Preparation of a porous carbon / hydrophobic carbon paper electrode from plane tree leaves and application to decomposition of water to produce h2o2

Abstract

This application discloses a method for preparing a porous carbon / hydrophobic carbon paper electrode based on paulownia leaves and its application in water decomposition to produce H2O2, belonging to the field of electrochemical synthesis technology. The method uses waste paulownia leaves as a precursor, which are pretreated and calcined at high temperature under a protective atmosphere to obtain raw biochar. This raw biochar is then activated with KOH to obtain paulownia leaf-based porous biochar. This biochar is then mixed with a perfluorinated resin solution and anhydrous ethanol to prepare a catalyst dispersion, which is drop-coated onto a hydrophobic carbon paper substrate containing 20%–80% polytetrafluoroethylene (PTFE) and dried to obtain a composite electrode. This electrode uses hydrophobic carbon paper as a substrate, with a layered porous structure of paulownia leaf-based porous biochar loaded on its surface, exhibiting a specific surface area ≥600 m². 2 / g、I D / I G The value is 0.85~1.05. Using this electrode in a potassium carbonate electrolyte, a two-electron water oxidation reaction with a voltage of 1.5~4V vs. RHE can efficiently synthesize hydrogen peroxide, with an optimal yield of 43.48 mg / L and a Faraday efficiency of 25.32%. This application utilizes green and inexpensive raw materials and a simple process, achieving high-value utilization of biomass waste and providing a reliable solution for the green industrial production of hydrogen peroxide.

Description

Technical Field

[0001] This application belongs to the field of electrochemical synthesis technology, and specifically relates to the preparation of a porous carbon / hydrophobic carbon paper electrode made from sycamore leaves and its application in the decomposition of water to produce H2O2. Background Technology

[0002] Hydrogen peroxide (H2O2), as an environmentally friendly oxidant, has wide applications in chemical synthesis, medical and health care, and environmental remediation. Its efficient and green preparation technology has become an important research direction. The traditional anthraquinone method for preparing H2O2 has inherent drawbacks such as cumbersome processes, high energy consumption, and large pollutant emissions, severely restricting its green industrialization. Electrochemical synthesis of H2O2, with its advantages of good environmental compatibility and simple operation, provides an effective way to overcome these technical bottlenecks.

[0003] In the oxidation of water with two electrons (2e The WOR (Works-Oriented Chemical) pathway for synthesizing H2O2 uses only water as a raw material, requiring no additional oxidants or reducing agents, aligning with the principles of green chemical engineering and becoming a research hotspot in the field of electrochemical synthesis. The core of this process lies in the anode catalyst material, whose performance directly determines the H2O2 generation rate, selectivity, and energy efficiency. However, existing electrode materials generally suffer from low catalytic selectivity, insufficient activity, and poor stability, making it difficult to effectively suppress the four-electron oxygen evolution side reaction. This results in low H2O2 yield and Faraday efficiency, failing to meet the demands of industrial applications.

[0004] Carbon-based materials have become ideal supports for electrode catalysts due to their good chemical stability, excellent electronic conductivity, and tolerance to strong oxidizing environments. In recent years, biomass-derived carbon materials have attracted widespread attention due to their advantages such as wide availability of raw materials, high renewability, and tunable structure. However, existing biomass carbon electrodes still suffer from problems such as complex preparation processes and the need to improve catalytic performance.

[0005] Therefore, developing a carbon-based composite electrode with green raw materials, simple preparation, and excellent catalytic performance is of great significance for promoting the industrial application of electrochemical synthesis of H2O2 technology. Summary of the Invention

[0006] The purpose of this application is to overcome the shortcomings of existing technologies in the electrochemical synthesis of hydrogen peroxide, such as poor catalytic performance of electrode materials, high raw material costs, and complex preparation processes. This application provides a method for preparing a porous carbon composite electrode based on *Platycladus orientalis* leaves, and also provides the composite electrode obtained by this method and its application in the electrochemical synthesis of hydrogen peroxide. Using waste *Platycladus orientalis* leaves as a biomass precursor, the composite electrode prepared exhibits excellent conductivity, high catalytic activity and selectivity for the two-electron water oxidation pathway, effectively suppresses the four-electron oxygen evolution side reaction, and utilizes green and inexpensive raw materials with a simple and environmentally friendly preparation process, providing a reliable solution for the green industrial production of hydrogen peroxide.

[0007] To achieve the above objectives, this application adopts the following technical solution: In a first aspect, this application provides a method for preparing a porous carbon composite electrode based on a sycamore leaf, comprising the following steps: After pretreatment, the fallen leaves of the Chinese parasol tree are calcined at high temperature under a protective atmosphere to obtain raw biochar. The original biochar was mixed with an alkaline activator and activated to obtain porous biochar based on sycamore leaves. The porous biochar based on sycamore leaves is mixed with a binder and a solvent to prepare a catalyst dispersion. The catalyst dispersion is loaded onto a hydrophobic carbon paper substrate and dried to obtain a porous carbon composite electrode based on sycamore leaves.

[0008] In one possible implementation, the pretreatment includes washing, drying, and ball milling; The ball mill speed for the ball milling process is 200-800 rpm, and the ball milling time is 0.5-6 h. The heating rate of the high-temperature calcination is 3~15℃ / min, the calcination temperature is 500~1000℃, and the calcination time is 0.5~3h.

[0009] In one possible implementation, the alkaline activator is KOH; The activation treatment includes mixing the raw biochar with KOH and water, followed by water bath incubation, high-temperature calcination, acid washing, and drying. The water bath incubation temperature is 60~80℃, and the time is 0.5~3h; The heating rate of the high-temperature calcination is 3~15℃ / min, the calcination temperature is 500~1000℃, and the calcination time is 0.5~3h.

[0010] In one possible implementation, the adhesive is a perfluorinated resin solution and the solvent is anhydrous ethanol; The hydrophobic carbon paper substrate contains 20% to 80% polytetrafluoroethylene. The load is applied using a drop-coating method, and then dried after being added in multiple drops.

[0011] Secondly, this application provides a porous carbon composite electrode based on sycamore leaf, the composite electrode comprising: a hydrophobic carbon paper substrate; and a porous carbon material layer loaded on the surface of the hydrophobic carbon paper substrate; The porous carbon material layer comprises porous biochar with a hierarchical porous structure obtained from the carbonization and activation treatment of sycamore leaves.

[0012] In one possible implementation, the specific surface area of ​​the porous biochar is ≥600 m². 2 / g, mainly composed of carbon and oxygen elements; The porous biochar contains 85% to 95% carbon and 5% to 15% oxygen.

[0013] In one possible implementation, the Raman spectrum of the porous biochar is I D / I G The value is 0.85~1.05.

[0014] Thirdly, this application provides an application of a sycamore leaf-based porous carbon composite electrode in the electrochemical synthesis of hydrogen peroxide. The composite electrode is used as the working electrode to carry out a two-electron water oxidation reaction in the electrolyte to generate hydrogen peroxide. The composite electrode uses hydrophobic carbon paper as a substrate, and its surface is loaded with porous biochar made from sycamore leaves through carbonization and activation treatment.

[0015] In one possible implementation, the electrolyte is a potassium carbonate electrolyte with a concentration of 0.1~3M; The potential range for the two-electron water oxidation reaction is 1.5~4V vs. RHE.

[0016] In one possible implementation, the two-electron water oxidation reaction is carried out in a three-electrode system, which uses a platinum sheet as the counter electrode and a saturated calomel electrode as the reference electrode.

[0017] Compared with the prior art, this application has the following beneficial effects: This application provides a method for preparing a porous carbon composite electrode based on sycamore leaves. Using waste sycamore leaves as the core precursor, the composite electrode is prepared through a simple process of pretreatment, high-temperature calcination, alkali activation, and loading molding. This method not only realizes the high-value utilization of biomass waste, but also utilizes widely available, easily accessible, and low-cost raw materials, aligning with the concept of green and low-carbon development. Furthermore, the entire process adopts routine laboratory operations, requiring no complex equipment or harsh reaction conditions. The process is highly controllable, with good batch repeatability, and is easy to scale up for industrial production. At the same time, the two-step process of calcination and alkali activation can construct a well-developed hierarchical porous structure in the sycamore leaf-based carbon material, laying the structural foundation for the high catalytic performance of the electrode. Moreover, the preparation process does not involve the addition of toxic or harmful reagents, resulting in low wastewater and waste residue emissions, making it an overall green and environmentally friendly process.

[0018] In one possible implementation, the pretreatment process and key parameters of high-temperature calcination in the preparation method are precisely defined. Micron-sized sycamore leaf powder allows for more complete calcination. A heating rate of 3~15℃ / min, a calcination temperature of 500~1000℃, and a calcination time of 0.5~3h can precisely control the degree of carbonization of the carbon material. This effectively avoids the problem of structural collapse of the carbon material due to excessively rapid heating or insufficient carbonization due to excessively slow heating and insufficient calcination, ensuring the basic structural stability of the original biochar and laying a good structural foundation for the subsequent preparation of a uniform porous structure through alkali activation.

[0019] In one possible implementation, the alkaline activator is specified as KOH, and the core steps of the activation treatment and the water bath incubation parameters are clearly defined. KOH, as an alkaline activator, can selectively etch carbon materials to efficiently construct a hierarchical porous structure. The water bath incubation at 60~80℃ for 0.5~3h allows KOH to fully penetrate into the pores of the original biochar, making the etching effect of subsequent activation and calcination more uniform, avoiding local over-activation or under-activation, and ensuring that the obtained porous biochar has a uniform specific surface area and abundant and uniformly distributed catalytic active sites.

[0020] In one possible implementation, the binder, solvent, and loading process of the catalyst dispersion are precisely defined. The combination of perfluorinated resin solution and anhydrous ethanol can uniformly disperse porous biochar and achieve a firm bond between the catalyst layer and the hydrophobic carbon paper substrate, preventing the catalyst layer from falling off during the electrochemical reaction. The hydrophobic carbon paper substrate with a polytetrafluoroethylene content of 20% to 80% is adapted to the characteristics of the catalyst layer. The loading method of multiple drop-coating and drying ensures that the catalyst layer is evenly distributed on the substrate surface without agglomeration, fully exposing the active sites, while ensuring the overall conductivity and structural integrity of the electrode.

[0021] A porous carbon composite electrode based on paulownia leaves is disclosed, employing a structure design of a hydrophobic carbon paper substrate combined with a layer of paulownia leaf-based porous biochar catalyst. The hydrophobic carbon paper substrate combines excellent conductivity and hydrophobicity, ensuring rapid electron conduction while reducing excessive electrolyte adsorption on the electrode surface, thus improving reaction mass transfer efficiency. The paulownia leaf-based porous biochar catalyst layer has a hierarchical porous structure, providing abundant two-electron water oxidation catalytic active sites, significantly improving the electrode's catalytic reaction efficiency. Simultaneously, the porous biochar is mainly composed of C and O elements, exhibiting excellent chemical stability and being resistant to corrosion in highly oxidizing water oxidation reaction systems, significantly extending the electrode's lifespan and electrochemical stability. The electrode as a whole can also directionally promote the two-electron water oxidation to hydrogen peroxide reaction pathway, effectively suppressing the four-electron oxygen evolution side reaction, thus solving the core problem of low selectivity in existing electrodes.

[0022] In one possible implementation, the specific surface area and elemental content of porous biochar are quantitatively defined, with a specific surface area ≥ 600 m². 2 The hierarchical porous structure of / g provides ample catalytic active sites, ensuring sufficient contact between reactants and active sites and improving catalytic reaction efficiency. The carbon content ratio of 85%~95% and oxygen content of 5%~15% not only ensures excellent electron conduction efficiency of the electrode, but also allows for precise control of the electrode's adsorption capacity for reaction intermediates through appropriate oxygen-containing functional groups, further enhancing the catalytic selectivity of the electrode for the two-electron water oxidation pathway, while also taking into account the chemical stability of carbon materials.

[0023] In one possible implementation, the Raman spectrum of porous biochar is defined as I. D / I G The value ranges from 0.85 to 1.05, indicating that porous biochar has moderate structural defects and abundant edge sites. These sites are highly efficient active sites for the oxidation of water with two electrons to generate hydrogen peroxide, which can directionally enhance the catalytic activity of the electrode for the oxidation pathway of water with two electrons. At the same time, the moderate degree of structural defects can ensure the overall structural stability of the carbon material, avoiding the problem that excessive defects can lead to easy corrosion of the carbon material in a strongly oxidizing reaction system and shorten the service life of the electrode, thus achieving dual optimization of electrode catalytic activity and structural stability.

[0024] An application of a porous carbon composite electrode based on *Platycladus orientalis* leaves in the electrochemical synthesis of hydrogen peroxide is presented. This composite electrode is used as the working electrode for a two-electron water oxidation reaction, using only water as a raw material without the need for additional oxidants or reductants. This single-source and environmentally friendly approach replaces the complex process of the traditional anthraquinone method, significantly reducing energy consumption and pollutant emissions in hydrogen peroxide production. Simultaneously, the composite electrode exhibits excellent catalytic activity and selectivity in the electrolyte, significantly improving the yield and Faradaic efficiency of hydrogen peroxide, surpassing traditional low-cost carbon-based electrodes. Furthermore, this application organically combines the high-value utilization of biomass waste with green electrochemical synthesis technology, providing a reliable technical path for the green industrial production of hydrogen peroxide. It can also be extended to other electrochemical catalysis fields, possessing broad industrial application prospects.

[0025] In one possible implementation, the type, concentration, and reaction potential of the electrolyte for the electrochemical synthesis of hydrogen peroxide are specified. A 0.1–3 M potassium carbonate electrolyte provides a suitable alkaline environment for the two-electron water oxidation reaction, effectively reducing the reaction overpotential and increasing the reaction rate. A potential range of 1.5–4 V vs. RHE ensures efficient and stable two-electron water oxidation while avoiding the aggravation of side reactions such as four-electron oxygen evolution caused by excessively high potentials. This also reduces electrode wear caused by high potentials, achieving a balance between electrode catalytic activity and operational stability. Furthermore, it maintains stable catalytic performance over a wide potential range, facilitating on-site industrial control and implementation. In one possible implementation, the composition of the three-electrode system for the electrochemical synthesis of hydrogen peroxide is limited. The classic combination of a platinum sheet counter electrode and a saturated calomel reference electrode ensures the electrochemical stability of the three-electrode system and the accuracy of potential detection. This allows the actual catalytic performance of the composite electrode to be reflected in a true and objective manner, avoiding misjudgments of performance due to system errors. At the same time, this three-electrode system is a conventional system in the field of electrochemical synthesis, requiring no additional customized special equipment. This significantly reduces the equipment modification costs for the industrial application of this technology and is more conducive to industrial implementation and promotion. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a scanning electron microscope (SEM) image of the porous biochar material based on the leaves of the Chinese parasol tree in the embodiments of this application; Figure 1Note: The porous biochar based on the leaves of the Chinese parasol tree exhibits the typical fragmented and blocky morphology of pyrolysis biochar. It has a rough surface and rich multi-scale pore structure. This structure not only provides a huge specific surface area, but also provides channels for the efficient transport of reactants, thereby improving the efficiency of catalytic reaction.

[0028] Figure 2 The total X-ray photoelectron x-ray spectroscopy (XPS) spectrum (a) and the XPS spectrum (b) of C1s of the porous biochar material based on the leaves of the Chinese parasol tree in the embodiments of this application are shown. The horizontal axis represents the binding energy and the vertical axis represents the photoelectron intensity. Figure 2 Note: The porous biochar based on the leaves of the Chinese parasol tree mainly contains two elements, C and O, with high purity. It is mainly composed of aromatic carbon skeleton and contains a small amount of active oxygen-containing functional groups. It has good chemical stability and moderate conductivity, making it suitable as an electrochemical catalytic electrode material.

[0029] Figure 3 This is the Raman spectrum of the porous biochar material based on the leaves of the Chinese parasol tree in the embodiments of this application. The horizontal axis is the Raman shift and the vertical axis is the photoelectron intensity. Figure 3 Note: Raman spectrum of porous biochar based on sycamore leaf base I D / I G The value is approximately 0.91, indicating that the material has moderate structural defects and abundant edge sites at the nanoscale, providing sufficient catalytic active sites for the two-electron water oxidation reaction.

[0030] Figure 4 This is a nitrogen adsorption-desorption isotherm diagram of the porous biochar material based on sycamore leaf in the embodiments of this application. The horizontal axis is the relative pressure and the vertical axis is the adsorption amount. Figure 4 Note: The nitrogen adsorption-desorption isotherm of the porous biochar based on *Firmiana simplex* leaves is type IV and exhibits an H3 type hysteresis loop, with a total specific surface area as high as 606.22 m². 2 / g has a well-developed hierarchical porous structure, which can achieve full contact between reactants and active sites, and improve mass transfer efficiency.

[0031] Figure 5 The bar chart shows the yield versus Faraday efficiency of the electrochemical synthesis of hydrogen peroxide using the composite electrodes prepared in Examples 1 and 2 of this application. Figure 5 Note: The composite electrode prepared in Example 1 produced 43.48 mg / L of hydrogen peroxide and had a Faraday efficiency of 25.32%, which was significantly better than that of Example 2 and traditional carbon-based electrode materials. This demonstrates that the process parameter control in this application can effectively improve the catalytic performance of the composite electrode. Detailed Implementation

[0032] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0033] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0034] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly defined. The specific embodiments of this application will be further described in detail below with reference to the accompanying drawings.

[0035] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0036] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0037] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0038] like Figures 1-5 As shown, all raw materials and reagents used in the embodiments of this application are commercially available; the hydrophobic carbon paper used is commercially available polytetrafluoroethylene modified hydrophobic carbon paper, and the polytetrafluoroethylene content can be selected from 20% to 80%; the perfluorinated resin solution is a commercial electrode-specific binder, anhydrous ethanol is analytical grade, KOH is analytical grade, and hydrochloric acid is a dilute hydrochloric acid solution (concentration 0.5 mol / L); the ball mill, tube furnace, ultrasonic disperser, electrochemical workstation, etc. used are all conventional laboratory equipment.

[0039] Example 1 This embodiment provides a method for preparing a porous carbon composite electrode based on a sycamore leaf, the specific steps of which are as follows: Pretreatment of fallen sycamore leaves and high-temperature calcination to produce original biochar: Fresh fallen sycamore leaves were collected, repeatedly rinsed with deionized water to remove surface dust, impurities and soluble pollutants, and then dried in a 100℃ electric heating oven for 24 hours until completely dehydrated; The dried sycamore leaves were placed in a ball mill and pulverized at 500 rpm for 3 hours to obtain micron-sized sycamore leaf powder. The above-mentioned sycamore leaf powder was placed in a tube furnace, and nitrogen gas was introduced as a protective atmosphere (flow rate 100 mL / min). The temperature was increased to 700℃ at a heating rate of 5℃ / min, and calcined at a constant temperature for 2 hours. After naturally cooling to room temperature, it was placed in a vacuum drying oven at 100℃ and dried for 12 hours to obtain sycamore leaf-based original biochar.

[0040] To prepare porous biochar based on sycamore leaf by activating raw biochar, weigh 1g of the above-mentioned raw biochar based on sycamore leaf, place it in a beaker, add 20mL of deionized water and 2g of KOH powder (alkaline activator), and stir thoroughly until evenly mixed; Place the beaker in a 60℃ constant temperature water bath for 1 hour to allow KOH to fully penetrate into the pores of the biochar; transfer the mixture to a tube furnace, introduce nitrogen as a protective atmosphere, heat to 700℃ at a heating rate of 5℃ / min, and calcine at a constant temperature for 1 hour for activation treatment. After naturally cooling to room temperature, the product was repeatedly washed with 0.5 mol / L dilute hydrochloric acid solution until the pH of the washing solution was 7.0. The washed product was then dried in a vacuum drying oven at 60℃ for 24 hours to obtain porous biochar based on sycamore leaves.

[0041] Testing revealed that the porous biochar possesses a hierarchical porous structure with a specific surface area of ​​606.22 m². 2 / g, mainly composed of carbon and oxygen (carbon content approximately 92%, oxygen content approximately 8%), Raman spectrum I D / I G The value is 0.91.

[0042] Catalyst dispersion preparation and composite electrode molding: 5 mg of the above-mentioned porous biochar based on paulownia leaves was accurately weighed and placed in a centrifuge tube. 30 μL of perfluorinated resin solution (binder) and 1 mL of anhydrous ethanol (solvent) were added sequentially. The centrifuge tube was placed in an ultrasonic disperser and ultrasonically dispersed for 1 h (conventional laboratory power) to obtain a uniform catalyst dispersion without precipitation. Hydrophobic carbon paper with a polytetrafluoroethylene content of 40% was selected, cut into 1 cm × 1 cm sizes, and immersed in anhydrous ethanol for ultrasonic cleaning for 5 min to remove surface oil and impurities. It was then air-dried. The above-mentioned catalyst dispersion was added to the surface of the hydrophobic carbon paper substrate in 4 drops using the drop-coating method. The amount added each time was 200 μL. After each drop, the solvent was dried by irradiation with an infrared lamp (60℃) for 12 min until all the dispersion was added and there was no obvious liquid residue on the substrate surface, thus obtaining the paulownia leaf-based porous carbon composite electrode.

[0043] The composite electrode was used as the working electrode in the electrochemical synthesis of hydrogen peroxide. A three-electrode test system was constructed by using the composite electrode prepared above as the working electrode, a platinum sheet as the counter electrode, and a saturated calomel electrode as the reference electrode. The system was placed in a 0.5 mol / L potassium carbonate electrolyte. Before the test, nitrogen gas was introduced into the electrolyte for 30 min to remove dissolved oxygen. The electrolyte temperature was controlled at 25 °C. The two-electron water oxidation reaction was carried out by chronoamperometry at a potential of 2.7 V vs. RHE for 10 min.

[0044] After the reaction was completed, the concentration of hydrogen peroxide in the electrolyte was determined using the titanium sulfate colorimetric method. The results showed that: The hydrogen peroxide yield was 43.48 mg / L, and the Faraday efficiency was 25.32%.

[0045] Example 2 This embodiment provides a method for preparing and applying a porous carbon composite electrode based on sycamore leaf. The difference from Embodiment 1 lies only in the adjustment of process parameters. The specific steps are as follows: Pretreatment of fallen sycamore leaves and high-temperature calcination to produce raw biochar: Fresh fallen sycamore leaves were washed with deionized water and dried in an electric heating oven at 80℃ for 36 hours. They were then ball-milled at 300 rpm for 1 hour to obtain micron-sized sycamore leaf powder. The powder was placed in a tube furnace, and argon gas (protective atmosphere, flow rate 80 mL / min) was introduced. The temperature was increased to 800℃ at a rate of 3℃ / min and calcined at a constant temperature for 1.5 hours. After cooling, the powder was dried with hot air at 80℃ for 20 hours to obtain raw biochar.

[0046] To prepare porous biochar based on *Firmiana simplex* leaves by activating raw biochar, weigh 0.5 g of raw biochar, add 15 mL of deionized water and 1 g of KOH powder, stir evenly, and incubate in a constant temperature water bath at 70 °C for 2 h; then heat to 800 °C at a rate of 3 °C / min under nitrogen atmosphere and calcine at a constant temperature for 1 h; after cooling, wash with 0.5 mol / L dilute hydrochloric acid until pH=6.8, and vacuum dry at 60 °C for 36 h to obtain porous biochar based on *Firmiana simplex* leaves.

[0047] The porous biochar was tested and found to have a specific surface area of ​​612.5 m². 2 / g, carbon content approximately 90%, oxygen content approximately 10%, Raman spectrum I D / I G The value is 0.88.

[0048] Catalyst dispersion preparation and composite electrode molding: 5 mg of porous biochar was mixed with 30 μL of perfluorinated resin solution and 1 mL of anhydrous ethanol and ultrasonically dispersed for 1 h to prepare catalyst dispersion. Select hydrophobic carbon paper (1cm×1cm) with 60% polytetrafluoroethylene content, ultrasonically clean it with anhydrous ethanol for 5 minutes and then air dry it. The dispersion was added dropwise in four portions (200 μL each time), and after each addition, the electrode was dried by irradiation with an infrared lamp at 70°C for 10 min to obtain the composite electrode.

[0049] The composite electrode was used in the electrochemical synthesis of hydrogen peroxide. The same three-electrode system, electrolyte, and testing conditions as in Example 1 were employed for the two-electrode water oxidation reaction, with a reaction time of 10 min. The hydrogen peroxide yield was measured to be 27.94 mg / L, and the Faraday efficiency was 16.27%.

[0050] Example 3 This embodiment provides a method for preparing and applying a porous carbon composite electrode based on sycamore leaf. The difference from Embodiment 1 lies only in the adjustment of process parameters. The specific steps are as follows: Pretreatment of fallen sycamore leaves and high-temperature calcination to produce original biochar: Fresh fallen sycamore leaves were washed with deionized water and then dried in an electric heating forced-air oven at 120℃ for 18 hours. Micron-sized sycamore leaf powder was obtained by ball milling at 700 rpm for 2 hours. The powder was placed in a tube furnace, nitrogen gas was introduced (flow rate 150 mL / min), and the temperature was increased to 900℃ at a rate of 10℃ / min. The mixture was calcined at a constant temperature for 1 hour, cooled, and then vacuum dried at 110℃ for 10 hours to obtain the original biochar.

[0051] To prepare porous biochar based on sycamore leaf by activating raw biochar, weigh 2g of raw biochar, add 40mL of deionized water and 4g of KOH powder, stir evenly, and incubate in a constant temperature water bath at 80℃ for 0.5h. The temperature was increased to 900℃ at a rate of 10℃ / min under a nitrogen atmosphere and calcined at a constant temperature for 0.5h. After cooling, it was washed with 0.5mol / L dilute hydrochloric acid until pH=7.2, and then vacuum dried at 60℃ for 18h to obtain porous biochar based on sycamore leaf.

[0052] The porous biochar was tested and found to have a specific surface area of ​​601.8 m². 2 / g, carbon content approximately 93%, oxygen content approximately 7%, Raman spectrum I D / I G The value is 0.95.

[0053] Catalyst dispersion preparation and composite electrode molding: 5 mg of porous biochar was mixed with 30 μL of perfluorinated resin solution and 1 mL of anhydrous ethanol and ultrasonically dispersed for 1 h to prepare catalyst dispersion. Select hydrophobic carbon paper (1cm×1cm) with 80% polytetrafluoroethylene content, ultrasonically clean it with anhydrous ethanol for 5 minutes and then air dry it. The dispersion was added dropwise in four portions (200 μL each time), and after each addition, the electrode was dried by irradiation with an infrared lamp at 80°C for 8 minutes to obtain the composite electrode.

[0054] The composite electrode was used in the electrochemical synthesis of hydrogen peroxide. The same three-electrode system, electrolyte, and testing conditions as in Example 1 were employed for the two-electrode water oxidation reaction, with a reaction time of 10 min. The hydrogen peroxide yield was measured to be 38.65 mg / L, and the Faraday efficiency was 22.15%.

[0055] Comparative Example Commercial graphite carbon powder was used to replace the sycamore leaf-based porous biochar of this application. The rest of the preparation process, raw material ratio and application test conditions were completely consistent with those in Example 1. A graphite carbon powder / hydrophobic carbon paper composite electrode was prepared and tested for electrochemical synthesis of hydrogen peroxide.

[0056] The results showed that the hydrogen peroxide yield of the electrode prepared in this comparative example was only 8.25 mg / L, and the Faraday efficiency was 4.18%, which was far lower than the test results of the various embodiments of this application. This proves that the porous biochar prepared by the application using sycamore leaves as raw material can significantly improve the catalytic activity and selectivity of the composite electrode for the two-electron water oxidation reaction.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them; although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications to the technical solutions described in the foregoing embodiments, or equivalent substitutions for some or all of the technical features, do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing a porous carbon composite electrode based on *Firmiana simplex* leaf, characterized in that, Includes the following steps: After pretreatment, the fallen leaves of the Chinese parasol tree are calcined at high temperature under a protective atmosphere to obtain raw biochar. The original biochar was mixed with an alkaline activator and activated to obtain porous biochar based on sycamore leaves. The porous biochar based on sycamore leaves is mixed with a binder and a solvent to prepare a catalyst dispersion. The catalyst dispersion is loaded onto a hydrophobic carbon paper substrate and dried to obtain a porous carbon composite electrode based on sycamore leaves.

2. The method for preparing the sycamore leaf-based porous carbon composite electrode according to claim 1, characterized in that, The pretreatment includes washing, drying, and ball milling; The ball mill speed for ball milling is 200~800 rpm, and the ball milling time is 0.5~6 h; The heating rate of the high-temperature calcination is 3~15℃ / min, the calcination temperature is 500~1000℃, and the calcination time is 0.5~3h.

3. The method for preparing the sycamore leaf-based porous carbon composite electrode according to claim 1, characterized in that, The alkaline activator is KOH; The activation treatment includes mixing the raw biochar with KOH and water, followed by water bath incubation, high-temperature calcination, acid washing, and drying. The water bath incubation temperature is 60~80℃, and the time is 0.5~3h; The heating rate of the high-temperature calcination is 3~15℃ / min, the calcination temperature is 500~1000℃, and the calcination time is 0.5~3h.

4. The method for preparing the sycamore leaf-based porous carbon composite electrode according to claim 1, characterized in that, The adhesive is a perfluorinated resin solution, and the solvent is anhydrous ethanol; The hydrophobic carbon paper substrate contains 20% to 80% polytetrafluoroethylene. The load is applied using a drop-coating method, and then dried after being added in multiple drops.

5. A porous carbon composite electrode based on *Platycodon grandiflorus* leaf, characterized in that, The composite electrode includes: a hydrophobic carbon paper substrate; and a porous carbon material layer loaded on the surface of the hydrophobic carbon paper substrate; The porous carbon material layer comprises porous biochar with a hierarchical porous structure obtained from the carbonization and activation treatment of sycamore leaves.

6. The sycamore leaf-based porous carbon composite electrode according to claim 5, characterized in that, The specific surface area of ​​the porous biochar is ≥600 m². 2 / g, mainly composed of carbon and oxygen elements; The porous biochar contains 85% to 95% carbon and 5% to 15% oxygen.

7. The sycamore leaf-based porous carbon composite electrode according to claim 5, characterized in that, Raman spectrum of the porous biochar I D / I G The value is 0.85~1.

05.

8. The application of a porous carbon composite electrode based on *Firmiana simplex* leaf in the electrochemical synthesis of hydrogen peroxide, characterized in that... Using the composite electrode as the working electrode, a two-electron water oxidation reaction is carried out in the electrolyte to generate hydrogen peroxide. The composite electrode uses hydrophobic carbon paper as a substrate, and its surface is loaded with porous biochar made from sycamore leaves through carbonization and activation treatment.

9. The application of the sycamore leaf-based porous carbon composite electrode according to claim 8 in the electrochemical synthesis of hydrogen peroxide, characterized in that, The electrolyte is a potassium carbonate electrolyte with a concentration of 0.1~3M; The potential range for the two-electron water oxidation reaction is 1.5~4V vs. RHE.

10. The application of the sycamore leaf-based porous carbon composite electrode according to claim 8 in the electrochemical synthesis of hydrogen peroxide, characterized in that, The two-electron water oxidation reaction is carried out in a three-electrode system, which uses a platinum sheet as the counter electrode and a saturated calomel electrode as the reference electrode.

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