Silicon-based gas diffusion membrane for electrocatalytic reduction of carbon dioxide to produce formic acid

Abstract

The present invention relates to a silicon-based gas diffusion membrane for preparing formic acid by a carbon dioxide electrocatalytic reduction method. The raw materials of the silicon-based gas diffusion membrane include the following components in parts by weight: 10 to 15 parts of polysiloxane, 1-2 parts of organic fluorine-modified multi-walled carbon nanotubes, 1-2 parts of a curing agent, and 50 to 60 parts of a solvent. The silicon-based gas diffusion membrane is a nano-composite porous material, which is composed of a polysiloxane porous elastomer and organic fluorine-modified multi-walled carbon nanotubes. The gas diffusion membrane obtained in the present invention not only has a lower cost than a traditional polytetrafluoroethylene gas diffusion membrane, but also has good mechanical properties and is suitable for flexible devices.

Description

Technical Field

[0001] The present invention relates to the field of new energy technology, and in particular to a silicon-based gas diffusion membrane used for preparing formic acid by electrocatalytic reduction of carbon dioxide. Background Art

[0002] Carbon dioxide electrocatalytic reduction is one of the important negative emission technologies. To improve the conversion efficiency of this technology, high current density must be achieved through heterogeneous electrocatalytic reactions on the gas / solid surface. The above process undoubtedly requires high-performance gas diffusion electrodes, among which the gas diffusion membrane composed of a hydrophobic porous structure is one of the key components. At present, almost all gas diffusion membranes are based on polytetrafluoroethylene (PTFE) porous materials. However, PTFE has a fatal disadvantage, that is, it is very easy to creep under long-term continuous load, which poses a hidden danger and is therefore not suitable for long-term application. The current carbon dioxide electrocatalytic reduction technology is still in the laboratory research and development stage. To move towards large-scale application, it is obviously necessary to solve the above problems. Silicone polymers also have excellent hydrophobic properties, but their tensile strength is low and they are prone to large deformations under high mechanical loads. At present, the industry mainly enhances tensile properties by adding nanoparticles such as silicon dioxide, but the latter often have a large number of hydrophilic groups such as hydroxyl groups on their surfaces, which will significantly reduce the hydrophobic properties of the gas diffusion membrane, leading to a series of potential problems such as electrode flooding and catalyst failure. Summary of the invention

[0003] In view of this, the purpose of the present invention is to provide a gas diffusion membrane based on silicon-based nanocomposite materials, in order to solve the creep problem of PTFE materials under long-term continuous load while ensuring that the hydrophobic performance is not affected. The silicon-based gas diffusion membrane provided by the present invention solves the creep problem of PTFE by using polysiloxane as a flexible porous polymer skeleton and using organic fluorine-modified multi-walled carbon nanotubes as a reinforcement, and improves its tensile strength while maintaining the ultra-high elongation at break characteristic of polysiloxane.

[0004] The objective of the present invention is achieved through the following technical solutions:

[0005] <First aspect>

[0006] The present invention provides a silicon-based gas diffusion membrane, wherein the raw materials of the silicon-based gas diffusion membrane include the following components in parts by weight:

[0007]

[0008]

[0009] The organic fluorine-modified multi-walled carbon nanotubes are prepared from the following raw materials in parts by weight:

[0010] Triazene fluoride reagent 500-550 parts

[0011] 8-10 parts of multi-walled carbon nanotubes

[0012] Emulsifier 100-150 parts.

[0013] The preparation method of the organic fluorine-modified multi-walled carbon nanotubes is as follows:

[0014] After the triazine fluoride reagent and multi-walled carbon nanotubes are mixed in an aqueous solution in the presence of an emulsifier, the pH value is adjusted to 2-3 using hydrochloric acid, and after stirring for 5-10 minutes, the pH value is adjusted to 10-11 using potassium hydroxide, and then stirred for 60-90 minutes. After the solution is precipitated, it is filtered and dried to obtain the product, which is the organic fluorine-modified multi-walled carbon nanotubes.

[0015] The triazene fluoride reagent is prepared from the following raw materials in parts by weight:

[0016]

[0017] The preparation method of the triazene fluoride reagent comprises the following steps:

[0018] 1) reacting p-fluoroaniline, dichloromethane, boron trifluoride ether solution and isoamyl nitrite under a nitrogen atmosphere at a temperature of 0-5° C. for 60-80 minutes;

[0019] 2) adding diethylamine and sodium carbonate to the reaction product of step 1) for further reaction at a temperature of 25-30° C. for a reaction time of 60-80 minutes; then separating the oil phase, concentrating it by rotary evaporation, and vacuum drying to obtain the product.

[0020] The multi-walled carbon nanotubes have a diameter of 15-20 nanometers and a length of 6-10 micrometers.

[0021] The solvent includes one of acetone, cyclohexane and isopropanol.

[0022] As an embodiment of the present invention, the method for preparing the organic fluorine-modified multi-walled carbon nanotubes comprises the following steps:

[0023] After the triazine fluoride reagent and multi-walled carbon nanotubes are mixed in an aqueous solution in the presence of an emulsifier, the pH value is adjusted to 2 using hydrochloric acid, and after stirring for 5 minutes, the pH value is adjusted to 10 using potassium hydroxide, and then stirred for 60-80 minutes. After the solution is precipitated in acetone, it is filtered and vacuum dried to obtain a product, which is organic fluorine-modified multi-walled carbon nanotubes.

[0024] The emulsifier includes sodium dibutylnaphthalene sulfonate.

[0025] The polysiloxane includes one of polydiethylsiloxane, polytrifluoropropylmethylsiloxane and polydimethyldiphenylsiloxane.

[0026] The method for preparing the silicon-based gas diffusion membrane comprises the following steps:

[0027] Step 1, polysiloxane, organic fluorine-modified multi-walled carbon nanotubes, a curing agent and cyclohexane are mixed in proportion, mechanically stirred evenly, and then cast into a mold, and preheated for a period of time to obtain a nanocomposite prepolymer;

[0028] Step 2: removing the solvent from the nanocomposite prepolymer under reduced pressure at ambient temperature, and heating for a period of time to solidify the polysiloxane to obtain a silicon-based gas diffusion membrane.

[0029] In step 1, the heating temperature is 150-160 degrees and the heating time is 2 hours;

[0030] In step 2, the pressure during the removal of the solvent is 0.1-1 Pa.

[0031] The silicon-based gas diffusion membrane is a nanocomposite porous material composed of polysiloxane porous elastomer and organic fluorine-modified multi-walled carbon nanotubes. The gas diffusion membrane obtained in the present invention not only has lower cost than the traditional polytetrafluoroethylene gas diffusion membrane, but also has good mechanical properties and is suitable for flexible devices.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. By using polysiloxane as the main matrix of the gas diffusion membrane, the creep problem of the PTFE gas diffusion membrane under long-term load is avoided, achieving the beneficial effect of increasing the service life of the gas diffusion membrane.

[0034] 2. The technical feature of using fluorine-modified carbon nanotubes as reinforcement for the polysiloxane matrix solves the problem of insufficient mechanical properties of polysiloxane used in gas diffusion membranes and the decrease in hydrophobic properties caused by traditional silica nanoparticle reinforcement, thereby achieving the effect of improving mechanical properties while ensuring electrocatalytic performance.

[0035] 3. A flexible porous structure is formed by removing a low-boiling point solvent under reduced pressure, thereby avoiding the melt spinning process with high process requirements and reducing the manufacturing cost of the gas diffusion membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0037] Figure 1This is a tensile test of the gas diffusion membrane prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0038] The present invention is described in detail below in conjunction with embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, some adjustments and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0039] Preparation Example 1 Preparation of triazine fluoride reagent

[0040] The triazene fluoride reagent comprises the following components in parts by weight:

[0041] Components content p-Fluoroaniline 5 servings Dichloromethane 25 servings Boron trifluoride ether solution 12 servings Isoamyl nitrite 12 servings Diethylamine 10 servings Sodium carbonate 20 servings.

[0042] The preparation method of the triazene fluoride reagent comprises the following steps:

[0043] 1) reacting p-fluoroaniline, dichloromethane, boron trifluoride ether solution and isoamyl nitrite under a nitrogen atmosphere at a reaction temperature of 5° C. for 60 minutes;

[0044] 2) adding diethylamine and sodium carbonate to the reaction product of step 1) for further reaction at a temperature of 25° C. for 60 minutes; then separating the oil phase, concentrating it by rotary evaporation, and drying it in vacuum to obtain the product.

[0045] Preparation Example 2 Preparation of organic fluorine-modified multi-walled carbon nanotubes

[0046] The organic fluorine-modified multi-walled carbon nanotubes include the following components in parts by weight:

[0047] Components content Triazene fluoride reagent (Preparation Example 1) 500 copies Multi-walled carbon nanotubes 10 servings Emulsifier 100 copies

[0048] Among them, the diameter of multi-walled carbon nanotubes is 15-20 nanometers and the length is 6-10 microns.

[0049] The preparation method of organic fluorine modified multi-walled carbon nanotubes comprises the following steps:

[0050] After the triazine fluoride reagent and multi-walled carbon nanotubes are mixed in an aqueous solution in the presence of an emulsifier, the pH value is adjusted to 2 using hydrochloric acid. After stirring for 5 minutes, the pH value is adjusted to 10 using potassium hydroxide and stirred for another 60 minutes. After the solution is precipitated in acetone, it is filtered and vacuum dried to obtain a product, namely, organic fluorine-modified multi-walled carbon nanotubes.

[0051] Examples 1-3

[0052] This embodiment provides a silicon-based gas diffusion membrane, wherein the raw materials of the silicon-based gas diffusion membrane include the following components in parts by weight:

[0053] Unit: weight parts

[0054]

[0055] The method for preparing the silicon-based gas diffusion membrane comprises the following steps:

[0056] Step 1, mixing the components in proportion, mechanically stirring them evenly, then casting them into a mold, and preheating them for a period of time to obtain a nanocomposite prepolymer;

[0057] Step 2: removing the solvent from the nanocomposite prepolymer under reduced pressure at ambient temperature, and heating for a period of time to solidify the polysiloxane to obtain a silicon-based gas diffusion membrane.

[0058] In step 1, the heating temperature is 150-160 degrees and the heating time is 2 hours;

[0059] In step 2, the pressure during the removal of the solvent is 0.1-1 Pa.

[0060] Comparative Example 1

[0061] The difference between Comparative Example 1 and Example 1 is that no organic fluorine-modified multi-walled carbon nanotubes are added.

[0062] Comparative Example 2

[0063] The difference between Comparative Example 2 and Example 1 is that the organic fluorine-modified multi-walled carbon nanotubes are replaced by gas-phase carbon black.

[0064] Comparative Example 3

[0065] The difference between Comparative Example 3 and Example 1 is that the added amount of the organic fluorine-modified multi-walled carbon nanotubes is 3 parts.

[0066] Comparative Example 4

[0067] The difference between Comparative Example 4 and Example 1 is that the added amount of the organic fluorine-modified multi-walled carbon nanotubes is 0.5 parts.

[0068] Application performance test 1:

[0069] The tensile test of the gas diffusion membranes prepared in Examples 1-3 and Comparative Examples 1-4 was performed using a DMA-800 dynamic mechanical analyzer. Figure 1 .

[0070] Application performance test 2:

[0071] The gas diffusion membranes prepared in Examples 1-3 and Comparative Examples 1-4 and the porous carbon membranes deposited with copper atoms, anion exchange membranes, iridium oxide-coated titanium meshes, solid electrolytes and Nafion membranes were laminated and assembled with cathode gas chamber flow channel plates, cathode current collectors and anode gas chamber flow channel plates to form a carbon dioxide electrocatalytic reduction performance detection unit. The linear voltammetry and chronoamperometric method were used to test the hydrogen reduction current and formic acid reduction current at different potentials using an electrochemical workstation. The results are shown in Tables 1 and 2.

[0072] Table 1 Hydrogen reduction current and formic acid reduction current of each embodiment and comparative example at different potentials (electrode area 2.25cm 2 )

[0073]

[0074] Table 2 Reduction current stability of various examples and comparative examples at -1.0 V (vs RHE) (electrode area 2.25 cm 2 )

[0075]

[0076]

[0077] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A silicon-based gas diffusion membrane, characterized in that: The raw materials of the silicon-based gas diffusion membrane include the following components in parts by weight: Polysiloxane 10-15 parts 1-2 parts of organic fluorine modified multi-walled carbon nanotubes 1-2 parts of curing agent 50-60 parts of solvent; The organic fluorine-modified multi-walled carbon nanotubes are prepared from the following raw materials in parts by weight: Triazene fluoride reagent 500-550 parts 8-10 parts of multi-walled carbon nanotubes Emulsifier 100-150 parts; The preparation method of the organic fluorine-modified multi-walled carbon nanotubes is as follows: After the triazine fluoride reagent and multi-walled carbon nanotubes are mixed in an aqueous solution in the presence of an emulsifier, the pH value is adjusted to 2-3 using hydrochloric acid, and after stirring for 5-10 minutes, the pH value is adjusted to 10-11 using potassium hydroxide, and then stirred for 60-90 minutes. After the solution is precipitated, it is filtered and dried to obtain the product, which is the organic fluorine-modified multi-walled carbon nanotubes.

2. The silicon-based gas diffusion membrane according to claim 1, characterized in that: The triazene fluoride reagent is prepared from the following raw materials in parts by weight:

3. The silicon-based gas diffusion membrane according to claim 2, characterized in that: The preparation method of the triazene fluoride reagent comprises the following steps: 1) reacting p-fluoroaniline, dichloromethane, boron trifluoride ether solution and isoamyl nitrite under a nitrogen atmosphere at a temperature of 0-5° C. for 60-80 minutes; 2) adding diethylamine and sodium carbonate to the reaction product of step 1) for further reaction at a temperature of 25-30° C. for a reaction time of 60-80 minutes; then separating the oil phase and concentrating and drying to obtain the triazene fluoride reagent.

4. The silicon-based gas diffusion membrane according to claim 1, characterized in that: The emulsifier includes sodium dibutylnaphthalene sulfonate.

5. The silicon-based gas diffusion membrane according to claim 1, characterized in that: The polysiloxane includes one of polydiethylsiloxane, polytrifluoropropylmethylsiloxane and polydimethyldiphenylsiloxane.

6. A method for preparing a silicon-based gas diffusion membrane according to any one of claims 1 to 5, characterized in that: The steps include: Step 1, polysiloxane, organic fluorine-modified multi-walled carbon nanotubes, a curing agent and cyclohexane are mixed in proportion, stirred evenly and then cast into a mold, and preheated to obtain a nanocomposite prepolymer; Step 2: removing the solvent from the nanocomposite prepolymer under reduced pressure at ambient temperature, and heating to solidify the polysiloxane to obtain a silicon-based gas diffusion membrane.

7. The preparation method according to claim 6, characterized in that: In step 1, the preheating temperature is 150-160 degrees, and the heating time is 2-3 hours; in step 2, the pressure during solvent removal is 0.1-1 Pa, and the heating temperature is 80-100 degrees.

8. Use of the silicon-based gas diffusion membrane according to any one of claims 1 to 5 in the preparation of formic acid by carbon dioxide electrocatalytic reduction.

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