A cathode electrode for alkaline water electrolysis to produce hydrogen.

Abstract

This invention relates to a cathode electrode for alkaline water electrolysis to produce hydrogen, belonging to the field of alkaline water electrolysis to produce hydrogen. The cathode electrode is composed of a porous carbon / carbon composite matrix and a water electrolysis catalyst supported on the porous carbon / carbon composite matrix; the porous carbon / carbon composite matrix has a graphitization degree of 90-99% and a specific surface area of ​​0.7-2.5 m². 2 / g, contact angle is 110~160° o The compressive strength is not less than 1.6 MPa. The cathode structure described in this invention is stable, resistant to strong alkali corrosion, can operate stably for a long time, has a low density, a high water electrolysis catalyst loading, and high hydrogen production efficiency, which is beneficial to reducing hydrogen production energy consumption. The preparation process is simple and easy to operate, with low cost, and has good application prospects in alkaline water electrolysis for hydrogen production.

Description

Technical Field

[0001] This invention relates to a cathode electrode for alkaline water electrolysis to produce hydrogen, belonging to the field of alkaline water electrolysis to produce hydrogen. Background Technology

[0002] Green hydrogen is generated by using renewable and clean energy sources such as solar and wind power to produce hydrogen through the electrolysis of water, thus 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. Commercial cathode electrodes use nickel mesh as a substrate, coated with Raney nickel powder to prepare the electrode material. This electrode material suffers from poor catalytic activity, poor resistance to strong alkali corrosion, short lifespan at high current densities, and weak adhesion to the catalyst coating, leading to easy peeling. These problems directly affect the electrolyzer's lifespan and hydrogen production efficiency. 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 for alkaline water electrolysis. This cathode electrode uses a porous carbon / carbon composite material as its matrix. The porous structure of the matrix not only provides channels for alkali and charge transfer during the water electrolysis process, but also gives it a large specific surface area, which is beneficial for increasing the effective loading of the water electrolysis catalyst and improving the bonding effect with the catalyst. Compared with metal matrix materials, this matrix also has the characteristics of low density and resistance to strong alkali corrosion. The cathode electrode made by loading the water electrolysis catalyst onto this matrix exhibits high hydrogen evolution catalytic activity and can operate stably for a long time, showing good 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, the cathode electrode being composed of a porous carbon / carbon composite matrix and a water electrolysis catalyst supported on the porous carbon / carbon composite matrix;

[0007] The porous carbon / carbon composite matrix has a graphitization degree of 90-99% and a specific surface area of ​​0.7-2.5 m². 2 / g, contact angle is 110~160° o The compressive strength is not less than 1.6 MPa.

[0008] Preferably, the porous carbon / carbon composite matrix is ​​pretreated with a roughening process before loading the water electrolysis catalyst. This roughening pretreatment further increases the specific surface area and reduces the contact angle of the porous carbon / carbon composite matrix, thereby improving the loading effect of the water electrolysis catalyst on the porous carbon / carbon composite matrix. More preferably, the specific surface area of ​​the porous carbon / carbon composite matrix after the roughening pretreatment is 1~4 m². 2 / g, contact angle 60~110 o .

[0009] 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.

[0010] 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 .

[0011] Preferably, the porosity of the porous framework carbon is 35-80%; more preferably, the pore size of the porous framework carbon is 50-500 μm.

[0012] 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.

[0013] Preferably, the porous skeletal carbon is prepared from carbon fiber woven fabric or foam carbon as a precursor.

[0014] Preferably, the porous skeleton carbon prepared from carbon fiber braid has a pore size of 100~500μm and a porosity of 35~60%; the porous skeleton carbon prepared from foam carbon has a pore size of 50~300μm and a porosity of 40~80%.

[0015] 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 1~5m3 / h, deposition time is 50~100h;

[0016] 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;

[0017] 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.

[0018] 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 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 .

[0019] 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 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 .

[0020] 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 foamed carbon, after roughening pretreatment, has a specific surface area of ​​1~2 m². 2 / g, contact angle is 70~110 o .

[0021] Preferably, the water electrolysis catalyst is at least one selected from the group consisting of a transition metal alloy, a transition metal oxide, and a transition metal carbide. More preferably, the transition metal alloy is a nickel-iron alloy, and the molar ratio of nickel to iron is further preferably 7:1 to 1:1; the transition metal oxide is a nickel-zinc oxide, and the molar ratio of nickel to zinc is further preferably 7:3 to 1:1; the transition metal carbide is nickel carbide; when the transition metal alloy, transition metal oxide, and transition metal carbide are used in combination, it is further preferably a composite of nickel-iron alloy and nickel carbide, and the molar ratio of nickel-iron alloy to nickel carbide is even more preferably 1:(1 to 3).

[0022] Preferably, the particle size of the water electrolysis catalyst supported on the porous carbon / carbon composite matrix is ​​0.005~2μm (i.e. 5nm~2μm).

[0023] Preferably, the thickness of the water electrolysis catalyst supported on the porous carbon / carbon composite matrix is ​​0.03~5μm (i.e. 30nm~5μm).

[0024] Preferably, the water electrolysis catalyst is loaded onto a porous carbon / carbon composite matrix using the following method:

[0025] Hydrothermal method: Transition metal salts and alkaline substances are dissolved in water, then transferred to a reaction vessel and a porous carbon / carbon composite matrix is ​​added. Through hydrothermal reaction, oxides of transition metals are formed on the porous carbon / carbon composite matrix.

[0026] Electrodeposition method: An electrolyte solution is prepared using transition metal salts, and a constant potential deposition method is used to deposit the transition metal alloy on a porous carbon / carbon composite matrix that serves as the cathode.

[0027] Vapor deposition: The process of depositing transition metal carbides on a porous carbon / carbon composite matrix using vapor deposition technology (physical vapor deposition and / or chemical vapor deposition).

[0028] Electrodeposition + Vapor Deposition: First, an alloy of transition metals is formed on a porous carbon / carbon composite matrix by electrodeposition. Then, a carbide of transition metals is formed on the porous carbon / carbon composite matrix by vapor deposition. In other words, a composite catalyst of alloy of transition metals and carbide of transition metals is formed on a porous carbon / carbon composite matrix.

[0029] Preferably, the specific surface area of ​​the cathode is 1.1~4.2 m². 2 / g, density is 0.5~1.8g / cm³ 3 .

[0030] Beneficial effects:

[0031] (1) The cathode of the present invention uses porous carbon / carbon composite material as the supporting matrix for supporting water electrolysis catalyst. On the one hand, its porous structure can provide channels for alkali solution and charge transfer. 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, which is conducive to increasing the effective loading of water electrolysis catalyst. Moreover, it has a better binding effect with water electrolysis catalyst, making the cathode structure stable and ensuring the excellent hydrogen evolution catalytic activity and long-term stable operation of cathode.

[0032] (2) The present invention performs a roughening pretreatment on the porous carbon / carbon composite matrix, which can further increase its surface area and further improve its binding effect with the water electrolysis catalyst, which is beneficial to further improve the hydrogen evolution catalytic activity and service life of the cathode.

[0033] (3) 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 and meeting the conductivity and strength requirements of the cathode for the loaded water electrolysis catalyst matrix in alkaline water electrolysis hydrogen production. Moreover, the matrix also 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 subsequent cathode.

[0034] (4) In the cathode of the present invention, the porous carbon / carbon composite matrix is ​​combined with an alloy of a transition metal with high conductivity and good catalytic activity, or with an oxide of a transition metal, or with a transition metal carbide with a similar electronic structure to a noble metal, or with an alloy of a transition metal and a carbide of a transition metal. The resulting integrated hydrogen evolution cathode has excellent electron transport performance, gas desorption effect, hydrogen evolution catalytic activity and hydrogen evolution efficiency.

[0035] In summary, the cathode structure of the present invention is stable with low density, high loading of water electrolysis catalyst, and high hydrogen production efficiency, which is beneficial to reducing hydrogen production energy consumption. The preparation process is simple and easy to operate with low cost, providing a feasible path for the large-scale and continuous promotion and application of alkaline water electrolysis for hydrogen production, and has good application prospects. Attached Figure Description

[0036] Figure 1 This is a SEM (scanning electron microscope) image of the cathode electrode prepared in Example 1.

[0037] Figure 2 This is a SEM image of the cathode prepared in Example 3.

[0038] Figure 3 Comparison of LSV (linear sweep voltammetry) curves for hydrogen evolution activity testing of the cathodes prepared in Examples 2, 5, and 6.

[0039] Figure 4 The stability test curve of the cathode prepared in Example 4 is shown. 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 is composed of a porous carbon / carbon composite matrix and a water electrolysis catalyst supported on the matrix. The specific preparation steps are as follows:

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

[0047] (1.1) The foam carbon precursor (polyurethane foam) is impregnated with phenolic resin. After thorough impregnation, excess phenolic resin is discharged, and the material is first placed at 170°C. o Curing at C for 2 hours, followed by curing under a nitrogen protective atmosphere and at 900°C. o Carbonization at C for 2 hours yielded a porous framework carbon with a surface covered by pyrolyzed carbon and a density of 0.09 g / cm³. 3The porosity is 75%, and the pore size is ~230 μm. It should be noted that the pyrolysis carbon covering the porous framework carbon is a portion of the second-phase carbon formed by pyrolysis on the porous framework carbon through a liquid-phase impregnation process (900...). o Carbonization at C for 2 hours (under which the phenolic resin is simultaneously decomposed) will be carried out in subsequent steps to deposit carbon on the porous framework carbon to form another part of the second phase carbon through vapor deposition process.

[0048] (1.2) The porous framework carbon with a surface covered by cracked carbon obtained in step (1.1) is loaded into a chemical vapor deposition furnace for further deposition of the second phase carbon, wherein the carbon source gas is propylene and the flow rate is 1.5 m³ / s. 3 / h, deposition temperature is 900 o C, with a deposition time of 80 hours, forms another second-phase carbon on the porous framework carbon through deposition; at this point, the density of the porous framework carbon after the deposition of the second-phase carbon is 0.15 g / cm³. 3 The degree of graphitization is 91%, and the resistivity is 38.7 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 2500 °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 96%, a resistivity of 11.7 mΩ·cm, and a specific surface area of ​​0.8 m². 2 / g, contact angle is 140° 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 550 °C. o Oxidation treatment at C for 20 minutes, followed by ultrasonic cleaning with deionized water, and then 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 ​​1.3 m². 2 / g, contact angle is 90° o ;

[0051] (2) A water electrolysis catalyst was loaded onto a porous carbon / carbon composite matrix using a hydrothermal method.

[0052] The roughened porous carbon / carbon composite matrix obtained in step (1.4), 0.214 g of NiCl2·6H2O, 0.066 g of Zn(OAC)2·2H2O, and 100 mL of deionized water were mixed and ultrasonically mixed until homogeneous. The mixture was then transferred to a reaction vessel and heated at 170 °C. oThe hydrothermal reaction was carried out at C for 12 hours. After the reaction was completed, the mixture was cooled, and the solid product was collected and washed with deionized water and anhydrous ethanol. Finally, it was placed in 60 °C. o Drying in an oven at C for 24 hours achieves loading of nickel-zinc oxide (the molar ratio of nickel to zinc in the nickel-zinc oxide is 7:3) on a porous carbon / carbon composite matrix, thereby obtaining the cathode electrode.

[0053] The specific surface area of ​​the cathode prepared in Example 1 is 1.5 m². 2 / g, density is 0.5g / cm³ 3 .

[0054] The morphology of the cathode prepared in Example 1 was characterized, from... Figure 1 The SEM images show that nickel-zinc oxide particles grew on the three-dimensional network framework of the porous carbon / carbon composite matrix. As the reaction proceeded, the grains grew larger, and the inherent properties of nanoparticle aggregation ensured that the catalyst uniformly coated the carbon matrix framework. The nickel-zinc oxide particle size ranged from 50 to 500 nm, which is beneficial for gas adsorption and desorption, and improves the hydrogen evolution performance of the cathode. Furthermore, SEM measurements revealed that the thickness of the nickel-zinc oxide loaded on the porous carbon / carbon composite matrix was ~1 μm.

[0055] The cathode prepared in Example 1 was subjected to an 80°C test. 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 417 mV, indicating that it has high hydrogen evolution activity.

[0056] The cathode prepared in Example 1 was subjected to a temperature of 25°C. o C. In a 30 wt.% potassium hydroxide alkaline solution, at 5000 A / m 2 Under a certain current density, it can operate stably for 500 hours without degradation, indicating that its structure is stable and its service life is long.

[0057] Example 2

[0058] A cathode for alkaline water electrolysis to produce hydrogen is composed of a porous carbon / carbon composite matrix and a water electrolysis catalyst supported on the matrix. The specific preparation steps are as follows:

[0059] (1) Preparation of porous carbon / carbon composite matrix

[0060] (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.

[0061] (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 1.5 m³ / s. 3 / h, deposition temperature is 900 o C, with a deposition time of 50 hours, a second-phase 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 0.8 g / cm³. 3 The degree of graphitization is 94%, and the resistivity is 8.9 mΩ·cm;

[0062] (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 2500 °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 4.6 mΩ·cm, and a specific surface area of ​​2.1 m². 2 / g, contact angle is 110° o The compressive strength is greater than 5 MPa;

[0063] (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 550 °C. o Oxidation treatment at C for 20 minutes, followed by ultrasonic cleaning with deionized water, and then 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 ​​2.5 m². 2 / g, contact angle is 70° o ;

[0064] (2) A water electrolysis catalyst was loaded onto a porous carbon / carbon composite matrix by electrodeposition.

[0065] Dissolve 9g of NiSO4·6H2O, 2g of FeSO4·7H2O, 4.5g of H3BO3, 3g of NaCl, and 2g of Na3C6H5O7·2H2O in 100mL of deionized water, mix well, and prepare an electrolyte solution. Deposit a nickel-iron alloy (the molar ratio of nickel to iron in the nickel-iron alloy is 4:1) on the roughened porous carbon / carbon composite matrix obtained in step (1.4) using a potentiostatic deposition method to obtain the corresponding cathode.

[0066] The specific surface area of ​​the cathode prepared in Example 2 is 2.8 m². 2 / g, density is 1.2g / cm³ 3 .

[0067] The cathode prepared in Example 2 was characterized by morphology. According to the SEM characterization results, nickel-iron alloy particles were uniformly deposited on the porous carbon / carbon composite matrix, with a particle size of ~80 nm. Meanwhile, SEM testing showed that the thickness of the nickel-iron alloy loaded on the porous carbon / carbon composite matrix was ~400 nm.

[0068] The cathode prepared in Example 2 was subjected to an 80°C test. 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 345 mV, indicating high hydrogen evolution activity. Figure 3 As shown.

[0069] The cathode prepared in Example 2 was subjected to a temperature of 25°C. o C. In a 30 wt.% potassium hydroxide alkaline solution, at 5000 A / m 2 Under a certain current density, it can operate stably for 500 hours without degradation, indicating that its structure is stable and its service life is long.

[0070] Example 3

[0071] A cathode for alkaline water electrolysis to produce hydrogen is composed of a porous carbon / carbon composite matrix and a water electrolysis catalyst supported on the matrix. The specific preparation steps are as follows:

[0072] (1) The preparation steps and process conditions of the porous carbon / carbon composite matrix are the same as those in step (1) of Example 2;

[0073] (2) A water electrolysis catalyst was loaded onto a porous carbon / carbon composite matrix by vapor deposition.

[0074] Under an argon atmosphere, a nickel layer with a thickness of ~100 nm was deposited on the roughened porous carbon / carbon composite matrix obtained in step (1.4) using physical vapor deposition. The porous carbon / carbon composite matrix with the nickel layer was then placed in a chemical vapor deposition furnace under a hydrogen atmosphere with a propylene flow rate of 1.0 m³ / h. 3 / h, deposition temperature is 900 o C. After deposition for 1 hour, the material is cooled to form nickel carbide on the porous carbon / carbon composite matrix, thus obtaining the cathode electrode.

[0075] The specific surface area of ​​the cathode prepared in Example 3 is 3.2 m². 2 / g, density is 1.6g / cm³ 3 .

[0076] The morphology of the cathode prepared in Example 3 was characterized, from... Figure 2The SEM images show that the preferentially oriented nickel carbide growth tends to be perpendicular to the porous carbon / carbon composite matrix, with a deposited nickel carbide particle size of ~700 nm. This structure further increases its specific surface area, which is beneficial for the full reaction of the alkaline solution on the cathode and improves the hydrogen evolution performance of the electrode. Meanwhile, SEM measurements show that the thickness of the nickel carbide loaded on the porous carbon / carbon composite matrix is ​​~2 μm.

[0077] The cathode prepared in Example 3 was at 80 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 332 mV, indicating that it has high hydrogen evolution activity.

[0078] 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 Under a certain current density, it can operate stably for 500 hours without degradation, indicating that its structure is stable and its service life is long.

[0079] Example 4

[0080] A cathode for alkaline water electrolysis to produce hydrogen is composed of a porous carbon / carbon composite matrix and a water electrolysis catalyst supported on the matrix. The specific preparation steps are as follows:

[0081] (1) Preparation of porous carbon / carbon composite matrix

[0082] (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.

[0083] (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 o C, with a deposition time of 50 hours, a second-phase 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;

[0084] (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. oThe 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;

[0085] (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 ​​first placed in a 600°C environment. 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 ;

[0086] (2) Loading water electrolysis catalysts onto porous carbon / carbon composite matrices using a combination of electrodeposition and vapor deposition methods

[0087] 9g of NiSO4·6H2O, 2g of FeSO4·7H2O, 4.5g of H3BO3, 3g of NaCl, and 2g of Na3C6H5O7·2H2O were dissolved in 100mL of deionized water and mixed thoroughly to prepare an electrolyte solution. A nickel-iron alloy (with a nickel to iron molar ratio of 4:1) was deposited on the roughened porous carbon / carbon composite matrix obtained in step (1.4) using a potentiostatic deposition method.

[0088] A porous carbon / carbon composite matrix loaded with nickel-iron alloy was treated in a 7 wt.% hydrochloric acid solution for 5 min, then removed, washed until neutral, and dried. It was then placed in a chemical vapor deposition furnace under a hydrogen atmosphere with a propylene flow rate of 1.0 m³ / min. 3 / h, deposition temperature is 900 o C. After deposition for 30 minutes and cooling, nickel carbide is formed on the porous carbon / carbon composite matrix loaded with nickel-iron alloy, that is, a water electrolysis catalyst composed of nickel-iron alloy and nickel carbide is formed on the porous carbon / carbon composite matrix (wherein the molar ratio of nickel-iron alloy to nickel carbide is 1:2), and the cathode electrode is obtained accordingly.

[0089] The specific surface area of ​​the cathode prepared in Example 4 is 3.6 m². 2 / g, density is 1.5g / cm³ 3 .

[0090] The morphology of the cathode prepared in Example 4 was characterized. According to the cross-sectional SEM characterization results, a nickel-iron alloy layer and a nickel carbide layer exist on the porous carbon / carbon composite matrix. Furthermore, SEM testing showed that the total thickness of the nickel-iron alloy layer and nickel carbide layer loaded on the porous carbon / carbon composite matrix was ~800 nm.

[0091] The cathode prepared in Example 4 was subjected to an 80°C test. 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 306 mV, indicating that it has high hydrogen evolution activity.

[0092] The cathode prepared in Example 4 was subjected to a temperature of 25°C. o C. In a 30 wt.% potassium hydroxide alkaline solution, at 5000 A / m 2 Under a given current density, it can operate stably for 500 hours without degradation, indicating that its structure is stable and its service life is long. Figure 4 As shown.

[0093] Example 5

[0094] A cathode for alkaline water electrolysis to produce hydrogen is composed of a porous carbon / carbon composite matrix and a water electrolysis catalyst supported on the matrix. The specific preparation steps are as follows:

[0095] (1) The preparation steps and process conditions of the porous carbon / carbon composite matrix are the same as those in step (1) of Example 2;

[0096] (2) A water electrolysis catalyst was loaded onto a porous carbon / carbon composite matrix by electrodeposition.

[0097] Dissolve 9g of NiSO4·6H2O, 8g of FeSO4·7H2O, 4.5g of H3BO3, 3g of NaCl, and 2g of Na3C6H5O7·2H2O in 100mL of deionized water and mix thoroughly to prepare an electrolyte solution. Deposit a nickel-iron alloy (with a nickel-iron alloy molar ratio of 1:1) onto the roughened porous carbon / carbon composite matrix obtained in step (1.4) using a potentiostatic deposition method to obtain the corresponding cathode.

[0098] The specific surface area of ​​the cathode prepared in Example 5 is 3.0 m². 2 / g, density is 1.4g / cm³ 3 .

[0099] The morphology of the cathode prepared in Example 5 was characterized. According to the SEM characterization results, nickel-iron alloy particles were uniformly deposited on the porous carbon / carbon composite matrix, with a particle size of ~100 nm. Meanwhile, SEM testing showed that the thickness of the nickel-iron alloy loaded on the porous carbon / carbon composite matrix was ~400 nm.

[0100] The cathode prepared in Example 5 was subjected to an 80°C test. 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 355 mV, indicating high hydrogen evolution activity. Figure 3 As shown.

[0101] The cathode prepared in Example 5 was subjected to a temperature of 25°C. o C. In a 30 wt.% potassium hydroxide alkaline solution, at 5000 A / m 2 Under a certain current density, it can operate stably for 500 hours without degradation, indicating that its structure is stable and its service life is long.

[0102] Example 6

[0103] Based on Example 2, except for step (1.4), all other steps and process conditions are the same as in Example 2. That is, in Example 6, the porous carbon / carbon composite matrix obtained in step (1.3) was not subjected to roughening pretreatment, and step (2) was to directly deposit nickel-iron alloy on the porous carbon / carbon composite matrix obtained in step (1.3).

[0104] The specific surface area of ​​the cathode prepared in Example 6 is 2.4 m². 2 / g, density is 1.06g / cm³ 3 .

[0105] The cathode prepared in Example 6 was subjected to an 80°C test. 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 415 mV, such as Figure 3 As shown.

[0106] 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 producing hydrogen through alkaline water electrolysis, characterized in that: The cathode is composed of a porous carbon / carbon composite matrix and a water electrolysis catalyst supported on the porous carbon / carbon composite matrix; Among them, the porous carbon / carbon composite matrix is ​​formed by graphitization of porous skeleton carbon and second-phase carbon covering the surface of porous skeleton carbon. The porous skeleton carbon is prepared by using carbon fiber braid 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 of 110~150°, compressive strength of not less than 1.6MPa; 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 degree of graphitization 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 of 130~160°, compressive strength of not less than 1.6Mpa; The water electrolysis catalyst is a nickel-iron alloy with a nickel to iron molar ratio of 7:1 to 1:1; or a nickel-zinc oxide with a nickel to zinc molar ratio of 7:3 to 1:1; or nickel carbide; or a composite of nickel-iron alloy and nickel carbide with a nickel-iron alloy to nickel carbide molar ratio of 1:(1 to 3).

2. The cathode electrode for alkaline water electrolysis to produce hydrogen according to claim 1, characterized in that: After roughening pretreatment, a porous carbon / carbon composite matrix is ​​loaded with a water electrolysis catalyst. This roughening pretreatment increases the specific surface area and reduces the contact angle of the porous carbon / carbon composite matrix, thus improving the loading effect of the water electrolysis catalyst on the matrix. Specifically, the porous carbon / carbon composite matrix prepared from porous framework carbon based on carbon fiber weave has a specific surface area of ​​2–4 m² after roughening pretreatment. 2 / g, with a contact angle of 60–90°; The porous carbon / carbon composite matrix prepared from porous framework carbon based on foamed carbon has a specific surface area of ​​1–2 m² after roughening pretreatment. 2 / g, with a contact angle of 70–110°.

3. The cathode electrode for alkaline water electrolysis to produce hydrogen according to claim 1, characterized in that: The particle size of the water electrolysis catalyst supported on the porous carbon / carbon composite matrix is ​​0.005–2 μm, and the thickness of the water electrolysis catalyst supported on the porous carbon / carbon composite matrix is ​​0.03–5 μm.

4. A cathode electrode for alkaline water electrolysis to produce hydrogen according to claim 1 or 2, characterized in that: The specific surface area of ​​the cathode is 1.1–4.2 m². 2 / g, density is 0.5~1.8g / cm³ 3 .

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