A method and apparatus for in-situ measurement of proton membrane decay in a membrane electrode

Abstract

This invention discloses a method and apparatus for in-situ determination of proton exchange membrane (PEM) degradation in a membrane electrode assembly (MEA). The invention assembles the PEM as a dummy MEA without a catalyst layer into a single cell, and then uses a short-stack fuel cell with a complete MEA as the object of simultaneous measurement experiments. During the measurement process, the actual operating conditions of the PEM during fuel cell operation are obtained through the actual operation of the short-stack. The temperature of the single cell is controlled based on the temperature of the short-stack, the voltage of the single cell is controlled based on the voltage of the short-stack, and the gas back pressure of the single cell is controlled based on the gas back pressure of the short-stack. Water generated during the actual operation of the short-stack is input into the cathode of the single cell. In other words, the PEM in the single cell is subjected to the same conditions and operating parameters as the PEM in the short-stack, thereby achieving the determination of PEM degradation.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell technology, specifically relating to a method and apparatus for in-situ measurement of proton membrane decay in membrane electrode assembly. Background Technology

[0002] The membrane electrode assembly (MEA) is the site of chemical reactions in a fuel cell, providing the catalyst for these reactions. It mainly consists of a proton exchange membrane (PEM), cathode catalyst, anode catalyst, cathode diffusion layer, anode diffusion layer, and sealing resin materials on both sides. The MEA is integrated through hot pressing and stack compaction, reducing the internal resistance of the electrochemical reaction. During the electrochemical reaction, there are failure issues such as platinum particle loss and agglomeration. Lost platinum particles can also enter the PEM and accumulate, increasing membrane resistance and decreasing proton conductivity. Stack start-up, shutdown, reverse polarity, and undergassing conditions can cause corrosion of the carbon support, platinum catalyst shedding, and carbon particle loss. The PEM is constantly affected by temperature changes during operation, leading to thermal stress fatigue failure. Platinum nanoparticles, metal plates, reactant gases, and impurity metal ions from pipelines can also enter the MEA and replace sulfonic acid groups, accumulating in the PEM and causing a decrease in water content and proton mobility. Metal ions, especially iron ions, in acidic solutions react with hydrogen peroxide via the Fenton effect, generating hydroxyl radicals. These hydroxyl radicals attack the sulfonic acid groups on the proton exchange membrane, causing oxidative thinning of the membrane. This leads to gas permeation and diffusion, reducing battery performance and causing abnormal overheating or even fires in the battery stack.

[0003] Therefore, it is necessary to detect the degradation of proton exchange membranes in order to screen and prepare proton exchange membranes that are more resistant to degradation.

[0004] The invention application with publication number CN110412103A discloses a method for evaluating the durability of membrane electrode in a proton exchange membrane fuel cell. The steps are as follows: based on the electrochemical performance data of the membrane electrode before and after the durability test, and the electrochemical performance data of the new membrane electrode and the aged gas diffusion layer membrane electrode obtained from the test, the diffusion polarization voltages Vd1, Vd2, Vd3, and Vd4 at the current density j are obtained respectively; the influence factor E of the gas diffusion layer on the diffusion polarization loss of the membrane electrode at the current density j is calculated, E=|(Vd4-Vd3) / (Vd2-Vd1)|×100%.

[0005] Chinese patent application CN113629276A discloses an accelerated testing method for the durability of the membrane electrode assembly (MEA) of a proton exchange membrane fuel cell. This method uses the pressure difference between the anode and cathode to forcibly generate a hydrogen-air interface, simulating the start-up / shutdown process of an unprotected proton exchange membrane fuel cell. Specifically, after the battery is shut down, hydrogen supply to the anode is stopped. A certain back pressure is set at the cathode outlet. Under the pressure difference between the anode and cathode, air on the cathode side permeates through the proton exchange membrane to the anode, generating a hydrogen-air interface on the anode side. This simulates the start-up / shutdown process and allows for the evaluation of the fuel cell MEA's durability.

[0006] In the aforementioned prior art, the degradation of the catalyst layer is detected, or the degradation of the membrane electrode where the proton exchange membrane and the catalyst layer are combined is detected.

[0007] In fuel cells, membrane electrode assembly (MEA) degradation includes both catalyst degradation and proton exchange membrane (PEM) degradation. Detecting the degradation of the PEM itself is also beneficial for improving MEA performance. Summary of the Invention

[0008] This application addresses the aforementioned shortcomings in the prior art by providing a method and apparatus for in-situ measurement of proton membrane decay in a membrane electrode. It distinguishes between the magnitude of the proton membrane decay itself and its proportion in the overall membrane electrode decay. Measuring the proton membrane decay itself allows technicians to better optimize catalysts and proton membranes, thereby improving the performance of the membrane electrode.

[0009] This invention first provides a method for in-situ measurement of proton membrane decay in membrane electrodes, using a short stack of fuel cells including multiple membrane electrodes as the first stack for actual operation of the membrane electrodes;

[0010] A single cell of a fuel cell containing the proton exchange membrane to be tested is used as the second stack, and the cathode catalyst layer and anode catalyst layer are not assembled on both sides of the proton exchange membrane to be tested, in order to simulate the actual operation of the proton exchange membrane to be tested in the fuel cell.

[0011] The method includes the following steps:

[0012] The first fuel cell stack was put into actual operation, and the water generated during the operation was input into the cathode of the second fuel cell stack to simulate the effect of the water generated by the reaction on the proton membrane.

[0013] Simultaneously, temperature control is applied to the second fuel cell stack, ensuring that the temperature changes are consistent with those of the first fuel cell stack during actual operation, thus simulating the effect of temperature changes on the proton exchange membrane.

[0014] A potential is applied to the second stack to simulate the working voltage of the membrane electrode. The magnitude of the voltage is the same as that of the first stack during actual operation, simulating the effect of the voltage on the proton membrane.

[0015] Hydrogen gas was introduced into the hydrogen side of the second fuel cell stack, and air was introduced into the air side. The pressure of the hydrogen and air introduced was the same as that in the first fuel cell stack to simulate the effect of the gas on the proton membrane.

[0016] Impedance tests were performed on the second electrode stack to detect the impedance change, and the conductivity change of the proton exchange membrane was calculated to obtain the proton exchange membrane attenuation.

[0017] Preferably, the area of ​​the membrane electrode in the first fuel cell stack is not less than the area of ​​the proton exchange membrane in the second fuel cell stack. The theoretical water production of the second fuel cell stack is calculated based on the area of ​​the proton exchange membrane, and the amount of water produced from the reaction in the first fuel cell stack is controlled according to this theoretical water production.

[0018] More preferably, the theoretical water production of the second fuel cell stack is calculated as: current density × proton membrane area × time × 18, where the unit of theoretical water production is ml / min and the unit of current density is A / cm². 2 The unit for proton membrane area is cm². 2 The unit of time is min.

[0019] The water produced by the fuel cell reaction contains sulfonate ions dissociated from the proton exchange membrane, trace dust particles entering the stack from compressed air, salt, hydrogen sulfide, organic oil, and other components. It also contains metal components introduced from the intake pipe, calcium and magnesium ions from the pure water in the anode and cathode humidifier tanks, and metal ions that have entered the stack after metal plate corrosion. These components migrate into the stack and undergo ion exchange reactions on the membrane electrodes. Some ions coat the catalyst surface, affecting the adsorption reaction of the reactant gas on the active catalyst surface, while others enter the proton exchange membrane, replacing sulfonate groups, causing a decrease in membrane water content and proton conductivity. Divalent and trivalent metal ions undergo the Fenton effect in a weakly acidic environment, generating free radicals. These highly oxidizing free radicals oxidize the proton exchange membrane, causing membrane thinning and increasing hydrogen permeability.

[0020] Preferably, an electrochemical workstation is used when applying a potential to the second fuel cell stack to simulate the working voltage of the membrane electrode. The positive electrode of the second fuel cell stack is used as the working electrode, and the negative electrode is used as the reference electrode. The potential to simulate the working voltage of the membrane electrode stack is applied to the second fuel cell stack through the electrochemical workstation. The electrochemical workstation also has an impedance testing module for performing impedance testing on the second fuel cell stack.

[0021] More preferably, during impedance testing, an electrochemical workstation is used to perform impedance EIS testing on the second stack, an equivalent circuit diagram of the impedance test is drawn, the obtained data is fitted to obtain a Z'-Z diagram, the intercept and radius of the arc with respect to the horizontal axis are read, and the conductivity of the proton membrane is calculated.

[0022] Preferably, in the second fuel cell stack, carbon paper is provided on both sides of the proton membrane to be tested, a flow field plate is provided on the outside of the carbon paper, and a current collector is provided on the outside of the flow field plate.

[0023] This invention further provides an apparatus for in-situ measurement of proton exchange membrane decay in a membrane electrode, as a dedicated device for the above-mentioned method. The proton exchange membrane to be measured is a catalyst-free proton exchange membrane, and the apparatus includes:

[0024] The first stack is a short stack of fuel cells that includes multiple membrane electrode assemblies (MEAs) for actual operation of the MEAs.

[0025] The second stack is a single cell of a fuel cell containing the proton exchange membrane to be tested, and the proton exchange membrane to be tested is not equipped with cathode catalyst layer and anode catalyst layer on both sides, which is used to simulate the actual operation of the proton exchange membrane to be tested in the fuel cell.

[0026] Water supply pipes are used to input the water generated in the reaction of the first fuel cell stack into the cathode of the second fuel cell stack;

[0027] A heating mechanism is used to heat the second fuel cell stack and control its temperature.

[0028] An electrochemical workstation uses the positive electrode of the second fuel cell stack as the working electrode and the negative electrode as the reference electrode. The electrochemical workstation applies a potential to the second fuel cell stack to simulate the working voltage of the membrane electrode. The electrochemical workstation also has an impedance testing module for performing impedance testing on the second fuel cell stack.

[0029] Hydrogen inlet pipeline, used to supply hydrogen to the second fuel cell stack;

[0030] The air inlet line is used to supply air to the second fuel cell stack.

[0031] Preferably, the device further includes a water storage tank connected to the water supply pipe, the water storage tank being used to store the excess water generated in the first fuel cell after deducting the amount used to input into the second fuel cell.

[0032] Preferably, in the second fuel cell stack, carbon paper is provided on both sides of the proton membrane to be tested, a flow field plate is provided on the outside of the carbon paper, and a current collector is provided on the outside of the flow field plate.

[0033] Preferably, the heating mechanism is a heating band wrapped around the surface of the second fuel cell stack, and / or a thermocouple located inside the second fuel cell stack.

[0034] The present invention provides a method for in-situ determination of proton exchange membrane (PEM) degradation in a membrane electrode assembly. This method assembles the PEM as a dummy membrane electrode assembly (without a catalyst layer) into a single cell (second stack). A short stack of a fuel cell with a complete PEM is then used as the object of simultaneous measurement experiments. During the measurement process, the actual operating conditions of the PEM during fuel cell operation are obtained through the actual operation of the short stack. The temperature of the single cell is controlled based on the temperature of the short stack, the voltage of the single cell is controlled based on the voltage of the short stack, and the gas back pressure of the single cell is controlled based on the gas back pressure of the short stack. Water generated during the actual operation of the short stack is input into the cathode of the single cell. In other words, the PEM in the single cell is subjected to the same conditions and operating parameters as the PEM in the short stack, thereby achieving the determination of PEM degradation.

[0035] The present invention can effectively separate the contribution rate of proton membrane to membrane electrode decay, provide a reference standard for the modification of membrane electrode manufacturing process, and establish performance evaluation specifications. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of the device of the present invention.

[0037] Figure 2 This is the equivalent circuit diagram for impedance testing.

[0038] Figure 3 The Nyquist plot is fitted to the impedance. Detailed Implementation

[0039] Example 1

[0040] like Figure 1 As shown, an apparatus for in-situ measurement of proton membrane decay in a membrane electrode assembly (MEA) includes a first fuel cell stack 1 and a second fuel cell stack 2. The first stack 1 is a short fuel cell stack including multiple MEAs, used for actual operation of the MEAs. In one embodiment, the MEA area in the first stack 1 is 350 cm². 2 It is equipped with bipolar plates and assembled to form a short stack including multiple membrane electrodes.

[0041] The second fuel cell stack 2 is a single cell containing the proton exchange membrane to be tested, but without cathode and anode catalyst layers on either side of the membrane, to simulate the actual operation of the proton exchange membrane in a fuel cell. In other words, the proton exchange membrane to be tested is assembled into a single cell without a catalyst. In one embodiment, the area of ​​the proton exchange membrane in the second fuel cell stack 2 is 25 cm². 2 When assembling into a single cell, carbon paper is provided on both sides of the proton membrane to be tested in the second stack 2, a flow field plate is provided on the outside of the carbon paper, and a current collector is provided on the outside of the flow field plate. The flow field plate can be a carbon plate with an engraved flow field (such as a graphite electrode plate), and the current collector can be a copper-plated gold current collector.

[0042] Water generated in the reaction of the first fuel cell stack 1 is fed into the cathode of the second fuel cell stack 2. A water supply pipe connects the first fuel cell stack 1 and the second fuel cell stack 2, with a T-junction in the middle of the pipe, one end of which connects to a water storage tank 4. The anode and cathode water generated in the first fuel cell stack 1 enters the cathode of the second fuel cell stack 2 through the water supply pipe. The amount of water entering the second fuel cell stack 2 is calculated based on the reaction area and controlled, while excess water is collected in the water storage tank 4. The amount of water entering the second fuel cell stack 2 can be controlled by installing a flow meter on the water supply pipe.

[0043] Since the area of ​​the membrane electrode in the first fuel cell stack 1 is larger than the area of ​​the proton membrane in the second fuel cell stack 2, the theoretical water production of the second fuel cell stack 2 is calculated based on the area of ​​the proton membrane, and the amount of water produced from the reaction in the first fuel cell stack 1 is controlled according to this theoretical water production.

[0044] The theoretical water production of the second fuel cell stack 2 = current density × proton membrane area × time × 18, where the unit of theoretical water production is ml / min and the unit of current density is A / cm². 2 The unit for proton membrane area is cm². 2 The unit of time is min.

[0045] The water produced by the fuel cell reaction contains sulfonate ions dissociated from the proton exchange membrane, trace dust particles entering the stack from compressed air, salt, hydrogen sulfide, organic oil, and other components. It also contains metal components introduced from the intake pipe, calcium and magnesium ions from the pure water in the anode and cathode humidifier tanks, and metal ions that have entered the stack after metal plate corrosion. These components migrate into the stack and undergo ion exchange reactions on the membrane electrodes. Some ions coat the catalyst surface, affecting the adsorption reaction of the reactant gas on the active catalyst surface, while others enter the proton exchange membrane, replacing sulfonate groups, causing a decrease in membrane water content and proton conductivity. Divalent and trivalent metal ions undergo the Fenton effect in a weakly acidic environment, generating free radicals. These highly oxidizing free radicals oxidize the proton exchange membrane, causing membrane thinning and increasing hydrogen permeability.

[0046] Therefore, by actually operating the first fuel cell stack 1, the water generated during the reaction is input into the cathode of the second fuel cell stack 2 to simulate the effect of the water generated on the proton exchange membrane. In this application, when the water generated in the first fuel cell stack 1 is input into the cathode of the second fuel cell stack 2, it flows through the second fuel cell stack 2 and is then discharged from the other end of the cathode.

[0047] The device of this application also includes a heating mechanism for heating the second fuel cell stack 2 and controlling its temperature. Preferably, the heating mechanism is at least one of a heating band 3 wrapped around the surface of the second fuel cell stack 2 and a thermocouple (not shown in the figure) located inside the second fuel cell stack 2, as long as it can achieve temperature control within the required range. Temperature control of the second fuel cell stack 2 ensures that its temperature changes are consistent with the temperature changes of the first fuel cell stack 1 during actual operation, simulating the effect of temperature changes on the proton exchange membrane. Maintaining the same temperature between the second fuel cell stack 2 and the first fuel cell stack 1 simulates the thermal expansion and contraction of the membrane electrode under conditions such as startup, idling, normal operation, and shutdown. Thermal stress is also an important factor affecting the performance of the membrane electrode.

[0048] The device of this application also includes a hydrogen inlet pipeline for introducing hydrogen into the second fuel cell stack. The device of this application also includes an air inlet pipeline for introducing air into the second fuel cell stack. Hydrogen is introduced into the hydrogen side of the second fuel cell stack 2, and air is introduced into the air side. The pressure of the introduced hydrogen and air is the same as that in the first fuel cell stack 1, simulating the effect of the gas on the proton exchange membrane. The hydrogen inlet pipeline is connected to a hydrogen storage tank 6, and the air inlet pipeline is connected to an air storage tank 7. The gas flow rate and back pressure entering the second fuel cell stack 2 are regulated by a pressure regulating valve, and the corresponding parameters are set to be the same as those in the first fuel cell stack 1.

[0049] The device in this application also includes an electrochemical workstation 5, which uses the positive electrode of the second fuel cell stack 2 as the working electrode and the negative electrode as the reference electrode. The electrochemical workstation applies a potential to the second fuel cell stack 2 to simulate the working voltage of the membrane electrode. The voltage applied to the second fuel cell stack 2 to simulate the working voltage of the membrane electrode is consistent with the voltage of the first fuel cell stack 1 during actual operation, simulating the effect of the voltage on the proton exchange membrane. The working potential range of a single cell in the fuel cell stack is between 0.3V and 0.9V. The potential applied to the second fuel cell stack 2 is achieved through the electrochemical workstation 5, which has a constant potential mode and can output the corresponding voltage.

[0050] Meanwhile, the electrochemical workstation 5 also has an impedance testing module for performing impedance testing on the second electrode stack 2. Impedance testing of the second electrode stack 2 detects impedance changes, calculates the change in conductivity of the proton exchange membrane, and thus obtains the proton exchange membrane attenuation. During impedance testing, the electrochemical workstation 5 performs an impedance EIS test on the second electrode stack 2, draws an equivalent circuit diagram of the impedance test, fits the obtained data to obtain a Z'-Z plot, reads the intercept and radius of the arc with the horizontal axis, and calculates the conductivity of the proton exchange membrane. The specific impedance model is a resistance R. i resistance R ct Capacitor C dl The series and parallel resistors formed are detailed in [reference needed]. Figure 2 The equivalent circuit diagram of series and parallel connections.

[0051] The impedance changes of the membrane electrode assembly (MEA) after 300 hours of operation of the second fuel cell stack 2 at different temperatures were simulated. During the impedance test, the MEA was affected by diffusion resistance, polarization resistance, and ohmic resistance. The effects of these resistances were fitted into an equivalent circuit, and the resistance of the MEA at different temperatures was calculated using a Nyquist plot. Figure 3 As can be seen, the resistance of the proton exchange membrane increases continuously with rising temperature, and its performance degrades at an accelerated rate. The higher the temperature, the faster the degradation.

Claims

1. A method for in-situ measurement of proton membrane attenuation in a membrane electrode, characterized in that, A short stack of fuel cells including multiple membrane electrode assemblies is used as the first stack for actual operation of the membrane electrode assemblies. A single cell of a fuel cell containing the proton exchange membrane to be tested is used as the second stack, and the cathode catalyst layer and anode catalyst layer are not assembled on both sides of the proton exchange membrane to be tested, in order to simulate the actual operation of the proton exchange membrane to be tested in the fuel cell. The method includes the following steps: The first fuel cell stack was put into actual operation. During the operation, the water generated by the reaction was input into the cathode of the second fuel cell stack to simulate the effect of the water generated by the reaction on the proton exchange membrane. The area of ​​the membrane electrode in the first fuel cell stack was not less than the area of ​​the proton exchange membrane in the second fuel cell stack. The theoretical amount of water generated by the second fuel cell stack was calculated based on the area of ​​the proton exchange membrane, and the amount of water generated from the reaction in the first fuel cell stack was controlled according to the theoretical amount of water generated. Simultaneously, temperature control is applied to the second fuel cell stack, ensuring that the temperature changes are consistent with those of the first fuel cell stack during actual operation, thus simulating the effect of temperature changes on the proton exchange membrane. A potential is applied to the second stack to simulate the working voltage of the membrane electrode. The magnitude of the voltage is the same as that of the first stack during actual operation, simulating the effect of the voltage on the proton membrane. Hydrogen gas was introduced into the hydrogen side of the second fuel cell stack, and air was introduced into the air side. The pressure of the hydrogen and air introduced was the same as that in the first fuel cell stack to simulate the effect of the gas on the proton membrane. Impedance tests were performed on the second electrode stack to detect the impedance change, and the conductivity change of the proton exchange membrane was calculated to obtain the proton exchange membrane attenuation.

2. The method for in-situ measurement of proton membrane attenuation in a membrane electrode according to claim 1, characterized in that, An electrochemical workstation is used to apply a potential to the second fuel cell stack to simulate the working voltage of the membrane electrode. The positive electrode of the second fuel cell stack is used as the working electrode, and the negative electrode is used as the reference electrode. The electrochemical workstation applies a potential to the second fuel cell stack to simulate the working voltage of the membrane electrode. The electrochemical workstation also has an impedance testing module for performing impedance testing on the second fuel cell stack.

3. The method for in-situ measurement of proton membrane attenuation in a membrane electrode according to claim 2, characterized in that, During impedance testing, an electrochemical workstation was used to perform EIS impedance testing on the second stack. An equivalent circuit diagram of the impedance test was drawn, and the obtained data was fitted to obtain a Z'-Z diagram. The intercept and radius of the arc with respect to the horizontal axis were read, and the conductivity of the proton membrane was calculated.

4. The method for in-situ measurement of proton membrane attenuation in a membrane electrode according to claim 1, characterized in that, In the second fuel cell stack, carbon paper is provided on both sides of the proton membrane to be tested, a flow field plate is provided on the outside of the carbon paper, and a current collector is provided on the outside of the flow field plate.

5. An apparatus for in-situ measurement of proton exchange membrane decay in a membrane electrode, wherein the proton exchange membrane to be measured is a catalyst-free proton exchange membrane, characterized in that, The device includes: The first stack is a short stack of fuel cells that includes multiple membrane electrode assemblies (MEAs) for actual operation of the MEAs. The second stack is a single cell of a fuel cell containing the proton exchange membrane to be tested, and the proton exchange membrane to be tested is not equipped with cathode catalyst layer and anode catalyst layer on both sides, which is used to simulate the actual operation of the proton exchange membrane to be tested in the fuel cell. A water supply pipe is used to input the water generated in the reaction of the first electric stack into the cathode of the second electric stack; the area of ​​the membrane electrode in the first electric stack is not less than the area of ​​the proton membrane in the second electric stack. The theoretical water generation of the second electric stack is calculated based on the area of ​​the proton membrane, and the amount of water generated in the reaction of the first electric stack is controlled according to the theoretical water generation. A heating mechanism is used to heat the second fuel cell stack and control its temperature. An electrochemical workstation uses the positive electrode of the second fuel cell stack as the working electrode and the negative electrode as the reference electrode. The electrochemical workstation applies a potential to the second fuel cell stack to simulate the working voltage of the membrane electrode. The electrochemical workstation also has an impedance testing module for performing impedance testing on the second fuel cell stack. The hydrogen inlet pipeline is used to supply hydrogen to the second fuel cell stack. The air inlet line is used to supply air to the second fuel cell stack.

6. The apparatus for in-situ measurement of proton membrane decay in a membrane electrode according to claim 5, characterized in that, The device also includes a water storage tank connected to the water supply pipe, the water storage tank being used to store the excess water generated in the first fuel cell after deducting the amount used to input into the second fuel cell.

7. The apparatus for in-situ measurement of proton membrane attenuation in a membrane electrode according to claim 5, characterized in that, In the second fuel cell stack, carbon paper is provided on both sides of the proton membrane to be tested, a flow field plate is provided on the outside of the carbon paper, and a current collector is provided on the outside of the flow field plate.

8. The apparatus for in-situ measurement of proton membrane decay in a membrane electrode according to claim 5, characterized in that, The heating mechanism is a heating band wrapped around the surface of the second fuel cell stack, and / or a thermocouple located inside the second fuel cell stack.

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