Method for optimizing cold start performance of PEMFC

Abstract

The invention belongs to the field of proton exchange membrane fuel cells, and provides a method for optimizing the cold start performance of a PEMFC (Proton Exchange Membrane Fuel Cell) aiming at the defects in the prior art, the improved PEMFC is obtained by carrying out layered design on a cathode catalyst layer of the PEMFC, the platinum loading capacity and the electrolyte content in the catalyst layer are optimized by carrying out positive layered design and negative layered design on a CCL (Copper Cathode Logic), and the cold start performance of the PEMFC is optimized under the low-temperature condition of-15 to 0 DEG C. And by loading different current modes, optimization of the cold start performance of the PEMFC is completed. Compared with the prior art, according to the technical scheme, the ice storage capacity of the CCL can be effectively improved, the freezing rate of water in the CCL is reduced, PEMFC cold starting is successfully achieved, and the cold starting time is shortened.

Description

Technical Field

[0001] The invention belongs to the field of proton exchange membrane fuel cells, and in particular relates to a method for optimizing the cold start performance of PEMFC. Background Art

[0002] Proton exchange membrane fuel cells (PEMFCs) are widely used in energy systems, transportation, and portable devices due to their high efficiency, high power density, water-only emissions, and excellent low-temperature startability. When a PEMFC is started under low-temperature conditions, water present or generated in the cathode catalyst layer (CCL) freezes in the pores, blocking the CCL pores. This leads to insufficient oxygen supply within the PEMFC and a reduction in the effective electrochemical reaction area, resulting in PEMFC cold-start failure. Currently, auxiliary heating methods are primarily used to improve PEMFC cold-start performance in low-temperature environments. For example, a mixture is passed through the anode for catalytic preheating, where the anode exhaust gas is passed to the cathode, causing a catalytic reaction at the cathode and simultaneously heating the anode and cathode. A cold-start loop is activated at low temperatures, where an electric heater is activated to assist in stack heating when the stack temperature falls below the self-starting lower limit. Furthermore, a small coolant circulation system is employed to improve cold-start efficiency and shorten cold-start time. However, the above method will increase the extra energy consumption and complexity of the battery, increase the production cost of PEMFC. In addition, the current loading mode also has a great impact on the cold start performance of PEMFC under low temperature conditions. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for optimizing the cold start performance of PEMFC in response to the deficiencies of the above-mentioned prior art. CCL is the main place where PEMFC ice forms. The layered design of CCL can effectively reduce the freezing rate of water present in or generated in the catalytic layer, and delay the coverage of the pores of the outer layer of the catalytic layer by ice, thereby achieving the purpose of optimizing the cold start performance of PEMFC. The present invention improves the performance of PEMFC by layering the CCL of PEMFC; by controlling the platinum loading and electrolyte content distribution of the CCL after the layered design, the cold start performance of PEMFC is optimized, thereby effectively shortening the cold start time of PEMFC and successfully achieving the cold start of PEMFC.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0005] A method for optimizing the cold start performance of a PEMFC is characterized by: performing a layered design on the cathode catalyst layer (CCL) of the PEMFC, wherein the inner layer is close to the proton exchange membrane (PEM) and the outer layer is close to the cathode microporous layer (MPL), wherein the electrolyte content and / or platinum loading in each layer of the CCL is gradiently distributed to obtain an improved PEMFC; and applying a current to both ends of the improved PEMFC at a temperature between -15°C and 0°C to successfully achieve a cold start of the PEMFC.

[0006] Preferably, the CCL layered design scheme is: along the direction perpendicular to the PEM, the CCL is divided into two sub-layers, the inner layer is close to the PEM, and the outer layer is close to the MPL, and the two sub-layers are equal in thickness.

[0007] Preferably, the CCL layered design scheme is as follows: the cathode catalyst layer is divided into three sub-layers along a direction perpendicular to the PEM, the inner layer is close to the PEM, the outer layer is close to the MPL, and the three sub-layers have equal thickness.

[0008] In the technical solution of the present invention, when designing the layered design of CCL, in addition to dividing the CCL into two or three sub-layers of equal thickness as mentioned above, the CCL can also be divided into four layers or more layers. Among them, when the CCL is divided into two or three sub-layers of equal thickness, the optimization effect on the cold start performance of PEMFC is more significant.

[0009] Preferably, after the CCL is layered, when the electrolyte content and / or platinum loading increases layer by layer from the inner layer to the outer layer, it is called a positive layered design of the CCL; when the electrolyte content and / or platinum loading decreases layer by layer from the inner layer to the outer layer, it is called a negative layered design of the CCL.

[0010] In the CCL layered design of the present invention, in the positive CCL layered design, the platinum loading or electrolyte content increases layer by layer from the inner layer to the outer layer of the CCL, that is, the platinum loading or electrolyte content in the outer layer of the CCL is greater than that in the inner layer; in the negative CCL layered design, the platinum loading or electrolyte content decreases layer by layer from the inner layer to the outer layer of the CCL, that is, the platinum loading or electrolyte content in the outer layer of the CCL is less than that in the inner layer.

[0011] Preferably, when the CCL is designed in a positive or negative layered manner, when the electrolyte content is evenly distributed from the inner layer to the outer layer, the platinum loading content varies from the inner layer to the outer layer in the range of 0.15 to 0.45 mg / cm 2 .

[0012] Preferably, when the CCL is positively layered or negatively layered, when the platinum loading is evenly distributed from the inner layer to the outer layer, the electrolyte content varies in the range of 0.1 to 0.5 from the inner layer to the outer layer.

[0013] Preferably, when the CCL is designed with positive or negative stratification, the platinum loading from the inner layer to the outer layer varies in the range of 0.15 to 0.45 mg / cm 2 , the electrolyte content varies from the inner layer to the outer layer in the range of 0.1 to 0.5.

[0014] In the CCL layered design of the present invention, the average platinum loading is close to 0.3 mg / cm 2 , the average value of electrolyte content is close to 0.3~0.35.

[0015] Preferably, the mode of loading current across the improved PEMFC is constant current or ramp current.

[0016] Preferably, the loading angle of the ramp current is 10° to 50°.

[0017] Preferably, the density of the loading current is 1000-2000A / m 2 .

[0018] Among the loading current modes of the present invention, the ramp current mode optimizes PEMFC cold start performance more than the constant current mode. Under -15 to 0°C temperatures, when the ramp current mode is used and the CCL layering design adopts a negative layering, the PEMFC can complete a cold start within 24 hours, varying the ramp current loading angle and loading density. Compared to existing technologies, the cold start time is significantly shortened.

[0019] The loading current mode of the present invention may be any other current loading mode, such as a gradually changing current loading mode, in addition to the constant current or ramp current loading mode described herein.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The present invention improves the CCL structure of the PEMFC and optimizes the PEMFC performance by performing a layered design on the CCL. By adopting a positive layered design or a negative layered design on the CCL, a constant current or a ramp current is applied to both ends of the PEMFC under low temperature conditions of -15 to 0°C, thereby achieving a successful cold start of the PEMFC without the need for auxiliary heating. Compared with the prior art, the present invention reduces the additional energy consumption of the PEMFC, simplifies the PEMFC structure, and reduces production costs.

[0022] (2) The negative stratification design of the CCL described in the present invention can effectively improve the ice storage capacity of the CCL and reduce the freezing rate of water in the CCL, thereby optimizing the cold start performance of the PEMFC and shortening the cold start time.

[0023] (3) The CCL is the main place for ice to form in the catalyst layer. The present invention can effectively increase the porosity of the outer layer of the CCL through the layered design of the CCL, thereby improving the ice storage capacity of the CCL, and fundamentally solving the problem of water ice existing in or generated in the catalyst layer covering the pores of the outer layer of the catalyst layer. This allows more oxygen to enter the inner layer through the outer layer of the CCL, thereby enhancing the electrochemical reaction of the PEMFC and optimizing the performance of the PEMFC, thereby shortening its cold start time and improving its cold start success efficiency;

[0024] (4) In the negative layered design of the CCL described in the present invention, under the ramp current mode, when the electrolyte content of the CCL is evenly distributed from the inner layer to the outer layer, the platinum loading is between 0.15 and 0.45 mg / cm 2 When the current density and loading angle increase, the CCL temperature rise rate increases, further shortening the PEMFC cold start time. The PEMFC cold start time is shortened to 30-45 seconds.

[0025] (5) In the technical solution of the present invention, under a low temperature environment of -15 to 0°C, the optimization effect of the CCL negative stratification design on the cold start performance of PEMFC is more significant than that of the CCL positive stratification design; under the CCL negative stratification design, the CCL ice storage capacity is stronger, and it can more effectively delay the coverage of the pores of the catalyst layer by the water existing in the CCL or the generated water after freezing, thereby enhancing the cold start capability of PEMFC and successfully achieving the cold start of PEMFC. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the membrane electrode structure of PEMFC;

[0027] Figure 2 Schematic diagram of the improved PEMFC membrane electrode structure;

[0028] Figure 3 Porosity distribution diagram of CCL in CCL layered design;

[0029] Figure 4 Theoretical ice capacity distribution diagram of CCL in CCL layered design;

[0030] Figure 5 Ice volume fraction distribution diagram of CCL in CCL layered design;

[0031] Figure 6 Oxygen concentration distribution on the platinum surface in the catalytic layer in the negative layered CCL design;

[0032] Figure 7 Relationship diagram among PEMFC cold start time, platinum loading, electrolyte content and ramp current loading density.

[0033] Description of Reference Numerals

[0034] 1—cathode gas diffusion layer, 2—cathode microporous layer, 3—cathode catalytic layer, 4—proton exchange membrane, 5—anode catalytic layer, 6—anode microporous layer, 7—anode gas diffusion layer, 31—cathode catalytic layer outer layer, 32—cathode catalytic layer inner layer. Specific embodiments

[0035] The technical solution of the present invention is further described below with reference to the accompanying drawings.

[0036] Example 1

[0037] In this embodiment, the method for optimizing the cold start performance of PEMFC is as follows: the CCL of PEMFC is designed in layers, and the CCL is divided into two sub-layers with equal thickness in a direction perpendicular to the PEM, with the inner layer close to the PEM and the outer layer close to the MPL, thereby obtaining an improved PEMFC; the low temperature condition is set to -15°C, the initial membrane water content of the battery is 2, the relative humidity at the anode and cathode inlets of the battery is 0%, and the battery operating pressure is 150kPa. A constant current is applied to both ends of the PEMFC, and the current loading density is 1000A / m 2 ; A positive layered design is adopted for CCL. From the inner layer to the outer layer of CCL, the electrolyte content is evenly distributed from the inner layer to the outer layer, which is 0.1, and the platinum loading is 0.15mg / cm 2 , outer layer 0.45mg / cm 2 (The layered design scheme of the CCL is recorded as: platinum forward layering); under the above conditions, the PEMFC was started, and finally the PEMFC cold start was successfully achieved with a start-up time of 300 to 320 seconds.

[0038] The improved membrane electrode structure of PEMFC in Example 1 is shown in FIG. Figure 2 As shown, the membrane electrode structure of the improved PEMFC includes, from top to bottom: cathode gas diffusion layer 1, cathode microporous layer 2, cathode catalyst layer 3, proton exchange membrane 4, anode catalyst layer 5, anode microporous layer 6, anode gas diffusion layer 7, wherein the cathode catalyst layer 3 includes two sub-layers of equal thickness, namely a cathode catalyst layer outer layer 31 and a cathode catalyst layer inner layer 32.

[0039] Example 2

[0040] In this embodiment, the method for optimizing the cold start performance of PEMFC is as follows: the CCL of PEMFC is designed in layers, and the CCL is divided into two sub-layers with equal thickness in a direction perpendicular to the PEM, with the inner layer close to the PEM and the outer layer close to the MPL, thereby obtaining an improved PEMFC; the low temperature condition is set to -14°C, the initial membrane water content of the battery is 2, the relative humidity at the anode and cathode inlets of the battery is 0%, the battery operating pressure is 150 kPa, and a constant current is applied to both ends of the PEMFC, with a current loading density of 1500 A / m 2 A positive layering design was adopted for the CCL. From the inner layer to the outer layer of the CCL, the electrolyte content distribution was 0.1 in the inner layer and 0.5 in the outer layer (this CCL layering design was recorded as: electrolyte positive layering). The platinum loading was evenly distributed from the inner layer to the outer layer at 0.35 mg / cm 2 ; Under the above conditions, PEMFC was started and successfully achieved cold start, with a cold start time of 310 to 330 seconds.

[0041] In the above embodiments 1 and 2, the loading current mode is replaced with a ramp current, and the current loading density is set to 1000-2000 A / m 2 , and then starting the PEMFC after the loading angle was 10-50°, the PEMFC cold start was also successfully achieved, and the cold start time was further shortened to less than 300s.

[0042] Example 3

[0043] In this embodiment, the method for optimizing the cold start performance of PEMFC is as follows: the CCL of PEMFC is designed in layers, and the CCL is divided into two sub-layers with equal thickness in a direction perpendicular to the PEM, with the inner layer close to the PEM and the outer layer close to the MPL, thereby obtaining an improved PEMFC; the low temperature condition is set to -15°C, the initial membrane water content of the battery is 2, the relative humidity at the anode and cathode inlets of the battery is 0%, and the battery operating pressure is 150kPa. A constant current is applied to both ends of the PEMFC, and the current loading density is 1000A / m 2 A negative layered design scheme is adopted for CCL. From the inner layer to the outer layer of CCL, the electrolyte content is evenly distributed from the inner layer to the outer layer, which is 0.35. The platinum loading in the inner layer is 0.45 mg / cm 2 , 0.15mg / cm in the outer layer 2 (The layered design of the CCL is denoted as: negative platinum layering). The PEMFC was started under the above conditions, and a PEMFC cold start was successfully achieved, with the cold start time shortened to less than 200 seconds.

[0044] The loading current mode of Examples 1 and 3 was replaced with a ramp current, and the loading density of the current was controlled to be 1000-2000 A / m 2, the loading angle is 50°, and the other conditions are the same as in Example 1 or 3. Then the PEMFC is started again, and the PEMFC cold start is successfully achieved, and the cold start time is shortened to less than 100s. The change of the cold start time with the loading current density is shown in Figure 2. Figure 7 As shown; when the loading current density is 1500A / m 2 When the oxygen concentration value of the platinum surface from the inner layer to the outer layer of the CCL changes in the range of Figure 6 As shown in the figure, when the platinum negative layering design is adopted, when the ramp current is loaded and the loading angle is 50°, the oxygen concentration value in the inner layer of the CCL is higher, which is more conducive to the electrochemical reaction of the battery and improves the battery performance.

[0045] Example 4

[0046] In this embodiment, the method for optimizing the cold start performance of PEMFC is as follows: the CCL of PEMFC is designed in layers, and the CCL is divided into two sub-layers with equal thickness in a direction perpendicular to the PEM, with the inner layer close to the PEM and the outer layer close to the MPL, thereby obtaining an improved PEMFC; the low temperature condition is set to -14°C, the initial membrane water content of the battery is 2, the relative humidity at the anode and cathode inlets of the battery is 0%, the battery operating pressure is 150 kPa, and a constant current is applied to both ends of the PEMFC, with a current loading density of 1500 A / m 2 A negative stratification design scheme was adopted for the CCL. From the inner layer to the outer layer of the CCL, the electrolyte content distribution was 0.5 in the inner layer and 0.1 in the outer layer (this CCL stratification design scheme is recorded as: negative electrolyte stratification). The platinum loading was evenly distributed from the inner layer to the outer layer at 0.35 mg / cm 2 ; 0.25mg / cm in the outer layer 2 ; Under the above conditions, PEMFC was started and PEMFC cold start was successfully achieved, and the cold start time was shortened to less than 180s.

[0047] Comparing Example 1 and Example 3, when the electrolyte content is evenly distributed from the inner layer to the outer layer of the CCL, and the platinum loading content in the inner layer is greater than that in the outer layer, the cold start time of the PEMFC is shorter. This is because the layering method can increase the oxygen concentration value in the inner layer of the CCL and enhance the electrochemical reaction in the inner layer of the CCL. The change curve of the oxygen concentration value is shown in FIG. Figure 6 Oxygen concentration change curve of negative platinum stratification.

[0048] Comparing Example 2 and Example 4, it can be seen that when other conditions remain unchanged and the platinum loading is evenly distributed, the negative electrolyte stratification design is adopted for the CCL, and the cold start of the PEMFC is shorter; the cold start time of Examples 2 and 4 varies with the loading current density. Figure 7 shown.

[0049] The loading current mode of Examples 2 and 4 was replaced with a ramp current, and the loading density of the current was controlled to be 1000-2000 A / m 2 , the loading angle is 50°, and the other conditions are the same as in Example 2 or 4, and then the PEMFC is started, the PEMFC cold start is successfully achieved, and the cold start time is shortened to less than 100s. The change of the cold start time with the loading current density is shown in Figure 2. Figure 7 shown.

[0050] In the technical solutions of Examples 1 to 4, the porosity and theoretical ice capacity of CCL are based on Figure 3 and 4 As shown; when constant current is loaded, the loading density is 1500A / m 2 When the ice volume fraction of the inner and outer layers of the CCL is Figure 5 As shown; In the technical solution of the present invention, the following formula is used to calculate the theoretical ice capacity per unit membrane area of ​​CCL, which is used to analyze the effects of positive and negative stratification designs of CCL on the ice storage capacity of CCL, and to compare the effects of different stratification designs of CCL on the optimization of PEMFC cold start performance;

[0051] The formula is:

[0052] Where: Q ice It represents the theoretical ice capacity of CCL per unit membrane area, in mg / cm 2 ρ ice Indicates the density of ice in kg / m 3 ; ε CL represents the porosity of the cathode catalyst layer; V CL Represents the volume of the cathode catalyst layer, in m 3 ; A PEM Represents the membrane area of ​​the proton exchange membrane, in m 2 ;

[0053] The calculation formula of the loading ramp current is: Where I represents the ramp current density, I0 represents the initial current density of the ramp current, and the unit is A / m 2 , α represents the loading angle, the unit is °.

[0054] like Figure 3 、 4As shown in Figure 5, when the CCL layered design adopts a negative layered design, its outer layer porosity and theoretical ice capacity are greater than those of the CCL's positive layered design, and the ice volume fraction is less than that of the CCL's positive layered design. It can be seen that in the technical solution of the present invention, the CCL adopts a negative layered design, that is, when the platinum catalyst or electrolyte content decreases layer by layer from the inner layer to the outer layer of the CCL, the porosity of the CCL outer layer is large and the ice storage capacity is strong, and the effect of optimizing the cold start performance of the PEMFC is more significant.

[0055] Example 5

[0056] In this embodiment, the method for optimizing the cold start performance of PEMFC is as follows: the CCL of PEMFC is designed in layers, and the CCL is divided into three sub-layers with equal thickness in a direction perpendicular to the PEM, with the inner layer close to the PEM and the outer layer close to the MPL, thereby obtaining an improved PEMFC; the low temperature condition is set to -15°C, the initial membrane water content of the battery is 2, the relative humidity at the anode and cathode inlets of the battery is 0%, the battery operating pressure is 150 kPa, and a ramp current is applied to both ends of the PEMFC, with a current loading density of 1000 A / m 2 , the loading angle is 10°; a negative layered design scheme is adopted for CCL, from the inner layer to the outer layer of CCL, the electrolyte content distribution is 0.10, and the platinum loading content distribution is 0.45 mg / cm in the inner layer. 2 , middle layer 0.30mg / cm 2 , outer layer 0.15mg / cm 2 , the PEMFC was started under the above conditions, and the PEMFC cold start was successfully achieved, and the cold start time was shortened to less than 80s.

[0057] Example 6

[0058] The method for optimizing the cold start performance of PEMFC is as follows: the CCL of PEMFC is designed in layers. In the direction perpendicular to the PEM, the CCL is divided into three sub-layers with equal thickness. The inner layer is close to the PEM and the outer layer is close to the MPL, thereby obtaining an improved PEMFC; the low temperature condition is set to -15°C, the initial membrane water content of the battery is 2, the relative humidity at the anode and cathode inlets of the battery is 0%, the battery operating pressure is 150kPa, and a ramp current is loaded at both ends of the PEMFC with a current loading density of 1500A / m 2 , the loading angle is 50°; a negative layered design scheme is adopted for CCL, from the inner layer to the outer layer of CCL, the electrolyte content distribution is 0.10, and the platinum loading content distribution is 0.45 mg / cm in the inner layer. 2 , middle layer 0.30mg / cm 2 , outer layer 0.15mg / cm 2, started the PEMFC under the above conditions, started the PEMFC under the above conditions, successfully achieved PEMFC cold start, and the cold start time was shortened to less than 40s.

[0059] By comparing Examples 5 and 6, it can be seen that as the density and angle of the ramp current loaded at both ends of the PEMFC increase, the cold start time of the PEMFC is further shortened. This is because the CCL temperature rise is gradually accelerated with the increase of the current loading density and the loading angle, and the oxygen transmission resistance of the inner layer of the CCL is low when the CCL negative layered design is adopted, so that the oxygen concentration on the surface of the catalyst platinum is higher, thereby enhancing the ability of the catalytic layer to withstand a wider range of current density and current loading angles. Such a virtuous cycle further optimizes the cold start performance of the PEMFC, significantly shortens the cold start time, and improves the cold start success rate.

[0060] Example 7

[0061] In this embodiment, the method for optimizing the cold start performance of PEMFC is as follows: the CCL of PEMFC is designed in layers, and the CCL is divided into three sub-layers with equal thickness in a direction perpendicular to the PEM, with the inner layer close to the PEM and the outer layer close to the MPL, thereby obtaining an improved PEMFC; the low temperature condition is set to -15°C, the initial membrane water content of the battery is 2, the relative humidity at the anode and cathode inlets of the battery is 0%, the battery operating pressure is 150 kPa, and a ramp current is applied to both ends of the PEMFC, with a current loading density of 1500 A / m 2 , the loading angle is 30°; a negative layered design scheme is adopted for CCL. From the inner layer to the outer layer of CCL, the electrolyte content distribution is 0.5 in the inner layer, 0.3 in the middle layer, and 0.1 in the outer layer. The platinum loading distribution is 0.35 mg / cm in the inner layer. 2 , middle layer 0.3mg / cm 2 , outer layer 0.25mg / cm 2 (The CCL layering technology is denoted as: platinum & negative layering). Under the above conditions, the PEMFC was started and the cold start of the PEMFC was successfully achieved. The cold start time was shortened to less than 50s. Among them, when the platinum & negative layering was used, the relationship between the cold start time of the PEMFC and the change of the loading current density is shown in the figure below. Figure 7 As shown, the oxygen concentration value on the platinum surface varies as follows Figure 6 As shown in the figure, it can be seen that its concentration value is lower than the oxygen concentration in the platinum negative stratification design.

[0062] When the negative CCL stratification scheme of Example 7 is replaced by a positive stratification scheme (this CCL stratification technology scheme is denoted as: Pt & Cd positive stratification), the time for successful cold start of the PEMFC is extended to less than 200s when other conditions remain unchanged. This is because in the CCL positive stratification scheme, the porosity of the outer layer of the CCL decreases, resulting in a weakened ice storage capacity, which prolongs the cold start time of the PEMFC. In the case of Pt & Cd positive stratification, the relationship between the cold start time of the PEMFC and the change of the loading current density is shown in the figure below. Figure 7 shown.

[0063] Example 8

[0064] In this embodiment, the method for optimizing the cold start performance of PEMFC is as follows: the CCL of PEMFC is designed in layers, and the CCL is divided into a plurality of sublayers in a direction perpendicular to the PEM, the number of sublayers being greater than 3, and the thickness of each sublayer being equal, with the inner layer close to the PEM and the outer layer close to the MPL, thereby obtaining an improved PEMFC; the low temperature condition is set to -15°C, the initial membrane water content of the battery is 2, the relative humidity at the anode and cathode inlets of the battery is 0%, the battery operating pressure is 150 kPa, and a ramp current is applied to both ends of the PEMFC, with a current loading density of 1500 A / m 2 , the loading angle is 10°; a negative layered design scheme is adopted for CCL. From the inner layer to the outer layer of CCL, the electrolyte content distribution is 0.5, 0.3, 0.1, and the platinum loading content is 0.45 mg / cm 2 , 0.3mg / cm 2 , 0.15mg / cm 2 (The CCL layering technology solution is recorded as: platinum & negative layering); under the above conditions, the PEMFC was started and the PEMFC cold start was successfully achieved within 150 seconds.

[0065] The CCL negative layered design scheme described in Example 8 is replaced by a positive layered design scheme (denoted as: platinum & electric positive layered design), and the other conditions are the same as those described in Example 8. Then the PEMFC is started again, and the PEMFC cold start can still be successfully achieved, and the cold start time will be extended to within 300s.

[0066] In Example 8 and its alternatives, the porosity of the CCL, the theoretical ice capacity, and the ice volume fraction of the inner and outer layers of the CCL are referenced to the following when the platinum & electron positive layer is layered and the platinum & electron negative layer is layered: Figure 3 、 4 As shown in Figure 5, it can be seen from the figure that the CCL layered design scheme using platinum & negative layering has a larger porosity and theoretical ice capacity in the CCL outer layer, which can improve the PEMFC performance.

[0067] The calculation method of the CCL ice storage capacity and the ramp current loading mode described in the present invention can be replaced by other calculation methods disclosed in the prior art, which does not affect the technical solution and the technical effects that can be achieved in the present invention.

[0068] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent variation made to the above embodiment based on the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for optimizing the cold start performance of PEMFC, characterized in that: The method comprises the following steps: performing a layered design on the cathode catalyst layer of the PEMFC, dividing the layer into multiple layers, wherein the inner layer is close to the proton exchange membrane and the outer layer is close to the cathode microporous layer. After the layered design of the cathode catalyst layer, the electrolyte content and / or platinum loading in each layer is distributed in a gradient, thereby obtaining an improved PEMFC; and loading current at both ends of the improved PEMFC at a temperature of -15 to 0°C, thereby successfully achieving a cold start of the PEMFC.

2. The method for optimizing the cold start performance of PEMFC according to claim 1, characterized in that: The cathode catalyst layer is designed in a layered manner as follows: along a direction perpendicular to the proton exchange membrane, the cathode catalyst is divided into two sub-layers, the inner layer is close to the proton exchange membrane, and the outer layer is close to the cathode microporous layer, and the two sub-layers have equal thickness.

3. The method for optimizing the cold start performance of PEMFC according to claim 1, characterized in that: The cathode catalyst layer is designed as follows: the cathode catalyst layer is divided into three sublayers along the direction perpendicular to the proton exchange membrane, the inner layer is close to the proton exchange membrane, the outer layer is close to the cathode microporous layer, and the three sublayers have equal thickness.

4. The method for optimizing the cold start performance of PEMFC according to claim 1, characterized in that: After the cathode catalyst layer is layered, when the electrolyte content and / or platinum loading increases layer by layer from the inner layer to the outer layer, it is called a positive layered design of the cathode catalyst layer; when the electrolyte content and / or platinum loading decreases layer by layer from the inner layer to the outer layer, it is called a negative layered design of the cathode catalyst layer.

5. The method for optimizing the cold start performance of PEMFC according to claim 4, characterized in that: When the cathode catalyst layer is designed in a positive or negative layered manner and the electrolyte content is evenly distributed from the inner layer to the outer layer, the platinum loading content varies from the inner layer to the outer layer in the range of 0.15 to 0.45 mg / cm 2 .

6. The method for optimizing the cold start performance of PEMFC according to claim 4, characterized in that: When the cathode catalyst layer is designed in a positive layered manner or a negative layered manner, and the platinum loading is evenly distributed from the inner layer to the outer layer, the electrolyte content varies in the range of 0.1 to 0.5 from the inner layer to the outer layer.

7. The method for optimizing the cold start performance of PEMFC according to claim 4, characterized in that: When the cathode catalyst layer is designed in a positive layered or negative layered manner, the platinum loading from the inner layer to the outer layer varies in the range of 0.15 to 0.45 mg / cm 2 , the electrolyte content varies from the inner layer to the outer layer in the range of 0.1 to 0.

5.

8. The method for optimizing the cold start performance of PEMFC according to claim 1, characterized in that: Current is loaded across the improved PEMFC, and the current mode is a constant current or a ramp current.

9. The method for optimizing the cold start performance of PEMFC according to claim 8, characterized in that: The loading angle of the ramp current is 10° to 50°.

10. The method for optimizing the cold start performance of PEMFC according to claim 1, characterized in that: The density of the loading current is 1000-2000A / m 2 .

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