Component optimization and hydrogen evolution catalysis method of imidazolium ionic liquid modified KOH electrolyte and application of imidazolium ionic liquid modified KOH electrolyte

Abstract

The invention relates to the related field of hydrogen production through electrolysis of water, in particular to a component optimization and hydrogen evolution catalysis method of an imidazolium ionic liquid modified KOH electrolyte and application of the imidazolium ionic liquid modified KOH electrolyte, the imidazolium ionic liquid modified KOH electrolyte comprises KOH with the concentration of 6-10 mol / L, the KOH is analytically pure, and the purity is larger than or equal to 85%; the concentration of the 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4) is 0.01 mol / L to 0.1 mol / L; the conductivity of the deionized water is less than or equal to 10 [mu] S / cm. Through systematic study on the ratio of the imidazolium ionic liquid (BMIM-BF4) to KOH, the electrolyte has the optimal hydrogen evolution performance when the concentration of KOH is 8M and the concentration of BMIM-BF4 is 0.05 M. The ratio not only considers the regulation and control effect of the ionic liquid on the interface property, but also considers the influence of the KOH concentration on the freezing point and the conductivity of the electrolyte, so that collaborative optimization of multiple parameters is realized. Through component optimization, action mechanism innovation and performance improvement, the electrolyte composition which is efficient, stable and wide in application range is provided for the alkaline water electrolysis hydrogen production technology, and remarkable technical progress and practical application value are achieved.

Description

Technical Field

[0001] The present invention relates to the field of hydrogen production by electrolysis of water, and in particular to a component optimization and hydrogen evolution catalytic method and application of an imidazole ionic liquid modified KOH electrolyte. Background Art

[0002] As the global energy transition progresses, "green hydrogen," a clean secondary energy source, plays a crucial role in energy storage and conversion. Water electrolysis has become a key method for producing "green hydrogen" due to its wide range of raw material sources and high product purity. Among various water electrolysis technologies, alkaline water electrolysis (AWE) has been widely researched and applied due to its low equipment cost and simple operation. This technology typically uses aqueous KOH or NaOH solutions as the electrolyte.

[0003] However, a key challenge facing alkaline water electrolysis hydrogen production technology is the high overpotential of the hydrogen evolution reaction (HER), which leads to increased energy consumption and reduced electrolysis efficiency. Theoretically, the decomposition voltage of water is 1.23V, but in practical applications, a voltage much higher than this needs to be applied. The higher overpotential significantly reduces the efficiency of water electrolysis, which is particularly evident in alkaline electrolysis cells.

[0004] To solve this problem, researchers have tried a variety of methods, including developing high-performance catalysts and optimizing the electrolyte composition. In terms of electrolyte optimization, reducing the overpotential by changing the type of interfacial cations, increasing the cation concentration, or adding appropriate additives is an effective way. For example, studies have found that adding a small amount of theophylline-like organic small molecules to potassium hydroxide solution can change the structural composition of interfacial water, thereby reducing the Tafel slope of alkaline hydrogen evolution and promoting the kinetics of hydrogen evolution reaction. In addition, there are also studies that add trifluoroacetic acid to the electrolyte to reduce the overpotential of the hydrogen evolution reaction at all pH levels.

[0005] However, these organic additives often have problems such as poor stability and poisoning of catalysts. In contrast, ionic liquids have shown unique advantages as electrolyte additives. Imidazole ionic liquids, as additives to water electrolysis hydrogen production electrolytes, can increase the current density of water electrolysis hydrogen production, reduce the overpotential of hydrogen evolution reaction, and improve the efficiency of HER. Despite this, there is still room for optimization in the use of imidazole ionic liquids in the existing technology, such as how to determine the optimal type of ionic liquid, concentration and its ratio with KOH to maximize the improvement of hydrogen evolution performance.

[0006] Therefore, developing a KOH electrolyte composition that can significantly reduce the hydrogen evolution overpotential, improve the hydrogen evolution efficiency and have good stability is of great significance for promoting the development of alkaline water electrolysis hydrogen production technology. Summary of the Invention

[0007] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a component optimization and hydrogen evolution catalytic method and application of an imidazole ionic liquid modified KOH electrolyte.

[0008] A KOH electrolyte composition modified with an imidazole ionic liquid, comprising:

[0009] KOH with a concentration of 6-10 mol / L, wherein the KOH is analytical grade and has a purity of ≥85%;

[0010] 1-Butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4) at a concentration of 0.01-0.1 mol / L;

[0011] The balance is deionized water, wherein the conductivity of the deionized water is ≤10 μS / cm.

[0012] Furthermore, the purity of the BMIM-BF4 is ≥99%, the cation thereof is 1-butyl-3-methylimidazolium cation (butyl chain length is C4), and the anion thereof is tetrafluoroborate ion (BF4 - ), and the BMIM-BF4 was filtered through a 0.22 μm filter membrane at least once to remove impurities.

[0013] Furthermore, the KOH concentration is preferably 8 mol / L, and the BMIM-BF4 concentration is preferably 0.05 mol / L; under this ratio, the electrolyte has a conductivity of ≥208 mS / cm at 25°C, a viscosity of ≤14.5 mPa·s at -40°C, and a flow rate of 10 mA / cm 2 The hydrogen evolution overpotential is ≤220mV at this current density.

[0014] A method for preparing the electrolyte composition, characterized in that it comprises the following steps:

[0015] S1. Add KOH pellets to deionized water at a constant temperature of 20°C and stir at a stirring rate of 150-250 rpm until completely dissolved to prepare a 6-10 mol / L KOH solution. During the dissolution process, the solution temperature is controlled to be ≤35°C.

[0016] S2. After the solution obtained in step S1 is cooled to room temperature, BMIM-BF4 is added thereto, and the mixture is stirred at a stirring rate of 250-350 rpm for 30-90 minutes at room temperature to prepare a homogeneous electrolyte.

[0017] Furthermore, after step S2, the method further includes: filtering the homogeneous electrolyte through a 0.22 μm polytetrafluoroethylene filter membrane, transferring the mixture into a volumetric flask, and diluting the mixture to a target volume with deionized water. After diluting, the solution volume error is ≤±0.5%, and the solution is colorless and transparent.

[0018] Furthermore, the electrolyte composition is used in alkaline water electrolysis to produce hydrogen, and is used for hydrogen evolution catalysis reaction, and the working electrode is selected from:

[0019] The nickel foam electrode, with a size of 1 cm × 1 cm, a thickness of 1.6 mm, and a porosity of 95%, was pretreated by ultrasonic cleaning with 1 M HCl for 10 minutes;

[0020] Nickel-iron alloy electrode, its hydrogen evolution active site density is 20% higher than that of pure nickel;

[0021] The platinum sheet electrode has a specification of 1 cm×1 cm, a thickness of 0.1-0.5 mm, a purity of 99.9%, and is pretreated by soaking in aqua regia for 5 minutes.

[0022] Furthermore, the electrolyte composition operates stably in the temperature range of -60°C to 80°C, with an optimal operating temperature of 70°C; the conductivity is ≥150mS / cm at -20°C, the weight loss rate is less than 1% after thermogravimetric analysis (TG) testing at 80°C, and there is no solidification phenomenon at -60°C.

[0023] Furthermore, the electrolyte composition is at 10 mA / cm 2 The hydrogen evolution overpotential under current density is 215-235mV, which is 20-50mV lower than that of pure KOH electrolyte with the same concentration; at a voltage of 1.6V, the current density is ≥30mA / cm 2 (When nickel foam electrode is the working electrode).

[0024] Furthermore, the interfacial charge transfer resistance (R2) between the electrolyte composition and the working electrode is reduced by ≥50% compared with pure KOH electrolyte; after 1000 cyclic voltammetry (CV) tests, the hydrogen evolution overpotential performance decay rate is ≤4.8%, wherein the life of the nickel foam electrode is ≥5000h, and the corrosion current density of the nickel-iron alloy electrode is ≤0.5mA / cm 2 .

[0025] Furthermore, the electrolyte composition is non-toxic when in contact with precious metal catalysts, and the activity decay rate of the platinum-based electrode is ≤5% after 1000 hours of continuous operation; in a 24-hour chronopotentiometry (CP) test, the cell voltage fluctuation range is ≤±1.7%, and the electrolyte always remains homogeneous and transparent.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The creativity of the present invention is mainly reflected in the following aspects:

[0028] 1. Through systematic research on the ratio of imidazole ionic liquid (BMIM-BF4) to KOH, it was found that when the KOH concentration was 8M and the BMIM-BF4 concentration was 0.05M, the electrolyte had the best hydrogen evolution performance. This ratio not only takes into account the regulatory effect of the ionic liquid on the interfacial properties, but also takes into account the influence of KOH concentration on the freezing point and conductivity of the electrolyte, achieving the coordinated optimization of multiple parameters. Compared with the existing technology, the component optimization scheme of the present invention can more significantly reduce the hydrogen evolution overpotential and improve the hydrogen evolution efficiency.

[0029] 2. This paper investigates the mechanism of action of imidazole-based ionic liquid-modified KOH electrolytes, finding that they not only reduce overpotential by altering the interfacial double-layer structure but also enhance hydrogen evolution performance through multiple synergistic mechanisms, including reconstructing hydrogen bonding networks, optimizing ion conduction, and promoting bubble desorption. This multi-faceted mechanism provides theoretical guidance for further optimization of electrolytes, whereas prior art understanding of these mechanisms is often limited.

[0030] 3. Compared with the traditional KOH electrolyte, the electrolyte composition of the present invention has significant advantages in hydrogen evolution overpotential, current density, temperature adaptability and stability. For example, at 10 mA / cm 2 Under the current density, the overpotential is reduced by 50mV, the current density is increased by 30%, and the freezing point is reduced by more than 20°C. These performance improvements are not simply superposition, but a synergistic effect achieved through component optimization.

[0031] 4. The electrolyte of the present invention is suitable for both non-precious metal and precious metal catalysts and maintains good performance over a wide temperature range, expanding the application of alkaline water electrolysis hydrogen production technology. Compared with additives in the prior art, the imidazolium ionic liquid of the present invention has better stability and applicability and does not poison the catalyst.

[0032] 5. The electrolyte preparation method of the present invention is simple and easy to implement, does not require complex equipment and processes, and is convenient for industrial production and application. An electrolyte with excellent performance can be prepared through simple dissolution and stirring operations, which is also one of the important innovations of the present invention.

[0033] In summary, the present invention provides an efficient, stable, and widely applicable electrolyte composition for alkaline water electrolysis hydrogen production technology through component optimization, innovative mechanism of action, and performance improvement, which has significant technological progress and practical application value. DETAILED DESCRIPTION

[0034] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0035] Example 1: 8M KOH+0.01M BMIM-BF4 electrolyte

[0036] S1. Preparation of KOH mother liquor: Slowly add 186.5 g of KOH (analytical grade, purity 85%) to 500 mL of deionized water at a constant temperature of 25°C. Stir at 200 rpm for 30 minutes until completely dissolved. The solution temperature is measured to be 32°C. After cooling to room temperature, transfer to a 1000 mL beaker.

[0037] S2. Adding ionic liquid: add 0.21 g BMIM-BF4 (purity 99.5%) and stir at 300 rpm for 60 minutes until it is completely dissolved and the solution becomes colorless and transparent.

[0038] S3. Volume adjustment and filtration: Transfer to a 1000 mL volumetric flask, adjust to volume with deionized water, and filter through a 0.22 μm polytetrafluoroethylene filter to obtain the target electrolyte.

[0039] Example 2: 8M KOH+0.05M BMIM-BF4 electrolyte

[0040] S1. Preparation of KOH mother liquor: Weigh 186.5 g of KOH and dissolve it in 500 mL of deionized water (25° C.). Stir at 200 rpm for 30 minutes and cool to 25° C.

[0041] S2. Adding ionic liquid: 1.05 g BMIM-BF4 (purity 99.5%) was added, and the mixture was stirred at 300 rpm for 60 minutes. The solution was transparent and uniform.

[0042] S3. Constant volume filtration: constant volume to 1000 mL, filter through a 0.22 μm filter membrane to obtain the electrolyte.

[0043] Example 3: 8M KOH+0.1M BMIM-BF4 electrolyte

[0044] S1. Preparation of KOH mother solution: prepare 8M KOH solution as in Example 2.

[0045] S2. Add ionic liquid: add 2.10 g BMIM-BF4 and stir for 90 minutes until dissolved.

[0046] S3. Constant volume filtration: set aside after constant volume filtration.

[0047] Example 4: 7M KOH+0.04M BMIM-BF4 electrolyte

[0048] S1. Preparation of KOH mother liquor: Slowly add 392.7 g KOH (analytical grade, purity 85%) to 800 mL of deionized water at a constant temperature of 20°C. Stir at 180 rpm for 40 minutes until completely dissolved. During this time, use circulating water cooling to control the temperature to ≤35°C. After cooling to 25°C, transfer to a 1000 mL beaker.

[0049] S2. Addition of ionic liquid: accurately weigh 9.04 g BMIM-BF4 (purity 99.5%), add KOH mother solution three times, each time with an interval of 10 minutes, increase the stirring speed to 300 rpm, and stir for a total of 60 minutes until the solution becomes clear.

[0050] S3. Fine preparation: The solution was filtered twice through a 0.22 μm polypropylene filter membrane, transferred to a 1000 mL volumetric flask, and diluted to the mark with deionized water to obtain the target electrolyte.

[0051] Performance parameters: Hydrogen evolution overpotential @10mA / cm 2 =230mV, conductivity@25℃=198mS / cm, viscosity@-40℃=16.2mPa·s.

[0052] Example 5: 9MKOH+0.06MBMIM-BF4 electrolyte

[0053] S1. Preparation of KOH mother liquor: Dissolve 504.9 g of KOH in 700 mL of deionized water at 25°C. Use magnetic stirring (220 rpm) and ultrasonic assistance (power 100 W) to accelerate dissolution. After 30 minutes, the solution temperature rises to 32°C and is naturally cooled to room temperature.

[0054] S2. Ionic liquid compounding: 13.56 g of BMIM-BF4 (purity 99.5%) was added, and the mixture was stirred at 350 rpm for 30 minutes, and then reduced to 250 rpm and stirred for 45 minutes to form a homogeneous solution.

[0055] S3. Constant volume filtration: The solution is filtered through a 0.1 μm ceramic filter membrane to remove possible KOH particle impurities, and the volume is constant to 1000 mL to prepare the electrolyte.

[0056] Performance parameters: Hydrogen evolution overpotential @10mA / cm 2 =228mV, conductivity@25℃=205mS / cm, viscosity@-40℃=17.0mPa·s.

[0057] Example 6: 6MKOH+0.03MBMIM-BF4 electrolyte

[0058] S1. Preparation of KOH mother liquor: Slowly add 336.6 g KOH (analytical grade) to 900 mL of deionized water at a constant temperature of 25°C. Stir at 200 rpm for 30 minutes until completely dissolved. Use a thermometer to monitor the dissolution temperature until it reaches a maximum of 33°C. Cool to room temperature and transfer to a 1000 mL beaker.

[0059] S2. Addition of ionic liquid: Accurately weigh 6.78 g of BMIM-BF4 (purity 99.5%) and dissolve it in 50 mL of deionized water to form a pre-solution. Add the KOH mother liquor dropwise five times with an interval of 5 minutes between each addition while maintaining a stirring rate of 300 rpm for a total addition time of 25 minutes. Continue stirring for 35 minutes until uniform.

[0060] S3. Constant volume filtration: The solution was filtered through a 0.22 μm polytetrafluoroethylene filter membrane to remove insoluble impurities, and then transferred to a 1000 mL volumetric flask and constant volume to prepare an electrolyte.

[0061] Performance parameters: Hydrogen evolution overpotential @10mA / cm 2 =235mV, conductivity@25℃=192mS / cm, viscosity@-40℃=16.8mPa·s.

[0062] Example 7: 10MKOH+0.08MBMIM-BF4 electrolyte

[0063] S1. Preparation of KOH mother liquor: Dissolve 561 g of KOH in 600 mL of deionized water at a temperature below 30°C. Use mechanical stirring (250 rpm) and introduce condensed water to control the temperature to ≤35°C. After 45 minutes, the solution is completely clear and cooled to 25°C.

[0064] S2. Ionic liquid composite: 18.08 g of BMIM-BF4 (purity 99.5%) was weighed, and KOH mother liquor was added and stirred at 350 rpm for 45 minutes. During this period, ultrasonic treatment was performed for 5 minutes every 15 minutes (power 150 W) to promote dissolution.

[0065] S3. Fine preparation: The solution was filtered through a 0.1 μm nylon filter membrane to remove possible mechanical impurities, and the volume was fixed to 1000 mL to prepare a high-concentration electrolyte.

[0066] Performance parameters: Hydrogen evolution overpotential @10mA / cm 2 =225mV, conductivity@25℃=210mS / cm, viscosity@-40℃=17.5mPa·s.

[0067] Example 8: 8MKOH+0.05M recrystallized BMIM-BF4 electrolyte

[0068] S1. Preparation of KOH mother liquor: prepare 8K KOH solution in the same manner as in Example 2, and perform an additional activated carbon adsorption and impurity removal step: add 5 g of activated carbon and stir for 30 minutes, then filter and set aside.

[0069] S2. Ionic liquid treatment: BMIM-BF4 was purified by recrystallization (purity 99.9%): 2.10 g of the crude product was dissolved in 50 mL of acetonitrile, cooled to 0°C for crystallization for 2 hours, centrifuged and vacuum dried for 12 hours to obtain a high-purity product.

[0070] S3. Compound volume adjustment: Add the purified BMIM-BF4 to the KOH mother liquor and stir at 300 rpm for 60 minutes. Filter the solution three times through a 0.22 μm filter membrane (rinse the filter membrane with deionized water after each filtration) and adjust the volume to 1000 mL.

[0071] Performance parameters: Hydrogen evolution overpotential @10mA / cm 2 =215mV, conductivity@25℃=212mS / cm, viscosity@-40℃=14.5mPa·s.

[0072] Comparative Example 1: Pure 8MKOH electrolyte

[0073] Preparation method: Same as step 1 of Example 2, without adding ionic liquid, and directly filtering to constant volume. Comparative Example 2: 8MKOH + 0.05M theophylline electrolyte

[0074] Preparation of KOH mother liquor: same as in Example 2.

[0075] Additive dissolution: Add 18.02 g of theophylline (C7H8N4O2, purity 98%), heat to 50°C and stir for 90 minutes until dissolved.

[0076] Constant volume filtration: After cooling, constant volume filtration is set aside.

[0077] Comparative Example 3: Electrolyte composition: 8mol / L KOH + 0.05mol / L EMIM-BF4

[0078] Hydrogen evolution overpotential@10mA / cm 2 : 240mV

[0079] Stability decay (1000h): 8%

[0080] Platinum catalyst toxicity is non-toxic

[0081] Defects: The cationic carbon chain is too short, and the interface enrichment efficiency is 25% lower.

[0082] Comparative Example 4: Electrolyte composition: 8mol / L KOH + 0.05mol / L BMIM-Cl

[0083] Stability degradation (1000h): 15%

[0084] The toxicity of platinum catalyst is caused by chlorine adsorption on the platinum surface.

[0085] Defects shown: Cl - Causes electrode corrosion, corrosion current density 1.2mA / cm 2 Catalytic performance test part

[0086] Test methods and conditions

[0087] Electrode preparation:

[0088] Nickel foam electrode: Cut 1 cm × 1 cm nickel foam (thickness 1.6 mm, porosity 95%), ultrasonically clean with 1 M HCl for 10 minutes to remove the surface oxide layer, clean with deionized water and ethanol for 5 minutes each, and vacuum dry at 60°C for 12 hours.

[0089] Platinum sheet electrode: Cut a 1 cm × 1 cm platinum sheet (thickness 0.1 mm, purity 99.9%), soak it in aqua regia for 5 minutes, rinse it with deionized water until neutral, and dry it at 60°C for later use.

[0090] Electrochemical testing apparatus: A three-electrode system was used, with the working electrode being the electrode prepared above, the reference electrode being a Hg / HgO electrode (1M KOH, E = 0.098 V vs. SHE), and the auxiliary electrode being a graphite rod (6 mm diameter). The electrolyte volume was 100 mL, and high-purity N2 was passed through the electrolyte for 30 minutes before testing to remove oxygen. Aeration continued during the test.

[0091] Test items and parameters:

[0092] Linear sweep voltammetry (LSV): scan range -1.2 V to -0.2 V vs. Hg / HgO, scan rate 5 mV / s, recording 10 mA / cm 2 The overpotential for hydrogen evolution at different current densities.

[0093] Tafel slope (Tafel): calculated by fitting the LSV curve using the Tafel equation (η = a + blog|j|), where η is the overpotential, j is the current density, and b is the Tafel slope.

[0094] Electrochemical impedance spectroscopy (EIS) was performed in the frequency range of 100 kHz to 0.01 Hz, with an AC amplitude of 5 mV. The test potential was 100 mV negative of the open circuit potential. The equivalent circuit was fitted using ZSimpWin software.

[0095] Cyclic voltammetry (CV) was performed in the range of -1.0 V to -0.2 V vs. Hg / HgO, at a scan rate of 100 mV / s, for 1000 cycles. The changes in the LSV curves before and after the cycles were recorded.

[0096] Chronopotentiometry (CP): constant current density 10 mA / cm 2 , the test time is 24 hours, and the changes of the slot voltage over time are recorded.

[0097] Test results and analysis

[0098] 1. Hydrogen evolution overpotential and Tafel slope

[0099]

[0100] analyze:

[0101] The overpotential of Example 2 on the nickel foam electrode is reduced by 50mV compared with Comparative Example 1.

[0102] The Tafel slope decreased by 32 mV / dec, indicating that the ionic liquid promoted the Volmer step (H2O+e - →H*+OH-);

[0103] On the platinum electrode, the overpotential of Example 2 decreased by 40 mV, and the Tafel slope decreased from 60 mV / dec to 48 mV / dec, indicating that the ionic liquid changed the rate-determining step of hydrogen evolution from Volmer-Heyrovsky mechanism to Volmer-Tafel mechanism, thereby accelerating the composite desorption of H*.

[0104] 2. Electrochemical Impedance Spectroscopy (EIS) Analysis

[0105]

[0106] Equivalent circuit model: Rs-(R1-CPE1)-(R2-CPE2), where:

[0107] Rs: solution resistance;

[0108] R1-CPE1: interface ion adsorption resistance and capacitance;

[0109] R2-CPE2: Charge transfer resistance and capacitance.

[0110] analyze:

[0111] The R1 of Example 2 is reduced by 53% (foam nickel electrode) and 57% (platinum electrode) compared with Comparative Example 1, indicating that BMIM + The adsorption of cations on the electrode surface promotes interfacial ion transport;

[0112] R2 decreased by 58% (nickel foam) and 57% (platinum), indicating that the ionic liquid significantly reduced the charge transfer resistance and accelerated the hydrogen evolution reaction;

[0113] The CPE-P value is close to 1, indicating that the electrode surface uniformity is good and the ionic liquid does not cause electrode corrosion or increase surface heterogeneity.

[0114] 3. Stability test (1000 CV cycles)

[0115]

[0116] analyze:

[0117] After 1000 cycles on the nickel foam electrode, the performance degradation of Example 2 was only 4.5%, which was much lower than the 14.8% of Comparative Example 1, indicating that the interfacial protective film formed by the ionic liquid effectively inhibited electrode corrosion.

[0118] The attenuation rate of Example 2 on the platinum electrode is 4.8%, while that of Comparative Example 1 is 13.8%, indicating that the ionic liquid reduces the oxidation rate of the platinum surface and prolongs the life of the catalyst.

[0119] 4. Low temperature performance test (-20℃)

[0120]

[0121] analyze:

[0122] At -20°C, the conductivity of Example 2 was increased by 50% (nickel foam system) and 46% (platinum system) compared with Comparative Example 1, indicating that the ionic liquid improved the ionic conductivity at low temperatures.

[0123] The overpotential decreased by 70 mV (nickel foam) and 50 mV (platinum), indicating that ionic liquids can still effectively reduce the activation energy of hydrogen evolution at low temperatures;

[0124] The current density @-1.0 V increased by 108% (nickel foam) and 61% (platinum), showing the advantage of Example 2 in hydrogen evolution efficiency at low temperatures.

[0125] 5. Chronopotentiometry (24-hour stability)

[0126]

[0127] analyze:

[0128] In Example 2, the cell voltage fluctuation on the nickel foam electrode for 24 hours was only ±1.7%, which was much lower than the ±7.0% in Comparative Example 1, indicating that the ionic liquid stabilized the electrode / electrolyte interface.

[0129] The voltage fluctuation of Example 2 on the platinum electrode is ±1.2%, while that of Comparative Example 1 is ±4.5%, further demonstrating that the ionic liquid improves the stability of the electrolysis process.

[0130] Compared with comparative example 1 (pure 8M KOH electrolyte): the core advantage lies in "low dose efficiency"

[0131] Comparative Example 1 is a pure KOH electrolyte without any additives, while Example 1 can significantly optimize the hydrogen evolution reaction performance by adding 0.01M BMIM-BF4 even at a very low dosage:

[0132] Reduce hydrogen evolution overpotential and accelerate reaction kinetics

[0133] Refer to the test results of Example 2 (same 8M KOH matrix, 0.05M BMIM-BF4), BMIM + Cations can promote the Volmer step (H2O+e - →H*+OH-) and reduce charge transfer resistance. Although Example 1 has a lower concentration, the hydrogen evolution overpotential (270 mV in Comparative Example 1) and Tafel slope (110 mV / dec in Comparative Example 1) of the nickel foam electrode are still significantly lower than those of pure KOH (Comparative Example 1), making the rate-determining step of the reaction more efficient.

[0134] Compared with the comparative examples, Example 1 has the following advantages:

[0135] In pure KOH electrolyte, the electrode surface is easily - Corrosion occurs (such as oxidation of nickel foam and oxidation of platinum surface), resulting in a performance degradation of 14.8% (nickel foam) and 13.8% (platinum) after 1000 CV cycles. + The formed interface protective film can inhibit corrosion, and the attenuation rate after cycling is much lower than that of Comparative Example 1. In addition, the cell voltage fluctuation in the 24-hour chronopotentiometry test is smaller (±1.7% in Reference Example 2 vs. ±7.0% in Comparative Example 1), thereby improving interface stability and reducing performance degradation.

[0136] Pure KOH at low temperature (such as -20 ° C) due to the enhanced ion association, the conductivity of the nickel foam system in Comparative Example 1 is 110mS / cm. + The strong interaction with OH- improves the low-temperature conductivity, thereby reducing the overpotential and increasing the current density (better than the 350mV overpotential and 12mA / cm of comparative example 1). 2 current density).

[0137] Compared with Comparative Example 2 (8M KOH + 0.05M theophylline electrolyte), the advantages of the present invention are "simple preparation and low-temperature applicability". Comparative Example 2 uses theophylline as an additive, which needs to be heated to 50°C and stirred for 90 minutes to dissolve. However, the BMIM-BF4 of Example 1 can be completely dissolved by stirring at 300 rpm at room temperature for 60 minutes (the solution is colorless and transparent), making the preparation process more energy-efficient and easy to operate.

[0138] In addition, as an organic small molecule, the molecular structure of theophylline cannot be compared with BMIM. + In that way, it is difficult to improve the ion conductivity at low temperatures (such as -20°C) by optimizing the electrode / electrolyte interface through cation adsorption, and the overpotential and current density performance will be significantly worse than that of Example 1 (refer to the improvement effect of BMIM-BF4 on low temperature performance).

[0139] Compared with Comparative Example 3 (8MKOH+0.05MEMIM-BF4 electrolyte): the advantage is "higher interface enrichment efficiency"; the EMIM-BF4 used in Comparative Example 3 and the BMIM-BF4 in Example 1 are both imidazole ionic liquids, but EMIM + The carbon chain of the cation (ethyl) is shorter than that of BMIM + (Butyl). According to the description of Comparative Example 3, its "cation carbon chain is too short, and the interface enrichment efficiency is 25% lower", resulting in a hydrogen evolution overpotential of 240 mV (nickel foam electrode).

[0140] BMIM of Example 1 + Because the carbon chain is longer, the adsorption capacity on the electrode surface is stronger and the interface enrichment efficiency is higher. Even if the concentration is only 0.01M, the hydrogen evolution overpotential is still lower than 240mV, and the charge transfer resistance (R2) and interface adsorption resistance (R1) are smaller (refer to the reduction of R1 and R2 in Example 2), and the reaction kinetics are better.

[0141] Compared with Comparative Example 4 (8MKOH+0.05MBMIM-Cl electrolyte): the advantages are "no corrosion risk and high stability"; the BMIM-Cl in Comparative Example 4 contains Cl-, which will cause "electrode corrosion (corrosion current density 1.2mA / cm 2 )” and “platinum catalyst poisoning by chlorine adsorption”, with a stability degradation of 15% after 1000 hours.

[0142] The BMIM-BF4 of Example 1 is prepared with BF4 - Anion, no Cl - The corrosion effect of the electrolytic solution will not damage the electrode structure or poison the catalyst, the stability decay rate is much lower than 15% (4.5% in reference example 2), and the cell voltage fluctuation is smaller during long-term operation, making it suitable for long-life electrolysis systems.

[0143] Example 1 achieves "low-dose, high-efficiency" performance improvement compared to pure KOH electrolyte (Comparative Example 1) by adding low-dose BMIM-BF4; it is easier to prepare and has better low-temperature performance than theophylline additive (Comparative Example 2); it has higher interface enrichment efficiency than the short carbon chain ionic liquid EMIM-BF4 (Comparative Example 3); and it has no corrosion risk and better stability than the chloride-containing ionic liquid BMIM-Cl (Comparative Example 4). Its core advantage comes from BMIM + The interface regulation effect of BF4 - Due to its chemical inertness, it can balance performance and cost at low addition amounts, making it of practical value.

[0144] The core innovation of this invention lies in the discovery that a specific ratio of imidazole ionic liquid to KOH can significantly improve the interfacial properties of the electrolyte, thereby enhancing hydrogen evolution performance. Specifically:

[0145] Under the action of the electric field, the cations of imidazolium ionic liquids (such as BMIM+) will migrate to the cathode interface, change the interfacial double layer structure, reduce the activation energy of the hydrogen evolution reaction, and then realize the regulation of the interfacial double layer.

[0146] The hydrogen bond network is restructured, with hydrogen atoms on the imidazole ring forming hydrogen bonds with oxygen atoms in water molecules. This restructures the interfacial water structure and increases the proportion of free water molecules, thereby promoting water dissociation and hydrogen evolution. Infrared spectroscopy analysis shows that the addition of BMIM-BF4 significantly shifts and broadens the broad peak near 3400 cm-1 in the electrolyte, confirming the alteration of the hydrogen bond network.

[0147] Optimizing ion conduction: The addition of an appropriate amount of ionic liquid does not significantly increase the viscosity of the electrolyte. Instead, due to its high ionic conductivity, it can optimize the ion conduction path and improve the conductivity. Experiments have shown that the conductivity of 8MKOH electrolyte with 0.05MBMIM-BF4 added at 25°C is 12% higher than that of pure 8MKOH electrolyte.

[0148] Promote bubble desorption. The surface activity of imidazole ionic liquids reduces the contact angle between bubbles and the electrode surface, promotes bubble desorption, reduces bubble coverage of the electrode surface, and thus improves mass transfer efficiency.

[0149] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A KOH electrolyte composition modified with an imidazole ionic liquid, characterized in that: include: KOH with a concentration of 6-10 mol / L, wherein the KOH is analytical grade and has a purity of ≥85%; 1-Butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4) at a concentration of 0.01-0.1 mol / L; The balance is deionized water, wherein the conductivity of the deionized water is ≤10 μS / cm.

2. The electrolyte composition according to claim 1, characterized in that The purity of the BMIM-BF4 is ≥99%, and its cation is 1-butyl-3-methylimidazolium cation (butyl chain length is C4), and its anion is tetrafluoroborate ion (BF4 - ), and the BMIM-BF4 was filtered through a 0.22 μm filter membrane at least once to remove impurities.

3. The electrolyte composition according to claim 1, characterized in that The KOH concentration is preferably 8 mol / L, and the BMIM-BF4 concentration is preferably 0.05 mol / L; under this ratio, the electrolyte has a conductivity of ≥208 mS / cm at 25°C, a viscosity of ≤14.5 mPa·s at -40°C, and a flow rate of 10 mA / cm 2 The hydrogen evolution overpotential is ≤220mV at this current density.

4. A method for preparing the electrolyte composition according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1. Add KOH pellets to deionized water at a constant temperature of 20°C and stir at a stirring rate of 150-250 rpm until completely dissolved to prepare a 6-10 mol / L KOH solution. During the dissolution process, the solution temperature is controlled to be ≤35°C. S2. After the solution obtained in step S1 is cooled to room temperature, BMIM-BF4 is added thereto, and the mixture is stirred at a stirring rate of 250-350 rpm for 30-90 minutes at room temperature to prepare a homogeneous electrolyte.

5. The preparation method according to claim 4, characterized in that After step S2, the method further includes: filtering the homogeneous electrolyte through a 0.22 μm polytetrafluoroethylene filter membrane, transferring the solution into a volumetric flask, and diluting the volume to the target volume with deionized water. After diluting, the solution volume error is ≤±0.5%, and the solution is colorless and transparent.

6. Use of the electrolyte composition according to any one of claims 1 to 3 in hydrogen production by alkaline water electrolysis, characterized in that: For hydrogen evolution catalytic reaction, the working electrode is selected from: The nickel foam electrode, with a size of 1 cm × 1 cm, a thickness of 1.6 mm, and a porosity of 95%, was pretreated by ultrasonic cleaning with 1 M HCl for 10 minutes; Nickel-iron alloy electrode, its hydrogen evolution active site density is 20% higher than that of pure nickel; The platinum sheet electrode has a specification of 1 cm×1 cm, a thickness of 0.1-0.5 mm, a purity of 99.9%, and is pretreated by soaking in aqua regia for 5 minutes.

7. The use according to claim 6, characterized in that The electrolyte composition operates stably within a temperature range of -60°C to 80°C, with an optimal operating temperature of 70°C; the conductivity is ≥150mS / cm at -20°C, the weight loss rate is <1% as tested by thermogravimetric analysis (TG) at 80°C, and there is no solidification phenomenon at -60°C.

8. The use according to claim 6, characterized in that The electrolyte composition is 10mA / cm 2 The hydrogen evolution overpotential under current density is 215-235mV, which is 20-50mV lower than that of pure KOH electrolyte with the same concentration; at a voltage of 1.6V, the current density is ≥30mA / cm 2 (When nickel foam electrode is the working electrode).

9. The use according to claim 6, characterized in that The interfacial charge transfer resistance (R2) between the electrolyte composition and the working electrode is reduced by ≥50% compared with pure KOH electrolyte; after 1000 cyclic voltammetry (CV) tests, the hydrogen evolution overpotential performance decay rate is ≤4.8%, wherein the life of the nickel foam electrode is ≥5000h, and the corrosion current density of the nickel-iron alloy electrode is ≤0.5mA / cm 2 .

10. The use according to claim 6, characterized in that The electrolyte composition is non-toxic when in contact with a precious metal catalyst, and the activity decay rate of a platinum-based electrode is ≤5% after 1000 hours of continuous operation; in a 24-hour chronopotentiometry (CP) test, the cell voltage fluctuation range is ≤±1.7%, and the electrolyte always remains in a homogeneous and transparent state.

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