A method for restoring fuel cell stack performance during parking

Abstract

The present invention discloses a method for restoring the performance of a fuel cell stack during parking, and belongs to the technical field of proton exchange membrane fuel cells. The method comprises three stages: step 1, introducing nitrogen into the cathode, maintaining the supply of hydrogen at the anode and applying a predetermined load; step 2, when the single-chip voltage of the fuel cell stack is reduced to a preset voltage value, disconnecting the load, reducing the cathode side back pressure, reducing the battery temperature to a first predetermined temperature value, reducing the flow of nitrogen on the cathode side, and continuing to purge; step 3, introducing nitrogen purge on both sides and reducing the stack temperature to a second predetermined temperature value. The present invention enables the fuel cell stack to quickly recover the performance degradation caused by reversible attenuation during parking, improve output efficiency, extend service life, and has high recovery efficiency, simple operation, and low cost.

Description

Technical Field

[0001] The invention belongs to the technical field of proton exchange membrane fuel cells, and in particular relates to a method for restoring the performance of a fuel cell stack during parking. Background Art

[0002] Proton exchange membrane fuel cells have attracted widespread attention due to their high efficiency, high power density, and environmental friendliness. As one of the most promising energy conversion devices, they have been widely used in industries such as transportation, transport, and energy. However, poor durability is one of the most critical reasons hindering the commercialization of fuel cells.

[0003] When proton exchange membrane fuel cells are operated for a long time, especially when they are operated under high potential dynamic circulation conditions, an oxide film will form on the surface of the Pt catalyst, making charge transfer difficult, reducing catalyst activity, slowing down the ORR reaction kinetics, and reducing the output performance of the fuel cell stack and the service life. The water generated by the long-term operation of the fuel cell will be retained in the flow channel on the one hand, and on the other hand, it will be retained in the mass transfer channel due to the influence of the hydrophilic oxygen-containing groups generated on the surface due to the oxidation of the carbon carrier. Both of these will lead to a decrease in mass transfer capacity and a decrease in battery output power. In addition, the long-term operation of the fuel cell will inevitably lead to ionomer degradation, and its degradation products such as SO4 2- It will be adsorbed on the surface of the catalyst layer. During the normal operation of the battery stack, the SO4 adsorbed on the surface of the catalyst layer is affected by the high potential. 2- Failure to desorb leads to a significant reduction in the activity of the Pt catalyst, which accelerates battery degradation and reduces its durability. The battery performance degradation caused by these degradation mechanisms can be restored through specific operating strategies, thereby improving the battery's output performance and extending its service life.

[0004] In the prior art, research on performance recovery mostly remains at the laboratory single-cell stage, and the recovery methods are mostly limited to the recovery of single reversible attenuation. The operation is cumbersome, the recovery efficiency is low, and it takes up a lot of battery stack operation time, and cannot be applied to actual operating battery stacks. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for restoring the performance of a fuel cell stack during parking, so as to overcome the defects of the prior art proton exchange membrane fuel cell stack performance recovery method that occupies a large amount of available operating time, is cumbersome to operate, and has low recovery efficiency.

[0006] The technical problem to be solved by the present invention can be achieved by the following technical solutions:

[0007] A method for restoring fuel cell stack performance during parking, comprising the following steps:

[0008] Step 1, introducing nitrogen into the cathode, maintaining the supply of hydrogen to the anode and applying a predetermined load;

[0009] Step 2, when the single-cell voltage of the fuel cell stack is reduced to a preset voltage value, disconnect the load, reduce the cathode side back pressure, reduce the battery temperature to a first predetermined temperature value, reduce the flow rate of the cathode side nitrogen, and continue purging;

[0010] Step 3, nitrogen is introduced into both sides for purging and the temperature of the stack is reduced to a second predetermined temperature value.

[0011] Furthermore, in step 1, the relative humidity of hydrogen and nitrogen is 100%, and the flow rate is the same and is between 0.1 and 0.4 SLPM·cm -2 between.

[0012] Furthermore, in step 1, the current value of the predetermined load is between 50 and 200 mA·cm -2 .

[0013] Furthermore, in step 2, the voltage value is preset to be between 0.1V and 0.3V.

[0014] Furthermore, in step 2, the cathode side back pressure is reduced so that the cathode side back pressure is 10 to 30 kPa lower than the anode side back pressure.

[0015] Further, in step 2, the first predetermined temperature value is predetermined to be between 45 and 60°C.

[0016] Furthermore, in step 2, the nitrogen flow rate on the cathode side is reduced to half of the nitrogen flow rate on the cathode side in step 1, the hydrogen flow rate on the anode side remains unchanged, and the relative humidity of the gases on both sides is the same and over-humidified. Over-humidification means that the relative humidity is greater than 100%.

[0017] Furthermore, in step 2, the duration of the purge is 30 to 50 minutes.

[0018] Further, in step 3, dry nitrogen is introduced into both sides for purging at a flow rate of 1 to 2 SLPM·cm -2 .

[0019] Furthermore, in step 3, nitrogen is introduced into both sides for 2 to 3 minutes.

[0020] Furthermore, in step 3, the second predetermined temperature value is between 25 and 40°C.

[0021] The recovery principle of the present invention is:

[0022] (1) Nitrogen is introduced into the cathode to maintain the supply of hydrogen at the anode and apply a predetermined load to consume the oxygen in the cathode, reduce the cathode potential, and artificially force a lack of gas to create "oxygen starvation", so that hydrogen evolution reaction occurs in the cathode area, and the hydrogen that penetrates into the cathode is combined to reduce the platinum oxide, restore the active surface of the catalyst, and improve the performance of the fuel cell stack.

[0023] (2) When the voltage drops to a predetermined voltage value, disconnect the load, reduce the flow rate of nitrogen on the cathode side, reduce the back pressure on the cathode side, generate a pressure difference on both sides, increase the permeation of hydrogen, and work together with the low cathode potential to reduce the platinum oxide. In addition, in an over-humidified environment, impurities or pollutants can also be desorbed from the surface of the platinum catalyst and washed out of the stack, making the recovery effect more significant.

[0024] (3) Dry nitrogen is introduced into both sides to purge water in the flow channel and mass transfer channel to prevent the accumulation of liquid water from occupying the catalyst surface or blocking the transmission path of the reaction gas, thereby improving the performance output of the battery.

[0025] The technical solution provided by the present invention has the following advantages:

[0026] (1) The recovery method provided by the present application effectively alleviates the attenuation of the membrane electrode of the fuel cell stack. By artificially forcing the gas shortage in step 1 to create "oxygen starvation" to cause hydrogen evolution reaction to reduce the platinum oxide, combined with step 2 to create a pressure difference on both sides and increase the hydrogen permeation, the platinum oxide reduction is more thorough and the performance recovery is more complete. In addition, the liquid water produced by the condensation of the over-humidified reaction gas in step 2 combined with the low cathode potential environment allows some impurities or pollutants (such as SO4 2- ) is desorbed and discharged from the stack along with the liquid water. Finally, the mass transfer channel is unblocked under the purge of dry nitrogen, which improves the output performance of the stack under high current load. The recovery method provided in this application can significantly restore the performance of the battery stack, extend its service life, and enhance its durability.

[0027] (2) The recovery method provided in this application can recover the performance degradation caused by three reversible attenuation mechanisms and has wide applicability.

[0028] (3) The recovery method provided by this application is suitable for recovery during parking and purging, which overcomes the problems of cumbersome operation and taking up a large amount of fuel cell stack operation time in the prior art, and can minimize efficiency loss; in addition, in the existing recovery technology, the single consumption of oxygen is used to create "oxygen starvation", which requires multiple cycles of consuming air / oxygen and introducing air / oxygen. When this operation is frequently performed, it will have an adverse effect on the constituent materials of the membrane electrode. The method of this application provides an economical, convenient, practical and efficient performance recovery strategy. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0030] Figure 1 This is a flow chart of a method for restoring fuel cell stack performance during parking according to Example 1 of the present invention.

[0031] Figure 2 This is a comparison diagram of the polarization curves of the second single cell in the fuel cell stack of Example 1 of the present invention after activation, attenuation and recovery.

[0032] Figure 3 This is a comparison chart of the EIS of the second single cell in the fuel cell stack of Example 1 of the present invention after activation, attenuation and recovery. Specific implementation methods

[0033] In order to make the technical personnel in the field of this invention understand the scheme and advantages of the present invention more clearly, the technical scheme in the embodiment of the present invention is described in detail below in conjunction with the drawings in the examples of the present invention. The specific embodiments described here are only used to explain the present invention and do not limit the present invention or its application.

[0034] In the following embodiments, a fuel cell stack composed of three single cells is used to implement the method of the present invention, and polarization curve and EIS characterization tests are performed on the second single cell in the stack.

[0035] Example 1

[0036] Step 1: The fuel cell stack is shut down, the load is turned off, the supply of reactant gas is interrupted, and other working parameters of the stack: the back pressure on the anode and cathode sides is 100 kPa, the stack temperature is 70°C, and the humidification tank temperature is 70°C, which remain unchanged.

[0037] Step 2: Start to introduce nitrogen to the cathode side and hydrogen to the anode side, with a flow rate of 0.2 SLPM cm -2 , relative humidity was 100%, and the applied current density was 100 mA cm -2 The load value.

[0038] Step 3: When the single-chip voltage of the fuel cell stack drops to 0.2V, disconnect the load and reduce the cathode back pressure by 10kPa, reduce the stack temperature to 60°C, and reduce the cathode nitrogen flow rate to 0.1SLPM·cm -2 , the other operating parameters of the stack remain unchanged, and the purge is continued for 30 minutes.

[0039] Step 4: The flow rate on both sides is 2SLPM·cm -2 The nitrogen was purged for 2 minutes and the stack temperature dropped to 30°C.

[0040] Figure 2This is the performance recovery effect diagram of the second cell in Example 1. It can be seen that after parking, discharging and purging, the performance of the second cell has been significantly restored in the full power density area. -2 At 1000mA·cm -2 Under this condition, the voltage increased by 29mV.

[0041] Figure 3 The second section of the single cell in Example 1 is at 1A·cm -2 From the EIS graph measured below, it can be seen that after parking, discharging and purging, the charge transfer impedance R ct and mass transfer impedance R mt This result shows that the stop discharge in step 2 and the continuous purge in step 3 improve the surface state of the catalyst, effectively restore the active area of ​​the catalyst, reduce the charge transfer resistance, and improve the ORR reaction kinetics. Under the combined effect of the continuous purge of gas in steps 3 and 4, the liquid water accumulated in the single cell is taken out, so that the mass transfer capacity of the single cell is enhanced and the limiting current density is improved.

[0042] It can be seen from this embodiment that the parking discharge and purging restore the active area of ​​the catalyst and the mass transfer capacity of the fuel cell stack, which is sufficient to prove that the present invention can effectively restore the reversible attenuation produced during the operation of the fuel cell stack, enhance the durability of the fuel cell stack, and extend its service life.

[0043] Example 2

[0044] Step 1: The fuel cell stack is shut down, the load is turned off, the supply of reactant gas is interrupted, and other working parameters of the stack: the back pressure on the anode and cathode sides is 100 kPa, the stack temperature is 70°C, and the humidification tank temperature is 70°C, which remain unchanged.

[0045] Step 2: Start to introduce nitrogen to the cathode side and hydrogen to the anode side, with a flow rate of 0.1 SLPM cm -2 , relative humidity was 100%, and the applied current density was 50 mA·cm -2 The load value.

[0046] Step 3: When the single-chip voltage of the fuel cell stack drops to 0.1V, disconnect the load and reduce the cathode back pressure by 10kPa, the stack temperature drops to 45°C, and the flow rate of nitrogen on the cathode side drops to 0.05SLPM·cm -2 , the other operating parameters of the stack remain unchanged, and the purge is continued for 30 minutes.

[0047] Step 4: The flow rate on both sides is 1 SLPM cm -2 The nitrogen was purged for 3 minutes and the stack temperature dropped to 25°C.

[0048] The effect of this embodiment is the same as that of embodiment 1.

[0049] Example 3

[0050] Step 1: The fuel cell stack is shut down, the load is turned off, the supply of reactant gas is interrupted, and other working parameters of the stack: the back pressure on the anode and cathode sides is 100 kPa, the stack temperature is 70°C, and the humidification tank temperature is 70°C, which remain unchanged.

[0051] Step 2: Start to introduce nitrogen to the cathode side and hydrogen to the anode side, with a flow rate of 0.4 SLPM cm -2 , relative humidity was 100%, and the applied current density was 200 mA cm -2 The load value.

[0052] Step 3: When the single-chip voltage of the fuel cell stack drops to 0.3V, disconnect the load and reduce the cathode back pressure by 30kPa, the stack temperature drops to 60°C, and the flow rate of nitrogen on the cathode side drops to 0.2SLPM·cm -2 , the other operating parameters of the stack remain unchanged, and the purge continues for 50 minutes.

[0053] Step 4: The flow rate on both sides is 2SLPM·cm -2 The nitrogen was purged for 2 minutes and the stack temperature dropped to 40°C.

[0054] The effect of this embodiment is the same as that of embodiment 1.

[0055] The above-described embodiments are intended to facilitate those skilled in the art to more clearly understand and use the present invention, rather than to limit the present invention. Those skilled in the art should understand that all modifications, substitutions and improvements made without departing from the technical principles and scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for restoring fuel cell stack performance during parking, characterized in that: The following steps are involved: Step 1, introducing nitrogen into the cathode, maintaining the supply of hydrogen to the anode and applying a predetermined load; Step 2, when the single-cell voltage of the fuel cell stack is reduced to a preset voltage value, disconnect the load, reduce the cathode side back pressure, reduce the battery temperature to a first predetermined temperature value, reduce the flow rate of the cathode side nitrogen, and continue purging; Step 3, nitrogen is introduced into both sides for purging and the temperature of the stack is reduced to a second predetermined temperature value; In step 1, the relative humidity of hydrogen and nitrogen is 100%, and the flow rates are the same.

2. The method for restoring fuel cell stack performance during parking according to claim 1, characterized in that: In step 1, the flow rate of hydrogen and nitrogen is between 0.1 and 0.4 SLPM·cm -2 between.

3. The method for restoring fuel cell stack performance during parking according to claim 1, characterized in that: The current value of the predetermined load in step 1 is between 50 and 200 mA cm -2 between.

4. The method for restoring fuel cell stack performance during parking according to claim 1, characterized in that: In step 2, the voltage value is preset to be between 0.1V and 0.3V.

5. The method for restoring fuel cell stack performance during parking according to claim 1, characterized in that: The step 2 of reducing the cathode back pressure is that the cathode back pressure is 10 to 30 kPa lower than the anode back pressure.

6. The method for restoring fuel cell stack performance during parking according to claim 1, characterized in that: In step 2, the first predetermined temperature value is between 45 and 60°C.

7. The method for restoring fuel cell stack performance during parking according to claim 1, characterized in that: In step 2, the nitrogen flow rate on the cathode side is reduced to half of the nitrogen flow rate on the cathode side in step 1, the hydrogen flow rate on the anode side remains unchanged, and the relative humidity of the gases on both sides is the same and over-humidified.

8. The method for restoring fuel cell stack performance during parking according to claim 1, characterized in that: The duration of the purge in step 2 is 30 to 50 minutes.

9. The method for restoring fuel cell stack performance during parking according to claim 1, characterized in that: In step 3, dry nitrogen was introduced into both sides for purging at a flow rate of 1-2 SLPM·cm -2 ; Nitrogen is passed into both sides for 2 to 3 minutes.

10. The method for restoring fuel cell stack performance during parking according to claim 1, characterized in that: In step 3, the second predetermined temperature value is between 25 and 40°C.

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