Methods and applications of using metal oxyacid anions to inhibit metal chloride corrosion

Abstract

This invention discloses a method for using metal oxyacid anions to inhibit chlorine corrosion of metals and its application. Specifically, it discloses a novel use of metal oxyacid anions to alleviate the chemical or electrochemical corrosion of metals by chlorine-containing solutions. In this invention, metal oxyacid anions form polymetallic oxyacid anion clusters during electrolytic or electrochemical corrosion, revealing that these clusters possess specific chemical adsorption properties on the surface of metal electrodes or metal substrates, and exhibit strong resistance to chlorine corrosion. ‑ The electrostatic repulsion and steric hindrance effects of the Cl- at the interface can reduce the interfacial Cl- ‑ The concentration can thus alleviate chlorine corrosion of metals and extend the service life of metal materials in chlorine-containing environments.

Description

Technical Field

[0001] This invention belongs to the field of metal corrosion and protection technology, specifically relating to a method and its application of using metal oxyacid anions to inhibit metal chlorine corrosion. Background Technology

[0002] Currently, freshwater resources are relatively scarce. In contrast, seawater resources are abundant and easily accessible; seawater accounts for over 97.5% of the world's water resources, thus it is considered an inexhaustible resource. However, due to the high concentration of ions in seawater, it can easily lead to structural damage to metal materials in contact with it. - Chlorine is the most abundant ion in seawater (approximately 0.5M). Due to its small radius, strong diffusion ability, high electronegativity, and strong complexing ability, it easily accelerates the chemical and electrochemical corrosion of metallic materials. Therefore, chlorine corrosion is the most important and serious type of corrosion involved in seawater corrosion.

[0003] Seawater electrolysis is a common method for fully developing seawater resources. However, chlorine corrosion causes electrochemical corrosion of the metal electrodes used in seawater electrolysis, which restricts the application of this technology. Summary of the Invention

[0004] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes the use of metal oxyacid ions to suppress chemical and electrochemical corrosion of metals by chlorine-containing solutions. Specifically, metal oxyacid ions form polymetallic oxyacid anion clusters during chemical corrosion, electrolysis, or electrochemical corrosion. These polymetallic oxyacid anion clusters can alleviate chlorine corrosion of metals in situ (such as seawater chlorine corrosion). When used in seawater electrolysis, they can alleviate the electrochemical corrosion of the metal electrodes used, showing promising application prospects.

[0005] The present invention also proposes an electrolyte for mitigating metal corrosion.

[0006] The present invention also proposes an electrolysis system.

[0007] The present invention also proposes a method to mitigate corrosion of metal electrodes.

[0008] In a first aspect, the present invention proposes the use of metal oxyacid anions to suppress chemical or electrochemical corrosion of metals by chlorine-containing solutions.

[0009] Metal oxyacid anions can form polymetallic oxyacid anion clusters during chemical corrosion, electrolysis, or electrochemical corrosion. These clusters exhibit specific chemical adsorption on the metal electrode surface or metal substrate surface, and react with Cl-. - The presence of electrostatic repulsion and steric hindrance between the interfacial surfaces allows for the achievement of low-interfacial Cl... -Concentration, mitigating chloride corrosion of metal electrodes. Specifically, this includes: metal oxyacid anion monomers and polymetallic oxyacid anion clusters repelling chloride ions (Cl-) at the metal-chlorine-containing solution (e.g., electrolyte) interface through electrostatic interactions. - This process mitigates the rate of chlorine corrosion. Oxygen-containing anions form a passivation layer on the metal surface through specific adsorption, reducing the rate of chlorine diffusion at the metal-chlorine-containing solution (e.g., electrolyte) interface and hindering the binding process between chlorine and metal sites, thus mitigating the chlorine corrosion rate. Polyoxygen-containing anion clusters have relatively large ionic radii, and due to their strong steric hindrance effect, they can reduce the chloride ion concentration at the metal-chlorine-containing solution (e.g., electrolyte) interface. - Concentration reduces the rate of chlorine corrosion.

[0010] Furthermore, metal oxyacid ions can be applied to seawater corrosion protection of equipment that comes into direct contact with seawater in closed systems, such as seawater desalination facilities, offshore wind power platforms, offshore oil and gas platforms, and offshore construction platforms; they can be used to couple with offshore photovoltaic and wind power generation systems in nearshore areas to achieve large-scale production of green hydrogen energy; and they can be used for seawater corrosion protection of metal components in scenarios such as railways, airports, highway bridges, ports and wharves, water conservancy projects, ships, aircraft, trains, coal industry, power systems, urban water supply, mariculture, cultural relics and historical sites, seawater desalination, marine new energy, marine platforms and equipment, submarine pipelines, marine oil equipment, construction, automobiles, oil and gas industry, metallurgy, electronics industry, papermaking industry, chemical industry, telecommunications, home appliances, pharmaceutical industry, mining industry, food processing, medical devices, and agriculture.

[0011] In some embodiments of the present invention, the chlorine-containing solution contains Cl. - Cl in chlorine-containing solutions - The concentration is 0.1–5 mol / L.

[0012] In some embodiments of the present invention, the pH range of the chlorine-containing solution is 0 to 14.

[0013] In some embodiments of the present invention, the chlorine-containing solution includes seawater, simulated seawater, industrial electrolyte, or tap water.

[0014] In some embodiments of the present invention, the metal element in the metal oxyacid ion includes at least one selected from chromium, molybdenum, or tungsten. Optionally, the metal oxyacid ion includes at least one selected from molybdate, chromate, or tungstate.

[0015] In some embodiments of the present invention, the initial concentration of metal oxyacid ions in the chlorine-containing solution, calculated as metal atoms, is 0.01-6 mol / L, and may be selected as 0.05-4 mol / L.

[0016] In some embodiments of the present invention, the temperature of the chlorine-containing solution is 10-90°C, and optionally 20-80°C.

[0017] In some embodiments of the present invention, a corrosion inhibitor containing metal oxyacid anions is added to a chlorine-containing solution for the protection of metal electrodes or metal substrates during electrochemical or chemical corrosion.

[0018] In some embodiments of the present invention, the metal oxyacid anions are used in the electrolyte of seawater electrolysis for corrosion protection of metal electrodes.

[0019] Through the above embodiments, metal oxyacid anions form polymetallic oxyacid anion clusters during seawater electrolysis. Due to the specific chemical adsorption of these polymetallic oxyacid anion clusters on the metal electrode surface, and their interaction with Cl... - Electrostatic repulsion and steric hindrance effects are formed between the surfaces, which can reduce the interfacial Cl. - Concentration, to alleviate chlorine corrosion of metal electrodes. Specifically, this includes: adding metal oxyacids to the electrolyte, which prevents corrosion ions from approaching the protected metal by forming polymetallic oxyacid anion clusters on the metal surface in situ, thus alleviating chlorine corrosion in seawater: (1) Interface-specific adsorption: Polymetallic oxyacid ions such as polymolybdate can form specific adsorption on the surface of the metal electrode and accumulate on the electrode surface in situ to play an anti-corrosion role. (2) Electrostatic repulsion between ions: Polymolybdate anion clusters can form charge repulsion against other negatively charged anions, reducing the concentration of anions on the electrode surface, thereby producing an anti-chlorine corrosion effect on the electrode surface. (3) Spatial hindrance effect of polyacids: The center, side edges and bottom edge of the polymolybdate anion cluster structure are usually distributed with molybdenum and oxygen atom species. The large spatial hindrance can inhibit chloride anions from approaching the electrode surface and produce an anti-corrosion effect.

[0020] In some embodiments of the present invention, the metal being protected or shielded includes at least one of Ni, Mo, Fe, Co, Ti, or Au.

[0021] In some embodiments of the present invention, the metal electrode comprises one or more of elemental Ni, Raney nickel, NiMo alloy, NiFe alloy, Co metal, CoFe alloy, or elemental Au.

[0022] In some embodiments of the present invention, the metal substrate includes one or more of elemental Ni, NiMo alloy, NiFe alloy, Co metal, CoFe alloy, or elemental Au.

[0023] In some embodiments of the present invention, a corrosion inhibitor containing metal oxyacid anions is added to a chlorine-containing solution for the protection of metal electrodes or metal substrates during electrochemical or chemical corrosion. The raw materials of the chlorine-containing solution include, but are not limited to, those containing Cl. - The solution can be one or more natural / artificial corrosive liquids, such as seawater, simulated seawater, industrial electrolytes, industrial wastewater, or tap water. Optionally, the raw material for the chlorine-containing solution may include Cl-containing... - At least one of the following: seawater, simulated seawater, industrial electrolyte, industrial wastewater, or tap water.

[0024] In some embodiments of the present invention, the corrosion inhibitor includes at least one of molybdate, chromate, or tungstate.

[0025] In some embodiments of the present invention, the molybdate includes at least one of sodium molybdate, potassium molybdate, ammonium molybdate, or ammonium heptamolybdate.

[0026] The aforementioned molybdates play roles including the formation of heptamolybdate or octamolybdate ions in the corrosive microenvironment, which are then specifically chemisorbed on the metal electrode surface by polymolybdenum oxyacid anion clusters and react with Cl-. - Electrostatic repulsion and steric hindrance effects reduce interfacial Cl - Concentration, to alleviate chlorine corrosion of metals.

[0027] In some embodiments of the present invention, the chromate includes at least one of sodium chromate, potassium chromate, magnesium chromate, or ammonium chromate.

[0028] In some embodiments of the present invention, the tungstate includes at least one of sodium tungstate, potassium tungstate, or ammonium tungstate.

[0029] In some embodiments of the present invention, the electrochemical reaction includes the electrolysis of seawater.

[0030] In some embodiments of the present invention, metal oxyacid anions are used for corrosion protection of layered bimetallic hydroxide catalysts for oxygen evolution reactions, corrosion protection of catalysts for oxygen evolution reactions, corrosion protection of catalysts for chlorine evolution reactions, corrosion protection of metal substrates for oxygen evolution reactions, corrosion protection of metal substrates for chlorine evolution reactions, or corrosion protection of alkaline anion exchange membrane electrolyzers. The electrochemical reactions that can occur in the alkaline anion exchange membrane electrolyzer include oxygen evolution reactions and chlorine evolution reactions.

[0031] The aforementioned method for inhibiting electrochemical corrosion of metals using metal oxyacid anions can be used to suppress electrochemical corrosion of electrocatalytic electrodes in chlorine-containing electrolytes, achieve high stability of seawater electrolysis catalysts, protect against corrosion of layered bimetallic hydroxides used in common oxygen evolution reaction catalysts, protect against corrosion of oxygen evolution reaction catalysts and chlorine evolution reaction catalysts and substrates, and protect against corrosion of seawater electrolysis hydrogen production electrodes and corresponding electrolytic cells. Specifically, this method for mitigating metal electrode corrosion can achieve in-situ mitigation of chlorine corrosion of metals using polymetallic oxyacid anion clusters, effectively reducing the chloride ion concentration on the metal surface from three aspects: ion electronegativity repulsion, specific adsorption, and steric hindrance. - This method effectively protected against chlorine corrosion of metals in simulated and real seawater electrolytes at various concentrations and pH levels. Particularly in alkaline anion exchange membrane electrolyzers for industrial seawater hydrogen production, this method also provided excellent corrosion protection for the metal catalyst electrodes and substrate. Furthermore, this method has broad applicability and can be used in a wide range of Cl concentrations. - It provides corrosion protection for Ni metal, NiMo alloy, NiFe alloy, Co metal, CoFe alloy, Au metal, etc. in corrosive media with varying concentrations and pH ranges. Optionally, in some embodiments of the present invention, the concentration of the corrosion inhibitor anion is also adjustable within the range of 0.05 to 4 mol / L, which is beneficial for achieving efficient utilization of seawater resources in multiple scenarios.

[0032] A second aspect of the invention provides an electrolyte capable of mitigating metal corrosion, the electrolyte comprising chloride ions (Cl... - It also includes at least one of metal oxyacid anions or polymetallic oxyacid anion clusters.

[0033] The electrolyte according to embodiments of the present invention, which can mitigate metal corrosion, has at least the following beneficial effects:

[0034] During the electrochemical corrosion process, hydroxide ions are consumed at the metal-electrolyte interface. The electrolyte of this invention can induce the formation of polymetallic oxyacid anion clusters from metal oxyacid anion monomers in situ. This polymetallic oxyacid anion clusters are then utilized in conjunction with Cl... - The electrostatic repulsion between electrodes, the specific adsorption to metal surfaces, and the steric hindrance effect enhance the resistance of electrode materials to chlorine corrosion, effectively mitigating the corrosion of various metal materials in chlorine-containing solutions (such as seawater) over a wide pH and temperature range. The electrolyte of this invention, capable of mitigating metal corrosion, is a method for in-situ constructing polymetallic oxyacid anion clusters to alleviate chlorine corrosion of metals (such as seawater chlorine corrosion).

[0035] In some embodiments of the present invention, the metal element in the metal oxyanion and the polymetallic oxyanion anion cluster is independently selected from at least one of chromium, molybdenum or tungsten.

[0036] In some embodiments of the present invention, the metal oxyacid ion includes at least one of molybdate, chromate or tungstate.

[0037] In some embodiments of the present invention, the polymetallic oxyacid anion cluster includes at least one of heptamolybdate, octamolybdate, chromate, dichromate, heptatungstate, decatungstate, and dodecatungstate.

[0038] In some embodiments of the present invention, the sum of the initial concentrations of the metal oxyacid ions and the polymetallic oxyacid anion clusters in the electrolyte, based on metal atoms, is 0.01-6 mol / L, and optionally 0.05-4 mol / L.

[0039] In some embodiments of the present invention, the electrolyte contains Cl - Cl - The concentration in the electrolyte is 0.1–5 mol / L, and can be selected as 0.5–1.25 mol / L.

[0040] In some embodiments of the present invention, the pH range of the electrolyte is 0 to 14.

[0041] In some embodiments of the present invention, the temperature of the electrolyte is 10-90°C, and optionally 20-80°C.

[0042] In some embodiments of the present invention, the raw materials for preparing the electrolyte include a corrosion inhibitor, which includes metal oxyacid anions.

[0043] In some embodiments of the present invention, the corrosion inhibitor includes at least one of molybdate, chromate, or tungstate.

[0044] In some embodiments of the present invention, the molybdate includes at least one of sodium molybdate, potassium molybdate, ammonium molybdate, or ammonium heptamolybdate.

[0045] In some embodiments of the present invention, the chromate includes at least one of sodium chromate, potassium chromate, magnesium chromate, or ammonium chromate.

[0046] In some embodiments of the present invention, the tungstate includes at least one of sodium tungstate, potassium tungstate, or ammonium tungstate.

[0047] In some embodiments of the present invention, the raw materials for preparing the electrolyte also include other materials as needed for electrolysis. Optionally, the raw materials for preparing the electrolyte also include aqueous fluids.

[0048] In some embodiments of the present invention, the aqueous fluid includes, but is not limited to, deionized water, seawater, tap water, and some industrial wastewater. The seawater may be simulated seawater or natural seawater. Optionally, the aqueous fluid includes at least one of natural seawater, simulated seawater, industrial electrolyte, industrial wastewater, or tap water.

[0049] In some embodiments of the present invention, the raw materials for preparing the electrolyte also include at least one of alkaline substances or electrolyte substances.

[0050] In some embodiments of the present invention, the alkaline substance includes, but is not limited to, at least one of sodium hydroxide, potassium hydroxide, etc. Optionally, the alkaline substance includes at least one of sodium hydroxide or potassium hydroxide.

[0051] In some embodiments of the present invention, the electrolyte substance includes metal chlorides.

[0052] In some embodiments of the present invention, the metal chloride includes at least one of sodium chloride or potassium chloride.

[0053] Depending on the electrolysis requirements, the electrolyte may also include other electrolysis additives.

[0054] In a third aspect, the present invention provides an electrolysis system comprising the above-described electrolyte.

[0055] In some embodiments of the present invention, the electrolysis system includes a seawater electrolysis hydrogen production electrolysis cell.

[0056] In some embodiments of the present invention, the seawater electrolysis hydrogen production electrolytic cell includes a working electrode, which comprises at least one of Ni, Fe, Co, or Au. Optionally, the working electrode may be one or more of Ni metal, NiMo alloy, NiFe alloy, Co metal, CoFe alloy, or Au metal.

[0057] In some embodiments of the present invention, the seawater electrolysis hydrogen production electrolyzer includes an alkaline electrolyzer or an alkaline anion exchange membrane electrolyzer. Optionally, an anion exchange membrane electrolyzer assembled from metallic nickel can achieve stable operation for over 800 hours.

[0058] In a fourth aspect, the present invention provides a method for mitigating corrosion of a metal electrode, comprising the following steps: when the metal electrode is placed in a chlorine-containing electrolyte for electrolysis, wherein the chlorine-containing electrolyte includes the electrolyte described in any of the second aspects of the present invention.

[0059] Through the above implementation method, during the electrochemical corrosion process, hydroxide ions are consumed at the metal-electrolyte interface, inducing the in-situ formation of polymetallic oxyacid anion clusters from metal oxyacid anion monomers. This utilizes the reaction between polymetallic oxyacid anions and Cl... - The electrostatic repulsion between electrodes, the specific adsorption of electrodes to metal surfaces, and the steric hindrance effect enhance the resistance of electrode materials to chlorine corrosion. This method can effectively alleviate the corrosion of various metal materials in chlorine-containing solutions (such as seawater) over a wide pH and temperature range. It is a method for in-situ construction of polymetallic oxyanion clusters to alleviate metal chlorine corrosion (such as seawater chlorine corrosion).

[0060] This method is applicable to metal corrosion under open-circuit potential or applied anodic potential, especially for the protection against seawater corrosion and chlorine corrosion. Specifically, it can be used to mitigate chlorine corrosion of metals or alloys such as Ni, NiMo alloys, NiFe alloys, Co, CoFe alloys, and Au.

[0061] Specifically, in some embodiments of the present invention, this method can be adapted to mitigate electrochemical corrosion under applied potential or open-circuit potential in an electrolyte composed of deionized water, simulated seawater, real seawater, and KOH and NaOH, within a pH range of 0–14 and a temperature range of 20–80°C. Simultaneously, the concentration of the corrosion-inhibiting anions involved in this method is adjustable within a concentration range of 0.05–4 mol / L. For electrochemical corrosion processes under applied anodic potential, this method can be successfully applied to alkaline electrolytic cells and alkaline anion exchange membrane devices. This method utilizes the process of consuming hydroxide ions during anodic electrochemical corrosion to induce the in-situ formation of polymetallic oxyacid anion clusters from metal oxyacid anions. Furthermore, it utilizes the electrostatic repulsion, interface-specific adsorption, and steric hindrance effects of the two types of ions to reduce the chloride ion concentration at the metal-electrolyte interface, effectively reducing the metal chloride corrosion rate. This is a metal corrosion protection technology applicable to a wide pH range, a wide temperature range, and various solution environments.

[0062] In some embodiments of the present invention, the pH range of the chlorine-containing electrolyte is 0–14, such as 7–14. Optionally, the pH value of the microenvironment at the interface between the metal electrode and the electrolyte is 0–6.

[0063] In some embodiments of the present invention, the temperature of the chlorine-containing electrolyte is 10-90°C, and can be selected as 20-80°C. Attached Figure Description

[0064] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0065] Figure 1 Mo7O in the electrolyte of Example 1 of this invention 246- Cluster structure diagram;

[0066] Figure 2 The above are the accelerated aging test time-potential curves of nickel electrodes in the electrolytic cells of Embodiment 1 and Comparative Examples 1-4 of this invention.

[0067] Figure 3 The graph shows the scanning polarization curves and key corrosion parameters of the nickel electrode in the electrolyte S1 and D1 of the electrolytic cell.

[0068] Figure 4 The diagram shows the surface morphology changes of the nickel electrode during the accelerated aging experiment of the electrolyte in Example 1 and Comparative Example 1 of this invention.

[0069] Figure 5 This is a statistical chart showing the percentage of nickel electrode corrosion area during the accelerated aging experiment of the electrolyte in Example 1 and Comparative Example 1 of the present invention.

[0070] Figure 6 The graph shows the test results of the electrostatic repulsion of ions during the accelerated aging experiment of the electrolyte in Example 1 and Comparative Example 1 of this invention.

[0071] Figure 7 The graph shows the test results of electrostatic repulsion of ions during the chronovoltammetry test of electrolytes under different current densities in Example 1 and Comparative Examples 1 and 4 of the present invention.

[0072] Figure 8 The figure shows the in-situ Raman signal test results of the electrolyte under different current densities in Example 1 of the present invention.

[0073] Figure 9 The graph shows the test results of the specific adsorption of ions during the accelerated aging experiment of the electrolyte in Example 1 and Comparative Example 4 of this invention.

[0074] Figure 10 The graph shows the test results of the percentage of chlorine atoms on the electrode surface during the accelerated aging experiment of the electrolyte in Example 1 and Comparative Examples 1, 3 and 4 of this invention;

[0075] Figure 11 This is a graph showing the in-situ Raman signal test results of polymolybdate ions in the electrolyte of Example 2 of the present invention;

[0076] Figure 12 This is a graph showing the response of the form of molybdenum in the electrolyte of the present invention, in which molybdenum is used as a metal oxyacid anion additive element, to pH.

[0077] Figure 13 This is a graph showing the form and content distribution of molybdenum in the electrolyte of this invention at pH = 3, 5, 7, and 9.

[0078] Figure 14This is a graph showing the in-situ Raman signal test results of polymolybdate ions in the electrolyte of Example 3 of the present invention;

[0079] Figure 15 This is a figure showing the temperature universality test results of the in-situ mitigation method for metal chloride corrosion by polymetallic oxyacid anion clusters in the electrolyte according to an embodiment of the present invention.

[0080] Figure 16 This is a time-potential curve of the accelerated aging test of the nickel electrode in the electrolytic cell of Example 4 and Comparative Example 1 of the present invention.

[0081] Figure 17 This is a graph showing the response of the molybdenum form in the electrolyte with a molybdenum concentration of 0.4 mol / L to pH.

[0082] Figure 18 The graph shows the stability test results of electrolyte S8 in Example 6 and electrolyte D5 in Comparative Example 5 in an alkaline anion exchange membrane electrolyzer.

[0083] Figure 19 The graph shows the test results of the resistance of electrolyte S1 in Example 1 and electrolyte D1 in Comparative Example 1 to chlorine corrosion of iron-doped nickel hydroxide.

[0084] Figure 20 The graph shows the test results of potential decay rate and performance decay rate of iron-doped nickel hydroxide in electrolyte S1 of Example 1 and electrolyte D1 of Comparative Example 1. Detailed Implementation

[0085] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0086] Unless otherwise specified, the experimental methods described in the following examples are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used are all commercially available from the conventional market unless otherwise specified.

[0087] Example 1

[0088] This embodiment discloses an electrolyte (electrolyte S1), the preparation process of which includes:

[0089] Weigh 4.04 g sodium hydroxide, 7.30 g sodium chloride, and 3.09 g sodium molybdate solid, dissolve them in deionized water, and transfer them to a 100 mL volumetric flask and make up to volume to obtain electrolyte S1, in which the concentration of molybdenum (in the form of molybdate and polymolybdate anions) is 0.15 mol / L and the pH is 14.

[0090] This embodiment also discloses an electrolysis system, including an electrolytic cell comprising a circular glass cell, an electrolyte S1 placed therein, and a three-electrode system. A treated nickel electrode is used as the working electrode, a graphite rod as the counter electrode, and Hg / HgO as the reference electrode. Each electrode is placed in the electrolyte S1, forming a three-electrode system within the circular glass electrolytic cell.

[0091] The pretreatment steps for the nickel electrode include: cutting a piece of foamed nickel (30mm×10mm×0.5mm in size), first placing it in 1.0mol / L hydrochloric acid and sonicating it for 40 minutes to remove the surface oxide layer, and then washing the surface with ethanol and deionized water to remove residual hydrochloric acid, thus obtaining the treated nickel electrode.

[0092] Example 2

[0093] This embodiment discloses an electrolyte (electrolyte S2), the preparation process of which includes:

[0094] Weigh 0.404 g sodium hydroxide, 7.30 g sodium chloride, and 3.09 g sodium molybdate solid, dissolve them in deionized water, and transfer them to a 100 mL volumetric flask and make up to volume to obtain the test electrolyte S2, in which the concentration of molybdenum (in the form of molybdate and polymolybdate anions) is 0.15 mol / L and the pH is 12.

[0095] This embodiment also discloses an electrolysis system, which differs from Embodiment 1 only in that the electrolyte S2 prepared in this embodiment is used instead of the electrolyte S1 in Embodiment 1.

[0096] Example 3

[0097] This embodiment discloses an electrolyte (electrolyte S3), the preparation process of which includes:

[0098] Weigh 0.0404 g sodium hydroxide, 7.30 g sodium chloride, and 3.09 g sodium molybdate solid, dissolve them in deionized water, and transfer them to a 100 mL volumetric flask and make up to volume to obtain test electrolyte S3, in which the concentration of molybdenum (in the form of molybdate and polymolybdate anions) is 0.15 mol / L and the pH is 8.

[0099] This embodiment also discloses an electrolysis system, including an electrolytic cell comprising an electrolyte S3 and a three-electrode system. A treated nickel electrode is used as the working electrode, a platinum wire as the counter electrode, and solid silver / silver chloride as the reference electrode. Each electrode is placed in the electrolyte S3, forming a three-electrode system in an in-situ Raman electrolysis cell. The electrolyte and ambient temperature are room temperature (20°C). The pretreatment steps for the nickel electrode are the same as in Embodiment 1.

[0100] Example 4

[0101] This embodiment discloses a series of electrolytes (electrolytes S4 to S6). The difference between electrolytes S4 to S6 and electrolyte S1 in Example 1 is that the molybdenum concentration based on molybdenum atoms is different. The molybdenum concentrations based on molybdenum atoms in electrolytes S4 to S6 are 10 mmol / L, 50 mmol / L, and 150 mmol / L, respectively.

[0102] This embodiment also discloses a series of electrolysis systems, which differ from Embodiment 1 only in that the electrolyte S4 to S6 prepared in this embodiment are used to replace the electrolyte S1 in Embodiment 1.

[0103] Example 5

[0104] This embodiment discloses an electrolyte (electrolyte S7), which differs from electrolyte S1 in Example 1 in that the molybdenum concentration, calculated as molybdenum atoms, is different. The molybdenum concentration in electrolyte S7, calculated as molybdenum atoms, is 0.4 mol / L.

[0105] This embodiment also discloses an electrolysis system, which differs from Embodiment 1 only in that the electrolyte S7 prepared in this embodiment is used instead of the electrolyte S1 in Embodiment 1.

[0106] Example 6

[0107] This embodiment discloses an electrolyte (electrolyte S8), the preparation process of which includes:

[0108] Seawater, sodium hydroxide, and sodium molybdate were mixed to obtain electrolyte S8. The concentration of sodium hydroxide in electrolyte S8 was 1 mol / L, the concentration of molybdenum (based on molybdenum atoms) was 0.15 mol / L, and the concentration of Cl... - The concentration is approximately 0.5 mol / L.

[0109] This embodiment discloses an electrolysis system, including an alkaline anion exchange membrane electrolytic cell. The electrolytic cell includes the electrolyte S8 prepared in this embodiment. In this embodiment, anion exchange membrane is used as an ion transport channel and a gas isolation barrier. After the pretreatment steps described in Example 1, the nickel metal electrode is combined with the anion exchange membrane and assembled to form an alkaline anion exchange membrane electrolytic cell. This electrolytic cell is a two-electrode system (working electrode and counter electrode), which can be connected to an electrochemical workstation to form a complete voltage and current loop. Stability testing can be performed using the chronopotential method, such as setting the constant current parameter to 1A.

[0110] Example 7

[0111] This embodiment discloses an electrolysis system, which differs from Embodiment 1 in that: this embodiment uses a layered bimetallic hydroxide catalyst electrode (30mm × 10mm × 0.5mm) instead of the nickel electrode in Embodiment 1. The layered bimetallic hydroxide catalyst electrode can be an oxygen evolution reaction catalyst or a chlorine evolution reaction catalyst.

[0112] Comparative Example 1

[0113] This comparative example discloses an electrolyte (electrolyte D1), the preparation process of which includes: weighing 4.04 g of sodium hydroxide and 7.30 g of sodium chloride, dissolving them in deionized water, and transferring them to a 100 mL volumetric flask and making up to volume to obtain electrolyte D1 (wherein, the concentration of NaOH is 1 mol / L and the concentration of NaCl is 1.25 mol / L).

[0114] This comparative example also discloses an electrolysis system, which differs from Example 1 only in that the electrolyte D1 prepared in this comparative example is used instead of the electrolyte S1 in Example 1.

[0115] Comparative Example 2

[0116] This comparative example discloses an electrolyte (electrolyte D2), the preparation process of which includes: weighing 4.04g sodium hydroxide, 7.30g sodium chloride, and 1.27g sodium nitrate solid, dissolving them in deionized water, and transferring them to a 100mL volumetric flask and making up to volume to obtain test electrolyte D2, wherein the concentration of nitrogen element (existing in the form of nitrate anion) is 0.15mol / L.

[0117] This comparative example also discloses an electrolysis system, which differs from Example 1 only in that the electrolyte D2 prepared in this comparative example is used instead of the electrolyte S1 in Example 1.

[0118] Comparative Example 3

[0119] This comparative example discloses an electrolyte (electrolyte D3), the preparation process of which includes: weighing 4.04 g sodium hydroxide, 7.30 g sodium chloride, and 2.13 g sodium sulfate solid, dissolving them in deionized water, and transferring them to a 100 mL volumetric flask and making up to volume to obtain test electrolyte D3, wherein the concentration of sulfur element (existing in the form of sulfate anion) is 0.15 mol / L.

[0120] This comparative example also discloses an electrolysis system, which differs from Example 1 only in that the electrolyte D3 prepared in this comparative example is used instead of the electrolyte S1 in Example 1.

[0121] Comparative Example 4

[0122] This comparative example discloses an electrolyte (electrolyte D4), the preparation process of which includes: weighing 4.04 g sodium hydroxide, 7.30 g sodium chloride, and 2.46 g sodium phosphate solid, dissolving them in deionized water, and transferring them to a 100 mL volumetric flask and making up to volume to obtain test electrolyte D4, wherein the concentration of phosphorus (existing in the form of phosphate anions) is 0.15 mol / L.

[0123] This comparative example also discloses an electrolysis system, which differs from Example 1 only in that the electrolyte D4 prepared in this comparative example is used instead of the electrolyte S1 in Example 1.

[0124] Comparative Example 5

[0125] This comparative example discloses an electrolyte (electrolyte D5), which differs from Example 6 in that electrolyte D5 does not contain molybdate. Specifically, the preparation process of electrolyte D5 includes: taking seawater and sodium hydroxide, mixing them, and obtaining electrolyte D5. The concentration of sodium hydroxide in electrolyte D5 is 1 mol / L, and Cl... - The concentration is approximately 0.5 mol / L.

[0126] This comparative example discloses an electrolysis system, including an alkaline anion exchange membrane electrolyzer, which differs from Example 6 only in that the electrolyte D5 in this comparative example is used instead of the electrolyte S8 in Example 6.

[0127] Test case

[0128] This experimental example tested the performance of the electrolytes and electrolysis systems in each embodiment and comparative example, specifically including:

[0129] 1. Establish an electrochemical corrosion research system and conduct accelerated aging experiments:

[0130] The three-electrode systems of the electrolysis systems in each embodiment and comparative example were connected to an electrochemical workstation to construct a complete voltage and current loop, thus establishing an electrochemical corrosion research system. The electrolyte and ambient temperature were set to room temperature (20°C). Accelerated aging tests were conducted with the constant current parameter of the chronopotential method set to 1A. The changes in system potential over time were recorded to investigate the enhancing effect of each electrolyte (such as the oxyacid ions corresponding to the four elements: nitrogen, sulfur, phosphorus, and molybdenum) on the metal's resistance to chloride corrosion.

[0131] To better illustrate the effect of oxyacid anions on improving the chloride corrosion resistance of metals, molybdate ions (MoO4) are first listed. 2- The reaction equilibrium and equilibrium constant between MoO4 and polymolybdate ions are detailed in Table 1 below. 2- Depending on its environment, it can spontaneously transform into different configurations, such as heptamolybdate (Mo7O). 24 6- ) or octamolate (Mo8O) 26 4- During corrosion induced by open circuit potential or applied anodic potential, H near the electrode surface + As concentration increases, MoO4 2- Polymolybdate clusters are formed in an electrolytic environment.

[0132] Table 1 Ionic equations for polymolybdate transformation

[0133]

[0134] Figure 1 Mo7O 24 6- A schematic diagram of the cluster structure, representing one of the forms in which molybdenum exists in electrolyte S1, Mo7O. 24 6- There are three types of molybdenum atom sites: M1 at the structural center, M2 on the structural side edges, and M4 at the bottom. There are six types of oxygen atom sites, as shown in the diagram (O1 to O6). In electrolytes used for the electrolysis of chlorine-containing solutions, a steric hindrance effect of polyammonium ions will occur. The polyammonium anion clusters have molybdenum and oxygen atom species distributed at their center, side edges, and bottom. This significant steric hindrance can inhibit chloride ions from approaching the electrode surface, thus providing corrosion protection.

[0135] Figure 2The potential-time curves for each accelerated aging experiment show that electrodes placed in different electrolytes exhibit varying stability times at the anodic potential under accelerated corrosion. The test duration indicates the strength of the corrosion inhibition effect of anions in the electrolyte on metal chloride corrosion. In electrolyte D1, which does not contain oxyacid anions, the metal electrode failed after 1 hour of stable operation (due to chloride corrosion). Using electrolyte D1 as a blank control, in electrolytes containing oxyacid anions (electrodes D2–D4 and S1), each ion showed varying degrees of corrosion inhibition, and the metal electrode's resistance to chloride corrosion was improved. Compared to electrolyte D1, the stability time of nickel metal in electrolytes D2 and D3 was slightly longer than 1 hour, indicating that nitrate and sulfate ions exhibited weak corrosion inhibition capabilities. In electrolyte D4, which added 0.15 mol / L phosphate ions, the electrode stability was extended to nearly 2 hours (double that of the blank control group), indicating that phosphate ions possess strong corrosion inhibition capabilities. In electrolyte S1 with a molybdenum content of 0.15 mol / L, the electrode can operate stably for 8 hours, exhibiting significant resistance to chlorine corrosion. (See Table 1 and...) Figure 1 Molybdenum in Mo7O 24 6- It exists in the form of corrosive microenvironments, therefore Figure 2 The results shown demonstrate the effectiveness of the in-situ mitigation strategy for metal chloride corrosion proposed in this invention using polymetallic oxyanion clusters, which also demonstrates the excellent role of molybdate and polymolybdate ions in resisting chloride corrosion of electrodes.

[0136] Figure 3 The image shows the scanning polarization curves and key corrosion parameters of the nickel electrode in electrolytes S1 and D1. pit This represents the pitting potential of the electrode, relative to electrolyte D1. In electrolyte S1, the nickel electrode E... pit The increase in voltage from 0.267V to 0.527V, indicating greater resistance to pitting corrosion, demonstrates that the polymolybdate ions in electrolyte S1 significantly enhance the nickel electrode's resistance to chloride corrosion. Simultaneously, the Tafel slope of the pitting process in electrolyte S1 increased from 50.99 mV / dec to 79.60 mV / dec, kinetically illustrating the effectiveness of the in-situ mitigation strategy for chloride corrosion of metals proposed in this invention using polymetallic oxyacid anion clusters.

[0137] Table 2 Summary of key parameters for corrosion of nickel electrodes in electrolyte

[0138] electrolyte Episode (V) Tafel slope (mV / dec) Electrolyte S1 0.527 79.60 Electrolyte D1 0.267 50.99

[0139] Figure 4 To accelerate the aging process, the surface morphology of the nickel electrode was observed in situ during the accelerated aging experiment. The black shadow areas that appeared on the electrode as the anodic potential increased were the corrosion areas. Figure 4 It is evident that the corrosion of the metal electrode in electrolyte S1 was significantly suppressed. Among these factors, the corrosion was significantly inhibited by… Figure 4 As shown in the figure above, the surface corrosion of the metal electrode in the simulated seawater electrolyte gradually deepens with increasing applied potential. However, using electrolyte S1, the polymetallic oxyacid anion clusters it contains provide in-situ corrosion protection, allowing the metal electrode to maintain good corrosion resistance under different potentials or current densities. The electrolyte of this invention is suitable for scenarios involving the protection of metal electrodes against seawater chlorine corrosion under high current density conditions. During electrolysis in seawater environments, the metal electrode exhibits higher oxidative corrosion activity at higher electrolysis voltages or current densities. Furthermore, in important fields such as renewable energy coupled with seawater electrolysis for hydrogen production, the corrosion protection strategy of using an electrolyte containing polymetallic oxyacid anion clusters is well-suited for applications with currents of 500-1000 mA / cm². -1 It operates at a high current density, far exceeding current application levels (200-300mA cm⁻¹). -1 This technology is expected to promote the industrialization of high-current-density seawater electrolysis, thereby reducing costs and increasing efficiency.

[0140] Figure 5 The statistics on the percentage of corrosion area during the accelerated aging experiment of nickel electrodes are a summary of... Figure 4 A quantitative description of the surface morphology changes of the nickel electrode during accelerated aging experiments is presented in the figure. As shown in the figure, for electrolyte D1, when the anolyte voltage exceeds 1.58V vs. RHE, the corrosion area of ​​the nickel electrode reaches 5%. When the voltage increases to 1.88V vs. RHE, the corrosion area exceeds 60%. When the voltage increases to 2.18V vs. RHE, nearly 80% of the electrode surface is corroded. In contrast, in electrolyte S1, as the voltage increases from 1.08V to 2.18V vs. RHE, the corrosion area remains close to 0, meaning no corrosion occurs on the electrode surface. The introduction of polymetallic oxyacid ions in electrolyte S1 significantly inhibits electrode corrosion.

[0141] Figure 6 This demonstrates the electrostatic repulsion of polymolybdate ions. Figure 6The horizontal axis represents the time at which the accelerated aging experiment began. In the accelerated aging experiment with applied anodic potential, an oxygen evolution reaction occurs at the anolyte. When ethylenediaminetetraacetic acid (EDTA) anions are instantaneously added to the electrolyte, the electrode potential decreases instantaneously due to the lower oxidation potential of the EDTA anion compared to the anodic oxygen evolution reaction. In this experimental example, when the same amount of EDTA anions were added to different electrolytes (electrolyte D1 and electrolyte S1) at the same time, the potential in electrolyte D1 decreased by 20 mV, while the potential in electrolyte S1 decreased by only 6 mV. This is because the electrostatic repulsion between the molybdenum species and the EDTA anions hinders the diffusion of these ions to the electrode surface, reducing the electrode potential drop caused by the oxidation reaction of the EDTA anions. This demonstrates the electrostatic repulsion effect of polymolybdate.

[0142] Furthermore, the parameter ΔE (mV) of the small molecule oxidation potential difference was introduced to explain the electrostatic repulsion of polymetallic oxyacid anion clusters. For example... Figure 7 As shown, chronovoltammetry tests were performed at different current densities in molybdate-containing electrolyte (electrolyte S1), phosphate electrolyte (electrolyte D4), and background electrolyte (electrolyte D1). Equal amounts of a small-molecule organic oxide (ethylenediaminetetraacetic acid) were instantaneously added to each electrolyte. A smaller potential change ΔE (mV) indicates a smaller impact of the added small-molecule organic compound on the original oxidation reaction, meaning a stronger corrosion resistance of the electrode surface under the original electrolyte conditions. Figure 7 It can be seen that (MoE, PE, and BE represent the test results of electrolyte S1, electrolyte D4, and electrolyte D1, respectively), the potential difference ΔE of different electrolytes does not change significantly at lower current densities, but increases with current density to 600, 700, and 1000 mA / cm². -1 It can be clearly observed that the change in ΔE in the molybdate-containing electrolyte under high current density is smaller than that in the control group. Figure 8 The in-situ Raman signals of molybdate and polymolybdate ions in electrolyte S1 at different current densities can be used to explain this phenomenon. The current range in the figure is 800-1000 mA cm⁻¹. -1 A Raman peak corresponding to polymolybdate ions appeared at wavenumber 940, indicating that polymetallic oxyacid anion clusters were generated in situ on the metal electrode surface under high current density, significantly improving the electrode's corrosion resistance. Furthermore, under high current conditions, the steric hindrance effect of polymetallic oxyacid anions was the main factor contributing to the improved electrode corrosion resistance.

[0143] Figure 9The specific adsorption of polymolybdate ions was demonstrated. After accelerated aging tests, electrode depth X-ray photoelectron spectroscopy (EDS) was performed at 0 nm and 5 nm on the nickel electrode surface to detect molybdenum and phosphorus signals. Molybdenum was detected at 0 nm in electrolyte S1, but not at 5 nm, indicating that molybdenum underwent specific adsorption on the electrode surface (see details). Figure 9 (Top image). In electrolyte D4, no phosphorus signal was detected at either 0 nm or 5 nm on the electrode, indicating that phosphorus did not undergo specific adsorption on the electrode surface (see details). Figure 9 (Lower middle image).

[0144] Figure 10 The percentage of chlorine atoms on the electrode surface and deep profile after 30 minutes of accelerated aging testing in electrolytes D1, D3, D4, and S1 is shown, illustrating the chlorine repulsion effect caused by the specific adsorption of polymolybdate ions. X-ray photoelectron spectroscopy was used to observe the chlorine atom percentages at 0 nm and 5 nm on the electrode surface. - Concentration. From Figure 10 It can be seen that in electrolyte D1, the Cl on the electrode surface - The atomic percentage was nearly 20%, indicating severe chloride corrosion of the electrode. In electrolyte D3, the atomic percentage of chloride on the electrode surface and at a depth of 5 nm was lower than that in electrolyte D1, suggesting that the sulfate anions in electrolyte D3 had a certain inhibitory effect on chloride corrosion of the nickel electrode. In electrolyte D4, a low concentration of Cl was detected at 0 nm on the electrode surface. - Cl was almost undetectable at a depth of 5nm. - This indicates that phosphate ions possess a more significant Cl- content compared to sulfate ions. - Despite exhibiting repulsive properties, chlorine corrosion still occurred on the electrode surface. However, in electrolyte S1, no Cl was detected on the electrode surface or in a 5 nm depth profile. - This indicates that the electrode did not experience chlorine corrosion, demonstrating the effectiveness of the in-situ mitigation strategy for metal chlorine corrosion proposed in this invention using polymetallic oxyacid anion clusters.

[0145] Figure 11 This represents the in-situ Raman signal of polymolybdate ions in electrolyte S2 (pH = 12). The current density first increases and then decreases with time. The in-situ Raman test results show that the current density of molybdate ions (corresponding to 896 cm⁻¹) initially increases and then decreases over time. -1 Raman vibrations are always present in the electrolyte, and when the current density increases to 200-500 mA / cm², they are observed to be present. -2 When the interval is reached, polymolybdate ions appear (corresponding to 940 cm⁻¹). -1 Raman vibration). As the current density of the oxygen evolution reaction at the anolyte increases, OH... -The increased consumption rate leads to a decrease in the local pH near the electrode, inducing the in-situ formation of polymolybdate clusters. When the current density decreases, the pH at the electrode surface rapidly returns to the alkaline environment of the bulk electrolyte, and the polymolybdate signal disappears, indicating that the formation of polymolybdate ion clusters is a reversible process.

[0146] Figure 12 To calculate the relationship between the existence form and relative percentage of molybdate ions and the pH response of the solution based on the polymolybdate ion transformation equation and transformation equilibrium constant, the following graph is used: The graph shows the pH response of the existence form of molybdenum in a molybdenum-containing solution with a molybdenum concentration of 0.15 mol / L (based on molybdenum atoms). The total molybdenum concentration in each solution is 0.15 mol / L. The upper left corner shows the distribution of molybdate and polymolybdate percentages as a function of pH. When pH > 7, molybdenum is almost entirely present as MoO4. 2- Molybdenum exists in various forms, and its form changes gradually as pH decreases. Below pH 6.5, Mo7O... 24 6- The formation of oxyanion clusters occurs, and at a pH of around 5, molybdenum mainly exists as Mo7O. 24 6- Molybdenum exists in the form of oxyanion clusters. When the pH continues to decrease below 4, molybdenum is released via hydrogen heptamolybdate (HMo7O). 24 5- The transitional form of ) is transformed into Mo8O 26 4- The upper right image shows Mo7O 24 6- With HMo7O 24 5- Simplified to Mo7O 24 6- The following figures illustrate the pH response of molybdate and polymolybdate ion concentrations to pH, specifically the lower left and lower right figures. This invention demonstrates the response relationship between polymetallic oxyanion anions and environmental pH, further illustrating that in-situ pH changes at the electrode surface can regulate the formation of in-situ polymetallic anion clusters. All figures above demonstrate that in alkaline environments, molybdenum primarily exists as MoO4. 2- It exists in the form of H, and as pH decreases, H... + As concentration increases, molybdate ions polymerize to form polymolybdate ions. Figure 11 For the nickel anode in the accelerated aging experiment, an oxygen evolution reaction occurs on the electrode surface, consuming OH groups. - The pH value near the electrode surface is reduced. At the same time, the electrochemical corrosion process under open circuit voltage will also result in a local pH decrease and induce the formation of polymolybdate. This clarifies the feasibility of the present invention to achieve metal seawater corrosion protection by in-situ inducing polymolybdate clusters during the electrochemical corrosion process.

[0147] 2. Establish an in-situ electrochemical corrosion research system and conduct accelerated aging experiments:

[0148] An in-situ electrochemical corrosion research system was constructed, including: using a treated nickel electrode (treatment steps as in Example 1) as the working electrode, a platinum wire as the counter electrode, and solid silver / silver chloride as the reference electrode, and placing them in separate electrolytes (electrolytes S1 and S3) to form a three-electrode system in an in-situ Raman electrolysis cell, with the electrolyte and ambient temperature at room temperature (20°C).

[0149] Accelerated aging experiment: The obtained three-electrode system was connected to an electrochemical workstation to construct a complete voltage and current loop. A chronopotential method was used with constant current parameters set at 500-second experimental cycles. The magnitude of the applied current at different time points was recorded. Simultaneously, under the in-situ condition of applied current, samples were collected at 850-1000 cm⁻¹. -1 Raman signal in the interval.

[0150] Figure 13 To calculate the relationship between the existence forms and relative percentage content of molybdate ions and the pH response of the solution, based on the polymolybdate ion transformation equation and the transformation equilibrium constant, the following graphs were calculated: distribution of molybdenum existence forms and content at pH = 3, 5, 7, and 9. Based on the equilibrium constants of the interconversion reactions between different molybdenum existence forms, in a strongly acidic environment at pH = 3, molybdenum mainly exists as Mo8O. 26 4- Molybdenum exists in the form of HMo7O. 24 5- It exists in the form of Mo7O, and its concentration increases linearly with increasing total molybdenum concentration. In a weakly acidic environment with pH=5, molybdenum exists primarily as Mo7O. 24 6- It exists in the form of HMo7O, with a small portion in the form of HMo7O. 24 5- It exists in the form of MoO4. In a neutral solution with pH = 7, MoO4... 2- MoO4 is the main form of molybdenum. When the molybdenum concentration increases to 4 mol / L (based on molybdenum atoms), some MoO4... 2- Polymerizes into Mo7O 24 6- In an alkaline environment with pH = 9, molybdenum exists as MoO4. 2- It exists in the form of.

[0151] Figure 14 This is the in-situ Raman signal of polymolybdate ions in electrolyte S3 (pH=8). When the current density increases to 100-150 mA / cm²... -2 Mo7O was detected at that time. 24 6-The signal indicates that the in-situ mitigation method for metal chloride corrosion using polymetallic oxyacid anion clusters is suitable for electrolytes with a pH of 8. Figure 11 The signal disappeared after the current density decreased. When the pH decreased from 12 to 8, the anodic oxidation current that induced the formation of polymolybdate ions also decreased accordingly, indicating the dependence of polymolybdate formation on the pH of the electrode surface micro-region.

[0152] Figure 8 , Figure 11 , Figure 14 This indicates that the in-situ method for mitigating metal chloride corrosion using polymetallic oxyacid anion clusters is applicable to electrolytes with a wide pH range.

[0153] In electrolytic systems where the solution pH is consistently maintained above 7, the in-situ corrosion inhibition strategy for polymetallic oxyanion clusters proposed in this invention remains significantly effective against chloride corrosion. In the electrolytic system, the pH observation can be divided into two parts: bulk pH and interface pH. Corrosion of the metal electrode occurs at the microenvironment of the interface between the metal and the electrolyte. For example... Figure 8 , Figure 11 , Figure 14 The figure shows in-situ Raman signal detection diagrams of polymolybdate ions in the electrolysis system under different pH conditions (pH = 8, 12, 14). This indicates the presence of OH groups during the electrolysis process. - The consumption of electrolytes alters the pH of the electrode surface microenvironment, inducing the in-situ formation of polymetallic oxyacid anion clusters on the electrode surface, thus enabling the metal to resist chloride ion corrosion. Furthermore, the bulk pH of the solution remains at a high level without significant change before and after electrolysis, demonstrating the wide pH range applicability of the polymetallic oxyacid anion cluster method for mitigating chloride corrosion of metals in situ.

[0154] 3. Temperature universality test:

[0155] The three-electrode systems of the electrolysis systems in Example 4 and Comparative Example 1 were connected to an electrochemical workstation to construct a complete voltage and current loop, thus establishing an electrochemical corrosion research system. Accelerated aging experiments were conducted at temperatures of 20℃, 40℃, 60℃, and 80℃: the constant current parameter of the chronopotential method was set to 1A, and accelerated aging tests were carried out. The changes in system potential over time were recorded to investigate the effect of the electrolyte on enhancing the metal's resistance to chloride corrosion at temperatures ranging from 20℃ to 80℃.

[0156] Figure 15 Figure 1 shows the temperature universality test results for the in-situ mitigation of metal chloride corrosion by polymetallic oxyacid anion clusters. Figure 15 It can be seen that MoO4 2- Increasing the concentration is beneficial for long-term electrode stability, while in MoO4 2-At the same concentration, temperature changes had no significant effect on the electrode stabilization time in the accelerated aging test, demonstrating the temperature universality of the method for in-situ mitigation of metal chloride corrosion by polymetallic oxyacid anion clusters.

[0157] 4. Universality test of molybdenum concentration:

[0158] The three-electrode systems of the electrolysis systems in Example 4 and Comparative Example 1 were connected to an electrochemical workstation to construct a complete voltage and current loop, thus establishing an electrochemical corrosion research system. Accelerated aging experiments were conducted using electrolytes with different molybdenum concentrations: the constant current parameter of the chronopotential method was set to 1A, and accelerated aging tests were carried out, recording the change in system potential over time. The results were as follows... Figure 16 The experimental results shown indicate that the introduction of molybdenum oxyacid ions of different concentrations all improve electrode stability, and this improvement increases with the increase of molybdenum concentration.

[0159] Figure 17 To calculate the relationship between the form and relative percentage of molybdate ions and the pH response of the solution, based on the polymolybdate ion transformation equation and the transformation equilibrium constant, a graph showing the effect of molybdate ion existence form on pH was calculated. Specifically, the graph shows the effect of molybdenum existence form on pH when the molybdenum concentration is 0.4 mol / L (calculated as molybdenum atoms). The upper left graph shows that when pH > 7, molybdenum is almost entirely present as MoO4 in neutral and alkaline solutions. 2- It exists in the form of Mo7O at a pH of around 5.5. 24 6- The percentage content of Mo7O reaches its highest level, and as pH continues to decrease, the percentage content of Mo7O... 24 6- Gradually transforms into HMo7O 24 5- The transition state is reached and peaks at around pH 4. When the pH decreases to 2, molybdenum is almost entirely converted into Mo8O. 26 4- It exists in the form of Mo7O. The upper right figure shows Mo7O. 24 6- With HMo7O 24 5- Combined into the same form, as shown in the figure, Mo7O 24 6- It begins to form at pH=7 and reaches its peak at around pH=5. Figure 17 The lower left and lower right figures show the distribution of molybdate and polymolybdate ion concentrations with respect to pH; the trends of each ion are the same as in the two figures above. (Summary) Figure 12 , Figure 13 and Figure 17The change in total molybdenum concentration does not affect the range of polymolybdate formation or the proportion of different species. Molybdenum solutions of different concentrations all exhibit the characteristic of polymerization under local acidic conditions, which demonstrates the universality of the in-situ mitigation of metal chloride corrosion by polymetallic oxyanion clusters for solutions of different molybdenum concentrations.

[0160] 6. Stability test of electrolyte used in alkaline anion exchange membrane electrolyzer:

[0161] The alkaline anion exchange membrane electrolyzers in Example 6 and Comparative Example 5 were connected to an electrochemical workstation to form a complete voltage and current loop. Stability tests were conducted using the chronopotential method, and the constant current parameter was set to 1A.

[0162] Figure 18 This presents the stability test results of an alkaline anion exchange membrane electrolyzer with nickel metal as the working electrode in electrolyte S8 (molybdenum metal oxyacid acid cluster electrolyte) and electrolyte D5. In electrolyte D5, the electrolyzer experienced electrode corrosion and failure after 12,000 seconds (3.3 hours) of operation, while in electrolyte S8, the electrolyzer achieved stable operation for over 800 hours. This indicates that the in-situ mitigation method of metal chloride corrosion by polymetallic oxyacid anion clusters can be successfully applied to alkaline anion exchange membrane electrolyzers.

[0163] 7. The effect of electrolyte on the corrosion protection of catalyst electrodes in electrochemical reactions of chlorine-containing electrolytes.

[0164] Figure 19 This study aimed to enhance the chloride corrosion resistance of iron-doped nickel hydroxide by utilizing the molybdenum metal oxyanion cluster. Iron-doped nickel hydroxide, a commonly used oxygen evolution reaction catalyst, was loaded onto a nickel metal electrode, constructing a three-electrode system similar to that in Example 1 and Comparative Example 1 (only the nickel metal electrode in Example 1 and Comparative Example 1 was replaced with the nickel metal electrode loaded with iron-doped nickel hydroxide; otherwise, the electrolysis systems were the same). Accelerated aging tests were conducted in electrolytes D1 and S1, with the electrolyte and ambient temperature at room temperature (20°C). The constant current parameter for the chronopotential method was set to 1 A. The method for loading iron-doped nickel hydroxide onto the nickel metal electrode is not limited; in this example, a hydrothermal method was used to prepare iron-doped nickel hydroxide on a foamed nickel metal electrode (Reference: Nature Communications, volume 14, Article number: 1686 (2023)).

[0165] Depend on Figure 19 It can be seen that the electrode in electrolyte D1 fails due to severe chloride corrosion after about 1 hour, while it can operate stably for more than 3 hours in electrolyte S1. This indicates that the in-situ mitigation method for chloride corrosion of metals provided by the present invention, using polymetallic oxyacid anion clusters, can be successfully applied to the corrosion protection of iron-doped nickel hydroxide catalysts.

[0166] Figure 20 Based on the accelerated aging test results of replacing the nickel metal electrodes in Example 1 and Comparative Example 1 with nickel metal electrodes supported by iron-doped nickel hydroxide, the potential decay rate (DV) and performance decay rate (also known as activity decay rate, DA) of iron-doped nickel hydroxide in electrolytes D1 and S1 were calculated respectively; the calculation formula is as follows:

[0167]

[0168] and The average voltage values ​​from the accelerated aging test (CP test) were taken during the initial 10% t time period and the final 10% t time period within the test time t, respectively, to eliminate fluctuations during long-term operation; (Calculation formula reference: Nature Communications volume 14, Article number: 3607(2023)). It can be seen that in electrolyte S1, the potential decay rate and performance decay rate of iron-doped nickel hydroxide are both lower than the corresponding values ​​in electrolyte D1.

[0169] This invention provides a method for in-situ mitigating chloride corrosion of metals using polymetallic oxyacid anion clusters. This in-situ corrosion prevention method is based on the phenomenon of pH differences between the bulk phase and the interface of a solution system. During metal corrosion at open-circuit potential or applied anodic potential, the local pH on the metal surface decreases, inducing the in-situ formation of polymetallic oxyacid anion clusters. These clusters are then specifically chemically adsorbed onto the metal electrode surface and react with Cl-. - Electrostatic repulsion and steric hindrance effects reduce interfacial Cl - This invention utilizes the concentration of OH groups to mitigate chlorine corrosion of metals during chemical and electrochemical corrosion processes in seawater. - Based on the properties of the metal, a method was developed to induce in-situ formation of polymetallic oxyanion clusters on the metal surface by altering the pH of the interfacial microenvironment, thus achieving corrosion protection of metals in seawater. This method does not require modification of the metal electrode structure and can achieve corrosion protection effects at corresponding interfacial microenvironments in bulk solutions with different pH values, demonstrating good applicability over a wide pH range. Target applications include corrosion protection of catalyst electrodes in electrochemical reactions involving chlorine-containing electrolytes, such as corrosion protection of oxygen evolution reaction catalysts and chlorine evolution reaction catalysts and substrates.

[0170] The metal electrode in this invention resists Cl - The corrosion strategy focuses on the corrosion resistance process under in-situ pH changes on the electrode surface. The chemical and electrochemical corrosion processes of metal electrodes are accompanied by OH groups. - The consumption of OH groups is also accompanied by the high current density of seawater electrolysis.- The consumption of [the material] causes a significant change in the in-situ pH of the corresponding electrode during the above process. The polymetallic oxyanion cluster structure described in this patent exhibits a reversible response relationship with pH.

[0171] Among them, based on the response change relationship between polymetallic oxyacid anions and environmental pH, it is explained that OH- ions are generated during the electrolysis of chlorine-containing solutions (which can also be seawater). - Consumption leads to in-situ pH changes on the electrode surface. This in-situ low pH environment induces the in-situ polymerization of molybdate monomers on the electrode surface, forming polymolybdate anionic clusters, which in turn affect the Cl- concentration in the solution. - Corrosion provides effective protection, and with the increase of seawater electrolysis current density, the degree of in-situ pH change and the degree of polymerization of polymetallic oxyacid anions both increase accordingly (e.g., Figure 11 ).

[0172] This invention utilizes the molybdate ion, representing metal oxyacid anions, which possess the property of polymerizing into metal oxyacid anion clusters, such as MoO4. 2- The monomer can be polymerized into Mo7O 24 6- Or octamolybdate (Mo8O) 26 4- Furthermore, there is a reversible response relationship between the polymeric ion form of molybdenum and the pH of the solution (e.g., Figure 12 , Figure 13 The resulting polymetallic oxyacid anion clusters exhibit significant and excellent resistance to chloride ion corrosion.

[0173] Unless otherwise specified, the term "about" in this invention actually means that the allowable error is within ±2%, for example, about 100 is actually 100 ± 2% × 100. The terms "room temperature" and "room temperature" in this invention, unless otherwise specified, are approximately 20-30°C. The phrase "between..." in this invention includes the number itself; for example, "between 2 and 3" includes the endpoints 2 and 3.

[0174] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. The application of metal oxyacid anions in the electrolyte of seawater electrolysis for chlorine corrosion protection of metal electrodes, characterized in that, The corrosion inhibitor containing metal oxyanion ions is added to the electrolyte, the metal oxyanion ions form poly-metal oxyanion anion clusters in the seawater electrolysis process, the metal oxyanion ions are molybdate, the poly-metal oxyanion anion clusters include at least one of heptamolybdate and octamolybdate, the current density of seawater electrolysis is 500-1000 mAcm -2 , and the preparation raw material of the electrolyte includes at least one of natural seawater and simulated seawater, and the temperature of the electrolyte is 10-90℃.

2. The use according to claim 1, characterized in that, The electrolyte contains Cl - Cl in the electrolyte - The concentration of the electrolyte is 0.1~5 mol / L, and / or the pH range of the electrolyte is 0~14.

3. The use according to claim 1, characterized in that, The metal electrode includes one or more of elemental Ni, Raney nickel, NiMo alloy, NiFe alloy, Co metal, CoFe alloy, or elemental Au.

4. The use according to claim 1, characterized in that, The corrosion inhibitor includes molybdate.

5. The use according to claim 4, characterized in that, The molybdate includes at least one of sodium molybdate, potassium molybdate, and ammonium molybdate.

6. The use according to claim 1, characterized in that, The raw materials for preparing the electrolyte also include at least one of alkaline substances or electrolyte substances.

7. The use according to claim 6, characterized in that, The electrolyte substance includes metal chlorides; and / or, the alkaline substance includes at least one of sodium hydroxide or potassium hydroxide.

8. The use according to claim 7, characterized in that, The metal chloride includes at least one of sodium chloride or potassium chloride.

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