A Cr-doped basic cobalt vanadate catalyst, its preparation method and application

Abstract

This invention discloses a Cr-doped basic cobalt vanadate catalytic material, its preparation method, and its applications, belonging to the field of electrocatalytic material preparation technology. It includes a conductive substrate and basic cobalt vanadate supported on the conductive substrate, wherein the crystal lattice of the basic cobalt vanadate is doped with chromium. This invention utilizes the doping modification of chromium in the basic cobalt vanadate crystal lattice to achieve the desired Cr content. 3+ With V 5+ / V 4+ The synergistic effect of redox pairs provides more electron transfer pathways for catalytic cycling, strengthens the crystal lattice framework, inhibits excessive loss of lattice oxygen and overall structural instability, and significantly improves the oxygen evolution reaction activity and long-term stability of the material.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic material preparation technology, specifically relating to a Cr-doped basic cobalt vanadate catalytic material, its preparation method, and its application. Background Technology

[0002] Against the backdrop of rapidly growing global energy demand, hydrogen energy (H2), as a high-energy-density and clean, pollution-free energy form, has attracted widespread attention. Electrolysis of water to produce hydrogen has become an important pathway due to its advantages such as a green and clean process, simple equipment requirements, and the absence of stringent conditions like high temperature and high pressure. However, in the electrocatalytic water splitting process, the oxygen evolution reaction (OER) at the anode involves a slow four-electron transfer process, requiring a high reaction energy barrier, which limits the overall efficiency of electrocatalytic water splitting.

[0003] The key to solving the problem lies in developing highly active catalysts. Currently, Ru / Ir-based noble metal catalysts exhibit high catalytic activity for OER, but they suffer from limitations such as high cost, resource scarcity, and poor cycle stability, making it difficult to meet the demands of large-scale commercial applications. Transition metal oxides, hydroxy oxides, and their derivatives are inexpensive catalysts that exhibit excellent activity and long-term stability in alkaline solution environments, making them potentially feasible alternatives to traditional noble metal-based electrocatalysts. In particular, basic transition metal salts can effectively promote the formation of high-valence active species in catalysts at low potentials, but their catalytic activity needs further improvement.

[0004] In the prior art, although the performance of catalysts can be improved by doping with a second metal, the doping effect of different metal elements in a specific crystal structure varies greatly, and the mechanism of influence of doping on the microstructure and electrochemical performance of the material is still unclear, making it difficult to significantly improve the OER activity and stability of the catalyst while controlling costs. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a Cr-doped basic cobalt vanadate catalytic material, its preparation method and application, so as to solve the problems of low activity and insufficient stability of transition metal basic salt catalysts in the oxygen evolution reaction.

[0006] To achieve the above objectives, the present invention employs the following technical solution: A first aspect of the present invention discloses a chromium-doped basic cobalt vanadate catalytic material, comprising a conductive substrate and basic cobalt vanadate supported on the conductive substrate, wherein the crystal lattice of the basic cobalt vanadate is doped with chromium.

[0007] The above scheme introduces chromium into the basic cobalt vanadate lattice, utilizing Cr3+ With V 5+ / V 4+ The synergistic effect of redox pairs provides more and more flexible electron transfer pathways for catalytic cycling, while strengthening the crystal lattice framework, inhibiting excessive loss of lattice oxygen and overall structural relaxation, thereby significantly improving the OER activity and long-term stability of the material.

[0008] In one implementation method, the molar ratio of cobalt to chromium in the basic cobalt vanadate is 10:1 to 3:1. By controlling the molar ratio of cobalt to chromium within a reasonable range, it is ensured that chromium can effectively enter the lattice sites to exert its doping modification effect, while avoiding the problem of severe lattice distortion or the covering of active centers due to excessive doping, thus maximizing catalytic activity.

[0009] In one embodiment, the molar ratio of cobalt to chromium is 4:1. This scheme determines the optimal doping ratio, at which the catalyst exhibits the best electrochemical active surface area and the lowest overpotential, demonstrating the superior oxygen evolution reaction performance.

[0010] As one embodiment, the basic cobalt vanadate has the general chemical formula Co3(OH)2V2O7·nH2O, where n≥0.

[0011] The above scheme clarifies the crystal structure of the basic cobalt vanadate matrix, which is conducive to the adsorption and activation of water molecules, and at the same time provides a stable lattice framework for chromium doping.

[0012] In one embodiment, the conductive substrate is selected from foamed metal, carbon cloth or metal mesh to adapt to different application scenarios and preparation process requirements, thus ensuring the conductivity and mechanical strength of the catalyst.

[0013] In one embodiment, the conductive substrate is copper foam. The three-dimensional porous structure of copper foam is beneficial for the uniform loading of the catalyst and the wetting of the electrolyte, thereby further improving the efficiency of the catalytic reaction.

[0014] In a second aspect, the present invention also provides a method for preparing a chromium-doped basic cobalt vanadate catalyst, comprising: placing a conductive substrate in a mixture containing a cobalt source, a chromium source and a vanadium source, and performing a hydrothermal reaction to obtain the chromium-doped basic cobalt vanadate catalyst.

[0015] The above scheme uses a one-step hydrothermal in-situ growth method to grow the catalyst. The process is simple and highly reproducible, which is conducive to the large-scale preparation of the catalyst. Furthermore, the hydrothermal reaction enables the effective doping of chromium in the basic cobalt vanadate lattice.

[0016] As one implementation method, the above preparation method specifically includes: Prepare a mixed solution of Co(NO3)2 and Cr(NO3)3; Preparation of NaVO3 solution; Then, the mixed solution of Co(NO3)2 and Cr(NO3)3 was slowly added dropwise to the NaVO3 solution and mixed thoroughly to obtain a suspension. A conductive substrate is added to the prepared suspension, and a hydrothermal reaction is carried out at 150-180℃ for 8-12 hours. The resulting product is washed and dried to obtain a Cr-doped basic cobalt vanadate catalyst.

[0017] In one embodiment, the hydrothermal reaction is carried out at a temperature of 150°C to 180°C for a duration of 8 to 12 hours.

[0018] The above scheme limits the key process parameter window for the hydrothermal reaction, under which chromium-doped cobalt vanadate crystals with good crystallinity and regular morphology can be formed.

[0019] In one embodiment, the hydrothermal reaction is carried out at a temperature of 160°C for 10 hours. This scheme represents the optimal hydrothermal reaction conditions, under which the catalyst prepared exhibits the best crystal structure and electrochemical performance.

[0020] In a third aspect, the present invention also provides the application of the above-mentioned chromium-doped basic cobalt vanadate catalyst in the oxygen evolution reaction of water electrolysis.

[0021] The above scheme expands the application range of chromium-doped basic cobalt vanadate catalysts. When applied to the oxygen evolution reaction in water electrolysis, it can significantly reduce the overpotential of the oxygen evolution reaction and improve the efficiency of hydrogen production from water electrolysis.

[0022] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a chromium-doped basic cobalt vanadate catalyst. By doping the basic cobalt vanadate catalyst with Cr, the synergistic effect of the element can be utilized to further improve the catalyst's activity and stability. Specifically, Cr... 3+ It can itself act as an additional redox pair, reacting with the original V 5+ / V 4+ The redox pair forms a synergistic effect, providing more and more flexible electron transport pathways for the catalytic cycle. Through the synergistic optimization of the electronic structure and oxygen species activity, the Cr-doped basic cobalt vanadate catalyst prepared in this invention exhibits a significantly reduced overpotential in the electrochemical oxygen evolution reaction. This is due to the easier generation and utilization of active oxygen species on the catalyst surface, as well as the enhanced electron transport capability. Furthermore, chromium (Cr) with a stable valence and suitable ionic radius... 3+Introducing ions into the lattice framework of basic cobalt vanadate can strengthen the lattice skeleton, suppress excessive loss of lattice oxygen and overall structural instability, and at the same time, partially occupy easily soluble sites in the lattice to stabilize the overall structure, reduce the exposure of defect sites, and meet the stringent requirements of industrial applications for catalyst stability and durability. Attached Figure Description

[0023] Figure 1 The image shows a scanning electron microscope (SEM) image of Cr-Co3(OH)2V2O7·2H2O / CF in Example 2.

[0024] Figure 2 The XRD diffraction patterns and standard card comparison diagrams of the materials in Example 1 (Co3(OH)2V2O7·2H2O / CF), Example 2 (Cr-Co3(OH)2V2O7·2H2O / CF), Example 3 (Fe-Co3(OH)2V2O7·2H2O / CF), and Example 4 (Mn-Co3(OH)2V2O7·2H2O / CF) are shown.

[0025] Figure 3 The image shows the Raman spectrum of Cr-Co3(OH)2V2O7·2H2O / CF in Example 2.

[0026] Figure 4 The OER polarization curves are for the materials in Example 1 (Co3(OH)2V2O7·2H2O / CF), Example 2 (Cr-Co3(OH)2V2O7·2H2O / CF), Example 3 (Fe-Co3(OH)2V2O7·2H2O / CF), and Example 4 (Mn-Co3(OH)2V2O7·2H2O / CF). Detailed Implementation

[0027] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0028] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0029] The present invention will now be described in further detail with reference to the accompanying drawings: This invention provides a method for preparing Cr-doped basic cobalt vanadate catalysts. This method primarily utilizes a hydrothermal process to prepare various basic cobalt vanadate catalysts supported on copper foam. The optimal catalyst is determined based on XRD and LSV performance. The introduction of the second metal Cr effectively improves OER activity and stability, increases the number of active sites on the catalyst, and results in faster OER kinetics. Specifically, to achieve the above objectives, this section includes two parts: the preparation of the basic cobalt vanadate material and the screening of the doping second metal.

[0030] I. Preparation of basic cobalt vanadate materials (Co3(OH)2V2O7·2H2O / CF) Example 1 This embodiment does not dope with a second metallic element, and its preparation method includes the following steps: A. Cut the copper foam into 2×3 cm pieces. 2 The sample was ultrasonicated in ethanol, 3 M HCl, and deionized water for 10 min each, and then dried with a hair dryer for later use. B. Weigh 1.2 mmol of Co(NO3)2·6H2O and dissolve it in 5 mL of deionized water, then stir until well mixed; C. Weigh 2.4 mmol NaVO3 and dissolve it in 20 mL of deionized water, then stir at 70°C for 20 min. D. Co(NO3)2 solution was added dropwise to NaVO3 solution, and a wine-red suspension was obtained under continuous stirring. The suspension was then transferred to a hydrothermal reactor. E. Add the pretreated copper foam from step A into a hydrothermal reactor and react at 160℃ for 10 h; F. Take out the sample synthesized in step E and wash it with deionized water and ethanol. Dry it in a vacuum oven at 70°C overnight to finally obtain the Co3(OH)2V2O7·2H2O / CF material.

[0031] II. Screening for doped second metallic elements Example 2 The preparation method of this embodiment, which involves doping with a second metallic element Cr, includes the following steps: A. Cut the copper foam into 2×3 cm pieces. 2 The sample was ultrasonicated in ethanol, 3 M HCl, and deionized water for 10 min each, and then dried with a hair dryer for later use. B. Weigh 0.96 mmol Co(NO3)2·6H2O and 0.24 mmol Cr(NO3)3·9H2O, dissolve them in 5 mL of deionized water, and stir well; C. Weigh 2.4 mmol NaVO3 and dissolve it in 20 mL of deionized water, then stir at 70°C for 20 min. D. Add the mixed solution of Co(NO3)2 and Cr(NO3)3 dropwise to the NaVO3 solution, and obtain a suspension by continuous stirring. Transfer the suspension to a hydrothermal reactor. E. Add the pretreated copper foam from step A into a hydrothermal reactor and react at 160℃ for 10 h; F. Take out the sample synthesized in step E and wash it with deionized water and ethanol. Dry it in a vacuum oven at 70°C overnight to finally obtain the Cr-Co3(OH)2V2O7·2H2O / CF material.

[0032] Example 3 The preparation method of this embodiment, which involves doping with a second metallic element Fe, includes the following steps: A. Cut the copper foam into 2×3 cm pieces. 2 The sample was ultrasonicated in ethanol, 3 M HCl, and deionized water for 10 min each, and then dried with a hair dryer for later use. B. Weigh 0.96 mmol Co(NO3)2·6H2O and 0.24 mmol Fe(NO3)3·9H2O, dissolve them in 5 mL of deionized water, and stir well; C. Weigh 2.4 mmol NaVO3 and dissolve it in 20 mL of deionized water, then stir at 70°C for 20 min. D. Add the mixed solution of Co(NO3)2 and Fe(NO3)3 dropwise to the NaVO3 solution, and obtain a suspension by continuous stirring. Transfer the suspension to a hydrothermal reactor. E. Add the pretreated copper foam from step A into a hydrothermal reactor and react at 160℃ for 10 h; F. Take out the sample synthesized in step E and wash it with deionized water and ethanol. Dry it in a vacuum oven at 70°C overnight to finally obtain the Fe-Co3(OH)2V2O7·2H2O / CF material.

[0033] Example 4 This embodiment is prepared by doping with a second metallic element, Mn, and includes the following steps: A. Cut the copper foam into 2×3 cm pieces. 2 The sample was ultrasonicated in ethanol, 3 M HCl, and deionized water for 10 min each, and then dried with a hair dryer for later use. B. Weigh 0.96 mmol Co(NO3)2·6H2O and 0.24 mmol Mn(NO3)3·9H2O, dissolve them in 5 mL of deionized water, and stir well; C. Weigh 2.4 mmol NaVO3 and dissolve it in 20 mL of deionized water, then stir at 70°C for 20 min. D. Add the mixed solution of Co(NO3)2 and Mn(NO3)3 dropwise to the NaVO3 solution, and obtain a suspension by continuous stirring. Transfer the suspension to a hydrothermal reactor. E. Add the pretreated copper foam from step A into a hydrothermal reactor and react at 160℃ for 10 h; F. Take out the sample synthesized in step E and wash it with deionized water and ethanol. Dry it in a vacuum oven at 70°C overnight to finally obtain the Mn-Co3(OH)2V2O7·2H2O / CF material.

[0034] As can be seen from the above examples, the difference between Example 1 and Example 2 is that no second metal is doped, and Example 3 can be used as a control group. The difference between Example 3 and Example 2 is that the second metal doped is different, and Example 3 can be used to test the effect of different second metals on OER activity. Similarly, the difference between Example 4 and Example 2 is that the second metal doped is different, and Example 4 can be used to test the effect of different second metals on OER activity.

[0035] III. Characterization and OER Activity Verification of the Products Obtained in the Above Examples To verify the microstructure and performance of the catalytic material prepared in this embodiment, the following characterization and testing were performed: Combination Figure 1 The image shown is a scanning electron microscope (SEM) image of the chromium-doped basic cobalt vanadate catalyst prepared in this embodiment. It can be clearly observed from the image that the material exhibits a regular microstructure, with the active material uniformly covering the surface of the copper foam framework and possessing a rich porous structure. This unique microstructure greatly increases the electrochemical active surface area of ​​the material, providing a large number of active sites for the oxygen evolution reaction, while also facilitating electrolyte wetting and gas diffusion.

[0036] Combination Figure 2 As shown, the materials prepared in Examples 1, 3, and 4 all exhibited diffraction peaks similar to those in Example 2, and the peak positions were basically consistent with those of the standard cards (PDF #50-0570, etc.). This indicates that the basic cobalt vanadate crystal structure was successfully synthesized via the hydrothermal method, and the introduction of Fe and Mn elements did not change the main crystal phase of the material. However, careful comparison of the intensity and full width at half maximum (FWHM) of the diffraction peaks reveals that the doping of different metal ions had different effects on the crystallinity and lattice microstress, suggesting that metal ions with different ionic radii exerted differentiated regulatory effects on crystal growth kinetics after entering the lattice.

[0037] Combination Figure 3 The image shows the Raman spectrum of the material prepared in this embodiment. The spectrum shows the spectrum at approximately 850 cm⁻¹. - A significant characteristic peak appears at ¹, corresponding to the vibrational mode of the VO bond, while at 300-600 cm⁻¹... -1 The spectral bands within the range are correlated with the vibrations of Co-O and Cr-O bonds. Raman spectroscopy results further confirm that chromium has been successfully doped into the crystal structure of basic cobalt vanadate and has formed stable chemical bonds with surrounding atoms. This bonding helps improve the structural stability of the material during electrochemical reactions.

[0038] Combination Figure 4 The figure shows the oxygen evolution reaction (OER) polarization curves of the catalytic material prepared in this embodiment and other comparative samples. The test results show that different doping elements have significantly different effects on the electrocatalytic performance of the material. Specifically, the undoped sample prepared in Example 1 exhibits significantly better performance at a current density of 10 mA cm⁻¹. - At 2000 mV, the overpotential was 215 mV. Although the OER performance of the iron-doped sample prepared in Example 3 and the manganese-doped sample prepared in Example 4 showed some changes compared to the undoped sample, neither reached the performance level of the chromium-doped sample in Example 2. This fully demonstrates that the Co3(OH)2V2O7·2H2O / CF electrode prepared in Example 2 exhibits excellent OER catalytic activity in 1 M KOH electrolyte. Specifically, at a current density of 10 mA cm⁻¹, the overpotential was 215 mV. -2 At this point, the required overpotential is only 135 mV, significantly lower than that of the undoped sample (215 mV) and other metal-doped samples. This data strongly demonstrates that the introduction of chromium significantly lowers the energy barrier of the oxygen evolution reaction and enhances the reaction kinetics. Furthermore, by calculating the double-layer capacitance (C0...),... dl It was found that the C material in this embodiment... dl The value is as high as 14.4 mFcm -2This indicates that it has a larger electrochemical active surface area and more active sites. This is mainly attributed to Cr 3+ Ions, acting as additional redox pairs, interact with the original V 5+ / V 4+ The redox pair produced a synergistic effect, optimized the electronic structure, and accelerated the electron transport rate, thereby achieving a qualitative leap in catalytic performance.

[0039] In summary, the comparative experimental results strongly demonstrate that the selection of chromium as a dopant in this invention yields unexpected technical effects. Although iron, manganese, and chromium are all transition metals and are close in position in the periodic table, their behavior is drastically different in the specific crystal system of basic cobalt vanadate. This invention, through innovative research, confirms that by doping basic cobalt vanadate catalysts with Cr, the synergistic effect of the elements can be leveraged to further improve the activity and stability of the catalyst. In contrast, when Fe or Mn ions enter the crystal lattice, their ionic radius, electron configuration, or valence state is not as well-matched to the crystal framework as that of Cr ions, failing to form an effective synergistic redox mechanism. They may even damage the original active site structure or hinder electron transport, resulting in limited or even decreased catalytic activity improvement.

[0040] Specifically, this invention introduces chromium ions of specific radius and valence state into a basic cobalt vanadate lattice, utilizing Cr... 3+ It itself acts as an additional redox pair, with the original V 5+ / V 4+ The redox pair exhibits a synergistic effect, providing more and more flexible electron transport pathways for the catalytic cycle. This synergistic optimization of the electronic structure and oxygen species activity makes it easier for active oxygen species to be generated and utilized on the catalyst surface, enhancing electron transport capacity and resulting in a significantly reduced overpotential in the electrochemical oxygen evolution reaction. Simultaneously, the introduction of chromium ions with stable valence and suitable ionic radius into the basic cobalt vanadate lattice framework strengthens the lattice skeleton, inhibits excessive lattice oxygen loss and overall structural instability, and partially occupies easily soluble sites in the lattice, thereby stabilizing the overall structure and reducing the exposure of defect sites. This meets the stringent requirements of industrial applications for catalyst stability and durability.

[0041] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A Cr-doped basic cobalt vanadate catalyst, characterized in that, It includes a conductive substrate and a basic cobalt vanadate supported on the conductive substrate, wherein Cr is doped in the crystal lattice of the basic cobalt vanadate.

2. The Cr-doped basic cobalt vanadate catalyst according to claim 1, characterized in that, The molar ratio of cobalt to chromium in the basic cobalt vanadate is 10:1 to 3:

1.

3. The Cr-doped basic cobalt vanadate catalyst according to claim 2, characterized in that, The molar ratio of cobalt to chromium in the basic cobalt vanadate is 4:

1.

4. The Cr-doped basic cobalt vanadate catalyst according to claim 1, characterized in that, The conductive substrate is selected from foamed metal, carbon cloth, or metal mesh.

5. The Cr-doped basic cobalt vanadate catalyst according to claim 4, characterized in that, The conductive substrate is copper foam.

6. A method for preparing the Cr-doped basic cobalt vanadate catalytic material according to any one of claims 1-5, characterized in that, include: A conductive substrate is placed in a mixture containing a cobalt source, a chromium source, and a vanadium source, and subjected to a hydrothermal reaction to obtain the Cr-doped basic cobalt vanadate catalyst.

7. The method for preparing the Cr-doped basic cobalt vanadate catalytic material according to claim 6, characterized in that, include: Prepare a mixed solution of Co(NO3)2 and Cr(NO3)3; Preparation of NaVO3 solution; Then, the mixed solution of Co(NO3)2 and Cr(NO3)3 was added to the NaVO3 solution and mixed thoroughly to obtain a suspension. A conductive substrate is added to the prepared suspension, and a hydrothermal reaction is carried out at 150-180℃ for 8-12 hours. The resulting product is washed and dried to obtain a Cr-doped basic cobalt vanadate catalyst.

8. The method for preparing the Cr-doped basic cobalt vanadate catalytic material according to claim 7, characterized in that, The hydrothermal reaction was carried out at a temperature of 160℃ for 10 hours.

9. The method for preparing the Cr-doped basic cobalt vanadate catalytic material according to claim 7, characterized in that, The conductive substrate undergoes pretreatment before hydrothermal reaction, including: cutting it to a suitable size, then sequentially washing it with alcohol, acid, and water, and finally drying it for later use.

10. The application of the Cr-doped basic cobalt vanadate catalyst according to any one of claims 1-5 in the oxygen evolution reaction of water electrolysis.

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