JPH0311559A - Operating method of fuel battery - Google Patents

Abstract

PURPOSE:To prevent electrodes from being locally deteriorated, and thereby stabilize electricity generation performance by detecting potential at the inlet and outlet port sides of a reaction gas passage, and thereby turning over the flow direction of reaction gas in the reaction gas passage when the difference in potential between both of the port sides comes up to a specified level. CONSTITUTION:As operating time passes on, detected potential from a voltage sensor 41 located at the inlet port side for reaction gas becomes lower, and detected potential from a voltage sensor 42 located at the outlet port side becomes higher so that the difference in potential between both of them is thereby increased. When the difference comes up to a specified level, a controller 44 opens valves 22 and 23, and 32 and 33 based on signals from a potential difference detector 43 so that the switch-over of exciting current is made in order to close valves 21 and 14, and 31 and 34. Which thereby permits the flow direction of combustion gas 27 in a reaction gas passage to be turned over to the direction indicated by a solid arrow head line 27B, and also permits the flow direction of an oxidizing agent 37 to be turned over to the direction indicated by a dotted arrow head line 37B. As a result, the distribution of reaction gas concentration in a fuel passage and an oxdizing agent passage and the distribution of output current density can almost completely be equalized so that electricity generation characteristics can thereby be stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of operating a stacked fuel cell having a manifold for supplying and discharging a reactant gas, and particularly to a method of supplying the reactant gas.

[Conventional technology]

As is well known, a fuel cell is a stack of single cells consisting of a fuel electrode, an oxidizer electrode, and an electrolyte IJx layer sandwiched between these two electrodes, which are airtightly connected to the sides of the stack. Power generation operation is performed by supplying fuel gas and oxidant gas to the unit cells through the manifold. Conventionally, as a method of supplying these reactive gases, the flow rate distribution of the reactive gas is completely uniformized by improving the reactive gas passage formed in the shape of a groove in the electrode base material or the separator, and the current density distribution is made uniform, which improves the battery performance. Stabilization has been carried out. However, power generation operation is performed with the supply and discharge directions of fuel gas and oxidant gas kept constant from the beginning of the operation.

[Problem to be solved by the invention]

Figure 6 shows the reaction gas passages such as the fuel passage and the oxidizer passage in the conventional method. Since the active substance is consumed by the power generation reaction, the reaction gas anchorage is high on the input 1 side and the output D (i+
! Dark I that decreases towards I]! Show the distribution.

FIG. 4 is a characteristic diagram showing the output current density distribution in the length direction of the reactant gas passage in the conventional method, and shows the reactant gas concentration,
In other words, as the hydrogen partial pressure or oxygen partial pressure decreases on the downstream side of the reaction gas passage, the amount of active material supplied to the electrode also decreases, so the output current density also decreases toward the outlet side of the reaction gas passage. Characteristic gold indicates.

As is well known, batteries exhibit polarization that is related to the withdrawal current density. In other words, the potential is high in areas with low current density;
Areas with high current density have low potential.

The lifespan of a fuel cell is completely influenced by the cell potential; the higher the potential, the more corrosion of the battery's constituent materials and the deterioration of the electrode catalyst, resulting in a shorter lifespan. If the direction of supply and discharge of reactant gases such as fuel gas and oxidizing gas is constant from the beginning of the operation head, corrosion of the reactant gas and catalyst deterioration on the first side (14) will progress and the fuel cell as a whole will deteriorate. There is a problem in that it shortens the lifespan of the

This is a problem that cannot be sufficiently compensated for by improving/removing the reaction gas passages in the base material or separator.

The purpose of this invention is to improve the method of supplying a reaction gas.
The objective is to equalize the distribution of the reaction gas intensities and the power generation current density within the reaction gas passage.

[Failure to solve the problem]

In order to solve all of the above problems, according to the present invention,
Consisting of a stack of unit cells in which a fuel electrode and an oxidizer electrode are arranged across the entire 14-layer, and a fuel passage and an oxidizer passage that supply fuel gas and oxidant gas to both electrodes, respectively, are formed in directions orthogonal to each other. In a fuel cell that performs power generation operation by supplying and discharging fuel gas to the fuel passage and oxidant gas to and from the oxidizer passage through a fuel manifold and an R-wave converter manifold that are airtightly connected to the side surface of the stacked body,
The potential of the unit cell during power generation operation is detected at a position close to the inlet side and outlet side of the fuel gas and oxidizing gas. When the voltage difference between the two detection IB potentials reaches a predetermined level, The flow direction of at least one of the fuel gas and the oxidant gas supplied to the oxidizer passages is reversed.

[Effect]

In the above means, the direction of flow of both or one of the fuel gas and oxidizing gas to the reaction gas passage is completely reversed based on a voltage difference at a point near the entrance and exit of the reaction gas of the unit cell. As a result, the distribution of the reactant gas concentration is reversed with each switching operation, and the position of the portion where the output current density is low and the potential is high is also reversed, making it possible to avoid the occurrence of a high potential depending on how the voltage difference is set. ,
The corrosion of the carbon-based electrode base material as a battery constituent material and the deterioration of the 741 electrode catalyst caused by the voltage difference are equivalently equalized, and therefore the deterioration of the outlet side of the reaction gas progresses locally, resulting in the fuel #F It is possible to completely avoid shortening the life of the battery as a whole.

〔Example〕

All embodiments of this invention will be explained below.

-5~ Figure 7 is a gas 70 diagram showing an embodiment method of the present invention, in which a stack of unit cells (hereinafter referred to as a cell stack) 1 has a pair of gas passages connected to the fuel passages of each unit cell on the side surface. Fuel manifolds 2A and 2B are provided, and a pair of oxidizer manifolds 3A and 3B, which communicate with the oxidizer passages of each unit cell, are hermetically coupled to side surfaces perpendicular to these, respectively.

The fuel pipe 2o shown by the solid line in the figure is connected to its inlet side 2OA, outlet side 20B, and manifold 2A via a pair of valves 2122, and the manifold 2B is connected to a pair of valves 23.2.
Connected via 4. Also, the pair of valves 21 and 22 are 2
When valve 1 opens, valve 22 closes.

They are switching valves that operate in opposition to each other in that when valve 22 opens, valve 21 closes, and the same applies to the other pair of valves 23 and 24. In addition, oxidizer piping 301-14 indicated by a broken line in the figure
．． It communicates with manifolds 3A and 3B via two pairs of valves 31, 32 and 63.64, respectively.

Reference numerals 41 and 42 designate voltage sensors, for example, a pair of platinum wires interposed between a unit battery and a separator sandwiching the unit battery. Voltage sensors 41 and 4
2 are provided on the diagonal of a rectangular unit cell with a distance as large as possible, and at a certain point the voltage sensor 41 is located close to the reactant gas inlet (11!lK) of the manifolds 2A and 3A. The voltage sensor 42 detects the entire side potential.
are manifolds 2B and 6B on the outlet side at the above point.
It is located close to the terminal and detects the entire potential on the exit side. The detected potentials of both voltage sensors 41 and 42 are led to a voltage difference detector 46, which detects the voltage difference between the inlet and outlet of the unit battery, and this voltage difference is set to a predetermined level, for example, about 10% to 20% of the rated output voltage of the unit battery. When the switching command signal is reached, the controller 44
output towards. The controller 44 controls switching valves (21, 22), (23, 24), (21, 22), (23, 24), (
31, 32) (33°34) excitation current switching f
IlJ controls.

In the fuel F4 battery configured in this way, first, the valve 21
Open 24 and close 22.23 to enter 2OA
The hydrogen-rich fuel gas 27 supplied from the cell stack 1 flows in the direction of the solid line arrow 27A through the fuel passage of the cell stack 1 and reaches the outlet 20.
Ejected from B, and again f'31.34 fully open, 32.3
3 is closed, the oxidizing agent 37U such as air flows in the same direction as the broken line arrow 37A from the inlet 30A, and is discharged from the outlet 30B to perform power generation operation. As the driving time passes,
The detection potential of the voltage sensor 41 disposed on the inlet side of the reactant gas is low, and the detection potential of the outlet side voltage sensor 42 is low, so that the voltage difference between the two increases. When this voltage difference reaches the predetermined level, the controller 44 is energized to fully open the valves 22, 26 and 32, 33, and close the valves 21, 24, and 31 and 64 based on the command signal from the voltage difference detector 46. Since all current switching operations are performed, the fuel gas 27 in the reaction gas passage
The flow direction of the oxidizing agent 37 is reversed to the direction of the solid arrow 27B.
The flow direction of is reversed to the direction of the broken line arrow 37B.

This kind of switching operation of the flow direction of the reactant gas can be easily performed by simply switching the valve automatically without stopping the power generation operation, so reversal and maintenance can be repeated repeatedly with a low voltage difference. be able to.

As a result, the distribution of reactant gas a degrees and the output current density distribution in the fuel passage and oxidizer passage are as shown in Figures 3 and 4.
As shown in the figure, if the inlet and outlet positions of the reactant gas on the IA thin axis are all alternated, a distribution will be obtained, and the distribution in the direction of the reactant gas passage can be almost completely equalized, so the output current density will decrease. Deterioration of electrode groups, electrode catalysts, etc. caused by high potential is equalized in each part of the reaction gas passage, stabilizing the power generation characteristics, and the progress of local deterioration reduces the life of the cell stack 1 as a whole. This can also be avoided. In addition, by reducing the voltage difference, the increase in potential that causes deterioration can be completely suppressed, which provides the advantage of extending the life of the fuel cell.

FIG. 2 shows a gas 70-
4A, 4B or 5A, 5B on one side of each of the fuel manifold and oxidizer manifold.
It is divided into the manifold 4C or 5 on the other side (4- This shows the application column to the fuel cell of the return flow where the fuel gas 27 or the oxidant gas is turned back as an intermediate manifold. 9- In this case, the fuel pipe 20 is a pair of manifolds 4A, 4B via two pairs of valves 21, 22 and 23, 24.
As in the previous embodiment, the valve k-! ;IJ
, the flow direction of the return flow 27U can be completely reversed by performing the D change operation. Further, the oxidizer pipe 30 is connected to a pair of manifolds 3A and 3B via two pairs of valves 31, 32 and 33, 34, and the oxidizer pipe 30 is connected to a pair of manifolds 3A and 3B through two pairs of valves 31, 32 and 33, 34. The flow direction of the return 70-37U can be reversed.

In this case, the method of arranging the voltage sensors differs depending on which two of the voltage sensors 51, 52, 53, and 54 placed at the four corners of the unit battery are used. For example, if the sensors 51 and 52 are combined, the fuel By combining the gas inlet and outlet concentration differences and the sensors 52 and 54, it is possible to detect the voltage difference that is most affected by the oxidizing gas inlet and outlet concentration differences. 51)
.

With the combination (53, 54), it is possible to detect a voltage difference corresponding to approximately half the concentration difference in the U-turn gas passage.

In addition, in the example method, it is preferable to reverse the flow direction for both the fuel gas and the oxidizing gas, but if the reaction gas passage is short and the influence on deterioration is small, either one of the gases may be reversed. It may also be configured to reverse only the gas flow.

〔Effect of the invention〕

As described above, this invention is configured to detect the potentials on the inlet side and the outlet side of the reaction gas passage, respectively, and to reverse the flow direction of the reaction gas in the reaction gas passage when the voltage difference reaches a predetermined level. . As a result, depending on how the voltage difference is determined, the flow direction of the reactant gas can be reversed before the potential at the outlet side of the unit cell becomes too high. The problem was that the concentration of the reactant gas and the output current density decreased toward the outlet side of the reactant gas, and the battery potential at the outlet side of the reactant gas became high, causing corrosion of the electrode group ions and the electrode catalyst. The problem of accelerated deterioration is eliminated by v1, and therefore local deterioration of the electrodes is reduced and equalized, making it possible to fully stabilize power generation performance and to provide a method of operating a fuel cell that can extend its life. . Furthermore, a score of 40 can be obtained in that the reversal operation of the flow direction of the reaction gas can be performed by automatic valve operation without completely stopping the power generation operation of the fuel cell.

[Brief explanation of drawings]

Fig. 1 is a gas 70-diagram showing an embodiment method of the present invention, Fig. 2 is a gas flow diagram showing a different embodiment method, Fig. 6 is a characteristic diagram showing the conventional reaction gas concentration distribution, and Fig. 4 The figure is a characteristic diagram showing the distribution of conventional output current density. 1... Laminated body of unit batteries (cell stack), 2A. 2B, 4A, 4B...Fuel manifold, 6A, 3B
, 5A, 5B... Oxidizer manifold, 4C15C・
...Intermediate manifold, 20...Fuel gas piping, 21
．． 22, 23, 24... Valve (fuel gas side), 27...
・Fuel gas, 60... Oxidizer piping, 31, 32, 36
．． 34... Valve (oxidizer side), 37... Oxidizer gas,
27A, 27B, 37A, 37B...Flow direction of reaction gas, 27U, 37U...Return 70-41°42
．． 51.52, 53.54... Voltage sensor, 43...
・Voltage difference detector, 44...tlilJ controller.

Claims (1)

[Claims] 1) From a stack of unit cells in which a fuel electrode and an oxidizer electrode are arranged with an electrolyte layer in between, and a fuel passage and an oxidizer passage that supply fuel gas and oxidant gas to both electrodes, respectively, are formed in directions orthogonal to each other. In a fuel cell that performs power generation operation by supplying and discharging fuel gas to the fuel passage and oxidant gas to and from the oxidizer passage through a fuel manifold and an oxidizer manifold that are airtightly connected to the side surface of the stacked body, The potential of the unit cell during power generation operation is detected at a position close to the inlet side and outlet side of the fuel gas and oxidant gas, and when the voltage difference between the two detected potentials reaches a predetermined level, the potential of the unit cell is detected in the fuel passage and the oxidant passage. 1. A method of operating a fuel cell, comprising reversing the flow direction of at least one of a fuel gas and an oxidant gas respectively supplied to the fuel cell.