JPH0336274B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains]

The present invention provides a method for determining when it is necessary to replenish electrolyte to a so-called matrix fuel cell, in which electrode layers are arranged on both sides of a matrix layer holding electrolyte to receive a reaction gas and generate electricity. The present invention relates to a method for intermittently monitoring the amount of electrolyte retained within a matrix layer.

[Prior art and its problems]

The above types of fuel cells, especially matrix fuel cells that use phosphoric acid as the electrolyte, hydrogen or reformed gas obtained by reforming natural gas as the fuel gas, and air or oxygen as the oxidizing gas, are close to It is attracting attention as a large-capacity fuel cell that is expected to be put to practical use or commercialized in the future. As is well known, in this type of fuel cell, the matrix layer that holds the electrolyte is a porous, electrically insulating thin sheet, and various improvements have been made to its porosity and pore size, and the electrolyte is absorbed into the pores within this matrix layer. It is held so that it completely fills the area. The fuel gas electrode layer and the oxidant gas electrode layer disposed in contact with this matrix layer are both gas permeable or gas diffusive, and therefore, during battery operation, the electrolyte retained within the matrix layer is These leached electrolytes also leak into the parts of the electrode layers that are in contact with the matrix layer, and the electrochemical reaction between this leached electrolyte and the reactant fuel gas or oxidizing gas that permeates or diffuses through the electrode layers generates electricity. carry out an action. The matrix layer plays the role of holding the electrolyte necessary for such electrochemical reactions and supplying it to the electrode layer, and it is also important to separate the reaction gases from each other so that the fuel gas and oxidizing gas do not come into contact with each other. It also serves a role. In other words, even if the reactant gas were to penetrate the gas-permeable electrode layer,
The electrolyte filled in the matrix layer prevents it from further permeating or diffusing to the opposite side. If the fuel gas and oxidizing gas mix outside the electrode layer, an extra combustion reaction that does not contribute to power generation may occur, or a detonating gas may be formed, which in the worst case may result in an explosion. The ability of the matrix layer to separate both reactant gases is an extremely important function both in maintaining high efficiency of the battery and in ensuring safe operation of the battery. By the way, a reaction product, usually water, is produced in the electrode layer by the aforementioned electrochemical reaction, and the electrolyte is diluted by this. This dilution naturally increases the amount of electrolyte containing electrolyte, and if left as it is, the amount of electrolyte will continue to increase as power generation continues. Therefore, the amount of water generated by the reaction is evaporated into the reaction gas. I have to do it. For this reason, the amount of reaction gas in excess of that consumed within the electrode layer, usually several times the amount, is flowed onto the surface of the electrode layer, promoting the evaporation of reaction product water.
However, at this time, the electrolyte tends to be taken out of the electrode layer along with the evaporated water, albeit in a small amount, and the amount of electrolyte initially retained in the matrix layer gradually decreases over a long period of operation. It turns out. Of course, even in such a case, if the matrix layer is replenished with electrolyte, the battery will return to its normal state. On the other hand, normal power generation occurs only when the electrolyte and reactive gas coexist in the electrode layer, so if the amount of electrolyte is excessive, the electrolyte will leach into the electrode layer and drive out the reactive gas. It is also undesirable to allow the matrix layer to retain excess electrolyte in advance, since this will impede the power generation action. of course,
Excessive electrolyte leaching into the electrode layer tends to scatter from the electrode layer relatively quickly as the water produced by the reaction evaporates, and in this sense the electrode layer has a self-adjusting effect, but this does not limit the amount of electrolyte consumed. In addition to this, the scattered electrolyte causes problems such as corrosion to the attached piping system of the battery. As mentioned above, managing the amount of electrolyte held in the matrix layer and replenishing the electrolyte at the correct time is extremely important to maintain battery operating performance and ensure safe operation. However, since the matrix layer exists inside the stacked battery body, there is no convenient means to measure the amount of electrolyte, and it is difficult to determine whether the appropriate amount of electrolyte is retained in the matrix layer and when to replenish the electrolyte. There is a need for the development of a practical method for knowing what to do.

[Purpose of the invention]

In view of the above-mentioned circumstances, the present invention enables relatively simple means to monitor the amount of electrolyte held in the matrix layer of the above-mentioned type of fuel cell and replenish the electrolyte to the cell at an appropriate time. By doing so, the purpose is to contribute to maintaining the operational performance of the fuel cell and ensuring operational reliability.

[Key points of the invention]

According to the method of the invention, this object is to electrically separate a part of the electrode plane of at least one of the two electrode layers sandwiching the matrix layer from the remaining part of the electrode plane in a fuel cell of the type mentioned at the outset. The separated part and the remaining part are connected to each other, and the battery is constantly operated with the two parts interconnected by a disconnectable opening/closing means, and the separated part is included in a state where both parts are separated from each other. This is achieved by measuring the cell voltage of the partial cell so that the amount of electrolyte in the matrix layer can be estimated from the measured voltage value. FIGS. 1 and 2 show the principle of construction of the present invention, and FIG. 1 shows the matrix layer 1 of one unit cell and a matrix layer 1 disposed in contact with both surfaces of the matrix layer 1 to supply reactant gas. A fuel gas electrode layer 2 and an oxidant gas electrode layer 3, which serve as electrode layers receiving electricity from the anti-matrix layer side and performing a power generation function, are shown taken out from the cell. In the figure, a part of the electrode surface of the upper oxidizing gas electrode layer 3 of both the electrode layers 2 and 3 is a separation part 13, and a remaining part 3a is formed by a separation layer to be described later in the defect indicated by 3b in the figure. It is electrically separated and fitted. FIG. 2a shows the state shown in FIG. 1 with this separated part 13 fitted.
A cross section is shown. FIG. 1A schematically shows a switch 21 as an opening/closing means for interconnecting the separated portion 13 and the remaining portion 3a, and a separation layer 11 for insulating them from each other. This switch 21 is normally closed during operation of the battery, but is opened as shown in the figure when measuring the voltage across the separation section 13 in order to estimate the amount of electrolyte in the matrix layer 1. The voltage V of the partial cell 10 formed by the fuel gas electrode layer 13 and the fuel gas electrode layer 2 corresponding thereto is measured by the voltage measuring means 30. Note that the portion corresponding to this separated electrode layer portion 13 may be the matrix layer 1 instead of the fuel gas electrode layer 2, and in this case, the partial cell consists of a matrix layer and two electrode layers sandwiching the matrix layer. It is configured as a so-called single battery formed by one of the two. The reason why the amount of electrolyte in the matrix layer 1 can be estimated by measuring the battery voltage of the partial battery described above will be explained with reference to FIGS. 3 and 4. Third
The horizontal axis of the graph in the figure is the elapsed operating time t of the battery, the vertical axis of the figure a is the battery voltage V, and the vertical axis of the figure b is the relative expansion value of the leakage amount Q of the reaction gas between the two electrodes. It shows. Also, between the two curves in figure a
Vo indicates the open circuit voltage of the battery, that is, the electromotive force of the battery when there is no load current, and Vi indicates the output voltage of the battery when the battery is at the rated load (in addition,
Both voltages are shown enlarged to clarify trends). As can be seen from both figures a and b, as time passes after the battery starts operating at time t0 and the amount of leakage Q gradually increases as the electrolyte decreases, it is clear that the open circuit voltage particularly tends to decrease accordingly. recognized. In this test, the electrolyte was replenished into the battery at time t1, and as can be seen from the figure, both the leakage amount Q and the battery voltage V showed remarkable recovery due to the replenishment of the electrolyte. Also, as can be seen from this figure, under certain conditions when the battery is under rated load, the drop in battery voltage due to electrolyte reduction is relatively small; It can be said that measuring the open circuit voltage at this time is advantageous in estimating the amount of electrolyte. Note that the value of the open circuit voltage Vo mentioned above is about 1 volt per single cell at the operation start time t0, and about 0.7 volt just before the electrolyte replenishment time t1, so
There is no difficulty in accurately measuring the 0.3 volt difference between the two values. On the other hand, Figure 4 shows the results of measuring the polarization characteristics of a fuel cell by separating the fuel gas electrode layer and the oxidizing gas electrode layer, and the horizontal axis shows the current density per unit area of the electrode. The vertical axis shows the potential E of the electrode layer, with the potential of the fuel gas electrode layer under no load being zero, the curve Ea shows the potential of the oxidizing gas electrode layer, and the curve Ef shows the potential of the fuel gas electrode layer. It shows. As can be seen from this figure, the polarization of the oxidizing gas electrode layer is larger than that of the fuel gas electrode layer, and the increase in polarization voltage during light loads is particularly significant in the oxidizing gas electrode layer. Due to these reasons, the tendency for the battery voltage to decrease due to a decrease in the amount of electrolyte is mainly caused by a decrease in the electromotive force on the oxidizing gas electrode layer side during both load and no-load conditions. It is advantageous to provide this on the oxidizing gas electrode layer 3 side. In addition, in FIG. 2b, the separated parts 12 and 13 are used as fuel,
When switches 21 and 22 for measuring battery voltage are provided on both oxidizing gas electrode layers 2 and 3, FIG. This is an example.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings. 5 and 6 show the structure of a fuel cell when the method of the present invention is applied to a fuel cell having a so-called ribbed electrode substrate structure. FIG. 6 shows a cell in longitudinal section. As shown in FIG. 5, the electrode layer section in this example includes an air-permeable electrode substrate 3d equipped with a plurality of grooves 3e for supplying reaction gases, and a gas-diffusive electrode substrate 3d provided on the bottom surface of the electrode substrate 3d, as shown in FIG. The active layer 3c contains an oxidizing gas electrode layer, and a separated portion 13 of the electrode layer is provided on the side of the oxidizing gas electrode layer, corresponding to FIG. 1 described above. The aforementioned defect 3b is therefore provided for both the electrode substrate 3d and the active layer 3c, and correspondingly, the separation portion 13 also consists of the electrode substrate 3d and the active layer 3c, and the groove 13e When the separation part 13 is placed in the cutout 3b, the groove 3e of the remaining part 3a
It is set up so that it is continuous. Further, the width of the left peak portion 13f of the separated portion 13 is the same as that of the remaining portion 3a.
It is about half the width of the mountain part 3f between the grooves, and the width of the 6th
Care is taken so that when assembled as shown in the figure, the position of the groove 13e in the partial battery 10 is approximately equal to the position of the groove 3e in the remaining part. FIG. 6, which shows the assembled state of the unit cell, shows that in addition to this oxidizing gas electrode layer, it also includes the matrix layer 1 below it, as well as an active layer 2c and an electrode plate 2d, similar to the oxidizing gas side, but separated. A fuel gas electrode layer separation section 2 with no section is shown, and an air-impermeable flat separator plate sandwiching the electrode layer sections 2 and 3 from above and below is also shown. As is well known, an actual fuel cell is constructed as a laminate in which a large number of single cells shown in the figure are stacked vertically, but the partial cells necessary for carrying out the present invention are contained in one or at key points in the laminate. It is sufficient to create a small number of them with a distribution of . Oxidizing gas, such as air A, is passed through the grooves 3e and 13e from the front and rear sides of the laminate as viewed in the figure, passes through the electrode substrates 3d and 13d, and reaches the active layers 3c and 13c on the oxidizing gas side. Similarly, the fuel gas F enters the groove 2e from the left and right side surfaces of the stack, passes through the electrode substrate 2d, and reaches the active layer 2c on the fuel gas side. In the figure, an electrolyte replenishment means 40 for the matrix layer 1 is shown on the left side of the figure opposite to the partial battery 10 of the electrode substrate 3d, and as shown in the figure, the electrolyte replenishment means 40 for the matrix layer 1 is
Electrolyte can be injected into an electrolyte reservoir 41 formed as a recess provided at d through an electrolyte supply pipe 42 that opens into the electrolyte reservoir 41 from the side of the battery. This electrolyte pool 41
is connected to the matrix layer 1 through the communication hole 44 at the bottom thereof.
The electrolyte injected into the electrolyte reservoir 41 during replenishment spreads to each part of the porous matrix layer 1 using the communication hole 44 as a replenishment point. Therefore, the part of the matrix layer located farthest from this replenishment point tends to run out of electrolyte earliest within the plane of the electrode layer, and by building the partial battery 10 at the position farthest from the electrolyte replenishment point as shown in the figure, the electrolyte can be reduced. shortage can be detected early. When the separation part 13 is assembled into a battery, the separation layer 11 is attached to the remaining part 3 so as to surround the three fitted sides of the separation part 13 shown in FIG.
Insert between a. This separation layer may be a sheet of fluororesin that is resistant to electrolytes, or may be made of the same resin in the form of a paste. In addition, an insulating plate 1 is placed on the top surface so that the top surface does not come into contact with the conductive separator plate 4 and be electrically connected to the remaining portion 3a.
After placing the separator plates 4, the separator plates 4 are laminated. Furthermore, when the partial battery 10 is provided at the periphery of the battery as in this example, the configuration shown in FIG. As shown in the example, it is preferable that the peripheral portion thereof be configured as an air-impermeable portion 13h. As an electrical measurement means, the leads 31 are pulled out from the side surface of the separation part 13 by a method such as erecting as shown in FIG. Also, the leads 33 from the opposing fuel gas electrode 2 side are similarly pulled out from the lower separator plate 4. These leads 31 to 33 insulatively and airtightly pass through a manifold lid attached to the side surface of the battery stack (not shown) and are drawn out of the battery. The battery voltage V between the leads 31 and 33 is measured. As shown in FIG. 5, sealing layers 3g and 13g are provided on the peripheral edges of the electrode substrates 3d and 13d, which are the side surfaces of the battery, to prevent the reaction gas from leaking to the side surfaces of the battery. A gasket 1b is also provided on the peripheral edge of the battery to prevent electrolyte from leaking to the side of the battery. FIG. 7 shows the structure of a fuel cell when the method of the present invention is applied to a fuel cell having a so-called ribbed separator structure, and the main parts of the cell are shown in a longitudinal sectional view. Further, in the illustrated example, the separation portions 12 and 13 of the electrode layers 2 and 3 are provided on both the fuel gas and oxidation gas sides, and the remaining portions are separated from the separation layer 1.
1 and 11. The air-impermeable separator 4 is provided with a large number of grooves 4a and 4b orthogonal to each other on both sides thereof, and the fuel gas F and the oxidizing gas A are passed through the grooves 4a and 4b, respectively, to the fuel gas electrode layer 2 and its separation portion 12. and is supplied to the oxidizing gas electrode layer 3 and its separated portion 13. Separated portions 12 and 13 of the electrode layer are separated from the separator 4 by the insulating plate 1.
4, and plate-shaped leads 31 and 34 are inserted between the insulating plate 14 and the separation parts 12 and 13 on the peripheral edge side of the battery. Potentials 12 and 13 are led out to the sides of the cell. Since the potential of the remaining portions of the electrode layers 2 and 3 can be derived from the conductive separator 4 that is in conductive contact with the remaining portions, as shown in the figure, the potential of the remaining portions of the electrode layers 2 and 3 can be derived from the battery sides of the separators 4 and 4 above and below the remaining portions 12 and 13. For example, the leads 32 and 33 that are set up
will be provided. switch 21 as opening/closing means;
22 interconnects these leads 31, 32 and 33, 34, respectively, when the battery is in operation, but is opened as shown during measurement to monitor the amount of electrolyte retained, and the voltage between the leads 31, 34 is It is measured as the battery voltage V of the partial battery 10. Note that the electrode layers 2 and 3 in this case are the same as the matrix layer 1.
In addition, the battery is often constructed as a stacked unit of batteries whose periphery is surrounded by a common sealing layer.
It is preferable that the aforementioned separation layer 11 is also built into this unit. The separation layer 11 may be a fluorocarbon resin sheet having phosphoric acid resistance, and is formed into a unit by adhering it to the electrode layer and the matrix layer during molding of the sealing layer 1b using the same resin adhesive. can be included. FIG. 8 illustrates some embodiments regarding the location of the separation portion indicated by the hatching within the electrode layer plane of the fuel cell, and also shows the arrangement of the electrolyte replenishment point 44 and the groove 3e for supplying the reactant gas. ing.
On the side a of the figure, a partial battery 10 is arranged on the opposite side of the left side of the electrode surface where the thin groove-shaped electrolyte replenishment point is arranged, and a groove 13e therein is provided independently from a groove 3e in the remaining part. It is being On the side shown in FIG. 5B, two electrolyte replenishment points 44, 44 are provided at diagonal corners in the electrode plane, so that the partial battery 10 is arranged across the center of the plane. In the example shown in FIG. It is provided continuously with the groove 3e. An example of an electrical measuring circuit for carrying out the method of the invention is shown in FIG. 9, which is similar to FIGS.
This corresponds to the arrangement example of the partial battery 10 shown in FIG.
In this figure, there are 10 cells connected in series with each other.
0, 101, and 102, of which a single cell 100 is provided with a partial battery 10. As mentioned above, the switches 21 and 22 as opening/closing means are always closed while the battery is in operation, so the partial battery 1
0 also performs a power generation function as a part of the unit cell 100, and as a result, the electrolyte retention state in the matrix layer of the partial electrode 10 is maintained at the unit cells 100, 10.
1,102. To start the measurement, there is no need to stop the operation of the fuel cell; simply open the switches 21 and 22 and measure the battery voltage V of the partial battery 10 between the leads 31 and 34 using the voltmeter 35. You can measure it. As described above, this battery voltage is the open circuit voltage Vo, that is, simply the voltmeter 35 connected to the partial battery 10.
It is advantageous to measure the voltage V when the electrodes are connected in order to accurately determine the state of electrolyte retention within the matrix layer. However, the open circuit electromotive force of a battery when the electrolyte is well maintained may be 1 volt or slightly higher than this, and if this high electromotive force is maintained for too long, the electrode layer, especially the oxidizing gas electrode layer Oxidation progresses on the side, and there is a risk of deterioration or corrosion of the active material in the electrode layer. Therefore, if necessary, an ammeter 37 should be connected to the high resistance 36 as a battery load, whose connection relationship is shown by the chain line in the figure. This allows the voltage generated by the battery to be kept within dangerous limits, for example 0.9 volts or less. In addition, in case of disconnection of the leads led out of the battery manifold,
One method is to connect the high resistance 36 in parallel to the partial batteries in the manifold in advance. When measuring with a light load applied to the partial battery, especially when placing emphasis on the voltage on the oxidizing gas electrode layer side,
It also has the meaning of knowing the polarization state on the oxidizing gas electrode layer side as explained in the figure, and depending on the purpose, it may be more advantageous than measuring the open circuit voltage. As is known, battery voltage is a function of temperature, and therefore the measurements obtained when carrying out the method of the invention may also be influenced by the operating temperature of the battery.
However, practical fuel cells are usually operated under a constant load condition, and the temperature of the cooling means and the like is precisely controlled, so there is almost no fluctuation in the operating temperature of the cell. In addition, in the method of the present invention, as mentioned above, there is no need to interrupt battery operation for electrical measurements, so the battery temperature during measurement is also maintained during the measurement period since all the surrounding cells are in operation. There is no need to take into account temperature fluctuations of the internal partial batteries. For this reason, in the case of the method of the present invention, it is not actually necessary to perform temperature correction on the measured values, but if the battery temperature tends to fluctuate depending on the operating conditions, the temperature of the partial battery can be measured by known means. Temperature compensation can be performed using The temperature dependence of battery voltage has been established both theoretically and experimentally, and there is extremely little risk of introducing uncertain factors into temperature correction. The measured value of battery voltage obtained as above,
Alternatively, as the case may be, the temperature-corrected measured value is compared with an experimentally determined lower limit value of the battery voltage, and when it falls below this, it is determined that electrolyte replenishment is necessary.

【Effect of the invention】

As explained above, the method of the present invention provides an effective and practical method for monitoring the amount of electrolyte retained in a matrix fuel cell in order to know when electrolyte replenishment is necessary, something for which there was no suitable means in the past. This is a new offering. A particular advantage of the invention for this purpose is that there is no need to stop or interrupt the operation of the battery for measurements during monitoring; in fact, measurements can be made more accurately without interruption; As a result, great benefits can be obtained from the operational economics of the fuel cell, and the amount of electrolyte retained can be accurately determined over time through detailed monitoring and measurement, thereby improving the operational reliability of the battery. . Furthermore, as mentioned above, the partial battery to be measured in the method of the present invention can be arbitrarily selected at the most advantageous position in relation to the electrolyte replenishment point within the plane of the electrode layer, and its area can also be arbitrarily selected. Therefore, the shortage of electrolyte in the matrix layer can be detected earlier than when monitoring the entire surface of the electrode layer. Another feature of the method of the present invention is that, as can be easily seen from the above description, the measured value does not essentially change depending on the area of the electrode layer in the partial cell. This provides the convenience of being able to quickly obtain the most useful information by appropriately selecting the location and area of the battery. The principle of the method of the present invention is that, as explained at the beginning, when the amount of electrolyte gradually decreases,
This method takes advantage of the fact that a small amount of reactant gas, especially hydrogen as a fuel gas, leaks inside the matrix layer to the oxidizing gas electrode side and lowers the electromotive force.However, such a small amount of leaked hydrogen molecules leak into the gas passage on the oxidizing gas side. Before exiting, the oxidizing gas always passes through the electrode layer and affecting the generated electromotive force, so there is no possibility of missed detection, and it is possible to analyze the trace amount of fuel gas mixed into the oxidizing gas side. This method has the advantage of being able to more sensitively detect signs that do not lead to actual leaks, and therefore can be detected earlier.

[Brief explanation of the drawing]

The drawings are all for explaining the contents of the method of the present invention, and FIG. 1 is a perspective view of the main parts in a cell equipped with a partial battery to show the principle of construction of the present invention, and FIG. A vertical cross-sectional view of the main parts of a unit cell showing some basic configuration examples of a partial battery, and FIG. 3 is an operational test result showing changes over time in battery voltage and reaction gas leakage amount to explain the principle of the method of the present invention. graph diagram,
FIG. 4 is a graph illustrating the polarization characteristics of the fuel gas electrode layer and the oxidizing gas electrode layer, also for explaining the principle, and FIGS. 5 and 6 show the method of the present invention applied to a fuel cell having a ribbed electrode substrate structure. The structure of the partial battery in the applied example is shown, in which FIG. 5 is a perspective view of the main part of the electrode layer, and FIG. 6 is a longitudinal sectional view of the unit cell. FIG. 7 is a vertical cross-sectional view of the main parts of a unit cell showing the configuration of a partial cell in an embodiment in which the method of the present invention is applied to a fuel cell with a ribbed separator structure, and FIG. FIG. 9 is a circuit diagram showing an electrical measuring circuit for carrying out the method of the present invention. In the figure, 1: matrix layer, 2: fuel gas electrode layer,
3: Oxidizing gas electrode layer, 3a: Remaining portion, 4: Separator, 10: Partial battery, 11: Separation layer that separates the separated portion from the remaining portion, 12, 13: Separating portion, 20: Opening/closing means, 21, 22: Switch as opening/closing means, 30: Battery voltage measuring means, 31:
40: electrolyte replenishment means; 44: electrolyte replenishment point; A: air as oxidizing gas; F: fuel gas.

Claims (1)

[Scope of Claims] 1. A fuel cell comprising a matrix layer holding an electrolyte, and electrode layers each disposed in contact with both sides of the matrix layer to receive a reaction gas and perform a power generation function. A method for monitoring the amount of oxidation, the method comprising electrically separating a part of the electrode surface of at least one of the two electrode layers sandwiching the matrix layer from the remaining part of the electrode surface, the separated part and the remaining part. The battery is constantly operated with both parts interconnected by an opening/closing means that can connect and disconnect them, and the battery voltage of the partial battery including the separated part is measured with both parts separated from each other. A method for monitoring the amount of electrolyte retained in a fuel cell, characterized in that the amount of electrolyte in a matrix layer can be estimated from a measured voltage value. 2. In the method described in claim 1,
A method for monitoring electrolyte retention in a fuel cell, characterized in that an open circuit voltage is measured as a cell voltage of a partial cell. 3. In the method described in claim 1,
1. A method for monitoring the amount of electrolyte retained in a fuel cell, characterized in that a separated part in the electrode plane is provided at a part of the plane opposite to a point at which electrolyte is supplied to the matrix layer.