Three-dimensional multi-stage needle tip array type Bi-CuO integral electrode as well as preparation method and application thereof

Abstract

The invention provides a three-dimensional multi-stage needle tip array type Bi-CuO integral electrode as well as a preparation method and application of the three-dimensional multi-stage needle tip array type Bi-CuO integral electrode. The integral electrode comprises foamy copper, a copper oxide needle tip array layer growing on the foamy copper and a bismuth nanosheet array layer uniformly covering the surface of a copper oxide needle tip. The integral electrode has a multi-stage self-supporting structure, so that catalyst aggregation or stacking is effectively avoided, and the specific surface area of exposed active sites is remarkably increased; and the electrode also has multiple heterogeneous interfaces, and shows excellent catalytic activity, selectivity and electrochemical window when being used as a working electrode for electrically reducing CO2 to prepare formate. The preparation method comprises the following steps: generating the copper hydroxide nanowire layer on foamy copper in situ by using a chemical oxidation method, performing annealing treatment in air to form the copper oxide needle tip array layer, and depositing the bismuth nanosheet array layer on the surface of the copper oxide needle tip by using a wet chemical method to obtain the integral electrode. The preparation method is novel and simple, the use of a binder is avoided, the operability is high, and the preparation method has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of carbon dioxide electrocatalysis technology, specifically relating to a three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode, its preparation method and application. Background Technology

[0002] Converting carbon dioxide into high-value-added industrial products using electricity not only significantly reduces the amount of carbon dioxide in the atmosphere but also achieves the conversion of electrical energy into chemical energy, realizing electrochemical energy storage. Although research on the electrochemical reduction of carbon dioxide has been ongoing for over thirty years, highly efficient catalysts for this process remain lacking. Bismuth (Bi), as one of the few metal catalysts capable of effectively electrocatalytically reducing CO2 to formate, has attracted widespread attention. While Bi-based catalysts have made significant progress in CO2 reduction, breakthroughs in selectivity and current density are still needed to overcome the bottlenecks in their industrial applications.

[0003] Patent application CN2023103585270 discloses a copper-bismuth bimetallic catalyst, its preparation method, and its application. The preparation method involves in-situ growth of copper hydroxide nanowires on a copper substrate, followed by a series of heat treatments, electrochemical reduction treatments, and electrodeposition to obtain the copper-bismuth bimetallic catalyst. The obtained copper-bismuth bimetallic catalyst includes a copper substrate and copper-bismuth nanowires grown on the copper substrate. The copper-bismuth nanowires consist of copper nanowires and a bismuth layer supported thereon, wherein the bismuth layer comprises several bismuth nanoparticles. The above preparation method requires first reducing the obtained copper oxide nanowires to metallic copper nanowires before further electrochemical deposition of the bismuth nanoparticle layer, making the process complex. Furthermore, the bismuth nanoparticles prepared by electrochemical deposition are relatively large (10–20 nm) and prone to aggregation, resulting in insufficient exposure of the catalyst's active sites and reduced catalytic performance. In addition, when this catalyst is used as an electrode for the electrocatalytic reduction of carbon dioxide, an applied potential of at least -1.1 V is required to achieve a formate selectivity of over 90%.

[0004] It is evident that existing electrodes for the electrocatalytic reduction of carbon dioxide still suffer from problems such as a limited number of surface catalytic active sites, low catalytic efficiency for carbon dioxide reduction over a wide potential window, and high overpotential. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode, its preparation method, and its application. This invention uses three-dimensional copper foam with excellent conductivity as a substrate. A primary structure of copper oxide needle-tip array layer is constructed in situ on the copper foam using a chemical oxidation-air annealing method. Subsequently, a secondary structure of bismuth nanosheet array layer is constructed on the surface of the copper oxide needle tips using a chemical deposition method, thereby fabricating a three-dimensional needle-tip array type Bi-CuO monolithic electrode with a multi-level micro / nano structure. The monolithic electrode of this invention has self-supporting, multi-level three-dimensional structural features, providing high specific surface area, abundant catalytic active sites, and multiple heterogeneous interfaces for the electroreduction of CO2, exhibiting excellent electrochemical activity, formic acid selectivity, and electrochemical window.

[0006] A three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode, wherein the monolithic electrode has a three-dimensional multi-level structure, including a copper foam substrate, a copper oxide needle-tip array layer grown in situ on the copper foam, and a bismuth nanosheet array layer uniformly covering the surface of the copper oxide needle tips.

[0007] In the aforementioned monolithic electrode, copper foam serves as the main conductive framework, copper oxide needle-tip array layer serves as the primary structure, and bismuth nanosheet array layer serves as the secondary structure.

[0008] Preferably, in the monolithic electrode, bismuth nanosheets are uniformly coated along the axial direction of the copper oxide needle tip. The bismuth nanosheets are approximately several nanometers thick and are cross-linked, exhibiting an open porous structure.

[0009] Preferably, in the integral electrode, the copper oxide needle tip has a length in the micrometer range and a diameter of approximately 200 nm.

[0010] A method for fabricating a three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode as described above includes the following steps:

[0011] S1. Using a chemical oxidation method, a copper hydroxide nanowire layer is grown in situ on the surface of a copper foam substrate to obtain copper foam loaded with copper hydroxide nanowires.

[0012] S2. Using air annealing, copper foam loaded with copper hydroxide nanowires is calcined in air and cooled to obtain copper foam loaded with copper oxide needle tip array.

[0013] S3. Using chemical deposition, a bismuth nanosheet array is grown on the surface of copper oxide needle tip to obtain the three-dimensional multi-level needle tip array type Bi-CuO monolithic electrode.

[0014] As a preferred embodiment, the specific process of step S1 is as follows:

[0015] The copper foam substrate was immersed in a sodium hydroxide solution containing ammonium persulfate, allowed to stand, and then removed. It was rinsed several times with deionized water and dried with an argon stream to obtain copper foam loaded with copper hydroxide nanowires.

[0016] The sodium hydroxide solution containing ammonium persulfate is prepared by the following method:

[0017] Sodium hydroxide is dissolved in deionized water to obtain a sodium hydroxide solution, then ammonium persulfate is added and stirred until fully dissolved and mixed. The stirring time is 5–15 minutes, preferably 10 minutes.

[0018] As a further preferred option, the foamed copper undergoes the following pretreatment before being immersed in a sodium hydroxide solution containing ammonium persulfate:

[0019] The copper foam was immersed in acetone, then sonicated, followed by sonication in hydrochloric acid solution. Finally, it was rinsed several times with deionized water and dried with an argon stream. The purpose of the pretreatment was to remove oxides, oil, and other impurities from the surface of the copper foam.

[0020] Specifically, the ultrasonic time for copper foam in acetone was 10 min; the ultrasonic time in hydrochloric acid solution was 10 min; and the concentration of hydrochloric acid solution was 1 mol / L.

[0021] As a further preferred option, in the sodium hydroxide solution, the mass-to-area ratio of ammonium persulfate to copper foam is 0.4–1 g / cm³. 2 A further preferred value is 0.5–0.6 g / cm³. 2 A further preferred value is 0.57 g / cm³. 2 .

[0022] As a further preferred embodiment, the standing time of the copper foam in the sodium hydroxide solution containing ammonium persulfate is 10–40 min. More preferably, it is 15–25 min. Even more preferably, it is 20 min.

[0023] As a further preferred embodiment, the concentration of the sodium hydroxide solution is 1–5 mol / L. Even more preferably, it is 2–3 mol / L. Even more preferably, it is 2.5 mol / L.

[0024] As a further preferred embodiment, the concentration of ammonium persulfate in the sodium hydroxide solution is 20–35 g / L. Even more preferably, it is 25–30 g / L. Even more preferably, it is 28.6 g / L.

[0025] Preferably, in step S2, the copper foam loaded with copper hydroxide nanowires is heated to 100-200°C in air at a rate of 2-10°C / min and calcined for 0.5-4 hours. After cooling, copper foam loaded with copper oxide needle tip array is obtained.

[0026] As a further preferred option, the heating rate is 4–6 °C / min. Even more preferred is 5 °C / min.

[0027] As a further preferred option, the calcination temperature is 140–160℃, and the calcination time is 1–3 hours. Even more preferred is that the calcination temperature is 150℃, and the calcination time is 2 hours.

[0028] As a preferred embodiment, the specific process of step S3 is as follows:

[0029] The copper foam loaded with copper oxide needle array was immersed in a dimethyl sulfoxide solution containing bismuth chloride, allowed to stand and deposit, and then removed, rinsed several times with deionized water and dried with argon gas to obtain the three-dimensional multi-level needle array type Bi-CuO monolithic electrode.

[0030] The dimethyl sulfoxide solution containing bismuth chloride is prepared by dissolving bismuth chloride in dimethyl sulfoxide. In the above steps, the dimethyl sulfoxide solution containing bismuth chloride is used as the deposition solution.

[0031] In the above steps, a wet chemical method is used, utilizing the reducing properties of dimethyl sulfoxide to directly react Bi with dimethyl sulfoxide. 3+ Restored to Bi 0 Ultimately, it is deposited on the surface of the CuO needle tip and forms an array of bismuth nanosheets.

[0032] As a further preferred embodiment, the concentration of bismuth chloride in the dimethyl sulfoxide solution is 4–8 g / L. Even more preferably, it is 6–7 g / L. Even more preferably, it is 6.32 g / L.

[0033] As a further preferred option, the mass-to-area ratio of bismuth chloride to copper foam in the dimethyl sulfoxide solution is 0.05–0.3 g / cm³. 2 A further preferred value is 0.1–0.15 g / cm³. 2 A further preferred value is 0.105 g / cm³. 2 .

[0034] As a further preferred embodiment, the standing deposition time of the copper foam supported on the copper oxide needle array in a dimethyl sulfoxide solution containing bismuth chloride is 12–48 h. More preferably, it is 20–40 h. Even more preferably, it is 30–40 h. As a further preferred embodiment, the standing deposition time is 36 h.

[0035] As a preferred embodiment, a method for fabricating a three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode specifically includes the following steps:

[0036] A. In-situ growth of copper hydroxide nanowire layers on the surface of a copper foam substrate via chemical oxidation method, specifically:

[0037] A1. Preparation of reaction solution: First, dissolve 3g of sodium hydroxide in 30mL of deionized water, then add 0.86g of ammonium persulfate and stir for 10min to fully dissolve it to obtain the reaction solution;

[0038] A2. Growth of copper hydroxide nanowires on the surface of copper foam substrate: The copper foam substrate is immersed in the reaction solution and left to stand for 20 minutes. After being taken out, it is rinsed several times with deionized water and dried under an argon flow to obtain copper foam loaded with copper hydroxide nanowires. The blue substance generated on the surface of the copper foam substrate is the copper hydroxide nanowire.

[0039] A3. Preparation of copper oxide needle tip array layer: The copper foam loaded with copper hydroxide nanowires obtained in step A2 is placed in a ceramic boat and calcined in air at a rate of 5℃ / min to 150℃ for 2h. After cooling, copper foam loaded with copper oxide needle tip array is obtained.

[0040] B. A bismuth nanosheet array layer is grown on a copper oxide needle tip using a chemical deposition method, specifically as follows:

[0041] B1. Preparation of deposition solution: Dissolve 0.158g of bismuth chloride in 25mL of dimethyl sulfoxide and stir to obtain the deposition solution;

[0042] B2. Deposition of the bismuth nanosheet array layer: Immerse the copper foam containing the copper oxide needle array prepared in step A3 into a deposition solution (containing Bi). 3+ In the process of static deposition, the material is rinsed several times with deionized water and dried under an argon flow to obtain the three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode.

[0043] The present invention describes a preparation method that uses three-dimensional copper foam as a substrate to synthesize copper hydroxide nanowires via chemical oxidation, followed by air annealing to obtain a three-dimensional needle-tip array type monolithic copper oxide electrode. Finally, a three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode is obtained using a wet chemical method (chemical deposition) with bismuth chloride as the Bi source, and is used as a catalytic electrode for the electrochemical reduction of carbon dioxide to formate. The monolithic electrode prepared by this method has a high specific surface area, effectively improving the shortcomings of traditional spray-coated electrodes, such as few catalytic active sites and easy catalyst aggregation or stacking. Furthermore, this electrode exhibits multiple interfacial electronic coupling effects, significantly improving the efficient conversion of carbon dioxide to formate and reducing the overpotential for formate formation. Moreover, this preparation method is novel and simple, avoids the use of binders, is highly operable, and has good application prospects.

[0044] Application of a three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode as described above in the electrochemical reduction of carbon dioxide.

[0045] Preferably, in the electrochemical reduction of carbon dioxide, the electrolytic cell is an H-type electrolytic cell; the reference electrode is a silver / silver chloride (Ag / AgCl) electrode, the counter electrode is a titanium mesh loaded with iridium oxide, the concentration of the reference solution KCl is 3-4 mol / L, and the electrolyte is a potassium bicarbonate solution with a concentration of 0.1-1 mol / L.

[0046] As a further preferred option, the concentration of the reference solution KCl is 3.5 mol / L.

[0047] As a further preferred option, the concentration of the potassium bicarbonate solution in the electrolyte is 0.5 mol / L.

[0048] The present invention discloses a three-dimensional multi-level tip array type Bi-CuO monolithic electrode, comprising a foamed copper conductive substrate, a primary structure of copper oxide tip array grown on the foamed copper substrate, and a secondary structure of bismuth nanosheet array uniformly covering the surface of the copper oxide tips. The preparation method of this monolithic electrode includes: synthesizing copper hydroxide nanowires on the foamed copper substrate via chemical oxidation, followed by annealing in air to obtain the copper oxide tip array, and finally constructing the bismuth nanosheet array in situ on the surface of the copper oxide tips using a wet chemical method, ultimately forming a three-dimensional multi-level tip array type Bi-CuO monolithic electrode, which is used as the working electrode for electrocatalytic carbon dioxide reduction. The monolithic electrode of the present invention, on the one hand, possesses a multi-level self-supporting structure, effectively avoiding catalyst aggregation or stacking, significantly increasing the specific surface area of ​​exposed active sites, and improving the shortcomings of traditional spray-coated electrodes with few catalytic active sites; on the other hand, it has a metal-oxide heterojunction interface, exhibiting excellent catalytic activity, selectivity, and electrochemical window for the electroreduction of CO2 to formate. Moreover, the preparation method is novel and simple, avoids the use of binders, is highly operable, and has good application prospects.

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0050] (1) The three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode of the present invention, using copper foam with excellent conductivity as a substrate, significantly improves the current density for electroreduction of carbon dioxide compared with traditional spray-coated electrocatalysts (substrate is hydrophobic carbon paper (model: H60)). At the same time, the monolithic electrode of the present invention contains a dual component (CuO / Bi), which utilizes the synergistic effect of the dual components to enrich the selectivity of electrochemical reduction of carbon dioxide and further improve the activity of electrochemical reduction of carbon dioxide.

[0051] (2) The three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode of the present invention uses foam copper with a three-dimensional porous structure as a conductive substrate, copper oxide needle-tip array layer as a primary structure, and metal bismuth nanosheet array layer uniformly coated on the surface of copper oxide needle tip as a secondary structure, so that the monolithic electrode forms a special multi-level sub-micro-nano structure, which significantly expands the working area participating in the electrochemical reduction of carbon dioxide, thereby increasing the catalytic reaction active sites.

[0052] (3) The preparation method of the integral electrode of the present invention is simple to operate, avoids the use of binders, is highly operable, and has good application prospects. Attached Figure Description

[0053] Figure 1 The X-ray diffraction (XRD) patterns of CF, CuO NWs / CF, and 36h-Bi-CuO in Example 1 are shown.

[0054] Figure 2 The image shown is a scanning electron microscope (SEM) image of CF in Example 1.

[0055] Figure 3 This is a scanning electron microscope image of the copper oxide needle tip array layer in Example 1;

[0056] Figure 4 The image shown is a scanning electron microscope (SEM) image (low magnification) of 36h-Bi-CuO in Example 1.

[0057] Figure 5 The image shown is a scanning electron microscope (SEM) image (high magnification) of 36h-Bi-CuO in Example 1.

[0058] Figure 6 The graph shows the electrochemical reduction performance of carbon dioxide by 36h-Bi-CuO in Example 1.

[0059] Figure 7 This is a scanning electron microscope image of 12h-Bi-CuO in Example 2;

[0060] Figure 8 The graph shows the electrochemical reduction performance of carbon dioxide by 12h-Bi-CuO in Example 2.

[0061] Figure 9 This is a scanning electron microscope image of 24h-Bi-CuO in Example 3;

[0062] Figure 10 The graph shows the electrochemical reduction performance of carbon dioxide by 24h-Bi-CuO in Example 3.

[0063] Figure 11 The graph shows the electrochemical reduction performance of carbon dioxide in CuO NWs / CF in Comparative Example 1.

[0064] Figure 12 Scanning electron microscope image of commercial bismuth powder in Comparative Example 2;

[0065] Figure 13 The graph shows the electrochemical carbon dioxide reduction performance of the working electrode made from commercial bismuth powder in Comparative Example 2.

[0066] Figure 14 The graph shows a comparison of the Faraday efficiency of the formate at various voltages for the monolithic electrodes in Examples 1-3 and the working electrode made from commercial bismuth powder in Comparative Example 2.

[0067] Figure 15 The graph shows a comparison of the current density of the monolithic electrode in Examples 1-3 and the working electrode made from commercial bismuth powder in Comparative Example 2 at various voltages. Detailed Implementation

[0068] The present invention will be further described in detail below through specific embodiments.

[0069] Example 1

[0070] A method for fabricating a three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode specifically includes the following steps:

[0071] (1) Pretreatment of the foamed copper conductive skeleton: with an area of ​​1.5 cm² 2 Using copper foam as a substrate, it was immersed in acetone and sonicated for 10 min; then it was transferred to a 1 mol / L hydrochloric acid solution and sonicated for 10 min; then it was rinsed several times with deionized water and dried under an argon flow to obtain pretreated copper foam (CF).

[0072] (2) Preparation of copper oxide needle tip array layer: Dissolve 3g sodium hydroxide in 30mL deionized water, then add 0.86g ammonium persulfate, stir for 10min to obtain reaction solution U; immerse CF in reaction solution U, let stand for 20min, take it out, rinse several times with deionized water, and dry under argon flow to obtain copper foam loaded with copper hydroxide nanowires.

[0073] Copper foam loaded with copper hydroxide nanowires was placed in a ceramic boat and calcined in air at a rate of 5 °C / min to 150 °C for 2 h. After cooling, copper foam loaded with copper oxide needle array (CuO NWs / CF) was obtained.

[0074] (3) Deposition of bismuth nanosheet array layer: 0.158 g of bismuth chloride was dissolved in 25 mL of dimethyl sulfoxide and stirred to obtain deposition solution V; CuO NWs / CF was immersed in deposition solution V, left to stand for 36 h, then taken out, rinsed several times with deionized water, and dried under argon flow to obtain a three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode, denoted as 36h-Bi-CuO.

[0075] Product structure characterization:

[0076] X-ray diffraction (XRD) analysis was performed on CF, CuO NWs / CF, and 36h-Bi-CuO in the above embodiments, as follows: Figure 1 As shown. Figure 1 The XRD patterns of CF, CuO NWs / CF, and 36h-Bi-CuO all show three typical diffraction peaks at 43.30°, 50.43°, and 74.13°, corresponding to the Cu(111), (200), and (220) crystal planes of CF, respectively. The XRD patterns of CuO NWs / CF and 36h-Bi-CuO show two diffraction peaks at 35.54° and 38.71°, corresponding to the CuO(11-1) and (111) crystal planes of the copper oxide needle array layer, respectively. After the deposition of the bismuth nanosheet array layer (36h-Bi-CuO), three diffraction peaks appear at 27.17°, 37.95°, and 39.62°, corresponding to the Bi(012), (104), and (110) crystal planes, respectively. The intensity of the diffraction peaks corresponding to copper oxide decreases accordingly, indicating that the bismuth nanosheet array layer is successfully attached (covered) on the surface of the copper oxide needle tip.

[0077] The SEM images of CF, CuO NWs / CF, and 36h-Bi-CuO in the above embodiments are shown below. Figures 2-5 As shown. (Through) Figure 2 The three-dimensional porous structure of copper foam can be observed using a scanning electron microscope (SEM) on a copper foam substrate; Figure 3 The SEM images of CuONWs / CF show that the CuO NWs grown by chemical oxidation are arranged in a neat and dense needle-like pattern on the surface of the copper foam substrate (CF). The copper oxide needles are micrometers long and approximately 200 nanometers in diameter. Figure 4 and 5 The SEM image of 36h-Bi-CuO shows that, after chemical deposition, bismuth nanosheets with a thickness of several nanometers are uniformly and neatly distributed along the axial direction of the copper oxide needle tip structure, forming a three-dimensional multi-level needle tip array type Bi-CuO monolithic electrode.

[0078] Performance testing:

[0079] The electrocatalytic performance of the 36h-Bi-CuO electrode was tested using a three-electrode system for carbon dioxide electrolysis. The prepared electrode (36h-Bi-CuO) was used as the working electrode; the counter electrode was a titanium mesh supported on iridium oxide; and the reference electrode was a silver / silver chloride (Ag / AgCl) electrode. The concentration of the reference solution KCl was 3.5 mol / L. The cathode and anode chambers were separated by a cation exchange membrane (Nafion 117), and the electrolyte was a 0.5 mol / L KHCO3 solution. During the 30-minute constant-pressure test, CO2 was continuously introduced at a flow rate of 10 mL / min to ensure CO2 saturation in the system. The obtained gaseous products were detected by gas chromatography (GC), and the liquid products were analyzed by... 1 H-NMR ( 1 H-NMR) detection.

[0080] Figure 6 The electrocatalytic performance of 36h-Bi-CuO on carbon dioxide was demonstrated in the voltage range of -0.8 to -1.4 V (vs. RHE). High product selectivity was observed, with HCOO being the most abundant component. - The formate is the main component, with only small amounts of H2 and CO. Among them, the formate has the highest Faraday efficiency at a potential of -0.8V (vs. RHE), reaching 98.4%; the Faraday efficiency of hydrogen is only 1.4%, and that of CO is 0.4%.

[0081] Example 2

[0082] A method for preparing a three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode, which differs from Example 1 in that the standing time for depositing the bismuth nanosheet array layer in step (3) is replaced with 12 hours, specifically including the following steps:

[0083] (1) Pretreatment of the foamed copper conductive skeleton: with an area of ​​1.5 cm² 2 Using copper foam as a substrate, it was immersed in acetone and sonicated for 10 min; then it was transferred to a 1 mol / L hydrochloric acid solution and sonicated for 10 min; then it was rinsed several times with deionized water and dried under an argon flow to obtain pretreated copper foam (CF).

[0084] (2) Preparation of copper oxide needle tip array layer: Dissolve 3g sodium hydroxide in 30mL deionized water, then add 0.86g ammonium persulfate, stir for 10min to obtain reaction solution U; immerse CF in reaction solution U, let stand for 20min and then take it out, rinse several times with deionized water, and dry under argon flow to obtain foam copper loaded with copper hydroxide nanowires.

[0085] Copper foam loaded with copper hydroxide nanowires was placed in a ceramic boat and calcined in air at a rate of 5 °C / min to 150 °C for 2 h. After cooling, copper foam loaded with copper oxide needle array (CuO NWs / CF) was obtained.

[0086] (3) Deposition of bismuth nanosheet array layer: 0.158 g of bismuth chloride was dissolved in 25 mL of dimethyl sulfoxide and stirred to obtain deposition solution V;

[0087] The CuO NWs / CF was immersed in deposition solution V, left to stand for 12 hours, then removed, rinsed several times with deionized water, and dried under an argon flow to obtain a Bi-CuO monolithic electrode, denoted as 12h-Bi-CuO.

[0088] The scanning electron microscope (SEM) image of the 12h-Bi-CuO prepared above is shown below. Figure 7 As shown. By Figure 7 It can be seen that after copper oxide nanowires are left to stand in deposition solution V for 12 hours, their originally relatively smooth surface is etched by dimethyl sulfoxide and a small amount of bismuth nanoparticles are initially deposited.

[0089] Performance testing:

[0090] The electrocatalytic performance of the 12h-Bi-CuO electrode was tested using a three-electrode system for carbon dioxide electrolysis. The prepared electrode (12h-Bi-CuO) was used as the working electrode; the counter electrode was a titanium mesh supported on iridium oxide; and the reference electrode was a silver / silver chloride (Ag / AgCl) electrode. The concentration of the reference solution KCl was 3.5 mol / L. The cathode and anode chambers were separated by a cation exchange membrane (Nafion 117), and the electrolyte was a 0.5 mol / L KHCO3 solution. During the 30-minute constant-pressure test, CO2 was continuously introduced at a flow rate of 10 mL / min to ensure CO2 saturation in the system. The obtained gaseous products were detected by gas chromatography (GC), and the liquid products were analyzed by... 1 H-NMR ( 1 H-NMR) detection.

[0091] Figure 8 The electrocatalytic performance of 12h-Bi-CuO on carbon dioxide was demonstrated in the voltage range of -0.8 to -1.4 V (vs. RHE). High product selectivity was observed, with HCOO being the most abundant component. - The formate was the main component, but the products H2 and CO increased relative to those using 36h-Bi-CuO as the working electrode. Among them, the formate had the highest Faradaic efficiency of 77.9% at a potential of -1.2V (vs. RHE); the Faradaic efficiency of hydrogen was 9.4%, and that of CO was 15.4%.

[0092] Example 3

[0093] A method for preparing a three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode, which differs from Example 1 in that the standing time for depositing the bismuth nanoarray layer in step (3) is replaced with 24 hours, specifically including the following steps:

[0094] (1) Pretreatment of the foamed copper conductive skeleton: with an area of ​​1.5 cm² 2 Using copper foam as a substrate, it was immersed in acetone and sonicated for 10 min; then it was transferred to a 1 mol / L hydrochloric acid solution and sonicated for 10 min; then it was rinsed several times with deionized water and dried under an argon flow to obtain pretreated copper foam (CF).

[0095] (2) Preparation of copper oxide needle tip array layer: Dissolve 3g sodium hydroxide in 30mL deionized water, then add 0.86g ammonium persulfate, stir for 10min to obtain reaction solution U; immerse CF in reaction solution U, let stand for 20min and then take it out, rinse several times with deionized water, and dry under argon flow to obtain foam copper loaded with copper hydroxide nanowires.

[0096] Copper foam loaded with copper hydroxide nanowires was placed in a ceramic boat and calcined in air at a rate of 5 °C / min to 150 °C for 2 h. After cooling, copper foam loaded with copper oxide needle array (CuO NWs / CF) was obtained.

[0097] (3) Deposition of bismuth nanosheet array layer: 0.158 g of bismuth chloride was dissolved in 25 mL of dimethyl sulfoxide and stirred to obtain deposition solution V;

[0098] CuO NWs / CF was immersed in deposition solution V, left to stand for 24 hours, then removed, rinsed several times with deionized water, and dried under an argon flow to obtain a three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode, denoted as 24h-Bi-CuO.

[0099] The scanning electron microscope (SEM) image of the 24h-Bi-CuO prepared above is shown below. Figure 9 As shown. Comparison Figure 7 and 9 It can be seen that, Figure 9 The diameter of the 24h-Bi-CuO nanowires is compared to Figure 7 There has been an increase. Figure 9 In the image, Bi nanosheets are clearly visible deposited on the CuO needle tip surface, arranged neatly, but they have not yet shown outward extension. However, in the SEM image of 36h-Bi-CuO, the Bi nanosheets are fully grown and extend outward (e.g., ...). Figure 4 , 5 As shown), the density is further increased, with 36h-Bi-CuO nanowires (as shown). Figure 5 ) diameter compared Figure 9 And it has increased further.

[0100] Performance testing:

[0101] The electrocatalytic performance of the above-mentioned 24h-Bi-CuO electrode was tested using a three-electrode system for carbon dioxide electrolysis. The prepared electrode (24h-Bi-CuO) was used as the working electrode; the counter electrode was a titanium mesh supported on iridium oxide; and the reference electrode was a silver / silver chloride (Ag / AgCl) electrode. The concentration of the reference solution KCl was 3.5 mol / L. The cathode and anode chambers were separated by a cation exchange membrane (Nafion 117), and the electrolyte was a 0.5 mol / L KHCO3 solution. During the 30-minute constant-pressure test, CO2 was continuously introduced at a flow rate of 10 mL / min to ensure CO2 saturation in the system. The obtained gaseous products were detected by gas chromatography (GC), and the liquid products were analyzed by... 1 H-NMR ( 1 H-NMR) detection.

[0102] Figure 10 The electrocatalytic performance of 24h-Bi-CuO on carbon dioxide was demonstrated in the voltage range of -0.8 to -1.4 V (vs. RHE). High product selectivity was observed, with HCOO being the most abundant component. - (Formate) is the main component. Among them, the formate has the highest Faraday efficiency at a potential of -1.4V (vs. RHE), reaching 95.1%; the Faraday efficiency of hydrogen is only 5.3%, and the Faraday efficiency of CO is 0.3%.

[0103] Comparative Example 1

[0104] A monolithic CuO electrode (CuO NWs / CF) was prepared according to the preparation method in Example 1, except that the deposition step of the bismuth nanoarray layer in step (3) was omitted. The performance of the CuO NWs / CF was analyzed using the performance testing process in Example 1, and the resulting product distribution is as follows. Figure 11 As shown. By Figure 11 It can be seen that the product selectivity of the CuO monolithic electrode (CuO NWs / CF) is relatively poor, with H2 as the main component and only a small amount of HCOO. - (Formate) and some C2 products and other byproducts.

[0105] Comparative Example 2

[0106] The sample selected in this comparative example is commercial bismuth powder, and its scanning electron microscope (SEM) results are as follows: Figure 12 As shown. By Figure 12It can be seen that the morphology of commercial bismuth powder consists of large, smooth particles with a diameter of approximately 1 μm. The performance of the commercial bismuth powder was analyzed using the performance testing procedure described in Example 1. Before the electrochemical testing (performance testing), a certain amount of commercial bismuth powder was mixed evenly with isopropanol and Nafion solution, and then sprayed onto carbon paper as the working electrode, with a loading of 1 mg / cm³. 2 The distribution of the obtained products is as follows Figure 13 As shown. By Figure 12 It can be seen that at -1.0V (vs. RHE), the Faraday efficiency of formate reaches the highest level of 84.7%; the Faraday efficiency of hydrogen is approximately 8.9%.

[0107] Performance comparison:

[0108] The comparison of the Faradaic efficiency and current density of the formate at different voltages for the monolithic electrodes (36h-Bi-CuO, 12h-Bi-CuO, 24h-Bi-CuO) prepared in Examples 1-3 and the working electrode prepared from commercial bismuth powder in Comparative Example 2 (shown as commercial bismuth powder in the figure) is shown in the figure. Figure 14 and 15 .Depend on Figure 14 , Figure 15 It can be seen that the 36h-Bi-CuO prepared in Example 1 exhibits the highest Faradaic efficiency of 98.4% formate at a potential of -0.8V (vs. RHE). Under other potential conditions, the Faradaic efficiency of formate is above 90%, which is superior to the Faradaic efficiency of formate in the monolithic electrodes of 12h-Bi-CuO and 24h-Bi-CuO in Examples 2 and 3, and the working electrode prepared from commercial bismuth powder in Comparative Example 2. This indicates that the 36h-Bi-CuO prepared in Example 1 possesses excellent catalytic selectivity, and at a potential of -1.2V (vs. RHE), the maximum current density of formate on 36h-Bi-CuO is -106.17 mA / cm². 2 This is significantly greater than that of commercial bismuth powder (-15.18 mA / cm). 2 This demonstrates that the three-dimensional needle-tip array type Bi-CuO monolithic electrode (36h-Bi-CuO) prepared in Example 1 has a multi-level self-supporting structure that can effectively prevent catalyst aggregation or stacking. By increasing the specific surface area of ​​exposed active sites, it improves the deficiency of the traditional spray-coated electrode surface having few catalytic active sites, and exhibits excellent catalytic activity, selectivity and electrochemical window for the electroreduction of CO2 to formate.

Claims

1. A three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode, characterized in that, The monolithic electrode has a three-dimensional multi-level structure, including a copper foam substrate, an array of copper oxide tips grown in situ on the copper foam, and an array of bismuth nanosheets uniformly covering the surface of the copper oxide tips.

2. The three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode according to claim 1, characterized in that, In the monolithic electrode, bismuth nanosheets are uniformly coated along the axial direction of the copper oxide needle tip.

3. A method for fabricating a three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode as described in claim 1 or 2, characterized in that, Includes the following steps: S1. Using a chemical oxidation method, a copper hydroxide nanowire layer is grown in situ on the surface of a copper foam substrate to obtain copper foam loaded with copper hydroxide nanowires. S2. Using air annealing, copper foam loaded with copper hydroxide nanowires is calcined in air and cooled to obtain copper foam loaded with copper oxide needle tip array. S3. Using chemical deposition, a bismuth nanosheet array is grown on the surface of copper oxide needle tip to obtain the three-dimensional multi-level needle tip array type Bi-CuO monolithic electrode.

4. The method for fabricating a three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode according to claim 3, characterized in that, The specific process of step S1 is as follows: The copper foam substrate was immersed in a sodium hydroxide solution containing ammonium persulfate, allowed to stand, and then removed. It was rinsed several times with deionized water and dried with an argon stream to obtain copper foam loaded with copper hydroxide nanowires.

5. The method for fabricating a three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode according to claim 4, characterized in that, The concentration of the sodium hydroxide solution is 1–5 mol / L; In sodium hydroxide solution, the concentration of ammonium persulfate is 20–35 g / L.

6. The method for fabricating a three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode according to claim 3, characterized in that, In step S2, the copper foam loaded with copper hydroxide nanowires is heated to 100-200°C in air at a rate of 2-10°C / min and calcined for 0.5-4 hours. After cooling, copper foam loaded with copper oxide needle tip array is obtained.

7. The method for fabricating a three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode according to claim 3, characterized in that, The specific process of step S3 is as follows: The copper foam loaded with copper oxide needle array was immersed in a dimethyl sulfoxide solution containing bismuth chloride, allowed to stand and deposit, and then removed, rinsed several times with deionized water and dried with argon gas to obtain the three-dimensional multi-level needle array type Bi-CuO monolithic electrode.

8. The method for fabricating a three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode according to claim 7, characterized in that, The static deposition time of copper foam loaded with copper oxide needle array in dimethyl sulfoxide solution containing bismuth chloride is 12–48 h.

9. The application of a three-dimensional multi-level needle-tip array type Bi-CuO monolithic electrode as described in claim 1 or 2 in the electrochemical reduction of carbon dioxide.

10. The application according to claim 9, characterized in that, In the electrochemical reduction of carbon dioxide, the electrolytic cell is an H-type electrolytic cell; the reference electrode is a silver / silver chloride electrode, the counter electrode is a titanium mesh loaded with iridium oxide, the concentration of the reference solution KCl is 3-4 mol / L, and the electrolyte is a potassium bicarbonate solution with a concentration of 0.1-1.0 mol / L.

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