A method for improving voltage consistency and starting performance of a proton exchange membrane fuel cell during low-temperature starting

Abstract

The application discloses a method for improving voltage consistency and starting performance in a low-temperature starting process of a proton exchange membrane fuel cell, which comprises the following steps: after a stable OCV is established before a low-temperature starting load of a fuel cell stack, a very low load current is applied for a period of time; and after the fuel cell stack voltage continuously rises for 3-10 seconds, subsequent loading is performed. The method has the advantages that: the current application time is short, the overall low-temperature starting speed is not affected; the load current is very low, and the electrode is not damaged; the phenomenon that the single-cell voltage is too low due to uneven initial water vapor distribution in the fuel cell stack at the initial loading stage is avoided, and the voltage consistency and low-temperature starting performance in the low-temperature starting process of the fuel cell stack are improved. The method is suitable for all low-temperature starting processes of fuel cells, and is simple to operate without any modification of the fuel cell system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of proton exchange membrane fuel cells, and particularly relates to a method for improving voltage consistency and starting performance of proton exchange membrane fuel cells in low-temperature starting process. BACKGROUND

[0002] The low-temperature starting performance of proton exchange membrane fuel cells has become a basic performance indicator for fuel cell applications. In a low-temperature environment, quickly and safely starting the fuel cell not only affects the overall service life of the stack, but also seriously affects the driving experience of the passenger. The core problem of low-temperature starting is the water and heat management problem in the battery during the starting process. At present, most of the patents are from the perspective of improving the heat generation of the fuel cell or providing additional heat to improve the low-temperature starting performance of the fuel cell. For example, Chinese patents CN109904488A, CN111180758A and CN111987336A disclose methods of providing heat to the stack by using electrically heated end plates or coolants; Chinese patents CN113675442A, CN108832158A and CN106558713B disclose methods of inputting heat to the stack by using hydrogen and oxygen catalytic combustion; Chinese patents CN105702979A, CN109921066A and CN111740132A disclose various starting methods of controlling the load current. Although the above methods are very helpful in improving the low-temperature starting ability of the fuel cell. However, due to different initial conditions inside the stack, the water vapor distribution near the end plate or in some cells in the stack is uneven, and the voltage of a single cell in the stack is prone to be too low at the initial stage of starting, the voltage consistency is poor, which causes the stack to alarm and directly leads to starting failure, and in severe cases, the polarity is reversed. In view of this problem, the present application combines experiments with practical applications and proposes a method for improving the voltage consistency and starting performance of proton exchange membrane fuel cells in low-temperature starting process. The method applies a very low current load for a period of time at the initial stage of starting to balance the water vapor distribution inside the stack, which can effectively avoid the situation of too low voltage at the initial stage of loading, and improve the voltage consistency and starting performance of the stack. SUMMARY

[0003] The purpose of the present application is to make up for the deficiencies of the prior art and provide a method for improving the voltage consistency and starting performance of proton exchange membrane fuel cells in low-temperature starting process.

[0004] The specific technical scheme of the present application is: a method for improving the voltage consistency and starting performance of proton exchange membrane fuel cells in low-temperature starting process, including establishing a stable OCV before the low-temperature starting load of the stack, controlling the load to make the stack output a current of 5-10 mA / cm 2 for a period of time, and running the subsequent starting program after detecting that the voltage of the stack continuously rises for 3-10 s.

[0005] The process of establishing OCV before starting the fuel cell stack refers to the process from starting to pass the reaction gas to the voltage of the stack reaching the stable open circuit voltage;

[0006] Preferably, the extremely low current load current range is 5-10 mA / cm2;

[0007] Further, in the above technical solution, the duration of the extremely low load current applied for a period of time is determined by the detection result of the stack voltage, specifically, when the stack voltage is detected continuously for 3-10 s, the process is stopped;

[0008] Further, in the above technical solution, the low-temperature starting method is suitable for a low-temperature environment of-5 to-40℃ for low-temperature starting;

[0009] Further, in the above technical solution, a voltage sensor is arranged on the fuel cell stack to measure the voltage of each single cell;

[0010] Further, in the above technical solution, the fuel cell control system collects voltage data and issues subsequent starting operation instructions at the same time;

[0011] Further, in the above technical solution, the subsequent starting program includes but is not limited to making the stack follow a specific loading program for loading;

[0012] Further, in the above technical solution, the starting process further includes providing heat to the stack, and at this time, the low-temperature starting temperature can be further reduced to-20 to-70℃.

[0013] Further, in the above technical solution, the method further includes purging and removing water after the battery is powered off.

[0014] The beneficial effects of the present application are:

[0015] (1) A low load current is applied for a period of time before the fuel cell stack is formally loaded and started, which makes the electrode internal ionomer pre-wet, and the internal battery is judged to reach a suitable starting state according to the continuous rise of the stack voltage for a period of time (3-10 s), which avoids the phenomenon of single low caused by poor voltage consistency due to uneven initial water content distribution in the battery, and improves the voltage consistency and the probability of successful starting in the low-temperature starting process of the fuel cell;

[0016] (2) The load current is extremely low, and the small amount of water produced is absorbed by the ionomer in the electrode, which does not cause freezing and electrode performance degradation, and at the same time, the short loading time does not affect the overall starting speed;

[0017] (3) Strong applicability, suitable for all low-temperature starting loading processes, especially when the starting temperature is lower than -20℃;

[0018] (4) Simple operation, the related operation can be completed according to the existing fuel cell system without any modification to the existing fuel cell system. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The starting process for applying a low current load for a period of time before starting loading at -15℃.

[0020] Figure 2 The starting process for directly loading at -15℃.

[0021] Figure 3 The stack voltage in the starting process for applying a low current load for a period of time before starting loading at -20℃.

[0022] Figure 4 The stack voltage in the starting process for directly loading at -20℃.

[0023] Figure 5 The consistency of the stack voltage in the starting process for applying a low current load for a period of time before starting loading at -20℃. DETAILED DESCRIPTION

[0024] Example 1

[0025] The embodiments of the present application will be described in detail below with reference to the accompanying drawings. The experimental object is a metal bipolar plate proton exchange membrane fuel cell stack composed of 46 single cells, and the fuel cell stack is provided with voltage inspection. After the stack is parked, it is purged of water through a predetermined purging program, and is placed in an environmental bin for more than 12h. The environmental temperature is -15℃, and the specific method for starting is as follows: air and hydrogen are respectively introduced into the cathode and anode of the stack, and after the stack establishes a stable OCV (referring to the process from the start of introducing the reaction gas to the stable open circuit voltage of the stack voltage), the load is controlled to make the stack work at an output current of 5mA / cm 2 ) for 8s, and then loaded at a loading rate of 30-50mA / (s·cm 2 ) until the starting is completed.

[0026] As Figure 1As shown, after the stack establishes a stable OCV, a current of 5mA / cm^2 is applied. At this time, the stack voltage decreases in a stepwise manner, then begins to stabilize and increase. During the entire startup process, the lowest voltage of a single cell appears on the 46th cell, which is closer to the anode plate, and the lowest value is higher than 0.2V. The lowest voltage of the 1st cell, which is closer to the cathode plate, is higher than 0.3V. The voltage is safe and healthy throughout the startup process.

[0027] Comparative Example 1

[0028] The fuel cell stack and ambient temperature in Comparative Example 1 were exactly the same as in Example 1. The difference in the startup method was that after the fuel cell stack established a stable OCV, Comparative Example 1 did not apply a very low load current. Instead, it directly performed a normal loading startup according to a preset loading program. The specific process was as follows: first, a current of 10-20 mA / (s·cm) was applied. 2 Loading at a rate of 8 seconds for 8 seconds, then at 30-50 mA / (s·cm) 2 The loading rate is adjusted to load until startup ends, from... Figure 2 As can be seen, as loading began immediately after the establishment of OCV, the battery voltage dropped rapidly. The 46th cell dropped to 0V directly at 7s, causing the stack to alarm and fail to start. It is worth noting that although the average voltage was close to that of Example 1, the stack had to be shut down due to the occurrence of a single low voltage, otherwise it could have caused serious consequences such as reverse polarity burning of the stack.

[0029] Example 2

[0030] Example 2 describes the startup process of a fuel cell stack (identical to that in Example 1) at -20°C. After establishing a stable OCV before startup, a load current of 5 mA / cm² was applied for 6 seconds. Figure 3 It can be seen that after applying a load current of 5 mA / cm², the voltage of each section of the fuel cell stack rapidly decreased and stabilized after 3 seconds, then rose continuously over the next 3 seconds. Subsequently, a low-temperature start-up was performed according to the set loading program. The specific process was as follows: first, a load current of 10-20 mA / (s·cm²) was applied... 2 Loading at a rate of 8 seconds for 8 seconds, then at 30-50 mA / (s·cm) 2 The loading rate is adjusted to load until startup ends, from... Figure 3 As can be seen, the voltage of each cell in the stack was relatively consistent during the subsequent loading process, and no cell voltage was too low during the entire startup process, indicating a safe and stable startup.

[0031] Comparative Example 2

[0032] Comparative Example 2 is a comparative example of Example 2, which is different from Example 2 in that the loading is directly performed at the initial stage, i.e. after the establishment of a stable OCV of the stack, a very low load current is not applied, but a normal loading start is directly performed according to a preset loading program, and the specific process is as follows: first, 10-20 mA / (s·cm 2 ) of the loading rate is loaded for 8 s, and then 30-50 mA / (s·cm 2 ) of the loading rate is loaded to the end of the start. Figure 4 It can be clearly seen that the consistency of the stack voltage in Comparative Example 2 is obviously poorer than that in Example 3, and the minimum voltage is reduced to below 0.2 V. Figure 5 The consistency of the stack voltage in the start process in Example 2 and Comparative Example 2 is shown by the voltage variance, and it can be clearly seen that in the initial stage of loading, the stack voltage will fluctuate obviously, and direct loading is easy to cause the voltage of some battery to be too low, and after the method described in the application is used, this stage can be perfectly avoided, so that the stack voltage distribution is more uniform, the fluctuation is smaller, and the low-temperature start performance of the fuel cell stack is improved.

Claims

1. A method for improving voltage consistency and start-up performance of a proton exchange membrane fuel cell during low temperature start-up, characterized by, Before the low temperature start-up of the stack, when the stable OCV is established, the load is controlled to make the stack output a current of 5-10 mA / cm 2 for a period of time, and when it is detected that the voltage of the stack continuously rises for 3-10 s, the subsequent start-up procedure is run. The establishing stable OCV refers to a process from starting to input reaction gas to reaching stable open circuit voltage of the stack voltage; The low-temperature environment for low-temperature starting is -5 to -40 ℃.

2. The method of claim 1, wherein, The fuel cell stack is provided with a voltage sensor for measuring the voltage of each single cell.

3. The method of claim 1, wherein, The starting process further includes providing heat to the stack, and the low-temperature starting temperature can be further reduced to -70 ℃.

4. The method of claim 1, wherein, The battery is purged to remove water after the parking.

Images