Ga-N-C catalyst as well as preparation method and application thereof

Abstract

The invention discloses a Ga-N-C catalyst as well as a preparation method and application thereof, and belongs to the technical field of catalysts. The preparation method of the Ga-N-C catalyst comprises the following steps: S1, mixing gallium oxide and halogenated ammonium salt to obtain mixed powder; placing the mixed powder in a porcelain boat and placing the porcelain boat at the upstream of a tubular furnace; placing the carbon carrier in a porcelain boat and placing the porcelain boat at the downstream of the tubular furnace; introducing carrier gas into the tubular furnace, heating to a set temperature, and carrying out vapor deposition to obtain a crude product; and S2, after pickling the crude product, washing and drying to obtain the Ga-N-C catalyst. According to the method disclosed by the invention, the dispersibility of Ga atoms and the nitrogen doping efficiency are remarkably improved, and the prepared Ga-N-C catalyst has excellent conductivity and efficient ORR catalytic performance.

Description

A Ga-NC catalyst, its preparation method, and its application Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a Ga-NC catalyst, its preparation method, and its application. Background Technology

[0002] The oxygen reduction reaction (ORR) is a key cathode reaction in electrochemical energy devices such as fuel cells and metal-air batteries, and it also has significant applications in the electrochemical synthesis of hydrogen peroxide (H₂O₂) and the degradation of water pollutants through the generation of oxygen free radicals (·OH). However, the ORR reaction kinetics are relatively slow, involving complex multi-electron transfer processes, resulting in high overpotentials and low reaction efficiency. Therefore, developing efficient and low-cost catalysts to lower the reaction energy barrier and improve catalytic performance has become a research focus. Traditionally, platinum-based noble metal catalysts have been widely used due to their excellent ORR performance, but their high cost and resource scarcity limit their widespread application in industrial settings.

[0003] In recent years, non-precious metal catalysts have attracted much attention due to their low cost, high activity, and environmental friendliness. Gallium (Ga), as a p-block metal element with a unique electronic structure, possesses redox properties and a strong coordination ability with nitrogen atoms, giving it potential advantages in the field of electrocatalysis. However, existing methods for preparing Ga-based catalysts mainly rely on traditional processes such as solution methods and impregnation methods. These methods struggle to achieve uniform dispersion of Ga atoms in a carbon matrix, easily leading to metal agglomeration and consequently reducing the utilization rate of active sites. Summary of the Invention

[0004] Therefore, the purpose of this invention is to provide a Ga-NC catalyst, its preparation method, and its application.

[0005] In a first aspect, the present invention provides a method for preparing a Ga-NC catalyst, comprising the following steps: S1: mixing gallium oxide and ammonium halide salt to obtain a mixed powder; placing the mixed powder in a ceramic boat and placing it upstream of a tube furnace; placing a carbon support in the ceramic boat and placing it downstream of the tube furnace; introducing a carrier gas into the tube furnace, then heating it to a set temperature and performing vapor phase deposition to obtain a crude product; S2: acid washing the crude product, followed by washing and drying to obtain the Ga-NC catalyst.

[0006] Preferably, in step S1, the ammonium halide salt is one or more of ammonium chloride, ammonium bromide, and ammonium iodide.

[0007] Preferably, in step S1, the carbon support is activated carbon.

[0008] Preferably, in step S1, the mass ratio of gallium oxide to ammonium halide is 1:(1~10), more preferably 1:(1.3~3); the mass ratio of gallium oxide to carbon support is 1:(0.1~10).

[0009] Preferably, in step S1, the carrier gas is one or two of nitrogen, argon, carbon monoxide, and hydrogen.

[0010] Preferably, in step S1, the flow rate of the carrier gas is (0.01~1) L / min.

[0011] Preferably, in step S1, the heating rate is 1~10℃ / min; the set temperature is 300~800℃, more preferably 550~750℃; and the vapor deposition time is 0.5~5h.

[0012] Preferably, in step S2, the acid used for pickling is one of hydrochloric acid, sulfuric acid, nitric acid, and acetic acid, and the concentration of the acid is 0.1~5 mol / L; the pickling time is 0.5~8 h.

[0013] Preferably, in step S2, the drying is vacuum drying, the drying temperature is 40~100℃, and the drying time is 1~12h.

[0014] Secondly, the present invention provides a Ga-NC catalyst, which is prepared by the aforementioned preparation method.

[0015] Thirdly, the Ga-NC catalyst provided by this invention is used in fuel cells, metal-air batteries, and the degradation of water pollutants.

[0016] Compared with existing technologies, one or more of the above technical solutions can achieve at least one of the following beneficial effects: In the method of the present invention, after mixing NH4X and Ga2O3, vapor deposition is performed. During the vapor deposition process, NH4X slowly decomposes into NH3 and HX. HX reacts in situ with Ga2O3 to generate GaX3, and ammonia reacts with the carbon support to generate N doping on the carbon support. The volatilized GaX3 travels downstream with the carrier gas and reacts with the N-doped carbon support to generate uniform Ga-N active sites in situ on the surface of the carbon support. This method can significantly improve the dispersion of Ga atoms and the nitrogen doping efficiency, and the prepared Ga-NC catalyst has excellent conductivity and high ORR catalytic performance. In addition, Ga-NC in the present invention has strong acid corrosion resistance. Impurities that are not Ga-N active sites can be removed by acid washing, avoiding the presence of impurities affecting the catalytic activity of Ga-NC. Attached Figure Description

[0017] Figure 1 is a schematic diagram of the principle of vapor deposition in the preparation method of the present invention.

[0018] Figure 2 is a scanning electron microscope image of the Ga-NC catalyst prepared in Example 1.

[0019] Figure 3 shows the X-ray diffraction patterns of the catalytic materials prepared in Example 1 and Comparative Example 1.

[0020] Figure 4 is a voltammetric curve of the Ga-NC catalyst prepared by Example 1 of the present invention.

[0021] Figure 5 shows the HO2 calculated in Figure 4 for the Ga-NC catalyst prepared according to Example 1 of the present invention. - The graph shows the change in the number of transferred electrons as a function of potential.

[0022] Figure 6 shows the voltammetric curves of the Ga-NC catalysts prepared in Examples 2-4.

[0023] Figure 7 shows the HO2 calculated in Figure 6 for the Ga-NC catalysts prepared in Examples 2-4. - The graph shows the change in the number of transferred electrons as a function of potential.

[0024] Figure 8 shows the voltammetric curves of the Ga-NC catalyst prepared in Examples 3-3.

[0025] Figure 9 shows the HO2 calculated in Figure 8 for the Ga-NC catalyst prepared in Examples 3-3. - The graph shows the change in the number of transferred electrons as a function of potential.

[0026] Figure 10 shows the voltammetric curve of the Ga-NC catalyst prepared in Example 4.

[0027] Figure 11 shows the HO2 of the Ga-NC catalyst prepared in Example 4 as calculated in Figure 10. - The graph shows the change in the number of transferred electrons as a function of potential.

[0028] Figure 12 shows the change in pollutant residue over time when the catalysts prepared in Example 1 and Comparative Example 1 degrade the organic pollutant Rhodamine B in situ. Detailed Implementation

[0029] To facilitate understanding of the present invention, it will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments. However, the scope of protection of the present invention is not limited to the specific embodiments described below. Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention.

[0030] As mentioned above, in a first aspect, the present invention provides a method for preparing a Ga-NC catalyst, comprising the following steps: S1: mixing gallium oxide and ammonium halide salt to obtain a mixed powder; placing the mixed powder in a ceramic boat and placing it upstream of a tube furnace; placing a carbon support in the ceramic boat and placing it downstream of the tube furnace; introducing a carrier gas into the tube furnace, then heating it to a set temperature and performing vapor phase deposition to obtain a crude product; S2: acid washing the crude product, followed by washing and drying to obtain the Ga-NC catalyst.

[0031] In the method of this invention, the thermal decomposition of NH4X to produce NH3 can dope nitrogen onto the carbon support. Simultaneously, the HX gas produced during decomposition can react with Ga2O3 to generate volatile GaX3, achieving co-deposition of gallium and nitrogen and forming a Ga-NC structure. A schematic diagram of the reaction apparatus is shown in Figure 1. The reaction process in the upstream region of Figure 1 is as follows: The reaction occurring in the upstream ceramic boat includes: In the equation, X represents one or more of chlorine, bromine, and iodine.

[0032] The downstream ceramic ark undergoes the following reactions: HX etches the carbon support, NH3, as a nitrogen source, reacts with the carbon support to generate the NC support, and GaX3 further reacts with the NC support to generate the Ga-NC structure.

[0033] The method of this invention uses the in-situ release of hydrogen halide gas through the thermal decomposition of ammonium salts, replacing the traditional process route of directly introducing halogenated hydrocarbons or adding external hydrogen halide. Since hydrogen halide gas is highly corrosive and environmentally hazardous, it easily causes severe corrosion to pipelines and equipment, and poses a high risk of environmental emissions. This invention, however, generates hydrogen halide slowly and controllably through the thermal decomposition of solid ammonium salts, and most of the generated hydrogen halide is absorbed and reacted by gallium oxide, resulting in a low content within the furnace. This not only significantly reduces corrosion of equipment and pipelines but also reduces the emission of harmful gases, significantly improving the safety and environmental friendliness of the process.

[0034] The method of this invention achieves in-situ reaction of ammonium salt and gallium oxide during the reaction process, combined with chemical vapor deposition, avoiding the cumbersome multi-step process of traditional impregnation-drying-calcination. This saves the steps of impregnation, solvent recovery, and drying, significantly shortening production time and process. Simultaneously, the in-situ reaction releases nitrogen-containing substances, enabling the simultaneous vapor deposition of gallium and nitrogen-containing components. Due to the excellent diffusion and coverage characteristics of vapor deposition, the active components can be more uniformly distributed on the surface of the support and the inner walls of the pores, solving the problems of agglomeration and uneven distribution that easily occur in traditional impregnation methods, thereby obtaining higher catalyst utilization and better catalytic performance.

[0035] The method of the present invention can prepare a Ga-NC catalyst with high catalytic activity in one step. The process is simple, environmentally friendly, and low in cost.

[0036] Preferably, in step S1, the ammonium halide salt is one or more of ammonium chloride, ammonium bromide, and ammonium iodide.

[0037] Preferably, in step S1, the carbon support is activated carbon.

[0038] Preferably, in step S1, the mass ratio of gallium oxide to ammonium halide is 1:(1~10), more preferably 1:(1.3~3), including but not limited to: 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, etc.; the mass ratio of gallium oxide to carbon support is 1:(0.1~10), including but not limited to: 1:0.1, 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, etc.

[0039] Preferably, in step S1, the carrier gas is one or two of nitrogen, argon, carbon monoxide, and hydrogen.

[0040] Preferably, in step S1, the flow rate of the carrier gas is (0.01~1) L / min, including but not limited to: 0.01L / min, 0.1L / min, 0.2L / min, 0.3L / min, 0.4L / min, 0.5L / min, 0.6L / min, 0.7L / min, 0.8L / min, 0.9L / min, 1L / min, etc.

[0041] Preferably, in step S1, the heating rate is 1~10℃ / min, including but not limited to: 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, etc.; the set temperature is 300~800℃, more preferably 550~750℃, including but not limited to: 300℃, 400℃, 500℃, 600℃, 700℃, 800℃, etc.; the vapor deposition time is 0.5~5h, including but not limited to: 0.5h, 1h, 2h, 3h, 4h, 5h, etc.

[0042] Preferably, in step S2, the acid used for pickling is one of hydrochloric acid, sulfuric acid, nitric acid, and acetic acid, and the concentration of the acid is 0.1~5 mol / L, including but not limited to: 0.1 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, etc.; the pickling time is 0.5~8h, including but not limited to: 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, etc.; the pickling temperature is 20~100℃, including but not limited to: 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, etc.

[0043] Preferably, in step S2, the drying is vacuum drying, and the drying temperature is 40~100℃, including but not limited to: 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, etc.; the drying time is 1~12h, including but not limited to: 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, etc.

[0044] Secondly, the present invention provides a Ga-NC catalyst, which is prepared by the aforementioned preparation method.

[0045] Thirdly, the Ga-NC catalyst provided by this invention is used in fuel cells, metal-air batteries, and the degradation of water pollutants.

[0046] The Ga-NC catalyst prepared in this invention not only enables the three-electron reduction pathway of the oxygen reduction reaction to generate active intermediates with strong oxidizing capabilities, but also directly acts on the organic pollutant Rhodamine B, achieving efficient in-situ degradation with over 95% degradation within 30 minutes. This function overcomes the limitations of traditional oxygen reduction reactions, which primarily utilize a four-electron pathway and are difficult to directly apply to pollutant degradation. It provides new possibilities for combining fuel cell catalysts and environmental catalysts, possessing dual value in energy conversion and environmental remediation.

[0047] In Example 1, 300 mg Ga2O3 and 800 mg NH4Cl were thoroughly ground to obtain a mixed powder. The mixed powder was placed in a ceramic boat and positioned upstream of a tube furnace as shown in Figure 1. 90 mg activated carbon was placed in the ceramic boat and positioned downstream of the tube furnace as shown in Figure 1. Nitrogen gas was introduced into the tube furnace at a rate of 0.6 L / min for 30 min to purge the furnace. The nitrogen flow rate was then adjusted to 0.1 L / min, and the temperature was raised to 650 °C and held for 30 min (heating rate of 5 °C / min) for gallium chemical vapor deposition to obtain a crude product. The crude product was placed in a 1 M HCl solution and acid-washed at 60 °C for 6 h. The acid-washed sample was then centrifuged and washed with deionized water until the conductivity of the supernatant was <2 µS / cm. Finally, it was vacuum-dried at 50 °C for 8 h to obtain the Ga-NC catalyst material.

[0048] The SEM image of the Ga-NC catalyst prepared in this embodiment is shown in Figure 2. It can be seen that the Ga-NC catalyst maintains the original morphology of the activated carbon support, and no nanoparticles were observed.

[0049] In Comparative Example 1, 800 mg of NH4Cl was placed in a ceramic boat and positioned upstream of a tube furnace as shown in Figure 1; 90 mg of activated carbon was placed in a ceramic boat and positioned downstream of the tube furnace as shown in Figure 1; nitrogen gas was introduced into the tube furnace at a flow rate of 0.6 L / min for 30 min to purge, then the flow rate was adjusted to 0.1 L / min, and the temperature was raised to 650 °C and held for 30 min at a heating rate of 5 °C / min. Subsequently, the deposited product was placed in a 1 M HCl solution and acid-washed at 60 °C for 6 h. The acid-washed sample was then centrifuged and washed with deionized water until the conductivity of the supernatant was <2 µS / cm. Finally, the acid-washed sample was vacuum-dried at 50 °C for 8 h to obtain the NC catalyst material.

[0050] The XRD patterns of the Ga-NC catalyst in Example 1 and the NC catalyst in Comparative Example 1 are shown in Figure 3. It can be seen that the XRD curve of the NC catalyst prepared in Comparative Example 1 has a narrower 26° carbon peak compared with that of the Ga-NC catalyst prepared in Example 1, indicating that Ga doping leads to local disordering of the carbon layer.

[0051] In Comparative Example 2, activated carbon and urea were mixed evenly at a mass ratio of 1:5. Water was then added, and the mixture was magnetically stirred at room temperature for 6 hours to ensure complete dissolution of the urea and thorough wetting of the carbon support. Subsequently, the solvent was evaporated under reduced pressure at 80°C to obtain a urea-loaded precursor. The obtained urea-loaded precursor was placed in a quartz boat, and the magnetic boat was placed in a tube furnace. Under a nitrogen atmosphere (flow rate of 0.1 L / min), the temperature was increased to 800°C at a rate of 5°C / min and held for 2 hours. The mixture was then allowed to cool naturally to room temperature to obtain a nitrogen-doped carbon support (denoted as NC).

[0052] 40 mg of Ga(NO3)3·9H2O was dissolved in 4 mL of a 1:1 mixture of deionized water and ethanol. The solution was sonicated for 10 min to obtain a gallium salt solution. The gallium salt solution was slowly added dropwise to an NC support (NC support to gallium salt solution mass-to-volume ratio of 1 g / 5 mL) using an equal-volume impregnation method, and stirred thoroughly until the solution just completely wetted the carbon support, resulting in an impregnated sample. The impregnated sample was dried in a vacuum drying oven at 60 °C for 12 h to obtain a dried sample. The dried sample was placed in a quartz boat, which was then placed in a tube furnace. The temperature was increased to 750 °C at a rate of 5 °C / min under a nitrogen atmosphere (100 mL / min) and held for 2 h. The sample was then allowed to cool naturally to room temperature to obtain the crude product. The crude product was placed in a 1M HCl solution and acid-washed at 60℃ for 6 hours. It was then repeatedly washed with deionized water until the conductivity of the supernatant was <2µS / cm. Finally, it was vacuum-dried at 50℃ for 8 hours to obtain the Ga-NC catalyst material.

[0053] The preparation methods of Example 2 and Example 1 are basically the same, except that the chemical vapor deposition temperature is different; specifically as follows: Example 2-1 The chemical vapor deposition temperature is 350℃.

[0054] Example 2-2: The chemical vapor deposition temperature was 450°C.

[0055] Examples 2-3: Chemical vapor deposition temperature was 550°C.

[0056] Examples 2-4: Chemical vapor deposition temperature was 750°C.

[0057] The preparation methods of Example 3 and Example 1 are basically the same, except that the mass ratio of Ga2O3 and NH4Cl is different.

[0058] Example 3-1: 300 mg Ga2O3 and 400 mg NH4Cl.

[0059] Example 3-2: 300 mg Ga2O3 and 1200 mg NH4Cl.

[0060] Example 4 is basically the same as Example 1, except that the subsequent pickling step is not performed.

[0061] In Example 5, 300 mg Ga2O3 and 800 mg NH4Br were thoroughly ground to obtain a mixed powder. The mixed powder was placed in a ceramic boat and positioned upstream of a tube furnace as shown in Figure 1. 60 mg activated carbon was placed in the ceramic boat and positioned downstream of the tube furnace as shown in Figure 1. Nitrogen gas was introduced into the tube furnace at a rate of 0.6 L / min for 30 min to purge the furnace. The flow rate was then adjusted to 0.05 L / min, and the temperature was raised to 500 °C and held for 3 h (heating rate of 1 °C / min) for gallium chemical vapor deposition to obtain a crude product. The crude product was placed in a 3 M HCl solution and acid-washed at 20 °C for 8 h. The acid-washed sample was then centrifuged and washed with deionized water until the conductivity of the supernatant was <2 µS / cm. Finally, the sample was vacuum-dried at 100 °C for 1 h to obtain the Ga-NC catalyst material.

[0062] In Example 6, 300 mg Ga2O3 and 900 mg NH4I were thoroughly ground to obtain a mixed powder. The mixed powder was placed in a ceramic boat and positioned upstream of a tube furnace as shown in Figure 1. 300 mg activated carbon was placed in the ceramic boat and positioned downstream of the tube furnace as shown in Figure 1. Argon gas at a flow rate of 0.6 L / min was introduced into the tube furnace for purging for 30 min, then the flow rate was adjusted to 0.2 L / min, and the temperature was raised to 800 °C and held for 1 h (heating rate of 3 °C / min) for gallium chemical vapor deposition to obtain a crude product. The crude product was placed in a 0.5 M HCl solution and acid-washed at 80 °C for 2 h. Then, the acid-washed sample was centrifuged and washed with deionized water until the conductivity of the supernatant was <2 µS / cm. Finally, it was vacuum-dried at 40 °C for 12 h to obtain the Ga-NC catalyst material.

[0063] XPS tests were performed on Examples 1, 2-4, 3-2, 4, and Comparative Example 1. The test results are shown in Table 1. It can be seen that the proportions of Ga and N elements in Example 1 are 0.13 at.% and 5.63 at.%, respectively. Gallium and nitrogen were also detected in Examples 2-4 and 3-2, indicating that Ga was successfully incorporated into the NC framework. No doping was performed in Comparative Example 1, and no Ga element was detected.

[0064] Table 1 RRDE electrochemical performance testing: The catalysts of Examples 1-6 and Comparative Examples 1-2 were prepared into catalyst slurries with a concentration of 5 mg / mL, and then subjected to a reaction at a concentration of 50 µg / cm³. 2 The loading capacity was achieved by spin-coating the catalyst onto an area of ​​0.196 cm². 2 On a rotating ring-disc electrode, the electrode was rotated at 1600 rpm and its disk current and ring current were tested in 0.1 M KOH solution. The changes in oxygen reduction selectivity and the number of transferred electrons with potential were calculated and plotted.

[0065] The calcination temperatures corresponding to Examples 2-1, 2-2, 2-3, 1, and 2-4 are 350℃, 450℃, 550℃, 650℃, and 750℃, respectively. As can be seen from Table 2 and Figures 4-7, the higher the calcination temperature, the higher the oxygen reduction initiation potential of the catalyst. In Examples 2-1 and 2-2, the calcination temperatures are relatively low, resulting in lower oxygen reduction initiation potentials for the corresponding catalysts, and these potentials are lower than those at 0.2V HO2. - The selectivity is relatively high and deviates significantly from 50%, with the electron transfer number biased towards 2e. - Path (n≈2.4 or n≈2.6); In Examples 2-3, with further increases in temperature compared to Example 1, the oxygen reduction onset potential of the catalyst increases compared to Example 2-2, and at 0.2V HO2 - Selectivity is moderate and closer to 50%, with the electron transfer number biased towards 3e. - Path (n≈2.8 or n≈3.1); In Examples 2-4, the temperature is further increased compared to Example 1, and the oxygen reduction initiation potential of the corresponding catalyst will further increase, but at 0.2V, HO2 - Selectivity is high and deviates significantly from 50%, with the electron transfer number biased towards 3e. - Path (n≈2.8). Overall, controlling the calcination temperature between 550 and 750℃ yields Ga-NC catalysts with superior performance.

[0066] The corresponding amounts of NH4Cl added in Examples 3-1, 1, and 3-2 were 400 mg, 800 mg, and 1200 mg, respectively. As can be seen from Table 2, Figures 3-4, and Figures 8-9, the variation of NH4Cl dosage from 400 mg, 800 mg to 1200 mg exhibits a clear volcanic-like pattern in the ORR performance of the final product: In Example 3-1, when the amount of NH4Cl was too small (e.g., 400 mg), GaCl... x Insufficient volatile matter generation leads to a lower actual Ga loading, lower active site density, and a lower ORR onset potential (approximately 0.8V). HO2 - High selectivity (62%), significant 50% offset, and electron transfer number biased towards 3e. - Path (n≈2.8); In Example 1, as NH4Cl increased to 800 mg, the Ga transfer efficiency reached its optimum, Ga-N x The number and quality of single-atom sites are optimal, and the ORR onset potential is increased (by approximately 0.84 V). HO2 - Selectivity is moderate and close to 50%, with the electron transfer number biased towards 3e. - Path (n≈3.1), and 3e -The pathway tendency is strongest; however, in Example 3-2, when NH4Cl is further increased to 1200 mg, the excess HCl causes the carbon support to be over-etched, resulting in decreased activity (initial potential approximately 0.82 V), HO2 - High selectivity (78%), electron transfer number biased towards 2e - The path is (n≈2.4). Therefore, 800mg is the optimal amount of NH4Cl for this system.

[0067] The difference between Example 4 and Example 1 is that no acid washing treatment was performed. As can be seen from Table 2 and Figures 10-11, the oxygen reduction initiation potential in Example 4 is 0.75V, and the HO2... - The selectivity is relatively high (70%), deviating significantly from 50%, and the electron transfer number is biased towards 2e. - The path (n≈2.6) may be because acid washing can effectively remove impurities and prevent them from affecting the activity of the Ga-NC catalyst.

[0068] In Examples 5 and 6, the process parameters were adjusted to correspond to the oxygen reduction onset potential (HO2) of the prepared Ga-NC catalyst. - Both selectivity and electron transfer number n fluctuate to some extent.

[0069] In Comparative Example 1, no Ga deposition was performed, resulting in a lower oxygen reduction onset potential for the NC catalyst and HO2. - It exhibits high selectivity and a bias towards 2e electrons. - Path. The Ga-NC catalyst prepared by the impregnation method in Comparative Example 2 has a higher oxygen reduction onset potential and HO2. - It has low selectivity and the electron transfer number is biased towards 4e. - path.

[0070] Table 2 Catalytic degradation of organic compound Rhodamine B: The catalytic materials of Example 1 and Comparative Example 1 were prepared into a catalytic slurry with a concentration of 5 mg / mL, and the catalytic concentration was 400 µg / cm³. 2 The catalyst loading was sprayed onto a hydrophobic carbon paper measuring 2cm × 2.5cm (actual reaction area 2cm × 2cm), ensuring thorough drying after spraying and no peeling or cracking of the catalyst layer. The catalyst-loaded carbon paper was placed in a flow reaction tank with a 50ppm Rhodamine B acidic solution as the electrolyte, a flow rate of 20mL / min, an oxygen flow rate of 50sccm (standard cubic centimeters per minute), and an applied potential of 0.2V vs. RHE to evaluate the Rhodamine B degradation performance of the catalyst.

[0071] The degradation ability of Ga-NC catalyst for the organic pollutant Rhodamine B is shown in Table 2 and Figure 12. It can be seen that the Ga-NC catalyst in Example 1 can achieve a degradation rate of up to 96% within 30 minutes. In Examples 2-1, 2-2, 2-3, 1, and 2-4, the calcination temperatures were 350℃, 450℃, 550℃, 650℃, and 750℃, respectively. As the preparation calcination temperature increased, the degradation ability of the corresponding catalyst for Rhodamine B first increased and then decreased. The catalytic degradation effect was better when the calcination temperature was in the range of 550~750℃.

[0072] In Examples 3-1, 1, and 3-2, the corresponding amounts of NH4Cl added were 400 mg, 800 mg, and 1200 mg, respectively; the degradation ability of the corresponding catalysts for Rhodamine B first increased and then decreased.

[0073] The difference between Example 4 and Example 1 is that no acid washing treatment was performed. The catalyst prepared in Example 4 showed a slight decrease in the catalytic degradation ability of Rhodamine B compared with Example 1. This may be because acid washing can effectively remove impurities, thereby improving the catalytic activity of the Ga-NC catalyst.

[0074] The process parameters for preparation in Examples 5 and 6 were adjusted, and the catalytic degradation ability of the corresponding Ga-NC catalysts for Rhodamine B fluctuated to some extent, but both showed good catalytic effects.

[0075] The catalyst without Ga deposition in Comparative Example 1 showed poor catalytic degradation of Rhodamine B, which indirectly confirms that Ga is the catalytically active site. The Ga-NC catalyst prepared by impregnation in Comparative Example 2 also showed poor degradation of Rhodamine B due to its tendency to follow the 4e- transfer pathway.

[0076] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a Ga-NC catalyst, characterized in that, Includes the following steps: S1: Gallium oxide and ammonium halide salt are mixed to obtain a mixed powder; the mixed powder is placed in a ceramic boat and positioned upstream of a tube furnace; a carbon support is placed in the ceramic boat and positioned downstream of the tube furnace; a carrier gas is introduced into the tube furnace, and then the temperature is raised to a set temperature for vapor deposition to obtain a crude product; S2: The crude product is acid-washed, washed, and dried to obtain a Ga-NC catalyst.

2. The method for preparing the Ga-NC catalyst according to claim 1, characterized in that, In step S1, the ammonium halide salt is one or more of ammonium chloride, ammonium bromide and ammonium iodide; and / or: the carbon support is activated carbon; and / or: the carrier gas is one or two of nitrogen, argon, carbon monoxide and hydrogen; and / or: the flow rate of the carrier gas is (0.01~1) L / min.

3. The method for preparing the Ga-NC catalyst according to claim 1, characterized in that, In step S1, the mass ratio of gallium oxide to ammonium halide is 1:(1~10); the mass ratio of gallium oxide to carbon support is 1:(0.1~10).

4. The method for preparing the Ga-NC catalyst according to claim 3, characterized in that, The mass ratio of gallium oxide to ammonium halide is 1:(1.3~3).

5. The method for preparing the Ga-NC catalyst according to claim 1, characterized in that, In step S1, the heating rate is 1~10℃ / min, the set temperature is 300~800℃, and the vapor deposition time is 0.5~5h.

6. The method for preparing the Ga-NC catalyst according to claim 5, characterized in that, The set temperature is 550~750℃.

7. The method for preparing the Ga-NC catalyst according to claim 1, characterized in that, In step S2, the acid used for pickling is one of hydrochloric acid, sulfuric acid, nitric acid, and acetic acid, with an acid concentration of 0.1~5 mol / L; the pickling time is 0.5~8 h.

8. The method for preparing the Ga-NC catalyst according to claim 1, characterized in that, In step S2, the drying is vacuum drying, the drying temperature is 40~100℃, and the drying time is 1~12h.

9. A Ga-NC catalyst, characterized in that, It is prepared by any of the preparation methods described in claims 1 to 8.

10. The application of the Ga-NC catalyst according to claim 8 in fuel cells, metal-air batteries, and degradation of water pollutants.

Images