WO2024219065A1 - Organic hydride production device and organic hydride production method - Google Patents

Abstract

This organic hydride production device 2 comprises, as an anode catalyst 11, an anode electrode 10 having a high entropy alloy containing a base metal element, a cathode electrode 8, and an electrolyte membrane 12 positioned between the anode electrode 10 and the cathode electrode 8. The anode electrode 10 oxidizes water or hydroxide ions. The cathode electrode 8 electrochemically reduces a hydride to generate an organic hydride.

Description

Organic hydride production apparatus and organic hydride production method

The present invention relates to an organic hydride production apparatus and an organic hydride production method.

Patent Document 1 describes a water electrolysis device that uses a high-entropy alloy as a catalyst for the oxygen generation reaction.

International Publication No. 2022/080142

In recent years, organic hydrides have been attracting attention as an energy carrier for the large-scale transport and storage of hydrogen derived from renewable energy sources. In addition, an organic hydride production device is known that produces protons from water at the anode electrode and hydrogenates the substance to be hydrided with the protons at the cathode electrode to produce an organic hydride.

As in the case of water electrolysis, the anode catalyst of an organic hydride production device is required to have oxygen evolution reaction (OER) activity, acid resistance, oxidation potential resistance, electrical conductivity, etc., and also to be resistant to the substances to be hydrided and organic hydrides that cross leak from the cathode electrode side. In conventional organic hydride production devices, Ir and the like have generally been used as the anode catalyst, but the inventors, after extensive investigations, have come to realize that there is room for improving the durability of the anode catalyst in conventional organic hydride production devices.

The present invention was made in consideration of these circumstances, and one of its objectives is to improve the durability of anode catalysts used in organic hydride production equipment.

One aspect of the present invention is an organic hydride production apparatus. This apparatus comprises an anode electrode having a high-entropy alloy containing a base metal element as an anode catalyst, a cathode electrode, and an electrolyte membrane located between the anode electrode and the cathode electrode. The anode electrode oxidizes water or hydroxide ions. The cathode electrode electrochemically reduces the substance to be hydrided to produce an organic hydride.

Another aspect of the present invention is a method for producing organic hydrides using an organic hydride production apparatus that includes an anode electrode having a high-entropy alloy containing a base metal element as an anode catalyst, a cathode electrode, and an electrolyte membrane located between the anode electrode and the cathode electrode. This production method includes oxidizing water or hydroxide ions at the anode electrode and electrochemically reducing the substance to be hydrided at the cathode electrode to produce an organic hydride.

Any combination of the above components, or any conversion of the expressions of this disclosure between methods, devices, systems, etc., are also valid aspects of this disclosure.

The present invention makes it possible to improve the durability of the anode catalyst used in an organic hydride production device.

1 is a schematic diagram of an organic hydride production system including an organic hydride production apparatus according to an embodiment. FIG. 13 is a diagram showing the current density of each cell in a toluene poisoning test. FIG. 1 shows by-products produced in potentiostatic electrolysis. 4A and 4B are diagrams showing the results of FT-IR analysis of the working electrode of Example 1 after a toluene poisoning test, and the results of FT-IR analysis of the working electrode of Comparative Example 1 after a toluene poisoning test. 5A and 5B are diagrams showing the current density of the cell of Example 1 and Comparative Example 1 in a toluene oxidation product poisoning test, respectively. 6A and 6B are diagrams showing the results of FT-IR analysis of the working electrode of Example 1 after a toluene oxidation product poisoning test, and the results of FT-IR analysis of the working electrode of Comparative Example 1 after a toluene oxidation product poisoning test.

The present invention will be described below with reference to the drawings based on preferred embodiments. The embodiments are illustrative and do not limit the technical scope of the present invention, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention. Therefore, many design changes such as changes, additions, and deletions of components are possible in the contents of the embodiments, as long as they do not deviate from the idea of the invention defined in the claims. A new embodiment with design changes has the effects of both the combined embodiments and modifications. In the embodiments, the contents for which such design changes are possible are emphasized by adding notations such as "in this embodiment" and "in this embodiment", but design changes are permitted even in contents without such notations. Any combination of the components described in the embodiments is also valid as an aspect of the present invention. The same or equivalent components, members, and processes shown in each drawing are given the same reference numerals, and duplicated explanations are omitted as appropriate. In addition, the scale and shape of each part shown in each drawing are set for convenience in order to facilitate explanation, and are not to be interpreted as being limited unless otherwise specified. Furthermore, when terms such as "first" and "second" are used in this specification or claims, these terms do not indicate any order or importance, but are used to distinguish one configuration from another. Also, in each drawing, some of the components that are not important for explaining the embodiment are omitted.

1 is a schematic diagram of an organic hydride production system 1 including an organic hydride production apparatus 2 according to an embodiment. The organic hydride production system 1, as an example, includes an organic hydride production apparatus 2, a cathode liquid tank 4, and an anode liquid tank 6. Although only one organic hydride production apparatus 2 is illustrated in FIG. 1, the organic hydride production system 1 may include multiple organic hydride production apparatuses 2. In this case, the organic hydride production apparatuses 2 are stacked in the same orientation so that the cathode electrodes 8 and anode electrodes 10 are aligned in the same order, and are electrically connected in series. The organic hydride production apparatuses 2 may be connected in parallel, or a combination of series and parallel connections may be used. The configuration of the organic hydride production system 1 is not limited to that described below, and the configuration of each part can be changed as appropriate.

The organic hydride manufacturing apparatus 2 is an electrolysis cell that generates organic hydrides by hydrogenating the material to be hydrided, which is a dehydrogenated form of organic hydride, through an electrochemical reduction reaction. The organic hydride manufacturing apparatus 2 has a cathode electrode 8 (negative electrode), an anode electrode 10 (positive electrode), an electrolyte membrane 12, a pair of plate members 14a, 14b, and a pair of gaskets 16a, 16b. The cathode electrode 8, the anode electrode 10, and the electrolyte membrane 12 constitute a membrane electrode assembly. Note that, although the present embodiment will be described using a membrane electrode assembly as an example, the organic hydride manufacturing apparatus 2 may have a so-called zero-gap electrode structure in which an electrode having an anode catalyst applied to a hard support substrate is in physical contact with the electrolyte membrane.

The cathode electrode 8 electrochemically reduces the material to be hydrided to produce an organic hydride. In this embodiment, "electrochemical" means that the reaction proceeds when a voltage or current is applied from outside the organic hydride production apparatus 2. The cathode electrode 8 has a cathode catalyst 9. For example, the cathode catalyst 9 is contained in a cathode catalyst layer. The cathode catalyst 9 includes precious metals such as Pt (platinum), Ru (ruthenium), and Pd (palladium), and base metals such as Ni (nickel). In the cathode catalyst layer, the cathode catalyst 9 can be supported by a porous catalyst carrier. The catalyst carrier is composed of an electron-conductive material such as porous carbon, porous metal, and porous metal oxide.

When the electrolyte membrane 12 has proton conductivity, the cathode catalyst 9 is coated with a cation exchange type ionomer. For example, the catalyst carrier supporting the cathode catalyst 9 is coated with an ionomer. Examples of cation exchange type ionomers include perfluorosulfonic acid polymers such as Nafion (registered trademark), Flemion (registered trademark), Aquivion (registered trademark), and Aciplex (registered trademark), and hydrocarbon-based sulfonic acid polymers. It is preferable that the ionomer partially coats the cathode catalyst 9. Preferably, 10% or more of the surface of each cathode catalyst 9 is coated with the ionomer. This allows the three elements necessary for the electrochemical reaction at the cathode electrode 8, namely, the hydrogenated material, protons, and electrons, to be efficiently supplied to the reaction field.

When the electrolyte membrane 12 has anion conductivity, the cathode catalyst 9 is coated with an anion exchange type ionomer. For example, the catalyst carrier supporting the cathode catalyst 9 is coated with an ionomer. An example of an anion exchange type ionomer is a polymer such as Fumion (registered trademark). It is preferable that the ionomer partially coats the cathode catalyst 9. Preferably, 10% or more of the surface of each cathode catalyst 9 is coated with the ionomer. This allows the three elements necessary for the electrochemical reaction at the cathode electrode 8, namely the material to be hydrided, water, and electrons, to be efficiently supplied to the reaction site.

The cathode electrode 8 may be provided with a cathode diffusion layer. As an example, the cathode catalyst layer is arranged so as to contact one of the main surfaces of the electrolyte membrane 12. The cathode diffusion layer is arranged so as to contact the main surface of the cathode catalyst layer opposite the electrolyte membrane 12. The cathode diffusion layer uniformly diffuses the material to be hydrided, which is supplied from the outside, into the cathode catalyst layer. The organic hydride generated in the cathode catalyst layer is discharged to the outside of the cathode electrode 8 through the cathode diffusion layer. The cathode diffusion layer is made of a conductive material such as carbon or metal. The cathode diffusion layer is a porous body such as a sintered body of fibers or particles, or a foam molded body. Examples of materials that constitute the cathode diffusion layer include woven carbon fabric (carbon cloth), nonwoven carbon fabric, and carbon paper. The cathode diffusion layer may be omitted.

The anode electrode 10 oxidizes water or hydroxide ions. If the electrolyte membrane 12 has proton conductivity, the anode electrode 10 oxidizes water to generate protons. If the electrolyte membrane 12 has anion conductivity, the anode electrode 10 oxidizes hydroxide ions to generate oxygen. The anode electrode 10 has an anode catalyst 11. For example, the anode catalyst 11 is included in the anode catalyst layer. In the anode catalyst layer, the anode catalyst 11 may be dispersed and supported on or coated on a substrate having electronic conductivity. The substrate is composed of a material whose main component is a metal such as Ti (titanium) or SUS (stainless steel). Examples of the form of the substrate include a woven or nonwoven sheet, a mesh, a porous sintered body, a foamed molded body (foam), and an expanded metal.

The anode electrode 10 of the present embodiment has a high-entropy alloy (HEA) containing a base metal element as the anode catalyst 11. The high-entropy alloy is a solid solution alloy in which the atomic composition ratios of five or more constituent elements are substantially equal. The entropy of mixing is increased by the atomic composition ratios of five or more constituent elements being substantially equal. In the present embodiment, "substantially equal" means that the atomic composition ratios of the elements are equal to the extent that the entropy is high, and a difference of the order of manufacturing error is allowed. For example, when the atomic composition ratio of the element with the highest atomic composition ratio among the five or more constituent elements is C _max and the atomic composition ratio of the element with the lowest atomic composition ratio is C _min , (C _max -C _min )/(C _max +C _min )≦0.2, and preferably (C _max -C _min )/(C _max +C _min )≦0.1. The atomic composition ratio of each metal element in the solid solution alloy is preferably 4 atm % or more and 24 atm % or less, and more preferably 5 atm % or more and 20 atm % or less.

As mentioned above, it is known to use high entropy alloys for oxygen generating electrodes in water electrolysis. However, a person skilled in the art would not easily come up with the idea of using a high entropy alloy containing a base metal element as the anode catalyst 11 of the organic hydride production apparatus 2, as in this embodiment.

Firstly, in the organic hydride manufacturing apparatus 2, the material to be hydrided and the organic hydride may leak from the cathode electrode 8 side to the anode electrode 10 side. For this reason, in the organic hydride manufacturing apparatus 2, the OER overvoltage at the anode electrode 10 tends to be larger than in the case of water electrolysis. Therefore, those skilled in the art consider that high-entropy alloys containing base metal elements that have lower OER activity than precious metals such as Ir are useless as the anode catalyst 11.

Secondly, the operating temperature of the organic hydride production apparatus 2 is set lower than that of water electrolysis so as not to exceed the boiling points of the material to be hydrided and the organic hydride. The electrolysis voltage of the organic hydride production apparatus 2 is highly dependent on temperature, and the lower the temperature, the higher the electrolysis voltage. Therefore, those skilled in the art believe that high-entropy alloys containing base metal elements, which are expected to increase the electrolysis voltage due to their low OER activity, are useless as the anode catalyst 11.

Thirdly, it is common technical knowledge that high entropy alloys containing base metals as constituent elements are less durable than precious metals such as Ir. Also, as stated in the first reason, the anode catalyst 11 is prone to deterioration in the organic hydride production apparatus 2 because the material to be hydrided and the organic hydride may leak. Therefore, those skilled in the art consider that high entropy alloys containing base metal elements, which are less durable, are useless as anode catalyst 11.

Thus, it is natural that one would not normally think of using a high-entropy alloy containing base metal elements as the anode catalyst 11 for producing organic hydrides. However, as a result of extensive research, the present inventors have discovered that, contrary to expectations, high-entropy alloys containing base metal elements have high durability against substances to be hydrided. This finding should not be considered as something that a person skilled in the art could easily arrive at.

Therefore, by using a high entropy alloy as the anode catalyst 11, the durability of the anode catalyst 11 can be improved. This allows the activity of the anode catalyst 11 to be maintained for a long period of time, improving the production efficiency of organic hydrides. Furthermore, since high entropy alloys containing base metal elements are cheaper than precious metals such as Ir, it is possible to reduce the costs involved in the production of organic hydrides. Furthermore, it is preferable that all of the constituent elements of a high entropy alloy containing a base metal element are base metal elements. Note that although Cu has a smaller ionization tendency than hydrogen and its standard electrode potential is positive relative to the hydrogen standard electrode, it is treated as a base metal in this application.

Preferably, the high entropy alloy contains at least one element selected from the group consisting of Mn, Fe, Co, Ni, Cr, Ti, Zr, Nb, Mo and Cu. More preferably, the high entropy alloy contains at least one element selected from the group consisting of Mn, Fe, Co and Ni (hereinafter referred to as the first group as appropriate) and at least one element selected from the group consisting of Cr, Ti, Zr, Nb, Mo and Cu (hereinafter referred to as the second group as appropriate).

The elements of the first group have higher catalytic activity than the elements of the second group. On the other hand, the elements of the second group have higher durability against the anode fluid LA than the elements of the first group. Therefore, by including elements of the first group and elements of the second group in the high entropy alloy, it is possible to improve both the catalytic performance and durability of the anode catalyst 11. The average particle size D50 of the high entropy alloy is, for example, 1 nm or more and 100 μm or less.

Furthermore, the anode catalyst 11 preferably has a dissolution rate of elements contained in the high entropy alloy of 60 μg/h or less per 1 g of anode catalyst when a rated current, i.e., a current during rated electrolysis in the organic hydride production apparatus 2, is applied, or when a rated voltage, i.e., a voltage during rated electrolysis in the organic hydride production apparatus 2, is applied, or when immersed in an acidic solution with a pH of 4.0 or less, the dissolution rate of elements contained in the high entropy alloy is 60 μg/h or less per 1 g of anode catalyst. In this way, by keeping the high entropy alloy in a stable state, dissolution of the constituent elements of the high entropy alloy from the anode catalyst 11 during operation of the organic hydride production system 1 can be suppressed.

The stable state of the high entropy alloy can be achieved by performing an aging treatment on the anode catalyst 11 in advance. The aging treatment includes at least one of electrolysis of an electrolyte using the anode catalyst 11 and immersion of the anode catalyst 11 in an acidic solution having a pH of 4.0 or less. In this embodiment, "in advance" means before the production of organic hydride is carried out in the organic hydride production apparatus 2. For example, "performing an aging treatment in advance" means immersing the anode electrode 10 alone in an electrolyte such as an aqueous sulfuric acid solution and applying an electrolytic current or an electrolytic voltage. Also, "performing an aging treatment in advance" means immersing the anode electrode 10 alone in an acidic solution having a pH of 4.0 or less.

The anode electrode 10 may be provided with an anode diffusion layer. As an example, the anode catalyst layer is disposed so as to be in contact with the other main surface of the electrolyte membrane 12. The anode diffusion layer is disposed so as to be in contact with the main surface of the anode catalyst layer opposite the electrolyte membrane 12. The anode diffusion layer may have a structure similar to that of the cathode diffusion layer.

The electrolyte membrane 12 is located between the cathode electrode 8 and the anode electrode 10. As an example, the electrolyte membrane 12 has proton conductivity. In this case, the electrolyte membrane 12 moves protons from the anode electrode 10 to the cathode electrode 8. As an example, the electrolyte membrane 12 is composed of a solid polymer electrolyte membrane (PEM) having proton conductivity. Examples of PEMs include fluorine-based ion exchange membranes having sulfonic acid groups, such as Nafion (registered trademark), and hydrocarbon-based ion exchange membranes, such as Fumasep (registered trademark).

Although FIG. 1 illustrates an electrolyte membrane 12 with proton conductivity, this is not particularly limited, and the electrolyte membrane 12 may also have anion conductivity. In this case, the electrolyte membrane 12 moves hydroxide ions from the cathode electrode 8 to the anode electrode 10. As an example, the electrolyte membrane 12 is composed of a solid polymer electrolyte membrane (AEM) with anion conductivity. Examples of AEM include known anion exchange membranes such as Fumasep (registered trademark), Pention, and Sustainion (registered trademark).

The plate members 14a and 14b are made of metals such as SUS and Ti. The plate member 14a is stacked on the membrane electrode assembly from the cathode electrode 8 side. The plate member 14b is stacked on the membrane electrode assembly from the anode electrode 10 side. Therefore, the membrane electrode assembly is sandwiched between the pair of plate members 14a and 14b. The gap between the plate member 14a and the membrane electrode assembly is sealed with a gasket 16a. The gap between the plate member 14b and the membrane electrode assembly is sealed with a gasket 16b. When the organic hydride production system 1 has only one organic hydride production device 2, the pair of plate members 14a and 14b can correspond to so-called end plates. When the organic hydride production system 1 has multiple organic hydride production devices 2 and another organic hydride production device 2 is arranged next to the plate member 14a or the plate member 14b, the plate member can correspond to so-called separators.

The cathode electrode 8 is connected to the cathode flow path 18. The cathode flow path 18 supplies and discharges the cathode liquid LC to the cathode electrode 8. A groove may be provided on the main surface of the plate member 14a facing the cathode electrode 8, and this groove may constitute the cathode flow path 18.

The anode electrode 10 is connected to the anode flow path 20. The anode flow path 20 supplies and discharges the anode liquid LA to the anode electrode 10. A groove may be provided on the main surface of the plate member 14b facing the anode electrode 10, and this groove may constitute the anode flow path 20.

The cathode fluid tank 4 is connected to the cathode flow path 18 via a first cathode pipe 24 and a second cathode pipe 26. The cathode fluid tank 4 stores cathode fluid LC. One end of the first cathode pipe 24 is connected to the cathode fluid tank 4, and the other end of the first cathode pipe 24 is connected to the inlet of the cathode flow path 18. A cathode pump 28 is provided in the middle of the first cathode pipe 24. The cathode pump 28 can be a known pump such as a gear pump or a cylinder pump. The flow of the cathode fluid LC may be achieved by a fluid delivery device other than a pump. One end of the second cathode pipe 26 is connected to the outlet of the cathode flow path 18, and the other end of the second cathode pipe 26 is connected to the cathode fluid tank 4.

The cathode liquid LC contains a hydrogenation target substance, which is a raw material for the organic hydride. As an example, the cathode liquid LC does not contain any organic hydride before the organic hydride production system 1 starts operating, and becomes a mixed liquid of the hydrogenation target substance and organic hydride when the organic hydride produced by electrolysis is mixed in after the operation starts. The hydrogenation target substance and the organic hydride are preferably liquid at 20°C and 1 atmosphere.

The substance to be hydrogenated and the organic hydride are not particularly limited as long as they are organic compounds to which hydrogen can be added/desorbed by reversibly causing hydrogenation/dehydrogenation reactions. A wide variety of substances such as acetone-isopropanol, benzoquinone-hydroquinone, and aromatic hydrocarbons can be used as the substance to be hydrogenated and the organic hydride used in this embodiment. Of these, aromatic hydrocarbons are preferred from the standpoint of transportability during energy transportation.

　The aromatic hydrocarbon compound used as the substance to be hydrogenated is a compound containing at least one aromatic ring. Examples of aromatic hydrocarbon compounds include benzene, alkylbenzene, naphthalene, alkylnaphthalene, anthracene, diphenylethane, tetralin, and the like. Alkylbenzene includes compounds in which 1 to 4 hydrogen atoms of an aromatic ring are substituted with a linear or branched alkyl group having 1 to 6 carbon atoms. Examples of such compounds include toluene, xylene, mesitylene, ethylbenzene, diethylbenzene, and the like. Alkylnaphthalene includes compounds in which 1 to 4 hydrogen atoms of an aromatic ring are substituted with a linear or branched alkyl group having 1 to 6 carbon atoms. Examples of such compounds include methylnaphthalene, and the like. These may be used alone or in combination.

The substance to be hydrogenated is preferably at least one selected from the group consisting of toluene, benzene, and xylene. Nitrogen-containing heterocyclic aromatic compounds such as quinoline, isoquinoline, N-alkylpyrrole, N-alkylindole, and N-alkyldibenzopyrrole can also be used as the substance to be hydrogenated. Organic hydrides are the above-mentioned substances to be hydrogenated that have been hydrogenated, and examples of such organic hydrides include cyclohexane, methylcyclohexane, dimethylcyclohexane, and decahydroquinoline.

The cathode liquid LC in the cathode liquid tank 4 flows into the cathode electrode 8 via the first cathode pipe 24 by driving the cathode pump 28. The cathode liquid LC that flows into the cathode electrode 8 is used for an electrode reaction at the cathode electrode 8. The cathode liquid LC in the cathode electrode 8 returns to the cathode liquid tank 4 via the second cathode pipe 26. As an example, the cathode liquid tank 4 also functions as a gas-liquid separator. At the cathode electrode 8, hydrogen gas may be generated due to a side reaction. Therefore, the cathode liquid LC discharged from the cathode electrode 8 may contain hydrogen gas. The cathode liquid tank 4 separates the hydrogen gas in the cathode liquid LC from the cathode liquid LC and discharges it outside the system.

A gas-liquid separator may be provided separately from the cathode liquid tank 4. The organic hydride production system 1 may also be provided with an oil-water separator for separating water from the cathode liquid LC as necessary. Alternatively, the cathode liquid tank 4 may function as the oil-water separator. In the organic hydride production system 1 of this embodiment, the cathode liquid LC is circulated between the cathode electrode 8 and the cathode liquid tank 4. However, this configuration is not limited, and the cathode liquid LC may be sent from the cathode electrode 8 to the outside of the system without being returned to the cathode liquid tank 4.

The anode fluid tank 6 is connected to the anode flow path 20 via the first anode pipe 30 and the second anode pipe 32. The anode fluid tank 6 stores the anode fluid LA. One end of the first anode pipe 30 is connected to the anode fluid tank 6, and the other end of the first anode pipe 30 is connected to the inlet of the anode flow path 20. An anode pump 34 is provided in the middle of the first anode pipe 30. The anode pump 34 can be a known pump such as a gear pump or a cylinder pump. The circulation of the anode fluid LA may be achieved by a fluid delivery device other than a pump. One end of the second anode pipe 32 is connected to the outlet of the anode flow path 20, and the other end of the second anode pipe 32 is connected to the anode fluid tank 6.

The anode liquid LA contains water. When the electrolyte membrane 12 has proton conductivity, examples of the anode liquid LA include acidic solutions such as an aqueous sulfuric acid solution, an aqueous nitric acid solution, and an aqueous hydrochloric acid solution; pure water; ion-exchanged water; and the like. Preferably, the pH of the anode liquid LA is 8 or less. When the electrolyte membrane 12 has anion conductivity, examples of the anode liquid LA include alkaline solutions such as an aqueous potassium hydroxide solution; ion-exchanged water; and an aqueous solution containing an inorganic electrolyte such as potassium sulfate; Preferably, the pH of the anode liquid LA is 6 or more.

The anode fluid LA in the anode fluid tank 6 flows into the anode electrode 10 via the first anode pipe 30 by driving the anode pump 34. If the electrolyte membrane 12 has proton conductivity, the water in the anode fluid LA that flows into the anode electrode 10 is used for the electrode reaction at the anode electrode 10. If the electrolyte membrane 12 has anion conductivity, the water in the anode fluid LA that flows into the anode electrode 10 diffuses through the electrolyte membrane 12 to the cathode electrode 8 side and is used for the electrode reaction at the cathode electrode 8. The anode fluid LA in the anode electrode 10 is returned to the anode fluid tank 6 via the second anode pipe 32. As an example, the anode fluid tank 6 also functions as a gas-liquid separator. Oxygen gas is generated by the electrode reaction at the anode electrode 10. Therefore, oxygen gas is mixed into the anode fluid LA discharged from the anode electrode 10. The anode liquid tank 6 separates the oxygen gas in the anode liquid LA from the anode liquid LA and discharges it outside the system.

A gas-liquid separator may be provided separately from the anode liquid tank 6. In the organic hydride manufacturing system 1 of this embodiment, the anode liquid LA is circulated between the anode electrode 10 and the anode liquid tank 6. However, this configuration is not limited, and the anode liquid LA may be sent from the anode electrode 10 to the outside of the system without being returned to the anode liquid tank 6.

The organic hydride manufacturing apparatus 2 is supplied with power from the power source 22. When power is supplied from the power source 22, a predetermined electrolysis voltage is applied between the cathode electrode 8 and the anode electrode 10, causing an electrolysis current to flow. The power source 22 sends power supplied from an external power supply device 38 to the organic hydride manufacturing apparatus 2. The power supply device 38 can be configured as a power generation device that generates power using renewable energy, such as a wind power generation device 40 or a solar power generation device 42. Note that the power supply device 38 is not limited to a power generation device that uses renewable energy, and may be a system power source, or a storage device that stores power from a renewable energy power generation device or a system power source. It may also be a combination of two or more of these.

When the electrolyte membrane 12 has proton conductivity, the reaction that occurs in the organic hydride production apparatus 2 is as follows. In the following reaction, toluene (TL) is shown as an example of the material to be hydrogenated. When toluene is used as the material to be hydrogenated, the obtained organic hydride is methylcyclohexane (MCH).
<Electrode reaction at the anode electrode>
3H ₂ O → 3/2O ₂ +6H ⁺ +6e ^-
<Electrode reaction at the cathode electrode>
TL+6H ⁺ +6e ^- →MCH

In other words, the electrode reaction at the anode electrode 10 and the electrode reaction at the cathode electrode 8 proceed in parallel. At the anode electrode 10, a water oxidation reaction occurs, producing oxygen, protons, and electrons. The produced protons pass through the electrolyte membrane 12 and move to the cathode electrode 8. The electrons are sent to the cathode electrode 8 via the power source 22. The oxygen is discharged from the anode flow path 20 to the outside of the organic hydride manufacturing apparatus 2. At the cathode electrode 8, the toluene contained in the cathode liquid LC reacts with the protons that have moved from the anode electrode 10 side, electrochemically hydrogenating (reducing) the toluene to produce methylcyclohexane. The produced methylcyclohexane is discharged from the cathode flow path 18 to the outside of the organic hydride manufacturing apparatus 2.

When the electrolyte membrane 12 has anion conductivity, the following reaction occurs in the organic hydride manufacturing apparatus 2. In the following reaction, toluene is shown as an example of the substance to be hydrogenated.
<Electrode reaction at the cathode electrode>
TL+6H ₂ O+6e ^- →MCH+6OH ^-
<Electrode reaction at the anode electrode>
6OH ^- →3/2O ₂ +3H ₂ O+6e ^-

In other words, the electrode reaction at the cathode electrode 8 and the electrode reaction at the anode electrode 10 proceed in parallel. At the cathode electrode 8, the toluene contained in the cathode liquid LC reacts with the water diffused from the anode electrode 10 side, and the toluene is electrochemically hydrogenated (reduced) to produce methylcyclohexane and hydroxide ions. The methylcyclohexane is discharged from the cathode flow path 18 to the outside of the organic hydride manufacturing apparatus 2. The hydroxide ions pass through the electrolyte membrane 12 and move to the anode electrode 10. At the anode electrode 10, an oxidation reaction of the hydroxide ions that have moved from the cathode electrode 8 side occurs, and oxygen, water, and electrons are produced. The electrons are supplied to the cathode electrode 8 via the power source 22 and are used in the electrode reaction at the cathode electrode 8. The oxygen and water are discharged from the anode flow path 20 to the outside of the organic hydride manufacturing apparatus 2.

Accordingly, according to the organic hydride manufacturing apparatus 2 of this embodiment, the electrolysis of water and the hydrogenation reaction of the material to be hydrogenated can be carried out in one step. Alternatively, the oxidation reaction of hydroxide ions and the hydrogenation reaction of the material to be hydrogenated can be carried out in one step. This improves the efficiency of organic hydride manufacturing compared to conventional techniques that manufacture organic hydrides in a two-stage process consisting of a process of manufacturing hydrogen by water electrolysis or the like and a process of chemically hydrogenating the material to be hydrogenated in a reactor of a plant or the like. In addition, since there is no need for a reactor for chemical hydrogenation or a high-pressure container for storing hydrogen produced by water electrolysis or the like, a significant reduction in equipment costs can be achieved.

The organic hydride manufacturing apparatus 2 according to this embodiment has a current drop rate of 1% or less after 10 hours when 200 ppm or more of a substance to be hydrided or an organic hydride is added to the anolyte LA supplied to the anode electrode 10 in a specified constant voltage electrolysis, or a voltage rise rate of 1% or less after 10 hours when 200 ppm or more of a substance to be hydrided or an organic hydride is added to the anolyte LA in a specified constant current electrolysis.

By keeping the current drop rate after 10 hours to 1% or less, it is possible to prevent the current drop from becoming significant over the lifetime of the organic hydride production apparatus 2. This makes it possible to maintain the equipment utilization rate of the organic hydride production system 1 and improve operating costs. In addition, by keeping the voltage rise rate after 10 hours to 1% or less, it is possible to suppress the increase in electricity costs required to operate the organic hydride production system 1 and improve operating costs.

In addition, when 200 ppm or more of the substance to be hydrogenated or organic hydride is added to the anode liquid LA supplied to the anode electrode 10 and electrolysis is performed for 50 hours, the organic hydride production apparatus 2 according to this embodiment has a Faraday efficiency of 0.1% or less for at least one product selected from the group consisting of a product in which a hydroxyl group is bonded to the substance to be hydrogenated or organic hydride (hereinafter referred to as oxidation product I as appropriate), a product in which an aldehyde group is bonded to the substance to be hydrogenated or organic hydride or a part of the substance to be hydrogenated or organic hydride is changed to an aldehyde group (hereinafter referred to as oxidation product II as appropriate), and a product in which a carboxyl group is bonded to the substance to be hydrogenated or organic hydride or a part of the substance to be hydrogenated or organic hydride is changed to a carboxyl group (hereinafter referred to as oxidation product III as appropriate).

This makes it possible to reduce the cost of removing the oxidation products I to III from the anolyte LA, thereby improving the operating costs of the organic hydride production system 1.

In addition, the organic hydride manufacturing apparatus 2 according to this embodiment allows the reaction to proceed at each electrode at a pressure of 1 atm or more and 3 atm or less and at a temperature of 20°C or more and 70°C or less. The reaction temperature is more preferably 20°C or more and 60°C or less. In addition, the potential of the anode electrode 10 is preferably 0 to 2.07 V vs. RHE.

The embodiment may be specified by the items described below.
[Item 1]
an anode electrode (10) having a high entropy alloy containing a base metal element as an anode catalyst (11);
A cathode electrode (8);
an electrolyte membrane (12) located between the anode electrode (10) and the cathode electrode (8);
The anode electrode (10) oxidizes water or hydroxide ions;
The cathode electrode (8) electrochemically reduces the substance to be hydrided to produce an organic hydride.
Organic hydride production equipment (2).
[Second Item]
The high entropy alloy comprises at least one element selected from the group consisting of Mn, Fe, Co, Ni, Cr, Ti, Zr, Nb, Mo, and Cu;
2. An organic hydride production apparatus (2) according to claim 1.
[Item 3]
The high entropy alloy comprises at least one element selected from the group consisting of Mn, Fe, Co, and Ni, and at least one element selected from the group consisting of Cr, Ti, Zr, Nb, Mo, and Cu;
Item 2. An organic hydride production apparatus (2).
[Fourth Item]
High entropy alloys are made up of all base metal elements.
4. An organic hydride manufacturing apparatus (2) according to any one of the first to third items.
[Item 5]
a current decrease rate after 10 hours is 1% or less when 200 ppm or more of a substance to be hydrided or an organic hydride is added to the anolyte (LA) supplied to the anode electrode (10) in a predetermined constant voltage electrolysis, or a voltage increase rate after 10 hours is 1% or less when 200 ppm or more of a substance to be hydrided or an organic hydride is added to the anolyte (LA) in a predetermined constant current electrolysis.
5. An organic hydride manufacturing apparatus (2) according to any one of the first to fourth items.
[Item 6]
when 200 ppm or more of a material to be hydrogenated or an organic hydride is added to an anolyte (LA) supplied to an anode electrode (10) and electrolysis is performed for 50 hours, the Faraday efficiency of formation of at least one selected from the group consisting of a product in which a hydroxy group is bonded to the material to be hydrogenated or the organic hydride, a product in which an aldehyde group is bonded to the material to be hydrogenated or the organic hydride or a part of the material to be hydrogenated or the organic hydride is changed to an aldehyde group, and a product in which a carboxy group is bonded to the material to be hydrogenated or the organic hydride or a part of the material to be hydrogenated or the organic hydride is changed to a carboxy group is 0.1% or less;
Item 5. An organic hydride manufacturing apparatus (2) according to any one of items 1 to 5.
[Item 7]
the anode catalyst (11) has a dissolution rate of elements contained in the high entropy alloy of 60 μg/h or less per 1 g of the anode catalyst (11) when a rated current or a rated voltage is applied thereto, or the dissolution rate of elements contained in the high entropy alloy of 60 μg/h or less per 1 g of the anode catalyst (11) when immersed in an acidic solution of pH 4.0 or less;
7. An organic hydride manufacturing apparatus (2) according to any one of items 1 to 6.
[Item 8]
A reaction is allowed to proceed at each electrode (8, 10) at a pressure of 1 atmosphere or more and 3 atmospheres or less and at a temperature of 20° C. or more and 70° C. or less.
8. An organic hydride manufacturing apparatus (2) according to any one of items 1 to 7.
[Item 9]
A method for producing an organic hydride using an organic hydride production apparatus (2) including an anode electrode (10) having a high-entropy alloy containing a base metal element as an anode catalyst (11), a cathode electrode (8), and an electrolyte membrane (12) located between the anode electrode (10) and the cathode electrode (8), comprising:
Oxidizing water or hydroxide ions at the anode electrode (10);
Electrochemically reducing the substance to be hydrided at the cathode electrode (8) to produce an organic hydride.
Organic hydride production methods.
[Item 10]
The method includes subjecting the anode catalyst (11) to a prior aging treatment,
The aging treatment includes at least one of electrolysis of an electrolyte using the anode catalyst (11) and immersion of the anode catalyst (11) in an acidic solution having a pH of 4.0 or less.
10. A method for producing an organic hydride according to item 9.

The following describes examples of the present invention, but these examples are merely illustrative examples for the purpose of explaining the present invention in a suitable manner and do not limit the present invention in any way.

[Preparation of anode electrode]
Example 1
Ingots of each metal, Mn, Fe, Co, Ni, Cr, Ti, Zr, Nb and Mo, were put into an arc melting furnace. The amount of each ingot was adjusted so that the composition ratio of each metal in the high entropy alloy was 11.1 atm%. Then, arc melting was performed under a pure Ar atmosphere. In the arc melting process, the operation of completely melting the base material and then rotating the ingot to remelt it was repeated six or more times to uniformly mix each metal. The obtained ingot of high entropy alloy (9eHEA) was formed into a sheet shape to have a predetermined area, and an anode electrode according to Example 1 was obtained.

Example 2
An anode electrode according to Example 2 made of a high entropy alloy (10eHEA) was produced in the same manner as in Example 1, except that Cu was added to the nine metals used in Example 1 to use ten metals. The input amount of each ingot was adjusted so that the composition ratio of each metal in the high entropy alloy was 10 atm %.

(Comparative Example 1)
According to the paper by Zhao et al., Electrochimica Acta 391, 2021, _IrOx was deposited on a Ti film by cyclic voltammetry to prepare an anode electrode according to Comparative Example 1.

[Preparation of organic hydride production apparatus]
An H-shaped cell was prepared, which was divided into two spaces by a proton exchange membrane Nafion 117 fixed in the center. In one space of the H-shaped cell, the anode electrode of Example 1, Example 2, or Comparative Example 1 was inserted as a working electrode. A reference electrode and a stirrer were also inserted in the space. In the other space of the H-shaped cell, a Pt mesh was inserted as a counter electrode. Then, 15 mL of 0.5 mol/L aqueous sulfuric acid solution was poured into each space, and an organic hydride manufacturing apparatus (hereinafter, referred to as a cell as appropriate) according to each Example and Comparative Example was prepared.

[Toluene poisoning test]
A 1/4-inch PTFE tube was inserted into the working electrode side of each cell. The PTFE tube was inserted until the tip reached the center of the aqueous solution in the cell. While stirring the aqueous solution on the working electrode side, constant potential electrolysis was performed at a potential where the potential of the working electrode was 2.0 V vs. RHE. In addition, the current in each cell was measured, and the current density was calculated. After the current was stabilized, a sufficient amount of toluene was dripped from the top end of the tube while continuing the electrolysis. This formed a two-layer structure of an aqueous sulfuric acid solution and toluene in the tube. As a result, the toluene was saturated in the aqueous sulfuric acid solution, and a state was obtained in which undissolved toluene did not adhere to the surface of the working electrode. In this state, constant potential electrolysis was continued.

Figure 2 shows the current density of each cell in the toluene poisoning test. As shown in Figure 2, in Comparative Example 1, a rapid decrease in current density was observed after the addition of toluene. On the other hand, in Examples 1 and 2, the decrease in current density was gradual even after the addition of toluene. This confirmed that high-entropy alloys have higher durability against hydrides than Ir. Therefore, it was shown that the durability of the anode catalyst is improved by using a high-entropy alloy as the anode catalyst.

After the test, the sulfuric acid aqueous solution on the working electrode side in each example and comparative example was collected. Then, each sulfuric acid aqueous solution was mixed with ether to extract the by-products in each sulfuric acid aqueous solution into ether. This ether was measured with a gas chromatograph mass spectrometer (GC/MS: JMS-T100 GCV, manufactured by JEOL) to analyze the components of the by-products. In addition, the components of the by-products were analyzed when constant potential electrolysis was performed at a potential of 1.6 V vs. RHE at the working electrode and when constant potential electrolysis was performed at a potential of 1.8 V vs. RHE at the working electrode. The results are shown in Figure 3.

Figure 3 shows by-products generated by constant potential electrolysis. As shown in Figure 3, in Comparative Example 1, benzaldehyde, benzyl alcohol, and benzoic acid, which are oxidation products of toluene, were detected at a potential of 2.0 V vs. RHE. Also, benzaldehyde and benzyl alcohol were detected at a potential of 1.6 V vs. RHE and a potential of 1.8 V vs. RHE. On the other hand, in Example 1, only benzaldehyde was detected at both potentials. Also, in Example 2, benzaldehyde and benzoic acid were detected at a potential of 2.0 V vs. RHE, and benzaldehyde was detected at a potential of 1.8 V vs. RHE. No oxidation products of toluene were detected at a potential of 1.6 V vs. RHE.

Benzaldehyde corresponds to part of the product to be hydrogenated, that is, the product in which the methyl group of toluene is converted to an aldehyde group. Benzyl alcohol corresponds to the product in which a hydroxyl group is bonded to toluene, which is the product to be hydrogenated. Benzoic acid corresponds to part of the product to be hydrogenated, that is, the product in which the methyl group of toluene is converted to a carboxyl group.

Furthermore, after the test, the working electrodes of Example 1 and Comparative Example 1 were removed, and FT-IR analysis was performed on each working electrode using a Fourier transform infrared spectrophotometer (FT-IR: IRTracer-100, manufactured by Shimadzu Corporation). The removed working electrodes were then immersed in ethanol for 5 days to clean them. Then, each cleaned working electrode was vacuum dried for 24 hours. After that, FT-IR analysis was performed on each cleaned working electrode using the FT-IR. The results are shown in Figures 4(A) and 4(B).

FIG. 4(A) is a diagram showing the results of FT-IR analysis of the working electrode of Example 1 after the toluene poisoning test. FIG. 4(B) is a diagram showing the results of FT-IR analysis of the working electrode of Comparative Example 1 after the toluene poisoning test. In FIG. 4(A) and FIG. 4(B), the results before cleaning are shown by solid lines, and the results after cleaning are shown by dashed lines. As shown in FIG. 4(B), in Comparative Example 1, peaks derived from toluene polymers and polymerization products of oxidation products, that is, peaks derived from CH ₂ and CH ₃ , were observed both before and after cleaning. On the other hand, as shown in FIG. 4(A), in Example 1, the peaks were not observed both before and after cleaning. From this, it was confirmed that the surface of the anode electrode containing a high entropy alloy is difficult to polymerize with the substance to be hydrided and its oxidation product, and therefore difficult to be poisoned by the substance to be hydrided, etc. It was therefore shown that the durability of the anode catalyst is improved by using a high entropy alloy as the anode catalyst.

[Toluene oxidation product poisoning test]
Using the cell of Example 1 described above, constant potential electrolysis was performed at a potential where the potential of the working electrode was 2.0 V vs. RHE. Also, using the cell of Comparative Example 1 described above, constant potential electrolysis was performed at a potential where the potential of the working electrode was 1.6 V vs. RHE. Also, the current in each cell was measured, and the current density was calculated. After constant potential electrolysis was performed for 2 hours while stirring the aqueous solution on the working electrode side, 0.2 mmol of benzyl alcohol, benzaldehyde, or benzoic acid was added to the aqueous solution on the working electrode side of each cell while continuing the electrolysis.

Figure 5(A) shows the current density of the cell of Example 1 in a toluene oxidation product poisoning test. Figure 5(B) shows the current density of the cell of Comparative Example 1 in a toluene oxidation product poisoning test. As shown in Figure 5(B), in Comparative Example 1, a significant decrease in current density was observed after the addition of all of benzyl alcohol, benzaldehyde, and benzoic acid. In particular, the current density of benzyl alcohol and benzoic acid decreased rapidly immediately after addition. On the other hand, as shown in Figure 5(A), in Example 1, the decrease in current density of all of benzyl alcohol, benzaldehyde, and benzoic acid was more gradual than that of Comparative Example 1. In particular, the current density of benzyl alcohol and benzaldehyde was maintained significantly more significantly than that of benzoic acid.

This confirmed that high entropy alloys are more durable against oxidation products of the material to be hydrided than Ir. Therefore, it was shown that the durability of the anode catalyst is improved by using a high entropy alloy as the anode catalyst. Furthermore, since benzoic acid was not produced in Example 1 (see Figure 3), it was shown that the anode electrode of Example 1 is even more durable than the anode electrode of Example 2. Furthermore, since benzoic acid was not produced at potentials of 1.8 V vs. RHE or less in Examples 1 and 2 (see Figure 3), it was shown that it is preferable to perform constant-potential electrolysis at a potential at which the anode electrode potential is 1.8 V vs. RHE or less.

Furthermore, after the test, the working electrodes of each cell were removed and washed by immersing them in ethanol for five days. Next, each washed working electrode was vacuum dried for 24 hours. After that, FT-IR analysis was performed on each washed working electrode using FT-IR. The results are shown in Figures 6(A) and 6(B). Note that Figures 6(A) and 6(B) also include the FT-IR analysis results shown in Figures 4(A) and 4(B) for reference.

FIG. 6(A) is a diagram showing the results of FT-IR analysis of the working electrode of Example 1 after the toluene oxidation product poisoning test. FIG. 6(B) is a diagram showing the results of FT-IR analysis of the working electrode of Comparative Example 1 after the toluene oxidation product poisoning test. As shown in FIG. 6(B), when benzyl alcohol and benzoic acid were added in Comparative Example 1, peaks derived from the polymerization product of the oxidation product, that is, peaks derived from CH ₂ and CH _3, were observed. On the other hand, as shown in FIG. 6(A), no such peaks were observed in Example 1 when any of the oxidation products was added. From this, it was confirmed that the oxidation product of the substance to be hydrided is difficult to polymerize on the surface of the anode electrode containing a high entropy alloy, and therefore it is difficult to be poisoned by the substance to be hydrided, etc. It was therefore shown that the durability of the anode catalyst is improved by using a high entropy alloy as the anode catalyst.

The present invention can be used in an organic hydride production apparatus and an organic hydride production method.

2 Organic hydride manufacturing equipment, 8 Cathode electrode, 9 Cathode catalyst, 10 Anode electrode, 11 Anode catalyst, 12 Electrolyte membrane.

Claims (10)

an anode electrode having a high entropy alloy containing a base metal element as an anode catalyst;
A cathode electrode;
an electrolyte membrane located between the anode electrode and the cathode electrode;
The anode electrode oxidizes water or hydroxide ions;
The cathode electrode electrochemically reduces the substance to be hydrided to produce an organic hydride.
Organic hydride production equipment. The high entropy alloy includes at least one element selected from the group consisting of Mn, Fe, Co, Ni, Cr, Ti, Zr, Nb, Mo, and Cu;
The organic hydride manufacturing apparatus according to claim 1 . The high entropy alloy includes at least one element selected from the group consisting of Mn, Fe, Co, and Ni, and at least one element selected from the group consisting of Cr, Ti, Zr, Nb, Mo, and Cu;
The organic hydride manufacturing apparatus according to claim 2 . The high entropy alloy has all of its constituent elements being base metal elements.
The organic hydride manufacturing apparatus according to claim 1 . a current decrease rate after 10 hours is 1% or less when 200 ppm or more of a substance to be hydrided or an organic hydride is added to the anolyte supplied to the anode electrode in a predetermined constant voltage electrolysis, or a voltage increase rate after 10 hours is 1% or less when 200 ppm or more of a substance to be hydrided or an organic hydride is added to the anolyte in a predetermined constant current electrolysis.
The organic hydride manufacturing apparatus according to any one of claims 1 to 4. when 200 ppm or more of a substance to be hydrogenated or an organic hydride is added to the anolyte supplied to the anode electrode and electrolysis is performed for 50 hours, the Faraday efficiency of formation of at least one selected from the group consisting of a product in which a hydroxyl group is bonded to the substance to be hydrogenated or the organic hydride, a product in which an aldehyde group is bonded to the substance to be hydrogenated or the organic hydride or a part of the substance to be hydrogenated or the organic hydride is changed to an aldehyde group, and a product in which a carboxyl group is bonded to the substance to be hydrogenated or the organic hydride or a part of the substance to be hydrogenated or the organic hydride is changed to a carboxyl group is 0.1% or less;
The organic hydride manufacturing apparatus according to any one of claims 1 to 4. The anode catalyst has a dissolution rate of elements contained in the high entropy alloy of 60 μg/h or less per 1 g of the anode catalyst when a rated current or a rated voltage is applied thereto, or has a dissolution rate of elements contained in the high entropy alloy of 60 μg/h or less per 1 g of the anode catalyst when immersed in an acidic solution of pH 4.0 or less.
The organic hydride manufacturing apparatus according to any one of claims 1 to 4. The reaction is carried out at each electrode at a pressure of 1 to 3 atmospheres and a temperature of 20 to 70° C.
The organic hydride manufacturing apparatus according to any one of claims 1 to 4. A method for producing an organic hydride using an organic hydride producing apparatus including an anode electrode having a high-entropy alloy containing a base metal element as an anode catalyst, a cathode electrode, and an electrolyte membrane located between the anode electrode and the cathode electrode, comprising:
Oxidizing water or hydroxide ions at the anode electrode;
and electrochemically reducing a substance to be hydrided at the cathode electrode to generate an organic hydride.
Organic hydride production methods. and subjecting the anode catalyst to a pre-aging treatment;
The aging treatment includes at least one of electrolysis of an electrolyte solution using the anode catalyst and immersion of the anode catalyst in an acidic solution having a pH of 4.0 or less.
The method for producing an organic hydride according to claim 9.

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