阅读说明：本技术 一种可调控型蛋黄-壳结构氮碳掺杂硫化钴钼对电极催化剂的制备方法 (Preparation method of adjustable and controllable yolk-shell structure nitrogen-carbon-doped cobalt molybdenum sulfide counter electrode catalyst ) 是由 钱兴 杨家辉 于 2019-10-12 设计创作，主要内容包括：本发明公开了一种可调控型蛋黄-壳结构的氮碳掺杂硫化钴钼NC-CoS<Sub>2</Sub>@Co-MoS<Sub>2</Sub>催化剂的制备方法。将硫化铵和钼酸铵溶解在水中,加入氨水后油浴反应,制得的溶液加入到ZIF-67多面体分散液中,混合后搅拌得到中间体ZIF-67@Co-MoS<Sub>2</Sub>；再将中间体进一步高温硫化,得到具有蛋黄-壳结构的NC-CoS<Sub>2</Sub>@Co-MoS<Sub>2</Sub>催化剂。该方法通过调控特定的反应时间和反应质量比来控制外壳厚度、内核大小以及蛋黄-壳的间距,从而形成不同形貌结构的催化剂来达到不同的催化效果。制备所得催化剂具有高的比表面积、孔隙率以及良好的电催化性能,用于染料敏化太阳能电池,其光电转化效率达到9.38％。(The invention discloses a nitrogen-carbon doped cobalt molybdenum sulfide NC-CoS with a controllable yolk-shell structure 2 @Co‑MoS 2 A method for preparing the catalyst. Dissolving ammonium sulfide and ammonium molybdate in water, adding ammonia water, carrying out oil bath reaction, adding the prepared solution into ZIF-67 polyhedron dispersion liquid, mixing, and stirring to obtain an intermediate ZIF-67@ Co-MoS 2 (ii) a Then the intermediate is further vulcanized at high temperature to obtain NC-CoS with a yolk-shell structure 2 @Co‑MoS 2 A catalyst. The method controls the shell thickness, the inner core size and the yolk-shell spacing by regulating and controlling specific reaction time and reaction mass ratio, thereby forming catalysts with different morphological structures to achieve different catalytic effects. The prepared catalyst has high specific surface area and poresThe porosity and good electrocatalysis performance are achieved, and the photoelectric conversion efficiency of the dye-sensitized solar cell is 9.38%.)

1. Nitrogen-carbon-doped cobalt molybdenum sulfide catalyst NC-CoS with adjustable yolk-shell structure₂@Co-MoS₂The preparation method is characterized by comprising the following steps:

1) Respectively dissolving cobalt nitrate hexahydrate and 2-methylimidazole in methanol at room temperature under normal pressure, mixing the two solutions, stirring uniformly, standing for 24 hours, and centrifugally drying to obtain a purple precipitate ZIF-67 polyhedron;

2) Dissolving ammonium molybdate and 20wt% ammonium sulfide solution in water, adding a certain amount of ammonia water, and reacting for a period of time under the condition of oil bath to obtain ammonium thiomolybdate solution;

3) Ultrasonically dispersing ZIF-67 polyhedron in ethanol, mixing with the ammonium thiomolybdate solution obtained in the step 2), stirring for reacting for a period of time, and centrifugally drying to obtain ZIF-67@ Co-MoS₂An intermediate;

4) The resulting ZIF-67@ Co-MoS₂Putting the intermediate and a certain amount of sulfur powder into a porcelain boat, and carrying out high-temperature calcination in a tube furnace to carry out secondary vulcanization on the catalyst to obtain the NC-CoS with the yolk-shell structure₂@Co-MoS₂A catalyst.

2. The preparation method according to claim 1, wherein the mass ratio of the cobalt nitrate hexahydrate to the 2-methylimidazole in the step 1) is 1:1 ~ 1.5.5, and the volume of the added methanol is 100 ml of methanol per gram of the cobalt nitrate hexahydrate and 100 ml of methanol per gram of the 2-methylimidazole.

3. The preparation method according to claim 1, wherein the volume ratio of the ammonia water to the 20wt% ammonium sulfide solution in the step 2) is 1:10 ~ 15, and the mass of ammonium molybdate is 10 ~ 15 mg of ammonium molybdate added for every 100 μ L of the 20wt% ammonium sulfide solution.

4. The method according to claim 1, wherein the volume of water in step 2) is 5mL per 45 mg of ammonium molybdate, the oil bath temperature is 50 ~ 80 ℃, and the reaction time is 0.5 ~ 1 h.

5. The method of claim 1, wherein the mass ratio of the ZIF-67 polyhedra to ammonium molybdate in step 3) is 1:0.15 ~ 1.5.5, the volume of ethanol added is 100 ml ethanol per 300 mg ZIF-67 polyhedra, and the reaction time is 0.5 ~ 2 h.

6. The method of claim 1, wherein step 4) is performed using ZIF-67@ Co-MoS₂The mass ratio of the intermediate to the sulfur powder is 1:2 ~ 4.

7. The preparation method of claim 1, wherein the tube furnace reaction temperature in the step 4) is 300 ~ 500 ℃, the holding reaction time is 1.5 ~ 3 h, and the heating rate is 1.5 ~ 3 ℃/min.

8. A controlled yolk-shell structured NC-CoS product prepared by the method of claim 1₂@Co-MoS₂The catalyst is applied to a counter electrode of a dye-sensitized solar cell.

Technical Field

The invention belongs to the field of material preparation, and particularly relates to a nitrogen-carbon-doped cobalt molybdenum sulfide catalyst NC-CoS with a controllable yolk-shell structure₂@Co-MoS₂The preparation method of (1).

Background

Based on the excessive development and consumption of fossil energy in the last century and the gradual deterioration of the environment, the development of a green energy conversion device has become a hot topic in recent decades. Among all renewable clean energy sources, solar energy is the most utilized. The solar energy has universality, and the utilization of the solar energy can be carried out in any place in the world where the sunlight can be irradiated; and the utilization of solar energy does not cause any secondary pollution, which also makes it one of the most environmentally-friendly available energy sources today. The high-efficiency utilization of solar energy can thoroughly change the existing energy utilization mode, and the society of people can enter a new era of pollution-free energy conservation.

In 1991, Gr ä tzel et al reported a new Solar energy conversion device named Dye Sensitized Solar Cell (DSSC). in the next few years, the photoelectric conversion efficiency of DSSC has been increasing, and it is likely to replace silicon-based cells to become the leading of Solar cells.

The DSSC consists of three parts of a sandwich-like structure, namely a counter electrode, an electrolyte and TiO loaded with dye₂And a photo-anode. The counter electrode is an important component of the DSSC, and the noble metal platinum (Pt) is widely applied to the DSSC as an industrial counter electrode material. Pt has good charge transfer and electrocatalytic capability and is used for catalyzing I₃ ^–/I^–Redox reaction of ion pair. However, large-scale commercial application of DSSCs is limited due to the scarce and expensive Pt reserves. Therefore, it has become the research direction to find a non-noble metal catalyst with higher catalytic activity and lower price to replace the noble metal Pt.

In recent years, various non-noble metal catalysts have been found to be useful for electrocatalysis of counter electrodes, such as carbon materials, alloy materials, composite materials and conductive polymer materials, each of which has advantages and disadvantages. For example, carbon materials have excellent catalytic activity and good corrosion resistance. But also has certain drawbacks: firstly, the carbon material is black and opaque, so that light is blocked from entering the battery, and the efficiency of the battery is greatly reduced; secondly, the carbon material has poor adhesion and is easy to fall off from the conductive glass to cause short circuit of the DSSC cell.

Among a plurality of materials, the ZIF-67 polyhedron has better chemical stability and thermal stability, can be used as a template agent, can also provide Co, N and C elements, and still keeps the shape of the polyhedron after being heated. In addition, the ZIF-67 polyhedron also has the advantages of high porosity, large specific surface area and the like, and is widely applied to preparation of an electrocatalytic material of DSSC. Additionally, transition metal chalcogenides such as MoS₂、CoS₂、CoS、FeS、NiS₂The electrochemical performance is more prominent due to the cheap price and excellent electrocatalytic activity, particularly those transition metal sulfides with yolk-shell structures. The catalyst nanoparticles are small in size, and the yolk-shell structure causes gaps in the nanoparticles, so that the specific surface area is increased, more active sites are exposed, more ion channels are provided, and the catalyst nanoparticles are expected to be a substitute for Pt in a DSSC counter electrode.

disclosure of Invention

The invention aims to provide a controllable yolk-shell structure nitrogen-carbon doped cobalt molybdenum sulfide catalyst (NC-CoS) with simple process and low cost₂@Co-MoS₂) The preparation method is used for replacing a noble metal Pt catalyst in the DSSC. The method has the advantages of simple synthesis process and easy operation, and the synthesized catalyst nanoparticles have small size, large specific surface area, controllable morphology and high catalytic activity.

In order to achieve the purpose, the invention adopts the following technical scheme:

A preparation method of a controllable yolk-shell structure nitrogen-carbon doped cobalt molybdenum sulfide catalyst is characterized by comprising the following steps:

1) Respectively dissolving cobalt nitrate hexahydrate and 2-methylimidazole in methanol at room temperature under normal pressure, mixing the two solutions, stirring uniformly, standing for 24 hours, and centrifugally drying to obtain a purple precipitate ZIF-67 polyhedron;

2) Dissolving ammonium molybdate and 20wt% ammonium sulfide solution in water, adding a certain amount of ammonia water, and reacting for 0.5 ~ 1 h under the condition of 50 ~ 80 ℃ oil bath to obtain ammonium thiomolybdate solution;

3) Ultrasonically dispersing ZIF-67 polyhedron in ethanol, mixing with the ammonium thiomolybdate solution obtained in the step 2), stirring for reacting for a period of time, and centrifugally drying to obtain ZIF-67@ Co-MoS₂An intermediate;

4) The resulting ZIF-67@ Co-MoS₂putting the intermediate and a certain amount of sulfur powder into a porcelain boat, calcining in a tubular furnace at 300 ~ 500 ℃ to carry out secondary vulcanization on the catalyst, and keeping the temperature for reaction for 1.5 ~ 3 h to obtain the NC-CoS with the yolk-shell structure₂@Co-MoS₂A catalyst.

The mass ratio of the cobalt nitrate hexahydrate and the 2-methylimidazole in the step 1) is 1:1 ~ 1.5.5, the volume of the added methanol is 100 ml of methanol corresponding to each gram of the cobalt nitrate hexahydrate, and 100 ml of methanol corresponding to each gram of the 2-methylimidazole.

The volume ratio of the ammonia water to the 20wt% ammonium sulfide solution in the step 2) is 1:10 ~ 15, the mass of ammonium molybdate is 10 ~ 15 mg of ammonium molybdate added to each 100 mu L of 20% ammonium sulfide solution, and the volume of water is 5mL of water to each 45 mg of ammonium molybdate.

The mass ratio of the ZIF-67 polyhedron to the ammonium molybdate in the step 3) is 1:0.15 ~ 1.5.5, the volume of the added ethanol is 100 ml of ethanol corresponding to each 300 mg of the ZIF-67 polyhedron, and the reaction time is 0.5 ~ 2 h.

Step 4) the ZIF-67@ Co-MoS₂The mass ratio of the intermediate to the sulfur powder is 1:2 ~ 4.

The obtained NC-CoS with the yolk-shell structure₂@Co-MoS₂The catalyst can be used for preparing a counter electrode of a dye-sensitized solar cell (DSSC).

NC-CoS₂@Co-MoS₂The mechanism of catalyst formation is explained as an etch/ion exchange process. The precursor ZIF-67 polyhedron is subjected to etching reaction with ammonium molybdate and ammonium thiomolybdate generated by ammonium sulfide under the condition of ammonia water, and Co in the ZIF-67 polyhedron²⁺Ions are gradually diffused to the edge, and are etched on the outer surface to generate Co-MoS with sulfur ions₂Shell to form intermediate ZIF-67@ Co-MoS₂. Secondary sulfurization through a tube furnace, intermediate ZIF-67@ Co-MoS₂By formation of nitrogen-carbon doped CoS₂A part of Co²⁺Continued CoS Generation at the Shell₂And finally forming the NC-CoS of the yolk-shell structure₂@Co-MoS₂A catalyst. As the reaction time increased, the interior of ZIF-67 lost Co²⁺The more ions, the smaller the core and the larger the gap with the shell. Wherein, the shape of the obtained catalyst can be regulated and controlled by accurately controlling the reaction time and the mass ratio of reactants. The reaction degree can be deepened by increasing the amount of ammonium molybdate and ammonium sulfide or prolonging the reaction time, the prepared catalyst has smaller kernel and larger space between the yolk and the shell, and even a hollow shell structure (Co-MoS) can be obtained₂). On the contrary, the amount of ammonium molybdate and ammonium sulfide is reduced or the reaction time is shortened, the obtained catalyst core is larger, the core is tightly attached to the shell, the gap is smaller, but the structure is more stable and firmer, so that the service life of the catalyst is prolonged. If the reaction is excessive, serious morphology breakage and shell collapse and fragmentation can be caused; if the reaction time is too short, the ZIF-67 polyhedron is not enough to be etched into an egg yolk-shell structure, and a formed sulfide shell is easy to fall off, so that the specific surface area and the active sites of the catalyst are seriously influenced, and the electrochemical catalytic performance is greatly reduced. Therefore, the specific mass ratio of the reactants and the reaction time regulate the morphology structure of the catalyst, and further control the catalytic activity of the catalyst.

The shape of the nitrogen-carbon-doped cobalt molybdenum sulfide catalyst with the adjustable and controllable yolk-shell structure keeps the shape of a ZIF-67 polyhedron, a spherical inner core of the nitrogen-carbon-doped cobalt disulfide is arranged inside the catalyst, a certain gap is reserved between the inner core and the outer shell, and the outer shell is the cobalt disulfide/molybdenum disulfide.

drawings

FIG. 1 is a ZIF-67@ Co-MoS polyhedral from example 2₂intermediates and NC-CoS₂@Co-MoS₂SEM image of catalyst. (a) (b) (c) is ZIF-67 polyhedron, (d) (e) (f) is ZIF-67@ Co-MoS₂Intermediate, (g) (h) (i) is NC-CoS₂@Co-MoS₂SEM image of catalyst.

FIG. 2 shows NC-CoS obtained in example 2 and example 3₂@Co-MoS₂TEM images of the catalyst. Wherein (a) and (b) are the NC-CoS prepared in example 2₂@Co-MoS₂Catalyst, (c) (d) is NC-CoS prepared in example 3₂@Co-MoS₂TEM images of the catalyst.

FIG. 3 shows the hollow Co-MoS obtained in example 6₂TEM images of the catalyst.

FIG. 4 shows NC-CoS obtained in example 2₂@Co-MoS₂XRD pattern of catalyst.

FIG. 5 shows NC-CoS obtained in example 2₂@Co-MoS₂Catalyst and hollow Co-MoS prepared in example 6₂Aperture distribution map of and N₂Adsorption and desorption curves.

FIG. 6 shows the results obtained using NC-CoS prepared in example 2₂@Co-MoS₂Catalyst, hollow Co-MoS prepared in example 6₂And Pt counter electrode to form DSSCJ-VCurve and photovoltaic parameters of the counter electrode prepared from the three materials.

FIG. 7 shows the NC-CoS obtained in example 2₂@Co-MoS₂Catalyst, hollow Co-MoS prepared in example 6₂And a Pt counter electrode are assembled into a cyclic voltammogram of the DSSC.

FIG. 8 shows the NC-CoS obtained in example 2₂@Co-MoS₂Catalyst, hollow Co-MoS prepared in example 6₂And the Pt counter electrode are assembled into a polarization curve of the DSSC.

FIG. 9 shows NC-CoS obtained in example 2₂@Co-MoS₂Catalyst, hollow Co-MoS prepared in example 6₂And Pt counter electrode.

Detailed Description

The present invention will be described in detail with reference to specific examples, but the use and purpose of these examples are merely to illustrate the present invention, and the present invention is not limited to the actual scope of the present invention in any form, and the present invention is not limited to these.