Pdag alloy electrocatalytic electrode, preparation method and application thereof
By forming a three-dimensional PdAg alloy catalytic layer on a conductive substrate, the problems of high oxidation voltage and mass transfer limitation in the electrochemical synthesis of ethylene oxide were solved, improving catalytic activity and stability, and achieving highly selective and efficient ethylene oxide production.
Patent Information
- Application Number
- CN202411691225.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-22
- Publication Date
- 2026-05-22
Smart Images
Figure CN122071803A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of electrocatalysis technology, and in particular to a PdAg alloy electrocatalytic electrode, its preparation method, and its application. Background Technology
[0002] Ethylene oxide, as a commonly used chemical raw material, is widely used in various fields such as daily chemicals, pharmaceuticals, construction, and pesticides. However, current industrial synthesis processes for ethylene oxide still heavily rely on high-temperature (200–260°C) and high-pressure (1–3 MPa) environments and highly efficient catalysts. This not only generates a large amount of pollutants but also tends to result in low ethylene oxide yields and selectivity. Therefore, the electrocatalytic synthesis of epoxides using renewable energy and with mild and environmentally friendly methods has attracted researchers' attention. Currently, the main electrosynthetic methods for ethylene oxide include solid-state electrolysis, direct oxidation, and halogen-mediated indirect oxidation. These reactions can also be coupled with CO2RR reactions to achieve continuous reactions, which is an important method for addressing the large-scale demand for ethylene oxide.
[0003] Patent CN104805465 employs a method for the electrocatalytic oxidation of ethylene to prepare ethylene oxide. First, a silver / carbon catalyst is prepared into a slurry and uniformly coated onto the electrode surface. Second, after complete drying, the prepared electrode is placed in an electrolyte, and ethylene gas and nitrogen gas are introduced at a flow rate of 1–600 mL / min. A reference electrode and a platinum counter electrode are inserted. Finally, ethylene oxide is obtained at a certain mild temperature. Although the reaction conditions of this method are relatively mild, the selectivity and current density of the ethylene oxide obtained by this reaction cannot meet the requirements for subsequent industrial applications.
[0004] Patent CN103566980 discloses a method for preparing an alumina support and a silver catalyst supported thereon, used for the oxidation of ethylene to produce ethylene oxide. The steps include: (1) adding a silicon-containing compound to a porous α-alumina support, adding nitric acid and formic acid as binders during the support modification process, kneading the mixture until homogeneous to form an aluminum sol, and finally extruding it into a paste. (2) impregnating the modified alumina support with a silver-containing catalyst impregnation solution, and then drying and activating it to obtain the silver catalyst. In the catalyst preparation process, the modification of the support is particularly crucial, but the preparation process is relatively cumbersome, and the yield of ethylene oxide obtained is low, making it unsuitable for large-scale industrial application.
[0005] It is evident that the current electrochemical synthesis of ethylene oxide still faces many problems and challenges that urgently need to be addressed: (1) Due to the high stability of ethylene, the electrochemical synthesis of ethylene oxide requires a high oxidation voltage. Under high current density conditions, the reaction is prone to ethylene peroxidation, generating CO2. However, if the current density is reduced, a larger electrode surface area is required, leading to high reaction costs. Therefore, it is necessary to design more efficient and stable catalysts to improve catalyst activity and thus enhance the Faradaic efficiency and yield of the reaction; (2) The low solubility of ethylene in polar solvents (electrolytes) limits the mass transfer process, resulting in low Faradaic efficiency at high current densities; (3) The strong acidity, strong corrosivity, and strong oxidizing environment formed during the reaction places extremely stringent requirements on the catalytic materials. Therefore, the electrochemical stability of the catalyst under current density must be considered to achieve good sustainability and economy. However, there are still few publicly available high-efficiency catalysts that can be applied to the electrochemical oxidation of ethylene to prepare ethylene oxide, which is insufficient to meet current application needs.
[0006] Therefore, it is necessary to solve the technical problem that the high stability of ethylene ne ne ne requires a high oxidation voltage for the electrochemical synthesis of ethylene oxide, and the reaction under high current density conditions is very easy to cause ethylene peroxidation and generate CO2. However, if the current density is reduced, a large electrode surface area is required, which leads to high reaction cost. Summary of the Invention
[0007] To address the aforementioned problems, the present invention aims to provide a PdAg alloy electrocatalytic electrode, its preparation method, and its applications. This electrode exhibits high selectivity and catalytic activity in electrocatalytic reactions.
[0008] To achieve the above objectives, the present invention provides a PdAg alloy electrocatalytic electrode, which includes a conductive substrate and a PdAg alloy catalytic layer deposited on the surface of the substrate; the PdAg alloy catalytic layer has a three-dimensional spatial structure formed by the accumulation of PdAg alloy particles.
[0009] In some specific implementations, the three-dimensional spatial structure can specifically be a three-dimensional dendritic vine structure formed by the accumulation of PdAg alloy particles (e.g., Figure 1 (As shown).
[0010] Compared to Ag and Pd alone, the Ag 3d phase of the Ag element in the PdAg alloy provided by this invention shifts towards the reduced state, and the Pd 3d phase of the Pd element shifts towards the oxidized state. That is, the electronic structures of Ag and Pd in the PdAg alloy are significantly different from those of Ag and Pd alone, exhibiting unique electronic structures that are beneficial for improving the catalytic activity of the electrode (e.g., ...). Figure 9 (As shown).
[0011] In the above-mentioned PdAg alloy electrocatalytic electrode, the particle size of the PdAg alloy particles can be 50-300nm, for example, it can be a specific value such as 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 150nm, 200nm, 250nm, 300nm, etc., and a range with any two of the above specific values as endpoints.
[0012] In some specific embodiments, the size of the PdAg alloy particles can be adjusted by the concentration of the depositable material (palladium and silver salt concentrations) in the molten salt electrolyte. For example, at a given electrolysis temperature and current density, a higher concentration of the depositable material results in a greater number of crystal nuclei forming rapidly on the substrate surface; conversely, a lower concentration results in fewer crystal nuclei. Within the same electrolysis time, a lower concentration of the depositable material leads to larger particle sizes.
[0013] In the above-mentioned PdAg alloy electrocatalytic electrode, the atomic ratio (i.e. molar ratio) of Pd and Ag in the PdAg alloy particles is (0.7-9):1, for example, specific values such as 0.7:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, etc., and a range with any two of the above specific values as endpoints.
[0014] In the above-mentioned PdAg alloy electrocatalytic electrode, the thickness of the PdAg alloy catalyst layer is 0.001-1000 μm, for example, it can be a specific value such as 0.001 μm, 1 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 1000 μm, etc., or a range with any two of the above specific values as endpoints.
[0015] In the aforementioned PdAg alloy electrocatalytic electrode, the bonding force of the PdAg alloy catalyst layer refers to the bonding force between the PdAg alloy catalyst layer and the conductive substrate. By adjusting the bonding force, the stability of the catalyst in the catalyst layer can be controlled. Specifically, the bonding force of the catalyst layer can be adjusted by the temperature and current density during the electrolysis process of the preparation method. In the electrode provided by this invention, the bonding force of the PdAg alloy catalyst layer is 0.1-100N, for example, specific values such as 0.1N, 0.5N, 1N, 5N, 10N, 20N, 30N, 40N, 50N, 60N, 70N, 80N, 90N, and 100N, as well as a range with any two of the above specific values as endpoints. The electrode provided by this invention has high bonding force and is prepared from high-temperature molten salt, making it resistant to gas erosion and corrosion; furthermore, the three-dimensional spatial structure of the electrode also has a good gas-clearing effect, ensuring high stability of the electrode.
[0016] This invention also provides a method for preparing a PdAg alloy electrocatalytic electrode, the method comprising:
[0017] Palladium salt, silver salt and supporting electrolyte are mixed and heated to a molten state in a protective atmosphere to obtain molten salt electrolyte;
[0018] A conductive substrate is used as the cathode, a molten salt electrolyte is used as the electrolyte, and an anode is set. Electrolysis is performed by applying a constant voltage or a constant current. After electrolysis, the cathode is removed and washed to obtain the PdAg alloy electrocatalytic electrode.
[0019] The preparation method provided by this invention employs molten salt electrochemical co-deposition to prepare a PdAg catalytic layer on the surface of a conductive substrate. In the molten salt, utilizing the principle of concentration polarization, the deposition rate of Pd and Ag is controlled by adjusting the concentrations of added Pd and Ag salts, the electrolysis temperature, and the electrolysis current density, resulting in a PdAg catalytic layer with a three-dimensional spatial structure formed by the stacking of PdAg alloy nanoparticles. This preparation method can be used to prepare the PdAg alloy electrocatalytic electrode provided by this invention.
[0020] In the above preparation method, the palladium salt comprises PdCl2 and / or Pd(NO3)2. In some specific embodiments, the palladium salt may be PdCl2.
[0021] In the above preparation method, the silver salt includes one or a combination of two or more of AgCl, Ag2SO4, and AgNO3. In some specific embodiments, the silver salt may be AgCl.
[0022] In the above preparation method, the molar ratio of palladium in the palladium salt and silver in the silver salt in the molten salt electrolyte can be controlled to be 0.6-9:1, for example, specific values such as 0.6:1, 0.7:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, etc., as well as a range with any two of the above specific values as endpoints.
[0023] In the above preparation method, the sum of the concentrations of the palladium salt and the silver salt in the molten salt electrolyte is 10-40 mM, for example, it can be a specific value such as 10 mM, 15 mM, 20 mM, 25 mM, 30 mM, 35 mM, 40 mM, etc., or a range with any two of the above specific values as endpoints.
[0024] In the above preparation method, the supporting electrolyte is a combination of two or more metal salts to give the supporting electrolyte a wide molten salt temperature range and reduce the minimum operating temperature of the molten salt. The supporting electrolyte is selected from molten sodium salts, molten lithium salts, and molten potassium salts. Specifically, the supporting electrolyte includes one or more combinations of LiCl-KCl, LiCl-LiF, LiCl-NaF, LiCl-KF, LiF-NaF, LiF-KF, and LiF-NaF-KF.
[0025] In the above preparation method, the composition of the supporting electrolyte can be determined according to the operating temperature of the molten salt and the phase diagram. The operating temperature of the molten salt is generally adjusted according to the electrolysis temperature.
[0026] In the above preparation method, the anode may include graphite.
[0027] In the above preparation method, the conductive substrate is a foam-like conductive substrate. The foam-like substrate can be a foam-like metal, which has a large surface area and good air permeability. Specifically, the foam-like conductive substrate can include one or more of foamed iron, foamed nickel, foamed copper, foamed cobalt, foamed nickel-iron, and foamed nickel-molybdenum. In some specific embodiments, the foam-like conductive substrate can be foamed nickel.
[0028] In the above preparation method, the electrolysis temperature can be controlled to be 400-600℃, for example, specific values such as 400℃, 450℃, 500℃, 550℃, 600℃, etc., and a range with any two of the above specific values as endpoints.
[0029] In the above preparation method, the heating temperature (i.e., the temperature at which the palladium salt, silver salt, and supporting electrolyte are heated to a molten state) is usually consistent with the electrolysis temperature, and can be 400-600℃, for example, specific values such as 400℃, 450℃, 500℃, 550℃, 600℃, etc., and a range with any two of the above specific values as endpoints.
[0030] In the above preparation method, the current density of the electrolysis can be 50-500 mA·cm. -2 For example, 50mA·cm -2 100mA·cm -2 150mA·cm -2 200mA·cm -2 250mA·cm -2 300mA·cm -2 350mA·cm -2 400mA·cm -2 450mA·cm-2 500mA·cm -2 The specific values and the range with any two of the above specific values as endpoints.
[0031] In the above preparation method, when electrolysis is performed using a constant voltage, the current density of the electrolysis can be controlled to be 50-500 mA·cm⁻¹. -2 When electrolysis is performed using a constant current method, the current density of the electrolysis can be controlled to be 50-500 mA·cm⁻¹. -2 .
[0032] In the above preparation method, the electrolysis time can be 1h-5h, for example, specific values such as 1h, 2h, 3h, 4h, 5h, and a range with any two of the above specific values as endpoints.
[0033] In the above preparation method, the protective atmosphere may include an argon atmosphere.
[0034] The electrode prepared by the above method provided by the present invention has a uniform elemental distribution and a unique electronic structure, thus exhibiting excellent electrocatalytic activity and stability.
[0035] This invention also provides the application of the above-mentioned PdAg alloy electrocatalytic electrode in the electrocatalytic preparation of ethylene oxide from ethylene. The PdAg alloy electrocatalytic electrode provided by this invention exhibits high selectivity and catalytic activity in the electrocatalytic oxidation of ethylene to ethylene oxide. In some specific embodiments, using this electrode to catalyze the ethylene to ethylene oxide reaction, the selectivity for ethylene oxide is >90%, and the electrocatalytic current density reaches 100-380 mA·cm⁻¹. -2 The ethylene conversion rate can reach over 18%, and the current efficiency can reach over 85%.
[0036] The beneficial effects of this invention include:
[0037] 1. The PdAg alloy electrocatalytic electrode provided by this invention exhibits high selectivity and catalytic activity in the electrocatalytic oxidation of ethylene to prepare ethylene oxide. The selectivity of ethylene oxide and the electrocatalytic current density are high, which has greater economic benefits compared with existing industrial technologies and is suitable for industrialization and promotion.
[0038] 2. The catalyst electrode provided by the present invention has a three-dimensional PdAg catalyst layer that can provide more active sites and gas entry / exit channels, which is beneficial to improving electrocatalytic activity; and the unique electronic structure between the active sites of Pd and Ag in the PdAg alloy is also beneficial to improving catalytic activity.
[0039] 3. The PdAg catalyst layer prepared by this invention has good adhesion and corrosion resistance, good resistance to gas erosion, and strong stability under operating conditions.
[0040] 4. The electrode preparation method provided by the present invention is simple and controllable, and the catalytic reaction equipment is simple and easy to scale up industrially. Attached Figure Description
[0041] Figure 1 The image shows the XRD pattern of the catalytic layer of the PdAg alloy catalytic electrode prepared in Example 1 of this invention.
[0042] Figure 2 This is a SEM image of the catalytic layer of the PdAg alloy catalytic electrode prepared in Example 1 of the present invention.
[0043] Figure 3 EDS image of the catalytic layer of the PdAg alloy catalytic electrode prepared in Example 1 of the present invention.
[0044] Figure 4 This is a TEM-EDS image of the catalytic layer of the PdAg alloy catalytic electrode prepared in Example 1 of the present invention.
[0045] Figure 5 This is a SEM image of the catalytic layer of the PdAg alloy catalytic electrode prepared in Example 2 of the present invention.
[0046] Figure 6 This is a SEM image of the catalytic layer of the PdAg alloy catalytic electrode prepared in Example 3 of the present invention.
[0047] Figure 7 This is a SEM image of the catalytic layer of the PdAg alloy catalytic electrode prepared in Example 4 of the present invention.
[0048] Figure 8 This is a SEM image of the catalytic layer of the PdAg alloy catalytic electrode prepared in Example 5 of the present invention.
[0049] Figure 9 XPS spectra of Pd 3d and Ag 3d in the catalyst layers of the electrodes prepared in Example 1, Comparative Example 1 and Comparative Example 2.
[0050] Figure 10 This is a SEM image of the catalytic layer of the PdAg alloy catalytic electrode prepared in Comparative Example 3 of this invention. Detailed Implementation
[0051] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.
[0052] In the following experiments, the catalyst layer bonding force refers to the bonding force between the catalyst layer and the foam-like conductive substrate, which is measured by a scratch tester.
[0053] Example 1
[0054] This embodiment provides a PdAg alloy electrocatalytic electrode, the preparation method of which includes the following steps:
[0055] A LiCl-KCl-PdCl2-AgCl molten salt electrolyte system was used: 500g of LiCl-KCl (molar ratio 1:1) was weighed, and 1.5g each of PdCl2 and AgCl were added. The mixture was prepared, placed in an alumina crucible, and dried in a 300℃ drying oven for 48 hours to remove moisture. The mixture was then placed in a high-temperature resistance furnace and heated to 500℃ at a rate of 3℃ / min under argon atmosphere protection, and held for 2 hours to obtain the molten salt electrolyte. The sum of the concentrations of palladium and silver salts in the molten electrolyte was 21.4 mM. Using nickel foam as the cathode and a graphite rod as the anode, the LiCl-KCl-PdCl2-AgCl molten salt electrolyte system was heated at 500℃ at a rate of 200 mA·cm2. -2 Electrolysis was performed for 2 hours. After electrolysis, the electrode was removed and allowed to cool. Then it was cleaned and dried to obtain a PdAg electrode with a Pd to Ag molar ratio of 0.81:1.
[0056] Figure 1 As shown, the PdAg electrode prepared in this embodiment exhibits Pd and Ag phases; Figure 2 The electrode surface shows a PdAg alloy layer with a three-dimensional spatial structure (specifically a three-dimensional dendritic vine structure) formed by the accumulation of PdAg alloy particles, with a particle size of approximately 50 nm. Figure 3 As can be seen, the EDS spectrum only shows Pd and Ag elements; Figure 4 The TEM image shows Pd and Ag lattices, with a catalyst layer thickness of approximately 50 μm and a bonding force of approximately 20 N.
[0057] The PdAg alloy electrocatalytic electrode obtained in this embodiment was used in the electrocatalytic preparation of ethylene oxide from ethylene. Under ambient temperature and pressure conditions, the PdAg alloy electrocatalytic electrode was used as the anode, and nickel foam was used as the cathode. 1M KOH was introduced into the cathode chamber, and 5% C2H4 / Ar was introduced into the anode chamber at a gas flow rate of 2 mL·min. -1 Apply 200 mA·cm -2 The current density was set at 30 min. After the reaction stabilized, the change rate of C2H4 content in 5% C2H4 / Ar before and after the reaction was determined by gas chromatography. The conversion rate of C2H4 was calculated to be approximately 20%, and the current efficiency was 85%.
[0058] Example 2
[0059] This embodiment provides a PdAg alloy electrocatalytic electrode, the preparation method of which includes the following steps:
[0060] A LiF-KF-Pd(NO3)2-AgNO3 molten salt electrolyte system was used: 500g of LiF-KF (molar ratio 5:4) was weighed, and 1.5g each of Pd(NO3)2 and AgNO3 were added. The mixture was prepared, placed in an alumina crucible, and dried in a 300℃ drying oven for 48h to remove moisture. The crucible was then placed in a high-temperature resistance furnace and heated to 500℃ at a rate of 3℃ / min under argon atmosphere protection, and held for 2h to obtain the molten salt electrolyte. The sum of the concentrations of palladium and silver salts in the molten electrolyte was 22.5mM. Using nickel-iron foam as the cathode and a graphite rod as the anode, the LiF-KF-Pd(NO3)2-AgNO3 molten salt electrolyte system was heated at 500℃ at a rate of 400mA·cm. -2 Electrolysis was performed for 1 hour. After electrolysis, the electrode was removed and cooled, then cleaned and dried to obtain a PdAg electrode with a Pd to Ag molar ratio of 0.78:1. The prepared PdAg electrode had a catalyst layer thickness of about 30 μm, a PdAg particle size of about 200 nm, and a catalyst layer bonding force of about 60 N.
[0061] The PdAg alloy electrocatalytic electrode obtained in this embodiment was used in the electrocatalytic preparation of ethylene oxide from ethylene. Under ambient temperature and pressure conditions, the PdAg alloy electrocatalytic electrode was used as the anode, and nickel foam was used as the cathode. 1M KOH was introduced into the cathode chamber, and 5% C2H4 / Ar was introduced into the anode chamber at a gas flow rate of 2 mL·min. -1 Apply 200 mA·cm -2 The current density was set at 30 min. After the reaction stabilized, the change rate of C2H4 content in 5% C2H4 / Ar before and after the reaction was determined by gas chromatography. The conversion rate of C2H4 was calculated to be approximately 18%, and the current efficiency was 90%.
[0062] Example 3
[0063] This embodiment provides a PdAg alloy electrocatalytic electrode, the preparation method of which includes the following steps:
[0064] A LiF-NaF-KF-Pd(NO3)2-Ag2SO4 molten salt electrolyte system was used: 500g of LiF-NaF-KF (molar ratio 5:1:4) was weighed, and 1.5g each of Pd(NO3)2 and Ag2SO4 were added. The mixture was prepared, placed in an alumina crucible, and dried in a 300℃ drying oven for 48h to remove moisture. The crucible was then placed in a high-temperature resistance furnace and heated to 550℃ for 2h under an argon atmosphere at a rate of 3℃ / min to obtain the molten salt electrolyte. The sum of the concentrations of palladium and silver salts in the molten electrolyte was 13.5mM. Using copper foam as the cathode and a graphite rod as the anode, the LiF-NaF-KF-Pd(NO3)2-Ag2SO4 molten salt electrolyte system was heated at 550℃ at a rate of 100mA·cm. -2 Electrolysis was performed for 1 hour. After electrolysis, the electrode was removed and cooled, then cleaned and dried to obtain a PdAg electrode with a Pd to Ag molar ratio of approximately 1:1. The prepared PdAg electrode had a catalyst layer thickness of approximately 20 μm, a PdAg particle size of approximately 60 nm, and a catalyst layer bonding force of approximately 80 N.
[0065] The PdAg alloy electrocatalytic electrode obtained in this embodiment was used in the electrocatalytic preparation of ethylene oxide from ethylene. Under ambient temperature and pressure conditions, the PdAg alloy electrocatalytic electrode was used as the anode, and nickel foam was used as the cathode. 1M KOH was introduced into the cathode chamber, and 5% C2H4 / Ar was introduced into the anode chamber at a gas flow rate of 2 mL·min. -1 Apply 300mA·cm -2 Electrolysis was carried out at a current density for 30 minutes. After the reaction stabilized, the change rate of C2H4 content in 5% C2H4 / Ar before and after the reaction was determined by gas chromatography. The conversion rate of C2H4 was calculated to be approximately 22%, and the current efficiency was 92%.
[0066] Example 4
[0067] This embodiment provides a PdAg alloy electrocatalytic electrode, the preparation method of which includes the following steps:
[0068] A LiF-NaF-KF-Pd(NO3)2-Ag2SO4 molten salt electrolyte system was used: 500g of LiF-NaF-KF (molar ratio 5:1:4) was weighed, and 2.78g of Pd(NO3)2 and 0.22g of Ag2SO4 were added respectively. The mixture was prepared and placed in an alumina crucible, which was then placed in a 300℃ drying oven for 48h to remove moisture. The crucible was then removed and placed in a high-temperature resistance furnace, where it was heated to 550℃ at a rate of 3℃ / min and held for 2h under an argon atmosphere to obtain the molten salt electrolyte. The sum of the concentrations of palladium and silver salts in the molten electrolyte was 23.6mM. Using nickel foam as the cathode and a graphite rod as the anode, the LiF-NaF-KF-Pd(NO3)2-Ag2SO4 molten salt electrolyte system was heated to 550℃ at a rate of 50mA·cm. -2 Electrolysis was performed for 1 hour. After electrolysis, the electrode was removed and cooled, then cleaned and dried to obtain a PdAg alloy electrode with a Pd to Ag molar ratio of 9:1. The prepared PdAg electrode catalyst layer was about 30 μm thick, the PdAg particle size was about 80 nm, and the bonding force of the catalyst layer was about 85 N.
[0069] The PdAg alloy electrocatalytic electrode obtained in this embodiment was used in the electrocatalytic preparation of ethylene oxide from ethylene. Under ambient temperature and pressure conditions, the PdAg alloy electrocatalytic electrode was used as the anode, and nickel foam was used as the cathode. 1M KOH was introduced into the cathode chamber, and 5% C2H4 / Ar was introduced into the anode chamber at a gas flow rate of 2 mL·min. -1 Apply 300mA·cm -2 The current density was set at 30 min. After the reaction stabilized, the change rate of C2H4 content in 5% C2H4 / Ar before and after the reaction was determined by gas chromatography. The conversion rate of C2H4 was calculated to be approximately 13%, and the current efficiency was 62%.
[0070] Example 5
[0071] This embodiment provides a PdAg alloy electrocatalytic electrode, the preparation method of which includes the following steps:
[0072] A LiF-NaF-KF-Pd(NO3)2-Ag2SO4 molten salt electrolyte system was used: 500g of LiF-NaF-KF (molar ratio 5:1:4) was weighed, and 2.43g of Pd(NO3)2 and 0.55g of Ag2SO4 were added respectively. The mixture was prepared and placed in an alumina crucible, which was then placed in a 300℃ drying oven for 48h to remove moisture. The crucible was then removed and placed in a high-temperature resistance furnace, where it was heated to 550℃ at a rate of 3℃ / min and held for 2h under an argon atmosphere to obtain the molten salt electrolyte. The sum of the concentrations of palladium and silver salts in the molten electrolyte was 15.4mM. Using nickel foam as the cathode and a graphite rod as the anode, the LiF-NaF-KF-Pd(NO3)2-Ag2SO4 molten salt electrolyte system was heated to 550℃ at a rate of 20mA·cm. -2 Electrolysis was performed for 5 hours. After electrolysis, the electrode was removed and cooled, then cleaned and dried to obtain a PdAg alloy electrode with a Pd to Ag molar ratio of 3:1. The prepared PdAg electrode catalyst layer was about 110 μm thick, the PdAg particle size was about 80 nm, and the bonding force of the catalyst layer was about 95 N.
[0073] The PdAg alloy electrocatalytic electrode obtained in this embodiment was used in the electrocatalytic preparation of ethylene oxide from ethylene. The reaction apparatus was operated at ambient temperature and pressure, with the PdAg alloy electrocatalytic electrode as the anode and nickel foam as the cathode. 1M KOH was introduced into the cathode chamber, and 5% C2H4 / Ar was introduced into the anode chamber at a gas flow rate of 2 mL / min. -1 Apply 300mA·cm -2 The current density was set at 30 min. After the reaction stabilized, the change rate of C2H4 content in 5% C2H4 / Ar before and after the reaction was determined by gas chromatography. The conversion rate of C2H4 was calculated to be approximately 63%, and the current efficiency was 71%.
[0074] Figures 5 to 8 The images show SEM images of the catalyst layer surface of the alloy electrodes prepared in Examples 2 to 5. As can be seen from the images, the catalyst layers in Examples 2 to 5 also exhibit a three-dimensional spatial structure formed by the accumulation of PdAg alloy particles.
[0075] Comparative Example 1
[0076] This comparative example provides a Pd electrocatalytic electrode, the preparation method of which includes the following steps:
[0077] A LiF-NaF-KF-Pd(NO3)2 molten salt electrolyte system was used: 500g of LiF-NaF-KF (molar ratio 4:1:5) was weighed, and 1.5g of Pd(NO3)2 was added. The mixture was prepared and placed in an alumina crucible, which was then placed in a 300℃ drying oven for 48h to remove moisture. The crucible was then removed and placed in a high-temperature resistance furnace, where it was heated to 550℃ at a rate of 3℃ / min and held for 2h under an argon atmosphere to obtain the molten salt electrolyte. Using copper foam as the cathode and a graphite rod as the anode, the electrolyte was prepared in the LiF-NaF-KF-Pd(NO3)2 molten salt electrolyte system at a rate of 100mA·cm⁻¹. -2 Electrolysis was performed for 1 hour. After electrolysis, the electrode was removed and cooled, then cleaned and dried to obtain the Pd electrode. The prepared Pd electrode had a catalyst layer thickness of about 20 μm, a Pd particle size of about 200 nm, and a catalyst layer bonding force of about 80 N.
[0078] The Pd electrode obtained in this comparative example was used in the electrocatalytic synthesis of ethylene oxide from ethylene. Under ambient temperature and pressure conditions, the Pd electrocatalytic electrode was used as the anode, and nickel foam was used as the cathode. 1M KOH was introduced into the cathode chamber, and 5% C2H4 / Ar was introduced into the anode chamber at a gas flow rate of 2 mL / min. -1 Apply 300mA·cm -2 The current density was set at 30 min. After the reaction stabilized, the change rate of C2H4 content in 5% C2H4 / Ar before and after the reaction was determined by gas chromatography. The conversion rate of C2H4 was calculated to be approximately 2%, and the current efficiency was 20%.
[0079] Comparative Example 2
[0080] This comparative example provides an Ag electrocatalytic electrode, the preparation method of which includes the following steps:
[0081] A LiF-NaF-KF-AgCl molten salt electrolyte system was used: 500g of LiF-NaF-KF (molar ratio 5:1:4) was weighed, and 1.5g of AgCl was added. The mixture was prepared, placed in an alumina crucible, and dried in a 300℃ drying oven for 48h to remove moisture. The crucible was then placed in a high-temperature resistance furnace and heated to 550℃ for 2h under an argon atmosphere at a rate of 3℃ / min to obtain the molten salt electrolyte. Using copper foam as the cathode and a graphite rod as the anode, the electrolyte was prepared in the LiF-NaF-KF-AgCl molten salt electrolyte system at a rate of 100mA·cm⁻¹. -2 Electrolysis was performed for 1 hour. After electrolysis, the electrode was removed and cooled, then cleaned and dried to obtain the Ag electrode. The prepared Ag electrode had a catalyst layer thickness of about 40 μm, an Ag particle size of about 300 nm, and a catalyst layer bonding force of about 80 N.
[0082] The Ag alloy electrocatalytic electrode obtained in this comparative example was used in the electrocatalytic preparation of ethylene oxide from ethylene. Under ambient temperature and pressure conditions, the Ag electrocatalytic electrode was used as the anode, and nickel foam was used as the cathode. 1M KOH was introduced into the cathode chamber, and 5% C2H4 / Ar was introduced into the anode chamber. The gas flow rate was 2 mL·min⁻¹, and 300 mA·cm⁻¹ was applied. -2 The current density was set at 30 min. After the reaction stabilized, the change rate of C2H4 content in 5% C2H4 / Ar before and after the reaction was determined by gas chromatography. The conversion rate of C2H4 was calculated to be approximately 6%, and the current efficiency was 32%.
[0083] Figure 9 XPS spectra of Pd 3d and Ag 3d in the PdAg alloy electrode (PdAg) of Example 1, the Pd electrode (Pd) prepared in Comparative Example 1, and the Ag electrode (Ag) prepared in Comparative Example 2 are compared.
[0084] from Figure 9 It can be seen that, compared to the XPS characteristic peaks of Ag alone, the XPS characteristic peaks of Ag 3d in the PdAg alloy show a significant shift towards the reduced state, while in the XPS spectrum of Pd 3d, the XPS characteristic peaks of Pd 3d in the PdAg alloy show a significant shift towards the oxidized state. This indicates that the electronic structures of Pd and Ag in the PdAg alloy have undergone significant changes, possessing unique electronic structures compared to Pd or Ag alone.
[0085] Comparing Comparative Examples 1 and 2 with Example 3, it can be seen that, compared with an electrode formed from a single metal element, the electrode formed from a binary alloy provided by the present invention has the advantages of small particle size, high ethylene conversion rate, and high current efficiency.
[0086] Comparative Example 3
[0087] This comparative example provides a PdAg alloy electrocatalytic electrode, the preparation method of which includes the following steps:
[0088] A LiCl-KCl-PdCl2-AgCl molten salt electrolyte system was used: 500g of LiCl-KCl (molar ratio 1:1) was weighed, and 1.5g each of PdCl2 and AgCl were added. The mixture was placed in an alumina crucible and dried in a 300℃ drying oven for 48 hours to remove moisture. The crucible was then placed in a high-temperature resistance furnace and heated to 500℃ at a rate of 3℃ / min under argon atmosphere protection, and held for 2 hours to obtain the molten salt electrolyte. Using nickel foam as the cathode and a graphite rod as the anode, the LiCl-KCl-PdCl2-AgCl molten salt electrolyte system was heated at 500℃ at a rate of 20mA·cm2. -2 Electrolysis is performed for 20 hours. After electrolysis, the electrode is removed and allowed to cool. Then it is cleaned and dried to obtain the PdAg alloy electrode.
[0089] The surface morphology of the catalyst layer of the PdAg alloy catalytic electrode prepared in this comparative example is as follows: Figure 10 As shown, the PdAg alloy layer formed by the stacking of PdAg alloy particles is planar and does not have a clear three-dimensional spatial structure. The prepared PdAg electrode catalyst layer is approximately 2 μm thick, the PdAg particle size is approximately 200 nm, and the bonding force of the catalyst layer is approximately 20 N.
[0090] The PdAg alloy electrocatalytic electrode obtained in this comparative example was used in the electrocatalytic preparation of ethylene oxide from ethylene. Under ambient temperature and pressure conditions, the PdAg alloy electrocatalytic electrode was used as the anode, and nickel foam was used as the cathode. 1M KOH was introduced into the cathode chamber, and 5% C2H4 / Ar was introduced into the anode chamber at a gas flow rate of 2 mL·min. -1 Apply 200 mA·cm -2 The current density was set at 30 min. After the reaction stabilized, the change rate of C2H4 content in 5% C2H4 / Ar before and after the reaction was determined by gas chromatography. The conversion rate of C2H4 was calculated to be approximately 8%, and the current efficiency was 35%.
[0091] Comparing Comparative Example 3 with the Examples, it can be seen that the preparation method of the present invention can regulate the deposition rate of silver salt and palladium salt by controlling the electrolysis conditions, thereby regulating the spatial morphology of the PdAg alloy particles. The catalytic layer of the electrode provided by the present invention has a three-dimensional spatial structure, which can provide more active sites and is beneficial to improving the catalytic activity of the electrode.
Claims
1. A PdAg alloy electrocatalytic electrode, wherein, The electrode includes a conductive substrate and a PdAg alloy catalyst layer deposited on the surface of the substrate; The PdAg alloy catalyst layer has a three-dimensional spatial structure composed of stacked PdAg alloy particles.
2. The PdAg alloy electrocatalytic electrode according to claim 1, wherein, The particle size of the PdAg alloy particles is 50-300 nm.
3. The PdAg alloy electrocatalytic electrode according to claim 1, wherein, In the PdAg alloy particles, the atomic ratio of Pd to Ag is 0.7-9:
1.
4. The PdAg alloy electrocatalytic electrode according to claim 1, wherein, The thickness of the PdAg alloy catalyst layer is 0.001-1000 μm.
5. The PdAg alloy electrocatalytic electrode according to claim 1, wherein, The bonding strength of the PdAg alloy catalyst layer is 0.1-100N.
6. A method for preparing a PdAg alloy electrocatalytic electrode, the method comprising: Palladium salt, silver salt and supporting electrolyte are mixed and heated to a molten state in a protective atmosphere to obtain molten salt electrolyte; A conductive substrate is used as the cathode, a molten salt electrolyte is used as the electrolyte, and an anode is set. Electrolysis is performed by applying a constant voltage or a constant current. After electrolysis, the cathode is removed and washed to obtain the PdAg alloy electrocatalytic electrode.
7. The preparation method according to claim 6, wherein, The palladium salt includes PdCl2 and / or Pd(NO3)2.
8. The preparation method according to claim 6, wherein, The silver salt includes one or more of AgCl, Ag2SO4, and AgNO3.
9. The preparation method according to claim 6, wherein, The supporting electrolyte includes one or more of the following: LiCl-KCl, LiCl-LiF, LiCl-NaF, LiCl-KF, LiF-NaF, LiF-KF, and LiF-NaF-KF.
10. The preparation method according to claim 6, wherein, The molar ratio of palladium in the palladium salt to silver in the silver salt is 0.6-9:1; The sum of the concentrations of the palladium salt and silver salt in the molten salt electrolyte is 10-40 mM.
11. The preparation method according to claim 6, wherein, The conductive substrate is a foam-like conductive substrate; The foam-like conductive substrate includes one or more of the following: foamed iron, foamed nickel, foamed copper, foamed cobalt, foamed nickel-iron, and foamed nickel-molybdenum.
12. The preparation method according to claim 6, wherein, The electrolysis temperature is 400-600℃; The current density of the electrolysis is 50-500 mA·cm. -2 The electrolysis time is 1-5 hours.
13. The application of the PdAg alloy electrocatalytic electrode according to any one of claims 1-5 in the electrocatalytic preparation of ethylene oxide from ethylene.