CeO2-Ni (OH) 2 composite catalyst and preparation method thereof

Abstract

The invention relates to the technical field of electrochemical catalytic ammoxidation, in particular to a CeO2-Ni (OH) 2 composite catalyst and a preparation method thereof. Oxidation overpotential of a conventional electrochemical ammoxidation catalyst is high, and development of an electrochemical ammoxidation catalysis technology is greatly restricted. In order to solve the technical problems, the invention provides the CeO2-Ni (OH) 2 composite catalyst, which is characterized in that nickel hydroxide and cerium oxide which have catalytic activity are combined to generate a synergistic effect, so that the electrochemical ammoxidation reaction rate is promoted, and the electro-catalytic performance of the composite catalyst is improved. Compared with other preparation methods, the CeO2-Ni (OH) 2 composite catalyst synthesized by the method disclosed by the invention has the advantages of high electrochemical specific surface area and more benefit for the proceeding of AOR, and compared with other preparation methods, the CeO2-Ni (OH) 2 composite catalyst synthesized by the method disclosed by the invention has more advantages in the aspect of electrochemical catalysis of AOR.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalytic ammonia oxidation, and particularly relates to a CeO2-Ni(OH)2 composite catalyst and a preparation method thereof. Background Art

[0002] Ammonia (NH3), as an excellent hydrogen carrier and a good hydrogen storage medium for carbon-free fuels, can effectively solve the hydrogen storage problem. As a carbon-neutral fuel, it has the characteristics of high energy density and easy liquefaction. At the same time, the industrial chain of ammonia production, storage, and transportation is mature, which can avoid the high utilization cost of pure hydrogen fuel and has a very broad application prospect. Using direct ammonia oxidation to supply power to a direct ammonia fuel cell (DAFC) made of a fuel cell can avoid carbon dioxide emissions from other carbon-based fuels and is a new type of clean energy conversion technology.

[0003] However, the development of electrocatalytic ammonia oxidation technology is restricted by various factors such as high oxidation overpotential, low current, and easy poisoning of the catalyst surface. Therefore, it is crucial to develop a high-performance anode ammonia oxidation reaction (AOR) catalyst.

[0004] Cerium oxide is a semiconductor metal oxide. It has characteristics such as good biocompatibility, large specific surface area, high chemical stability, good electrical conductivity, and high isoelectric point, and has been widely used in the preparation of lithium-air batteries (Chinese Patent CN 117352756A), heavy metal wastewater treatment (Chinese Patent CN 115722197A), the preparation of photocatalytic materials (Chinese Patent CN 118788361A), and other fields.

[0005] However, there is no relevant research or report on the application of the composite catalyst formed by CeO2 and Ni(OH)2 in the field of electrocatalytic ammonia oxidation. Summary of the Invention

[0006] The problems existing in the prior art are that the oxidation overpotential of conventional catalysts for electrocatalytic ammonia oxidation is relatively high, the energy consumption is high, which greatly restricts the development of electrocatalytic ammonia oxidation technology. To solve the above technical problems, the present invention provides a CeO2-Ni(OH)2 composite catalyst, which includes the following preparation steps:

[0007] (1) Ammonium cerium nitrate, nickel sulfate hexahydrate, acrylamide, and hexamethylenetetramine are added to deionized water, and after stirring evenly, a mixed solution is prepared;

[0008] (2) The mixed solution is transferred to a high-pressure reaction kettle with a polytetrafluoroethylene lining and reacted at a constant temperature;

[0009] (3) After the isothermal reaction is completed, cool it to room temperature, take out the reaction kettle, and after centrifugal washing and drying of the obtained reaction solution in sequence, a light green powder is obtained, which is the CeO2-Ni(OH)2 composite catalyst.

[0010] Preferably, the mass ratio of nickel sulfate hexahydrate to acrylamide and hexamethylenetetramine is 0.624:0.12:0.8.

[0011] Preferably, the mass concentration of nickel sulfate hexahydrate in deionized water is 0.0150 mL - 0.0160 g / mL.

[0012] Preferably, the mass concentration of nickel sulfate hexahydrate in deionized water is 0.0156 ± 0.0002 g / mL.

[0013] Preferably, the reaction temperature in step (2) is 180 ± 2 °C.

[0014] Preferably, the reaction time in step (2) is at least 6 h.

[0015] Preferably, the washing in step (3) includes water washing and anhydrous ethanol washing in sequence.

[0016] Preferably, the drying temperature in step (3) is 45 - 70 °C.

[0017] Preferably, the mass percentage of CeO2 in the CeO2-Ni(OH)2 composite catalyst is 30%.

[0018] The present invention has the following beneficial effects:

[0019] (1) The present invention provides a preparation method of a CeO2-Ni(OH)2 composite catalyst, specifically by combining two catalytically active substances, nickel hydroxide and cerium oxide, to produce a synergistic effect, promoting the rate of the electrochemical ammonia oxidation reaction and improving its electrocatalytic performance; at the same current density, the initial potential of the CeO2-Ni(OH)2 composite catalyst obtained in the present invention is reduced from 0.60 (V vs RHE) to 0.53 (V vs RHE), and at the same voltage, the current density of the CeO2-Ni(OH)2 composite catalyst obtained in the present invention is increased from 31.76 mA / cm 2 to 97.61 mA / cm 2 , thus proving that the CeO2-Ni(OH)2 composite catalyst obtained in the present invention has excellent catalytic activity in AOR;

[0020] (2) The present invention obtains CeO2-Ni(OH)2 composite catalysts with different mass percentages of CeO2 by means of a hydrothermal method at high temperature. The CeO2-Ni(OH)2 composite catalysts have a relatively high electrochemically specific surface area, which is more conducive to the AOR. In the present invention, nickel sulfate hexahydrate is preferably used as the nickel source, and ammonium cerium nitrate is preferably used as the cerium source. The present invention preferably uses a mass ratio of nickel sulfate hexahydrate to ammonium cerium nitrate of 0.624:0.3, and the maximum current density of the obtained catalyst can reach 97.61 mA / cm 2 , and the initial potential can be as low as 0.53 (V vs RHE), with the best catalytic activity;

[0021] (3) By changing the concentration of the precursors in the hydrothermal reaction at high temperature and controlling the nickel / cerium ratio, the present invention changes the catalytic performance of the catalyst. Compared with other preparation methods, the CeO2-Ni(OH)2 composite catalyst synthesized by the method of the present invention has more advantages in AOR. Description of the Drawings

[0022] Figure 1 : It is the XRD pattern of 30% CeO2-Ni(OH)2 obtained in Example 3 of the present invention.

[0023] Figure 2 : It is a performance comparison diagram of AOR and OER of the catalysts obtained in Examples 1-5 and Comparative Examples 1-2 of the present invention respectively; among them, (a) and (b) are CV and LSV curves respectively, showing the performance comparison diagram of AOR in a mixed solution formed by 1M KOH aqueous solution and 0.5M NH4Cl aqueous solution; (c) and (d) are CV and LSV curves respectively, showing the performance comparison diagram of oxygen evolution reaction (OER) in 1M KOH aqueous solution.

[0024] Figure 3 : It is the double-layer capacitance (Cdl) diagram of the catalysts obtained in Examples 1-5 and Comparative Examples 1-2 of the present invention respectively in a mixed solution formed by 1M KOH aqueous solution and 0.5M NH4Cl aqueous solution.

[0025] Figure 4 : It is a performance comparison diagram of AOR and OER of the samples of CeO2-Ni(OH)2 composite catalysts synthesized with different nickel sources obtained in Example 3 and Examples 6-8 of the present invention respectively; among them, (a) and (b) are CV and LSV curves respectively, showing the performance comparison diagram of AOR in a mixed solution formed by 1M KOH and 0.5M NH4Cl; (c) and (d) are CV and LSV curves respectively, showing the performance comparison diagram of OER in 1M KOH aqueous solution.

[0026] Figure 5: It is a performance comparison diagram of AOR and OER of the catalysts synthesized by using different cerium sources in Example 3 and Examples 9-11 of the present invention; among them, (a) and (b) are CV and LSV curves respectively, representing the AOR performance comparison diagram in a mixed solution formed by 1M KOH and 0.5M NH4Cl; (c) and (d) are CV and LSV curves respectively, representing the OER performance comparison diagram in a mixed solution formed by 1M KOH and 0.5M NH4Cl.

[0027] Figure 6 : It is a performance comparison diagram of AOR and OER of the catalysts obtained by Example 3 and Comparative Examples 3-4 of the present invention according to different methods respectively; among them, (a) and (b) are CV and LSV curves respectively, representing the AOR performance comparison diagram in a mixed solution formed by 1M KOH and 0.5M NH4Cl; (c) and (d) are CV and LSV curves respectively, representing the OER performance comparison diagram in 1M KOH aqueous solution.. Detailed implementation manners

[0028] The present invention will be described in detail below with reference to examples. It should be understood, however, that the following examples are merely illustrative of the implementation manners of the present invention and do not limit the scope of the present invention.

[0029] The preparation method of the working electrode in the following examples of the present invention is as follows:

[0030] First, weigh 2.5 mg of CeO2-Ni(OH)2 composite catalyst and 2.5 mg of activated carbon and add them to a mixed solution formed by 1 mL of absolute ethanol and 50 μL of Nafion aqueous solution with a mass concentration of 5%, and ultrasonically mix evenly to prepare a catalyst suspension. The catalyst suspension is added dropwise to the surface of the glassy carbon electrode head with an effective active area of 0.1256 cm 2 in small amounts and dried naturally to prepare a working electrode with a catalyst loading of 0.35 mg / cm 2 .

[0031] The electrochemical ammonia oxidation ammonia test is carried out in an electrode electrolytic cell reaction device, and the specific experimental conditions are as follows:

[0032] The working electrode uses a glassy carbon electrode loaded with a catalyst, the reference electrode uses an Ag / AgCl electrode (saturated KCl) (the final potential is corrected to the standard hydrogen electrode), and the counter electrode uses a platinum wire. The three electrodes are respectively connected to the corresponding electrode interfaces of the electrochemical workstation to form a three-electrode system.

[0033] Cyclic voltammetry (CV) is an experimental method based on the principle of the response of current to external potential to reflect the characteristics of an electrochemical system. Before the test, the working electrode is activated by rapid scanning to increase the active sites and generate active groups (such as ·OH, etc.), so as to achieve the purpose of improving the catalytic performance of the electrode material. The voltage test range is 0 - 0.8V. First, scan at a rate of 50 mV / s until the curves coincide, and then change the scan rate to 25 mV / s for scanning until the curves coincide.

[0034] Linear sweep voltammetry (LSV) is used to test the oxidation onset potential and current response value of the working electrode during the electrocatalytic oxidation of ammonia. The scan rate is 2 mV / s.

[0035] The double-layer capacitance (Cdl) is proportional to the electrochemically active specific surface area of the catalyst. It refers to the cyclic voltammetry scan carried out at scan rates of 20 mV / s, 40 mV / s, 60 mV / s, 80 mV / s, and 100 mV / s respectively within the non-Faraday reaction interval to obtain the relationship curve of scan rate - current density, and the linear fitting curve calculated on this basis.

[0036] Example 1

[0037] A preparation method of a CeO2-Ni(OH)2 composite catalyst (denoted as 10% CeO2-Ni(OH)2) is as follows:

[0038] (1) Weigh 0.025 g of ammonium cerium nitrate, 0.624 g of nickel sulfate hexahydrate, 0.12 g of acrylamide, and 0.8 g of hexamethylenetetramine, add them to 40 mL of deionized water, and stir evenly to obtain a mixed solution;

[0039] (2) Transfer the mixed solution to a high-pressure reaction kettle lined with polytetrafluoroethylene, and react at a constant temperature of 180 °C in an oven for 6 h;

[0040] (3) After the reaction is completed, cool to room temperature, take out the reaction kettle, and centrifuge and wash the precipitate obtained by filtering the reaction solution 3 times with deionized water and absolute ethanol respectively;

[0041] (4) After washing, dry the collected solid product in a drying oven at 70 °C for 7 h to obtain a light green powder, namely the CeO2-Ni(OH)2 composite catalyst. The mass percentage of CeO2 in the obtained CeO2-Ni(OH)2 composite catalyst is 10%.

[0042] The CeO2-Ni(OH)2 composite catalyst obtained in Example 1 was made into a working electrode and subjected to electrocatalytic ammonia oxidation testing. The test results are shown in the attached Figure 2As shown, (a) and (b) are the CV and LSV curves respectively, showing the comparison diagram of the catalytic effect of the AOR (AOR) performance of the working electrode in a mixed solution formed by 1M KOH aqueous solution and 0.5M NH4Cl aqueous solution in a volume ratio of 2:1; (c) and (d) are the CV and LSV curves respectively, showing the comparison diagram of the catalytic effect of the OER (OER) performance of the working electrode in 1M KOH aqueous solution. As shown in the attached Figure 2 From (b), it can be seen that the initial potential of the working electrode obtained in Example 1 is 0.61 (V vs RHE), and the current density at 0.78V is 28.79mA / cm 2 .

[0043] Example 2 is the same as Example 1, except that the addition amount of ammonium cerium nitrate in Example 2 is 0.18g. The mass percentage of CeO2 in the CeO2-Ni(OH)2 composite catalyst obtained in Example 2 is 20%, and the CeO2-Ni(OH)2 composite catalyst obtained in Example 2 is denoted as 20% CeO2-Ni(OH)2. After testing, as shown in the attached Figure 2 From (b), it can be seen that the initial potential of the working electrode obtained in Example 2 is 0.56 (V vs RHE), and the current density at 0.78V is 74.09mA / cm 2 .

[0044] Example 3 is the same as Example 1, except that the addition amount of ammonium cerium nitrate in Example 3 is 0.30g. The mass percentage of CeO2 in the CeO2-Ni(OH)2 composite catalyst obtained in Example 3 is 30%, and the CeO2-Ni(OH)2 composite catalyst obtained in Example 3 is denoted as 30% CeO2-Ni(OH)2. After testing, as shown in the attached Figure 2 From (b), it can be seen that the initial potential of the working electrode obtained in Example 3 is 0.53 (V vs RHE), and the current density at 0.78V is 97.61mA / cm 2 .

[0045] Example 4 is the same as Example 1, except that the addition amount of ammonium cerium nitrate in Example 4 is 0.378g. The mass percentage of CeO2 in the CeO2-Ni(OH)2 composite catalyst obtained in Example 4 is 35%, and the CeO2-Ni(OH)2 composite catalyst obtained in Example 4 is denoted as 35% CeO2-Ni(OH)2. After testing, as shown in the attached Figure 2 From (b), it can be seen that the initial potential of the working electrode obtained in Example 4 is 0.62 (V vs RHE), and the current density at 0.78V is 19.26mA / cm 2 .

[0046] Example 5 is the same as Example 1, except that the addition amount of ammonium cerium nitrate in Example 5 is 0.468 g. The mass percentage of CeO2 in the CeO2-Ni(OH)2 composite catalyst obtained in Example 5 is 40%, and the CeO2-Ni(OH)2 composite catalyst obtained in Example 5 is denoted as 40% CeO2-Ni(OH)2. After testing, as shown in Figure 2 (b) of the specification, the initial potential of the working electrode obtained in Example 5 is 0.64 (V vs RHE), and the current density at 0.78 V is 13.53 mA / cm 2 .

[0047] Comparative Example 1 is the same as Example 3, except that nickel sulfate hexahydrate is not added in Comparative Example 1. The catalyst obtained in Comparative Example 1 is denoted as CeO2. After testing, as shown in Figure 2 (b) of the specification, the initial potential of the working electrode obtained in Comparative Example 1 is 0.79 (V vs RHE), and the current density at 0.78 V is 2.03 mA / cm 2 .

[0048] Comparative Example 2 is the same as Example 3, except that ammonium cerium nitrate is not added in Comparative Example 2. The catalyst obtained in Comparative Example 2 is denoted as Ni(OH)2. After testing, as shown in Figure 2 (b) of the specification, the initial potential of the working electrode obtained in Comparative Example 2 is 0.6 (V vs RHE), and the current density at 0.78 V is 31.76 mA / cm 2 .

[0049] Example 6 is the same as Example 3, except that nickel chloride hexahydrate is used to replace nickel sulfate hexahydrate in Example 6, and the addition amount of nickel chloride hexahydrate is 0.69 g. The mass percentage of CeO2 in the composite catalyst obtained in Example 6 is 30%, and the composite catalyst obtained in Example 6 is denoted as 30% CeO2-Ni(OH)2-Ni(NO3)2. As shown in Figure 4 (b) of the specification, the initial potential of the working electrode obtained in Example 6 is 0.62 (V vs RHE), and the current density at 0.78 V is 25.81 mA / cm 2 .

[0050] Example 7 is the same as Example 3, except that nickel nitrate hexahydrate is used to replace nickel sulfate hexahydrate in Example 7, and the addition amount of nickel nitrate hexahydrate is 0.56 g. The mass percentage of CeO2 in the composite catalyst obtained in Example 7 is 30%, and the composite catalyst obtained in Example 7 is denoted as 30% CeO2-Ni(OH)2-NiCl2. As shown in Figure 4As can be seen from (b), the initial potential of the working electrode obtained in Example 7 is 0.63 (V vs RHE), and the current density at 0.78 V is 28.12 mA / cm 2 .

[0051] Example 8 is the same as Example 3, except that nickel acetate tetrahydrate is used to replace nickel sulfate hexahydrate in Example 8, and the addition amount of nickel acetate tetrahydrate is 0.587 g. The mass percentage of CeO2 in the composite catalyst obtained in Example 8 is 30%, and the composite catalyst obtained in Example 8 is denoted as 30% CeO2-Ni(OH)2-Ni(CH3COO)2. As shown in the attached Figure 4 As can be seen from (b), the initial potential of the working electrode obtained in Example 8 is 0.61 (V vs RHE), and the current density at 0.78 V is 45.64 mA / cm 2 .

[0052] Example 9 is the same as Example 3, except that cerium nitrate hexahydrate is used to replace ammonium cerium nitrate in Example 9, and the addition amount of cerium nitrate hexahydrate is 0.24 g. The mass percentage of CeO2 in the composite catalyst obtained in Example 9 is 30%, and the composite catalyst obtained in Example 9 is denoted as 30% CeO2-Ni(OH)2-Ce(NO3)3. As shown in the attached Figure 5 As can be seen from (b), the initial potential of the working electrode obtained in Example 9 is 0.64 (V vs RHE), and the current density at 0.78 V is 12.01 mA / cm 2 .

[0053] Example 10 is the same as Example 3, except that cerium chloride heptahydrate is used to replace ammonium cerium nitrate in Example 10, and the addition amount of cerium chloride heptahydrate is 0.20 g. The mass percentage of CeO2 in the composite catalyst obtained in Example 10 is 30%, and the composite catalyst obtained in Example 10 is denoted as 30% CeO2-Ni(OH)2-CeCl3. As shown in the attached Figure 5 As can be seen from (b), the initial potential of the working electrode obtained in Example 10 is 0.53 (V vs RHE), and the current density at 0.78 V is 47 mA / cm 2 .

[0054] Example 11 is the same as Example 3, except that cerium acetate tetrahydrate is used to replace ammonium cerium nitrate in Example 11, and the addition amount of cerium acetate tetrahydrate is 0.17 g. The mass percentage of CeO2 in the composite catalyst obtained in Example 10 is 30%, and the composite catalyst obtained in Example 11 is denoted as 30% CeO2-Ni(OH)2-(CH3COO)3. As shown in the attached Figure 5(b) It can be seen that the initial potential of the working electrode obtained in Example 11 is 0.64 (V vs RHE), and the current density at 0.78 V is 11.83 mA / cm 2 .

[0055] Comparative Example 3

[0056] The CeO2-Ni(OH)2 composite catalyst was synthesized by the coprecipitation method, and the specific method is as follows:

[0057] (1) Weigh 0.3 g of ammonium cerium nitrate and 0.624 g of nickel sulfate hexahydrate, add them to 30 mL of deionized water, and stir evenly to obtain a mixed solution;

[0058] (2) Add 1 mol / L NaOH solution dropwise to the mixed solution, adjust the solution pH = 13, let it stand and age for 24 hours, and then centrifuge and wash it 3 times with deionized water and absolute ethanol in turn;

[0059] (3) The obtained centrifuged solid separation was dried in an oven at 70 °C for 7 h, and then calcined in a muffle furnace. It was calcined at 200 °C for 3 h to obtain the CeO2-Ni(OH)2 composite catalyst. The mass percentage content of CeO2 in the composite catalyst was 30%. The obtained CeO2-Ni(OH)2 composite catalyst was denoted as 30% CeO2-Ni(OH)2-coprecipitation. As shown in the appendix of the specification Figure 6 (b) It can be seen that the initial potential of the working electrode obtained in Comparative Example 3 is 0.53 (V vs RHE), and the current density at 0.78 V is 50 mA / cm 2 .

[0060] Comparative Example 4

[0061] The CeO2-Ni(OH)2 composite catalyst was synthesized by the impregnation method, and the specific method is as follows:

[0062] (1) Weigh 0.624 g of nickel sulfate hexahydrate, add it to 30 mL of deionized water, and stir evenly to obtain a nickel sulfate solution;

[0063] (2) Add 0.078 g of the catalyst CeO2 obtained in Comparative Example 1 to the nickel sulfate solution and stir and impregnate for 6 h;

[0064] (3) After the stirring impregnation is completed, add 1 mol / L NaOH aqueous solution dropwise to the reaction system, adjust the solution pH = 13, and then place the solution in an oven and dry it at a constant temperature of 70 °C to obtain a light green powder, and obtain the composite catalyst, denoted as 30% CeO2-Ni(OH)2-impregnation. As shown in the appendix of the specification Figure 6 (b) It can be seen that the initial potential of the working electrode obtained in Comparative Example 4 is 0.58 (V vs RHE), and the current density at 0.78 V is 28 mA / cm2 。

[0065] The XRD pattern of the 30% CeO2-Ni(OH)2 obtained in Example 3 is shown in the appendix of the specification Figure 1 As shown, the characteristic diffraction peaks of the 30% CeO2-Ni(OH)2 obtained in Example 3 are in agreement with the standard cards of α-Ni(OH)2 (No. JCPDS 22-0444) and CeO2 (No. JCPDS 78-0694), indicating that the CeO2-Ni(OH)2 composite catalyst was successfully synthesized in Example 3.

[0066] The performance comparison diagrams of AOR and OER of the catalysts obtained in Examples 1-5 and Comparative Examples 1-2 are shown in the appendix of the specification Figure 2 as shown.

[0067] From the comparison between Figure 2 (a) in the appendix of the specification and Figure 2 (c) in the appendix of the specification, it can be known that, that is, the comparison of CV curves. In the positive scan, for the same catalyst, in the mixed solution formed by KOH and NH4Cl, the current density of the working electrode increases significantly, indicating that the CeO2-Ni(OH)2 composite catalyst has an obvious catalytic effect on ammonia oxidation, and with the increase of the cerium oxide composite amount, the current density shows a trend of first rising and then falling. Among them, the maximum current density of the working electrode obtained in Example 3 reaches 97.61 mA / cm 2 , and the initial potential is as low as 0.53 (V vs RHE), with the best catalytic activity.

[0068] From the comparison between Figure 2 (b) in the appendix of the specification and Figure 2 (d) in the appendix of the specification, it can be known that, that is, the comparison of LSV curves, which further verifies that with the increase of the CeO2 content in the composite catalyst, the working electrode has a higher selectivity for AOR and has an advantage in the competition with OER, and its current density is much larger than that of OER, and the initial potential is lower.

[0069] The double-layer capacitance (Cdl) diagrams of the catalysts obtained in Examples 1-5 and Comparative Examples 1-2 in the mixed solution formed by 1M KOH and 0.5M NH4Cl according to the volume ratio of 2:1 are shown in the appendix of the specification Figure 3 as shown; the double-layer capacitance value of the working electrode obtained in Example 3 is the largest, which is 1.67 mF / cm 2 , having the best electrochemically active specific surface area and the highest catalytic activity, and its trend is consistent with the activity curve.

[0070] The performance comparison diagrams of AOR and OER of the catalysts obtained in Example 3 and Examples 6-8 are shown in the appendix of the specification Figure 4 as shown.

[0071] From the appended specification Figure 4 (a) and the appended specification Figure 4 (c) comparison shows that, namely the CV curve comparison. In the forward scan, for the same catalyst, in a mixed solution formed by 1M KOH aqueous solution and 0.5M NH4Cl aqueous solution in a volume ratio of 2:1, its current density increases significantly, indicating that the CeO2-Ni(OH)2 composite catalyst has an obvious catalytic effect on AOR, and with different nickel sources, its ammonia electrooxidation performance has significant differences;

[0072] Among them, the catalytic activity of 30% CeO2-Ni(OH)2 synthesized with nickel sulfate as the nickel source in Example 3 is the best, and its maximum current density reaches 97.61 mA / cm 2 , and the starting potential is as low as 0.53 (V vs RHE).

[0073] From the appended specification Figure 4 (b) and the appended specification Figure 4 (d) comparison shows that, namely the LSV curve comparison, further verifying that with different nickel sources, the AOR activity of the obtained CeO2-Ni(OH)2 composite catalyst is different.

[0074] The performance comparison diagrams of AOR and OER of the catalysts obtained in Example 3 and Examples 9 - 11 respectively are as shown in the appended specification Figure 5 as shown

[0075] From as shown in the appended specification Figure 5 (a) and as shown in the appended specification Figure 5 (c) comparison shows that, namely the CV curve comparison. In the forward scan, for the same catalyst, in a mixed solution formed by 1M KOH aqueous solution and 0.5M NH4Cl aqueous solution in a volume ratio of 2:1, its current density increases significantly, indicating that the CeO2-Ni(OH)2 composite catalyst has an obvious catalytic effect on AOR, and with different cerium sources, its ammonia electrooxidation performance has significant differences;

[0076] Among them, the catalytic activity of 30% CeO2-Ni(OH)2 synthesized with ammonium cerium nitrate as the cerium source in Example 3 is the best, and the maximum current density of the working electrode obtained in Example 3 reaches 97.61 mA / cm 2 , and the starting potential is as low as 0.53 (V vs RHE).

[0077] From the appended specification Figure 5 (b) and the appended specification Figure 5 (d) comparison shows that, namely the LSV curve comparison, further verifying that with different cerium sources, its AOR activity is different.

[0078] The performance comparison diagrams of AOR and OER of the catalysts obtained in Example 3 and Comparative Examples 3-4 are shown in the attached Figure 6 specification.

[0079] As can be seen from the attached Figure 6 specification, compared with other synthesis methods, the CeO2-Ni(OH)2 catalyst synthesized by the method provided in the embodiments of the present invention has its catalytic activity for AOR increased several times.

[0080] Taking the above ideal embodiments based on the present invention as an inspiration, through the above description, relevant staff can completely make various changes and modifications without departing from the technical idea of this invention. The technical scope of this invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A CeO2-Ni(OH)2 composite catalyst, characterized in that, It includes the following preparation steps: (1) Add ammonium cerium nitrate, nickel sulfate hexahydrate, acrylamide and hexamethylenetetramine into deionized water. After stirring evenly, a mixed solution is prepared. (2) Transfer the mixed solution to a high-pressure reactor with a polytetrafluoroethylene lining and carry out a constant-temperature reaction. (3) After the constant-temperature reaction is completed, cool it to room temperature, take out the reactor. The obtained reaction solution is successively centrifuged, washed and dried to obtain a solid powder, which is the CeO2-Ni(OH)2 composite catalyst.

2. The CeO2-Ni(OH)2 composite catalyst according to claim 1, wherein The mass ratio of nickel sulfate hexahydrate to acrylamide and hexamethylenetetramine is 0.624:0.12:0.

8.

3. The CeO2-Ni(OH)2 composite catalyst according to claim 2, characterized in that, The mass concentration of nickel sulfate hexahydrate in deionized water is 0.0150 mL - 0.0160 g / mL.

4. The CeO2-Ni(OH)2 composite catalyst according to claim 3, characterized in that, The mass concentration of nickel sulfate hexahydrate in deionized water is 0.0156 ± 0.0002 g / mL.

5. The CeO2-Ni(OH)2 composite catalyst according to claim 1, wherein, The reaction temperature in step (2) is 180 ± 2 °C.

6. The CeO2-Ni(OH)2 composite catalyst according to claim 1, wherein The reaction time in step (2) is at least 6 h.

7. A CeO2-Ni(OH)2 composite catalyst according to claim 1, wherein, The washing in step (3) successively includes water washing and anhydrous ethanol washing.

8. The CeO2-Ni(OH)2 composite catalyst according to claim 1, characterized in that, The drying temperature in step (3) is 45 - 70 °C.

9. The CeO2-Ni(OH)2 composite catalyst according to claim 1, wherein, The mass percentage of CeO2 in the CeO2-Ni(OH)2 composite catalyst is 30%.

10. An electrochemical catalytic system for AOR, characterized in that, Use the CeO2-Ni(OH)2 composite catalyst described in any one of claims 1 - 9 as the electrocatalytic active substance on the surface of the working electrode.

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