JP2006351252A - Deterioration diagnosis method of polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a deterioration diagnosis device of a PEFC capable of correctly diagnosing deterioration by measuring internal resistance and an I-V characteristic so as not to diagnose temporary voltage drop due to flooding or the like as deterioration of a cell and capable of diagnosing deterioration without measuring all cells. <P>SOLUTION: In this deterioration diagnosis device of a polymer electrolyte fuel cell having a structure composed by catching a fuel electrode, an air electrode and a polymer electrolyte membrane (ion exchange membrane) arranged between them by a separator, the deterioration of a cell located at an end part of a supply passage for a fuel gas to the fuel electrode is intensively diagnosed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a method for diagnosing deterioration of a fuel cell, particularly a polymer electrolyte fuel cell using a polymer as an electrolyte.

Fuel cell technology is attracting attention as a power source or power source with clean exhaust and high energy efficiency against recent environmental problems, especially air pollution due to automobile exhaust gas and global warming due to carbon dioxide . In particular, attention has been focused on a polymer electrolyte fuel cell (hereinafter referred to as PEFC) that can be reduced in size and weight at an operating temperature of about 80 ° C.

  PEFC is usually used by laminating a plurality of single cells. In a single cell, a polymer ion exchange membrane and a fuel electrode and an air electrode are arranged on both sides thereof, and these are integrated as a membrane / electrode assembly (hereinafter referred to as MEA). A separator also serves as a reaction gas supply passage such as hydrogen gas or oxygen gas (air) outside the fuel electrode and the air electrode. The PEFC has a structure in which the MEA is held between the separators. In addition, the separator is engraved with a plurality of grooves so that hydrogen gas or oxygen gas flows uniformly in contact with the entire surface of the ion exchange membrane.

  The PEFC power generation mechanism is as follows. As shown in FIG. 1, a single cell 11 of PEFC includes an ion exchange membrane 131, a porous fuel electrode 134 and an air electrode 135 that are disposed opposite to each other, and the ion exchange membrane 131 and each electrode 134. , 135, respectively, and a separator layer 12 installed on the back surface of each electrode 134, 135. The separator 12 has a large number of grooves 121, and the fuel gas 111 and the oxidant gas 112 are supplied through the grooves 121, so that the fuel gas (hydrogen) is hydrogen ions and electrons on the catalyst layer 132 of the fuel electrode 134. Divided into Then, hydrogen ions move together with water in a cluster of 131 in the ion exchange membrane, and electrons move to the air electrode 135 through the separator 12, and oxygen, electrons, and hydrogen ions react in the air electrode 135. Water 113 is produced. Electric power is obtained by the difference in electromotive force generated between the fuel electrode 134 and the air electrode 135, respectively.

By the way, as a factor of the performance deterioration of the PEFC stack or the cell, there is a characteristic deterioration due to a decrease in ion conductivity of the polymer electrolyte membrane due to insufficient supply of water. Conversely, excessive supply of water is likely to cause clogging of pores (called flooding) necessary for gas diffusion on the air electrode side, resulting in deterioration of characteristics due to oxygen diffusion inhibition. As a method for evaluating performance degradation and characteristic degradation of PEFC, voltage measurement, internal resistance measurement, and the like are performed.

For example, in a fuel cell configured by stacking a plurality of blocks composed of an arbitrary number of cells stacked in series, a light emitting device that emits light when a predetermined voltage is applied to both ends of the block, and a light emitting device And a light receiving element that constitutes a photocoupler to determine a cell in which the voltage drops abnormally when the block voltage falls below a threshold (Patent Document 1), or a PEFC cell or stack during normal power generation AC impedance is measured in advance for a specific frequency, and the impedance reference value and an allowable value that can allow an increase in impedance are determined. When these values are compared with the actual value and exceeded the allowable value, it is judged abnormal. (Patent Document 2) and the like are performed.

JP 2005-26239 A JP 2002-367650 A

However, in the diagnostic methods disclosed in Patent Documents 1 and 2, since the battery voltage and internal resistance of the entire fuel cell are measured to detect an abnormality, the entire fuel cell must be replaced after detection. Will also be replaced, resulting in waste. In order to prevent this, it is possible to measure all the battery voltages and internal resistances of a single cell. Moreover, it was not possible to diagnose whether the abnormality was due to deterioration. PEFC cannot transport hydrogen ions without power in the electrolyte membrane (ion exchange membrane) and cannot generate electricity. Therefore, the fuel and the oxidant are operated with humidification, and water is generated by the reduction reaction of the air electrode. However, when the moisture in the PEFC becomes excessive, water accumulates in the gas flow path, stops the gas flow, and the voltage decreases (referred to as flooding). Further, when water is pushed out of the fuel cell due to an increase in internal pressure, the cell voltage is recovered. At this time, even if the voltage decreases, the internal resistance does not necessarily increase.

Under such a background, it is desired to improve the PEFC deterioration diagnosis apparatus in which the accurate deterioration diagnosis is performed by measuring the internal resistance and IV characteristics of the PEFC, and the number of objects to be measured is suppressed.

The present invention relates to a solid polymer fuel cell having a fuel electrode, an air electrode, and a polymer electrolyte membrane comprising an ion exchange membrane disposed between the fuel electrode and the air electrode. It is characterized by diagnosing deterioration by concentrating a single cell at the end portion.

Moreover, the performance fall of a fuel cell is detected by internal resistance and IV characteristic.

In addition, after detecting the degradation of the performance of the fuel cell, the degradation of the performance is recovered by increasing the supply pressure of the fuel and the oxidant, and when it does not recover, the degradation is diagnosed and replaced with a new cell. .

In the present invention, focusing on the deterioration of a single cell (near the end) farthest from the inlet of the fuel gas supply path, the deterioration of the single cell near the end of the fuel cell is intensively diagnosed. Thus, it is possible to provide a degradation diagnosis apparatus for a polymer electrolyte fuel cell capable of performing accurate degradation diagnosis while suppressing the number of measurement objects.

An embodiment of the present invention will be described with reference to FIGS. In addition, the same number is attached to the same component.

FIG. 2 is a schematic diagram of a PEFC deterioration diagnosis apparatus showing an embodiment of the present invention. 1 is a fuel cell stack formed by stacking a number of single cells shown in FIG. 1, 2 is a pressure regulator for adjusting pressure, and 3 is a flow rate measuring device for measuring flow rate. 4 is an inverter for converting the electric power generated by the fuel cell stack 1 into an alternating current, and 5 is a load. 6 is a measuring device for measuring internal resistance and voltage that can be measured for each single cell, 7 is a pressure measuring device for measuring the pressure near the end of the fuel gas supply path, 8 is an internal resistance and It is a deterioration determination device that performs comprehensive diagnosis by measuring voltage and pressure.

In the PEFC stack 1 configured as described above, hydrogen gas as a fuel gas is supplied to the PEFC stack 1 via the pressure regulator 2 and the flow rate measuring device 3 according to the supply path indicated by the arrow 136. On the other hand, power is generated by supplying air as an oxidant gas through the supply path indicated by an arrow 137. In the present invention, the oxidant gas 135 is air and is naturally aspirated. The fuel gas is constantly supplied by the pressure regulator 2 and the flow rate measuring device 3. And since the electric power generated by the PEFC stack 1 is a direct current, when the load 5 is an alternating current load, the inverter 4 converts the electric power and uses it.

The deterioration diagnosis of the PEFC stack 1 is performed by three of the internal resistance measurement device and voltage measurement device 6, the pressure measurement device 7, and the deterioration determination device 8. In the internal resistance measurement and the voltage measurement, a diagnosis is performed by concentrating the farthest location (near the end portion) from the supply port of the fuel gas 111, and in other locations, the diagnosis is performed. This is because the fuel gas is depleted in the vicinity of the end portion of the supply path, and the internal resistance increases due to concentration polarization, so that it is more likely to deteriorate near the end portion of the PEFC stack.

Next, the PEFC deterioration diagnosis performed by the deterioration determination device 8 will be described with reference to FIG. In the present invention, the range of the normal value of the internal resistance serving as a reference, the IV characteristic (see FIG. 4) serving as a reference for deterioration, the pressure near the end of the fuel gas supply path of the stack, and the maximum supply pressure of the stack are determined in advance. Keep it. The normal value range of the internal resistance was set to a value not more than 2 to 3 times the internal resistance value of the single cell in the initial stage of use. The IV characteristic was measured at the initial stage of use, and the reference value was a value that was 30% lower than this, that is, a value at which the voltage dropped to 70% of the initial value at a specific current. . Further, the pressure near the end of the fuel gas supply passage was set so that the pressure at the PEFC rated operation in the initial stage of use was a reference value, and the operation was performed so that the gas pressure near the end did not fall below this. Further, the maximum supply pressure was set to a pressure that can withstand the ion exchange membrane of a single cell and can safely operate the PEFC. The measuring device 6 measures the internal resistance and voltage of the single cell to be measured, the pressure measuring device 7 measures the gas pressure near the end, determines whether the gas pressure is higher than a predetermined pressure, and is high. Next, it is determined whether or not the voltage of a single cell exceeds the reference value. If it is higher, then it is determined whether or not the internal resistance value is within the normal value range. If it is within the range, the PEFC is determined to be normal. To do.

On the other hand, when the pressure is low, the voltage is low, or the internal resistance is out of range, it is determined whether the supply pressure of the fuel gas is the maximum supply pressure, which is the limit pressure, If it is not the maximum supply pressure, the pressure is increased to the maximum supply pressure, and the pressure, voltage, and internal resistance are measured and judged again. If all are normal, the fuel gas supply pressure is restored to the original and the measurement judgment is repeated.
If the voltage is low or the internal resistance is outside the range even when the maximum supply pressure is raised, it is judged that the battery has deteriorated.

Embodiments of the present invention will be described below with reference to FIGS.

The PEFC stack used in the present invention was a rated operation of 12V / 12W (8W during continuous operation). The number of single cells is 20, and a PEFC stack is formed by stacking these cells. The structure of a single cell is circular, and as shown in FIG. 1, a fuel electrode and an air electrode composed of a catalyst layer and a diffusion layer are integrally formed on both sides of an ion exchange membrane to form an MEA. Hold it. Hydrogen gas is used as the fuel gas to be supplied to the PEFC stack, and hydrogen gas is supplied through a pipe whose tip is closed at the center of the circle. The pressure is adjusted by a pressure regulator and a flow meter as shown in FIG. The flow rate was 0.07 MPa, and the flow rate was about 80 ml / min. A large number of holes are formed around the portion of the pipe where the separator is located, and hydrogen gas is supplied into the grooves formed radially in the separator through the holes. The generated power is about 8 W during continuous operation. In this example, an inverter was not used, and a light bulb that was a DC load was used as the load. In addition, when recognizing that the performance of the cell is deteriorated, the pressure of the gas is controlled by the pressure regulator. This pressure regulator is capable of pressure control with an analog input signal, and when the cell performance deteriorates, the supply pressure automatically increases as the input signal from the deterioration determining device changes. In addition, a large number of air is horizontally formed on the side opposite to the groove for supplying hydrogen gas so as to be naturally supplied.

The deterioration diagnosis of the PEFC stack was performed during the power generation in which the PEFC stack is operating at rated power. The deterioration diagnosis was performed by measuring the internal resistance of a single cell, the voltage, the current, and the pressure at the end of the pipe that is the supply path of the fuel gas. The internal resistance, current and voltage are measured every four cells from the single cell on the inlet side of the fuel gas supply, and the single cell near the end of the fuel gas supply path is continuous including the single cell at the end. Three single cells were measured in a concentrated manner, and a total of seven single cells were measured. In the present invention, the measurement of all single cells was not performed because it was confirmed that the vicinity of the end of the fuel gas supply path was significantly deteriorated, and many measurements of a single cell near the end were performed. Measured and concentrated.

The internal resistance measuring apparatus measured using the AC four-terminal method. A current source and a voltmeter are built in the internal resistance measuring device. A constant current is passed through a single measured cell of the PEFC by the former, and each single cell voltage is measured by the latter. The internal resistance was calculated from the value of the flowing alternating current and the single cell voltage measured with a voltmeter. Moreover, the pressure measuring device measured pressure by using a pressure sensor.

FIG. 4 is an IV characteristic curve of PEFC. The vertical axis represents the voltage of a single cell, and the horizontal axis represents the current. It can be seen that the voltage decreases as the flowing current increases as shown. In the figure, the solid line is the characteristic curve of the initial PEFC, that is, the new PEFC, and the dotted line is the characteristic curve when deteriorated by long-term use. As is apparent from the figure, the voltage drops greatly even with the same current due to deterioration. Degradation can be determined using this characteristic. In this embodiment, the initial value of use, that is, a value that is 30% lower than the solid line value is used as the reference value for deterioration.

FIG. 5 shows changes over time in the voltage of a single cell at the inlet side and a single cell at the end of the fuel gas supply path of PEFC. It can be seen that the voltage at the end single cell drops faster than the single cell at the inlet side compared to the single cell at the inlet side of the fuel gas. This is thought to be due to the lack of fuel gas near the gas outlet and an increase in internal resistance due to concentration polarization. Further, it is considered that the activation polarization increases by operating at a high temperature for a long period of time, and the output voltage decreases by increasing the internal resistance. Therefore, it can be seen that it is effective to measure a single cell at the end.

FIG. 6 is a diagram showing the voltage for each single cell of the PEFC stack, where the vertical axis indicates the single cell voltage and the horizontal axis indicates the single cell number. The single cell at the inlet of the fuel gas supply path is numbered 1 and the single cell at the end is designated n (20 in this case). In the normal state indicated by the solid line, the output voltage of the single cell farthest from the entrance (the single cell at the end) is slightly lower than the others, but the output voltage is significantly higher than the others when it is degraded. It turns out that it has fallen and it has deteriorated. As described above, it is conceivable that the output voltage decreases due to the increase in internal resistance.

  FIG. 7 is an IV characteristic diagram showing that the performance deterioration is recovered by increasing the supply pressure of the fuel gas. The pressure of the supply gas at low pressure indicated by a dotted line is 0.06 MPa, and the pressure of the supply gas at high pressure indicated by a solid line is 0.08 MPa. As can be seen from FIG. 7, when the performance is recovered by increasing the pressure of the supply gas, it is considered that the internal resistance is temporarily increased or the voltage is decreased due to flooding or the like, not cell deterioration. However, if the performance does not recover even when the maximum supply pressure of the PEFC stack is applied, it is determined that the PEFC cell is deteriorated. When the single cell of the PEFC determined to be degraded is only the terminal portion, only the single cell at the terminal portion is replaced with a normal single cell. In addition, when the single cell determined to be deteriorated is other than the end portion or is generated at the end portion, the entire PEFC is replaced.

In the present invention, the oxidant gas is naturally aspirated, but similar results were obtained when oxygen gas was used as the oxidant.

From the above results, it is possible to suppress the number of measurement objects by intensively diagnosing deterioration of cells near the end of the fuel cell supply path. In addition, it is possible to provide a degradation diagnosis apparatus for a polymer electrolyte fuel cell capable of performing accurate degradation diagnosis by measuring gas pressure, cell voltage, and internal resistance.

1 is an explanatory diagram of a single cell of PEFC showing an embodiment of the present invention. FIG. 1 is a schematic diagram of a PEFC deterioration diagnosis apparatus showing an embodiment of the present invention. The flowchart of the deterioration diagnosis of PEFC which shows one Embodiment of this invention. Judgment of performance deterioration by IV characteristics of fuel cell stack. Change in voltage of fuel gas inlet and outlet cells over time. The voltage of each cell in the fuel cell stack. Recovery performance of the fuel cell stack.

Explanation of symbols

1 Fuel cell 11 Single cell 111 Fuel gas (hydrogen gas)
112 Oxidant gas (air or oxygen gas)
113 Water 12 Separator 121 Groove 13 MEA
131 Ion Exchange Membrane 132 Catalyst Layer 133 Diffusion Layer 134 Fuel Electrode 135 Air Electrode 2 Pressure Regulator 3 Flow Rate Measuring Device 4 Inverter 5 Load 6 Internal Resistance Measuring Device and Voltage Measuring Device (Single Cell)
7 Pressure measuring device (near fuel gas outlet)
8 Degradation judgment device

Claims (3)

In a degradation diagnosis method for a polymer electrolyte fuel cell having a fuel electrode, an air electrode, and a polymer electrolyte membrane disposed therebetween, a cell located at the end of a fuel gas supply path to the fuel electrode is provided. A method for diagnosing deterioration of a solid polymer fuel cell, characterized by intensively diagnosing deterioration. 2. The deterioration diagnosis method for a polymer electrolyte fuel cell according to claim 1, wherein the deterioration diagnosis is detected by an internal resistance and IV characteristics of the cell. After detecting a decrease in performance based on the internal resistance or IV characteristics of the fuel cell, if the fuel gas supply pressure to the fuel electrode and the oxidant gas supply pressure to the oxygen electrode do not recover, the deterioration is diagnosed. 3. A method for diagnosing deterioration of a polymer electrolyte fuel cell according to claim 1 or 2.