CN112466668B - Tungsten sulfide-doped cobalt sulfide copper counter electrode catalyst with hollow nanotube structure and preparation method and application thereof - Google Patents

Tungsten sulfide-doped cobalt sulfide copper counter electrode catalyst with hollow nanotube structure and preparation method and application thereof Download PDF

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CN112466668B
CN112466668B CN202011399048.6A CN202011399048A CN112466668B CN 112466668 B CN112466668 B CN 112466668B CN 202011399048 A CN202011399048 A CN 202011399048A CN 112466668 B CN112466668 B CN 112466668B
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cuco
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ethanol
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钱兴
黄杰
杨亚杰
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Fuzhou University
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Abstract

The invention discloses a tungsten sulfide doped cobalt copper sulfide counter electrode catalyst (CuCo) with a hollow nanotube structure2S4/WS2) Compared with single metal sulfide, the catalyst has richer oxygenA redox couple and more excellent conductivity, and is doped with WS2A large number of active sites are provided; meanwhile, the hollow structure provides a larger specific surface area and more exposed active sites, the larger void space of the hollow structure can also effectively reduce the ion migration resistance, so that the electrochemical performance is more excellent, the photoelectric conversion efficiency reaches 9.50 percent when the hollow structure is applied to a counter electrode of the DSSC, and the I & lt/EN & gt3 −/I−The electrolyte system has good electrochemical stability, and the photoelectric conversion efficiency can still keep 88.3% of the initial value after 1000 times of continuous cyclic voltammetry scanning.

Description

Tungsten sulfide-doped cobalt sulfide copper counter electrode catalyst with hollow nanotube structure and preparation method and application thereof
Technical Field
The invention belongs to the field of material preparation, and particularly relates to a tungsten sulfide-doped cobalt sulfide copper counter electrode catalyst CuCo with a hollow nanotube structure2S4/WS2And a preparation method and application thereof.
Background
Solar energy has a wide development prospect in various currently known renewable green energy sources due to its huge capacity, strong versatility, safety and environmental protection advantages. The dye-sensitized solar cell (DSSC) has the advantages of low cost, simple structure, environmental protection and the like, and is composed of a photoanode for absorbing dye and an electrolyte (containing I)3 −/I−Redox couple) and a counter electrode, which can convert solar energy into electrical energy. As an extremely important part of DSSC, the role of the counter electrode is to catalyze I in the electrolyte by collecting electrons from an external circuit3 −Reducing it to I−Thereby reducing and regenerating the dye in the oxidation state. In most cases, platinum (Pt) has abundant catalytically active sites, excellent electrical conductivity and excellent electron/ion mobility, and can be used as a conventional counter electrode catalyst. However, the problems of high cost, low reserves and susceptibility to corrosion in the electrolyte of Pt-based counter electrodes have limited their large-scale low-cost commercial use. Therefore, a great number of researchers have been studying economic efficiency and haveExcellent electrochemical performance and Pt-free catalysts that are chemically stable in the electrolyte, to replace the noble metal Pt and to promote the development of DSSCs.
The transition metal compound has great potential due to the outstanding electrochemical performance, and can be used as a substitute material of Pt in the DSSC. Among them, the monometallic sulfides have been widely studied and applied, for example, CoS2，CuS2，Cu2S，Co9S8And MoS2. Due to its sandwich structure like sandwich (S ‒ W ‒ S), large specific surface area and large number of exposed edge electrocatalytic active sites, WS2Also has very wide development prospect. In addition, bimetallic sulfides such as CuCo2S4The conductive material has the advantages of more abundant redox pairs, more excellent conductivity, excellent stability and the like, and is widely applied to the field of new energy. Meanwhile, the hollow structure is widely designed as a unique advanced structure of the DSSC due to its special structural characteristics. Such a structure with a larger specific surface area generally provides more exposed active sites for the catalyst, and its larger void space can also effectively reduce the ion migration resistance. Therefore, the multi-element transition metal sulfide catalyst with a hollow structure is expected to become a replaceable material of the noble metal Pt in the DSSC counter electrode.
Disclosure of Invention
The invention aims to prepare a tungsten sulfide-doped cobalt sulfide copper counter electrode catalyst (CuCo) with a hollow nanotube structure by a simple, feasible and low-cost method2S4/WS2) The catalyst prepared by the method has a stable hollow structure, higher specific surface area, porosity and electrocatalytic activity, and therefore, has good battery performance and electrochemical stability.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a preparation method of a tungsten sulfide-doped cobalt copper sulfide counter electrode catalyst with a hollow nanotube structure comprises the following steps:
1) dissolving polyvinylpyrrolidone (PVP) in ethanol, mixing the ethanol solution with ethanol solution of cobalt acetate and copper acetate, and carrying out water bath heating reaction at a certain temperature for a period of time to obtain Cu-Co nanotube precursor precipitate;
2) washing and drying the obtained Cu-Co nanotube precursor precipitate, dispersing the precipitate in ethanol, dissolving ammonium tetrathiotungstate in deionized water to obtain an aqueous solution, dropwise adding the aqueous solution into the ethanol solution containing the Cu-Co nanotube precursor, stirring at normal temperature and reacting for a period of time to obtain the Cu-CoWSx；
3) The obtained Cu-CoWSxAt H2Further calcining under the atmosphere of/Ar to obtain the tungsten sulfide doped cobalt copper sulfide CuCo with the hollow nano tube structure2S4/WS2A counter electrode catalyst;
further, the mass ratio of the cobalt acetate, the copper acetate and the PVP in the step 1) is 2:1: 8-12, the volume ratio of the dissolved PVP to the ethanol for dissolving the cobalt acetate and the copper acetate is 3:1, the water bath reaction temperature is 70-110 ℃, and the reaction time is 1-4 hours.
Further, the Cu-Co nanotube precursor precipitation of step 2) is mixed with (NH)4)2WS4The mass ratio of ethanol to deionized water is 0.5-3: 1, the volume ratio of ethanol to deionized water is 3-7: 1, and the reaction time of stirring at normal temperature is 0.5-2 h.
Further, the calcining temperature in the step 3) is 200-400 ℃, the heat preservation time is 1-2 hours, and the heating rate in the calcining process is 1-3 ℃/min.
The invention also discloses the application of the catalyst: the tungsten sulfide doped with cobalt copper sulfide CuCo in the hollow nanotube structure2S4/WS2The counter electrode catalyst can be used for preparing a counter electrode of a dye-sensitized solar cell (DSSC).
CuCo2S4/WS2The mechanism of formation of the hollow nanotube catalyst can be explained by the diffusion effect of different cationic and anionic species. Firstly, a rapid ion exchange process is utilized, and a Cu-Co nanotube precursor is used as a self-sacrifice template and (NH) used as a multifunctional vulcanizing agent4)2WS4Reacting to form an intermediate product Cu-CoWSxHollow nanotubes, and the evolution process of their hollow structure can be attributed toDiffusion effects from different cationic and anionic species. In the chemical conversion process, small ions are continuously diffused outwards from the precursor of the Cu-Co nanotube, so that the Cu-CoWS is drivenxStable growth of thin layers and as physical barriers to prevent external WS4 2‒With internal Co2+、Cu2+Direct chemical reaction between the two, leading the whole chemical conversion process to occur in the pre-formed Cu-CoWSxForming a hollow structure on the thin layer, and completely converting the precursor of the Cu-Co nanotube into Cu-CoWSxHollow nanotubes. The subsequent tube furnace calcination procedure, the purpose of which is to increase the crystallinity of the product and to form a new crystalline phase (CuCo)2S4And WS2) Finally successfully preparing CuCo2S4/WS2A hollow nanotube catalyst.
Has the advantages that: (1) the tungsten sulfide-doped cobalt sulfide copper counter electrode catalyst with the hollow nanotube structure synthesized by the method keeps the shape of the Cu-Co nanotube, and the inside of the catalyst is of a hollow structure. The catalyst shell is uniformly distributed with a proper amount of nano particles, which greatly enhances the specific surface area and also exposes more active sites. The hollow structure provides more ion exchange channels, and the internal gaps and the porous substances are more beneficial to the transmission and exchange of electrolyte ions, so that the hollow structure has more excellent electrocatalytic performance. At the same time, WS is doped2And a large number of active sites are provided, so that the electrocatalytic performance of the catalyst is enhanced. In addition, the catalyst is not protected by3 −/I−Corrosion or decomposition of the redox couple, in I3 −/I−The electrolyte system has good electrochemical stability. The synthetic raw materials of the tungsten sulfide-doped cobalt copper sulfide counter electrode catalyst with the hollow nanotube structure are cheap and easy to obtain, so that the catalyst has greater advantages compared with a Pt catalyst.
(2) The method has the advantages of mild and controllable operation conditions, short reaction time, low cost and easy large-scale production. Prepared hollow nanotube CuCo2S4/WS2The material has the advantages of high specific surface area, high porosity, good electrochemical performance, good electrochemical stability and the like, and is used for preparing the materialAs a counter electrode of a dye-sensitized solar cell, the photoelectric conversion efficiency can reach 9.50 percent, and the counter electrode is shown in the specification I3 −/I−The electrolyte system has good electrochemical stability, and the photoelectric conversion efficiency can still keep 88.3% of the initial value after 1000 times of continuous cyclic voltammetry scanning.
Drawings
FIG. 1 shows Cu-Co nanotubes and CuCo prepared in examples 6, 7 and 82S4/WS2Catalysts (respectively named CuCo)2S4/WS2-2/1，CuCo2S4/WS2-1/1 and CuCo2S4/WS2-1/2) in the SEM images, where (a) (b) is Cu-Co nanotubes and (c) (d) is CuCo prepared in example 62S4/WS2Catalyst-2/1, CuCo obtained in example 7 (e) - (g)2S4/WS2Catalyst 1/1, (h) (i) CuCo from example 82S4/WS2-1/2 catalyst;
FIG. 2 shows CuCo prepared in examples 6, 7 and 82S4/WS2-2/1，CuCo2S4/WS2-1/1 and CuCo2S4/WS2TEM image of-1/2 catalyst, (a) CuCo prepared in example 62S4/WS2Catalyst-2/1, (b) CuCo prepared in example 72S4/WS2Catalyst-1/1, (c) CuCo prepared in example 82S4/WS2-1/2 catalyst;
FIG. 3 shows CuCo prepared in examples 6, 7 and 82S4/WS2-2/1，CuCo2S4/WS2-1/1 and CuCo2S4/WS2-an XRD pattern of 1/2 catalyst;
FIG. 4 shows CuCo prepared in examples 6, 7 and 82S4/WS2-2/1，CuCo2S4/WS2-1/1 and CuCo2S4/WS2Pore size distribution of-1/2 catalyst and N2An adsorption-desorption curve;
FIG. 5 shows examples 6 and 7,8 prepared CuCo2S4/WS2-2/1，CuCo2S4/WS2-1/1 and CuCo2S4/WS2-1/2 Assembly of catalyst and Pt counter electrode into DSSCsJ-VCurve and photovoltaic parameters of the counter electrode prepared from the three materials;
FIG. 6 shows CuCo prepared for examples 6, 7 and 82S4/WS2-2/1，CuCo2S4/WS2-1/1 and CuCo2S4/WS2-1/2 cyclic voltammograms of catalyst and Pt counter electrode assembled into DSSCs;
FIG. 7 shows CuCo prepared for examples 6, 7 and 82S4/WS2-2/1，CuCo2S4/WS2-1/1 and CuCo2S4/WS2-1/2 polarization curves of DSSCs assembled by the catalyst and Pt counter electrode;
FIG. 8 shows CuCo prepared in examples 6, 7 and 82S4/WS2-2/1，CuCo2S4/WS2-1/1 and CuCo2S4/WS 21/2 electrochemical impedance curves of DSSCs assembled with a Pt counter electrode;
FIG. 9 shows CuCo obtained in examples 6, 7 and 82S4/WS 2100 continuous cyclic voltammograms of DSSCs assembled from the catalyst, (a) CuCo prepared in example 62S4/WS2Catalyst-2/1, (b) CuCo prepared in example 72S4/WS2Catalyst-1/1, (c) CuCo prepared in example 82S4/WS2-1/2 catalyst, (d) is a Pt counter electrode;
FIG. 10 is a graph of CuCo obtained in example 72S4/WS2-1/1 assembling DSSCs after 1000 continuous cyclic voltammetric scansJ-VA curve;
FIG. 11 is a graph of CuCo obtained in example 72S4/WS2-1/1 SEM images of DSSCs assembled after 1000 consecutive cyclic voltammetry scans.
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.
Example 1
Dissolving 2.4 g of PVP in 180 mL of ethanol to obtain a solution A; 600 mg of cobalt acetate and 300 mg of copper acetate were dissolved in 60 mL of an ethanol solution, and the resulting solution was solution B. And slowly pouring the solution B into the solution A, and stirring for 1 h in a water bath at 70 ℃ to obtain a Cu-Co nanotube precursor precipitate. Washing and drying the obtained Cu-Co nanotube precursor precipitate, dispersing 200 mg of the precipitate in 60 mL of ethanol, and then dispersing 300 mg (NH)4)2WS4Dissolving in 20 mL of deionized water; dripping the aqueous solution into the ethanol solution, stirring for 0.5 h at normal temperature, centrifuging, washing and drying to obtain the Cu-CoWSx. The obtained Cu-CoWSx150 mg of the powder was placed in a porcelain boat in H2Heating to 200 ℃ in a tube furnace under Ar atmosphere, preserving heat for 1 h at the heating rate of 1 ℃/min, and finally obtaining the tungsten sulfide doped cobalt copper sulfide CuCo with the hollow nanotube structure2S4/WS2A counter electrode catalyst.
Example 2
Dissolving 2.7 g of PVP in 180 mL of ethanol to obtain a solution A; 600 mg of cobalt acetate and 300 mg of copper acetate were dissolved in 60 mL of an ethanol solution, and the resulting solution was solution B. And slowly pouring the solution B into the solution A, and stirring for 1 h in a water bath at the temperature of 80 ℃ to obtain a Cu-Co nanotube precursor precipitate. Washing and drying the obtained Cu-Co nanotube precursor precipitate, dispersing 400 mg of the precipitate in 60 mL of ethanol, and then dispersing 300 mg of (NH)4)2WS4Dissolving in 15 mL of deionized water; dripping the aqueous solution into the ethanol solution, stirring for 1 h at normal temperature, centrifuging, washing and drying to obtain the Cu-CoWSx. The obtained Cu-CoWSx150 mg of the powder was placed in a porcelain boat in H2Heating to 200 ℃ in a tube furnace under Ar atmosphere, keeping the temperature for 1.5 h, and heating at the rate of 2 ℃/min to finally obtain the tungsten sulfide doped cobalt copper sulfide CuCo with the hollow nanotube structure2S4/WS2A counter electrode catalyst.
Example 3
Dissolving 3.0 g of PVP in 180 mL of ethanol to obtain a solution A; 600 mg of cobalt acetate and 300 mg of copper acetate were dissolved in 60 mL of an ethanol solution, and the resulting solution was solution B. And slowly pouring the solution B into the solution A, and stirring for 2 hours in a water bath at the temperature of 80 ℃ to obtain a Cu-Co nanotube precursor precipitate. Washing and drying the obtained Cu-Co nanotube precursor precipitate, dispersing 480 mg in 60 mL ethanol, and then dispersing 320 mg (NH)4)2WS4Dissolving in 12 mL of deionized water; dripping the aqueous solution into the ethanol solution, stirring for 0.5 h at normal temperature, centrifuging, washing and drying to obtain the Cu-CoWSx. The obtained Cu-CoWSx150 mg of the powder was placed in a porcelain boat in H2Heating to 200 ℃ in a tube furnace under Ar atmosphere, keeping the temperature for 1.5 h, and heating at the rate of 3 ℃/min to finally obtain the tungsten sulfide doped cobalt copper sulfide CuCo with the hollow nanotube structure2S4/WS2A counter electrode catalyst.
Example 4
Dissolving 3.3 g of PVP in 180 mL of ethanol to obtain a solution A; 600 mg of cobalt acetate and 300 mg of copper acetate were dissolved in 60 mL of an ethanol solution, and the resulting solution was solution B. And slowly pouring the solution B into the solution A, and stirring for 1 h in a water bath at the temperature of 90 ℃ to obtain a Cu-Co nanotube precursor precipitate. Washing and drying the obtained Cu-Co nanotube precursor precipitate, dispersing 800 mg of the precipitate in 60 mL of ethanol, and then dispersing 320 mg of (NH)4)2WS4Dissolving in 10 mL of deionized water; dripping the aqueous solution into the ethanol solution, stirring for 2 hours at normal temperature, centrifuging, washing and drying to obtain the Cu-CoWSx. The obtained Cu-CoWSx150 mg of the powder was placed in a porcelain boat in H2Heating to 300 ℃ in a tube furnace under Ar atmosphere, preserving heat for 1 h at the heating rate of 2 ℃/min, and finally obtaining the tungsten sulfide doped cobalt copper sulfide CuCo with the hollow nano tube structure2S4/WS2A counter electrode catalyst.
Example 5
Dissolving 3.6 g of PVP in 180 mL of ethanol to obtain a solution A; dissolving 600 mg of cobalt acetate and 300 mg of copper acetate in 60 mL of ethanol solution to obtain a solutionAnd (B) liquid. And slowly pouring the solution B into the solution A, and stirring for 2 hours in a water bath at the temperature of 110 ℃ to obtain a Cu-Co nanotube precursor precipitate. Washing and drying the obtained Cu-Co nanotube precursor precipitate, dispersing 960 mg of the precipitate in 60 mL of ethanol, and then dispersing 320 mg (NH)4)2WS4Dissolving in 9 mL of deionized water; dripping the aqueous solution into the ethanol solution, stirring for 1 h at normal temperature, centrifuging, washing and drying to obtain the Cu-CoWSx. The obtained Cu-CoWSx150 mg of the powder was placed in a porcelain boat in H2Heating to 400 ℃ in a tube furnace under Ar atmosphere, preserving heat for 2h at the heating rate of 2 ℃/min, and finally obtaining the tungsten sulfide doped cobalt copper sulfide CuCo with the hollow nano tube structure2S4/WS2A counter electrode catalyst.
Example 6
Dissolving 3.0 g of PVP in 180 mL of ethanol to obtain a solution A; 600 mg of cobalt acetate and 300 mg of copper acetate were dissolved in 60 mL of an ethanol solution, and the resulting solution was solution B. And slowly pouring the solution B into the solution A, and stirring for 2 hours in a water bath at the temperature of 85 ℃ to obtain a Cu-Co nanotube precursor precipitate. Washing and drying the obtained Cu-Co nanotube precursor precipitate, dispersing 320 mg in 60 mL ethanol, and then dispersing 160 mg (NH)4)2WS4Dissolving in 12 mL deionized water; dripping the aqueous solution into the ethanol solution, stirring for 1 h at normal temperature, centrifuging, washing and drying to obtain the Cu-CoWSx. The obtained Cu-CoWSx150 mg of the powder was placed in a porcelain boat in H2Heating to 350 ℃ in a tube furnace under Ar atmosphere, preserving the heat for 2 hours at the heating rate of 2 ℃/min, and finally obtaining the tungsten sulfide doped cobalt copper sulfide CuCo with the hollow nano tube structure2S4/WS2A counter electrode catalyst.
Example 7
Dissolving 3.0 g of PVP in 180 mL of ethanol to obtain a solution A; 600 mg of cobalt acetate and 300 mg of copper acetate were dissolved in 60 mL of an ethanol solution, and the resulting solution was solution B. And slowly pouring the solution B into the solution A, and stirring for 2 hours in a water bath at the temperature of 85 ℃ to obtain a Cu-Co nanotube precursor precipitate. Washing and drying the obtained Cu-Co nanotube precursor precipitate, dispersing 320 mg in 60 mL ethanol, and then dispersing 320 mg (NH)4)2WS4Dissolving in 12 mL deionized water; dripping the aqueous solution into the ethanol solution, stirring for 0.5 h at normal temperature, centrifuging, washing and drying to obtain the Cu-CoWSx. The obtained Cu-CoWSx150 mg of the powder was placed in a porcelain boat in H2Heating to 350 ℃ in a tube furnace under Ar atmosphere, preserving heat for 2h at the heating rate of 2 ℃/min, and finally obtaining the tungsten sulfide doped cobalt copper sulfide CuCo with the hollow nano tube structure2S4/WS2A counter electrode catalyst.
Example 8
Dissolving 3.0 g of PVP in 180 mL of ethanol to obtain a solution A; 600 mg of cobalt acetate and 300 mg of copper acetate were dissolved in 60 mL of an ethanol solution, and the resulting solution was solution B. And slowly pouring the solution B into the solution A, and stirring for 2 hours in a water bath at the temperature of 85 ℃ to obtain a Cu-Co nanotube precursor precipitate. Washing and drying the obtained Cu-Co nanotube precursor precipitate, dispersing 320 mg in 60 mL ethanol, and then dispersing 640 mg (NH)4)2WS4Dissolving in 12 mL deionized water; dripping the aqueous solution into the ethanol solution, stirring for 0.5 h at normal temperature, centrifuging, washing and drying to obtain the Cu-CoWSx. The obtained Cu-CoWSx150 mg of the powder was placed in a porcelain boat in H2Heating to 350 ℃ in a tube furnace under Ar atmosphere, preserving heat for 2h at the heating rate of 2 ℃/min, and finally obtaining the tungsten sulfide doped cobalt copper sulfide CuCo with the hollow nano tube structure2S4/WS2A counter electrode catalyst.
Example 9
Dissolving 2.4 g of PVP in 180 mL of ethanol to obtain a solution A; 600 mg of cobalt acetate and 300 mg of copper acetate were dissolved in 60 mL of an ethanol solution, and the resulting solution was solution B. And slowly pouring the solution B into the solution A, and stirring for 2 hours in a water bath at the temperature of 90 ℃ to obtain a Cu-Co nanotube precursor precipitate. Washing and drying the obtained Cu-Co nanotube precursor precipitate, dispersing 480 mg in 60 mL ethanol, and then dispersing 320 mg (NH)4)2WS4Dissolving in 15 mL of deionized water; dripping the aqueous solution into the ethanol solution, stirring for 0.5 h at normal temperature, centrifuging, washing and drying to obtain the Cu-CoWSx. The obtained Cu-CoWSx150 mg of the powder was placed in a porcelain boat in H2Heating to 250 deg.C in a tube furnace under Ar atmosphereThe temperature is 2h, the heating rate is 2 ℃/min, and finally the tungsten sulfide doped cobalt copper sulfide CuCo with the hollow nanotube structure is obtained2S4/WS2A counter electrode catalyst.
Assembling:
first, a photo-anode is prepared using a screen printing process. Specifically, nano titanium dioxide (20 nm and 200 nm in size, 5 times and 2 times for coating, respectively, and 12 μm and 4 μm in coating thickness, respectively) was coated on FTO conductive glass by a screen printing technique; then placing the FTO glass coated with the titanium dioxide in a muffle furnace to be calcined for 1 h at 500 ℃, taking out the FTO glass after the FTO glass is naturally cooled to room temperature, and then taking out the FTO glass again in 0.04M TiCl4Soaking in the water solution for 1 h, placing in a muffle furnace, and calcining at 500 deg.C for 0.5 h; then the prepared photo-anode is sensitized, firstly cut into small pieces with proper size (1.5 cm multiplied by 1.5 cm), and then the small pieces are soaked in N719 dye ethanol solution (0.03M) in dark for 12 h.
Secondly, the counter electrode is prepared by using a spin coating technique. Specifically, 20 mg of the tungsten sulfide doped with cobalt copper sulfide CuCo in the hollow nanotube structure prepared in example 7 was taken2S4/WS2Dispersing a counter electrode catalyst in 2 mL of isopropanol, uniformly spin-coating the dispersion liquid on cleaned FTO glass at a rotating speed of 600-650 r/min for 8 seconds each time, repeating the spin-coating for 3-4 times, wherein the loading amount of the catalyst on each piece of FTO glass is about 0.44 mg cm–2. Meanwhile, a Pt counter electrode was fabricated for comparison, and a 20 mM ethanol solution of chloroplatinic acid was spin-coated on the cleaned FTO glass as described above at a rotation speed of 500 r/min for 1 time for 8 seconds, and then it was calcined in a muffle furnace at 450 ℃ for 0.5 h.
And finally, packaging the counter electrode and the photo-anode by using a Shalin heat sealing film, injecting electrolyte between the counter electrode and the photo-anode, and fixing and clamping to assemble the dye-sensitized cell with the sandwich structure. Wherein the electrolyte is 0.1M LiI, 0.05M I20.3M DMPII (1, 2-dimethyl-3-propylimidazolium iodide) and 0.5M tert-butylpyridine in acetonitrile. The assembled cell was placed in standard simulated solar conditions (AM 1.5G, 100 mW cm)–2) To carry outAnd (6) testing.
The following analysis is made in conjunction with the accompanying drawings
FIG. 1 shows Cu-Co nanotubes, CuCo prepared in examples 6, 7 and 82S4/WS2SEM image of catalyst. As can be seen from (a) and (b) in FIG. 1, the Cu-Co nanotube precursor is a regular nanotube structure, and has a uniform size, a length of about 5 μm and a width of about 400-500 nm. In FIG. 1, (c) and (d) show CuCo obtained in example 62S4/WS2SEM image of-2/1 catalyst, surface depressed compared to the precursor Cu-Co nanotubes, but still maintaining the framework structure of the nanotubes and due to (NH) participating in the reaction during preparation4)2WS4The amount is small, and therefore a small amount of nanoparticles are distributed on the surface. In FIG. 1, (e) - (g) show CuCo obtained in example 72S4/WS2SEM picture of-1/1 catalyst, which is hollow nanotube structure, shortens charge transport path while accelerating charge transfer process, and is due to (NH) participating in reaction at the time of preparation4)2WS4Moderate amount, has proper amount of uniformly distributed WS on the surface2And the nano particles can increase the contact area of the catalyst and the electrolyte, expose more active sites and improve the electrochemical catalytic capability of the catalyst. In FIG. 1, (h) (i) shows CuCo obtained in example 82S4/WS2SEM picture of-1/2 catalyst, which retains the framework structure of nanotubes but is due to (NH) that participates in the reaction during preparation4)2WS4Too much, so that a considerable part of the WS is broken and a large amount of agglomerated WS is attached to the surface2The nano-particles cover the effective active sites of the catalyst, and prevent the catalyst from contacting with electrolyte, thereby reducing the electrochemical catalytic capability of the catalyst.
FIG. 2 shows CuCo prepared in examples 6, 7 and 82S4/WS2-2/1，CuCo2S4/WS2-1/1 and CuCo2S4/WS2TEM image of the catalyst-1/2. As can be seen from the figure, all three catalysts prepared are of hollow nanotube structure. Wherein the CuCo produced in example 6 in FIG. (a)2S4/WS 22/1 minimal surface attachment of nanoparticles, CuCo from example 8 in Panel (c)2S4/WS 21/2 the catalyst surface had the most nanoparticles attached and agglomeration, while the CuCo prepared in example 7 in the graph (b)2S4/WS2The nano particles attached to the surface of the-1/1 catalyst are moderate and uniformly distributed, so that the specific surface area is increased, more effective active sites are provided, and the electrochemical catalytic performance is improved.
FIG. 3 shows CuCo prepared in examples 6, 7 and 82S4/WS2-2/1，CuCo2S4/WS2-1/1 and CuCo2S4/WS2-XRD pattern of 1/2 catalyst. As can be seen from FIG. 3, CuCo2S4/WS2-2/1, CuCo2S4/WS2-1/1 and CuCo2S4/WS2The-1/2 catalysts may each be combined with WS2And CuCo2S4The standard cards of (1) prove that the three catalysts all contain WS2And CuCo2S4And the difference is with (NH)4)2WS4Increase of the mass ratio of/Cu-Co nanotube precursor, WS2The peaks at 14.5 °, 33.3 °, 58.3 ° and 60.4 ° also gradually increased.
FIG. 4 shows CuCo prepared in examples 6, 7 and 82S4/WS2-2/1，CuCo2S4/WS2-1/1 and CuCo2S4/WS2Pore size distribution of-1/2 catalyst and N2Adsorption and desorption curves. Wherein CuCo2S4/WS2-2/1, CuCo2S4/WS2-1/1 and CuCo2S4/WS2The specific surface areas of the catalysts-1/2 were respectively 26 m2 g–1，36 m2 g–1And 15 m2 g–1. As shown in the figure, the P/P ratio is between 0.5 and 1.00The presence of the type IV curve with typical hysteresis characteristics below, all catalysts show mesoporous characteristics and the dominance of the pore diameters of the three catalysts calculated by Barrett Joyner Halenda (BJH)To be distributed around 4.3 nm. And the electrolyte solution is easier to permeate into the catalyst with small pore diameter, high specific surface and large pore volume, which provides a plurality of effective active sites for the catalytic material and shows more efficient electrocatalytic performance in the DSSCs.
FIG. 5 shows CuCo prepared in examples 6, 7 and 82S4/WS2-2/1，CuCo2S4/WS2-1/1 and CuCo2S4/WS2-1/2 Assembly of catalyst and Pt counter electrode into DSSCsJ-VCurve and photovoltaic parameters of the counter electrode prepared from the three materials. As can be seen from FIG. 5, CuCo is used2S4/WS2-2/1 open circuit voltage of DSSCS prepared with catalyst as counter electrodeV oc809 mV, current densityJ scIs 16.8 mA cm–2Fill factor FF of 62.9%, photoelectric conversion efficiencyη8.55 percent, and has higher efficiency (the Pt is 8.32 percent) than a battery consisting of a Pt counter electrode under the same condition; with CuCo2S4/WS2-1/2 open circuit voltage of DSSCS prepared with catalyst as counter electrodeV oc798 mV, current densityJ scIs 14.8 mA cm–2Fill factor FF of 62.1%, photoelectric conversion efficiencyη7.34 percent; under the same conditions, the CuCo of the invention2S4/WS2-1/1 open circuit voltage of DSSCs prepared from catalystV oc818 mV, current densityJ scIs 18.4 mA cm–2Fill factor FF of 63.1%, photoelectric conversion efficiencyη9.50%, i.e., CuCo2S4/WS2-2/1, CuCo2S4/WS2The catalyst 1/2 and Pt have higher conductivity and catalytic efficiency. This indicates that CuCo2S4/WS2Large specific surface area and proper amount of WS adhered to surface of-1/1 catalyst2The nanoparticles can provide more active sites, thereby achieving higher catalytic efficiency.
FIG. 6 shows CuCo prepared in examples 6, 7 and 82S4/WS2-2/1，CuCo2S4/WS2-1/1 and CuCo2S4/WS 21/2 Cyclic voltammograms of DSSCs assembled from catalyst and Pt counter electrode. As can be seen from FIG. 6, all CV curves have two distinct redox peaks, and the left peak pair (Red-1/Ox-1) can be attributed to I3 − + 2e− ↔ 3I−Another pair of peaks (Red-2/Ox-2) is attributed to equation 3I2 + 2e− → 2I3 −And redox pair I−/I3 −The reaction between them has a great influence on the whole electrochemical catalytic process. At the same time, the electrocatalytic performance of the triiodide ion reduction and the cathodic current density of the Red-1 peak: (J Red-1) Are directly related. The study shows that3 −Reduction rate ofJ Red-1A positive correlation is obtained. In addition, the potential difference between the first oxidation peak and the first reduction peak (E pp) Is also an important indicator for evaluating electrochemical catalytic performance, since it is compatible with I−/I3 −The reversibility of the redox reaction is relevant. The study showed that between the peaks of Ox-1 and Red-1E ppThe smaller the value, the better the electrochemical performance. As can be seen in FIG. 6, CuCo2S4/WS2Redox couple I in the circulation curve of the-1/1 catalyst3 ‒/I‒First reduction peak-to-peak ratio CuCo of (1)2S4/WS2-2/1，CuCo2S4/WS2Both-1/2 and Pt are high and the area enclosed by the CV curve is larger, indicating that CuCo2S4/WS2The catalytic activity of the-1/1 catalyst on the electrode is better than both the others. Further, CuCo2S4/WS2-1/1 potential difference between the first oxidation peak and the first reduction peak of the catalystE ppAround 238 mV compared to CuCo2S4/WS2284 mV, CuCo, of-2/1 catalyst2S4/WS2The 382 mV of the-1/2 catalyst and the 337 mV of Pt are both small. Thus CuCo2S4/WS2The-1/1 catalyst possesses stronger electrocatalytic activity.
FIG. 7 shows CuCo prepared in examples 6, 7 and 82S4/WS2-2/1，CuCo2S4/WS2-1/1 and CuCo2S4/WS2-1/2 polarization curves of DSSCs assembled with a Pt counter electrode. There are two important indicators in the polarization curve (Tafel) test, namely the limiting diffusion current density: (J lim) And exchange current density: (J 0 ) And can be used for evaluating the electrocatalytic performance of the CE. When the voltage is-1.0V,J limis determined by the y-axis value, andJ 0 the values of (d) are calculated from the cathodic or anodic branch of the Tafel curve. In general, higherJ 0 AndJ limthe values indicate that the catalyst has superior performance for reducing I3 ‒Electrocatalytic performance of. As can be seen from fig. 7, the exchange current densities are arranged in the following order: CuCo2S4/WS2Catalyst-1/1 (0.642 log (mA cm)–2)) > CuCo2S4/WS2Catalyst 2/1 (0.480 log (mA cm)–2)) > Pt (0.441 log (mA cm–2)) > CuCo2S4/WS2Catalyst-1/2 (0.217 log (mA cm)–2) ); the limiting diffusion current density arrangement order is as follows: CuCo2S4/WS2Catalyst-1/1 (2.10 log (mA cm)–2)) > CuCo2S4/WS2Catalyst-2/1 (1.71 log (mA cm)–2)) > Pt (1.51 log (mA cm–2)) > CuCo2S4/WS2Catalyst-1/2 (1.12 log (mA cm)–2) Namely CuCo-2S4/WS2The catalyst-1/1 has the highest exchange current densityJ 0And ultimate diffusion current densityJ limThis indicates CuCo2S4/WS2The catalyst-1/1 possesses the highest electrocatalytic activity.
FIG. 8 shows CuCo prepared in examples 6, 7 and 82S4/WS2-2/1，CuCo2S4/WS2-1/1 and CuCo2S4/WS 21/2 electrochemical impedance curves of DSSCs assembled from catalyst and Pt counter electrode. In the Electrochemical Impedance (EIS) curve, all electrodesThe material exhibits two semicircles, where the semicircle located in the high frequency region (left) reflects the charge transfer kinetics between the electrolyte interface and the electrode material, and the first intersection with the x-axis represents the series impedance: (R s ) And generally represents the series resistance between the FTO substrate, electrolyte and catalyst; the diameter of which reflects the interfacial charge transfer impedance between the surface of the electrode material and the electrolyte solutionR ct ). The semicircle (right) located in the low frequency region reflects the charge transfer condition in the electrolyte, and the corresponding equivalent circuit diagram is simulated by Z-view software. The results show that all samples show approximationsR s Due to the several electrode materialsR s The value is determined primarily by the impedance of the FTO substrate and the FTO/electrode material interfacial impedance, and thus its reference to the electrocatalytic performance of the electrode material is negligible. Of the prepared samplesR ct Are arranged in order: CuCo2S4/WS2-1/2 catalyst (8.78 Ω)> Pt (4.28 Ω) > CuCo2S4/WS2-2/1 catalyst (3.86 Ω)> CuCo2S4/WS 21/1 catalyst (1.64 Ω). In general, the catalytic activity of the catalyst is dependent onR ct Is increased, it can be seen that the catalytic activity of the catalyst is in order from small to large: CuCo2S4/WS2-1/2 catalyst, Pt, CuCo2S4/WS2-2/1 catalyst, CuCo2S4/WS2-1/1 catalyst.
FIG. 9 shows CuCo obtained in examples 6, 7 and 82S4/WS2The catalyst was assembled into 1000 continuous cyclic voltammograms of DSSCs. With CuCo2S4/WS2Catalyst-2/1, CuCo2S4/WS2CuCo was observed for the-1/2 catalyst and the Pt counter electrode2S4/WS2The current density decay of the-1/1 catalyst was smaller and the change in the position of the redox peak was also smaller. Furthermore, after being subjected to continuous scanning, CuCo2S4/WS2The-1/1 catalyst did not detach from the FTO substrate. TheThe results show that CuCo obtained in example 72S4/WS2The catalyst-1/1 has good stability at I3 −/I−The electrolyte is not corroded or decomposed. In contrast, after 1000 consecutive scans, CuCo2S4/WS2The catalyst-1/2 shows less overlap of CV curves, significant change in redox peak position, sharp decrease in current density, and slight peeling from the FTO substrate, indicating poor stability.
FIG. 10 is a graph of CuCo obtained in example 72S4/WS2-1/1 assembling DSSCs after 1000 continuous cyclic voltammetric scansJ-VCurve line. As can be seen in FIG. 10, the CuCo obtained in example 7 was obtained after 1000 consecutive CV scans2S4/WS2-1/1 method for assembling DSSCs from catalystJ-VThe test still has good performance, open circuit voltageV oc817 mV of current densityJ scIs 16.4 mA cm–2The fill factor FF is 62.6%. Photoelectric conversion efficiencyηThe content was 8.39%. In addition, after 1000 consecutive CV cycles, CuCo2S4/WS2The PCE of the-1/1 catalyst dropped to 8.39%, 88.3% (9.50%) of the initial value, indicating its good electrochemical stability.
FIG. 11 is a graph of CuCo obtained in example 72S4/WS2-1/1 SEM images of DSSCs assembled after 1000 consecutive cyclic voltammetry scans. As can be seen from the figure, CuCo obtained in example 72S4/WS2The 1/1 catalyst assembled into DSSCs, after the stability test of 1000 continuous cyclic voltammetry scans, the overall morphology of the DSSCs is kept good and the DSSCs show good electrochemical stability, although part of the outer shell is slightly damaged and part of the column is broken.
The above description is only a preferred embodiment of the present invention, and all the equivalent changes and modifications made according to the claims of the present invention should be covered by the present invention.

Claims (1)

1. A tungsten sulfide-doped cobalt sulfide copper counter electrode catalyst with a hollow nanotube structure is characterized in that: the preparation method comprises the following steps:
1) mixing ethanol solutions of cobalt acetate and copper acetate with ethanol solution of polyvinylpyrrolidone, and then carrying out water-bath heating reaction to obtain Cu-Co nanotube precursor precipitate;
2) washing and drying the Cu-Co nanotube precursor precipitate obtained in the step 1), dispersing the precipitate in ethanol, dissolving ammonium tetrathiotungstate in deionized water to obtain an aqueous solution, dropwise adding the aqueous solution into the ethanol solution containing the Cu-Co nanotube precursor, stirring at normal temperature, and reacting for a period of time to obtain Cu-CoWSx；
3) Subjecting the Cu-CoWS obtained in the step 2) toxAt H2Calcining in Ar atmosphere to obtain hollow nanotube CuCo2S4/WS2A counter electrode catalyst;
the reaction temperature of the water bath in the step 1) is 85 ℃, and the reaction time is 2 hours; the mass ratio of the Cu-Co nanotube precursor precipitate to the ammonium tetrathiotungstate in the step 2) is 1: 1; in the step 3), the calcination temperature is 350 ℃, the heat preservation is carried out for 2h, and the heating rate is 2 ℃/min; the mass ratio of cobalt acetate, copper acetate and PVP in the step 1) is 2:1: 10; the volume ratio of PVP dissolved to cobalt acetate and copper acetate dissolved in the step 1) is 3: 1; the volume ratio of the ethanol to the deionized water in the step 2) is 5: 1; the reaction time of stirring at normal temperature in the step 2) is 0.5 h.
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