CN114457363A

CN114457363A - For electrochemical reduction of CO2Electrode and preparation method thereof

Info

Publication number: CN114457363A
Application number: CN202210287039.0A
Authority: CN
Inventors: 张霞; 焦学然; 毛艳丽; 朱新峰; 康海彦; 延旭; 宋忠贤; 闫晓乐; 谷得明; 韩昌睿; 崔璐雪; 张珂梦
Original assignee: Henan University of Urban Construction
Current assignee: Henan University of Urban Construction
Priority date: 2022-03-22
Filing date: 2022-03-22
Publication date: 2022-05-10
Anticipated expiration: 2042-03-22
Also published as: CN114457363B

Abstract

The invention discloses a method for electrochemically reducing CO₂The electrode comprises a conductive substrate, wherein metal bismuth and lead are loaded on the conductive substrate. Also provides a corresponding preparation method. The electrode prepared by the invention loads bismuth-lead material, has bismuth metal phase and bismuth-lead mixed phase, and has abundant electrochemical reduction CO₂The active site can stably work for more than 50 hours, and because the material has very good conductivity and the contact resistance between the catalyst and the substrate is extremely small, the active site can be controlled at 15.56 mA cm/cm when the external potential is-0.96V/s.RHE^‑2The formic acid is produced under lower stability, and the method has extremely high formic acid Faraday efficiency (more than 90 percent), simultaneously effectively inhibits the hydrogen evolution reaction, and solves the problem of the prior artElectrocatalytic CO₂Too low reduction current density and poor stability in the process.

Description

For electrochemical reduction of CO2Electrode and preparation method thereof

Technical Field

The invention belongs to the technical field of electrochemistry.

Background

Electrochemical carbon dioxide reduction (CO) reaction powered by renewable energy₂RR) can effectively reduce greenhouse effect and counteract artificial carbon emission [ chem. Soc. Rev. 2014, 45, 631-]However, CO₂Can be converted into various products, such as acids, alcohols, hydrocarbons and syngas, resulting in CO₂The selectivity of RR is poor. Among the numerous conversion products, formic acid or formic acid (HCOOH) fuel is produced via two electron transfer reaction pathways, and thus, the efficiency of electron utilization per mole is highest [ Joule. 2018, 2, 825-832-]. Formic acid, a portable liquid fuel, has a high energy density and can be used as a hydrogen storage material and a chemical fuel for fuel cells [ nat. Catal. 2018, 2(1), 55-61 ]]. Heretofore, formic acid-selective electrocatalysts have been reported, mainly comprising Sn, Bi, In, Pb and Pd, etc., but CO₂RR has many challenges such as slow reaction kinetics, low selectivity of target product, competitive Hydrogen Evolution (HER), etc., and thus there is still a need to develop a catalyst with high selectivity, high activity, and high stability.

Disclosure of Invention

The invention aims to provide a method for electrochemically reducing CO₂And an electrode ofA corresponding process for their preparation is a further object of the present invention.

Based on the purpose, the invention adopts the following technical scheme:

for electrochemical reduction of CO₂The electrode comprises a conductive substrate, wherein metal bismuth and lead are loaded on the conductive substrate.

The conductive substrate is foam copper.

Preparation of CO for electrochemical reduction₂The method of electrode of (1), comprising the steps of:

1) pretreating the conductive substrate;

2) preparing an electroplating solution: dissolving bismuth salt, lead salt, composite complexing agent and ammonium formate in an inorganic solvent according to the mass ratio of (0.001-0.01): (0.006-0.06): 0.002-0.02) to obtain a mixed solution, and adjusting the pH value of the mixed solution by using a buffering agent to obtain an electroplating solution;

3) placing a counter electrode and the conductive substrate pretreated in the step 1) as working electrodes into the electroplating solution in the step 2), and electroplating by adopting a pulse electrodeposition method to obtain the bismuth and lead loaded conductive substrate for electrochemical reduction of CO₂The electrode of (1).

The compound complexing agent in the step 2) is triammonium citrate (C)₆H₅O₇ (NH₄)₃) Thiourea (CH)₄N₂S), disodium edetate (C)₁₀H₁₄N₂Na₂O₈) And (4) forming.

In the step 2), the ratio of the amounts of the triammonium citrate, the thiourea and the disodium ethylene diamine tetraacetate is (0.002-0.02) to (0.002-0.02); the bismuth salt is bismuth chloride (BiCl)₃) The lead salt is lead chloride (PbCl)₂) (ii) a The inorganic solvent is deionized water, and the dosage ratio of the bismuth salt, the lead salt and the inorganic solvent is (0.001-0.01) mol, (90-110) mL; the buffering agent is hydrochloric acid or ammonia water; and adjusting the pH value of the mixed solution to 3-10 by using a buffering agent.

The conditions of the pulse electrodeposition method in the step 3) are as follows: 10-50 cycle periods with a potential of 0-4V, each cycle period comprising one minuteClock 0.1-1.5 mA/cm²And half minute 3-10 mA/cm²The constant current electrodeposition module of (1); the counter electrode is a graphite rod.

The pretreatment method of the conductive substrate in the step 1) comprises the following steps: the conductive substrate was sequentially treated with 1M H₂SO₄And ultrasonically cleaning with acetone and deionized water for 20-40 min.

Compared with the prior art, the invention has the following beneficial effects:

1) the preparation method of the electrode directly reduces Bi and Pb on the foam copper substrate in situ by using a pulse electrodeposition method, enables the metal bismuth and lead to present a bismuth metal phase and a bismuth-lead mixed phase by effectively regulating and controlling the mixture ratio of different metal precursors in electroplating solution, the current density and other conditions in the electroplating process, has a three-dimensional porous structure, is beneficial to the mass transfer of reducing substances, has good conductivity, presents the synergistic effect of the metal bismuth and bismuth-lead alloy on the catalytic performance, generates a large number of interface active sites, and greatly adsorbs CO in electrolyte₂Molecule, realization of CO₂The molecule is converted into formic acid;

2) in the pulse electrodeposition process, a mode of alternating low current density and high current density is adopted in a cycle period, metal ions in electroplating solution migrate to the surface of an electrode due to electric field force at low current density, and then rapid reduction of bismuth ions and lead ions is realized at high current density, so that the shape and the crystal phase of bismuth and lead are regulated and controlled, wherein metal bismuth and bismuth-lead alloy provide a large amount of catalytic active sites, the formic acid Faraday efficiency of the electrode can reach more than 90%, and the competitive reaction (hydrogen evolution effect) in electrochemical reduction of carbon dioxide is greatly inhibited;

3) the prepared electrode-loaded bismuth-lead material has a bismuth metal phase and a bismuth-lead mixed phase, and is rich in electrochemical reduction CO₂The active site can stably work for more than 50 hours, and because the material has very good conductivity and the contact resistance between the catalyst and the substrate is extremely small, the active site can be controlled at 15.56 mA cm when the external potential is-0.96V vs. RHE^-2The stable formic acid production is realized, the high formic acid Faraday efficiency (more than 90 percent) is realized, and the hydrogen evolution reaction is effectively inhibited, thereby solving the problem ofExisting electrocatalytic CO₂Too low reduction current density and poor stability in the process.

Drawings

In order to more clearly illustrate the technical solution of the present invention, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.

FIG. 1 is a schematic view of pulse electrodeposition of an electrode in example 1;

FIGS. 2 and 2a show the Bi and Bi-Pb alloys (Bi @ Pb) on the electrodes prepared in example 1₁) The SEM topography of the material, FIG. 2b is the SEM image of a pure bismuth material on an electrode prepared in comparative example 1, and FIG. 2c is the SEM image of a bismuth-lead bimetallic material on an electrode prepared in comparative example 3 under constant current conditions;

FIG. 3 is an XRD (X-ray diffraction) pattern of the metal material when the electrodes prepared in example 1 and comparative examples 1-2 are used for depositing metal bismuth lead, pure bismuth and pure lead;

FIG. 4 shows the results of the preparation of the electrodes of examples 1 and comparative examples 1 to 2 in CO₂Saturated 0.5M KHCO₃A lower product distribution diagram;

FIG. 5 is a time-course plot of the-0.96V vs RHE conditions of example 1;

FIG. 6 is a bismuth lead alloy electrode (Bi @ Pb electrode) prepared in comparative example 4;

fig. 7 is an enlarged view of fig. 2 a.

Detailed Description

The technical solution of the present invention will be described in detail below in order to make the objects, technical solutions and advantages of the present invention clearer, but the following embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the examples given herein without any inventive step, are within the scope of the present invention.

In the present invention, the copper foam used in the following examples was purchased from Kunshan Guanjia-sourced New Material Co., Ltd, bismuth chloride (BiCl)₃) Lead chloride (PbCl)₂) Triammonium citrate (C)₆H₅O₇ (NH₄)₃) Thiourea (CH)₄N₂S) and disodium ethylenediaminetetraacetate (C)₁₀H₁₄N₂Na₂O₈) Purchased from Shanghai Aladdin Biotechnology Ltd.

Example 1

For electrochemical reduction of CO₂The electrode comprises a conductive substrate, wherein metal bismuth and lead are loaded on the conductive substrate, and the conductive substrate is foam copper.

1) pretreatment of the copper foam: cutting the foam copper into 1 x 2 cm²In turn using 1M H₂SO₄Ultrasonic cleaning with acetone and deionized water for 30 min;

2) preparing an electroplating solution: respectively dissolving 0.001mol of bismuth chloride, 0.001mol of lead chloride, 0.01mol of triammonium citrate, 0.01mol of thiourea, 0.01mol of disodium ethylene diamine tetraacetate and 0.01mol of ammonium formate in 100ml of deionized water, fully stirring until the solution is clear and transparent to obtain a mixed solution, and adjusting the pH value of the mixed solution to 5 by using 0.1M hydrochloric acid to obtain an electroplating solution;

3) the graphite rod is used as a counter electrode, the foamy copper pretreated in the step 1) is used as a working electrode, the working electrode is placed in the electroplating solution in the step 2), a pulse electrodeposition method is adopted to carry out electroplating under a two-electrode system, bismuth ions and lead ions are reduced on the foamy copper in situ, and the electrochemical reduction CO loaded with metal bismuth and lead for electrochemical reduction is obtained₂Electrode (Bi @ Pb)₁An electrode); the conditions of the pulse electrodeposition method are as follows: 30 cycle periods, each cycle period comprising 1 mA/cm in one minute²And half a minute 5 mA/cm²The constant current electrodeposition module. The specific schematic diagram is shown in fig. 1 below.

As can be seen from FIG. 1, when the current is 1 mA/cm²While the voltage was rapidly increased from 0V to 1.462V, it is considered that bismuth ions and lead ions in the plating solution continuously moved to the surface of the growth substrate when the current became 5 mA/cm²At the same time, the voltage rapidly changes from 1.462VIncreased to 1.656V due to rapid deposition of bismuth and lead ions at high current densities.

Example 2

The difference from example 1 is that step 2) prepares a plating solution: respectively dissolving 0.01mol of bismuth chloride, 0.001mol of lead chloride, 0.008mol of triammonium citrate, 0.006mol of thiourea, 0.005mol of disodium ethylene diamine tetraacetate and 0.008mol of ammonium formate in 100ml of deionized water;

step 3) the conditions of the pulse electrodeposition method are as follows: 40 cycle periods, each cycle period comprising 1.5 mA/cm per minute²And half a minute 3 mA/cm²The constant current electrodeposition module.

Example 3

The difference from example 1 is that step 2) prepares a plating solution: respectively dissolving 0.005mol of bismuth chloride, 0.01mol of lead chloride, 0.005mol of triammonium citrate, 0.004mol of thiourea, 0.004mol of disodium ethylene diamine tetraacetate and 0.02mol of ammonium formate in 100ml of deionized water;

step 3) the conditions of the pulse electrodeposition method are as follows: 50 cycle periods, each cycle period comprising 0.5 mA/cm for one minute²And 8 mA/cm for half a minute²The constant current electrodeposition module.

Example 4

The difference from example 1 is that step 2) prepares a plating solution: respectively dissolving 0.002mol of bismuth chloride, 0.008mol of lead chloride, 0.02mol of triammonium citrate, 0.02mol of thiourea, 0.02mol of disodium ethylene diamine tetraacetate and 0.002mol of ammonium formate in 100ml of deionized water;

step 3) the conditions of the pulse electrodeposition method are as follows: 20 cycle periods, each cycle period comprising 0.2 mA/cm for one minute²And half a minute 10 mA/cm²The constant current electrodeposition module.

Example 5 electrochemical Performance test

The electrochemical performance test is carried out on the electrochemical workstation CHI760e of Shanghai Chenghua company by carrying out the electrochemical performance test on the example 1 and the comparative examples 1-7, a three-electrode system is adopted, the electrodes prepared in the example 1 and the comparative examples 1-2 are used as working electrodes, Ag/AgCl electrodes are used as reference electrodes, foamed nickel is used as a counter electrode, and electricity is carried outThe hydrolysate is 0.5M KHCO₃The solution was subjected to electrochemical performance test in H tank, and Sustainable X37-50 alkaline film of Dioxide materials, USA was used as intermediate membrane. The morphology diagrams of the electrodes obtained in the example 1 and the comparative examples 1, 3 and 4 are respectively shown in fig. 2a, 2b, 2c and 6, the XRD diagrams of the examples 1 and the comparative examples 1-2 are shown in fig. 3, and the product distribution diagrams are respectively shown in fig. 4c, 4b and 4 a. The electrode long-term test pattern of example 1 is shown in fig. 5.

Comparative example 1

The difference from example 1 is that lead chloride was not included in the plating solution and the resulting supported metallic bismuth was used for electrochemical reduction of CO₂Electrode (pure Bi electrode).

Comparative example 2

The difference from example 1 was that bismuth chloride was not included in the plating solution, and the resulting electrode carrying metallic lead (pure Pb electrode) was obtained.

Comparative example 3

The difference from example 1 is that the constant current electrodeposition method is used to reduce bismuth ions and lead ions in situ on the copper foam, i.e. at 5 mA/cm²And electrodeposition was carried out for 15 minutes, and an electrode (Bi-Pb electrode) supporting metallic bismuth and lead was obtained.

Comparative example 4

The difference from example 1 was that ammonium formate was not added to the plating solution, and the resulting electrode (Bi @ Pb electrode) was loaded with metallic bismuth and lead.

As can be seen from FIG. 2a, Bi @ Pb prepared in example 1₁Has a sheet-like and needle-point-like structure, and the special structure can be used for electrochemical reduction of CO₂Providing more active sites. As can be seen from fig. 2b, the pure bismuth electrode prepared in comparative example 1 exhibited a needle-tip-like morphology, which indicates that bismuth lead can be induced to grow into a two-dimensional sheet-like structure in example 1 when lead ions are present in the plating solution. As can be seen from FIG. 2c, the morphology of the Bi-Pb bimetallic electrode prepared in comparative example 3 is similar to that of the pure Bi electrode in FIG. 2b under constant current conditions, mainly because the standard reduction potentials of Bi ions (0.32V vs. RHE) and Pb ions (-0.126V vs. RHE) in the aqueous solution are different, so that Bi ions are easier to co-react with each other than Pb ionsThe solution is precipitated and the morphology of fig. 2c is closer to that of fig. 2 b.

As can be seen from FIG. 3, the pure bismuth electrode exhibited a metallic bismuth phase alone (JCPDS PDF #44-1246) and the pure lead exhibited a metallic lead phase alone (JCPDS PDF #04-0686), while Bi @ Pb in example 1 was used as the @ Pb phase₁The electrodes showed a metallic bismuth phase (JCPDS PDF #44-1246) and an alloyed bismuth lead phase (Pb)₇Bi₃ JCPDS PDF#39-1087）。

From FIG. 4a, it can be seen that the pure lead electrode of comparative example 2 is in CO₂Saturated 0.5M KHCO₃Lower product profile, formic acid faradaic efficiency not exceeding 60% over the whole potential range; FIG. 4b shows the pure bismuth electrode of comparative example 1 in CO₂Saturated 0.5M KHCO₃Lower product profile, from figure 4b, the formic acid faradaic efficiency starts to decrease after increasing to 71.53%; FIG. 4c shows Bi @ Pb in example 1₁Electrode in CO₂Saturated 0.5M KHCO₃The lower product distribution plot, from figure 4c, shows that the faraday trend of the electrode is similar to that of pure bismuth, both increasing and decreasing, but the highest faraday efficiency of the mixed phase can be as high as 91.86% at-0.96V vs. RHE.

FIG. 5 shows Bi @ Pb in example 1₁Long term test patterns of the electrodes under-0.96V vs RHE conditions. As can be seen from FIG. 5, the current density was maintained at 15.56 mA/cm despite the replacement of the electrolyte during the first 20 hours of continuous operation²And the formic acid faradaic efficiency can be maintained at 90%, so that the electrode can be continuously operated for at least 50 hours.

FIG. 6 shows the plating solution of comparative example 4 without ammonium formate, resulting in an electrode loaded with metallic bismuth and lead (Bi @ Pb electrode), and it can be seen from FIG. 6 that without ammonium formate, Bi @ Pb do not have the lamellar structure shown in FIG. 2a, and that the addition of ammonium formate may affect the phase composition of Bi @ Pb and CO₂The reducing property of (2). The reason is that ammonium formate is introduced into the electroplating solution system, the aqueous solution of ammonium ions is acidic, the conductivity of the electroplating solution can be improved, and the existence of the ammonium formate can improve the active sites on the surface of bismuth and lead in situ during the deposition of the bismuth and lead and is used for subsequent CO₂The excellent performance of the formic acid provides a solid foundation; in addition, aim atThe reduction potential of bismuth and lead in the aqueous solution is different, under the low current density, metal ions in the electroplating solution migrate to the surface of the electrode due to the electric field force, and then under the high current density, the bismuth ions and the lead ions are rapidly reduced, so that the shape and the crystal phase of bismuth and lead are regulated and controlled.

Therefore, the preparation method of the electrode directly reduces Bi and Pb on the foam copper substrate in situ by using the pulse electrodeposition method, enables the metal bismuth and lead to present a bismuth metal phase and a bismuth-lead mixed phase by effectively regulating and controlling the mixture ratio of different metal precursors in electroplating solution, the current density in the electroplating process and other conditions, has a three-dimensional porous structure, is beneficial to the mass transfer of reducing substances, has good conductivity, presents the synergistic effect of the metal bismuth and bismuth-lead alloy on the catalytic performance, generates a large number of interface active sites, and greatly adsorbs CO in the electrolyte₂Molecule, realization of CO₂The molecule is converted to formic acid.

In the pulse electrodeposition process, a mode of alternating low current density and high current density is adopted in a cycle period, metal ions in electroplating solution migrate to the surface of an electrode under the low current density due to electric field force, and then rapid reduction of bismuth ions and lead ions is realized under the high current density, so that the shape and the crystal phase of bismuth and lead are regulated and controlled, wherein metal bismuth and bismuth-lead alloy provide a large amount of catalytic active sites, the formic acid Faraday efficiency of the electrode can reach more than 90%, and the competitive reaction (hydrogen evolution effect) in the electrochemical reduction of carbon dioxide is greatly inhibited.

The prepared electrode-loaded bismuth-lead material has a bismuth metal phase and a bismuth-lead mixed phase, and is rich in electrochemical reduction CO₂The active site can stably work for more than 50 hours, and because the material has very good conductivity and the contact resistance between the catalyst and the substrate is extremely small, the active site can be controlled at 15.56 mA cm when the external potential is-0.96V vs. RHE^-2Stable formic acid production, high formic acid Faraday efficiency (more than 90 percent), effective inhibition of hydrogen evolution reaction, and solving the problem of the existing electrocatalysis of CO₂Too low reduction current density and poor stability in the process.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. For electrochemical reduction of CO₂The electrode of (2), characterized by comprising a conductive substrate on which metallic bismuth and lead are supported.

2. The method of claim 1 for electrochemical reduction of CO₂The electrode of (1), wherein the conductive substrate is copper foam.

3. Preparation of CO for electrochemical reduction according to claim 1 or 2₂The method of (3), comprising the steps of:

1) pretreating the conductive substrate;

2) preparing an electroplating solution: dissolving bismuth salt, lead salt, composite complexing agent and ammonium formate in an inorganic solvent according to the mass ratio of (0.001-0.01) to (0.006-0.06) to (0.002-0.02) to obtain a mixed solution, and adjusting the pH value of the mixed solution by using a buffering agent to obtain an electroplating solution;

4. The method of claim 3 for the preparation of CO for electrochemical reduction₂The method of (1), characterized in that,

the composite complexing agent in the step 2) consists of triammonium citrate, thiourea and disodium ethylene diamine tetraacetate.

5.The method of claim 4 for the preparation of CO for electrochemical reduction₂The method of (1), characterized in that,

in the step 2), the ratio of the amounts of the triammonium citrate, the thiourea and the disodium ethylene diamine tetraacetate is (0.002-0.02) to (0.002-0.02); the bismuth salt is bismuth chloride, and the lead salt is lead chloride; the inorganic solvent is deionized water, and the dosage ratio of the bismuth salt, the lead salt and the inorganic solvent is (0.001-0.01) mol, (90-110) mL; the buffering agent is hydrochloric acid or ammonia water; and adjusting the pH value of the mixed solution to 3-10 by using a buffering agent.

6. The method of claim 5 for the preparation of CO for electrochemical reduction₂The method of (1), characterized in that,

the conditions of the pulse electrodeposition method in the step 3) are as follows: 10 to 50 cycle periods with a potential of 0 to 4V, each cycle period comprising 0.1 to 1.5 mA/cm per minute²And half minute 3-10 mA/cm²The constant current electrodeposition module of (1); the counter electrode is a graphite rod.

7. The method of claim 3 for the preparation of CO for electrochemical reduction₂The method for preparing the electrode, wherein the pretreatment method of the conductive substrate in the step 1) is as follows: the conductive substrate was sequentially treated with 1M H₂SO₄And ultrasonically cleaning with acetone and deionized water for 20-40 min.