Electrochemical Reactors

Abstract

To suppress outflow of an unreduced gas and an unoxidized gas to the outside.SOLUTION: An electrochemical reactor is provided in a casing (120) of an exhaust flow passage of an internal combustion engine (110), and purifies exhaust discharged from the internal combustion engine by an electrochemical reaction corresponding to application of a voltage. The electrochemical reactor (100) is configured by laminating multiple cells (10) composed of a cathode electrode layer (80) as a porous member capable of reducing an unreduced substance contained in the exhaust, an anode electrode layer (50) as a porous member capable of oxidizing an unoxidized substance contained in the exhaust, and a solid electrolyte layer (70) clamped by the anode electrode layer and the cathode electrode layer. In at least one of the anode electrode layer and the cathode electrode layer positioned in the outermost part in a lamination direction, one portion (51) of the porous member is configured densely so as to inhibit outflow of exhaust to a downstream side within the porous member.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to an electrochemical reactor. [Background technology]

[0002] Exhaust from vehicle engines contains nitrogen oxides (NOx), which must be reduced using a three-way catalyst or other device before being discharged outside the vehicle. However, in situations where there is an excess of oxygen, the reducing power of the three-way catalyst decreases, so other reduction methods must be considered.

[0003] Patent Document 1 discloses a technology that uses an electrochemical reactor configured by stacking MEAs (Membrane and Electrode Assembly) each having a cathode surface and an anode surface via a metal porous body as a reduction means by electrochemical reaction. In the MEA, nitrogen oxides are reduced at the cathode electrode, and oxygen ions are released to generate nitrogen gas. The released oxygen ions are then conducted through the electrolyte layer inside the MEA to move to the anode electrode, where they are oxidized and released as oxygen gas.

[0004] In an electrochemical reactor, which is a stack of MEAs, a reduction reaction does not take place at the anode located at the outermost position in the stacking direction, so if nitrogen oxides flow between the outermost anode and the housing, there is a risk that unreduced nitrogen oxides will flow downstream. Therefore, according to the technology disclosed in Patent Document 1, the outermost anode is separated from the exhaust flow path as a flow path, thereby making it possible to suppress the release of unreduced nitrogen oxides to the outside.

[0005] Similarly, unoxidized substances such as carbon monoxide are oxidized at the anode, but since no oxidation reaction takes place at the cathode located at the outermost side in the stacking direction, if the unoxidized substances flow between the outermost cathode and the housing, there is a risk that the unoxidized substances will flow downstream. Therefore, by isolating the outermost cathode as a flow path different from the exhaust flow path, it is possible to suppress the release of unoxidized gas to the outside.

[0006] However, the above-mentioned method has a problem in that the structure of the flow path becomes complicated. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2010-270720 A Summary of the Invention

[0008] The present invention has been made in consideration of the above problems, and has an object to provide an electrochemical reactor that suppresses the outflow of unreduced substances and unoxidized substances to the outside without complicating the structure of the flow path.

[0009] According to one aspect of the present invention, an electrochemical reactor is provided inside a housing of an exhaust passage of an internal combustion engine, and purifies exhaust gas discharged from the internal combustion engine by an electrochemical reaction in response to application of a voltage. The electrochemical reactor is configured by stacking a plurality of cells, each of which is configured with a cathode layer that is a porous member capable of reducing unreduced substances contained in the exhaust gas, an anode layer that is a porous member capable of oxidizing unoxidized substances contained in the exhaust gas, and a solid electrolyte layer sandwiched between the anode layer and the cathode layer. At least one of the anode layer and the cathode layer located at the outermost position in the stacking direction has a portion of the porous member densely configured so that the exhaust gas is prevented from flowing downstream within the porous member. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a block diagram of an exhaust system including an electrochemical reactor according to an embodiment of the present invention. [Diagram 2] FIG. 2 is an exploded perspective view of the electrochemical reactor. [Diagram 3] FIG. 3 is an exploded perspective view of a cell unit. [Figure 4] FIG. 4 is an exploded perspective view of the metal support cell assembly. [Diagram 5]FIG. 5 is a partial cross-sectional view of an electrochemical reactor. [Figure 6] FIG. 6 is a cross-sectional view taken along line kI in FIG. [Figure 7] FIG. 7 is a cross-sectional view of the exhaust flow passage in a plane including the exhaust flow direction and the stacking direction of the electrochemical reactor. [Figure 8] FIG. 8 is a top view of the end of the cathode layer of the electrochemical reactor as seen from XIII in FIG. [Figure 9] FIG. 9 is a cross section taken along line IX of FIG. [Figure 10] FIG. 10 is a cross-sectional view of an exhaust flow passage in the first modified example. [Figure 11] FIG. 11 is a top view of the end of the cathode layer of the electrochemical reactor in the second modification. [Figure 12] FIG. 12 is a cross-sectional view of an exhaust flow passage in a plane including the stacking direction of an electrochemical reactor in a third modified example. [Figure 13] FIG. 13 is a top view of the fixing member. [Figure 14] FIG. 14 is a cross-sectional view of an exhaust flow passage in a plane including the stacking direction of an electrochemical reactor in a fourth modified example. [Figure 15] FIG. 15 is a cross-sectional view of an exhaust flow passage in a plane including the exhaust flow direction and the stacking direction of the electrochemical reactor in the second embodiment. [Figure 16] FIG. 16 is a cross section taken along line XVI of FIG. [Figure 17] FIG. 17 is a cross-sectional view of an exhaust flow passage in a plane including the stacking direction of an electrochemical reactor in another modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0012] (First embodiment) FIG. 1 is a block diagram of an exhaust system equipped with an electrochemical reactor according to a first embodiment.

[0013] In an exhaust system 200 equipped with an electrochemical reactor 100, a three-way catalyst 130, the electrochemical reactor 100, and a muffler 140 are provided in an exhaust flow path 120 along the flow direction of exhaust gas discharged from an internal combustion engine 110. The three-way catalyst 130 and the electrochemical reactor 100 are provided in the exhaust flow path 120, and the muffler 140 is configured integrally with the exhaust flow path 120.

[0014] The internal combustion engine 110 runs on, for example, a hydrocarbon fuel. When the internal combustion engine 110 is mounted on a vehicle, it may directly drive the wheels, or it may be a source of power generation for a motor that drives the vehicle. Exhaust gas discharged from the internal combustion engine 110 includes unburned fuel (HC), carbon oxides (CO), nitrogen oxides (NOx), and the like.

[0015] The three-way catalyst 130 is made of, for example, a platinum material, and reduces unburned fuel and carbon oxides contained in the exhaust gas from the internal combustion engine 110. Nitrogen oxides contained in the exhaust gas that has passed through the three-way catalyst 130 are reduced by the electrochemical reactor 100. Then, the exhaust gas that has passed through the three-way catalyst 130 and the electrochemical reactor 100 is discharged to the outside through the muffler 140.

[0016] Here, the electrochemical reactor 100 is configured by stacking a plurality of MEAs (Membrane and Electrode Assembly). As described later, the MEA has a cathode where a reduction reaction takes place and an anode where an oxidation reaction takes place stacked with an electrolyte layer interposed between them. By applying a DC voltage to the electrochemical reactor 100, the following reactions take place in the anode, electrolyte layer, and cathode.

[0017] Cathode (reduction reaction): 2NO+4e - →N2+2O 2- Electrolyte layer :O 2- Conduction of Anode (oxidation reaction): 2O 2- →O2+4e-

[0018] In this embodiment, a plurality of MEAs are stacked via stacking members to form an electrochemical reactor 100. Note that, although an example in which a metal plate-shaped separator is used as the stacking member in this embodiment will be described, a leaf spring as shown in the third modified example or a porous metal as shown in the fourth modified example may also be used.

[0019] 2 to 4 are diagrams illustrating the configuration of an electrochemical reactor 100 according to an embodiment of the present invention. As shown in Fig. 2 and Fig. 3, the electrochemical reactor 100 is composed of a plurality of cell units 1, and each cell unit 1 is composed of a metal support cell assembly 10 and a laminate member 20. In addition, as shown in Fig. 4, the metal support cell assembly 10 is composed of a metal support cell 11 and a cell frame 12.

[0020] 2 is an exploded perspective view of the electrochemical reactor 100. The electrochemical reactor 100 is configured by stacking a plurality of cell units 1 formed in a plate shape.

[0021] FIG. 3 is an exploded perspective view of the cell unit 1. The cell unit 1 is formed by stacking a metal support cell assembly (electrochemical reaction unit) 10 and a lamination member 20. The metal support cell assembly 10 and the lamination member 20 are formed in a plate shape. A gas flow path forming section 21 is provided in the center of the lamination member 20. As shown in FIG. 3, the gas flow path forming section 21 is formed in a substantially linear shape such that the concave and convex shape extends in the short side direction of the lamination member 20. The gas flow path forming section 21 is provided with a plurality of fine holes penetrating in the lamination direction.

[0022] When the lamination member 20 is laminated on the metal support cell assembly 10, a gas flow path 40 (see Figs. 5 and 6) partitioned by the gas flow path forming portion 21 is formed between the upper surface of the metal support cell assembly 10 and the lower surface of the lamination member 20 adjacent to the upper part of the metal support cell assembly 10. In addition, the metal support cell assembly 10 of another cell unit 1 is laminated on the gas flow path forming portion 21 of the lamination member 20. As a result, another gas flow path 40 (see Figs. 5 and 6) partitioned by the gas flow path forming portion 21 is formed between the upper surface of the lamination member 20 and the lower surface of another metal support cell assembly 10 (not shown) adjacent to the upper part of the lamination member 20. As described above, since the gas flow path forming portion 21 has a plurality of fine holes, exhaust gas communicates between the gas flow path 40 on the lower surface side of the lamination member 20 and the gas flow path 40 on the upper surface side of the lamination member 20.

[0023] 4 is an exploded perspective view of the metal support cell assembly 10. The metal support cell assembly 10 has a metal support cell 11 and a cell frame 12 that surrounds the outer periphery of the metal support cell 11 and holds it.

[0024] The metal support cell 11 is formed by laminating an anode layer 50, a cathode layer 60, and a solid electrolyte layer 70 sandwiched between the anode layer 50 and the cathode layer 60 on a metal support 80, with the solid electrolyte layer 70 being made of a solid oxide. That is, the metal support cell assembly 10 is an electrochemical unit having the solid electrolyte layer 70. The anode layer 50, the cathode layer 60, the solid electrolyte layer 70, and the metal support 80 will be described in detail later.

[0025] The cell frame 12 is made of, for example, a plate-shaped metal, and has an opening 12A in the center in which the metal support cell 11 is placed. The solid electrolyte layer 70 of the metal support cell 11 is surface-bonded to the inner peripheral surface of the opening 12A of the cell frame 12 by sintering bonding or the like. In this way, the metal support cell 11 is held by the cell frame 12.

[0026] As described above, the electrochemical reactor 100 is configured by stacking the cell units 1, each of which is made up of a metal support cell assembly 10 and a lamination member 20. In this embodiment, the electrochemical reactor 100 reduces nitrogen oxides contained in the exhaust gas by application of a DC voltage.

[0027] Next, the gas flow in the electrochemical reactor 100 will be described.

[0028] In the electrochemical reactor 100, nitrogen oxides (NOx) in the exhaust gas are reduced in the cathode layer 60, and oxygen gas is discharged from the anode layer 50. As described later, if unoxidized substances are contained in the exhaust gas, the unoxidized substances are oxidized in the anode layer 50.

[0029] 2 are stacked, exhaust flow paths are formed between each cell unit 1 along the gas flow path forming portion 21. Exhaust air flowing in from one side in the formation direction of the gas flow path forming portion 21 is supplied to two gas flow paths 40 (first flow path 41, second flow path 42) defined by the gas flow path forming portion 21 of the laminate member 20 in each cell unit 1. These two gas flow paths 40 (first flow path 41, second flow path 42) are separated by the laminate member 20 having micropores, and therefore communicate with each other.

[0030] 5 and 6 are partial cross-sectional views of the electrochemical reactor 100 according to this embodiment, showing a gas flow path 40 and two adjacent metal support cell assemblies 10 stacked above and below the gas flow path 40. Fig. 5 is a cross-sectional view seen from the front of the gas flow path 40, and Fig. 6 is a cross-sectional view taken along line VI in Fig. 5. That is, in Fig. 5, the exhaust gas flows in the direction of the page, and in Fig. 6, the exhaust gas flows in the left-right direction.

[0031] As described above, the cell unit 1 of the electrochemical reactor 100 includes the metal support cell assembly 10 and the laminated member 20. Also, as shown in Figures 5 and 6, the metal support cell assembly 10 includes a solid electrolyte layer 70, a cathode layer 60 disposed on one surface of the solid electrolyte layer 70, an anode layer 50 disposed on the other surface of the solid electrolyte layer 70, and a metal support 80 provided to support the cathode layer 60.

[0032] The solid electrolyte layer 70 is a thin film formed of an oxide having oxygen ion conductivity, and is sandwiched between the anode electrode layer 50 and the cathode electrode layer 60. As the oxide, for example, yttria-stabilized zirconia (YSZ), scandium-stabilized zirconia (SSZ), samarium-doped ceria (SDC), gadolinium-doped ceria (GDC), lanthanum strontium magnesium gallate (LSGM), etc. can be used.

[0033] The anode layer 50 is a plate-shaped member formed of, for example, lanthanum strontium cobalt composite oxide (LSC), lanthanum strontium cobalt iron oxide (LSCF), or the like, and is provided so as to be in contact with the upper surface of the solid electrolyte layer 70. In the anode layer 50, unoxidized substances contained in the exhaust gas are oxidized.

[0034] The cathode layer 60 is a plate-like member formed of a metal such as nickel (Ni) and an oxide such as yttria-stabilized zirconia (YSZ). The anode layer 50 is provided in contact with the lower surface of the solid electrolyte layer 70 and placed on a metal support 80. In the cathode layer 60, unreduced substances (nitrogen oxides) contained in the exhaust gas are reduced.

[0035] The metal support 80 is a porous plate-like member configured not to impede gas conduction, is provided to support the anode layer 50, and functions as a structural member for reinforcing the strength of the metal support cell assembly 10. In this manner, the metal support cell assembly 10 is of a so-called metal support type in which the cathode layer 60, the solid electrolyte layer 70, and the anode layer 50 are laminated on the metal support 80 as a support.

[0036] The laminated member 20 is disposed between two adjacent metal support cell assemblies 10, and forms gas flow paths 40 (first flow path 41, second flow path 42) between the metal support cell assemblies 10. Since the laminated member 20 has fine pores, the exhaust gas flowing through the two gas flow paths 40 (first flow path 41, second flow path 42) is mixed while flowing from upstream to downstream.

[0037] The material for forming the lamination members 20 is not particularly limited as long as it is an electrically conductive and thermally conductive material, but for example, an alloy or metal containing iron (Fe) or chromium (Cr) is used, and preferably, ferritic heat-resistant stainless steel is used. Examples of ferritic stainless steel include SUS430, SUS434, ZMG (registered trademark), and Crofer (registered trademark). The lamination members 20 may be austenitic stainless steel. The lamination members 20 are plate-shaped members formed by press-molding the above-mentioned electrically conductive and thermally conductive material.

[0038] 5, the lamination member 20 includes a first abutment portion 22 that abuts against a metal support 80 (anode layer side) that supports a cathode layer 60 of a metal support cell assembly 10 stacked on the lamination member 20, and a second abutment portion 23 that abuts against an anode layer 50 of the metal support cell assembly 10 located below the lamination member 20. The first abutment portion 22 and the second abutment portion 23 are connected by a connecting portion 24.

[0039] The laminated member 20 is configured as an uneven member by connecting the first contact portions 22 and the second contact portions 23 arranged alternately (in order) in a predetermined direction (separator width direction) with the connecting portions 24. By having such an uneven structure, the laminated member 20 has a plurality of first flow paths 41 on one side surface and a plurality of second flow paths 42 on the other side surface. Note that in FIG. 5, the connecting portions 24 are formed linearly and the first flow paths 41 are formed so that the cross-sectional area in the front direction of the flow path is trapezoidal, but this is not necessarily limited to this. For example, the connecting portions 24 may be formed in a curved shape and the first flow paths 41 may be configured so that the cross-sectional area of ​​the flow path is curved.

[0040] The first abutment portion 22 and the second abutment portion 23 of the lamination member 20 are formed as flat surfaces, the first abutment portion 22 abuts against the metal support 80 of the metal support cell assembly 10, and the second abutment portion 23 abuts against the anode layer 50 of the metal support cell assembly 10. The connecting portion 24 of the lamination member 20 is formed as a wall portion connecting an end of the first abutment portion 22 and an end of the second abutment portion 23. In this manner, a first flow path 41, which is a space formed by the connecting portion 24, the second abutment portion 23, and the metal support 80, and a second flow path 42, which is a space formed by the connecting portion 24, the first abutment portion 22, and the anode layer 50, are formed.

[0041] Next, the gas flowing through the first flow passage 41 and the second flow passage 42 when a DC voltage is applied to the electrochemical reactor 100 to purify exhaust gas (when reducing nitrogen oxides) will be described.

[0042] As shown in FIG. 5, in the metal support cell assembly 10, when nitrogen oxides (NOx) contained in the exhaust gas flow from the lower side into the cathode layer 60 through the metal support 80, a reduction reaction (2NO+4e - →N2+2O 2- The nitrogen gas (N2) produced by the reduction is discharged again to the flow path below the metal support cell assembly 10.

[0043] In the cathode layer 60, oxygen ions (O 2- The oxygen ions (not shown) are conducted through the solid electrolyte layer 70 and reach the anode layer 50. Then, the oxygen ions are oxidized in the anode layer 50 (2O 2- →O2+4e - ), oxygen gas (O2) is generated and discharged to the flow path above the metal support cell assembly 10. In this manner, in the electrochemical reactor 100, nitrogen oxides are reduced in the cathode layer 60 to generate nitrogen gas, and oxygen gas is generated in the anode layer 50.

[0044] Since the laminated member 20 has micropores 20A, the first flow path 41 and the second flow path 42 are connected to each other. Therefore, nitrogen oxides contained in the exhaust gas flowing through the second flow path 42 flow into the first flow path 41 through the micropores 20A, and then reach the cathode layer 60 via the metal support 80 and are reduced there. In this way, the electrochemical reactor 100 reduces the nitrogen oxides contained in the exhaust gas flowing between the two metal support cell assemblies 10 to produce nitrogen gas and oxygen gas.

[0045] 7 to 9 are diagrams showing the arrangement inside an exhaust flow path 120 of an electrochemical reactor 100 in this embodiment. Fig. 7 is a cross-sectional view of the exhaust flow path 120 in a plane including the exhaust flow direction and the lamination direction of the electrochemical reactor 100. Fig. 8 is a top view of an end of an anode layer 50 of the electrochemical reactor 100 as viewed from XIII (lamination direction) in Fig. 7. Fig. 9 is a cross-sectional view perpendicular to the exhaust flow direction at IX in Fig. 7.

[0046] As shown in FIG. 9, the exhaust flow path 120 has a rectangular cross section, and as shown in FIG. 7, the exhaust flow path 120 has a large cross section in the center relative to the inlet and outlet in the flow direction, and the electrochemical reactor 100 is provided at the point where the cross section is large.

[0047] 9 again, exhaust flow path 120 has an insulating portion 121 on a side surface thereof. Insulating portion 121 is provided so as to surround exhaust flow path 120 in a strip shape, and insulates conductive upper housing 122 and lower housing 123 that constitute exhaust flow path 120.

[0048] 7, the upper housing 122 and the lower housing 123 are connected so that a DC voltage can be applied from a power source 300. The gas flow path between the anode layer 50, which is the uppermost layer of the electrochemical reactor 100, and the upper housing 122 is referred to as an upper flow path 124, and the gas flow path between the metal support 80, which is the lowermost layer of the electrochemical reactor 100, and the lower housing 123 is referred to as a lower flow path 125.

[0049] In the upper flow path 124, the anode layer 50, which is the top layer of the electrochemical reactor 100, is fixed to the upper housing 122 via a gas sealing member 111 and a fixing member 112 provided in the upper flow path 124. The gas sealing member 111 and the fixing member 112 are members made of a conductive material, and are fixed to the anode layer 50 and the upper housing 122 by welding. In the lower flow path 125, the metal support 80 supporting the cathode layer 60, which is the bottom layer of the electrochemical reactor 100, is fixed to the lower housing 123 by two fixing members 112 provided in the lower flow path 125.

[0050] When the electrochemical reactor 100 receives power supply from the power source 300, an oxidation reaction proceeds in the anode layer 50, and a reduction reaction proceeds in the cathode layer 60. The gas sealing member 111 and the fixing member 112 are fixed by welding, so that the electrical connection is strengthened and the current collection resistance is reduced, thereby suppressing a decrease in the efficiency of power supply to the electrochemical reactor 100.

[0051] Here, the gas sealing member 111 is configured to cross the upper flow passage 124 in the width direction (the vertical direction in FIG. 8) and close the upper flow passage 124. In addition, the inside of the uppermost anode layer 50 is not configured uniformly as a porous member, and the region 51 connected to the gas sealing member 111 is configured densely, thereby blocking gas permeating through the anode layer 50. With this configuration, gas is prevented from flowing from the upstream side to the downstream side of the gas sealing member 111 in the upper flow passage 124.

[0052] The fixing member 112, like the gas sealing member 111, is provided across the upper flow passage 124 in the width direction. However, the region of the anode layer 50 connected to the fixing member 112 is not densely configured like the region 51, and gas can permeate inside. Therefore, gas can flow from the upstream side to the downstream side of the fixing member 112 in the upper flow passage 124. As shown in FIG. 8, the gas sealing member 111 and the fixing member 112 are provided symmetrically on the upstream and downstream sides with respect to the center line M of the electrochemical reactor 100 in the flow direction. With this configuration, it is possible to suppress shaking in the plane perpendicular to the airflow direction of the electrochemical reactor 100.

[0053] 7, in the metal support cell assembly 10, nitrogen oxides (NOx) flowing from below through the metal support 80 into the cathode layer 60 are reduced and released as nitrogen gas (N2), and at the same time, oxygen gas (O2) is released from the anode layer 50 above. That is, in the gas flow path 40 sandwiched between two metal support cell assemblies 10, nitrogen gas is released from the cathode layer 60 through the metal support 80 from the metal support cell assembly 10 in contact with the upper side, and oxygen gas is released from the anode layer 50 from the metal support cell assembly 10 in contact with the lower side. Note that, between the gas sealing member 111 and the fixing member 112 in the upper flow path 124, oxygen gas is released from the anode layer 50, and the released oxygen gas flows out to the downstream side of the fixing member 112.

[0054] Here, the upper flow passage 124 faces the cathode layer 60 but is not in contact with the anode layer 50 where the reduction reaction takes place. Therefore, if nitrogen oxides (NOx) flow into the upper flow passage, there is a risk that they will flow downstream without being reduced. Therefore, by providing the gas sealing member 111 and forming the region 51 of the anode layer 50, which is a porous member, densely, the upper flow passage 124 is blocked, and it is possible to prevent unreduced nitrogen oxides from flowing downstream. Note that oxygen gas released from the cathode layer 60 in the upper flow passage 124 passes through the inside of the cathode layer 60 and flows out downstream of the fixing member 112.

[0055] The lower flow passage 125 is in contact with the anode layer 50, in which a reduction reaction takes place, via the metal support 80. Therefore, in the lower flow passage 125, nitrogen oxides (NOx) are reduced by the anode layer 50. In the lower flow passage 125, no gas sealing member 111 is provided, and instead, two fixing members 112 are provided, so that the reduced nitrogen gas flows downstream through the fixing members 112.

[0056] In the above description, oxygen ions are oxidized in the anode layer 50, but this is not limiting. If unburned fuel (HC) and carbon oxides (CO) are not oxidized in the three-way catalyst 130, these unoxidized substances are oxidized in the anode layer 50. That is, by operating the electrochemical reactor 100, unreduced substances (nitrogen oxides) in the exhaust gas are reduced in the cathode layer 60, and unoxidized substances (unburned fuel, carbon oxides) are oxidized in the anode layer 50.

[0057] Here, the lower flow passage 125 contacts the cathode layer 60 via the metal support 80, and does not face the anode layer 50 that performs oxidation. Therefore, in order to suppress the outflow of unoxidized substances downstream in the lower flow passage 125, it is necessary to configure some regions of the metal support 80 and the cathode layer 60 densely and provide the gas sealing member 111 in the densely configured region. With this configuration, the outflow of unoxidized substances from the upstream to the downstream of the gas sealing member 111 is prevented in the lower flow passage 125.

[0058] In the present embodiment, both the gas sealing member 111 and the fixing member 112 in the upper flow path 124 are made of a conductive material, but this is not limited thereto. At least one of the gas sealing member 111 and the fixing member 112 may be made of a conductive material to electrically connect the upper housing 122 and the anode layer 50. By making the other of the gas sealing member 111 and the fixing member 112 of a non-conductive material, the number of members through which a current flows can be reduced, thereby reducing the risk of a short circuit. Similarly, at least one of the two fixing members 112 provided in the lower flow path 125 may be made of a conductive material.

[0059] According to the first embodiment, the following effects can be obtained.

[0060] The electrochemical reactor 100 of the first embodiment is provided in an exhaust flow path 120, and purifies exhaust gas by an electrochemical reaction in response to application of a voltage from a power source 300. The electrochemical reactor 100 is configured by stacking a plurality of cells (metal support cell assemblies 10) each including a cathode layer 60 capable of reducing nitrogen oxides (unreduced substances) contained in the exhaust gas, an anode layer 50 capable of oxidizing unburned fuel and carbon oxides (unoxidized substances) contained in the exhaust gas, and a solid electrolyte layer 70 sandwiched between the anode layer 50 and the cathode layer 60. The anode layer 50 located at the outermost side of the stacked metal support cell assemblies 10 has a part of a region 51 densely configured to prevent exhaust gas from flowing downstream.

[0061] Here, the upper flow passage 124 in contact with the outermost anode layer 50 of the electrochemical reactor 100 is not in contact with the cathode layer 60 where the reduction reaction takes place, so there is a risk that unreduced nitrogen gas will flow downstream. In addition, since the anode layer 50 is a porous member, gas will permeate through the inside. Therefore, the gas sealing member 111 is provided and a partial region 51 of the anode layer 50 is densely configured, so that the exhaust gas is prevented from flowing downstream in the upper flow passage 124 and the gas permeating through the anode layer 50 is blocked. As a result, the risk that unreduced nitrogen oxides will flow downstream of the gas sealing member 111 can be reduced.

[0062] Furthermore, when unoxidized substances are contained in the exhaust gas, the lower flow passage 125 that contacts the outermost cathode layer 60 (including the metal support 80) at the bottom of the electrochemical reactor 100 is not in contact with the anode layer 50 where the oxidation reaction takes place, so that unoxidized carbon compounds and the like may flow downstream. Therefore, a part of the region of the cathode layer 60 (including the metal support 80) is densely configured, and a gas sealing member 111 that closes the lower flow passage 125 is provided in the densely configured part. In this way, the exhaust gas is prevented from flowing downstream in the lower flow passage 125, and the gas that permeates the cathode layer 60 is blocked. As a result, the risk of unoxidized substances flowing downstream can be reduced.

[0063] According to the electrochemical reactor 100 of the first embodiment, the electrochemical reactor 100 is configured by stacking a plurality of cells (metal support cell assemblies 10) each composed of a cathode layer 60, an anode layer 50, and a solid electrolyte layer 70 sandwiched between the anode layer 50 and the cathode layer 60, via a lamination member 20 through which exhaust gas can pass. With this configuration, a flow path through which exhaust gas passes is formed by the lamination member 20 between the two cells, so that unburned fuel and carbon oxides (unoxidized substances) are oxidized in the anode layer 50 in contact with one side of the lamination member, and nitrogen oxides (unreduced substances) contained in the exhaust gas are easily reduced in the cathode layer 60 in contact with the other side of the lamination member.

[0064] According to the electrochemical reactor 100 of the first embodiment, the upper flow path 124 (wall flow path) is provided with a gas sealing member 111 and further provided with a fixing member 112. Here, if only the gas sealing member 111 is provided, the gas sealing member 111 may vibrate due to the flow of exhaust gas, causing the fixed state between the electrochemical reactor 100 and the exhaust flow path 120 to become loose. However, by fixing the electrochemical reactor 100 at two points, the gas sealing member 111 and the fixing member 112, the electrochemical reactor 100 can be fixed more reliably.

[0065] According to the electrochemical reactor 100 of the first embodiment, the gas sealing member 111 and the fixing member 112 are paired on the upstream side and downstream side in the exhaust flow direction, and are arranged symmetrically with respect to the center line M in the flow path direction of the electrochemical reactor 100. By arranging them in this manner, the forces applied to the gas sealing member 111 and the fixing member 112 on the upstream side and downstream side with respect to the center line M become uniform, and the generation of torque in the rotation direction around the flow direction can be suppressed, so that the electrochemical reactor 100 can be fixed more reliably.

[0066] According to the electrochemical reactor 100 of the first embodiment, the gas sealing member 111 is provided upstream of the fixing member 112. Oxygen gas discharged from the anode layer 50 upstream of the gas sealing member 111 does not flow downstream of the gas sealing member 111 but flows toward the upstream side, goes around the metal support cell assembly 10, and flows into the gas flow path 40. In addition, oxygen gas discharged from the anode layer 50 downstream of the gas sealing member 111 can pass through the inside of the anode layer 50 and flow to the downstream side of the fixing member 112. By providing the gas sealing member 111 upstream of the fixing member 112, the route through which the oxygen gas goes around the upstream side of the gas sealing member 111 can be shortened, and the flow path of the oxygen gas downstream of the gas sealing member 111 can be lengthened, so that the exhaust flow can be stabilized.

[0067] According to the electrochemical reactor 100 of the first embodiment, at least one of the gas sealing member 111 and the fixing member 112 is made of a conductive material. In this way, the gas sealing member 111 and the fixing member 112 can be used as a power supply terminal (bus bar) from the power source 300, thereby reducing the number of parts.

[0068] According to the electrochemical reactor 100 of the first embodiment, one of the gas sealing member 111 and the fixing member 112 is made of a conductive material, and the other is made of a non-conductive material. By using a non-conductive material for some of the members in this manner, the risk of a short circuit can be reduced.

[0069] According to the electrochemical reactor 100 of the first embodiment, at least one of the gas sealing member 111 and the fixing member 112, which are made of a conductive material, is fixed to the anode layer 50 and the upper housing 122 by welding. By fixing the gas sealing member 111 and the fixing member 112 by welding, the electrical connection becomes strong and the current collection resistance can be reduced. As a result, the operating efficiency of the electrochemical reactor 100 can be improved.

[0070] (First Modification) In the first embodiment, an example has been described in which a gas sealing member 111 that blocks the upper flow passage 124 is provided on the outermost anode layer 50 side of the electrochemical reactor 100, thereby preventing exhaust gas passing through the upper flow passage 124 from flowing downstream in an unreduced state. In the first modified example, an example will be described in which the outermost anode layer 50 side of the electrochemical reactor 100 contacts the inner surface of the upper housing 122.

[0071] FIG. 10 is a diagram showing the configuration of the first modified example, and is a cross-sectional view of the exhaust flow path 120 along a plane including the exhaust flow direction and the stacking direction of the electrochemical reactor 100, and corresponds to FIG.

[0072] According to this figure, in the electrochemical reactor 100, the anode layer 50, which is the outermost surface at the top in the stacking direction, is in contact with the inner surface of the upper housing 122 and fixed by an adhesive member (not shown). The anode layer 50 is a porous member into which gas can permeate, so there is a risk that exhaust gas that has permeated from the upstream end face will pass through the inside without being reduced and be released from the downstream side. Therefore, by forming a part of the region 51 of the anode layer 50 densely, it is possible to block the permeation of gas within the anode layer 50, and therefore the release of unreduced nitrogen oxides downstream is suppressed.

[0073] Thus, according to the first modification, the anode layer 50, which is the outermost surface in the stacking direction of the electrochemical reactor 100, is in contact with the inner surface of the upper housing 122, and further, a partial region 51 of the anode layer 50 is configured to be dense. By configuring in this manner, it is possible to prevent unreduced nitrogen oxides from flowing downstream without providing a gas sealing member 111.

[0074] (Second Modification) In the first embodiment, an example has been described in which fixing member 112 is provided so as to cover the entire upper flow path 124. In the second modified example, an example will be described in which fixing member 112 is provided so as to cover a portion of the upper flow path 124 and an opening that allows flow through the upper flow path 124 is formed.

[0075] FIG. 11 is a top view of the end portion of the anode layer 50 of the electrochemical reactor 100 of the second modified example, as viewed from the stacking direction, and corresponds to FIG.

[0076] According to this figure, the fixing member 112 is provided so as to cover a part of the upper flow passage 124 provided between the cathode layer 60, which is the end of the electrochemical reactor 100, and the upper housing 122, and an opening that allows flow in the upper flow passage 124 is formed on the side in the width direction. In detail, the fixing member 112 is configured to be shorter than the width of the exhaust flow passage 120 in the direction perpendicular to the stacking direction (the width direction, the top and bottom in FIG. 11), and is disposed so as to be spaced apart from the side surface of the upper housing 122.

[0077] In the electrochemical reactor 100 of the second modification, the fixing member 112 is provided to cover a part of the upper flow passage 124 so as to provide an opening that allows flow in the upper flow passage 124. This makes it easier for oxygen gas released from the anode layer 50 upstream of the fixing member 112 to flow downstream of the fixing member 112. As a result, it is possible to prevent the oxygen gas from accumulating between the gas sealing member 111 and the fixing member 112 and increasing the pressure in a part of the exhaust flow passage 120, and therefore the electrochemical reaction can proceed stably.

[0078] (Third Modification) In the first embodiment, an example in which a plurality of metal support cell assemblies 10 constituting the electrochemical reactor 100 are stacked via bent stacking members 20 has been described, but the present invention is not limited to this. In the fourth modified example, an example in which a plurality of metal support cell assemblies 10 are stacked via leaf springs 25 will be described.

[0079] Fig. 12 is a cross-sectional view of the gas flow path 40 as viewed from the front direction, and corresponds to Fig. 5. Fig. 13 is a top view of the leaf spring 25 as viewed from above in the stacking direction. That is, in this figure, the exhaust gas flows along the paper surface.

[0080] 12, the leaf spring 25 is configured by providing a contact portion 251 for fixing the metal support cell assembly 10 in contact with the upper side, and an inclined portion 252 for separating the vertically adjacent metal support cell assemblies 10, on a plate portion 253. As shown in FIG. 13, the leaf springs 25 are provided at multiple points on one plate portion 253.

[0081] According to the electrochemical reactor 100 of the third modification, a leaf spring 25 is provided between adjacent metal support cell assemblies 10, and exhaust gas flows through the region where the leaf spring 25 is provided. In one (upper part of the figure) of the two metal support cell assemblies 10 facing each other through the leaf spring 25, nitrogen oxides (NOx) are reduced in the cathode layer 60 supported by the metal support 80 in a region other than the region in contact with the abutment part 251. In the other (lower part of the figure) of the metal support cell assembly 10, oxygen gas is released from the anode layer 50 at an opening provided by a notch in the plate part 253. In this way, by using the leaf spring 25, the lamination member 20 can be configured with a simpler structure than the separator shown in the first embodiment.

[0082] (Fourth Modification) In the first embodiment, a plurality of metal support cell assemblies 10 constituting the electrochemical reactor 100 are stacked via bent stacking members 20, and in the third modified example, via leaf springs 25, but the present invention is not limited to this. In the fourth modified example, an example in which metal support cell assemblies 10 are stacked via porous metal will be described.

[0083] Fig. 14 is a cross-sectional view of the gas flow passage 40 as viewed from the front direction, and corresponds to Fig. 5. That is, in this figure, the exhaust gas flows along the paper surface direction.

[0084] As shown in the figure, the metal support cell assembly 10 is constructed by stacking a cathode layer 60, a solid electrolyte layer 70, and an anode layer 50 between two metal supports 80. The metal support cell assembly 10 is further sandwiched between two gas-permeable porous metal layers 26 in the stacking direction, thereby forming an electrochemical cell 10A. A plurality of such electrochemical cells 10A (two in the figure) are stacked to form an electrochemical reactor 100. In the electrochemical reactor 100 finally constructed, the anode layer 50 or the cathode layer 60 is arranged on the outermost side in the stacking direction, instead of the porous metal layer 26 or the metal support 80. In the outermost anode layer 50, a part of the region 51 (not shown) is densely configured, thereby suppressing the outflow of unreduced nitrogen oxides downstream.

[0085] According to the electrochemical reactor 100 of the fourth modification, two gas-permeable porous metal layers 26 are provided between one metal support 80 of one metal support cell assembly 10 and the metal support 80 of the other opposing metal support cell assembly 10. Exhaust gas flows inside the porous metal layer 26, and unreduced nitrogen oxides contained in the exhaust gas are reduced in the cathode layer 60 of one metal support cell assembly 10. At the same time, unoxidized unburned fuel and carbon oxides are oxidized in the anode layer 50 of the other metal support cell assembly 10. Even with this configuration, oxidation and reduction reactions can be carried out.

[0086] Second embodiment In the first embodiment, an example has been described in which an exhaust inlet and an exhaust outlet are provided opposite each other in the exhaust flow path 120. In the second embodiment, an example will be described in which an exhaust inlet and an exhaust outlet are provided on one side of the exhaust flow path 120.

[0087] Fig. 15 is a cross-sectional view of the exhaust flow path 120 in a plane including the exhaust flow direction and the lamination direction of the electrochemical reactor 100, and corresponds to Fig. 7. Fig. 16 is a cross-sectional view taken along XVI in Fig. 15, which is a cross-sectional view taken along a direction perpendicular to the exhaust flow direction. In this embodiment, the electrochemical reactor 100 is configured by laminating the metal support cell assemblies 10 shown in the fourth modified example via the porous metal layer 26. The outermost part of the upper part of the lamination direction of the electrochemical reactor 100 is the anode layer 50, and the outermost part of the lower part is the cathode layer 60.

[0088] In this embodiment, the electrochemical reactor 100 is housed in a rectangular exhaust flow path 120. The exhaust flow path 120 is composed of an upper housing 122 and a lower housing 123 that face each other via an insulating part 121 that surrounds the side in a band shape. An exhaust inlet 126 and an exhaust outlet 127 are provided at both ends of the lower surface of the lower housing 123. As in the first embodiment, the outermost part of the upper part of the electrochemical reactor 100 is connected to the inner surface of the upper housing 122 by a gas sealing member 111 and a fixing member 112, and the outermost part of the lower part of the electrochemical reactor 100 is connected to the inner surface of the lower housing 123 by two fixing members 112. The gas sealing member 111 is connected to a region 51 that is densely formed in the anode layer 50.

[0089] As shown in FIG. 16, when viewed from the flow path direction, a plastically deformable gasket 128 is provided between the electrochemical reactor 100 and the exhaust flow path 120 in a direction perpendicular to the stacking direction to suppress lateral outflow of gas.

[0090] According to the electrochemical reactor 100 of the second embodiment, exhaust gas flowing into the exhaust passage 120 from the inlet 126 passes through the porous metal layer 26 of the electrochemical reactor 100 and flows out from the outlet 127. Unreduced nitrogen oxides contained in the exhaust gas flowing through the porous metal layer 26 are reduced in the cathode layer 60 of the metal support cell assembly 10 that contacts one side of the porous metal layer 26, and unoxidized unburned fuel and carbon oxides are oxidized in the anode layer 50 of the metal support cell assembly 10 that contacts the other side of the porous metal layer 26. Even with this configuration, it is possible to reduce nitrogen oxides while suppressing the outflow of unreduced nitrogen oxides to the downstream side in the upper passage that contacts the cathode layer 60.

[0091] In the first and second embodiments, an example has been described in which a plurality of metal support cell assemblies 10 each composed of an anode layer 50, a solid electrolyte layer 70, and a cathode layer 60 are stacked via a metal plate-shaped lamination member 20 (separator, first embodiment), a leaf spring 25 (third modified example), and a porous metal layer 26 (fourth modified example), but the present invention is not limited to this.

[0092] For example, multiple metal support cell assemblies 10 may be stacked apart from each other using some kind of fixing member without using these stacking members. In this case, exhaust gas flows through the gap. Between the anode electrode layer 50 of one metal support cell assembly 10 and the cathode electrode layer 60 of the other adjacent metal support cell assembly 10, a bus bar is provided to connect the two so as to ensure electrical conductivity.

[0093] Alternatively, multiple metal support cell assemblies 10 may be stacked without these stacking members and without being spaced apart. In this case, the metal support cell assemblies 10 are adjacent to each other, and the anode layer 50 of one metal support cell assembly 10 is adjacent to the cathode layer 60 of the other metal support cell assembly 10. Since the anode layer 50 and the cathode layer 60 are porous members, the anode layer 50 and the cathode layer 60 themselves act as exhaust flow paths, and exhaust gas flows in from the sides.

[0094] In the first embodiment, the metal support 80 is provided so as to contact the lower surface of the cathode layer 60, but this is not limited thereto. The metal support 80 may be provided so as to contact the upper surface of the anode layer 50. When the anode layer 50 or the cathode layer 60 and the metal support 80 are integrally formed, the members thus integrally formed may be referred to as the anode layer and the cathode layer.

[0095] Alternatively, metal support cell assemblies 10 may be adjacently configured with a conductive adhesive interposed between them, with a solid electrolyte layer interposed therebetween, as shown in Fig. 17. Fig. 17 is a cross-sectional view of the gas flow passage 40 as viewed from the front direction, and corresponds to Fig. 5.

[0096] According to this figure, like other configurations, the metal support cell assembly 10 is configured by stacking a cathode layer 60, a solid electrolyte layer 70, and an anode layer 50. Each of the metal support cell assemblies 10 has a conductive adhesive 27 on the upper and lower surfaces in the stacking direction, and is stacked via a porous metal layer 26. The conductive adhesive 27 is a porous member through which exhaust gas can pass. As a result, the porous metal layer 26 and the conductive adhesive 27 become an exhaust gas flow path, and electrical conductivity in the stacking direction of the multiple metal support cell assemblies 10 is ensured. The anode layer 50 and the cathode layer 60 are supported by a metal support 80, and the conductive adhesive 27 may be provided on the metal support 80. In this case, exhaust gas flows through the metal support 80 in addition to the porous metal layer 26 and the conductive adhesive 27.

[0097] Although the embodiments of the present invention have been described above, the above-mentioned embodiments merely show some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above-mentioned embodiments. [Explanation of symbols]

[0098] 1 cell unit, 10 electrochemical cell (metal support cell assembly), 20 laminated member, 40 gas flow path, 50 anode electrode layer, 51 region, 60 cathode electrode layer, 70 solid electrolyte layer, 80 metal support, 100 electrochemical reactor, 111 gas sealing member, 112 fixing member, 120 exhaust flow path

Claims

1. An electrochemical reactor that is provided inside a housing of an exhaust passage of an internal combustion engine and purifies exhaust gas discharged from the internal combustion engine by an electrochemical reaction in response to application of a voltage, the electrochemical reactor is configured by stacking a plurality of cells, each cell being configured with a cathode layer being a porous member capable of reducing unreduced substances contained in the exhaust gas, an anode layer being a porous member capable of oxidizing unoxidized substances contained in the exhaust gas, and a solid electrolyte layer sandwiched between the anode layer and the cathode layer; A gas flow path through which the exhaust gas flows is formed between the cells adjacent to each other in the stacking direction, the plurality of cells are stacked such that an anode layer of one of the cells adjacent to each other in the stacking direction faces a cathode layer of the other cell via the gas flow path; a wall flow path is formed between at least one of the anode layer and the cathode layer located at the outermost position in the stacking direction and a wall surface of the housing, a gas sealing portion that prevents the exhaust gas from flowing downstream is provided in the wall surface flow path, an electrochemical reactor, wherein at least one of the anode layer and the cathode layer facing the wall surface flow path has a portion of the porous member that is densely configured at a portion that overlaps with the gas sealing portion so that the exhaust gas is prevented from flowing downstream within the porous member.

2. An electrochemical reactor provided inside a housing of an exhaust passage of an internal combustion engine, which purifies exhaust gas discharged from the internal combustion engine by an electrochemical reaction in response to application of a voltage, comprising: the electrochemical reactor is configured by stacking a plurality of cells, each cell being configured with a cathode layer being a porous member capable of reducing unreduced substances contained in the exhaust gas, an anode layer being a porous member capable of oxidizing unoxidized substances contained in the exhaust gas, and a solid electrolyte layer sandwiched between the anode layer and the cathode layer; A gas flow path through which the exhaust gas flows is formed between the cells adjacent to each other in the stacking direction, the plurality of cells are stacked such that an anode layer of one of the cells adjacent to each other in the stacking direction faces a cathode layer of the other cell via the gas flow path; a wall surface flow path is formed between the anode layer located at the outermost position in the stacking direction and a wall surface of the housing, a gas sealing portion that prevents the exhaust gas from flowing downstream is provided in the wall surface flow path, an anode layer positioned at the outermost position in the stacking direction, the porous member being densely configured at a portion overlapping the gas sealing portion so that the exhaust gas is prevented from flowing downstream within the porous member;

3. 3. The electrochemical reactor according to claim 1 or 2, an electrochemical reactor, wherein a plurality of cells each including the cathode layer, the anode layer, and a solid electrolyte layer sandwiched between the anode layer and the cathode layer are stacked via a stacking member through which the exhaust gas can pass.

4. 4. The electrochemical reactor according to claim 1 , moreover, An electrochemical reactor comprising: a fixing portion that fixes the electrochemical reactor to the housing.

5. 5. The electrochemical reactor of claim 4, An electrochemical reactor, wherein the gas sealing portion and the fixing portion form a pair and are arranged symmetrically on the upstream side and the downstream side with respect to the center of the cell in the flow direction of the exhaust gas.

6. 6. The electrochemical reactor according to claim 4 or 5, The gas sealing portion is provided upstream of the fixed portion in a flow of the exhaust gas.

7. 7. The electrochemical reactor according to claim 4, The fixing portion is provided so as to close a part of the wall surface flow path.

8. 8. The electrochemical reactor according to claim 4, At least one of the gas sealing portion and the fixing portion provided in the wall surface flow path is made of a conductive material.

9. 8. The electrochemical reactor according to claim 4, one of the gas sealing portion and the fixing portion is made of a conductive material; The other of the gas sealing portion and the fixed portion is made of a non-conductive material.

10. 10. The electrochemical reactor according to claim 8 or 9, At least one of the gas sealing portion and the fixing portion, which are made of the conductive material, is fixed by welding.

11. 9. The electrochemical reactor of claim 8, one of the anode layer and the cathode layer located at one outermost position in a stacking direction of the stacked cells is connected to a part of the conductive casing via at least one of the gas sealing portion and the fixing portion, which are made of the conductive material; the other of the anode layer and the cathode layer located at the outermost position of the other of the stacked cells is connected to another conductive portion insulated from the part of the casing by at least one of the gas sealing portion and the fixing portion, which are made of the conductive material; The voltage is applied to the electrochemical reactor by connecting the first portion and the second portion of the housing to a voltage supply terminal.

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