JP6962202B2 - Fuel cell separator inspection method - Google Patents

Description

The present invention relates to a method for inspecting a fuel cell separator for inspecting the presence or absence of pinholes.

As a fuel cell separator of this type, one in which a carbon layer that imparts corrosion resistance is formed on the entire surface of the base material is disclosed (see Patent Document 1). This fuel cell separator constitutes a fuel cell stack, and the fuel cell stack is formed by pressing a Ti roll of a metal plate having a titanium (Ti) thin film formed on its surface, as shown in FIG. 10 (a). After cleaning, a carbon layer is formed by carbon-based surface treatment (PAC: Pi-conjugated Amorphous Carbon treatment, hereinafter referred to as PAC treatment), and after visual inspection, cells are formed to be integrated with the fuel cell separator and other components. It is completed and shipped through each process such as.

Instead of this PAC treatment, as shown in FIG. 10B, there is a fuel cell stack that is subjected to nanocarbon treatment (hereinafter referred to as NC treatment). This fuel cell stack is completed and shipped through various steps such as forming a carbon layer on a Ti roll by NC treatment, pressing to form a separator material, cleaning, and cell formation. In the cleaning process, the fuel cell stack to be NC-treated is cleaned by immersing the separator material in the liquid in the cleaning tank, dried, and then subjected to a gas leak inspection to detect the presence or absence of pinholes. ..

Japanese Unexamined Patent Publication No. 2005-251618

However, the gas leak inspection in the fuel cell stack subjected to the NC treatment is performed after the separator material has dried. If there are pinholes in this separator material, carbon that has fallen off from the carbon layer will enter during cleaning of the separator material, and the pinholes will be blocked. Furthermore, the carbon in the pinholes will aggregate and clog the pinholes due to drying. It ends up. As a result, there is a problem that in the gas leak inspection, erroneous detection may occur in which the pinhole is detected even though it is present.

The present invention has been made to solve such a problem, and it is possible to prevent erroneous detection of the presence or absence of pinholes formed in the separator material and accurately detect the presence or absence of pinholes. An object of the present invention is to provide a method for inspecting a fuel cell separator.

The method for inspecting a fuel cell separator according to the present invention includes a first step of cleaning a separator material having a carbon layer on a base material with a liquid, and a surface of the separator material before the washed separator material is dried. It is characterized by including a second step of applying an external force and a third step of inspecting a pinhole of the separator material in a step after the second step.

In the fuel cell separator inspection method according to the present invention, a second step of applying an external force to the surface of the separator material is provided before the separator material washed in the first step is dried. With this configuration, even if carbon that has fallen off from the carbon layer during cleaning enters the pinhole, an external force is applied to the surface of the separator material before the carbon in the pinhole aggregates due to drying and the pinhole is clogged. The carbon in the pinhole is surely removed by the external force. Then, the third step of inspecting the pinhole of the separator material is performed after the carbon in the pinhole is surely removed by an external force in the second step, so that the presence or absence of the pinhole is accurately detected in the third step. Will be done.

According to the present invention, it is possible to provide a fuel cell separator inspection method capable of preventing erroneous detection of the presence or absence of pinholes formed in a separator material and accurately detecting the presence or absence of pinholes. ..

A partial cross-sectional view of a fuel cell cell provided with a fuel cell separator to be inspected by the fuel cell separator inspection method according to the embodiment of the present invention is shown. FIG. 3 is a process diagram showing the production of a fuel cell stack including a method for inspecting a fuel cell separator according to an embodiment of the present invention. It is a figure of the cleaning process in the inspection method of the fuel cell separator which concerns on embodiment of this invention, FIG. 3A shows the formula for obtaining the surface tension in a pinhole, and FIG. 3B is a fuel cell separator. A graph showing the relationship between time and pressure at the inlet and outlet and a pressurizing device that applies pressure to the fuel is shown, and FIG. 3 (c) shows a graph showing a specific relationship between time and pressure at the inlet and outlet. It is a figure of the cleaning process in the inspection method of the fuel cell separator which concerns on embodiment of this invention, FIG. 4A shows the graph which shows the gas leak test result before drying, and FIG. 4B is before drying. And the graph showing the test result after drying is shown. It is a figure of the fuel cell separator in the inspection method of the fuel cell separator which concerns on embodiment of this invention, FIG. 5A shows the perspective view of the fuel cell separator with a pinhole, and FIG. 5B is a figure. A cross-sectional view taken along the line AA of 5 (a) is shown, and FIG. 5 (c) shows a schematic view of a cross section of the fuel cell separator having a pinhole. A cross-sectional view of a pinhole portion of the fuel cell separator in the method for inspecting a fuel cell separator according to the embodiment of the present invention is shown, and a state in which gas escapes through the pinhole by boosting the pressure is shown. It is a figure of the cleaning process in the inspection method of the fuel cell separator which concerns on embodiment of this invention, FIG. 7A shows the graph which shows the gas leak test result after drying, and FIG. 7B shows after drying. The formula for calculating the pressure required to release the carbon in the pinhole is shown. It is a figure of the cleaning process in the inspection method of the fuel cell separator which concerns on the modification of embodiment of this invention, and FIG. 8A shows the time when the fuel cell separator was immersed in pure water, and the inlet pressure. 8 (b) shows a perspective view of a state in which the fuel cell separator is immersed in pure water. It is a figure of the cleaning process in the inspection method of the fuel cell separator which concerns on the modification of embodiment of this invention, and FIG. 9 (b) shows a graph showing the relationship between time and carbon concentration, and FIG. 9 (c) shows the pinhole detection result with respect to the carbon concentration. , FIG. 9 (d) shows the result of performing a light transmission test on a pinhole. It is a process drawing of manufacturing of the conventional fuel cell stack, FIG. 10A shows the process drawing including PAC processing, and FIG. 10B shows the process drawing including NC processing.

The drawing of the method for inspecting the fuel cell separator 40 according to the embodiment to which the method for inspecting the fuel cell separator according to the present invention is applied, including the production of a fuel cell stack composed of the fuel cell 10 provided with the fuel cell separator 40. Will be described with reference to.

First, the configuration of the fuel cell 10 will be described. As shown in FIG. 1, the fuel cell 10 is composed of a membrane electrode gas diffusion layer assembly (MEGA: Membrane Electrode & Gas Diffusion Layer Assembly, hereinafter referred to as MEGA) 20, a sealing member 30, and a fuel cell separator 40. It is configured.

The MEGA 20 is composed of a membrane electrode assembly (MEA: Membrane Electrode Assembly, hereinafter referred to as MEA) 21, an anode side gas diffusion layer (GDL: Gas Diffusion Layer, hereinafter referred to as GDL) 22, and a cathode side GDL 23. There is.

The MEA 21 is composed of an electrolyte membrane (not shown), an anode catalyst layer, and a cathode catalyst layer junction. The electrolyte membrane is formed of a polyelectrolyte resin which is a solid polymer material such as perfluorosulfonic acid (PFSA) ionomer, and is composed of an ion exchange membrane using a polymer membrane having ionic conductivity as an electrolyte. The electrolyte membrane has a function of blocking the flow of electrons and gas and moving protons from the anode catalyst layer to the cathode catalyst layer.

The anode catalyst layer is made of a conductive carrier carrying a catalyst such as platinum or a platinum alloy. For example, an electrode catalyst layer formed by coating carbon particles such as catalyst-supported carbon particles with an ionomer having proton conductivity. Consists of. The ionomer is made of a polyelectrolyte resin which is a solid polymer material such as a fluororesin having the same quality as the electrolyte membrane, and has proton conductivity due to its ion exchange group. The anode catalyst layer has a _{function of decomposing hydrogen gas (H 2} ) into protons and electrons. The cathode catalyst layer is made of the same material as the anode catalyst layer, but unlike the anode catalyst layer, it has a function of generating water from protons, electrons, and oxygen.

The anode-side GDL22 is formed of a gas-permeable and conductive material, for example, a carbon fiber such as carbon paper or a porous fiber base material such as graphite fiber. The anode-side GDL 22 is bonded to the outside of the anode catalyst layer, and has a function of diffusing hydrogen gas as a fuel gas to make it uniform and spreading it to the anode catalyst layer.

Like the anode-side GDL22, the cathode-side GDL23 is formed of a gas-permeable and conductive material, for example, a carbon fiber such as carbon paper or a porous fiber base material such as graphite fiber. The cathode side GDL 23 is bonded to the outside of the cathode catalyst layer, and has a function of diffusing air as an oxidant gas to make it uniform and spreading it to the cathode catalyst layer.

The seal member 30 is made of synthetic resin, is formed in a frame shape, and is joined with MEGA 20. The seal member 30 prevents so-called cross leaks and electrical short circuits between catalyst electrodes, in which _{hydrogen gas (H 2} ) at the fuel electrode and oxygen gas (O _{2) at the air electrode pass through the electrolyte membrane in a small amount.} Has a function for

The fuel cell separator 40 is composed of an anode side separator 41 and a cathode side separator 42. The anode-side separator 41 is made of a metal plate such as an iron steel plate, a stainless steel plate, and an aluminum plate, and is manufactured through an inspection step described later. The anode-side separator 41, the cathode-side separator 42, and the fuel cell separator 40 of the present embodiment correspond to the separator material in the fuel cell separator inspection method according to the present invention.

The anode-side separator 41 is joined to the anode-side GDL 22 of MEGA 20, and a fuel gas flow path 41a through which hydrogen as a fuel gas flows is formed along the surface of the anode-side GDL 22. On the surface of the anode-side separator 41, a titanium (Ti) thin film is formed on the surface in the Ti roll process described later, and a carbon layer is formed in the titanium thin film in the NC conversion process.

Like the anode-side separator 41, the cathode-side separator 42 is made of a metal plate, and is manufactured through an inspection step described later. The cathode side separator 42 is bonded to the cathode side GDL 23 of the MEGA 20, and an oxidant gas flow path 42a through which air as an oxidant gas flows is formed along the surface of the cathode side GDL 23. Similar to the anode side separator 41, a titanium (Ti) thin film is formed on the surface of the cathode side separator 42 in the Ti roll process described later, and a carbon layer is formed in the titanium thin film in the NC conversion process.

Next, the production of the fuel cell stack composed of the fuel cell 10 will be described including the inspection method of the fuel cell separator 40. The fuel cell separator 40 is composed of an anode-side separator 41 and a cathode-side separator 42. However, since the anode-side separator 41 and the cathode-side separator 42 are similarly configured, hereinafter, mainly the anode-side separator 41 Will be described.

As shown in FIG. 2, the production of the fuel cell stack composed of the fuel cell 10 according to the present embodiment includes a Ti roll process, an NC processing process, a pressing process, and a cleaning process. It includes a cell-forming process and a stack shipping process. Each step is performed in sequence. The Ti roll step, the NC treatment step, and the cleaning step of the present embodiment are included in the fuel cell separator inspection method according to the present invention.

In the Ti roll process, a titanium (Ti) thin film is formed on the surface of the base material of the anode side separator 41 made of a metal plate such as an iron steel plate, a stainless steel plate, and an aluminum plate, and is formed in a roll shape (step). S1). By forming the titanium thin film, a passivation oxide film is formed on the surface of the metal plate, and the corrosion resistance of the base material of the anode side separator 41 is improved.

In the NC treatment process, the base material of the roll-shaped anode side separator 41 is unwound, and carbon black (CB: Carbon Black) and titanium oxide (TIO) are formed on the surface of the titanium thin film of the base material of the anode side separator 41. _A carbon layer composed of the mixed layer of 2) is formed (step S2). Carbon black is fine particles of carbon having a diameter of about 3 to 500 nm, and is made of so-called nanocarbon. The conductivity of the base material of the anode side separator 41 is ensured by the NC treatment.

In the pressing process, the base material of the anode side separator 41 is cut so as to match the shape of the anode side separator 41, and press molding is performed on the cut base material. By this press molding, a concave-convex shape anode-side separator 41 having the fuel gas flow path 41a shown in FIG. 1 is formed (step S3).

As shown in FIG. 2, the cleaning step includes a step of putting it in a washing tank, a first step, a second step, a drying step, and a gas leak inspection step. Each step is performed in sequence. The gas leak inspection step of the present embodiment corresponds to the third step of performing a pinhole inspection in the fuel cell separator inspection method according to the present invention. Further, the first step, the second step, the drying step, and the gas leak inspection step of the present embodiment are also included in the fuel cell separator inspection method according to the present invention.

In the step of putting in the washing tank, the anode side separator 41 is put in the washing tank after the pressing step (step S11). The cleaning tank is filled with a known cleaning solution, for example, cleaning water or an alkaline solution heated at room temperature or heated.

In the first step, foreign matter and dirt adhering to the surface of the anode-side separator 41 provided with the carbon layer on the base material are removed by a known cleaning method (step S12). Known cleaning methods include, for example, cleaning with room temperature or heated cleaning water, cleaning with an alkaline solution, and cleaning with ultrasonic waves.

In the second step, an external force is applied to the surface of the cleaned anode-side separator 41 (step S13). Specifically, as shown in FIGS. 3A and 3B, an external force is applied to the anode side separator 41 by the pressurizing device 50. The pressurizing device 50 includes a pressure vessel 51, pipes 52 and 53, a pump Pi, a valve V, a plurality of pressure sensors (not shown), and a controller (not shown) that controls each component. The pressure vessel 51 is configured so that the anode-side separator 41 can be mounted in the center, and by mounting the anode-side separator 41, the inside of the pressure vessel 51 is partitioned by an in-side chamber 51a and an out-side chamber 51b. It is configured to.

One end of the pipe 52 is connected to the chamber 51a on the in side, and the other end is connected to a storage container (not shown) for storing a pressure supply medium such as _{nitrogen gas (N 2).} Further, the pipe 52 is connected to the pump Pi, and is configured so that the pressure (kPa) is supplied to the chamber 51a on the in side by the pump Pi. One end of the pipe 53 is connected to the out-side chamber 51b, and the other end is open to the atmosphere.

The valve V is provided in the pipe 52, and is configured to open and close the passage of the pressure supply medium of the pipe 52. Pressure sensors are provided in the in-side chamber 51a and the out-side chamber 51b, respectively, to detect the pressure in the in-side chamber 51a and the pressure in the out-side chamber 51b, and send the detection information to the controller. It is configured in.

In the second step, by applying an external force to the surface of the anode-side separator 41, the cleaning liquid and carbon that have entered the pinhole existing in the anode-side separator 41 are discharged to the outside of the pinhole. When the pinhole is filled with a cleaning liquid containing carbon, as shown in FIG. 3A, the radius of the pinhole is r = 2.5 μm, and the contact angle of the cleaning liquid in the pinhole is θ = 40 °. The surface tension of the liquid in the pinhole was calculated to be 56 kPa. If a pressure larger than the surface tension of the liquid, that is, an external force is applied to the pinhole, the cleaning liquid and carbon that fill the inside of the pinhole can be discharged.

For example, as shown in FIG. 3B, the pump Pi supplies a maximum pressure of 354 kPa to gradually increase the pressure in the chamber 51a on the in side from the normal pressure. On the other hand, the pressure in the chamber 51b on the out side is maintained at normal pressure for a while. Then, when the pressure in the chamber 51a on the in side exceeds the above-mentioned 56 kPa, the cleaning liquid and carbon filling the pinhole are discharged from the pinhole into the chamber 51b on the out side. As a result, the pressure in the chamber 51b on the out side rises.

Specifically, as shown in FIG. 3C, pressure was applied to the anode-side separator 41 having pinholes within 1 hour after washing and before drying by the pressurizing device 50. As a result, the pressure in the chamber 51a on the inlet side, that is, the in side became 75 kPa about 80 minutes after the start of pressurization, and at this time, the pressure in the chamber 51b on the outlet side, that is, the out side started to rise. As a result, it was confirmed that the pressure in the chamber 51a on the in side was 75 kPa, and the cleaning liquid and carbon filling the inside of the pinhole could be discharged.

Further, as shown in FIG. 4A, the pressurizing device 50 determines whether or not it is possible to prevent erroneous detection of the presence or absence of pinholes in the anode-side separator 41 having pinholes. The test was conducted. As shown in the graph of FIG. 4 (b), this test is performed with respect to a predetermined inlet pressure (kPa), that is, when a predetermined pressure is applied into the chamber 51a on the in side, the inlet pressure time (min) is applied. The presence or absence of pinholes is determined by the change. The curve shown by the broken line in the graph indicates that the pressure leaks from the inside of the chamber 51a on the in side to the inside of the chamber 51b on the out side due to the pinhole, and the inlet pressure decreases. Since there are no pinholes, there is no pressure leak from the inside of the chamber 51a on the in side to the inside of the chamber 51b on the out side, indicating that the inlet pressure hardly drops.

The straight line shown by the thick solid line shows the result of the gas leak test after drying, and the curve shown by the thin solid line shows the result of the gas leak test before drying. The curve shown by the broken line and the curve shown by the thin solid line indicate that there is no difference in the amount of leakage and there is no undetected pinhole. The curve shown by the broken line and the curve shown by the thick solid line indicate that there is a difference in the amount of leakage and that there is an undetected pinhole.

The gas leak test before drying shown in FIG. 4 (a) was specifically performed on the central portion of the anode side separator 41 as shown in FIGS. 5 (a), 5 (b) and 5 (c). It was done for those with pinholes. Further, FIG. 6 shows the state of the pinhole before the pressure exceeding 56 kPa of the liquid surface tension described above is applied into the chamber 51a on the in side, and the state of the pinhole before the pressure exceeding 56 kPa of the liquid surface tension is applied to the chamber 51a on the in side due to the pressure increase. It shows the state of the pinhole after the pressure is applied, that is, the state in which the gas escapes into the pinhole due to the pressure increase. FIG. 6 shows that the liquid and carbon in the pinhole are removed by boosting the pressure inside the chamber 51a on the in side.

In the test of gas leak before drying shown in FIG. 4A, water was dropped into the pinholes in the initial case where the pinholes penetrated the anode side separator 41 before drying in which the pinholes were present. The case was divided into a case where a liquid of 0.014 wt% of aqua black was dropped on the pinhole and a case where the liquid was dropped. FIG. 4A shows a change in pressure with the passage of time (min) when a pressure of about 355 kPa is supplied to the chamber 51a on the in side, and the pressure is provided in the chamber 51a on the in side. Measured with a pressure sensor.

Aqua Black (registered trademark) is made of carbon black (CB: Carbon Black), and is composed of carbon fine particles having a diameter of about 3 to 500 nm and having an affinity for water. Aqua Black 0.014 wt% assumes the amount of carbon that has fallen off from the carbon layer present in the cleaning liquid when the anode side separator 41 is washed, that is, the carbon concentration of the actual cleaning liquid.

As a result of the gas leak test before drying shown in FIG. 4A, the inlet pressure was changed from the start in both the initial case, when water was dropped and when a liquid of 0.014 wt% of aqua black was dropped. It gradually decreased from about 355 kPa to about 250 kPa after about 60 minutes, and it was found that the anode side separator 41 had pinholes. By applying pressure to the anode side separator 41 before drying, the liquid in the pinholes and It was confirmed that carbon was removed and the occurrence of false positives could be prevented.

In contrast to the pre-drying gas leak test shown in FIG. 4 (a), the post-drying gas leak test shown in FIG. 7 (a) was performed, and the results of both were compared. The test for the gas leak after drying shown in FIG. 7 (a) is the same as the test for the gas leak before drying shown in FIG. 4 (a). The initial case of penetrating and the case of dropping 0.014 wt% of aqua black liquid into the pinhole were performed separately. FIG. 7A shows a change in pressure with the passage of time (min) when a pressure of about 355 kPa is supplied to the chamber 51a on the in side, and the pressure is provided in the chamber 51a on the in side. Measured with a pressure sensor.

As shown in FIG. 7B, when the radius of the pinhole is 2.5 μm and carbon of about 500 nm is deposited in the pinhole, in order to remove the carbon, the pressure P to be removed is friction. It is obtained by multiplying the coefficient (μ) by the sum of the intermolecular force (Fw) and the liquid cross-linking force (Fc) and dividing by the cross-sectional area (S). From this calculation formula, it can be seen that the pressure P to be removed is about 974 kPa. That is, it can be seen that the gas does not escape at a pressure of about 355 kPa.

As a result of the gas leak test after drying shown in FIG. 7 (a), in the initial case where the pinhole penetrates, the inlet pressure increases from about 355 kPa to about 250 kPa about 60 minutes after the start, as shown by the broken line. On the other hand, when the liquid of 0.014 wt% of Aqua Black was dropped, there was no change in the inlet pressure as shown by the thick solid line. This indicates that even if pressure is applied to the anode side separator 41 after drying, the liquid and carbon in the pinhole are not removed, and the occurrence of false detection cannot be prevented.

In the drying step, the foreign matter and dirt adhering to the surface are removed in the first step, and the anode side separator 41 from which the liquid and carbon in the pinhole are removed by applying an external force in the second step. The anode-side separator 41 is dried in a relatively high-temperature drying furnace, for example, a vacuum drying furnace at about 100 ° C. to 300 ° C. (step S14).

In the gas leak inspection step, the presence or absence of pinholes in the dried anode-side separator 41 is detected by the pressurizing device 50 in the same manner as in the gas leak test described above, and pass / fail is determined (step S15). As shown in FIG. 2, the anode-side separator 41 determined to be acceptable in the gas leak inspection is sent to the cell formation step, and the anode-side separator 41 determined to be unacceptable is sent to the defective product processing (step S16). Be done.

In the cell formation step, as shown in FIG. 1, in the gas leak inspection step, the anode side separator 41 and the cathode side separator 42 in which pinholes were not detected, the MEGA 20 manufactured in another step, and the seal member The fuel cell cell 10 is completed (step S5) by being integrated with the 30th unit, that is, being made into a cell.

In the stack shipping process, a plurality of fuel cell cells 10 completed in the cell formation process are stacked to produce a fuel cell stack, and the fuel cell stack is confirmed and the number of shipments is confirmed. The fuel cell stack is sent to a predetermined destination (step S6).

The effect of the inspection method of the fuel cell separator 40 according to the embodiment configured as described above will be described.

In the method for inspecting the fuel cell separator 40 according to the present embodiment, the surface of the fuel cell separator 40 is before the fuel cell separator 40 washed in the first step (step S12) is dried in the drying step (step S14). Is provided with a second step (step S13) of applying pressure as an external force by the pressurizing device 50. With this configuration, even if carbon that has fallen off from the carbon layer during cleaning of the fuel cell separator 40 enters the pinhole, the surface of the fuel cell separator 40 is before the carbon in the pinhole aggregates due to drying and the pinhole is clogged. Since the pressure is applied to the fuel, the carbon in the pinhole is surely removed by the pressure, and an effect that false detection can be prevented can be obtained.

Further, in the fuel cell separator 40 inspection method according to the present embodiment, the gas leak inspection step (step S15) of the fuel cell separator 40 is a step, and in the second step, carbon in the pinhole is surely removed by the pressure. Since it is performed later, the effect of being able to accurately detect the presence or absence of pinholes in the gas leak inspection process can be obtained.

<Modified example of the embodiment>
In the method for inspecting the fuel cell separator 40 according to the present embodiment, in the second step, the pressurizing device 50 is configured to apply an external force to the surface of the anode side separator 41. However, in the second step, an external force may be applied to the surface of the anode side separator 41 by a device other than the pressurizing device 50.

Hereinafter, a method for inspecting the fuel cell separator 40 according to a modified example of the embodiment in which an external force is applied to the surface of the anode side separator 41 by another device in the second step will be described with reference to the drawings.

In the method for inspecting the fuel cell separator 40 according to the modified example of the embodiment, first, whether or not the carbon in the pinhole can be removed only by immersing the anode side separator 41 in which the pinhole exists in pure water. I examined whether. As shown in FIGS. 8 (a) and 8 (b), the pure water immersion was performed by immersing in pure water at 60 ° C. and leaving it to stand for 15 hours.

Specifically, the anode-side separator 41 is immersed in a carbon solution of 0.014 wt% of aqua black, soaked in the pure water described above, and before the anode-side separator 41 is dried, the fuel cell separator 40 according to the embodiment is used. In the second step of the inspection method of the above, the gas leak test of the anode side separator 41 immersed in pure water was tested by the same method as the method of applying pressure by the pressurizing device 50.

As for the result of the gas leak test, as shown in the graph of FIG. 8 (a), pinholes were detected in the early ones not immersed in 0.014 wt% of aqua black, as shown by the thick solid line. .. On the other hand, after immersing in 0.014 wt% of Aqua Black and immersing in pure water as described above, pinholes could not be detected as shown by a thin solid line. Therefore, it was confirmed that the carbon in the pinhole cannot be removed only by immersing the anode-side separator 41 in which the pinhole is present in pure water.

Further, from the results calculated based on the concentration gradient and the concentration diffusion formula, it was found that the carbon in the pinhole cannot be removed only by immersing the anode side separator 41 in which the pinhole exists in pure water. The calculation result by the concentration conversion formula will be described below.

The anode-side separator 41 is immersed in 0.014 wt% of aqua black, but in general, substances such as carbon in the liquid tend to flow from the higher concentration to the lower concentration. The fact that there is a high or low concentration indicates that there is a slope in the concentration with respect to each position, and this slope is referred to as a concentration gradient. When the x-axis is taken in the direction in which the concentration is inclined, the concentration gradient is simply represented by ΔC / Δx. Consider how much flow is actually occurring when diffusion, which represents the microscopic movement of atoms in a substance, is occurring in the presence of a concentration gradient.

The amount of this flow is expressed by the amount of a substance flowing in a unit time in a unit area, and is referred to as a flow velocity and is represented by the symbol J. The unit is usually expressed in mol. J is expressed by the following equation. The proportional coefficient D is referred to as a diffusion coefficient.
J = −D × (ΔC / Δx)
Based on this equation, the concentration gradient corresponding to the above-mentioned external force, ΔP = 56 kPa, required for removing carbon from the pinhole can be calculated.

In general, the diffusion driving force for moving a substance is given by a concentration gradient, and the concentration gradient and the diffusion driving force are in a proportional relationship. By diffusion of the concentration, the concentration corresponding to ΔP = 56 kPa becomes 9.87 × 10 ² wt% (carbon concentration 100% or more). From this result, it can be seen that the diffusion driving force of the assumed cleaning tank concentration is insufficient for the external force equivalent to ΔP = 56 kPa or more required to remove the carbon in the pinhole.

Based on the above examination results, the inspection method of the fuel cell separator 40 according to the modified example of the embodiment is configured to remove carbon in the pinhole by applying ultrasonic vibration before drying.

In the ultrasonic cleaning in the inspection method of the fuel cell separator 40 according to the modified example of the embodiment, as shown in FIG. 9A, the anode side separator 41 is put in the cleaning tank, and the ultrasonic vibration is applied to the anode side separator 41. In addition, this is done by reducing the carbon concentration in the pinhole of the anode side separator 41. If the carbon concentration is low, the carbon in the pinhole can be removed by the cleaning liquid in the cleaning tank. Specifically, as shown by the circles in the table of FIG. 9 (c), when the carbon concentration in the pinhole becomes 5.0 × 10 ^-4 wt% or less, the carbon in the pinhole is removed by the cleaning liquid. It becomes possible to do. Although the cleaning tank for cleaning the anode side separator 41 is composed of a plurality of cleaning tanks, it is preferable to remove the carbon clogged in the pinholes at the concentration of the first tank.

Factors for optimal ultrasonic cleaning include (1) cleaning time (min), (2) ultrasonic frequency (Hz), and (3) cleaning first, as shown in the graph of FIG. 9B. There are elements of carbon concentration (wt%) in one tank and (4) carbon concentration in the final cleaning tank. In particular, (1) cleaning time (min) and (2) ultrasonic frequency (Hz) are appropriately changed to control the external force applied to the pinhole, and the carbon concentration of the first cleaning tank is less than or equal to the required final cleaning tank. By reducing the frequency to, the carbon in the pinhole can be removed.

Specifically, as shown in the graph of FIG. 9A, the inlet pressure of both the initial one through which the pinhole penetrates and the one after ultrasonic cleaning has passed about 60 minutes from the start. By then, it gradually decreased from about 355 kPa to about 250 kPa, and on the graph, they completely overlap each other. Therefore, it is found that the anode side separator 41 has a pinhole, and by applying an external force to the anode side separator 41 by ultrasonic vibration before drying, carbon in the pinhole is removed and the occurrence of false detection is prevented. It was confirmed that it could be done.

Further, as shown in FIG. 9 (d), pore size to prepare a sample having pinholes 8.67Myuemu, carbon concentration in the pinholes immersed for 10 minutes in a 1.0 × ¹⁰ -2 wt% of the cleaning solution , 40 kHz ultrasonic waves were vibrated and washed for 5 minutes. Then, when the pinhole of the sample was inspected by light transmission, no clogging of foreign matter such as carbon was confirmed in the pinhole. As a result, it was confirmed that the carbon in the pinhole was removed by ultrasonic vibration even when the carbon concentration in the pinhole was 1.0 × ^{10-2 wt%.}

In the method for inspecting the fuel cell separator 40 according to the modified example of the present embodiment, the same effect as the inspection method for the fuel cell separator 40 according to the embodiment can be obtained. That is, before the fuel cell separator 40 washed in the first step (step S12) is dried in the drying step (step S14), an external force is applied to the surface of the fuel cell separator 40 by ultrasonic vibration in the second step (step). S13) is provided. With this configuration, even if carbon that has fallen off from the carbon layer during cleaning of the fuel cell separator 40 enters the pinhole, the surface of the fuel cell separator 40 is before the carbon in the pinhole aggregates due to drying and the pinhole is clogged. Since an external force is applied to the fuel cell, the carbon in the pinhole is surely removed by the external force, and an effect that false detection can be prevented can be obtained.

Further, in the method for inspecting the fuel cell separator 40 according to the modified example of the present embodiment, the step of inspecting the gas leak of the fuel cell separator 40 (step S15) is carried out, and in the second step, the carbon in the pinhole is surely removed by an external force. Since it is performed after the fuel is removed, the effect that the presence or absence of pinholes can be accurately detected in the gas leak inspection process can be obtained.

Although the embodiments of the present invention and variations thereof have been described in detail above, the present invention is not limited to the above-described embodiments and variations thereof, and the spirit of the present invention described in the claims is expressed. Various design changes can be made without deviation.

10 ... Fuel cell, 20 ... MEGA, 21 ... MEA, 22 ... Anode side GDL, 23 ... Cathode side GDL, 30 ... Seal member, 40 ... Fuel cell separator (Separator material), 41 ... Anode side separator (separator material), 41a ... Fuel gas flow path, 42 ... Cathode side separator (separator material), 42a ... Oxidizer gas flow path, 50.・ ・ Pressurizing device, 51 ・ ・ ・ Pressure vessel, 52, 53 ・ ・ ・ Piping, 51a ・ ・ ・ In side chamber, 51b ・ ・ ・ Out side chamber

Claims (1)

It is an inspection method for fuel cell separators.
The first step of cleaning the separator material with the carbon layer on the base material with a liquid, and
A second step of applying an external force to the surface of the separator material before drying the washed separator material,
A third step of inspecting the pinhole of the separator material in a subsequent step according to the second step is provided .
In the second step, the separator material is arranged in the pressure vessel, the pressure vessel is divided into one chamber and the other chamber by the separator material, and the pressure supply medium is supplied to the one chamber. A method for inspecting a fuel cell separator , which comprises pressurizing the chamber on one side and applying a pressure larger than the surface tension of the liquid in the pinhole to the surface on one side of the separator material.

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