Ru-CeO2 / NC catalyst as well as preparation method and application thereof

Abstract

The invention discloses a Ru-CeO2 / NC catalyst as well as a preparation method and application thereof, and belongs to the field of hydrogen production by electrolysis of water. The Ru-CeO2 / NC catalyst is prepared through a soft template method and one-step pyrolysis of a metal ion impregnated MOFs material. The Ru-CeO2 / NC catalyst has the advantages that the conductivity, the stability and the catalytic activity are good; an electrochemical test shows that the Ru-CeO2 / NC catalyst only needs 20 mV overpotential at 10 mA / cm, and the overpotential is far lower than 50 mV of a commercial 20 wt% Pt / C catalyst.

Description

Technical Field

[0001] The present invention relates to the field of hydrogen production by electrolysis of water, and in particular to a Ru-CeO 2 / NC catalyst, preparation method and application. Background Art

[0002] Hydrogen production by water electrolysis provides a feasible and low-cost method to alleviate the environmental and energy crisis caused by fossil energy consumption. Designing catalysts for hydrogen evolution reaction (HER) is one of the main focuses of water electrolysis research. Among them, Pt-based catalysts supported on high specific surface area supports are widely considered to be the most effective HER catalysts, but their application in industry is still restricted by their inherent defects, especially their rarity, high cost and low stability. Therefore, it is urgent to find a Pt-based catalyst alternative material with advantages such as high catalytic efficiency, high stability and low cost, or to significantly reduce the amount of catalyst without affecting the catalytic activity and stability. Ruthenium (Ru), a precious metal with only 1 / 4 the price of platinum, has become the most promising alternative to platinum (Pt)-based catalysts due to its similar hydrogen binding energy (~65 kcal / mol) to platinum. The inherent high surface free energy of precious metal atoms makes them tend to agglomerate into large particles during preparation or catalysis, affecting the catalytic activity. Therefore, the development of Ru-based catalysts with high activity and stability remains a huge challenge.

[0003] One feasible method is to use metal oxide supports to stabilize metal nanoparticles. With the help of the strong metal-support interaction (SMSI), metal particles can be stably loaded on the metal oxide surface even under harsh reaction conditions. In addition, the alkaline HER process includes water dissociation into adsorbed H* and OH*, and H* recombination into H 2 , and the resolution of OH*, among which the water dissociation step is the only different and difficult-to-overcome step between alkaline HER and acidic HER, and metal oxides can promote the dissociation of water to produce a local acidic environment around it that is conducive to HER. However, the poor conductivity of the metal oxide support itself seriously hinders its application in HER catalysis. In contrast, carbon supports have the advantages of flexible structure, high stability and excellent conductivity and are widely used as supports for active centers in various catalytic reactions, but their weak interaction with metal active centers in the actual catalytic process usually leads to the agglomeration of metal active centers, affecting the catalytic efficiency. Therefore, there is an urgent need to develop new synthesis methods to integrate the strong interaction and conductivity of metal supports into supported HER catalysts. Summary of the invention

[0004] The purpose of the present invention is to provide a Ru-CeO 2 / NC catalyst and preparation method and application thereof, the method of the present invention is to 3+ The ions were impregnated into SGPN-UIO-66 (Ce) MOFs synthesized by using P123 as a soft template, and then carbonized under the protection of an inert atmosphere. The pyrolysis of MOFs resulted in the conversion of the organic part into a carbon-based material with a porous structure and good conductivity. In addition, during the pyrolysis process, the Ce nodes evolved into chemically stable CeO embedded in the carbon support. 2 Nanoparticles, thanks to the strong interaction between the metal support and the Ru nanoparticles and CeO 2 Due to the strong chemical interaction between the particles, the precious metal Ru is stably loaded on its surface, limiting the agglomeration of Ru.

[0005] The present invention first provides a Ru-CeO 2 A method for preparing a NC catalyst comprises the following steps: (1) Mixing polyether, glacial acetic acid, 1,3,5-trimethylbenzene and water to prepare a microemulsion solution; (2) mixing the microemulsion solution, ammonium cerium nitrate and terephthalic acid to react and obtain three-dimensional porous spherical UIO-66 (Ce) MOFs; (3) mixing a soluble ruthenium salt, cyanamide, a three-dimensional porous spherical UIO-66 (Ce) MOFs and water to obtain a mixed solution; freeze-drying the mixed solution, and then annealing to obtain the Ru-CeO 2 / NC catalyst.

[0006] In the above preparation method, the polyether is polyether 123.

[0007] In the above-mentioned preparation method, in steps (1) and (2), the mass ratio of the ammonium cerium nitrate to the polyether is 1:1.5-3, specifically 1:1.9; The mass ratio of the cerium ammonium nitrate to the volume ratio of the glacial acetic acid is 1 g:1-3 mL, specifically 1 g:1.8 mL; The mass ratio of the cerium ammonium nitrate to the volume ratio of 1,3,5-trimethylbenzene is 1 g:20-80 mL, specifically 1 g:22 mL; The mass ratio of the ammonium cerium nitrate to the volume ratio of water is 1 g:100-400 mL, specifically 1 g:109 mL; The mass ratio of the ammonium cerium nitrate to terephthalic acid is 1:2-4, specifically 1:3.

[0008] In the above preparation method, in step (2), the reaction temperature is 35°C-45°C, specifically 45°C; The reaction time is 30 min-60 min, specifically 50 min.

[0009] In the above preparation method, after the reaction in step (2), there is a step of centrifuging to obtain a solid and washing and drying the solid; specifically, the washing is carried out using DMF and anhydrous ethanol; and the drying is carried out in a vacuum oven at 30° C. for 24 h.

[0010] In the above-mentioned preparation method, in step (3), the soluble ruthenium salt is ruthenium chloride; In the mixed solution, the concentration of the soluble ruthenium salt is 0.5 μg / mL-1.2 μg / mL; specifically, it can be 1 μg / mL; The concentration of the cyanamide is 5 mg / mL-15 mg / mL; specifically, it can be 9.8 mg / mL; The concentration of the three-dimensional porous spherical UIO-66 (Ce) MOFs is 8 mg / mL-12 mg / mL, specifically 10 mg / mL.

[0011] In the above preparation method, in step (3), the freeze-drying temperature is -60°C to -80°C; The freeze-drying time is 20-30 h.

[0012] In the above preparation method, in step (3), the annealing temperature is 600°C-900°C, specifically 600°C, 675°C, 750°C / 825°C or 900°C; The annealing time is 1 h-3 h, specifically 3 h; The heating rate of the annealing is 2°C / min-10°C / min, specifically 5°C / min; The annealing is performed in an inert atmosphere, specifically an argon or nitrogen atmosphere.

[0013] The present invention also provides Ru-CeO prepared by the above preparation method 2 / NC catalyst.

[0014] Finally, the present invention provides the above-mentioned Ru-CeO 2 / Application of NC catalysts in hydrogen production by water electrolysis.

[0015] The Ru-CeO 2 The rich pore structure on the surface of the NC catalyst carrier can effectively limit the aggregation of cerium oxide nanoparticles during high-temperature conversion and HER reactions. In addition, the presence of cerium oxide nanoparticles also effectively limits the agglomeration of metallic ruthenium during the high-temperature preparation process.

[0016] The present invention has the following advantages: (1) The present invention prepares highly efficient and stable carbon and metal oxides (CeO 2 ) supported Ru-based catalyst (Ru-CeO 2 / NC); Uio-66(Ce) was impregnated with Ru ions and then pyrolyzed to obtain hexagonal CeO embedded in the carbon support. 2 Nanoparticles loaded with precious metal Ru; CeO 2 The oxygen vacancies on the surface are beneficial to the uniform dispersion of Ru metal on the nanoparticles and improve the stability of the catalyst during hydrogen evolution; (2) The present invention uses a method of embedding metal oxides in carbon carriers as carriers, which helps solve the problem of insufficient conductivity of metal oxides as carriers and improves the conductivity of the catalyst; (3) After the introduction of cerium oxide nanoparticles, Ru and CeO 2 The strong interaction between the metal carrier and Ru-CeO promoted the electron transfer between the two, optimized the adsorption strength of the intermediates in the hydrogen evolution reaction, and improved the catalytic activity. Electrochemical tests showed that Ru-CeO 2 The Pt / NC catalyst only requires an overpotential of 20 mV at 10 mA / cm², which is much lower than the 50 mV of the Pt / C catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Ru-CeO 2 / NC preparation process.

[0018] Figure 2 For SGPN-UIO-66 (Ce) and Ru-CeO 2 / NC catalyst SEM image; among them, Figure 2 (a) and (b) are SEM images of SGPN-UIO-66(Ce); (c) and (d) are SEM images of Ru-CeO 2 / NC catalyst SEM image.

[0019] Figure 3 Ru-CeO 2 TEM images and HRTEM images of / NC catalyst at 50nm, 20nm, 10nm and 5nm respectively; Figure 3 (a), (b) and (c) are TEM images; (d) is a HRTEM image.

[0020] Figure 4 For SGPN-UIO-66 (Ce) and Ru-CeO 2 N / NC catalyst 2 Adsorption-desorption isotherm and pore size distribution diagram; Among them, Figure 4 (a) is the isotherm curve; (b) is the pore size distribution.

[0021] Figure 5 Ru-CeO 2 Comparison of XRD results of / NC catalysts prepared at different temperatures (600℃-900℃).

[0022] Figure 6 CeO 2 / NC、Ru / NC、Ru-CeO 2 / C、Ru-CeO 2 / NC, Pt / C HER catalytic activity; among them, Figure 6 (a) is the linear voltammetric scan curve LSV; (b) is the Tafel curve and Tafel slope; (c) is the Nengquist impedance diagram; (d) is the active area comparison diagram.

[0023] Figure 7 For commercial Pt / C, Ru-CeO 2 100h stability test of Ru / NC and Ru / NC catalysts. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below in conjunction with specific embodiments. The given examples are only for illustrating the present invention, but not for limiting the scope of the present invention.

[0025] The experimental methods in the following examples are all conventional methods unless otherwise specified.

[0026] The quantitative tests in the following examples were performed three times unless otherwise specified, and the results were averaged.

[0027] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0028] Example 1 1. Preparation of three-dimensional porous spherical UIO-66 (Ce) MOFs (SGPN-UIO-66 (Ce)) The soft template method was used to prepare three-dimensional porous spherical UIO-66 (Ce) MOFs with uniform particle size as the precursor of the subsequent carbon carrier. The preparation method is as follows: First, prepare a 25 mL beaker, then dissolve 176.6 mg of polyether P123 in 10 mL of deionized water, and then add 170 μL of glacial acetic acid and 2 mL of 1,3,5-trimethylbenzene to the above solution. Then add a rotor to stir continuously to form a microemulsion solution A for use. Then weigh 92 mg (NH 4 )Ce(NO 3 )6 (cerium ammonium nitrate) and 280 mg of terephthalic acid were added to microemulsion A to obtain solution B. After sealing with plastic wrap, solution B was stirred in an oil bath at 45°C, and a milky white product was obtained after 50 min of reaction. The obtained product was poured into a 50 mL centrifuge tube and stirred at 10,000 rpm / min for 7 min. The milky white turbid liquid obtained by centrifugation was introduced into a waste liquid bucket. The obtained light yellow solid was washed several times with DMF (N,N-dimethylformamide) and anhydrous ethanol to remove the soft template P123 and excess reactants. The obtained sample was placed in a vacuum oven and dried at 30°C for 24 h to obtain three-dimensional porous spherical UIO-66 (Ce) MOFs.

[0029] 2. Ru-CeO 2 Preparation of NC catalyst Ru-CeO 2 The preparation steps of NC catalyst are as follows: Figure 1 As shown, the specific preparation method is as follows: First, use a pipette to draw 80 μL of RuCl 3 Solution (0.066 mg / mL), 1 mL of cyanamide solution (50 mg / mL) and 4 mL of deionized water were placed in a 10 mL beaker and dispersed evenly by low-temperature ultrasound to obtain solution A. In the second step, 0.05 g of the three-dimensional porous spherical UIO-66 (Ce) MOFs prepared above was weighed and placed in solution A. After being dispersed evenly by low-temperature ultrasound for 60 min, it was placed in a freeze dryer and freeze-dried at -70°C for 24 h. In the third step, the freeze-dried solid was placed in a corundum magnetic boat, and heated to 750°C in an argon atmosphere using a tubular furnace at a heating rate of 5°C / min, and kept at this temperature for 3 h to obtain Ru-CeO 2 / NC catalyst.

[0030] Scanning electron microscopy (SEM) was used to characterize the SGPN-UIO-66 (Ce) and Ru-CeO 2 / NC catalyst materials were subjected to morphological analysis ( Figure 2 ).like Figure 2 As shown in (a, b), the SEM images reveal that SGPN-UIO-66 (Ce) exhibits a uniform spherical morphology with a diameter of about 570 nm. Figure 2 As can be seen in (b), the surface of SGPN-UIO-66 (Ce) has an ordered pore structure. Figure 2 (c, d) show the Ru-CeO prepared by impregnation and carbonization. 2The SEM image of the / NC catalyst shows that no obvious metal particles are observed at the micrometer scale, indicating that the metal particles formed during the synthesis process are small in size. The SEM image also clearly shows that the Ru-CeO 2 There are mesoporous structures on the surface of the / NC catalyst, which are beneficial to improving the mass transfer rate of the catalyst and facilitating the exposure of the active centers, thereby optimizing the hydrogen evolution reaction (HER) performance of the catalyst.

[0031] In order to further confirm the Ru and CeO 2 The distribution and morphology of Ru-CeO 2 The / NC catalyst samples were analyzed by transmission electron microscopy (TEM). Figure 3 Transmission electron microscopy (a) shows Ru-CeO at a scale of 50 nm. 2 The / NC catalyst exhibits a spherical porous structure with a diameter of about 370 nm, and abundant mesoporous structures are also observed in the figure. The surface of the spherical structure is magnified, as shown in Figure 3 As shown in (b), a large number of metal particles are uniformly loaded on the carbon layer structure, and no significant particle aggregation phenomenon is found. This result shows that under the heat treatment condition of 750℃, Ru-CeO 2 / NC exhibits excellent metal dispersion. In order to more accurately determine the size of metal nanoparticles on the carbon support surface, Figure 3 The red dashed box area in (b) is further magnified and observed. Figure 3 In (c), the size of the metal nanoparticles fluctuates around 5 nm, and no larger nanoparticles are found. In order to determine the specific metal type of the metal nanoparticles loaded on the surface of the carrier, high-resolution transmission electron microscopy (HRTEM) was used to characterize them. Figure 3 As shown in (d) Figure 3 The lattice fringes of the metal nanoparticles in the red box area in (d) were measured and found to be 0.311 nm in size. Further crystal plane analysis confirmed that these nanoparticles correspond to CeO 2 The (111) crystal plane of the cerium oxide was found to be present on the surface of the support in the form of nanoparticles. In addition, after screening the lattice fringes of the metal nanoparticles, no lattice fringes belonging to Ru were detected. Based on this, it is inferred that Ru metal is dispersed on the surface of cerium oxide in the form of extremely fine particles, and this phenomenon may be due to the strong interaction between the metal support and the support.

[0032] In order to further study the pore structure of the catalyst surface as well as its specific surface area and pore size distribution, SGPN-UIO-66 (Ce) and Ru-CeO 2 The / NC catalysts were characterized by BET. Figure 4 (a) is SGPN-UIO-66(Ce) and Ru-CeO 2 The nitrogen adsorption-desorption isotherms of SGPN-UIO-66 (Ce) and Ru-CeO 2 / NC catalysts all show typical IV-type isotherms, and their adsorption-desorption curves have H4-type hysteresis loops, proving that both have rich mesoporous structures on their surfaces. In addition, the nitrogen adsorption-desorption curve of SGPN-UIO-66 (Ce) rises rapidly at low P / P0 and then flattens in the region, indicating that the material has a microporous structure, but in Ru-CeO 2 The nitrogen adsorption-desorption curves of the SGPN-UIO-66 (Ce) catalysts do not show this phenomenon. The main reason is that the decomposition of organic components and the collapse of the microstructure during the carbonization process of the SGPN-UIO-66 (Ce) lead to the blockage of micropores, and the Ce nodes in the SGPN-UIO-66 (Ce) are converted into CeO 2 Nanoparticles will also block some micropores. The specific surface area of ​​SGPN-UIO-66 (Ce) is 751.51 m 2 / g, while Ru-CeO 2 The specific surface area of ​​the NC catalyst is 235.9241 m 2 / g, which shows that the specific surface area of ​​SGPN-UIO-66 (Ce) decreases during annealing due to the decomposition of organic components and the collapse of some pores, but Ru-CeO 2 / NC catalyst still maintains a large specific surface area. Figure 4 From the pore size distribution curve (b), it can be observed that SGPN-UIO-66 (Ce) has a large number of micropores and mesopores with pore sizes mainly distributed around 30 nm, while Ru-CeO 2 The mesopore size of the / NC catalyst is mainly distributed around 17 nm due to the pore shrinkage caused by the decomposition of the organic components in the precursor during the high-temperature carbonization process. Therefore, it can be known from Brunauer-Emmett-Teller data, SEM and TEM characterization that Ru-CeO 2 There are micropores and mesopores on the surface of NC catalysts. The mesopores and micropores on the surface of the catalyst provide a large number of active sites for it, while improving the mass transfer rate between the metal active center and the electrolyte.

[0033] Example 2 In order to further explore the effect of temperature on the metal nanoparticles on the surface of the sample catalyst during the annealing process, this experiment synthesized a series of Ru-CeO 2 / NC catalyst, denoted as Ru-CeO 2 / NC-x (x=600℃, 675℃, 750℃, 825℃ and 900℃), and its structure was analyzed by X-ray diffraction (XRD) technique.

[0034] The Ru-CeO 2 The preparation method of the / NC-x catalyst is the same as that in Example 1, except that the temperature of "heating the tubular furnace to 750°C at a heating rate of 5°C / min" is changed.

[0035] like Figure 5 , by Ru-CeO 2 From the analysis of the XRD spectrum of the / NC-750℃ sample, it can be found that in addition to the diffraction peak of the C(002) crystal plane detected at 22°, there are characteristic peaks belonging to the (111), (200), (220), (311) and (331) crystal planes of cerium oxide at 28°, 33°, 47° and 56°, respectively. No obvious characteristic diffraction peaks belonging to Ru were observed. Moreover, from the figure, we can clearly observe that even when the preparation temperature is 900℃, no strong characteristic peaks of cerium oxide and characteristic diffraction peaks of Ru are observed in the XRD data diagram, which further proves the confinement effect of the three-dimensional porous spherical structure on cerium oxide nanoparticles and the anchoring effect of cerium oxide nanoparticles on ruthenium.

[0036] Example 3 In order to explore the 2 The strong interaction between the metal support and the nitrogen doping on the hydrogen evolution performance of the catalyst were compared. The electrochemical activity of a series of samples, such as CeO 2 / NC (Comparative Example 1), Ru / NC (Comparative Example 2), Ru-CeO 2 / C (Comparative Example 3), Ru-CeO 2 / NC (Example 1), commercial Pt / C catalyst. The electrochemical activity test method is as follows: a. Preparation of working electrode Before dripping the catalyst ink on the surface of the working electrode, the surface of the working electrode needs to be polished with alumina polishing powder of different particle sizes, and the order of the polishing particle size follows 1.0 μm-0.5 μm-0.03 μm. After polishing, the residual alumina on the surface is removed by ultrasonic technology, and then thoroughly cleaned with deionized water and ethanol, and wiped dry with lens paper for subsequent use. The measured catalyst is then pretreated to ensure that it is evenly distributed on the surface of the working electrode. The processing flow is as follows: First, a small amount of catalyst is finely ground in an agate mortar, 2.5 mg of sample is accurately weighed and placed in a centrifuge tube, 235 μL of deionized water and 235 μL of anhydrous ethanol, and 30 μL of Nafion are added as a binder. The mixed solution is ultrasonically treated for 30 minutes until the catalyst is evenly dispersed, and then 6 μL of the solution is pipetted with a pipette and dropped onto a glassy carbon electrode with a diameter of 3 mm (area 0.07 cm²) and dried; among them, the catalyst loading is 0.428 mg / cm².

[0037] Comparative sample: Commercial Pt / C (P822267-1g purchased from Shanghai MacLean Biochemical Technology Co., Ltd.) was used as a comparative sample. The preparation steps are as follows: 2.5 mg of 20 wt% Pt / C catalyst (wherein the Pt content in 50 mg Pt / C catalyst is 10 mg) was placed in a centrifuge tube, 235 μL of anhydrous ethanol and 235 μL of deionized water, and 30 μL of Nafion were used as a binder, and after ultrasonication for 30 min, it was dropped on a 3 mm glassy carbon electrode and dried.

[0038] The electrolytic cell system used for the following LSV, cyclic voltammetry analysis, electrochemical impedance spectroscopy analysis and long-term stability performance evaluation tests is as follows: a three-electrode system was selected: the working electrode was a catalyst drop-coated on a commercial glassy carbon electrode, the counter electrode was a carbon rod (purchased from Tianjin Gaoshi Ruilian (Tianjin) Optoelectronic Technology Co., Ltd.), the reference electrode was a mercury oxide electrode (purchased from Tianjin Gaoshi Ruilian (Tianjin) Optoelectronic Technology Co., Ltd.), the electrolytic cell was a 50 mL glass electrolytic cell (purchased from Tianjin Gaoshi Ruilian (Tianjin) Optoelectronic Technology Co., Ltd.), and the electrode liquid was a 1 mol / L potassium hydroxide solution.

[0039] b. LSV test Linear sweep voltammetry (LSV) is performed by applying a time-dependent potential change to the working electrode (relative to the reference electrode), that is, the potential increases or decreases monotonically at a certain scan rate. Through LSV, the overpotential of the electrode at a specific current density (such as 10 mA / cm² and 50 mA / cm²) can be determined to evaluate the hydrogen evolution reaction (HER) performance of the prepared catalyst. The specific parameters of the LSV test in this experiment are as follows: the HER potential scan range is -0.8 V to -1.3 V, the scan rate is 5 mV / s, the IR compensation is automatically compensated by the electrochemical workstation at 95%, and the overpotential is calculated according to formula (1).

[0040] (1) Select the part of the processed linear sweep voltammetry (LSV) curve that follows the Tafel equation, according to formula (2): (2) (η: overpotential; i: current density) plot. In this equation, the Tafel slope a is an intrinsic parameter reflecting the characteristics of the electrocatalyst and is closely related to the kinetics of the hydrogen evolution reaction (HER). At the same time, the magnitude of the Tafel slope reveals the reaction mechanism of HER (see Table 1). Generally speaking, a lower Tafel slope means a faster and more efficient catalytic process.

[0041] Table 1 HER mechanism

[0042] c. Cyclic voltammetry (CV) In this study, CV scanning is used to calculate the electrochemically active area (ECSA). The electrochemically active area is an important data to measure the number of active sites of electrocatalytic materials. It is calculated based on the double-layer capacitance (Cdl) and is proportional to: (3) In formula (3), Cs: specific capacitance of the catalyst material; Cdl: double-layer capacitance. The double-layer capacitance is measured by cyclic voltammetry (CV) in the non-Faraday range of the material. The current difference obtained by gradually increasing the scan rate under the same voltage range is linearly fitted, and its slope is Cdl. The specific parameters of the CV test in this experiment are as follows: the HER potential scanning range is -0.55V to -0.8V, and the scan rates are 20, 40, 60, 80, 100, and 120 mV / s, respectively.

[0043] d. Electrochemical impedance spectroscopy (EIS) Electrochemical impedance spectroscopy (EIS) is a characterization method for evaluating the electron transfer rate of catalysts and the conductivity of materials. By fitting the measured data with an equivalent circuit model, a semicircular figure in the Nyquist diagram can be obtained, and its diameter represents the charge transfer impedance (Rct). A smaller Rct value represents a higher electron transfer efficiency. In this paper, the sample catalyst was selected to conduct a charge transfer test at a current density of 10 mA / cm 2 The impedance test is performed with a voltage of 0.1 Hz to 106 Hz.

[0044] The CeO was investigated in alkaline electrolyte at a scan rate of 5 mV / s. 2 / NC、Ru / NC、Ru-CeO 2 / C、Ru-CeO 2 The electrochemical hydrogen evolution activity LSV curves of Pt / NC and commercial Pt / C catalysts are shown in Figure 6 As shown in (a) in the figure. First, we compared Ru-CeO 2 / NC and CeO 2 / NC catalyst for hydrogen evolution in water electrolysis, Ru-CeO 2 The overpotential of the NC catalyst (η 10 =20 mV, η 100 =77 mV) is much lower than its comparative sample CeO 2 / NC(η 10 =520 mV), CeO 2 / NC samples showed almost no hydrogen evolution activity, which further proved that 2 The real HER active center in the / NC catalyst is the precious metal Ru. 2 / NC、Ru-CeO 2 / C and Ru / NC catalysts have good hydrogen evolution activity in water electrolysis. 2 The / C catalyst was not subjected to nitrogen doping modification, but it still showed good HER performance at low current density (η 10 =24.2 mV). However, due to the lack of nitrogen doping, its poor conductivity leads to 2 The HER activity of the / C catalyst decreased significantly at high current density, and η 100 Relative to Ru-CeO 2 / NC catalyst increased by 68 mV. Figure 6 It can be clearly seen from (a) that the Ru / NC catalyst also exhibits good HER performance in the hydrogen evolution process (η 10 =30.2 mV, η 100 =162 mV), but when CeO is introduced 2 Ru-CeO after site2 The η of Ru / NC catalyst is relative to that of Ru / NC 10 , η 100 10.2 mV and 85 mV, respectively, so the introduction of cerium oxide sites can promote the water molecules in CeO 2 The dissociation of the nanoparticle surface creates a local acidic environment around the Ru nanoparticles, which improves the hydrogen evolution performance. In addition, due to the strong interaction between the metal support, the Ru metal and CeO 2 The electrons were rearranged between the nanoparticles and the hydrogen adsorption free energy was optimized, which improved the hydrogen evolution activity of the Ru-based catalyst. Finally, the 20% commercial Pt / C catalyst and Ru-CeO 2 The HER performance of the / NC catalyst at a current density of 10 mA / cm 2 The overpotential of Pt / C is 50 mV, and its activity is much worse than that of Ru-CeO 2 / NC catalyst, especially at high current density, the performance is more obvious at 100 mA / cm 2 Under the overpotential of 2 / NC catalyst increased by 135 mV, and according to the ICP-OES results, Ru-CeO 2 The Ru-CeO / NC catalyst has only 2.3 wt% Ru, and its manufacturing cost is much lower than that of the 20% Pt / C catalyst, but it does have a much higher hydrogen evolution performance than the commercial glassy carbon catalyst. 2 / NC catalysts have great potential for widespread commercial applications.

[0045] The Tafel slopes were then obtained from the polarization curves (LSV) to reveal the kinetic mechanism of hydrogen evolution in alkaline conditions for all sample catalysts. Figure 6 As shown in (b), CeO 2 The Tafel value of the / NC catalyst is 694.5 mV / dec, indicating that the Volmer step related to water adsorption and dissociation is the absolute step of the reaction. 2 / NC, prepared Ru-CeO 2 / NC catalyst has the smallest Tafel slope (34.12 mV / dec) and follows the Volmer-Tafel mechanism, with faster kinetic performance, and this value is lower than the Tafel slope of commercial platinum carbon catalyst (51.15 mV / dec). 2 / NC and Ru / NC (92.21 mV / dec), Ru-CeO 2 / C (87.53 mV / dec), which indicates that nitrogen-doping modification and SMSI-induced changes in the electronic structure of the catalyst active sites play a crucial role in favoring the Volmer–Tafel step and improving the kinetics of hydrogen evolution of the catalyst in alkaline media.

[0046] from Figure 6 (c) Electrochemical impedance spectroscopy shows that Ru-CeO 2 The / NC catalyst has the best electron transfer ability at the electrolyte / catalyst interface (Rct=27.63 Ω). In addition, Ru / NC (Rct=80.88 Ω), Ru-CeO 2 / C(Rct=72.11 Ω)、Ru-CeO 2 / NC impedance comparison found that heteroatom N and CeO 2 The introduction of nanoparticles reduces the catalyst interface kinetic path resistance, further proving that Ru metal and CeO 2 The interaction between nanoparticles. 2 A comparative analysis of Ru-CeO / NC and Pt / C catalysts revealed that 2 / NC catalyst exhibits excellent electrical conductivity and hydrogen evolution reaction kinetics, and the change trend of EIS data also matches the change trend of Tafel slope.

[0047] Finally, the double-layer capacitance (C dl ), which is proportional to its electrochemically active specific surface area (ECSA), and this parameter is one of the key factors affecting the overall HER catalytic performance of the catalyst. Ru-CeO 2 The strong interaction between the metal and the support makes the surface active sites of the NC catalyst evenly dispersed, resulting in the largest double-layer capacitance (C dl =92.38 mF / cm 2 ), indicating that it is relatively weaker than CeO at the solid-liquid interface. 2 / NC(C dl =3.29mF / cm 2 )、Ru / NC(C dl =43.47 mF / cm 2 )、Ru-CeO 2 / C(C dl =64.86 mF / cm 2 )、Pt / C(C dl =48.59 mF / cm 2 ) have more abundant HER active sites.

[0048] The long-term operational stability of the catalyst is related to the structural stability of the test sample and is also an important performance parameter to measure whether a catalyst has the potential for industrial application. The chronovoltametry (vt) method was used to evaluate the performance of commercial Pt / C, Ru-CeO 2 / NC and Ru / NC (Comparative Example 2) catalysts for hydrogen evolution reaction stability in 1 M KOH electrolyte. The specific test method is as follows: Chronovoltametry (VT): In this study, the chronovoltametry (VT) method was used to evaluate the long-term stability of the sample catalyst. Specifically, a constant current (-0.07 mA) was applied to test the voltage change curve over time. A smaller voltage loss indicates that the catalyst has good stability.

[0049] The results are as follows Figure 7 As shown in the figure, when the current density is maintained at 10 mA / cm², the overpotential of the catalyst does not increase by more than 100 mV after 100 h of continuous electrolysis, while the overpotential of the commercial Pt / C catalyst and Ru / NC catalyst increases by more than 200 mV after 100 h of continuous electrolysis, which indicates that the Ru-CeO 2 The NC catalyst has good stability in the HER process. The key factors are the excellent structural stability, alkali corrosion resistance and CeO 2 Corrosion resistance and CeO 2 The strong interaction between the nanoparticles and the Ru metal support prevents the dissolution and agglomeration of the HER active centers of the catalyst during the catalytic process.

[0050] Comparative Example 1, CeO 2 Preparation of NC catalyst First, use a pipette to place 1 mL of cyanamide solution (50 mg / mL) and 4 mL of deionized water in a 10 mL beaker, and then disperse them evenly at low temperature using ultrasound to obtain solution A. In the second step, weigh 0.05 g of three-dimensional porous spherical UIO-66 (Ce) MOFs (preparation method is the same as in Example 1) and put them into solution A. After being dispersed evenly by low temperature ultrasound for 60 min, put them into a freeze dryer and freeze-dried at -70°C for 24 h. In the third step, the freeze-dried solid was placed in a corundum magnetic boat, and heated to 750°C in an argon atmosphere using a tubular furnace at a heating rate of 5°C / min, and kept at this temperature for 3 h to obtain CeO 2 / NC catalyst.

[0051] Comparative Example 2: Preparation of Ru / NC Catalyst (1) First, use a pipette to draw 80 μL of RuCl 3Solution (0.066 mg / mL), 1 mL of cyanamide solution (50 mg / mL) and 4 mL of deionized water were placed in a 10 mL beaker and dispersed evenly by low-temperature ultrasound to obtain solution A. In the second step, 0.05 g of three-dimensional porous spherical UIO-66 (Ce) MOFs (prepared by the same method as in Example 1) was weighed and placed in solution A. After being dispersed evenly by low-temperature ultrasound for 60 min, it was placed in a freeze dryer and freeze-dried at -70°C for 24 h. In the third step, the freeze-dried solid was placed in a corundum magnetic boat, and heated to 750°C in a tube furnace at a heating rate of 5°C / min under an argon atmosphere, and kept at this temperature for 3 h to obtain Ru-CeO 2 / NC catalyst.

[0052] (2) Weigh 50 mg of the Ru-CeO prepared in step (1). 2 The / NC catalyst was placed in a 25 mL beaker, and then 20 mL of 1 mol / L sulfuric acid solution was added. After ultrasonic dispersion, it was placed in an oil bath at 50°C for 24 h. It was then filtered and washed with deionized water until the filtrate pH was 7, and then placed in an oven at 60°C for 12 h to obtain Ru / NC.

[0053] Comparative Example 3: Ru-CeO 2 Preparation of / C catalyst First, use a pipette to draw 80 μL of RuCl 3 The solution (0.066 mg / mL) and 4 mL of deionized water were placed in a 10 mL beaker and dispersed evenly by low temperature ultrasonication to obtain solution A. In the second step, 0.05 g of three-dimensional porous spherical UIO-66 (Ce) MOFs (prepared by the same method as in Example 1) was weighed and placed in solution A. After being dispersed evenly by low temperature ultrasonication for 60 min, the solution was placed in a freeze dryer and freeze-dried at -70 °C for 24 h. In the third step, the freeze-dried solid was placed in a corundum magnetic boat and heated to 750 °C in an argon atmosphere using a tubular furnace at a heating rate of 5 °C / min, and kept at this temperature for 3 h to obtain Ru-CeO 2 / C catalyst.

Claims

1. A method for preparing a Ru-CeO2 / NC catalyst, comprising the following steps: (1) Mixing polyether, glacial acetic acid, 1,3,5-trimethylbenzene and water to prepare a microemulsion solution; (2) mixing the microemulsion solution, ammonium cerium nitrate and terephthalic acid to react and obtain three-dimensional porous spherical UIO-66 (Ce) MOFs; (3) Mixing a soluble ruthenium salt, cyanamide, three-dimensional porous spherical UIO-66 (Ce) MOFs and water to obtain a mixed solution; freeze-drying the mixed solution, and then annealing it to obtain the Ru-CeO2 / NC catalyst.

2. The preparation method according to claim 1, characterized in that: In steps (1) and (2), the mass ratio of the ammonium cerium nitrate to the polyether is 1:1.5-3; The mass ratio of the ammonium cerium nitrate to the volume ratio of glacial acetic acid is 1 g: 1-3 mL; The mass ratio of the cerium ammonium nitrate to the volume ratio of 1,3,5-trimethylbenzene is 1 g:20-80 mL; The mass ratio of the ammonium cerium nitrate to the volume of water is 1 g: 100-400 mL; The mass ratio of the ammonium cerium nitrate to terephthalic acid is 1:2-4.

3. The preparation method according to claim 1 or 2, characterized in that: In step (2), the reaction temperature is 35°C-45°C; The reaction time is 30 min-60 min.

4. The preparation method according to any one of claims 1 to 3, characterized in that: In step (3), the soluble ruthenium salt is ruthenium chloride; In the mixed solution, the concentration of the soluble ruthenium salt is 0.5 μg / mL-1.2 μg / mL; The concentration of the cyanamide is 5 mg / mL-15 mg / mL; The concentration of the three-dimensional porous spherical UIO-66 (Ce) MOFs is 8 mg / mL-12 mg / mL.

5. The preparation method according to any one of claims 1 to 4, characterized in that: In step (3), the freeze-drying temperature is -60°C to -80°C; The freeze-drying time is 20-30 h.

6. The preparation method according to any one of claims 1 to 5, characterized in that: In step (3), the annealing temperature is 600°C-900°C; The annealing time is 1 h-3 h; The heating rate of the annealing is 2°C / min-10°C / min; The annealing is performed in an inert atmosphere.

7. The Ru-CeO2 / NC catalyst prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the Ru-CeO2 / NC catalyst according to claim 7 in hydrogen production by water electrolysis.

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