Preparation methods and applications of Ca-doped RuO2

Abstract

The application provides a preparation method of Ca-doped RuO2, and adopts the following technical scheme: the preparation method of the Ca-doped RuO2 is as follows: grinding +3 valence Ru salt, +2 valence Ca salt and fused salt in a mortar, then pouring into a crucible, keeping at 350 DEG C in a tube furnace for 3h-6h, taking out after natural cooling, cleaning and drying to obtain the Ca-doped RuO2; and one of lithium nitrate, potassium nitrate and sodium nitrate and a mixture thereof are selected; the molar feeding ratio of Ru and Ca is 10:4-10:12, and the mass of the fused salt corresponding to 0.2-0.4mmol of Ru is 2.5-5g. In the application, Ca atoms replace part of Ru atoms in RuO2, slow down the dissolution rate of Ru, and improve the catalytic activity and stability of RuO2 in acid OER. The method is simple and has the potential for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of catalysts, and particularly to a method for preparing Ca-doped RuO2 and its applications. Background Technology

[0002] Electrochemical splitting of water into H2 and O2 is considered a promising hydrogen production technology. Among various water electrolysis technologies, alkaline water electrolysis is relatively mature and has been applied industrially, but it faces challenges such as product gas cross-contamination, high ohmic resistance, and limited current density. Proton exchange membrane (PEM) electrolysis, on the other hand, has attracted attention due to its advantages such as high current density, high efficiency, and more compact equipment.

[0003] Due to the harsh acidic medium and the high overpotential of the oxygen evolution reaction (OER), most metals face dissolution problems in acidic OER processes. Currently, most commercial PEM electrolyzers use IrO2 catalysts, but the high cost of Ir-based catalysts limits the further development of PEM electrolyzers. RuO2, with its good OER performance, is considered a promising candidate catalyst, exhibiting better OER activity than IrO2. However, RuO2 is easily oxidized to higher valence Ru (>+4) during acidic OER reactions, resulting in generally poor stability, which severely hinders its further development. Improving the stability of RuO2 while maintaining its high catalytic activity is a pressing challenge.

[0004] In existing technologies, ruthenium dioxide is typically prepared by heating metallic ruthenium powder at 800–900°C for 1 hour in an oxygen atmosphere, followed by cooling to obtain the final product. While the synthesized RuO2 exhibits good catalytic activity, it suffers from poor stability and rapid deactivation. Summary of the Invention

[0005] This invention employs a molten salt synthesis method to prepare Ca-doped RuO2, which significantly improves its catalytic performance and stability. The method is simple and has the potential for large-scale production.

[0006] The present invention adopts the following technical solution: a method for preparing Ca-doped RuO2, wherein the method is as follows: grinding +3 valence Ru salt, +2 valence Ca salt and molten salt in a mortar, then pouring into a crucible, keeping it at 350°C for 3h-6h in a tube furnace, taking it out after natural cooling, washing and drying to obtain Ca-doped RuO2; and using one of lithium nitrate, potassium nitrate, sodium nitrate and a mixture thereof; the molar ratio of Ru to Ca is 10:4-10:12, and the mass of molten salt corresponding to 0.2-0.4 mmol of Ru is 2.5-5g.

[0007] Furthermore, the +3 valence Ru salt is ruthenium chloride, ruthenium nitrate, or ruthenium chloride hydrate.

[0008] Furthermore, the +2 valence Ca salt is calcium chloride.

[0009] Furthermore, the molar ratio of Ru to Ca is 10:4.

[0010] Furthermore, the heating rate of the tube furnace is 5℃ / min-15℃ / min.

[0011] Furthermore, the holding time in the tubular furnace is 6 hours.

[0012] Furthermore, the cleaning process includes: first soaking in deionized water to remove molten salt, then acid soaking, and finally rinsing with deionized water. The acid can be 1 mol / L hydrochloric acid or 0.5 mol / L sulfuric acid.

[0013] This invention also provides the application of the above-mentioned catalyst as an acidic OER catalyst, which exhibits excellent catalytic performance in 0.5 mol / L H2SO4 and at 10 mA / cm². 2 It can maintain stability for more than 100 hours at a current density.

[0014] The beneficial effects of this invention are as follows: This invention uses Ca atoms to replace some Ru atoms in RuO2, which slows down the dissolution rate of Ru and improves the catalytic activity of RuO2 in acidic OER. Attached Figure Description

[0015] Figure 1 These are SEM images of the products obtained in Examples 1-3; Figure 2 The images show the XRD patterns of the products obtained in Examples 1-3. As can be seen from the images, the obtained products are rutile phase. Figure 3 The figure shows the EDS elemental distribution of the products obtained in Examples 1-3. As can be seen from the figure, Ca, Ru, and O are evenly distributed in the obtained products. Figure 4 The products obtained in Examples 1-3 are at 10 mA / cm 2 The graph shows the ICP test data of the dissolved Ru under current. Figure 5 C is the product obtained in Examples 1-3 dl picture; Figure 6 This is a normalized LSV diagram of the products obtained in Examples 1-3; Figure 7 The LSV diagrams are of the products obtained in Examples 1-3. Figure 8 The samples of the products obtained in Examples 1-3 are at 10 mA / cm 2 Stability test results under current; Figure 9 The LSV plots for the first and fifth iterations of the product obtained in Comparative Example 1 are shown. Figure 10 These are the LSV diagrams of the first and fifth iterations of the product obtained in Comparative Example 2. Detailed Implementation

[0016] The present invention will be further described below with reference to the embodiments and accompanying drawings, but is not limited thereto.

[0017] Example 1

[0018] Grind and mix 0.2 mmol RuCl3 powder, 0.08 mol CaCl2·2H2O powder and 2.5 g LiNO3, pour the mixture into a crucible, place it in a tube furnace, heat it to 350 °C at 5 °C / min, hold it at that temperature for 6 h, and then let it cool naturally.

[0019] After removing the sample from the tube furnace, first immerse the sample in deionized water to remove the molten salt, then soak it in 1 mol / L hydrochloric acid for 1 hour, then wash it several times with deionized water, and finally dry it before testing.

[0020] Example 2

[0021] 0.2 mmol RuCl3 powder, 0.24 mol CaCl2·2H2O powder and 2.5 g KNO3 were ground and mixed, poured into a crucible, and heated to 350 °C at 15 °C / min in a tube furnace, held for 6 h, and then cooled naturally.

[0022] After removing the sample from the tube furnace, first immerse the sample in deionized water to remove molten salt, then soak it in 0.5 mol / L sulfuric acid for 1 hour, then wash it several times with deionized water, and finally dry it before testing.

[0023] Implementation 3

[0024] 0.4 mmol RuCl3 powder, 0.16 mol CaCl2·2H2O powder and 5 g NaNO3 were ground and mixed, poured into a crucible, and heated to 350 °C at 7 °C / min in a tube furnace, held for 6 h, and then cooled naturally.

[0025] After removing the sample from the tube furnace, first immerse the sample in deionized water to remove molten salt, then soak it in 1 mol / L hydrochloric acid for 0.5 h, then wash it several times with deionized water, and finally dry it before testing.

[0026] Comparative Example 1 By replacing CaCl2·2H2O in Example 1 with an equimolar amount of hydrated magnesium chloride, Mg-RuO2 synthesized using the molten salt method was obtained.

[0027] Comparative Example 2 The specific steps for synthesizing Ca-RuO2 using the sol-gel method are as follows: 0.2 mmol RuCl3, 0.08 mol CaCl2·2H2O, and 50 mg PVP powder were dissolved in 10 mL of ethanol. The solution was then sonicated for 10 minutes, followed by stirring at 80°C for 6 hours. After stirring, the ethanol was evaporated, and the powder was incubated at 350°C for 6 hours. The powder was then soaked in 1 mol / L hydrochloric acid for 0.5 hours, washed several times with deionized water, and dried before testing.

[0028] 10 mg of the samples obtained in Examples 1-3 above were loaded onto a 1 cm² substrate. 2 On a Ti substrate, at 10 mA / cm 2 Under current, the dissolved Ru was tested by ICP. After 10 hours, the Ru concentrations in the solutions of Examples 1-3 were 287.83 ug / L, 320.58 ug / L, and 312.17 ug / L, respectively. The results obtained in Example 1 are shown in [reference needed]. Figure 4 The Ru dissolution rate of Ca-RuO2 was significantly lower than that of RuO2, indicating that Ca-RuO2 had a lower Ru dissolution rate and better sample stability during acidic OER.

[0029] The C of the sample was measured by the CV cycle method. dl Value, C of Examples 1-3 dl The values ​​were 14.4 mF cm. -2 11.2mF cm -2 11.6mF cm -2 C obtained in Example 1 dl Worth seeing Figure 5 It can be seen that the C of Ca-RuO2 dl The concentration of Ca was significantly higher than that of RuO2, indicating that the incorporation of Ca can significantly increase the density of active sites.

[0030] Dividing the current density in the LSV curve by the electrochemically active area yields the normalized LSV plot of the sample. Figure 6 The specific activity of Ca-RuO2 is higher than that of RuO2, indicating that the intrinsic OER activity of the Ca-RuO2 catalyst is improved due to the introduction of Ca.

[0031] The samples obtained in Examples 1-3 and the samples in Comparative Examples 1-2 were subjected to OER performance tests, and the test methods are as follows: First, a catalyst slurry is prepared. The specific preparation method is as follows: the catalyst is added to 400 μL of isopropanol containing 40 μL of naphthol, and sonicated for one hour until the catalyst is uniformly dispersed. 4 μL of the uniformly dispersed catalyst slurry is then dropped onto a surface with a surface area of ​​0.07065 cm². 2 The RuO2 electrode was dried at room temperature on a glassy carbon electrode. A three-electrode cell was used for testing, with the glassy carbon electrode as the working electrode, a platinum sheet as the counter electrode, and a calomel electrode as the reference electrode. The electrolyte was 0.5 mol / L H2SO4, and the scan rate was 1 mV / s. The OER performance of RuO2 was tested under the same conditions.

[0032] Among them, the Ca-RuO2 obtained in Example 1 has a strength of 10 mA / cm². 2 The overpotential was 206 mV (see LSV diagram of sample from Example 1). Figure 7 The Ca-RuO2 obtained in Example 2 has a 10 mA / cm² value. 2 The overpotential was 226 mV, and the Ca-RuO2 obtained in Example 3 had an overpotential of 10 mA / cm. 2 The overpotential is 225mV, and the overpotential of RuO2 is 10mA / cm. 2 The overpotential was 303 mV. The overpotential of Ca-RuO2 was significantly lower than that of RuO2, proving that the catalytic performance of Ca-RuO2 in acidic OER was significantly better than that of RuO2.

[0033] Furthermore, the samples from Examples 1-3 and Comparative Examples 1-2 were tested at 10 mA / cm². 2 For stability testing under current, see Figure 8-10 Among them, RuO2 was deactivated in less than 10 hours. Comparative Example 1, Mg-RuO2 synthesized using the molten salt method, had an overpotential of 246 mV at a current density of 10 mA / cm², but its performance significantly decreased after only 5 LSV cycles. Comparative Example 2, Ca-RuO2 synthesized using the sol-gel method, had an overpotential of 245 mV at a current density of 10 mA / cm², but its performance also significantly decreased after only 5 LSV cycles. In contrast, the Ca-RuO2 obtained in Examples 1-3 remained stable after 100 h, 80 h, and 80 h, respectively, demonstrating a significant improvement in its stability.

[0034] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing Ca-doped RuO2, characterized in that, The method is as follows: +3 valence Ru salt, +2 valence Ca salt and molten salt are ground in a mortar, then poured into a crucible and kept at 350℃ for 3h-6h in a tube furnace. After natural cooling, the mixture is taken out, cleaned and dried to obtain Ca-doped RuO2. The molten salt is selected from one of lithium nitrate, potassium nitrate and sodium nitrate. The molar ratio of Ru to Ca is 10:4-10:12, and the mass of molten salt corresponding to 0.2-0.4 mmol of Ru is 2.5-5g.

2. The preparation method according to claim 1, characterized in that, The +3 valence Ru salt is ruthenium chloride, ruthenium nitrate, or ruthenium chloride hydrate.

3. The preparation method according to claim 1, characterized in that, The +2 valence Ca salt is calcium chloride.

4. The preparation method according to claim 1, characterized in that, The molar ratio of Ru to Ca is 10:

4.

5. The preparation method according to claim 1, characterized in that, The heating rate of the tube furnace is 5℃ / min-15℃ / min.

6. The preparation method according to claim 1, characterized in that, The heat preservation time in the tubular furnace is 6 hours.

7. The preparation method according to claim 1, characterized in that, The cleaning process includes: first soaking in deionized water to remove molten salt, then acid soaking, and then rinsing with deionized water; the acid used is 1 mol / L hydrochloric acid and 0.5 mol / L sulfuric acid.

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