JP4794843B2 - Method for operating a solid oxide fuel cell having a heat-resistant alloy interconnector - Google Patents

Description

  The present invention relates to a solid oxide fuel cell having a heat-resistant alloy interconnector and a method for operating the solid oxide fuel cell, and more particularly, to stably provide a solid oxide fuel cell having a heat-resistant alloy interconnector containing chromium over a long period of time. The present invention relates to a solid oxide fuel cell that can be operated and a method for operating the same.

  A solid oxide fuel cell (SOFC (= Solid Oxide Fuel Cell), hereinafter abbreviated as SOFC as appropriate) generally has an operating temperature as high as about 800 to 1000 ° C. An operating temperature of 650-800 ° C. is also being developed. The SOFC has an anode and a cathode arranged with an electrolyte material in between, and is composed of a three-layer unit of anode / electrolyte / cathode.

  SOFC has such a high operating temperature that (1) the electrochemical reaction at the electrode proceeds smoothly, resulting in low energy loss and high power generation efficiency. (2) In addition to hydrogen, carbon monoxide ( CO) can also be involved in the power generation reaction, so the fuel can be diversified. (3) All the constituent materials are solid and easy to handle. (4) The exhaust heat temperature is high, so it is used in multiple stages. By doing so, there is an advantage that it is possible to further increase the power generation efficiency, and research and development are being promoted for practical use.

  The SOFC includes a flat plate method, a cylindrical method, and an integral lamination method, and these are the same in principle. Among them, flat plate type SOFCs include (a) a self-supporting membrane type SOFC that retains its structure with the electrolyte membrane itself, and (b) a support membrane type SOFC that supports the electrolyte membrane with a thick anode. FIGS. 1A to 1B are diagrams for explaining examples of these modes.

  FIG. 1A shows a self-supporting membrane type SOFC. The cell 1 is configured such that the anode 2 is disposed on the lower surface of the electrolyte membrane 3, the cathode 4 is disposed on the upper surface of the electrolyte membrane 3, and the anode 2 and the cathode 4 are supported by the thick electrolyte membrane 3. FIG. 1B shows a support membrane type SOFC. The cell 1 is configured by disposing an electrolyte membrane 3 on an anode 2 and a cathode 4 on the electrolyte membrane 3. In the support membrane type cell, the thickness of the electrolyte membrane 3 can be reduced to about 10 μm, for example, and can be operated at a low temperature of 650 to 850 ° C. For this reason, it is possible to use a heat-resistant alloy, for example, an inexpensive material such as stainless steel as the constituent material, and there are various advantages such as being able to reduce the size.

  In any of these SOFCs, since a high voltage cannot be obtained with one cell, the cells and the cells are alternately stacked through an interconnector to be stacked. That is, in a flat SOFC stack, interconnectors and cells are alternately stacked for the purpose of distributing and supplying and discharging air and fuel to and from the cathode and anode at the same time as electrically connecting adjacent cells. Is done.

  FIG. 2 shows a configuration example of a SOFC stack incorporating a single cell constructed as described above, and shows a case of a support membrane type cell. FIG. 2B is a perspective view of the support membrane cell viewed from the cathode side. In FIG. 2A, air is required to flow between the cathode and the interconnector A, and the cathode and the interconnector A must be in electrical contact. For this reason, a conductive interconnector having a groove for air circulation is provided between the cathode and the interconnector A, but the illustration is omitted. The interconnector may be provided separately from the interconnector A or may be provided integrally therewith.

  As shown in FIG. 2A, in the support membrane type SOFC stack, the interconnector A, interconnector B, interconnector C, cell, interconnector D are sequentially arranged from the top to the bottom. Of these, the interconnector C is also referred to as a cell support foil. A current collector plate and the like are disposed above the interconnector A and below the interconnector D, but are not shown. The interconnectors A to D are made of a heat-resistant alloy containing chromium such as stainless steel.

  In FIG. 2 (a), a gap is shown between the anode and the current collector plate, but both need to be in electrical contact. For this reason, the lower surface of the anode and the current collector plate may be in direct contact with each other, and nickel felt or the like may be interposed therebetween. Since the anode is a porous body, fuel contributes to power generation through the anode and its lower surface.

  By the way, also in the support membrane type SOFC operated at a low temperature as described above, since the voltage of one single cell is low, the single cell is usually configured by stacking a plurality of layers electrically in series. A single cell is joined to a cell support foil (ie, interconnector C in FIG. 2), and is placed and joined so that it fits in a manifold (interconnectors B and D in FIG. 2). A stack is formed by joining to the next unit via the interconnector.

  In addition, the fuel that flows through the SOFC stack, oxidant gas such as air, anode off gas, and cathode off gas are all gas, so they are gas sealed. It is necessary to sandwich the material.

  FIG. 3 is a diagram showing an example of the configuration. In FIG. 3, the members of the flat plate-type SOFC stack are shown at intervals in order to show the positional relationship. Shown is a stack with two cells 1 and one interconnector 6 between them, and an interconnector 6 (this interconnector is also a frame) on the upper surface of the upper cell and the lower surface of the lower cell. ing. The interconnector 6 is formed with a plurality of groove-like gas flow paths for supplying air and fuel to the cells. These are laminated by applying a load, for example.

  By the way, an interconnector used in such a manner is required to have many properties such as the following (1) to (8). (1) It is dense and does not allow gas to permeate or leak, (2) It has high electronic conductivity, (3) Ion conductivity is negligibly small, (4) In both oxidizing and reducing atmospheres at high temperatures The material itself is chemically stable. (5) There is no reaction with other members such as two electrodes or excessive interdiffusion. (6) The thermal expansion coefficient is consistent with other battery components. (7) The dimensional change due to the change in atmosphere is small, and (8) it has sufficient strength.

Due to such severe requirements, materials that can be used as an interconnector are limited under conditions of high-temperature operation of 850 to 1000 ° C. In order to satisfy these requirements as much as possible, conductive ceramics such as LaCrO ₃ group oxide solid solution (lanthanum chromite) are most commonly used. The properties of this material are improved by substituting part of La with alkaline earth metal elements such as Ca and Sr, or substituting part of Cr with 3d transition metal elements such as Mg, Co, Mn, and Ni. ing.

  Since the interconnector has severe requirements as described above, its constituent material is limited. Even in the case of a SOFC with an operating temperature of medium to low temperature (about 650 to 850 ° C.), a heat-resistant alloy containing Cr is used to satisfy these requirements as much as possible. Using a heat-resistant alloy containing Cr as a material for the manifold and interconnector is advantageous from the viewpoint of cost in addition to the above properties and performance.

  By the way, when the SOFC stack is started up, the temperature is normally raised in an open circuit state, and during that time, a reducing gas such as hydrogen is supplied to the anode side and an oxidizing gas such as air is supplied to the cathode side. . However, it has been found that when the SOFC stack is actually operated through such a temperature raising process, the voltage decreases, and the battery performance deteriorates by, for example, 5 to 20% in 1000 hours of operation time.

  The present invention has been made in order to solve the above problems at the time of starting the SOFC, and has been made to solve these problems. An SOFC comprising a heat-resistant alloy interconnector containing chromium as a constituent material is long. Provided is a method for operating a solid oxide fuel cell that can be stably operated over a period of time, and the present invention provides a solid that can stably operate a SOFC having an interconnector made of a heat-resistant alloy containing chromium as a constituent material over a long period of time. An object of the present invention is to provide an oxide fuel cell.

  The present invention relates to (1) a method for operating a solid oxide fuel cell using a heat-resistant alloy containing chromium as an interconnector, and at the time of start-up, an oxidant gas is allowed to flow to the cathode side while the circuit is raised in an open circuit state. A method of operating a solid oxide fuel cell, characterized by maintaining the temperature in the range of 650 to 850 ° C. for at least 30 hours or more while flowing the oxidant gas to the cathode side in the open circuit state after heating. I will provide a.

  The present invention relates to (2) a method of operating a solid oxide fuel cell using a heat-resistant alloy containing chromium as an interconnector, and at the start-up, an inert gas or a reducing gas is flowed to the anode side, The temperature is raised in an open circuit state while flowing an oxidant gas, and subsequently, in an open circuit state, an inert gas or a reducing gas is flowed to the anode side, and an oxidant gas is flowed to the cathode side to 650 to 850 ° C. The solid oxide fuel cell operating method is characterized in that it is maintained in a temperature range of at least 30 hours or more.

As for the present application, a part thereof was switched to a divisional application. In the present specification, the invention according to the present application is referred to as “present invention (1) to (2)”, and the invention related to the divisional application related thereto is “related”. Inventions (a) to (b) ”are described.
The related invention (a) is a solid oxide fuel cell using a heat-resistant alloy containing chromium as an interconnector , and the interconnector made of a heat-resistant alloy containing chromium is previously oxidized at a temperature in the range of 650 to 850 ° C. Ru SOFC der characterized by comprising incorporating the interconnector formed by oxidation treatment retains at least 30 hours or more in a gas atmosphere.

The related invention (b) is a method of operating a solid oxide fuel cell using a heat-resistant alloy containing chromium as an interconnector , and the interconnector made of the heat-resistant alloy containing chromium is previously in a range of 650 to 850 ° C. A solid oxide fuel cell incorporating an interconnector that is maintained in an oxidizing gas atmosphere at a temperature of at least 30 hours and is subjected to oxidation treatment. At the start-up, a reducing gas is supplied to the anode side, and the cathode side while flowing an oxidant gas, the temperature was raised in an open circuit condition, Ru operation method der of the solid oxide fuel cell characterized by power switch to closed circuit state.

  According to the present invention (1), after the start-up operation of the SOFC by a conventional method, in an open circuit state, the oxidant gas is allowed to flow to the cathode side and kept in a temperature range of 650 to 850 ° C. for at least 30 hours or more. By doing so, the SOFC can be stably operated over a long period of time without causing the performance deterioration of the SOFC cell. Further, as in the present invention (2), while maintaining an inert gas or a reducing gas on the anode side and an oxidant gas on the cathode side, the temperature is maintained in a temperature range of 650 to 850 ° C. for at least 30 hours or more. By doing so, the SOFC can be stably operated over a long period of time without causing the performance deterioration of the SOFC cell.

Moreover, according to related invention (a)-(b) , as an interconnector of a solid oxide fuel cell, an interconnector made of a heat-resistant alloy containing chromium is preliminarily oxidized gas atmosphere at a temperature in the range of 650-850 ° C. Incorporating an interconnector that is held for at least 30 hours and then oxidized to allow the SOFC to be stably operated over a long period of time without degrading the performance of the SOFC cell.

  The present invention (1) is a method for operating a solid oxide fuel cell using a heat-resistant alloy containing chromium as an interconnector. Then, at the time of start-up, the temperature is raised in an open circuit state while flowing an oxidant gas to the cathode side, and then in the open circuit state, a temperature range of 650 to 850 ° C. while flowing the oxidant gas to the cathode side. For at least 30 hours.

  The present invention (2) is a method for operating a solid oxide fuel cell using a heat-resistant alloy containing chromium as an interconnector. Then, at the start-up, an inert gas or a reducing gas is supplied to the anode side, and the temperature is raised in an open circuit state while an oxidant gas is supplied to the cathode side. Then, in the open circuit state, the inert gas is continuously supplied to the anode side. Alternatively, a reducing gas is allowed to flow, and an oxidant gas is allowed to flow to the cathode side, and the temperature is maintained within a range of 650 to 850 ° C. for at least 30 hours.

The related invention (a) is a solid oxide fuel cell using a heat-resistant alloy containing chromium as an interconnector. And the interconnector formed by hold | maintaining the interconnector which consists of a heat-resistant alloy containing chromium in the oxidizing gas atmosphere of the temperature of the range of 650-850 degreeC beforehand for at least 30 hours or more is integrated, It is characterized by the above-mentioned. .

Further, the related invention (b) is a method for operating the SOFC of the related invention (a) . At the start-up, a reducing gas is supplied to the anode side and an oxidant gas is supplied to the cathode side so that an open circuit state is obtained. After the temperature is raised, the power is switched to a closed circuit state to generate power. Here, the reducing gas may be an SOFC fuel gas. In this case, the fuel gas can continue to flow when the power is switched to the closed circuit state after the temperature rises.

SOFCs targeted in the present invention (1) to (2) and related inventions (a) to (b) are heat resistant chromium-containing iron-based alloys, heat-resistant chromium-containing nickel-based alloys, heat-resistant The SOFC uses a heat-resistant alloy containing chromium, such as a chromium-containing cobalt-based alloy and a heat-resistant chromium-based alloy. Examples of these heat-resistant alloys containing chromium include various stainless steels such as ferrite, but are not limited to these stainless steels.

Moreover, this invention (1)- (2) and related invention (a)-(b) used SOFC which has the interconnector made from a heat-resistant alloy containing chromium, ie, the heat-resistant alloy containing such chromium as an interconnector. The SOFC is applicable to any type of SOFC such as a self-supporting membrane type, a supporting membrane type, a cylindrical type, or an integral lamination type.

  In the present invention (1), first, at the time of starting the SOFC, the temperature is raised in an open circuit state while flowing an oxidant gas to the cathode side. The temperature raising temperature in this step is preferably the operating temperature of SOFC or in the vicinity thereof, but is not limited thereto, and can be raised to a temperature in the range of 650 to 850 ° C. Then, following the temperature raising step, also in an electrically open circuit state, the oxidant gas is allowed to flow to the cathode side, and the temperature is maintained in the temperature range of 650 to 850 ° C. for at least 30 hours, more preferably 60 hours or more. To do.

  The holding step is a very important step in the operation method of the present invention (1), whereby the SOFC can be stably operated over a long period of time without causing the performance deterioration of the SOFC cell. As the oxidant gas, air, oxygen-enriched air, oxygen or the like is used.

  Next, in the present invention (2), at the start of SOFC, first, an inert gas or a reducing gas is supplied to the anode side and an oxidant gas is supplied to the cathode side, so that it is electrically raised in an open circuit state. Warm up. When reducing gas is allowed to flow to the anode side in this step, it is the same step as in the conventional method, and the temperature rise temperature is preferably at or near the SOFC operating temperature, but is not limited to that, 650-850 ° C. The temperature can be raised to a temperature in the range of.

  Then, following the temperature raising step, in the same electrically open circuit state, an inert gas or a reducing gas is allowed to flow on the anode side, and an oxidizing gas is allowed to flow on the cathode side. The temperature is maintained for at least 30 hours, more preferably 60 hours or more. This step is a very important step in the operation method of the present invention (2), whereby the SOFC can be stably operated over a long period of time without causing the performance deterioration of the SOFC cell.

  Here, nitrogen, argon, or the like is used as the inert gas, and hydrogen, a gas containing hydrogen, or the like is used as the reducing gas. Examples of the gas containing hydrogen include a gas containing carbon monoxide, methane and the like in addition to hydrogen. As the oxidant gas, air, oxygen-enriched air, oxygen or the like is used.

In the SOFC of the related invention (a) , as an interconnector, an interconnector made of a heat-resistant alloy containing chromium is previously maintained in an oxidizing gas atmosphere at a temperature in the range of 650 to 850 ° C. for at least 30 hours to oxidize. It is configured by incorporating a processed interconnector. This process for the interconnector is a very important step in the related invention (a) , so that the SOFC can be stably operated over a long period of time without degrading the performance of the SOFC cell during the operation of the SOFC. be able to. As the oxidizing gas, air, oxygen-enriched air, oxygen or the like is used.

Further, the related invention (b) is a method for operating the SOFC of the related invention (a) . At the start-up, a reducing gas is supplied to the anode side and an oxidant gas is supplied to the cathode side so that an open circuit state is obtained. After the temperature rises, the power is switched to a closed circuit state. As SOFC, an SOFC in which an interconnector made of a heat-resistant alloy containing chromium is previously held in an oxidizing gas atmosphere at a temperature in the range of 650 to 850 ° C. for at least 30 hours is used. The SOFC can be stably operated over a long period of time without causing performance degradation. As the oxidizing gas, air, oxygen-enriched air, oxygen or the like is used.

  Exactly what kind of mechanism (the mechanism) achieves such an effect obtained in the present invention, that is, an effect capable of operating the SOFC stably over a long period of time without causing deterioration of the performance of the SOFC cell. Although it is not clear, this is probably because, on the cathode side, a film composed of a composite oxide of the alloy component is formed on the surface of the heat-resistant alloy containing chromium by oxidation with an oxidizing gas or oxidizing gas. It is presumed that this prevents the scattering of chromium and suppresses the deterioration of battery performance due to chromium poisoning. Further, when reducing gas is allowed to flow to the anode side, it is presumed that the anode is sufficiently reduced.

  EXAMPLES Hereinafter, although this invention is demonstrated in more detail based on an Example, it cannot be overemphasized that this invention is not limited to an Example. A plurality of cells as shown in FIG. 1B were produced, interconnectors were produced, and performance tests were performed using these.

<Production of cell>
A solid oxide electrolyte material (YSZ-based electrolyte) was disposed on the upper surface of the anode [Ni-YSZ cermet, planar size 11 cm × 11 cm (121 cm ² )]. A cathode made of (La, Sr) (Co, Fe) O ₃ (LaCoO ₃ doped with Sr and Fe) is arranged on the upper surface of the electrolyte, and a plurality of flat SOFC cells as shown in FIG. Individually produced. Each cell thus produced was used in the following performance test.

A plurality of heat-resistant alloy interconnectors containing Cr having a planar dimension of 11 cm × 11 cm (121 cm ² ) and a thickness of about 0.8 mm were formed. The composition of the heat-resistant alloy containing Cr is as follows. Cr = 22 (% by weight, the same applies hereinafter), Mn = 1.00, Si = 1.00, Ni = 0.50, Zr = 0.33, Al = 0.50, La = 0.04, C = 0 .10, P = 0.03, S = 0.03, Fe = balance (electric resistance at 750 ° C. = about 23 mΩ · cm ² ).

  Thus, a plurality of interconnectors were produced. FIG. 4 is a perspective view of the interconnector. A performance test was conducted using these interconnectors.

<performance test>
A performance test was conducted using the SOFC cell prepared in <Preparation of Cell> and the interconnector. In this performance test method, the cell and each interconnector are set as shown in FIG. 5, and (1) hydrogen is supplied as a reducing gas on the anode side, air is supplied on the cathode side, and the circuit is electrically opened. After the temperature was raised and the cell temperature was raised to 750 ° C., (2) it was kept in an electrically open circuit state and kept at this temperature for a predetermined time of 1 to 300 hours. Thereafter, (3) the cell voltage was measured over time with the current density kept constant at 0.2 A / cm ² by switching electrically to a closed circuit state.

Among the processes (1) to (3), the process of (1), which is a stage from when the temperature is electrically raised in an open circuit state and the cell temperature is raised to 750 ° C., is the same as the conventional start-up process. . Following the process of (1), the process of (2), which is an electrically open circuit state and is maintained at this temperature for a predetermined time between 1 and 300 hours, is the time that the effect of the present invention appears and is obtained. This corresponds to the “pre-oxidation time” of the cathode air. After the process (2), the process is a step of electrically switching to a closed circuit state and measuring the cell voltage over time with a constant current density of 0.2 A / cm ^2. Is the process of obtaining

  In the process of (2), as described above, on the cathode side, a film composed of a complex oxide of the alloy component is generated on the surface of the heat-resistant chromium-containing iron-based alloy by the oxidizing action of air on the cathode side, Since it is presumed that this coating prevents the scattering of chromium and suppresses the deterioration of the battery performance due to the chromium poisoning, the process of (2) is performed by the cathode “ This is described as “pre-oxidation time”.

  6 to 9 are diagrams showing the results of this performance test. 6 to 9, the horizontal axis represents time (h), and the vertical axis represents the stack voltage. First, as shown in FIG. 6, the cell voltage in the case of “pre-oxidation time” of 10 hours has fluctuations up and down immediately after the start of power generation, but shows 0.860 V when 10 hours have elapsed, and gradually decreases thereafter. The voltage is about 0.800 V when 400 hours elapse and decreases to 0.660 V when 1000 hours elapses. The performance deterioration rate at this time was 23%.

  Next, as shown in FIG. 7, the cell voltage in the case of “pre-oxidation time” of 30 hours is 0.850 V at the start of power generation, and then increases slightly until 100 hours have elapsed, at which time it reaches 0.860 V. Become. Since then, it has decreased very little and shows a value of 0.840 V after 600 hours. Although not shown in the figure, the same tendency was shown thereafter, and the performance deterioration rate after 1000 hours was 4.7%.

  Further, as shown in FIG. 8, the cell voltage in the case of “pre-oxidation time” of 60 hours gradually increases gradually from the start of power generation, becomes 0.736 V after 200 hours have elapsed, and thereafter maintains substantially the same voltage, 800 0.735V is maintained also at the time passage. There is no change even after 1000 hours, and there is no performance degradation.

  Furthermore, as shown in FIG. 9, the cell voltage in the case of “preliminary oxidation time” of 280 hours becomes a steady voltage of 0.800 V in just a few hours from the start of power generation, hardly changes thereafter, and 0.800 V even after 600 hours have elapsed. The value of is maintained. Although illustration is omitted, since then, there was no change until 1000 hours, and there was no performance deterioration. The same was true when the same test was conducted with the heating temperature set at 700 ° C and 780 ° C.

  In addition to the results of the above <performance test>, Table 1 shows that the “pre-oxidation time” is 2.5 hours, including the case of using an interconnector made of a heat-resistant chromium-containing iron-based alloy having another composition. This is a summary of the results of performance tests that were carried out at different times and 40 hours. As shown in Table 1, when the “pre-oxidation time” is less than 30 hours, the cell performance deterioration suppressing effect is not recognized. Although it is not complete from 30 hours to about 50 hours, the cell performance deterioration suppressing effect appears. On the other hand, if it is about 50 hours or more, especially 60 hours or more, it has shown that the performance degradation of a cell can be suppressed completely.

The figure explaining the example of an aspect of various flat type SOFC cells The figure which shows the example of composition of the SOFC stack which incorporates the flat type SOFC cell A diagram showing a configuration example in which flat plate SOFC cells are stacked. The figure which shows the interconnector produced in the Example The figure which shows the performance test equipment which is used with execution example The figure which shows the result of the performance test of an Example The figure which shows the result of the performance test of an Example The figure which shows the result of the performance test of an Example The figure which shows the result of the performance test of an Example

Explanation of symbols

1 cell 2 anode 3 electrolyte membrane 4 cathode A to D, 5 interconnector

Claims (7)

A method of operating a solid oxide fuel cell using a heat-resistant alloy containing chromium as an interconnector, and at the first start-up, the temperature is raised in an open circuit state while flowing an oxidant gas to the cathode side, and then continues to open. A method for operating a solid oxide fuel cell, characterized in that, in a circuit state, the gas is maintained in a temperature range of 650 to 850 ° C. for at least 30 hours while flowing an oxidant gas to the cathode side.   2. The solid oxide according to claim 1, wherein in the open circuit state, the time for maintaining in the temperature range of 650 to 850 ° C. is set to 60 hours or longer while flowing the oxidant gas to the cathode side. Fuel cell operation method. An operation method of a solid oxide fuel cell using a heat-resistant alloy containing chromium as an interconnector, and at the first start-up, an inert gas or a reducing gas is flowed to the anode side, and an oxidant gas is flowed to the cathode side. However, after raising the temperature in the open circuit state, in the open circuit state, an inert gas or a reducing gas is allowed to flow to the anode side, and an oxidant gas is allowed to flow to the cathode side, and a temperature range of 650 to 850 ° C. A method for operating a solid oxide fuel cell, wherein the method is maintained for at least 30 hours.   Subsequently, in the open circuit state, an inert gas or a reducing gas is allowed to flow on the anode side, and an oxidant gas is allowed to flow on the cathode side, while maintaining the temperature range of 650 to 850 ° C. for 60 hours or more. The method for operating a solid oxide fuel cell according to claim 3.   The method for operating a solid oxide fuel cell according to claim 3 or 4, wherein the reducing gas flowing to the anode side is hydrogen or a gas containing hydrogen.   6. The method for operating a solid oxide fuel cell according to claim 1, wherein the oxidant gas flowing to the cathode side is air.   The solid oxide fuel cell is a self-supporting membrane type solid oxide fuel cell, a support membrane type solid oxide fuel cell, a cylindrical solid oxide fuel cell, or a monolithic solid oxide fuel. It is a battery, The operating method of the solid oxide fuel cell of any one of Claims 1-6 characterized by the above-mentioned.

Images