RuO2 acidic oxygen evolution reaction catalyst based on grain boundary engineering and preparation method of RuO2 acidic oxygen evolution reaction catalyst

Abstract

The invention provides a RuO2 acidic oxygen evolution reaction catalyst based on grain boundary engineering and a preparation method thereof, the RuO2 acidic oxygen evolution reaction catalyst based on grain boundary engineering is Zn-xRuO2 (at) ZnO nanoparticles, and x is 0.5-0.67. According to the Zn-RuO2 (at) ZnO adopting the technical scheme, the ruthenium gradient concentration is achieved in the radial direction, ultralow overpotential is achieved in a 0.5 M H2SO4 solution under the current density of 10 mAcm <-2 >, and the Zn-RuO2 (at) ZnO has excellent stability. The catalyst has a lattice oxygen mechanism (LOM) at the grain boundary and an adsorbate evolution mechanism (AEM) in nanoparticles during the OER process. At the grain boundary, zinc doping reduces the formation energy of oxygen vacancy, improves the formation energy of ruthenium vacancy, activates LOM and inhibits dissolution of ruthenium, so that the OER activity and stability are enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of oxygen evolution catalysts, and in particular to a RuO2 acidic oxygen evolution reaction catalyst based on grain boundary engineering and a preparation method thereof. Background Art

[0002] As the burning of fossil fuels continues to exacerbate energy demand and environmental problems, the pursuit of renewable energy has once again stimulated interest in producing hydrogen through water electrolysis. Hydrogen production by water electrolysis consists of two half reactions, namely HER at the cathode and OER at the anode. However, water electrolysis technology faces major challenges in achieving large-scale industrial applications due to the activity, stability and cost of the anode oxygen evolution reaction (OER) electrocatalyst. Compared with the two-electron transfer process of the cathode hydrogen evolution reaction, OER is an electrochemical process involving the transfer of 4 electrons and 4 protons, following the traditional adsorbate evolution mechanism (AEM, that is, adsorbed H2O is converted to OH*, then to O*, followed by OOH*, and finally to O 2 ), and generally speaking, the process of converting the intermediate *O to the *OOH intermediate is considered to be the rate-limiting step (RDS) in the OER process, with a theoretical overpotential of up to 370mV. Therefore, it is necessary to construct an efficient electrocatalyst to reduce the activation energy barrier and thus reduce the overpotential. In addition, in the OER process, in addition to metal sites that can serve as active sites, lattice oxygen can also participate in the OER process, which is called the lattice oxygen oxidation mechanism. LOM is a more efficient catalytic pathway. First, similar to the AEM pathway, the first two steps are continuous deprotonation, forming *OH and *O intermediates on the Ru site in sequence, and then the surface-adsorbed *O intermediate reacts with lattice O to form O2 and generate O vacancies, which are then refilled by another H2O. Unlike traditional AEM, LOM breaks the scale relationship by introducing lattice oxygen redox reactions and non-coordinated proton-electron transfer steps, and exhibits pH-dependent OER activity. On the one hand, AEM is limited by the adsorption and desorption of oxygen-containing intermediates, which can promote the development of LOM. On the other hand, LOM is usually accompanied by severe metal dissolution and O vacancy formation, which leads to the instability of the crystalline structure of the catalyst. In principle, catalysts based on AEM will not experience such severe surface changes or even structural collapse. Currently, the top catalysts for OER are oxides of ruthenium (Ru) and iridium (Ir), which are precious metals. Compared with iridium (price is US$60,670 per kilogram), the price of ruthenium (US$9,523 per kilogram) is relatively low, so it has more advantages in economic cost. Despite this, existing ruthenium oxide-based catalysts still face the problems of insufficient activity (the theoretical overpotential based on AEM is about 370 millivolts) and poor stability (lifespan is only tens of hours). These problems are mainly caused by the dissolution of active ruthenium in strongly acidic and oxidizing environments.

[0003] Generally speaking, RuO2 will dissolve due to excessive oxidation at a potential of 1.39V and is therefore unstable: RuO2+2H2O→RuO4(aq)+4H + (aq)+4e - (U0 = 1.39V). In addition to the dissolution problem, RuO2 catalysts may also be deactivated through various other mechanisms, such as catalyst phase transition, morphology change, passivation, and catalyst detachment from the electrode. In addition, previous studies have shown that the activity and stability of RuO2 catalysts in acidic OER are much lower than those in alkaline electrolytes. Therefore, to meet the high demand for industrial applications, it is imperative to improve the OER activity and stability of RuO2 and RuO2-based electrocatalysts. Summary of the Invention

[0004] In response to the above technical problems, the present invention discloses a RuO2 acidic oxygen evolution reaction catalyst based on grain boundary engineering and a preparation method thereof, which has low overpotential and better stability.

[0005] To this end, the technical solution adopted in the present invention is:

[0006] A RuO2 acidic oxygen evolution reaction catalyst based on grain boundary engineering is Zn-xRuO2@ZnO nanoparticles, wherein x is 0.5 to 0.67.

[0007] As a further improvement of the present invention, the RuO2 acidic oxygen evolution reaction catalyst based on grain boundary engineering is Zn-0.5RuO2@ZnO or Zn-0.67RuO2@ZnO nanoparticles.

[0008] The present invention discloses a method for preparing the RuO2 acidic oxygen evolution reaction catalyst based on grain boundary engineering as described above, comprising the following steps:

[0009] Step S1, preparing ZnO nanoparticles;

[0010] Step S2, preparing Zn-RuO2@ZnO nanoparticles by a cation exchange method, specifically comprising: dissolving RuCl3 in deionized water and stirring to obtain a RuCl3 solution; dispersing the ZnO nanoparticles in deionized water to obtain a ZnO suspension; adding the ZnO suspension to the RuCl3 solution and stirring to perform ion exchange, and filtering to obtain a Zn-RuO2@ZnO precursor; washing and drying the Zn-RuO2@ZnO precursor, and calcining it at 430-480°C in an inert gas atmosphere for 1-3 hours to obtain Zn-xRuO2@ZnO nanoparticles.

[0011] As a further improvement of the present invention, in step S1 , ZnO nanoparticles are prepared by electrospinning.

[0012] As a further improvement of the present invention, step S1 includes: dissolving C4H6O4Zn powder in a mixed solution of DMF and water, stirring until clear and transparent, then adding PVP, and stirring to form a stable sol; using the sol to prepare a ZnO precursor by electrospinning, after drying the precursor, annealing at a temperature of 480-520°C for more than 3 hours, and naturally cooling to room temperature to obtain ZnO nanoparticles.

[0013] As a further improvement of the present invention, in the electrospinning process, the pump speed is 1.3 to 1.7 mL·h -1 , the voltage range is -1kV to 20kV.

[0014] As a further improvement of the present invention, in step S1, the volume ratio of DMF to water in the mixed solution of DMF and water is 13 to 15:1; and the mass of the PVP is 1.1 to 1.2 times the mass of the C4H6O4Zn powder.

[0015] As a further improvement of the present invention, in step S1, C4H6O4Zn powder is dissolved in a mixed solution of DMF and water, and the concentration of the C4H6O4Zn powder is 0.09-0.15 g / mL.

[0016] As a further improvement of the present invention, in step S2, the mass ratio of ZnO in the ZnO suspension to RuCl3 in the RuCl3 solution is 1:1.5-1.65.

[0017] The present invention also discloses the application of the above-mentioned RuO2 acidic oxygen evolution reaction catalyst based on grain boundary engineering. The RuO2 acidic oxygen evolution reaction catalyst based on grain boundary engineering is used in water electrolysis as an anode catalyst.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The Zn-RuO2@ZnO prepared by the present invention has a ruthenium gradient concentration along the radial direction. The catalyst is heated to 10 mA cm in a 0.5 M H3SO4 solution. -2 At a current density of 170 mV, it exhibits ultra-low overpotential (e.g., 170 mV) and excellent stability (e.g., 600 hours), breaking through the linear ratio limitation between oxygen intermediates OOH and OH based on the traditional adsorption enhancement mechanism (AEM) pathway. 18O-labeled in situ differential electrochemical mass spectrometry (DEMS) tests revealed the presence of lattice oxygen in the oxygen evolution reaction (OER) of Zn-RuO2@ZnO. This participation decreases with decreasing grain boundary density, exhibiting a clear dependence on grain boundary density. Furthermore, the material's excellent OER stability is primarily attributed to the Zn doping, which effectively inhibits Ru dissolution. Furthermore, the catalyst's synthesis method is simple and easy to control. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the preparation process of a RuO2 acidic oxygen evolution reaction catalyst based on grain boundary engineering according to an embodiment of the present invention; in the figure, pink: Ru; green: Zn; orange: O.

[0021] Figure 2 is a HR-TEM image of the Zn-RuO2@ZnO catalyst according to an embodiment of the present invention.

[0022] Figure 3 These are the OER characteristics of Zn-RuO2@ZnO of the embodiment of the present invention and commercial RuO2 in 0.5M H2SO4 solution, where (a) is the geometric area normalized LSV curve; (b) is the Tafel slope.

[0023] Figure 4 The Zn-0.67RuO2@ZnO in the present invention and the commercial RuO2 are -2 Chronopotentiometry curves at different current densities.

[0024] Figure 5 These are the in-situ DEMS signals of Zn-0.5RuO2@ZnO and Zn-0.67RuO2@ZnO and the ratio of 34O2 to 32O2 obtained during the LSV test of an embodiment of the present invention; wherein, (a) and (b) are the in-situ DEMS signal of Zn-0.5RuO2@ZnO and the ratio of 34O2 to 32O2, respectively, and (c) and (d) are the in-situ DEMS signal of Zn-0.67RuO2@ZnO and the ratio of 34O2 to 32O2, respectively. DETAILED DESCRIPTION

[0025] The preferred embodiments of the present invention are described in further detail below.

[0026] A RuO2 acidic oxygen evolution reaction catalyst based on grain boundary engineering, using Figure 1 The preparation process shown is prepared as follows:

[0027] (1) Preparation of ZnO nanoparticles.

[0028] ZnO nanoparticles were prepared by electrospinning, specifically:

[0029] In a 25 mL glass bottle, 1.65 g of C4H6O4Zn powder was dissolved in a mixture of 14 mL of DMF and 1 mL of deionized water and stirred until clear. 1.85 g of PVP was then added to the mixture and stirred for 12 h to form a stable sol. The ZnO precursor was prepared by electrospinning using the sol solution at a pump rate of 1.5 mL h. -1 The electrospinning voltage range is -1kV to 20kV. The precursor is dried in a 60℃ oven for 12h, transferred to a muffle furnace and annealed at 500℃ for 4h, and then naturally cooled to room temperature to obtain ZnO nanoparticles.

[0030] (2) Preparation of Zn-RuO2@ZnO nanoparticles: Zn-RuO2@ZnO nanoparticles were prepared by cation exchange method. First, 300 mg of RuCl3·xH2O (AR) was dissolved in 10 mL of deionized water and stirred to obtain a uniform RuCl3 solution for use. Then, 50 mg of ZnO nanoparticles were dispersed in 10 mL of deionized water and stirred for 10 minutes. Finally, 2.50 or 2.75 mL of the above RuCl3 solution was added to the ZnO suspension at room temperature and stirred for 24 hours to allow ion exchange. The precursor of Zn-RuO2@ZnO was then filtered and washed with deionized water three times and then dried under an infrared lamp. Finally, the precursor was calcined at 450 °C for 2 hours in an argon atmosphere to obtain Zn-0.5RuO2@ZnO or Zn-0.67RuO2@ZnO nanoparticles.

[0031] The resulting Zn-0.5RuO2@ZnO or Zn-0.67RuO2@ZnO nanoparticles were tested. All electrochemical measurements were performed using a conventional three-electrode system connected to an electrochemical workstation. An Ag / AgCl electrode (saturated with KCl solution) and a graphite rod (3 mm diameter) served as the reference and auxiliary electrodes, respectively. The prepared electrode served as the working electrode, and a 0.5 M H2SO4 solution was used as the electrolyte. A closed electrolytic cell was assembled, and oxygen was introduced into the cell for 30 minutes to create an oxygen-saturated environment.

[0032] Preparation of the working electrode: First, the platinum carbon electrode (GCE, diameter: 3mm) was polished on a polishing machine with a mixture of Al2O3 polishing powder and anhydrous ethanol for 5 to 10 minutes, and then the polished GCE electrode was rinsed with deionized water and anhydrous ethanol in turn, and then dried with lens paper, and then placed under an infrared lamp to dry for use. The catalyst (4mg) and CNT (1mg) were dispersed in a mixed solution of 400μL anhydrous ethanol and 0.5wt% Nafion solution, wherein the volume ratio of the mixed solution was 1:1. The above suspension was placed in an ultrasonic bath for at least 15 minutes to obtain a uniform ink, and then 6μL of ink was evenly applied on the GCE with a pipette (chronopotentiometry test: 400μL of ink was applied on 1cm 2 The working electrode was prepared by drying the film on carbon cloth under infrared light.

[0033] OER activity test: Linear sweep voltammetry (LSV) test voltage range is 1.0~1.6Vvs.RHE, and the scan rate is 10mV·s -1 Without iR compensation, each working electrode needs to be tested for about 15 cycles to obtain the final stable LSV curve of the catalyst. Commercial RuO2 was used as a comparison sample.

[0034] OER stability test: The stability test is to control the current density at 10 mA cm -2 The potential variation with time was tested under the following conditions until a significant increase in potential occurred. Commercial RuO2 was used as a comparison sample.

[0035] pass Figure 2 The HR-TEM images of Zn-RuO2@ZnO show that there are abundant grain boundaries and sub-grain lattice stripes, and the sub-grain size of Zn-0.5RuO2@ZnO is smaller than that of Zn-0.67RuO2@ZnO, which indicates that Zn-0.5RuO2@ZnO with low Ru content has more abundant grain boundaries; the interplanar spacings of RuO2(110) and (101) in Zn-RuO2@ZnO are about 3.15 and 1.25, respectively. Smaller than the (110) and (101) interplanar spacings of commercial RuO2 (3.18 and ).

[0036] A standard three-electrode system was used in 0.5 M H2SO4 solution at 10 mV·s -1 The OER performance of commercial RuO2 and Zn-RuO2@ZnO was evaluated by LSV curves at the scan rate. Figure 3 As shown in the figure, the LSV curves normalized based on geometric area show that Zn-0.5RuO2@ZnO and Zn-0.67RuO2@ZnO have the highest thermal conductivity at 10 mA·cm -2The overpotentials under current density are both 170mV, which is significantly lower than the value of commercial RuO2 (273mV). It can be seen that when the atomic content of Ru is greater than 0.50, the catalyst has excellent OER activity. Among them, due to the small amount of current contributed by the double layer capacitance, the current density of the LSV curve of Zn-0.5RuO2@ZnO is not zero before the potential of 1.35V vs. RHE. The corresponding Tafel slope is obtained by converting the LSV curve, such as Figure 3 As shown in Figure 2, the Tafel slopes of Zn-0.5RuO2@ZnO and Zn-0.67RuO2@ZnO are 63.97 and 64.29 mV·dec, respectively. -1 , which is significantly smaller than the value of commercial RuO2 (99.0mV·dec -1 ), indicating that Zn-RuO2@ZnO exhibits faster reaction kinetics in the OER process.

[0037] like Figure 4 As shown, commercial RuO2 at 10 mA cm -2 It is completely deactivated within 20 hours of operation at the current density. In sharp contrast, Zn-0.67RuO2@ZnO is -2 It can operate stably for more than 600 h at the current density without a significant increase in overpotential, indicating that the unique crystal structure of Zn-RuO2@ZnO gives it outstanding OER stability.

[0038] The Zn-RuO2@ZnO catalyst exhibits an impressively low overpotential in the acidic oxygen evolution reaction (OER), breaking the linear proportional relationship between the oxygen intermediates OOH and OH. In order to explore the root cause of this deviation, the isotope 18 O labeling was used to conduct in situ differential electrochemical mass spectrometry (DEMS) measurements to reveal the OER reaction pathway of Zn-RuO2@ZnO. Figure 5 As shown, in the OER products catalyzed by Zn-0.5RuO2@ZnO and Zn-0.67RuO2@ZnO, 18 O and 16 The mass signals of O were all detected, and the signal ratio of 34O2 to 32O2 increased with the increase of potential, reaching about 17.4 atomic percent and 12.4 atomic percent at 1.55 V relative to the reversible hydrogen electrode (RHE), respectively. This ratio significantly exceeded that in water. 18The natural isotopic abundance of O indicates that the OER mechanism of Zn-0.5RuO2@ZnO and Zn-0.67RuO2@ZnO involves a high degree of lattice oxygen participation. In contrast, the signal ratio of 34O2 to 32O2 in pure RuO2 is much lower (about 2 atomic percent) throughout the linear sweep voltammetry (LSV) test, revealing that the adsorption enhancement mechanism (AEM) dominates the OER mechanism of pure RuO2. In addition, there are more grain boundaries in Zn-0.5RuO2@ZnO, and its 34O2 to 32O2 signal ratio is much larger than that of Zn-0.67RuO2@ZnO, further indicating that the LOM path exists on the grain boundaries.

[0039] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A RuO2 acidic oxygen evolution reaction catalyst based on grain boundary engineering, characterized by: It is Zn-xRuO2@ZnO nanoparticles, wherein x is 0.5 to 0.

67.

2. The RuO2 acidic oxygen evolution reaction catalyst based on grain boundary engineering according to claim 1, characterized in that: They are Zn-0.5RuO2@ZnO or Zn-0.67RuO2@ZnO nanoparticles.

3. The method for preparing a RuO2 acidic oxygen evolution reaction catalyst based on grain boundary engineering according to claim 1 or 2, wherein: The steps include: Step S1, preparing ZnO nanoparticles; Step S2, dissolving RuCl3 in deionized water and stirring evenly to obtain a RuCl3 solution; dispersing the ZnO nanoparticles in deionized water to obtain a ZnO suspension; adding the ZnO suspension to the RuCl3 solution and stirring to perform ion exchange, filtering to obtain a Zn-RuO2@ZnO precursor; washing and drying the Zn-RuO2@ZnO precursor, and calcining it at 430-480°C in an inert gas atmosphere for 1-3 hours to obtain Zn-xRuO2@ZnO nanoparticles.

4. The method for preparing a RuO2 acidic oxygen evolution reaction catalyst based on grain boundary engineering according to claim 3, characterized in that: In step S1, ZnO nanoparticles are prepared by electrospinning.

5. The method for preparing a RuO2 acidic oxygen evolution reaction catalyst based on grain boundary engineering according to claim 4, characterized in that: Step S1 comprises: dissolving C4H6O4Zn powder in a mixed solution of DMF and water, stirring until the solution becomes clear and transparent, then adding PVP and stirring to form a stable sol; preparing a ZnO precursor by electrospinning the sol, drying the precursor, annealing the precursor at a temperature of 480-520°C for more than 3 hours, and naturally cooling the precursor to room temperature to obtain ZnO nanoparticles.

6. The method for preparing a RuO2 acidic oxygen evolution reaction catalyst based on grain boundary engineering according to claim 5, characterized in that: In the electrospinning process, the pump speed is 1.3-1.7 mL·h -1 , the voltage range is -1kV to 20kV.

7. The method for preparing a RuO2 acidic oxygen evolution reaction catalyst based on grain boundary engineering according to claim 5, characterized in that: In step S1, the volume ratio of DMF to water in the mixed solution of DMF and water is 13-15:1; the mass of the PVP is 1.1-1.2 times the mass of the C4H6O4Zn powder.

8. The method for preparing a RuO2 acidic oxygen evolution reaction catalyst based on grain boundary engineering according to claim 5, characterized in that: In step S2, the mass ratio of ZnO in the ZnO suspension to RuCl3 in the RuCl3 solution is 1:1.5-1.

65.

9. The use of a RuO2 acidic oxygen evolution reaction catalyst based on grain boundary engineering according to claim 1 or 2, characterized in that: The RuO2 acidic oxygen evolution reaction catalyst based on grain boundary engineering is used as an anode catalyst in water electrolysis.

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