Method for detecting local mass transfer state of fuel cell and fuel cell

Abstract

The invention relates to a fuel cell local mass transfer state detection method and a fuel cell, and the method comprises the following steps: continuously measuring the current and voltage of each region of a partitioned fuel cell, and executing the following steps: applying a first load to the partitioned fuel cell until the cell voltage stops fluctuating, and applying a second load to the partitioned fuel cell in a step mode; calculating a gas concentration index of each region according to the current change process of each region of the partitioned fuel cell; and judging the mass transfer state of each region according to the gas concentration index of each region. Compared with the prior art, the method has the advantages of high anti-interference performance, high accuracy, high calculation speed and the like.

Description

Technical Field

[0001] The present invention relates to the field of fuel cells, and in particular to a method for detecting a local mass transfer state of a fuel cell and a fuel cell. Background Art

[0002] Automobile manufacturers and parts suppliers are committed to the research and development and promotion of new energy vehicles. Pure electric vehicles, hybrid vehicles and fuel cell vehicles are developing rapidly. Among them, proton exchange membrane fuel cells (PEMFC) have the advantages of zero emissions, no pollution, high efficiency, and low operating temperature, and are used as a power source for fuel cell vehicles. When used as a fixed energy source, the life of PEMFC can reach 30,000 hours, but when used as a vehicle power source, the life is only 2,500-3,000 hours. The life of fuel cells has seriously restricted the large-scale commercialization of fuel cell vehicles.

[0003] Insufficient supply of reaction gas and uneven internal gas distribution caused by complex and changeable vehicle operating conditions are one of the important reasons for the decline in fuel cell life. Lack of gas can lead to corrosion of carbon carriers and loss of catalysts, causing serious decline in fuel cell life and performance. To reduce the decline caused by lack of gas, it is necessary to accurately characterize the local gas mass transfer state.

[0004] At present, when designing the operating conditions of fuel cells, the output performance is mainly considered, and the voltage and current parameters are used to evaluate whether the fuel cell operating conditions are good or not. However, these overall parameters are difficult to characterize the local characteristics of the fuel cell. In the characterization methods of the local performance of fuel cells, more attention is paid to the current density distribution of the fuel cell. Since the current density is affected by activation polarization, ohmic polarization, and concentration polarization, it cannot accurately reflect the internal mass transfer situation. For example, there will be situations such as poor mass transfer in some locations, but due to the high contact pressure, the ohmic resistance is low and the current does not show a significant decrease, resulting in the failure of the diagnosis of the local mass transfer situation. Therefore, a characterization method that can decouple the mass transfer capacity from other factors is proposed, which has positive significance for the design of fuel cell flow channels and the optimization of operating conditions. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a method for detecting the local mass transfer state of a fuel cell and a fuel cell.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A method for detecting a local mass transfer state of a fuel cell comprises the following steps:

[0008] A1: continuously measuring the current and voltage of each area of ​​the partitioned fuel cell, and executing: applying a first load to the partitioned fuel cell until the battery voltage stops fluctuating, and then applying a second load to the partitioned fuel cell in a step manner;

[0009] A2: Calculate the gas concentration index of each area according to the current change process of each area of ​​the partitioned fuel cell;

[0010] A3: Determine the mass transfer status of each area based on the gas concentration index of each area.

[0011] Furthermore, the parameters of the current change process include: the current value of each area at each moment, the moment when the second load is applied, and the moment when the current response reaches a steady state after the second load is applied; the gas concentration index is calculated based on the moment when the second load is applied and the moment when the current response reaches a steady state after the second load is applied, and the difference in gas concentration between each area is judged based on the current value of each area at each moment.

[0012] Furthermore, the calculation expression of the gas concentration index is:

[0013]

[0014] Where t3 is the time when the current response reaches a steady state, t1 is the time when the load is applied, S is the area of ​​the current partition of the partitioned fuel cell, and I static is the current value of the current partition when the current response reaches the steady state after the second load, I phase1 It is the current value of the current partition when the battery voltage stops fluctuating after the first load is applied.

[0015] Furthermore, when the gas concentration index is a positive value, the gas reserve is sufficient; when the gas concentration index is a negative value, the gas reserve is insufficient.

[0016] Furthermore, the first load is 0.05A·cm -2 , the second load is 1A·cm -2 .

[0017] Furthermore, after the cell voltage stops fluctuating, if the gas concentration index decreases in each partition along the flow channel direction of the partitioned fuel cell, it indicates that the gas distribution in the partitioned fuel cell is normal.

[0018] Furthermore, the current and voltage of each area of ​​the partitioned fuel cell satisfy:

[0019]

[0020] Where U n is the voltage of region n, I n is the current in region n, U is the plate voltage, I loadis the external load current.

[0021] Furthermore, the partitioned fuel cell is a proton exchange membrane fuel cell.

[0022] Furthermore, the current response of the partitioned fuel cell includes a gas transport current response, a membrane water state rebalancing current response and a mechanical pressure current response.

[0023] A second aspect of the present invention is a fuel cell, which is divided into multiple regions, each region is provided with an air duct, and when the fuel cell is working, the air intake of each region is adjusted according to the gas concentration index obtained by any of the above fuel cell local mass transfer state detection methods.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1) The present invention utilizes the time difference between the dynamic response time caused by gas transmission and the response time caused by water redistribution, and proposes to use current as an indicator to evaluate gas concentration, so as to quickly and accurately evaluate gas concentration, which is more conducive to the optimization design of flow channels and working conditions for improving gas mass transfer capacity, and is of great significance to the research on improving fuel cell performance and durability.

[0026] 2) The present invention can effectively decouple the gas mass transfer process from other polarization processes, such as the influence of intake air humidity on the polarization process, so that the result is not interfered by other processes and has strong anti-interference ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The figure is a flow chart of the method of the present invention.

[0028] Figure 2 Schematic diagram of the current change process in the embodiment.

[0029] Figure 3 It is a comparison chart of gas concentration indicators in various regions in the embodiment.

[0030] Figure 4 This is a graph showing the change in gas concentration index with humidity and cathode stoichiometric ratio. DETAILED DESCRIPTION

[0031] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0032] Example 1

[0033] The present invention is a method for detecting the local mass transfer state of a fuel cell and a fuel cell, such as Figure 1 As shown, the method comprises the following steps:

[0034] A1: continuously measuring the current and voltage of each area of ​​the partitioned fuel cell, and executing: applying a first load to the partitioned fuel cell until the battery voltage stops fluctuating, and then applying a second load to the partitioned fuel cell in a step manner;

[0035] A2: Calculate the gas concentration index of each area according to the current change process of each area of ​​the partitioned fuel cell;

[0036] A3: Determine the mass transfer status of each area based on the gas concentration index of each area.

[0037] Principle of implementing the scheme of the present invention:

[0038] A fuel cell monolithic chip can be regarded as a structure composed of multiple small-area monolithic chips connected in parallel. After an external load is connected, ignoring the potential difference on the plate surface, the relationship between the current and voltage in each area can be expressed as:

[0039]

[0040] Where U n is the voltage of region n, I n is the current in region n, U is the plate voltage, I load is the external load current. When the voltage is U, the current reflects the polarization state of the region. In static state, since the polarization state is affected by the three processes of activation polarization, ohmic polarization, and concentration polarization, it is impossible to distinguish the influence of each process, and it is difficult to characterize the gas mass transfer state.

[0041] Under dynamic loading, since the proton exchange membrane hydration process and the gas transfer process have different magnitudes of time parameters, the response of the fuel cell after loading can be divided into three main parts: the current response generated by the gas transfer process, the current response generated by the membrane water state rebalance process, and the current response generated by the constant mechanical pressure, etc. The current response process generated by gas transfer and membrane water state rebalance is dynamic and changes with time, while the current response generated by mechanical pressure is static.

[0042] The dynamic response time caused by gas transmission is on the order of 1 second, and the response time caused by water redistribution is on the order of 10 seconds. Therefore, the current dynamic response can be divided into three stages: gas response stage, water redistribution stage, and steady-state stage. Within 1 second after loading, the water state does not have time to change and cannot dominate the response. By capturing the current response within 1 second, the influence of the water state can be excluded and the state related to gas transmission can be obtained.

[0043] The specific implementation method is:

[0044] First, a small load is applied to the partitioned fuel cell, which in this embodiment is 0.05 A·cm-2 After the fuel cell is working stably, that is, the voltage no longer fluctuates, a larger load is applied to the fuel cell in a step-by-step manner. In this embodiment, the load is 1A·cm -2 After the step load is applied, the current response in each region shows a trend of first increasing (or first decreasing) and then flattening.

[0045] like Figure 2 As shown, the present invention applies a current step at time t1, and the current in the S1 and S2 regions shows a trend of first rising and then flattening, and the current in the S3 and S4 regions shows a trend of first falling and then flattening. In addition, the amplitude of the rise or fall is different, and the current change speed begins to decline at time t2. The rising and falling trends and amplitude values ​​within t1 and t3 can reflect the gas transmission situation.

[0046] Therefore, the present invention needs to record the current value of each area at each time, the time when the second load is applied, and the time when the current response reaches a steady state after the second load is applied; the gas concentration index is calculated according to the time when the second load is applied and the time when the current response reaches a steady state after the second load is applied. The calculation expression of the gas concentration index is:

[0047]

[0048] Where t3 is the time when the current response reaches a steady state, t1 is the time when the load is applied, S is the area of ​​the current partition of the partitioned fuel cell, and I static is the current value of the current partition when the current response reaches the steady state after the second load, I phase1 is the current value of the current partition when the battery voltage stops fluctuating after the first load is applied. This index is obtained by calculating the integral of the difference between the transient current and the steady-state current, taking into account the two indicators of response amplitude and steady-state time. t The value reflects the mass transfer capacity of the area, Q t When it is a negative value, it indicates that the gas is insufficient and it is difficult to maintain a high current load. The current decreases and Q t A positive value indicates that the current rises after loading, the gas reserve is sufficient, and the mass transfer capacity is good.

[0049] During the current loading process, the load current increases from a small value to a large value. When the load is small, the gas supply in each area is relatively sufficient. At the moment of applying the load, due to the delay in gas consumption, the current in each area can reach a higher value. Figure 3As shown in the figure, as the load continues, the gas continues to be consumed, and the gas concentration in the upstream area decreases mainly due to the consumption in this area, while the change in the gas concentration in the downstream area is the superposition of the upstream consumption and its own consumption, with a larger amplitude. The decrease in downstream concentration leads to an increase in the downstream mass transfer resistance, thereby increasing the concentration polarization. Therefore, under the same external voltage, the downstream current gradually decreases. However, due to the external constant current, in order to meet the total load requirements, the current in the area with relatively good upstream mass transfer capacity increases. This process is the current redistribution process after loading, which actually reflects the gas concentration and mass transfer capacity in different regions. In addition, the higher the concentration, the faster the diffusion process of the gas from the flow channel to the reaction interface, which leads to a faster current redistribution process. Therefore, the dynamic current response amplitude and steady-state time after loading can reflect the gas concentration and mass transfer capacity of the area.

[0050] like Figure 4 As shown, the experiment was repeated in turn under different intake air humidity and intake air flow rates, and the standard deviation of Qt in all areas was calculated to obtain the standard deviation of Qt under all working conditions. The standard deviation of Qt reflects the uneven distribution of the mass transfer capacity obtained by diagnosis. It can be seen that the standard deviation of Qt changes significantly with the cathode stoichiometric ratio, but hardly changes with the change of intake air humidity. This shows that Qt is closely related to the gas concentration and is not affected by the membrane hydration process, which proves the effectiveness of the decoupling process of this method and can avoid the interference of humidity on the evaluation results. This embodiment successfully characterizes the mass transfer situation within the surface of the fuel cell.

[0051] Based on the method of the present invention, the present invention also designs a fuel cell, in which each partition of the fuel cell is provided with an independent air intake duct. When the fuel cell is working, the gas concentration index of each area is calculated according to the method of the present invention, and the air intake volume of each air intake duct is adjusted in a targeted manner, thereby intervening in gas deficiency, thereby reducing the battery performance degradation and shortened service life caused by gas deficiency.

[0052] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for detecting the local mass transfer state of a fuel cell, characterized in that: The following steps are involved: A1: continuously measuring the current and voltage of each area of ​​the partitioned fuel cell, and executing: applying a first load to the partitioned fuel cell until the battery voltage stops fluctuating, and then applying a second load to the partitioned fuel cell in a step manner; A2: Calculate the gas concentration index of each area according to the current change process of each area of ​​the partitioned fuel cell; A3: Determine the mass transfer status of each area based on the gas concentration index of each area.

2. A method for detecting a local mass transfer state of a fuel cell according to claim 1, characterized in that: The parameters included in the current change process include: the current value of each area at each moment, the moment when the second load is applied, and the moment when the current response reaches a steady state after the second load is applied; the gas concentration index is calculated according to the moment when the second load is applied and the moment when the current response reaches a steady state after the second load is applied, and the gas concentration difference between each area is judged according to the current value of each area at each moment.

3. A method for detecting a local mass transfer state of a fuel cell according to claim 2, characterized in that: The calculation expression of the gas concentration index is: Where t3 is the time when the current response reaches a steady state, t1 is the time when the load is applied, S is the area of ​​the current partition of the partitioned fuel cell, and I static is the current value of the current partition when the current response reaches the steady state after the second load, I phase1 It is the current value of the current partition when the battery voltage stops fluctuating after the first load is applied.

4. A method for detecting a local mass transfer state of a fuel cell according to claim 3, characterized in that: When the gas concentration index is a positive value, the gas reserve is sufficient; when the gas concentration index is a negative value, the gas reserve is insufficient.

5. A method for detecting a local mass transfer state of a fuel cell according to claim 1, characterized in that: The first load is 0.05A·cm -2 , the second load is 1A·cm -2 .

6. A method for detecting a local mass transfer state of a fuel cell according to claim 1, characterized in that: When the cell voltage stops fluctuating, if the gas concentration index decreases in each partition along the flow direction of the partitioned fuel cell, it means that the gas distribution in the partitioned fuel cell is normal.

7. A method for detecting a local mass transfer state of a fuel cell according to claim 1, characterized in that: The current and voltage of each area of ​​the partitioned fuel cell meet the following requirements: Where U n is the voltage of region n, I n is the current in region n, U is the plate voltage, I load is the external load current.

8. A method for detecting a local mass transfer state of a fuel cell according to claim 1, characterized in that: The partitioned fuel cell is a proton exchange membrane fuel cell.

9. A method for detecting a local mass transfer state of a fuel cell according to claim 8, characterized in that: The current response of the partitioned fuel cell includes a gas transmission current response, a membrane water state rebalancing current response and a mechanical pressure current response.

10. A fuel cell, characterized in that: The fuel cell is divided into multiple areas, each area is provided with an airway, and when the fuel cell is working, the air intake of each area is adjusted according to the gas concentration index obtained by the fuel cell local mass transfer state detection method as described in any one of claims 1-9.

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