A bifunctional catalyst and a bifunctional catalyst based on rare earth gadolinium doping, and a preparation method and application thereof

Abstract

The application discloses a kind of bifunctional catalyst and based on rare earth gadolinium doped bifunctional catalyst and its preparation method and application.The ZIF-8 is prepared first;Cobalt source methanol solution and 2-methyl imidazole methanol solution are poured into ZIF-8 methanol solution simultaneously, and ZIF-8@ZIF-67 is obtained by stirring;Tris (hydroxymethyl) aminomethane aqueous solution and dopamine hydrochloride aqueous solution are added to ZIF-8@ZIF-67 ethanol aqueous solution in turn, and ZIF-8@ZIF-67@PDA is obtained by stirring;Co@NC is obtained by calcining under protective gas atmosphere;Co@NC and sulfur source are placed downstream and upstream of protective gas flow respectively, and double functional catalyst is obtained by firing treatment.Cobalt source is replaced by cobalt source and gadolinium source, and based on rare earth gadolinium doped bifunctional catalyst is obtained.The two kinds of bifunctional catalysts of the application are used for electrocatalytic oxygen evolution and oxygen reduction, and have high catalytic activity and good stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy nanomaterials, in particular to a bifunctional catalyst and a bifunctional catalyst based on rare earth gadolinium doping and a preparation method and application thereof. BACKGROUND

[0002] At present, the energy structure of countries all over the world is still mainly traditional fossil fuels, but fossil fuels are not renewable, and the massive emission of carbon dioxide, a combustion product of fossil fuels, has caused serious environmental problems. The development and use of environmentally friendly renewable energy is the key to solving the energy crisis and environmental problems, among which the zinc-air battery in the clean and environmentally friendly metal-air battery has a capacity and energy density several times higher than the dominant battery on the market, can be repeatedly charged and discharged, has good stability, is safer, and has lower cost, and has great development potential. However, due to the energy consumption of the battery structure itself and the voltage drop inside the battery during actual use, the zinc-air battery is still difficult to achieve the theoretical energy density and theoretical battery voltage. Its performance is mainly limited by the efficiency of air cathode oxygen reduction (ORR) and oxygen evolution reaction (OER), so it is necessary to develop new, low-cost, high-efficiency and stable bifunctional electrocatalysts to accelerate the kinetics of the entire reaction.

[0003] In recent years, a variety of transition metal (TM) compounds have been reported as candidate electrocatalysts to replace noble metal-based catalysts. Impressively, transition metal sulfides (TMS) have become a research hotspot for electrocatalytic water splitting due to their simple preparation process, high activity and good electrical conductivity. In order to further improve the catalytic activity and stability in ORR and OER, a large number of optimization strategies have been introduced into TMS, such as morphology engineering, composition adjustment, heteroatom doping and introduction of conductive base materials, etc.

[0004] In recent years, rare earth metals have attracted widespread attention in adjusting electronic structure and improving the catalytic performance of various transition metal-based materials due to their unique chemical and electronic properties of 4f subshell electrons. The variability of coordination number of rare earth elements determines their "remaining valence". The 4f orbit of rare earth elements has 7 valence electron orbits, which can form bonds, which is a kind of "reserve bond". Therefore, rare earth elements can be used as additives or promoters to improve the catalytic performance of the host material. SUMMARY

[0005] In order to overcome the deficiencies existing in the prior art, the purpose of the present application is to provide a bifunctional catalyst Co / CoS2@NC and a bifunctional catalyst based on rare earth gadolinium doping Gd-Co / CoS2@NC and a preparation method and application thereof.

[0006] The purpose of the present application is at least realized by one of the following technical solutions.

[0007] A preparation method of a bifunctional catalyst, comprising the following steps:

[0008] (1) Dissolve a zinc source and 2-methylimidazole in methanol respectively, stir them uniformly, and make them completely dissolved in methanol;

[0009] (2) Pour the methanol solution of 2-methylimidazole obtained in step (1) into the methanol solution containing zinc to obtain a mixed solution, and stir it at room temperature to obtain a dodecahedron ZIF-8;

[0010] (3) Disperse the dodecahedron ZIF-8 obtained in step (2) in methanol, dissolve a cobalt source and 2-methylimidazole in methanol respectively, pour the methanol solution of the cobalt source and the methanol solution of 2-methylimidazole into the methanol solution of ZIF-8 at the same time to obtain a mixed solution, and stir it at room temperature to obtain ZIF-8@ZIF-67;

[0011] (4) Disperse ZIF-8@ZIF-67 obtained in step (3) in a mixed solvent of water and ethanol, add an aqueous solution of tris(hydroxymethyl)aminomethane and an aqueous solution of dopamine hydrochloride into the ethanol aqueous solution of ZIF-8@ZIF-67 in sequence to obtain a mixed solution, and stir it at room temperature to obtain ZIF-8@ZIF-67@PDA;

[0012] (5) Calcine ZIF-8@ZIF-67@PDA obtained in step (4) under a protective gas atmosphere to obtain a carbonization product Co@NC;

[0013] (6) Place Co@NC obtained in step (5) and a sulfur source downstream and upstream of a protective gas flow respectively, and perform a sintering treatment to obtain a bifunctional catalyst Co / CoS2@NC.

[0014] Preferably, the zinc source in step (1) is zinc nitrate;

[0015] Preferably, the stirring time in step (2) is 20-28 h;

[0016] Preferably, the concentration of zinc ions in the mixed solution in step (2) is 0.04-0.05 M; and the molar ratio of zinc ions to 2-methylimidazole in the mixed solution is 1:12-13.

[0017] Preferably, the cobalt source in step (3) is cobalt nitrate;

[0018] Preferably, the concentration of cobalt ions in the mixed solution in step (3) is 4-7 mM; and the molar ratio of cobalt ions to 2-methylimidazole in the mixed solution is 1:12-13.

[0019] Preferably, the ratio of the mass of the dodecahedral ZIF-8 to the molar amount of cobalt ions in the mixed solution of step (3) is 1-2 g:6 mMol;

[0020] Preferably, the stirring time of step (3) is 10-20 min;

[0021] Preferably, the volume ratio of water to ethanol in the mixed solution of step (4) is 1-1.5:1;

[0022] Preferably, the concentration of tris(hydroxymethyl)aminomethane in the mixed solution of step (4) is 18-24 mM;

[0023] Preferably, the concentration of dopamine hydrochloride in the mixed solution of step (4) is 1.5-1.8 mM;

[0024] Preferably, the content of ZIF-8@ZIF-67 in the mixed solution of step (4) is 1.0-1.2 g / L;

[0025] Preferably, the stirring time of step (4) is 1-2 h.

[0026] Preferably, the volume ratio of water to ethanol in the ethanol aqueous solution of ZIF-8@ZIF-67 of step (4) is 1:2.5-3.0;

[0027] Preferably, the content of ZIF-8@ZIF-67 in the ethanol aqueous solution of ZIF-8@ZIF-67 of step (4) is 1.8-2.0 g / L;

[0028] Preferably, the concentration of tris(hydroxymethyl)aminomethane in the aqueous solution of step (4) is 80-100 mM;

[0029] Preferably, the concentration of dopamine hydrochloride in the aqueous solution of step (4) is 10-11 mM;

[0030] Preferably, the volume ratio of the ethanol aqueous solution of ZIF-8@ZIF-67, the aqueous solution of tris(hydroxymethyl)aminomethane, and the aqueous solution of dopamine hydrochloride in step (4) is 1.0-1.2:0.3-0.5:0.3.

[0031] Preferably, the temperature of the calcination of step (5) is set as follows: first heated to 150-250°C at a heating rate of 2-5°C / min -1 , kept at the same temperature for 2-5 h, then heated to 700-900°C at a heating rate of 2-5°C / min -1 , and kept for 2-5 h;

[0032] Further preferably, the temperature of the calcination of step (5) is set as follows: first heated to 200°C at a heating rate of 2°C / min-1 , and then heated to 800℃ at a heating rate of 2℃ / min, and kept at 800℃ for 2h. -1 , and kept at 800℃ for 2h.

[0033] Preferably, the sulfur source in step (6) is sulfur powder; the mass ratio of the sulfur source to Co@NC is 5-10:1; the temperature of the calcination treatment is 300-450℃, and the time of the calcination treatment is 1.5-2.5h.

[0034] Preferably, the protective gas in step (5) and step (6) is nitrogen or inert gas (argon, etc.).

[0035] The bifunctional catalyst Co / CoS2@NC prepared by the preparation method.

[0036] A preparation method of a bifunctional catalyst based on rare earth gadolinium doping, comprising the following steps:

[0037] (a) Dissolve a zinc source and 2-methylimidazole in methanol respectively, stir until completely dissolved in methanol;

[0038] (b) Pour the methanol solution of 2-methylimidazole obtained in step (a) into the methanol solution containing zinc to obtain a mixed solution, and stir at room temperature to obtain dodecahedral ZIF-8;

[0039] (c) Disperse the dodecahedral ZIF-8 obtained in step (b) in methanol, dissolve a cobalt source and a gadolinium source in methanol, and dissolve 2-methylimidazole in methanol, then pour the cobalt source and gadolinium source methanol solution and the 2-methylimidazole methanol solution into the ZIF-8 methanol solution at the same time to obtain a mixed solution, and stir at room temperature to obtain ZIF-8@ZIF-67@Gd;

[0040] (d) Disperse the ZIF-8@ZIF-67@Gd obtained in step (c) in a mixed solvent of water and ethanol, and sequentially add a tris(hydroxymethyl)aminomethane aqueous solution and a dopamine hydrochloride aqueous solution to the ZIF-8@ZIF-67@Gd ethanol aqueous solution to obtain a mixed solution, and stir at room temperature to obtain ZIF-8@ZIF-67@Gd@PDA;

[0041] (e) Calcine the ZIF-8@ZIF-67@Gd@PDA obtained in step (d) under a protective gas atmosphere to obtain a carbonized product Gd-Co@NC;

[0042] (f) Place the Gd-Co@NC obtained in step (e) and a sulfur source downstream and upstream of a protective gas flow respectively, and perform calcination treatment to obtain a bifunctional catalyst Gd-Co / CoS2@NC based on rare earth gadolinium doping.

[0043] Preferably, the gadolinium source in step (c) is gadolinium nitrate; the molar ratio of cobalt ions in the zinc source to gadolinium ions in the gadolinium source is 30:1 to 5:1 (30:1, 10:1; 5:1).

[0044] Preferably, the zinc source in step (a) is zinc nitrate;

[0045] Preferably, the stirring time in step (b) is 20 to 28 h;

[0046] Preferably, the concentration of zinc ions in the mixed solution in step (b) is 0.04 to 0.05 M; the molar ratio of zinc ions to 2-methylimidazole in the mixed solution is 1:12 to 13;

[0047] Preferably, the cobalt source in step (c) is cobalt nitrate;

[0048] Preferably, the total concentration of cobalt ions and gadolinium ions in the mixed solution in step (c) is 4 to 7 mM; the molar ratio of the total amount of cobalt ions and gadolinium ions to 2-methylimidazole in the mixed solution is 1:12 to 13;

[0049] Preferably, the ratio of the mass of the dodecahedral ZIF-8 to the total molar amount of cobalt ions and gadolinium ions in the mixed solution in step (c) is 1 to 2 g:6 mMol;

[0050] Preferably, the stirring time in step (c) is 10 to 20 min;

[0051] Preferably, the volume ratio of water to ethanol in the mixed solution in step (d) is 1 to 1.5:1;

[0052] Preferably, the concentration of tris(hydroxymethyl)aminomethane in the mixed solution in step (d) is 18 to 24 mM;

[0053] Preferably, the concentration of dopamine hydrochloride in the mixed solution in step (d) is 1.5 to 1.8 mM;

[0054] Preferably, the content of ZIF-8@ZIF-67@Gd in the mixed solution in step (d) is 1.0 to 1.2 g / L;

[0055] Preferably, the stirring time in step (d) is 1 to 2 h;

[0056] Preferably, the volume ratio of water to ethanol in the ethanol aqueous solution of ZIF-8@ZIF-67@Gd in step (d) is 1:2.5 to 3.0;

[0057] Preferably, the content of ZIF-8@ZIF-67 in the ethanol aqueous solution of ZIF-8@ZIF-67@Gd in step (d) is 1.8 to 2.0 g / L;

[0058] Preferably, the concentration of the tris(hydroxymethyl)aminomethane aqueous solution in step (d) is 80–100 mM;

[0059] Preferably, the concentration of the dopamine hydrochloride aqueous solution in step (d) is 10–11 mM;

[0060] Preferably, the volume ratio of the ZIF-8@ZIF-67@Gd aqueous ethanol solution, tris(hydroxymethyl)aminomethane aqueous solution, and dopamine hydrochloride aqueous solution in step (d) is 1.0-1.2:0.3-0.5:0.3.

[0061] Preferably, the calcination temperature in step (e) is set as follows: first heat to 150–250°C, with a heating rate of 2–5°C / min. -1 Hold at the same temperature for 2–5 hours, then raise the temperature to 700–900℃ at a rate of 2–5℃ / min. -1 Keep warm for 2-5 hours;

[0062] More preferably, the calcination temperature in step (e) is set as follows: first heat to 200°C, with a heating rate of 2°C / min. -1 The temperature was kept at the same temperature for 2 hours, and then raised to 800℃ at a rate of 2℃ / min. -1 Keep warm for 2 hours.

[0063] Preferably, the sulfur source in step (f) is sulfur powder; the mass ratio of the sulfur source to Gd-Co@NC is 5 to 10:1; the firing temperature is 300 to 450°C, and the firing time is 1.5 to 2.5 hours.

[0064] Preferably, the protective gas in steps (e) and (f) is nitrogen or an inert gas (such as argon).

[0065] The above-described method prepares a bifunctional catalyst, Gd-Co / CoS2@NC, based on rare earth gadolinium doping.

[0066] Application of the aforementioned bifunctional catalyst Co / CoS2@NC or the aforementioned rare earth gadolinium-doped bifunctional catalyst Gd-Co / CoS2@NC in electrocatalytic oxygen evolution and oxygen reduction.

[0067] The Co / CoS2@NC catalyst of this invention uses ZIF-8 as a sacrificial matrix, and in order to prevent the dodecahedron from collapsing under high temperature calcination, a rigid polydopamine film is wrapped around its outer layer to form a hollow dodecahedron. This not only has a high effective specific surface area, providing abundant electrochemical active sites, but also the internal cavity structure can buffer the volume expansion during charge and discharge, improving the cycle stability of the material. Furthermore, the hollow shell structure has better mechanical properties due to the mutual support of different shells.

[0068] This invention proposes to utilize rare-earth gadolinium doping to modulate the electronic structure of Co / CoS2@NC, and successfully prepares a Gd x -Co / CoS2@NC catalyst. First, ZIF-8 was prepared, and the amount of gadolinium doping was adjusted. Then, the successfully prepared ZIF-8@ZIF-67@Gd was coated with polydopamine, and the resulting Gd-Co / CoS2@NC was directly used as a catalyst for electrocatalytic oxygen production and oxygen reduction after high-temperature calcination and sulfidation.

[0069] This invention uses gadolinium doping to prepare Gd x -Co / CoS2@NC catalyst, utilizing gadolinium doping to modulate the electronic structure of Co / CoS2@NC, and taking advantage of the good conductivity of the outer carbon film, yields hollow dodecahedral Gd x -Co / CoS2@NC catalysts can be used for electrocatalytic oxygen production and oxygen reduction, exhibiting good catalytic properties.

[0070] This invention synthesizes hollow dodecahedral Gd by coordination pyrolysis and sulfidation of ZIF precursor. x The catalytic sites of Co / CoS2@NC were constructed, and their interfacial assembly on ultrathin hollow nitrogen-doped carbon nanocages (Co / CoS2@NC) was achieved through physical stress stretching during pyrolysis. Gadolinium doping was used to modulate the electronic structure of Co / CoS2@NC, thereby further enhancing its electrocatalytic performance. Specifically, ZIF-8 polyhedral nanocrystals were first prepared as a sacrificial matrix. Considering the similar topological structure and cellular parameters of ZIF-8 nanocrystals, a thin layer of Co-containing ZIF-67 was epitaxially grown on the ZIF-8 nanocrystals (ZIF-8@ZIF-67). To introduce rare earth gadolinium, some Co was replaced with Gd in ZIF-8@ZIF-67, forming (ZIF-8@ZIF-67@Gd). Gd doping was used to ensure that Co and Gd coexisted in the ZIF-67 layer. Subsequently, an ultrathin polydopamine (PDA) shell was coated onto the surface of ZIF-8@ZIF-67@Gd. During pyrolysis, the relatively hard carbonized PDA shell, formed very early in the process, acts as a framework, inhibiting the shrinkage of the internal ZIF components and inducing the accumulation of pyrolysis species on the shell, forming a hollow structure. Correspondingly, the Gd and Co-containing ZIF-67 layer transforms into a carbon shell. Finally, sulfidation occurs, forming a hollow dodecahedral Gd... x -Co / CoS2@NC. The non-noble metal catalyst prepared using the method of this invention exhibits high catalytic activity and good stability in the electrocatalytic oxygen evolution and oxygen reduction reactions. This catalytic material has been shown to be a promising industrial-scale cathode catalyst for zinc-air batteries, thereby significantly improving the theoretical performance of zinc-air batteries.

[0071] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0072] (1) The catalyst prepared by the method provided in this invention has a porous carbon structure and a hollow structure. The porous carbon structure has high porosity and high conductivity; the hollow structure has a high effective specific surface area, which can provide abundant electrochemical active sites. The internal cavity structure can buffer the volume expansion during charge and discharge, improve the cycle stability of the material, and the multi-shell hollow structure has better mechanical properties due to the mutual support of different shells. The high porosity allows the electrolyte to enter the interior of the hollow structure material, thereby improving the wettability of the electrolyte and shortening the transport paths of ions and electrons, giving the catalyst excellent bifunctional performance, thereby significantly improving the reaction kinetics.

[0073] (2) This invention uses rare earth gadolinium-doped Co / CoS2@NC catalyst. Rare earth gadolinium doping regulates the electronic structure of cobalt and increases the number of mesopores in the material, and the catalytic performance of gadolinium-doped catalyst is significantly improved. This invention uses non-precious metal-based catalyst instead of commonly used precious metal catalysts on the market, which reduces the cost of catalyst.

[0074] (3) The hollow dodecahedron Gd prepared by the present invention x -Co / CoS2@NC catalyst exhibits low oxygen evolution overpotential and high oxygen reduction half-wave potential, demonstrating excellent catalytic performance and stability, and has broad application prospects in the field of zinc-air batteries. Attached Figure Description

[0075] Figure 1 Gd in Examples 2-4 x - Co / CoS2@NC and X-ray diffraction (XRD) patterns of Co / CoS2@NC in Example 1;

[0076] Figure 2 Gd in Example 3 x - Co / CoS2@NC and Co / CoS2@NC N2 adsorption / desorption curves of Example 1;

[0077] Figure 3 Gd in Example 3 x -NL-DFT pore size distribution curves of Co / CoS2@NC and Co / CoS2@NC in Example 1;

[0078] Figure 4 The image shows a scanning electron microscope (SEM) image of Co / CoS2@NC from Example 1.

[0079] Figure 5 Gd in Example 2 xScanning electron microscope (SEM) image of -Co / CoS2@NC;

[0080] Figure 6 Gd in Example 3 x Scanning electron microscope (SEM) image of -Co / CoS2@NC;

[0081] Figure 7 Gd in Example 4 x Scanning electron microscope (SEM) image of -Co / CoS2@NC;

[0082] Figure 8 This is a transmission electron microscope (TEM) image of Co / CoS2@NC from Example 1;

[0083] Figure 9 Gd in Example 2 x Transmission electron microscopy (TEM) image of Co / CoS2@NC;

[0084] Figure 10 Gd in Example 3 x Transmission electron microscopy (TEM) image of Co / CoS2@NC;

[0085] Figure 11 Gd in Example 4 x Transmission electron microscopy (TEM) image of Co / CoS2@NC;

[0086] Figure 12 Gd in Embodiments 2-4 of the present invention x - Linear sweep voltammograms (LSV) of oxygen reduction reaction of Co / CoS2@NC and Co / CoS2@NC in Example 1;

[0087] Figure 13 Gd in Embodiment 3 of the present invention x - Co / CoS2@NC timing current response at a fixed potential (0.85V);

[0088] Figure 14 Gd in Embodiments 2-4 of the present invention x - Linear sweep voltammograms (LSV) of the oxygen evolution reaction of Co / CoS2@NC and Co / CoS2@NC in Example 1;

[0089] Figure 15 Gd in Embodiment 3 of the present invention x -Co / CoS2@NC at 10mA·cm -2 Chronopotential curves at current density for 20 hours. Detailed Implementation

[0090] The following examples further illustrate specific implementations of the present invention, but the implementation and protection of the present invention are not limited thereto. It should be noted that any processes not specifically described below are those that can be implemented or understood by those skilled in the art by referring to existing technology. Reagents or instruments whose manufacturers are not specified are considered to be conventional products that can be purchased commercially.

[0091] The electrochemical performance characterization (linear voltammetric scan) methods for the catalysts prepared in the following examples and comparative examples are as follows:

[0092] 4.0 mg of the catalysts prepared in Examples 1, 2, 3, and 4 were prepared into 1.0 mL of catalyst ink, which was then dropped onto the surface of a glassy carbon electrode. After drying, the ink was used as the working electrode for linear voltammetry scanning.

[0093] All electrochemical measurements were performed at room temperature. Catalyst performance was tested using a three-electrode system: a glassy carbon electrode coated with the catalyst as the working electrode, a platinum wire electrode as the counter electrode, and a silver / silver chloride electrode (filled with a saturated KCl solution) as the reference electrode. Catalyst performance was obtained by linear sweep voltammetry (LSV). For bifunctional catalysts, the test medium for ORR testing was a 0.1M KOH solution saturated with O2; the test medium for OER testing was a 1M KOH solution.

[0094] Example 1

[0095] A method for preparing a Co / CoS2@NC catalyst includes the following steps:

[0096] Zn(NO3)2·6H2O (2g) and 2-methylimidazole (7g) were dissolved in 100mL and 50mL of anhydrous methanol, respectively, and stirred at room temperature to obtain clear solutions. Then, the 2-methylimidazole solution was quickly poured into zinc nitrate solution, and the mixture was reacted slowly (400rpm) at room temperature for 24h. The white precipitate ZIF-8 was obtained by centrifugation, washed three times with anhydrous methanol, and dried under vacuum at 60℃ for 12h for later use.

[0097] 150 mg of the prepared ZIF-8 was dispersed in 50 mL of anhydrous methanol. 0.175 g of Co(NO3)2·6H2O and 0.6 g of 2-methylimidazole were dissolved in 25 mL of anhydrous methanol, respectively. The solutions were stirred at room temperature to obtain a clear solution. Then, the 2-methylimidazole solution and cobalt nitrate solution were rapidly poured into the dispersed ZIF-8 methanol solution simultaneously under vigorous stirring (800 rpm). The mixture was then reacted at room temperature for 15 min with slow stirring (400 rpm). The purple precipitate ZIF-8@ZIF-67 was obtained by centrifugation, washed three times with anhydrous methanol, and dried under vacuum at 60 °C for 12 h for later use.

[0098] The prepared ZIF-8@ZIF-67 (200 mg) was dispersed in a mixed solvent of 30 mL water and 80 mL anhydrous ethanol. 40 mL of a 100 mM tris(hydroxymethyl)aminomethane aqueous solution was added under vigorous stirring (800 rpm). After stirring for 30 min at room temperature, 30 mL of an aqueous solution containing 60 mg dopamine hydrochloride was added to the suspension, and the mixture was reacted under slow stirring (400 rpm) at room temperature for 60 min. The black precipitate ZIF-8@ZIF-67@PDA was obtained by centrifugation, washed three times each with water and ethanol, and then vacuum dried at 60 °C for 12 h for later use.

[0099] Take the prepared ZIF-8@ZIF-67@PDA (40mg) and place it in a quartz boat. Put it in a tube furnace and heat it to 200℃ at a heating rate of 2℃ / min under an argon atmosphere. Hold it at 200℃ for 2h. Then heat it to 800℃ at a heating rate of 2℃ / min and hold it at 800℃ for 2h. Then let it cool naturally to room temperature. The black powder obtained is Co@NC.

[0100] Weigh 400 mg of sulfur powder and place it in a ceramic boat. Put Co@NC (40 mg) in another ceramic boat and place the two ceramic boats upstream and downstream of a tube furnace, respectively. Heat the furnace to 450 °C at a heating rate of 5 °C / min under an argon atmosphere and maintain the temperature at 450 °C for 2 hours. Then let it cool naturally to room temperature. The resulting black powder is the final catalyst Co / CoS2@NC.

[0101] Example 2

[0102] A method for preparing a gadolinium-doped Co / CoS2@NC catalyst includes the following steps:

[0103] Zn(NO3)2·6H2O (2g) and 2-methylimidazole (7g) were dissolved in 100mL and 50mL of anhydrous methanol, respectively, and stirred at room temperature to obtain clear solutions. Then, the 2-methylimidazole solution was quickly poured into zinc nitrate solution, and the mixture was reacted slowly (400rpm) at room temperature for 24h. The white precipitate ZIF-8 was obtained by centrifugation, washed three times with anhydrous methanol, and dried under vacuum at 60℃ for 12h for later use.

[0104] 150 mg of the prepared ZIF-8 was dispersed in 50 mL of anhydrous methanol. 0.169 g of Co(NO3)2·6H2O and 0.009 g of Gd(NO3)3·6H2O were dissolved in 25 mL of anhydrous methanol, and 0.6 g of 2-methylimidazole was dissolved in 25 mL of anhydrous methanol. The mixture was stirred at room temperature to obtain a clear solution. Then, the 2-methylimidazole solution and cobalt nitrate solution were rapidly poured into the dispersed ZIF-8 methanol solution while stirring vigorously (800 rpm). The mixture was then stirred slowly (400 rpm) and reacted at room temperature for 15 min. The purple precipitate ZIF-8@ZIF-67@Gd was obtained by centrifugation, washed three times with anhydrous methanol, and dried under vacuum at 60 °C for 12 h for later use.

[0105] The prepared ZIF-8@ZIF-67@Gd (200 mg) was dispersed in a mixed solvent of 30 mL water and 80 mL anhydrous ethanol. 40 mL of a 100 mM tris(hydroxymethyl)aminomethane aqueous solution was added under vigorous stirring (800 rpm). After stirring for 30 min at room temperature, 30 mL of an aqueous solution containing 60 mg dopamine hydrochloride was added to the suspension, and the mixture was reacted under slow stirring (400 rpm) at room temperature for 60 min. The black precipitate ZIF-8@ZIF-67@Gd@PDA was obtained by centrifugation, washed three times each with water and ethanol, and then vacuum dried at 60 °C for 12 h for later use.

[0106] Take the prepared ZIF-8@ZIF-67@Gd@PDA (40mg) and place it in a quartz boat. Put the boat into a tube furnace and heat it to 200℃ at a heating rate of 2℃ / min under an argon atmosphere. Hold the temperature at 200℃ for 2h. Then heat it to 800℃ at a heating rate of 2℃ / min and hold the temperature at 800℃ for 2h. Then let it cool naturally to room temperature. The black powder collected is Gd-Co@NC.

[0107] Weigh 400 mg of sulfur powder and place it in a ceramic boat. Put Gd-Co@NC (40 mg) in another ceramic boat and place the two ceramic boats upstream and downstream of a tube furnace, respectively. Heat the furnace to 450 °C at a heating rate of 5 °C / min under an argon atmosphere and maintain the temperature at 450 °C for 2 hours. Then let it cool naturally to room temperature. The resulting black powder is the final catalyst Gd-Co / CoS2@NC.

[0108] Example 3

[0109] A method for preparing a gadolinium-doped Co / CoS2@NC catalyst includes the following steps:

[0110] Zn(NO3)2·6H2O (2g) and 2-methylimidazole (7g) were dissolved in 100mL and 50mL of anhydrous methanol, respectively, and stirred at room temperature to obtain clear solutions. Then, the 2-methylimidazole solution was quickly poured into zinc nitrate solution, and the mixture was reacted slowly (400rpm) at room temperature for 24h. The white precipitate ZIF-8 was obtained by centrifugation, washed three times with anhydrous methanol, and dried under vacuum at 60℃ for 12h for later use.

[0111] 150 mg of the prepared ZIF-8 was dispersed in 50 mL of anhydrous methanol. 0.157 g of Co(NO3)2·6H2O and 0.027 g of Gd(NO3)3·6H2O were dissolved in 25 mL of anhydrous methanol, and 0.6 g of 2-methylimidazole was dissolved in 25 mL of anhydrous methanol. The mixture was stirred at room temperature to obtain a clear solution. Then, the 2-methylimidazole solution and cobalt nitrate solution were rapidly poured into the dispersed ZIF-8 methanol solution while stirring vigorously (800 rpm). The mixture was then reacted slowly (400 rpm) at room temperature for 15 min. The purple precipitate ZIF-8@ZIF-67@Gd was obtained by centrifugation, washed three times with anhydrous methanol, and dried under vacuum at 60 °C for 12 h for later use.

[0112] The prepared ZIF-8@ZIF-67@Gd (200 mg) was dispersed in a mixed solvent of 30 mL water and 80 mL anhydrous ethanol. 40 mL of a 100 mM tris(hydroxymethyl)aminomethane aqueous solution was added under vigorous stirring (800 rpm). After stirring for 30 min at room temperature, 30 mL of an aqueous solution containing 60 mg dopamine hydrochloride was added to the suspension, and the mixture was reacted under slow stirring (400 rpm) at room temperature for 60 min. The black precipitate ZIF-8@ZIF-67@Gd@PDA was obtained by centrifugation, washed three times each with water and ethanol, and then vacuum dried at 60 °C for 12 h for later use.

[0113] Take the prepared ZIF-8@ZIF-67@Gd@PDA (40mg) and place it in a quartz boat. Put the boat into a tube furnace and heat it to 200℃ at a heating rate of 2℃ / min under an argon atmosphere. Hold the temperature at 200℃ for 2h. Then heat it to 800℃ at a heating rate of 2℃ / min and hold the temperature at 800℃ for 2h. Then let it cool naturally to room temperature. The black powder collected is Gd-Co@NC.

[0114] Weigh 400 mg of sulfur powder and place it in a ceramic boat. Put Gd-Co@NC (40 mg) in another ceramic boat and place the two ceramic boats upstream and downstream of a tube furnace, respectively. Heat the furnace to 450 °C at a heating rate of 5 °C / min under an argon atmosphere and maintain the temperature at 450 °C for 2 hours. Then let it cool naturally to room temperature. The resulting black powder is the final catalyst Gd-Co / CoS2@NC.

[0115] Example 4

[0116] A method for preparing a gadolinium-doped Co / CoS2@NC catalyst includes the following steps:

[0117] Zn(NO3)2·6H2O (2g) and 2-methylimidazole (7g) were dissolved in 100mL and 50mL of anhydrous methanol, respectively, and stirred at room temperature to obtain clear solutions. Then, the 2-methylimidazole solution was quickly poured into zinc nitrate solution, and the mixture was reacted slowly (400rpm) at room temperature for 24h. The white precipitate ZIF-8 was obtained by centrifugation, washed three times with anhydrous methanol, and dried under vacuum at 60℃ for 12h for later use.

[0118] 150 mg of the prepared ZIF-8 was dispersed in 50 mL of anhydrous methanol. 0.145 g of Co(NO3)2·6H2O and 0.045 g of Gd(NO3)3·6H2O were dissolved in 25 mL of anhydrous methanol, and 0.6 g of 2-methylimidazole was dissolved in 25 mL of anhydrous methanol. The mixture was stirred at room temperature to obtain a clear solution. Then, the 2-methylimidazole solution and cobalt nitrate solution were rapidly poured into the dispersed ZIF-8 methanol solution while stirring vigorously (800 rpm). The mixture was then stirred slowly (400 rpm) and reacted at room temperature for 15 min. The purple precipitate ZIF-8@ZIF-67@Gd was obtained by centrifugation, washed three times with anhydrous methanol, and dried under vacuum at 60 °C for 12 h for later use.

[0119] The prepared ZIF-8@ZIF-67@Gd (200 mg) was dispersed in a mixed solvent of 30 mL water and 80 mL anhydrous ethanol. 40 mL of a 100 mM tris(hydroxymethyl)aminomethane aqueous solution was added under vigorous stirring (800 rpm). After stirring for 30 min at room temperature, 30 mL of an aqueous solution containing 60 mg dopamine hydrochloride was added to the suspension, and the mixture was reacted under slow stirring (400 rpm) at room temperature for 60 min. The black precipitate ZIF-8@ZIF-67@Gd@PDA was obtained by centrifugation, washed three times each with water and ethanol, and then vacuum dried at 60 °C for 12 h for later use.

[0120] Take the prepared ZIF-8@ZIF-67@Gd@PDA (40mg) and place it in a quartz boat. Put the boat into a tube furnace and heat it to 200℃ at a heating rate of 2℃ / min under an argon atmosphere. Hold the temperature at 200℃ for 2h. Then heat it to 800℃ at a heating rate of 2℃ / min and hold the temperature at 800℃ for 2h. Then let it cool naturally to room temperature. The black powder collected is Gd-Co@NC.

[0121] Weigh 400 mg of sulfur powder and place it in a ceramic boat. Put Gd-Co@NC (40 mg) in another ceramic boat and place the two ceramic boats upstream and downstream of a tube furnace, respectively. Heat the furnace to 450 °C at a heating rate of 5 °C / min under an argon atmosphere and maintain the temperature at 450 °C for 2 hours. Then let it cool naturally to room temperature. The resulting black powder is the final catalyst Gd-Co / CoS2@NC.

[0122] Data Analysis:

[0123] Figure 1 The X-ray diffraction (XRD) patterns are shown in Examples 1-4;

[0124] Figure 2 Co / CoS2@NC from Example 1 and Gd from Example 3 x -Co / CoS2@NC N2 adsorption / desorption curves;

[0125] Figure 3 Co / CoS2@NC from Example 1 and Gd from Example 3 x NL-DFT pore size distribution curve of -Co / CoS2@NC N2;

[0126] Figure 4 The image shows a scanning electron microscope (SEM) image of Co / CoS2@NC from Example 1.

[0127] Figure 5 Gd in Example 2 x Scanning electron microscope (SEM) image of -Co / CoS2@NC;

[0128] Figure 6 Gd in Example 3 x Scanning electron microscope (SEM) image of -Co / CoS2@NC;

[0129] Figure 7 Gd in Example 4 x Scanning electron microscope (SEM) image of -Co / CoS2@NC;

[0130] Figure 8 This is a transmission electron microscope (TEM) image of Co / CoS2@NC from Example 1;

[0131] Figure 9 Gd in Example 2 x Transmission electron microscopy (TEM) image of Co / CoS2@NC;

[0132] Figure 10 Gd in Example 3 x Transmission electron microscopy (TEM) image of Co / CoS2@NC;

[0133] Figure 11 Gd in Example 4 x Transmission electron microscopy (TEM) image of Co / CoS2@NC;

[0134] Figure 12 Linear sweep voltammograms (LSVs) of the oxygen reduction reaction in Examples 1-4 of this invention;

[0135] Figure 13 Gd in Embodiment 3 of the present invention x - Co / CoS2@NC timing current response at a fixed potential (0.85V);

[0136] Figure 14 Linear sweep voltammograms (LSVs) of the oxygen evolution reaction in Examples 1-4 of this invention;

[0137] Figure 15 Gd in Embodiment 3 of the present invention x -Co / CoS2@NC at 10mA·cm -2 Chronopotential curves at current density for 20 hours.

[0138] from Figure 1 It can be seen that the successful preparation of Examples 1, 2, 3 and 4 proves that the materials all contain CoS2 and Co, and the position of the peak shifts to the left with the increase of rare earth Gd doping. This is because the atomic radius of rare earth Gd is larger than that of Co. When some Co is replaced by Gd, it leads to lattice distortion.

[0139] from Figure 2 It can be seen that both Examples 1 and 3 exhibit typical Type IV curves and have H3-type hysteresis loops. The larger specific surface area after rare earth doping is likely due to the higher bond energy between rare earth elements and sulfur atoms. The reduced lattice volume effectively increases the specific surface area of ​​the material, leading to a more stable structure.

[0140] from Figure 3It can be seen that although Example 1 has more micropores than Example 3, Example 3 has significantly more mesopores than Example 1. More micropores result in a larger apparent surface area, which is beneficial for the distribution of active sites and increases the contact between active sites and the substrate. However, the relatively long spacing between micropores hinders reactant diffusion, thus negatively impacting reaction kinetics. In contrast, mesopores are more conducive to the transport of reactants or solvents.

[0141] from Figure 4 , 5 As can be seen from points 6 and 7, gadolinium doping does not change the morphology and size of the dodecahedron in the material.

[0142] from Figure 8 , 9 As can be seen from 10 and 11, the hollow dodecahedron was successfully prepared.

[0143] from Figure 12 It can be seen that the doping of rare earth gadolinium improves the electrocatalytic performance of oxygen reduction. The oxygen reduction half-wave potential (0.852V) with the optimal doping amount is higher than that of commercial catalyst Pt / C (0.848V). As the amount of gadolinium increases, the half-wave potential of the catalyst also increases, indicating the improvement of electrocatalytic performance. However, when the amount of gadolinium increases to a certain extent (Example 4), the half-wave potential shows a downward trend, thus finding the optimal doping amount (Example 3).

[0144] from Figure 13 It can be seen that the catalytic stability of Example 3 under 0.1m KOH conditions was further investigated by chronoamperometry (it). Example 3 exhibits excellent stability, with a current retention rate of 91% after 30,000 s.

[0145] from Figure 14 It can be seen that the trend of gadolinium doping on the catalytic activity of oxygen evolution reaction is consistent with that of oxygen reduction, with the overpotential of Example 3 being 343mV.

[0146] from Figure 15 It can be seen that at 10mA·cm -2 At the specified current density, the oxygen evolution performance of Example 3 remained stable over 21 hours, with no significant change in voltage, indicating that the catalyst exhibits good stability.

[0147] The above embodiments are merely preferred embodiments of the present invention and are only used to explain the present invention, not to limit the present invention. Any changes, substitutions, modifications, etc., made by those skilled in the art without departing from the spirit and essence of the present invention should be within the protection scope of the present invention.

Claims

1. A method for the preparation of a bifunctional catalyst based on rare earth gadolinium doping, characterized by, Comprising the following steps: (a) separately dissolving a zinc source and 2-methylimidazole in methanol, stirring to make them completely dissolved in methanol; (b) pouring the methanol solution of 2-methylimidazole obtained in step (a) into the methanol solution containing zinc to obtain a mixed solution, stirring at room temperature to obtain a dodecahedron ZIF-8; the concentration of zinc ions in the mixed solution is 0.04-0.05 M; (c) dispersing the dodecahedron ZIF-8 obtained in step (b) in methanol, dissolving a cobalt source and a gadolinium source in methanol, dissolving 2-methylimidazole in methanol, pouring the cobalt source and gadolinium source methanol solution and the 2-methylimidazole methanol solution into the ZIF-8 methanol solution at the same time to obtain a mixed solution, stirring at room temperature to obtain ZIF-8@ZIF-67@Gd; the gadolinium source is gadolinium nitrate; the molar ratio of cobalt ions in the zinc source to gadolinium ions in the gadolinium source is 30:1-5:1; the total concentration of cobalt ions and gadolinium ions in the mixed solution is 4-7 mM; the mass of dodecahedron ZIF-8, the total molar amount of cobalt ions and gadolinium ions in the mixed solution is 1-2 g:6 mmol; (d) dispersing the ZIF-8@ZIF-67@Gd obtained in step (c) in a mixed solvent of water and ethanol, sequentially adding a tris(hydroxymethyl)aminomethane aqueous solution and a dopamine hydrochloride aqueous solution to the ethanol aqueous solution of ZIF-8@ZIF-67@Gd to obtain a mixed solution, stirring at room temperature to obtain ZIF-8@ZIF-67@Gd@PDA; (e) calcining the ZIF-8@ZIF-67@Gd@PDA obtained in step (d) under a protective gas atmosphere to obtain a carbonized product Gd-Co@NC; the temperature of the calcining is set as: first heated to 150-250℃, the heating rate is 2-5℃ / min -1 , and kept at the same temperature for 2-5 h, and then heated to 700-900℃, the heating rate is 2-5℃ / min -1 , and kept for 2-5 h; (f) placing the Gd-Co@NC obtained in step (e) and a sulfur source downstream and upstream of a flow of protective gas respectively, and performing a calcination treatment to obtain a rare earth gadolinium-doped bifunctional catalyst Gd-Co / CoS2@NC; the sulfur source is sulfur powder; the mass ratio of the sulfur source to Gd-Co@NC is 5-10:1; the calcination treatment temperature is 300-450℃, and the calcination treatment time is 1.5-2.5 h.

2. The method for preparing a bifunctional catalyst based on rare-earth gadolinium doping according to claim 1, characterized in that, The zinc source in step (a) is zinc nitrate; The stirring time in step (b) is 20-28 h; The molar ratio of zinc ions to 2-methylimidazole in the mixed solution in step (b) is 1:12-13; The cobalt source in step (c) is cobalt nitrate; The molar ratio of the total amount of cobalt ions and gadolinium ions to 2-methylimidazole in the mixed solution in step (c) is 1:12-13; The stirring time in step (c) is 10-20 min; The volume ratio of water to ethanol in the mixed solution in step (d) is 1-1.5:1; The concentration of tris(hydroxymethyl)aminomethane in the mixed solution in step (d) is 18-24 mM; The concentration of dopamine hydrochloride in the mixed solution in step (d) is 1.5-1.8 mM; The content of ZIF-8@ZIF-67@Gd in the mixed solution in step (d) is 1.0-1.2 g / L; The stirring time in step (d) is 1-2 h.

3. The rare earth gadolinium-doped bifunctional catalyst Gd-Co / CoS2@NC prepared by the preparation method of any one of claims 1-2.

4. The use of the bifunctional catalyst based on rare earth gadolinium doping Gd-Co / CoS2@NC of claim 3 in electrocatalytic oxygen evolution and oxygen reduction.

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