Composite alkaline electrolyte for protecting anion exchange membrane in electrolysis process

Abstract

The invention belongs to the field of new energy, and discloses a composite alkaline electrolyte for protecting an anion exchange membrane in an electrolysis process, which comprises the following components in percentage by mass: 0.6-5.6% of strong base, 0.1-5% of strong base weak acid salt, 0.01-0.3% of surfactant and the balance of water. According to the composite alkaline electrolyte disclosed by the invention, the OH concentration is remarkably reduced through the pH regulation effect of the buffer salt, and the corrosion damage of traditional alkaline liquor to the surface of an anion exchange membrane is effectively inhibited; the surfactant can promote bubble coalescence and rapid separation from the surface of the electrode, improve the available area of the surface of the electrode, reduce the mass transfer resistance of the edge of the anion-exchange membrane, improve the electrochemical reaction efficiency, significantly improve the overall performance of the battery, and effectively solve the problem of corrosion degradation of the anion-exchange membrane in a high-temperature and strong-alkali environment. And the performance of the electrolyte can be kept stable within the temperature range of 40-90 DEG C, so that the long-term operation stability of the battery is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of new energy, especially the field of hydrogen energy, and specifically relates to a composite alkaline electrolyte for protecting anion exchange membranes during electrolysis. Background Technology

[0002] Hydrogen energy, with its inherently clean and environmentally friendly characteristics, large-scale and long-term energy storage potential, and wide applicability across various fields, has demonstrated unprecedented development prospects and profound industrial value in key areas such as industrial heating, green power supply, low-carbon chemical raw materials, and clean transportation power.

[0003] Among numerous hydrogen production technologies, water electrolysis is widely recognized as the most promising green hydrogen production technology. Currently, the three low-temperature water electrolysis hydrogen production technologies with high commercial development and application potential are: alkaline (ALK) water electrolysis, proton exchange membrane (PEM) water electrolysis, and anion exchange membrane (AEM) water electrolysis.

[0004] Alkaline electrolysis (AEM) technology combines the advantages of alkaline water electrolysis (ALK) and polymethyl methacrylate (PEM) technologies, overcoming their respective shortcomings. ALK relies on high-concentration alkaline electrolytes (such as 20-30 wt% KOH solution), which are prone to corrosion and have poor dynamic response characteristics; PEM requires precious metal catalysts (such as platinum and iridium), which are costly and scarce. AEM generally uses low-concentration alkaline electrolytes (such as 0.1-1M KOH solution), which reduces corrosion risk and improves durability; at the same time, it can use non-precious metal catalysts (such as nickel and iron-based materials), significantly reducing costs.

[0005] In anion exchange membrane (AEM) water electrolysis technology, the traditional use of 0.1-1M KOH solution as the electrolyte, while increasing current density by operating at high temperatures of 40-90℃ to enhance OH⁻ migration rate and reaction kinetic efficiency, presents a dual challenge: Firstly, under high temperature and high current density conditions, the intense gas evolution on the electrode surface generates bubbles that accumulate in large quantities at the membrane edge—leading to excessively high mass transfer resistance at the edge, ultimately resulting in higher temperatures at the membrane edge and increased susceptibility to failure. This severely restricts the system's reaction efficiency and long-term stability. Secondly, high concentrations of OH⁻ cause drastic pH fluctuations at the three-phase interface, accelerating the chemical erosion of the anion exchange membrane.

[0006] Chinese patent application CN119736641A discloses a method for improving the efficiency of alkaline water electrolysis. This method involves adding a buffer to the alkaline water electrolysis reaction system to maintain local pH stability at the electrode surface, thereby reducing overpotential and improving electrolysis efficiency. The electrolyte in this system is an aqueous solution of KOH, with a concentration ranging from 0.1M to 8M. While this electrolyte can effectively stabilize the pH value at the membrane surface, its pH remains extremely high, leading to significant chemical degradation of the ion exchange membrane during operation. Summary of the Invention

[0007] The purpose of this invention is to overcome at least one deficiency of the prior art and to provide a composite alkaline electrolyte that protects the anion exchange membrane during electrolysis.

[0008] The technical solution adopted in this invention is: The first aspect of the present invention provides: A composite alkaline electrolyte comprises, by mass: 0.6-5.6% strong alkali, 0.1-5% strong alkali-weak acid salt, 0.01-0.3% surfactant, with the balance being water.

[0009] In some instances, the strong base is selected from at least one of KOH, NaOH, LiOH, and CsOH.

[0010] In some instances, the anion of the strong base-weak acid salt is selected from PO4. 3- CO3 2- CH3COO - B4O7 2 HCO3 - H2PO4 - HPO4 2- SiO3 2- At least one of them.

[0011] In some instances, the cation of the strong base-weak acid salt is selected from K. + Na + Li + Cs + At least one of the following.

[0012] In some instances, the surfactant is anionic, cationic, or neutral nonionic surfactant.

[0013] In some instances, the surfactant is selected from at least one of AEO-15, NP-15, polyether F68, APG, SXP-107, SAG-622, Corning-7610, and CTAB.

[0014] In some instances, the strong base-weak acid salt is selected from at least one of Na2CO3, K2CO3, K3PO4, NaHCO3, KHCO3, and Na2B4O7.

[0015] A second aspect of the present invention provides: A method for producing hydrogen by electrolysis of water, wherein the composite alkaline electrolyte described in the first aspect of the present invention is used during water electrolysis.

[0016] A third aspect of the present invention provides: An electrolytic water hydrogen production device, wherein the electrolyte used is the composite alkaline electrolyte described in the first aspect of the present invention.

[0017] A fourth aspect of the present invention provides: The application of the composite alkaline electrolyte described in the first aspect of this invention in the preparation of a water electrolysis hydrogen production device.

[0018] The beneficial effects of this invention are: The composite alkaline electrolyte of some examples of this invention significantly reduces the OH concentration through the pH adjustment effect of the buffer salt, effectively inhibiting the corrosion damage of traditional alkaline solutions to the surface of anion exchange membranes; the surfactant promotes bubble aggregation and rapid detachment from the electrode surface, increasing the usable area of ​​the electrode surface while reducing the mass transfer resistance at the edge of the anion exchange membrane, thereby improving the efficiency of electrochemical reactions.

[0019] During AEM electrolysis, a strong alkaline electrolyte can provide OH- - Constructing a basic ion conduction pathway is crucial. During electrolysis, a locally strong alkaline environment forms on the surface of the anion exchange membrane. The membrane gradually degrades due to the large amount of OH- attack, leading to corrosion and deterioration, which prevents the hydrogen production unit from operating sustainably. Adding buffer salts not only improves the conductivity of the solution but also reduces the OH concentration, maintaining pH stability in the local environment on the anion exchange membrane surface, thereby improving the long-term stability of the battery. However, under high current density, bubbles accumulate in large quantities at the membrane edge. The addition of surfactants can disrupt foam stability, accelerate bubble collapse, reduce the mass transfer resistance at the membrane electrode edge, and increase the effective reaction area on the electrode surface, thus improving electrochemical reaction efficiency.

[0020] The composite alkaline electrolytes of some embodiments of this invention not only significantly improve the overall performance of the battery, but also effectively solve the corrosion and deterioration problem of anion exchange membranes under high-temperature and strong alkaline conditions, thereby greatly improving the long-term operational stability of the battery. When a surfactant is added, it reduces the specific surface energy associated with bubble formation and growth, resulting in smaller bubbles, reduced bubble adhesion, and faster detachment of bubbles from the electrode surface, thus improving the durability of the anion exchange membrane edges. The buffer salt reduces the OH concentration in low-concentration strong alkaline electrolytes, forming a dynamic pH buffer system that maintains electrolyte performance stability within a temperature range of 40-90℃, inhibiting the accelerated corrosion of membrane surface materials by strong alkali. The addition of the buffer salt optimizes the ionic conductivity of the electrolyte and reduces OH concentration. - The low-concentration strong alkaline electrolyte (0.1-1M) combined with buffer salt reduces raw material costs and maintenance requirements compared to traditional AEM electrolytes. Attached Figure Description

[0021] Figure 1 The figure shows the results of the AST accelerated test conducted in 1M KOH electrolyte for Comparative Example 1.

[0022] Figure 2 The polarization curves are for Comparative Example 2 (without surfactant) and Example 11 (with surfactant).

[0023] Figure 3 The polarization curves are for Comparative Example 3 (without surfactant) and Example 12 (with surfactant).

[0024] Figure 4 This is a diagram showing the burn-out of the membrane electrode after the AST accelerated test in Comparative Example 1.

[0025] Figure 5 This is a magnified microscopic image of the damaged edge of the membrane electrode after the AST acceleration experiment in Comparative Example 3.

[0026] Figure 6 The figure shows the results of the AST accelerated test conducted in Example 1 with 1.12% KOH + 2.12% K3PO4 + 0.03% NP-15 electrolyte.

[0027] Figure 7 The figure shows the results of the AST accelerated test conducted in Example 3 with 1.12% KOH + 0.4% NaOH + 2.12% K3PO4 + 0.02% polyether F68 electrolyte.

[0028] Figure 8 The image shows the polarization curves before and after the AST accelerated experiment conducted in Example 7 with 0.4% NaOH + 1.06% Na2CO3 + 0.89% K2HPO4 + 0.05% CTAB electrolyte.

[0029] Figure 9 The polarization curves before and after the AST accelerated experiment in Example 8 were obtained using 1.96% KOH + 1.01% Na2B4O7 + 1.06% K3PO4 + 0.53% Na2CO3 + 0.02% Dow Corning-7610 electrolyte.

[0030] Figure 10 This is a magnified image of the membrane edge under a microscope after the AST acceleration experiment in Example 7.

[0031] Figure 11 The anion exchange membrane surface image after the AST accelerated experiment in Example 8. Detailed Implementation

[0032] The technical solution of the present invention will be further illustrated below with examples.

[0033] The following examples are intended to illustrate, not limit, the invention. In these examples, unless otherwise specified, all parts and percentages are by weight.

[0034] Construction of the electrolytic cell: For ease of comparison, the electrolytic cells are constructed uniformly according to the following method.

[0035] 1. First, weigh ethanol (7.0g), ultrapure water (3.0g), catalyst (0.5g) and 5% ionomer (8.0g), place them in a sealed sample bottle, and then, under ice bath conditions, use mechanical stirring to form a uniformly dispersed system. Continue sonication for 1 hour to obtain the required catalyst slurry.

[0036] 2. Then, the membrane electrode assembly is prepared. The coating process of the membrane electrode is mainly divided into two types: CCM (catalyst coated membrane) and CCS (catalyst coated substrate). (1) CCM preparation process: The anion exchange membrane (2.5cm×2.5cm) is heated at 80℃ for 30min to remove the adsorbed water on the surface of the anion exchange membrane. Then, the prepared catalyst slurry is uniformly sprayed on both sides of the membrane with a spray gun so that the catalyst loading of the anode and cathode is 1.0mg / cm. 2 Finally, a three-in-one membrane electrode assembly was obtained. (2) CCS preparation process: The nickel felt (2cm×2cm) was fixed on a horizontal substrate, and the prepared anode catalyst slurry was uniformly sprayed onto the nickel felt with a spray gun. It was dried at 80℃ for 2h to make the catalyst loading 1.0mg / cm 2 The cathode CCS is prepared using the same process to ensure that the loading of the anode and cathode catalyst layers is the same.

[0037] 3. Next, place the nickel-plated stainless steel bipolar plate (channel size 2cm×2cm), then sequentially stack a 370μm thick PTFE gasket, a 400μm thick nickel felt gas diffusion layer (size 2cm×2cm), an anion exchange membrane, and the PTFE gasket and gas diffusion layer on the other side. Finally, cover the bipolar plate. After assembly, use a torque wrench to tighten the bolts to 7.5Nm in a diagonal sequence.

[0038] 4. Immediately afterwards, a 0.5-1.5 mol / L KOH solution is introduced into the electrolytic cell at a flow rate of 20 mL / min and the treatment is continued for 12 hours to allow the anion exchange membrane to fully complete the ion exchange.

[0039] The electrolyte compositions for different examples are as follows: Example 1: KOH 1.12%, K3PO4 2.12%, NP-15 0.03%.

[0040] Example 2: NaOH 0.80%, Na3PO4 0.82%, AEO-15 0.02%, NP-15 0.01%.

[0041] Example 3: KOH 1.12%, NaOH 0.40%, K3PO4 2.12%, polyether F68 0.02%.

[0042] Example 4: NaOH 0.40%, LiOH 0.24%, Na3PO4 0.82%, polyether F68 0.01%, SXP-107 0.02%.

[0043] Example 5: NaOH 0.80%, K2CO3 0.69%, KH2PO4 0.27%, SXP-107 0.02%.

[0044] Example 6: KOH 2.80%, Na2CO3 0.53%, K3PO4 2.12%, SAG-622 0.05%.

[0045] Example 7: NaOH 0.40%, Na2CO3 1.06%, K2HPO4 0.89%, CTAB 0.05%.

[0046] Example 8: KOH 1.12%, Na2B4O7 1.01%, K3PO4 1.06%, Na2CO3 0.53%, Dow Corning-7610 0.02%.

[0047] Example 9: NaOH 0.80%, Na2CO3 1.06%, K3PO4 0.42%, CH3COONa 0.16%, APG 0.04%, AEO-15 0.04%.

[0048] Example 10: CsOH 2.25%, K2CO3 1.38%, sodium silicate 0.61%, APG 0.05%.

[0049] Example 11: NaOH 0.40%, Na2CO3 1.06%, K2HPO4 0.89%, AEO-15 0.08%.

[0050] Example 12: NaOH 0.80%, Na2CO3 1.06%, K3PO4 0.42%, CH3COONa 0.16%, polyether F68 0.05%, SAG-622 0.10%.

[0051] Comparative Example 1: KOH 5.60%.

[0052] Comparative Example 2: NaOH 0.40%, Na2CO3 1.06%, K2HPO4 0.89%.

[0053] Comparative Example 3: NaOH 0.80%, Na2CO3 1.06%, K3PO4 0.42%, CH3COONa 0.16%.

[0054] Electrolyte performance testing The testing system consists of a data acquisition system and a circulating temperature control system. The main testing methods include polarization curve testing, AST accelerated durability testing, and AST post-acceleration testing and analysis.

[0055] (1) Data acquisition system: The Blue Electric Test System is used in conjunction with host computer software to monitor and record electrochemical performance parameters in real time.

[0056] (2) Circulating temperature control system: The closed-loop system consists of a storage tank, a magnetically driven circulating pump, a constant temperature heating platform, and corrosion-resistant pipelines. The connection sequence is: storage tank → circulating pump → AEM electrolytic cell → storage tank. During system operation, the electrolyte circulation rate is controlled to (60±2) mL / min by a precision flow regulating valve, and the working temperature of the electrolytic cell is maintained within the set range of 40-90℃ by the temperature control system. After the system stabilizes, a constant voltage of 2.0 V is applied for continuous activation treatment for 24 h.

[0057] (3) Polarization curve test: The electrochemical performance was characterized using a quasi-steady-state scanning method. The test voltage range was set to 1.45-2.00 V, and the scan step size was 50 mV. The polarization time was maintained for 300 s at each test potential point. After the current change rate was lower than 1% / min (reaching the quasi-steady-state condition), the stable current value was recorded. Finally, the voltage-current density polarization curve of the electrolytic cell was plotted based on the measured data to evaluate the electrochemical behavior characteristics of the system under different overpotentials.

[0058] (4) AST Accelerated Durability Testing: Based on the actual operating characteristics of the photovoltaic power generation system, the long-term durability of the electrolyzer is evaluated using a dynamic voltage scanning mode. The method includes the following steps: a) Dynamic voltage loading: A periodically varying voltage is applied to the working electrode of the electrolytic cell, with the voltage range set from 1.5V to 2.0V, to simulate the actual output fluctuation characteristics of the photovoltaic power generation system; b) Cyclic test control: Each voltage fluctuation cycle is 15 seconds, and the total number of cycles is 6000 to accelerate the simulation of long-term operating conditions; c) Real-time data acquisition: During the test, the voltage, current and temperature parameters of the electrolytic cell are monitored and recorded simultaneously to build a performance degradation database; d) Attenuation law analysis: Based on the collected data, the performance degradation rate of the electrolyzer is calculated using statistical modeling methods to evaluate its long-term operational stability.

[0059] (5) AST accelerated test analysis: After completing the AST accelerated durability test, the same polarization curve test method as the initial test was used to compare and analyze the change law of the curve characteristic parameters before and after aging.

[0060] The experimental results are shown in Table 1.

[0061] Table 1. Polarization performance and accelerated attenuation results at high temperature (80℃)

[0062] As shown in Table 1, under a strongly alkaline environment of 80℃ and pH 13-14, the battery system using this electrolyte exhibits a maximum voltage decay of 7.38 mA·cm⁻¹. -2 ·h -1 The operational stability is 2.37 times higher than that of Comparative Example 1.

[0063] Figure 1 The figure shows the results of the AST accelerated test conducted in 1M KOH electrolyte for Comparative Example 1.

[0064] Figure 2 The polarization curves are for Comparative Example 2 (without surfactant) and Example 11 (with surfactant).

[0065] Figure 3 The polarization curves are for Comparative Example 3 (without surfactant) and Example 12 (with surfactant).

[0066] like Figure 2 , 3As shown, the surfactant added to the electrolyte can unexpectedly reduce the coverage of the electrode active sites by bubbles, increase the effective reaction area, and thus improve the efficiency of the electrochemical reaction.

[0067] Figure 4 This is a diagram showing the burn-out of the membrane electrode after the AST accelerated test in Comparative Example 1.

[0068] Figure 5 This is a magnified microscopic image of the damaged edge of the membrane electrode after the AST acceleration experiment in Comparative Example 3.

[0069] Figure 10 This is a magnified image of the membrane edge under a microscope after the AST acceleration experiment in Example 7.

[0070] Figure 11 The anion exchange membrane surface image after the AST accelerated experiment in Example 8.

[0071] like Figure 4 , Figure 5 , Figure 10 , Figure 11 As shown, this composite alkaline electrolyte effectively inhibits the aggregation of OH⁻ ions, significantly reducing their chemical erosion on the surface of the anion exchange membrane; at the same time, it inhibits the aggregation of bubbles at the membrane edge under high current density conditions, effectively reducing mass transfer resistance and heat generation, thereby better protecting the edge of the membrane electrode.

[0072] Figure 6 The figure shows the results of the AST accelerated test conducted in Example 1 with 1.12% KOH + 2.12% K3PO4 + 0.03% NP-15 electrolyte.

[0073] Figure 7 The figure shows the results of the AST accelerated test conducted in Example 3 with 1.12% KOH + 0.4% NaOH + 2.12% K3PO4 + 0.02% polyether F68 electrolyte.

[0074] Depend on Figure 6 and Figure 7 It can be seen that under accelerated experimental conditions, the electrolyte exhibits excellent performance, with relatively gradual changes in current density and minimal decay over time, indicating that the electrolyte provides good protection for the anion exchange membrane.

[0075] Figure 8 The image shows the polarization curves before and after the AST accelerated experiment conducted in Example 7 with 0.4% NaOH + 1.06% Na2CO3 + 0.89% K2HPO4 + 0.05% CTAB electrolyte.

[0076] Figure 9The polarization curves before and after the AST accelerated experiment in Example 8 were obtained using 1.96% KOH + 1.01% Na2B4O7 + 1.06% K3PO4 + 0.53% Na2CO3 + 0.02% Dow Corning-7610 electrolyte.

[0077] Depend on Figure 8 and Figure 9 It can be seen that the polarization curves before and after the accelerated experiment basically overlap below 1.7V. At higher voltages, the current density only decreases slightly, indicating that the electrolyte has a good protective effect on the anion exchange membrane.

[0078] The above is a further detailed description of the present invention and should not be considered as a limitation on the specific implementation of the present invention. For those skilled in the art, simple deductions or substitutions without departing from the concept of the present invention are all within the protection scope of the present invention.

Claims

1. A composite alkaline electrolyte, characterized in that, Its composition includes: 0.6-5.6% strong alkali, 0.1-5% strong alkali-weak acid salt, 0.01-0.3% surfactant, and the balance being water.

2. The composite alkaline electrolyte according to claim 1, characterized in that, The strong base is selected from at least one of KOH, NaOH, LiOH, and CsOH.

3. The composite alkaline electrolyte according to claim 1, characterized in that, The anion of the strong base-weak acid salt is selected from PO4. 3- CO3 2- CH3COO - B4O7 2 HCO3 - H2PO4 - HPO4 2- SiO3 2- At least one of them.

4. The composite alkaline electrolyte according to claim 1, characterized in that, The cation of the strong base weak acid salt is selected from K. + Na + Li + Cs + At least one of the following.

5. The composite alkaline electrolyte according to claim 1, characterized in that, The surfactant is an anionic, cationic, or neutral nonionic surfactant.

6. The composite alkaline electrolyte according to claim 1, characterized in that, The surfactant is selected from at least one of AEO-15, NP-15, polyether F68, APG, SXP-107, SAG-622, Corning-7610 and CTAB.

7. The composite alkaline electrolyte according to claim 1, characterized in that, The strong base weak acid salt is selected from at least one of Na2CO3, K2CO3, K3PO4, NaHCO3, KHCO3, and Na2B4O7.

8. A method for producing hydrogen by electrolysis of water, characterized in that, The composite alkaline electrolyte according to any one of claims 1 to 7 is used during water electrolysis.

9. A device for producing hydrogen by electrolysis of water, characterized in that, The electrolyte used is the composite alkaline electrolyte as described in any one of claims 1 to 7.

10. The application of the composite alkaline electrolyte according to any one of claims 1 to 7 in the preparation of a water electrolysis hydrogen production device.

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