An electrode and method of manufacture, and an electrochemical water softening method

Abstract

The present application provides an electrode and a preparation method thereof, and a method for electrochemical scale removal using the electrode. The electrode has a surface with a plurality of multi-prism protrusions. The electrode is obtained by processing with a multi-prism mold. The electrode is used for electrochemical scale removal as a cathode, and wastewater is fed from the cathode inlet and discharged from the cathode outlet. The electrode has a large specific surface area, and based on its specific shape, forms a plurality of specific regions. When applied to an electrochemical reaction, a reaction region with a specific environment is formed on the surface, thereby increasing the rate of the reaction to be performed. During electrochemical scale removal, an alkaline region is mainly generated at the tip of the prism, and the tip surface of the multi-prism protrusion reduces the adhesion of scale, moves the deposition reaction from the cathode surface to the bulk solution, thereby avoiding the scaling of the cathode surface to some extent, prolonging the deactivation time of the cathode, and allowing the cathode to maintain a high scale removal rate for a longer period of time.

Description

TECHNICAL FIELD

[0001] The present application relates to an electrode and a preparation method thereof, and a method for electrochemical scale removal using the same. It belongs to the technical field of electrochemistry and water treatment. BACKGROUND

[0002] Circulating cooling water is a necessary heat transfer medium in the production process of equipment manufacturing, thermal power, metallurgy, petrochemical and coal chemical industries. The stable operation of the circulating cooling water system is of great significance to ensure the safe and stable production of enterprises. However, the phenomenon of scaling is widespread in the circulating cooling water system, which can cause the heat transfer efficiency of circulating water to decrease and energy consumption to increase. Therefore, the control and elimination of scale are of great significance to energy saving and safety production in energy-intensive industries.

[0003] At present, the common solutions to the scaling problem in industrial circulating cooling water mainly include chemical method, physical scale inhibition method and removal of scale-forming ions in water. Each method has its own advantages and disadvantages, but none of them can fundamentally solve the scaling problem in the cooling water system. The chemical method has problems such as high operating cost, non-compliance of wastewater discharge, secondary pollution caused by chemical agents, etc. in the actual application process. The physical scale inhibition method mainly acts on the water body through ultrasonic waves, electromagnetic fields and electrostatic repulsion to change the physical properties of the water to achieve the goal of scale removal. However, this method only inhibits the tendency of scale formation, and the application range is still very limited, only suitable for water with low hardness. When the hardness of the raw water is high, the effect of physical scale inhibition treatment will decrease significantly. The methods of removing scale-forming ions in the system include ion exchange, membrane separation, capacitive deionization, electrocoagulation and electrochemical scale removal technology. Among them, electrochemical scale removal technology is a typical active scale removal and inhibition technology, which has the advantages of precipitating scale-forming ions from water in the form of scale deposition, thereby increasing the concentration multiple of circulating cooling water, reducing the amount of wastewater and makeup water, and saving water resources. At the same time, a large amount of strong oxidizing active substances can be produced by the electrochemical anode in the reaction process, which also has a good killing and inhibiting effect on microorganisms and algae. Although electrochemical scale removal technology has the above advantages, there are still some problems to be solved: the small existing cathode area of electrochemical scale removal technology leads to the need to improve the scale removal rate; the energy consumption required to remove unit mass of scale is high; and the effective scale removal technology is not mature, which cannot guarantee the excellent scale removal performance of the equipment after a long time of operation.

[0004] Patent CN114105320A discloses a method for inhibiting electrode surface scaling by using nano and micro bubbles to induce liquid phase nucleation of scale-forming substances. The method includes: electrode construction with continuous multi-channel and nano tip covered surface; size regulation of nano and micro bubbles; control of liquid phase nucleation of scale-forming substances. The electrode preparation process of the method is complicated, and the requirements for the electrode are high, which limits the actual application.

[0005] Patent CN113151891A discloses a method for softening water body and preparing calcium carbonate whiskers by using electrochemistry. The method achieves the effect of softening water body through periodic electrolysis. The generated scale is still on the surface of the cathode plate, and a large amount of scale deposition reduces the treatment capacity and electrode life.

[0006] In view of the above problems, for the electrochemical hardness removal technology, how to accelerate the scaling rate and reduce the energy consumption of scale removal on the basis of effectively reducing the hardness still needs further improvement. SUMMARY

[0007] To solve the problems of low scaling rate and high energy consumption in the prior art, the present application provides an electrode and a preparation method thereof, and a method for electrochemical hardness removal using the same. By changing the structure and morphology of the electrode, the diffusion rate of the alkaline region of the cathode during electrochemical reaction is improved, thereby accelerating the scaling rate during electrochemical hardness removal and increasing the size of the scaling particles, effectively reducing the energy consumption of scale removal.

[0008] To achieve the above technical purposes, the technical solutions of the present application are as follows:

[0009] The first aspect of the present application is to provide an electrode with a plurality of multi-pyramidal protrusions on the surface.

[0010] Further, the positive multi-pyramidal protrusion is an electrode with a surface in the shape of a positive triangular pyramid, a positive quadrangular pyramid, a positive pentagonal pyramid or a positive hexagonal pyramid, which is a protrusion in one shape or a combination of protrusions in multiple shapes.

[0011] Further, the edge length of the multi-pyramidal protrusion is 0.2-1.5 cm, preferably 0.4-1.0 cm, and more preferably 0.4-0.8 cm; and the edge length of the corresponding base polygon is 0.2-1.5 cm, preferably 0.4-1.0 cm, and more preferably 0.4-0.8 cm.

[0012] Further, as one of the more specific embodiments, the multi-pyramidal protrusion is a positive triangular pyramid, and the edge length of the positive triangular pyramid is 0.2-1.0 cm, preferably 0.4-0.6 cm. The edge length of the base triangle is 0.2-1.0 cm, preferably 0.4-0.7 cm.

[0013] Further, as one of the more specific embodiments, the multi-pyramidal protrusion is a positive quadrangular pyramid, and the edge length of the positive quadrangular pyramid is 0.2-1.0 cm, preferably 0.5-0.8 cm. The edge length of the base square is 0.2-1.2 cm, preferably 0.5-0.8 cm.

[0014] Further, as one of the more specific embodiments, the polyhedral pyramid protrusions are regular pentagonal pyramid protrusions, the edge length of the regular pentagonal pyramid protrusions is 0.2-1.0 cm, preferably 0.5-0.8 cm, and the edge length of the base regular pentagon is 0.2-1.2 cm, preferably 0.5-0.8 cm.

[0015] Further, as one of the more specific embodiments, the polyhedral pyramid protrusions are regular hexagonal pyramid protrusions, the edge length of the regular hexagonal pyramid protrusions is 0.2-1.0 cm, preferably 0.6-0.8 cm, and the edge length of the base regular hexagon is 0.2-1.2 cm, preferably 0.4-0.8 cm.

[0016] Further, on the same electrode, there are polyhedral pyramid protrusions of different shapes, and the vertex of each polyhedral pyramid protrusion is at a height corresponding to the bottom surface of the electrode.

[0017] Further, the distance between adjacent vertices of the polyhedral pyramid protrusions is 0.1-4.0 cm, preferably 0.15-1.4 cm.

[0018] Further, the electrode is a plate-shaped or mesh-shaped graphite electrode, a carbon felt electrode, a copper-nickel alloy electrode, a titanium electrode, an iron electrode, a copper electrode, or a stainless steel electrode, preferably a mesh-shaped iron electrode, a copper electrode, or a stainless steel electrode, and most preferably a mesh-shaped stainless steel electrode.

[0019] Further, the electrode is a mesh-shaped electrode of 10-200 mesh, preferably a mesh-shaped stainless steel electrode of 10-200 mesh, and most preferably a mesh-shaped stainless steel electrode of 50-100 mesh.

[0020] The technical purpose of the second aspect of the present application is to provide a preparation method of an electrode with a surface having a plurality of polyhedral pyramid protrusions, comprising the step of processing the electrode through a polyhedral pyramid mold.

[0021] Further, the preparation method further comprises the step of pretreating the electrode to remove surface oxides and obtain a rough surface. The pretreatment is activation with 0.1-10 mol / L sulfuric acid for 18-24 h, and the activated electrode is washed with deionized water and then dried.

[0022] The technical purpose of the third aspect of the present application is to provide a method for electrochemical hardness removal, which uses an electrochemical device with a cathode and an anode to treat wastewater, the wastewater is fed from the cathode and discharged from the cathode, and the cathode is an electrode with a surface having a plurality of polyhedral pyramid protrusions.

[0023] Further, the anode is a DSA electrode, a graphite plate electrode, a lead dioxide electrode, a tin dioxide electrode, or other non-sacrificial electrodes.

[0024] Further, the distance between the anode and the cathode of the electrochemical device is 2-10 cm, preferably 4-8 cm.

[0025] Further, the current density of the electrochemical device is 2-30 mA / cm 2 .

[0026] Further, the residence time of the material in the electrochemical device is 10-120 min, preferably 30-60 min.

[0027] Further, the wastewater is wastewater with calcium ion concentration of 200-1000 mg·L -1 , bicarbonate ion concentration of 300-3000 mg·L -1 .

[0028] Further, the hardness removal method further comprises directly introducing the reacted wastewater into a solid-liquid separation device for treatment by standing sedimentation, centrifugation, cyclone or filtration, so as to reduce the hardness of the industrial wastewater to be treated.

[0029] Further, the standing sedimentation, centrifugation, cyclone or filtration solid-liquid separation structure treatment time is 10-30 min.

[0030] The technical scheme of the present application has the following advantages:

[0031] (1) The electrode surface provided by the present application has a plurality of multi-pyramidal protrusions, has a large specific surface area, and based on its specific shape, forms a plurality of specific regions, which can form a reaction region with a specific environment on the surface when applied to an electrochemical reaction, thereby increasing the rate of the reaction to be performed.

[0032] (2) In the electrochemical hardness removal method provided by the present application, the electrode with a plurality of multi-pyramidal protrusions on the surface is used as the cathode, the multi-pyramidal protrusions can increase the local current density of the cathode region during the electrochemical reaction, increase the area of the alkaline region, and make the alkaline region mainly generated at the tip of the pyramid, and the tip surface of the multi-pyramidal protrusion reduces the adhesion of scale, moves the deposition reaction from the cathode surface to the bulk solution, thereby to a certain extent avoiding the scaling of the cathode surface, prolonging the deactivation time of the cathode, and making the cathode can maintain a high scale removal rate for a long time.

[0033] (3) The hydrogen bubbles rapidly emanating from the cathode play a site-occupying role in the growth of scale, not only causing the scale to grow rapidly outward in the form of dendrites, but also resulting in a lower coverage and weaker binding force of the scale layer on the cathode grid, allowing the crystal nuclei to grow large enough that the diameter of the scale particles generated in the method of this invention is at least 1 μm. These particles can then be separated from the electrochemical reaction device by gravity settling, saving crystal waiting time and reducing energy consumption during the reaction process. The average energy consumption of the electrochemical descaling device in the method of this invention, calculated based on the electrode working cycle, is typically 1.2-11.6 kW·h / kg CaCO3. This invention not only reduces the risk of scaling and clogging in chemical hardening devices and achieves efficient and stable operation of the electrochemical hardening process, but also reduces the addition of flocculants, saving costs.

[0034] (4) The preparation process of the electrode with several pyramidal protrusions on the surface of the present invention is simple and easy to scale up and manufacture.

[0035] (5) The hardness removal method of the present invention can achieve a hardness removal rate of 70-95%, and the homogeneous nucleation rate can reach more than 60%. In the preferred technical solution, it can even reach more than 90%, and the operating cycle of a single electrode can reach more than 8 months.

[0036] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0037] Figure 1 Schematic diagram of the electrode with regular triangular pyramidal protrusions on the surface used in Example 1.

[0038] Figure 2 Example 2 shows a schematic diagram of an electrode with a regular square pyramidal protrusion on its surface.

[0039] Figure 3 Schematic diagram of the electrode with a regular pentagonal pyramidal protrusion on the surface used in Example 3.

[0040] Figure 4 Example 4 uses an electrode with a surface having regular hexagonal pyramidal protrusions.

[0041] Figure 5 Schematic diagram of the sawtooth-folded electrode used in Comparative Example 2. Detailed Implementation

[0042] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.

[0043] The experimental methods in the following examples are the conventional methods in the art, unless otherwise specified. The experimental materials used in the following examples are purchased from the conventional biochemical reagent stores, unless otherwise specified.

[0044] The pH value in the present application is determined by the method of “Determination of pH of Water Glass Electrode Method” (GB / T6920), the suspended solids are determined by the method of “Determination of Suspended Solids of Water Gravimetric Method” (GB / T 11901), and the metal ions are determined by the method of “Microwave Digestion / Inductively Coupled Plasma Mass Spectrometry” (ICP-MS).

[0045] Homogeneous nucleation rate = homogeneous nucleation amount / (homogeneous nucleation amount + heterogeneous nucleation amount) * 100%

[0046] Wherein, the heterogeneous nucleation is obtained by subtraction method, and the mass change of the electrode before and after descaling is the heterogeneous nucleation amount; and the homogeneous nucleation amount is obtained by subtracting the heterogeneous nucleation amount from the total hardness removal amount.

[0047] The average energy consumption of the electrochemical device descaling in the present application is represented by the electricity consumption for removing unit mass of hardness, and the energy consumption for removing unit mass of hardness is calculated according to the following formula.

[0048] E = UIt / VC * 1000

[0049] Wherein, E represents the energy consumption for removing unit mass; U represents the voltage, V; I represents the current, A; t represents the electrolysis time, h; V represents the water sample volume, L; and C represents the concentration difference of hardness change before and after treatment, mg / L.

[0050] Example 1

[0051] The electrode with a plurality of right triangular pyramid-shaped protrusions on the surface is a 70-mesh stainless steel mesh electrode, as shown in the figure. Figure 1 As shown in the figure, the edge length L1 of the right triangular pyramid-shaped protrusion is 0.5 cm, the base is an equilateral triangle, the edge length a1 is 0.6 cm, and the distance between the two adjacent vertices C1 and D1 of the right triangular pyramid-shaped protrusion is -0.35 cm. The right triangular pyramid-shaped protrusions are continuously distributed.

[0052] The wastewater to be treated is a certain coal chemical circulating water, and the water quality characteristics are as follows: total hardness is 700 mg / L, calcium content is 419 mg / L, magnesium content is 281 mg / L, and total alkalinity is 1002 mg / L.

[0053] The anode of the electrochemical hardness removal device is a DSA electrode, and the cathode is the electrode with a plurality of right triangular pyramid-shaped protrusions on the surface as described above. The insulating pad of different sizes is adjusted to make the distance between the cathode and the anode plate 5 cm.

[0054] The wastewater to be treated is pumped into the electrochemical hardness removal device by the cathode by the water inlet pump, and the water is discharged from the cathode. A downward-upward mode is adopted. During the hardness removal process, the direct current constant current source is adjusted so that the current density is 12 mA / cm 2 The stirring speed is adjusted to 200 rpm / min. After 30 minutes of reaction, the average particle size of the scale particles is about 5 μm. The water discharged from the electrochemical reaction device is directly transferred to the solid-liquid separation device. After 10 minutes of sedimentation, the water is discharged through the water outlet, and the generated scale is discharged through the slag outlet.

[0055] After the above reaction treatment, the total hardness of the wastewater is 84 mg / L, the calcium content is 56 mg / L, the magnesium content is 28 mg / L, the total alkalinity is 103 mg / L, the hardness removal rate is 91.1%, the homogeneous nucleation rate is 83.3%, the electrode single operation cycle can reach more than 6 months, and the average energy consumption of the device running for 6 months is 4.3 kW·h / kg CaCO3.

[0056] Example 2

[0057] The electrode with a plurality of right tetrahedral pyramid-shaped protrusions on the surface is a 70-mesh stainless steel mesh electrode, as shown in Figure 2 The edge length L2 of the right tetrahedral pyramid-shaped protrusion is 0.6 cm, the base is a square with a side length a2 of 0.6 cm, and the distance between two adjacent vertices C2 and D2 of the right tetrahedral pyramid-shaped protrusion is 0.6 cm. The right tetrahedral pyramid-shaped protrusions are continuously distributed.

[0058] The industrial wastewater to be treated is the same as in Example 1, and the industrial wastewater treated by the electrochemical hardness removal process is a certain coal chemical circulating water. The water quality characteristics are as follows: total hardness is 700 mg / L, calcium content is 419 mg / L, magnesium content is 281 mg / L, and total alkalinity is 1002 mg / L.

[0059] The anode of the electrochemical hardness removal device is a DSA electrode, and the cathode is the above-mentioned electrode with a plurality of right tetrahedral pyramid-shaped protrusions on the surface. The insulating pad of different sizes is adjusted to make the distance between the anode and the cathode plate 5 cm.

[0060] The wastewater to be treated is pumped into the electrochemical hardness removal device by the cathode by the water inlet pump, and the water is discharged from the cathode. A downward-upward mode is adopted. During the hardness removal process, the direct current constant current source is adjusted so that the current density is 12 mA / cm 2 The stirring speed is adjusted to 200 rpm / min. After 30 minutes of reaction, the average particle size of the scale particles is about 10 μm. The water discharged from the electrochemical reaction device is directly transferred to the solid-liquid separation device. After 10 minutes of sedimentation, the water is discharged through the water outlet, and the generated scale is discharged through the slag outlet.

[0061] After the above reaction treatment, the total hardness of the wastewater is 62 mg / L, the calcium content is 36 mg / L, the magnesium content is 26 mg / L, the total alkalinity is 83 mg / L, the hardness removal rate is 95.3%, the homogeneous nucleation rate is 90.2%, the single running period of the electrode can reach more than 8 months, and the average energy consumption for descaling of the device running for 8 months is 2.6 kW·h / kg CaCO3.

[0062] Example 3

[0063] The electrode with a plurality of regular pentagonal pyramid protrusions on the surface is a 70-mesh stainless steel mesh electrode, as shown in Figure 3 As shown in the figure, the edge length L3 of the regular pentagonal pyramid protrusion is 0.8 cm, the bottom is a regular pentagon with an edge length a3 of 0.6 cm, the distance between the minimum distance C3 and the distance D3 between the two adjacent vertices of the regular pentagonal pyramid protrusion is -0.83 cm. The regular pentagonal pyramid protrusions are discontinuously distributed.

[0064] The treated industrial wastewater is the same as in Example 1, and the industrial wastewater treated by the electrochemical hardness removal process is a certain coal chemical circulating water, and the water quality characteristics are as follows: total hardness is 700 mg / L, calcium content is 419 mg / L, magnesium content is 281 mg / L, and total alkalinity is 1002 mg / L.

[0065] The anode of the electrochemical hardness removal device is a DSA electrode, and the cathode is the above-mentioned electrode with a plurality of regular tetragonal pyramid protrusions on the surface. The insulating pad of different sizes is adjusted to make the distance between the anode and the cathode plate 5 cm.

[0066] The wastewater to be treated is pumped into the electrochemical hardness removal device by the cathode pump, and the water is discharged from the cathode. The down-up mode is adopted, and the direct current constant current source is adjusted during the hardness removal process to make the current density 12 mA / cm 2 ; the stirrer is adjusted to make the stirring speed 200 rpm / min, and after 30 minutes of reaction, the average particle size of the scale particles is measured to be 3 μm. The water discharged from the electrochemical reaction device is directly transferred to the solid-liquid separation device, settled for 10 minutes, and then discharged from the water outlet. The generated scale is discharged from the slag outlet.

[0067] After the above reaction treatment, the total hardness of the wastewater is 62 mg / L, the calcium content is 36 mg / L, the magnesium content is 26 mg / L, the total alkalinity is 83 mg / L, the hardness removal rate is 95.3%, the homogeneous nucleation rate is 90.2%, the single running period of the electrode can reach more than 8 months, and the average energy consumption for descaling of the device running for 8 months is 2.6 kW·h / kg CaCO3.

[0068] Example 4

[0069] The electrode with a plurality of regular hexagonal pyramid protrusions on the surface is a 70-mesh stainless steel mesh electrode, as shown in Figure 4As shown, the edge length L4 of the regular hexagonal pyramid-shaped protrusion is 0.7 cm, the bottom is a regular hexagon with an edge length a4 of 0.6 cm, and the distance between two adjacent vertices C3 and D3 of the regular hexagonal pyramid-shaped protrusion is 1.04 cm. The regular hexagonal pyramid-shaped protrusions are continuously distributed.

[0070] The treated industrial wastewater is the same as in Example 1, and the industrial wastewater treated by the electrochemical hardness removal is a circulating water of a coal chemical industry, and the water quality characteristics are as follows: total hardness is 700 mg / L, calcium content is 419 mg / L, magnesium content is 281 mg / L, and total alkalinity is 1002 mg / L.

[0071] The anode of the electrochemical hardness removal device is a DSA electrode, and the cathode is the electrode with the surface provided with the regular hexagonal pyramid-shaped protrusions, and the distance between the anode and the cathode is adjusted to be 5 cm by adjusting the insulating pad of different sizes.

[0072] The wastewater to be treated is pumped into the electrochemical hardness removal device by the cathode pump, and the water is discharged from the cathode, and the down-up mode is adopted. During the hardness removal process, the direct current constant current source is adjusted so that the current density is 12 mA / cm 2 ; the stirring speed is adjusted to be 200 rpm / min, and after 30 minutes of reaction, the average particle size of the scale particles is measured to be 4 μm. The water discharged from the electrochemical reaction device is directly transferred to the solid-liquid separation device, and after 10 minutes of sedimentation, the water is discharged from the water outlet, and the generated scale is discharged from the slag outlet.

[0073] After the above reaction treatment, the total hardness of the wastewater is 97 mg / L, the calcium content is 66 mg / L, the magnesium content is 31 mg / L, the total alkalinity is 140 mg / L, the hardness removal rate is 86.7%, the homogeneous nucleation rate is 79.9%, the single running period of the electrode can reach more than 6 months, and the average energy consumption for scale removal of the device during 6 months of operation is 4.9 kW·h / kg CaCO3.

[0074] Comparative Example 1

[0075] The same as in Example 1, except that the cathode is a two-dimensional stainless steel mesh. After the reaction treatment, the total hardness of the wastewater is 353 mg / L, the calcium content is 210 mg / L, the magnesium content is 143 mg / L, the total alkalinity is 502 mg / L, the hardness removal rate is 50.5%, the homogeneous nucleation rate is 21.3%, and the average particle size of the scale particles is 0.2 μm. The single running period of the electrode is only 0.5 months, and the average energy consumption for scale removal of the device during 0.5 months of operation is 21 kW·h / kg CaCO3. And it is found that there are mainly two problems during the experiment: (1) the scale is deposited on the surface of the cathode, which needs to be treated, causing damage to the electrode and reducing the service life; (2) the size of the scale particles is very small, and it must be flocculated by adding chemicals to make it settle.

[0076] Comparative Example 2

[0077] The same as example 1, except that the cathode is a sawtooth corrugated electrode, as shown in Figure 5 The sawtooth is a 70-mesh, three-dimensional sawtooth stainless steel mesh with a corrugation angle a of 80°, and the single-side length of the sawtooth is 0.8 cm. After the reaction treatment, the total hardness of the wastewater is 154 mg / L, the calcium content is -84 mg / L, the magnesium content is -70 mg / L, the total alkalinity is 222 mg / L, the hardness removal rate is 79.8%, the homogeneous nucleation rate is 75.5%, and the average particle size of the scale particles is 0.6 μm. The single operation cycle of the electrode is 4.5 months, and the average energy consumption of the device during the 4.5 months of operation is 14 kW·h / kg CaCO3. During the experiment, it is found that the size of the scale particles is very small, and they must be flocculated by adding chemicals to be settled, which increases the treatment cost.

Claims

1. A hydrogen evolution cathode, characterized in that, It is a hydrogen evolution cathode with several pyramidal protrusions on its surface, the top of which is a pointed tip.

2. The hydrogen evolution cathode according to claim 1, characterized in that, The multi-faceted pyramidal protrusion can be a triangular pyramidal protrusion, a quadrangular pyramidal protrusion, a pentagonal pyramidal protrusion, or a hexagonal pyramidal protrusion, and can be a protrusion of one shape or a combination of protrusions of multiple shapes.

3. The hydrogen evolution cathode according to claim 1, characterized in that, The polygonal pyramidal protrusion is a regular polygonal pyramidal protrusion.

4. The hydrogen evolution cathode according to claim 3, characterized in that, The pyramidal protrusion is a regular triangular pyramidal protrusion, a regular square pyramidal protrusion, a regular pentagonal pyramidal protrusion, or a regular hexagonal pyramidal protrusion.

5. The hydrogen evolution cathode according to claim 1, characterized in that, The length of the edge of the pyramidal protrusion is 0.2-1.5cm, and the side length of the corresponding base polygon is 0.2-1.5cm.

6. The hydrogen evolution cathode according to claim 5, characterized in that, The length of the edge of the pyramidal protrusion is 0.4-1.0 cm, and the side length of the corresponding base polygon is 0.4-1.0 cm.

7. The hydrogen evolution cathode according to claim 6, characterized in that, The length of the edge of the pyramidal protrusion is 0.4-0.8cm, and the length of the corresponding base polygon is 0.4-0.8cm.

8. The hydrogen evolution cathode according to claim 1, characterized in that, On the same electrode, there are pyramidal protrusions of different shapes, and the apex of each pyramidal protrusion is at the same height as the bottom surface of the electrode.

9. The hydrogen evolution cathode according to claim 1, characterized in that, The distance between adjacent vertices of the pyramidal protrusion is 0.1-4.0 cm.

10. The hydrogen evolution cathode according to claim 1, characterized in that, The hydrogen evolution cathode is a plate-shaped or mesh-shaped graphite electrode, carbon felt electrode, copper-nickel alloy electrode, titanium electrode, iron electrode, copper electrode, or stainless steel electrode.

11. The hydrogen evolution cathode according to claim 10, characterized in that, The hydrogen evolution cathode is a 10-200 mesh electrode.

12. The method for preparing the hydrogen evolution cathode according to any one of claims 1-11, comprising the step of processing the electrode through a polygonal mold.

13. The preparation method according to claim 12, characterized in that, It also includes a step of pretreating the electrodes to remove surface oxides and obtain a rough surface.

14. An electrochemical method for hardening removal, comprising treating wastewater using an electrochemical device having a cathode and an anode, wherein the wastewater enters through the cathode and exits through the cathode, characterized in that, The cathode is the hydrogen evolution cathode according to any one of claims 1-11.

15. The method according to claim 14, characterized in that, The distance between the anode and cathode of the electrochemical device is 2-10 cm, and the current density is 2-30 mA / cm². 2 The residence time of materials in the electrochemical device is 10-120 min.

16. The method according to claim 14, characterized in that, The method for removing hardness also includes the step of introducing the wastewater after the reaction into a solid-liquid separation device for treatment.

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