Preparation Method and Application of a Dual-Gradient Self-Supported Hydrogen Evolution Electrode

Abstract

The present invention relates to the technical field of electrocatalytic hydrogen evolution, and discloses a preparation method and application of a dual-gradient self-supporting hydrogen evolution electrode. The preparation method includes the following steps: forming oxygen-containing hydrophilic groups on the surface of a conductive carbon cloth to obtain a pretreated carbon cloth; in-situ self-growing a metal-organic framework composed of Co and 2-methylimidazole on the surface of the pretreated carbon cloth, the metal-organic framework forming triangular protrusions on the surface of the pretreated carbon cloth, and roasting to obtain a geometric gradient electrode; covering a mask with a plurality of through holes on the surface of the geometric gradient electrode, and applying a hydrophobic and air-permeable coating through the through holes on the surface of the geometric gradient electrode to form a plurality of hydrophobic and air-permeable regions on the surface of the geometric gradient electrode. By adopting the preparation method of the present invention, the overpotential and the overpotential growth rate of the electrode at a high current density can be effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalytic hydrogen evolution, and particularly relates to a preparation method and application of a double-gradient self-supporting hydrogen evolution electrode. Background Art

[0002] Hydrogen has always been regarded as an ideal energy carrier due to its advantages such as zero emissions and high energy density. For the source of hydrogen, electrocatalytic hydrogen evolution is a key technology that can be coupled with renewable energy sources such as photovoltaics and wind energy. However, due to the high cost of its noble metal catalysts and the rapid decline of electrolysis performance at actual high current densities, it has hindered the further industrial application of the electrolytic hydrogen evolution technology.

[0003] For electrocatalytic hydrogen evolution, most current studies mainly focus on developing new catalysts and electrode materials to reduce the manufacturing and use costs of electrolyzers. However, in the actual operation process, the effects of electrolysis products and bubbles on the performance of electrolyzers are often ignored. During the process of electrocatalytic hydrogen evolution, bubbles are adsorbed and attached to the electrode surface and fluid channels for a long time, covering the noble metal catalytic active sites on the electrode surface with gas, resulting in the loss of catalytic active sites and insufficient local supply of electrolyte, leading to a high overpotential for oxygen evolution, especially a too high overpotential at high current densities, making it difficult to increase the current density. Generally speaking, the reduction of effective catalytic sites makes it difficult to reduce the loading of noble metal catalysts, resulting in a high cost of the electrode per unit electrode area and making it difficult for the electrolytic water hydrogen production technology to be applied on a large scale in the industry.

[0004] The existing means to solve the above problems mainly include constructing catalyst microstructures with different morphologies (such as leaf-shaped, needle-shaped, sheet-shaped, etc.), and adjusting the wettability of electrode materials by acid etching and loading hydrophilic groups to control the bubble migration process on the electrode surface. However, the uneven distribution and disordered arrangement of catalysts with different morphologies on the electrode substrate will still lead to the cross-coverage of effective active sites, and it is difficult to directionally control the morphological characteristics and hydrophilicity of the catalysts, resulting in very difficult bubble management and induced migration on the electrode surface and very serious coverage of active sites. Therefore, there is an urgent need to design a more efficient and effective surface for bubble directional migration to prepare electrodes with high hydrogen evolution activity and stability. Summary of the Invention

[0005] In order to solve the technical problems of high overpotential of the electrode and difficult increase of current density caused by bubble coverage during the electrocatalytic hydrogen evolution process, the present invention provides a preparation method and application of a double-gradient self-supporting hydrogen evolution electrode. By using the preparation method of the present invention, it is possible to reduce the aggregation of gas on the electrode surface, promote the in-situ separation of hydrogen on the electrode surface, thereby reducing the overpotential of the electrode at high current densities. At the same time, it can also improve the stability of the electrode during long-term operation at high current and reduce the overpotential growth rate.

[0006] The specific technical solution of the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing a dual-gradient self-supporting hydrogen evolution electrode, comprising the following steps:

[0008] S1: Form oxygen-containing hydrophilic groups on the surface of the conductive carbon cloth to obtain pretreated carbon cloth;

[0009] S2: In-situ self-grow a metal-organic framework composed of Co and 2-methylimidazole on the surface of the pretreated carbon cloth. The metal-organic framework forms triangular protrusions on the surface of the pretreated carbon cloth, and then calcinates to obtain a geometric gradient electrode;

[0010] S3: Cover a mask with a number of through holes on the surface of the geometric gradient electrode, and apply a hydrophobic and gasophilic coating through the through holes on the surface of the geometric gradient electrode to form a number of hydrophobic and gasophilic regions on the surface of the geometric gradient electrode.

[0011] By adopting the above method, the present invention can form a longitudinal (i.e., perpendicular to the electrode surface) geometric gradient and a transverse (i.e., parallel to the electrode surface) infiltration gradient on the surface of the conductive carbon cloth. Specifically: after the conductive carbon cloth is pretreated, oxygen-containing hydrophilic groups are formed on the surface. These groups can serve as nucleation sites for the metal-organic framework, coordinate and anchor free 2-methylimidazole on the carbon cloth surface. This organic coordination then self-assembles with cobalt metal ions to form a network topology structure. Subsequently, under the restriction of the water molecule crystal plane, triangular protrusions grow perpendicular to the carbon cloth surface, that is, a longitudinal geometric gradient is formed. And Co in the metal-organic framework can play a catalytic role in electrocatalytic hydrogen evolution. Subsequently, after applying the hydrophobic and gasophilic coating, the regions covered by the mask on the surface of the geometric gradient electrode are not coated with the hydrophobic and gasophilic coating, which are hydrophilic and gasophobic regions, and the regions not covered by the template (i.e., the regions corresponding to the through holes) are coated with the hydrophobic and gasophilic coating, which are hydrophobic and gasophilic regions. The adjacent hydrophilic and gasophobic regions and hydrophobic and gasophilic regions can form a transverse infiltration gradient on the electrode surface.

[0012] The migration mechanism of water on the longitudinal geometric gradient is as follows: as the electrolysis current density increases, the surface of the triangular protrusions composed of the metal-organic framework is gradually covered by bubbles. The difference in the apparent contact angle will generate a shape gradient force acting on the liquid droplet. The triangular protrusions have a structural gradient, resulting in unbalanced surface tension of the liquid on them. Due to the different contact areas, the apparent contact angles of the electrolyte droplets are different, which can guide the liquid to transport from the tip of the triangle to the root of the catalyst under the action of the Laplace force, supplement fresh electrolyte and hydrogen ions in water to the electrode surface, ensure the stable existence of catalytic active sites at high current density, reduce the coverage time of bubbles on the hydrogen evolution catalytic active sites, and thus improve the efficiency of hydrogen production.

[0013] The migration mechanism of bubbles on the lateral wetting gradient is as follows: The hydrophilic and gasophobic regions and the hydrophobic and gasophilic regions formed on the electrode surface by using a mask can function as the electrolytic hydrogen evolution region and the gas transport region respectively. The hydrophilic and gasophobic regions and the hydrophobic and gasophilic regions on the electrode surface form a wetting gradient at the interactive boundary. When bubbles are generated in the electrolytic hydrogen evolution region, the bubbles will be affected by the gradient wetting gradient and, under the action of surface tension, laterally move from the electrolytic hydrogen evolution region with a small bubble wetting angle to the gasophilic gas transport region, thereby ensuring that the catalytic active sites in the electrolytic hydrogen evolution region under high current are not covered by bubbles. At the same time, the hydrogen partial pressure on its surface is also reduced, enabling the electrolytic water reaction to proceed in the forward direction, thus helping to improve the hydrogen production efficiency.

[0014] By the above method, using the dual gradients of the longitudinal geometric gradient and the lateral wetting gradient on the electrode surface, the aggregation of gas on the electrode surface can be reduced, and the in-situ separation of hydrogen on the electrode surface can be promoted, thereby reducing the overpotential of electrocatalytic hydrogen evolution (especially the overpotential at high current densities). At the same time, the triangular protrusions are composed of metal-organic frameworks and have an open porous structure, which can expose more active sites, facilitate the full contact between the active sites on the catalyst surface and the electrolyte, improve the intrinsic performance of the hydrogen evolution electrode, and enable the hydrogen evolution electrode to have a lower overpotential.

[0015] In addition to being able to reduce the overpotential, the dual gradients of the electrode in the present invention can also control the growth process of bubbles, and the bubble size can be reduced from more than 200 microns to 20 microns. This helps to reduce the impact on the electrode surface during the coalescence process of small bubbles, thereby reducing the possibility of catalyst shedding. Moreover, the self-supported synthesized catalyst of the present invention does not require the use of additional binders. These characteristics can ensure the stable operation of the hydrogen evolution electrode under high current for a long time and reduce the overpotential growth rate.

[0016] Preferably, in step S3, the shape of the through hole is triangular.

[0017] Adopting a triangular through hole design can make the hydrophobic and gasophilic regions formed on the electrode surface be triangular, which can constitute another geometric shape gradient. During the process of electrocatalytic hydrogen evolution, when the tip of the triangular hydrophobic and gasophilic region is below the electrolyte liquid level and the bottom edge is above the electrolyte liquid level, the triangular shape gradient will help the bubbles to quickly migrate from the tip of the triangle to the space outside the electrolyte, thereby reducing to a greater extent the coverage of the catalytic active sites in the electrolytic hydrogen evolution region under high current by bubbles and reducing the hydrogen partial pressure on its surface, thereby further reducing the overpotential of the hydrogen evolution electrode.

[0018] Preferably, in step S3, the apex angle of the through hole is 10° - 30°, the height is 10 - 20 mm, and the distance between the bottom edges of adjacent through holes is 100 - 200 μm.

[0019] When the apex angle of the triangular through-hole is too large, that is, when the apex angle of the formed triangular hydrophobic and gasophilic region is too large, the Laplace force induced by the geometric effect will fail, and the directional transportation of bubbles cannot be induced by the tip effect. Instead, bubbles will accumulate inside the hydrophobic and gasophilic layer, resulting in too high local hydrogen concentration, which is not conducive to the hydrogen evolution reaction.

[0020] Preferably, in step S3, the total area of the hydrophobic and gasophilic region accounts for 10-60% of the area on the electrode surface.

[0021] Preferably, in step S3, the hydrophobic and gasophilic coating is composed of a polydimethylsiloxane layer and hydrophobic nano-SiO2 bonded to the polydimethylsiloxane layer.

[0022] Preferably, step S1 specifically includes: cleaning and drying the conductive carbon cloth with water and absolute ethanol, heating it to 450-550 °C at a rate of 10-15 °C / min and holding for 2-5 h, and then cleaning with water and ethanol.

[0023] Preferably, step S2 specifically includes: preparing a solution containing dimethylimidazole and Co 2+ suspending the pretreated carbon cloth in it, with the inclination angle relative to the vertical direction not greater than 45°, and standing and aging at 30-35 °C for 2-5 h; the molar ratio of dimethylimidazole and Co 2+ is 1-12:1; in the solution containing dimethylimidazole and Co 2+ the concentration of Co 2+ is 0.03-0.4 mol / L.

[0024] Preferably, in step S2, the roasting process specifically includes: heating to 550-650 °C at a rate of 2-5 °C / min and holding for 3-4 h.

[0025] Preferably, in step S3, the process of applying the hydrophobic and gasophilic coating specifically includes: immersing the geometric gradient electrode covered with a mask in a solution containing a polydimethylsiloxane prepolymer and a curing agent for 10-100 s, taking it out and placing it in the air for 10-40 s to form a prepolymer layer; then depositing hydrophobic nano-SiO2 on the prepolymer layer and curing.

[0026] Furthermore, in the solution containing the polydimethylsiloxane prepolymer and the curing agent, the concentrations of the polydimethylsiloxane prepolymer and the curing agent are 0.6-0.9 g / mL and 0.1-0.4 g / mL respectively.

[0027] Furthermore, the curing temperature is 80-100 °C and the time is 2-5 h.

[0028] Preferably, in step S3, the thickness of the mask is 10-200 μm.

[0029] In a second aspect, the present invention provides an application of a dual-gradient self-supporting hydrogen evolution electrode in electrocatalytic hydrogen evolution, and the dual-gradient self-supporting hydrogen evolution electrode is prepared by the above preparation method.

[0030] Preferably, the dual-gradient self-supporting hydrogen evolution electrode is partially immersed in the electrolyte; the hydrophobic and gasophilic region is triangular, and the bottom edge of each hydrophobic and gasophilic region at the electrolyte liquid level is above the electrolyte liquid level, and the apex angle is below the electrolyte liquid level.

[0031] Preferably, during the electrocatalytic hydrogen evolution process, the dual-gradient self-supporting hydrogen evolution electrode is used as the working electrode cathode, a graphite rod electrode is used as the counter electrode, an Ag / AgCl electrode is used as the reference electrode, and a potassium hydroxide solution is used as the electrolyte.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] (1) By constructing a longitudinal geometric gradient composed of cobalt-based metal-organic frameworks and a transverse wetting gradient composed of adjacent hydrophobic and gasophilic regions and hydrophilic and gasophobic regions on the electrode surface, the present invention can largely reduce the accumulation of gas on the electrode surface, promote the in-situ separation of hydrogen on the electrode surface, and thus effectively reduce the overpotential of the electrode at high current densities. After testing, when the present invention only uses non-precious metal Co as the catalytic metal, the overpotential at a current density of 100 mA / cm 2 can be as low as 80-87 mV, which is significantly lower than that of the conventional noble metal platinum-carbon coated hydrogen evolution electrode (100-170 mV). It not only effectively reduces the overpotential of the electrode at high current densities, but also can effectively reduce the raw material cost due to the avoidance of the use of noble metals.

[0034] (2) By constructing a dual gradient of longitudinal geometric gradient and transverse wetting gradient on the electrode surface, the present invention can reduce the impact on the electrode surface during the coalescence process of small bubbles, and the self-supporting synthesized catalyst of the present invention does not require the use of additional binders, so it can improve the stability of the electrode during long-term operation at high current and reduce the overpotential growth rate. After testing, the overpotential growth of the hydrogen evolution electrode prepared by the present invention is only 10 μV / h within 100 h at a current density of 100 mA / cm 2 and the growth rate is only 10% of that of the conventional platinum-carbon electrode. Description of the Drawings

[0035] Figure 1 It is the SEM image of the surface of the hydrogen evolution electrode prepared in Example 1.

[0036] Figure 2Schematic diagram of the mask surface structure used in Example 1.

[0037] The reference numeral is: via hole 1. Detailed implementation manners

[0038] The present invention will be further described below in conjunction with embodiments.

[0039] A preparation method of a dual-gradient self-supporting hydrogen evolution electrode includes the following steps:

[0040] S1: Form oxygen-containing hydrophilic groups on the surface of the conductive carbon cloth to obtain pretreated carbon cloth;

[0041] S2: In-situ self-grow a metal-organic framework composed of Co and dimethylimidazole on the surface of the pretreated carbon cloth. The metal-organic framework forms triangular protrusions on the surface of the pretreated carbon cloth, and then calcine to obtain a geometric gradient electrode;

[0042] S3: Cover a mask with a number of through holes on the surface of the geometric gradient electrode, apply a hydrophobic and gasophilic coating through the through holes on the surface of the geometric gradient electrode, and form a number of hydrophobic and gasophilic regions on the surface of the geometric gradient electrode.

[0043] In some specific implementation manners, step S1 specifically includes: After cleaning and drying the conductive carbon cloth with water and absolute ethanol, heat it to 450-550 °C at a rate of 10-15 °C / min and hold for 2-5 h, and then clean it with water and ethanol.

[0044] In some specific implementation manners, step S2 specifically includes: Prepare a solution containing dimethylimidazole and Co 2+ Suspend the pretreated carbon cloth in it, and the inclination angle relative to the vertical direction is not greater than 45 °, and let it stand and age at 30-35 °C for 2-5 h; the molar ratio of dimethylimidazole and Co 2+ is 1-12:1; in the solution containing dimethylimidazole and Co 2+ the concentration of Co 2+ is 0.03-0.4 mol / L.

[0045] In some specific implementation manners, in step S2, the calcination process specifically includes: Heat it to 550-650 °C at a rate of 2-5 °C / min and hold for 3-4 h.

[0046] In some specific implementation manners, in step S3, the shape of the through hole is triangular, the apex angle is 10°-30°, the height is 10-20 mm, and the distance between the bottom edges of adjacent through holes is 100-200 μm.

[0047] In some specific implementation manners, in step S3, the thickness of the mask is 10-200 μm.

[0048] In some specific embodiments, in step S3, the total area of the hydrophobic and gasophilic region accounts for 10% to 60% of the area on the electrode surface.

[0049] In some specific embodiments, in step S3, the hydrophobic and gasophilic coating is composed of a polydimethylsiloxane layer and hydrophobic nano-SiO2 bonded to the polydimethylsiloxane layer.

[0050] In some specific embodiments, in step S3, the process of applying the hydrophobic and gasophilic coating specifically includes: immersing the geometric gradient electrode covered with a mask in a solution containing 0.6 to 0.9 g / mL of polydimethylsiloxane prepolymer and 0.1 to 0.4 g / mL of curing agent for 10 to 100 s, taking it out and placing it in the air for 10 to 40 s to form a prepolymer layer; then depositing hydrophobic nano-SiO2 onto the prepolymer layer and curing it at 80 to 100 °C for 2 to 5 h.

[0051] An application of a dual-gradient self-supporting hydrogen evolution electrode in electrocatalytic hydrogen evolution, wherein the dual-gradient self-supporting hydrogen evolution electrode is prepared by the above preparation method.

[0052] In some specific embodiments, the dual-gradient self-supporting hydrogen evolution electrode is partially immersed in the electrolyte; the hydrophobic and gasophilic region is triangular, with the bottom edge of each hydrophobic and gasophilic region at the electrolyte liquid level above the liquid surface and the apex below the electrolyte liquid level.

[0053] In some specific embodiments, during the electrocatalytic hydrogen evolution process, the dual-gradient self-supporting hydrogen evolution electrode is used as the working electrode cathode, a graphite rod electrode is used as the counter electrode, an Ag / AgCl electrode is used as the reference electrode, and a potassium hydroxide solution is used as the electrolyte.

[0054] The present invention will be described below through specific examples. It should be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. Without departing from the spirit and scope of the inventive concept, changes and advantages that can be conceived by those skilled in the art are included in the present invention, and the scope of protection of the present invention is defined by the appended claims and any equivalents thereof.

[0055] Example 1

[0056] The steps for preparing the hydrogen evolution electrode in this example are as follows:

[0057] (1) Select a 4 cm 2 flexible conductive carbon cloth, wash it alternately with deionized water and absolute ethanol 3 times, and then dry it in a vacuum oven for 24 h.

[0058] (2) Heat the dried carbon cloth in a muffle furnace at a heating rate of 10 °C / min to 450 °C, and heat it at this temperature for 3 h. Then wash it alternately with deionized water and absolute ethanol three times, and then dry it overnight in a vacuum oven to obtain the pretreated carbon cloth.

[0059] (3) Add dimethylimidazole to deionized water and ultrasonicate for 45 min to fully dissolve it, and prepare 50 mL of a dimethylimidazole solution with a concentration of 0.4 mol / L; add Co(NO3)2·6H2O to deionized water and ultrasonicate for 45 min to fully dissolve it, and prepare 50 mL of a cobalt nitrate solution with a concentration of 0.08 mol / L.

[0060] (4) Quickly pour the prepared cobalt nitrate solution into the dimethylimidazole solution and stir at a stirring speed of 50 r / min for 1 min to fully mix the solution and obtain a mixed solution.

[0061] (5) Vertically suspend the pretreated carbon cloth in the mixed solution, place it in a constant temperature oven at 30 °C, and let it stand for 5 h to age, so that the grown triangular flake-like two-dimensional cobalt-based metal-organic framework (Co-MOF) catalyst grows in-situ on the surface of the carbon cloth, forming triangular protrusions epitaxially grown from the electrode catalyst substrate. Then, under the protection of argon, heat it in a tube furnace at a heating rate of 2 °C / min to 550 °C and anneal for 3 h to obtain a geometric gradient electrode.

[0062] (6) Take a PET plastic mask with a thickness of 10 μm, the size of which is slightly larger than that of the carbon cloth, and cut out triangular through-holes by laser. The apex angle of the triangular through-holes is 10°, the height is 20 mm, and the bottom edge interval between adjacent triangular through-holes is 200 μm (see the arrangement method of the triangular through-holes in the mask in Figure 2 , that is: there is a row of triangular through-holes 1 arranged on the mask, the shape and direction of each triangular through-hole are the same, and there is a gap between adjacent triangular through-holes), and then clamp the mask and cover it on the front and back surfaces of the geometric gradient electrode.

[0063] (7) Dissolve 1.0 g of polydimethylsiloxane (PDMS) prepolymer containing 10 wt% curing agent (Dow Corning DC184 PDMS polydimethylsiloxane high-transparency curing agent) in 10 mL of n-hexane and stir well to prepare a dipping solution. Immerse the geometric gradient electrode covered with the mask in the dipping solution for 15 s, take it out and place it in the air at room temperature for 30 s to make a layer of PDMS prepolymer layer adhere to the electrode surface.

[0064] (8) Hydrophobic nano-SiO₂ particles (average particle size 16 nm) were uniformly deposited on the surface of the electrode with a PDMS prepolymer layer. It was heated at 80 °C for 2 h to cure the PDMS prepolymer layer and tightly attach the hydrophobic nano-SiO₂ particles at the same time. Then it was carefully rinsed with sufficient ethanol to remove the unbound hydrophobic nano-SiO₂ particles, and then dried under a nitrogen stream for 24 h.

[0065] (9) The PET plastic mask sandwiched between the front and back of the electrode was removed to obtain a hydrogen evolution electrode. On the surface of the hydrogen evolution electrode, the area covered by the mask was not attached with hydrophobic nano-SiO₂ particles, which was a hydrophilic and gasophobic area, and the adjacent mask gap area was a hydrophobic and gasophilic area, forming a lateral wetting gradient. The total area of the hydrophobic and gasophilic area accounted for 43% of the area on the electrode surface.

[0066] The surface structure of the hydrogen evolution electrode prepared in this example is as Figure 1 shown.

[0067] Example 2

[0068] The steps for preparing the hydrogen evolution electrode in this example are as follows:

[0069] (1) A flexible conductive carbon cloth with a size of 8 cm 2 was alternately cleaned 4 times with deionized water and absolute ethanol, and then dried in a vacuum oven for 36 h.

[0070] (2) The dried carbon cloth was heated in a muffle furnace at a heating rate of 12 °C / min to 500 °C, and heated at this temperature for 3 h. Then it was alternately cleaned 4 times with deionized water and absolute ethanol, and then dried overnight in a vacuum oven to obtain a pretreated carbon cloth.

[0071] (3) Dimethylimidazole was added to deionized water and ultrasonically dissolved for 45 min to prepare 50 mL of a dimethylimidazole solution with a concentration of 0.4 mol / L; Co(NO₃)₂·6H₂O was added to deionized water and ultrasonically dissolved for 45 min to prepare 50 mL of a cobalt nitrate solution with a concentration of 0.08 mol / L.

[0072] (4) The prepared cobalt nitrate solution was quickly poured into the dimethylimidazole solution and stirred at a stirring speed of 100 r / min for 1.5 min to fully mix the solution and obtain a mixed solution.

[0073] (5) Vertically suspend the pretreated carbon cloth in the mixed solution, place it in an incubator at 35 °C, and let it stand for 3 h for aging, so that the grown triangular flake-like two-dimensional cobalt-based metal-organic framework (Co-MOF) catalyst grows in-situ on the surface of the carbon cloth, forming triangular protrusions epitaxially grown from the electrode catalyst substrate. Subsequently, under the protection of argon, heat it to 500 °C at a heating rate of 4 °C / min in a tubular furnace and anneal for 3.5 h to obtain a geometric gradient electrode.

[0074] (6) Take a PET plastic mask with a thickness of 10 μm, which is slightly larger than the size of the carbon cloth, and cut out triangular through-holes by laser. The apex angle of the triangular through-holes is 20°, the height is 20 mm, and the bottom edges of adjacent triangular through-holes are spaced 150 μm apart (the arrangement of the triangular through-holes in the mask is the same as that in Example 1, and the difference from Example 1 is only the through-hole size and spacing). Then clamp the mask and cover the front and back surfaces of the geometric gradient electrode.

[0075] (7) Dissolve 1.0 g of polydimethylsiloxane (PDMS) prepolymer containing 10 wt% curing agent (Dow Corning DC184 PDMS polydimethylsiloxane high-transparency curing agent) in 10 mL of n-hexane and stir well to make a dipping solution. Immerse the geometric gradient electrode covered with the mask in the dipping solution for 60 s, take it out and place it in the air at room temperature for 30 s to attach a layer of PDMS prepolymer layer on the electrode surface.

[0076] (8) Uniformly deposit hydrophobic nano-SiO2 particles (average particle size 16 nm) on the surface of the electrode with the PDMS prepolymer layer. Heat it at 85 °C for 3 h to cure the PDMS prepolymer layer and at the same time tightly attach the hydrophobic nano-SiO2 particles. Then carefully rinse with sufficient ethanol to remove the unbound hydrophobic nano-SiO2 particles, and dry it under a nitrogen stream for 24 h.

[0077] (9) Remove the PET plastic mask clamped on the front and back surfaces of the electrode to obtain a hydrogen evolution electrode. On the surface of the hydrogen evolution electrode, the area covered by the mask is not attached with hydrophobic nano-SiO2 particles, which is a hydrophilic and hydrophobic gas area, and the adjacent mask void area is a hydrophobic and hydrophilic gas area, forming a lateral infiltration gradient. The total area of the hydrophobic and hydrophilic gas area accounts for 58% of the area on the electrode surface.

[0078] Example 3

[0079] The steps for preparing the hydrogen evolution electrode in this example are as follows:

[0080] (1) Select a 16 cm 2 flexible conductive carbon cloth, and alternately wash it 6 times with deionized water and absolute ethanol, and then dry it in a vacuum oven for 48 h.

[0081] (2) Heat the dried carbon cloth in a muffle furnace at a heating rate of 15 °C / min to 550 °C, heat it at this temperature for 5 h, then wash it alternately with deionized water and absolute ethanol 6 times, and then dry it overnight in a vacuum oven to obtain the pretreated carbon cloth.

[0082] (3) Add dimethylimidazole to deionized water and ultrasonicate for 45 min to fully dissolve it, and prepare 50 mL of a dimethylimidazole solution with a concentration of 0.4 mol / L; add Co(NO3)2·6H2O to deionized water and ultrasonicate for 45 min to fully dissolve it, and prepare 50 mL of a cobalt nitrate solution with a concentration of 0.08 mol / L.

[0083] (4) Quickly pour the prepared cobalt nitrate solution into the dimethylimidazole solution and stir at a stirring speed of 200 r / min for 3 min to fully mix the solution and obtain a mixed solution.

[0084] (5) Vertically suspend the pretreated carbon cloth in the mixed solution, place it in a constant temperature oven at 35 °C, and let it stand for 5 h to age, so that the grown triangular flake-like two-dimensional cobalt-based metal-organic framework (Co-MOF) catalyst grows in-situ on the surface of the carbon cloth, forming triangular protrusions epitaxially grown from the electrode catalyst substrate. Then, under the protection of argon, heat it in a tube furnace at a heating rate of 5 °C / min to 650 °C and anneal for 4 h to obtain a geometric gradient electrode.

[0085] (6) Take a PET plastic mask with a thickness of 10 μm, the size of which is slightly larger than the size of the carbon cloth, and cut out triangular through-holes by laser. The apex angle of the triangular through-holes is 30°, the height is 20 mm, and the bottom edge interval between adjacent triangular through-holes is 200 μm (the arrangement of the triangular through-holes in the mask is the same as that in Example 1, and the difference from Example 1 is only the through-hole size and interval). Then clamp the mask and cover it on the front and back surfaces of the geometric gradient electrode.

[0086] (7) Dissolve 1.0 g of a polydimethylsiloxane (PDMS) prepolymer containing 10 wt% curing agent (Dow Corning DC184 PDMS polydimethylsiloxane high-transparency curing agent) in 10 mL of n-hexane and stir well to prepare a dipping solution. Immerse the geometric gradient electrode covered with the mask in the dipping solution for 100 s, take it out and place it in the air at room temperature for 40 s to attach a layer of PDMS prepolymer layer to the electrode surface.

[0087] (8) Hydrophobic nano-SiO₂ particles (average particle size 16 nm) were uniformly deposited on the surface of the electrode with a PDMS prepolymer layer. It was heated at 100 °C for 5 h to cure the PDMS prepolymer layer while tightly adhering the hydrophobic nano-SiO₂ particles. Then it was carefully rinsed with sufficient ethanol to remove the unbound hydrophobic nano-SiO₂ particles and dried under a nitrogen stream for 24 h.

[0088] (9) The PET plastic mask sandwiched between the front and back sides of the electrode was removed to obtain a hydrogen evolution electrode. On the surface of the hydrogen evolution electrode, the area covered by the mask was not attached with hydrophobic nano-SiO₂ particles and was a hydrophilic and hydrophobic gas area, and the adjacent mask gap area was a hydrophobic and hydrophilic gas area, forming a lateral wetting gradient. The total area of the hydrophobic and hydrophilic gas area accounted for 60% of the area on the electrode surface.

[0089] Comparative Example 1

[0090] This comparative example is a conventional platinum-carbon electrode.

[0091] Comparative Example 2

[0092] The difference between this comparative example and Example 1 is only that: in this comparative example, a lateral wetting gradient was not constructed on the electrode surface, that is, steps (6) to (9) were not carried out. Specifically, the steps for preparing the hydrogen evolution electrode in this comparative example are as follows:

[0093] (1) A 4 cm 2 flexible conductive carbon cloth was selected and alternately cleaned 3 times with deionized water and absolute ethanol, and then dried in a vacuum oven for 2 forty-four hours.

[0094] (2) The dried carbon cloth was heated in a muffle furnace at a heating rate of 10 °C / min to 450 °C and heated at this temperature for 3 h, then alternately cleaned 3 times with deionized water and absolute ethanol, and then dried overnight in a vacuum oven to obtain a pretreated carbon cloth.

[0095] (3) Dimethylimidazole was added to deionized water and ultrasonically dissolved for 45 min to prepare 50 mL of a dimethylimidazole solution with a concentration of 0.4 mol / L; Co(NO₃)₂·6H₂O was added to deionized water and ultrasonically dissolved for 45 min to prepare 50 mL of a cobalt nitrate solution with a concentration of 0.08 mol / L.

[0096] (4) The prepared cobalt nitrate solution was quickly poured into the dimethylimidazole solution and stirred at a stirring speed of 50 r / min for 1 min to fully mix the solution and obtain a mixed solution.

[0097] (5) Vertically suspend the pretreated carbon cloth in the mixed solution, place it in an incubator at 30 °C, and let it stand for 5 h for aging, so that the grown triangular flake-like two-dimensional cobalt-based metal-organic framework (Co-MOF) catalyst grows in-situ on the surface of the carbon cloth, forming triangular protrusions epitaxially grown from the electrode catalyst substrate. Subsequently, under the protection of argon, heat it to 550 °C at a heating rate of 2 °C / min in a tubular furnace and anneal for 3 h to obtain a hydrogen evolution electrode.

[0098] Comparative Example 3

[0099] The difference between this comparative example and Example 1 is only that: the shape of the through-hole in the mask used in this comparative example is linear. Specifically, the steps for preparing the hydrogen evolution electrode in this comparative example are as follows:

[0100] (1) Select a 4 cm 2 flexible conductive carbon cloth, and alternately wash it 3 times with deionized water and absolute ethanol, and then dry it in a vacuum oven for 24 h.

[0101] (2) Heat the dried carbon cloth in a muffle furnace to 450 °C at a heating rate of 10 °C / min, and heat it at this temperature for 3 h. Then, alternately wash it 3 times with deionized water and absolute ethanol, and then dry it overnight in a vacuum oven to obtain a pretreated carbon cloth.

[0102] (3) Add dimethylimidazole to deionized water and ultrasonicate for 45 min to fully dissolve it, and prepare 50 mL of a dimethylimidazole solution with a concentration of 0.4 mol / L; add Co(NO3)2·6H2O to deionized water and ultrasonicate for 45 min to fully dissolve it, and prepare 50 mL of a cobalt nitrate solution with a concentration of 0.08 mol / L.

[0103] (4) Quickly pour the prepared cobalt nitrate solution into the dimethylimidazole solution and stir at a stirring speed of 50 r / min for 1 min to fully mix the solution and obtain a mixed solution.

[0104] (5) Vertically suspend the pretreated carbon cloth in the mixed solution, place it in an incubator at 30 °C, and let it stand for 5 h for aging, so that the grown triangular flake-like two-dimensional cobalt-based metal-organic framework (Co-MOF) catalyst grows in-situ on the surface of the carbon cloth, forming triangular protrusions epitaxially grown from the electrode catalyst substrate. Subsequently, under the protection of argon, heat it to 550 °C at a heating rate of 2 °C / min in a tubular furnace and anneal for 3 h to obtain a geometric gradient electrode.

[0105] (6) A PET plastic mask with a thickness of 10 μm, slightly larger than the size of the carbon cloth, is taken. Vertical and parallel linear through-holes are cut out by laser. The width of the linear through-holes is 640 μm, and the interval between adjacent through-holes is 1000 μm. Then the mask is clamped and covered on the front and back surfaces of the geometric gradient electrode.

[0106] (7) 1.0 g of a polydimethylsiloxane (PDMS) prepolymer containing 10 wt% of a curing agent (Dow Corning DC184 PDMS polydimethylsiloxane high-transparency curing agent) is dissolved in 10 mL of n-hexane and stirred thoroughly to prepare a dipping solution. The geometric gradient electrode covered with the mask is immersed in the dipping solution for 15 s, taken out and placed in the air at room temperature for 30 s to attach a layer of PDMS prepolymer layer on the electrode surface.

[0107] (8) Hydrophobic nano-SiO2 particles (average particle size 16 nm) are uniformly deposited on the surface of the electrode with the PDMS prepolymer layer. It is heated at 80 °C for 2 h to cure the PDMS prepolymer layer and tightly attach the hydrophobic nano-SiO2 particles at the same time. Then it is carefully rinsed with sufficient ethanol to remove the unbonded hydrophobic nano-SiO2 particles and dried under a nitrogen stream for 24 h.

[0108] (9) The PET plastic mask clamped on the front and back sides of the electrode is removed to obtain a hydrogen evolution electrode. On the surface of the hydrogen evolution electrode, the area covered by the mask is not attached with hydrophobic nano-SiO2 particles, which is a hydrophilic and hydrophobic gas area, and the adjacent mask void area is a hydrophobic and hydrophilic gas area, forming a horizontal infiltration gradient. The total area of the hydrophobic and hydrophilic gas area accounts for 43% of the area on the electrode surface.

[0109] Comparative Example 4

[0110] The difference between this comparative example and Example 1 is only that: the shape of the through-holes in the mask used in this comparative example is circular. Specifically, the steps for preparing the hydrogen evolution electrode in this comparative example are as follows:

[0111] (1) A 4 cm 2 flexible conductive carbon cloth is selected and alternately washed 3 times with deionized water and absolute ethanol, and then dried in a vacuum oven for 24 h.

[0112] (2) The dried carbon cloth is heated in a muffle furnace at a heating rate of 10 °C / min to 450 °C and heated at this temperature for 3 h, then alternately washed 3 times with deionized water and absolute ethanol, and then dried overnight in a vacuum oven to obtain a pretreated carbon cloth.

[0113] (3) Add dimethylimidazole to deionized water and ultrasonicate for 45 min to fully dissolve it, and prepare 50 mL of a dimethylimidazole solution with a concentration of 0.4 mol / L; add Co(NO3)2·6H2O to deionized water and ultrasonicate for 45 min to fully dissolve it, and prepare 50 mL of a cobalt nitrate solution with a concentration of 0.08 mol / L.

[0114] (4) Quickly pour the prepared cobalt nitrate solution into the dimethylimidazole solution and stir at a stirring speed of 50 r / min for 1 min to fully mix the solution and obtain a mixed solution.

[0115] (5) Vertically suspend the pretreated carbon cloth in the mixed solution, place it in a constant temperature oven at 30 °C, and let it stand for 5 h for aging, so that the grown triangular flake-like two-dimensional cobalt-based metal-organic framework (Co-MOF) catalyst grows in-situ on the surface of the carbon cloth, forming triangular protrusions epitaxially extending from the electrode catalyst substrate. Subsequently, under the protection of argon, heat it to 550 °C at a heating rate of 2 °C / min in a tubular furnace and anneal for 3 h to obtain a geometric gradient electrode.

[0116] (6) Take a PET plastic mask with a thickness of 10 μm, the size of which is slightly larger than that of the carbon cloth, and cut out circular through-holes by laser. The diameter of the circular through-holes is 400 μm, and the interval between adjacent through-holes is 1000 μm (the arrangement of the circular through-holes in the mask is the same as that in Example 1). Then clamp the mask and cover the front and back surfaces of the geometric gradient electrode.

[0117] (7) Dissolve 1.0 g of a polydimethylsiloxane (PDMS) prepolymer containing 10 wt% curing agent (Dow Corning DC184 PDMS polydimethylsiloxane high-transparency curing agent) in 10 mL of n-hexane and stir well to make a dipping solution. Immerse the geometric gradient electrode covered with the mask in the dipping solution for 15 s, take it out and place it in the air at room temperature for 30 s to attach a layer of PDMS prepolymer layer on the electrode surface.

[0118] (8) Uniformly deposit hydrophobic nano-SiO2 particles (average particle size 16 nm) on the surface of the electrode with the PDMS prepolymer layer. Heat it at 80 °C for 2 h to cure the PDMS prepolymer layer and at the same time tightly attach the hydrophobic nano-SiO2 particles. Then carefully rinse it with sufficient ethanol to remove the unbound hydrophobic nano-SiO2 particles, and dry it under a nitrogen stream for 24 h.

[0119] (9) Remove the PET plastic mask sandwiched between the front and back sides of the electrode to obtain a hydrogen evolution electrode. On the surface of the hydrogen evolution electrode, the area covered by the mask is not attached with hydrophobic nano-SiO2 particles, which is a hydrophilic and hydrophobic gas area, and the adjacent mask void area is a hydrophobic and hydrophilic gas area, forming a horizontal wetting gradient. The total area of the hydrophobic and hydrophilic gas area accounts for 43% of the area on the electrode surface.

[0120] Comparative Example 5

[0121] The difference between this comparative example and Example 1 is only that: the apex angle of the through-hole in the mask used in this comparative example is 5°. Specifically, the steps for preparing the hydrogen evolution electrode in this comparative example are as follows:

[0122] (1) Select a flexible conductive carbon cloth of 4 cm 2 and wash it alternately with deionized water and absolute ethanol three times, and then dry it in a vacuum oven for 24 h.

[0123] (2) Heat the dried carbon cloth in a muffle furnace at a heating rate of 10 °C / min to 450 °C, and heat it at this temperature for 3 h. Then wash it alternately with deionized water and absolute ethanol three times, and then dry it overnight in a vacuum oven to obtain a pretreated carbon cloth.

[0124] (3) Add dimethylimidazole to deionized water and ultrasonically dissolve it for 45 min to prepare 50 mL of a dimethylimidazole solution with a concentration of 0.4 mol / L; add Co(NO3)2·6H2O to deionized water and ultrasonically dissolve it for 45 min to prepare 50 mL of a cobalt nitrate solution with a concentration of 0.08 mol / L.

[0125] (4) Quickly pour the prepared cobalt nitrate solution into the dimethylimidazole solution and stir it at a stirring speed of 50 r / min for 1 min to fully mix the solution and obtain a mixed solution.

[0126] (5) Vertically suspend the pretreated carbon cloth in the mixed solution, place it in a constant temperature oven at 30 °C, and let it stand for 5 h for aging, so that the grown triangular flake two-dimensional cobalt-based metal-organic framework (Co-MOF) catalyst grows in-situ on the surface of the carbon cloth, forming a triangular protrusion extending from the electrode catalyst substrate. Then, under the protection of argon, heat it in a tube furnace at a heating rate of 2 °C / min to 550 °C and anneal it for 3 h to obtain a geometric gradient electrode.

[0127] (6) Take a PET plastic mask with a thickness of 10 μm, the size of which is slightly larger than the size of the carbon cloth, and cut out triangular through-holes by laser. The apex angle of the triangular through-holes is 5°, and the height is 20 mm (the arrangement of the triangular through-holes in the mask is the same as that in Example 1). Then clamp and cover the mask on the front and back surfaces of the geometric gradient electrode.

[0128] (7) Dissolve 1.0 g of polydimethylsiloxane (PDMS) prepolymer containing 10 wt% curing agent (Dow Corning DC184 PDMS polydimethylsiloxane high-transparency curing agent) in 10 mL of n-hexane, and stir well to prepare a dip-coating solution. Immerse the geometric gradient electrode covered with a mask into the dip-coating solution for 15 s, take it out and place it in the air at room temperature for 30 s to attach a layer of PDMS prepolymer layer on the electrode surface.

[0129] (8) Uniformly deposit hydrophobic nano-SiO₂ particles (average particle size 16 nm) on the surface of the electrode with a PDMS prepolymer layer. Heat at 80 °C for 2 h to cure the PDMS prepolymer layer and tightly attach the hydrophobic nano-SiO₂ particles at the same time. Then carefully rinse with sufficient ethanol to remove the unbound hydrophobic nano-SiO₂ particles, and dry under a nitrogen stream for 24 h.

[0130] (9) Remove the PET plastic mask sandwiched on both sides of the electrode to obtain a hydrogen evolution electrode. On the surface of the hydrogen evolution electrode, the area covered by the mask is not attached with hydrophobic nano-SiO₂ particles, which is a hydrophilic and gas-phobic area, and the adjacent mask gap area is a hydrophobic and gas-philic area, forming a lateral infiltration gradient. The area ratio of the hydrophobic and gas-philic area on the electrode surface is 43%.

[0131] Comparative Example 6

[0132] The difference between this comparative example and Example 1 is only that: the top angle of the inner through-hole of the mask used in this comparative example is 60°. Specifically, the steps for preparing the hydrogen evolution electrode in this comparative example are as follows:

[0133] (1) Select a 4 cm 2 flexible conductive carbon cloth, wash it alternately with deionized water and absolute ethanol three times, and then dry it in a vacuum oven for 24 h.

[0134] (2) Heat the dried carbon cloth in a muffle furnace at a heating rate of 10 °C / min to 450 °C, and heat at this temperature for 3 h. Then wash it alternately with deionized water and absolute ethanol three times, and then dry it overnight in a vacuum oven to obtain a pretreated carbon cloth.

[0135] (3) Add dimethylimidazole to deionized water and ultrasonically dissolve it for 45 min to prepare 50 mL of a dimethylimidazole solution with a concentration of 0.4 mol / L; add Co(NO₃)₂·6H₂O to deionized water and ultrasonically dissolve it for 45 min to prepare 50 mL of a cobalt nitrate solution with a concentration of 0.08 mol / L.

[0136] (4) Rapidly pour the prepared cobalt nitrate solution into the 2-methylimidazole solution, and stir at a stirring speed of 50 r / min for 1 min to fully mix the solution and obtain a mixed solution.

[0137] (5) Vertically suspend the pretreated carbon cloth in the mixed solution, place it in an incubator at 30 °C, and let it stand for 5 h for aging, so that the grown triangular flake two-dimensional cobalt-based metal-organic framework (Co-MOF) catalyst grows in-situ on the surface of the carbon cloth, forming a triangular protrusion epitaxially grown from the electrode catalyst substrate. Subsequently, under the protection of argon, heat it to 550 °C at a heating rate of 2 °C / min in a tube furnace and anneal for 3 h to obtain a geometric gradient electrode.

[0138] (6) Take a PET plastic mask with a thickness of 10 μm, the size of which is slightly larger than that of the carbon cloth, and cut out triangular through-holes by laser. The apex angle of the triangular through-holes is 40°, and the height is 20 mm (the arrangement of the triangular through-holes in the mask is the same as that in Example 1). Then clamp the mask and cover the front and back surfaces of the geometric gradient electrode.

[0139] (7) Dissolve 1.0 g of polydimethylsiloxane (PDMS) prepolymer containing 10 wt% curing agent (Dow Corning DC184 PDMS polydimethylsiloxane high-transparency curing agent) in 10 mL of n-hexane, and stir well to prepare a dip-coating solution. Immerse the geometric gradient electrode covered with the mask in the dip-coating solution for 15 s, take it out and place it in the air at room temperature for 30 s to attach a layer of PDMS prepolymer layer on the electrode surface.

[0140] (8) Uniformly deposit hydrophobic nano-SiO2 particles (average particle size 16 nm) on the surface of the electrode with the PDMS prepolymer layer. Heat at 80 °C for 2 h to cure the PDMS prepolymer layer and at the same time tightly attach the hydrophobic nano-SiO2 particles. Then carefully rinse with sufficient ethanol to remove the unbound hydrophobic nano-SiO2 particles, and dry under a nitrogen stream for 24 h.

[0141] (9) Remove the PET plastic mask clamped on the front and back surfaces of the electrode to obtain a hydrogen evolution electrode. On the surface of the hydrogen evolution electrode, the area covered by the mask is not attached with hydrophobic nano-SiO2 particles, which is a hydrophilic and gasophobic area, and the adjacent mask gap area is a hydrophobic and gasophilic area, forming a horizontal wetting gradient. The area ratio of the hydrophobic and gasophilic area on the electrode surface is 43%.

[0142] Application Example

[0143] Assemble a single-chamber three-electrode system electrolytic cell. In the electrolytic cell, use the hydrogen evolution electrodes prepared in each of the examples and comparative examples as the working electrode cathode. When using the hydrogen evolution electrodes in Examples 1 to 3 and Comparative Examples 5 and 6, make the bottom edge of each hydrophobic and gasophilic region at the electrolyte liquid level 2 mm above the electrolyte liquid level; when using the hydrogen evolution electrode in Comparative Example 3, make the upper edge of each hydrophobic and gasophilic region at the electrolyte liquid level 2 mm above the electrolyte liquid level; when using the hydrogen evolution electrode in Comparative Example 4, make the upper edge of each hydrophobic and gasophilic region at the electrolyte liquid level 40 μm above the electrolyte liquid level. Use a standard Ag / AgCl electrode as the reference electrode and a graphite rod electrode as the counter electrode. Inject a 1 mol / L potassium hydroxide solution into the electrolytic cell as the electrolyte, adjust the pH value to 14, and perform electrolytic hydrogen evolution reaction.

[0144] At a current density of 100 mA / cm 2 , perform a constant current test. Record the overpotential at the 0th h and record the overpotential again at the 100th h, and calculate the overpotential growth rate. The results are shown in Table 1. The calculation formula for the overpotential growth rate is as follows: overpotential growth rate = (overpotential at the 100th h - overpotential at the 0th h) / 100 h.

[0145] Table 1 Test results of hydrogen evolution electrode performance

[0146]

[0147] Analysis of test results:

[0148] (1) Comparing Examples 1 to 3 with Comparative Example 1, it can be seen that: compared with the conventional platinum-carbon electrode, by using the method of the present invention, the overpotential and overpotential growth rate of the hydrogen evolution electrode can be effectively reduced.

[0149] (2) Comparing Example 1 with Comparative Example 2, it can be seen that: the present invention uses a mask to form a lateral infiltration gradient on the electrode surface, which can reduce the overpotential and overpotential growth rate of the hydrogen evolution electrode. The reason for the analysis is that: the hydrophilic and gasophobic regions and hydrophobic and gasophilic regions formed on the electrode surface by using the mask can respectively function as the electrolytic hydrogen evolution region and the gas transport region; the hydrophilic and gasophobic regions and hydrophobic and gasophilic regions on the electrode surface form an infiltration gradient at the interactive boundary; when bubbles are generated in the electrolytic hydrogen evolution region, the bubbles will be affected by the gradient infiltration gradient and move laterally from the electrolytic hydrogen evolution region with a small bubble infiltration angle to the gasophilic gas transport region under the action of surface tension, so as to ensure that the catalytic active sites in the electrolytic hydrogen evolution region under high current are not covered by bubbles, and at the same time reduce the hydrogen partial pressure on its surface, making the electrolytic water reaction proceed in the forward direction, thus contributing to improving the hydrogen production efficiency and reducing the impact of the small bubble coalescence process on the electrode surface.

[0150] (3) By comparing Example 1 with Comparative Example 3 and Comparative Example 4, it can be seen that: compared with the linear and circular shapes, designing the shape of the through-holes on the mask as triangular in the present invention is beneficial to reducing the overpotential and the overpotential growth rate of the hydrogen evolution electrode. The reason for the analysis is as follows: The hydrophobic and gasophilic regions formed by the triangular through-holes can form a geometric shape gradient, thus effectively inducing the migration of bubbles from the tip to the bottom, and then being beneficial to the transfer of bubbles in the hydrophilic and gasophobic regions to the hydrophobic and gasophilic regions; while the hydrophobic and gasophilic regions formed by the linear through-holes lack unbalanced surface tension, and the directional transportation of bubbles will be restricted, so the effect of reducing the overpotential and the overpotential growth rate is poor; it is difficult for the hydrophobic and gasophilic regions formed by the circular through-holes to induce the bubbles to be sent out to the external space of the electrolyte, and they accumulate on the electrode surface and cannot achieve the directional transportation of bubbles.

[0151] (4) By comparing Example 1 with Comparative Example 6, it can be seen that: when the apex angle of the triangular through-hole is too large, it will lead to a larger overpotential and overpotential growth rate of the hydrogen evolution electrode. The reason for the analysis is as follows: when the apex angle of the triangular through-hole is too large, the apex angle of the formed triangular hydrophobic and gasophilic region is too large, which will cause the Laplace force induced by the geometric effect to fail, and it is impossible to induce the directional transportation of bubbles through the tip effect. Instead, it will cause the bubbles to accumulate inside the hydrophobic and gasophilic layer, resulting in too high a local hydrogen concentration.

[0152] Unless otherwise defined, all technical terms and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the art to which the present disclosure belongs. The raw materials and equipment used in the present invention are conventional raw materials and equipment in the art and can be obtained from conventional commercial channels without special instructions; the methods used in the present invention are conventional methods in the art without special instructions.

[0153] The above are only the preferred embodiments of the present invention and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent transformations made to the above embodiments according to the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A preparation method of a dual-gradient self-supporting hydrogen evolution electrode, characterized in that, It includes the following steps: S1: Form oxygen-containing hydrophilic groups on the surface of the conductive carbon cloth to obtain a pretreated carbon cloth; S2: In-situ self-grow a metal-organic framework composed of Co and dimethylimidazole on the surface of the pretreated carbon cloth. The metal-organic framework forms triangular protrusions on the surface of the pretreated carbon cloth, and then calcine to obtain a geometric gradient electrode; S3: Cover a mask with a number of through-holes on the surface of the geometric gradient electrode, apply a hydrophobic and air-permeable coating through the through-holes on the surface of the geometric gradient electrode, and form a number of hydrophobic and air-permeable regions on the surface of the geometric gradient electrode; The shape of the through-hole is triangular, the apex angle is 10° - 30°, the height is 10 - 20 mm, and the distance between the bottom edges of adjacent through-holes is 100 - 200 μm.

2. The preparation method according to claim 1, wherein, In step S3, the total area of the hydrophobic and air-permeable regions accounts for 10% - 60% of the area of the electrode surface.

3. The preparation method according to claim 1 or 2, characterized in that, In step S3, the hydrophobic and air-permeable coating is composed of a polydimethylsiloxane layer and hydrophobic nano-SiO₂ bonded to the polydimethylsiloxane layer.

4. The preparation method according to claim 1, characterized in that, Step S1 specifically includes: After cleaning and drying the conductive carbon cloth with water and absolute ethanol, heat it to 450 - 550 °C at a rate of 10 - 15 °C / min and hold for 2 - 5 h, and then clean it with water and ethanol.

5. The preparation method according to claim 1, characterized in that, Step S2 specifically includes: preparing a solution containing dimethylimidazole and Co 2+ , suspending the pretreated carbon cloth therein, with the inclination angle relative to the vertical direction not greater than 45°, and standing and aging at 30-35°C for 2-5 h.

6. The preparation method according to claim 5, characterized in that, The dimethylimidazole and Co 2+ have a molar ratio of 1 to 12:1; in the solution containing dimethylimidazole and Co 2+ , the concentration of Co 2+ is 0.03 to 0.4 mol / L.

7. The preparation method according to claim 3, characterized in that, In step S3, the process of applying the hydrophobic and air-permeable coating specifically includes: Immerse the geometric gradient electrode covered with the mask in a solution containing a polydimethylsiloxane prepolymer and a curing agent for 10 - 100 s, take it out and place it in the air for 10 - 40 s to form a prepolymer layer; Then deposit hydrophobic nano-SiO₂ on the prepolymer layer and cure it.

8. Application of a dual-gradient self-supporting hydrogen evolution electrode in electrocatalytic hydrogen evolution, characterized in that, The dual-gradient self-supporting hydrogen evolution electrode is prepared by the preparation method according to any one of claims 1 - 7.

9. The application according to claim 8, wherein During the electrocatalytic hydrogen evolution process, the dual-gradient self-supporting hydrogen evolution electrode is partially immersed in the electrolyte; The hydrophobic and air-permeable regions are triangular, the bottom edge of each hydrophobic and air-permeable region at the electrolyte liquid level is above the electrolyte liquid level, and the apex angle is below the electrolyte liquid level.

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