CN116240582A - Tricobalt tetraoxide/bismuth molybdate composite electrocatalyst for HER/OER double functions and preparation method and application thereof - Google Patents

Tricobalt tetraoxide/bismuth molybdate composite electrocatalyst for HER/OER double functions and preparation method and application thereof Download PDF

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CN116240582A
CN116240582A CN202310253788.6A CN202310253788A CN116240582A CN 116240582 A CN116240582 A CN 116240582A CN 202310253788 A CN202310253788 A CN 202310253788A CN 116240582 A CN116240582 A CN 116240582A
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oer
bismuth molybdate
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卢启芳
刘梦雨
姜怡林
韩秀君
司聪慧
郭恩言
魏明志
陈顺伟
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Qilu University of Technology
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Abstract

The invention provides a cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER double functions, and a preparation method and application thereof. The preparation method comprises the following steps: dissolving a bismuth source, a molybdenum source and citric acid in a mixed solvent of absolute ethyl alcohol and DMF, and then adding an acid solution and a cobalt source to obtain a precursor solution; dissolving polyvinylpyrrolidone in a mixed solvent of absolute ethyl alcohol and DMF, and then adding a precursor solution to obtain a precursor sol; and then carrying out electrostatic spinning, drying and calcining to obtain the product. According to the invention, the electrostatic spinning technology is adopted for the first time to prepare the cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER double functions, the bismuth molybdate is modified by compositing bismuth molybdate and cobaltosic oxide to form a heterostructure, the bismuth molybdate electronic structure is optimized, the obtained composite electrocatalyst shows excellent HER and OER performances, the preparation method is simple and environment-friendly, the raw material cost is low, the environment is friendly, and the potential of large-scale production is provided.

Description

Tricobalt tetraoxide/bismuth molybdate composite electrocatalyst for HER/OER double functions and preparation method and application thereof
Technical Field
The invention relates to a cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER double functions, and a preparation method and application thereof, and belongs to the technical field of electrocatalysts.
Background
With the development of global economy, the demand of human beings for energy is increasing, so that fossil fuels with limited reserves are being excessively consumed, and the development and utilization of clean energy are accelerated along with environmental deterioration problems such as greenhouse effect. Hydrogen is considered as one of the most promising substitutes for fossil fuels, and has the advantages of no pollution of combustion products, high energy density, high energy utilization rate, abundant raw materials and the like. In the existing hydrogen production technology, the electrolytic water hydrogen production is considered to be a very attractive hydrogen production method because of the characteristics of green color, high hydrogen purity, sustainability and the like. However, oxygen Evolution Reaction (OER) and Hydrogen Evolution Reaction (HER) in the water electrolysis process involve multiple electron transfer, the dynamics process is slow, the hydrogen production rate is low, the actual requirements cannot be met, and the two reactions of HER and OER have large overpotential and high energy consumption, so the development of efficient dual-functional electrocatalysts for the Hydrogen Evolution Reaction (HER) and the Oxygen Evolution Reaction (OER) is a key of the water electrolysis hydrogen production technology. Although noble metal catalysts have high catalytic activity and can effectively solve the problem, the reserves of noble metals in nature are rare and expensive, which severely limits their large-scale application. Therefore, the development of a novel dual-function electrocatalyst with high activity and low cost is a key for realizing high-efficiency electrocatalytic full water decomposition.
The molybdate material belongs to a transition metal-based catalyst, has low cost and abundant reserves, but has general intrinsic electrocatalytic performance and low utilization rate of active sites. The electronic structure of the molybdate can be optimized by adopting the regulation and control schemes such as heterojunction, doping and the like, the catalytic potential of the molybdate is stimulated, the efficient catalytic reaction is realized, and the electrocatalytic performance of the material is further improved. The bismuth molybdate has strong oxidation-reduction capability and good conductivity, has wide application prospect in the field of electrocatalysis, but has the defects of lower electrocatalysis and the like, and is mainly used as a photocatalytic material at present, so that few reports about the application of bismuth molybdate in the field of electrocatalysis are provided.
Therefore, a new regulation and control method is adopted to optimize the bismuth molybdate electronic structure, so that the bismuth molybdate-based electrocatalyst with high-efficiency electrocatalytic hydrogen evolution and oxygen evolution reaction capacity is obtained, and the method has important significance for reducing the overpotential of the electrolysis reaction and realizing low-energy consumption hydrogen preparation.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER double functions, and a preparation method and application thereof. According to the invention, the electrostatic spinning technology is adopted for the first time to prepare the cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER double functions, the bismuth molybdate is modified by forming a heterostructure through compositing bismuth molybdate and cobaltosic oxide, the bismuth molybdate electronic structure is optimized, the obtained composite electrocatalyst shows excellent HER and OER performances, and the preparation process is simple and environment-friendly.
Description of the terminology:
room temperature: has the meaning known to those skilled in the art and means 25.+ -. 5 ℃.
The technical scheme of the invention is as follows:
the microcosmic appearance of the composite electrocatalyst is nanofiber, and the diameter of the nanofiber is 200-400nm, and the length of the nanofiber is 5-20 mu m.
The invention also provides a preparation method of the cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER double functions, which comprises the following steps:
(1) Dissolving a bismuth source, a molybdenum source and citric acid in a mixed solvent of anhydrous ethanol and N, N-Dimethylformamide (DMF), then adding an acid solution, adding a cobalt source, and uniformly stirring to obtain a precursor solution;
(2) Dissolving polyvinylpyrrolidone (PVP) in a mixed solvent of anhydrous ethanol and N, N-Dimethylformamide (DMF), and then adding the precursor solution prepared in the step (1) to obtain precursor sol; and then carrying out electrostatic spinning, drying and calcining to obtain the cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER double functions.
Preferably according to the invention, the bismuth source in step (1) is bismuth nitrate pentahydrate; the molybdenum source is ammonium molybdate or sodium molybdate dihydrate; the cobalt source is cobalt nitrate hexahydrate or cobalt acetate tetrahydrate; the molar ratio of the molybdenum element in the molybdenum source to the bismuth element in the bismuth source is 1 (1-3), and is more preferably 1:2; the molar ratio of the cobalt source to the bismuth source is (0.9-1.5): 1, more preferably 1:1.
According to the invention, the mass ratio of the bismuth source to the citric acid in the step (1) is (0.5-1): 0.8-1.3; the bi-tooth chelation of citrate radical in the citric acid, bismuth and cobalt ions plays a role in stabilizing colloid, not only can improve the stability of the colloid, but also is beneficial to the formation of linear polymer molecules in the polymerization and polycondensation processes, thereby improving the spinnability and the fiber forming property of the colloid.
According to the invention, the ratio of the number of moles of the bismuth source to the volume of the mixed solvent in the step (1) is preferably (1-2) mmol (8-15) mL.
According to the invention, preferably, the volume ratio of the absolute ethanol to the N, N-Dimethylformamide (DMF) in the mixed solvent in the step (1) is 1:1; the solvent of the invention is the result of the inventor through a great deal of experimental optimization, if only ethanol or N, N-dimethylformamide or other organic solvents are used, the prepared precursor sol is sprayed on a copper mesh to form fibers with discontinuity, the precursor sol has great loss, the electrospinning yield is greatly reduced, and the morphology and the properties of the prepared catalyst are also influenced.
According to the invention, the acid solution in the step (1) is hydrochloric acid solution, nitric acid solution or acetic acid solution, wherein the mass concentration of the hydrochloric acid solution is 37wt%, the mass concentration of the nitric acid solution is 66wt%, and the mass concentration of the acetic acid solution is 99wt%; the ratio of the volume of the acid solution to the mole number of the bismuth source is (1-2) mL to 2mmol; the acid solution is dripped into the system, and the dripping speed is 1-2 drops/s; the addition of the acid solution can provide an acidic environment, so that the solute can be dispersed and dissolved conveniently to form a uniform spinning precursor solution.
According to the invention, the stirring time in the step (1) is preferably 100-200min.
According to a preferred embodiment of the invention, the polyvinylpyrrolidone (PVP) of step (2) has a weight average molecular weight of 100 to 150 ten thousand; further preferably, the polyvinylpyrrolidone has a weight average molecular weight of 130 ten thousand.
According to a preferred embodiment of the present invention, the ratio of the mass of polyvinylpyrrolidone (PVP) to the volume of absolute ethanol in step (2) is (0.6-1.6) g (8-15) mL; the ratio of the mass of polyvinylpyrrolidone (PVP) to the volume of N, N-Dimethylformamide (DMF) is (0.6-1.6) g (2-5) mL.
According to a preferred embodiment of the invention, the ratio of the volume of the precursor solution in step (2) to the mass of polyvinylpyrrolidone (PVP) is (3-5) mL 1g.
According to the invention, the voltage of the electrostatic spinning in the step (2) is 12-28kV, the relative humidity is 10-35%, the receiving distance is 10-30cm, the advancing speed is 0.8-1.2mL/h, and the temperature of the electrostatic spinning is room temperature; the reception distance means: the vertical distance from the electrostatic spinning needle head to the receiving device; further preferably, the voltage of the electrostatic spinning is 15-25kV.
According to the invention, the drying temperature in step (2) is 40-60 ℃ and the drying time is 12-18h.
According to the invention, the temperature of the calcination in the step (2) is 400-550 ℃, and the temperature rising rate in the calcination process is 1-5 ℃/min; the calcination time is 60-180min.
The invention adopts an electrostatic spinning technology and a calcination process to prepare the cobaltosic oxide/bismuth molybdate composite electrocatalyst, and the fiber membrane is dried and then calcined to obtain the cobaltosic oxide/bismuth molybdate nanofiber with the diameter of 200-400 nm.
According to the invention, the application of the cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER double functions is applied to electrocatalytic Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER) as a catalyst.
All chemicals used in the present invention were equally divided into analytically pure and not further treated.
Compared with the prior art, the invention has the following advantages:
1. according to the invention, an electrostatic spinning technology is utilized for the first time to prepare the cobaltosic oxide/bismuth molybdate composite bifunctional electrocatalyst, and the cobaltosic oxide and bismuth molybdate are compounded to form a heterostructure to regulate and control the electronic structure of bismuth molybdate, so that the intrinsic activity of the bismuth molybdate composite bifunctional electrocatalyst is improved, the electrocatalytic activity of a material is enhanced, and the prepared bifunctional electrocatalyst has high active site utilization rate, excellent HER and OER performances and good application prospect in the field of electrocatalysis.
2. The cobaltosic oxide/bismuth molybdate composite bifunctional electrocatalyst prepared by the invention has high activity, fast electron transmission and small overpotential in the electrocatalytic hydrogen evolution reaction and the oxygen evolution reaction, and has excellent electrocatalytic oxygen evolution and hydrogen evolution performances; experiments prove that the HER overpotential of the cobaltosic oxide/bismuth molybdate composite bifunctional electrocatalyst is as low as 198mV, and is respectively reduced by 44.5 percent and 31.8 percent compared with that of the bismuth molybdate and the cobaltosic oxide single-phase electrocatalyst under the same test condition; the OER overpotential is as low as 348mV, which is respectively reduced by 32.9 percent and 15.5 percent compared with the single-phase electrocatalyst of bismuth molybdate and cobaltosic oxide under the same test condition; HER test results in Tafel curves with slopes as low as 130mV dec -1 Compared with bismuth molybdate and cobaltosic oxide single-phase electrocatalyst, the single-phase electrocatalyst is respectively reduced by 39.5 percent and 19.3 percent under the same test condition, and the gradient of Tafel curve obtained by OER test is as low as 103mV dec -1 The ratio of bismuth molybdate and cobaltosic oxide electrocatalyst is reduced by 27.5 percent and 15.6 percent respectively under the same test condition.
3. The preparation method of the invention is a method combining electrostatic spinning and calcination, and the proportion of raw materials, the selection of solvents and high molecular binders, the sequence of adding the raw materials, the dissolution degree of precursor solution, the electrostatic spinning condition and the calcination condition can all have different degrees of influence on the prepared electrocatalyst and the properties thereof. According to the invention, by combining the influence factors in various aspects, the most suitable proportion and conditions are found out, and the prepared electrocatalyst shows excellent properties; the preparation method is simple and convenient to operate, low in raw material cost, simple in process equipment, free of waste water and waste gas emission in the preparation process, environment-friendly and potential for large-scale production.
4. The prepared bifunctional electrocatalyst is green and pollution-free, has good stability, does not produce secondary pollution to the environment in the application process, and has good circulation stability.
Drawings
FIG. 1 is an X-ray diffraction pattern of the tricobalt tetraoxide/bismuth molybdate composite electrocatalyst prepared in example 1, the bismuth molybdate electrocatalyst prepared in comparative example 1, and the tricobalt tetraoxide electrocatalyst prepared in comparative example 2.
FIG. 2 is a scanning electron micrograph of the tricobalt tetraoxide/bismuth molybdate composite electrocatalyst prepared in example 1; wherein a is a low power Scanning Electron Microscope (SEM) photograph; b is a high power Scanning Electron Microscope (SEM) photograph.
Fig. 3 is a transmission electron micrograph of the bismuth molybdate electrocatalyst prepared in comparative example 1.
FIG. 4 is a scanning electron micrograph of the tricobalt tetraoxide electrocatalyst prepared in comparative example 2; wherein a is a low power Scanning Electron Microscope (SEM) photograph; b is a high power Scanning Electron Microscope (SEM) photograph.
FIG. 5 shows the tricobalt tetraoxide/bismuth molybdate composite electrocatalysts prepared in examples 1-3, comparative examples 3-4, the bismuth molybdate electrocatalyst prepared in comparative example 1, and the tricobalt tetraoxide electrocatalyst prepared in comparative example 2 in N 2 In saturated 1mol/L KOH solution, the scanning rate is 10mV s -1 Is a LSV plot of HER.
Fig. 6 is a Tafel plot of HER for the tricobalt tetraoxide/bismuth molybdate composite electrocatalysts prepared in examples 1-3, comparative examples 3-4, the bismuth molybdate electrocatalyst prepared in comparative example 1, and the tricobalt tetraoxide electrocatalyst prepared in comparative example 2.
FIG. 7 is a view showing a tricobalt tetraoxide/bismuth molybdate composite electrocatalyst prepared in example 1, comparative examples 3 to 4, and a bismuth molybdate electrocatalyst prepared in comparative example 1And the tricobalt tetraoxide electrocatalyst prepared in comparative example 2 in O 2 In saturated 1mol/L KOH solution, the scanning rate is 10mV s -1 The LSV profile of OER.
Fig. 8 is a Tafel plot of OER for the tricobalt tetraoxide/bismuth molybdate composite electrocatalysts prepared in example 1, comparative examples 3-4, the bismuth molybdate electrocatalyst prepared in comparative example 1, and the tricobalt tetraoxide electrocatalyst prepared in comparative example 2.
Detailed Description
The present invention is further illustrated by the following specific examples and figures, but is not intended to limit the scope of the invention as claimed. All chemicals used in the present invention were equally divided into analytically pure and not further treated.
The raw materials used in the examples were all conventional, and the equipment used was all conventional equipment and commercially available.
The polyvinylpyrrolidone (PVP) used in the examples had a weight average molecular weight of 130 ten thousand.
Example 1
The preparation method of the cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER double functions comprises the following steps:
(1) Bismuth nitrate pentahydrate 0.971g, 0.1765g ammonium molybdate ((NH) 4 ) 6 Mo 7 O 24 ·4H 2 O) and 1g of citric acid are dissolved in a mixed solvent of 5mL of absolute ethyl alcohol and 5mL of DMF, then 1mL of hydrochloric acid solution with the mass concentration of 37wt% is added dropwise, the dropping rate is 1 drop/s, and then 0.498g of cobalt acetate tetrahydrate is added, and stirring is carried out for 180min, so as to obtain a precursor solution;
(2) 1g of polyvinylpyrrolidone (PVP) is weighed and dissolved in a mixed solvent of 8mL of absolute ethyl alcohol and 2mL of DMF, and the mixture is stirred uniformly; then adding 3mL of the precursor solution prepared in the step (1), and uniformly stirring to obtain precursor sol; and (3) carrying out electrostatic spinning on the obtained precursor sol under the conditions of 20kV voltage, 30% relative humidity and room temperature, wherein the spinning receiving distance is 20cm, and the advancing speed is 1mL/h, so as to obtain the precursor fiber.
(3) Drying the precursor fiber prepared in the step (2) for 12 hours at 40 ℃, then placing the precursor fiber in a tube furnace, heating to 500 ℃ at a heating rate of 2 ℃/min, and preserving heat at 500 ℃ for 120min to obtain the cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER dual functions.
The X-ray diffraction pattern (XRD) of the cobaltosic oxide/bismuth molybdate composite electrocatalyst prepared in this example is shown in fig. 1. As can be seen from FIG. 1, the obtained product Bi 2 MoO 6 /Co 3 O 4 Diffraction peaks of (2) respectively correspond to low-temperature phase gamma-Bi 2 MoO 6 (JCPDS No. 21-0102), high Wen Xiang' -Bi 2 MoO 6 (JCPDS No. 22-0112) and Co 3 O 4 The standard spectrogram (JCPDS No. 43-1003) of the obtained composite electrocatalyst shows that bismuth molybdate in the obtained composite electrocatalyst has a low-temperature phase and a high-temperature phase at the same time, forms an in-phase heterojunction, enhances the electrocatalytic activity of the material, and then is combined with Co 3 O 4 The heterostructure is formed by compounding to further regulate and control the electronic structure of bismuth molybdate, so that HER and OER performances are improved.
A Scanning Electron Microscope (SEM) of the cobaltosic oxide/bismuth molybdate composite electrocatalyst prepared in this example is shown in FIG. 2. As can be seen from FIG. 2, the prepared sample is a nanofiber with a diameter of about 200-400nm, and has a larger length-diameter ratio and uniform and continuous morphology.
Example 2
The preparation method of the cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER double functions comprises the following steps:
(1) Bismuth nitrate pentahydrate 0.971g, 0.1765g ammonium molybdate ((NH) 4 ) 6 Mo 7 O 24 ·4H 2 O) and 1g of citric acid are dissolved in a mixed solvent of 5mL of absolute ethyl alcohol and 5mL of DMF, then 1mL of hydrochloric acid solution with the mass concentration of 37wt% is added dropwise, the dropping rate is 1 drop/s, and then 0.498g of cobalt acetate tetrahydrate is added, and stirring is carried out for 180min, so as to obtain a precursor solution;
(2) 1g of polyvinylpyrrolidone (PVP) is weighed and dissolved in a mixed solvent of 8mL of absolute ethyl alcohol and 2mL of DMF, and the mixture is stirred uniformly; then adding 3mL of the precursor solution prepared in the step (1), and uniformly stirring to obtain precursor sol; and (3) carrying out electrostatic spinning on the obtained precursor sol under the conditions of 20kV voltage, 30% relative humidity and room temperature, wherein the spinning receiving distance is 20cm, and the advancing speed is 1mL/h, so as to obtain the precursor fiber.
(3) Drying the precursor fiber prepared in the step (2) for 12 hours at 40 ℃, then placing the precursor fiber in a tube furnace, heating to 500 ℃ at a heating rate of 2 ℃/min, and preserving heat at 500 ℃ for 180 minutes to obtain the cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER dual functions.
Example 3
The preparation method of the cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER double functions comprises the following steps:
(1) Bismuth nitrate pentahydrate 0.971g, 0.1765g ammonium molybdate ((NH) 4 ) 6 Mo 7 O 24 ·4H 2 O) and 1g of citric acid are dissolved in a mixed solvent of 5mL of absolute ethyl alcohol and 5mL of DMF, then 1mL of hydrochloric acid solution with the mass concentration of 37wt% is added dropwise, the dropping rate is 1 drop/s, and then 0.622g of cobalt acetate tetrahydrate is added, and stirring is carried out for 180min, so as to obtain a precursor solution;
(2) 1g of polyvinylpyrrolidone (PVP) is weighed and dissolved in a mixed solvent of 8mL of absolute ethyl alcohol and 2mL of DMF, and the mixture is stirred uniformly; then adding 3mL of the precursor solution prepared in the step (1), and uniformly stirring to obtain precursor sol; and (3) carrying out electrostatic spinning on the obtained precursor sol under the conditions of 20kV voltage, 30% relative humidity and room temperature, wherein the spinning receiving distance is 20cm, and the advancing speed is 1mL/h, so as to obtain the precursor fiber.
(3) Drying the precursor fiber prepared in the step (2) for 12 hours at 40 ℃, then placing the precursor fiber in a tube furnace, heating to 500 ℃ at a heating rate of 2 ℃/min, and preserving heat at 500 ℃ for 120min to obtain the cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER dual functions.
Comparative example 1
The preparation method of the bismuth molybdate electrocatalyst comprises the following steps:
(1) Bismuth nitrate pentahydrate 0.971g, 0.1765g ammonium molybdate ((NH) 4 ) 6 Mo 7 O 24 ·4H 2 O) and 1g of citric acid are dissolved in a mixed solvent of 5mL of absolute ethanol and 5mL of DMF, then 1mL of hydrochloric acid solution with the mass concentration of 37wt% is added dropwise, the adding speed is 1 drop/s, and stirring is carried out for 180min, thus obtaining the productA precursor solution;
(2) 1g of polyvinylpyrrolidone (PVP) is weighed and dissolved in a mixed solvent of 8mL of absolute ethyl alcohol and 2mL of DMF, and the mixture is stirred uniformly; then adding 3mL of the precursor solution prepared in the step (1), and uniformly stirring to obtain precursor sol; and (3) carrying out electrostatic spinning on the obtained precursor sol under the conditions of 20kV voltage, 30% relative humidity and room temperature, wherein the spinning receiving distance is 20cm, and the advancing speed is 1mL/h, so as to obtain the precursor fiber.
(3) Drying the precursor fiber prepared in the step (2) for 12 hours at 40 ℃, then placing the precursor fiber in a tube furnace, heating to 500 ℃ at a heating rate of 2 ℃/min, and preserving heat for 120 minutes at 500 ℃ to obtain the bismuth molybdate electrocatalyst.
The X-ray diffraction pattern (XRD) of the bismuth molybdate electrocatalyst prepared in this comparative example is shown in FIG. 1. As can be seen from FIG. 1, the obtained product Bi 2 MoO 6 Diffraction peaks of (2) respectively correspond to low-temperature phase gamma-Bi 2 MoO 6 (JCPDS No. 21-0102) and high Wen Xiang' -Bi 2 MoO 6 (JCPDS No. 22-0112) diffraction pattern of two phases coexisting.
A Transmission Electron Microscope (TEM) of the bismuth molybdate electrocatalyst prepared in this comparative example is shown in FIG. 3. As can be seen from FIG. 3, the prepared sample is a nanofiber with a diameter of about 400nm, and has a larger length-diameter ratio and uniform and continuous morphology.
Comparative example 2
The preparation method of the cobaltosic oxide electrocatalyst comprises the following steps:
(1) Dissolving 0.249g of cobalt acetate tetrahydrate in a mixed solvent of 5mL of absolute ethyl alcohol and 5mL of DMF, and stirring for 180min to obtain a precursor solution;
(2) Weighing 1g of polyvinylpyrrolidone (PVP) and dissolving in the precursor solution in the step (1), and uniformly stirring to obtain precursor sol; and (3) carrying out electrostatic spinning on the obtained precursor sol under the conditions of pressure of 20kV, relative humidity of 30%, spinning receiving distance of 20cm and advancing speed of 1mL/h at room temperature to obtain precursor fibers.
(3) Drying the precursor fiber prepared in the step (2) for 12 hours at 40 ℃, then placing the precursor fiber in a tube furnace, heating to 500 ℃ at a heating rate of 2 ℃/min, and preserving heat at 500 ℃ for 120 minutes to obtain the cobaltosic oxide electrocatalyst.
The X-ray diffraction pattern (XRD) of the cobaltosic oxide electrocatalyst prepared in this comparative example is shown in fig. 1. As can be seen from FIG. 1, the obtained product Co 3 O 4 The diffraction peak of the material corresponds to Co 3 O 4 (JCPDS No.43-1003)。
A Scanning Electron Microscope (SEM) of the tricobalt tetraoxide electrocatalyst prepared in this comparative example is shown in FIG. 4. As can be seen from fig. 4, the prepared sample is a nanofiber with a diameter of about 300nm, and has a larger length-diameter ratio and uniform and continuous morphology.
Comparative example 3
The preparation method of the cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER double functions comprises the following steps:
(1) Bismuth nitrate pentahydrate 0.971g, 0.1765g ammonium molybdate ((NH) 4 ) 6 Mo 7 O 24 ·4H 2 O) and 1g of citric acid are dissolved in a mixed solvent of 5mL of absolute ethyl alcohol and 5mL of DMF, then 1mL of hydrochloric acid solution with the mass concentration of 37wt% is added dropwise, the dropping rate is 1 drop/s, and then 0.498g of cobalt acetate tetrahydrate is added, and stirring is carried out for 180min, so as to obtain a precursor solution;
(2) 1g of polyvinylpyrrolidone (PVP) is weighed and dissolved in a mixed solvent of 8mL of absolute ethyl alcohol and 2mL of DMF, and the mixture is stirred uniformly; then adding 3mL of the precursor solution prepared in the step (1), and uniformly stirring to obtain precursor sol; and (3) carrying out electrostatic spinning on the obtained precursor sol under the conditions of 20kV voltage, 30% relative humidity and room temperature, wherein the spinning receiving distance is 20cm, and the advancing speed is 1mL/h, so as to obtain the precursor fiber.
(3) Drying the precursor fiber prepared in the step (2) for 12 hours at 40 ℃, then placing the precursor fiber in a tube furnace, heating to 600 ℃ at a heating rate of 2 ℃/min, and preserving heat at 600 ℃ for 120 minutes to obtain the cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER dual functions.
The calcination temperature was too high in this comparative example.
Comparative example 4
The preparation method of the cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER double functions comprises the following steps:
(1) Bismuth nitrate pentahydrate 0.971g, 0.1765g ammonium molybdate ((NH) 4 ) 6 Mo 7 O 24 ·4H 2 O) and 1g of citric acid are dissolved in a mixed solvent of 5mL of absolute ethyl alcohol and 5mL of DMF, then 1mL of hydrochloric acid solution with the mass concentration of 37wt% is added dropwise, the dropping rate is 1 drop/s, and then 0.373g of cobalt acetate tetrahydrate is added, and stirring is carried out for 180min, so as to obtain a precursor solution;
(2) 1g of polyvinylpyrrolidone (PVP) is weighed and dissolved in a mixed solvent of 8mL of absolute ethyl alcohol and 2mL of DMF, and the mixture is stirred uniformly; then adding 3mL of the precursor solution prepared in the step (1), and uniformly stirring to obtain precursor sol; and (3) carrying out electrostatic spinning on the obtained precursor sol under the conditions of 20kV voltage, 30% relative humidity and room temperature, wherein the spinning receiving distance is 20cm, and the advancing speed is 1mL/h, so as to obtain the precursor fiber.
(3) Drying the precursor fiber prepared in the step (2) for 12 hours at 40 ℃, then placing the precursor fiber in a tube furnace, heating to 500 ℃ at a heating rate of 2 ℃/min, and preserving heat at 500 ℃ for 120min to obtain the cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER dual functions.
The ratio of cobalt source to bismuth source in this comparative example is small.
Test example 1
The electrocatalysts prepared in examples 1-3 and comparative examples 1-4 were tested for electrocatalytic hydrogen evolution performance, as follows:
(1) Preparing a catalyst ink: weighing 5mg of the prepared electrocatalyst material and 1mg of conductive carbon black, adding the electrocatalyst material and the conductive carbon black into 1mL of mixed solvent with the volume ratio of isopropanol to naphthol solution of 3:1, uniformly dispersing by ultrasonic, and transferring 10 mu L of solution by using a pipette, namely, the electrode loading capacity is 255 mu g cm -2 The prepared electrocatalyst material is dripped on the rotary disk electrode to be used as a working electrode, and the vacuum drying time is 10 hours;
(2) LSV test method for electrocatalytic HER: the three-electrode system is adopted, the prepared catalyst ink is used as a working electrode, a graphite rod is used as a counter electrode, an Hg/HgO electrode is used as a reference electrode, and the concentration of the electrolyte KOH is 1mol L -1 . Introducing nitrogen before testing to make nitrogen in electrolyteSaturation is reached. Setting the scanning speed to 10mV s -1 The rotational speed was 1600rpm.
FIG. 5 shows the tricobalt tetraoxide/bismuth molybdate composite electrocatalysts prepared in examples 1-3, comparative examples 3-4, the bismuth molybdate electrocatalyst prepared in comparative example 1, and the tricobalt tetraoxide electrocatalyst prepared in comparative example 2 in N 2 In saturated 1mol/L KOH solution, the scanning rate is 10mV s -1 Is a LSV plot of HER.
Fig. 6 is a Tafel plot of HER for the tricobalt tetraoxide/bismuth molybdate composite electrocatalysts prepared in examples 1-3, comparative examples 3-4, the bismuth molybdate electrocatalyst prepared in comparative example 1, and the tricobalt tetraoxide electrocatalyst prepared in comparative example 2.
As can be seen from FIG. 5, the electrocatalysts obtained in examples 1-3 and comparative examples 1-4 were measured at 10mA cm -2 Over-potentials of 198mV, 238mV, 276mV, 357mV, 286mV, 385mV, 354mV, respectively, corresponding Tafel slopes of 130mV dec, respectively -1 、155mV dec -1 、158mV dec -1 、215mV dec -1 、161mV dec -1 、270mV dec -1 、210mV dec -1 . From the experimental results, it can be seen that the overpotential and Tafel slope of the cobaltosic oxide/bismuth molybdate composite electrocatalyst prepared in example 1 are significantly lower than those of Bi obtained in comparative examples 1 and 2 2 MoO 6 And Co 3 O 4 Electrocatalyst, indicating Bi 2 MoO 6 /Co 3 O 4 The composite bifunctional electrocatalyst has higher electrocatalytic HER activity; and it can be seen from examples 1 to 3 and comparative examples 3 to 4 that the calcination conditions and the raw material ratio in the present invention have an important influence on the performance of the resulting electrocatalyst.
Test example 2
The electrocatalysts prepared in example 1 and comparative examples 1-4 were tested for electrocatalytic oxygen evolution performance, as follows:
(1) Preparing a catalyst ink: weighing 5mg of the prepared electrocatalyst material and 1mg of conductive carbon black, adding the electrocatalyst material and the 1mg of conductive carbon black into 1mL of mixed solution with the volume ratio of isopropanol to naphthol solution of 3:1, uniformly dispersing by ultrasonic, and transferring 10 mu L of solution by using a pipette, namely, the electrode loading capacity is 255 mu g cm -2 Prepared electric catalystThe chemical agent material is dripped on the rotary disk electrode to be used as a working electrode, and the vacuum drying time is 10 hours;
(2) LSV test method for electrocatalytic OER: adopting a three-electrode system, taking the prepared electrocatalyst ink as a working electrode, taking a graphite rod as a counter electrode and a Hg/HgO electrode as a reference electrode, wherein the concentration of the electrolyte KOH is 1mol L -1 . Oxygen is introduced before the test to saturate the oxygen in the electrolyte. Setting the scanning speed to 10mV s -1 The rotational speed was 1600rpm.
FIG. 7 is a graph showing the presence of a tricobalt tetraoxide/bismuth molybdate composite electrocatalyst prepared in example 1, a bismuth molybdate electrocatalyst prepared in comparative example 1, a tricobalt tetraoxide electrocatalyst prepared in comparative example 2, and tricobalt tetraoxide/bismuth molybdate composite electrocatalyst prepared in comparative examples 3 to 4 in O 2 In saturated 1mol/L KOH solution, the scanning rate is 10mV s -1 The LSV profile of OER.
Fig. 8 is a Tafel plot of OER for the tricobalt tetraoxide/bismuth molybdate composite electrocatalyst prepared in example 1, the bismuth molybdate electrocatalyst prepared in comparative example 1, the tricobalt tetraoxide electrocatalyst prepared in comparative example 2, and the tricobalt tetraoxide/bismuth molybdate composite electrocatalysts prepared in comparative examples 3-4.
As can be seen from FIG. 7, the electrocatalysts obtained in example 1 and comparative examples 1 to 4 were measured at 10mA cm -2 Over-potentials of 348mV, 519mV, 412mV, 490mV and 534mV respectively at current densities corresponding to Tafel slopes of 103mV dec respectively -1 、142mV dec -1 、122mV dec -1 、164mV dec -1 、182mV dec -1 . From the experimental results, it can be seen that the overpotential and Tafel slope of the cobalt oxide/bismuth molybdate composite electrocatalyst of example 1 are significantly lower than those of Bi obtained in comparative examples 1 and 2 2 MoO 6 And Co 3 O 4 Electrocatalyst, indicating Bi 2 MoO 6 /Co 3 O 4 The composite bifunctional electrocatalyst has higher electrocatalytic OER activity.
The invention adopts an electrostatic spinning method to prepare the cobaltosic oxide/bismuth molybdate composite bifunctional electrocatalyst, and the catalyst prepared after the compounding has excellent performance of electrocatalytic HER and OER, and is a bifunctional electrocatalyst with good application prospect.

Claims (10)

1. The cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER double functions is characterized in that the electrocatalyst has a microcosmic appearance of nanofibers, and the diameter of the nanofibers is 200-400nm, and the length of the nanofibers is 5-20 mu m.
2. The method for preparing the cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER double functions as recited in claim 1, comprising the following steps:
(1) Dissolving a bismuth source, a molybdenum source and citric acid in a mixed solvent of anhydrous ethanol and N, N-dimethylformamide, then adding an acid solution, then adding a cobalt source, and uniformly stirring to obtain a precursor solution;
(2) Dissolving polyvinylpyrrolidone in a mixed solvent of anhydrous ethanol and N, N-dimethylformamide, and then adding the precursor solution prepared in the step (1) to obtain precursor sol; and then carrying out electrostatic spinning, drying and calcining to obtain the cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER double functions.
3. The method of preparing a bi-functional tricobalt tetraoxide/bismuth molybdate composite electrocatalyst for HER/OER according to claim 2, wherein the bismuth source in step (1) is bismuth nitrate pentahydrate; the molybdenum source is ammonium molybdate or sodium molybdate dihydrate; the cobalt source is cobalt nitrate hexahydrate or cobalt acetate tetrahydrate; the molar ratio of the molybdenum element in the molybdenum source to the bismuth element in the bismuth source is 1 (1-3), preferably 1:2; the molar ratio of the cobalt source to the bismuth source is (0.9-1.5): 1, preferably 1:1.
4. The method for preparing the bi-functional cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER according to claim 2, wherein the mass ratio of bismuth source to citric acid in step (1) is (0.5-1): 0.8-1.3;
the ratio of the mole number of the bismuth source to the volume of the mixed solvent is (1-2) mmol (8-15) mL;
according to the invention, the volume ratio of the absolute ethanol to the N, N-Dimethylformamide (DMF) in the mixed solvent in the step (1) is preferably 1:1.
5. The method for preparing the bi-functional cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER according to claim 2, wherein the acid solution in step (1) is a hydrochloric acid solution, a nitric acid solution or an acetic acid solution, the mass concentration of the hydrochloric acid solution is 37wt%, the mass concentration of the nitric acid solution is 66wt%, and the mass concentration of the acetic acid solution is 99wt%; the ratio of the volume of the acid solution to the mole number of the bismuth source is (1-2) mL to 2mmol; the stirring time is 100-200min.
6. The method for preparing a bi-functional tricobalt tetraoxide/bismuth molybdate composite electrocatalyst for HER/OER according to claim 2, wherein the weight average molecular weight of the polyvinylpyrrolidone in step (2) is 100 to 150 tens of thousands; preferably, the polyvinylpyrrolidone has a weight average molecular weight of 130 ten thousand;
the ratio of the mass of the polyvinylpyrrolidone to the volume of the absolute ethyl alcohol is (0.6-1.6) g (8-15) mL; the ratio of the mass of the polyvinylpyrrolidone to the volume of the N, N-dimethylformamide is (0.6-1.6) g (2-5) mL.
7. The method for preparing a bi-functional cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER according to claim 2, wherein the ratio of the volume of the precursor solution to the mass of polyvinylpyrrolidone in step (2) is (3-5) mL:1g.
8. The method for preparing a bi-functional cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER according to claim 2, wherein the voltage of the electrospinning in step (2) is 12-28kV, the relative humidity is 10-35%, the receiving distance is 10-30cm, the advancing speed is 0.8-1.2mL/h, and the temperature of the electrospinning is room temperature; the reception distance means: the vertical distance from the electrostatic spinning needle head to the receiving device; preferably, the voltage of the electrostatic spinning is 15-25kV;
the drying temperature is 40-60 ℃, and the drying time is 12-18h.
9. The method for preparing a bi-functional cobaltosic oxide/bismuth molybdate composite electrocatalyst for HER/OER according to claim 2, wherein the calcination temperature in step (2) is 400-550 ℃ and the temperature rise rate during calcination is 1-5 ℃/min; the calcination time is 60-180min.
10. The use of the cobalt oxide/bismuth molybdate composite electrocatalyst for HER/OER dual function according to claim 1 as a catalyst for electrocatalytic hydrogen evolution reactions and oxygen evolution reactions.
CN202310253788.6A 2023-03-16 2023-03-16 Tricobalt tetraoxide/bismuth molybdate composite electrocatalyst for HER/OER double functions and preparation method and application thereof Pending CN116240582A (en)

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