Method for simply synthesizing honeycomb Fe3O4 / Fe2O3 / CeO2 nano-composite as efficient OER electrocatalyst and application of honeycomb Fe3O4 / Fe2O3 / CeO2 nano-composite

Abstract

The invention discloses a method for simply synthesizing a honeycomb Fe3O4 / Fe2O3 / CeO2 nano-composite as a high-efficiency OER electrocatalyst and application of the nano-composite, and belongs to the field of electrocatalysis. The method comprises the following steps: sequentially dissolving polyvinylpyrrolidone and urea in deionized water, and magnetically stirring until a clear and transparent solution is formed; then sequentially adding Fe (NO3) 3.9 H2O and Ce (NO3) 3.6 H2O, continuously stirring at room temperature until the materials are fully mixed, standing and drying to obtain a fluffy precursor; and grinding into fine powder, calcining in an inert atmosphere, and naturally cooling to room temperature to obtain the Fe3O4 / Fe2O3 / CeO2 catalyst. The catalyst provided by the invention has a honeycomb pore structure, provides a high specific surface area and abundant active sites, and enhances the transport and conduction capabilities of electrolyte and electrons.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of OER electrocatalysis, in particular, a method for simply synthesizing a honeycomb Fe3O4 / Fe2O3 / CeO2 nanocomposite as a high-efficiency OER electrocatalyst and application thereof. BACKGROUND

[0002] The water electrolysis hydrogen production technology is composed of a cathode hydrogen evolution reaction (HER) and an anode oxygen evolution reaction (OER). Among them, the OER process is relatively complex, involving a four-electron transfer process, and passing through multiple intermediates such as OH*, O*, OOH* in sequence, which requires a high reaction barrier, thus leading to slow kinetics. Currently, commercial OER catalysts still rely on noble metal materials (such as Ru / Ir-based catalysts). However, the scarcity of noble metals, high cost and poor stability hinder their wide application, so it is of great research value and industrial significance to develop cheap and efficient and stable OER non-noble metal electrocatalysts.

[0003] So far, transition metal oxides are considered as ideal candidate materials to replace noble metal catalysts due to their abundant reserves, low price and controllable electronic structure. Iron (Fe), as one of the transition metals with the highest content in the earth's crust, has a significant cost advantage, but the activity of pure Fe-based catalysts still needs to be improved.

[0004] Cerium (Ce), as the most abundant and lowest cost element in the rare earth family, has been widely used in the field of photocatalysis, etc., but its research in electrocatalysis (especially OER and ORR) is still in the exploratory stage. SUMMARY

[0005] The application constructs a Fe3O4 / Fe2O3 / CeO2 nanocomposite catalyst with a three-dimensional "honeycomb structure", and adjusts the electrocatalytic performance of the product by adjusting the input amount of metal raw materials, carbonization temperature and other conditions. The optimized sample exhibits OER electrocatalytic activity comparable to that of commercial RuO2 catalyst. The method is simple and easy to operate, the raw material cost is low, the electrochemical performance is excellent, and the performance limitation of single metal catalyst is broken through.

[0006] In order to solve the above technical problems, the application adopts the following technical solutions: The application aims to provide a method for simply synthesizing a honeycomb Fe3O4 / Fe2O3 / CeO2 nanocomposite as a high-efficiency OER electrocatalyst and application thereof, comprising the following steps: Step 1, dissolving polyvinylpyrrolidone and urea in deionized water in turn, and magnetically stirring until a clear transparent solution is formed; Step 2, then Fe(NO3)3·9H2O and Ce(NO3)3·6H2O are added in turn, continuously stirred at room temperature until fully mixed, and dried by standing, to obtain fluffy precursor; Step 3, then ground into fine powder, calcined under inert atmosphere, and naturally cooled to room temperature to obtain Fe3O4 / Fe2O3 / CeO2 catalyst. Further limitation, in step 1, the weight average molecular weight (MW) of polyvinylpyrrolidone is 1300000.

[0007] Further limitation, in step 1, the ratio of polyvinylpyrrolidone, urea and deionized water is 1.0 g:0.5 g:30 mL.

[0008] Further limitation, in step 1, the speed of magnetic stirring is 500 rpm.

[0009] Further limitation, in step 2, the mass ratio of polyvinylpyrrolidone, Fe(NO3)3·9H2O and Ce(NO3)3·6H2O is 1.0:1.2:0.15.

[0010] Further limitation, in step 2, the standing and drying at 95 ℃ for 16 h.

[0011] Further limitation, in step 3, the inert atmosphere is N2.

[0012] Further limitation, in step 3, the calcination is to heat to 700 ℃ at a rate of 5 ℃ / min, and keep constant temperature for 1 h.

[0013] A Fe3O4 / Fe2O3 / CeO2 nanocomposite catalyst with honeycomb porous structure prepared by any of the above-mentioned methods.

[0014] The Fe3O4 / Fe2O3 / CeO2 nanocomposite catalyst with honeycomb porous structure prepared by any of the above-mentioned methods is used as OER electrocatalytic reaction.

[0015] Compared with the prior art, the present application has the following beneficial effects: Structural advantage: the unique honeycomb pore structure provides high specific surface area and rich active sites, and enhances the transport and conduction capacity of electrolyte and electrons.

[0016] Performance advantage: in OER test, the catalyst shows better catalytic activity and stability than commercial RuO2 at large current density. At 100 mA / cm 2 , the overpotential is only 1.55 V, less than 1.58 V of commercial RuO2 catalyst; at 200 mA / cm 2At high current density, the overpotential is as low as 1.56 V, which is less than 1.62 V of the commercial RuO2 catalyst.

[0017] Cost advantage: The use of cheap and readily available Fe and Ce elements (the mass of the Ce raw material is only 10% of the mass of the Fe raw material), greatly reducing the production cost of the catalyst, and having the potential for large-scale application.

[0018] The present application provides a new idea for designing efficient and stable non-noble metal water electrolysis anode catalyst, and promotes the development of low-cost water electrolysis technology.

[0019] For a better understanding of the features and technical content of the present application, please refer to the detailed description and drawings attached. It should be noted that the drawings are provided for illustrative purposes only and are not intended to limit the present application. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 a is different Fe 3+ and Ce 3+ XRD comparison chart of Fe3O4 / Fe2O3 / CeO2 samples obtained by carbonization at 700 DEG C at different raw material input ratios; Figure 1 b is the XRD comparison chart of Fe3O4 / Fe2O3 / CeO2 samples obtained by carbonization at different temperatures (600 DEG C, 700 DEG C, 800 DEG C) with a fixed raw material input (Fe:Ce = 1.2 g:0.15 g); Figure 2 is the SEM photo of the Fe3O4 / Fe2O3 / CeO2 sample; Figure 3 (a) is an OER comparison chart of Fe3O4 / Fe2O3 / CeO2 samples in 1M KOH at different raw material input amounts at a carbonization temperature of 700 DEG C; Figure 3 (b) is an OER comparison chart of Fe3O4 / Fe2O3 / CeO2 and commercial RuO2 in 1M KOH at different temperatures with a fixed raw material input; DETAILED DESCRIPTION The present application will be described in detail below with specific examples. These examples help those skilled in the art to further understand the present application, but should not be regarded as limiting the present application. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made. These all belong to the protection scope of the present application.

[0021] In this embodiment, the preparation method of the Fe3O4 / Fe2O3 / CeO2 composite OER catalyst with a honeycomb-like porous structure is as follows: Dissolve 1.0 g of polyvinylpyrrolidone (MW 1300000) and 0.5 g of urea in 30 mL of deionized water, respectively, and magnetically stir (500 rpm) until a clear transparent solution is formed.

[0022] Add 1.2 g of Fe(N03)3 9 H20 and 0.15 g of Ce(N03)3 6 H20 to the above solution, respectively, and continue stirring at room temperature for 5 h to ensure thorough mixing.

[0023] Transfer the mixed solution to a 95 °C blast drying oven and let it dry for 16 h to obtain a fluffy precursor.

[0024] Grind the dried precursor into fine powder and place it in a tube furnace under N2 atmosphere, program the temperature to rise to 700 °C at a rate of 5 °C / min, keep the temperature constant for 1 h, and then naturally cool to room temperature to obtain Fe304 / Fe203 / Ce02 nanocomposite catalyst.

[0025] Electrochemical tests All electrochemical tests were performed on a CHI 760E workstation using a typical three-electrode setup with 1.0 M KOH solution as the electrolyte, and a (1.0 x 1.0) cm 2 catalyst as the working electrode, a graphite rod and Hg / HgO as the counter and reference electrodes, respectively. Linear sweep voltammetry (LSV) was used to evaluate the OER electrochemical performance of the catalysts, with a scan rate of 5 mV / s, and the potential measurement was calibrated using 95% infrared compensation; cyclic voltammetry (CV) was used to measure the non-faradic electrochemical double-layer capacitance, from which the effective electrochemical surface area (ECSA) was calculated.

[0026] Preparation of working electrode Disperse 5.0 mg of sample, 1.0 mg of carbon black, and 40 μL of 5wt% Nafion solution uniformly in 1.0 mL of water / ethanol (1:2 v / v), and ultrasonicate for 15 min to obtain a uniform catalyst ink. Then, apply the catalyst ink to a treated nickel foam (1 x 1 cm 2 ) and dry it in a 60 °C oven for 24 h. Using the same method, apply a commercial Ru02 catalyst to the nickel foam.

[0027] Structure and performance characterization Characterize the crystal structure of the synthesized Fe304 / Fe203 / Ce02 by X-ray diffraction spectroscopy (XRD). Figure 1 a is different Fe 3+ and Ce 3+XRD patterns of Fe3O4 / Fe2O3 / CeO2 samples carbonized at 700 °C with different input amounts. As shown in the figure, the signal peaks at 2q = 30.1°, 35.4°, 62.5° and 66.8° are attributed to the XRD characteristic diffraction peaks of Fe3O4crystal (JCPDS No. 74-0748). The signal peaks at 2q = 24.1°, 33.1°, 40.8°, 43.5°, 54.1° and 57.5° are in full agreement with the standard characteristic peaks of Fe2O3(JCPDS No. 72-0469). The signal peaks at 2q = 28.5°, 47.5° and 56.3° are attributed to CeO2(JCPDS No. 78-0694). The above results show that Fe3O4 / Fe2O3 / CeO2 composites are successfully prepared under the above different input amounts. Then, we find that with the increase of Fe 3+ content, the XRD diffraction peaks of Fe2O3and CeO2components do not change significantly, but the XRD diffraction peak intensity of Fe3O4significantly increases, indicating that the more Fe 3+ content, the more conducive to the crystallization of Fe3O4. Figure 1 b is the input mass of Fe 3+ and Ce 3+ , i.e. Fe: Ce = 1.20 g : 0.15 g, and the XRD comparison chart of the products obtained by changing the carbonization temperature. We find that with the increase of carbonization temperature from 600 °C to 800 °C, the characteristic diffraction peaks of Fe3O4do not change significantly, but the characteristic peaks of Fe2O3and CeO2crystals significantly increase. Combined with the results of Figure 1 a, it is shown that the composition and crystallization of the product are closely related to the metal input amount and reaction temperature.

[0028] The morphology and microstructure of the samples are further characterized by scanning electron microscopy (SEM). Figure 2 The Fe3O4 / Fe2O3 / CeO2 sample obtained by carbonization at 700 °C is shown to have a similar "honeycomb" three-dimensional network structure, each "nest" is framed by carbonaceous sheets, and the nests are connected to each other to form an open, three-dimensional, ordered three-dimensional framework structure. This rich porous structure will be conducive to the transport of electrolyte and the formation of electrochemical three-phase interface. At the same time, the dispersion of particles inside the pore can be seen, i.e. Fe3O4 / Fe2O3 / CeO2 composite nanoparticles.

[0029] In order to evaluate the electrocatalytic performance of the series of Fe3O4 / Fe2O3 / CeO2 samples, electrochemical performance characterization was carried out in 1M KOH solution using a three-electrode system, and a commercial RuO2 catalyst was used as a reference sample. Figure 3aTo maintain a constant carbonization temperature (700 °C), the electrochemical polarization curves of Fe3O4 / Fe2O3 / CeO2 samples with different metal feed amounts were investigated. As shown in the figure, at 10 mA cm⁻¹... -2 At the given current density, the overpotential of the Fe3O4 / Fe2O3 / CeO2 (Fe:Ce=1.20 g:0.15 g) catalyst was 280 mA, the overpotential of the Fe3O4 / Fe2O3 / CeO2 (Fe:Ce=1.35 g:0.15 g) catalyst was 290 mA, the overpotential of the Fe3O4 / Fe2O3 / CeO2 (Fe:Ce=1.05 g:0.15 g) catalyst was 310 mA, and the overpotential of the Fe3O4 / Fe2O3 / CeO2 (Fe:Ce=0.90 g:0.15 g) catalyst was 330 mA. These results indicate that the dosage of different metal feedstocks directly affects the electrocatalytic activity of OER, with the Fe3O4 / Fe2O3 / CeO2 (Fe:Ce=1.20 g:0.15 g) catalyst exhibiting the most superior OER electrocatalytic performance. Figure 3b The electrochemical polarization curves of Fe3O4 / Fe2O3 / CeO2 samples at different carbonization temperatures with a fixed metal dosage (Fe:Ce = 1.20 g: 0.15 g) were investigated. As shown in the figure, the Fe3O4 / Fe2O3 / CeO2-700 catalyst only requires an overpotential of 320 mV to achieve 100 mAcm. -2 The current density of [the material] is superior to that of commercial RuO2 (350 mV), Fe3O4 / Fe2O3 / CeO2-600 (460 mV), and Fe3O4 / Fe2O3 / CeO2-800 (470 mV), respectively; further investigation revealed that at 200 mA cm⁻¹... -2 At high current densities, the overpotential of the Fe3O4 / Fe2O3 / CeO2-700 catalyst is 330 mV, which is superior to that of commercial RuO2 (390 mV), Fe3O4 / Fe2O3 / CeO2-600 (540 mV), and Fe3O4 / Fe2O3 / CeO2 / C-800 (560 mV), respectively. Experimental results show that the difference in required overpotential increases with increasing current density, indicating that the Fe3O4 / Fe2O3 / CeO2-700 catalyst possesses excellent OER catalytic performance.

[0030] The specific embodiments of the present invention have been described in detail above. It should be noted that the present invention is not limited to the specific embodiments described above. Various modifications or alterations can be made by those skilled in the art without departing from the scope of protection defined by the claims, and all such modifications or alterations fall within the scope of the present invention.

Claims

1. A method for simple synthesis of honeycomb-like Fe3O4 / Fe2O3 / CeO2 nanocomposites as high-efficient OER electrocatalysts, characterized in that, The method comprises the following steps: Step 1, polyvinylpyrrolidone, urea are sequentially dissolved in deionized water, and magnetic stirring is performed until a clear and transparent solution is formed; Step 2, then Fe(NO3)3·9H2O and Ce(NO3)3·6H2O are sequentially added, stirring is continuously performed at room temperature until they are fully mixed, and then the mixture is left to dry, thereby obtaining a fluffy precursor; Step 3, then the precursor is ground into fine powder, calcination is performed in an inert atmosphere, and natural cooling is performed to room temperature, thereby obtaining the Fe3O4 / Fe2O3 / CeO2 catalyst.

2. The method of claim 1, wherein, The weight average molecular weight (MW) of the polyvinylpyrrolidone is 1,300,000.

3. The method of claim 1, wherein, The ratio of polyvinylpyrrolidone, urea and deionized water is 1.0 g:0.5 g:30 mL.

4. The method of claim 1, wherein, The speed of magnetic stirring is 500 rpm.

5. The method of claim 1, wherein, The mass ratio of polyvinylpyrrolidone, Fe(NO3)3·9H2O and Ce(NO3)3·6H2O is 1.0:1.2:0.

15.

6. The method of claim 1, wherein, The mixture is left to dry at 95 ℃ for 16 h.

7. The method of claim 1, wherein, The inert atmosphere is N2.

8. The method of claim 1, wherein, The calcination is performed at a rate of 5 ℃ / min to 700 ℃, and the temperature is kept constant for 1 h.

9. A honeycomb porous structure Fe3O4 / Fe2O3 / CeO2 heterojunction catalyst prepared by the method of any one of claims 1-8.

10. A honeycomb porous structure Fe3O4 / Fe2O3 / CeO2 heterojunction for OER electrocatalytic reaction prepared by the method of any one of claims 1-8.

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