Method for synthesizing hydrogen peroxide through efficient electrocatalytic oxygen reduction

Abstract

The invention discloses a method for synthesizing hydrogen peroxide through high-efficiency electro-catalysis oxygen reduction, which comprises the following steps: in an electro-catalysis system, ZnS is loaded on an atomic catalyst Co-NC to form a heterogeneous interface ZnS / Co-NC as an electro-catalyst for synthesizing hydrogen peroxide through oxygen reduction, and ZnS / Co-NC regulates and controls the 3d orbital electron spin state of an active site of monatomic Co-NC to synthesize hydrogen peroxide. Therefore, an oxygen reduction path is converted from a four-electron reduction path to two-electron oxygen reduction to produce hydrogen peroxide; wherein ZnS redistributes charges on a monatomic C carrier and adjusts the spin state of Co < 2 + >, so that the activity of an oxygen reduction process is ensured, a two-electron reaction process is ensured to be a leading process in a reaction process, and high-selectivity and high-activity conversion of oxygen into an ideal H2O2 product can be effectively promoted.

Description

Technical Field

[0001] The invention relates to the technical field of clean energy production, and in particular to a method for synthesizing hydrogen peroxide by high-efficiency electrocatalytic oxygen reduction. Background Art

[0002] Hydrogen peroxide (H2O2) is considered to be an environmentally friendly substance with a wide range of uses in chemical raw materials, water treatment, chemical synthesis, disinfection, papermaking and other fields. Currently, more than 95% of H2O2 on the market is synthesized by the anthraquinone method, which requires a lot of infrastructure and produces a lot of organic waste, hindering its further application. In recent years, the two-electron oxygen reduction reaction (2e - ORR) has attracted considerable research attention. Due to its ready-to-use and environmentally friendly characteristics, it provides a new alternative to anthraquinone synthesis.

[0003] Recently, carbon-based non-noble metal single-atom catalysts (SACs) have shown great potential in achieving efficient two-electron oxygen reduction to hydrogen peroxide due to their maximum utilization of metal atoms, tunable coordination environment of coordinated metals, and high electronic conductivity. - ORR (to generate H2O2) and 4e - However, Co-NCs are more likely to react with 4e oxygen during the oxygen reduction reaction. - ORR, its low H2O2 selectivity cannot achieve the desired catalytic performance for H2O2 synthesis. - ORR involves two consecutive proton-mediated electron transfer steps (O2→OOH * →H2O2), usually accompanied by a competing four-electron pathway to form H2O (O2→OOH * →O * →OH * →H2O), so the ORR process of O2 to H2O2 or H2O depends on the competitive relationship between the dissociation and desorption of OOH at the active site during the reduction process, which is related to the different oxygen-containing intermediates (OOH * ,OH * ,O * ) is closely related to the binding strength at the active site. HO * can be a general descriptor, i.e.,

[0004] △G HOO * =△G HO * +3.2eV (1)

[0005] △GO * =2△G HO * . (2)

[0006] From the above formula, we can see that 4e - ORR key intermediates ( * OH) and 2e - ORR key intermediates ( * OOH) has a scaling relationship, which makes Co-NC * OH has a stronger adsorption strength. * OOH tends to dissociate into * OH, thus making the overall performance good 4e - The ORR reaction activity is very low, but the H2O2 selectivity is very low. Therefore, due to the "leverage effect" generated by this scaling relationship, high H2O2 selectivity and high ORR activity cannot be achieved at the same time. Therefore, it is urgent to explore methods to break this limitation and transform the oxygen reduction pathway of the single-atom catalyst Co-NC from a highly active four-electron process to a two-electron pathway with both high activity and high selectivity, so as to achieve efficient electrosynthesis of H2O2 in the ORR process.

[0007] Based on the above problems, the present invention provides a method for synthesizing hydrogen peroxide by highly efficient electrocatalytic oxygen reduction. Summary of the invention

[0008] The purpose of the present invention is to solve the technical problems existing in the prior art and to provide a method for synthesizing hydrogen peroxide by high-efficiency electrocatalytic oxygen reduction.

[0009] To achieve the above object, the technical solution provided by the present invention is: a method for synthesizing hydrogen peroxide by highly efficient electrocatalytic oxygen reduction, wherein ZnS is loaded on an atomic catalyst Co-NC in an electrocatalytic system to form a heterogeneous interface ZnS / Co-NC as an electrocatalyst for synthesizing hydrogen peroxide by oxygen reduction, and oxygen is efficiently converted into H2O2 with high activity and high selectivity, as follows:

[0010] ZnS / Co-NC regulates the 3d orbital electron spin state of the single-atom Co-NC active site, thereby converting the oxygen reduction pathway from a four-electron reduction pathway to a two-electron oxygen reduction pathway to produce hydrogen peroxide; ZnS redistributes the charge on the single-atom C carrier and 2+ The spin state of ZnS is adjusted. After ZnS loading, Co 2+ The electron spin of Co changes from low spin to high spin; and according to the Tafel slope result, the high spin Co 2+ More inclined to adsorption * OOH, and *The interaction between OH is weakened, which is used to hinder the two-electron key intermediate * OOH to four-electron ORR key intermediate * The conversion of OH ensures the activity of the oxygen reduction process and the dominant process of the two-electron reaction.

[0011] Preferably, oxygen is used as a raw material for electrochemical conversion in the electrocatalytic system; the cathode material in the electrocatalytic system is a carbon cloth electrode loaded with ZnS / Co-NC, the cathode material is a Pt sheet electrode, and the electrochemical workstation provides a constant voltage.

[0012] Preferably, 100 mL of KOH is used as the electrolyte solution in the electrocatalytic system, and the pH range is 11-14.

[0013] Preferably, the reaction device in the electrocatalytic system is a 100 mL H-type electrolytic cell reactor.

[0014] Beneficial effects of the present invention:

[0015] In the electrocatalytic oxygen synthesis H2O2 system of the present invention, ZnS is loaded on the atomic catalyst Co-NC to form a heterogeneous interface ZnS / Co-NC as an electrocatalyst for oxygen reduction synthesis of hydrogen peroxide, which can effectively promote the high selectivity and high activity of oxygen to realize the conversion of oxygen into the ideal H2O2 product.

[0016] In addition, the rational selection of reaction conditions in this system can effectively realize the generation of H2O2 while strictly inhibiting the double decomposition of H2O2, effectively resolving the contradictory relationship between selectivity and activity in the traditional H2O2 conversion process, and opening up a new method for the design of safe and efficient H2O2 electrocatalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings described herein are used to provide further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0018] Figure 1 LSV diagrams of two-electron oxygen reduction of ZnS / Co-NC, Co-NC, and ZnS / NC;

[0019] Figure 2 The electron transfer number diagram of two-electron oxygen reduction of ZnS / Co-NC, Co-NC and ZnS / NC;

[0020] Figure 3 The H202 selectivity of two-electron oxygen reduction of ZnS / Co-NC, Co-NC and ZnS / NC;

[0021] Figure 4The yield and Faraday efficiency of two-electron oxygen reduction of H2O2 by ZnS / Co-NC;

[0022] Figure 5 Lsv curves of ZnS / Co-NC and Co-NC in nitrogen and in nitrogen environment with 10 mM H2O2 added;

[0023] Figure 6 It is the dynamic current density diagram of ZnS / Co-NC and ZnS / NC;

[0024] Figure 7 This is the graph of ZnS / Co-NC after 2000 cycles of CV;

[0025] Figure 8 Comparison of the temperature-dependent magnetic moments of ZnS / Co-NC, Co-NC, and ZnS / NC. DETAILED DESCRIPTION

[0026] This section will describe in detail the specific embodiments of the present invention. The preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the accompanying drawings is to supplement the description of the text part of the specification with graphics, so that people can intuitively and vividly understand each technical feature and the overall technical solution of the present invention, but it cannot be understood as a limitation on the scope of protection of the present invention.

[0027] The purpose of the present invention is to make the single-atom catalyst Co-NC react with high activity to form a four-electron oxygen reduction reaction (4e - The ORR is transformed into a two-electron oxygen reduction reaction (2e - This solves the "leverage effect" that high H2O2 selectivity and high ORR activity cannot be achieved at the same time, making it possible to achieve high selectivity and high activity in the production of H2O2.

[0028] Reference Figure 1-Figure 8 The preferred embodiment of the present invention is a method for synthesizing hydrogen peroxide by high-efficiency electrocatalytic oxygen reduction. The method uses ZnS loaded on the atomic catalyst Co-NC in the electrocatalytic system to form a heterogeneous interface ZnS / Co-NC as an electrocatalyst for synthesizing hydrogen peroxide by oxygen reduction, and efficiently realizes the high activity and high selectivity of oxygen into H2O2, as follows:

[0029] ZnS / Co-NC regulates the 3d orbital electron spin state of the single-atom Co-NC active site, thereby converting the oxygen reduction pathway from a four-electron reduction pathway to a two-electron oxygen reduction pathway to produce hydrogen peroxide; ZnS redistributes the charge on the single-atom C carrier and 2+ The spin state of ZnS is adjusted. After ZnS loading, Co 2+The electron spin of Co changes from low spin to high spin; and according to the Tafel slope result, the high spin Co 2+ More inclined to adsorption * OOH, and * The interaction between OH is weakened, which is used to hinder the two-electron key intermediate * OOH to four-electron ORR key intermediate * The conversion of OH ensures the activity of the oxygen reduction process and the dominant process of the two-electron reaction.

[0030] Specifically, the present invention uses ZnS loaded on the single-atom catalyst Co-NC to redistribute the charge on the C carrier and 2+ The spin state of Co changes from low spin before loading to high spin. According to the Tafel slope results, the high spin Co 2+ With the best * OOH adsorption, which is beneficial to * Desorption of OOH to avoid dissociation of 4e - ORR key intermediates * OH, in addition, ZnS can accelerate the generated H2O2 to quickly move away from the active site and avoid the decomposition of H2O2. Therefore, this can promote the constructed ZnS / Co-NC to achieve high selectivity and high yield of hydrogen peroxide production.

[0031] In this embodiment, oxygen is used as a raw material for electrochemical conversion in the electrocatalytic system; the cathode material in the electrocatalytic system is a carbon cloth electrode loaded with ZnS / Co-NC, the cathode material is a Pt sheet electrode, and an electrochemical workstation (CHI 760E, Shanghai Chenhua, China) provides a constant voltage of 0.2-0.6 V vs RHE.

[0032] In this embodiment, 100 mL of KOH is used as the electrolyte solution in the electrocatalytic system, and the pH range is 11-14.

[0033] In this embodiment, the reaction device in the electrocatalytic system is a 100 mL H-type electrolytic cell reactor.

[0034] Furthermore, before the reaction started, the two electrodes were inserted into the solution with an immersion area of ​​1 cm 2 , pass oxygen for 0.5h to reach oxygen saturation.

[0035] Furthermore, oxygen saturation is maintained during the reaction, and after 1 hour of electrolysis, the cathode electrolyte rich in H2O2 is collected.

[0036] The specific determination method of the content of each product in the present invention is as follows:

[0037] The concentration of H2O2 in the reaction system was determined by iodine titration spectrophotometry using a spectrophotometer model U-3900, Hitachi Ltd, Japan.

[0038] Example 1

[0039] Oxygen is electrochemically synthesized into H2O2.

[0040] In the present embodiment, pure oxygen is used as the treatment object. First, 100 ml of KOH with a pH of 11-14 is added to the cathode and anode of the H-type reactor as the electrolyte, and oxygen is introduced into the cathode for 0.5 h to achieve oxygen saturation. A Pt sheet electrode is used as the anode and the electrocatalyst loading is 0.05 mg cm -2 1cm -2 The carbon cloth was used as cathode. The electrochemical workstation CHI 760E provided a certain voltage for electrolysis to generate H2O2.

[0041] The specific preparation method of the cathode electrode material in this example is as follows:

[0042] 1. Cut the carbon cloth into 1cm×1cm size. Place the cut carbon cloth in a tube furnace and calcine it at 500℃ for 2h, then immerse it in H2O and ethanol for 15min respectively, dry it, seal it and set it aside.

[0043] 2. Preparation of ZnS / Co-NC: First, Co-Zif-8 was synthesized. 0.12g of Co(acac)3 and 1.07g of Zn(NO3)2 were added to a mixed solution of 30ml DMF and methanol (volume ratio of 4:1) and stirred for 30min. Then, 1.16g of 2-methylimidazole was dissolved in a mixture of 30ml DMF and methanol and added to the above solution, and stirred for 12 hours. The obtained Co-ZIF-8 powder was washed with methanol several times and dried in a vacuum oven at 65°C overnight. 400mg of Co-ZIF-8 powder was dissolved in 30mL of a mixed solution of CS2 and ethanol (volume ratio of 4:1), 20mg, 40mg, and 60mg of S powder were added, and then ultrasonicated for 30min and vacuum evaporated to obtain S-doped precursor, which was then directly annealed at 900°C for 3 hours in a N2 atmosphere to obtain ZnS / Co-NC.

[0044] 3. Mix ZnS / Co-NC powder with 700 μL of water, 300 μL of ethanol and 15 μL of Nafion, and ultrasonicate for 0.5 h. Use a pipette to take 10 μL and drop it on the treated carbon cloth.

[0045] like Figure 1-3As shown in the figure, taking the S doping amount of 20 mg as an example, in the system of preparing H2O2 by electrocatalytic oxygen reduction, compared with Co-NC and ZnS / NC, ZnS / Co-NC shows a starting potential closer to the theoretical value of 0.75V and the number of electron transfers in the oxygen reduction process is closer to 2, and the H2O2 selectivity is higher. This indicates that in the reaction process, ZnS regulates the oxygen reduction pathway of Co-NC to a two-electron process, and Co 2+ As an active center, it ensures the activity of two-electron reduction to H2O2.

[0046] The preparation of H2O2 by ZnS / Co-NC under actual conditions was determined. Figure 4-5 As shown in the figure, during the reaction, as the voltage increases, the yield of H2O2 gradually decreases and the Faraday efficiency gradually increases. This is because when the voltage is close to the starting potential, the reaction current is small and the side reactions are less, so the selectivity of H2O2 is higher. At 0.2V, the yield of H2O2 can reach 3.125mol·g -1 ·h -1 The Faraday efficiency is 96%, which is higher than that of ZnS / NC, which reflects the superiority of ZnS / Co-NC in H2O2 production. And for the further reduction of H2O2 to water, ZnS / Co-NC is also negligible, which is conducive to the accumulation of H2O2 in production.

[0047] Figure 6 It shows that the dynamic current density of ZnS / Co-NC is always greater than that of ZnS / NC and Co-NC during the two-electron oxygen reduction process, which indicates that the source of the activity and selectivity of ZnS / Co-NC is the active center Co 2+ , and ZnS plays a role in regulating the oxygen reduction pathway of Co-NC. Figure 7 It shows that after 2000 cycles of CV, ZnS / Co-NC still maintains high H2O2 selectivity, indicating that ZnS / Co-NC has good stability. The temperature-varying magnetic moment shows that compared with Co-NC and ZnS / NC, ZnS / Co-NC has the largest magnetic moment and the largest number of unpaired electrons in the d orbital, which can determine the Co 2+ The spin state is high spin.

[0048] It can be seen from the above examples that the present invention realizes the efficient conversion of oxygen to H2O2 by constructing ZnS / Co-NC. In this system, ZnS is used to adjust the Co in the single-atom catalyst Co-NC. 2+ The redistribution of spin states and surface charges induces the active site Co 2+ The spin state of the molecule changes from low spin to high spin, thereby effectively adjusting the binding strength with the oxygen-containing intermediate, thereby making the two-electron oxygen reduction key intermediate* OOH is more favorable to desorb and form H2O2, rather than dissociate to form H2O, achieving high activity and high selectivity in the preparation of H2O2. In addition, since ZnS / Co-NC is inert to the further conversion of H2O2 into H2O, it also ensures that it will not be decomposed during the production of H2O2. At 0.2V, the H2O2 yield of ZnS / Co-NC can reach 3.125mol·g -1 ·h -1 , the Faradaic efficiency is 96%.

[0049] Under the premise that no conflict occurs, those skilled in the art may freely combine and superimpose the above-mentioned additional technical features.

[0050] The above description is only a preferred implementation mode of the present invention. Any technical solution that achieves the purpose of the present invention by substantially the same means belongs to the protection scope of the present invention.

Claims

1. A method for synthesizing hydrogen peroxide by high-efficiency electrocatalytic oxygen reduction, characterized in that: The method uses ZnS loaded on the atomic catalyst Co-NC in the electrocatalytic system to form a heterogeneous interface ZnS / Co-NC as an electrocatalyst for oxygen reduction to synthesize hydrogen peroxide, and efficiently realizes the high activity and high selectivity of oxygen conversion into H2O2, as follows: ZnS / Co-NC regulates the 3d orbital electron spin state of the single-atom Co-NC active site, thereby converting the oxygen reduction pathway from a four-electron reduction pathway to a two-electron oxygen reduction pathway to produce hydrogen peroxide; ZnS redistributes the charge on the single-atom C carrier and 2+ The spin state of ZnS is adjusted. After ZnS loading, Co 2+ The electron spin of Co changes from low spin to high spin; and according to the Tafel slope result, the high spin Co 2+ More inclined to adsorption * OOH, and * The interaction between OH is weakened, which is used to hinder the two-electron key intermediate * OOH to four-electron ORR key intermediate * The conversion of OH ensures the activity of the oxygen reduction process and the dominant process of the two-electron reaction.

2. The method for synthesizing hydrogen peroxide by high-efficiency electrocatalytic oxygen reduction according to claim 1, characterized in that: In the electrocatalytic system, oxygen is used as a raw material for electrochemical conversion; the cathode material in the electrocatalytic system is a carbon cloth electrode loaded with ZnS / Co-NC, the cathode material is a Pt sheet electrode, and the electrochemical workstation provides a constant voltage.

3. The method for synthesizing hydrogen peroxide by high-efficiency electrocatalytic oxygen reduction according to claim 1, characterized in that: In the electrocatalytic system, 100 mL of KOH was used as the electrolyte solution, and the pH range was 11-14.

4. The method for synthesizing hydrogen peroxide by high-efficiency electrocatalytic oxygen reduction according to claim 1, characterized in that: The reaction device in the electrocatalytic system is a 100 mL H-type electrolytic cell reactor.

Images