Biochar-based enzyme electrode for CO2 reduction as well as preparation method and application of biochar-based enzyme electrode

Abstract

The invention belongs to the technical field of bioelectrocatalytic reduction of CO2, and relates to a charcoal-based enzyme electrode for CO2 reduction as well as a preparation method and application of the charcoal-based enzyme electrode. Firstly, SBA-15 is used as a template, microcrystalline cellulose is used as a carbon source, ordered porous biochar is constructed through temperature programming carbonization and template removal with strong base, then copper nanoparticles are formed in a CuSO4 electrolyte through cyclic voltammetry electrodeposition, and formate dehydrogenase and carbonic anhydrase are synergistically fixed on the surface of an electrode. The porous biochar provides a mass transfer channel with a high specific surface area and high efficiency, the copper nanoparticles improve the electron transfer efficiency, and formate dehydrogenase and carbonic anhydrase are combined to simulate a microbial carbon concentration mechanism, so that the CO2 concentration and reduction specificity of an interface are improved. Under the voltage of-0.3 V to-0.8 V (vs Ag / AgCl), CO2 is selectively reduced into formic acid, the process conditions are mild, the cost is low, and a feasible strategy is provided for high-selectivity formic acid preparation and CO2 recycling.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of bio-electrocatalytic reduction of CO2, and relates to a biochar-based enzyme electrode for CO2 reduction and a preparation method and application thereof. BACKGROUND

[0002] The conversion of CO2 into high-value chemicals by carbon capture and utilization (CCU) technology is an effective way to achieve a carbon cycle economy. Among the many CO2 conversion technologies, electrocatalytic CO2 reduction (CO2RR) is considered one of the important means to achieve CCU because of its mild reaction conditions, renewable energy driving, and diverse product types. However, the traditional electrocatalytic process still has the following shortcomings: first, the product types are complex, making it difficult to achieve high selectivity synthesis of a single target product; second, the stability of some catalysts is insufficient in long-term reactions; and finally, the electrochemical reaction process lacks precise regulation of the molecular level reaction path.

[0003] In order to further improve the CO2 conversion efficiency, bio-electrocatalysis has gradually attracted attention. Unlike traditional inorganic catalysts, bio-electrocatalytic systems can achieve high selectivity and high reaction rate under mild conditions by introducing biological molecules such as enzymes or microorganisms. Compared with microorganisms, enzymes break through the limitations of biological membranes, are not limited by complex metabolic regulation and slow strain growth cycles, have high catalytic activity and strong specificity, so enzyme electrocatalysis is an ideal method for CO2 reduction.

[0004] However, enzyme electrocatalytic systems are still limited in practical applications. The most important problem is that the reaction rate is usually limited by the efficiency of electron transfer. Since the active center of the enzyme is usually buried inside the protein, the efficiency of electron transfer between the electrode and the enzyme is limited, which in turn limits the overall reaction rate. At the same time, enzyme molecules have poor stability in the system and are prone to inactivation, making it difficult to maintain long-term catalytic performance.

[0005] To solve the above problems, carbon materials have been gradually introduced as intermediates for enzyme immobilization and electron transfer. Carbon materials have excellent electrical conductivity and can be easily functionalized on the surface, providing a stable microenvironment for enzyme molecules while improving the electron coupling between the electrode and the enzyme. However, traditional carbon materials still have deficiencies in terms of pore size regulation, specific surface area, and compatibility with enzyme molecules.

[0006] In contrast, biochar is environmentally friendly, low-cost, and can precisely control the pore structure, making it an ideal choice for enzyme electrode construction. In particular, porous biochar prepared by a hard template method not only provides a high specific surface area and regular pore structure, but also facilitates enzyme immobilization and mass transfer of reaction substrates. In addition, it also has good electrical conductivity and surface activity, which can further improve the electron transfer process.

[0007] As disclosed in patent CN202111177307.5, a method for biological electrocatalytic reduction of carbon dioxide by immobilized enzyme on mesoporous material is provided. Formic dehydrogenase is immobilized on glutaraldehyde cross-linked PEI modified mesoporous material SBA-15, and neutral red is used to regenerate coenzyme. Although this technology realizes biological electrocatalytic reduction of CO2, reduces coenzyme consumption, and improves CO2 conversion rate. However, during the reaction process, the inevitable dimerization reaction of neutral red and the accumulation of dimers (NR2 + ) will lead to a sharp decline in coenzyme regeneration efficiency, and the system is difficult to operate for a long time.

[0008] Patent application CN202310129743.8 discloses a copper-based formate dehydrogenase catalyst. A coupling electrocatalytic method of formate dehydrogenase and Cu / CuSiO3 nanocatalyst is adopted. The copper-based nanocatalyst is prepared by hydrothermal synthesis method and formate dehydrogenase is immobilized. The expensive NADH coenzyme is replaced to improve the stability and reaction efficiency of the catalyst. However, the Cu / CuSiO3 nanocatalyst used in the catalytic system is mainly synthesized by hydrothermal method, which has a relatively complex preparation process and high energy consumption. On the other hand, the catalyst uses CuSiO3 as the substrate, and the conductivity is limited, which affects the electron transfer efficiency to some extent.

[0009] Therefore, it is urgent to develop a new type of carbon material-based composite enzyme electrode to improve the stability of enzyme loading and the efficiency of electron transfer, so as to realize efficient and stable CO2 reduction. SUMMARY

[0010] The purpose of the present application is to overcome at least one of the above technical problems, and to provide a biochar-based enzyme electrode for CO2 reduction and a preparation method and application thereof, so as to solve the problems of low electron transfer efficiency between the electrode and the enzyme, poor enzyme stability, and low CO2 concentration in the aqueous phase in the prior art, thereby realizing efficient and stable CO2 conversion.

[0011] The technical scheme adopted by the present application to solve the technical problems is: a preparation method of a biochar-based enzyme electrode for CO2 reduction, comprising the following steps: S1, preparing a porous biochar-based material by a hard template method; S2, loading the porous biochar-based material prepared in step S1 on a carbon paper substrate to obtain a porous biochar / carbon paper composite electrode; S3, drying the porous biochar / carbon paper composite electrode prepared in step S2, and placing it in an electrolyte. Metal nanoparticles are loaded on the surface of the porous biochar / carbon paper composite electrode by electrodeposition to obtain a porous biochar / carbon paper electrode loaded with metal nanoparticles; S4, fixing the formic acid dehydrogenase and the carbonic anhydrase on the metal nanoparticle loaded porous biochar / carbon paper electrode of step S3 through a crosslinking agent to obtain a biochar-based enzyme electrode.

[0012] Further, in step S1, SBA-15 is used as a template agent, SBA-15 is mixed with microcrystalline cellulose, and then added to a solvent, and ultrasonic treatment is performed for 0.5-2 h to obtain a precursor mixture; an acidic additive is added to the precursor mixture to promote uniform wrapping of the carbon source around the template or filling of the pores, and drying is performed to obtain an SBA-15 / cellulose composite precursor; the SBA-15 / cellulose composite precursor is carbonized to obtain a carbide, and then the template is removed to obtain a porous biochar.

[0013] Still further, in step S1, the pore size of SBA-15 is 6-11 nm; The mass ratio of SBA-15 to microcrystalline cellulose is 1:0.8-1:3.0, preferably 1:1.5-1:2.5, and more preferably 1:2; The solvent is a mixture of ethanol and deionized water in a volume ratio of (0.8-1.2):(0.8-1.2), and preferably in a volume ratio of 1:1; The acidic additive is hydrochloric acid with a concentration of 0.05-0.5 mol / L, and preferably 0.1 mol / L dilute hydrochloric acid, to promote wrapping of the carbon source around the template or filling of the pores; The drying temperature is 40-120 °C; The carbonization is performed in an N2 atmosphere, first heating to 150-350 °C for 1-3 h, then heating to 300-600 °C for 0.5-1.5 h, and finally heating to 700-900 °C for 1-3 h; During the carbonization process, the N2 flow rate is 100-300 SCCM, and preferably 200 SCCM; The template removal is performed by mixing the carbide with a 2-3 mol / L NaOH solution in a solid-liquid ratio of 1:50-1:100 (g:mL) and stirring in a water bath at 80-90 °C for 6-12 h; the supernatant is removed by centrifugation, the collected carbide is washed with deionized water until neutral, then washed with ethanol, and finally dried at 80-100 °C for 6-12 h, and preferably dried at 90 °C for 8 h.

[0014] The specific surface area of the porous biochar-based material is 300-400 m 2 / g, the average pore size is 3-4 nm, and the total pore volume is 0.3-0.4 cm 3 / g, and further preferably, the specific surface area of the porous biochar-based material is 342.63 m 2 / g, the average pore size is 3.62 nm, and the total pore volume is 0.323 cm 3 / g. The present application realizes the regulation of the pore size of the biochar by selecting a template with a suitable particle size. Specifically, by wrapping a carbon source around a template with a suitable particle size, carbonizing, and then etching to remove the template, precise regulation of the pore channels is achieved. The porous structure can be obtained according to the BET results (specific surface area, average pore size, and total pore volume).

[0015] Further, the specific preparation method of the porous biochar / carbon paper composite electrode in step S2 is as follows: dispersing the porous biochar-based material in an organic solvent to obtain a porous biochar suspension; uniformly dropping the porous biochar suspension on the surface of the carbon paper substrate at a coating amount of 0.5-2 mg / cm 2 , preferably 1 mg / cm 2 , and then drying at room temperature to obtain the porous biochar / carbon paper composite electrode.

[0016] Still further, the organic solvent is N, N-dimethylformamide (DMF) with a concentration of 1-10 mg / mL, preferably 5 mg / mL.

[0017] The carbon paper substrate is a carbon paper substrate ultrasonically cleaned with a mixture of isopropanol / deionized water=1:1.

[0018] The carbon paper has a size of 10*10 mm, is ultrasonically cleaned with a mixture of isopropanol / deionized water=1:1 for 10-20 min, and is dried for standby use.

[0019] Further, in step S3, the electrolyte is a CuSO4 solution with a concentration of 0.01-0.1 mol / L. Step S3 adopts a three-electrode system, the working electrode is the porous biochar / carbon paper composite electrode, the reference electrode is an Ag / AgCl electrode, and the counter electrode is a platinum sheet. The electrodeposition method adopts cyclic voltammetric electrodeposition, the electrodeposition potential range is-0.1--1.2 V (vs. Ag / AgCl), the scanning rate is 20-70 mV / s, and the scanning is performed for 20-60 cycles. The metal nanoparticles are copper nanoparticles with a particle size of 4-6 nm, and preferably, the average particle size is 5.245 nm.

[0020] Further, in step S4, the porous biochar / carbon paper electrode loaded with metal nanoparticles is placed in a buffer solution, a formate dehydrogenase and carbonic anhydrase mixed enzyme solution is added, and the mixture is allowed to stand for adsorption at room temperature for 2-4 h, a crosslinking agent is then added for reaction for 0.5-2 h to enhance the binding force between the enzyme and the carbon material, and then the mixture is washed with a buffer solution to remove the unbound enzyme molecules, thereby obtaining a biochar-based enzyme electrode.

[0021] Further, the mixed enzyme solution of formic acid dehydrogenase and carbonic anhydrase is prepared by using formic acid dehydrogenase and carbonic anhydrase with a mass ratio of (1-2):(1-2) as solutes and PBS as a solvent. The total concentration of the enzyme solution is 0.1-1.0 mg / mL. The formic acid dehydrogenase (FDH) is derived from Candida boidinii The carbonic anhydrase (CA) is derived from bovine red blood cells. The cross-linking agent is glutaraldehyde solution with a concentration of 0.05-0.2 wt%.

[0022] The application further provides a biochar-based enzyme electrode prepared by the method.

[0023] The application further provides an application of the biochar-based enzyme electrode, which is applied to the bioelectrocatalytic reduction of CO2.

[0024] Further, in the H-type three-electrode reactor, the biochar-based enzyme electrode is used as the working electrode in the cathode chamber, the Ag / AgCl electrode is used as the reference electrode, the platinum electrode is used as the counter electrode in the anode chamber, and the electrolyte is the PB buffer solution; a potential of-0.3 V to-0.8 V (vs. Ag / AgCl) is applied to the system, CO2 gas is continuously introduced into the cathode at a gas flow rate of 5-15 mL / min, and 0.1-0.3 mmol / L of NADH is added into the cathode chamber before the introduction of CO2, so as to ensure that the formic acid dehydrogenase realizes the conversion of CO2, and the reaction product is formic acid.

[0025] The NADH is an essential electron donor for the CO2 conversion of the formic acid dehydrogenase and provides core reducing power for the reaction. The NADH directly provides two electrons and one proton to the CO2 molecule through a hydrogen anion (H - ) transfer mechanism, drives the formic acid dehydrogenase to complete the conversion of CO2 to formic acid, and is converted into NAD + .

[0026] Compared with the prior art, the application has the following beneficial effects: (1) Firstly, ordered porous biochar was constructed by using SBA-15 as a template, microcrystalline cellulose as a carbon source, and removing the template by programmed temperature carbonization and strong alkali. Then, copper nanoparticles were formed by cyclic voltammetry electrodeposition in CuSO4 electrolyte, and formate dehydrogenase and carbonic anhydrase were co-immobilized on the electrode surface. The porous biochar provides a high specific surface area and an efficient mass transfer channel, and the copper nanoparticles significantly improve the electron transfer efficiency. The combination of formate dehydrogenase and carbonic anhydrase simulates the microbial carbon concentration mechanism, improves the interface CO2 concentration and reduction specificity. At a voltage of-0.3 to-0.8 V (vs Ag / AgCl), CO2 can be selectively reduced to formic acid. This method has mild process conditions and low cost, and provides a feasible strategy for high selectivity formic acid preparation and CO2 resource utilization.

[0027] (2) The porous biochar prepared by the hard template method has a high specific surface area and an ordered mesoporous structure, which can significantly improve the loading capacity of enzyme molecules and provide a through and ordered mass transfer channel for the reaction substrate, avoiding enzyme molecule accumulation and inactivation.

[0028] (3) The porous biochar has excellent electrical conductivity, and the copper nanoparticles deposited on the surface can further provide an efficient electron transport channel, reducing the electron transfer resistance between the electrode and the enzyme, thereby improving the overall reaction rate.

[0029] (4) The combination of formate dehydrogenase and carbonic anhydrase realizes the high selectivity reduction of CO2 to formic acid, and the latter promotes the hydration and dissolution of CO2, significantly improving the effective concentration of CO2 at the electrode interface and the reaction efficiency.

[0030] (5) The biochar-based enzyme electrode obtained in the present application has high yield and Faraday efficiency in the process of CO2 electroreduction, and can realize the efficient synthesis of formic acid, which is superior to the existing single electrocatalytic system or biological catalytic system, and provides a green, economic and sustainable strategy for CO2 conversion. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings needed to be used in the embodiments.

[0032] Figure 1 is a schematic diagram of the working principle of the biochar-based enzyme electrode of Example 1 of the present application in the process of CO2 electroreduction; Figure 2 is a TEM image and a particle size distribution diagram of the biochar-based enzyme electrode of Example 1 of the present application (a) and (b); Figure 3 is a SEM image of the biochar-based enzyme electrode of Example 1 of the present application. DETAILED DESCRIPTION

[0033] The application will be further described below with reference to the drawings. The following examples are only used to more clearly illustrate the technical solutions of the application, and cannot be used to limit the protection scope of the application.

[0034] In order to realize efficient conversion of CO2, solve the problems of low electron transfer rate between enzyme and electrode, poor enzyme stability, and low concentration of CO2 in water phase, the application provides a preparation method of a biochar-based enzyme electrode for CO2 reduction. The method uses porous biochar as a substrate to construct a composite biochar-based enzyme electrode for improving the CO2 conversion efficiency. First, a biochar-based material with ordered mesoporous structure is prepared by a hard template method, the obtained biochar-based material is loaded on a substrate, metal nanoparticles are electrodeposited on the composite electrode to improve the electron transfer rate, formic acid dehydrogenase and carbonic anhydrase are fixed on the composite electrode, and finally the composite electrode is used in a CO2 electroreduction system.

[0035] In multiple embodiments, the Faradaic efficiency (FE) is calculated by formula (1): Wherein is the number of moles of formic acid produced; 2 is the number of electrons transferred when one CO2 molecule is converted into formic acid; is the current intensity; is the reaction time.

[0036] In multiple embodiments, the carbonization is first carried out at 150-350 ℃ for 1-3 h, at 300-600 ℃ for 0.5-1.5 h, and at 700-900 ℃ for 1-3 h. Preferably, the N2 gas flow rate during pyrolysis is 100-300 SCCM, preferably 200 SCCM.

[0037] Example 1 A preparation method of a biochar-based enzyme electrode for CO2 reduction, i.e. a porous biochar / metal nanoparticle / FDH+CA composite enzyme electrode. In the composite enzyme electrode, the porous biochar protects the enzyme and promotes mass transfer at the same time, the metal nanoparticles promote electron transfer, and the combination of formic acid dehydrogenase and carbonic anhydrase has a similar effect to the carbon concentration mechanism in microorganisms, which increases the concentration of the substrate CO2 and promotes CO2 conversion together. The method specifically includes the following steps: S1, a porous biochar-based material is prepared by a hard template method; In the present embodiment, SBA-15 with a pore size of 6-11 nm is used as a template agent, SBA-15 is mixed with microcrystalline cellulose at a mass ratio of 1:2, an ethanol / deionized water mixed solution (volume ratio 1:1) is added, and ultrasonic treatment is performed for 30 min to obtain a precursor mixture; dilute hydrochloric acid with a concentration of 0.1 mol / L is added to the precursor mixture to promote uniform wrapping of the carbon source around the template or filling of the channels.

[0038] 80 ℃ for 10 h to obtain an SBA-15 / cellulose composite precursor. The SBA-15 / cellulose composite precursor is placed in a tube furnace under N2 atmosphere, heated to 250 ℃ for 2 h, then to 450 ℃ for 1 h, and finally to 800 ℃ for 2 h, and then cooled to room temperature. The obtained carbonized product is uniformly mixed with a 2.5 mol / L NaOH solution at a solid-liquid ratio of 1:80 (g:mL), and stirred in a water bath at 80 ℃ for 8 h to remove the template. The supernatant is removed by centrifugation, and the collected carbonized product is washed with deionized water until neutral, then washed with ethanol, and finally dried at 90 ℃ for 8 h to obtain a porous biochar-based material.

[0039] The specific surface area of the obtained porous biochar-based material is 342.63 m 2 / g, the average pore size is 3.62 nm, and the total pore volume is 0.323 cm 3 / g.

[0040] S2, loading the porous biochar-based material of step S1 on a carbon paper substrate; The obtained porous biochar-based material is dispersed in N,N-dimethylformamide at a concentration of 5 mg / mL, and ultrasonic treatment is performed for 30 min to obtain a uniform porous biochar suspension. The carbon paper substrate has a size of 10×10 mm, and is cleaned by ultrasonic treatment with a mixture of isopropanol / deionized water=1:1 for 15 min and then dried. 200 μL of the porous biochar suspension is uniformly dropped and coated on the surface of the carbon paper substrate using a pipette, and the coating amount is 2 mg / cm 2 , and the porous biochar / carbon paper composite electrode sheet is obtained after drying at room temperature for 4 h.

[0041] S3, after drying the porous biochar / carbon paper composite electrode prepared in step S2 at room temperature, metal nanoparticles are loaded on the surface of the porous biochar / carbon paper composite electrode by electrodeposition, specifically as follows: The porous biochar / carbon paper composite electrode sheet obtained in step S2 was clamped with a platinum electrode clamp and placed as a working electrode in a three-electrode system, a platinum sheet electrode (10x10 mm) was used as a counter electrode, and an Ag / AgCl electrode was used as a reference electrode. The electrolyte was 0.05 mol / L CuSO4 and 0.1 mol / L K2SO4 as a supporting electrolyte. The scanning was performed at a voltage of -0.6 V (vs Ag / AgCl) and a scanning rate of 50 mV / s for 50 cycles. After deposition, the electrode was washed with deionized water and dried to obtain a porous biochar / carbon paper electrode uniformly loaded with copper nanoparticles on the surface.

[0042] The porous biochar / carbon paper electrode loaded with copper nanoparticles was taken, and the copper nanoparticles deposited on the surface were scraped off. The copper nanoparticles were dispersed uniformly in an ethanol solution and then characterized by TEM. The test was performed at a magnification of 12000 times with a scale of 50 nm. The results showed that the average particle size of the copper nanoparticles was 5.245 nm (see Figure 2 a); the overall particle size distribution of the copper nanoparticles is shown in Figure 2 b; and Figure 2 It can be seen from Figure 3 b that most of the copper nanoparticles have a particle size of about 5.245 nm, indicating that the copper nanoparticles formed in the electrodeposition process have uniform particle sizes. It can be seen from the SEM test results (see

[0043] S4, formate dehydrogenase and carbonic anhydrase were immobilized on the porous biochar / carbon paper electrode loaded with metal nanoparticles obtained in step S3 by a crosslinking agent: The porous biochar / carbon paper electrode loaded with copper nanoparticles obtained in step S3 was dried and then immersed in a mixed enzyme solution (total concentration of 0.5 mg / mL, mass ratio of formate dehydrogenase to carbonic anhydrase of 1:1, and solvent of PBS buffer with pH 7.4) of formate dehydrogenase and carbonic anhydrase. The electrode was placed in a glove box at room temperature for 3 h of adsorption, followed by the addition of 0.1 wt% glutaraldehyde solution for crosslinking for 1 h. The electrode surface was then washed with PBS to obtain the final biochar-based enzyme electrode.

[0044] S5, the biochar-based enzyme electrode prepared in step S4 was used in an electrocatalytic system for CO2 electroreduction.

[0045] The reaction was carried out in an H-type three-electrode reactor, in the cathode chamber, the biochar-based enzyme electrode prepared in step S4 was used as the working electrode, Ag / AgCl was used as the reference electrode, and a platinum sheet electrode in the anode chamber was used as the counter electrode, and the electrolyte was PB buffer (pH 6.0). A potential of-0.5 V (vs. Ag / AgCl) was applied to the system, and CO2 gas was continuously introduced into the cathode at a gas flow rate of 10 mL / min. Before the introduction of CO2, 0.2 mmol / L of NADH was added to the cathode chamber. The reaction product was formic acid. The working principle of the biochar-based enzyme electrode in the process of CO2 electroreduction is shown in Figure 1 As shown in the figure, the porous biochar protects the enzyme and simultaneously forms a gas-liquid-solid three-phase interface to efficiently enrich CO2 and promote mass transfer; the carbonic anhydrase accelerates the conversion of HCO3 - to CO2, increases the substrate concentration; the copper nanoparticles mediate the NADH cycle regeneration, and NADH provides reducing equivalents for formate dehydrogenase to drive the directional conversion of CO2 to formic acid. Through multi-enzyme cooperation and three-phase interface construction, efficient electron transfer and substrate conversion are realized.

[0046] The formic acid concentration was determined by liquid chromatography, and the formic acid yield, current density and faradic efficiency are shown in Table 1.

[0047] Comparative Example 1 Unlike Example 1, in this example, porous biochar / carbon paper is directly used for enzyme immobilization and in the CO2 reduction system.

[0048] S1, prepare the porous biochar-based material according to step S1 of Example 1.

[0049] S2, load the porous biochar-based material on the carbon paper substrate according to step S2 of Example 1 to obtain a porous biochar / carbon paper composite electrode.

[0050] S3, immobilize FDH and CA on the porous biochar / carbon paper composite electrode: The porous biochar / carbon paper composite electrode obtained in step S2 was immersed in a mixed solution of FDH and CA (total concentration of 0.5 mg / mL, mass ratio of FDH to CA of 1:1, solvent of PBS buffer at pH 7.4). After 3 h of adsorption at room temperature in a glove box, 0.1 wt% glutaraldehyde solution was added and cross-linked for 1 h, and then the electrode surface was rinsed with PBS to obtain the final biochar-based enzyme electrode.

[0051] S4, perform CO2 electrocatalytic conversion according to step S5 of Example 1.

[0052] The formic acid concentration was determined by liquid chromatography, and the formic acid yield, current density and faradic efficiency are shown in Table 1.

[0053] Comparative Example 2 Different from Example 1, this example directly applies the porous biochar / copper nanoparticle electrode to the CO2 electrocatalytic system.

[0054] S1, prepare the porous biochar-based material according to step S1 of Example 1; S2, load the porous biochar on the carbon paper substrate according to step S2 of Example 1 to obtain a porous biochar / carbon paper composite electrode; S3, deposit copper nanoparticles on the surface of the porous biochar / carbon paper composite electrode according to step S3 of Example 1 to obtain a porous biochar / carbon paper electrode loaded with copper nanoparticles; S4, apply the porous biochar / carbon paper electrode loaded with copper nanoparticles obtained in step S3 to the CO2 electrocatalytic system: Take the porous biochar / carbon paper electrode loaded with copper nanoparticles obtained in step S3 as the working electrode, Ag / AgCl as the reference electrode, and platinum sheet as the counter electrode. In the PB buffer solution (pH 6.0), apply a potential of -0.5 V, and continuously introduce CO2 gas into the cathode at a flow rate of 10 mL / min. Before introducing CO2, add 0.2 mmol / L of NADH to the cathode chamber. The reaction product is formic acid.

[0055] Determine the formic acid concentration by liquid chromatography. The formic acid yield, current density, and Faraday efficiency are shown in Table 1.

[0056] Comparative Example 3 Different from Example 1, this example prepares a porous biochar / copper nanoparticle / FDH enzyme electrode and applies it to the electrocatalytic CO2 system.

[0057] S1, prepare the porous biochar-based material according to step S1 of Example 1; S2, load the porous biochar on the carbon paper substrate according to step S2 of Example 1 to obtain a porous biochar / carbon paper composite electrode; S3, deposit copper nanoparticles on the surface of the porous biochar / carbon paper composite electrode according to step S3 of Example 1 to obtain a porous biochar / carbon paper electrode loaded with copper nanoparticles; S4, immerse the porous biochar / carbon paper electrode loaded with copper nanoparticles obtained in S3 in an FDH solution (concentration of 0.25 mg / mL, solvent is PBS buffer solution at pH 7.4). Place it in a glove box at room temperature for 3 h of adsorption. Then add 0.1 wt% glutaraldehyde solution, crosslink for 1 h, and then rinse the electrode surface with PBS to obtain a biochar-based enzyme electrode.

[0058] S5, perform CO2 electrocatalytic conversion according to step S5 of Example 1.

[0059] The concentration of formic acid was determined by liquid chromatography, and the formic acid yield, current density and faradic efficiency are shown in Table 1.

[0060] Comparative Example 4 Different from Example 1, no cofactor NADH was added in the electrocatalytic CO2 system in this example.

[0061] S1, the porous biochar-based material was prepared according to step S1 of Example 1; S2, the porous biochar was loaded on the carbon paper substrate according to step S2 of Example 1 to obtain a porous biochar / carbon paper composite electrode; S3, the copper nanoparticles were deposited on the porous biochar / carbon paper composite electrode according to step S3 of Example 1 to obtain a porous biochar / carbon paper electrode loaded with copper nanoparticles; S4, the enzyme was immobilized on the porous biochar / carbon paper electrode loaded with copper nanoparticles according to step S4 of Example 1 to obtain a biochar-based enzyme electrode; S5, the biochar-based enzyme electrode obtained in step S4 was used as the working electrode, Ag / AgCl was used as the reference electrode, and platinum plate was used as the counter electrode. In the PB buffer (pH 6.0), a potential of-0.5 V was applied, and CO2 gas was continuously introduced into the cathode at a flow rate of 10 mL / min. The reaction product was formic acid, and the concentration of formic acid was determined by liquid chromatography. The formic acid yield, current density and faradic efficiency are shown in Table 1.

[0062] The results of the reaction of the electrodes prepared in Example 1 and Comparative Examples 1-4 in the CO2 electroreduction system are shown in Table 1.

[0063] Table 1 As can be seen from the above examples and comparative examples, the present application realizes the efficient and selective conversion of CO2 to formic acid through the electrode structure of "porous biochar / copper nanoparticles / two-enzyme synergy". The porous biochar protects the enzyme while promoting mass transfer, the copper nanoparticles enhance electron transfer and increase the effect, and the two-enzyme synergy increases the substrate concentration, promotes CO2 electroreduction, and significantly improves the electrocatalytic performance. At the same time, the cofactor NADH is also crucial for electron transfer and CO2 conversion.

[0064] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for the preparation of a biochar-based enzyme electrode for CO2 reduction, characterized by, The method comprises the following steps: S1, a porous biochar-based material is prepared by a hard template method; S2, the porous biochar-based material prepared in step S1 is loaded on a carbon paper substrate to obtain a porous biochar / carbon paper composite electrode; S3, the porous biochar / carbon paper composite electrode prepared in step S2 is dried, placed in an electrolyte, and metal nanoparticles are loaded on the surface of the porous biochar / carbon paper composite electrode by electrodeposition to obtain a porous biochar / carbon paper electrode loaded with metal nanoparticles; S4, formate dehydrogenase and carbonic anhydrase are fixed on the porous biochar / carbon paper electrode loaded with metal nanoparticles in step S3 by a crosslinking agent to obtain a biochar-based enzyme electrode.

2. The method for the preparation of biochar-based enzyme electrodes for CO2 reduction according to claim 1, characterized in that, In step S1, SBA-15 is used as a template agent, SBA-15 is mixed with microcrystalline cellulose, and then a solvent is added to obtain a precursor mixture; an acidic additive is added to the precursor mixture, and drying is performed to obtain an SBA-15 / cellulose composite precursor; the SBA-15 / cellulose composite precursor is carbonized to obtain a carbide, and then the template is removed to obtain a porous biochar.

3. The method for the preparation of biochar-based enzyme electrodes for CO2 reduction according to claim 2, characterized in that, In step S1, the pore size of SBA-15 is 6-11 nm; The mass ratio of SBA-15 to microcrystalline cellulose is 1:0.8-1:3.0; The solvent is a mixture of ethanol and deionized water in a volume ratio of (0.8-1.2):(0.8-1.2); The acidic additive is hydrochloric acid with a concentration of 0.05-0.5 mol / L; The drying temperature is 40-120 ℃; The carbonization is carried out in an N2 atmosphere, first heated to 150-350 ℃ for 1-3 h, then heated to 300-600 ℃ for 0.5-1.5 h, and finally heated to 700-900 ℃ for 1-3 h; The template removal is to mix the carbide with NaOH solution uniformly, stir in a water bath at 80-90 ℃ for 6-12 h; centrifugal removal of supernatant, the collected carbide is washed and dried; The specific surface area of the porous biochar-based material is 300-400 m 2 / g, the average pore size is 3-4 nm, and the total pore volume is 0.3-0.4 cm 3 / g.

4. The method for the preparation of biochar-based enzyme electrodes for CO2 reduction according to claim 1, characterized in that, The specific preparation method of the porous biochar / carbon paper composite electrode in step S2 is as follows: dispersing the porous biochar-based material in an organic solvent to obtain a porous biochar suspension; uniformly dropping the porous biochar suspension on the surface of a carbon paper substrate, and the coating amount is 0.5-2 mg / cm 2 and then drying at room temperature to obtain the porous biochar / carbon paper composite electrode.

5. The method for the preparation of biochar-based enzyme electrodes for CO2 reduction according to claim 4, characterized in that, The organic solvent is N,N-dimethylformamide with a concentration of 1-10 mg / mL.

6. The method for the preparation of biochar-based enzyme electrodes for CO2 reduction according to claim 1, characterized in that, In step S3, the electrolyte is a CuSO4 solution with a concentration of 0.01-0.1 mol / L; The electrodeposition method is cyclic voltammetry electrodeposition, the electrodeposition potential range is -0.1 to -1.2 V (vs. Ag / AgCl), the scanning rate is 20-70 mV / s, and the scanning is 20-60 cycles; The metal nanoparticles are copper nanoparticles with a particle size of 4-6 nm.

7. The method for the preparation of biochar-based enzyme electrodes for CO2 reduction according to claim 1, characterized in that, In step S4, the porous biochar / carbon paper electrode loaded with metal nanoparticles is placed in a mixed enzyme solution of formate dehydrogenase and carbonic anhydrase, and adsorbed at room temperature for 2-4 h, then a crosslinking agent is added for 0.5-2 h, and then washed with a buffer solution to obtain a biochar-based enzyme electrode.

8. The method for the preparation of a biochar-based enzyme electrode for CO2 reduction according to claim 7, characterized in that, The mixed enzyme solution of formate dehydrogenase and carbonic anhydrase uses formate dehydrogenase and carbonic anhydrase as solutes in a mass ratio of (1-2):(1-2), and a buffer solution PBS as a solvent; The total concentration of the mixed enzyme solution is 0.1-1.0 mg / mL; The cross-linking agent is glutaraldehyde solution with a concentration of 0.05-0.2 wt%.

9. A biochar-based enzyme electrode, characterized in that, The method is prepared by any one of claims 1-8.

10. Use of a biochar-based enzyme electrode, characterized in that, The charcoal-based enzyme electrode is applied to bioelectrocatalytic reduction of CO2.

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