A ferrous oxide-graphene composite electrode, a preparation method and use thereof

Abstract

The application belongs to the technical field of chlorine precipitation electrocatalysis, and particularly relates to a ferrous oxide-graphene composite electrode and a preparation method and application thereof. The application provides a ferrous oxide-graphene composite structure obtained by simply ball milling a mixture of graphite powder and ferric nitrate, wherein the graphite powder is converted into graphene with a smaller size and a thinner thickness, and the surface of the graphene is loaded with ferrous oxide nanoparticles. The composite structure is dispersed in anhydrous ethanol, Nafion solution is added, and then the composite structure is coated on the surface of carbon cloth and naturally dried to obtain the ferrous oxide-graphene composite electrode. The composite electrode does not use noble metal, and the CER electrocatalytic activity of the composite electrode is higher than that of DSA, and the composite electrode has the characteristics of low cost and high activity.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of chlorine evolution electrocatalysis, and particularly relates to a ferrous oxide-graphene composite electrode and a preparation method and application thereof. BACKGROUND

[0002] Chlorine evolution reaction (CER) electrocatalysts can reduce the CER barrier and reduce energy consumption, and thus have wide applications in the fields of chlor-alkali industry, seawater electrolysis, salt-containing wastewater treatment, hydrogen-chlorine regenerative fuel cells, etc. At present, the commercial CER electrocatalyst is a dimensionally stable anode (DSA), which comprises 30% of ruthenium oxide and 70% of titanium oxide. Since the content of ruthenium oxide in the earth's crust is very low and the price is high, the cost of the DSA is difficult to be further reduced. In addition, most of the reported CER electrocatalysts also contain rare noble metals (such as platinum) or oxides (iridium oxide), for example, in the article “Atomically dispersed Pt–N4 sites as efficient and selective electrocatalysts for the chlorine evolution reaction” Nat. Commun., 2020, 11, 412, researchers prepared a platinum / carbon nanotube composite structure as a CER electrocatalyst. In addition, in the article “Rational surface and interfacial engineering of IrO2 / TiO2 nanosheet arrays toward high-performance chlorine evolution electrocatalysis and practical environmental remediation.” Small 2021, 17, 2006587, researchers designed an iridium oxide / titanium oxide nanosheet array. Therefore, it is of great significance to prepare a CER electrocatalyst without noble metal components. SUMMARY

[0003] One of the objectives of the application is to provide a preparation method of a ferrous oxide-graphene composite electrode without noble metal components and with high activity.

[0004] To achieve the above object, the application adopts the following technical scheme: a preparation method of ferrous oxide-graphene composite electrode, comprising the following steps:

[0005] S1, mixing graphite powder and ferric nitrate according to a mass ratio of 1:0.3, then sealing and ball milling, soaking the ball milling product in inorganic acid to remove impurities, and then freeze-drying to obtain a ferrous oxide-graphene composite structure;

[0006] S2, dispersing the ferrous oxide-graphene composite structure in anhydrous ethanol, then adding a Nafion solution to the anhydrous ethanol, and then ultrasonic treating to obtain an ink with uniformly dispersed sample, coating the ink on the surface of carbon cloth, and making the dispersion quality of the ferrous oxide-graphene composite structure on the carbon cloth be 1 mg / cm 2 , and naturally drying at room temperature to obtain the ferrous oxide-graphene composite electrode.

[0007] Further improvement of the preparation method of the ferrous oxide-graphene composite electrode:

[0008] Preferably, the particle size of the graphite powder in step S1 is 0.3-1 μm.

[0009] Preferably, the specific process of the ball milling in step S1 is ball milling at a speed of 500 rpm for 56 hours.

[0010] Preferably, the concentration of the inorganic acid in step S1 is 5-10 wt%.

[0011] Preferably, the inorganic acid in step S1 is one of hydrochloric acid, sulfuric acid or nitric acid.

[0012] Preferably, the specific process of the freeze-drying in step S1 is freeze-drying at a vacuum degree of 0.05 mmHg and a temperature of-120℃ for 12 hours.

[0013] Preferably, the ink in step S2 is prepared by dispersing 10 mg of the ferrous oxide-graphene composite structure in 1 ml of anhydrous ethanol, and then adding 10 μL of a 0.5 wt% Nafion solution.

[0014] The second object of the application is to provide a ferrous oxide-graphene composite electrode prepared by the preparation method.

[0015] The third object of the application is to provide a use of the ferrous oxide-graphene composite electrode in a chlorine evolution reaction.

[0016] The application has the following beneficial effects compared with the prior art:

[0017] 1) This invention provides a method for obtaining a ferrous oxide@graphene composite structure by simply ball milling a mixture of graphite powder and ferric nitrate. The ball milling process transforms the graphite powder into smaller, thinner graphene particles, and ferrous oxide nanoparticles are loaded onto the graphene surface. This composite structure is then dispersed in anhydrous ethanol, Nafion solution is added, and the mixture is coated onto a carbon cloth surface and allowed to dry naturally.

[0018] 2) Electrochemical measurements revealed that the ferrous oxide@graphene composite electrode prepared in this invention exhibits superior CER electrocatalytic activity, exceeding that of DSA. Since it does not use precious metals, it features low cost and high activity. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the preparation of the ferrous oxide@graphene composite structure according to the present invention.

[0020] Figure 2 (a) is a scanning electron microscope (SEM) image of graphite powder. (b) is a scanning electron microscope (SEM) image of the ferrous oxide@graphene composite structure of Example 1. (c) is a high-magnification scanning electron microscope (SEM) image of the ferrous oxide@graphene composite structure of Example 1. (d) is a transmission electron microscope (TEM) image of the ferrous oxide@graphene composite structure of Example 1.

[0021] Figure 3 The image shows the X-ray photoelectron spectrum of the ferrous oxide@graphene composite structure in Example 1.

[0022] Figure 4 The image shows the X-ray diffraction pattern of the ferrous oxide@graphene composite structure in Example 1.

[0023] Figure 5 The results show the CER electrocatalytic activity of the ferrous oxide@graphene composite electrode, size stability anode (DSA), and graphite prepared in Example 1; where (a) is the linear sweep voltammetry curve, (b) is the Tafel polarization curve, and (c) is the electrochemical impedance spectroscopy. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0025] Example 1

[0026] This embodiment provides a method for preparing an ferrous oxide@graphene composite electrode, which specifically includes the following steps:

[0027] S1. Place 5 g of graphite powder, 1.5 g of ferric nitrate, and 250 g of stainless steel balls in a ball mill jar. Then, seal the ball mill jar, place it in a planetary ball mill, and run the ball mill at 500 rpm for 56 hours. Next, soak the sample in dilute hydrochloric acid to remove impurities, and then dry it in a freeze dryer (vacuum: 0.05 mmHg) for 12 hours. The resulting product is a ferrous oxide@graphene composite structure.

[0028] S2. 10 mg of ferrous oxide@graphene composite structure was dispersed in 1 mL of anhydrous ethanol, and then 10 μL of Nafion solution was added. After ultrasonic treatment, a uniformly dispersed ink was obtained. Next, 100 μL of ink was pipetted onto a 1 cm... 2 The carbon cloth surface was naturally dried at room temperature, resulting in an iron oxide@graphene composite structure with a mass of approximately 1 mg / cm³ on the carbon cloth. -2 That is, ferrous oxide@graphene composite electrode is prepared.

[0029] like Figure 1 The diagram shown is a schematic of the preparation of the ferrous oxide@graphene composite structure in step S1. The ball milling process transforms graphite powder into graphene with smaller size and thinner thickness, and ferrous oxide nanoparticles are loaded on the surface of the graphene to obtain the ferrous oxide@graphene composite structure.

[0030] Scanning electron microscopy (SEM) images of graphite powder and the ferrous oxide@graphene composite structure prepared in step S1 were obtained, and the results are shown below. Figure 2 As shown in (a) and (b), by Figure 2 It can be seen that the size of the iron oxide@graphene composite structure is significantly smaller than that of graphite powder. Figure 2 (c) is a high-magnification scanning electron microscope image of the ferrous oxide@graphene composite structure. It can be clearly seen that there are a large number of nanoparticles on the graphene surface. Figure 2 (d) is a transmission electron microscope (TEM) image of the ferrous oxide@graphene composite structure. The inset is a high-magnification TEM image of the ferrous oxide nanoparticles. The interplanar spacing of the lattice fringes proves that the main component of the nanoparticles on the graphene surface is ferrous oxide.

[0031] Figure 3 The image shows the X-ray photoelectron spectrum of the ferrous oxide@graphene composite structure prepared in step S1. Figure 3 It can be seen that the composite structure contains three elements: carbon, iron, and oxygen.

[0032] Figure 4 The X-ray diffraction pattern of the ferrous oxide@graphene composite structure prepared in step S1 is obtained from... Figure 4 It can be seen that the composite structure has obvious FeO

[101] and FeO

[102] peaks, proving that the nanoparticles on the graphene surface are ferrous oxide nanoparticles.

[0033] Using a Chenhua electrochemical workstation (CHI 760E), a three-electrode system was employed, with a graphite rod as the counter electrode, a silver / silver chloride electrode as the reference electrode, and an ferrous oxide@graphene composite electrode as the working electrode. The voltage range was 0.8–1.5 V (vs Ag / AgCl), and the scan rate was 5 mV / s. -1 When testing electrochemical impedance spectroscopy, the frequency range was 0.1-100000 Hz, the amplitude was 5 mV, and linear sweep voltammetry curves were measured. The results are as follows: Figure 5 As shown, by Figure 5 (a) It can be seen that the voltages corresponding to a current density of 10 mA / cm² for the ferrous oxide@graphene composite structure and graphite are 1.15 V (vs Ag / AgCl) and 1.36 V (vs Ag / AgCl), respectively. This indicates that the ferrous oxide@graphene composite structure has a much higher CER electrocatalytic activity than graphite, and also proves that modifying the graphene surface with ferrous oxide by ball milling can indeed improve the CER electrocatalytic activity of graphene. Furthermore, under the same conditions, the voltage corresponding to a current density of 10 mA / cm² for the size-stability anode (DSA) in commercial CER electrocatalysts is 1.18 V (vs Ag / AgCl). Therefore, the CER electrocatalytic activity of the ferrous oxide@graphene composite structure is also significantly higher than that of DSA.

[0034] Tafel polarization curve test, as follows Figure 5 As shown in (b), the Tafel slope of the ferrous oxide@graphene composite structure is 58 mV dec. -1 It is significantly smaller than the Tafel slope of DSA (68mV dec). -1 This indicates that, compared with DSA, the ferrous oxide@graphene composite structure has more favorable CER catalytic kinetics.

[0035] Electrochemical impedance spectroscopy (EIS) testing, such as Figure 5 As shown in (c), the interfacial charge transfer resistance (Rct, 3.0 Ω) of the ferrous oxide@graphene composite structure is less than that of DSA (3.3 Ω) and much less than that of graphite (>6.3 Ω). This indicates that the ferrous oxide@graphene composite structure has faster electron transport performance than both DSA and graphite.

[0036] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments. It should be noted that many modifications and improvements can be made by those skilled in the art, and all modifications or improvements not exceeding the scope of the claims should be considered within the protection scope of the present invention.

Claims

1. A method for preparing an ferrous oxide@graphene composite electrode, characterized in that, Includes the following steps: S1. Graphite powder and ferric nitrate were mixed at a mass ratio of 1:0.3 and sealed. The mixture was ball-milled at 500 rpm for 56 hours. The ball-milled product was soaked in inorganic acid to remove impurities, and then freeze-dried at a vacuum of 0.05 mmHg and a temperature of -120℃ for 12 hours to obtain a ferrous oxide@graphene composite structure. The particle size of the graphite powder was 0.3-1 μm. S2. 10 mg of ferrous oxide@graphene composite structure was dispersed in 1 ml of anhydrous ethanol, and then 10 μL of 0.5 wt% Nafion solution (a perfluorosulfonic acid polymer) was added. The mixture was ultrasonically treated to obtain a uniformly dispersed ink. This ink was then coated onto the surface of carbon cloth, ensuring that the ferrous oxide@graphene composite structure was dispersed at a mass of 1 mg / cm³ on the carbon cloth. 2 The ferrous oxide@graphene composite electrode is prepared by naturally drying at room temperature and used for chlorine evolution reaction.

2. The method for preparing the ferrous oxide@graphene composite electrode according to claim 1, characterized in that, The concentration of the inorganic acid in step S1 is 5-10 wt%.

3. The method for preparing the ferrous oxide@graphene composite electrode according to claim 1 or 2, characterized in that, The inorganic acid mentioned in step S1 is one of hydrochloric acid, sulfuric acid, or nitric acid.

4. A ferrous oxide@graphene composite electrode prepared by the preparation method according to any one of claims 1-3.

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