JP4488284B2 - Soundness evaluation method and soundness evaluation apparatus for solid oxide fuel cell - Google Patents

Description

  The present invention relates to a soundness evaluation method and a soundness evaluation apparatus for a flat oxide fuel cell (SOFC: Solid Oxide Fuel Cell).

  As is well known, solid oxide fuel cells are being researched and developed as third-generation power generation fuel cells. Three types of solid oxide fuel cells are currently proposed: a cylindrical type, a monolith type, and a flat plate type. Among these structures, a low temperature operation type solid oxide fuel cell is proposed. The flat plate type structure is widely adopted.

  In this flat plate type solid oxide fuel cell, a separator, a fuel electrode current collector, a power generation cell, and an air electrode current collector are sequentially stacked to form a single cell unit, and a plurality of the single cell units are stacked. Thus, a cell stack is configured. Each power generation cell has a laminated structure in which a solid electrolyte made of an oxide ion conductor is sandwiched between an air electrode (cathode) and a fuel electrode (anode).

In the cell stack having the above configuration, oxygen supplied to the air electrode side of the power generation cell via the separator and the air electrode current collector passes through the pores in the air electrode layer and reaches the vicinity of the interface with the solid electrolyte, In this portion, electrons are received from the air electrode and ionized to oxide ions (O ²⁻ ). The oxide ions diffuse and move in the solid electrolyte layer toward the fuel electrode. Oxide ions that have reached the vicinity of the interface with the fuel electrode react with the fuel gas at this portion to generate a reaction product (H ₂ O or the like), and discharge electrons to the fuel electrode. When these electrons are taken out by the anode current collector, a current flows and a predetermined electromotive force is obtained.

Incidentally, the electrode reaction when hydrogen is used as the fuel is as follows.
Air electrode: 1/2 O ₂ + 2e ⁻ → O ²⁻
Fuel electrode: H ₂ + O ²⁻ → H ₂ O + 2e ⁻
Overall: H ₂ +1/2 O ₂ → H ₂ O

  By the way, in the cell stack of the flat plate type solid oxide fuel cell, as the evaluation items of its soundness, (1) appearance and dimensions, (2) presence or absence of gas leak in the supply gas pipe, (3) electrical There are presence / absence of short circuit, (4) uniformity of flow rate of fuel gas supplied to each power generation cell, and (5) internal resistance of each single cell unit (internal resistance between separators). Among the evaluation items (1) to (3), after assembling the cell stack, its soundness can be confirmed by a known method using calipers, soapy water, a tester, and the like. On the other hand, for the evaluation items of (4) and (5), since a method for directly obtaining after assembling the cell stack has not been established, conventionally, power is actually generated and the voltage between the separators is set. The soundness was confirmed by measuring.

  However, in the above conventional method, when any of the single cell units does not satisfy the required performance for at least one of the evaluation items (4) and (5), the single cell unit is determined based on the voltage value. However, it is impossible to distinguish whether the cause is caused by the supply flow rate of the fuel gas or the variation of the internal resistance of each single cell unit. For this reason, when any of the single cell units constituting the cell stack has a performance defect or a problem, there is a problem that an appropriate countermeasure cannot be taken.

  The present invention has been made in view of such circumstances, and the soundness of the cell stack can be easily and appropriately evaluated. If any of the single cell units has a performance defect or a malfunction, the cause can be accurately determined. It is an object of the present invention to provide a soundness evaluation method and a soundness evaluation apparatus for a solid oxide fuel cell that can be grasped in a short time.

  As a result of intensive studies to solve the above problems, the present inventors have varied the fuel gas flow rate with a constant current loaded on a single cell unit of practical scale that has a large concentration distribution inside the cell. When measuring the AC impedance and taking the Cole-Cole plot, it is found that the size of the arc on the low frequency side changes according to the flow rate of the fuel gas, and with the real axis on the high frequency side of the arc. It has been found that the impedance value at the intercept changes according to the internal resistance of the single cell unit. And if such a principle is applied, the performance can be estimated from the impedance characteristics of the single cell unit, and in the cell stack having a plurality of single cell units, the impedance characteristics between the separators are compared with each other. The inventors have found that the soundness of the cell stack can be easily and appropriately evaluated, such as the uniformity of the gas supply flow rate between the power generation cells and the uniformity of the internal resistance between the separators, and the present invention has been completed.

  In other words, the soundness evaluation method for a solid oxide fuel cell according to the first aspect of the present invention includes a cell stack in which power generation cells and separators are alternately stacked, and reacts with each of the power generation cells. In a solid oxide fuel cell that generates a power generation reaction by supplying a gas for a test, a test signal is sent between both ends in the stacking direction of the cell stack with the reaction gas supplied to each of the power generation cells. It is characterized in that the soundness of the cell stack is evaluated by applying and measuring the impedance between the separators and comparing the impedance characteristics with each other.

  Here, the test signal includes, for example, an AC sine wave signal, a current step, white noise, a delta function, and the like, and includes a case where these signals are superimposed on DC. The method for obtaining impedance data includes, for example, a method for comparing and obtaining AC waveforms of voltage and current at each frequency, a method for obtaining by a known impedance analyzer, a method for obtaining by Fourier analysis, a method for obtaining by Laplace transform, and the like. Further, the data analysis method includes, for example, a method using a complex impedance curve, a method using a Bode diagram, or a method of directly analyzing by a computer without using these visual diagrams. For example, when measuring impedance using an AC signal, an AC signal is applied between both ends in the stacking direction of the cell stack, a response signal between the separators is measured, and each response signal is determined from the applied AC signal and the response signal. What is necessary is just to derive | lead-out the alternating current impedance between separators by a calculation.

The invention according to claim 2 is the soundness evaluation method for a solid oxide fuel cell according to claim 1, wherein impedance characteristics between the separators are measured, and components having a large time constant of each measurement data are analyzed. By comparing each, the uniformity of the flow rate of the reaction gas supplied to each of the power generation cells is evaluated.
Here, when analyzing the impedance characteristics between the separators, for example, when using complex impedance curves, arcs appearing on the low frequency side of each complex impedance curve (gas flow rate) after obtaining each complex impedance curve. Each of the above-mentioned power generation cells by calculating the size of each of the above-mentioned arcs, which vary depending on the gas flow path conditions, etc. It is possible to evaluate the uniformity of the flow rate of the reaction gas supplied to the reactor.

The complex impedance curve is a curve obtained by drawing a locus of impedance accompanying a frequency change on the complex plane with the real component of impedance on the horizontal axis and the imaginary component on the vertical axis, and is also called a Cole-Cole plot.
The method for obtaining the size of the arc (semicircle) appearing on the low frequency side of the complex impedance curve is, for example, the distance between the end points of the arc with the point where the imaginary component of the impedance is almost zero as the end point of the arc. And a method for obtaining the radius from the distance between the vertex of the circular arc where the absolute value of the imaginary component is a maximum and the end point. It is also possible to estimate the radius of the arc from the absolute value of the imaginary component at the vertex. Such a method can be performed without bothering plotting data or drawing a curve on the drawing. Here, in order to simplify the explanation, an analysis using a complex impedance curve is shown as an example. The same applies to the following.

  The size of the arc that appears on the low-frequency side is roughly inversely proportional to the reaction gas supply flow rate, and tends to increase as the gas supply flow rate decreases. By comparing, the uniformity of the gas supply flow rate between the power generation cells can be grasped, and the power supply cell with a smaller gas supply flow rate than other power generation cells (that is, the reaction gas supply system has some sort of It is possible to easily detect problematic power generation cells.

  According to a third aspect of the present invention, in the soundness evaluation method for a solid oxide fuel cell according to the second aspect, the impedance characteristics between the separators are measured, and the impedance obtained by removing the component having a large time constant is analyzed. Then, by comparing these with each other, the uniformity of the internal resistance between the separators is evaluated.

In this specification, the impedance of a cell that is derived from the material of the cells existing between the separators, the manufacturing process, etc. and does not depend on the gas flow rate is defined as “internal resistance”.
In the soundness evaluation method for a solid oxide fuel cell according to claim 3, when analyzing the impedance characteristics between the separators, for example, when using a complex impedance curve, a low frequency is represented by each complex impedance curve. The impedance values of the intercepts when the high-frequency ends of the arcs observed on the side are extrapolated to the real axis are obtained, and the impedance values are compared with each other to evaluate the uniformity of the internal resistance between the separators. It is possible.

  That is, when an arc is drawn using data on the low frequency side in the complex impedance curve, the impedance value of the intercept with the real axis on the high frequency side of the arc is higher as the internal resistance of the single cell unit is larger. Therefore, by comparing the impedance values with each other, the uniformity of the internal resistance between the separators can be grasped, and the internal resistance is different from that of other single cell units. A single cell unit larger than that can be easily detected.

  According to a fourth aspect of the present invention, in the solid oxide fuel cell soundness evaluation method according to any one of the first to third aspects, the solid oxide fuel cell has a gas manifold around the cell stack. A solid oxide fuel cell that supplies a reaction gas from the gas manifold to each separator through a conductive gas pipe. In measuring the impedance between the separators, the gas manifold and the gas manifold Insulating the gas pipe, bringing a probe into contact with the gas pipe, measuring a response signal to the test signal with the probe, and obtaining an impedance between the separators from the response signal and the test signal To do.

  The invention according to claim 5 is a solid oxide type having a cell stack formed by alternately stacking power generation cells and separators, and generating a power generation reaction by supplying a reaction gas to each of the power generation cells. In a fuel cell, a soundness evaluation apparatus for evaluating the soundness of the cell stack, the test signal applying means for applying a test signal between both ends in the stacking direction of the cell stack, and the test signal between each separator A probe for detecting a response signal to the cell, and an evaluation means for evaluating the soundness of the cell stack by obtaining an impedance between the separators from the response signal and the test signal and comparing the impedance characteristics with each other. It is characterized by this.

  According to the invention of any one of claims 1 to 5, the soundness of the cell stack such as the uniformity of the supply flow rate of the reaction gas supplied to each power generation cell and the uniformity of the internal resistance between the separators. Can be evaluated easily and appropriately, and when any of the single cell units has a performance defect or a malfunction, the cause can be accurately grasped.

Hereinafter, an embodiment of a soundness evaluation method and a soundness evaluation apparatus for a solid oxide fuel cell according to the present invention will be described with reference to the drawings.
FIG. 1 shows a main configuration of a flat plate type solid oxide fuel cell to be evaluated by the soundness evaluation method and the soundness evaluation apparatus. In this solid oxide fuel cell, a separator 11 is shown. (Or the end plates 11a and 11b), the fuel electrode current collector 12, the power generation cell 13, and the air electrode current collector 14 are sequentially stacked to form a single cell unit 10, and a plurality of the single cell units 10 are stacked. A cell stack 20 is configured.

Here, the separator 11 is made of stainless steel, the fuel electrode current collector 12 is made of a sponge-like porous sintered metal plate such as a Ni-based alloy, and the air electrode current collector 14 is made of a sponge such as an Ag-based alloy. It is comprised with the shape of a porous sintered metal plate. The power generation cell 13 has a laminated structure in which a solid electrolyte is sandwiched between a fuel electrode and an air electrode. The solid electrolyte is composed of stabilized zirconia (YSZ) to which yttria is added, and the fuel electrode is Ni, A metal such as Co or a cermet such as Ni—YSZ or Co—YSZ is used, and the air electrode is made of LaMnO ₃ , LaCoO ₃ or the like.

  Further, on the side of the cell stack 20, a fuel gas manifold 15 that supplies fuel gas to the fuel passages (not shown) of each separator 11 through the conductive gas pipe 17, and an oxidant passage (not shown) of each separator 11. ) And an oxidant gas manifold 16 for supplying air as an oxidant gas through the conductive gas pipe 18, extending in the stacking direction of the cell stack 20. The gas pipes 17 and 18 are insulated from the gas manifolds 15 and 16 so that the voltage between the separators 11 can be easily measured by bringing a probe 31 (described later) into contact with each of the gas pipes 17 and 18. It is configured.

  In the solid oxide fuel cell having the above-described configuration, the fuel gas introduced into the separator 11 from the fuel gas manifold 15 through the gas pipe 17 is discharged toward the anode current collector 12, and the oxidant gas. The air introduced into the separator 11 from the manifold 16 through the gas pipe 18 is discharged toward the air electrode current collector 14, and these gases diffuse from the center of the power generation cell 13 to the outer peripheral direction while being diffused to the fuel electrode and the air electrode. The power generation reaction described above occurs by spreading over the entire surface with a good distribution. Moreover, in this embodiment, since it is set as the sealless structure which does not dare provide the gas leak prevention seal in the outer peripheral part of the electric power generation cell 13, the gas produced | generated by the said electric power generation reaction, or the residual gas which was not used for the said electric power generation reaction Then, it is discharged from the outer peripheral portion of the power generation cell 13.

Next, an embodiment of a soundness evaluation apparatus for evaluating the soundness of the cell stack 20 of the solid oxide fuel cell having the above configuration will be described. As shown in FIG. 2, the soundness evaluation apparatus is roughly configured by a probe 31 and an impedance analysis apparatus 32.
The probe 31 has a plurality of contacts 33 arranged in a comb shape, and collects a measurement signal by bringing these contacts 33 into contact with a measurement target site (separator 11, gas pipes 17, 18, etc.). And output to the impedance analyzer 32. Note that the interval between the contactors 33 is set in advance to an interval at which the separators 11 or the gas pipes 17 and 18 in the cell stack 20 can be simultaneously contacted.

  On the other hand, the impedance analysis device 32 includes a control unit (evaluation means) having a CPU (Central Processing Unit), a RAM (Random Access Memory), a storage device, an input device, a display device, an interface, and the like, and the cell stack 20 in the stacking direction. A signal applying unit (test signal applying means) that applies a test signal (for example, an alternating current) between both ends is provided. The storage device of the control unit is provided with a storage area for storing impedance measurement data and the like in addition to a storage area for storing various processing programs executed by the CPU and control data.

  The CPU reads and executes various processing programs stored in the storage device, thereby controlling the signal application unit to apply a predetermined test signal to the cell stack 20, and a response signal to the test signal. Is received from the probe 31 and stored in the storage device, the impedance between the separators 11 is obtained from the response signal and the test signal, and stored in the storage device, and the impedance characteristics between the separators 11 are compared with each other. Accordingly, processing for evaluating the soundness of the cell stack 20 is performed.

Next, an embodiment of a soundness evaluation method for the cell stack 20 using the soundness evaluation apparatus having the above configuration will be described.
First, as shown in FIG. 3, the soundness evaluation apparatus is set in the cell stack 20 to be evaluated (step S1). That is, the contacts 33 of the probe 31 are brought into contact with the separators 11 or the gas pipes 17 and 18 of the cell stack 20 and the test signal application cables 34a and 34b are connected to the end plates 11a of the cell stack 20, respectively. , 11b.
Next, the valve (not shown) of the supply piping for supplying the reaction gas (fuel gas, oxidant gas) to each gas manifold 15, 16 is opened, and the fuel gas is supplied to the fuel electrode side of each power generation cell 13. Air as an oxidant gas is supplied to the air electrode side (step S2).

Then, a test signal (alternating current) is applied between both ends of the cell stack 20 in the stacking direction with the reaction gas supplied. Here, the CPU of the impedance analysis device 32 controls the signal application unit based on an instruction input from the input device and performs a process of applying a test signal to the cell stack 20. This process may be performed in an open circuit state or in a power generation state.
Next, a response signal (response voltage) to the test signal is sampled by the probe 31, and the impedance between the separators 11 is obtained from the response signal and the test signal (step S3). Here, the CPU of the impedance analyzer 32 receives the response signal from the probe 31, calculates the impedance between the separators 11 from the response signal and the test signal, and stores the calculation result in the storage device. Perform the process.

Next, the soundness of the cell stack 20 is evaluated by comparing impedance characteristics between the separators 11 (step S4).
That is, the CPU of the impedance analyzer 32 reads the impedance measurement data stored in the storage device, analyzes the impedance characteristics of each single cell unit 10, and compares these characteristics with each other. 10 is performed to evaluate the uniformity of the performance of 10 and diagnose the soundness of the cell stack 20.

For example, when evaluating the uniformity of the supply flow rate of the fuel gas between the power generation cells 13, the resistance component having a large time constant in the obtained impedance characteristic (low resistance with respect to the real axis of the arc C of the Cole-Cole plot). (Corresponding to the impedance L of the value obtained by subtracting the value of the high frequency side intercept from the value of the frequency side intercept), and the magnitudes thereof are compared with each other.
That is, when the impedance characteristics between the separators 11 are represented by, for example, a complex impedance curve, a large arc C appears on the low frequency side, and the diameter of the arc C approximately corresponds to the fuel gas supply flow rate as shown in FIG. It is inversely proportional and tends to increase as the fuel gas supply flow rate decreases. Therefore, by comparing the diameters of the arcs C with each other, the uniformity of the supply flow rate of the fuel gas between the power generation cells 13 can be grasped, and the supply flow rate of the fuel gas is compared with the other power generation cells 13. Therefore, it is possible to easily detect a small number of power generation cells (that is, power generation cells having some problem in the gas supply system).

For example, assuming a hydrogen / water vapor partial pressure corresponding to a fuel utilization rate of 50% at 750 ° C., assuming that the supply flow rate of fuel gas to each power generation cell 13 is 1 cc / min / cm ² , the low frequency side of the complex impedance curve As shown in FIG. 4, the impedance L of the difference between both intercepts from the real axis of the arc C that can be drawn from the data is about 1 Ωcm ² , and the fuel gas supply flow rate is about 3 cc / min / cm ² . 4Omucm ² next, when the supply flow rate of the fuel gas and 5cc / min / cm ^2, to be approximately 0.3Omucm ^2, has been confirmed by experiments by the present inventors. Therefore, under the above conditions, when the fuel gas supply flow rate is set to 1 cc / min / cm ² , the impedance L of the difference between both intercepts from the real axis of each arc C is approximately the same value (1 Ωcm ^When each variation is statistically within the allowable error range in ² ), it can be diagnosed that the supply flow rate of the fuel gas to each power generation cell 13 is almost uniform and normal. When the diameter of the arc C is significantly different from the diameters of the other arcs C and exceeds the allowable error range, the fuel gas supply flow rate is uneven between the power generation cells 13 and corresponds to the part of the arcs C. It can be diagnosed that the fuel gas supply system of the power generation cell 13 is abnormal.

Further, for example, when evaluating the uniformity of the internal resistance of the single cell unit 10, taking the analysis by the complex impedance curve as an example, the intercept of the complex impedance curve with the real axis on the high frequency side of the low frequency arc C The impedance values of P are obtained, and the impedance values are compared with each other.
That is, the impedance value of the intercept P with respect to the real axis at the high frequency end of the low frequency arc C in the complex impedance curve tends to shift to the high impedance side as the internal resistance of the single cell unit 10 increases. Therefore, by comparing the impedance value of the intercept P at the high frequency end of the arc C on the low frequency side between the separators 11, it is possible to grasp the uniformity of the internal resistance between the separators 11 and The single cell unit 10 having a resistance larger than that of the other single cell units 10 can be easily detected.

  In addition to the internal resistance of the single cell unit 10 and the fuel gas supply flow rate, if some of the single cell units 10 have performance problems, characteristic differences appear in each part of the complex impedance curve. Therefore, by comparing the impedance L of the difference between both intercepts where the arc C on the low frequency side of the complex impedance curve intersects the real axis and the portion other than the position of the intercept P at the high frequency end, The uniformity of various performances of the single cell unit 10 can be grasped, and when there is a single cell unit 10 that includes some problem in terms of performance, the single cell unit 10 can be easily identified. .

  As described above, according to the present embodiment, a test signal is applied between both ends in the stacking direction of the cell stack 20 with the reaction gas (fuel gas, oxidant gas) supplied to each of the power generation cells 13. Since the impedance between the separators 11 is measured and the soundness of the cell stack 20 is evaluated by comparing the impedance characteristics with each other, the fuel gas supply flow rate between the single cell units 10 and the internal Even when there is a performance failure or malfunction that was difficult to determine by conventional voltage measurement due to resistance variation, etc., it is possible to accurately grasp the cause and take measures according to the cause. Can be done appropriately.

  In the present embodiment, the impedance characteristics are measured for each single cell unit 10, but the impedance characteristics are measured for each power generation block using a predetermined number of single cell units 10 as power generation blocks. Good. Also in this case, it is possible to appropriately evaluate the soundness of the cell stack 20 by comparing the impedance characteristics with each other.

  Moreover, in this embodiment, although illustrated about the case where the soundness is evaluated after the assembly of the cell stack 20, this invention is not limited to this, For example, the soundness evaluation apparatus of this embodiment is equipped. By operating the solid oxide fuel cell as it is and periodically evaluating the soundness of the cell stack 20 during operation, abnormalities in the cell stack 20 such as cracking of the power generation cell 13 and separation of the fuel electrode occur. It is also possible to monitor.

It is a figure which shows the principal part structure of a flat plate type solid oxide fuel cell. It is a schematic block diagram which shows one Embodiment of the soundness evaluation apparatus of the solid oxide fuel cell which concerns on this invention. It is a flowchart for demonstrating one Embodiment of the soundness evaluation method of the solid oxide fuel cell which concerns on this invention. It is a figure which shows an example of a complex impedance curve.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Single cell unit 11 Separator 13 Power generation cell 15, 16 Gas manifold 17, 18 Gas piping 20 Cell stack 31 Probe 32 Impedance analysis apparatus (test signal application means, analysis means)

Claims (5)

In a solid oxide fuel cell having a cell stack in which power generation cells and separators are alternately stacked, and generating a power generation reaction by supplying a reaction gas to each of the power generation cells,
With the reaction gas supplied to each of the power generation cells, a test signal is applied across the cell stack in the stacking direction, the impedance between the separators is measured, and the impedance characteristics are compared with each other. A method for evaluating the soundness of a solid oxide fuel cell, wherein the soundness of the cell stack is evaluated.   Measure impedance characteristics between separators, analyze components with large time constants in each measurement data, and compare them to evaluate the uniformity of the flow rate of the reaction gas supplied to each of the power generation cells The soundness evaluation method for a solid oxide fuel cell according to claim 1, wherein:   The impedance characteristic between each separator is measured, the impedance excluding the component having the large time constant is analyzed, and the internal resistance uniformity between the separators is evaluated by comparing the impedances with each other. The soundness evaluation method of the solid oxide fuel cell according to claim 2. The solid oxide fuel cell is a solid oxide fuel cell having a gas manifold around the cell stack and supplying a reaction gas from the gas manifold to each separator through a conductive gas pipe. Yes,
In measuring the impedance between the separators, the gas manifold and the gas pipe are insulated, a probe is brought into contact with the gas pipe, a response signal to the test signal is measured by the probe, and the response signal and 4. The method for evaluating the integrity of a solid oxide fuel cell according to claim 1, wherein an impedance between the separators is obtained from the test signal. In a solid oxide fuel cell having a cell stack in which power generation cells and separators are alternately stacked and supplying a reaction gas to each of the power generation cells to generate a power generation reaction, the cell stack is sound A soundness evaluation device for evaluating sex,
Test signal applying means for applying a test signal between both ends in the stacking direction of the cell stack;
A probe for detecting a response signal to the test signal between each separator,
Solid oxide form characterized by comprising evaluation means for obtaining the impedance between the separators from the response signal and the test signal and evaluating the soundness of the cell stack by comparing the impedance characteristics with each other Fuel cell soundness evaluation device.

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