Method for preparing surface metal atom-doped ru-based oxide catalyst by ion exchange method and application thereof

Abstract

The application relates to a method for preparing a Ru-based oxide catalyst doped with surface metal atoms by an ion exchange method and application thereof. The method comprises three steps of preparing a Ru hydrate by a hydrothermal method, preparing a metal atom doped Ru hydrate by an ion exchange method and preparing a metal atom doped Ru-based oxide catalyst by high-temperature calcination. The application introduces metal atoms and oxygen vacancies on the surface of the Ru-based oxide by the ion exchange method, causes a certain degree of compressive strain on the surface of the composite catalyst, shortens the distance between Ru-O bonds, enhances the bond energy of the Ru-O bonds, makes the lattice oxygen more stable, thereby inhibits the lattice oxygen mechanism and improves the stability of the Ru-based oxide catalyst. The introduction of the metal atoms and the existence of the oxygen vacancies change the electronic structure of Ru, optimize the bonding strength between the oxygen evolution catalyst and the oxygen evolution reaction molecules, and improve the oxygen evolution reaction activity.

Description

Technical Field

[0001] The present invention belongs to the field of new material preparation and electrochemical catalysis, and in particular relates to the preparation of a surface metal atom-doped material and its application as a catalyst in electrocatalytic acidic oxygen evolution. Background Art

[0002] Proton exchange membrane water electrolysis (PEMWE) technology offers advantages such as low energy consumption, high efficiency, and high hydrogen quality. In particular, it features rapid startup and power regulation, making it ideally suited to the volatility of renewable energy sources such as wind, solar, and water. It is a strategic technology for producing high-purity green hydrogen and addressing carbon neutrality. The high overpotential, poor stability, and high cost of anodic oxygen evolution reaction (OER) catalysts are among the major bottlenecks limiting the development of this technology. Therefore, the development of highly active and stable acidic OER catalysts is crucial for the large-scale application of PEMWE. Compared with Ir-based catalysts, Ru-based catalysts are relatively inexpensive and highly active. However, Ru-based oxide catalysts are generally unstable in acidic OER. This is related to the lattice oxygen reaction mechanism (LOM). In this mechanism, the lattice oxygen of RuO2 participates in the reaction, leading to crystal structure collapse, accelerated leaching of active Ru, and poor operational stability. Therefore, stabilizing the lattice oxygen and thereby suppressing the LOM mechanism can improve the stability of Ru-based oxide catalysts. Summary of the Invention

[0003] The present invention aims to address the poor stability and inactivity of existing Ru-based oxide catalysts by providing a method for preparing a Ru-based oxide catalyst doped with surface metal atoms and its application as an acidic OER electrocatalyst. This material can significantly reduce the OER overpotential and extend the stable operating time of the Ru-based catalyst.

[0004] Manipulating the electronic structure of Ru-based catalysts is a common strategy for improving their activity and stability. Heteroatom doping can effectively alter the electronic structure of catalysts by changing the coordination environment of active sites, introducing defects (cation defects, anion defects, and unsaturated coordination sites) and strain (compressive strain, tensile strain), thereby suppressing the occurrence of the LOM mechanism, thereby improving the poor stability of Ru-based catalysts and enhancing their OER activity.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The method for preparing a Ru-based oxide catalyst M-RuO2 doped with surface metal atoms by an ion exchange method comprises the following steps:

[0007] (1) Synthesis of Ru hydrate precursor: Disperse the Ru metal source in pure water, mix well at room temperature, perform a one-step hydrothermal reaction at 120-150°C for 6-10 h, wash by centrifugation, and dry in vacuum at 40-80°C to obtain Ru hydrate;

[0008] (2) adding the Ru hydrate synthesized in step (1) to a metal chloride aqueous solution, performing an ion exchange reaction in a water bath at 40-80° C., and then centrifugally washing and vacuum drying to obtain a Ru hydrate doped with surface metal atoms;

[0009] (3) The metal atom-doped Ru hydrate synthesized in step (2) is placed in a tube furnace and calcined at high temperature, and then naturally cooled to room temperature to obtain a Ru-based oxide catalyst M-RuO2.

[0010] In step (1), the Ru metal source is RuCl3·6H2O, wherein the mass fraction of Ru is at least 47%. The concentration of the Ru metal source dispersed in pure water is 10-15 mmol / L.

[0011] In step (2), the water bath temperature is preferably 60-80° C., and the reaction time is preferably 2-6 hours. The metal chloride salt is chloroplatinic acid, chloroauric acid, rhenium chloride, manganese chloride or titanium chloride, preferably chloroplatinic acid.

[0012] In step (2), the mass ratio of the metal chloride to the Ru hydrate is 0.35 to 3.25:1, more preferably 0.65:1. The solvent of the metal chloride aqueous solution is pure water, and the concentration is 4-20 mmol / L, more preferably 8 mmol / L.

[0013] In step (3), the calcination temperature is 300-500°C, the sintering heating rate is 2-5°C / min, the holding time is 1-5h, and the sintering atmosphere is air.

[0014] The present invention also provides a surface metal atom-doped Ru-based oxide catalyst M-RuO2 prepared by the above method. The catalyst has excellent acidic OER electrocatalytic activity and stability and can be used as an acidic OER electrocatalyst.

[0015] Advantages and beneficial effects of the present invention:

[0016] Compared with the prior art, the method of the present invention uses a wide range of raw materials, requires mild reaction conditions, is suitable for large-scale production and has high reproducibility. 4+ Diffusion from the crystal structure to the solution, the M n+Diffusion into the RuO2 crystal structure, thus achieving metal doping. The high temperature conditions of the ion exchange process cause the RuO2 lattice to vibrate, the anions as the skeleton will be "squeezed out" by the cations, and the loss of surface oxygen atoms will form oxygen vacancies. Since oxygen vacancies are positively charged, they interact with Ru 4+ Mutual repulsion leads to compressive stress in RuO2. At the same time, when the atomic radius of the doped metal is larger than that of Ru, the introduction of large ions near the surface causes the volume to increase, thus generating compressive stress in the ion exchange area.

[0017] In summary, the large-radius ion doping and oxygen vacancies caused by cation exchange induce a certain amount of compressive strain on the catalyst surface. This lattice strain caused by cation exchange is different from the epitaxial strain generated in the core-shell structure. The core-shell strain is gradually released from the core-shell interface to the outermost atomic layer, which greatly limits the ability of strain to regulate catalytic activity. In contrast, the compressive strain induced by cation exchange is mainly located on the surface of the RuO2 catalyst, which can fine-tune the surface electronic structure, which is very beneficial for electrocatalytic reactions occurring on the surface. The presence of compressive strain increases the interaction between Ru and O, thereby increasing the bond energy of the Ru-O bond and improving the stability of the Ru-O bond, thereby stabilizing the lattice oxygen, hindering the occurrence of the LOM mechanism, and improving the stability of the Ru-based oxide catalyst. The introduction of metal atoms and the presence of oxygen vacancies change the electronic structure of Ru, optimize the bond strength between the oxygen evolution catalyst and the oxygen evolution reaction molecules, and enhance the oxygen evolution reaction activity. Therefore, the surface metal-doped Ru-based oxide material (M-RuO2) prepared by the ion exchange method provided by the present invention has excellent OER electrocatalytic activity and stability under acidic conditions, and can be used as an acidic OER electrocatalyst with excellent performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the XRD spectra of the prepared Pt-RuO2 and RuO2 catalysts;

[0019] Figure 2 TEM morphology of the prepared Pt-RuO2 catalyst;

[0020] Figure 3 is the EPR pattern of the prepared Pt-RuO2 catalyst;

[0021] Figure 4 (a) LSV performance test curve and (b) stability test curve of the prepared Pt-RuO2, RuO2 catalyst and commercial RuO2;

[0022] Figure 5 The stability test curves of the prepared Pt-RuO2 / CP and RuO2 / CP catalysts;

[0023] Figure 6 For the preparation of Pt 0.35 -RuO2、Pt 1.3 -RuO2 and Pt 3.25 -RuO2 catalyst (a) XRD spectrum and (b) LSV performance test curve;

[0024] Figure 7 The LSV performance test curves of the prepared Au-RuO2 and Re-RuO2 catalysts before and after 10,000 CV cycles;

[0025] Figure 8 (a) LSV performance test curve and (b) stability test curve of the prepared Mn-RuO2 and Ti-RuO2 catalysts. DETAILED DESCRIPTION

[0026] Example 1: A method for preparing a Pt-doped RuO2 catalyst, comprising the following steps:

[0027] (1) First, synthesize the Ru hydrate precursor: 0.25 mmol of hydrated ruthenium trichloride is evenly dispersed in 20 mL of pure water, mixed and stirred at room temperature for 0.5 h. After stirring, a one-step hydrothermal reaction is carried out at 120°C for 10 h. The mixture is washed with pure water and anhydrous ethanol three times by centrifugation, and dried in a vacuum environment at 60°C for 12 h to obtain Ru hydrate;

[0028] (2) adding 20 mg of the Ru hydrate synthesized in step (1) to a chloroplatinic acid aqueous solution, with a mass ratio of chloroplatinic acid to Ru hydrate of 0.65:1, and conducting an ion exchange reaction in a 60°C water bath for 2 h. The mixture was centrifugally washed once with pure water and once with anhydrous ethanol, and then dried in a vacuum environment at 60°C for 12 h to obtain Pt-doped Ru hydrate;

[0029] (3) The Pt-doped Ru hydrate synthesized in step (2) was placed in a tubular furnace for high-temperature calcination. The sintering atmosphere was air, the sintering heating rate was 5°C / min, the reaction temperature was 400°C, the reaction time was 2h, and the mixture was naturally cooled to room temperature to obtain a Pt-RuO2 electrocatalyst.

[0030] The Ru hydrate synthesized in step (1) is calcined at high temperature in the same manner to obtain a RuO2 electrocatalyst.

[0031] ICP detected that the doping amount of Pt was 0.2 wt%. The XRD pattern of the Pt-RuO2 catalyst prepared above is as follows: Figure 1As shown, only the peak of the rutile phase of RuO2 appears, indicating that the introduction of Pt did not form a new phase, but rather that Pt was doped into the RuO2 crystal structure. Compared with the peak of undoped RuO2, the Pt-RuO2 peak is broadened, indicating that the introduction of Pt reduces the crystallinity of RuO2.

[0032] The transmission electron microscopy (TEM) particle morphology and particle size distribution statistics of the Pt-RuO2 catalyst prepared above are as follows: Figure 2 As shown in the figure, the catalyst particle size is about 17.76 nm.

[0033] The EPR spectrum of the Pt-RuO2 catalyst prepared above Figure 3 As shown, it shows that there are a large number of oxygen vacancies in Pt-RuO2.

[0034] The Pt-RuO2 catalyst prepared above was subjected to OER performance test, and the test method was as follows:

[0035] (1) First, prepare Pt-RuO2 catalyst ink. The specific preparation method is as follows: add 5 mg of Pt-RuO2 catalyst to 260 μL of a mixed solution of water and ethanol containing 10 μL of Nafion (volume ratio of 3:2), and then ultrasonicate for 1 hour to obtain a uniform black catalyst ink.

[0036] (2) Draw 5 μL of the ink droplet onto a surface area of ​​0.196 cm 2 A working electrode film is formed on the glassy carbon electrode and dried at room temperature.

[0037] (3) A three-electrode cell test was performed, with a glassy carbon electrode as the working electrode, a carbon rod as the counter electrode, Hg / Hg2SO4 (0.70 V vs. RHE) as the reference electrode, and 0.5 M H2SO4 as the electrolyte. The test voltage range was 0.5-0.9 V vs. Hg / Hg2SO4.

[0038] For comparison purposes, the OER performance of undoped RuO2 and commercial RuO2 was tested under the same test conditions.

[0039] Test results: Figure 4 The LSV comparison diagram of different samples and the voltage-time diagram of drop coating on glassy carbon electrode, Pt-RuO2, RuO2 and commercial RuO2 at 10mAcm -2 At current densities of 100, 240, and 300 mV, respectively, the overpotential of Pt-RuO2 is the lowest, so the activity is the highest, and Pt-RuO2 can operate stably on the glassy carbon electrode for 100 hours.

[0040] When testing the stability of the catalyst on a glassy carbon electrode, the generation of bubbles can cause the catalyst to fall off, making it impossible to accurately assess the stability of the catalyst. Therefore, we used the following method to prepare a Pt-RuO2 / CP self-supporting electrode sprayed on carbon paper (CP) to test the stability of the catalyst.

[0041] (1) First, prepare Pt-RuO2 catalyst ink. The specific preparation method is to add 5 mg of Pt-RuO2 catalyst to 2 mL of isopropanol solution containing 30 μL of Nafion, and then ultrasonicate for 1 hour to obtain a uniform black catalyst ink.

[0042] (2) Use a spray gun to spray the ink onto an area of ​​2*2cm 2 The carbon paper was placed on a hot plate at 70 ° C and dried to obtain a Pt-RuO2 / CP self-supporting electrode with a loading of 2 mg / cm 2 .

[0043] (3) Tested with a three-electrode battery, 1*1cm 2 The Pt-RuO2 / CP is a self-supporting working electrode, the counter electrode is a carbon rod, the reference electrode is Hg / Hg2SO4 (0.70Vvs.RHE), the electrolyte is 0.5MH2SO4, and the test constant current is 10mA.

[0044] For comparison, the OER stability of undoped RuO2 was tested under the same test conditions.

[0045] Test results: Figure 5 This is the voltage-time diagram of different samples. It can be seen from the figure that the undoped RuO2 catalyst is completely deactivated after 200 hours of operation, while the Pt-RuO2 catalyst can operate stably for more than 2000 hours, reflecting excellent OER stability.

[0046] Example 2-3: Example 1 was repeated, except that the mass ratio of chloroplatinic acid to Ru hydrate was changed to 0.35:1, 1.3:1 and 3.25:1. The obtained catalysts were recorded as Pt 0.35 -RuO2、Pt 1.3 -RuO2 and Pt 3.25 -RuO2. Figure 6 The XRD patterns and LSV patterns of the catalysts synthesized in Examples 2-3 are shown. In the XRD pattern, only the peak of rutile phase RuO2 appears, indicating that the introduction of Pt does not form a new phase. As the amount of chloroplatinic acid added increases, the broadening of the XRD peak increases, indicating that the higher the amount of Pt doping, the lower the crystallinity of RuO2. The results of the LSV test show that Pt 0.35 -RuO2、Pt 1.3 -RuO2 and Pt 3.25-RuO2 have overpotentials of 203, 223 and 236 mV, respectively.

[0047] Example 4-5: Example 1 was repeated, with the only difference being that chloroplatinic acid was replaced by other noble metal chlorides, namely chloroauric acid and rhenium chloride. The obtained catalysts were denoted as Au-RuO2 and Re-RuO2. Figure 7 The LSV curves of the catalyst synthesized in Example 4-5 before and after 10,000 cycles are shown. Figure 7 It can be found that before the cycle, the -2 At a current density of 10000, the overpotentials of Au-RuO2 and Re-RuO2 were 231 and 237 mV, respectively. After 10,000 cycles, the Au-RuO2 and Re-RuO2 catalysts were -2 The OER overpotential at current density of 100 nm and 100 nm increased by 23 mV and 32 mV, respectively. Compared with the undoped RuO2 catalyst, the activity and stability of Au-RuO2 and Re-RuO2 catalysts were improved.

[0048] Example 6-7: Example 1 was repeated, with the only difference being that chloroplatinic acid was replaced by transition metal chlorides, namely manganese chloride and titanium chloride. The resulting catalysts were denoted as Mn-RuO2 and Ti-RuO2. Figure 8 The LSV comparison diagram of the catalyst synthesized in Example 6-7 and the voltage-time diagram of the catalyst drop-coated on the glassy carbon electrode are shown in Figure 6-7. -2 At a current density of 1.5 Å, the overpotentials were 235 and 236 mV, respectively, both lower than that of the undoped RuO2 sample (240 mV), indicating that Mn-RuO2 and Ti-RuO2 are more active than RuO2. Furthermore, both Mn-RuO2 and Ti-RuO2 were able to operate stably on the glassy carbon electrode for over 30 hours, longer than the undoped RuO2 sample (<20 hours), indicating improved stability of the Mn-RuO2 and Ti-RuO2 catalysts.

Claims

1. A method for preparing a Ru-based oxide catalyst doped with surface metal atoms by ion exchange, comprising the following preparation steps: (1) Synthesis of Ru hydrate precursor: The Ru metal source is dispersed in pure water, mixed evenly at room temperature, subjected to a one-step hydrothermal reaction at 120-150°C, centrifuged and washed, and vacuum dried to obtain Ru hydrate; (2) adding the Ru hydrate synthesized in step (1) to a metal chloride aqueous solution, wherein the mass ratio of the metal chloride to the Ru hydrate is 0.35-3.25:1, the metal chloride is chloroplatinic acid, chloroauric acid, rhenium chloride, manganese chloride or titanium chloride, the solvent of the metal chloride aqueous solution is pure water, and the concentration is 4-20 mmol / L, performing an ion exchange reaction in a water bath at 40-80°C, and then centrifugally washing and vacuum drying to obtain Ru hydrate doped with surface metal atoms; (3) The metal atom-doped Ru hydrate synthesized in step (2) is placed in a tube furnace for high-temperature calcination and naturally cooled to room temperature to obtain a Ru-based oxide catalyst M-RuO2.

2. The method according to claim 1, wherein: The Ru metal source is RuCl3·6H2O, wherein the mass fraction of Ru is at least 47%.

3. The method according to claim 1, characterized in that In step (1), the hydrothermal reaction time is 6-10 h, and the vacuum drying temperature is 40-80°C.

4. The method according to claim 1, wherein the crystal particle size of the Ru-based oxide catalyst M-RuO2 is between 10 nm and 30 nm.

5. The Ru-based oxide catalyst M-RuO2 prepared by the method according to any one of claims 1 to 4.

6. Use of the Ru-based oxide catalyst M-RuO2 according to claim 5 as an acidic OER electrocatalyst.

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