New compound exhibiting hydride ionic conduction performance, method for producing same, and use thereof

Abstract

Provided are: a new compound exhibiting hydride ionic conduction performance with high conductivity; a method for producing the same; and a use for batteries or the like using the same.　A compound represented by general formula (I).　(I): Ba1.75-xSrxLiHaOb (In the formula, x represents a number satisfying 0<x≤1.65, b represents a number satisfying 0<b≤1.5, and a represents a number satisfying charge compensation for b.)

Description

New compounds exhibiting hydride ion conductivity, their production methods and uses

[0001] The present invention relates to a compound exhibiting unique physical properties such as hydride ion conductivity, a method for producing the same, and applications such as batteries using the same.

[0002] Energy storage and power generation devices play a major role in building a sustainable society. Ionic conductors used in the electrodes and solid electrolytes of these electrochemical devices are the key materials that determine their operating principles and performance. Protons and oxide ions are used as mobile ions in energy conversion devices such as fuel cells and electrolysis.

[0003] Recently, hydrides (H - Hydride ions are monovalent, have an ionic radius of approximately 1.2 angstroms, and have a large polarizability, making them more suitable for fast ionic conduction than protons and oxygen ions. Furthermore, H2 + 2e - →2H - Since the oxidation-reduction potential of this compound is as high as −2.25 V (vs. SHE), it has the potential to create new high-potential energy storage devices or highly reactive energy / material conversion devices.

[0004] Materials containing rare earth elements, alkali metal elements, and alkaline earth metal elements have been proposed as materials exhibiting hydride ion conductivity (Patent Documents 1 to 3). 1.75 LiH 2.7 O 0.9 was discovered, and it went through a structural phase transition at around 300°C. -2 S.cm. -1 It has been found that an extremely high conductivity exceeding 1000 kJ / cm is exhibited (Non-Patent Document 1).

[0005] JP 2011-204632 A JP 2017-098067 A JP 2023-128076 A

[0006] F. Takeiri et.al, Nature Materials 2022, 21, 325-330.

[0007] However, further reduction of the phase transition temperature at which the conductivity increases sharply may expand the range of application as a solid electrolyte. 1.75 LiH 2.7 O 0.9 Since ZnO becomes unstable against metal electrodes such as Pt and Pd at temperatures above 300°C, this can limit the temperature range in which it can be used as a solid electrolyte. Furthermore, a dense sintered body is essential for use as a solid electrolyte, but no research has been conducted to date with this goal in mind.

[0008] An object of the present invention is to provide a compound that exhibits high hydride ion conductivity, a method for producing the same, and uses thereof, such as batteries, etc. In particular, an object of the present invention is to provide a compound that exhibits good hydride ion conductivity over a medium temperature range (e.g., 200°C to 400°C, 275°C to 400°C, or 300°C to 400°C), a method for producing the same, and uses thereof, such as batteries, etc.

[0009] In view of the above problems, the present disclosure provides the following invention: [1] A compound represented by the following general formula (I): Ba 1.75-x Sr x LiH a O b (I) (wherein x is 0<x≦1.65, b is 0<b≦1.5, and a is a number that satisfies charge compensation for b.) [2] A compound represented by the following general formula (Ia): Ba 1.75-x Sr x LiH 2.7-2y O 0.9+y (Ia) (wherein x is 0<x≦1.65, -0.9<y≦0.6). [3] The compound according to [1] or [2], wherein the X-ray powder diffraction pattern at a temperature of 25°C shows a diffraction pattern of a layered perovskite structure of an orthorhombic system and space group Pnm21. [4] The compound according to any one of [1] to [3], wherein 0<x≦1.0. [5] The compound according to any one of [1] to [4], wherein 0.01≦x≦0.15. [6] The compound according to any one of [1] to [5], wherein -0.89≦y≦0.6. [7] The compound according to any one of [1] to [6], represented by the following general formula (II): Ba 1.75-x Srx LiH 2.7 O 0.9 (II) (x has the same meaning as in formula (I) and formula (Ia)). [8] A method for producing the compound according to any one of [1] to [7], comprising mixing two or more raw materials containing one or more elements selected from Ba, Sr, and Li to obtain a mixture, and calcining the mixture. [9] A method for producing a hydride ion conductor, comprising exposing a powder of the compound according to any one of [1] to [7] to a high temperature under pressure to form a sintered body.

[10] A hydride ion conductor comprising at least one compound according to any one of [1] to [7].

[11] A hydride ion conductor comprising an oxyhydride having a layered structure of Ba, Li, H, and O, in which part of the Ba is substituted with Sr.

[12] The hydride ion conductor according to

[11] , whose X-ray powder diffraction pattern at 25°C shows a diffraction pattern of a layered perovskite structure with an orthorhombic system and space group Pnm21.

[13] A battery, fuel cell, or electrolysis cell having a hydride ion conductive layer containing at least one compound according to any one of [1] to [7].

[14] An electrochemical cell comprising at least a pair of electrodes and a hydride ion conductive layer disposed therebetween, wherein a reduction reaction by hydride ions proceeds at one of the electrodes when a current is applied to the pair of electrodes.

[15] The electrochemical cell according to

[13] , wherein the reduction reaction is a reaction in which nitrogen (N2) is reduced by hydride ions to produce ammonia (NH3).

[16] An electrochemical cell comprising at least a pair of electrodes and a hydride ion conductive layer disposed therebetween, wherein the reduction reaction by hydride ions proceeds at one of the electrodes when a current is applied to the pair of electrodes.

[17] The electrochemical cell according to claim 16, wherein the reduction reaction is a reaction in which nitrogen (N2) is reduced by hydride ions to produce ammonia (NH3).

[0010] The present invention provides a novel compound that exhibits high hydride ion conductivity, particularly good hydride ion conductivity over a medium temperature range, a method for producing the compound, and applications of the compound in batteries, etc. The compound is also stable against metal electrodes even over such a temperature range, and the temperature range in which it can be used as a solid electrolyte, etc., can be expanded.

[0011] Ba produced in the examples 1.75-x Sr x LiH 2.7 O 0.9 (x=0.03, 0.05, 0.07, 0.10) is a diagram showing the powder X-ray diffraction patterns of Ba produced in the examples. 1.75-x Sr x LiH 2.7 O 0.9 1 is a graph showing the change in the phase transition temperature (phase transition accompanied by a steep improvement in electrical conductivity) with respect to the degree of Sr substitution (x=0.03, 0.05, 0.07, 0.10). 1.75 LiH 2.7 O 0.9 The phase transition temperature of the laminate (top and bottom metal layers (Mo, Pt, Pd) and Ba in between) manufactured in the example 1.65 Sr 0.10 LiH 2.7 O 0.9 1 is a Cole-Cole plot (330°C) obtained from AC impedance measurement of the laminate (a laminate having Mo layers (blocking electrodes) on the top and bottom and Ba layers between them) manufactured in the example. 1.65 Sr 0.10 LiH 2.7 O 0.91 shows the results of measuring the conductivity (S / cm) of a laminate (a laminate in which a conductive layer of the present invention is arranged) at temperatures of 200°C to 400°C. The conductivities of other materials are quoted from literature. 1 shows a longitudinal cross-sectional view schematically illustrating the structure of a cell used for the synthesis of ammonia in the examples. 2 shows the IV characteristics when current is applied when ammonia is synthesized using the cell of the examples. 3 shows a GC spectrum when current is applied when ammonia is synthesized using the cell of the examples. 4 shows the gas concentration evolved at the positive electrode with application of current when ammonia is synthesized using the cell of the examples. 5 shows a comparison with the theoretical NH3 conversion efficiency when ammonia is synthesized using the cell of the examples. 6 shows the results of measuring the conductivity (S / cm) of a laminate (a laminate in which a conductive layer of the present invention is arranged) at temperatures of 200°C to 400°C. The conductivities of other materials are quoted from literature. 7 shows the results of measuring the conductivity (S / cm) of a laminate (a laminate in which a conductive layer of the present invention is arranged) at temperatures of 200°C to 400°C. The conductivities of other materials are quoted from literature. 8 shows a longitudinal cross-sectional view schematically illustrating the structure of a cell used for the synthesis of ammonia in the examples. 9 shows the IV characteristics when current is applied when ammonia is synthesized using the cell of the examples. 10 shows the GC spectrum when current is applied when ammonia is synthesized using the cell of the examples. 2 1 shows the change over time in the amount of ammonia generated in the cell. (a) shows gas chromatograms of gas collected during electrochemical ammonia synthesis in an open circuit state, where (a) is a gas chromatogram at 0 hours, (b) is a gas chromatogram at 240 hours, and (c) is a gas chromatogram of gas collected when the anode side flow was switched from N to Ar after ammonia synthesis. (b) shows the XRD pattern of the hydride conductive layer after the reaction when ammonia synthesis was performed using the cell of the example, where (a) is a pattern before the ammonia synthesis experiment, (b) is a pattern after impedance measurement, and (c) is a pattern after the ammonia synthesis experiment.

[0012] The present invention will be described in detail below.

[0013] The compound of the present invention is represented by the following general formula (I): 1.75-x Sr x LiH a O b (I) In formula (I), x is 0<x≦1.65, b is 0<b≦1.5, and a is a number that satisfies charge compensation for b.

[0014] In particular, the compound of the present invention is represented by the following general formula (Ia): 1.75-x Sr x LiH 2.7-2y O 0.9+y (Ia) (In formula (Ia), x is 0<x≦1.65, and −0.9<y≦0.6).

[0015] In general formulas (I) and (Ia), x is preferably 0<x≦1.0, more preferably 0.01≦x≦0.15. In general formula (Ia), y is preferably −0.89≦y≦0.6.

[0016] In a preferred example, the compound of the present invention is represented by the following general formula (II): 1.75-x Sr x LiH 2.7 O 0.9 (II) In formula (II), x has the same meaning as in formula (I) and formula (Ia).

[0017] In a preferred example, the compound of the present invention exhibits an X-ray powder diffraction pattern at a temperature of 25° C. that is a diffraction pattern of a layered perovskite structure of an orthorhombic system and space group Pnm21.

[0018] One of the features of the compound of the present invention is that part of Ba is replaced by Sr. This lowers the phase transition temperature, which is the temperature at which the electrical conductivity increases rapidly. 1.75 LiH 2.7 O 0.9 It is known that Ba undergoes a phase transition at 300°C, which is accompanied by a rapid increase in electrical conductivity (Non-Patent Document 1). However, if part of the Ba is substituted with Sr, the phase transition temperature decreases.

[0019] Furthermore, the compound of the present invention in which part of the Ba is replaced by Sr does not chemically react with metal electrodes such as Pt, Pd, or Mo even at temperatures above 300°C, and does not impair hydride ion conductivity even in such a temperature range.

[0020] The compound of the present invention can be produced by a method including, for example, mixing two or more raw materials containing one or more elements selected from Ba, Sr, and Li to obtain a mixture, and calcining the mixture. Specific examples of the process for obtaining a mixture include a process for mixing a raw material containing Ba, a raw material containing Sr, and a raw material containing Li to obtain a mixture. Furthermore, examples of the raw material containing one or more elements selected from Ba, Sr, and Li include a process for using a raw material containing two or more elements selected from Ba, Sr, and Li, and mixing this with another raw material containing one or more elements selected from Ba, Sr, and Li to obtain a mixture. That is, the molar ratio of each element in the raw material as a whole is not particularly limited as long as it is such that the molar ratio of each element is the desired stoichiometric ratio in consideration of formula (I).

[0021] As raw materials, hydrides or oxides of Ba, Sr, and Li can be used. Examples of hydrides include BaH2, SrH2, and LiH. Examples of oxides include BaO, SrO, and LiO2. The raw materials are preferably in powder form. When mixing two or more of these raw materials to prepare a mixture, the elements are blended in a molar ratio that achieves the desired stoichiometric ratio, taking into account formula (I). Mixing may be performed using an agate mortar, a ball mill, or the like. The mixture may also be used in powder form, or may be formed into pellets before use.

[0022] The mixture is preferably fired in a hydrogen atmosphere. The pressure conditions of the hydrogen atmosphere are not particularly limited, and firing may be performed at normal pressure. For example, firing can be performed in a hydrogen gas atmosphere at a pressure of 0.1 MPa to 2 GPa. The firing temperature is also not particularly limited, and firing can be performed at a temperature high enough for firing. The firing temperature is not particularly limited, but can be, for example, 550 to 700°C. The firing time is also not particularly limited depending on the reaction conditions, but can be, for example, 0.5 to 6 hours.

[0023] A hydride ion conductor can be produced using the compound of the present invention by a method comprising exposing a powder of the compound to high temperature under pressure to sinter the powder.

[0024] For example, a powder of the compound is pressurized and heated in the gap of a heatable clamping device such as a hot press to form a sintered body. Pressurization and heating are preferably carried out in an inert gas atmosphere such as argon. The pressure is not particularly limited, but can be, for example, 100 to 300 MPa. The temperature is not particularly limited, but can be, for example, 350 to 500°C. The pressurization and heating time depends on the reaction conditions and is not particularly limited, but can be, for example, 0.5 to 1 hour.

[0025] The relative density of the sintered body of the compound of the present invention, which is a hydride ion conductor, is not particularly limited, but in order to obtain a dense sintered body, it is preferably 90% or more, more preferably 95% or more, at a temperature of 25°C. The relative density can be further increased by sintering under pressure as described above. 1.75 LiH 2.7 O 0.9 In the previous study, pellets were sintered in a hydrogen atmosphere under normal pressure, but as described above, sintering can be performed under pressure in an inert gas atmosphere such as argon to achieve densification.

[0026] The relative density can be further increased by heat treating the sintered body in a hydrogen atmosphere, i.e., annealing it. Annealing can be carried out, for example, in a hydrogen gas atmosphere at a pressure of 0.05 to 0.2 MPa. The annealing temperature is not particularly limited, but can be, for example, 550 to 650°C. The annealing time is not particularly limited, but can be, for example, 3 to 6 hours.

[0027] The hydride ion conductor of the present invention exhibits high hydride ion conductivity, and is in a superionic conductive state particularly over a medium temperature range (e.g., 200°C to 400°C, 275°C to 400°C, or 300°C to 400°C), exhibiting good hydride ion conductivity.

[0028] The hydride ion conductor of the present invention is preferably provided with electrodes. Examples of the electrodes include a blocking electrode that blocks mobile hydride ions and a transmitting electrode that can convert hydrogen gas supplied from the outside into hydride ions and supply them to the hydride ion conductor. The material for the blocking electrode is not particularly limited, but examples thereof include Mo and Ta. The material for the transmitting electrode is not particularly limited, but examples thereof include Pd and TiN. The blocking electrode and the transmitting electrode may be a single layer or multiple layers, or both the blocking electrode and the transmitting electrode may be stacked.

[0029] The electrodes are provided in layers on the surfaces of the layered hydride ion conductor to form a laminate. For example, when a powder of the compound of the present invention is pressurized and heated to form a sintered body, electrode layers are placed above and below the powder layer, and then pressurized and heated to obtain a laminate in which the electrode layers are directly placed above and below the sintered body.

[0030] Ba 1.75 LiH 2.7 O 0.9 However, the problem is that the hydride ion conductor of the present invention is chemically unstable with electrodes, reacting with metal electrodes such as Pt and Pd to precipitate impurities with low ionic conductivity. It also reacts with blocking electrodes such as Mo, and therefore its conductivity behavior at high temperatures has not been clarified. By substituting a portion of the Ba with Sr, chemical stability with electrodes is increased, allowing conductivity measurement without reaction with metal electrodes such as Pt and Pd. Furthermore, even when using a blocking electrode such as Mo, conductivity measurement is possible up to approximately 370°C. By enabling measurements up to high temperatures, the hydride ion conductor of the present invention exhibits a superionic conductive state, particularly over a medium temperature range (e.g., 200°C to 400°C, 275°C to 400°C, or 300°C to 400°C), exhibiting good hydride ion conductivity, thereby expanding the temperature range in which it can be used as a solid electrolyte, etc.

[0031] The hydride ion conductor of the present invention is also specified as a hydride ion conductor in which a portion of the Ba in a conventional hydride ion conductor containing an oxyhydride having a layered structure of Ba, Li, H, and O is substituted with Sr. Its typical X-ray powder diffraction pattern at 25°C shows a diffraction pattern of a layered perovskite structure of an orthorhombic system and space group Pnm21.

[0032] The compound of the present invention exhibits high hydride ion conductivity, and therefore can provide a hydride ion conductor with high ionic conductivity in a solid state. This hydride ion conductor can be used as a battery, fuel cell, or electrolytic cell having a hydride ion conductive layer containing the compound. For example, the compound can be suitably used in solid-state batteries such as hydride ion secondary batteries and ammonia fuel cells, particularly all-solid-state batteries. Examples of all-solid-state batteries include a positive electrode containing a hydride ion donor, a negative electrode containing a hydrogen storage metal or alloy, and the above-mentioned hydride ion conductor disposed between the positive electrode and the negative electrode. Furthermore, there is potential for the development of new energy devices using hydride ion conductors.

[0033] The present invention also relates to an electrochemical cell comprising at least a pair of electrodes and a hydride ion conductive layer disposed therebetween, wherein a reduction reaction by hydride ions proceeds at one of the electrodes when a current is applied to the pair of electrodes. Because hydride ions have a high reducing power, the present invention utilizes this reducing power. One example is an electrochemical cell in which a reduction reaction proceeds at one electrode, in which nitrogen (N) is reduced by hydride ions to convert to ammonia (NH). In this example, nitrogen (N) is preferably supplied to at least the electrode where the reduction reaction proceeds. Hydrogen (H) may be supplied to the other electrode, but if the hydride ion conductive layer is made of a material that releases hydride ions when a current is applied, the reduction reaction can proceed by applying a current without supplying hydrogen.

[0034] The hydride ion conductive layer containing at least one compound of the present invention is preferable in that it not only conducts hydride ions but also releases hydride ions when current is applied. Furthermore, the conductive layer containing the compound of the present invention is also preferable in that it is easy to manufacture, since, as described above, by placing electrode layers on the top and bottom of a powder layer containing a powder of the compound of the present invention and applying pressure and heat, a laminate in which electrode layers are directly placed on the top and bottom of a sintered body can be obtained.

[0035] The configuration of the electrochemical cell of the present invention is not particularly limited. Depending on the application, a catalyst layer or a gas diffusion layer such as a metal foam may be disposed between each of the pair of electrodes and the hydride ion conductive layer.

[0036] The following examples illustrate specific embodiments of the present disclosure, but the invention is not limited thereto. All parts and percentages are by weight unless otherwise specified.

[0037] 1. Example of the production of hydride ion conductive compound Raw material powders (BaH2, BaO, SrO, LiH) were mixed in various molar ratios in a glove box and fired at 650°C for 6 hours in a hydrogen atmosphere. 1.75-x Sr x LiH 2.7 O 0.9 Powders with x = 0, 0.03, 0.05, 0.07, and 0.10 were obtained, respectively. The powder X-ray diffraction patterns at room temperature (25°C) are shown in Figure 1. The results in Figure 1 indicate that all of these powders have a layered perovskite structure with an orthorhombic system and space group Pnm21 at 25°C.

[0038] 2. Production Example of Sintered Body (Hydride Ion Conductor) The obtained powders were pulverized and mixed, and sintered in a hot press at 400°C for 1 hour at 300 MPa in an Ar atmosphere to obtain sintered bodies. Note that Mo layers were placed above and below the powder layer during hot press pressure application. As a result, a laminate was obtained in which Mo layers functioning as blocking electrodes were directly placed above and below the sintered body (hydride ion conductor). The relative density of each sintered body was approximately 93%. Further, each sintered body was treated in a H2 atmosphere at 650°C for 6 hours, resulting in a dense sintered body with a relative density (at 25°C) of 98%. The following measurements of conductivity and other properties were performed using sintered bodies with a relative density of 98%. Note that when sintered bodies were obtained under the same conditions without pressure but at normal pressure, the relative density was approximately 88%. This demonstrates that sintering under pressure improves the relative density.

[0039] 3. Relationship between Sr substitution and hydride ion conductivity Ba 1.75 LiH 2.7 O 0.9 It is known that Ba undergoes a phase transition at 300°C, which leads to a rapid increase in electrical conductivity. 1.75 LiH 2.7 O 0.9 The temperature at which the conductivity suddenly increases (=phase transition temperature) was measured for each of the above compounds in which part of the Ba was replaced with Sr. The results are shown in Figure 2. As shown in Figure 2, it can be seen that the phase transition temperature was lowered by the replacement of Sr. 1.75-x Sr x LiH 2.7 O 0.9 It was found that the phase transition occurs at the lowest temperature (279°C) when x = 0.1, which is the maximum amount of Sr dissolved in solid solution.

[0040] 4. Relationship between Sr substitution and chemical stability of the electrode Ba 1.75 LiH 2.7 O 0.9However, at temperatures above 300°C, the compound of the present invention, in which part of the Ba is replaced with Sr, does not chemically react with the metal electrodes (Pt, Pd) even at temperatures above 300°C. Figure 3 shows the behavior of a laminate (top and bottom metal layers (Pd, Pt, Mo) with Ba in between) at 330°C. 1.65 Sr 0.10 LiH 2.7 O 0.9 The graph shows a cole-cole plot obtained from the AC impedance measurement of a laminate in which the conductive layer of Ba is arranged as a hydride ion conductor. 1.65 Sr 0.10 LiH 2.7 O 0.9 From the results shown in FIG. 3, it can be seen that at 330° C., no chemical reaction occurs with either the metal electrodes (Pt, Pd) or the blocking electrode (Mo).

[0041] 5. Measurement of Electrical Conductivity The electrical conductivity (S / cm) was measured at temperatures of 200°C to 400°C using the laminate produced in "2.". 1.65 Sr 0.10 LiH 2.7 O 0.9 The results are shown in Figure 4 together with data on known hydride ion conductors (cited from the literature). 1.65 Sr 0.10 LiH 2.7 O 0.9 It can be seen that this material is in a superionic conductive state and exhibits the highest hydride conductivity at 330-370°C.

[0042] 6. Preparation of a laminate for an electrochemical cell In the same manner as above, Ba was placed between a pair of electrodes. 1.65 Sr 0.10 LiH 2.7 O 0.9A laminate was obtained in which a Pt-C layer (a layer of platinum powder supported on commercially available carbon) was placed between one electrode and the hydride ion conductive layer 2, and a Ru-Pt-C layer 3b (a layer of a ruthenium-platinum mixed powder supported on commercially available carbon) was placed between the other electrode and the hydride ion conductive layer 2 (Figure 5). Furthermore, gas diffusion layers 4 (Cu foam, SUS foam, or a combination thereof) were also placed between each of the Pt-C layer and the Ru-Pt-C layer and the electrode. Furthermore, gas pipes capable of introducing and evacuating gas were attached to each of the pair of electrodes. In Figure 5, the upper and lower components through which the gas pipes pass are SUS current collectors, and the current collectors, metal foam 4, and Pt-supported carbon electrodes 3a and 3b function as electrodes.

[0043] 7. Synthesis of ammonia using an electrochemical cell 1 The following experiment was carried out using an electrochemical cell 1 having the configuration shown in Figure 5. The fabricated electrochemical cell was placed in a space filled with a hydrogen atmosphere at a temperature of 350°C. The voltage between the electrodes at this time was 9 mV. Nitrogen gas and hydrogen gas were then supplied. The current flow was increased stepwise up to 1000 μA. As the current was increased, the gas discharged from the gas pipe on the anode side was analyzed by gas chromatography. The voltage decreased with increasing current, confirming power generation. The maximum output density was (7.6 x 10 -5 A / cm 2 ) 1.8 μW / cm 2 In addition, when the gas extracted from the anode side was analyzed by GC, an ammonia peak was detected. As the ammonia generation rate calculated from the GC detection peak increased, the nitrogen generation rate decreased, and after the ammonia generation rate peaked, it decreased, and the nitrogen generation rate increased. From this, it can be understood that the reduction reaction from nitrogen to ammonia is progressing on the anode.

[0044] 8. Synthesis of ammonia using an electrochemical cell 2 The following experiment was further carried out using the electrochemical cell 1 configured as shown in Figure 5. The fabricated electrochemical cell was placed in a space filled with a hydrogen atmosphere at a temperature of 350°C, and nitrogen gas and hydrogen gas were both supplied at 10 mml / min. As the current was increased, the gas discharged from the anode gas pipe was analyzed by gas chromatography. Figure 6 shows the IV characteristics when current was applied. E we indicates the voltage of the working electrode, and W indicates the output density. A voltage drop was confirmed with the application of current. Figure 7 shows the GC spectrum when current was applied. An increase in the amount of NH3 generated was confirmed with an increase in current density. These results confirmed the generation of NH3 due to an electrochemical reaction at the anode. Figure 8 shows the gas concentration generated on the anode with the application of current. With an increase in current density, N2 decreased and NH3 increased. This indicates that the electrochemical reaction was 1 / 2N2 + 3H - →NH3 + 3e - This indicates that hydrogen evolution (2H - →H2 + 2e - ) was mainly generated. Figure 9 shows a comparison with the theoretical NH conversion efficiency. By applying a current, the theoretical conversion efficiency (0.92%) at 350 °C and 1 atm was exceeded. - This shows the advantage of electrochemical reactions that supply r to the reaction field. The conversion efficiency was calculated using the following formula: NH3 is the amount of NH3 generated, r N2 , r H2 indicates the supply amount of N2 and H2. Conversion efficiency = r NH3 / (r N2 +r H2 +r NH3 ) Figure 10 shows the current density of 1.27 mA / cm 2The graph shows the change in the amount of ammonia generated over time. Figure 11 shows gas chromatograms of gas collected during electrochemical ammonia synthesis under open-circuit conditions. (a) is a gas chromatogram at 0 hours, (b) is a gas chromatogram at 240 hours, and (c) is a gas chromatogram of gas collected after ammonia synthesis when the anode flow was switched from N to Ar. The amount of NH3 generated was maintained for 10 days, and the hydride ion conductive layer was stable under device operation. Figure 12 shows the XRD pattern of the hydride ion conductive layer after the reaction. (a) is before the ammonia synthesis experiment, (b) is after impedance measurement, and (c) is after the ammonia synthesis experiment. There was no significant change in the XRD of the hydride ion conductive layer even after the reaction using the device, indicating that the hydride ion conductive layer was stable under device operation.

[0045] 1 Electrochemical cell 2 Ba 1.65 Sr 0.10 LiH 2.7 O 0.9 Layer (hydride ion conductive layer) 3a Pt—C layer 3b Ru—Pt—C layer 4 Metal foam (gas diffusion layer) 5 Al2O3 tube

Claims

1. A compound represented by the following general formula (I): 1.75-x Sr x LiH a O b (I) (In the formula, x is 0<x≦1.65, b is 0<b≦1.5, and a is a number that satisfies charge compensation for b.) 2. A compound represented by the following general formula (Ia): 1.75-x Sr x LiH 2.7-2y O 0.9+y (Ia) (wherein x is 0<x≦1.65 and −0.9<y≦0.6).

3. The compound according to claim 1 or 2, which exhibits an X-ray powder diffraction pattern at 25°C which is a diffraction pattern of a layered perovskite structure having an orthorhombic system and space group Pnm21.

4. The compound according to any one of claims 1 to 3, wherein 0<x≦1.

0.

5. The compound according to any one of claims 1 to 4, wherein 0.01≦x≦0.

15.

6. The compound according to any one of claims 1 to 5, wherein -0.89≦y≦0.

6.

7. The compound according to any one of claims 1 to 6, represented by the following general formula (II): 1.75-x Sr x LiH 2.7 O 0.9 (II) (x has the same meaning as in formula (I) and formula (Ia)).

8. A method for producing the compound according to any one of claims 1 to 7, comprising mixing two or more raw materials containing one or more elements selected from Ba, Sr, and Li to obtain a mixture, and calcining the mixture.

9. A method for producing a hydride ion conductor comprising exposing a powder of a compound according to any one of claims 1 to 7 to high temperatures under pressure to sinter said powder.

10. A hydride ion conductor comprising at least one compound according to any one of claims 1 to 7.

11. A hydride ion conductor containing an oxyhydride having a layered structure of Ba, Li, H, and O, in which some of the Ba is replaced with Sr.

12. The hydride ion conductor according to claim 11, which exhibits an X-ray powder diffraction pattern at a temperature of 25° C. that is indicative of a layered perovskite structure having an orthorhombic system and space group Pnm21.

13. A battery, fuel cell or electrolysis cell having a hydride ion conductive layer comprising at least one compound according to any one of claims 1 to 7.

14. An electrochemical cell comprising at least a pair of electrodes and a hydride ion conductive layer disposed therebetween, in which, when a current is passed through the pair of electrodes, a reduction reaction by hydride ions proceeds at one of the electrodes.

15. The electrochemical cell according to claim 14, wherein the reduction reaction is a reaction in which nitrogen (N2) is reduced by hydride ions to produce ammonia (NH3).

16. An electrochemical cell comprising at least a pair of electrodes and a hydride ion conductive layer disposed between the electrodes, the layer containing at least one of the compounds according to any one of claims 1 to 7, in which a reduction reaction by hydride ions proceeds in one of the electrodes when a current is passed through the pair of electrodes.

17. The electrochemical cell according to claim 16, wherein the reduction reaction is a reaction in which nitrogen (N2) is reduced by hydride ions to produce ammonia (NH3).