KR101791658B1 - A method for preparing electrocatalyst for carbon dioxide selective reduction - Google Patents
A method for preparing electrocatalyst for carbon dioxide selective reduction Download PDFInfo
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- KR101791658B1 KR101791658B1 KR1020150096971A KR20150096971A KR101791658B1 KR 101791658 B1 KR101791658 B1 KR 101791658B1 KR 1020150096971 A KR1020150096971 A KR 1020150096971A KR 20150096971 A KR20150096971 A KR 20150096971A KR 101791658 B1 KR101791658 B1 KR 101791658B1
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- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/0009—Use of binding agents; Moulding; Pressing; Powdering; Granulating; Addition of materials ameliorating the mechanical properties of the product catalyst
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- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
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- B01J2231/60—Reduction reactions, e.g. hydrogenation
- B01J2231/62—Reductions in general of inorganic substrates, e.g. formal hydrogenation, e.g. of N2
- B01J2231/625—Reductions in general of inorganic substrates, e.g. formal hydrogenation, e.g. of N2 of CO2
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Abstract
The present invention relates to a method for producing an electrocatalyst for the selective reduction of carbon dioxide, comprising the steps of: (A) dissolving a metal precursor in an organic solvent and then subjecting the metal precursor to a first heat treatment to prepare a metal precursor solution; (B) dispersing the carbon support in a mixed solution of a fixing agent and an organic solvent by ultrasonic to prepare a carbon support solution; (C) adding the carbon support solution to the metal precursor solution and performing the second heat treatment for 1 to 3 hours, thereby improving the ferrode efficiency and lowering the over-potential in the selective reduction from CO 2 to CO.
Description
The present invention relates to a process for the preparation of an electrocatalyst which exhibits enhanced ferroefficiency and low overvoltage during the selective reduction of CO 2 to CO in an aqueous solution.
The atmospheric concentration of CO 2 , a greenhouse gas, continues to increase due to the continued use of traditional fossil fuels and has adversely affected the global climate. Global dependency and CO have to be emphasized more and more development of renewable energy sources in an effort to mitigate the emissions, more proactive response as a transition to a possible carbon forms CO 2 re-use of fossil fuel, that is sustainable carbon recycling system Lt; / RTI >
Of the various methods for CO 2 conversion, electrochemical CO 2 reduction in aqueous solution is environmentally clean and can be combined with renewable energy sources such as solar and wind energy to store in the form of chemical energy. However, it is difficult to achieve high efficiency because of the large overvoltage required for electrochemical CO 2 reduction, difficulty in controlling the selectivity between various reduction products, and hydrogen production reaction in aqueous solution. Therefore, development of new catalysts with high efficiency and selectivity is required.
Compared to good hydrogen-producing electrocatalysts such as platinum, gold, silver, and copper are promising CO 2 reduction electrocatalysts because CO is relatively weakly bonded at its surface. In particular, Au and Ag have been reported to be good catalysts for the selective production of CO in the electrochemical CO 2 reduction reaction, and Cu is a mixture of more reduced forms of hydrocarbon products such as CH 4 , C 2 H 4 , Respectively. Although the Ag exhibits a selectivity as high as Au and is inexpensive, Ag has not been widely studied relative to Au since it has a large overcharge potential. Ag based CO2 reduction catalysts have been studied in nonaqueous electrolytes such as ionic liquids.
Recently, a modified surface of a bulk polycrystalline metal has been developed to form a nanostructure to improve catalytic activity for a CO 2 reduction reaction. For example, oxide-derived Au nanoparticles or Ag nanoporous exhibited low overvoltage and high stability to CO generation, suggesting that the high purity crystalline surface of the curved surface is associated with high activity. In addition, the size effect of nanoparticles associated with changes in the ratio between edge and corner regions has been demonstrated in relation to metals such as Au and Cu in aqueous electrolyte.
It has been suggested that edge portions of Au nanoparticles favor CO generation, but corner portions have been suggested to favor competing H 2 production, so that an optimal particle size is desirable to have high CO 2 reducing activity and selectivity. Uniform synthesis is important to understand the effect of the nano-form on the CO 2 reduction reaction activity, as the amount of high-purity crystalline or edge regions can change as nanoparticle morphology and size change.
Wet chemical synthesis has the advantage that a large amount of metal nanoparticles having uniformly controlled sizes and shapes can be synthesized. Nanoparticle size and shape are typically controlled using surface sequestrants in wet chemistry, which are stabilizers that can aid in the dispersion of colloidal nanoparticles and control agents that can determine the growth direction of the metal in solution Lt; / RTI > However, since the catalytically active sites may be blocked by the surface sequestering agent due to the strong bonding at the metal surface, the organic surface sequestering agent has been removed before the catalytic reaction to expose the active sites. More preferably, direct growth of nanoparticles on a carbon support without a surface sequestering agent is desirable as a heterogeneous catalyst for electrocatalyst applications.
It is an object of the present invention to provide a process for preparing an electrocatalyst which exhibits improved ferrodefficiency and low overvoltage in the selective reduction of CO 2 to CO 2 in an aqueous solution.
Another object of the present invention is to provide an electrocatalyst prepared according to the above production method.
(A) dissolving a metal precursor of the present invention in an organic solvent and then subjecting the metal precursor to a first heat treatment to prepare a metal precursor solution;
(B) dispersing the carbon support in a mixed solution of a fixing agent and an organic solvent by ultrasonic to prepare a carbon support solution; And
(C) adding the carbon support solution to the metal precursor solution and performing a second heat treatment for 1 to 3 hours.
In the step (A), the first heat treatment is performed by raising the temperature from room temperature to T1, and T1 may be any temperature between 40 and 60 ° C.
In the step (A), the metal of the metal precursor may be silver, gold or zinc.
In the above steps (A) and (B), the organic solvent may be at least one selected from the group consisting of ethylene glycol, pentanediol, 1-octadecyne and benzyl ether.
In the step (B), the fixing agent may be cysteamine or acetyl cysteine, and the fixing agent and the carbon support may be mixed in a weight ratio of 1:10 to 30.
In the step (B), the carbon support may be one selected from the group consisting of carbon black, acetylene black, carbon nanotubes (CNT), graphite, graphene, graphite nanofiber (GNF) It can be more than a species.
In the step (C), the second heat treatment is performed by raising the temperature from T1 to T2, T1 is the first heat treatment temperature, and T2 is any temperature between 150 and 250 ° C.
And maintaining the temperature at T1 for 5 to 30 minutes before the second heat treatment.
The first and second heat treatments may be performed at a heating rate of 1 to 5 DEG C / min.
The metal of the metal precursor is silver and the fixing agent is cysteamine.
According to another aspect of the present invention, there is provided an electrocatalyst for CO 2 selective reduction according to the present invention.
In general, the smaller the particle size of the catalyst, the better the effect. The electrocatalyst for CO 2 selective reduction of the present invention can be produced with an average particle size of 2 to 15 nm. Among these, the average particle size is 4 to 8 nm, Shows the lowest over-potential, the highest mass activity, the highest CO feraday efficiency and improved durability in the selective reduction of CO 2 to CO in CO 2 . Specifically, when the average particle diameter is 4 to 8 nm, the exchange current density is increased more than 60 times and the ferrodefficiency is improved four times as compared with the foil in general.
In addition, the electrocatalyst for CO 2 selective reduction of the present invention can easily control the size.
1A to 1C are photographs of a catalyst prepared according to Examples 1 to 3 of the present invention, respectively, by transmission electron microscopy (TEM).
FIG. 1D is a photograph of a catalyst prepared according to Example 2 of the present invention by a high-resolution transmission electron microscope (HR-TEM). FIG.
FIG. 1E is a graph showing the X-ray photoelectron spectroscopy (XPS) of the catalyst prepared according to the control group, Example 2 and Comparative Example 1 for
2 is a graph showing the X-ray diffraction (XRD) of the catalyst prepared according to Example 2 of the present invention.
3 is a photograph of the catalyst prepared according to Comparative Example 2 taken by TEM.
4A is a graph of CO partial current density according to the applied electric potential of the catalyst prepared according to Examples and Comparative Examples of the present invention.
FIG. 4B is an over-potential graph at a fixed current density of the catalyst prepared according to Examples and Comparative Examples of the present invention. FIG.
FIG. 4C is the CO ferard efficiency according to the applied potential of the catalyst prepared according to Examples and Comparative Examples of the present invention.
4D is a graph of CO feraday efficiency at a fixed potential of -0.75 V (vs. RHE) of the catalyst prepared according to Examples and Comparative Examples of the present invention.
5 is (A) TEM image and (B) HR-TEM image of the catalyst prepared according to Example 2 of the present invention after CO 2 reduction.
FIG. 6A is a graph of the CO partial current density on overcharge of the catalyst prepared according to Examples and Comparative Examples of the present invention. FIG.
6B is a graph of mass activity according to the applied potential of the catalyst prepared according to Examples 1 to 3 of the present invention.
7 is a graph showing the total current density according to the applied electric potential of the catalyst prepared according to Examples and Comparative Examples of the present invention.
8 is a graph of H 2 and CO ferrate efficiency of the catalyst prepared according to Example 2 according to the applied potential.
FIG. 9 is a graph of the durability of a catalyst prepared according to Example 2 of the present invention (A) and the foil (B).
10 is a mass GC chromatogram of (A) the normal CO 2 reduction product and (B) 13 CO 2 isotope product for the catalyst prepared according to Example 2 of the present invention.
The present invention relates to a process for preparing an electrocatalyst having improved ferrode efficiency and low overvoltage in the selective reduction of CO 2 to CO in an aqueous solution, and an electrocatalyst prepared thereby.
The electrocatalyst of the present invention is a metal / C structure catalyst, which is directly synthesized on a carbon support by a one-pot reaction using a fixing agent to obtain a metal / C structure catalyst.
Hereinafter, the present invention will be described in detail.
The method for preparing an electrocatalyst for CO 2 selective reduction according to the present invention comprises the steps of: (A) dissolving a metal precursor in an organic solvent and then subjecting the metal precursor to a first heat treatment to prepare a metal precursor solution; (B) dispersing the carbon support in a mixed solution of a fixing agent and an organic solvent by ultrasonic to prepare a carbon support solution; And (C) adding the carbon support solution to the metal precursor solution and performing a second heat treatment for 1 to 3 hours.
In the step (A), a metal precursor solution is prepared by dissolving a metal precursor in an organic solvent, followed by first heat treatment.
The first heat treatment is performed by raising the temperature from room temperature to T1 at a temperature raising rate of 1 to 5 占 폚 / min, preferably 1 to 2 占 폚 / min. At this time, it is preferable that the normal temperature is 23 to 25 ° C, and the T1 is a temperature between 40 and 60 ° C, and the temperature is slowly increased from room temperature to the T1 for 15 to 20 minutes.
If the temperature of T1 is lower than the lower limit, the metal precursor may not be dissolved on the carbon support, so that the size of the particles may not be uniform. If the temperature is higher than the upper limit, the carbon support solution It is necessary to mix the metal precursor solution. However, since the metal precursor solution has a high temperature, it is difficult for the metal precursor to directly support (grow) on the carbon support, and there is a great possibility that the silver nano impurity exists.
If the rate of temperature rise is less than the lower limit, it takes a long time to reach the target temperature. If the rate is above the upper limit, the yield of the CO 2 selective reduction electrocatalyst may decrease.
The metal of the metal precursor may be silver, gold or zinc, preferably a silver precursor consisting of AgNO 3, Ag (acac) and Ag 2 SO 4 ; A gold precursor consisting of KAuCl 4 , NaAuCl 4 , NH 4 AuCl 4 , HAuCl 4 , LiAuCl 4 , KAuBr 4 , NaAuBr 4 and HAuBr 4 ; Zn (NO 3 ) 2 and (Zn (CH 3 COO) 2 2H 2 O). It is more preferable to use a silver precursor in view of the fact that the over-potential is so high that it is not used in the catalyst field and that the over-potential can be lowered and used as a catalyst.
In addition, the organic solvent is a substance that helps metal to be supported directly on the carbon support by the fixing agent while dissolving the metal precursor, and specifically includes a compound consisting of ethylene glycol, pentane diol, 1-octadecine, benzyl ether . ≪ / RTI > When an alcohol or water is used as the solvent, the metal may not be directly supported on the carbon support.
Next, in the step (B), the carbon support is dispersed by ultrasonication in a mixture of the fixing agent and the organic solvent to prepare a carbon support solution.
The fixing agent is a metal precursor to be directly supported on the carbon support by the thiol group (-SH) and the amine group (-NH 2 ) contained in the fixing agent, and is mixed with the carbon support and electrodeposited on the surface of the carbon support And reacts with the metal precursor to support the metal on the carbon support. At this time, when the fixing agent is first mixed with the metal precursor and reacts with the carbon support later, the metal precursor is not directly grown on the carbon support, and even if a small amount of metal is supported on the carbon support, , The size of the catalyst can not be controlled.
The fixing agent includes cysteamine or acetyl cysteine, preferably cysteamine.
The fixing agent and the carbon support are mixed at a weight ratio of 1:10 to 30, preferably 1:15 to 20. If the content of the carbon support is less than the lower limit based on the fixing agent, the catalyst can not be produced in a uniform particle size. If the content is above the upper limit, there are many carbon supports on which the metal is not supported, have.
The carbon support may include at least one selected from the group consisting of carbon black, acetylene black, carbon nanotubes (CNT), graphite, graphene, graphite nanofiber (GNF) .
The organic solvent may be the same or different from the organic solvent in the step (A).
The ultrasonic condition is an intensity of 75 to 400 W, preferably 100 to 200 W; The frequency is 5,000 to 30,000 times / second, preferably 10,000 to 15,000 times / second. When the ultrasonic intensity and / or frequency is below the lower limit, the catalyst can not be produced with a uniform particle size. If the ultrasonic intensity and / or frequency is above the upper limit, the carbon support is damaged and the desired catalyst can not be obtained.
Next, in step (C), the carbon support solution prepared in step (B) is added to the metal precursor solution prepared in step (A) and subjected to a second heat treatment for 1 to 3 hours.
The second heat treatment is performed for 1 to 3 hours by raising the temperature from T1 to T2 at a heating rate of 1 to 5 占 폚 / min, preferably at a heating rate of 3 to 4 占 폚 / min. In this case, T1 is the same as the first heat treatment temperature in the step (A), and T2 is any temperature between 150 and 250 ° C.
When the temperature of T2 is less than the lower limit value, a catalyst having a very small particle size is produced, the ferrode efficiency is not improved and a low overpotential can not be obtained. If the temperature is above the upper limit, a catalyst having a non- The ferrode efficiency is not improved and a low overvoltage can not be obtained.
If the rate of temperature rise is less than the lower limit value, a catalyst having a uniform size can not be obtained. If the rate is above the upper limit value, the yield of the CO 2 selective reduction catalyst may be reduced.
Specifically, performing a second heat treatment at 150 to 170 占 폚 for 50 to 80 minutes produces a catalyst having an average particle size of 3 nm; When the second heat treatment is performed at 150 to 170 ° C for 150 to 200 minutes, a catalyst having an average particle diameter of 5 nm is produced. When the second heat treatment is performed at 190 to 210 ° C for 50 to 80 minutes, Is generated. As described above, according to the present invention, the desired uniform size catalyst can be obtained by controlling the temperature and time.
Maintaining the temperature at T1 for 5 to 30 minutes to obtain a more uniform size catalyst prior to the second heat treatment. If the temperature holding time is less than the lower limit value, the effect of obtaining a more uniform size catalyst may be insignificant. If the temperature holding time is higher than the upper limit value, no further effect is expected.
In the electrocatalyst prepared as may be prepared mean a particle diameter of 2 to 15 nm, the above in the average particle diameter is the lowest overcurrent during the selective reduction in CO 2 to the CO when the 4 to 8 nm, preferably 5 to 6 nm , The highest mass activity, the highest CO ferrady efficiency and the most enhanced durability.
It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention. Such variations and modifications are intended to be within the scope of the appended claims.
Control group.
Carbon black (Ketjen black) was used.
Example 1 Preparation of an Ag / C catalyst having an average particle diameter of 3 nm
20 mg of silver nitrate (AgNO 3 ; Aldrich, 99.9999%) was dissolved in 10 mL of ethylene glycol (EG; Aldrich, 99.8%) while stirring vigorously and the solution was gradually heated to 50 ° C for 20 minutes to prepare a silver nitrate solution. On the other hand, 20 mg of carbon black (Ketjen black) was ultrasonicated for 30 minutes and dispersed in a solution containing 10 mL of ethylene glycol and 1 mg of cysteamine solution (Aldrich) to prepare a carbon black solution. The prepared carbon black solution was added to the silver nitrate solution at 50 占 폚, maintained at 50 占 폚 for 10 minutes, and then heated at 160 占 폚 for 1 hour at an ascending rate of 3 to 4 占 폚 / min to obtain Ag / C .
Example 2. 5 nm average particle size Ag / C catalyst preparation
The procedure of Example 1 was repeated except that the mixture was heated to 160 ° C for 3 hours to prepare Ag / C having an average particle diameter of 5 nm.
Example
3.
(Ag (acac); Aldrich, 98%) was used as a silver precursor, and at 200 ° C. for 1 hour in a second heat treatment, the same procedure as in Example 1 was carried out except that 1-octadecine was used as an organic solvent, silver acetylacetonate Followed by heating to prepare Ag / C having an average particle diameter of 10 nm.
Comparative Example 1. Cysteamine-C
20 mg of carbon black (Ketjen black) was ultrasonicated for 30 minutes without using a metal precursor and dispersed in a solution of 10 mL of ethylene glycol and 1 mg of cysteamine solution (Aldrich) to prepare a carbon black solution The mixture was maintained at 50 캜 for 10 minutes and then heated at 160 캜 for 1 hour at an increasing rate of 3 to 4 캜 / minute to prepare cysteamine-C.
Comparative Example 2. Cysteamine Not used
A catalyst was prepared in the same manner as in Example 1 except that cysteamine was not used.
Comparative Example 3. Silver foil
A silver foil with a thickness of 0.5 mm was used.
<Test Example>
The products prepared according to Examples and Comparative Examples were cooled to room temperature, washed with isopropanol, filtered and dried.
Test Example One. TEM , XRD And XPS Measure
1A to 1C are photographs of a catalyst prepared according to Examples 1 to 3, respectively, by a transmission electron microscope (TEM; TECNAI F20 G 2 , 200 kV); 1D is a photograph of the catalyst prepared according to Example 2 taken with a high-resolution transmission electron microscope (HR-TEM; JEM-ARM200F, 200 kV); FIG. 1E is a graph of the catalysts prepared according to the control group, Example 2 and Comparative Example 1, measured by X-ray photoelectron spectroscopy (XPS; Thermo Scientific K-Alpha) against
2 is a graph showing the X-ray diffraction (XRD; Shimadzu XRD-6000) of the catalyst prepared according to Example 2; 3 is a photograph of the catalyst prepared according to Comparative Example 2 taken by TEM.
As shown in FIG. 1, it was confirmed that Example 1 was fabricated at 3.4 ± 0.6 nm, Example 2 was fabricated at 5.0 ± 0.9 nm, and Example 3 was fabricated at 10.6 ± 2.8 nm (FIGS. 1A to 1C). In addition, HR-TEM images confirmed single crystal Ag nanoparticles with a d-spacing of 0.23 nm, corresponding to a (111) crystal face of the face-centered cubic silver (Fig. 1D).
Further, as shown in FIG. 2, XRD data confirmed that the Ag nanoparticles were plane-centered cubic Ag crystal structures.
Also, as shown in Fig. 3, it was found from the TEM image that in the absence of cysteamine (Comparative Example 2), the Ag particles could not be grown directly on the carbon support and the size of the nanoparticles was not controlled, It seems that the amine molecule helps to fix the nanoparticles in the initial nucleation step.
In addition, as shown in FIG. 1E, a
Test Example 2. Electrochemical activity measurement
FIG. 4A is a graph of CO partial current density according to the applied electric potential of the catalyst prepared according to Examples and Comparative Examples, FIG. 4B is an over-potential graph of the catalyst prepared according to Examples and Comparative Examples at a fixed current density, FIG. 4D is a graph of CO feraday efficiency at a fixed potential of -0.75 V (vs. RHE) of the catalyst prepared according to Examples and Comparative Examples. FIG. CO 2 electrochemical reduction was performed in CO 2 -saturated 0.5 M KHCO 3 .
FIG. 5 is a TEM image (FIG. 5A) and HR-TEM (FIG. 5B) images of the catalyst prepared according to Example 2 after CO 2 reduction.
6A is a graph of CO partial current density on overcharge of the catalyst prepared according to Examples and Comparative Examples; FIG. 6B is a mass activity graph according to the applied electric potential of the catalyst prepared according to Examples 1 to 3. FIG.
7 is a graph of the total current density according to the applied electric potential of the catalyst prepared according to Examples and Comparative Examples; 8 is a graph of H 2 and CO ferrate efficiency of the catalyst prepared according to Example 2 according to the applied potential.
As shown in Figs. 4 and 6, the catalyst prepared according to Examples 1 to 3 exhibited enhanced catalytic activity for CO production as compared to the foil of the polycrystalline of Comparative Example 3 (Fig. 4A). Figure 4A shows the iR -corrected potential-dependent CO partial current density, which was measured at the rectified current density from chronoam ferrometry. Example 2 The CO partial current density of the catalyst showed the highest value in the low cathode potential range (-0.3 to -0.9 V vs. RHE).
On the other hand, in Example 1 and the catalyst of Example 3, Example was at a higher biased potential region than the catalyst of the second start indicate the CO partial current density, the foil I of the larger cathode initiation potential which CO 2 Which means that the overvoltage required for the reduction reaction is greater.
To further compare over-potential, we obtained over-potential and over-potential dependent CO partial current densities at a fixed current density (FIG. 4B and FIG. 6A). The thermodynamic reduction potential of CO 2 to CO is -0.11 V for RHE. All of the catalysts prepared according to Examples 1 to 3 exhibited a significant reduction in over-potential, with the catalyst of Example 2 showing the greatest attenuation. Specifically, the catalyst of Example 2 exhibited migration toward the anode at about 300 mV anode at 1 mA / cm 2 as compared to the Ag foil. Moreover, as shown in FIG. 6B, the mass activity of the three catalysts of Examples 1 to 3 at various potentials followed a trend similar to the CO current density normalized to the electrode area, indicating that the amount of Ag metal content Because it was controlled using inductively coupled plasma (ICP) results.
In order to confirm that the CO 2 reducing activity of the Ag / C catalysts (Examples 1 to 3) was attributed to the Ag nanoparticles rather than the carbon support itself or the cysteamine, the CO 2 reduction reaction was carried out under the same conditions . Low CO partial current densities were detected in carbon black and cysteamine-C (Fig. 4A), and their total current density increased sharply as the applied potential exceeded -0.8 V vs. RHE (Fig. 7). These results indicate that both the carbon support and the cysteamine-C were converted into the hydrogen production reaction in place of the CO 2 reduction reaction.
The identification of the gaseous products by gas chromatography (GC) also confirmed that a large amount of hydrogen was produced as the main product when Ag was not supported on the carbon support.
In addition, the selectivity of the CO 2 reduction reaction to CO on the Ag / C catalyst electrode prepared by varying the applied potential was studied (FIG. 4C). Enhanced CO generation selectivity compared to the hydrogen production reaction (HER) was common in the low cathode potential region in the Ag / C catalysts of Examples 1 to 3 compared to the Ag foil. Specifically, the catalyst of Example 2 exhibited the highest CO 2 reduction performance, reached the maximum CO ferrored efficiency at the minimum over-potential (635 mV), and the Ag / C catalyst of Example 3 and Example 1 and the Ag foil were in turn I followed it.
The maximum CO ferrude efficiency was 76.8%, 84.4%, 72.6%, and 70.5% for the Ag / C catalyst and Ag foil of Examples 1 to 3, respectively, and the Ag / C catalyst of Example 2 achieved the highest CO ferrude efficiency Respectively. The CO ferrude efficiency of all samples was compared at a fixed potential of -0.75 V versus RHE, the maximum selectivity potential for the Ag / C catalyst of Example 2 (Figure 4D), the FERDETE of the Ag / C catalyst of Example 2 It was confirmed that the efficiency was improved 4 times compared with Ag foil (FE CO = 21.3%).
As a result of mass activity, overcharge and CO feraday efficiency analysis, it was proved that the Ag / C catalyst of Example 2 was the optimum Ag nanoparticle size for the CO 2 reduction reaction in an aqueous solution.
The, 8 as shown in Figure 8 is H 2 And the Faraday efficiency of the Ag / C catalyst of Example 2 for the CO product. Methane (CH 4 ) is also one of the gaseous products, but with less than 1% peraday efficiency at all potentials, regardless of the type of working electrode. The main products are H 2 and CO, and the sum of their faraday efficiencies is close to 100% for each sample as a result of GC measurement, which means that liquid products such as formic acid are negligible, . In addition, the TEM and HR-TEM images after the CO 2 reduction showed no change in the size of the Ag / C catalyst of Example 2 and showed an average particle size of 5.0 ± 1.0 nm (FIG. 5).
In general, the large surface area of the nanostructured metal can be advantageous for catalyst applications due to increased catalyst sites, and therefore it is desirable that the size of the nanoparticles is small for highly active catalysts. However, in the case of the Ag / C catalyst according to the invention having an average particle diameter of 5 nm in Example 2 of the catalyst with a higher current density and selectivity than the catalyst of Example 1, the average of particle diameter of 3 nm for the CO conversion of the CO 2 , And it was confirmed that the catalyst of Example 2 was the optimum size among three different size catalysts.
This size dependence on selectivity can be understood by competition of catalytic active sites. In the case of Au nanoparticles, previous studies have shown that edge portions may be more effective in stabilizing CO 2 reduction intermediates than in corner portions, which may be beneficial for CO generation, but corner portions present in larger portions in small nanoparticles More active. In the catalyst according to the present invention, the optimum size of the Ag nanoparticles capable of maximizing the selectivity of the CO 2 -CO reduction reaction is 5 nm. These results are in agreement with previous studies carried out on organic electrolytes, suggesting that the catalyst of Example 2 with an average particle size of 5 nm had the best CO partial current density at a given deflection potential.
In addition, the over-potential reduction in the Ag / C catalyst according to the present invention is noteworthy. In addition to the mass activity in the Ag / C catalyst of Example 2 as well as the increase in CO ferrude efficiency, the initiation potential (FIG. 4) for the CO 2 reduction reaction and the overcharge (FIG. 4) at the maximum CO ferrude efficiency , Indicating that both the overpotential of CO generation is reduced on the Ag / C catalyst.
The low overvoltage in the Ag / C catalyst of Examples 1 to 3 according to the present invention is expected to be related to the terminal group of -SH in the cysteamine as a fixing agent, .
9 is a graph of the durability of a catalyst prepared according to (A) a foil and (B) Example 2; 10 is a mass GC chromatogram of (A) the normal CO 2 reduction product and (B) 13 CO 2 isotope product for the catalyst prepared according to Example 2. FIG.
As shown in Fig. 9, the Ag / C catalyst of Example 2 exhibited enhanced durability as compared to polycrystalline Ag foil. The durability test was carried out using Ag foil and the Ag / C catalyst of Example 2 at a specified potential for 5 hours (-1.1 V vs. RHE for Ag foil -0.8 V versus RHE for Ag / C catalyst of Example 2) Lt; / RTI > During the 5 hour durability test, both the Ag foil and the Ag / C catalyst of Example 2 had a steady current density, but the reduction in CO ferrude efficiency was very different. The decrease in CO feraday efficiency in Ag foil after 5 hours was 58.2% (from 70.1% to 29.3%).
On the other hand, after 5 hours, the CO feraday efficiency of the Ag / C catalyst of Example 2 decreased by only 18.9% (from 78.3% to 63.5%).
When the durability test of the Ag foil was carried out at -0.8 V versus RHE, which was the same as the potential applied to the Ag / C catalyst of Example 2, the CO ferrude efficiency decreased from 19.2% to 7.7% within 1 hour and was a HER catalyst . In both samples, the CO ferrude efficiency loss was transferred to H 2 Faraday efficiency.
Finally, from the results of the 13 CO 2 isotope experiments, it was confirmed that the source of C was derived entirely from CO 2 dissolved in aqueous solution (FIG. 10), and C from the carbon support or cysteamine molecule was not involved in the reduction reaction .
(nm)
(mA / mg)
(mV)
(mV)
Ag / C catalysts of three different sizes successfully carried nanoparticles on a carbon support directly by a one-port method using a cysteamine initiating nucleation on a carbon support. Further, the Ag / C catalyst prepared in Example was applied as the electrocatalyst for CO 2 reduction reaction in an aqueous system without the organic substance removing process of any more, 13 CO 2 isotope result CO 2 is the carbon source to produce a CO Respectively. A comparison of the CO 2 reduction activity of the 3 nm, 5 nm and 10 nm Ag / C catalysts and the Ag foil showed that the 5 nm Ag / C catalyst (Example 2) exhibited low overvoltage, high mass activity, It was confirmed that the best CO 2 reduction activity was achieved in terms of enhanced durability. In the case of Ag nanoparticles grown directly on a carbon support, a significant reduction in over-potential was associated with the cysteamine fixative that enhanced the Ag-S interaction. It is suggested that the wet chemically synthesized Ag / C catalyst is a promising CO 2 reduction catalyst with high mass activity and low overvoltage for CO production.
- Working Electrode Fabrication -
The catalyst was dispersed in a mixture of isopropanol and Nafion solution (5 wt%, Dupont) and the catalyst ink was prepared by sonication for 30 minutes. The amount of actual metal in solution was measured by inductively coupled plasma (ICP) elemental analysis. The mirror-like carbon plate (Alfa Aesar) was thoroughly cleaned with mechanical polishing and deionized water and used as an electrode substrate, and the catalyst ink solution was sprayed onto the mirror-like carbon plate. The active area of the electrode is 0.5 cm 2 and the atomized amount of the metal catalyst is 0.045 ± 0.005 mg Ag / cm 2 .
The carbon and cysteamine-C ink solution was prepared by the same procedure, sprayed onto an enamel carbon plate, and for comparison, an Ag foil was used as the working electrode after surface machine polishing, the active area of which is also 0.5 cm < 2 > .
- electrochemical measurement -
Platinum and Ag / AgCl (saturated KCl) were used as the counter and reference electrodes, respectively. Electrochemical measurements were carried out in a two chamber electrochemical cell using Ivium potentiostat (Iviumtechnology) and a proton exchange membrane Nafion 117 was used to separate the catholyte and anolyte. The electrolyte solution (0.5 M KHCO 3 ) was purged with high purity CO 2 gas for at least 1 hour and the pH after saturation was 7.0. To obtain a stable electrochemical signal, chronoam ferrometry was performed at -2.0 V ( vs. Ag / AgCl) for 10 minutes before the CO 2 reduction reaction measurement. The CO 2 reduction reaction was measured using chronoam ferrometry at each fixed potential and the gaseous product (i.e., H 2 And CO) were quantified by gas chromatography (GC) (Younglin 6500 GC) equipped with a pulse discharge detector (PDD). Ultra high purity helium (He: 99.9999%) was used as the carrier gas. The CO 2 average flow rate was 120 cc / min as measured by a universal flow meter (Agilent Technologies ADM 2000) at the exit of the electrochemical cell. H 2 Or partial-current and fractional efficiency ( i H2 or CO and FE H2 or CO ) of CO generation are calculated from the peak area of the GC chromatogram, where V H2 or CO is calculated from the H 2 Or CO, i total is the measured current, F is the Faraday constant, p 0 is the pressure, T is the temperature and R is the ideal gas constant of 8.314 J · mol · K -1 ( 11, 28 ).
The durability test was carried out for 5 hours in CO 2 -saturated 0.5 M KHCO 3 solution by chronoam ferrometry at fixed potential, which caused the highest ferrodefficiency.
Solution resistance was measured by electrochemical impedance spectroscopy (EIS) at various potentials. The potential measured in the CO 2 reduction reaction was compensated for the iR loss and was recorded for the reversible hydrogen electrode (RHE) using the following equation: .
E ( vs. RHE) = E ( vs. Ag / AgCl) + 0.197 V + 0.0591 VX pH
Claims (12)
(B) dispersing the carbon support in a mixed solution of a fixing agent and an organic solvent by ultrasonic to prepare a carbon support solution; And
(C) adding the carbon support solution to the metal precursor solution and performing a second heat treatment for 1 to 3 hours,
Metal of the metal precursor is, the fixing agent is a process for producing a cis-Te CO 2 selective reduction electrocatalyst for the characterized minin.
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| KR20210017421A (en) * | 2019-08-08 | 2021-02-17 | 한양대학교 에리카산학협력단 | Metal oxide-carbon nitride composite nano-fibers for reducing carbon dioxide and method of fabricating of the same |
| KR102247105B1 (en) | 2019-08-08 | 2021-04-30 | 한양대학교 에리카산학협력단 | Metal oxide-carbon nitride composite nano-fibers for reducing carbon dioxide and method of fabricating of the same |
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