Method for preparing carbonyl regulation type gas diffusion electrode based on defect engineering

Abstract

The invention discloses a high-performance gas diffusion electrode and a preparation method thereof, and the method is characterized in that a modified commercial carbon black material catalyst is loaded on a hydrophobic gas diffusion layer in a spray gun spraying mode to obtain the high-performance gas diffusion electrode. Wherein the modified carbon-based catalyst is obtained by carrying out mechanical ball milling and oxidation treatment on original commercial carbon black. The commercial carbon black is used as a catalyst modification precursor, so that the preparation cost of the catalyst can be reduced, and the characteristics of greenness, environmental protection and no metal leaching in actual production are ensured. According to the preparation method, the original carbon black is modified by adopting a mechanical ball milling method, so that the purpose of solvent-free material modification is achieved, and a target catalytic material can be prepared on a large scale. In the ball milling process, many defect structures are generated on the surface of the carbon black, the defect structures can serve as catalytic sites of electrochemical reaction, conditions are provided for subsequent loading of oxygen-containing functional groups, and the gas diffusion electrode loaded with the modified carbon material shows ideal performance in the oxygen reduction reaction; the method can be used for efficiently synthesizing hydrogen peroxide. The gas diffusion electrode not only has the advantages of simplicity in preparation, no need of a metal-based catalyst, low cost and the like, but also has the advantages of large-scale preparation, environmental friendliness and the like, and has good application value and prospect.

Description

Technical Field

[0001] The present invention relates to a gas diffusion electrode modified by defect engineering of a carbon-based catalyst and a preparation method thereof, belonging to the technical field of electrode preparation. Background Art

[0002] In the two-electron oxygen reduction reaction (2e – ORR), in order to increase the mass transfer of O2, gas diffusion electrodes (GDEs) have been widely used. The gas diffusion layer (GDL) is usually composed of a carbon substrate of a hydrophobic layer, serving as the substrate of the cathode catalyst layer (CL), forming a GDE and promoting O2 diffusion. This structure can effectively enrich O2 near the electrode surface, promote rapid mass transfer and increase the reaction rate.

[0003] So far, various cathode electrocatalysts have been developed as the CL layer, including noble metal alloys, non-noble metals, and metal-free materials. Among the reported electrocatalysts, carbon-based catalysts have become a promising 2e – ORR catalytic material due to their rich resources and low cost. However, unmodified carbon-based catalysts generally have poor catalytic activity and are difficult to operate at an ampere-level current density. Oxygen-containing functional groups on the surface of carbon materials can effectively enhance their electrochemical activity. However, the types of oxygen-containing functional groups will affect the catalytic activity and selectivity, and it is difficult to achieve directional regulation of the types of functional groups.

[0004] In the present invention, we propose a method for modifying raw commercial carbon black by mechanical ball milling and oxidation treatment, preparing the modified carbon black material into catalyst ink, and loading it onto the GDL by spraying with a spray gun, and obtaining the GDE after natural drying. The carbon black treated by ball milling will have more defect structures, and defect engineering realizes the targeted regulation of oxygen-containing functional groups on the surface of carbon black, enabling it to be loaded with carbonyl functional groups with high 2e – ORR activity and selectivity, and can still maintain a high H2O2 synthesis efficiency at an ampere-level current density. In addition, compared with traditional metal-based electrocatalysts, this GDE has a considerable cost advantage and no risk of metal leaching, and has broad application prospects. Summary of the Invention

[0005] The present invention provides a modified carbon-based catalyst gas diffusion electrode and a preparation method thereof, and the prepared electrode can operate efficiently at an ampere-level current.

[0006] The present invention adopts the following technical solutions:

[0007] Commercial carbon black was treated by mechanical ball milling and oxidation, and the modified carbon black catalyst was loaded onto hydrophobic carbon paper by spraying to prepare a gas diffusion electrode. After the original carbon black was treated by mechanical ball milling, the defect content of the ball-milled oxidized carbon black catalyst increased significantly. It can not only serve as the active site for 2e – ORR, but also achieve targeted regulation of carbonyl formation in the subsequent nitric acid oxidation step, further improving the activity and selectivity of 2e – ORR. Compared with unmodified carbon black, its electrochemical activity has been greatly improved (at a constant current density of 100 mA cm –2 , only a cell voltage of 3.45 V is required, which is lower than 4.3 V for oxidized carbon black, 4.6 V for ball-milled carbon black, and 6 V for original carbon black).

[0008] In the above method, further improved, the preparation method of the modified ball-milled oxidized carbon black catalyst includes the following steps:

[0009] S1. Using a planetary ball mill, commercially available carbon black was mechanically ball milled to obtain a ball-milled carbon black material;

[0010] S2. The ball-milled carbon black material obtained in step S1 was mixed with a nitric acid solution, heated and condensed for reflux, and then washed and freeze-dried to obtain a modified ball-milled oxidized carbon black catalyst.

[0011] In the above method, further improved, in step S1, the ball milling beads used in the mechanical ball milling process are one of zirconia, agate, and stainless steel. The mass ratio of balls to materials is 20-80:1, the ball milling time is 1-48 h, and the ball milling direction is changed every half hour.

[0012] In the above method, further improved, in step S2, the concentration of the nitric acid solution is 3-16 mol / L, the heating temperature is 50-90 °C, and the condensation reflux time is 1-48 h.

[0013] In the above method, further improved, in step S2, the freeze-drying time is 48-72 h. After drying, the following treatment is also included: grinding the dried product and passing it through a 200-mesh sieve.

[0014] In the above method, further improved, the process of spraying with a spray gun is as follows: Solvent and binder are added to the modified ball-milled oxidized carbon black powder, and after ultrasonic treatment, a catalyst ink is dispersed and sprayed onto one of the gas diffusion layers of commercial hydrophobic carbon paper, carbon felt, and carbon cloth by spraying with a spray gun. After natural drying, a modified carbon-based catalyst gas diffusion electrode can be obtained.

[0015] In the above method, further improved, the catalyst ink solvent is one or more of isopropanol, methanol, N,N–dimethylformamide, and dimethyl sulfoxide, the binder is one or more of Nafion solution and polytetrafluoroethylene dispersion, and the ratio of the modified ball-milled oxidized carbon black catalyst in the catalyst ink to the solvent and the binder is 1-100 mg: 0.1-10 mL: 0.01-1 mL. The ultrasonic power is 5-500 W, the time is 15-180 min, and the spraying amount is 0.1-10 mg of catalyst loaded on each square centimeter of the electrode.

[0016] Compared with the prior art, the advantages of the present invention are as follows:

[0017] (1) The present invention adopts the mechanical ball milling defect engineering technology to mechanically ball mill the unmodified carbon black to generate more carbon defects on its surface, and then through nitric acid oxidation treatment, oxygen-containing functional groups are loaded on its surface. The defect engineering not only increases the active sites on the surface of the carbon material, but also can achieve targeted regulation of the oxygen-containing functional groups on the surface of the carbon material during the oxidation process, increasing the carbonyl content. The carbonyl has ideal 2e – ORR activity and selectivity. Therefore, the GDE prepared by the targeted regulation of oxygen-containing functional groups technology through mechanochemical defect engineering has ideal H2O2 synthesis efficiency and selectivity.

[0018] (2) The present invention uses commercial carbon black as the precursor for preparing the cathode CL catalyst, saving production costs. Using the means of mechanical ball milling to modify the precursor, the procedure is simple and easy to operate, and large-scale production of the catalyst can be achieved. The obtained modified carbon black material GDE does not contain metals and has no risk of metal leaching. Using the obtained GDE as the cathode, the electro-synthesis of H2O2 has high efficiency and can still maintain a high Faraday efficiency at an amperometric current density. Description of the Drawings

[0019] Figure 1 It is the preparation flow chart of GDE in Example 1 of the present invention.

[0020] Figure 2 It is the Raman spectrogram of the original commercial carbon black and the prepared modified carbon black catalysts (CB, MCB, OCB, MOCB) in Example 1 of the present invention.

[0021] Figure 3 It is the infrared spectrogram of the original commercial carbon black and the prepared modified carbon black catalysts (CB, MCB, OCB, MOCB) in Example 1 of the present invention.

[0022] Figure 4 It is the 2e – ORR-related volcano plot calculated for the oxygen electroreduction to H2O2 of the present invention.

[0023] Figure 5 Schematic diagram of the relationship between the GDE cell voltage and the current density in Examples 1-4 of the present invention.

[0024] Figure 6 Digital photo of the 10×10 cm 2 GDE prepared in Example 5 of the present invention.

[0025] Figure 7 Schematic diagram of the relationship between the cell voltage and the total current of the 10×10 cm 2 GDE prepared in Example 5 of the present invention, and the Faraday efficiency of H2O2 production at the corresponding current. Detailed implementation manners

[0026] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific preferred embodiments, but the protection scope of the present invention is not limited thereby. Unless otherwise specified, the materials and instruments used in the following embodiments are all commercially available.

[0027] Example 1:

[0028] (1) Put 2 g of commercial carbon black and 80 g of zirconia (ZrO2) balls into an agate grinding jar (50 mL) equipped with a stainless steel container. Then, under solvent-free conditions, perform ball milling treatment at a speed of 500 rpm for 7 hours. During the ball milling process, change the ball milling direction every 30 minutes. Then, sieve the dried solid sample with a 200-mesh sieve and label it as MCB.

[0029] (2) Mix 1.5 g of MCB evenly with 500 ml of 12.0 mol nitric acid, and then reflux the above solution in an oil bath at 85 °C for 24 h. After natural cooling, take out the slurry, centrifuge and wash it until the pH value is neutral. Finally, freeze-dry the sample for 48 hours. Grind the dried solid sample into fine powder, sieve it with a 200-mesh sieve, store it in a sealed container, and label it as MOCB. The oxidized carbon black of the control group, labeled as OCB, is obtained by directly soaking commercial carbon black without mechanical ball milling treatment under the same conditions.

[0030] (3) The preparation method of the catalyst ink is as follows: 20 mg of catalyst, 1.92 mL of isopropanol, and 0.08 mL of 5% Nafion solution are combined and ultrasonicated to form a homogeneous solution. The ultrasonic power is 40 W, the time is more than 60 min, and the temperature is 25 °C.

[0031] (4) The catalyst ink is sprayed on a hydrophobic carbon paper (Sigracet 28BC) and dried naturally until the catalyst loading is 0.5 mg cm –2 , and the GDE loaded with ball-milled oxidized carbon black is obtained.

[0032] (5)GDE electrocatalytic activity test: Cut the GDE into 2×2 cm 2 size, which serves as the cathode of the H2O2-producing reactor. Connect the DC power supply. When the cell voltage is about 3.45 V, the current density can reach 100 mA cm –2 .

[0033] Example 2:

[0034] As described in Example 1, the difference is that:

[0035] In step (1), mechanical ball milling treatment is not required.

[0036] In step (5), when the cell voltage is about 4.3 V, the current density can reach 100 mA cm –2 .

[0037] Example 3:

[0038] As described in Example 1, the difference is that:

[0039] In step (2), nitric acid oxidation treatment is not required.

[0040] In step (5), when the cell voltage is about 4.6 V, the current density can reach 100 mA cm –2 .

[0041] Example 4:

[0042] As described in Example 1, the difference is that:

[0043] In step (1), mechanical ball milling treatment is not required.

[0044] In step (2), nitric acid oxidation treatment is not required.

[0045] In step (5), when the cell voltage is about 6 V, the current density can reach 100 mA cm –2 .

[0046] Example 5:

[0047] As described in Example 1, the difference is that:

[0048] In step (5), cut the GDE into 10×10 cm 2 size. When the cell voltage is about 4.8 V, the total reaction current can reach 8 A. In the cell voltage range of 1.6 - 4.8 V, the Faraday efficiency of H2O2 production can be maintained above 80%.

[0049] The above are only the preferred embodiments of the present invention, and do not impose any formal limitations on the present invention. Any person skilled in the art can make many possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above, or modify it into equivalent embodiments with equivalent changes, without departing from the spirit and technical solution of the present invention. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A modified carbon-based catalyst gas diffusion electrode and a preparation method, characterized in that: The method comprises the following steps: using mechanical ball milling and oxidation treatment of commercial carbon black, loading the modified carbon black catalyst onto hydrophobic carbon paper by spraying, and preparing a gas diffusion electrode; the ball milled oxidized carbon black catalyst is prepared by mechanical ball milling and nitric acid oxidation of the original carbon black.

2. A modified carbon-based catalyst gas diffusion electrode and preparation method according to claim 1, characterized in that: The preparation method of the modified ball-milled oxidized carbon black catalyst comprises the following steps: S1. Using a planetary ball mill, mechanically ball-milling commercial carbon black to obtain a ball-milled carbon black material; S2. The ball-milled carbon black material obtained in step S1 is mixed with a nitric acid solution, and then heated, condensed and refluxed, and then washed and freeze-dried to obtain a modified ball-milled oxidized carbon black catalyst.

3. A modified carbon-based catalyst gas diffusion electrode and preparation method according to claim 2, characterized in that: In step S1, the ball milling beads used in the mechanical ball milling process are made of one of zirconium oxide, agate, and stainless steel, the ball-to-material mass ratio is 20-80:1, the ball milling time is 1-48 hours, and the ball milling direction is changed every half an hour.

4. A modified carbon-based catalyst gas diffusion electrode and preparation method according to claim 3, characterized in that: In step S2, the concentration of the nitric acid solution is 3-16 mol / L, the heating temperature is 50-90° C., and the condensation reflux time is 1-48 h.

5. A modified carbon-based catalyst gas diffusion electrode and a preparation method according to any one of claims 1 to 4, characterized in that: In step S2, the freeze-drying time is 48-72 hours, and the following treatment is also included after drying: the dried product is ground and passed through a 200-mesh sieve.

6. A modified carbon-based catalyst gas diffusion electrode and a preparation method according to any one of claims 1 to 4, characterized in that: The spray gun spraying process is as follows: adding a solvent and a binder to the modified ball-milled oxidized carbon black powder, dispersing the catalyst ink through ultrasonic treatment, and spraying the ink onto a gas diffusion layer of commercial hydrophobic carbon paper, carbon felt, or carbon cloth through a spray gun spraying method. After natural drying, a modified carbon-based catalyst gas diffusion electrode can be obtained.

7. A modified carbon-based catalyst gas diffusion electrode and preparation method according to claim 6, characterized in that: The catalyst ink solvent is one or more of isopropanol, methanol, N,N-dimethylformamide, and dimethyl sulfoxide; the binder is one or more of Nafion solution and polytetrafluoroethylene dispersion; the ratio of the catalyst ink modified ball-milled oxidized carbon black catalyst to the solvent to the binder is 1-100 mg: 0.1-10 mL: 0.01-1 mL; the ultrasonic power is 5-500 W, the time is 15-180 min, and the spraying amount is 0.1-10 mg of catalyst loaded on each square centimeter of electrode.

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