阅读说明：本技术 一种自支撑氧还原催化剂及其制备方法、应用 (Self-supporting oxygen reduction catalyst and preparation method and application thereof ) 是由 方剑 江珊 于 2020-05-11 设计创作，主要内容包括：本发明公开了一种自支撑氧还原催化剂及其制备方法、应用,以廉价易得的纯棉织物为碳源,在二氧化碳气氛中进行热解,制得多孔碳布,然后将此碳布浸泡在含有金属离子和含氮配体的混合溶液中,最后将负载金属离子和含氮配体的碳布在氮气气氛中进行热解,生成自支撑氧还原催化剂。本发明制备的催化剂比表面积高达1769±2m<Sup>2</Sup>/g,在碱性环境下的催化活性与商业Pt/C(20wt％)相当,具有良好的抗甲醛毒化能力和稳定性,且所用原料成本低,制备方法简单,能够应用于电池阴极材料中,并表现出良好的电池性能和柔韧性,具有非常好的工业应用前景。(The invention discloses a self-supporting oxygen reduction catalyst and a preparation method and application thereof. The specific surface area of the catalyst prepared by the invention is as high as 1769 +/-2 m 2 The catalytic activity of the catalyst is equivalent to that of commercial Pt/C (20 wt%) in an alkaline environment, the catalyst has good formaldehyde poisoning resistance and stability, the used raw materials are low in cost, the preparation method is simple, the catalyst can be applied to a battery cathode material, and the battery has good battery performance and flexibility and has a good industrial application prospect.)

1. A method of preparing a self-supporting oxygen reduction catalyst, comprising the steps of:

pyrolyzing a pure cotton fabric in a carbon dioxide atmosphere to obtain a porous carbon cloth;

soaking the carbon cloth in a mixed solution containing metal ions and nitrogen-containing ligands so that the carbon cloth can fully adsorb the metal ions and the nitrogen-containing ligands;

and (3) pyrolyzing the carbon cloth loaded with the metal ions and the nitrogen-containing ligand in a nitrogen atmosphere to obtain the self-supporting oxygen reduction catalyst.

2. The method for preparing a self-supporting oxygen-reducing catalyst according to claim 1, wherein in the step of "pyrolyzing a pure cotton fabric in a carbon dioxide atmosphere to obtain a porous carbon cloth", the pyrolysis reaction conditions are as follows: heating to 900 deg.C at 5 deg.C/min for 2 h.

3. The method of preparing a self-supporting oxygen-reducing catalyst according to claim 2, wherein the porous carbon cloth has a specific surface area of 1226 ± 2m²/g。

4. The method for preparing a self-supporting oxygen-reducing catalyst according to claim 1, wherein the step of "immersing the carbon cloth in a mixed solution containing a metal ion and a nitrogen-containing ligand so that the carbon cloth sufficiently adsorbs the metal ion and the nitrogen-containing ligand" comprises ferric nitrate and dicyandiamide, wherein the ferric nitrate is present at a concentration of 1000ppm and the dicyandiamide is present at a concentration of 20 g/L.

5. The method of preparing a self-supporting oxygen-reducing catalyst according to claim 4, wherein the metal ion is Fe³⁺And the nitrogen-containing ligand is dicyandiamide.

6. The method of preparing a self-supporting oxygen-reducing catalyst according to claim 1, wherein the step of "immersing the carbon cloth in a mixed solution containing a metal ion and a nitrogen-containing ligand so that the carbon cloth sufficiently adsorbs the metal ion and the nitrogen-containing ligand" has a ratio of a grammage of the carbon cloth to a volume of the mixed solution of 20mg:20 mL.

7. The method for preparing a self-supporting oxygen-reducing catalyst according to claim 1, wherein in the step of "pyrolyzing a carbon cloth supporting metal ions and a nitrogen-containing ligand in a nitrogen atmosphere to obtain a self-supporting oxygen-reducing catalyst", the pyrolysis reaction conditions are as follows: heating to 800-1000 ℃ at a speed of 5 ℃/min and keeping for 1 h.

8. The preparation method of the self-supported oxygen reduction catalyst according to claim 7, wherein the specific surface area of the iron-nitrogen co-doped porous biomass carbon self-supported oxygen reduction catalyst is 1195 +/-2 m²/g～1769±2m²/g。

9. The self-supporting oxygen reduction catalyst is characterized by comprising a flaky porous carbon cloth main body, wherein the porous carbon cloth main body is provided with Fe elements and N elements, the content of the Fe elements is 0.8 +/-0.02%, and the content of the N elements is 1.0 +/-0.03%.

10. Use of a self-supporting oxygen reduction catalyst according to claim 9 in a battery cathode material.

Technical Field

The invention belongs to the technical field of non-noble metal catalysts in electrocatalysis, and particularly relates to a self-supporting oxygen reduction catalyst, and a preparation method and application thereof.

Background

Over-utilization of traditional fossil energy by humans has caused serious resource exhaustion and environmental pollution problems in the past decades, and development of novel forms of energy storage and energy conversion has become an important issue for development of new era. As a new energy technology, a fuel cell can directly and efficiently convert chemical energy contained in a fuel and an oxidant into electric energy, and only generates water that does not pollute the environment. The fuel cell has the characteristics of light weight, high efficiency, long service life, low corrosivity, environmental friendliness, recyclability and the like, and has a very wide application prospect in the aspects of mobile power supplies, electric automobile power supplies, power station systems, aerospace and the like. Nevertheless, the development and application of fuel cells are severely restricted due to the fact that the cathodic oxygen reduction (ORR) rate is 5-6 orders of magnitude slower than the anodic oxidation rate, and the exchange current density is low. Therefore, the development of an efficient ORR catalyst is of great importance. At present, the ORR catalyst for fuel cells is mainly a noble metal Pt-based catalyst with excellent performance. However, the metal Pt has a small storage amount, is expensive, is easily poisoned by methanol, and has poor chemical stability, which greatly limits the development of direct alcohol fuel cells. Therefore, the development of non-noble metal cathode catalysts is very important.

In the currently more studied non-platinum ORR catalysts, a carbon material (M-N) co-doped with a transition metal and nitrogen element_x/C), are of great interest due to their excellent catalytic activity and good chemical stability over Pt-based catalysts. The preparation of such catalysts places high demands on the physical properties of the carbon-based material, including high electrical conductivity, large specific surface area, and good corrosion resistance. In the reported M-N_xIn the/C catalyst, the carbon sources used are more as follows: commercially available activated carbon, graphene, carbon nanotubes, and the like. However, these carbon materials are expensive in raw material, harsh and complicated in conditions, low in product yield, and difficult in post-treatment. In recent years, biomass resources have been receiving increasing attention as a source of carbon structures. A large amount of biomass resources in the world can not be reasonably utilized every year, and a considerable part of biomass resources even decay and deteriorate to become environmental pollutants. Therefore, if the ORR catalyst can be produced using a biomass material as a carbon source, the production cost of the carbon material can be greatly reduced, and sustainable use of biomass resources can be realized.

At present, most of the reported catalysts exist in powder form. Therefore, in practical battery device applications, it is generally necessary to adhere the powdered catalyst to the electrode using an organic binder, and this process has many adverse effects such as active site clogging, deterioration in conductivity, and complication of electron transfer paths. Therefore, it is a trend in the future to synthesize an active ORR catalytic substance, i.e., a self-supporting catalyst, on a conductive material, and use it directly as a cathode material of a battery.

Disclosure of Invention

In order to overcome the defects in the prior art, the embodiment of the invention provides a self-supporting oxygen reduction catalyst, and a preparation method and application thereof, wherein the catalytic activity of the self-supporting oxygen reduction catalyst in an alkaline environment is equivalent to that of commercial Pt/C (20 wt%), the self-supporting oxygen reduction catalyst has good formaldehyde poisoning resistance and stability, the used raw materials are low in cost, the preparation method is simple, the self-supporting oxygen reduction catalyst can be applied to a battery cathode material, and the self-supporting oxygen reduction catalyst shows good battery performance and flexibility, and has a very good industrial application prospect.

The invention discloses a preparation method of a self-supporting oxygen reduction catalyst, which comprises the following steps:

pyrolyzing a pure cotton fabric in a carbon dioxide atmosphere to obtain a porous carbon cloth;

soaking the carbon cloth in a mixed solution containing metal ions and nitrogen-containing ligands so that the carbon cloth can fully adsorb the metal ions and the nitrogen-containing ligands;

and (3) pyrolyzing the carbon cloth loaded with the metal ions and the nitrogen-containing ligand in a nitrogen atmosphere to obtain the self-supporting oxygen reduction catalyst.

Preferably, in the step of "pyrolyzing a pure cotton fabric in a carbon dioxide atmosphere to obtain a porous carbon cloth", the pyrolysis reaction conditions are as follows: heating to 900 deg.C at 5 deg.C/min for 2 h.

Preferably, the specific surface area of the porous carbon cloth is 1226 ± 2m²/g。

Preferably, the step of "immersing the carbon cloth in a mixed solution containing a metal ion and a nitrogen-containing ligand so that the carbon cloth sufficiently adsorbs the metal ion and the nitrogen-containing ligand" includes ferric nitrate and dicyandiamide, wherein the ferric nitrate is present at a concentration of 1000ppm, and the dicyandiamide is present at a concentration of 20 g/L.

More preferably, the metal ion is Fe³⁺And the nitrogen-containing ligand is dicyandiamide.

Preferably, in the step of "immersing the carbon cloth in a mixed solution containing metal ions and nitrogen-containing ligands so that the carbon cloth sufficiently adsorbs the metal ions and the nitrogen-containing ligands", the ratio of the gram weight of the carbon cloth to the volume of the mixed solution is 20mg:20 mL.

Preferably, in the step of pyrolyzing the carbon cloth loaded with metal ions and nitrogen-containing ligands in a nitrogen atmosphere to obtain the self-supporting oxygen reduction catalyst, the pyrolysis reaction conditions are as follows: heating to 800-1000 ℃ at a speed of 5 ℃/min and keeping for 1 h.

Further preferably, the specific surface area of the iron-nitrogen co-doped porous biomass carbon self-supporting oxygen reduction catalyst is 1195 +/-2 m²/g～1769±2m²/g。

The invention provides a self-supporting oxygen reduction catalyst, which comprises a flaky porous carbon cloth main body, wherein the porous carbon cloth main body is provided with Fe elements and N elements, the content of the Fe elements is 0.8 +/-0.02%, and the content of the N elements is 1.0 +/-0.03%.

The invention relates to an application of a self-supporting oxygen reduction catalyst in a battery cathode material.

The invention has the following beneficial effects:

the self-supporting oxygen reduction catalyst has equivalent oxygen reduction performance to that of a 20 wt% Pt/C catalyst in 0.1M potassium hydroxide solution, the catalyst has higher stability and better methanol poisoning resistance, and the activity of the catalyst is hardly attenuated by adding 1M methanol into 0.1M KOH electrolyte.

The self-supporting oxygen reduction catalyst is applied to a self-made solid zinc-air battery, and shows good battery performance and flexibility.

The raw material used by the self-supporting oxygen reduction catalyst is the most common cotton fabric in the textile field, and the self-supporting oxygen reduction catalyst has wide sources, lower price and low cost of large-scale preparation, thereby reducing the production cost of the catalyst material and realizing the sustainable utilization of biomass resources.

The preparation method of the self-supporting oxygen reduction catalyst has the advantages of simple synthetic route, no use of any toxic gas, controllable operation and easy large-scale production.

In order to make the aforementioned and other objects, features and advantages of the invention comprehensible, preferred embodiments accompanied with figures are described in detail below.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a graph showing the N of comparative example 1 catalyst CC and catalyst FeN @ CC of example 1 in accordance with the present invention₂Adsorption/desorption isotherm curves;

FIG. 2 is an XPS spectrum of the nitrogen element in the catalyst FeN @ CC of example 1 of the present invention;

FIG. 3 is a plot of the catalytic ORR polarization curves for comparative example 1 catalyst CC, comparative example 2 catalyst Fe @ CC, and comparative example 3 catalyst N @ CC, and example 1 catalyst FeN @ CC, in accordance with the present invention;

FIG. 4 is a plot of the catalytic ORR polarization of the catalyst FeN @ CC at various rotational speeds in accordance with example 1 of the present invention;

FIG. 5 is a graph of the corresponding K-L fit of FIG. 4;

FIG. 6 is a graph of I-t at a constant pressure of 0.67V for the catalyst FeN @ CC of example 1 in accordance with the present invention;

FIG. 7 is a methanol poisoning resistance map of the catalyst FeN @ CC of example 1 of the present invention;

FIG. 8 is a graph of the catalytic ORR polarization curves for the catalyst FeN @ CC of example 1, the catalyst FeN @ CC-800 of example 2, and the catalyst FeN @ CC-1000 of example 3 in accordance with the present invention;

fig. 9 is a structural view of a solid zinc-air battery prepared in example 1 of the present invention;

reference numerals in fig. 9: 1-zinc flake, 2-solid electrolyte; 3-carbon cloth.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Comparative example 1

1. Preparation of catalyst CC

(1) Soaking the pure cotton fabric in deionized water, heating and stirring at 60 ℃ for 24h, and then drying at 80 ℃ to remove impurities on the surface of the pure cotton fabric. Placing the purified cotton fabric with impurities removed in a tubular furnace in active gas CO₂Heating to 900 ℃ at a speed of 5 ℃/min and keeping for 2h, cooling to room temperature to obtain the porous carbon cloth with the mesoporous and microporous structures, wherein the specific surface area of the porous carbon cloth is 1226 +/-2 m²/g；

(2) Soaking the porous carbon cloth obtained in the step (1) in pure water, wherein the ratio of the gram weight of the carbon cloth to the volume of the pure water is 20mg:20mL, oscillating for 5h, taking out the carbon cloth, placing the taken-out carbon cloth in a tubular furnace, and carrying out reaction under inert gas N₂Under the protection of (2), heating to 900 ℃ at the speed of 5 ℃/min, keeping for 1h, and cooling to room temperature to obtain the undoped porous biomass carbon self-supporting oxygen reduction catalyst, which is marked as CC.

2. Electrochemical testing

(1) Preparation of electrodes

Weighing 5mg of fully ground undoped porous biomass carbon self-supporting oxygen reduction catalyst powder, adding 1mL of isopropanol and 20 mu L of Nafion (0.5 wt%) solution (perfluorosulfonic acid type polymer solution), carrying out ultrasonic treatment for 30min, and uniformly coating 10 mu L of the solution on a glassy carbon electrode.

(2) Activity assay

A rotating disc electrode device is adopted to carry out testing in a three-electrode system, wherein a Pt wire electrode is a counter electrode, an Ag/AgCl electrode is a reference electrode, a glassy carbon electrode coated with a catalyst is a working electrode, oxygen saturated solution of 0.1M KOH is electrolyte, and the working electrode is the rotating disc electrode.

The ORR catalytic activity of the catalyst was tested by Linear Sweep Voltammetry (LSV) and the results are shown in FIG. 3. As can be seen from the ORR polarization curve of CC catalyst in FIG. 3, the initial oxygen reduction potential of the catalyst of this example is 0.77V at 1600 rmp.

3、N₂Adsorption/desorption isotherm curve

N of catalyst CC₂The absorption/desorption isothermal curve is shown in the attached figure 1, and it can be seen that the undoped porous biomass carbon self-supporting oxygen reduction catalyst prepared by the method has rich micropore and mesoporous structures.

Comparative example 2

1. Preparation of catalyst Fe @ CC

(1) Soaking the pure cotton fabric in deionized water, heating and stirring at 60 ℃ for 24h, and then drying at 80 ℃ to remove impurities on the surface of the pure cotton fabric. Placing the purified cotton fabric with impurities removed in a tubular furnace in active gas CO₂Heating to 900 ℃ at a speed of 5 ℃/min and keeping for 2h, cooling to room temperature to obtain the porous carbon cloth with the mesoporous and microporous structures, wherein the specific surface area of the porous carbon cloth is 1226 +/-2 m²/g；

(2) Soaking the porous carbon cloth obtained in the step (1) in 1000ppm ferric nitrate aqueous solution, wherein the ratio of gram weight of the carbon cloth to volume of the ferric nitrate aqueous solution is 20mg:20mL, and oscillating for 5h to enable metal ions Fe³⁺Uniformly and fully absorbed in carbon cloth, and then loaded with Fe³⁺Taking out the carbon cloth and placing the carbon cloth in a tube furnace in inert gas N₂Under the protection of (1), heating to 900 ℃ at a speed of 5 ℃/min, keeping for 1h, and cooling to room temperature to obtain the iron-doped porous biomass carbon self-supporting oxygen reduction catalyst, wherein the label is Fe @ CC.

2. Electrochemical testing

(1) Preparation of electrodes

Weighing 5mg of fully ground iron-doped porous biomass carbon self-supporting oxygen reduction catalyst powder, adding 1mL of isopropanol and 20 mu L of Nafion (0.5 wt%) solution, carrying out ultrasonic treatment for 30min, and uniformly coating 10 mu L of the solution on a glassy carbon electrode.

(2) Activity assay

A rotating disc electrode device is adopted to carry out testing in a three-electrode system, wherein a Pt wire electrode is a counter electrode, an Ag/AgCl electrode is a reference electrode, a glassy carbon electrode coated with a catalyst is a working electrode, oxygen saturated solution of 0.1M KOH is electrolyte, and the working electrode is the rotating disc electrode.

The catalysts were tested for ORR catalytic activity using Linear Sweep Voltammetry (LSV) and the results are shown in figure 3. As can be seen from the catalytic ORR polarization curve of Fe @ CC in FIG. 3, the oxygen reduction initiation potential of the sample Fe @ CC was 0.82V at a rotating disk electrode speed of 1600 rmp.

Comparative example 3

1. Preparation of catalyst N @ CC

(1) Soaking the pure cotton fabric in deionized water, heating and stirring at 60 ℃ for 24h, and then drying at 80 ℃ to remove impurities on the surface of the pure cotton fabric. Placing the purified cotton fabric with impurities removed in a tubular furnace in active gas CO₂Heating to 900 ℃ at a speed of 5 ℃/min and keeping for 2h, cooling to room temperature to obtain the porous carbon cloth with the mesoporous and microporous structures, wherein the specific surface area of the porous carbon cloth is 1226 +/-2 m²/g；

(2) Soaking the porous carbon cloth obtained in the step (1) in a dicyandiamide aqueous solution with the concentration of 20g/L, wherein the ratio of the gram weight of the carbon cloth to the volume of the dicyandiamide aqueous solution is 20mg:20mL, oscillating for 5h until the nitrogen-containing ligand is uniformly and fully adsorbed in the carbon cloth, taking out the carbon cloth loaded with the nitrogen-containing ligand, placing the carbon cloth in a tubular furnace, and carrying out N gas inert gas treatment on the carbon cloth₂Under the protection of (1), heating to 900 ℃ at a speed of 5 ℃/min, keeping for 1h, and cooling to room temperature to obtain the nitrogen-doped porous biomass carbon self-supporting oxygen reduction catalyst, wherein the label is N @ CC.

2. Electrochemical testing

(1) Preparation of electrodes

Weighing 5mg of fully ground nitrogen-doped porous biomass carbon self-supporting oxygen reduction catalyst powder, adding 1mL of isopropanol and 20 mu L of Nafion (0.5 wt%) solution, carrying out ultrasonic treatment for 30min, and uniformly coating 10 mu L of the solution on a glassy carbon electrode.

(2) Activity assay

A rotating disc electrode device is adopted to carry out testing in a three-electrode system, wherein a Pt wire electrode is a counter electrode, an Ag/AgCl electrode is a reference electrode, a glassy carbon electrode coated with a catalyst is a working electrode, oxygen saturated solution of 0.1M KOH is electrolyte, and the working electrode is the rotating disc electrode.

The ORR catalytic activity of the catalyst was tested using Linear Sweep Voltammetry (LSV) and the results are shown in FIG. 3. As can be seen from the catalytic ORR polarization curve of N @ CC in FIG. 3, the oxygen reduction onset potential of the sample N @ CC was 0.87V at a rotating disk electrode speed of 1600 rmp.