A biochar-based gas diffusion electrode with porous channels, its preparation method and application

Abstract

The present invention discloses a biochar-based gas diffusion electrode with porous channels, a preparation method thereof, and an application thereof. The biochar-based gas diffusion electrode with porous channels comprises a biochar-based material with porous channels and a catalyst loaded on the biochar-based material with porous channels. In the present invention, wood is calcined in an H2 / Ar atmosphere to obtain the biochar-based material with porous channels; the catalyst is loaded on the biochar-based material with porous channels to obtain the biochar-based gas diffusion electrode with porous channels. The biochar-based gas diffusion electrode with porous channels prepared in the present invention has good electrical conductivity and hydrophilicity, which is beneficial to improving the efficiency of the electrocatalytic reaction; the biochar-based gas diffusion electrode with porous channels loaded with cuprous oxide obtained in the present invention plays a significant role in enhancing the performance of electrocatalytic synthesis of urea and has good application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas diffusion electrodes, and particularly relates to a biochar-based gas diffusion electrode with porous channels, a preparation method thereof, and an application thereof. Background Art

[0002] Urea (CO(NH 2 ) 2 ) is an important chemical raw material. Due to its high nitrogen content and easy conversion to ammonia in the soil, it is the most widely used nitrogen fertilizer in the world. Currently, the production of urea in industry is mainly completed through the reaction of NH 3 and CO 2 under high temperature and high pressure. However, this method not only consumes relatively more energy, with the energy consumption accounting for more than 3% of the global annual energy consumption, but also relies on some complex equipment and multi-cycle processes to improve the conversion efficiency. Therefore, there is an urgent need for a green urea synthesis technology that can be carried out under mild conditions. The electrocatalytic technology can couple the reduction of carbon dioxide and nitrate to urea under room temperature and atmospheric pressure conditions, and technically achieve zero carbon emissions, providing a reliable strategy for the green transformation of the urea industry.

[0003] In the reaction of electrocatalytic synthesis of urea, the efficiency of C-N coupling in the solution is one of the main factors affecting the urea yield. The separate reduction of CO 2 and nitrate are two competing reactions in urea synthesis, which leads to a complex reaction product distribution and a low Faraday efficiency of urea. In addition, during the reaction process, the reduction rate of nitrate is much higher than that of carbon dioxide. The mismatch between the reaction rates of the two leads to excessive nitrate reduction reaction directly generating stable by-products ammonia, thus severely limiting the selectivity of urea. Therefore, the collision adsorption efficiency of carbon dioxide molecules with the catalyst is an important direction to improve the reaction kinetics of CO 2 reduction. And currently, there is still no electrode with a gas diffusion structure used in the field of electrocatalytic synthesis of urea to improve the efficiency of C-N coupling.

[0004] Therefore, developing an electrode with a gas diffusion structure can effectively improve the efficiency of CO 2 reduction and C-N coupling to promote the synthesis of urea, which is of great significance for inhibiting the generation of by-products such as ammonia and hydrogen and improving the yield of urea. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a biochar-based gas diffusion electrode with porous channels and a preparation method thereof. The gas diffusion electrode obtained by the preparation method provided by the present invention can construct a pipeline with sufficient contact of gas-liquid-solid three-phase interfaces, thereby improving the efficiency of electrocatalytic synthesis of urea.

[0006] Another object of the present invention is to use a gas diffusion electrode as a carrier to load cuprous oxide as a catalyst for improving the performance of electrocatalytic synthesis of urea.

[0007] The object of the present invention is achieved by the following technical solutions:

[0008] A porous-channel biochar-based gas diffusion electrode, comprising a porous-channel biochar-based and a catalyst loaded on the porous-channel biochar-based.

[0009] Preferably, the catalyst is cuprous oxide.

[0010] More preferably, the preparation method of the loaded cuprous oxide is as follows:

[0011] (1) Immerse the porous-channel biochar-based in a soluble copper salt solution, take it out, wash and dry it, then immerse it in a KOH or NaOH solution, take it out, wash and dry it;

[0012] (2) Perform constant current reduction on the product obtained in step (1) in a soluble sulfate solution, wash and dry it to obtain a porous-channel biochar-based gas diffusion electrode loaded with cuprous oxide.

[0013] More preferably, in step (1), the soluble copper salt is copper sulfate; the concentration of the soluble copper salt is 10-30 mmol / L; the concentration of the KOH or NaOH solution is 10-30 mmol / L; the impregnation time in the soluble copper salt solution is 2-30 min; the impregnation time in the KOH or NaOH solution is 2-30 min; the washing is with deionized water; the drying temperature is 40-80 °C, and the drying time is 4-12 h;

[0014] Most preferably, in step (1), the concentration of the soluble copper salt is 20 mmol / L; the concentration of the KOH or NaOH solution is 20 mmol / L; the drying temperature is 60 °C, and the drying time is 12 h;

[0015] More preferably, in step (2), the soluble sulfate is sodium sulfate or potassium sulfate; the concentration of the soluble sulfate solution is 0.1 mol / L; the current of the constant current reduction is -5 mA, and the time is 15-60 min. The washing is with deionized water, and the drying temperature is 40-80 °C, and the drying time is 4-12 h.

[0016] Most preferably, in step (2), the time of the constant current reduction is 30 min.

[0017] The preparation method of the above-mentioned porous-channel biochar-based gas diffusion electrode includes the following steps:

[0018] S1: Calcinate the wood in an H 2 / Ar atmosphere to obtain a porous biochar-based material;

[0019] S2: Load a catalyst on the porous biochar-based material obtained in step S1 to obtain a porous biochar-based gas diffusion electrode.

[0020] Preferably, in step S1, the calcination temperature is 700 - 1000 °C, and the calcination time is 1 - 4 h; the H 2 in the H 2 / Ar atmosphere has a volume fraction of 5 - 10%; the wood is basswood.

[0021] More preferably, the calcination temperature is 800 °C, the calcination time is 2 h, and the heating rate is 5 °C / min; the H 2 in the H 2 / Ar atmosphere has a volume fraction of 8%.

[0022] Application of the above-mentioned porous biochar-based gas diffusion electrode loaded with cuprous oxide in electrocatalytic synthesis of urea.

[0023] Preferably, the porous biochar-based gas diffusion electrode is used as the working electrode to form a three-electrode system, and the electrolyte is 0.1 M KHCO 3 and 0.001 - 0.02 M KNO 3 ; CO 2 gas is introduced into the porous biochar-based gas diffusion electrode under the condition of a voltage of (-0.5) - (-1.1) V.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The main body of the gas diffusion electrode of the present invention comes from natural basswood, with a low acquisition cost, and it can be used through simple calcination, which is economical and efficient.

[0026] (2) The porous biochar-based electrode of the present invention has good electrical conductivity and hydrophilicity.

[0027] (3) The present invention realizes the electrocatalytic synthesis of urea reaction under mild conditions, and the reaction potential is relatively low.

[0028] (4) Compared with the traditional electrocatalytic synthesis of urea reaction, the use of the gas diffusion electrode structure in the present invention can significantly improve the yield and Faraday efficiency of urea synthesis. Description of the Drawings

[0029] Figure 1It is a comparative diagram of the raw materials of the gas diffusion electrode carrier described in Embodiment 1 of the present invention and after calcination treatment, and a schematic diagram of the gas diffusion electrode prepared therefrom.

[0030] Figure 2 It is a scanning electron microscope image of the cross-section of the gas diffusion electrode carrier obtained by calcining at different temperatures described in Embodiments 1-3 of the present invention.

[0031] Figure 3 It is the scanning electron microscope image of the gas diffusion electrode carrier described in Embodiment 1 of the present invention after loading Cu 2 O.

[0032] Figure 4 It is a diagram of urea production rate and Faraday efficiency of the gas diffusion electrode described in Embodiment 1 of the present invention at different potentials.

[0033] Figure 5 It is a comparison diagram of urea production rate and Faraday efficiency of the gas diffusion electrode carriers obtained at different calcination temperatures described in Embodiments 1-3 of the present invention.

[0034] Figure 6 It is a diagram of urea production rate and Faraday efficiency of the gas diffusion electrodes described in Embodiments 1, 4-6 of the present invention at different KNO 3 concentrations.

[0035] Figure 7 It is a diagram of urea production rate and Faraday efficiency of the gas diffusion electrode using carbon cloth in Comparative Example 1 of the present invention at different potentials. Detailed implementation manners

[0036] The following further illustrates the present invention in conjunction with specific embodiments and drawings, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the technical field.

[0037] Unless otherwise specified, the reagents and materials used in the present invention are all commercially available.

[0038] Embodiment 1

[0039] A preparation method of a copper oxide-loaded biochar-based gas diffusion electrode with porous channels is as follows:

[0040] Step 1: Take a 1×1×2 cm basswood in a porcelain boat and place it in a tube furnace. After introducing 8% H 2 / Ar, heat it to 800 °C at a heating rate of 5 °C / min and hold for 2 h. When the tube furnace program automatically ends and the temperature drops to room temperature, stop ventilation to obtain a black block material.

[0041] Step 2: Immerse the black block material in a 20 mmol / L copper sulfate solution for 10 min, wash it with deionized water, and dry it in an oven at 60 °C for 12 h. After drying, take out the material and immerse it in a 20 mmol / L KOH solution for 15 min, then wash it with deionized water and dry it in an oven at 60 °C for 12 h.

[0042] Step 3: Place the material in a 0.1 mol / L sodium sulfate solution, reduce it at a reduction current of -5 mA for 30 min, then take it out and dry it in an oven at 60 °C for 12 h. The obtained material is a biochar-based gas diffusion electrode with porous channels, labeled as W800-Cu.

[0043] The comparison diagram of the raw material basswood of the gas diffusion electrode carrier described in Example 1 before and after calcination treatment and the schematic diagram of the prepared gas diffusion electrode are as Figure 1 shown.

[0044] The scanning electron microscope image of the cross-section of the gas diffusion electrode carrier calcined at the temperature described in Example 1 is as Figure 2 shown.

[0045] The scanning electron microscope image of the gas diffusion electrode carrier described in Example 1 after loading Cu 2 O is as Figure 3 shown.

[0046] Step 4: Use the gas diffusion electrode W800-Cu as the working electrode to form a three-electrode system, introduce high-purity CO 2 gas (60 mL / min) into the gas diffusion electrode, and the electrolyte is 0.1 M KHCO 3 and 0.01 M KNO 3 , and perform a constant potential test with the voltage set to -0.6 V.

[0047] According to Figure 5 the test results, the urea synthesis yield of the W800-Cu gas diffusion electrode in the electrocatalytic reaction is 1401.8 μg h -1 mg cat. -1 , and the Faraday efficiency is 11.9%.

[0048] Change the voltage in Step 4 to -0.5 V, -0.7 V, -0.8 V, -0.9 V, -0.10 V, -0.11 V; the urea synthesis yield and Faraday efficiency are as Figure 4 shown.

[0049] Example 2

[0050] Preparation method of cuprous oxide-loaded biochar-based gas diffusion electrode with porous channels, the method is as follows:

[0051] Step 1: Take a 1×1×2 cm basswood and place it in a porcelain boat, and then put it into a tube furnace. After introducing 8% H 2 / Ar, heat it to 700 °C at a heating rate of 5 °C / min and hold for 2 h. Wait for the tube furnace program to end automatically. When the temperature drops to room temperature, stop the ventilation to obtain a black block material.

[0052] Step 2: Immerse the black block material in a 20 mmol / L copper sulfate solution for 10 min, wash it with deionized water and dry it in an oven at 60 °C for 12 h. After drying, take out the material and immerse it in a 20 mmol / L KOH solution for 15 min, then wash it with deionized water and dry it in an oven at 60 °C for 12 h.

[0053] Step 3: Place the material in a 0.1 mol / L sodium sulfate solution, reduce it at a reduction current of -5 mA for 30 min and then take it out, and dry it in an oven at 60 °C for 12 h. The obtained material is the biochar-based gas diffusion electrode with porous channels, marked as W700-Cu.

[0054] The scanning electron microscope image of the cross-section of the gas diffusion electrode carrier obtained by calcining at the temperature described in Example 2 is as Figure 2 shown.

[0055] Step 4: Use the gas diffusion electrode W700-Cu as the working electrode to form a three-electrode system, introduce high-purity CO 2 gas (60 mL / min) into the gas diffusion electrode, and the electrolyte is 0.1 M KHCO 3 and 0.01 M KNO 3 , and perform a constant potential test with the voltage set to -0.6 V.

[0056] According to Figure 5 the test results, the urea synthesis yield of the W700-Cu gas diffusion electrode in the electrocatalytic reaction is 699 μg h -1 mg cat. -1 , and the Faraday efficiency is 4.9%.

[0057] Example 3

[0058] Preparation method of cuprous oxide-loaded biochar-based gas diffusion electrode with porous channels, the method is as follows:

[0059] Step 1: Take a 1×1×2 cm basswood and place it in a porcelain boat, and then put it into a tube furnace. After introducing 8% H 2After Ar, it was heated to 900 °C at a heating rate of 5 °C / min and held for 2 h. When the program of the tubular furnace automatically ended and the temperature dropped to room temperature, the gas supply was stopped to obtain a black bulk material.

[0060] Step 2: The black bulk material was fully immersed in a 20 mmol / L copper sulfate solution for 10 min, then washed with deionized water and dried in an oven at 60 °C for 12 h. After drying, the material was taken out and fully immersed in a 20 mmol / L KOH solution for 15 min, and then washed with deionized water and dried in an oven at 60 °C for 12 h.

[0061] Step 3: The material was placed in a 0.1 mol / L sodium sulfate solution and reduced at a reduction current of -5 mA for 30 min and then taken out, and dried in an oven at 60 °C for 12 h. The obtained material was a biochar-based gas diffusion electrode with porous channels, labeled as W900-Cu.

[0062] The scanning electron microscope image of the cross-section of the gas diffusion electrode support obtained by calcination at the temperature described in Example 3 is as Figure 2 shown.

[0063] Step 4: Using this gas diffusion electrode W900-Cu as the working electrode, a three-electrode system was formed, and high-purity CO 2 gas (60 mL / min) was introduced into the gas diffusion electrode, and the electrolyte was 0.1 M KHCO 3 and 0.01 M KNO 3 , and a constant potential test was carried out with the voltage set at -0.6 V.

[0064] According to Figure 5 the test results, the urea synthesis yield of the W900-Cu gas diffusion electrode in the electrocatalytic reaction was 428.7 μg h -1 mg cat. -1 , and the Faraday efficiency was 1.2%.

[0065] Example 4

[0066] A preparation method of a cuprous oxide-loaded biochar-based gas diffusion electrode with porous channels, the method is as follows:

[0067] Step 1: Take a 1×1×2 cm basswood and place it in a porcelain boat, and put it into a tubular furnace. After introducing 8% H 2 / Ar, it was heated to 800 °C at a heating rate of 5 °C / min and held for 2 h. When the program of the tubular furnace automatically ended and the temperature dropped to room temperature, the gas supply was stopped to obtain a black bulk material.

[0068] Step 2: Immerse the black block material in 20 mmol / L copper sulfate solution for 10 min, wash it with deionized water, and dry it in an oven at 60 °C for 12 h. After drying, take out the material and immerse it in 20 mmol / L KOH solution for 15 min, then wash it with deionized water and dry it in an oven at 60 °C for 12 h.

[0069] Step 3: Place the material in 0.1 mol / L sodium sulfate solution, reduce it at a reduction current of -5 mA for 30 min, then take it out and dry it in an oven at 60 °C for 12 h. The obtained material is a biochar-based gas diffusion electrode with porous channels, labeled as W800-Cu.

[0070] Step 4: Use this gas diffusion electrode as the working electrode to form a three-electrode system, and introduce high-purity CO 2 gas (60 mL / min), with the electrolyte being 0.1 M KHCO 3 and 0.001 M KNO 3 , and conduct a potentiostatic test with the voltage set at -0.6 V.

[0071] According to Figure 6 the test results, the urea synthesis yield of the W800-Cu gas diffusion electrode in the electrocatalytic reaction is 79.7 μg h -1 mg cat. -1 , and the Faraday efficiency is 0.65%.

[0072] Example 5

[0073] A preparation method of a cuprous oxide-loaded biochar-based gas diffusion electrode with porous channels, the method is as follows:

[0074] Step 1: Take a 1×1×2 cm basswood and place it in a porcelain boat, and then put it into a tube furnace. After introducing 8% H 2 / Ar, raise the temperature to 800 °C at a heating rate of 5 °C / min and keep it for 2 h. When the tube furnace program automatically ends and the temperature drops to room temperature, stop the gas supply to obtain a black block material.

[0075] Step 2: Immerse the black block material in 20 mmol / L copper sulfate solution for 10 min, wash it with deionized water, and dry it in an oven at 60 °C for 12 h. After drying, take out the material and immerse it in 20 mmol / L KOH solution for 15 min, then wash it with deionized water and dry it in an oven at 60 °C for 12 h.

[0076] Step 3: Place the material in a 0.1 mol / L sodium sulfate solution, reduce it at a reduction current of -5 mA for 30 min, then take it out and dry it in an oven at 60 °C for 12 h. The obtained material is a biochar-based gas diffusion electrode with porous channels, labeled as W800-Cu.

[0077] Step 4: Use this gas diffusion electrode as the working electrode to form a three-electrode system, and introduce high-purity CO 2 gas (60 mL / min) into the gas diffusion electrode. The electrolyte is 0.1 M KHCO 3 and 0.005 M KNO 3 , and conduct a potentiostatic test with the voltage set at -0.6 V.

[0078] According to Figure 6 the test results, the urea synthesis yield of the W800-Cu gas diffusion electrode in the electrocatalytic reaction is 738.6 μg h -1 mg cat. -1 , and the Faraday efficiency is 6.1%.

[0079] Example 6

[0080] A preparation method of a cuprous oxide-loaded biochar-based gas diffusion electrode with porous channels, the method is as follows:

[0081] Step 1: Take a 1×1×2 cm basswood and place it in a porcelain boat, then put it into a tubular furnace. After introducing 8% H 2 / Ar, heat it to 800 °C at a heating rate of 5 °C / min and hold for 2 h. When the program of the tubular furnace automatically ends and the temperature drops to room temperature, stop the gas supply to obtain a black block material.

[0082] Step 2: Immerse the black block material in a 20 mmol / L copper sulfate solution for 10 min, wash it with deionized water and dry it in an oven at 60 °C for 12 h. After drying, take out the material and immerse it in a 20 mmol / L KOH solution for 15 min, then wash it with deionized water and dry it in an oven at 60 °C for 12 h.

[0083] Step 3: Place the material in a 0.1 mol / L sodium sulfate solution, reduce it at a reduction current of -5 mA for 30 min, then take it out and dry it in an oven at 60 °C for 12 h. The obtained material is a biochar-based gas diffusion electrode with porous channels, labeled as W800-Cu.

[0084] Step 4: Use this gas diffusion electrode as the working electrode to form a three-electrode system, and introduce high-purity CO 2Gas (60 mL / min), and the electrolyte is 0.1 M KHCO 3 and 0.02 M KNO 3 , and a potentiostatic test is carried out with the voltage set at -0.6 V.

[0085] According to Figure 6 the test results, the urea synthesis yield of the W800-Cu gas diffusion electrode in the electrocatalytic reaction is 671.5 μg h -1 mg cat. -1 , and the Faraday efficiency is 4.8%.

[0086] Comparative Example 1

[0087] A preparation method of a cuprous oxide-loaded carbon cloth electrode, and the method is as follows:

[0088] Step 1: Take a 1×1.5 cm carbon cloth and place it in a porcelain boat, and then put it into a tube furnace. After introducing Air, heat it to 600 °C at a heating rate of 5 °C / min and hold for 2 h. When the tube furnace program automatically ends and the temperature drops to room temperature, stop ventilation to obtain a hydrophilic carbon cloth.

[0089] Step 2: Immerse the carbon cloth in a 20 mmol / L copper sulfate solution for 10 min, then wash it with deionized water and dry it in an oven at 60 °C for 12 h. After drying, take out the carbon cloth and immerse it in a 20 mmol / L KOH solution for 15 min, and then wash it with deionized water and dry it in an oven at 60 °C for 12 h.

[0090] Step 3: Place the carbon cloth in a 0.1 mol / L sodium sulfate solution, reduce it at a reduction current of -5 mA for 30 min and then take it out, and dry it in an oven at 60 °C for 12 h. What is obtained is the cuprous oxide-loaded carbon cloth, marked as CC600-Cu.

[0091] Step 4: Clamp the carbon cloth on the working electrode to form a three-electrode system, and introduce high-purity CO 2 gas (60 mL / min), and the electrolyte is 0.1 M KHCO 3 and 0.01 M KNO 3 , and a potentiostatic test is carried out with the voltage set at (-0.5 V) to (-1.1 V).

[0092] According to Figure 7 the test results, the highest urea synthesis yield of the CC600-Cu control group in the electrocatalytic reaction is only 441.7 μg h -1 mg cat. -1 , and the highest Faraday efficiency is only 3.9%.

[0093] In summary, the above are only the preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A biochar-based gas diffusion electrode with porous channels, characterized in that, it includes a biochar-based material with porous channels and a catalyst supported on the biochar-based material with porous channels, and the catalyst is cuprous oxide; The preparation method of the supported cuprous oxide is as follows: (1) Immerse the biochar-based material with porous channels in a soluble copper salt solution, take it out, wash and dry it, then immerse it in a KOH or NaOH solution, take it out, wash and dry it; (2) Carry out constant current reduction on the product obtained in step (1) in a soluble sulfate solution, wash and dry it to obtain a biochar-based gas diffusion electrode with porous channels loaded with cuprous oxide.

2. The biochar-based gas diffusion electrode with porous channels according to claim 1, characterized in that, In step (1), the soluble copper salt is copper sulfate; the concentration of the soluble copper salt is 10-30 mmol / L; the concentration of the KOH or NaOH solution is 10-30 mmol / L; the immersion time in the soluble copper salt solution is 2-30 min; the immersion time in the KOH or NaOH solution is 2-30 min; the washing is with deionized water; the drying temperature is 40-80 °C, and the drying time is 4-12 h; In step (2), the soluble sulfate is sodium sulfate or potassium sulfate; the concentration of the soluble sulfate solution is 0.1 mol / L; the current of the constant current reduction is -5 mA, and the time is 15-60 min. The washing is with deionized water, and the drying temperature is 40-80 °C, and the drying time is 4-12 h.

3. The biochar-based gas diffusion electrode with porous channels according to claim 2, characterized in that, In step (1), the concentration of the soluble copper salt is 20 mmol / L; the concentration of the KOH or NaOH solution is 20 mmol / L; the drying temperature is 60 °C, and the drying time is 12 h; In step (2), the time of the constant current reduction is 30 min.

4. The preparation method of the biochar-based gas diffusion electrode with porous channels according to claim 1, characterized in that, it includes the following steps: S1: Calcinate the wood in an H 2 / Ar atmosphere to obtain a porous biochar-based material; S2: Load a catalyst on the biochar-based material with porous channels in step S1 to obtain a biochar-based gas diffusion electrode with porous channels.

5. The preparation method according to claim 4, characterized in that, In step S1, the temperature of the calcination is 700 to 1000 °C, and the time of the calcination is 1 to 4 h; the H 2 volume fraction of H in the H 2 / Ar atmosphere is 5 to 10%; the wood is basswood.

6. The preparation method according to claim 5, characterized in that, The calcination temperature is 800 °C, the calcination time is 2 h, and the heating rate is 5 °C / min; the H 2 / Ar atmosphere, the volume fraction of H 2 is 8%.

7. The application of the biochar-based gas diffusion electrode with porous channels according to claim 1 in the electrocatalytic synthesis of urea.

8. The application according to claim 7, characterized in that, The biochar-based gas diffusion electrode with porous channels is used as the working electrode to form a three-electrode system, and the electrolyte is 0.1 M KHCO 3 and 0.001 - 0.02 M KNO 3 ; CO 2 gas is introduced into the biochar-based gas diffusion electrode with porous channels under the condition that the voltage is (-0.5) - (-1.1) V.

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