High-stability CQDs modified Cu-based catalyst as well as preparation and application thereof

Abstract

The invention creatively provides the CQDs modified Cu-based catalyst with high stability. The modified copper-based catalyst is composed of a copper-based catalyst and a proper amount of CQDs dispersed on the surface of the copper-based catalyst, and the weight ratio of the copper-based catalyst to the CQDs is (100: 2)-(100: 20). Wherein the copper-based catalyst is Cu < 2-x > Se, CuO, Cu2O, CuS, Cu2S or Cu3N. According to the CQDs modified Cu-based catalyst, reduction of Cu < + > is avoided by adopting the electron storage performance of the carbon quantum dots, and long-term stability of Cu < + > is achieved. The invention also provides an application of the CQDs modified Cu-based catalyst in an electrochemical reaction. On the basis, the invention further provides a method for efficiently carrying out electrochemical reaction by adopting the CQDs modified Cu-based catalyst, CQDs storage and electron release circulation are realized by adjusting proper pulse time and pulse potential, and the technical problem that the electron storage capacity of CQDs is limited is fundamentally solved.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemical technology and relates to a highly stable Cu-based catalyst, in particular to a CQDs-modified Cu-based catalyst and its preparation and application in electrochemical reactions. Background Art

[0002] Copper (Cu)-based catalysts play an extremely important role in electrochemical reactions due to their unique electronic structure, adjustable oxidation state (Cu 0 / Cu + / Cu 2+ ) and cost advantages, and is widely used in a variety of key electrocatalytic processes. Among them, in the CO2 reduction reaction, Cu + It is a key active species in C2 products, which can accelerate the activation of inert CO2 molecules and significantly reduce the CC coupling energy barrier. In the nitrate electroreduction reaction, Cu-based catalysts (such as Cu2O) can efficiently reduce nitrate (NO3-) in water to ammonia (NH3) or nitrogen (N2), solving the problem of water pollution. In the oxygen reduction reaction (ORR), Cu-NC single-atom catalysts (Cu-N4 sites) show ORR activity close to that of Pt, and at a lower cost. However, due to the high overpotential required in actual operation, the applied potential is often significantly higher than that of Cu. + / Cu 0 reduction potential, resulting in Cu + Inevitably reduced to Cu during the reaction 0 , which leads to performance degradation. Therefore, how to maintain Cu under high overpotential conditions + The stable existence of Cu has become one of the key challenges to improving the performance of Cu-based catalysts.

[0003] In order to stabilize Cu + To modify the electronic structure of Cu species, various strategies have been adopted, including heteroatom doping, construction of metastable states, defect engineering, interface engineering, and construction of heterojunctions, with the goal of adjusting the electronic structure of Cu species by changing the coordination environment. However, the catalysts modified by the above methods are more prone to structural deterioration and may be limited by too low current density and narrow potential window. Especially when the CO2 gas feed supply is insufficient or at a more negative reduction potential, the catalyst will inevitably undergo reconstruction, resulting in Cu + Therefore, how to maintain Cu in a harsh reducing environment + The long-term stability of electrochemical reactions is a technical problem that needs to be solved urgently.

[0004] Carbon quantum dots (CQDs), as a unique nanomaterial, exhibit a discrete energy level structure due to its quantum size effect; its lowest unoccupied molecular orbital (LUMO) energy level is relatively low and can be adjusted through chemical modification or physical regulation. When the energy of external electrons is higher than the LUMO energy level of CQDs, the electrons will spontaneously transfer into the interior of the CQDs. In addition, CQDs usually have a highly delocalized π-electron system. This structural feature not only helps to disperse and stabilize electrons, but also gives CQDs efficient electron acceptance and transfer capabilities, thus giving them excellent electron storage performance. Based on this feature, carbon quantum dots are currently widely used in fields such as energy storage and conversion. As supercapacitor electrode materials, their high specific surface area and delocalized π-electron system can accelerate charge adsorption / desorption, achieving high energy density (>200F / g) and long cycle stability (>10,000 times). In lithium / sodium ion batteries, CQDs can not only serve as negative electrode materials to alleviate volume expansion, but also as conductive additives to reduce interfacial impedance, thereby improving battery rate performance (>5C) and cycle life. In addition, by regulating the LUMO energy level and light absorption characteristics, CQDs can promote the electron transfer efficiency in photocatalytic water splitting, and the hydrogen production rate can reach μmol·h-1·g-1. Flexible modification of surface functional groups can also anchor active sites, further synergistically optimizing the electrochemical and light energy conversion processes, and providing an innovative path for the development of clean energy technologies.

[0005] Currently, the existing technology does not use the electron storage properties of carbon quantum dots to avoid Cu + Reduction, maintaining Cu + There are no reports on the long-term stability of the product, nor are there any relevant technical insights. Summary of the Invention

[0006] In view of this, the present invention innovatively proposes a CQDs-modified Cu-based catalyst with high stability. The CQDs-modified Cu-based catalyst utilizes the electron storage properties of carbon quantum dots to avoid Cu + The reduction of Cu + The present application also provides the application of the CQDs-modified Cu-based catalyst in an electrochemical reaction. On this basis, the present application also provides a method for efficiently performing an electrochemical reaction using the CQDs-modified Cu-based catalyst as described above, by adjusting the appropriate pulse time and pulse potential to achieve CQDs storage and release electron cycles, fundamentally solving the technical problem of CQDs' limited ability to store electrons.

[0007] The technical solution of the present invention:

[0008] A highly stable CQDs-modified Cu-based catalyst, wherein the modified copper-based catalyst is composed of a copper-based catalyst and an appropriate amount of CQDs dispersed on the surface of the copper-based catalyst, wherein the weight ratio of the copper-based catalyst to the CQDs is 100:2-100:20. 2-x Se, CuO, Cu2O, CuS, Cu2S or Cu3N.

[0009] The applicant unexpectedly discovered that by adding a small amount of CQDs during the hydrothermal synthesis of Cu-based catalysts, the catalytic activity of Cu-based catalysts can be significantly improved. The inventors believe that this is based on the electron storage properties of carbon quantum dots. + The reduction of species is essentially driven by the electron transfer process from the cathode to the catalyst surface. From a thermodynamic point of view, the energy is higher than that of Cu + / Cu 0 The electrons at the reduction potential can be + Spontaneous capture, resulting in Cu + to Cu 0 In the CQDs-modified Cu-based catalyst, the applicant found that the LUMO energy level of CQDs is just slightly lower than that of Cu + / Cu 0 Potential, through precise energy level matching, the effect of CQDs as an electron storage pool is achieved, preventing excess unreacted electrons from transferring active Cu + Reduced to poorly active Cu 0 ——Store the electrons originally used to reduce the oxidation state of Cu in the π electron conjugated structure, avoiding Cu + The reduction of Cu + That is to say, the CQDs-modified Cu-based catalyst effectively resists the reconstruction of the catalyst by switching the thermodynamically preferred reaction path of electrons, thereby achieving Cu + Long-term stability of species.

[0010] The method for preparing the CQD-modified Cu-based catalyst described above comprises the following steps: adding CQDs and raw materials for preparing the copper-based catalyst to a reaction apparatus, and performing a hydrothermal synthesis reaction to obtain the CQD-modified Cu-based catalyst. The hydrothermal synthesis is performed at 160-200°C for 18-30 hours.

[0011] The aforementioned application of a CQD-modified Cu-based catalyst in an electrochemical reaction is specifically as follows: use as an electrode for an electrochemical reaction having a reduction potential exceeding -0.37 V vs. RHE. Furthermore, the CQD-modified Cu-based catalyst also acts as a catalyst in the electrochemical reaction.

[0012] Preferably, the electrochemical reaction is specifically CO2 reduction, HER, OER, ORR, N2 reduction or NO3 - reduction.

[0013] However, electroreduction reactions usually require continuous electrolysis at harsh reduction potentials to achieve long-term reactions, while the electron storage capacity of CQDs is limited. Therefore, the aforementioned CQDs-modified Cu-based catalysts have achieved an improvement in the stability of Cu-based catalysts to a certain extent, but have not fundamentally solved the problem.

[0014] Based on this, the present invention also provides a method for efficiently carrying out electrochemical reactions using the aforementioned CQDs-modified Cu-based catalyst, specifically using pulse electrolysis to carry out electrochemical reactions. The inventor unexpectedly discovered that by adopting the pulse electrolysis method, by adjusting the appropriate pulse time and pulse potential, the aforementioned technical problems were effectively solved, and the high stability of the CQDs-modified Cu-based catalyst was achieved. The inventor speculates that this is because, by applying an oxidizing pulse potential, the electrons stored in the CQDs are released and converted into "active electrons", thereby breaking through the limitations of their electron storage capacity. In other words, combining the electron storage of CQDs with pulse electrolysis realizes the periodic storage and release of electrons, forming a reversible energy storage cycle similar to charging and discharging. Therefore, this method makes full use of the electron storage and release capabilities of carbon quantum dots, effectively avoiding the problem of Cu + Reduced to Cu by excess electrons 0 , fundamentally achieving the high stability of CQDs-modified Cu-based catalysts, not only achieving significant progress in technical effects compared with the existing technology; but also solving the aforementioned technical problems existing in the application of CQDs-modified Cu-based catalysts in electrochemical reactions.

[0015] The pulse potential of the pulse electrolysis is 0.2-0.8V vs. RHE, and the pulse time is 2-10s. When the parameters of the pulse electrolysis are used to electrocatalyze CO2 reduction to prepare C2 products, the selectivity and reaction efficiency of C2 products are significantly improved. By applying a low pulse potential and precisely controlling the pulse electrolysis parameters to switch the electrode reaction path to release the electrons stored in CQDs, the electron storage capacity limit of CQDs is broken, thereby achieving Cu + Therefore, under the aforementioned pulse electrolysis conditions, the method achieves optimal utilization of the electron storage and release capacity of carbon quantum dots, thereby significantly improving the selectivity and reaction efficiency of CO2 electrocatalytic reduction to C2 products, providing a new technical path for achieving efficient and green CO2 conversion.

[0016] Preferably, the potential of the pulse electrolysis is 0.4-0.6 V vs. RHE, and the pulse time is 4-8 s.

[0017] Beneficial effects of the present invention:

[0018] (1) The present invention innovatively proposes a CQDs-modified Cu-based catalyst with high stability. The CQDs-modified Cu-based catalyst utilizes the electron storage properties of carbon quantum dots to avoid Cu + The reduction of Cu + The long-term stability of the system has produced unexpected technical effects.

[0019] (2) The present application provides a method for efficiently performing electrochemical reactions using a CQDs-modified Cu-based catalyst as described above. By adjusting the appropriate pulse time and pulse potential, the CQDs can store and release electrons in a cycle, thereby fundamentally solving the technical problem of the limited electron storage capacity of CQDs.

[0020] (3) The method described in the present invention significantly improves the selectivity and reaction efficiency of CO2 electrocatalytic reduction to generate C2 products, providing a new technical path for achieving efficient and green CO2 conversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Attachment Figure 1 This is a diagram of the strategy mechanism based on energy level matching;

[0022] Attachment Figure 2 The Cu prepared in Example 1 2-x TEM morphology of Se / CQD;

[0023] Attachment Figure 3 Cu in Example 2 2-x Se / CQD、Cu 2-x Cyclic voltammetry curves of Se and CQDs;

[0024] Attachment Figure 4 For the pulse electrolysis of Cu in Example 3 2-x In situ XRD of Se / CQDs;

[0025] Attachment Figure 5 Cu in Example 3 2-x In situ Raman spectra of Se / CQDs under constant potential / pulsed potential.

[0026] Attachment Figure 6 Cu under constant potential and pulse electrolysis conditions in Example 4 2-x Se and Cu 2-x Performance of Se / CQDs in CO2 electroreduction reaction. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the embodiments.

[0028] Example 1: Preparation of CQDs-modified copper-based catalyst

[0029] (1) Preparation of CQDs by citric acid hydrothermal synthesis

[0030] A variety of methods for preparing CQDs have been publicly reported in the prior art. In this embodiment, CQDs are prepared by citric acid hydrothermal synthesis. Specifically, citric acid (1.751 g) and ethylenediamine (558.3 μL) are dissolved in an appropriate amount of deionized water (16.67 mL). The solution is then transferred to a polytetrafluoroethylene-lined autoclave and heated at 180-200°C for 3-5 hours. After the reaction is completed, it is naturally cooled to room temperature to obtain a brown-black, transparent product, which is dialyzed and freeze-dried to obtain CQDs.

[0031] (2) Preparation of CQDs-modified Cu-based catalysts

[0032] The CQDs and the raw materials for preparing the copper-based catalyst were added to a reaction apparatus and reacted using a hydrothermal synthesis method to obtain the CQD-modified Cu-based catalyst. The specific Cu-based catalyst, reaction conditions, and corresponding products are detailed in Table 1.

[0033] Table 1. Conditions and corresponding products for the preparation of CQDs-modified Cu-based catalysts by hydrothermal synthesis

[0034] Copper-based catalysts <![CDATA[Cu 2-x With]]> CuO <![CDATA[Cu2O]]> CuS <![CDATA[Cu2S]]> <![CDATA[Cu3N]]> Reaction temperature 180℃ 200℃ 160℃ 200℃ 160℃ 200℃ Reaction time 24h 30h 18h 30h 18h 30h Weight ratio 100：6 100：2 100：20 100：2 100：20 100：12 product <![CDATA[Cu 2-x Se / CQD]]> CuO / CQD <![CDATA[Cu2O / CQD]]> CuS / CQD <![CDATA[Cu2S / CQD]]> <![CDATA[Cu3N / CQD]]>

[0035] Note: (1) The weight ratio refers to the weight ratio of copper-based catalyst and CQDs.

[0036] Since the preparation methods of the Cu-based catalysts have been disclosed in the prior art, this embodiment only uses Cu 2- x Se / CQD is used as an example. Cu 2-x The specific preparation steps of Se / CQD are as follows: 0.2g of copper acetate monohydrate (Cu(CH3COO)2·H2O) is dissolved in 20ml of diethylenetriamine (DETA), and the solution gradually turns blue; 10ml of deionized water containing 6mg of CQDs is added under stirring. Then, 1.0mmol (0.173g) of sodium selenite (Na2SeO3) is added to the above solution under continuous stirring at room temperature for 20 minutes. Subsequently, the obtained mixed solution is placed in a sealed kettle and reacted at 180℃ for 24 hours. After precipitation, centrifugation, washing, and drying by freeze drying, Cu 2-x Se / CQD. Cu 2-x In Se / CQD, Cu 2-x The weight ratio of Se to CQDs was 100:6.

[0037] The CQDs modified copper-based catalyst prepared above was characterized by TEM, and the results were similar. 2-x Se / CQD is used as an example to illustrate. 2-x The morphology and structure of Se / CQD are detailed in Figure 2 , Figure 2 The scale of a-2d is reduced from 200nm to 10nm, thus gradually magnifying the morphology. Figure 2 As shown in a-2d, Cu 2-x CQDs are evenly distributed on the surface of the Se material, which indicates that the CQDs-modified copper-based catalyst was successfully prepared in this example.

[0038] Example 2: Determination of the Redox Potential of Cu-based Catalysts, CQDs-Modified Cu-based Catalysts, and CQDs

[0039] The redox potential of the Cu-based catalyst, CQDs-modified Cu-based catalyst, and CQDs described in Example 1 was detected by cyclic voltammetry.

[0040] The specific method is as follows: electrochemical measurements were performed using a conventional three-electrode system. The material was coated on a glassy carbon electrode and polished with alumina slurry (0.3 mm). It was then sonicated in ethanol. 2 μl of the catalyst suspension was coated on a glassy carbon electrode and tested in a dimethylformamide (DMF) solution containing 0.1 M tetrabutylammonium tetrafluoroborate ((Bu)4NBF4) over a voltage range of -1.6–0.6 V vs. Ag / AgCl at a scan rate of 200 mV s. -1 The results are shown in Table 2-3.

[0041] Table 2. Cyclic voltammetry test results of Cu-based catalysts

[0042]

[0043] As shown in Table 2, the copper-based catalyst (Cu 2-x Se, CuO, Cu2O, CuS, Cu2S or Cu3N)Cu + / Cu 0 The reduction potentials are -0.91 to -0.95 V vs. Ag / AgCl, which are relatively close to each other.

[0044] Table 3. Redox potential of CQDs-modified Cu-based catalysts

[0045]

[0046] As shown in Table 3, the CQDs modified Cu-based catalyst (Cu 2-xSe / CQD, CuO / CQD, Cu2O / CQD, CuS / CQD, Cu2S / CQD or Cu3N / CQD), the Cu of CQDs modified Cu-based catalysts + / Cu 0 The reduction potential of CQDs is -0.81~-0.85V vs.Ag / AgCl, which is also relatively close to each other. At the same time, the storage potential of CQDs is -0.80V vs.Ag / AgCl. This shows that in the CQDs-modified Cu-based catalyst, due to the presence of CQDs, the electrons originally used to reduce the oxidation state of Cu are stored in the π-electron conjugated structure of CQDs. Therefore, the Cu in Table 3 + →Cu 0 The reduction potential is actually the storage potential of CQDs. This also fully proves that compared with the aforementioned Cu-based catalysts, the CQDs-modified Cu-based catalysts all show CV characteristic signals consistent with CQDs.

[0047] The following Cu 2-x Se, Cu 2-x Se / CQD and CQDs are used as examples for specific description. First, Cu is dissolved in 0.1M (Bu)4NBF4 DMF electrolyte. 2-x Se, Cu 2-x Se / CQD and CQDs were tested by CV, and the results are shown in Figure 3 .like Figure 3 As shown, pure Cu 2-x Se exhibits two typical redox pairs corresponding to Cu + / Cu 0 and Cu 2+ / Cu + The redox potential of Cu + The reduction potential of Cu is -0.91V vs.Ag / AgCl (ie -0.37V vs.RHE). 2-x SeCu 0 The oxidation peak area is significantly smaller than that of Cu + The reduction peak area of Cu + / Cu 0 The redox reaction of Cu is irreversible. + Reduced to Cu 0 It is difficult to return to Cu by electrochemical oxidation + CQDs exhibit significant electron absorption and release peaks, indicating their excellent electron storage and release capabilities; and their absorption peak position (-0.80V vs.Ag / AgCl) is slightly lower than that of Cu + / Cu 0 This thermodynamic advantage proves that it can be reduced by storing the original Cu+ electrons to protect Cu + More importantly, Cu 2-x Se / CQDs exhibited similar CV signals to CQDs, further demonstrating that CQDs protected Cu by their excellent electron storage properties. + .

[0048] Example 3: Pulse electrolysis to maintain Cu 2-x Cu in Se / CQD catalyst + Stability research

[0049] In this example, in-situ XRD and in-situ Raman were used to measure the evolution of Cu valence in CQDs-modified Cu-based catalysts under pulse electrolysis (pulse parameters are detailed in Table 4), and the results were consistent. 2-x The results of Se / CQD under a pulse potential of 0.6 V vs. RHE and a pulse time of 5.0 s are used as an example for specific description.

[0050] Table 4. Maintaining Cu 2-x Cu in Se / CQD catalyst + Stability of pulse parameters

[0051] Pulse parameters Experiment 1 Experiment 2 Experiment 3 Experiment 4 Pulse potential / V vs.RHE 0.2 0.4 0.6 0.8 Pulse time / s 2.0 8.0 5.0 10.0

[0052] The in situ XRD results are detailed in Figure 4 .like Figure 4 As shown, due to Cu 2-x Thermodynamic instability of Se, Cu 2-x Se / CQDs were first rapidly reconstructed under pulse electrolysis to form a mixed phase of Cu2Se (PDF#04-0839) and CuSe (PDF#27-0184) rich in high Cu oxidation state sites. More importantly, the Cu sites can be stably present under strong reduction reaction conditions, avoiding the high oxidation state of Cu + / Cu 2+ The site is attacked by high potential electrons to generate Cu 0 Therefore, the reversible cyclic process consisting of the electron storage property of CQDs coupled with the electron release by pulse electrolysis can effectively maintain the highly active oxidation state of Cu, thereby exhibiting high C2 product selectivity.

[0053] The in-situ Raman test results are detailed in Figure 5 .like Figure 5 As shown, Cu 2-x Se under constant potential, the Cu-Se bond signal disappears within tens of seconds, indicating that its Cu + The species is decreasing rapidly. 2-x Se / CQD can significantly prolong the Cu-Se bond signal intensity, indicating that the electron storage liquid of CQDs can protect Cu+ However, due to the limited storage capacity of CQDs, the overflow electrons will continue to reduce the Cu + Subsequently, the electrolysis conditions were switched from constant potential to pulse potential. Under pulse potential, the initial Cu 2-x The peak of Se bond signal can maintain the intensity for a certain period of time, but the peak gradually becomes wider and eventually disappears. This indicates that under the pulse oxidation potential, Cu 2-x Cu in Se + Species can be partially composed of Cu 0 Oxidized to Cu + , but Cu 2-x The structure of Se is finally due to the irreversible Cu + / Cu 0 This shows that only when the CQD load and pulse conditions (pulse potential of 0.2-0.8V vs.RHE, pulse time of 2-10s) are met at the same time, Cu 2-x Se / CQD can achieve Cu + long-term stability.

[0054] Example 4: Application of CQDs-modified Cu-based catalysts in CO2 electroreduction reaction

[0055] Based on the results of Examples 1-3, the inventors believe that CQDs modified Cu-based catalysts can be used as electrodes for electrochemical reactions whose reduction potential exceeds that of Cu + / Cu 0 The redox potential of Figure 3 It can be seen that Cu + / Cu 0 The reduction potential of Cu is -0.91V vs.Ag / AgCl. According to the formula E(RHE)=E(Ag / AgCl)+0.0591pH+0.197, + / Cu 0 The reduction potential is -0.37V vs. RHE. The electrochemical reactions include but are not limited to CO2 reduction, HER, OER, ORR, N2 reduction or NO3 - The applied potential of these electrochemical reactions exceeds -0.37 V vs. RHE, which inevitably leads to Cu + The reduction of species leads to a decrease in catalytic activity.

[0056] Now let’s take CO2 reduction as an example to explain in detail. The electrochemical measurement is carried out in a flow cell, with a gas diffusion electrode as the working electrode, Ni foam as the counter electrode, and Hg / HgO as the reference electrode. The cathode electrolytic cell and the anode electrolytic cell are separated by a Nafion117 proton exchange membrane. The cathode and anode electrolytes are both 1.0M potassium hydroxide solutions, and a peristaltic pump is used to achieve liquid phase circulation. CO2 gas is introduced as a reactant, and its flow rate is controlled by a mass flow meter. Both the working electrode and the counter electrode are fixed with conductive copper tape. The CO2ER experiment was carried out for 15 minutes at different applied potentials to obtain relatively stable and reliable performance parameters, which were then quantitatively analyzed. Cu 2-x Se, Cu 2-x Se / CQD was used for CO2 electroreduction experiments under constant potential and pulse electrolysis. The analysis results are detailed in Figure 6 a-6d; wherein, the reduction potential of the pulse electrolysis is -0.6 to -2.4 vs. RHE, the electrolysis time is 30 to 70 s, the pulse potential is 0.6 V vs. RHE, and the electrolysis time is 5.0 s.

[0057] Depend on Figure 6 It can be seen that pure Cu 2-x The C2 Faraday efficiency (FE) of Se catalyst under constant potential (optimal production potential -1.6 V vs. RHE, the selectivity of C2 product at this potential is the highest) electrolysis conditions C2 ) is only 28.6%, which is due to the fact that too many electrons that do not participate in the reaction will + Reduction to Cu 0 This results in low selectivity for C2 products.

[0058] Depend on Figure 6 b As can be seen, CQDs are used as a storage pool for Cu 2-x After Se, the FE of the sample can be clearly found C2 Significantly improved, at the applied potential of -1.6 V vs. RHE, FE C2 It increased to 45.5%, but it is still not ideal. This shows that although the electron storage effect of CQDs can protect Cu + , but excessive reduction electrolysis will still reduce the overflowed electrons to Cu + species.

[0059] Depend on Figure 6 c shows that under the action of pulse potential electrolysis, Cu 2-x The selectivity of C2 products of Se can be increased to 45.5%. This may be due to the fact that when the oxidizing potential is applied, part of Cu 0 Oxidized to Cu + This shows that pulse electrolysis has a significant contribution to performance improvement, but the FE C2 Not high.

[0060] Depend on Figure 6 d, Cu 2-x Se / CQDs exhibit the highest FE at -1.6 V vs. RHE C2 , reaching 85.3%; Figure 6 Cu 2-x Se achieved a significant improvement. This shows that although pulse electrolysis has a significant contribution to the performance improvement, the electron storage effect of CQDs is indispensable. In addition, almost no CO generation was detected, which shows that the efficiency of CC coupling is much greater than the rate of CO generation; that is, the generated *CO is almost completely converted into C2 products through the CC coupling pathway. In addition, Cu 2-x Se / CQD also did not observe excessive occurrence of hydrogen evolution reaction side reaction under the extremely negative applied potential of -2.4V vs.RHE. More importantly, the selectivity of C2 product was still as high as 77.4%. This shows that Cu 2-x Se / CQDs can effectively protect Cu + , even at high overpotential, high selectivity for C2 products can be achieved. And under pulse electrolysis conditions, Cu 2-x Se / CQDs exhibit an ultra-wide C2 product potential window, up to 1.6 V, and FE C2 >70%.

[0061] The above results show that CQDs as electron storage pools coupled with pulse electrolysis play a key role in improving the performance of C2 products. Only by combining the electron storage effect of CQDs with pulse potential electrolysis can the selectivity of C2 products be maximized. In other words, Cu 2-x Se / CQDs exhibit excellent selectivity in CO2 electroreduction to C2 products.

[0062] In summary, the CQDs modified Cu-based catalyst proposed in this application reduces the amount of electrons that do not participate in the reaction to transfer Cu + Reduction to Cu 0 On this basis, under the action of pulse potential electrolysis, CQDs modified Cu-based catalysts overcome the technical problem of CQDs' limited ability to store electrons, and fundamentally realize the Cu + long-term stability.

Claims

1. A highly stable CQDs-modified Cu-based catalyst, characterized by: The modified copper-based catalyst consists of a copper-based catalyst and an appropriate amount of CQDs dispersed on the surface of the copper-based catalyst, and the weight ratio of the copper-based catalyst to the CQDs is 100:2-100:

20.

2. The CQDs-modified Cu-based catalyst according to claim 1, characterized in that: The copper-based catalyst Cu 2- x Se, CuO, Cu2O, CuS, Cu2S or Cu3N.

3. The method for preparing a CQDs-modified Cu-based catalyst according to claim 1 or 2, wherein: The method comprises the following steps: adding CQDs and raw materials for preparing the copper-based catalyst into a reaction device, and carrying out the reaction by a hydrothermal synthesis method to obtain the CQDs-modified Cu-based catalyst.

4. The method for preparing a CQDs-modified Cu-based catalyst according to claim 3, wherein: The hydrothermal synthesis conditions are 160-200° C. and 18-30 hours.

5. Use of the CQDs-modified Cu-based catalyst as claimed in claim 1 or 2 in an electrochemical reaction.

6. The use of the CQDs-modified Cu-based catalyst in an electrochemical reaction according to claim 5, characterized in that: The application is specifically: being used as an electrode for an electrochemical reaction, wherein the reduction potential of the electrochemical reaction exceeds -0.37 V vs. RHE.

7. The use of the CQDs-modified Cu-based catalyst in an electrochemical reaction according to claim 5, characterized in that: The electrochemical reaction is specifically CO2 reduction, HER, OER, ORR, N2 reduction or NO3 - reduction.

8. A method for efficiently performing an electrochemical reaction using the CQDs-modified Cu-based catalyst according to claim 1 or 2, characterized in that: The electrochemical reaction was carried out using pulse electrolysis.

9. The method for efficiently performing electrochemical reactions using a CQDs-modified Cu-based catalyst according to claim 8, wherein: The pulse electrolysis potential is 0.2-0.8 V vs. RHE, and the pulse time is 2-10 s.

10. The method for efficiently performing electrochemical reactions using a CQDs-modified Cu-based catalyst according to claim 8 or 9, wherein: The electrochemical reaction is the electrocatalytic reduction of CO2 to produce C2 products.

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