Carbon sequestration type zinc oxide-based bifunctional catalyst as well as preparation method and application thereof

Abstract

The invention discloses a carbon sequestration type zinc oxide-based bifunctional catalyst and a preparation method and application thereof, the catalyst has an MOx-ZnOy heterostructure, M represents a transition metal in a d region, the value range of x is 0.5-1, and the value range of y is 0.5-1; the MOx-ZnOy heterostructure has the following characteristics: (1) MOx is uniformly embedded in ZnOy, and MOx and ZnOy form a uniformly distributed heterojunction interface on the nanoscale; (2) exposing the (100) crystal face of ZnOy; and (3) oxygen vacancies exist in the heterojunction interface area, and a built-in electric field is formed on the heterojunction interface. The preparation method comprises the following steps: S1, adding oxygen-containing zinc salt, metal chlorate and melamine into an alcohol solvent, and stirring to obtain a precursor solution; s2, drying the precursor solution under reduced pressure to obtain a solid precursor; s3, calcining the solid precursor under the protection of inert gas to obtain the zinc oxide-based bifunctional catalyst. When the catalyst is used for electrocatalytic synthesis of hydrogen peroxide, the catalyst is simultaneously used as a catalyst for a cathode two-electron oxygen reduction reaction and an anode two-electron water oxidation reaction.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical catalysis, and in particular to a carbon-fixing zinc oxide-based bifunctional catalyst and a preparation method thereof, as well as application of the catalyst in driving the synthesis of hydrogen peroxide in a carbon-fixing electrocatalytic device. Background Art

[0002] Hydrogen peroxide is a green, efficient, and widely used oxidant, widely used in environmental protection (such as wastewater treatment and disinfection), fine chemicals (such as pharmaceutical intermediate synthesis), pulp bleaching, and energy storage. Currently, the main industrial production method for hydrogen peroxide is the anthraquinone process. This method is complex, has high investment costs, and generates large amounts of organic waste liquid. This method poses significant environmental pollution and safety risks, making it difficult to adapt to the development trend of distributed, green chemical production.

[0003] In recent years, electrocatalytic in-situ hydrogen peroxide synthesis has become a research hotspot. This method uses water and oxygen as raw materials, generating hydrogen peroxide through an electrochemical reaction under mild conditions. It boasts advantages such as ease of operation, safety, environmental protection, and low cost. In particular, electrocatalytic hydrogen peroxide synthesis can be used simultaneously in distributed water treatment, medical disinfection, and emergency oxidation applications, eliminating the risks associated with the storage and transportation of highly concentrated hydrogen peroxide.

[0004] The core reactions of the electrocatalytic synthesis of hydrogen peroxide mainly include the two-electron oxygen reduction reaction (cathode) and the two-electron water oxidation reaction (anode). At present, most research focuses on the development of cathode catalysts to improve the selectivity and activity of two-electron oxygen reduction, while the research on the two-electron water oxidation reaction at the anode is relatively lagging behind. Some studies have used different materials to optimize the cathode and anode respectively, which leads to catalyst mismatch and electrochemical environment asymmetry, making it difficult to build a stable and efficient coupling system. On the other hand, the electrocatalytic synthesis of hydrogen peroxide system usually relies on a rectifier or inverter to convert the AC power output of renewable energy into DC power to drive the electrolyzer operation. However, this power conversion process not only increases the complexity and cost of the system, but also brings additional energy loss and equipment maintenance problems, which seriously restricts the practical application of hydrogen peroxide electrosynthesis in the in-situ utilization of renewable energy.

[0005] At present, there is still a lack of electrocatalytic systems that are compatible with alternating current, do not rely on power electronic equipment, and can drive cathode and anode reactions at the same time. Especially when using intermittent and highly volatile renewable energy as a power source, the system places higher demands on bidirectional catalytic ability and dynamic response capabilities. At the same time, with the advancement of the "dual carbon" strategy, there is an urgent need to develop green, low-carbon, and resource-saving chemical synthesis pathways. In this context, hydrogen peroxide, as a zero-carbon byproduct, high-value-added liquid oxidant, has become a research hotspot for its green synthesis through electrocatalytic pathways. Compared with the traditional carbon-containing source preparation route, the direct use of renewable energy to drive the two-electron reduction of oxygen in water (2e - ORR) and two-electron water oxidation (2e - The WOR reaction process has significant carbon sequestration and emission reduction benefits. Therefore, the development of a bifunctional catalyst that can simultaneously catalyze two-electron oxygen reduction and two-electron water oxidation, and achieve direct drive from renewable energy AC power without rectifier conditions, has important application value in promoting the development of green electrosynthesis technology for carbon-fixing hydrogen peroxide. Summary of the Invention

[0006] In view of this, the present invention proposes a zinc oxide-based bifunctional catalyst and its preparation method and application to solve the problems of catalyst mismatch and electrochemical environment asymmetry in existing electrocatalytic hydrogen peroxide synthesis schemes, which make it difficult to build a stable and efficient coupling system, and improve the adaptability of AC-driven efficient hydrogen peroxide synthesis systems.

[0007] In order to solve the above problems, the present invention first proposes a carbon-fixing zinc oxide-based bifunctional catalyst that can simultaneously drive the cathode two-electron oxygen reduction reaction and the anode two-electron water oxidation reaction. The zinc oxide-based bifunctional catalyst has MO x -ZnO y Heterostructure, wherein M represents a d-block transition metal, x ranges from 0.5 to 1, and y ranges from 0.5 to 1; the MO x -ZnO y Heterostructures have the following characteristics: ①MO x Uniformly embedded in ZnO y and the two form a uniformly distributed heterojunction interface at the nanoscale; ② Exposing ZnO y (100) crystal plane; ③ There are oxygen vacancies in the heterojunction interface region, and a built-in electric field is formed at the heterojunction interface.

[0008] Furthermore, in the MO x -ZnO y In heterostructures, MO x With (200) crystal plane, (111) crystal plane and (100) crystal plane, ZnO yIt has (002), (100) and (110) crystal planes.

[0009] Furthermore, in the MO x -ZnO y In heterostructures, MO x The particle size is 2nm~5nm, ZnO y The particle size is 500nm~1μm.

[0010] The carbon-fixing zinc oxide-based bifunctional catalyst proposed in the above technical solution of the present invention has at least the following beneficial technical effects compared to the catalyst used in the existing electrocatalytic synthesis of hydrogen peroxide solution:

[0011] 1) Clear and tight interface bonding: In the catalyst of the present invention, MO x (d-zone transition metal oxides, such as CuO, NiO, CoO, FeO x Nanoparticles (such as) are uniformly embedded in ZnO y The two form a uniformly distributed heterojunction interface at the nanoscale, with a clear and tight interface, free of significant gaps or impurities, ensuring efficient electron and ion transport. This interface promotes rapid carrier transfer between the two phases, effectively reducing the reaction activation energy (here activation energy refers to the adsorption energy of the key hydrogen peroxide intermediates *OOH and *OH), making the catalytic reaction more likely to occur.

[0012] 2) Spatial uniformity of nanostructure: In the catalyst of the present invention, MO x Nanoparticles are evenly dispersed in ZnO y In the matrix, agglomeration is avoided and a rich interface distribution is formed;

[0013] 3) Crystal plane directional exposure and morphology control: The present invention uses the Kirkendall effect to control the coupling and exposure of the heterojunction interface, so that the heterostructure of the catalyst of the present invention presents a specific crystal plane (such as ZnO y The preferential exposure of the (100) crystal plane improves the electronic structure and surface energy of the active sites and enhances the adsorption and conversion capabilities of reaction intermediates;

[0014] 4) Oxygen vacancy regulation: In the catalyst of the present invention, due to element diffusion and structural stress, abundant oxygen vacancies are generated in the heterogeneous interface region. These oxygen vacancies serve as active centers, which are conducive to promoting the efficient progress of the two-electron oxygen reduction reaction and the two-electron water oxidation reaction. Crystal surface exposure and oxygen vacancies jointly regulate the reaction path and reaction activation energy through structural coupling and electronic synergy during the catalytic process, thereby significantly improving the reaction activity and selectivity in the electrocatalytic reaction.

[0015] 5) Electronic structure regulation effect: The catalyst of the present invention generates carrier redistribution and energy band regulation at the heterostructure interface, forming a built-in electric field, which effectively regulates the adsorption energy and reaction path of the catalyst surface, thereby improving the reaction selectivity and rate.

[0016] In summary, the zinc oxide-based bifunctional catalyst of the present invention solves the problems of disordered structure, loose interface bonding, limited number of active sites and obstructed electron transport in existing catalysts, and achieves the technical effect of being able to efficiently catalyze the two-electron oxygen reduction reaction and the two-electron water oxidation reaction on the same catalyst surface, significantly improving the electrosynthesis efficiency of hydrogen peroxide and realizing the synergistic coupling of the anode and cathode.

[0017] In addition, the present invention also proposes a preparation method of the aforementioned zinc oxide-based bifunctional catalyst, comprising the following steps: S1, adding an oxygen-containing zinc salt, a metal chloride and melamine to an alcohol solvent and stirring to obtain a precursor solution; S2, drying the precursor solution under reduced pressure to obtain a solid precursor; S3, calcining the solid precursor under the protection of an inert gas to obtain the zinc oxide-based bifunctional catalyst.

[0018] Furthermore, the oxygen-containing zinc salt is at least one of zinc nitrate, zinc acetate, and zinc carbonate; the metal chloride is at least one of nickel chloride, ferric chloride, cobalt chloride, and copper chloride; and the alcohol solvent is ethanol or isopropanol.

[0019] Furthermore, the molar ratio of the oxygen-containing zinc salt to the metal chloride is 6:1 to 2:5, and the amount of melamine used is 1% to 10% of the mass of the metal chloride.

[0020] Furthermore, the calcination in step S3 is carried out at a temperature of 550-1050° C., and the heating rate during the calcination process is 2-5° C. / min.

[0021] The preparation method of the zinc oxide-based bifunctional catalyst proposed in the above technical solution of the present invention has at least the following beneficial technical effects compared with the existing preparation methods:

[0022] This invention utilizes the Kirkendall effect as a key structural control mechanism in the preparation process. Through the heterogeneous diffusion of different metal ions under high-temperature calcination conditions, it induces the formation of a catalyst with a hollow porous structure and rich heterojunction interfaces. This process innovation is reflected in: on the one hand, it achieves spontaneous regulation of the catalyst's internal structure without the need for complex templates or multi-step assembly processes; on the other hand, through rapid and efficient ion migration and diffusion, it promotes the exposure of active sites on the catalyst surface and the formation of oxygen vacancies, significantly enhancing catalytic activity.

[0023] Traditional methods struggle to precisely control the nanostructure and interface properties of catalysts, leading to unstable performance and low catalytic efficiency. However, a preparation method utilizing Kirkendall effect regulation not only simplifies the process but also significantly enhances the catalyst's structural order and functional synergy, thereby improving bifunctional catalytic performance and long-term stability, meeting the demands of efficient hydrogen peroxide electrosynthesis.

[0024] Furthermore, the present invention further proposes the use of the aforementioned zinc oxide-based bifunctional catalyst for electrocatalytic synthesis of hydrogen peroxide, serving as a catalyst for both the cathode two-electron oxygen reduction reaction and the anode two-electron water oxidation reaction.

[0025] Furthermore, in an apparatus or method for electrocatalytic synthesis of hydrogen peroxide, the zinc oxide-based bifunctional catalyst is loaded on carbon paper at the cathode and anode during use.

[0026] Furthermore, when applied to the electrocatalytic synthesis of hydrogen peroxide, alternating current is directly used to drive the carbon fixation device to synthesize hydrogen peroxide.

[0027] The application of the zinc oxide-based bifunctional catalyst proposed in the above technical solution of the present invention has the following beneficial technical effects: the zinc oxide-based bifunctional catalyst of the present invention is used to construct a hydrogen peroxide electrosynthesis catalytic system, and the catalyst acts as a catalyst for the two-electron oxygen reduction reaction and the two-electron water oxidation reaction at the cathode and anode respectively, realizing the synergy of bifunctional catalysis, solving the problems of mismatch between the yin and yang two-stage catalysts and the asymmetry of the electrochemical environment in the existing solution, constructing a stable and efficient catalytic system, and can directly utilize renewable energy in the form of AC output such as solar energy and wind energy without the need for a rectifier or inverter, directly drive the reaction with AC power, avoiding the energy loss and system cost brought by traditional power conversion equipment, and is suitable for green, carbon fixation, and distributed energy application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the X-ray diffraction pattern of the zinc oxide-based bifunctional catalyst prepared in Example 1 of the present invention.

[0029] Figure 2 This is a scanning electron microscope image of the zinc oxide-based bifunctional catalyst prepared in Example 1 of the present invention.

[0030] Figure 3 This is a transmission electron microscope image of the zinc oxide-based bifunctional catalyst prepared in Example 1 of the present invention.

[0031] Figure 4 This is the X-ray diffraction pattern of the zinc oxide-based bifunctional catalyst prepared in Example 2 of the present invention.

[0032] Figure 5This is the X-ray diffraction pattern of the zinc oxide-based bifunctional catalyst prepared in Example 3 of the present invention.

[0033] Figure 6 This is a performance diagram of the zinc oxide-based bifunctional catalyst used as a cathode for two-electron oxygen reduction to synthesize hydrogen peroxide in Example 4 of the present invention.

[0034] Figure 7 Schematic diagram of the synthesis of hydrogen peroxide by alternating current in Example 5 of the present invention.

[0035] Figure 8 This is a diagram showing the effect of using the zinc oxide-based bifunctional catalyst synthesized in Example 1 as both a cathode and an anode catalyst for alternating current synthesis of hydrogen peroxide in Example 5 of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be further described below with reference to the accompanying drawings, specific implementation methods, and examples. The examples are provided for illustration only and are not intended to limit the scope of protection of the present invention.

[0037] The specific embodiment of the present invention first provides a zinc oxide-based bifunctional catalyst, which has MO x -ZnO y Heterostructure, wherein M represents a d-block transition metal (such as Fe, Co, Ni, Cu, etc.), x and y represent the presence of oxygen vacancies in the heterostructure, wherein x ranges from 0.5 to 1, and y ranges from 0.5 to 1; MO of the catalyst x -ZnO y Heterostructures must have at least the following characteristics:

[0038] ①MO x Uniformly embedded in ZnO y In the nanometer scale, the two form a uniformly distributed heterojunction interface. Specifically, MO x (Metal oxides, such as NiO, CoO, FeO x etc.) and ZnO y (Zinc oxide) forms a uniformly distributed heterojunction interface at the nanoscale. There is no obvious gap or impurity between the two interfaces, and they are nested or wrapped with each other, ensuring efficient transmission of electrons and ions.

[0039] ② Exposure of ZnO y Specifically, in this heterostructure, MO x With (200) crystal plane, (111) crystal plane and (100) crystal plane, ZnO y It has (002), (100) and (110) crystal planes, and ZnO y The (100) crystal plane is preferentially exposed.

[0040] The Kirkendall effect refers to the phenomenon that the interface migration and vacancy formation occur during the solid-state diffusion process of high-temperature calcination due to the different diffusion rates of two atoms. In the synthesis of metal oxide heterostructures (such as ZnO / NiO), Zn 2+ and Ni 2 The difference in the diffusion rate of + drives the spontaneous reorganization of the structure. In the process of forming the heterostructure, the component with faster diffusion rate (such as Zn 2+ ) is more likely to migrate outward, gradually forming a coating structure around the slow-diffusing component (such as NiO). In this process, in order to reduce the interfacial energy and minimize the stress, the material tends to form a directional coupling relationship between specific crystal planes, such as NiO (200) / / ZnO (110) coupled crystal planes. Once the coupled crystal planes are stably formed, they can play a role similar to "end-capping agents" in the early stage of heterostructure formation. These heterogeneous crystal planes selectively inhibit the further growth of the coupled crystal planes, and the crystal planes that are not end-capped (such as ZnO (100) crystal planes) will be more likely to continue crystal growth along this direction, eventually showing the preferential growth and exposure of the (100) crystal plane. In the case of NiO x -ZnO y Taking heterostructure as an example, the outer layer of ZnO tends to couple with the NiO(200) crystal plane, forming a directional relationship of NiO(200) / / ZnO(110). Due to the high lattice matching, the heterogeneous crystal plane is first stably generated and suppresses the growth direction. Since these "coupling positions" are stably locked, other uncoupled directions, such as ZnO(100), will gradually be exposed in the subsequent expansion, and eventually form a quasi-cubic appearance dominated by the (100) crystal plane. This is also the reason why NiO x -ZnO y Microscopic causes of preferential exposure of the (100) crystal plane in heterostructures.

[0041] ③ Oxygen vacancies exist at the heterojunction interface. Specifically, due to element diffusion and structural stress, the interface region generates abundant oxygen vacancies, which are conducive to promoting the efficient two-electron oxygen reduction reaction and two-electron water oxidation reaction.

[0042] ④ Spatial uniformity of nanostructure: MO in catalyst x Nanoparticles are evenly dispersed in ZnO y In the matrix, agglomeration is avoided and a rich interface distribution is formed.

[0043] ⑤ Electronic structure regulation effect: The heterostructure interface produces carrier redistribution and energy band regulation, forming a built-in electric field, which effectively regulates the adsorption energy and reaction path of the catalyst surface, and improves the reaction selectivity and rate.

[0044] Catalyst MO of the embodiment of the present invention x -ZnO yIn heterostructures, MO x The particle size of ZnO is 2nm~5nm, and the particle size of ZnOy is 500nm~1μm.

[0045] The specific embodiment of the present invention also provides a method for preparing the aforementioned zinc oxide-based bifunctional catalyst, comprising the following steps S1 to S3:

[0046] Step S1: Add an oxygen-containing zinc salt, a metal chloride, and melamine to an alcoholic solvent and stir to obtain a precursor solution. The oxygen-containing zinc salt may be one or a combination of two or more of zinc nitrate, zinc acetate, and zinc carbonate; the metal chloride may be one or a combination of two or more of nickel chloride, ferric chloride, cobalt chloride, and copper chloride; and the alcoholic solvent may be a highly polar, non-aqueous alcohol, such as ethanol or isopropanol. In some specific embodiments, the molar ratio of the oxygen-containing zinc salt to the metal chloride is 6:1 to 2:5, and the amount of melamine used is 1% to 10% of the mass of the metal chloride.

[0047] Step S2: drying the precursor solution obtained in step S1 under reduced pressure in a rotary evaporator or a vacuum oven for preferably 6 to 12 hours to obtain a solid precursor.

[0048] Step S3: calcining the solid precursor obtained in step S2 under an inert gas (e.g., argon) to obtain the desired zinc oxide-based bifunctional catalyst. In this step, calcination is performed at a temperature of 550-1050°C at a heating rate of 2-5°C / min. After calcination, the catalyst is naturally cooled to obtain the zinc oxide-based bifunctional catalyst.

[0049] The zinc oxide-based bifunctional catalyst of the present invention can be applied to a carbon-fixing electrocatalytic device for electrosynthesis of hydrogen peroxide, and simultaneously serves as a catalyst for the cathode two-electron oxygen reduction reaction and the anode two-electron water oxidation reaction. The embodiment of the present invention provides a carbon-fixing electrocatalytic device for electrosynthesis of hydrogen peroxide, with reference to Figure 7 The device includes: an AC power supply 10, a cathode 21, an anode 22 and an electrolyte chamber. Among them, the cathode and the anode both use metal titanium plates as the plates, and the metal titanium plates are provided with serpentine air flow channels. The serpentine air flow channels can enhance the distribution uniformity and utilization efficiency of the gas on the electrode surface, improve the effective transmission of oxygen reactants (or products) at the three-phase interface, and suppress local polarization and bubble accumulation. It is particularly suitable for the rapid exchange and dynamic stability environment required for the periodic reaction of gas under AC conditions, and significantly improves the efficiency of hydrogen peroxide electrosynthesis and the stability of the device. The cathode electrode and the anode electrode both include a catalyst layer, a carbon paper support and a binder. The catalyst layer uses the zinc oxide-based bifunctional catalyst prepared in the above embodiment and is loaded on the carbon paper supports 210 and 220. The electrolyte chamber is made of PEEK material and is provided with a liquid inlet and a liquid outlet to form a single-pass flow or circulating flow system.

[0050] The carbon-fixing electrocatalytic device of the embodiment of the present invention can directly use alternating current to achieve 2e - ORR / 2e - The WOR dual-site (two-electron oxygen reduction and two-electron water oxidation) electrocatalytic synthesis of hydrogen peroxide system fills the gap in AC drive adaptation of this type of device. Traditional electrolysis devices are mostly based on constant direction DC, while this device is specially designed with a symmetrical structure and double-sided catalysis to adapt to the periodic reversal of current. It solves the problems of decreased electrolysis efficiency, electrode depolarization, and uneven gas evolution under AC reverse current. The bipolar electrode structure + catalyst layer design in this device can not only perform 2e - ORR and 2e - WOR, and can operate synchronously under AC drive conditions. This device can operate stably without a rectifier, significantly improving hydrogen peroxide yield and energy efficiency. It overcomes the multiple technical difficulties of traditional DC electrolysis devices in gas supply, electrode depolarization, and reaction coupling, and has clear system innovation and industrial application prospects.

[0051] In some specific embodiments, the reserved electrode area on the cathode plate and the anode plate is 1 cm 2 ~6.25cm 2 The width of the air flow channel is 0.5mm to 2mm, and the channel spacing is 0.1cm to 1cm. The area of ​​carbon paper used for cathode and anode is 1cm 2 ~6.25cm 2 The catalyst is used in an amount of 0.2 mg to 13 mg. The binder is polyvinylidene fluoride (PVDF) and / or polytetrafluoroethylene (PTFE). The electrolyte is at least one of KOH, Na2SO4, KHCO3, or K2CO3 at a concentration of 0.5 to 4 mol / L. The electrolyte is operated in a single-inlet and single-outlet or circulating flow mode.

[0052] The electrosynthesis of hydrogen peroxide using the aforementioned device is performed using a zinc oxide-based bifunctional catalyst. The general operating procedure is as follows: The device is connected to an AC power source, and a two-electron oxygen reduction reaction and a two-electron water oxidation reaction are carried out at the cathode and anode, respectively, to synthesize hydrogen peroxide (H2O2) in situ. The AC power used is a low-frequency, periodic reversing current (cycle of 0.5 to 5 minutes); the electrolyte pH is 7 to 14, and the reaction current density is 50 to 300 mA cm -2 , the concentration of hydrogen peroxide can reach 30000mg·L -1 Above, the Faradaic efficiency is higher than 85%.

[0053] The AC-driven continuous flow reactor constructed in the above-mentioned embodiments of the present invention boasts a compact structure, compatibility with a variety of proton exchange membranes and electrolyte systems, and suitability for in-situ hydrogen peroxide synthesis in neutral, weakly alkaline, and even highly alkaline environments. It exhibits excellent industrial scale-up potential and environmental adaptability. It avoids the organic solvent pollution and high energy consumption associated with the traditional anthraquinone method. The catalyst synthesis process utilizes inexpensive raw materials and a simple process, offering the dual advantages of sustainable chemical synthesis and low-carbon manufacturing.

[0054] Example 1: Preparation of zinc oxide-based bifunctional catalyst

[0055] First, 60 mmol of Zn(NO3)2·6H2O, 10 mmol of metal salt NiCl2, and 1 mmol of melamine were weighed and added to 50 mL of ethanol, and stirred to form a uniform precursor solution;

[0056] Then, the obtained precursor solution was vacuum dried at 80°C to obtain a solid precursor;

[0057] Next, the solid precursor was ground in an agate mortar for 30 min;

[0058] Finally, the ground precursor was calcined at 950°C under an argon atmosphere with a heating rate of 5°C / min to obtain a ZnO composite material embedded with metal oxide NiO nanoparticles.

[0059] Figure 1 The X-ray diffraction (XRD) image of the prepared ZnO composite material (i.e., the zinc oxide-based bifunctional catalyst) is shown. The horizontal axis in the figure is the diffraction angle, and the vertical axis is the diffraction intensity, which respectively represent the angle at which the corresponding crystal plane undergoes Bragg diffraction in the X-ray diffraction and the relative orientation number or crystallinity of the crystal plane in the sample. The "NiO-PDF#47-1049" and "ZnO-PDF#36-1451" marked in the figure correspond to the standard card numbers included in the International Diffraction Data Center, respectively, which are used to identify the matching of the detected crystal phase with the standard in the reference database. It can be seen that the zinc oxide-based bifunctional catalyst prepared in Example 1 of the present invention is composed of zinc oxide and nickel oxide.

[0060] Figure 2 This is a scanning electron microscope (SEM) image of the prepared catalyst. It can be seen that the prepared catalyst has a microscopic morphology that is approximately cubic. Figure 3This is a high-resolution transmission electron microscope (HRTEM) image. The left and right images are observed at 10nm and 5nm resolutions, respectively. The darker particles in the image represent nickel oxide nanoclusters, and the lighter part is zinc oxide. It can be seen that the catalyst is composed of nickel oxide clusters uniformly embedded in a zinc oxide matrix. At the same time, in the structure of the catalyst, there are ZnO (002) crystal planes (crystal plane size of approximately 0.248nm), (100) crystal planes (crystal plane size of approximately 0.28nm), and NiO (200) crystal planes (crystal plane size of approximately 0.209nm). Other crystal planes are not marked, but this does not mean that the zinc oxide-based bifunctional catalyst of the embodiment of the present invention only has the crystal planes shown in the figure. This is only an example.

[0061] Example 2: Preparation of zinc oxide-based bifunctional catalyst

[0062] First, 40 mmol of Zn(NO3)2·6H2O, 30 mmol of metal salt NiCl2, and 1 mmol of melamine were weighed and added to 50 mL of ethanol, and stirred to form a uniform precursor solution;

[0063] Then, the obtained precursor solution was vacuum dried at 80°C to obtain a solid precursor;

[0064] Next, the solid precursor was ground in an agate mortar for 30 min;

[0065] Finally, the ground precursor was calcined at 950°C under an argon atmosphere with a heating rate of 5°C / min to obtain a ZnO composite material embedded with metal oxide NiO nanoparticles.

[0066] Figure 4 : This is an X-ray diffraction (XRD) image of the prepared ZnO composite material (ie, the zinc oxide-based bifunctional catalyst). It can be seen that the zinc oxide-based bifunctional catalyst prepared in Example 2 of the present invention is composed of a composite of zinc oxide and nickel oxide.

[0067] Example 3: Preparation of zinc oxide-based bifunctional catalyst

[0068] First, 60 mmol of Zn(NO3)2·6H2O, 10 mmol of CoCl2, and 1 mmol of melamine were weighed and added to 50 mL of ethanol, and stirred to form a uniform precursor solution.

[0069] Then, the obtained precursor solution was vacuum dried at 80°C to obtain a solid precursor;

[0070] Next, the solid precursor was ground in an agate mortar for 30 min;

[0071] Finally, the ground precursor was calcined at 950 °C under argon atmosphere with a heating rate of 5 °C / min.

[0072] Figure 5 This is an X-ray diffraction (XRD) pattern of the prepared ZnO composite material (i.e., the zinc oxide-based bifunctional catalyst). The "CoO–PDF#43-1004" and "ZnO–PDF#36-1451" labeled in the figure correspond to the standard card numbers included in the International Diffraction Data Center, indicating whether the detected crystal phase matches the standards in the reference database. It can be seen that the zinc oxide-based bifunctional catalyst prepared in Example 3 of the present invention is composed of a composite of zinc oxide and cobalt oxide.

[0073] Example 4: Direct current driven hydrogen peroxide electrosynthesis method

[0074] The zinc oxide-based bifunctional catalyst prepared in Example 1 was used for the electrosynthesis of hydrogen peroxide at the cathode. The specific steps were as follows: By constructing a flow cell system with simultaneous circulation of anode and cathode electrolytes, the practical application potential of hydrogen peroxide synthesis based on the two-electron oxygen reduction reaction was evaluated. During the preparation of the cathode electrode, the catalyst was evenly coated on a 1 cm 2 0.25 wt% polytetrafluoroethylene was added as a binder on the hydrophobic carbon paper, and the catalyst loading was 0.2 mg / cm 2 The anode uses a platinum electrode, and the cathode and anode are separated by a proton exchange membrane. Figure 6 As shown in the figure, the Faradaic efficiency (FE) of the catalyst for hydrogen peroxide synthesis at potentials of 0.3, 0.4, 0.5, and 0.6 V vs. RHE was higher than 90%, and the synthesis rate exceeded 0.28 mol g catalysts -1 min -1 , which can achieve efficient and rapid synthesis of hydrogen peroxide. Here vs. RHE means that the potential here is relative to the reversible hydrogen electrode.

[0075] Example 5: AC-driven hydrogen peroxide electrosynthesis device and method

[0076] The electrocatalytic synthesis under simulated alternating current conditions was carried out in a single-pass flow reactor with a liquid intermediate chamber (see Figure 7 ), electrolysis adopts a single-input and single-output flow mode. The alternating current switches direction once per minute. Both the anode and cathode are made by dripping catalyst ink onto carbon cloth, with a catalyst loading of 2mg / cm 2, 0.25wt% PTFE was added. The electrolyte used was a 2mol / L KHCO3 / K2CO3 mixture with a pH adjusted to approximately 13. Stability tests were conducted over 4 hours under these conditions, demonstrating the ability to continuously produce H2O2 at concentrations of 349-427mg / L, with the cell voltage fluctuating within a narrow range of approximately 0.5V. It can be seen that the catalyst exhibited excellent performance in both two-electron oxygen reduction and two-electron water oxidation, such as Figure 8 As shown, hydrogen peroxide is stably synthesized under electric current at an industrial scale via cathode-anode coupling, while also demonstrating its electrocatalytic potential under alternating current, which can directly integrate intermittent renewable energy.

[0077] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. Those skilled in the art will recognize that several equivalent substitutions or obvious variations can be made without departing from the scope of the present invention, and that any equivalent performance or application should be considered to fall within the scope of protection of the present invention.

Claims

1. A carbon-fixing zinc oxide-based bifunctional catalyst, characterized in that: With MO x -ZnO y Heterostructure, where M represents a d-block transition metal, x ranges from 0.5 to 1, and y ranges from 0.5 to 1; The MO x -ZnO y Heterostructures have the following characteristics: ①MO x Uniformly embedded in ZnO y In the nanometer scale, the two form a uniformly distributed heterojunction interface; ② Exposure of ZnO y (100) crystal plane; ③ Oxygen vacancies exist in the heterojunction interface region, and a built-in electric field is formed at the heterojunction interface.

2. The zinc oxide-based bifunctional catalyst according to claim 1, wherein In the MO x -ZnO y In heterostructures, MO x With (200) crystal plane, (111) crystal plane and (100) crystal plane, ZnO y It has (002), (100) and (110) crystal planes.

3. The zinc oxide-based bifunctional catalyst according to claim 1, wherein In the MO x -ZnO y In heterostructures, MO x The particle size is 2nm~5nm, ZnO y The particle size is 500nm~1μm.

4. The method for preparing a zinc oxide-based bifunctional catalyst according to any one of claims 1 to 3, wherein: The following steps are involved: S1. Adding oxygen-containing zinc salt, metal chloride and melamine into an alcohol solvent and stirring to obtain a precursor solution; S2, drying the precursor solution under reduced pressure to obtain a solid precursor; S3. calcining the solid precursor under the protection of an inert gas to obtain the zinc oxide-based bifunctional catalyst.

5. The preparation method according to claim 4, wherein The oxygen-containing zinc salt is at least one of zinc nitrate, zinc acetate, and zinc carbonate; the metal chloride is at least one of nickel chloride, ferric chloride, cobalt chloride, and copper chloride; and the alcohol solvent is ethanol or isopropanol.

6. The preparation method according to claim 4 or 5, characterized in that The molar ratio of the oxygen-containing zinc salt to the metal chloride is 6:1 to 2:5, and the amount of melamine used is 1% to 10% of the mass of the metal chloride.

7. The preparation method according to any one of claims 4 to 6, characterized in that The calcination in step S3 is carried out at a temperature of 550-1050° C., and the heating rate during the calcination process is 2-5° C. / min.

8. Use of the zinc oxide-based bifunctional catalyst according to any one of claims 1 to 3, characterized in that When used in the electrocatalytic synthesis of hydrogen peroxide, it acts as a catalyst for both the two-electron oxygen reduction reaction at the cathode and the two-electron water oxidation reaction at the anode.

9. The use of the zinc oxide-based bifunctional catalyst as claimed in claim 8, characterized in that: The invention is applied to a device or method for electrocatalytic synthesis of hydrogen peroxide. When in use, the zinc oxide-based bifunctional catalyst is loaded on carbon paper of the cathode and the anode.

10. Use of the zinc oxide-based bifunctional catalyst according to claim 9, characterized in that: When applied to electrocatalytic synthesis of hydrogen peroxide, alternating current is directly used to drive the device to synthesize hydrogen peroxide.

Images