阅读说明：本技术 一种化学转化石墨烯负载Co卟啉复合物电催化剂的制备及应用 (Preparation and application of chemical conversion graphene loaded Co porphyrin complex electrocatalyst ) 是由 徐宇曦 崔凯 于 2021-08-11 设计创作，主要内容包括：本发明公开了一种化学转化石墨烯负载Co卟啉复合物电催化剂的制备及应用。采用改进的hummers法制备纯化的氧化石墨烯水溶液,再还原氧化石墨烯得到在水溶液中分散性很好、带负电的化学转化石墨烯；利用带负电的化学转化石墨烯与带正电荷的钴卟啉之间的静电与π-π协同作用诱导钴卟啉侧链发生偏转,得到化学转化石墨烯负载Co卟啉电催化剂。本发明利用超分子策略调控钴卟啉分子构象,显著改善钴卟啉本征催化活性,得到的电催化剂展现出优异的电催化性能,组装的可充电锌空电池比容量高,功率密度大,分子水平上调控了电催化剂的本征催化活性。(The invention discloses preparation and application of a chemical conversion graphene loaded Co porphyrin compound electrocatalyst. Preparing a purified graphene oxide aqueous solution by adopting an improved hummers method, and reducing graphene oxide to obtain chemically converted graphene with good dispersibility and negative charge in the aqueous solution; inducing the cobalt porphyrin side chain to deflect by utilizing the electrostatic and pi-pi synergistic effect between the negatively charged chemically converted graphene and the positively charged cobalt porphyrin to obtain the chemically converted graphene loaded Co porphyrin electrocatalyst. The invention utilizes a supermolecule strategy to regulate and control the molecular conformation of cobalt porphyrin, obviously improves the intrinsic catalytic activity of the cobalt porphyrin, obtains the electrocatalyst with excellent electrocatalysis performance, has high specific capacity and high power density of the assembled rechargeable zinc-air battery, and regulates and controls the intrinsic catalytic activity of the electrocatalyst at the molecular level.)

1. A preparation method of a chemical conversion graphene loaded Co porphyrin compound electrocatalyst is characterized by comprising the following specific steps:

(1) preparing a purified graphene oxide aqueous solution by adopting an improved hummers method:

(2) preparing a chemically converted graphene aqueous dispersion:

(3) preparing the cobalt porphyrin composite material electrocatalyst loaded by the chemical conversion graphene.

2. The method of claim 1, wherein: the step (1) is specifically as follows:

(1.1) taking 0.5-5 g of 325-8000 mesh flake graphite powder, adding 0.2-2.5 g of sodium nitrate powder, then adding 10-120 mL of acid, stirring for 5-30 min, adding 2-20 g of potassium salt under the condition of ice-water bath, stirring for 0.5-3 h in water bath at 30-40 ℃, then adding water, continuing to react for 10-30 min, adding water, reacting for 5-20 min, and then adding hydrogen peroxide until the solution turns golden yellow;

(1.2) standing and settling the solution, then decanting to remove supernatant, adding hydrochloric acid with the mass fraction of 5% -10%, subpackaging in centrifuge tubes for centrifugation, discarding supernatant, then washing with deionized water to be neutral, collecting washed products, adding deionized water, performing ultrasonic dispersion to obtain a graphene oxide aqueous solution, and finally purifying graphene oxide through long-time dialysis to remove residual metal to obtain a purified graphene oxide solution with the mass concentration of 0.1-0.4 mg/mL.

3. The method of claim 2, wherein: in the step (1), the acid is one or more of concentrated sulfuric acid, concentrated hydrochloric acid and concentrated nitric acid, and the potassium salt is one or more of potassium permanganate, potassium perchlorate and potassium carbonate.

4. The method of claim 1, wherein: the step (2) is specifically as follows: mixing 30-70 mL of purified graphene oxide dispersion liquid with 10-30 mu L of reducing agent and 100-300 mu L of pH regulator to obtain a mixture, continuing the mixture at 70-120 ℃ for 0.5-2 h to obtain a uniform black dispersion after reduction, and filtering the black dispersion to remove precipitates to obtain the stable black chemically converted graphene dispersion liquid.

5. The method of claim 4, wherein: in the step (2), the reducing agent is one or more of ascorbic acid, sodium ascorbate, sodium sulfite and hydrazine hydrate; the pH regulator is one or more of sodium dihydrogen phosphate solution, sodium hydroxide solution and ammonia water.

6. The method of claim 4, wherein: in the step (2), one or more of gauze, filter paper and cotton are used for filtering and removing the precipitate.

7. The method of claim 1, wherein: the step (3) is specifically as follows: and (3) dropwise adding 9-15 mL of the chemically converted graphene dispersion solution into 100-200 mL of Co porphyrin aqueous solution with the concentration of 2-8 mu M under stirring at normal temperature, and finally centrifuging, washing, and freeze-drying the solution to obtain the composite electrocatalyst.

8. The method of claim 1, wherein: in the step (3), the rotation speed of centrifugation is 5000-10000 rpm, and the freeze drying time is 20-70 h.

9. A chemically converted graphene-supported Co porphyrin complex electrocatalyst material obtained by the preparation method according to any one of claims 1 to 8.

Technical Field

The invention belongs to a preparation method of a composite electrocatalyst in the technical field of catalysts, and particularly relates to preparation and application of a chemically converted graphene loaded Co porphyrin composite electrocatalyst.

Background

There is a great deal of attention paid to green and renewable technologies for water electrolysis, fuel cells and metal-air batteries, which are dominated by Oxygen Reduction Reaction (ORR), Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER). However, both of these reactions require a catalyst to accelerate their reaction kinetics. Unfortunately, noble metal (Pt, Ru) based catalysts are costly and rare and therefore difficult to use commercially on a large scale. Therefore, the development of non-noble metal electrocatalysts instead of noble metal catalysts is a necessary choice for future large-scale production.

Molecular catalysts have received much attention because of their well-defined molecular structure, stable active sites and controllable structure. The metalloporphyrin is a conjugated, polar and highly delocalized organic molecule, has a stable metal coordination environment, and can be combined with other molecules through intermolecular interaction to form a complex and organized molecular aggregate with a definite microstructure. These properties make metalloporphyrins and their derivatives promising electrocatalysts. However, metalloporphyrin has poor catalytic performance due to problems such as poor conductivity and low electrocatalytic activity. Accordingly, a great deal of research effort has been devoted to overcoming these problems. On the one hand, it has been proved that the combination of metalloporphyrin and highly conductive carriers such as graphene or carbon nanotubes can effectively promote charge transfer. On the other hand, effective strategies for improving the electrocatalytic activity of metalloporphyrin mainly focus on adjusting coordination environment around active sites by expanding/modifying metalloporphyrin molecular structures, such as axial coordination, construction of crystalline porous materials, introduction of functional groups, and the like, which all involve relatively complex chemical processes to change molecular configurations. To the best of knowledge, no reports have been made on the regulation of the intrinsic activity of metalloporphyrins by modulating the conformation of the molecule.

Disclosure of Invention

In order to solve the problems faced by molecular catalysts, the invention utilizes the electrostatic and pi-pi synergistic effect between the negatively charged chemical conversion graphene and the positively charged cobalt porphyrin to induce the cobalt porphyrin side chain to deflect, so as to change the electronic environment of a metal active center, obviously enhance the electrocatalytic activity and improve the performance of a zinc-air battery. The catalyst prepared by the preparation method disclosed by the invention has excellent catalytic performance and zinc-air battery performance.

The technical scheme of the invention comprises the following specific steps:

(1) preparing a purified graphene oxide aqueous solution by adopting an improved hummers method:

(2) preparing a chemically converted graphene aqueous dispersion:

(3) preparing the cobalt porphyrin composite material electrocatalyst loaded by the chemical conversion graphene.

The step (1) is specifically as follows:

(1.1) taking 0.5-5 g of 325-8000 mesh flake graphite powder, adding 0.2-2.5 g of sodium nitrate powder, then adding 10-120 mL of acid, stirring for 5-30 min, slowly adding 2-20 g of potassium salt under the condition of ice-water bath, stirring for 0.5-3 h in water bath at 30-40 ℃, then adding a small amount of water below 100mL, continuing to react for 10-30 min, adding a large amount of water above 100mL, reacting for 5-20 min, and then adding a proper amount of hydrogen peroxide until the solution turns golden yellow;

(1.2) standing and settling the solution, then decanting to remove supernatant, adding hydrochloric acid with the mass fraction of 5% -10%, subpackaging in centrifuge tubes for high-speed centrifugation, discarding the supernatant, then washing with deionized water to be neutral, collecting washed products, adding deionized water, performing ultrasonic dispersion to obtain a graphene oxide aqueous solution, and finally purifying graphene oxide through long-time dialysis to remove residual metal to obtain a purified graphene oxide solution with the mass concentration of 0.1-0.4 mg/mL.

In the step (1), the acid is one or more of concentrated sulfuric acid, concentrated hydrochloric acid and concentrated nitric acid, and the potassium salt is one or more of potassium permanganate, potassium perchlorate and potassium carbonate.

The step (2) is specifically as follows: mixing 30-70 mL of purified graphene oxide dispersion liquid with 10-30 mu L of reducing agent and 100-300 mu L of pH regulator, wherein the mass concentration of the pH regulator is 20-35 wt%, obtaining a mixture, continuously maintaining the mixture at 70-120 ℃ for 0.5-2 h, reducing to obtain a uniform black dispersion liquid with a small amount of black precipitate, and filtering the black dispersion liquid to remove the precipitate, thereby obtaining the stable black chemically converted graphene dispersion liquid.

In the step (2), the reducing agent is one or more of ascorbic acid, sodium ascorbate, sodium sulfite and hydrazine hydrate; the pH regulator is one or more of sodium dihydrogen phosphate solution, sodium hydroxide solution and ammonia water.

In the step (2), one or more of gauze, filter paper and cotton are used for filtering and removing the precipitate.

The step (3) is specifically as follows: and slowly dropwise adding 9-15 mL of the chemically converted graphene dispersion solution into 100-200 mL of Co porphyrin aqueous solution with the concentration of 2-8 mu M under stirring at normal temperature, and finally centrifuging, washing, and freeze-drying the solution to obtain the composite electrocatalyst.

In the step (3), the rotation speed of centrifugation is 5000-10000 rpm, and the freeze drying time is 20-70 h.

The invention loads cobalt porphyrin on chemically converted graphene through electrostatic and pi-pi interaction in aqueous solution, and synthesizes a supramolecular complex. Firstly, the chemically converted graphene with good dispersibility in aqueous solution and negative charge is obtained by reducing graphene oxide. And then inducing the cobalt porphyrin side chain to deflect by utilizing the electrostatic and pi-pi synergistic effect between the negatively charged chemical conversion graphene and the positively charged cobalt porphyrin to obtain the chemical conversion graphene loaded Co porphyrin electrocatalyst.

The invention induces the rotation of four pyridine side groups by the electrostatic and pi-pi synergistic action between the chemically converted graphene and the cobalt porphyrin so as to flatten the molecules of the cobalt porphyrin. This change in molecular conformation results in compression of the Co-N bond and transfer of electrons from the porphyrinic macrocycle to the metal ion in the cobalt porphyrin molecule. The contraction of the Co-N bond length also facilitates the acceleration of electron (N → Co) transport, allowing more charge to accumulate around the metal ion of the active center, resulting in a higher charge density around the active center. The electrocatalytic performance of cobalt porphyrin is obviously improved, and the assembled zinc-air battery shows excellent performance.

Compared with the prior art, the invention has the advantages and positive effects that:

the intrinsic catalytic activity of the molecular catalyst is regulated and controlled by changing the molecular conformation, and the cobalt porphyrin is loaded on the chemically converted graphene by a simple method, so that the chemically converted graphene not only ensures the good conductivity of the catalyst and prevents the dissolution of the cobalt porphyrin, but also induces the change of the molecular conformation of the cobalt porphyrin.

The invention solves the problems of poor conductivity and low catalytic activity of the molecular catalyst, and simultaneously the composite material prepared by the method has excellent electrocatalytic performance in the field of the molecular catalyst, and the assembled zinc-air battery has excellent performance.

Drawings

Fig. 1 is an ultraviolet-visible spectrum diagram of a chemically converted graphene-supported cobalt porphyrin composite material.

Fig. 2 is a scanning electron microscope image of the chemically converted graphene-supported cobalt porphyrin composite material.

Fig. 3 is a diagram of oxygen reduction reaction LSV of the chemically converted graphene-supported cobalt porphyrin composite material.

Fig. 4 is a diagram of a hydrogen evolution reaction LSV of a chemically converted graphene-supported cobalt porphyrin composite material.

Fig. 5 is an LSV diagram of oxygen evolution reaction of the chemically converted graphene-supported cobalt porphyrin composite material.

Fig. 6 is a graph of specific capacity of a zinc-air battery of a chemically converted graphene-supported cobalt porphyrin composite material.

Fig. 7 is a charge-discharge diagram of a zinc-air battery with a chemically converted graphene-supported cobalt porphyrin composite material.

Detailed Description

The technical solutions of the present invention are further described below with reference to the following examples, but the present invention is not limited to the following examples, and all modifications or equivalent substitutions that do not depart from the scope of the technical solutions of the present invention are intended to fall within the scope of the present invention.

The examples of the invention are as follows:

example 1

(1) Preparing graphene oxide:

preparing graphene oxide by adopting an improved hummers method: taking 0.5g (325 meshes) of flake graphite powder, adding 0.2g of sodium nitrate powder, then adding 10mL of concentrated sulfuric acid, stirring for 5min, slowly adding 2g of potassium permanganate under the condition of ice-water bath, stirring for 0.5h in water bath at 30 ℃, then adding a small amount of water, continuing to react for 10min, then adding 200mL of distilled water, reacting for 5min, and then adding a proper amount of hydrogen peroxide until the solution turns golden yellow; standing and settling the solution, decanting to remove supernatant, adding a proper amount of 5% hydrochloric acid, subpackaging in a centrifuge tube, centrifuging at high speed, discarding supernatant, washing with deionized water to neutrality, collecting washed products, adding a proper amount of deionized water, performing ultrasonic dispersion to obtain a graphene oxide aqueous solution, and finally purifying graphene oxide through long-time dialysis to remove residual metal;

(2) preparing a chemically converted graphene aqueous dispersion:

30mL (0.25mg/mL) of the purified graphene oxide dispersion was mixed with 20. mu.L of ascorbic acid and 150. mu.L of sodium dihydrogen phosphate solution (35 wt%). The mixture was left at 70 ℃ for 0.5h and after reduction a homogeneous black dispersion was obtained with a small amount of black precipitate. Then, filtering the dispersion with gauze to remove precipitates to obtain a stable black chemically converted graphene dispersion liquid;

(3) preparing a cobalt porphyrin composite material electrocatalyst loaded by chemically converted graphene:

the chemically converted graphene dispersion (9mL) was added dropwise to an aqueous solution of cobalt porphyrin (2. mu.M, 100mL) slowly with stirring at room temperature. Finally, the composite was centrifuged (5000rpm), washed and freeze-dried (20 h).

Example 2

A0.25 mg/mL aqueous solution of graphene oxide was obtained as in example 1 above. 35mL (0.25mg/mL) of the above purified graphene oxide dispersion was mixed with 20. mu.L of sodium sulfite and 150. mu.L of an aqueous ammonia solution (35 wt%). The mixture was kept at 95 ℃ for 2h and after reduction a homogeneous black dispersion was obtained with a small amount of black precipitate. Subsequently, the dispersion was filtered with cotton to remove precipitates, resulting in a stable black chemically converted graphene dispersion. The chemically converted graphene dispersion (13mL) was added dropwise slowly to an aqueous solution of cobalt porphyrin (5. mu.M, 150mL) with stirring at room temperature. The cobalt porphyrin molecule conformation is found to be significantly changed by ultraviolet spectrum test (figure 1). Finally, the composite was centrifuged (8000rpm), washed and freeze dried (30 h). The resulting composite electrocatalyst (figure 2).

The catalyst is used as a three-functional molecular catalyst for the first time, the high half-wave potential of the oxygen reduction reaction is 0.824V (figure 3), and when the current density is 10mA cm^-2When the reaction is carried out, the overpotentials for the hydrogen evolution reaction and the oxygen evolution reaction are 320mV (figure 4) and 379mV (figure 5), respectively, and are smaller. The specific capacity of the assembled rechargeable zinc-air battery is 793mAh g^-1(FIG. 6) the power density was 225.4mW cm^-2(FIG. 7). It can be seen that this example achieved excellent electrocatalytic performance.

Example 3

A0.25 mg/mL aqueous GO solution was obtained as described above in example 1. 30mL (0.25mg/mL) of the purified graphene oxide dispersion was mixed with 20. mu.L of ascorbic acid and 150. mu.L of sodium dihydrogen phosphate solution (35 wt%). The mixture was kept at 95 ℃ for 1h and after reduction a homogeneous black dispersion was obtained with a small amount of black precipitate. Subsequently, the dispersion was filtered with cotton to remove precipitates, resulting in a stable black chemically converted graphene dispersion. The chemically converted graphene dispersion (11mL) was added dropwise slowly to an aqueous solution of cobalt porphyrin (5. mu.M, 150mL) with stirring at room temperature. Finally, the composite was centrifuged (7000rpm), washed and freeze-dried (40 h).

The obtained composite material electrocatalyst is used as a three-functional molecular catalyst, the high half-wave potential of the oxygen reduction reaction is 0.765V, and when the current density is 10mA cm^-2When the reaction is carried out, overpotentials of hydrogen evolution reaction and oxygen evolution reaction are 368mV and 408mV respectively. The specific capacity of the assembled rechargeable zinc-air battery is 775mAh g^-1The power density is 201mW cm^-2。

Example 4

A0.25 mg/mL aqueous GO solution was obtained as described above in example 1. 40mL (0.25mg/mL) of the purified graphene oxide dispersion was mixed with 20. mu.L of sodium ascorbate and 150. mu.L of sodium hydroxide solution (35 wt%). The mixture was kept at 95 ℃ for 1h and after reduction a homogeneous black dispersion was obtained with a small amount of black precipitate. Subsequently, the dispersion was filtered with cotton to remove precipitates, resulting in a stable black chemically converted graphene dispersion. The chemically converted graphene dispersion (13mL) was added dropwise slowly to an aqueous solution of cobalt porphyrin (5. mu.M, 150mL) with stirring at room temperature. Finally, the composite was centrifuged (8000rpm), washed and freeze dried (50 h).

The obtained composite material electrocatalyst is used as a three-functional molecular catalyst, the high half-wave potential of the oxygen reduction reaction is 0.803V, and when the current density is 10mA cm^-2The overpotentials of the hydrogen evolution reaction and the oxygen evolution reaction are 346mV and 386mV respectively. The specific capacity of the assembled rechargeable zinc-air battery is 782mAh g^-1The power density is 213mW cm^-2。

Example 5

The only difference between this example and example 1 is that the final composite centrifuge speed was 9000rpm, the wash time and the freeze-drying time was 24 h.

The obtained composite material electrocatalyst is used as a three-functional molecular catalyst, the high half-wave potential of the oxygen reduction reaction is 0.775V, and the current density is 10mA cm^-2When the reaction is carried out, overpotentials of hydrogen evolution reaction and oxygen evolution reaction are 393mV and 416mV respectively. The specific capacity of the assembled rechargeable zinc-air battery is 765mAh g^-1The power density is 214mW cm^-2。

Example 6

This example only differs from example 1 in that the final composite material was centrifuged at 10000rpm, washed and freeze-dried for 72 hours.

The obtained composite material electrocatalyst is used as a three-functional molecular catalyst, the high half-wave potential of the oxygen reduction reaction is 0.815V, and the current density is 10mA cm^-2When the reaction is carried out, overpotentials of hydrogen evolution reaction and oxygen evolution reaction are 329mV and 381mV respectively. The specific capacity of the assembled rechargeable zinc-air battery is 789mAh g^-1The power density is 219mW cm^-2。

Therefore, the implementation shows that the supermolecule strategy is utilized to regulate and control the molecular conformation of the cobalt porphyrin, the intrinsic catalytic activity of the cobalt porphyrin is obviously improved, the obtained electrocatalyst shows excellent electrocatalytic performance, and the assembled rechargeable zinc-air battery has high specific capacity and high power density. The intrinsic catalytic activity of the electrocatalyst is regulated and controlled at the molecular level, and a new way is provided for improving the catalytic performance of the molecular catalyst.