A cerium-based cobalt oxide electrocatalyst with an interface structure and a preparation method thereof

Abstract

The present invention relates to a cerium-based cobalt oxide electrocatalyst with an interfacial structure, a preparation method thereof, and an application thereof. The preparation method of the present invention is simple and does not require complex experimental equipment such as tube furnaces and muffle furnaces. Cobalt oxide nanosheets can be obtained only by impregnation, and the growth of the nanosheets can be controlled by adjusting the pH value of the solution. Among the electrocatalysts of the same kind with cobalt as the active site, the CoO / CeO2 catalyst obtained in the present invention has good oxygen evolution performance in water electrolysis, a large transfer current, and outstanding stability under high current conditions. At 10 mA / cm 2 and 100 mA / cm 2 , it can be continuously stable for 170 h at a large current density.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and particularly relates to a cerium-based cobalt oxide electrocatalyst with an interfacial structure and a preparation method thereof. Background Art

[0002] As an emerging green hydrogen production method, electrolysis of water has been widely studied. It consists of a hydrogen evolution reaction (HER) at the cathode and an oxygen evolution reaction (OER) at the anode. It should be noted that the oxygen evolution reaction at the anode is a slow four-electron transfer process, resulting in a high overpotential and energy consumption. Therefore, the development of efficient oxygen evolution electrocatalysts has become a research hotspot in recent years. Iridium oxide (IrO 2 ) and ruthenium oxide (RuO 2 ) are generally considered to be the best electrocatalysts for the oxygen evolution reaction, but the disadvantage is that these precious metals are scarce and expensive. Therefore, a large number of non-precious metal-based electrocatalysts have also been studied, and transition metal-based oxygen evolution catalysts with oxygen evolution performance comparable to that of IrO 2 / RuO 2 have been successfully developed, especially the first group of transition elements represented by oxides or hydroxides of Fe / Co / Ni.

[0003] Cerium is a rare earth element that is abundant and inexpensive. Due to the special properties of cerium oxide (CeO 2 ), whether as a dopant, a carrier, or an interfacial component, it plays an important role in improving the oxygen evolution performance of transition metal catalysts. The valence state of Ce ions in CeO 2 is easily convertible between +3 and +4, and this property is beneficial to: 1) optimizing the electronic structure and coordination environment of transition metals to obtain high intrinsic activity; 2) promoting charge transfer and electron conduction; 3) introducing abundant oxygen vacancies as active sites for the oxygen evolution reaction. Patent application 201811255715.6 discloses a cobalt oxide cerium dioxide composite oxide, a preparation method and uses thereof. However, it uses a high-temperature synthesis method, requires a H 2 / Ar atmosphere tube furnace, the reaction is violent and the requirements are high; and the CoO-CeO 2 composite nanoparticles synthesized in this patent application need to add a binder and then be loaded onto a suitable current collector when used as an electrocatalyst, and the oxygen production performance is average. The oxygen evolution overpotential at 10 mA / cm 2 reaches 319 mV, and the overpotential increases significantly during the 50 h stability test at this current.

[0004] The interfacial effect refers to the formation of an interface between two active materials. Due to its strong bonding, electron interaction, or synergy, more active centers can be formed than those composed of individual components, and the interfacial active sites also have higher intrinsic activity. Therefore, the interfacial effect has been widely applied to the design of electrocatalysts. However, the reported studies on CeO 2 acting as an interfacial component to exert the interfacial effect have all focused on the hydrogen evolution reaction, and its application in the oxygen evolution reaction remains to be further studied. SUMMARY OF THE INVENTION

[0005] The purpose of the present invention is to solve the problems existing in traditional noble metal oxygen evolution electrocatalysts in the prior art, such as high cost, low current density of traditional non-noble metal oxygen evolution electrocatalysts, and poor stability at high currents. Thus, a cerium-based cobalt oxide electrocatalyst with an interfacial structure is provided, which has good water electrolysis performance and can be stable for a long time at a relatively high current density.

[0006] To solve the above technical problems, the present invention is achieved through the following technical solutions.

[0007] The first aspect of the present invention provides a preparation method of a cerium-based cobalt oxide electrocatalyst with an interfacial structure, comprising the following steps:

[0008] (1) Take a mixed solution containing a cerium salt and a sodium salt, and perform electrodeposition on the surface of nickel foam under a water bath condition to prepare a CeO 2 thin film;

[0009] (2) Immerse the CeO 2 thin film prepared in step (1) in a cobalt salt solution, adjust the pH value of the solution, and then thoroughly wash the excess solution on the surface of the sample with ultrapure water; after natural drying, the CoO / CeO 2 catalyst is obtained.

[0010] Preferably, the cerium salt in step (1) is selected from one or more of cerium nitrate, cerium acetate, and cerium chloride; most preferably, the cerium salt is selected from cerium nitrate.

[0011] Preferably, the sodium salt in step (1) is selected from one or more of sodium chloride, sodium carbonate, sodium bicarbonate, sodium sulfate, and sodium sulfite; most preferably, the sodium salt in step (1) is selected from sodium chloride.

[0012] Preferably, the cerium ion concentration in the solution in step (1) is 1-5 mM; most preferably, the cerium ion concentration in the solution in step (1) is 2 mM.

[0013] Preferably, the sodium ion concentration in the solution in step (1) is 5-20 mM; most preferably, the sodium ion concentration in the solution in step (1) is 10 mM.

[0014] Preferably, the temperature of the water bath in step (1) is 50-100°C; more preferably, the temperature of the water bath is 65-80°C; most preferably, the temperature of the water bath is 70°C.

[0015] Preferably, the current of the electrodeposition in step (1) is 0.1-0.5 mA / m 2 , and the electrodeposition time is 5-30 min; most preferably, the current of the electrodeposition is 0.25 mA / m 2 , and the electrodeposition time is 10-20 min.

[0016] Preferably, a three-electrode system is used for the electrodeposition in step (1).

[0017] Preferably, Ag / AgCl is used as the reference electrode, nickel foam is used as the cathode, and platinum wire is used as the anode in the three-electrode system.

[0018] Preferably, the cobalt salt in step (2) is selected from one or more of cobalt nitrate, cobalt chloride, and cobalt acetate; most preferably, the cobalt salt is selected from cobalt nitrate.

[0019] Preferably, the concentration of cobalt ions in the cobalt salt solution in step (2) is 0.1-1 M; most preferably, the concentration of cobalt ions in the cobalt salt solution is 0.3 M.

[0020] Preferably, the pH value of the solution is adjusted to 1.0-3.0 in step (2); more preferably, the pH value of the solution is adjusted to 1.5-2.5 in step (2); most preferably, the pH value of the solution is adjusted to 1.56 in step (2).

[0021] Preferably, the reagent used to adjust the pH value of the solution in step (2) is selected from one or more of hydrochloric acid and nitric acid.

[0022] Preferably, the impregnation time in step (2) is 30-100 min; most preferably, the impregnation time is 60 min.

[0023] The second aspect of the present invention provides a cerium-based cobalt oxide electrocatalyst with an interfacial structure prepared according to the above preparation method.

[0024] The third aspect of the present invention provides the application of a cerium-based cobalt oxide electrocatalyst with an interfacial structure prepared according to the above preparation method in the oxygen evolution reaction of water electrolysis.

[0025] The present invention has the following technical effects compared with the prior art:

[0026] (1) The preparation method of the present invention is simple and does not require complex experimental equipment such as tube furnaces and muffle furnaces. Only conventional equipment or devices such as ordinary beakers can be used to obtain cobalt oxide nanosheets through impregnation. The reaction conditions are mild, and the growth of nanosheets can be controlled by adjusting the pH value of the solution, which is more suitable for large-scale production.

[0027] (2) Among the similar electrocatalysts with cobalt as the active site, the CoO / CeO 2 catalyst obtained in the present invention has good oxygen evolution performance for water electrolysis. The self-supporting electrode with CoO nanosheets grown on the CeO 2 film can be directly used. The catalyst of the present invention has a large current transmission. To reach a current density of 10 mA / cm 2 , only a overpotential of 291 mV is required, and it has outstanding stability under high current conditions. It can continuously and stably operate for 170 h at large current densities of 10 mA / cm 2 and 100 mA / cm 2 , and the performance basically does not decay. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic diagram of the preparation process of the CoO / CeO 2 catalyst of the present invention.

[0029] Figure 2 is a morphology diagram of the CeO 2 film prepared in Example 1 of the present invention.

[0030] Figure 3 is a morphology diagram of the CoO / CeO 2 catalyst prepared in Example 1 of the present invention.

[0031] Figure 4 is a morphology diagram of the CoO / CeO 2 -L catalyst prepared in Example 4 of the present invention.

[0032] Figure 5 is a morphology diagram of the CoO catalyst prepared in Comparative Example 1 of the present invention.

[0033] Figure 6 is a schematic diagram of the test results of the oxygen evolution performance of the CoO / CeO 2 catalyst prepared in Example 1 of the present invention and the CoO / CeO 2 -L catalyst prepared in Example 4 for water electrolysis.

[0034] Figure 7 is a schematic diagram of the test results of the oxygen evolution performance of the CoO / CeO 2 catalyst prepared in Example 1 of the present invention and the CoO catalyst for water electrolysis.

[0035] Figure 8 CoO / CeO prepared in Example 1 of the present invention 2 Schematic diagram of the detection result of the catalyst stability Detailed implementation manners

[0036] To make the objectives, technical solutions and effects of the present invention clearer and more definite, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention

[0037] Example 1

[0038] A cerium-based cobalt oxide electrocatalyst with an interfacial structure, the preparation process of which is as Figure 1 shown, and specifically includes the following steps

[0039] (1) Take 100 mL of a mixed solution containing 2 mM Ce(NO 3 ) 3 and 10 mM NaCl, and perform electrodeposition on the surface of nickel foam at 70 °C in a water bath under a constant current condition of 0.25 mA / cm 2 for 10 min to prepare a CeO 2 thin film (see Figure 2 ); The electroplating uses a three-electrode system, with Ag / AgCl as the reference electrode, nickel foam as the cathode, and platinum wire as the anode

[0040] (2) Immerse the CeO 2 thin film prepared in step (1) in a solution of Co(NO 3 ) 2 with a concentration of 0.3 M, adjust the pH value of the solution to 1.56 with hydrochloric acid, and the immersion time is 60 min; then wash the excess solution on the surface of the sample thoroughly with ultrapure water; after natural drying, the CoO / CeO 2 catalyst is obtained, and its morphology diagram is as Figure 3 shown

[0041] Example 2

[0042] A cerium-based cobalt oxide electrocatalyst with an interfacial structure, the preparation method of which includes the following steps

[0043] (1) Take 100 mL of a mixed solution containing 1 mM Ce(NO 3 ) 3 and 5 mM NaCl, and perform electrodeposition on the surface of nickel foam at 65 °C in a water bath under a constant current condition of 0.2 mA / cm 2 for 20 min to prepare a CeO 2The thin film; electroplating uses a three - electrode system, with Ag / AgCl as the reference electrode, nickel foam as the cathode, and platinum wire as the anode;

[0044] (2) Immerse the CeO 2 thin film prepared in step (1) in a Co(NO 3 ) 2 solution with a concentration of 0.2 M. Use hydrochloric acid to adjust the pH value of the solution to 1.8, and the immersion time is 100 min; then wash the excess solution on the surface of the sample thoroughly with ultrapure water; after natural drying, the CoO / CeO 2 catalyst is obtained.

[0045] Example 3

[0046] A cerium - based cobalt oxide electrocatalyst with an interfacial structure, and its preparation method includes the following steps:

[0047] (1) Take 100 mL of a mixed solution containing 4 mM Ce(NO 3 ) 3 and 20 mM NaCl, and perform electrodeposition on the surface of nickel foam at 80 °C in a water bath under a constant current condition of 0.4 mA / cm 2 for 5 min to prepare a CeO 2 thin film; electroplating uses a three - electrode system, with Ag / AgCl as the reference electrode, nickel foam as the cathode, and platinum wire as the anode;

[0048] (2) Immerse the CeO 2 thin film prepared in step (1) in a Co(NO 3 ) 2 solution with a concentration of 0.8 M. Use nitric acid to adjust the pH value of the solution to 2.5, and the immersion time is 30 min; then wash the excess solution on the surface of the sample thoroughly with ultrapure water; after natural drying, the CoO / CeO 2 catalyst is obtained.

[0049] Example 4

[0050] A cerium - based cobalt oxide electrocatalyst with an interfacial structure, and its preparation method includes the following steps:

[0051] (1) Take 100 mL of a mixed solution containing 2 mM Ce(NO 3 ) 3 and 10 mM NaCl, and perform electrodeposition on the surface of nickel foam at 70 °C in a water bath under a constant current condition of 0.25 mA / cm 2 for 10 min to prepare a CeO 2 thin film; electroplating uses a three - electrode system, with Ag / AgCl as the reference electrode, nickel foam as the cathode, and platinum wire as the anode;

[0052] (2) Immerse the CeO 2 thin film in a Co(NO 3 ) 2 solution with a concentration of 0.3 M. Adjust the pH value of the solution to 1.0 using hydrochloric acid, and the immersion time is 30 min; then wash the excess solution on the surface of the sample thoroughly with ultrapure water; after natural drying, the CoO / CeO 2 -L catalyst is obtained, and its morphology diagram is as shown in Figure 4 .

[0053] Comparative Example 1

[0054] A cobalt oxide reference electrocatalyst with a nanosheet structure, and its preparation method includes the following steps: Immerse the nickel foam directly in a Co(NO 3 ) 2 solution with a concentration of 0.3 M. Adjust the pH value of the solution to 1.56 using hydrochloric acid, and the immersion time is 60 min; then wash the excess solution on the surface of the sample thoroughly with ultrapure water; after natural drying, the CoO catalyst is obtained, and its morphology diagram is as shown in Figure 5 .

[0055] Verification Example 1

[0056] In the present invention, by adjusting the pH value of the solution during the preparation process, the growth and size of the nanosheets are adjusted. Through a large number of experiments, it is found that within a certain range, the lower the pH value of the solution, the larger the size of the cobalt oxide nanosheets prepared. In the CoO / CeO 2 catalyst, the size of the cobalt oxide nanosheets is about 50 nm, while in the CoO / CeO 2 -L catalyst, the size of the cobalt oxide nanosheets reaches several hundred nanometers. This is because hydrogen ions can not only create an acidic environment that hinders the growth of nanosheets, but also fill the positive charges missing due to the decrease in Co 2+ concentration in the solution to maintain the electrical neutrality of the solution. Therefore, within a certain range, as the pH value of the solution decreases, the size of the cobalt oxide nanosheets increases.

[0057] Subsequently, the CoO / CeO 2 catalyst prepared in Example 1 and the CoO / CeO 2 -L catalyst prepared in Example 4 are respectively taken for the oxygen evolution performance test of water electrolysis, and the test results are as shown in Figure 6 . The results show that the oxygen evolution performance of the CoO / CeO 2 catalyst for water electrolysis is much better than that of the CoO / CeO 2 -L catalyst. Although the CoO / CeO 2In the -L catalyst, the cobalt oxide nanosheets are larger in size and have a larger contact area with the electrolyte. However, the Co-O-Ce active substance with higher intrinsic oxygen evolution activity at the Co / Ce interface is more difficult to contact with the electrolyte and thus undergo the oxygen evolution reaction.

[0058] Furthermore, the CoO catalyst prepared in Comparative Example 1 and the CoO / CeO 2 catalyst prepared in Example 1 were respectively taken for the oxygen evolution performance test of electrolytic water. The test used a three-electrode system, with the CoO and CoO / CeO 2 catalysts as the working electrode, the Pt electrode as the counter electrode, and Hg / HgO as the reference electrode. First, 20 cycles of cyclic voltammetry tests were carried out to activate the samples. After the curve stabilized, linear voltammetry tests were carried out, and the test results are as Figure 7 shown. The results show that the oxygen evolution performance of electrolytic water is far superior to that of the single cobalt oxide sample. This is because the electron reconstruction at the CoO / CeO 2 interface forms a new Co-O-Ce active substance, optimizing the adsorption energy of the reaction intermediate products during the oxygen evolution reaction, making the reactants easy to adsorb and transform, and the products easy to desorb. Therefore, the intrinsic activity and apparent oxygen evolution performance of the CoO / CeO 2 catalyst are improved.

[0059] Even further, the CoO / CeO 2 catalyst prepared in Example 1 was taken for the stability detection of constant current. The test used a three-electrode system, with the CoO / CeO 2 catalyst as the working electrode, the Pt electrode as the counter electrode, and Hg / HgO as the reference electrode. Tests were carried out successively at current densities of 10 mA / cm 2 and 100 mA / cm 2 , and the detection results are as Figure 8 shown. The results show that the CoO / CeO 2 catalyst can be continuously stable for 170 h at large current densities of 10 mA / cm 2 and 100 mA / cm 2 .

[0060] The above specific implementation part has specifically introduced the analysis method involved in the present invention. It should be noted that the above introduction is only to help those skilled in the art better understand the method and idea of the present invention, rather than a limitation on the relevant content. Without departing from the principle of the present invention, those skilled in the art can also make appropriate adjustments or modifications to the present invention, and the above adjustments and modifications should also fall within the protection scope of the present invention.

Claims

1. A method for preparing a cerium-based cobalt oxide electrocatalyst having an interface structure, characterized in that: The steps include: (1) taking a mixed solution containing cerium salt and sodium salt, and electro-depositing it on the surface of nickel foam in a water bath to prepare a CeO2 film; (2) Immersing the CeO2 film prepared in step (1) in a cobalt salt solution, adjusting the pH value of the solution to 1.0-3.0, and then thoroughly washing the excess solution on the surface of the sample with ultrapure water; after natural drying, a CoO / CeO2 catalyst is obtained.

2. The preparation method according to claim 1, characterized in that: The cerium salt in step (1) is selected from one or more of cerium nitrate, cerium acetate and cerium chloride.

3. The preparation method according to claim 1, characterized in that: The sodium salt in step (1) is selected from one or more of sodium chloride, sodium carbonate, sodium bicarbonate, sodium sulfate and sodium sulfite.

4. The preparation method according to claim 1, characterized in that: The temperature of the water bath in step (1) is 50-100°C.

5. The preparation method according to claim 1, characterized in that: The current of the electrodeposition in step (1) is 0.1-0.5 mA / m 2 The electrodeposition time is 5-30min.

6. The preparation method according to claim 1, characterized in that: The cobalt salt in step (2) is selected from one or more of cobalt nitrate, cobalt chloride and cobalt acetate.

7. The preparation method according to claim 1, characterized in that: The immersion time in step (2) is 30-100 minutes.

8. A cerium-based cobalt oxide electrocatalyst with an interface structure prepared according to the preparation method according to any one of claims 1 to 7.

9. Use of a cerium-based cobalt oxide electrocatalyst having an interface structure prepared by the preparation method according to any one of claims 1 to 7 in an oxygen evolution reaction by electrolysis of water.

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