Electrolytic separation tank and electrochemical nitrogen generator applying same
By employing an ion exchange membrane and optimizing the cathode gas diffusion layer in electrolysis cells, the nitrogen production efficiency and purity in electric chemical generators are enhanced, addressing the inefficiencies of PPS membranes.
Patent Information
- Application Number
- CN202510353777.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-24
- Publication Date
- 2025-07-15
AI Technical Summary
In existing electrochemical nitrogen generators, the membrane electrode structure leads to low nitrogen production efficiency and high energy consumption, and the commonly used PPS membrane has poor gas barrier properties, which cannot effectively isolate the gas produced by the female and anodes, resulting in a decrease in nitrogen purity and yield.
An ion exchange membrane is used to replace the PPS separator, and the porosity and hydrophobic capacity of the cathode gas diffusion layer are optimized. Combined with the cathode catalytic layer with specific porosity and contact angles, an improved membrane electrode structure is formed to ensure gas inlet and water separation.
It significantly improves the yield and purity of nitrogen, reduces energy consumption, and improves reaction efficiency and current density.
Smart Images
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Figure BDA0005326768050000091
Abstract
Description
Technical Field
[0001] The present invention belongs to the field of nitrogen generators, and particularly relates to an electrolytic separation cell and an electrochemical nitrogen generator using the same. Background Art
[0002] Nitrogen generators have the advantages of low operating cost, convenient operation, low noise, safety and stability, long service life, etc., and are widely used in various fields. In the chemical industry, nitrogen is used as a protective gas to prevent the oxidation of reactants and catalysts. In the electronics industry, nitrogen is used in the production and processing of precision electronic products to provide a high-purity nitrogen environment. In addition, nitrogen also plays an important role in many industries such as medicine, food, and metallurgy, such as for the packaging of drugs and food, metal welding and heat treatment, etc.
[0003] At present, nitrogen production technologies are mainly divided into three types: membrane separation nitrogen production, pressure swing adsorption nitrogen production, and electrochemical nitrogen production.
[0004] Among them, the membrane separation nitrogen production method is a device that uses gas separation technology to separate nitrogen from compressed air. Its core component is the gas separation membrane, and this membrane material can selectively permeate according to the size and polarity differences of gas molecules. Compressed air first undergoes pretreatment to remove oil, water, and particulate matter, and then enters the membrane separation module. In the membrane separation module, since nitrogen molecules are larger than oxygen molecules and have a slower permeation rate, under a certain pressure drive, nitrogen is enriched on one side of the membrane, while oxygen quickly passes through the membrane to achieve the purpose of separation. Finally, the system outputs high-purity nitrogen, and the oxygen-enriched air is discharged or reused. However, the disadvantage of this method is that the nitrogen purity cannot reach the high-purity level, and currently all membrane modules are imported and cannot be provided domestically, resulting in a relatively high cost.
[0005] The principle of electrochemical nitrogen production is the constant potential electrolysis method (electrocatalysis method), that is, oxygen and nitrogen in the air are separated through an electrolytic cell. Specifically, when stable and pure raw material air enters the electrolytic cell, oxygen in the air is adsorbed at the cathode and obtains electrons, reacts with water to generate hydroxide ions, and then migrates to the anode, where it loses electrons and oxygen is evolved. In this way, oxygen in the air is continuously separated, and nitrogen is output along the gas path. High-purity nitrogen can be obtained through electrochemical nitrogen production, which is suitable for application scenarios with high requirements for nitrogen purity. However, since the reaction process has high requirements for the electrolytic cell manufacturing technology, inappropriate electrolytic cell manufacturing technology will cause a reduction in the nitrogen purity by several orders of magnitude. Therefore, there are relatively few electrochemical nitrogen generators available on the market currently, and the cost is relatively high when there is a large-flow nitrogen demand. Summary of the Invention
[0006] In order to improve the efficiency of producing nitrogen by an electrochemical nitrogen generator, the present invention provides an electrolytic separation cell and an electrochemical nitrogen generator using the same.
[0007] According to one aspect of the present application, there is provided an electrolytic separation cell, which includes a membrane electrode; the membrane electrode includes an anode gas diffusion layer, an anode catalyst layer, an ion exchange membrane, a cathode catalyst layer, and a cathode gas diffusion layer stacked in sequence; wherein, the contact angle of the cathode gas diffusion layer > 90°, and the porosity of the cathode gas diffusion layer is 20-50%.
[0008] Currently, the efficiency of generating nitrogen in electrochemical nitrogen generators on the market is relatively low. The inventor found that this is caused by the following reasons: The structural composition of the membrane electrode of the electrolytic separation cell currently applicable to electrochemical nitrogen generators is usually formed by stacking an anode gas diffusion layer, a diaphragm, and a cathode gas diffusion layer, that is, the anode gas diffusion and the cathode gas diffusion are sandwiched on both sides of the gas diffusion to form a membrane electrode, and finally, an anode plate and a cathode plate are added on both sides of the electrode to form an electrolytic cell. Among them, in the field of existing electrochemical nitrogen generators, the commonly used diaphragm is a polyphenylene sulfide (PPS) diaphragm, which is mainly used to prevent the mixing of hydrogen and oxygen and maintain stability under the corrosion of high-concentration alkali solution. However, the PPS diaphragm has poor gas barrier performance and poor ionic conductivity, resulting in low nitrogen production efficiency and high energy consumption.
[0009] Therefore, in order to improve the efficiency of generating nitrogen in electrochemical nitrogen generators, the inventor replaces the commonly used PPS diaphragm with an ion exchange membrane. However, an improper cathode structure will cause a flooding problem (liquid water exists in the cathode, blocking the pores, resulting in a decrease in the efficiency of generating nitrogen). In the new energy field, ion exchange membranes are mainly applied to fuel cells. Although both fuel cells and electrochemical nitrogen generators use the cathode as the core reaction site, consume oxygen in the air to produce the target gas, and the presence of liquid water in the cathode will hinder the entry of oxygen into the catalyst layer to participate in the reaction. In fuel cells, the following measures are taken to enable more gas to enter the catalyst layer to participate in the reaction: respectively, introducing excessive air and applying backpressure (backpressure: adding a valve at the gas outlet to hold the gas inside and pressing the gas in the flow channel into the catalyst layer to participate in the reaction) to improve the problem of reduced yield caused by flooding. However, electrochemical nitrogen generators cannot adopt the above methods for the following two reasons: On the one hand, when excessive air is introduced, the unreacted oxygen cannot be completely removed, resulting in a decrease in the purity of the produced nitrogen, which deviates from the advantages of electrochemical nitrogen generators; on the other hand, when there is backpressure, the reacted nitrogen cannot be discharged. When new air is introduced, the concentration of oxygen in the device will be further reduced, resulting in a sharp drop in current, greatly reducing the reaction efficiency and sharply increasing the energy consumption.
[0010] Thus, based on the problems discovered above, the inventor was able to significantly improve the nitrogen production efficiency and purity at the device level by improving the membrane electrode structure of the electrolytic separation cell applicable to the electrochemical nitrogen generator. Specifically, in the present application, by introducing an ion exchange membrane as a separator in the membrane electrode, the gases generated at the cathode and anode can be effectively isolated, thereby improving the purity of the generated nitrogen. Moreover, by combining with a cathode gas diffusion layer having hydrophobic ability and a specific porosity, it is possible to ensure that the cathode gas diffusion layer can isolate water molecules while maintaining a good ability to admit air.
[0011] Preferably, the porosity of the cathode gas diffusion layer is 20-50%. By further optimizing the porosity, the contact efficiency between the reactants and the electrode can be improved.
[0012] Preferably, the thickness of the ion exchange membrane < 50 μm. Further, by controlling the thickness of the ion exchange membrane, the ionic conductivity can be increased, thereby reducing the internal resistance of the device.
[0013] Preferably, the ion exchange membrane includes at least one of a proton exchange membrane, an anion exchange membrane, and an amphoteric ion exchange membrane.
[0014] Preferably, the contact angle of the cathode gas diffusion layer is 110°-140°.
[0015] Preferably, the cathode gas diffusion layer includes a substrate layer and a hydrophobic layer, the hydrophobic layer covering the substrate layer, and calculated by thickness ratio, substrate layer:hydrophobic layer = 8-20:1-3. Further, by controlling the thickness of the substrate layer and the hydrophobic layer, it helps to further enhance the hydrophobic ability of the cathode gas diffusion layer.
[0016] Preferably, the thickness of the substrate layer is 50-200 μm.
[0017] Preferably, the raw materials for preparing the hydrophobic layer include at least one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and ethylene propylene copolymer.
[0018] Preferably, the substrate layer includes at least one of a stainless steel mesh, a stainless steel felt, a titanium mesh, a titanium felt, a nickel mesh, a nickel felt, a carbon paper, and a carbon cloth.
[0019] Preferably, the porosity of the cathode catalytic layer is 20%-50%. Further, by controlling the porosity of the cathode catalytic layer, more gas can enter the gas diffusion layer, reducing the gas transmission resistance, thereby improving the gas production efficiency.
[0020] Preferably, the contact angle of the cathode catalytic layer is 100°-120°.
[0021] Preferably, the cathode catalyst layer includes a cathode catalyst, a hydrophobic material, and an ionomer. Calculated by mass ratio, the cathode catalyst:hydrophobic material:ionomer = 8:1-2:1-3. In the electrochemical nitrogen generator, the role of the cathode catalyst layer is to cause the reduction reaction of oxygen in the air and consume the oxygen in the air. By introducing the hydrophobic material and the ionomer in this application, it helps to prevent flooding of the catalyst layer, enables the gas to reach the surface of the catalyst to participate in the reaction, and improves the ion transport rate.
[0022] Preferably, the hydrophobic material includes at least one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and perfluoroethylene propylene copolymer.
[0023] Preferably, the ionomer includes at least one of ALkymer ionomer, Fumasep ionomer, Ionomr ionomer, Versogen ionomer, and Sustainion ionomer.
[0024] Preferably, the cathode catalyst includes at least one of a platinum-based catalyst, a nickel-based catalyst, an iron-based catalyst, a cobalt-based catalyst, a molybdenum-based catalyst, and a manganese-based catalyst.
[0025] In another aspect of this application, an electrochemical nitrogen generator is provided, and this electrochemical nitrogen generator includes the electrolytic separation cell as described above. Detailed implementation manners
[0026] In order to enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the scope of protection of this application.
[0027] Embodiment 1
[0028] In this embodiment, the membrane electrode and the electrolytic separation cell using it are prepared according to the following steps.
[0029] (1) Anode catalyst layer
[0030] The preparation raw materials of the anode catalyst layer include an anode catalyst and an anode ionomer. The anode catalyst is nickel-iron layered double hydroxide (NiFe LDH), the anode ionomer is ALkymer ionomer, the solvent is a mixed solution of alcohol and water, and the volume ratio of alcohol to water is 1:2. Calculated by mass ratio, the anode catalyst:anode ionomer = 5:1.5.
[0031] The preparation method of the anode catalyst layer includes the following operations: Mix the raw materials for preparing the above anode catalyst layer evenly to form an anode catalyst layer slurry. By adjusting the addition amount of the solvent, the concentration of the anode catalyst in the anode catalyst layer slurry is 20 mg / mL. Mix the anode catalyst, ionomer and solvent evenly by high-speed shearing, and then ultrasonicate for 30 min with the ultrasonic temperature less than 5 °C. Finally, coat the anode catalyst layer slurry on one side of the anion exchange membrane, and maintain the substrate temperature at 80 °C during the coating process, thereby obtaining a hydrophobic anode catalyst layer, wherein the loading of the anode catalyst is 1 mg / cm 2 .
[0032] (2) Cathode catalyst layer
[0033] The raw materials for preparing the cathode catalyst layer include a cathode catalyst, a hydrophobic material, an ionomer, and a solvent. The cathode catalyst is a platinum-carbon catalyst, the hydrophobic material is a polytetrafluoroethylene emulsion (the mass concentration of polytetrafluoroethylene in the emulsion is 20%), the ionomer is an ALkymer ionomer, and the solvent is a mixed solution of ethanol and water with a volume ratio of ethanol to water of 1:2. Calculated by mass ratio, cathode catalyst: polytetrafluoroethylene emulsion: cathode ionomer = 8:1:1.5.
[0034] The preparation method of the cathode catalyst layer includes the following operations: Mix the raw materials for preparing the above cathode catalyst layer evenly to form a cathode catalyst layer slurry. By adjusting the addition amount of the solvent, the concentration of the anode catalyst in the anode catalyst layer slurry is 20 mg / mL. Mix the cathode catalyst, polytetrafluoroethylene emulsion, ionomer and solvent evenly by high-speed shearing, and then ultrasonicate for 30 min with the ultrasonic temperature less than 5 °C. Finally, coat the cathode catalyst layer slurry on the other side of the anion exchange membrane, and maintain the substrate temperature at 80 °C during the coating process, thereby obtaining a cathode catalyst layer, wherein the loading of the cathode catalyst is 0.2 mg / cm 2 .
[0035] (3) Cathode gas diffusion layer
[0036] Soak a nickel mesh felt with a porosity of 40% in a 20% polytetrafluoroethylene emulsion for 30 min, then heat it up in a nitrogen environment at a rate of 5 °C / min and keep it at 350 °C for 30 minutes, thereby obtaining a cathode gas diffusion layer (the contact angle of the cathode gas diffusion layer is 140°).
[0037] (4) Electrolytic cell
[0038] The electrolytic separation cell includes a screw, a nut, an end plate, an insulating gasket, a current collector plate, a flow field plate, a sealing gasket, and a membrane electrode;
[0039] Using a stainless steel mesh felt as the anode gas diffusion layer, an ALkymer W-25 with a thickness of 25 μm as the anion exchange membrane (AEM), and stacking the above-prepared anode catalyst layer, cathode catalyst layer, and cathode gas diffusion layer in sequence as the anode gas diffusion layer, anode catalyst layer, anion exchange membrane, cathode catalyst layer, and cathode gas diffusion layer to obtain a membrane electrode.
[0040] A preparation method of an electrolytic cell includes the following operations: Stacking a cathode end plate, a cathode insulating gasket, a cathode current collector plate, a cathode flow field plate, a cathode sealing gasket, a cathode gas diffusion layer, a cathode catalyst layer, an anion exchange membrane, an anode catalyst layer, an anode diffusion layer, an anode sealing gasket, an anode flow field plate, an anode current collector plate, an anode insulating gasket, and an anode end plate on a screw in sequence, screwing on a nut, and using a torque wrench to tighten the nut with torques of 1 N·m, 3 N·m, and 5 N·m in sequence.
[0041] Example 2
[0042] In this example, a membrane electrode and an electrolytic separation cell were prepared with reference to the formula and method provided in Example 1. The difference from Example 1 is that when preparing the cathode gas diffusion layer in this example, the contact angle of the cathode gas diffusion layer is 110°. Except for the above difference, the operation steps for preparing the membrane electrode and the electrolytic separation cell in this example are strictly the same as those in Example 1.
[0043] Example 3
[0044] In this example, a membrane electrode and an electrolytic separation cell were prepared with reference to the formula and method provided in Example 1. The difference from Example 1 is that when preparing the cathode gas diffusion layer in this example, the porosity of the cathode gas diffusion layer is 20%. Except for the above difference, the operation steps for preparing the membrane electrode and the electrolytic separation cell in this example are strictly the same as those in Example 1.
[0045] Example 4
[0046] In this example, a membrane electrode and an electrolytic separation cell were prepared with reference to the formula and method provided in Example 1. The difference from Example 1 is that when preparing the cathode gas diffusion layer in this example, the porosity of the cathode gas diffusion layer is 50%. Except for the above difference, the operation steps for preparing the membrane electrode and the electrolytic separation cell in this example are strictly the same as those in Example 1.
[0047] Example 5
[0048] In this example, a membrane electrode and an electrolytic separation cell were prepared with reference to the formula and method provided in Example 1. The difference from Example 1 is that when preparing the membrane electrode in this example, the thickness of the used anion exchange membrane is 75 μm. Except for the above difference, the operation steps for preparing the membrane electrode and the electrolytic separation cell in this example are strictly the same as those in Example 1.
[0049] Example 6
[0050] In this example, the membrane electrode and the electrolytic separation cell were prepared with reference to the formula and method provided in Example 1. The difference from Example 1 is that when preparing the cathode catalyst layer, an ionomer of equal mass parts was used to replace the hydrophobic material (that is, no hydrophobic material was added when preparing the cathode catalyst layer). Except for the above differences, the operating steps for preparing the membrane electrode and the electrolytic separation cell in this example were strictly the same as those in Example 1.
[0051] Comparative Example 1
[0052] In this comparative example, the membrane electrode and the electrolytic separation cell were prepared with reference to the formula and method provided in Example 1. The difference from Example 1 is that when preparing the membrane electrode, a PPS diaphragm was used to replace the anion exchange membrane, and neither the cathode catalyst layer nor the gas diffusion layer was hydrophobically treated (contact angle < 90°C). Except for the above differences, the operating steps for preparing the membrane electrode and the electrolytic separation cell in this comparative example were strictly the same as those in Example 1.
[0053] Comparative Example 2
[0054] In this comparative example, the membrane electrode and the electrolytic separation cell were prepared with reference to the formula and method provided in Example 1. The difference from Example 1 is that when preparing the membrane electrode, a PPS diaphragm was used to replace the anion exchange membrane, and both the cathode catalyst layer and the gas diffusion layer were hydrophobically treated (contact angle > 90°C). Except for the above differences, the operating steps for preparing the membrane electrode and the electrolytic separation cell in this comparative example were strictly the same as those in Example 1.
[0055] Comparative Example 3
[0056] In this comparative example, the membrane electrode and the electrolytic separation cell were prepared with reference to the formula and method provided in Example 1. The difference from Example 1 is that when preparing the cathode gas diffusion layer, the porosity of the cathode gas diffusion layer was 10%. Except for the above differences, the operating steps for preparing the membrane electrode and the electrolytic separation cell in this comparative example were strictly the same as those in Example 1.
[0057] Comparative Example 4
[0058] In this comparative example, the membrane electrode and the electrolytic separation cell were prepared with reference to the formula and method provided in Example 1. The difference from Example 1 is that when preparing the cathode catalyst layer, no polytetrafluoroethylene emulsion was added, and when preparing the membrane electrode, a nickel mesh felt with a porosity of 40% was used as the cathode gas diffusion layer. Except for the above differences, the operating steps for preparing the membrane electrode and the electrolytic separation cell in this comparative example were strictly the same as those in Example 1.
[0059] Test Example
[0060] 1. Test Object
[0061] The membrane electrodes and electrolytic separation cells prepared in Examples 1 to 6 and Comparative Examples 1 to 4.
[0062] 2. Test methods
[0063] (1) Contact angle: Referring to the test method in "GB / T 30693-2014 Measurement of the contact angle of plastic films with water", the contact angles of the cathode catalyst layer and the cathode gas diffusion layer were respectively tested.
[0064] (2) Porosity: Referring to the test method in "GB / T21650.1-2008 Determination of pore size distribution and porosity of solid materials by mercury intrusion method and gas adsorption method. Part 1: Mercury intrusion method", the porosity of the cathode gas diffusion layer was tested.
[0065] (3) Current density: A constant voltage was applied across the electrolytic cell using a charge and discharge instrument, and the current reading at the interface of the charge and discharge instrument was read. The current density was obtained by dividing the current by the active area.
[0066] 3. Test results and analysis
[0067] The test results of this test example are shown in Table 1. Among them, through the test data of Examples 1 to 6 and Comparative Examples 1 to 4, it can be proved that by improving the membrane electrode structure of the electrolytic separation cell applicable to the electrochemical nitrogen generator, the nitrogen production efficiency and nitrogen production purity can be greatly improved at the device level (represented by the current density, generally the higher the current density, the higher the nitrogen production efficiency and nitrogen production purity).
[0068] Furthermore, from the data of Examples 1 to 2, it can be seen that when the contact angle of the cathode gas diffusion layer is between 110° and 140°, it has better nitrogen production efficiency and nitrogen production purity. Based on the porosity of the cathode gas diffusion layer in Example 1 and Examples 3 to 4 and Comparative Example 3, it can be known that as the porosity increases, the nitrogen production efficiency and nitrogen production purity also increase. And from the data of Example 1 and Example 5, it can be seen that the thickness of the anion exchange membrane will affect the internal resistance during this period, thereby affecting the nitrogen production efficiency and nitrogen production purity. Based on the test data of Example 1 and Example 6, it can be known that hydrophobic modification of the cathode catalyst layer can further enhance the efficiency of generating nitrogen by the electrochemical nitrogen generator.
[0069] In addition, in the present invention, the porosity of the cathode gas diffusion layer mainly depends on the porosity of the nickel mesh felt itself and is not affected by the hydrophobic layer. This is mainly because in this application, the mass concentration of the hydrophobic material in the hydrophobic layer can be regulated to ensure that the coating of the hydrophobic layer does not reduce the porosity of the substrate layer, but can effectively enhance the hydrophobic effect of the nickel mesh felt. Specifically, it can be achieved by controlling the mass concentration of the hydrophobic material to be 5 to 20% when preparing the cathode gas diffusion layer.
[0070] Table 1. Test results of this test example
[0071]
[0072]
[0073] The above embodiments are only used to illustrate the technical solutions of this application rather than to limit the protection scope of this application. Although this application has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of this application can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of this application.
Claims
1. An electrolytic separation cell, characterized in that, The electrolytic separation cell includes a membrane electrode; the membrane electrode comprises an anode gas diffusion layer, an anode catalyst layer, an ion exchange membrane, a cathode catalyst layer, and a cathode gas diffusion layer that are sequentially stacked; Among them, the contact angle of the cathode gas diffusion layer > 90°, and the porosity of the cathode gas diffusion layer is 20 - 50%.
2. The electrolytic separation cell according to claim 1, wherein, The thickness of the ion exchange membrane < 50 μm.
3. The electrolytic separation cell according to claim 1, characterized in that, The cathode gas diffusion layer includes a substrate layer and a hydrophobic layer, the hydrophobic layer covers the substrate layer, and calculated by thickness ratio, the substrate layer: the hydrophobic layer = 8 - 20: 1 - 3.
4. The electrolytic separation cell according to claim 3, wherein, The thickness of the substrate layer is 50 - 200 μm.
5. The electrolytic separation cell according to claim 1, wherein, The porosity of the cathode catalyst layer is 20% - 50%.
6. The electrolytic separation cell according to claim 5, wherein The cathode catalyst layer includes a cathode catalyst, a hydrophobic material, and an ionomer. Calculated by mass ratio, the cathode catalyst: the hydrophobic material: the ionomer = 8: 1 - 2: 1 - 3.
7. The electrolytic separation cell according to claim 6, wherein The hydrophobic material includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, and perfluoroethylene propylene copolymer.
8. The electrolytic separation cell according to claim 6, wherein The ionomer includes at least one of ALkymer ionomer, Fumasep ionomer, Ionomr ionomer, Versogen ionomer, and Sustainion ionomer.
9. The electrolytic separation cell according to claim 6, characterized in that, The cathode catalyst includes at least one of a platinum-based catalyst, a nickel-based catalyst, an iron-based catalyst, a cobalt-based catalyst, a molybdenum-based catalyst, and a manganese-based catalyst.
10. An electrochemical nitrogen generator, characterized in that, The electrochemical nitrogen generator includes the electrolytic separation cell according to any one of claims 1 - 9.