Composite reference electrode and preparation method thereof

Abstract

The invention discloses a composite reference electrode and a preparation method thereof, and relates to the technical field of reference electrodes. According to the method, firstly, a silver bar / silver mesh composite substrate is prepared through blue laser welding, so that the specific surface area is increased; then, a rare earth-nano particle doped silver halide functional layer is formed on the substrate through a melt impregnation and anodic polarization process, and the structural stability and ionic conductivity of the silver halide functional layer are enhanced. Secondly, preparing double-ion imprinted polymer powder capable of specifically capturing sulfur ions and heavy metal ions, and compounding the double-ion imprinted polymer powder with sulfonated polyether ether ketone, thiolated graphene oxide, imidazole ionic liquid and other components to prepare interface strengthening slurry; and finally, carrying out oxygen plasma treatment on an electrode, coating the slurry, and carrying out curing, heat treatment and activation to obtain a finished product electrode. The reference electrode prepared by the method has good foreign ion interference resistance.

Description

Technical Field

[0001] This invention relates to the field of reference electrode technology, specifically to a composite reference electrode and its preparation method. Background Technology

[0002] Reference electrodes are indispensable core measurement components in cathodic protection systems for metallic structures in marine environments. Their potential stability and response accuracy directly determine the accuracy of cathodic protection effect assessment, which in turn relates to the corrosion safety and service life of critical metallic structures such as ships, offshore platforms, ports, and subsea oil pipelines. Among various types of reference electrodes, traditional silver / silver chloride reference electrodes have long been widely used in marine cathodic protection potential measurement scenarios due to their outstanding advantages such as fast response speed, stable basic potential, and relatively controllable manufacturing costs, becoming the mainstream choice in this field. However, the complexity and uniqueness of the marine environment present a severe challenge of interference from impurity ions, a core defect that seriously restricts their practical application value. Summary of the Invention

[0003] The purpose of this invention is to provide a composite reference electrode and its preparation method to solve the technical problems mentioned in the background.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A method for preparing a composite reference electrode includes the following steps:

[0006] (1) Provide a pure silver rod and a pure silver mesh, process a spiral groove on the surface of the pure silver rod, embed the pure silver mesh into the spiral groove, fix it by blue laser welding, and then clean and dry it to obtain a silver rod / silver mesh composite substrate;

[0007] (2) Cerium nitrate, lanthanum nitrate, citric acid, nano titanium dioxide and nano hydroxyapatite were mixed and treated, and then calcined to obtain rare earth-nanoparticle doped precursor powder;

[0008] (3) Mix silver chloride, silver bromide, silver iodide, rare earth-nanoparticle doped precursor powder and lithium fluoride, and heat to melt to form a ternary solid solution melt;

[0009] (4) Immerse the silver rod / silver mesh composite substrate in the molten ternary solid solution, pull it out and cool it, and then use it as the anode in the mixed sodium halide solution for constant current polarization. Repeat the immersion and polarization operation to obtain the pretreated electrode.

[0010] (5) Using lead nitrate as a heavy metal template molecule and thiourea as a simulated template molecule of sulfur, a polymerization reaction is carried out with 4-vinylpyridine, ethylene glycol dimethacrylate and initiator AIBN to obtain a polymer; the polymer is eluted with nitric acid solution to remove template ions and then dried to obtain a dual-ion imprinted polymer powder.

[0011] (6) Dissolve sulfonated polyether ether ketone in N-methylpyrrolidone, add polyvinylpyrrolidone, dual ion-imprinted polymer powder, silane coupling agent KH-550, epoxy resin, mercaptoized graphene oxide and imidazole ionic liquid, and disperse to form a slurry;

[0012] (7) The pretreated electrode is subjected to oxygen plasma treatment, then immersed in slurry, pulled up and dried and cured. The coating and curing operations are repeated, and after vacuum heat treatment, it is placed in potassium chloride solution for immersion and activation to obtain a composite reference electrode.

[0013] The present invention improves the anti-interference performance of the reference electrode from the following aspects: Firstly, the anti-interference performance is intrinsically enhanced by optimizing the microstructure of the composite silver halide layer. Rare earth ions enter the silver halide lattice through doping, repair point defects using charge compensation effects, and pin the ions at grain boundaries to inhibit grain coarsening, significantly strengthening the chemical and thermodynamic stability of the lattice. Simultaneously, dispersed high surface energy nanoparticles (nano-titanium dioxide and nano-hydroxyapatite) construct a complex physical barrier in the silver halide matrix, greatly increasing the tortuosity of the path for external interfering ions to penetrate into the electrode. Combined with the Frenkel defects introduced by lithium fluoride, this modification internally constructs a strengthening mechanism of grain boundary pinning, dispersion blocking, and defect regulation. This not only improves the resistance of the functional layer to single impurity erosion but also ensures the stability of the Nernst response by optimizing ionic conductivity, thus building a solid internal structural foundation for the electrode. On the other hand, by constructing a multifunctional composite barrier on the electrode surface to achieve synergistic enhancement of resistance to impurity interference, ion-imprinted polymers utilize specific holes that match the size and charge of sulfide ions and heavy metal ions to precisely capture and lock impurities before they reach the electrode surface. The dense network structure formed by the crosslinking of sulfonated polyether ether ketone and epoxy resin utilizes its strong negative charge property to strongly repel negatively charged interfering ions, synergistically blocking the penetration of harmful anions such as sulfide ions. At the same time, the covalent crosslinking system formed by silane coupling agent and thermosetting process greatly improves the interfacial adhesion between the organic film layer and the inorganic silver halide substrate, eliminating the risk of peeling and lateral penetration pathways. This modification constructs multiple external defenses of specific capture, electrostatic repulsion, and interfacial shielding, significantly reducing the risk of synergistic corrosion of the electrode by composite impurities in complex marine environments and significantly extending the precise service life of the electrode.

[0014] This invention reveals that the composite interface between an inorganic silver halide layer and a flexible organic polymer membrane, under the complex stresses of the marine environment (high osmotic pressure, pressure cycling, and temperature fluctuations), experiences physical stress mismatch due to the difference in the thermal expansion coefficients and mechanical moduli of the two materials. This leads to a high susceptibility to microscopic delamination and stress cracks at the interface, resulting in a severe "bypass permeation" effect. Specifically, interfering ions in seawater (such as sulfide ions) can bypass specific trapping sites in the polymer membrane and directly attack the inner silver halide crystals through interface defects, causing electrode poisoning and failure. Simultaneously, discontinuous ion conduction at the interface also causes excessive electrochemical impedance and severe lag in potential response, significantly affecting measurement accuracy and stability. To further address this technical problem, this invention incorporates thiolized graphene oxide (SH-GO) and imidazole ionic liquids into the polymer slurry. SH-GO acts as a molecular-level chemical anchor; its surface thiol groups can form strong Ag-S covalent bonds with the underlying silver or silver halide, powerfully anchoring the polymer membrane to the inorganic substrate and fundamentally eliminating interfacial gaps. Simultaneously, its two-dimensional layered structure creates a labyrinth effect within the membrane, forcibly altering and extending the diffusion path of interfering ions, forcing them to pass through more ion-imprinted capture sites, thereby exponentially improving impurity blocking efficiency. Furthermore, as an interfacial electrochemical bridging agent, the ionic liquid's liquid properties can fill all nanoscale voids, constructing a continuous and efficient ion conduction channel, significantly reducing interfacial resistance. More importantly, it acts as a dynamic buffer, maintaining the dynamic balance of ion activity at the interface when external salinity or osmotic pressure fluctuates drastically, thus ensuring a rapid and stable potential response. Through the combined effects of chemical anchoring and ion bridging, not only are interfacial stripping and bypass permeation problems solved, but also, by constructing a low-impedance, highly dynamically balanced ion transport interface, the electrode exhibits excellent mechanical stability, long-term anti-interference capability, and rapid potential response performance in extreme environments such as the deep sea.

[0015] Preferably, in step (2), the molar ratio of cerium nitrate to lanthanum nitrate is 2:(1-2).

[0016] Preferably, in step (2), the mass ratio of nano-titanium dioxide to nano-hydroxyapatite is 15:(4-6).

[0017] Preferably, in step (3), the mass ratio of silver chloride, silver bromide, silver iodide, rare earth-nanoparticle doped precursor, and lithium fluoride is 100:(4~6):(1~2):(0.5~1):(0.5~1).

[0018] Preferably, in step (5), the molar ratio of lead nitrate to thiourea is 1:(1-2).

[0019] Preferably, in step (5), the molar ratio of 4-vinylpyridine to ethylene glycol dimethacrylate is 6:(10-15).

[0020] Preferably, in step (6), the mass ratio of sulfonated polyether ether ketone to dual ion-imprinted polymer powder is 8:(0.3-0.8).

[0021] Preferably, in step (6), the mass ratio of mercapto-modified graphene oxide to imidazole ionic liquid is 2:(0.5-1.0).

[0022] Preferably, in step (7), the concentration of the potassium chloride solution is 0.1 to 0.2 mol / L.

[0023] A composite reference electrode, characterized in that it is prepared by the method described above.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] 1. By doping the internal silver halide layer with rare earth elements and nanoparticles, the structural stability and ionic conductivity are enhanced at the lattice and grain boundary levels. The external coating consists of a multi-polymer barrier that combines specific ion trapping, electrostatic repulsion, and strong interfacial bonding (silane coupling). The combined internal and external coatings effectively resist the erosion of impurities such as sulfur ions, significantly extending the precision service life of the electrode.

[0026] 2. The introduced thiolized graphene oxide achieves a strong chemical bond between the polymer film and the inorganic substrate through Ag-S bonds, eliminating interfacial gaps. At the same time, its maze effect, combined with the dynamic buffering and bridging effect of ionic liquids, forces interfering ions to diffuse through the capture sites and constructs a continuous, low-impedance ion transport channel, ensuring a rapid and stable potential response of the electrode under osmotic pressure and pressure fluctuations. Attached Figure Description

[0027] Figure 1 This is a SEM image of the surface of the composite reference electrode prepared in Example 1 of the present invention.

[0028] Figure 2 The XPS spectrum of the composite reference electrode prepared in Example 1 of this invention is shown. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1

[0031] A method for preparing a composite reference electrode includes the following steps:

[0032] Step 1: Select a pure silver rod with a purity of 99.9% and a size of Φ6mm×50mm. Use wire cutting to machine three evenly distributed spiral grooves (groove width 1.5mm, groove depth 1mm, pitch 8mm) on its surface. Select a 20-mesh pure silver mesh, cut it into strips of 2.5cm×12cm, and embed them into the grooves. Use a 450nm blue laser welding machine for fixation, setting the welding power to 350W, spot welding time to 20ms, and weld spot spacing to 3mm. Then, ultrasonically clean it in anhydrous ethanol for 20 minutes, rinse with deionized water, and dry it in a 60℃ vacuum drying oven for 2 hours to obtain the silver rod / silver mesh composite substrate.

[0033] Step 2: Weigh 0.02 mol cerium nitrate and 0.018 mol lanthanum nitrate and dissolve them in 150 mL deionized water. Add 0.08 mol citric acid and stir in a 70 °C water bath for 2 h to form a transparent sol. Separately weigh 1.5 g nano TiO2 (10 nm) and 0.55 g nano hydroxyapatite and disperse them in 80 mL anhydrous ethanol. Disperse them using high-power ultrasonication for 1 h. Mix the two and stir at 80 °C under nitrogen protection until the solvent is completely evaporated. Collect the solid and grind it through a 300-mesh sieve using an agate mortar. Finally, calcine it in a muffle furnace at 500 °C for 3 h to obtain rare earth-nanoparticle-doped precursor powder.

[0034] Step 3: Weigh silver chloride, silver bromide, silver iodide, rare earth-nanoparticle doped precursor powder, and anhydrous lithium fluoride in a mass ratio of 100:5.5:1.8:0.9:0.8, and grind and mix them thoroughly in a dark room. Place the mixture in a quartz crucible, heat it to 580℃ at a rate of 10℃ / min, hold it at this temperature for 2 hours, stirring with a quartz rod every 20 minutes, and then cool it down to 520℃ and hold it at this temperature to form a ternary solid solution molten liquid.

[0035] Step 4: Slowly immerse the silver rod / silver mesh composite substrate into the molten ternary solid solution for 20 seconds, then lift it out at a speed of 0.5 cm / s and allow it to cool naturally to room temperature. Use the resulting electrode as the anode and the carbon rod as the cathode, placing it in a 1.0 mol / L mixed sodium halide solution (NaCl:NaBr = 9:1), and set a constant current density of 2 mA / cm². 2 Perform anodic polarization for 15 minutes; repeat the above immersion and polarization process 3 times to obtain the pretreated electrode;

[0036] Step 5: Weigh 0.01 mol of lead nitrate as the heavy metal template molecule and 0.017 mol of thiourea as the simulated template molecule of sulfur, dissolve them in 50 mL of methanol solution, add 0.06 mol of 4-vinylpyridine, 0.14 mol of ethylene glycol dimethacrylate and 0.005 mol of initiator AIBN, and react at 65 °C for 24 h under nitrogen protection; grind the obtained product through a 400-mesh sieve, and repeatedly elute the template ions with 0.5 mol / L nitric acid solution until lead and sulfur are undetectable in the eluent, and dry to obtain the dual-ion imprinted polymer powder;

[0037] Step 6: Weigh 8g of sulfonated polyether ether ketone (SPEEK, sulfonation degree 65%) and dissolve it in 90g of N-methylpyrrolidone. Add 2g of polyvinylpyrrolidone as a film-forming aid. Add 0.7g of dual ion-imprinted polymer powder, 1.0g of silane coupling agent KH-550, 0.5g of bisphenol A epoxy resin (E-51), 0.2g of mercapto-modified graphene oxide (SH-GO), and 0.09g of imidazole ionic liquid to the solution in sequence. Disperse the mixture with high-power ultrasonication for 2 hours to form a homogeneous slurry.

[0038] Step 7: Treat the pretreated electrode with oxygen plasma for 10 min, then immerse it in the above interface strengthening slurry using the dip-coating method (speed 1 mm / s). After removal, pre-dry it at 60℃ for 30 min, then heat it to 130℃ at a rate of 2℃ / min and hold it at that temperature for 2 h. Repeat the coating and curing process twice, then place it in a vacuum oven at 150℃ for final heat treatment for 1.5 h, and then immerse it in a 0.15 mol / L KCl solution for equilibration activation for 48 h. After activation, remove the electrode and immediately seal it with a rubber sleeve containing saturated KCl solution on the electrode head. Cover the outside with black aluminum foil to block light, thus obtaining the composite reference electrode.

[0039] Example 2

[0040] A method for preparing a composite reference electrode includes the following steps:

[0041] Step 1: Select a pure silver rod with a purity of 99.9% and a size of Φ6mm×50mm. Use wire cutting to machine three evenly distributed spiral grooves (groove width 1.5mm, groove depth 1mm, pitch 8mm) on its surface. Select a 20-mesh pure silver mesh, cut it into strips of 2.5cm×12cm, and embed them into the grooves. Use a 450nm blue laser welding machine for fixation, setting the welding power to 350W, spot welding time to 20ms, and weld spot spacing to 3mm. Then, ultrasonically clean it in anhydrous ethanol for 20 minutes, rinse with deionized water, and dry it in a 60℃ vacuum drying oven for 2 hours to obtain the silver rod / silver mesh composite substrate.

[0042] Step 2: Weigh 0.02 mol cerium nitrate and 0.012 mol lanthanum nitrate and dissolve them in 150 mL deionized water. Add 0.08 mol citric acid and stir in a 70 °C water bath for 2 h to form a transparent sol. Separately weigh 1.5 g nano TiO2 (10 nm) and 0.45 g nano hydroxyapatite and disperse them in 80 mL anhydrous ethanol. Disperse them using high-power ultrasonication for 1 h. Mix the two and stir at 80 °C under nitrogen protection until the solvent is completely evaporated. Collect the solid and grind it through a 300-mesh sieve using an agate mortar. Finally, calcine it in a muffle furnace at 500 °C for 3 h to obtain rare earth-nanoparticle-doped precursor powder.

[0043] Step 3: Weigh silver chloride, silver bromide, silver iodide, rare earth-nanoparticle doped precursor powder, and anhydrous lithium fluoride in a mass ratio of 100:4.5:1.2:0.6:0.6, and grind and mix them thoroughly in a dark room. Place the mixture in a quartz crucible, heat it to 580℃ at a rate of 10℃ / min, hold it at this temperature for 2 hours, stirring with a quartz rod every 20 minutes, and then cool it down to 520℃ and hold it at this temperature to form a ternary solid solution molten liquid.

[0044] Step 4: Slowly immerse the silver rod / silver mesh composite substrate into the molten ternary solid solution for 20 seconds, then lift it out at a speed of 0.5 cm / s and allow it to cool naturally to room temperature. Use the resulting electrode as the anode and the carbon rod as the cathode, placing it in a 1.0 mol / L mixed sodium halide solution (NaCl:NaBr = 9:1), and set a constant current density of 2 mA / cm². 2 Perform anodic polarization for 15 minutes; repeat the above immersion and polarization process 3 times to obtain the pretreated electrode;

[0045] Step 5: Weigh 0.01 mol of lead nitrate as the heavy metal template molecule and 0.012 mol of thiourea as the simulated template molecule of sulfur, dissolve them in 50 mL of methanol solution, add 0.06 mol of 4-vinylpyridine, 0.12 mol of ethylene glycol dimethacrylate and 0.005 mol of initiator AIBN, and react at 65 °C for 24 h under nitrogen protection; grind the obtained product through a 400-mesh sieve, and repeatedly elute the template ions with 0.5 mol / L nitric acid solution until no lead and sulfur elements are detected in the eluent. After drying, the dual-ion imprinted polymer powder is obtained.

[0046] Step 6: Weigh 8g of sulfonated polyether ether ketone (SPEEK, sulfonation degree 65%) and dissolve it in 90g of N-methylpyrrolidone. Add 2g of polyvinylpyrrolidone as a film-forming aid. Add 0.4g of dual ion-imprinted polymer powder, 1.0g of silane coupling agent KH-550, 0.5g of bisphenol A epoxy resin (E-51), 0.2g of mercapto-modified graphene oxide (SH-GO), and 0.06g of imidazole ionic liquid to the solution in sequence. Disperse the mixture with high-power ultrasonication for 2 hours to form a homogeneous slurry.

[0047] Step 7: Treat the pretreated electrode with oxygen plasma for 10 min, then immerse it in the above interface strengthening slurry using the dip-coating method (speed 1 mm / s). After removal, pre-dry it at 60℃ for 30 min, then heat it to 130℃ at a rate of 2℃ / min and hold it at that temperature for 2 h. Repeat the coating and curing process twice, then place it in a vacuum oven at 150℃ for final heat treatment for 1.5 h, and then immerse it in a 0.15 mol / L KCl solution for equilibration activation for 48 h. After activation, remove the electrode and immediately seal it with a rubber sleeve containing saturated KCl solution on the electrode head. Cover the outside with black aluminum foil to block light, thus obtaining the composite reference electrode.

[0048] Example 3

[0049] A method for preparing a composite reference electrode includes the following steps:

[0050] Step 1: Select a pure silver rod with a purity of 99.9% and a size of Φ6mm×50mm. Use wire cutting to machine three evenly distributed spiral grooves (groove width 1.5mm, groove depth 1mm, pitch 8mm) on its surface. Select a 20-mesh pure silver mesh, cut it into strips of 2.5cm×12cm, and embed them into the grooves. Use a 450nm blue laser welding machine for fixation, setting the welding power to 350W, spot welding time to 20ms, and weld spot spacing to 3mm. Then, ultrasonically clean it in anhydrous ethanol for 20 minutes, rinse with deionized water, and dry it in a 60℃ vacuum drying oven for 2 hours to obtain the silver rod / silver mesh composite substrate.

[0051] Step 2: Weigh 0.02 mol cerium nitrate and 0.015 mol lanthanum nitrate and dissolve them in 150 mL deionized water. Add 0.08 mol citric acid and stir in a 70 °C water bath for 2 h to form a transparent sol. Separately weigh 1.5 g nano TiO2 (10 nm) and 0.5 g nano hydroxyapatite and disperse them in 80 mL anhydrous ethanol. Disperse them using high-power ultrasonication for 1 h. Mix the two and stir at 80 °C under nitrogen protection until the solvent is completely evaporated. Collect the solid and grind it through a 300-mesh sieve using an agate mortar. Finally, calcine it in a muffle furnace at 500 °C for 3 h to obtain rare earth-nanoparticle-doped precursor powder.

[0052] Step 3: Weigh silver chloride, silver bromide, silver iodide, rare earth-nanoparticle doped precursor powder, and anhydrous lithium fluoride in a mass ratio of 100:5:1.5:0.0.7:0.7, and grind and mix them thoroughly in a dark room. Place the mixture in a quartz crucible, heat it to 580℃ at a rate of 10℃ / min, hold it at this temperature for 2 hours, stirring with a quartz rod every 20 minutes, and then cool it down to 520℃ and hold it at this temperature to form a ternary solid solution molten liquid.

[0053] Step 4: Slowly immerse the silver rod / silver mesh composite substrate into the molten ternary solid solution for 20 seconds, then lift it out at a speed of 0.5 cm / s and allow it to cool naturally to room temperature. Use the resulting electrode as the anode and the carbon rod as the cathode, placing it in a 1.0 mol / L mixed sodium halide solution (NaCl:NaBr = 9:1), and set a constant current density of 2 mA / cm². 2 Perform anodic polarization for 15 minutes; repeat the above immersion and polarization process 3 times to obtain the pretreated electrode;

[0054] Step 5: Weigh 0.01 mol of lead nitrate as the heavy metal template molecule and 0.015 mol of thiourea as the simulated template molecule of sulfur, dissolve them in 50 mL of methanol solution, add 0.06 mol of 4-vinylpyridine, 0.13 mol of ethylene glycol dimethacrylate and 0.005 mol of initiator AIBN, and react at 65 °C for 24 h under nitrogen protection; grind the obtained product through a 400-mesh sieve, and repeatedly elute the template ions with 0.5 mol / L nitric acid solution until no lead and sulfur elements are detected in the eluent. After drying, the dual-ion imprinted polymer powder is obtained.

[0055] Step 6: Weigh 8g of sulfonated polyether ether ketone (SPEEK, sulfonation degree 65%) and dissolve it in 90g of N-methylpyrrolidone. Add 2g of polyvinylpyrrolidone as a film-forming aid. Then, add 0.5g of dual ion-imprinted polymer powder, 1.0g of silane coupling agent KH-550, 0.5g of bisphenol A epoxy resin (E-51), 0.2g of mercapto-modified graphene oxide (SH-GO), and 0.07g of imidazole ionic liquid to the solution in sequence. Disperse the mixture using high-power ultrasonication for 2 hours to form a homogeneous slurry.

[0056] Step 7: Treat the pretreated electrode with oxygen plasma for 10 min, then immerse it in the above interface strengthening slurry using the dip-coating method (speed 1 mm / s). After removal, pre-dry it at 60℃ for 30 min, then heat it to 130℃ at a rate of 2℃ / min and hold it at that temperature for 2 h. Repeat the coating and curing process twice, then place it in a vacuum oven at 150℃ for final heat treatment for 1.5 h, and then immerse it in a 0.15 mol / L KCl solution for equilibration activation for 48 h. After activation, remove the electrode and immediately seal it with a rubber sleeve containing saturated KCl solution on the electrode head. Cover the outside with black aluminum foil to block light, thus obtaining the composite reference electrode.

[0057] Example 4

[0058] A method for preparing a composite reference electrode includes the following steps:

[0059] Step 1: Select a pure silver rod with a purity of 99.9% and a size of Φ6mm×50mm. Use wire cutting to machine three evenly distributed spiral grooves (groove width 1.5mm, groove depth 1mm, pitch 8mm) on its surface. Select a 20-mesh pure silver mesh, cut it into strips of 2.5cm×12cm, and embed them into the grooves. Use a 450nm blue laser welding machine for fixation, setting the welding power to 350W, spot welding time to 20ms, and weld spot spacing to 3mm. Then, ultrasonically clean it in anhydrous ethanol for 20 minutes, rinse with deionized water, and dry it in a 60℃ vacuum drying oven for 2 hours to obtain the silver rod / silver mesh composite substrate.

[0060] Step 2: Weigh 0.02 mol cerium nitrate and 0.02 mol lanthanum nitrate and dissolve them in 150 mL deionized water. Add 0.08 mol citric acid and stir in a 70 °C water bath for 2 h to form a transparent sol. Separately weigh 1.5 g nano TiO2 (10 nm) and 0.6 g nano hydroxyapatite and disperse them in 80 mL anhydrous ethanol. Disperse them using high-power ultrasonication for 1 h. Mix the two and stir at 80 °C under nitrogen protection until the solvent is completely evaporated. Collect the solid and grind it through a 300-mesh sieve using an agate mortar. Finally, calcine it in a muffle furnace at 500 °C for 3 h to obtain rare earth-nanoparticle-doped precursor powder.

[0061] Step 3: Weigh silver chloride, silver bromide, silver iodide, rare earth-nanoparticle doped precursor powder, and anhydrous lithium fluoride in a mass ratio of 100:6:2:1:1, and grind and mix them thoroughly in a dark room. Place the mixture in a quartz crucible, heat it to 580℃ at a rate of 10℃ / min, hold it at this temperature for 2 hours, stirring with a quartz rod every 20 minutes, and then cool it down to 520℃ and hold it at this temperature to form a ternary solid solution molten liquid.

[0062] Step 4: Slowly immerse the silver rod / silver mesh composite substrate into the molten ternary solid solution for 20 seconds, then lift it out at a speed of 0.5 cm / s and allow it to cool naturally to room temperature. Use the resulting electrode as the anode and the carbon rod as the cathode, placing it in a 1.0 mol / L mixed sodium halide solution (NaCl:NaBr = 9:1), and set a constant current density of 2 mA / cm². 2 Perform anodic polarization for 15 minutes; repeat the above immersion and polarization process 3 times to obtain the pretreated electrode;

[0063] Step 5: Weigh 0.01 mol of lead nitrate as the heavy metal template molecule and 0.02 mol of thiourea as the simulated template molecule of sulfur, dissolve them in 50 mL of methanol solution, add 0.06 mol of 4-vinylpyridine, 0.15 mol of ethylene glycol dimethacrylate and 0.005 mol of initiator AIBN, and react at 65 °C for 24 h under nitrogen protection; grind the obtained product through a 400-mesh sieve, and repeatedly elute the template ions with 0.5 mol / L nitric acid solution until no lead and sulfur elements are detected in the eluent. After drying, the dual-ion imprinted polymer powder is obtained.

[0064] Step 6: Weigh 8g of sulfonated polyether ether ketone (SPEEK, sulfonation degree 65%) and dissolve it in 90g of N-methylpyrrolidone. Add 2g of polyvinylpyrrolidone as a film-forming aid. Add 0.8g of dual ion-imprinted polymer powder, 1.0g of silane coupling agent KH-550, 0.5g of bisphenol A epoxy resin (E-51), 0.2g of mercapto-modified graphene oxide (SH-GO), and 0.1g of imidazole ionic liquid to the solution in sequence. Disperse the mixture with high-power ultrasonication for 2 hours to form a homogeneous slurry.

[0065] Step 7: Treat the pretreated electrode with oxygen plasma for 10 min, then immerse it in the above interface strengthening slurry using the dip-coating method (speed 1 mm / s). After removal, pre-dry it at 60℃ for 30 min, then heat it to 130℃ at a rate of 2℃ / min and hold it at that temperature for 2 h. Repeat the coating and curing process twice, then place it in a vacuum oven at 150℃ for final heat treatment for 1.5 h, and then immerse it in a 0.2 mol / L KCl solution for equilibration activation for 48 h. After activation, remove the electrode and immediately seal it with a rubber sleeve containing saturated KCl solution on the electrode head. Cover the outside with black aluminum foil to block light, thus obtaining the composite reference electrode.

[0066] Example 5

[0067] A method for preparing a composite reference electrode includes the following steps:

[0068] Step 1: Select a pure silver rod with a purity of 99.9% and a size of Φ6mm×50mm. Use wire cutting to machine three evenly distributed spiral grooves (groove width 1.5mm, groove depth 1mm, pitch 8mm) on its surface. Select a 20-mesh pure silver mesh, cut it into strips of 2.5cm×12cm, and embed them into the grooves. Use a 450nm blue laser welding machine for fixation, setting the welding power to 350W, spot welding time to 20ms, and weld spot spacing to 3mm. Then, ultrasonically clean it in anhydrous ethanol for 20 minutes, rinse with deionized water, and dry it in a 60℃ vacuum drying oven for 2 hours to obtain the silver rod / silver mesh composite substrate.

[0069] Step 2: Weigh 0.02 mol cerium nitrate and 0.01 mol lanthanum nitrate and dissolve them in 150 mL deionized water. Add 0.08 mol citric acid and stir in a 70 °C water bath for 2 h to form a transparent sol. Separately weigh 1.5 g nano TiO2 (10 nm) and 0.4 g nano hydroxyapatite and disperse them in 80 mL anhydrous ethanol. Disperse them using high-power ultrasonication for 1 h. Mix the two and stir at 80 °C under nitrogen protection until the solvent is completely evaporated. Collect the solid and grind it through a 300-mesh sieve using an agate mortar. Finally, calcine it in a muffle furnace at 500 °C for 3 h to obtain rare earth-nanoparticle-doped precursor powder.

[0070] Step 3: Weigh silver chloride, silver bromide, silver iodide, rare earth-nanoparticle doped precursor powder, and anhydrous lithium fluoride in a mass ratio of 100:4:1:0.5:0.5, and grind and mix them thoroughly in a dark room. Place the mixture in a quartz crucible, heat it to 580℃ at a rate of 10℃ / min, hold it at this temperature for 2 hours, stirring with a quartz rod every 20 minutes, and then cool it down to 520℃ and hold it at this temperature to form a ternary solid solution molten liquid.

[0071] Step 4: Slowly immerse the silver rod / silver mesh composite substrate into the molten ternary solid solution for 20 seconds, then lift it out at a speed of 0.5 cm / s and allow it to cool naturally to room temperature. Use the resulting electrode as the anode and the carbon rod as the cathode, placing it in a 1.0 mol / L mixed sodium halide solution (NaCl:NaBr = 9:1), and set a constant current density of 2 mA / cm². 2 Perform anodic polarization for 15 minutes; repeat the above immersion and polarization process 3 times to obtain the pretreated electrode;

[0072] Step 5: Weigh 0.01 mol of lead nitrate as the heavy metal template molecule and 0.01 mol of thiourea as the simulated template molecule of sulfur, dissolve them in 50 mL of methanol solution, add 0.06 mol of 4-vinylpyridine, 0.1 mol of ethylene glycol dimethacrylate and 0.005 mol of initiator AIBN, and react at 65 °C for 24 h under nitrogen protection; grind the obtained product through a 400-mesh sieve, and repeatedly elute the template ions with 0.5 mol / L nitric acid solution until lead and sulfur are undetectable in the eluent, and dry to obtain the dual-ion imprinted polymer powder;

[0073] Step 6: Weigh 8g of sulfonated polyether ether ketone (SPEEK, sulfonation degree 65%) and dissolve it in 90g of N-methylpyrrolidone. Add 2g of polyvinylpyrrolidone as a film-forming aid. Add 0.3g of dual ion-imprinted polymer powder, 1.0g of silane coupling agent KH-550, 0.5g of bisphenol A epoxy resin (E-51), 0.2g of mercapto-modified graphene oxide (SH-GO), and 0.05g of imidazole ionic liquid to the solution in sequence. Disperse the mixture with high-power ultrasonication for 2 hours to form a homogeneous slurry.

[0074] Step 7: Treat the pretreated electrode with oxygen plasma for 10 min, then immerse it in the above interface strengthening slurry using the dip-coating method (speed 1 mm / s). After removal, pre-dry it at 60℃ for 30 min, then heat it to 130℃ at a rate of 2℃ / min and hold it at that temperature for 2 h. Repeat the coating and curing process twice, then place it in a vacuum oven at 150℃ for final heat treatment for 1.5 h, and then immerse it in a 0.1 mol / L KCl solution for equilibration activation for 48 h. After activation, remove the electrode and immediately seal it with a rubber sleeve containing saturated KCl solution on the electrode head. Cover the outside with black aluminum foil to block light, thus obtaining the composite reference electrode.

[0075] Comparative Example 1: Comparative Example 1 uses commercially available industrial-grade silver / silver chloride reference electrodes.

[0076] Comparative Example 2 (without rare earth nanoparticle doping): The difference between Comparative Example 2 and Example 1 is that step 2 is omitted. In step 3, no rare earth nanoparticle doping precursor powder is added. Instead, silver chloride, silver bromide, silver iodide and anhydrous lithium fluoride are weighed according to the mass ratio and melted.

[0077] Comparative Example 3 (without dual ion-imprinted polymer powder): The difference between Comparative Example 3 and Example 1 is that step 5 is omitted, and dual ion-imprinted polymer powder is not added when preparing the slurry in step 6.

[0078] Comparative Example 4: The difference between Comparative Example 4 and Example 1 is that in step 6, when preparing the slurry, thiolized graphene oxide and imidazole ionic liquid are not added.

[0079] Performance testing:

[0080] 1. Sulfide ion interference resistance test: 5 mg / L of sulfide ions (provided by Na2S) were added to simulated seawater (3.5% NaCl solution). The test electrode was completely immersed in the solution and left to stand at a constant temperature of 25℃ for 30 days. Electrochemical workstations were used to record the electrode potential changes in real time, and the maximum potential drift value of the electrode over 30 days was calculated. The smaller the potential drift value, the stronger the resistance to sulfide ion corrosion. The test results are shown in Table 1.

[0081] 2. Resistance to heavy metal ion interference test: 10 mg / L of lead ions (provided by Pb(NO3)2) were added to simulated seawater and the electrode was immersed at a constant temperature of 25°C for 30 days. The amount of lead ions adsorbed on the electrode surface was detected by inductively coupled plasma mass spectrometry (ICP-MS). Simultaneously, the potential fluctuation amplitude during the immersion period was recorded using an electrochemical workstation. The lower the adsorption amount and the smaller the potential fluctuation amplitude, the better the electrode's resistance to heavy metal ion interference. The test results are shown in Table 1.

[0082] 3. Resistance to Bromine / Iodide Ion Interference Test: The simulated seawater system was adjusted to achieve a bromide ion concentration of 100 mg / L (provided by NaBr) and an iodide ion concentration of 1 mg / L (provided by NaI). The system was continuously immersed at 25°C for 60 days. X-ray diffraction was used to analyze the compositional changes of the silver halide layer on the electrode surface, and the silver chloride retention rate was calculated. Simultaneously, the Nernst response deviation of the electrode was tested using an electrochemical workstation. Higher silver chloride retention rates and smaller Nernst response deviations indicated stronger resistance to bromide / iodide ion displacement interference. The test results are shown in Table 1.

[0083] 4. Long-term potential stability test: The electrode was placed in a standard 3.5% NaCl solution and continuously monitored at a constant temperature of 25℃ for 180 days. The electrode potential value was recorded at a fixed time each day using an electrochemical workstation, and the standard deviation of the potential data over the 180 days was calculated. The smaller the standard deviation, the better the long-term stability of the electrode potential. The test results are shown in Table 1.

[0084] 5. In simulated seawater containing complex impurities (sulfide ions, lead ions, and organic matter), linear polarization scanning was performed on the electrodes to calculate their polarization resistance. The rate of change of the electrodes at the initial stage of immersion and after 30 days of immersion was compared. This indicator reflects the adsorption and scaling of impurity ions on the electrode surface and the degree of erosion of the electrode's functional layer. A lower rate of change indicates stronger anti-interference and self-cleaning performance. The test results are shown in Table 1.

[0085] Table 1:

[0086]

[0087] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a composite reference electrode, characterized in that, Includes the following steps: (1) Provide a pure silver rod and a pure silver mesh, process a spiral groove on the surface of the pure silver rod, embed the pure silver mesh into the spiral groove, fix it by blue laser welding, and then clean and dry it to obtain a silver rod / silver mesh composite substrate; (2) Cerium nitrate, lanthanum nitrate, citric acid, nano titanium dioxide and nano hydroxyapatite were mixed and treated, and then calcined to obtain rare earth-nanoparticle doped precursor powder; (3) Mix silver chloride, silver bromide, silver iodide, rare earth-nanoparticle doped precursor powder and lithium fluoride, and heat to melt to form a ternary solid solution melt; (4) Immerse the silver rod / silver mesh composite substrate in the molten ternary solid solution, pull it out and cool it, and then use it as the anode in the mixed sodium halide solution for constant current polarization. Repeat the immersion and polarization operation to obtain the pretreated electrode. (5) Using lead nitrate as a heavy metal template molecule and thiourea as a simulated template molecule of sulfur, a polymerization reaction is carried out with 4-vinylpyridine, ethylene glycol dimethacrylate and initiator AIBN to obtain a polymer; the polymer is eluted with nitric acid solution to remove template ions and then dried to obtain a dual-ion imprinted polymer powder. (6) Dissolve sulfonated polyether ether ketone in N-methylpyrrolidone, add polyvinylpyrrolidone, dual ion-imprinted polymer powder, silane coupling agent KH-550, epoxy resin, mercaptoized graphene oxide and imidazole ionic liquid, and disperse to form a slurry; (7) The pretreated electrode is subjected to oxygen plasma treatment, then immersed in slurry, pulled up and dried and cured. The coating and curing operations are repeated, and after vacuum heat treatment, it is placed in potassium chloride solution for immersion and activation to obtain a composite reference electrode.

2. The method for preparing a composite reference electrode according to claim 1, characterized in that, In step (2), the molar ratio of cerium nitrate to lanthanum nitrate is 2:(1-2).

3. The method for preparing a composite reference electrode according to claim 1, characterized in that, In step (2), the mass ratio of nano-titanium dioxide to nano-hydroxyapatite is 15:(4-6).

4. The method for preparing a composite reference electrode according to claim 1, characterized in that, In step (3), the mass ratio of silver chloride, silver bromide, silver iodide, rare earth-nanoparticle doped precursor, and lithium fluoride is 100:(4~6):(1~2):(0.5~1):(0.5~1).

5. The method for preparing a composite reference electrode according to claim 1, characterized in that, In step (5), the molar ratio of lead nitrate to thiourea is 1:(1-2).

6. The method for preparing a composite reference electrode according to claim 1, characterized in that, In step (5), the molar ratio of 4-vinylpyridine to ethylene glycol dimethacrylate is 6:(10-15).

7. The method for preparing a composite reference electrode according to claim 1, characterized in that, In step (6), the mass ratio of sulfonated polyether ether ketone to dual ion-imprinted polymer powder is 8:(0.3-0.8).

8. The method for preparing a composite reference electrode according to claim 1, characterized in that, In step (6), the mass ratio of mercapto-modified graphene oxide to imidazole ionic liquid is 2:(0.5-1.0).

9. The method for preparing a composite reference electrode according to claim 1, characterized in that, In step (7), the concentration of potassium chloride solution is 0.1-0.2 mol / L.

10. A composite reference electrode, characterized in that, Its features are, It is prepared by the method described in any one of claims 1 to 9 above.

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