A method for activating a fuel cell stack

Abstract

The present invention relates to the technical field of fuel cells, and in particular to an activation method for a fuel cell stack. The activation method provided by the present invention first determines the rated current through polarization testing. In the medium current region, all activations are based on the rated current, making the rated value after activation larger. Subsequently, it rapidly increases in the high current region, avoiding the phenomenon of cathode flooding caused by staying in the high current region for too long. The present invention not only improves the activation time but also greatly enhances the performance of the entire membrane electrode, having broad application prospects. At the same time, the activation method described in the present invention reduces the consumption of hydrogen, lowers the cost, and has broad application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to an activation method for a fuel cell stack. Background Art

[0002] A fuel cell stack is composed of multiple single cells connected in series, plus end plates and current collectors, and is assembled by bundling and bolting methods. After the fuel cell is assembled, it needs to be installed on a test system for performance testing. Before performance testing, the stack needs to be activated. After activation, the overall performance of the stack will gradually increase. When the stack reaches equilibrium, the activation ends. Since the activation mechanism is very complex, it can be summarized as the following points: 1) Complete the humidification process of the proton exchange membrane; 2) Open the micropores with different structures in the catalyst layer to expose more crystal planes of Pt; 3) Construct gas, proton, and water three-phase reaction channels.

[0003] The activation of fuel cells can be classified as follows: 1) Constant current natural activation; 2) Variable current natural activation. Among them, the constant current activation has the worst effect and cannot open the different micropore structures in the catalyst layer to complete the exposure of Pt crystal planes; while the variable current natural activation uses the purging of different currents to change the different micropore structures and improve the activity of the catalyst layer, but the improvement degree is limited. Summary of the Invention

[0004] The purpose of the present invention is to provide an activation method for a fuel cell stack, which greatly improves the performance of the entire membrane electrode.

[0005] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0006] The present invention provides an activation method for a fuel cell stack, including the following steps:

[0007] After purging the cathode and anode of the fuel cell stack with humidified nitrogen respectively, change the humidified nitrogen at the anode to humidified hydrogen and preheat the stack, and then change the humidified nitrogen at the cathode to humidified air and perform a polarization test to obtain the rated current at a standard condition of 0.65V.

[0008] Activate the fuel cell stack: The activation includes a first activation and a second activation performed in sequence; the first activation includes: after adjusting the current of the fuel cell stack to 180 A, adjusting it to the rated current for a first residence, adjusting it to A1 for a second residence, adjusting it to the rated current for a third residence, adjusting it to A2 for a fourth residence, adjusting it to the rated current for a fifth residence, adjusting it to A3 for a sixth residence,..., until the current is adjusted to 360 A; A1, A2, A3,..., and 360 A show a monotonically increasing trend, and the monotonically increasing interval is 30 A; the second activation includes: after adjusting the current of the fuel cell stack from 360 A to 570 A and then performing a residence, reducing the current of the fuel cell stack to 30 A.

[0009] After repeating the above processes of stack preheating and activation, repeat the above process of polarization test.

[0010] Preferably, the humidity of the humidified nitrogen is RH 70%;

[0011] When performing the purge, the purge time is 30 - 40 min; the stoichiometric ratio of the anode is 2.5 - 3, and the anode back pressure is 120 - 140 kPa; the stoichiometric ratio of the cathode is 3.5 - 4, and the cathode back pressure is 90 - 110 kPa;

[0012] The temperature of the fuel cell stack after the purge is 70 - 80 °C.

[0013] Preferably, the humidity of the humidified hydrogen is RH 70%;

[0014] The stoichiometric ratio of the humidified hydrogen at the anode is 2.5 - 3, and the back pressure is 120 - 140 kPa.

[0015] Preferably, the process of stack preheating includes: after adjusting the current of the fuel cell stack from 30 A to 180 A, performing a residence for 300 - 360 s;

[0016] The rising rate of the current is 5 - 15 A / s.

[0017] Preferably, the humidity of the humidified air is RH 70%;

[0018] The stoichiometric ratio of the humidified air at the cathode is 2.5 - 3, and the back pressure is 120 - 140 kPa.

[0019] Preferably, the scanning current for the polarization test is 30 - 570 A, and the scanning rate is 15 A / s.

[0020] Preferably, the residence time corresponding to the currents of A1, A2, A3,..., and 360 A is 30 - 50 s;

[0021] The residence time corresponding to the rated current is 20 to 40 s.

[0022] Preferably, during the first activation process: the humidity of the anode is 50% to 70%, the stoichiometric ratio is 1.8 to 2.5, and the back pressure is 110 to 150 kPa; the humidity of the cathode is 60% to 80%, the stoichiometric ratio is 3 to 3.5, and the back pressure is 90 to 110 kPa.

[0023] Preferably, the residence time after adjusting the current of the fuel cell stack from 360 A to 570 A is 120 to 180 s;

[0024] The rising rate of the current is 15 to 30 A / s.

[0025] Preferably, the number of membrane electrode sheets of the fuel cell stack is 90 to 120, and the power is 30 to 50 kW.

[0026] The present invention provides a method for activating a fuel cell stack, including the following steps: after purging the cathode and anode of the fuel cell stack with humidified nitrogen respectively, changing the humidified nitrogen at the anode to humidified hydrogen and preheating the stack, then changing the humidified nitrogen at the cathode to humidified air and performing a polarization test to obtain the rated current under standard conditions at 0.65 V; activating the fuel cell stack: the activation includes a first activation and a second activation performed in sequence; the first activation includes: after adjusting the current of the fuel cell stack to 180 A, adjusting to the rated current for a first residence, adjusting to A1 for a second residence, adjusting to the rated current for a third residence, adjusting to A2 for a fourth residence, adjusting to the rated current for a fifth residence, adjusting to A3 for a sixth residence,..., until the current is adjusted to 360 A; the A1, A2, A3,..., 360 A show a monotonically increasing trend, and the monotonically increasing interval is 30 A; the second activation includes: after adjusting the current of the fuel cell stack from 360 A to 570 A and performing a residence, reducing the current of the fuel cell stack to 30 A; repeating the above processes of stack preheating and activation, and repeating the above process of polarization test. The present invention first determines the rated current through a polarization test. In the medium current region, all activations are based on the rated current, making the rated value after activation larger, and then rapidly increasing in the high current region, avoiding the phenomenon of cathode flooding caused by staying in the high current region for too long. The present invention not only improves the activation time but also greatly enhances the performance of the entire membrane electrode, having a wide range of application prospects; at the same time, the activation method described in the present invention reduces the consumption of hydrogen and lowers the cost, having a wide range of application prospects. Description of the Drawings

[0027] Figure 1 The polarization curves of the fuel cell stack described in Example 1 before and after activation;

[0028] Figure 2 The polarization curves after activation for the fuel cell stacks described in Examples 1 and 2. Detailed implementation manners

[0029] The present invention provides an activation method for a fuel cell stack, comprising the following steps:

[0030] After purging the cathode and anode of the fuel cell stack with humidified nitrogen respectively, change the humidified nitrogen at the anode to humidified hydrogen and perform stack preheating, then change the humidified nitrogen at the cathode to humidified air and perform polarization testing to obtain the rated current under standard conditions at 0.65V.

[0031] Activate the fuel cell stack: the activation includes a first activation and a second activation performed in sequence; the first activation includes: after adjusting the current of the fuel cell stack to 180A, adjust to the rated current for a first dwell, adjust to A1 for a second dwell, adjust to the rated current for a third dwell, adjust to A2 for a fourth dwell, adjust to the rated current for a fifth dwell, adjust to A3 for a sixth dwell,..., until the current is adjusted to 360A; A1, A2, A3,..., 360A show a monotonically increasing trend, and the monotonically increasing interval is 30A; the second activation includes: after adjusting the current of the fuel cell stack from 360A to 570A and performing a dwell, reduce the current of the fuel cell stack to 30A.

[0032] After repeating the above processes of stack preheating and activation, repeat the above process of polarization testing.

[0033] In the present invention, during the whole process of the activation method, the minimum voltage is preferably set to 0.4V. After it is lower than 0.4V, the system will automatically stop.

[0034] In the present invention, after purging the cathode and anode of the fuel cell stack with humidified nitrogen respectively, change the humidified nitrogen at the anode to humidified hydrogen and perform stack preheating, then change the humidified nitrogen at the cathode to humidified air and perform polarization testing to obtain the rated current under standard conditions at 0.65V.

[0035] In the present invention, the number of membrane electrode sheets of the fuel cell stack is preferably 90 - 120 sheets, more preferably 95 - 115 sheets, and most preferably 100 - 110 sheets; the power of the fuel cell stack is preferably 30 - 50kW, more preferably 35 - 45kW, and most preferably 38 - 42kW.

[0036] Before purging, the present invention preferably conducts airtightness tests on the fuel cell stack in sequence. The present invention has no special limitation on the process of the airtightness test, and the process well-known to those skilled in the art can be adopted. If the airtightness test fails, it is preferred to reassemble the fuel cell stack and conduct the airtightness test until the airtightness test is qualified.

[0037] In the present invention, the humidity of the humidified nitrogen is preferably RH 70%; when conducting the purging, the stoichiometric ratio of the anode is preferably 2.5 - 3, more preferably 2.6 - 2.8; the anode back pressure is preferably 120 - 140 kPa, more preferably 125 - 135 kPa, and most preferably 128 - 132 kPa; the stoichiometric ratio of the cathode is preferably 3.5 - 4, more preferably 3.6 - 3.8; the cathode back pressure is preferably 90 - 110 kPa, more preferably 95 - 105 kPa, and most preferably 98 - 102 kPa; the purging time is preferably 30 - 40 min, more preferably 32 - 38 min, and most preferably 34 - 36 min. In the present invention, the conditions described in the above technical solutions can adjust the temperature of the fuel cell stack to 70 - 80 °C.

[0038] In the present invention, the humidity of the humidified hydrogen is preferably RH 70%; the stoichiometric ratio of the humidified hydrogen at the anode is preferably 2.5 - 3, more preferably 2.6 - 2.8; the back pressure is preferably 120 - 140 kPa, more preferably 125 - 135 kPa, and most preferably 128 - 132 kPa.

[0039] In the present invention, the process of preheating the stack preferably includes: after adjusting the current of the fuel cell stack from 30 A to 180 A, staying for 300 - 360 s; the rising rate of the current is preferably 5 - 15 A / s, more preferably 8 - 12 A / s.

[0040] In the present invention, the function of preheating the stack is to preheat the fuel cell stack, so that the voltage of each membrane electrode sheet is stable, and the stack will not be broken down due to excessive current.

[0041] In the present invention, the humidity of the humidified air is preferably RH 70%; the stoichiometric ratio of the humidified air at the cathode is 2.5 - 3, more preferably 2.6 - 2.8; the back pressure is preferably 120 - 140 kPa, more preferably 125 - 135 kPa, and most preferably 128 - 132 kPa.

[0042] In the present invention, the scanning current of the polarization test is preferably 30 - 570 A, and the scanning rate is preferably 15 A / s.

[0043] After obtaining the rated current under standard conditions at 0.65V, the present invention activates the fuel cell stack: the activation includes first activation and second activation performed in sequence; the first activation includes: after adjusting the current of the fuel cell stack to 180A, adjusting it to the rated current for a first dwell, adjusting it to A1 for a second dwell, adjusting it to the rated current for a third dwell, adjusting it to A2 for a fourth dwell, adjusting it to the rated current for a fifth dwell, adjusting it to A3 for a sixth dwell, ……, until the current is adjusted to 360A; A1, A2, A3, ……, 360A show a monotonically increasing trend, and the interval of the monotonically increasing is 30A; the second activation includes: after adjusting the current of the fuel cell stack from 360A to 570A and performing a dwell, reducing the current of the fuel cell stack to 30A.

[0044] In the present invention, the first activation includes: after adjusting the current of the fuel cell stack to 180A, adjusting it to the rated current for a first dwell, adjusting it to A1 for a second dwell, adjusting it to the rated current for a third dwell, adjusting it to A2 for a fourth dwell, adjusting it to the rated current for a fifth dwell, adjusting it to A3 for a sixth dwell, ……, until the current is adjusted to 360A; A1, A2, A3, ……, 360A show a monotonically increasing trend, and the interval of the monotonically increasing is 30A.

[0045] In the present invention, the dwell time corresponding to the currents of A1, A2, A3, …… and 360A is preferably 30 - 50s, more preferably 35 - 45s, and most preferably 38 - 42s. In the present invention, the dwell time corresponding to the rated current is preferably 20 - 40s, more preferably 25 - 35s, and most preferably 28 - 32s.

[0046] In the present invention, the heating rate from the rated current to A1, A2, A3, …… or 360A is preferably 5 - 15A / s, more preferably 8 - 12A / s.

[0047] In the present invention, during the first activation: the humidity of the anode is preferably 50% - 70%, the stoichiometric ratio is preferably 1.8 - 2.5, and the back pressure is preferably 110 - 150kPa; the humidity of the cathode is preferably 60% - 80%, the stoichiometric ratio is preferably 3 - 3.5, and the back pressure is preferably 90 - 110kPa.

[0048] In the present invention, the process of the first activation is the most important part of the entire activation process, which can enable Pt with different pore structures in the catalyst layer to all exhibit activity and can also reduce platinum oxides.

[0049] In the present invention, during the second activation process, the time for staying after adjusting the current of the fuel cell stack from 360 A to 570 A is preferably 120 - 180 s, more preferably 130 - 170 s, and most preferably 140 - 150 s; the rising rate of the current is preferably 15 - 30 A / s, more preferably 18 - 26 A / s, and most preferably 21 - 23 A / s.

[0050] In the present invention, during the second activation process: the humidity of the anode is preferably 50% - 70%, the stoichiometric ratio is preferably 1.8 - 2.5, and the back pressure is preferably 110 - 150 kPa; the humidity of the cathode is preferably 60% - 80%, the stoichiometric ratio is preferably 3 - 3.5, and the back pressure is preferably 90 - 110 kPa.

[0051] In the present invention, the number of times of repeating the above stack preheating and activation is preferably 3 - 5 times.

[0052] Note: The "stoichiometric ratio" involved in the above activation process can be understood as the volume ratio of the purge gas to air.

[0053] The activation method of the fuel cell stack provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0054] Example 1

[0055] Assemble a 90 - membrane - electrode stack with a power of 30 kW, and conduct an airtightness test. After the airtightness test is qualified, conduct a stack - loading test;

[0056] Switch the cathode and anode gas paths of the fuel cell stack to humidified nitrogen (both with a humidity of RH 70%). The stoichiometric ratio of the cathode is 3.5, the cathode back pressure is 90 kPa, the stoichiometric ratio of the anode is 3, and the anode back pressure is 130 kPa, and operate for 30 min; after heating up to 78°C, switch the anode to humidified hydrogen (with a humidity of RH 70%) for stack preheating, and keep other parameters unchanged (including the stoichiometric ratio and back pressure). Adjust the current from 30 A to 180 A at a rate of 5 A / s and stay for 300 s; then switch the humidified nitrogen at the cathode to humidified air (with a humidity of 70%) for polarization test, and keep other parameters unchanged (including the stoichiometric ratio and back pressure). The scanning current of the polarization test is 30 - 570 A, and the scanning rate is 15 A / s, to obtain the polarization curve in the pre - activation stage (as Figure 1 shown), and obtain the rated current of 480 A under standard conditions at 0.65 V according to the polarization curve;

[0057] Set the cathode stoichiometry to 3.5, the cathode back pressure to 150 kPa, the anode stoichiometry to 3, the anode back pressure to 120 kPa, and the humidity of the cathode and anode to 70%; perform the first activation on the fuel cell stack. The process of the first activation is as follows: After adjusting the current of the fuel cell stack to 180 A, then adjust it to 480 A at a rate of 15 A / s and stay for 30 s, adjust the current to 210 A and stay for 30 s, then adjust it to 480 A at a rate of 15 A / s and stay for 30 s, adjust the current to 240 A and stay for 30 s, then adjust it to 480 A at a rate of 15 A / s and stay for 30 s, adjust the current to 270 A and stay for 30 s, and so on, until the current is adjusted to 360 A and stays for 300 s (as shown in Table 1); perform the second activation. The process of the second activation is as follows: Adjust from 360 A to 480 A at a rate of 30 A / s and stay for 120 s, then reduce the current to 30 A;

[0058] Repeat the above processes of stack preheating and activation four times, repeat the above process of polarization test, and the polarization curve is as Figure 1 shown;

[0059] Table 1 Program table of the first activation described in Example 1

[0060]

[0061] Figure 1 are the polarization curves of the fuel cell stack described in Example 1 before and after activation. It can be seen from Figure 1 that before and after activation, at a rated voltage of 0.65 V, the current density increases from 1.6 A / cm 2 to 1.72 A / cm 2 . It proves that the activation method described in the present invention has a very high improvement in activation performance in the short term.

[0062] Example 2

[0063] Assemble a stack of 90 membrane electrode assemblies with a power of 30 kW, and perform an airtightness test. After the airtightness test meets the standard, perform a stack test;

[0064] Switch the cathode and anode gas paths of the fuel cell stack to humidified nitrogen (both with a humidity of 70%). The stoichiometric ratio of the cathode is 3.8, the cathode back pressure is 100 kPa, the stoichiometric ratio of the anode is 2.8, and the anode back pressure is 120 kPa. Operate for 40 min. After heating to 80 °C, switch the anode to humidified hydrogen (humidity of 70%) for stack preheating, and keep other parameters unchanged (including stoichiometric ratio and back pressure). Adjust the current from 30 A to 180 A at a rate of 10 A / s and stay for 360 s. Then switch the humidified nitrogen at the cathode to humidified air (humidity of 70%) for polarization testing, and keep other parameters unchanged (including stoichiometric ratio and back pressure). The scanning current of the polarization testing is 30 - 570 A, and the scanning rate is 10 A / s to obtain the polarization curve in the pre-activation stage. According to the polarization curve, the rated current at a standard condition of 0.65 V is 450 A;

[0065] Set the cathode stoichiometric ratio to 3.5, the cathode back pressure to 140 kPa, the anode stoichiometric ratio to 2.5, the anode back pressure to 110 kPa, the humidity of the cathode to 80%, and the humidity of the anode to 70%. After adjusting the current of the fuel cell stack to 180 A, then adjust it to 450 A at a rate of 10 A / s and stay for 40 s, adjust the current to 210 A and stay for 40 s, then adjust it to 450 A at a rate of 10 A / s and stay for 40 s, adjust the current to 240 A and stay for 40 s, then adjust it to 450 A at a rate of 10 A / s and stay for 30 s, adjust the current to 270 A and stay for 40 s, and so on until the current is adjusted to 360 A. After staying for 360 s, adjust it from 360 A to 570 A at a rate of 20 A / s and stay for 180 s, and then reduce the current to 30 A;

[0066] Repeat the above processes of stack preheating and activation four times, and repeat the above process of polarization testing.

[0067] Figure 2 For the polarization curves of the fuel cell stacks after activation described in Examples 1 and 2, from Figure 2 it can be seen that by comparing the polarization curves of Examples 1 and 2 after activation, at 0.65 V, the current density is within the range of 1.72 A / cm 2 which proves that the activation efficiency is very high and the performance is stable. Thus, it can be seen that the activation method described in the present invention has a broad application prospect.

[0068] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for activating a fuel cell stack, characterized in that, It includes the following steps: After purging the cathode and anode of the fuel cell stack with humidified nitrogen respectively, change the humidified nitrogen at the anode to humidified hydrogen and preheat the stack, then change the humidified nitrogen at the cathode to humidified air and conduct a polarization test to obtain the rated current under standard conditions at 0.65V; Activate the fuel cell stack: The activation includes a first activation and a second activation carried out in sequence; The first activation includes: After adjusting the current of the fuel cell stack to 180A, adjust it to the rated current for the first residence, adjust it to A1 for the second residence, adjust it to the rated current for the third residence, adjust it to A2 for the fourth residence, adjust it to the rated current for the fifth residence, adjust it to A3 for the sixth residence,..., until the current is adjusted to 360A; The A1, A2, A3,..., 360A show a monotonically increasing trend, and the monotonically increasing interval is 30A; The second activation includes: After adjusting the current of the fuel cell stack from 360A to 570A and carrying out a residence, reduce the current of the fuel cell stack to 30A; After repeating the processes of stack preheating and activation, repeat the process of the above polarization test.

2. The activation method according to claim 1, wherein The humidity of the humidified nitrogen is RH 70%; When conducting the purging, the purging time is 30 - 40 min; The stoichiometric ratio of the anode is 2.5 - 3, and the anode back pressure is 120 - 140 kPa; The stoichiometric ratio of the cathode is 3.5 - 4, and the cathode back pressure is 90 - 110 kPa; The temperature of the fuel cell stack after purging is 70 - 80 °C.

3. The activation method according to claim 1, characterized in that, The humidity of the humidified hydrogen is RH 70%; The stoichiometric ratio of the humidified hydrogen at the anode is 2.5 - 3, and the back pressure is 120 - 140 kPa.

4. The activation method according to claim 1 or 3, characterized in that, The process of stack preheating includes: After adjusting the current of the fuel cell stack from 30A to 180A, carry out a residence for 300 - 360 s; The rising rate of the current is 5 - 15 A / s.

5. The activation method according to claim 1, characterized in that, The humidity of the humidified air is RH 70%; The stoichiometric ratio of the humidified air at the cathode is 2.5 - 3, and the back pressure is 120 - 140 kPa.

6. The activation method according to claim 1 or 5, characterized in that, The scanning current of the polarization test is 30 - 570A, and the scanning rate is 15 A / s.

7. The activation method according to claim 1, characterized in that, The residence time corresponding to the currents of A1, A2, A3,..., and 360A is 30 - 50 s; The residence time corresponding to the rated current is 20 - 40 s.

8. The activation method according to claim 1 or 7, characterized in that, During the first activation process: The humidity of the anode is 50% - 70%, the stoichiometric ratio is 1.8 - 2.5, and the back pressure is 110 - 150 kPa; The humidity of the cathode is 60% - 80%, the stoichiometric ratio is 3 - 3.5, and the back pressure is 90 - 110 kPa.

9. The activation method according to claim 1, wherein The residence time after adjusting the current of the fuel cell stack from 360A to 570A is 120 - 180 s; The rising rate of the current is 15 - 30 A / s.

10. The activation method according to claim 1, wherein The number of membrane electrode sheets of the fuel cell stack is 90 - 120, and the power is 30 - 50 kW.

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