JP7540645B2 - Organic hydride production apparatus and method for producing membrane electrode assembly - Google Patents

Description

Article 30, paragraph 2 of the Patent Act applies. Abstracts of the 87th Annual Meeting of the Electrochemical Society, 2020, https://confit.atlas.jp/guide/event/ecsj2020s/proceedings/list (publication address), March 10, 2020 (publication date) [Publications, etc.] Web Discussion Meeting of the 87th Annual Meeting of the Electrochemical Society, 2020 (meeting name), March 17-19, 2020 (held date)

The present invention relates to an organic hydride production apparatus and a method for producing a membrane electrode assembly.

In recent years, the use of renewable energy sources such as solar, wind, hydroelectric, and geothermal power has been expected to reduce carbon dioxide emissions during the energy generation process. As an example, a system has been devised that produces hydrogen by electrolyzing water using electricity derived from renewable energy. In addition, organic hydride systems have attracted attention as an energy carrier for the large-scale transport and storage of hydrogen derived from renewable energy.

Regarding organic hydride production technology, a conventional organic hydride production apparatus is known that includes an oxidizing electrode that generates protons from water and a reducing electrode that hydrogenates an organic compound having an unsaturated bond (see, for example, Patent Document 1). In this organic hydride production apparatus, water is supplied to the oxidizing electrode, and a substance to be hydrogenated is supplied to the reducing electrode while a current is passed between the oxidizing electrode and the reducing electrode, whereby hydrogen is added to the substance to be hydrogenated, producing an organic hydride.

International Publication No. 2012/091128

As a result of extensive research into the above-mentioned organic hydride manufacturing technology, the inventors have come to realize that there is room for improvement in the current efficiency of organic hydride manufacturing devices in conventional technology.

The present invention was made in consideration of these circumstances, and its purpose is to provide a technology that improves the current efficiency of an organic hydride production device.

One aspect of the present invention is an organic hydride manufacturing apparatus. This apparatus includes an electrolyte membrane having a first surface and a second surface facing each other and for transferring protons, a cathode provided on the first surface side of the electrolyte membrane, and an anode provided on the second surface side of the electrolyte membrane. The cathode has a cathode catalyst layer that hydrogenates a substance to be hydrided with protons to produce an organic hydride. The anode oxidizes water to produce protons. The cathode catalyst layer has a plurality of protrusions that protrude in the stacking direction of the electrolyte membrane and the cathode. The plurality of protrusions are distributed in the in-plane direction of the first surface, either independently of each other or connected to each other at their bases.

Another aspect of the present invention is a method for manufacturing a membrane electrode assembly for use in an organic hydride manufacturing apparatus. The membrane electrode assembly has an electrolyte membrane and a cathode, and the cathode has a cathode catalyst layer. This manufacturing method includes forming a cathode catalyst layer having a plurality of protrusions by pressing a dot layer in which catalyst ink constituting the cathode catalyst layer is dispersed and a continuous layer in which the catalyst ink is continuous. The plurality of protrusions protrude in the stacking direction of the electrolyte membrane and the cathode, and are connected to each other at their bases and dispersed in the in-plane direction of the electrolyte membrane.

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

The present invention can improve the current efficiency of an organic hydride production device.

1 is a cross-sectional view of an organic hydride manufacturing apparatus according to an embodiment. 2A and 2B are enlarged cross-sectional views showing a part of the organic hydride manufacturing apparatus. 5A to 5C are diagrams illustrating a method for forming a cathode catalyst layer. 4(A) to 4(C) are schematic diagrams of masks used in forming the cathode catalyst layer. 5A to 5C are schematic diagrams for explaining the function of a plurality of protrusions. FIG. 13 is a diagram showing the relationship between cell voltage (U _{iR free} ) and current density (i), and the relationship between internal resistance (R) and current density (i). 7A and 7B are diagrams showing the polarization curves of an anode and a cathode, respectively. FIG. 1 is a graph showing the relationship between current density (i) and current efficiency (ε). FIG. 13 is a diagram showing the relationship between cell voltage (U _{iR free} ) and current density (i), and the relationship between internal resistance (R) and current density (i). 10A and 10B are diagrams showing the polarization curves of an anode and a cathode, respectively. FIG. 1 is a graph showing the relationship between current density (i) and current efficiency (ε). FIG. 13 is a graph showing the relationship between the dot layer ratio (rdot) and the current density (i) (solid line) when the current efficiency is constant, and the relationship between the dot layer ratio (rdot) and the cathode potential (E) (dashed line).

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 invention, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention. The same or equivalent components, members, and processes shown in each drawing are given the same reference numerals, and duplicated descriptions are omitted as appropriate. The scale and shape of each part shown in each drawing are set for convenience to facilitate explanation, and are not to be interpreted as being limiting unless otherwise specified. In addition, 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 intended to distinguish one configuration from another. In addition, some of the members that are not important for explaining the embodiment are omitted in each drawing.

Figure 1 is a cross-sectional view of an organic hydride manufacturing apparatus according to an embodiment. In Figure 1, the shape of each part is illustrated in a simplified form. The organic hydride manufacturing apparatus 1 is an electrolysis cell that hydrogenates a substance to be hydrogenated by an electrochemical reduction reaction, and mainly comprises an electrolyte membrane 2, a cathode 4, an anode 6, and a pair of end plates 8. The electrolyte membrane 2, the cathode 4, the anode 6, and the pair of end plates 8 are each approximately flat or thin-film shaped.

The electrolyte membrane 2 is disposed between the cathode 4 and the anode 6, and is a membrane that transfers protons from the anode 6 side to the cathode 4 side. The electrolyte membrane 2 has a first surface 2a and a second surface 2b that face each other, with the first surface 2a facing the cathode 4 and the second surface 2b facing the anode 6. The electrolyte membrane 2 is, for example, composed of a solid polymer electrolyte membrane having proton conductivity. The solid polymer electrolyte membrane is not particularly limited as long as it is a material that conducts protons, and examples of the solid polymer electrolyte membrane include fluorine-based ion exchange membranes having sulfonic acid groups, such as Nafion (registered trademark).

The electrolyte membrane 2 selectively conducts protons while suppressing the mixing and diffusion of substances between the cathode 4 and the anode 6. The thickness of the electrolyte membrane 2 is not particularly limited, but is, for example, 5 to 300 μm. By making the thickness of the electrolyte membrane 2 5 μm or more, the desired strength of the electrolyte membrane 2 can be obtained more reliably. In addition, by making the thickness of the electrolyte membrane 2 300 μm or less, excessive ion migration resistance can be suppressed.

The cathode 4 is provided on the first surface 2a side of the electrolyte membrane 2. The cathode 4 has a cathode catalyst layer 10 and a cathode diffusion layer 12. The cathode catalyst layer 10 is disposed closer to the electrolyte membrane 2 than the cathode diffusion layer 12. In this embodiment, the cathode catalyst layer 10 is in contact with the first surface 2a of the electrolyte membrane 2. In order to increase the strength of the electrolyte membrane 2, the electrolyte membrane 2 may contain a reinforcing material. By adding a reinforcing material, it is possible to suppress swelling of the electrolyte and suppress a decrease in the strength of the electrolyte membrane 2.

The cathode catalyst layer 10 is a layer that hydrogenates the substance to be hydrogenated with protons to generate an organic hydride. The cathode catalyst layer 10 has a cathode catalyst such as platinum (Pt) or ruthenium (Ru). The cathode catalyst layer 10 also has a catalyst carrier that supports the cathode catalyst. The catalyst carrier is made of an electron-conductive material such as porous carbon, porous metal, or porous metal oxide. The thickness of the cathode catalyst layer 10 is not particularly limited, but is, for example, 20 to 50 μm. By making the thickness of the cathode catalyst layer 10 20 μm or more, the amount of catalyst required for the electrolytic reaction can be more reliably obtained. In addition, by making the thickness of the cathode catalyst layer 10 50 μm or less, excessive reduction in the diffusibility of the substance to be hydrogenated can be suppressed.

The cathode diffusion layer 12 is a layer that uniformly diffuses the liquid material to be hydrogenated, which is supplied from the outside, into the cathode catalyst layer 10. The organic hydride generated in the cathode catalyst layer 10 is discharged to the outside of the cathode catalyst layer 10 through the cathode diffusion layer 12. In this embodiment, the cathode diffusion layer 12 is in contact with the main surface of the cathode catalyst layer 10 on the side opposite the electrolyte membrane 2.

The cathode diffusion layer 12 is made of a conductive material such as carbon or metal. The cathode diffusion layer 12 is a porous body such as a sintered body of fibers or particles, or a foam molded body. Specific examples of materials constituting the cathode diffusion layer 12 include woven carbon fabric (carbon cloth), nonwoven carbon fabric, and carbon paper. The thickness of the cathode diffusion layer 12 is not particularly limited, but is, for example, 200 to 700 μm. By making the thickness of the cathode diffusion layer 12 200 μm or more, the diffusivity of the material to be hydrided can be more reliably increased. Furthermore, by making the thickness of the cathode diffusion layer 12 700 μm or less, excessive electrical resistance can be suppressed.

The anode 6 is provided on the second surface 2b of the electrolyte membrane 2. In this embodiment, the anode 6 is in contact with the second surface 2b of the electrolyte membrane 2. The anode 6 has an anode catalyst, such as iridium (Ir), ruthenium (Ru), platinum, or an oxide of these metals, and oxidizes water to generate protons. The anode catalyst may be dispersed or coated on a substrate having electronic conductivity. The substrate is composed of a material mainly composed of a metal, such as titanium (Ti) or stainless steel (SUS). Examples of the form of the substrate include a woven or nonwoven sheet (fiber diameter: for example, 10 to 30 μm), a mesh (diameter: for example, 500 to 1000 μm), a porous sintered body, a foamed molded body (foam), and an expanded metal.

When the anode 6 has a structure in which the anode catalyst is dispersed or coated on the substrate, the thickness of the anode 6 including the anode catalyst and substrate is, for example, 0.05 to 1 mm, but is not particularly limited. By making the thickness of the anode 6 0.05 mm or more, the amount of catalyst required for the electrolytic reaction can be obtained more reliably. In addition, by making the thickness of the anode 6 1 mm or less, excessive reduction in the diffusivity of the substance to be hydrided can be suppressed.

When the anode catalyst is coated on the substrate to form a layer, the thickness of the layer is not particularly limited, but is, for example, 0.1 to 50 μm. The anode 6 may also be formed of a layer formed by directly coating the anode catalyst on the main surface of the electrolyte membrane 2. In this case, the thickness of the layer constituting the anode 6 is not particularly limited, but is, for example, 0.1 to 50 μm. By making these layers 0.1 μm or more thick, the amount of catalyst required for the electrolytic reaction can be obtained more reliably. Furthermore, by making these layers 50 μm or less thick, excessive reduction in the diffusivity of the substance to be hydrided can be suppressed.

The pair of end plates 8 are made of a metal such as stainless steel or titanium. The thickness of each end plate 8 is not particularly limited, but is, for example, 1 to 30 mm. By making the thickness of the end plate 8 1 mm or more, it is possible to avoid significant impairment of workability. In addition, by making the thickness of the end plate 8 30 mm or less, it is possible to suppress increases in costs.

One end plate 8a is installed on the opposite side of the cathode 4 from the electrolyte membrane 2. In this embodiment, the end plate 8a is in contact with the main surface of the cathode diffusion layer 12. The organic hydride manufacturing apparatus 1 has a frame-shaped spacer 14 arranged between the electrolyte membrane 2 and the end plate 8a. The end plate 8a, the electrolyte membrane 2, and the spacer 14 define a cathode chamber in which the cathode 4 is housed. The spacer 14 also serves as a sealant that prevents the cathode fluid from leaking out of the cathode chamber.

The cathode fluid is a mixture of the material to be hydrogenated and organic hydride that is supplied to the cathode chamber. The material to be hydrogenated is a compound that is hydrogenated to become an organic hydride by an electrochemical reduction reaction in the organic hydride production apparatus 1, in other words, a dehydrogenated form of an organic hydride. The material to be hydrogenated is preferably liquid at 20°C and 1 atmosphere. As an example, the cathode fluid does not contain organic hydride before the organic hydride production apparatus 1 starts operating, and becomes a mixture of the material to be hydrogenated and organic hydride by mixing with the organic hydride generated by electrolysis after the operation starts.

The substance to be hydrogenated and the organic hydride used in this embodiment are not particularly limited as long as they are organic compounds that can add/desorb hydrogen by reversibly causing hydrogenation/dehydrogenation reactions, and a wide range of compounds such as acetone-isopropanol, benzoquinone-hydroquinone, and aromatic hydrocarbons can be used. 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, and examples thereof include benzene, alkylbenzene, naphthalene, alkylnaphthalene, anthracene, diphenylethane, and the like. Alkylbenzene includes compounds in which 1 to 4 hydrogen atoms in the aromatic ring are substituted with linear or branched alkyl groups 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 in the aromatic ring are substituted with linear or branched alkyl groups 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 of toluene and benzene. Nitrogen-containing heterocyclic aromatic compounds such as pyridine, pyrimidine, pyrazine, 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 piperidine.

The end plate 8a has a supply flow path 16 and a discharge flow path 18 on the main surface facing the cathode diffusion layer 12. In this embodiment, the supply flow path 16 and the discharge flow path 18 are formed by grooves provided on the main surface of the end plate 8a. The supply flow path 16 is in contact with one end side of the cathode diffusion layer 12 in the in-plane direction, and the cathode fluid supplied to the cathode 4 flows inside the supply flow path 16. The discharge flow path 18 is in contact with the other end side of the cathode diffusion layer 12 in the in-plane direction, and the cathode fluid discharged from the cathode 4 flows inside the discharge flow path 18. The in-plane direction of the cathode diffusion layer 12 is the direction in which a plane perpendicular to the stacking direction of the electrolyte membrane 2 and the cathode 4 extends.

In this embodiment, the supply flow passage 16 contacts the lower end of the cathode diffusion layer 12 in the vertical direction, and the discharge flow passage 18 contacts the upper end of the cathode diffusion layer 12. Each flow passage extends horizontally. A groove-shaped flow passage that connects the supply flow passage 16 and the discharge flow passage 18 may be provided on the surface of the end plate 8a. This can prevent the drift of the substance to be hydrogenated in the cathode chamber and the pressure loss caused when the cathode liquid passes through the cathode chamber from becoming excessive. The extension direction and shape of the supply flow passage 16, the discharge flow passage 18, and the flow passage connecting both flow passages are not limited to those described above and can be set appropriately by the implementer.

A cathode fluid storage tank (not shown) is connected to the supply flow path 16. The cathode fluid storage tank contains the cathode fluid. Between the supply flow path 16 and the cathode fluid storage tank, a cathode fluid supply device (not shown) consisting of various pumps such as gear pumps and cylinder pumps, or a gravity flow device is provided. The cathode fluid contained in the cathode fluid storage tank is sent to the supply flow path 16 by the cathode fluid supply device and supplied to the cathode catalyst layer 10 via the cathode diffusion layer 12. The discharge flow path 18 is connected to the cathode fluid storage tank as an example. The cathode fluid containing the organic hydride generated in the cathode catalyst layer 10 and the unreacted hydrogenated material is returned to the cathode fluid storage tank via the discharge flow path 18.

The other end plate 8b is placed on the opposite side of the anode 6 from the electrolyte membrane 2. The organic hydride manufacturing apparatus 1 has a frame-shaped spacer 20 placed between the electrolyte membrane 2 and the end plate 8b. The end plate 8b, the electrolyte membrane 2, and the spacer 20 define an anode chamber in which the anode 6 is housed. The spacer 20 also serves as a sealant that prevents the anode fluid from leaking out of the anode chamber. The anode fluid is a liquid that contains water and is supplied to the anode chamber. Examples of the anode fluid include an aqueous sulfuric acid solution, an aqueous nitric acid solution, an aqueous hydrochloric acid solution, pure water, and ion-exchanged water.

The end plate 8b has a supply flow path 22, a discharge flow path 24, and a connecting flow path 26 on the main surface facing the anode 6. In this embodiment, the supply flow path 22, the discharge flow path 24, and the connecting flow path 26 are formed by grooves provided on the main surface of the end plate 8b. The supply flow path 22 is in contact with one end side of the anode 6 in the in-plane direction, and the anode fluid supplied to the anode 6 flows inside the supply flow path 22. The discharge flow path 24 is in contact with the other end side of the anode 6 in the in-plane direction, and the anode fluid discharged from the anode 6 flows inside the discharge flow path 24. One end of the connecting flow path 26 is connected to the supply flow path 22, and the other end is connected to the discharge flow path 24.

In this embodiment, the supply flow path 22 contacts the lower end of the anode 6 in the vertical direction, and the discharge flow path 24 contacts the upper end of the anode 6. The supply flow path 22 and the discharge flow path 24 extend in the horizontal direction, and the connecting flow path 26 extends in the vertical direction. In addition, a plurality of connecting flow paths 26 are provided on the end plate 8b, and each connecting flow path 26 is arranged at a predetermined interval in the horizontal direction. The extension direction and shape of the supply flow path 22, discharge flow path 24, and connecting flow path 26 are not limited to those described above, and can be set appropriately by the implementer.

The anode chamber may contain an electronically conductive buffer material disposed between the anode 6 and the end plate 8b to press the anode 6 against the electrolyte membrane 2. The buffer material can reduce the contact resistance between the electrolyte membrane 2 and the anode 6. The buffer material may be pressed against the anode 6 by a biasing member such as a spring. The buffer material may also be composed of a flow path block having slits that form the supply flow path 22, the discharge flow path 24, and the connecting flow path 26. In this case, the end plate 8b may be composed of a flat plate that does not have the grooves that form each flow path.

An anode fluid storage tank (not shown) is connected to the supply flow path 22. The anode fluid storage tank contains anode fluid. Between the supply flow path 22 and the anode fluid storage tank, an anode fluid supply device (not shown) is provided, which is composed of various pumps such as gear pumps and cylinder pumps, or a gravity flow device. The anode fluid contained in the anode fluid storage tank is sent to the supply flow path 22 by the anode fluid supply device, and a portion of the anode fluid is supplied to the anode 6 directly and another portion is supplied via the connecting flow path 26. The discharge flow path 24 is connected to the anode fluid storage tank, as an example. The anode fluid supplied to the anode 6 is returned to the anode fluid storage tank via the discharge flow path 24.

A control unit (not shown) may be connected to the organic hydride manufacturing apparatus 1. The control unit controls the cell voltage (electrolysis voltage) of the organic hydride manufacturing apparatus 1 or the current flowing through the organic hydride manufacturing apparatus 1. The control unit is realized as a hardware configuration by elements and circuits including a computer CPU and memory, and as a software configuration by a computer program, etc.

A signal indicating the potential of each electrode or the cell voltage of the organic hydride manufacturing apparatus 1 is input to the control unit from a potential detection unit (not shown) provided in the organic hydride manufacturing apparatus 1. The potential of each electrode and the cell voltage of the organic hydride manufacturing apparatus 1 can be detected by a known method. As an example, a reference electrode is provided on the electrolyte membrane 2. The reference electrode is held at a reference electrode potential. For example, the reference electrode is a reversible hydrogen electrode (RHE). The potential detection unit detects the potential of each electrode relative to the reference electrode and transmits the detection result to the control unit. The potential detection unit is composed of, for example, a known voltmeter.

The control unit controls the output of the power supply and the driving of the cathode fluid supply device and the anode fluid supply device during operation of the organic hydride manufacturing apparatus 1 based on the detection result of the potential detection unit. The power source of the organic hydride manufacturing apparatus 1 is preferably renewable energy obtained from solar, wind, hydroelectric, geothermal power generation, etc., but is not limited to these.

The reaction that occurs when toluene (TL) is used as an example of the substance to be hydrogenated in the organic hydride production apparatus 1 is as follows: When toluene is used as the substance to be hydrogenated, the resulting organic hydride is methylcyclohexane (MCH).
<Electrode reaction at the anode>
3H ₂ O → 3/2O ₂ +6H ⁺ +6e ^-
<Electrode reaction at the cathode>
TL+6H ⁺ +6e ^- →MCH

That is, the electrode reaction at the cathode catalyst layer 10 and the electrode reaction at the anode 6 proceed in parallel. Protons generated by the electrolysis of water at the anode 6 are supplied to the cathode catalyst layer 10 via the electrolyte membrane 2. Electrons generated by the electrolysis of water are supplied to the cathode catalyst layer 10 via the end plate 8b, the external circuit, and the end plate 8a. The protons and electrons supplied to the cathode catalyst layer 10 are used to hydrogenate toluene in the cathode catalyst layer 10. As a result, methylcyclohexane is produced.

Therefore, according to the organic hydride manufacturing apparatus 1 of this embodiment, the electrolysis of water and the hydrogenation reaction of the substance to be hydrogenated can be carried out in one step. This improves the efficiency of organic hydride manufacturing compared to the conventional technology in which organic hydrides are manufactured in a two-step process consisting of a process for manufacturing hydrogen by water electrolysis or the like and a process for chemically hydrogenating toluene 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 manufactured by water electrolysis or the like, a significant reduction in equipment costs can be achieved.

In addition to the main reaction, the hydrogenation reaction of toluene, a side reaction, a hydrogen generation reaction, shown below, may occur in the cathode 4. The side reaction may occur when the amount of toluene supplied to the cathode catalyst layer 10 is insufficient, for example.
<Possible side reactions at the cathode>
2H ⁺ +2e ^- →H ₂

Next, the cathode catalyst layer 10 provided in the organic hydride production apparatus 1 according to this embodiment will be described in detail. Figures 2(A) and 2(B) are cross-sectional views showing an enlarged portion of the organic hydride production apparatus 1. Figure 2(A) shows an example of the cathode catalyst layer 10. Figure 2(B) shows another example of the cathode catalyst layer 10.

The cathode catalyst layer 10 has multiple protrusions 28 that protrude in the stacking direction X of the electrolyte membrane 2 and the cathode 4. As shown in FIG. 2(A), in one example of the cathode catalyst layer 10, the multiple protrusions 28 are independent of one another and are distributed in the in-plane direction of the first surface 2a. As shown in FIG. 2(B), in another example of the cathode catalyst layer 10, the multiple protrusions 28 are connected to one another at their bases and are distributed in the in-plane direction of the first surface 2a. The in-plane direction of the first surface 2a is the direction in which a plane perpendicular to the stacking direction X extends, in other words, the direction in which the first surface 2a extends.

The cathode catalyst layer 10 has a structure in which multiple protrusions 28 and multiple recesses 30 are arranged alternately. In other words, the cathode catalyst layer 10 has multiple thick layer sections formed by each protrusion 28 and multiple thin layer sections formed by each recess 30. When the multiple protrusions 28 are independent of each other, the first surface 2a is exposed at the recess 30. In this case, each protrusion 28 is also called an isolated section. The thickness of each recess 30 or the thickness of each thin layer section is zero. When the multiple protrusions 28 are connected to each other at their bases, the connected base portions form the recess 30.

Preferably, the multiple protrusions 28 are arranged in a matrix when viewed from the stacking direction X. Therefore, the protrusions 28 and the recesses 30 are periodically repeated in the vertical and horizontal directions. Also preferably, the multiple protrusions 28 are arranged at equal intervals. The "equally spaced" preferably means that the vertices of each protrusion 28 are equally spaced. However, this is not limited to this, and it can also include a case where the multiple protrusions 28 correspond to a plurality of imaginary points arranged at equal intervals, and each protrusion 28 is arranged with a shift within a range in which each imaginary point is included within the extension range of each protrusion 28 when viewed from the stacking direction X. The distance between the vertices of two adjacent protrusions 28, or the distance between two adjacent imaginary points, is, for example, 1 mm to 3 mm.

The thickness of the recess 30 in the stacking direction X is preferably 90% or less of the thickness of the protrusion 28 in the stacking direction X, and more preferably 80% or less of the thickness of the protrusion 28. The thickness of the protrusion 28 is, for example, the average thickness of the multiple protrusions 28, and the thickness of the recess 30 is, for example, the average thickness of the multiple recesses 30. In addition, the thickness of the protrusion 28 may be the thickness of the thickest part of the cathode catalyst layer 10, and the thickness of the recess 30 may be the thickness of the thinnest part of the cathode catalyst layer 10.

The cathode catalyst layer 10 having multiple protrusions 28 and multiple recesses 30 can be formed by the method described below. Figure 3 is a diagram for explaining the method for forming the cathode catalyst layer 10. Figures 4(A) to 4(C) are schematic diagrams of masks used to form the cathode catalyst layer 10.

That is, as shown in FIG. 3, the cathode catalyst layer 10 having a plurality of protrusions 28 and a plurality of recesses 30 is formed by pressing a dot layer 32 in which the catalyst ink constituting the cathode catalyst layer 10 is dispersed and a continuous layer 34 in which the catalyst ink is continuous. The protrusions 28 are formed by overlapping the continuous layer 34 with the coated portion of the dot layer 32 in which the catalyst ink is applied, and the recesses 30 are formed by overlapping the continuous layer 34 with the uncoated portion of the dot layer 32 in which the catalyst ink is not applied. The continuous layer 34 has a substantially uniform thickness. The catalyst ink is, for example, a mixture of a cathode catalyst, a catalyst carrier, pure water, an ionomer, etc.

For example, the dot layer 32 is laminated on one of the electrolyte membrane 2 and the cathode diffusion layer 12. The continuous layer 34 is laminated on the other of the electrolyte membrane 2 and the cathode diffusion layer 12. In this embodiment, as shown in FIG. 3, the dot layer 32 is laminated on the electrolyte membrane 2, and the continuous layer 34 is laminated on the cathode diffusion layer 12. However, this is not limited to this, and the continuous layer 34 may be laminated on the electrolyte membrane 2, and the dot layer 32 may be laminated on the cathode diffusion layer 12. In addition, each figure of this embodiment shows a shape in which the convex portion protrudes from the first surface 2a to the cathode diffusion layer 12 side, but the convex portion may protrude from the main surface of the cathode diffusion layer 12 to the electrolyte membrane 2 side. In other words, the multiple convex portions 28 only need to protrude in the stacking direction X, and may protrude to the electrolyte membrane 2 side, the cathode diffusion layer 12 side, or both.

To form the dot layer 32, a mask M2 shown in FIG. 4(B) or a mask M3 shown in FIG. 4(C) is used. A plurality of openings H2, H3 arranged in a matrix are provided in the masks M2, M3. The masks M2, M3 are obtained by forming a plurality of openings H2, H3 in a resin sheet such as FEP using a laser cutter or the like.

Each opening H2 in the mask M2 is rectangular, with two sides of each opening H2 extending vertically and the remaining two sides extending horizontally. In the following, the dot layer 32 formed using the mask M2 is referred to as a square dot layer. Each opening H3 in the mask M3 is rectangular, with one diagonal of each opening H3 extending vertically and the other diagonal extending horizontally. In the following, the dot layer 32 formed using the mask M3 is referred to as a diamond dot layer. The mask M1 shown in FIG. 4A is used to form the continuous layer 34. The mask M1 is made of, for example, stainless steel, and has one rectangular opening H1. As an example, the total area of the openings H2 and H3 is 50% of the area of the opening H1. In other words, the opening ratio of the masks M2 and M3 is 50% of the opening ratio of the mask M1.

For example, masks M2 and M3 are laminated on a resin sheet such as PTFE, and catalyst ink is applied to the surface of the resin sheet through the masks M2 and M3. As a result, the catalyst ink enters the multiple openings H2 and H3, and a dot layer 32 is formed on the resin sheet. Next, the electrolyte membrane 2 and the resin sheet on which the dot layer 32 is formed are pressed together while being pressurized (hot press). As a result, the dot layer 32 is laminated (transferred) onto the electrolyte membrane 2. In addition, a mask M1 is laminated on the cathode diffusion layer 12, and catalyst ink is applied to the surface of the cathode diffusion layer 12 through the mask M1. As a result, the catalyst ink enters the openings H1, and a continuous layer 34 is laminated on the cathode diffusion layer 12.

Then, the electrolyte membrane 2 and the cathode diffusion layer 12 are pressed against each other while being heated, so that the dot layer 32 and the continuous layer 34 are pressed together. This forms the cathode catalyst layer 10 having a plurality of protrusions 28 and a plurality of recesses 30. This also results in a membrane electrode assembly 36 having the electrolyte membrane 2 and the cathode 4. Note that if the electrolyte membrane 2 and the cathode diffusion layer 12 are hot pressed without forming the continuous layer 34 on the cathode diffusion layer 12, a cathode catalyst layer 10 is obtained in which the plurality of protrusions 28 are spaced apart from each other, i.e., the thickness of the recesses 30 is zero.

Preferably, the ratio of the thickness of the dot layer 32 to the thickness of the continuous layer 34 is 1:9 to less than 10:0. That is, T in FIG. 3 is 1 or more and less than 10. The ratio of the thickness of the dot layer 32 to the thickness of the continuous layer 34 (T:10-T) is more preferably 1:9 to 5:5, and even more preferably 3:7. The thickness of the dot layer 32 can be adjusted by changing the thickness of the masks M2 and M3. The thickness of the continuous layer 34 can be adjusted by changing the thickness of the mask M1.

Figures 5(A) to 5(C) are schematic diagrams for explaining the function of multiple protrusions 28. Figures 5(A) to 5(C) show an example in which toluene is used as the substance to be hydrogenated. As shown in Figure 5(A), when the cathode catalyst layer 10 does not have multiple protrusions 28 and has a uniform thickness, the reaction to produce methylcyclohexane occurs uniformly over the entire surface of the cathode catalyst layer 10. As a result, methylcyclohexane tends to remain on the surface of the cathode catalyst layer 10 facing the cathode diffusion layer 12, resulting in the formation of a layer L of methylcyclohexane.

In particular, the denser the substrate of the anode 6, the greater the contact area between the anode 6 and the electrolyte membrane 2, and therefore the more uniformly the protons are transferred to the cathode catalyst layer 10. For example, if the substrate of the anode 6 is changed from a substrate made of a woven mesh of metal fibers or expanded metal to a web of sintered fine metal fibers, the protons are transferred more uniformly to the cathode catalyst layer 10. This increases the utilization rate of the cathode catalyst in the cathode catalyst layer 10, thereby reducing the cell voltage of the organic hydride manufacturing apparatus 1 and making it easier to form the methylcyclohexane layer L.

When the methylcyclohexane layer L is formed, the layer L inhibits the supply of toluene to the cathode catalyst layer 10, and the amount of toluene supplied to the cathode catalyst layer 10 decreases. If the amount of toluene supplied is insufficient, a side reaction occurs in the cathode catalyst layer 10, and hydrogen is generated. The progression of the side reaction leads to a decrease in the current efficiency of the organic hydride production apparatus 1.

In response to this, as shown in FIG. 5(B), by forming the cathode catalyst layer 10 with multiple convex portions 28 spaced apart from each other, that is, by forming the cathode catalyst layer 10 in a dot shape, it is possible to make the production of methylcyclohexane non-uniform in the in-plane direction of the cathode catalyst layer 10. This makes it possible to suppress the formation of a methylcyclohexane layer L and to suppress a decrease in the amount of toluene supplied to the cathode catalyst layer 10. This makes it possible to suppress the progression of side reactions and increase the current efficiency of the organic hydride manufacturing apparatus 1.

However, in a structure in which each protrusion 28 is isolated, protons and current may concentrate at each protrusion 28, further promoting the reaction to produce methylcyclohexane. In this case, the amount of toluene consumed at each protrusion 28 exceeds the amount of toluene supplied, resulting in a shortage of toluene supply and causing a side reaction to proceed. The decrease in current efficiency caused by the structure in which each protrusion 28 is spaced apart is smaller than the decrease in current efficiency caused by the methylcyclohexane layer L. Therefore, although the effect of improving current efficiency can be obtained even with a structure in which multiple protrusions 28 are spaced apart from each other, there is room for further improvement.

In response to this, as shown in FIG. 5(C), by pressing the dot layer 32 and the continuous layer 34 together to form a shape in which multiple protrusions 28 are connected at their bases, it is possible to maintain non-uniform production of methylcyclohexane while mitigating excessive current concentration on each protrusion 28 and suppressing the progression of side reactions. This makes it possible to further improve the current efficiency of the organic hydride manufacturing apparatus 1.

In addition, by making the thickness of the recess 30 90% or less (more than 0%) of the thickness of the protrusion 28, the current density can be increased compared to when the multiple protrusions 28 are spaced apart from each other. By increasing the current density of the organic hydride production apparatus 1, the amount of methylcyclohexane produced per unit time can be increased. Alternatively, the size of the electrode required to produce a certain amount of methylcyclohexane can be reduced. In other words, by making the difference between the thickness of the recess 30 and the thickness of the protrusion 28 10% or more of the thickness of the cathode catalyst layer 10, the performance improvement effect of the organic hydride production apparatus 1 can be more reliably obtained.

Increasing the difference between the thickness of the protrusions 28 and the thickness of the recesses 30 promotes non-uniform production of methylcyclohexane. On the other hand, decreasing this difference suppresses current concentration in the cathode catalyst layer 10. Therefore, by adjusting the balance between the thickness of the protrusions 28 and the thickness of the recesses 30, the performance of the organic hydride manufacturing apparatus 1 can be further improved. The thickness of the protrusions 28 and the thickness of the recesses 30 can be adjusted by changing the ratio between the thickness of the dot layer 32 and the thickness of the continuous layer 34.

Specifically, by setting the ratio of the thickness of the dot layer 32 to the thickness of the continuous layer 34 to 1:9 to less than 10:0, the current density can be increased more than when only the dot layer 32 is used. In addition, by setting the ratio of the thickness of the dot layer 32 to the thickness of the continuous layer 34 to 1:9 to 5:5, the current density can be further increased. Furthermore, by setting the ratio of the thickness of the dot layer 32 to the thickness of the continuous layer 34 to 3:7, the current density can be maximized. In addition, by setting the ratio of the thickness of the dot layer 32 to the thickness of the continuous layer 34 to 3:7 to 7:3, the current efficiency can be improved more reliably than when only the dot layer 32 is used.

As described above, the organic hydride manufacturing apparatus 1 according to this embodiment includes an electrolyte membrane 2 having a first surface 2a and a second surface 2b facing each other, which transfers protons, a cathode 4 provided on the first surface 2a side of the electrolyte membrane 2, and an anode 6 provided on the second surface 2b side of the electrolyte membrane 2. The cathode 4 has a cathode catalyst layer 10 that hydrogenates a substance to be hydrogenated with protons to generate an organic hydride. The anode 6 oxidizes water to generate protons. The cathode catalyst layer 10 has a plurality of protrusions 28 that protrude in the stacking direction X of the electrolyte membrane 2 and the cathode 4. The plurality of protrusions 28 are distributed in the in-plane direction of the first surface 2a, either independently of each other or connected to each other at their bases.

In this way, by providing multiple protrusions 28 on the cathode catalyst layer 10, it is possible to suppress uniform production of organic hydride in the in-plane direction of the cathode catalyst layer 10. This makes it possible to suppress a decrease in the supply amount of the material to be hydrogenated to the cathode catalyst layer 10 and suppress the progression of side reactions. Therefore, according to this embodiment, the current efficiency of the organic hydride production apparatus 1 can be improved.

The cathode catalyst layer 10 of this embodiment has a structure in which multiple protrusions 28 and multiple recesses 30 are arranged alternately, and preferably, the thickness of the recesses 30 in the stacking direction X is 90% or less of the thickness of the protrusions 28 in the stacking direction X. This allows the current density of the organic hydride manufacturing apparatus 1 to be further increased.

In addition, in this embodiment, the multiple convex portions 28 and the multiple concave portions 30 are formed by pressing a dot layer 32 in which the catalyst ink is dispersed and a continuous layer 34 in which the catalyst ink is continuous. The ratio of the thickness of the dot layer 32 to the thickness of the continuous layer 34 is preferably 1:9 to less than 10:0, more preferably 1:9 to 5:5, and even more preferably 3:7. This allows the current density of the organic hydride manufacturing apparatus 1 to be further increased.

In addition, in this embodiment, the multiple protrusions 28 are arranged in a matrix. This allows the organic hydride generation to be non-uniform over a wider range of the cathode catalyst layer 10, so that the effect of improving current efficiency can be more reliably achieved.

Above, the embodiments of the present invention have been described in detail. The above-mentioned embodiments merely show specific examples of implementing the present invention. The contents of the embodiments do not limit the technical scope of the present invention, and many design changes such as changing, adding, and deleting components are possible within the scope of the idea of the invention defined in the claims. A new embodiment with design changes has the effects of both the combined embodiment and modification. In the above-mentioned 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 above-mentioned components is also valid as an aspect of the present invention.

The embodiment may be specified by the items described below.
[Item 1]
A method for producing a membrane electrode assembly (36) for use in an organic hydride production apparatus (1), comprising the steps of:
The membrane electrode assembly (36) has an electrolyte membrane (2) and a cathode (4),
The cathode (4) has a cathode catalyst layer (10);
The manufacturing method includes forming a cathode catalyst layer (10) having a plurality of convex portions (28) by pressing a dot layer (32) in which a catalyst ink constituting the cathode catalyst layer (10) is dispersed and a continuous layer (34) in which the catalyst ink is continuous,
A method for manufacturing a membrane electrode assembly (36) in which a plurality of protrusions (28) protrude in a stacking direction (X) of an electrolyte membrane (2) and a cathode (4), are connected to each other at their bases, and are dispersed and arranged in an in-plane direction of the electrolyte membrane (2).
[Item 2]
The cathode (4) has a cathode catalyst layer (10) and a cathode diffusion layer (12);
The manufacturing method includes:
A dot layer (32) is laminated on one of the electrolyte membrane (2) and the cathode diffusion layer (12);
A continuous layer (34) is laminated on the other of the electrolyte membrane (2) and the cathode diffusion layer (12);
A method for producing a membrane electrode assembly (36), comprising pressing an electrolyte membrane (2) and a cathode diffusion layer (12) together to pressure-bond a dot layer (32) and a continuous layer (34).

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 are not intended to limit the present invention in any way.

(Preparation of catalyst ink)
A PtRu/C catalyst (TEC61E54E, Tanaka Kikinzoku Kogyo Co., Ltd.), pure water, 5 wt% Nafion (registered trademark) solution (DuPont), and 1-propanol (Wako) were mixed in a ball mill container to prepare a catalyst ink for the cathode catalyst layer. The Nafion/carbon ratio of the catalyst ink was 0.8.

(Preparation of Membrane Electrode Assembly)
Using the above-mentioned mask M3, the catalyst ink was applied in a dot shape to the PTFE sheet. Then, this PTFE sheet and Nafion (registered trademark) N117 (manufactured by DuPont) as an electrolyte membrane were hot-pressed at 130 ° C. and 5 MPa for 5 minutes. As a result, the dot-shaped catalyst ink was transferred to the electrolyte membrane to form a diamond-shaped dot layer. In addition, using the above-mentioned mask M1, the catalyst ink was uniformly applied to carbon paper (35BC, manufactured by SGL Carbon, 4 cm x 4 cm) as a cathode diffusion layer to form a continuous layer. The cathode diffusion layer on which the continuous layer was formed was processed with a cutter to be a rectangle of 3.3 cm in length and 3.5 cm in width. Then, the electrolyte membrane on which the diamond-shaped dot layer was formed and the cathode diffusion layer on which the continuous layer was formed were hot-pressed at 120 ° C. and 2.5 MPa for 3 minutes to produce a membrane electrode assembly (diamond type).

When producing the membrane electrode assembly (diamond type), the thickness of the masks M1 and M3 was changed to adjust the thickness of the dot layer and the continuous layer. As a result, membrane electrode assemblies (diamond type 3:7, diamond type 5:5, diamond type 7:3) with ratios of the thickness of the dot layer to the thickness of the continuous layer of 3:7, 5:5, and 7:3 were produced. In addition, an electrolyte membrane with a diamond-shaped dot layer formed thereon and a cathode diffusion layer without a continuous layer formed thereon were hot pressed to produce a membrane electrode assembly (diamond type 10:0) with a ratio of the thickness of the dot layer to the thickness of the continuous layer of 10:0.

In addition, an electrolyte membrane on which a square-type dot layer was formed and a cathode diffusion layer on which a continuous layer was not formed were hot-pressed using the mask M2 to produce a membrane electrode assembly (square type 10:0) in which the ratio of the thickness of the dot layer to the thickness of the continuous layer was 10:0. Furthermore, an electrolyte membrane on which a dot layer was not formed and a cathode diffusion layer on which a continuous layer was formed were hot-pressed to produce a membrane electrode assembly (continuous type 0:10) in which the ratio of the thickness of the dot layer to the thickness of the continuous layer was 0:10. In each membrane electrode assembly, the amount of catalytic metal in the convex portion (the amount of catalytic metal in the continuous layer in the case of only the continuous layer) was 0.75 mg/ ^cm2 .

(Preparation of organic hydride production device)
A web-shaped DSE (Dimensionally Stable Electrode) electrode (manufactured by De Nora Permelec) was prepared as the anode, which was a 1 mm thick Ti substrate coated with IrTa oxide. The geometric area of the anode was 12.25 ^cm2 . Then, each membrane electrode assembly and the anode were stacked. In addition, a flow path block with a vertical slit was pressed against the anode by a spring. These were sandwiched between a pair of end plates and fastened with bolts and nuts. In this way, an organic hydride manufacturing device (electrolytic cell) having each membrane electrode assembly was obtained.

(Electrochemical Measurement)
A RHE was connected to each organic hydride production apparatus as a reference electrode. In addition, each organic hydride production apparatus was connected to an electrochemical property evaluation device (NF, manufactured by NF Corporation). The electrochemical property evaluation device includes an electrolytic cell operation property analyzer (As-510-4 100/20), an electrolytic cell electrochemical property analyzer (MTB55867), and an AC impedance measuring device (FRA5014). As pretreatment, circulation of the anolyte to the anode, circulation of the catholyte to the cathode, and constant voltage electrolysis were performed.

Using each pretreated organic hydride production device, an electrolytic reduction reaction of toluene was carried out under the specified conditions described below. Then, electrochemical evaluation of each organic hydride production device was carried out using known measurement methods such as linear sweep voltammetry, chronoamperometry, AC impedance measurement, and current efficiency measurement.

In the current efficiency measurement, the amount (volume) of hydrogen gas generated by a side reaction in the cathode reaction was calculated by comparing the mass of the solution in the flow path when no voltage was applied with the mass of the solution in the flow path when a certain voltage was applied. The amount of hydrogen generated when all the current was used for hydrogen generation was also calculated. The hydrogen generation efficiency was calculated from the two amounts of hydrogen generated, and this value was subtracted from 100 to obtain the current efficiency of the electrolytic hydrogenation reaction of toluene. It was assumed that no reactions other than the electrolytic hydrogenation reaction of toluene and the hydrogen generation reaction were occurring at the cathode.

[Evaluation of the effect of multiple protrusions on electrochemical properties]
Using organic hydride production equipment having a membrane electrode assembly (diamond type 10:0), a membrane electrode assembly (square type 10:0) and a membrane electrode assembly (continuous type 0:10), respectively, toluene with a concentration of 10% was supplied to the cathode at a flow rate of 5 mL/min, sulfuric acid with a concentration of 1 M was supplied to the anode at a flow rate of 10 mL/min, and the operating temperature was set to 60° C., to carry out an electrolytic reduction reaction of toluene. Then, the electrochemical characteristics of each organic hydride production equipment were evaluated.

FIG. 6 shows the relationship between the cell voltage (U _{iR free} ) and the current density (i), and the relationship between the internal resistance (R) and the current density (i). The current density is a value obtained by chronoamperometry, and the IR loss is corrected using the high-frequency intercept obtained by AC impedance measurement. The internal resistance of each organic hydride production device was about 0.4 to 0.5 Ω cm ² , and no significant difference was observed. There was also almost no difference in the cell voltage, and it was confirmed that the cell voltage was maintained even when multiple protrusions were provided on the cathode catalyst layer.

Figure 7 (A) shows the polarization curve of the anode. Figure 7 (B) shows the polarization curve of the cathode. Each polarization curve is a steady-state polarization obtained by chronoamperometry, and IR losses are corrected using the high-frequency intercept obtained by AC impedance measurement. In each organic hydride production device, there was almost no difference between the anode polarization curve and the cathode polarization curve, and it was confirmed that overvoltage was maintained even when multiple protrusions were provided on the cathode catalyst layer. Therefore, it is believed that the catalyst utilization rate was maintained for both the anode and the cathode.

The electrochemical properties were evaluated by carrying out an electrolytic reduction reaction of toluene under the same conditions as above, except that the flow rate of toluene was set to 20 mL/min. FIG. 8 is a diagram showing the relationship between current density (i) and current efficiency (ε). The current efficiency of the membrane electrode assembly (diamond type 10:0) and the membrane electrode assembly (square type 10:0) was improved compared to the membrane electrode assembly (continuous type 0:10) (the current efficiency obtained is increased when viewed at the same current density). In other words, it was confirmed that the current efficiency can be improved by providing a plurality of convex parts spaced apart from each other on the cathode catalyst layer. The diamond-shaped dot layer showed a larger increase in current efficiency than the square-shaped dot layer. In the square-shaped dot layer, two sides of each dot, which is approximately rectangular, extend parallel to the vertical direction in which the supply flow path 16 and the discharge flow path 18 are aligned. On the other hand, in the diamond-shaped dot layer, four sides of each dot, which is approximately rectangular, extend in a direction intersecting the vertical direction in which the supply flow path 16 and the discharge flow path 18 are aligned. Therefore, the diamond-shaped dot layer can reduce the amount of toluene that passes through without contacting each dot, compared to the square-shaped dot layer. In other words, the diamond-shaped dot layer supplies more toluene than the square-shaped dot layer. For this reason, it is believed that the diamond-shaped dot layer had a greater increase in current efficiency than the square-shaped dot layer.

[Evaluation of the effect of the ratio of dot layer to continuous layer on electrochemical properties]
Using organic hydride production equipment having a membrane electrode assembly (continuous type 0:10), a membrane electrode assembly (diamond type 3:7), a membrane electrode assembly (diamond type 5:5), a membrane electrode assembly (diamond type 7:3) and a membrane electrode assembly (diamond type 10:0), toluene with a concentration of 10% was supplied to the cathode at a flow rate of 5 mL/min, sulfuric acid with a concentration of 1 M was supplied to the anode at a flow rate of 10 mL/min, and the operating temperature was set to 60° C., and an electrolytic reduction reaction of toluene was carried out. Then, the electrochemical characteristics of each organic hydride production equipment were evaluated.

FIG. 9 shows the relationship between the cell voltage (U _{iR free} ) and the current density (i), and the relationship between the internal resistance (R) and the current density (i). The current density is a value obtained by chronoamperometry, and the IR loss is corrected using the high-frequency intercept obtained by AC impedance measurement. The internal resistance of each organic hydride production device was about 0.4 to 0.5 Ω cm ² , and no significant difference was observed. There was also almost no difference in the cell voltage, and it was confirmed that the cell voltage was maintained even if the ratio of the dot layer to the continuous layer was changed.

Figure 10 (A) shows the polarization curve of the anode. Figure 10 (B) shows the polarization curve of the cathode. Each polarization curve is a steady-state polarization obtained by chronoamperometry, and IR losses are corrected using the high-frequency intercept obtained by AC impedance measurement. In each organic hydride production device, there was almost no difference between the polarization curves of the anode and the cathode, and it was confirmed that the overvoltage was maintained even when the ratio of the dot layer to the continuous layer was changed. Therefore, it is considered that the catalyst utilization rate was maintained in both the anode and the cathode.

The electrochemical properties were evaluated by carrying out an electrolytic reduction reaction of toluene under the same conditions as above, except that the flow rate of toluene was set to 20 mL/min. FIG. 11 is a diagram showing the relationship between current density (i) and current efficiency (ε). The current efficiency of the membrane electrode assembly (diamond type 3:7), the membrane electrode assembly (diamond type 5:5), and the membrane electrode assembly (diamond type 7:3) was higher than that of the membrane electrode assembly (diamond type 10:0). In other words, it was confirmed that the current efficiency can be improved by providing multiple convex portions connected to each other in the cathode catalyst layer compared to the case where multiple convex portions independent of each other are provided. It was also confirmed that the current efficiency can be improved more reliably by setting the ratio of the thickness of the dot layer 32 to the thickness of the continuous layer 34 to 3:7 to 7:3. Furthermore, it was confirmed that the highest current efficiency was obtained among the measured values by setting the ratio to 3:7.

12 is a diagram showing the relationship (solid line) between the dot layer ratio (r _dot ) and the current density (i) when the current efficiency is constant, and the relationship (dashed line) between the dot layer ratio (r _dot ) and the cathode potential (E). The dot layer ratio is the ratio of the thickness of the dot layer to the total thickness of the dot layer and the continuous layer. It was confirmed that by making the dot layer ratio 10% or more and less than 100%, that is, by making the ratio of the dot layer to the continuous layer 1:9 to less than 10:0, the current density is increased to a level higher than when the dot layer ratio is 100%.

It was also confirmed that the current density was increased by setting the ratio of the dot layer 32 to 10% or more and 50% or less, that is, by setting the ratio of the dot layer to the continuous layer to 1:9 to 5:5. Furthermore, it was confirmed that the current density was maximized by setting the ratio of the dot layer to 30% (dot layer:continuous layer = 3:7). When the ratio of the dot layer was 30%, the cathode potential was the lowest, but the current efficiency was maintained at 90, 95, and 100%. Therefore, it is believed that the selectivity of toluene hydrogenation is not governed by the kinetics of charge transfer on the catalyst, but is strongly dependent on the mass transfer process in the cathode catalyst layer.

Theoretically, the thickness of the convex portion is equal to the sum of the thickness of the dot layer and the thickness of the continuous layer, and the thickness of the concave portion is equal to the thickness of the continuous layer. Therefore, when the proportion of the dot layer is 10%, the thickness of the concave portion is 90% of the thickness of the convex portion. Therefore, from the results when the proportion of the dot layer is 10% or more, it can be confirmed that the current density is improved by making the thickness of the concave portion 90% or less of the thickness of the convex portion.

However, in reality, when the dot layer and the continuous layer are bonded by hot pressing, the catalyst ink flows from the parts corresponding to the convex parts to the parts corresponding to the concave parts, and the thickness of the convex parts may become smaller than the theoretical value, and the thickness of the concave parts may become larger than the theoretical value. However, as shown in FIG. 12, the current density increases as the proportion of the dot layer increases from 10%. Therefore, a cathode catalyst layer in which the thickness of the concave parts is 90% of the thickness of the convex parts is formed by a combination of a dot layer and a continuous layer that obtains a higher current density than when the proportion of the dot layer is 10%. Therefore, it can be understood that a high current density can be obtained if the thickness of the concave parts is 90% or less of the thickness of the convex parts.

1 organic hydride manufacturing apparatus, 2 electrolyte membrane, 2a first surface, 2b second surface, 4 cathode, 6 anode, 10 cathode catalyst layer, 12 cathode diffusion layer, 28 convex portion, 30 concave portion, 32 dot layer, 34 continuous layer, 36 membrane electrode assembly.

Claims (11)

an electrolyte membrane having a first surface and a second surface opposed to each other and allowing protons to move;
a cathode provided on the first surface side of the electrolyte membrane;
an anode provided on the second surface side of the electrolyte membrane,
the cathode has a cathode catalyst layer that hydrogenates a substance to be hydrogenated with protons to produce an organic hydride;
The anode oxidizes water to produce protons;
the cathode catalyst layer has a plurality of convex portions protruding in a stacking direction of the electrolyte membrane and the cathode, and is formed by pressing a dot layer in which a catalyst ink constituting the cathode catalyst layer is dispersed and disposed, and a continuous layer in which the catalyst ink is continuous,
The plurality of protrusions are connected to each other at their bases and are dispersed and disposed in the in-plane direction of the first surface. the cathode catalyst layer has a structure in which the plurality of protrusions and the plurality of recesses are alternately arranged,
2. The organic hydride manufacturing apparatus according to claim 1, wherein a thickness of the recessed portion in the stacking direction is 90% or less of a thickness of the protruding portion in the stacking direction, the thickness of the protruding portion is a thickness of a thickest portion of the cathode catalyst layer, and the thickness of the recessed portion is a thickness of a thinnest portion of the cathode catalyst layer . 3. The organic hydride manufacturing apparatus according to claim 1, wherein the ratio of the thickness of the dot layer to the thickness of the continuous layer is 1:9 to less than 10:0. The organic hydride manufacturing apparatus according to claim 3, wherein the ratio of the thickness of the dot layer to the thickness of the continuous layer is 1:9 to 5:5. The organic hydride manufacturing apparatus according to claim 4, wherein the ratio of the thickness of the dot layer to the thickness of the continuous layer is 3:7. The organic hydride manufacturing apparatus according to any one of claims 1 to 5, wherein the plurality of protrusions are arranged in a matrix. A method for producing a membrane electrode assembly for use in an organic hydride production apparatus, comprising the steps of:
the membrane electrode assembly has an electrolyte membrane and a cathode,
The cathode has a cathode catalyst layer,
The manufacturing method includes forming the cathode catalyst layer having a plurality of convex portions by pressure-bonding a dot layer in which the catalyst ink constituting the cathode catalyst layer is dispersed and a continuous layer in which the catalyst ink is continuous,
The plurality of protrusions protrude in a stacking direction of the electrolyte membrane and the cathode, are connected to each other at their bases, and are distributed in an in-plane direction of the electrolyte membrane. the cathode has the cathode catalyst layer and a cathode diffusion layer,
The manufacturing method includes:
The dot layer is laminated on one of the electrolyte membrane and the cathode diffusion layer;
laminating the continuous layer on the other of the electrolyte membrane and the cathode diffusion layer;
The method for producing a membrane electrode assembly according to claim 7 , further comprising pressing the electrolyte membrane and the cathode diffusion layer together to pressure-bond the dot layer and the continuous layer. The method for producing a membrane electrode assembly according to claim 7 or 8, wherein the ratio of the thickness of the dot layer to the thickness of the continuous layer is 1:9 to less than 10:0. The method for producing a membrane electrode assembly according to claim 9, wherein the ratio of the thickness of the dot layer to the thickness of the continuous layer is 1:9 to 5:5. The method for manufacturing a membrane electrode assembly according to claim 10, wherein the ratio of the thickness of the dot layer to the thickness of the continuous layer is 3:7.

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