JP2015097149A - Solid oxide fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress deterioration in power generation performance in a solid oxide fuel cell that uses a separator comprising a chromium-containing alloy material.SOLUTION: A solid oxide fuel cell includes a reaction layer 106 comprising a nickel cobalt alloy, between an air electrode side separator 105 and an air electrode 101. The reaction layer 106 includes a plurality of holes communicating between a side of the air electrode 101 and a side of the air electrode side separator 105. The reaction layer 106 may be constituted, for example, from foam metal of a nickel cobalt alloy, and also may be a nonwoven cloth of thread comprising a nickel cobalt alloy.

Description

  The present invention relates to a solid oxide fuel cell using a separator made of an alloy containing chromium.

  In recent years, fuel cells have attracted attention as power generation means used in next-generation cogeneration systems because high efficiency can be obtained regardless of the size. A fuel cell is a cell that utilizes a chemical reaction between an oxidant gas such as oxygen and a fuel gas such as hydrogen. In a fuel cell, a plurality of single cells are used in which an electrolyte layer is sandwiched between an anode called an air electrode and a cathode called a fuel electrode.

  The voltage obtained in one set of cells (single cells) is about 0.7 V, but a desired voltage can be supplied by using a plurality of single cells in an overlapping manner. Such fuel cells include a solid polymer type using a polymer material for the electrolyte layer, and a solid oxide type using an oxide such as ceramics for the electrolyte layer. Solid oxide fuel cells are expected to have high power generation efficiency among fuel cells.

  A solid oxide fuel cell is configured by stacking a plurality of single cells each composed of a solid oxide electrolyte, an air electrode, and a fuel electrode as described above. In such a cell stack configuration, each of the separators for supplying air to the air electrode, supplying fuel gas to the fuel electrode, exhausting used or unused fuel gas, and taking out electric power from the cell, Arranged between single cells.

  As the separator material, stainless steel is generally used from the viewpoint of cost and workability. Further, since the operating temperature of the solid oxide fuel cell is 600 ° C. to 800 ° C., chromium-containing heat resistant stainless steel is used.

N. Sakai, T. Horita, K. Yamaji, YP Xiong, H. Kishimoto, ME Brito, H. Yokokawa, "Material transport and degradation behavior of SOFC interconnects", Solid State Ionics, vol.177, pp.1933-1939 , 2006.

  However, when heat-resistant stainless steel containing chromium is used, there is a problem in that the chromium contained in the separator evaporates to deteriorate the air electrode and reduce the power generation performance under the temperature conditions during operation. In order to solve this problem, attempts have been made to lower the vapor pressure of chromium by coating the separator surface with oxide or metal. However, there has been a problem that, due to long-term use and thermal cycle, the coating film is cracked and chromium is evaporated. Thus, when the separator comprised from the alloy material containing chromium was used, there existed a problem that the case where the power generation performance in a solid oxide fuel cell fell occurred.

  The present invention has been made to solve the above-described problems, and is capable of suppressing a decrease in power generation performance in a solid oxide fuel cell using a separator composed of an alloy material containing chromium. For the purpose.

  A solid oxide fuel cell according to the present invention includes a plurality of single cells each having an air electrode, an electrolyte, and a fuel electrode, and a separator made of an alloy including chromium disposed between the single cells; And a reaction layer made of a nickel-cobalt alloy that is disposed between the separator and the air electrode and includes a plurality of holes that communicate the air electrode side and the separator side.

  In the solid oxide fuel cell, the reaction layer may be made of a nickel cobalt alloy foam metal. Moreover, the reaction layer should just be the nonwoven fabric by the thread | yarn comprised from the nickel cobalt alloy.

  As described above, according to the present invention, since the reaction layer composed of the nickel-cobalt alloy is provided, the power generation performance of the solid oxide fuel cell using the separator composed of the alloy material containing chromium is improved. An excellent effect that the reduction can be suppressed is obtained.

FIG. 1 is a configuration diagram showing a configuration of a solid oxide fuel cell according to an embodiment of the present invention. FIG. 2 is a configuration diagram showing a more detailed state of the solid oxide fuel cell according to the embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing a configuration of a solid oxide fuel cell according to an embodiment of the present invention. FIG. 1 schematically shows a cross section.

  The solid oxide fuel cell includes a plurality of unit cells 104 each having an air electrode 101, an electrolyte 102, and a fuel electrode 103. In FIG. 1, the portion of one single cell 104 is shown enlarged. Although not shown, a plurality of single cells 104 are stacked in the vertical direction of the drawing in FIG. Further, an air electrode side separator 105 made of an alloy containing chromium is disposed between the stacked single cells 104. A fuel electrode side separator (not shown) is disposed on the fuel electrode 103 side, and the fuel electrode side separator is disposed on the air electrode side separator 105 between the single cells. Details of these basic solid oxide fuel cell configurations are omitted.

  In addition to the basic structure of the solid oxide fuel cell described above, the present invention is characterized in that a reaction layer 106 made of a nickel cobalt alloy is provided between the air electrode side separator 105 and the air electrode 101. is there. The reaction layer 106 includes a plurality of holes that communicate the air electrode 101 side and the air electrode side separator 105 side. The reaction layer 106 may be made of, for example, a foamed metal of a nickel cobalt alloy. Further, the reaction layer 106 may be a nonwoven fabric made of a thread made of a nickel cobalt alloy. The reaction layer 106 only needs to be made of such a porous (continuous porous structure) material.

  For example, when the reaction layer 106 is composed of foam metal, the reaction layer 106 is overlaid on the air electrode 101 of the single cell 104, and further, the air electrode side separator 105 is overlaid on the reaction layer 106, and pressure is applied. The air electrode 101, the reaction layer 106, and the air electrode side separator 105 are brought into close contact with each other.

  As is well known, a channel groove for uniformly supplying an oxidizing gas such as air is formed on the single cell 104 side (air electrode 101 side) of the air electrode side separator 105. If the air electrode 101 is pressed against such an air electrode side separator 105 with a reaction layer 106 made of foam metal and deformable, the reaction layer is interposed between the air electrode 101 and the air electrode side separator 105. 106 is sandwiched without a gap. The reaction layer 106 can be deformed by the application of stress, and an adhesion state as described above can be realized.

  For example, in the manufacture of a solid oxide fuel cell, a slurry of a powder or mixed powder of the material constituting each electrode is prepared, and a film (layer) of this slurry is formed at 1000 to 1200 ° C. The above layers are produced by firing. For example, the air electrode 101, the reaction layer 106, and the air electrode side separator 105 may be stacked in a close contact state as described above in an unfired state, and then fired.

  As described above in the unfired state, the air electrode 101, the reaction layer 106, and the air electrode side separator 105 are in close contact with each other in the solid oxide fuel cell that is completed by firing, as described above. It is laminated in a state. In this close contact state, the electrical resistance between the air electrode 101 and the air electrode side separator 105 is reduced.

  Further, when a plurality of unit cells 104 are stacked and connected in a stack, the occurrence of poor contact portions on the stacked surface due to variations in the thickness and shape of the unit cells 104 is caused by the pressure during assembly of the solid oxide fuel cell. This is advantageous because it is eliminated by deformation of the reaction layer 106.

  Hereinafter, it demonstrates in detail using FIG. FIG. 2 is a configuration diagram showing a more detailed state of the solid oxide fuel cell according to the embodiment of the present invention. FIG. 2 schematically shows the state of each component before assembly.

  As shown in FIG. 2, the solid oxide fuel cell includes a single cell 104 having an air electrode 101, an electrolyte 102, and a fuel electrode 103. An air electrode side separator 105 made of an alloy containing chromium is disposed on the air electrode 101 side, and a reaction layer 106 is disposed between the air electrode 101 and the air electrode side separator 105.

  On the other hand, a fuel electrode side separator 107 is disposed on the fuel electrode 103 side. A mesh-shaped fuel electrode side current collecting layer 108 is provided between the fuel electrode side separator 107 and the fuel electrode 103. A cell holder 109 for storing the single cell 104 is disposed between the air electrode side separator 105 and the fuel electrode side separator 107 around the single cell 104. Further, an insulating portion 110 made of a heat-resistant insulating material such as mica is disposed between the cell holder 109 and the air electrode side separator 105. Further, a seal member 111 provided between the cell holder 109 and the single cell 104 is disposed inside the cell holder 109.

  Here, the air electrode side separator 105 and the fuel electrode side separator 107 are provided with a manifold (not shown) through which an oxidant gas supplied to the air electrode 101 is circulated and a manifold (not shown) through which the fuel gas supplied to the fuel electrode 103 is circulated. (Shown) is formed. The cell holder 109 has a thickness sufficient for storing the single cell 104. The cell holder 109 is also provided with a manifold (not shown) for communicating the manifolds of the air electrode side separator 105 and the fuel electrode side separator 107 disposed between the cell holders 109.

  When assembling the above parts, for example, in the solid oxide fuel cell, the cell holder 109 is disposed on the fuel electrode side separator 107 in a state where the parts of the manifolds are aligned, and the air electrode side separator is disposed on the cell holder 109. 105 is arranged. Further, a fuel electrode side current collecting layer 108 is arranged in the arrangement region of the unit cell 104 of the fuel electrode 103 and the fuel electrode side separator 107, and the fuel electrode 103 is arranged on the fuel electrode side current collecting layer 108. Like that. These assemblies may be performed on the insulating plate 212 by providing the insulating plate 212 on the pedestal 211 made of a heat-resistant alloy.

  A mesh-like current collecting layer similar to the fuel electrode side current collecting layer 108 may be provided between the air electrode side separator 105 and the air electrode 101. In this case, the current collecting layer is preferably provided between the air electrode side separator 105 and the reaction layer 106.

  Further, the side surface of the unit cell 104 and the inner peripheral surface of the cell holder 109 are sealed by the seal member 111, so that the air electrode side separator 105 side and the fuel electrode side separator 107 are spatially separated via the unit cell 104. To separate. Thus, the supplied oxidant gas and fuel gas are prevented from being mixed. Further, the insulating portion 110 electrically insulates and separates the air electrode side separator 105 and the fuel electrode side separator 107 with the cell holder 109 interposed therebetween.

  Next, the power generation operation of the solid oxide fuel cell configured as described above will be briefly described. First, when an oxidant gas such as oxygen is introduced into a manifold for supplying an oxidant gas, the oxidant gas passes through a flow path (not shown) formed inside the air electrode side separator 105 and passes through the air electrode. 101 side is reached. The oxidant gas thus introduced is supplied in a uniform state over the entire area of the air electrode 101 by a flow channel groove (not shown) formed in the air electrode side separator 105 on the air electrode 101 side. Become. Further, unused exhaust gas is exhausted outward from the side portion between the air electrode 101 and the air electrode side separator 105.

  On the other hand, when a fuel gas such as hydrogen is introduced into the fuel gas supply manifold, the fuel gas passes through a flow path (not shown) formed in the fuel electrode side separator 107 and is on the fuel electrode 103 side. To reach. The fuel gas introduced in this way is supplied in a uniform state over the entire area of the fuel electrode 103 by a channel groove (not shown) formed in the fuel electrode side separator 107 on the fuel electrode 103 side. . Further, the exhaust gas is discharged from a space sealed between the fuel electrode 103 and the fuel electrode side separator 107 through an exhaust passage (not shown) provided in the fuel electrode side separator 107, and then a fuel gas exhaust manifold. Exhausted from.

As described above, when the oxidizing gas is supplied to the air electrode 101 and the fuel gas is introduced to the fuel electrode 103, it contributes to the electrode reaction at the interface where the particles of the electrolyte 102 and the air electrode 101 are in contact. The triple layer interface becomes the active point of the electrochemical reaction on the air electrode 101 side, and the oxygen of the supplied oxidant gas is generated by the air electrode reaction represented by the chemical formula “1 / 2O ₂ + 2e ⁻ → O ²⁻ ”. Electrons react to generate oxygen ions.

The oxygen ions generated in the air electrode 101 in this way move inside the electrolyte 102 and reach the fuel electrode 103. In the fuel electrode 103, the oxygen ions that have moved inside the electrolyte 102 are supplied to the fuel electrode 103 by a fuel electrode reaction represented by the chemical formula “H ₂ + O ^{2 −} → H ₂ O + 2e ⁻ ”. Reacts with hydrogen. As a result, water vapor and electrons are generated at the fuel electrode 103.

  The electrons generated at the fuel electrode 103 as described above move through the external circuit and reach the air electrode 101. The electrons that have reached the air electrode 101 react with oxygen by the air electrode reaction described above. In the process that the electrons move through the external circuit, electric energy can be taken out as a direct current output of the solid oxide fuel cell.

  Here, in this solid oxide fuel cell, since the reaction layer 106 is provided as described above, even when the fuel electrode support type single cell 104 having a variation in shape is used, at the manufacturing (assembly) stage. The variation in the cell shape can be absorbed by the shape change caused by the stress of the reaction layer 106 that is easily changed by the application of the stress. As a result, a uniform output can be expected from each of the stacked single cells.

  Next, a method for manufacturing a solid oxide fuel cell will be briefly described. First, a plate-like fuel electrode made of Ni-ScSZ is prepared, and a plate-like electrolyte layer made of ScSZ is placed thereon, on which LNF having an average particle size of 0.5 to 1.0 μm is placed. A plate-shaped (disc) air electrode composed of a sintered body is placed, and a single cell is configured. Three such single cells are produced.

  Next, a nickel cobalt alloy foam having a porosity of 95% to 97% is disposed on the air electrode of each single cell, and a reaction layer is formed on the air electrode of each single cell.

  Next, the fuel electrode side separator is fixed on a pedestal made of a heat resistant alloy via an insulating plate. In this example, the fuel electrode side separator is a lower end separator.

  Next, the single cell described above is placed on the fuel electrode side separator. At this time, the fuel electrode current collector layer is disposed on the surface of the fuel electrode side separator where the fuel gas flow path is formed, and the single cell fuel electrode is disposed thereon. The anode current collecting layer should be made of metal such as platinum, silver, gold, palladium, iridium, rhodium, mesh or non-woven fabric made of fine wire of ferritic heat-resistant alloy, expanded metal, or foam metal. Good. For example, nickel foam, which is a nickel foam, may be disposed and used as the fuel electrode current collecting layer.

  Next, the air electrode side separator was placed on the reaction layer arranged on the air electrode of the single cell arranged as described above so that the surfaces on which the oxidant gas flow paths are formed face each other. State. Note that a fuel electrode side separator is disposed on the air electrode side separator.

  On the surface of the fuel electrode side separator, which is overlaid on the air electrode side separator, on the surface on which the fuel gas flow path is formed, the same fuel electrode current collecting layer as described above is disposed. As described above, the next single cell is stacked. In addition, the cell holder is arranged at the periphery of the cell, and the insulating member is arranged thereon. After repeating these steps, a predetermined number of single cells (power generation units) are stacked, and then the upper end separator is placed on the reaction layer of the last (uppermost) single cell. The upper end separator is an air electrode side separator and is placed so that the surface on which the oxidant gas flow path is formed is brought into contact with the reaction layer.

  As described above, in a state where a plurality of separators and single cells are stacked, first, a load is applied from the top of the upper separator to the pedestal so that pressure is applied to each single cell. The reaction layer is deformed according to the applied pressure and is in close contact with the air electrode and the air electrode side separator.

  In such a state where the layers are stacked and loaded, the solid oxide fuel cell is placed inside a predetermined electric furnace, and the solid oxide fuel cell is heated to 800 ° C. Next, when the fuel gas is supplied to the fuel electrode via the fuel gas supply manifold and the oxidant gas is supplied to the air electrode via the oxidant gas supply manifold, the power generation state can be obtained.

  Next, the output of the case where a plurality of single cells are stacked via a separator using a reaction layer and the output when a plurality of single cells are stacked via a separator without using a reaction layer are compared. It was.

  In the case of using the reaction layer, single cells were stacked by the method described above, and ripened to 800 ° C. to obtain a power generation state. Moreover, when not using the reaction layer, the air electrode side separator was arrange | positioned directly on the air electrode, the single cell was laminated | stacked, and it was set as the electric power generation state by heating to 800 degreeC. For each condition, 5 single cells were stacked in series.

Further, hydrogen gas was supplied as the fuel gas, and mixed air in which nitrogen and oxygen were mixed as the oxidant gas was supplied. Furthermore, a load of 100 kg was applied from the upper end separator to the pedestal. The voltage drop rates at a current density of 0.3 A / cm ^{2 at} this time are compared and shown in Table 1. As shown in Table 1, it was demonstrated that by using the reaction layer, the voltage drop rate was suppressed and deterioration could be suppressed.

  As described above, according to the present invention, since the reaction layer composed of the nickel cobalt alloy is provided between the air electrode and the separator on the air electrode side, it is composed of the alloy material containing chromium. A reduction in power generation performance in a solid oxide fuel cell using a separator can be suppressed.

  Here, the nickel-cobalt alloy has a different thermal expansion coefficient from surrounding members such as a separator and an air electrode made of an alloy containing chromium. However, as described above, since the reaction layer is porous, the stress due to the difference in thermal expansion coefficient is relieved. In addition, being porous does not hinder the flow of the oxidant gas supplied to the air electrode, increases the specific surface area of the reaction layer, and has the effect of promoting the reaction with chromium evaporated from the separator.

  By the way, in order to sufficiently capture chromium evaporated from the separator, the thickness of the reaction layer is preferably at least 0.1 mm or more in the operation state of the solid oxide fuel cell. On the other hand, when the reaction layer is thicker than necessary, the reaction layer is porous and easily deforms in shape. Therefore, when the surface pressure is applied, the gas flow path portion of the air electrode side separator may be filled. For this reason, the upper limit of the thickness of a reaction layer should just be less than the groove depth of the gas flow path part currently formed in the separator. Since the depth of the groove arranged in the separator depends on gas distribution and stack height limitation, the depth of the groove cannot be determined by fixing the thickness of the reaction layer. Therefore, the difference in the reaction layer may be determined as appropriate for the set (designed) depth of the separator groove.

  Further, there is an upper limit to the amount of chromium that can be reacted by the reaction layer. However, when the solid oxide fuel cell is actually operated, a behavior is observed in which the evaporation amount of chromium decreases as an oxide film grows on the surface of the separator. For this reason, even if it is a comparatively thin reaction layer of 0.1 mm or more, it becomes possible to effectively suppress the deterioration of the air electrode due to chromium.

  On the other hand, when the surface of the separator is coated with a metal or the like to suppress the evaporation of chromium, the growth of the oxide film on the surface of the chromium-containing heat resistant stainless steel may be suppressed. In such a situation, when the surface coating is peeled off, the evaporation of chromium is newly started to cause deterioration of the air electrode. As described above, in the technology for covering and suppressing the evaporation of chromium, the surface coating needs to be maintained semipermanently. On the other hand, it can be said that by using the reaction layer of the present invention, it is possible to more stably suppress deterioration of the air electrode due to chromium.

  The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious.

  DESCRIPTION OF SYMBOLS 101 ... Air electrode, 102 ... Electrolyte, 103 ... Fuel electrode, 104 ... Single cell, 105 ... Air electrode side separator, 106 ... Reaction layer.

Claims (3)

A plurality of single cells configured with an air electrode, an electrolyte, and a fuel electrode;
A separator made of an alloy containing chromium disposed between the single cells;
And a reaction layer made of a nickel-cobalt alloy provided between the separator and the air electrode and having a plurality of holes communicating the air electrode side and the separator side. Solid oxide fuel cell. The solid oxide fuel cell according to claim 1, wherein
2. The solid oxide fuel cell according to claim 1, wherein the reaction layer is made of a nickel cobalt alloy foam metal. The solid oxide fuel cell according to claim 1, wherein
2. The solid oxide fuel cell according to claim 1, wherein the reaction layer is a non-woven fabric made of nickel cobalt alloy.

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