CN101915794B - Preparation method of all-solid-state reference electrode - Google Patents

Abstract

The invention provides an all-solid reference electrode based on thick film printing technology, which includes a substrate, an electrode base system, an electrolyte layer, a reference film and an insulating layer. The electrode base system consists of a reaction electrode on the substrate, a contact electrode and a lead wire connecting the two electrodes. The electrolyte layer is located on the reaction electrode of the electrode base system. The electrolyte layer is covered with a reference film, and the insulating layer wraps the reference film. The insulating layer is provided with an opening to expose the reference film, and the opening area is used as a reaction area where the reference film contacts the solution to be measured in actual measurement. The all-solid-state reference electrode of the present invention abandons the traditional internal electrolytic solution, and eliminates the unfavorable factors in terms of carrying and storage due to the liquid component. The invention also provides a preparation method of the all-solid reference electrode, which has the advantages of simple manufacturing process, suitable for mass production and low cost.

Description

A kind of preparation method of all-solid-state reference electrode

technical field

The invention relates to the technical field of chemical sensors, in particular to an all-solid-state reference electrode and a preparation method thereof. the

Background technique

In electrochemical measurement, an electrode whose electrode potential is stable, accurate and whose value is known is required as a reference electrode. The hydrogen electrode device is often used as a primary reference electrode due to its stable performance. However, the hydrogen electrode device and the experimental process using the device are cumbersome. In practice, slightly soluble salt electrodes such as calomel electrodes, silver chloride electrodes, or mercurous sulfate electrodes are commonly used as secondary reference electrodes. These electrodes are called reference electrodes. than the electrode. the

Electrolyte refers to a class of substances that can dissociate into charged ions in solution and have conductivity. At present, the electrolytes used to detect body fluids and environmental water are ion selective electrodes (ISE for short). This is a type of electrochemical sensor that uses membrane potential to measure the activity or concentration of a specific ion in a solution. During the measurement, it is necessary to combine the ion-selective electrode with the reference electrode and immerse it in the solution to be measured to form an electrochemical cell. The reference electrode is used as a reference comparison when measuring the potential of the ion-selective electrode, and the electrode potential is required to be stable and have good reproducibility. the

Commonly used reference electrodes are silver/silver chloride reference electrode and calomel reference electrode. These two reference electrodes are prepared by coating the corresponding metal surface with a coating of the metal's refractory salt. When measuring, it is immersed in the solution with the same anion as the insoluble metal salt, and its electrode potential changes with the anion activity of the insoluble salt in the solution. When the anion activity in the solution remains constant, the electrode potential remains stable. However, if the solution to be tested contains other anions that can form insoluble salts with the metal cations (mercury, silver ions), these anions will interfere with the electrode potential of the reference electrode. the

Because the traditional reference electrode contains a liquid inner electrolyte, it is subject to many restrictions in transportation, storage and use, and cannot work under high temperature and high pressure. The all-solid-state external reference electrode can overcome the above-mentioned shortcomings because it does not contain a liquid part. At present, a considerable part of the research on the all-solid-state external reference electrode is based on the Ag/AgCl mechanism, that is, the Ag/AgCl is used as the substrate, and the Ag/AgCl electrode is coated with a hydrogel containing a fixed concentration of chloride ions or High polymer film, etc., to keep the potential of the electrode stable. However, the loss of water in the hydrogel will cause the volume change of the hydrogel layer, which will lead to the change of the chloride ion concentration in the hydrogel, resulting in the potential instability. This is a major drawback of this type of solid reference electrode. the

As the properties of conducting polymers to convert ion conduction to electron conduction are gradually discovered, the research on using various modified conducting polymers for all-solid-state external reference electrodes has attracted more and more interest of scientists from various countries. These conducting polymers cover a variety of polymer materials with ion-conducting and/or electronic-conducting capabilities, including: 1) doped conjugated polymers; 2) redox polymers; 3) synthetic polymers; 4) polymeric matter electrolyte. Among them, p-type doped conjugated conductive polymers, such as polypyrrole, polyaniline, polythiophene and their derivatives, are suitable for solid-state filling electrolytes for reference electrodes due to their ability to convert ion conduction into electron conduction. Material. Among them, poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrenesulfonate (poly(styrenesulfonate), PSS) is a new type of conductive polymer with relatively stable potential. It has excellent characteristics of insensitivity to O ₂ and CO ₂ (pH), and is suitable for use as an internal reference electrolyte. By introducing a pH buffer system containing sulfo groups into PEDOT (PSS), the electrode has the dual advantages of a conductive polymer solid electrolyte and a pH buffer system, thereby achieving stable electrode potential in a wide range of liquids to be tested. .

Screen printing technology belongs to stencil printing, and it is called the four major printing methods together with offset printing, letterpress printing and gravure printing. In stencil printing, the most widely used is screen printing. Stretch silk, nylon, polyester fiber or stainless steel wire mesh on the screen frame to make it tensioned and fixed, and make screen printing plates by hand engraving paint film or photochemical plate making. The more common use in modern times is the photochemical plate-making method. Photochemical plate-making technology is to use photosensitive materials to make screen printing plates by means of photographic plate making, so that the screen holes of the graphic part on the screen printing plate are transparent holes, and the screen holes of the non-graphic part are blocked. Put the slurry (ink) for screen printing into the screen frame, pressurize and scrape the screen frame with a squeegee, and transfer the slurry to the substrate through the mesh of the graphic part to form the same pattern as the original. graphic. This process belongs to thick film film forming technology. Screen printing equipment is simple, easy to operate, easy to print and plate-making, and low in cost, easy to operate, and strong in adaptability. Thin-film film-forming technology uses the principle of high-temperature evaporation or plasma sputtering to accumulate materials on the surface of the substrate to form a thin film. Compared with screen printing, the film-forming is uniform, but the price is higher. the

Contents of the invention

The invention provides a flat-plate all-solid-state reference electrode, which can measure the ion concentration in body fluid and environmental water quality when paired with an ion-selective electrode. The invention also provides a preparation method of the all-solid reference electrode, which simplifies the production process and is suitable for mass production. the

An all-solid-state reference electrode, including a substrate, an electrode base system, an electrolyte layer, a reference membrane and an insulating layer;

The electrode base system is composed of a reaction electrode on the substrate, a contact electrode and a lead wire connecting the two electrodes;

The electrolyte layer is located on the reaction electrode of the electrode base system, and the electrolyte layer is covered with a reference membrane;

The insulating layer covers the reference film, and an opening for exposing the reference film is provided on the insulating layer, and the opening area is used as a reaction area where the reference film contacts the solution to be measured in actual measurement. the

The preparation method of above-mentioned all-solid-state reference electrode, comprises the following steps:

(1) Use screen printing method to print conductive screen printing materials on organic polymer material substrates (such as polypropylene, polyester, polyethylene or polyvinyl chloride, etc.) to form reaction electrodes, contact electrodes and connect these two electrodes conductive leads;

The reaction electrodes can be made of stable conductive materials such as carbon, gold, platinum or titanium, and the conductive leads and contact electrodes can be made of materials such as silver, carbon, gold, platinum or titanium. The electrochemical properties of silver are unstable. However, it has good electrical conductivity, so it is generally not used to make reaction electrodes, but can be used to make contact electrodes and conductive leads;

The above-mentioned conductive material can also be evaporate-coated on the substrate as an evaporation material by thin film evaporation technology; or the above-mentioned conductive material can be used as a target material and sputtered onto the substrate to form a reaction electrode, a contact electrode and a conductive lead. the

(2) Use a surfactant solution to pretreat the surface of the reaction electrode to clean the surface of the reaction electrode, enhance the hydrophilicity of the reaction electrode, and strengthen the adhesion between the reaction electrode and the solid electrolyte layer. the

The surfactant solution can be 1‰～1% carboxymethylcellulose sodium (CMC) solution or hydroxyethylcellulose sodium (HEC) solution;

(3) Dispersing the conductive polymer in water to form a suspension, the preparation ratio is conductive polymer: water = 1:99 to 5:95, based on the total amount of the suspension, adding 0.1 to 1% by mass to the suspension ‰ treatment agent and 1.5-5.0% by mass of CMC or HEC, prepared as electrolyte slurry, and coated with the electrolyte slurry on the surface of the reaction electrode by dot spraying, spin coating or screen printing, and dried in the dark , forming an electrolyte layer. the

The conductive polymer is selected from one of P-type doped polypyrrole and its derivatives, polyaniline and its derivatives, polythiophene and its derivatives. the

Preferably, the conductive polymer is selected to be doped with polystyrene sulfonic acid (PSS) poly-3,4-ethylenedioxythiophene (hereinafter referred to as PEDOT/PSS), this conductive polymer is to _O in the solution and CO ₂ (pH) insensitive, so that the reference electrode can keep the electrode potential stable in various types of solutions to be tested.

Described treatment agent can adopt polyethylene glycol isooctylphenol ether (Triton X-100), and treatment agent can make electrolyte layer and reaction electrode better bonding;

(4) Dissolving lipophilic macromolecular substances and non-conductive macromolecular polymers in plasticizers to form a mixture, based on the total mass of the mixture, the mass percentage of lipophilic macromolecular substances is 1.1 to 2.6%, and lipophilic macromolecular substances Including lipophilic anionic macromolecular substances and lipophilic cationic macromolecular substances, wherein the mass ratio of lipophilic anionic macromolecular substances to lipophilic cationic macromolecular substances is 0.8:1 to 1.2:1, and the mass of non-conductive polymers The percentage is 32.0-38.0%, and the mass percentage of the plasticizer is 58.0-66.0%; the mixture is dissolved in tetrahydrofuran or cyclohexanone solvent, and prepared as a reference membrane solution, so that the non-conductive high molecular polymer in the solution The concentration is 46.8-72.6 mg/mL, and the reference film solution is coated on the surface of the electrolyte layer by dot spraying, spin coating or screen printing, and dried in the dark to form a solid hydrophobic reference film. The reference membrane can protect the electrolyte layer covered by it with poor mechanical properties, so that the electrolyte layer can maintain a stable potential during the measurement. the

The lipophilic anionic macromolecular substance is selected from one or more of sodium tetraphenylborate, potassium tetrachlorophenylborate, tetrakis [3,5-bis(trifluoromethyl)phenyl]potassium borate. The lipophilic cationic macromolecular substance adopts methyl tridodecyl ammonium chloride. Lipophilic macromolecular substances can eliminate the interference of lipophilic ions (such as long-chain fatty acids, long-chain alkyl sulfonates or long-chain dialkyl phosphates, etc.) in the solution to be tested on the reference membrane, and can reduce the resistance of the electrode . the

The non-conductive polymer is selected from one or more of polyvinyl chloride (PVC), polyurethane (PU), polyvinyl acetate (PVA) and polymethyl methacrylate (PMMA). the

Described plasticizer is selected from dibutyl sebacate, dioctyl adipate, bis(1-butylpentane) adipate, dinitrophenyl octyl ether, di-sec-octyl sebacate , one or more of diethyloctyl maleate and dioctyl fumarate. Plasticizers can improve the plasticity of the mixture, which facilitates molding in subsequent screen printing. the

(5) Print an insulating layer on the substrate by screen printing, the insulating layer covers the reference film, and is provided with an opening where the reference film is exposed. This opening area is where the actual measurement reference film contacts the solution to be measured. The reaction area is the all-solid-state reference electrode. the

In order to achieve a better effect of the reference electrode, before performing the above step (4), soak the electrolyte layer on the substrate in 0.1mol/L sulfosalicylic acid (SSA) buffer for 12 to 24 hours , and dry in the dark, the sulfosalicylic acid buffer must be adjusted to pH 7 with NaOH. In this step, the electrode is modified. By introducing a pH buffer system containing a sulfo group into PEDOT/PSS, the electrode has the dual advantages of a conductive polymer solid electrolyte and a pH buffer system, so as to achieve a wide range of liquids to be tested. to keep the electrode potential stable. the

In the actual measurement, the prepared all-solid-state reference electrode is combined with the ion-selective electrode, and immersed in the measured solution to form an electrochemical cell. The reference electrode is connected with the external measuring device through the contact electrode on the substrate. The conductive polymer in the electrolyte layer has the function of an electron acceptor, which can convert ion conduction to electron conduction, and the process can be written as:

Among them, M ⁺ represents the oxidized conductive polymer unit in the electrolyte layer; e is an electron; M represents a neutral conductive polymer unit; A ^- represents a negatively charged doping component in the conductive polymer. Since the ratio of M ⁺ /M in the conductive polymer is constant, the potential of the solid electrolyte layer is kept constant, which acts as a traditional reference electrode. Conductive polymer, as an electronically conductive material, forms an ohmic contact between the electrolyte layer and the reaction electrode, effectively reduces the resistance of the electrode, converts the ion signal in the solution to be tested detected by the reference membrane into an electronic signal, and passes the reaction The electrodes, conductive leads, and contact electrodes are used for detection by an external test circuit. In actual measurement, the electrode potential of the reference electrode remains stable, providing a stable reference potential for the ion-selective electrode.

The all-solid-state reference electrode of the present invention adopts a solid internal charge electrolyte, abandons the traditional internal charge electrolyte, and eliminates the unfavorable factors in terms of carrying and storage caused by containing liquid components. At the same time, the flat plate structure of the present invention realizes the miniaturization of the reference electrode, shortens the reaction time of the reference electrode, and can perform measurement under high temperature and high pressure. the

Description of drawings

Fig. 1 is the schematic diagram of the structure of the all-solid-state reference electrode;

Fig. 2 is the top view of all-solid-state reference electrode shown in Fig. 1;

Fig. 3 is the potential response of the all-solid-state reference electrode prepared in embodiment 1 in different concentrations of NaCl solutions;

Fig. 4 is the potential response of the all-solid-state reference electrode prepared in embodiment 1 in different concentrations of KCl solutions;

Fig. 5 is the potential response of the all-solid-state reference electrode prepared in embodiment 2 in different concentrations of _{CaCl2solutions} ;

Fig. 6 is the potential response of the all-solid-state reference electrode prepared in Example 2 in Tris-HCl buffer solutions with different pHs. the

Detailed ways

As shown in Figure 1, a kind of all-solid-state reference electrode comprises substrate 1, electrode base system, electrolyte layer 3, reference film 4 and insulating layer 5;

The electrode substrate system consists of a reaction electrode 2a on the substrate 1, a contact electrode 2c, and a lead wire 2b connecting the two electrodes; it can be seen from Fig. 2 that the reaction electrode 2a and the contact electrode 2c are rectangular, and the connection electrode 2 The lead wire 2b is elongated, and such a shape makes it easier to make the screen printing plate during the preparation process by the screen printing method;

The electrolyte layer 3 is located on the reaction electrode 2a of the electrode base system, the electrolyte layer 2a is covered with a reference membrane 4, and the reference membrane 4 completely covers the electrolyte layer 3;

The insulating layer 5 is located on the surface of the reference film 4, and the insulating layer 5 is provided with an opening 6 that exposes the reference film 4, and the opening area serves as a reaction area where the reference film 4 contacts the solution to be measured in actual measurement. As shown in Figure 1, the insulating layer 5 completely covers the reaction electrode 2a, and partially covers the lead wire 2b, and the contact electrode 2c is completely exposed without the insulating layer 5, and the contact electrode 2c is connected to an external measuring device during measurement. the

Example 1

A kind of preparation of all-solid-state reference electrode comprises the following steps:

(1) The carbon printing material is printed on the polypropylene substrate by screen printing technology to form a reaction electrode, a contact electrode and a lead connecting the two electrodes;

(2) Use a CMC aqueous solution with a mass fraction of 3‰ to scrub the surface of the reaction electrode, and then wipe it clean. the

(3) Disperse PEDOT/PSS (Clevios P from HC Starck, Germany, CAS No. 155090-83-8) in water to form a suspension, the configuration ratio is PEDOT/PSS: H ₂ O = 1:99, in the suspension Add 0.5‰ of Triton X-100 and 2% of HEC to form an electrolyte slurry with a certain viscosity. The prepared electrolyte slurry was printed on the reaction electrode by screen printing, and after drying in the dark, an electrolyte layer was formed, and the thickness of the electrolyte layer was about 20 μm. The screen used is 150 mesh, the screen distance is 1 mm, the scraper speed is 8 mm/s, and the pressure is 1.8 kg/cm ² .

(4) Soak the electrolyte layer area on the polypropylene substrate in 0.1mol/L sulfosalicylic acid solution for 12 hours, and the sulfosalicylic acid solution must be adjusted to pH 7 with NaOH;

(5) Add 33.9 mg of sodium tetrachlorophenylborate, 35.1 mg of methyl docosyl ammonium chloride and 1120 mg of high molecular weight PVC to 1.2 mL of dibutyl sebacate. After shaking for 1 minute, add 8 mL of cyclohexanone , shake and dissolve to obtain a uniform transparent viscous liquid. The viscous solution was printed on the electrolyte layer by screen printing, and dried in the dark to form a reference film. The stencil used is 150 mesh, the mesh distance is 1mm, the scraper speed is 8mm/s, and the pressure is 1.8kg/cm ² ;

(6) The insulating layer is printed by screen printing, and a circular opening with a diameter of 1 mm is provided on the insulating layer to partially expose the reference film. The material of the insulating layer is the insulating dye SS8391 produced by Baohua Industrial China Co., Ltd. the

Measure the electrode potential of the prepared all-solid-state reference electrode relative to the Ag/AgCl|(3mol/LKCl) standard reference electrode in various standard solutions with different ion concentrations, record the potential value at 15s, and take the ion concentration as horizontal axis, the response potential value is on the vertical axis, and the results are shown in Figures 3 and 4, respectively. the

Figure 3 is the potential response of the prepared all-solid-state reference electrode in different concentrations of NaCl (the solution contains 1mmol/LCaCl2 and 4mmol/LKCl background electrolyte), and the measured potential fluctuation range is 199.5±0.7mV. the

Figure 4 is the potential response of the prepared all-solid-state reference electrode in different concentrations of KCl solutions (the solution contains 140mmol/LNaCl and 1mmol/ _LCaCl2 background electrolyte), and the measured potential fluctuation range is 109.4±0.6mV .

Example 2

A kind of preparation of all-solid-state reference electrode comprises the following steps:

(1) Print the carbon printing material on the polypropylene substrate by screen printing technology to form reaction electrodes, conductive leads and contact electrodes;

(2) Use the HEC aqueous solution with a mass fraction of 2‰ to scrub the surface of the reaction electrode, and then wipe it clean;

(3) Disperse PEDOT/PSS (Clevios P from HC Starck, Germany, CAS No. 155090-83-8) in water to form a suspension, the configuration ratio is PEDOT/PSS: H ₂ O = 1:99, Add 0.5‰ Triton X-100 and 2% HEC to the solution to form an electrolyte slurry with a certain viscosity, and print the electrolyte slurry on the surface of the reaction electrode by screen printing, and form an electrolyte layer after drying in the dark. The thickness of the layer is about 20 μm, the stencil used is 150 mesh, the mesh distance is 1mm, the scraper speed is 8mm/s, and the pressure is 1.8kg/cm ² ;

(4) Add 0.9 mg of potassium tetrachlorophenyl boride, 1.1 mg of methyl docosyl ammonium chloride, 17 mg of PVA and 68 mg of PU in 56.2 μL of bis(1-butylpentane) adipate, After shaking for 1 minute, add 300 μL of cyclohexanone, shake and dissolve to obtain a uniform, transparent and viscous reference film solution, take 0.5 μL of the reference film solution and apply it on the surface of the electrolyte layer by spot spraying, and dry it in the dark Form a reference film;

(5) The insulating layer is printed by screen printing, and a square opening of 2×2 cm ² is arranged on the insulating layer to partially expose the reference film. The material of the insulating layer is the insulating dye SS8391 produced by Baohua Industrial China Co., Ltd.

Measure the potential response of the prepared all-solid-state reference electrode in different concentrations of _CaCl2 solutions (the solution contains 140mmol/LNaCl and 4mmol/LKCl background electrolyte), and the results are shown in Figure 5. The calcium ion concentration ranges from 0.1 to Within the range of 5mmol/L, the measured potential fluctuation range of the all-solid-state reference electrode is 182.7±0.5mV.

Measure the potential response of the prepared all-solid-state reference electrode in tris-hydrochloric acid (Tris-HCl) buffers with different pHs. The results are shown in Figure 6. The pH of the Tris-HCl buffer is 5.91 ~8.67, the measured potential fluctuation range of the all-solid-state reference electrode is 182.7±0.5mV. the

From the above experimental results, it can be seen that the all-solid-state reference electrode of the present invention can maintain stable potential in different ion types, different ion concentrations, and different pH solutions, and has good working stability. the

Claims (8)

1. A method for preparing an all-solid-state reference electrode, characterized in that, The all-solid-state reference electrode includes a substrate, an electrode base system, an electrolyte layer, a reference film and an insulating layer; The electrode substrate system is composed of a reaction electrode on the substrate, a contact electrode and a lead connecting the reaction electrode and the contact electrode; The electrolyte layer is located on the reaction electrode of the electrode base system, and the electrolyte layer is covered with a reference membrane; The insulating layer covers the reference film, and the insulating layer is provided with an opening for exposing the reference film; The all-solid-state reference electrode is prepared by the following method: (1) Coating conductive materials on organic polymer material substrates to form reaction electrodes, contact electrodes and conductive leads; (2) Pretreat the surface of the reaction electrode with an aqueous surfactant solution; (3) Disperse the conductive polymer in water to form a suspension, the preparation ratio is conductive polymer: water = 1:99-5:95, based on the total amount of the suspension, the mass percentage added to the suspension is 0.1-1‰ The treating agent and sodium carboxymethylcellulose or sodium hydroxyethylcellulose with a mass percentage of 1.5 to 5.0% are prepared into an electrolyte slurry, and the electrolyte slurry is coated on the surface of the reaction electrode to form an electrolyte layer; (4) Dissolving lipophilic anionic macromolecular substances, lipophilic cationic macromolecular substances, and non-conductive polymers in plasticizers to form a mixture, based on the total mass of the mixture, the lipophilic anionic macromolecular substances and lipophilic The mass percentage of cationic macromolecular substances is 1.1 to 2.6%, the mass ratio of lipophilic anionic macromolecular substances to lipophilic cationic macromolecular substances is 0.8:1 to 1.2:1, and the mass percent of non-conductive polymers is 32.0% ~38.0%, the mass percentage of plasticizer is 58.0~66.0%; The mixture is dissolved in tetrahydrofuran or cyclohexanone solvent to prepare a reference membrane solution, and the membrane solution is coated on the surface of the electrolyte layer to form a reference membrane; (5) Print an insulating layer on the substrate, the insulating layer covers the reference film, and the insulating layer is provided with an opening to expose the reference film; The lipophilic anionic macromolecular substance is selected from potassium tetrachlorophenyl boride, and the lipophilic cationic macromolecular substance is selected from methyl docosyl ammonium chloride. 2. the preparation method of all-solid-state reference electrode according to claim 1, is characterized in that, described surface active agent aqueous solution that is carried out pretreatment to reaction electrode surface is the carboxymethyl cellulose of mass fraction 0.1～1%. Sodium solution or sodium hydroxyethylcellulose solution. 3. the preparation method of all-solid-state reference electrode according to claim 1 is characterized in that, described conductive polymer is selected from polypyrrole and derivative thereof, polyaniline and derivative thereof, polythiophene and derivative thereof One of. 4. The preparation method of the all-solid-state reference electrode according to claim 1, characterized in that, the treating agent added in the conductive polymer suspension adopts polyethylene glycol isooctylphenol ether. 5. the preparation method of all-solid-state reference electrode according to claim 1 is characterized in that, described non-conductive polymer is selected from polyvinyl chloride, polyurethane, polyvinyl acetate, polymethyl methacrylate one or more of. 6. The method for preparing an all-solid-state reference electrode according to claim 1, characterized in that the concentration of the non-conductive polymer in the reference membrane liquid in the step (4) is 46.8-72.6 mg/mL . 7. The method for preparing an all-solid-state reference electrode according to claim 1, wherein the conductive polymer is poly-3,4-ethylenedioxythiophene doped with polystyrenesulfonic acid. 8. The method for preparing an all-solid-state reference electrode according to claim 1, characterized in that, before step (4), the electrolyte layer on the substrate is mixed with 0.1mol/L sulfosalicylic acid buffer Soak in water for 12 to 24 hours, avoid light and dry, and adjust the pH value of the solution to 7 with sodium hydroxide in the sulfosalicylic acid buffer.

Images