Preparation method and application of an iron-doped basic cobalt silicate electrocatalyst

Abstract

This invention relates to a method for preparing and applying an iron-doped basic cobalt silicate electrocatalyst. The method includes the following steps: (1) placing natural halloysite powder in a muffle furnace, dispersing the calcined halloysite in hydrochloric acid, and stirring to obtain a first suspension; (2) transferring the first suspension to a reaction vessel, sealing it, and reacting it at 100–140°C for 10–14 h to obtain silicon oxide (SiO2). x (3) Nanotubes; SiO x Nanotubes, cobalt nitrate hexahydrate, and ferric nitrate nonahydrate were added to a mixed solvent, stirred, and then ammonia was added dropwise. NH4Cl was then added, and the mixture was stirred continuously for 20–40 min. The resulting suspension was transferred to a reaction vessel, sealed, and reacted at 130–170 °C for 12–20 h to obtain the CoFeSi electrocatalyst. The CoFeSi electrocatalyst synthesized in this invention has the advantages of low cost, simple synthesis, high oxygen evolution efficiency, and excellent stability.

Description

Technical Field

[0001] This invention belongs to the field of inorganic electrocatalytic materials technology, specifically relating to a method for preparing and applying an iron-doped basic cobalt silicate electrocatalyst. Background Technology

[0002] Basic cobalt silicate (CoSi) is a novel electrocatalyst for the oxygen evolution reaction (OER). Its structure is similar to the layered structure of hydroxyl oxides, but its synthesis cost is lower, and it possesses abundant hydroxyl and metal active sites on its surface. Its unique structure and electron transfer pathway make it a promising OER catalyst. Currently, the silicon sources required for CoSi synthesis are generally industrially synthesized Na₂SiO₃·9H₂O and SiO₂ synthesized through various methods. However, when using traditional silicon sources such as Na₂SiO₃·9H₂O or SiO₂ as raw materials to synthesize CoSi, the reaction process is difficult to control, and the nanostructure cannot extend uniformly under alkaline conditions, making controllable synthesis difficult. Materials with high silicon content and unique structures can not only serve as silicon sources for the controllable synthesis of CoSi but also as templates for growing nanoscale CoSi on their surfaces. Based on this, silicon oxides (SiO₂) derived from silicate minerals, which are low-cost and widely available, are a promising candidate for OER catalysts. x It began to attract attention.

[0003] Meanwhile, the electrocatalytic activity of CoSi still needs further improvement. For a given catalyst structural framework, introducing cations through chemical methods to achieve cation diversity is one of the simple ways to improve electrocatalytic performance. This is because different metals in the catalyst will interact, further affecting the electronic structure and causing strain in the original geometry, thus optimizing the energy of intermediates involved in the OER process. For example, Chinese patent CN 115386908 A discloses a method for preparing iron-cobalt-nickel double hydroxide (LDH) nanocage electrocatalytic oxygen evolution material. Based on the strong coupling synergistic effect of Fe, Co, and Ni active sites, the catalytic activity of Fe-Co-Ni LDH-based electrocatalyst is further improved. However, its preparation cost is still higher than that of basic cobalt silicate-based electrocatalysts prepared using silicate minerals as silicon sources. Chinese patent CN 118326451 A prepares a nickel-doped cobalt MOF-74 electrocatalytic oxygen evolution material. The doping of nickel adjusts the electronic structure of the material and improves the catalytic activity, but the preparation process requires the use of toxic reagents such as methanol. Summary of the Invention

[0004] The purpose of this invention is to address the problems of low oxygen evolution efficiency, high synthesis cost, and poor stability of current electrocatalysts by providing a method for preparing iron-doped basic cobalt silicate electrocatalysts. This method uses natural tubular halloysite as the silicon source, and through calcination activation and purification treatment, obtains high-purity SiO₂.x Nanotubes were used as raw materials to synthesize iron-doped basic cobalt silicate (CoFeSi) electrocatalysts via a simple hydrothermal reaction. The CoFeSi electrocatalysts synthesized in this invention possess advantages such as low cost, simple synthesis, high oxygen evolution efficiency, and excellent stability.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A method for preparing an iron-doped basic cobalt silicate electrocatalyst, the method comprising the following steps:

[0007] (1) Place natural halloysite powder in a muffle furnace and calcine at 700-750°C for 2-4 hours; disperse the calcined halloysite in hydrochloric acid and stir to obtain the first suspension;

[0008] The product of calcination of natural halloysite powder is added to every 60 mL of hydrochloric acid; the concentration of hydrochloric acid is 1–2 mol / L.

[0009] (2) The first suspension was transferred to a reaction vessel, sealed, and reacted at 100–140°C for 10–14 h. The mixture was then washed and dried to obtain silicon oxide (SiO2). x Nanotubes, for later use;

[0010] (3) Silicon oxide (SiO) x Nanotubes, cobalt nitrate hexahydrate and ferric nitrate nonahydrate were added to a mixed solvent and stirred to obtain a second suspension.

[0011] In this process, 0.02–0.04 g of SiO2 is added to every 10–12 mL of mixed solvent. x Nanotubes, 0.2–0.5 g of Co(NO3)2·6H2O, and 0.1–0.3 g of Fe(NO3)3·9H2O; the mixed solvent consists of ethanol and deionized water in a volume ratio of 4:1 to 2:1.

[0012] (4) Add ammonia water dropwise to the second suspension, then add NH4Cl and stir continuously for 20-40 min. Transfer the resulting suspension to the reaction vessel, seal it and react at 130-170℃ for 12-20 h. After the reaction, wash and dry to obtain CoFeSi electrocatalyst.

[0013] For every 10–12 mL of the second suspension, add 2–4 mL of ammonia water and 0.4–0.6 g of NH4Cl; the concentration of ammonia water is 1.0–1.5 mol / L.

[0014] The iron-doped basic cobalt silicate electrocatalyst prepared by the method is used in the oxygen evolution reaction of water electrolysis.

[0015] Specifically, this includes: a three-electrode system performing constant current electrolysis on a KOH solution, where hydrogen evolution reaction (HER) occurs at the cathode to produce hydrogen gas, and oxygen evolution reaction (OER) occurs at the anode to produce oxygen gas;

[0016] The electrocatalyst containing iron-doped basic cobalt silicate is used as the working electrode (anode), Hg / HgO is selected as the reference electrode, and a carbon rod is used as the counter electrode (cathode); the current density is 5–20 mA·cm⁻¹. -2 ;

[0017] The concentration of the KOH solution is 0.5–2 M;

[0018] The method for preparing the working electrode is as follows: an iron-doped basic cobalt silicate electrocatalyst is added to a mixed solution to obtain a suspension, and then the suspension is coated onto carbon cloth and dried to obtain the working electrode.

[0019] In this process, 1–10 mg of catalyst is added to every 500 μL of mixed solution; and 20–100 μL of suspension is coated per square centimeter of carbon cloth.

[0020] The mixed solution consists of water, Nafion, and isopropanol in a volume ratio of 14:35:1.

[0021] The raw materials, reagents and equipment involved in the preparation method of the above-mentioned iron-doped basic cobalt silicate electrocatalyst are all obtained through known means, and the operation process is mastered by those skilled in the art.

[0022] The essential features of this invention are:

[0023] Iron-doped basic cobalt silicate nanosheets were successfully synthesized using halloysite, a natural clay mineral, as the silicon source and template. Iron doping modified the basic cobalt silicate, resulting in the synthesized CoFeSi without impurity phases. Furthermore, its lower crystallinity exposed more vacancy defects, which improved the catalytic efficiency. The hollow structure formed by the CoFeSi nanosheets assembled on the surface of one-dimensional halloysite nanotubes greatly exposed the reactive sites. The specific surface area of ​​CoFeSi is much larger than that of CoSi, which facilitates the participation of more catalytically active sites in the catalytic reaction. The larger pore size distribution and the bimetallic synergistic effect generated by Fe doping also significantly improved the OER performance of the material.

[0024] The beneficial effects of this invention are:

[0025] (1) Using halloysite, a natural clay mineral, as the silicon source to replace industrial raw materials such as sodium silicate or tetraethyl orthosilicate to prepare CoFeSi nanosheets can effectively reduce the preparation cost, and the tubular structure of halloysite can provide a template for the growth of CoFeSi nanosheets.

[0026] (2) Fe doping causes the binding energy of Co 2p to migrate to a lower position, and the bimetallic synergistic effect generated by doping greatly improves the OER reaction performance of the catalyst.

[0027] (3) The present invention uses a hydrothermal method to prepare CoFeSi nanosheet electrocatalysts. The preparation process is relatively simple and has high tolerance for experimental parameters.

[0028] (4) The CoFeSi electrocatalyst disclosed in this application operates at a current density of 10 mA·cm⁻¹. -2 The overvoltage is only 282mV, far lower than that of commercial RuO2 (321mV) and CoSi in the comparative example (347mV), and the Tafel slope is only 57mV·dec. -1 It is also far lower than that of commercial RuO2 (71mV·dec) -1 ) and CoSi (97mV·dec) in the comparative example -1 It has an earlier start-up potential and faster reaction kinetics, and exhibits good long-term stability.

[0029] (5) The silicon source used in the synthesis of the CoFeSi electrocatalyst disclosed in this application is not limited to halloysite. This research result provides an important reference for the subsequent research and preparation of natural clay mineral-based OER catalysts.

[0030] This invention provides a method for preparing and applying an iron-doped basic cobalt silicate electrocatalyst. Using natural tubular halloysite as the silicon source, and through calcination activation and purification treatment, high-purity SiO₂ is first obtained. x Nanotubes were then used as raw materials to synthesize an iron-doped basic cobalt silicate electrocatalyst (CoFeSi) via a simple hydrothermal reaction. The catalytic activity of the obtained electrocatalyst was significantly improved compared to CoSi, with the overpotential decreasing from 347 mV to 282 mV and the Tafel slope decreasing from 97 mV·dec. -1 Decreased to 57mV·dec -1 . Attached Figure Description

[0031] Figure 1 XRD patterns of CoSi prepared in Comparative Example 1 and CoFeSi prepared in Examples 1-3 with different iron additions.

[0032] Figure 2 FT-IR images of CoSi prepared in Comparative Example 1 and CoFeSi prepared in Examples 1-3 with different iron additions.

[0033] Figure 3 SEM images of CoSi prepared in Comparative Example 1 and CoFeSi prepared in Examples 1-3 with different iron addition amounts; wherein, Figure 3(a) is the SEM image of CoSi. Figure 3 (b) is a SEM image of 5 wt.% iron doping. Figure 3 (c) is a SEM image of 10 wt.% iron doping. Figure 3 (d) is a SEM image of 15 wt.% iron doping.

[0034] Figure 4 The images show BET analysis chromatograms of CoFeSi prepared in Example 1 and CoSi prepared in Comparative Example 1; wherein, Figure 4 (a) shows the N2 adsorption-desorption isotherms of CoFeSi and CoSi. Figure 4 (b) shows the pore size distribution curves of CoFeSi and CoSi.

[0035] Figure 5 The electrochemical performance curves of CoFeSi prepared in Examples 1-3 with different iron addition amounts are shown. Figure 5 (a) is the LSV curve. Figure 5 (b) is the Tafel slope plot. Figure 5 (c) is C dl picture, Figure 5 (d) is the Nyquist plot.

[0036] Figure 6 The results show the stability test results of the CoFeSi electrocatalyst prepared in Example 1; wherein, Figure 6 (a) LSV polarization curves of CoFeSi before and after 3000 CV cycles. Figure 6 (b) CoFeSi at 10 mA·cm -2 The results of the time-potential method test are shown below. Detailed Implementation

[0037] The present invention will be described below with specific embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0038] Example 1

[0039] Weigh 2g of natural halloysite powder and place it in a crucible. Transfer the crucible to a muffle furnace and calcine at 730℃ for 3h. Disperse the calcined halloysite in 60mL of 2mol / L hydrochloric acid solution, stir for 30min, transfer to a reaction vessel, seal, and react at 120℃ for 12h. Then wash and dry to obtain SiO2. x Nanotubes; Weigh 0.03g SiO2 xNanotubes, 0.3 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 0.2 g of ferric nitrate nonahydrate (Fe(NO3)3·9H2O) were added to a mixture of 8 mL of ethanol and 2 mL of deionized water. After stirring, 3 mL of 1.5 mol / L ammonia water was added dropwise to the suspension, followed by the addition of 0.53 g of NH4Cl and continuous stirring for 30 min. The resulting suspension was transferred to a reaction vessel, sealed, and reacted at 150 °C for 16 h. After the reaction, the mixture was washed and dried to obtain the CoFeSi electrocatalyst.

[0040] Example 2

[0041] The other steps are the same as in Example 1, except that "2g halloysite" is replaced with "1g halloysite", "2mol / L hydrochloric acid solution" is replaced with "1mol / L hydrochloric acid solution", "0.2g Fe(NO3)3·9H2O" is replaced with "0.1g Fe(NO3)3·9H2O", "2mL deionized water" is replaced with "4mL deionized water", "3mL 1.2mol / L ammonia water" is replaced with "4mL 1.0mol / L ammonia water", and "0.53g NH4Cl and continuous stirring for 30min" is replaced with "0.4g NH4Cl and continuous stirring for 20min". The obtained CoFeSi electrocatalyst still exhibits good electrocatalytic activity.

[0042] Example 3

[0043] The other steps are the same as in Example 2, except that "0.2g Fe(NO3)3·9H2O" is replaced with "0.3g Fe(NO3)3·9H2O", "3mL 1.2mol / L ammonia water" is replaced with "2mL 1.5mol / L ammonia water", and "0.53g NH4Cl and stirring continuously for 30min" is replaced with "0.6g NH4Cl and stirring continuously for 40min". The obtained CoFeSi electrocatalyst still exhibits good electrocatalytic activity.

[0044] Comparative Example 1

[0045] The other steps are the same as in Example 1, except that Fe(NO3)3·9H2O is not added during the preparation process. After the reaction, the obtained CoSi nanosheets are washed and dried for later use.

[0046] From the appendix Figure 1 As can be seen, the characteristic peak positions of CoFeSi obtained with all Fe addition amounts are the same as those of CoSi, indicating that Fe doping did not cause a shift in the diffraction peak positions. Furthermore, the intensity of the diffraction peaks hardly changes with the Fe content, suggesting that Fe doping did not affect the crystallinity of the catalyst.

[0047] From the appendix Figure 2 As can be seen, the bonding characteristics of the functional groups in CoSi and CoFeSi conform to the characteristics of layered silicates. Among them, 3627 cm⁻¹... -1 The position corresponds to the OH stretching vibration mode of OH-3M (M: Co / Fe), indicating that MO6 in silicates has a top hydroxyl group (-OH). 1009 cm -1 and 460cm -1 The values ​​at points represent the bending vibration modes of Si-O and asymmetric Si-O, respectively. Changes in the amount of Fe added did not lead to the appearance or disappearance of new functional groups. 3434 cm⁻¹ -1 and 1643cm -1 The absorption vibration peaks at the locations correspond to the tensile vibrations of adsorbed water and surface OH functional groups on the sample surface, respectively.

[0048] From the appendix Figure 3 As shown in the SEM image in (a), the CoSi nanosheets self-assemble into a typical one-dimensional rod-like structure, with a thickness of approximately 10 nm; from the attached... Figure 3 (b)- Figure 3 (d) SEM images show that the basic cobalt-iron silicate nanosheets prepared under different Fe addition conditions are arranged along SiO₂. x Nanotubes grow on the surface, and the nanosheets are relatively thin and interwoven. As the Fe content increases, the nanosheets become thicker, but their length does not change significantly.

[0049] From the appendix Figure 4 (a) The N2 adsorption-desorption isotherms show that CoFeSi exhibits classic type IV isotherms with type H3 hysteresis loops, confirming the mesoporous nature of CoFeSi. More tightly connected nanosheets enhance the S... BET Reaching 244m 2 / g, proving that the CoFeSi catalyst has more reaction sites than CoSi. From the attached... Figure 4 As can be seen from the pore size distribution curve in (b), the average pore size of CoFeSi is 18 nm, which is much larger than that of CoSi. The larger pore size provides more diffusion possibilities.

[0050] Appendix Figure 5 (a) Polarization curves for CoFeSi and commercial RuO2 with three different Fe additions are shown. (When the current density is 10 mA·cm⁻¹) -2 At that time, the overpotentials of CoFeSi-5 and CoFeSi-15 were 334 mV and 313 mV, respectively, while the polarization of CoFeSi-10 occurred at a lower potential, with the lowest overpotential, reaching 10 mA·cm⁻¹. -2Only 282mV is required. CoFeSi-10 exhibits excellent OER activity, far exceeding that of commercial RuO2 electrocatalysts (overpotential of 321mV). (See attached...) Figure 5 (b) It can be seen that, in the CoFeSi samples prepared under different Fe addition conditions, the Tafel slope of CoFeSi-5 is 62 mV·dec. -1 The Tafel slope of CoFeSi-15 is 66 mV·dec -1 CoFeSi-10 has the smallest Tafel slope, at only 57 mV·dec. -1 The lower Tafel slope indicates that CoFeSi-10 exhibits a faster OER process, allowing the catalyst to achieve a relatively high catalytic current at a lower overpotential. (From the attached...) Figure 5 (c) It can be seen that there is a linear relationship between Δj and the scanning speed. Calculations using the slope show that the double-layer capacitance of CoFeSi-10 is 35.7 mF·cm. -2 Compared to CoFeSi-5 (29.8 mF·cm⁻¹), -2 ) and CoFeSi-15 (34.5 mF·cm -2 It has a higher double-layer capacitance value due to the electrochemical active surface area and C dl The relationship is linear, therefore CoFeSi-10 has more exposed active sites. (From the attached...) Figure 5 (d) It can be seen that the Nyquist plot fits well with the dual time constant and equivalent circuit model, and CoFeSi-10 exhibits the lowest R0. ct (4.05Ω), corresponding to a faster electron transfer rate. This is because the appropriate amount of Fe added leads to a favorable bimetallic synergistic effect between Fe and Co, and the electron transfer between Fe and Co under this addition condition is more conducive to the OER reaction.

[0051] The oxygen evolution reaction (OER) performance of all electrocatalysts was tested using a three-electrode system. The electrocatalysts were drop-coated onto carbon cloth as the working electrode, Hg / HgO was selected as the reference electrode, and a carbon rod was used as the counter electrode. All electrochemical performance tests were conducted at room temperature using 1M KOH solution. The conversion formula between Hg / HgO and RHE, and the equation corresponding to the overpotential (η) are as follows:

[0052] E RHE =E Hg / HgO +0.059×pH+0.098

[0053] η = E RHE -1.23V

[0054] The preparation steps of the working electrode are as follows: Take 5 mg of catalyst powder and add it to a mixture of water, Nafion and isopropanol (140 μL of water, 350 μL of isopropanol and 10 μL of Nafion solution), sonicate until it is mixed evenly, then take 50 μL of suspension and drop it onto the cut carbon cloth (1 cm × 1 cm), and let it air dry at room temperature for later use.

[0055] The polarization curves were obtained by linear sweep voltammetry. In this experiment, the LSV test scan rate was 5 mV·s. -1 The iR compensation is 90%. The Tafel slope curve is a curve that conforms to the Tafel relationship and is obtained by transforming the LSV curve according to the following formula:

[0056] η = alogj + b

[0057] Where η is the overpotential, j is the current density, and the values ​​of a and b are determined by the material itself.

[0058] Catalyst stability testing is a crucial indicator for evaluating a catalyst's long-term performance stability and applicability. Currently, methods for testing the stability of catalysts in classic three-electrode systems include cyclic voltammetry and chronopotentialography (CP). This work assessed the catalyst's stability through 3000 consecutive cyclic voltammetric tests at a constant current density of 10 mA·cm⁻¹. -2 Under these conditions, 10 were recorded. 5 Chronopotential curves were used to further evaluate the long-term stability of the catalyst.

[0059] From the appendix Figure 6 (a) As can be seen, the stability of CoFeSi was verified by 3000 consecutive CV tests. The polarization curve of CoFeSi shows that its performance improved after 3000 CV cycles, which may be due to the exposure of more metal active sites during the testing process. Chronopotentiometric method (CP) is also an important parameter for measuring catalyst stability, at j = 10 mA·cm⁻¹. -2 The stability of CoFeSi was analyzed using the chronopotential method under constant conditions. (From the attached...) Figure 6 (b) It can be seen that CoFeSi at 10 5 The potential within s did not change significantly, indicating that no structural degradation occurred on the CoFeSi surface during the test. The results demonstrate that the electrocatalyst maintained excellent durability and stability throughout the entire test process.

[0060] As can be seen from the above examples and comparative examples, the present invention successfully synthesized basic cobalt silicate using a hydrothermal method with halloysite, a natural clay mineral, as a silicon source and template. Furthermore, the oxygen evolution reaction performance of the basic cobalt silicate nanosheets was improved by the bimetallic synergistic effect generated by iron doping.

[0061] The foregoing description illustrates the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

[0062] Matters not covered in this invention are common knowledge.

Claims

1. A method for preparing an iron-doped basic cobalt silicate electrocatalyst, characterized in that the method includes the following steps: (1) Place natural halloysite powder in a muffle furnace and calcine at 700~750 ℃ ​​for 2~4 h; disperse the calcined halloysite in hydrochloric acid and stir to obtain the first suspension; The product of calcination of natural halloysite powder is added to every 60 mL of hydrochloric acid. (2) The first suspension was transferred to the reaction vessel, sealed, and reacted at 100~140 °C for 10~14 h. Then it was washed and dried to obtain silicon oxide nanotubes. (3) Add silicon oxide nanotubes, cobalt nitrate hexahydrate and ferric nitrate nonahydrate to a mixed solvent and stir to obtain a second suspension; The mixture consists of 0.02–0.04 g of silicon oxide nanotubes, 0.2–0.5 g of Co(NO3)2·6H2O, and 0.1–0.3 g of Fe(NO3)3·9H2O added per 10–12 mL of mixed solvent. The mixed solvent is composed of ethanol and deionized water, with a volume ratio of ethanol to deionized water of 4:1 to 2:

1. (4) Add ammonia water dropwise to the second suspension, then add NH4Cl and stir continuously for 20-40 min. Transfer the resulting suspension to the reaction vessel, seal it and react at 130-170 °C for 12-20 h. After the reaction, wash and dry to obtain CoFeSi electrocatalyst. For every 10-12 mL of the second suspension, add 2-4 mL of ammonia and 0.4-0.6 g of NH4Cl.

2. The preparation method of the iron-doped basic cobalt silicate electrocatalyst as described in claim 1, characterized in that: In step (1), the concentration of hydrochloric acid is 1~2 mol / L.

3. The preparation method of the iron-doped basic cobalt silicate electrocatalyst as described in claim 1, characterized in that: In step (4), the concentration of ammonia water is 1.0~1.5 mol / L.

4. The application of the iron-doped basic cobalt silicate electrocatalyst prepared by the method described in claim 1, characterized in that it is used in the oxygen evolution reaction of water electrolysis.

5. The application as described in claim 4, characterized in that a three-electrode system performs constant current electrolysis on KOH solution, with hydrogen evolution reaction (HER) occurring at the cathode to obtain hydrogen gas and oxygen evolution reaction (OER) occurring at the anode to obtain oxygen gas; in, An iron-doped basic cobalt silicate electrocatalyst was used as the anode, Hg / HgO was selected as the reference electrode, and a carbon rod was used as the cathode; the current density was 5~20 mA·cm. -2 ; The concentration of the KOH solution is 0.5~2 M.

6. The application as described in claim 5, characterized in that the anode is prepared by: adding an iron-doped basic cobalt silicate electrocatalyst to a mixed solution to obtain a suspension, then coating the suspension onto carbon cloth, and drying it to obtain the anode; in, Add 1–10 mg of catalyst to every 500 μL of mixed solution; coat each square centimeter of carbon cloth with 20–100 μL of suspension.

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