Mononuclear ruthenium-based water oxidation catalyst based on negatively-charged ligand and preparation method and application of mononuclear ruthenium-based water oxidation catalyst

Abstract

The invention discloses a mononuclear ruthenium-based water oxidation catalyst based on a negative-electricity ligand, and a preparation method and application thereof, and belongs to the technical field of catalyst preparation. The catalyst contains an electronegative tridentate ligand with a conjugated system, the electronegative ligand can reduce the overpotential of the molecular catalyst, and meanwhile, pyridine groups are introduced into the molecular catalyst, so that the molecular catalyst can be better combined with water. Therefore, the water oxidation catalyst shows relatively good electrochemical performance in electro-catalysis water oxidation, so that the catalyst provides an effective half reaction for water oxidation.

Description

Technical Field

[0001] The present invention relates to a mononuclear ruthenium-based water oxidation catalyst based on a negatively charged ligand, a preparation method and an application thereof, belonging to the technical field of catalyst preparation. Technical Background

[0002] Artificial photosynthesis (AP) is to simulate the basic principle of natural photosynthesis, use sunlight and water as basic raw materials, under the action of a catalyst, make water undergo an oxidation decomposition reaction, and convert the protons and electrons released by the hydrolysis of water into available chemical energy, thereby realizing the conversion of solar energy into chemical energy. Among them, the occurrence of the water oxidation half-reaction is a crucial step in photosynthesis and also an important challenge faced by the development of artificial photosynthesis systems. Therefore, efficient catalysts are needed to overcome the high reaction barrier, reduce the requirement for overpotential, and accelerate the reaction rate. To obtain catalysts with high intrinsic activity, low overpotential and high catalytic rate, developing molecular catalysts is the most promising approach.

[0003] Mononuclear Ru catalysts provide a structural basis for precisely regulating catalytic performance with clear atomic-level structural characteristics and reaction paths. The design freedom of their independent catalytic centers is significantly better than that of multinuclear systems. Due to the uniform chemical environment of mononuclear sites, the synthesis selectivity of this type of catalyst is higher, which can effectively improve the product purity without complex multi-component regulation strategies. In addition, the synthesis process of mononuclear Ru catalysts is more simplified, which is conducive to large-scale production applications. At the same time, their clear intermediate adsorption configuration and electron transfer path can more clearly reveal the microscopic mechanism of the water oxidation reaction, so it is easy to explore the details in the reaction process.

[0004] Based on the research on mononuclear Ru water oxidation catalysts in recent years, it is known that the introduction of electronegative ligands is beneficial to reducing the potential energy of high-valence reaction intermediates, which can effectively reduce the overpotential of the catalyst, thereby accelerating the kinetic process of the water oxidation reaction. In 2023, Marta et al. developed a new member [Ru(tda)(pyrS)2] of the Ru-tda complex family. This complex is functionalized with thiophene groups and a composite electrode is prepared by polymerization on the surface of a carbon electrode. The electrocatalytic activity of this electrode is significant, and a current density of up to 90 mA cm -2 can be achieved at 1.40 V, and a TON of more than 5×10 4 can be achieved within just 30 minutes, but 30% of Ru is lost during the activation process, and the stability is poor. Summary of the Invention

[0005] To solve the problems existing in the prior art, the present invention provides a mononuclear ruthenium-based water oxidation catalyst based on a negatively charged ligand, a preparation method and an application thereof. This novel, highly efficient and stable water oxidation catalyst is used to study the influence of an electronegative ligand on the water oxidation reaction. The electronegative ligand H2tda is selected and 4-picoline is introduced axially to synthesize a novel Ru mononuclear catalyst [Ru(tda)(4-pic)2] (H2tda = [2,2’:6’,2”-terpyridine]-6,6”-dicarboxylic acid, 4-pic = 4-picoline). By testing and studying its electrochemical performance, spectral performance, water oxidation performance, and catalytic mechanism, the activity change of the modified catalyst is revealed.

[0006] To achieve this purpose, the technical solution adopted by the present invention is as follows: A mononuclear ruthenium-based water oxidation catalyst based on a negatively charged ligand, the catalyst structure is as follows: 。

[0007] A preparation method of a mononuclear ruthenium-based water oxidation catalyst based on a negatively charged ligand, comprising the following steps:

[0008] (1) Add m-chloroperbenzoic acid to a 2,2’:6’,2”-terpyridine solution and stir at room temperature. After the reaction is completed, wash and purify to obtain intermediate R1a; The molar ratio of the 2,2’:6’,2”-terpyridine to the m-chloroperbenzoic acid is 1:(2.5 - 4); (2) Add intermediate R1a to dichloromethane of trimethylcyanosilane and stir; then add benzoyl chloride, stir overnight, extract and purify to obtain intermediate R2a; The molar ratio of the intermediate R1a to the trimethylcyanosilane is 1:(8 - 12); the molar ratio of the intermediate R1a to the benzoyl chloride is 1:(3 - 5); (3) Add solid KOH to a mixed solution of ethanol and water of intermediate R2a; reflux and stir; after the reaction is completed, evaporate the solvent under reduced pressure, disperse the residue in water, adjust the solution to pH = 3; filter and collect the white solid, wash; then disperse the solid in a mixed solution of H2SO4 and CH3COOH and reflux; after the reaction, cool and pour into cold water, filter, wash and dry to obtain H2tda;

[0009] (4) Ru(DMSO)4Cl2 and H2tda are refluxed and reacted in a mixed solution of triethylamine and methanol; after cooling, filter and collect the solid, dissolve the solid in a mixed solution of water and 4-picoline, and reflux overnight; cool to room temperature, extract and then rotary evaporate to obtain a red solid, purify and dry to obtain the catalyst.

[0010] Further, step (4) is carried out under anaerobic conditions.

[0011] Application of a mononuclear ruthenium-based water oxidation catalyst based on a negatively charged ligand, said catalyst being used in the electrocatalytic water oxidation half-reaction.

[0012] A composite electrode, said electrode being prepared using the above catalyst.

[0013] Further, the preparation method of the electrode is: adding catalyst powder and carboxylated multi-walled carbon nanotubes into a mixed solution of nafion and methanol, and ultrasonically obtaining a uniformly dispersed slurry; under the irradiation of an infrared lamp, drop-coating on carbon paper, and waiting for the methanol to completely volatilize to obtain the composite electrode Ru / MWCNTs-COOH / CP.

[0014] Further, the mass ratio of the catalyst powder to the carboxylated multi-walled carbon nanotubes is 1:1.

[0015] Further, the composite electrode is applied to the electrocatalytic water oxidation half-reaction.

[0016] A mononuclear ruthenium-based water oxidation catalyst based on a negatively charged ligand, comprising the following steps:

[0017] Ru(DMSO)4Cl2 and H2tda are refluxed in triethylamine and methanol for 6 hours. After cooling, the brown solid is collected by filtration, the solid is dissolved in water and 4-methylpyridine, and refluxed overnight. Cool to room temperature, extract with dichloromethane, rotary evaporate the organic phase to obtain a red solid, dissolve it with methanol and then precipitate with ether, and dry to obtain the target product. All the above steps are carried out under anaerobic conditions.

[0018] The beneficial effects of the present invention are: The catalyst contains a negatively charged tridentate ligand with a conjugated system. The negatively charged ligand can reduce the overpotential of the molecular catalyst, and at the same time introduce pyridine groups into the molecular catalyst, enabling it to better bind to water. Therefore, this water oxidation catalyst exhibits good electrochemical performance in electrocatalytic water oxidation, and thus this catalyst provides an effective half-reaction for water oxidation.

[0019] (1) The ligand of the ruthenium water oxidation catalyst of the present invention has a large conjugated system, effectively enhancing the oxidation activity of the catalyst, and the cumulative turnover number (TON) breaks through 8.2×10 6 . It is confirmed by gas chromatography quantitative analysis that the system has a Faraday efficiency of 96%, highlighting its practical application potential.

[0020] (2)The preparation method of the ruthenium-based water oxidation catalyst of the present invention is simple and feasible, with a relatively high yield and is easy to industrialize. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the 1 1H NMR spectrum of the complex [Ru(tda)(4-pic)2].

[0022] Figure 2 are (a) CV diagrams of 0.144 mM [Ru(tda)(4-pic)2] at different scan rates in Na2SO4 solution; (b) the relationship diagram between peak current density and the square root of scan rate.

[0023] Figure 3 are (a) CV diagrams of [Ru(tda)(4-pic)2] at different concentrations in Na2SO4 solution; (b) the relationship diagram between catalyst concentration and current density at 1.8 V vs. NHE.

[0024] Figure 4 is j c / j p versus v -1 / 2 relationship diagram.

[0025] Figure 5 is the scanning electron microscope image of the composite electrode Ru / MWCNTs-COOH / CP.

[0026] Figure 6 is the EDX image of the composite electrode Ru / MWCNTs-COOH / CP.

[0027] Figure 7 is the elemental distribution map of the composite electrode Ru / MWCNTs-COOH / CP.

[0028] Figure 8 is the cyclic voltammetry scanning test image of the composite electrode Ru / MWCNTs-COOH / CP.

[0029] Figure 9 is the current density test image of the composite electrode Ru / MWCNTs-COOH / CP under different potential conditions.

[0030] Figure 10 is the TOF value and Tafel slope diagram of the composite electrode Ru / MWCNTs-COOH / CP under different potential conditions.

[0031] Figure 11 is the TOF value and Tafel slope diagram of the composite electrode Ru / Ti3C2T x / CP under different potential conditions.

[0032] Figure 12 It is the long-term electrolysis test chart of the composite electrode Ru / MWCNTs-COOH / CP.

[0033] Figure 13 It is the Faraday efficiency chart of the composite electrode Ru / MWCNTs-COOH / CP. Specific embodiments

[0034] The present invention will be described in detail below through specific embodiments, but the scope of protection required by the present invention is not limited to the scope described in the embodiments.

[0035] A method for preparing a mononuclear ruthenium-based water oxidation catalyst based on a negatively charged ligand is as follows: Example 1 Preparation of the electronegative ligand H2tda

[0036] 2,2':6',2''-Bipyridine-1,1''-dioxide: Dissolve 2,2’:6’,2”-terpyridine (1 g, 4.29 mmol) in 30 mL of dry DCM, and add meta-chloroperoxybenzoic acid m-CPBA (85%, 2.177 g, 10.72 mmol; 2.5 eq). Stir at room temperature for 3 hours, and a white precipitate appears. Then add m-CPBA (0.435 g; 0.5 eq) and stir for another 6 hours. Dilute with DCM (120 mL) and quench with saturated sodium carbonate solution. Wash the organic phase with saturated NaCl solution (100 mL). Extract the aqueous phase with CHCl3, evaporate to dryness, and then purify by short column chromatography (CH2Cl2 / MeOH: 20 / 1, 9 / 1), evaporate the solvent under vacuum, and dry to obtain a white to pale yellow solid. (587 mg, 2.21 mmol, yield 51.6%). 1H-NMR (500 MHz, CDCl3) δ: 8.94 (d, J = 8.0 Hz, 2H); 8.34 (dd, J = 6.5 Hz, J = 0.5 Hz, 2H); 8.20 (dd, J = 8.0 Hz, J = 2.0 Hz, 2H); 7.98 (t, J = 8.0 Hz, 1H); 7.38 (td, J = 8.0 Hz, J = 1.0 Hz, 2H); 7.30 (td, J = 6.5 Hz, J = 2.0 Hz, 2H).

[0037] [2,2’:6’,2’-Bipyridine]-6,6’-dicarbonitrile (R2a): R1a (2,2':6',2''-bipyridine-1,1''-dioxide) (515 mg, 1.94 mmol) was added to 20 mL of dichloromethane containing trimethylcyanosilane (1.927 g, 19.43 mmol; 10 eq), and the mixture was stirred evenly in the flask. After 5 minutes, benzoyl chloride (10.92 g, 7.77 mmol; 4 eq) was added dropwise. After stirring overnight, the reaction was quenched with saturated sodium carbonate solution (100 mL). The reaction mixture was extracted with chloroform (5 × 20 mL), the organic phase was collected and the solvent was removed by rotary evaporation. The residue was recrystallized from acetonitrile / tetrahydrofuran, filtered under reduced pressure, the filter cake was collected, and dried in vacuo to obtain a white powder (336 mg, 1.19 mmol, yield 61.1%). 1 H NMR (500 MHz, CDCl3) δ 8.82 (d, J J = 8.0Hz, 2H), 8.58 (d, J J = 7.7 Hz, 2H), 8.03 (dt, J J = 20.0, 7.8 Hz, 3H), 7.75 (d, J J = 7.6 Hz, 2H).

[0038] [2,2’:6’,2”-Terpyridine]-6,6”-dicarboxylic acid (H2tda): Solid KOH (118 mg, 2.103 mmol) was added to a mixed solution of R2a (56 mg, 0.198 mmol) in ethanol (20 mL) and water (4 mL). The mixture was refluxed at 100 °C and stirred overnight, and then the solvent was evaporated under reduced pressure. The residue was dispersed in water, and the solution was adjusted to pH = 3 with concentrated hydrochloric acid. The white solid was collected by filtration, washed with cold water (40 mL) and acetonitrile (40 mL) respectively, and then the solid was dispersed in a mixed solution of H2SO4 / CH3COOH (10 mL, 1:1) and refluxed for 5 hours. After the reaction, the mixture was cooled to room temperature and poured into 40 mL of cold water, and a white precipitate was formed. The precipitate was filtered under reduced pressure, washed with cold water (40 mL) and acetonitrile (40 mL), and dried in vacuo to obtain a white solid (51 mg, 0.159 mmol, yield 80.3%). 1 H NMR (500 MHz, d6-DMSO) δ 8.87 (d, J J = 7.8 Hz, 1H), 8.65 (d, J J = 7.7 Hz,1H), 8.26 – 8.12 (m, 3H).

[0039] Example 2 Synthesis of Ru(DMSO)4Cl2

[0040] Under nitrogen protection, RuCl3•3H2O (5.2 g, 20 mol) and 25 mL of purified DMSO were added to a flask, and the mixture was heated under reflux for 5 min. The solution changed from black to dark red. A small amount of DMSO was distilled off under reduced pressure until yellow solid appeared in the solution. After cooling to room temperature, acetone (30 mL) was added to the reaction solution, and a large amount of yellow precipitate appeared. The solid was filtered under reduced pressure and washed successively with acetone (30 mL) and ether (30 mL), and then dried in vacuo to obtain a yellow powder (7.80 g, yield 80%). 1 1H NMR(400 MHz, CDCl3): d δ (ppm) 3.52 (d, J J = 11.0 Hz, 3H), 3.44 (s, 3H), 3.33 (s,2H), 2.74 (s, 2H), 2.63 (s, 1H).

[0041] Example 3 Synthesis of Complex [Ru(tda)(4-pic)2]

[0042] Under nitrogen protection, Ru(DMSO)4Cl2 (150 mg, 0.31 mmol), [2,2’:6’,2”-terpyridine]-6,6”-dicarboxylic acid (H2tda) (99 mg, 0.31 mmol), triethylamine (0.3 mL), and methanol (6 mL) were added to a reaction flask and refluxed for 6 hours. After cooling to room temperature, brown solid appeared in the reaction mixture, which was collected by filtration and washed with methanol and ether. The solid was dissolved in water (5mL) and 4-methylpyridine (15ml), and refluxed overnight. The resulting red solution was cooled to room temperature, extracted with dichloromethane (3×100mL), and the organic phase was rotary evaporated to obtain a red solid. The solid was dissolved in methanol and then precipitated with ether, and dried to obtain the target product (95 mg, 0.16 mmol, yield 51%). 1 1H NMR (400 MHz, MeOD) δ 8.58 (d, J J = 8.1Hz, 2H), 8.43 (dd, J J = 7.8, 1.4 Hz, 2H), 8.06 – 7.89 (m, 9H), 6.90 (d, J J =5.7 Hz, 4H), 2.16 (s, 6H).

[0043] Electrochemical Testing Method of the Catalyst in Example 4 To study the electrochemical properties of the catalyst [Ru(tda)(4-pic)2], cyclic voltammetry was used to determine the redox range, and differential pulse voltammetry was used to determine the oxidation peaks. The experiments were carried out using a CHI660E electrochemical workstation. A three-electrode system was adopted for the test, with a glassy carbon electrode with a diameter of 3 mm as the working electrode, a platinum wire as the counter electrode, and an Ag / AgCl electrode as the reference electrode. Before the test, the glassy carbon electrode was polished with alumina powder for 5 minutes, washed with deionized water, then ultrasonically cleaned for 10 minutes, and dried for standby. Before performing the electrochemical test on the catalyst, the reference electrode Ag / AgCl electrode needs to be calibrated with Ru(bpy)3 2+ (Ru Ⅱ / Ru Ⅲ = 1.26 V vs. NHE).

[0044] Study on the Electrochemical Properties of the Catalyst in Example 5 Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) tests were respectively carried out on the catalyst under the conditions of pH = 7.0 (0.1 M Na2SO4 solution) and pH = 1.0 (0.1 M CF3SO3H solution). The test results are as Figure 2 shown. Under the condition of pH = 7.0, CV shows that two sets of reversible redox peaks appear near E 1 / 2 = 0.52 V and E 1 / 2 = 1.01 V, which are respectively attributed to the redox processes of Ru Ⅱ / Ru Ⅲ , Ru Ⅲ / Ru Ⅳ . DPV shows that two sets of oxidation peaks of the catalyst appear at 0.47 V and 1.0 V, which are respectively attributed to the oxidation peaks of Ru Ⅱ / Ru Ⅲ , Ru Ⅲ / Ru Ⅳ ; Under the condition of pH = 1.0, CV shows that two sets of reversible redox peaks appear near E 1 / 2 = 0.60 V and E 1 / 2 = 1.05 V, which are respectively attributed to the redox processes of Ru Ⅱ / Ru Ⅲ , Ru Ⅲ / Ru Ⅳ . DPV shows that two sets of oxidation peaks of the catalyst appear at 0.57 V and 0.99 V, which are respectively attributed to the oxidation peaks of Ru Ⅱ / RuⅢ , Ru Ⅲ / Ru Ⅳ oxidation peak.

[0045] Water Oxidation Kinetics Study of the Catalyst in Example 6 Under the condition of pH = 7.0, the CV diagram shows that at E 1 / 2 = 0.52 V, a set of reversible redox peaks appear, which are attributed to the redox process of Ru Ⅱ / Ru Ⅲ . By changing the scan rate, the relationship between the oxidation peak current of its Ru Ⅱ / Ru Ⅲ and the scan rate was studied, and it was found that the current density was linearly related to the square root of the scan rate ( Figure 3 b in), indicating that the redox process of the catalyst is diffusion-controlled and conforms to the Randles-Sevcik relationship, which can be expressed by the following formula: (Equation 1) In Equation 1, is the peak current density, is the number of electrons transferred during the catalytic process, is the Faraday constant, is the diffusion coefficient of the catalyst in the system, A is the working electrode surface area, [cat] is the catalyst concentration, v is the scan rate, R is the standard gas constant, and T is the Kelvin temperature. According to the above formula, the diffusion coefficient of the catalyst in the system was calculated to be 5.766×10 -4 cm 2 s -1 .

[0046] The relationship between the catalytic current density and the catalyst concentration was studied. As Figure 4 shown, the catalytic current density at 1.8 V vs. NHE shows a linear relationship with the catalyst concentration, which conforms to the first-order kinetic reaction process, indicating that the catalyst reaction is a unimolecular mechanism and can be shown by the following formula: (Equation 2) In Equation 2, is the catalytic current density, is the number of electrons transferred during the catalytic process, is the Faraday constant, is the diffusion coefficient of the catalyst in the system, A is the working electrode surface area, [cat] is the catalyst concentration, is the reaction rate constant.

[0047] Preparation of the Composite Electrode in Example 7 Compared with ordinary carbon nanotubes, carboxylated carbon nanotubes have a certain hydrogen bond interaction with water molecules, which can improve the activity of the electrode for electrochemically catalyzing water oxidation. Nafion itself is a polymer with a certain viscosity and excellent electrical conductivity, which can well modify the electrode. Therefore, in this chapter, carboxylated multi-walled carbon nanotubes produced by Aladdin Reagent Company are selected as the carrier material for loading molecular catalysts, and carbon paper with good electrical conductivity is selected as the substrate material, and it is loaded onto the surface of the carbon paper by a simple drop-coating method to prepare a composite electrode. This preparation method is simple and easy to operate and has good repeatability. Carbon paper pretreatment: Cut the carbon paper in advance and soak it in concentrated nitric acid overnight, then ultrasonically treat it with absolute ethanol and deionized water for 30 min to remove the oxide layer and impurities on the surface, and then put it into a vacuum drying oven and dry it at 60 °C overnight for use.

[0048] (1)Preparation of electrode MWCNTs-COOH / CP Weigh 3 mg of carboxylated multi-walled carbon nanotubes MWCNTs-COOH and place them in a mixed solution of 0.03 mL of nafion (N 117, 5wt%) and 0.57 mL of methanol, and ultrasonically treat for 30 min to obtain a methanol dispersion of MWCNTs-COOH. Under the irradiation of an infrared lamp, use a pipette to transfer 50 μL of the dispersion and drop it onto the surface of the carbon paper. After the methanol has completely volatilized, the MWCNTs-COOH / CP electrode is obtained and reserved for use.

[0049] (2)Preparation of electrode Ru / MWCNTs-COOH / CP Weigh 3 mg (0.005 mmol) of [Ru(tda)(4-pic)2] catalyst powder and 3 mg of MWCNTs-COOH, add them to a mixed solution containing 0.03 mL of nafion (N 117, 5 wt%) and 0.57 mL of methanol, and ultrasonically treat for 30 min to obtain a uniformly dispersed slurry. Subsequently, under the irradiation of an infrared lamp, use a pipette to take 50 μL of the slurry and evenly drop it on the carbon paper. After the methanol has completely volatilized, the composite electrode Ru / MWCNTs-COOH / CP is obtained and reserved for use.

[0050] (3)Comparative electrode Ru / Ti3C2T x / CP preparation Weigh 3 mg (0.005 mmol) of [Ru(tda)(4-pic)2] catalyst powder and 3 mg of Ti3C2T with an analytical balance x, add it to a mixed solution containing 0.03 mL of nafion (N117, 5 wt%) and 0.57 mL of methanol, and ultrasonicate for 30 min to obtain a uniformly dispersed slurry. Subsequently, under the irradiation of an infrared lamp, use a pipette to take 50 μL of the slurry and evenly drop-coat it on a 1 cm × 1 cm carbon paper. After the methanol has completely evaporated, obtain the composite electrode Ru / Ti3C2T x / CP for standby.

[0051] From the scanning electron microscope of the composite electrode Figure 5 It can be seen that the helical carboxylated multi-walled carbon nanotubes on the surface of the carbon paper electrode are successfully loaded onto the carbon fiber and intertwined and overlapped with each other, presenting a disordered porous structure. Therefore, it has a large specific surface area, providing a guarantee for the loading of the molecular catalyst. In addition, through the energy-dispersive X-ray spectroscopy of the composite electrode Figure 6 test results, the presence of ruthenium metal element on the composite electrode can be clearly observed, proving that the molecular catalyst is indeed loaded onto the electrode. While conducting the scanning electron microscope test, the main element distribution on the electrode surface was analyzed ( Figure 7 ), and in a randomly selected area, the distributions of C element and Ru element on the electrode surface are very uniform, indicating that the molecular catalyst is uniformly distributed on the surface of the composite electrode.

[0052] Example 8 Electrochemical test method of the composite electrode Ru / MWCNTs-COOH / CP Select a CHI 760E electrochemical workstation from Shanghai Huachen Company to conduct cyclic voltammetry and potentiostatic electrolysis tests on the composite electrode. In a phosphate buffer solution with a pH of 6.86, use a platinum wire as the counter electrode and Ag / AgCl as the reference electrode. Before the test, calibrate the reference electrode Ag / AgCl electrode with Ru(bpy)3 2+ (RuⅡ / RuⅢ = 1.26 V vs. NHE).

[0053] Example 9 Application of the composite electrode Ru / MWCNTs-COOH / CP in electrocatalytic water oxidation By conducting cyclic voltammetry scanning tests on the composite electrode Ru / MWCNTs-COOH / CP, Figure 8 it can be observed that the composite electrode Ru / MWCNTs-COOH / CP exhibits obvious electrocatalytic water oxidation activity. At E 1 / 2 0.46 V and 0.96 V, two pairs of oxidation peaks can be clearly observed. This redox process corresponds to Ru Ⅱ / Ru Ⅲ and Ru Ⅲ / Ru ⅣProcess. Cyclic voltammetry tests also show that the onset potential for the electrocatalytic water oxidation of this composite electrode is approximately 1.36 V, and the overpotential is 710 mV. By integrating the peak currents of the Ru II / Ru III redox peaks, the charge obtained is 3.261 × 10 -4 C. Then, through the Faraday's law formula Γ = Q / (ns F ), where n is the number of electrons transferred, equal to 1; s is the working area of the electrode, equal to 1 cm 2 ; F is the Faraday constant, equal to 96485 C mol -1 ), the adsorption amount of the catalyst on this composite electrode can be calculated to be 3.38 × 10 -9 mol cm -2 . For the MWCNTs-COOH / CP electrode without the modified catalyst, no redox peaks are observed within the cyclic voltammetry scanning range, indicating that this electrode has almost no electrocatalytic water oxidation activity.

[0054] (1) Tafel and TOF tests of the composite electrode Ru / MWCNTs-COOH / CP The electrocatalytic water oxidation test of the composite electrode Ru / MWCNTs-COOH / CP was carried out under controlled time at different bias voltages to obtain the catalytic current density under different overpotential conditions. Figure 9 It can be seen that the catalytic activity is significantly improved as the bias voltage increases.

[0055] Taking the logarithm of the catalytic current density obtained at different overpotentials as the ordinate and the overpotential as the abscissa to plot a graph, the Tafel plot of the composite electrode can be obtained. Figure 10 It can be seen that as the overpotential increases, the current density gradually increases. In the overpotential range of 383 mV to 783 mV, the Tafel of the composite electrode is a straight line, indicating that there is an effective electron transfer process at the interface. Through the formula TOF = Q / (4tFΓ) (Q is the charge passed during the electrolysis process, in units of C; F is the Faraday constant, t is the time of the electrolysis reaction, and Γ is the adsorption amount of the catalyst), the TOF values of the composite electrode at different overpotentials can be calculated. As the overpotential increases from 383 mV to 783 mV, the TOF value of the electrode increases from 14.99 s -1 to 191.66 s -1 .

[0056] (2) Tafel and TOF tests of the composite electrode Ru / Ti3C2T x / CP For the composite electrode Ru / Ti3C2T xThe / CP was subjected to controlled-time electrocatalytic water oxidation testing at the same bias voltage (1.2 V to 1.6 V) as the electrode Ru / MWCNTs-COOH / CP to obtain the catalytic current density under different overpotential conditions. Then, the logarithm of the catalytic current density was taken as the ordinate and the overpotential was taken as the abscissa to plot a graph ( Figure 11 ), and the Tafel plot of the composite electrode could be obtained. It can be seen that as the overpotential increases, the current density gradually increases. As can be seen from the figure, in the overpotential range of 383 mV to 783 mV, the Tafel of the composite electrode is a straight line. From the TOF values of the composite electrode at different overpotentials, it can be seen that as the overpotential increases from 383 mV to 783 mV, the TOF value of the electrode increases from 0.54 s -1 to 0.89 s -1 .

[0057] The comparison results show that the synergistic effect after the catalyst containing strongly electronegative ligands is combined with carboxylated multi-walled carbon nanotubes significantly enhances the catalytic water oxidation performance of the catalyst.

[0058] (3) Electrochemical catalytic water oxidation stability test of the composite electrode Ru / MWCNTs-COOH / CP To further investigate the electrocatalytic water oxidation activity of the composite electrode Ru / MWCNTs-COOH / CP, a phosphate buffer solution with pH 6.86 was used as the electrolyte, and the working area of the electrode was controlled to be 1 cm 2 . A potentiostatic electrolysis experiment was carried out at a potential of 1.4 V vs. NHE for 1 hour, and the results are as Figure 12 shown. During the electrolysis process, a large number of bubbles could be clearly observed continuously forming and releasing from the cathode and anode surfaces. After gas chromatography detection, they were determined to be hydrogen and oxygen respectively. After 1 hour of electrolysis experiment, the current density remained at about 0.92 mA cm -2 without attenuation, indicating that the composite electrode has good stability for the electrochemical catalytic water oxidation reaction.

[0059] (4) Faraday efficiency test of the composite electrode Ru / MWCNTs-COOH / CP The Faradaic Efficiency (FE) is a key parameter for quantifying reaction selectivity and energy utilization efficiency, defined as the ratio of the amount of charge actually generated for the target product (O2) to the total charge transfer. Its calculation formula is: n = 4n(O2)F / Q × 100%, where 4n(O2) is the amount of oxygen generated during the electrolysis process, F is the Faraday constant, and Q is the total charge of the electrolysis. In the catalytic reaction, the Turnover Number (TON) is the core parameter for measuring the catalyst efficiency, indicating the number of substrate molecules converted by a single active site during the reaction process. Its calculation formula is: TON = n (amount of product generated in the reaction) / n (amount of catalyst loaded). In a closed electrolytic cell, a long-term electrolysis test was carried out at a voltage of 1.4 V. The gas in the electrolytic cell was quantitatively analyzed for oxygen by gas chromatography every hour. After 12 hours of electrolysis, the amount of oxygen generated was detected to be 27.98 mmol, and the electric charge was 27 C, which was consistent with the electric charge of 27.99 C generated during the electrolysis process, as Figure 13 , after calculation, the Faraday efficiency of the composite electrode for catalytic water oxidation reaction was as high as 96.46%, and the TON value reached 8.28×10 6 . At the same time, the amount of hydrogen generated in the electrolytic cell was detected to be 56 mmol, which was twice the amount of oxygen generated.

Claims

1. A mononuclear ruthenium-based water oxidation catalyst based on a negatively charged ligand, characterized in that, The catalyst structure is as follows: 。 2. The preparation method of a mononuclear ruthenium-based water oxidation catalyst based on a negatively charged ligand according to claim 1, characterized in that, It includes the following steps: ； (1) Add m-chloroperbenzoic acid to a 2,2’:6’,2”-terpyridine solution and stir at room temperature. After the reaction is completed, wash and purify to obtain intermediate R1a; The molar ratio of 2,2’:6’,2”-terpyridine to m-chloroperbenzoic acid is 1:(2.5 - 4); (2) Add intermediate R1a to dichloromethane of trimethylcyanosilane and stir; then add benzoyl chloride, stir overnight, extract and purify to obtain intermediate R2a; The molar ratio of intermediate R1a to trimethylcyanosilane in terms of dosage is 1:(8 - 12); the molar ratio of intermediate R1a to benzoyl chloride in terms of dosage is 1:(3 - 5); (3) Add solid KOH to a mixed solution of ethanol and water of intermediate R2a; reflux and stir; after the reaction is completed, evaporate the solvent under reduced pressure, disperse the residue in water, and adjust the solution to pH = 3; Filter to collect the white solid and wash it; Then disperse the solid in a mixed solution of H2SO4 and CH3COOH and reflux; after the reaction, cool and pour it into cold water, filter, wash and dry to obtain H2tda; ； (4) Ru(DMSO)4Cl2 and H2tda are refluxed and reacted in a mixed solution of triethylamine and methanol; after cooling, filter to collect the solid, dissolve the solid in a mixed solution of water and 4-methylpyridine, and reflux overnight; cool to room temperature, extract and then rotary evaporate to obtain a red solid, purify and dry to obtain the catalyst.

3. The preparation method of a mononuclear ruthenium-based water oxidation catalyst based on a negatively charged ligand according to claim 2, wherein, Step (4) is carried out under anaerobic conditions.

4. Use of a mononuclear ruthenium-based water oxidation catalyst based on a negatively charged ligand according to claim 1, characterized in that: The catalyst is used in the electrocatalytic water oxidation half-reaction.

5. A composite electrode, characterized in that, The electrode is prepared by using the catalyst described in Claim 1.

6. The composite electrode according to claim 5, characterized in that, The preparation method of the electrode is: Add catalyst powder and carboxylated multi-walled carbon nanotubes to a mixed solution of nafion and methanol, and ultrasonically obtain a uniformly dispersed slurry; under the irradiation of an infrared lamp, drop-coat it on carbon paper, and wait for the methanol to volatilize completely to obtain a composite electrode Ru / MWCNTs-COOH / CP.

7. A composite electrode according to claim 6, characterized in that, The mass ratio of the catalyst powder to the carboxylated multi-walled carbon nanotubes is 1:

1.

8. Use of a composite electrode according to any one of claims 5-7, characterized in that: The composite electrode is applied to the electrocatalytic water oxidation half-reaction.

Images