CN112877725A - Ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material and preparation method and application thereof - Google Patents

Abstract

The invention discloses a ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material, which is prepared from RuCl₃·3H₂And performing hydrothermal reaction on the O, the graphene oxide and the polypyrrole in deionized water to obtain aerogel, and oxidizing the aerogel and the calcium carbonate to obtain a final product. The material has double active centers as a catalyst, and has the characteristics of low overpotential, high activity and good stability in the process of water decomposition by electrocatalysis. The invention also discloses a preparation method of the composite material, and the preparation process is simple to operate, low in cost, controllable in reaction process and high in yield. The invention also provides application of the ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material as a catalyst in electrocatalytic water decomposition, and the catalyst shows good HER and OER performances and good stability in different electrolytes. The invention discloses a low overpotential, bifunctional electrocatalyst for reducing energy consumption andthe simplification of the whole electrolytic water system design has important significance.

Description

Ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material and preparation method and application thereof

Technical Field

The invention relates to the field of electrochemistry, and relates to a ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material, and a preparation method and application thereof.

Background

Hydrogen energy is considered as the secondary energy with the most development potential in the 21 st century, and hydrogen element is the most common element existing in nature and has the highest specific energy density. The process of hydrogen powering takes place as a combustion reaction, the product of which is water, without producing any greenhouse gases and pollutants. Water is also a raw material for preparing hydrogen, and the preparation and combustion of the hydrogen supply realize the cyclic utilization of resources. Therefore, the hydrogen is used as a clean energy carrier and has important significance for solving the problems of energy and pollution.

Electrolyzed water has received much attention as an economical and efficient method for producing high purity hydrogen. Water splitting consists of two parts: the cathode is subjected to a reduction reaction to generate hydrogen and the anode is subjected to an oxidation reaction to generate oxygen. The theoretical electromotive force of water decomposition is 1.23V, but the electromotive force of water decomposition in the actual production operation process is far greater than 1.23V, because the cathode and the anode can generate electrochemical polarization respectively in the electrocatalysis process, the Hydrogen (HER) Oxygen Evolution (OER) process can be realized only by overcoming the overpotential (eta) generated by the electrochemical polarization, and the energy consumption of the electrocatalysis process is increased due to the existence of the overpotential. In addition, because the catalytic mechanisms of hydrogen evolution and oxygen evolution are different, the different reaction processes of hydrogen evolution and oxygen evolution present challenges to the design of full hydrolysis hydro-catalysts. Therefore, the research of the bifunctional electrocatalyst with hydrogen/oxygen evolution and low overpotential simultaneously has important significance for reducing energy consumption and simplifying the whole system design.

The key and key points of research in the field of electrocatalysis are to realize a fully water-splitting bifunctional electrocatalyst, namely, the same catalyst can separate out hydrogen and oxygen when electrolyzing water, so that the activity of an electrode catalytic material is improved, the overpotential in the reaction process is reduced, and the stability of the electrode material is improved. Three-dimensional graphene is receiving attention due to its unique structural and electronic properties, such as an ordered network structure, a large specific surface area, a diverse pore distribution, and excellent conductivity. Three-dimensional graphene, which contributes to the exposure of active sites, promotes electron transfer and diffusion of gaseous products, is considered to be a promising electrocatalytic material based on the above characteristics. It is known that metallic ruthenium has good metal-hydrogen adsorption and desorption capabilities, and that electrocatalysts based on metallic ruthenium show good catalytic activity and catalytic stability in electrocatalytic hydrogen evolution reactions. Meanwhile, ruthenium oxide is considered as an optimal catalyst for electrocatalytic oxygen evolution.

However, the metal ruthenium-based electrocatalyst still has more problems, one of which is the stability and the cyclability of the electrode, the stability of the metal ruthenium-based catalyst in an alkaline solution is poor, and the catalytic efficiency of the catalyst is low; secondly, the metal ruthenium-based catalyst still has over-high overpotential in the catalysis process; thirdly, the preparation method of the prior electrocatalyst is complex. Therefore, designing and preparing an electrocatalytic material with high catalytic activity and good stability and having dual-function full water decomposition is a problem to be solved at present.

Disclosure of Invention

In order to overcome the defects of the prior art, one of the purposes of the invention is to provide a ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material which can be used as a catalyst and has the characteristics of low overpotential, high catalytic activity and good catalytic stability in the process of water electrocatalytic decomposition.

The invention also aims to provide a preparation method of the ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material.

The invention also aims to provide application of the ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material as a catalyst in electrocatalytic decomposition of water.

One purpose of the invention is to provide a ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material, wherein the composite material is made of RuCl₃·3H₂Performing hydrothermal reaction on O, graphene oxide and polypyrrole in deionized water to obtain aerogel, and oxidizing the aerogel and calcium carbonate to obtain the final productAnd (3) obtaining the product.

Further, the mass ratio of the calcium carbonate to the aerogel is 1: 2-5. Preferably, the mass ratio of calcium carbonate to aerogel is 1: 4.

Further, the RuCl₃·3H₂The mass ratio of the O to the graphene oxide is 1: 2-6. Preferably, RuCl₃·3H₂The mass ratio of O to graphene oxide is 1: 4.

Further, the mass ratio of the polypyrrole to the graphene oxide is 1: 1-10. Preferably, the mass ratio of polypyrrole to graphene oxide is 1: 4.

Further, the ratio of the graphene oxide to the deionized water is 1: 0.25-2. Preferably, the ratio of the graphene oxide mass mg to the deionized water volume mL is 1: 0.5.

The second purpose of the invention is realized by the following technical scheme:

1) adding RuCl₃·3H₂Adding O, graphene oxide and polypyrrole into deionized water, ultrasonically oscillating and dispersing for 1-5h, and carrying out hydrothermal reaction for 10-20h at the temperature of 100-200 ℃ to obtain aerogel;

2) roasting the aerogel obtained in the step 1) and calcium carbonate at the temperature of 500-900 ℃ for 1-4h to obtain a final product.

Preferably, the ultrasonic oscillation time is 3-4 h.

Preferably, the hydrothermal reaction temperature is 180 ℃ and the time is 10-14 h.

Preferably, the roasting temperature is 600-700 ℃ and the time is 2-3 h.

Preferably, the calcination environment is an inert atmosphere, and the inert gas is selected from one or more of nitrogen, argon or helium.

The invention also aims to provide application of the ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material as a catalyst in electrocatalytic decomposition of water.

Compared with the prior art, the invention has the beneficial effects that:

1. the ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material provided by the invention adopts RuCl₃·3H₂Subjecting O, graphene oxide and polypyrrole to deionized waterObtaining aerogel through hydrothermal reaction, and oxidizing the aerogel and calcium carbonate to obtain a final product.

According to the invention, calcium carbonate is used as an oxidant to carry out high-temperature reaction with aerogel, so that a ruthenium simple substance and ruthenium oxide compound is successfully formed on the surface of the nitrogen-doped graphene three-dimensional material, a bifunctional active center is formed, and the prepared final product has excellent electrocatalytic hydrogen evolution and oxygen evolution performances;

the polypyrrole selected by the invention plays a role in stabilizing the three-dimensional structure of the graphene in the high-temperature calcination process, so that the specific surface area of the composite material is improved, the contact between the catalyst and the electrolyte is increased, the mass transfer process is promoted, and the reaction activity is increased. The polypyrrole selected by the invention also provides an N source to realize nitrogen-doped graphene, so that the conductivity of the material is improved, and the improvement of the conductivity is beneficial to reducing the polarization effect in the electrocatalytic reaction process and reducing the overpotential of the reaction.

2. The invention also provides a preparation method of the material, and the two-step preparation process has the advantages of simple operation, low cost, controllable reaction process and high yield.

3. The invention also provides the application of the material as a catalyst in water electrocatalytic decomposition, and the catalyst has double active centers and has the characteristics of low overpotential, high activity and good stability in the water electrocatalytic decomposition process. The catalyst provided by the invention improves the HER performance and the OER performance, has good stability no matter hydrogen evolution and oxygen evolution under an acidic condition or hydrogen evolution and oxygen evolution under an alkaline condition, and has lower reaction overpotential and better performance than that of the current commercial electrocatalyst; has important significance for reducing energy consumption and simplifying the design of the whole electrolytic water system.

Drawings

FIG. 1 is a synthetic scheme of examples 1 to 3 of the present invention;

FIG. 2 is an XRD pattern of the products obtained in examples 1 to 3 of the present invention;

FIG. 3 is a comparison of XRD patterns of Graphene Oxide (GO) with the product obtained in example 1 of the present invention;

FIG. 4 is an SEM photograph of the products obtained in examples 1 to 3 of the present invention;

FIG. 5 is a TEM image of the products obtained in examples 1 to 3 of the present invention;

FIG. 6 is a HRTEM image of the product obtained in example 1 of the present invention;

FIG. 7 is an EDX mapping chart of the product obtained in example 1 of the present invention;

FIG. 8 is an XPS spectrum of the product obtained in example 1 of the present invention;

FIG. 9 is an XPS analysis spectrum of Ru element in a product obtained in example 1 of the present invention;

FIG. 10 is a BET plot of the product obtained in example 1 of the present invention;

FIG. 11 shows the results of examples 1 to 3 of the present invention at 0.5mol/L H₂SO₄Hydrogen evolution in solution linear sweep voltammetry;

FIG. 12 shows the results of comparative examples 1 to 3 according to the invention at 0.5mol/L H₂SO₄Hydrogen evolution in solution linear sweep voltammetry;

FIG. 13 shows that the products obtained in examples 1 to 3 of the present invention are at 0.5mol/L H₂SO₄Linearly scanning a voltammogram by oxygen evolution in a solution;

FIG. 14 shows the results of comparative examples 1 to 3 according to the invention at 0.5mol/L H₂SO₄Linearly scanning a voltammogram by oxygen evolution in a solution;

FIG. 15 is a hydrogen evolution linear sweep voltammogram of the products obtained in examples 1 to 3 of the present invention in a 1.0mol/L KOH solution;

FIG. 16 is a hydrogen evolution linear sweep voltammogram of the products obtained in comparative examples 1 to 3 of the present invention in a 1.0mol/L KOH solution;

FIG. 17 is an oxygen evolution linear sweep voltammogram of the products obtained in examples 1 to 3 of the present invention in a 1.0mol/L KOH solution;

FIG. 18 is an oxygen evolution linear sweep voltammogram of the products obtained in comparative examples 1 to 3 of the present invention in a 1.0mol/L KOH solution;

FIG. 19 shows stability tests of hydrogen evolution and oxygen evolution in a 1.0mol/L KOH solution for the product obtained in example 1 of the present invention.

Detailed Description

The present invention will be further described with reference to the accompanying drawings and the detailed description, and it should be noted that any combination of the embodiments or technical features described below can be used to form a new embodiment without conflict.

Synthetic schemes for examples 1, 2 and 3 are shown in fig. 1.

Example 1

1) Weighing 5mg of RuCl₃·3H₂O, 5mg of polypyrrole and 20mg of Graphene Oxide (GO) are added into 10mL of deionized water, and the mixture is subjected to ultrasonic oscillation for 4 hours to form a uniformly dispersed solution. And transferring the prepared solution to a hydrothermal reaction kettle, and carrying out hydrothermal reaction at 180 ℃ for 12 hours to obtain Graphene Oxide (GO) aerogel. Washing the graphene oxide aerogel with deionized water for three times, and then freezing and drying;

2) placing 2.5mg of calcium carbonate at an upper air inlet of a tubular furnace, calcining 10.0mg of aerogel obtained in the step 1) in a nitrogen atmosphere, wherein the heating rate is 5 ℃/min, and the calcining temperature is 700 ℃ for reacting for 2 h. And cooling to room temperature after calcining to obtain the ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material.

Example 2

1) Weighing 5mg of RuCl₃·3H₂O, 10mg of polypyrrole and 20mg of Graphene Oxide (GO) are added into 40mL of deionized water, and the mixture is subjected to ultrasonic oscillation for 4 hours to form a uniformly dispersed solution. And transferring the prepared solution to a hydrothermal reaction kettle, and carrying out hydrothermal reaction for 12 hours at 160 ℃ to obtain Graphene Oxide (GO) aerogel. Washing the graphene oxide aerogel with deionized water for three times, and then freezing and drying;

2) placing 1.5mg of calcium carbonate on an upper air inlet of a tubular furnace, calcining 5.0mg of aerogel obtained in the step 1) in a nitrogen atmosphere, wherein the heating rate is 5 ℃/min, and the calcining temperature is 750 ℃ for reacting for 2 h. And cooling to room temperature after calcining to obtain the ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material.

Example 3

1) Weighing 4mg of RuCl₃·3H₂O, 20mg polypyrrole and 20mg Graphene Oxide (GO) plusAdding the mixture into 5mL of deionized water, and carrying out ultrasonic oscillation for 2h to form a uniformly dispersed solution. And transferring the prepared solution to a hydrothermal reaction kettle, and carrying out hydrothermal reaction for 16h at 180 ℃ to obtain Graphene Oxide (GO) aerogel. Washing the graphene oxide aerogel with deionized water for three times, and then freezing and drying;

2) placing 4.0mg of calcium carbonate on an upper air inlet of a tubular furnace, calcining 12.0mg of aerogel obtained in the step 1) in a nitrogen atmosphere, wherein the heating rate is 5 ℃/min, and the calcining temperature is 800 ℃ for reacting for 2 h. And cooling to room temperature after calcining to obtain the ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material.

Comparative example 1

Comparative example 1 differs from example 1 in that calcium carbonate, an oxidizing agent, is not added, and the rest is the same as example 1. Finally obtaining the ruthenium modified nitrogen-doped graphene three-dimensional composite material.

Comparative example 2

The difference between the comparative example 2 and the example 1 is that the ratio of the added calcium carbonate to the aerogel is 2:1, the Ru element is completely oxidized into ruthenium oxide, and the rest is the same as that in the example 1, so that the ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material is finally obtained.

Comparative example 3

The difference between the comparative example 3 and the example 1 is that the ratio of the added calcium carbonate to the aerogel is 1:10, and the rest is the same as that in the example 1, so that the ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material is finally obtained.

The products obtained in examples 1 to 3 were subjected to systematic study on their morphology, composition, chemical bond and microstructure by modern nano-test analysis techniques such as XRD, SEM, TEM, HRTEM, EDX, XPS, BET, etc., and the results are as follows:

the XRD characterization of the product obtained in each example was performed first (FIG. 2), and the XRD spectrum was compared with Ru and RuO₂The standard cards correspond. The results show that the products obtained in examples 1 to 3 all contain Ru and RuO₂Characteristic peak, proving that the final product contains Ru simple substance and RuO₂. In addition, when the XRD pattern of graphene oxide was compared with that of example 1 (fig. 3), the characteristic peak at the 10-degree position disappeared, indicating that graphene oxide had been reducedIs graphene.

The products obtained in each example were further characterized by SEM (FIG. 4) and TEM (FIG. 5), in which a, b and c represent example 1, example 2 and example 3, respectively. The results show that the composite materials obtained in examples 1 to 3 have unique three-dimensional structures (fig. 4), and spherical nanoparticles can be seen on the surface thereof (fig. 5).

The microstructure of the product obtained in example 1 was further analyzed by HRTEM, and the result is shown in FIG. 6, FIG. 6b is an enlarged view of FIG. 6a, FIG. 6b clearly shows that the lattice fringes of the nanoparticles have two different orientations, and the parts c, d, e and f (indicated by square boxes in the figure) with clear lattice fringes are further enlarged and analyzed to obtain lattice spacings of 0.21m, 0.19nm, 0.216nm and 0.213nm, respectively, wherein the lattice spacings obtained from the parts c and d are equal to the XRD RuO in FIG. 2₂The lattice spacing obtained from the e and f parts is consistent with the lattice spacing of the crystal face (002) corresponding to the characteristic peak of XRD Ru in figure 2, which shows that the nanoparticles in the product of example 1 are Ru and RuO₂Consistent with XRD results.

To further analyze the elemental composition of the product, the product obtained in example 1 was subjected to EDX mapping analysis (fig. 7), which indicated that the product obtained in example 1 contained C, N, O, Ru four elements.

In order to determine the chemical bonding state of each element in the product, XPS full spectrum analysis was performed on the product obtained in example 1, and the results are shown in fig. 8, and the XPS full spectrum analysis shows that the results are consistent with EDX mapping, which also indicates that the product contains C, N, O, Ru four elements, and the doping of N element into graphene is successfully achieved. FIG. 9 is a fitting analysis of the characteristic energy spectrum of Ru 3p orbit, wherein 464.1eV and 486.4eV represent that Ru has a valence of +4, and 462.1eV and 484.6eV represent that Ru has a valence of 0, i.e., the Ru element in the product obtained in example 1 exists in the form of a simple substance of ruthenium and ruthenium oxide, which is consistent with the XRD result.

FIG. 10 shows BET analysis of the product obtained in example 1, and the specific surface area of the product obtained in example 1 was 351.6m by subjecting the material to a nitrogen adsorption/desorption test³In terms of/g (FIG. 10a), the pore size is predominantly distributed between 2 and 5 nm.

The above characterization and analysis results show that polypyrrole, graphene oxide and RuCl are adopted in the invention₃And compounding, namely preparing the ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material by using calcium carbonate as an oxidant. The polypyrrole can play a role in stabilizing the graphene and maintaining a three-dimensional structure in a high-temperature calcination process, so that the structure collapse is prevented, and the composite material obtained by the method has a large specific surface area. And simultaneously reducing the graphene oxide and the polypyrrole in a high-temperature calcination process to obtain nitrogen-doped three-dimensional graphene, and simultaneously adjusting the dosage ratio of the calcium carbonate oxidant to the aerogel to obtain the ruthenium/ruthenium oxide with double active sites.

Experimental example 1

The ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite materials prepared in examples 1 to 3 and comparative examples 1 to 3 are used as catalysts and have the concentration of H at 0.5mol/L₂SO₄And respectively carrying out electrolytic water hydrogen evolution and oxygen evolution tests in the solution. The electrode preparation process is as follows: 5mg of the composite materials obtained in example 1, example 2 and example 3 as a catalyst and 100. mu.L of an Afion solution (5 wt%) were added to 1000. mu.L of a mixture of water and ethanol (volume ratio: 1), and sonicated for 2 hours to obtain a uniform dispersion. And (3) dripping 30 mu L of the dispersion liquid on carbon paper of 0.5 multiplied by 0.5cm, and drying at room temperature to obtain the working electrode for the electrocatalytic reaction.

1.1 acid condition Hydrogen Evolution Reaction (HER)

An electrode prepared by using the ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite materials prepared in the examples 1 to 3 and the comparative examples 1 to 3 as a catalyst is used as a working electrode, a commercial Pt/C electrode is used as a control group, Ag/AgCl is used as a reference electrode, a graphite rod is used as an auxiliary electrode, and the concentration of the active carbon in the electrode is 0.5mol/L H₂SO₄And carrying out linear sweep voltammetry in the solution to carry out electrocatalytic hydrogen evolution reaction. Voltage scan range: -0.2 to-0.5 (V vs Ag/AgCl). The iR compensation formula is E-iR × 90%.

Along with the negative increase of the voltage, the current density begins to increase, bubbles are generated on the surface of the working electrode, and the occurrence of the electrocatalytic hydrogen evolution reaction is proved. The results of the experiment are shown in FIGS. 11 and 12, at a current density of 10mAcm^-2In the case of the catalyst, the overpotential η for hydrogen evolution of the Pt/C electrode under acidic conditions was 38mV, and the overpotential η for the catalyst electrodes of examples 1 to 3 were 20mV, 60mV, and 50mV, respectively. The overpotential η of the catalyst electrodes of comparative examples 1 to 3 were 71mV, 173mV, and 65mV, respectively. The hydrogen evolution overpotential of the catalyst electrode of example 1 is lower than that of a commercial Pt/C electrode, and the performance is better.

1.2 acid condition Oxygen Evolution Reaction (OER)

An electrode prepared by taking the ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material prepared in the examples 1 to 3 and the comparative examples 1 to 3 as a catalyst is taken as a working electrode, and the commercial RuO₂The electrode is a control group, Ag/AgCl is a reference electrode, a graphite rod is an auxiliary electrode, and the concentration is 0.5mol/L H₂SO₄Linear sweep voltammetry is carried out in the solution to carry out electrocatalytic oxygen evolution reaction. Voltage scan range: 1.0 to 1.5 (Vvsag/AgCl). The iR compensation formula is E-iR × 90%.

Along with the positive increase of the voltage, the current density is increased, bubbles are generated on the surface of the working electrode, and the occurrence of the electrocatalytic oxygen evolution reaction is proved. The results of the experiment are shown in FIGS. 13 and 14 at a current density of 10mAcm^-2In acidic condition, RuO₂The overpotential η of the electrode for oxygen evolution is 258mV, and the overpotential η of the catalyst electrodes of examples 1 to 3 are 235mV, 265mV and 330mV, respectively. The overpotential eta of the catalyst electrodes of the comparative example 2 and the comparative example 3 are 315mV and 368mV respectively, and the overpotential of the catalyst obtained in the comparative example 1 is too high and almost has no oxygen evolution performance. Example 1 oxygen evolution overpotential ratio of catalyst electrode commercial RuO₂The electrode has lower oxygen evolution overpotential and better performance.

Experimental example 2

The ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite materials prepared in examples 1 to 3 and comparative examples 1 to 3 are used as catalysts to respectively perform an electrolytic water hydrogen evolution and oxygen evolution test in a 1.0mol/L KOH solution. The electrode was prepared in the same manner as in experimental example 1.

2.1 basic conditions Hydrogen Evolution Reaction (HER)

An electrode prepared by using the ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material prepared in the examples 1 to 3 and the comparative examples 1 to 3 as a catalyst is used as a working electrode, a commercial Pt/C electrode is used as a control group, Ag/AgCl is used as a reference electrode, a graphite rod is used as an auxiliary electrode, and a linear sweep voltammetry is performed in a 1.0mol/L KOH solution to perform an electrocatalytic hydrogen evolution reaction. -0.2 to-0.4 (V vs Ag/AgCl). The iR compensation formula is E-iR × 90%.

Along with the negative increase of the voltage, the current density begins to increase, bubbles are generated on the surface of the working electrode, and the occurrence of the electrocatalytic hydrogen evolution reaction is proved. The results of the experiment are shown in FIGS. 15 and 16, at a current density of 10mAcm^-2In the case of alkaline conditions, the overpotential η for hydrogen evolution of the Pt/C electrode was 25mV, and the overpotential η for the catalyst electrodes of examples 1 to 3 were 11mV, 42mV, and 43mV, respectively. The overpotential η of the catalyst electrodes of comparative examples 1 to 3 were 87mV, 214mV, and 68mV, respectively. The hydrogen evolution overpotential of the catalyst electrode of example 1 is lower than that of a commercial Pt/C electrode, and the performance is better.

2.2 basic conditions Oxygen Evolution Reaction (OER)

An electrode prepared by taking the ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material prepared in the examples 1 to 3 and the comparative examples 1 to 3 as a catalyst is taken as a working electrode, and the commercial RuO₂The electrode is a control group, Ag/AgCl is a reference electrode, a graphite rod is an auxiliary electrode, and electrocatalytic oxygen evolution reaction is carried out by carrying out linear sweep voltammetry in a 1.0mol/L KOH solution. Voltage scan range: 1.0 to 1.5(V vs Ag/AgCl). The iR compensation formula is E-iR × 90%.

Along with the positive increase of the voltage, the current density begins to increase, bubbles are generated on the surface of the working electrode, and the occurrence of the electrocatalytic oxygen evolution reaction is proved. The results of the experiment are shown in FIGS. 17 and 18, at a current density of 10mAcm^-2In alkaline condition, RuO₂The overpotential η for hydrogen evolution at the electrode was 265mV, and the overpotential η for the catalyst electrodes of examples 1 to 3 were 255mV, 270mV, and 342mV, respectively. The overpotential η of the catalyst electrodes of comparative examples 1 to 3 were 692mV, 344mV, and 415mV, respectively. Example 1 oxygen evolution overpotential ratio of catalyst electrode commercial RuO₂The electrode has lower oxygen evolution overpotential and better performance.

The catalyst obtained in the embodiment 1 to the embodiment 3 contains ruthenium and ruthenium oxide double-activity sites, and has poor catalytic activity, so that the performance of HER and OER cannot be ensured to have better performance. In comparative example 3, where the ratio of calcium carbonate to aerogel was 1:10, the final product did not allow the hydrogen and oxygen evolution properties of the catalyst to be improved simultaneously.

To sum up, the oxidizing agent calcium carbonate is added, the ratio of calcium carbonate to aerogel is set to be 1:2-5, the finally obtained ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material has double active sites, and the hydrogen evolution performance and the oxygen evolution performance are improved at the same time.

Experimental example 3

Stability test of hydrogen evolution and oxygen evolution by electrolyzed water

Using the catalyst prepared in example 1 as a working electrode (the electrode preparation method is the same as in example 1), Ag/AgCl as a reference electrode, and a graphite rod as an auxiliary electrode, a constant voltage stability test of electrolyzed water was performed in a KOH solution of 1.0mol/L, that is, a constant current density of 10mAcm was set^-2(OER 10 mAcm)^-2HER is-10 mAcm^-2) The change in voltage at the working electrode is measured. As shown in fig. 19, the OER and HER tests each for 10h showed almost constant working electrode voltage at constant current density, indicating that the catalyst obtained in example 1 has good stability during the hydrogen evolution and oxygen evolution reaction.

The invention provides a ruthenium/ruthenium oxide modified doped graphene three-dimensional composite material, which is characterized in that N element doping is introduced into graphene, so that the conductivity of a catalyst is increased, the polarization in the electrocatalytic reaction process is reduced, and the overpotential of the reaction is reduced; the graphene three-dimensional structure has a large specific surface area, so that the contact area of the catalyst and the electrolyte is increased, the mass transfer process is promoted, and the reaction activity is increased; the metal ruthenium and the ruthenium oxide nucleate and grow on the nitrogen-doped graphene to form a bifunctional active site, so that the ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material is obtained, and the HER performance and the OER performance are improved. No matter hydrogen and oxygen are separated under an acidic condition or under an alkaline condition, the catalytic effect is lower than the reaction overpotential of the current commercial electrocatalyst, and the performance is better; and under the alkaline condition, the hydrogen evolution and oxygen evolution processes of the catalyst have good stability.

The above embodiments are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited thereby, and any insubstantial changes and substitutions made by those skilled in the art based on the present invention are within the protection scope of the present invention.

Claims (7)

1. The ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material is characterized by being prepared from RuCl₃·3H₂And performing hydrothermal reaction on the O, the graphene oxide and the polypyrrole in deionized water to obtain aerogel, and oxidizing the aerogel and the calcium carbonate to obtain a final product.

2. The ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material according to claim 1, wherein the mass ratio of calcium carbonate to aerogel is 1: 2-5.

3. The ruthenium/ruthenium oxide-modified nitrogen-doped graphene three-dimensional composite material of claim 1, wherein the RuCl is₃·3H₂The mass ratio of the O to the graphene oxide is 1: 2-6.

4. The ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material according to claim 1, wherein the mass ratio of polypyrrole to graphene oxide is 1: 1-10.

5. The ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material according to claim 1, wherein the ratio of the mass mg of graphene oxide to the volume mL of deionized water is 1: 0.25-2.

6. The method for preparing the ruthenium/ruthenium oxide modified nitrogen-doped graphene three-dimensional composite material according to any one of claims 1 to 5, comprising the following steps:

1) adding RuCl₃·3H₂Adding O, graphene oxide and polypyrrole into deionized water, ultrasonically oscillating and dispersing for 1-5h, and carrying out hydrothermal reaction for 10-20h at the temperature of 100-200 ℃ to obtain aerogel;

2) roasting the aerogel obtained in the step 1) and calcium carbonate at the temperature of 500-900 ℃ for 1-4h to obtain a final product.

7. The use of the ruthenium/ruthenium oxide-modified nitrogen-doped graphene three-dimensional composite material according to any one of claims 1 to 5 as a catalyst for electrocatalytic decomposition of water.

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