An Ag / AgCl reference electrode and its preparation method

Abstract

The present invention discloses an Ag / AgCl reference electrode and a preparation method thereof, belonging to the field of electrochemistry. The preparation method includes: using the pretreated clean Ag as the anode and platinum as the cathode, placing them in an electrolyte solution containing carbamide and betaine, and applying a current to generate the Ag / AgCl reference electrode through electrochemical in-situ conversion. The preparation method of the Ag / AgCl reference electrode provided by the present invention uses a brand-new silver electrode and a used silver electrode as the silver electrode matrix. Under the action of adding additives to the electrolyte solution, an AgCl conversion film layer is formed through electrochemical in-situ conversion. The AgCl conversion film has good uniformity and compactness, and the film layer has strong binding force, so that the film layer has strong adhesion and is not easy to fall off, and can meet the harsh use requirements of some electrochemical sensors. At the same time, the AgCl film layer is composed of uniformly distributed AgCl nanoparticles, which increases the specific surface area of the electrode. The prepared electrode has extremely high electrochemical stability; and the thickness is uniformly controllable, and the practicability is stronger.

Description

Technical Field

[0001] The present invention relates to the field of electrochemistry, and particularly to an Ag / AgCl reference electrode and a preparation method thereof. Background Art

[0002] Ag / AgCl electrodes have the advantages of simple structure, stable performance, good reversibility, and small temperature coefficient. Especially under high temperature and high pressure, AgCl has very low solubility and extremely high stability in aqueous solution systems. These characteristics enable it to be widely used in measuring some electrochemical parameters (such as current density and anode voltage) in some demanding environments. Currently, the preparation methods of Ag / AgCl electrodes include electrolysis method, thermal decomposition method, powder pressing method, and thermal dipping method, etc.

[0003] (1) Electrolysis method: The silver wire is polished clean to remove surface sulfides and oxides, and surface pretreatment work such as degreasing, activation, and cleaning is carried out. Then, the silver wire is placed in hydrochloric acid or NaCl solution for electrolysis to obtain the electrode. Due to its own characteristics, such as the ability to selectively adjust and control potential or current density and current mode, the electrolysis method provides a convenient and feasible experimental method for preparing nano-particles with controllable particle size and shape. However, the AgCl prepared by the traditional electrolysis method has a large particle size, poor film layer uniformity and compactness, low mechanical strength, and is easy to fall off.

[0004] (2) Thermal decomposition method: A mixture paste of Ag2O and AgClO3 is coated on a spiral platinum wire, and then reacted at 650 °C in a crucible furnace to decompose the coating into Ag and AgCl. The prepared electrode is immersed in dilute hydrochloric acid for a period of time to form the electrode. Due to impure products and difficult control of the production amount in the thermal decomposition method, the measurement accuracy is insufficient.

[0005] (3) Powder pressing method: The powder pressing method is prepared based on the principle of solid-phase reaction. Since the Ag / AgCl electrode prepared by the powder pressing method is easy to powder and peel off, the conductivity of the electrode becomes poor, and the limited exposed area makes the electrode vulnerable to contamination coverage, affecting the electrode sensitivity.

[0006] (4) Thermal dipping method: A certain proportion of insoluble metal salt raw materials are heated to a certain temperature to keep them in a molten state. Then, the metal matrix of this kind of salt is immersed in the molten raw material, taken out and cooled to make a certain amount of metal salt adhere to the surface of the metal matrix, and then part of the metal salt is reduced to metal to obtain the electrode. After thermal dipping, the electrode needs to be reduced, which is divided into chemical reduction (hydrogen reduction) and electrochemical reduction (passing a cathode current). The surface uniformity of the Ag / AgCl electrode prepared by the thermal dipping method is poor, which is caused by crystal defects on the electrode surface and different surface energies. Summary of the Invention

[0007] The object of the present invention is to provide an Ag / AgCl reference electrode and a preparation method thereof, which solve the problems of impure silver chloride film layer products, easy pulverization and peeling, uneven film layer, and uncontrollable film layer thickness in the Ag / AgCl reference electrode.

[0008] The present invention is realized through the following technical solutions:

[0009] The present invention provides a preparation method of an Ag / AgCl reference electrode, including:

[0010] Using the pretreated clean Ag as the anode and platinum as the cathode, placing them in an electrolyte solution containing carbamide and betaine, and applying a current to generate an Ag / AgCl reference electrode through in-situ electrochemical conversion.

[0011] Further, in the preparation method of the Ag / AgCl reference electrode, the pretreatment method of Ag includes: polishing the surface of the Ag electrode with sandpaper of 1000 - 1200 mesh and 1600 - 1800 mesh respectively for the initially used Ag electrode until the surface of the Ag electrode is bright and has no obvious scratches, ultrasonically cleaning in water and ethanol respectively, and then air-drying naturally.

[0012] Further, in the preparation method of the Ag / AgCl reference electrode, the pretreatment method of Ag includes: immersing the used Ag electrode in concentrated ammonia water until the AgCl on the surface of the Ag electrode completely falls off, rinsing with water, activating in concentrated nitric acid, then washing with water, and air-drying naturally.

[0013] Further, in the preparation method of the Ag / AgCl reference electrode, the main body of the electrolyte solution is a KCl solution.

[0014] Further, in the preparation method of the Ag / AgCl reference electrode, the concentration of the electrolyte solution is 0.5 mol / L - 1.5 mol / L.

[0015] Further, in the preparation method of the Ag / AgCl reference electrode, the preparation of the electrolyte solution containing carbamide and betaine includes: dissolving carbamide in betaine to form a mixed solution of 0.5 g / L - 2 g / L, and mixing the mixed solution and the electrolyte solution according to a volume ratio of (1 - 10):1000.

[0016] Further, in the preparation method of the Ag / AgCl reference electrode, the applied current is a constant current or an intermittent current of 1.5 mA / cm 2 ~6 mA / cm 2 of.

[0017] Further, in the preparation method of the Ag / AgCl reference electrode, when a constant current is adopted, the current duration is 30 min - 50 min.

[0018] Further, in the preparation method of the Ag / AgCl reference electrode, when intermittent current is adopted, a cycle is defined as the current lasting for 25 s - 35 s and then stopping for 80 s - 100 s, and this cycle is repeated 12 - 20 times.

[0019] The present invention also provides an Ag / AgCl reference electrode prepared by the above - mentioned preparation method of the Ag / AgCl reference electrode.

[0020] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0021] The preparation method of the Ag / AgCl reference electrode provided by the present invention is simple and easy to control the conditions, greatly improving the feasibility of the operation. This method uses a brand - new silver electrode and a used silver electrode as the silver electrode substrate, and generates an Ag / AgCl reference electrode through in - situ electrochemical conversion. Under the action of adding additives to the electrolyte, the uniformity and compactness of the silver chloride conversion film layer formed by in - situ electrochemical conversion are good, and the film layer has a strong binding force, so that the film layer has a strong adhesion and is not easy to fall off, which can meet the harsh use requirements of some electrochemical sensors. At the same time, the silver chloride film layer is composed of uniformly distributed silver chloride nanoparticles, increasing the specific surface area of the electrode. The prepared electrode has extremely high electrochemical stability; and the thickness is uniformly controllable, making it more practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings. In the drawings:

[0023] Figure 1 is the surface morphology diagram of the silver chloride film layer in Test Example 1 of the present invention; among them, Figure 1 (a), (b), and (c) respectively correspond to currents of 6 mA / cm 2 , 3 mA / cm 2 , 1.5 mA / cm 2 , with the current lasting for 30 s and stopping for 90 s as a cycle, and this cycle is repeated 15 times;

[0024] Figure 2 is the surface morphology diagram of the silver chloride film layer in Test Example 2 of the present invention; among them, Figure 2 (a), (b), and (c) are currents of 3 mA / cm 2 , and the current - lasting times are 30, 40, and 50 min respectively;

[0025] Figure 3 This is the cross-sectional view of the silver chloride film layer in Test Example 2 of the present invention; Figure 3 (a), (b), and (c) are when the current is 3 mA / cm 2 , and the current duration is 30, 40, and 50 minutes respectively. Specific Embodiments

[0026] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the embodiments and the accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention. For those conditions not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0027] The solution of the present invention is as follows:

[0028] A preparation method of an Ag / AgCl reference electrode, comprising:

[0029] Using the pre-treated clean Ag as the anode and platinum as the cathode, placing them in an electrolyte solution containing carbamide and betaine, and applying a current to generate an Ag / AgCl reference electrode through in-situ electrochemical conversion.

[0030] This solution first pre-treats the Ag electrode to make the surface of the Ag electrode bright, providing conditions for the uniform growth of the AgCl conversion film on the surface of the Ag electrode. Both carbamide and betaine are added as film-forming promoters in the electrolyte solution, promoting the formation of an AgCl conversion film with good uniformity, compactness, and strong film adhesion on the surface of the Ag electrode.

[0031] Pre-treatment: There are two pre-treatment methods for Ag, which are for the Ag electrode used for the first time and the Ag electrode that has been used. The pre-treatment method for the Ag electrode used for the first time includes: using sandpaper with 1000 - 1200 meshes and 1600 - 1800 meshes to polish the surface of the Ag electrode until the surface of the Ag electrode is bright and has no obvious scratches, and then ultrasonically cleaning in water and ethanol respectively, and naturally drying. The pre-treatment method for the Ag electrode that has been used includes: putting the used Ag electrode into concentrated ammonia water and soaking until the AgCl on the surface of the Ag electrode completely falls off, rinsing with water, activating in concentrated nitric acid, then washing with water, and naturally drying. These two pre-treatment methods are simple and fast, providing conditions for the uniform growth of the AgCl conversion film on the surface of the Ag electrode.

[0032] Among them, the electrolyte is a KCl solution with a concentration of 0.5 mol / L - 1.5 mol / L. The preparation of the electrolyte containing urea and betaine includes: dissolving urea in betaine to form a mixed solution with a concentration of 0.5 g / L - 2 g / L, and mixing the mixed solution and the electrolyte in a volume ratio of (1 - 10):1000.

[0033] During the in-situ electrochemical conversion, the applied current is 1.5 mA / cm 2 ~6 mA / cm 2 of constant current or intermittent current. When using constant current, the current duration is 30 min - 50 min. When using intermittent current, a cycle consists of a current duration of 25 s - 35 s and a stop of 80 s - 100 s, and it cycles 12 - 20 times. By controlling the current duration or the number of cycle times, the thickness of the silver chloride film layer of the Ag / AgCl reference electrode can be achieved.

[0034] Example 1:

[0035] A preparation method of an Ag / AgCl reference electrode in this example includes:

[0036] (1) Pretreatment: The surface of the Ag electrode for the first use is polished with 1000-mesh sandpaper and 1600-mesh sandpaper until the surface of the Ag electrode is bright and has no obvious scratches. After ultrasonic cleaning in water and ethanol for 1 min respectively, it is naturally air-dried.

[0037] (2) Using a KCl solution with a concentration of 0.5 mol / L as the electrolyte, dissolving urea in betaine to form a mixed solution with a concentration of 0.5 g / L, and mixing the mixed solution and the electrolyte in a volume ratio of 1:1000 to obtain an electrolyte containing urea and betaine. The pretreated clean Ag is used as the anode and platinum is used as the cathode, and they are placed in the electrolyte containing urea and betaine. The applied current is 1.5 mA / cm 2 of constant current, and the current duration is 30 min. An Ag / AgCl reference electrode is generated through in-situ electrochemical conversion.

[0038] Example 2:

[0039] A preparation method of an Ag / AgCl reference electrode in this example includes:

[0040] (1) Pretreatment: The surface of the Ag electrode for the first use is polished with 1100-mesh sandpaper and 1700-mesh sandpaper until the surface of the Ag electrode is bright and has no obvious scratches. After ultrasonic cleaning in water and ethanol for 1 min respectively, it is naturally air-dried.

[0041] (2) Using a KCl solution with a concentration of 1.2 mol / L as the electrolyte, dissolve carbamide in betaine to prepare a mixed solution with a concentration of 1.5 g / L. Mix the mixed solution and the electrolyte in a volume ratio of 5:1000 to obtain an electrolyte containing carbamide and betaine. Use the pre-cleaned Ag as the anode and platinum as the cathode, place them in the electrolyte containing carbamide and betaine, and apply a constant current of 3.5 mA / cm 2 , and the current duration is 40 min. Generate an Ag / AgCl reference electrode through in-situ electrochemical conversion.

[0042] Example 3:

[0043] A preparation method of an Ag / AgCl reference electrode in this example includes:

[0044] (1) Pretreatment: Use 1200-mesh sandpaper and 1800-mesh sandpaper to polish the surface of the Ag electrode for the first time until the surface of the Ag electrode is bright and has no obvious scratches. Ultrasonically clean it in water and ethanol for 1 min respectively, and then air-dry it naturally.

[0045] (2) Using a KCl solution with a concentration of 1.5 mol / L as the electrolyte, dissolve carbamide in betaine to prepare a mixed solution with a concentration of 2 g / L. Mix the mixed solution and the electrolyte in a volume ratio of 10:1000 to obtain an electrolyte containing carbamide and betaine. Use the pre-cleaned Ag as the anode and platinum as the cathode, place them in the electrolyte containing carbamide and betaine, and apply a constant current of 6 mA / cm 2 , and the current duration is 50 min. Generate an Ag / AgCl reference electrode through in-situ electrochemical conversion.

[0046] Example 4:

[0047] A preparation method of an Ag / AgCl reference electrode in this example includes:

[0048] (1) Pretreatment: Immerse the used Ag electrode in concentrated ammonia water until the AgCl on the surface of the Ag electrode completely falls off. After rinsing with water, activate it in concentrated nitric acid, then wash it with water and air-dry it naturally.

[0049] (2) Using a KCl solution with a concentration of 0.5 mol / L as the electrolyte, dissolve carbamide in betaine to prepare a mixed solution with a concentration of 0.5 g / L. Mix the mixed solution and the electrolyte in a volume ratio of 1:1000 to obtain an electrolyte containing carbamide and betaine. Use the pre-cleaned Ag as the anode and platinum as the cathode, place them in the electrolyte containing carbamide and betaine, and apply a constant current of 1.5 mA / cm 2The intermittent current, with a current duration of 25 s and a stop of 80 s as a cycle, circulates for 12 cycles to generate an Ag / AgCl reference electrode through in-situ electrochemical conversion.

[0050] Example 5:

[0051] A preparation method of an Ag / AgCl reference electrode in this example includes:

[0052] (1) Pretreatment: The used Ag electrode is immersed in concentrated ammonia water until the AgCl on the surface of the Ag electrode completely falls off, rinsed with water, activated in concentrated nitric acid, then washed with water and air-dried naturally.

[0053] (2) Using a KCl solution with a concentration of 1 mol / L as the electrolyte, dissolve carbamide in betaine to form a mixed solution of 1 g / L. The mixed solution and the electrolyte are mixed at a volume ratio of 5:1000 to obtain an electrolyte containing carbamide and betaine. The pretreated clean Ag is used as the anode and platinum as the cathode, placed in the electrolyte containing carbamide and betaine, and the applied current is 4 mA / cm 2 of intermittent current, with a current duration of 30 s and a stop of 90 s as a cycle, circulates for 15 cycles to generate an Ag / AgCl reference electrode through in-situ electrochemical conversion.

[0054] Example 6:

[0055] A preparation method of an Ag / AgCl reference electrode in this example includes:

[0056] (1) Pretreatment: The used Ag electrode is immersed in concentrated ammonia water until the AgCl on the surface of the Ag electrode completely falls off, rinsed with water, activated in concentrated nitric acid, then washed with water and air-dried naturally.

[0057] (2) Using a KCl solution with a concentration of 1.5 mol / L as the electrolyte, dissolve carbamide in betaine to form a mixed solution of 2 g / L. The mixed solution and the electrolyte are mixed at a volume ratio of 10:1000 to obtain an electrolyte containing carbamide and betaine. The pretreated clean Ag is used as the anode and platinum as the cathode, placed in the electrolyte containing carbamide and betaine, and the applied current is 6 mA / cm 2 of intermittent current, with a current duration of 35 s and a stop of 90 s as a cycle, circulates for 20 cycles to generate an Ag / AgCl reference electrode through in-situ electrochemical conversion.

[0058] Test Example 1

[0059] Referring to the preparation method of the Ag / AgCl reference electrode in Example 5, the pretreated Ag electrode was placed in the electrolyte solution, and a platinum electrode was used as the counter electrode. An AgCl conversion film was in-situ prepared by applying an intermittent current to the Ag electrode. The current magnitudes were 6 mA / cm 2 , 3 mA / cm 2 , 1.5 mA / cm 2 . The current application method was that 30 s of continuous application and 90 s of stop constituted one cycle, and the cycle was repeated 15 times to prepare the Ag / AgCl reference electrode.

[0060] The silver chloride film layer in Test Example 1 was scanned by electron microscopy. The results are shown in Figure 1 .

[0061] From Figure 1 (a), Figure 1 (b) and Figure 1 (c) of the surface morphology diagrams, it can be seen that a dense film layer composed of uniformly distributed silver chloride nanoparticles was formed on the surface of the Ag electrode, and the larger the applied current, the larger the diameter of the generated silver chloride particles.

[0062] Test Example 2

[0063] Referring to the preparation method of the Ag / AgCl reference electrode in Example 5, the pretreated Ag electrode was placed in the electrolyte solution, and a platinum electrode was used as the counter electrode. An Ag / AgCl reference electrode was in-situ prepared by applying a constant current to the Ag electrode. The current magnitude was 3 mA / cm 2 , and the durations were 30, 40, and 50 min respectively.

[0064] The silver chloride film layer and the cross-section of the silver chloride film layer in Test Example 2 were scanned by electron microscopy. The results are shown in Figure 2 and Figure 3 .

[0065] From Figure 2 (a), Figure 2 (b) and Figure 2 (c) of the surface morphology diagrams, it can be seen that a dense film layer composed of uniformly distributed silver chloride nanoparticles was formed on the surface of the Ag electrode, and the longer the current application time, the larger the silver chloride particles and the denser the film layer.

[0066] From Figure 3 (a), Figure 3 (b) and Figure 3 (c) of the cross-section diagrams, it can be seen that the silver chloride film layers with different constant current application times were all very dense, and the longer the current application time, the thicker the film layer.

[0067] Control Example 1

[0068] The preparation method of the Ag / AgCl reference electrode in this comparative example is the same as that in Example 5, except that the electrolyte does not contain carbamide and betaine. The silver chloride prepared by this method has larger particles, and the film layer is loose and easy to fall off.

[0069] Comparative Example 2

[0070] The preparation method of the Ag / AgCl reference electrode in this comparative example is the same as that in Example 5, except that the electrolyte only contains carbamide. The silver chloride prepared by this method has larger particles, shows uneven distribution, and is easy to fall off.

[0071] Comparative Example 3

[0072] The preparation method of the Ag / AgCl reference electrode in this comparative example is the same as that in Example 5, except that the electrolyte only contains betaine. The silver chloride prepared by this method has larger particles, and the film layer is loose and easy to fall off.

[0073] Comparative Example 4

[0074] The preparation method of the Ag / AgCl reference electrode in this comparative example is the same as that in Example 5, except that the electrolyte is HCl solution. The silver chloride prepared by this method is needle-shaped, has weak adhesion to the substrate, and is easy to fall off.

[0075] The specific embodiments described above have further elaborated on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of an Ag / AgCl reference electrode, characterized in that, Comprising: Using pre-treated clean Ag as the anode and platinum as the cathode, placing them in an electrolyte solution containing carbamide and betaine, and applying a current to generate an Ag / AgCl reference electrode through in-situ electrochemical conversion; The main body of the electrolyte solution is a KCl solution, and the concentration of the electrolyte solution is 0.5 mol / L - 1.5 mol / L; The preparation of the electrolyte solution containing carbamide and betaine includes: dissolving carbamide in betaine to form a mixed solution with a concentration of 0.5 g / L - 2 g / L, and mixing the mixed solution and the electrolyte solution in a volume ratio of (1 - 10):1000.

2. The preparation method of the Ag / AgCl reference electrode according to claim 1, wherein The pre-treatment method of Ag includes: for a newly used Ag electrode, polishing the surface of the Ag electrode with sandpaper of 1000 - 1200 mesh and 1600 - 1800 mesh respectively until the surface of the Ag electrode is bright and has no obvious scratches, then ultrasonically cleaning in water and ethanol respectively, and naturally drying.

3. The preparation method of the Ag / AgCl reference electrode according to claim 1, characterized in that, The pre-treatment method of Ag includes: putting a used Ag electrode into concentrated ammonia water and soaking it until the AgCl on the surface of the Ag electrode completely falls off, rinsing with water, activating in concentrated nitric acid, then cleaning with water, and naturally drying.

4. The preparation method of the Ag / AgCl reference electrode according to claim 1, characterized in that, The applied current is 1.5 mA / cm 2 to 6 mA / cm 2 of constant current or intermittent current.

5. The preparation method of the Ag / AgCl reference electrode according to claim 4, wherein, When using a constant current, the current duration is 30 min - 50 min.

6. The preparation method of the Ag / AgCl reference electrode according to claim 4, characterized in that, When using an intermittent current, taking a cycle of the current lasting for 25 s - 35 s and stopping for 80 s - 100 s, and cycling for 12 - 20 cycles.

7. An Ag / AgCl reference electrode prepared by the preparation method of the Ag / AgCl reference electrode according to any one of claims 1 - 6.

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