A method for enhancing the conductivity of conductive carbon black and its application in ORR catalyst

Abstract

The present invention discloses a method for enhancing the conductivity of conductive carbon black and its application in ORR catalyst. The invention is based on the preparation of grafted polyvinyl pyrrolidone (PVP) by free radical polymerization reaction on the basis of commercially available conductive carbon black, and the use of a phosphating agent to perform trace phosphorus doping under high temperature conditions to obtain modified conductive carbon black. The trace phosphorus element in the product can not only improve the electronic structure of commercially available conductive carbon black, making it electron-rich and increasing its intrinsic conductivity; it can also cause its spherical structure to collapse during high temperature, further increase the specific surface area, and form more conductive channels. The addition of PVP can increase the carbon chain structure of conductive carbon black, so that the phosphorus-doped carbon black can further exert its high conductive properties. Through microscopic electronic structure optimization and macroscopic structural engineering regulation, the synergistic effect between the two has a leverage effect, so that the carbon black prepared by this method has a higher conductivity than general commercially available carbon black.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemical catalysis, and specifically relates to a carbon material, in particular a method for modifying conductive carbon black to enhance its conductivity and its application in ORR catalyst Background Art

[0002] Conductive carbon black is the oldest nanocarbon material on the commercial market. It is a carbonaceous material produced by the thermal decomposition of various carbon-rich hydrocarbons (solid, liquid, or gaseous) under strictly controlled inert (pyrolysis) or oxygen-deficient (partial combustion) conditions. With the rapid development of new energy vehicles and wearable electronic devices, batteries and capacitors are being used in large quantities, and global demand for conductive additives has steadily increased. Conductive carbon black offers advantages such as high electrical and thermal conductivity, low production cost, oxidative stability, and low density, offering significant advantages over metal powders or fiber fillers. Water-soluble carbon black, also known as hydrophilic carbon black, is commonly used in electrocatalysis. Compared to conventional carbon black, hydrophilic carbon black has more hydrophilic functional groups on its surface and extremely low surface energy, allowing it to dissolve and disperse rapidly in water without the need for dispersing agents. It is not only water-soluble but also exhibits high jetness, excellent gloss, strong tinting strength, and good dispersibility. Its conductivity is primarily influenced by factors such as the carbon black's surface chemical composition, aggregate structure, porosity, and the crystallite morphology of the primary particles.

[0003] Proton exchange membrane fuel cells are considered to be mobile energy devices with great application prospects. Oxygen reduction reaction (ORR) occurs on their cathode. In the study of ORR catalysts, the carrier has a supporting and dispersing effect on the catalyst. Therefore, optimizing the properties of the carbon carrier is a very important task. The characteristics of the carbon carrier material will have a significant impact on the preparation steps and the performance of the synthesized catalyst. Carbon black is one of the common catalyst carriers, but its conductivity, porosity, specific surface area, etc. often cannot meet the expected requirements. This requires first modifying the hydrophilicity of carbon black. The main methods to improve its hydrophilicity include adding dispersants, oxidative modification, water-soluble polymer grafting and polymer coating. Among them, grafting modification is a common method in the laboratory, but the effect is not ideal. Based on this, in the present invention, we prepared grafted polyvinyl pyrrolidone (PVP) and carbon black doped with trace phosphorus by high-temperature reaction through free radical polymerization. The modified carbon black obtained can not only be well dispersed in water, but also its conductivity has been greatly improved. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the present invention proposes a method for enhancing the conductivity of conductive carbon black and its application in ORR catalyst to solve the problems faced in the above technical background.

[0005] To achieve the above object, the present invention is implemented through the following technical solutions:

[0006] S1, pretreatment of commercially available carbon black: 10-50g of carbon black was added to 500-2000mL of 10% hydrochloric acid solution, stirred evenly, and allowed to stand for a period of time. The supernatant was first removed, and then 500mL of deionized water was added. After standing, the supernatant was again poured out, and the deionized water addition process was repeated three times. The mixture was then transferred to an 80°C vacuum drying oven for drying before use;

[0007] S2, 8-15 g of carbon black, 40-60 g of N-vinyl pyrrolidone (NVP), 0.1-0.8 g of 2,2'-azobisisobutyronitrile (AIBN) and 15-25 mL of tetrahydrofuran (THF) were added to a 200 mL beaker, and the mixture was heated at 50-80°C for 5-8 h. The reaction mixture was then centrifuged several times to remove ungrafted polymer and AIBN, and dried in a vacuum oven overnight to obtain a solid for standby use;

[0008] S3, the solid obtained from S2 is further purified by Soxhlet extraction with THF for 18-54 h, and then dried under vacuum at 40 °C to obtain modified carbon black for future use;

[0009] S4, use a high-temperature tubular furnace for trace phosphorus doping, select an inorganic phosphorus source (such as NaH2PO2, NH4H2PO4, (NH4)2HPO4, etc.) and calcine at 300-400℃ under N2 atmosphere for 1.5-3h. After cooling to room temperature, collect the product to obtain modified carbon black doped with trace phosphorus.

[0010] Preferably, in step S1, the mass of carbon black is 30 g, and the amount of 10% hydrochloric acid solution is 1200 mL.

[0011] Preferably, in step S2, the masses of carbon black, NVP, and AIBN are 10 g, 45 g, and 0.5 g, respectively, and the amount of THF is 20 mL.

[0012] Preferably, the THF Soxhlet extraction time in step S3 is 40 hours.

[0013] Preferably, in step S4, an inorganic phosphorus source NaH2PO2 is selected, and the calcination temperature and time are 300°C and 2h, respectively.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] The trace phosphorus in the modified carbon black not only improves the electronic structure of commercially available conductive carbon black, increasing its intrinsic conductivity; it also causes its spherical structure to collapse during high-temperature processing, further increasing its specific surface area and forming more conductive pathways. Furthermore, the addition of PVP increases the carbon chain structure of the conductive carbon black, further enhancing the high conductivity of the phosphorus-doped carbon black. The synergistic effect of these two factors makes the carbon black prepared by this method more conductive than standard commercially available carbon black. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a flow chart of obtaining modified carbon black by grafting PVP in Examples 2 and 3 of the present invention and Comparative Examples 2 and 3.

[0017] Figure 2 These are SEM images of modified carbon black obtained by grafting PVP in Examples 2 and 3 of the present invention.

[0018] Figure 3 This is a bar chart comparing the electrical conductivity of the carbon black obtained in Comparative Examples 1-3 and Examples 1-3 of the present invention.

[0019] Figure 4 TEM images of Comparative Example 1 and Example 3 and their respective dispersibility in water.

[0020] Figure 5 This is the electrochemical impedance spectroscopy (EIS) test of the same ORR catalyst using homemade carbon black as a conductive agent.

[0021] Table 1 shows the specific surface area and pore size test data of different carbon blacks. DETAILED DESCRIPTION

[0022] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. The details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other unless they conflict.

[0023] The present invention provides a method for enhancing the conductivity of conductive carbon black and its application in ORR catalyst, which specifically comprises the following steps:

[0024] S1, pretreatment of commercially available carbon black: 10-50g of carbon black was added to 500-2000mL of 10% hydrochloric acid solution, stirred evenly, and allowed to stand for a period of time. The supernatant was first removed, and then 500mL of deionized water was added. After standing, the supernatant was again poured out, and the deionized water addition process was repeated three times. The mixture was then transferred to an 80°C vacuum drying oven for drying before use;

[0025] S2, 8-15 g of carbon black, 40-60 g of N-vinylpyrrolidone (NVP), 0.1-0.8 g of 2,2'-azobisisobutyronitrile (AIBN) and 15-25 mL of tetrahydrofuran (THF) were added to a 200 mL beaker, and the mixture was heated at 50-80°C for 5-8 h. The reaction mixture was then centrifuged several times to remove ungrafted polymer and AIBN, and dried in a vacuum drying oven overnight to obtain a solid for standby use;

[0026] S3, the solid obtained from S2 is further purified by Soxhlet extraction with THF for 18-54 h, and then dried in vacuo at 40 °C to obtain modified carbon black for future use;

[0027] S4, use a high-temperature tubular furnace for trace phosphorus doping, select an inorganic phosphorus source (such as NaH2PO2, NH4H2PO4, (NH4)2HPO4, etc.) and calcine at 300-400℃ under N2 atmosphere for 1.5-3h. After cooling to room temperature, collect the product to obtain modified carbon black doped with trace phosphorus.

[0028] Based on commercially available carbon black, the present invention prepares grafted PVP through a free radical polymerization reaction, and then dopes a trace amount of phosphorus under high temperature conditions. Under the optimization of microscopic electronic structure and the regulation of macroscopic structural engineering, the synergistic effect between the two plays a leverage effect, making the carbon black prepared by the present invention more conductive than general commercially available carbon black.

[0029] Comparative Example 1:

[0030] S1, pretreatment of commercially available carbon black: 30 g of carbon black was added to 1000 mL of 10% hydrochloric acid solution, stirred evenly, and allowed to stand for a period of time. The supernatant was removed, and then 500 mL of deionized water was added. After standing, the supernatant was discarded again, and the deionized water addition process was repeated three times. The mixture was then transferred to an 80°C vacuum drying oven for drying before use;

[0031] Example 1:

[0032] S1, pretreatment of commercially available carbon black: 30 g of carbon black was added to 1000 mL of 10% hydrochloric acid solution, stirred evenly, and allowed to stand for a period of time. The supernatant was removed, and then 500 mL of deionized water was added. After standing, the supernatant was discarded again, and the deionized water addition process was repeated three times. The mixture was then transferred to an 80°C vacuum drying oven for drying before use;

[0033] S2, 10 g of carbon black, 50 g of N-vinylpyrrolidone (NVP), 0.5 g of 2,2'-azobisisobutyronitrile (AIBN), and 20 mL of tetrahydrofuran (THF) were added to a 200 mL beaker, and the mixture was heated at 60 °C for 6 h. The reaction mixture was then centrifuged several times to remove ungrafted polymer and AIBN, and dried in a vacuum oven overnight to obtain a solid for later use;

[0034] Example 2:

[0035] S1, pretreatment of commercially available carbon black: 30 g of carbon black was added to 1000 mL of 10% hydrochloric acid solution, stirred evenly, and allowed to stand for a period of time. The supernatant was removed, and then 500 mL of deionized water was added. After standing, the supernatant was discarded again, and the deionized water addition process was repeated three times. The mixture was then transferred to an 80°C vacuum drying oven for drying before use;

[0036] S2, 10 g of carbon black, 50 g of N-vinylpyrrolidone (NVP), 0.5 g of 2,2'-azobisisobutyronitrile (AIBN), and 20 mL of tetrahydrofuran (THF) were added to a 200 mL beaker, and the mixture was heated at 60 °C for 6 h. The reaction mixture was then centrifuged several times to remove ungrafted polymer and AIBN, and dried in a vacuum oven overnight to obtain a solid for later use;

[0037] S3, the solid obtained from S2 was further purified by Soxhlet extraction with THF for 36 h, and then dried under vacuum at 40 °C to obtain modified carbon black for future use;

[0038] Comparative Example 2:

[0039] S1, pretreatment of commercially available carbon black: 30 g of carbon black was added to 1000 mL of 10% hydrochloric acid solution, stirred evenly, and allowed to stand for a period of time. The supernatant was removed, and then 500 mL of deionized water was added. After standing, the supernatant was discarded again, and the deionized water addition process was repeated three times. The mixture was then transferred to an 80°C vacuum drying oven for drying before use;

[0040] S2, 10 g of carbon black, 50 g of N-vinylpyrrolidone (NVP), 0.5 g of 2,2'-azobisisobutyronitrile (AIBN), and 20 mL of tetrahydrofuran (THF) were added to a 200 mL beaker, and the mixture was heated at 60 °C for 6 h. The reaction mixture was then centrifuged several times to remove ungrafted polymer and AIBN, and dried in a vacuum oven overnight to obtain a solid for later use;

[0041] S3, the solid obtained from S2 was further purified by Soxhlet extraction with THF for 48 h, and then dried under vacuum at 40 °C to obtain modified carbon black for future use;

[0042] Example 3:

[0043] S1, pretreatment of commercially available carbon black: 30 g of carbon black was added to 1000 mL of 10% hydrochloric acid solution, stirred evenly, and allowed to stand for a period of time. The supernatant was removed, and then 500 mL of deionized water was added. After standing, the supernatant was discarded again, and the deionized water addition process was repeated three times. The mixture was then transferred to an 80°C vacuum drying oven for drying before use;

[0044] S2, 10 g of carbon black, 50 g of N-vinylpyrrolidone (NVP), 0.5 g of 2,2'-azobisisobutyronitrile (AIBN), and 20 mL of tetrahydrofuran (THF) were added to a 200 mL beaker, and the mixture was heated at 60 °C for 6 h. The reaction mixture was then centrifuged several times to remove ungrafted polymer and AIBN, and dried in a vacuum oven overnight to obtain a solid for later use;

[0045] S3, the solid obtained from S2 was further purified by Soxhlet extraction with THF for 36 h, and then dried under vacuum at 40 °C to obtain modified carbon black for future use;

[0046] S4, using a high-temperature tube furnace for trace phosphorus doping, select the inorganic phosphorus source NaH2PO2 and calcine it at 300℃ for 2h under N2 atmosphere. After cooling to room temperature, collect the product to obtain modified carbon black doped with trace phosphorus.

[0047] Figure 2 This is the SEM image of the modified carbon black obtained by grafting PVP in Examples 2 and 3 of the present invention. It can be seen from the figure that the modified carbon black is uniformly dispersed and basically no aggregation occurs. This makes the specific surface area of ​​the modified carbon black higher than that of commercially available carbon black, which is beneficial to improving the conductivity. More importantly, the high surface area carbon black can effectively support highly dispersed catalyst nanoparticles, making it difficult for the catalyst dripped on the glassy carbon electrode to fall off during the ORR test.

[0048] Comparative Example 3:

[0049] S1, pretreatment of commercially available carbon black: 30 g of carbon black was added to 1000 mL of 10% hydrochloric acid solution, stirred evenly, and allowed to stand for a period of time. The supernatant was removed, and then 500 mL of deionized water was added. After standing, the supernatant was discarded again, and the deionized water addition process was repeated three times. The mixture was then transferred to an 80°C vacuum drying oven for drying before use;

[0050] S2, 10 g of carbon black, 50 g of N-vinylpyrrolidone (NVP), 0.5 g of 2,2'-azobisisobutyronitrile (AIBN), and 20 mL of tetrahydrofuran (THF) were added to a 200 mL beaker, and the mixture was heated at 60 °C for 6 h. The reaction mixture was then centrifuged several times to remove ungrafted polymer and AIBN, and dried in a vacuum oven overnight to obtain a solid for later use;

[0051] S3, the solid obtained from S2 was further purified by Soxhlet extraction with THF for 36 h, and then dried under vacuum at 40 °C to obtain modified carbon black for future use;

[0052] S4, using a high-temperature tubular furnace for trace phosphorus doping, select the inorganic phosphorus source NaH2PO2 and calcine it at 350℃ for 2h under N2 atmosphere. After cooling to room temperature, collect the product to obtain modified carbon black doped with trace phosphorus.

[0053] The electrical conductivity of all carbon black powders used in this invention was measured using a Keithley RTS-8 digital four-probe resistance meter equipped with a semi-automatic wafer tungsten probe. Prior to measurement, an appropriate amount of carbon black was placed in a circular mold with a diameter of 13 mm. The carbon black was then pressed into 2 mm thick discs using an infrared tablet press at a pressure of 15 MPa.

[0054] Figure 3 This is a bar chart comparing the conductivity of the carbon black obtained in Comparative Examples 1-3 and Examples 1-3 of the present invention. As can be seen from the figure, the conductivity of Example 3 is as high as 20.3 S / cm, which is more than 20 times higher than that of commercially available carbon black. The conductivity of the carbon black in Comparative Example 1 without PVP grafting and Example 1 is also very different. The conductivity of the carbon black after trace phosphating is greatly improved, which indicates that the addition of PVP and trace phosphating have a synergistic effect, thereby showing excellent conductivity.

[0055] Figure 4 TEM images of Comparative Example 1 and Example 3 and their respective dispersibility in water. Figure 4 The left side in the middle shows the sample obtained after pretreatment of commercial carbon black, and the right side shows the sample obtained by grafting PVP and doping with trace phosphorus at high temperature. From the TEM image, it can be clearly seen that their aggregation degree and dispersibility in water are significantly different, which will affect the stability of carbon black and the performance of the ORR catalyst after being loaded with carbon.

[0056] Figure 5This is an electrochemical impedance spectroscopy (EIS) test of the same ORR catalyst using homemade carbon black as a conductive agent. Before the test, carbon was loaded at a ratio of catalyst: carbon black = 5:1, and then a slurry was prepared according to a certain ratio. 15μL was evenly dripped on a polished clean platinum carbon electrode, and an electrochemical test was performed using a rotating disk. As shown in the figure, in the high-frequency region, the EIS curve is semicircular, while in the low-frequency region, the EIS curve is linear. For the ORR catalytic process, R ct It represents the charge transfer resistance. The smaller its value is, the smaller the resistance to ion transport is. It can be obtained by fitting the semicircular part in the EIS curve. It can be seen from the figure that Example 3 has the smallest resistance value, which is more favorable for the ORR catalyst reaction.

[0057]

[0058]

[0059] Table 1

[0060] Table 1 shows the specific surface area and pore size test data of different carbon blacks. It can be seen from the experimental data that adding PVP to commercially available carbon black can greatly increase the specific surface area of ​​carbon black, increase the pore volume of carbon black and change the pore size distribution of carbon black. At the same time, trace phosphating at different temperatures will also have a great impact on the specific surface area, pore volume and size. The synergistic treatment of PVP and trace phosphating is beneficial to expand the pore size distribution of carbon black while maintaining a high specific surface area, thereby affecting its conductivity.

[0061] The above-described embodiments merely represent specific implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A method for enhancing the electrical conductivity of conductive carbon black used in ORR catalysts, characterized by: The specific steps include: S1. Pretreatment of commercially available carbon black: 10-50g of carbon black was added to 500-2000mL of 10% hydrochloric acid solution, stirred, and allowed to stand for a period of time. The supernatant was removed, and then 500mL of deionized water was added. After standing, the supernatant was again discarded. The deionized water addition process was repeated three times. The mixture was then transferred to an 80°C vacuum drying oven and dried until ready for use. S2. Add 8-15 g of carbon black, 40-60 g of N-vinyl pyrrolidone, 0.1-0.8 g of 2,2'-azobisisobutyronitrile, and 15-25 mL of tetrahydrofuran to a 200 mL beaker and heat the mixture at 50-80°C for 5-8 h. The reaction mixture is then centrifuged several times to remove ungrafted polymer and azobisisobutyronitrile and dried in a vacuum oven overnight to obtain a solid for later use. S3. The solid obtained from S2 was further purified by Soxhlet extraction with tetrahydrofuran for 36 h, and then dried in vacuo at 40 ° C to obtain a modified carbon black for use; S4. Use a high-temperature tube furnace for trace phosphorus doping, select an inorganic phosphorus source, calcine at 300 ° C for 1.5-3h under N2 atmosphere, and collect the product after cooling to room temperature to obtain a modified carbon black doped with trace phosphorus; Among them, inorganic phosphorus sources include NaH2PO2, NH4H2PO4, and (NH4)2HPO4.

2. The method according to claim 1, wherein: In step S1, the mass of carbon black is 30 g, and the amount of 10% hydrochloric acid solution is 1000 mL.

3. The method according to claim 1, wherein: In step S2, the masses of carbon black, N-vinyl pyrrolidone, and azobisisobutyronitrile are 10 g, 50 g, and 0.5 g, respectively, and the amount of tetrahydrofuran is 18 mL.

4. The method according to claim 1 or 3, characterized in that: The heating temperature and time in step S2 are 65° C. and 6.5 h, respectively.

5. The method according to claim 3, wherein: The heating temperature and time in step S2 are 70° C. and 6 h, respectively.

6. The method according to claim 1, wherein: In step S4, an inorganic phosphorus source NaH2PO2 is selected and calcined at 300°C for 2h.

7. Conductive carbon black prepared according to the method according to any one of claims 1 to 6.

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