In-situ generated amorphous carbon-coated noble metal catalyst electrode and its preparation method

Abstract

The present invention belongs to the technical field of catalysts, and specifically relates to an in-situ generated amorphous carbon-coated noble metal composite catalyst electrode and a preparation method thereof. Through simple ultrasonic thermal decomposition, the present invention directly grows the catalyst in-situ on the gas diffusion layer, integrating the synthesis and loading of the catalyst into one step, effectively reducing the preparation time and cost of the electrode; the effective active component in the prepared electrode is noble metal nanoparticles, and a special core-shell structure is generated between the noble metal element as the catalytic active site and the amorphous carbon carrier, which can enhance the interaction between the active component and the carrier, is beneficial to charge transfer and the adsorption of reactants, promotes the occurrence of reactions, and improves the catalyst activity. The preparation process of the present invention is simple, and the obtained cathode has the characteristics of high activity and has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and particularly relates to an in-situ generated amorphous carbon-coated noble metal composite catalyst electrode and a preparation method thereof. Background Art

[0002] The continuous development of industry has led to a continuous increase in the content of greenhouse gas carbon dioxide in the atmosphere. The continuous increase in global temperature has brought many environmental problems, seriously affecting human production and life. Among the many methods for treating carbon dioxide, electrochemical reduction is promising because it can not only efficiently utilize renewable energy, but also produce fuels for production and life. Therefore, electrocatalytic reduction of carbon dioxide is very promising to achieve "carbon neutrality".

[0003] The anodic reaction in the electrocatalytic carbon dioxide reduction electrolytic cell is an oxidation reaction, and the cathodic reaction is a carbon dioxide reduction reaction. Among them, there are many products of the cathodic carbon dioxide reduction reaction, mainly C1 products (carbon monoxide, formate, etc.), C2 products (acetic acid, ethanol, ethylene, etc.) and C3 products (n-propanol, etc.). The carbon dioxide reduction reaction involves complex multi-electron and proton transfer processes, including a series of complex catalytic reaction processes. The reaction pathway is affected by various factors such as the catalyst, the pH of the electrolyte, and cations. For electrocatalytic carbon dioxide reduction to be industrialized, it is required that the catalyst achieve the performance of a single product at a high current density. Among the many products, carbon monoxide and formate can relatively easily achieve a selectivity of more than 90%. However, in actual economic analysis, carbon monoxide is more economically valuable. Existing catalysts can easily achieve high carbon monoxide selectivity, but it is still difficult to maintain high selectivity at a high current density, which greatly limits the industrialization of carbon dioxide reduction electrolytic cells. Therefore, finding a high-performance, low-cost, and simple-to-synthesize carbon dioxide reduction catalyst electrode has become one of the urgent problems to be solved by those skilled in the art. Summary of the Invention

[0004] The purpose of the present invention is to provide an in-situ generated amorphous carbon-coated noble metal catalyst electrode and a preparation method thereof, which can improve the efficiency of electrocatalytic carbon dioxide reduction while reducing the electrode preparation time and production cost.

[0005] The preparation method of the in-situ generated amorphous carbon-coated noble metal catalyst electrode provided by the present invention specifically comprises the following steps:

[0006] (1) Add an amorphous carbon support, a noble metal precursor salt, and a binder to a mixed solution of water and an organic solvent, and use an ultrasonic instrument to ultrasonically disperse the amorphous carbon support to obtain a dispersion solution;

[0007] (2) Spray or drop the dispersion solution onto a gas diffusion layer placed on a hot stage, and evaporate the solvent;

[0008] (3) Place the above gas diffusion layer in a tube furnace for annealing, introduce a protective gas, and decompose the noble metal precursor salt into noble metal particles at a certain temperature. At the same time, the amorphous carbon support forms a spherical shell coating on the noble metal particles, thus obtaining a composite catalyst electrode.

[0009] Further, in step (1), the noble metal element is selected from one of Ag, Au, Pt, and Pd. The molar ratio of the amorphous carbon support to the noble metal element is 1:(0.1 - 0.33).

[0010] Further, in step (1), the noble metal precursor salt is one of noble metal halides, noble metal nitrates, noble metal sulfates, noble metal phosphates, noble metal acetates, or noble metal esters.

[0011] Further, in step (1), the amorphous carbon support is selected from one of conductive carbon black super P, conductive carbon black XC - 72, conductive carbon black acetylene black, and conductive carbon black BP2000.

[0012] Further, in step (1), the binder is selected from at least one of Nafion solution, polyvinylidene fluoride solution, and polytetrafluoroethylene solution.

[0013] Further, in the mixed solution in step (1), the organic solvent is at least one of methanol, ethanol, propylene glycol, acetone, N,N - dimethylformamide, ethyl acetate, dimethyl sulfoxide, and tetrahydrofuran, and the volume ratio of water to the organic solvent is 1:(0.1 - 5).

[0014] Further, in step (1), the ultrasonic temperature is 0°C to 45°C, and the ultrasonic time is 1 hour to 12 hours.

[0015] Further, in step (2), the gas diffusion layer material is selected from one of carbon paper, carbon cloth, carbon felt, and PTFE film; the thickness of the gas diffusion layer is 0.1 mm to 2.0 mm, and the loading amount of the noble metal catalyst in the formed gas diffusion electrode is 1 mg / cm 2 to 10 mg / cm 2 .

[0016] Further, in step (2), the temperature of the hot stage is 45°C to 90°C.

[0017] Further, in step (3), when the gas diffusion layer is annealed in a tube furnace, the introduced gas is one of air, nitrogen, argon, and a mixed gas of hydrogen and argon with different hydrogen volume concentrations.

[0018] Further, in step (3), the bulk diffusion layer is annealed in a tube furnace at a temperature of 200 °C to 550 °C, and the heating rate is controlled at 1 °C / min to 10 °C / min.

[0019] The in-situ generated amorphous carbon-coated noble metal catalyst electrode provided by the present invention directly grows the catalyst in-situ on the gas diffusion layer through simple ultrasonic thermal decomposition, integrating the synthesis and loading of the catalyst into one step, effectively reducing the preparation time and cost of the electrode. The effective active component in the prepared electrode is noble metal nanoparticles. The noble metal element serves as a catalytic active site, generating a special core-shell structure with the amorphous carbon carrier, enhancing the interaction between the active component and the carrier, facilitating charge transfer and the adsorption of reactants, promoting the occurrence of reactions, and enhancing the catalyst activity.

[0020] The present invention also provides a carbon dioxide reduction electrolytic cell test device, using the in-situ generated amorphous carbon-coated noble metal composite catalyst electrode as the cathode; the anode is one of a platinum sheet, a titanium felt, and a nickel foam; the cathode electrolyte and the anode electrolyte are any one of alkaline KOH, neutral solution KHCO3, and KCl. The diaphragm between the cathode and the anode is one of a cation exchange membrane, an anion exchange membrane, and a bipolar membrane.

[0021] Further, humid carbon dioxide gas is introduced into the cathode.

[0022] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0023] (1) The in-situ generated amorphous carbon-coated noble metal catalyst electrode provided by the present invention directly grows the catalyst in-situ on the gas diffusion layer through simple ultrasonic thermal decomposition, integrating the preparation of the amorphous carbon-coated noble metal composite catalyst and the loading of the catalyst on the gas diffusion layer into one process, effectively reducing the time and cost of electrode preparation;

[0024] (2) The in-situ generated amorphous carbon-coated noble metal catalyst electrode provided by the present invention is detected by experimental detection techniques such as XRD, HRTEM, and TPD. The amorphous carbon-coated noble metal forms a special core-shell structure, which is conducive to charge transfer and the adsorption of reactants, promoting the occurrence of reactions. This amorphous carbon-coated noble metal composite catalyst electrode has excellent carbon dioxide reduction performance. The preparation process of the present invention is simple, and the obtained cathode has the characteristics of high activity, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the synthesis scheme of the Ag / C composite catalyst in Example 1 of the present invention.

[0026] Figure 2This is the high-resolution transmission electron microscopy (HRTEM) image of the Ag / C composite catalyst in Example 1 of the present invention.

[0027] Figure 3 This is the X-ray diffraction (XRD) pattern of the Ag / C composite catalyst, commercial silver powder (Ag nano), pure silver powder (Ag), and hydrophobic carbon paper (Carbon paper, CP) in Example 1 of the present invention.

[0028] Figure 4 This is the electrochemical impedance spectroscopy of the Ag / C composite catalyst, commercial silver powder (Ag nano), and pure silver powder (Ag) in Example 1 of the present invention.

[0029] Figure 5 This is the carbon dioxide adsorption graph of the Ag / C composite catalyst, commercial silver powder (Ag nano), and pure silver powder (Ag) in Example 1 of the present invention.

[0030] Figure 6 This is the temperature-programmed desorption of carbon dioxide (TPD) graph of the Ag / C composite catalyst, commercial silver powder (Ag nano), and pure silver powder (Ag) in Example 1 of the present invention.

[0031] Figure 7 This is the in-situ infrared spectroscopy of the Ag / C composite catalyst, commercial silver powder (Ag nano), and pure silver powder (Ag) in Example 1 of the present invention.

[0032] Figure 8 This is the performance of the carbon dioxide reduction electrolytic cell device using the Ag / C composite catalyst, commercial silver powder (Ag nano), and pure silver powder (Ag) as the cathode catalyst in Example 1 of the present invention. The cathode electrolyte and the anode electrolyte are alkaline KOH. Moist carbon dioxide gas is introduced into the cathode. An anion exchange membrane is used as the diaphragm between the cathode and the anode. The anode is nickel foam, and the mercury / mercuric oxide electrode is used as the reference electrode.

[0033] Figure 9 This is the comparison of the Ag / C composite catalyst in Example 1 of the present invention.

[0034] Figure 10 This is the high-resolution transmission electron microscopy (HRTEM) image of the Ag / BP composite catalyst in Example 2 of the present invention.

[0035] Figure 11 This is the performance of the carbon dioxide reduction electrolytic cell device using the Ag / BP composite catalyst as the cathode catalyst in Example 2 of the present invention.

[0036] Figure 12 This is the high-resolution transmission electron microscopy (HRTEM) image of the Au / C composite catalyst in Example 3 of the present invention.

[0037] Figure 13 Performance of the carbon dioxide reduction electrolytic cell device with the Au / C composite catalyst as the cathode catalyst in Example 3 of the present invention. Detailed implementation mode

[0038] Currently, the catalysts for electrocatalytic reduction of carbon dioxide to carbon monoxide that have been successfully developed are mainly Au, Ag, and Zn. Among them, Ag has attracted wide attention because of its lower price compared to Au and better carbon monoxide selectivity compared to Zn. However, maintaining a carbon monoxide Faradaic efficiency of over 90% at a high current density (≥500 mA cm -2 ) required for industrialization is still a challenge for Ag-based catalysts.

[0039] The present invention will be further described below through examples in conjunction with the accompanying drawings.

[0040] Example 1, Preparation of Ag / C catalyst

[0041] A special structure composite catalyst of carbon-coated silver in-situ grown on a gas diffusion layer is synthesized by ultrasonic pyrolysis, which is beneficial to charge transfer and adsorption of reactants, and promotes the occurrence of reactions. The specific steps are as follows:

[0042] First, weigh commercial conductive carbon powder XC-72 (for example, 4 mg) and silver acetate (16.7 mg) and add them to a mixed solution of 2 ml of water and 1 ml of isopropanol. Add 5% Nafion binder (40 μl) dropwise to the solution, and use an ultrasonic instrument to ultrasonically disperse the commercial amorphous carbon powder evenly in the solution at 30 °C for 2 hours. Then, drop the ultrasonicated solution onto a hydrophobic carbon paper and dry it with a 90 °C hot stage. Put the dried carbon paper into a tube furnace and heat it to 250 °C at a rate of 1 °C / min under air conditions and hold for 2 hours.

[0043] In this example, the specific synthesis scheme is as Figure 1 shown. At the same time, with the help of currently common analysis means, such as HRTEM, XRD, TPD, etc., the structure of the amorphous carbon-coated noble metal composite catalyst Ag / C is characterized. Through HRTEM (as Figure 2 shown), it is found that the Ag / C catalyst forms a carbon-coated structure, the size of Ag particles is about several tens of nanometers, and the outer carbon layer is about 2 nm thick. Through XRD (as Figure 3 shown), it is found that the active component Ag in the Ag / C catalyst exists in the form of elemental Ag nanoparticles in the catalyst. Through the electrochemical impedance diagram (as Figure 4 shown), it can be seen that this special carbon-coated structure promotes charge transfer. Through the carbon dioxide adsorption diagram (as Figure 5 shown) and the carbon dioxide temperature-programmed desorption diagram (asFigure 6 As shown in the figure, it is found that the presence of the carbon shell improves the adsorption of carbon dioxide by the catalyst itself. Through the in-situ infrared spectrum (as Figure 7 shown), during the carbon dioxide reduction reaction, the carbon shell promotes the adsorption of CO2, thereby improving the reaction activity.

[0044] The present invention also provides a battery testing device. The battery testing device uses the above Ag / C composite catalyst as the electrode catalyst. The cathode electrolyte and the anode electrolyte are alkaline KOH. Moist carbon dioxide gas is introduced into the cathode. The diaphragm between the cathode and the anode uses an anion exchange membrane. The anode is nickel foam, and the mercury / mercuric oxide electrode is the reference electrode. Further, the battery testing device is an electrocatalytic carbon dioxide reduction electrolytic cell testing device. As Figure 8 shown, the Ag / C composite catalyst can achieve a carbon monoxide Faraday efficiency of more than 95% at 800 mA cm -2 . Its performance is much higher than that of commercial silver powder and pure silver powder. As Figure 9 shown, by coating a layer of carbon shell outside the silver nanoparticles, the adsorption of carbon dioxide is improved, thereby improving the catalyst activity. At a high current density such as 700 mA cm -2 , the carbon monoxide Faraday efficiency of the Ag / C catalyst is much higher than that of commercial silver powder and pure silver powder.

[0045] Example 2. Preparation of Ag / BP catalyst

[0046] The specific steps are as follows: First, weigh commercial conductive carbon black BP2000 (for example, 8 mg) and silver acetate (16.7 mg) and add them to a mixed solution of 2 ml of water and 1 ml of isopropanol. Add 5% Nafion binder (40 μl) dropwise to the solution. Use an ultrasonic instrument to ultrasonically disperse the commercial conductive carbon black BP2000 evenly in the solution at 40 °C for 4 hours. Then, drop the ultrasonicated solution onto the hydrophobic carbon paper and dry it with a 90 °C hot stage. Put the dried carbon paper into a tubular furnace and heat it to 350 °C at a rate of 1 °C / min under nitrogen conditions and hold for 2 hours.

[0047] In this example, through HRTEM (as Figure 10 shown) characterization, it is found that the Ag / BP catalyst forms a carbon-coated structure. The size of the Ag particles is about several tens of nanometers, and the outer carbon layer is about 2-5 nm thick. The battery testing device uses the above Ag / BP composite catalyst as the electrode catalyst. The cathode electrolyte and the anode electrolyte are alkaline KOH. Moist carbon dioxide gas is introduced into the cathode. The diaphragm between the cathode and the anode uses a cation exchange membrane. The anode is nickel foam, and the mercury / mercuric oxide electrode is the reference electrode. Further, the battery testing device is an electrocatalytic carbon dioxide reduction electrolytic cell testing device. As Figure 11As shown, the Ag / BP composite catalyst can achieve a carbon monoxide Faraday efficiency of over 90% at 500 mA cm -2 −2.

[0048] Example 3: Preparation of Au / C Catalyst

[0049] The specific steps are as follows: First, weigh commercial conductive carbon black XC-72 (e.g., 4 mg) and chloroauric acid (34 mg) and add them to a mixed solution of 2 ml of water and 2 ml of ethanol. Then, add 5% Nafion binder (40 μl) dropwise to the solution, and use an ultrasonic instrument to ultrasonically disperse the commercial conductive carbon black XC-72 evenly in the solution at 30 °C for 5 hours. Then, drop the ultrasonicated solution onto a hydrophobic carbon paper and dry it on a hot stage at 90 °C. Place the dried carbon paper in a tubular furnace and heat it to 350 °C at a rate of 1 °C / min under a mixed gas condition with a volume concentration ratio of hydrogen to argon of 1:9 and hold for 2 hours.

[0050] In this example, through HRTEM (as Figure 12 shown), it was found that the Au / C catalyst formed a carbon-coated structure, the Au particle size was about several tens of nanometers, and the outer carbon layer was about 2 nm thick. The battery test device uses the above Au / C composite catalyst as the electrode catalyst, the cathode electrolyte and the anode electrolyte are alkaline KOH, humidified carbon dioxide gas is introduced into the cathode, the diaphragm between the cathode and the anode uses an anion exchange membrane, the anode is nickel foam, and the mercury / mercuric oxide electrode is the reference electrode. Further, the battery test device is an electrocatalytic carbon dioxide reduction electrolytic cell test device. As Figure 13 shown, the Au / C composite catalyst can achieve a carbon monoxide Faraday efficiency of over 90% at 700 mA cm -2 −2.

Claims

1. A preparation method of an in-situ generated amorphous carbon-coated noble metal catalyst electrode, characterized in that, The specific steps are as follows: (1) Add the amorphous carbon carrier, the precursor salt of the noble metal, and the binder into a mixed solution of water and an organic solvent, and use an ultrasonic instrument to ultrasonically disperse the amorphous carbon carrier to obtain a dispersed solution; (2) Spray or drop the dispersed solution onto the gas diffusion layer placed on a hot stage, and evaporate the solvent; (3) Place the above-mentioned gas diffusion layer in a tube furnace for annealing. The annealing temperature is 200 °C to 550 °C, and a protective gas is introduced to decompose the noble metal precursor salt into noble metal particles. At the same time, the amorphous carbon carrier forms a spherical shell covering the noble metal particles, thus obtaining a composite catalyst electrode.

2. The preparation method according to claim 1, characterized in that, In step (1), the noble metal element is selected from one of Ag, Au, Pt, and Pd; the precursor salt of the noble metal is one of the halides of the noble metal, noble metal nitrates, noble metal sulfates, noble metal phosphates, noble metal acetates, or noble metal esters; control the molar ratio of the amorphous carbon carrier to the noble metal to be 1:(0.1 - 0.33).

3. The preparation method according to claim 1, characterized in that, In step (1), the amorphous carbon carrier is selected from one of conductive carbon black super P, conductive carbon black XC - 72, conductive carbon black acetylene black, and conductive carbon black BP2000.

4. The preparation method according to claim 1, characterized in that, In step (1), the binder is selected from at least one of Nafion solution, polyvinylidene fluoride solution, and polytetrafluoroethylene solution.

5. The preparation method according to claim 1, characterized in that, In the mixed solution, the organic solvent is at least one of methanol, ethanol, propylene glycol, acetone, N, N - dimethylformamide, ethyl acetate, dimethyl sulfoxide, and tetrahydrofuran, and the volume ratio of water to the organic solvent is 1:(0.1 - 5); The ultrasonic temperature is 0 °C to 45 °C, and the ultrasonic time is 1 hour to 12 hours.

6. The preparation method according to claim 1, characterized in that, The gas diffusion layer material described in step (2) is selected from one of carbon paper, carbon cloth, carbon felt, and PTFE film; the thickness of the gas diffusion layer is 0.1 mm to 2.0 mm, and the loading of the noble metal catalyst in the formed gas diffusion electrode is 1 mg / cm 2 to 10 mg / cm 2 ; The temperature of the hot stage is 45 °C to 90 °C.

7. The preparation method according to claim 1, characterized in that, In step (3), the gas diffusion layer is annealed in a tube furnace, and the gas introduced is one of air, nitrogen, argon, and a mixed gas of hydrogen and argon.

8. The preparation method according to claim 1, characterized in that, In step (3), the bulk diffusion layer is in a tube furnace, and the annealing temperature control heating rate is 1 °C / min to 10 °C / min.

9. An in-situ generated amorphous carbon-coated noble metal catalyst electrode obtained by the preparation method according to any one of claims 1-8; wherein, The catalyst grows in situ on the gas diffusion layer, and the noble metal element and the amorphous carbon carrier form a core - shell structure as the catalytic active site.

10. A carbon dioxide reduction electrolytic cell test device with the catalyst electrode described in claim 9 as the cathode; its anode is one of a platinum sheet, titanium felt, and nickel foam; the cathode electrolyte and the anode electrolyte are any one of KOH, KHCO3, and KCl; the diaphragm between the anode and the cathode is one of a cation - exchange membrane, an anion - exchange membrane, and a bipolar membrane.

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