Preparation method and application of a copper-based electrode material

Abstract

The application belongs to the field of electrode materials, and particularly relates to a preparation method and application of a copper-based electrode material. After cleaning, the foamed copper is placed in a mixed solution of sodium hydroxide and hydrogen peroxide for stirring and reaction, and is cleaned and vacuum dried to obtain foamed copper loaded with copper hydroxide on the surface. The cobalt salt and conductive carbon black are placed in a mixed solution of isopropyl alcohol and naphthol, and are ultrasonically dispersed to obtain a suspension. The suspension is coated on the surface of the foamed copper loaded with copper hydroxide on the surface, and is vacuum dried, and is placed in an electrolyte for reduction reaction, and is washed and dried to obtain the copper-based electrode material. The method does not involve high-temperature treatment, the preparation of copper hydroxide is realized by controlling the proportion of hydrogen peroxide and sodium hydroxide, and when cobalt is introduced by electrochemical reduction, a carbon protective shell is simultaneously formed, so that the efficiency and stability of the nitrate reduction cathode are greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of electrode materials, specifically relating to a method for preparing and applying a copper-based electrode material. Background Technology

[0002] Electrochemical reduction for treating nitrate wastewater has attracted much attention due to its advantages such as high controllability and no secondary pollution. Copper (Cu)-based electrode materials are one of the most critical factors affecting the electrocatalytic reduction of nitrates.

[0003] Chinese patent document CN119553302A discloses a method for preparing a Co / Cu nanoalloy catalyst for the electrocatalytic reduction of nitrate to ammonia. The method involves impregnating copper foam in an ammonium persulfate and sodium hydroxide solution to form copper hydroxide, followed by electrodeposition and heat treatment with a hydrogen-argon mixed gas to synthesize Cu and Co, thus obtaining a catalyst with a nanoneedle structure for nitrate-to-ammonia reduction. However, although this technical solution uses a Cu substrate to prepare the Cu / Co nanoneedle structure catalyst, its preparation method still involves high-temperature treatment, and at a voltage of 0.5V, its ammonia yield is only 16.76 mg / h / cm³. 2 Its activity and stability need to be improved. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a highly active and structurally stable copper-based electrode material.

[0005] To achieve the above objectives, the present invention includes the following steps:

[0006] (1) The cleaned copper foam is placed in a mixture of sodium hydroxide and hydrogen peroxide and stirred to react. After the reaction is complete, it is cleaned and vacuum dried to obtain copper foam with copper hydroxide loaded on the surface. The concentration of hydrogen peroxide in the mixture is 0.3~1.5 mol / L.

[0007] (2) Cobalt salt and conductive carbon black are placed in a mixed solution of isopropanol and naphthol and ultrasonically dispersed to obtain a suspension; the suspension is coated on the surface of copper foam loaded with copper hydroxide, vacuum dried, and placed in an electrolyte for reduction reaction. After the reaction is completed, it is washed and dried to obtain copper-based electrode material.

[0008] Furthermore, in step (1), the concentration of the sodium hydroxide solution is 1~5 mol / L; the stirring reaction time is 1~12 h.

[0009] Furthermore, in step (2), the cobalt salt is one of cobalt chloride, cobalt nitrate, cobalt sulfate, and cobalt acetate; in the mixed solution of propanol and naphthol, the volume fraction of naphthol is 1-5%; the mass concentration of the cobalt salt is 10-20 mg / mL; the mass ratio of cobalt salt to conductive carbon black is 1:0.1-1; and the loading of cobalt salt on the surface of copper hydroxide-loaded foam is 1-10 mg / cm³. 2 The reduction reaction potential is -0.5 to -1.0 V (Vs. Ag / AgCl), and the reduction time is 0.5 to 1 h.

[0010] Compared with the prior art, the present invention has the following beneficial effects:

[0011] (1) The inventors discovered that Chinese patent document CN119553302A discloses a method for preparing a Co / Cu nano-alloy catalyst for electrocatalytic reduction of nitrate to ammonia. The Co / Cu nano-alloy is prepared from copper foam. The key to the formation of the Co / Cu nano-alloy is to use hydrogen and argon gas to reduce it at high temperature (250~550℃) for 200~400min. The material preparation process is complicated, and hydrogen atoms will penetrate into the copper matrix at high temperature, causing hydrogen embrittlement on the surface or inside of the copper foam. This will significantly reduce the thermal conductivity and mechanical strength of the material, resulting in a significant reduction in its toughness and rigidity, and thus affecting its stability. Therefore, this invention provides a method for preparing copper-based electrode materials and their application. Using copper foam as the cathode material, copper hydroxide is loaded onto the copper foam by oxidation with hydrogen peroxide and sodium hydroxide solution. The electrode material is prepared by coating its surface with cobalt salt and conductive carbon black suspension, followed by further electrochemical reduction. This method avoids the damage to the toughness and rigidity of the copper foam caused by high-temperature treatment during material preparation, and significantly shortens and simplifies the preparation process, reduces energy consumption, and shortens the time required, thereby saving costs.

[0012] (2) The inventors discovered that Chinese patent document CN119553302A discloses a method for preparing a Co / Cu nanoalloy catalyst for the electrocatalytic reduction of nitrate to ammonia. The prepared Co / Cu nanoalloy catalyst, when tested using cyclic voltammetry in a mixed solution of 0.1 mol / L KNO3 and 1 mol / L KOH, involved a low current density, requiring only 10 cycles, and the reaction time was also too short, far from meeting the requirements. The reason is that under high current, NO2... - Accumulation can poison active sites and interfere with subsequent hydrogenation steps. Furthermore, nitrates are reduced to NH3, which exists as NH3 under alkaline conditions. NH3 can then form [Cu(NH3)4] through complexation. 2+This invention accelerates the dissolution of copper. Addressing the problems of existing technologies, this invention prepares a suspension by mixing cobalt salt and conductive carbon black, coats it onto a prepared Cu(OH)2 / CF substrate, and electrochemically reduces it to obtain a cathode. During reduction, a carbon protective shell is formed on the cathode. This carbon protective shell provides physical and chemical protection for the catalyst in high-temperature or corrosive environments, giving it excellent stability and enabling it to maintain stability in the electrode solution for over 100 hours.

[0013] (3) The inventors discovered that in the prior art, due to the large difference in reduction potential between cobalt and copper, the order in which copper and cobalt are reduced during electrochemical reduction differs greatly, which leads to the segregation of copper and cobalt on the electrode surface and causes instability of the surface metal. In contrast, the present invention uses a mixture of cobalt salt and conductive carbon black to prepare a suspension. The conductive carbon black has abundant oxygen-containing functional groups, which can uniformly adsorb cobalt ions. The suspension is then coated on the surface of the copper-based material to form a coating layer. Compared with the prior art, the present invention uniformly adsorbs cobalt ions on the conductive carbon black in the coating layer. During electrochemical reduction, it can not only better stabilize the active sites of copper and cobalt ions on the surface, but also accelerate the transfer of electrons from the copper substrate to the active sites on the surface during reduction, thereby effectively avoiding the large difference in reduction potential between cobalt and copper and preventing segregation.

[0014] (4) The inventors discovered that the materials prepared in the prior art have a low ammonia yield in the application of nitrate reduction to ammonia production. Chinese patent document CN119553302A shows an ammonia yield of only 16.76 mg / h / cm³ at 0.5V. 2 The ammonia yield needs improvement. The core reason for the low ammonia yield lies in the competition between the hydrogen evolution reaction (HER) and the nitrate reduction of ammonia reaction, both of which are cathodes, leading to insufficient selectivity. In particular, the HER reaction in solution is a 2-electron process, which is much simpler than the nitrate reduction of ammonia reaction, which involves the transfer of 8 electrons. Therefore, in order to improve the catalytic selectivity, this invention avoids the thermal decomposition of copper hydroxide at high temperatures through electrochemical reduction during the preparation process, retaining the hydroxyl (-OH) groups of Cu(OH)2 to enhance surface hydrophilicity and preferentially adsorb NO3. - Instead of H + This reduces the competition for the HER reaction, and by introducing conductive carbon black, whose high conductivity (~1000 S / m) forms a three-dimensional conductive network on the copper foam skeleton, it accelerates the transfer of electrons from the current collector to the active sites (Cu, Co), speeds up the reaction rate, and increases the ammonia yield. Attached Figure Description

[0015] Figure 1 Transmission electron microscope image of the material prepared in Example 1 of this invention;

[0016] Figure 2This is a magnified transmission electron microscope image of the material prepared in Example 1 of the present invention;

[0017] Figure 3 For the stability test of the prepared material in Example 1 of the present invention;

[0018] Figure 4 This is for stability testing of the material prepared in Comparative Example 2 of the present invention. Detailed Implementation

[0019] The present invention will be further described below with reference to embodiments and accompanying drawings, but the scope of protection of the present invention is not limited thereto. Example 1

[0020] (1) Take 2×2cm 2 Copper foam was ultrasonically cleaned in methanol solution, dilute sulfuric acid and distilled water solution in sequence, and then vacuum dried. The clean copper foam was then immersed in a mixed solution of 10 mL of 1 mol / L sodium hydroxide and 2 mL of 0.3 mol / L hydrogen peroxide and stirred for 12 h. After the reaction was completed, the copper foam was removed, cleaned and vacuum dried to obtain copper foam loaded with copper hydroxide.

[0021] (2) Dissolve 10 mg of metallic cobalt chloride and 5 mg of conductive carbon black in a mixed solution of 0.99 mL isopropanol and 0.01 mL naphthol, and sonicate to prepare a suspension of 10 mg / mL. Coat 0.4 mL of the suspension onto the surface of Cu(OH)2 / CF, with a cobalt salt loading of 1 mg / cm³. 2 After vacuum drying, the material is used as the cathode and graphite as the anode. The reaction is carried out in 0.5M sodium sulfate electrolyte at a potential of -1.0V (hereinafter abbreviated as Vs.Ag / AgCl when Ag / AgCl is used as the reference electrode) for 0.5h. After washing and drying, the copper-based electrode material is obtained. Example 2

[0022] (1) Take 2×2cm 2 Copper foam was ultrasonically cleaned in methanol solution, dilute sulfuric acid and distilled water solution in sequence, and then vacuum dried. The clean copper foam was then immersed in a mixed solution of 10 mL of 3 mol / L sodium hydroxide and 2 mL of 0.9 mol / L hydrogen peroxide and stirred for 6 h. After the reaction was completed, the copper foam was removed, cleaned and vacuum dried to obtain copper foam loaded with copper hydroxide.

[0023] (2) Dissolve 20 mg of metallic cobalt nitrate and 5 mg of conductive carbon black in a mixed solution of 1.95 mL isopropanol and 0.05 mL naphthol, and sonicate to prepare a suspension of 10 mg / mL. Coat 2 mL of the suspension onto the surface of Cu(OH)2 / CF, with a cobalt salt loading of 5 mg / cm³. 2After vacuum drying, the material is used as the cathode and graphite as the anode. The reaction is carried out in 0.5M sodium sulfate electrolyte at a potential of -0.7V (Vs. Ag / AgCl) for 0.8h. After washing and drying, copper-based electrode material is obtained. Example 3

[0024] (1) Take 2×2cm 2 Copper foam was ultrasonically cleaned in methanol solution, dilute sulfuric acid and distilled water solution in sequence, and then vacuum dried. The clean copper foam was then immersed in a mixed solution of 10 mL of 5 mol / L sodium hydroxide and 2 mL of 1.5 mol / L hydrogen peroxide and stirred for 1 h. After the reaction was completed, the copper foam was removed, cleaned and vacuum dried to obtain copper foam loaded with copper hydroxide.

[0025] (2) Dissolve 40 mg of cobalt sulfate and 10 mg of conductive carbon black in a mixed solution of 1.9 mL of isopropanol and 0.1 mL of naphthol, and sonicate to prepare a suspension of 20 mg / mL. Coat 2 mL of the suspension onto the surface of Cu(OH)2 / CF, with a cobalt salt loading of 10 mg / cm³. 2 After vacuum drying, the material is used as the cathode and graphite as the anode. The reaction is carried out in 0.5M sodium sulfate electrolyte at a potential of -0.5V (Vs. Ag / AgCl) for 1 hour. After washing and drying, copper-based electrode material is obtained.

[0026] Comparison Example 1

[0027] Except for the use of 2 mL of 3 mol / L hydrogen peroxide solution in the mixture in step 1, the rest is the same as in Example 1.

[0028] Comparison Example 2

[0029] Except for step 2, which does not use conductive carbon black, the rest is the same as in Example 1.

[0030] Application Example 1

[0031] The cathode materials prepared in Examples 1-3 and Comparative Examples 1-2 were used for the reduction of nitrate wastewater to produce ammonia under alkaline conditions, including the following application steps:

[0032] In an H-type electrolytic cell, a proton exchange membrane was used to separate the cathode and anode chambers. 45 mL of 0.1 M PBS buffer solution was placed in each chamber. The cathode chamber contained 50 mM NaNO3 aqueous solution. The mixture was stirred continuously at 400 rpm to maintain a uniform distribution of the solution.

[0033] The testing procedure is as follows: First, a silver-silver chloride electrode and a platinum sheet electrode were used as the reference electrode and counter electrode, respectively. The working electrode was the cathode material prepared in the examples and comparative examples. The assembled standard three-electrode electrolytic cell was subjected to cyclic voltammetry (CV) testing in a CHI760. The working area of ​​the working electrode immersed in the electrolyte was 2 × 1 cm. The voltammetry was first performed at a voltage of 0.25 to -0.95 V (vs. RHE) at 100 mV s. -1 CV curve activation was performed at a scan rate to ensure the catalyst remained stable in subsequent tests. Electrolysis was then carried out for 1 hour at -0.5 V using chronoamperometry (It). The electrolyte was then collected for further product analysis. Nitrate content and NH4+ were measured. + The ammonia yield was obtained from the content.

[0034] The method for determining nitrate content is as follows: First, take 1.0 mL of the reacted electrolyte from the cathode chamber of the H-type electrolytic cell and dilute it to a suitable detection range. Then, add 1 mL of 1M HCl and 0.1 mL of 0.8wt% aminosulfonic acid solution to the above solution in sequence, shake well, and let stand for 10 minutes. Measure the absorbance of the prepared mixture at wavelengths of 220 nm and 275 nm using ultraviolet-visible spectrophotometry.

[0035] NH4 + Determination method: Take 1.0 mL of the reacted electrolyte from the cathode chamber of the H-type electrolytic cell and dilute it to a suitable detection range. First, add 1.0 mL of 500 g / L potassium sodium tartrate solution to the above 50 mL diluent and shake well. Then, add Nessler's reagent (1 mL) and shake well. After standing for 10 minutes, measure the absorbance in a UV spectrophotometer at a wavelength of 420 nm, using deionized water as a reference.

[0036] Experimental Example 1

[0037] A portion of the copper-based electrode material prepared in Example 1 was subjected to transmission electron microscopy (TEM) analysis. The results are as follows: Figure 1-2 As shown, the results indicate that the prepared cathode material exists in the form of particles, and Figure 2 This indicates that there is a carbon shell on the outer layer of the particles. The carbon shell can prevent the active components of the catalyst from coming into direct contact with the external environment, reducing the oxidation, sintering or poisoning of the active components. The carbon material itself has good chemical inertness and can protect the catalyst from corrosive media (such as acids and alkalis).

[0038] The nitrate reduction application tests were conducted on Examples 1-3. Electrolysis was performed at -0.5V for 1 hour, and the NH4+ produced after the reaction was analyzed. + The content was determined, and the results showed that after 1 hour of reaction, NH4+ The significant increase in content demonstrates that the prepared cathode material has excellent reduction properties.

[0039] According to the formula, the ammonia yields in Examples 1-3 were calculated to be 19.34 mg / h / cm³. 2 20.27 mg / h / cm 2 23.49 mg / h / cm 2 The excellent ammonia yield demonstrates the superior nitric acid reduction potential of the present invention. The stability of the cathode material prepared in Example 1 was tested at -0.5V. During a long electrolysis process of 100 hours, the current did not decrease significantly, proving the excellent stability of the cathode material.

[0040] Experimental Example 2

[0041] Using the same testing methods, comparative examples 1-2 were tested, and their ammonia yields are shown in the table below, demonstrating that the technical solution of this invention has an irreplaceable role.

[0042] In Comparative Example 1, the concentration of hydrogen peroxide in the mixed solution was increased. However, during the experiment, excess hydrogen peroxide acted as an oxidant under alkaline conditions, oxidizing metallic copper (Cu). Copper was oxidized from 0 valence to +2 valence, generating a large amount of blue precipitate, accompanied by the release of oxygen. Therefore, the excess hydrogen peroxide led to a vigorous reaction, generating a large amount of blue precipitate, some of which detached from the surface and entered the solution, making it impossible to prepare the catalyst on the foamed copper. When controlling the concentration and volume of sodium hydroxide and hydrogen peroxide, a low H2O2 concentration resulted in a slower oxidation reaction rate for Cu. 2+ Cu is locally enriched on the surface of the copper foam. 2+ Gradually released on the surface and reacting with OH - The precipitate preferentially forms a stable Cu(OH)₂ layer. In Comparative Example 1, the precipitate was collected, coated onto a new sheet of clean copper foam, and subsequent steps were performed. The resulting material had an ammonia yield of only 9.25 mg / h / cm². 2 .

[0043] In Comparative Example 2, conductive carbon black was not used; otherwise, it was the same as in Example 1. The prepared cathode material exhibited an ammonia yield of 14.21 mg / h / cm³ during nitrate reduction. 2 However, its stability is poor. In the stability test by chronoamperometry, its performance degraded by 20% within 7 hours, and by 68% of its initial value within 15 hours. The results are as follows. Figure 4 As shown.

[0044]

Claims

1. A method for preparing a copper-based electrode material, characterized in that, Includes the following steps: (1) The cleaned copper foam is placed in a mixture of sodium hydroxide and hydrogen peroxide and stirred to react. After the reaction is complete, it is cleaned and vacuum dried to obtain copper foam with copper hydroxide loaded on the surface. The concentration of hydrogen peroxide in the mixture is 0.3~1.5 mol / L. (2) Cobalt salt and conductive carbon black were placed in a mixed solution of isopropanol and naphthol and ultrasonically dispersed to obtain a suspension; the suspension was coated on the surface of copper foam loaded with copper hydroxide, vacuum dried, and placed in an electrolyte for reduction reaction. After the reaction was completed, the material was washed and dried to obtain copper-based electrode material. In step (1), the concentration of sodium hydroxide in the mixture is 1~5 mol / L; the stirring reaction time is 1~12 h.

2. The method for preparing the copper-based electrode material according to claim 1, characterized in that, In step (2), the cobalt salt is one of cobalt chloride, cobalt nitrate, cobalt sulfate, and cobalt acetate; in the mixed solution of isopropanol and naphthol, the volume fraction of naphthol is 1-5%; the mass concentration of the cobalt salt is 10-20 mg / mL; the mass ratio of cobalt salt to conductive carbon black is 1:0.1-1; and the loading of cobalt salt on the surface of copper foam loaded with copper hydroxide is 1-10 mg / cm³. 2 When Ag / AgCl is used as the reference electrode, the reduction reaction potential is -0.5 to -1.0 V, and the reduction time is 0.5 to 1 h.

3. The application of a copper-based electrode material prepared by the preparation method according to any one of claims 1 to 2, characterized in that, The prepared copper-based electrode material was applied to the electrochemical reduction of nitrate wastewater to produce ammonia.

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