Cobalt-based electrocatalyst and preparation method and application thereof

Abstract

The invention discloses a cobalt-based electrocatalyst and a preparation method and application thereof.The preparation method of the cobalt-based electrocatalyst comprises the following steps that a cobalt-based pre-catalyst is activated under constant current or constant voltage, so that the cobalt-based pre-catalyst is partially or completely converted into beta-Co (OH) 2, and the cobalt-based electrocatalyst is prepared; and the cobalt-based pre-catalyst is selected from at least one of Co3O4, alpha-Co (OH) 2, CoN, CoS2, CoP and CoSe2. According to the method, the cobalt-based pre-catalyst (alpha-Co (OH) 2, CoP, CoN, Co3O4, CoSe2 and CoS2) is subjected to constant-current activation or constant-voltage activation, so that the cobalt-based pre-catalyst is reconstructed, and part or all of the cobalt-based pre-catalyst is converted into a beta-Co (OH) 2 phase, and therefore, the ammonia production yield of nitrate radicals of the prepared cobalt-based electro-catalyst and the Faraday efficiency are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the field of catalysts, and in particular relates to a cobalt-based electrocatalyst and a preparation method and application thereof. Background Art

[0002] With the rapid increase in the emission of nitrogen-containing pollutants, nitrates in groundwater continue to accumulate, water bodies become eutrophic, and excessive nitrates in surface water and drinking water all pose certain threats to human health. Therefore, it is necessary to remove nitrates from surface water and drinking water. Among the many technologies for removing nitrates, electrocatalytic nitrate removal is considered to be a very promising solution that is expected to meet the growing demand for nitrate removal. In addition, the traditional ammonia production method (Haber-Bosch process) consumes a large amount of fossil fuels and releases a large amount of greenhouse gases, resulting in inevitable energy scarcity and environmental pollution problems. "Green ammonia" refers to ammonia (NH3) produced using renewable energy. At present, among the many methods for producing "green ammonia", the electrocatalytic nitrate reduction reaction (e-NO3RR) is considered to be a very promising way to produce ammonia. Therefore, reducing nitrates to high-value ammonia provides great possibilities for environmental remediation and energy transformation. How to improve the industrial application efficiency of e-NO3RR has attracted more and more attention, and the design of new catalysts is one of the key factors. At present, there is no catalyst that can achieve efficient electrocatalytic nitrate reduction reaction. Summary of the invention

[0003] In order to overcome the problems existing in the prior art, one of the objectives of the present invention is to provide a cobalt-based electrocatalyst.

[0004] A second object of the present invention is to provide a method for preparing the above-mentioned cobalt-based electrocatalyst.

[0005] A third object of the present invention is to provide application of the above-mentioned cobalt-based electrocatalyst and / or the method for preparing the cobalt-based electrocatalyst in the field of electrocatalytic nitrate reduction.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A first aspect of the present invention provides a cobalt-based electrocatalyst comprising β-Co(OH)2.

[0008] Preferably, the cobalt-based electrocatalyst is β-Co(OH)2.

[0009] Preferably, the cobalt-based electrocatalyst further comprises at least one compound selected from Co3O4, CoS2, CoP, and CoSe2.

[0010] The second aspect of the present invention provides a method for preparing the cobalt-based electrocatalyst according to the first aspect of the present invention, comprising the following steps:

[0011] The cobalt-based precatalyst is activated under constant current or constant voltage to obtain a catalyst;

[0012] The cobalt-based precatalyst is selected from at least one of Co3O4, α-Co(OH)2, CoN, CoS2, CoP, and CoSe2.

[0013] Preferably, the preparation method is: assembling electrodes containing cobalt-based pre-catalysts into a three-electrode system, activating them in an electrolyte using a constant current method or a constant voltage method, so that the cobalt-based pre-catalyst is partially or completely converted into β-Co(OH)2.

[0014] Preferably, the electrolyte contains potassium nitrate and potassium hydroxide.

[0015] Preferably, in the electrolyte, the molar ratio of potassium nitrate to potassium hydroxide is 1:(8-12).

[0016] Preferably, when the activation method is constant current, the activation current is -10 to -200 mA / cm -2 .

[0017] Preferably, when the constant current method is used for activation, the activation time is 1 to 15 hours.

[0018] Preferably, when the activation is performed by a constant voltage method, the activation voltage is -0.1 to -0.5V.

[0019] Preferably, when the activation method is adopted, the activation time is 1 to 2 hours.

[0020] The third aspect of the present invention provides the use of the cobalt-based electrocatalyst described in the first aspect of the present invention and / or the method for preparing the cobalt-based electrocatalyst described in the second aspect of the present invention in the field of electrocatalytic nitrate reduction.

[0021] The beneficial effect of the present invention is that the present invention reconstructs the cobalt-based precatalyst (α-Co(OH)2, CoP, CoN, Co3O4, CoSe2, CoS2) by constant current activation or constant voltage activation, and partially or completely converts it into β-Co(OH)2 phase, thereby significantly improving the yield and Faraday efficiency of the prepared cobalt-based electrocatalyst in electrocatalytic nitrate reduction to produce ammonia. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 2 is the XRD pattern of the Co3O4 precatalyst and the cobalt-based electrocatalyst in Example 2.

[0023] Figure 2This is a test chart of the yield and Faraday efficiency of nitrate reduction to ammonia using the Co3O4 precatalyst and cobalt-based electrocatalyst in Example 2.

[0024] Figure 3 : XRD patterns of the CoN precatalyst and the cobalt-based electrocatalyst in Example 4.

[0025] Figure 4 This is a test graph of the yield and Faraday efficiency of nitrate reduction to ammonia using the CoN precatalyst and cobalt-based electrocatalyst in Example 4.

[0026] Figure 5 : XRD patterns of CoP precatalyst and cobalt-based electrocatalyst in Example 5.

[0027] Figure 6 This is a test graph of the yield and Faraday efficiency of nitrate reduction to ammonia using CoP precatalyst and cobalt-based electrocatalyst in Example 5.

[0028] Figure 7 2. XRD patterns of CoSe2 precatalyst and cobalt-based electrocatalyst in Example 6.

[0029] Figure 8 This is a test chart of the yield and Faraday efficiency of nitrate reduction to ammonia using CoSe2 precatalyst and cobalt-based electrocatalyst in Example 6. DETAILED DESCRIPTION

[0030] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that if there are processes that are not particularly described in detail below, they can be implemented or understood by those skilled in the art with reference to the prior art. The reagents or instruments used that do not indicate the manufacturer are all conventional products that can be purchased commercially.

[0031] The preparation method of the precatalyst used in the embodiment of the present invention is as follows:

[0032] (1) Synthesis of α-Co(OH)2: α-Co(OH)2 nanosheets were synthesized by rapid electrochemical deposition. The specific steps are as follows: a three-electrode system was used, with carbon cloth as the working electrode, platinum sheet as the counter electrode, saturated calomel electrode as the reference electrode, and 0.15 mol / L cobalt nitrate solution as the electrolyte. The constant current method was used to electro-deposit at a constant current of -25 mA for 10 minutes.

[0033] The carbon cloth must be processed before use: cut it into a size of 1.25 cm × 2 cm, soak it in piranha solution (concentrated sulfuric acid and hydrogen peroxide prepared in a volume ratio of 3:1) for 15 minutes, and then rinsed with deionized (DI) water to remove surface impurities.

[0034] (2) Synthesis of Co3O4: The prepared α-Co(OH)2 was placed in a tubular furnace and heated to 400°C at a rate of 2°C / min. The temperature was kept at that temperature for 2 hours. The sample obtained after cooling in the furnace was Co3O4.

[0035] (3) Synthesis of CoP: CoP was synthesized by phosphating α-Co(OH)2. 1 g of NaH2PO2 was used as a phosphorus source, nitrogen was introduced as a protective gas and carrier gas, α-Co(OH)2 was placed downstream of the gas flow, the temperature was raised to 400°C at a rate of 2°C / min, maintained for 2 hours, and CoP was obtained after cooling.

[0036] (4) Synthesis of CoN: CoN is obtained by nitriding α-Co(OH)2. In an Ar / NH3 gas mixture, α-Co(OH)2 is heated to 400°C at a rate of 2°C / min, maintained for 2 hours, and cooled to obtain CoN.

[0037] (5) Synthesis of CoS2: CoS2 was prepared by sulfiding α-Co(OH)2. α-Co(OH)2 was placed in a tube furnace, and 1 g of sulfur powder was placed upstream of the tube furnace. CoS2 was synthesized by annealing at 400°C at a rate of 2°C / min and holding for 2 hours under a N2 atmosphere.

[0038] (6) Synthesis of CoSe2: CoSe2 was prepared by selenization of α-Co(OH)2. α-Co(OH)2 was placed on a glass boat, and 2 g of Se powder was placed upstream of a tube furnace. In an Ar / H2 atmosphere, annealing was performed at 600°C and maintained for 2 hours, and CoSe2 was obtained after cooling.

[0039] The nitrate reduction performance test method in the embodiment of the present invention is: the carbon cloth loaded with cobalt-based electrocatalyst prepared in the embodiment is used as the working electrode, the Pt sheet is used as the counter electrode, the mercury-mercury oxide electrode is used as the reference electrode, the electrolyte is a mixed solution of 1 mol / L KOH and 0.1 mol / L KNO3, the test voltage range is 0 to -0.6 V (vs. RHE), a constant voltage test is performed for one hour at each potential, the electrolyte in the cathode tank is taken for product concentration analysis, and the yield and Faraday efficiency are calculated.

[0040] Example 1

[0041] This example provides a method for preparing a cobalt-based electrocatalyst, and the specific steps are as follows:

[0042] 1) Prepare 100 mL of 1 mol / L potassium hydroxide (KOH) solution, add 1.01 g of potassium nitrate (KNO3) to the solution, mix well, and use it as an electrolyte.

[0043] 2) Using a three-electrode system, the carbon cloth loaded with α-Co(OH)2 precatalyst is used as the working electrode, the Pt sheet is used as the counter electrode, the mercury-mercury oxide electrode is used as the reference electrode, and the electrolyte is the electrolyte prepared in step 1). The activation is carried out in a constant current manner, and the current density used for activation is -10 mA cm -2 The activation time is 12 hours. After activation, the sample is cleaned with deionized water to obtain the cobalt-based electrocatalyst in this example. The cobalt-based electrocatalyst in this example is the reconstructed phase β-Co(OH)2.

[0044] The nitrate reduction performance of the α-Co(OH)2 precatalyst and the cobalt-based electrocatalyst samples in this example was tested, and the specific test results are shown in Table 1 below.

[0045] Table 1 Ammonia yield and Faraday efficiency test results

[0046]

[0047] From the test results in Table 1, it can be seen that the yield of ammonia produced by nitrate and the Faraday efficiency of the cobalt-based electrocatalyst obtained after activation in this example are improved.

[0048] Example 2

[0049] This example provides a method for preparing a cobalt-based electrocatalyst, and the specific steps are as follows:

[0050] 1) Prepare 100 mL of 1 mol / L potassium hydroxide (KOH) solution, add 1.01 g of potassium nitrate (KNO3) to the solution, mix well, and use it as an electrolyte.

[0051] 2) Using a three-electrode system, the carbon cloth loaded with Co3O4 precatalyst was used as the working electrode, the Pt sheet was used as the counter electrode, and the mercury-mercury oxide electrode was used as the reference electrode. The activation was carried out in a constant current manner. The activation process was accompanied by structural evolution. The electrolyte was the electrolyte in step 1). The current density used for activation was -10 mA cm -2 The activation time is 12 hours, and the obtained sample is washed with deionized water to obtain the cobalt-based electrocatalyst in this example. The cobalt-based electrocatalyst in this example contains Co3O4 and β-Co(OH)2 generated after partial reconstruction of Co3O4.

[0052] The XRD patterns of the Co3O4 precatalyst and the activated cobalt-based electrocatalyst in this example were measured by X-ray diffractometer. Figure 1 As shown by Figure 1 It can be seen that the Co3O4 precatalyst was activated under constant current, and part of the Co3O4 underwent structural reconstruction to generate β-Co(OH)2.

[0053] The nitrate reduction performance of the Co3O4 precatalyst and the activated cobalt-based electrocatalyst in this example was tested. The specific test results are shown in Figure 2 As shown in Table 2, Figure 2 The bar graph in the figure represents the ammonia production rate, and the dotted line graph represents the Faraday efficiency of ammonia production.

[0054] Table 2 Ammonia yield and Faraday efficiency test results

[0055]

[0056] Depend on Figure 2 As shown in Table 2, compared with the Co3O4 pre-catalyst, the yield and Faraday efficiency of nitrate production of ammonia in the activated cobalt-based electrocatalyst in this example are significantly improved.

[0057] Example 3

[0058] This example provides a method for preparing a cobalt-based electrocatalyst, and the specific steps are as follows:

[0059] 1) Prepare 100 ml of 1 mol / L potassium hydroxide (KOH) solution, add 1.01 g of potassium nitrate (KNO3) to the solution, mix well, and use it as an electrolyte.

[0060] 2) Using a three-electrode system, the carbon cloth loaded with CoS2 precatalyst is used as the working electrode, the Pt sheet is used as the counter electrode, and the mercury-mercury oxide electrode is used as the reference electrode. The activation is carried out in a constant current manner, and the activation process is accompanied by structural evolution. The electrolyte is the electrolyte prepared in step 1). The current density used for activation is -10mA·cm -2 The time is 12 hours. The obtained sample is cleaned with deionized water to obtain the cobalt-based electrocatalyst in this example. The cobalt-based electrocatalyst in this example contains CoS2 and a phase β-Co(OH)2 generated by partial reconstruction of CoS2.

[0061] The nitrate reduction performance of the CoS2 precatalyst and cobalt-based electrocatalyst samples in this example was tested, and the specific test results are shown in Table 3 below.

[0062] Table 3 Ammonia yield and Faraday efficiency test results

[0063]

[0064]

[0065] It can be seen from the test results in Table 3 that the yield of ammonia produced by nitrate and the Faraday efficiency of the cobalt-based electrocatalyst obtained after activation in this example are improved.

[0066] Example 4

[0067] This example provides a method for preparing a cobalt-based electrocatalyst, and the specific steps are as follows:

[0068] 1) Prepare 100 ml of 1 mol / L potassium hydroxide (KOH) solution, add 1.01 g of potassium nitrate (KNO3) to the solution, mix well, and use it as an electrolyte.

[0069] 2) Using a three-electrode system, the carbon cloth loaded with CoN precatalyst is used as the working electrode, the Pt sheet is used as the counter electrode, and the mercury-mercury oxide electrode is used as the reference electrode. The activation is carried out in a constant current manner, and the structural evolution is accompanied by the activation process. The electrolyte is the electrolyte in step 1). The current density used for activation is -10mA·cm -2 The time is 1 hour. The obtained sample is cleaned with deionized water to obtain the cobalt-based electrocatalyst in this example. The cobalt-based electrocatalyst in this example is the phase β-Co(OH)2 reconstructed by CoN.

[0070] The XRD patterns of the CoN precatalyst and the activated cobalt-based electrocatalyst in this example were measured by X-ray diffractometer. Figure 3 As shown by Figure 3 It can be seen that the CoN precatalyst was activated under constant current and its structure was reconstructed to generate β-Co(OH)2.

[0071] The nitrate reduction performance of the CoN precatalyst and the activated cobalt-based electrocatalyst in this example was tested, and the results were as follows: Figure 4 As shown in Table 4 below, Figure 4 The bar graph in the figure represents the ammonia production rate, and the dotted line graph represents the Faraday efficiency of ammonia production.

[0072] Table 4 Ammonia yield and Faraday efficiency test results

[0073]

[0074]

[0075] Depend on Figure 4 As shown in Table 4, compared with the CoN pre-catalyst, the yield and Faraday efficiency of nitrate production of ammonia in the activated cobalt-based electrocatalyst in this example are significantly improved.

[0076] Example 5

[0077] This example provides a method for preparing a cobalt-based electrocatalyst, and the specific steps are as follows:

[0078] 1) Prepare 100 ml of 1 mol / L potassium hydroxide (KOH) solution, add 1.01 g of potassium nitrate (KNO3) to the solution, mix well, and use it as an electrolyte.

[0079] 2) Using a three-electrode system, the carbon cloth loaded with CoP precatalyst is used as the working electrode, the Pt sheet is used as the counter electrode, and the mercury-mercury oxide electrode is used as the reference electrode. The activation is carried out in a constant current manner, and the activation process is accompanied by structural evolution. The electrolyte is the electrolyte prepared in step 1). The current density used for activation is -10 mA cm -2 The sample was washed with deionized water to obtain the cobalt-based electrocatalyst in this example. The cobalt-based electrocatalyst in this example contained CoP and a phase β-Co(OH)2 generated by partial reconstruction of CoP.

[0080] The XRD patterns of the CoP precatalyst and the activated cobalt-based electrocatalyst in this example were measured by X-ray diffractometer. Figure 5 As shown by Figure 5 It can be seen that the CoP precatalyst was partially activated under constant current and its structure was reconstructed to generate β-Co(OH)2.

[0081] The nitrate reduction performance of the CoP precatalyst and the activated cobalt-based electrocatalyst in this example was tested, and the results were as follows: Figure 6 As shown in Table 5, Figure 6 The bar graph in the figure represents the ammonia production rate, and the dotted line graph represents the Faraday efficiency of ammonia production.

[0082] Table 5 Ammonia yield and Faraday efficiency test results

[0083]

[0084]

[0085] Depend on Figure 6 As shown in Table 5, compared with the CoP pre-catalyst, the yield of ammonia produced by nitrate and the Faradaic efficiency of the activated cobalt-based electrocatalyst in this example are significantly improved.

[0086] Example 6

[0087] This example provides a method for preparing a cobalt-based electrocatalyst, and the specific steps are as follows:

[0088] 1) Prepare 100 ml of 1 mol / L potassium hydroxide (KOH) solution, add 1.01 g of potassium nitrate (KNO3) to the solution, mix well, and use it as an electrolyte.

[0089] 2) Using a three-electrode system, the carbon cloth loaded with CoSe2 precatalyst is used as the working electrode, the Pt sheet is used as the counter electrode, and the mercury-mercury oxide electrode is used as the reference electrode. The activation is carried out in a constant current manner, and the activation process is accompanied by structural evolution. The electrolyte is the electrolyte prepared in step 1). The current density used for activation is -100 mA cm -2 The time is 12 hours. The obtained sample is cleaned with deionized water to obtain the cobalt-based electrocatalyst in this example. The cobalt-based electrocatalyst in this example contains CoSe2 and a phase β-Co(OH)2 generated by partial reconstruction of CoSe2.

[0090] The XRD patterns of CoSe2 and the activated cobalt-based electrocatalyst in this example were measured by X-ray diffractometer. Figure 7 As shown by Figure 7 It can be seen that the CoSe2 precatalyst was partially activated under constant current and its structure was reconstructed to generate β-Co(OH)2.

[0091] The nitrate reduction performance of the CoSe2 precatalyst and the activated cobalt-based electrocatalyst in this example was tested, and the results were as follows: Figure 8 As shown in Table 6, Figure 8 The bar graph in the figure represents the ammonia production rate, and the dotted line graph represents the Faraday efficiency of ammonia production.

[0092] Table 6 Ammonia yield and Faraday efficiency test results

[0093]

[0094]

[0095] Depend on Figure 8 As shown in Table 6, compared with the CoSe2 pre-catalyst, the yield of ammonia produced by nitrate and the Faradaic efficiency of the activated cobalt-based electrocatalyst in this example are significantly improved.

[0096] Example 7

[0097] This example provides a method for preparing a cobalt-based electrocatalyst, and the specific steps are as follows:

[0098] 1) Prepare 100 ml of 1 mol / L potassium hydroxide (KOH) solution, add 1.01 g of potassium nitrate (KNO3) to the solution, mix well, and use it as an electrolyte.

[0099] 2) Using a three-electrode system, the carbon cloth loaded with Co3O4 precatalyst is used as the working electrode, the Pt sheet is used as the counter electrode, and the mercury-mercury oxide electrode is used as the reference electrode. The activation is carried out in a constant current manner, and the activation process is accompanied by structural evolution. The electrolyte is the electrolyte prepared in step 1). The current density used for activation is -100 mA cm -2 The time is 12 hours. The obtained sample is cleaned with deionized water to obtain the cobalt-based electrocatalyst in this example. The cobalt-based electrocatalyst in this example contains Co3O4 and β-Co(OH)2 generated by partial reconstruction of Co3O4.

[0100] The nitrate reduction performance of the Co3O4 precatalyst and the cobalt-based electrocatalyst samples in this example was tested, and it was found that the yield of nitrate to produce ammonia and the Faraday efficiency of the cobalt-based electrocatalyst obtained after activation were improved.

[0101] Example 8

[0102] This example provides a method for preparing a cobalt-based electrocatalyst, and the specific steps are as follows:

[0103] 1) Prepare 100 ml of 1 mol / L potassium hydroxide (KOH) solution, add 1.01 g of potassium nitrate (KNO3) to the solution, mix well, and use it as an electrolyte.

[0104] 2) Using a three-electrode system, the carbon cloth loaded with Co3O4 precatalyst is used as the working electrode, the Pt sheet is used as the counter electrode, and the mercury-mercury oxide electrode is used as the reference electrode. The activation is carried out in a constant current manner, and the activation process is accompanied by structural evolution. The electrolyte is the electrolyte prepared in step 1). The current density used for activation is -200mA·cm -2 The time is 15 hours. The obtained sample is cleaned with deionized water to obtain the cobalt-based electrocatalyst in this example. The cobalt-based electrocatalyst in this example contains Co3O4 and β-Co(OH)2 generated by partial reconstruction of Co3O4.

[0105] The nitrate reduction performance of the Co3O4 precatalyst and the cobalt-based electrocatalyst samples in this example was tested, and it was found that the yield of nitrate to produce ammonia and the Faraday efficiency of the cobalt-based electrocatalyst obtained after activation were improved.

[0106] The cobalt-based electrocatalysts in Examples 1 to 8 were all activated by a constant current method to obtain activated cobalt-based electrocatalysts. The types of precatalysts, current density, current action time, and phase compositions of the reconstructed cobalt-based electrocatalysts used in the preparation of the cobalt-based electrocatalysts in Examples 1 to 8 are shown in Table 7 below.

[0107] Table 7 Preparation conditions of cobalt-based electrocatalysts in Examples 1 to 8

[0108]

[0109] Example 9

[0110] This example provides a method for preparing a cobalt-based electrocatalyst, and the specific steps are as follows:

[0111] 1) Prepare 100 ml of 1 mol / L potassium hydroxide (KOH) solution, add 1.01 g of potassium nitrate (KNO3) to the solution, mix well, and use it as an electrolyte.

[0112] 2) Using a three-electrode system, the carbon cloth loaded with α-Co(OH)2 precatalyst is used as the working electrode, the Pt sheet is used as the counter electrode, and the mercury-mercury oxide electrode is used as the reference electrode, and activation is carried out in a constant potential manner, and the activation process is accompanied by structural evolution. The electrolyte is the electrolyte prepared in step 1). The potential used for activation is -0.3V (relative to the reversible hydrogen electrode potential) and the time is 1 hour. The obtained sample is cleaned with deionized water to obtain the cobalt-based electrocatalyst in this example. The cobalt-based electrocatalyst in this example is the phase β-Co(OH)2 generated by the reconstruction of α-Co(OH)2.

[0113] The nitrate reduction performance of the α-Co(OH)2 precatalyst and cobalt-based electrocatalyst samples in this example was tested, and it was found that the yield of nitrate to ammonia and the Faraday efficiency of the cobalt-based electrocatalyst obtained after activation were improved.

[0114] Example 10

[0115] This example provides a method for preparing a cobalt-based electrocatalyst, and the specific steps are as follows:

[0116] 1) Prepare 100 ml of 1 mol / L potassium hydroxide (KOH) solution, add 1.01 g of potassium nitrate (KNO3) to the solution, mix well, and use it as an electrolyte.

[0117] 2) Using a three-electrode system, the carbon cloth loaded with α-Co(OH)2 precatalyst is used as the working electrode, the Pt sheet is used as the counter electrode, and the mercury-mercury oxide electrode is used as the reference electrode, and activation is carried out in a constant potential manner, and the activation process is accompanied by structural evolution. The electrolyte is the electrolyte prepared in step 1). The potential used for activation is -0.5V (relative to the reversible hydrogen electrode potential) and the time is 1 hour. The obtained sample is cleaned with deionized water to obtain the cobalt-based electrocatalyst in this example. The cobalt-based electrocatalyst in this example is the phase β-Co(OH)2 generated by the reconstruction of α-Co(OH)2.

[0118] The nitrate reduction performance of the α-Co(OH)2 precatalyst and cobalt-based electrocatalyst samples in this example was tested, and it was found that the yield of nitrate to ammonia and the Faraday efficiency of the cobalt-based electrocatalyst obtained after activation were improved.

[0119] Embodiment 11

[0120] This example provides a method for preparing a cobalt-based electrocatalyst, and the specific steps are as follows:

[0121] 1) Prepare 100 ml of 1 mol / L potassium hydroxide (KOH) solution, add 1.01 g of potassium nitrate (KNO3) to the solution, mix well, and use it as an electrolyte.

[0122] 2) Using a three-electrode system, the carbon cloth loaded with CoN precatalyst is used as the working electrode, the Pt sheet is used as the counter electrode, and the mercury-mercury oxide electrode is used as the reference electrode, and activation is carried out in a constant potential manner, and the activation process is accompanied by structural evolution. The electrolyte is the electrolyte prepared in step 1). The potential used for activation is -0.5V (relative to the reversible hydrogen electrode potential) and the time is 2 hours. The obtained sample is cleaned with deionized water to obtain the cobalt-based electrocatalyst in this example. The cobalt-based electrocatalyst in this example is the phase β-Co(OH)2 generated by the reconstruction of CoN.

[0123] The nitrate reduction performance of the CoN precatalyst and the cobalt-based electrocatalyst samples in this example was tested, and it was found that the yield of nitrate to ammonia and the Faraday efficiency of the cobalt-based electrocatalyst obtained after activation were improved.

[0124] Example 12

[0125] This example provides a method for preparing a cobalt-based electrocatalyst, and the specific steps are as follows:

[0126] 1) Prepare 100 ml of 1 mol / L potassium hydroxide (KOH) solution, add 1.01 g of potassium nitrate (KNO3) to the solution, mix well, and use it as an electrolyte.

[0127] 2) Using a three-electrode system, a carbon cloth loaded with a Co3O4 precatalyst is used as a working electrode, a Pt sheet is used as a counter electrode, and a mercury-mercury oxide electrode is used as a reference electrode, and activation is performed in a constant potential manner, and the activation process is accompanied by structural evolution. The electrolyte is the electrolyte prepared in step 1). The potential used for activation is -0.5V (relative to the reversible hydrogen electrode potential) and the time is 2 hours. The obtained sample is cleaned with deionized water to obtain the cobalt-based electrocatalyst in this example. The cobalt-based electrocatalyst in this example contains Co3O4 and a phase β-Co(OH)2 obtained by partial reconstruction of Co3O4.

[0128] The nitrate reduction performance of the Co3O4 precatalyst and the cobalt-based electrocatalyst samples in this example was tested, and it was found that the yield of nitrate to produce ammonia and the Faraday efficiency of the cobalt-based electrocatalyst obtained after activation were improved.

[0129] The cobalt-based electrocatalysts in Examples 9 to 12 were all activated by a constant voltage method to obtain activated cobalt-based electrocatalysts. The types of precatalysts, current density, current action time, and phase compositions of the reconstructed cobalt-based electrocatalysts used in the preparation of the cobalt-based electrocatalysts in Examples 9 to 12 are shown in Table 8 below.

[0130] Table 8 Preparation conditions of cobalt-based electrocatalysts in Examples 9 to 12

[0131]

[0132]

[0133] In summary, the present invention reconstructs the cobalt-based precatalyst (α-Co(OH)2, CoP, CoN, Co3O4, CoSe2, CoS2) by constant current activation or constant voltage activation, and partially or completely converts it into β-Co(OH)2 phase, thereby significantly improving the yield of nitrate to ammonia production and the Faraday efficiency of the prepared cobalt-based electrocatalyst.

[0134] The above is a detailed description of the embodiments of the present invention, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. A cobalt-based electrocatalyst, characterized in that: Including β-Co(OH)2.

2. The cobalt-based electrocatalyst according to claim 1, characterized in that: The cobalt-based electrocatalyst further comprises at least one compound selected from Co3O4, CoS2, CoP, and CoSe2.

3. The method for preparing a cobalt-based electrocatalyst according to any one of claims 1 to 2, characterized in that: The following steps are involved: The cobalt-based precatalyst is activated under constant current or constant voltage to obtain a catalyst; The cobalt-based precatalyst is selected from at least one of Co3O4, α-Co(OH)2, CoN, CoS2, CoP, and CoSe2.

4. The method for preparing a cobalt-based electrocatalyst according to claim 3, characterized in that: The preparation method comprises the following steps: assembling electrodes containing cobalt-based pre-catalysts into a three-electrode system, and activating the electrodes in an electrolyte by a constant current method or a constant voltage method.

5. The method for preparing a cobalt-based electrocatalyst according to claim 4, characterized in that: The electrolyte contains potassium nitrate and potassium hydroxide.

6. The method for preparing a cobalt-based electrocatalyst according to claim 4, characterized in that: When the activation method is constant current, the activation current is -10~-200mA / cm -2 .

7. The method for preparing a cobalt-based electrocatalyst according to claim 4, characterized in that: When the constant current method is used for activation, the activation time is 1 to 15 hours.

8. The method for preparing a cobalt-based electrocatalyst according to claim 4, characterized in that: When the constant voltage method is used for activation, the activation voltage is -0.1 to -0.5V.

9. The method for preparing a cobalt-based electrocatalyst according to claim 4, characterized in that: When the activation method is adopted, the activation time is 1 to 2 hours.

10. Use of the cobalt-based electrocatalyst according to any one of claims 1 to 2 and / or the method for preparing the cobalt-based electrocatalyst according to any one of claims 3 to 9 in the field of electrocatalytic nitrate reduction.

Images