A nano-platinum-rare earth alloy and its preparation method and use

Abstract

The present invention discloses a nano-platinum-rare earth alloy catalyst and its preparation method and use. The nano-platinum-rare earth alloy catalyst is prepared by high-temperature molten salt electrochemical deoxidation, comprising the following steps: A) a nano-precursor (Pt-RE x O y / C) Preparation; B) cathode sheet (Pt-RE x O y / C) preparation; C) preparation of nano platinum-rare earth (Pt-RE) alloy material; D) product treatment. The method is suitable for large-scale synthesis, low energy consumption, and pollution-free. The prepared platinum-rare earth (Pt-RE) alloy material has an orderly structure, uniform nanometer size, high dispersion, and good catalytic stability, and can be used as a proton exchange membrane fuel cell ORR catalyst.

Description

Technical Field

[0001] The invention relates to the field of electrochemical technology, in particular to a method for preparing a platinum-rare earth alloy by an electrochemical method. Background Art

[0002] As a type of fuel cell, proton exchange membrane fuel cell (PEMFC) has the advantages of safety, high efficiency, wide fuel sources and pollution-free emissions, and has been gradually used in various energy fields. When hydrogen is used as fuel, the proton exchange membrane fuel cell realizes the conversion of chemical energy into electrical energy through the oxidation reaction of hydrogen at the anode and the reduction reaction of oxygen at the cathode. Both the anode and cathode reactions need to be completed with the assistance of nano-platinum (Pt) catalysts. At present, commercial nano-Pt / C catalysts are used for cathode oxygen reduction reaction (ORR), and their activity and long-term stability are poor, resulting in the mass of platinum catalysts required for cathode oxygen reduction reaction (ORR) being much higher than the mass of platinum catalysts required for anode hydrogen oxidation reaction. Pt reserves are scarce and expensive, resulting in the high cost of proton exchange membrane fuel cells.

[0003] In recent years, theoretical predictions and experimental verifications have shown that platinum-rare earth (Pt-RE) alloys have excellent ORR catalytic activity and good stability, but there is no mature, commercially available method for producing platinum-rare earth alloy catalysts for proton exchange membrane fuel cells.

[0004] Magnetron sputtering is the earliest method reported in the literature to synthesize Pt-RE alloy catalysts. The main literature is as follows: 1) The method was used to synthesize Pt with a thickness of nanometer scale. xGd film, verifying that its catalytic performance is superior to that of traditional commercial Pt / C catalysts. (See reference: A. Vel′azquez-Palenzuela, F. Masini, AF Pedersen, ME Escribano, D. Deiana, P. Malacrida, TW Hansen, D. Friebel, A. Nilsson, IEL Stephens, I. Chorkendorff. The enhanced activity of mass-selected PtxGd nanoparticles for oxygen electroreduction [J]. Journal of Catalysis. 2015, 328: 297–307). 2) Escudero-Escribano et al. also used magnetron sputtering to synthesize platinum-rare earth (Pt-RE) alloy catalysts such as Pt5La, Pt5Ce, Pt5Gd, and Pt5Tm with a thickness of nanometers. The study confirmed that the catalytic activity of Pt-RE alloys was significantly improved, and the catalyst showed extremely high stability. (See reference: M. Escudero-Escribano, P. Malacrida, MH Hansen, UG Vej-Hansen, A. Velázquez-Palenzuela, V. Tripkovic, I. Chorkendorff. Tuning the activity of Pt alloy electrocatalysts by means of the lanthanide [J]. Science. 2016, 352 (6281): 73-76.). 3) Malacrida prepared nanoscale Pt5La, Pt5Ce and Pt5Gd alloy catalysts by magnetron sputtering, and the alloy catalysts showed excellent stability. (See literature: P. Malacrida, MEEscribano, A. Verdaguer-Casadevall, IEL Stephens, I. Chorkendorff. Enhanced activity and stability of Pt–La and Pt–Ce alloys for oxygen electroreduction: the elucidation of the active surface phase [J]. Journal of Materials Chemistry A. 2014, 2(12): 4234–4243.)

[0005] The above literatures all adopt the magnetron sputtering method to prepare alloys. This method has the following disadvantages: the prepared alloy is a single film layer. During use, the particles are very easy to aggregate and grow. It cannot be used to assemble the membrane electrode of the proton exchange membrane fuel cell and is not suitable for practical application. The quality of the synthesized alloy is 10 -3 The deposition rate is slow; the Pt-RE alloy prepared by magnetron sputtering can only be used for mechanism research, which is far from meeting the needs of large-scale synthesis; in the process of preparing the alloy, an ultra-high vacuum system is required, with a pressure of 10 -9 Pa, the synthesis conditions are extremely harsh. Therefore, the magnetron sputtering method has great limitations in the large-scale synthesis of nano Pt-RE alloys.

[0006] The Pt-based catalyst required for the oxygen reduction reaction of the proton exchange membrane fuel cell needs to be loaded on a carbon carrier with a high specific surface area to achieve a high dispersion of nano-platinum particles, so that the nano-platinum particles maintain good ORR catalytic activity. However, the Pt-RE alloy prepared by magnetron sputtering is a single film layer, which cannot achieve a high dispersion of the alloy catalyst, and therefore cannot meet the requirements of being a catalyst for the ORR reaction of the proton exchange membrane fuel cell.

[0007] In addition to the magnetron sputtering method (a physical method), there are also reports on the synthesis of Pt-RE alloys by chemical methods, as described below.

[0008] R.Brandiele et al. used a mixture of diacetylacetonate platinum (Pt(acac)2) and yttrium nitrate hexahydrate (Y(NO3)3·6H2O) as a precursor and synthesized Pt with a Y atomic content of about 41% by hydrogen reduction reaction in a high temperature H2 / N2 atmosphere. x Compared with commercial Pt / C (Pt content 50wt%) catalyst, Pt x The ORR area specific activity and mass specific activity of Y increased by 2 times and 3 times, respectively. However, there are many uncertainties and deficiencies in the synthesis process: it is impossible to determine whether Pt x Y; and Pt cannot be determined xThe specific composition of Y; the synthesized product contains a large amount of Y2O3 and YC, that is, the purity of the alloy is not high. (See: Brandiele R, Durante C, Gradzka E, et al. One step forward to a scalable synthesis of platinum-yttrium alloy nanoparticles on mesoporous carbon for the oxygen reduction reaction [J]. Journal of Materials Chemistry A. 2016: 10.1039.C6TA04498K.)

[0009] Claudie et al. used a mixture of Pt / C and YCl3 as a precursor and prepared nanoscale Pt by H2 reduction at 800°C. x Y / C catalyst. This process has the following shortcomings: during the preparation of the alloy, high vacuum conditions need to be controlled; in particular, the H2O and O2 contents need to be controlled below 20 ppm, which greatly increases the difficulty of preparing the alloy; and the particle size distribution of the obtained alloy particles is uneven, and the generated hydrogen chloride gas corrodes the equipment. (See the literature: Roy C, Knudsen BP, Pedersen CM, Amado Andrés Velázquez Palenzuela, & Chorkendor FfI. Scalable synthesis of carbon supported platinum-lanthanide and rare earthalloys for oxygen reduction [J]. ACS Catalysis. 2018, 8 (3).)

[0010] Hu et al. first prepared a Pt-RE-NC compound precursor using hydrated metal salts as raw materials. The compound precursor anchored Pt and RE metal ions with a CN network, and then subjected it to high-temperature heat treatment in a 3.3% H2 / Ar atmosphere. During this process, the CN network collapsed, and the metal ions were converted into rare earth cyanamide (RE2(CN2)3) and Pt particles, which were then reduced by H2 to form Pt xRE nanoalloy. HCN is produced during the synthesis process, which brings safety issues to the synthesis process and the environment, and the preparation process is relatively complicated. (See reference: HuY, Jensen JO, Cleemann LN, Brandes BA, & Li Q. Synthesis of pt-rare earth metal nanoalloys [J]. Journal of the American Chemical Society. 2020, 142: 953-961.)

[0011] Kanady et al. used a homogeneous mixture of PtCl4, YCl3 and K(Na)Et3BH as a precursor and heated it to above the melting point of the mixture. Among them, potassium (sodium) triethylborohydride (K(Na)Et3BH) was used as a molten salt medium and reducing agent, and a Pt3Y nano alloy supported on a carbon carrier was obtained through the reduction reaction of potassium (sodium) triethylborohydride. This method uses molten salt as a medium and reducing agent. The prepared Pt-RE alloy particles are easy to aggregate and dissolve in the molten salt, resulting in a relatively large particle size of the alloy, and the reducing ability of potassium (sodium) triethylborohydride reducing agent is fixed and cannot be adjusted; the literature does not characterize the ORR catalytic performance. (See literature: Kanady JS, Leidinger P, Haas A, et al.Synthesis of Pt3Yand other early–late intermetallic nanoparticles by way of a molten reducing agent[J].Journal of the American Chemical Society.2017,139(16):5672-5675.)

[0012] Kobayashi et al. obtained nano-intermetallic compound Pt2Y (28nm) by reducing CaH2 in a LiCl-CaH2 molten salt containing a mixture of H2PtCl6·6H2O and Y2O3, with CaH2 as a reducing agent, at a temperature of 600°C. This method uses molten salt as a medium, and the reduction reaction of CaH2 is carried out in the molten salt. Since nanoparticles are easy to aggregate and grow in the high-temperature molten salt medium, the synthesized intermetallic compound Pt2Y particles are relatively large, and therefore the prepared intermetallic compound Pt2Y cannot be used for the preparation of membrane electrodes for fuel cells; CaH2 as a reducing agent has a fixed reducing ability and cannot be adjusted; the literature does not characterize the ORR catalytic performance. (See the literature: Kobayashi Y, Tada S, Kikuchi R. Simplechemical synthesis of intermetallic Pt2Y bulk nanopowder [J]. Materials Advances. 2020, 1 (7): 2202-2205.)

[0013] At present, there are still huge challenges in the chemical synthesis of Pt-RE alloys, nano Pt-RE alloys, and highly dispersed nano Pt-RE alloys. There are the following difficulties in the chemical synthesis of Pt-RE alloys: the reduction potential of rare earth elements is much more negative than that of Pt, and it is difficult for the two to be co-reduced; rare earth metals are highly active, and the extraction process from rare earth metal compounds to single substances cannot be completed in oxygen-containing or water-containing media; the alloying process of platinum and rare earths can only be achieved at high temperatures. Furthermore, the preparation of nano Pt-RE alloys and highly dispersed nano Pt-RE alloys has exacerbated the difficulty of preparation. Because platinum and rare earths need to be at high temperatures to form alloys, and high temperatures will cause the alloy particles to grow rapidly, it is difficult to obtain low-nano-sized alloys at high temperatures, and at the same time, it is difficult to maintain the high dispersion of the alloy at high temperatures.

[0014] The molten salt electrochemical deoxidation method (FFC method) has attracted attention in the preparation of bulk inert metal materials. When the reduction potentials of two elements are not much different, it is appropriate to use the molten salt electrochemical deoxidation method to prepare metal alloys. However, the reduction potentials of rare earth Tb and Fe (Co, Ni) are relatively large, so it is more difficult to use the molten salt electrochemical deoxidation method to prepare metal alloys. Through in-depth exploration by researchers, the preparation of alloys of rare earth metals and transition metals, including TbFe2, Dy-Fe, CeCo5, and CeNi4Cu alloys, has been reported. This is the alloy with the largest potential difference prepared by the molten salt electrochemical deoxidation method reported in the literature. Moreover, the purpose of the molten salt electrochemical deoxidation method is to prepare bulk alloys. (1) Wang et al. sintered the mixed oxides Tb4O7 and Fe2O3, and then prepared bulk TbFe2 alloys composed of micron-sized particles (0.3-3μm) by molten salt electrochemical deoxidation. (See reference: G. Qiu, D. Wang, M. Ma, X. Jin, G. Z. Chen. Electrolytic synthesis of TbFe2 from Tb4O7 and Fe2O3 powders in molten CaCl2 [J]. Journal of Electroanalytical Chemistry. 2006, 589 (1): 139-147.). (2) Wang Zhonglei et al. used Dy2O3 and Fe2O3 as raw materials and explored the possibility of synthesizing Dy-Fe alloy by molten salt electrochemical deoxidation method, and prepared bulk Dy-Fe alloy composed of particles of 0.2-1 μm (See reference: Wang Zhonglei, Tang Huiqing, Guo Zhancheng, Cai Zhuofei, Ye Wei, Zhao Zhilong. Study on cathode reduction process of Dy-Fe alloy prepared by molten salt electrochemical deoxidation method [C]. National Conference on Metallurgical Physical Chemistry. 2010.). (3) Dai et al. pressed a mixture of Co3O4 and CeO2 into an electrode sheet and sintered it at 850℃. They prepared a rare earth CeCo5 alloy consisting of particles of about 5μm by molten salt electrochemical deoxidation at a voltage of 3.1V (see reference: Dai.L, Wang.S, Yue.H, LI, Wang.L, & Shao.GJ Direct electrochemical preparation of ceco5 alloy from mixed oxides [J]. Transactions of Nonferrous Metals Society of China. 2012, 22 (8): 2007-2013.). (4) Kang et al. used CeO2, NiO and CuO as raw materials, prepared cylindrical electrodes by pressure molding, and sintered them at 950℃ for 4h.Afterwards, CeNi4Cu alloy consisting of particles of about 4 μm was prepared by molten salt electro-deoxidation at 650°C using LiCl-KCl electrolyte (see reference: Xue.K, Qian.X, Ximei.Y, Qiushi.S. Electrochemical synthesis of CeNi4Cualloy from the mixed oxides and in situ heat treatment in a eutectic LiCl-KClmelt[J].Materials Letters.2010,64(20):2258-2260.).

[0015] The above-mentioned molten salt electro-deoxidation method for preparing rare earth alloys is carried out in high-temperature molten salt, and the synthesized products are binary or ternary alloys of rare earth and transition elements, and are not Pt rare earth alloys; and the purpose of the molten salt electro-deoxidation method is to prepare large-scale alloys.

[0016] Since the potential difference between Pt and rare earth metal elements is nearly 4V, it is difficult to prepare Pt rare earth alloys through the existing molten salt electro-deoxidation method with such a large potential difference, and there is no literature report. Moreover, the alloys reported by the molten salt electro-deoxidation method are all bulk; and for the oxygen reduction reaction (ORR) of proton exchange membrane fuel cells (PEMFC), the size of its commercial Pt / C catalyst is less than 3.5nm, and it is impossible to use the above-mentioned high-temperature molten salt electrochemical deoxidation to prepare highly dispersed, nano-scale Pt rare earth alloys. Summary of the invention

[0017] In order to overcome the limitations of existing technologies in the large-scale synthesis of Pt rare earth alloys, we adopted a new molten salt electrochemical deoxidation method, which is suitable for the large-scale preparation of nano Pt rare earth alloys, and the Pt rare earth alloys prepared by this method can meet the application of proton exchange membrane fuel cells.

[0018] The purpose of the present invention is to use high-temperature molten salt as a medium and prepare low-nanoscale platinum-rare earth (Pt-RE) alloy materials by a molten salt electro-deoxidation method, which solves the problems existing in the prior art: first, the problem that Pt-RE alloy is difficult to be co-reduced due to excessive potential difference is solved; second, the reduction ability can be adjusted by changing the applied voltage, which solves the problem of fixed reduction ability, so that the composition of the obtained product can be regulated; third, a highly dispersed, low-nanoscale Pt-RE alloy can be obtained; fourth, by increasing the molar ratio of rare earth elements to platinum elements in rare earth oxides and synergistically controlling the electrolysis voltage, the aggregation and growth of platinum rare earth alloy particles can be prevented; fifth, products of gram, kilogram, hundred kilograms and other scales can be obtained; sixth, it is environmentally friendly and no pollutants or toxic substances are produced. The problem of synthesizing highly dispersed, low-nanoscale Pt-RE alloys at high temperatures is solved, and a method for preparing nano Pt-RE alloy catalysts suitable for proton exchange membrane fuel cells (PEMFC) oxygen reduction reaction (ORR) at low cost and large scale is provided.

[0019] The present invention provides a method for preparing a PEMFC cathode ORR nano Pt-RE alloy catalyst, wherein the rare earth (RE) element can be a light rare earth element or a heavy rare earth element. Light rare earth elements such as scandium (Sc), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu); heavy rare earth elements such as yttrium (Y), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu). The preparation method of the nano platinum rare earth alloy comprises the following steps:

[0020] A) Nano-precursor (Pt-RE x O y / C) preparation: the carbon carrier, platinum source and rare earth source are uniformly dispersed in deionized water to obtain Pt nanoparticles uniformly distributed on the carbon carrier, and then the solution pH is adjusted to allow the rare earth source to hydrolyze on the Pt nanoparticles and the carbon carrier, and then the obtained powder is washed, filtered, dried and calcined to obtain nano Pt and RE supported on the carbon carrier. x O y Mixture, namely nano-Pt-RE x O y / C precursor.

[0021] The carbon carrier is a carbon material with large specific surface area, good electrical conductivity, stable structure and porous characteristics, such as one or more of Vulcan XC-72 carbon black, hollow carbon spheres, ordered mesoporous carbon, nanocarbon fibers, carbon nanotubes and graphene.

[0022] The platinum source can directly use commercial platinum nanoparticles, or chloroplatinic acid, platinum chloride, potassium chloroplatinate, etc. can be used as the platinum source, and new platinum nanoparticles can be obtained by reduction with a reducing agent, such as hexahydrate chloroplatinic acid (H2PtCl6·6H2O) as the platinum source, and platinum nanoparticles can be obtained by reduction with a reducing agent. The reducing agent for reducing the platinum source is preferably a reducing agent such as sodium borohydride (NaBH4), ethylene glycol (C2H6O2), formic acid (CH2O2), ascorbic acid (C6H8O6), etc.

[0023] The rare earth source can be a rare earth nitrate, a rare earth halide, a rare earth oxide, a rare earth hydroxide, etc., preferably a hexahydrated rare earth nitrate or a rare earth chloride, such as neodymium nitrate hexahydrate (Nd(NO3)3·6H2O), dysprosium nitrate hexahydrate (Dy(NO3)3·6H2O) or neodymium chloride (NdCl3), dysprosium chloride (DyCl3).

[0024] The pH is adjusted with an alkaline solution so that the pH is maintained in the range of 8-14, preferably 9-12. The alkaline solution is preferably aqueous ammonia, sodium hydroxide, potassium hydroxide, etc.

[0025] The ratio of the molar number of platinum in the platinum source to the molar number of rare earth elements in the rare earth source (Pt / RE) is in the range of 5:1 to 1:30. The preferred ratio of Pt / RE is 1:1-1:20.

[0026] It is preferred that the molar number of the carbon support is 4 times or more the molar number of the rare earth element in the rare earth source.

[0027] Preferably, the calcination process is carried out in a N2 atmosphere at a temperature range of 500-900°C and the sintering time is 1-4h.

[0028] B) Electrolysis: Nano-Pt-RE x O y / C precursor is pressed into a cathode and electrolyzed in a molten salt to obtain a nano-platinum-rare earth (Pt-RE) alloy.

[0029] The preferred pressure for pressing into the cathode is 10-20 MPa, and the holding time is 2-10 min.

[0030] The molten salt is commonly used in the prior art, and can be molten LiCl or a binary or multinary halide system of an alkali metal or alkaline earth metal based on LiCl, such as LiCl-KCl, LiCl-CsCl, which can contain one or more halides of the lanthanide or ruthenium series; or a binary or multinary halide system of an alkali metal or alkaline earth metal based on CaCl2 or CaCl2, such as CaCl2-LiCl, CaCl2-NaCl, which can contain one or more halides of the lanthanide or ruthenium series. The temperature range used can be determined by those skilled in the art according to the selected molten salt. For example, the temperature range of LiCl-KCl molten salt is 450-800°C, and the temperature range of CaCl2 or CaCl2-based molten salt is 500-900°C.

[0031] The electrolysis adopts a two-electrode system to Pt-RE x O y / C cathode plate is subjected to constant voltage electrolysis for 2-6h. The voltage range adopted can be adjusted by technicians in this field according to different molten salt systems. In the LiCl-KCl molten salt system, the voltage range is 2.8-3.5V; for the CaCl2-based molten salt system, the voltage range is 2.8-3.2V.

[0032] The electrolysis voltage can also be controlled as needed to form products in different proportions, such as Pt5RE, Pt3RE, Pt2RE. Rare earth alloys with different compositions have different catalytic properties. Therefore, by adjusting the applied voltage, the composition of the product can be adjusted, and then the catalytic properties of the material can be adjusted.

[0033] C) Product treatment: The electrolysis products are washed and dried.

[0034] Washing and drying can remove the remaining rare earth oxides in the product. For example, the electrolysis product is 0.5 mol·L -1 The product after acid washing was washed and filtered, and then dried in a constant temperature vacuum oven at 70-100°C for 5-10 hours.

[0035] The nano-platinum-rare earth alloy material obtained by the present invention can be used as a proton exchange membrane fuel cell ORR catalyst. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) tests are used to characterize the catalytic activity and stability of the nano-platinum-rare earth alloy material as a proton exchange membrane fuel cell ORR catalyst.

[0036] The platinum-rare earth alloy particles prepared by the above method in the present invention are between 5-15 nm, and obtain catalytic activity close to or better than commercial JM Pt / C, and catalytic stability better than commercial JM Pt / C. Among them, Pt-Nd nano alloy can obtain catalytic activity and catalytic stability better than commercial JM Pt / C.

[0037] The advantages of the present invention are:

[0038] 1. The raw materials are easily available, the operation is simple, the experimental conditions are easy to meet, it is suitable for large-scale synthesis, low energy consumption, and no pollutants or toxic substances are produced.

[0039] The raw materials used in the present invention are mainly carbon black, chloroplatinic acid hexahydrate, neodymium nitrate hexahydrate, dysprosium nitrate hexahydrate and neodymium chloride, and the solvent is lithium chloride, potassium chloride or calcium chloride; compared with physical metallurgical methods such as magnetron sputtering, the present invention has a lower temperature and is carried out under normal pressure, and can perform electrolysis operations continuously, and the product scale can be increased from gram level to kilogram level and hundred kilogram level; lithium chloride, potassium chloride or calcium chloride molten salt can be recycled and reused to achieve the recycling of raw materials, and the entire production process is green and pollution-free.

[0040] 2. The alloy structure is ordered, the size is uniform and highly dispersed, and the composition of the alloy can be controlled.

[0041] The nano platinum-rare earth alloy particles prepared by the present invention have good crystallinity, orderly structure and are highly dispersed on the surface of the carbon carrier, wherein the average particle size of Pt2Nd is 13.4nm, the average particle size of Pt5Nd is 11.5nm and the average particle size of Pt3Dy is 9.2nm, and the alloy particles are uniform in size and are all at the nanometer level.

[0042] 3. Nano-platinum-rare earth (Pt-RE) alloy materials have good catalytic activity and stability.

[0043] The Pt5Nd / C alloy material prepared by the present invention has good performance as a proton exchange membrane fuel cell ORR catalyst, and its mass specific activity at 0.9V (69.03mA·mg -1 ) and area specific activity (0.22 mA cm -2 ), reaching 2.58 and 5.5 times that of the commercial JM Pt / C catalyst. After 10,000 cycles, the half-wave potential of the Pt5Nd / C alloy catalyst decreased by only 21 mV, which is superior to the stability of the commercial JM Pt / C catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is the XRD phase analysis spectrum of the Pt5Nd / C alloy material obtained in Example 1.

[0045] Figure 2 This is the TEM microscopic morphology of the Pt5Nd / C alloy material obtained in Example 1.

[0046] Figure 3 This is the XRD phase analysis spectrum of the Pt2Nd / C alloy material obtained in Example 2.

[0047] Figure 4 This is the XRD phase analysis spectrum of the Pt3Dy / C alloy material obtained in Example 3.

[0048] Figure 5 To characterize the oxygen reduction performance of the Pt5Nd / C alloy catalyst obtained in Example 1.

[0049] Figure 6 To characterize the oxygen reduction durability of the Pt5Nd / C alloy catalyst obtained in Example 1. DETAILED DESCRIPTION

[0050] The specific implementation methods provided by the present invention are described in detail below in conjunction with implementation examples.

[0051] Example 1: Preparation of Pt5Nd / C Nanoalloy

[0052] (1) Preparation of nano-precursor: 145 mg of carbon black (Vulcan XC-72R) was weighed and ultrasonically mixed and magnetically stirred in a NaBH4 solution (73 mg) for 30 min each. Then, Nd(NO3)3·6H2O (845 mg) and 0.0193 mol·L -1 10 ml of H2PtCl6·6H2O solution was added and stirred vigorously for 1 hour. Ammonia water was added to ensure that the solution pH was 10 and magnetic stirring was continued for 1 hour. Filter and wash until the last filtrate is neutral, vacuum dry at 80℃, grind into powder carefully and calcine at 700℃ in N2 atmosphere for 2 hours;

[0053] (2) Preparation of cathode sheet: The nano-Pt-Nd2O3 / C powder precursor was pressed into a sheet under a pressure of 15 MPa and connected to a conductor as a cathode;

[0054] (3) Preparation for electrolysis experiment: The experiment adopts a two-electrode system. The distance between the electrodes is kept consistent in each experiment. Pt-Nd2O3 / C flakes are used as cathodes, graphite flakes are used as anodes, and LiCl-KCl with an equal molar ratio is used as the molten salt medium;

[0055] (4) Electrochemical deoxidation: The Pt-Nd2O3 / C cathode was electrolyzed in molten LiCl-KCl (equimolar ratio) at 700°C at a constant voltage of 3.2 V for 2 h.

[0056] (5) Product treatment: The electrolysis product was cooled to room temperature in a N2 atmosphere. After being taken out, the electrolysis product was soaked in deionized water, then washed, filtered and vacuum dried at 80°C. The evenly ground black powder was poured into the bottom of a beaker and 0.5 mol·L -130 mL of dilute sulfuric acid (H2SO4) was added, and magnetic stirring was performed at 80°C for 1 h to remove the remaining Nd2O3 in the product by acid washing. The product after acid washing was washed, filtered, and dried at 80°C in a constant temperature vacuum oven for 8 h.

[0057] The above embodiment obtains a nano alloy with a composition of Pt5Nd / C. The diffraction peak 2θ position of the Pt5Nd alloy coincides with the standard PDF card. The alloy structure is orderly ( Figure 1 The average particle size of the alloy particles is 11.5nm, with less agglomeration and better dispersion ( Figure 2 ).

[0058] Example 2: Preparation of Pt2Nd / C Nanoalloy

[0059] (1) Preparation of nano-precursor: 145 mg of carbon black (Ketjen EC 300J) was weighed and ultrasonically mixed and magnetically stirred in 100 mL of ethylene glycol (C2H6O2) solution for 30 min each. Then, NdCl3 (966 mg) and 0.0193 mol·L -1 10 ml of H2PtCl6·6H2O solution was added, and the uniformly mixed slurry was kept at 130℃ for 3 hours. Ammonia water was added dropwise to adjust the pH of the slurry to 11, and stirring was continued for 1 hour. Filter and wash until the last filtrate is neutral, vacuum dry at 90℃, carefully grind into powder and calcine at 500℃ in N2 atmosphere for 4 hours;

[0060] (2) Cathode sheet preparation: The nano-Pt-Nd2O3 / C powder precursor was pressed into a cylindrical sheet under a pressure of 10 MPa and connected to a conductor as a cathode;

[0061] (3) Preparation for electrolysis experiment: The experiment adopts a two-electrode system. The distance between the electrodes is kept consistent in each experiment. Pt-Nd2O3 / C flakes are used as cathodes, graphite flakes are used as anodes, and LiCl-KCl with an equal molar ratio is used as the molten salt medium;

[0062] (4) Electrochemical deoxidation: The Pt-Nd2O3 / C cathode sheet was electrolyzed at a constant voltage of 2.8 V for 6 h in molten LiCl-KCl (equimolar ratio) at 500°C.

[0063] (5) Product treatment: The electrolysis product was cooled to room temperature in a N2 atmosphere. The electrolysis product was taken out and soaked in deionized water. Then, it was washed, filtered and vacuum dried at 90°C. The evenly ground black powder was poured into the bottom of a beaker and 0.5 mol·L -1 30 mL of dilute sulfuric acid (H2SO4) was added, and magnetic stirring was performed at 90°C for 1 h to remove the remaining Nd2O3 in the product by acid washing. The product after acid washing was washed, filtered, and dried at 90°C in a constant temperature vacuum oven for 8 h.

[0064] The above embodiment obtains an alloy with a composition of Pt2Nd / C. The diffraction peak 2θ position of the Pt2Nd alloy coincides with the standard PDF card. The alloy has an orderly structure ( Figure 3 ).

[0065] Example 3: Preparation of Pt3Dy / C Nanoalloy

[0066] (1) Preparation of nano-precursor: 192 mg of ordered mesoporous carbon (CMK-5) was weighed and ultrasonically mixed and magnetically stirred in a NaBH4 solution (37 mg) for 30 min each. Dy(NO3)3·6H2O (88.1 mg) and 0.0193 mol·L -1 10 ml of H2PtCl6·6H2O solution was added and stirred vigorously for 1 hour. Ammonia water was added to ensure that the solution pH was 9 and magnetic stirring was continued for 1 hour. Filter and wash until the last filtrate was neutral, vacuum dry at 80℃, grind into powder carefully and calcine at 900℃ in N2 atmosphere for 1 hour;

[0067] (2) Preparation of cathode sheet: Pt-Dy2O3 / C powder precursor is pressed into a sheet under a pressure of 20 MPa and connected to a conductor as a cathode;

[0068] (3) Preparation for electrolysis experiment: The experiment adopts a two-electrode system. The distance between the electrodes is kept consistent in each experiment. Pt-Dy2O3 / C flakes are used as cathodes, graphite flakes are used as anodes, and CaCl2 is used as molten salt medium;

[0069] (4) Electrochemical deoxidation: The Pt-Dy2O3 / C cathode sheet was electrolyzed at a constant voltage of 3.0 V for 4 h in molten CaCl2 at 900°C.

[0070] (5) Product treatment: The electrolysis product was cooled to room temperature in a N2 atmosphere. The electrolysis product was taken out and soaked in deionized water. Then, it was washed, filtered and vacuum dried at 100°C. The evenly ground black powder was poured into the bottom of a beaker and 0.5 mol·L -1 30 mL of dilute sulfuric acid (H2SO4) was added, and magnetic stirring was performed at 100°C for 1 h. The remaining Dy2O3 in the product was removed by acid washing. The product after acid washing was washed, filtered, and dried at 100°C in a constant temperature vacuum oven for 8 h.

[0071] The above embodiment obtains an alloy with a composition of Pt3Dy / C. The diffraction peak 2θ position of the Pt3Dy alloy coincides with the standard PDF card. The alloy structure is orderly ( Figure 4 ).

[0072] Example 4: Redox performance test:

[0073] Characterization content: Catalytic performance of cathode oxygen reduction reaction (ORR) of proton exchange membrane fuel cell (PEMFC); Characterization methods: Cyclic voltammetry (CV) test and linear sweep voltammetry (LSV) test.

[0074] The working electrode used in the catalytic performance characterization was a glassy carbon electrode loaded with nano-Pt5Nd / C, Pt2Nd / C and Pt3Dy / C alloy catalysts prepared in Examples 1 to 3, ensuring that the Pt loading on the surface of the glassy carbon electrode was 20 μg cm -2 ; Counter electrode: Pt wire; Reference electrode: saturated calomel electrode (SCE). All electrode potentials in this part of the experiment were corrected to the potential of the standard hydrogen electrode (RHE).

[0075] Before the cyclic voltammetry (CV) test, according to the internationally accepted test standards, N2 was first passed through the 0.1M HClO4 solution for 30 min, and the potential was scanned clockwise for 20 cycles (scan rate: 100 mV·s) in the potential range of 0.05 to 1.25 V (vs. RHE) starting from the open circuit potential. -1 ), which plays an activation role. Then, in the potential range of 0.05-1.20 V, the sample was scanned clockwise for 20 cycles (scan rate: 50 mV·s -1 ). Select the last cycle of the CV curve and calculate the hydrogen adsorption / desorption peak area S in the CV curve. H (minus the double layer area) to obtain the electrochemically active area (ECSA).

[0076] Before the linear sweep voltammetry (LSV) test, according to the internationally accepted test standards, a large flow rate of O2 was passed through the 0.1M HClO4 solution for 30 minutes to reach oxygen saturation. Test conditions: Rotation speed of the rotating disk electrode: 1600rpm; Scanning range: 0.05-1.1V (vs. RHE); Scanning rate: 5mV·s -1 According to the LSV curve of the catalyst, the half-wave potential (E 1 / 2 ), and the mass specific activity (M) at potentials of 0.85 and 0.90 V (vs. RHE) A ) and area specific activity (S A ).

[0077] The catalyst was subjected to an accelerated aging test in a 0.1M HClO4 solution saturated with N2. Test conditions: Scanning range: 0.6-1.0V (vs. RHE); Scanning rate: 100mV·s -1; Cycle number: 40, 5000, 10000. After 40, 5000, and 10000 cycles, each catalyst was tested again for CV and LSV. The stability of the catalyst was determined based on the following data: electrochemically active area (ECSA), half-wave potential (E 1 / 2 ) and quality (M A ), Area (S A ) specific activity.

[0078] Figure 5 The CV and LSV curves of the Pt5Nd / C alloy and JM-Pt / C catalyst (Shanghai Hesen Electric Co., Ltd., hispee3000) obtained in Example 1; the performance parameters of the Pt5Nd / C, Pt2Nd / C and Pt3Dy / C alloy catalysts for oxygen reduction in Examples 1 to 3 are shown in Table 1 below.

[0079] Figure 6 The CV and LSV curves of the Pt5Nd / C alloy and JM Pt / C catalyst in Example 1 after 40, 5000, and 10000 cycles of stability testing are shown in Table 2 below.

[0080] Table 1 Performance parameters of alloy catalysts for oxygen reduction in Examples 1 to 3

[0081]

[0082]

[0083] Table 2 Oxygen reduction durability parameters of Pt5Nd / C alloy and JM-Pt / C catalyst in Example 1

[0084]

[0085] The Pt5Nd / C alloy material prepared in Example 1 has good performance as a cathode catalyst for proton exchange membrane fuel cells. Its mass specific activity at 0.9 V (69.03 mA·mg -1 ) and area specific activity (0.22 mA cm -2 ), reaching 2.58 times and 5.5 times that of the commercial JM-Pt / C catalyst. After 10,000 cycles, the half-wave potential of the Pt5Nd / C alloy catalyst only decreased by 21 mV, which has a better stability than the commercial JM-Pt / C catalyst. It can be seen that the Pt-RE alloy prepared by the present invention can be applied to the cathode oxygen reduction reaction (ORR) of proton exchange membrane fuel cells (PEMFC).

[0086] The nano-Pt2Nd / C alloy material prepared in Example 2 is used as a cathode catalyst for a proton exchange membrane fuel cell. Its mass specific activity at 0.9V (20.32 mA·mg -1 ) and area specific activity (0.17 mA cm -2 ), its mass specific activity is slightly lower than that of the commercial JM-Pt / C catalyst, while its area specific activity is 4.25 times that of the commercial JM Pt / C catalyst.

[0087] The nano-Pt3Dy / C alloy material prepared in Example 3 was used as a proton exchange membrane fuel cell ORR catalyst, and its mass specific activity at 0.9V (41.33 mA·mg -1 ) and area specific activity (0.25 mA cm -2 ), reaching 1.55 and 6.25 times that of the commercial JM-Pt / C catalyst.

[0088] In the described embodiments, the prepared nano Pt-RE alloys all showed excellent area specific activity, the nano Pt5Nd / C alloy and Pt3Dy / C alloy catalysts showed excellent mass specific activity, and the prepared nano Pt-RE alloy had excellent long-term stability.

Claims

1. A method for preparing a nano-platinum-rare earth (Pt-RE) alloy, characterized in that Nano-Pt-RExOy / C precursor is used as cathode to electrolyze nano-platinum-rare earth (Pt-RE) alloy in molten salt at constant voltage. x O y The preparation method of / C is as follows: a carbon carrier, a platinum source and a rare earth source are uniformly dispersed in deionized water, wherein the ratio of the molar number of platinum in the platinum source to the molar number of rare earth elements in the rare earth source (Pt / RE) is 1:10-1:30, to obtain Pt nanoparticles uniformly distributed on the carbon carrier, adjust the pH of the solution to hydrolyze the rare earth source, wash, filter, dry and calcine the obtained powder, and obtain nano Pt and RE loaded on the carbon carrier. x O y Mixture, namely nano-Pt-RE x O y / C precursor, wherein the calcination process is carried out in a N2 atmosphere at a temperature range of 500-900°C, and the sintering time is 1-4h; the molten salt is a LiCl-KCl or CaCl2-based molten salt system, when the molten salt is LiCl-KCl, the temperature is 450-800°C, and the voltage range is 2.8-3.5V; when the molten salt is a CaCl2-based molten salt system, the temperature is 500-900°C, and the voltage range is 2.8-3.2V, and the CaCl2-based molten salt is selected from CaCl2-LiCl or CaCl2-NaCl; the electrolysis adopts a two-electrode system, and the Pt-RE x O y / C cathode sheet constant voltage electrolysis time is 2-6h.

2. The method for preparing a nano-platinum-rare earth (Pt-RE) alloy according to claim 1, characterized in that The carbon carrier is selected from one or more of Vulcan XC-72 carbon black, hollow carbon spheres, ordered mesoporous carbon, nanofiber carbon, carbon nanotubes or graphene.

3. The method for preparing nano platinum-rare earth (Pt-RE) alloy according to claim 1, characterized in that The platinum source is selected from platinum nanoparticles, chloroplatinic acid, platinum chloride, and potassium chloroplatinate. When the platinum source is chloroplatinic acid, platinum chloride, or potassium chloroplatinate, it is reduced with a reducing agent.

4. The method for preparing nano platinum-rare earth (Pt-RE) alloy according to claim 1, characterized in that The rare earth source is selected from rare earth nitrates, rare earth halides, rare earth oxides and rare earth hydroxides.

5. The method for preparing nano platinum-rare earth (Pt-RE) alloy according to claim 3, characterized in that The reducing agent is selected from sodium borohydride (NaBH4), ethylene glycol (C2H6O2), formic acid (CH2O2), and ascorbic acid (C6H8O6).

6. The method for preparing nano-platinum-rare earth (Pt-RE) alloy according to claim 3, characterized in that The molar number of the reducing agent is more than 1 times the molar number of platinum in the platinum source.

7. The method for preparing nano-platinum-rare earth (Pt-RE) alloy according to claim 1, characterized in that The ratio of the molar number of platinum in the platinum source to the molar number of rare earth elements in the rare earth source (Pt / RE) is 1:20-1:

30.

8. The method for preparing nano-platinum-rare earth (Pt-RE) alloy according to claim 1, characterized in that The molar number of the carbon carrier is more than 4 times the molar number of the rare earth element in the rare earth source.

9. The method for preparing nano-platinum-rare earth (Pt-RE) alloy according to claim 1, characterized in that The pH is adjusted by using an alkaline solution selected from aqueous ammonia, sodium hydroxide and potassium hydroxide so that the pH is maintained at 8-14.

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