CN112864405B

CN112864405B - Oxygen-reduced cobalt @ nitrogen-doped graphite crystal nanobelt-Keqin carbon black composite catalyst and preparation method and application thereof

Info

Publication number: CN112864405B
Application number: CN202110008483.XA
Authority: CN
Inventors: 钱东; 苏侃达; 张志良; 龙炫达; 刘灿辉; 郭江南; 李俊华
Original assignee: Central South University
Current assignee: Central South University
Priority date: 2021-01-05
Filing date: 2021-01-05
Publication date: 2022-05-06
Anticipated expiration: 2041-01-05
Also published as: CN112864405A

Abstract

The invention discloses a high-performance oxygen-reduced cobalt @ nitrogen-doped graphite crystal nanobelt-Keqin carbon black composite catalyst, a preparation method and application thereof, wherein the catalyst is formed by inlaying simple substance cobalt particles in a nitrogen-doped carbon material; the nitrogen-doped carbon material is formed by compounding a nitrogen-doped graphite crystal nanobelt and nitrogen-doped ketjen black in situ; the preparation method comprises the steps of mixing cobalt salt, a nitrogen-containing organic micromolecule compound and carbon black, placing the mixture in a protective atmosphere, and carrying out two-stage roasting treatment to obtain the catalyst; the catalyst has simple preparation process, convenient operation and low cost, and is beneficial to large-scale production; the prepared composite catalyst is applied to the oxygen reduction process of the fuel cell, has the characteristics of high activity, good stability and the like, has comprehensive performance exceeding 20 wt% of a Pt/C commercial catalyst, and shows good application prospect.

Description

Oxygen-reduced cobalt @ nitrogen-doped graphite crystal nanobelt-Keqin carbon black composite catalyst and preparation method and application thereof

Technical Field

The invention relates to an oxygen reduction (ORR) composite catalyst, a preparation method and application thereof, in particular to a high-performance Co @ N-C-KB composite catalyst and a preparation method thereof, and also relates to application of the Co @ N-C-KB composite catalyst in a fuel cell, belonging to the technical field of electrocatalysis.

Technical Field

The oxygen reduction (ORR) catalysts currently used in fuel cells are mainly noble metal Pt-based catalysts. However, the Pt-based catalyst has the defects of rare reserves, high price, poor stability and the like, and seriously hinders the wide use of the fuel cell. The development of a cheap and commercialized substitute of the Pt-based catalyst becomes a primary task for large-scale popularization and application of fuel cells.

Currently some scientists are working on developing non-noble metal ORR electrocatalysts in which a transition metal compound is composited with a functional carbon material. The composite catalysts utilize high electrocatalytic activity of transition metal compounds, high conductivity and large specific surface area of functional carbon materials, and have certain improvement on performance, but have certain distance from practical application. Besides transition metal oxygen group and nitrogen group compounds, the transition metal simple substance group ORR catalysts reported in recent years are poor in performance except for transition metal single atom catalysts reported in recent years (generally, the preparation process of the transition metal single atom catalysts has high requirements on operation skills, the comprehensive performance of the transition metal single atom catalysts is still to be improved, and the transition metal single substance group ORR catalysts are far away from practical application). The development of a high-efficiency transition metal elementary substance-based ORR catalyst with simple preparation process and low cost is undoubtedly of great significance for large-scale commercial application of fuel cells.

Disclosure of Invention

Aiming at the defects of poor comprehensive performance and complex preparation of a pure cobalt simple substance based composite material as an ORR electrocatalyst in the prior art, the invention aims to provide the ORR electrocatalyst formed by embedding simple substance cobalt particles in a nitrogen-doped carbon material formed by in-situ compounding of a nitrogen-doped graphite crystal nano-belt and nitrogen-doped ketjen black carbon, and the comprehensive catalytic performance of the ORR electrocatalyst exceeds that of a commercial Pt/C catalyst.

The second purpose of the invention is to provide a preparation method of the high-performance oxygen reduction Co @ N-C-KB composite catalyst, which is extremely simple and low in cost and meets the application requirements of industrial production.

The third purpose of the invention is to provide the application of the high-performance oxygen reduction Co @ N-C-KB composite catalyst in a fuel cell, wherein the ORR comprehensive catalytic performance of the Co @ N-C-KB composite catalyst exceeds that of a commercial 20% Pt/C catalyst in an alkaline medium.

In order to realize the technical purpose, the invention provides a high-performance oxygen reduction Co @ N-C-KB composite catalyst which is formed by inlaying simple substance cobalt particles in a nitrogen-doped carbon material; the nitrogen-doped carbon material is formed by compounding a nitrogen-doped graphite crystal nanobelt and nitrogen-doped ketjen black in situ.

The main active components in the high-performance oxygen reduction Co @ N-C-KB composite catalyst provided by the invention are derived from simple substance cobalt and nitrogen-doped functional carbon materials, and organic combination between the simple substance cobalt and the nitrogen-doped functional carbon materials can increase defects and active sites, so that the catalytic activity and the stability of the composite material are improved. On the other hand, the nitrogen-doped graphite crystal nanobelt-ketjen black carbon composite carbon material has a large specific surface area and high conductivity, and particularly, the nitrogen-doped graphite crystal nanobelt is highly crystalline graphene, so that the catalytic performance of the composite material is further improved.

In a preferred scheme, the high-performance oxygen reduction Co @ N-C-KB composite catalyst comprises the following components in percentage by mass: 1% -15% of cobalt simple substance; 5% -39% of nitrogen-doped graphite crystal nanobelts; 60% -80% of nitrogen-doped Keqin carbon black; wherein, the mass percent of nitrogen is 1-10%. In a more preferable scheme, the high-performance oxygen reduction Co @ N-C-KB composite catalyst consists of the following components in percentage by mass: elementary cobalt: 3% -10%; nitrogen-doped graphite crystal nanobelts: 15% -30%; nitrogen-doped ketjen black: 65% -75%; wherein, the mass percent of nitrogen is 3% -7%.

The nitrogen-doped carbon material is formed by in-situ doping and carbonizing a mixture of a nitrogen-containing organic micromolecule compound and carbon black at high temperature.

The invention also provides a preparation method of the high-performance oxygen reduction Co @ N-C-KB composite catalyst, which comprises the following steps: mixing cobalt salt, nitrogen-containing organic micromolecule compound and carbon black, placing in protective atmosphere, and carrying out two-stage roasting treatment to obtain the catalyst.

In a preferred scheme, the cobalt salt is a water-soluble cobalt salt, such as cobalt chloride, cobalt nitrate, cobalt acetate and the like.

Preferably, the nitrogen-containing organic small molecule compound consists of at least one of urea, melamine, cyanuric chloride, cyanamide and dicyanodiamide and amino acid in a mass ratio of (70-85) to (5-15). The amino acid is added to increase the nitrogen doping of the carbon material in the product. The urea, melamine, cyanuric chloride, cyanamide, dicyandiamide, etc. are added to coordinate and capture metal Co²⁺And further carrying out in-situ carbonization to obtain the nitrogen-doped graphite crystal nanobelt with high conductivity and high specific surface area.

In a preferred embodiment, the amino acid includes at least one of alanine, phenylalanine, lysine, glycine, valine, leucine, proline, serine, tryptophan, and glutamic acid.

In a preferred embodiment, the carbon black material includes at least one of ketjen black, cabot conductive carbon black, and acetylene black.

Preferably, the mass ratio of the cobalt salt, the nitrogen-containing organic micromolecule compound and the carbon black is (5-15): 70-95): 5-10. In a more preferable scheme, the mass ratio of the cobalt salt, the nitrogen-containing organic small molecular compound and the carbon black is (7-10): (81-89): 6-9).

In a preferred scheme, the two-stage roasting treatment process is to carry out roasting treatment at 500-600 ℃ and 650-900 ℃ in sequence.

In a more preferable scheme, the roasting treatment time is 0.5-4 h at 500-600 ℃; the roasting treatment time is 0.5-4 h at 650-900 ℃. In the first stage of heating to 500-600 deg.c, the nitrogen-containing organic small molecular compound is pyrolyzed to produce polymerized graphite-phase carbon nitride (g-C)₃N₄)，g-C₃N₄Provides abundant pyridine nitrogen with lone pair electrons to coordinate and capture metal Co²⁺. Taking into account g-C₃N₄No ORR electrocatalytic activity per se and low conductivity and specific surface area, and g-C in the subsequent second-stage heating process to 650-900 DEG C₃N₄Further decomposition into nitrogen and cyano fragments in Co²⁺Under the catalytic action of the catalyst, the in-situ carbonization is carried out to form the nitrogen-doped graphite crystal nanobelt with high conductivity and high specific surface area, and meanwhile, cobalt ions are efficiently reduced to form simple substance cobalt.

In a preferred embodiment, the protective atmosphere is generally an inert atmosphere or a nitrogen atmosphere.

The invention also provides application of the high-performance oxygen reduction Co @ N-C-KB composite catalyst as a fuel cell oxygen reduction catalyst.

Compared with the prior art, the technical scheme of the invention has the beneficial technical effects that:

1. the oxygen reduction Co @ N-C-KB composite catalyst disclosed by the invention is formed by organically combining elemental cobalt and nitrogen-doped graphite crystal nanobelts with high conductivity and large specific surface area, namely Keqin carbon black, the substances have obvious synergistic interaction effect, and the composite catalyst shows high catalytic activity and stability.

2. The preparation method of the high-performance oxygen reduction Co @ N-C-KB composite catalyst is extremely simple, low in cost, easy to operate and beneficial to industrial production.

3. The simple substance cobalt and the nitrogen-doped graphite crystal nanobelt in the high-performance oxygen reduction Co @ N-C-KB composite catalyst are generated through in-situ reaction, the simple substance Co is embedded in the nitrogen-doped graphite crystal nanobelt-Keqin carbon black composite structure, and the physicochemical stability is good.

4. The oxygen evolution Co @ N-C-KB composite catalyst provided by the invention has the characteristics of high activity and good stability when being applied to the oxygen reduction process of a fuel cell, exceeds a commercial 20% Pt/C catalyst, greatly reduces the cost of an ORR catalyst, and shows good application prospect.

Drawings

FIG. 1 is an XRD pattern of Co @ N-C-KB from example 1, indicating that the Co @ N-C-KB composite contains elemental Co and carbon materials, and no cobalt oxide phase is present.

FIG. 2 is SEM (a, b and C) and TEM (d, e and f) images of Co @ N-C-KB in example 1, and shows that elemental Co particles are embedded in the carbon layer and a large number of graphitic nanobelts with a width of 2-8 nm are present.

FIG. 3 is a linear sweep voltammogram at 1600rpm for Co @ N-C-KB, 20 wt% Pt/C, Co @ N-C-KB-NL, Co @ N-KB, Co @ N-C, N-C-KB-1, and N-C-KB-2 from example 1, comparative example 2, comparative example 3, comparative example 4, comparative example 5, and comparative example 6.

FIG. 4 is a linear sweep voltammogram of Co @ N-C-KB in example 1 at different rotation speeds; (b) is a graph of the electron transfer number during ORR with Co @ N-C-KB as catalyst in example 1.

FIG. 5 is a graph of chronoamperometry plots for Co @ N-C-KB and 20 wt% Pt/C in example 1 and comparative example 1.

Detailed Description

The following examples are given to illustrate the present invention in more detail, but do not limit the scope of the claims of the present invention.

Example 1

Preparation of Co @ N-C-KB: 0.3g KB, 0.3g 0.3g L-alanine, 3g urea and 0.25g cobalt chloride hexahydrate were weighed and ground in an agate mortar for 30min to obtain a uniformly mixed precursor powder. And (3) putting the ground precursor powder into a tube furnace, heating to 550 ℃ at the speed of 5 ℃/min in the nitrogen protective atmosphere, preserving heat for 2h, then continuously heating to 750 ℃ at the speed of 3 ℃/min, preserving heat for 2h, and naturally cooling to room temperature to obtain Co @ N-C-KB.

The X-ray diffractometer (XRD, Bruke D8 Advance, Cu ka,

) Performing phase analysis on the product; the morphology of the product was observed by means of a scanning electron microscope (SEM, Zeiss HD,10kV) and a transmission electron microscope (TEM, JEOL-2010,200 kV).

The ORR activity of the samples was evaluated by rotating the disk electrode (RDE) via the CHI760D electrochemical workstation testing the limiting current density of the samples in a three-electrode system. Preparation of a working electrode: 5mg of sample to be detected is weighed and dispersed in 1mL of mixed solution (volume ratio is 9:10:1) of ethanol, water and 5% Nafion solution, and ultrasonic treatment is carried out for 1h to obtain 5mg/mL of dispersion liquid. And drawing 10 mu L of suspension by using a pipette, dripping the suspension on a glassy carbon electrode with the diameter of 5mm, and drying at room temperature to be tested. During the test, the counter electrode was a platinum electrode and the reference electrode was an Hg/HgO electrode. In evaluating the ORR activity of the samples, the electrolyte was an oxygen-saturated 0.1M KOH solution, at 1600rpm, at a sweep rate of 5mV/s, and at a sweep voltage in the range of 0.15V to-0.7V (vs. Under different rotating speed conditions, the electron transfer number in the oxygen reduction process is calculated by a Koutech-Levich formula. The stability of ORR catalysis was compared by chronoamperometry with a test voltage of-0.5V (vs. Hg/HgO) and an electrolyte of 0.1M KOH saturated with oxygen.

The initial potential of the Co @ N-C-KB composite as the ORR catalyst was 0.04V (vs. Hg/HgO), the half-wave potential was-0.037V (vs. Hg/HgO), and the limiting current density was-5.56 mA/cm². The oxygen reduction average electron transfer number in the potential range of-0.4V to-0.6V (vs. Hg/HgO) is about 4.03, tending toward the 4 electron transfer pathway. In the amperometric evaluation, the current density retention rate was about 97% after 18000s of continuous operation.

Comparative example 1

Commercial 20 wt% Pt/C was used as ORR catalyst.

The catalytic performance was evaluated in the same manner as in example 1.

The 20 wt% Pt/C as ORR catalyst had an initial potential of 0.08V (vs. Hg/HgO), a half-wave potential of-0.025V (vs. Hg/HgO), and a limiting current density of-5.5 mA/cm². In the amperometric evaluation, the current density retention was about 86% after 18000s of continuous operation.

Comparative example 2

Co @ N-C-KB-NL was prepared as in example 1, without adding L-alanine to the preparation of Co @ N-C-KB.

The catalytic performance was evaluated in the same manner as in example 1.

Co @ N-C-KB-NL as the ORR catalyst has an initial potential of-0.028V (vs. Hg/HgO), a half-wave potential of-0.10V (vs. Hg/HgO), and a limiting current density of-4.8 mA/cm²。

Comparative example 3

Co @ N-KB was prepared as in example 1, without urea in the preparation of Co @ N-C-KB.

The catalytic performance was evaluated in the same manner as in example 1.

The initial potential of Co @ N-KB as the ORR catalyst was 0.02V (vs. Hg/HgO), the half-wave potential was-0.055V (vs. Hg/HgO), and the limiting current density was-4.9 mA/cm²。

Comparative example 4

Co @ N-C was prepared as in example 1, without adding Keqin carbon to the preparation of Co @ N-C-KB.

The catalytic performance was evaluated in the same manner as in example 1.

Co @ N-C as ORR catalyst has an initial potential of-0.045V (vs. Hg/HgO) and a current density of-3.7 mA/cm at-0.7V (vs. Hg/HgO)²。

Comparative example 5

N-C-KB-1 was prepared as in example 1, without adding cobalt chloride hexahydrate in the preparation of Co @ N-C-KB. The catalytic performance was evaluated in the same manner as in example 1.

The initial potential of N-L-KB as the ORR catalyst was-0.08V (vs. Hg/HgO), the half-wave potential was-0.19V (vs. Hg/HgO), and the limiting current density was-4.8 mA/cm²。

Comparative example 6

N-C-KB-2 was prepared as in example 1, without addition of L-alanine and cobalt chloride hexahydrate in the preparation of Co @ N-C-KB.

The catalytic performance was evaluated in the same manner as in example 1.

The initial potential of N-C-KB-2 as the ORR catalyst is-0.058V (vs. Hg/HgO), the half-wave potential is-0.17V (vs. Hg/HgO), and the limiting current density is-4.8 mA/cm²。

Claims

1. The application of the high-performance oxygen reduction Co @ N-C-KB composite catalyst is characterized in that: the catalyst is applied as an oxygen reduction catalyst of a fuel cell; the high-performance oxygen reduction Co @ N-C-KB composite catalyst is formed by inlaying simple substance cobalt particles in a nitrogen-doped carbon material; the nitrogen-doped carbon material is formed by compounding a nitrogen-doped graphite crystal nanobelt and nitrogen-doped ketjen black in situ;

the high-performance oxygen reduction Co @ N-C-KB composite catalyst comprises the following components in percentage by mass:

simple cobalt substance: 3% -10%;

nitrogen-doped graphite crystal nanobelts: 15% -30%;

nitrogen-doped ketjen black: 65% -75%;

wherein the content of the first and second substances,

the mass percent content of nitrogen is 3% -7%;

the high-performance oxygen reduction Co @ N-C-KB composite catalyst is prepared by the following preparation method: mixing cobalt salt, a nitrogen-containing organic micromolecule compound and carbon black, placing in a protective atmosphere, and performing two-stage roasting treatment to obtain the catalyst; wherein, the mass ratio of the cobalt salt, the nitrogen-containing organic micromolecule compound and the carbon black is (7-10): 81-89): 6-9, and the nitrogen-containing organic micromolecule compound is composed of at least one of urea, melamine, cyanuric chloride, cyanamide and dicyanodiamide and amino acid according to the mass ratio of (70-85): 5-15.

2. The use of a high performance oxygen reduced Co @ N-C-KB composite catalyst as defined in claim 1, wherein:

the cobalt salt is water-soluble cobalt salt;

the amino acid comprises at least one of alanine, phenylalanine, lysine, glycine, valine, leucine, proline, serine, tryptophan and glutamic acid;

the carbon black material comprises at least one of Keqin carbon black, Cabot conductive carbon black and acetylene carbon black.

3. The use of a high performance oxygen reduced Co @ N-C-KB composite catalyst as defined in claim 1, wherein: the two-stage roasting treatment process is sequentially 500^oC–600^oC and 650^oC–900^oAnd C, roasting.

4. The use of a high performance oxygen reduced Co @ N-C-KB composite catalyst as defined in claim 3, wherein:

at 500^oC–600^oThe roasting time of C is 0.5-4 h;

at 650^oC–900^oThe time of the C roasting treatment is 0.5-4 h.