An efficient self-supported cobalt molybdenum oxide-based heterostructure catalyst, its preparation method, and application

Abstract

The present invention relates to a highly efficient self-supporting cobalt-molybdenum oxide-based heterostructure catalyst and its preparation method and application. First, the foamed copper is immersed in a mixed solution containing ammonium persulfate and potassium hydroxide to react, so that the foamed copper is reacted with Cu(OH) 2 The nanorods are covered, thereby obtaining Cu(OH) 2 / CF; then Cu(OH) 2 / CF was added to the Co(NO 3 ) 2 and Na 2 MoO 4 In the precursor solution, a hydrothermal reaction was carried out at 100-200℃ to grow a layer of nanoflowers on the originally smooth nanorods, thereby obtaining a highly efficient self-supporting cobalt-molybdenum oxide-based heterostructure catalyst Cu(OH) 2 @CoMoO 4 0.9H 2 O / CF. The present invention uses one-dimensional nanorod Cu(OH) 2 Coated with a two-dimensional nanosheet and Cu(OH) 2 With CoMoO 4 0.9H 2 O recombination and other methods effectively increased the specific surface area of ​​the catalyst, accelerated the electron transfer efficiency, and significantly improved the catalyst performance, providing a new idea for the design and preparation of high-performance bifunctional electrocatalysts.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalytic materials, and particularly relates to a highly efficient self-supporting cobalt molybdate-based heterostructure catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] To cope with the increasingly serious energy crisis and environmental pollution, hydrogen has been identified as a clean and carbon-free energy carrier, and is expected to replace the current fossil fuel-based economy through a renewable energy economy. As a secondary energy source, hydrogen has the advantages of being clean, pollution-free, efficient, and storable, and is regarded as the most ideal clean energy at present. Among various hydrogen production technologies, hydrogen production by electrolysis of water has low cost and high purity of hydrogen obtained, and is a hydrogen production method with good application prospects. Electrolysis of water is divided into two half-reactions: hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Among them, HER catalysts usually have the problem of high overpotential during the electrolysis of water, which means that more energy needs to be consumed. In addition, the high overpotential of OER catalysts will significantly reduce the efficiency of the entire electrolysis of water process. From the perspective of industrial applications, this will greatly hinder the production of hydrogen. So far, the most effective and stable catalysts for HER and OER are noble metals / metal oxides. However, due to disadvantages such as high cost, scarcity, and instability, their large-scale commercial applications in the entire water splitting are limited.

[0003] Transition metal molybdates have received extensive attention due to their various forms, excellent electrical conductivity, and electrochemical activity. Among these transition metal molybdates, CoMoO 4 is considered to be a promising OER electrocatalyst because of the synergistic effect between the excellent redox ability of the internal Co element and the high electrical conductivity of Mo, which can increase the OER performance of the material. Cobalt molybdate has three different crystal structures, namely α-type (α-CoMoO 4 ), β-type (β-CoMoO 4 ), and hydrated (hydrated (H)-CoMoO 4 ). The α-type and β-type crystals are obtained by calcining the hydrated crystal at 600 °C and 340 °C for 2 hours, respectively. Through electrochemical tests and simulation calculations, it can be known that compared with the other two crystal structures, H-CoMoO 4 has a larger electrochemical active area and specific surface area, which indicates that the hydrated crystal structure has more active sites.

[0004] In the present invention, a two-dimensional structure of Cu(OH) 2 nanorods (Cu(OH) 2 / CF) is in-situ grown on copper foam (CF), and then a layer of cobalt molybdate hydrate is coated on the outer layer of the Cu(OH) 2 nanorods by a hydrothermal method (Cu(OH)2 @CoMoO 4 ·0.9H 2 O), thus forming a core-shell heterostructure. This heterostructure can effectively increase the specific surface area of H-CoMoO 4 , greatly accelerate the electron conduction rate of the material, and improve the catalytic performance of H-CoMoO 4 . This study also proves that hydrates have great research significance in the field of electrocatalysis, providing a new idea for the design and preparation of high-performance bifunctional electrocatalysts. SUMMARY OF THE INVENTION

[0005] One of the objectives of the present invention is to provide a preparation method for an efficient self-supporting cobalt molybdenum oxide-based heterostructure catalyst, which mainly includes the following steps: (a) Dissolve ammonium persulfate and potassium hydroxide in water to obtain a mixed solution, and then add copper foam for reaction to obtain Cu(OH) 2 / CF; (b) Dissolve cobalt salt and molybdenum salt in water to obtain a precursor solution, and add Cu(OH) 2 / CF for hydrothermal reaction.

[0006] Furthermore, in step (a), the molar ratio of ammonium persulfate to potassium hydroxide is 20-30:1.

[0007] Furthermore, in step (a), the copper foam is pre-washed repeatedly with at least one of alcohol solvent and water before the reaction, and then dried for standby.

[0008] Furthermore, in step (a), the reaction temperature is room temperature, the static reaction time is 15-30 min, after the reaction, the copper foam is taken out and washed with water, and then freeze-dried.

[0009] Furthermore, in step (b), the cobalt salt is cobalt nitrate or its hydrate, and the molybdenum salt is sodium molybdate or its hydrate.

[0010] Furthermore, in step (b), the molar ratio of cobalt salt to molybdenum salt is 1:0.5-1:3.

[0011] Furthermore, in step (b), the hydrothermal reaction temperature is 100-200 °C, the reaction time is 1-4 h, after the reaction, the solid product is taken out, washed and dried.

[0012] Another objective of the present invention is to provide an efficient self-supporting cobalt molybdenum oxide-based heterostructure catalyst, with the chemical formula Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF, which has a core-shell wrapped heterostructure.

[0013] The third object of the present invention is to provide the application of the above-mentioned highly efficient self-supporting cobalt molybdenum oxide-based heterostructure catalyst in electrocatalytic hydrogen evolution.

[0014] Compared with the existing similar catalysts and their preparation methods, the present invention has significant advantages in the following aspects:

[0015] (1) In the present invention, copper foam is used as the growth substrate, and Cu(OH) 2 nanorods are in-situ grown at room temperature, and then Cu(OH) 2 / CF is used as the growth template core, and CoMoO 4 ·0.9H 2 O shell is prepared by hydrothermal method to form a core-shell wrapped heterostructure. There is a strong synergistic coupling effect between the inner and outer layers, and the inner layer of Cu(OH) 2 can accelerate the adsorption of water molecules.

[0016] (2) By coating a layer of two-dimensional nanosheets on the one-dimensional nanorod material, the present invention effectively increases the specific surface area of the material and constructs an effective connected structure to accelerate the electron transport efficiency. Subsequently, Cu(OH) 2 is compounded with CoMoO 4 ·0.9H 2 O, and the synergistic effect between the two significantly improves the catalyst performance.

[0017] (3) The prepared Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF exhibits the optimal electrocatalytic activity. When the current density is 10 mA·cm -2 , the HER overpotential of the material is 59 mV, and 80% of the performance remains after a stability test of up to 22 hours.

[0018] (4) The OER performance of the prepared Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF is also competitive. When the current density is 10 mA·cm -2 , 20 mA·cm -2 and 100 mA·cm -2 , the overpotentials are 159 mV, 259 mV and 365 mV respectively.

[0019] (5) The present invention proves that hydrates have great research significance in the field of electrocatalysis, providing a new idea for the design and preparation of high-performance bifunctional electrocatalysts. Brief Description of the Drawings

[0020] Figure 1 For Cu(OH) in Example 1 2 / CF and Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF SEM image;

[0021] Figure 2 For Cu(OH) in Example 1 2 / CF and Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF XRD pattern;

[0022] Figure 3 For Cu(OH) in Example 1 2 @CoMoO 4 ·0.9H 2 O / CF application diagram in a zinc-air battery;

[0023] Figure 4 For the Cu(OH) prepared in Example 1 2 / CF, Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF and the CoMoO·0.9H 4 ·0.9H 2 O / CF prepared in Example 2 impedance diagram;

[0024] Figure 5 For the CF, Cu(OH) / CF, Cu(OH)@CoMoO·0.9H 2 / CF, Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF, the CoMoO·0.9H 4 ·0.9H 2 O / CF prepared in Example 2 and the HRE polarization curve diagram of Pt / C prepared in Example 3;

[0025] Figure 6 For the CF, Cu(OH) / CF, Cu(OH)@CoMoO·0.9H 2 / CF, Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF, the CoMoO·0.9H 4 ·0.9H 2 O / CF prepared in Example 2 and the Tafel slope diagram of Pt / C prepared in Example 3;

[0026] Figure 7 For the CF, Cu(OH) prepared in Example 12 / CF, Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF, CoMoO prepared in Example 2 4 ·0.9H 2 O / CF and RuO prepared in Example 4 2 OER polarization curve;

[0027] Figure 8 CF, Cu(OH) prepared in Example 1 2 / CF, Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF, CoMoO prepared in Example 2 4 ·0.9H 2 O / CF and RuO prepared in Example 4 2 Tafel slope diagram. Detailed implementation method

[0028] To enable those of ordinary skill in the art to fully understand the technical solutions and beneficial effects of the present invention, the following further description is provided in conjunction with specific embodiments and the accompanying drawings.

[0029] Example 1

[0030] First, put the copper foam (CF) with a geometric area of 2*4 cm into absolute ethanol and ultrasonically clean it for 20 minutes to remove the surface oil stain. After taking it out, put it into clean water and wash it 2-3 times, and then dry it for standby.

[0031] Dissolve 10.1 g of KOH in 30 mL of pure water to obtain an aqueous potassium hydroxide solution, and dissolve 1.6432 g of (NH 4 ) 2 S 2 O 8 in 30 mL of pure water to obtain an aqueous ammonium persulfate solution. Mix the aqueous potassium hydroxide solution and the aqueous ammonium persulfate solution and ultrasonically vibrate for 5 minutes, and then immediately immerse a cleaned CF into the mixed solution at room temperature and let it stand for reaction for more than 20 minutes. After the reaction is completed, take out the CF, wash it 3-5 times with water to remove the unreacted substances on the surface, and then freeze-dry it for 4-6 hours to obtain Cu(OH) 2 / CF.

[0032] Prepare 30 mL of a solution containing 1 mmol of Co(NO 3 ) 2 ·6H 2 O and 1 mmol of Na 2 MoO 4 ·2H 2The precursor solution of O was poured into the inner shell of an autoclave with a capacity of 50 mL, and then a dried Cu(OH) flake was added. 2 / CF, and the resulting mixture was heated to 160 °C for hydrothermal reaction for 2 h. After the reaction, the solid sample was taken out, washed 2 - 3 times with clear water, and then freeze-dried for 4 - 5 h to obtain the target product Cu(OH). 2 @CoMoO 4 ·0.9H 2 O / CF.

[0033] The Cu(OH) prepared in this example 2 / CF and Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF's SEM is as Figure 1 shown, where a - c are the SEM images of Cu(OH) 2 SEM, and d - f are the SEM images of Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF. It can be seen from a - c that the substrate copper foam is basically covered by Cu(OH) 2 nanorods and is uniformly distributed. From the high - magnification SEM images (b, c) of Cu(OH) 2 / CF, it can be known that the diameter of the Cu(OH) 2 nanorods is about 200 - 230 nm, and the surface is smooth without extra impurities, and the morphology is regular and uniform. After the second hydrothermal method, it can be found from d - f that a layer of nanoflowers has grown on the originally smooth nanorods, showing a significant change compared with the morphology of pure Cu(OH) 2 / CF. From the high - magnification SEM images (e, f), it can be known that the CoMoO 2 grown on the surface of Cu(OH) 4 ·0.9H 2 O is a nanoflower arranged by nanosheets, with regular and uniform morphology, and it can be seen from Figure f that the surface of the nanosheets is smooth, without wrinkles and particle attachment.

[0034] XRD analysis tests were carried out on the Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF and Cu(OH) 2 / CF prepared in Example 1, and the results are as Figure 2 shown. It can be seen from Figure 2 that Cu(OH) 2The diffraction peaks of the nanorods at 16.71°, 23.84°, 34.06° and 39.8° correspond to the (020), (021), (002) and (130) crystal planes respectively, which proves that the in-situ grown Cu(OH) 2 nanorods on the copper foam have been successfully prepared. After the second hydrothermal reaction, the diffraction peaks of the Cu(OH) 2 nanorods still exist, and the remaining diffraction peaks belong to CoMoO 4 ·0.9H 2 O (JCPDS No.14-0086), thus confirming the existence of the core-shell heterostructure and also determining the types of the inner and outer layer materials.

[0035] Figure 3 For the application of the Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF prepared in Example 1 in a zinc-air battery, where a is the open-circuit potential test diagram of the zinc-air battery. The open-circuit potential of the prepared Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF catalyst-based battery can reach 1.261 V, and a small light bulb with a specification of 1.5 V and 0.1 A is successfully lit (upper right corner). b is a picture of a small car driven by a zinc-air battery based on the Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF catalyst as the power system. These results indicate that Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF can be used as a zinc-air battery.

[0036] Example 2

[0037] First, put the CF with a geometric area of 2*4 cm into an ethanol solution and ultrasonically clean it for 20 min. After taking it out, wash it 2-3 times with clean water and dry it for later use.

[0038] Refer to the method in Example 1 to prepare the precursor solution required for the hydrothermal reaction. Pour the precursor solution into the inner liner of a 50 mL autoclave, and then add a piece of clean pure copper foam (without growing Cu(OH) 2 ), heat the resulting mixture to 160 °C for a hydrothermal reaction for 2 h. After the reaction, take out the solid sample and wash it 2-3 times with clean water, and then freeze-dry it for 4-5 h to obtain the target product CoMoO 4 ·0.9H 2 O / CF.

[0039] The Cu(OH) prepared in Example 1 2 / CF, Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF and the CoMoO prepared in Example 2 4 ·0.9H 2 O / CF were subjected to electrochemical impedance spectroscopy (EIS) tests in the range of 100 kHz to 0.01 Hz with an amplitude of 5 mV. The test results are as Figure 4 shown. It can be seen from Figure 4 that the transfer resistance of Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF with a core-shell heterostructure during the reaction is much smaller than that of Cu(OH) 2 / CF and CoMoO 4 ·0.9H 2 O / CF. The reason for the decrease in transfer resistance may be due to the strong electron flow between the inner layer of Cu(OH) 2 and the outer layer of CoMoO 4 ·0.9H 2 O. The core-shell heterostructure of Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF creates a large number of interfaces, and the interface effect greatly reduces the internal resistance and transfer resistance of the catalyst.

[0040] Example 3

[0041] First, copper foam (CF) with a geometric area of 2 * 4 cm was placed in an ethanol solution and ultrasonically cleaned for 20 min. After taking it out, it was then placed in clean water and washed 2 - 3 times, and dried for later use.

[0042] 4 mg of commercial Pt / C catalyst (20 wt%) and 40 μL of nafion solution (5 wt%) were ultrasonically dispersed in 960 μL of a mixed solvent (720 μL of deionized water and 240 μL of absolute ethanol) to obtain a homogeneous dispersion. 188 μL of the homogeneous dispersion was dropped onto the surface of the copper foam drop by drop and dried thoroughly at room temperature to obtain a Pt / C catalytic electrode.

[0043] Figure 5 is the HRE polarization curve graph of a series of catalyst materials prepared in Examples 1 - 3. It can be seen from the figure that the HER performance of the catalyst Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF is excellent. When the current density is 10 mA·cm -2, 20 mA·cm -2 and 100 mA·cm -2 When the current densities are 20 mA·cm -2 and 100 mA·cm 2 respectively, the overpotentials are 59 mV, 94 mV and 213 mV in sequence. The performance of pure copper foam is the worst, and the overpotential is 334 mV when the current density is 10 mA·cm 4 ·0.9H 2 O / CF and CoMoO 2 @CoMoO 4 ·0.9H 2 O / CF have extremely different overpotentials compared with Cu(OH) -2 @CoMoO 2 ·0.9H 4 O / CF. The overpotentials are 317 mV and 200 mV respectively when the current density is 10 mA·cm 2 . Compared with most hydrogen evolution catalysts, the hydrogen evolution performance of Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF is better than that of most catalysts reported so far. This is because the inner layer of Cu(OH)

[0044] The Tafel slope of the material can be used to study the kinetic reaction steps and control steps of the material in the hydrogen evolution reaction. Figure 6 Figure 3 is the Tafel slope of a series of catalyst materials prepared in Examples 1-3. The Tafel slope of Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF is 72.8 mV·dec -1 , which is close to the Tafel slope of 20% Pt / C (39 mV·dec -1 ). In addition, the Tafel slopes of Cu(OH) 2 / CF and CoMoO 4 ·0.9H 2 O / CF are much larger than the Tafel slope of the catalyst Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF, indicating that their hydrogen evolution reaction rates are much smaller than that of Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF.

[0045] Example 4

[0046] First, put the CF with a geometric area of 0.5 * 0.5 cm into an ethanol solution and ultrasonically clean it for 20 min. After taking it out, put it into clean water and wash it 2 - 3 times, then dry it for standby.

[0047] Weigh 4 mg of commercial RuO 2 , disperse it in 960 μL of a mixed solution (720 μL of pure water and 240 μL of ethanol), then add 40 μL of Nafion solution (5 wt%) as an adhesive, and ultrasonically disperse the mixture for 30 - 60 min. After the ultrasonic treatment is completed, drop the dispersion onto the CF to obtain a RuO 2 electrode, ensuring that the loading amount of RuO 2 on the CF is 4 mg·cm -2 .

[0048] Figure 7 Figure 1 is the OER polarization curve of a series of catalyst materials prepared in Example 1, Example 2, and Example 4. As can be seen from Figure 7 it, the OER performance of the catalyst Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF is the best. When the current density is 10 mA·cm -2 , 20 mA·cm -2 and 100 mA·cm -2 , the overpotentials are 159 mV, 159 mV, and 365 mV respectively. The catalytic performance of this catalyst is even much better than that of the noble metal catalyst RuO 2 which is currently considered to have the best OER performance. Among the many OER catalysts reported so far, the OER performance of Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF is still better than that of most other materials.

[0049] Figure 8 Figure 2 is the Tafel slope of a series of catalyst materials prepared in Example 1, Example 2, and Example 4. The Tafel slope of Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF is 70.2 mV·dec –1 , while the Tafel slope of RuO 2 is 83.3 mV·dec –1 . This indicates that the OER reaction rate of Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF is greater than that of the noble metal catalyst RuO 2 . In addition, Cu(OH)2 The Tafel slope of / CF is 188.3 mV·dec –1 , CoMoO 4 ·0.9H 2 The Tafel slope of O / CF is 127.8 mV·dec –1 , and the Tafel slope of pure copper foam is 192.5 mV·dec –1 , and their Tafel slopes are all much larger than that of Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF. These data all indicate that Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF is an effective substitute for noble metal catalysts for OER in alkaline media and has great application potential in the industrial field.

Claims

1. A preparation method of an efficient self-supporting cobalt molybdenum oxide-based heterostructure catalyst, characterized in that, The method comprises the following steps: (a) Dissolve ammonium persulfate and potassium hydroxide in water, then add copper foam for reaction to in-situ grow Cu(OH) 2 nanorods on the copper foam to obtain Cu(OH) 2 / CF; (b) Dissolve cobalt salt and molybdenum salt in water according to a molar ratio of 1:0.5 - 1:3 to obtain a precursor solution, then add Cu(OH) 2 / CF and perform hydrothermal reaction at 100 - 200 °C for 1 - 4 h to coat a layer of CoMoO 2 ·0.9H 4 O two-dimensional nanosheets on the one-dimensional Cu(OH) 2 nanorods to form a core-shell wrapped heterostructure, obtaining Cu(OH) 2 @CoMoO 4 ·0.9H 2 O / CF.

2. The preparation method according to claim 1, characterized in that: In step (a), the molar ratio of ammonium persulfate to potassium hydroxide is 20-30:

1.

3. The preparation method according to claim 1, characterized in that: Before the reaction in step (a), the copper foam is repeatedly washed with an alcohol solvent and water and dried for standby.

4. The preparation method according to claim 1, characterized in that: In step (a), the reaction temperature is room temperature, the static reaction time is 15-30 min, after the reaction, the copper foam is taken out, washed and then freeze-dried.

5. The preparation method according to claim 1, characterized in that: The cobalt salt in step (b) is specifically cobalt nitrate or its hydrate, and the molybdenum salt is specifically sodium molybdate or its hydrate.

6. An efficient self-supporting cobalt molybdenum oxide-based heterostructure catalyst, characterized in that: This catalyst is prepared by any one of the methods according to claims 1-5.

7. Application of the efficient self-supporting cobalt molybdenum oxide-based heterostructure catalyst according to claim 6 in electrocatalytic hydrogen evolution.

Images