Electrocatalytic hydrogen evolution catalyst and preparation and application thereof

Abstract

The invention discloses an electro-catalytic hydrogen evolution catalyst and preparation and application thereof, the catalyst comprises a porous carbon carrier loaded with metal elements capable of catalyzing electro-catalytic hydrogen evolution reaction, the porous carbon carrier contains hierarchical pore channels in which micropores, mesopores and macropores coexist, and the porous carbon carrier is doped with non-metal elements. The preparation method comprises the following steps: by taking heteroatom-doped graphene quantum dots (GQDs) as a carbon source and M / Zn-ZIF-8 as a metal source and a self-sacrifice template, adding Ru salt, and performing freeze drying to obtain a precursor; by regulating and controlling the mass ratio of GQDs, M / Zn-ZIF-8 and Ru salt in a precursor, a tightly connected mesoporous / macroporous structure is constructed, so that MRu alloy nanoparticles are uniformly distributed on a carbon wall with a cavity, the hierarchical pore MRu catalyst is formed, and the difficulty that a GQDs derivative catalyst only contains micropores is overcome. The catalyst has excellent mass transfer characteristic and high specific surface area, and the reaction activity of HER is remarkably improved.

Description

Technical Field

[0001] The invention relates to a catalyst and a preparation method thereof, and in particular to an electrocatalytic hydrogen evolution catalyst and a preparation and application thereof. Background Art

[0002] The electrocatalytic hydrogen evolution reaction (HER) is an efficient and environmentally friendly method for hydrogen production. HER relies on the participation of hydrogen evolution catalysts. However, the commonly used hydrogen evolution catalysts currently have problems such as high cost, low activity, and poor stability, which seriously limit their large-scale application.

[0003] Non-precious metal or low-precious metal catalysts such as ruthenium (Ru) have shown potential to replace Pt-based materials in the hydrogen evolution reaction (HER) due to their moderate hydrogen adsorption energy and low price. The d-band center of Ru is relatively high, resulting in a higher adsorption energy (ΔG-H) for H*. The preparation of Ru-based alloys can regulate the electronic structure of Ru through the alloying effect, reduce its d-band center, and thus weaken the adsorption strength of H*. In addition, the heterojunction formed at the metal interface in the Ru-based alloy provides an efficient channel for the migration of hydrogen atoms, significantly improving the hydrogen overflow efficiency. H* adsorbed on the Ru site can quickly migrate to the metal site or the carrier surface (such as the carbon substrate), accelerating the generation and desorption of H2.

[0004] However, Ru-based catalysts generally face the problem of metal nanoparticle agglomeration during the synthesis and catalytic process: Ru nanoparticles with high surface energy are prone to migration and aggregation during high-temperature carbonization or electrochemical cycles, resulting in a decrease in active site density and deterioration in stability. For example, after 100 hours of operation, the average particle size of Ru catalysts supported by traditional carbon carriers (such as activated carbon and carbon nanotubes) can increase from the initial 3nm to more than 10nm, and the activity loss exceeds 50%. Therefore, how to achieve high-dispersion anchoring of Ru-based metal nanoparticles through carrier design has become the key to improving the performance of Ru-based catalysts.

[0005] As a new type of carbon nanomaterial, graphene quantum dots (GQDs) provide innovative ideas for the dispersion of metal catalysts due to their unique edge functional groups (such as carboxyl, hydroxyl, etc.) and tunable surface chemical properties. The abundant oxygen-containing functional groups on the surface of GQDs can efficiently capture metal ions (such as Ru 3+), and in the subsequent carbonization process, the excessive migration and aggregation of metal species are suppressed through the spatial confinement effect, thereby achieving uniform dispersion of nanoparticles. For example, studies have shown that in Ru-based catalysts prepared with GQDs as precursors, the average size of Ru nanoparticles can be controlled below 2nm, and the dispersion density is increased by 3-5 times compared with traditional carriers. This high dispersion characteristic stems from the following advantages of GQDs: 1) The small size effect of quantum dots (1-10nm) provides high-density anchoring sites; 2) The strong chemical bonding and electrostatic interaction between edge functional groups and metal ions can stabilize the precursor complex; 3) The local reduction environment generated by the decomposition of functional groups during carbonization promotes the nucleation and confined growth of metal nanocrystals. Although GQDs-derived carbon materials perform well in metal dispersion, there is still room for optimization of their inherent properties. For example, GQDs-derived carbon materials are usually dominated by micropores (pore size < 2nm). Although this type of pore structure is conducive to metal dispersion, it seriously restricts the mass transfer dynamics in the catalytic process: the tortuous micropores significantly extend the diffusion path of active hydrogen, and the generated H2 bubbles are easily retained in the pores to form a gas barrier effect, resulting in a sharp decrease in the accessibility of active sites under high current density. This contradiction highlights the limitations of existing strategies - how to build efficient mass transfer channels while ensuring high metal dispersion has become a core challenge in the design of Ru-based alloy catalysts. Summary of the invention

[0006] Purpose of the invention: The purpose of the present invention is to provide an electrocatalytic hydrogen evolution catalyst to solve the problem that the existing graphene quantum dot-derived carbon carrier is dominated by micropores, resulting in a sharp decrease in the accessibility of active sites of the catalyst at high current density. Another purpose of the present invention is to propose a method for preparing an electrocatalytic hydrogen evolution catalyst to solve the problem of how to prepare an electrocatalytic hydrogen evolution catalyst. The third purpose of the present invention is to provide an application of an electrocatalytic hydrogen evolution catalyst in the electrolysis of water to produce hydrogen to solve the problem of how to efficiently electrolyze water to produce hydrogen.

[0007] Technical solution: The electrocatalytic hydrogen evolution catalyst described in the present invention includes a porous carbon carrier loaded with a metal element that can catalyze the electrocatalytic hydrogen evolution reaction, the porous carbon carrier contains multi-level pores in which micropores, mesopores and macropores coexist, and the porous carbon carrier is doped with non-metallic elements.

[0008] Preferably, the metal elements are M and Ru, wherein M includes at least one of Co, Ni, and Mn, and the non-metal elements include at least one of N, P, and S.

[0009] The present invention overcomes the shortcomings of existing GQDs-derived porous carbon materials in terms of porosity. It can not only realize the flexible preparation of Ru-based alloys, but also utilize the unique stress difference effect of the display structure to realize the preparation of multi-level porous substrates, thereby solving the problems of easy agglomeration of Ru-based catalysts and poor mass transfer efficiency.

[0010] The second aspect of the present invention discloses a method for preparing the above-mentioned electrocatalytic hydrogen evolution catalyst, comprising the following steps:

[0011] (1) dissolving citric acid and a heteroatom compound containing at least one of N, P, and S in water to obtain a first reaction solution, and subjecting the first reaction solution to a hydrothermal reaction to obtain heteroatom-doped graphene quantum dots;

[0012] (2) dissolving a zeolite imidazolate framework structure material doped with at least one of Co, Ni, and Mn, heteroatom-doped graphene quantum dots, and Ru salt in water, mixing them to obtain a mixed colloid, freezing the mixed colloid with liquid nitrogen, and then freeze-drying it to obtain an intermediate;

[0013] (3) calcining the intermediate under an inert atmosphere to obtain an electrocatalytic hydrogen evolution catalyst.

[0014] This method uses heteroatom-doped graphene quantum dots (GQDs) as a carbon source, M / Zn-ZIF-8 as a metal source (M = Ni, Co, Mn) and a self-sacrificial template, and RuCl3·3H2O as a Ru source, and freeze-drying to obtain a precursor. By adjusting the mass ratio of GQDs, M / Zn-ZIF-8 and Ru salt in the precursor, the strength of the outward contraction stress generated by GQDs during the carbonization process is optimized, the hollowing of nanoparticles is promoted, and a closely connected mesoporous / macroporous structure is constructed, so that MRu alloy nanoparticles are evenly distributed on the carbon wall with cavities, forming a multi-level porous MRu catalyst, overcoming the difficulty that GQDs-derived catalysts only contain micropores.

[0015] Preferably, in step (1), the heteroatom compound includes at least one of urea, ethylenediamine, melamine, ammonium dihydrogen phosphate, phytic acid, thiourea, and L-cysteine. GQDs have good water phase dispersibility, which is conducive to promoting the formation of stable coordination bonds between metal ions and oxygen-containing functional groups (such as -OH, -C=O), and preventing metal ions from migrating and agglomerating during carbonization; changing the type of additional heteroatom compounds added during the synthesis process can achieve flexible preparation of N-GQDs, P-GQDs, P,N-GQDs, S,N-GQDs with single or co-doping of N, P or S.

[0016] Preferably, in step (1), the mass ratio of citric acid to heteroatom compound is 4-4.5:3.5-4.5, the hydrothermal reaction method is to react at 150-170°C for 2-6h, the product is cooled and immersed in ethanol, sealed and allowed to stand, and after the product changes from dark green to dark blue, centrifuge to obtain the solid, wash the solid with ethanol and then vacuum dry to obtain heteroatom-doped graphene quantum dots.

[0017] Preferably, in step (2), the preparation method of the zeolite imidazolate framework structure material is: dissolving at least one of Co salt, Ni salt, Mn salt, zinc salt, 2-methylimidazole and hexadecyltrimethylammonium bromide in water, stirring the reaction to obtain M / Zn-ZIF-8. M / Zn-ZIF-8, as a metal M source, can realize the controllable preparation of MRu multi-element alloy (M=Ni, Co, Mn, etc.). M / Zn-ZIF-8 nanoparticles can use different metal salts as dopants to replace the Zn sites in the crystal, thereby realizing the preparation of M / Zn-ZIF-8 particles doped with different metals.

[0018] Preferably, the zinc salt, Co salt, Ni salt and Mn salt are all metal carboxylates; for example, zinc acetate, cobalt acetate, nickel acetate, manganese acetate, zinc formate, cobalt formate, nickel formate, manganese formate and the like.

[0019] The Ru salt includes at least one of ruthenium chloride, ruthenium nitrate and ruthenium sulfate.

[0020] Preferably, in step (2), the mass ratio of the zeolite imidazolate framework material, the heteroatom-doped graphene quantum dots and the Ru salt is 50-150:250-350:10-20.

[0021] The nanosize of GQDs limits the growth direction of the carbon skeleton during the carbonization process, resulting in the formation of only micropores. With an appropriate ratio of M / Zn-ZIF-8 particles as a self-sacrificial template, a hollow macroporous structure is formed during the carbonization process. This not only overcomes the shortcoming that GQDs-derived catalysts only contain microporous characteristics, but also does not require additional acid washing to remove the template, making it environmentally friendly.

[0022] Preferably, in step (3), the calcination conditions are to increase the temperature to 800-1000°C at 1-5°C / min, calcine at a constant temperature for 1-5h, and then cool to room temperature at a cooling rate of 5-15°C / min. The inert atmosphere can be Ar or N2 atmosphere, and the flow rate of the inert gas is 50-150mL / min.

[0023] The two-dimensional hybrid array structure precursor is obtained by freeze drying. During the heating process, the stress difference generated can be used to obtain a multi-level porous catalyst rich in micropores / mesopores / macropores loaded with MRu alloy nanoparticles. Zn will volatilize at high calcination temperatures, so there is almost no Zn in the product.

[0024] The third aspect of the present invention discloses the application of the electrocatalytic hydrogen evolution catalyst in the production of hydrogen by electrolysis of water. The specific application method is: take the electrocatalytic hydrogen evolution catalyst and mix it with a binder (such as Nafion), ethanol and water, drip the slurry evenly onto carbon paper, and obtain the cathode of the electrolytic water hydrogen production device after drying.

[0025] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0026] 1) The present invention realizes the flexible functional application of GQDs through freeze-drying, and then accurately constructs a two-dimensional multi-level porous structure of MRu (M = Ni, Co, Mn) alloy catalyst, breaking through the limitations of the traditional GQDs direct carbonization process and providing a new method for the design of high-performance catalytic materials.

[0027] 2) The present invention uses heteroatom doping GQDs@M / Zn-ZIF-8@Ru 3+ The array structure precursor is carbonized. Since the thermal stability of GQDs is low and the thermal stability of ZIF-8 is high, GQDs are first carbonized on the surface of ZIF to produce a rigid carbon layer. The stress difference generated under different heating times causes the ZIF to shrink outward from the sacrificial template to form macropores, which can realize a multi-level porous catalyst rich in micropores / mesopores / macroporous. The present invention overcomes the problem that the GQDs-derived catalyst contains only micropores. The catalyst prepared by the present invention has excellent mass transfer characteristics and a high specific surface area, which significantly improves the reaction activity of HER. The preparation method provided by the present invention is simple and efficient, and the obtained catalyst has broad application prospects in the field of energy conversion.

[0028] 3) The GQDs@M / Zn-ZIF-8@Ru array structure precursor pyrolysis method adopted in the present invention can achieve the doping of heteroatoms such as N, P, and S in the product by changing the raw material composition of GQDs, thereby enhancing the conductivity of the carbon substrate, adjusting the d-band center position of Ru, and optimizing its adsorption energy for reaction intermediates.

[0029] 4) The present invention utilizes the good water phase dispersibility of GQDs to promote Ru 3+ It forms a stable coordination bond with oxygen-containing functional groups (such as -OH, -C=O) to prevent metal ions from migrating and agglomerating during the carbonization process, thereby realizing the preparation of alloy particle catalysts.

[0030] 5) The two-dimensional multi-level porous MRu (M = Ni, Co, Mn) alloy catalyst derived from graphene quantum dots prepared by the present invention has flexible preparation with high metal dispersion and alloy degree, as well as structural advantages such as high specific surface area and multi-level pore size distribution. The catalyst prepared by the present invention has excellent intrinsic activity, efficient active site utilization and excellent mass transfer performance, and exhibits excellent hydrogen evolution performance and kinetic characteristics in the water electrolysis device. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a transmission electron microscope (TEM) photograph of the two-dimensional multi-level porous CoRu alloy catalyst derived from graphene quantum dots prepared in Example 1 (under 200 nm scale);

[0032] Figure 2 The nitrogen adsorption-desorption curve of the two-dimensional multi-level porous CoRu alloy catalyst derived from graphene quantum dots prepared in Example 1;

[0033] Figure 3 The linear sweep voltammetry (LSV) curve of the two-dimensional multi-level porous CoRu alloy catalyst derived from graphene quantum dots prepared in Example 1 in the hydrogen evolution reaction;

[0034] Figure 4 This is the Tafel slope diagram of the two-dimensional multi-level porous CoRu alloy catalyst derived from graphene quantum dots prepared in Example 1. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0036] Example 1: A method for preparing an electrocatalytic hydrogen evolution catalyst is as follows:

[0037] (1) Preparation of N-GQDs

[0038] Weigh 4.2g of citric acid and 3.6g of urea and dissolve them in 100mL of water. After ultrasonic dissolution, transfer them to a reactor and heat them at 160°C for 4 hours. After the product is naturally cooled to room temperature, transfer it to a beaker. Wash the reactor with anhydrous ethanol, and soak the product in 500mL of ethanol. Seal it and let it stand for 3-4 days. After the solution changes from dark green to dark blue, centrifuge the product, wash it with ethanol several times, and vacuum dry it to obtain a bright dark blue powder.

[0039] (2) Preparation of Co / Zn-ZIF-8

[0040] Weigh Zn(CH3COO)2·2H2O (1.40 g, 6.36 mmol) and Co(CH3COO)2·4H2O (0.10 g, 0.46 mmol) respectively and dissolve them in 25 mL of water, then pour them into a 25 mL aqueous solution containing 2-methylimidazole (5.60 g, 68 mmol) and hexadecyltrimethylammonium bromide (CTAB) (5.0 mg, 0.014 mmol) under stirring, and stop stirring until the solution becomes turbid, about 1 minute. After standing at room temperature for 2 hours, ZnCo-ZIF-8 nanoparticles were obtained by centrifugation and washing with water 3 times.

[0041] (3) Two-dimensional layered N-GQDs@Co / Zn-ZIF-8@Ru 3+ Preparation of hybrid array structures

[0042] 300 mg of Co / Zn-ZIF-8 nanoparticles obtained in step (2) were dispersed in 30 mL of water, and a total of 100 mg of N-GQDs obtained in step (1) was added, and 1.5 mL of RuCl3·3H2O aqueous solution (10 mg / mL) was added, and fully ultrasonicated to form a stable and concentration-controllable mixed colloid system. The mixed colloid was quickly frozen by liquid nitrogen and then transferred to a freeze dryer for freeze drying, and finally a material with a two-dimensional layered array structure was obtained.

[0043] (4) Preparation of two-dimensional multi-level pore-supported CoRu alloy catalyst

[0044] The two-dimensional layered N-GQDs@Co / Zn-ZIF-8@Ru 3+ The hybrid array structure was transferred to a tube furnace. Under the protection of inert gas (Ar), the flow rate of inert gas was 150 mL / min, and the temperature was increased to 900 °C at a rate of 3 °C / min. After constant temperature calcination for 3 hours, the temperature was cooled to room temperature at a rate of 10 °C / min to obtain a two-dimensional multi-level pore-supported CoRu alloy catalyst. Its microstructure is as follows Figure 1 As shown, the two-dimensional multi-level pore structure derived from graphene quantum dots presents a highly ordered arrangement state, and obviously has a highly developed hollow feature. This unique hollow structure not only significantly improves the specific surface area of ​​the material, but also provides an efficient channel for the transmission of reactants and products. The multi-level pore structure is interconnected by an ultra-thin carbon shell layer to form a continuous three-dimensional conductive network, which not only enhances the mechanical stability of the material, but also optimizes the electron transmission path. In addition, the CoRu alloy particles are dispersed in the two-dimensional multi-level pore structure in the form of fine particles, avoiding a large amount of agglomeration between particles.

[0045] 5 mg of catalyst was mixed with 40 uL of 5% Nafion solution, 800 uL of ethanol and 160 uL of water. After ultrasonic treatment for 2 h, the slurry was evenly dropped onto carbon paper and dried. It was used as the working electrode of the water electrolysis hydrogen production device. A three-electrode system was used on an electrochemical workstation (CHI-760E), with the carbon rod and Hg / HgO electrode as the counter electrode and reference electrode, respectively. Figure 3 and Figure 4 LSV curves and current density at 20 mA cm for the two-dimensional hierarchical CoRu alloy catalyst derived from graphene quantum dots in hydrogen evolution reaction -2 The corresponding Tafel slope graph under the conditions. It can be seen that the catalyst prepared in this example has a catalytic activity significantly better than commercial Pt / C in the electrocatalytic hydrogen evolution reaction.

[0046] Example 2: A method for preparing an electrocatalytic hydrogen evolution catalyst is as follows:

[0047] (1) Preparation of N-GQDs

[0048] Weigh 4.2g of citric acid and 3.6g of urea and dissolve them in 100ml of water. After ultrasonic dissolution, transfer them to a reactor and heat them at 150°C for 6 hours. After the product is naturally cooled to room temperature, transfer it to a beaker. Wash the reactor with anhydrous ethanol, and soak the product in 500mL of ethanol. Seal it and let it stand for 3-4 days. After the solution changes from dark green to dark blue, centrifuge the product, wash it with ethanol several times, and vacuum dry it to obtain a bright dark blue powder.

[0049] (2) Preparation of Ni / Zn-ZIF-8

[0050] Weigh Zn(CH3COO)2·2H2O (1.40 g, 6.36 mmol) and Ni(CH3COO)2·4H2O (0.1 g, 0.40 mmol) respectively and dissolve them in 25 mL of water, then pour them into a 25 mL aqueous solution containing 2-methylimidazole (5.60 g, 68 mmol) and hexadecyltrimethylammonium bromide (CTAB) (5.0 mg, 0.014 mmol) under stirring, and stop stirring until the solution becomes turbid, about 1 minute. After standing at room temperature for 2 hours, NiCo-ZIF-8 nanoparticles were obtained by centrifugation and washing with water 3 times.

[0051] (3) Two-dimensional layered N-GQDs@Ni / Zn-ZIF-8@Ru 3+ Preparation of hybrid array structures

[0052] 300 mg of Ni / Zn-ZIF-8 nanoparticles obtained in step (2) were dispersed in 30 mL of water, and a total of 90 mg of N-GQDs obtained in step (1) were added, and 1.5 mL of RuCl3·3H2O aqueous solution (10 mg / mL) was added, and a stable mixed colloid system with controllable concentration was formed by full ultrasonication. The mixed colloid was quickly frozen by liquid nitrogen and then transferred to a freeze dryer for freeze drying, and finally a material with a two-dimensional layered array structure was obtained.

[0053] (4) Preparation of two-dimensional multi-level pore-supported NiRu alloy catalyst

[0054] The two-dimensional layered N-GQDs@Ni / Zn-ZIF-8@Ru 3+ The hybrid array structure was transferred to a tube furnace and heated to 800°C at a rate of 3°C / min under the protection of inert gas (Ar). After calcination at constant temperature for 5 hours, the temperature was cooled to room temperature at a rate of 10°C / min to obtain a two-dimensional multi-level pore-supported NiRu alloy catalyst. The flow rate of the inert gas was 100 mL / min.

[0055] Example 3: A method for preparing an electrocatalytic hydrogen evolution catalyst is as follows:

[0056] (1) Preparation of N-GQDs

[0057] Weigh 4.2g of citric acid and 3.6g of urea and dissolve them in 100ml of water. After ultrasonic dissolution, transfer them to a reactor and heat them at 170°C for 2 hours. After the product is naturally cooled to room temperature, transfer it to a beaker. Wash the reactor with anhydrous ethanol, and soak the product in 500mL of ethanol. Seal it and let it stand for 3-4 days. After the solution changes from dark green to dark blue, centrifuge the product, wash it with ethanol several times, and vacuum dry it to obtain a bright dark blue powder.

[0058] (2) Preparation of Ni / Co / Mn / Zn-ZIF-8

[0059] Zn(CH3COO)2·2H2O (1.40 g, 6.57 mmol), Ni(CH3COO)2·4H2O (0.02 g, 0.1 mmol), Co(CH3COO)2·4H2O (0.02 g, 0.1 mmol), Mn(CH3COO)2·2H2O (0.02 g, 0.1 mmol) were weighed and dissolved in 25 mL of water, and then poured into a 25 mL aqueous solution containing 2-methylimidazole (5.60 g, 68 mmol) and hexadecyltrimethylammonium bromide (CTAB) (5.0 mg, 0.014 mmol) under stirring, and the stirring was stopped until the solution became turbid, about 1 minute. After standing at room temperature for 3 hours, Ni / Co / Mn / Zn-ZIF-8 nanoparticles were obtained by centrifugation and washing with water 3 times.

[0060] (3) Two-dimensional layered N-GQDs@Ni / Co / Mn / Zn-ZIF-8@Ru 3+ Preparation of hybrid array structures

[0061] 300 mg of Ni / Co / Mn / Zn-ZIF-8 nanoparticles obtained in step (2) were dispersed in 30 mL of water, and a total of 110 mg of N-GQDs obtained in step (1) were added, and 1.5 mL of RuCl3·3H2O aqueous solution (10 mg / mL) was added, and a stable and concentration-controllable mixed colloid system was formed by full ultrasonication. The mixed colloid was quickly frozen by liquid nitrogen and then transferred to a freeze dryer for freeze drying, and finally a material with a two-dimensional layered array structure was obtained.

[0062] (4) Preparation of two-dimensional multi-level porous NiCoMnRu multi-element alloy catalyst

[0063] The two-dimensional layered N-GQDs@Ni / Co / Mn / Zn-ZIF-8@Ru3+ The hybrid array structure was transferred to a tube furnace, and under the protection of inert gas (Ar), the temperature was raised to 1000°C at a rate of 5°C / min, and after constant temperature calcination for 1 hour, the temperature was lowered at a rate of 15°C / min until it cooled to room temperature to obtain a two-dimensional multi-level porous supported NiCoMnRu multi-element alloy catalyst. The flow rate of the inert gas was 50 mL / min.

[0064] Example 4: A method for preparing an electrocatalytic hydrogen evolution catalyst is as follows:

[0065] (1) Preparation of S,N-GQDs

[0066] Weigh 4.2g of citric acid, 1.8g of urea and 2.2g of thiourea and dissolve them in 100ml of water. After ultrasonic dissolution, transfer them to a reactor and heat them at 160°C for 4 hours. After the product is naturally cooled to room temperature, transfer it to a beaker. Wash the reactor with anhydrous ethanol and soak the product in 500mL of ethanol. Seal and let it stand for 3-4 days. After the solution changes from dark green to dark blue, centrifuge and separate the product. After washing with ethanol several times, vacuum dry it to obtain S,N-GQDs.

[0067] (2) Preparation of Co / Zn-ZIF-8

[0068] Weigh Zn(CH3COO)2·2H2O (1.45 g, 6.57 mmol) and Co(CH3COO)2·4H2O (0.05 g, 0.23 mmol) respectively and dissolve them in 25 mL of water, then pour them into a 25 mL aqueous solution containing 2-methylimidazole (5.60 g, 68 mmol) and hexadecyltrimethylammonium bromide (CTAB) (5.0 mg, 0.014 mmol) under stirring, and stop stirring until the solution becomes turbid, about 1 minute. After standing at room temperature for 2 hours, ZnCo-ZIF-8 nanoparticles were obtained by centrifugation and washing 3 times.

[0069] (3) Two-dimensional layered S,N-GQDs@Co / Zn-ZIF-8@Ru 3+ Preparation of hybrid array structures

[0070] 300 mg of Co / Zn-ZIF-8 nanoparticles obtained in step (2) were dispersed in 30 mL of water, and a total of 120 mg of S,N-GQDs obtained in step (1) were added, and 1.5 mL of RuCl3·3H2O aqueous solution (10 mg / mL) was added, and a stable and concentration-controllable mixed colloid system was formed by full ultrasonication. The mixed colloid was quickly frozen by liquid nitrogen and then transferred to a freeze dryer for freeze drying, and finally a material with a two-dimensional layered array structure was obtained.

[0071] (4) Preparation of two-dimensional multi-level pore-supported CoRu alloy catalyst

[0072] The two-dimensional layered S,N-GQDs@Co / Zn-ZIF-8@Ru obtained in step (3) 3+ The hybrid array structure was transferred to a tubular furnace and, under the protection of inert gas (N2), the temperature was increased to 900°C at a heating rate of 4°C / min. After constant temperature calcination for 3 hours, the temperature was cooled to room temperature at a cooling rate of 5°C / min to obtain a two-dimensional multi-level pore-loaded CoRu alloy catalyst. The flow rate of the inert gas was 100 mL / min.

[0073] Example 5: A method for preparing an electrocatalytic hydrogen evolution catalyst is as follows:

[0074] (1) Preparation of P,N-GQDs

[0075] Weigh 4.2g of citric acid, 2.0g of urea and 1.8g of ammonium dihydrogen phosphate and dissolve them in 100ml of water. After ultrasonic dissolution, transfer them to a reactor and heat them at 170°C for 3 hours. After the product is naturally cooled to room temperature, transfer it to a beaker. Wash the reactor with anhydrous ethanol and soak the product in 500mL of ethanol. Seal it and let it stand for 3-4 days. After the solution changes from dark green to dark blue, centrifuge the product, wash it with ethanol several times, and vacuum dry it to obtain P,N-GQDs.

[0076] (2) Preparation of Mn / Zn-ZIF-8

[0077] Weigh Zn(CH3COO)2·2H2O (1.40 g, 6.36 mmol) and Mn(CH3COO)2·2H2O (0.10 g, 0.37 mmol) respectively and dissolve them in 25 mL of water, then pour them into a 25 mL aqueous solution containing 2-methylimidazole (5.60 g, 68 mmol) and hexadecyltrimethylammonium bromide (CTAB) (5.0 mg, 0.014 mmol) under stirring, and stop stirring until the solution becomes turbid, about 1 minute. After standing at room temperature for 2 hours, ZnCo-ZIF-8 nanoparticles were obtained by centrifugation and washing 3 times.

[0078] (3) Two-dimensional layered P,N-GQDs@Mn / Zn-ZIF-8@Ru 3+ Preparation of hybrid array structures

[0079] 300 mg of Mn / Zn-ZIF-8 nanoparticles obtained in step (2) were dispersed in 30 mL of water, and a total of 80 mg of P,N-GQDs obtained in step (1) were added, and 1.5 mL of RuCl3·3H2O aqueous solution (10 mg / mL) was added, and the mixture was fully ultrasonicated to form a stable and concentration-controllable mixed colloid system. The mixed colloid was quickly frozen by liquid nitrogen and then transferred to a freeze dryer for freeze drying, and finally a material with a two-dimensional layered array structure was obtained.

[0080] (4) Preparation of two-dimensional multi-level pore-supported MnRu alloy catalyst

[0081] The two-dimensional layered P,N-GQDs@Mn / Zn-ZIF-8@Ru 3+ The hybrid array structure was transferred to a tubular furnace and, under the protection of inert gas (Ar), the temperature was increased to 800°C at a rate of 2°C / min. After constant temperature calcination for 4 hours, the temperature was cooled to room temperature at a rate of 10°C / min to obtain a two-dimensional multi-level pore-loaded MnRu alloy catalyst. The flow rate of the inert gas was 100 mL / min.

[0082] Comparative Example 1: The rest is the same as Example 1, except that:

[0083] In step (3), the mass ratio of N-GQDs:Co / Zn-ZIF-8:RuCl3·3H2O is 50:300:15.

[0084] Comparative Example 2: The rest is the same as Example 1, except that:

[0085] In step (3), the mass ratio of N-GQDs:Co / Zn-ZIF-8:RuCl3·3H2O is 150:300:15.

[0086] The nitrogen adsorption-desorption curves of the catalysts prepared in Example 1, Comparative Example 1 and Comparative Example 2 were measured respectively. The results are as follows: Figure 2 As shown in the figure, when the mass ratio of the precursor raw materials is 50:300:15, the adsorption amount of the sample in the low pressure area (P / P0<0.1) is large, the hysteresis loop is small, and the specific surface area is 940m 2 / g, with a total pore volume of 0.65 cm 3 / g, of which micropores account for about 52%, indicating that the sample is mainly composed of micropores. This is because the proportion of graphene quantum dots is small and the outward contraction stress is weak. When the mass ratio of the precursor raw materials is 100:300:15, the sample presents a typical type IV isotherm accompanied by an H3 type hysteresis loop, indicating that the material has both mesopores and macropores, forming a multi-level pore system with coexistence of micropores / mesopores / macropores. The specific surface area of ​​the sample is 835m 2 / g, and the total pore volume is 1.02cm 3 / g, of which micropores account for about 30%, mesopores and macropores account for 43% and 27% respectively, proving the coordinated distribution of multi-level channels. When the mass ratio of the precursor raw materials is 150:300:15, the value of the micropore area in the sample is significantly reduced, and the specific surface area of ​​the sample is reduced to 695m 2 / g, and the total pore volume is 1.24 cm 3 / g, of which micropores contribute only 25%. This is because the high proportion of graphene quantum dots produces stronger outward contraction stress, resulting in a decrease in specific surface area.

[0087] Comparative Example 3: The rest is the same as Example 1, except that:

[0088] The Co / Zn-ZIF-8 nanoparticles were replaced with the N-GQDs prepared in step (1), i.e., 400 mg of N-GQDs were dispersed in 30 mL of water, and 1.5 mL of RuCl3·3H2O aqueous solution (10 mg / mL) was added, and the mixture was thoroughly ultrasonically mixed. The mixture was quickly frozen by liquid nitrogen and then transferred to a freeze dryer for freeze drying.

[0089] The pore data and catalytic activity in HER of the catalysts prepared in Examples 1-5 and Comparative Examples 1-3 were tested respectively, and the results are as follows:

[0090] Table 1 Pore data and catalytic activity test results of different catalysts

[0091]

[0092] Comparison of Example 1 and Comparative Example 3 shows that the pores in the porous carbon support prepared only by N-GQDs are mainly micropores, resulting in a significant reduction in the catalytic activity of the catalyst. Comparison of Example 1 and Comparative Examples 1 and 2 shows that the mass ratio of N-GQDs: Co / Zn-ZIF-8: RuCl3·3H2O directly affects the pore structure and specific surface area of ​​the catalyst. The wrong ratio cannot form the expected multi-level synergistic pores, which leads to a significant reduction in the catalytic activity of the catalyst.

Claims

1. An electrocatalytic hydrogen evolution catalyst, characterized in that The invention comprises a porous carbon carrier loaded with a metal element capable of catalyzing an electrocatalytic hydrogen evolution reaction, wherein the porous carbon carrier contains multi-level pores in which micropores, mesopores and macropores coexist, and the porous carbon carrier is doped with a non-metallic element.

2. The electrocatalytic hydrogen evolution catalyst according to claim 1, characterized in that: The metal elements are M and Ru, wherein M includes at least one of Co, Ni, and Mn, and the non-metal elements include at least one of N, P, and S.

3. The method for preparing the electrocatalytic hydrogen evolution catalyst according to claim 1 or 2, characterized in that: The steps include: (1) dissolving citric acid and a heteroatom compound containing at least one of N, P, and S in water to obtain a first reaction solution, and subjecting the first reaction solution to a hydrothermal reaction to obtain heteroatom-doped graphene quantum dots; (2) dissolving a zeolite imidazolate framework structure material doped with at least one of Co, Ni, and Mn, heteroatom-doped graphene quantum dots, and Ru salt in water, mixing them to obtain a mixed colloid, freezing the mixed colloid with liquid nitrogen, and then freeze-drying it to obtain an intermediate; (3) calcining the intermediate under an inert atmosphere to obtain an electrocatalytic hydrogen evolution catalyst.

4. The method for preparing the electrocatalytic hydrogen evolution catalyst according to claim 3, characterized in that: In step (1), the heteroatom compound includes at least one of urea, ethylenediamine, melamine, diammonium phosphate, phytic acid, thiourea, and L-cysteine.

5. The method for preparing the electrocatalytic hydrogen evolution catalyst according to claim 3, characterized in that: In step (1), the mass ratio of citric acid to heteroatom compound is 4-4.5:3.5-4.5, the hydrothermal reaction method is to react at 150-170°C for 2-6h, the product is cooled and immersed in ethanol, sealed and allowed to stand, and after the product changes from dark green to dark blue, centrifuge to obtain the solid, wash the solid with ethanol and then vacuum dry to obtain heteroatom-doped graphene quantum dots.

6. The method for preparing the electrocatalytic hydrogen evolution catalyst according to claim 3, characterized in that: In step (2), the preparation method of the zeolite imidazolate framework structure material is: dissolving at least one of Co salt, Ni salt, Mn salt, zinc salt, 2-methylimidazole and hexadecyltrimethylammonium bromide in water, stirring and reacting to obtain M / Zn-ZIF-8.

7. The method for preparing the electrocatalytic hydrogen evolution catalyst according to claim 6, characterized in that: The zinc salt, Co salt, Ni salt and Mn salt are all metal carboxylates; the Ru salt includes at least one of ruthenium chloride, ruthenium nitrate and ruthenium sulfate.

8. The method for preparing the electrocatalytic hydrogen evolution catalyst according to claim 3, characterized in that: In step (2), the mass ratio of the zeolite imidazolate framework material, the heteroatom-doped graphene quantum dots and the Ru salt is 50-150:250-350:10-20.

9. The method for preparing the electrocatalytic hydrogen evolution catalyst according to claim 3, characterized in that: In step (3), the calcination conditions are to increase the temperature to 800-1000°C at a rate of 1-5°C / min, calcine at a constant temperature for 1-5h, and then cool to room temperature at a cooling rate of 5-15°C / min.

10. Use of the electrocatalytic hydrogen evolution catalyst according to claim 1 or 2 in producing hydrogen by electrolysis of water.

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