CN112510221B

CN112510221B - Fuel cell electrocatalyst and preparation method and application thereof

Info

Publication number: CN112510221B
Application number: CN202110144650.3A
Authority: CN
Inventors: 刘建国; 陈雅文; 李佳
Original assignee: Nanjing University
Current assignee: Nanjing University
Priority date: 2021-02-03
Filing date: 2021-02-03
Publication date: 2021-05-11
Anticipated expiration: 2041-02-03
Also published as: CN112510221A

Abstract

The invention discloses a fuel cell electrocatalyst, a preparation method and application thereof. The preparation method of the catalyst comprises the following steps: (1) preparing a metal-nitrogen-carbon support; (2) preparing a catalyst precursor; (3) the platinum reduced by the electrochemical reduction method forms an alloy with the transition metal in the carrier. The catalyst utilizes metal-nitrogen-carbon as a carrier to adsorb platinum salt, the limitation effect of a pore passage limits the particle size of platinum particles, the transition metal contained in the carrier and Pt form alloy, the Pt loading capacity can be reduced, the Pt utilization rate is improved, the preparation process is simple, the product has excellent oxygen reduction activity, and the catalyst can be applied to proton exchange membrane fuel cells.

Description

Fuel cell electrocatalyst and preparation method and application thereof

Technical Field

The invention relates to an electrocatalyst and a preparation method and application thereof, in particular to a fuel cell electrocatalyst and a preparation method and application thereof.

Background

The proton exchange membrane fuel cell electrocatalyst that is widely used commercially remains a Pt/C catalyst. However, the platinum metal is scarce in resources and expensive, and the development of the fuel cell is seriously hindered. Therefore, the problem to be solved is to reduce the amount of noble metal platinum and find a cheap substitute. Researchers have found that Pt-M (M is typically Ti, Cr, Mn, Fe, Co, Ni) alloy catalysts can improve the activity and stability of the catalyst. In the preparation method of the alloy catalyst, a chemical reduction method is a relatively common method, and generally, a precursor of the catalyst and a carrier are uniformly mixed, and then a reducing agent is added or the precursor is reduced by a high-temperature roasting method in a reducing atmosphere to obtain the alloy catalyst, but the chemical reduction method has complicated steps and long synthesis time, and the particle size of formed alloy particles is difficult to control. The microwave-assisted glycol reduction method utilizes the advantages of rapid and uniform microwave heating, can synthesize the alloy catalyst rapidly, but high heat generated by microwave heating easily causes particle agglomeration, and has requirements on the use amount of a precursor and a carrier, such as excessive carrier, which is easy to cause explosion. The electrochemical reduction method adopted by the invention can control the particle size in a proper range, the preparation method is simple and quick, the energy consumption is low, and the obtained alloy catalyst has excellent oxygen reduction performance.

Disclosure of Invention

The purpose of the invention is as follows: the invention aims to provide a fuel cell electrocatalyst with small platinum particle size, low Pt loading capacity, high utilization rate and good oxygen reduction activity, and also aims to provide a preparation method of the electrocatalyst, which can control the Pt particle size and has simple preparation process, and the application of the electrocatalyst.

The technical scheme is as follows: the fuel cell electrocatalyst comprises a metal-nitrogen-carbon carrier material, wherein a platinum precursor is adsorbed in micropores of the metal-nitrogen-carbon carrier material, the platinum precursor on the metal-nitrogen-carbon carrier material is subjected to in-situ reduction and forms Pt-transition metal alloy nanoparticles with transition metals in a carrier, and the loading amount of platinum is 0.2wt% -1.1 wt%.

Wherein the metal in the metal-nitrogen-carbon carrier is Fe, Co or Mn, and the metal is prepared from at least one of chlorides, nitrates, acetates, carbonates, phosphates, sulfates, oxalates, citrates and acetylacetonato compounds of Fe, Co and Mn.

The preparation method of the fuel cell electrocatalyst comprises the following steps:

(1) dissolving 2-methylimidazole in methanol to obtain a solution A, dissolving zinc nitrate hexahydrate and metal salt in methanol to obtain a solution B, uniformly mixing the solution A and the solution B for hydrothermal reaction, and centrifuging, washing and drying a precipitate to obtain a metal-nitrogen-carbon precursor; roasting the metal-nitrogen-carbon precursor, and then cooling to room temperature to obtain a metal-nitrogen-carbon carrier material;

(2) adding a metal-nitrogen-carbon carrier material into a metal platinide solution, refluxing and stirring, carrying out suction filtration and washing, and carrying out vacuum drying to obtain a catalyst precursor;

(3) uniformly mixing the catalyst precursor with ethanol, ultrapure water and Nafion to obtain slurry with the catalyst precursor uniformly dispersed, dripping the slurry on an electrode, treating by using an electrochemical workstation, reducing platinum, and alloying the reduced platinum and transition metal in a carrier to obtain the alloy catalyst.

In the step (1), the hydrothermal reaction temperature is 100-160 ℃, the roasting temperature is 400-1200 ℃ in protective gas when the metal-nitrogen-carbon precursor is roasted, and the metal salt is at least one of chlorides, nitrates, acetates, carbonates, phosphates, sulfates, oxalates, citrates and acetylacetonato compounds of Fe, Co and Mn.

Wherein, in the step (2), the reflux temperature is 25-80 ℃, the metal platinum compound is chloroplatinic acid, potassium chloroplatinate, sodium chloroplatinate, potassium chloroplatinate, platinum acetylacetonate, and the concentration of the metal platinum compound solution is 0.1-50 mol/L.

In the step (3), the volume fraction of Nafion in the slurry is 3% -8%, the volume fraction of ultrapure water is 10% -20%, the volume fraction of ethanol is 80% -95%, the treatment method in the electrochemical workstation is cyclic voltammetry, linear voltammetry or potentiostatic voltammetry, and the electrolyte in the electrochemical workstation is O₂/N₂A saturated perchloric acid electrolyte; the concentration of the slurry on the rotating disk electrode is 0.2-1.0mg/cm²。

Wherein, during the cyclic voltammetry scanning in the step (3), the scanning potential is 0-1.5V, the scanning speed is 10-100 mv/s, and the number of scanning circles is 1-100 circles; the scanning potential is 0-1.5V during linear volt-ampere scanning, the scanning speed is 5-20 mv/s, the rotating speed is 500-2000 rpm, and the scanning times are 1-10 times; when constant potential volt-ampere scanning is carried out, the scanning potential is-1.0V-0.68V, and the scanning time is 10-10000 s.

The fuel cell electrocatalyst is applied to a proton exchange membrane fuel cell.

Has the advantages that: compared with the prior art, the invention has the following remarkable advantages: 1. the metal-nitrogen-carbon containing abundant micropores is used as a carrier to adsorb platinum salt, and the limitation of pore channels limits the particle size of reduced platinum particles. The platinum particles obtained by electrochemical reduction cannot grow up, and meanwhile, because the metal-nitrogen-carbon carrier contains uniformly distributed transition metal, the reduced Pt can form alloy with the metal-nitrogen-carbon carrier, so that the Pt loading capacity is reduced, and the Pt utilization rate is improved; 2. the preparation process is simple, the operation is easy, and the rapid preparation can be realized; 3. has excellent oxygen reduction activity and can be applied to proton exchange membrane fuel cells.

Drawings

FIG. 1 is a cyclic voltammogram of an electrochemical reduction process of the present invention;

FIG. 2 is a linear sweep voltammogram of the electrochemical reduction process of the invention;

FIG. 3 shows Pt in example 1₃Transmission electron microscope pictures of 10nm size of Fe alloy;

FIG. 4 shows Pt in example 2₃A transmission electron microscope picture of 5nm size of Fe alloy;

FIG. 5 is a graph comparing the oxygen reduction activity of the electrocatalysts of example 1 and example 9;

FIG. 6 is a transmission electron microscope photograph of an iron-nitrogen-carbon support in example 1;

FIG. 7 is an oxygen reduction test curve for the iron-nitrogen-carbon support of example 1;

FIG. 8 is a graph of the oxygen reduction test of the iron-nitrogen-carbon support in example 1

FIG. 9 is a graph of XPS data for an iron-nitrogen-carbon support in example 1;

fig. 10 is a graph of BET data for the iron-nitrogen-carbon support of example 1.

Detailed Description

Example 1

(1) 1418mg of 2-methylimidazole is dissolved in 180ml of methanol to obtain a solution A, 1220mg of zinc nitrate hexahydrate and 30mg of ferric nitrate nonahydrate are dissolved in 180ml of methanol to obtain a solution B, and the solution A and the solution B are respectively subjected to ultrasonic treatment for half an hour to be uniformly dispersed; then pouring the solution A into the solution B, carrying out ultrasonic treatment for 3min, transferring the mixed solution into a hydrothermal kettle, and carrying out hydrothermal reaction for 6h in a forced air oven at 120 ℃; pouring the solution into a centrifuge tube after the hydrothermal reaction, centrifugally washing the solution for three times by using methanol at 12000rpm for 5min, putting the obtained precipitate into an air-blast drying oven for drying at 60 ℃ for 12h, pouring the dried sample into a mortar for fully grinding to obtain about 300mg of light yellow powder, pouring the powder into a porcelain boat, placing the porcelain boat in a quartz tube of a tube furnace, carrying out heat treatment under the protection of nitrogen, raising the temperature to 1000 ℃ at the heating rate of 5 ℃/min, preserving the heat for 3h, taking out the powder after the temperature is reduced to the room temperature, fully grinding the obtained iron-nitrogen-carbon by using the mortar, and weighing the weight of the obtained iron-nitrogen-carbon to be about 60 mg. Fig. 6 is a TEM picture of the resulting iron-nitrogen-carbon support, and it can be seen that the support exhibits a regular polyhedral shape. Fig. 7 and 8 are electrochemical test curves of the carrier of iron, nitrogen and carbon, and it can be seen that the carrier has oxygen reduction activity. FIG. 9 is an XPS picture of an iron nitrogen carbon support, which shows that the support contains rich Fe-Nx oxygen reduction active sites. Fig. 10 is a BET data graph of an iron nitrogen carbon support, and it can be seen that the support has a large specific surface area and is rich in micropores.

(2) Taking 0.62ml of prepared chloroplatinic acid solution (wherein the concentration of Pt is 3.77 mg/ml), dripping the solution into 50ml of ultrapure water, stirring at room temperature for 30min, weighing 60mg of iron-nitrogen-carbon powder, adding the powder into the aqueous solution of chloroplatinic acid, stirring at room temperature for 8h, performing suction filtration and washing by using a suction filtration device after stirring and adsorption are finished, performing suction filtration by using the ultrapure water, performing suction filtration by using about 5L of ultrapure water to completely wash and remove redundant chloroplatinic acid so that adsorbed platinum ions only exist in micropores of a carrier, taking down filter paper after the suction filtration is finished, putting the filter paper into a beaker, sealing by using a sealing film, leaving a small air-permeable hole, drying the filter paper in a vacuum oven at 60 ℃ for 12h, and fully grinding by using a mortar after the drying is finished to obtain;

(3) pouring 0.1M perchloric acid into two electrolytic cells, respectively introducing nitrogen and oxygen into the two electrolytic cells, saturating the electrolytic cells after 30min, putting the hydrogen label into an electrolytic cell after electrolysis, putting a carbon rod into the electrolytic cell after being cleaned by perchloric acid, weighing 6mg of catalyst precursor, pouring the catalyst precursor into a glass vial, then adding 50ml of ultrapure water, 432uL of ethanol and 18uL of 5% Nafion into the small bottle, carrying out ultrasonic treatment for 10min to obtain uniform slurry, sucking 10uL of slurry by using a liquid transfer gun and dripping the slurry on a glassy carbon electrode, drying the slurry, then installing the electrode on a rotating device, connecting an electrode wire of an electrochemical workstation with a hydrogen label and a carbon rod, wherein the hydrogen mark is used as a reference electrode, the carbon rod is used as a counter electrode, the glassy carbon electrode is used as a working electrode, CHI760 is opened after the connection is finished, the cyclic voltammetry scanning is selected for 60 circles, the scanning speed is 50mv/s, and the scanning potential interval is 0-1.2V. And after 60 circles of scanning is finished, the catalyst with the theoretical Pt loading of 1% is prepared, and the oxygen reduction activity of the catalyst is tested by scanning linear sweep voltammetry once again every 10 circles.

As can be seen from fig. 1, the first turnThe CV curve is the curve of Fe-N-C, the Fe-N-C has oxygen reduction activity, the oxygen reduction peak position continuously moves to the right along with the rising of the number of cycles of cyclic voltammetry scanning from the 1 st cycle to the 5 th cycle, the 10 th cycle and the 15 th cycle, which shows that Pt is continuously reduced, the LSV curve in figure 2 shows that the half-wave potential continuously rises, the oxygen reduction activity is continuously enhanced, the stable state is reached after the cyclic voltammetry scanning is carried out for 60 cycles, the half-wave potential of the formed alloy catalyst reaches 0.815V, and the TEM picture in figure 3 shows that the reduced Pt and transition metal Fe in the carrier form Pt₃An Fe alloy.

Example 2

The difference between this example and example 1 is: the volumes of the chloroplatinic acid solution added in the step 2 are respectively 1.24ml, 2.48ml, 4.96ml and 9.92ml, and as can be seen from the TEM picture of FIG. 4, the reduced Pt and the transition metal Fe in the carrier form Pt₃An Fe alloy.

Example 3

The difference between this example and example 1 is: potassium chloroplatinate was used in step 2, the volume of potassium chloroplatinate being 6.42ml, with the concentration of Pt being 3.77 mg/ml.

Example 4

The difference between this example and example 1 is: in step 1, 1220mg of zinc nitrate hexahydrate and 80mg of ferric ammonium citrate were dissolved in 180ml of methanol to obtain a solution B

Example 5

The difference between this example and example 1 is: the solution B obtained in step 1 was prepared by dissolving 1220mg of zinc nitrate hexahydrate and 65mg of iron acetylacetonate in 180ml of methanol

Example 6

The difference between this example and example 1 is: the solution B obtained in step 1 was prepared by dissolving 1220mg of zinc nitrate hexahydrate and 48mg of ferric chloride in 180ml of methanol

Example 7

The difference between this example and example 1 is: and 3, cyclic voltammetry scanning is performed for 10 circles.

Example 8

The difference between this example and example 1 is: and 3, performing Pt reduction by adopting a linear scanning voltammetry method, wherein the scanning speed is 10mv/s, the scanning potential interval is 0-1.2V, the times are 10 times, Pt is gradually reduced along with the increase of the scanning times, and the Pt reaches an equilibrium state after 10 times of scanning.

Example 9

The difference between this example and example 1 is: in the step 3, a constant potential voltammetry is adopted for Pt reduction, the scanning potential is 0V, the scanning time is 5000s, and as can be seen from fig. 4, the Pt can also be reduced by the method, but after the reduction equilibrium is reached, the oxygen reduction activity of the sample is not as good as that of the sample reduced by the cyclic voltammetry.

Claims

1. The fuel cell electrocatalyst is characterized by comprising a metal-nitrogen-carbon carrier material, wherein a platinum precursor is adsorbed in micropores of the metal-nitrogen-carbon carrier material, and the platinum precursor on the metal-nitrogen-carbon carrier material is subjected to in-situ reduction to form alloy nanoparticles with transition metals in a carrier, wherein the loading amount of platinum is 0.2-1.1 wt%;

the metal in the metal-nitrogen-carbon carrier is Fe, Co or Mn;

the preparation method of the fuel cell electrocatalyst specifically comprises the following steps:

(1) dissolving 2-methylimidazole in methanol to obtain a solution A, dissolving zinc nitrate hexahydrate and metal salt in methanol to obtain a solution B, uniformly mixing the solution A and the solution B for hydrothermal reaction, and centrifuging, washing and drying a precipitate to obtain a metal-nitrogen-carbon precursor; roasting the metal-nitrogen-carbon precursor, and then cooling to room temperature to obtain a metal-nitrogen-carbon carrier;

(2) adding the metal-nitrogen-carbon carrier into a metal platinide solution, refluxing and stirring, carrying out suction filtration and washing, and carrying out vacuum drying to obtain a catalyst precursor;

(3) uniformly mixing the catalyst precursor with ethanol, ultrapure water and Nafion to obtain slurry with the catalyst precursor uniformly dispersed, dripping the slurry on an electrode, treating by using an electrochemical workstation to reduce platinum, and alloying the reduced platinum and transition metal in a carrier to obtain an alloy catalyst;

wherein, in the step (1), the hydrothermal reaction temperature is 100-160 ℃, and the roasting temperature is 400-1200 ℃ in the protective gas during roasting of the metal-nitrogen-carbon precursor;

the metal salt is at least one of chlorides, nitrates, acetates, carbonates, phosphates, sulfates, oxalates, citrates and acetylacetonato compounds of Fe, Co and Mn;

in the step (2), the reflux temperature is 25-80 ℃, and the metal platinum compounds are chloroplatinic acid, potassium chloroplatinate, sodium chloroplatinate, potassium chloroplatinate and platinum acetylacetonate; the concentration of the metal platinum compound solution is 0.1 mmol/L-50 mol/L;

in the step (3), the volume fraction of Nafion in the slurry is 3% -8%, the volume fraction of ultrapure water is 10% -20%, the volume fraction of ethanol is 80% -95%, the processing method in the electrochemical workstation is cyclic voltammetry, linear voltammetry or potentiostatic voltammetry, and the electrolyte in the electrochemical workstation is O₂And N₂A saturated perchloric acid electrolyte; the concentration of the slurry on the electrode is 0.2-1.0mg/cm²；

In cyclic voltammetry scanning, the scanning potential is 0-1.5V, the scanning speed is 10-100 mv/s, and the number of scanning circles is 1-100 circles; the scanning potential is 0-1.5V during linear volt-ampere scanning, the scanning speed is 5-20 mv/s, the rotating speed is 500-2000 rpm, and the scanning times are 1-10 times; when constant potential volt-ampere scanning is carried out, the scanning potential is-1.0V-0.68V, and the scanning time is 10-10000 s.

2. Use of the fuel cell electrocatalyst according to claim 1 as an electrocatalyst in a proton exchange membrane fuel cell.