Silver-coated copper powder and preparation method thereof

Abstract

The invention relates to silver-coated copper powder and a preparation method thereof.The preparation method comprises the following steps that S1, a dispersing agent, water, a first reducing agent and a first pH regulator are mixed, a mixed solution is obtained and then heated, a copper source water solution is dropwise added, centrifuging, washing and drying are conducted after reaction, and copper powder is obtained; s2, mixing copper powder, water and a second pH regulator to obtain a copper particle dispersion system; s3, mixing a silver source, water, ammonia water and a third pH regulator to obtain a silver-ammonia solution; and S4, the silver-ammonia solution, the copper particle dispersion system and the second reducing agent aqueous solution are mixed for a reaction, and after the reaction is completed, centrifugation, washing and drying are conducted to obtain the silver-coated copper powder. Compared with the prior art, the high conductivity of the silver-coated copper powder is achieved through the low silver coating amount, no toxic solvent participates in, the steps are simple, the cost is low, and environment friendliness is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of metal powder processing, in particular to silver-coated copper powder and a preparation method thereof. Background Art

[0002] With the advancement of science and technology, the research and development of new materials has become a key driving force for social progress and economic development. Metal materials, due to their unique properties, are widely used in fields such as optics, magnetism, heat, electricity, catalysis, and information storage. Silver is a scarce metal, with a content of only 0.07 ppm in the Earth's crust. It has attracted much attention for its excellent electrical and thermal conductivity, but its high price limits its widespread application. In contrast, copper is widely used due to its lower cost, but its susceptibility to oxidation leads to a decrease in electrical and thermal conductivity. These shortcomings of both silver and copper limit their practical applications.

[0003] Silver-coated copper powder is a core-shell composite metal powder produced by coating copper powder with silver. This composite powder not only solves the problem of silver migration but also improves the copper powder's conductivity and oxidation resistance, while significantly reducing production costs. Combining the advantages of silver and copper, silver-coated copper powder maintains its high conductivity while offering high oxidation resistance and heat resistance.

[0004] Patent Publication No. CN115805310A discloses a method for preparing silver-coated copper powder. The method comprises mixing a silver salt, a ligand (such as diethylenetriamine, triethylenetetramine, or tetraethylenepentamine), a surface modifier (such as a fatty acid, a fatty acid salt, or a silane coupling agent), and a solvent (such as water or a combination of water and an alcoholic solvent) to obtain a silver complex solution. The copper powder solution and the silver complex solution are then mixed, reacted, and dried to obtain the silver-coated copper powder. Patent Publication No. CN116393696A discloses a method for producing silver-coated copper powder. The method comprises sensitizing and activating the copper powder, preparing a reducing solution, performing a chemical reduction reaction with the reducing solution, and adding the prepared silver ammonia solution to the mixture, so that the reduced silver is uniformly and densely coated on the copper surface. Patent Publication No. CN103752842A discloses a method for preparing nano-silver-coated copper powder by a combined replacement and chemical deposition method. The method first prepares nano-copper powder by hydrazine hydrate reduction, then adds the silver ammonia solution and formaldehyde to the reaction system to silver-plate the copper surface to prepare the silver-coated copper powder. However, the above three methods all increase the conductivity of silver-coated copper powder by increasing the amount of silver coating, which is costly; the steps are cumbersome, involve a lot of organic reagents, and are not environmentally friendly. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a silver-coated copper powder and a preparation method thereof, which achieves high conductivity of the silver-coated copper powder by a lower silver coating amount, without the involvement of toxic solvents, simple steps, low cost, and environmental friendliness.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] In one aspect, the present invention provides a method for preparing silver-coated copper powder, comprising the following steps:

[0008] S1, a dispersant, water, a first reducing agent, and a first pH adjuster are mixed to obtain a mixed solution, which is then heated, and a copper source aqueous solution is added dropwise. After the reaction, the solution is centrifuged, washed, and dried to obtain copper powder;

[0009] S2, copper powder, water, and a second pH adjuster are mixed to obtain a copper particle dispersion system;

[0010] S3, mixing the silver source, water, ammonia water, and a third pH adjuster to obtain a silver ammonia solution;

[0011] S4. Mixing the silver ammonia solution, the copper particle dispersion system, and the second reducing agent aqueous solution, and heating the mixture for reaction. After the reaction is completed, centrifuging, washing, and drying the mixture to obtain silver-coated copper powder.

[0012] Further, in step S1, the dispersant includes polyvinyl pyrrolidone K12, polyvinyl pyrrolidone K13-18, polyvinyl pyrrolidone molecular weight 30000, polyvinyl pyrrolidone K30, polyvinyl pyrrolidone K90;

[0013] The first reducing agent includes one or more of ascorbic acid, glucose, sodium borohydride, hydrazine hydrate, sodium citrate, sodium hypophosphite, and oleic acid;

[0014] The first pH adjuster includes sodium hydroxide, ammonia water, potassium hydroxide, acetic acid, and sodium acetate, and the pH of the mixed solution is 3 to 14;

[0015] The copper source in the copper source aqueous solution includes copper sulfate, copper chloride and copper nitrate, and the concentration is 0.03-0.1 g / mL.

[0016] Furthermore, the first reducing agent includes a first strong reducing agent and a first mild reducing agent, the first strong reducing agent includes sodium borohydride, hydrazine hydrate, and sodium hypophosphite, the first mild reducing agent includes ascorbic acid, glucose, sodium citrate, and oleic acid, and the mass ratio of the first strong reducing agent to the first mild reducing agent is 1:80-120;

[0017] A single first mild reducing agent has moderate reducing power and a controllable reduction process. However, moderate reducing power can lead to larger and more uneven copper powder particles at the same time, affecting performance. Excessively strong reducing power in a single first strong reducing agent can result in the formation of fine nano-copper particles and severe particle agglomeration. The synergistic effect of the first strong reducing agent and the first mild reducing agent allows the first strong reducing agent to rapidly reduce metal ions while the first mild reducing agent provides sustained and mild subsequent reduction, resulting in a copper powder with small particle size, good dispersion, and high purity.

[0018] Furthermore, in step S1, the usage ratio of the dispersant, the first reducing agent, the copper source in the copper source aqueous solution, and water is 1.5-3.5 g: 5-15 g: 3-10 g: 200 mL.

[0019] Furthermore, in step S1, the heating temperature of the mixed solution is 50 to 90°C;

[0020] In step S4, the heating reaction process temperature is 50-90° C., and the heating reaction time is 2-3 hours.

[0021] Furthermore, in step S1, the centrifugal speed is 6000-10000 rpm, anhydrous ethanol is used for washing, and the drying temperature is 40-80°C.

[0022] Furthermore, in step S2, the concentration of copper powder in the copper particle dispersion system is 0.01 to 0.1 g / mL;

[0023] The second pH adjuster includes sodium hydroxide, ammonia water, potassium hydroxide, acetic acid, and sodium acetate. The pH of the copper particle dispersion system is 7-14.

[0024] Furthermore, a uniformly dispersed copper particle dispersion system is obtained by ultrasound, with an ultrasound frequency of 40 to 80 Hz. Furthermore, the ultrasound can remove oil and other impurities on the surface of the copper powder, thereby improving the silver coating effect on the copper powder surface.

[0025] Further, in step S3, the silver source includes silver nitrate, silver oxide, and silver chloride;

[0026] The silver source, ammonia water, and water are used in a ratio of 0.01-0.02 g: 10-30 mL: 10 mL, wherein the ammonia water acts as a complexing agent;

[0027] The third pH adjuster includes sodium hydroxide, ammonia water, potassium hydroxide, acetic acid, and sodium acetate, and the pH of the silver ammonia solution is 7-14.

[0028] Furthermore, in step S4, the second reducing agent in the second reducing agent aqueous solution includes one or more reducing agents selected from the group consisting of ascorbic acid, glucose, sodium borohydride, sodium citrate, sodium hypophosphite, hydrazine hydrate, and oleic acid.

[0029] Furthermore, the second reducing agent includes a second strong reducing agent and a second mild reducing agent, the second strong reducing agent includes sodium borohydride, hydrazine hydrate, sodium hypophosphite, and the second mild reducing agent includes ascorbic acid, glucose, sodium citrate, and oleic acid;

[0030] The mass ratio of the second strong reducing agent to the second mild reducing agent is 1:80-120. A single second mild reducing agent has moderate reducing power and a controllable reduction process, but moderate reducing power can lead to uneven silver coating at the same time, affecting performance. Excessive reducing power of a single second strong reducing agent can cause particle agglomeration, resulting in performance degradation. The synergistic effect of the second strong reducing agent and the second mild reducing agent allows the second strong reducing agent to rapidly reduce metal ions, while the second mild reducing agent provides sustained, mild subsequent reduction, resulting in a product with better performance than a single reducing agent.

[0031] Furthermore, in step S4, the mass of the silver source in the silver ammonia solution is 1.9% to 3.5% of the mass of the copper powder in the copper particle dispersion system, preferably 2% to 3%, and more preferably 2.2% to 2.7%.

[0032] Furthermore, in step S4, the volume ratio of the silver ammonia solution, the copper particle dispersion system, and the second reducing agent aqueous solution is 5-10:8-16:1-2;

[0033] The molar concentration of the second reducing agent in the second reducing agent aqueous solution is 0.018 mol / L.

[0034] Furthermore, in step S4, the centrifugal speed is 6000-10000 rpm, anhydrous ethanol is used for washing, and the drying temperature is 40-80°C.

[0035] On the other hand, the present invention also provides a silver-coated copper powder, which is prepared by the preparation method.

[0036] Compared with the prior art, the present invention has the following advantages:

[0037] (1) The silver-coated copper powder prepared by the present invention has a low silver content. The mass of the silver source in the silver ammonia solution is 0.3% to 4% of the mass of the copper powder in the copper particle dispersion system. The high conductivity of the silver-coated copper powder is achieved by a relatively low silver coating amount, and the cost is low.

[0038] (2) The present invention uses a second pH regulator to adjust the dispersion liquid to an alkaline environment, which can clean impurities on the surface of the copper powder and provide silver coating reaction conditions, thereby simplifying the process steps and improving the production efficiency of silver-coated copper powder.

[0039] (3) The copper powder of the present invention is subjected to ultrasound to remove oil and other impurities on the surface of the copper powder, thereby improving the silver coating effect on the surface of the copper powder. After the surface of the copper powder is cleaned, it is finally washed with ethanol and dried to obtain silver-coated copper powder.

[0040] (4) The present invention does not involve any toxic organic solvents in the entire process, which is lower in cost and environmentally friendly.

[0041] (5) The homemade copper powder of the present invention can control the formation and growth of silver particles by adjusting conditions such as reaction time and silver coating amount, and can well control the preparation of silver-coated copper powder with different particle sizes and excellent conductive properties.

[0042] (6) The present invention innovatively adopts a dual reduction system of a strong reducing agent to initiate the reaction and a mild reducing agent to control the deposition rate. First, the high-speed reduction of copper ions is quickly completed, and then the excessive aggregation and growth of crystal nuclei is suppressed by a slow reduction rate, achieving controllable nucleation-growth separation, and obtaining copper powder with small particle size and uniform dispersion. It not only quickly triggers the reduction of silver ions on the surface of the copper core, but also promotes the directional and uniform growth of silver atoms by a slow reduction rate, forming a continuous and dense thin silver layer. While significantly reducing the amount of silver used, the present invention avoids the use of organic reagents or protective agents and uses water as the reaction medium throughout the process, only using ethanol for washing, greatly simplifying the process and improving environmental protection, ultimately achieving low-cost, efficient, and green preparation of high-performance silver-coated copper powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The electrochemical impedance spectroscopy of the silver-coated copper powder prepared in Examples 1 and 2 is shown;

[0044] Figure 2 The electrochemical impedance spectra of the silver-coated copper powder prepared in Examples 1, 3, and 4 are shown;

[0045] Figure 3 The electrochemical impedance spectra of the silver-coated copper powder prepared in Example 1 and Comparative Examples 1 to 4 are shown;

[0046] Figure 4 The photoelectric response spectra of the silver-coated copper powder prepared in Example 1 and Comparative Examples 1 to 4 are shown;

[0047] Figure 5 The electrochemical impedance spectra of the silver-coated copper powder prepared in Example 2 and Comparative Examples 5 to 8 are shown;

[0048] Figure 6 The photoelectric response spectra of the silver-coated copper powder prepared in Example 2 and Comparative Examples 5 to 8 are shown;

[0049] Figure 7 This is a scanning electron microscope image of the silver-coated copper powder prepared in Example 1. DETAILED DESCRIPTION

[0050] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the scope of protection of the present invention is not limited to the following embodiments. Based on the given embodiments, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0051] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention are conventional reagents, methods, instruments and equipment in the art.

[0052] In the following examples, all the following chemicals were used as received without further purification. Copper sulfate pentahydrate has a CAS number of 7758-99-8 and a brand name of Greagent, purchased from Shanghai Titan Technology Co., Ltd.; sodium hydroxide has a CAS number of 1310-73-2 and a brand name of Greagent, purchased from Shanghai Titan Technology Co., Ltd.; ammonia has a CAS number of 1336-21-6 and a brand name of Greagent, purchased from Shanghai Titan Technology Co., Ltd.; polyvinylpyrrolidone K30 has a CAS number of 9003-39-8 and a brand name of Greagent, purchased from Shanghai Titan Technology Co., Ltd.; ascorbic acid has a CAS number of 50-81-7 and a brand name of Greagent, purchased from Shanghai Titan Technology Co., Ltd.; sodium borohydride has a CAS number of 16940-66-2 and a brand name of Greagent, purchased from Shanghai Titan Technology Co., Ltd.; silver nitrate has a CAS number of 7761-88-8, AR., ≥99.8%, purchased from Sinopharm Chemical Reagent Co., Ltd. Polyvinyl pyrrolidone with a molecular weight of 30,000, a CAS number of 9003-39-8, a brand of Yuanye Bio, was purchased from Shanghai Naicheng Biotechnology Co., Ltd.

[0053] A method for preparing silver-coated copper powder comprises the following steps:

[0054] S1, a dispersant, water, a first reducing agent, and a first pH adjuster are mixed to obtain a mixed solution, which is then heated, and a copper source aqueous solution is added dropwise. After the reaction, the solution is centrifuged, washed, and dried to obtain copper powder;

[0055] S2, copper powder, water, and a second pH adjuster are mixed to obtain a copper particle dispersion system;

[0056] S3, mixing the silver source, water, ammonia water, and a third pH adjuster to obtain a silver ammonia solution;

[0057] S4. Mixing the silver ammonia solution, the copper particle dispersion system, and the second reducing agent aqueous solution, and heating the mixture for reaction. After the reaction is completed, centrifuging, washing, and drying the mixture to obtain silver-coated copper powder.

[0058] In some specific embodiments, in step S1, the dispersant includes polyvinyl pyrrolidone K12, polyvinyl pyrrolidone K13-18, polyvinyl pyrrolidone with a molecular weight of 30,000, polyvinyl pyrrolidone K30, and polyvinyl pyrrolidone K90;

[0059] The first reducing agent includes one or more of ascorbic acid, glucose, sodium borohydride, hydrazine hydrate, sodium citrate, sodium hypophosphite, and oleic acid;

[0060] The first pH adjuster includes sodium hydroxide, ammonia water, potassium hydroxide, acetic acid, and sodium acetate, and the pH of the mixed solution is 3 to 14;

[0061] The copper source in the copper source aqueous solution includes copper sulfate, copper chloride and copper nitrate, and the concentration is 0.03-0.1 g / mL.

[0062] In some specific embodiments, the first reducing agent includes a first strong reducing agent and a first mild reducing agent, the first strong reducing agent includes sodium borohydride, hydrazine hydrate, and sodium hypophosphite, the first mild reducing agent includes ascorbic acid, glucose, sodium citrate, and oleic acid, and the mass ratio of the first strong reducing agent to the first mild reducing agent is 1:80-120;

[0063] A single first mild reducing agent has moderate reducing power and a controllable reduction process. However, moderate reducing power can lead to larger and more uneven copper powder particles at the same time, affecting performance. Excessively strong reducing power in a single first strong reducing agent can result in the formation of fine nano-copper particles and severe particle agglomeration. The synergistic effect of the first strong reducing agent and the first mild reducing agent allows the first strong reducing agent to rapidly reduce metal ions while the first mild reducing agent provides sustained and mild subsequent reduction, resulting in a copper powder with small particle size, good dispersion, and high purity.

[0064] In some specific embodiments, in step S1, the usage ratio of the dispersant, the first reducing agent, the copper source in the copper source aqueous solution, and water is 1.5-3.5 g: 5-15 g: 3-10 g: 200 mL.

[0065] In some specific embodiments, in step S1, the heating temperature of the mixed solution is 50-90°C;

[0066] In step S4, the heating reaction process temperature is 50-90° C., and the heating reaction time is 2-3 hours.

[0067] In some specific embodiments, in step S1, the centrifugal speed is 6000-10000 rpm, anhydrous ethanol is used in the washing process, and the drying temperature is 40-80°C.

[0068] In some specific embodiments, in step S2, the concentration of copper powder in the copper particle dispersion system is 0.01 to 0.1 g / mL;

[0069] The second pH adjuster includes sodium hydroxide, ammonia water, potassium hydroxide, acetic acid, and sodium acetate. The pH of the copper particle dispersion system is 7-14.

[0070] In some specific embodiments, a uniformly dispersed copper particle dispersion is obtained by ultrasound at a frequency of 40 to 80 Hz. Furthermore, ultrasound can remove oil and other impurities from the surface of the copper powder, thereby improving the silver coating effect on the copper powder surface.

[0071] In some specific embodiments, in step S3, the silver source includes silver nitrate, silver oxide, or silver chloride;

[0072] The silver source, ammonia water, and water are used in a ratio of 0.01-0.02 g: 10-30 mL: 10 mL, wherein the ammonia water acts as a complexing agent;

[0073] The third pH adjuster includes sodium hydroxide, ammonia water, potassium hydroxide, acetic acid, and sodium acetate, and the pH of the silver ammonia solution is 7-14.

[0074] In some specific embodiments, in step S4, the second reducing agent in the second reducing agent aqueous solution includes one or more of ascorbic acid, glucose, sodium borohydride, sodium citrate, sodium hypophosphite, hydrazine hydrate, and oleic acid.

[0075] In some specific embodiments, the second reducing agent includes a second strong reducing agent and a second mild reducing agent, the second strong reducing agent includes sodium borohydride, hydrazine hydrate, sodium hypophosphite, and the second mild reducing agent includes ascorbic acid, glucose, sodium citrate, and oleic acid;

[0076] The mass ratio of the second strong reducing agent to the second mild reducing agent is 1:80-120. A single second mild reducing agent has moderate reducing power and a controllable reduction process, but moderate reducing power can lead to uneven silver coating at the same time, affecting performance. Excessive reducing power of a single second strong reducing agent can cause particle agglomeration, resulting in performance degradation. The synergistic effect of the second strong reducing agent and the second mild reducing agent allows the second strong reducing agent to rapidly reduce metal ions, while the second mild reducing agent provides sustained, mild subsequent reduction, resulting in a product with better performance than a single reducing agent.

[0077] In some specific embodiments, in step S4, the mass of the silver source in the silver ammonia solution is 1.9% to 3.5% of the mass of the copper powder in the copper particle dispersion system, preferably 2% to 3%, and more preferably 2.2% to 2.7%.

[0078] In some specific embodiments, in step S4, the volume ratio of the silver ammonia solution, the copper particle dispersion system, and the second reducing agent aqueous solution is 5-10:8-16:1-2;

[0079] The molar concentration of the second reducing agent in the second reducing agent aqueous solution is 0.018 mol / L.

[0080] In some specific embodiments, in step S4, the centrifugal speed is 6000-10000 rpm, anhydrous ethanol is used in the washing process, and the drying temperature is 40-80°C.

[0081] A silver-coated copper powder is prepared by adopting the preparation method.

[0082] The above embodiments may be implemented individually or in any combination of two or more.

[0083] The following describes the details with reference to specific embodiments.

[0084] Example 1

[0085] A method for preparing silver-coated copper powder comprises the following steps:

[0086] S1. Preparation of copper powder:

[0087] Weigh 2.56g of polyvinylpyrrolidone K30 and add 200mL of deionized water, stirring and dissolving to obtain a dispersant aqueous solution; weigh 8.8g of ascorbic acid and 0.095g of sodium borohydride and add them to the dispersant aqueous solution, stirring and dissolving to obtain a first reducing agent aqueous solution, add 2mol / L NaOH solution to adjust the pH, and heat the obtained mixed solution to 80°C. Weigh 5g of copper sulfate pentahydrate and add 100mL of deionized water, stirring and dissolving to obtain a copper source aqueous solution. Slowly add the copper source aqueous solution dropwise to the heated mixed solution, react for 60 minutes, centrifuge at 8500rpm for 3 minutes, wash three times with anhydrous ethanol, and dry at 60°C for 120 minutes to obtain copper powder.

[0088] S2. Preparation of copper particle dispersion system:

[0089] 0.5 g of copper powder was weighed and added to 10 mL of deionized water for ultrasonication. The pH was adjusted to 13 with 2 mol / L NaOH to obtain a copper particle dispersion system.

[0090] S3. Preparation of silver ammonia solution:

[0091] Weigh 0.0127 g of silver nitrate and dissolve it in 10 mL of deionized water. Add 20 mL of ammonia water and adjust the pH to 13 with 2 mol / L NaOH to prepare a silver ammonia solution.

[0092] S4. Preparation of silver-coated copper powder:

[0093] 1.232 g of ascorbic acid and 0.0133 g of sodium borohydride were weighed and dissolved in 20 mL of deionized water to obtain a second reducing agent aqueous solution. 1.36 mL of the second reducing agent aqueous solution and 30 mL of the silver ammonia solution were added to 20 mL of the copper particle dispersion. The reaction was controlled at 75°C for 3 hours. After completion of the reaction, the mixture was centrifuged at 8500 rpm for 3 minutes, washed three times with anhydrous ethanol, and dried at 60°C for 120 minutes to obtain silver-coated copper powder (the mass of the silver source in the silver ammonia solution in this example was 2.52% of the mass of the copper powder in the copper particle dispersion).

[0094] Example 2

[0095] Compared with Example 1, except that the dispersant in step S1 is replaced from polyvinyl pyrrolidone K30 to polyvinyl pyrrolidone with a molecular weight of 30,000, the rest are the same.

[0096] Example 3

[0097] Compared with Example 1, except that the reaction time in step S4 is adjusted to 2 hours, the rest are the same.

[0098] Example 4

[0099] Compared with Example 1, except that the reaction time in step S4 is adjusted to 2.5 h, the rest are the same.

[0100] Comparative Example 1

[0101] Compared with Example 1, except that the mass of silver nitrate in step S3 was adjusted to 0.0018 g, all other aspects were the same. (In this comparative example, the mass of the silver source in the silver ammonia solution was 0.36% of the mass of the copper powder in the copper particle dispersion system).

[0102] Comparative Example 2

[0103] Compared with Example 1, except that the mass of silver nitrate in step S3 was adjusted to 0.0054 g, all other aspects were the same. (In this comparative example, the mass of the silver source in the silver ammonia solution was 1.08% of the mass of the copper powder in the copper particle dispersion system).

[0104] Comparative Example 3

[0105] Compared with Example 1, except that the mass of silver nitrate in step S3 was adjusted to 0.009 g, all other aspects were the same. (In this comparative example, the mass of the silver source in the silver ammonia solution was 1.8% of the mass of the copper powder in the copper particle dispersion system).

[0106] Comparative Example 4

[0107] Compared with Example 1, except that the mass of silver nitrate in step S3 was adjusted to 0.018 g, all other aspects were the same. (In this comparative example, the mass of the silver source in the silver ammonia solution was 3.6% of the mass of the copper powder in the copper particle dispersion system).

[0108] Comparative Example 5

[0109] Compared with Example 2, except that the reducing agent in step S1 was adjusted to 10.56 g of ascorbic acid and the reducing agent in step S4 was adjusted to 1.47 g of ascorbic acid, the rest were the same.

[0110] Comparative Example 6

[0111] Compared with Example 2, except that the reducing agent in step S1 is adjusted to 0.57 g of sodium borohydride and the reducing agent in step S4 is adjusted to 0.0794 g of sodium borohydride, the rest are the same.

[0112] Comparative Example 7

[0113] Compared with Example 2, except that the reducing agent in step S1 is adjusted to 7.04 g of ascorbic acid and 0.1892 g of sodium borohydride, and the reducing agent in step S4 is adjusted to 0.9856 g of ascorbic acid and 0.0266 g of sodium borohydride, the rest are the same.

[0114] Comparative Example 8

[0115] Compared with Example 2, except that the reducing agent in step S1 is adjusted to 7.744 g of ascorbic acid and 0.1514 g of sodium borohydride, and the reducing agent in step S4 is adjusted to 1.0842 g of ascorbic acid and 0.0213 g of sodium borohydride, the rest are the same.

[0116] The silver-coated copper powders prepared in Examples 1 to 4 and Comparative Examples 1 to 8 were characterized and tested.

[0117] like Figure 1 Shown are the electrochemical impedance spectra of the silver-coated copper powders prepared in Examples 1 and 2. It can be seen that the semicircular diameters of the silver-coated copper powders prepared in Examples 1 and 2 are small in the electrochemical impedance spectra, indicating that both have good electrical conductivity. The semicircular diameter of Example 1 in the high-frequency region is smaller than that of Example 2, indicating that its charge transfer resistance is lower. This may be attributed to the high molecular weight characteristics of polyvinyl pyrrolidone K30, whose long chain structure provides a stronger steric effect, effectively inhibiting the agglomeration of copper powder and forming a more uniform particle distribution, thereby reducing the interface resistance. Example 2 has a larger semicircular diameter, which may be due to the weak steric effect provided by the low molecular weight characteristics of the polyvinyl pyrrolidone with a molecular weight of 30,000 used, resulting in slight agglomeration of particles and increased charge transfer resistance.

[0118] like Figure 2Shown are the electrochemical impedance spectra of the silver-coated copper powders prepared in Example 1, 3, and 4. It can be seen that the semicircle diameter of Example 1 is significantly the smallest, indicating that it has the lowest charge transfer resistance, which is attributed to the formation of the densest and continuous silver coating layer on its surface, which reduces interface defects and electron transfer resistance. In contrast, Example 3 has the largest semicircle diameter and shows the highest charge transfer resistance, proving that its silver coating layer has defects, such as insufficient coverage or poor density, which leads to obstruction of the charge transfer process; the impedance of Example 4 is between the two, indicating that extending the reaction time to 2.5 hours improves the coating effect. The above results show that the silver-coated copper powders under the three reaction times all have good electrical conductivity, while insufficient silver coating reaction time leads to partial defects in the silver layer and a significant increase in interface resistance; extending the reaction time can form an ideal silver-coated structure with lower impedance and high conductivity, optimize the charge transfer efficiency, and provide silver-coated copper powders with different conductive properties for different application scenarios.

[0119] like Figure 3 The electrochemical impedance spectra of the silver-coated copper powder prepared in Example 1 and Comparative Examples 1 to 4 are shown. It can be seen that the semicircle diameter of Example 1 is the smallest and its charge transfer resistance is the lowest. This shows that the silver coating amount in Example 1 is moderate, and the silver layer effectively covers the surface of the copper powder, reducing interface defects and electron transfer resistance. Comparative Example 1 has the largest semicircle diameter and the highest charge transfer resistance. This may be due to insufficient silver content, resulting in discontinuous silver layer, causing the copper matrix to be exposed, and the interface resistance is significantly increased. The semicircle diameters of Comparative Examples 2 to 3 gradually decrease, and the charge transfer resistance decreases, indicating that the continuity of the silver layer is improved and the silver layer is initially formed. The semicircle diameter of Comparative Example 4 is slightly larger than that of Example 1, which may be due to the agglomeration or excessive accumulation of silver particles, resulting in roughening of the interface microstructure and increased resistance. The above results show that the interface performance of the silver-coated copper powder in Example 1 is significantly better than that of all comparative examples, and too low a silver loading will lead to incomplete coating, while too high a silver loading will cause degradation of the microstructure, both of which will damage the electrochemical transmission efficiency of the interface.

[0120] like Figure 4The photoelectric response spectra of the silver-coated copper powder prepared in Example 1 and Comparative Examples 1 to 4 are shown. It can be seen that when the light is turned on, the photocurrent of various samples increases, indicating that the samples are photosensitivity. Among them, the photocurrent response of Comparative Example 1 is the weakest, indicating that the light absorption efficiency and carrier separation ability of the material are limited at low silver coating. As the silver coating increases, the photocurrent intensity of Comparative Examples 2 and 3 gradually increases, which may be because the increase in silver layer coverage promotes the effective separation of visible light absorption and electron-hole pairs. The photocurrent of Comparative Example 4 has a strong response in the initial stage, but rapidly decays to a level lower than that of Comparative Example 1 over time, indicating that excessive silver loading may cause silver particle agglomeration or interface defects, hinder carrier transport, or induce recombination losses of photogenerated carriers. The above results show that Example 1 achieves continuous and uniform coverage of the silver layer on the copper core surface by precisely controlling the silver coating, thereby synergistically optimizing light absorption, carrier separation and carrier transport, effectively suppressing carrier recombination losses, and ultimately obtaining the strongest and most stable photocurrent response.

[0121] like Figure 5 The electrochemical impedance spectra of the silver-coated copper powder prepared in Example 2 and Comparative Examples 5 to 8 are shown. Example 2 forms a dense and continuous silver coating in a highly alkaline environment due to the synergistic reduction effect of ascorbic acid and sodium borohydride, significantly reducing interfacial defects, resulting in the smallest semicircular diameter. Comparative Example 5 may have slowed reduction kinetics due to excessive ascorbic acid, resulting in discontinuous silver layer deposition and exposure of the copper substrate, causing interfacial charge accumulation and an increase in the semicircular diameter. Comparative Example 6 may have experienced a vigorous reduction due to excessive sodium borohydride, causing heterogeneous nucleation and agglomeration of silver particles to form a porous structure, resulting in the largest semicircular diameter and the highest charge transfer resistance. Comparative Example 7 may have induced local coarsening of silver particles due to an excessively high sodium borohydride ratio, resulting in a semicircular diameter between Comparative Examples 5 and 8. Comparative Example 8 may have weakened the continuity of the silver layer due to the increase in ascorbic acid, resulting in a semicircular diameter close to that of Comparative Example 5. This confirms that the reducing agent ratio controls the coating morphology integrity and interfacial electron conduction efficiency by regulating the nucleation rate and growth continuity.

[0122] like Figure 6The photoelectric response spectra of the silver-coated copper powder prepared in Example 2 and Comparative Examples 5 to 8 are shown. According to the analysis of the photocurrent response curve shown in the figure, the silver-coated copper powder prepared in Example 2 exhibits significantly optimized photoelectrochemical performance, with the highest initial photocurrent response intensity, and maintains the most stable photocurrent output during the illumination test period, and the decay rate is extremely small, which is significantly better than Comparative Examples 5 to 8. In contrast, the initial photocurrent response intensity of Comparative Example 5 drops sharply and continues to decay; Comparative Example 6 has the worst performance, and its photocurrent decays rapidly; although the photocurrents of Comparative Examples 7 and 8 are improved compared to the single-component system, they are still significantly lower than the performance level of Example 2. This phenomenon is attributed to the synergistic effect of the precise ratio of the two reducing agents in Example 2. The two synergistically optimize the density and thickness uniformity of the silver shell layer on the copper core surface, thereby enhancing the carrier separation efficiency and inhibiting interfacial recombination. The imbalance of the reducing agent ratio in the comparative group leads to incomplete silver shell coating or increased lattice defects, which aggravates the recombination of photogenerated electron-hole pairs, and ultimately manifests as a weakening of the photocurrent response intensity and deterioration of stability.

[0123] like Figure 7 Shown is a scanning electron micrograph of the silver-coated copper powder prepared in Example 1. The sample consists of submicron particles covered with a continuous and dense nanosilver shell. The silver phase exhibits a typical polyhedral arrangement, with an average grain size of approximately 80-120 nm, forming a uniform coating structure. The overall particle morphology is irregular, polyhedral, with a concentrated particle size distribution and high silver shell coverage, consistent with a high-integrity core-shell structure. Residual impurities on the surface are minimal, meeting the microscopic morphology requirements for functional conductive fillers.

[0124] Although the present invention has been described in detail above using general explanations, specific embodiments, and experiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A method for preparing silver-coated copper powder, characterized in that: The following steps are involved: S1, a dispersant, water, a first reducing agent, and a first pH adjuster are mixed to obtain a mixed solution, which is then heated, and a copper source aqueous solution is added dropwise. After the reaction, the solution is centrifuged, washed, and dried to obtain copper powder; S2, copper powder, water, and a second pH adjuster are mixed to obtain a copper particle dispersion system; S3, mixing the silver source, water, ammonia water, and a third pH adjuster to obtain a silver ammonia solution; S4. Mixing the silver ammonia solution, the copper particle dispersion system, and the second reducing agent aqueous solution, and heating the mixture for reaction. After the reaction is completed, centrifuging, washing, and drying the mixture to obtain silver-coated copper powder.

2. The method for preparing silver-coated copper powder according to claim 1, wherein: In step S1, the dispersant includes polyvinyl pyrrolidone K12, polyvinyl pyrrolidone K13-18, polyvinyl pyrrolidone molecular weight 30000, polyvinyl pyrrolidone K30, and polyvinyl pyrrolidone K90; The first reducing agent includes a first strong reducing agent and a first mild reducing agent, wherein the first strong reducing agent includes sodium borohydride, hydrazine hydrate, and sodium hypophosphite, and the first mild reducing agent includes ascorbic acid, glucose, sodium citrate, and oleic acid, and the mass ratio of the first strong reducing agent to the first mild reducing agent is 1:80-120; The first pH adjuster includes sodium hydroxide, ammonia water, potassium hydroxide, acetic acid, and sodium acetate, and the pH of the mixed solution is 3 to 14; The copper source in the copper source aqueous solution includes copper sulfate, copper chloride and copper nitrate, and the concentration is 0.03-0.1 g / mL.

3. The method for preparing silver-coated copper powder according to claim 1, wherein: In step S1, the dispersant, the first reducing agent, the copper source in the copper source aqueous solution, and water are used in a ratio of 1.5-3.5 g: 5-15 g: 3-10 g: 200 mL.

4. The method for preparing silver-coated copper powder according to claim 1, wherein: In step S1, the mixed solution is heated to a temperature of 50 to 90°C; In step S4, the heating reaction process temperature is 50-90°C.

5. The method for preparing silver-coated copper powder according to claim 1, wherein: In step S2, the concentration of copper powder in the copper particle dispersion system is 0.01 to 0.1 g / mL; The second pH adjuster includes sodium hydroxide, ammonia water, potassium hydroxide, acetic acid, and sodium acetate. The pH of the copper particle dispersion system is 7-14.

6. The method for preparing silver-coated copper powder according to claim 1, wherein: In step S3, the silver source includes silver nitrate, silver oxide, and silver chloride; The usage ratio of the silver source, ammonia water and water is 0.01-0.02 g: 10-30 mL: 10 mL; The third pH adjuster includes sodium hydroxide, ammonia water, potassium hydroxide, acetic acid, and sodium acetate, and the pH of the silver ammonia solution is 7-14.

7. The method for preparing silver-coated copper powder according to claim 1, wherein: In step S4, the second reducing agent in the second reducing agent aqueous solution includes a second strong reducing agent and a second mild reducing agent, the second strong reducing agent includes sodium borohydride, hydrazine hydrate, and sodium hypophosphite, and the second mild reducing agent includes ascorbic acid, glucose, sodium citrate, and oleic acid; The mass ratio of the second strong reducing agent to the second mild reducing agent is 1:80-120.

8. The method for preparing silver-coated copper powder according to claim 1, wherein: In step S4, the mass of the silver source in the silver ammonia solution is 1.9% to 3.5% of the mass of the copper powder in the copper particle dispersion system.

9. The method for preparing silver-coated copper powder according to claim 1, wherein: In step S4, the volume ratio of the silver ammonia solution, the copper particle dispersion system, and the second reducing agent aqueous solution is 5-15:8-16:0.1-2; The molar concentration of the second reducing agent in the second reducing agent aqueous solution is 0.01 to 0.03 mol / L.

10. Silver-coated copper powder, prepared by the preparation method according to any one of claims 1 to 9.

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