Alkaline electrolysis cell bipolar plate with corrosion-resistant composite coating on the surface

Abstract

The application discloses a bipolar plate of an alkaline electrolytic cell with a surface corrosion-resistant composite coating. The bipolar plate comprises a base material, a pre-coating layer and a composite coating, the composite coating is attached to the surface of the pre-coating layer, and the pre-coating layer is attached to the surface of the base material. The base material is Q235B carbon steel, the pre-coating layer is a nickel layer, and the composite coating is a Ni-P / NbC composite coating. The application also provides a preparation method of the bipolar plate of the alkaline electrolytic cell with the surface corrosion-resistant composite coating. The bipolar plate prepared by the application has high hardness, excellent corrosion resistance, wear resistance, electrical conductivity and high-temperature resistance due to the superior comprehensive performance of NbC nanoparticles. In addition, the composite coating has an ultrathin thickness, thereby reducing the overall weight of the bipolar plate, making the electrolytic cell more portable and reducing the manufacturing cost.

Description

Technical Field

[0001] This invention relates to the field of bipolar plate material technology, specifically to an alkaline electrolytic cell bipolar plate with a corrosion-resistant Ni-P / NbC composite coating on its surface. Background Technology

[0002] Hydrogen production via water electrolysis using renewable energy has garnered widespread attention as a clean and renewable energy source. Currently, water electrolysis hydrogen production technologies mainly include alkaline (ALK) water electrolysis, proton exchange membrane (PEM) water electrolysis, solid oxide electrolytic cell (SOEC) water electrolysis, and anion exchange membrane (AEM) water electrolysis. Among these, ALK water electrolysis is the most mature and promising technology, leading to a sustained increase in market demand for water electrolysis hydrogen production equipment. Consequently, the market for bipolar plates, an indispensable component of ALK hydrogen electrolyzers, is also booming.

[0003] Bipolar plates play a crucial role in ALK hydrogen production electrolyzers, supporting the electrodes, diaphragm, and ensuring conductivity. They are the most numerous components in the electrolyzer, accounting for 20% to 30% of the total cost. In existing technologies, ALK hydrogen production electrolyzers use carbon steel sheets for the bipolar plates, with the main plate and frame welded together. This results in an extremely heavy electrolyzer and high raw material costs. Furthermore, the need for sealing rings between the frames complicates the manufacturing process, and the frames are susceptible to corrosion, leading to internal short circuits. Additionally, the alkaline electrolyte within the battery, operating at 80-90°C, falls within the range where carbon steel main plates are prone to alkaline corrosion. Therefore, the bipolar plates must also possess corrosion resistance in alkaline media.

[0004] Because nickel does not react with strong alkalis and has excellent resistance to alkali corrosion, it is currently commonly used to obtain Ni-P coatings by electroless nickel plating on carbon steel to protect bipolar plates. While electroless nickel plating is widely used for corrosion protection on carbon steel, its performance on bipolar plates still needs improvement. Electroless composite nickel plating technology is one effective way to improve the performance of nickel plating layers. This involves adding insoluble microparticles with specific properties to the electroless plating solution and co-depositing them on a Ni-P alloy to obtain composite coatings with different physicochemical properties, thereby improving the corresponding properties of the coating. With the continuous deepening of research on nanomaterials and nanotechnology, introducing nanoscale insoluble microparticles into composite coatings has become a development trend in electroless composite coatings. Currently, composite coatings with different functions, such as Ni-P / Al2O3, Ni-P / SiO2, Ni-P / SiC, Ni-P / PTFE, and Ni-P / Ti4O7, have been prepared and applied. These insoluble microparticles can enhance the wear resistance, corrosion resistance, creep resistance, and conductivity of the coating.

[0005] Chinese Patent CN 116516328 A discloses a process for preparing a Ni-P / Ti4O7 composite coating by chemical plating on the surface of a carbon steel bipolar plate. This process improves the corrosion resistance of the coating and reduces contact resistance by introducing Ti4O7 particles with excellent corrosion resistance and conductivity into the Ni-P plating solution, thereby extending the service life of the carbon steel bipolar plate. When the bipolar plate with this composite coating was subjected to potentiodynamic polarization testing in an acidic environment, the lowest corrosion current density in the characterization data was 10.28 ± 0.15 μA / cm². 2 This indicates that the introduction of Ti4O7 particles can effectively improve the acid corrosion resistance of Ni-P coatings, but there is still room for improvement, and its alkali corrosion resistance still needs to be explored.

[0006] Chinese patent CN 117867479 A discloses a method for preparing a SiC particle-reinforced Ni-P coating. This method involves pre-plating a Ni-P coating on the sample surface, followed by a second Ni-P-SiC composite plating in a composite plating solution containing SiC particles. The resulting double-layer composite coating is used for the protection of oil well pipes, exhibiting good morphology, high hardness, and strong wear and corrosion resistance. However, this method uses 0.5 μm SiC particles, which are micro-nano scale particles. Applying them to bipolar plate coatings may result in a thicker coating. Existing nanocomposite coatings have higher hardness and corrosion resistance than micron composite coatings, but nanoparticles are more prone to agglomeration during plating.

[0007] Therefore, it is still necessary to develop an alkaline electrolytic cell bipolar plate with a corrosion-resistant nanocomposite coating on its surface. This nanocomposite coating is extremely thin and simultaneously possesses properties such as high hardness, excellent corrosion resistance, wear resistance, conductivity, and high temperature resistance. This not only enables the bipolar plate to achieve better performance but also reduces the manufacturing cost of the electrolytic cell. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of existing technologies and provide an alkaline electrolytic cell bipolar plate with a corrosion-resistant composite coating. Specifically, niobium carbide (NbC) nanoparticles are introduced into the Ni-P coating on the carbon steel substrate of the bipolar plate to prepare a Ni-P / NbC composite coating. The bipolar plate with the corrosion-resistant Ni-P / NbC composite coating has high hardness, excellent corrosion and wear resistance, and excellent electrical conductivity and high temperature resistance. The composite coating has an ultra-thin thickness (6~8 μm), which can reduce the overall weight of the bipolar plate, thereby making the electrolytic cell lighter and reducing manufacturing costs.

[0009] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0010] A bipolar plate for an alkaline electrolytic cell with a corrosion-resistant composite coating on its surface, the bipolar plate comprising a substrate material, a pre-plating layer, and a composite coating, wherein the composite coating is attached to the surface of the pre-plating layer, and the pre-plating layer is attached to the surface of the substrate material; the substrate material is Q235B carbon steel, the pre-plating layer is a nickel layer, and the composite coating is a Ni-P / NbC composite coating.

[0011] Furthermore, the thickness of the Ni-P / NbC composite coating is 6~8 μm.

[0012] Furthermore, the phosphorus (P) content in the Ni-P / NbC composite coating is in the range of 11-14%. At low phosphorus contents, the Ni-P coating has a mixed-crystalline structure; when the phosphorus content is greater than 8%, the structure becomes amorphous. At high phosphorus contents, phosphorus may participate in the deformation of the nickel lattice, reducing the microhardness of the nickel layer. The corrosion resistance of the coating increases with increasing phosphorus content, resulting in better corrosion resistance in alkaline media. Compared to a conventional Ni-P coating with a phosphorus content of 10%, the Ni-P coating with phosphorus content within the above range exhibits a higher degree of amorphization, enabling the bipolar plate to achieve corrosion resistance.

[0013] A method for preparing an alkaline electrolytic cell bipolar plate with a corrosion-resistant composite coating on its surface includes the following steps:

[0014] (1) Pretreatment: The Q235B carbon steel is subjected to surface pretreatment by mechanical polishing, ultrasonic degreasing, alkaline washing and acid washing to ensure that the sample surface is free of oil, grease, dirt and oxide layer, so as to prevent it from affecting the subsequent plating process, hindering the bonding between the composite coating and the substrate material, and causing the coating to separate from the substrate material.

[0015] (2) Pre-plating nickel layer: The pre-treated Q235B carbon steel is used as the cathode and the nickel plate is used as the anode. By electroplating, an external power supply is applied to introduce current into the pre-plating nickel solution, so that the nickel ions in the plating solution are reduced to metallic nickel on the surface of Q235B carbon steel to form a nickel layer. The pre-plating nickel layer can make the subsequent plating layer adhere better and improve the adhesion of the plating layer. The nickel layer itself also has a good corrosion resistance, which is equivalent to a double anti-corrosion layer.

[0016] (3) Chemical composite plating of Ni-P / NbC composite coating: The Ni-P / NbC composite coating is prepared on the surface of the material after the above-mentioned pre-nickel plating treatment by chemical composite plating process. The chemical composite plating is performed by immersing the above-mentioned pre-nickel-plated sample in a prepared chemical composite plating solution. The chemical composite plating solution is prepared by mixing a conventional chemical plating solution with a suspension containing insoluble NbC nanoparticles. The NbC nanoparticles in the composite plating solution are co-deposited on the Ni-P alloy to obtain a uniform and smooth Ni-P / NbC composite coating.

[0017] Further, the preprocessing step (1) includes:

[0018] (1.1) Mechanical polishing: The Q235 B carbon steel sample was first ground with coarse sandpaper, and then mechanical equipment (such as polishing machine) and grinding tools (such as sandpaper) were used to mechanically grind and polish the carbon steel surface. Different grits (100#, 400#, 600#, 800#, 1000#, 1200#, 1500#) of abrasive paper or grinding wheel were used to polish the surface in multiple passes, from rough to fine, to gradually improve the surface finish.

[0019] (1.2) Ultrasonic degreasing: The carbon steel that has been mechanically polished is placed in an organic solvent for ultrasonic degreasing to remove residual grease from the sample surface; the organic solvent is either anhydrous ethanol or anhydrous acetone; the ultrasonic degreasing cleaning time is 5-6 min.

[0020] (1.3) Alkaline degreasing: The carbon steel after ultrasonic degreasing is immersed in an alkaline degreasing solution for further alkaline degreasing to remove rust-preventive oil, lubricating oil and other greases and dirt remaining on the surface of the plated parts during machining or storage; the alkaline degreasing solution has the following composition: sodium hydroxide (NaOH) 35~45 g / L, sodium carbonate (Na2CO3) 95~105 g / L; the degreasing temperature is 70~80℃, and the alkaline washing time is 8~12 min;

[0021] (1.4) Pickling: The carbon steel that has been degreased by alkaline washing is immersed in pickling solution for pickling to remove the oxide film, oxide scale and other rust products on the surface of the sample; the pickling solution is a hydrochloric acid solution with a mass fraction of 15~25%; the pickling temperature is room temperature and the pickling time is 1~3 min.

[0022] Further, in the (2) pre-plating nickel layer step, the pre-plating nickel solution comprises: nickel chloride hexahydrate (NiCl2·6H2O) 40~50 g / L, nickel sulfate hexahydrate (NiSO4·6H2O) 240~260 g / L, boric acid (H3BO3) 25~35 g / L, sodium dodecyl sulfate 0.20~0.30 g / L, sodium hydroxymethylsulfonate (PN) 35~45 mg / L, and propynyl alcohol propoxy ether (PAP) 25~35 mg / L; the temperature is 20~30℃, the pH is 3~4, the plating time is 1~2 min, and the current density during plating is 2~3 A / dm³. 2 .

[0023] Further, in the step (3) of chemically plating Ni-P / NbC composite coating, the chemical plating solution consists of: main salt NiCl2·6H2O 25~35 g / L, reducing agent sodium hypophosphite (NaH2PO2·H2O) 15~25 g / L, complexing agent sodium citrate (Na3C6H5O7·2H2O) 8~12 g / L, complexing agent aminoacetic acid [CH2(NH2)COOH] 4~6 g / L, buffer sodium acetate (CH3COONa) 8~12 g / L, surfactant sodium dodecylbenzenesulfonate 0.25~0.35 g / L, and stabilizer zinc molybdate 75~85 mg / L; the temperature is 80~85℃, the pH is 5~6, and the plating time is 0.5~1.5 h; the NbC nanoparticles are purchased NbC powder (purity 99.9%, average particle size 100 μm). The NbC nanoparticles (nm) were pretreated by ball milling in a ball mill, resulting in small and uniform particle size. The NbC nanoparticle suspension was obtained by ultrasonically dispersing the pretreated NbC nanoparticles in deionized water.

[0024] The advantages and beneficial effects of this invention are as follows:

[0025] 1. The present invention relates to an alkaline electrolytic cell bipolar plate with a corrosion-resistant composite coating. First, a nickel layer is pre-plated on the surface of the carbon steel substrate material of the bipolar plate. The pre-plated nickel layer can make the subsequent coating adhere better and improve the bonding force of the coating. The nickel layer itself also has good corrosion resistance, which is equivalent to a double anti-corrosion layer.

[0026] Next, NbC nanoparticles were introduced into the Ni-P coating system. Through chemical deposition, the NbC nanoparticles were well embedded in the Ni-P coating, resulting in a uniform, dense, and smooth Ni-P / NbC composite coating. The phosphorus (P) content in the Ni-P / NbC composite coating ranged from 11% to 14%. Compared to a conventional Ni-P coating with a phosphorus content of 10%, it exhibited a higher degree of amorphization, which enhanced the corrosion resistance of the bipolar plate. Although the addition of NbC nanoparticles inhibited phosphorus deposition on the composite coating, reducing the phosphorus content, it formed a stable physical barrier. This made the path for corrosive media to enter the coating longer and more complex, significantly increasing the degradation time of the coating and thus improving its corrosion resistance, allowing it to better serve in the operating environment of the bipolar plate.

[0027] 2. This invention performs potentiodynamic polarization tests on carbon steel substrates, carbon steel with Ni-P coatings, and carbon steel with Ni-P / NbC composite coatings, and measures the self-corrosion potential of carbon steel with Ni-P / NbC composite coatings (…). E corr ) and self-corrosion current density ( I corr The maximum (-0.485 V) and minimum (3.50 μA / cm) values ​​were respectively. 2 Due to the protection of NbC nanoparticles, the corrosion rate of carbon steel with a Ni-P / NbC composite coating was reduced compared to both the carbon steel substrate and the carbon steel with a Ni-P coating. After neutral salt spray testing, rust spots only appeared on the surface of the Q235B carbon steel sample with the Ni-P / NbC composite coating after 1080 hours. This indicates that the Ni-P / NbC composite coating effectively improves the corrosion resistance of the Q235B carbon steel substrate.

[0028] 3. Since the NbC nanoparticles introduced in this invention are a type of metal carbide, they have the advantages of high hardness (harder than corundum, microhardness >23.5 GPa), high strength, high melting point (3500℃), high conductivity (resistivity 35 μΩ·cm) and high corrosion resistance. They can be used as an additive in composite coatings to improve the overall performance of the coating, thereby giving the bipolar plate high hardness, excellent corrosion resistance, wear resistance, and excellent conductivity and high temperature resistance.

[0029] 4. The Ni-P / NbC composite coating of the present invention, due to its ultra-thin thickness (6~8 μm), can reduce the overall weight of the bipolar plate, thereby making the electrolytic cell lighter and reducing manufacturing costs. Detailed Implementation

[0030] The specific embodiments of the present invention will be further described below with reference to examples. These examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0031] Example 1

[0032] A bipolar plate for an alkaline electrolytic cell with a corrosion-resistant coating on its surface, the bipolar plate comprising a substrate material and a pre-plating layer, the pre-plating layer being attached to the surface of the substrate material; the substrate material is Q235B carbon steel, and the pre-plating layer is a nickel layer.

[0033] A method for preparing an alkaline electrolytic cell bipolar plate with a corrosion-resistant coating on its surface includes the following steps:

[0034] (1) Pretreatment: The Q235B carbon steel is subjected to surface pretreatment by mechanical polishing, ultrasonic degreasing, alkaline washing and acid washing to ensure that the sample surface is free of oil, grease, dirt and oxide layer.

[0035] (2) Pre-plating nickel layer: The pre-treated Q235B carbon steel is used as the cathode and the nickel plate is used as the anode. By electroplating, an external power supply is applied to introduce current into the pre-plating nickel solution, so that the nickel ions in the plating solution are reduced to metallic nickel on the surface of Q235B carbon steel to form a nickel layer.

[0036] (3) Chemical plating of Ni-P coating: The Ni-P coating is prepared by chemical plating on the surface of the material after the above-mentioned pre-plating of nickel layer. The chemical plating is performed by immersing the above-mentioned pre-plated nickel sample in a prepared chemical plating solution to obtain the Ni-P coating.

[0037] The mechanical polishing process involves first grinding the edges of the Q235 B carbon steel sample with coarse sandpaper, and then using mechanical equipment and grinding tools to mechanically grind and polish the surface of the carbon steel. Multiple polishing passes are performed using abrasive paper or grinding wheels of different grit sizes (100#, 400#, 600#, 800#, 1000#, 1200#, 1500#).

[0038] The ultrasonic degreasing process involves immersing the mechanically polished carbon steel in an organic solvent for ultrasonic degreasing; the organic solvent used is anhydrous ethanol; the ultrasonic degreasing cleaning time is 5 minutes.

[0039] The alkaline degreasing involves immersing the carbon steel, which has undergone ultrasonic degreasing, in an alkaline degreasing solution for further alkaline degreasing. The alkaline degreasing solution has the following composition: NaOH 40 g / L, Na2CO3 100 g / L; the degreasing temperature is 75℃, and the alkaline washing time is 10 min.

[0040] The pickling process involves immersing the carbon steel, which has been degreased by alkaline washing, into a pickling solution for pickling; the pickling solution is a 20% hydrochloric acid solution by mass; the pickling temperature is room temperature, and the pickling time is 2 minutes.

[0041] The pre-plating nickel solution consisted of 45 g / L NiCl2·6H2O, 250 g / L NiSO4·6H2O, 30 g / L H3BO3, 0.25 g / L sodium dodecyl sulfate, 40 mg / L sodium hydroxymethylsulfonate, and 30 mg / L propynyl alcohol propoxy ether; the temperature was 25℃, the pH was 3.8, the plating time was 1.5 min, and the current density during plating was 2.5 A / dm³. 2 .

[0042] The chemical plating solution consists of: NiCl2·6H2O 30 g / L, NaH2PO2·H2O 20 g / L, Na3C6H5O7·2H2O 10 g / L, [CH2(NH2)COOH] 5 g / L, CH3COONa 10 g / L, sodium dodecylbenzenesulfonate 0.30 g / L, and zinc molybdate 80 mg / L; the temperature is 82℃, the pH is 5.8, and the plating time is 1.0 h.

[0043] Example 2

[0044] The difference between this embodiment and Embodiment 1 is that:

[0045] A bipolar plate for an alkaline electrolytic cell with a corrosion-resistant coating, wherein the pre-plating nickel solution comprises 40 g / L NiCl2·6H2O, 240 g / L NiSO4·6H2O, 25 g / L H3BO3, 0.20 g / L sodium dodecyl sulfate, 35 mg / L sodium hydroxymethanesulfonate, and 25 mg / L propynyl alcohol propoxy ether; the temperature is 20℃, the pH is 3.0, the plating time is 1.0 min, and the current density during plating is 2.0 A / dm³. 2 .

[0046] The chemical plating solution consists of: NiCl2·6H2O 25 g / L, NaH2PO2·H2O 15 g / L, Na3C6H5O7·2H2O 8 g / L, [CH2(NH2)COOH] 4 g / L, CH3COONa 8 g / L, sodium dodecylbenzenesulfonate 0.25 g / L, and zinc molybdate 75 mg / L; the temperature is 80℃, the pH is 5.0, and the plating time is 0.5 h.

[0047] Example 3

[0048] The difference between this embodiment and Embodiment 1 is that:

[0049] A bipolar plate for an alkaline electrolytic cell with a corrosion-resistant coating, wherein the pre-plating nickel solution comprises 50 g / L NiCl2·6H2O, 260 g / L NiSO4·6H2O, 35 g / L H3BO3, 0.30 g / L sodium dodecyl sulfate, 45 mg / L sodium hydroxymethanesulfonate, and 35 mg / L propynyl alcohol propoxy ether; the temperature is 30℃, the pH is 4.0, the plating time is 2.0 min, and the current density during plating is 3.0 A / dm³. 2 .

[0050] The chemical plating solution consisted of: NiCl2·6H2O 35 g / L, NaH2PO2·H2O 25 g / L, Na3C6H5O7·2H2O 12 g / L, [CH2(NH2)COOH] 6 g / L, CH3COONa 12 g / L, sodium dodecylbenzenesulfonate 0.35 g / L, and zinc molybdate 85 mg / L; the temperature was 85℃, the pH was 6.0, and the plating time was 1.5 h.

[0051] Example 4

[0052] A bipolar plate for an alkaline electrolytic cell with a corrosion-resistant composite coating on its surface, the bipolar plate comprising a substrate material, a pre-plating layer, and a composite coating, wherein the composite coating is attached to the surface of the pre-plating layer, and the pre-plating layer is attached to the surface of the substrate material; the substrate material is Q235B carbon steel, the pre-plating layer is a nickel layer, and the composite coating is a Ni-P / NbC composite coating.

[0053] A method for preparing an alkaline electrolytic cell bipolar plate with a corrosion-resistant composite coating on its surface includes the following steps:

[0054] (1) Pretreatment: The Q235B carbon steel is subjected to surface pretreatment by mechanical polishing, ultrasonic degreasing, alkaline washing and acid washing to ensure that the sample surface is free of oil, grease, dirt and oxide layer.

[0055] (2) Pre-plating nickel layer: The pre-treated Q235B carbon steel is used as the cathode and the nickel plate is used as the anode. By electroplating, an external power supply is applied to introduce current into the pre-plating nickel solution, so that the nickel ions in the plating solution are reduced to metallic nickel on the surface of Q235B carbon steel to form a nickel layer.

[0056] (3) Chemical composite plating of Ni-P / NbC composite coating: The Ni-P / NbC composite coating is prepared on the surface of the material after the above-mentioned pre-nickel plating treatment by chemical composite plating process. The chemical composite plating is performed by immersing the above-mentioned pre-nickel-plated sample in a prepared chemical composite plating solution. The chemical composite plating solution is prepared by mixing a conventional chemical plating solution with a suspension containing insoluble NbC nanoparticles. The NbC nanoparticles in the composite plating solution are co-deposited on the Ni-P alloy to obtain a uniform and smooth Ni-P / NbC composite coating.

[0057] The mechanical polishing process involves first grinding the edges of the Q235 B carbon steel sample with coarse sandpaper, and then using mechanical equipment and grinding tools to mechanically grind and polish the surface of the carbon steel. Multiple polishing passes are performed using abrasive paper or grinding wheels of different grit sizes (100#, 400#, 600#, 800#, 1000#, 1200#, 1500#).

[0058] The ultrasonic degreasing process involves immersing the mechanically polished carbon steel in an organic solvent for ultrasonic degreasing; the organic solvent used is anhydrous ethanol; the ultrasonic degreasing cleaning time is 5 minutes.

[0059] The alkaline degreasing involves immersing the carbon steel, which has undergone ultrasonic degreasing, in an alkaline degreasing solution for further alkaline degreasing. The alkaline degreasing solution has the following composition: NaOH 40 g / L, Na2CO3 100 g / L; the degreasing temperature is 75℃, and the alkaline washing time is 10 min.

[0060] The pickling process involves immersing the carbon steel, which has been degreased by alkaline washing, into a pickling solution for pickling; the pickling solution is a 20% hydrochloric acid solution by mass; the pickling temperature is room temperature, and the pickling time is 2 minutes.

[0061] The pre-plating nickel solution consisted of 45 g / L NiCl2·6H2O, 250 g / L NiSO4·6H2O, 30 g / L H3BO3, 0.25 g / L sodium dodecyl sulfate, 40 mg / L sodium hydroxymethylsulfonate, and 30 mg / L propynyl alcohol propoxy ether; the temperature was 25℃, the pH was 3.8, the plating time was 1.5 min, and the current density during plating was 2.5 A / dm³. 2 .

[0062] The chemical plating solution consists of: NiCl2·6H2O 30 g / L, NaH2PO2·H2O 20 g / L, Na3C6H5O7·2H2O 10 g / L, [CH2(NH2)COOH] 5 g / L, CH3COONa 10 g / L, sodium dodecylbenzenesulfonate 0.30 g / L, and zinc molybdate 80 mg / L; the temperature is 82℃, the pH is 5.8, and the plating time is 1.0 h.

[0063] The NbC nanoparticles were obtained by ball milling purchased NbC powder (99.9% purity, average particle size 100 nm) to achieve small and uniform particle size. The NbC nanoparticle suspension was obtained by ultrasonically dispersing the pretreated NbC nanoparticles in deionized water.

[0064] With the addition of second-phase particles (NbC nanoparticles), the coating surface becomes uniform and smooth, the grain size decreases, and the bonding between cells becomes more compact. The composite coating surface exhibits fewer irregular protrusions and depressions in the cell shapes. This is likely because the addition of NbC particles increases the number of active deposition sites during the deposition process due to the impact of the plating solution on the substrate, resulting in a more uniform distribution and better protection of the substrate.

[0065] Example 5

[0066] The difference between this embodiment and embodiment 4 is that:

[0067] A bipolar plate for an alkaline electrolytic cell with a corrosion-resistant composite coating on its surface, wherein the pre-plating nickel solution comprises 40 g / L NiCl2·6H2O, 240 g / L NiSO4·6H2O, 25 g / L H3BO3, 0.20 g / L sodium dodecyl sulfate, 35 mg / L sodium hydroxymethanesulfonate, and 25 mg / L propynyl alcohol propoxy ether; the temperature is 20℃, the pH is 3.0, the plating time is 1.0 min, and the current density during plating is 2.0 A / dm³. 2 .

[0068] The chemical plating solution consists of: NiCl2·6H2O 25 g / L, NaH2PO2·H2O 15 g / L, Na3C6H5O7·2H2O 8 g / L, [CH2(NH2)COOH] 4 g / L, CH3COONa 8 g / L, sodium dodecylbenzenesulfonate 0.25 g / L, and zinc molybdate 75 mg / L; the temperature is 80℃, the pH is 5.0, and the plating time is 0.5 h.

[0069] Example 6

[0070] The difference between this embodiment and embodiment 4 is that:

[0071] A bipolar plate for an alkaline electrolytic cell with a corrosion-resistant composite coating on its surface, wherein the pre-plating nickel solution comprises 50 g / L NiCl2·6H2O, 260 g / L NiSO4·6H2O, 35 g / L H3BO3, 0.30 g / L sodium dodecyl sulfate, 45 mg / L sodium hydroxymethanesulfonate, and 35 mg / L propynyl alcohol propoxy ether; the temperature is 30℃, the pH is 4.0, the plating time is 2.0 min, and the current density during plating is 3.0 A / dm³. 2 .

[0072] The chemical plating solution consisted of: NiCl2·6H2O 35 g / L, NaH2PO2·H2O 25 g / L, Na3C6H5O7·2H2O 12 g / L, [CH2(NH2)COOH] 6 g / L, CH3COONa 12 g / L, sodium dodecylbenzenesulfonate 0.35 g / L, and zinc molybdate 85 mg / L; the temperature was 85℃, the pH was 6.0, and the plating time was 1.5 h.

[0073] Comparative Example 1

[0074] An alkaline electrolytic cell bipolar plate, the bipolar plate comprising a substrate material, the substrate material being Q235B carbon steel.

[0075] In this comparative example, only Q235B carbon steel was subjected to mechanical polishing pretreatment. The mechanical polishing involved first grinding the edges of the Q235B carbon steel sample with coarse sandpaper, and then using mechanical equipment and grinding tools to mechanically grind and polish the surface of the carbon steel. Multiple polishing passes were performed using abrasive paper or grinding wheels of different grit sizes (100#, 400#, 600#, 800#, 1000#, 1200#, 1500#).

[0076] The Ni-P coatings and Ni-P / NbC composite coatings prepared in Examples 1 and 4 were characterized by scanning electron microscopy.

[0077] The Ni-P coating completely covers the carbon steel substrate without obvious defects, although some bubble-like structures are visible on the surface. The coating surface consists of granular clusters with similarly sized spheres, evenly distributed, and a few noticeable cellular protrusions. Fine boundaries are visible between the spherical cluster particles. With the addition of NbC nanoparticles (the second phase), the coating surface becomes more uniform and smooth, the grain size decreases, and the bonding between cells becomes denser. The composite coating surface shows fewer irregular protrusions and depressions, which may be because the addition of NbC nanoparticles increases the number of active deposition sites during the deposition process due to the impact of the plating solution on the substrate, resulting in a more uniform distribution and better protection of the carbon steel substrate.

[0078] The coating thickness was measured using a cross-sectional method under a scanning electron microscope. The thickness of the visible Ni-P coating was 6.1 μm, and the thickness of the Ni-P / NbC composite coating was 7.8 μm. Energy-dispersive X-ray spectroscopy (EDS) was used to analyze the surface composition of the Ni-P and Ni-P / NbC composite coatings. The weight percentages of phosphorus and nickel on the Ni-P coating surface were as follows: phosphorus 13.8%, nickel 86.9%; and for the Ni-P / NbC composite coating surface, phosphorus 11.7%, nickel 85.4%. The lower phosphorus content on the Ni-P / NbC composite coating surface compared to the Ni-P coating indicates that the addition of NbC nanoparticles (the second-phase particles) inhibits phosphorus deposition on the composite coating.

[0079] Electrochemical tests were performed on the bipolar plates obtained in Examples 1-6 and Comparative Example 1: the potentiodynamic polarization curves of the samples in 3.5% NaCl solution were measured, and the Tafel polarization curves were fitted and analyzed using Zahner Analysis software. A three-electrode system was used, with a platinum electrode as the auxiliary electrode, a saturated calomel electrode (SCE) as the reference electrode, and the electroless plated sample as the working electrode. The electroless plated sample was placed aligned with a circular hole in the single-layer plate etching cell; the hole area was 1 cm². 2 This ensures that the sample area participating in the corrosion reaction is 1 cm². 2 During testing, the open-circuit potential (OCP) was first measured after stabilizing at room temperature for 120 s. Then, the polarization curve was measured within a potential range of ±300 mV relative to the open-circuit potential, at a scan rate of 1 mV / s. The test results are shown in Table 1.

[0080] Table 1. Electrochemical test results of bipolar plates prepared in Examples 1-6 and Comparative Example 1.

[0081] category <![CDATA[ E corr (V)]]> <![CDATA[ I corr (μA / cm 2 )]]> Example 1 -0.503 6.80 Example 2 -0.510 7.20 Example 3 -0.498 6.50 Example 4 -0.485 3.50 Example 5 -0.488 3.57 Example 6 -0.486 3.53 Comparative Example 1 -1.019 16.20

[0082] This invention performs potentiodynamic polarization tests on bipolar plates prepared in Examples 1-3 (Q235B carbon steel samples with Ni-P coating), Examples 4-6 (Q235B carbon steel samples with Ni-P / NbC composite coating), and Comparative Example 1 (Q235B carbon steel substrate sample), and derives the results through the Tafel region. I corr and E corr .generally I corr The smaller the value, the slower the corrosion rate of the sample. Examples 4-6 E corr and I corr The maximum (-0.485 V) and minimum (3.50 μA / cm) values ​​were respectively. 2Due to the protection of NbC nanoparticles, the corrosion rates of Examples 4-6 were reduced compared to Examples 1-3 and Comparative Example 1, indicating that the Ni-P / NbC composite coating effectively improved the corrosion resistance of the Q235B carbon steel substrate.

[0083] The bipolar plates prepared in Examples 1, 4, and Comparative Example 1 of this invention were subjected to neutral salt spray tests to investigate their corrosion resistance.

[0084] According to the test standards of GB / T 10125-2012 "Artificial Atmosphere Corrosion Test - Salt Spray Test" and GB / T 6458-86 "Neutral Salt Spray Test (NSS Test) for Metal Coatings", the neutral salt spray test was conducted using the LYW-015 salt spray corrosion test chamber produced by Shanghai Yiheng Technology Co., Ltd. The salt spray corrosion resistance of the coating was evaluated by observing the time when rust spots first appeared on the sample surface and the changes in surface morphology.

[0085] In Comparative Example 1, the Q235B carbon steel sample (top) showed a large number of rust spots on its surface after 1 hour; in Example 1, the Q235B carbon steel sample with Ni-P coating (middle) showed a small number of rust spots on its surface after 160 hours; and in Example 4, the Q235B carbon steel sample with Ni-P / NbC composite coating (bottom) showed visible rust spots on its surface only after 1080 hours. This demonstrates that the Ni-P / NbC composite coating has excellent salt spray corrosion resistance, enabling the Q235B carbon steel substrate to achieve excellent corrosion resistance.

[0086] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An alkaline electrolysis cell bipolar plate with a corrosion resistant composite coating on the surface, characterized in that, The bipolar plate includes a substrate material, a pre-plated layer, and a composite plating layer, wherein the composite plating layer is attached to the surface of the pre-plated layer, and the pre-plated layer is attached to the surface of the substrate material. The substrate material is Q235B carbon steel, the pre-plating layer is a nickel layer, and the composite plating layer is a Ni-P / NbC composite plating layer. The phosphorus (P) content in the Ni-P / NbC composite coating is 11-14%. The Ni-P / NbC composite coating includes NbC nanoparticles and a Ni-P alloy. The NbC nanoparticles are co-deposited on the Ni-P alloy, and the NbC nanoparticles inhibit the deposition of phosphorus in the composite coating.

2. The bipolar plate of claim 1, wherein The thickness of the Ni-P / NbC composite coating is 6~8 μm.

3. A method for producing an alkaline electrolysis cell bipolar plate with a corrosion-resistant composite coating on the surface, characterized in that, Includes the following steps: S10. Pretreatment: The Q235B carbon steel is subjected to surface pretreatment, which includes mechanical polishing, ultrasonic degreasing, alkaline washing, and acid pickling. S20, Pre-plated nickel layer: The pre-treated Q235B carbon steel is used as the cathode and the nickel plate is used as the anode. By electroplating, an external power supply is applied to introduce current into the pre-plated nickel solution, so that the nickel ions in the plating solution are reduced to metallic nickel on the surface of Q235B carbon steel to form a nickel layer. S30. Chemical composite plating of Ni-P / NbC composite coating: A Ni-P / NbC composite coating is prepared on the surface of the material after the above-mentioned pre-plating of nickel layer by a chemical composite nickel plating process; the chemical composite nickel plating involves immersing the sample after the above-mentioned pre-plating of nickel into a prepared chemical composite plating solution for plating, the chemical composite plating solution containing NbC nanoparticles, and the NbC nanoparticles in the composite plating solution are co-deposited on the Ni-P alloy to obtain a uniform and smooth Ni-P / NbC composite coating.

4. The preparation method according to claim 3, characterized in that, The preprocessing steps include: S11. Mechanical polishing: The Q235B carbon steel sample is first ground with coarse sandpaper, and then the surface of the Q235B carbon steel is mechanically ground and polished using mechanical equipment and grinding tools. Multiple polishing passes are performed using abrasive paper or grinding wheels with different grit sizes of 100#, 400#, 600#, 800#, 1000#, 1200#, and 1500#. S12. Ultrasonic degreasing: The Q235B carbon steel that has been mechanically polished is placed in an organic solvent for ultrasonic degreasing; the organic solvent is either anhydrous ethanol or anhydrous acetone; the ultrasonic degreasing cleaning time is 5-6 minutes. S13. Alkaline degreasing: The Q235B carbon steel after ultrasonic degreasing is immersed in an alkaline degreasing solution for further alkaline degreasing; the alkaline degreasing solution has the following composition: sodium hydroxide 35~45 g / L, sodium carbonate 95~105 g / L; the degreasing temperature is 70~80℃, and the alkaline washing time is 8~12 min. S14. Pickling: The Q235B carbon steel that has been degreased by alkaline washing is immersed in a pickling solution for pickling; the pickling solution is a hydrochloric acid solution with a mass fraction of 15~25%, the pickling temperature is room temperature, and the pickling time is 1~3 min.

5. The preparation method according to claim 3, characterized in that, In the pre-plating nickel layer step, the pre-plating nickel solution comprises: nickel chloride hexahydrate 40-50 g / L, nickel sulfate hexahydrate 240-260 g / L, boric acid 25-35 g / L, sodium dodecyl sulfate 0.20-0.30 g / L, sodium hydroxymethylsulfonate 35-45 mg / L, and propynyl alcohol propoxy ether 25-35 mg / L; the temperature is 20-30 ℃, the pH is 3-4, the plating time is 1-2 min, and the current density during plating is 2-3 A / dm³. 2 .

6. The preparation method according to claim 3, characterized in that, In the chemical composite plating step of Ni-P / NbC composite coating, the chemical plating solution consists of: nickel chloride hexahydrate (main salt) 25-35 g / L, sodium hypophosphite (reducing agent) 15-25 g / L, sodium citrate (complexing agent) 8-12 g / L, glycine (complexing agent) 4-6 g / L, sodium acetate (buffer) 8-12 g / L, sodium dodecylbenzenesulfonate (surfactant) 0.25-0.35 g / L, and zinc molybdate (stabilizer) 70-80 mg / L; the temperature is 80-85℃, the pH is 5-6, and the plating time is 0.5-1.5 h; the NbC nanoparticles are obtained by ball milling pretreatment; and the NbC nanoparticle suspension is obtained by ultrasonic dispersion in deionized water.