CN113584512B

CN113584512B - Preparation method of cobalt/cobalt oxide/molybdenum oxide in-situ electrode

Info

Publication number: CN113584512B
Application number: CN202110950901.7A
Authority: CN
Inventors: 黄妞; 李佳乐; 骆禅; 杨柳
Original assignee: China Three Gorges University CTGU
Current assignee: China Three Gorges University CTGU
Priority date: 2021-08-18
Filing date: 2021-08-18
Publication date: 2022-08-05
Anticipated expiration: 2041-08-18
Also published as: CN113584512A

Abstract

The invention provides a preparation method of a cobalt/cobalt oxide/molybdenum oxide in-situ electrode. Preparing a precursor solution containing cobalt/molybdenum oxide or cobalt/molybdenum hydroxide, attaching the precursor solution to the surface of foam Nickel (NF), and applying a constant potential in a specific electrolyte for reduction by using an electrochemical reduction method to reduce precursor substances attached to the surface of the foam Nickel (NF) into cobalt and generate cobalt oxide and molybdenum oxide. The technical scheme of the invention has the advantages of no pollution of required raw materials, low cost, simple operation, quick preparation and the like; the prepared molybdenum oxide passivated cobalt/cobalt oxide in-situ electrode shows excellent catalytic activity as a bifunctional electrocatalyst for Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER), and has good prospect of being applied to electrocatalytic decomposition of water.

Description

Preparation method of cobalt/cobalt oxide/molybdenum oxide in-situ electrode

Technical Field

The invention relates to preparation of a multi-component multifunctional material, and belongs to the field of electrocatalysis and energy conversion materials and devices.

Background

The problem of energy consumption is a bottleneck problem restricting the development of the world. With the gradual depletion of conventional fossil fuels, the problems of energy shortage and global environmental pollution become increasingly severe. The development of efficient, economical and renewable green energy sources to alleviate these problems is a great pursuit. The hydrogen energy has the advantages of high energy conversion efficiency, cleanness, renewability, zero carbon emission and the like, and is considered to be a novel energy carrier with high efficiency (wherein the electrocatalytic decomposition of water under alkaline conditions is considered to be one of the most potential ways for industrial application). Water splitting involves two half-reactions, namely an Oxygen Evolution Reaction (OER) occurring at the anode and an oxygen evolution reaction (HER) occurring at the cathode. Currently, the most efficient HER and OER catalysts are platinum-based materials and noble metal oxides of iridium and ruthenium, respectively, but the expensive price, rare reserves and poor stability of these materials severely limit their large-scale commercial application. Therefore, the search and preparation of non-noble metal-based materials which are free of pollution, low in price and efficient and stable become an important research direction in the field of electrocatalytic water decomposition. Wherein, the cobalt and nickel-based non-noble materials not only have low price and rich reserves, but also show excellent performance in the aspect of water decomposition, thereby showing huge commercial application prospect.

Molybdenum-based compounds are important materials (as electrical, photocatalyst and other catalysts) in many fields. The tuning state of molybdenum and its easy binding to various anions diversify the application of molybdenum-based materials in different fields (Catalysis Science)&Technology, 2016, 6(7): 2403-. To date, various cobalt-based materials have been reported for use in HER, e.g., metals Co, CoS ₂ CoP and CoSe, show high catalytic activity. Cobalt oxide/(oxy) hydroxide showed better catalytic activity for OER. This means that cobalt-based materials with different cobalt active species are able to complete the total water splitting to produce hydrogen and oxygen. However, metal Co or Co _x O _y Materials have many disadvantageous characteristics such as easy build-up and low conductivity. (Chemical communications, 2016, 52(35): 5946-.

Based on the research, the invention adopts an electrochemical reduction mode to prepare the molybdenum oxide passivated cobalt/cobalt oxide in-situ electrode, utilizes a larger negative potential to convert an attached hydroxide into an oxide, reduces a cobalt oxide or cobalt salt into metal cobalt, simultaneously exposes more active sites, and optimizes the ratio of the metal cobalt to the cobalt oxide in the electrode by adjusting the time of electrochemical reduction, so that the prepared molybdenum oxide passivated cobalt/cobalt oxide in-situ electrode is expected to have high HER and OER electrocatalytic activity and high stability.

Disclosure of Invention

In view of the above, the present invention provides a method for preparing a molybdenum oxide passivated cobalt/cobalt oxide in-situ electrode, which comprises the following steps:

s1, preparing a precursor of cobalt/molybdenum oxide or cobalt/molybdenum hydroxide: dissolving cobalt chloride without crystal water in a mixed solution of ethanol and glacial acetic acid, adding molybdenum acetylacetonate while stirring, adding the mixed solution of water and ethanol, continuously stirring until the solution is clear to form a cobalt/cobalt (hydrogen) oxide solution, placing the solution in a hydrothermal tank, preserving the temperature for a period of time, immersing foam Nickel (NF) in the solution after cooling, taking out the solution, throwing the solution out by a homogenizer, and drying the solution for later use.

S2, electroreduction: and (3) placing the NF attached with the precursor in an electrolyte of sodium sulfate and boric acid, and performing electro-reduction on the NF for a period of time by using an electrochemical workstation in a constant-current mode. The surface electrolyte was then rinsed with UP water and dried.

And S3, the steps of attaching and electrochemical reduction are cycled for multiple times to prepare the electrode, or the steps of attaching are cycled for multiple times and electrochemical reduction is carried out to prepare the molybdenum oxide passivated cobalt/cobalt oxide in-situ electrode.

Further, in S1, the concentration of cobalt chloride is 0.5-1 mol/L, and the molar ratio of cobalt chloride to molybdenum acetylacetonate is 1: 0.1 to 0.2.

Further, in S1, the first solvent is a mixed solution of ethanol and glacial acetic acid, wherein a volume ratio of ethanol to glacial acetic acid is 1: 0.02-0.04, wherein the second solvent is a water-ethanol mixed solution, and the volume ratio of ethanol to water is 1: 0.03-0.07, wherein the volume ratio of the first solvent to the second solvent is 1: 0.1 to 0.3.

Further, the heat preservation temperature of the hydrothermal box in S1 is 80-120 ℃, and the heat preservation time is 4 hours.

Further, the drying in S1 and S2 is 70-90 ℃.

Further, in S2, the constant potential is in the range of-2.5 to-3.0V relative to the saturated calomel electrode.

Furthermore, the time in S2 is 600-3000 seconds.

Further, the number of cycles mentioned in S3 is 0-5.

The invention also relates to the application of the material obtained by the preparation method in HER/OER bifunctional catalytic electrolysis water.

The invention has the following beneficial effects:

1. when the molybdenum oxide passivated cobalt/cobalt oxide in-situ electrode material is prepared, a precursor solution is prepared, and Co and Mo elements are mixed at a molecular level, so that the particle size of a product is favorably refined, more active areas are favorably exposed, and the catalytic performance of the material is improved; on the other hand, the subsequent molybdenum oxide passivated Co/cobalt oxide in-situ electrode is convenient for Co and CoO _x 、MoO _y Corresponding or called componentUniform dispersion, and is favorable for synergistically improving the electrocatalytic activity and stability of HER and OER.

2. And (3) placing the NF attached with the precursor into a mixed solution of sodium sulfate and boric acid, and performing electro-reduction on the NF for a certain time by using an electrochemical workstation in a constant potential mode. And (3) generating oxide by utilizing an electrical reduction mode to the hydroxide attached to the NF surface, and reducing the cobalt oxide or cobalt salt into metallic cobalt.

3. The multiple attachment step is to increase the load capacity of NF to increase the number of active sites, thereby increasing the number of active sites

HER and OER electrocatalytic activity and stability.

Drawings

Fig. 1 shows HER linear voltammetry scans and OER linear voltammetry scans measured on samples prepared in example 1, wherein a is HER linear voltammetry scan (LSV) and b is OER linear voltammetry scan (LSV).

Fig. 2 shows HER linear voltammetry scans and OER linear voltammetry scans measured on the samples prepared in example 2, wherein a is HER linear voltammetry scan (LSV) and b is OER linear voltammetry scan (LSV).

Fig. 3 shows HER linear voltammetry scans and OER linear voltammetry scans measured on samples prepared in example 3, wherein a is HER linear voltammetry scan (LSV) and b is OER linear voltammetry scan (LSV).

Figure 4 is a plot of HER linear voltammetry scans measured on samples prepared in example 4.

Fig. 5 shows HER linear voltammetry scans and OER linear voltammetry scans measured on samples prepared in example 5, wherein a is HER linear voltammetry scan (LSV) and b is OER linear voltammetry scan (LSV).

Fig. 6 shows HER linear voltammetry scans and OER linear voltammetry scans measured on samples prepared in example 6, wherein a is HER linear voltammetry scan (LSV) and b is OER linear voltammetry scan (LSV).

FIG. 7 is an SEM photograph of a sample prepared in example 3, wherein a is an SEM photograph at a magnification of 11000 and b is an SEM photograph at a magnification of 50000.

FIG. 8 is an SEM photograph of a sample prepared in example 5, wherein a is an SEM photograph at a magnification of 10000 and b is an SEM photograph at a magnification of 50000.

FIG. 9 is an SEM photograph of a sample prepared in example 6, wherein a is an SEM photograph at a magnification of 10000 and b is an SEM photograph at a magnification of 50000.

Characterizing conditions

The HER and OER test method in the invention embodiment comprises the following steps: foamed nickel is used as a working electrode, a carbon rod is used as a counter electrode, a saturated Hg/HgO electrode is used as a reference electrode, and the used electrolytes are as follows: 1M KOH aqueous solution, and the scanning speed is 5-10 mV/s. The HER test was performed with nitrogen, and the OER test was performed with oxygen. Oxygen and nitrogen were naturally saturated in 1M aqueous KOH and stirred at 200 rpm during the test. The saturated Hg/HgO electrodes were corrected with a reversible hydrogen electrode, and the potentials described hereinafter are all relative to the reversible hydrogen electrode. The electric potential is automatically carried out by using the Shanghai Chen chemical workstation in the LSV testIR) And (6) compensation. An X-ray diffraction (SEM) pattern of the sample was obtained using a SMART LAB-9 type X-ray diffractometer. Scanning electron microscope (XRD) images were acquired using an aspect F50 scanning electron microscope (FEI America).

Example 1

At room temperature, 2.475 g of CoCl ₂ Dissolved in a mixture of 21.99 mL of ethanol and 0.72 mL of glacial acetic acid, then 0.877 g of molybdenum acetylacetonate is added while stirring, then a mixture of 6 mL of ethanol and 0.3 mL of water is added dropwise, and stirring is continued until the solution is clear to form a solution. Then sealing the nickel foam, preserving the heat for 4 hours at 80 ℃ in a hydrothermal chamber, soaking the Nickel Foam (NF) for ten minutes after cooling, taking out the nickel foam, throwing out redundant solution by using a uniform glue machine, and then drying the nickel foam at 80 ℃. 7.102 g of sodium sulfate and 3.0915 g of boric acid were weighed out to prepare 100 mL of an electrolyte, and the solvent was UP water. And (3) performing electric reduction on the treated NF by using an electrochemical workstation, wherein a calomel electrode is used as a reference electrode, a platinum sheet is used as a counter electrode, the potential is set to be-2.5V, and the time is 600 seconds. The surface electrolyte was washed off with UP water and dried.

Figure 1 is a linear voltammetric scan (LSV) of HER and OER measured on the samples prepared in example 1. As can be seen from FIG. 1 (a), the current density when the electrode passes through the electrode was 10 mA/cm ² In alkaline aqueous solution, the HER reaction corresponds toThe overpotential of (a) is 106 mV; as can be seen from FIG. 1 (b), the current density when the electrode passes through the electrode was 10 mA/cm ² In this case, the overpotential for the OER reaction in the aqueous alkaline solution was 280 mV.

Example 2

At room temperature, 2.475 g of CoCl ₂ Dissolved in a mixture of 21.99 mL of ethanol and 0.72 mL of glacial acetic acid, then 0.877 g of molybdenum acetylacetonate is added while stirring, then a mixture of 6 mL of ethanol and 0.3 mL of water is added dropwise, and stirring is continued until the solution is clear to form a solution. Then sealing the nickel foam, preserving the heat for 4 hours at 80 ℃ in a hydrothermal chamber, soaking the Nickel Foam (NF) for ten minutes after cooling, taking out the nickel foam, throwing out redundant solution by using a uniform glue machine, and then drying the nickel foam at 80 ℃. 7.102 g of sodium sulfate and 3.0915 g of boric acid were weighed out to prepare 100 mL of an electrolyte, and the solvent was UP water. And (3) performing electric reduction on the treated NF by using an electrochemical workstation, wherein a calomel electrode is used as a reference electrode, a platinum sheet is used as a counter electrode, the potential is set to be-3.0V, and the time is 600 seconds. The surface electrolyte was washed off with UP water and dried. And (5) recycling the attaching solution and the electroreduction process once again to obtain the electrode.

Figure 2 is a graph of HER and OER linear voltammetric scans (LSVs) measured for the samples prepared in example 2. As can be seen from FIG. 2 (a), the current density when the electrode passes through the electrode was 10 mA/cm ² When the reaction is carried out, the overpotential corresponding to the HER reaction in the alkaline aqueous solution is 124 mV; as can be seen from FIG. 2 (b), the current density when the electrode passes through the electrode was 10 mA/cm ² In this case, the overpotential for the OER reaction in the aqueous alkaline solution was 280 mV.

Example 3

At room temperature, 2.475 g of CoCl ₂ Dissolved in a mixture of 21.99 mL of ethanol and 0.72 mL of glacial acetic acid, then 0.877 g of molybdenum acetylacetonate is added while stirring, then a mixture of 6 mL of ethanol and 0.3 mL of water is added dropwise, and stirring is continued until the solution is clear to form a solution. Then sealing the nickel foam, preserving the heat for 4 hours at 80 ℃ in a hydrothermal chamber, soaking the Nickel Foam (NF) for ten minutes after cooling, taking out the nickel foam, throwing out redundant solution by using a uniform glue machine, and then drying the nickel foam at 80 ℃. 7.102 g of sodium sulfate and 3.0915 g of boric acid were weighed out to prepare 100 mL of an electrolyte, and the solvent was UP water. Using electrochemical workstation to treat NFAnd (3) electroreduction, namely performing electroreduction, wherein a calomel electrode is used as a reference electrode, a platinum sheet is used as a counter electrode, the potential is set to be-3.0V, and the time is 600 seconds. The surface electrolyte was washed off with UP water and dried.

Figure 3 is a graph of HER and OER linear voltammetric scans (LSVs) measured for the samples prepared in example 3. As can be seen from FIG. 3 (a), the current density when the electrode passes through the electrode was 10 mA/cm ² When the reaction is carried out, the overpotential corresponding to the HER reaction in the alkaline aqueous solution is 210 mV; as can be seen from FIG. 3 (b), the current density when the electrode passes through the electrode was 10 mA/cm ² The overpotential for the OER reaction in the alkaline aqueous solution is 280 mV.

FIG. 7 is an SEM photograph of example 3 showing that the prepared sample adhered to nickel foam and was observed to be in a state of fine particle connection at a high magnification and uniformly distributed on the surface.

Example 4

At room temperature, 2.475 g of CoCl ₂ Dissolving the mixture in a mixed solution of 21.99 mL of ethanol and 0.72 mL of glacial acetic acid, then adding 0.877 g of molybdenum acetylacetonate while stirring, then dropwise adding a mixed solution of 6 mL of ethanol and 0.3 mL of water, and continuing stirring until the solution is clear to form a precursor solution. Then sealing the precursor solution, preserving the heat for 4 hours at 120 ℃ in a hydrothermal chamber, taking out 2 mL of precursor solution after cooling, completely dripping the precursor solution on foam Nickel (NF), and drying the precursor solution at 90 ℃ in the whole process. 7.102 g of sodium sulfate and 3.0915 g of boric acid were weighed out to prepare 100 mL of electrolyte, and 2 mL of precursor solution was added thereto. And (3) performing electric reduction on the treated NF by using an electrochemical workstation, wherein a calomel electrode is used as a reference electrode, a platinum sheet is used as a counter electrode, the potential is set to be-3.0V, and the time is 1800 seconds. The surface electrolyte was washed off with UP water and dried. The obtained product is placed in a tube furnace with Ar gas as protective gas to be annealed for 1 hour at the temperature of 350 ℃.

Figure 4 is a HER linear voltammetric scan (LSV) measured on the samples prepared in example 4. The current density when the electrode passes through is 10 mA/cm ² When the reaction is carried out, the overpotential corresponding to the HER reaction in the alkaline aqueous solution is 11 mV;

example 5

At room temperature, 2.475 g of CoCl ₂ Dissolving in a mixture of 21.99 mL ethanol and 0.72 mL glacial acetic acid, and mixingWhile stirring, 0.877 g of molybdenum acetylacetonate was added, followed by dropwise addition of a mixture of 6 mL of ethanol and 0.3 mL of water, and stirring was continued until the solution became clear to form a solution. Then sealing the nickel foam, preserving the heat for 4 hours at 80 ℃ in a hydrothermal chamber, soaking the Nickel Foam (NF) for ten minutes after cooling, taking out the nickel foam, throwing out redundant solution by using a uniform glue machine, and then drying the nickel foam at 80 ℃. 7.102 g of sodium sulfate and 3.0915 g of boric acid were weighed out to prepare 100 mL of an electrolyte, and the solvent was UP water. And (3) performing electric reduction on the treated NF by using an electrochemical workstation, wherein a calomel electrode is used as a reference electrode, a platinum sheet is used as a counter electrode, the potential is set to be-3.0V, and the time is 600 seconds. The surface electrolyte was washed off with UP water and dried. And (5) repeating the steps of attaching the solution and performing electro-reduction twice to obtain the electrode.

Figure 5 is a HER and OER linear voltammetric scan (LSV) measured on the samples prepared in example 5. As can be seen from FIG. 5 (a), the current density when the electrode passes through the electrode was 10 mA/cm ² When the reaction is carried out, the overpotential corresponding to the oxygen production of HER reaction in the alkaline aqueous solution is only 22 mV; as can be seen from FIG. 5 (b), the current density when the electrode passes through the electrode was 10 mA/cm ² When the reaction is carried out, the overpotential corresponding to the oxygen production by the OER reaction in the alkaline aqueous solution is 280 mV.

FIG. 8 is an SEM photograph of example 5 showing that the prepared sample adhered to nickel foam and was observed to be spherical and uniformly distributed on the surface at a high magnification.

Example 6

At room temperature, 2.475 g of CoCl ₂ Dissolved in a mixture of 21.99 mL of ethanol and 0.72 mL of glacial acetic acid, then 0.877 g of molybdenum acetylacetonate is added while stirring, then a mixture of 6 mL of ethanol and 0.3 mL of water is added dropwise, and stirring is continued until the solution is clear to form a solution. And then sealing the nickel foam and the solution, preserving the heat for 4 hours at the temperature of 80 ℃ in a hydrothermal chamber, soaking the Nickel Foam (NF) for ten minutes after cooling, taking out the nickel foam and the solution, throwing the nickel foam and the solution out of the nickel foam by using a spin coater, drying the nickel foam and the solution at the temperature of 80 ℃, recycling the operation of the step, attaching the solution twice, and attaching the solution on the NF for three times. 7.102 g of sodium sulfate and 3.0915 g of boric acid were weighed out to prepare 100 mL of an electrolyte, and the solvent was UP water. Performing electric reduction on the treated NF by using an electrochemical workstation, wherein a calomel electrode is used as a reference electrode, a platinum sheet is used as a counter electrode, and the set potential is3.0V, time 1800 seconds. The surface electrolyte was washed off with UP water and dried.

Figure 6 is a HER and OER linear voltammetric scan (LSV) measured on the samples prepared in example 6. As can be seen from FIG. 6 (a), the current density when the electrode passes through the electrode was 10 mA/cm ² When the reaction is carried out, the overpotential corresponding to the HER reaction in the alkaline aqueous solution is 150 mV; as can be seen from FIG. 6 (b), the current density when the electrode passes through the electrode was 10 mA/cm ² In this case, the overpotential for the OER reaction in the aqueous alkaline solution is 290 mV.

FIG. 9 is an SEM photograph of example 6 showing that the prepared sample adhered to nickel foam and observed to be spherical at a high magnification, and the surface of the sample was uniformly distributed with pores.

Claims

1. A preparation method of a cobalt/cobalt oxide/molybdenum oxide in-situ electrode is characterized by comprising the following specific preparation methods:

s1, preparing a precursor of cobalt/molybdenum oxide or cobalt/molybdenum hydroxide: dissolving cobalt chloride without crystal water in a first solvent, adding molybdenum acetylacetonate while stirring, adding a second solvent, continuously stirring until the solution is clear to form an oxide or hydroxide solution of cobalt/molybdenum, placing the solution in a hydrothermal tank, keeping the temperature at 80-120 ℃ for 4 hours, immersing foam nickel NF in the solution after cooling, taking out the solution, throwing the solution out by using a homogenizer, and drying the solution for later use;

the first solvent is a mixed solution of ethanol and glacial acetic acid, wherein the volume ratio of the ethanol to the glacial acetic acid is 1: 0.02-0.04, wherein the second solvent is a water-ethanol mixed solution, and the volume ratio of ethanol to water is 1: 0.03-0.07, wherein the volume ratio of the first solvent to the second solvent is 1: 0.1 to 0.3;

the concentration of the cobalt chloride is 0.5-1 mol/L, and the molar ratio of the cobalt chloride to the molybdenum acetylacetonate is 1: 0.1 to 0.2;

s2, electroreduction: placing NF attached with the precursor in electrolyte of sodium sulfate and boric acid, performing electro-reduction on the NF for a period of time by using an electrochemical workstation in a constant potential mode, wherein the constant potential is in a range of-2.5V to-3.0V relative to a saturated calomel electrode, and then flushing the electrolyte on the surface by using UP water and drying;

s3, cycling the step S1 and the step S2 for multiple times to prepare the electrode, or cycling the step S1 for multiple times to prepare the cobalt/cobalt oxide/molybdenum oxide in-situ electrode by electrochemical reduction.

2. The method of claim 1, wherein the drying process of the cobalt/cobalt oxide/molybdenum oxide in-situ electrode is 70-90 ℃ in S1 and S2.

3. The method for preparing the cobalt/cobalt oxide/molybdenum oxide in-situ electrode according to claim 1, wherein the time in S2 is 600-3000 seconds.

4. The method for preparing the cobalt/cobalt oxide/molybdenum oxide in-situ electrode according to claim 1, wherein the number of cycles in S3 is 1-5.