PtCu oxygen reduction catalyst with hcp phase ordered structure and preparation method of PtCu oxygen reduction catalyst

Abstract

The invention relates to an hcp phase ordered structure PtCu oxygen reduction catalyst and a preparation method thereof.The preparation method comprises the steps that carbon black and a Cu metal precursor are mixed, and a Cu / C precursor is obtained under the action of a reducing agent; pt and Cu / C are compounded through an impregnation method; the PtCu alloy loaded on the conductive carbon black is ordered through high-temperature gas reduction, and the loaded PtCu intermetallic compound catalyst is obtained. The catalyst nanoparticles prepared by the invention are uniformly distributed on the carbon carrier, the size of the nanoparticles is about 3-5nm, and the alloy structure is an intermetallic compound structure. The preparation process is simple, environment-friendly and suitable for large-scale batch production; the prepared catalyst has high oxygen reduction activity and stability, and can be directly applied to fuel cells.

Description

Technical Field

[0001] The invention belongs to the technical field of platinum-based catalysts for proton exchange membrane fuel cells, and particularly relates to a PtCu oxygen reduction catalyst with an hcp phase ordered structure and a preparation method thereof. Background Art

[0002] At present, the global energy demand is soaring, environmental problems are becoming increasingly prominent, and it is urgent to gradually replace fossil fuels with sustainable clean energy. Proton exchange membrane fuel cells (PEMFCs) are an effective clean energy conversion device with the advantages of high capacity density, no restrictions on the Carnot cycle, and zero pollution emissions. They can be widely used in transportation, stationary power generation, portable power sources and other fields. The anode oxidation reaction of PEMFCs uses hydrogen as fuel, and the cathode undergoes oxygen reduction reaction (ORR). The cathode ORR has a complex reaction mechanism and slow reaction kinetics, making it a key step in restricting the efficiency of fuel cells. The precious metal platinum (Pt) is currently the most effective catalyst, which can greatly improve the reaction kinetics of ORR and increase the reaction rate. However, due to the high price of Pt and its small reserves in the earth's crust, its commercial application is limited.

[0003] Research has found that introducing other transition metals (such as Fe, Co, Ni, Cu, Ag, Zn, etc.) to form a multi-metal Pt-based alloy is one of the effective strategies to reduce the Pt content and improve the catalytic activity. This is due to the synergistic effect of multi-metals and the electronic structure strain effect between different metals, which reduces the adsorption energy of oxygen species by the platinum-based catalyst, thereby improving the catalytic performance for ORR. However, when the transition metal atoms in the alloy are exposed to acidic high potential conditions for a long time, they will segregate and gradually migrate to the crystal surface, dissolve, and cause the collapse of the catalyst structure and changes in the crystal face type, thus causing the catalyst activity to decay sharply.

[0004] Intermetallic compounds are a highly ordered alloy structure formed by multiple metal elements. In platinum-based intermetallic compounds, Pt atoms and other transition metal atoms are arranged in a certain way. The highly ordered structure makes the interaction between metal atoms stronger than that of solid solution alloys, which can prevent other transition metal atoms from segregating to the surface, and thus theoretically has stronger corrosion resistance. The preparation of intermetallic compounds usually requires high-temperature annealing to overcome the interatomic migration energy barrier to achieve reordering. However, during the high-temperature treatment process, the nanoparticles will obviously sinter and then coarsen into larger particles, resulting in a decrease in the utilization rate of platinum atoms and a decrease in the quality and activity of the catalyst. Summary of the invention

[0005] The object of the present invention is to provide a PtCu oxygen reduction catalyst with an ordered structure of an hcp phase and a preparation method thereof, thereby improving the technical problem that the catalytic activity and stability of the catalyst formed by alloying transition metal elements with platinum are not ideal;

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A PtCu oxygen reduction catalyst with an hcp phase ordered structure and a preparation method thereof, comprising the following steps:

[0008] Step 1: Add the copper salt solution to the carrier dispersion under magnetic stirring, stir evenly, adjust the pH value of the solution with sodium hydroxide or ammonia water, and slowly add hydrazine hydrate;

[0009] Step 2: After the reaction of the reaction solution in step 1 is completed, the precipitate is collected by filtration or centrifugation, washed to neutrality, and then the washed precipitate is dried and ground to obtain Cu / C powder;

[0010] Step 3: Disperse the Cu / C powder in chloroform, add platinum acetylacetonate, and heat with magnetic stirring at a temperature of 65-70°C until the chloroform is completely evaporated to obtain a mixture of platinum salt and Cu / C;

[0011] Step 4: placing the platinum salt and Cu / C mixture in a heating furnace for heating, and introducing a reducing gas into the heating furnace to form a PtCu / C intermetallic compound powder;

[0012] Step 5: Disperse the PtCu / C intermetallic compound powder in a mineral acid, stir overnight, then wash with a mixed solution of distilled water and ethanol until neutral, filter or centrifuge to obtain a precipitate, and dry the precipitate overnight to obtain an hcp-PtCu ordered structure catalyst.

[0013] Preferably, in step 1, the carrier dispersion is prepared by dispersing a conductive carbon black carrier in an aqueous solution containing glacial acetic acid to obtain a carrier dispersion; and the concentration of hydrazine hydrate is 6-8%.

[0014] Preferably, the conductive carbon black material is one of VULCAN XC-72R or Ketjen 300.

[0015] Preferably, in step 1, the copper salt solution is any one of copper sulfate, copper nitrate, copper chloride, copper acetate and copper carbonate.

[0016] Preferably, in step 2, drying the washed precipitate comprises the following steps: vacuum drying the washed precipitate for 6 hours, placing it in a tubular furnace, and drying it at 120° C. for 4 hours under an inert gas atmosphere.

[0017] Preferably, in step 3, platinum acetylacetonate is added to obtain a metal precursor, wherein the mass ratio of Pt to Cu in the metal precursor is 3:1, and the stirring speed is 800-900 rpm.

[0018] Preferably, in step 4, the platinum salt and Cu / C mixture are placed in a heating furnace, reducing gas is first introduced into the heating furnace to drive out the air in the furnace, and then the heating furnace is set to have a heating rate of 10°C / min and calcined at 900°C for 1.5h.

[0019] Preferably, in step 4, the reducing gas is a mixture of hydrogen and inert gas, wherein the volume ratio of hydrogen is 10%.

[0020] Preferably, in step 5, the mineral acid is nitric acid.

[0021] Another aspect of the present invention provides a PtCu oxygen reduction catalyst with an hcp phase ordered structure, which is prepared by the preparation method as described above.

[0022] The invention adopts a step-by-step reduction method, firstly prepares a Cu / C precursor at room temperature, then combines Pt with Cu / C by an impregnation method, and finally obtains a Pt-based ordered structure alloy catalyst supported on conductive carbon black through high-temperature gas reduction. The method is simple to operate and has a low operating temperature, and can be used for industrial mass preparation. The carbon black has a large specific surface area, so the nanoparticles will not sinter at high temperatures. The prepared catalyst particles are evenly distributed on the carbon carrier, have a small size, have high ORR catalytic activity, and have strong durability.

[0023] The present invention adopts hydrazine hydrate to reduce copper salt, and hydrazine hydrate has strong reducing property, and copper salt can be reduced at room temperature without heating. In addition, chloroform is adopted to disperse Cu / C, and chloroform has low boiling point and is easy to volatilize, and heating and stirring can make platinum salt uniformly adsorbed on the Cu / C solid surface, and after chloroform is completely volatilized, solid product can be directly obtained without further separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the XRD characterization result of the catalyst prepared in Example 1 of the present invention.

[0025] Figure 2 This is the TEM characterization result of the catalyst prepared in Example 1 of the present invention.

[0026] Figure 3 This is the cyclic voltammetry test result of the catalyst prepared in Example 1 of the present invention in a N2-saturated 0.1M HClO4 electrolyte.

[0027] Figure 4 This is the test result of the polarization curve of the catalyst prepared in Example 1 of the present invention in an O2-saturated 0.1M HClO4 electrolyte.

[0028] Figure 5 These are the polarization curve test results of the catalyst prepared in Example 1 of the present invention after 5000 cycles and 10000 cycles. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0030] Embodiment 1

[0031] A PtCu oxygen reduction catalyst with an hcp phase ordered structure and a preparation method thereof, comprising the following steps:

[0032] Preparation of 10% Cu / C: Weigh 4.5 g Ketjen 300 conductive carbon black, add it to 0.3% glacial acetic acid aqueous solution, and stir vigorously for 20 minutes.

[0033] Weigh 1.9 g Cu(NO3)2·3H2O into another beaker, add 50 mL distilled water and ultrasonically dissolve it, mix it with the dispersed Ketjen 300 under magnetic stirring, and continue stirring for 30 minutes to allow the copper ions to be fully adsorbed on Ketjen 300.

[0034] After sufficient stirring, adjust the solution pH to 8 with sodium hydroxide or ammonia, add 20mL of 6% hydrazine hydrate solution at a rate of 1ml / min, and react for 1h after the addition of hydrazine hydrate to ensure that the copper ions are completely converted into a metallic state. Collect the precipitate by centrifugation, wash the precipitate with distilled water, dry it in a vacuum for 6h to remove most of the water, then put it in a tube furnace, dry it at 120℃ for 4h under Ar atmosphere, take it out, grind it to obtain a dry powder, recorded as 10% Cu / C.

[0035] Preparation of hcp-PtCu ordered structure catalyst: Take 100mg 10% Cu / C powder after drying into a 20mL ampoule, add it into 10mL chloroform and ultrasonically disperse it for 10min. Weigh 60mg Pt(acac)2 into the ampoule, the mass ratio of Pt to Cu in the metal precursor is about 3:1, and ultrasonically dissolve it. Then use magnetic stirring to heat for 3h, the temperature is set to 70℃, the speed is 900rpm, and the bottle mouth is wrapped with tin foil with small holes until the chloroform evaporates to obtain the metal precursor powder.

[0036] The metal precursor powder was transferred into a quartz boat and placed in a tube furnace. The mixture of 10% H2 / 90% Ar (volume ratio) was first ventilated for 30 minutes to drive out the air in the furnace. The gas flow rate was 18 mL / min, and the heating rate was set to 10°C / min. The mixture was calcined at 900°C for 1.5 hours. Pt was reduced by H2 and alloyed with Cu at high temperature. The platinum salt on Cu / C was reduced to metallic platinum by introducing reducing gas, and a platinum-copper intermetallic compound was formed under high temperature conditions. The calcined powder was dissolved in 5 mL of 0.1 M dilute nitric acid, acid-washed and stirred overnight to remove unreacted Cu particles, and then washed with a mixed solution of distilled water and ethanol, centrifuged, and vacuum dried overnight to obtain a hcp-PtCu ordered structure catalyst.

[0037] Embodiment 2

[0038] A PtCu oxygen reduction catalyst with an hcp phase ordered structure and a preparation method thereof, comprising the following steps:

[0039] Preparation of 10% Cu / C: Weigh 4.5 g Ketjen 300 conductive carbon black, add it to 0.3% glacial acetic acid aqueous solution, and stir vigorously for 20 minutes.

[0040] Weigh 1.9 g Cu(NO3)2·3H2O into another beaker, add 50 mL distilled water and ultrasonically dissolve it, mix it with the dispersed Ketjen 300 under magnetic stirring, and continue stirring for 30 minutes to allow the copper ions to be fully adsorbed on Ketjen 300.

[0041] After sufficient stirring, adjust the solution pH to 8 with sodium hydroxide or ammonia, add 20mL of 6% hydrazine hydrate solution at a rate of 1ml / min, and react for 1h after the addition of hydrazine hydrate to ensure that the copper ions are completely converted into a metallic state. Collect the precipitate by centrifugation, wash the precipitate with distilled water, dry it in a vacuum for 6h to remove most of the water, then put it in a tube furnace, dry it at 120℃ for 4h under Ar atmosphere, take it out, grind it to obtain a dry powder, recorded as 10% Cu / C.

[0042] Take 1g 10% Cu / C powder after drying and put it into a 250mL single-neck round-bottom flask, and add it to 100mL chloroform for ultrasonic dispersion for 10 minutes. Weigh 0.6g Pt(acac)2 and add it into a single-neck round-bottom flask. The mass ratio of Pt to Cu in the metal precursor is about 3:1. Ultrasonicate it to dissolve it. Then use magnetic stirring to heat for 3h, set the temperature to 70℃, the speed to 900rpm, and wrap the bottle mouth with tin foil with small holes, and remove the unvolatile chloroform by rotary evaporation to obtain the metal precursor powder.

[0043] The metal precursor powder was transferred into a quartz boat and placed in a tube furnace. The mixture was ventilated with 10% H2 / 90% Ar (volume ratio) for 30 minutes to drive out the air in the furnace. The gas flow rate was 19 mL / min, and the heating rate was set to 10°C / min. The mixture was calcined at 900°C for 1.5 hours. Pt was reduced with H2 and alloyed with Cu at high temperature. The calcined powder was dissolved in 50 mL of 0.1 M dilute nitric acid, acid-washed and stirred overnight to remove unreacted Cu particles, and then washed with a mixed solution of distilled water and ethanol, centrifuged, and vacuum dried overnight to obtain a hcp-PtCu ordered structure catalyst.

[0044] Embodiment 3

[0045] A PtCu oxygen reduction catalyst with an hcp phase ordered structure and a preparation method thereof, comprising the following steps:

[0046] Preparation of 10% Cu / C: Weigh 4.5 g Ketjen 300 conductive carbon black, add it to 0.3% glacial acetic acid aqueous solution, and stir vigorously for 20 minutes.

[0047] Weigh 1.9 g Cu(NO3)2·3H2O into another beaker, add 50 mL distilled water and ultrasonically dissolve it, mix it with the dispersed Ketjen 300 under magnetic stirring, and continue stirring for 30 minutes to allow the copper ions to be fully adsorbed on Ketjen 300.

[0048] After sufficient stirring, adjust the solution pH to 8 with sodium hydroxide or ammonia, add 20mL of 6% hydrazine hydrate solution at a rate of 1ml / min, and react for 1h after the addition of hydrazine hydrate to ensure that the copper ions are completely converted into a metallic state. Collect the precipitate by centrifugation, wash the precipitate with distilled water, dry it in a vacuum for 6h to remove most of the water, then put it in a tube furnace, dry it at 120℃ for 4h under Ar atmosphere, take it out, grind it to obtain a dry powder, recorded as 10% Cu / C.

[0049] Take 2g of 10% Cu / C powder after drying and put it into a 500mL single-neck round-bottom flask, and add it to 300mL chloroform for ultrasonic dispersion for 10min. Weigh 1.2g Pt(acac)2 and add it into a single-neck round-bottom flask. The mass ratio of Pt to Cu in the metal precursor is about 3:1. Ultrasonication is used to dissolve it. Then use magnetic stirring to heat for 3h, the temperature is set to 70℃, the speed is 900rpm, and the bottle mouth is wrapped with tin foil with small holes, and the non-volatile chloroform is removed by rotary evaporation to obtain the metal precursor powder.

[0050] The metal precursor powder was transferred into a quartz boat and placed in a tube furnace. The mixture was ventilated with 10% H2 / 90% Ar (volume ratio) for 30 minutes to drive out the air in the furnace. The gas flow rate was 20 mL / min, and the heating rate was set to 10°C / min. The mixture was calcined at 900°C for 1.5 hours. Pt was reduced with H2 and alloyed with Cu at high temperature. The calcined powder was dissolved in 50 mL of 0.1 M dilute nitric acid, acid-washed and stirred overnight to remove unreacted Cu particles, and then washed with a mixed solution of distilled water and ethanol, centrifuged, and vacuum dried overnight to obtain a hcp-PtCu ordered structure catalyst.

[0051] The catalyst performance of Example 1 was evaluated and characterized as follows:

[0052] Catalyst performance evaluation:

[0053] The obtained catalyst was tested for electrochemical activity and stability using a rotating disk electrode. The test conditions were a three-electrode test system, with a glassy carbon electrode (area 0.196 cm 2 ) as the working electrode of the disk, saturated calomel electrode as the corresponding reference electrode, the reference electrode is connected to the Luggin capillary to reduce the liquid junction potential and protect the reference electrode, and the platinum sheet is used as the corresponding counter electrode. The electrolyte used is 0.1M perchloric acid.

[0054] Weigh 2 mg of the catalyst sample, add 500 μL of isopropanol, 500 uL of distilled water and 5 μL of 5 wt% Nafion solution, and perform low-temperature ultrasonic dispersion for about 1.5 h to prepare a uniform mixed slurry. Transfer a certain volume of the catalyst slurry for electrochemical evaluation.

[0055] like Figure 3 As shown, CV test was carried out in N2 saturated 0.1M HClO4 electrolyte, the potential scanning range was 0.1~1.1Vvs RHE, the scanning rate was 50mV / s, and the electrochemical active area ECSA of the electrode catalyst could be calculated according to the calculation formula.

[0056] like Figure 4 As shown, the LSV test was carried out in an O2-saturated 0.1M HClO4 electrolyte, with a scan rate of 20mV / s and a scan range of 0.2-1.1V vs RHE. The rotating disk electrode was rotated at 1600rpm. The half-wave potential (E 1 / 2 , mass activity (MA), and Tafel slope were used to evaluate the oxygen reduction activity performance.

[0057] The stability test was carried out in an O2-saturated 0.1M HClO4 electrolyte. The voltage range was set to 0.6-1.0V vsRHE and the scan rate was 100mV / s. CV uninterrupted scanning was performed as an accelerated stability test (ADT). The changes in the CV and LSV curves before and after the scan were observed, and the performance of the obtained catalyst was evaluated.

[0058] Catalyst Characterization:

[0059] The XRD data of the prepared catalyst are shown in Figure 1 It can be clearly seen that the prepared catalyst overlaps with the standard hcp-PtCu ordered structure card, and combined with transmission electron microscopy characterization, it can be seen that Figure 2 As shown, the size of the prepared catalyst is about 3-5nm and is evenly dispersed. The ICP analysis results show that the atomic ratio of Pt and Cu in the prepared catalyst is 52:48. Therefore, the prepared catalyst is an hcp-PtCu ordered structure.

[0060] Further electrochemical characterization showed that the half-wave potential of the prepared electrocatalyst was 0.903 V, which was higher than the half-wave potential of the commercial JM-Pt / C catalyst (0.851 V), and the Tafel slope was 81.7 mV dec. -1 , which is smaller than the 149.8mV dec of commercial JM-Pt / C -1 , mass specific activity is 0.54A mgPt -1 , is a commercial JM-Pt / C (0.11AmgPt -1 ). Figure 5 As shown in the figure, after 10,000 cycles of accelerated scanning, the half-wave potential of the prepared catalyst shifted negatively by only 3 mV, and the mass activity increased from the initial 0.54 AmgPt -1 Down to 0.45AmgPt -1 In summary, the hcp-PtCu ordered structure oxygen reduction electrocatalyst was prepared, which has excellent electrocatalytic performance.

Claims

1. A method for preparing a hcp phase ordered structure PtCu oxygen reduction catalyst, It is characterized in that The following steps are involved: Step 1: Add the copper salt solution to the carrier dispersion, stir evenly, adjust the pH value of the solution, and slowly add hydrazine hydrate; Step 2: Filter or centrifuge the reaction solution of step 1 to collect the precipitate, wash it to neutrality, and then dry and grind the washed precipitate to obtain Cu / C powder; Step 3: Disperse Cu / C powder in chloroform, add platinum acetylacetonate, stir and heat at 65-70°C until the chloroform evaporates completely to obtain a mixture of platinum salt and Cu / C; Step 4: placing the platinum salt and Cu / C mixture in a heating furnace for heating, and introducing a reducing gas into the heating furnace to form a PtCu / C intermetallic compound powder; Step 5: Disperse the PtCu / C intermetallic compound powder in a mineral acid, stir, and then wash with a mixed solution of distilled water and ethanol until neutral, filter or centrifuge to obtain a precipitate, and dry the precipitate to obtain an hcp-PtCu ordered structure catalyst.

2. The preparation method according to claim 1, It is characterized in that In step 1, the carrier dispersion is prepared by dispersing a conductive carbon black carrier into an aqueous solution containing glacial acetic acid to obtain a carrier dispersion; and the concentration of the hydrazine hydrate is 6-8%.

3. The preparation method according to claim 2, It is characterized in that The conductive carbon black material is one of VULCAN XC-72R and Ketjen 300.

4. The preparation method according to claim 1, It is characterized in that In step 1, the copper salt solution is any one of copper sulfate, copper nitrate, copper chloride, copper acetate and copper carbonate.

5. The preparation method according to claim 1, It is characterized in that In step 2, drying the washed precipitate comprises the following steps: vacuum drying the washed precipitate for 6 hours, placing it in a tubular furnace, and drying it at 120° C. for 4 hours in an inert gas atmosphere.

6. The preparation method according to claim 1, It is characterized in that In step 3, platinum acetylacetonate is added to obtain a metal precursor, wherein the mass ratio of Pt to Cu in the metal precursor is 3:1, and the stirring speed is 800-900 rpm.

7. The preparation method according to claim 1, It is characterized in that In step 4, the platinum salt and Cu / C mixture are placed in a heating furnace, reducing gas is first introduced into the heating furnace to drive out the air in the furnace, and then the heating furnace is set to have a heating rate of 10°C / min and calcined at 900°C for 1.5h.

8. The preparation method according to claim 1 or 7, It is characterized in that The reducing gas is a mixture of hydrogen and inert gas, wherein the volume ratio of hydrogen is 10%.

9. The preparation method according to claim 1, It is characterized in that In step 5, the mineral acid is nitric acid.

10. A hcp phase ordered structure PtCu oxygen reduction catalyst, It is characterized in that The method is described in any one of claims 1 to 9.

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