Composite electrocatalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of electrocatalytic materials and electrolytic hydrogen production, and particularly relates to a composite electrocatalyst and a preparation method and application thereof. According to the preparation method of the Ni single active center composite electrocatalyst based on the high-rubidium high-silicon lithium ore base as the carrier, uniform loading and efficient activation of the Ni single active center on the ore carrier are achieved through the steps of pretreatment, acid etching activation, lithiation regulation and control, Ni active solution preparation, solvothermal loading, roasting shaping and the like on the high-rubidium high-silicon lithium ore. When the catalyst is applied to urea electrolytic hydrogen production, the catalyst has the advantages of low initial potential, low overpotential and high stability.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic materials and electrolytic hydrogen production technology, specifically relating to a composite electrocatalyst, its preparation method, and its application. Background Technology

[0002] Hydrogen energy is considered a promising secondary energy source, boasting advantages such as cleanliness, low carbon footprint, high calorific value, and high conversion efficiency. Water electrolysis for hydrogen production, as the name suggests, utilizes electricity to decompose water (H2O) into hydrogen (H2) and oxygen (O2). It is a green and efficient method of hydrogen production, especially when the electricity used comes from renewable energy sources (such as solar and wind power), enabling zero-carbon production of "green hydrogen" and widely regarded as a key technological pillar of the future hydrogen society. Water electrolysis for hydrogen production is one of the core technologies for achieving this goal. With the explosive growth in global demand for green hydrogen and strong support from governments worldwide, water electrolysis technology is experiencing unprecedented development opportunities.

[0003] While water electrolysis is a core technology for obtaining clean hydrogen energy, the high overpotential of the oxygen evolution reaction (OER) typically leads to enormous energy consumption. However, the theoretical potential of the urea electrolysis reaction (UOR) (0.37V vs RHE) is much lower than that of the OER (1.23V vs RHE). Therefore, replacing the OER with UOR can significantly reduce the energy consumption of hydrogen production and has significant application value.

[0004] In recent years, Ni-based catalysts have attracted attention due to their excellent catalytic activity for UOR (unstable oxygen regeneration). However, traditional Ni-based catalysts suffer from poor dispersion of active sites and insufficient stability. Furthermore, in water electrolysis for hydrogen production, natural ores, rich in multiple elements and possessing potentially porous structures, can be used as catalyst supports. However, general high-rubidium, high-silicon lithium ores suffer from poor performance due to their complex composition. For example, high-rubidium, high-silicon lithium ores contain impurities such as Fe, which easily interfere with Ni active sites; and their underdeveloped mesoporous structure leads to insufficient Ni loading sites. More importantly, their poor conductivity hinders electron conduction. Currently, research on Ni electrocatalysts based on natural ores is scarce. How to remove ore impurities, construct mesoporous structures, optimize conductivity, and achieve uniform loading and efficient activation of Ni active sites are urgent technical challenges to be solved. Summary of the Invention

[0005] The first objective of this invention is to provide a method for preparing a Ni single-active-center composite electrocatalyst based on a high-rubidium, high-silicon lithium ore substrate, which effectively solves the problems of interference from natural ore impurities, insufficient mesopores, poor conductivity, and poor dispersion / stability of Ni active centers, so that the catalyst has both high activity and high stability when applied to urea electrolysis for hydrogen production. The second objective of this invention is to provide a Ni single-active-center composite electrocatalyst based on high-rubidium and high-silicon lithium ore and its application in urea electrolysis for hydrogen production.

[0006] To address the aforementioned technical problems, this invention provides a method for preparing a composite electrocatalyst, comprising the following steps: (1) Take high rubidium and high silicon lithium raw ore and pre-treat it to obtain ore material; (2) The ore material is added to an acid solution for acid etching and activation to obtain activated material; (3) The activated material is added to the lithium source solution and mixed to perform lithiation control to obtain a lithiation carrier; (4) Prepare a Ni active solution containing a nickel source and a slow-release alkali source; mix the lithiation support with the Ni active solution and carry out a loading reaction to obtain a loaded precursor; (5) The precursor is calcined and shaped to obtain the final product.

[0007] Specifically, in the preparation method of the composite electrocatalyst, step (1) includes the pretreatment steps of crushing, sieving, washing, drying, and magnetically separating iron from the high-rubidium, high-silicon lithium ore; wherein, The crushing step crushes the high-rubidium, high-silicon lithium ore to a particle size ≤ 5 mm; and / or, The sieving step collects powder with a particle size <75μm; and / or, The cleaning step includes ultrasonic cleaning at 200-400W; and / or, The drying step includes vacuum drying at a vacuum degree of -0.08 to -0.10 MPa and a temperature of 75-85°C for 5-7 hours; and / or, The magnetic separation iron removal step includes the step of magnetically separating powder with an Fe content of <0.05%.

[0008] Specifically, in the preparation method of the composite electrocatalyst, in step (2): The acid solution includes at least one of hydrochloric acid solution, sulfuric acid solution, nitric acid solution, or phosphoric acid solution; and / or, The liquid-to-solid ratio of the ore to the acid solution is 8:1-15:1; and / or, The reaction temperature for the acid etching activation step is 25-30℃; and / or, The reaction time for the acid etching activation step is 1.5-2 hours; and / or, The acid etching activation step further includes washing the activation material until the filtrate pH is 5-6 and / or drying it at 95-105°C for 9-11 hours.

[0009] Specifically, in the preparation method of the composite electrocatalyst, in step (3): The lithium source solution includes at least one of lithium carbonate solution, lithium hydroxide solution, lithium nitrate solution, or lithium chloride solution; and / or, The liquid-to-solid ratio of the activating material to the lithium source solution is 7:1-9:1; and / or, The temperature for the lithiation control step is 40-55°C; and / or, The lithiation control step takes 1-1.5 hours.

[0010] Specifically, in the preparation method of the composite electrocatalyst, in step (4): In the Ni active solution, the nickel source includes at least one of nickel nitrate, nickel sulfate, nickel chloride, or nickel acetate; and / or, In the Ni active solution, the slow-release alkali source includes at least one of urea, ammonium carbonate, or ammonium bicarbonate; and / or, In the Ni active solution, the molar ratio of the slow-release alkali source to Ni element is 0.8:1-1.2:1; and / or, In the Ni active solution, the concentration of the nickel source is 0.20-0.28 mol / L; and / or, The Ni active solution contains at least one solvent selected from ethylene glycol or glycerol; and / or, The solid-liquid ratio of the lithium-ion carrier to the Ni active solution is 10 g: 50-60 mL; and / or, The temperature of the loading reaction is 160-170℃; and / or, The loading reaction time is 7-8 hours; and / or, The loading reaction also includes the step of drying the precursor at 75-85°C for 5-7 hours.

[0011] Specifically, in the preparation method of the composite electrocatalyst, in step (5): The temperature for the roasting and shaping step is 280-320℃; and / or, The roasting and shaping step takes 1.5-2.5 hours; and / or, The heating rate for the roasting and shaping step is 5°C / min.

[0012] The present invention also discloses a composite electrocatalyst prepared by the method described above.

[0013] The present invention also discloses a catalytic electrode, wherein the active component of the catalytic electrode includes the composite electrocatalyst.

[0014] The present invention also discloses a method for preparing the catalytic electrode, comprising the steps of preparing a slurry containing 4-6 mg / mL of the composite catalyst, and the step of coating the slurry onto the surface of a substrate electrode.

[0015] The present invention also discloses the application of the composite electrocatalyst or the catalytic electrode in the field of catalytic urea electrolysis for hydrogen production.

[0016] The present invention also discloses a method for producing hydrogen by catalytic electrolysis of urea, the method comprising the step of electrocatalytically degrading urea to produce hydrogen in the presence of the composite electrocatalyst or the catalytic electrode.

[0017] The present invention describes a method for preparing a Ni single-active-center composite electrocatalyst based on a high-rubidium, high-silicon lithium ore substrate. This method involves pretreatment of the high-rubidium, high-silicon lithium ore (impurity removal, particle size control), acid etching activation (mesoporous structure construction), lithiation regulation (conductivity optimization), Ni active solution preparation, solvothermal loading, and calcination to achieve uniform loading and efficient activation of Ni single active centers on the ore substrate. When applied to urea electrolysis for hydrogen production, this catalyst exhibits advantages such as low onset potential, low overpotential, and high stability, solving the problems of interference from impurities in natural ores, insufficient mesoporous structures, poor conductivity, and poor dispersion / stability of Ni active centers.

[0018] The present invention discloses a method for preparing a Ni single-active-center composite electrocatalyst based on a high-rubidium, high-silicon lithium ore substrate. The pretreatment step employs impurity removal and particle size control, involving coarse crushing, grinding, and sieving to control the uniformity of ore particle size, increasing the initial specific surface area and laying the foundation for the uniform formation of mesopores in subsequent acid etching. The pretreatment step utilizes ultrasonic cleaning to remove surface dirt and soluble salts (such as Li₂SO₄) from the ore, reducing interference from impurities in subsequent steps. The pretreatment step also employs magnetic separation to remove Fe impurities, preventing Fe from competing with Ni for adsorption and thus preventing contamination of the active centers.

[0019] The present invention describes a method for preparing a Ni single-active-center composite electrocatalyst based on a high-rubidium, high-silicon lithium ore substrate. This method involves acid etching activation treatment to construct a mesoporous structure. Hydrochloric acid is used to etch 25-50 nm mesopores into the pretreated ore, increasing the specific surface area from an initial ≥10 nm. 2 / g increased to 120-140m 2 / g, with a mesoporous content of ≥80%, providing sufficient loading sites for Ni active components.

[0020] The present invention describes a method for preparing a Ni single-active-center composite electrocatalyst based on a high-rubidium, high-silicon lithium ore substrate. This method employs lithium source solutions such as lithium carbonate to treat acid-etched ore for lithiation regulation and conductivity optimization, utilizing Li... + With Rb in ore +The synergistic effect optimizes the conductivity of the ore and meets the requirements of electrocatalytic electron conduction.

[0021] The present invention describes a method for preparing a Ni single-active-center composite electrocatalyst based on a high-rubidium, high-silicon lithium ore substrate. This method utilizes a Ni active solution for loading, employing solvents such as ethylene glycol (to delay Ni crystallization) and slow-release alkaline sources such as urea (to prevent premature Ni(OH)₂ precipitation) to prepare a stable Ni active solution (with no impurity peak at 230 nm and stable absorbance), thus achieving uniform Ni loading. Under solvothermal conditions, the Ni active component forms chemical bonds with the hydroxyl groups on the surface of the lithiated support, achieving uniform Ni loading (without agglomeration) and a Ni loading of 12%-15%.

[0022] The present invention describes a method for preparing a Ni single-active-center composite electrocatalyst based on a high-rubidium, high-silicon lithium ore-based support. This method involves calcining and shaping the Ni-supported precursor to form a "support-Ni active layer." Through programmed temperature calcination, Ni(OH)₂ is converted into a NiO / Ni(OH)₂ composite active structure, thereby enhancing the Ni... 3+ A proportion (≥40%) enhances catalyst activity and alkali resistance.

[0023] The method for preparing Ni single-active-center composite electrocatalyst based on high-rubidium, high-silicon lithium ore as a support described in this invention uses high-rubidium, high-silicon lithium ore as raw material. The ore has sufficient mesoporous structure, with a mesoporous content ≥80% after acid etching, increasing the specific surface area to 120-140 μm². 2 / g, providing ample sites for Ni loading, exhibiting excellent conductivity, Li + With Rb + Synergistic optimization of conductivity meets the requirements of electrocatalytic electron conduction, enhances reaction kinetics, efficiently loads Ni active centers, and ensures uniform Ni dispersion (without agglomeration) through solvothermal loading, guaranteeing high catalytic activity. It exhibits outstanding urea electrolysis performance and excellent stability. Attached Figure Description

[0024] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein... Figure 1 The XRD pattern of the composite electrocatalyst prepared in Example 1 shows the characteristic peaks of NiO / Ni(OH)2; Figure 2 The image shows the SEM image of the electrocatalyst prepared in Example 1. The top left tab represents a size of 8 μm, and the other tabs represent a size of 6 μm, indicating no agglomeration. Detailed Implementation

[0025] In the following embodiments of the present invention, a Ni single-active-center composite electrocatalyst based on rubidium high-silicon lithium ore as a carrier is provided. The composite electrocatalyst effectively solves the problems of interference from impurities in natural ore, insufficient mesopores, poor conductivity, and poor dispersion / stability of Ni active centers, so that the catalyst has both high activity and high stability when applied to urea electrolysis for hydrogen production.

[0026] The present invention provides a method for preparing a composite electrocatalyst in the following embodiments, comprising the following steps: (1) Take high rubidium and high silicon lithium raw ore and pre-treat it to obtain ore material; (2) The ore material is added to an acid solution for acid etching and activation to obtain activated material; (3) The activated material is added to the lithium source solution and mixed to perform lithiation control to obtain a lithiation carrier; (4) Prepare a Ni active solution containing a nickel source and a slow-release alkali source; mix the lithiation support with the Ni active solution and carry out a loading reaction to obtain a loaded precursor; (5) The precursor is calcined and shaped to obtain the final product.

[0027] In some specific embodiments, step (1) includes the pretreatment steps of crushing, screening, washing, drying, and magnetically separating iron from the high-rubidium, high-silicon lithium ore; wherein, The crushing step crushes the high-rubidium, high-silicon lithium ore to a particle size ≤ 5 mm; and / or, The sieving step collects powder with a particle size <75μm; and / or, The cleaning step includes ultrasonic cleaning at 200-400W; and / or, The drying step includes vacuum drying at a vacuum degree of -0.08 to -0.10 MPa and a temperature of 75-85°C for 5-7 hours; and / or, The magnetic separation iron removal step includes the step of magnetically separating powder with an Fe content of <0.05%.

[0028] In some specific embodiments, in step (2): The acid solution includes at least one of hydrochloric acid solution, sulfuric acid solution, nitric acid solution, or phosphoric acid solution; and / or, The liquid-to-solid ratio of the ore to the acid solution is 8:1-15:1; and / or, The reaction temperature for the acid etching activation step is 25-30℃; and / or, The reaction time for the acid etching activation step is 1.5-2 hours; and / or, The acid etching activation step further includes washing the activation material until the filtrate pH is 5-6 and / or drying it at 95-105°C for 9-11 hours.

[0029] As an exemplary embodiment, the acid solution is preferably a hydrochloric acid solution, and the introduced chloride ions can be washed away by washing, which makes it easier to operate.

[0030] As an exemplary embodiment, the acid solution can be sulfuric acid (concentration 15-25wt%): the liquid-solid ratio can be maintained at 8:1-12:1, preferably 15-20% by mass concentration. Since sulfuric acid has a slightly stronger acid etching ability, the concentration can be reduced accordingly, and the reaction temperature can be reduced by 1-2 degrees. Alternatively, a higher concentration can be selected, and the reaction time can be shortened by 1.3-1.8 hours. The washing and drying conditions remain unchanged, but since sulfate ions are relatively difficult to wash, it may be necessary to wash several times. The drying time can be slightly shorter, which can be adjusted to 8-10 hours, or it can remain unchanged, except for the energy consumption.

[0031] As an exemplary embodiment, the acid solution can be nitric acid (concentration 20-30wt%): the liquid-to-solid ratio can be adjusted to 10:1-14:1. Due to its strong oxidizing properties, increasing the amount used avoids excessive local etching. The reaction temperature remains unchanged, and the reaction time is 1-1.6 hours. This reaction is very fast, and washing and drying remain unchanged. However, nitrate is easier to wash than sulfate.

[0032] As an exemplary embodiment, the acid solution can be phosphoric acid (10-20wt%): the liquid-to-solid ratio is adjusted to 10:1-15:1. Because the etching rate is slow, the amount of liquid needs to be increased, and the reaction temperature is increased by 2-3 degrees. Phosphoric acid has a relatively mild effect, so the reaction time also needs to be increased slightly, to about 1.8-2.5 minutes. The number of washing cycles increases and the drying time is extended. However, the use of phosphoric acid is not recommended, as it will form complexes, which is not good. When changing the acid, only sulfuric acid and nitric acid are recommended.

[0033] In some specific embodiments, in step (3): The lithium source solution includes at least one of lithium carbonate solution, lithium hydroxide solution, lithium nitrate solution, or lithium chloride solution; and / or, The liquid-to-solid ratio of the activating material to the lithium source solution is 7:1-9:1; and / or, The temperature for the lithiation control step is 40-55°C; and / or, The lithiation control step takes 1-1.5 hours.

[0034] In some exemplary embodiments, the lithium source solution is selected as a lithium hydroxide solution, preferably with a concentration of 0.02-0.04 mol / L, a liquid-solid ratio controlled at 7:1-9:1, and a temperature of 40-50°C.

[0035] In some exemplary embodiments, the lithium source solution is selected as lithium nitrate solution, preferably with a concentration of 0.03-0.06 mol / L, a liquid-solid ratio controlled at 7:1-9:1, and a temperature of 45-55°C.

[0036] In some exemplary embodiments, the lithium source solution is selected as a lithium chloride solution, preferably with a concentration of 0.04-0.07 mol / L, a liquid-solid ratio controlled at 7:1-9:1, and a temperature of 45-55°C.

[0037] In some specific embodiments, in step (4): In the Ni active solution, the nickel source includes at least one of nickel nitrate, nickel sulfate, nickel chloride, or nickel acetate; and / or, In the Ni active solution, the slow-release alkali source includes at least one of urea, ammonium carbonate, or ammonium bicarbonate; and / or, In the Ni active solution, the molar ratio of the slow-release alkali source to Ni element is 0.8:1-1.2:1; and / or, In the Ni active solution, the concentration of the nickel source is 0.20-0.28 mol / L; and / or, The Ni active solution contains at least one solvent selected from ethylene glycol or glycerol; and / or, The solid-liquid ratio of the lithium-ion carrier to the Ni active solution is 10 g: 50-60 mL; and / or, The temperature of the loading reaction is 160-170℃; and / or, The loading reaction time is 7-8 hours; and / or, The loading reaction also includes the step of drying the precursor at 75-85°C for 5-7 hours.

[0038] In some specific embodiments, in step (5): The temperature for the roasting and shaping step is 280-320℃; and / or, The roasting and shaping step takes 1.5-2.5 hours; and / or, The heating rate for the roasting and shaping step is 5°C / min.

[0039] As an exemplary embodiment, the present invention provides a specific method for preparing a Ni single-active-center composite electrocatalyst based on rubidium-rich high-silicon lithium ore as a support, which specifically includes the following steps: (1) Ore pretreatment ① Crushing and Screening: Take 400g-600g of high-rubidium, high-silicon lithium ore and coarsely crush it to a particle size ≤5mm using a jaw crusher. Then, grind it in an agate ball mill (ball-to-material ratio 5:1, 300rpm) for 1.5h-2.5h. Collect the powder with a particle size <75μm through a 200-mesh sieve (particles above the sieve are returned for re-grinding). The powder specific surface area should be ≥10m². 2 / g; ② Ultrasonic cleaning: Take 100g of sieved powder and add 250-350mL of deionized water (i.e., liquid-solid ratio 2.5:1-3.5:1), ultrasonically clean for 10-20min × 3 times at 300W, after the supernatant is clear, vacuum dry at -0.08~-0.10MPa and 75-85℃ for 5-7h, with a moisture content ≤0.5%; ③ Magnetic separation for iron removal: The dried powder is spread evenly (thickness ≤ 2 mm) and magnetically separated 3 times by a 15000 Gs flat plate magnetic separator (feeding speed 5 cm / min). The Fe content is <0.05% according to AAS test. If it exceeds the standard, soak it in 0.08-0.12 mol / L EDTA for 0.8-1.2 h and then dry it again. (2) Acid etching activation Take 40g of magnetically separated powder and add 320-480mL of 18%-27% hydrochloric acid (i.e., liquid-solid ratio 8:1-12:1). Stir in a constant temperature water bath at 25-30℃ (280-320rpm) for 1.5-2h. Filter through a 0.22μm filter membrane. Wash with deionized water until the pH of the filtrate is 5-6. Dry in a forced-air dryer at 95-105℃ for 9-11h. (3) Lithification regulation Take 30g of acid-etched powder and add 210-270mL of 0.03-0.05mol / L lithium carbonate solution (liquid-solid ratio 7:1-9:1). If the ore Rb + ≥0.3%, lithium carbonate concentration reduced to 0.03mol / L, stirred at 45-55℃ (180-220rpm) for 1-1.5h, filtered, and then vacuum dried at 80℃ for 8h; (4) Preparation of Ni active solution and solvent thermal load Take 50 mL of ethylene glycol and add 3.3-4.3 g of nickel nitrate (0.20-0.28 mol / L), then add 8-12 mL of 0.4-0.6 mol / L urea solution (urea:Ni molar ratio 0.8:1-1.2:1), stir at 450-550 rpm for 10-20 min, and use within 1 hour; Take 10g of lithium-ionized support and add Ni active solution. Stir for 30min and then transfer to 100mL reactor. React in oven at 160-170℃ for 7-8h. Then dry at 75-85℃ for 5-7h. After natural cooling, filter, wash 3 times with deionized water, and dry at 80℃ for 6h. (5) Firing and shaping: Place the dried product into a porcelain boat (thickness ≤ 3 mm), heat it in a muffle furnace to 280-320℃ at 5℃ / min, keep it at that temperature for 1.5-2.5 hours, then let it cool naturally and seal it in a desiccator.

[0040] In the following embodiments of the present invention, in step (1), the specific surface area of ​​the ore powder is verified by the BET nitrogen adsorption method and is ≥10m². 2 / g.

[0041] In the following embodiments of the present invention, in step (1), the moisture content of the ore powder is verified by gravimetric method and is ≤0.5%.

[0042] In the following embodiments 1-3 of the present invention, as exemplary implementations, the composition information of the selected high rubidium and high silicon lithium ore is shown in Tables 1-2 below.

[0043] Table 1. Semi-quantitative analysis results of X-ray fluorescence spectra of raw ore.

[0044] Table 2. Results of multi-element chemical analysis of the ore.

[0045] Example 1 The preparation method of the Ni single-active-center composite electrocatalyst based on high-rubidium, high-silicon lithium ore as a support described in this embodiment specifically includes the following steps: (1) Ore pretreatment Crushing and Screening: 500g of high-rubidium, high-silicon lithium ore was coarsely crushed to ≤5mm, ground in an agate ball mill (ball-to-material ratio 5:1, 300rpm) for 2 hours, and passed through a 200-mesh sieve to obtain <75μm powder. BET analysis showed a specific surface area of ​​11m². 2 / g; Ultrasonic cleaning: 100g powder was added to 300mL of deionized water, ultrasonicated at 300W for 15min × 3 times, dried at -0.09MPa and 80℃ for 6h, and the moisture content was determined by gravimetric method to be 0.4%. Magnetic separation for iron removal: The powder was spread into a 1.5mm thick layer and subjected to magnetic separation three times by a 15000Gs magnetic separator. The Fe content was measured to be 0.04% (<0.05%) by AAS. (2) Acid etching activation 40g of magnetically separated powder was added to 400mL of 25% hydrochloric acid and stirred at 28℃ and 300rpm for 1.8h. The mixture was then filtered, washed until pH=5.5, and dried at 100℃ for 10h. The specific surface area determined by BET was 135m². 2 / g, mesoporous content is 85%; (3) Lithification regulation 30g acid etching powder (Rb) +Add 240 mL of 0.05 mol / L lithium carbonate solution (content 0.25% < 0.3%), stir at 50℃ and 200 rpm for 1.2 h, filter, and dry at 80℃ for 8 h; (4) Preparation of Ni active solution and solvent thermal load Add 3.8 g of nickel nitrate (0.24 mol / L) to 50 mL of ethylene glycol, stir at 500 rpm for 15 min to dissolve, add 10 mL of 0.5 mol / L urea solution, stir for another 15 min, and no impurity peaks are observed at 230 nm. Solvothermal: 10g of lithium-ion support was added to Ni active solution, stirred for 30min and then transferred to 100mL reactor (75% filling degree), reacted at 165℃ for 7.5h, filtered, washed and dried at 80℃ for 6h, ICP-OES showed Ni loading of 14% and SEM showed no agglomeration. (5) Firing and shaping The dried product was placed in a porcelain boat (2 mm thick), heated to 300 °C in a muffle furnace at a rate of 5 °C / min, held for 2 hours, and then cooled. XRD detected characteristic peaks for NiO / Ni(OH)2, and XPS detected Ni... 3+ It accounts for 42%.

[0046] The XRD pattern of the composite electrocatalyst prepared in this embodiment is attached. Figure 1 As shown, the characteristic peaks of NiO / Ni(OH)2 are as follows: Ni(OH)2 (β type) characteristic peaks: diffraction peaks at 2θ≈19.3°, 33.0°, and 38.54°, corresponding to the (001), (100), and (101) crystal planes of Ni(OH)2; diffraction peaks at 2θ≈37.2° and 43.3°, corresponding to the (111) and (200) crystal planes of NiO.

[0047] The SEM images of the composite electrocatalyst prepared in this embodiment are attached. Figure 2 As shown, there is no agglomeration. O element is widely and continuously distributed, covering the entire ore carrier area. Ni element is uniformly dispersed on the surface of the ore carrier, with no local dense agglomeration areas. The distribution areas of O element and Ni element highly overlap, indicating that the active phase has uniform coverage on the carrier surface and no areas lacking active sites.

[0048] This embodiment uses the aforementioned composite electrocatalyst to prepare a catalytic electrode for use in the urea electrolysis hydrogen production process.

[0049] Take 5 mg of composite electrocatalyst, add 900 μL of water, 100 μL of ethanol and 50 μL of Nafion, mix and sonicate at 300 W for 30 min to obtain slurry.

[0050] 5 μL of slurry was drop-coated onto a 5 mm glassy carbon electrode and allowed to air dry at room temperature for 12 hours. The coating amount was 0.25 mg / cm². 2The working electrode is obtained.

[0051] Example 2 The preparation method of the Ni single-active-center composite electrocatalyst based on high-rubidium, high-silicon lithium ore as a support described in this embodiment specifically includes the following steps: (1) Ore pretreatment Crushing and screening: 400g of raw ore was coarsely crushed to ≤5mm, ground in an agate ball mill (ball-to-material ratio 5:1, 300rpm) for 1.5h, and passed through a 200-mesh sieve to obtain <75μm powder; Ultrasonic cleaning: Add 250mL of deionized water to 100g of powder, sonicate at 300W for 10min × 3 times, dry at -0.08MPa and 75℃ for 5h, and determine the moisture content by gravimetric method as ≤0.5%; Magnetic separation for iron removal: The powder was spread into a 1.5mm thick layer and subjected to magnetic separation three times by a 15000Gs magnetic separator. The Fe content was measured to be 0.04% (<0.05%) by AAS. (2) Acid etching activation Add 320 mL of 18% hydrochloric acid to 40 g of magnetically separated powder, stir at 25 °C and 280 rpm for 1.5 h, filter, wash until pH=5.0, and dry at 95 °C for 9 h; (3) Lithification regulation 30g acid etching powder (Rb) + Add 210 mL of 0.05 mol / L lithium carbonate solution (content 0.25% < 0.3%), stir at 45℃ and 180 rpm for 1 h, filter, and dry at 80℃ for 8 h; (4) Preparation of Ni active solution and solvent thermal load Take 50 mL of ethylene glycol and add 3.3 g of nickel nitrate, stir at 500 rpm for 15 min to dissolve, add 8 mL of 0.4 mol / L urea solution, and stir for another 10 min; Take 10g of lithium-ionized support and add Ni active solution. Stir for 30min and then transfer to 100mL reactor (75% filling). React at 160℃ for 7h. Filter, wash and dry at 75℃ for 5h. SEM observation showed no agglomeration. (5) Firing and shaping The dried product was placed in a ceramic boat (2 mm thick), heated to 280 °C in a muffle furnace at a rate of 5 °C / min, held for 1.5 h, and then cooled. The characteristic peaks of NiO / Ni(OH)2 were detected by XRD.

[0052] This embodiment uses the aforementioned composite electrocatalyst to prepare a catalytic electrode for use in the urea electrolysis hydrogen production process.

[0053] Take 4 mg of composite electrocatalyst, add 900 μL of water, 100 μL of ethanol and 50 μL of Nafion, mix and sonicate at 300 W for 30 min to obtain slurry.

[0054] 5 μL of slurry was drop-coated onto a 5 mm glassy carbon electrode and allowed to air dry at room temperature for 12 hours. The coating amount was 0.25 mg / cm². 2 The working electrode is obtained.

[0055] Example 3 The preparation method of the Ni single-active-center composite electrocatalyst based on high-rubidium, high-silicon lithium ore as a support described in this embodiment specifically includes the following steps: (1) Ore pretreatment Crushing and screening: 600g of raw ore was coarsely crushed to ≤5mm, ground in an agate ball mill (ball-to-material ratio 5:1, 300rpm) for 2.5h, and passed through a 200-mesh sieve to obtain <75μm powder; Ultrasonic cleaning: Add 100g of powder to 350mL of deionized water, sonicate at 300W for 20min × 3 times, dry at -0.10MPa and 85℃ for 7h, and determine the moisture content by gravimetric method as ≤0.5%; Magnetic separation for iron removal: The powder was spread into a 1.5mm thick layer and subjected to magnetic separation three times by a 15000Gs magnetic separator. The Fe content was measured to be 0.04% (<0.05%) by AAS. (2) Acid etching activation Take 40g of magnetic separation powder, add 480mL of 27% hydrochloric acid, stir at 30℃ and 320rpm for 2h, filter, wash until pH=6.0, and dry at 105℃ for 11h; (3) Lithification regulation Take 30g of acid etching powder (Rb) + Add 270 mL of 0.05 mol / L lithium carbonate solution (content 0.25% < 0.3%), stir at 55℃ and 220 rpm for 1.5 h, filter, and dry at 80℃ for 8 h; (4) Preparation of Ni active solution and solvent thermal load Take 50 mL of ethylene glycol and add 4.3 g of nickel nitrate. Stir at 550 rpm for 20 min to dissolve. Add 12 mL of 0.6 mol / L urea solution and stir for another 10 min. Take 10g of lithium-ionized support and add Ni active solution. Stir for 30min and then transfer to 100mL reactor (75% filling). React at 170℃ for 8h. Filter, wash and dry at 85℃ for 7h. SEM observation showed no agglomeration. (5) Firing and shaping The dried product was placed in a ceramic boat (2 mm thick), heated to 320 °C in a muffle furnace at a rate of 5 °C / min, held for 2.5 h, and then cooled. XRD detected characteristic peaks of NiO / Ni(OH)2.

[0056] This embodiment uses the aforementioned composite electrocatalyst to prepare a catalytic electrode for use in the urea electrolysis hydrogen production process.

[0057] Take 6 mg of composite electrocatalyst, add 900 μL of water, 100 μL of ethanol and 50 μL of Nafion, mix and sonicate at 300 W for 30 min to obtain slurry.

[0058] 5 μL of slurry was drop-coated onto a 5 mm glassy carbon electrode and allowed to air dry at room temperature for 12 hours. The coating amount was 0.25 mg / cm². 2 The working electrode is obtained.

[0059] Comparative Example 1 The preparation method of the composite electrocatalyst described in this comparative example is the same as that in Example 1, except that urea is not added when preparing the Ni active solution, and the other steps are the same as in Example 1.

[0060] The preparation method of the catalytic electrode described in this comparative example is the same as that in Example 1.

[0061] Comparative Example 2 The preparation method of the composite electrocatalyst described in this comparative example is the same as that in Example 1, except that the magnetic separation iron removal step is omitted in the ore pretreatment step, and the other steps are the same as in Example 1.

[0062] The preparation method of the catalytic electrode described in this comparative example is the same as that in Example 1.

[0063] Comparative Example 3 The preparation method of the composite electrocatalyst described in this comparative example is the same as that in Example 1, except that 20wt% sulfuric acid is used instead of hydrochloric acid during acid etching activation, and the remaining acid etching conditions are adjusted accordingly. The remaining steps are the same as in Example 1.

[0064] The preparation method of the catalytic electrode described in this comparative example is the same as that in Example 1.

[0065] Comparative Example 4 The preparation method of the composite electrocatalyst described in this comparative example is the same as that in Example 1, except that the lithiation control step is omitted, and the acid-etched powder is directly used for Ni loading; the remaining steps are the same as in Example 1. The preparation method of the catalytic electrode described in this comparative example is the same as that in Example 1.

[0066] Experimental Example 1. Performance Testing This experimental example is based on the working electrodes of Examples 1-3 and Comparative Examples 1-4 mentioned above, to test electrocatalytic activity and application stability.

[0067] The electrocatalytic activity test was conducted using a three-electrode system, and the electrolyte system consisted of 30 mL of 1 mol / L KOH and 0.33 mol / L urea.

[0068] CV test: 0-0.8V vs Hg / HgO, 50mV / s, stabilized after 10 cycles.

[0069] LSV test: 0-0.8V vs Hg / HgO, 5mV / s, UOR onset potential 0.36V (vs RHE), 10mA / cm 2 Overpotential 85mV, Tafel slope 48mV / dec.

[0070] The control parameters for stability testing are as follows: Constant current: 100mA / cm 2 After 120 hours of electrolysis, the voltage increased from 1.45V to 1.55V, an increase of 6.9% (≤10%).

[0071] Cyclic stability: After 10,000 cycles at 100 mV / s, 10 mA / cm 2 The overpotential increased from 85mV to 92mV, an increase of 7mV (≤10mV).

[0072] In this embodiment, the performance test results of the working electrode are shown in Tables 3-4 below.

[0073] Table 3 Performance test results of Schemes 1-3 in Examples 1-3

[0074] Table 4 Performance test results of comparative examples 1-4

[0075] As can be seen from the data in Table 3 above, the detection parameters of the composite electrocatalyst prepared by the method of this invention are as follows: 1. Overpotential data can reflect the "extra energy to overcome the reaction energy barrier", and also shows that the mesoporous support provides sufficient mass transfer channels + uniform Ni dispersion (SEM verification) to make the reaction energy barrier of urea oxidation low; the overpotential data of the catalysts prepared by the schemes in Examples 1-3 are better, among which the Ni loading (14%) of Example 1 is the highest and the overpotential is the lowest. 2. The smaller the slope of the Tafel slope, the faster the reaction kinetics (the higher the electron transfer / urea adsorption rate); the catalysts prepared by the schemes in Examples 1-3 all have good reaction kinetic performance; 3. The CV cycle stability shows the situation where Ni forms strong chemical bonds with the hydroxyl groups of the support by the solvothermal loading method. The CV curves of the catalysts prepared by the schemes in Examples 1-3 show no peak shift, current fluctuation ≤3%, and no loss of active centers, indicating good stability. 4. The constant current stability characterization of the catalysts prepared by the schemes in Examples 1-3 shows that the ore support has good alkali resistance, and the NiO / Ni(OH)2 active phase is stable. During long-term electrolysis, there is no aggregation / detachment of active components and the voltage rise is small. 5. The cycling stability of the catalysts prepared by the schemes in Examples 1-3 showed that the Ni active centers were uniformly dispersed (SEM-EDS verification), there was no agglomeration during cycling, the number of active sites remained stable, and the performance degradation was within an acceptable range.

[0076] As can be seen, the composite electrocatalyst prepared under the scheme of this invention allows the Ni active centers (NiO / Ni(OH)2) to be fully exposed based on the mesopores (25-50 nm) constructed by hydrochloric acid etching; Li + With Rb in ore + The conductivity was optimized to bring the potential required for reaction initiation close to the theoretical UOR potential. In particular, the optimization of parameters under Example 1 made the potential required for reaction initiation reach 0.37VvsRHE, which is close to the theoretical UOR potential.

[0077] As can be seen from the data in Table 4 above, the electrocatalyst prepared under Comparative Example 1, due to the absence of urea-released OH... - Affecting Ni 2+ Rapid precipitation and aggregation lead to reduced exposure of active sites and increased onset potential. Aggregation also hinders mass transfer / electron transfer, resulting in a sharp increase in overpotential and Tafel slope. In particular, the active sites are prone to detachment after aggregation, causing a sharp drop in stability. Therefore, the addition of urea in the catalyst preparation method can ensure uniform dispersion of Ni.

[0078] As can be seen from the data in Table 4 above, the electrocatalyst prepared under Comparative Example 2 exhibits an increased onset potential due to Fe residue competing with Ni for active sites and Fe contaminating Ni active centers. Furthermore, Fe forms electron transport barriers, slowing down reaction kinetics; and especially, Fe dissolution contaminates the active layer, leading to decreased stability. Therefore, magnetic separation for iron removal during catalyst preparation can prevent contamination of active centers.

[0079] As can be seen from the data in Table 4 above, the electrocatalyst prepared under Comparative Example 3, when etched with sulfuric acid, has certain drawbacks: firstly, there are insufficient Ni loading sites; secondly, sulfate residues adsorbed on the support surface hinder electron transfer; and thirdly, sulfate accelerates the collapse of the support structure, affecting stability. Therefore, the method described above, which utilizes hydrochloric acid etching, can construct sufficient loading sites.

[0080] As can be seen from the data in Table 4 above, the electrocatalyst prepared under Comparative Example 3, due to the lack of lithiation treatment, has slightly lower conductivity, but the number of Ni active centers is sufficient, resulting in a smaller increase in onset potential. Furthermore, the electron transport is hindered, slowing down the reaction kinetics. In particular, insufficient conductivity accelerates the oxidation of the active phase, leading to decreased stability. Therefore, lithiation control can optimize its conductivity.

[0081] In summary, the performance of the composite electrocatalyst described in this invention is based on the synergistic effect of multiple processes, including ore pretreatment (impurity removal), hydrochloric acid etching (mesoporosis), lithiation regulation (conductivity), and urea slow release (Ni dispersion). The synergistic effect of each step effectively increases its catalytic activity. The Ni single-active-center composite electrocatalyst based on high-rubidium, high-silicon lithium ore as a support described in this invention exhibits superior application performance.

[0082] 2. Electrochemical impedance This experimental example uses the working electrodes from Examples 1-3 and Comparative Examples 1-4 to perform electrochemical impedance spectroscopy. The results are shown in Table 5 below.

[0083] Table 5 Results of electrochemical impedance spectroscopy tests

[0084] Charge transfer resistance (Rct) is a core parameter in electrochemical impedance spectroscopy (EIS), reflecting the resistance to electron transfer at the electrode-electrolyte interface and between active sites. A smaller Rct indicates higher electron transport efficiency, resulting in better electrocatalytic reaction kinetics and energy utilization efficiency. The data shown in Table 5 conforms to this trend. Specifically: As shown in the process flow of Examples 1-3, Rct is concentrated in 1.6-1.9Ω and is significantly lower than that of the comparative example. Among them, Example 1 has the best performance with the smallest Rct of 1.6Ω, while Examples 2 and 3 have slightly lower Rct because the process parameters are close to the upper and lower limits of the optimization range, the proportion of mesopores and the Ni dispersion are slightly worse than those of Example 1. As shown in Comparative Examples 1-4, due to the lack of core process steps, the electron transport resistance is significantly increased, with Rct generally ranging from 2.4 to 3.8 Ω. This difference in Rct is related to the electrocatalytic performance data in Tables 3 and 4. The low Rct in the examples corresponds to a smaller Tafel slope and a lower overpotential, while the high Rct in the comparative examples is accompanied by a larger Tafel slope and a higher overpotential. This fully demonstrates that the synergistic effect of the process of "lithiation regulation to optimize conductivity + mesoporous construction to reduce transport resistance + uniform Ni dispersion to eliminate the influence of agglomeration" can improve the overall performance of the catalyst.

[0085] As can be seen, the composite electrocatalyst prepared by this invention has lower electrochemical impedance and better application performance. The embodiments of this invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, for those skilled in the art, based on the ideas of this invention, there will be changes in specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for preparing a composite electrocatalyst, characterized in that, Includes the following steps: (1) Take high rubidium and high silicon lithium raw ore and pre-treat it to obtain ore material; (2) The ore material is added to an acid solution for acid etching and activation to obtain activated material; (3) The activated material is added to the lithium source solution and mixed to perform lithiation control to obtain a lithiation carrier; (4) Prepare a Ni active solution containing a nickel source and a slow-release alkali source; mix the lithiation support with the Ni active solution and carry out a loading reaction to obtain a loaded precursor; (5) The precursor is calcined and shaped to obtain the final product.

2. The method for preparing the composite electrocatalyst according to claim 1, characterized in that, In step (1), the pretreatment includes crushing, screening, washing, drying, and magnetic separation to remove iron from the high-rubidium, high-silicon lithium ore; wherein, The crushing step crushes the high-rubidium, high-silicon lithium ore to a particle size ≤ 5 mm; and / or, The sieving step collects powder with a particle size <75μm; and / or, The cleaning step includes ultrasonic cleaning at 200-400W; and / or, The drying step includes vacuum drying at a vacuum degree of -0.08 to -0.10 MPa and a temperature of 75-85°C for 5-7 hours; and / or, The magnetic separation iron removal step includes the step of magnetically separating powder with an Fe content of <0.05%.

3. The method for preparing the composite electrocatalyst according to claim 1, characterized in that, In step (2): The acid solution includes at least one of hydrochloric acid solution, sulfuric acid solution, nitric acid solution, or phosphoric acid solution; and / or, The liquid-to-solid ratio of the ore to the acid solution is 8:1-15:1; and / or, The reaction temperature for the acid etching activation step is 25-30℃; and / or, The reaction time for the acid etching activation step is 1.5-2 hours; and / or, The acid etching activation step further includes washing the activation material until the filtrate pH is 5-6, and / or drying it at 95-105°C for 9-11 hours.

4. The method for preparing the composite electrocatalyst according to claim 1, characterized in that, In step (3): The lithium source solution includes at least one of lithium carbonate solution, lithium hydroxide solution, lithium nitrate solution, or lithium chloride solution; and / or, The liquid-to-solid ratio of the activating material to the lithium source solution is 7:1-9:1; and / or, The temperature for the lithiation control step is 40-55°C; and / or, The duration of the lithiation control step is 1-1.5 hours.

5. The method for preparing the composite electrocatalyst according to claim 1, characterized in that, In step (4): In the Ni active solution, the nickel source includes at least one of nickel nitrate, nickel sulfate, nickel chloride, or nickel acetate; and / or, In the Ni active solution, the slow-release alkali source includes at least one of urea, ammonium carbonate, or ammonium bicarbonate; and / or, In the Ni active solution, the molar ratio of the slow-release alkali source to Ni element is 0.8:1-1.2:1; and / or, In the Ni active solution, the concentration of the nickel source is 0.20-0.28 mol / L; and / or, The Ni active solution contains at least one solvent selected from ethylene glycol or glycerol; and / or, The solid-liquid ratio of the lithium-ion carrier to the Ni active solution is 10 g: 50-60 mL; and / or, The temperature of the loading reaction is 160-170℃; and / or, The loading reaction time is 7-8 hours; and / or, The loading reaction also includes the step of drying the precursor at 75-85°C for 5-7 hours.

6. The method for preparing the composite electrocatalyst according to claim 1, characterized in that, In step (5): The temperature for the roasting and shaping step is 280-320℃; and / or, The roasting and shaping step takes 1.5-2.5 hours; and / or, The heating rate for the roasting and shaping step is 5°C / min.

7. A composite electrocatalyst prepared by the method according to any one of claims 1-6.

8. A catalytic electrode, characterized in that, The active component of the catalytic electrode includes the composite electrocatalyst described in claim 7.

9. A method for preparing the catalytic electrode as described in claim 8, characterized in that, The process includes the steps of preparing a slurry containing 4-6 mg / mL of the composite catalyst, and the step of coating the slurry onto the surface of the substrate electrode.

10. The application of the composite electrocatalyst of claim 7 or the catalytic electrode of claim 8 in the field of catalytic urea electrolysis for hydrogen production.

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