CN113201750A

CN113201750A - Fluorine modified copper cobaltate modified carbon nanotube electrode catalyst

Info

Publication number: CN113201750A
Application number: CN202110342479.7A
Authority: CN
Inventors: 曾庆钢
Original assignee: Guangzhou Fisher Artificial Intelligence Technology Co ltd
Current assignee: Guangzhou Fisher Artificial Intelligence Technology Co ltd
Priority date: 2021-03-30
Filing date: 2021-03-30
Publication date: 2021-08-03

Abstract

The invention discloses a fluorine modified copper cobaltate modified carbon nanotube electrode catalyst, and a preparation method thereof comprises the following steps: mixing cobalt chloride hexahydrate and copper chloride into an ethanol solution containing ammonia water, adding a hydroxyl carbon nanotube, mixing and dispersing to obtain a precursor mixed solution, carrying out 16-hour oil bath reaction at 80 ℃, then adding ammonium fluoride, continuing to carry out 3-hour hydrothermal reaction at 140 ℃, filtering, washing and drying to obtain a solid. The electrode catalyst has a one-dimensional tubular structure, is loaded with nanoparticles with high intrinsic activity, and has excellent oxygen reduction catalytic performance comparable to noble metals. The preparation method is simple, low in cost and easy to popularize.

Description

Fluorine modified copper cobaltate modified carbon nanotube electrode catalyst

Technical Field

The invention belongs to the technical field of new energy and new material application, and particularly relates to a preparation method and application of a fluorine modified copper cobaltate modified carbon nanotube oxygen reduction electrode catalyst.

Background

Spinel-type transition metal oxides are abundant in natural resources and low in price, and the catalytic activity of the spinel-type transition metal oxides as catalysts depends on the coordination environment of the transition metals in the crystal structure. Under alkaline conditions, copper cobaltate exhibits catalytic properties for ORR due to its unique d-electron structure and crystal structure. However, pure-phase copper cobaltate is poor in conductivity, so that hydroxyl carbon nanotubes coupled with copper cobaltate are used for constructing an electron transport channel and increasing the number of active sites. The resulting composites have a gap in their ability to catalyze ORR as compared to platinum. Therefore, in order to realize a practical use scene of the copper cobaltate modified carbon nanotube catalyst, a research on how to generate intrinsic activity of the high spinel oxide and improve the density of active sites is needed.

Disclosure of Invention

Aiming at some defects in the prior art, the invention provides a preparation method of a fluorine modified copper cobaltate modified carbon nanotube oxygen reduction electrode catalyst, which comprises the following steps:

(1) weighing 0.05g of hydroxyl carbon nanotube oCNT, 0.05-1 mmol of cobalt chloride hexahydrate and 0.025-0.5 mmol of copper chloride, wherein the molar ratio of the cobalt chloride hexahydrate to the copper chloride is 2: 1, placing them in a 100mL round-bottom flask, adding 0.8mL ammonia water and 70mL absolute ethyl alcohol, and then carrying out ultrasonic treatment for 30min for dispersion and mixing.

(2) Placing the round-bottom flask in an oil bath kettle at 80 ℃ for refluxing for 16 hours to perform first-step heat treatment, and then adding the copper chloride in the step (1) in a molar ratio of (1-2): (1-2), transferring the mixed liquid into a 100mL hydrothermal reaction kettle, and further reacting in an oven at 140 ℃ for 3 hours. And (3) carrying out suction filtration and washing at normal temperature, and drying in an oven at 50 ℃ for 4 hours to obtain the fluorine modified copper cobaltate modified carbon nanotube electrode catalyst.

In the above preparation method, preferably, 0.2mmol of cobalt chloride hexahydrate and 0.1mmol of copper chloride are used in the step (1);

as another object of the present invention, the present invention provides a fluorine modified copper cobaltate modified carbon nanotube electrode catalyst which can be used in electrochemical oxygen reduction reaction;

as another object of the invention, the invention provides a fluorine modified copper cobaltate modified carbon nanotube electrode catalyst which can be used in a liquid zinc-air battery cathode.

The invention has the beneficial effects that:

1. according to the invention, the hydroxyl carbon nanotube material is used as a carrier, and is coupled with the fluorine modified copper cobaltate spinel material with high intrinsic activity to construct a heterogeneous interface, so that the material has catalytic oxygen reduction performance comparable to that of noble metal platinum, and compared with noble metal platinum, the fluorine modified copper cobaltate modified carbon nanotube has lower cost.

2. The electronegativity of the fluorine negative ions is higher than that of the oxygen negative ions, and the connected cobalt atoms can be kept to have the valence +3 with high catalytic activity in the catalytic oxygen reduction reaction process, so that the electrochemical catalytic reaction activity is improved; in addition, the radius of the fluorine negative ions is smaller, the stability of a metal-oxygen bond can be enhanced, the dissolution of cations in the discharging process can be inhibited, and the stability of the catalyst is further improved.

3. The fluorine modified copper cobaltate modified carbon nano tube obtained by the invention is applied to a liquid zinc-air battery, the open-circuit potential is 1.52V, and the power density is 98.2mW/cm^-2。

Drawings

FIG. 1 is a linear voltammogram for oxygen reduction reaction of the electrode catalysts of examples 1 to 3 and comparative examples 1 to 3.

FIG. 2 shows Tafel slopes of oxygen reduction reactions of the electrode catalysts of examples 1 to 3 and comparative examples 1 to 3.

FIG. 3 is a characterization of the electrochemical performance of example 2. Where FIG. 3a is a plot of electron transfer number, hydrogen peroxide yield, calculated at RRDE, and FIG. 3b is a plot of raw disc current and ring current.

Fig. 4 is a topographical characterization of example 2 and comparative example 1. Wherein FIG. 4a is a comparative example 1F-CuCo₂O₄-oCNT scanning Electron microscopy, FIG. 4b is example 2F-CuCo₂O₄-scanning electron micrograph of oCNT-2.

Fig. 5 is a structure-characterizing X-ray diffraction pattern of example 2 and comparative example 1.

Fig. 6 is an open circuit potential diagram applied to the air cathode of the zinc-air battery in example 2.

Fig. 7 is a graph of the discharge curve and power density of the air cathode of the zinc-air battery applied in example 2.

FIG. 8 shows 25mA cm of zinc-air battery air cathode in example 2^-2Discharge curve stability plot.

Detailed Description

The present invention will be described in more detail with reference to the following examples, which should not be construed as limiting the scope of the present invention.

Example 1

The preparation method of the fluorine modified copper cobaltate modified carbon nanotube electrode catalyst comprises the following steps:

(1) 0.05g of hydroxyl carbon nanotube oCNT, 0.0476g (0.2mmol) of cobalt chloride hexahydrate and 0.0170g (0.1mmol) of copper chloride are weighed and placed in a 100mL round-bottom flask, 0.8mL of ammonia water and 70mL of absolute ethyl alcohol are added, and then ultrasonic treatment is carried out for 30min for dispersion and mixing.

(2) The round-bottomed flask was put in an 80 ℃ oil bath and refluxed for 16 hours to perform the first-step heat treatment, and then 0.0019g (0.05mmol) of ammonium fluoride was added, and the mixed liquid was transferred to a 100mL hydrothermal reaction vessel and further reacted in an oven at 140 ℃ for 3 hours. Filtering and washing at normal temperature, drying in a 50 ℃ oven for 4 hours, collecting a sample, and marking the sample as F-CuCo₂O₄-oCNT-1。

Example 2

Ammonium fluoride was added in an amount of 0.0037g (0.1 mmol); other preparation processes and parameters are the same as those of the example 1; the resulting sample was labeled F-CuCo₂O₄-oCNT-2。

Example 3

Ammonium fluoride was added in an amount of 0.0056g (0.15 mmol); other preparation processes and parameters are the same as those of the example 1; the resulting sample was labeled F-CuCo₂O₄-oCNT-3。

Comparative example 1

The procedure in comparative example 1 was substantially the same as in example 1 above, except that: no fluorine source was introduced, i.e. no ammonium fluoride was added, between the two heat treatments. Sample designation CuCo₂O₄-oCNT。

Comparative example 2

The hydroxyl carbon nanotube otcnt is commonly used on the market.

Comparative example 3

Pt/C platinum carbon catalyst is commonly used on the market.

Example 4 electrochemical Performance characterization test

(1) ORR performance research of the carbon nano tube modified by the fluorine modified copper cobaltate with different degrees.

Redox performance analysis was performed on the samples obtained in examples 1 to 3 and comparative examples 1 to 3, and the ORR performance of the fluorine-modified copper cobaltate-modified carbon nanotubes with different degrees was studied.

Preparing a working electrode: weighing 3mg of catalyst sample, adding the catalyst sample into a mixed solution of 0.5mL of deionized water, 0.5mL of isopropanol and 20 mu L of Nafion, carrying out ultrasonic treatment for 15min to uniformly disperse the catalyst sample and prepare catalyst ink, using a liquid transfer gun to transfer 5 mu L of catalyst ink, dropwise adding the catalyst ink on the surface of a glassy carbon working electrode, and drying.

Linear sweep voltammetry: a standard three-electrode system is adopted, a glassy carbon electrode dripped with a catalyst is used as a working electrode, a spectral pure graphite carbon rod is used as a counter electrode, and an Hg/HgO electrode is used as a reference electrode. The electrolyte solution was 0.1M KOH. The Hg/HgO electrode reference electrode voltage relative to the RHE electrode in 0.1M KOH was 0.86708V. Introducing oxygen for 30 minutes before testing, testing an LSV curve after waiting for oxygen saturation, and scanning at a speed of 10mV s^-1The rotation speed is 1600rpm, the voltage interval of ORR reaction is 0.2-1.0V vs. RHE, and the data is recorded, and the specific results are shown in Table 1 and figure 1.

TABLE 1 electrochemical ORR data for different degrees of fluorine modified copper cobaltate modified carbon nanotubes and comparative examples

As can be seen from Table 1, all fluorine-modified copper cobaltate modified carbon nanotube catalysts have better initial potential, half-wave potential and limiting current density than CuCo which is not modified by fluorine₂O₄-oCNT (comparative example 1), better than unmodified oCNT (comparative example 2). It can therefore be concluded that: the introduction of the fluorine element can effectively improve the catalytic capability of copper cobaltate modified carbon nano tube on ORR. In general, a more positive peaking potential means a smaller overpotential for the oxygen reduction reaction, O₂The more readily electrons are received and participate in the reaction, the more likely it is to improve the discharge efficiency of the air fuel cell when applied as a cathode catalyst. FIG. 1 is a linear sweep voltammogram of different fluorine-modified copper cobaltates modified carbon nanotubes, wherein F-CuCo₂O₄The initial potential of-oCNT-2 is larger than that of F-CuCo₂O₄-oCNT-1 and F-CuCo₂O₄-oCNT-3, which indicates that the amount of fluorine source introduced needs to be adaptedWhen too little or too much ammonium fluoride precursor may affect the spinel structure and eventually fail to achieve efficient oxygen reduction catalysis; and F-CuCo₂O₄The initial potential of-oCNT-2 was 0.91V as Pt/C (comparative example 3), and the limiting current density was higher than Pt/C, indicating that F-CuCo₂O₄-oCNT-2 possesses ORR catalytic properties comparable to noble metals Pt/C.

TABLE 2 electrochemical Tafel data for different degrees of fluorine modified copper cobaltate modified carbon nanotubes and comparative examples

Fig. 2 and table 2 show the tafel slope corresponding to the oxygen reduction process of the electrode catalyst, which is used to characterize the kinetics speed of catalytic ORR. Wherein, F-CuCo₂O₄The Tafel slope of-oCNT-2 was the lowest and was 63.4 mV dec^-1This means that F-CuCo₂O₄the-oCNT-2 has the advantages over other fluorine modified copper cobaltate modified carbon nanotubes in catalytic oxygen reduction reaction kinetics. Furthermore, F-CuCo₂O₄The lower tafel slope of-oCNT-2 compared to the noble metal Pt/C also further demonstrates its potential to replace noble metals as oxygen reduction electrode catalysts.

FIG. 3 further characterizes F-CuCo using rotating ring disk electrochemical electrodes₂O₄-oxygen reduction electrochemical performance of otnt-2. From FIG. 3a, F-CuCo can be calculated₂O₄-oCNT-2 is in the voltage window range of 0.2V to 0.8V, the electron transfer number of the reaction is between 3.56 and 3.65, corresponding to a hydrogen peroxide yield of between 22.1% and 17.5%, which means F-CuCo₂O₄The reaction path of the-oCNT-2 is mainly a reaction which occurs through four electron transfer when catalyzing oxygen reduction reaction.

Example 5CuCo₂O₄-oCNT and F-CuCo₂O₄-structural morphology characterization of oCNT-2

Modification of carbon nanotube CuCo by Scanning Electron Microscope (SEM) copper cobaltate₂O₄-oCNT and fluorine modified cobaltic acidCopper-modified carbon nanotube F-CuCo₂O₄-oCNT-2, see FIG. 4. The tubular morphology of CuCo can be clearly seen in FIG. 4a₂O₄-oCNT are randomly dispersed and stacked together, and CuCo with different sizes is dispersed on the tube wall₂O₄Nanoparticles. FIG. 4b F-CuCo which has been fluorinated₂O₄The significant blocking between-oCNT-2 tube walls indicates that the introduction of the fluorine modification source is to CuCo₂O₄The morphological structure of the-oCNT has certain influence.

FIG. 5 shows CuCo₂O₄-oCNT and F-CuCo₂O₄-X-ray diffraction pattern of otnt-2. From FIG. 4, CuCo can be seen₂O₄-oCNT and F-CuCo₂O₄the-oCNT-2 catalyst has diffraction signal peaks at 26.2 degrees and 44.4 degrees and is the (002) and (101) crystal planes of graphite carbon corresponding to the structure of the carbon nanotube. Despite the fluorinated F-CuCo₂O₄The morphology of the-oCNT-2 is adhered, but the diffraction signal peak of the active substance is not obviously different no matter whether the peak is CuCo₂O₄-oCNT or F-CuCo₂O₄-oCNT-2, all of which can find the characteristic diffraction peak corresponding to CuCo at 36.7 DEG₂O₄The (311) crystal plane of (a), indicating that the fluorine modification does not affect the spinel structure of the active site.

Example 6F-CuCo₂O₄-oCNT-2 is applied to air cathode analysis of zinc-air battery

F-CuCo of example 2 was selected₂O₄-oCNT-2 was used for analysis in air cathode of zinc-air battery. Study of its open circuit potential, discharge curve and power density and at 25mA cm^-2And (4) stability of discharge curve.

Assembling a zinc-air battery device: a single chamber reactor of 28mL capacity was used. The anode is a polished zinc sheet with the thickness of 0.5mm, the electrolyte is a mixed solution of 6mol/L potassium hydroxide and 0.2mol/L zinc acetate, the cathode substrate is hydrophobic carbon cloth, and the loading amount of the hydrophobic carbon cloth is 4.5mg/cm²F-CuCo of₂O₄-oCNT-2 catalyst.

FIG. 6 shows F-CuCo₂O₄-oCNT-2 is applied to the battery switch of the air cathode of the zinc-air batteryThe open-circuit potential of the battery is stabilized to 1.52V in a circuit potential-time diagram, and the high open-circuit potential proves that F-CuCo₂O₄-oCNT-2 is an ideal material as an air cathode catalyst. FIG. 6 is a graph showing the charge/discharge characteristics of the battery at 50mA/cm²And 100mA/cm²The corresponding discharge voltage under the current is 1.04V and 0.84V respectively, which shows that F-CuCo₂O₄the-oCNT-2 electrode catalyst has the potential of being applied to a high-current discharge scene. FIG. 7 shows that F-CuCo can be calculated from the discharge curve₂O₄The power density of the-oCNT-2 air cathode zinc-air battery is 98.2mW/cm²High power density. FIG. 8 shows the zinc-air battery fixed at 25mA cm^-2The current density is continuously discharged for 12 hours, the discharge voltage is only attenuated by 0.04V, which further proves that F-CuCo₂O₄Practical significance of application of-oCNT-2 to zinc-air battery air cathodes.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention.

Claims

1. The fluorine modified copper cobaltate modified carbon nanotube electrode catalyst is characterized in that the preparation method comprises the following steps:

(1) weighing 0.05g of hydroxyl carbon nanotube oCNT, 0.05-1 mmol of cobalt chloride hexahydrate and 0.025-0.5 mmol of copper chloride, wherein the molar ratio of the cobalt chloride hexahydrate to the copper chloride is 2: 1, placing the materials in a 100mL round-bottom flask, adding 0.8mL ammonia water and 70mL absolute ethyl alcohol, and performing ultrasonic treatment for 30min to perform dispersion and mixing;

2. The method for preparing the fluorine modified copper cobaltate modified carbon nanotube electrode catalyst according to claim 1, wherein the dosage of the cobalt chloride hexahydrate in the step (1) is 0.2mmol, and the dosage of the copper chloride is 0.1 mmol.

3. The fluorine modified copper cobaltate modified carbon nanotube electrode catalyst as claimed in claim 1, which can be used in electrochemical oxygen reduction reaction.

4. The fluorine modified copper cobaltate modified carbon nanotube electrode catalyst as claimed in claim 1, which can be used in liquid zinc-air battery cathodes.