A method for preparing a rare earth-site-modified hydrotalcite-based oxygen evolution catalyst

Abstract

The present invention provides a method for preparing a rare earth-site-modified hydrotalcite-based oxygen evolution catalyst. The preparation method comprises the following steps: constructing a hydrotalcite precursor with selective metal vacancies by hydrothermal-alkali etching, and then introducing rare earth elements into the hydrotalcite precursor at specific points to obtain a rare earth-precisely modified hydrotalcite-based oxygen evolution catalyst. The hydrotalcite-based oxygen evolution catalyst of the present invention has a stable structure, abundant active sites, excellent oxygen evolution catalytic performance and stability, and has a prospect for large-scale promotion and application.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to a method for preparing a rare earth-site-modified hydrotalcite-based oxygen evolution catalyst. Background Art

[0002] Water electrolysis has been considered one of the most reliable ways to obtain hydrogen energy and high-purity oxygen. Among them, alkaline water electrolysis is widely used and relatively mature in technology, and the reaction equation is: 2H2O→2H2+O2. However, in the actual process of water electrolysis, the oxygen evolution reaction at the anode involves a four-electron transfer process, and the entire oxygen production reaction kinetics process is relatively slow, which is the key bottleneck affecting the efficiency of water electrolysis. At present, precious metal materials (IrO2 and RuO2) have better catalytic effects, but they are relatively expensive. Therefore, designing and preparing high-performance, low-cost water electrolysis catalysts is of great significance to improving reaction efficiency and reducing production costs.

[0003] Hydrotalcite materials have the advantages of adjustable layer metals and controllable interlayer ions, and currently have achieved industrial production of thousands of tons. These characteristics give them a very broad application space in the field of catalysis. Hydrotalcite catalytic materials can not only participate in catalytic reactions as catalysts themselves, but can also be used as catalyst precursors or even carriers to synthesize a variety of catalysts. However, the oxygen evolution stability of today's hydrotalcite catalysts needs to be further improved, and their poor conductivity is not conducive to electron transfer during the reaction. In addition, due to the inherent lamellar structure of hydrotalcite, the layers overlap each other, which is not conducive to the exposure of active sites.

[0004] CN111450881A discloses a modified Cu-Al hydrotalcite catalyst for hydrogen chloride oxidation, wherein the catalyst comprises, based on the total weight of the catalyst, active material: Cu-Al hydrotalcite intercalated with oleate, the content of which is 2-30%; additives: rare earth elements and alkali metal elements, the content of the rare earth elements calculated as rare earth oxides is 2-12%, and the content of the alkali metal elements calculated as alkali metal oxides is 0.1-5%; and an aluminum-containing carrier, the content of which is 53-95.9%.

[0005] CN105514450A discloses a non-precious metal bifunctional oxygen catalyst of nitrogen-doped graphene / nickel-iron hydrotalcite, a preparation method thereof, and an electrocatalytic application of the catalyst to oxygen evolution reaction and oxygen reduction reaction in alkaline medium. The catalyst uses micelles as templates, assembles nickel-iron hydrotalcite onto graphene oxide under hydrothermal conditions to form a spherical porous composite, and then, under hydrothermal conditions, reduces the graphene oxide while doping carbonized nitrogen nanosheets to obtain a nitrogen-doped graphene / nickel-iron hydrotalcite oxygen catalyst. The method comprises: first dispersing graphene oxide and a metal salt into micelles, hydrothermally synthesizing a graphene oxide / hydrotalcite composite under alkaline conditions, and doping the product with carbonized nitrogen nanosheets under hydrothermal conditions to obtain the oxygen catalyst.

[0006] However, the preparation method of the above catalyst is relatively costly, and the stability of the prepared catalyst needs to be further improved.

[0007] Therefore, developing a method for preparing a rare earth-site-modified hydrotalcite-based oxygen evolution catalyst is of great significance for improving the oxygen evolution stability of the catalyst during water electrolysis. Summary of the invention

[0008] In view of the problems existing in the prior art, the present invention provides a method for preparing a rare earth-site-modified hydrotalcite-based oxygen evolution catalyst, wherein a hydrotalcite precursor with selective metal vacancies is constructed by a hydrothermal method-alkaline etching, and then rare earth elements are site-specifically introduced into the hydrotalcite precursor to obtain a rare earth-precisely modified hydrotalcite-based oxygen evolution catalyst; the hydrotalcite-based oxygen evolution catalyst has a stable structure, abundant active sites, and excellent oxygen evolution catalytic performance and stability, and has a prospect for large-scale promotion and application.

[0009] To achieve this object, the present invention adopts the following technical solutions:

[0010] The present invention provides a method for preparing a rare earth-site-modified hydrotalcite-based oxygen evolution catalyst, the preparation method comprising the following steps:

[0011] (1) mixing a transition metal salt solution, an alkali metal salt solution and an alkaline solution, and performing a hydrothermal reaction to obtain a first product; the alkali metal in the alkali metal salt solution comprises Zn or Al;

[0012] (2) dispersing the first product in an alkaline solution and etching it to obtain a second product;

[0013] (3) After the second product is dispersed in an aqueous solution, a solution containing rare earth ions is added dropwise, the pH is adjusted, and after stirring under an inert atmosphere, a first solid-liquid separation, water washing, and a first drying are performed in sequence to obtain the rare earth site-modified hydrotalcite-based oxygen evolution catalyst.

[0014] The method for preparing the rare earth-site-modified hydrotalcite-based oxygen evolution catalyst of the present invention first utilizes alkali metal (Zn or Al) to dope hydrotalcite to achieve site-specific substitution of divalent and trivalent sites in the hydrotalcite; then, the Zn or Al metal ions are removed by alkali etching, and hydrotalcite materials with different metal vacancies are selectively constructed; finally, the rare earth metal ions are adsorbed and anchored at the metal vacancies of the above-mentioned hydrotalcite material to complete the preparation of the rare earth-site-modified hydrotalcite-based oxygen evolution catalyst. The present invention uses the "selective metal vacancy construction" strategy to accurately control the incorporation sites of rare earth ions on the hydrotalcite layer plate, achieve precise regulation of the electronic structure of the hydrotalcite, and then achieve the regulation of the oxygen evolution reaction rate by the rare earth-site-modified hydrotalcite-based oxygen evolution catalyst. At the same time, the oxygen affinity of the rare earth elements is used to stabilize the surface oxygen of the hydrotalcite, inhibit the surface reconstruction of the hydrotalcite-based catalyst during the electrocatalytic process, and thus improve its catalytic stability.

[0015] The alkali metal in the alkali metal salt solution of step (1) of the present invention includes Zn or Al, and other alkali metals such as Mg cannot be used because other alkali metals cannot be subsequently etched away after being combined with the hydrotalcite material, so that the rare earth ions cannot be combined with the hydrotalcite material, and ultimately the rare earth-site-modified hydrotalcite-based oxygen evolution catalyst cannot be prepared.

[0016] Preferably, the transition metal salt solution comprises a divalent transition metal salt solution and a trivalent transition metal salt solution.

[0017] Preferably, the molar ratio of the divalent transition metal salt solution to the trivalent transition metal salt solution is (2-3):1, for example, it can be 2:1, 2.2:1, 2.5:1, 2.7:1, 2.9:1 or 3:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] The preferred molar ratio of the divalent transition metal salt solution to the trivalent transition metal salt solution is (2-3):1. When the molar ratio is too large, the hydrotalcite material cannot be obtained; when the molar ratio is too small, the obtained hydrotalcite is impure.

[0019] Preferably, the divalent transition metal in the divalent transition metal salt solution comprises Ni 2+ 、Co 2+ , Mn 2+ Cu 2+ Any one or a combination of at least two of the following, wherein a typical but non-limiting combination includes Ni 2+ and Co 2+ Combination of Mn 2+ and Cu 2+ The combination of Ni 2+ and Mn 2+ Combination or Cu 2+、Ni 2+ and Co 2+ A combination of all three.

[0020] Preferably, the trivalent transition metal in the trivalent transition metal salt solution includes Fe 3+ 、V 3+ Cr 3+ or Co 3+ Any one or a combination of at least two of the following, wherein a typical but non-limiting combination includes Fe 3+ and V 3+ The combination of Cr 3+ and Co 3+ Combination of Fe 3+ and Cr 3+ Combination or Co 3+ , Fe 3+ and Cr 3+ A combination of all three.

[0021] Preferably, the transition metal salt solution comprises any one of chloride, nitrate, acetate, sulfate, acetylacetonate or phthalocyanine salt of the transition metal or a combination of at least two thereof, wherein typical but non-limiting combinations include a combination of chloride and nitrate, a combination of acetate and sulfate, a combination of acetylacetonate and phthalocyanine, or a combination of chloride, acetate and acetylacetonate.

[0022] Preferably, the alkaline solution in step (1) comprises any one of NaHCO3, Na2CO3, NaOH or urea, or a combination of at least two of them, wherein typical but non-limiting combinations include a combination of NaHCO3 and Na2CO3, a combination of NaOH and urea, a combination of NaHCO3 and NaOH, or a combination of urea, NaHCO3 and NaOH.

[0023] Preferably, the concentration of the alkaline solution is 0.5-2 mol / L, for example, it can be 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.3 mol / L, 1.5 mol / L or 2 mol / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] Preferably, the hydrothermal reaction in step (1) is stirred for 1 to 4 hours before reaction, for example, 1 hour, 1.2 hours, 1.5 hours, 2 hours, 3 hours or 4 hours, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0025] Preferably, the temperature of the hydrothermal reaction is 100-180°C, for example, it can be 100°C, 120°C, 130°C, 150°C, 170°C or 180°C, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably 100-150°C.

[0026] Preferably, the hydrothermal reaction time is 6 to 30 h, for example, 6 h, 8 h, 10 h, 20 h or 30 h, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] Preferably, in step (1), the first product is sequentially washed, subjected to a second solid-liquid separation and a second drying before being dispersed in an alkaline solution.

[0028] Preferably, the second drying is carried out in an oven.

[0029] Preferably, the second drying temperature is 60-100°C, for example, 60°C, 70°C, 80°C, 90°C or 100°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] Preferably, the alkaline solution in step (2) comprises NaOH solution or KOH solution.

[0031] Preferably, the concentration of the alkaline solution is 1 to 5 mol / L, for example, 1 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 4 mol / L or 5 mol / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] The present invention preferably has a concentration of 1 to 5 mol / L of the alkaline solution. When the concentration of the alkaline solution is too low, the alkali metal Zn or Al doped on the hydrotalcite material cannot be etched away, and the rare earth metal ions cannot be subsequently adsorbed and anchored at the metal vacancies of the hydrotalcite material, and a rare earth-site-modified hydrotalcite-based oxygen evolution catalyst cannot be obtained. When the concentration of the alkaline solution is too high, the catalyst structure is destroyed, and the reaction equipment is corroded, which also increases the preparation cost.

[0033] Preferably, stirring is performed during the etching process in step (2).

[0034] Preferably, the etching time is 10 to 24 hours, for example, 10 hours, 12 hours, 16 hours, 20 hours or 24 hours, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] Preferably, the molar ratio of the rare earth ion-containing solution in step (3) to the transition metal salt solution in step (1) is (1-20):(80-99), for example, it can be 1:99, 5:95, 1:9, 15:85, 17:83 or 2:8, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] The present invention preferably has a molar ratio of the rare earth ion-containing solution to the transition metal salt solution of step (1) of (1-20):(80-99). When the rare earth ion-containing solution is relatively large, the crystal structure of the hydrotalcite will be destroyed, thereby affecting the performance of the rare earth-site-modified hydrotalcite-based oxygen evolution catalyst; when the rare earth ion-containing solution is relatively small, the catalytic stability of the finally prepared catalyst will not be significantly improved.

[0037] Preferably, the dripping rate of the solution containing rare earth ions is 10 to 50 μL / s, for example, it can be 10 μL / s, 15 μL / s, 20 μL / s, 30 μL / s, 40 μL / s or 50 μL / s, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0038] The preferred dripping rate of the rare earth ion-containing solution of the present invention is 10 to 50 μL / s. When the dripping rate is too fast, the rare earth ions cannot be well adsorbed and anchored at the metal vacancies of the hydrotalcite material, and the performance of the obtained rare earth site-modified hydrotalcite-based oxygen evolution catalyst is poor; when the dripping rate is too slow, the preparation time of the rare earth site-modified hydrotalcite-based oxygen evolution catalyst is long.

[0039] Preferably, the rare earth ions contained in the rare earth ion-containing solution include any one of Y, La, Ce, Pr, Nd, Sm or Gd.

[0040] Preferably, the pH value in step (3) is adjusted to 9-11, for example, 9, 9.5, 10, 10.5 or 11, etc., but is not limited to the listed values, and other listed values ​​within the numerical range are also applicable.

[0041] In the present invention, the pH is adjusted using a NaOH solution with a concentration of 0.01 to 0.1 mol / L, for example, 0.01 mol / L, 0.03 mol / L, 0.05 mol / L, 0.08 mol / L, 0.09 mol / L or 0.1 mol / L, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0042] Preferably, the first drying comprises any one of air drying, vacuum drying or freeze drying.

[0043] There is no limitation on the first solid-liquid separation and the second solid-liquid separation in the present invention, and any method for solid-liquid separation known to those skilled in the art may be used, such as filtration, sedimentation or centrifugation, preferably centrifugation.

[0044] Preferably, the centrifugal rotation speed is 5000-12000 rpm, for example, it can be 5000 rpm, 6000 rpm, 7000 rpm, 8000 rpm, 10000 rpm or 12000 rpm, but it is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably 6000 rpm.

[0045] Preferably, the centrifugation time is 1 to 10 min, for example, 1 min, 3 min, 5 min, 8 min, 9 min or 10 min, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 3 min.

[0046] In the present invention, the second product is also sequentially subjected to a first solid-liquid separation, water washing and a first drying before being dispersed in an aqueous solution, which is the same as the operation after adjusting the pH and stirring under an inert atmosphere in step (3).

[0047] As a preferred technical solution of the present invention, the preparation method comprises the following steps:

[0048] (1) mixing a transition metal salt solution, an alkali metal salt solution and an alkaline solution, stirring for 1 to 4 hours, and performing a hydrothermal reaction at a temperature of 100 to 180° C. for 6 to 30 hours to obtain a first product; the alkali metal in the alkali metal salt solution comprises Zn or Al;

[0049] The transition metal salt solution comprises a divalent transition metal salt solution and a trivalent transition metal salt solution; the molar ratio of the divalent transition metal salt solution to the trivalent transition metal salt solution is (2-3):1; the divalent transition metal in the divalent transition metal salt solution comprises Ni 2+ 、Co 2+ , Mn 2+ Cu 2+ Any one or a combination of at least two of the following; the trivalent transition metal in the trivalent transition metal salt solution includes Fe 3+ 、V 3+ Cr 3+ or Co 3+ Any one or a combination of at least two of the following: the transition metal salt solution comprises any one or a combination of at least two of the following: chloride, nitrate, acetate, sulfate, acetylacetonate or phthalocyanine salt of the transition metal;

[0050] The alkaline solution includes any one of NaHCO3, Na2CO3, NaOH or urea or a combination of at least two thereof; the concentration of the alkaline solution is 0.5 to 2 mol / L;

[0051] (2) the first product is sequentially washed, subjected to a second solid-liquid separation, and subjected to a second drying at a temperature of 60 to 100° C., and then dispersed in an alkaline solution with a concentration of 1 to 5 mol / L and etched for 10 to 24 hours to obtain a second product;

[0052] The second drying is performed in an oven; the alkaline solution includes a NaOH solution or a KOH solution; stirring is performed during the etching process;

[0053] (3) After the second product is dispersed in an aqueous solution, a solution containing rare earth ions is added dropwise at a rate of 10 to 50 μL / s, the pH is adjusted to 9 to 11, and after stirring under an inert atmosphere, a first solid-liquid separation, water washing, and a first drying are performed in sequence to obtain the rare earth site-modified hydrotalcite-based oxygen evolution catalyst;

[0054] The molar ratio of the solution containing rare earth ions to the transition metal salt solution in step (1) is (1-20):(80-99); the rare earth ions contained in the solution containing rare earth ions include any one of Y, La, Ce, Pr, Nd, Sm or Gd; and the first drying includes any one of forced air drying, vacuum drying or freeze drying.

[0055] Compared with the prior art, the present invention has at least the following beneficial effects:

[0056] (1) The preparation method of the rare earth site-modified hydrotalcite-based oxygen evolution catalyst provided by the present invention is simple to operate and has a precise synthesis process. The finally obtained rare earth site-modified hydrotalcite-based oxygen evolution catalyst has a clear structure and can achieve precise modification of different rare earth elements at different sites of the hydrotalcite;

[0057] (2) The method for preparing a rare earth-site-modified hydrotalcite-based oxygen evolution catalyst provided by the present invention utilizes the oxophilicity of rare earth elements to stabilize the surface oxygen of hydrotalcite, inhibit the surface reconstruction of the hydrotalcite-based catalyst during the electrocatalytic process, and thus improve the catalytic stability;

[0058] (3) The method for preparing a rare earth-site-modified hydrotalcite-based oxygen evolution catalyst provided by the present invention has a higher catalytic activity than commercial RuO2 and excellent stability, and has a good application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 The present invention is a flow chart of a method for preparing a rare earth-site-modified hydrotalcite-based oxygen evolution catalyst.

[0060] Figure 2 This is the XRD diagram of the rare earth site-modified hydrotalcite-based oxygen evolution catalyst prepared in Example 1.

[0061] Figure 3 This is a normalized oxygen evolution activity curve of the rare earth site-modified hydrotalcite-based oxygen evolution catalyst prepared in Example 1.

[0062] Figure 4 This is a constant current curve diagram of the rare earth site-modified hydrotalcite-based oxygen evolution catalyst prepared in Example 1. DETAILED DESCRIPTION

[0063] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0064] The present invention provides a method for preparing a rare earth-site-modified hydrotalcite-based oxygen evolution catalyst, the flow chart of which is as follows: Figure 1 shown.

[0065] The preparation method comprises the following steps:

[0066] (1) mixing a transition metal salt solution, an alkali metal salt solution and an alkaline solution, stirring for 1 to 4 hours, and performing a hydrothermal reaction at a temperature of 100 to 180° C. for 6 to 30 hours to obtain a first product; the alkali metal in the alkali metal salt solution comprises Zn or Al;

[0067] The transition metal salt solution comprises a divalent transition metal salt solution and a trivalent transition metal salt solution; the molar ratio of the divalent transition metal salt solution to the trivalent transition metal salt solution is (2-3):1; the divalent transition metal in the divalent transition metal salt solution comprises Ni 2+ 、Co 2+ , Mn 2+ Cu 2+ Any one or a combination of at least two of the following; the trivalent transition metal in the trivalent transition metal salt solution includes Fe 3+ 、V 3+ Cr 3+ or Co 3+ Any one or a combination of at least two of the following: the transition metal salt solution comprises any one or a combination of at least two of the following: chloride, nitrate, acetate, sulfate, acetylacetonate or phthalocyanine salt of the transition metal;

[0068] The alkaline solution includes any one of NaHCO3, Na2CO3, NaOH or urea or a combination of at least two thereof; the concentration of the alkaline solution is 0.5 to 2 mol / L;

[0069] (2) the first product is sequentially washed, subjected to a second solid-liquid separation, and subjected to a second drying at a temperature of 60 to 100° C., and then dispersed in an alkaline solution with a concentration of 1 to 5 mol / L and etched for 10 to 24 hours to obtain a second product;

[0070] The second drying is performed in an oven; the alkaline solution includes a NaOH solution or a KOH solution; stirring is performed during the etching process;

[0071] (3) After the second product is dispersed in an aqueous solution, a solution containing rare earth ions is added dropwise at a rate of 10 to 50 μL / s, the pH is adjusted to 9 to 11, and after stirring under an inert atmosphere, a first solid-liquid separation, water washing, and a first drying are performed in sequence to obtain the rare earth site-modified hydrotalcite-based oxygen evolution catalyst;

[0072] The molar ratio of the solution containing rare earth ions to the transition metal salt solution in step (1) is (1-20):(80-99); the rare earth ions contained in the solution containing rare earth ions include any one of Y, La, Ce, Pr, Nd, Sm or Gd; and the first drying includes any one of forced air drying, vacuum drying or freeze drying.

[0073] The present invention is further described in detail below. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0074] Example 1

[0075] This embodiment provides a method for preparing a rare earth-site-modified hydrotalcite-based oxygen evolution catalyst, the preparation method comprising the following steps:

[0076] (1) Dissolve 13.5mmol NiCl2·6H2O, 4.5mmol FeCl3·6H2O and 1.5mmol ZnCl2·6H2O in 40ml water, sonicate and stir until the solution is uniformly dispersed, then add 40ml 1mol L -1 NaHCO3 solution, stirred for 2 hours, and subjected to hydrothermal reaction at 100°C for 20 hours to obtain the first product;

[0077] (2) The first product was washed alternately with deionized water and ethanol for 3 times, centrifuged at 6000 rpm for 3 min, and then dried for 12 h at 80° C., and 100 mg was dispersed in a 2 mol / L NaOH solution and etched for 10 h to obtain a second product; the second drying was performed in an oven;

[0078] (3) After the second product is dispersed in the aqueous solution, 0.2 ml of 10 mmol mL -1 CeCl3·6H2O solution, add 0.01 mol L -1 The pH value is adjusted to 10 by using a NaOH solution, and after stirring for 12 hours under an inert atmosphere, the mixture is centrifuged, washed with water until neutral, and dried for the first time to obtain the rare earth site-modified hydrotalcite-based oxygen evolution catalyst; the first drying is forced air drying; the molar ratio of the rare earth ion-containing solution to the transition metal salt solution in step (1) is 1:9.

[0079] The XRD pattern of the rare earth site-modified hydrotalcite-based oxygen evolution catalyst prepared in this example is as follows: Figure 2 As shown. Figure 2 It can be seen that the crystal form of the catalyst is the same as that of NiFe-LDH, indicating that the introduction of Ce does not change the crystal structure of LDH.

[0080] The normalized oxygen evolution activity curve of the rare earth site-modified hydrotalcite-based oxygen evolution catalyst prepared in this example is shown in FIG. Figure 3 As shown. Figure 3 It can be seen that the oxygen evolution overpotential of the NiFe-LDH catalyst after the introduction of the rare earth element Ce is 220mV, which is 20mV lower than the original NiFe-LDH, and is far superior to the commercial precious metal catalyst RuO2, with an overpotential 40mV lower than it, and the oxygen evolution effect is significant.

[0081] The constant current curve of the rare earth site-modified hydrotalcite-based oxygen evolution catalyst prepared in this example is shown in FIG. Figure 4 As shown. Figure 4 It can be seen that the stability of the NiFe-LDH catalyst without rare earth elements is poor, and the overpotential increases at the 10th hour and continues to increase. However, the stability of the NiFe-LDH catalyst after the introduction of the rare earth element Ce is significantly improved. The overpotential hardly increases after 50 hours of constant current testing, and the catalytic effect of the catalyst remains relatively stable during the entire test process.

[0082] Example 2

[0083] This embodiment provides a method for preparing a rare earth-site-modified hydrotalcite-based oxygen evolution catalyst, the preparation method comprising the following steps:

[0084] (1) mixing a transition metal salt solution, an alkali metal salt solution and an alkaline solution, stirring for 1 hour, and performing a hydrothermal reaction at a temperature of 180° C. for 6 hours to obtain a first product; the alkali metal in the alkali metal salt solution includes Al;

[0085] The transition metal salt solution comprises a divalent transition metal salt solution and a trivalent transition metal salt solution; the molar ratio of the divalent transition metal salt solution to the trivalent transition metal salt solution is 2.5:1; the divalent transition metal in the divalent transition metal salt solution is Co 2+ The trivalent transition metal in the trivalent transition metal salt solution is V 3+ ; The transition metal salt solution is an acetate of a transition metal;

[0086] The amount of alkaline solution added is 40ml 0.5mol L -1 NaOH solution;

[0087] (2) The first product was sequentially washed, centrifuged for a second time, and dried for a second time at 60° C., and then dispersed in an alkaline solution with a concentration of 1 mol / L and etched for 24 h to obtain a second product;

[0088] The second drying is performed in an oven; the alkaline solution is a KOH solution; stirring is performed during the etching process;

[0089] (3) After the second product is dispersed in an aqueous solution, a solution containing rare earth ions is added dropwise at a rate of 10 μL / s, the pH is adjusted to 11, and after stirring under an inert atmosphere, the solution is subjected to a first centrifugation, a water wash, and a first drying to obtain the rare earth site-modified hydrotalcite-based oxygen evolution catalyst;

[0090] The molar ratio of the solution containing rare earth ions to the transition metal salt solution in step (1) is 1:99; the rare earth ions contained in the solution containing rare earth ions are Pr; and the first drying is forced air drying.

[0091] Example 3

[0092] This embodiment provides a method for preparing a rare earth-site-modified hydrotalcite-based oxygen evolution catalyst, the preparation method comprising the following steps:

[0093] (1) mixing a transition metal salt solution, an alkali metal salt solution and an alkaline solution, stirring for 4 hours, and performing a hydrothermal reaction at a temperature of 150° C. for 30 hours to obtain a first product; the alkali metal in the alkali metal salt solution includes Al;

[0094] The transition metal salt solution comprises a divalent transition metal salt solution and a trivalent transition metal salt solution; the molar ratio of the divalent transition metal salt solution to the trivalent transition metal salt solution is 2:1; the divalent transition metal in the divalent transition metal salt solution is Cu 2+ The trivalent transition metal in the trivalent transition metal salt solution is Cr 3+ ; The transition metal salt solution is a phthalocyanine salt of a transition metal;

[0095] The alkaline solution is 40 ml of 2 mol L -1 Na2CO3 solution;

[0096] (2) The first product was sequentially washed, centrifuged and dried at 100° C., and then dispersed in an alkaline solution with a concentration of 5 mol / L and etched for 10 h to obtain a second product;

[0097] The second drying is performed in an oven; the alkaline solution is a KOH solution; stirring is performed during the etching process;

[0098] (3) After the second product is dispersed in the aqueous solution, a solution containing rare earth ions is added dropwise at a rate of 50 μL / s, the pH is adjusted to 9, and after stirring under an inert atmosphere, the solution is subjected to a first centrifugation, a water wash, and a first drying in sequence to obtain the rare earth site-modified hydrotalcite-based oxygen evolution catalyst;

[0099] The molar ratio of the solution containing rare earth ions to the transition metal salt solution in step (1) is 1:4; the rare earth ions contained in the solution containing rare earth ions are Nd; and the first drying is vacuum drying.

[0100] Example 4

[0101] This embodiment provides a method for preparing a rare earth site-modified hydrotalcite-based oxygen evolution catalyst. The preparation method is the same as that of Embodiment 1 except that the concentration of the NaOH solution in step (2) is replaced with 0.5 mol / L.

[0102] Example 5

[0103] This embodiment provides a method for preparing a rare earth site-modified hydrotalcite-based oxygen evolution catalyst. The preparation method is the same as that of Embodiment 1 except that the concentration of the NaOH solution in step (2) is replaced with 6 mol / L.

[0104] Example 6

[0105] This embodiment provides a method for preparing a rare earth site-modified hydrotalcite-based oxygen evolution catalyst, the preparation method is the same as that of Example 1 except that the molar ratio of the CeCl3·6H2O solution in step (3) to the NiCl2·6H2O and FeCl3·6H2O in step (1) is replaced with 5:985.

[0106] Example 7

[0107] This embodiment provides a method for preparing a rare earth site-modified hydrotalcite-based oxygen evolution catalyst, the preparation method is the same as that of Example 1 except that the molar ratio of the CeCl3·6H2O solution in step (3) to the NiCl2·6H2O and FeCl3·6H2O in step (1) is replaced with 3:7.

[0108] Example 8

[0109] This embodiment provides a method for preparing a rare earth site-modified hydrotalcite-based oxygen evolution catalyst, which is the same as that of Example 1 except that the CeCl3·6H2O solution in step (3) is replaced by an equimolar amount of YCl3·6H2O.

[0110] Example 9

[0111] This embodiment provides a method for preparing a rare earth-site-modified hydrotalcite-based oxygen evolution catalyst. The preparation method is the same as that of Embodiment 1 except that the CeCl3·6H2O solution in step (3) is replaced by an equimolar amount of LaCl3·6H2O.

[0112] Example 10

[0113] This embodiment provides a method for preparing a rare earth site-modified hydrotalcite-based oxygen evolution catalyst, which is the same as that of Embodiment 1 except that the CeCl3·6H2O solution in step (3) is replaced by an equimolar amount of SmCl3·6H2O.

[0114] Embodiment 11

[0115] This embodiment provides a method for preparing a rare earth site-modified hydrotalcite-based oxygen evolution catalyst, which is the same as that of embodiment 1 except that the CeCl3·6H2O solution in step (3) is replaced by an equimolar amount of GdCl3·6H2O.

[0116] Comparative Example 1

[0117] This comparative example provides a method for preparing a hydrotalcite-based oxygen evolution catalyst. The preparation method is the same as Example 1 except that the alkali metal salt solution in step (1) is replaced by an equimolar amount of MgCl2·6H2O.

[0118] The catalysts obtained in the above examples and comparative examples were tested by LSV linear sweep voltammetry. The test method parameters were set as follows: scanning voltage 0.8-2V (vs. RHE), scanning rate 10mV / s, and the mass of the catalyst dropped on the carbon paper was 1mg cm -2 The overpotential results of the catalysts obtained in the above examples and comparative examples and the results of whether the overpotential has obvious changes after 50h constant current test are shown in Table 1.

[0119] Table 1

[0120]

[0121]

[0122] From Table 1 we can see that:

[0123] (1) It can be seen from Example 1 and Examples 4 to 5 that the concentration of the alkaline solution during the alkaline etching process should not be too high or too low. In Example 5, the concentration of the alkaline solution is too high, resulting in the destruction of the catalyst structure. In Example 4, the concentration of the alkaline solution is too low, resulting in the inability to completely etch away the alkali metal, thereby affecting the subsequent adsorption of rare earth ions.

[0124] (2) It can be seen from the combination of Example 1 and Examples 6 to 7 that in Example 1, when the ratio of divalent to trivalent transition metal ions is 3:1 and the ratio of rare earth ions to transition metal ions is 1:9, the catalytic performance is relatively optimal, the overpotential is 220 mV, and there is no significant change in the overpotential in the constant current test; when the rare earth content in Example 6 is relatively low, the improvement in catalyst stability is relatively unobvious, and when the rare earth content in Example 7 is relatively high, the original structure of nickel-iron hydrotalcite will be changed, resulting in no significant improvement in performance, the overpotential is 248 mV, and the overpotential changes slightly in the constant current test.

[0125] (3) It can be seen from Examples 1 and 8 to 11 that Ce has the best catalytic activity among the rare earth elements.

[0126] (4) From Example 1 and Comparative Example 1, it can be seen that in step (1) of Comparative Example 1, the alkali metal salt solution is replaced with an equimolar amount of MgCl2·6H2O, and the final catalyst overpotential is 270 mV. The overpotential changes significantly in the constant current test. This is because after Mg is combined with the hydrotalcite material, it cannot be subsequently etched away, so that the rare earth ions cannot be combined with the hydrotalcite material, and ultimately the rare earth site-modified hydrotalcite-based oxygen evolution catalyst cannot be prepared.

[0127] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a rare earth-site-modified hydrotalcite-based oxygen evolution catalyst, characterized in that: The preparation method comprises the following steps: (1) mixing a transition metal salt solution, an alkali metal salt solution and an alkaline solution, and performing a hydrothermal reaction to obtain a first product; the alkali metal in the alkali metal salt solution comprises Zn or Al; (2) dispersing the first product in an alkaline solution and etching it to obtain a second product; (3) After the second product is dispersed in an aqueous solution, a solution containing rare earth ions is added dropwise, the pH is adjusted, and after stirring under an inert atmosphere, a first solid-liquid separation, water washing, and a first drying are performed in sequence to obtain the rare earth site-modified hydrotalcite-based oxygen evolution catalyst; The transition metal salt solution in step (1) includes a divalent transition metal salt solution and a trivalent transition metal salt solution; The molar ratio of the divalent transition metal salt solution to the trivalent transition metal salt solution is (2-3): 1; The divalent transition metal in the divalent transition metal salt solution includes Ni 2+ 、Co 2+ , Mn 2+ Cu 2+ Any one or a combination of at least two of the following: The trivalent transition metal in the trivalent transition metal salt solution includes Fe 3+ 、V 3+ Cr 3+ or Co 3+ Any one or a combination of at least two of the following: Among them, the transition metal salt solution cannot contain only Co 2+ and Co 3+ .

2. The preparation method according to claim 1, characterized in that: The transition metal salt solution includes any one of transition metal chlorides, nitrates, acetates, sulfates, acetylacetonates or phthalocyanine salts, or a combination of at least two of the transition metals.

3. The preparation method according to claim 1, characterized in that: The alkaline solution in step (1) includes any one of NaHCO3, Na2CO3, NaOH or urea, or a combination of at least two of them.

4. The preparation method according to claim 1, characterized in that: The concentration of the alkaline solution is 0.5-2 mol / L.

5. The preparation method according to claim 1, characterized in that: The hydrothermal reaction in step (1) is stirred for 1 to 4 hours.

6. The preparation method according to claim 1, characterized in that: The temperature of the hydrothermal reaction is 100-180°C.

7. The preparation method according to claim 6, characterized in that: The temperature of the hydrothermal reaction is 100-150°C.

8. The preparation method according to claim 1, characterized in that: The hydrothermal reaction time is 6 to 30 h.

9. The preparation method according to claim 1, characterized in that: Step (1) The first product is sequentially washed, subjected to a second solid-liquid separation and a second drying before being dispersed in an alkaline solution.

10. The preparation method according to claim 9, characterized in that: The second drying is performed in an oven.

11. The preparation method according to claim 9, characterized in that: The second drying temperature is 60-100°C.

12. The preparation method according to claim 1, characterized in that: The alkaline solution in step (2) includes NaOH solution and / or KOH solution.

13. The preparation method according to claim 1, characterized in that: The concentration of the alkaline solution is 1-5 mol / L.

14. The preparation method according to claim 1, characterized in that: Stirring is performed during the etching process in step (2).

15. The preparation method according to claim 1, characterized in that: The etching time is 10 to 24 h.

16. The preparation method according to claim 1, characterized in that: The molar ratio of the rare earth ion-containing solution in step (3) to the transition metal salt solution in step (1) is (1-20):(80-99).

17. The preparation method according to claim 1, characterized in that: The droplet acceleration rate of the rare earth ion-containing solution is 10-50 μL / s.

18. The preparation method according to claim 1, characterized in that: The rare earth ions contained in the rare earth ion-containing solution include any one of Y, La, Ce, Pr, Nd, Sm or Gd.

19. The preparation method according to claim 1, characterized in that: In step (3), the pH is adjusted to 9-11.

20. The preparation method according to claim 1, characterized in that: The first drying includes any one of air drying, vacuum drying or freeze drying.

21. The preparation method according to claim 1, characterized in that: The preparation method comprises the following steps: (1) mixing a transition metal salt solution, an alkali metal salt solution and an alkaline solution, stirring for 1 to 4 hours, and performing a hydrothermal reaction at a temperature of 100 to 180° C. for 6 to 30 hours to obtain a first product; the alkali metal in the alkali metal salt solution comprises Zn or Al; The transition metal salt solution comprises a divalent transition metal salt solution and a trivalent transition metal salt solution; the molar ratio of the divalent transition metal salt solution to the trivalent transition metal salt solution is (2-3): 1; the divalent transition metal in the divalent transition metal salt solution comprises Ni 2+ 、Co 2+ , Mn 2+ Cu 2+ Any one or a combination of at least two of the following; the trivalent transition metal in the trivalent transition metal salt solution includes Fe 3+ 、V 3+ Cr 3+ or Co 3+ Any one or a combination of at least two of the following: Among them, the transition metal salt solution cannot contain only Co 2+ and Co 3+ ; The transition metal salt solution includes any one of transition metal chlorides, nitrates, acetates, sulfates, acetylacetonates or phthalocyanine salts, or a combination of at least two thereof; The alkaline solution includes any one of NaHCO3, Na2CO3, NaOH or urea or a combination of at least two thereof; the concentration of the alkaline solution is 0.5-2 mol / L; (2) The first product is sequentially washed, subjected to a second solid-liquid separation, and subjected to a second drying at a temperature of 60 to 100 °C, and then dispersed in an alkaline solution having a concentration of 1 to 5 mol / L and etched for 10 to 24 h to obtain a second product; The second drying is performed in an oven; the alkaline solution includes a NaOH solution or a KOH solution; stirring is performed during the etching process; (3) After the second product is dispersed in an aqueous solution, a solution containing rare earth ions is added dropwise at a rate of 10 to 50 μL / s, the pH is adjusted to 9 to 11, and after stirring under an inert atmosphere, a first solid-liquid separation, water washing and a first drying are performed in sequence to obtain the rare earth site-modified hydrotalcite-based oxygen evolution catalyst; The molar ratio of the solution containing rare earth ions to the transition metal salt solution in step (1) is (1-20):(80-99); the rare earth ions contained in the solution containing rare earth ions include any one of Y, La, Ce, Pr, Nd, Sm or Gd; and the first drying includes any one of forced air drying, vacuum drying or freeze drying.

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