Cobalt-ruthenium double-metal doped cerium dioxide catalytic electrode and preparation and application thereof
By preparing a cobalt-ruthenium bimetallic doped cerium dioxide catalyst, the problem of poor catalytic performance in the nitrate reduction reaction under alkaline conditions was solved, achieving efficient and selective ammonia synthesis and improving the ammonia generation rate and Faraday efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-06
- Publication Date
- 2026-04-14
AI Technical Summary
Existing technologies exhibit poor catalytic performance and selectivity in the nitrate reduction reaction (NO3-RR) under alkaline conditions, resulting in low ammonia generation rate, Faraday efficiency, and energy utilization efficiency, making it difficult to achieve highly selective and efficient ammonia synthesis from nitrate wastewater.
The preparation method of cobalt-ruthenium bimetallic doped cerium dioxide catalyst includes mixing cerium salt with sodium hydroxide aqueous solution, precipitation, washing, vacuum drying and calcination, followed by mixing with cobalt salt and ruthenium salt, and loading onto a conductive substrate to form a cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode.
It exhibits high redox potential and high current density in alkaline environments, with an ammonia yield of up to 82.54 mg/h/cm2 and a Faraday efficiency of 97.42%. It also maintains high selectivity and applicability at low NO3- concentrations.
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Figure CN121853036A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of catalyst technology, specifically relating to a cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode and its preparation and application. Background Technology
[0002] Nitrate anion NO3 - Widely present in industrial wastewater and polluted groundwater, NO3 has adverse effects on the environment and human health, and poses a significant threat to the sustainable development of industry and agriculture. - Reducing NH3 to a green and valuable product is a sustainable solution. NH3, as a widely used chemical raw material, is crucial for global industrial and agricultural development. Currently, the main route for NH3 synthesis is the Haber-Bosch process, which requires high temperatures of 400–500°C and high pressures of 130–170 bar. This process consumes approximately 1.4% of global energy and generates about 1% of global carbon dioxide emissions.
[0003] In the redox reaction of nitrates (NO3-RR), the NO bond energy is only 204 kJ / mol. From a thermodynamic perspective, the NO bond is more prone to breakage, which is why NO3-... - The conversion offers a natural advantage. Furthermore, nitrates are among the most common pollutants in natural aquatic environments, not only seriously endangering human health but also significantly disrupting the nitrogen balance in ecosystems. Therefore, using renewable energy to power the electrocatalytic synthesis of NH3 from nitrates in wastewater under normal temperature and pressure conditions is considered a green synthesis method that can replace the traditional Haber-Bosch process while simultaneously achieving waste resource conversion and environmental remediation.
[0004] In recent years, research on electrocatalytic NO3-RR has become increasingly extensive, but it still faces many challenges. The redox reaction of nitrates (NO3-RR) involves eight electron transfer steps, has slow reaction kinetics, and is further complicated by competition from side reactions such as hydrogen evolution and nitrite formation. This results in low NH3 formation rates, Faraday efficiency, and energy utilization efficiency, far from meeting industrial requirements. Therefore, achieving highly selective and efficient NH3 synthesis from nitrate wastewater remains a significant challenge. Summary of the Invention
[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing cobalt-ruthenium bimetallic doped cerium dioxide catalysts.
[0006] Another object of the present invention is to provide a cobalt-ruthenium bimetallic doped cerium dioxide catalyst obtained by the above method.
[0007] Another objective of this invention is to provide a method for preparing a cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode.
[0008] Another object of the present invention is to provide a cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode (CoRu / CeO2) obtained by the above preparation method.
[0009] Another objective of this invention is to provide the application of the aforementioned cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode in the electrocatalytic nitrate reduction reaction to synthesize ammonia, in order to solve the problems of poor catalytic performance and selectivity of NO3-RR under alkaline conditions.
[0010] The objective of this invention is achieved through the following technical solutions.
[0011] A method for preparing a cobalt-ruthenium bimetallic doped cerium dioxide catalyst includes the following steps:
[0012] Step 1: Mix cerium salt and water evenly, add sodium hydroxide aqueous solution, stir for at least 20 minutes to obtain the first solution, let the first solution stand at 100~120℃ for 20~24 hours, discard the supernatant to obtain the first precipitate, wash the first precipitate in sequence, vacuum dry and calcine to obtain cerium dioxide support, wherein, by molar fraction, the ratio of cerium element in cerium salt to sodium hydroxide in sodium hydroxide aqueous solution is 0.002: (0.021~0.025);
[0013] In step 1, the ratio of the molar amount of cerium in the cerium salt to the volume fraction of water in step 1 is 0.002:(5~10), where the molar amount is in mol and the volume fraction is in mL.
[0014] In step 1, the stirring time is 30-60 minutes and the stirring speed is 400-500 rpm.
[0015] In step 1, the mixing process includes stirring at a speed of 400-500 rpm for 10-20 minutes.
[0016] In step 1, the concentration of sodium hydroxide in the sodium hydroxide aqueous solution is 6~7 mol / L.
[0017] In step 1, the cerium salt includes cerium nitrate hexahydrate.
[0018] In step 1, the washing includes rinsing the first precipitate sequentially with water and anhydrous ethanol.
[0019] In step 1, the vacuum drying temperature is 60~80℃ and the vacuum drying time is 8~12h.
[0020] In step 1, the calcination includes: heating to 400-500°C at a rate of 5-10°C / min, and calcining for 4-6 hours.
[0021] Step 2: Mix the cerium dioxide support and water evenly, add cobalt salt and ruthenium salt, stir for 4-6 hours, centrifuge to obtain a second precipitate, wash the second precipitate, vacuum dry and calcine it to obtain a cobalt-ruthenium bimetallic doped cerium dioxide catalyst, wherein the ratio of cerium element in cerium salt, cobalt element in cobalt salt and ruthenium element in ruthenium salt by molar amount is 10.28:3:(1-5).
[0022] In step 2, the ratio of the molar amount of cerium salt to the volume fraction of water in step 2 is 0.00023:(30~40), where the molar amount is in mol and the volume fraction is in mL.
[0023] In step 2, the mixing process includes stirring at a speed of 400-500 rpm for 10-20 minutes.
[0024] In step 2, the cobalt salt includes cobalt nitrate hexahydrate, and the ruthenium salt includes ruthenium trichloride.
[0025] In step 2, the centrifugation speed is 8000~10000 rpm and the centrifugation time is 3~5 min.
[0026] In step 2, the washing includes rinsing the second precipitate sequentially with water and anhydrous ethanol.
[0027] In step 2, the vacuum drying temperature is 60~80℃, and the vacuum drying time is 8~12h.
[0028] In step 2, the calcination includes: heating to 400-500°C at a rate of 5-10°C / min, and calcining for 2-4 hours.
[0029] The cobalt-ruthenium bimetallic doped cerium dioxide catalyst obtained by the above method.
[0030] A cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode includes: a conductive substrate and the cobalt-ruthenium bimetallic doped cerium dioxide catalyst, wherein the cobalt-ruthenium bimetallic doped cerium dioxide catalyst is supported on the conductive substrate.
[0031] In the above technical solution, the loading of cobalt-ruthenium bimetallic doped cerium dioxide catalyst in the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode is at least 0.2 mg per square centimeter.
[0032] In the above technical solution, the conductive substrate includes carbon, preferably a carbon fiber substrate or a carbon-based composite substrate.
[0033] A method for preparing a cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode includes: mixing a cobalt-ruthenium bimetallic doped cerium dioxide catalyst with a second solution, sonicating for at least 20 minutes to obtain a mixed solution, dripping the mixed solution onto the surface of a conductive substrate to uniformly load the cobalt-ruthenium bimetallic doped cerium dioxide catalyst onto the conductive substrate, and drying to obtain a cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode, wherein the second solution is a mixture of anhydrous ethanol and Nafion dispersion.
[0034] In the above technical solution, the ratio of the mass fraction of the cobalt-ruthenium bimetallic doped cerium dioxide catalyst to the volume fraction of the second solution is (0.2~1):0.35, where the mass fraction is in mg and the volume fraction is in mL.
[0035] In the above technical solution, the ratio of anhydrous ethanol to Nafion dispersion in the second solution is 0.3: (0.05~0.1) by volume.
[0036] In the above technical solution, the drying temperature is room temperature, and the drying time is 6-8 hours.
[0037] The above-mentioned cobalt-ruthenium bimetallic doped cerium dioxide catalyst is used in the redox reaction of nitrate to synthesize ammonia.
[0038] The above-mentioned cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode is used in the redox reaction of nitrate to synthesize ammonia.
[0039] In the above technical solution, a cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode catalyzes the synthesis of ammonia from nitrate anions.
[0040] Compared with the prior art, the present invention has the following beneficial effects:
[0041] 1. The cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode prepared by this invention exhibits a high redox potential in an alkaline environment, with a current density of -100 mA / cm². 2 The overpotential at that time was -0.765 V vs. RHE.
[0042] 2. The cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode prepared in this invention achieves an ammonia yield of up to 82.54 mg / h / cm³ in an H-type electrolytic cell. 2 It also has extremely high Faraday efficiency (97.42%).
[0043] 3. The cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode prepared in this invention operates under low NO3 conditions. - It still exhibits high ammonia production performance, high selectivity, and strong applicability at a concentration (5mM). Attached Figure Description
[0044] Figure 1 Figure a shows the microstructure of the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode in Example 4. Figure 1 b represents the distribution of cobalt in the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode of Example 4. Figure 1 c represents the distribution of ruthenium in the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode of Example 4;
[0045] Figure 2 X-ray diffraction patterns of the cerium dioxide support in Comparative Example 3 and the cobalt-ruthenium bimetallic doped cerium dioxide catalysts in Examples 1-5;
[0046] Figure 3 LSV curves of NO3-RR were obtained using the carbon felt-based ruthenium-doped cerium dioxide catalytic electrode of Comparative Example 1, the carbon felt-based cobalt-doped cerium dioxide catalytic electrode of Comparative Example 2, the cerium dioxide electrode of Comparative Example 3, and the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode of Example 4 as working electrodes.
[0047] Figure 4 The Tafel slope of NO3-RR is shown when the carbon felt-based ruthenium-doped cerium dioxide catalytic electrode of Comparative Example 1, the carbon felt-based cobalt-doped cerium dioxide catalytic electrode of Comparative Example 2, the cerium dioxide electrode of Comparative Example 3, and the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode of Example 4 are used as working electrodes.
[0048] Figure 5 The cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrodes of Examples 1-5 were used as working electrodes to conduct NO3-RR NH3 production at a voltage of -0.7 to -1.3 V vs. RHE;
[0049] Figure 6 The cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode of Example 4 was used as the working electrode to perform NO3-RR NH3 production and Faraday efficiency at -0.7 to -1.3 V vs. RHE.
[0050] Figure 7 Using the carbon felt-based ruthenium-doped cerium dioxide catalytic electrode of Comparative Example 1, the carbon felt-based cobalt-doped cerium dioxide catalytic electrode of Comparative Example 2, the cerium dioxide electrode of Comparative Example 3, and the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode of Example 4 as working electrodes, the NH3 production of NO3-RR, the Faradaic efficiency of ammonia synthesis, the Faradaic efficiency of nitrite production, and the Faradaic efficiency of hydrogen production were measured at a voltage of -1.0V vs. RHE.
[0051] Figure 8 The proton NMR spectrum of the electrolyte used in the NO3-RR reaction with the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode of Example 4 as the working electrode;
[0052] Figure 9 The cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode used in Example 4 was used as the working electrode in a low-concentration nitrate saline solution (5 mM) for NO3-RR performance testing. - NO2 - and NH4 + The concentration change. Detailed Implementation
[0053] The technical solution of the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.
[0054] The purity and source of the reagents involved in the following examples are as follows:
[0055]
[0056] In the following examples, the Nafion dispersion (D-521) was purchased from Tianjin Yanshen Technology Co., Ltd.
[0057] The instrument models and manufacturers involved in the following embodiments are as follows:
[0058]
[0059] In the following examples, the water used is deionized water.
[0060] In the following examples, the stirring speed is 400 rpm.
[0061] Examples 1-5
[0062] A method for preparing a cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode includes:
[0063] A cobalt-ruthenium bimetallic doped cerium dioxide catalyst was mixed with a second solution and sonicated for 20 min to obtain a mixed solution. 0.35 mL of this mixed solution was dropwise applied to the surface of a carbon fiber felt (conductive substrate, 10 mm × 10 mm × 3 mm) to uniformly load the cobalt-ruthenium bimetallic doped cerium dioxide catalyst onto the carbon fiber felt. The mixture was then dried at room temperature for 8 h to obtain a cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode. The second solution was a mixture of anhydrous ethanol and Nafion dispersion, with a volume ratio of 0.3:0.05. The mass fraction of the cobalt-ruthenium bimetallic doped cerium dioxide catalyst was in the volume fraction ratio of 0.2:0.35 to the second solution. (Mass fractions are in mg, and volume fractions are in mL.)
[0064] The loading of cobalt-ruthenium bimetallic doped cerium dioxide catalyst in the above-mentioned cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode is 0.2 mg.
[0065] The method for preparing a cobalt-ruthenium bimetallic doped cerium dioxide catalyst includes the following steps:
[0066] Step 1: Mix cerium salt (cerium nitrate hexahydrate) with water and stir for 10 min to ensure uniform mixing. Add sodium hydroxide aqueous solution (sodium hydroxide concentration in the sodium hydroxide aqueous solution is 6 mol / L) and stir for 30 min to completely precipitate cerium element to obtain the first solution. Let the first solution stand at 100℃ for 24 h, discard the supernatant to obtain the first precipitate, wash the first precipitate (washing with water and anhydrous ethanol in sequence), vacuum dry at 60℃ for 12 h, then heat to 400℃ at a rate of 5℃ / min and calcine at 400℃ for 4 h to obtain cerium dioxide support (CeO2). The ratio of cerium element in the cerium salt to sodium hydroxide in the sodium hydroxide aqueous solution is 0.002:0.21 by molar amount.
[0067] The ratio of the molar amount of cerium in the cerium salt to the volume fraction of water in step 1 is 0.002:5. The molar amount is expressed in mol and the volume fraction is expressed in mL.
[0068] Step 2: Cerium dioxide support and water are mixed and stirred for 10 min to ensure uniform mixing. Cobalt salt (cobalt nitrate hexahydrate) and ruthenium salt (ruthenium trichloride) are added and stirred for 4 h. The mixture is then centrifuged at 10000 rpm for 3 min to obtain a second precipitate. The second precipitate is washed (sequentially with water and anhydrous ethanol), dried under vacuum at 60 °C for 12 h, and then calcined at 400 °C for 2 h at a rate of 5 °C / min to obtain a cobalt-ruthenium bimetallic doped cerium dioxide catalyst. The ratio of cerium element in the cerium salt, cobalt element in the cobalt salt, and ruthenium element in the ruthenium salt, by molar amount, is X. The molar amount of cerium salt to the volume fraction of water from Step 2 is 0.00023:40. The units of molar amount are mol, and the units of volume fraction are mL. The values of X are shown in Table 1.
[0069]
[0070] Comparative Example 1
[0071] A method for preparing a carbon felt-based ruthenium-doped cerium dioxide catalytic electrode is basically the same as that in Example 1, except that cobalt salt (cobalt nitrate) is not added in step 2 of this comparative example.
[0072] Comparative Example 2
[0073] A method for preparing a carbon felt-based cobalt-doped cerium dioxide catalytic electrode is basically the same as that in Example 1, except that ruthenium salt (ruthenium chloride) is not added in step 2 of this comparative example.
[0074] Comparative Example 3
[0075] A method for preparing a cerium dioxide electrode includes: mixing a cerium dioxide support with a second solution, sonicating for 20 min to obtain a mixed solution, dripping 0.35 mL of the mixed solution onto the surface of a carbon fiber felt (10 mm × 10 mm × 3 mm) to uniformly load the cerium dioxide support onto the carbon fiber felt, and drying at room temperature for 8 h to obtain a cerium dioxide electrode. The second solution is a mixture of anhydrous ethanol and Nafion dispersion, with a volume ratio of 0.3:0.05. The mass fraction of the cerium dioxide support is in the ratio of the volume fraction of the second solution to 0.2:0.35. The mass fractions are expressed in mg, and the volume fractions are expressed in mL.
[0076] The cerium dioxide support is the cerium dioxide support obtained in step 1 of the preparation of the cobalt-ruthenium bimetallic doped cerium dioxide catalyst in Example 1.
[0077] The microstructure and surface elemental composition of the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode of Example 4 were observed using transmission electron microscopy. The results are as follows: Figure 1 As shown. By Figure 1 As can be seen from a, the cerium dioxide support in the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode of Example 4 has a rod-like structure. Figure 1 b and Figure 1 As can be seen from c, cobalt and ruthenium were successfully doped onto the surface of the carbon fiber felt.
[0078] The X-ray diffraction patterns of the cobalt-ruthenium bimetallic doped cerium dioxide catalysts of Examples 1-5 and the cerium dioxide support of Comparative Example 3 were measured using an X-ray diffractometer. The results are as follows: Figure 2 As shown. By Figure 2 It can be seen that the characteristic diffraction peaks of the cobalt-ruthenium bimetallic doped cerium dioxide catalysts in Examples 1-5 are not significantly different from those of the cerium dioxide support in Comparative Example 3, indicating that the doping method of the cobalt-ruthenium bimetallic doped cerium dioxide catalysts in Examples 1-5 is such that both cobalt and ruthenium are doped into the cerium dioxide support in a single-atom manner.
[0079] Example 6
[0080] NO3-RR Performance Test: At room temperature, the redox reaction of nitrate (NO3-RR) was conducted in an H-type electrolytic cell using a three-electrode system on an electrochemical workstation. The three electrodes were the working electrode, the counter electrode, and the reference electrode. The working electrode was one of the following: the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode of Example 4; the carbon felt-based ruthenium doped cerium dioxide catalytic electrode of Comparative Example 1; the carbon felt-based cobalt doped cerium dioxide catalytic electrode of Comparative Example 2; and the cerium dioxide electrode of Comparative Example 3. The counter electrode was a platinum electrode, and the reference electrode was a saturated silver chloride electrode. The working electrode and the reference electrode were placed in the cathode chamber of the H-type electrolytic cell (with the working electrode and reference electrode separated). Argon gas was pre-introduced into the cathode chamber to prevent the working electrode from being affected by dissolved oxygen or other substances. The counter electrode was placed in the anode chamber of the H-type electrolytic cell. The cathode chamber and the anode chamber were separated by a proton exchange membrane. 10 ml of electrolyte was added to each of the cathode and anode chambers. The electrolyte consisted of potassium hydroxide and potassium nitrate. 14 N(K) 14 A mixture of NO3 and water, wherein the concentration of KOH in the electrolyte is 0.1M, and the concentration of K in the electrolyte is... 14 The concentration of NO3 is 0.5M.
[0081] The voltage of the working electrode was scanned from -0.2 V vs. RHE to -1.3 V vs. RHE at a rate of 20 mV / s, and the current density between the working electrode and the counter electrode was recorded to obtain the LSV curve as shown below. Figure 3 As shown, by Figure 3 The LSV curve shown is fitted to calculate the Tafel slope, as shown in the figure. Figure 4 As shown in Table 3.
[0082] Depend on Figure 3 It can be seen that the current density of the working electrode in Example 4 is much greater than that in Comparative Examples 1-3 (by comparing the absolute values on the vertical axis), indicating that simultaneous doping of cobalt and ruthenium on the cerium dioxide support is beneficial to improving its electron transport capability. Table 2 shows the current density at a current density of -100 mA / cm². 2 The overpotentials of the working electrodes in Examples 4 and Comparative Examples 1-3 were compared. The overpotential of the working electrode in Example 4 was -0.765 V vs. RHE, which was higher than that in Comparative Examples 1-3, indicating that the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode exhibited extremely high NO3 content. - Electroreduction capability.
[0083] The Tafel slope of the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode in Example 4 was 358 mV / dec, which was much lower than that of Comparative Examples 1-3. This indicates that the NO3-RR kinetic rate of the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode in Example 4 was the fastest, suggesting that the synergistic doping of cobalt and ruthenium improved its NO3-RR performance.
[0084] Table 2
[0085]
[0086] Table 3
[0087]
[0088] Example 7
[0089] Ammonia production test: Using the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrodes of Examples 1-5 as working electrodes, the ammonia production of their NO3-RR reaction for 20 min was tested, including: using the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrodes of Examples 1-5 as working electrodes, the "NO3-RR performance test" of Example 6 was performed, and the voltage of the working electrodes was set to -0.7 V vs. RHE, -0.8 V vs. RHE, -0.9 V vs. RHE, -1.0 V vs. RHE, -1.1 V vs. RHE, -1.2 V vs. RHE, and -1.3 V vs. RHE, respectively. RHE was performed, and NO3-RR reaction was carried out for 20 min. After the NO3-RR reaction, 2 mL of electrolyte in the cathode chamber was taken, and 3.2 mL of indophenol blue mixed solution was added. The mixture was shaken well and allowed to stand for 2 h to obtain the sample to be tested. The absorbance of the sample at 650 nm was measured using a UV-Vis spectrophotometer. The absorbance was then substituted into the first standard curve to obtain the ammonium ion concentration (NH4+) in the electrolyte of the cathode chamber after the working electrode was activated. + The concentration of );
[0090] The method for plotting the first standard curve includes: preparing standard ammonium sulfate aqueous solutions with concentrations of 0.0005 mM, 0.025 mM, 0.05 mM, and 0.125 mM using ammonium sulfate with a purity of 99% purchased from Shanghai Maclean Biochemical Technology Co., Ltd., and water, respectively. The standard ammonium sulfate aqueous solution contains ammonium ions (NH4+). + The concentrations of ammonium sulfate were 0.001 mM, 0.05 mM, 0.1 mM, and 0.25 mM, respectively. The absorbance of the standard ammonium sulfate aqueous solution at 650 nm was measured using a UV-Vis spectrophotometer. The absorbance of ammonium ions (NH4+) was used as the absorbance. + The concentration of α is plotted on the x-axis and absorbance on the y-axis to generate the first standard curve: y = 0.4392x + 0.2855 (R²). 2 =0.9855);
[0091] The method for obtaining the indophenol blue mixed solution includes: dissolving 5 g of salicylic acid and 5 g of sodium citrate dihydrate in 100 mL of a first sodium hydroxide aqueous solution (the concentration of NaOH in the first sodium hydroxide aqueous solution is 1M) to obtain a first indophenol blue solution; dissolving 1.861 g of sodium hypochlorite (with an available chlorine content greater than or equal to 30%, purchased from Maclean) in 100 mL of a second sodium hydroxide aqueous solution (the concentration of NaOH in the second sodium hydroxide aqueous solution is 2M) to obtain a second indophenol blue solution; dissolving 0.1 g of sodium nitrosoferricyanide dihydrate in 100 mL of water to obtain a third indophenol blue solution; and mixing 2 mL of the first indophenol blue solution, 1 mL of the second indophenol blue solution, and 0.2 mL of the third indophenol blue solution to obtain 3.2 mL of the indophenol blue mixed solution.
[0092] Since ammonium ions can be converted into ammonia (NH3) through bubbling or heating, the concentration of ammonia (NH3) is usually characterized by the concentration of ammonium ions in the art. The yield of NH3 is then calculated using the concentration of ammonium ions, as shown in the following formula:
[0093]
[0094] Where Y of NH3 is the NH3 production (mg / h / mg) cata C represents ammonium ions (NH4+) in the electrolyte of the cathode chamber after the NO3-RR reaction. + The concentration of NH3 is (mol / L), V is the volume of electrolyte in the cathode chamber (mL), M is the relative molecular mass of NH3 (M=17g / mol), t is the reaction time (h), and m is the mass of the cobalt-ruthenium bimetallic doped cerium dioxide catalyst supported on the working electrode (m=0.2 mg).
[0095] The NH3 yields of the working electrodes in Examples 1-5 after 20 min of NO3-RR reaction at different voltages were obtained as follows: Figure 5 As shown. By Figure 5 It can be seen that the working electrode of Example 4 has the highest NH3 yield at voltages of -0.7 to -1.3 V vs. RHE.
[0096] Example 8
[0097] Faraday efficiency calculation: Using the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode of Example 4 as the working electrode, the "NO3-RR performance test" of Example 6 was performed. The reaction time was 20 min, and the voltages were -0.7V vs. RHE, -0.8V vs. RHE, -0.9V vs. RHE, -1.0V vs. RHE, -1.1V vs. RHE, -1.2V vs. RHE, and -1.3V vs. RHE. The ammonia yield of the working electrode at different voltages was calculated according to the method of Example 7. Furthermore, the Faraday efficiency of the working electrode of Example 4 for NO3-RR ammonia synthesis at voltages of -0.7V vs. RHE, -0.8V vs. RHE, -0.9V vs. RHE, -1.0V vs. RHE, -1.1V vs. RHE, -1.2V vs. RHE, and -1.3V vs. RHE was calculated. The calculation formula is as follows:
[0098]
[0099] Where FE(NH3) is the Faradaic efficiency (%) of ammonia synthesis by the working electrode NO3-RR, n is the number of electrons transferred (n=8 for 1 mol of NH3), V is the volume of electrolyte in the cathode chamber (mL), and C1 is the concentration of ammonium ions (NH4+) in the electrolyte in the cathode chamber after the working electrode has been operating for 20 min. + The concentration of ) (mol / L), F is the Faraday constant (F=96485C / mol), and Q is the total charge (C) applied in the NO3-RR reaction.
[0100] The results are as follows Figure 6 As shown. By Figure 6 As can be seen from the overall trend, the ammonia production of the working electrode in Example 4 increases with the increase of voltage, and its Faraday efficiency for ammonia synthesis fluctuates less with voltage changes, and its minimum value is still greater than 90%. This indicates that the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode in Example 4 still has high selectivity for NO3-RR ammonia synthesis over a wide voltage range.
[0101] Example 9
[0102] To clarify the effects of cobalt and ruthenium doping, the cerium dioxide electrode of Comparative Example 3, the carbon felt-based ruthenium-doped cerium dioxide catalytic electrode of Comparative Example 1, the carbon felt-based cobalt-doped cerium dioxide catalytic electrode of Comparative Example 2, and the cobalt-ruthenium bimetallic-doped cerium dioxide catalytic electrode of Example 4 were used as working electrodes. The "NO3-RR performance test" of Example 6 was performed, with a reaction time of 20 min and a voltage of -1.0 V vs. RHE. The NH3 yield was calculated according to the method of Example 7, the Faradaic efficiency of NO3-RR ammonia synthesis for each working electrode was calculated according to the method of Example 8, and the Faradaic efficiency of nitrite formation was calculated according to the following formula:
[0103]
[0104] Among them, FE (NO2) - ) represents the Faraday efficiency (%) of nitrite formation at the working electrode NO3-RR, where n is the number of electrons transferred (for 1 mol of NO2). - (n=2), V is the volume of electrolyte in the cathode chamber (mL), and C2 is the concentration of nitrite ions (NO2) in the electrolyte in the cathode chamber after the working electrode has been in operation for 20 minutes. - The concentration of ) (mol / L), F is the Faraday constant (F=96485C / mol), and Q is the total charge (C) applied in the NO3-RR reaction.
[0105] Among them, NO2 - The concentration test method includes: mixing 5 mL of electrolyte from the cathode chamber with 0.1 mL of naphthylethylenediamine hydrochloride solution, shaking well, and letting stand for 2 hours to obtain the sample to be tested. The absorbance value of the sample at 540 nm is measured using a UV-Vis spectrophotometer, and the result is substituted into the second standard curve to obtain the NO2 concentration in the electrolyte of the cathode chamber. - The concentration of N-(1-naphthyl)ethylenediamine dihydrochloride; a method for obtaining a mixed solution of N-(1-naphthyl)ethylenediamine dihydrochloride, comprising: mixing 4 g of p-aminobenzenesulfonamide, 0.2 g of N-(1-naphthyl)ethylenediamine dihydrochloride, 10 mL of phosphoric acid aqueous solution (the concentration of H3PO4 in the phosphoric acid aqueous solution is 75 wt%) and 50 mL of water to obtain a mixed solution of N-(1-naphthyl)ethylenediamine dihydrochloride;
[0106] The method for plotting the second standard curve includes: preparing standard sodium nitrite aqueous solutions with concentrations of 0.001 mM, 0.005 mM, 0.01 mM, and 0.025 mM using sodium nitrite with a purity of 99% purchased from Shanghai Maclean Biochemical Technology Co., Ltd., wherein the concentrations of nitrite ions in the standard sodium nitrite aqueous solutions are 0.001 mM, 0.005 mM, 0.01 mM, and 0.025 mM, respectively; measuring the absorbance of the standard sodium nitrite aqueous solutions at 540 nm using a UV-Vis spectrophotometer; and generating the second standard curve with nitrite ion concentration as the abscissa and absorbance as the ordinate: y = 0.5878x + 0.0437 (R 2 =0.9962).
[0107] In the nitrate reduction reaction system of this study, it is assumed that electrons are used only to generate three products: ammonia, nitrite, and hydrogen gas, with no other side reactions. The sum of the Faraday efficiencies of all products is 100%. Therefore, the Faraday efficiency of hydrogen gas can be expressed as:
[0108]
[0109] Wherein, FE(H2) is the Faradaic efficiency (%) of hydrogen production by the working electrode NO3-RR, FE(NH3) is the Faradaic efficiency (%) of ammonia synthesis by the working electrode NO3-RR, and FE(NO2) is the Faradaic efficiency (%) of ammonia synthesis by the working electrode NO3-RR. - The value is the Faraday efficiency (%) of nitrite formation at the working electrode NO3-RR.
[0110] The results of the NO3-RR reaction at the working electrode under a voltage of -1.0 V vs. RHE for 20 min, including NH3 production, Faradaic efficiency of ammonia synthesis, Faradaic efficiency of nitrite formation, and Faradaic efficiency of hydrogen formation, are as follows: Figure 7 As shown. By Figure 7 It can be seen that the NH3 production of the working electrode in Example 4 is much higher than that of the working electrodes in Comparative Examples 1-3, and its ammonia production selectivity is also much higher than that of the working electrodes in Comparative Examples 1-3. The ammonia production selectivity of the working electrodes in Comparative Examples 1 and 2 is higher than that of the working electrode in Comparative Example 3. This indicates that the doping of cobalt and ruthenium will have different degrees of promoting effect on the NO3-RR ammonia synthesis of the working electrode, and the cobalt and ruthenium bimetallic doping will have a better effect.
[0111] Example 10
[0112] Using the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode from Example 4 as the working electrode, the NO3-RR reaction was carried out for 1 hour at -1.0V vs. RHE. The results were essentially the same as the "NO3-RR performance test" in Example 6, except that the electrolyte in the cathode chamber was either the first cathode chamber electrolyte or the second cathode chamber electrolyte. The first cathode chamber electrolyte was potassium hydroxide and potassium nitrate. 14 N(K) 14 A mixed solution of NO3 and water, wherein the concentration of potassium hydroxide in the electrolyte of the first cathode chamber is 0.1M, and the concentration of potassium hydroxide in the electrolyte of the first cathode chamber is... 14 The NO3 concentration is 0.5 M; the electrolyte in the second cathode chamber is potassium hydroxide and potassium nitrate. 15 N(K) 15 A mixed solution of NO3 and water, wherein the concentration of potassium hydroxide in the electrolyte of the second cathode chamber is 0.1M, and the concentration of K in the electrolyte of the second cathode chamber is... 15 The concentration of NO3 is 0.5 M.
[0113] After the NO3-RR test, 5 mL of electrolyte from the cathode chamber was taken and 2 mL of sulfuric acid aqueous solution (H2SO4 concentration in the sulfuric acid aqueous solution was 4 M) was added to obtain the sample to be tested. The proton NMR spectrum of the sample was measured using a nuclear magnetic resonance spectrometer, and the results are as follows. Figure 8 As shown. By Figure 8 As can be seen, the proton NMR spectrum corresponding to the electrolyte in the first cathode chamber is as follows: Figure 8 The "H NMR spectrum corresponding to the first cathode chamber" in the image shows a clear... 14 NH4 + The characteristic peaks, and the corresponding proton NMR spectrum of the electrolyte in the second cathode chamber ( Figure 8 The "H NMR spectrum corresponding to the second cathode chamber" in the image only has... 15 NH4 + The characteristic peaks were absent, indicating that NO3 in the electrolyte was present in the NO3-RR reaction. - It is the only source of synthesized ammonium ions (not from other substances).
[0114] Example 11
[0115] Using the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode from Example 4 as the working electrode, NO3-RR testing was performed at -1.0V vs. RHE. The results were essentially the same as the "NO3-RR performance test" in Example 6, except that the NO3-RR in the electrolyte of the cathode chamber... -The concentration of NO2 was 5 mM, and the concentration of NO2 in the electrolyte of the cathode chamber was measured at 0 min, 10 min, 20 min, 30 min, 40 min, 50 min, and 60 min during the NO3-RR test. - concentration of NO3 - concentration and NH4 + The concentration was measured;
[0116] Among them, NO2 - The concentration test method refers to "NO2" in Example 9. - "Methods for testing concentration";
[0117] NO3 - The concentration test method includes: mixing 4 mL of electrolyte from the cathode chamber, 1 mL of hydrochloric acid (HCl concentration of 1.0 M), and 0.1 mL of aminosulfonic acid aqueous solution (aminosulfonic acid concentration of 0.8 wt.%), allowing the mixture to stand at room temperature for 20 min to react, and obtaining the sample to be tested. The absorbance of the sample at wavelengths of 220 nm and 275 nm is determined using ultraviolet-visible spectrophotometry. The combined absorbance is calculated and substituted into the third standard curve to obtain the NO3 concentration in the electrolyte from the cathode chamber. - concentration;
[0118] The method for plotting the third standard curve includes: preparing standard potassium nitrate aqueous solutions with concentrations of 0.1 mM, 0.5 mM, 1 mM, and 5 mM using potassium nitrate with a purity of 99% purchased from Shanghai Maclean Biochemical Technology Co., Ltd., wherein the nitrate concentrations in the standard potassium nitrate aqueous solutions are 0.1 mM, 0.5 mM, 1 mM, and 5 mM, respectively; measuring the absorbance at wavelengths of 220 nm and 275 nm using ultraviolet-visible spectrophotometry; and calculating the overall absorbance using the following formula:
[0119]
[0120] Where A is the total absorbance (Abs), A 220 Abs is the absorbance at a wavelength of 220 nm. 275 Absorbance at 275 nm wavelength (Abs);
[0121] With nitrate concentration (NO3) - A third standard curve was generated with concentration on the x-axis and total absorbance on the y-axis: y = 3.1097x + 0.0074 (R² + π / 4)². 2 =0.9981);
[0122] NH4 + For the concentration test method, please refer to Example 7.
[0123] The working electrode of Example 4 was tested for NO2 in the electrolyte of the cathode chamber at different reaction times during the NO3-RR test. - concentration of NO3 - concentration and NH4 + The concentration results are as follows Figure 9 As shown, by Figure 9 It can be seen that as the reaction time increases, the NO2 in the electrolyte of the cathode chamber increases. - The concentration of NO3 did not change significantly. - The concentration of NH4 gradually decreased. + The concentration of NO3 gradually increases, meaning that in the NO3-RR reaction, NO3 is continuously produced. - Converted to NH4 + This indicates that at extremely low NO3 levels... - In environments with high concentrations of NO3, the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode also exhibits excellent NO3-RR performance. After 1 hour of NO3-RR reaction, the NO3 concentration in the electrolyte of the cathode chamber... - The concentration was 16.43 mg / L, NH4 + The concentration of NO2 was 223 mg / L. - The concentration remained consistently around 2.6 mg / L, indicating that the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode of Example 4 of this invention completely removed NO3. - It has good application potential in converting it into NH3.
[0124] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.
Claims
1. A method for preparing a cobalt-ruthenium bimetallic doped cerium dioxide catalyst, characterized in that, Includes the following steps: Step 1: Mix cerium salt and water evenly, add sodium hydroxide aqueous solution, stir for at least 20 minutes to obtain the first solution, let the first solution stand at 100~120℃ for 20~24 hours, discard the supernatant to obtain the first precipitate, wash the first precipitate in sequence, vacuum dry and calcine to obtain cerium dioxide support, wherein, by molar fraction, the ratio of cerium element in cerium salt to sodium hydroxide in sodium hydroxide aqueous solution is 0.002: (0.021~0.025); Step 2: Mix the cerium dioxide support and water evenly, add cobalt salt and ruthenium salt, stir for 4-6 hours, centrifuge to obtain a second precipitate, wash the second precipitate, vacuum dry and calcine it to obtain a cobalt-ruthenium bimetallic doped cerium dioxide catalyst, wherein the ratio of cerium element in cerium salt, cobalt element in cobalt salt and ruthenium element in ruthenium salt by molar amount is 10.28:3:(1-5).
2. The method according to claim 1, characterized in that, In step 1, the ratio of the molar amount of cerium in the cerium salt to the volume fraction of water in step 1 is 0.002:(5~10), where the molar amount is in mol and the volume fraction is in mL.
3. The method according to claim 1, characterized in that, In step 1, the concentration of sodium hydroxide in the sodium hydroxide aqueous solution is 6~7 mol / L.
4. The method according to claim 1, characterized in that, In step 1, the calcination includes calcining at 400~500℃ for 4~6 hours; in step 2, the calcination includes calcining at 400~500℃ for 2~4 hours.
5. The method according to claim 1, characterized in that, In step 2, the ratio of the molar amount of cerium salt to the volume fraction of water in step 2 is 0.00023:(30~40), where the molar amount is in mol and the volume fraction is in mL.
6. The cobalt-ruthenium bimetallic doped cerium dioxide catalyst obtained by the method according to any one of claims 1 to 5.
7. A cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode, characterized in that, include: The conductive substrate and the cobalt-ruthenium bimetallic doped cerium dioxide catalyst of claim 6, wherein the cobalt-ruthenium bimetallic doped cerium dioxide catalyst is supported on the conductive substrate.
8. The method for preparing the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode as described in claim 7, characterized in that, include: The cobalt-ruthenium bimetallic doped cerium dioxide catalyst was mixed with a second solution and sonicated for at least 20 minutes to obtain a mixed solution. The mixed solution was then dripped onto the surface of a conductive substrate to uniformly load the cobalt-ruthenium bimetallic doped cerium dioxide catalyst onto the conductive substrate. After drying, a cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode was obtained. The second solution was a mixture of anhydrous ethanol and Nafion dispersion.
9. The application of the cobalt-ruthenium bimetallic doped cerium dioxide catalyst as described in claim 6 in the redox reaction of nitrate to synthesize ammonia.
10. The application of the cobalt-ruthenium bimetallic doped cerium dioxide catalytic electrode as described in claim 7 in the redox reaction of nitrate to synthesize ammonia.