Nickel-graphene oxide gradient composite coating and preparation method and application thereof

Abstract

The invention discloses a nickel-graphene oxide gradient composite coating and a preparation method and application thereof. The nickel-graphene oxide gradient composite coating comprises a first coating and a second coating which are sequentially formed on the surface of a base body, and the first coating is formed by first electro-deposition liquid containing a first standard nickel plating solution and first graphene oxide dispersion liquid; the second plating layer is formed by a second electrodeposition solution containing a second standard nickel plating solution and a second graphene oxide dispersion solution, and the concentration of graphene oxide in the second electrodeposition solution is higher than that of graphene oxide in the first electrodeposition solution. The composite coating provided by the invention has excellent hydrogen resistance and corrosion resistance, provides an efficient and economic solution for protection of key parts in the fields of hydrogen energy infrastructure, ocean engineering, aerospace and the like, and has great social and economic values.

Description

Technical Field

[0001] This invention belongs to the field of metal surface protection technology, and particularly relates to a nickel-graphene oxide gradient composite coating, its preparation method and application. Background Technology

[0002] Hydrogen energy, as a crucial carrier of next-generation clean energy, plays a key role in the energy transition. However, during the storage, transportation, and application of hydrogen, hydrogen atoms can easily penetrate into the interior of metal structures, causing hydrogen embrittlement. This leads to reduced plasticity of metal materials, accelerated fatigue crack propagation rates, and even sudden fracture accidents. This problem is particularly prominent in high-pressure hydrogen pipelines, PEM electrolyzers, marine equipment, and aerospace, severely hindering the industrialization of hydrogen energy technology.

[0003] To address the problem of hydrogen permeation, hydrogen barrier coating technology has emerged and been extensively studied. An ideal hydrogen barrier coating should possess low hydrogen permeability, good adhesion, thermal shock resistance, and environmental durability. Early hydrogen barrier coatings primarily relied on oxide ceramic materials (such as... Nitride / carbide coatings (such as TiN and CrN) enhance hydrogen barrier performance by increasing hydrogen diffusion resistance and path tortuosity through the dense barrier they form on the metal surface. For example, plasma-enhanced chemical vapor deposition (PECVD) can be used to prepare hydrogen barrier coatings on stainless steel surfaces. The composite film exhibits excellent deuterium blocking properties below 350°C. Furthermore, the sintered film... Composite oxide coatings have also achieved good hydrogen barrier properties on 316L stainless steel. For example, a method for preparing a graphite-like carbon nitride-yttrium stabilized zirconium oxide composite hydrogen barrier coating (CN118847476B) involves sintering to obtain the graphite-like carbon nitride-yttrium stabilized zirconium oxide composite coating.

[0004] With technological advancements, multilayer composite coatings and novel two-dimensional material composite coatings have gradually become research focuses. For example, physical vapor deposition (PVD) is used to construct multilayer coatings with a hydrogen-solidifying underlayer, a hydrogen-blocking layer, and a GO-rich region that inhibits hydrogen dissociation, thereby further improving the overall performance of the coating. For instance, a yttrium / yttrium oxide composite hydrogen-blocking coating (CN113046695A) discloses a yttrium / yttrium oxide composite hydrogen-blocking coating, which is formed on a metal substrate with the following composition: A single-layer coating.

[0005] Although hydrogen barrier coating technology has made some progress, existing technologies, especially coatings used in conventional aqueous / humid environments (such as marine environments and underground pipelines) and under medium and low temperature conditions, struggle to simultaneously achieve hydrogen barrier properties and other performance characteristics (such as corrosion resistance). Good corrosion resistance is crucial for hydrogen barrier coatings because it effectively blocks the penetration of corrosive media such as water and chloride ions into the coating's interior, inhibiting hydrogen evolution reactions on the substrate surface at the source. This prevents the formation of localized corrosion pits or cracks that provide a rapid pathway for hydrogen atoms to invade the substrate, thus synergistically maintaining and enhancing the overall hydrogen barrier performance and structural integrity of the coating during long-term service.

[0006] Therefore, developing a novel hydrogen barrier coating that can adapt to conventional industrial environments, possesses excellent hydrogen barrier properties, corrosion resistance, good adhesion and durability, and has a simple process and controllable cost has become an urgent need for technological development in this field. Summary of the Invention

[0007] The main objective of this invention is to address the problems and shortcomings of existing technologies by providing a nickel-graphene oxide gradient composite coating with excellent hydrogen barrier properties, corrosion resistance, good adhesion, and durability, as well as its preparation method and application.

[0008] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: A nickel-graphene oxide gradient composite coating includes a first coating and a second coating sequentially formed on the surface of a substrate. The first coating is formed by a first electrodeposition solution comprising a first standard nickel plating solution and a first graphene oxide dispersion. The second coating is formed by a second electrodeposition solution comprising a second standard nickel plating solution and a second graphene oxide dispersion. The concentration of graphene oxide in the second electrodeposition solution is higher than the concentration of graphene oxide in the first electrodeposition solution.

[0009] In the above scheme, the concentration of graphene oxide in the first electrodeposition solution is greater than or equal to 200 mg / L and less than 350 mg / L, and the concentration of graphene oxide in the second electrodeposition solution is greater than or equal to 350 mg / L and less than or equal to 500 mg / L.

[0010] In the above scheme, the thickness of the first coating is 15-20 μm, and the thickness of the second coating is 5-15 μm.

[0011] In the above scheme, both the first and second graphene oxide dispersions are composed of graphene oxide and a dispersant, wherein the dispersant is sodium dodecyl sulfate.

[0012] In the above scheme, the first and second standard nickel plating solutions both include the following components: nickel sulfate hexahydrate 280-320 g / L, nickel chloride hexahydrate 45-55 g / L, boric acid 35-45 g / L, trisodium citrate 0.2-0.4 g / L, and surfactant OP-10 0.5-0.7 g / L.

[0013] A method for preparing a nickel-graphene oxide gradient composite coating includes the following steps: Pretreatment of the metal substrate includes surface grinding, degreasing, and pickling; Prepare a first electrodeposition solution, comprising a first standard nickel plating solution and a first graphene oxide dispersion; The pretreated metal substrate is placed in the first electrodeposition solution for electrodeposition to form the first coating layer; A second electrodeposition solution is prepared, comprising a second standard nickel plating solution and a second graphene oxide dispersion, wherein the concentration of graphene oxide in the second electrodeposition solution is higher than the concentration of graphene oxide in the first electrodeposition solution. The metal substrate with the first coating layer is placed in the second electrodeposition solution for electrodeposition to form the second coating layer.

[0014] In the above scheme, the current density of the electrodeposition process is 3-5 A / dm²; the electrodeposition time of the first coating is 15-18 min, and the electrodeposition time of the second coating is 12-15 min.

[0015] In the above scheme, the preparation of the graphene oxide dispersion includes: mixing graphene oxide and sodium dodecyl sulfate in water at a mass ratio of 1:1 to 1:2; and ultrasonically dispersing the dispersion for 0.5 to 1.5 h using an ultrasonic cell disruptor in a pulse mode with a power of 250-350 W and a start-stop-1-second cycle.

[0016] In the above scheme, the electrodeposition process is carried out in a water bath at 50 ± 5 ℃, accompanied by mechanical stirring at a stirring speed of 15 - 25 RPM.

[0017] The application of the nickel-graphene oxide gradient composite coating in the surface protection of metal parts.

[0018] This invention provides a method for preparing a nickel-graphene oxide gradient composite coating by electrodeposition at room temperature. The graphene oxide content in the coating is adjusted by regulating the graphene oxide concentration in the composite electrodeposition solution. This invention relates to a nickel-graphene oxide gradient composite coating prepared by room-temperature electrodeposition. Its core mechanism lies in achieving multifunctional synergistic protection through gradient structure design: On one hand, the nickel-rich region maintains a high nickel content to form a dense metal matrix, enhancing its bonding with the substrate through metallic bonding. On the other hand, in the Ni-GO composite coating, graphene oxide plays a crucial role in hydrogen blocking due to its unique two-dimensional sheet-like structure. These randomly oriented or parallel-to-the-substrate GO sheets form a complex labyrinthine physical barrier within the nickel matrix, forcing extremely small hydrogen atoms to traverse winding paths within the coating, significantly extending their diffusion distance and reducing their penetration rate. Simultaneously, the dense sp² hybrid carbon mesh structure of the GO sheets themselves exhibits extremely low inherent permeability to hydrogen atoms, forming an impenetrable nanoscale barrier. Furthermore, the numerous interfaces formed between the GO sheets and nickel grain boundaries serve as effective hydrogen trapping sites, fixing and delaying hydrogen atom migration. The grain-refining effect of the GO sheets on nickel grains further increases grain boundary density, collectively significantly enhancing the activation energy for hydrogen diffusion, thus achieving synergistic hydrogen blocking.

[0019] Its anti-corrosion mechanism mainly stems from the following synergistic effect: GO nanosheets are oriented within the nickel matrix, forming a dense physical barrier layer, which, through the "maze effect," greatly extends and hinders the penetration of corrosive media (such as... ion, molecular, The diffusion path of GO into the interior of the coating is facilitated; at the same time, the abundant oxygen-containing functional groups (such as carboxyl groups and epoxy groups) on the surface of GO sheets can effectively adsorb or bond these polar media molecules, reducing their chemical activity at the interface; in addition, the introduction of GO refines the nickel grains and reduces the structural defects of the coating itself, thereby further reducing the tendency for localized corrosion.

[0020] This gradient structure transitions from a "hydrogen barrier" to a "corrosion barrier" through a transition from a nickel-rich region to a GO-rich region, achieving a synergistic enhancement of hydrogen barrier and corrosion resistance. This precise structure can be controlled through a simple room-temperature electrodeposition process by adjusting the GO concentration. By controlling the core process parameter of graphene oxide (GO) concentration, multiple performance improvements in the composite coating, including hydrogen barrier, corrosion resistance, and strong adhesion, can be achieved simultaneously. The fundamental reason is that the GO concentration directly dominates the evolution of the coating's microstructure, triggering a series of synergistic enhancement effects. In the low-concentration region, an appropriate amount of GO acts as a nucleation site, effectively refining the nickel grains and increasing grain boundary density. This not only provides more hydrogen atom capture sites to improve hydrogen barrier properties but also inhibits the formation of corrosion channels by breaking continuous grain boundaries. Simultaneously, the high nickel content in this region ensures a strong bond with the substrate through metallic bonding. As the GO concentration gradient increases to the high-concentration region, numerous GO sheets are oriented and interwoven within the nickel matrix, constructing a dense nanoscale network structure—a structure that effectively resists extremely small hydrogen atoms and corrosive media (such as...). In contrast, the GO surface, together with other components, forms a tortuous "maze-like" physical barrier, significantly extending its diffusion path. Furthermore, the abundant oxygen-containing functional groups on the GO surface can chemically adsorb and immobilize polar corrosion molecules, further delaying interfacial reactions. Therefore, what appears to be a single concentration gradient variable actually achieves, on a macroscopic level, the integrated construction from a "strongly bonded substrate" to a "multifunctional protective surface layer" through a multi-level synergistic mechanism of "grain refinement - maze barrier - chemical adsorption," ultimately endowing the coating with superior comprehensive performance.

[0021] Compared with existing technologies, the beneficial effects of this invention are as follows: By constructing a nickel-graphene oxide (Ni-GO) composite coating with a compositional gradient and employing an optimized electrodeposition process, this invention effectively overcomes the shortcomings of existing technologies, such as the difficulty in simultaneously achieving hydrogen barrier and corrosion resistance, and the complexity of the process. The composite coating provided by this invention possesses both excellent hydrogen barrier and corrosion resistance, significantly extending the service life of metal components under harsh operating conditions such as high-pressure hydrogen pipelines, inner wall coatings of hydrogen storage tanks, PEM electrolyzers, offshore platform structural components, and liquid hydrogen storage tank accessories. It reduces failures and maintenance costs caused by hydrogen embrittlement and corrosion, providing an efficient and economical solution for the protection of key components in hydrogen energy infrastructure, marine engineering, and aerospace, and has significant social and economic value. Attached Figure Description

[0022] Figure 1 A schematic diagram of the hydrogen barrier coating provided in Example 1; Figure 2 Electrochemical hydrogen permeation curves for Example 1 and Comparative Examples 1, 2, 3, and 5; Figure 3 The potentiodynamic polarization curves are for Example 1 and Comparative Examples 1, 2, and 4. Figure 4 The SEM scan images are those of Example 1 and Comparative Example 2; Figure 5 This is the SEM scan image of Comparative Example 3.

[0023] Figure 6 The images shown are cross-sectional SEM scans of Example 1 and Comparative Example 5. Detailed Implementation

[0024] The principles and features of this invention are described below with reference to examples. These examples are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it is worth noting that, unless otherwise specified, all raw materials involved in this invention are commercially available products.

[0025] Example 1

[0026] like Figure 1 As shown, this embodiment provides a nickel-graphene oxide gradient composite coating, which sequentially includes a first coating layer 2 and a second coating layer 3 directly electrodeposited on the surface of a metal substrate 1. The first coating layer 2 is a nickel-rich region, and the second coating layer 3 is a GO-rich region. The first coating layer 2 is electrodeposited by a first electrodeposition solution composed of a first standard nickel plating solution and a first graphene oxide dispersion, and has a high nickel content. The second coating layer 3 is also electrodeposited by a second electrodeposition solution composed of a second standard nickel plating solution and a second graphene oxide dispersion, but has a higher graphene oxide content. The metal substrate is low-carbon steel, offshore platform steel, etc.

[0027] In this embodiment, the metal substrate 1 is X80 pipeline steel, cut into steel sheet samples with dimensions of 20mm×30mm×1mm, and after being sanded to 3000#, the surface oil and dust are cleaned, and after acid pickling and activation, it is dried.

[0028] In this embodiment, the first quasi-nickel plating solution and the second standard nickel plating solution are the same, both containing nickel sulfate hexahydrate. 300g / L, nickel chloride hexahydrate 50g / L, boric acid 40 g / L of sodium citrate, 0.3 g / L of trisodium citrate, and 0.6 g / L of surfactant OP-10 were prepared and placed in a magnetic stirrer at 20 RPM for one hour.

[0029] In this embodiment, the graphene oxide concentration in the first electrodeposition solution is 300 g / L, and the graphene oxide concentration in the second electrodeposition solution is 400 g / L. A sodium dodecyl sulfate solution is prepared and magnetically stirred for half an hour at 20 RPM. The desired amount of graphene oxide is then added to the sodium dodecyl sulfate solution and stirred for another half hour at 20 RPM. The mass ratio of graphene oxide to sodium dodecyl sulfate is 1:1. The stirred dispersions are then placed in an ice-water bath and then into an ultrasonic cell disruptor. Ultrasonic dispersion is performed for one hour at a preset power of 300 W with a 2-second start-1-second stop frequency to obtain well-dispersed first and second graphene oxide dispersions.

[0030] Take an appropriate amount of well-dispersed first graphene oxide dispersion and add it to the first standard nickel plating solution to prepare a first pre-electrodeposition solution with a graphene oxide content of 300 mg / L. Then take an appropriate amount of well-dispersed second graphene oxide dispersion and add it to the second standard nickel plating solution to prepare a second pre-electrodeposition solution with a graphene oxide content of 400 mg / L. Then, put the two pre-electrodeposition solutions into an ice-water bath and place them together in an ultrasonic cell disruptor for ultrasonic dispersion for half an hour to obtain the first electrodeposition solution and the second electrodeposition solution respectively.

[0031] In this embodiment, the X80 pipeline steel sheet is sequentially immersed in a first electrodeposition solution (nickel-rich region) and a second electrodeposition solution (GO-rich region) for electrodeposition. The electrodeposition parameters are a current density of 4 A / dm³. 2 The electrodeposition time for the nickel-rich region was 18 min, and the thickness was 15 μm. The electrodeposition time for the GO-rich region was 12 min, and the thickness was 7 μm.

[0032] In this embodiment, electrodeposition was performed with stirring in a 50°C water bath at a rotation speed of 20 RPM. The resulting sample is as follows: Figure 4 As shown in (#2), the obtained sample cross-section is as follows Figure 6 As shown in (#2).

[0033] The experiment used a Davanathan-Stachursky dual electrolytic cell, with the sample fixed between the cathode and anode chambers, and the effective detection area was 1 cm². 2 The side with the second coating faces the cathode chamber. On the anode chamber side, a three-electrode system is used, with the sample as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum electrode as the auxiliary electrode, connected to the electrochemical workstation by wires; on the cathode chamber side, a two-electrode method is used, with the sample as the cathode and a platinum sheet as the anode.

[0034] In the experiment, a 0.1 mol / L sodium hydroxide solution (to remove dissolved oxygen) was first placed in the anode chamber, and the anode potential was controlled at the open circuit potential +250 mV (relative to the reference electrode). When the background current measured in the anode chamber was less than 0.1 μA / cm², a 0.1 mol / L sulfuric acid solution was then added to the cathode chamber, and a 10 mA / cm² current was applied between the anode and cathode electrodes. 2 The current is applied to the cathode chamber. After applying the current, the hydrogen atom oxidation current in the anode chamber is recorded using an electrochemical workstation, thus obtaining the electrochemical hydrogen permeation curve. The steady-state segment of this curve is positively correlated with the number of hydrogen atoms that permeate through the hydrogen barrier coating; that is, the lower the value of the steady-state segment, the less hydrogen atoms permeate through the hydrogen barrier coating, and the better the effect of the hydrogen barrier coating. The electrochemical permeation curve measured at this time is as follows: Figure 2 As shown in #3.

[0035] The experiment employed a standard three-electrode electrolytic cell system to evaluate the corrosion resistance of the coating. The sample served as the working electrode, with an effective exposed area of ​​1 cm². A saturated calomel electrode served as the reference electrode, and a platinum sheet served as the auxiliary electrode; both were placed in an electrolytic cell containing electrolyte. All electrodes were connected to an electrochemical workstation via wires.

[0036] The electrolyte used in the test was a 3.5 wt% sodium chloride solution to simulate a neutral corrosive environment. At the start of the experiment, the prepared sample was immersed in the electrolyte and allowed to stand for 30 minutes until its open-circuit potential stabilized before the potentiodynamic polarization curve was measured. The test scan started from an initial potential of -0.5 V relative to the open-circuit potential and proceeded towards the positive potential up to +0.5 V (relative to the open-circuit potential), with a scan rate set to 1 mV / s. The current response of the working electrode as a function of potential was recorded using an electrochemical workstation, thus obtaining the potentiodynamic polarization curve.

[0037] Tafel extrapolation analysis of the curve yielded key parameters such as the self-corrosion potential (E_corr) and corrosion current density (i_corr). A higher self-corrosion potential indicates a more thermodynamically stable coating, making it less susceptible to corrosion; a lower corrosion current density indicates a stronger kinetic resistance to corrosion, resulting in a slower corrosion rate. In other words, compared to the control sample, the sample with a significantly positive shift in self-corrosion potential and a significantly lower corrosion current density exhibits superior corrosion resistance.

[0038] The measured potentiodynamic polarization curve at this time is as follows: Figure 3 As shown in #3.

[0039] Comparative Example 1

[0040] X80 pipeline steel is cut into steel sheets with dimensions of 20mm×30mm×1mm. After being sanded to 3000#, the surface is cleaned of oil and dust, and then acid-washed and activated before drying.

[0041] The experiment used a Davanathan-Stachursky dual electrolytic cell, with the sample fixed between the cathode and anode chambers, and the effective detection area was 1 cm². 2 The side with the second coating faces the cathode chamber. On the anode chamber side, a three-electrode system is used, with the sample as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum electrode as the auxiliary electrode, connected to the electrochemical workstation by wires; on the cathode chamber side, a two-electrode method is used, with the sample as the cathode and a platinum sheet as the anode.

[0042] During the experiment, a 0.1 mol / L sodium hydroxide solution (with dissolved oxygen removed) was first placed in the anode chamber. The anode potential was controlled at the open-circuit potential +250 mV (relative to the reference electrode). When the background current measured in the anode chamber was less than 0.1 μA / cm... 2 Then, add 0.1 mol / L sulfuric acid solution to the cathode chamber and apply 10 mA / cm² between the cathode and anode. 2 The current. The electrochemical permeation curve measured at this time is as follows: Figure 2 As shown in #1.

[0043] The experiment employed a standard three-electrode electrolytic cell system to evaluate the corrosion resistance of the coating. The sample served as the working electrode, with an effective exposed area of ​​1 cm². A saturated calomel electrode served as the reference electrode, and a platinum sheet served as the auxiliary electrode; both were placed in an electrolytic cell containing electrolyte. All electrodes were connected to an electrochemical workstation via wires.

[0044] The electrolyte used in the test was a 3.5 wt% sodium chloride solution to simulate a neutral corrosive environment. At the start of the experiment, the prepared sample was immersed in the electrolyte and allowed to stand for 30 minutes until its open-circuit potential stabilized before the potentiodynamic polarization curve was measured. The test scan started from an initial potential of -0.5 V relative to the open-circuit potential and proceeded towards the positive potential up to +0.5 V (relative to the open-circuit potential), with a scan rate set to 1 mV / s. The current response of the working electrode as a function of potential was recorded using an electrochemical workstation, thus obtaining the potentiodynamic polarization curve. The measured potentiodynamic polarization curve is shown below. Figure 3 As shown in #1.

[0045] Comparative Example 2

[0046] X80 pipeline steel is cut into steel sheets with dimensions of 20mm×30mm×1mm. After being sanded to 3000#, the surface is cleaned of oil and dust, and then acid-washed and activated before drying.

[0047] In this comparative example, the nickel plating solution contains nickel sulfate hexahydrate. 300g / L, nickel chloride hexahydrate 50g / L, boric acid 40 g / L of sodium citrate, 0.3 g / L of trisodium citrate, and 0.6 g / L of surfactant OP-10 were prepared and placed in a magnetic stirrer at 20 RPM for one hour.

[0048] In this comparative example, X80 pipeline steel sheets were electrodeposited in a nickel plating solution. The electrodeposition parameters were a current density of 4 A / dm³. 2 The electrodeposition time was 30 min, and the thickness was 20-30 μm.

[0049] In this comparative example, electrodeposition was performed with stirring in a 50°C water bath at a rotation speed of 20 RPM. The resulting sample is as follows. Figure 4 As shown in (#1).

[0050] The experiment used a Davanathan-Stachursky dual electrolytic cell, with the sample fixed between the cathode and anode chambers, and the effective detection area was 1 cm². 2 The side with the second coating faces the cathode chamber. On the anode chamber side, a three-electrode system is used, with the sample as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum electrode as the auxiliary electrode, connected to the electrochemical workstation by wires; on the cathode chamber side, a two-electrode method is used, with the sample as the cathode and a platinum sheet as the anode.

[0051] During the experiment, a 0.1 mol / L sodium hydroxide solution (with dissolved oxygen removed) was first placed in the anode chamber. The anode potential was controlled at the open-circuit potential +250 mV (relative to the reference electrode). When the background current measured in the anode chamber was less than 0.1 μA / cm... 2 Then, add 0.1 mol / L sulfuric acid solution to the cathode chamber and apply 10 mA / cm² between the cathode and anode. 2 The current. The electrochemical permeation curve measured at this time is as follows: Figure 2 As shown in #2.

[0052] The experiment employed a standard three-electrode electrolytic cell system to evaluate the corrosion resistance of the coating. The sample served as the working electrode, with an effective exposed area of ​​1 cm². A saturated calomel electrode served as the reference electrode, and a platinum sheet served as the auxiliary electrode; both were placed in an electrolytic cell containing electrolyte. All electrodes were connected to an electrochemical workstation via wires.

[0053] The electrolyte used in the test was a 3.5 wt% sodium chloride solution to simulate a neutral corrosive environment. At the start of the experiment, the prepared sample was immersed in the electrolyte and allowed to stand for 30 minutes until its open-circuit potential stabilized before the potentiodynamic polarization curve was measured. The test scan started from an initial potential of -0.5 V relative to the open-circuit potential and proceeded towards the positive potential up to +0.5 V (relative to the open-circuit potential), with a scan rate set to 1 mV / s. The current response of the working electrode as a function of potential was recorded using an electrochemical workstation, thus obtaining the potentiodynamic polarization curve. The measured potentiodynamic polarization curve is shown below. Figure 3 As shown in #2.

[0054] Comparative Example 3

[0055] Cut the X80 pipeline steel into steel sheets measuring 20mm×30mm×1mm, sand them with sandpaper to 3000#, clean off any oil and dust from the surface, and then dry them.

[0056] In this comparative example, graphene oxide was prepared into a uniform dispersion with a concentration of 8.4 mg / mL. The graphene oxide concentration in this dispersion was significantly higher than the 300-400 mg / L graphene oxide concentration in the electrodeposition solution of Example 1. The dispersion was uniformly sprayed onto the surface of an X80 pipeline steel sheet using a spraying device, and then dried and cured at 80°C. The spray-drying process was repeated 10 times to obtain sufficient coating thickness, with the final dry film thickness controlled at 15-20 μm.

[0057] The experiment used a Davanathan-Stachursky dual electrolytic cell, with the sample fixed between the cathode and anode chambers, and the effective detection area was 1 cm². 2 The side with the second coating faces the cathode chamber. On the anode chamber side, a three-electrode system is used, with the sample as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum electrode as the auxiliary electrode, connected to the electrochemical workstation by wires; on the cathode chamber side, a two-electrode method is used, with the sample as the cathode and a platinum sheet as the anode.

[0058] In the experiment, a 0.1 mol / L sodium hydroxide solution (to remove dissolved oxygen) was first placed in the anode chamber, and the anode potential was controlled at the open circuit potential +250 mV (relative to the reference electrode). When the background current measured in the anode chamber was less than 0.1 μA / cm², a 0.1 mol / L sulfuric acid solution was then added to the cathode chamber, and a 10 mA / cm² current was applied between the anode and cathode electrodes. 2 The current. The electrochemical permeation curve measured at this time is as follows: Figure 2 As shown in #4.

[0059] Comparative Example 4

[0060] This comparative example is largely the same as Example 1, except that the two electrodepositions of the gradient graphene oxide coating with concentrations of 300 mg / L and 400 mg / L in Example 1 are replaced by a single electrodeposition of a single concentration graphene oxide coating with a concentration of 300 mg / L. The electrodeposition time is 30 min and the thickness is 25 μm.

[0061] The corrosion resistance test for this comparative example is the same as that in Example 1. The measured potentiodynamic polarization curve is as follows: Figure 3 As shown in #4.

[0062] Comparative Example 5

[0063] This comparative example is largely the same as Example 1, except that the step of using the ultrasonic cell disruptor in Example 1, which involves placing the stirred dispersion in an ice-water bath and then into the ultrasonic cell disruptor, and ultrasonically dispersing it for one hour at a preset power of 300W with a 2s start-1s stop frequency to obtain well-dispersed first and second graphene oxide dispersions, is replaced with a conventional ultrasonic oscillator for one hour. Additionally, the step of "again placing the two pre-electrodeposition solutions in an ice-water bath and then into the ultrasonic cell disruptor for ultrasonic dispersion for half an hour to obtain the first and second electrodeposition solutions" in Example 1 is replaced with a conventional ultrasonic oscillator for half an hour. The electrodeposition time is 30 minutes, and the thickness is 24 μm. The resulting sample is as follows. Figure 6 As shown in (#1).

[0064] The hydrogen permeation test in this comparative example was the same as in Example 1. The electrochemical permeation curve obtained at this time is as follows: Figure 2 As shown in #5.

[0065] Significantly improved hydrogen barrier performance: as shown in the attached document Figure 2 As shown in Example 1, the steady-state hydrogen permeation current density of the gradient Ni-GO composite coating (#3) of the present invention is significantly reduced to 1-2 μA / cm². This effect stems from the "maze effect" formed by the GO sheets within the coating and the numerous hydrogen traps formed by the GO sheets and nickel grain boundaries, which greatly increases the tortuosity and energy barrier of hydrogen diffusion. Compared with the uncoated substrate (#1) in Comparative Example 1, the hydrogen barrier efficiency is improved by 71%. Compared with the pure nickel coating (#2) in Comparative Example 2, the hydrogen barrier efficiency is improved by 83%, and it can be seen that the pure nickel coating plays a certain role in promoting hydrogen permeation. Compared with the pure graphene oxide coating (#4) in Comparative Example 3, the hydrogen barrier efficiency is improved by 34%, and the surface of the pure graphene oxide coating is uneven with many wrinkles, such as... Figure 5As shown, this will lead to poor adhesion. This invention achieves better hydrogen barrier effect with less GO and does not have the problem of poor adhesion. Compared with the conventionally dispersed graphene oxide (#5) in Comparative Example 5, the hydrogen barrier efficiency is improved by 57%, and the conventionally dispersed graphene oxide is prone to agglomeration in the coating, resulting in a large number of protrusions on the surface, such as... Figure 6 As shown, agglomeration leads to a decrease in hydrogen barrier performance. This invention uses a two-step ultrasonic cell disruption method to obtain a well-dispersed graphene oxide dispersion that does not agglomerate in the coating.

[0066] Corrosion resistance is enhanced simultaneously: such as Figure 3 As shown in the potentiodynamic polarization test results of Example 1, the self-corrosion potential (E_corr) of the composite coating (#3) of the present invention in 3.5 wt% NaCl solution is significantly more positively shifted compared to the uncoated substrate (#1) of Comparative Example 1, the pure nickel coating (#2) of Comparative Example 2, and the coating of graphene oxide with a concentration of 300 mg / L in Comparative Example 4 (#4), and the self-corrosion current density is lower than that of the substrate. This is mainly due to the dense physical barrier formed by the high concentration of GO in the GO-rich region, which effectively blocks the penetration of corrosive media, and the two-step ultrasonic pulverization and dispersion, which ensures that the graphene oxide is uniformly distributed without agglomeration, further improving performance.

[0067] Excellent coating adhesion and structural stability: Through gradient structure design, the nickel-rich area maintains a high nickel content, and the metal bonding effect ensures a strong bond between the coating and the metal substrate, avoiding the risk of peeling due to stress or thermal shock during service, and ensuring the stability of long-term protection.

[0068] This invention employs a room-temperature electrodeposition process, eliminating the need for the high temperatures, high vacuum, or complex equipment required by existing technologies (such as PVD, CVD, or sintering), thus significantly reducing equipment investment and energy costs. By simply adjusting the GO concentration and electrodeposition time in the electrodeposition solution, precise control of the gradient structure can be achieved. The process is simple, highly repeatable, and well-suited for large-scale industrial production and uniform coating of complex-shaped components. The composite coating provided by this invention possesses both excellent hydrogen barrier properties and corrosion resistance, significantly extending the service life of metal components under harsh conditions such as high-pressure hydrogen pipelines, inner wall coatings of hydrogen storage tanks, PEM electrolyzers, offshore platform structural components, and liquid hydrogen storage tank accessories. It reduces failures and maintenance costs caused by hydrogen embrittlement and corrosion, providing an efficient and economical solution for the protection of critical components in hydrogen energy infrastructure, marine engineering, and aerospace, demonstrating significant social and economic value.

[0069] It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept, and these all fall within the scope of protection of this invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A nickel-graphene oxide gradient composite coating, characterized in that, The nickel-graphene oxide gradient composite coating includes a first coating and a second coating sequentially formed on the surface of a substrate. The first coating is formed by a first electrodeposition solution comprising a first standard nickel plating solution and a first graphene oxide dispersion. The second coating is formed by a second electrodeposition solution comprising a second standard nickel plating solution and a second graphene oxide dispersion. The concentration of graphene oxide in the second electrodeposition solution is higher than the concentration of graphene oxide in the first electrodeposition solution.

2. The nickel-graphene oxide gradient composite coating as described in claim 1, characterized in that, The concentration of graphene oxide in the first electrodeposition solution is greater than or equal to 200 mg / L and less than 350 mg / L, and the concentration of graphene oxide in the second electrodeposition solution is greater than or equal to 350 mg / L and less than or equal to 500 mg / L.

3. The nickel-graphene oxide gradient composite coating as described in claim 1, characterized in that, The thickness of the first coating is 15-20 μm, and the thickness of the second coating is 5-15 μm.

4. The nickel-graphene oxide gradient composite coating as described in claim 1, characterized in that, Both the first and second graphene oxide dispersions are composed of graphene oxide and a dispersant, wherein the dispersant is sodium dodecyl sulfate.

5. The nickel-graphene oxide gradient composite coating as described in claim 1, characterized in that, The first and second standard nickel plating solutions both contain the following components: nickel sulfate hexahydrate 280-320 g / L, nickel chloride hexahydrate 45-55 g / L, boric acid 35-45 g / L, trisodium citrate 0.2-0.4 g / L, and surfactant OP-10 0.5-0.7 g / L.

6. A method for preparing a nickel-graphene oxide gradient composite coating, characterized in that, Includes the following steps: Pretreatment of the metal substrate includes surface grinding, degreasing, and pickling; Prepare a first electrodeposition solution, comprising a first standard nickel plating solution and a first graphene oxide dispersion; The pretreated metal substrate is placed in the first electrodeposition solution for electrodeposition to form the first coating layer; A second electrodeposition solution is prepared, comprising a second standard nickel plating solution and a second graphene oxide dispersion, wherein the concentration of graphene oxide in the second electrodeposition solution is higher than the concentration of graphene oxide in the first electrodeposition solution. The metal substrate with the first coating layer is placed in the second electrodeposition solution for electrodeposition to form the second coating layer.

7. The preparation method according to claim 6, characterized in that, The current density of the electrodeposition process is 3-5 A / dm²; the electrodeposition time of the first coating is 15-18 min, and the electrodeposition time of the second coating is 12-15 min.

8. The preparation method according to claim 6, characterized in that, The preparation of the graphene oxide dispersion includes: mixing graphene oxide and sodium dodecyl sulfate in water at a mass ratio of 1:1 to 1:2; and ultrasonically dispersing the mixture for 0.5 to 1.5 h using an ultrasonic cell disruptor in a pulse mode with a power of 250-350 W and a start-stop-1-second cycle.

9. The preparation method according to claim 6, characterized in that, The electrodeposition process was carried out in a water bath at 50 ± 5 ℃ with mechanical stirring at a speed of 15 - 25 RPM.

10. The application of the nickel-graphene oxide gradient composite coating as described in claim 1 in the surface protection of metal parts.

Images