Hollow spherical phosphorus-doped CuO composite electrocatalyst as well as preparation method and application thereof

Abstract

The invention discloses a hollow spherical phosphorus-doped CuO composite electrocatalyst as well as a preparation method and application thereof, and belongs to the technical field of biomass cracking. The hollow spherical phosphorus-doped CuO composite electrocatalyst is of a hollow sphere structure with a porous surface, and is prepared by compounding a nitrogen-doped carbon skeleton, CuO and CuPO3. The material has a larger specific surface area, excellent conductivity, abundant pore structures and edge defects, and the catalytic activity of oxygen reduction reaction (ORR) is remarkably improved; the hollow shell structure can significantly increase the number of active sites, provides an effective way for transmission of electrons, electrolyte and oxygen, is beneficial to desorption of an. OOH intermediate, and has double functions of high electrocatalytic activity and stability. Benefited from the hollow porous structure, compared with single photocatalysis or electro-catalysis, the conversion rates of the lignin are respectively increased by 124.89% and 11.36% in photoelectric concerted catalysis, and the total product yields are respectively increased by 73.81% and 215.80%.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomass cracking, and in particular relates to a hollow spherical phosphorus-doped CuO composite electrocatalyst and a preparation method and application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Lignin is nature's most abundant renewable aromatic resource. Converting lignin into value-added fuels and chemicals can reduce dependence on fossil fuel resources. Lignin is composed of methoxylated phenylpropane units connected by a variety of carbon-oxygen (CO) and carbon-carbon (CC) bonds. The key to its cracking to obtain monomers lies in the efficient and selective cleavage of these two connecting bonds. Existing CC bond cracking technologies, such as oxidation, pyrolysis, and hydrogenolysis, are energy-intensive and cannot effectively address the re-condensation of aldehydes and phenolic compounds.

[0004] At present, some studies have used the photocatalytic method to cleave the CC bond, and the photocatalytic system is responsible for the oxidation of C β The electrocatalytic system is responsible for reducing the radical intermediate to form OOH. The oxidizing and reducing groups can be spatially separated, avoiding mutual quenching. Although photocatalytic synergy has advantages over other methods in cleaving CC bonds, the key to photocatalytic cleavage of CC bonds lies in the efficient and selective generation of OOH. Therefore, the catalytic activity of the electrocatalyst in the electrocatalytic system becomes a new limiting factor. Therefore, selecting an electrocatalyst that can efficiently and selectively generate OOH is crucial to improving the conversion rate and product yield of lignin.

[0005] Some studies have used the ball milling method to dope copper oxide with phosphorus, and changed the type of CuO adsorption to O2 by phosphorus doping, thereby controlling the production of OOH radicals, which cooperates with the photogenerated holes h in the photocatalytic process. + , effectively breaking CC bonds and increasing the yield of aromatic monomers from lignin cracking. Due to high-speed collisions, the prepared material is spherical, and the active sites are not fully utilized. OOH has a low Faradaic efficiency, and monomer yields still need to be improved. Summary of the Invention

[0006] In order to address the deficiencies of the prior art, the purpose of the present invention is to provide a phosphorus-doped hollow porous electrocatalyst and its preparation method and application. The present invention provides surface-porous phosphorus-doped copper oxide hollow spheres as electrocatalysts. By controlling the morphology of the electrocatalyst, the number of active sites is effectively increased, thereby improving the catalytic efficiency.

[0007] In order to achieve the above object, the technical solution of the present invention is:

[0008] The first aspect of the present invention provides a hollow spherical phosphorus-doped CuO composite electrocatalyst having a porous surface.

[0009] The hollow sphere is made of a composite of nitrogen-doped carbon skeleton, CuO and CuPO3.

[0010] The hollow spherical phosphorus-doped CuO composite electrocatalyst provided by the present invention has a porous surface, a large specific surface area, excellent conductivity, and a rich pore structure. As an electrocatalyst, it exhibits high electrocatalytic activity and stability. Furthermore, the hollow shell structure significantly increases the number of active sites and provides an efficient pathway for the transport of electrons, electrolytes, and oxygen, facilitating the desorption of the OOH intermediate.

[0011] In some embodiments of the present invention, the particle size of the hollow spherical phosphorus-doped CuO composite electrocatalyst is 150-200 nm. The surface of the hollow spherical structure is rough, which is conducive to increasing the specific surface area and enhancing the adsorption of oxygen.

[0012] Preferably, the specific surface area of the hollow spherical phosphorus-doped CuO composite electrocatalyst reaches 95-100m 2 g -1 The larger specific surface area can provide more active sites, which helps to improve its catalytic performance.

[0013] The present invention uses phosphorus-doped copper oxide, and phosphorus doping does not change the crystal plane of copper oxide. Compared with other heteroatoms (such as N, S, B, etc.), the atomic radius of P atoms is the largest, resulting in the largest substitution defects. The CP bond length formed is significantly longer than the CX (X = N, S, B) bond length. The incorporation of phosphorus atoms brings greater structural deformation to the electrocatalytic material. In terms of electronegativity, the electronegativity of N (3.04) and S (2.58) is greater than that of carbon (2.55), while the electronegativity of phosphorus (2.19) is smaller than that of C. The polarity of the CP bond is opposite to that of the CN and CS bonds. Therefore, phosphorus doping can produce more defects and new active sites different from nitrogen and sulfur doping.

[0014] It should be noted that the hollow spherical phosphorus-doped CuO composite electrocatalyst provided by the present invention has a high phosphorus content and is evenly distributed.

[0015] In some embodiments of the present invention, the phosphorus atoms in the hollow spherical phosphorus-doped CuO composite electrocatalyst account for 0.5-1at%, for example, 0.5-0.9at%, 0.6-0.9at%, 0.7-0.9at%, 0.8-0.9at%, 0.8-0.85at%, 0.8at%, 0.81at%, 0.82at%, 0.83at%, etc.

[0016] It should be noted that the term atomic percentage (Atomic Percent, abbreviated as At.%) is a unit used to express the ratio of the number of atoms of different elements in a chemical composition, and is commonly used to describe the relative content of each element in a material. In this representation method, the sum of the atomic percentages of all elements is 100%. The calculation method of atomic percentage usually involves determining the number of atoms of each element in the sample, dividing the number of atoms of each element by the total number of atoms, and then multiplying by 100 to obtain the percentage.

[0017] For example, in the hollow spherical phosphorus-doped CuO composite electrocatalyst, the atomic percentage of phosphorus is 0.5-1 at %, which means that among every 100 atoms, 0.5-1 are phosphorus atoms.

[0018] Preferably, the hollow spherical phosphorus-doped CuO composite electrocatalyst comprises 78-82 at% carbon atoms, 10-14 at% copper atoms, 5-6 at% oxygen atoms, 1-2 at% nitrogen atoms, and 0.5-1 at% phosphorus atoms. With this atomic ratio, the phosphorus-doped hollow porous electrocatalyst has a stable structure and high catalytic activity.

[0019] In some embodiments of the present invention, C, O, Cu, N and P elements are uniformly distributed in the hollow spherical phosphorus-doped CuO composite electrocatalyst.

[0020] A second aspect of the present invention provides a method for preparing the hollow spherical phosphorus-doped CuO composite electrocatalyst, comprising:

[0021] The polyether block copolymer is dissolved in water, a spherical template is added, and after mixing, acid, 1,3,5-trimethylbenzene (TMB) and triphenylphosphine (PPh3) are added and stirred until a microemulsion state is formed; copper salt and 2-aminoterephthalic acid (APDC, providing nitrogen doping) are then added, heated and stirred, and the solid-liquid separation is performed. The obtained solid is dried and calcined in a protective gas to obtain a phosphorus-doped hollow porous electrocatalyst.

[0022] The prior art generally uses phosphorus-containing precursors such as phosphorus tribromide, sodium dihydrogen phosphate and phosphoric acid to prepare phosphorus-doped electrocatalysts. However, the electrocatalyst materials prepared using these precursors have the problems of low phosphorus content and uneven distribution of phosphorus. In addition, the existing phosphorus doping methods include hydrothermal method, high-temperature pyrolysis method, impregnation-high-temperature treatment combination method, sol-gel-high-temperature treatment combination method, high-temperature and high-pressure method, etc., with a long preparation cycle and a complicated process, and low phosphorus utilization rate. In this regard, the present invention provides a method for constructing a hollow spherical phosphorus-doped CuO composite electrocatalyst by a hard template method, using triphenylphosphine as a phosphorus precursor. Triphenylphosphine can achieve effective doping by forming a strong CP bond to obtain an electrocatalyst with a high phosphorus content and uniform distribution.

[0023] This paper uses the hard template method to prepare a hollow spherical phosphorus-doped CuO composite electrocatalyst for the first time. The advantages of the hollow porous morphology, abundant oxygen vacancies, and P doping to control the electronic structure and enhance oxygen adsorption capacity all contribute to efficient production. · OOH.

[0024] The preparation method provided by the invention is simple, has low energy consumption, does not pollute the environment, and is safe and environmentally friendly.

[0025] In some embodiments of the present invention, the polyether block copolymer is a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer. P-123, abbreviated as P123, has a molecular formula of PEO-PPO-PEO and a molecular weight of 5800. It is a typical nonionic surfactant that acts as a template in the synthesis reaction of the present invention, forming regular micelles through self-assembly, thereby guiding the material to form a mesoporous structure. In the present invention, the P123 also has the following functions:

[0026] (1) Improve crystallinity and promote the uniform growth of MOF particles.

[0027] (2) Forming a mesoporous structure, improving the specific surface area of MOF, and enhancing the catalytic and adsorption properties.

[0028] P123 is a commercially available product and can be purchased.

[0029] In some embodiments of the present invention, the acid includes acetic acid (HAC) and phosphoric acid, preferably acetic acid. Acid is added to the reaction system to form acidic conditions, causing the polyether block copolymer to aggregate. Under acidic conditions, the PEO hydrophilic segments of the polyether block copolymer P123 interact with the solution, while the PPO hydrophobic segments aggregate to form micelle cores. These micelles can serve as "templates" to guide the deposition of inorganic precursors around them, ultimately forming a mesoporous material with uniform pores. After the reaction is completed, P123 is removed to obtain a porous structure.

[0030] In some embodiments of the present invention, TMB (1,3,5-trimethylbenzene) acts as a pore-expanding agent, increasing the specific surface area and porosity, thereby enhancing the catalytic, adsorption, and energy storage properties of the electrocatalyst. Furthermore, as an organic cosolvent, TMB can improve the solubility of certain hydrophobic precursors (such as organic ligands and metal salts), making the reaction more uniform and promoting the uniform growth of MOF crystals.

[0031] In some embodiments of the present invention, the spherical template is preferably polystyrene spheres (PS spheres).

[0032] The present invention uses PS spheres as a template. The main advantage of using PS spheres as a template is that the MOF framework material controls the attachment of individual spherical polystyrene (PS) particles to each surface of the polyhedron particles. The shape of the polyhedron determines the final coordination number, which is equal to the number of faces and geometric shape of the final assembled colloidal cluster. Secondly, using a hard template strategy, a suitable solvent is selected to control the nucleation and growth rate of the precursor, achieving strictly confined growth of MOFs within the template. In addition, the PS spheres are easily melted and decomposed during the subsequent heating process without destroying the outer MOF framework structure.

[0033] It is understandable that the spherical template can also be selected from silica, ZIF-8, etc. as a template, but the pores formed therein are not as large as those of PS spheres. Therefore, PS spheres are preferably used as the template.

[0034] It is understood that the polystyrene microspheres are obtained by polymerization of styrene, and can be purchased or prepared by oneself. The preparation method of the polystyrene microspheres is a commonly used polymerization method in the art. For example, the following method can be used to synthesize polystyrene microspheres:

[0035] The styrene monomer is dissolved in water, an initiator is added under anaerobic conditions, and the reaction is heated to obtain polystyrene, which is then ground to a target particle size to obtain polystyrene spheres.

[0036] It should be noted that if the styrene monomer contains a stabilizer, the stabilizer needs to be washed away with an alkaline solution before the reaction, and the residual alkali in the styrene needs to be washed away with water before the polymerization reaction is carried out.

[0037] It should be noted that the particle size of the polystyrene spheres synthesized from styrene monomers is relatively uniform, which ensures the stable performance of the obtained hollow spherical phosphorus-doped CuO composite electrocatalyst. The particle size of the polystyrene spheres is 200-300 nm.

[0038] In some embodiments of the present invention, the copper salt comprises any one of copper nitrate, copper chloride, and copper sulfate, preferably copper nitrate, and more preferably copper nitrate trihydrate. Copper is a key metal in many electrocatalytic reactions, particularly in oxygen reduction reactions. In the present invention, the copper salt provides copper ions as catalytically active centers, ultimately forming a copper-based catalytic material.

[0039] In some embodiments of the present invention, the ratio of the polyether block copolymer, water, spherical template, acetic acid, 1,3,5-trimethylbenzene, triphenylphosphine, copper salt, and 2-aminoterephthalic acid is: 800-900 mg: 40-60 mL: 1500-2500 mg: 0.5-1 mL: 5-15 mL: 250-1250 mg: 1200-1300 mg: 1000-2000 mg. Within this range, the resulting hollow spherical phosphorus-doped CuO composite electrocatalyst exhibits good catalytic activity and stability.

[0040] Preferably, the polyether block copolymer, water, spherical template, acetic acid, 1,3,5-trimethylbenzene, triphenylphosphine, copper salt, and 2-aminoterephthalic acid are used in a ratio of 800-850 mg:50 mL:1800-2200 mg:0.8-0.9 mL:8-12 mL:250-1250 mg:1200-1250 mg:1300-1700 mg. Within this dosage range, the resulting hollow spherical phosphorus-doped CuO composite electrocatalyst exhibits better catalytic activity and stability.

[0041] In order to further improve the catalytic activity and stability of the obtained hollow spherical phosphorus-doped CuO composite electrocatalyst, the usage ratio of the polyether block copolymer, water, spherical template, acetic acid, 1,3,5-trimethylbenzene, triphenylphosphine, copper salt and 2-aminoterephthalic acid is: 833 mg: 50 mL: 2000 mg: 0.83 mL: 10 mL: 250-1250 mg: 1210.8 mg: 1500 mg;

[0042] The polyether block copolymer is P123, the spherical template is PS sphere, and the copper salt is copper nitrate trihydrate.

[0043] It is understood that the amount of phosphorus incorporated into the hollow spherical phosphorus-doped CuO composite electrocatalyst can be changed by controlling the amount of triphenylphosphine. Specifically, the amount of triphenylphosphine can be 250 mg, 500 mg, 750 mg, 1000 mg, or 1250 mg. The amount of triphenylphosphine is preferably 1000 mg. At this time, the amount ratio of the polyether block copolymer, water, spherical template, acetic acid, 1,3,5-trimethylbenzene, triphenylphosphine, copper salt, and 2-aminoterephthalic acid is: 833 mg:50 mL:2000 mg:0.83 mL:10 mL:1000 mg:1210.8 mg:1500 mg.

[0044] In some embodiments of the present invention, the calcination temperature is 200-1000°C and the calcination time is 1-3 hours. The calcination temperature can be 200°C, 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, or a range consisting of any two temperatures.

[0045] It is understood that since the calcination temperature affects the structure of the resulting electrocatalyst, the optimal calcination temperature can be determined based on the optimal phosphorus doping amount. The calcination temperature is preferably 600° C. At this temperature, the electrocatalyst structure is stable and the catalytic activity is high.

[0046] A third aspect of the present invention provides a use of the above-mentioned hollow spherical phosphorus-doped CuO composite electrocatalyst or the hollow spherical phosphorus-doped CuO composite electrocatalyst prepared by the above-mentioned preparation method in the cracking of lignin model compounds.

[0047] In some embodiments of the present invention, the application is the catalytic cracking of a lignin model compound by a hollow spherical phosphorus-doped CuO composite electrocatalyst under photoelectric synergistic conditions.

[0048] The fourth aspect of the present invention provides a method for cracking a lignin model compound, comprising: loading the above-mentioned hollow spherical phosphorus-doped CuO composite electrocatalyst or the hollow spherical phosphorus-doped CuO composite electrocatalyst prepared by the above-mentioned preparation method on the surface of carbon paper, and using it as a cathode, in combination with an anode platinum sheet, to electrocatalytically crack the lignin model compound.

[0049] The hollow spherical phosphorus-doped CuO composite electrocatalyst provided by the present invention can improve the conversion rate of lignin model compounds and increase the yield of products.

[0050] In some embodiments of the present invention, during electrocatalytic cracking, the electrocatalytic chamber and the photocatalytic chamber are separated by a microporous membrane, free radicals move freely in the two reaction chambers, and the lignin model compound is cracked by photoelectric synergistic catalysis.

[0051] It should be noted that when using photoelectric synergistic catalysis, the photoelectric synergistic system used is mainly composed of three parts. The leftmost part is the electric anode chamber, the middle part is the electric reduction chamber, which is used to form a closed electric circuit. The electric anode chamber and the electric reduction chamber are connected by an ion exchange membrane, and the rightmost part is the photooxidation chamber. The photooxidation chamber and the electric reduction chamber are connected by a 0.45 micron microporous membrane. The membrane pore size of 0.45 microns can meet the transmembrane transport of ·OOH radicals and Cβ· radicals. The photooxidation chamber is responsible for oxidizing to form Cβ· radical intermediates, and the electric reduction chamber is responsible for reducing to form · In the photoelectric synergistic system, not only can the oxidizing and reducing groups be spatially separated to avoid mutual quenching, but the hydrogen sources are also more diverse.

[0052] It should be noted that the electrocatalytic chamber and the photocatalytic chamber are both conventional structures.

[0053] The hollow spherical phosphorus-doped CuO composite electrocatalyst provided by the present invention significantly improves the conversion rate of lignin model compounds during photoelectric synergistic catalysis compared with single electrocatalysis and single photocatalysis.

[0054] The beneficial effects of the present invention are:

[0055] The present invention provides a hollow spherical phosphorus-doped CuO composite electrocatalyst, which has a larger specific surface area, excellent electrical conductivity, rich pore structure and edge defects, significantly improving its catalytic activity for the oxygen reduction reaction (ORR). The hollow shell structure can significantly increase the number of active sites and provide an effective pathway for the transmission of electrons, electrolytes and oxygen, which is beneficial to the desorption of OOH intermediates. When used as an electrocatalyst, the hollow spherical phosphorus-doped CuO composite electrocatalyst has the dual functions of high electrocatalytic activity and stability.

[0056] Thanks to the material's hollow, porous structure, the concentration of ·OOH doubled compared to a simple spherical phosphorus-doped copper oxide electrocatalyst. As the ·OOH concentration increased, the photocatalytic and synergistic lignin conversion increased by 124.89% and 11.36%, respectively, compared to photocatalysis or electrocatalysis alone, and the total product yield increased by 73.81% and 215.80%, respectively.

[0057] This invention uses a hard template method to prepare hollow spherical phosphorus-doped CuO composite electrocatalysts using triphenylphosphine as a phosphorus precursor. Triphenylphosphine can effectively dope the material by forming strong C-P bonds, increasing the phosphorus content in the electrocatalyst and achieving uniform phosphorus distribution. The preparation method provided by the invention is simple, has low energy consumption, is environmentally friendly, and is safe and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding 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.

[0059] Figure 1 The conversion rates (a) and product yields (b) of the hollow spherical phosphorus-doped CuO composite electrocatalysts with different phosphorus doping amounts obtained in Examples 1 and 2 of the present invention during photoelectric synergistic catalysis of lignin model compounds;

[0060] Figure 2 Figure 1 is a morphological representation of Cu-1000P obtained in Example 1 of the present invention, wherein a is a SEM image of PS spheres, b is a SEM image of PS@Cu-MOF, c is a SEM image of Cu-1000P, df are TEM images of Cu-1000P, and the scale bars are 50 nm, 5 nm, and 5 nm, respectively. g1 are the distribution diagrams of all elements, Cu, P, C, N, and O in Cu-1000P, respectively.

[0061] Figure 3 The energy spectrum element content of Cu-1000P obtained in Example 1 of the present invention;

[0062] Figure 4 XRD patterns (a) and FT-IR spectra (b) of PS spheres, Cu-1000P-S, PS@Cu-MOF, Cu-250P, Cu-500P, Cu-750P, Cu-1000P, and Cu-1250P in Examples 1 and 2 of the present invention;

[0063] Figure 5 XRD patterns (a) and FT-IR spectra (b) of PS spheres, Cu-1000P-S, PS@Cu-MOF, Cu-1000P / 200, Cu-1000P / 400, Cu-1000P / 600, Cu-1000P / 800, and Cu-1000P / 1000 in Examples 1 and 3 of the present invention;

[0064] Figure 6 XPS spectra of PS@Cu-MOF and Cu-1000P obtained in Example 1 of the present invention, where a is the full spectrum, b is C1s, c is N1s, d is O1s, e is Cu2p, and f is P2p;

[0065] Figure 7 Thermogravimetric curves of PS, PS@Cu-MOF, and Cu-1000P obtained in Example 1 of the present invention, a is the TG curve, and b is the DTA curve;

[0066] Figure 8N2 adsorption / desorption isotherms of PS, PS@Cu-MOF and Cu-1000P obtained in Example 1 of the present invention;

[0067] Figure 9 The pp-ol conversion rate (a) and product yield (b) of Cu-1000P obtained in Example 1 of the present invention in single photocatalysis, single electrocatalysis, and photoelectric synergistic systems;

[0068] Figure 10 The conversion rates (a) and product yields (b) of the hollow spherical phosphorus-doped CuO composite electrocatalysts with different phosphorus doping amounts obtained in Examples 1 and 3 of the present invention during the photoelectric synergistic catalysis of the lignin model compound. DETAILED DESCRIPTION

[0069] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0070] The materials and equipment used in the following examples and comparative examples are all conventional commercially available products and can be purchased.

[0071] The synthesis method of the PS spheres used in the following examples and comparative examples comprises the following steps:

[0072] (1) Add 13 mL of styrene to a separatory funnel, then add 20 mL of NaOH solution (10 wt%), shake, rinse, let stand, and then discard the NaOH solution layer. Repeat the NaOH solution washing step three times to remove the stabilizer from the styrene.

[0073] (2) Add 5 mL of deionized water to the styrene washed with NaOH solution, shake, rinse, let stand, and separate the layers. Discard the aqueous layer. Repeat the water washing step three times to wash away the residual NaOH in the styrene.

[0074] (3) The cleaned styrene monomer was added to a round-bottom flask, and 100 mL of deionized water (in which 0.5 g of polyvinyl pyrrolidone was dissolved) was quickly added. Nitrogen was bubbled for 30 minutes to remove oxygen from the solution, and then the mixture was stirred in an 80°C water bath for 30 minutes.

[0075] (4) Under continuous stirring, 5 mL of an aqueous solution (0.3 g of potassium persulfate, potassium persulfate as an initiator) was quickly added. After the initiator was rapidly injected, the reaction system was stirred at 80°C in an oxygen-free environment for 24 hours. During the reaction, condensation reflux was maintained and nitrogen was purged.

[0076] (5) Finally, a white emulsion was obtained by centrifugal washing three times, and the solid was dried in a vacuum at 60 °C and ground to obtain PS spheres (particle size of about 250 nm) as the subsequent hard template.

[0077] 1. Material preparation

[0078] Example 1

[0079] A method for preparing a phosphorus-doped hollow porous electrocatalyst comprises the following steps:

[0080] (1) Preparation of composite electrocatalyst precursor PS@Cu-MOF

[0081] (1) Dissolve 833 mg of P123 in 50 mL of deionized water, add 2000 mg of PS spheres, and disperse by ultrasonication.

[0082] (2) Add 0.83 mL of HAC and 10 mL of TMB to the solution, then add 1000 mg of PPh3 and stir until a microemulsion forms.

[0083] (3) 1210.8 mg of Cu(NO3)2·3H2O and 1500 mg of APDC were added to the above mixed solution and stirred in 45°C water for 50 min (stirring speed was 800 rpm / min);

[0084] (4) The obtained product was centrifuged (9000 rpm / min, 8 min), washed three times with water and ethanol respectively, and dried under vacuum at 40 °C to obtain PS@Cu-MOF powder;

[0085] (2) Preparation of composite electrocatalyst Cu-XP

[0086] (1) 1.0 g of PS@Cu-MOF was placed in a quartz boat and heated in a tube furnace under a nitrogen atmosphere at a heating rate of 5°C / min to the target temperature (600°C) for 2 h. The resulting powder was ground and named Cu-1000P or Cu-1000P / 600, depending on the amount of triphenylphosphine added.

[0087] Example 2

[0088] A method for preparing a phosphorus-doped hollow porous electrocatalyst, which is different from Example 1 in that the addition amount of PPh3 is replaced by 250mg, 500mg, 750mg or 1250mg, and the remaining steps are consistent with those of Example 1. The obtained samples are respectively named Cu-250P, Cu-500P, Cu-750P and Cu-1250P according to the addition amount of triphenyl phosphine. Wherein, Cu-250P represents that the addition amount of triphenyl phosphine is 250mg, Cu-500P represents that the addition amount of triphenyl phosphine is 500mg, Cu-750P represents that the addition amount of triphenyl phosphine is 750mg, and Cu-1250P represents that the addition amount of triphenyl phosphine is 1250mg.

[0089] Example 3

[0090] A method for preparing a phosphorus-doped hollow porous electrocatalyst, which differs from Example 1 in that the calcination temperature is replaced by 200°C, 400°C, 800°C or 1000°C, and the remaining steps are consistent with Example 1. The obtained samples are named Cu-1000P / 200, Cu-1000P / 400, Cu-1000P / 800, and Cu-1000P / 1000 according to the calcination temperature. Among them, Cu-1000P / 200 means the calcination temperature is 200°C, Cu-1000P / 400 means the calcination temperature is 400°C, Cu-1000P / 800 means the calcination temperature is 800°C, and Cu-1000P / 1000 means the calcination temperature is 1000°C.

[0091] Comparative Example 1

[0092] A method for preparing a phosphorus-doped porous electrocatalyst comprises the following steps:

[0093] (1) Dissolve 833 mg of P123 in 50 mL of deionized water and disperse by ultrasonication.

[0094] (2) Add 0.83 mL of HAC and 10 mL of TMB to the solution, then add 1000 mg of PPh3 and stir until a microemulsion forms.

[0095] (3) 1210.8 mg of Cu(NO3)2·3H2O and 1500 mg of APDC were added to the above mixed solution and stirred in 45°C water for 50 min (stirring speed was 800 rpm / min);

[0096] (4) The obtained product was centrifuged (9000 rpm / min, 8 min), washed with water and ethanol three times respectively, and dried under vacuum at 40°C. The obtained powder was the intermediate.

[0097] (5) 1.0 g of the intermediate was placed in a quartz boat and heated in a tube furnace under a nitrogen atmosphere at a heating rate of 5°C / min to the target temperature (600°C) for 2 h. The resulting powder was ground and named Cu-1000P-S. Electron microscopy revealed a solid electrocatalyst structure.

[0098] 2. Material structure characterization and performance testing

[0099] 1. Determination of the optimal addition amount of triphenylphosphine

[0100] The catalytic activity of the samples obtained in Example 1 and Example 2 was tested to determine the optimal addition amount of triphenylphosphine.

[0101] Detection method:

[0102] The experiment was conducted in a 40 mL quartz reactor. 4 mg of the lignin model compound 2-phenoxy-1-phenylethanol (pp-ol) was added, followed by 20 mL of acetonitrile and 20 mL of water. The pH of the mixed solution was adjusted to 3 with phosphoric acid. The quartz reactor was separated by a microporous membrane, with one side being the photooxidation chamber and the other the electroreduction chamber. The membrane allowed free radical movement between the two reaction chambers.

[0103] Photooxidation chamber: under the irradiation of a xenon lamp with a total power of 300 W, and 20 mg of g-C3N4 (photocatalyst, suspended on the surface of the solution) was added.

[0104] Electroreduction chamber: 16 mg of electrocatalyst (Cu-1000P) was evenly covered on both sides of the carbon paper (2 cm × 2 cm), with a loading of 2 mg / cm 2 The prepared catalyst-loaded carbon paper was used as the cathode, a platinum electrode (2 cm × 2 cm) was used as the anode, and a saturated silver-silver chloride electrode was used as the reference electrode. Oxygen was passed through the electrocatalytic chamber throughout the process to assist in the formation of OOH radicals.

[0105] 1 mL of sample was taken every hour, and the sample after passing through a 0.22 μm organic filter membrane was analyzed by liquid chromatography for the cracking rate of the lignin model compound pp-ol and the yield of the product.

[0106] like Figure 1 As shown, the conversion rates of electrocatalysts with different phosphorus contents are different, and Cu-1000P has the highest conversion rate for pp-ol ( Figure 1 (a)), the yield is also the highest ( Figure 1 Therefore, the optimal amount of triphenylphosphine to be added is determined to be 1000 mg.

[0107] At the optimal phosphorus addition level, more oxygen vacancies are created, enhancing oxygen adsorption capacity. This increases the output of ·OOH, thereby improving the PP-OL conversion rate. Weak electronegativity results in weak electron control in the surrounding metal outer layer. Oxygen absorption at the metal terminal sites allows for easier stable absorption, leading to a more favorable Yeager-type adsorption pattern. The more ·OOH formed, the higher the PP-OL conversion rate.

[0108] 2. Determination of the optimal calcination temperature

[0109] The samples obtained in Example 1 and Example 3 were tested using the same testing method as described in "1. Determination of the Optimal Addition Amount of Triphenylphosphine". The optimal calcination temperature was determined based on the catalytic activity.

[0110] like Figure 10As shown in Figure 2, the conversion rates of electrocatalysts obtained at different calcination temperatures are different, and Cu-1000P / 600 has the highest conversion rate for pp-ol ( Figure 10 (a)), the yield is also the highest ( Figure 10 Therefore, the optimal calcination temperature was determined to be 600°C.

[0111] The Cu-1000P prepared in Example 1 at the optimal triphenylphosphine addition amount and the optimal calcination temperature was used for subsequent characterization and performance testing.

[0112] 3. Morphology characterization

[0113] Figure 2 Figures (a), (b) and (c) show the morphologies of PS spheres, PS@Cu-MOF (Example 1) and Cu-1000P, respectively. Figure 2 As shown in (a), the PS spheres are standard spherical structures with a particle size of about 250nm. After combining with Cu-MOF, the particle size of the PS spheres increases significantly, reaching about 800nm ( Figure 2 (b)). In the subsequent pyrolysis treatment, the PS spheres as hard templates decomposed, resulting in a hollow structure. The hollow structure of Cu-1000P collapsed and carbonized, and the particle size was reduced to 150-200nm ( Figure 2 (c)). The surface of the shell structure becomes rough, which is beneficial to increase the specific surface area and enhance the adsorption of oxygen.

[0114] Figure 2 The transmission electron microscopy (TEM) images in (d) and (e) further confirm the existence of the hollow structure of Cu-1000P. The crystal planes of Cu-1000P correspond to (202) and (111), respectively, which indicates that phosphorus doping does not change the crystal plane of CuO ( Figure 2 (f)).

[0115] To verify the uniform distribution of elements in the Cu-1000P prepared by the present invention, elemental analysis of Cu-1000P was performed. Energy dispersive spectroscopy (EDS) elemental mapping proved that C, O, Cu, N and P elements were uniformly distributed in Cu-1000P ( Figure 2 (g)-(l)). P is evenly distributed in Cu-1000P, rather than aggregated. Energy spectrum element content analysis of Cu-1000P is performed, as shown in Figure 2. Figure 3 The EDS element content results show that the proportion of P atoms in Cu-1000P is 0.81at%, which further proves that P has been successfully doped into Cu-1000P.

[0116] Figure 4Panel (a) shows the XRD patterns of PS spheres, Cu-1000P-S, PS@Cu-MOF, Cu-250P, Cu-500P, Cu-750P, Cu-1000P, and Cu-1250P. The peak at 19.59° corresponds to the amorphous state of PS. After the PS spheres are coated with Cu-MOF (i.e., PS@Cu-MOF), new peaks at 5.89°, 9.85°, 19.14°, and 26.92° are associated with the crystal planes of Cu-MOF. For Cu-1000P-S, the peaks at 35.50°, 38.73°, 48.73°, and 61.53° correspond to (002), (111), (-202), and (-113), respectively, indicating that during the pyrolysis of Cu-1000P-S, Cu exists primarily as CuO (PDF#45 -0937). After pyrolysis to remove PS spheres, the characteristic peaks of Cu-250P, Cu-500P, Cu-750P, Cu-1000P, and Cu-1250P change significantly compared to PS@Cu-MOF. The peaks at 43.25° and 50.36° are associated with the characteristic peaks of CuPO3 (PDF#21 -0300), while the peak at 74.13° is associated with the (220) crystal plane of Cu (PDF#04 -0836). This indicates that PS spheres can not only serve as hard templates to prepare hollow electrocatalysts, but also affect the distribution of phosphorus during pyrolysis, thereby affecting the composition and morphology of the electrocatalysts.

[0117] Figure 4 (b) shows the Fourier transform infrared (FT-IR) spectra of PS spheres, Cu-1000P-S, PS@Cu-MOF, Cu-250P, Cu-500P, Cu-750P, Cu-1000P, and Cu-1250P. For PS spheres, 3430 cm -1 Corresponding to the stretching vibration of OH, 2926 cm -1 The peak at 1450-1650cm is related to the stretching vibration of CH. -1 The four peaks at 1158 cm correspond to the skeleton vibration of C=C in the benzene ring. After the introduction of Cu-MOF on the surface of PS sphere (i.e., PS@Cu-MOF), the peak at 1158 cm -1 and 609cm -1 The new peaks at 370°C correspond to P=O and Cu-O, respectively. After pyrolysis at 600°C, the characteristic peaks of the benzene ring disappear, indicating that the PS spheres decompose during the pyrolysis process. However, the characteristic peaks of C=O, P=O, and Cu-O remain, indicating the presence of residual carbon and CuPO3 in the electrocatalyst after pyrolysis.

[0118] In order to further explore the effect of PS balls on phosphorus conversion during pyrolysis, X-ray diffraction (XRD) patterns of Cu-1000P at different calcination temperatures were obtained. Figure 5 As shown in (a), when the calcination temperature is 200°C, the crystalline phase of the calcined product is still primarily CuO. When the calcination temperature is increased to 400°C, characteristic peaks at 43.25° and 50.36° begin to appear, indicating the presence of CuPO3 in the crystalline phase of the calcined product. As the temperature increases (600-1000°C), the intensities of the characteristic peaks at 43.25° and 50.36° gradually increase, indicating that higher temperatures facilitate the stabilization of phosphorus by the PS spheres, ultimately leading to the formation of the CuPO3 crystalline phase.

[0119] Figure 5 Panel (b) shows the Fourier transform infrared spectra of PS spheres, Cu-1000P-S, PS@Cu-MOF, Cu-1000P / 200, Cu-1000P / 400, Cu-1000P / 600, Cu-1000P / 800, and Cu-1000P / 1000. After pyrolysis at 200°C, the characteristic peaks of benzene rings in Cu-1000P / 200 still exist, indicating that the PS spheres did not decompose during the pyrolysis process. After pyrolysis at 400°C, the characteristic peaks of benzene rings in Cu-1000P / 400 partially disappear, indicating that the PS spheres decomposed during the pyrolysis process but not completely. After pyrolysis at 600°C, the characteristic peaks of benzene rings in Cu-1000P / 600 disappear, indicating that the PS spheres decomposed completely during the pyrolysis process. However, the characteristic peaks of C=O, P=O, and Cu-O are retained, indicating the presence of residual carbon and CuPO3 in the electrocatalyst after pyrolysis.

[0120] To further explore the binding of copper, oxygen, and phosphorus, the X-ray photoelectron spectra (XPS) of PS@Cu-MOF and Cu-1000P were recorded, e.g. Figure 6 shown.

[0121] like Figure 6 As shown in (a), Cu2p3, O1s, N1s, and C1s were detected in PS@Cu-MOF, but phosphorus was not detected. Peaks of all elements in PS@Cu-MOF were detected in Cu-1000P. Compared with PS@Cu-MOF, a new peak at 132.8 eV was observed in Cu-1000P ( Figure 6 This further demonstrates that the PS spheres preferentially arrange phosphorus around the periphery, making it impossible for the surface detection technique XPS to detect the presence of phosphorus deep in the PS@Cu-MOF. The thermal decomposition of the PS spheres and the thermal collapse of the Cu-MOF result in a thinner shell, allowing XPS to detect phosphorus in Cu-1000P.

[0122] The C1s spectra of PS@Cu-MOF and Cu-1000P are shown in Figure 2. Figure 6 As shown in (b), for PS@Cu-MOF, the peaks at 284.20, 285.60, and 288.20 eV can be attributed to three different carbon states, corresponding to various carbon states, CC (sp2), OCO, and CN, respectively. Compared to Cu-1000P, the peak areas at 285.41 and 287.37 eV decrease after pyrolysis, indicating that the contents of OCO and CN decrease during the pyrolysis process.

[0123] Figure 6 (c) shows the N1s spectrum. In PS@Cu-MOF, the peaks at 400.70 eV and 399.10 eV are attributed to NH and C=N, respectively. For Cu-1000P, the peak shape changes significantly. The peaks at 399.80 eV and 397.89 eV correspond to C=N and Cu-N, respectively.

[0124] Figure 6 (d) shows the O1s spectrum. In PS@Cu-MOF, the peaks at 532.90 eV and 531.55 eV correspond to C=O and Cu-O, respectively. For Cu-1000P, the peaks at 533.10 eV, 532.30 eV, and 531.00 eV correspond to C=O, P=O, and Cu-O, respectively.

[0125] Figure 6 (e) shows the spectrum of Cu2p. In PS@Cu-MOF, the peaks at 962.20 eV, 953.80 eV, 940.30 eV, and 933.60 eV are attributed to the Cu2p1 / 2 satellite peak, Cu2p1 / 2, Cu2p3 / 2 satellite peak, and Cu2p3 / 2, respectively. For Cu-1000P, the peaks at 951.50 eV and 931.70 eV are attributed to Cu2p3 and Cu-O, respectively.

[0126] Figure 6 (f) shows the P2p spectrum. In Cu-1000P, the peaks at 133.70 eV and 132.80 eV correspond to O=P and OP, respectively.

[0127] Figure 6 XPS results and Figure 4 The FT-IR results of (b) are consistent, indicating that phosphorus has been successfully doped into CuO and exists mainly in the form of PO-Cu.

[0128] Figure 7Thermogravimetric curves of PS, PS@Cu-MOF, and Cu-1000P are presented. For PS, three decomposition stages are observed: 0.91% between 30°C and 270°C, 87.83% between 270°C and 412°C, and 4.11% between 412°C and 487°C, corresponding to adsorbed water, polymer chain scission, and benzene ring decomposition, respectively. The remaining 7.15% is the residue after PS combustion. After the introduction of Cu-MOF onto the surface of the PS spheres, the residue rate increases to 15.5%, corresponding to carbon residue and phosphorus-doped CuO. Compared to PS and PS@Cu-MOF, Cu-1000P does not decompose upon calcination at 600°C, indicating that the Cu-1000P structure is stable and free of decomposable substances.

[0129] For electrocatalysts, specific surface area is a very important indicator. The specific surface area is studied using N2 adsorption / desorption isotherms. Figure 8 As shown in Figure 2, the hysteresis loop of PS shows a type II isotherm, indicating that PS is a solid sphere without pores. The hysteresis loop of PS@Cu-MOF shows a type IV isotherm and an H3 type hysteresis loop, indicating that there are layered slit-like mesopores (2-50nm) in PS@Cu-MOF. As for Cu-1000P, its hysteresis loop shows a type IV isotherm and an H1-H2 type hysteresis loop, indicating that there are cage-like mesopores in Cu-1000P, which is consistent with the Figure 1 The results of scanning electron microscopy images are consistent with those of the previous one. The specific surface areas of PS, PS@Cu-MOF and Cu-1000P are 2.262, 10.733 and 96.941 m 2 g -1 Cu-1000P has a larger specific surface area, which can provide more active sites and help improve its catalytic performance.

[0130] 4. Catalytic performance verification

[0131] A method for cracking a lignin model compound comprises the following steps:

[0132] (1) Photocatalysis alone:

[0133] In the photooxidation chamber, the photocatalytic reaction was carried out in a 40 mL quartz reactor under irradiation with a 300 W xenon lamp. To the reactor were added 4 mg of the lignin model compound pp-ol and 20 mg of g-C3N4 (the photocatalyst, suspended on the surface of the solution). Then, 20 mL of acetonitrile and 20 mL of water were added. Furthermore, the pH of the mixed solution was adjusted to 3 with phosphoric acid.

[0134] (2) Electrocatalysis alone:

[0135] Electroreduction chamber: 16 mg of electrocatalyst (Cu-1000P) was evenly coated on both sides of a 2 cm × 2 cm carbon paper sheet, with a loading of 2 mg / L. The prepared catalyst-loaded carbon paper served as the cathode, a platinum electrode (2 cm × 2 cm) was used as the anode, and a saturated silver-silver chloride electrode was used as the reference electrode. A 40 mL aqueous solution containing 100.0 mg / L of the lignin model compound pp-ol and 0.1 mol / L of sodium chloride was then introduced, with oxygen flowing throughout to assist in the formation of OOH radicals. Furthermore, the pH of the mixed solution was adjusted to 3 with phosphoric acid.

[0136] (3) Photocatalytic synergy

[0137] The reaction was conducted in a 40 mL quartz reactor. 4 mg of pp-ol was added, followed by 20 mL of acetonitrile and 20 mL of water. The pH of the mixed solution was adjusted to 3 with phosphoric acid. The quartz reactor was separated by a microporous membrane, with one side being the photooxidation chamber and the other the electroreduction chamber. The membrane allowed free radical movement between the two reaction chambers.

[0138] Photooxidation chamber: under the irradiation of a xenon lamp with a total power of 300 W, and 20 mg of g-C3N4 (photocatalyst, suspended on the surface of the solution) was added.

[0139] Electroreduction chamber: 16 mg of electrocatalyst (Cu-1000P) was evenly coated on both sides of a 2 cm × 2 cm carbon paper sheet, with a loading of 2 mg / L. The prepared catalyst-loaded carbon paper served as the cathode, a platinum electrode (2 cm × 2 cm) was used as the anode, and a saturated silver-silver chloride electrode was used as the reference electrode. Oxygen was flowed through the electrocatalytic chamber throughout the process to assist in the formation of OOH radicals.

[0140] When using photoelectric synergistic catalysis, the photoelectric synergistic system used is mainly composed of three parts. The leftmost part is the electric anode chamber, the middle part is the electric reduction chamber, which is used to form a closed electric circuit. The electric anode chamber and the electric reduction chamber are connected by an ion exchange membrane. The rightmost part is the photooxidation chamber. The photooxidation chamber and the electric reduction chamber are connected by a 0.45 micron microporous membrane. The membrane pore size of 0.45 microns can meet the transmembrane transport of ·OOH radicals and Cβ· radicals. The photooxidation chamber is responsible for oxidation to form Cβ· radical intermediates, and the electric reduction chamber is responsible for reduction to form · In the photoelectric synergistic system, not only can the oxidizing and reducing groups be spatially separated to avoid mutual quenching, but the hydrogen sources are also more diverse.

[0141] 1 mL of sample was taken every hour, and the sample after passing through a 0.22 μm organic filter membrane was analyzed by liquid chromatography for the cracking rate of the lignin model compound pp-ol and the yield of the product.

[0142] Figure 9The conversion rate and product yield of the lignin model compound pp-ol in the single photocatalytic, single electrocatalytic and photoelectric synergistic systems are shown.

[0143] like Figure 9 As shown in (a), in the single photocatalysis, single electrocatalysis and photoelectric synergistic systems, the conversion rates of pp-ol were 41.67%, 76.47%, 93.71% (electroreduction chamber) and 84.91% (photooxidation chamber), respectively. Compared with the single photocatalysis and electrocatalysis, the conversion rates of pp-ol in the photoelectric synergistic system increased by 124.89% (electroreduction chamber) and 11.36% (photooxidation chamber), respectively, indicating that photoelectric synergy can effectively avoid the mutual quenching of oxidizing and reducing groups, thereby improving the conversion rate of pp-ol. In addition, the conversion rate of phenol in the electroreduction chamber (93.71%) was higher than that in the photooxidation chamber (84.91%).

[0144] Compared with the photooxidation chamber, the electroreduction chamber showed higher conversion rate and lower product yield ( Figure 9 (b)). In addition, the product yield of the photoelectric synergistic system was improved compared with that of electrocatalysis and photocatalysis alone. Compared with photocatalysis alone, the yield of benzoic acid in the photooxidation chamber decreased from 28.15% to 25.99%, the yield of benzaldehyde increased from 18.68% to 112.37%, and the yield of phenyl formate increased from 11.41% to 45.53%. Compared with electrocatalysis alone, the yield of benzoic acid in the electroreduction chamber increased from 23.81% to 36.08%, and the yield of benzaldehyde increased from 12.71% to 26.48%. These results indicate that the OOH radicals and C β Free radicals improve reaction efficiency and selectivity.

[0145] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A hollow spherical phosphorus-doped CuO composite electrocatalyst, characterized in that: It is a hollow sphere structure with a porous surface; The hollow sphere is made of a composite of nitrogen-doped carbon skeleton, CuO and CuPO3.

2. The hollow spherical phosphorus-doped CuO composite electrocatalyst according to claim 1, characterized in that: The particle size of the phosphorus-doped hollow porous electrocatalyst is 150-200 nm.

3. The hollow spherical phosphorus-doped CuO composite electrocatalyst according to claim 1, characterized in that: In the phosphorus-doped hollow porous electrocatalyst, the phosphorus atoms account for 0.5-1 at %.

4. A method for preparing the hollow spherical phosphorus-doped CuO composite electrocatalyst according to any one of claims 1 to 3, characterized in that: include: The polyether block copolymer is dissolved in water, a spherical template is added, and after mixing, acetic acid, 1,3,5-trimethylbenzene and triphenylphosphine are added and stirred until a microemulsion state is formed; copper salt and 2-aminoterephthalic acid are then added, the mixture is heated and stirred, and the solid-liquid separation is performed. The obtained solid is dried and calcined in a protective gas to obtain a hollow spherical phosphorus-doped CuO composite electrocatalyst.

5. The preparation method according to claim 1, wherein The polyether block copolymer is a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer; Preferably, the spherical template is a polystyrene sphere with a particle size of 200-300 nm; Preferably, the copper salt includes any one of copper nitrate, copper chloride and copper sulfate, preferably copper nitrate, and more preferably copper nitrate trihydrate.

6. The preparation method according to claim 1, wherein The usage ratio of the polyether block copolymer, water, spherical template, acetic acid, 1,3,5-trimethylbenzene, triphenylphosphine, copper salt and 2-aminoterephthalic acid is: 800-900 mg: 40-60 mL: 1500-2500 mg: 0.5-1 mL: 5-15 mL: 250-1250 mg: 1200-1300 mg: 1000-2000 mg.

7. The preparation method according to claim 1, wherein The calcination temperature is 200-1000° C. and the calcination time is 1-3 hours.

8. Use of the hollow spherical phosphorus-doped CuO composite electrocatalyst according to any one of claims 1 to 3 or the hollow spherical phosphorus-doped CuO composite electrocatalyst prepared by the preparation method according to any one of claims 4 to 7 in the cracking of a lignin model compound; Preferably, the application is the catalytic cracking of lignin model compounds by hollow spherical phosphorus-doped CuO composite electrocatalyst under photoelectric synergistic conditions.

9. A method for cracking a lignin model compound, characterized in that: include: The hollow spherical phosphorus-doped CuO composite electrocatalyst described in any one of claims 1 to 3 or the hollow spherical phosphorus-doped CuO composite electrocatalyst prepared by the preparation method described in any one of claims 4 to 7 is loaded on the surface of carbon paper, and used as a cathode in combination with an anode platinum sheet to electrocatalyze the cracking of a lignin model compound.

10. The cracking method according to claim 9, wherein: During electrocatalytic cracking, the electrocatalytic chamber and the photocatalytic chamber are separated by a microporous membrane, free radicals move freely in the two reaction chambers, and the lignin model compound is cracked by photoelectric synergistic catalysis.

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