Catalytically active Co3O4@Fe-BO heterogeneous catalyst and its preparation and application

Abstract

The present invention belongs to the technical field of metal electrocatalysts, and specifically relates to a catalytically active Co3O4@Fe‑B‑O heterogeneous catalyst, its preparation, and application. The present invention prepares the heterogeneous catalyst Co3O4@Fe‑B‑O by a simple and convenient alternating immersion method. The catalytic performance of Co3O4@Fe‑B‑O can be effectively regulated by controlling the number of alternating immersions. Test results show that the prepared Co3O4@Fe‑B‑O exhibits excellent OER catalytic performance under both alkaline and neutral conditions, and also has great potential as an anode catalyzer for full hydrolysis and CO2 reduction reactions. This work provides a simple and effective strategy for the preparation of efficient multifunctional catalysts.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal electrocatalysts, and in particular relates to a Co3O4@Fe-BO heterogeneous catalyst with catalytic activity and its preparation and application. Background Art

[0002] The increasingly serious energy crisis and environmental pollution have forced mankind to seek a renewable clean energy to replace traditional fossil energy. Hydrogen energy is considered an ideal alternative because of its zero emissions and high combustion calorific value. The technology for hydrogen production by electrolysis of water is mature and the process is simple. It is an efficient way to produce hydrogen. Water electrolysis consists of two half reactions. Compared with the hydrogen evolution reaction (HER) at the cathode, the oxygen evolution reaction (OER) at the anode involves a complex proton-electron coupling process with slow kinetics, which is the main factor limiting the production of hydrogen by electrolysis of water. The preparation of efficient OER catalysts can accelerate the efficiency of water decomposition. Precious metal-based catalysts such as Ir- and Ru- have outstanding electrocatalytic performance, but their high cost limits their large-scale application. Therefore, the development of efficient catalysts with abundant reserves and low prices has great practical value.

[0003] Transition metal oxide Co3O4 has high intrinsic catalytic activity and electrochemical stability, and is very low in cost, and is considered one of the most promising electrochemical catalytic materials. However, the electrocatalytic performance of Co3O4 still cannot meet the requirements of industrial hydrogen production, and its catalytic performance needs to be further improved to meet industrial needs. Constructing a heterostructure can combine the advantages of two heterogeneous components and is a feasible strategy to improve the electrocatalytic performance of the material, such as Xie (Xu, W.; Xie, W.; Wang, Y. Co3O 4-x -Carbon@Fe 2-y Co y O3 Heterostructural Hollow Polyhedrons for the Oxygen EvolutionReaction.ACS Applied Materials&Interfaces 2017,9(34),28642-28649.) and others constructed Co3O 4-x -carbon@Fe 2-y Co y O3 heterostructure, combined with Fe 2-y Co y O3 has large specific surface area and Co3O 4-xThe advantages of surface defects significantly improve the catalytic performance of Co3O4. In addition, the introduction of borate ions has been shown to effectively promote OER. For example, Ni-Fe-OB prepared by Wang et al. (You, C.; Ji, Y.; Liu, Z.; Xiong, X.; Sun, X. Ultrathin CoFe-Borate Layer Coated CoFe-Layered Double Hydroxide Nanosheets Array: A Non-Noble-Metal 3D Catalyst Electrode for Efficient and Durable Water Oxidation in Potassium Borate. ACSSustainable Chemistry & Engineering 2018, 6(2): 1527-1531.) has excellent OER performance. However, most heterostructures are constructed using hydrothermal methods, electrodeposition methods, etc., which are relatively complex processes and have high requirements for equipment. Therefore, developing a simple and convenient method to construct a heterostructure of Co3O4 and borate is expected to improve the electrocatalytic performance of Co3O4 and further broaden its application range. Summary of the Invention

[0004] The purpose of the present invention is to develop a simple and convenient method, the alternating immersion method, to prepare a catalytically active heterogeneous catalyst Co3O4@Fe-BO.

[0005] The technical problem solved by the present invention can be achieved through the following technical solutions:

[0006] A method for preparing a catalytically active Co3O4@Fe-BO heterogeneous catalyst is described. The alternating immersion method is used to construct a Co3O4@Fe-BO heterogeneous core-shell structure. The specific process steps are as follows:

[0007] Step 1, preparation of Co3O4, comprises the following steps:

[0008] Step 1.1, adding cobalt nitrate hexahydrate, urea and ammonium fluoride to the lining of a reactor, then adding deionized water, and stirring the mixture evenly;

[0009] Step 1.2: vertically immerse a piece of pretreated nickel foam in the reactor liner, transfer the liner to the stainless steel reactor shell, and perform a hydrothermal reaction. After the reaction is completed, remove the reactor and naturally cool to room temperature, and then remove the sample;

[0010] Step 1.3, rinse the sample with excess deionized water and anhydrous ethanol, and dry it to obtain Co(OH)2;

[0011] Step 1.4, placing the obtained Co(OH)2 sample in a muffle furnace, heating it to 375°C at a rate of 5°C / min, and keeping it at that temperature for 4 hours, then cooling it to room temperature at the same rate and taking out the sample to obtain Co3O4;

[0012] Step 2, preparation of Co3O4@Fe-BO, comprises the following steps:

[0013] Co3O4 was alternately soaked in a sodium borohydride aqueous solution and an ferric nitrate nonahydrate aqueous solution, and this step was repeated 5 times. The sample was then rinsed with excess deionized water and anhydrous ethanol and dried to obtain the Co3O4@Fe-BO heterogeneous catalyst.

[0014] Preferably, in step 1.1, the molar ratio of cobalt nitrate hexahydrate, urea and ammonium fluoride is 1:5:2.

[0015] Preferably, the hydrothermal reaction temperature in step 1.2 is 120° C. and the time is 6 h.

[0016] Preferably, the drying in step 1.3 is performed in a vacuum oven at 60° C. for 5 h.

[0017] Preferably, in step 2, the concentration of the sodium borohydride aqueous solution is 0.5 mol / L, and the concentration of the ferric nitrate nonahydrate aqueous solution is 0.1 mol / L.

[0018] Preferably, the alternating soaking time in step 2 is 1 min.

[0019] Preferably, the drying in step 2 is carried out in a vacuum oven at 60° C. overnight.

[0020] The present invention also relates to the application of the above-mentioned Co3O4@Fe-BO heterogeneous catalyst in the oxygen evolution reaction of alkaline and neutral water electrolysis. The prepared Co3O4@Fe-BO heterogeneous catalyst is used as a working electrode, and the electrochemical performance is tested in 1M KOH electrolyte with a pH of 13.6 and 0.1M PBS electrolyte with a pH of 7, respectively.

[0021] The present invention also relates to the application of the above-mentioned Co3O4@Fe-BO heterogeneous catalyst in the CO2 reduction reaction. The prepared Co3O4@Fe-BO heterogeneous catalyst is used as an anode, and its catalytic performance for the full hydrolysis CO2 reduction reaction is tested using a membrane electrode assembly.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This study has developed a simple and convenient alternating immersion method for rapidly preparing a catalytically active heterogeneous material, Co3O4@Fe-BO, at room temperature. The Co3O4 is fixed in sodium borohydride and ferric nitrate nonahydrate solutions for 1 minute, respectively. The catalytic activity of the Co3O4@Fe-BO heterogeneous material can be optimized simply by varying the number of alternating immersion cycles. Test results demonstrate that the prepared Co3O4@Fe-BO exhibits excellent OER catalytic performance under both alkaline and neutral conditions, and also shows great potential as an anode catalyst for full hydrolysis and CO2 reduction reactions. This work provides a simple and effective strategy for preparing highly efficient and multifunctional catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is the transmission electron microscopy (TEM) image of Co3O4 and Co3O4@Fe-BO in Examples 1 and 2;

[0025] Figure 2 The oxygen evolution activity polarization curves (LSV) of Co3O4, Fe-BO and Co3O4@Fe-BO in Examples 1 and 2 under alkaline (1M KOH) and neutral (0.1M PBS) conditions are shown;

[0026] Figure 3 The oxygen evolution activity polarization curves (LSV) were obtained by varying the number of times Co3O4 was alternately immersed in sodium borohydride and ferric nitrate nonahydrate solutions in Example 1 under alkaline (1M KOH) and neutral (0.1M PBS) conditions.

[0027] Figure 4 This is the polarization curve diagram (LSV) of Co3O4@Fe-BO as the anode catalyzing the full water split and electrocatalytic CO2 reduction reaction in Examples 1 and 2. DETAILED DESCRIPTION

[0028] The present invention will be further described below through specific implementations. The following examples are merely illustrative and non-restrictive, and should not be used to limit the scope of protection of the present invention.

[0029] Examples 1 and 2 are the preparation method of the catalytically active Co3O4@Fe-BO catalyst synthesized by the alternating immersion method described in the present invention and its application in the electrolytic water oxygen evolution reaction and the electrocatalytic CO2 reduction reaction.

[0030] Example 1

[0031] (1) Preparation of Co3O4@Fe-BO

[0032] a) Accurately weigh 5 mmol of Co(NO₃)₂·6H₂O, 10 mmol of NH₄F, and 25 mmol of urea into a 50 mL reactor liner. Then, add 40 mL of deionized water and stir the mixture thoroughly using a rotor and magnetic stirrer. A 2 cm x 3 cm piece of pretreated nickel foam is vertically immersed in the reactor liner. The liner is transferred to a stainless steel shell and placed in a 120°C constant-temperature electric oven for 6 h. After the reaction, the reactor is removed and cooled naturally to room temperature, and the sample is removed. The sample is rinsed with excess deionized water and anhydrous ethanol and dried in a 60°C vacuum oven for 5 h to obtain Co(OH)₂. The resulting Co(OH)₂ sample is placed in a porcelain boat and transferred to a muffle furnace. The temperature is increased to 375°C at a rate of 5°C / min and maintained for 4 h. The temperature is then lowered to room temperature at the same rate, and the sample is removed to obtain Co₃O₄.

[0033] b) The product from step (1) was alternately immersed in a 0.5 M aqueous sodium borohydride solution and a 0.1 M aqueous ferric nitrate nonahydrate solution for 1 minute, and this step was repeated five times. The sample was then rinsed with excess deionized water and anhydrous ethanol and dried overnight in a vacuum oven at 60°C to obtain the Co3O4@Fe-BO heterogeneous catalyst.

[0034] Example 2

[0035] The Co3O4 obtained in Example 1a) was replaced by pretreated nickel foam, and other conditions were the same as in Example 1b). The obtained catalytic material was recorded as Fe-BO.

[0036] The prepared catalytic material was used as a working electrode and the electrochemical performance was tested in 1M KOH electrolyte (pH = 13.6) and 0.1M PBS electrolyte (pH = 7). The test results showed that the Co3O4@Fe-BO catalytic material only required an overpotential of 233mV in 1M KOH to drive a charge of 20mA cm -2 The current density is 10 mA cm-2, and an overpotential of 395 mV is required in 0.1 M PBS. -2 The current density is high and the stability is excellent.

[0037] The prepared catalytic material was used as an anode and its catalytic performance for full water splitting and CO2 reduction reactions was tested using a membrane electrode assembly (MEA). The test results showed that it required a battery voltage of 2.35V and 3.66V to drive 200mAcm at room temperature, respectively. -2 The current density of Co3O4@Fe-BO was higher than that of commercial IrO2 for full hydrolysis and CO2 reduction reactions. The above results show that Co3O4@Fe-BO has good catalytic activity as a catalytic material.

[0038] Figure 1This is the transmission electron microscopy (TEM) image of Co3O4 and Co3O4@Fe-BO in Example 1. It can be seen from the figure that Co3O4 presents a nanoneedle morphology, Co3O4@Fe-BO maintains the original Co3O4 nanoneedle morphology and uniformly grows many nanoparticles around it, forming a typical core-shell heterostructure.

[0039] Figure 2 The LSV curves of Co3O4, Fe-BO and Co3O4@Fe-BO in Example 1 and Example 2 are shown in 1MKOH at 20mAcm -2 Under the current density of Co3O4(η 20 =289mV,η 100 =372mV) and Fe-BO(η 20 =283V,η 100 =329mV,η 20 =440mV), Co3O4@Fe-BO(η 20 =233mV,η 100 =271mV) showed the best catalytic activity; in 0.1MPBS, Co3O4@Fe-BO required 395mV to drive 10mAcm -2 The current density is better than that of Co3O4(η 10 =605mV) and Fe-BO(η 10 =548mV), which shows that the oxygen evolution performance of Co3O4 in water electrolysis under alkaline and neutral conditions is significantly improved by constructing a heterostructure.

[0040] Figure 3 The LSV curves obtained by fixing the immersion time of Co3O4 in sodium borohydride and ferric nitrate nonahydrate solutions in Example 1 to 1 min and changing the number of alternating immersions are as follows. In 1MKOH, the catalytic performance of the Co3O4@Fe-BO heterostructure obtained after alternating immersion once is significantly improved compared to that of pure Co3O4. The heterogeneous material obtained after alternating immersion 5 times shows the best OER catalytic activity. In 0.1MPBS, when the number of alternating immersions is 1, the catalytic performance of the obtained Co3O4@Fe-BO heterogeneous material is not much different from that of pure Co3O4. When the number of alternating immersions is 5, the OER catalytic performance reaches the best. This shows that the catalytic performance of the Co3O4@Fe-BO heterogeneous material can be effectively regulated by changing the number of alternating immersions. Figure 4 The LSV curves of Co3O4@Fe-BO as the anode catalyzing the full hydrolysis reaction and CO2 reduction reaction in Example 1 are shown. Co3O4@Fe-BO / NF requires a battery voltage of 2.35V and 3.66V to drive 200mA cm -2The current density of Co3O4@Fe-BO / NF was higher than that of commercial IrO2 (the battery voltages of 2.44 V and 4.65 V were required to drive the same current density), which indicated that Co3O4@Fe-BO / NF has great potential for industrial application.

[0041] The above is an exemplary description of the technical solution of the present invention. It should be noted that without departing from the core of the technical solution, any simple deformation, modification or other equivalent replacement that can be made by other technical personnel in this field without expending creative labor falls within the scope of protection of this patent.

Claims

1. A method for preparing a catalytically active Co3O4@Fe-BO heterogeneous catalyst, characterized in that: The Co3O4@Fe-BO heterogeneous core-shell structure was constructed by alternating immersion method. The specific process steps are as follows: Step 1, preparation of Co3O4, comprises the following steps: Step 1.1, adding cobalt nitrate hexahydrate, urea and ammonium fluoride to the lining of a reactor, then adding deionized water, and stirring the mixture evenly; Step 1.2: vertically immerse a piece of pretreated nickel foam in the reactor liner, transfer the liner to the stainless steel reactor shell, and perform a hydrothermal reaction. After the reaction is completed, remove the reactor and naturally cool to room temperature, and then remove the sample; Step 1.3, rinse the sample with excess deionized water and anhydrous ethanol, and dry it to obtain Co(OH)2; In step 1.4, the obtained Co(OH)2 sample was placed in a muffle furnace, heated to 375°C at a heating rate of 5°C / min, and kept at that temperature for 4 h. The temperature was then lowered to room temperature at the same rate and the sample was removed to obtain Co3O4. Step 2, preparation of Co3O4@Fe-BO, comprises the following steps: Co3O4 was alternately soaked in a sodium borohydride aqueous solution and an ferric nitrate nonahydrate aqueous solution, and this step was repeated 5 times. The sample was then rinsed with excess deionized water and anhydrous ethanol and dried to obtain the Co3O4@Fe-BO heterogeneous catalyst.

2. The method for preparing a catalytically active Co3O4@Fe-BO heterogeneous catalyst according to claim 1, characterized in that: In the step 1.1, the molar ratio of cobalt nitrate hexahydrate, urea and ammonium fluoride is 1:5:

2.

3. The method for preparing a catalytically active Co3O4@Fe-BO heterogeneous catalyst according to claim 1, characterized in that: The hydrothermal reaction temperature in step 1.2 is 120° C. and the reaction time is 6 h.

4. The method for preparing a catalytically active Co3O4@Fe-BO heterogeneous catalyst according to claim 1, characterized in that: The drying in step 1.3 is performed in a vacuum oven at 60°C for 5 h.

5. The method for preparing a catalytically active Co3O4@Fe-BO heterogeneous catalyst according to claim 1, characterized in that: In step 2, the concentration of the sodium borohydride aqueous solution is 0.5 mol / L, and the concentration of the ferric nitrate nonahydrate aqueous solution is 0.2 mol / L.

6. The method for preparing a catalytically active Co3O4@Fe-BO heterogeneous catalyst according to claim 1, characterized in that: The alternating soaking time in step 2 is 1 min.

7. The method for preparing a catalytically active Co3O4@Fe-BO heterogeneous catalyst according to claim 1, characterized in that: The drying in step 2 is carried out in a vacuum oven at 60° C. overnight.

8. Use of a Co3O4@Fe-BO heterogeneous catalyst prepared by the method for preparing a catalytically active Co3O4@Fe-BO heterogeneous catalyst according to any one of claims 1 to 7 in an alkaline or neutral water electrolysis oxygen evolution reaction, characterized in that: The prepared Co3O4@Fe-BO heterogeneous catalyst was used as the working electrode, and the electrochemical performance was tested in 1 M KOH electrolyte with pH = 13.6 and 0.1 M PBS electrolyte with pH = 7, respectively.

9. A use of a Co3O4@Fe-BO heterogeneous catalyst prepared by the method for preparing a catalytically active Co3O4@Fe-BO heterogeneous catalyst according to any one of claims 1 to 7 in a CO2 reduction reaction, wherein the prepared Co3O4@Fe-BO heterogeneous catalyst is used as an anode, and its catalytic performance in the CO2 reduction reaction is tested in a membrane electrode assembly.

Images