Method for judging low-temperature cold start purging degree of fuel cell stack
By monitoring high-frequency impedance and stack voltage changes through electrochemical impedance spectroscopy, combined with a low-current, high-flow-rate purging method, the problem of determining water content during low-temperature cold start of fuel cell stacks is solved, ensuring proper purging, preventing performance degradation, simplifying operation, and reducing costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHENZHEN SENERGY FUEL CELL TECH CO LTD
- Filing Date
- 2024-12-30
- Publication Date
- 2026-06-02
AI Technical Summary
Existing technologies cannot directly or indirectly observe the water content within the fuel cell stack, and lack specific criteria for assessing the degree of purging, leading to performance degradation during cold starts.
By monitoring high-frequency impedance and stack voltage changes using electrochemical impedance spectroscopy (EIS), and combining this with a small-current, high-flow-rate purging method, the appropriate purging time and extent can be determined to avoid excessive dryness or wetness.
It enables accurate determination of the purging degree during low-temperature cold start, avoids damage to membrane electrodes, simplifies operation and reduces costs.
Smart Images
Figure CN119764490B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of fuel cell technology, and in particular relates to a method for judging the degree of low-temperature cold start purging of fuel cell stacks. Background Technology
[0002] In the process of further commercialization and promotion of fuel cell vehicles, there are many key factors that restrict their development. Among them, the cold start problem of fuel cells caused by extremely cold regions and climate is one of the main obstacles to the commercialization of fuel cells.
[0003] During cold start, the output performance of a fuel cell will decrease to some extent. The main reasons for this decrease are: during the start-up process, water produced by the electrochemical reaction freezes as it flows from the core (CL) to the gas delivery system (GDL) and flow channels. This ice covers the reactive sites of the catalyst in the CL and blocks the gas channels in the GDL and flow channels, thus affecting the normal progress of the electrochemical reaction. Moreover, freezing can damage the internal structure of the fuel cell, leading to catalyst layer shedding and diffusion layer damage. At the same time, the formation of ice will increase the contact resistance, which will also increase the overall impedance of the cell. These factors ultimately lead to a decrease in output performance.
[0004] It can be seen that the key to a successful cold start lies in water management; the lower the water content of the fuel cell stack in the initial stage of cold start, the greater the success rate. The most effective way to reduce the water content of the fuel cell stack is to properly purge the stack. However, existing literature lacks a clear and effective standard for judging the degree of purging; excessively dry purging of the membrane electrode assembly (MEA) can lead to accelerated mechanical degradation of the proton exchange membrane; insufficient purging can result in residual water inside the membrane, increasing the risk of icing. How to quickly and accurately determine whether the purging has reached the required level is a technical challenge. Currently, most existing technologies use high-flow-rate nitrogen or air for purging over a certain period, which cannot directly or indirectly show the water content within the stack, and there is no specific numerical standard for judging the degree of purging. Summary of the Invention
[0005] This invention provides a method for judging the degree of purging during low-temperature cold start of a fuel cell stack, aiming to solve the problems of existing technologies that cannot directly or indirectly observe the water content state inside the stack and that the degree of purging does not have a specific numerical value as an evaluation standard.
[0006] To achieve the above objectives, the present invention provides a method for determining the degree of low-temperature cold start purging of a fuel cell stack, comprising the following steps:
[0007] S01. Connect the battery stack to be purged to EIS (Electrochemical Impedance Spectroscopy), then activate the battery stack to be purged, and calibrate the performance of the battery stack to be purged.
[0008] S02. Raise the temperature of the fuel cell stack to be purged to 65℃~80℃, maintain the temperature at 65℃~80℃, and then set the back pressure of the fuel cell stack to be purged.
[0009] S03. Introduce fuel gas into the fuel cell stack to be purged, and then apply current to the fuel cell stack to be purged.
[0010] S04. When the average voltage in the inspection voltage diagram and the impedance value in the high-frequency impedance spectrum trend diagram both tend to be constant, record the purging time and end the purging.
[0011] In a preferred embodiment, in step S01,
[0012] The EIS is preferably an EIS with 1A perturbation; the high-frequency impedance frequency of the EIS is preferably 1000Hz.
[0013] The activation is achieved by the following method: the stack to be purged is subjected to gradient loading, the slope of each loading is preferably 10A / s to 50A / s, the constant current is maintained for 2min to 10min for each gradient, and the constant current is maintained for 1h after loading to the rated electrical density; the above steps are repeated 3 to 6 times.
[0014] The performance calibration is achieved by the following method: performing a transformer-on-polarization test on the fuel cell stack to be purged to obtain a polarization curve; and calibrating the performance of the fuel cell stack to be purged based on the performance shown by the polarization curve.
[0015] In a preferred embodiment, in step S02,
[0016] The back pressure is set in accordance with the temperature.
[0017] The back pressure is preferably 50 kPa to 100 kPa.
[0018] In a preferred embodiment, in step S03...
[0019] The humidity of the fuel gas is preferably 0%RH to 40%RH.
[0020] The fuel gas is hydrogen and air; air is introduced into the cathode inlet of the fuel cell stack to be purged, and hydrogen is introduced into the anode inlet of the fuel cell stack to be purged.
[0021] The preferred current density of the hydrogen gas is 0.5 A / cm. 2~1.0A / cm 2 The preferred current density of the air is 0.5 A / cm³. 2 ~1.0A / cm 2 .
[0022] According to the metering ratio, the supply flow rate of the anode of the fuel cell stack to be purged is 1.6 to 1.8 of the corresponding current metering ratio; the supply flow rate of the cathode of the fuel cell stack to be purged is 1.8 to 2.0 of the corresponding current metering ratio.
[0023] The current load follows the principle of small current density and large current flow, and the preferred current density of the current load is 0.05 A / cm². 2 ~0.1A / cm 2 .
[0024] In a preferred embodiment, in step S04,
[0025] The preferred purging time is 5 to 10 minutes.
[0026] When purging fuel cells of the same model and power in the future, quantitative purging can be performed based on the purging time and average voltage value obtained from the previous experiments, without the need to connect auxiliary equipment or high-frequency impedance.
[0027] In this embodiment, the fuel cell stack is kept at a constant temperature of 65°C to 80°C during the purging process. This temperature can accelerate the evaporation of residual liquid water in the stack and shorten the purging time. During the purging process, the fuel cell stack is purged with a small current and a large flow rate. This purging method can quickly reduce the water content in the fuel cell stack, avoid excessive water freezing in sub-zero environments which could damage the membrane electrode assembly, and effectively prevent excessive water loss from the membrane electrode assembly, thus affecting the performance of the fuel cell stack.
[0028] This application is based on the inverse relationship between high-frequency impedance and corresponding water content, and the direct proportionality between the hydration state of the proton exchange membrane and the stack performance. It uses high-frequency impedance and stack voltage to determine the water content within the fuel cell stack during purging, thereby confirming the purging time. This method facilitates accurate assessment of the purging degree during low-temperature cold storage, cold start-up, or purging of the fuel cell stack during shutdown, locking in the purging time and preventing excessive or insufficient purging that leaves residual moisture. Furthermore, when purging the same model and power fuel cell stack again, the purging standard can be directly determined based on the previously obtained voltage value and purging time, reducing the need for impedance equipment as an auxiliary basis for judgment, thus saving operating costs and simplifying operation. Attached Figure Description
[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.
[0030] Figure 1 This is a schematic diagram showing the relationship between impedance values and purging time in an impedance spectrum diagram according to an embodiment of the present invention;
[0031] Figure 2 This is a schematic diagram showing the correspondence between purging time and high-frequency impedance spectrum according to an embodiment of the present invention;
[0032] Figure 3 This is a schematic diagram showing the relationship between the purging time and the average voltage of the fuel cell stack according to an embodiment of the present invention.
[0033] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation
[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0035] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, top, bottom, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.
[0036] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.
[0037] It should be noted that when a component is described as "fixed to" or "set on" another component, it can be directly on the other component or there may be an intervening component. When a component is described as "connected to" another component, it can be directly connected to the other component or there may be an intervening component.
[0038] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.
[0039] Generally, the water content in a fuel cell stack is mainly distributed in the flow channels, diffusion layer, and proton exchange membrane, among which:
[0040] 1) Due to the water absorption properties of the proton exchange membrane, water is stored inside the membrane in a hydrated form.
[0041] 2) The gas diffusion layer is commonly made of porous carbon paper or carbon cloth. Liquid water is adsorbed in the porous structure due to surface tension. In addition, carbon materials themselves can adsorb a small amount of liquid water.
[0042] 3) The electrode plates are filled with channels for gas flow. The channels are where water is most abundant, mainly consisting of large water droplets, which are also the easiest water to blow away.
[0043] The different components in a fuel cell stack interact with liquid water in different ways, resulting in varying degrees of difficulty in removing the liquid water from different components during the purging process.
[0044] In the embodiments of this application, we use electrochemical impedance spectroscopy and stack voltage to describe this process. Electrochemical impedance spectroscopy is a common method for studying proton exchange membrane fuel cells, which can characterize various impedance states in the current electrochemical reaction of the fuel cell stack online. Among them, high-frequency impedance is the main means of characterizing the water content of the fuel cell.
[0045] The purging process of a fuel cell stack can be mainly divided into three stages: a slow rise stage, a rapid rise stage, and a tendency to equilibrium stage. The corresponding high-frequency impedance spectra are as follows: Figure 1 As shown; the meanings represented are as follows:
[0046] a. Slow rising phase: This phase sweeps away the moisture inside the flow channel;
[0047] b. Rapid ascent phase: The water in the diffusion layer and proton membrane is swept away;
[0048] c. Equilibrium stage: At this point, the amount of water produced inside the membrane and the amount of water carried away by the gas reach a balance.
[0049] like Figure 1 As shown, when the impedance spectrum detects that the high-frequency impedance value is about to reach equilibrium, that is, when the rapid rise phase is about to enter the equilibrium phase, it indicates that the water content inside the fuel cell stack is suitable. At this time, the fuel cell stack purging time and voltage value are recorded, and the purging ends.
[0050] In the embodiments of this application, the range of each parameter can be set according to actual needs, and the solution of this application can be achieved as long as it is within the range required by this application.
[0051] Specifically, this application provides a method for determining the degree of cold start purging of a fuel cell stack, including the following steps:
[0052] S01. Connect the battery stack to be purged to EIS (Electrochemical Impedance Spectroscopy), then activate the battery stack to be purged, and calibrate the performance of the battery stack to be purged.
[0053] S02. Raise the temperature of the fuel cell stack to be purged to 65℃~80℃, maintain the temperature at 65℃~80℃, and then set the back pressure of the fuel cell stack to be purged.
[0054] S03. Introduce fuel gas into the fuel cell stack to be purged, and then apply current to the fuel cell stack to be purged.
[0055] S04. When the average voltage in the inspection voltage diagram and the impedance value in the high-frequency impedance spectrum trend diagram both tend to be constant, record the purging time and end the purging.
[0056] In a preferred embodiment, in step S01,
[0057] The EIS is preferably an EIS with 1A perturbation; the high-frequency impedance frequency of the EIS is preferably 1000Hz.
[0058] The activation is achieved by the following method: the stack to be purged is subjected to gradient loading, the slope of each loading is preferably 10A / s to 50A / s, the constant current is maintained for 2min to 10min for each gradient, and the constant current is maintained for 1h after loading to the rated electrical density; the above steps are repeated 3 to 6 times.
[0059] The performance calibration is achieved by the following method: performing a transformer-on-polarization test on the fuel cell stack to be purged to obtain a polarization curve; and calibrating the performance of the fuel cell stack to be purged based on the performance shown by the polarization curve.
[0060] In the embodiments of this application, the transformer polarization test can be performed using conventional test methods and test conditions.
[0061] In a preferred embodiment, in step S02,
[0062] The back pressure is set in accordance with the temperature.
[0063] The back pressure is preferably 50 kPa to 100 kPa.
[0064] In a preferred embodiment, in step S03...
[0065] The humidity of the fuel gas is preferably 0%RH to 40%RH.
[0066] The fuel gas is hydrogen and air; air is introduced into the cathode inlet of the fuel cell stack to be purged, and hydrogen is introduced into the anode inlet of the fuel cell stack to be purged.
[0067] The preferred current density (i.e., electrical density) of the hydrogen gas is 0.5 A / cm. 2 ~1.0A / cm 2 The preferred current density (i.e., electrical density) of the air is 0.5 A / cm². 2 ~1.0A / cm 2 .
[0068] According to the metering ratio, the supply flow rate of the anode of the fuel cell stack to be purged is 1.6 to 1.8 of the corresponding current metering ratio; the supply flow rate of the cathode of the fuel cell stack to be purged is 1.8 to 2.0 of the corresponding current metering ratio.
[0069] The current load follows the principle of small current density and large current flow, and the preferred current density of the current load is 0.05 A / cm². 2 ~0.1A / cm 2 .
[0070] In a preferred embodiment, in step S04,
[0071] The preferred purging time is 5 to 10 minutes.
[0072] When purging fuel cells of the same model and power in the future, quantitative purging can be performed based on the purging time and average voltage value obtained from the previous experiments, without the need to connect auxiliary equipment or high-frequency impedance.
[0073] In one embodiment, a method for determining the degree of purging during cryogenic storage of a fuel cell stack includes the following steps:
[0074] S01. Connect the EIS to the battery stack to be purged, fully activate the battery stack to be purged and calibrate its performance (activation and performance calibration can be performed according to the above method);
[0075] S02. Control the stack temperature of the fuel cell stack to be purged at 70℃, and set the back pressure to 67 kPa for the anode and 57 kPa for the cathode.
[0076] S03, according to 1.0A / cm 2 The electrical density and metering ratio are 1.8, and the hydrogen supply flow rate is 1.0 A / cm³. 2 The electrical density and metering ratio are 2.0, and the air supply flow rate is 0.1 A / cm. 2 Load current;
[0077] S04. Observe the trend of high-frequency impedance spectrum and average voltage. When the average voltage and impedance values tend to stabilize, record the purging time, end the purging, and the results are as follows. Figure 2 and Figure 3 As shown. From Figure 2 and Figure 3 As can be seen, the high-frequency impedance diagram shows the relationship between the water content inside the fuel cell stack and the impedance, as well as the voltage relationship. The impedance spectrum changes are divided into three stages: a slow rise period, a rapid rise period, and an equilibrium period.
[0078] In this embodiment, the fuel cell stack is kept at a constant temperature of 65°C to 80°C during the purging process. This temperature can accelerate the evaporation of residual liquid water in the stack and shorten the purging time. During the purging process, the fuel cell stack is purged with a small current and a large flow rate. This purging method can quickly reduce the water content in the fuel cell stack, avoid excessive water freezing in sub-zero environments which could damage the membrane electrode assembly, and effectively prevent excessive water loss from the membrane electrode assembly, thus affecting the performance of the fuel cell stack.
[0079] This application is based on the inverse relationship between high-frequency impedance and corresponding water content, and the direct proportionality between the hydration state of the proton exchange membrane and the stack performance. It uses high-frequency impedance and stack voltage to determine the water content within the fuel cell stack during purging, thereby confirming the purging time. This method facilitates accurate assessment of the purging degree during low-temperature cold storage, cold start-up, or purging of the fuel cell stack during shutdown, locking in the purging time and preventing excessive or insufficient purging that leaves residual moisture. Furthermore, when purging the same model and power fuel cell stack again, the purging standard can be directly determined based on the previously obtained voltage value and purging time, reducing the need for impedance equipment as an auxiliary basis for judgment, thus saving operating costs and simplifying operation.
[0080] In the description of this specification, references to terms such as "an embodiment," "example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.
[0081] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style of the specification is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.
[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for determining the degree of cold start purging of a fuel cell stack, characterized in that, Includes the following steps: S01. Connect the fuel cell stack to be purged to the EIS, then activate the fuel cell stack to be purged, and calibrate the performance of the fuel cell stack to be purged. S02. Raise the temperature of the fuel cell stack to be purged to 65℃~80℃, maintain the temperature at 65℃~80℃, and then set the back pressure of the fuel cell stack to be purged. S03. Introduce fuel gas into the fuel cell stack to be purged, and then apply current to the fuel cell stack to be purged. S04. When the average voltage in the inspection voltage diagram and the impedance value in the high-frequency impedance spectrum trend diagram both tend to be constant, record the purging time and end the purging. In step S01, the performance calibration is achieved by the following method: performing a transformer-on-polarization test on the fuel cell stack to be purged to obtain a polarization curve; and calibrating the performance of the fuel cell stack to be purged based on the performance shown by the polarization curve. In step S02, the back pressure is set to be compatible with the temperature; the pressure of the back pressure is 50 kPa to 100 kPa.
2. The method for determining the degree of low-temperature cold start purging of a fuel cell stack according to claim 1, characterized in that, In step S01, the EIS is an EIS with 1A perturbation; the high-frequency impedance frequency of the EIS is 1000Hz.
3. The method for determining the degree of low-temperature cold start purging of a fuel cell stack according to claim 1, characterized in that, In step S01, the activation is achieved by the following method: the stack to be purged is subjected to gradient loading, with the slope of each loading being 10A / s to 50A / s, and constant current for 2min to 10min for each gradient, and constant current for 1h after loading to the rated electrical density; the above steps are repeated 3 to 6 times.
4. The method for determining the degree of low-temperature cold start purging of a fuel cell stack according to claim 1, characterized in that, In step S03, the humidity of the fuel gas is 0%RH to 40%RH.
5. The method for determining the degree of low-temperature cold start purging of a fuel cell stack according to claim 1, characterized in that, In step S03, the fuel gas is hydrogen and air; air is introduced into the cathode inlet of the fuel cell stack to be purged, and hydrogen is introduced into the anode inlet of the fuel cell stack to be purged.
6. The method for determining the degree of low-temperature cold start purging of a fuel cell stack according to claim 5, characterized in that, In step S03, the current density of the hydrogen gas is 0.5 A / cm². 2 ~1.0A / cm 2 The current density of the air is 0.5 A / cm³. 2 ~1.0A / cm 2 .
7. The method for determining the degree of low-temperature cold start purging of a fuel cell stack according to claim 1, characterized in that, In step S03, according to the metering ratio, the supply flow rate of the anode of the fuel cell stack to be purged is 1.6 to 1.8 of the corresponding current metering ratio; the supply flow rate of the cathode of the fuel cell stack to be purged is 1.8 to 2.0 of the corresponding current metering ratio. The current density of the current load is 0.05 A / cm². 2 ~0.1A / cm 2 .
8. The method for determining the degree of low-temperature cold start purging of a fuel cell stack according to claim 1, characterized in that, In step S04, the purging time is 5 min to 10 min.