A method for preparing a cathode coating resistant to reverse current erosion and a cathode

Abstract

The application relates to a preparation method of a reverse current erosion-resistant cathode coating and a cathode, and the method comprises the following steps: S1, pretreating a cathode base material; S2, loading a precursor of an N-type semiconductor on the surface of the cathode base material and performing sintering to form an N-type semiconductor coating on the surface of the cathode base material; S3, loading a precursor of a P-type semiconductor on the surface of the N-type semiconductor coating and performing sintering to form a P-type semiconductor coating on the surface of the N-type semiconductor coating; and S4, sintering the material obtained in S3 to obtain the reverse current erosion-resistant cathode coating. The application solves the technical problem that the cathode coating is easy to be dissolved and consumed due to reverse current in the existing water electrolysis hydrogen production technology or chlor-alkali electrolysis technology.

Description

Technical Field

[0001] This invention relates to the field of electrolysis technology, and in particular to a method for preparing a cathode coating resistant to reverse current erosion and a cathode. Background Technology

[0002] Precious metals are widely used due to their unique electronic structure and their ability to significantly enhance reactivity and efficiency during electrolysis when used in suitable electrolysis systems. In existing water electrolysis for hydrogen production or chlor-alkali electrolysis technologies, a precious metal coating (including pure precious metal coatings and precious metal oxide coatings) is typically applied to the cathode to reduce the overpotential of the hydrogen evolution reaction and enable more stable operation at high current densities. However, during the use of this precious metal coating, when the electrolysis cell is shut down (when the electrolysis reaction stops), electrons transfer from the cathode to the anode. The branch pipes and main pipe for entering and exiting the electrolyte provide electron transfer channels for the redox reactions of the electrodes, creating a reverse current. This causes the precious metals in the coating to dissolve into the electrolyte, leading to rapid coating wear and a decrease in electrolysis efficiency.

[0003] Existing technologies generally reduce the loss of precious metal coatings by introducing additional polarization current into the electrodes during shutdown. However, this method is not ideal in actual electrolysis operations. In practical chlor-alkali electrolysis and photovoltaic electrolysis for hydrogen production, frequent occurrences include unexpected shutdowns of chlor-alkali electrolyzers, slow polarization current input leading to reverse current and precious metal dissolution, and repeated start-ups and shutdowns of the electrolyzer during photovoltaic hydrogen production, generating reverse current. These situations cause precious metals in the cathode coating to dissolve into the electrolyte, resulting in significant unnecessary dissolution and loss. This leads to a substantial reduction in the lifespan of the active cathode, decreased electrolysis efficiency, and increased costs. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a method for preparing a cathode coating resistant to reverse current erosion, which solves the technical problem that the cathode coating in the existing water electrolysis hydrogen production technology or chlor-alkali electrolysis technology is prone to large unnecessary dissolution and loss due to reverse current.

[0006] (II) Technical Solution

[0007] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0008] In a first aspect, the present invention provides a method for preparing a cathode coating resistant to reverse current erosion, comprising the following steps:

[0009] S1: Pretreatment of the cathode substrate;

[0010] S2: Load the N-type semiconductor precursor onto the surface of the cathode substrate and burn it to form an N-type semiconductor coating on the surface of the cathode substrate;

[0011] S3: Load the P-type semiconductor precursor onto the surface of the N-type semiconductor coating and burn it off to form a P-type semiconductor coating on the surface of the N-type semiconductor coating, and form a PN junction at the interface between the N-type semiconductor coating and the P-type semiconductor coating.

[0012] S4: The material obtained in S3 is sintered to obtain a cathode coating resistant to reverse current erosion.

[0013] Optionally, the precursor of the N-type semiconductor includes a ruthenium metal salt precursor with donor impurities; the precursor of the P-type semiconductor includes a ruthenium metal salt precursor with acceptor impurities; the total weight of the N-type semiconductor coating does not exceed the total weight of the P-type semiconductor coating.

[0014] Optionally, the atomic ratio of ruthenium to donor impurities in the precursor of N-type semiconductors is 0.80-0.95:0.05-0.20; the atomic ratio of ruthenium to acceptor impurities in the precursor of P-type semiconductors is 0.80-0.95:0.05-0.20; the donor impurities include one of Co, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, Eu, and Gd; and the acceptor impurities include one of Mn, La, Ce, Pr, Nd, and Pm.

[0015] Optionally, the precursor of the N-type semiconductor includes at least one of ruthenium nitrate, chlorate or acetate and at least one of donor impurity nitrate, chlorate or acetate; the precursor of the P-type semiconductor includes at least one of ruthenium nitrate, chlorate or acetate and at least one of acceptor impurity nitrate, chlorate or acetate.

[0016] Optionally, in S1, the cathode substrate is a nickel plate or nickel mesh; the pretreatment also includes an air burn treatment: the cathode substrate is placed at 450-550℃ for 30-40 minutes to form a dense oxide layer on the surface of the cathode substrate.

[0017] Optionally, in S2, the process of loading the N-type semiconductor precursor and burning it is repeated multiple times, so that the total weight of the N-type semiconductor coating on the cathode substrate surface reaches the range of 3.6-6.0 g / m2.

[0018] Optionally, in S3, the process of loading the P-type semiconductor precursor and burning it is repeated multiple times, so that the total weight of the P-type semiconductor coating on the surface of the N-type semiconductor coating reaches the range of 6.0-10.8 g / m2.

[0019] Optionally, in S2 and S3, the initial firing temperature is 200-300℃, and then the firing temperature is increased to 350-550℃ within 5-10 minutes and held for 10-30 minutes.

[0020] Optionally, in S4, the sintering temperature is 450-550℃, and the holding time after reaching the sintering temperature is 60-90 minutes.

[0021] Secondly, the present invention also provides a cathode resistant to reverse current erosion, comprising a cathode substrate, an N-type semiconductor coating covering the cathode substrate, and a P-type semiconductor coating covering the N-type semiconductor coating; a PN junction is formed between the N-type semiconductor coating and the P-type semiconductor coating; both the N-type semiconductor coating and the P-type semiconductor coating are metal composite oxide coatings with noble metal as the main component.

[0022] (III) Beneficial Effects

[0023] This invention provides a method for preparing a cathode coating resistant to reverse current erosion. By sequentially depositing two semiconductor coatings with P-type and N-type conductivity on the cathode substrate, compared to existing technologies, a PN junction can be formed at the interface between the two semiconductor coatings, generating a built-in electric field. When the electrolytic cell stops and a reverse current is generated, the current flows from the N-type semiconductor coating to the P-type semiconductor coating, generating a reverse bias, enhancing the built-in electric field, and preventing the PN junction from conducting. This significantly reduces or directly eliminates the reverse current, thereby protecting the cathode coating, preventing the dissolution of noble metal components in the cathode coating, enabling the cathode coating to maintain its catalytic ability for a long time, and extending the service life of the cathode. Detailed Implementation

[0024] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below through specific embodiments.

[0025] This invention provides a method for preparing a cathode coating resistant to reverse current erosion, specifically comprising the following steps:

[0026] S1: Pretreatment: The cathode substrate is pretreated to roughen and clean its surface. Pretreatment creates a good adhesion environment for the subsequent coating of the N-type semiconductor coating, ensuring the bonding effect between the N-type semiconductor coating and the cathode substrate, and enabling the N-type coating to adhere better to the cathode substrate.

[0027] S2: Preparation of N-type semiconductor coating: The precursor of N-type semiconductor is loaded onto the surface of the cathode substrate and sintered to form an N-type semiconductor coating.

[0028] Preferably, the precursor of the N-type semiconductor includes one of a noble metal host and a metal salt precursor of donor impurities, a nano-metal powder precursor, or a pre-oxidized oxide precursor. The N-type semiconductor precursor is loaded onto the cathode substrate by liquid phase deposition / vapor phase deposition / sputtering.

[0029] More preferably, the precursor of the N-type semiconductor includes a noble metal host and a metal salt precursor of donor impurities. The N-type semiconductor precursor is loaded onto the cathode substrate by roller coating, dip coating, or spray coating.

[0030] More preferably, the noble metal matrix is ​​ruthenium, and the precursor of the N-type semiconductor is a ruthenium-donor impurity metal salt precursor. The metal salt precursor is loaded onto the cathode substrate by roller coating, dip coating, or spray coating. A sintering furnace is used to sinter the metal salt precursor, causing it to decompose (thermal decomposition) and react with oxygen at high temperature (oxidative sintering), forming a uniform ruthenium-doped donor impurity metal composite oxide with a specific crystal structure. This results in a more uniform crystal structure and higher stability.

[0031] Specifically, when using a metal salt precursor, in step S2, an N-type semiconductor precursor slurry is first coated onto the surface of the cathode substrate. The solute in the N-type semiconductor precursor slurry includes ruthenium and a metal salt precursor containing donor impurities. Then, the cathode substrate is dried to remove the solvent from the N-type semiconductor precursor slurry, allowing the solute (i.e., the N-type semiconductor precursor) to deposit onto the cathode substrate. Finally, sintering is performed, i.e., sintering the cathode substrate with the deposited N-type semiconductor precursor under specific temperature conditions. This allows the ruthenium and donor impurity precursor to react with oxygen at high temperature (oxidative sintering), forming a uniform first metal composite oxide (i.e., forming an N-type semiconductor) with a specific crystal lattice structure. This metal composite oxide is thermally bonded to the surface of the cathode substrate, forming an N-type semiconductor coating, i.e., forming the first metal composite oxide coating, thus obtaining the primary substrate. In practice, the process of coating the precursor slurry of the N-type semiconductor, drying, and then sintering can be repeated multiple times to ensure that the thickness or total weight of the final metal composite oxide reaches the predetermined standard.

[0032] S3: P-type semiconductor coating preparation: A P-type semiconductor precursor is loaded onto the surface of an N-type semiconductor coating and sintered to form a P-type semiconductor coating on the surface of the N-type semiconductor coating. At this time, a PN junction is initially formed between the P-type semiconductor coatings on the surface of the N-type semiconductor coating.

[0033] Preferably, the precursor for the P-type semiconductor includes one of a noble metal host and acceptor impurity metal salt precursor, a nano-metal powder precursor, or a pre-formed oxide precursor. The P-type semiconductor precursor is loaded onto the surface of the N-type semiconductor coating via liquid phase deposition / vapor phase deposition / sputtering.

[0034] More preferably, the precursor of the P-type semiconductor includes a noble metal host and a metal salt precursor of donor impurities. The P-type semiconductor precursor is loaded onto the N-type semiconductor coating by roller coating, dip coating, or spray coating. More preferably, the noble metal host is ruthenium, and the P-type semiconductor precursor is a ruthenium and acceptor impurity metal salt precursor. The metal salt precursor is loaded onto the surface of the N-type semiconductor coating by roller coating, dip coating, or spray coating. Specifically, when using a metal salt precursor, in S3, a P-type semiconductor precursor slurry is first coated on the surface of the primary substrate. The solute in the P-type semiconductor precursor slurry includes ruthenium and acceptor impurity metal salt precursor. Then, the secondary substrate is dried to remove the solvent in the P-type semiconductor precursor slurry, so that the solute in the P-type semiconductor precursor slurry (i.e., the P-type semiconductor precursor) is deposited on the primary substrate. Finally, sintering is performed, which involves sintering the primary substrate with the deposited P-type semiconductor precursor at a specific temperature. Ruthenium and the acceptor impurity precursor react with oxygen at high temperature to form a uniform ruthenium-doped acceptor impurity second metal composite oxide (i.e., forming a P-type semiconductor) according to a specific crystal lattice structure. This metal composite oxide is thermally bonded to the surface of the first metal composite oxide coating on the primary substrate, forming a P-type semiconductor coating, i.e., forming the second metal composite oxide coating, thus obtaining the secondary substrate. In practice, the process of coating the P-type semiconductor precursor slurry, drying, and then sintering can be repeated multiple times to ensure that the thickness or total weight of the final metal composite oxide reaches a predetermined standard.

[0035] S4: Firing: Sintering the secondary substrate to obtain a cathode coating resistant to reverse current erosion. Firing involves further calcining the secondary substrate using a sintering method, allowing any residual ruthenium, donor impurities, and acceptor impurities in the secondary substrate to more completely combine with oxygen to form a first metal composite oxide or a second metal composite oxide. Simultaneously, firing enables the existing first and second metal composite oxides to oxidize more fully and completely, resulting in a tighter bond between the first and second metal composite oxide coatings, thus obtaining a cathode coating resistant to reverse current erosion, or in other words, forming a cathode coating resistant to reverse current erosion on the surface of the cathode substrate.

[0036] The N-type semiconductor coating is preferably a ruthenium-based metal composite oxide coating doped with donor impurities, meaning the first metal composite oxide coating is an N-type semiconductor coating. The P-type semiconductor coating is preferably a ruthenium-based metal composite oxide coating doped with acceptor impurities, meaning the second metal composite oxide coating is a P-type semiconductor coating. The thickness of the first metal composite oxide coating does not exceed the thickness of the second metal composite oxide coating.

[0037] Ruthenium, as a precious metal, possesses high catalytic activity. Compared to other non-precious metals, it can catalyze reactions such as chlor-alkali or water electrolysis, significantly improving electrolysis efficiency. Furthermore, compared to precious metals like platinum, the first and second metal composite oxide coatings prepared using ruthenium as the main component not only exhibit better catalytic activity but also are less prone to catalyst poisoning and failure. Their catalytic activity is more stable, enabling long-term, stable, and rapid catalytic electrolysis reactions in chlor-alkali or water electrolysis. This invention provides a method for preparing a cathode coating resistant to reverse current erosion. By sequentially depositing two ruthenium-based metal composite oxide coatings with different conductivity properties on the cathode substrate, and utilizing the N-type and P-type semiconductor properties of these two metal composite oxide coatings, a PN junction is formed at the interface between the two coatings, generating a built-in electric field. Compared to existing technologies, during normal electrolysis (current flows from the anode to the cathode), the current flows from the second metal composite oxide coating to the first metal composite oxide coating, i.e., from the P-type semiconductor coating to the N-type semiconductor coating. The direction of the current is opposite to the direction of its built-in electric field, resulting in a positive bias. This offsets the built-in electric field, allowing charge carriers to move normally and forming a positive current. This does not affect the catalytic effect of ruthenium on the electrolysis reaction, nor does it affect the normal progress of the electrolysis reaction. When the electrolytic cell is shut down and a reverse current is generated (current flows from the cathode to the anode), the current flows from the first metal composite oxide coating to the second metal composite oxide coating, i.e., from the N-type semiconductor coating to the P-type semiconductor coating. The direction of the current is the same as the direction of the built-in electric field, resulting in a reverse bias. This strengthens the built-in electric field, preventing the PN junction from conducting, thereby significantly reducing or directly eliminating the reverse current. This protects the cathode coating, prevents ruthenium from dissolving in the coating, and extends the cathode's lifespan.

[0038] Meanwhile, in the event of an unexpected situation such as an open circuit in the electrolytic cell, which may cause a potential shift in the cathode, the built-in electric field can also resist the potential shift (the behavior of an open circuit in the electrolytic cell is very similar to the situation of generating reverse current, which can essentially be regarded as the electrolytic cell transforming into a galvanic cell. At this time, the cathode of the electrolytic cell becomes the positive electrode of the battery to conduct electricity, which will also enhance the built-in electric field, making the battery unable to form or operate effectively). The cathode potential is controlled within a certain range to avoid a large shift in the cathode potential, reduce the dissolution of the ruthenium body, and avoid ruthenium loss.

[0039] Preferably, in steps S2 and S3, after coating the N-type semiconductor precursor slurry or the P-type semiconductor precursor slurry onto the surface of the cathode substrate, drying is performed at a temperature of 60°C-100°C for 2-5 minutes. Drying rapidly evaporates the solvent in the N-type semiconductor precursor slurry or the P-type semiconductor precursor slurry and allows the precursor to deposit onto the cathode substrate or primary substrate, resulting in a more uniform precursor distribution and preventing uneven coating thickness after firing.

[0040] Preferably, the donor impurity is a transition metal element with a valence electron count greater than that of ruthenium, or a lanthanide or actinide metal element. More preferably, the donor impurity includes one of Co, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, Eu, and Gd. Even more preferably, it includes one of Co, Ir, Ni, Pd, Pt, and Cu. These donor impurities possess better stability and conductivity, ensuring the formation of the N-type semiconductor and improving the conductivity of the resulting first metal composite oxide coating during conduction. Pt is more preferred because its ionic radius is similar to that of Ru. Choosing Pt as the donor impurity effectively reduces lattice distortion, maintains the stability of the crystal structure of the formed metal composite oxide, improves the conductivity of the cathode during conduction, makes the cathode more stable under long-term, high-current conditions, and improves electrolysis efficiency.

[0041] Preferably, the acceptor impurity is a transition metal element with fewer valence electrons than ruthenium, or a lanthanide or actinide metal element. More preferably, the acceptor impurity includes one of Mn, La, Ce, Pr, Nd, and Pm. When these metal materials are mixed in the lattice structure of ruthenium oxide, they form more holes, causing the second metal composite oxide coating to exhibit a P-type semiconductor coating. La, Ce, and Pr are preferred. Compared to the other elements mentioned above, lanthanides have more flexible valence state switching and are more uniform after doping, improving the doping effect. They can also further improve the high-temperature stability of the coating and reduce high-temperature precipitation. Ce is more preferred, as it has even higher flexibility in valence state switching and higher catalytic activity.

[0042] Furthermore, since both the first and second metal composite oxide coatings of this invention are based on ruthenium, they exhibit a high degree of lattice matching and a small difference in their coefficients of thermal expansion. This allows for coherent growth during sintering and firing, ensuring the stability of the interface composite center (i.e., the interface) and carrier transport efficiency. This not only reduces the hydrogen evolution overpotential to a certain extent and further improves the coating's resistance to reverse current dissolution, but also avoids large interfacial resistance that could affect electrolysis. It also enhances the strength of the interfacial connection, preventing delamination and extending the coating's lifespan. Simultaneously, the identical noble metal substrate prevents large corrosion potential differences between the two coatings, avoiding galvanic corrosion and further improving the coating's corrosion resistance and the cathode's resistance to dissolution during potential shifts.

[0043] Furthermore, since the radii and valence states of the different metal ions incorporated are not the same as those of ruthenium, the lattice matching degrees of their oxides also differ. Incorporating too many types of metal impurities can lead to severe lattice distortion, resulting in decreased crystal integrity, defects such as dislocations and stacking faults, and even phase transitions (e.g., transforming the stable rutile form of RuO2 into an amorphous form), thus disrupting the conductive structure of the semiconductor. Simultaneously, too many types of impurities can easily aggregate to form nanoparticles or a second phase (such as composite oxides of elemental metals or impurities), introducing additional interfaces that become carrier scattering centers, affecting the conductivity and electrical properties of the coating. Choosing a single metal as the donor or acceptor impurity avoids conflicts between multiple metal components, prevents lattice distortion and structural instability, and ensures the stability of the semiconductor and conductivity properties of the formed metal composite oxide.

[0044] Preferably, the atomic (or ionic) ratio of ruthenium to donor impurities in the precursor slurry of the N-type semiconductor is 0.80-0.95:0.05-0.20, and the atomic (or ionic) ratio of ruthenium to acceptor impurities in the precursor slurry of the P-type semiconductor is 0.80-0.95:0.05-0.20. Alternatively, the atomic ratio of ruthenium to donor impurities in the first metal composite oxide coating is 0.80-0.95:0.05-0.20, and the atomic ratio of ruthenium to donor impurities in the second metal composite oxide coating is 0.80-0.95:0.05-0.20.

[0045] More preferably, the atomic ratio of ruthenium to donor impurities in the precursor slurry of the N-type semiconductor is 0.9-0.95:0.05-0.15, and the atomic ratio of ruthenium to acceptor impurities in the precursor slurry of the P-type semiconductor is 0.80-0.90:0.10-0.20. The ratio of ruthenium atoms to their corresponding donor and acceptor impurities has a significant impact on the conductivity of the first and second metal composite oxide coatings. An excessively high proportion of donor or acceptor impurities will affect the carrier generation and recombination rates, resulting in decreased conductivity.

[0046] An excessively high proportion of donor or acceptor impurities may also lead to changes or damage to the crystal structure of the coating, resulting in increased coating resistance, decreased conductivity, and increased hydrogen evolution overpotential.

[0047] If the donor or acceptor impurities are not sufficiently present, the conductivity of the coating will not be optimal, and there will still be room for the hydrogen evolution overpotential to decrease, resulting in a reduction in the ability of the final PN junction to resist reverse current.

[0048] Furthermore, it should be noted that the present invention forms a continuous and stable PN junction, or PN junction interface, between two coatings with different conductivity properties, thereby stably resisting reverse current. If its conductivity deteriorates, even if the coating has corresponding semiconductor properties, it will affect the stability of the coating interface, causing the reverse current erosion resistant cathode coating of the present invention to decrease its resistance to reverse current.

[0049] Preferably, in S1, the cathode substrate is a nickel plate or nickel mesh. Other materials besides nickel, such as carbon steel, can also be used for the cathode substrate, but nickel is preferred considering its applicability and conductivity. This invention does not have special requirements for the shape of the cathode substrate; the reverse current erosion resistant cathode coating of this invention can be applied to a cathode substrate of any shape. However, for practicality and the uniformity of coating application, a mesh-like cathode substrate is preferred.

[0050] Preferably, in S1, the pretreatment includes degreasing, sandblasting, and pickling. The pretreatment removes dirt and deposits from the cathode substrate surface, ensuring its cleanliness, and also increases the surface roughness to a certain extent, providing a good foundation for the adhesion of the first metal composite oxide.

[0051] Preferably, in step S1, after the pretreatment, the cathode substrate also needs to undergo an air-firing treatment: the cathode substrate is placed at a certain temperature and calcined for a certain time to form an oxide layer on its surface. Since the metal salt precursor in the precursor slurry of the N-type semiconductor generally makes its solution (i.e., the precursor slurry) acidic, to avoid significant corrosion of the cathode substrate by these acidic solutions and the metal salt precursors themselves during coating and firing, the air-firing treatment oxidizes the surface of the cathode substrate, forming a dense oxide film that protects the cathode substrate from corrosion. Furthermore, if nano-metal powder precursors or pre-oxide precursors are used, and acidic or corrosive substances are not involved, the air-firing treatment may be omitted.

[0052] Furthermore, it is very important that after the dense oxide layer is formed by air firing, during the repeated coating and firing processes in S2 and S3, the dense oxide layer can also prevent the metal components of the cathode substrate from entering the precursor slurry in the form of ions after being corroded by the acidic precursor slurry (such as nickel ions generated by the corrosion of the nickel cathode entering the precursor slurry), and then entering the N-type or P-type semiconductor coating of the present invention, which would cause changes in the elements and proportions in the coating, and lead to problems such as a decrease in the ability to resist reverse current and a deterioration in the conductivity of the cathode coating of the present invention.

[0053] More preferably, when the cathode substrate is made of nickel, the dry firing temperature is 450-550°C and the holding time is 30-40 minutes to ensure that a dense oxide film can be formed.

[0054] Preferably, in S2, the solute (precursor) of the N-type semiconductor precursor slurry includes at least one of ruthenium nitrate, chlorate, or acetate, and at least one of donor impurity nitrate, chlorate, or acetate. The solvent in the N-type semiconductor precursor slurry is water or ethanol, preferably water.

[0055] Preferably, in S3, the solute (precursor) of the P-type semiconductor precursor slurry includes at least one of ruthenium nitrate, chlorate, or acetate, and at least one of acceptor impurity nitrate, chlorate, or acetate. The solvent in the P-type semiconductor precursor slurry is water or ethanol, preferably water.

[0056] Among them, ruthenium, donor impurities, and acceptor impurities such as nitrates, chlorates, and acetates generally have good solubility and can dissolve better in water. Furthermore, these salts can be decomposed relatively completely during calcination and firing when used as precursors for metal salts.

[0057] More preferably, the solute in the precursor slurry of the N-type semiconductor is ruthenium acetate with donor impurities, and the solute in the precursor slurry of the P-type semiconductor is ruthenium acetate with acceptor impurities. As a precursor, acetate can be decomposed relatively completely, resulting in lower acidity of the coating solution and preventing excessive corrosion of the cathode substrate.

[0058] Preferably, in step S2, an N-type semiconductor precursor slurry is coated onto the cathode substrate, dried, and then fired. After cooling, the N-type semiconductor precursor slurry is coated onto the cathode substrate again, dried, and fired. This process is repeated multiple times until the total weight (total weight: the total loading of the coating per unit area) of the ruthenium-doped donor impurity metal composite oxide coating on the cathode substrate reaches 3.6-6.0 g / m². 2 Within the specified range, a first metal composite oxide coating is obtained. In S3, following the same method as in S2, the precursor slurry of the P-type semiconductor is coated multiple times, dried, and sintered to achieve a total weight of 6.0-10.8 g / m² of ruthenium-doped acceptor impurities in the primary substrate. 2 After being within the specified range, a second metal composite oxide coating is obtained.

[0059] In this invention, the relatively low total weight of the first metal composite oxide coating and the second metal composite oxide coating can lead to several issues. Firstly, the inability to form a PN junction or a reduced barrier effect may result in decreased conductivity, making it difficult to achieve high current densities. Similarly, a relatively low total weight of the second metal composite oxide coating can also prevent PN junction formation or reduce barrier effect. Furthermore, it may result in insufficient active sites on the cathode coating surface to resist reverse current erosion, leading to decreased electrolysis efficiency. Additionally, the dissolution of the active component (noble metal) during normal electrolysis is also a contributing factor to coating failure. In this invention, the dissolution of the active component mainly occurs on the outer P-type semiconductor coating. A thicker P-type semiconductor coating can maintain catalytic activity for a longer period, further extending the service life of the cathode coating and the cathode.

[0060] Finally, controlling the overall weight can also, to a certain extent, ensure the tightness of the bonding between the cathode coating resisting reverse current erosion of the present invention and the cathode substrate, and ensure that there is sufficient bonding strength between the first metal composite oxide coating and the cathode substrate, as well as between the first and second metal composite oxide coatings, so that they are not easily peeled off from the cathode substrate.

[0061] Preferably, the total weight of the first metal composite oxide coating is controlled to not exceed the total weight of the second metal composite oxide. By matching the corresponding total weights, it is ensured that the final PN junction has sufficient barrier capability.

[0062] Preferably, in S2 and S3, during the firing process, the initial firing temperature is 200-300°C, and then the firing temperature is increased to 350-550°C within 5-10 minutes, and held for 10-30 minutes. More preferably, the heating begins at an initial firing temperature of 200-250°C, and then the firing temperature is increased to 400-550°C within 8-10 minutes, held for 10-20 minutes, and the firing is completed. More preferably, the heating begins at an initial firing temperature of 200-250°C, the temperature is increased for 10 minutes, the firing temperature is increased to 450-550°C, and held for 10-20 minutes, and the firing is completed.

[0063] In steps S2 and S3, the cathode substrate or primary substrate is directly placed in an environment with a high initial temperature and sintered at a high initial sintering temperature. This avoids abnormal stacking of the crystal structures of the first and second metal composite oxide coatings due to the low-temperature environment during sintering, thus improving the stability of the final crystal lattice structure. Simultaneously, controlling the rate of increase in sintering temperature within an appropriate range further enhances the stability of the crystal structure, ensuring stable crystal growth and guaranteeing the semiconductor properties and crystal structure stability of the first and second metal composite oxide coatings. Preferably, in step S4, the sintering temperature is 450-550°C, and after reaching the sintering temperature, the temperature is held for 60-90 minutes to complete the sintering process, forming the reverse current erosion resistant cathode coating of the present invention. In this process, prolonged sintering allows for the complete oxidation / decomposition of incompletely oxidized / decomposed components in both the first and second metal composite oxide coatings (e.g., the complete decomposition of residual ruthenium acetate in the second metal composite oxide coating to produce ruthenium oxide and carbon dioxide). This also makes both coatings denser, reducing unnecessary porosity and preventing excessive porosity from causing current to flow through and dissolving precious metals or the substrate, thus reducing or even eliminating the reverse current erosion resistance of the cathode coating. During sintering, the fully oxidized first and second metal composite oxide coatings bond more tightly, further combining (bonding) to obtain the reverse current erosion resistant cathode coating of this invention.

[0064] If the sintering temperature is too high during firing, some metals in the coating may transform from an oxidized state to an elemental state. For example, when platinum is used as a donor impurity in the first metal composite oxide coating, an excessively high sintering temperature may cause platinum to transform from an oxidized state to an elemental state (which can be seen as the decomposition of platinum oxide to produce elemental platinum and oxygen). If the firing temperature is too low or firing is not performed, problems such as incomplete oxidation of the first and second metal composite oxide coatings or poor bonding and interfacial adhesion between the two may occur. This leads to a significant reduction in the service life of the cathode coating resistant to reverse current erosion or unstable and uneven conductivity, and the PN junction cannot effectively resist reverse current or potential shift.

[0065] More preferably, in S4, the sintering temperature is 500-550°C during the sintering process, and the oxidation of the first metal composite oxide coating and the second metal composite oxide coating is further ensured by appropriately increasing the temperature.

[0066] Preferably, after firing, the resulting material undergoes an alkaline washing treatment: the secondary substrate is immersed in a 5-10% NaOH solution at room temperature for 4-8 hours, then washed and dried to obtain a cathode coating resistant to reverse current corrosion. Preferably, it is immersed in a 6-8% NaOH solution at room temperature for 6-8 hours. Alkaline washing removes any residual acidic substances from the cathode coating resistant to reverse current corrosion, preventing these residues from affecting the coating's performance and lifespan. It should be noted that if a nano-metal powder precursor or pre-oxide precursor is used, and no acidic substances remain, alkaline washing may not be necessary.

[0067] Furthermore, it should be noted that in S2, S3, or S4, when using metal salt precursors for sintering or firing, or when using nano-metal powder precursors or pre-oxide precursors for sintering, the corresponding sintering operations can be carried out under a conventional oxygen-containing oxidizing atmosphere. However, the oxygen concentration should be between 15% and 80%, preferably between 15% and 25%. Sintering or firing should not be carried out in an oxidizing atmosphere with excessively high oxygen content, especially not in a pure oxygen environment, to avoid problems such as over-oxidation, volatilization of precious metals, and deterioration of the crystal structure.

[0068] Secondly, the present invention also provides a cathode resistant to reverse current erosion, comprising a cathode substrate and a cathode coating resistant to reverse current erosion as described in the first aspect of the present invention disposed on the surface of the cathode substrate. Specifically, the cathode coating resistant to reverse current erosion comprises a first metal composite oxide coating coated on the cathode substrate and a second metal composite oxide coating coated on the first metal oxide coating. The first metal composite oxide coating is an N-type semiconductor coating, the composition of which is a metal composite oxide of ruthenium and its donor impurity. The second metal composite oxide coating is a P-type semiconductor coating, the composition of which is a metal composite oxide of ruthenium and its acceptor impurity. A PN junction is formed between the first metal oxide coating and the second metal composite oxide coating. The total weight of the first metal oxide coating does not exceed the total weight of the second metal composite oxide coating. To better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present invention can be understood more clearly and thoroughly, and that the scope of the present invention can be fully conveyed to those skilled in the art.

[0069] Example 1

[0070] This embodiment provides a method for preparing a cathode coating resistant to reverse current erosion and a cathode resistant to reverse current erosion, including the following steps:

[0071] S1: Pretreatment: The cathode substrate is pretreated and then fired at 500°C for 40 minutes.

[0072] S2: Preparation of N-type semiconductor coating: An N-type semiconductor precursor slurry was coated onto the surface of the cathode substrate and dried at 80°C for 5 min. The cathode substrate was then placed in a sintering environment at 250°C, and the temperature was increased to 500°C over 10 min, held at that temperature for 15 min, and then cooled. This process was repeated four times, resulting in a total weight of 4.8 g / m³. 2 A first metal composite oxide coating is formed, resulting in a primary substrate.

[0073] S3: Preparation of P-type semiconductor coating: A P-type semiconductor precursor slurry was coated onto the surface of the primary substrate and held at 80°C for 5 min. The cathode substrate was then placed in a sintering environment at 250°C. The temperature of the sintering environment was increased to 500°C over 10 min, held for 25 min, and then cooled. This process was repeated 7 times to achieve a total weight of 9.6 g / m² for the second metal composite oxide coating. 2 Secondary substrate is obtained.

[0074] S4: Firing: The secondary substrate is placed in a sintering environment, the sintering temperature is increased to 500℃, then held for 80 minutes, cooled and alkali washed to obtain a cathode coating resistant to reverse current erosion.

[0075] The solutes (precursors) of the N-type semiconductor precursor slurry are ruthenium nitrate and platinum nitrate, and the solvent is water. The atomic ratio of ruthenium to platinum in the N-type semiconductor precursor slurry is Ru:Pt = 0.85:0.15. The solutes (precursors) of the P-type semiconductor precursor slurry are ruthenium nitrate and cerium nitrate, and the solvent is water. The atomic ratio of ruthenium to cerium in the P-type semiconductor precursor slurry is Ru:Ce = 0.85:0.15.

[0076] A 3cm×30cm nickel mesh with a wire diameter of 0.16mm and a 40-mesh diameter was used as the cathode substrate. The reverse current erosion resistant cathode coating preparation method of this embodiment was used to prepare a reverse current erosion resistant cathode on this substrate, resulting in a reverse current erosion resistant cathode. The performance of the reverse current erosion resistant cathode coating was then tested: the reverse current erosion resistant cathode was immersed in a 90℃, 32% NaOH aqueous solution, and the hydrogen evolution potential was first detected using a three-electrode method. Then, electrolysis was performed at 60℃ in 32% NaOH according to the steps and parameters in Table 1 below. The percentage of residual cathode coating before and after electrolysis was measured and calculated using X-ray fluorescence spectrometry. After electrolysis detection, the hydrogen evolution potential was detected again using the three-electrode method, and the results are shown in Table 2 below.

[0077] Table 1. Electrolysis steps and parameters for testing coating performance

[0078]

[0079]

[0080] Example 2

[0081] This embodiment provides a method for preparing a cathode coating resistant to reverse current erosion and a cathode resistant to reverse current erosion. The difference from Embodiment 1 is that in S2, the process of coating the N-type semiconductor precursor slurry, drying, and sintering is repeated three times, resulting in a total weight of 3.6 g / m³ for the first metal composite oxide coating. 2 A primary substrate was obtained. In S3, the process of coating the precursor slurry of the P-type semiconductor, drying, and sintering was repeated eight times, resulting in a total weight of 10.6 g / m² for the second metal composite oxide coating. 2 Secondary substrate is obtained.

[0082] Using the same cathode substrate as in Example 1, a cathode coating resistant to reverse current erosion was prepared on the cathode substrate according to the method of this example, and the performance of the obtained cathode coating resistant to reverse current erosion was tested in the manner of Example 1. The test results are shown in Table 2.

[0083] Example 3

[0084] This embodiment provides a method for preparing a cathode coating resistant to reverse current erosion and a cathode resistant to reverse current erosion. The difference from Embodiment 1 is that in S2, the process of coating the N-type semiconductor precursor slurry, drying, and sintering is repeated 5 times, and the total weight of the first metal composite oxide coating is 6 g / m. 2 A primary substrate is obtained. In S3, the process of coating the P-type semiconductor precursor slurry, drying, and sintering is repeated five times to achieve a total weight of 6.8 g / m² for the second metal composite oxide coating. 2 Secondary substrate is obtained.

[0085] The performance of the reverse current erosion resistant cathode coating obtained in this embodiment was tested using the same method as in Example 1, and the test results are shown in Table 2.

[0086] Example 4

[0087] This embodiment provides a method for preparing a cathode coating resistant to reverse current erosion and a cathode resistant to reverse current erosion. The difference from Embodiment 1 is that in the precursor slurry of the N-type semiconductor, the atomic ratio of ruthenium to platinum is Ru:Pt = 0.80:0.20. In the precursor slurry of the P-type semiconductor, the atomic ratio of ruthenium to cerium is Ru:Ce = 0.95:0.05.

[0088] Using the same cathode substrate as in Example 1, a cathode coating resistant to reverse current erosion was prepared on the cathode substrate according to the method of this example, and the performance of the obtained cathode coating resistant to reverse current erosion was tested in the manner of Example 1. The test results are shown in Table 2.

[0089] Example 5

[0090] This embodiment provides a method for preparing a cathode coating resistant to reverse current erosion and a cathode resistant to reverse current erosion. The difference from Embodiment 1 is that in the precursor slurry of the N-type semiconductor, the atomic ratio of ruthenium to platinum is Ru:Pt = 0.93:0.07. In the precursor slurry of the P-type semiconductor, the atomic ratio of ruthenium to cerium is Ru:Ce = 0.85:0.15.

[0091] Using the same cathode substrate as in Example 1, a cathode coating resistant to reverse current erosion was prepared on the cathode substrate according to the method of this example, and the performance of the obtained cathode coating resistant to reverse current erosion was tested in the manner of Example 1. The test results are shown in Table 2.

[0092] Example 6

[0093] This embodiment provides a method for preparing a cathode coating resistant to reverse current erosion and a cathode resistant to reverse current erosion. The difference from Embodiment 1 is that the solutes in the precursor slurry for the N-type semiconductor are ruthenium acetate and cobalt acetate, with an atomic ratio of Ru:Co = 0.80:0.20. The solutes in the precursor slurry for the P-type semiconductor are ruthenium nitrate and praseodymium nitrate, with an atomic ratio of Ru:Pr = 0.80:0.20.

[0094] Using the same cathode substrate as in Example 1, a cathode coating resistant to reverse current erosion was prepared on the cathode substrate according to the method of this example, and the performance of the obtained cathode coating resistant to reverse current erosion was tested in the manner of Example 1. The test results are shown in Table 2.

[0095] Example 7

[0096] This embodiment provides a method for preparing a cathode coating resistant to reverse current erosion and a cathode resistant to reverse current erosion. The difference from Embodiment 1 is that in S2, the process of coating the N-type semiconductor precursor slurry, drying, and sintering is repeated eight times, resulting in a total weight of 9.6 g / m² for the first metal composite oxide coating. 2 In step S3, the process of coating the P-type semiconductor precursor slurry, drying, and sintering was repeated four times, resulting in a total weight of 5.3 g / m² for the formed second metal composite oxide coating. 2 .

[0097] Using the same cathode substrate as in Example 1, a cathode coating was prepared on the cathode substrate according to the method of this comparative example, and the performance of the obtained cathode coating was tested in the manner described in Example 1. The test results are shown in Table 2.

[0098] Comparative Example 1

[0099] This comparative example provides a method for preparing a cathode coating resistant to reverse current erosion and a cathode resistant to reverse current erosion. The difference from Example 1 is that it includes the following steps:

[0100] S1: Pretreatment: The cathode substrate is pretreated and then fired at 500°C for 40 minutes.

[0101] S2: Coating Preparation: An N-type semiconductor precursor slurry was coated onto the surface of the cathode substrate and dried at 80°C for 5 min. The cathode substrate was then placed in a sintering environment at 250°C, and the temperature was increased to 500°C over 10 min. After holding at this temperature for 15 min, the substrate was removed and cooled. This process was repeated 12 times to achieve a total weight of 14.4 g / m² for the metal composite oxide coating. 2 This yields a primary substrate.

[0102] S3: Firing: The primary substrate is placed in a sintering environment and held at a sintering temperature of 500℃ for 80 minutes. Then it is taken out, cooled and alkali washed to obtain a cathode coating resistant to reverse current erosion. The cathode substrate and the cathode coating resistant to reverse current erosion are combined to form a cathode resistant to reverse current erosion.

[0103] The solutes in the precursor slurry of the N-type semiconductor are ruthenium nitrate and platinum nitrate, and the solvent is water. The atomic ratio of ruthenium to platinum in the precursor slurry of the N-type semiconductor is Ru:Pt = 0.85:0.15.

[0104] Using the same cathode substrate as in Example 1, a cathode coating was prepared on the cathode substrate according to the method of this comparative example, and the performance of the obtained cathode coating was tested in the manner described in Example 1. The test results are shown in Table 2.

[0105] Comparative Example 2

[0106] This comparative example provides a method for preparing a cathode coating resistant to reverse current erosion and a cathode resistant to reverse current erosion. The difference from Comparative Example 1 is that in step S2, the process of coating the P-type semiconductor precursor slurry, drying, and sintering is repeated 11 times, resulting in a total weight of 14.4 g / m² for the first metal composite oxide coating. 2 The solutes in the precursor slurry for P-type semiconductors are ruthenium nitrate and cerium nitrate. The atomic ratio of ruthenium to cerium in the precursor slurry for P-type semiconductors is Ru:Ce = 0.85:0.15.

[0107] Using the same cathode substrate as in Example 1, a cathode coating was prepared on the cathode substrate according to the method of this comparative example, and the performance of the obtained cathode coating was tested in the manner described in Example 1. The test results are shown in Table 2.

[0108] Comparative Example 3

[0109] This comparative example provides a method for preparing a cathode coating resistant to reverse current erosion and a cathode resistant to reverse current erosion. The difference from Example 1 is that the solutes in the precursor slurry for the N-type semiconductor are ruthenium nitrate and platinum nitrate, and the atomic ratio of ruthenium to platinum in the N-type semiconductor precursor slurry is Ru:Pt = 0.70:0.30. The solutes in the precursor slurry for the P-type semiconductor are ruthenium nitrate and cerium nitrate, and the atomic ratio of ruthenium to cerium in the P-type semiconductor precursor slurry is Ru:Ce = 0.70:0.30.

[0110] Using the same cathode substrate as in Example 1, a cathode coating was prepared on the cathode substrate according to the method of this comparative example, and the performance of the obtained cathode coating was tested in the manner described in Example 1. The test results are shown in Table 2.

[0111] Comparative Example 4

[0112] This comparative example provides a method for preparing a cathode coating resistant to reverse current erosion and a cathode resistant to reverse current erosion. The difference from Example 1 is that, in S2, the solute of the precursor slurry for the N-type semiconductor is ruthenium nitrate and cobalt nitrate, and the atomic ratio of ruthenium to cobalt is Ru:Co = 0.85:0.15. In S3, the precursor slurry for the N-type semiconductor is used instead of the precursor slurry for the P-type semiconductor, and the precursor used is ruthenium nitrate and platinum nitrate, and the atomic ratio of ruthenium to platinum is Ru:Pt = 0.85:0.15.

[0113] Using the same cathode substrate as in Example 1, a cathode coating was prepared on the cathode substrate according to the method of this comparative example, and the performance of the obtained cathode coating was tested in the manner described in Example 1. The test results are shown in Table 2.

[0114] Note: In the above embodiments and comparative examples, the changes in the ratio of ruthenium to donor impurities or acceptor impurities, but without mentioning the changes in the total weight of the first metal composite oxide coating, were all achieved by slightly adjusting the concentration of the precursor in the corresponding precursor slurry or the weight of the precursor slurry in a single coating to keep the total weight of the coating stable. Such slight adjustments have virtually no impact on the performance of the obtained cathode coating resistant to reverse current erosion.

[0115] Table 2. Test Results

[0116]

[0117] Note: The percentage of coating residue reflects the degree of coating loss, and the change in hydrogen evolution potential before and after electrolysis reflects the change in the coating's electrolytic performance.

[0118] From the above, it can be seen that, compared to Example 1, Example 2 has a relatively low total weight of the first metal composite oxide coating and a relatively high total weight of the second metal composite oxide coating. The PN junction formed between them has a weaker resistance to reverse current erosion, leading to increased losses and reduced coating residue in the cathode coating obtained in Example 2 before and after electrolysis. Compared to Example 1, although Example 3 has a relatively high total weight of the first metal composite oxide coating, its relatively low total weight of the second metal composite oxide coating means that while it can better resist reverse current erosion, the larger forward electrolysis current accelerates the dissolution of the P-type coating during enhanced electrolysis, resulting in a significant increase in the hydrogen evolution potential before and after electrolysis. Compared to Example 1, Example 4 further increases the proportion of donor impurities, increases carrier recombination rate, deteriorates conductivity, and results in a higher hydrogen evolution potential. Compared to Example 1, Example 5, with its lower proportion of donor impurities, exhibits a more suitable P-type characteristic in its second metal composite oxide coating. This results in better carrier generation and recombination rates, and a more stable PN junction formed between the coatings. This not only more effectively combats reverse current and reduces coating losses, but also leads to a lower hydrogen evolution potential before electrolysis. Compared to Example 1, Example 6 uses a higher proportion of cobalt as a donor impurity and a higher proportion of praseodymium as an acceptor impurity, also achieving good resistance to reverse current erosion. In Example 7, the first metal composite oxide coating has a higher total weight, while the second metal composite oxide coating has a lower total weight. Although it also resists reverse current erosion, the stability of the PN junction formed between the coatings is poor, resulting in a higher interfacial resistance and a higher hydrogen evolution potential before and after electrolysis.

[0119] Compared to Example 1, Comparative Examples 1 and 2, with essentially the same coating weight as Example 1, achieved higher pre-electrolysis hydrogen evolution potentials through a single coating with more active sites. However, since both relied solely on the material's inherent properties to resist reverse current erosion, their coatings suffered significant losses after electrolysis testing, and the hydrogen evolution potential increased substantially, indicating their inability to resist reverse current. Comparative Example 3 used a coating similar to that of Example 1, but due to excessively high proportions of donor and acceptor impurities in its first and second metal composite oxide coatings, its lattice structure was significantly distorted, leading to instability in the P-type or N-type semiconductor properties. The PN junction formed between the two coatings was not stable enough to effectively resist reverse current erosion, resulting in significant coating losses and changes in hydrogen evolution potential before and after electrolysis. In Comparative Example 4, since both the first and second metal composite oxide coatings are ruthenium-doped donor impurity metal composite oxide coatings, although the two coating materials are different, they are both N-type semiconductor materials (the two coatings have the same conductivity). It is difficult to form a PN junction between the two coatings to resist reverse current. After electrolysis testing, the coating loss and the changes in hydrogen evolution potential before and after electrolysis are also relatively large.

[0120] A comparison of the embodiments and comparative examples reveals that the cathode coating of the present invention, resistant to reverse current erosion, effectively prevents the dissolution of precious metals in the coating when facing reverse current, reduces coating loss, maintains the catalytic capacity of the cathode coating for a long time, and improves the service life of the cathode. This solves the technical problem in existing water electrolysis hydrogen production technology or chlor-alkali electrolysis technology where the cathode coating is easily dissolved and lost due to reverse current.

[0121] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a cathode coating resistant to reverse current erosion, characterized in that, The steps include the following: S1: Pretreatment of the cathode substrate; S2: Load the precursor of the N-type semiconductor onto the surface of the cathode substrate and burn it to form an N-type semiconductor coating on the surface of the cathode substrate; S3: Load the P-type semiconductor precursor onto the surface of the N-type semiconductor coating and burn it off to form a P-type semiconductor coating on the surface of the N-type semiconductor coating, and form a PN junction at the interface between the N-type semiconductor coating and the P-type semiconductor coating. S4: The material obtained in S3 is sintered to obtain a cathode coating resistant to reverse current erosion; The precursor of the N-type semiconductor includes a ruthenium and a metal salt precursor of donor impurities; the precursor of the P-type semiconductor includes a ruthenium and a metal salt precursor of acceptor impurities; the total weight of the N-type semiconductor coating does not exceed the total weight of the P-type semiconductor coating; wherein, the total weight refers to the total load of the coating per unit area. The atomic ratio of ruthenium to donor impurity in the precursor of the N-type semiconductor is 0.80-0.95:0.05-0.20; the atomic ratio of ruthenium to acceptor impurity in the precursor of the P-type semiconductor is 0.80-0.95:0.05-0.20; the donor impurity is one of Co and Pt; the acceptor impurity is one of Ce and Pr.

2. The method for preparing a cathode coating resistant to reverse current erosion as described in claim 1, characterized in that, The precursor of the N-type semiconductor includes at least one of the nitrate or acetate of ruthenium and at least one of the nitrate or acetate of the donor impurity; the precursor of the P-type semiconductor includes at least one of the nitrate or acetate of ruthenium and at least one of the nitrate or acetate of the acceptor impurity.

3. The method for preparing a cathode coating resistant to reverse current erosion as described in claim 1, characterized in that, In S1, the cathode substrate is a nickel plate or nickel mesh; the pretreatment also includes an air burn-in process: the cathode substrate is placed at 450-550℃ for 30-40 minutes to form a dense oxide layer on the surface of the cathode substrate.

4. The method for preparing a cathode coating resistant to reverse current erosion as described in claim 1, characterized in that, In step S2, the process of loading the N-type semiconductor precursor and firing it is repeated multiple times, so that the total weight of the N-type semiconductor coating on the surface of the cathode substrate reaches 3.6-6.0 g / m³. 2 Within the range.

5. The method for preparing a cathode coating resistant to reverse current erosion as described in claim 1, characterized in that, In step S3, the process of loading the P-type semiconductor precursor and firing it is repeated multiple times, so that the total weight of the P-type semiconductor coating on the surface of the N-type semiconductor coating reaches 6.0-10.8 g / m³. 2 Within the range.

6. The method for preparing a cathode coating resistant to reverse current erosion as described in claim 1, characterized in that, In S2 and S3, the initial firing temperature is 200-300℃, and then the firing temperature is increased to 350-550℃ within 5-10 minutes, and held for 10-30 minutes.

7. The method for preparing a cathode coating resistant to reverse current erosion as described in claim 1, characterized in that, In S4, the firing temperature is 450-550℃, and the holding time after reaching the firing temperature is 60-90 minutes.

8. A cathode resistant to reverse current erosion prepared by the method for preparing a cathode coating resistant to reverse current erosion as described in any one of claims 1-7, characterized in that, It includes a cathode substrate, an N-type semiconductor coating covering the cathode substrate, and a P-type semiconductor coating covering the N-type semiconductor coating; A PN junction is formed between the N-type semiconductor coating and the P-type semiconductor coating; The N-type semiconductor coating is a ruthenium-based metal composite oxide coating doped with Co or Pt; the P-type semiconductor coating is a ruthenium-based metal composite oxide coating doped with Ce or Pr.

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