A phosphide-induced PtM ordered alloy composite catalyst and its preparation method and application

Abstract

A phosphide-induced PtM ordered alloy composite catalyst and its preparation method and application, which relates to a composite catalyst and its preparation method and application, and solves the technical problems of low catalytic activity and poor stability of existing Pt-based catalysts. The catalyst of the present invention is composed of an ordered PtM alloy and a M x P is uniformly loaded on a carbon support, and the ordered PtM alloy is composed of M x The catalyst is obtained by inducing a high-temperature phase transition of P; wherein M is Co, Fe, or Ni, and x = 0.5 to 3. It is obtained by impregnating the surface of a carbon support with Pt, P, and M precursors, evaporating them to dryness, and then annealing and grinding them in an inert gas. The mass activity of the catalyst of the present invention is 0.384 to 0.321 mA / μg. Pt , approximately 3.4 times that of commercial 10% Pt / C. PtCo-Co2P / C exhibited a half-wave potential decay of only 5mV after 30,000 cycles, with a mass activity decay rate of 13.44%. It can be used in fuel cell applications.

Description

Technical Field

[0001] The present invention relates to the preparation of PtM (M = Co, Fe, Ni, etc.) ordered alloys and M x The invention relates to a method and application of a P composite catalyst, belonging to the field of new energy materials. Background Art

[0002] Proton exchange membrane fuel cells (PEMFCs) are playing an increasingly important role in their field as a clean energy source. Traditional Pt / C catalysts remain the most widely used, but their slow cathode oxygen reduction reaction (ORR), low intrinsic activity, and high cost limit their further application. Furthermore, the harsh operating environment of electrocatalysts places high demands on catalyst stability. The activity and stability of the most commonly used commercial 20% Pt / C are still unsatisfactory.

[0003] Currently, alloying Pt with transition metals can significantly enhance the intrinsic activity of catalysts while reducing Pt usage and thus costs. Of the numerous alloy catalysts, only PtCo alloys—mesoporous carbon-supported PtCo alloy catalysts—have been commercialized. However, Pt-based alloys suffer from issues such as metal nanoparticle dissolution, which compromises their stability. Summary of the Invention

[0004] The present invention aims to solve the technical problems of poor catalytic activity and stability of existing Pt-based catalysts, and to provide a phosphide-induced PtM ordered alloy composite catalyst and its preparation method and application. The present invention uses transition metal phosphide as a precursor, adopts impregnation and evaporation and multi-stage high-temperature heat treatment to obtain PtM-M x P / C (M = Co, Fe or Ni) composite catalysts improve the stability of alloy catalysts by increasing the degree of alloy order and enhancing the metal-support interaction. The resulting catalyst Pt activity and stability are significantly higher than the latest commercial Pt / C catalysts.

[0005] The phosphide-induced PtM ordered alloy composite catalyst of the present invention is composed of ordered PtM alloy and M x P is uniformly loaded on a carbon support, and the ordered PtM alloy is composed of M x P is induced by high-temperature phase transformation; wherein M is Co, Fe or Ni, and x is 0.5 to 3.

[0006] Furthermore, the loading amount of precious metal Pt in the phosphide-induced PtM ordered alloy composite catalyst is 5 to 20 wt.%.

[0007] The preparation method of the phosphide-induced PtM ordered alloy composite catalyst of the present invention is carried out according to the following steps:

[0008] 1. Precursor impregnation and evaporation: Disperse the carbon support in ultrapure water, then add Pt source, P source, and M source aqueous solutions, stir and disperse for 8 to 12 hours, ultrasonically disperse for 3 to 4 hours, and then place in a water bath and rotary evaporate to dryness to obtain a black solid powder;

[0009] 2. Preparation of PtM-M by Multi-stage High-temperature Heat Treatment x P / C composite catalyst: The black powder obtained in step 1 is placed in a high-temperature furnace and calcined and annealed in multiple stages under an inert atmosphere. After cooling and grinding, a PtM ordered alloy composite catalyst is obtained, which is denoted as PtM-M. x P / C.

[0010] Furthermore, the carbon support described in step 1 is ECP600-jD, EC300J, BP-2000 or XC-72.

[0011] Furthermore, the platinum source in step 1 is an aqueous solution of chloroplatinic acid;

[0012] Furthermore, the M source in step 1 is cobalt chloride, cobalt nitrate, nickel chloride, nickel nitrate, ferric chloride or ferric nitrate.

[0013] Furthermore, the concentration of M in the M source aqueous solution in step 1 is 0.025 to 5 mol / L.

[0014] Furthermore, the phosphorus source described in step 1 is a sodium hypophosphite aqueous solution with a concentration of 0.025 to 5 mol / L;

[0015] Furthermore, the molar ratio of Pt to M in step 1 is 1:(0.25-5), and the molar ratio of phosphorus to M is 1:(0.5-5).

[0016] Furthermore, the water bath evaporation temperature in step 1 is 70°C to 80°C.

[0017] Furthermore, the inert gas in step 2 is argon.

[0018] Furthermore, the multi-stage calcination conditions described in step 2 are: the first stage annealing temperature is 200-500°C, the heating rate is 5-10°C / min, and the annealing time is 2-4h; the second stage annealing temperature is 400-800°C, the heating rate is 5-10°C / min, and the annealing time is 2-4h.

[0019] The application of the above-mentioned PtM ordered alloy composite catalyst is to use the catalyst in the oxygen reduction reaction (ORR) of a fuel cell.

[0020] The beneficial effects of the present invention compared to the prior art are:

[0021] (1) The present invention can adsorb Pt, P, M (M = Co, Fe, Ni) precursor salts onto a carbon support by an impregnation evaporation method, and then anneal PtM and M by multiple high-temperature annealing steps. x P is uniformly loaded on the carbon support to obtain the composite catalyst PtM-M x P / C;

[0022] (2) By controlling the high temperature annealing conditions, multi-stage calcination is performed on the first formed Pt and M x P, and then induced by high temperature M x P undergoes partial phase transformation and decomposition, and Pt forms PtM intermetallic compound with M by diffusion, and at the same time, it x P formed a heterogeneous composite structure; the resulting PtM-M x The P / C catalyst is evenly dispersed on the surface of the carbon support; the resulting PtM intermetallic compound can effectively enhance the activity and stability of the catalyst. x The presence of P not only regulates the adsorption capacity of Pt for reaction intermediates, but also enhances the metal-support interaction (SMSI) between the carbon support and PtM, further improving the activity and stability of the catalyst.

[0023] The mass activity (MA) of the phosphide-induced PtM ordered alloy composite catalyst of the present invention is 0.384-0.321 mA / μg Pt , approximately 3.4 times that of the latest commercial 10% Pt / C. After 30,000 cycles of testing, the half-wave potential of PtCo-Co2P / C decreased by only 5mV, with a mass activity decay rate of 13.44%, demonstrating excellent stability. It can be used in the fuel cell field. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 1 is an XRD pattern of PtCo-Co2P / C prepared in Example 1 and 10% Pt / C prepared in Comparative Example 1;

[0025] Figure 2 is a high magnification TEM image of PtCo-Co2P / C prepared in Example 1;

[0026] Figure 3 is a high magnification TEM image of PtCo-Co2P / C prepared in Example 1;

[0027] Figure 4 1 is the ORR polarization diagram of PtCo-Co2P / C prepared in Example 1 and 10%Pt / C prepared in Comparative Example 1;

[0028] Figure 5The mass specific activity graphs of PtCo-Co2P / C prepared in Example 1 and Example 2 and 10% Pt / C prepared in Comparative Example 1 and Comm.10% Pt / C prepared in Comparative Example 2 are shown;

[0029] Figure 6 This is the ORR polarization diagram of PtCo-Co2P / C prepared in Example 1 before and after aging. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the spirit and scope of the technical solution of the present invention should be included in the scope of protection of the present invention.

[0031] Example 1: The preparation method of the phosphide-induced PtM ordered alloy composite catalyst of this embodiment is carried out according to the following steps:

[0032] 1. Precursor impregnation and evaporation: 50 mg of carbon support EC300J was dispersed in 60 mL of ultrapure water, and 0.59 mL of 0.0489 mol / L chloroplatinic acid aqueous solution, 0.5 mL of 0.1 mol / L cobalt chloride aqueous solution, and 0.25 mL of 0.05 mol / L sodium hypophosphite aqueous solution were added. After stirring and dispersing for 12 hours, ultrasonic dispersion was performed for 3 hours, and then the mixture was placed in a water bath and rotary evaporated at 75 ° C to obtain a black solid powder.

[0033] 2. Preparation of PtCo-Co2P / C composite catalyst: The black solid powder obtained in step 1 is placed in a corundum magnetic boat, and then the magnetic boat is placed in a tubular furnace, argon is introduced to form an inert atmosphere, and the temperature is increased to 400°C at a heating rate of 10°C / min and maintained for 2 hours for the first annealing, and then the temperature is increased to 700°C at a heating rate of 10°C / min and maintained for 2 hours for the second annealing. After cooling to room temperature, the material is taken out and ground evenly to obtain a PtM ordered alloy composite catalyst, which is recorded as PtCo-Co2P / C.

[0034] The XRD pattern of the PtCo-Co2P / C catalyst prepared in this example is shown in Figure 2. Figure 1 As shown, from Figure 1 It can be seen that the diffraction peaks of the obtained catalyst sample match well with the standard pdf cards of PtCo and Co2P, indicating the coexistence of PtCo and Co2P.

[0035] TEM images of the PtCo-Co2P / C catalyst prepared in this example are as follows: Figure 2 and 3 As shown, from Figure 2 It can be seen that the catalyst particles are well dispersed on the surface of the carbon support and no obvious agglomeration occurs. Figure 3 It can be seen that the PtCo particles are about 4 nm in size and form a heterostructure with the Co2P particles.

[0036] Comparative Example 1: In this comparative example, no M source or P source was added, and the Pt nanoparticle oxygen reduction catalyst was directly loaded by the impregnation method. The specific preparation steps are as follows:

[0037] 1. Precursor impregnation and evaporation: 50 mg of carbon support EC300J was dispersed in 60 mL of ultrapure water, and 0.59 mL of a 0.0489 mol / L chloroplatinic acid aqueous solution was added. After stirring and dispersing for 12 hours, ultrasonic dispersion was performed for 3 hours, and then the mixture was placed in a water bath and rotary evaporated at 75 ° C to obtain a black solid powder.

[0038] 2. Preparation of catalyst: The powder obtained in step 1 was placed in a corundum magnetic boat, and then the magnetic boat was placed in a tubular furnace. Argon was introduced to form an inert atmosphere. The temperature was raised to 400°C at a heating rate of 10°C / min and maintained for 2h. The mixture was cooled to room temperature and ground evenly to obtain a Pt / C catalyst.

[0039] The ORR polarization curves of PtCo-Co2P / C prepared in Example 1 and 10% Pt / C prepared in Comparative Example 1 were tested. The specific testing method was as follows: the electrochemical properties of the catalyst were tested with the help of the RRDE testing system and the electrochemical workstation of Shanghai Chenhua Instrument Co., Ltd. The testing system is a three-electrode system, with a glassy carbon electrode as the working electrode, a reversible hydrogen electrode (RHE) as the reference electrode, a platinum wire as the auxiliary electrode, and a 0.1M HClO4 aqueous solution as the electrolyte. The steps for making the thin film electrode are as follows: weigh 2.5mg of catalyst, add 1000μl of dispersion liquid (a mixed liquid of anhydrous ethanol, ultrapure water, and Nafion solution), ultrasonicate for 40min to obtain a uniformly dispersed catalyst dispersion, take 20μL and add it dropwise to an area of 0.2472cm 2 The working electrode was baked on a glassy carbon electrode with a catalyst surface loading of 0.2 mg Pt / cm 2 ORR polarization curves were measured using linear sweep voltammetry. O2 was introduced into the electrolyte for 20 minutes until saturation, and the disk electrode was rotated at 1600 rpm. The scan rate was 10 mV / s, and the potential range was 0.05–1.2 V. Figure 4 is the ORR polarization diagram of PtCo-Co2P / C prepared in Example 1 and 10%Pt / C prepared in Comparative Example 1; Figure 4 It can be seen that the half-wave potential of PtCo-Co2P / C is 0.905V and the mass activity (MA) is 0.384mA / μg Pt , which is significantly higher than 10% Pt / C. The latter has a half-wave potential of 0.872 V and a mass activity (MA) of 0.0839 mA / μg Pt .

[0040] Comparative Example 2: Purchase the latest commercial 10% Pt / C (Comm.10% Pt / C) from a certain company and use it directly for testing without any treatment. The mass activity (MA) of the Comm.10% Pt / C is 0.112 mA / μg Pt .

[0041] The mass activity of the PtCo-Co2P / C prepared in Example 1 and the Comm.10%Pt / C prepared in Comparative Example 2 was tested by first determining the kinetic current of the catalyst at 0.9V based on the oxygen reduction polarization curve, and reading the current j at 0.9V in the curve. A and the limiting diffusion current j L , then the kinetic current needs to be calculated according to the Koutechy-Levich equation (abbreviated as KL equation):

[0042] 1 / j A =1 / j K +1 / j L +1 / j f

[0043] where 1 / j f is very small and can be ignored during calculation, so the KL equation can be simplified to:

[0044] 1 / j A =1 / j K +1 / j L

[0045] Where: j A ——Current at 0.9V in the LSV curve (mA)

[0046] j K ——Calculated kinetic current at 0.9V (mA)

[0047] j L ——Limiting diffusion current in the LSV curve, usually the current at 0.4V (mA)

[0048] Then, using the above kinetic current j K The mass specific activity of the catalyst was calculated based on the mass of Pt on the electrode.

[0049] MA=j K / m Pt

[0050] Where: MA——mass specific activity (mA / μg Pt )

[0051] j K ——Calculated kinetic current at 0.9V (mA)

[0052] m Pt ——Mass of Pt on the glassy carbon electrode (ug)

[0053] Figure 5 The mass activity diagram of PtCo-Co2P / C prepared in Example 1, 10%Pt / C prepared in Comparative Example 1, and Comm.10%Pt / C prepared in Comparative Example 2 is shown. Figure 5 It can be seen that the oxygen reduction mass activity of PtCo-Co2P / C prepared in Example 1 is better than that of Comparative Example 1 and Comparative Example 2. The mass activity (MA) of PtCo-Co2P / C prepared in Example 1 is 0.384 mA / μg Pt , which is about 3.4 times that of the latest commercial 10% Pt / C (Comparative Example 2).

[0054] The PtCo-Co2P / C catalyst prepared in Example 1 was subjected to ORR aging testing. Specifically, the catalyst stability was assessed using an accelerated aging test. Cyclic voltammetry was performed in an O2-saturated electrolyte at a sweep potential of 0.6 V to 0.95 V and a sweep rate of 0.2 V / s. LSV tests were performed before and after the accelerated aging test to compare the ORR polarization curves. Figure 6 The ORR polarization diagram of the PtCo-Co2P / C catalyst prepared in Example 1 before and after aging is shown in FIG. Figure 6 It can be seen that after 30,000 cycles of testing, the half-wave potential decayed by only 5 mV, and the mass activity decay rate was 13.44%. The PtCo-Co2P / C catalyst prepared in Example 1 has good stability.

[0055] Comparative Example 3: This comparative example adopts a high-temperature annealing step. The preparation method of the catalyst of this comparative example is carried out according to the following steps:

[0056] 1. Preparation of black solid powder: This step is the same as Example 1;

[0057] 2. Preparation of PtCo-Co2P / C composite catalyst: The black solid powder obtained in step 1 was placed in a corundum magnetic boat, and then the magnetic boat was placed in a tube furnace. Argon was introduced to form an inert atmosphere. The temperature was increased to 700°C at a heating rate of 10°C / min and maintained for 2 hours for annealing. After cooling to room temperature, the catalyst was taken out and ground evenly to obtain the catalyst.

[0058] The catalyst obtained in this comparative example has a half-wave potential of 0.895 V and a MA of 0.263 mA / μg. Pt , which is lower than the performance of the two-stage annealing in Example 1, indicating that the staged annealing is more beneficial to the oxygen reduction performance.

[0059] Example 2: The preparation method of the phosphide-induced PtM ordered alloy composite catalyst of this embodiment is carried out according to the following steps:

[0060] 1. Precursor impregnation and evaporation: 50 mg of carbon support ECP600-JD was dispersed in 60 mL of ultrapure water, and 0.59 mL of 0.0489 mol / L chloroplatinic acid aqueous solution, 0.5 mL of 0.1 mol / L cobalt chloride aqueous solution, and 0.25 mL of 0.05 mol / L sodium hypophosphite aqueous solution were added. After stirring and dispersing for 12 hours, ultrasonic dispersion was performed for 3 hours, and then placed in a water bath and rotary evaporated at 75 ° C to obtain a black solid powder;

[0061] 2. Preparation of PtCo-Co2P / C composite catalyst: The black solid powder obtained in step 1 is placed in a corundum magnetic boat, and then the magnetic boat is placed in a tubular furnace, argon is introduced to form an inert atmosphere, and the temperature is increased to 400°C at a heating rate of 10°C / min and maintained for 2 hours for the first annealing, and then the temperature is increased to 700°C at a heating rate of 10°C / min and maintained for 2 hours for the second annealing. After cooling to room temperature, the material is taken out and ground evenly to obtain a PtM ordered alloy composite catalyst, which is recorded as PtCo-Co2P / C.

[0062] The difference between Example 2 and Example 1 is that the carbon carrier is different. The ORR half-wave potential of the obtained PtCo-Co2P / C catalyst is 0.902V and MA is 0.363mA / μg. Pt .

[0063] Example 3: The preparation method of the phosphide-induced PtM ordered alloy composite catalyst of this embodiment is carried out according to the following steps:

[0064] 1. Precursor impregnation and evaporation: 50 mg of carbon support EC300J was dispersed in 60 mL of ultrapure water, and 0.59 mL of 0.0489 mol / L chloroplatinic acid aqueous solution, 0.5 mL of 0.1 mol / L nickel chloride aqueous solution, and 0.25 mL of 0.05 mol / L sodium hypophosphite aqueous solution were added. After stirring and dispersing for 12 hours, ultrasonic dispersion was performed for 3 hours, and then placed in a water bath and rotary evaporated at a temperature of 75 ° C to obtain a black solid powder;

[0065] 2. Preparation of PtNi-Ni2P / C composite catalyst: The black solid powder obtained in step 1 is placed in a corundum magnetic boat, and then the magnetic boat is placed in a tubular furnace, argon is introduced to form an inert atmosphere, and the temperature is increased to 400°C at a heating rate of 10°C / min and maintained for 2 hours for the first annealing, and then the temperature is increased to 600°C at a heating rate of 10°C / min and maintained for 2 hours for the second annealing. After cooling to room temperature, the material is taken out and ground evenly to obtain a PtM ordered alloy composite catalyst, which is recorded as PtNi-Ni2P / C.

[0066] The difference between Example 3 and Example 1 is that the metal is different. The half-wave potential of the PtNi-Ni2P / C catalyst obtained is 0.899V and MA is 0.321mA / μg. Pt .

[0067] The present invention uses transition metal phosphide as a precursor, adopts impregnation evaporation and multi-stage high temperature annealing to obtain PtM-M x P / C composite catalyst. The introduced Pt source first decomposes into Pt during the first high temperature annealing process, and the M source and P source form M at high temperature. x P, by controlling the annealing conditions, finally forms PtM intermetallic compound and M x Composite structure with coexistence of P. M x The presence of P not only regulates the adsorption capacity of Pt for reaction intermediates and has a strong electronic regulation and anchoring effect on PtNPs, but also enhances the metal-support interaction (SMSI) between the carbon support and PtM, thereby improving the activity and stability of the catalyst.

Claims

1. A method for preparing a phosphide-induced PtM ordered alloy composite catalyst, characterized in that: The method proceeds as follows:

1. Precursor impregnation and evaporation: Disperse the carbon support in ultrapure water, then add Pt source, P source, and M source aqueous solutions, stir and disperse for 8-12 hours, ultrasonically disperse for 3-4 hours, and then place in a water bath and rotary evaporate to dryness to obtain a black solid powder; 2. Preparation of PtM-M by Multi-stage High-temperature Heat Treatment x P / C composite catalyst: The black powder obtained in step 1 is placed in a high-temperature furnace and calcined and annealed in multiple stages under an inert atmosphere. The calcination conditions are as follows: the first stage annealing temperature is 200-400 °C, the heating rate is 5-10 °C / min, and the annealing time is 2-4 h; the second stage annealing temperature is 600-800 °C, the heating rate is 5-10 °C / min, and the annealing time is 2-4 h; after cooling and grinding, a PtM ordered alloy composite catalyst is obtained, which is denoted as PtM-M x P / C; the catalyst is composed of ordered PtM alloy and M x P is uniformly loaded on a carbon support, and the ordered PtM alloy is composed of M x P is induced by high-temperature phase transformation; where M is Co, Fe or Ni, and x=0.5~3.

2. The method for preparing a phosphide-induced PtM ordered alloy composite catalyst according to claim 1, characterized in that: The carbon support described in step 1 is ECP600-jD, EC300J, BP-2000 or XC-72.

3. The method for preparing a phosphide-induced PtM ordered alloy composite catalyst according to claim 1 or 2, characterized in that: The platinum source described in step 1 is an aqueous solution of chloroplatinic acid.

4. The method for preparing a phosphide-induced PtM ordered alloy composite catalyst according to claim 1 or 2, characterized in that: The M source described in step 1 is cobalt chloride, cobalt nitrate, nickel chloride, nickel nitrate, ferric chloride or ferric nitrate.

5. The method for preparing a phosphide-induced PtM ordered alloy composite catalyst according to claim 1 or 2, characterized in that: The phosphorus source described in step 1 is an aqueous solution of sodium hypophosphite.

6. The method for preparing a phosphide-induced PtM ordered alloy composite catalyst according to claim 1 or 2, characterized in that: The molar ratio of Pt to M in step 1 is 1:(0.25 ~ 5), and the molar ratio of phosphorus to M is 1:(0.5 ~ 5).

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