Preparation method and application of CeO2-Ni (OH) 2 heterojunction electrocatalyst

Abstract

The invention discloses a preparation method of a CeO2-Ni (OH) 2 heterojunction electrocatalyst, which comprises the following steps: firstly, carrying out pretreatment on foamed nickel to remove nickel oxide on the surface of the foamed nickel, then dissolving water-soluble cerium salt and nickel salt in deionized water according to a preset proportion to obtain a deposition solution, and finally, taking the pretreated foamed nickel as a working electrode to prepare the CeO2-Ni (OH) 2 heterojunction electrocatalyst. And carrying out electro-deposition in the deposition solution to obtain the CeO2-Ni (OH) 2 heterojunction. The CeO2-Ni (OH) 2 heterojunction electrocatalyst accelerates electron transfer by establishing an electric field in an interface, optimizes space charge distribution, remarkably improves oxygen evolution efficiency, reduces water electrolysis anode side reaction energy consumption, realizes long-term stable operation under industrial-grade current density, has the advantages of simple preparation process, low cost, high efficiency, strong activity and good stability, and has wide application prospects. And the method has excellent industrial application potential.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalysis, and in particular relates to a preparation method of a CeO2-Ni(OH)2 heterojunction electrocatalyst and application thereof. Background Art

[0002] Energy issues are one of the hot issues in the 21st century. Renewable energy sources such as solar energy and wind energy have problems such as unstable output power and difficulty in connecting to the grid. Hydrogen energy, as a green and pollution-free energy source, shows good application prospects. At present, the main way to produce hydrogen is through the combustion and cracking of fossil energy such as coal and oil. Hydrogen production by electrolysis of water converts excess electricity produced by renewable energy sources such as solar energy and wind energy into clean and more energy-dense hydrogen energy, which can not only fundamentally reduce environmental pollution problems, but also solve the energy crisis facing mankind.

[0003] Water electrolysis is usually divided into two half reactions, namely the cathode hydrogen evolution reaction (HER) and the anode oxygen evolution reaction (OER). Compared with the cathode 2-electron process of hydrogen evolution reaction, the anode OER is a more complex 4-electron reaction, including four proton-coupled electron transfer and the formation of OO bonds. The intermediates formed include HO*, O* and HOO*, and follow ΔG (*OOH) =ΔG (*OH) +3.2eV scaling relationship. Due to the slow reaction kinetics and high overpotential, the industrial-scale application of water electrolysis is seriously hindered. Therefore, OER determines the overall efficiency of water electrolysis.

[0004] Currently, most oxygen evolution catalysts used in industry are precious metals, such as platinum, iridium, palladium, etc. Although they have high activity and stability, their high cost limits their future development. Therefore, it is of vital importance to find oxygen evolution reaction electrocatalysts that are abundant in the earth's crust and still have high activity and durability in alkaline environments in the scalable application of water electrolysis.

[0005] However, it is difficult to achieve high activity for non-precious metal-based (transition metals such as nickel, cobalt, iron, etc.) catalysts even after modification. -2Under current density conditions, the overpotential of most non-metallic catalysts cannot exceed 200mV, and their stability cannot be compared with that of precious metal-based catalysts. In recent years, in order to speed up the reaction rate of OER, researchers have focused on designing efficient water electrolysis OER catalysts from the two aspects of the number of active sites and the intrinsic activity of the active sites, so as to improve its reaction kinetics and reduce the overpotential. Among them, heterojunction catalysts have attracted widespread attention due to their unique structure, which can form a built-in electric field, thereby accelerating the spontaneous transfer of charges and optimizing the charge distribution. However, in the prior art, the preparation of heterojunction catalysts still has problems such as complex process, high cost and low efficiency. At the same time, the prepared catalysts do not have high activity and high stability under alkaline OER conditions, which makes it difficult to meet the requirements of actual industrial applications and needs further improvement.

[0006] Therefore, this paper proposes a preparation method and application of CeO2-Ni(OH)2 heterojunction electrocatalyst. Summary of the invention

[0007] The present invention designs a preparation method of a CeO2-Ni(OH)2 heterojunction electrocatalyst and its application to solve the problems existing in the above-mentioned background technology.

[0008] In order to achieve the above technical effects, the present invention is implemented through the following technical solutions:

[0009] A method for preparing a CeO2-Ni(OH)2 heterojunction electrocatalyst, characterized in that it comprises the following steps:

[0010] S1: pre-treating the nickel foam to remove nickel oxide on its surface;

[0011] S2: dissolving water-soluble cerium salt and nickel salt in deionized water in a predetermined ratio to obtain a deposition solution;

[0012] S3: Using the pretreated nickel foam as the working electrode, electrodeposition is performed in a deposition solution to obtain a CeO2-Ni(OH)2 heterojunction.

[0013] Furthermore, the pretreatment in S1 includes sequentially acid washing, water washing and vacuum drying the nickel foam.

[0014] Furthermore, the water-soluble cerium salt and nickel salt in S2 are cerium nitrate hexahydrate (Ce(NO3)3﹒6H2O) and nickel nitrate hexahydrate (Ni(NO3)3﹒6H2O), respectively.

[0015] Furthermore, the molar ratio of cerium to nickel in the deposition solution in S2 is 0-3:7-10, and the total molar concentration of cerium and nickel is 4-6 mmol / L.

[0016] Furthermore, the electrodeposition current in S3 is -50 to -200 mA cm -2 , the deposition time is 100 to 2000 seconds, and the electrodeposition process is carried out in the following three-electrode system: nickel foam is the working electrode, saturated Ag / AgCl is the reference electrode, and graphite rod is the counter electrode.

[0017] Another object of the present invention is to provide an application of CeO2-Ni(OH)2 heterojunction electrocatalyst in the anode oxygen evolution reaction under alkaline conditions.

[0018] The beneficial effects of the present invention are:

[0019] 1. The present invention uses a simple one-step electrodeposition method to prepare CeO2-Ni(OH)2 heterojunction electrocatalyst. The built-in electric field formed between the interfaces realizes rapid electron transmission and induces charge redistribution to achieve optimal adsorption energy of OH* intermediates at the catalytic sites.

[0020] 2. The present invention has the characteristics of simple preparation, high efficiency and low cost. The prepared CeO2-Ni(OH)2 heterojunction electrocatalyst has excellent performance and only needs about 170mV to reach 10mA cm -2 The current density is 1000 mA cm -2 Under current density conditions, it has a long continuous operation time and almost no performance degradation, and has excellent potential for industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0022] Figure 1 is an X-ray diffraction (XRD) pattern of CeO2-Ni(OH)2 of Example 1 and Ni(OH)2 of Comparative Example 1;

[0023] Figure 2 is a scanning electron microscope (SEM) image of CeO2-Ni(OH)2 of Example 1 and Ni(OH)2 of Comparative Example 1;

[0024] Figure 3 is a transmission electron microscope (TEM) image of CeO2-Ni(OH)2 of Example 1;

[0025] Figure 4 is the ultraviolet photoelectron spectrum (UPS) and energy band structure schematic diagram of Ni(OH)2 of Comparative Example 1 and CeO2 of Comparative Example 2;

[0026] Figure 5 is an X-ray photoelectron spectroscopy (XPS) graph of CeO2-Ni(OH)2 of Example 1, Ni(OH)2 of Comparative Example 1, and CeO2 of Comparative Example 2;

[0027] Figure 6 Linear sweep voltammetry (LSV) graphs of CeO2-Ni(OH)2 of Examples 1-5 and Ni(OH)2 of Comparative Example 1;

[0028] Figure 7 Methanol oxidation reaction (MOR) diagram of CeO2-Ni(OH)2 of Example 1, Ni(OH)2 of Comparative Example 1 and CeO2 of Comparative Example 2;

[0029] Figure 8 This is the stability test of CeO2-Ni(OH)2 of Example 1. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Example 1

[0032] See also Figures 1 to 8 As shown, the preparation of CeO2-Ni(OH)2 heterojunction electrocatalyst:

[0033] 1. Cut the nickel foam into 1cm×1cm size, put it into 6mol / L hydrochloric acid and ultrasonicate it for 10min to remove the oxide (NiO X ), washed several times with deionized water to remove the residual hydrochloric acid on the nickel foam, and vacuum dried at 60° C. for 2 hours for use.

[0034] 2. Disperse 0.25 mmol of cerium nitrate hexahydrate (Ce(NO3)3﹒6H2O) and 4.75 mmol of nickel nitrate hexahydrate (Ni(NO3)3﹒6H2O) in 100 mL of deionized water and ultrasonicate for 10 minutes to obtain a uniformly mixed electrochemical deposition electrolyte.

[0035] 3. A three-electrode system was used, with the treated nickel foam as the working electrode, the graphite rod as the counter electrode, and the saturated Ag / AgCl electrode as the reference electrode. The electrodes were placed in the deposition electrolyte at -100 mA cm -2The current density was maintained for 500 seconds to obtain the CeO2-Ni(OH)2 heterojunction electrocatalyst.

[0036] Embodiment 2-5

[0037] The specific preparation steps of Examples 2-5 are the same as the preparation process of the CeO2-Ni(OH)2 heterojunction electrocatalyst in Example 1. The only difference is that when preparing the CeO2-Ni(OH)2 heterojunction catalyst, the ratio of Ce and Ni is changed. In this example, the molar amounts of Ce and Ni are adjusted to 0.125mmol and 4.875mmol, 0.5mmol and 4.5mmol, 1mmol and 4mmol, and 1.5mmol and 3.5mmol, respectively.

[0038] Comparative Example 1-2

[0039] Comparative Examples 1-2 are respectively: nickel foam loaded nickel hydroxide electrocatalyst (Ni(OH)2) and nickel foam loaded cerium dioxide electrocatalyst (CeO2). The specific preparation steps of Comparative Examples 1-2 are the same as the preparation process of CeO2-Ni(OH)2 heterojunction catalyst in Example 1, the only difference is that when preparing Ni(OH)2 electrocatalyst, no cerium source (Ce(NO3)3﹒6H2O) is added to the deposition solution, and no nickel source (Ni(NO3)3﹒6H2O) is added when preparing the corresponding CeO2 electrocatalyst.

[0040] Catalyst structure and morphology analysis:

[0041] Figure 1 The XRD patterns of CeO2-Ni(OH)2 and Ni(OH)2 electrocatalysts are shown in Figure 2. Figure 1 As can be seen from a, the crystal structure of CeO2-Ni(OH)2 corresponds to nickel hydroxide (JCPDS NO.014-0117), indicating that the catalyst exists mainly in the form of Ni(OH)2 phase; in addition, Figure 1 The local magnified image of b clearly shows that CeO2-Ni(OH)2 has two weak cerium dioxide diffraction peaks (JCPDS NO.004-0593), indicating that the catalyst also has a small amount of CeO2 phase with low crystallinity. Ni(OH)2 only has nickel hydroxide phase (JCPDS NO.014-0117). The above results show that CeO2-Ni(OH)2 contains both Ni(OH)2 and CeO2 structures, and has the prerequisites for forming a heterogeneous structure.

[0042] Figure 2 This is the TEM image of CeO2-Ni(OH)2. Figure 2As can be seen in a, CeO2-Ni(OH)2 has two distinct lattice fringes in different directions, which are marked as regions A and B respectively. Figure 2 be shown, further measurement of its lattice fringes, two different crystal plane spacings (0.271 and 0.310nm) correspond to the (100) plane of Ni(OH)2 and the (110) plane of CeO2, respectively, providing strong evidence for the formation of heterogeneous structures. At the same time, the close connection between the two components of Ni(OH)2 and CeO2 enables them to build a stable charge transfer channel, which is beneficial to improving the stability of the catalyst.

[0043] Figure 3 This is the SEM image of CeO2-Ni(OH)2. Figure 3 As can be seen in a, CeO2-Ni(OH)2 is composed of a large number of two-dimensional nanosheets; Figure 3 The Ni(OH)2 shown in b is composed of numerous nanoparticles, indicating that the formation of heterogeneous structure changes the morphology of CeO2-Ni(OH)2, changing it from nanoparticles to two-dimensional nanosheets. This structure is conducive to the exposure of more active sites, increasing the number of active sites, and thus improving the catalytic activity of CeO2-Ni(OH)2.

[0044] Figure 4 Figure 1 is a schematic diagram of the energy bands of Ni(OH)2 and CeO2 before and after the UPS and heterostructure formation. Figure 4 As shown in a, it can be seen from the UPS results that the Fermi level of Ni(OH)2 is 3.72eV away from the vacuum energy level, while that of CeO2 is 3.92eV away from the vacuum energy level, indicating that the Fermi level of Ni(OH)2 is higher than that of CeO2; thus, the energy band diagram of the CeO2-Ni(OH)2 heterostructure before and after formation can be obtained, as shown in Figure 4 As shown in ab, when Ni(OH)2 and CeO2 form a heterojunction, due to the difference in Fermi levels, a built-in electric field is formed between the two components, accelerating the transfer of electrons from Ni(OH)2 to CeO2 until the Fermi levels of the two reach equilibrium. This process accelerates the redistribution of electrons between heterogeneous components, regulates the electronic structure of the active site, and thus optimizes the adsorption energy of the intermediate.

[0045] Figure 5 The XPS graphs of CeO2-Ni(OH)2, Ni(OH)2 and CeO2 are shown below. Figure 5As shown in a, Ni 2p of CeO2-Ni(OH)2 moves to a high energy position relative to Ni(OH)2, indicating the loss of Ni electrons; while Ce 3p of CeO2-Ni(OH)2 moves to a low energy position relative to CeO2, indicating that Ce gains electrons. XPS results again show that electrons are transferred from Ni(OH)2 to CeO2, thereby optimizing the charge distribution, which is consistent with the above UPS results.

[0046] Alkaline OER reaction electrocatalytic performance test:

[0047] Under the conditions of 1 mol / L KOH solution and a scan rate of 1 mV / s, the electrochemical test was carried out using a CHI760e electrochemical workstation with the prepared catalyst as the working electrode, a graphite rod as the counter electrode, and saturated Ag / AgCl as the reference electrode.

[0048] Figure 6 This is a LSV comparison diagram of CeO2-Ni(OH)2 electrocatalysts prepared by introducing different amounts of Ce in Examples 1-5 and Ni(OH)2 electrocatalysts prepared without introducing Ce in Comparative Example 1. It can be seen that under the premise that the total molar concentration of Ce and Ni in the deposition solution remains unchanged, the content of Ce and Ni will affect the OER performance. An appropriate amount of Ce element can effectively improve the OER performance. However, when Ce is too much or too little, the OER performance is attenuated. When the deposition solution contains 0.25mmol of cerium nitrate hexahydrate (Ce(NO3)3﹒6H2O) and 4.75mmol of nickel nitrate hexahydrate (Ni(NO3)3﹒6H2O), that is, the molar ratio of Ce:Ni is 5:95 (the ratio of Example 1), the CeO2-Ni(OH)2 heterojunction electrocatalyst has the highest OER activity.

[0049] Figure 7 The MOR graphs of CeO2-Ni(OH)2, Ni(OH)2, and CeO2 are shown in Figure 2. The adsorption behavior of the key OER intermediate OH* on the three catalysts was further studied by MOR, thereby revealing the potential mechanism for the improvement of OER performance. MOR is a method for directly detecting OH* intermediates. Since OH* produced under OER conditions can also oxidize alcohol molecules, the greater the current density difference between MOR and OER, the stronger the adsorption of OH*. As shown in the figure, in an alkaline electrolyte containing methanol, the current density difference of CeO2-Ni(OH)2 is significantly smaller than that of Ni(OH)2 and CeO2, indicating that the formation of a heterogeneous structure weakens the adsorption energy of CeO2-Ni(OH)2 to *OH, thereby reducing the reaction energy barrier and improving the reaction efficiency.

[0050] Figure 8This is a stability test curve of CeO2-Ni(OH)2 heterojunction electrocatalyst. As shown in the figure, CeO2-Ni(OH)2 heterojunction electrocatalyst can withstand an industrial-grade 1000mA cm -2 Under the current density, it can run stably for more than 300 hours without obvious potential decay, indicating that CeO2-Ni(OH)2 has long-term durability under alkaline OER high current conditions and has good industrial application potential.

[0051] In summary, the present invention synthesized CeO2-Ni(OH)2 heterojunction electrocatalysts through a simple one-step electrodeposition method. The catalysts are mainly composed of cerium dioxide and nickel hydroxide. The heterostructure formed drives the built-in electric field to accelerate the charge transfer from Ni(OH)2 to CeO2, optimizes the electronic structure of the active site, and weakens the adsorption energy of the intermediate OH*, thereby effectively reducing the reaction energy consumption and significantly improving the efficiency of the oxygen evolution reaction by electrolysis of water. In addition, the CeO2-Ni(OH)2 heterojunction electrocatalyst can achieve long-term stable operation at industrial-grade current density. It also has the advantages of simple preparation process, low cost and high efficiency, and has the advantages of high activity and strong stability under alkaline OER conditions, and has excellent industrial application potential.

Claims

1. A method for preparing a CeO2-Ni(OH)2 heterojunction electrocatalyst, characterized in that: The steps include: S1: pre-treating the nickel foam to remove nickel oxide on its surface; S2: dissolving water-soluble cerium salt and nickel salt in deionized water in a predetermined ratio to obtain a deposition solution; S3: Using the pretreated nickel foam as the working electrode, electrodeposition is performed in a deposition solution to obtain a CeO2-Ni(OH)2 heterojunction.

2. The method for preparing a CeO2-Ni(OH)2 heterojunction electrocatalyst according to claim 1, characterized in that: The pretreatment in S1 includes sequentially acid washing, water washing and vacuum drying of the nickel foam.

3. The method for preparing a CeO2-Ni(OH)2 heterojunction electrocatalyst according to claim 1, characterized in that: The water-soluble cerium salt and nickel salt in the S2 are cerium nitrate hexahydrate (Ce(NO3)3﹒6H2O) and nickel nitrate hexahydrate (Ni(NO3)3﹒6H2O) respectively.

4. The method for preparing a CeO2-Ni(OH)2 heterojunction electrocatalyst according to claim 1, characterized in that: The molar ratio of cerium to nickel in the deposition solution in S2 is 0-3:7-10, and the total molar concentration of cerium and nickel is 4-6 mmol / L.

5. The method for preparing a CeO2-Ni(OH)2 heterojunction electrocatalyst according to claim 1, characterized in that: The electrodeposition current in S3 is -50 to -200 mA cm -2 , the deposition time is 100 to 2000 seconds, and the electrodeposition process is carried out in the following three-electrode system: nickel foam is the working electrode, saturated Ag / AgCl is the reference electrode, and graphite rod is the counter electrode.

6. Use of the CeO2-Ni(OH)2 heterojunction electrocatalyst prepared by the preparation method according to any one of claims 1 to 5 in the anode oxygen evolution reaction under alkaline conditions.

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