A Co-Sn / biochar thin film electrode for electrochemical reduction and its preparation method and application

Abstract

The present invention discloses a Co-Sn / biochar thin film electrode for electrochemical reduction, and its preparation method and application. The porous carbon is used as a substrate. Due to its porous structure, it has a large specific surface area. The N-P element doped in the porous carbon can significantly enhance the electrochemical catalytic performance. At the same time, the electrode has a Co-Sn composite metal film layer. When the Co-Sn / biochar thin film electrode is applied to the electrochemical reduction of CO2 to produce formic acid, it can significantly improve the directional conversion of CO2 to formic acid and achieve a high product generation rate. It has good application prospects in the field of electrochemistry.

Description

Technical Field

[0001] The invention discloses a Co-Sn / biochar film electrode for electrochemical reduction, a preparation method and an application thereof. Background Art

[0002] With the rapid development of the global economy, fossil fuel consumption has gradually increased, and CO2 emissions in the air have continued to rise, leading to a series of environmental problems such as global warming. Therefore, it is necessary to develop effective CO2 conversion technologies that can not only reduce the CO2 content in the atmosphere and improve the greenhouse effect, but also obtain high-value fuels or industrially useful chemicals such as formate, thus achieving a virtuous carbon cycle. Currently, CO2 conversion methods mainly include photochemical, biochemical, electrochemical, and thermochemical methods. Among them, electrochemical methods have attracted extensive attention and research due to their advantages such as simple operation, green and clean environment, mild reaction conditions, easy engineering, and the ability to control product formation by optimizing reaction conditions. However, due to the insufficient stability and low efficiency of catalytic electrode materials, electrochemical CO2 reduction has not yet been widely applied. Therefore, it is necessary to develop catalytic reduction electrodes with high selectivity, high catalytic efficiency, and high stability.

[0003] To date, a variety of catalytic materials, including precious metals, non-precious metals, metal oxides, organic frameworks, and carbon-based materials, have been screened for electrocatalytic CO2 reduction. Metal catalytic materials for CO2 conversion have low product selectivity and are prone to blockage of active sites, resulting in rapid performance degradation. Organic framework materials are complex to prepare and relatively expensive. Carbon-based materials are increasingly being used for CO2 reduction due to their durability and low cost. For example, patent application number 201710009138.1 discloses a method for preparing melamine as a nitrogen source by mechanically mixing it with a carbon-containing precursor and then combining it with high-temperature treatment. However, simple mechanical mixing cannot effectively dope the external nitrogen source into the carbon material, thereby reducing the physical and chemical properties of the nitrogen-doped carbon material; patent application number 201711083142.9 discloses a method for preparing nitrogen-doped porous carbon materials using two-dimensional graphene oxide as a template, biomass sugars as a carbon source, and amino acids as a nitrogen source. However, the use of bio-sugar and amino acids obtained through fine processing as raw materials greatly increases the preparation cost of the carbon material. At the same time, the production process of two-dimensional graphene oxide is relatively complicated and the production process has certain pollution to the environment.

[0004] Based on this, it is meaningful to develop carbon-based materials with excellent performance for the electrocatalytic reduction of CO2. Summary of the Invention

[0005] 1. Problem to be solved

[0006] In view of the problem that the electrocatalytic reduction of CO2 by existing carbon-based materials is not ideal, especially the problem of low efficiency, the present invention provides a Co-Sn / biochar thin film electrode with electrocatalytic reduction ability;

[0007] At the same time, the present invention provides a method for preparing a catalyst capable of highly efficient electrocatalytic reduction of CO2;

[0008] And it is applied to the electrocatalytic reduction of CO2 to form formic acid.

[0009] 2. Technical solution

[0010] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0011] [1] In a first aspect, the present invention provides a Co-Sn / biochar thin film electrode for electrochemical reduction, the electrode comprising:

[0012] Porous carbon, and a metal film layer located on the surface of the porous carbon;

[0013] The porous carbon includes N and P elements;

[0014] The metal of the metal film layer includes cobalt and tin.

[0015] In the Co-Sn / biochar thin film electrode for electrochemical reduction according to any embodiment of the first aspect of the present invention, the mass ratio of the N element to the P element is 0.25 to 4, preferably 1.5 to 2.5. NP doping can enhance the stability and conductivity of the porous carbon substrate, increase the interlayer spacing of the porous carbon, accelerate ion diffusion and electron transfer, and thus enhance electrochemical catalytic performance.

[0016] In the Co-Sn / biochar thin film electrode for electrochemical reduction according to any embodiment of the first aspect of the present invention, the mass ratio of cobalt to tin in the metal film layer is 0.25 to 4, preferably 4:1. The cobalt (Co) and tin (Sn) composite metal film layer can significantly enhance the directional conversion of CO2 to formic acid through elemental coupling, achieving a high product yield.

[0017] In the Co-Sn / biochar thin film electrode for electrochemical reduction according to any embodiment of the first aspect of the present invention, the thickness of the metal film layer is 10 to 100 nm; the Co-Sn / biochar thin film electrode is used for the reduction of carbon dioxide.

[0018] [2] A second aspect of the present invention provides a method for preparing a Co-Sn / biochar thin film electrode for electrochemical reduction, comprising the following steps:

[0019] S1. Preparation of porous carbon

[0020] Provide carbon source;

[0021] Providing a treatment liquid; the treatment liquid includes nitrogen and phosphorus, and the mass ratio of the nitrogen and phosphorus is 0.25 to 4.0;

[0022] Mix the carbon source and treatment solution and let it stand for 20 to 60 minutes;

[0023] Then, a high-temperature pre-carbonization treatment is carried out at a temperature of 100 to 300°C; and then a high-temperature carbonization treatment is carried out again at a temperature of 600 to 1000°C in an inert gas atmosphere;

[0024] Finally, a binder is added to form porous carbon doped with nitrogen and phosphorus elements;

[0025] S2. Coating

[0026] A metal film containing cobalt and tin is prepared on the surface of porous carbon by thermal evaporation.

[0027] The mass ratio of cobalt to tin is 0.25 to 4.0.

[0028] In the method for preparing a Co-Sn / biochar thin film electrode according to any embodiment of the second aspect of the present invention, the carbon source is biomass, which is crushed, passed through a 200-mesh sieve, and dried in a drying oven at a temperature not exceeding 80° C.; preferably, the drying time is 18 to 30 hours;

[0029] By limiting the particle size of the biomass and drying it, and then placing it in a treatment solution for static treatment, it is possible to achieve a better penetration effect of the N and P element compounds within the biomass structure, so that the subsequent N and P element doping effect can be guaranteed. In addition, it should be noted that in fact, too short a static time will lead to insufficient N and P element doping. Based on this, it is not necessarily the case that the longer the static time, the better. Too long a static time will lead to excessive penetration of N and P elements, affecting the stability and conductivity of the biomass structure itself. Therefore, in S1, the carbon source and the treatment solution are mixed and allowed to stand for 20 to 60 minutes, preferably 20 to 40 minutes, and most preferably 30 minutes.

[0030] Based on the above, the prepared porous carbon is also called biochar.

[0031] Based on the preparation method of the Co-Sn / biochar thin film electrode of any embodiment of the second aspect of the present invention, the treatment liquid contains a substance for providing the N element and a substance for providing the P element, and the sum of the mass concentrations of the two substances (hereinafter referred to as NP dopants) in the solution is 5% to 20%.

[0032] The nitrogen element in the treatment liquid is derived from any one or both of ammonium bicarbonate and urea; the phosphorus element in the treatment liquid is derived from any one or both of phosphorus-containing substances such as sodium dihydrogen phosphate and disodium hydrogen phosphate; and the solvent of the treatment liquid is any one or more of water, ethanol, acetic acid, and acetone.

[0033] In the method for preparing a Co-Sn / biochar thin film electrode according to any embodiment of the second aspect of the present invention, the concentration of the biomass in the treatment solution is 0.5 to 2.0 g / mL.

[0034] Furthermore, in S1, the carbon source and the treatment solution are mixed and allowed to stand for 20 to 40 minutes, preferably 30 minutes;

[0035] The high temperature treatment is carried out at a temperature of 100 to 300°C for 3 to 6 hours, preferably at 200°C for 4 hours;

[0036] The high temperature treatment is carried out at a temperature of 600 to 1000° C. for 1 to 3 hours, preferably at 800° C. for 2 hours.

[0037] Furthermore, in S2, the cobalt source and the tin source are placed separately to form a cobalt evaporation source and a tin evaporation source;

[0038] The sum of the thermal evaporation rates of cobalt and tin is controlled to be 0.05-0.20 nm / s;

[0039] During the thermal evaporation coating process, precise and accurate control of the thermal evaporation rates of different metals is crucial. Thermal evaporation allows for precise control of the evaporation rates of Co and Sn, controlling the metal coating synthesis ratio, providing a larger specific surface area, and improving catalytic efficiency. However, it is important to keep the sum of the thermal evaporation rates of cobalt and tin within a certain range. If the evaporation rate is too low, the residual gas contained in the deposited film will increase excessively, resulting in insufficient purity of the deposited film. If the evaporation rate is too high, it may increase the internal stress of the film, causing defects within the film layer to increase, and even leading to film rupture.

[0040] In addition, the evaporation rates of Co and Sn are different, and the ratio of the thermal evaporation rates of cobalt and tin is controlled to be 0.25-4.0; further, the thermal evaporation rate of cobalt needs to be controlled to be 0.04-0.16 nm / s to ensure the ratio of cobalt to tin.

[0041] Any of the above-described Co-Sn / biochar thin film electrodes, or the Co-Sn / biochar thin film electrodes prepared by any of the above-described methods, are used for electrochemical reduction of carbon dioxide to form formic acid.

[0042] Beneficial effects

[0043] (1) The Co-Sn / biochar thin film electrode provided by the present invention is based on porous carbon. Due to its porous structure, it has a large specific surface area. The NP element doped with the porous carbon can significantly enhance the stability and conductivity of the porous carbon substrate, expand the pore structure of the porous carbon, and increase the interlayer spacing, thereby accelerating ion diffusion and electron transfer, thereby enhancing the electrochemical catalytic performance.

[0044] At the same time, the Co-Sn composite metal film layer of the electrode can enhance the reaction stability and reusability of the electrode. Applying the Co-Sn / biochar thin film electrode to the electrochemical reduction of CO2 to produce formic acid can significantly improve the directional conversion of CO2 to formic acid, achieve a high product generation rate, and continuously produce formic acid with a Faradaic efficiency of 92.8%±2.3% within 5 hours, which has good application prospects in the field of electrochemistry.

[0045] (2) The preparation method of the Co-Sn / biochar thin film electrode provided by the present invention uses biomass (straw and peel) that is widely present in nature as raw materials, which is not only beneficial to environmental improvement but also realizes resource recycling;

[0046] By pulverizing, drying, and finely treating the biomass in a treatment solution, NP elements can be effectively doped into biochar (i.e., porous carbon);

[0047] The thermal evaporation coating method can accurately control the evaporation rate of Co and Sn, control the synthesis ratio of metal coating, and provide a larger specific surface area to improve catalytic efficiency.

[0048] (3) Based on the porous structure, high conductivity and large specific surface area of ​​doped biochar, as well as the synergistic effect of the coupling of composite metals Co and Sn, the Co-Sn / biochar thin film electrode provided by the present invention or the Co-Sn / biochar thin film electrode prepared by the method of the present invention is applied to the electrochemical reduction of CO2 to produce formic acid, which has the effect of significantly improving the directional conversion of CO2 to formic acid, achieving a high product generation rate, and having excellent stability and repeatability, and has good application prospects in the field of electrochemistry. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 Schematic diagram of the catalytic reduction mechanism of the Co-Sn / biochar thin film electrode in the present invention;

[0050] Figure 2 Comparison of the Faradaic efficiency of the NP-C-1 electrode of the present invention and the NP-C-10 electrode for the reduction of carbon dioxide to formic acid;

[0051] Figure 3 Comparison of the Faradaic efficiency of the NP-C-1 to 10 electrodes of the present invention for carbon dioxide reduction;

[0052] Figure 4 The kinetic process of reducing carbon dioxide to formic acid by the NP-C-1 electrode and the Co-Sn (NP-C-1) electrode of the present invention;

[0053] Figure 5 Comparison of the Faradaic efficiencies of the Co-Sn(NP-C-1) and Co-Sn(NP-C-1)-11-16 electrodes of the present invention for the reduction of carbon dioxide to formic acid;

[0054] Figure 6 This is a graph showing the degradation changes in the stability experiment of the Co-Sn / biochar thin film electrode of the present invention for the Faradaic efficiency of reducing carbon dioxide to formic acid. DETAILED DESCRIPTION

[0055] The present invention is further described below with reference to specific examples, but the examples do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art;

[0056] The essential features and significant effects of the present invention can be reflected in the following embodiments. The described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Therefore, they do not limit the present invention in any way. Those skilled in the art may make some non-essential improvements and adjustments based on the contents of the present invention, which all fall within the scope of protection of the present invention.

[0057] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs; and the terms used herein include any and all combinations of one or more of the associated listed items.

[0058] In more detail, the implementation and operation of the technical solution of the present invention are as follows:

[0059] 1) Mix a certain proportion of straw and peel, place in an 80℃ drying oven and dry for 24 hours, then grind into powder using a grinder, pass through a 200-mesh sieve, and set aside;

[0060] 2) Mix 200-mesh biomass powder and treatment solution evenly, let it stand for 20-60 minutes to allow the structure to penetrate, and then place it in a drying oven at 100-300°C for pre-carbonization for 3-6 hours;

[0061] 3) placing the pre-carbonized material into a tube furnace, introducing inert gas, starting the temperature ramp to 600-1000°C, and carbonizing at a constant temperature for 1-3 hours. After cooling to room temperature, the material is taken out, a certain amount of polyvinyl chloride is added, mixed evenly, and placed in a mold for high pressure shaping to obtain an NP-doped biochar electrode substrate;

[0062] 4) Co particles and Sn particles are placed at different positions in the thermal evaporation chamber as different evaporation sources, and the electrode substrate is attached to the thermal evaporation tray and fixed on the turntable above the evaporation source;

[0063] 5) After evacuating to a vacuum state, a thermal evaporation process is started to control the thermal evaporation rates of Co and Sn to produce a Co-Sn / biochar thin film electrode in which the ratio of Co to Sn is adjustable.

[0064] The mass ratio of peel in the mixed biomass of straw and peel is controlled to be 10% to 30%.

[0065] The treatment liquid formula is: ammonium bicarbonate, urea and other N-containing substances, sodium dihydrogen phosphate, disodium hydrogen phosphate and other P-containing substances, and the solution is one of water, ethanol, acetic acid, acetone and the like.

[0066] Preferably, the N:P ratio is 1.5 to 2.5.

[0067] Preferably, the concentration of the NP dopant in the solution is 5% to 20%.

[0068] Preferably, the concentration of the mixed biomass in the treatment solution is 0.5 to 1.0 g / mL.

[0069] Preferably, the standing time of the biomass powder and the treatment liquid is preferably 30 minutes, the pre-carbonization temperature is preferably 200° C., and the pre-carbonization time is preferably 4 hours.

[0070] Preferably, the carbonization temperature is 800° C. and the carbonization time is 2 h.

[0071] The present invention provides a Co-Sn / biochar thin film electrode for efficient carbon dioxide electroreduction and a preparation method thereof. A polyvinyl chloride binder is added to make the NP-doped biochar electrode substrate structure more stable.

[0072] By adjusting the instrument's P, I, and D parameters, the sum of the thermal evaporation rates of Co and Sn is controlled to be 0.05-0.20 nm / s, preferably 0.10 nm / s. The thermal evaporation rate of Co is basically limited to 0.08 nm / s.

[0073] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0074] Example 1

[0075] In this embodiment,

[0076] 1. Preparation of NP-doped biochar series (abbreviated as NP-C):

[0077] NP-C-1: 80% straw and 20% peel were mixed and dried in an 80°C drying oven for 24 hours. The mixture was then crushed into powder using a grinder and passed through a 200-mesh sieve. The 200-mesh biomass powder was evenly mixed with the treatment liquid and allowed to stand for 30 minutes to allow the structure to penetrate. The mixture was then placed in a 200°C drying oven for pre-carbonization for 4 hours. The pre-carbonized material was then placed in a tubular furnace, inert gas was introduced, and the temperature was raised to 800°C. The mixture was carbonized at a constant temperature for 2 hours. After cooling to room temperature, the mixture was taken out and a certain amount of polyvinyl chloride was added and mixed evenly. The mixture was then placed in a mold and shaped under high pressure to obtain an NP-doped biochar electrode.

[0078] The treatment liquid formula is: nitrogen element comes from urea, phosphorus element comes from disodium hydrogen phosphate, and is prepared with a nitrogen to phosphorus element mass ratio of 2. Ethanol is used as the solvent, and the mass concentration of urea and disodium hydrogen phosphate in ethanol is 10%.

[0079] NP-C-2: Its preparation is basically the same as NP-C-1, except that the biomass is not dried in an 80°C drying oven for 24 hours. Then, the 200-mesh biomass powder is mixed evenly with the treatment liquid, and the standing time is extended to 50 minutes to allow the structure to penetrate;

[0080] NP-C-3: Its preparation is basically the same as NP-C-1, except that the 200-mesh biomass powder is mixed evenly with the treatment solution, and the standing time is extended to 90 min to allow the structure to penetrate;

[0081] NP-C-4: Its preparation is basically the same as NP-C-1, except that the 200-mesh biomass powder is mixed evenly with the treatment solution, and the standing time is changed to 10 minutes to allow the structure to penetrate;

[0082] NP-C-5: Its preparation is basically the same as NP-C-1, except that the 200-mesh biomass powder is mixed evenly with the treatment solution, and the standing time is changed to 20 minutes to allow the structure to penetrate;

[0083] NP-C-6: Its preparation is basically the same as NP-C-1, except that the phosphorus-containing substance in the treatment solution formula is replaced with a corresponding amount of nitrogen-containing substance (calculated according to the content of nitrogen and phosphorus elements);

[0084] NP-C-7: Its preparation is basically the same as NP-C-1, except that the nitrogen-containing substance in the treatment solution formula is replaced with a corresponding amount of phosphorus-containing substance (calculated according to the content of nitrogen and phosphorus elements);

[0085] NP-C-8: Its preparation is basically the same as NP-C-1, except that in the treatment solution formula, the ratio of the amount of N element to the amount of P element is modified to: N element amount / P element amount = 1;

[0086] NP-C-9: Its preparation is basically the same as NP-C-1, except that in the treatment solution formula, the ratio of the amount of N element to the amount of P element is modified to: N element amount / P element amount = 4;

[0087] NP-C-10: Its preparation is basically the same as NP-C-1, except that the 200-mesh biomass powder is not mixed with the treatment liquid and is directly subjected to the carbonization step to obtain the biochar electrode.

[0088] Figure 1 The diagram shows the catalytic reduction mechanism of the Co-Sn / biochar film electrode in the present invention. In the experiment, multiple 200mL electrolyte solutions with a concentration of 0.05mol / L were taken, CO2 was continuously introduced to form an electrolyte, a ruthenium-iridium-titanium electrode was used as the anode, and NP-C-1 electrode and NP-C-10 electrode were used as the cathode, respectively. The CO2 chronoamperometric reduction was performed at different potentials. The results are shown in FIG. Figure 2 As shown. The Faradaic efficiency of NP-C-1 electrode for CO2 reduction can reach more than 90%, while that of NP-C-10 electrode is only about 70%. However, due to the poor selectivity of the electrode for CO2 products, products such as CO, HCOOH, and CH4 will be generated. Taking HCOOH as a comparison, under the optimal voltage condition of -1.0V, the Faradaic efficiency of CO2 reduction to HCOOH of NP-C-1 electrode reaches 55.6%±2.7%, while the Faradaic efficiency of CO2 reduction to HCOOH of NP-C-10 electrode is 40.9%±2.1%. In addition, under the voltage condition of -1.0V, the differences in the CO2 reduction performance of NP-C-1 to 10 electrodes were further compared, and the results are shown as follows. Figure 3 The NP-C-1 electrode showed the best performance, with a Faradaic efficiency of 94.3% ± 2.4% for CO2 reduction, which was better than that of other electrodes (56.5% to 91.6%).

[0089] Example 2

[0090] In this embodiment,

[0091] 1. Prepare a series of Co-Sn / biochar thin film electrodes (abbreviated as Co-Sn(NP-Cx)), x = 1 to 10:

[0092] On the basis of NP-C preparation, Co particles and Sn particles were placed in different positions of the thermal evaporation chamber as different evaporation sources, and then the electrode substrate was attached to the thermal evaporation tray and fixed on the turntable above the evaporation source; after evacuation to vacuum, the thermal evaporation program was started, and the thermal evaporation rates of Co and Sn were controlled (the sum of the rates was 0.10nm / s) to prepare Co-Sn (NP-C-1) thin film electrodes, in which the ratio of Co to Sn was 0.8:0.2 and the thickness was 100nm. In the experiment, two 200mL electrolyte solutions with a concentration of 0.05mol / L were taken, and CO2 was continuously introduced to form an electrolyte. The ruthenium iridium titanium electrode was used as the anode, the NP-C-1 electrode and the Co-Sn (NP-C-1) electrode were used as the cathode, respectively. A DC voltage of 1.0V was applied between the positive and negative plates, and the reaction was carried out for 5h. The results are as follows Figure 4 The yield of CO2 reduction to HCOOH on the Co-Sn(NP-C-1) electrode reached 93.4±1.9 nmol dm -3 However, the yield of CO2 reduction to HCOOH at NP-C-1 electrode was only 58.3±2.6 nmol dm -3 This further indicates that the addition of Co-Sn promotes the directional reduction of CO2 to HCOOH.

[0093] 2. Based on the preparation of NP-C-1, the ratio of Co and Sn was adjusted to obtain:

[0094] Electrode Co-Sn(NP-C-1)-11: The ratio of Co to Sn is 0.10, which is achieved by controlling the ratio of Co and Sn thermal evaporation rates to 0.10;

[0095] Electrode Co-Sn(NP-C-1)-12: The ratio of Co to Sn is 9, which is achieved by controlling the ratio of Co and Sn thermal evaporation rates to 9;

[0096] Electrode Co-Sn(NP-C-1)-13: does not contain Co, only contains Sn, and the Sn content is the sum of the aforementioned Co and Sn contents;

[0097] Electrode Co-Sn(NP-C-1)-14: does not contain Sn, only contains Co, the Co content is the sum of the aforementioned Co and Sn contents;

[0098] Electrode Co-Sn(NP-C-1)-15: Control the sum of the thermal evaporation rates of Co and Sn to 0.02 nm / s;

[0099] Electrode Co-Sn(NP-C-1)-16: The combined thermal evaporation rate of Co and Sn is 0.30 nm / s;

[0100] In the experiment, multiple 200mL electrolyte solutions with a concentration of 0.05mol / L were taken and CO2 was continuously introduced to form an electrolyte. The ruthenium-iridium-titanium electrode was used as the anode, and the Co-Sn(NP-C-1) and Co-Sn(NP-C-1)-11~16 electrodes were used as the cathodes respectively. A DC voltage of 1.0V was applied between the positive and negative plates and the reaction was carried out for 5h. The results are as follows Figure 5 The yield of CO2 reduction to HCOOH on the Co-Sn(NP-C-1) electrode reached 93.4±1.9 nmol dm -3 , which is significantly better than the yield of other electrodes (71.5~85.2nmol dm -3 ).

[0101] Example 3

[0102] In the experiment, two 200mL electrolyte solutions with a concentration of 0.05mol / L were taken and CO2 was continuously introduced to form an electrolyte. The ruthenium-iridium-titanium electrode was used as the anode and the Co-Sn(NP-C-1) thin film electrode was used as the cathode. A DC voltage of 1.0V was applied between the positive and negative plates. The reaction was repeated for 5h and 20 times. The results are as follows: Figure 6 As shown in the figure, it can be seen that the Faradaic efficiency of the Co-Sn (NP-C-1) thin film electrode for the reduction of CO2 to HCOOH is stable at above 90%, and only slightly decreases by 2% to 3% with the accumulation of times, indicating that the composite electrode has excellent stability.

[0103] It should be noted that other coating wastewaters can also be treated using the treatment method of the present invention. Although the present invention has been disclosed above with reference to preferred embodiments, this is not intended to limit the present invention. Those skilled in the art will be able to make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A method for preparing a Co-Sn / biochar thin film electrode for electrochemical reduction, characterized in that: S1. Preparation of porous carbon Provide carbon source; Providing a treatment liquid; the treatment liquid includes nitrogen and phosphorus, and the mass ratio of the nitrogen and phosphorus is 0.25~4.0; Mix the carbon source and treatment solution and let it stand for 20-60 minutes; Then, a high-temperature pre-carbonization treatment is carried out at a temperature of 100-300°C; and then a high-temperature carbonization treatment is carried out again at a temperature of 600-1000°C in an inert gas atmosphere; Finally, a binder is added to form porous carbon doped with nitrogen and phosphorus elements; S2. Coating A metal film containing cobalt and tin is prepared on the surface of porous carbon by thermal evaporation. The mass ratio of cobalt to tin is 0.25 to 4.0; The electrode comprises: Porous carbon, and a metal film layer located on the surface of the porous carbon; The porous carbon comprises N and P elements, and the mass ratio of the nitrogen element to the phosphorus element is 0.25-4.0; The metal of the metal film layer includes cobalt and tin, and the mass ratio of the cobalt to the tin is 0.25-4.

0.

2. The method for preparing a Co-Sn / biochar thin film electrode for electrochemical reduction according to claim 1, characterized in that: The carbon source is biomass, which is sieved through a 200-mesh sieve and dried.

3. The method for preparing a Co-Sn / biochar thin film electrode for electrochemical reduction according to claim 2, characterized in that: The treatment solution contains a substance for providing the N element and a substance for providing the P element, and the sum of the mass concentrations of the two substances in the solution is 5% to 20%.

4. The method for preparing a Co-Sn / biochar thin film electrode for electrochemical reduction according to claim 3, characterized in that: The biomass has a concentration in the treatment liquid of 0.5-2.0 g / mL.

5. The method for preparing a Co-Sn / biochar thin film electrode for electrochemical reduction according to any one of claims 1 to 4, characterized in that: In S1, the carbon source and the treatment solution are mixed and allowed to stand for 20 to 40 minutes; The high temperature treatment time is 3 to 6 h at a temperature of 100 to 300 °C; The high temperature treatment time is 1 to 3 hours at a temperature of 600 to 1000 °C.

6. The method for preparing a Co-Sn / biochar thin film electrode for electrochemical reduction according to any one of claims 1 to 4, characterized in that: In S2, the cobalt source and the tin source are placed separately to form a cobalt evaporation source and a tin evaporation source; The sum of the thermal evaporation rates of cobalt and tin is controlled to be 0.05~0.20 nm / s.

7. The method for preparing a Co-Sn / biochar thin film electrode for electrochemical reduction according to claim 6, characterized in that: The ratio of the thermal evaporation rates of cobalt and tin is controlled to be 0.25~4.

0.

8. The method for preparing a Co-Sn / biochar thin film electrode for electrochemical reduction according to claim 5, characterized in that: In S2, the cobalt source and the tin source are placed separately to form a cobalt evaporation source and a tin evaporation source; The sum of the thermal evaporation rates of cobalt and tin is controlled to be 0.05~0.20 nm / s.

9. The method for preparing a Co-Sn / biochar thin film electrode for electrochemical reduction according to claim 8, characterized in that: The ratio of the thermal evaporation rates of cobalt and tin is controlled to be 0.25~4.

0.

10. A Co-Sn / biochar thin film electrode for electrochemical reduction, characterized in that: The Co-Sn / biochar thin film electrode is prepared according to the preparation method of the Co-Sn / biochar thin film electrode for electrochemical reduction according to any one of claims 1 to 9. The thickness of the metal film layer is 10-100 nm; The Co-Sn / biochar thin film electrode is used for reducing carbon dioxide.

11. A Co-Sn / biochar thin film electrode prepared by the method according to any one of claims 1 to 9, or a use of the Co-Sn / biochar thin film electrode according to claim 10, characterized in that: Used for the electrochemical reduction of carbon dioxide to form formic acid.

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