Cathode capable of resisting iron ion deposition, preparation method and equipment

Abstract

The invention discloses an iron ion deposition resistant cathode, a preparation method and equipment wherein the cathode comprises a hydrogen evolution electrode substrate and a composite layer formed on the surface of the electrode substrate, the composite layer is a porous and hydrophobic polytetrafluoroethylene functional layer, and the thickness of the polytetrafluoroethylene functional layer is 50-200 nm. According to the scheme, optimization is conducted from the two aspects of the electrode structure and the film layer composition, iron ions are prevented from approaching and being reduced to the active surface of the electrode in a long-acting mode, and therefore performance degradation caused by iron pollution is greatly relieved, and the long-term operation efficiency and service life of the electrolytic cell are guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of water electrolysis hydrogen production technology, specifically relating to a cathode resistant to iron ion deposition, its preparation method and equipment, particularly to a hydrogen evolution cathode for alkaline water electrolysis cells, and especially to a surface composite layer that can effectively resist the electrochemical deposition of iron ions and its preparation method. Background Technology

[0002] Water electrolysis technology is one of the core pathways to achieve large-scale green hydrogen production. Among them, alkaline water electrolysis technology dominates due to its mature technology and relatively low cost. In this system, the hydrogen evolution reaction cathode is a key component determining the efficiency and lifespan of the electrolyzer. In the actual industrial operation of alkaline water electrolysis, a long-standing and difficult-to-eradicate problem is the electrochemical deposition and contamination of iron impurities on the surface of the hydrogen evolution cathode. This problem mainly stems from the following aspects: the electrolyte (KOH / NaOH) itself may contain trace amounts of iron impurities; stainless steel pipes, valves, circulating pumps, and other components widely used in the electrolyzer system continuously dissolve iron species under the corrosive effects of high temperature and high concentration of alkaline solution, mainly existing in the form of soluble ferrates (such as K2FeO4) in the electrolyte. These iron ions undergo electrochemical reduction deposition at the cathode potential, forming Fe or Fe(OH)2 deposition layers. This leads to the following problems: the active sites on the cathode surface are covered, physically blocking the hydrogen evolution reaction; the adsorption energy of metallic iron for hydrogen intermediates (H*) is usually different from that of highly active cathode catalysts (such as Raney nickel), resulting in an increase in hydrogen evolution overpotential and energy consumption; the initially deposited iron layer increases the specific surface area and reduces the hydrogen evolution overpotential, but at the same time provides nucleation sites for subsequent iron deposition, accelerating performance degradation; under shutdown or operating condition fluctuations, the deposited iron may redissolve and migrate within the electrolyzer, even contaminating the diaphragm or other components, causing more widespread systemic problems.

[0003] To address the iron deposition problem, several approaches have been explored, but all have significant limitations. Using high-purity KOH and deionized water is costly and difficult to maintain long-term, representing passive and temporary mitigation measures. Replacing some stainless steel components with more corrosion-resistant materials like titanium drastically increases costs and cannot completely eliminate iron introduction. Adding chelating agents (such as EDTA) can lead to decomposition and contamination over long-term operation. Introducing a protective layer on the electrode surface, while traditional dense coatings block iron ions, also severely hinders mass transfer between reactants and products, leading to an increase in hydrogen evolution overpotential.

[0004] In summary, current technologies lack an effective method to fundamentally and sustainably prevent iron ions from approaching and being reduced to the electrode surface without significantly affecting the intrinsic hydrogen evolution activity of the cathode. There is an urgent need to develop a cathode with an intrinsic resistance to Fe deposition, controllable cost, and long-term stability, featuring a surface composite layer.

[0005] Therefore, in order to address the above-mentioned technical problems, it is necessary to provide a cathode resistant to iron ion deposition, its preparation method, and equipment. Summary of the Invention

[0006] The purpose of this invention is to provide a cathode, preparation method and equipment for resisting iron ion deposition, so as to achieve the dual goals of "not significantly affecting hydrogen evolution activity" and "long-term resistance to iron deposition", and to ensure the long-term operating efficiency and life of alkaline water electrolyzers.

[0007] To achieve the above objectives, a specific embodiment of the present invention provides the following technical solution:

[0008] The cathode resistant to iron ion deposition includes a hydrogen evolution electrode substrate and a composite layer formed on the surface of the electrode substrate. The composite layer is a porous and hydrophobic polytetrafluoroethylene (PTFE) functional layer with a thickness of 50-200 nm. Preferably, the hydrogen evolution electrode substrate is a Raney nickel electrode or other electrode with hydrogen evolution catalytic activity.

[0009] In one or more embodiments of the present invention, the polytetrafluoroethylene functional layer is formed by coating a slurry comprising polytetrafluoroethylene particles.

[0010] In one or more embodiments of the present invention, the particle size of polytetrafluoroethylene is 50~200nm.

[0011] In one or more embodiments of the present invention, the pore density of the polytetrafluoroethylene functional layer is 10. 3 -10 4 / cm 2 .

[0012] In one or more embodiments of the present invention, the pore size of the polytetrafluoroethylene functional layer is 10-80 nm.

[0013] In one or more embodiments of the present invention, a method for preparing a cathode resistant to iron ion deposition includes the following steps:

[0014] a. Provide a catalytically active hydrogen evolution electrode substrate and a polytetrafluoroethylene suspension with a concentration of 0.1~5wt%;

[0015] b. Uniformly coat the polytetrafluoroethylene suspension onto the surface of the electrode substrate;

[0016] c. Place the coated electrode in an environment of 80~150℃ and dry for 10~60 minutes to melt the polytetrafluoroethylene particles and form a continuous nanoporous network structure.

[0017] d. Repeat steps b to c3 to 10 times to form a PTFE coating on the electrode surface.

[0018] In one or more embodiments of the present invention, the concentration of polytetrafluoroethylene in the polytetrafluoroethylene suspension is 0.1-5 wt%. Preferably, the particle size of polytetrafluoroethylene in the suspension is 50-200 nm.

[0019] In one or more embodiments of the present invention, the solvent in the polytetrafluoroethylene suspension is an organic solvent or deionized water that does not react with polytetrafluoroethylene and is easily volatile.

[0020] In one or more embodiments of the present invention, the coating process is selected from: immersion, spin coating, or spray coating. The spraying pressure of the spray coating process is 0.1~0.3MPa, and the spraying distance is 10~20cm.

[0021] In one or more embodiments of the present invention, an alkaline water electrolysis device includes an electrolytic electrode, wherein the cathode is an anti-ferric ion deposition cathode. (The following appears to be a separate, unrelated description: In a 30wt% KOH solution, at 80°C and 3000 A / m...) 2 At the specified current density, the hydrogen evolution overpotential of the hydrogen evolution cathode is ≤250mV; in a current density containing 30ppm FeO4 - After being polarized at a constant potential of 1.8V at 80℃ for 4 hours in a 30wt% KOH solution, the amount of iron deposited decreased by more than 90%, and the overpotential change was ≤5mV.

[0022] Compared with the prior art, the cathode, preparation method and equipment for resisting iron ion deposition of the present invention are optimized from two aspects: electrode structure and film composition. The strong negative electrostatic repulsion of FeO4 by polytetrafluoroethylene is utilized. - The combined effect of nanopore size and exclusion mechanism reduces iron deposition by more than 90%. At the same time, the porous structure ensures mass transfer and conductivity, with hydrogen evolution overpotential increase ≤10mV and overpotential change after deposition ≤5mV. This effectively prevents iron ions from approaching and being reduced to the active surface of the electrode, thereby greatly alleviating the performance degradation caused by iron contamination and ensuring the long-term operating efficiency and lifespan of the electrolyzer. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 The graphs show the overpotential changes of the electrode (original electrode) in Comparative Example 1 and the polytetrafluoroethylene coated electrode in Example 1 of this invention. Detailed Implementation

[0025] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments disclosed herein. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0026] To achieve the above objectives, the core technical solution proposed in this invention for the anti-iron ion deposition cathode, preparation method, and equipment is: to construct an ultra-thin, porous, and hydrophobic polytetrafluoroethylene functional layer on the surface of the hydrogen evolution electrode, thereby blocking the adsorption and deposition of iron ions through both physical and chemical actions, while ensuring mass transfer and conductivity, and guaranteeing the intrinsic hydrogen evolution activity of the electrode.

[0027] The specific preparation method is as follows:

[0028] 1. Provide a hydrogen evolution electrode substrate with catalytic activity: Raney nickel electrode is preferred, but other electrode materials with hydrogen evolution catalytic activity (such as Ni-Co alloy electrode) can also be selected.

[0029] 2. Preparation of polytetrafluoroethylene suspension: Dilute high-concentration polytetrafluoroethylene emulsion with particle size of 50~200nm with solvent (such as deionized water or ethanol) to prepare a suspension with a concentration of 0.1~5wt%; the solvent must meet the requirements of not reacting with polytetrafluoroethylene and being volatile, and ensure that there is no residue after drying;

[0030] 3. Coating process: The polytetrafluoroethylene suspension is uniformly covered on the surface of the electrode substrate by immersion, spin coating or spray coating process; if the spray coating process is used, the preferred spraying pressure is 0.1~0.3MPa and the spraying distance is 10~20cm to ensure the uniformity of the coating.

[0031] 4. Drying and film formation: Place the coated electrode in an environment of 80~150℃ for 10~60 minutes to dry, so that the polytetrafluoroethylene particles melt and form a continuous nanoporous network structure; if the drying temperature is too low, the polytetrafluoroethylene particles will not melt sufficiently, and if it is too high, it may cause the polytetrafluoroethylene to decompose or the electrode substrate performance to degrade.

[0032] 5. Repeat coating: Repeat the above coating-drying steps 3 to 10 times to ensure the formation of a polytetrafluoroethylene composite layer with uniform thickness and continuous structure, while controlling the total thickness to be ultra-thin to avoid affecting mass transfer and conductivity.

[0033] The mechanism of iron deposition resistance of this invention is as follows:

[0034] Chemical repulsion: The inherent strong negative charge of polytetrafluoroethylene (PTFE) material is incompatible with the positively charged FeO4. -The ions generate a strong electrostatic repulsion, reducing the migration of iron ions to the electrode surface;

[0035] Physical barrier: The nanoscale porous network structure of the polytetrafluoroethylene composite layer has a pore size that matches the size of hydrated iron ions, forming an effective size barrier that prevents iron ions from penetrating the coating and reaching the active surface of the electrode.

[0036] Structural adaptation: The ultra-thin porous structure ensures both the continuity of the coating (blocking iron ions) and the mass transfer channels (without affecting the hydrogen evolution reaction), achieving a balance between "anti-deposition" and "maintaining activity".

[0037] Example 1

[0038] In the electrodes of this embodiment:

[0039] Electrode substrate: Commercial Raney nickel electrode (5cm×5cm, 0.5mm thickness) is selected. Before use, it is ultrasonically cleaned with deionized water for 10 minutes to remove surface oil and impurities, and then dried for later use.

[0040] Preparation of polytetrafluoroethylene suspension: A high-concentration polytetrafluoroethylene emulsion with a particle size of 100 nm was selected, diluted with deionized water to 1 wt%, and stirred for 30 minutes until uniformly dispersed.

[0041] Coating process: The Raney nickel electrode is immersed in a polytetrafluoroethylene suspension for 5 minutes after cleaning, and then allowed to drip naturally for 1 minute to remove excess suspension.

[0042] Drying process: The coated electrode is placed in a 120℃ oven and dried for 30 minutes to melt the polytetrafluoroethylene particles and form a preliminary nanoporous structure.

[0043] Repeated coating: Repeat a total of 5 times to form a uniform polytetrafluoroethylene composite layer on the electrode surface.

[0044] Performance testing:

[0045] Hydrogen evolution overpotential: The measured value was 246 mV at 30 wt% KOH solution, 80 ℃, and a current density of 3000 A / m².

[0046] Anti-iron deposition performance: in a solution containing 30 ppm FeO4 - After being polarized at a constant potential of 1.8V at 80℃ for 4 hours in a 30wt% KOH solution, the amount of iron deposited decreased by 92%, and the overpotential change was 3mV.

[0047] Comparative Example 1

[0048] The difference between this comparative example and Example 1 is that the electrode is a commercial Raney nickel electrode (5cm×5cm, 0.5mm thick) without a surface composite layer.

[0049] Performance comparison between Example 1 and Comparative Example 1

[0050] (1) The polytetrafluoroethylene coating has minimal effect on the intrinsic hydrogen evolution activity of the electrode.

[0051] The hydrogen evolution performance of the uncoated polytetrafluoroethylene electrode (Comparative Example 1 electrode) and the electrode coated with a polytetrafluoroethylene composite layer were tested under the conditions of 30wt% KOH solution and 80℃.

[0052] Experimental results: At a current density of 3000 A / m², the hydrogen evolution overpotential of the electrode in Comparative Example 1 was 239, while that of the polytetrafluoroethylene composite layer electrode was 248. The difference between the two was ≤10 mV.

[0053] The results demonstrate that the polytetrafluoroethylene composite layer constructed in this invention possesses excellent proton / electron conductivity, and its porous structure ensures the smooth transport of reactants (H2O) and products (H2). Therefore, it has almost no negative impact on the core hydrogen evolution function of the electrode, overcoming the technical obstacle of a sharp increase in overpotential caused by traditional dense protective layers.

[0054] (2) The polytetrafluoroethylene coating can effectively block the adsorption and deposition of iron ions, and significantly maintain the long-term stability of the electrode.

[0055] To verify the coating's resistance to iron deposition, two electrodes (the electrode of Example 1 and the original electrode of Comparative Example 1) were placed in a 30wt% KOH solution containing 30ppm FeO4⁻ and subjected to constant potential polarization at 1.8V for 4 hours at 80°C.

[0056] Comparison of iron adsorption: After the experiment, the elemental composition of the electrode surface was analyzed by XRF (X-ray fluorescence spectrometry). The results showed that the iron content on the original electrode surface was as high as 18.74%, while the iron content on the polytetrafluoroethylene composite layer electrode surface was only 0.41%, representing a reduction of more than 90% in iron deposition.

[0057] Post-deposition performance comparison: The hydrogen evolution performance of the two electrodes after iron adsorption was tested again. At a current density of 3000 A / m², the overpotential of the original electrode increased significantly by Δη (≥30 mV) due to iron deposition; while the overpotential of the polytetrafluoroethylene composite layer electrode only changed negligibly (Δη≤5 mV).

[0058] like Figure 1As shown in the figure, it is clearly evident that the overpotential of the original electrode increases significantly after iron deposition, while the overpotential of the PTFE-coated electrode remains almost unchanged, verifying the anti-iron deposition effect of this invention. This series of experiments demonstrates that the PTFE composite layer of this invention possesses excellent resistance to iron ion penetration. Its mechanism of action lies in the fact that the inherent strong negative charge of the PTFE layer generates a strong electrostatic repulsion effect on FeO4⁻ ions, while its nanoscale pores effectively restrict the size of hydrated iron ions. Therefore, it can effectively prevent iron ions from approaching and being reduced to the active surface of the electrode from both physical and chemical perspectives, thereby greatly alleviating the performance degradation caused by iron contamination and ensuring the long-term operating efficiency and lifespan of the electrolytic cell.

[0059]

[0060] Example 2

[0061] In the electrodes of this embodiment:

[0062] Electrode substrate: Ni-Co alloy hydrogen evolution electrode (5cm×5cm, 0.5mm thickness) was selected, ultrasonically cleaned and then air-dried;

[0063] Preparation of polytetrafluoroethylene suspension: A high-concentration polytetrafluoroethylene emulsion with a particle size of 50 nm was selected, diluted with ethanol to 0.1 wt%, and stirred for 60 minutes until uniformly dispersed;

[0064] Coating process: A spraying process is adopted, with a spraying pressure of 0.1MPa and a spraying distance of 10cm, to uniformly spray the polytetrafluoroethylene suspension onto the electrode surface;

[0065] Drying process: Place the coated electrode in an 80℃ oven and dry for 60 minutes;

[0066] Repeat coating: Repeat a total of 10 times to form a polytetrafluoroethylene composite layer.

[0067] Performance testing:

[0068] Hydrogen evolution overpotential: The measured value was 242mV at 30wt% KOH solution, 80℃, and a current density of 3000A / m².

[0069] Iron deposition resistance: After being polarized at a constant potential of 1.8V for 4 hours at 80℃ in a 30wt% KOH solution containing 30ppm FeO4⁻, the iron deposition amount decreased by 95%, and the overpotential change was 2mV.

[0070] Example 3

[0071] In the electrodes of this embodiment:

[0072] Electrode substrate: Raney nickel electrode is selected, cleaned and dried;

[0073] Preparation of polytetrafluoroethylene suspension: A high-concentration polytetrafluoroethylene emulsion with a particle size of 200 nm was selected, diluted to 5 wt% with deionized water, and stirred for 30 minutes.

[0074] Coating process: Spin coating process is adopted, with a spin coating speed of 3000 rpm and a spin coating time of 30 seconds;

[0075] Drying process: Place the coated electrode in a 150℃ oven and dry for 10 minutes;

[0076] Repeat coating: Repeat a total of 3 times to form a polytetrafluoroethylene composite layer.

[0077] Performance testing:

[0078] Hydrogen evolution overpotential: The measured value was 249 mV at 30 wt% KOH solution, 80 ℃, and a current density of 3000 A / m².

[0079] Iron deposition resistance: After being polarized at 1.8V at 80℃ for 4 hours in a 30wt% KOH solution containing 30ppm FeO4⁻, the iron deposition amount decreased by 91%, and the overpotential change was 4mV.

[0080] In summary, the above embodiments demonstrate that the technical solution of the present invention possesses excellent proton / electron conductivity, and the porous structure ensures smooth transport of reactants (H2O) and products (H2), with almost no negative impact on the hydrogen evolution function of the electrode core. Simultaneously, the polytetrafluoroethylene composite layer effectively repels FeO4 through its strong negative electrostatic repulsion. - The dual effect of "nanopore size blocking hydrated iron ions" effectively prevents iron ions from approaching and being reduced to the active surface of the electrode, significantly improving the long-term stability of the electrode.

[0081] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this disclosure. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0082] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A cathode resistant to iron ion deposition, comprising a hydrogen evolution electrode substrate and a composite layer formed on the surface of the electrode substrate, wherein the composite layer is a porous and hydrophobic polytetrafluoroethylene functional layer, and the thickness of the polytetrafluoroethylene functional layer is 50-200 nm.

2. The cathode against iron ion deposition according to claim 1, characterized in that, The polytetrafluoroethylene functional layer is formed by coating a slurry containing polytetrafluoroethylene particles.

3. The cathode against iron ion deposition according to claim 2, characterized in that, The particle size of the polytetrafluoroethylene is 50~200nm.

4. The cathode against iron ion deposition according to claim 1, characterized in that, The pore density of the polytetrafluoroethylene functional layer is 10. 3 -10 4 / cm 2 .

5. The cathode against iron ion deposition according to claim 4, characterized in that, The pore size of the polytetrafluoroethylene functional layer is 10-80 nm.

6. A method for preparing a cathode resistant to iron ion deposition according to any one of claims 1-5, comprising the following steps: a. Provide a catalytically active hydrogen evolution electrode substrate and a polytetrafluoroethylene suspension with a concentration of 0.1~5wt%; b. Uniformly coat the polytetrafluoroethylene suspension onto the surface of the electrode substrate; c. Place the coated electrode in an environment of 80~150℃ and dry for 10~60 minutes to melt the polytetrafluoroethylene particles and form a continuous nanoporous network structure. d. Repeat steps b to c3 to 10 times to form a PTFE coating on the electrode surface.

7. The preparation method according to claim 6, characterized in that, The concentration of polytetrafluoroethylene in the polytetrafluoroethylene suspension is 0.1~5wt%.

8. The preparation method according to claim 7, characterized in that, The solvent in the polytetrafluoroethylene suspension is an organic solvent or deionized water that does not react with polytetrafluoroethylene and is easily volatile.

9. The preparation method according to claim 6, characterized in that, The coating process is selected from: immersion, spin coating or spray coating.

10. An alkaline water electrolysis device, characterized in that, Includes an electrolytic electrode, wherein the cathode is an anti-iron ion deposition cathode according to any one of claims 1 to 5.

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