A cobalt-ruthenium oxide catalytic electrode for nitrate reduction and a method for preparing the same

Abstract

The application discloses a cobalt-ruthenium oxide catalytic electrode for nitrate reduction and a preparation method thereof. Two solutions of Co(NO3)2.6H2O and cyclohexane-1,2,3,4,5,6-hexamine are mixed, fully stirred, centrifuged, and dried to obtain yellow precipitate; the yellow precipitate is uniformly ultrasonically treated in water, and a RuCl3 solution is added, fully stirred, centrifuged, and dried to obtain brown precipitate; the brown precipitate is annealed to obtain black precursor; the precursor is added to an alcohol solution containing a binder, uniformly ultrasonically treated, and coated on an electrode substrate to obtain a catalytic electrode containing cobalt-ruthenium oxide ultrathin nanosheets. The catalytic electrode provided by the application exhibits excellent Faraday efficiency (>=96%) and cycle stability (still higher than 94.5% after 8 cycles of test) in electrocatalytic nitrate reduction reaction.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation, and particularly relates to a cobalt ruthenium oxide catalytic electrode for nitrate reduction and its preparation method. Background Technology

[0002] Rapid societal development is highly dependent on the consumption of fossil fuels, leading to a continuous stream of environmental problems and energy crises. Ammonia, a raw material for the fertilizer industry and the world's second-largest produced chemical, is a potential carrier of hydrogen energy. As a fertilizer and neutralizing agent, ammonia is widely used in various industries, including wastewater treatment, leather, papermaking, and the food and beverage sectors. Currently, the main method for industrial ammonia production is the Haber-Bosch process (H2 + N2 → NH3). This process is highly energy-intensive due to the need for high temperatures (300-500 degrees Celsius) and high pressures (15-35 MPa). Because of the enormous annual production of ammonia, the synthetic ammonia industry consumes approximately 1-2% of the world's energy supply. The H2 used in this process is mainly produced from coal or natural gas, thus also generating a large amount of carbon dioxide (CO2).

[0003] Currently, researchers are exploring routes for ammonia synthesis using electricity generated from renewable energy sources, including: (1) electrochemical reduction of nitrogen (N2) to ammonia (NH3); (2) plasma-driven synthesis of ammonia (NH3) from nitrogen (N2) and hydrogen (H2); and (3) electrocatalytic synthesis of nitrogen oxides (NO3). x For example, nitrite ions NO2 in the liquid phase - nitrate ions NO3 - The process converts nitrogen (N2) into ammonia (NH3). Meanwhile, compared to high-cost technologies such as compressed hydrogen and hydrogen liquefaction, utilizing sustainable energy supplies to achieve electrocatalytic ammonia synthesis is a promising technological route. The electrocatalytic nitrogen reduction reaction (NRR) process uses electricity to convert nitrogen (N2) into ammonia (NH3) at room temperature, representing a potential alternative for industrial ammonia production. However, the Faraday efficiency and yield of ammonia synthesized by the NRR process are relatively low, mainly due to the extreme stability of the N-N bond (941 kJ / mol) and the competing mechanism of the hydrogen evolution reaction (HER). Additionally, at room temperature and pressure, N2 has low solubility in electrolytes due to its non-polar nature, resulting in slow reaction kinetics at the gas-liquid-solid interface.

[0004] In contrast, the electrocatalytic reduction of nitrates (NO3RR) to ammonia is thermodynamically more feasible because NO3RR involves a higher theoretical electrode potential (NO3). - +8e - +6H2O - →NH3+9OH- The energy input required to break the NO bond is lower (204 kJ / mol), while the energy input required to break the NO bond is lower (-0.12V vs. SHE), and nitrate (NO3) - Nitrates possess low dissociation energy, high solubility, and rapid reduction kinetics at the liquid-solid interface, which helps reduce mass transfer resistance and energy consumption during electrolysis. Furthermore, nitrates are widely present in industrial wastewater and polluted groundwater, and may be converted into harmful nitrites (NO2). - Concentrated nitrates can damage aquatic ecosystems and pose serious health risks to humans. In recent years, the use of renewable and clean energy and electrocatalytic technology to reduce nitrates to ammonia has attracted increasing attention due to its advantages such as mild operating conditions and high controllability. This technology may not only solve the problems of nitrate and nitrite pollution but also provide a potential green and sustainable solution for ammonia production, contributing to the goal of carbon neutrality.

[0005] The selectivity of NO3RR is affected by overpotential and current density. Good Faradaic efficiency and selectivity can only be achieved at low potentials. To meet industrial requirements, such as high current density and Faradaic efficiency (FE, the percentage of actual products to theoretical products) at low potentials, the reaction kinetics of the NO3RR process need to be significantly improved. - +6H2O+8e - →NH3+9OH - The catalytic electrode significantly affects the conversion rate, product selectivity, and catalytic stability.

[0006] Researchers are dedicated to designing and preparing electrocatalysts for the electrochemical NO3RR process to achieve efficient NH3 production, which has become a recent hot topic in the field of electrocatalysis. Currently, various materials, including metals, alloys, metal oxides, atomic catalysts, and non-metallic materials, have been systematically explored as catalysts for NO3RR. Transition metal compounds, including transition metal oxides, nitrides, sulfides, etc., are widely available, inexpensive, and possess excellent electrocatalytic capabilities, making them promising replacements for currently available commercial precious metal catalysts and holding significant future application value.

[0007] Currently, there are reports on the technology for synthesizing catalytic electrodes for the electrocatalytic reduction of nitrate to ammonia. Patent CN105198046 discloses a Ti-graphene catalytic electrode made with the assistance of graphene oxide. When the initial nitrate concentration is 50 mg N / L, the removal rate is 41.8% after 1 hour of reaction, which is not ideal.

[0008] Patent CN 114369841 discloses a cobalt nanowire electrode prepared by in-situ growth using cobalt foam and oxalic acid as raw materials, which is used for electrocatalytic reduction of nitrate to ammonia. After 6 hours of reaction, the nitrate removal rate is 84.1% and the ammonia generation rate is 77.7%. The deep removal of nitrate and the high efficiency of ammonia conversion are not high.

[0009] Patent CN 112206797 discloses a method based on copper sulfate and Ti3C2T x Cu(I)@Ti3C2T prepared from MXene x The MXene catalyst converted 77.1% of nitrate to ammonia in 6 hours, but the ammonia conversion rate gradually decreased with the increase of electrode recycling, which limited the further practical application of the catalyst. Summary of the Invention

[0010] The purpose of this invention is to provide a cobalt ruthenium oxide catalytic electrode and its preparation method that have excellent nitrate removal efficiency, ammonia generation rate and cycle stability, for the efficient electrocatalytic reduction of nitrate to ammonia.

[0011] According to a first aspect of the present invention, a method for preparing a cobalt ruthenium oxide catalytic electrode for nitrate reduction is provided, comprising the following steps:

[0012] Step 1: Mix Co(NO3)2·6H2O solution and cyclohexamethylenetetramine solution in a 1:1 ratio, stir thoroughly, centrifuge, and dry to obtain a yellow precipitate;

[0013] Step 2: The yellow precipitate obtained in Step 1 is sonicated in water until homogeneous, RuCl3 solution is added, and after thorough stirring, it is centrifuged and dried to obtain a brown precipitate;

[0014] Step 3: Anneal the brown precipitate obtained in Step 2 to obtain the black precursor.

[0015] Step 4: Add the precursor obtained in Step 3 to an alcohol solution containing a binder, sonicate it until homogeneous, and then coat it onto an electrode substrate to obtain a cobalt ruthenium oxide catalytic electrode.

[0016] Preferably, the mass concentration of the Co(NO3)2·6H2O solution in step one is 0.2–1.5 g / L, the mass concentration of the cyclohexamethylenetetramine solution is 0.5–2.0 g / L, and the solvent for both the Co(NO3)2·6H2O solution and the cyclohexamethylenetetramine solution is methanol.

[0017] Preferably, the concentration of the RuCl3 solution is 50 g / L, and the volume of the RuCl3 solution is 0–300 μL.

[0018] Preferably, the annealing atmosphere in step three is air, the annealing temperature is 250–500°C, and the annealing time is 1–5 hours.

[0019] Preferably, the binder in step four is one or a combination of perfluorosulfonic acid resin, polytetrafluoroethylene, and polyvinylidene fluoride, and the loading of the precursor is 0.1–5 mg / cm³. 2 .

[0020] Preferably, in step four, the electrode substrate is one of the following: nickel foam, titanium foam, copper foam, cobalt foam, nickel mesh, titanium mesh, copper mesh, cobalt mesh, carbon paper, carbon felt, or glassy carbon; and the coating technique is one or a combination of several of the following: drop coating, spray coating, sputtering, or brush coating.

[0021] According to a second aspect of the present invention, the present invention provides a cobalt ruthenium oxide catalytic electrode for nitrate reduction, wherein the cobalt ruthenium oxide material on the electrode is in the form of ultrathin nanosheets with an average thickness of 2-50 nm;

[0022] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0023] (1) This invention achieves in-situ growth of sub-nanometer RuO by loading a certain amount of Ru onto the surface of Co3O4 nanosheets. x The cluster achieves highly efficient electrocatalytic reduction of nitrate to ammonia through the synergistic effect of cobalt and ruthenium. The Ru-O-Co bond in the catalytic electrode provided by this invention can prevent RuO... x Its solubility in electrolytes has great potential to achieve long-life nitrate reduction;

[0024] (2) The preparation method of the present invention consists of a simple liquid phase reaction and a low temperature annealing reaction. The steps are simple, the reaction time is short, the operation is convenient, the environment is very friendly, and the repeatability is strong.

[0025] (3) The catalytic electrode obtained by the preparation method provided by the present invention has a cobalt ruthenium oxide ultrathin nanosheet as its catalytic active material, which has a high specific surface area and can expose abundant highly active sites, which is beneficial to the efficient catalysis of nitrate reduction reaction;

[0026] (4) The support of carbon paper is conducive to promoting the diffusion of electrolytes and reactants and the release of bubbles, and avoids poisoning of active sites. These factors work together to enhance the electrocatalytic ability of the material in the electrolyte.

[0027] (5) The catalytic electrode provided by the present invention can effectively realize the electrocatalytic reduction of nitrate to ammonia under normal temperature and pressure conditions, and exhibits excellent NO3RR (electrochemical nitrate reduction reaction) Faradaic efficiency (higher than 96%) at a relatively low reduction potential (-1.2V);

[0028] (6) The catalytic electrode provided by the present invention has excellent cycle stability and still maintains a NO3RR Faraday efficiency of more than 94.5% after 8 cycles. Attached Figure Description

[0029] Figure 1 This is a flowchart of the preparation process of cobalt-ruthenium oxide catalyst.

[0030] Figure 2 This is a SEM image of the cobalt-ruthenium oxide catalytic electrode prepared in Example 1.

[0031] Figure 3 The image shows the X-ray diffraction (XRD) pattern of the cobalt-ruthenium oxide catalytic electrode prepared in Example 1.

[0032] Figure 4 Raman spectra of the cobalt ruthenium oxide catalytic electrode and Co3O4 powder provided in Example 1.

[0033] Figure 5 Scanning linear voltammetry curves of the cobalt-ruthenium oxide catalytic electrode material provided in Example 1 for electrocatalytic nitrate reduction and hydrogen evolution reactions;

[0034] Figure 6 The diagram shows the cyclic stability of the cobalt ruthenium oxide catalytic electrode provided in Example 1 for the electrocatalytic reduction of nitrate to ammonia.

[0035] Figure 7 Raman spectra of the cobalt ruthenium oxide catalytic electrode and Co3O4 powder provided in Example 2.

[0036] Figure 8 Scanning linear voltammetry curves of the cobalt-ruthenium oxide catalytic electrode material provided in Example 2 for electrocatalytic nitrate reduction and hydrogen evolution reactions;

[0037] Figure 9 The diagram shows the cyclic stability of the cobalt ruthenium oxide catalytic electrode provided in Example 2 for the electrocatalytic reduction of nitrate to ammonia.

[0038] Figure 10 Raman spectra of the cobalt ruthenium oxide catalytic electrode and Co3O4 powder provided in Example 3.

[0039] Figure 11 Scanning linear voltammetry curves of the cobalt-ruthenium oxide catalytic electrode material provided in Example 3 for electrocatalytic nitrate reduction and hydrogen evolution reactions;

[0040] Figure 12 The diagram shows the cyclic stability of the cobalt ruthenium oxide catalytic electrode provided in Example 3 for the electrocatalytic reduction of nitrate to ammonia. Detailed Implementation

[0041] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The following content is merely illustrative and explanatory of the inventive concept. Various modifications or additions to the described specific embodiments by those skilled in the art, or the use of similar methods to replace them, shall fall within the protection scope of the present invention as long as they do not depart from the inventive concept or exceed the scope defined by the claims.

[0042] Example 1

[0043] The cobalt ruthenium oxide catalytic electrode for the electrocatalytic reduction of nitrate to ammonia was prepared using the following steps:

[0044] Step 1: Add 0.65g Co(NO3)2·6H2O and 1.35g cyclohexamethylenetetramine to 20mL of methanol, stir at 60℃ for 6h, centrifuge 5 times, filter, and then dry to obtain a yellow precipitate;

[0045] Step 2: Dissolve 80mg of yellow precipitate in 50ml of water, sonicate for 10min, add 100μL of 50g / L RuCl3 solution, stir for 5h, centrifuge 5 times, and then dry to obtain brown precipitate;

[0046] Step 3: Anneal the brown precipitate in air at 250°C for 3 hours to obtain the black precursor;

[0047] Step 4: Add the black precursor to an ethanol solution containing 5% perfluorosulfonic acid resin, sonicate to form a homogeneous suspension, and drop it onto a carbon paper substrate to achieve a precursor loading of 0.4 mg / cm³. 2 After thorough drying, the following is obtained: Figure 2 The catalytic electrode shown is a cobalt-ruthenium oxide catalytic electrode, which, according to SEM, exhibits an ultrathin nanosheet structure with an average thickness of approximately 20 nm. This morphology results in a large specific surface area and a greater number of reaction sites. Its XRD pattern is shown below. Figure 3 As shown, its Raman spectrum is similar to that of Co3O4 powder. Figure 4 As shown in the figure. The XRD pattern shows the presence of the Co3O4 phase in the catalytic electrode, and the absence of RuO. x Crystal phase, proving RuO x The clusters are anchored at the atomic level on Co3O4 nanosheets. Raman spectroscopy reveals the Ao of this catalytic electrode. 1g The peak showed a redshift relative to Co3O4, indicating that the addition of ruthenium affected the stretching vibration of the Co-O bond, and that high-energy Ru-O-Co bonds were formed at the interface of the Co3O4 nanosheets. The Ru-O-Co bonds can accelerate the NO3-... - The adsorption of RuO promotes ammonia synthesis, and their strong interaction can prevent RuO from being adsorbed. xDissolution in electrolytes is beneficial for achieving a long cycle life.

[0048] The cobalt-ruthenium oxide catalytic electrode obtained in the above steps was used in the electrocatalytic reduction of nitrate. The catalytic electrode prepared in the above steps was cut to a length of 1 cm and a width of 1 cm to serve as the working electrode. A carbon rod was used as the counter electrode, and potassium chloride-saturated Ag / AgCl was used as the reference electrode. In a standard three-electrode system two-chamber electrolytic cell, using a mixture of 0.1 M sodium sulfate and 0.5 M potassium nitrate as the electrolyte, the scanning linear voltammetry curve was measured at room temperature and pressure. Figure 5 As shown by the solid line, the scan rate is 5 mV / s.

[0049] The catalytic electrode prepared in the above steps was cut to a length of 1 cm and a width of 1 cm to serve as the working electrode. A carbon rod was used as the counter electrode, and potassium chloride-saturated Ag / AgCl was used as the reference electrode. The HER hydrogen evolution reaction was tested in a standard three-electrode system two-chamber electrolytic cell using 0.25 M sodium sulfate solution as the electrolyte at room temperature and pressure. The linear voltammetric curve is shown below. Figure 5 The dashed line indicates a scan rate of 5 mV / s. As the HER (hydrogen evolution reaction) is a competing reaction for nitrate reduction, its performance influences the electrocatalytic activity for nitrate reduction. For example... Figure 5 As shown, the difference between the solid and dashed lines indicates that a nitrate reduction reaction has occurred, and the larger the difference, the greater the current density of the nitrate reduction reaction.

[0050] The cobalt-ruthenium oxide catalytic electrode obtained in the above steps was used in the electrocatalytic reduction of nitrate. The catalytic electrode prepared in Example 1 was cut to a length of 1 cm and a width of 1 cm to serve as the working electrode. A carbon rod was used as the counter electrode, and potassium chloride-saturated Ag / AgCl was used as the reference electrode. In a standard three-electrode system two-chamber electrolytic cell, a mixture of 0.1 M sodium sulfate and 0.5 M potassium nitrate was used as the electrolyte. The electrolyte was applied at room temperature and pressure at -1.2 V for 30 min. The ammonia concentration in the electrolyte was determined spectrophotometrically, and the analysis yielded a Faradaic efficiency of 96% reduction of nitrate to ammonia.

[0051] The catalytic electrode prepared in the above steps was cut to a length of 1 cm and a width of 1 cm to serve as the working electrode. A carbon rod was used as the counter electrode, and potassium chloride-saturated Ag / AgCl was used as the reference electrode. In a two-chamber electrolytic cell with a three-electrode system, a mixture of 0.1 M sodium sulfate and 0.5 M potassium nitrate was used as the electrolyte. The system was treated at room temperature and pressure at -1.2 V for 30 min. The electrolyte was then replaced, and the same cycle was repeated 7 times. The ammonia concentration in the electrolyte was determined spectrophotometrically. Figure 6 As shown, analysis revealed that the Faraday efficiency for reducing nitrate to ammonia remained above 94.5%.

[0052] For comparison, a cobalt oxide catalytic electrode was prepared, and the preparation steps are as follows:

[0053] Step 1: Add 0.65g Co(NO3)2·6H2O and 1.35g cyclohexamethylenetetramine to 20mL of methanol, stir at 60℃ for 6h, centrifuge 5 times, filter, and then dry to obtain a yellow precipitate;

[0054] Step 2: Anneal 80 mg of the yellow precipitate in air at 250 °C for 3 h to obtain the black precursor;

[0055] Step 3: Add the black precursor to an ethanol solution containing 5% perfluorosulfonic acid resin, sonicate to form a homogeneous suspension, and drop it onto a carbon paper substrate to achieve a precursor loading of 0.4 mg / cm³. 2 After thorough drying, a cobalt oxide catalytic electrode is obtained.

[0056] The cobalt oxide catalytic electrode obtained in the above steps was used in the electrocatalytic nitrate reduction reaction. The prepared cobalt oxide catalytic electrode was cut to a length of 1 cm and a width of 1 cm to serve as the working electrode. A carbon rod was used as the counter electrode, and potassium chloride-saturated Ag / AgCl was used as the reference electrode. In a standard three-electrode system two-chamber electrolytic cell, a mixture of 0.1 M sodium sulfate and 0.5 M potassium nitrate was used as the electrolyte. The electrolyte was treated at room temperature and pressure at -1.2 V for 30 min. The ammonia concentration in the electrolyte was determined spectrophotometrically. Analysis showed a Faradaic efficiency of 82% for the reduction of nitrate to ammonia, which is significantly different from the 96% Faradaic efficiency of the cobalt-ruthenium oxide catalytic electrode described above. This demonstrates that the addition of ruthenium has a significant promoting effect on the nitrate reduction reaction.

[0057] Example 2

[0058] A method for preparing a cobalt ruthenium oxide catalytic electrode for the electrocatalytic reduction of nitrate to ammonia includes the following steps:

[0059] Step 1: Add 0.65g Co(NO3)2·6H2O and 1.35g cyclohexamethylenetetramine to 20mL of methanol, stir at 60℃ for 6h, centrifuge 5 times, filter, and then dry to obtain a yellow precipitate;

[0060] Step 2: Dissolve 80mg of yellow precipitate in water, sonicate for 10min, add 300μL of 50g / L RuCl3 solution, stir for 5h, centrifuge 5 times, and then dry to obtain brown precipitate;

[0061] Step 3: Anneal the brown precipitate in air at 350°C for 5 hours to obtain the black precursor;

[0062] Step 4: Add the black precursor to an ethanol solution containing 5% polytetrafluoroethylene, sonicate to form a uniform suspension, and spray it onto a carbon paper substrate to achieve a precursor loading of 1 mg / cm³. 2 After thorough drying, a catalytic electrode was obtained. Its Raman spectrum is compared with that of the Co3O4 powder as follows: Figure 7 As shown, Raman spectroscopy reveals the A of this catalytic electrode. 1g The peak showed a redshift relative to Co3O4, indicating that the addition of ruthenium affected the stretching vibration of the Co-O bond, and that high-energy Ru-O-Co bonds were formed at the interface of the Co3O4 nanosheets. The Ru-O-Co bonds can accelerate the NO3-... - The adsorption of RuO promotes ammonia synthesis, and their strong interaction can prevent RuO from being adsorbed. x Dissolution in electrolytes is beneficial for achieving a long cycle life.

[0063] The cobalt-ruthenium oxide catalytic electrode obtained in the above steps was used in the electrocatalytic reduction of nitrate. The catalytic electrode prepared in the above steps was cut to a length of 1 cm and a width of 1 cm to serve as the working electrode. A carbon rod was used as the counter electrode, and potassium chloride-saturated Ag / AgCl was used as the reference electrode. In a standard three-electrode system two-chamber electrolytic cell, using a mixture of 0.1 M sodium sulfate and 0.5 M potassium nitrate as the electrolyte, the scanning linear voltammetry curve was measured at room temperature and pressure at a scan rate of 5 mV / s. Figure 8 As shown by the solid line in the image.

[0064] The catalytic electrode prepared in the above steps was cut to a length of 1 cm and a width of 1 cm to serve as the working electrode. A carbon rod was used as the counter electrode, and potassium chloride-saturated Ag / AgCl was used as the reference electrode. The HER hydrogen evolution reaction was tested in a standard three-electrode system two-chamber electrolytic cell using 0.25 M sodium sulfate solution as the electrolyte at room temperature and pressure. The linear voltammetric curve is shown below. Figure 8 The dashed line indicates a scan rate of 5 mV / s. As the HER (hydrogen evolution reaction) is a competing reaction for nitrate reduction, its performance influences the electrocatalytic activity for nitrate reduction. For example... Figure 8 As shown, the difference between the solid and dashed lines indicates that a nitrate reduction reaction has occurred, and the larger the difference, the greater the current density of the nitrate reduction reaction.

[0065] The cobalt-ruthenium oxide catalytic electrode obtained in the above steps was used in the electrocatalytic reduction of nitrate. The catalytic electrode prepared in the above steps was cut to a length of 1 cm and a width of 1 cm to serve as the working electrode. A carbon rod was used as the counter electrode, and potassium chloride-saturated Ag / AgCl was used as the reference electrode. In a standard three-electrode system two-chamber electrolytic cell, a mixture of 0.1 M sodium sulfate and 0.5 M potassium nitrate was used as the electrolyte. The electrolyte was treated at room temperature and pressure at -1.2 V for 30 min. The ammonia concentration in the electrolyte was determined spectrophotometrically, and the Faradaic efficiency for reducing nitrate to ammonia was obtained at 92%.

[0066] The catalytic electrode prepared in the above steps was cut to a length of 1 cm and a width of 1 cm to serve as the working electrode. A carbon rod was used as the counter electrode, and potassium chloride-saturated Ag / AgCl was used as the reference electrode. In a two-chamber electrolytic cell with a three-electrode system, a mixture of 0.1 M sodium sulfate and 0.5 M potassium nitrate was used as the electrolyte. The system was treated at room temperature and pressure at -1.2 V for 30 min. The electrolyte was then replaced, and the same cycle was repeated 7 times. The ammonia concentration in the electrolyte was determined spectrophotometrically. Figure 9 As shown, the Faraday efficiency for reducing nitrate to ammonia remained above 90%.

[0067] Example 3

[0068] A method for preparing a cobalt ruthenium oxide catalytic electrode for the electrocatalytic reduction of nitrate to ammonia includes the following steps:

[0069] Step 1: Add 0.65g Co(NO3)2·6H2O and 1.35g cyclohexamethylenetetramine to 20mL of methanol, stir at 60℃ for 6h, centrifuge 5 times, filter, and then dry to obtain a yellow precipitate;

[0070] Step 2: Dissolve 80 mg of yellow precipitate in water, sonicate for 10 min, add 200 μL of 50 mg / mL RuCl3 solution, stir for 5 h, centrifuge 5 times, and then dry to obtain brown precipitate;

[0071] Step 3: Anneal the brown precipitate in air at 500°C for 1 hour to obtain the black precursor;

[0072] Step 4: Add the black precursor to an ethanol solution containing 5% polyvinylidene fluoride, sonicate to form a uniform suspension, and brush it onto a cobalt mesh substrate to achieve a precursor loading of 3 mg / cm³. 2 After thorough drying, a catalytic electrode was obtained. Its Raman spectrum is compared with that of the Co3O4 powder as follows: Figure 10 As shown, Raman spectroscopy reveals the A of this catalytic electrode. 1gThe peak showed a redshift relative to Co3O4, indicating that the addition of ruthenium affected the stretching vibration of the Co-O bond, and that high-energy Ru-O-Co bonds were formed at the interface of the Co3O4 nanosheets. The Ru-O-Co bonds can accelerate the NO3-... - The adsorption of RuO promotes ammonia synthesis, and their strong interaction can prevent RuO from being adsorbed. x Dissolution in electrolytes is beneficial for achieving a long cycle life.

[0073] The cobalt-ruthenium oxide catalytic electrode obtained in the above steps was used in the electrocatalytic reduction of nitrate. The catalytic electrode prepared in the above steps was cut to a length of 1 cm and a width of 1 cm to serve as the working electrode. A carbon rod was used as the counter electrode, and potassium chloride-saturated Ag / AgCl was used as the reference electrode. In a standard three-electrode system two-chamber electrolytic cell, using a mixture of 0.1 M sodium sulfate and 0.5 M potassium nitrate as the electrolyte, the scanning linear voltammetry curve was measured at room temperature and pressure at a scan rate of 5 mV / s. Figure 11 As shown by the solid line in the image.

[0074] The catalytic electrode prepared in the above steps was cut to a length of 1 cm and a width of 1 cm to serve as the working electrode. A carbon rod was used as the counter electrode, and potassium chloride-saturated Ag / AgCl was used as the reference electrode. The HER hydrogen evolution reaction was tested in a standard three-electrode system two-chamber electrolytic cell using 0.25 M sodium sulfate solution as the electrolyte at room temperature and pressure. The linear voltammetric curve is shown below. Figure 11 The dashed line indicates a scan rate of 5 mV / s. As the HER (hydrogen evolution reaction) is a competing reaction for nitrate reduction, its performance influences the electrocatalytic activity for nitrate reduction. For example... Figure 11 As shown, the difference between the solid and dashed lines indicates that a nitrate reduction reaction has occurred, and the larger the difference, the greater the current density of the nitrate reduction reaction.

[0075] The cobalt-ruthenium oxide catalytic electrode obtained in the above steps was used in the electrocatalytic reduction of nitrate. The catalytic electrode prepared in the above steps was cut to a length of 1 cm and a width of 1 cm to serve as the working electrode. A carbon rod was used as the counter electrode, and potassium chloride-saturated Ag / AgCl was used as the reference electrode. In a standard three-electrode system two-chamber electrolytic cell, a mixture of 0.1 M sodium sulfate and 0.5 M potassium nitrate was used as the electrolyte. The electrolyte was treated at room temperature and pressure at -1.2 V for 30 min. The ammonia concentration in the electrolyte was determined spectrophotometrically, and the analysis showed a Faradaic efficiency of 91% for the reduction of nitrate to ammonia.

[0076] The catalytic electrode prepared in the above steps was cut to a length of 1 cm and a width of 1 cm to serve as the working electrode. A carbon rod was used as the counter electrode, and potassium chloride-saturated Ag / AgCl was used as the reference electrode. In a two-chamber electrolytic cell with a three-electrode system, a mixture of 0.1 M sodium sulfate and 0.5 M potassium nitrate was used as the electrolyte. The system was treated at room temperature and pressure at -1.2 V for 30 min. The electrolyte was then replaced, and the same cycle was repeated 7 times. The ammonia concentration in the electrolyte was determined spectrophotometrically. Figure 12 As shown, analysis revealed that the Faraday efficiency for reducing nitrate to ammonia remained above 89.5%.

[0077] The above are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a cobalt-ruthenium oxide catalytic electrode for nitrate reduction, characterized in that, Includes the following steps: Step 1: Mix Co(NO3)2·6H2O solution and cyclohexamethylenetetramine solution, stir thoroughly, centrifuge, and dry to obtain a yellow precipitate; Step 2: The yellow precipitate obtained in Step 1 is sonicated in water until homogeneous, RuCl3 solution is added, and after thorough stirring, it is centrifuged and dried to obtain a brown precipitate. Step 3: Anneal the brown precipitate obtained in Step 2 to obtain the black precursor; Step 4: Add the precursor obtained in Step 3 to an alcohol solution containing a binder, sonicate it until homogeneous, and then coat it onto an electrode substrate to obtain a cobalt ruthenium oxide catalytic electrode. In step one, the mass concentration of the Co(NO3)2·6H2O solution is 0.2~1.5 g / L, the mass concentration of the cyclohexamethylenetetramine solution is 0.5~2.0 g / L, and the solvent for both the Co(NO3)2·6H2O solution and the cyclohexamethylenetetramine solution is methanol; In step two, the concentration of the RuCl3 solution is 50 g / L, and the volume of the RuCl3 solution is 100~300 μL.

2. The method for preparing a cobalt ruthenium oxide catalytic electrode for nitrate reduction according to claim 1, characterized in that, In step three, the annealing atmosphere is air, the annealing temperature is 250~500℃, and the annealing time is 1~5h.

3. The method for preparing a cobalt-ruthenium oxide catalytic electrode for nitrate reduction according to claim 2, characterized in that, In step four, the binder is one or a combination of perfluorosulfonic acid resin, polytetrafluoroethylene, and polyvinylidene fluoride, and the precursor loading is 0.1~5 mg / cm³. 2 .

4. The method for preparing a cobalt-ruthenium oxide catalytic electrode for nitrate reduction according to claim 3, characterized in that, In step four, the electrode substrate is one of the following: nickel foam, titanium foam, copper foam, cobalt foam, nickel mesh, titanium mesh, copper mesh, cobalt mesh, carbon paper, carbon felt, or glassy carbon; the coating technology is one or a combination of several of the following: drop coating, spray coating, sputtering, or brush coating.

5. A cobalt ruthenium oxide catalytic electrode for nitrate reduction prepared according to any one of claims 1-4, characterized in that, The cobalt ruthenium oxide is in the form of ultrathin nanosheets with a thickness of 2-50 nm.

Images