Method for improving reaction efficiency of alkaline electrolyzed water

Abstract

The invention relates to a method for improving the reaction efficiency of alkaline electrolyzed water, a buffering agent is added into an alkaline electrolyzed water reaction system to maintain the local pH stability of the surface of an electrode so as to reduce the overpotential, the buffering agent forms a buffering system, and the buffering system is composed of one or more chemical substances of K3PO4, K2HPO4, Na2SiO3 and organic amine buffering agents. Compared with the prior art, the method has the advantages that the buffer agent is added into the alkaline electrolyzed water reaction system to maintain the stability of the local pH of the surface of the electrode, so that the overpotential is reduced, and the electrolysis efficiency is improved. The buffer system disclosed by the invention is composed of a plurality of chemical substances, and can be independently used or used in proportion in a combined manner so as to adapt to different alkaline electrolysis conditions and electrolysis process requirements.

Description

Technical Field

[0001] The invention relates to alkaline water electrolysis technology, and in particular to a method for improving the reaction efficiency of alkaline water electrolysis. Background Art

[0002] As an important means of hydrogen production, alkaline water electrolysis technology has been widely used in industrial production. In this process, potassium hydroxide (KOH) is usually used as an electrolyte to produce hydrogen and oxygen through electrolysis. This reaction depends on the hydroxide ion (OH - ) participate in the electrolysis of water. The efficiency of the water electrolysis reaction is closely related to the pH value near the electrode surface. Under normal conditions, as the electrolysis of water proceeds, the hydroxide ions on the electrode surface are rapidly consumed, resulting in a decrease in the local pH, which in turn affects the water electrolysis efficiency and electrode life.

[0003] In order to maintain an efficient electrolysis reaction, it is particularly important to maintain a stable pH near the electrode surface. A local decrease in pH will lead to an increase in the oxygen evolution reaction (OER) overpotential, resulting in a decrease in energy efficiency. Therefore, how to effectively alleviate the fluctuation of local pH and maintain a stable supply of hydroxide ions has become a key technical issue in improving the efficiency of alkaline water electrolysis.

[0004] In the prior art, researchers have tried to increase the KOH concentration or optimize the electrolysis efficiency. However, too high a KOH concentration will increase the difficulty of operation and may cause corrosion problems in equipment in some cases. At the same time, simply relying on physical means such as stirring or flowing the electrolyte to increase the replenishment rate of hydroxide, although it can improve the stability of the local electrolysis reaction to a certain extent, it cannot fundamentally solve the problem of pH drop near the electrode surface.

[0005] In similar electrochemical processes (such as electroplating reactions), the pH stability of the solution is usually maintained by introducing appropriate pH buffers. Common buffers such as boric acid effectively alleviate pH fluctuations caused by changes in hydrogen ion concentration during electroplating. However, in an alkaline water electrolysis environment, traditional buffers such as boric acid are not applicable, so it is crucial to find a system that can effectively buffer local pH changes under strong alkaline conditions. Summary of the invention

[0006] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a method for improving the efficiency of alkaline water electrolysis reaction, which aims to introduce a buffer system into KOH, adjust the hydroxide concentration in the solution under an alkaline environment, maintain the pH stability near the electrode surface, thereby improving the water electrolysis efficiency and extending the service life of the electrode.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] The present invention provides a method for improving the efficiency of alkaline water electrolysis reaction, wherein a buffer is added to the alkaline water electrolysis reaction system to maintain the local pH stability of the electrode surface, thereby reducing the overpotential, wherein the buffer constitutes a buffer system, and the buffer system consists of K 3 PO 4 , K 2 HPO 4 、Na 2 SiO 3 , and one or more chemical substances in organic amine buffers.

[0009] The present invention adds a buffer to the alkaline water electrolysis reaction system to maintain the local pH stability of the electrode surface, thereby reducing the overpotential and improving the electrolysis efficiency. The buffer system of the present invention is composed of a variety of chemical substances, which can be used alone or in combination in proportion to adapt to different alkaline electrolysis conditions and electrolysis process requirements.

[0010] Furthermore, the organic amine buffer is triethanolamine.

[0011] Furthermore, when the buffer system is K 3 PO 4 When used alone, K 3 PO 4 The concentration is 0.05M to 0.1M, used to maintain the electrolyte pH between 12 and 14.

[0012] Furthermore, when the buffer system is K 3 PO 4 With K 2 HPO 4 When used in combination, K 3 PO 4 With K 2 HPO 4 The mass ratio of 5:1 to 8:1 is 80:20 to 50:50, which is used to expand the pH buffer range.

[0013] Furthermore, the electrolyte of the alkaline water electrolysis reaction system is composed of a KOH aqueous solution, and the concentration of KOH is 0.1M to 8M.

[0014] Furthermore, when the buffer system is K 3 PO 4 with Na 2 SiO 3 When used in combination, Na 2 SiO 3 The concentration range is 0.01M to 0.05M and is used under conditions of high current density or rapid consumption of hydroxide ions.

[0015] Furthermore, it is characterized in that the concentration of KOH aqueous solution in the electrolyte is 1M, and K 3 PO 4 With K 2 HPO 4 Mix in a ratio of 80:20, with a total buffer concentration of 0.05 M;

[0016] The electrolysis reaction temperature is 25 degrees Celsius, the anode and cathode are both nickel mesh electrodes, and the current density is 500mA / cm 2 , and through and The chemical equilibrium reaction adjusts the pH value near the electrode surface to maintain a stable local alkaline environment and reduce the overpotential during the electrolysis process.

[0017] Furthermore, the buffer system maintains local pH stability through the following buffering mechanisms:

[0018] K 3 PO 4 Dissociates in aqueous solution to form PO 4 3- , through the reaction Regulate hydroxide ion concentration;

[0019] K 2 HPO 4 Dissociate to form hydrogen phosphate ion HPO 4 2- , through the reaction Regulate hydroxide ion concentration;

[0020] Na 2 SiO 3 Dissociation to form silicate ions SiO 3 2- , through the reaction pH changes under buffered alkaline conditions;

[0021] Triethanolamine reacts under alkaline conditions. Buffers changes in hydroxide.

[0022] Furthermore, the amount of the buffer added is adjusted according to the initial pH of the electrolyte, the reaction temperature, and the current density, and the total concentration of the buffer ranges from 0.01M to 0.1M.

[0023] Furthermore, during the electrolysis process, K 3 PO 4 With K 2 HPO 4 The combined buffer system adjusts the pH value near the electrode surface through the following chemical equilibrium reaction:

[0024]

[0025]

[0026] When OH near the electrode surface - When the local pH drops, the phosphate ions PO 4 3- and hydrogen phosphate ion HPO 4 2- By reacting with water to generate hydroxide ions OH - , thereby maintaining the stability of the local alkaline environment, allowing the oxygen evolution reaction and hydrogen evolution reaction to proceed under optimal conditions, reducing the overpotential during the electrolysis process.

[0027] The buffer system of the present invention is applicable to various alkaline water electrolysis reaction systems, including but not limited to: industrial hydrogen production systems, laboratory electrolysis systems, and systems combining renewable energy storage with water electrolysis hydrogen production.

[0028] Compared with the prior art, the present invention overcomes the problems of reduced efficiency and shortened electrode life caused by pH fluctuation in the traditional electrolysis process by introducing a buffer system into the alkaline water electrolysis system, and has significant advantages:

[0029] First, the present invention effectively improves the electrolysis efficiency. By adding phosphate, silicate or organic amine buffers to the electrolyte, the hydroxide ion concentration on the electrode surface can be quickly adjusted, local pH fluctuations can be reduced, and the overpotential of the electrolysis reaction can be reduced, thereby improving the production efficiency of hydrogen and oxygen.

[0030] Secondly, the addition of the buffer system can form a stable pH environment on the electrode surface, preventing electrode corrosion and passivation caused by drastic changes in pH, significantly extending the service life of the electrode and reducing maintenance and replacement costs. In addition, the buffer system can enhance the stability of the entire water electrolysis system, especially under conditions of high current density or rapid hydroxide consumption. The buffer system can ensure the pH balance of the electrolyte, thereby maintaining the continuity and efficiency of the reaction.

[0031] More importantly, the buffer system of the present invention has strong adaptability and is suitable for a variety of different working conditions and application scenarios, including industrial hydrogen production, laboratory electrolysis, and systems combined with renewable energy storage. The buffer used is low-cost, easy to obtain, and has excellent environmental performance. It will not produce harmful by-products during use, and meets the production requirements of green environmental protection. At the same time, the buffer system of the present invention is easy to integrate and apply, and can be quickly deployed in existing alkaline water electrolysis systems without equipment changes, and has good operability and promotion prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The pH change curve near the electrode when using / not using buffer;

[0033] Figure 2 The electrode OER performance curve with and without buffer;

[0034] Figure 3 The durability data of electrolyzing water for 3000 hours under the buffer system of this embodiment;

[0035] Figure 4 Surface morphology before and after electrode reaction in the buffer system of this embodiment. DETAILED DESCRIPTION

[0036] In general, the present invention provides a method for reducing overpotential and improving electrolysis efficiency by adding a buffer to an alkaline water electrolysis reaction system to maintain local pH stability on the electrode surface. The buffer system of the present invention is composed of a variety of chemical substances, which can be used alone or in combination in proportion to adapt to different alkaline electrolysis conditions and electrolysis process requirements.

[0037] 1. Composition of buffer system

[0038] The buffer system of the present invention is composed of one or more of the following chemical substances:

[0039] (1) Tripotassium phosphate (K 3 PO 4 )

[0040] K 3 PO 4 It is a strong alkaline buffer suitable for the pH range of 12-14, which can release hydroxide ions (OH - ), by quickly adjusting the local pH to stabilize the reaction environment. In alkaline electrolyzed water, K 3 PO 4 After dissolution, phosphate ions (PO 4 3- ), which can react with hydrogen ions (H + ) or water interactions, providing rapid pH adjustment capability and reducing pH fluctuations on the electrode surface.

[0041] (2) Potassium hydrogen phosphate (K 2 HPO 4 )

[0042] K 2 HPO 4 It is a buffer suitable for pH 11-12. Its function is to 3 PO 4Used together, a wider pH buffer range is formed. When the pH fluctuates greatly, K 2 HPO 4 Can be used with K 3 PO 4 Used in combination to achieve effective regulation of pH near the electrode surface. 2 HPO 4 Through its hydrogen phosphate ion (HPO 4 2- ) to adjust the alkalinity of the electrolyte and moderate OH - consumption rate.

[0043] (3) Sodium silicate (Na 2 SiO 3 )

[0044] Na 2 SiO 3 It is a buffer suitable for high pH environments and is suitable for rapid replenishment of hydroxide ions under strong alkaline conditions (pH>13). It is stable in alkaline environments and can provide additional pH stability support under high current density water electrolysis conditions, especially for OH - Rapidly consumed reaction system. 2 SiO 3 It can form a good synergistic effect with the phosphate buffer system to further improve the pH stability of the electrode surface.

[0045] (4) Organic amine buffers (such as triethanolamine, TEA)

[0046] Organic amine buffers can provide buffering under alkaline conditions, and when used in combination with inorganic buffers (such as phosphates and silicates), they can enhance the pH adjustment capacity of the buffer system. Triethanolamine (TEA), as an optional buffer, can provide additional pH adjustment capacity in environments with large pH fluctuations, while also having good electrochemical stability.

[0047] 2. Combination of buffer systems

[0048] The buffer system of the present invention can select different buffers for combination use according to the actual application scenario to meet different pH adjustment requirements. Common combination schemes include but are not limited to the following:

[0049] (1) K 3 PO 4 Used alone: ​​When the pH of the electrolyte needs to be maintained between 12-14, K 3 PO 4 It can be used alone as the main buffer at a concentration of 0.05M to 0.1M.

[0050] (2) K 3 PO 4 With K 2 HPO 4 Combination use: When it is necessary to expand the pH buffer range, K can be used in combination in proportion. 3 PO 4 With K 2 HPO 4 , the ratio is 80:20 to 50:50, and the specific ratio can be adjusted according to the actual pH fluctuation of the electrolysis reaction. 3 PO 4 Provides buffering capacity under high pH conditions, K 2 HPO 4 It plays an auxiliary role in a relatively low pH range.

[0051] (3)K 3 PO 4 with Na 2 SiO 3 Combination use: Under conditions of high current density or rapid consumption of hydroxide ions, K 3 PO 4 with Na 2 SiO 3 The former maintains pH stability, while the latter provides rapid OH - Supplement, Na 2 SiO 3 The concentration range is 0.01M to 0.05M.

[0052] (4)K 3 PO 4 Used in combination with organic amine buffers (such as TEA): In systems with complex reaction conditions and large pH fluctuations, the pH adjustment ability can be further enhanced by adding organic amine buffers. The concentration range of TEA is 0.01M to 0.05M.

[0053] 3. Application of buffer system

[0054] The buffer system of the present invention can be directly added to the electrolyte of the alkaline water electrolysis reaction. The amount of the buffer added is adjusted according to specific conditions such as the initial pH of the electrolyte, the reaction temperature, and the current density. Generally, the total concentration of the buffer ranges from 0.01M to 0.1M, and the specific ratio depends on the pH fluctuation range and the consumption rate of hydroxide ions during the electrolysis process.

[0055] (1) Composition of the electrolyte: The electrolyte is usually composed of potassium hydroxide (KOH), and the mass concentration of KOH is usually 0.1M to 8M, which can be adjusted according to the requirements of the electrolysis system.

[0056] (2) Addition of buffer: When preparing the electrolyte, add the selected buffer into the electrolyte in a certain proportion, stir evenly and then carry out the electrolysis reaction.

[0057] 4. Regulation mechanism of buffer system

[0058] During the electrolysis of water, hydroxide ions (OH - ) participates in the reaction and is consumed, resulting in a decrease in local pH. The buffer system of the present invention provides hydroxide ion supplementation through the chemical equilibrium reaction of the buffer, thereby maintaining local pH stability.

[0059] (1) Tripotassium phosphate (K 3 PO 4 ) Buffering mechanism

[0060] Tripotassium phosphate (K 3 PO 4 ) dissociates in aqueous solution to form phosphate ions (PO_4^{3-}). Under alkaline conditions, the concentration of hydroxide ions is adjusted by the following reaction:

[0061]

[0062] (2) Potassium hydrogen phosphate (K 2 HPO 4 ) Buffering mechanism

[0063] Potassium hydrogen phosphate (K 2 HPO 4 ) dissociates to form hydrogen phosphate ions (HPO_4^{2-}), which regulate the hydroxide ion concentration through the following reaction:

[0064]

[0065] (3) Sodium silicate (Na 2 SiO 3 ) Buffering mechanism

[0066] Sodium silicate (Na 2 SiO 3 ) dissociates to form silicate ions (SiO_3^{2-}), and buffers pH changes under alkaline conditions through the following reaction:

[0067]

[0068] (4) Buffering mechanism of organic amine buffers (such as triethanolamine, TEA)

[0069] Triethanolamine (TEA) buffers the change of hydroxide ions under alkaline conditions through the following reaction:

[0070]

[0071] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. Any features such as preparation means, materials, structures or composition ratios not clearly described in this technical solution are regarded as common technical features disclosed in the prior art.

[0072] Example 1

[0073] This example introduces a method of introducing tripotassium phosphate (K 3 PO 4 ) and potassium dihydrogen phosphate (K 2 HPO 4 ) combined buffer system, an application method for adjusting the pH of the electrode surface, improving the electrolysis efficiency and extending the life of the electrolytic cell.

[0074] 1. Preparation of Electrolyte

[0075] Potassium hydroxide (KOH) was prepared into a 1M solution as the base component of the electrolyte. Then, K 3 PO 4 With K 2 HPO 4 Mix and set the total concentration of the buffer to 0.05 M. Add tripotassium phosphate and dipotassium hydrogen phosphate buffers to the 1 M KOH solution and stir thoroughly to make them evenly dissolved in the electrolyte. This mixed buffer system can stabilize the hydroxide ion (OH - ) concentration to prevent drastic fluctuations in local pH.

[0076] 2. Setting the conditions for electrolysis reaction

[0077] The temperature of the electrolysis reaction was controlled at 25 degrees Celsius and maintained at room temperature. Nickel mesh electrodes were used as the anode and cathode in the electrolysis reaction, and the current density was set to 500 mA / cm 2 Immerse the electrode in the pre-prepared 1M KOH solution containing a buffer, ensuring that the electrode surface is completely in contact with the electrolyte.

[0078] 3. pH adjustment during electrolysis

[0079] During the electrolysis process, K 3 PO 4 With K 2 HPO 4 The combined buffer system adjusts the pH value near the electrode surface through the following chemical equilibrium reaction:

[0080]

[0081]

[0082] When OH near the electrode surface - When the local pH drops, phosphate ions (PO 4 3- ) and hydrogen phosphate ions (HPO 4 2- ) reacts with water to generate hydroxide ions (OH - ), thereby maintaining the stability of the local alkaline environment, ensuring that the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) proceed under optimal conditions, and reducing the overpotential during the electrolysis process.

[0083] 4. Improvement of electrolysis efficiency

[0084] Figure 1 The pH curve near the electrode when using / not using buffer. Figure 2 The figure shows the electrode OER performance curve with and without buffer. When the buffer system is used, the pH near the anode surface is maintained above 13.6 during the electrolysis reaction, and the pH near the anode surface in the buffer-free system is reduced to about 12.8. In addition, the water electrolysis efficiency is improved when the buffer system is used. The presence of the buffer system reduces the negative impact of electrolyte pH fluctuations on the reaction efficiency, ensures the continuous supply of hydroxide ions, and significantly improves the water electrolysis efficiency.

[0085] 5. Extended electrode life

[0086] Figure 3 In order to obtain the 3000-hour durability data of water electrolysis under this buffer system, the pH on the electrode surface was effectively controlled during the long-term electrolysis reaction, avoiding electrode corrosion and passivation caused by pH fluctuations. After 3000 hours of continuous electrolysis operation, Figure 4 This is the surface morphology diagram before and after the electrode reaction in this buffer system. The electrode surface with the buffer system added is still smooth, with no obvious corrosion phenomenon, and the electrode performance has no obvious decline.

[0087] 6. Buffer compatibility

[0088] Visible K 3 PO 4 With K 2 HPO 4 The combined buffer system has good compatibility with KOH solution. During the entire electrolysis process, the electrolyte remains transparent and no precipitation is generated, ensuring the stability of the reaction. At the same time, the addition of the buffer does not significantly affect the conductivity of the electrolyte. The resistance is low during the entire electrolysis process, ensuring the efficiency of energy conversion.

[0089] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for improving the efficiency of alkaline water electrolysis reaction, characterized in that: A buffer is added to the alkaline water electrolysis reaction system to maintain the local pH stability of the electrode surface, thereby reducing the overpotential. The buffer constitutes a buffer system, which is composed of one or more chemical substances selected from K3PO4, K2HPO4, Na2SiO3, and organic amine buffers.

2. A method for improving the efficiency of alkaline water electrolysis reaction according to claim 1, characterized in that: The organic amine buffer is triethanolamine.

3. A method for improving the efficiency of alkaline water electrolysis reaction according to claim 1, characterized in that: When the buffer system is K3PO4 used alone, the concentration of K3PO4 is 0.05M to 0.1M, which is used to maintain the pH of the electrolyte between 12 and 14.

4. A method for improving the efficiency of alkaline water electrolysis reaction according to claim 1, characterized in that: When the buffer system is a combination of K3PO4 and K2HPO4, the mass ratio of K3PO4 to K2HPO4 is 80:20 to 50:50, which is used to expand the pH buffer range.

5. A method for improving the efficiency of alkaline water electrolysis reaction according to claim 1, characterized in that: The electrolyte of the alkaline water electrolysis reaction system is composed of a KOH aqueous solution, and the concentration of KOH is 0.1M to 8M.

6. A method for improving the efficiency of alkaline water electrolysis reaction according to claim 1, characterized in that: When the buffer system is a combination of K3PO4 and Na2SiO3, the concentration of Na2SiO3 ranges from 0.01M to 0.05M, which is used under conditions of high current density or rapid consumption of hydroxide ions.

7. A method for improving the efficiency of alkaline water electrolysis reaction according to claim 6, characterized in that: The concentration of KOH aqueous solution in the electrolyte is 1M, and K3PO4 and K2HPO4 are mixed in a ratio of 80:20, and the total concentration of the buffer is 0.05M; The electrolysis reaction temperature is 25 degrees Celsius, the anode and cathode are both nickel mesh electrodes, and the current density is 500mA / cm 2 , and through and The chemical equilibrium reaction adjusts the pH value near the electrode surface to maintain a stable local alkaline environment and reduce the overpotential during the electrolysis process.

8. A method for improving the efficiency of alkaline water electrolysis reaction according to claim 1, characterized in that: The buffer system maintains local pH stability through the following buffering mechanisms: K3PO4 dissociates in aqueous solution to form PO4 3- , through the reaction Regulate the hydroxide ion concentration; K2HPO4 dissociates to form hydrogen phosphate ions HPO4 2- , through the reaction Regulate the hydroxide ion concentration; Na2SiO3 dissociates to form silicate ions SiO3 2- , through the reaction pH changes under buffered alkaline conditions; Triethanolamine reacts under alkaline conditions. Buffers changes in hydroxide.

9. A method for improving the efficiency of alkaline water electrolysis reaction according to claim 1, characterized in that: The amount of the buffer added is adjusted according to the initial pH of the electrolyte, the reaction temperature, and the current density, and the total concentration of the buffer is in the range of 0.01M to 0.1M.

10. A method for improving the efficiency of alkaline water electrolysis reaction according to claim 6, characterized in that: During the electrolysis process, the combined buffer system of K3PO4 and K2HPO4 adjusts the pH value near the electrode surface through the following chemical equilibrium reaction: When the OH- near the electrode surface is consumed faster and the local pH drops, the phosphate ion PO4 3- and hydrogen phosphate ion HPO4 2- By reacting with water to generate hydroxide ions OH-, the local alkaline environment is maintained stable, so that the oxygen evolution reaction and the hydrogen evolution reaction proceed under optimal conditions, reducing the overpotential during the electrolysis process.

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