CN113136591B

CN113136591B - Ruthenium and nitrogen co-doped porous carbon catalyst, preparation method thereof and application thereof in hydrogen electrolysis

Info

Publication number: CN113136591B
Application number: CN202110441290.3A
Authority: CN
Inventors: 谢建晖; 李懿君; 刘慧婧; 潘运玲; 李兵
Original assignee: Hefei University of Technology
Current assignee: Hefei University of Technology
Priority date: 2021-04-23
Filing date: 2021-04-23
Publication date: 2022-07-12
Anticipated expiration: 2041-04-23
Also published as: CN113136591A

Abstract

The invention discloses a ruthenium and nitrogen codoped porous carbon catalyst, a preparation method thereof and application thereof in hydrogen electrolysis. The catalyst has high-efficiency hydrogen evolution activity, lasting stability and wide application prospect.

Description

Ruthenium and nitrogen co-doped porous carbon catalyst, preparation method thereof and application thereof in hydrogen electrolysis

Technical Field

The invention belongs to the field of electrochemistry, relates to a preparation method of an electrocatalyst applied to an electrochemical hydrogen evolution reaction, and particularly relates to a preparation method of a ruthenium and nitrogen co-doped porous carbon catalyst.

Background

The hydrogen is not only an important industrial raw material, but also a clean energy and a good energy carrier, can meet the requirements of long period and large capacity of electrochemical energy storage and heat storage, and effectively ensures the safe and stable operation of a future high-proportion renewable energy system. The development prospect of hydrogen energy is wide, but the production of hydrogen mainly depends on non-renewable fossil energy sources, such as methane steam reforming, water gas shift and the like. The shortage of fossil energy and the environmental pollution caused by it compel people to find environmentally friendly renewable energy sources for producing hydrogen. Renewable energy sources such as wind energy, water energy and solar energy can provide abundant electric power, and hydrogen is produced by electrolyzing water by using the electric power, so that pollution-free production of hydrogen and storage of the renewable energy sources can be realized.

The water electrolysis process involves two electrode reactions, oxidation and reduction of water, and therefore requires an oxygen evolution catalyst and a hydrogen evolution catalyst to catalyze the oxidation and reduction of water, respectively. In view of the fact that the existing oxygen evolution catalysts only show good catalytic performance and stability under alkaline conditions, the development of hydrogen evolution catalysts under alkaline conditions is needed to complete water decomposition reaction together with the oxygen evolution catalysts. However, the non-noble metal hydrogen evolution catalyst under basic conditions is subject to a water dissociation step, and the catalytic activity and stability are still poor. Although platinum-based electrocatalysts have excellent hydrogen evolution catalytic activity and stability under alkaline conditions, the expensive cost and shortage of platinum metal reserves greatly limit the large-scale application of platinum metals. Therefore, the development of other alkaline hydrogen evolution catalysts with low cost and good performance is urgently needed.

Ruthenium metal not only can well catalyze water dissociation, but also is cheaper than platinum, so that the ruthenium metal is expected to be used for designing an excellent ruthenium-based alkaline hydrogen evolution catalyst. On the other hand, porous carbon materials are widely used as a framework of various metal catalysts due to their excellent electrical conductivity, large specific surface area, and good corrosion resistance. However, the directly supported metal often falls off or accumulates during the catalytic reaction. The ruthenium-carbon composite material prepared by the ruthenium complex precursor is beneficial to obtaining a catalyst with strong interaction of metal carriers, so that the stability and catalytic activity of the obtained catalyst are improved.

Disclosure of Invention

The invention aims to provide a preparation method of a ruthenium and nitrogen co-doped porous carbon catalyst which shows excellent hydrogen evolution performance under alkaline conditions.

The invention adopts the following technical scheme for realizing the purpose:

a preparation method of a ruthenium and nitrogen co-doped porous carbon catalyst is characterized by comprising the following steps: ruthenium salt and ethylene diamine tetraacetate are used as raw materials, are uniformly mixed in water and are stirred at room temperature for reaction, and then are dried in vacuum to obtain a ruthenium complex precursor; and pyrolyzing the ruthenium complex precursor at high temperature under the condition of inert gas, and then carrying out acid washing and drying to prepare the ruthenium and nitrogen co-doped porous carbon catalyst.

Preferably, the ruthenium salt is ruthenium trichloride, and the ethylenediamine tetraacetate (used as a ligand and a carbon source) is tetrasodium ethylenediamine tetraacetate tetrahydrate.

Preferably, the molar ratio of the ruthenium salt to the ethylenediamine tetraacetate is 1: 5-20, and preferably 1: 8-12.

Preferably, the stirring reaction time is 0.5-1 h.

Preferably, the inert gas is nitrogen or argon.

Preferably, the high-temperature pyrolysis temperature is 750-950 ℃ (preferably 800-900 ℃) and the time is 1-4 h.

Preferably, the acid washing is to add the material into sulfuric acid with the concentration of 0.05-1M and stir for 12 hours, and preferably sulfuric acid with the concentration of 0.1-0.5M.

In the ruthenium and nitrogen co-doped porous carbon catalyst obtained by the preparation method, the nitrogen doping amount is 3-4% and the ruthenium doping amount is 15-25%, the catalyst can be used as an electrochemical hydrogen evolution catalyst in electrochemical reaction, and the catalyst has excellent electrochemical hydrogen evolution effect and stability under alkaline conditions.

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

1. according to the invention, the ruthenium and nitrogen co-doped porous carbon catalyst is prepared by taking the ruthenium complex containing the ethylene diamine tetraacetate ligand as a precursor for the first time, and the ruthenium atom can be anchored due to the chelation of the ligand, so that the dispersion degree of ruthenium is improved, the agglomeration of the ruthenium atom is limited, a small ruthenium nano cluster is obtained, and the activity and the stability of the catalyst are improved.

2. In the pyrolysis process of the precursor ruthenium complex, the ruthenium metal center can catalyze the pyrolysis process of the ligand, and the finally obtained carbon material has a porous honeycomb shape which has large specific surface area and porosity and is beneficial to improving and exposing more catalytic active sites. Meanwhile, the ruthenium complex precursor pyrolysis method adopted by the invention can ensure that the carbon skeleton and the ruthenium metal nanoparticles simultaneously form the structure of the carbon-coated metal nanoparticles in situ, thereby limiting the aggregation of the ruthenium metal nanoparticles and improving the stability of the ruthenium metal nanoparticles.

3. The synthesis process is simple, has good repeatability and is easy for large-scale production.

4. The ruthenium and nitrogen co-doped porous carbon catalyst prepared by the invention has high-efficiency hydrogen evolution activity, and also has lasting stability, even superior to that of a commercial Pt/C catalyst.

Drawings

FIG. 1 is a Scanning Electron Microscope (SEM) image of the ruthenium and nitrogen co-doped porous carbon catalyst obtained in example 1;

FIG. 2 is an X-ray photoelectron spectrum (XPS) of the ruthenium and nitrogen co-doped porous carbon catalyst obtained in example 1;

FIG. 3 is an X-ray diffraction pattern (XRD) of the ruthenium and nitrogen co-doped porous carbon catalyst obtained in example 1;

FIG. 4 is a linear sweep voltammogram of hydrogen evolution in alkali for the ruthenium and nitrogen co-doped porous carbon catalyst and the commercial platinum carbon catalyst obtained in example 1;

FIG. 5 is a stability test curve of hydrogen evolution current-time (i-t) of the ruthenium and nitrogen co-doped porous carbon catalyst obtained in example 1 in alkali;

FIG. 6 is a linear sweep voltammogram of hydrogen evolution in alkali of the ruthenium and nitrogen co-doped porous carbon catalyst obtained in example 2;

FIG. 7 is a linear sweep voltammogram of hydrogen evolution in alkali of the ruthenium and nitrogen co-doped porous carbon catalyst obtained in example 3.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. The following disclosure is merely exemplary and illustrative of the inventive concept, and those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

The chemicals used in the following examples were all chemically pure and were freely available in the market.

Example 1

(1) 20.7mg (1mmol) of ruthenium trichloride and 452mg (10mmol) of tetrasodium ethylenediaminetetraacetate tetrahydrate were added to 10mL of water, respectively, and dissolved by sonication at room temperature, followed by stirring for 0.5 h. And (3) completely evaporating the solvent of the reaction solution by using a rotary evaporator, and finally placing the residual solid in a vacuum drying oven at 60 ℃ for vacuum drying for 12h to obtain the ruthenium complex precursor.

(2) And (3) under the protection of inert gas argon, heating the precursor obtained in the step (1) to 850 ℃ at the speed of 5 ℃/min in a tube furnace, pyrolyzing for 2h at constant temperature, and naturally cooling to room temperature.

(3) Subjecting the product obtained in the step (2)The black granular product was ground to a powder and dispersed in 0.5M H₂SO₄Stirring for 12h at a medium room temperature, cleaning with deionized water, and vacuum drying to obtain the ruthenium and nitrogen co-doped porous carbon catalyst.

The catalyst obtained in this example had a specific surface area of 452.916m²g^-1Pore volume of 0.766cm³g^-1。

The catalyst obtained in this example had a ruthenium mass doping amount of 22.7% and a nitrogen mass doping amount of 3.3%.

The SEM image of the catalyst obtained in the example is shown in FIG. 1, and the product can be seen to have a honeycomb-shaped porous carbon morphology.

The XPS chart of the catalyst obtained in this example is shown in fig. 2, and it can be seen that the catalyst contains Ru, C, N and O elements.

The XRD pattern of the catalyst obtained in this example is shown in FIG. 3, and it can be seen that the pattern includes a metallic ruthenium peak.

The catalyst obtained in this example was subjected to electrochemical tests as follows:

and taking 2mg of the obtained catalyst, adding 500 mu L of methanol and 20 mu L of a liquid-phase solvent, performing ultrasonic treatment for 5min to uniformly disperse the catalyst, transferring 10 mu L of the catalyst on the surface of a glassy carbon electrode by using a liquid transfer gun, and drying the catalyst at room temperature. The electrode is used as a working electrode, saturated calomel is used as a reference electrode, a graphite rod is used as a counter electrode, the electrolyte is 1M KOH, and the reaction temperature is 25 ℃ at room temperature.

1M KOH solution was saturated with argon and 5mV S^-1Electrochemical LSV testing was performed at rates ranging from-0.9 to-1.6V voltage window, followed by 10mAcm^-2Stability testing was performed at current density. As can be seen from FIG. 4, the catalyst obtained in this example (molar ratio of ruthenium trichloride to tetrasodium ethylenediaminetetraacetate tetrahydrate of 1:10) was reacted with commercial Pt-C (20 wt%) (commercial carbon catalyst containing 20% by mass of platinum) at 10mA/cm²The overpotentials at the current density were 14mV and 17mV, respectively, and it was found that the catalyst obtained in this example was superior in hydrogen evolution performance and superior to the commercial platinum-carbon catalyst. The time-current stability test (it) records that the experimental current changes along with the time within 14h under a certain potential (-1.08V)Change the situation. As can be seen from fig. 5, the current did not fluctuate greatly with the lapse of time within 14 hours, thus indicating that the catalyst obtained in this example is very stable in properties.

Example 2

This example prepared a ruthenium-doped porous carbon electrocatalyst in the same manner as in example 1, except that the amount of the raw material tetrasodium ethylenediaminetetraacetate tetrahydrate in step (1) was changed to 226mg (5 mmol).

The electrocatalyst obtained in this example was electrochemically tested in the same manner as in example 1.

As shown in FIG. 6, the catalyst of this example reached 10mAcm in 1M KOH at room temperature^-2The current density required 75mV overpotential.

Example 3

This example prepared a ruthenium-doped porous carbon electrocatalyst in the same manner as in example 1, except that the amount of tetrasodium ethylenediaminetetraacetate tetrahydrate as the raw material in step (1) was changed to 678mg (15 mmol).

As shown in FIG. 7, the catalyst of this example reached 10mAcm in 1M KOH at room temperature^-2The current density required 95mV overpotential.

The present invention is not limited to the above exemplary embodiments, and any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The preparation method of the ruthenium and nitrogen co-doped honeycomb porous carbon catalyst is characterized by comprising the following specific steps:

(1) adding 1mmol of ruthenium trichloride and 10mmol of tetrasodium ethylene diamine tetraacetate tetrahydrate into 10mL of water, ultrasonically dissolving at room temperature, and then stirring for reacting for 0.5 h; completely evaporating the solvent of the reaction solution by using a rotary evaporator, and finally placing the residual solid in a vacuum drying oven at 60 ℃ for vacuum drying for 12h to obtain a ruthenium complex precursor;

(2) under the protection of inert gas argon, heating the precursor obtained in the step (1) to 850 ℃ at the speed of 5 ℃/min in a tube furnace, carrying out constant-temperature pyrolysis for 2h, and then naturally cooling to room temperature;

(3) grinding the black granular product obtained in the step (2) into powder, and dispersing in 0.5M H₂SO₄Stirring for 12h at a medium room temperature, cleaning with deionized water, and vacuum drying to obtain the ruthenium and nitrogen co-doped honeycomb porous carbon catalyst.

2. The ruthenium and nitrogen co-doped honeycomb porous carbon catalyst obtained by the preparation method of claim 1.

3. The application of the ruthenium and nitrogen co-doped honeycomb porous carbon catalyst in the electrolytic hydrogen evolution according to claim 2 is characterized in that: the catalyst is used as an electrochemical hydrolysis hydrogen evolution catalyst.

4. Use according to claim 3, characterized in that: the ruthenium and nitrogen co-doped honeycomb porous carbon catalyst shows excellent electrocatalytic hydrogen evolution performance under an alkaline condition.