CN112941553A

CN112941553A - Preparation method and application of three-dimensional nano tip copper electrode

Info

Publication number: CN112941553A
Application number: CN202110108784.XA
Authority: CN
Inventors: 赵建
Original assignee: Tianjin University of Technology
Current assignee: Tianjin University of Technology
Priority date: 2021-01-27
Filing date: 2021-01-27
Publication date: 2021-06-11

Abstract

The invention provides a preparation method and application of a three-dimensional nanometer tip copper electrode, and belongs to the technical field of electrocatalysis. The invention prepares the three-dimensional nanometer tip copper electrode by simple in-situ electrodeposition method regulation and control under a three-electrode system,and active sites are raised by oxidation-reduction treatment. The prepared electrode has good stability, and compared with commercial copper foil, the electrode has the advantages of high stability at 0.1M KHCO₃The water solution is used as electrolyte in an electrocatalytic carbon dioxide system, and the excellent catalytic activity is shown. The preparation method provided by the invention is simple in process, convenient to operate and easy for large-scale preparation.

Description

Preparation method and application of three-dimensional nano tip copper electrode

Technical Field

The invention belongs to the technical field of electrocatalysis, and particularly relates to a preparation method of a three-dimensional nanometer tip copper electrode and application of the three-dimensional nanometer tip copper electrode in electrocatalysis carbon dioxide reduction.

Background

With the development of industry and the excessive consumption of fossil energy, energy crisis and environmental problems become more serious. Electrocatalysis is carried out to reduce carbon dioxide to generate fuel and high-value chemicals, so that not only can the cyclic utilization of energy be realized, but also a series of ecological problems caused by greenhouse effect can be solved, and the electrocatalysis reduction method becomes a research hotspot in related fields.

Since the Hori group examined the pioneer work of carbon dioxide reduction activity of different metal electrodes in 1989, copper electrodes have attracted much attention because of their abundant reserves, low cost and unique advantages in producing hydrocarbons. However, the copper electrode needs higher overvoltage in the process of catalyzing carbon dioxide reduction, and the product has wide distribution and low selectivity. Therefore, the design and preparation of the copper electrode with rich active sites have very important significance for enhancing the reduction activity of the electrocatalytic carbon dioxide.

Disclosure of Invention

The invention aims to design and prepare efficient electrocatalytic CO₂Reduced three-dimensional nanotip copper electrodes. According to the invention, the three-dimensional copper nanometer tip electrode is prepared in situ by a simple electrodeposition method in a three-electrode system, and the morphology and the active sites of the prepared electrode are regulated and controlled by the electrodeposition process and the oxidation-reduction treatment process, so that the electrode has higher catalytic activity, selectivity and stability in the electrocatalytic carbon dioxide reduction.

In order to solve the technical problems, the invention adopts the following technical scheme:

the preparation method of the three-dimensional nanometer tip copper electrode for electrocatalysis carbon dioxide reduction comprises the following steps:

(1) electro-polishing the copper foil: electropolishing for 1min under the action of 4V constant potential by using phosphoric acid (purity 85%) as electropolishing liquid, a graphite rod as a counter electrode and copper foil as a working electrode; then washing the residual polishing solution by ultrapure water; the electrode was immediately blow-dried with nitrogen for further use.

Preparing a three-dimensional nanometer tip copper electrode:

(2) measuring a certain volume of 0.02M CuSO₄And 0.1M KH₂PO₄Stirring the solution to uniformly mix the solution;

(3) taking the mixed solution in the step (2) as an electrodeposition solution, taking an electropolished copper foil as a working electrode, a platinum sheet as a counter electrode and Ag/AgCl as a reference electrode, and depositing for 800s under a certain potential;

(4) putting the electrode prepared in the step (3) into a muffle furnace, calcining at 250 ℃ for 15min, and raising the temperature at a rate of 2 ℃/min;

(5) and (3) carrying out in-situ reduction for 1h at a certain potential before carrying out electrocatalytic carbon dioxide reduction on the electrode obtained in the step (4) to obtain a three-dimensional nanometer tip copper electrode subjected to oxidation-reduction treatment, and marking as: 3D Cu NST-CR.

The electrode prepared by the method is used for electrocatalytic carbon dioxide reduction.

The invention has the beneficial effects that: the invention provides a method for preparing a three-dimensional nanometer tip copper electrode in situ, which is used for electrocatalysis carbon dioxide reduction. The method uses CuSO₄As a raw material, KH₂PO₄As an additive, a three-dimensional nanotip copper electrode was prepared by in-situ electrodeposition and oxidation-reduction treatment. The preparation method is simple and easy to operate, and 0.1M KHCO is added₃In a carbon dioxide reduction system with the aqueous solution as the electrolyte, the prepared electrode shows good catalytic activity.

The electrochemical active surface area test shows that the three-dimensional nano tip copper electrode has higher electrochemical active surface area than an electropolished copper foil electrode and a nano particle copper electrode, and can provide more active sites.

Through design experiments and inductive coupling plasma tests, the fact that the nanometer tip structure can locally enrich K relative to the appearance of nanometer particles is proved⁺And the corresponding anionic HCO₃ ^-Thereby improving the carbon dioxide reduction activity.

The current density is basically maintained at 32.4mA/cm through continuous 5h catalytic activity test²，C₂H₄/CH₄The ratio was stable at 21.7 and from the above results, the stability of the catalyst was good.

Drawings

Fig. 1 is a physical diagram in the process of preparing a three-dimensional nanotip copper electrode.

Fig. 2 is an XRD pattern of the sample: electropolished copper foil (a), untreated three-dimensional nanotip copper electrode (b), oxidation treated (c) and oxidation-reduction treated (d) three-dimensional nanotip copper electrode.

FIG. 3 is a scanning electron micrograph of a sample: an untreated three-dimensional nanotip copper electrode (a), an oxidation treated (b) and an oxidation-reduction treated (c).

Fig. 4 is a three-dimensional nanotip copper electrode electrochemically active surface area (ECSA).

Figure 5 shows faradaic efficiency of carbon dioxide reduction at different voltages: electropolished copper electrode (a), untreated three-dimensional nanotip copper electrode (b), oxidation treated (c) and oxidation-reduction treated (d) three-dimensional nanotip copper electrode.

FIG. 6 is a three-dimensional nanotip copper electrode, continuously reacted for 5h stability test at-1.2V vs.

FIG. 7 shows three-dimensional nanotip and nanoparticle copper electrode adsorption K⁺Concentration profile (unit electrochemically active surface area). Measurement of K by inductively coupled plasma spectroscopy⁺Concentration, inset shows adsorption K⁺The experimental procedure of (1).

Detailed Description

EXAMPLE 1 preparation of electrode

(1) Treatment of copper substrates

Cutting the copper sheet into electrodes with the specification of 1 multiplied by 2.5cm2, winding the electrodes by using an insulating tape to enable the working area to be 1 multiplied by 0.5cm2, using phosphoric acid (the purity is 85%) as an electric polishing solution, using a graphite rod as a counter electrode, performing electric polishing for 1min under the action of a constant potential of 4V of a direct current stabilized power supply, then flushing residual polishing solution by using ultrapure water, and finally drying the electrodes by using nitrogen for later use.

(2) Preparation of three-dimensional nano tip copper electrode

Firstly, 18ml of 0.02M CuSO is prepared₄Adding the solution into stirring rotor, stirring, adding 2ml 0.1M KH₂PO₄And (3) solution mixing the solution uniformly, and taking the mixed solution as an electrodeposition solution. Then, the above electrodeposition solution was poured into a beaker and deposited for 800s using a three-electrode system at-0.6V vs. Ag/AgCl potential to give a three-dimensional copper nanotip electrode (3D Cu NST) in which to treatThe good copper substrate is a working electrode, an Ag/AgCl (1M KCl) electrode is a reference electrode, and a platinum sheet is used as an auxiliary electrode. And finally, placing the deposited electrode into a muffle furnace, calcining for 15min at the temperature rise speed of 2 ℃/min and the temperature of 250 ℃, and reducing the electrode for 1h at the potential of-1.5V vs. And finally obtaining the calcined and reduced three-dimensional copper nanometer tip electrode, which is recorded as: 3D Cu NST-CR.

(3) Preparation of copper nanoparticle electrode

Firstly, 18ml of 0.02M CuSO is prepared₄And (3) adding 2ml of ultrapure water into the solution to mix in order to ensure that the copper content is consistent with the preparation of the three-dimensional tip electrode, taking the mixed solution as the solution for preparing the copper nanoparticle electrode, and keeping the rest steps consistent with the step (2).

(4) Characterization of three-dimensional copper nanotip electrodes

XRD characterization tests are carried out on the electropolished copper foil electrode, the 3D Cu NST electrode, the roasted 3D Cu NST electrode and the 3D Cu NST-CR electrode, and the test results are shown in figure 2, wherein the 3D Cu NST electrode has 3 peaks at 43 degrees, 50 degrees and 74 degrees and belongs to crystal planes (111), (200) and (220) respectively. The 3D Cu NST electrode was fired to increase its surface oxidation state, a weak oxidation peak at 36.5 ° was seen, which disappeared after reduction to form a 3D Cu NST-CR electrode. The prepared three-dimensional copper nanotip electrode was analyzed by Scanning Electron Microscopy (SEM) for morphology change at different processing stages, and the results are shown in fig. 3: wherein the diameter of the tip of the 3D Cu NST electrode obtained by electrodeposition is about 58.3nm, in order to maintain the oxidation state of the electrode surface, the 3D Cu NST electrode is calcined at 250 ℃ for 15min, the tip structure still exists and the diameter of the tip is about 94.5nm as can be seen by SEM, and the calcined 3D Cu NST electrode is reduced for 1h at the potential of-1.5 Vvs. RHE to obtain the 3D Cu NST-CR electrode, wherein the diameter of the tip of the electrode is about 210 nm.

Example 2 electrochemical property testing of three-dimensional copper nanotip electrodes

Electrochemically active surface area (ECSA), Inductively Coupled Plasma (ICP) and electrochemical stability tests.

Mining in a beakerECSA test is carried out by using a three-electrode system, a three-dimensional tip copper electrode is taken as a working electrode, a platinum electrode is taken as a counter electrode, an Ag/AgCl (1M KCl solution) electrode is taken as a reference electrode, and CO₂Saturated 0.1M KHCO₃The solution (pH 6.8) was an electrolyte solution, and then the cyclic voltammograms were scanned at different scan rates, and finally the electrochemically active surface area was obtained, and the results are shown in fig. 4. To better illustrate that the tip structure is capable of inducing KHCO₃The electrolyte is used as a positive ion, and the prepared copper nanoparticle electrode and the 3D Cu NST electrode are subjected to an Inductively Coupled Plasma (ICP) test under the following conditions, and are firstly subjected to 0.1M KHCO₃Applying a potential of-1.0 vvs. rhe for 120s to the 3D Cu NST electrode and the copper nanoparticle electrode under ambient conditions, then taking both electrodes out of the solution simultaneously, immersing in 10ml of an ultrapure aqueous solution and stopping the application of voltage, and finally testing the K in the solution by ICP⁺Content, results are shown in fig. 7, field-induced 3D Cu NST and copper nanoparticle electrodes adsorption K normalized for electrochemically active surface area (ECSA)⁺Concentration profile.

The electrochemical stability test was performed for 5h at-1.2V vs. RHE, gas phase products were tested every 1h using gas chromatography, and liquid phase products were tested using NMR spectroscopy. As shown in FIG. 6, the current density was maintained at 32.4mA/cm at all times during the reaction for 5 hours²，C₂H₄/CH₄The ratio was maintained at 21.7, indicating that the three-dimensional copper nanotip electrode had good stability during catalytic carbon dioxide reduction.

Example 3 application of three-dimensional copper nanotip electrode

The experiment adopts an online system to carry out carbon dioxide reduction test, in the catalysis process, the gas product amount generated by the electrolytic cell is detected on line by using gas chromatography every 1h, the liquid product amount is detected by using nuclear magnetic resonance hydrogen spectrum, and the generated main gas product is C₂H₄The liquid product in the electrolyte is qualitatively and quantitatively analyzed by using nuclear magnetic resonance hydrogen spectrum, and the result shows that HCOO exists^-Liquid phase product formation, which indicates that the three-dimensional copper nanotip electrode pair electrocatalyzes carbon dioxide reduction to form C₂H₄And HCOO^-Has good selectivity. As shown in the figure5, the faradaic efficiencies of different materials producing different products in the same voltage range at the same reaction time are compared. Wherein the Faraday efficiencies of the carbon dioxide reduction products of the electropolished copper foil at different potentials are consistent with those reported in the literature, except that C is at a potential of-1.1 Vvs₂H₄The results are shown in FIG. 5a, which is probably due to the volume of the conducting solution (30 cm) of the H-cell in the current work, in addition to the lower Faraday efficiency than reported in the literature³) Larger, at the same constant gas flow, CO₂The usability of (a) is reduced. FIG. 5b shows 3D Cu NST electrocatalytic CO under the same experimental conditions₂Faraday efficiency values of the reduced product, HCOO, compared to electropolished copper foil (FIG. 5a)^-The faraday efficiency of (a) is significantly increased, reaching 33.5% at-0.9V vs. Simultaneous CH₄The Faraday efficiency of (A) is sharply reduced, and C is at the potential of-1.2V vs₂H₄/CH₄The ratio reaches a relatively high value of 3.57. The distribution of faradaic efficiency of electrocatalytic carbon dioxide reduction products of the 3D Cu NST-CR electrode is shown in FIG. 5D, C at a potential of-1.2V vs. RHE₂H₄Faraday efficiency up to 42.4%, and corresponding C₂H₄/CH₄The ratio reaches 21.7, which is 90.6 times of that of the electropolished copper foil. HCOO at-0.9V vs. RHE potential^-The Faraday efficiency of (A) was 36% which was 6.8 times that of the electropolished copper foil. The 3D Cu NST-CR electrode exhibits a higher C at the same overpotential than the 3D Cu NST electrode₂H₄The faraday efficiency of. The results show that the redox treatment increases CO₂C in the reduction process₂H₄Selectivity of (2). This enhanced performance of the 3D Cu NST-CR electrode may be due to its rich active site formation during oxidation-reduction.

To fully understand how the three-dimensional nanotip improves the electrocatalytic CO₂Reduction activity and selectivity, we compared three-dimensional copper nanoparticles with 3D Cu NST-CR electrode activity to generate the highest HCOO^-The potential required for faraday efficiency was shifted from-1.0V vs. rhe to-0.9V vs. rhe. C of the nano-particle structure electrode under-1.2V vs₂H₄The Faraday efficiency is only 19.9%, and C is added₂H₄/CH₄The ratio was 15.1, which is lower than the activity of the tip structure electrode under the same conditions. These results indicate that the 3D Cu nanotip structure indeed increases C₂H₄Selectivity and reduction of HCOO^-The overpotential to the potential required to reach the maximum value is due to the ability of the nanotip structure to locally enrich K⁺And adsorbing the corresponding HCO₃ ^-The anion further promotes CO₂And (4) reducing.

The foregoing is directed to preferred embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. However, any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present invention are within the protection scope of the technical solution of the present invention.

Claims

1. A preparation method of a three-dimensional nanometer tip copper electrode is characterized by comprising the following steps:

(1) electro-polishing the copper foil: performing electropolishing for 1-3min under the action of 4V constant potential by using phosphoric acid as electropolishing liquid, a graphite rod as a counter electrode and copper foil as a working electrode; then washing the residual polishing solution by ultrapure water; immediately drying the electrode by using nitrogen for later use;

preparing a three-dimensional nanometer tip copper electrode:

(2) measuring 13-18ml of 0.02M CuSO₄And 2-4ml of 0.1M KH₂PO₄Stirring the solution to uniformly mix the solution;

(3) taking the mixed solution in the step (2) as an electrodeposition solution, taking an electropolished copper foil as a working electrode, a platinum sheet as a counter electrode and Ag/AgCl as a reference electrode, and depositing for 600-1000s at a potential of-0.6V to-0.8 Vvs. Ag/AgCl;

(4) placing the electrode prepared in the step (3) into a muffle furnace, calcining at the temperature of 250-300 ℃ for 0.25-1h, and raising the temperature at the rate of 2-3 ℃/min;

(5) and (3) carrying out in-situ reduction on the electrode obtained in the step (4) for 0.5-1h at a potential of-0.8V to-1.5 Vvs. RHE before carrying out electrocatalytic carbon dioxide reduction, thus obtaining the three-dimensional nanometer tip copper electrode subjected to oxidation-reduction treatment.

2. The method for preparing a three-dimensional nanotip copper electrode as claimed in claim 1, wherein: the preparation steps of the three-dimensional nanometer tip copper electrode are as follows:

(1) electro-polishing the copper foil: performing electropolishing for 1min under the action of a 4V constant potential by using phosphoric acid as electropolishing liquid, a graphite rod as a counter electrode and a copper foil as a working electrode; then washing the residual polishing solution by ultrapure water; immediately drying the electrode by using nitrogen for later use;

preparing a three-dimensional nanometer tip copper electrode:

(2) measuring 18ml of 0.02M CuSO₄And 2ml of 0.1M KH₂PO₄Stirring the solution to uniformly mix the solution;

(3) taking the mixed solution in the step (2) as an electrodeposition solution, taking an electropolished copper foil as a working electrode, a platinum sheet as a counter electrode and Ag/AgCl as a reference electrode, and depositing for 800s under the potential of-0.6 Vvs. Ag/AgCl;

(5) and (3) reducing the electrode obtained in the step (4) in situ for 1h at-1.5 Vvs. RHE potential before carrying out electrocatalytic carbon dioxide reduction to obtain the three-dimensional nanometer tip copper electrode subjected to oxidation-reduction treatment.

3. The method for preparing a three-dimensional nanotip copper electrode according to any one of claims 1 or 2, characterized in that: the purity of the phosphoric acid is 85%.

4. Use of the three-dimensional nanotip copper electrode of claim 1 for electrocatalytic carbon dioxide reduction.