Data mining method, electrolytic apparatus, catalyst layer, electrolysis method, and oxygen reduction catalyst

Abstract

To provide an electrolytic device using metal oxides that are inexpensive and have excellent catalytic performance. [Solution] The electrolytic apparatus of the present invention comprises a first electrode 101, a first catalyst layer 103 provided on the first electrode 101, a second electrode 102, a second catalyst layer 104 provided on the second electrode 102, an electrolyte 105 sandwiched between the first electrode 101 and the second electrode 102, and a container 106 that houses the first electrode 101, the first catalyst layer 103, the second electrode 102, the second catalyst layer 104, and the electrolyte 105, wherein the first catalyst layer 103 contains Sb2WO6 molecules.

Description

[Technical Field]

[0001] This invention relates to a data mining method, an electrolytic apparatus, a catalyst layer, an electrolytic method, and an oxygen reduction catalyst. [Background technology]

[0002] Fuel cells include hydrogen-oxygen secondary batteries and metal-air secondary batteries, and in both cases, the positive electrode is equipped with oxygen supplied from an external source as the positive electrode active material. The negative electrode of a hydrogen-oxygen secondary battery is equipped with hydrogen as the negative electrode active material. The negative electrode of a metal-air secondary battery is equipped with a metal as the negative electrode active material. Charging and discharging can be performed by an electrolytic reaction on the positive electrode side. As a catalyst for the positive electrode, platinum compounds are generally used from the viewpoint of chemical stability (Patent Document 1, etc.), but a challenge is to reduce the operating cost of fuel cells using electrolytic reactions with these compounds. There is a need for an inexpensive catalyst with catalytic performance equivalent to that of platinum compounds.

[0003] Data mining using computational materials databases is a common method for searching for unknown metal oxides. This data mining method can search for metal oxides with a predetermined catalytic performance. However, the results expected from data mining may not match experimental results. If the data mining method does not take into account the surface state of the metal oxide, metal oxides may be overlooked or incorrectly identified. There is a need for a data mining method that can search for metal oxides with a predetermined catalytic performance with high accuracy. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2018 / 194008 [Overview of the project] [Problems that the invention aims to solve]

[0005] This invention has been made in view of the above circumstances, and aims to provide an electrolytic apparatus, an electrolytic method, a catalyst layer (oxygen reduction catalyst) used in electrolysis, and a data mining method that enables the search for such a metal oxide from among multiple materials, using an inexpensive metal oxide with excellent catalytic performance. [Means for solving the problem]

[0006] To solve the above problems, the present invention employs the following means.

[0007] (1) An oxygen reduction catalyst according to one aspect of the present invention contains an Sb2WO6 molecule.

[0008] (2) An electrolytic apparatus according to one aspect of the present invention comprises a first electrode, a first catalyst layer provided on the first electrode, a second electrode, a second catalyst layer provided on the second electrode, an electrolyte sandwiched between the first electrode and the second electrode, and a container for housing the first electrode, the first catalyst layer, the second electrode, the second catalyst layer, and the electrolyte, wherein the first catalyst layer contains Sb2WO6 molecules.

[0009] (3) A catalyst layer according to one aspect of the present invention is a catalyst layer provided on an electrode constituting an electrolytic device, which promotes an electrolytic reaction and contains Sb2WO6 molecules.

[0010] (4) An electrolytic method according to one aspect of the present invention comprises the steps of generating a potential difference between two electrodes sandwiching an electrolyte, supplying oxygen molecules to a first electrode which is on the higher potential side of the electrodes, and supplying a reducing agent for the oxygen molecules to a second electrode which is on the lower potential side of the electrodes, wherein a catalyst layer containing Sb2WO6 molecules is provided on the surface of the first electrode.

[0011] (5) In the electrolysis method described in (4) above, it is preferable to cause an oxygen reduction reaction in the catalyst layer to produce water.

[0012] (6) In the electrolysis method described in either (4) or (5) above, a hydrogen molecule or a hydrogen compound molecule may be used as the reducing agent.

[0013] (7) In the electrolysis method described in any one of (4) to (6) above, it is preferable that the pH of the electrolyte around the catalyst layer and the potential of the first electrode are adjusted so that they fall within the region between the first line segment and the second line segment in the Pourbet diagram, wherein the first line segment is a line segment connecting a point where the pH is 0 and the potential is 0.6V and a point where the pH is 14 and the potential is -0.226V, and the second line segment is a line segment connecting a point where the pH is 0 and the potential is 1V and a point where the pH is 14 and the potential is 0.174V.

[0014] (8) In the electrolysis method described in any one of (4) to (7) above, the pH around the catalyst layer may be set to 1.3 or higher and 12.6 or lower.

[0015] (9) A data mining method according to one aspect of the present invention is a data mining method for searching for metal oxides as catalysts for oxygen reduction reactions, comprising: a first step of selecting a predetermined metal oxide from metal oxides recorded in a database; and from the metal oxide selected in the first step, E hull A second step of selecting a metal oxide that satisfies the condition that E becomes 0, and from the metal oxide selected in the second step, Form A third step involves selecting a metal oxide that satisfies the condition for minimizing the Gibbs free energy, and for each of the metal oxides selected in the third step, the Gibbs free energy being 0.5eVatom -1 The method comprises a fourth step of creating a Pourbet diagram with the following pH and potential ranges as the stable region, and a fifth step of selecting a metal oxide as an electrode catalyst from among the Pourbet diagrams created in the fourth step that gives a Pourbet diagram showing the presence of a solid phase in a predetermined reaction.

[0016] (10) In the data mining method according to (9) above, a combination of the metal oxide selected in the third step and the Pourbaix diagram created in the fourth step is recorded in a predetermined recording device, and the selection of the metal oxide to be the electrode catalyst may be performed by searching the recording of the recording device.

[0017] (11) In the data mining method according to any one of (9) or (10) above, a step of selecting, from the metal oxides selected in the third step, those containing a predetermined number of metal elements may be further included.

Advantages of the Invention

[0018] According to the present invention, it is possible to provide an electrolysis device, an electrolysis method, a catalyst layer (oxygen reduction catalyst) used for electrolysis, and a data mining method that uses a metal oxide that is inexpensive and has excellent catalyst performance and enables searching for the metal oxide from among a plurality of materials.

Brief Description of the Drawings

[0019] [Figure 1] It is a configuration diagram of a fuel cell used in an electrolysis method according to an embodiment of the present invention. [Figure 2] It is a process flow of a data mining method according to an embodiment of the present invention. [Figure 3] It is a graph showing the number of metal oxides selected in each step of the examples. [Figure 4] It is a graph in which the metal oxides after the third step are classified according to the number of metal elements they contain. [Figure 5] (a) to (c) are diagrams classifying reactions in which each metal element exhibits thermodynamic stability in solutions with pH of 0, 7, and 14. [Figure 6] It is a graph showing the results of X-ray diffraction measurement of Sb2WO6 synthesized in the examples. [Figure 7] It is an image of Sb2WO6 obtained using a scanning electron microscope. [Figure 8]This image shows the results of elemental mapping of Sb2WO6 using energy-dispersive X-ray spectroscopy. [Figure 9] This is an image of Sb2WO6 obtained by ICP-OES measurement. [Figure 10] (a) This is the spectrum obtained by X-ray photoelectron spectroscopy measurement of Sb2WO6. (b) and (c) are magnified portions of the spectrum in (a). [Figure 11] This graph shows the LSV curve measured using the rotating ring disk electrode method. [Figure 12] This graph shows the number of electrons contributing to the oxygen reduction reaction, as measured by the rotating ring disk electrode method. [Figure 13] This graph shows the LSV curve measured using the rotating ring disk electrode method. [Figure 14] This graph shows the results of chronoamperometry measurements performed on Sb2WO6 in acidic and alkaline solutions. [Figure 15] This graph shows the results of applying a correction based on density functional theory to the X-ray diffraction measurement results shown in Figure 6. [Figure 16] (a) and (b) are graphs showing the results of X-ray photoelectron spectroscopy measurements in Figures 10(b) and (c), after applying corrections based on density functional theory. [Figure 17] (a) TEM image (top) and EDS elemental mapping image (bottom) of Sb2WO6 in an acidic electrolyte. (b) TEM image (top) and EDS elemental mapping image (bottom) of Sb2WO6 in an alkaline electrolyte. [Figure 18] This is a Pourbet diagram showing the surface state of the catalyst layer. [Figure 19] This graph shows the relationship between the binding energy of OH- to the catalyst layer and the current density due to oxygen reduction. [Modes for carrying out the invention]

[0020] Hereinafter, an electrolysis method and a data mining method according to embodiments of the present invention will be described in detail with reference to the drawings. Note that, for the sake of clarity, the drawings used in the following description may show enlarged versions of key features, and the dimensional ratios of each component may not be the same as those in reality. Furthermore, the materials, dimensions, etc., exemplified in the following description are merely examples, and the present invention is not limited to these; it can be implemented with appropriate modifications without altering its essence.

[0021] [Electrolyzer] Figure 1 is a schematic diagram showing the configuration of a fuel cell 100 as an electrolytic device used in an electrolytic method according to one embodiment of the present invention. The fuel cell 100 mainly consists of two electrodes (first electrode 101, second electrode 102), catalyst layers (first catalyst layer 103, second catalyst layer 104) provided on each electrode to promote the electrolytic reaction, an electrolyte 105 sandwiched between the two electrodes, a container 106 that houses them, and a power generation unit (power generation element) 108 connected between the two electrodes by wiring 107.

[0022] The first electrode 101 and the second electrode 102 are made of a chemically stable and conductive material (such as platinum). The electrolyte 105 is made of a chemically stable material (such as sulfuric acid) that readily transmits a reducing agent for oxygen molecules O2. Preferably, the electrolyte 105 is provided not only between the first electrode 101 and the second electrode 102, but also around the entire circumference of the first electrode 101 and the entire circumference of the second electrode 102.

[0023] The first catalyst layer (catalyst layer) 103 formed on the surface of the first electrode 101 contains Sb2WO6 molecules as an essential material. It may contain only Sb2WO6 molecules, or it may contain Sb2WO6 molecules as the main component, preferably 10% or more, for example, 90%. The suitable catalyst material to be included in the first catalyst layer 103 can be selected using the data mining method described later. The thickness of the first catalyst layer 103 is not particularly limited. The material of the second catalyst 104 formed on the surface of the second electrode 102 is not particularly limited, and any chemically stable material that has the function of promoting the reduction of the material supplied to the second electrode 102 (in this case, hydrogen molecules H2) is acceptable.

[0024] The formation of the first catalyst layer (oxygen reduction catalyst) 103 containing Sb2WO6 molecules is not particularly limited, but can be carried out, for example, by the following procedure: Dissolve SbCl3 and Na2WO·2H2O in water and stir. Add tungstic acid solution to the stirred solution and stir again. Heat the re-stirred solution at a predetermined temperature for a predetermined time, and then recover the Sb2WO6 molecule powder (solid) by centrifugation, drying, etc. By coating the recovered powder onto the surface of the first electrode 101, the first catalyst layer 103 can be formed.

[0025] The oxygen reduction reaction in the first catalyst layer 103 containing Sb2WO6 molecules is a four-electron reaction that produces water, similar to the oxygen reduction reaction in the catalyst layer containing platinum compound molecules. Therefore, a larger current can be supplied to the power generation unit 108 compared to a two-electron reaction. Furthermore, by using chemically stable Sb2WO6 molecules as the catalyst material, the magnitude of the current supplied to the power generation unit 108, i.e., the current generated by the fuel cell, can be maintained for a long period of time.

[0026] [Electrolysis method] The electrolysis method of this embodiment is a method for reducing oxygen and mainly comprises the following first, second, and third steps.

[0027] (First step) A potential difference is generated between the first electrode 101 and the second electrode 102. This potential difference can be generated by applying a voltage between the first electrode 101 (positive electrode) and the second electrode 102 (negative electrode). In this case, the first electrode 101 will have a relatively higher potential, and the second electrode 102 will have a relatively lower potential.

[0028] From the viewpoint of chemical stability, it is preferable to adjust the pH of the electrolyte 105 surrounding the first catalyst layer 103 and the potential of the redox reaction at the first electrode 101 so that they fall within the region between the first and second line segments defined below in the Pourbet diagram. The first line segment is defined as the line segment connecting the point where the pH is 0 and the potential is 0.6V and the point where the pH is 14 and the potential is -0.226V. The second line segment is defined as the line segment connecting the point where the pH is 0 and the potential is 1V and the point where the pH is 14 and the potential is 0.174V. Furthermore, from the viewpoint of obtaining high catalytic activity, it is preferable that the pH around the first catalyst layer 103 be between 1.3 and 12.6.

[0029] (Second process) Oxygen molecules O2 are supplied to the first electrode (air electrode) 101. The supply of oxygen molecules O2 may be done using an oxygen supply source 109 as shown in Figure 1, or by exposing a part of the first electrode 101 to the atmosphere.

[0030] (Third step) A reducing agent consisting of oxygen molecules (O2) is supplied to the second electrode (fuel electrode) 102. It is preferable to use hydrogen molecules or hydrogen compound molecules as the reducing agent. Here, we assume that hydrogen molecules (H2) are used as the reducing agent for oxygen molecules (O2). The reducing agent (hydrogen molecules (H2)) is supplied using a reducing agent supply source (hydrogen supply source) 110, as shown in Figure 1.

[0031] Hydrogen molecules H2 supplied to the second electrode (fuel electrode) 102, which is on the lower potential side, separate into two hydrogen atoms on the second electrode 102 and produce electrons e - It releases hydrogen ions H + This is what happens when electrons are emitted. -It reaches the first electrode 101 through the wiring 107. The oxygen molecules O2 supplied to the first electrode 101 on the high potential side are separated into two oxygen atoms on the first electrode 101 and receive this electron e - to become oxygen ions O 2- .

[0032] On the other hand, hydrogen ions H + propagate through the electrolyte 105 and reach the first electrode 101, and react with the oxygen ions O 2- on the first electrode 101 to generate water molecules H2O. The reaction in this case is a four-electron reaction represented by O2 + 4H + + 4e - → 2H2O, and can generate a larger current compared to the case of a two-electron reaction. In this way, the supplied oxygen molecules O2 can be reduced.

[0033] As described above, according to the electrolysis method of the present embodiment, the first electrode 101 that supplies oxygen molecules O2 is provided with the first catalyst layer 103 containing Sb2WO6 molecules. Sb2WO6 is cheaper than platinum compounds and can be synthesized, and has catalyst performance equivalent to that of platinum compounds. The oxygen reduction reaction occurring at the first electrode 101 becomes a four-electron reaction that generates water by interposing Sb2WO6 molecules, so a large current can be extracted. In addition, since Sb2WO6 molecules are composed of chemically stable elements, the catalyst performance can be maintained over a long period, and as a result, a large current can be extracted.

[0034] (Data mining method) FIG. 2 is a process flow of the data mining method according to an embodiment of the present invention. The data mining method of the present embodiment is a method for searching (retrieving) an electrode catalyst of a metal oxide, and mainly has the following steps.

[0035] (First step) From the metal oxides recorded in the database, a predetermined metal oxide is selected, and other metal oxides are excluded. Examples of metal oxides to be selected include metal oxides that can be obtained at low cost, or metal oxides that do not contain radioactive elements, halogen elements, elements that are gaseous at room temperature and pressure, organic elements, etc.

[0036] (Second process) From the metal oxide selected in the first step, the Energy above hull (E) is used as an indicator of relative thermodynamic stability. hull Select the metal oxides that satisfy the condition that ) becomes 0, and exclude the other metal oxides. hull This can be determined by first-principles calculations, and metal oxides with lower values ​​are more stable and easier to produce.

[0037] (Third step) From the metal oxide selected in the second step, the formation energy E Form Select a metal oxide that satisfies the condition of minimizing and exclude all other metal oxides. After the third step, there may be a further step of selecting from the metal oxides selected in the third step those containing a predetermined number of metal elements.

[0038] (Fourth step) For each metal oxide selected in the third step, the Gibbs free energy is 0.5 eV·atom. -1 Create a Pourbet diagram that defines the stable region as the following pH and potential range.

[0039] (Fifth step) In the fourth step, a stable metal oxide is selected as the electrode catalyst from among the Pourbet diagrams created, which give a Pourbet diagram showing the presence of a solid phase in a predetermined reaction (such as an oxygen reduction reaction). For example, when using an acidic solution as the electrolyte, a stable metal oxide is selected in the Pourbet diagram within the potential range corresponding to the pH range of the acidic solution. Similarly, when using an alkaline solution as the electrolyte, a stable metal oxide is selected in the Pourbet diagram within the potential range corresponding to the pH range of the alkaline solution.

[0040] The combination of the metal oxide selected in the third step and the Pourbet diagram created in the fourth step may be recorded in a predetermined recording device, and the selection of a new metal oxide to be used as an electrode catalyst may be performed by searching the records in this recording device. This recording device may also be an online search engine that enables searching in a network environment connected to the internet.

[0041] The data mining method described above allows for the exploration of not only commonly known monometallic oxides (compounds of one metal element and oxygen) but also multimetallic oxides (compounds of multiple metal elements and oxygen) that are stable in oxygen reduction reactions (ORR) under acidic conditions. Examples of monometallic oxides that can be explored include Sb2O and W2O3. Examples of multi-component metal oxides to be explored include Hg(SbO3)2, Cd(SbO3)2, Zn(SbO3)2, Mn(SbO3)2, Ni(SbO3)2, Co(SbO3)2, Fe(SbO3)2, Sc2(MoO4)3, Fe2(MoO4)3, GaSbO4, BiSbO4, CsSbWO6, RbSbWO6, Ge3Sb2O9, MgCr2O4, Sb2WO6, TiSnO3, RbSbWO6, and Li4CrFe3O8.

[0042] As monometallic oxides, metal oxides containing Sb (such as Sb2O) are excellent as electrode catalysts for oxygen evolution and oxygen reduction reactions. Furthermore, since W has the second highest stability after Sb, as a multimetallic oxide, metal oxides containing both Sb and W (such as Sb2WO6) are excellent as electrode catalysts that promote oxygen evolution and oxygen reduction reactions.

[0043] As described above, the data mining method of this embodiment is a method for searching for metal oxides without considering the surface state of the catalyst layer. Therefore, the data mining method of this embodiment identifies Sb2WO6 that is stable only under acidic conditions. However, if the surface state and microkinetic modeling are considered, it is thought that metal oxides that are stable under alkaline conditions can also be searched. According to the data mining method of this embodiment, metal oxides that function as electrode catalysts in a predetermined reaction can be easily and accurately searched. In the fourth step, for each metal oxide, the Gibbs free energy is 0.5 eVatom -1 The following pH and potential ranges are identified. This allows for the highly accurate identification of metal oxides that possess thermodynamic stability and are suitable for a given reaction. [Examples]

[0044] The effects of the present invention will be made clearer by the following examples. However, the present invention is not limited to the following examples and can be modified as appropriate without altering its essence.

[0045] (Data mining) The data mining method of the embodiment described above was applied to various metal oxides recorded in the database. Figure 3 is a graph showing the number of metal oxides selected after the first, second, and third steps. By performing up to the third step, the number of candidate metal oxides to be selected has been narrowed down to 1159.

[0046] Figure 4 is a graph showing the 1159 selected metal oxides categorized by the number of constituent metal elements. Among the 1159 selected metal oxides, those containing two metal elements and those containing three metal elements are particularly numerous. Of the explored metal oxides, Sb2WO6 was evaluated.

[0047] Figures 5(a) to (c) are graphs comparing the thermodynamic stability of metal elements in various reactions (nitrogen reduction reaction (NRR), hydrogen evolution reaction (HER), chlorine evolution reaction (CER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR)) in aqueous solutions with pH values ​​of 0, 7, and 14, respectively. Regardless of the state of the aqueous solution, Sb exhibits the best stability in OER and ORR.

[0048] These results indicate that, as a single-component metal oxide, metal oxides containing Sb (Sb2O) are excellent as electrode catalysts for oxygen evolution and oxygen reduction reactions. Furthermore, since the stability of W is the second highest after the stability of Sb, it can be seen that, as a multi-component metal oxide, metal oxides containing both Sb and W are excellent as electrode catalysts.

[0049] (Synthesis of Sb2WO6) Nanoplates (average thickness 20 nm) of Sb2WO6, which were discovered using data mining methods, were synthesized by hydrothermal synthesis. Specifically, Sb2WO6 was synthesized using the following procedure: SbCl3 powder (137 mg) and Na2WO4 / 2H2O (99 mg) were dissolved in deionized water (15 mL) and stirred, and then W solution was added and stirred further. The stirred solution was placed in a Teflon® autoclave (45 mL) and heated at 180 °C for 12 hours. Furthermore, centrifugation was performed, washed with deionized water, and finally dried overnight at 70 °C to obtain Sb2WO6 nanoplates.

[0050] (Sb2WO6's evaluation) X-ray diffraction (XRD) measurements were performed on this Sb2WO6. Figure 6 shows a graph of the measurement results. The position of the diffraction peak of the synthesized Sb2WO6 is in close agreement with the position of the diffraction peak of standard Sb2WO6. From this result, it can be seen that the synthesized Sb2WO6 has an orthorhombic crystal structure similar to that of standard Sb2WO6.

[0051] Images of synthesized Sb2WO6 were acquired using a high-angle annular dark-field scanning electron microscope (HAADF-STEM). Figure 7 shows the acquired images. From these images, the synthesized Sb2WO6 can be observed.

[0052] Elemental mapping was performed on the synthesized Sb2WO6 using energy-dispersive X-ray (EDX) spectroscopy. Figure 8 shows the results of the elemental mapping. The elemental ratio Sb:W:O is 2.00:0.99:6.04, which is in close agreement with the theoretical chemical values.

[0053] ICP-OES measurements were performed on the synthesized Sb2WO6. Figure 9 shows an image of the measurement results. From this image, spaced lattice fringes can be seen in the (002) plane of the orthorhombic crystal structure.

[0054] X-ray photoelectron spectroscopy (XPS) measurements were performed on the synthesized Sb2WO6. Figure 10(a) is a graph showing the spectrum across the entire range of photoelectron energies obtained by the measurement. Peaks corresponding to the Sb, W, and O photoelectron orbitals can be seen. Figure 10(b) is a magnified view of the spectrum from Figure 10(a) showing the peaks of W in the 4f orbital and Sb in the 4d orbital. Figure 10(c) is a magnified view of the spectrum from Figure 10(a) showing the peaks of O in the 1s orbital and Sb in the 3d orbital.

[0055] Oxygen reduction reactions were induced in an acidic solution of 1 M HClO4 (pH=1.3) and an alkaline solution of 0.1 M KOH (pH=12.6) using the rotating ring-disk electrode method (RRDE). A catalyst layer containing Sb2WO6 molecules was placed on the disk electrode (carbon black substrate), and the oxygen reduction reaction was mediated by this catalyst layer. Here, the disk electrode corresponds to the first electrode, and the ring electrode corresponds to the second electrode.

[0056] Figure 11 is a graph showing the LSV curve obtained at this time. Reversible hydrogen electrode V RHEFor this, the onset potential is 0.94V, the half-wave potential is 0.78V, and the current is 0.05mA / cm². 2 The disk current density is obtained. This characteristic is as good as that obtained when using commercially available catalyst layers containing Pt and C.

[0057] In the same oxygen reduction reaction using the rotating ring disk electrode method, the number of electrons contributing to the reaction was measured. Figure 12 is a graph showing the measurement results. It can be seen that the 4-electron oxygen reduction reaction is maintained in both acidic and alkaline solutions, and that almost no H2O2 is produced. The high current density shown in Figure 11 is thought to be due to this 4-electron reaction.

[0058] When no catalyst layer was formed on the disk electrode, an oxygen reduction reaction without a catalyst layer was generated, and similar measurements were performed. Figure 13 is a graph comparing the current density obtained by the oxygen reduction reaction with and without a catalyst layer containing Sb2WO6 molecules. The current density with the catalyst layer is 2 to 5 times higher than the current density without the catalyst layer. From the comparison of the two current densities, it is considered that the effect of increased current density is due to the oxygen reduction reaction involving 4 electrons, rather than the influence of Sb2WO6.

[0059] Chronoamperometry measurements were performed using Sb2WO6 as a catalyst mounted on a carbon cloth electrode in acidic and alkaline solutions, respectively. Figure 14 shows the measurement results. The currents that flowed continuously in the acidic and alkaline solutions after 12 hours were 95.1% and 102.6% of the initial current, respectively, both showing higher retention rates compared to commercially available catalysts containing Pt and C. This is thought to be because the Sb and W contained in the catalyst layer have high chemical stability.

[0060] The results of X-ray diffraction and X-ray electron spectroscopy measurements of Sb2WO6, obtained immediately after the stability evaluation, were corrected using density functional theory (DFT) to reflect the crystal structure of Sb2WO6 when placed in an acidic electrolyte and an alkaline electrolyte, respectively. Figure 15 shows the graphs before and after correction for the X-ray diffraction measurement results in Figure 6. Figures 16(a) and (b) show the graphs before and after correction for the X-ray photoelectron spectroscopy measurement results in Figures 10(b) and (c), respectively.

[0061] In the graph in Figure 15, the uncorrected Sb2WO6 (Pristine) shows strong peaks at diffraction angles of 25 and 42 degrees, but these peaks disappear in the corrected Sb2WO6 (Acid, Alkaline). The full width at half maximum (FMAX) of the peaks in the acidic electrolyte is 20-30% of the FMAX of the peaks in the alkaline electrolyte. These results can also be confirmed from the Raman spectrum measurements.

[0062] In the spectrum of Figure 16(a), the Sb peak in the 4d orbital is blueshifted by approximately 0.1 eV compared to the same peak in the spectrum of Figure 10(b). Similarly, in the spectrum of Figure 16(b), the Sb peak in the 3d orbital is blueshifted by approximately 0.2 eV compared to the same peak in the spectrum of Figure 10(b).

[0063] Figure 17(a) shows a TEM image (top) and an EDS elemental mapping image (bottom) of Sb2WO6 in an acidic electrolyte. In this Sb2WO6, the (041) plane extends from the interior toward the surface, and almost no structural changes are observed.

[0064] Figure 17(b) shows a TEM image (top) and an EDS elemental mapping image (bottom) of Sb2WO6 in an alkaline electrolyte. The surface layer of this Sb2WO6 shows a structure that has been reduced and whose order has been diminished.

[0065] Comparing the EDS elemental mapping images, Sb, W, and O are uniformly distributed in both cases, but the ratio of Sb to W (Sb / W) differs between the acidic and alkaline electrolytes. In the acidic electrolyte, the ratio of Sb to W remains unchanged at 2.00±0.02 compared to immediately after the stability evaluation, while in the alkaline electrolyte, it increases to 2.03±0.02 compared to immediately after the stability evaluation.

[0066] Figure 18 is a Pourbet diagram showing the surface state of the catalyst layer containing Sb2WO6 molecules. When pH=0 and V>0, the catalyst layer surface is stable when covered with oxygen. When pH=0 and V<0, the catalyst layer surface is stable when covered with hydrogen. The potential window (the region between the two dashed lines) is approximately 1.5V.

[0067] The current density was measured in the pH range of 1.3 to 12.6 around the catalyst layer, corresponding to the binding energy of hydroxide ions to the catalyst layer. Figure 19 is a graph showing the results. A volcanic plot is shown according to Sabatier's principle. That is, there is a peak in current density for each pH, ​​and the magnitude of the current density is proportional to the pH. [Explanation of Symbols]

[0068] 100...fuel cell 101...first electrode 102...Second electrode 103...first catalyst layer 104...Second catalyst layer 105...electrolyte 106...container 107...Wiring 108...Power Generation Department 109... Oxygen supply source 110... Reducing agent supply source

Claims

1. Sb ２ WO ６ An oxygen reduction catalyst characterized by containing molecules.

2. First electrode and The first catalyst layer provided on the first electrode, The second electrode and The second catalyst layer provided on the second electrode, The electrolyte sandwiched between the first electrode and the second electrode, The system comprises the first electrode, the first catalyst layer, the second electrode, the second catalyst layer, and a container for housing the electrolyte. The first catalyst layer is Sb ２ WO ６ An electrolytic device characterized by containing molecules.

3. A catalyst layer provided on an electrode constituting an electrolytic device, which promotes the electrolytic reaction, Sb ２ WO ６ A catalyst layer characterized by containing molecules.

4. A process of generating a potential difference between two electrodes that sandwich an electrolyte, A step of supplying oxygen molecules to the first electrode, which is on the higher potential side of the aforementioned electrodes, The process includes supplying the oxygen molecule reducing agent to the second electrode, which is on the lower potential side of the aforementioned electrodes. The surface of the first electrode contains Sb ２ WO ６ An electrolytic method characterized by having a catalyst layer containing molecules.

5. The electrolysis method according to claim 4, characterized in that an oxygen reduction reaction occurs in the catalyst layer to produce water.

6. The electrolysis method according to either claim 4 or 5, characterized in that a hydrogen molecule or a hydrogen compound molecule is used as the reducing agent.

7. The pH of the electrolyte surrounding the catalyst layer and the potential of the first electrode are adjusted so that they fall within the region between the first line segment and the second line segment in the Pourbet diagram. The aforementioned first line segment is a line segment connecting a point where the pH is 0 and the potential is 0.6V, and a point where the pH is 14 and the potential is -0.226V. The electrolysis method according to either 4 or 5, characterized in that the second line segment is a line segment connecting a point where the pH is 0 and the potential is 1 V and a point where the pH is 14 and the potential is 0.174 V.

8. The electrolysis method according to either claim 4 or 5, characterized in that the pH around the catalyst layer is 1.3 or higher and 12.6 or lower.

9. A data mining method for searching for metal oxides as catalysts for oxygen reduction reactions, The first step is to select a specific metal oxide from the metal oxides recorded in the database, From the metal oxide selected in the first step, select a metal oxide that satisfies the condition that E ｈｕｌｌ becomes 0 in a second step. From the metal oxide selected in the second step, E Ｆｏｒｍ A third step involves selecting a metal oxide that satisfies the condition for minimizing [the value], For each of the metal oxides selected in the third step, the Gibbs free energy is 0.5 eVatom －１ The fourth step involves creating a Pourbet diagram that defines the stable region as the following pH and potential ranges, A data mining method characterized by comprising: a fifth step of selecting, from among the Pourbet diagrams created in the fourth step, a metal oxide that gives a Pourbet diagram showing the presence of a solid phase in a predetermined reaction, as an electrode catalyst.

10. The data mining method according to claim 9, characterized in that the combination of the metal oxide selected in the third step and the Pourbet diagram created in the fourth step is recorded in a predetermined recording device, and the selection of the metal oxide to be used as the electrode catalyst is performed by searching the records of the previous recording device.

11. The data mining method according to either 9 or 10, further comprising the step of selecting from the metal oxides selected in the third step that contain a predetermined number of metal elements.

Images