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

Abstract

The invention discloses an alkaline electrolytic cell bipolar plate with a corrosion-resistant composite coating on the surface. The bipolar plate comprises a substrate material, a pre-plating layer and a composite plating layer, the composite plating layer 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 is made of 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 invention further provides a preparation method of the alkaline electrolytic cell bipolar plate with the corrosion-resistant composite coating on the surface. According to the bipolar plate with the corrosion-resistant Ni-P / NbC composite coating on the surface, the NbC nanoparticles have excellent comprehensive performance, so that the prepared bipolar plate has high hardness, excellent corrosion resistance, excellent wear resistance, excellent conductivity and excellent high temperature resistance; and the composite coating has ultra-thin thickness, so that the overall mass of the bipolar plate is reduced, the electrolytic bath is lighter, and the manufacturing cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of bipolar plate materials, and specifically refers to an alkaline electrolytic cell bipolar plate with a corrosion-resistant Ni-P / NbC composite coating on its surface. Background Art

[0002] The use of renewable energy to electrolyze water to produce hydrogen has received wide attention as a clean new energy production method. Currently, the electrolytic water hydrogen production technology mainly includes alkaline (ALK) electrolytic water hydrogen production technology, proton exchange membrane (PEM) electrolytic water hydrogen production technology, solid oxide electrolytic cell (SOEC) hydrogen production technology, and anion exchange membrane (AEM) electrolytic water hydrogen production technology. Among them, ALK electrolytic water hydrogen production is the most mature and most promising electrolytic water hydrogen production technology, which has led to a continuous increase in the market demand for electrolytic water hydrogen production equipment. As an indispensable component of the ALK hydrogen production electrolytic cell - the market for bipolar plates has also developed vigorously accordingly.

[0003] The bipolar plate plays a key role in supporting the electrodes, diaphragms, and conducting electricity in the ALK hydrogen production electrolytic cell. It is the component with the largest quantity in the electrolytic cell, and its cost accounts for 20% - 30% of the total cost. In the prior art, the bipolar plates of the ALK hydrogen production electrolytic cell are integrally made of carbon steel metal plates, and the main plate and the electrode frame are formed by welding, which makes the electrolytic cell extremely heavy and the manufacturing raw material cost is also relatively high. Moreover, due to the need to set sealing rings between the electrode frames, the processing process is complex, and the electrode frame part is also easily corroded, resulting in internal short-circuit problems. In addition, since the electrolyte in the battery is alkaline and the working temperature is 80 - 90°C, such an alkaline environment and temperature happen to be within the range where the carbon steel main plate is prone to alkali corrosion. Therefore, the bipolar plate must also have the property of being corrosion-resistant in an alkaline medium.

[0004] Since nickel does not react with strong alkalis and has excellent alkali corrosion resistance, Ni-P coatings are usually obtained by electroless nickel plating on carbon steel to protect bipolar plates. The anticorrosion application of electroless nickel plating on carbon steel has been very extensive, but its performance on bipolar plates still needs to be improved. Electroless composite nickel plating technology is one of the effective ways to improve the performance of nickel plating layers. Insoluble particles with specific properties are added to the electroless plating solution and co-deposited on the Ni-P alloy to obtain composite coatings with different physical and chemical properties, and at the same time, the corresponding performance of the coating can be enhanced. With the continuous in-depth research of nanomaterials and nanotechnology, introducing nanoscale insoluble particles into composite coatings has become the development trend of electroless composite coatings. At present, composite coatings with different functions such as Ni-P / Al2O3, Ni-P / SiO2, Ni-P / SiC, Ni-P / PTFE, Ni-P / Ti4O7 have been prepared and applied. These insoluble particles can enhance the wear resistance, corrosion resistance, creep resistance, conductivity and other properties of the coating.

[0005] A preparation process of electroless Ni-P / Ti4O7 composite coating on the surface of carbon steel bipolar plates disclosed in Chinese Patent CN 116516328 A. This process introduces Ti4O7 particles with excellent corrosion resistance and conductivity into the Ni-P plating solution system to improve the anti-corrosion performance of the coating, reduce the contact resistance, and increase the service life of carbon steel bipolar plates. The bipolar plates with this composite coating are subjected to potentiodynamic polarization tests in an acidic environment, and the lowest corrosion current density in the characterization data is 10.28±0.15 μA / cm 2 , indicating that the introduction of Ti4O7 particles can effectively improve the acid corrosion resistance of the Ni-P coating, but there is still room for improvement, and its alkali corrosion resistance still needs to be explored.

[0006] A preparation method of SiC particle-reinforced Ni-P coating disclosed in Chinese Patent CN 117867479 A. This method pre-plates a Ni-P coating on the surface of the sample, and then performs a second Ni-P-SiC composite plating in a composite plating solution containing SiC particles. The obtained double-layer composite coating is applied to the protection of oil well pipes. The double-layer composite coating has a good morphology, high hardness, strong wear resistance and corrosion resistance. However, the SiC particles used in this method are 0.5 μm, which belong to micro-nano scale particles. Applying them to the bipolar plate coating may result in a relatively thick coating. The hardness and corrosion resistance of existing nano-composite coatings are higher than those of micro-composite coatings, but nano-particles are more likely to agglomerate during plating.

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

[0008] The purpose of the present invention is to overcome the deficiencies existing in the prior art and provide an alkaline electrolytic cell bipolar plate with a corrosion-resistant composite coating on its surface. Specifically, a niobium carbide (NbC) nanoparticle is introduced into the Ni-P coating on the surface of the carbon steel substrate material 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 resistance, wear resistance, electrical conductivity, and high-temperature resistance; the composite coating has an ultra-thin thickness (6-8 μm), which can reduce the overall mass of the bipolar plate, making the electrolytic cell lighter and reducing the manufacturing cost.

[0009] To achieve the above-mentioned invention purpose, the technical solution adopted by the present invention is as follows: An alkaline electrolytic cell bipolar plate with a corrosion-resistant composite coating on its surface, the bipolar plate includes a substrate material, a pre-coating layer, and a composite coating layer. The composite coating layer is attached to the surface of the pre-coating layer, and the pre-coating layer is attached to the surface of the substrate material; the substrate material is Q235B carbon steel, the pre-coating layer is a nickel layer, and the composite coating layer is a Ni-P / NbC composite coating.

[0010] Further, the thickness of the Ni-P / NbC composite coating layer is 6-8 μm.

[0011] Further, the content of phosphorus P in the Ni-P / NbC composite coating layer is in the range of 11-14%. When the phosphorus content in the Ni-P coating layer is low, the coating layer structure is a mixed crystal structure. When the phosphorus content of the coating layer is greater than 8%, the coating layer structure is an amorphous structure. Since when the phosphorus content is high, phosphorus may participate in the deformation of the nickel lattice, resulting in a decrease in the microhardness of the nickel layer, while the corrosion resistance of the coating layer increases with the increase of the phosphorus content and has better corrosion resistance in an alkaline medium. Compared with the conventional Ni-P coating layer with a phosphorus content of 10%, the Ni-P coating layer with the phosphorus content in the above range has a higher degree of amorphousness and can endow the bipolar plate with corrosion resistance.

[0012] A preparation method of an alkaline electrolytic cell bipolar plate with a corrosion-resistant composite coating on its surface, including the following steps: (1) Pretreatment: Perform surface pretreatment on the Q235B carbon steel. Through mechanical polishing, ultrasonic degreasing, alkali washing, and acid pickling treatments, ensure that the surface of the sample is free of oil, grease, dirt, and oxide layer, preventing it from affecting the subsequent plating process, hindering the bonding between the composite coating layer and the substrate material, and causing the separation of the coating layer from the substrate material;

[0013] (2)Pre - nickel plating layer: The pretreated Q235B carbon steel is used as the cathode, and the nickel plate is used as the anode. By electroplating, an external power supply introduces current into the pre - nickel plating solution, enabling nickel ions in the plating solution to be reduced to metallic nickel on the surface of Q235B carbon steel to form a nickel layer. The pre - nickel plating layer can make the subsequent plating adhere better, improving the bonding strength of the plating layer. The nickel layer itself also has good corrosion resistance, equivalent to a double - layer corrosion - resistant layer;

[0014] (3)Chemical composite plating Ni - P / NbC composite coating: The Ni - P / NbC composite coating is prepared on the surface of the material after the above pre - nickel plating layer treatment through a chemical composite plating process. The chemical composite plating is carried out by putting the above pre - nickel - plated specimen into the prepared chemical composite plating solution. The chemical composite plating solution is prepared by mixing a conventional electroless 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 flat Ni - P / NbC composite coating.

[0015] Further, the pretreatment step in (1) includes: (1.1)Mechanical polishing: First, the edges of the Q235 B carbon steel specimen are ground with coarse sandpaper, and then mechanical grinding and polishing are carried out on the surface of the carbon steel using mechanical equipment (such as a polishing machine) and grinding tools (such as sandpaper). Multiple - pass polishing is carried out successively using abrasive papers or grinding wheels with different grit sizes (100#, 400#, 600#, 800#, 1000#, 1200#, 1500#), gradually improving the surface finish from rough to delicate; (1.2)Ultrasonic degreasing: The carbon steel after mechanical polishing above is put into an organic solvent for ultrasonic degreasing to remove the residual grease on the surface of the specimen. The organic solvent is one of anhydrous ethanol or anhydrous acetone. The cleaning time for ultrasonic degreasing is 5 - 6 min; (1.3)Alkaline degreasing: The carbon steel after ultrasonic degreasing above is immersed in an alkaline degreasing solution for further alkaline degreasing to remove the rust - preventive oil, lubricating oil and other greases and dirt residues on the surface of the workpiece during machining or storage. The composition of the alkaline degreasing solution is: sodium hydroxide (NaOH) 35 - 45 g / L, sodium carbonate (Na2CO3) 95 - 105 g / L; the degreasing temperature is 70 - 80 °C, and the alkali - washing time is 8 - 12 min; (1.4)Pickling: The carbon steel after alkali - washing degreasing above is immersed in a pickling solution for pickling to remove the rust products such as oxide films and scale on the surface of the specimen. 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.

[0016] Further, in the step (2) of pre-plating a nickel layer, the composition of the pre-plating nickel solution is 40-50 g / L of nickel chloride hexahydrate (NiCl2·6H2O), 240-260 g / L of nickel sulfate hexahydrate (NiSO4·6H2O), 25-35 g / L of boric acid (H3BO3), 0.20-0.30 g / L of sodium dodecyl sulfate, 35-45 mg / L of sodium hydroxymethyl sulfonate (PN), and 25-35 mg / L of propynol propoxy ether (PAP); the temperature is 20-30 °C, the pH is 3-4, the plating time is 1-2 min, and the current density during plating is 2-3 A / dm 2 .

[0017] Further, in the step (3) of electroless composite plating of Ni-P / NbC composite coating, the composition of the electroless plating solution is: 25-35 g / L of main salt NiCl2·6H2O, 15-25 g / L of reducing agent sodium hypophosphite (NaH2PO2·H2O), 8-12 g / L of complexing agent sodium citrate (Na3C6H5O7·2H2O), 4-6 g / L of complexing agent glycine [CH2(NH2)COOH], 8-12 g / L of buffer sodium acetate (CH3COONa), 0.25-0.35 g / L of surfactant sodium dodecylbenzenesulfonate, and 75-85 mg / L of stabilizer zinc molybdate; the temperature is 80-85 °C, the pH is 5-6, and the plating time is 0.5-1.5 h; the NbC nanoparticles are obtained by pre-treating the purchased NbC powder (purity 99.9%, average particle size 100 nm) in a ball mill, with small and uniform particle size. The NbC nanoparticle suspension is obtained by ultrasonically dispersing the pre-treated NbC nanoparticles in deionized water.

[0018] The advantages and beneficial effects of the present invention are as follows: 1. For the bipolar plate of an alkaline electrolytic cell with a corrosion-resistant composite coating on the surface involved in the present invention, first, a pre-plated nickel layer is formed on the surface of the carbon steel substrate material of the bipolar plate. The pre-plated nickel layer can make the subsequent coatings adhere better, improve the adhesion of the coatings, and the nickel layer itself also has good corrosion resistance, equivalent to a double-layer corrosion-resistant layer.

[0019] 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, obtaining a uniform, dense and flat Ni-P / NbC composite coating. The phosphorus (P) content in the Ni-P / NbC composite coating is in the range of 11-14%. Compared with the conventional Ni-P coating with a phosphorus content of 10%, the degree of amorphousness is higher, which can endow the bipolar plate with corrosion resistance. Although the addition of NbC nanoparticles will inhibit the deposition of phosphorus elements on the composite coating and reduce the phosphorus content, it can form a stable physical barrier, making the path for corrosive media to enter the coating longer and more complex, greatly increasing the deterioration time of the coating, thereby improving the corrosion resistance of the coating and enabling it to better serve in the operating environment of the bipolar plate.

[0020] 2. The present invention carried out potentiodynamic polarization tests on carbon steel substrates, carbon steel with Ni-P coatings, and carbon steel with Ni-P / NbC composite coatings. The self-corrosion potential ( E corr ) and self-corrosion current density ( I corr ) of the carbon steel with Ni-P / NbC composite coating were the largest (-0.485 V) and the smallest (3.50 μA / cm 2 ), respectively. Due to the protection of NbC nanoparticles, the corrosion rate of the carbon steel with Ni-P / NbC composite coating was reduced compared to that of the carbon steel substrate and the carbon steel with Ni-P coating; after neutral salt spray testing, rust spots appeared on the surface of the Q235B carbon steel sample with Ni-P / NbC composite coating at 1080 h. This shows that the Ni-P / NbC composite coating effectively improved the corrosion resistance of the Q235B carbon steel substrate.

[0021] 3. Since the NbC nanoparticles introduced in the present invention are a kind of metal carbide, they have the advantages of high hardness (harder than corundum, microhardness > 23.5 GPa), high strength, high melting point (3500 °C), high electrical conductivity (resistivity 35 μΩ·cm), and high corrosion resistance. They can be used as additives for composite coatings to improve the overall performance of the coatings, so that the bipolar plate has high hardness, excellent corrosion resistance and wear resistance, excellent electrical conductivity and high temperature resistance.

[0022] 4. The Ni-P / NbC composite coating of the present invention, due to its ultra-thin thickness (6-8 μm), can reduce the overall mass of the bipolar plate, thereby making the electrolytic cell lighter and reducing the manufacturing cost. Specific Embodiments

[0023] The following combines examples to further describe the specific embodiments of the present invention. The following examples are only used to more clearly illustrate the technical solutions of the present invention and cannot be used to limit the protection scope of the present invention.

[0024] Example 1 An alkaline electrolytic cell bipolar plate with a corrosion-resistant coating on its surface. The bipolar plate includes a base material and a pre-coating layer, and the pre-coating layer adheres to the surface of the base material. The base material is Q235B carbon steel, and the pre-coating layer is a nickel layer.

[0025] A method for preparing an alkaline electrolytic cell bipolar plate with a corrosion-resistant coating on its surface, comprising the following steps: (1) Pretreatment: The Q235B carbon steel is subjected to surface pretreatment, including mechanical polishing, ultrasonic degreasing, alkaline washing, and acid pickling, to ensure that the surface of the specimen is free of oil, grease, dirt, and oxide layer.

[0026] (2) Pre-plating nickel layer: The pretreated Q235B carbon steel is used as the cathode, and a nickel plate is used as the anode. By electroplating, an external power source is used to introduce current into the pre-plating nickel solution, so that nickel ions in the plating solution are reduced to metallic nickel on the surface of the Q235B carbon steel to form a nickel layer.

[0027] (3) Electroless plating Ni-P layer: The Ni-P layer is prepared by electroless plating process on the surface of the material after the pre-plating nickel layer treatment. The electroless plating is carried out by immersing the specimen after pre-plating nickel into the prepared electroless plating solution to obtain the Ni-P layer.

[0028] The mechanical polishing is to first grind the edge of the Q235B carbon steel specimen with a coarse sandpaper, and then use mechanical equipment and grinding tools to mechanically grind and polish the surface of the carbon steel. Different grit sizes (100#, 400#, 600#, 800#, 1000#, 1200#, 1500#) of abrasive papers or grinding wheels are used for multiple polishing steps.

[0029] The ultrasonic degreasing is to put the carbon steel after mechanical polishing into an organic solvent for ultrasonic degreasing. The organic solvent uses anhydrous ethanol, and the cleaning time for ultrasonic degreasing is 5 min. The alkaline degreasing is to immerse the carbon steel after ultrasonic degreasing into an alkaline degreasing solution for further alkaline degreasing. The composition of the alkaline degreasing solution is: NaOH 40 g / L, Na2CO3 100 g / L; the degreasing temperature is 75 °C, and the alkaline washing time is 10 min. The acid pickling is to immerse the carbon steel after alkaline washing and degreasing into an acid pickling solution for acid pickling. The acid pickling solution is a hydrochloric acid solution with a mass fraction of 20%; the acid pickling temperature is room temperature, and the acid pickling time is 2 min.

[0030] The composition of the pre - nickel - plating solution is: NiCl2·6H2O 45 g / L, NiSO4·6H2O 250 g / L, H3BO3 30 g / L, sodium dodecyl sulfate 0.25 g / L, sodium hydroxymethyl sulfonate 40 mg / L, propynol propoxy ether 30 mg / L; the temperature is 25 °C, the pH is 3.8, the plating time is 1.5 min, and the current density during plating is 2.5 A / dm 2 .

[0031] The composition of the electroless plating solution is: 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, zinc molybdate 80 mg / L; the temperature is 82 °C, the pH is 5.8, and the plating time is 1.0 h.

[0032] Example 2 The difference between this example and Example 1 is that: For an alkaline electrolytic cell bipolar plate with a corrosion - resistant coating on the surface, the composition of the pre - nickel - plating solution is: NiCl2·6H2O 40 g / L, NiSO4·6H2O 240 g / L, H3BO3 25 g / L, sodium dodecyl sulfate 0.20 g / L, sodium hydroxymethyl sulfonate 35 mg / L, propynol propoxy ether 25 mg / L; the temperature is 20 °C, the pH is 3.0, the plating time is 1.0 min, and the current density during plating is 2.0 A / dm 2 .

[0033] The composition of the electroless plating solution is: 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, zinc molybdate 75 mg / L; the temperature is 80 °C, the pH is 5.0, and the plating time is 0.5 h.

[0034] Example 3 The difference between this example and Example 1 is that: An alkaline electrolytic cell bipolar plate with a corrosion-resistant coating on its surface. The composition of the pre-nickel plating solution is 50 g / L of NiCl2·6H2O, 260 g / L of NiSO4·6H2O, 35 g / L of H3BO3, 0.30 g / L of sodium dodecyl sulfate, 45 mg / L of sodium hydroxymethyl sulfonate, and 35 mg / L of propynol propoxy ether; the temperature is 30 °C, the pH is 4.0, the plating time is 2.0 min, and the current density during plating is 3.0 A / dm 2 .

[0035] The composition of the electroless plating solution is: 35 g / L of NiCl2·6H2O, 25 g / L of NaH2PO2·H2O, 12 g / L of Na3C6H5O7·2H2O, 6 g / L of [CH2(NH2)COOH], 12 g / L of CH3COONa, 0.35 g / L of sodium dodecylbenzenesulfonate, and 85 mg / L of zinc molybdate; the temperature is 85 °C, the pH is 6.0, and the plating time is 1.5 h.

[0036] Example 4 An alkaline electrolytic cell bipolar plate with a corrosion-resistant composite coating on its surface. The bipolar plate includes a substrate material, a pre-coating layer, and a composite coating layer. The composite coating layer adheres to the surface of the pre-coating layer, and the pre-coating layer adheres to the surface of the substrate material; the substrate material is Q235B carbon steel, the pre-coating layer is a nickel layer, and the composite coating layer is a Ni-P / NbC composite coating layer.

[0037] A preparation method of an alkaline electrolytic cell bipolar plate with a corrosion-resistant composite coating on its surface, comprising the following steps: (1) Pretreatment: The Q235B carbon steel is subjected to surface pretreatment, including mechanical polishing, ultrasonic degreasing, alkali washing, and acid pickling to ensure that the surface of the sample is free of oil, grease, dirt, and oxide layer.

[0038] (2) Pre-nickel plating layer: The pretreated Q235B carbon steel is used as the cathode, and a nickel plate is used as the anode. By electroplating, an external power source is used to introduce current into the pre-nickel plating solution, so that nickel ions in the plating solution are reduced to metallic nickel on the surface of the Q235B carbon steel to form a nickel layer.

[0039] (3) Chemical composite plating of Ni-P / NbC composite coating layer: The Ni-P / NbC composite coating layer is prepared on the surface of the material after the pre-nickel plating layer treatment through a chemical composite plating process. The chemical composite plating is to place the pre-nickel plated sample into the prepared chemical composite plating solution for plating. The chemical composite plating solution is prepared by mixing a conventional electroless 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 flat Ni-P / NbC composite coating layer.

[0040] The mechanical polishing is to first grind the edges of the Q235 B carbon steel specimen with coarse sandpaper, and then use mechanical equipment and grinding tools to mechanically grind and polish the surface of the carbon steel. Successive multi-pass polishing is carried out using abrasive papers or grinding wheels with different grit sizes (100#, 400#, 600#, 800#, 1000#, 1200#, 1500#).

[0041] The ultrasonic degreasing is to put the carbon steel after the above-mentioned mechanical polishing into an organic solvent for ultrasonic degreasing; the organic solvent used is anhydrous ethanol; the cleaning time of the ultrasonic degreasing is 5 min; The alkaline degreasing is to immerse the carbon steel after the above-mentioned ultrasonic degreasing into an alkaline degreasing solution for further alkaline degreasing; the composition of the alkaline degreasing solution is: 40 g / L of NaOH and 100 g / L of Na2CO3; the degreasing temperature is 75 °C, and the alkali washing time is 10 min; The pickling is to immerse the carbon steel after the above-mentioned alkali washing degreasing into a pickling solution for pickling; the pickling solution is a hydrochloric acid solution with a mass fraction of 20%; the pickling temperature is room temperature, and the pickling time is 2 min.

[0042] The composition of the pre-nickel plating solution is 45 g / L of NiCl2·6H2O, 250 g / L of NiSO4·6H2O, 30 g / L of H3BO3, 0.25 g / L of sodium dodecyl sulfate, 40 mg / L of sodium hydroxymethylsulfonate, and 30 mg / L of propynol propoxy ether; the temperature is 25 °C, the pH is 3.8, the plating time is 1.5 min, and the current density during plating is 2.5 A / dm 2 .

[0043] The composition of the electroless plating solution is: 30 g / L of NiCl2·6H2O, 20 g / L of NaH2PO2·H2O, 10 g / L of Na3C6H5O7·2H2O, 5 g / L of [CH2(NH2)COOH], 10 g / L of CH3COONa, 0.30 g / L of sodium dodecylbenzenesulfonate, and 80 mg / L of zinc molybdate; the temperature is 82 °C, the pH is 5.8, and the plating time is 1.0 h.

[0044] The NbC nanoparticles are obtained by ball milling pretreatment of purchased NbC powder (purity 99.9%, average particle size 100 nm), with small and uniform particle sizes. The NbC nanoparticle suspension is obtained by ultrasonically dispersing the pretreated NbC nanoparticles in deionized water.

[0045] With the addition of the second-phase particles (NbC nanoparticles), the surface of the coating is uniform and flat, the grain size becomes smaller, and the bonding between cells is denser. There are fewer irregular protrusions and depressions on the surface cells of the composite coating, which may be because with the addition of NbC particles, during the deposition process, with the impact of the plating solution on the substrate, the active points of deposition increase and are more evenly distributed, providing better protection for the substrate.

[0046] Example 5 The difference between this example and Example 4 is as follows: An alkaline electrolytic cell bipolar plate with a corrosion-resistant composite coating on its surface. The composition of the pre-plated nickel solution is 40 g / L of NiCl2·6H2O, 240 g / L of NiSO4·6H2O, 25 g / L of H3BO3, 0.20 g / L of sodium dodecyl sulfate, 35 mg / L of sodium hydroxymethyl sulfonate, and 25 mg / L of propynol propoxy ether; the temperature is 20 °C, the pH is 3.0, the plating time is 1.0 min, and the current density during plating is 2.0 A / dm 2 。

[0047] The composition of the electroless plating solution is: 25 g / L of NiCl2·6H2O, 15 g / L of NaH2PO2·H2O, 8 g / L of Na3C6H5O7·2H2O, 4 g / L of [CH2(NH2)COOH], 8 g / L of CH3COONa, 0.25 g / L of sodium dodecylbenzenesulfonate, and 75 mg / L of zinc molybdate; the temperature is 80 °C, the pH is 5.0, and the plating time is 0.5 h.

[0048] Example 6 The difference between this example and Example 4 is as follows: An alkaline electrolytic cell bipolar plate with a corrosion-resistant composite coating on its surface. The composition of the pre-plated nickel solution is 50 g / L of NiCl2·6H2O, 260 g / L of NiSO4·6H2O, 35 g / L of H3BO3, 0.30 g / L of sodium dodecyl sulfate, 45 mg / L of sodium hydroxymethyl sulfonate, and 35 mg / L of propynol propoxy ether; the temperature is 30 °C, the pH is 4.0, the plating time is 2.0 min, and the current density during plating is 3.0 A / dm 2 。

[0049] The composition of the electroless plating solution is as follows: 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, zinc molybdate 85 mg / L; the temperature is 85 °C, the pH is 6.0, and the plating time is 1.5 h.

[0050] Comparative Example 1 An alkaline electrolytic cell bipolar plate, the bipolar plate includes a base material, and the base material is Q235B carbon steel.

[0051] In this comparative example, it was only prepared by mechanical polishing pretreatment of Q235B carbon steel. The mechanical polishing is to first grind the edges of the Q235B carbon steel specimen with coarse sandpaper, and then use mechanical equipment and grinding tools to perform mechanical grinding and polishing on the surface of the carbon steel, and use abrasive papers or grinding wheels with different grit sizes (100#, 400#, 600#, 800#, 1000#, 1200#, 1500#) for multiple polishing steps in sequence.

[0052] The Ni-P coating and Ni-P / NbC composite coating prepared in Example 1 and Example 4 were characterized by scanning electron microscopy: The Ni-P coating has completely covered the carbon steel substrate without obvious defects, and there are bubble-like structures locally on the surface of the coating; the surface of the coating is composed of granular clusters, and the sizes of the cluster spheres are not very different, and they are evenly distributed. There are a few obvious cellular protrusions on the surface, and fine boundaries can be seen between the spherical cluster particles. With the addition of the second-phase particle NbC nanoparticles, the surface of the coating becomes more uniform and flat, the grain size becomes smaller, and the bonding between cells is denser; the irregular protrusions and depressions on the surface of the composite coating are less, which may be because with the addition of NbC nanoparticles, during the deposition process, with the impact of the plating solution on the substrate, the active points of deposition are increased and are more evenly distributed, providing better protection for the carbon steel substrate.

[0053] The thickness of the coating was measured by cross-sectional measurement under a scanning electron microscope. The visible Ni-P coating thickness was 6.1 μm, and the Ni-P / NbC composite coating thickness was 7.8 μm. The surface compositions of the Ni-P coating and the Ni-P / NbC composite coating were analyzed by energy-dispersive X-ray spectroscopy (EDS). The weight percentages of phosphorus and nickel components on the surface of the Ni-P coating were as follows: phosphorus 13.8%, nickel 86.9%; the weight percentages of phosphorus and nickel components on the surface of the Ni-P / NbC composite coating were as follows: phosphorus 11.7%, nickel 85.4%. The phosphorus element content on the surface of the Ni-P / NbC composite coating was lower than that of the Ni-P coating, indicating that the addition of the second-phase particles NbC nanoparticles would inhibit the deposition of phosphorus elements on the composite coating.

[0054] The bipolar plates obtained in Examples 1-6 and Comparative Example 1 were subjected to electrochemical tests: the potentiodynamic polarization curves of the test specimens in 3.5% NaCl solution were tested, and the Tafel polarization curves were fitted and analyzed using the supporting software of Zahner Analysis. The three-electrode system was used for the test, where the auxiliary electrode was a platinum electrode, the reference electrode was a saturated calomel electrode (SCE), and the working electrode was the electroless plating specimen. The electroless plating specimen was placed opposite the round hole of the single-layer flat corrosion cell, and the area of the round hole was 1 cm 2 , ensuring that the area of the specimen participating in the corrosion reaction was 1 cm 2 . During the test, the open-circuit potential (OCP) was first stabilized at room temperature for 120 s, and then the polarization curve was tested in the potential range of ±300 mV relative to the open-circuit potential, with a scanning rate of 1 mV / s. The test results are shown in Table 1: Table 1 Electrochemical test result data of the bipolar plates prepared in Examples 1-6 and Comparative Example 1 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 The present invention conducted potentiodynamic polarization tests on the bipolar plates prepared in Examples 1-3 (Q235B carbon steel samples with Ni-P coatings), Examples 4-6 (Q235B carbon steel samples with Ni-P / NbC composite coatings), and Comparative Example 1 (Q235B carbon steel substrate samples), and derived I corr and E corr . Generally I corr the smaller the value, the slower the corrosion rate of the sample. The E corr and I corr of Examples 4-6 were the largest (-0.485 V) and the smallest (3.50 μA / cm 2), due to the protection of NbC nanoparticles, the corrosion rates of Examples 4-6 were lower than those of 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.

[0055] The bipolar plates prepared in Example 1, Example 4 and Comparative Example 1 of the present invention were subjected to neutral salt spray tests to explore the corrosion resistance of the bipolar plates: According to the test standards of GB / T 10125-2012 "Artificial Atmosphere Corrosion Test - Salt Spray Test" and GB / T 6458-86 "Metallic Coatings - Neutral Salt Spray Test (NSS Test)", a LYW-015 type salt spray corrosion test chamber produced by Shanghai Yiheng Technology Co., Ltd. was used for the neutral salt spray test. The salt spray corrosion resistance of the coating was evaluated by observing the time when rust spots began to appear on the surface of the sample and the changes in the surface morphology.

[0056] For the Q235B carbon steel sample of Comparative Example 1 (upper), a large number of rust spots appeared on its surface at 1 h; for the Q235B carbon steel sample with Ni-P coating of Example 1 (middle), a small amount of rust spots appeared on its surface at 160 h; for the Q235B carbon steel sample with Ni-P / NbC composite coating of Example 4 (lower), rust spots visible to the naked eye appeared on its surface only at 1080 h. It shows that the Ni-P / NbC composite coating has excellent salt spray corrosion resistance and can endow the Q235B carbon steel substrate with excellent corrosion resistance.

[0057] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. An alkaline electrolytic cell bipolar plate with a corrosion-resistant composite coating on its surface, characterized in that, The bipolar plate includes a base material, a pre-plated layer, and a composite coating. The composite coating is attached to the surface of the pre-plated layer, and the pre-plated layer is attached to the surface of the base material. The base material is Q235B carbon steel, the pre-plated layer is a nickel layer, and the composite coating is a Ni-P / NbC composite coating.

2. The bipolar plate for an alkaline electrolytic cell with a corrosion-resistant composite coating on the surface according to claim 1, characterized in that, The thickness of the Ni-P / NbC composite coating is 6 - 8 μm.

3. The bipolar plate for an alkaline electrolytic cell with a corrosion-resistant composite coating on the surface according to claim 1, wherein, The content of phosphorus P in the Ni-P / NbC composite coating is in the range of 11 - 14%.

4. A preparation method of an alkaline electrolytic cell bipolar plate with a corrosion-resistant composite coating on the surface, characterized in that, It includes the following steps: (1) Pretreatment: Perform surface pretreatment on the Q235B carbon steel. The pretreatment includes mechanical polishing, ultrasonic degreasing, alkaline cleaning, and pickling. (2) Pre-plated nickel layer: Use the pretreated Q235B carbon steel as the cathode and a nickel plate as the anode. By electroplating, an external power supply is used to introduce current into the pre-plated nickel solution, so that nickel ions in the plating solution are reduced to metallic nickel on the surface of the Q235B carbon steel to form a nickel layer. (3) Chemical composite plating of Ni-P / NbC composite coating: On the surface of the material after the pre-plated nickel layer treatment above, a Ni-P / NbC composite coating is prepared by chemical composite plating of nickel. The chemical composite plating of nickel is to put the above pre-plated nickel sample into the prepared chemical composite plating solution for plating. The chemical composite plating solution is prepared by mixing a conventional electroless plating solution and a NbC nanoparticle suspension. The NbC nanoparticles in the composite plating solution are co-deposited on the Ni-P alloy to obtain a uniform and flat Ni-P / NbC composite coating.

5. The preparation method of an alkaline electrolytic cell bipolar plate with a corrosion-resistant composite coating on the surface according to claim 4, characterized in that, The (1) pretreatment step includes: (1.1) Mechanical polishing: First, grind the edges of the Q235 B carbon steel sample with coarse sandpaper, and then use mechanical equipment and grinding tools to perform mechanical grinding and polishing on the surface of the carbon steel. Use abrasive papers or grinding wheels with different grits of 100#, 400#, 600#, 800#, 1000#, 1200#, and 1500# for multiple polishing steps in sequence. (1.2) Ultrasonic degreasing: Put the carbon steel after the above mechanical polishing into an organic solvent for ultrasonic degreasing. The organic solvent is one of anhydrous ethanol or anhydrous acetone. The cleaning time for ultrasonic degreasing is 5 - 6 min. (1.3) Alkaline degreasing: Immerse the carbon steel after the above ultrasonic degreasing into an alkaline degreasing solution for further alkaline degreasing. The composition of the alkaline degreasing solution is: 35 - 45 g / L of sodium hydroxide and 95 - 105 g / L of sodium carbonate. The degreasing temperature is 70 - 80°C, and the alkaline cleaning time is 8 - 12 min. (1.4) Pickling: Immerse the carbon steel after the above alkaline cleaning and degreasing into 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.

6. The preparation method of an alkaline electrolytic cell bipolar plate with a corrosion-resistant composite coating on the surface according to claim 4, characterized in that, In the step of the pre-plated nickel layer (2), the composition of the pre-plated nickel solution is 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 hydroxymethyl sulfonate 35-45 mg / L, propynol propoxy ether 25-35 mg / L; the temperature is 20-30 °C, the pH is 3-4, the plating time is 1-2 min, and the current density during plating is 2-3 A / dm 2 .

7. The preparation method of an alkaline electrolytic cell bipolar plate with a corrosion-resistant composite coating on the surface according to claim 4, characterized in that, In the step of chemical composite plating of Ni-P / NbC composite coating (3), the composition of the electroless plating solution is as follows: the main salt nickel chloride hexahydrate is 25 - 35 g / L, the reducing agent sodium hypophosphite is 15 - 25 g / L, the complexing agent sodium citrate is 8 - 12 g / L, the complexing agent glycine is 4 - 6 g / L, the buffer sodium acetate is 8 - 12 g / L, the surfactant sodium dodecylbenzenesulfonate is 0.25 - 0.35 g / L, and the stabilizer zinc molybdate is 70 - 80 mg / L; the temperature is 80 - 85 °C, the pH is 5 - 6, and the plating time is 0.5 - 1.5 h; the NbC nanoparticles are obtained by pre-treating the purchased NbC powder through ball milling in a ball mill, with small and uniform particle size; the NbC nanoparticle suspension is obtained by ultrasonically dispersing the above-mentioned pre-treated NbC nanoparticles in deionized water.