Manganese monatomic catalysts modified with carbonyl functional groups, methods of making and using the same

Abstract

The application discloses a carbonyl functional group modified manganese monatomic catalyst and a manufacturing method and application thereof. The manganese monatomic catalyst is modified by a carbonyl functional group. The metal manganese is dispersed on a carbon carrier in a monatomic form. The manganese atom is connected with a nitrogen atom, and the manganese atom is modified by oxygen in the carbonyl group. The oxygen-coupled manganese-containing catalyst precursor with the required active center is prepared by taking a carbon carrier containing a specific oxygen-containing functional group and a Mn metal salt as raw materials. The catalyst precursor obtained is pyrolyzed in a specific molten salt environment, so that the Mn monatomic catalyst MnNOC with the carbonyl functional group modified active center is prepared. The MnNOC exhibits extremely high catalytic activity, selectivity and stability in electrocatalytic ORR.

Description

Technical Field

[0001] This invention belongs to the technical field of single-atom catalysts, and particularly relates to a carbonyl functional group modified manganese single-atom catalyst, its preparation method, and its application. Background Technology

[0002] Single-atom catalysts (SACs) are a class of catalysts in which the active metal component is supported on a support as a single atom and participates in catalytic reactions. The concept of SACs was proposed by Zhang Tao et al. in 2011, and it quickly became a research hotspot in the field of catalysis. Single-atom catalysts possess the highest apparent atom utilization rate, a well-defined active center structure, and a tunable coordination environment, thus exhibiting excellent catalytic activity and selectivity in many electrocatalytic reactions (such as ORR, OER, HER, and carbon dioxide reduction). The type of coordinating atoms and the coordination environment of the metal atom at the active center of SACs have a significant impact on their intrinsic activity, selectivity, and stability. Therefore, research on altering the intrinsic activity of catalysts by adjusting the local environment of the active center has attracted considerable attention. Controlling the type, coordination number, and high-coordination shell of the metal center can not only effectively improve the performance of SACs but also has important significance for deepening the understanding of the structure-activity relationship of catalysts.

[0003] Hu et al. [1] prepared Co single-atom catalysts with different coordination numbers by controlling the synthesis temperature, namely CoN4, CoN3, and CoN2. Through activity testing, it was found that SACs with different coordination structures had different conversion performance for persulfate, and their activity from high to low was CoN2 > CoN3 > CoN4. That is, the lower the coordination number of Co atoms, the higher the specific activity of CoNx active sites. Xiong et al. [2] prepared Fe-NC catalysts with precisely controllable number of metal atoms in active sites by using MOF channels to confine metal precursors containing different numbers of Fe atoms. The coordination structures of Fe in the samples were FeN4, Fe2N6, and Fe3N4, respectively. As the number of Fe atoms increases, the adsorption configuration of O2 in the catalytic center changes from superoxide adsorption to peroxide adsorption, and the adsorption energy and activation degree of oxygen are significantly improved. Therefore, Fe3N4 catalyst has the best electrocatalytic ORR activity. Jiang et al. [3] modified the high coordination shell of Cu atoms through the atomic interface strategy and finally obtained the active site structure with CuN4-C8S2. S atoms shorten the bond length of Cu-N bond through long-range interaction, increase the charge density of metal center, and thus reduce the reaction energy barrier of RDS. In alkaline electrolyte, the ORR half-wave potential of CuN4-C8S2 is as high as 0.89V, which is much higher than that of catalyst with CuN4 site. At present, the methods for regulating the coordination structure of SACs active center are mainly focused on regulating the number or type of coordination atoms, or regulating the electronic structure of metal center by doping with heteroatoms such as S and P. However, this method of using heteroatoms for modification still faces the problem of unclear action site and insignificant effect.

[0004] Using the bonding effect of functional groups at specific sites can not only effectively determine the specific location of the regulatory site, but also regulate the activity of the metal center through the specific electron absorption / donation effect of the functional group. Han et al. [4] introduced S-type functional groups around the FeN4 site and found that the lone pair electrons in the sulfur-benzene S can become strong electron donors of the carbon plane, thereby increasing the electron density of the carbon plane and increasing the energy of the Fe atom d orbital. The strong adsorption energy brought by the electron donor further reduced the activity of the FeN4 site. When oxidizing S is modified around the metal center, its electron absorption characteristics will reduce the d band center of Fe, weaken the adsorption of intermediates by the Fe center, and improve the ORR activity of the FeN4 site. Although using functional groups to regulate the coordination environment of the metal center is an efficient way to enhance catalytic activity, there is still a lack of effective synthetic methods for customizing functional group modification sites, so it is impossible to accurately design the target catalyst.

[0005] Electrocatalytic ORR is one of the core reactions in fuel cells, and its slow kinetics are a key obstacle to improving fuel cell efficiency. The main reason for the slow ORR kinetics is its complexity, involving multiple electron and proton transfer steps, each of which affects the entire ORR process. Traditional commercial Pt / C catalysts are not only expensive but also have significant shortcomings in terms of stability and resistance to methanol poisoning. Therefore, developing low-cost, highly active, and highly stable catalysts is an important research area for enhancing ORR kinetics and promoting the development of fuel cells.

[0006] In summary, it is of great significance to use precise and efficient preparation methods to accurately control the coordination environment of metal active centers and significantly improve the ORR activity and stability of SACs. Summary of the Invention

[0007] In view of this, the present invention provides a carbonyl functional group-modified manganese single-atom catalyst, its preparation method, and its application. The present invention uses a carbon support containing specific oxygen-containing functional groups and a Mn-containing metal salt as raw materials to prepare the desired oxygen-coupled manganese catalyst precursor. The obtained catalyst precursor is then pyrolyzed in a specific molten salt environment to prepare a Mn single-atom catalyst MnNOC with carbonyl functional group-modified active centers, exhibiting extremely high catalytic activity, selectivity, and stability in electrocatalytic ORR.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: The first aspect of this invention provides a method for preparing a carbonyl functional group-modified manganese single-atom catalyst, comprising the following steps: S1: Preparation of oxygen-coupled manganese-containing catalyst precursor: S101: Disperse disodium ethylenediaminetetraacetate in an organic solvent, then add manganese salt, mix well and let stand overnight; S102: After heating the mixed solution obtained in step S101 in a water bath for a period of time, the mixed solution is evaporated to obtain a light brown powder, and then the light brown powder is ground evenly using a ball milling method. S2: Preparation of carbonyl functional group modified manganese single-atom catalysts: The oxygen-coupled manganese catalyst precursor obtained in step S1 is mixed evenly with molten salt, transferred to a high-temperature furnace, calcined under an inert atmosphere, and then naturally cooled. The cooled product is washed and dried to obtain the carbonyl functional group modified manganese single-atom catalyst.

[0009] Preferably, the mass ratio of disodium ethylenediaminetetraacetate, manganese salt, and molten salt is 25-75:1:500, and more preferably 25-50:1:500.

[0010] Preferably, the manganese salt is manganese acetylacetonate, and the molten salt is sodium chloride and / or potassium chloride. The molten salt can be sodium chloride or potassium chloride, or it can be a mixed salt of sodium chloride and potassium chloride, for example, a mixture of sodium chloride and potassium chloride in a mass ratio of 1:1.

[0011] Preferably, in step S2, the calcination temperature is 700-800℃, the calcination time is 2-2.5h, and the heating rate during the calcination process is 2-5℃ / min. Controlling the heating rate helps to control the yield of the calcination decomposition products, and controlling the calcination temperature can control carbonization. The calcination temperature of 700-800℃ ensures that the carbon substrate of the final catalyst is graphitized carbon.

[0012] Preferably, the water bath heating in step S102 specifically involves heating the mixed solution in a 70°C water bath for 12 hours.

[0013] Preferably, the organic solvent in step S101 is a mixed solution of water and isopropanol, wherein the volume ratio of water to isopropanol is 1:1.

[0014] The second aspect of the present invention provides a carbonyl functional group modified manganese single-atom catalyst, wherein metallic manganese is dispersed in single-atom form on a carbon support, manganese atoms are connected to nitrogen atoms, and the MnN4 site is modified by carbonyl oxygen. In the carbonyl functional group modified manganese single-atom catalyst MnNOC, the mass fraction of carbon is 70.0-75.0%; the mass fraction of nitrogen is 10.0-15.0%; the mass fraction of oxygen is 10.0-20.0%; and the mass fraction of manganese is 0.5-1.0%.

[0015] The third aspect of this invention provides an application of a carbonyl functional group-modified manganese single-atom catalyst in electrocatalytic redox reactions.

[0016] Preferably, it includes the following steps: Preparation of catalyst solution: The carbonyl functional group modified manganese single-atom catalyst was dispersed in ethanol, ball-milled and sonicated, then Nafion binder was added, and sonicated for another 1 hour. The catalyst solution prepared above was dropped onto the surface of a glassy carbon electrode. After natural evaporation, the catalyst was left behind, forming a complete working electrode. The activity of the catalyst was tested using 0.1M KOH as the electrolyte, a carbon rod electrode as the reference electrode, and a silver / silver chloride electrode as the counter electrode.

[0017] Because the present invention adopts the above technical solution, it has the following advantages and positive effects compared with the prior art: The carboxyl-modified manganese single-atom catalyst provided in this application uses a specific oxygen-containing functional group, namely disodium ethylenediaminetetraacetate (EDTA-2Na), whose molecular structure contains multiple carboxyl groups (-COONa) and amino groups (-N). When it is mixed with manganese acetylacetone, the nitrogen and oxygen atoms on EDTA react with Mn... 2+ The ions undergo strong coordination to form a stable "Mn-N / O" complex. This is equivalent to pre-locking Mn, N, and O atoms together at the molecular level in the catalyst precursor before calcination. During the subsequent calcination process, the catalyst precursor is mixed with molten salt and calcined at high temperature. The molten salt medium formed at high temperature acts like a "cage," binding the Mn atoms and preventing them from migrating and agglomerating during carbonization, ensuring final atomic-level dispersion. Simultaneously, under an inert atmosphere and high temperature, the EDTA organic framework "locked" around Mn gradually carbonizes. During this process, the nitrogen atoms coordinated with Mn form Mn-N coordination bonds. As carbonization proceeds, some of the carboxyl oxygen groups in the original EDTA are converted to carbonyl oxygen groups (C=O). Due to the "pre-locking" in the precursor stage, these carbonyl oxygen groups are retained in the second coordination shell of the Mn atom or in a nearby position, thus modifying the Mn sites. Therefore, this invention first prepares an oxygen-coupled manganese catalyst precursor by using specific oxygen-containing functional groups and Mn metal salts as raw materials, and then calcines and pyrolyzes the oxygen-coupled manganese catalyst precursor in a specific molten salt environment to prepare a single-atom catalyst with carbonyl functional group modified Mn sites.

[0018] The manganese single-atom catalyst prepared in this application, being a Mn single-atom catalyst, exhibits significantly improved stability due to its resistance to the Fenton reaction in the ORR process. Furthermore, the carbonyl-modified metal center demonstrates a markedly enhanced intrinsic ORR catalytic activity. Under alkaline conditions, the half-wave potential of the LSV curve reaches 0.93 V, far exceeding that of commercial Pt / C catalysts, with an H₂O₂ yield of less than 10%. It maintains good stability even after 10,000 to 100,000 CV cycles. In addition, it exhibits excellent resistance to methanol poisoning. This manganese single-atom catalyst possesses advantages such as stable and reliable preparation process, low preparation cost, high catalytic activity, and good stability, and holds promise for replacing commercial Pt / C catalysts in ORR and fuel cells. Attached Figure Description

[0019] Figure 1 This is a high-angle annular dark-field scanning transmission electron microscope image with sub-angstrom resolution and elemental diagram of the corresponding region of the MnNOC manganese single-atom catalyst prepared in Example 1 of the present invention. Figure 2 Synchrotron radiation data for the MnNOC manganese single-atom catalyst prepared in Example 1 of this invention; Figure 3The O energy spectra of the MnNOC manganese single-atom catalyst prepared in Example 1 of this invention and the NC catalyst of Comparative Example 1 are characterized by XPS. Figure 4 The infrared spectra of the MnNOC manganese single-atom catalyst prepared in Example 1 of this invention and the NC catalyst in Comparative Example 1 are shown. Figure 5 The XRD patterns are those of the MnNOC manganese single-atom catalyst prepared in Example 1 of this invention, the NC catalyst of Comparative Example 1, and the MnNP catalyst of Comparative Example 2. Figure 6 The infrared spectra of the MnNOC manganese single-atom catalyst prepared in Example 1 and the MnNC prepared in Comparative Example 3 are shown. Figure 7 This is a comparison of the LSV curves of the MnNOC manganese single-atom catalyst prepared in Example 1 of the present invention with those of the commercial Pt / C catalyst and the NC catalyst of Comparative Example 1. Figure 8 The LSV curves of the MnNOC manganese single-atom catalyst prepared in Example 1 of this invention and the MnNC catalyst in Comparative Example 3 are shown. Figure 9 The LSV curves are for the MnNOC manganese single-atom catalyst prepared in Example 1 and the MnNOC 0.5 manganese single-atom catalyst prepared in Example 2 of this invention. Figure 10 LSV curves of the MnNOC manganese single-atom catalyst prepared in Example 1 of this invention and catalysts with different metal substitutions are shown. Figure 11 Selectivity test of the MnNOC manganese single-atom catalyst prepared in Example 1 of this invention; Figure 12 Stability testing of the MnNOC manganese single-atom catalyst prepared in Example 1 of this invention; Figure 13 This is a test of the methanol resistance of the MnNOC manganese single-atom catalyst prepared in Example 1 of the present invention. Detailed Implementation

[0020] The following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a carbonyl functional group-modified manganese single-atom catalyst, its preparation method, and its applications. The advantages and features of the present invention will become clearer from the following description.

[0021] Example 1 Dissolve 1000 mg of disodium ethylenediaminetetraacetate in a mixture of 100 mL of isopropanol and water. Sonicate for 30 min, then add 20 mg of manganese acetylacetone and sonicate for 10 min to disperse evenly. Stir for 12 h. Evaporate the solution to dryness in a 70°C water bath to obtain a light brown powder for later use. The light brown powder and 10g of molten salt (sodium chloride / potassium chloride) were placed into a ball mill jar and ball milled using a ball mill with a vibration frequency of 50Hz to ensure uniform dispersion. After ball milling for 10 minutes, the powder was transferred to a corundum boat. In an inert atmosphere, the above mixture was heated to 700℃ in a tube furnace at a rate of 2℃ / min, held at that temperature for 2 hours, and then cooled to room temperature to prepare a MnNOC manganese single-atom catalyst. Its transmission electron microscopy (TEM) image and elemental distribution of the contrast region are shown below. Figure 1 In (a) and (b), bright spots of Mn atoms can be clearly seen in the sample, proving that Mn atoms are dispersed on the carbon support in the form of individual atoms. Meanwhile, the elemental distribution maps of C, O, N, and Mn are shown below. Figure 1 As shown in (c), (d), (e), and (f). At the same time... Figure 2 Synchrotron radiation data of the prepared MnNOC manganese single-atom catalyst are presented, showing that Mn in MnNOC mainly exists in the Mn-N coordination mode.

[0022] Comparative Example 1 The preparation process is the same as in Example 1, except that Mn salt is not added to the solution of disodium ethylenediaminetetraacetate. Otherwise, all operating steps and amounts are the same, and the obtained sample is denoted as NC. Figure 3 XPS O2 spectra of the samples from Example 1 and the comparative example are provided. The significant difference in oxygen functional group content between the two examples indicates that the steps in preparing the oxygen-coupled manganese-containing catalyst precursor have a significant impact on the oxygen content in the samples. Figure 4 Infrared spectra of the samples from Example 1 and the comparative example are provided, mainly illustrating the types of oxygen-containing functional groups in the samples. Together with XPS characterization, these spectra confirm the presence of carbonyl functional groups in the samples.

[0023] Comparative Example 2 The preparation process is the same as in Example 1, except that the light brown powder is directly calcined without molten salt mixing. The sample obtained in this way is denoted as MnNP.

[0024] like Figure 5 The XRD patterns of the samples obtained in Example 1 and Comparative Examples 1-2 are shown. It can be seen that when no molten salt is used during the calcination process, obvious characteristic peaks of metal particles appear, that is, the obtained samples are metal nanoparticles.

[0025] Comparative Example 3 The preparation process was the same as in Example 1, except that disodium ethylenediaminetetraacetate was not used as the carbon and nitrogen source; instead, graphene was used. Otherwise, all operating steps and amounts were identical to those in Example 1. The resulting sample was designated MnNC.

[0026] Figure 6The infrared spectrum of the sample prepared in Example 3 is shown. As can be seen from the figure, there are no abundant oxygen-containing functional groups in the MnNC sample.

[0027] Example 2 Similar to Example 1, except that the amount of ethylenediaminetetraacetic acid (EDTA) was reduced to half that of Example 1. Specifically, 500 mg of disodium EDTA was dissolved in a mixture of 100 mL of isopropanol and water, sonicated for 30 min, and then 20 mg of manganese acetylacetone was added. The mixture was sonicated for 10 min to ensure uniform dispersion, and then stirred for 12 h. The solution was then evaporated to dryness in a 70°C water bath to obtain a light brown powder for later use. The light brown powder and 10g of molten salt (sodium chloride / potassium chloride) were placed into a ball mill jar and ball milled using a ball mill with a vibration frequency of 50Hz to ensure uniform dispersion. After ball milling for 10 minutes, the powder was transferred to a corundum boat. In an inert atmosphere, the above mixture was heated to 700°C at 2°C / min in a tube furnace, held at that temperature for 2 hours, and then cooled to room temperature to obtain a MnNOC0.5 manganese single-atom catalyst.

[0028] Comparative Example 4 Similar to Example 1, the difference lies in the type of metal salt added. 20 mg of cobalt / nickel / chromium / copper acetylacetonate metal salts were added to a mixed solution of disodium ethylenediaminetetraacetate to obtain single-atom materials of Co, Ni, Cu and Cr.

[0029] Catalytic activity test: The application of the prepared single-atom catalyst in electrocatalytic ORR was tested using a rotating disk electrode. A Shanghai Chenhua CHI660 workstation was selected, with a silver / silver chloride electrode as the counter electrode, a carbon rod electrode as the reference electrode, and a glassy carbon electrode (0.5 mm in diameter) as the working electrode. The electrolyte was 0.1 M KOH. Specifically: ① Take 5 mg of the single-atom catalysts of Example 1 MnNOC, Example 2 MnNOC0.5 and Comparative Examples 3 and 4 and disperse them in 960 μL of ethanol. After ball milling and sonication for 1 h, add 40 μL of Nafion binder and sonicate for another 1 h. ② Use a pipette to draw 10 μL of the prepared ink and drop it onto the surface of the glassy carbon electrode. After natural evaporation, the catalyst is left behind, forming a complete working electrode. ③ Test the prepared working electrolyte in the electrolyte solution.

[0030] like Figure 7 The LSV curves of the MnNOC manganese single-atom catalyst and the commercial Pt / C catalyst in Example 1 are shown in the figure. It can be seen from the figure that the catalyst has a good reduction effect on ORR and its half-wave reduction potential is better than that of the commercial catalyst.

[0031] Figure 8 The LSV curves of the MnNOC manganese single-atom catalyst in Example 1 and the MnNC prepared in Comparative Example 3 are compared. It can be seen from the figure that the carbonyl-modified manganese single-atom catalyst improves the half-wave potential and current density.

[0032] Figure 9 The figures show the LSV curves of the manganese single-atom catalysts in Examples 1 and 2. As can be seen from the figures, reducing the precursor ratio affects the activity of the samples. The main reason is that reducing the amount of disodium ethylenediaminetetraacetate (EDTA) causes a significant change in the surface morphology of the samples, preventing oxygen adsorption and transfer during the ORR process, thus reducing the activity of the samples.

[0033] Figure 10 The figures show the LSV curves of single-atom catalysts of different metals. As can be seen from the figures, the Mn single-atom catalyst sample has the best ORR activity.

[0034] Selective testing: The MnNOC manganese single-atom catalyst prepared in Example 1 was subjected to a selectivity test method. The specific test method was similar to the catalytic activity test method, except that a rotating ring-disc electrode was used. The sample ink prepared above was dropped onto the ring-disc electrode, and after the solution naturally evaporated, a catalyst film was formed. The test was then conducted in the electrolyte. The results are as follows: Figure 11 As shown in the figure, its selectivity is excellent, with a hydrogen peroxide yield of less than 4%.

[0035] Stability test: The ORR of the MnNOC manganese single-atom catalyst prepared in Example 1 and the commercial Pt / C catalyst were tested after 20,000 and 100,000 cycles, respectively. The results are as follows: Figure 12 The comparison of stability tests is shown. As can be seen from the figure, the half-wave potential of the commercial catalyst decays after 20,000 cycles, while the half-wave potential of MnNOC remains basically unchanged after 100,000 cycles, demonstrating good stability.

[0036] Methanol resistance test: The MnNOC manganese single-atom catalyst prepared in Example 1 was subjected to a methanol resistance test. The method was similar to the catalytic activity test, except that 5 mL of a solution containing 5% methanol was added to the test system before testing the sample activity. The results are as follows: Figure 13 As shown, MnNOC exhibits good resistance to methanol.

[0037] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments. Even if various changes are made to the present invention, if these changes fall within the scope of the claims of the present invention and their equivalents, they shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a carbonyl functional group-modified manganese single-atom catalyst, characterized in that, Includes the following steps: S1: Preparation of oxygen-coupled manganese-containing catalyst precursor: S101: Disperse disodium ethylenediaminetetraacetate in an organic solvent, then add manganese salt, mix well and let stand overnight; S102: After heating the mixed solution obtained in step S101 in a water bath for a period of time, the mixed solution is evaporated to obtain a light brown powder, and then the light brown powder is ground evenly using a ball milling method. S2: Preparation of carbonyl functional group modified manganese single-atom catalysts: The oxygen-coupled manganese catalyst precursor obtained in step S1 is mixed evenly with molten salt, transferred to a high-temperature furnace, calcined under an inert atmosphere, and then naturally cooled. The cooled product is washed and dried to obtain the carbonyl functional group modified manganese single-atom catalyst.

2. The method for preparing the carbonyl functional group-modified manganese single-atom catalyst according to claim 1, characterized in that, The mass ratio of disodium ethylenediaminetetraacetate, manganese salt, and molten salt is 25-75:1:

500.

3. The method for preparing the carbonyl functional group-modified manganese single-atom catalyst according to claim 1, characterized in that, The manganese salt is manganese acetylacetonate, and the molten salt is sodium chloride and / or potassium chloride.

4. The method for preparing the carbonyl functional group-modified manganese single-atom catalyst according to claim 1, characterized in that, In step S2, the calcination temperature is 700℃-800℃, the calcination time is 2h-2.5h, and the heating rate during the calcination process is 2-5℃ / min.

5. The method for preparing the carbonyl functional group-modified manganese single-atom catalyst according to claim 1, characterized in that, In step S102, the water bath heating specifically involves heating the mixed solution in a water bath at 70℃-75℃ for 12 hours.

6. The method for preparing the carbonyl functional group-modified manganese single-atom catalyst according to claim 1, characterized in that, In step S101, the organic solvent is a mixed solution of water and isopropanol, wherein the volume ratio of water to isopropanol is 1:

1.

7. A carbonyl-functionalized manganese single-atom catalyst prepared by the method according to any one of claims 1-6, characterized in that, Metallic manganese is dispersed in a single-atom form on a carbon support, with manganese atoms connected to nitrogen atoms, and the MnN4 site is modified by carbonyl oxygen. In the carbonyl functional group modified manganese single-atom catalyst MnNOC, the mass fraction of carbon is 70.0-75.0%; the mass fraction of nitrogen is 10.0-15.0%; the mass fraction of oxygen is 10.0-20.0%; and the mass fraction of manganese is 0.5-1.0%.

8. The application of a carbonyl functional group-modified manganese single-atom catalyst prepared by the preparation method according to any one of claims 1-6 in electrocatalytic redox reactions.

9. The application of the carbonyl functional group-modified manganese single-atom catalyst as described in claim 8 in electrocatalytic redox reactions, characterized in that, Includes the following steps: Preparation of catalyst solution: The carbonyl functional group modified manganese single-atom catalyst was dispersed in ethanol, ball-milled and sonicated, then Nafion binder was added, and sonicated for another 1 hour. The catalyst solution prepared above was dropped onto the surface of a glassy carbon electrode. After natural evaporation, the catalyst was left behind, forming a complete working electrode. The activity of the catalyst was tested using 0.1M KOH as the electrolyte, a carbon rod electrode as the reference electrode, and a silver / silver chloride electrode as the counter electrode.

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