A method for regenerating a copper-based electrocatalyst based on intermittent shutdowns

Abstract

The application relates to the field of catalysis, and discloses a copper-based electrocatalyst regeneration method based on intermittent stoppage, which comprises the following steps: 1) a working stage: under electrolysis conditions, a nitrate reduction reaction is carried out by taking a copper-based electrocatalyst as an electrode; 2) a stoppage stage: under the condition that the copper-based electrocatalyst has performance attenuation, electrolysis is stopped, and the electrode is taken out; 3) a regeneration stage: the attenuation degree is divided into slight, moderate and deep; according to the attenuation degree, primary regeneration, conventional regeneration and deep regeneration are respectively carried out; and 4) steps 1) to 3) are repeated. By arranging the periodical stoppage-regeneration link, the copper-based electrocatalyst with different attenuation degrees is placed in a controllable regeneration environment to recover the catalytic activity. By only adjusting the environmental parameters, the Cu + / Cu 2+ active phase can be recovered, and the method has the advantages of simple operation, low energy consumption and long-term stable operation.

Description

Technical Field

[0001] This invention relates to the field of catalysis technology, and in particular to a method for regenerating copper-based electrocatalysts based on intermittent shutdown. Background Technology

[0002] Copper-based electrocatalysts are widely used in the electrocatalytic nitrate reduction reaction (NO3RR) due to their low cost and high selectivity, enabling efficient ammonia production. However, during long-term continuous electrolysis, the oxidized copper on the surface of the copper-based catalyst is gradually reduced to elemental copper, leading to Cu... + / Cu 2+ The loss of the active phase results in a reduction of active sites, a decrease in Faraday efficiency, and insufficient stability.

[0003] In existing technologies, to restore the surface oxidation state of copper-based catalysts, researchers typically employ surface re-oxidation steps such as external oxidation potential scanning and chemical oxidant treatment (e.g., CN105057009A, CN 107954464A). However, these operations are mostly scattered methods used in scientific experiments to regulate surface valence states or explore active species, and have not formed a systematic regeneration process suitable for continuous operation systems. Furthermore, the above methods are usually complex to operate and energy-intensive, making them difficult to apply in long-term electrolysis environments driven by intermittent renewable energy sources such as wind and solar power.

[0004] Therefore, developing a regeneration strategy that can automatically match different regeneration intensities according to the degree of catalyst failure, and that is low in energy consumption, simple to operate, and suitable for continuous electrolysis systems, has become a key requirement for the practical application of copper-based NO3RR catalysts. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for regenerating copper-based electrocatalysts based on intermittent shutdown. This invention restores catalytic activity by incorporating periodic shutdown-regeneration cycles, placing copper-based electrocatalysts with varying degrees of degradation in a controlled regeneration environment. This method can restore Cu formation simply by adjusting environmental parameters. + / Cu 2 + The active phase has the advantages of simple operation, low energy consumption and long-term stable operation.

[0006] The specific technical solution of the present invention includes: a method for regenerating a copper-based electrocatalyst based on intermittent shutdown, which includes the following steps: 1) Working stage: Nitrate reduction reaction is carried out under electrolysis conditions using copper-based electrocatalysts as electrodes; 2) Stop phase: When the copper-based electrocatalyst experiences performance degradation, electrolysis is stopped and the electrodes are removed; 3) Regeneration stage: The degree of decay is divided into mild, moderate, and deep; primary regeneration, conventional regeneration, and deep regeneration are performed according to the degree of decay; after regeneration, some of the metallic copper in the copper-based electrocatalyst is oxidized and restored to Cu. + / Cu 2+ Active phase; 4) Repeat steps 1)-3) to form a cycle of working-stopping-regenerating-resuming working, thus realizing the copper-based electrocatalyst Cu + / Cu 2+ Periodic regeneration and long-term stable operation of the active phase.

[0007] This invention incorporates a periodic stop-and-regenerate cycle in the electrolysis system. Depending on the degree of decay, the electrodes are placed in different controllable regeneration environments (temperature, humidity, oxygen content, etc.), allowing the elemental copper formed on the surface of the copper-based electrocatalyst during electrolysis to gradually re-oxidize and form Cu. + / Cu 2+ The active phase is activated, and surface reconstruction and defect generation are promoted under appropriate humidity and temperature conditions, thereby restoring the active sites of the catalyst. Compared with existing regeneration methods such as electrochemical oxidation or chemical treatment, the method of this invention does not require additional chemical or electrochemical treatment; Cu can be regenerated simply by adjusting environmental parameters. + / Cu 2+ The reversible recovery of the active phase has the advantages of simple operation, low energy consumption and long-term stable operation, and is especially suitable for intermittent power supply and periodic electrolysis systems.

[0008] Preferably, in step 3), the conditions for primary regeneration, conventional regeneration, and deep regeneration are as follows: Primary regeneration: Let stand for 10-15 hours at room temperature, humidity 30-40%, and oxygen concentration 0.1-1 vol%. Conventional regeneration: Let stand for 20-30 hours under the conditions of 20-50℃, humidity 10-20%, purging with 1-5 sccm of inert gas, and oxygen concentration of 0.2-0.4 vol%. Deep regeneration: Let stand for 4-8 hours under the conditions of 80-150℃, 0-5% humidity, 1-5 sccm inert gas purging, and O2 / N2 mixed atmosphere with oxygen concentration of 1-5 vol%.

[0009] Compared to existing technologies that use a uniform regeneration process without differentiating the degree of electrode performance degradation, this invention designs targeted regeneration conditions for electrodes with different degrees of degradation. The differences in regeneration conditions at different levels stem from the different failure mechanisms of copper-based electrocatalysts. This invention discovers that mild failure of copper-based electrocatalysts is mainly due to adsorption coverage, moderate failure involves oxidation state and surface structure regulation, and deep failure involves defect reconstruction and active phase regeneration. Based on these characteristics, this invention designs regeneration conditions with different characteristics. Specifically: Primary regeneration is mainly used to remove weak adsorbates or slight oxidation state shifts on the electrode surface; therefore, primary regeneration is characterized by standing under low temperature and limited dilute oxygen (0.1-1 vol%) conditions.

[0010] Conventional regeneration is suitable for surfaces with unbalanced oxidation states or partial blockage. Therefore, conventional regeneration is characterized by purging with an appropriate flow rate (1-5 sccm) of inert gas under low temperature, low humidity, and weak oxidation (0.2-0.4 vol%) conditions. The inert gas is used to carry away the desorbed weak adsorbates and stabilize the oxygen partial pressure, avoiding localized strong oxidation or secondary adsorption, thereby achieving mild and controllable surface re-oxidation.

[0011] Deep regeneration is used for electrodes with significantly degraded structures; therefore, conventional regeneration is characterized by surface reconstruction under conditions of high temperature, low humidity, and moderate oxygen content (1-5 vol% O2 / N2) combined with inert gas purging at an appropriate flow rate (1-5 sccm). The inert gas can adjust the actual oxygen partial pressure, remove high-temperature byproducts, and avoid local overheating, thereby ensuring that surface reconstruction is carried out uniformly under controlled conditions.

[0012] The present invention found in experiments that if a lower level of regeneration process is used to regenerate the electrode, the activity of the electrode cannot be effectively restored; conversely, if a higher level of regeneration process is used to regenerate the electrode, over-regeneration may damage the electrode structure.

[0013] Preferably, in step 3), the criteria for determining the degree of attenuation are as follows: mild attenuation: current density fluctuation ≤10%, Faraday efficiency >85%; moderate attenuation: current density increases by 10-30%, Faraday efficiency is 80-70%; deep attenuation: current density increases by >30%, Faraday efficiency <70%.

[0014] This invention reveals that, under conditions of current density fluctuation ≤10% and Faraday efficiency >85%, the failure of copper-based electrocatalysts is mainly due to adsorption coverage, which meets the definition of mild degradation; under conditions of current density increase of 10-30% and Faraday efficiency of 80-70%, the failure of copper-based electrocatalysts mainly involves oxidation state and surface structure adjustment, which meets the definition of moderate degradation; under conditions of current density increase >30% and Faraday efficiency <70%, the failure of copper-based electrocatalysts mainly involves defect reconstruction and active phase regeneration, which meets the definition of deep degradation.

[0015] Preferably, in step 3), the inert gas is argon.

[0016] Preferably, in step 1), the copper-based electrocatalyst is copper oxide nanowires doped with transition metals.

[0017] Further preferably, in step 1), the transition metal is nickel and / or cobalt.

[0018] Further preferably, in step 1), the doping method is to immerse copper oxide nanowires in a transition metal nitrate solution.

[0019] Further preferably, in step 1), the ratio of the copper oxide nanowires to the transition metal nitrate solution is 40-60 mL of transition metal nitrate solution per square centimeter of catalytic area. Further preferably, in step 1), the concentration of the transition metal nitrate solution is 0.1-0.5 mol / L.

[0020] Further preferred, in step 1), the soaking time is 18-22 hours.

[0021] Preferably, in step 1), the electrolysis conditions are as follows: the electrolyte is an alkaline system containing potassium hydroxide and potassium nitrate; and the electrolysis process uses a potential of -0.2V to -0.4V relative to the reversible hydrogen electrode.

[0022] Preferably, in step 1), the concentration of potassium hydroxide is 0.1-2 mol / L; and the concentration of potassium nitrate is 0.005-0.5 mol / L.

[0023] Preferably, in step 2), the electrode is cleaned after it is removed.

[0024] Compared with the prior art, the beneficial effects of the present invention are: (1) The regeneration method of the present invention is simple. It only requires placing the electrode in a controlled environment during the rest period to achieve regeneration. No additional chemical or electrochemical treatment is required, which reduces operating costs and operational complexity.

[0025] (2) The present invention achieves differentiated regeneration by controlling the parameters of the regeneration environment (temperature, humidity, oxygen content, etc.) to avoid damage to the structure of copper-based electrocatalysts caused by over-regeneration treatment.

[0026] (3) The regeneration method of the present invention is particularly suitable for intermittent energy supply conditions (such as renewable energy-driven electrolysis) and has good application prospects. Attached Figure Description

[0027] Figure 1 This is a SEM image of the electrode after long-term electrolysis in Example 1.

[0028] Figure 2 This is a SEM image of the electrode after primary regeneration in Example 1.

[0029] Figure 3 The image shows the SEM image of the electrode after conventional regeneration in Comparative Example 1-1.

[0030] Figure 4 The image shows the SEM images of the electrodes after deep regeneration in Comparative Examples 1-2.

[0031] Figure 5 This is a SEM image of the electrode after conventional regeneration in Example 2.

[0032] Figure 6 The image shows the SEM image of the electrode after primary regeneration in Comparative Example 2-1.

[0033] Figure 7 The image shows the SEM image of the electrode after deep regeneration in Comparative Example 2-2.

[0034] Figure 8 This is a SEM image of the electrode after deep regeneration in Example 3.

[0035] Figure 9 The image shows the SEM image of the electrode after primary regeneration in Comparative Example 2-1.

[0036] Figure 10 The image shows the SEM image of the electrode after conventional regeneration in Comparative Example 2-2. Detailed Implementation

[0037] The present invention will be further described below with reference to embodiments.

[0038] A method for regenerating a copper-based electrocatalyst based on intermittent shutdown includes the following steps: 1) Working stage: Nitrate reduction reaction is carried out under electrolysis conditions using copper-based electrocatalysts as electrodes.

[0039] In some preferred embodiments, in step 1), the copper-based electrocatalyst is copper oxide nanowires doped with transition metals.

[0040] In some more preferred embodiments, in step 1), the transition metal is nickel and / or cobalt.

[0041] In some more preferred embodiments, in step 1), the doping method is to immerse copper oxide nanowires in a transition metal nitrate solution.

[0042] In some more preferred embodiments, in step 1), the ratio of the copper oxide nanowires to the transition metal nitrate solution is 40-60 mL of transition metal nitrate solution per square centimeter of catalytic area.

[0043] In some more preferred embodiments, in step 1), the concentration of the transition metal nitrate solution is 0.1-0.5 mol / L.

[0044] In some more preferred embodiments, in step 1), the immersion time is 18-22 hours.

[0045] In some preferred embodiments, in step 1), the electrolysis conditions are: the electrolyte is an alkaline system containing potassium hydroxide and potassium nitrate; and the electrolysis process uses a potential of -0.2V to -0.4V relative to the reversible hydrogen electrode.

[0046] In some more preferred embodiments, in step 1), the concentration of potassium hydroxide is 0.1-2 mol / L; and the concentration of potassium nitrate is 0.005-0.5 mol / L.

[0047] 2) Stopping phase: When the copper-based electrocatalyst experiences performance degradation, electrolysis is stopped and the electrodes are removed.

[0048] In some preferred embodiments, in step 2), the electrode is cleaned after it is removed.

[0049] 3) Regeneration stage: The degree of decay is divided into mild, moderate, and deep; based on the degree of decay, primary regeneration, conventional regeneration, and deep regeneration are performed respectively: Primary regeneration: Let stand for 10-15 hours at room temperature, humidity 30-40%, and oxygen concentration 0.1-1 vol%. Conventional regeneration: Let stand for 20-30 hours under the conditions of 20-50℃, humidity 10-20%, purging with 1-5 sccm of inert gas, and oxygen concentration of 0.2-0.4 vol%. Deep regeneration: Let stand for 4-8 hours under the conditions of 80-150℃, humidity 0-5%, 1-5sccm inert gas purging, and O2 / N2 mixed atmosphere with oxygen concentration of 1-5vol%. After regeneration, some of the elemental copper in the copper-based electrocatalyst is oxidized back to Cu. + / Cu2+ Active phase.

[0050] In some preferred embodiments, in step 3), the criterion for determining the degree of attenuation is: Mild attenuation: current density fluctuation ≤10%, Faraday efficiency >85%; Moderate attenuation: Current density increases by 10-30%, Faraday efficiency remains at 80-70%; Deep decay: Current density increases by >30%, Faraday efficiency <70%.

[0051] In some preferred embodiments, in step 3), the inert gas is argon.

[0052] 4) Repeat steps 1)-3) to form a cycle of working-stopping-regenerating-resuming working, thus realizing the copper-based electrocatalyst Cu + / Cu 2+ Periodic regeneration and long-term stable operation of the active phase.

[0053] Specific embodiments and comparative examples (I) Comparison of regeneration effects of mildly decayed copper-based electrocatalysts under different regeneration conditions.

[0054] Example 1 (Mild Attenuation + Primary Regeneration) (1) Preparation of copper-based electrocatalyst: Copper foam was washed in isopropanol and 0.1 mol / L dilute hydrochloric acid solution, and then transferred to a mixed solution containing 1 mol / L sodium hydroxide and 0.11 mol / L ammonium persulfate for 1 hour to obtain copper hydroxide. The prepared copper hydroxide was dried in a vacuum drying oven at 70°C for 1.5 hours for later use. Copper oxide was obtained by annealing in a tube furnace at 200°C for 2.5 hours under an Ar atmosphere with an Ar flow rate of 100 sccm. Copper oxide was immersed in 0.2 mol / L nickel nitrate solution for 20 hours according to 50 mL of nickel nitrate solution per square centimeter of catalytic area. After rinsing, nickel-supported copper oxide nanowires were obtained, which are the copper-based electrocatalyst.

[0055] (2) Working stage: Nitrate reduction reaction was carried out under electrolytic conditions using copper-based electrocatalyst as electrodes. Specifically, the stability was tested in an H-type electrolytic cell at a potential of -0.3V vs RHE in an electrolyte containing 1 mol / L KOH and 0.01 mol / L KNO3.

[0056] (3) Stopping phase: After the electrode has been running continuously for about 45 hours, the current density fluctuation is ≤10%, and the Faraday efficiency remains at about 86%, which meets the mild decay standard. Stop electrolysis, remove and clean the electrode.

[0057] (4) Primary regeneration: The electrode was placed in a sealed container at room temperature, 35% humidity, and 0.5 vol% oxygen concentration for 12 hours. After regeneration, some of the elemental copper in the copper-based electrocatalyst was oxidized and restored to Cu. + / Cu 2+ Active phase.

[0058] (5) After repeated operation, the current density recovered to about 94% of the level before decay, and the Faraday efficiency rose to about 93%. After regeneration, the total lifespan of the electrode was extended by about 1.2 times, and the performance was maintained for about 75 hours before significant decay occurred.

[0059] Comparative Example 1-1 (Mild Attenuation + Conventional Regeneration) (1) Preparation of copper-based electrocatalyst: Same as in Example 1.

[0060] (2) Working stage: Same as Example 1.

[0061] (3) Stopping phase: After the electrode has been running continuously for about 45 hours, the current density fluctuation is ≤10% and the Faraday efficiency is about 86%, which meets the mild decay standard. Stop electrolysis and clean the electrode.

[0062] (4) Routine regeneration: The electrode is placed in a closed device with a temperature of 35°C, humidity of 15%, oxygen concentration of 0.3 vol%, and argon gas purged at a low flow rate of 3 sccm for 24 hours.

[0063] (5) After repeated operation, the current density recovers to about 91%, and the Faraday efficiency recovers to about 88%. The total service life is extended by about 68 hours.

[0064] Comparative Examples 1-2 (Mild Attenuation + Deep Regeneration) (1) Preparation of copper-based electrocatalyst: Same as in Example 1.

[0065] (2) Working stage: Same as Example 1.

[0066] (3) Stopping phase: After the electrode has been running continuously for about 45 hours, the current density fluctuation is ≤10% and the Faraday efficiency is about 86%, which meets the mild decay standard. Stop electrolysis and clean the electrode.

[0067] (4) Deep regeneration: The electrode is placed in a closed device with a temperature of 100℃, humidity of 2%, oxygen concentration of 2vol% and argon purging at a low flow rate of 3sccm for 6 hours.

[0068] (5) After repeated operation, the current density recovers to about 87%, and the Faraday efficiency recovers to about 87%. The total service life is extended by about 60 hours.

[0069] Comparison of regeneration effects Figure 1The image shows the SEM morphology of the electrode after 45 hours of electrolysis in Example 1. As can be seen from the image, the original nanowires of the electrode exhibit an aggregated, irregular blocky / flocculent stacking morphology.

[0070] Example 1, Comparative Examples 1-2 and 1-2's regeneration data are shown in Table 1: Table 1

[0071] Example 1 employs a primary regeneration process, which can match a slight degree of degradation and can gently recover Cu. + / Cu 2+ The active phase, after regeneration, can restore the Faraday efficiency to about 93%, with a lifespan of 75 hours, and the recovery effect is optimal. Figure 2 The image shows the SEM morphology of the electrode after regeneration using the primary regeneration process in Example 1. As can be seen from the image, the original nanowire morphology is significantly restored, exhibiting a relatively regular one-dimensional linear structure with only slight surface agglomeration. The effective restoration of the microstructure corresponds to the good recovery of its Faraday efficiency after regeneration.

[0072] Comparative Example 1-1 used a conventional regeneration process, which had slightly stronger oxidizing properties and time, resulting in a decreased recovery effect. After regeneration, the Faraday efficiency recovered to approximately 88%, and the lifespan was 68 hours. Figure 3 The image shows the SEM morphology of the electrode after regeneration using a conventional regeneration process, as shown in Comparative Example 1-1. As can be seen from the image, the nanowire structure was not effectively restored, exhibiting a rough, agglomerated "beaded" stacking morphology, and the original one-dimensional features remained blurred. The insufficient degree of morphology restoration is an important reason for its poor Faraday efficiency after regeneration.

[0073] Comparative Examples 1-2 employed a deep regeneration process, but due to excessive oxidation and temperature, some surface active sites were lost. After regeneration, the Faraday efficiency recovered to approximately 87%, and the lifespan was 60 hours. Figure 4 The images show the SEM morphology of the electrodes after deep regeneration process in Comparative Examples 1-2. As can be seen from the images, the morphology of the nanowires was almost not restored, exhibiting an irregular blocky agglomeration structure, which is similar to the deteriorated morphology after long-term electrolysis. The microstructure repair effect was poor, corresponding to a significantly lower Faraday efficiency after regeneration compared to Example 1.

[0074] (II) Comparison of regeneration effects of moderately decaying copper-based electrocatalysts under different regeneration conditions.

[0075] Example 2 (Moderate Attenuation + Conventional Regeneration) (1) Preparation of copper-based electrocatalyst: Same as in Example 1.

[0076] (2) Working stage: Same as Example 1.

[0077] (3) Stoppage phase: After the electrode has been running continuously for about 75 hours, the current density increases by about 15%, and the Faraday efficiency decreases to about 72%, which meets the criteria for moderate degradation. Electrolysis is stopped, and the electrode is removed and cleaned. Within this degradation range, the failure of the copper-based electrocatalyst mainly involves changes in oxidation state and surface structure adjustment, rather than adsorption coverage or defect reconstruction.

[0078] (4) Routine regeneration: The electrode was placed in a sealed apparatus at 35°C, 15% humidity, 0.3 vol% oxygen concentration, and purged with argon gas at a low flow rate of 3 sccm for 24 hours. After regeneration, some Cu in the copper-based electrocatalyst was removed. 0 It is oxidized back to Cu + / Cu 2+ Active phase.

[0079] (5) After repeated operation, the current density drops back to about 95% of the original level, the Faraday efficiency rises to about 85%, and the lifespan is extended to about 280 hours.

[0080] Comparative Example 2-1 (Moderate Attenuation + Primary Regeneration) (1) Preparation of copper-based electrocatalyst: Same as in Example 1.

[0081] (2) Working stage: Same as Example 1.

[0082] (3) Stopping phase: After the electrode has been running continuously for about 75 hours, the current density increases by about 15% and the Faraday efficiency decreases to about 72%, which meets the moderate decay standard. Stop electrolysis, remove and clean the electrode.

[0083] (4) Primary regeneration: The electrode is placed in a sealed container at room temperature, 35% humidity, and 0.5 vol% oxygen concentration for 12 hours. After regeneration, Cu 0 Partially oxidized and restored to Cu + / Cu 2+ The active phase was recovered, but not completely.

[0084] (5) After repeated operation, the current density drops back to about 90% of the original level, and the Faraday efficiency rises back to about 75%.

[0085] Comparative Example 2-2 (Moderate Attenuation + Deep Regeneration) (1) Preparation of copper-based electrocatalyst: Same as in Example 1.

[0086] (2) Working stage: Same as Example 1.

[0087] (3) Stopping phase: After the electrode has been running continuously for about 75 hours, the current density increases by about 15% and the Faraday efficiency decreases to about 72%. Electrolysis is stopped, and the electrode is removed and cleaned.

[0088] (4) Deep regeneration: The electrode was placed in a sealed apparatus at 100℃, 2% humidity, and 2 vol% oxygen concentration (O2 / N2 mixed atmosphere) and purged with argon at a low flow rate of 3 sccm for 6 hours. After regeneration, Cu 0 Partially oxidized to Cu + / Cu 2+ However, high-temperature treatment may cause slight reconstruction of the microstructure, which may affect the recovery effect of moderate degradation.

[0089] (5) After repeated operation, the current density dropped back to about 92% of the original level, and the Faraday efficiency rose back to about 76%.

[0090] Comparison of regeneration effects Example 2, the regeneration data of Comparative Example 2-2 and Comparative Example 2-2 are shown in Table 2: Table 2

[0091] Table 2 shows that for electrodes with moderate degradation, Example 2 using the conventional regeneration process showed the best recovery effect under moderate degradation, with both current density and Faraday efficiency able to recover to a high level. Figure 5 The image shows the SEM morphology of the electrode after regeneration using a conventional regeneration process in Example 2. As can be seen from the image, the original nanowire morphology was well restored, exhibiting a relatively regular one-dimensional structure with only slight particle agglomeration in some areas. The effective repair of the microstructure corresponds to the good recovery of its Faraday efficiency after regeneration.

[0092] Comparative Example 2-1 uses a primary regeneration process. The results show that the Faraday efficiency is not fully recovered after electrode regeneration. This is because the temperature and oxidation conditions of the primary regeneration are too mild and cannot effectively restore the moderately decayed oxidation state and surface structure. Figure 6 The image shows the SEM morphology of the electrode after regeneration using a conventional regeneration process, as shown in Comparative Example 2-1. As can be seen from the image, the nanowire structure was not fully restored, exhibiting a loose and fragmented particle accumulation morphology, and the original one-dimensional features were weakened. The insufficient degree of morphology restoration is an important reason for its poor Faraday efficiency after regeneration.

[0093] Comparative Example 2-2 uses a deep regeneration process. The results show that the Faraday efficiency recovery after electrode regeneration is slightly worse. This is because the high-temperature treatment of deep regeneration causes local microstructure reconstruction. For electrodes with moderate decay, excessive treatment can actually affect performance. Figure 7 The image shows the SEM morphology of the electrode after deep regeneration process in Comparative Example 2-2. As can be seen from the image, the morphology of the nanowires is severely degraded, exhibiting a disordered agglomeration structure of mixed flakes and particles, and the original one-dimensional features have basically disappeared; the microstructure repair effect is poor.

[0094] (III) Comparison of regeneration effects of deep-degradation copper-based electrocatalysts under different regeneration conditions.

[0095] Example 3 (Deep Attenuation + Deep Regeneration) (1) Preparation of copper-based electrocatalyst: Same as in Example 1.

[0096] (2) Working stage: Same as Example 1.

[0097] (3) Stoppage phase: After the electrode has been running continuously for about 280 hours, the current density increases by about 35%, and the Faraday efficiency decreases to about 65%, meeting the deep decay standard. Electrolysis is stopped, and the electrode is removed and cleaned. Within this decay range, the failure of the copper-based electrocatalyst mainly involves the reconstruction of defects in the active phase and insufficient regeneration of the oxidation state.

[0098] (4) Deep regeneration: The electrode was placed in a sealed apparatus at 100℃, 2% humidity, and 2 vol% oxygen concentration (O2 / N2 mixed atmosphere) and purged with argon at a low flow rate of 3 sccm for 6 hours. After regeneration, Cu 0 It is oxidized back to Cu + / Cu 2+ The active phase simultaneously completes partial structural reconstruction.

[0099] (5) After repeated operation, the current density drops back to about 94% of the original level, the Faraday efficiency rises to about 83%, and the lifespan is extended to about 450 hours.

[0100] Comparative Example 3-1 (Deep Attenuation + Primary Regeneration) (1) Preparation of copper-based electrocatalyst: Same as in Example 1.

[0101] (2) Working stage: Same as Example 1.

[0102] (3) Stopping phase: After the electrode has been running continuously for about 280 hours, the current density increases by about 35% and the Faraday efficiency decreases to about 65%, which meets the deep decay standard. Stop electrolysis, remove and clean the electrode.

[0103] (4) Primary regeneration: The electrode is placed in a sealed container at room temperature, 35% humidity, and 0.5 vol% oxygen concentration for 12 hours. After regeneration, some Cu... 0 It was oxidized, but due to insufficient temperature and oxidation conditions, the active phase was not fully reconstructed.

[0104] (5) After repeated operation, the current density dropped back to about 88% of the original level, and the Faraday efficiency rose back to about 67%.

[0105] Comparative Example 3-2 (Deep Attenuation + Conventional Regeneration) (1) Preparation of copper-based electrocatalyst: Same as in Example 1.

[0106] (2) Working stage: Same as Example 1.

[0107] (3) Stopping phase: After the electrode has been running continuously for about 280 hours, the current density increases by about 35% and the Faraday efficiency decreases to about 65%, which meets the deep decay standard. Stop electrolysis, remove and clean the electrode.

[0108] (4) Routine regeneration: The electrode was placed in a sealed apparatus at 35°C, 15% humidity, 0.3 vol% oxygen concentration, and purged with argon gas at a low flow rate of 3 sccm for 24 hours. After regeneration, Cu 0 Partially oxidized to Cu + / Cu 2+ However, the high-temperature structural reconstruction is insufficient, and the active phase of the deeply decayed electrode cannot be fully restored.

[0109] (5) After repeated operation, the current density drops back to about 90% of the original level, and the Faraday efficiency rises back to about 73%.

[0110] Comparison of regeneration effects Example 3, the regeneration data of Comparative Example 3-2 and Comparative Example 3-2 are shown in Table 3: Table 3

[0111] Table 3 shows that the deep attenuation electrode is best suited for the deep regeneration process of Example 3, and the Faraday efficiency recovery effect is the best. Figure 8 The image shows the SEM morphology of the electrode after regeneration using the deep regeneration process in Example 3. As can be seen from the image, the one-dimensional structure of the original nanowires is restored to a certain extent. Although there are still particles attached to the surface, the overall linear morphology tends to be more regular. The microstructure is effectively reconstructed, so the Faraday efficiency can be restored to a good level after regeneration.

[0112] Comparative Example 3-1 used a primary regeneration process, but due to insufficient temperature and oxidation conditions, the active phase reconstruction was incomplete, resulting in poor recovery. Figure 9 The image shows the SEM morphology of the electrode after primary regeneration process in Comparative Example 3-1. As can be seen from the image, the nanowires completely lose their one-dimensional structure, exhibiting high-density blocky agglomeration with blurred boundaries between particles. Due to insufficient primary regeneration temperature / oxidation conditions, the active phase reconstruction is inadequate, resulting in the most severe damage to the microstructure, which leads to a significantly lower Faraday efficiency after regeneration compared to Example 3.

[0113] Comparative Example 3-2 uses a conventional regeneration process. Due to the lower temperature, structural reconstruction is limited, and the recovery effect is significantly lower than that of the deep regeneration in Example 3. Figure 10The image shows the SEM morphology of the electrode after conventional regeneration process in Comparative Example 3-2. As can be seen from the image, although the nanowires have not completely recovered their regular shape, some linear outlines are visible. The particle aggregation density is lower than that in Comparative Example 3-1, indicating that conventional regeneration conditions are better than primary regeneration, and the structural repair is more obvious. Correspondingly, its Faraday efficiency after regeneration is higher than that in Comparative Example 3-1, but still not as good as that in Example 3.

[0114] The data comparison above shows that regeneration conditions must be matched with the degree of degradation in order to achieve optimal performance recovery and lifespan extension.

[0115] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0116] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for regenerating a copper-based electrocatalyst based on intermittent shutdown, characterized in that: include: 1) Working stage: Nitrate reduction reaction is carried out under electrolysis conditions using copper-based electrocatalysts as electrodes; 2) Shutdown phase: Electrolysis is stopped when the copper-based electrocatalyst experiences performance degradation; 3) Regeneration stage: The degree of decay is divided into mild, moderate, and severe; Mild attenuation: current density fluctuation ≤10%, Faraday efficiency >85%; Moderate attenuation: Current density increases by 10-30%, Faraday efficiency remains at 80-70%; Deep decay: Current density increase >30%, Faraday efficiency <70%; Based on the degree of attenuation, the electrodes are subjected to primary regeneration, conventional regeneration, and deep regeneration: Primary regeneration: Let stand for 10-15 hours at room temperature, humidity 30-40%, and oxygen concentration 0.1-1 vol%. Conventional regeneration: Let stand for 20-30 hours under the conditions of 20-50℃, humidity 10-20%, purging with 1-5 sccm of inert gas, and oxygen concentration of 0.2-0.4 vol%. Deep regeneration: Let stand for 4-8 hours under the conditions of 80-150℃, 0-5% humidity, 1-5 sccm inert gas purging, and O2 / N2 mixed atmosphere with oxygen concentration of 1-5 vol%.

2. The method according to claim 1, characterized in that: In step 3), the inert gas is argon.

3. The method according to claim 1, characterized in that: In step 1), the copper-based electrocatalyst is copper oxide nanowires doped with transition metals.

4. The method according to claim 3, characterized in that: In step 1), the transition metal is nickel and / or cobalt.

5. The method according to claim 3 or 4, characterized in that: In step 1), the doping method is to immerse copper oxide nanowires in a transition metal nitrate solution.

6. The method according to claim 5, characterized in that: In step 1), The ratio of copper oxide nanowires to transition metal nitrate solution is 40-60 mL of transition metal nitrate solution per square centimeter of catalytic area. The concentration of the transition metal nitrate solution is 0.1-0.5 mol / L; The soaking time is 18-22 hours.

7. The method according to claim 1, 3, or 4, characterized in that: In step 1), the electrolysis conditions are as follows: The electrolyte is an alkaline system containing potassium hydroxide and potassium nitrate; During electrolysis, the potential is maintained at -0.2V to -0.4V relative to the reversible hydrogen electrode.

8. The method according to claim 7, characterized in that: In step 1), The concentration of potassium hydroxide is 0.1-2 mol / L; and / or The concentration of potassium nitrate is 0.005-0.5 mol / L.

9. The method according to claim 1, 3, or 4, characterized in that: In step 2), the electrode is cleaned after it is removed.

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