, has few usage restrictions, and has high power generation efficiency. As a result, they discovered that a power generation element that is advantageous in terms of power generation efficiency can be obtained when the electrolyte is a specific fluid. Based on this new finding, the present inventors have completed the power generation element according to the present disclosure.

[0014] (Embodiments of the Present Disclosure) Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0015] FIG. 1 is a diagram illustrating an example of a power generating element and its power generation principle according to the present disclosure. As shown in FIG. 1 , the power generating element 1a includes a first electrode 11, a second electrode 12, and an electrolyte 15. The first electrode 11 splits water. Water can exist in either a liquid or gas phase in the environment surrounding the first electrode 11. When water comes into contact with the first electrode 11, the water splits and generates specific ions. The electrolyte 15 is disposed between the first electrode 11 and the second electrode 12. The electrolyte 15 conducts the ions generated by the splitting of water at the first electrode 11 toward the second electrode 12. The splitting of water at the first electrode 11 and the generation of ions in the electrolyte 15 create a potential difference between the first electrode 11 and the second electrode 12, generating a current through ion conduction. This allows the power generating element 1a to supply electrical energy to the outside of the power generating element 1a. The electrolyte 15 is, for example, in a semi-solid or plastic state. This allows the power generating element 1a to easily achieve high power generation efficiency.

[0016] 2 is a graph showing the relationship between the volume of the electrolyte and the water content ratio. In the graph shown in FIG. 2, a, b, c, and d indicate that the electrolyte is in a solid, semi-solid, plastic, and liquid state, respectively. S , W P , and W L are the water content ratios corresponding to the shrinkage limit, plastic limit, and liquid limit, respectively. The shrinkage limit of an electrolyte is determined, for example, in accordance with or with reference to Japanese Industrial Standards (JIS) A 1209:2020. The plastic limit and liquid limit of an electrolyte are determined in accordance with or with reference to JIS A 1205:2020. For example, the shrinkage limit, plastic limit, and liquid limit of an electrolyte can be determined by testing using an air-dried sample. For example, an air-dried sample can be obtained by pulverizing and / or crushing the dried material obtained by air-drying the electrolyte. The water content of an electrolyte is determined, for example, in accordance with or with reference to JIS A 1203:2020.

[0017] When the electrolyte 15 is in a semi-solid or plastic state, the electrolyte 15 is likely to retain water, making it easier to handle the power generating element 1a.

[0018] For example, in a fuel cell, a fuel gas containing hydrogen gas is generally supplied to the fuel cell. Meanwhile, in the power generation element 1a, power generation occurs by decomposition of water at the first electrode 11. Therefore, the power generation element 1a can generate power in an environment where hydrogen gas is not supplied to the power generation element 1a and moisture is present. Generally, a fuel cell has a catalyst layer and a gas diffusion layer on both sides of the electrolyte. Meanwhile, since the power generation element 1a can generate power without being supplied with hydrogen gas, the first electrode 11 in the power generation element 1a may have a single-layer structure.

[0019] FIG. 3 is a schematic diagram illustrating an example of a thermochemical battery. As shown in FIG. 3 , 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.

[0020] The thermochemical battery 9 uses an electrolyte 95, and when heat is supplied to the thermochemical battery 9, the solvent in the electrolyte 95 may evaporate, reducing the amount of the electrolyte 95. In addition, there is a possibility that the electrolyte 95 may leak from the thermochemical battery 9. For this reason, the thermochemical battery 9 requires predetermined maintenance. On the other hand, the power generation element 1a generates power 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. Therefore, there are few restrictions on the use of the power generation element 1a.

[0021] As described above, the electrolyte 15 exhibits ionic conductivity with respect to ions generated by the decomposition of water. The electrolyte 15 has ionic conductivity with respect to at least one ion selected from the group consisting of protons, oxide ions, hydronium ions, and hydroxide ions. In the example shown in FIG. 1 , the electrolyte 15 has proton conductivity.

[0022] When the electrolyte 15 is in a semi-solid or plastic state, the electrolyte 15 is not limited to a specific fluid, and may be, for example, a non-Newtonian fluid.

[0023] The power generating element 1a will be described in more detail using an example in which protons are conducted through the 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. The first electrode 11 splits water using, for example, thermal energy supplied to the power generating element 1a. 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.

[0024] 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 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 electrolyte 15. Excess chemical energy associated with the generation of water at the second electrode 12 is extracted as electrical energy.

[0025] According to the first law of thermodynamics, the extracted free energy G is defined as follows using enthalpy H, thermodynamic temperature T, and entropy S: G = H - TS Equation (1)

[0026] 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, E is the standard electromotive force, and F is the Faraday constant 96485 Cmol-1 ΔG0 = -nE0F Equation (2)

[0027] 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 electrons transferred, and F is the Faraday constant. 0 +(RT / zF)ln(a Ox / a Red ) Formula (3)

[0028] The power generating element 1 a can generate electricity by utilizing water present in the environment in contact with the first electrode 11 even when ions other than protons generated by the decomposition of water are conducted through the electrolyte 15 .

[0029] In this way, the power generating element 1a is a 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 even without the temperature difference required for the Seebeck effect, for example. As described above, the power generating element 1a can be configured such that 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. When the power generating element 1a has such a configuration, the power generating element 1a can generate electricity even if the water vapor concentration around the power generating element 1a is uniform.

[0030] 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.

[0031] A power generation method can be provided, which includes placing the power generation element 1a in an environment where moisture is present, generating a potential difference between the first electrode 11 and the second electrode 12, and supplying electrical energy to the outside of the power generation element 1a.

[0032] 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.

[0033] 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, and Zn. In this case, the first electrode 11 can exhibit high catalytic activity for water decomposition.

[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. 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 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.

[0037] The material of the first electrode 11 and the material of the second electrode 12 may each be a simple substance or an alloy. Examples of alloys include Au—Al alloys, Pt—Ru alloys, Ag—Pd alloys, brass, and stainless steel. An example of stainless steel is austenitic stainless steel.

[0038] For example, the first electrode 11 may contain a first conductive material, and the second electrode 12 may contain a second conductive material having a composition different from that of the first conductive material. The power generating element 1a may, for example, satisfy the following condition (ia) or (ib). With such a configuration, the power generating element 1a has fewer restrictions on use and can exhibit high power generation efficiency. (ia) The ionization tendency of the first element contained in the first conductive material in the largest amount on a molar basis is greater than the ionization tendency of the second element contained in the second conductive material in the largest amount on a molar basis. (ib) The ionization tendency of the first element is greater than the ionization tendency of Au, and the second element is C.

[0039] The power generating element 1a may satisfy, for example, the following condition (ii) in addition to the condition (ia) or (ib): (ii) The first element and the second element are selected from combinations other than Ag and Au, Ni and Cu, Pd and Au, and Ru and Au.

[0040] The first element is preferably Mg, Al, Cu, Zn, Ni, Fe, or Ti. In this case, the power generating element 1a is more likely to exhibit high power generation efficiency.

[0041] The first element is more preferably Al or Cu. In this case, the power generating element 1a is more likely to exhibit high power generation efficiency.

[0042] The second element is preferably Pt, C, Fe, W, Ni, Ag, Cu, Pd, or Au. In this case, the power generating element 1a is more likely to exhibit high power generation efficiency.

[0043] The second element is more preferably C, W, Ni, or Cu. In this case, the power generating element 1a is more likely to exhibit high power generation efficiency.

[0044] 1 , in the power generating element 1a, for example, a catalyst 20 is attached to the surface of at least one selected from the group consisting of the first electrode 11 and the second electrode 12. With such a configuration, power generation efficiency is likely to be higher than when the catalyst 20 is not attached to the surfaces of the first electrode 11 and the second electrode 12. In the power generating element 1a, the catalyst 20 may be attached only to the surface of the first electrode 11, or may be attached only to the surface of the second electrode 12. In the power generating element 1a, the catalyst 20 does not have to be attached to the surface of both the first electrode 11 and the second electrode 12.

[0045] The catalyst 20 has a catalytic effect on, for example, the decomposition of water. The catalyst 20 contains, for example, at least one element selected from the group consisting of Pt, Pd, Ir, Rh, Ru, and Au. In this case, the power generation efficiency of the power generation element 1a is likely to be higher.

[0046] The shape of the catalyst 20 is not limited to a particular shape as long as it is attached to the surface of the first electrode 11. The catalyst 20 may be in the form of particles, fibers, or a film.

[0047] 1 , the catalyst 20 may be disposed between the first electrode 11 or the second electrode 12 and the electrolyte 15. The catalyst 20 may be disposed, for example, away from the electrolyte 15. For example, when the first electrode 11 or the second electrode 12 is a porous body, the catalyst 20 may be attached to the inner surface of the porous body.

[0048] When the catalyst 20 is attached to the surface of at least one selected from the group consisting of the first electrode 11 and the second electrode 12, the material of the first electrode 11 is not limited to a specific material as long as it can decompose water. The element most abundant in the first electrode 11 on a molar basis is, for example, Al or Cu. In this case, the power generation efficiency of the power generation element 1a is likely to be higher. In particular, the power generation efficiency of the power generation element 1a is likely to be higher when the catalyst 20 is attached to the surface of such a first electrode 11.

[0049] When the catalyst 20 is attached to the surface of at least one selected from the group consisting of the first electrode 11 and the second electrode 12, the material of the second electrode 12 is not limited to a specific material. The element most abundant on a molar basis in the second electrode 12 is, for example, C, W, Pt, or Cu. In this case, the power generation efficiency of the power generation element 1a is likely to be higher. In particular, the power generation efficiency of the power generation element 1a is likely to be higher when the catalyst 20 is attached to the surface of the second electrode 12 whose element most abundant on a molar basis is C, W, or Cu.

[0050] The shapes of the first electrode 11 and the second electrode 12 are not limited to a specific shape. Each of the first electrode 11 and the second electrode 12 may be, for example, a plate, foil, film, layer, mesh, woven fabric, nonwoven fabric, or punched metal. When the first electrode 11 or the second electrode 12 is a film or layer, the first electrode 11 or the second electrode 12 can be obtained, for example, by forming a film of a paste containing a predetermined conductive material by printing or coating and then baking the film. The first electrode 11 or the second electrode 12 may also be formed by sputtering, thermal spraying, plating, or pressure bonding.

[0051] The ionic conductivity σ of the 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 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 electrolyte 15 has a conductivity σ≧10 at 20° C. or higher. -5 SCM -1 The 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.

[0052] The material of the electrolyte 15 is not limited to a specific material as long as it conducts ions generated by the decomposition of water. The electrolyte 15 contains, for example, at least one selected from the group consisting of water molecules and hydroxide ions. In this case, the ionic conductivity of the electrolyte 15 is likely to be high when the power generating element 1a generates electricity.

[0053] The electrolyte 15 may include an inorganic solid electrolyte. The electrolyte 15 may include, for example, a mineral. The mineral may be a natural mineral or an artificial mineral. The 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 ionic conductivity of the electrolyte 15 is likely to be higher. In addition, the power generation element 1a is likely to have high durability even when heat is supplied to the power generation element 1a, and there are fewer restrictions on the use of the power generation element 1a.

[0054] Each of the oxide minerals, carbonate minerals, phosphate minerals, and silicate minerals contained in the 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 composition of silicon oxide, 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, hectorite, 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. In this basic composition, x is a positive integer. The basic composition of zeolite A-4 is Na 12 [(AlO) 12 (SiO2) 12 ]·yH2O, where y is a positive integer.

[0055] The electrolyte 15 may be a material having a layered crystal structure. In this case, hydration is likely to occur in the electrolyte 15, and the ionic conductivity of the electrolyte 15 is likely to be higher. For example, in smectite, cations exist between the layers, and these cations exhibit very high water adsorption properties. This can increase the ionic conductivity of the electrolyte 15.

[0056] The thickness of the electrolyte 15 is not limited to a specific value. The thickness is, for example, 3 mm or less, and may be 2 mm or less, 1 mm or less, 0.5 mm or less, 0.3 mm or less, or 0.2 mm or less. The thickness of the electrolyte 15 is, for example, 0.01 mm or more.

[0057] 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.

[0058] Fig. 4 is an exploded perspective view schematically showing an example of a power generation device according to the present disclosure. As shown in Fig. 4, 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.

[0059] 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 electrolyte 15 and the adsorbent / desorbent 21. The adsorbent / desorbent 21 may be disposed away from the first electrode 11, or another member may be disposed between the adsorbent / desorbent 21 and the first electrode 11.

[0060] 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.

[0061] 4 , 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.

[0062] 4, 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.

[0063] Fig. 5 is an exploded perspective view schematically illustrating another example of a power generation device according to the present disclosure. As shown in Fig. 5, 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.

[0064] 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.

[0065] 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.

[0066] As shown in FIG. 5 , 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.

[0067] 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.

[0068] 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.

[0069] 5, 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.

[0070] 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.

[0071] (Additional Notes) The above disclosure discloses the following technologies. (Technology 1) A power generating element comprising: a first electrode that splits water; a second electrode; and an electrolyte disposed between the first electrode and the second electrode and conducting ions generated by the splitting of water at the first electrode toward the second electrode, wherein the electrolyte is in a semi-solid or plastic state. (Technology 2) The first electrode includes a first conductive material; and the second electrode includes a second conductive material having a different composition from the first conductive material. The power generating element according to Technology 1 satisfies the following condition (ia) or (ib): The electrolyte contains at least one selected from the group consisting of water molecules and hydroxide ions. (ia) The ionization tendency of the first element contained in the first conductive material in the largest amount on a molar basis is greater than the ionization tendency of the second element contained in the second conductive material in the largest amount on a molar basis. (ib) The ionization tendency of the first element is greater than the ionization tendency of Au, and the second element is C. (Technology 3) The power generating element according to Technology 2, further satisfying the following condition (ii): (ii) the first element and the second element are selected from combinations other than Ag and Au, Ni and Cu, Pd and Au, and Ru and Au. (Technology 4) The power generating element according to Technology 2 or 3, wherein the first element is Mg, Al, Cu, Zn, Ni, Fe, or Ti. (Technology 5) The power generating element according to any one of Technology 2 to 4, wherein the first element is Al or Cu. (Technology 6) The power generating element according to any one of Technology 2 to 5, wherein the second element is Pt, C, Fe, W, Ni, Ag, Cu, Pd, or Au. (Technology 7) The power generating element according to any one of Technology 2 to 6, wherein the second element is C, W, Ni, or Cu. (Technology 8) The power generating element according to Technology 2, wherein a catalyst is attached to a surface of at least one selected from the group consisting of the first electrode and the second electrode. (Technology 9) The power generating element according to Technology 8, wherein the catalyst includes at least one selected from the group consisting of Pt, Pd, Ir, Rh, Ru, and Au. (Technology 10) The power generating element according to Technology 8 or 9, wherein the element most abundant in the first electrode on a molar basis is Al or Cu.(Technology 11) The power generating element according to any one of Technologies 8 to 10, wherein the element most abundant in the second electrode on a molar basis is C, W, Pt, or Cu. (Technology 12) The power generating element according to any one of Technologies 1 to 11, wherein the power generating element is capable of generating electricity in an environment where hydrogen gas is not supplied to the power generating element and moisture is present. (Technology 13) The power generating element according to any one of Technologies 1 to 12, wherein the electrolyte is a non-Newtonian fluid. (Technology 14) The power generating element according to any one of Technologies 1 to 13, wherein the electrolyte contains at least one selected from the group consisting of water molecules and hydroxide ions. (Technology 15) The power generating element according to any one of Technologies 1 to 14, wherein the electrolyte includes an inorganic solid electrolyte. (Technology 16) The power generating element according to any one of Technologies 1 to 15, wherein the electrolyte contains at least one selected from the group consisting of oxide minerals, carbonate minerals, phosphate minerals, and silicate minerals. (Technology 17) The power generating element according to any one of Technologies 1 to 16, wherein the electrolyte has a layered crystal structure. (Technology 18) The power generating element according to any one of Technologies 1 to 17, wherein the electrolyte is conductive to at least one ion selected from the group consisting of protons, oxide ions, hydronium ions, and hydroxide ions. (Technology 19) A power generating method, comprising placing the power generating element according to any one of Technologies 1 to 18 in an environment where moisture is present, and generating a potential difference between the first electrode and the second electrode to supply electrical energy to the outside of the power generating element.

[0072] 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.

[0073] Example 1-1: Ultrapure water was added to Kunipia F montmorillonite manufactured by Kunimine Industries Co., Ltd., and the mixture was mixed with a reagent spoon until uniform, yielding a mixture according to Example 1-1. Montmorillonite is a type of smectite. The water content of this mixture was 50% by mass. According to Non-Patent Document 1, the average plastic limit and liquid limit of Kunipia F calculated according to JIS A 1205:2020 are 67.9% by mass and 964.7% by mass, respectively. Therefore, the mixture according to Example 1-1 was in a semi-solid state. The mixture according to Example 1-1 was placed in a metal die with an opening of 30 mm in diameter and compressed using a hydraulic press. During compression of the mixture according to Example 1-1, the first and second electrodes were positioned so that the mixture according to Example 1-1 was located between them. The first electrode was an aluminum electrode. The aluminum electrode was aluminum foil, and platinum particles were attached to the surface of the aluminum foil as a catalyst. A water dispersion of platinum particles provided by Sigma-Aldrich was applied to an Al electrode with an area of ​​1 cm. 2 The platinum particles were deposited in an amount of 0.14 mL per electrode and heated at 120°C to deposit them on the surface of the carbon electrode. The average primary particle diameter of the platinum particles in the aqueous dispersion of platinum particles was 3 nm, and the concentration of the platinum particles in the aqueous dispersion of platinum particles was 1,000 parts per million (ppm) by mass. The second electrode was a carbon electrode. The carbon electrode was carbon paper. Platinum particles were supported on the surface of the carbon paper in the same manner as the Al electrode. Each of the first and second electrodes had a diameter of 30 mm. In this way, a sample according to Example 1-1 was obtained. The thickness of the mixture in this sample was 0.5 cm.

[0074] Example 1-2: Montmorillonite Kunipia F manufactured by Kunimine Industries Co., Ltd. was added to ultrapure water and uniformly dispersed using a homogenizer. The paste according to Example 1-2 was then deaerated for 20 minutes using a vacuum device. The water content of this paste was 93% by mass. According to Non-Patent Document 1, the paste according to Example 1-2 was in a plastic state. A plastic frame having a width of 0.5 cm and a thickness of 0.5 cm was placed on a first electrode having a diameter of 3 cm. The first electrode was configured similarly to the first electrode in Example 1-1. The frame had a rectangular opening with long sides of 3.4 cm and short sides of 2.6 cm in plan view. The paste according to Example 1-2 was placed on the first electrode. A second electrode was placed on the paste according to Example 1-2, and the second electrode was pressed against the paste according to Example 1-2 with a flat plate to squeeze out excess paste from between the first and second electrodes. In this manner, the sample according to Example 1-2 was obtained. The second electrode was configured similarly to the second electrode in Example 1-1. The first and second electrodes each had a diameter of 30 mm.

[0075] (Comparative Example 1-1) A sample according to Comparative Example 1-1 was obtained in the same manner as in Example 1-1, except that Kunipia F to which no ultrapure water had been added was used instead of the mixture according to Example 1-1. Kunipia F to which no ultrapure water had been added was in a solid state.

[0076] (Evaluation of power generation characteristics) A sealed container filled with water was prepared in a room with a room temperature of approximately 25°C. A stand was placed inside the sealed container to provide a horizontal surface above the water surface. Each of the above samples was placed on this stand. The relative humidity inside the sealed container was maintained at approximately 90% RH. In this state, I-V curve characteristics were measured using a potentiostat ALS Model 660E manufactured by BAS Corporation or a PARSTAT 4000 manufactured by Ametech Science Instruments, and the output P[W] was calculated from the relationship P[W] = V[V] × I[A]. The calculated output P[W] was divided by the area of ​​the electrode to obtain the power density [W / cm 2 ] was calculated.

[0077] 6 is a graph showing the relationship between the ratio of the power density of the samples according to Examples 1-1 and 1-2 to the power density of the sample according to Comparative Example 1-1 and the time elapsed from the start of measurement. As shown in FIG. 6, the samples according to Examples 1-1 and 1-2 exhibited higher power densities than the sample according to the comparative example for most of the period up to 60 hours after the start of measurement. This suggests that if the electrolyte in the power generation element is not a solid but a non-Newtonian fluid such as a fluid in a semi-solid and plastic state, the power density of the power generation element is likely to be high, which is advantageous from the perspective of power generation efficiency.

[0078] Example 2-1: Montmorillonite Kunipia F (Kunimine Industries Co., Ltd.) was added to ultrapure water and uniformly dispersed using a homogenizer. The mixture was then deaerated for 20 minutes using a vacuum device to obtain a montmorillonite paste. The water content of this paste was 93% by mass. According to Non-Patent Document 1, the paste according to Example 2-1 was in a plastic state. A frame with a width of 0.5 cm and a thickness of 0.05 cm was placed on a square Al electrode with sides measuring 5 cm in plan view. The frame had a square opening with sides measuring 4 cm in plan view. The opening was filled with montmorillonite paste. A carbon electrode was placed on the paste, and a flat plate was pressed against the carbon electrode to remove excess paste around the opening. In this manner, a sample according to Example 2-1 was obtained. The Al electrode was aluminum foil, and the carbon electrode was carbon paper.

[0079] Example 2-2 A sample according to Example 2-2 was obtained in the same manner as in Example 2-1, except that a copper electrode was used instead of the carbon electrode. The copper electrode was a plate-shaped electrode.

[0080] (Evaluation of power generation characteristics) Each of the above samples was placed in a thermostatic chamber set at 25°C or 30°C to measure the power generation characteristics. A container filled with water was placed in the thermostatic chamber, and the relative humidity in the thermostatic chamber was maintained at approximately 90% RH. In this state, I-V curve characteristics were measured using a potentiostat ALS Model 660E manufactured by BAS Corporation or a PARSTAT 4000 manufactured by Ametech Science Instruments, and the output P[W] was calculated from the relationship P[W] = V[V] × I[A]. The calculated output P[W] was divided by the area of ​​the electrode to obtain the power density [W / cm 2 The results are shown in Table 1.

[0081] As shown in Table 1, the power density of the samples according to each example was high, suggesting that the power generation element is advantageous in terms of power generation efficiency when the above condition (ia) or (ib) is satisfied.

[0082]

[0083] Example 3-1: Montmorillonite Kunipia F (Kunimine Industries Co., Ltd.) was added to ultrapure water and uniformly dispersed using a homogenizer. The mixture was then deaerated for 20 minutes using a vacuum device to obtain a montmorillonite paste. The water content of this paste was 93% by mass, and according to Non-Patent Document 1, this paste was in a plastic state. Using a cylindrical plastic container, the space between the Al electrode and Cu electrode was filled with the paste. The distance between the Al electrode and Cu electrode was adjusted to 9.4 mm. The container had an inner diameter of 30 mm. The Al electrode and Cu electrode were positioned at both ends of the container. The Al electrode and Cu electrode were disk-shaped and had a diameter of 30 mm. In this manner, a sample according to Example 3-1 was obtained.

[0084] Example 3-2 A sample according to Example 3-2 was obtained in the same manner as in Example 3-1, except that the water content in the montmorillonite paste was adjusted to 90 mass %. According to Non-Patent Document 1, this paste was in a plastic state.

[0085] Example 3-3 A sample according to Example 3-3 was obtained in the same manner as in Example 3-1, except that the water content in the montmorillonite paste was adjusted to 70 mass %. According to Non-Patent Document 1, this paste was in a plastic state.

[0086] Comparative Example 2 A sample according to Comparative Example 2 was obtained in the same manner as in Example 3-1, except that Kunipia F to which no ultrapure water had been added was used instead of the montmorillonite paste.

[0087] (Evaluation of power generation characteristics) Each of the above samples was placed in a thermostatic chamber set at 25°C or 30°C to measure the power generation characteristics. A container filled with water was placed in the thermostatic chamber, and the relative humidity in the thermostatic chamber was maintained at approximately 90% RH. In this state, I-V curve characteristics were measured using a potentiostat ALS Model 660E manufactured by BAS Corporation or a PARSTAT 4000 manufactured by Ametech Science Instruments, and the output P[W] was calculated from the relationship P[W] = V[V] × I[A]. The calculated output P[W] was divided by the area of ​​the electrode to obtain the power density [W / cm 2 The results are shown in Table 2.

[0088] As shown in Table 2, it can be seen that when the electrolyte is in a plastic state, the power generation characteristics of the sample are high.

[0089]

[0090] Example 4: Montmorillonite Kunipia F (Kunimine Industries Co., Ltd.) was added to ultrapure water and uniformly dispersed using a homogenizer. The mixture was then deaerated for 20 minutes using a vacuum device to obtain a montmorillonite paste. The water content of this paste was 93% by mass. According to Non-Patent Document 1, this paste was in a plastic state. The paste was filled into the space between an Al-Mg electrode and a carbon electrode, which were spaced 1.5 mm apart. Each of the Al-Mg electrode and the carbon electrode had a square shape with a side length of 40 mm in plan view. In this way, a sample according to Example 4 was obtained. The Al-Mg electrode was an electrode made of an alloy of Al and Mg containing less than 6% by mass of Mg.

[0091] <Comparative Example 3> Montmorillonite Kunipia F manufactured by Kunimine Industries Co., Ltd. was placed in a metal die with an inner diameter of 10 mm and pressed using a hydraulic press. An Al-Mg electrode with a diameter of 10 mm and a carbon electrode with a diameter of 10 mm were arranged so that the montmorillonite was located between them. The distance between the Al-Mg electrode and the carbon electrode was 1.4 mm. In this way, a sample according to Comparative Example 3 was obtained. The Al-Mg electrode was an electrode made of an alloy of Al and Mg containing less than 6% by mass of Mg.

[0092] (Evaluation of power generation characteristics) Each of the above samples was placed in a thermostatic chamber set at 25°C or 30°C to measure the power generation characteristics. A container filled with water was placed in the thermostatic chamber, and the relative humidity in the thermostatic chamber was maintained at approximately 90% RH. In this state, I-V curve characteristics were measured using a potentiostat ALS Model 660E manufactured by BAS Corporation or a PARSTAT 4000 manufactured by Ametech Science Instruments, and the output P[W] was calculated from the relationship P[W] = V[V] × I[A]. The calculated output P[W] was divided by the area of ​​the electrode to obtain the power density [W / cm 2 The results are shown in Table 3.

[0093] As shown in Table 3, it can be seen that when the electrolyte is in a plastic state, the power generation characteristics of the sample are high.

[0094]

[0095] The power generating element of the present disclosure can be used in a variety of applications, including applications for conventional power generating elements.

Claims

1. A power generating element comprising: a first electrode containing a first conductive material and capable of splitting water; a second electrode containing a second conductive material having a different composition from the first conductive material; and an inorganic solid electrolyte disposed between the first electrode and the second electrode and conducting ions generated by the splitting of water at the first electrode toward the second electrode, wherein the element satisfies the following condition (ia) or (ib): the inorganic solid electrolyte contains at least one selected from the group consisting of water molecules and hydroxide ions, and is in a semi-solid or plastic state. (ia) The ionization tendency of the first element contained in the first conductive material is greater than the ionization tendency of the second element contained in the second conductive material. (ib) The ionization tendency of the first element is greater than the ionization tendency of Au, and the second element is C.

2. The power generating element according to claim 1, wherein the power generating element is capable of generating electricity in an environment where hydrogen gas is not supplied to the power generating element and moisture is present.

3. The power generating element according to claim 1, wherein a catalyst is attached to a surface of at least one selected from the group consisting of the first electrode and the second electrode, and the catalyst includes at least one selected from the group consisting of Pt, Pd, Ir, Rh, Ru, and Au.

4. The power generating element according to claim 1, wherein the inorganic solid electrolyte is a non-Newtonian fluid.

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

6. The power generating element according to claim 1, wherein the inorganic solid electrolyte has a layered crystal structure.

7. The power generating element according to claim 1, wherein the inorganic solid electrolyte is conductive to at least one ion selected from the group consisting of protons, oxide ions, hydronium ions, and hydroxide ions.

8. A method of generating electricity, comprising placing the power generating element according to claim 1 in an environment where moisture is present, generating a potential difference between the first electrode and the second electrode, and supplying electrical energy to the outside of the power generating element.

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