A cathode electrode for alkaline water electrolysis to produce hydrogen containing a transition layer

Abstract

This invention relates to a cathode electrode for alkaline water electrolysis hydrogen production containing a transition layer, belonging to the field of alkaline water electrolysis hydrogen production technology. The cathode electrode is composed of a porous carbon / carbon composite matrix, a transition layer, and a water electrolysis catalyst layer. The transition layer is located between the porous carbon / carbon composite matrix and the water electrolysis catalyst layer. The transition layer is composed of an elemental transition metal or an alloy of transition metals. The presence of the transition layer not only improves the conductivity of the porous carbon / carbon composite matrix but also synergistically enhances the hydrogen evolution catalytic performance with the water electrolysis catalyst. The cathode electrode of this invention features high specific surface area, low density, resistance to strong alkali corrosion, and good hydrogen evolution catalytic activity. It can also operate stably for extended periods, showing promising application prospects in alkaline water electrolysis hydrogen production.

Description

Technical Field

[0001] This invention relates to a cathode electrode for alkaline water electrolysis hydrogen production containing a transition layer, belonging to the field of alkaline water electrolysis hydrogen production technology. Background Technology

[0002] Hydrogen energy is a green, low-carbon, high-calorific-value, renewable green energy source with diverse storage and transportation methods and wide application scenarios. It is regarded as the ultimate energy source under the "dual carbon" goal. Green hydrogen is generated by using renewable and clean energy sources such as solar and wind power to produce hydrogen gas through water electrolysis, effectively solving the problem of new energy consumption and truly achieving the "decarbonization" of energy.

[0003] Alkaline water electrolysis (ALK) is the largest-scale and commercially applied green hydrogen production technology to date. The electrolyzer is the key equipment in ALK hydrogen production, and the quality of its core component, the cathode electrode, directly determines the hydrogen production efficiency and capacity. Currently, commercially available cathode electrodes use nickel mesh as a substrate, with nickel-based catalyst powder loaded onto the substrate via thermal spraying to form the electrode. However, electrode materials prepared using this technology suffer from low catalytic activity, poor resistance to strong alkali corrosion, short lifespan at high current densities, and easy coating peeling, directly affecting the electrolyzer's lifespan and hydrogen production efficiency. Therefore, the development of high-performance novel cathode electrode materials is urgently needed. Summary of the Invention

[0004] To address the shortcomings of current cathode electrode materials in alkaline water electrolysis for hydrogen production, this invention provides a cathode electrode with a transition layer for alkaline water electrolysis. This cathode electrode uses a porous carbon / carbon composite material as its matrix, which features low density, high specific surface area, and resistance to strong alkali corrosion. Its porous structure ensures rapid transport of reaction ions with the alkaline solution. A transition layer is introduced onto the matrix before loading a water electrolysis catalyst. This transition layer not only improves the conductivity of the matrix, allowing electrons to diffuse rapidly on the cathode surface and supplying sufficient electrons for the reduction reaction at the cathode to produce hydrogen, but also possesses certain catalytic properties. Working synergistically with the water electrolysis catalyst, it exhibits superior catalytic effects, thus giving the cathode electrode excellent hydrogen evolution catalytic activity and enabling stable operation over long periods. This demonstrates promising application prospects in alkaline water electrolysis for hydrogen production.

[0005] The objective of this invention is achieved through the following technical solutions.

[0006] A cathode electrode for alkaline water electrolysis to produce hydrogen containing a transition layer, the cathode electrode being composed of a porous carbon / carbon composite matrix, a transition layer, and a water electrolysis catalyst layer, wherein the transition layer is located between the porous carbon / carbon composite matrix and the water electrolysis catalyst layer;

[0007] The transition layer is composed of an elemental transition metal or an alloy of transition metals.

[0008] Preferably, the thickness of the transition layer is 0.1~200μm (i.e. 100nm~200μm).

[0009] Preferably, the elemental transition metal is nickel (Ni) or cobalt (Co), and the alloy of the transition metal is a nickel-iron alloy. More preferably, the molar ratio of nickel to iron in the nickel-iron alloy is 10:1 to 15:1.

[0010] Preferably, a transition layer is prepared on a porous carbon / carbon composite matrix using a thermal spraying method, a chemical reaction synthesis method, or a hydrothermal electrodeposition method.

[0011] Preferably, the water electrolysis catalyst layer is composed of a water electrolysis catalyst containing a transition metal, but the composition of the water electrolysis catalyst layer differs from that of the transition layer. More preferably, when the transition layer is composed of an elemental transition metal, the water electrolysis catalyst layer is composed of an alloy of the transition metal, an oxide of the transition metal, or a carbide of the transition metal; when the transition layer is composed of an alloy of the transition metal, the water electrolysis catalyst layer is composed of a carbide of the transition metal.

[0012] Preferably, the transition metal alloy in the water electrolysis catalyst layer is a copper-vanadium-zinc-nickel alloy, the transition metal oxide is a nickel-zinc-iron oxide, and the transition metal carbide is tungsten carbide or molybdenum carbide. More preferably, the molar ratio of copper, vanadium, zinc, and nickel in the copper-vanadium-zinc-nickel alloy is 1:1:1:(1.5~3), and the molar ratio of nickel, zinc, and iron in the nickel-zinc-iron oxide is (4~5):1:1.

[0013] Preferably, the particle size of the water electrolysis catalyst in the water electrolysis catalyst layer is 0.005~2μm (i.e. 5nm~2μm).

[0014] Preferably, the thickness of the water electrolysis catalyst layer is 0.03~5μm (i.e. 30nm~5μm).

[0015] Preferably, the water electrolysis catalyst layer is prepared on the transition layer by electrodeposition, vapor deposition or hydrothermal method.

[0016] Preferably, the degree of graphitization of the porous carbon / carbon composite matrix is ​​85-99%, and the specific surface area is 0.7-3 m². 2 / g, contact angle is 100~160° o The compressive strength is not less than 1.6 MPa.

[0017] Preferably, the porous carbon / carbon composite matrix undergoes a roughening pretreatment before the transition layer is prepared. This roughening pretreatment further increases the specific surface area of ​​the porous carbon / carbon composite matrix and reduces its contact angle, thereby improving the bonding effect between the transition layer and the porous carbon / carbon composite matrix. More preferably, the specific surface area of ​​the porous carbon / carbon composite matrix after the roughening pretreatment is 1~5 m². 2 / g, contact angle 50~110 o .

[0018] Preferably, the porous carbon / carbon composite matrix is ​​pretreated by gas-phase oxidation, liquid-phase oxidation, or a combination of both; more preferably, the gas-phase oxidation method involves placing the porous carbon / carbon composite matrix at 350-600°C. o Oxidation treatment at C for 15-50 min, or liquid phase oxidation treatment by placing the porous carbon / carbon composite matrix in a 5-30 wt.% acid solution for 10-30 min.

[0019] Preferably, the porous carbon / carbon composite matrix is ​​formed by graphitizing porous framework carbon and a second-phase carbon covering the surface of the porous framework carbon. More preferably, the density of the porous framework carbon is 0.05~0.7 g / cm³. 3 The density of the porous framework carbon coated with a second phase of carbon is 0.14~1 g / cm³. 3 .

[0020] Preferably, the porosity of the porous framework carbon is 20-80%. More preferably, the pore size of the porous framework carbon is 0.07-500 μm (i.e. 70 nm-500 μm).

[0021] Preferably, after coating the porous framework carbon with a second phase of carbon, the temperature is between 2000 and 2800 °C. o Graphitization treatment at C for 1~6 hours forms the porous carbon / carbon composite matrix.

[0022] Preferably, the porous skeletal carbon is prepared from carbon fiber woven fabric, biochar, or foam carbon as a precursor.

[0023] Preferably, the porous framework carbon prepared from carbon fiber woven fabric has a pore size of 100~500μm and a porosity of 35~60%; the porous framework carbon prepared from biochar has a pore size of 70nm~200μm and a porosity of 20~50%; and the porous framework carbon prepared from foamed carbon has a pore size of 50~300μm and a porosity of 40~80%.

[0024] Preferably, the second phase carbon is formed by depositing a carbon source gas onto a porous framework carbon using a chemical vapor deposition (CVD) process; more preferably, the carbon source gas includes, but is not limited to, natural gas, propylene, or acetylene, and the deposition temperature of the CVD process is 800~1100°C. o C, the carbon source gas flow rate is 1~5m 3 / h, deposition time is 50~100h;

[0025] Alternatively, the second phase carbon is formed by the pyrolysis of a carbon source liquid on a porous framework carbon through a liquid-phase impregnation process; more preferably, the carbon source liquid includes, but is not limited to, asphalt, phenolic resin, or epoxy resin, and the pyrolysis temperature of the liquid-phase impregnation process is 900~1000℃. o C, the pyrolysis time is 1~5h;

[0026] Alternatively, part of the second phase carbon is formed by depositing carbon source gas onto porous framework carbon via chemical vapor deposition, and another part is formed by pyrolyzing carbon source liquid onto porous framework carbon via liquid phase impregnation.

[0027] Preferably, the porous framework carbon is prepared from carbon fiber woven fabric, and the density of the porous framework carbon is 0.6~0.7 g / cm³. 3 The density of the porous framework carbon coated with a second phase of carbon is 0.8~1 g / cm³. 3 Porous framework carbon prepared from biochar, with a density of 0.1~0.3 g / cm³. 3 The density of the porous framework carbon coated with a second phase of carbon is 0.3~0.5 g / cm³. 3 Porous framework carbon prepared from foamed carbon, with a density of 0.05~0.12 g / cm³. 3 The density of the porous framework carbon coated with a second phase of carbon is 0.14~0.25 g / cm³. 3 .

[0028] Preferably, the porous carbon / carbon composite matrix formed by graphitization of the porous carbon skeletal carbon prepared from carbon fiber braids has a graphitization degree of 96-99%, a resistivity of 1-10 mΩ·cm, and a specific surface area of ​​1-2.5 m². 2 / g, contact angle is 110~150° o The porous carbon / carbon composite matrix formed by graphitization of porous carbon prepared from biomass char has a graphitization degree of 85-92%, a resistivity of 15-30 mΩ·cm, and a specific surface area of ​​1.5-3 m². 2 / g, contact angle is 100~140° o The porous carbon / carbon composite matrix formed by graphitization of porous carbon based on foamed carbon has a graphitization degree of 90-97%, a resistivity of 10-20 mΩ·cm, and a specific surface area of ​​0.7-1 m².2 / g, contact angle is 130~160° o .

[0029] Preferably, the porous carbon / carbon composite matrix prepared based on porous skeleton carbon made from carbon fiber braided fabric has a specific surface area of ​​2-4 m² after roughening pretreatment. 2 / g, contact angle 60~90 o The porous carbon / carbon composite matrix prepared from porous framework carbon based on biochar, after roughening pretreatment, has a specific surface area of ​​2.5~5 m². 2 / g, contact angle 50~80 o The porous carbon / carbon composite matrix prepared based on porous framework carbon from foamed carbon, after roughening pretreatment, has a specific surface area of ​​1~2 m². 2 / g, contact angle is 70~110 o .

[0030] Preferably, the specific surface area of ​​the cathode is 0.8~4.2m². 2 / g, density is 0.32~1.85g / cm³ 3 .

[0031] Beneficial effects:

[0032] (1) The cathode of this invention uses a porous carbon / carbon composite material as the matrix. On the one hand, its porous structure provides channels for alkali solution and charge transfer, ensuring rapid transfer of reaction ions with the alkali solution. On the other hand, compared with metal matrix, porous carbon / carbon composite material matrix has lower density, higher specific surface area, and excellent resistance to strong alkali corrosion, resulting in better bonding with subsequent coatings and increasing the effective loading of water electrolysis catalyst. Introducing a transition layer between the matrix and the water electrolysis catalyst layer not only improves the conductivity of the matrix, allowing electrons to diffuse rapidly on the cathode surface and supplying sufficient electrons for hydrogen production in the reduction reaction on the cathode, but also has certain catalytic properties, working synergistically with the water electrolysis catalyst to exhibit a superior catalytic effect. The cathode of this invention has the characteristics of high specific surface area, low density, and good hydrogen evolution catalytic activity, enabling stable operation for a long time. It provides a feasible solution for the continued promotion and application of alkaline water electrolysis hydrogen production technology and has good application prospects.

[0033] (2) When the transition layer component of the present invention is an elemental transition metal, although the catalytic activity of the transition metal itself is relatively poor, its main function is to provide sufficient electrons for the hydrogen evolution reaction. By using it in conjunction with a transition metal-based water electrolysis catalyst with excellent hydrogen evolution catalytic activity, the potential barrier required for the entire reduction reaction can be effectively reduced, thereby achieving an overall improvement in the hydrogen evolution reaction rate at the cathode. When the transition layer component is an alloy of transition metals, it is used in conjunction with a transition metal carbide-based water electrolysis catalyst. The main function is to utilize the transition metal alloy to redistribute the valence electrons of the transition metal carbides, increase the hydrogen binding energy, and accelerate the desorption of hydrogen atoms, thereby effectively improving the hydrogen evolution reaction rate at the cathode. In addition, the transition layer of the present invention itself has a certain hydrogen evolution catalytic activity. The introduction of the transition layer can prevent the formation of areas with poor catalytic activity due to the local exposure of the substrate caused by the thin water electrolysis catalyst layer.

[0034] (3) The present invention performs a roughening pretreatment on the porous carbon / carbon composite matrix, which can further increase its surface area and thus increase the effective loading of the water electrolysis catalyst. On the other hand, it can further improve its bonding effect with the transition layer, which is beneficial to further improve the hydrogen evolution catalytic activity and service life of the cathode.

[0035] (4) The porous carbon / carbon composite matrix of the present invention is formed by graphitization of porous framework carbon and second phase carbon covering the surface of porous framework carbon. The porous framework carbon as the matrix and the second phase carbon as the reinforcing phase are used in combination to achieve a higher degree of graphitization, so that the carbon atoms in the porous carbon / carbon composite matrix are arranged in a more ordered manner, thereby improving the conductivity of the porous carbon / carbon composite matrix. This meets the conductivity and strength requirements of the cathode for the loaded water electrolysis catalyst matrix in alkaline water electrolysis hydrogen production. In addition, it has a small density, a high specific surface area, and excellent resistance to strong alkali corrosion, which lays the foundation for the excellent hydrogen evolution catalytic performance of the cathode. Attached Figure Description

[0036] Figure 1 This is a comparison of XRD (X-ray diffraction) images before and after loading a Co layer onto a porous carbon / carbon composite matrix in Example 1.

[0037] Figure 2 This is a comparison of the HER (hydrogen evolution reaction) performance of Example 1 before and after loading a Co layer onto a porous carbon / carbon composite matrix.

[0038] Figure 3 This is a surface SEM (scanning electron microscope) image of the water electrolysis catalyst layer prepared on the transition layer in Example 3.

[0039] Figure 4The polarization curves of the cathode prepared in Example 5 are compared with those of the cathode prepared in Comparative Example 1. Detailed Implementation

[0040] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Unless otherwise specified, the methods described are conventional methods, and the raw materials described are obtainable from publicly available commercial sources.

[0041] In the following examples, porosity, pore size, density, and specific surface area were tested according to standard GB / T 21650.1-2008; resistivity was tested according to standard GB / T 1552-1995; compressive strength was tested according to standard GB / T 1448-2005; and contact angle was tested according to standard ASTM D724-1999. The relationship between the lattice constant and the degree of graphitization of the artificial graphite material was derived from Franklin's method.

[0042] g=[(0.3440-c0 / 2) / 0.0086]×100%

[0043] Where g is the degree of graphitization (%), and c0 is the lattice constant of the c-axis of hexagonal graphite (nm). When c0 = 0.6708 nm, g = 100%; when c0 = 0.6880 nm, g = 0%. Standard QJ2507-93 specifies the method for determining the structural parameters of carbon materials by XRD. Substituting the interplanar spacings d002 and d004 of carbon (002) and (004) obtained by XRD into the above formula, the degree of graphitization g of the sample can be calculated.

[0044] Example 1

[0045] A cathode for alkaline water electrolysis to produce hydrogen containing a transition layer is composed of a porous carbon / carbon composite matrix, a transition layer, and a water electrolysis catalyst layer. The specific preparation steps are as follows:

[0046] (1) Preparation of porous carbon / carbon composite matrix

[0047] (1.1) Under a nitrogen atmosphere, for a density of 0.6 g / cm³ 3 Carbon fiber woven fabric with a porosity of 60% and a pore size of ~300μm was subjected to 900... o C. After 2 hours of debinding treatment, the sizing agent on its surface is removed, and porous framework carbon is obtained.

[0048] (1.2) The porous framework carbon obtained in step (1.1) is loaded into a chemical vapor deposition furnace for the deposition of second-phase carbon, wherein the carbon source gas is propylene and the flow rate is 2 m³ / s. 3 / h, deposition temperature is 1000 oC, with a deposition time of 50 hours, a second phase of carbon is deposited on the porous framework carbon; at this time, the density of the porous framework carbon after the deposition of the second phase carbon is 0.9 g / cm³. 3 The degree of graphitization is 95%, and the resistivity is 4.3 mΩ·cm;

[0049] (1.3) The porous framework carbon after the deposition of the second phase carbon in step (1.2) is loaded into a graphitization furnace and subjected to argon protection atmosphere and 2800 °C. o The porous carbon / carbon composite matrix was obtained by high-temperature graphitization treatment at C for 1 hour, with a graphitization degree of 99%, a resistivity of 2.0 mΩ·cm, and a specific surface area of ​​1.2 m². 2 / g, contact angle is 115 o The compressive strength is greater than 5 MPa;

[0050] (1.4) Further, the porous carbon / carbon composite matrix obtained in step (1.3) is subjected to a roughening pretreatment, namely: the porous carbon / carbon composite matrix is ​​placed at 600°C. o Oxidation treatment at C for 20 min, followed by oxidation treatment in 15 wt.% nitric acid solution for 10 min, then ultrasonic cleaning with deionized water, and finally immersion in 120 °C. o The porous carbon / carbon composite matrix was dried in an oven at C for 24 hours to obtain a roughened matrix with a specific surface area of ​​2.3 m². 2 / g, contact angle is 66 o ;

[0051] (2) Preparation of a transition layer on a porous carbon / carbon composite matrix

[0052] (2.1) Add 72.75g of Co(NO3)2·6H2O to 1000mL of water, and then sonicate for 2h to obtain a homogeneous cobalt nitrate solution;

[0053] (2.2) The cobalt nitrate solution prepared in step (2.1) is uniformly sprayed onto the porous carbon / carbon composite matrix roughened in step (1.4) using a sprayer, and then transferred to a freeze dryer at -60°C. o Freeze-dry at C for 24 hours, then transfer to a reduction furnace and freeze-dry at 650°C under H2 atmosphere. o If the C reaction lasts for 2 hours, a Co layer with a thickness of ~260 nm (abbreviated as Co-C / C composite material) is formed on the porous carbon / carbon composite matrix. At this time, the Co layer is the transition layer.

[0054] (3) Preparation of a water electrolysis catalyst layer on the transition layer

[0055] Under an argon atmosphere, a Cu-V-Zn-Ni alloy layer with a thickness of ~100 nm is deposited on the transition layer prepared in step (2.2) by physical vapor deposition (the molar ratio of Cu, V, Zn and Ni elements in the Cu-V-Zn-Ni alloy layer is 1:1:1:3). At this time, the Cu-V-Zn-Ni alloy layer is the water electrolysis catalyst layer, and the preparation of the cathode is completed accordingly.

[0056] Phase analysis was performed on the porous carbon / carbon composite matrix before and after the Co layer was loaded in step (1.4), according to... Figure 1 The XRD pattern characterization results show that the Co-loaded layer has characteristic diffraction peaks of the Co phase and no other impurity elements were introduced.

[0057] The hydrogen evolution reaction (HER) performance of the porous carbon / carbon composite matrix before and after the Co layer loading in step (1.4) was tested. Specifically, in a 30 wt.% KOH solution, using the sample as the working electrode, graphite as the counter electrode, and a saturated calomel electrode as the reference electrode, the linear sweep voltammetry (LSV) curve of the hydrogen evolution reaction of the sample at room temperature was measured using a three-electrode method. The HER catalytic activity of the sample was determined by the overpotential magnitude. Detailed test results can be found in [link to relevant documentation]. Figure 2 .from Figure 2 As can be seen from the data, after loading through the Co transition layer, the overpotential of the hydrogen evolution reaction of the material decreases significantly under the same current density, which means that the catalytic activity of the material for hydrogen evolution is greatly improved.

[0058] The microstructure of the water electrolysis catalyst layer prepared on the transition layer in step (3) was characterized. According to the surface SEM test results, the water electrolysis catalyst layer is a continuous layer formed by the stacking of spherical nanoparticles with a size of about 10 nm.

[0059] The specific surface area of ​​the cathode prepared in Example 1 is 2.13 m². 2 / g, density is 1.05g / cm³ 3 .

[0060] The cathode prepared in Example 1 was used at 25°C. o C. In a 30 wt.% potassium hydroxide alkaline solution, at 5000 A / m 2 At a given current density, the hydrogen evolution overpotential of this cathode is 389 mV, indicating its high hydrogen evolution activity; moreover, it can operate stably for 450 hours without degradation, indicating its structural stability and long service life.

[0061] Example 2

[0062] A cathode for alkaline water electrolysis to produce hydrogen containing a transition layer is composed of a porous carbon / carbon composite matrix, a transition layer, and a water electrolysis catalyst layer. The specific preparation steps are as follows:

[0063] (1) The preparation steps and process conditions of the porous carbon / carbon composite matrix are the same as those in step (1) of Example 1;

[0064] (2) Preparation of a transition layer on a porous carbon / carbon composite matrix

[0065] (2.1) Add 59.42 g of NiCl2·6H2O to 1000 mL of water, and then sonicate for 2 h to obtain a homogeneous nickel chloride solution;

[0066] (2.2) The nickel chloride solution prepared in step (2.1) is uniformly sprayed onto the porous carbon / carbon composite matrix roughened in step (1.4) using a sprayer, and then transferred to a freeze dryer at -60°C. o Freeze-dry at C for 24 hours, then transfer to a reduction furnace and freeze-dry at 550°C under H2 atmosphere. o If the reaction proceeds for 2 hours, a Ni layer with a thickness of ~300 nm (referred to as Ni-C / C composite material) is formed on the porous carbon / carbon composite matrix. At this time, the Ni layer is the transition layer.

[0067] (3) Preparation of a water electrolysis catalyst layer on the transition layer

[0068] Under an argon atmosphere, a Cu-V-Zn-Ni alloy layer with a thickness of ~100 nm is deposited on the transition layer prepared in step (2.2) by physical vapor deposition (the molar ratio of Cu, V, Zn and Ni elements in the Cu-V-Zn-Ni alloy layer is 1:1:1:3). At this time, the Cu-V-Zn-Ni alloy layer is the water electrolysis catalyst layer, and the preparation of the cathode is completed accordingly.

[0069] The hydrogen evolution reaction (HER) performance of the porous carbon / carbon composite matrix before and after loading with the Ni layer in step (1.4) was tested. Specifically, in a 30 wt.% KOH solution, using the sample as the working electrode, graphite as the counter electrode, and a saturated calomel electrode as the reference electrode, the linear sweep voltammetry (LSV) curve of the hydrogen evolution reaction of the sample at room temperature was measured using a three-electrode method. The HER catalytic activity of the sample was determined by the magnitude of the overpotential. The test results show that after loading with the Ni transition layer, the HER overpotential of the material at the same current density decreased significantly, indicating a substantial improvement in the HER catalytic activity.

[0070] The microstructure of the water electrolysis catalyst layer prepared on the transition layer in step (3) was characterized. According to the test results, the water electrolysis catalyst layer is a continuous layer formed by the stacking of spherical nanoparticles with a size of about 10 nm.

[0071] The specific surface area of ​​the cathode prepared in Example 2 is 2.08 m². 2 / g, density is 1.1g / cm³3 .

[0072] The cathode prepared in Example 2 was used at 25°C. o C. In a 30 wt.% potassium hydroxide alkaline solution, at 5000 A / m 2 At a given current density, the hydrogen evolution overpotential of this cathode is 415mV, indicating its high hydrogen evolution activity; moreover, it can operate stably for 500 hours without degradation, indicating its structural stability and long service life.

[0073] Example 3

[0074] A cathode for alkaline water electrolysis to produce hydrogen containing a transition layer is composed of a porous carbon / carbon composite matrix, a transition layer, and a water electrolysis catalyst layer. The specific preparation steps are as follows:

[0075] (1) The preparation steps and process conditions of the porous carbon / carbon composite matrix are the same as those in step (1) of Example 1;

[0076] (2) Preparation of a transition layer on a porous carbon / carbon composite matrix

[0077] Nickel powder with a particle size of 20~50μm was uniformly sprayed onto the porous carbon / carbon composite matrix after roughening in step (1.4) using plasma thermal spraying. The powder feeding speed was 70g / min and the spray gun scanning speed was 300mm / s. After spraying, the matrix was ultrasonically cleaned in 7wt.% hydrochloric acid solution for 15min to remove nickel oxide. A Ni layer with a thickness of ~80μm (referred to as Ni-C / C composite material) was formed on the porous carbon / carbon composite matrix. At this time, the Ni layer is the transition layer.

[0078] (3) Preparation of a water electrolysis catalyst layer on the transition layer

[0079] (3.1) Add 0.95g of NiCl2·6H2O, 0.22g of Zn(CH3COO)2·2H2O, 0.28g of FeSO4·7H2O, 0.04g of urea and 50mL of deionized water to a beaker, and then stir on a magnetic stirrer for 30min to obtain a well mixed solution;

[0080] (3.2) Add the mixed solution prepared in step (3.1) and the Ni-C / C composite material prepared in step (2) into the reactor. After sealing the reactor, place it in a forced-air drying oven and set the temperature parameter to 170°C. o C, react for 5 hours. After the reaction is complete, cool to room temperature, collect the solid product, and ultrasonically wash it three times alternately with distilled water and ethanol. Then place it in an oven at 60°C. oDrying at C for 10 hours forms a Ni-Zn-Fe alloy layer with a thickness of ~500 nm on the transition layer (the molar ratio of Ni, Zn, and Fe elements in the Ni-Zn-Fe alloy layer is 4:1:1). At this time, the Ni-Zn-Fe alloy layer is the water electrolysis catalyst layer, and the preparation of the cathode is completed accordingly.

[0081] The hydrogen evolution reaction (HER) performance of the porous carbon / carbon composite matrix before and after loading with the Ni layer in step (1.4) was tested. Specifically, in a 30 wt.% KOH solution, using the sample as the working electrode, graphite as the counter electrode, and a saturated calomel electrode as the reference electrode, the linear sweep voltammetry (LSV) curve of the hydrogen evolution reaction of the sample at room temperature was measured using a three-electrode method. The HER catalytic activity of the sample was determined by the overpotential magnitude. The test results showed that after loading with the Ni transition layer, the HER overpotential of the material decreased significantly at the same current density, indicating a significant improvement in the HER catalytic activity. However, compared to the Ni-C / C composite material in Example 2, the HER catalytic activity of the Ni-C / C composite material in Example 3 was slightly lower. This is mainly because the nickel particles in the Ni transition layer prepared in Example 3 were micrometer-sized, which, compared to the nanometer-sized nickel particles prepared in Example 2, had a relatively smaller specific surface area, resulting in fewer exposed active sites and thus lower HER catalytic activity.

[0082] The microstructure of the water electrolysis catalyst layer prepared on the transition layer in step (3) was characterized. According to the test results, the water electrolysis catalyst layer is a three-dimensional flower-like structure formed by the assembly of nanosheets with a thickness of about 30 nm, such as... Figure 3 As shown.

[0083] The specific surface area of ​​the cathode prepared in Example 3 is 1.77 m². 2 / g, density is 1.73g / cm³ 3 .

[0084] The cathode prepared in Example 3 was used at 25°C. o C. In a 30 wt.% potassium hydroxide alkaline solution, at 5000 A / m 2 At the specified current density, the hydrogen evolution overpotential of the cathode is 395mV, indicating its high hydrogen evolution activity; moreover, it can operate stably for 550 hours without degradation, indicating its structural stability and long service life.

[0085] Example 4

[0086] Based on Example 3, except that the mass of NiCl2·6H2O in step (3) is changed to 1.19g, the other steps and process conditions are the same as in Example 3. Accordingly, a Ni-Zn-Fe alloy layer with a thickness of ~500nm is formed on the transition layer (the molar ratio of Ni, Zn and Fe elements in the Ni-Zn-Fe alloy layer is 5:1:1). At this time, the Ni-Zn-Fe alloy layer is the water electrolysis catalyst layer.

[0087] The specific surface area of ​​the cathode prepared in Example 4 is 1.8 m². 2 / g, density is 1.75g / cm³ 3 .

[0088] The cathode prepared in Example 4 was used at 25°C. o C. In a 30 wt.% potassium hydroxide alkaline solution, at 5000 A / m 2 At a given current density, the hydrogen evolution overpotential of this cathode is 427 mV, indicating its high hydrogen evolution activity; moreover, it can operate stably for 550 hours without degradation, indicating its structural stability and long service life.

[0089] Example 5

[0090] Based on Example 3, except for step (3) of preparing the water electrolysis catalyst layer on the transition layer, all other steps and process conditions are the same as in Example 3. The specific steps for preparing the water electrolysis catalyst layer on the transition layer in Example 5 are as follows:

[0091] Under an argon atmosphere, a molybdenum carbide (Mo2C) layer with a thickness of ~200 nm is deposited on the transition layer prepared in step (2) by physical vapor deposition. At this time, the Mo2C layer is the water electrolysis catalyst layer, and the preparation of the cathode is completed accordingly (the composition of the cathode can be simply referred to as Mo2-Ni-C / C).

[0092] The microstructure of the water electrolysis catalyst layer prepared on the transition layer in step (3) was characterized. According to the test results, the water electrolysis catalyst layer is a continuous layer formed by the stacking of spherical nanoparticles with a size of about 50 nm.

[0093] The specific surface area of ​​the cathode prepared in Example 5 is 1.63 m². 2 / g, density is 1.85g / cm³ 3 .

[0094] The cathode prepared in Example 5 was used at 25°C. o C. In a 30 wt.% potassium hydroxide alkaline solution, at 5000 A / m 2 At a given current density, the hydrogen evolution overpotential of this cathode is 483 mV, indicating high hydrogen evolution activity. Figure 4As shown; moreover, it can operate stably for 500 hours without degradation, indicating that its structure is stable and its service life is long.

[0095] Example 6

[0096] Based on Example 3, except for step (3) of preparing the water electrolysis catalyst layer on the transition layer, all other steps and conditions are the same as in Example 3. The specific steps for preparing the water electrolysis catalyst layer on the transition layer in Example 6 are as follows:

[0097] Under an argon atmosphere, a tungsten carbide (WC) layer with a thickness of ~100 nm is deposited on the transition layer prepared in step (2) by physical vapor deposition. At this time, the WC layer is the water electrolysis catalyst layer, and the preparation of the cathode is completed accordingly.

[0098] The microstructure of the water electrolysis catalyst layer prepared on the transition layer in step (3) was characterized. According to the test results, the water electrolysis catalyst layer is a continuous layer formed by the stacking of spherical nanoparticles with a size of about 60 nm.

[0099] The specific surface area of ​​the cathode prepared in Example 6 is 1.58 m². 2 / g, density is 1.8g / cm³ 3 .

[0100] The cathode prepared in Example 6 was at 25°C. o C. In a 30 wt.% potassium hydroxide alkaline solution, at 5000 A / m 2 At a given current density, the hydrogen evolution overpotential of this cathode is 418 mV, indicating its high hydrogen evolution activity; moreover, it can operate stably for 520 hours without degradation, indicating its structural stability and long service life.

[0101] Example 7

[0102] A cathode for alkaline water electrolysis to produce hydrogen containing a transition layer is composed of a porous carbon / carbon composite matrix, a transition layer, and a water electrolysis catalyst layer. The specific preparation steps are as follows:

[0103] (1) The preparation steps and process conditions of the porous carbon / carbon composite matrix are the same as those in step (1) of Example 1;

[0104] (2) Preparation of a transition layer on a porous carbon / carbon composite matrix

[0105] Add 19g of NiSO4·6H2O, 2g of FeSO4·7H2O, 4.5g of H3BO3, 3g of NaCl, and 2g of Na3C6H5O7·2H2O to 100mL of deionized water and mix thoroughly to obtain an electrolyte solution; heat the electrolyte solution to 140°C. oC. Set the voltage to 5V and deposit carbon / carbon composite material on the roughened porous matrix obtained in step (1.4) using hydrothermal electrodeposition. After 50 minutes of deposition, remove the material and ultrasonically clean it with deionized water and anhydrous ethanol. Then place it in an oven at 60°C. o After drying at C for 24 hours, a nickel-iron alloy layer with a thickness of ~2μm (abbreviated as Ni-Fe-C / C composite material, the molar ratio of Ni to Fe in the Ni-Fe alloy layer is 10:1) is formed on the porous carbon / carbon composite matrix. At this time, the Ni-Fe alloy layer is the transition layer.

[0106] (3) Preparation of a water electrolysis catalyst layer on the transition layer

[0107] Under an argon atmosphere, a tungsten carbide (WC) layer with a thickness of ~100 nm is deposited on the transition layer prepared in step (2) by physical vapor deposition. At this time, the WC layer is the water electrolysis catalyst layer, and the preparation of the cathode is completed accordingly.

[0108] The hydrogen evolution reaction (HER) performance of the porous carbon / carbon composite matrix before and after loading with the Ni-Fe alloy layer was tested in step (1.4). Specifically, in a 30 wt.% KOH solution, using the sample as the working electrode, graphite as the counter electrode, and a saturated calomel electrode as the reference electrode, the linear sweep voltammetry (LSV) curve of the hydrogen evolution reaction of the sample at room temperature was measured using a three-electrode method. The HER catalytic activity of the sample was determined by the magnitude of the overpotential. The test results show that after loading with the Ni-Fe alloy transition layer, the HER overpotential of the material decreased significantly at the same current density, indicating a substantial improvement in the HER catalytic activity.

[0109] The specific surface area of ​​the cathode prepared in Example 7 is 2.54 m². 2 / g, density is 1.25g / cm³ 3 .

[0110] The cathode prepared in Example 7 was used at 25°C. o C. In a 30 wt.% potassium hydroxide alkaline solution, at 5000 A / m 2 At a given current density, the hydrogen evolution overpotential of this cathode is 375mV, indicating its high hydrogen evolution activity; moreover, it can operate stably for 500 hours without degradation, indicating its structural stability and long service life.

[0111] Comparative Example 1

[0112] A cathode for alkaline water electrolysis to produce hydrogen without a transition layer is composed of a porous carbon / carbon composite matrix and a water electrolysis catalyst layer. The specific preparation steps are as follows:

[0113] (1) The preparation steps and process conditions of the porous carbon / carbon composite matrix are the same as those in step (1) of Example 1;

[0114] (2) Preparation of water electrolysis catalyst layer on porous carbon / carbon composite matrix

[0115] Under an argon atmosphere, a molybdenum carbide (Mo2C) layer with a thickness of ~200 nm is deposited on the porous carbon / carbon composite matrix roughened in step (1.4) by physical vapor deposition. At this time, the Mo2C layer is the water electrolysis catalyst layer, and the cathode is prepared accordingly (the composition of the cathode can be simply referred to as Mo2-C / C).

[0116] The cathode prepared in Comparative Example 1 was at 25°C. o C. In a 30 wt.% potassium hydroxide alkaline solution, at 5000 A / m 2 At a current density of , the hydrogen evolution overpotential of the cathode is 710 mV, such as Figure 4 As shown.

[0117] Comparative Example 2

[0118] The porous carbon / carbon composite matrix with Ni layer prepared in step (2) of Example 3 was directly used as the cathode electrode for alkaline water electrolysis to produce hydrogen.

[0119] The cathode described in Comparative Example 2 at 25 o C. In a 30 wt.% potassium hydroxide alkaline solution, at 5000 A / m 2 At the given current density, the hydrogen evolution overpotential of the cathode is 519 mV.

[0120] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A cathode electrode for alkaline water electrolysis to produce hydrogen containing a transition layer, characterized in that: The cathode is composed of a porous carbon / carbon composite matrix, a transition layer, and a water electrolysis catalyst layer, with the transition layer located between the porous carbon / carbon composite matrix and the water electrolysis catalyst layer. The transition layer is composed of nickel or cobalt, and the water electrolysis catalyst layer is composed of a copper-vanadium-zinc-nickel alloy, tungsten carbide, or molybdenum carbide with a molar ratio of copper, vanadium, zinc, and nickel of 1:1:1:(1.5~3); or, the transition layer is composed of a nickel-iron alloy with a molar ratio of nickel to iron of 10:1~15:1, and the water electrolysis catalyst layer is composed of tungsten carbide or molybdenum carbide; the porous carbon / carbon composite matrix is ​​formed by graphitizing porous framework carbon and a second phase carbon covering the surface of the porous framework carbon, and the porous framework carbon is prepared by using carbon fiber weave, biochar, or foam carbon as a precursor; The porous skeletal carbon prepared from carbon fiber braids has a pore size of 100–500 μm, a porosity of 35–60%, and a density of 0.6–0.7 g / cm³. 3 The density of the porous framework carbon coated with a second phase of carbon is 0.8~1 g / cm³. 3 In this case, the degree of graphitization of the porous carbon / carbon composite matrix formed by graphitization is 96-99%, the resistivity is 1-10 mΩ·cm, and the specific surface area is 1-2.5 m². 2 / g, contact angle is 110~150° o ; The porous framework carbon prepared from biochar has a pore size of 70 nm to 200 μm, a porosity of 20% to 50%, and a density of 0.1 to 0.3 g / cm³. 3 The density of the porous framework carbon coated with a second phase of carbon is 0.3~0.5 g / cm³. 3 In this case, the degree of graphitization of the porous carbon / carbon composite matrix formed by graphitization is 85-92%, the resistivity is 15-30 mΩ·cm, and the specific surface area is 1.5-3 m². 2 / g, contact angle is 100~140° o ; The porous framework carbon prepared from foamed carbon has a pore size of 50–300 μm, a porosity of 40–80%, and a density of 0.05–0.12 g / cm³. 3 The density of the porous framework carbon coated with a second phase of carbon is 0.14~0.25 g / cm³. 3 In this case, the graphitization degree of the porous carbon / carbon composite matrix formed by graphitization is 90-97%, the resistivity is 10-20 mΩ·cm, and the specific surface area is 0.7-1 m². 2 / g, contact angle is 130~160° o .

2. The cathode electrode for alkaline water electrolysis to produce hydrogen containing a transition layer according to claim 1, characterized in that: The thickness of the transition layer is 0.1~200μm.

3. A cathode electrode for alkaline water electrolysis to produce hydrogen containing a transition layer according to claim 1 or 2, characterized in that: The thickness of the water electrolysis catalyst layer is 0.03~5μm, and the particle size of the water electrolysis catalyst in the water electrolysis catalyst layer is 0.005~2μm.

4. The cathode electrode for alkaline water electrolysis to produce hydrogen containing a transition layer according to claim 1, characterized in that: A transition layer is prepared after the porous carbon / carbon composite matrix undergoes roughening pretreatment. The roughening pretreatment increases the specific surface area and reduces the contact angle of the porous carbon / carbon composite matrix, thus improving the bonding effect between the transition layer and the porous carbon / carbon composite matrix. When porous carbon frameworks are prepared from carbon fiber braids, the porous carbon / carbon composite matrix, after roughening pretreatment, has a specific surface area of ​​2-4 m². 2 / g, contact angle 60~90 o ; When preparing porous framework carbon from biochar, the porous carbon / carbon composite matrix, after roughening pretreatment, has a specific surface area of ​​2.5~5 m². 2 / g, contact angle 50~80 o ; When preparing porous framework carbon from foamed carbon, the porous carbon / carbon composite matrix, after roughening pretreatment, has a specific surface area of ​​1~2 m². 2 / g, contact angle is 70~110 o .

5. A cathode electrode for alkaline water electrolysis to produce hydrogen containing a transition layer according to claim 1, 2, or 4, characterized in that: The specific surface area of ​​the cathode is 0.8~4.2m². 2 / g, density is 0.32~1.85g / cm³ 3 .

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