Method for reducing high potential after shutdown of electrolytic cell

Abstract

The invention provides a method for reducing the high potential after shutdown of an electrolytic cell, and belongs to the technical field of hydrogen production through water electrolysis. The electrolytic cell in a specific placement mode is adopted for hydrogen production operation, the electrolytic cell is laterally placed, namely, the membrane electrode of the electrolytic cell faces the vertical direction, gas generated in the operation process floats upwards to the main pipe opening side to be accumulated under the action of buoyancy, and the gas accumulation position is not located in an active area of the membrane electrode; and a two-step purging mode is combined, so that the bubble discharging speed can be remarkably increased, the purging time is greatly shortened, and the problem of high potential after the electrolytic cell is shut down under high current density is effectively solved.

Description

Technical Field

[0001] This invention relates to the field of water electrolysis for hydrogen production, and in particular to a method for reducing high potential after an electrolyzer is shut down. Background Technology

[0002] Proton exchange membrane electrolysis (PEMWE) for hydrogen production is currently the lowest carbon emission process among various hydrogen source options, and therefore it has received widespread attention in green hydrogen production technologies. Furthermore, it boasts advantages such as fast response speed, adaptability to wide power fluctuations, and high flexibility. Therefore, PEMWE technology has a very broad application prospect.

[0003] While PEM electrolyzers hold great promise, the current hydrogen production per cell is generally low, ranging from 10 to 100 Nm³. 3 The range is very small, with very few reaching 200 Nm. 3 The above. The hydrogen production capacity of alkaline electrolyzers is all around 1000 Nm³. 3 In summary, PEM electrolyzers still lag behind alkaline electrolyzers in hydrogen production capacity. The future trend for high hydrogen production in PEM electrolyzers lies in increasing the number of electrolyzer cells and the active area of ​​each cell. Furthermore, the overall operating point will also be increased accordingly.

[0004] As the number of chambers and their active area increase, and even the operating point rises, a large number of bubbles are generated inside. Removing these bubbles becomes a pressing issue. Failure to remove them promptly will cause the electrolyzer to maintain a high potential even after shutdown, affecting its durability. This is related to the residual hydrogen and oxygen inside; these two gases will continue to cause galvanic cell reactions within the electrolyzer, and prolonged high voltage will reduce the lifespan of the proton exchange membrane.

[0005] To address the issue of residual high voltage during electrolyzer shutdown, some researchers have employed a systematic strategy for control. After shutdown, the hydrogen side is first purged with nitrogen to remove residual hydrogen; then, both the water and hydrogen sides are simultaneously purged with nitrogen until the voltage drops to a reasonable level. This method can reduce the residual potential during electrolyzer shutdown to some extent. However, as the number of electrolyzer plates and the active area increase, the difficulty of removing residual gases from the inside increases, leading to longer purging times and a significant waste of nitrogen.

[0006] Therefore, in view of the above technical problems, how to obtain a method to reduce the high potential after the electrolytic cell is shut down is a technical problem that needs to be solved. Summary of the Invention

[0007] The purpose of this invention is to provide a method for reducing the high potential after an electrolytic cell is shut down, in order to solve the above-mentioned technical problems.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for reducing high potential after an electrolytic cell is shut down, comprising the following steps: (1) The electrolyzer with a specific placement method is used for hydrogen production operation. The electrolyzer is placed on the side, that is, the membrane electrode of the electrolyzer is oriented vertically, so that the gas generated during operation floats to the side of the main pipe under the action of buoyancy and accumulates, and the gas accumulation position is not located in the active area of ​​the membrane electrode. (2) After the electrolyzer stops producing hydrogen and the current is cut off, perform a two-step nitrogen purging process: a. Cathode purging stage: Keep the pure water on the anode side running continuously, and purge the cathode side with nitrogen until the average single-chamber voltage of the electrolyzer fed back by the inspection controller drops below 0.6V, then stop cathode purging; b. Simultaneous purging stage of anode and cathode: Keep the pure water on the anode side running continuously, and purge the cathode and anode sides with nitrogen gas simultaneously until the average single-chamber voltage of the electrolyzer reported by the inspection controller drops below 0.3V, then stop purging.

[0009] Furthermore, in step (1), during hydrogen production, the gas generation rate of the electrolyzer is positively correlated with the current density, the number of membrane electrode plates, and the active area of ​​a single chamber.

[0010] Furthermore, in step (2), the flow rate of nitrogen purging is the hydrogen production flow rate within the range of 5~120% power of the electrolyzer.

[0011] Furthermore, in step (2), the cathode purging method is constant current and / or pulsed.

[0012] Furthermore, in step (2), the simultaneous purging of the anode and cathode is carried out by constant current and / or pulsed current.

[0013] Furthermore, in step (2), the nitrogen purging flow rate on the cathode side may be the same as or different from the nitrogen purging flow rate on the anode side.

[0014] The beneficial effects of this invention are: This invention, through a combination of "side placement + two-step purging", can significantly accelerate the bubble discharge speed, greatly shorten the purging time, reduce nitrogen consumption, effectively solve the problem of high potential after the electrolytic cell is shut down under high current density, and the effect is significantly better than the traditional vertical placement method. Attached Figure Description

[0015] Figure 1 This diagram shows the placement of the electrolytic cell during operation; where "100" represents the lower end plate; "101" represents the upper end plate; "102" represents the screw and disc spring; and "103" represents the electrolytic cell core.

[0016] Figure 2 This diagram illustrates the generation of bubbles inside a small chamber under high current density; where "200" represents the cathode plate; "201" represents the flow channel inside the cathode plate; "202" represents the flow channel inside the anode plate; "203" represents the diffusion layer; "204" represents the proton exchange membrane; "205" represents oxygen bubbles; and "206" represents the anode side plate.

[0017] Figure 3 This is a flowchart of the electrolytic cell shutdown and purging process.

[0018] Figure 4 This is a comparison chart showing the purging process under different placement methods of the electrolytic cell. Detailed Implementation

[0019] This invention provides a method for reducing high potential after an electrolytic cell is shut down, comprising the following steps: (1) The electrolyzer with a specific placement method is used for hydrogen production operation. The electrolyzer is placed on the side, that is, the membrane electrode of the electrolyzer is oriented vertically, so that the gas generated during operation floats to the side of the main pipe under the action of buoyancy and accumulates, and the gas accumulation position is not located in the active area of ​​the membrane electrode. (2) After the electrolyzer stops producing hydrogen and the current is cut off, perform a two-step nitrogen purging process: a. Cathode purging stage: Keep the pure water on the anode side running continuously, and purge the cathode side with nitrogen until the average single-chamber voltage of the electrolyzer fed back by the inspection controller drops below 0.6V, then stop cathode purging; b. Simultaneous purging stage of anode and cathode: Keep the pure water on the anode side running continuously, and purge the cathode and anode sides with nitrogen gas simultaneously until the average single-chamber voltage of the electrolyzer reported by the inspection controller drops below 0.3V, then stop purging.

[0020] In this invention, the electrolytic cell generates hydrogen and oxygen during operation; the cathode is at a low potential to generate hydrogen, and the anode is at a high potential to generate oxygen.

[0021] In this invention, during hydrogen production in step (1), the gas generation rate of the electrolyzer is positively correlated with the current density, the number of membrane electrode plates, and the active area of ​​a single chamber. That is, the more plates, the larger the active area of ​​a single chamber, and the greater the current, the greater the gas generation rate.

[0022] In this invention, the electrolytic cell targeted by the method is a PEM electrolytic cell.

[0023] In this invention, when the electrolyzer stops producing hydrogen, if hydrogen and oxygen are still present inside the electrolyzer, although there is no current load driving it, it remains in a closed loop with the outside world. Therefore, a galvanic cell reaction occurs between the hydrogen and oxygen inside. Specifically, on the cathode side, hydrogen loses electrons through the catalyst and is converted into hydrogen protons. These protons then pass through the proton exchange membrane to the oxygen side on the anode side and combine with oxygen to form water. Because the galvanic cell reaction continues inside the electrolyzer, it causes the electrolyzer to maintain a high potential even after shutdown, leading to a decrease in the durability of the proton exchange membrane.

[0024] In this invention, after the electrolyzer stops producing hydrogen and cuts off the current, the main purpose of performing the two-step nitrogen purging step is to vent the hydrogen and oxygen inside the electrolyzer, avoid galvanic cell reaction, and keep it in a low potential state after shutdown; at the same time, the venting of hydrogen also reduces the safety risk of the electrolyzer after shutdown.

[0025] In this invention, in step (2), the flow rate of nitrogen purging is the hydrogen production flow rate within the range of 5~120% power of the electrolyzer.

[0026] In this invention, in step (2), the cathode purging method is constant current and / or pulsed.

[0027] In this invention, in step (2), the simultaneous purging of the anode and cathode is carried out by constant current and / or pulse.

[0028] In this invention, in step (2), the nitrogen purging flow rate on the cathode side is the same as or different from the nitrogen purging flow rate on the anode side.

[0029] In this invention, the principle of improving bubble discharge by placing the electrolytic cell is that the bubbles are discharged upward due to buoyancy, and the water is discharged by gravity and water pressure. By placing the electrolytic cell, the bubble discharge method can be appropriately adjusted so that the bubbles can be quickly discharged from the electrolytic cell when the machine is stopped, thereby reducing the occurrence of galvanic cell reactions and reducing the high potential problem after the machine is stopped.

[0030] The electrolytic cell can be placed in three orientations: vertical (Type 1), vertical (Type 2), and side-mounted. In vertical (Type 1) electrolytic cell, the membrane electrode oriented is anode downwards and cathode upwards; in vertical (Type 2) electrolytic cell, the membrane electrode oriented is anode upwards and cathode downwards; and in side-mounted electrolytic cell, the membrane electrode oriented is vertical. The following description uses anode gas discharge as an example.

[0031] The vertical membrane electrode of the electrolytic cell is oriented with the anode facing down and the cathode facing up. The bubbles generated at this time will float up due to buoyancy and accumulate on the surface of the anode catalyst layer of the membrane electrode. If the machine is suddenly stopped at this time, the bubbles will preferentially accumulate in the micropores of the membrane electrode catalyst layer and will not be easy to expel, which will make purging difficult.

[0032] In the vertical electrolytic cell 2, the membrane electrode oriented is with the anode facing upwards and the cathode facing downwards. The generated bubbles rise due to buoyancy and accumulate above the membrane electrode (on the surface of the upper electrode plate). This change in bubble position makes it less likely for bubbles to remain on the anode surface compared to the vertical electrolytic cell 1, thus promoting bubble expulsion from the anode catalyst layer and facilitating mass transfer. If the system is suddenly shut down, the gas will adhere to the bipolar plate side and is difficult to expel, requiring a continuous supply of pure water to carry the gas away.

[0033] The membrane electrode assembly (MEA) on the side of the electrolyzer is oriented vertically. The bubbles generated at this time rise due to buoyancy. Since the MEA is vertically positioned, the bubbles eventually rise to the side of the main pipe and accumulate. At this point, the bubble accumulation location is not in the active zone. If the electrolyzer is suddenly stopped, the gas in the active zone will rise to the main pipe opening due to buoyancy. The active zone will then contain only liquid water, thus reducing the occurrence of the galvanic cell reaction.

[0034] The technical solutions 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 scope of protection of the present invention.

[0035] Example 1

[0036] In this embodiment, the electrolytic cell is placed on its side (e.g., Figure 2 As shown in the diagram, the membrane electrode is oriented vertically, causing the gas generated during electrolyzer operation to rise to the main pipe inlet side under buoyancy and accumulate far from the active area of ​​the membrane electrode. The purging process involves a two-step nitrogen purging procedure: a. Cathode purging stage: Keep the pure water on the anode side running continuously, and purge the cathode side with nitrogen until the average single-chamber voltage of the electrolyzer fed back by the inspection controller drops below 0.6V, then stop cathode purging; b. Simultaneous purging stage of anode and cathode: Keep the pure water on the anode side running continuously, and purge the cathode and anode sides with nitrogen gas simultaneously until the average single-chamber voltage of the electrolyzer reported by the inspection controller drops below 0.3V, then stop purging.

[0037] In this embodiment, during the cathode purging stage, the average single-chamber voltage of the electrolytic cell was reduced to below 0.6V in just 125 seconds. After entering the simultaneous anode and cathode purging stage, the average single-chamber voltage further decreased to below 0.3V after 25 seconds of purging. The entire purging process took a total of 175 seconds. Experimental phenomena showed that after shutdown, the gas in the active zone of the electrolytic cell could quickly rise to the main pipe opening. There was no obvious bubble retention during the purging process, and the average single-chamber voltage showed a steady downward trend, eventually stabilizing at 0.28V, consistent with the attached... Figure 4 The trend shown by the "side view of the electrolytic cell" curve is consistent.

[0038] Comparative Example 1

[0039] In this comparative example, the electrolytic cell is placed vertically (e.g., ...). Figure 2 As shown, the membrane electrode is oriented with the anode facing down and the cathode facing up. This placement causes the gas generated during the operation of the electrolyzer to accumulate on the surface of the anode catalyst layer and inside the micropores. The purging process is completely consistent with Example 1, also using a two-step constant flow purging method. The purging flow rate, judgment criteria, and other parameters are all kept the same as in Example 1.

[0040] During the cathode purging stage, a large number of air bubbles remained in the micropores of the catalyst layer after shutdown, resulting in a slow voltage drop in the initial stage of purging. It took 510 seconds of continuous purging to reduce the average single-chamber voltage below 0.6V. In the subsequent simultaneous anode and cathode purging stage, a prolonged purging process was still required to gradually remove the residual air bubbles, taking 605 seconds for the average single-chamber voltage to drop below 0.3V. The total purging time was 850 seconds, 6.8 times that of Example 1. Experimental phenomena and appendices... Figure 4 The curve of the "vertical electrolytic cell" is consistent with the flat first half, which requires continuous high-pressure purging to gradually remove the bubbles, resulting in extremely poor purging efficiency.

[0041] This invention provides a method for reducing high potential after an electrolytic cell is shut down. Example 1 of this invention employs a combination of "side-mounted placement + two-step purging," with a total purging time of only 175 seconds and a final stable voltage below 0.05V, demonstrating significant advantages in terms of shortest purging time and stable voltage. Comparative Example 1 uses a vertical placement method; due to bubbles remaining in the catalyst layer, the total purging time is as long as 850 seconds, with a final stable voltage of 0.1V, resulting in the worst purging efficiency. In summary, this invention, through the combination of "side-mounted placement + two-step purging," can significantly accelerate bubble removal, greatly shorten purging time, reduce nitrogen consumption, and effectively solve the problem of high potential after electrolytic cell shutdown under high current density, with significantly better results than the traditional vertical placement method.

[0042] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for reducing high potential after an electrolytic cell is shut down, characterized in that, Includes the following steps: (1) The electrolyzer with a specific placement method is used for hydrogen production operation. The electrolyzer is placed on the side, that is, the membrane electrode of the electrolyzer is oriented vertically, so that the gas generated during operation floats to the side of the main pipe under the action of buoyancy and accumulates, and the gas accumulation position is not located in the active area of ​​the membrane electrode. (2) After the electrolyzer stops producing hydrogen and the current is cut off, perform a two-step nitrogen purging process: a. Cathode purging stage: Keep the pure water on the anode side running continuously, and purge the cathode side with nitrogen until the average single-chamber voltage of the electrolyzer fed back by the inspection controller drops below 0.6V, then stop cathode purging; b. Simultaneous purging stage of anode and cathode: Keep the pure water on the anode side running continuously, and purge the cathode and anode sides with nitrogen gas simultaneously until the average single-chamber voltage of the electrolyzer reported by the inspection controller drops below 0.3V, then stop purging.

2. The method for reducing high potential after electrolytic cell shutdown according to claim 1, characterized in that, In step (1), during hydrogen production, the gas generation rate of the electrolyzer is positively correlated with the current density, the number of membrane electrode plates, and the active area of ​​a single chamber.

3. The method for reducing high potential after electrolytic cell shutdown according to claim 1 or 2, characterized in that, In step (2), the flow rate of nitrogen purging is the hydrogen production flow rate within the range of 5~120% power of the electrolyzer.

4. The method for reducing high potential after electrolytic cell shutdown according to claim 3, characterized in that, In step (2), the cathode purging method is constant current and / or pulsed.

5. The method for reducing high potential after electrolytic cell shutdown according to claim 2 or 4, characterized in that, In step (2), the simultaneous purging of the anode and cathode is carried out by constant current and / or pulse.

6. The method for reducing high potential after electrolytic cell shutdown according to claim 5, characterized in that, In step (2), the nitrogen purging flow rate on the cathode side may be the same as or different from the nitrogen purging flow rate on the anode side.

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