Electrocatalytic plating

Abstract

The invention discloses a process for plating a polar plate of an electrolytic bath. The process comprises the following steps: pretreating the polar plate and plating a nickel-cobalt alloy on the polar plate through electro-deposition. A nickel-cobalt alloy is electrodeposited from the eutectic solvent to form a nanocrystalline electrocatalytic coating having corrosion resistance.

Description

Technical Field

[0001] This invention relates to the electrocatalytic coating of electrolytic cell plates. Background Technology

[0002] Compared to other energy sources, hydrogen is an ideal clean energy source due to its high calorific value, high energy density, and multiple storage options. There are various methods for hydrogen production. Hydrogen production through water electrolysis has gained a foothold in the market due to its high purity, simple operation, and zero pollution, and is the most commonly used method for converting renewable energy into hydrogen storage. However, currently less than 4% of hydrogen production is based on electrolysis, with the majority being hydrogen produced as a byproduct of chlorine production. Therefore, the majority of the required hydrogen relies on fossil fuel routes such as natural gas steam reforming. This is because high electricity costs and related laws and regulations make the production cost of electrolysis higher than that of traditional fossil fuels. To reduce CO2 emissions and reduce dependence on fossil fuels, a significant increase in the share of hydrogen produced using renewable energy sources is needed in the coming decades. Therefore, water electrolysis is a key technology for using renewable energy to decompose water into hydrogen and oxygen. After drying and removal of oxygen impurities, the hydrogen purity is higher than 99.9% and can be used directly.

[0003] There are three commonly used technologies for water electrolysis: alkaline water electrolysis (AWE), proton exchange membrane (or polymer electrolyte membrane) electrolysis (PEMEL), and solid oxide electrolysis (SOEL). While low-temperature technologies AWE and PEMEL have high technological maturity, high-temperature SOEL technology is still under development. Therefore, investment cost and service life determine the most advantageous system design for large-scale application of AWE or PEMEL. Currently, the investment cost of AWE is lower than that of PEMEL. Furthermore, compared to PEMEL systems, alkaline water electrolyzers have a longer service life and lower annual maintenance costs.

[0004] The shortcomings of AWE are being gradually overcome with further technological advancements. Because it does not require precious metals, AWE systems have lower capital expenditures, but they face the challenge of corrosion that affects durability and efficiency.

[0005] Therefore, the object of the present invention is to improve the efficiency of alkaline water electrolysis (AWE) by providing an electrocatalytic coating on the electrode plates of the electrolyzer. Summary of the Invention

[0006] One aspect of the present invention provides a plating process for electrolytic cell electrode plates, the steps of which include: The electrode plates are pretreated; and A nickel-cobalt alloy is plated onto the electrode plate by electrodeposition. The nickel-cobalt alloy is electrodeposited from a eutectic solvent to form a corrosion-resistant nanocrystalline electrocatalytic coating.

[0007] Advantageously, pretreatment ensures that the electrode plate is free of any impurities or foreign matter, thereby enabling the coating to adhere firmly to the surface of the substrate.

[0008] Advantageously, electrodeposition is performed using a eutectic solvent (DES); a non-aqueous electrolyte is chosen because gas escape at the anode / solution interface is negligible, high current efficiency can be obtained, and the eutectic solvent is mild and non-corrosive compared to aqueous acidic solutions.

[0009] Preferably, the electrode plate is made of 316 stainless steel (SS316).

[0010] In one embodiment, the pretreatment of the electrode plate can be achieved by grinding, pickling, chromium removal, Wood's nickel impact plating, or a combination thereof.

[0011] In one embodiment, the molar ratio of nickel to cobalt is preferably in the range of 0.1:0.1 to 2:2.

[0012] Preferably, the molar ratio of nickel to cobalt is 2:1.

[0013] In one embodiment, the eutectic solvent is a mixture of choline chloride, ethylene glycol, nickel chloride, and cobalt chloride.

[0014] In one embodiment, a nickel-cobalt alloy is deposited on the electrode plate using a time-potential electrodeposition method with an applied current of 1 mA to 3 mA for a duration of up to 20 minutes.

[0015] In one embodiment, the average grain size of the coating is less than 500 nm.

[0016] Advantageously, compared to bare SS316 (without Ni-Co alloy coating), Ni-Co alloy-plated SS316 exhibits better durability in alkaline water electrolysis, and there is no obvious catalyst layer peeling off the electroplated SS316 surface.

[0017] Advantageously, this process provides a feasible method for depositing a smooth nanocrystalline Ni-Co alloy coating on SS316 using a eutectic solvent under ambient conditions via time-potential electrodeposition.

[0018] Another aspect of the present invention provides an electrode plate comprising: Nickel-cobalt alloy coating; The nickel-cobalt alloy is electrodeposited from a eutectic solvent to form a corrosion-resistant nanocrystalline electrocatalytic coating.

[0019] Another aspect of the present invention provides an electrode plate for alkaline water electrolysis and anion exchange membrane electrolysis.

[0020] Advantageously, the electrode plate improves the efficiency of alkaline water electrolysis, thereby potentially reducing the cost of hydrogen. Attached Figure Description

[0021] The present invention will now be further described with reference to the accompanying drawings, which illustrate possible embodiments of the invention. Of course, other embodiments of the invention may also be employed; therefore, the specific details shown in the drawings should not be construed as replacing the general description of the invention above.

[0022] Figure 1a This shows the effect of a constant current of 1 mA / cm. 2 Timing potential deposition curves under these conditions; Figure 1b A stainless steel plate coated with a Ni-Co alloy is shown, prepared by chronopotential electrodeposition. Figure 1c A scanning electron microscope (SEM) image of a stainless steel plate coated with a Ni-Co alloy, prepared by chronopotential electrodeposition, is shown. Figure 2 The image shows a pretreated stainless steel plate coated with a Ni-Co alloy, prepared by chronopotential electrodeposition. Figure 3 The image shows Ni-Co alloy nanocrystals deposited on a pretreated stainless steel plate; Figure 4a and 4b Scanning electron microscopy-energy dispersive X-ray diffraction (SEM-EDX) analysis of pretreated stainless steel plates coated with Ni-Co alloy under different chronopotential electrodeposition times and applied currents is shown. Figure 5 The corrosion analysis of the anodic polarization curves of pretreated bare stainless steel plates and Ni-Co plated stainless steel plates before and after alkaline water electrolysis is shown. Figure 6 The hydrogen evolution reaction (HER) potentials measured in cyclic voltammetry plots are shown using pretreated bare stainless steel plates and stainless steel plates plated with Ni-Co alloy. Detailed Implementation

[0023] This invention discloses a process for depositing an electrocatalytic coating on the electrode plate of an electrolytic cell, wherein the coating remains stable in a strongly alkaline medium.

[0024] The application of platinum as a catalyst in water electrolysis is limited by its cost and supply. Non-platinum group metals such as nickel and nickel-cobalt alloys can be used as catalytic coatings for alkaline water electrolysis.

[0025] This invention discloses a method for electrodepositing a nickel (Ni) and cobalt (Co) alloy on an electrolytic cell electrode plate using a eutectic solvent (DES) to form a smooth electrocatalytic coating for alkaline water electrolysis (AWE).

[0026] The process steps for coating the electrode plate include pretreatment of the electrode plate and electrodeposition of a nickel-cobalt alloy onto the electrode plate by electrodeposition. The nickel-cobalt alloy is electrodeposited from a eutectic solvent to form a nanocrystalline electrocatalytic coating with an average grain size of less than 500 nm. Preferably, the electrode plate is 316 stainless steel (SS316), and the electrolyte used for electrodeposition contains a eutectic solvent of choline chloride and ethylene glycol, wherein nickel chloride and cobalt chloride are dissolved. The molar ratio of Ni:Co is from 0.1:0.1 to 2:2. Preferably, the molar ratio of Ni:Co is 2:1.

[0027] Pretreatment requires cleaning the surface of the stainless steel plate to ensure that there are no impurities or foreign objects on the electrode plate, so that the coating can adhere firmly to the substrate surface. Examples of pretreatment include polishing, grinding, acid treatment, chromium removal, Wood's nickel impact plating, or a combination thereof. The pretreatment is preferably Wood's nickel impact plating because the Ni-Co alloy coating will not peel off when the resulting electrode plate is used for alkaline water electrolysis.

[0028] Electrodeposition of the electrocatalytic coating was performed using a eutectic solvent (DES). A non-aqueous electrolyte was chosen because gas escape at the anode / solution interface is negligible, resulting in high current efficiency. Furthermore, compared to aqueous acidic solutions, the DES is mild and non-corrosive. Using DES also avoids the use of corrosive acidic electrolytes and environmentally harmful volatile solvents. On the other hand, non-aqueous volatile solvents limit the solubility and electrochemical stability of the metal precursor. Additionally, hydrogen embrittlement occurs when depositing metals using conventional aqueous electrolytes.

[0029] The current range is 1mA / cm 2 Up to 3mA / cm 2 A chronopotential electrodeposition method with a duration of up to 20 minutes was used to deposit Ni-Co alloy onto the electrode plate. The chronopotential method was selected based on physical observation of the deposited coating and scanning electron microscopy (SEM) analysis of the coating morphology on the electrode plate.

[0030] In multivariate testing, compared to the reversible hydrogen electrode (RHE), the method using a eutectic solvent and a current density of 2 mA / cm² showed better performance. 2The electrode prepared by electrodeposition time of 10 minutes and molar ratio of Ni-Co alloy coating of 2:1 exhibits a reduced hydrogen evolution reaction (HER) overpotential of -0.20 V, and its overpotential is reduced by nearly 30% compared with the bare electrode, thus improving efficiency.

[0031] Figure 1a It shows 1mA / cm 2 The chronopotential deposition curves under constant current show the formation of a smooth coating on the electrode plate. This figure depicts typical voltage-time curves for transient nucleation and diffusion-limited island growth. Initially, the double-layer charging potential is more negative and the overpotential increases; when a sufficient potential favorable for ion discharge is reached, transient nucleation, representing electrodeposition, occurs. The potential then decreases, indicating an increase in the electroactive area on the stainless steel plate serving as the working electrode.

[0032] Figure 1b Stainless steel plates coated with Ni-Co alloys, prepared by chronopotential electrodeposition, are shown. The stainless steel plates, labeled Ni-Co 1, Ni-Co 2, and Ni-Co 3, were prepared by chronopotential electrodeposition at 1 mA / cm². 2 2mA / cm 2 and 3 mA / cm 2 Timing potential electrodeposition of Ni-Co alloy was performed at a current of 2:1 molar ratio for 5 minutes. Under the same deposition time, a higher current density resulted in a thicker coating.

[0033] Figure 1c This image shows a scanning electron microscope (SEM) image of a stainless steel plate coated with a Ni-Co alloy, prepared by chronopotential electrodeposition. The SEM image on the left is of a Ni-Co alloy with a molar ratio of 2:1 (Ni: 20.945 wt.%; Co: 9.823 wt.%) at 1 mA / cm². 2 The image shows the morphology obtained by electrodeposition at a current of 1 mA / cm² for 5 minutes, while the image on the right shows a Ni-Co alloy with a molar ratio of 1:1 (Ni: 14.70 wt.%; Co: 22.71 wt.%) at 1 mA / cm². 2 The morphology obtained by electrodeposition at a given current for 5 minutes is shown in the images. The obtained images show that the Ni-Co alloy coating deposited on the stainless steel plate showed no cracks. The smooth, crack-free coating has better adhesion to the substrate (SS316 plate), thereby increasing the electrocatalytic active area and reducing the possibility of accelerated corrosion due to exposure of the stainless steel plate surface to alkaline media. Changing the Ni:Co ratio in the DES electrolyte can alter the Ni-Co alloy content in the electrodeposited layer. The Ni-rich coating exhibits superior performance in the hydrogen evolution reaction (HER).

[0034] Figure 2This paper shows a pretreated stainless steel sheet coated with a Ni-Co alloy, prepared by time-potential electrodeposition. The stainless steel sheet underwent polishing pretreatment before the Ni-Co alloy coating was deposited, followed by the application of different electrodeposition parameters (Ni-Co alloy ratio, electrodeposition time) to achieve the Ni-Co alloy coating. Compared to the stainless steel sheet shown in Figure 1, Figure 2 The pretreated stainless steel plate shown has a smoother Ni-Co alloy coating deposited on it.

[0035] Figure 3 This study demonstrates the deposition of Ni-Co alloy nanocrystals on a pretreated stainless steel plate. A smooth and dense Ni-Co alloy (2:1 molar ratio) nanocrystal coating with an average grain size of less than 500 nm was obtained by electrodeposition on stainless steel using a choline chloride and ethylene glycol eutectic solvent (DES) as the electrolyte. The submicron-scale smooth coating exhibits better adhesion to the substrate (SS316 plate), thereby increasing the electrocatalytic active area and reducing the likelihood of faster corrosion of the substrate surface when exposed to alkaline media.

[0036] Figure 4a and 4b The deposition of Ni-Co alloy on pretreated stainless steel plates is shown, depending on the electrodeposition time and applied current, according to different timing potentials. Figure 4a It can be seen that a 10-minute electrodeposition time yields a thicker Ni-Co alloy coating with a thickness of 598.4 nm, compared to electrodeposition times of 5 and 15 minutes. Although the coating thickness is positively correlated with the electrodeposition time, the thicker electrodeposited coating is formed by 3D nucleation of the electrodeposited material, making it prone to cracking and ultimately leading to detachment due to poor adhesion to the stainless steel electrode. Figure 4b As shown, with 1mA / cm 2 and 3mA / cm 2 Compared to the electrodeposition current, when the electrodeposition current is 2mA / cm 2 At this time, a Ni-Co alloy coating with a thickness of 598.4 nm can be obtained, and this current density is determined to be the optimal current density.

[0037] To test the durability of the Ni-Co alloy coating deposited on a pretreated stainless steel (SS316) substrate, alkaline water electrolysis was performed continuously for more than 40 minutes using 1.0M KOH as the electrolyte. Compared with the bare substrate (without Ni-Co alloy coating), the Ni-Co alloy-coated substrate exhibited better durability, and there was no obvious catalyst layer peeling on the surface of the coated substrate.

[0038] Table 1: Alkaline water electrolysis of substrates plated with Ni-Co alloy (plating area 0.5 cm²)2 )

[0039] Table 1 Ni-Co alloys can be used as electrocatalytic coatings for alkaline water electrolysis. Compared with bare stainless steel, they can maintain the durability of alkaline water electrolysis systems under harsh conditions such as alkaline media.

[0040] Figure 5 Corrosion analysis of bare stainless steel substrates and coated stainless steel substrates before and after alkaline water electrolysis is shown. Polarization curves show similar trends for both the bare substrate and the substrate with Ni-Co alloy coating; after water electrolysis, the Ecorr values ​​(Table 2) all show a positive shift. This positive shift in Ecorr values ​​after electrolysis indicates a thicker passivation layer and enhanced corrosion resistance. The Ecorr values ​​for the bare substrate (after electrolysis) and the substrate with Ni-Co alloy coating (after electrolysis) shift positively to -0.26877 V and -0.23963 V, respectively. Comparing corrosion rate values, the corrosion rate values ​​for both the substrate with Ni-Co alloy coating (before and after electrolysis) and the bare substrate (after electrolysis) are higher than those for the bare substrate, indicating improved corrosion resistance of the stainless steel substrate. However, for the bare substrate, a higher degree of passivation may lead to an increased overpotential during alkaline water electrolysis, resulting in greater energy consumption during the electrolysis process. In the passivation zone (region 3), the current of the substrate with the Ni-Co alloy coating did not change significantly before and after water electrolysis, indicating that the coating was stable. In region 4, the current slope of the bare substrate was higher than that of the substrate with the Ni-Co alloy coating. This indicates that the overpassivation rate of the Ni-Co alloy is slower, meaning that the coating effectively slows down corrosion. Even after electrolysis, the slope of the substrate with the Ni-Co alloy coating remained unchanged, indicating good coating stability and improved corrosion resistance.

[0041] Table 2: I of bare substrates and substrates with Ni-Co alloy coating CORR and E CORR value

[0042] Table 2 Figure 6 The hydrogen evolution reaction (HER) potentials on cyclic voltammograms are shown for a bare substrate after pretreatment and a substrate with a Ni-Co alloy coating. Compared to the bare substrate, the HER overpotential of the coated substrate is reduced by up to 30%, indicating that it has electrocatalytic activity.

[0043] Table 3: Comparison of HER electrochemical overpotentials between bare substrates and substrates with Ni-Co alloy coatings

[0044] Table 3 This invention provides a feasible method for depositing a smooth nanocrystalline Ni-Co alloy coating on SS316 using a eutectic solvent under environmental conditions via a time-potential electrodeposition method. The SS316 coated in this way can be used for alkaline water electrolysis and anion exchange membrane electrolysis.

Claims

1. A plating process for electrolytic cell electrode plates, comprising the following steps: Pre-treatment of the electrode plates; as well as Nickel-cobalt alloy was plated onto the electrode plate by electrodeposition. The feature is that the nickel-cobalt alloy is electrodeposited from a eutectic solvent to form a corrosion-resistant nanocrystalline electrocatalytic coating.

2. The process according to claim 1, characterized in that: The electrode plate is preferably made of 316 stainless steel (SS316).

3. The process according to claim 1, characterized in that: The pretreatment of the electrode plate includes: polishing, pickling, chromium removal, Wood's nickel impact plating, or any combination thereof.

4. The process according to claim 1, characterized in that: The molar ratio of nickel to cobalt is in the range of 0.1:0.1 to 2:

2.

5. The process according to claim 1, characterized in that: The preferred molar ratio of nickel to cobalt is 2:

1.

6. The process according to claim 1, characterized in that: The eutectic solvent is a mixture of choline chloride, ethylene glycol, nickel chloride, and cobalt chloride.

7. The process according to claim 1, characterized in that: The applied current is 1 mA / cm 2 Up to 3mA / cm 2 A nickel-cobalt alloy is deposited on the electrode plate by a time-potential electrodeposition method with a duration of up to 20 minutes.

8. The process according to claim 1, characterized in that: The average grain size of the coating is less than 500 nm.

9. The electrode plate obtained by the process according to claim 1, comprising: Coating of nickel-cobalt alloy; The feature is that the nickel-cobalt alloy is electrodeposited from a eutectic solvent to form a corrosion-resistant nanocrystalline electrocatalytic coating.

10. The application of the electrode plate as described in claim 9 in alkaline water electrolysis and anion exchange membrane electrolysis.

Images