JPH0324745B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention provides an electrolyte in which an electrolyte is held in a porous matrix layer, and a fuel gas electrode layer and an oxidant gas electrode layer that are gas permeable on both sides of the porous matrix layer and in contact with the matrix layer. Indirectly measuring or estimating the amount of electrolyte or electrolyte held in the matrix layer of a so-called matrix fuel cell, especially a stacked fuel cell including a ribbed separator, from the power generation characteristics of the cell. Regarding the method.

[Prior art and its problems]

The above types of fuel cells, especially so-called matrix cells, which use phosphoric acid as the electrolyte, use reformed hydrogen gas containing carbon dioxide obtained by reforming hydrogen or natural gas as the fuel gas, and use oxygen or air as the oxidizing gas. BACKGROUND ART Fuel cells are attracting attention as high-capacity fuel cells that can be put into practical use or commercialized in the near 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 oxidizing gas electrode layer disposed in contact with this matrix layer are both gas permeable or gas diffusive,
Therefore, during battery operation, the electrolyte held within the matrix layer also leaches into the electrode layers in contact with the matrix layer, and this leached electrolyte and the reactive gas that permeates or diffuses through the electrode layer. The fuel gas or oxidizing gas reacts electrochemically to generate electricity.

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. That is, even if the reaction gas were to penetrate through the gas-permeable electrode layer, the electrolyte filled in the matrix layer would prevent it from further permeating or diffusing to the opposite side. If the fuel gas and oxidizing gas come into contact outside the electrode layer, an extra combustion reaction that does not contribute to power generation will occur, or a detonating gas may be formed, which in the worst case may lead to an explosion. The ability of the 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.

Incidentally, within the electrode layer, a reaction product, usually water, is produced 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, so the amount of water produced by the reaction will evaporate into the reaction gas. I have to let it happen. 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 carried away from the electrode layer along with the evaporated water, albeit in small amounts, and during long-term operation, the electrolyte initially retained in the matrix layer gradually decreases, causing the concentration of the electrolyte. will continue to decline. Of course, even in such cases, if electrolyte is replenished into the matrix layer, the battery will operate without problems, but replenishing electrolyte is not always easy, so the question is when should electrolyte be replenished? remains.

In addition, as can be seen from the above description, the amount of electrolyte including the amount that oozes into the electrode layer is determined by the generation rate of reaction product water and the rate of its evaporation, so if the balance between the two is disrupted, the amount of electrolyte The amount will deviate from the desired value. If the reaction product water is evaporated in excess, especially if the amount of electrolyte has decreased to the limit, the amount of electrolyte will easily become insufficient, and the two reaction gases mentioned above will be isolated from each other. There is a risk that the matrix layer will not be able to fully fulfill its role of preserving the matrix. Practical fuel cells are constructed as a laminate made up of a large number of single cells, and excess or deficiency in the amount of electrolyte or electrolyte can occur for each single cell. It is easy for something to run out of electrolyte or electrolyte.

As mentioned above, although management of the amount of electrolyte held in the matrix layer is an important matter for maintaining battery operating performance and ensuring safe operation, it is important to note that the amount of electrolyte retained in the matrix layer is Due to its internal and distributed presence, there is no convenient way to measure the amount of electrolyte, and there is no practical way to know if the proper amount of electrolyte is retained within the matrix layer and when to replenish it. was desired. Note that if an excessive amount of electrolyte is retained in the matrix layer at all times, a large amount of the excess electrolyte will seep into the electrode layer, worsening or losing the gas diffusivity of the electrode layer, which may reduce or stop the power generation effect of the battery. It is well known that this can lead to

[Purpose of the invention]

Based on the state of the art as described above, the present invention provides a practical method for estimating the amount of electrolyte held within the matrix layer of a fuel cell of the above type with a relatively simple operation, thereby determining the amount of electrolyte. The purpose is to assist in the rational management of

[Key points of the invention]

According to the present invention, this purpose is to supply a test gas, which can act on both the fuel gas electrode and the oxidizing gas electrode and carry out an electrochemical reaction together with the electrolyte to generate electricity, at different concentrations to both electrode layers. ,
This is achieved by estimating the amount of electrolyte held in the matrix layer from the electromotive force generated by the fuel cell at this time.

When the electrolyte is phosphoric acid, hydrogen gas is an example of a gas that can act on both electrode layers and cause an electrochemical reaction, and the same gas can act on both the positive and negative electrode layers to cause electrolyte or electrolytic solution. Any material that can be an anion or a cation may be used. In particular, in devices that use hydrogen gas as the fuel gas, the active substances in the electrode layer are often carbon and noble metal catalysts for both the fuel gas and the oxidizing gas, so hydrogen gas itself is used as the test gas in both electrode layers. It can act on For example, in order to supply such hydrogen gas as a test gas at different concentrations to both electrode layers, for example, pure hydrogen is supplied to the fuel gas electrode layer side, and pure hydrogen is supplied to the oxidation gas electrode layer side. It may be supplied after being diluted with nitrogen as an active gas. At this time, it is desirable that the pressure of the pure hydrogen gas be equal to the pressure of the mixed gas of hydrogen and nitrogen so that stress due to differential pressure does not occur in the electrode layer or matrix layer. Further, in this case, the test gas source is not limited to pure hydrogen, but may be other gases that are inactive to both electrode layers, such as hydrogen containing carbon dioxide gas.

When test gases with different concentrations are supplied to both electrode layers in this way, an electromotive force is generated in each electrode layer according to the concentration of the test gas, and the difference between these two electromotive forces is the electromotive force generated by the battery. It appears. Therefore, the electromotive force generated by the battery during such a test is lower than the electromotive force generated when normal fuel gas and oxidizing gas are supplied to both electrode layers. This is advantageous in that the battery is not damaged during this type of test. That is, if a fuel cell is exposed to a high open-circuit voltage, loss of active material due to oxidation or corrosion may progress on the oxidizing gas electrode side, resulting in loss or inactivation of the active material. In the method of the present invention, the electromotive force generated by the battery during the test always appears as the difference between the electromotive forces of the two electrode layers, so there is no such fear at all.Moreover, if a fuel gas system is used as the test gas, the oxidation of the active material can be avoided. The problem essentially disappears.

The electromotive force generated by such a battery becomes abnormally small if the amount of electrolyte in the matrix layer is too small. In other words, when the electrolyte is no longer able to fill all the pores in the porous matrix layer, a small amount of test gas leaks from the higher concentration side to the lower concentration side, and as a result, the difference in electromotive force between the two electrode layers decreases. , the electromotive force generated by the battery decreases.
As a result of experiments, it was found that this process occurs more rapidly and is more sensitive than expected. Accordingly, the method of the present invention makes it possible to detect that the amount of electrolyte in the matrix layer is on the verge of becoming insufficient before the amount of electrolyte in the matrix layer has fallen to a level that requires replenishment.

A slightly theoretical explanation of this process is as follows. Assuming that the test gas concentration on the fuel gas electrode layer side is α, that on the oxidizing gas electrode layer side is β, and the pressures of the test gas applied to both electrode layers are equal to each other and P, the partial pressure of the test gas is equal to that of the fuel gas electrode layer. Pf=αP on the gas electrode layer side, Po=βP on the oxidizing gas electrode layer side, and from the known electromotive force formula, the electromotive force of both electrode layers is as follows.

Ef=Ff0+(RT/F)・ln(CH/√) Eo=Eo0+(RT/F)・ln(CH/√) However, Ef and Eo are the electromotive force on the fuel gas electrode layer side and the electromotive force on the oxidizing gas electrode layer side, respectively. The electromotive force, Ef0, Eo0 is the standard electrode potential on both electrode layers (Ef0=Eo0
), R is the gas constant, T is the absolute temperature, F is the Faraday constant, and CH is the hydrogen ion concentration in the electrolyte.

Therefore, the electromotive force V0 generated by the battery is V0=(RT/2F)lnα/β (assuming α>β), and the battery has a ratio of the test gas concentrations supplied to the fuel and oxidation gas electrode layers. It can be seen that the electromotive force of the function is generated. moreover,
When α > β, the test gas slightly leaks through the matrix layer from the higher concentration side to the lower concentration side, and the concentration β on the lower side is
If the voltage rises to β + Δβ, the electromotive force of the battery at that time is V = (RT / 2F) lnα / (β + Δβ), so the difference ΔV from the electromotive force V0 when there is no leakage is ΔV = V0 - V = (RT/2F)ln(1+Δβ/β). From this, it can be seen that the smaller the test gas concentration β of the lower concentration is, the better the detection sensitivity is.
However, if the value of this low concentration β is set to zero, the electromotive force itself of the electrode layer on the low concentration side will not necessarily become stable.
In addition, the above-mentioned problem of oxidation of the active substance, etc. also occurs, so it is not necessarily advantageous. From experience,
This value β on the low concentration side is preferably at least 0.1%, and practically desirably about 1%.

Other preferred embodiments of the present invention are as described in the second and subsequent claims and in the following embodiments.

[Embodiments of the invention]

Hereinafter, embodiments of the method of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an example of the basic configuration of a fuel cell to which the method of the present invention is applied, and the figure shows a single cell taken out. As mentioned above, the matrix layer 1 is a sheet made of a porous and electrically insulating material, and in contact with the matrix layer 1 are the fuel gas electrode layer 2 and the oxidant gas electrode layer 3, both of which are gas permeable. The matrix layer is placed between the upper and lower sides of the figure, and gas-impermeable ribbed separators 4, 4 are placed above and below the matrix layer.
This separator 4 is provided with a large number of grooves 4a and 4b that are orthogonal to each other on both sides, and fuel gas flows through the grooves 4a and oxidizing gas flows through the grooves 4b between the fuel gas electrode layer 2 and the oxidizing gas electrode layer 3. Supplied to the anti-matrix layer side. For example, in this example, the electrolyte held in matrix layer 1 is phosphoric acid, the fuel gas and oxidizing gas are hydrogen and air, respectively, and the active material contained in the fuel and oxidizing gas electrode layer is carbon and some It is a precious metal catalyst. Also, hydrogen as a fuel gas is usually a reformed gas of natural gas containing a significant amount of carbon dioxide.

If, as in this example, both electrode layers contain substantially the same active material, hydrogen as fuel gas can act on both electrode layers and qualify as a test gas in the method of the invention. There is.
Of course, the test gas can be appropriately selected depending on the type of electrolyte and the type of active substance contained in the electrode layer, but for the sake of simplicity, the case where hydrogen is used as the test gas will be described below.

Figure 2 shows the equipment necessary to carry out the present invention and its arrangement. In the center of the figure is a battery stack consisting of a large number of single cells stacked vertically in the figure as shown in Figure 1. A cell 10 is shown, and a unit cell 10a consisting of a matrix layer 1, a fuel gas electrode layer 2, an oxidizing gas electrode layer 3, and separators 4 is shown enlarged in the center thereof. A plurality of unit cells 10a are stacked to form a stacked unit block 10b, and a plurality of these stacked unit blocks 10b are further stacked to form the battery stack 10 described above, and clamping plates 11, 11 are attached from above and below. They are integrated by being tightened via a tightening means (not shown). Manifold lids 12, 13, 14, and 15 are attached to the four side surfaces of this battery stack 10 (however, the manifold lid 12 is at the rear of the paper and cannot be seen). During normal operation of the fuel cell, air A as an oxidizing gas enters the oxidizing gas inlet manifold 14b through the oxidizing gas introduction valve 18a of the oxidizing gas introduction system 18 and the inlet 14a of the manifold lid 14, and from there it oxidizes the separator. The oxidizing gas enters the gas groove 4b and is supplied to the oxidizing gas electrode layer 3. The air that is not consumed within the battery is led out from the outlet 15a of the manifold lid 15 on the right side of the figure through the outlet valve 15a of the oxidizing gas outlet system 19 toward the right side of the figure, and is disposed of or reformed (not shown). Used as combustion gas for equipment. The same applies to the fuel gas system, and hydrogen F as the fuel gas is
The fuel gas enters the fuel gas groove 4a of the separator 4 from the rear of the page through the introduction valve 16a of the fuel gas introduction system 16 and the introduction port 12a of the manifold lid 12 shown in the upper left of the figure, and is supplied to the fuel gas electrode layer 2. Further, the fuel gas that is not consumed within the battery is led out from the outlet 13a of the manifold lid 13 through the outlet valve 17a of the fuel gas outlet system 17 to the right in the figure. Note that in this figure, the means for extracting the electrical output of the battery is completely omitted for the sake of simplicity.

Now, the test gas, hydrogen, used in carrying out the method of the invention is supplied from test gas sources 21, 23, shown as cylinders at the lower left of the figure, and an inert gas, such as nitrogen, is used as a type of auxiliary test gas. is supplied from an inert gas source 22, also shown in the form of a cylinder. To start measurement in the method of the present invention, first close the aforementioned fuel gas introduction valve 16a and oxidant gas introduction valve 18a to cut off the supply of hydrogen F and air A to the battery, and Open the load switch to reduce its electrical output to zero. Then, the supply valve 22a of the inert gas source 22 is opened, and the switching valve 2 shown above is opened.
4 to pass the inert gas from the supply valve 22a, and open the test gas supply valve 25 shown above, to supply the inert gas to the oxidizing gas supply system 18.
will be used to introduce it into a fuel cell. At the same time, the oxidizing gas outlet valve 19a is closed, and instead, the test gas exhaust valve 26 shown below is opened to exhaust the inert gas that has passed through the battery to the outside air. By maintaining this state for a short time, all the oxygen in the air remaining in the battery after the battery stops operating is exhausted from the battery along with the inert gas. After this oxygen discharge is completed, the opening degrees of the supply valve 23a of the test gas source 23 and the other supply valve 22b of the inert gas source 22 are adjusted appropriately so that the concentration of the test gas reaches the specified value (the above β).
After switching the switching valve 24, a mixed test gas of hydrogen and nitrogen is introduced into the oxidizing gas electrode layer 3 inside the battery through the test gas supply valve 25 as before, and the gas passing through the battery is is discharged to the outside air from the test gas discharge valve 26.

On the other hand, the test gas is supplied to the fuel gas electrode layer 2 from the test gas supply source 2 immediately after the above-mentioned operation of the battery is stopped or after the oxygen discharge work from the battery section is completed.
The supply valve 21a of No. 1 is opened to introduce hydrogen as a test gas from the fuel gas supply system 16 into the battery. Therefore, in this example, the concentration of the test gas in the example fuel gas electrode layer is α=1, or 100%.
This test gas that has passed through the battery is passed through the fuel gas outlet valve 1.
Either leave the valve 9a open and let the gas out to the outside, or close this valve and open the on-off valve 27b of the test gas circulation system 27 instead.
This causes the water to flow back into the inlet 12a. Since this test gas circulation system is often originally attached to the battery as a fuel gas circulation system, such an attached system can be used as is. In this way, when circulating the test gas on the fuel gas electrode layer side, if the test gas supply valve 21a is slightly opened after the test gas supply is completed, some hydrogen will be consumed within the battery during the test. Also, the shortage can be automatically replenished.

In addition, in the above test gas supply system, the mixture of test gas and inert gas on the oxidizing gas electrode layer side is provided with a circulation system 28 shown by a chain line in the figure as on the fuel gas electrode layer side, and the above-mentioned method is provided. Instead of closing the test gas exhaust valve 26, the on-off valve 28b in the circulation system may be closed, and the test gas from the outlet 15a may be circulated back to the inlet 14a using another gas pump 28a.

As described above, the supply of the test gas to both the fuel and oxidizing gas electrode layers is completed, and the generated electromotive force is measured after the battery voltage is set. In this example,
As shown in the figure, a plurality of measurement leads 31 for measuring electromotive force are attached to the battery device in advance,
The potential detection ends of the measurement conductors are attached not only to the potential detection points 31a and 31b at both ends of the battery, but also to the intermediate potential measurement point 31c between the laminated unit blocks 10b. These potential detection points 31a, 31b, 31c
The potential of the manifold lid 14 is measured by a measuring lead.
The terminals 33a, 33b, and 33c of the measurement terminal board 33 located outside the battery compartment are respectively led out through the insulative insulation. A high-precision voltmeter with high input impedance is used as the electromotive force measuring device 32,
Connect the measurement lead wire 32a to the desired measurement terminal 33a.
33c, it is considered that the electromotive force between both ends of the battery as well as each laminated unit block can be measured separately. As for this measurement condition, it is desirable to measure the open-circuit voltage of the battery, that is, the pure electromotive force, with no load on the battery, from the viewpoint of estimating the amount of electrolyte held in the matrix as accurately as possible. . In addition, in the case of the method of the present invention, this open electromotive force value appears as a difference in the electromotive force values of the fuel and oxidation gas electrode layers as described above, so it does not have any harmful effect on the battery, but if If you are still unsure, you can measure the battery voltage with a very light load applied to the battery. In this case, the sensitivity for estimating the amount of electrolyte is slightly lower than in the case of open electromotive force measurement, but on the other hand, it has the advantage that the battery voltage is more likely to be stabilized. Furthermore, since the open-circuit electromotive force or battery voltage of this battery is a function of temperature as described above, it is desirable to measure the battery while keeping the battery temperature as constant as possible and making the temperature distribution within the stack uniform. In this sense, it is better to carry out measurements when the temperature distribution has become uniform due to heat conduction, rather than immediately after the battery has stopped operating. Furthermore, since it is also possible to measure the internal temperature of the battery, it is also possible to correct the measured value using the relationship that the electromotive force or battery voltage is proportional to the absolute temperature T. Furthermore, in cases where precision is required, a cooling plate is usually installed in each stacked unit block in the battery stack, so hot water at a constant temperature is passed through the cooling plate to maintain the temperature inside the battery. It is also possible to actively make the distribution uniform. This means is particularly useful in estimating the distribution of electrolyte retention within the matrix for each stacked unit block.

Figure 3 shows the relationship between the amount of electrolyte held in the matrix layer and the open electromotive force for a model battery. ² ) The vertical axis shows the open electromotive force V (volts) of the battery. As can be seen from the figure, when the electrolyte is sufficiently retained in the matrix layer, the curve is flat and the electromotive force has a constant value V0, and as the amount of electrolyte retained approaches its minimum limit value Qm, the open electromotive force value V
gradually decreases. Therefore, the permissible decrease ΔV from a constant value V0 is experimentally determined in advance, and when the decrease in the electromotive force value approaches this value, electrolyte replenishment work is performed to bring the battery into the best operating condition. can be maintained.

The method of the present invention is not limited to the best embodiment described above, and can be implemented in various modified forms. In particular, regarding the means for introducing the test gas, as can be seen from the principle of the method of the present invention, the concentration ratio of the test gas on the fuel gas electrode layer side and the oxidizing gas electrode layer side is varied to the degree required from the measurement. Therefore, each concentration value can be selected to a desired value by suitably mixing an inert gas with the test gas. Further, the type of test gas itself can be selected depending on the type of the electrode layer, especially the type of active substance contained therein, and can be used alone or in a mixed form.

〔Effect of the invention〕

As can be seen from the above explanation, according to the method of the present invention, it is possible to measure the amount of electrolyte held in the matrix layer of a fuel cell, which was previously thought to be practically impossible or extremely difficult, although it is an indirect estimate. Quantitative information can be used to determine when electrolyte replenishment work is required. The reproducibility of the battery open-circuit electromotive force value or battery voltage value in the method of the present invention is good, and these values can be measured with an accuracy of 0.1% or more using existing measuring instruments, so the estimation results by the method of the present invention are has sufficient accuracy for practically managing the amount of electrolyte retained.

When carrying out the method of the present invention, there is no need to remove piping or equipment around the battery body or disassemble the battery itself, and all that is required is to operate the valves, so the measurement work is relatively simple. It can be done easily. Furthermore, as mentioned above, the open-circuit electromotive force or cell voltage of the battery that is the object of measurement in the method of the present invention appears as a difference between the values generated in the fuel and oxidation gas electrode layers. Batteries are tested in inherently safe conditions, with no risk of exposing materials to hazardous conditions such as oxidative degradation or corrosion.

As described above, the method of the present invention is expected to be a practical method for estimating the amount of electrolyte retained, and can contribute to maintaining the operating efficiency of fuel cells, especially large-capacity batteries, at a high level and improving their operating reliability. .

[Brief explanation of the drawing]

Figure 1 is a perspective view showing the basic structure of a fuel cell to which the method of the present invention is applied;
The figures and subsequent figures are for explaining embodiments of the method of the present invention, of which Figure 2 shows the equipment and arrangement around the fuel cell necessary to implement the method of estimating the amount of electrolyte held in the matrix of a fuel cell according to the present invention. FIG. 3 is a graph diagram showing the relationship between electrolyte retention and battery electromotive force as an example of the results obtained by implementing the method of the present invention. In the figure, 1: matrix layer, 2: fuel gas electrode layer,
3: Oxidizing gas electrode layer, 10: Cell stack as fuel cell main body, 10b: Laminated unit block, 2
0: Test gas supply system, 21, 23: Hydrogen cylinder as test gas source, 22: Nitrogen cylinder as inert gas supply source as test gas concentration adjustment gas, 30: Measurement system, 31: Battery origin 32: a voltmeter as a means for measuring battery electromotive force.

Claims (1)

[Scope of Claims] 1. The matrix of a fuel cell, in which an electrolyte is held within a porous matrix layer, and a gas permeable fuel gas electrode layer and an oxidizing gas electrode layer are arranged on both sides of the matrix layer in contact with the matrix layer. A method for indirectly measuring or estimating the amount of electrolyte held in a layer, which involves applying a test gas to both electrode layers that can act on both of the electrode layers and cause an electrochemical reaction together with the electrolyte to generate electricity. 1. A method for estimating the amount of electrolyte held in a fuel cell, characterized in that the amount of electrolyte held in a matrix layer is estimated from the electromotive force generated by the fuel cell when the fuel cells are supplied at different concentrations. 2. In the method described in claim 1,
A method for estimating the amount of electrolyte retained in a fuel cell, characterized in that one type of gas is used as a test gas. 3. A method for estimating the amount of electrolyte retained in a fuel cell, characterized in that in the method according to claim 1 or 2, a fuel gas is used as the test gas. 4. In the method described in claim 3,
A method for estimating the amount of electrolyte retained in a fuel cell, characterized in that the fuel gas is hydrogen gas. 5. In the method described in claim 3,
A method for estimating the amount of electrolyte retained in a fuel cell, characterized in that the fuel gas is reformed hydrogen gas containing carbon dioxide. 6. In the method recited in claim 1,
A method for estimating the amount of electrolyte retained in a fuel cell, characterized in that at least one of the test gases supplied to both electrode layers contains an inert gas, and the pressures of the gases applied to both electrode layers are made approximately equal. 7. The method according to claim 1 or 6, wherein the lower concentration test gas supplied to the electrode layer contains at least 0.1% of the test gas. Estimation method. 8. In the method described in claim 1,
A method for estimating the amount of electrolyte retained in a fuel cell, characterized in that the fuel cell is a stacked fuel cell including a ribbed separator. 9. In the method recited in claim 1,
A method for estimating the amount of electrolyte retained in a fuel cell, characterized in that the electromotive force of the fuel cell is measured in a no-load state or an extremely light load state of the cell. 10. In the method according to claim 1, the fuel cell is a stacked fuel cell, and the electromotive force of the fuel cell is measured for each unit cell in the stacked battery or for each unit block in which the unit cells are stacked, A method for estimating the amount of electrolyte held in a fuel cell, characterized in that the amount of electrolyte held in a matrix layer is estimated separately for each unit cell or unit block.