A shell structure solid-phase catalytic electrode, a preparation method thereof and application of the electrode in electro-synthesis of sodium borohydride

Abstract

The application discloses a shell structure solid-phase catalytic electrode and a preparation method thereof and application of the shell structure solid-phase catalytic electrode in electrochemical synthesis of sodium borohydride. The shell structure solid-phase catalytic electrode is divided into an electrode inner core and an electrode outer shell body. A coating of the electrode inner core comprises sodium metaborate, a catalyst and a binder. A coating of the electrode outer shell body comprises the catalyst and the binder. The shell structure solid-phase catalytic electrode is prepared by combining the electrode inner core and the electrode outer shell body, and the shell structure solid-phase catalytic electrode solves the problem of low reaction efficiency caused by large migration resistance of anions to a cathode in a liquid-phase electrolysis method. The shell structure solid-phase catalytic electrode is used for electrochemical reduction of sodium metaborate to synthesize sodium borohydride, has low cost and high efficiency, and the current efficiency of the electrochemical reduction of sodium borohydride in an alkaline aqueous solution can reach more than 60%.

Description

TECHNICAL FIELD

[0001] The present application relates to a shell structure solid phase catalytic electrode and its preparation method and application of electrochemical synthesis of sodium borohydride, and belongs to the field of hydrogen storage materials. BACKGROUND

[0002] Hydrogen energy as a green, environmentally friendly, high-purity energy has been rapidly developed, and as a raw material for producing hydrogen energy, it has inevitably been widely concerned. Hydrogen production by hydrogen storage materials has become a major hotspot. Sodium borohydride as a hydrogen storage material has high hydrogen storage density, high safety, long storage time, high hydrogen purity, and no harm to the environment, and the decomposition products can be recycled, which has great potential in hydrogen production.

[0003] In industry, sodium borohydride is mainly prepared by Schlesinger method and Bayer method. The synthesis route of Schlesinger method is to heat and react NaH and gaseous trimethyl borate (B(OCH3)3) without solvent to generate NaBH4 and sodium methoxide (NaOCH3). Bayer method reacts borax (Na2B4O7), sodium metal (Na), H2 and silicon dioxide (SiO2) in a reaction kettle at 700 DEG C to obtain sodium borohydride. Although the above technologies are relatively mature, high pressure and high temperature conditions, high-precision reaction kettles and active reducing agents are required in the reaction process, and the reaction process is relatively dangerous.

[0004] Electrochemical synthesis technology uses electrons as reagents, has little environmental pollution, can be carried out at normal temperature and pressure, saves energy, and has low investment cost. It has been widely used in the fields of chemical industry, metallurgy, machinery, aviation, medicine, materials, energy, environmental science and other technologies. However, the reported product amount of sodium borohydride synthesized by electro-reduction is very small, and the current efficiency is low. The main problem is that liquid phase electrolysis method is used, and the reactant metaborate ion and the intermediate product in the reaction are all anions, which have great resistance to migrate to the cathode, and the diffusion process is hindered, so the reaction is difficult to proceed. The core technology of the present application is to design a shell structure solid phase catalytic electrode, which solves the repulsion between metaborate anion and cathode, so as to realize the efficient electro-reduction of sodium metaborate to synthesize sodium borohydride.

[0005] In view of the technical problems existing in the present liquid phase electro-reduction process, the purpose of the present application is to provide a shell structure solid phase catalytic electrode and its preparation method and application of electrochemical synthesis of sodium borohydride, to solve the influence of mutual repulsion between metaborate anion and cathode, to improve the current efficiency, to have low cost and high efficient electro-catalytic performance.

[0006] The purpose of the present application is realized by the following technical scheme:

[0007] In the preparation process of the novel shell structure solid-phase catalytic electrode of the present application, sodium metaborate is used to prepare a cathode together with catalyst powder, conductive material, additive and binder to reduce the mutual repulsion between metaborate anion and the cathode.

[0008] Further, the preparation method of the shell structure solid-phase catalytic electrode comprises the following steps:

[0009] 1) The coating raw material of the electrode inner core comprises sodium metaborate micron powder, catalyst powder and binder, which are uniformly mixed and then adjusted into slurry with a solvent to obtain a coating slurry for preparing the electrode inner core;

[0010] The coating raw material of the electrode outer shell comprises catalyst powder and binder, which are uniformly mixed and then adjusted into slurry with a solvent to obtain a coating slurry for preparing the electrode outer shell;

[0011] 2) The two slurries prepared in step 1) are respectively coated on the outer surface of the foam metal substrate, and then dried to obtain the electrode inner core and the electrode outer shell, respectively;

[0012] 3) The electrode inner core and the electrode outer shell are combined to obtain the shell structure solid-phase catalytic electrode.

[0013] Further, the sodium metaborate in step 1) comprises at least one of sodium metaborate tetrahydrate, sodium metaborate dihydrate or sodium metaborate anhydrous, and the particle size range is 400-800 mesh.

[0014] Further, the catalyst in step 1) comprises one or a mixture of several of the following:

[0015] (1) metal hydride: ionic metal hydride LiH, NaH, KH, CaH2 or BaH2, and metallic metal hydride CrH2, NiH, CuH, ZnH2 or PdH 0.8 , or a mixture of one or more thereof;

[0016] (2) metal boride: monoboride Mn4B or Co3B, diboride ZrB2, TiB2 or Ta3B2, triboride Cr5B3 or Rh7B3, and polyboride Ti3B4, CaB6, LaB6 or Ru 11 B8, or a mixture of one or more thereof;

[0017] (3) metal oxide: a mixture of one or more of CuO, FeO, PbO, Fe2O3, PbO2, Pb3O4.

[0018] Further, the binder in step 1) comprises a mixture of one or more of polytetrafluoroethylene emulsion, polyvinylidene fluoride emulsion, methyl cellulose, polyvinyl alcohol.

[0019] Further, in step 1), the coating raw material of the electrode inner core has a sodium metaborate powder mass of 0.5-5 times the mass of the catalyst, and a binder mass of 0.025-0.3 times the mass of the catalyst; the coating raw material of the electrode outer shell has a binder mass of 0.025-0.3 times the mass of the catalyst.

[0020] Further, in step 1), the solvent includes a mixture of one or more of deionized water, acetone, isopropyl alcohol, ethylene glycol, N-dimethylformamide, and N-dimethylpyrrolidone.

[0021] Further, in step 1), the coating raw material of the electrode inner core and the electrode outer shell respectively further has one or both of an additive and a conductive material; the coating raw material of the electrode inner core or the electrode outer shell has an additive mass of 0-4 times, preferably 0.47-4 times, the mass of the catalyst, and a conductive material mass of 0-0.5 times, preferably 0.055-5 times, the mass of the catalyst; the additive includes a mixture of one or more of Hg, Pb, Cd, Zn, Ni, and Co; the conductive material includes a mixture of one or more of carbon nanotubes, activated carbon, conductive graphite, and amorphous carbon.

[0022] Further, in step 2), the foam metal substrate includes any one of foam nickel, foam copper, foam titanium, and foam stainless steel.

[0023] As a preferred, in step 3), the combination form is as shown in Figure 1 The electrode outer shell is provided with a slot matched with the outer shape of the electrode inner core, and the electrode inner core is inserted into the slot of the electrode outer shell to form a shell structure solid-phase catalytic electrode.

[0024] The novel shell structure solid-phase catalytic electrode prepared by the application has good application in the synthesis of sodium borohydride from the electro-reduction of sodium metaborate in an alkaline aqueous solution. The novel shell structure solid-phase catalytic electrode is used as a cathode in a double-electrode chamber electrolytic cell with a cationic diaphragm, and a lead or graphite material is used as an anode. The concentration of sodium metaborate in the solution is 0.2 mol / L, and the concentration of sodium hydroxide is 0.5 mol / L.

[0025] The above scheme of the application has the following beneficial effects:

[0026] 1. The new shell structure solid phase catalytic electrode prepared by the present application has high efficiency of electric reduction of sodium borohydride, solves the mutual repulsion between the metaborate anion and the cathode, and has good selectivity for sodium metaborate reduction. The shell structure solid phase catalytic electrode of the present application is divided into an electrode inner core and an electrode outer shell. The coating of the electrode inner core is sodium metaborate, a catalyst, a conductive material, an additive and a binder. The reaction raw material sodium metaborate exists in a solid phase in the cathode, and the role is to solve the mutual repulsion between the metaborate anion and the cathode. The coating of the electrode outer shell is a catalyst, a conductive material, an additive and a binder, and the role is to inhibit the diffusion of the intermediate product generated in the sodium metaborate reduction process to the electrolyte body. The shell structure solid phase catalytic electrode prepared by combining the electrode inner core and the electrode outer shell solves the problem of high resistance of anion migration to the cathode in the liquid phase electrolysis method, which leads to low reaction efficiency.

[0027] 2. The present application uses an electrochemical reduction method in an alkaline solution to prepare sodium borohydride, which is carried out at normal temperature and pressure without the need for additional additives, and has the advantages of green energy saving and environmental protection.

[0028] 3. The present application uses a coating method to prepare a catalytic electrode, which has simplicity and operability.

[0029] 4. The shell structure solid phase catalytic electrode of the present application is used for electrochemical reduction of sodium metaborate to synthesize sodium borohydride, has low cost and high efficiency, and the current efficiency of the electrochemical reduction of sodium borohydride in an alkaline aqueous solution can reach more than 60%. The examples of the present application have been verified. The new shell structure solid phase catalytic electrode prepared by the present application is put into an electrolysis device, and the current efficiency can reach as high as 68% after electrolysis for 0.5h, which greatly improves the current efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a preparation flow chart of the new shell structure solid phase catalytic electrode of the present application.

[0031] Figure 2 is the XRD pattern of the electric reduction product NaBH4 prepared in Example 1 of the present application.

[0032] Figure 3 is the change of the concentration and current efficiency of the electric synthesis of sodium borohydride using the shell structure solid phase catalytic electrode of Example 1 of the present application with electrolysis time.

[0033] Figure 4 is the change of the concentration and current efficiency of the electric synthesis of sodium borohydride using the electrode inner core as the electrode in Comparative Example 1 of the present application with electrolysis time.

[0034] Figure 5 is the change of the concentration and current efficiency of the electric synthesis of sodium borohydride using the electrode outer shell as the electrode in Comparative Example 2 of the present application with electrolysis time. DETAILED DESCRIPTION

[0035] The application will be further described in connection with the following specific examples, but the scope of the application is not limited thereto.

[0036] Unless otherwise defined, all terms used in the connection with the present application, such as the technical terms used by those skilled in the art, have the same meaning as commonly understood by one of ordinary skill in the art. The technical terms used herein are only for the purpose of describing specific embodiments of the present application and are not intended to limit the scope of the present application.

[0037] Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by the existing methods.

[0038] Example 1

[0039] 12 g of anhydrous sodium metaborate powder (particle size range of 400-800 mesh), 8 g of metal hydride (MgH), 4 g of metal oxide (PbO), 1.5 g of polytetrafluoroethylene emulsion (60 wt%), and 4 g of metal boride (NiB) were mixed, a small amount of deionized water was added, and stirred into a slurry, which was then coated on a foamed stainless steel and dried at 65°C to obtain an electrode inner core. 4 g of metal hydride (MgH), 4 g of metal oxide (PbO), and 1 g of polytetrafluoroethylene emulsion (60 wt%) were mixed, a small amount of deionized water was added, and stirred into a slurry, which was then coated on a foamed stainless steel and dried at 60°C to obtain an outer shell electrode. The electrode inner core and the outer shell electrode were combined according to the structure to obtain a shell structure solid-phase catalytic electrode. Figure 1 The electrolysis experiment was carried out in a two-electrode cell electrolyzer with a cationic membrane, in which the anode was lead and the cathode was the obtained shell structure solid-phase catalytic electrode, and a constant current electrolysis was used with a current density of 20 mA / cm 2 .

[0040] According to the above operation process, the concentration and current efficiency of sodium borohydride electrochemically synthesized in 0.2 mol / L NaBO2+0.5 mol / L NaOH aqueous solution by the shell structure solid-phase catalytic electrode prepared in Example 1 are shown in the graph of Figure 3 After 0.5 h of electrolysis, the current efficiency reached 68.12%, and the calculation method of the current efficiency was that the amount of electricity required to generate the target product / the total amount of electricity*100% within a certain period of electrolysis. The concentration of sodium borohydride produced after 4 h was 1.378×10 -2 mol / L.

[0041] Comparative Example 1

[0042] The electrode preparation steps were repeated in Example 1, except that the cathode used in the operation was replaced with an electrode core, and direct electrolysis was performed in a 0.2 mol / L NaBO2 + 0.5 mol / L NaOH aqueous solution. The concentration and current efficiency of the electrochemical synthesis of sodium borohydride are shown in the figure below. Figure 4 As shown, the current efficiency reached 55.8% after 0.5 hours of electrolysis. The concentration of sodium borohydride produced after 4 hours was 6.2 × 10⁻⁶. -3 The reaction current efficiency is lower than that of the shell-structured solid-phase catalytic electrode in Example 1 due to the diffusion of intermediate products.

[0043] Compare with Example 2:

[0044] The electrode preparation steps were repeated in Example 1, except that the cathode used in the operation was replaced with a shell electrode, and direct electrolysis was performed in a 0.2 mol / L NaBO2 + 0.5 mol / L NaOH aqueous solution. The concentration and current efficiency of the electrochemical synthesis of sodium borohydride are shown in the figure below. Figure 5 As shown. This process is a liquid-phase electrolysis, with extremely low current efficiency. After 0.5 hours of electrolysis, the current efficiency is only 0.36%, and after 4 hours, the concentration of sodium borohydride produced is 0.149 × 10⁻⁶. -3 mol / L.

[0045] Example 2:

[0046] 10g of sodium metaborate dihydrate powder (particle size range 400-800 mesh), 2.5g of metal hydride (CuH), 8g of metal oxide (HgO), 0.5g of polytetrafluoroethylene emulsion (60wt%), and 8g of metal boride (NiB2) were mixed, a small amount of isopropanol was added, and the mixture was stirred into a slurry. This slurry was then filled onto nickel foam and dried at 75℃ to obtain the electrode core. Alternatively, 2.5g of metal hydride (CuH), 8g of metal oxide (HgO), and 0.5g of polytetrafluoroethylene emulsion (60wt%) were mixed, a small amount of isopropanol was added, and the mixture was stirred into a slurry. This slurry was then filled onto nickel foam and dried at 70℃ to obtain the outer shell electrode. The electrode core and the outer shell electrode were combined to obtain a shell-structured solid-phase catalytic electrode. Electrolysis experiments were conducted in a dual-electrode chamber electrolytic cell with a cation separator. The anode was graphite, and the cathode was the obtained shell-structured solid-phase catalytic electrode. Constant current electrolysis was used, with a current density of 25mA / cm². 2 .

[0047] Following the above operating procedure, the shell-structured solid-phase catalytic electrode prepared in Example 2 exhibited a current efficiency of 50% in synthesizing sodium borohydride through electrolysis in a 0.2 mol / L NaBO2 + 0.5 mol / L NaOH aqueous solution for 0.5 h, and the concentration of sodium borohydride produced after 4 h was 1.1 × 10⁻⁶. -2 mol / L.

[0048] Example 3:

[0049] An inner core electrode was prepared by mixing 10 g of sodium metaborate decahydrate powder (particle size range 400-800 mesh), 6 g of metal hydride (CrH), 6 g of metal oxide (FeO), 0.5 g of methyl cellulose and 8 g of metal boride (CoB), adding a small amount of N-dimethyl pyrrolidone, stirring into a slurry, and then filling into a foamed stainless steel, and drying at 80 °C. An outer shell electrode was prepared by mixing 6 g of metal hydride (CrH), 6 g of metal oxide (FeO), 0.5 g of methyl cellulose, adding a small amount of N-dimethyl pyrrolidone, stirring into a slurry, and then filling into a foamed stainless steel, and drying at 80 °C. The inner core electrode was combined with the outer shell electrode to obtain a solid phase catalytic electrode with a shell structure. Electrolysis experiments were carried out in a two-electrode cell with a cationic membrane, where the anode was lead and the cathode was the obtained solid phase catalytic electrode with a shell structure, using constant voltage electrolysis at a voltage of 5 V.

[0050] According to the above procedure, the solid phase catalytic electrode with a shell structure prepared in Example 3 had a current efficiency of 52.8% for the synthesis of sodium borohydride in 0.2 mol / L NaB02+ 0.5 mol / L NaOH aqueous solution for 0.5 h, and the concentration of sodium borohydride produced after 4 h was 1.136 x 10 -2 mol / L.

[0051] Example 4:

[0052] An inner core electrode was prepared by mixing 5 g of sodium metaborate decahydrate powder (particle size range 400-800 mesh), 3 g of metal hydride (ZnH), 2 g of metal oxide (CuO), 1 g of carbon nanotubes and 1.5 g of polytetrafluoroethylene emulsion (60 wt%), adding a small amount of ethylene glycol, stirring into a slurry, and then filling into a foamed copper, and drying at 75 °C. An outer shell electrode was prepared by mixing 3 g of metal hydride (ZnH), 2 g of metal oxide (CuO), 1 g of carbon nanotubes and 1.5 g of polytetrafluoroethylene emulsion (60 wt%), adding a small amount of ethylene glycol, stirring into a slurry, and then filling into a foamed copper, and drying at 70 °C. The inner core electrode was combined with the outer shell electrode to obtain a solid phase catalytic electrode with a shell structure. Electrolysis experiments were carried out in a two-electrode cell with a cationic membrane, where the anode was lead and the cathode was the obtained solid phase catalytic electrode with a shell structure, using constant voltage electrolysis at a voltage of 4.5 V.

[0053] According to the above procedure, the solid phase catalytic electrode with a shell structure prepared in Example 4 had a current efficiency of 48.5% for the synthesis of sodium borohydride in 0.2 mol / L NaB02+ 0.5 mol / L NaOH aqueous solution for 0.5 h, and the concentration of sodium borohydride produced after 4 h was 0.98 x 10-2 mol / L.

[0054] Example 5:

[0055] 5g of sodium metaborate tetrahydrate powder (particle size range 400-800 mesh), 1g of metal oxide (Fe2O3), 0.5g of polyvinyl alcohol, 0.5g of conductive graphite powder, and 4g of Ni powder were mixed, a small amount of deionized water was added, and the mixture was stirred into a slurry. This slurry was then filled onto nickel foam and dried at 65℃ to obtain the electrode core. The outer shell electrode was obtained by combining the electrode core and the outer shell electrode. Electrolysis experiments were conducted in a dual-electrode chamber electrolytic cell with a cation separator. The anode was lead, and the cathode was the obtained shell-structured solid-phase catalytic electrode. Constant current electrolysis was used with a current density of 30mA / cm². 2 .

[0056] Following the above operating procedure, the shell-structured solid-phase catalytic electrode prepared in Example 5 exhibited a current efficiency of 56% in synthesizing sodium borohydride through electrolysis in a 0.2 mol / L NaBO2 + 0.5 mol / L NaOH aqueous solution for 0.5 h. After 4 h, the concentration of sodium borohydride produced was 1.21 × 10⁻⁶. -2 mol / L.

[0057] Example 6:

[0058] A mixture of 6g sodium metaborate tetrahydrate powder (particle size range 400-800 mesh), 2.5g metal hydride (NiH), 4g Co powder, 0.5g polytetrafluoroethylene emulsion (60wt%), 6g metal boride (ZrB2), and 0.5g activated carbon was prepared. A small amount of N-dimethylformamide was added, and the mixture was stirred into a slurry. This slurry was then filled onto titanium foam and dried at 75℃ to obtain the electrode core. Alternatively, a mixture of 2.5g metal hydride (NiH), 4g Co powder, 0.5g polytetrafluoroethylene emulsion (60wt%), 6g metal boride (ZrB2), and 0.5g activated carbon was prepared. A small amount of N-dimethylformamide was added, and the mixture was stirred into a slurry. This slurry was then filled onto titanium foam and dried at 65℃ to obtain the outer shell electrode. The electrode core and the outer shell electrode were combined to obtain a shell-structured solid-phase catalytic electrode. The electrolysis experiment was carried out in a two-electrode chamber electrolytic cell with a cation diaphragm, wherein the anode was graphite and the cathode was the obtained shell-structured solid-phase catalytic electrode. Constant voltage electrolysis was used with a voltage of 3.5V.

[0059] According to the above procedure, the current efficiency of the shell-structured solid-phase catalytic electrode prepared in Example 6 for synthesizing sodium borohydride in 0.2 mol / L NaBO2+0.5 mol / L NaOH aqueous solution was 55.2% after 0.5 h of electrolysis, and the concentration of sodium borohydride produced was 1.19 x 10 -2 mol / L after 4 h.

[0060] Example 7:

[0061] A mixture of 10 g of sodium metaborate decahydrate powder (particle size range of 400-800 mesh), 2 g of metal hydride (PdH 0.8 ), 4 g of metal oxide (ZnO), 0.5 g of polyvinylidene fluoride emulsion, and 1 g of carbon nanotubes was mixed with a small amount of deionized water, stirred into a slurry, and then filled into a foamed stainless steel to obtain an electrode core. A mixture of 2 g of metal hydride (PdH 0.8 ), 4 g of metal oxide (ZnO), 0.5 g of polyvinylidene fluoride emulsion, and 1 g of carbon nanotubes was mixed with a small amount of deionized water, stirred into a slurry, and then filled into a foamed stainless steel to obtain an electrode shell. The electrode core and the electrode shell were combined to obtain a shell-structured solid-phase catalytic electrode. The electrolysis experiment was performed in a two-electrode electrolytic cell with a cationic membrane, in which the anode was platinum and the cathode was the obtained shell-structured solid-phase catalytic electrode, and constant current electrolysis was used with a current density of 25 mA / cm 2 .

[0062] According to the above procedure, the current efficiency of the shell-structured solid-phase catalytic electrode prepared in Example 7 for synthesizing sodium borohydride in 0.2 mol / L NaBO2+0.5 mol / L NaOH aqueous solution was 60% after 0.5 h of electrolysis, and the concentration of sodium borohydride produced was 1.217 x 10 -2 mol / L after 4 h.

[0063] Example 8:

[0064] An inner core of the electrode was prepared by mixing 4 g of anhydrous sodium metaborate powder (particle size range 400-800 mesh), 1 g of polytetrafluoroethylene emulsion (60 wt%), 4 g of metal boride (NiB2) and 2 g of conductive carbon powder, adding a small amount of deionized water, stirring into a slurry, and then filling it into a foamed stainless steel, and drying at 65°C to obtain the inner core of the electrode. An outer shell of the electrode was prepared by mixing 1 g of polytetrafluoroethylene emulsion (60 wt%), 4 g of metal boride (NiB2) and 2 g of conductive carbon powder, adding a small amount of deionized water, stirring into a slurry, and then filling it into a foamed stainless steel, and drying at 60°C to obtain the outer shell of the electrode. The inner core of the electrode was combined with the outer shell of the electrode to obtain a solid-phase catalytic electrode with a shell structure. The electrolysis experiment was carried out in a two-electrode cell with a cationic membrane, where the anode was platinum and the cathode was the solid-phase catalytic electrode with a shell structure obtained, and a constant voltage of 5 V was applied.

[0065] According to the above procedure, the current efficiency of the solid-phase catalytic electrode with a shell structure prepared in Example 8 for the synthesis of sodium borohydride in 0.2 mol / L NaBO2+0.5 mol / L NaOH aqueous solution was 55.6% after 0.5 h of electrolysis, and the concentration of sodium borohydride produced was 1.156 x 10 -2 mol / L after 4 h.

[0066] The content described in the specification is merely a list of implementations of the inventive concept, and the protection scope of the present application should not be regarded as limited to the specific forms described in the examples.

Claims

1. A method for preparing a shell-structured solid-phase catalytic electrode, characterized in that... Includes the following steps: 1) The coating materials for the electrode core include sodium metaborate micron-sized fine powder, catalyst powder and binder. After uniformly mixing them, they are prepared into a slurry with a solvent to obtain the coating slurry used to prepare the electrode core. The coating material for the electrode shell includes catalyst powder and binder. After uniformly mixing them, they are prepared into a slurry with a solvent to obtain a coating slurry for preparing the electrode shell. 2) The two slurries prepared in step 1) are coated on the outer surface of the foam metal substrate and dried to obtain the electrode core and electrode shell respectively; 3) Combining the inner core and outer shell of the electrode yields a shell-structured solid-phase catalytic electrode.

2. The method for preparing a shell-structured solid-phase catalytic electrode as described in claim 1, characterized in that... The sodium metaborate mentioned in step 1) includes at least one of sodium metaborate tetrahydrate, sodium metaborate dihydrate, or anhydrous sodium metaborate, with a particle size range of 400-800 mesh.

3. The method for preparing a shell-structured solid-phase catalytic electrode as described in claim 1, characterized in that... The catalyst described in step 1) comprises one or a mixture of the following: (1) LiH, NaH, KH, CaH2, BaH2, CrH2, NiH, CuH, ZnH2 or PdH 0.8 One or more mixtures thereof; (2) Mn4B, Co3B, ZrB2, TiB2, Ta3B2, Cr5B3, Rh7B3, Ti3B4, CaB6, LaB6 or Ru 11 One or more mixtures of B8; (3) A mixture of one or more of CuO, FeO, PbO, Fe2O3, PbO2, and Pb3O4.

4. The method for preparing a shell-structured solid-phase catalytic electrode as described in claim 1, characterized in that... The adhesive mentioned in step 1) includes one or more of polytetrafluoroethylene emulsion, polyvinylidene fluoride emulsion, methylcellulose, and polyvinyl alcohol.

5. The method for preparing a shell-structured solid-phase catalytic electrode as described in claim 1, characterized in that... In step 1), the mass of sodium metaborate powder in the coating material of the electrode core is 0.5-5 times the mass of the catalyst, and the mass of binder is 0.025-0.3 times the mass of the catalyst; in the coating material of the electrode shell, the mass of binder is 0.025-0.3 times the mass of the catalyst.

6. The method for preparing a shell-structured solid-phase catalytic electrode as described in claim 1, characterized in that... In step 1), the solvent includes one or more of the following: deionized water, acetone, isopropanol, ethylene glycol, N-dimethylformamide, and N-dimethylpyrrolidone.

7. The method for preparing a shell-structured solid-phase catalytic electrode as described in claim 1, characterized in that... In step 1), the coating materials of the electrode core and the electrode shell are respectively doped with one or two of the following: additives and conductive materials; in the coating materials of the electrode core or the electrode shell, the mass of the additives is 0-4 times the mass of the catalyst, and the mass of the conductive materials is 0-0.5 times the mass of the catalyst. The additives include one or more of Hg, Pb, Cd, Zn, Ni, and Co; the conductive materials include one or more of carbon nanotubes, activated carbon, conductive graphite, or amorphous carbon.

8. The method for preparing a shell-structured solid-phase catalytic electrode as described in claim 7, characterized in that... In the coating material of the electrode core or electrode shell, the mass of the additive is 0.47-4 times the mass of the catalyst, and the mass of the conductive material is 0.055-5 times the mass of the catalyst.

9. The method for preparing a shell-structured solid-phase catalytic electrode as described in claim 1, characterized in that... In step 2), the foamed metal matrix includes any one of foamed nickel, foamed copper, foamed titanium, and foamed stainless steel.

10. A shell-structured solid-phase catalytic electrode prepared by the method according to any one of claims 1-9, characterized in that... The electrode outer shell is provided with a slot that matches the shape of the electrode inner core. The electrode inner core is inserted into the slot of the electrode outer shell to form a shell-structured solid-phase catalytic electrode.

11. The application of the shell-structured solid-phase catalytic electrode as described in claim 10 in the electroreduction of sodium metaborate to synthesize sodium borohydride in alkaline aqueous solution.

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