Preparation method of a fuel cell catalyst with ultra-low platinum loading

Abstract

The present invention provides a method for preparing an ultra-low platinum loading fuel cell catalyst. This method first prepares a nitrogen-doped carbon support loaded with single-atom transition non-precious metals, then reduces ultra-small high-entropy alloy nanoparticles by microwave ethylene glycol and loads them on the support, and then anneals in a reducing atmosphere. After natural cooling, the powder is collected to obtain the ultra-low platinum loading fuel cell catalyst. Through the synergistic effect of ultra-small high-entropy alloy nanoparticles and single-atom transition non-precious metals, the present invention greatly reduces the platinum loading while maintaining high-efficiency oxygen reduction performance and stability, and to a certain extent solves the high-cost problem of fuel cell catalysts caused by low platinum utilization rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel cells, and particularly relates to a method for preparing a fuel cell catalyst with an ultra-low platinum loading through synergistic effects. Background Art

[0002] Platinum is considered the most active element in the energy conversion during the oxygen reduction reaction. However, the high loading of platinum in fuel cell catalysts results in too high costs of fuel cells, thus limiting the development of fuel cells. Therefore, the development of electrocatalysts with ultra-low platinum loadings is crucial for proton exchange membrane fuel cells. Currently, the main methods for reducing the use of platinum are to replace platinum-based catalysts with transition metal single atoms and to alloy platinum with transition metals. Due to the low selectivity of non-noble metal single atom catalysts and the problems of atomization limitation of particles and low stability caused by too low platinum loadings in intermetallic compounds, these are several major problems currently faced.

[0003] Some preparation methods of ultra-low platinum loading catalysts have been previously reported. Although the platinum loading has been greatly reduced to a certain extent, their oxygen reduction performance is low. For example, in a method for preparing an ultra-low platinum fuel cell catalyst and the catalyst (CN115133051A), the platinum loading is reduced to about 5% - 10%, but its half-wave potential is only about 0.83V. Subsequently, some preparation methods of catalysts with better oxygen reduction performance have been reported, but their platinum loadings are still high. For example, in a method for preparing and applying low-platinum high-entropy alloy nanoparticles (CN 115570143 A), although its half-wave potential reaches 0.91V, its platinum loading reaches more than 20%. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the present invention provides a method for preparing a fuel cell catalyst with good oxygen reduction performance and ultra-low platinum loading. Through the synergistic effects of ultra-small high-entropy alloy nanoparticles and transition non-noble metal single atoms, while improving the stability of the catalyst, the platinum loading is greatly reduced to solve the problems of too high costs and low stability of fuel cell catalysts.

[0005] The method for preparing the fuel cell catalyst with ultra-low platinum loading provided by the present invention includes the following steps:

[0006] 1. Dissolve aniline in hydrochloric acid, add any one of transition non-noble metal salts, stir to uniformly mix the non-noble metal salts, then add ammonium persulfate, continue to stir evenly, add carbon black, stir to uniformly mix the carbon black with the solution, then heat the solution to 80 - 90°C, reflux for 4 - 6 hours, and then dry. After drying, collect the powder, and then anneal at 600 - 900°C under nitrogen protection. After natural cooling, a nitrogen-doped carbon support loaded with single-atom transition non-noble metals is obtained.

[0007] 2. Ultrasonically disperse the nitrogen-doped carbon support loaded with single-atom transition non-noble metals in a mixed solution of ethylene glycol and isopropanol. Then add platinum salt and any four transition non-noble metal salts, and stir under the protection of inert gas to uniformly disperse the platinum salt and transition non-noble metal salts therein. Add sodium hydroxide to the dispersed solution to adjust the pH of the solution to 9 - 11, and then heat it to 160 - 180 °C in a microwave oven. Then naturally cool the solution to room temperature, add nitric acid to adjust the pH of the solution to 1 - 3, then wash with deionized water, filter by suction, dry, and finally anneal at 600 - 900 °C in a reducing atmosphere. After natural cooling, collect the powder to obtain an ultra-low platinum-loading fuel cell catalyst, the particle size of which is about 2 - 5 nm; based on the mass of the catalyst being 100%, the loading amount of the transition non-noble metal in the ultra-low platinum-loading fuel cell catalyst is 5% - 7.5%, and the loading amount of platinum is 2.5% - 4.5%.

[0008] In the above step 1, preferably, the mass ratio of the transition non-noble metal salt to carbon black is 1 - 2:1.

[0009] In the above step 1, the transition non-noble metal salt is selected from any one of ferric chloride, cobalt chloride, nickel chloride, manganese chloride, copper chloride, molybdenum chloride, zirconium chloride, titanium chloride, niobium chloride, chromium chloride, etc.

[0010] In the above step 1, it is further preferred to anneal at 900 °C for 2 hours under nitrogen protection.

[0011] In the above step 2, the transition non-noble metal salts are selected from any four of cobalt chloride, manganese chloride, zinc chloride, nickel chloride, ferric chloride, copper chloride, and zirconium nitrate, and the mass ratio of the four transition non-noble metal salts is 1 - 2:1 - 2:1 - 2:1 - 2.

[0012] In the above step 2, it is further preferred to anneal at 700 °C for 2 hours in a reducing atmosphere.

[0013] In the above steps 1 and 2, it is further preferred that the heating rate of annealing is 3 - 8 °C / min.

[0014] In the above step 2, the reducing atmosphere is a mixed gas of hydrogen and argon, in which the volume fraction of hydrogen is 5% - 10%.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] The present invention first prepares a nitrogen-doped carbon support loaded with single-atom transition non-noble metals by providing nitrogen coordination with aniline and carrying out a reflux reaction at high temperature. This support is beneficial for providing more active sites and improving stability. Then, platinum salt and any four transition non-noble metal salts are reduced by the microwave ethylene glycol method using the nitrogen-doped carbon loaded with single-atom transition non-noble metals as the support, and ultra-small nanoparticles are loaded on the nitrogen-doped carbon support to prepare an ultra-low platinum loading fuel cell catalyst. This catalyst, through the synergistic effect of single atoms and ultra-small high-entropy alloy nanoparticles, can not only increase the number of active sites and improve the catalyst activity, but also reduce the platinum loading to a certain extent. Moreover, the present invention further improves the stability of the catalyst through a high-temperature annealing method. Through the synergistic effect of non-noble metal single atoms and ultra-small high-entropy alloy nanoparticles, the platinum loading is greatly reduced (the platinum loading is 2.5% - 4.5%), while its oxygen reduction performance is still very high (the half-wave potential is 0.97V), and high efficiency and stability are maintained (the half-wave potential remains basically unchanged after 30,000 cycles). To a certain extent, the problems of high platinum usage and low stability faced in current fuel cell catalysts are solved. It has a great technological breakthrough. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the XRD pattern of the nitrogen-doped carbon support loaded with single-atom iron in Example 1.

[0018] Figure 2 It is the aberration-corrected HAADF-STEM image of the nitrogen-doped carbon support loaded with single-atom iron in Example 1.

[0019] Figure 3 It is the XRD pattern of the ultra-low platinum loading fuel cell catalyst prepared in Example 1.

[0020] Figure 4 It is the TEM image of the ultra-low platinum loading fuel cell catalyst prepared in Example 1.

[0021] Figure 5 It is the LSV curve of the ultra-low platinum loading fuel cell catalyst prepared in Example 1.

[0022] Figure 6 It is the stability test of the ultra-low platinum loading fuel cell catalyst prepared in Example 1 before and after the reaction. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0024] Example 1

[0025] 1. Dissolve 5 mL of aniline in 200 mL of 0.5 mol / L hydrochloric acid solution, then add 0.6 g of ferric chloride to the solution and stir. After the ferric chloride is evenly mixed, add 3.2 g of ammonium persulfate, continue to stir evenly, then add 0.5 g of carbon black to the solution, stir for 12 hours, then heat the solution to 85 °C, reflux for 5 hours, then dry the solution at 80 °C, collect the powder after drying, and then heat it to 900 °C at a heating rate of 5 °C / min under nitrogen protection, and anneal at a constant temperature for 2 hours. After natural cooling, a nitrogen-doped carbon support loaded with single-atom iron is obtained. By Figure 1 and Figure 2 it can be seen that the iron in the nitrogen-doped carbon support appears in the form of single atoms.

[0026] 2. Disperse 100 mg of the nitrogen-doped carbon support loaded with single-atom iron in a mixed solution of 100 mL of ethylene glycol and isopropyl alcohol with a volume ratio of 4:1 and sonicate for 3 hours. Then add 20 mg of cobalt chloride hexahydrate, 20 mg of nickel chloride hexahydrate, 15 mg of ferric chloride, 25 mg of copper chloride, and 25 mg of platinum chloride hexahydrate, and stir for 2 hours. During the stirring process, continuously introduce N2 to evenly disperse the metal salts in the solution; add sodium hydroxide to the dispersed solution to adjust the pH to 10, then heat the solution to 160 °C in a microwave oven, then naturally cool the solution to room temperature, add nitric acid to adjust the pH to 1, then wash with 2 L of deionized water, filter by suction, dry, and finally heat it to 700 °C at a heating rate of 5 °C / min in a reducing atmosphere (5% H2 / 95% Ar, V / V), and anneal at a constant temperature for 2 hours. After annealing, naturally cool and collect the powder to obtain an ultra-low platinum loading fuel cell catalyst (HENS-Fe / C-700). Based on the mass of the catalyst being 100%, the platinum loading in this catalyst is 3.0%, the loading of transition non-noble metals is 5.8%, and the particle size of the catalyst is between 2 and 3 nm. And Figure 3 and Figure 4 it can be seen that there are very small nanoparticles on the surface of the catalyst. Therefore, the high-efficiency oxygen reduction performance of this catalyst is triggered by the combined action of non-noble metal single atoms and ultra-small high-entropy alloy nanoparticles. Figure 5 The LSV curve was measured in 0.1 M perchloric acid. It can be seen that the half-wave potential is 0.97 V, which proves that the catalyst has high-efficiency oxygen reduction performance. Figure 6 The stability test of the catalyst was carried out. It can be seen that the half-wave potential of the catalyst remains basically unchanged after 30,000 cycles, which proves that the catalyst has high stability.

[0027] In step 2 of Example 1 above, the annealing temperature was adjusted to 600 °C, 800 °C, and 900 °C respectively for annealing, and the obtained catalysts were labeled as HENS-Fe / C-600, HENS-Fe / C-800, and HENS-Fe / C-900 respectively.

[0028] The above catalysts were respectively tested for their half-wave potentials, and the test results are shown in Table 1.

[0029] Table 1 Comparison of the half-wave potentials of the catalysts prepared at different annealing temperatures

[0030] catalyst <![CDATA[E 1 / 2 (V)]]> test solution HENS-Fe / C-600 0.94 <![CDATA[0.1M HCLO4]]> HENS-Fe / C-700 0.97 <![CDATA[0.1M HCLO4]]> HENS-Fe / C-800 0.95 <![CDATA[0.1M HCLO4]]> HENS-Fe / C-900 0.93 <![CDATA[0.1M HCLO4]]>

[0031] As can be seen from Table 1, the catalysts annealed at 600 - 900 °C all have relatively high half-wave potentials. Among them, the catalyst annealed at 700 °C has a more positive half-wave potential, showing better oxygen reduction performance. This is attributed to the fact that the alloying of metal elements to form particles requires a certain temperature, but too high a temperature will cause the formed particles to be too large, thereby affecting the activity. Therefore, in step 2 of the following examples, the annealing temperature is 700 °C.

[0032] Example 2

[0033] In step 1 of this example, 0.6 g of cobalt chloride hexahydrate was used to replace ferric chloride in Example 1, and the other steps were the same as those in Example 1, obtaining an ultra-low platinum loading fuel cell catalyst. Based on the mass of the catalyst being 100%, the platinum loading in this catalyst is 3.5%, the loading of transition non-noble metals is 5.4%, and the catalyst particle size is between 2 - 3 nm.

[0034] Example 3

[0035] In step 1 of this example, 0.6 g of nickel chloride hexahydrate was used to replace ferric chloride in Example 1, and the other steps were the same as those in Example 1, obtaining an ultra-low platinum loading fuel cell catalyst. Based on the mass of the catalyst being 100%, the platinum loading in this catalyst is 3.8%, the loading of transition non-noble metals is 5.5%, and the catalyst particle size is between 2 - 3 nm.

[0036] Example 4

[0037] In step 1 of this example, 0.6 g of manganese chloride was used to replace ferric chloride in Example 1, and the other steps were the same as those in Example 1, obtaining an ultra-low platinum loading fuel cell catalyst. Based on the mass of the catalyst being 100%, the platinum loading in this catalyst is 3.0%, the loading of transition non-noble metals is 5.0%, and the catalyst particle size is between 2 - 3 nm.

[0038] Example 5

[0039] In step 1 of this example, 0.6 g of manganese chloride was used to replace ferric chloride in Example 1, and the other steps were the same as those in Example 1, obtaining an ultra-low platinum loading fuel cell catalyst. Based on the mass of the catalyst being 100%, the platinum loading in this catalyst is 4.3%, the loading of transition non-noble metals is 4.5%, and the catalyst particle size is between 2 - 3 nm.

[0040] Example 6

[0041] In step 1 of this example, 0.6 g of copper chloride was used to replace ferric chloride in Example 1, and the other steps were the same as those in Example 1, obtaining an ultra-low platinum loading fuel cell catalyst. Based on the mass of the catalyst being 100%, the platinum loading in this catalyst was 2.5%, the loading of transition non-noble metals was 7.0%, and the catalyst particle size was between 2 and 3 nm.

[0042] Example 7

[0043] In step 1 of this example, 0.65 g of molybdenum chloride was used to replace ferric chloride in Example 1, and the other steps were the same as those in Example 1, obtaining an ultra-low platinum loading fuel cell catalyst. Based on the mass of the catalyst being 100%, the platinum loading in this catalyst was 2.7%, the loading of transition non-noble metals was 6.5%, and the catalyst particle size was between 2 and 3 nm.

[0044] Example 8

[0045] In step 1 of this example, 0.65 g of zirconium chloride was used to replace ferric chloride in Example 1, and the other steps were the same as those in Example 1, obtaining an ultra-low platinum loading fuel cell catalyst. Based on the mass of the catalyst being 100%, the platinum loading in this catalyst was 3.3%, the loading of transition non-noble metals was 6.5%, and the catalyst particle size was between 2 and 3 nm.

[0046] Example 9

[0047] In step 1 of this example, 0.7 g of titanium chloride was used to replace ferric chloride in Example 1, and the other steps were the same as those in Example 1, obtaining an ultra-low platinum loading fuel cell catalyst. Based on the mass of the catalyst being 100%, the platinum loading in this catalyst was 4.5%, the loading of transition non-noble metals was 6.0%, and the catalyst particle size was between 2 and 3 nm.

[0048] Example 10

[0049] In step 1 of this example, 0.7 g of niobium chloride was used to replace ferric chloride in Example 1, and the other steps were the same as those in Example 1, obtaining an ultra-low platinum loading fuel cell catalyst. Based on the mass of the catalyst being 100%, the platinum loading in this catalyst was 2.8%, the loading of transition non-noble metals was 6.4%, and the catalyst particle size was between 2 and 3 nm.

[0050] Example 11

[0051] In step 1 of this example, 0.7 g of chromium chloride was used to replace ferric chloride in Example 1, and the other steps were the same as those in Example 1, obtaining an ultra-low platinum-loading fuel cell catalyst. Based on the mass of the catalyst being 100%, the platinum loading in this catalyst was 3.0%, the loading of transition non-noble metals was 6.0%, and the catalyst particle size was between 2 and 3 nm.

[0052] Example 12

[0053] In step 2 of this example, 100 mg of the nitrogen-doped carbon support loaded with single-atom iron was dispersed in a mixed solution of 100 mL of ethylene glycol and isopropanol with a volume ratio of 4:1 and ultrasonicated for 3 hours. Then, 20 mg of cobalt chloride hexahydrate, 15 mg of manganese chloride, 20 mg of zinc chloride hexahydrate, 15 mg of ferric chloride, and 25 mg of platinum chloride hexahydrate were added and stirred for 2 hours. The other steps were the same as those in Example 1, obtaining an ultra-low platinum-loading fuel cell catalyst. Based on the mass of the catalyst being 100%, the platinum loading in this catalyst was 3.5%, the loading of transition non-noble metals was 5.0%, and the catalyst particle size was between 2 and 4 nm.

[0054] Example 13

[0055] In step 2 of this example, 100 mg of the nitrogen-doped carbon support loaded with single-atom iron was dispersed in a mixed solution of 100 mL of ethylene glycol and isopropanol with a volume ratio of 4:1 and ultrasonicated for 3 hours. Then, 20 mg of cobalt chloride hexahydrate, 15 mg of copper chloride, 20 mg of zinc chloride hexahydrate, 15 mg of ferric chloride, and 25 mg of platinum chloride hexahydrate were added and stirred for 2 hours. The other steps were the same as those in Example 1, obtaining an ultra-low platinum-loading fuel cell catalyst. Based on the mass of the catalyst being 100%, the platinum loading in this catalyst was 3.2%, the loading of transition non-noble metals was 5.2%, and the particle size was between 2 and 5 nm.

[0056] Example 14

[0057] In step 2 of this example, 100 mg of the nitrogen-doped carbon support loaded with single-atom iron was dispersed in a mixed solution of 100 mL of ethylene glycol and isopropanol with a volume ratio of 4:1 and ultrasonicated for 3 hours. Then, 20 mg of cobalt chloride hexahydrate, 15 mg of manganese chloride, 20 mg of zinc chloride hexahydrate, 15 mg of ferric chloride, and 25 mg of platinum chloride hexahydrate were added and stirred for 2 hours. The other steps were the same as those in Example 1, obtaining an ultra-low platinum-loading fuel cell catalyst. Based on the mass of the catalyst being 100%, the platinum loading in this catalyst was 4.0%, the loading of transition non-noble metals was 4.8%, and the catalyst particle size was between 2 and 4 nm.

[0058] Example 15

[0059] In step 2 of this embodiment, 100 mg of the nitrogen-doped carbon support loaded with single-atom iron was dispersed in 100 mL of a mixed solution of ethylene glycol and isopropanol with a volume ratio of 4:1 and ultrasonicated for 3 hours. Then, 30 mg of zirconium nitrate, 15 mg of manganese chloride, 20 mg of zinc chloride hexahydrate, 15 mg of iron chloride, and 25 mg of platinum chloride hexahydrate were added and stirred for 2 hours. Other steps were the same as those in Example 1, and an ultra-low platinum-loading fuel cell catalyst was obtained. Based on the mass of the catalyst being 100%, the platinum loading in this catalyst was 3.5%, the loading of transition non-noble metals was 4.8%, and the catalyst particle size was between 3 and 5 nm.

[0060] The half-wave potential tests were respectively carried out on the catalysts obtained in the above Examples 2 to 15, and the test results are shown in Table 2.

[0061] Table 2 Comparison of the half-wave potentials of the catalysts prepared in Examples 2 to 15:

[0062] catalyst <![CDATA[E 1 / 2 (V)]]> test solution Example 2 0.95 <![CDATA[0.1M HCLO4]]> Example 3 0.95 <![CDATA[0.1M HCLO4]]> Example 4 0.94 <![CDATA[0.1M HCLO4]]> Example 5 0.96 <![CDATA[0.1M HCLO4]]> Example 6 0.94 <![CDATA[0.1M HCLO4]]> Example 7 0.93 <![CDATA[0.1M HCLO4]]> Example 8 0.93 <![CDATA[0.1M HCLO4]]> Example 9 0.95 <![CDATA[0.1M HCLO4]]> Example 10 0.94 <![CDATA[0.1M HCLO4]]> Example 11 0.93 <![CDATA[0.1M HCLO4]]> Example 12 0.95 <![CDATA[0.1M HCLO4]]> Example 13 0.96 <![CDATA[0.1M HCLO4]]> Example 14 0.95 <![CDATA[0.1M HCLO4]]> Example 15 0.95 <![CDATA[0.1M HCLO4]]>

Claims

1. A preparation method of an ultra-low platinum loading fuel cell catalyst, characterized in that, It includes the following steps: (1) Dissolve aniline in hydrochloric acid, add any one of transition non-noble metal salts, stir to make the non-noble metal salts uniformly mixed, then add ammonium persulfate, continue to stir evenly, add carbon black, stir to make the carbon black uniformly mixed with the solution, heat the solution to 80 - 90 °C, reflux for 4 - 6 hours, then dry, collect the powder after drying, and then anneal at 600 - 900 °C under nitrogen protection. After natural cooling, a nitrogen-doped carbon support loaded with single-atom transition non-noble metal is obtained; (2) Ultrasonically disperse the nitrogen-doped carbon support loaded with single-atom transition non-noble metal in a mixed solution of ethylene glycol and isopropyl alcohol, then add platinum salt and any four transition non-noble metal salts, and stir under inert gas protection to make the platinum salt and transition non-noble metal salts uniformly dispersed therein. Add sodium hydroxide to the dispersed solution to adjust the pH of the solution to 9 - 11, then heat to 160 - 180 °C in a microwave oven, then naturally cool the solution to room temperature, add nitric acid to adjust the pH of the solution to 1 - 3, then wash with deionized water, filter by suction, dry, and finally anneal at 600 - 900 °C in a reducing atmosphere. After natural cooling, collect the powder to obtain an ultra-low platinum loading fuel cell catalyst with a particle size of 2 - 5 nm; Based on the mass of the catalyst being 100%, the loading amount of the transition non-noble metal in the ultra-low platinum loading fuel cell catalyst is 4.5% - 7.5%, and the loading amount of platinum is 2.5% - 4.5%.

2. The preparation method of the ultra-low platinum loading fuel cell catalyst according to claim 1, characterized in that, In step (1), the mass ratio of the transition non-noble metal salt to carbon black is 1 - 2:

1.

3. The preparation method of the ultra-low platinum loading fuel cell catalyst according to claim 1 or 2, characterized in that, In step (1), the transition non-noble metal salt is any one of ferric chloride, cobalt chloride, nickel chloride, manganese chloride, copper chloride, molybdenum chloride, zirconium chloride, titanium chloride, niobium chloride, chromium chloride.

4. The preparation method of the ultra-low platinum loading fuel cell catalyst according to claim 1, characterized in that, In step (1), anneal at 900 °C for 2 hours under nitrogen protection.

5. The preparation method of the ultra-low platinum loading fuel cell catalyst according to claim 1, wherein, In step (2), the transition non-noble metal salts are any four of cobalt chloride, manganese chloride, zinc chloride, nickel chloride, ferric chloride, copper chloride, zirconium nitrate.

6. The preparation method of the ultra-low platinum loading fuel cell catalyst according to claim 1 or 5, characterized in that, In step (2), the mass ratio of the four transition non-noble metal salts is 1 - 2:1 - 2:1 - 2:1 - 2.

7. The preparation method of the ultra-low platinum loading fuel cell catalyst according to claim 1, characterized in that, In step (2), anneal at 700 °C for 2 hours in a reducing atmosphere.

8. The preparation method of the ultra-low platinum loading fuel cell catalyst according to claim 1 or 5 or 7, characterized in that, In steps (1) and (2), the heating rate of annealing is 3 - 8 °C / min.

9. The preparation method of the ultra-low platinum loading fuel cell catalyst according to claim 1 or 7, characterized in that, In step (2), the reducing atmosphere is a mixture of hydrogen and argon, in which the volume fraction of hydrogen is 5% - 10%.

Images