AU2023323068A1

AU2023323068A1 - Apparatus for producing organic hydride

Info

Publication number: AU2023323068A1
Application number: AU2023323068A
Authority: AU
Inventors: Atsushi Fukazawa; Koji Matsuoka; Kota Miyoshi; Kaori Takano
Original assignee: Eneos Corp
Current assignee: Eneos Corp
Priority date: 2022-08-10
Filing date: 2023-07-31
Publication date: 2025-02-20
Also published as: WO2024034444A1

Abstract

An apparatus 2 for producing an organic hydride according to the present invention is provided with: an anode electrode 10 which generates protons by oxidizing water; a cathode electrode 12 which generates an organic hydride by hydrogenating an object to be hydrogenated with protons; an electrolyte membrane 14 which has an EW of less than 980 and is arranged between the anode electrode 10 and the cathode electrode 12 so as to transfer protons from the anode electrode 10 side to the cathode electrode 12 side; and a low moisture content layer 44 which is arranged between the electrolyte membrane 14 and the cathode electrode 12, while having a lower moisture content than the electrolyte membrane 14.

Description

DESCRIPTION TITLE OF INVENTION: APPARATUS FOR PRODUCING ORGANIC HYDRIDE TECHNICAL FIELD

[0001] The present invention relates to an apparatus for

producing an organic hydride.

BACKGROUND ART

[0002] In recent years, in order to suppress the carbon

dioxide emission amount in the energy generation process,

renewable energy is expected to be used, which is obtained by

solar light, wind power, hydraulic power, geothermal power

generation, and the like. As an example, a system for

generating hydrogen by performing water electrolysis using

power derived from renewable energy has been devised. In

addition, an organic hydride system has attracted attention

as an energy carrier for large-scale transportation and

storage of hydrogen derived from renewable energy.

[0003] Regarding the technology for producing an organic

hydride, there has been known an apparatus for producing an

organic hydride having an anode electrode that generates

protons from water, a cathode electrode that hydrogenates an

organic compound having an unsaturated bond (a substance to

be hydrogenated), and an electrolyte membrane that separates

the anode electrode and the cathode electrode (see, for

example, Patent Literature 1). In this apparatus for

producing an organic hydride, water is supplied to the anode electrode, a substance to be hydrogenated is supplied to the cathode electrode, and an electric current is passed between the anode electrode and the cathode electrode, whereby hydrogen is added to the substance to be hydrogenated so as to produce an organic hydride.

RELATED-ART LITERATURE PATENT LITERATURE

[0004] Patent Literature 1: WO 2012/091128

SUMMARY OF INVENTION TECHNICAL PROBLEM

[0005] As a result of intensive studies of apparatuses

for producing an organic hydride, the present inventors have

come to recognize the following issues. That is, apparatuses

for producing an organic hydride can increase the reaction

rate by increasing the current density. Thereby, it is

possible to improve the production efficiency of an organic

hydride and reduce the size of the apparatuses. However,

increasing the current density can increase the cell voltage

in organic hydride production. Therefore, if an electrolyte

membrane with a high water content and low resistance is used

to suppress the increase in cell voltage, the Faradaic

efficiency may decrease.

[0006] The present invention has been made in view of

such a situation, and a purpose thereof is to provide a

technology for suppressing an increase in cell voltage while

suppressing a decrease in the Faradaic efficiency in the production of organic hydrides.

SOLUTION TO PROBLEM

[0007] One embodiment of the present invention relates

to an apparatus for producing an organic hydride. This

apparatus for producing an organic hydride includes: an anode

electrode that generates protons by oxidizing water; a

cathode electrode that generates an organic hydride by

hydrogenating a substance to be hydrogenated with the

protons; an electrolyte membrane that has an equivalent

weight (EW) of less than 980 and is arranged between the

anode electrode and the cathode electrode so as to transfer

the protons from the anode electrode side to the cathode

electrode side; and a low water content layer that is

arranged between the electrolyte membrane and the cathode

electrode and that has a lower water content than that of the

electrolyte membrane.

[0008] Optional combinations of the aforementioned

constituting elements, and implementations of the present

disclosure in the form of methods, apparatuses, and systems

may also be practiced as additional modes of the present

disclosure.

ADVANTAGEOUS EFFECTS OF INVENTION

[0009] According to the present invention, it is

possible to suppress an increase in cell voltage while

suppressing a decrease in the Faradaic efficiency in the

production of organic hydrides.

BRIEF DESCRIPTION OF DRAWINGS

[0010] [Fig. 1] Fig. 1 is a schematic diagram of an

organic hydride production system according to an embodiment.

[Fig. 2] Fig. 2 is a cross-sectional view of an

apparatus for producing an organic hydride.

[Fig. 3] Fig. 3 is a diagram showing the

characteristics of respective electrolytic cells according to

exemplary embodiments and comparative examples, the

improvement rate of the Faradaic efficiency, and the amount

of change in voltage.

DESCRIPTION OF EMBODIMENTS

[0011] Hereinafter, the present invention will be

described based on preferred embodiments with reference to

the drawings. The embodiments do not limit the technical

scope of the present invention and are shown for illustrative

purposes, and not all the features described in the

embodiments and combinations thereof are necessarily

essential to the invention. Therefore, regarding the details

of the embodiments, many design modifications such as change,

addition, deletion, etc., of the constituent elements may be

made without departing from the spirit of the invention

defined in the claims. New embodiments resulting from added

design change will provide the advantages of the embodiments

and variations that are combined. In the embodiments, the

details for which such design change is possible are

emphasized with the notations "according to the embodiment,"

"in the embodiment," etc. However, design change is also

allowed for those without such notations. Optional

combinations of the constituting elements described in the

embodiments are also valid as embodiments of the present

invention. The same or equivalent constituting elements,

members, and processes illustrated in each drawing shall be

denoted by the same reference numerals, and duplicative

explanations will be omitted appropriately. The scales and

shapes of parts shown in each figure are set for the sake of

convenience in order to facilitate the explanation and shall

not be interpreted in a limited manner unless otherwise

mentioned. Terms like "first," "second," etc., used in the

specification and claims do not indicate an order or

importance by any means and are used to distinguish a certain

feature from the others. Some of the components in each

figure may be omitted if they are not important for

explanation.

[0012] Fig. 1 is a schematic diagram of an organic

hydride production system 1 according to an embodiment. The

organic hydride production system 1 as an example includes an

apparatus 2 for producing an organic hydride, an anolyte

supply device 4, and a catholyte supply device 6. In Fig. 1,

a part of the structure of the apparatus 2 for producing an

organic hydride is omitted. Although only one apparatus 2

for producing an organic hydride is shown in Fig. 1, the

organic hydride production system 1 may include a plurality of apparatuses 2 for producing an organic hydride. In this case, the respective apparatuses 2 for producing an organic hydride are stacked in the same direction such that the anode electrode 10 and the cathode electrode 12 are arranged in the same direction, and electrically connected in series. Note that the apparatuses 2 for producing an organic hydride may be connected in parallel, or may be a combination of series connection and parallel connection.

[0013] The apparatus 2 for producing an organic hydride

is an electrolysis cell for generating an organic hydride by

hydrogenating a substance to be hydrogenated, which is a

dehydrogenated product of the organic hydride, by an

electrochemical reduction reaction. The apparatus 2 for

producing an organic hydride includes a membrane electrode

assembly 8, a pair of plate members 16a and 16b, and a pair

of gaskets 18a and 18b. The membrane electrode assembly 8

includes an anode electrode 10 (anode), a cathode electrode

12 (cathode), and an electrolyte membrane 14.

[0014] The anode electrode 10 generates protons by

oxidizing water. The anode electrode 10 has, for example, a

metal such as iridium (Ir), ruthenium (Ru), or platinum (Pt),

or a metal oxide thereof as an anode catalyst that oxidizes

water. The anode catalyst may be dispersedly supported or

coated on a base material having electron conductivity. The

base material includes a material containing, for example, a

metal such as titanium (Ti) or stainless steel (SUS) as a main component. Examples of the form of the base material include a woven fabric sheet or a nonwoven fabric sheet, a mesh, a porous sintered body, a foamed molded body (foam), and an expanded metal.

[0015] The cathode electrode 12 generates an organic

hydride by hydrogenating a substance to be hydrogenated with

protons. The cathode electrode 12 contains, for example,

platinum or ruthenium as a cathode catalyst for hydrogenating

the substance to be hydrogenated. It is preferable that the

cathode electrode 12 also contains a porous catalyst support

that supports the cathode catalyst. The catalyst support

includes an electron-conductive material such as porous

carbon, a porous metal, or a porous metal oxide.

[0016] Furthermore, the cathode catalyst is coated with

an ionomer (cation exchange ionomer). For example, the

catalyst support, which is in the state of supporting the

cathode catalyst, is coated with an ionomer. Examples of the

ionomer include a perfluorosulfonic acid polymer such as

Nafion (registered trademark), Flemion (registered

trademark), Fumion (registered trademark), or Aciplex

(registered trademark). It is preferable that the cathode

catalyst is partially coated with the ionomer. As a result,

it is possible to efficiently supply three elements (the

substance to be hydrogenated, a proton, and an electron)

necessary for an electrochemical reaction in the cathode

electrode 12 to the reaction field.

[0017] The cathode electrode 12 according to the present

embodiment has a catalyst layer 12a and a diffusion layer

12b. The catalyst layer 12a is disposed closer to the

electrolyte membrane 14 than the diffusion layer 12b. The

catalyst layer 12a contains the cathode catalyst, the

catalyst support, and the ionomer described above. The

diffusion layer 12b is in contact with a main surface of the

catalyst layer 12a on a side opposite to the electrolyte

membrane 14. The diffusion layer 12b uniformly diffuses the

substance to be hydrogenated supplied from the outside into

the catalyst layer 12a. The organic hydride generated in the

catalyst layer 12a is discharged to the outside of the

cathode electrode 12 through the diffusion layer 12b. The

diffusion layer 12b includes a conductive material such as

carbon or a metal. In addition, the diffusion layer 12b is a

porous body such as a sintered body of fibers or particles or

a foamed molded body. Examples of the material included in

the diffusion layer 12b include a carbon woven fabric (carbon

cloth), a carbon nonwoven fabric, and carbon paper. Note

that the diffusion layer 12b may be omitted.

[0018] The electrolyte membrane 14 is disposed between

the anode electrode 10 and the cathode electrode 12. The

electrolyte membrane 14 moves protons from the anode

electrode 10 side to the cathode electrode 12 side. The

electrolyte membrane 14 as an example is composed of a solid

polymer electrolyte membrane having protonic conductivity.

[0019] The plate member 16a and the plate member 16b are

made of a metal such as stainless steel or titanium, for

example. The plate member 16a is stacked on the membrane

electrode assembly 8 from the side of the anode electrode 10.

The plate member 16b is stacked on the membrane electrode

assembly 8 from the side of the cathode electrode 12.

Accordingly, the membrane electrode assembly 8 is sandwiched

between the pair of plate members 16a and 16b. A gap between

the plate member 16a and the membrane electrode assembly 8 is

sealed with the gasket 18a. A gap between the plate member

16b and the membrane electrode assembly 8 is sealed with the

gasket 18b. When the organic hydride production system 1

includes only one apparatus 2 for producing an organic

hydride, the pair of plate members 16a and 16b can correspond

to so-called end plates. When the organic hydride production

system 1 includes a plurality of apparatuses 2 for producing

an organic hydride, and another apparatus 2 for producing an

organic hydride is arranged next to the plate member 16a or

the plate member 16b, the plate member can correspond to a

so-called separator.

[0020] The anode flow path 20 is connected to the anode

electrode 10. The anode flow path 20 feeds and discharges

the anolyte LA to and from the anode electrode 10. A groove

may be provided on a main surface facing the anode electrode

10 side in the plate member 16a, and this grove may

constitute the anode flow path 20.

[0021] The cathode flow path 22 is connected to the

cathode electrode 12. The cathode flow path 22 feeds and

discharges the catholyte LC to and from the cathode electrode

12. A groove may be provided on a main surface facing the

cathode electrode 12 side in the plate member 16b, and this

grove may constitute the cathode flow path 22.

[0022] The anolyte LA is supplied to the anode electrode

10 by the anolyte supply device 4. The anolyte supply device

4 includes an anolyte tank 24, a first anode pipe 26, a

second anode pipe 28, and an anode pump 30. The anolyte LA

is stored in the anolyte tank 24. The anolyte LA contains

water to be supplied to the anode electrode 10. Examples of

the anolyte LA include an aqueous sulfuric acid solution, an

aqueous nitric acid solution, an aqueous hydrochloric acid

solution, pure water, and ion-exchanged water.

[0023] The anolyte tank 24 is connected to the anode

electrode 10 by the first anode pipe 26. One end of the

first anode pipe 26 is connected to the anolyte tank 24, and

the other end of the first anode pipe 26 is connected to the

anode flow path 20. The anode pump 30 is provided in the

middle of the first anode pipe 26. The anode pump 30 can be

constituted by a known pump such as a gear pump or a cylinder

pump, for example. Note that the anolyte supply device 4 may

circulate the anolyte LA using a liquid feeding device other

than the pump. The anolyte tank 24 is connected to the anode

electrode 10 by the second anode pipe 28. One end of the second anode pipe 28 is connected to the anode flow path 20, and the other end of the second anode pipe 28 is connected to the anolyte tank 24.

[0024] The anolyte LA in the anolyte tank 24 flows into

the anode electrode 10 through the first anode pipe 26 by

driving of the anode pump 30. The anolyte LA flowing into

the anode electrode 10 is subjected to an electrode reaction

in the anode electrode 10. The anolyte LA in the anode

electrode 10 is returned to the anolyte tank 24 through the

second anode pipe 28. As an example, the anolyte tank 24

also functions as a gas-liquid separator. In the anode

electrode 10, oxygen gas is generated by the electrode

reaction. Therefore, the oxygen gas is mixed into the

anolyte LA discharged from the anode electrode 10. The

anolyte tank 24 separates the oxygen gas in the anolyte LA

from the anolyte LA and discharges the oxygen gas to the

outside of the system.

[0025] In the anolyte supply device 4 according to the

present embodiment, the anolyte LA is circulated between the

anode electrode 10 and the anolyte tank 24. However, the

present invention is not limited to this configuration, and

the anolyte LA may be sent from the anode electrode 10 to the

outside of the system without being returned to the anolyte

tank 24.

[0026] The catholyte LC is supplied to the cathode

electrode 12 by the catholyte supply device 6. The catholyte supply device 6 includes a catholyte tank 32, a first cathode pipe 34, a second cathode pipe 36, a third cathode pipe 38, a cathode pump 40, and a separator 42. The catholyte LC is stored in the catholyte tank 32. The catholyte LC contains an organic hydride raw material (substance to be hydrogenated) to be supplied to the cathode electrode 12. As an example, the catholyte LC does not contain an organic hydride before the start of the operation of the organic hydride production system 1, and after the start of the operation, the organic hydride generated by electrolysis is mixed in, whereby the catholyte becomes the liquid mixture of the substance to be hydrogenated and the organic hydride.

The substance to be hydrogenated and the organic hydride are

preferably a liquid at 200C and 1 atm.

[0027] The substance to be hydrogenated and the organic

hydride are not particularly limited as long as they are

organic compounds capable of adding/desorbing hydrogen by

reversibly causing a hydrogenation reaction/dehydrogenation

reaction. As the substance to be hydrogenated and the

organic hydride used in the present embodiment, an acetone

isopropanol type, a benzoquinone-hydroquinone type, an

aromatic hydrocarbon type, and the like can be widely used.

Among these, the aromatic hydrocarbon type is preferable from

the viewpoint of transportability during energy transport or

the like. In general, aromatic hydrocarbon-based substances

to be hydrogenated and organic hydrides are hydrophobic.

[0028] An aromatic hydrocarbon compound used as the

substance to be hydrogenated is a compound containing at

least one aromatic ring. Examples of the aromatic

hydrocarbon compound include benzene, alkylbenzene,

naphthalene, alkylnaphthalene, anthracene, and

diphenylethane. The alkylbenzene contains a compound in

which 1 to 4 hydrogen atoms in the aromatic ring are

substituted with a linear alkyl group or a branched alkyl

group having 1 to 6 carbons. Examples of such a compound

include toluene, xylene, mesitylene, ethylbenzene, and

diethylbenzene. The alkylnaphthalene contains a compound in

which 1 to 4 hydrogen atoms in the aromatic ring are

substituted with a linear alkyl group or a branched alkyl

group having 1 to 6 carbons. Examples of such a compound

include methylnaphthalene. These compounds may be used alone

or in combination.

[0029] The substance to be hydrogenated is preferably at

least one of toluene and benzene. It is also possible to use

a nitrogen-containing heterocyclic aromatic compound such as

quinoline, isoquinoline, N-alkylpyrrole, N-alkylindole, or N

alkyldibenzopyrrole as the substance to be hydrogenated. The

organic hydride is obtained by hydrogenating the above

described substance to be hydrogenated, and examples thereof

include cyclohexane, methylcyclohexane, dimethylcyclohexane,

and decahydroquinoline.

[0030] The catholyte tank 32 is connected to the cathode electrode 12 by the first cathode pipe 34. One end of the first cathode pipe 34 is connected to the catholyte tank 32, and the other end of the first cathode pipe 34 is connected to the cathode flow path 22. The cathode pump 40 is provided in the middle of the first cathode pipe 34. The cathode pump

40 can by constituted by a known pump such as a gear pump or

a cylinder pump, for example. Note that the catholyte supply

device 6 may circulate the catholyte LC using a liquid

feeding device other than the pump.

[0031] The separator 42 is connected to the cathode

electrode 12 by the second cathode pipe 36. One end of the

second cathode pipe 36 is connected to the cathode flow path

22, and the other end of the second cathode pipe 36 is

connected to the separator 42. The separator 42 has a known

gas-liquid separator and a known oil-water separator. The

separator 42 is connected to the catholyte tank 32 by the

third cathode pipe 38. One end of the third cathode pipe 38

is connected to the separator 42, and the other end of the

third cathode pipe 38 is connected to the catholyte tank 32.

[0032] The catholyte LC in the catholyte tank 32 flows

into the cathode electrode 12 through the first cathode pipe

34 by driving of the cathode pump 40. The catholyte LC

flowing into the cathode electrode 12 is subjected to an

electrode reaction in the cathode electrode 12. The

catholyte LC in the cathode electrode 12 flows into the

separator 42 through the second cathode pipe 36. The hydrogen gas may be generated by the side reaction in the cathode electrode 12. Therefore, the hydrogen gas may be mixed in the catholyte LC discharged from the cathode electrode 12. The separator 42 separates the hydrogen gas in the catholyte LC from the catholyte LC and discharges the hydrogen gas to the outside of the system. In addition, water moves from the anode electrode 10 to the cathode electrode 12 together with protons. Therefore, the water may be mixed in the catholyte LC discharged from the cathode electrode 12. The separator 42 separates the water in the catholyte LC from the catholyte LC and discharges the water to the outside of the system. The catholyte LC from which the hydrogen gas and the water have been separated is returned to the catholyte tank 32 through the third cathode pipe 38.

[00331 In the catholyte supply device 6 according to the

present embodiment, the catholyte LC is circulated between

the cathode electrode 12 and the catholyte tank 32. However,

the present invention is not limited to this configuration,

and the catholyte LC may be sent to the outside of the system

from the cathode electrode 12 without being returned to the

catholyte tank 32.

[0034] A reaction that occurs in a case where toluene

(TL) is used as an example of the substance to be

hydrogenated in the apparatus 2 for producing an organic

hydride is as follows. The organic hydride obtained in a case where toluene is used as the substance to be hydrogenated is methylcyclohexane (MCH).

3H 2 0 - 3/202 + 6H+ + 6e

TL + 6H+ + 6e- - MCH

[00351 That is, the electrode reaction in the anode

electrode 10 and the electrode reaction in the cathode

electrode 12 proceed in parallel. The protons generated by

electrolysis of water at the anode electrode 10 pass through

the electrolyte membrane 14 together with water molecules and

move to the cathode electrode 12. Electrons generated by

electrolysis of water are supplied to the cathode electrode

12 via an external circuit. The protons and electrons

supplied to the cathode electrode 12 are used for the

hydrogenation of toluene in the cathode electrode 12. As a

result, methylcyclohexane is generated.

[00361 Therefore, according to the organic hydride

production system 1 according to the present embodiment, the

electrolysis of water and the hydrogenation reaction of the

substance to be hydrogenated can be performed in one step.

For this reason, organic hydride production efficiency can be

increased as compared with a conventional technique in which

the organic hydride is produced by a two-step process which

includes a process of producing hydrogen by water

electrolysis or the like and a process of chemically hydrogenating the substance to be hydrogenated in a reactor such as a plant. Furthermore, since the reactor for performing the chemical hydrogenation and a high-pressure vessel for storing the hydrogen produced by the water electrolysis or the like are not required, a significant reduction in facility cost can be achieved.

[0037] In the cathode electrode 12, the following

hydrogen gas generation reaction may occur as a side reaction

together with the hydrogenation reaction of the substance to

be hydrogenated which is the main reaction. As the supply

amount of the substance to be hydrogenated to the cathode

electrode 12 becomes insufficient, this side reaction is

likely to occur.

2H+ + 2e- - H2

[0038] The apparatus 2 for producing an organic hydride

is supplied with power from an external power supply (not

shown). When power is supplied from the power supply to the

apparatus 2 for producing an organic hydride, a predetermined

cell voltage is applied between the anode electrode 10 and

the cathode electrode 12 of the apparatus 2 for producing an

organic hydride, and an electrolytic current flows. The

power supply sends power supplied from a power supply device

to the apparatus 2 for producing an organic hydride. The

power supply device can be constituted by a power generation

device that generates power using renewable energy, for example, a wind power generation device, a solar power generation device, or the like. Note that the power supply device is not limited to the power generation device using renewable energy, and may be a system power supply, a storage device storing power from the power generation device using renewable energy or the system power supply, or the like. A combination of two or more of these devices may be used.

Further, the configuration of the organic hydride production

system 1 is not limited to those described above, and the

configuration of each part can be appropriately changed.

[00391 Next, a structure of the apparatus 2 for

producing an organic hydride will be described in detail.

Fig. 2 is a cross-sectional view of the apparatus 2 for

producing an organic hydride. The apparatus 2 for producing

an organic hydride according to the present embodiment

includes a low water content layer 44 and a high water

content layer 46 in addition to the above-described

configuration.

[0040] The electrolyte membrane 14 has an equivalent

weight (EW) of less than 980. EW is the dry mass of the

electrolyte per mol of sulfonic acid groups in the

electrolyte membrane 14. The lower the EW, the more

hydrophilic sulfonic acid groups the electrolyte membrane 14

has, and therefore the higher the water content. The EW of

the electrolyte membrane 14 is preferably 950 or less, more

preferably 900 or less, and even more preferably 870 or less.

For example, the electrolyte membrane 14 is formed of a

polymer having an EW of less than 980. Examples of the

polymer that can be used for the electrolyte membrane 14

include a perfluorosulfonic acid polymer and the like. By

lowering the EW of the electrolyte membrane 14 to less than

980, the water content of the electrolyte membrane 14 can be

increased compared to a case where the EW is 980 or more.

Thereby, the ion transfer resistance of the electrolyte

membrane 14 can be reduced. Therefore, the cell voltage in

the organic hydride production can be reduced.

[0041] Therefore, by increasing the water content of the

electrolyte membrane 14, the resistance of the electrolyte

membrane 14 is reduced, and the current density can be

increased while suppressing the increase in the cell voltage.

On the other hand, when the water content of the electrolyte

membrane 14 is increased, the affinity of the electrolyte

membrane 14 for the substance to be hydrogenated decreases.

For this reason, the hydrophobic substance to be hydrogenated

is less likely to be supplied to the reaction field. As a

result, side reactions are likely to occur due to

insufficient substance to be hydrogenated in the reaction

field. Therefore, the efficiency of the electrode reaction

at the cathode electrode 12, that is, the Faradaic

efficiency, can be reduced.

[0042] On the other hand, in the present embodiment, the

low water content layer 44 is arranged between the electrolyte membrane 14 and the cathode electrode 12. One main surface of the low water content layer 44 is in contact with the electrolyte membrane 14, and the other main surface of the low water content layer 44 is in contact with the catalyst layer 12a. The low water content layer 44 has a lower water content (higher EW) than that of the electrolyte membrane 14 when the low water content layer 44 has ion exchange ability and is therefore more hydrophobic than the electrolyte membrane 14. For example, the low water content layer 44 is formed of a polymer (for example, ionomer) having a lower water content than that of the polymer constituting the electrolyte membrane 14. The water content (%) in the present embodiment is defined by the following equation (1).

The expression "polymer in hydrous state" in equation (1)

means, for example, a polymer after immersion in pure water

for one hour.

(1) water content = (weight of water contained in

polymer / weight of polymer in hydrous state) x 100

[0043] The method for forming the low water content

layer 44 is not particularly limited, and a known method can

be employed. For example, a method may be employed where a

polymer constituting the low water content layer 44 is

applied to the surface of the electrolyte membrane 14 or the

surface of the cathode electrode 12 or where a thin film of

the polymer is pressed on the surface of the electrolyte

membrane 14 or the surface of the cathode electrode 12.

[0044] Examples of the polymer that can be used for the

low water content layer 44 include Nafion (registered

trademark), Fumion (registered trademark), and the like. The

low water content layer 44 may or may not function as an ion

exchange membrane. By making the water content of the low

water content layer 44 lower than the water content of the

electrolyte membrane 14, it is possible to make it easier for

the substance to be hydrogenated to reach the reaction field.

Thereby, the shortage of the substance to be hydrogenated can

be avoided, and the occurrence of side reactions can be

suppressed.

[0045] That is, the combination of setting the EW of the

electrolyte membrane 14 to less than 980 and installing the

low water content layer 44 between the electrolyte membrane

14 and the cathode electrode 12 allows for both the

suppression of the increase in the cell voltage in the

organic hydride production and the suppression of the

decrease in Faradaic efficiency. Further, since the current

density can be easily increased, the production efficiency

per unit time of the organic hydride can be improved.

Further, the miniaturization and the like of the apparatus 2

for producing an organic hydride can be realized, and the

cost of members for the apparatus 2 for producing an organic

hydride can be thereby reduced. Further, by suppressing the

increase in the cell voltage, the cost of measures against

heat generation required for the apparatus 2 for producing an organic hydride can be reduced.

[0046] In the present embodiment, the high water content

layer 46 is arranged between the electrolyte membrane 14 and

the anode electrode 10. One main surface of the high water

content layer 46 is in contact with the electrolyte membrane

14, and the other main surface of the high water content

layer 46 is in contact with the anode electrode 10. The high

water content layer 46 has a higher water content (lower EW)

than that of the electrolyte membrane 14 and is therefore

more hydrophilic than the electrolyte membrane 14. For

example, the high water content layer 46 is formed of a

polymer having a higher water content than that of the

polymer constituting the electrolyte membrane 14. The method

for forming the high water content layer 46 is not

particularly limited, and a known method can be employed.

For example, a method may be employed where a polymer

constituting the high water content layer 46 is applied to

the surface of the electrolyte membrane 14 or the surface of

the anode electrode 10 or where a thin film of the polymer is

pressed on the surface of the electrolyte membrane 14 or the

surface of the anode electrode 10.

[0047] Examples of the polymer that can be used for the

high water content layer 46 include Aquivion (registered

trademark), Fumion (registered trademark), and the like,

which have a higher water content than that of the

electrolyte membrane 14. By interposing the high water content layer 46 between the electrolyte membrane 14 and the anode electrode 10, the access of water in the anode catalyst is improved, and the increase in the cell voltage and the decrease in the Faradaic efficiency can be further suppressed. Note that the high water content layer 46 may be omitted. In this case, the electrolyte membrane 14 and the anode electrode 10 are in contact with each other.

[0048] (Exemplary Variations)

The apparatus 2 for producing an organic hydride

according to the above-described embodiment can include the

following exemplary variations. That is, the cathode

electrode 12 may contain an ionomer having a lower water

content than that of the electrolyte membrane 14. Examples

of such a low water content ionomer include Nafion

(registered trademark) and the like. By adding a low water

content ionomer to the cathode electrode 12, the substance to

be hydrogenated can easily reach the reaction field in the

same manner as in the case when the low water content layer

44 is installed, and the occurrence of side reactions can be

thus suppressed. Therefore, the same effect as that of the

low water content layer 44 can be achieved.

[0049] The addition of a low water content ionomer to

the cathode electrode 12 may be performed instead of the

installation of the low water content layer 44, or may be

performed along with the installation of the low water

content layer 44. That is, the apparatus 2 for producing an organic hydride only needs to include at least one of the low water content layer 44 and the low water content ionomer contained in the cathode electrode 12. When the apparatus 2 for producing an organic hydride does not include the low water content layer 44, the electrolyte membrane 14 and the cathode electrode 12 are in contact with each other.

[00501 Further, a water-repellent layer (hydrophobic

layer) may be provided between the low water content layer 44

and the cathode catalyst layer 12a. Examples of such a

water-repellent layer include a layer made of a material in

which a water-repellent fluororesin such as a copolymer of

tetrafluoroethylene and hexafluoropropylene (FEP) is added to

ketjen black. The water-repellent layer can be formed by a

known method, for example, by applying a dispersion liquid of

the material to the surface of the catalyst layer 12a. This

allows the substance to be hydrogenated to reach the reaction

field more easily, and the Faradaic efficiency can be

improved.

[0051] The embodiments may be defined by the items

described in the following.

[Item 1]

An apparatus (2) for producing an organic hydride

including:

an anode electrode (10) that generates protons by

oxidizing water;

a cathode electrode (12) that generates an organic hydride by hydrogenating a substance to be hydrogenated with the protons; an electrolyte membrane (14) that has an equivalent weight (EW) of less than 980 and is arranged between the anode electrode (10) and the cathode electrode (12) so as to transfer the protons from the anode electrode (10) side to the cathode electrode (12) side; and a low water content layer (44) that is arranged between the electrolyte membrane (14) and the cathode electrode (12) and that has a lower water content than that of the electrolyte membrane (14).

[Item 2]

The apparatus (2) for producing an organic hydride

according to Item 1, including:

a high water content layer (46) that is arranged

between the electrolyte membrane (14) and the anode electrode

(10) and that has a higher water content than that of the

electrolyte membrane (14).

Exemplary Embodiments

[0052] Hereinafter, exemplary embodiments of the present

invention will be explained. However, these exemplary

embodiments are merely examples for suitably explaining the

present invention and do not limit the present invention in

any way.

(First Exemplary Embodiment)

[0053] As the electrolyte membrane, a polyfluorosulfonic acid cation exchange membrane (Aquivion (registered trademark) E87-05S, manufactured by Solvay) was prepared.

The EW of this electrolyte membrane is 870, and the film

thickness is 50 pm.

[0054] The water content of the electrolyte membrane was

measured by the following procedure. That is, the

electrolyte membrane cut out into 2 cm squares was dried in a

dryer for 24 hours. The weight of the electrolyte membrane

was measured after the drying. Subsequently, the dried

electrolyte membrane was immersed in pure water for one hour.

Then, the water attached to the surface of the electrolyte

membrane was wiped off, and the weight of the electrolyte

membrane containing water was measured. The weight of the

water contained in the electrolyte membrane was obtained from

the difference between the weight of the electrolyte membrane

after the drying and the weight of the electrolyte membrane

containing the water. Then, the water content (%) of the

electrolyte membrane was calculated based on the following

equation (2).

(2) water content = (weight of water contained in

electrolyte membrane / weight of electrolyte membrane in

hydrous state) x 100

[0055] A polyfluorosulfonic acid cation-exchange ionomer

(Nafion (registered trademark) D2020CS, EW: 1100,

manufactured by DuPont) was applied to one surface of the

electrolyte membrane so as to form a low water content layer.

The thickness of the low water content layer was 10 pm.

[00561 The water content of the low water content layer

was measured by the following procedure. That is, the weight

of a 12 cm square aluminum foil was measured, and the weight

per 2 cm square of aluminum foil was calculated. An ionomer

was spray-applied to this aluminum foil such that the

aluminum foil was laminated with a low water content layer

having a thickness of 10 pm. An aluminum foil with a low

water content layer cut out into 2 cm squares (hereinafter

referred to as laminated aluminum foil) was dried in a dryer

for 24 hours. The weight of the laminated aluminum foil was

measured after the drying. Subsequently, the dried laminated

aluminum foil was immersed in pure water for one hour. Then,

the water attached to the surface of the laminated aluminum

foil was wiped off, and the weight of the laminated aluminum

foil containing water in the low moisture content layer was

measured. The weight of the water contained in the low water

content layer was obtained from the difference between the

weight of the laminated aluminum foil after the drying and

the weight of the laminated aluminum foil containing the

water. Further, the weight of the low water content layer in

a hydrous state was obtained from the difference between the

weight of the laminated aluminum foil containing water and

the weight per 2 cm square of the aluminum foil. Then, the

water content (%) of the low water content layer was

calculated based on the following equation (3).

(3) water content = (weight of water contained in low

water content layer / weight of low water content layer in

hydrous state) x 100

[0057] A cathode catalyst ink was prepared by mixing a

PtRu/C catalyst (TEC61E54, manufactured by TANAKA PRECIOUS

METAL TECHNOLOGIES Co., Ltd.), a polyfluorosulfonic acid

cation exchange ionomer (Nafion (registered trademark)

D2020CS, EW: 1100, manufactured by DuPont), pure water, and

1-propanol (manufactured by Wako). The catalyst loading

density of the catalyst ink was 1 mg/cm 2 , and the

ionomer/carbon ratio (I/C) was 0.5. The prepared cathode

catalyst ink was applied to the surface of the low water

content layer so as to form a cathode catalyst layer.

[0058] As the anode electrode, a dimensionally stable

electrode (DSE) (manufactured by De Nora Permelec Ltd.)

coated with IrO2 on a Ti substrate was prepared. Then, this

DSE electrode was stacked on the other surface of the

electrolyte membrane. Thereby, the electrolytic cell

(apparatus for producing an organic hydride) according to the

first exemplary embodiment was obtained.

[0059] Toluene serving as a cathode liquid was

circulated to the cathode of the obtained apparatus for

producing an organic hydride at a flow rate of 20 mL/min.

Further, a 1 mol/L sulfuric acid aqueous solution serving as

an anode liquid was circulated on the anode side at a flow

rate of 60 mL/min. Then, constant-current electrolysis was performed at a temperature of 600C and a current density of 1

A/cm 2 . In addition, the voltage at the time of the constant

current electrolysis was measured. Then, the amount of

change in voltage with respect to the voltage in the second

comparative example described later was calculated. Further,

the Faradaic efficiency was calculated from the amount of

electricity consumed by the constant-current electrolysis and

the amount of organic hydride generated. Then, the

improvement rate (%) of the Faradaic efficiency with respect

to the Faradaic efficiency in the second comparative example

described later was calculated based on the following

equation (4).

(4) improvement rate = [1 - (100 - Faradaic efficiency

in exemplary embodiment) / (100 - Faradaic efficiency in

second comparative example)] x 100

(Second Exemplary Embodiment)

[00601 An electrolysis cell was prepared, constant

current electrolysis was performed, and the voltage change

amount and the improvement rate were calculated in the same

manner as in the first exemplary embodiment, except that a

low water content layer was formed by pressing a thin film of

ionomer onto the electrolyte membrane instead of applying an

ionomer.

(Third Exemplary Embodiment)

[0061] An electrolysis cell was prepared, constant

current electrolysis was performed, and the voltage change amount and the improvement rate were calculated in the same manner as in the first exemplary embodiment, except that

Fumion (registered trademark) FSLA-1020 (EW: 960-1000,

manufactured by FUMATECH) was used as the polyfluorosulfonic

acid-based cation exchange ionomer instead of Nafion

(registered trademark) D2020CS.

(Fourth Exemplary Embodiment)

[0062] An electrolysis cell was prepared, constant

current electrolysis was performed, and the voltage change

amount and the improvement rate were calculated in the same

manner as in the first exemplary embodiment, except that a

high water content layer was provided between the electrolyte

membrane and the anode electrode. The high water content

layer was formed by applying a polyfluorosulfonic acid

cation-exchange ionomer (Fumion (registered trademark) FSLA

710, EW: 710-740, manufactured by FUMATECH) to the other

surface of the electrolyte membrane. The thickness of the

high water content layer was 10 pm. Further, the water

content of the high water content layer was measured in the

same procedure as that in the case of the low water content

layer.

(Fifth Exemplary Embodiment)

[0063] An electrolysis cell was prepared, constant

current electrolysis was performed, and the voltage change

amount and the improvement rate were calculated in the same

manner as in the first exemplary embodiment, except that a water-repellent layer was provided between the low water content layer and the cathode catalyst layer. The water repellent layer was formed by applying a Nafion (registered trademark) dispersion liquid to which Ketjen Black (EC600JD, manufactured by Lion Corporation) containing FEP (120-JRB, manufactured by Chemours-Mitsui Fluoroproducts Co.,Ltd.) was added to the surface of the low water content layer facing opposite to the electrolyte membrane. The thickness of the water-repellent layer was 10 pm, and the I/C was 0.5.

(First Comparative Example)

[0064] An electrolysis cell was prepared, constant

current electrolysis was performed, and the improvement rate

was calculated in the same manner as in the first exemplary

embodiment, except that Aquivion (registered trademark) E98

05S was used as the electrolyte membrane instead of Aquivion

(registered trademark) E87-05S and that no low water content

layer was provided. The EW of this electrolyte membrane is

980.

(Second Comparative Example)

[0065] An electrolysis cell was prepared, constant

current electrolysis was performed, and the voltage and the

Faradaic efficiency were calculated in the same manner as in

the first exemplary embodiment, except that no low water

content layer was provided.

[0066] Fig. 3 is a diagram showing the characteristics

of respective electrolytic cells according to exemplary embodiments and comparative examples, the improvement rate of the Faradaic efficiency, and the amount of change in voltage.

As shown in Fig. 3, compared to the second comparative

example where the electrolyte membrane had an EW of less than

980 but did not have a low water content layer, the Faradaic

efficiency was improved by 20% or more in the first to fifth

exemplary embodiments where the electrolyte membrane had an

EW of less than 980 and had a low water content layer.

Further, the improvement rate was higher than that in the

first comparative example where the EW of the electrolyte

membrane was 980. Further, the Faradaic efficiency was

further improved in the fifth exemplary embodiment with a

water-repellent layer compared to the first to fourth

exemplary embodiments without a water-repellent layer.

Further, the increase in voltage with respect to that in the

second comparative example was able to be suppressed to 25 mV

or less in the first to fifth exemplary embodiments. The

voltage was able to be further reduced in the fourth

exemplary embodiment with a high water content layer.

[0067] From the above, it has been confirmed that by

using an electrolyte membrane having an EW of less than 980

and providing a low water content layer between the

electrolyte membrane and the cathode electrode, it is

possible to suppress both the increase in cell voltage and

the decrease in the Faradaic efficiency in the production of

organic hydrides. Further, it has been confirmed that the cell voltage can be further reduced by providing a high water content layer between the electrolyte membrane and the anode electrode. Also, it has been confirmed that the Faradaic efficiency can be further improved by providing a water repellent layer between the low water content layer and the cathode electrode.

INDUSTRIAL APPLICABILITY

[00681 The present invention can be used in an apparatus

for producing an organic hydride.

REFERENCE SIGNS LIST

[00691 2 apparatus for producing an organic hydride, 10

anode electrode, 12 cathode electrode, 14 electrolyte

membrane, 44 low water content layer, 46 high water content

layer

Claims

[Claim 1]

An apparatus for producing an organic hydride

comprising:

an anode electrode that generates protons by oxidizing

water;

a cathode electrode that generates an organic hydride

by hydrogenating a substance to be hydrogenated with the

protons;

an electrolyte membrane that has an equivalent weight

(EW) of less than 980 and is arranged between the anode

electrode and the cathode electrode so as to transfer the

protons from the anode electrode side to the cathode

electrode side; and

a low water content layer that is arranged between the

electrolyte membrane and the cathode electrode and that has a

lower water content than that of the electrolyte membrane.
[Claim 2]

The apparatus for producing an organic hydride

according to Claim 1, comprising:

a high water content layer that is arranged between the

electrolyte membrane and the anode electrode and that has a

higher water content than that of the electrolyte membrane.