Bifunctional catalytic electrode as well as preparation method and application thereof

Abstract

The invention provides a bifunctional catalytic electrode as well as a preparation method and application thereof. The bifunctional catalytic electrode comprises carbon paper and a catalytic material loaded on the surface of the carbon paper, the catalytic material comprises cobalt hydroxide and basic copper salt loaded on the cobalt hydroxide, the crystal form of the cobalt hydroxide is beta type, and the basic copper salt is selected from Cu2 (OH) 3Cl or Cu2 (OH) 3NO3. The catalytic electrode provided by the invention adopts the cobalt hydroxide catalytic material modified by the basic copper salt, has more catalytic active sites and synergistic catalytic effect, has high activity and excellent stability in the reaction process of electro-catalytic synthesis of ammonia and co-production of formate, and has good catalytic activity in a wide potential window. The catalytic electrode can achieve more than 90% of ammonium and formate Faraday efficiency, and has excellent stability in a cycle test process.

Description

Technical Field

[0001] The invention relates to the technical field of electrocatalytic nanomaterials, and in particular to a dual-functional catalytic electrode and a preparation method and application thereof. Background Art

[0002] Electrocatalysis is an effective means to efficiently process and utilize biomass resources to prepare high value-added chemicals. Nitrite is an organic pollutant widely used in various organisms and the environment. It is not only an important factor causing environmental pollution, but also has serious harm to the health of humans and animals. Therefore, it is of great significance to study nitrite pollution control technology. Glycerol is a representative polyol and a major by-product of the biofuel industry. It is one of the products with the highest yield among hundreds of biomass-derived intermediates. Glycerol can be converted into upgraded products (such as formic acid, etc.) with good economic benefits. In the past few decades, various metal-based materials have been developed into electroactive catalysts for electrocatalytic nitrate reduction to ammonia or electrocatalytic glycerol oxidation to formate. Among these catalysts, cobalt-based materials have attracted widespread attention due to their relatively high activity, low cost and good stability. However, these electrocatalysts often have too high potentials and are far from meeting practical applications. Summary of the invention

[0003] 1. Technical issues to be solved

[0004] In view of the deficiencies in the prior art, the present invention provides a bifunctional catalytic electrode and a preparation method and application thereof, and adopts basic copper salt and cobalt hydroxide material to form a composite catalytic material, which solves the problems raised in the above background technology.

[0005] (II) Technical solution

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0007] According to a first aspect of the present invention, a bifunctional catalytic electrode is provided, comprising carbon paper and a catalytic material loaded on the surface of the carbon paper, wherein the catalytic material comprises cobalt hydroxide and a basic copper salt loaded on the cobalt hydroxide, wherein the cobalt hydroxide has a β-type crystal form, and the basic copper salt is selected from Cu2(OH)3Cl or Cu2(OH)3NO3.

[0008] Preferably, the catalytic material is in the form of a sheet-like nanostructure, and the size of the sheet-like nanostructure is 50 to 200 nm.

[0009] Preferably, the molar ratio of the basic copper salt to cobalt hydroxide is 1:5 to 15, wherein the basic copper salt and cobalt hydroxide are calculated based on the molar amounts of copper and cobalt, respectively;

[0010] The loading amount of the catalytic material on the carbon paper is 2-3 mg / cm 2 .

[0011] According to a second aspect of the present invention, there is provided a method for preparing a bifunctional catalytic electrode, comprising the following steps:

[0012] Step 1, mixing cobalt salt, copper salt, hexamethylenetetraammonium, ethanol and water, and stirring to obtain a mixed solution;

[0013] Step 2, refluxing the mixed solution at 95° C. to obtain a solid powder;

[0014] Step 3, dispersing the solid powder in a mixed solution containing ethanol and naphthol, and subjecting the mixture to ultrasonic treatment to obtain a catalyst slurry;

[0015] Step 4: spray the catalyst slurry onto carbon paper and dry it naturally to obtain the bifunctional catalytic electrode.

[0016] Preferably, in step 1, the cobalt salt is selected from cobalt chloride hexahydrate or cobalt nitrate hexahydrate;

[0017] The copper salt is selected from copper chloride dihydrate or copper nitrate trihydrate.

[0018] Further preferably, when the cobalt salt is selected from cobalt chloride hexahydrate, the copper salt is selected from copper chloride dihydrate;

[0019] When the cobalt salt is selected from cobalt nitrate hexahydrate, the copper salt is selected from copper nitrate trihydrate.

[0020] Preferably, in step 1, the molar ratio of the cobalt salt to the copper salt is 5 to 15:1;

[0021] The molar ratio of the cobalt salt to the hexamethylenetetraammonium is 1:1 to 3;

[0022] The mass ratio of the cobalt salt to the volume ratio of the ethanol is 1 g: 10-20 mL;

[0023] The mass ratio of the cobalt salt to the volume of the water is 1 g: 120-160 mL.

[0024] Further preferably, the molar ratio of the cobalt salt to the copper salt is 10:1;

[0025] The molar ratio of the cobalt salt to hexamethylenetetraammonium is 1:2.

[0026] Further preferably, when the cobalt salt is selected from cobalt chloride hexahydrate, the mass ratio of cobalt chloride hexahydrate to ethanol is 1 g: 15-20 mL, and the mass ratio of cobalt chloride hexahydrate to water is 1 g: 150-160 mL;

[0027] When the cobalt salt is selected from cobalt nitrate hexahydrate, the mass ratio of cobalt nitrate hexahydrate to ethanol is 1g:10-15mL, and the mass ratio of hexahydrate and cobalt nitrate to water is 1g:120-130mL.

[0028] Further preferably, the volume ratio of ethanol to water is 1:9.

[0029] Preferably, in step 1, the stirring time is 15 to 30 minutes.

[0030] Preferably, in step 2, the reflux treatment time is 1 to 1.5 hours.

[0031] Preferably, in step 3, the volume ratio of the solid powder to ethanol is 1 g: 100-200 mL;

[0032] The volume ratio of the ethanol to naphthol is 200:7.

[0033] According to a third aspect of the present invention, there is provided a bifunctional catalytic electrode or a bifunctional catalytic electrode obtained according to the above preparation method for use in electrosynthesis of ammonia and coproduction of formate.

[0034] (III) Beneficial effects

[0035] The present invention provides a dual-functional catalytic electrode and a preparation method and application thereof, which has the following beneficial effects:

[0036] (1) This scheme provides a bifunctional catalytic electrode, which induces the simultaneous synthesis of β-cobalt hydroxide and basic copper salt by the introduction of copper salt. This one-step synthesized composite material helps to expose more catalytic active sites and improve the kinetics of the electrocatalytic reaction, thereby significantly improving the catalytic activity of the material.

[0037] (2) This scheme provides a method for preparing a bifunctional catalytic electrode, which uses a heating, condensation and reflux method to directionally synthesize a composite catalytic material of β-Co(OH)2 and different basic copper salts (Cu2(OH)3Cl or Cu2(OH)3NO3). The preparation method is simple, the raw materials are common, easy to control and low in cost. The rapid mass production of the electrocatalyst can be achieved only through a reflux device, with high production efficiency and environmental friendliness.

[0038] (3) The present invention provides a bifunctional catalytic electrode for use in electrocatalytic synthesis of ammonia and co-production of formate. The electrode has high activity and excellent stability during the electrocatalytic synthesis of ammonia and co-production of formate. Within a wide potential window, the electrode can achieve a Faradaic efficiency of over 90% for ammonium ion and formate, and has excellent stability during cyclic testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1X-ray diffraction patterns of the β-Co(OH)2 / Cu2(OH)3Cl catalytic material prepared in Example 1 of the present invention and the β-Co(OH)2 / Cu2(OH)3NO3 catalytic material prepared in Example 2, wherein Figure a is the X-ray diffraction pattern of the β-Co(OH)2 / Cu2(OH)3Cl catalytic material, and Figure b is the X-ray diffraction pattern of the β-Co(OH)2 / Cu2(OH)3NO3 catalytic material;

[0040] Figure 2 The transmission electron microscope morphology of the β-Co(OH)2 / Cu2(OH)3Cl catalytic material prepared in Example 1 of the present invention, wherein Figure a is a transmission electron microscope image of β-Co(OH)2 / Cu2(OH)3Cl at 200nm, and Figure b is a high-resolution electron microscope image of β-Co(OH)2 / Cu2(OH)3Cl at 5nm;

[0041] Figure 3 This is an X-ray photoelectron spectrum of the β-Co(OH)2 / Cu2(OH)3Cl catalytic material prepared in Example 1 of the present invention, wherein Figure a is the XPS spectrum of Co 2p, and Figure b is the XPS spectrum of Cu 2p;

[0042] Figure 4 The electrocatalytic nitrite reduction performance test graphs of the catalytic materials prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 of the present invention, wherein Figure a is a linear voltammetric curve of nitrite reduction in a mixed solution of 0.1M NaNO2 and 1M KOH, and Figure b is a Faraday efficiency comparison graph of ammonium radical products;

[0043] Figure 5 The electrocatalytic glycerol oxidation performance test diagrams of the catalytic materials prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 of the present invention, wherein Figure a is a linear voltammetric curve of glycerol oxidation in a mixed solution of 0.1M glycerol and 1M KOH, and Figure b is a comparison diagram of formate Faraday efficiency;

[0044] Figure 6 The β-Co(OH)2 / Cu2(OH)3Cl catalytic material prepared in Example 1 of the present invention before and after the electrocatalytic glycerol reaction 1 H NMR spectrum;

[0045] Figure 7The chronoamperometric curves of the β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode prepared in Example 1 of the present invention are obtained by a three-electrode method, wherein Figure a is a NO2RR chronoamperometric curve obtained by a three-electrode method in a mixed solution of 0.1M NaNO2 and 1M KOH, and Figure b is a chronoamperometric curve of glycerol oxidation obtained by a three-electrode method in a mixed solution of 0.1M glycerol and 1M KOH;

[0046] Figure 8 A linear voltammetric curve of the β-Co(OH)2 / Cu2(OH)3Cl catalytic material prepared in Example 1 of the present invention assembled into a membrane electrode assembly under the conditions of a mixed solution of 0.1M NaNO2 and 1M KOH and a mixed solution of 0.1M glycerol and 1M KOH;

[0047] Fig. 9 The electrolytic stability curves of the β-Co(OH)2 / Cu2(OH)3Cl catalytic material prepared in Example 1 of the present invention assembled into a membrane electrode assembly under the conditions of a mixed solution of 0.1M NaNO2 and 1M KOH and a mixed solution of 0.1M glycerol and 1M KOH;

[0048] Fig.10 This is a performance comparison chart of catalytic materials prepared at different Co / Cu molar ratios according to Examples 1 to 6 of the present invention and Comparative Examples 1 and 2 for electrocatalytic glycerol oxidation. DETAILED DESCRIPTION

[0049] In order to better illustrate the content of the present invention, a detailed description is given below in conjunction with specific embodiments.

[0050] Example 1

[0051] A method for preparing a bifunctional catalytic electrode comprises the following steps:

[0052] Step 1, dissolve 476 mg of cobalt chloride hexahydrate, 35 mg of cupric chloride dihydrate, and 561 mg of hexamethylenetetraammonium in 8 mL of anhydrous ethanol and 72 mL of deionized water, and stir for 30 min to obtain a pink mixed solution;

[0053] Step 2, placing the pink mixed solution in a round-bottom flask, heating in a 95°C water bath for condensation and reflux for 1 hour, centrifuging, washing and drying the product to obtain β-Co(OH)2 / Cu2(OH)3Cl powder;

[0054] Step 3, dispersing 5 mg of β-Co(OH)2 / Cu2(OH)3Cl powder in a mixed solution of 1 mL of anhydrous ethanol and 35 μL of 5 wt% naphthol, and ultrasonically treating for 30 min to form a uniform catalyst slurry;

[0055] Step 4: Take 500 μL of catalyst slurry and spray it evenly on a 1×1 cm 2 The catalytic electrode was obtained after natural drying on a hydrophilic carbon paper, denoted as β-Co(OH)2 / Cu2(OH)3Cl, with a copper / cobalt molar ratio of 10%.

[0056] Example 2

[0057] The preparation method of this embodiment is the same as that of Example 1, except that the mixed solution in step 1 contains 582 mg of cobalt nitrate hexahydrate, 48 mg of copper nitrate trihydrate, 561 mg of hexamethylenetetraammonium, 8 mL of anhydrous ethanol and 72 mL of deionized water, and the prepared catalytic electrode is recorded as β-Co(OH)2 / Cu2(OH)3NO3, and the copper / cobalt molar ratio is 10%.

[0058] Example 3

[0059] The preparation method of this embodiment is the same as that of Example 1, except that the mixed solution in step 1 contains 476 mg of cobalt chloride hexahydrate, 17.5 mg of cupric chloride dihydrate, 561 mg of hexamethylenetetraammonium, 8 mL of anhydrous ethanol and 72 mL of deionized water, and the prepared catalytic electrode is recorded as β-Co(OH)2 / Cu2(OH)3Cl, and the copper / cobalt molar ratio is 5%.

[0060] Example 4

[0061] The preparation method of this embodiment is the same as that of Example 1, except that the mixed solution in step 1 contains 476 mg of cobalt chloride hexahydrate, 52.5 mg of cupric chloride dihydrate, 561 mg of hexamethylenetetraammonium, 8 mL of anhydrous ethanol and 72 mL of deionized water, and the prepared catalytic electrode is recorded as β-Co(OH)2 / Cu2(OH)3Cl, and the copper / cobalt molar ratio is 15%.

[0062] Example 5

[0063] The preparation method of this embodiment is the same as that of Example 1, except that the mixed solution in step 1 contains 582 mg of cobalt nitrate hexahydrate, 24 mg of copper nitrate trihydrate, 561 mg of hexamethylenetetraammonium, 8 mL of anhydrous ethanol and 72 mL of deionized water, and the prepared catalytic electrode is recorded as β-Co(OH)2 / Cu2(OH)3NO3, and the copper / cobalt molar ratio is 5%.

[0064] Example 6

[0065] The preparation method of this embodiment is the same as that of Example 1, except that the mixed solution in step 1 contains 582 mg of cobalt nitrate hexahydrate, 72 mg of copper nitrate trihydrate, 561 mg of hexamethylenetetraammonium, 8 mL of anhydrous ethanol and 72 mL of deionized water, and the prepared catalytic electrode is recorded as β-Co(OH)2 / Cu2(OH)3NO3, and the copper / cobalt molar ratio is 15%.

[0066] Comparative Example 1

[0067] The preparation method of α-Co(OH)2 catalytic electrode comprises the following steps:

[0068] Step 1, dissolve 476 mg of cobalt chloride hexahydrate and 561 mg of hexamethylenetetraammonium in 8 mL of anhydrous ethanol and 72 mL of deionized water, and stir for 30 min to obtain a pink mixed solution;

[0069] Step 2: Place the pink mixed solution in a round-bottom flask, heat in a 95°C water bath to condense and reflux for 1 h, centrifuge, wash and dry the product to obtain α-Co(OH)2 powder;

[0070] Step 3, dispersing 5 mg of α-Co(OH)2 powder in a mixed solution of 1 mL of anhydrous ethanol and 35 μL of 5 wt% naphthol, and ultrasonically treating for 30 min to form a uniform slurry;

[0071] Step 4: Take 500 μL of slurry and spray it evenly on a 1×1 cm 2 The catalytic electrode was obtained after natural drying on the hydrophilic carbon paper and was recorded as α-Co(OH)2.

[0072] Comparative Example 2

[0073] The preparation method of this comparative example is the same as that of Example 1, except that the mixed solution in step 1 contains 582 mg of cobalt nitrate hexahydrate, 561 mg of hexamethylenetetraammonium, 8 mL of anhydrous ethanol and 72 mL of deionized water, and the prepared catalytic electrode is recorded as β-Co(OH)2.

[0074] Performance Testing

[0075] XRD analysis was performed on the catalytic electrodes prepared in Example 1 and Example 2. Figure 1As shown, Figure a shows that the prepared β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode consists of two physical phases, β-Co(OH)2 and Cu2(OH)3Cl, which matches the standard sample of Figure a card PDF#86-1391; Figure b shows that the synthesized β-Co(OH)2 / Cu2(OH)3NO3 catalytic electrode consists of two physical phases, β-Co(OH)2 and Cu2(OH)3NO3, which matches the standard sample of Figure b card PDF#84-0599. This proves that the catalyst on the catalytic electrode prepared by the present invention includes two phases, cobalt hydroxide and basic copper salt, and the cobalt hydroxide contains β-type.

[0076] The β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode prepared in Example 1 was subjected to TEM analysis. Figure 2 As shown, according to Figure 2 As shown in Figures a and b, the β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode presents a sheet-like nanostructure, with a small amount of Cu2(OH)3Cl with a size of 5 to 200 nm loaded on β-Co(OH)2. This supported nanosheet electrocatalyst helps to expose more catalytic active sites and improve the electrocatalytic performance.

[0077] The β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode prepared in Example 1 was subjected to X-ray photoelectron spectroscopy analysis. Figure 3 From Figures a to c, it can be seen that Co, Cu and O elements exist in the β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode. In the β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode, Cu mainly exists in the +2 valence, and Co exists in the +2 and +3 valences. This is mainly due to the increase in the valence state of some elements after the introduction of Cu2(OH)3Cl substance. In O1s, M-OH bonds and MO bonds are observed. According to the above test results, the successful preparation of the β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode is proved.

[0078] The catalytic electrodes prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 were tested by linear sweep voltammetry. The electrolyte was a mixed solution of 0.1 M NaNO2 and 1 M KOH. Figure 4 As shown; Figure a is a linear voltammetric scan of electrocatalytic nitrite reduction, and Figure b is a Faraday efficiency comparison of ammonium radical products; according to Figure 4It can be seen from Figure a that the prepared β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode has better catalytic performance. Compared with the Co(OH)2 samples prepared in Comparative Examples 1 and 2, the β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode has better current density and potential performance, and at a potential of -0.2V vs.RHE, the β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode can achieve an ammonium root Faraday efficiency of 90.3%, proving that the introduction of Cu2(OH)3Cl substance can significantly improve the cathode electrocatalytic performance of the Co(OH)2 catalyst.

[0079] The catalytic electrodes prepared in Example 1, Example 2, Comparative Examples 1 and 2 were tested by linear sweep voltammetry. The electrolyte was a mixed solution of 0.1 M glycerol and 1 M KOH. Figure 5 As shown; Figure a is a linear voltammetric scan of electrocatalytic glycerol oxidation, and Figure b is a comparison of the Faraday efficiencies of formate products; compared with the Co(OH)2 samples prepared in Comparative Examples 1 to 2, the β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode has better current density and potential performance, from which it can be seen that the β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode prepared in Example 1 of the present invention has the most excellent glycerol oxidation activity, and at a potential of 1.45V vs.RHE, the β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode can achieve a formate Faraday efficiency of 93.8%, proving that the introduction of Cu2(OH)3Cl substance can significantly improve the anode electrocatalytic performance of the Co(OH)2 catalyst.

[0080] The solution of the β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode prepared in Example 1 of the present invention before and after the electrocatalytic glycerol reaction was subjected to 1 H NMR test, the test results are as follows Figure 6 As shown in Figure 2, after 1 h of constant potential reaction, the 1 The H NMR signal weakened, and a signal peak of formic acid appeared at 8.3 ppm, indicating that the β-Co(OH)2 / Cu2(OH)3Cl electrocatalyst prepared in Example 1 can effectively electrocatalyze the oxidation of glycerol to formate.

[0081] In order to evaluate the stability of the β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode in the long-term cycle test, the β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode prepared in Example 1 was placed in a mixed solution of 0.1M NaNO2 and 1M KOH, and the NO2RR chronoamperometric curve was tested by the three-electrode method. Figure 7 As shown in a, the electrode is at -40 mA cm -2The electrolysis can be stable for more than 24 hours at the current density; Figure 7 As shown in b, in a mixed solution of 0.1 M glycerol and 1 M KOH, the GOR chronoamperometric curve was tested by the three-electrode method. The electrode was at 20 mA cm -2 The electrolysis can be stably carried out for more than 24 hours at a current density of 1.5 Å. It can be seen that the β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode prepared by the preparation method provided by the present invention has excellent bifunctional catalytic activity and high cycle test stability, showing great market application prospects.

[0082] The performance of the β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode prepared in Example 1 was tested by a flow membrane electrode assembly (MEA) method in a mixed solution of 0.1M NaNO2 and 1M KOH and in a mixed solution of 0.1M glycerol and 1M KOH. Figure 8 As shown in the figure, compared with the traditional water electrolysis cell, the electrolysis cell with coupled nitrite reduction and glycerol oxidation has a higher -2 Under the current density, the required voltage was significantly reduced by 300mV, indicating that the β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode can be used as a bifunctional catalytic electrode for glycerol oxidation coupled with nitrite reduction to synthesize ammonia.

[0083] The electrolytic stability of the MEA of the β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode prepared in Example 1 was further tested in a mixed solution of 0.1M NaNO2 and 1M KOH and in a mixed solution of 0.1M glycerol and 1M KOH. Fig. 9 As shown, the assembled electrolytic cell can sustain electrolysis for more than 17 h at a potential of 1.5 V vs. RHE, and can maintain stability in voltage and current density during the continuous electrolysis process, indicating that the β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode of the present invention has excellent catalytic stability for the co-production of formate and ammonium salt.

[0084] The catalytic electrodes prepared in Examples 1 to 6 and Comparative Examples 1 to 2 at different Co / Cu molar ratios were subjected to GOR tests. Fig.10 As shown in Figure a and Figure b, it is found through comparison that the optimal Co / Cu molar ratio of the β-Co(OH)2 / Cu2(OH)3Cl catalytic electrode prepared by the present invention is 10:1, and the catalytic electrode under this ratio has better GOR catalytic performance.

[0085] Through the above performance tests, it can be known that the present invention provides a bifunctional catalytic electrode and its preparation method and application. The catalytic electrode prepared by the synthesis method provided by the present invention has a flaky nanostructure, good crystallinity and stability, and exhibits high activity and excellent stability in the reaction of electrocatalytic synthesis of ammonia and co-production of formate. Within a wide potential window, the catalytic electrode can achieve more than 90% of the Faradaic efficiency of ammonium ions and formate, and shows good stability in cycle tests.

[0086] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A bifunctional catalytic electrode, characterized in that: It includes carbon paper and a catalytic material loaded on the surface of the carbon paper. The catalytic material includes cobalt hydroxide and a basic copper salt loaded on the cobalt hydroxide. The crystal form of the cobalt hydroxide is β-type. The basic copper salt is selected from Cu2(OH)3Cl or Cu2(OH)3NO3.

2. A bifunctional catalytic electrode according to claim 1, characterized in that: The catalytic material is in the form of a sheet-like nanostructure, and the size of the sheet-like nanostructure is 50-200 nm.

3. A bifunctional catalytic electrode according to claim 1, characterized in that: The molar ratio of the basic copper salt to the cobalt hydroxide is 1:5 to 15, wherein the basic copper salt and the cobalt hydroxide are calculated based on the molar amounts of copper and cobalt, respectively; The loading amount of the catalytic material on the carbon paper is 2-3 mg / cm 2 .

4. A method for preparing a bifunctional catalytic electrode according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step 1, mixing cobalt salt, copper salt, hexamethylenetetraammonium, ethanol and water, and stirring to obtain a mixed solution; Step 2, refluxing the mixed solution at 95° C. to obtain a solid powder; Step 3, dispersing the solid powder in a mixed solution containing ethanol and naphthol, and subjecting the mixture to ultrasonic treatment to obtain a catalyst slurry; Step 4: spray the catalyst slurry onto carbon paper and dry it naturally to obtain the bifunctional catalytic electrode.

5. The method for preparing a bifunctional catalytic electrode according to claim 4, characterized in that: In step 1, the cobalt salt is selected from cobalt chloride hexahydrate or cobalt nitrate hexahydrate; The copper salt is selected from copper chloride dihydrate or copper nitrate trihydrate.

6. The method for preparing a bifunctional catalytic electrode according to claim 4, characterized in that: In step 1, the molar ratio of the cobalt salt to the copper salt is 5 to 15:1; The molar ratio of the cobalt salt to the hexamethylenetetraammonium is 1:1 to 3; The mass ratio of the cobalt salt to the volume ratio of the ethanol is 1 g: 10-20 mL; The mass ratio of the cobalt salt to the volume of the water is 1 g: 120-160 mL.

7. The method for preparing a bifunctional catalytic electrode according to claim 4, characterized in that: In step 1, the stirring time is 15 to 30 minutes.

8. The method for preparing a bifunctional catalytic electrode according to claim 4, characterized in that: In step 2, the reflux treatment time is 1 to 1.5 hours.

9. The method for preparing a bifunctional catalytic electrode according to claim 4, characterized in that: In step 3, the volume ratio of the solid powder to ethanol is 1 g: 100-200 mL; The volume ratio of the ethanol to naphthol is 200:

7.

10. Use of a bifunctional catalytic electrode according to any one of claims 1 to 3 or a bifunctional catalytic electrode obtained according to the preparation method according to any one of claims 4 to 9 in electrosynthesis of ammonia and coproduction of formate.

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