KR20160057009A - Photo-electrode for Photoelectronchemical cell, method of manufacturing the same - Google Patents

Abstract

The present invention provides a photo-electrode for a photo-electrochemical cell including: a substrate; a transparent electrode provided on the substrate; a buffer layer provided on the transparent electrode and including graphite connected to a plurality of fullerenes; and a semiconductor layer provided on the buffer layer. The photo-electrode for a photo-electrochemical cell including a buffer layer according to the present invention can achieve an improved sunlight-hydrogen conversion efficiency by selectively rapidly separating and moving charges generated by the photo-electrode.

Description

Field of the Invention [0001] The present invention relates to photoelectrodes for photoelectrochemical cells,

The present invention relates to a photoelectrode for a photoelectrochemical cell and a method of manufacturing the same.

Currently, many studies are being actively conducted around the world to solve energy and environmental problems. Among them, research on the development of new and renewable energy is overwhelming. New and renewable energy is a sustainable renewable energy source that can replace fossil fuels. It will be able to solve energy and environmental problems simultaneously with a clean energy supply system. . In order to develop a system in which new and renewable energy sources such as solar energy, wind energy, geothermal energy, marine energy, biomass energy and hydrogen energy can be effectively produced and consumed, Is in progress.

Among new renewable energy in particular, and can be produced from sustainable energy hydrogen (H ₂₎ is water (H ₂ O) rich in resources, after use in the fuel is capable of reproduction because the water again. In addition, it is eco-friendly because it does not emit not only carbon dioxide, which is a greenhouse gas, but also substances causing air pollution such as sulfuric acid gas (SO _x ), nitric acid gas (NO _x ), dust,

It is possible to obtain much more energy than other energy sources of the same amount because it has a high energy density and is easy to move in the form of high-pressure gas or liquid hydrogen, and it is also easy to store using a hydrogen storage alloy or the like. Therefore, it is being used in various fields from basic materials to hydrogen cars, fuel cells, rocket fuels, etc. throughout the industry and it is receiving great social interest as a renewable energy source.

Although electrolysis of water is very simple and reliable, and it has the advantage of mass production of hydrogen energy, the cost of electric energy used in the electrolysis of water is high and produces expensive hydrogen energy.

Therefore, a hydrogen production method using a photovoltaic effect using solar energy has been devised to effectively decompose water at low cost.

The water splitting method using photoelectrochemical cell was reported by Professor Fujishima and Professor Honda of Tokyo University in 1972 on the decomposition reaction of water using photon with TiO ₂ . It has been progressed.

Photochemically, the technology to produce hydrogen chemically is similar to that of a solar cell system, but the electron-hole pair (EHP) generated by the photon induces the redox reaction of water And the generation of hydrogen gas and oxygen gas is induced through the hydrogen gas.

Through the decomposition of water using PEC Cells as described above, hydrogen energy can be produced by using renewable and clean system using infinite solar energy and earth's abundant resources. In addition, water decomposition using a photoelectrochemical cell produces oxygen as well as hydrogen energy, so it can be used for decomposition and purification of organic matter, and it can be applied to a suitable place by synthesis with ozone.

Photoelectrochemical cells are similar in mechanism to widely known solar cells, but in the case of photoelectrochemical cells, there is a difference in that the movement of electrons is used to produce hydrogen by direct water reduction without inducing electricity production.

A photoelectrode including a semiconductor oxide constituting a photoelectric chemical cell absorbs sunlight to form an exciton of an electron-hole, and is connected to an external electrode through an external circuit. The two electrodes are in contact with the aqueous electrolyte, and the oxidation and reduction reactions of water are produced at the two electrodes, respectively, to produce oxygen and hydrogen. If the photoelectrode is an n-type semiconductor, oxygen is generated in the oxidation reaction and reduction reaction is generated in the photoelectrode, thereby generating hydrogen. If the photoelectrode is a p-type semiconductor, the opposite reaction occurs. The photoelectrochemical decomposition method is a method of manufacturing hydrogen energy without using a conventional high-cost system which requires simultaneous use of a solar cell and a water decomposition electrolytic cell.

Generally, photoelectrochemical degradation cells can be fabricated by using an inorganic semiconductor having a band gap of 1.23 eV or more. However _, in the case of a cell made of a single-layer inorganic material such as TiO _{2 and} WO ₃ , , The solar-to-hydrogen conversion efficiency is as low as less than 1%. SrTiO ₃ , TiO ₂ , and WO ₃ , which have a bandgap of 2.5 eV or more, are mainly used. However, materials with a band gap of 2.5 eV or more mainly absorb holes and electrons by absorbing ultraviolet wavelengths of less than 4% Solar - hydrogen energy conversion efficiency is very low and not economical.

Also, the generated electron / hole pairs are rapidly recombined, the reverse reaction easily occurs, and the activation of the inorganic semiconductor by visible light is low.

In order to solve the above problems, Korean Patent Laid-Open Publication No. 10-2014-0119314 discloses a TiO ₂ nanotube; And a TiO ₂ layer coated on the surface of the TiO ₂ nanotube. The present invention provides a photoelectrode having improved hydrogen conversion efficiency. The TiO ₂ nanotube type is characterized in that the efficiency of light absorption is increased by increasing light scattering, and the efficiency is about 5 times higher than that of the conventional thin film type TiO ₂ because electrons can stay in a free state for a long time.

In addition, U.S. Patent No. 6936143 discloses a photo-electrode for a photoelectrochemical cell comprising a photoactive oxide layer such as WO ₃ or Fe ₂ O ₃ and a dye-sensitized TiO ₂ layer on both sides of a conductive substrate (F-doped tin oxide) And decomposing the aqueous electrolyte in contact therewith to generate hydrogen.

Korean Patent Laid-Open No. 10-2011-0107112 discloses a method for producing oxide nanoparticles by dispersing oxide nanoparticles into yeast or ink (step 1); (Step 2) of forming a coating film on the other surface of the conductive substrate composed of the oxide nano-particle paste or ink, the conductive substrate having one side made of the photo-electrode; And a step of subjecting the coating film formed in the step 3 to a low-temperature heat treatment (step 3). The photoelectrochemical cell can be formed as a single body of a photoelectrode-catalyst film by preparing a catalyst film on one surface of a conductive substrate, and can easily coat oxide nano-particles on a conductive substrate. And thus can be advantageously used as an oxidizing electrode catalyst film for photoelectrochemical batteries.

Accordingly, the inventors of the present invention developed a photoelectrode for a photoelectrochemical cell having a buffer layer containing graphitic carbon connected with a plurality of fullerenes while studying to improve the solar-hydrogen energy conversion efficiency, - the hydrogen conversion efficiency is improved, and the present invention has been completed.

It is an object of the present invention to provide a photoelectrode for a photoelectrochemical cell and a method of manufacturing the same.

In order to achieve the above object,

The present invention

Board;

A transparent electrode provided on the substrate;

A buffer layer disposed on the transparent electrode, the buffer layer including graphitic carbon having a plurality of fullerenes connected thereto; And

And a semiconductor layer provided on the buffer layer.

Further, according to the present invention,

Coating a mixed solution of fullerene and an organic solvent on the upper portion of the transparent electrode, and then heat-treating the mixed solution to form a buffer layer (Step 1); And

And forming a semiconductor layer by coating a semiconductor oxide solution on the buffer layer and then performing a heat treatment on the buffer layer to form a photoelectrode for a photoelectrochemical cell.

Further,

An optical electrode manufactured through the above manufacturing method; A reference electrode; A counter electrode; And an electrolyte,

And the photoelectrode and the counter electrode are electrically connected to each other.

By providing a photoelectrode for a photoelectrochemical cell having a buffer layer comprising graphitic connected in part by a plurality of fullerenes according to the present invention, it is possible to rapidly and selectively remove and transfer the charge generated in the photoelectrode So that an improved solar-to-hydrogen conversion efficiency can be obtained.

In addition, the manufacturing method of the photoelectrode for the photoelectrochemical battery according to the present invention can be easily manufactured compared to other carbon-based materials such as carbon nanotube and graphene, It is easier to manufacture.

1 is a graph showing the results of X-ray diffraction (XRD) of the photoelectrode prepared in Example 3 and Comparative Example 3;
2 is a graph showing the results of X-ray diffraction analysis of the buffer layer according to the present invention before and after firing;
FIG. 3 is a photograph of the photoelectrode prepared in Example 3 and Comparative Example 3 through a high resolution scanning transmission electron microscopy (HR-STEM); FIG.
4 is a photograph of a section of the photoelectrode prepared in Comparative Example 3 through a field emission scanning electron microscope (FE-SEM);
5 shows the Raman spectrum of the photoelectrode prepared in Comparative Example 3 and Example 3;
6 shows Raman spectrum before and after firing of fullerene;
7 is a schematic view schematically showing the structure of a photoelectrochemical cell including a photoelectrode according to the present invention;
8 is a graph showing the results of a solar simulator using photoelectrochemical cells including the photoelectrode manufactured in Examples 1 to 5 and Comparative Examples 1 to 5;
9 is a graph showing a result of a solar simulator using photovoltaic cells including the photoelectrode manufactured in Examples 1, 6, 7 and Comparative Examples 6 and 7;
10 is a graph showing the results of photoluminescence and time-resolved photoluminescence analysis of the photoelectrode prepared in Example 3 and Comparative Example 3;
11 is a photograph of the photoelectrode prepared in Example 3 and Comparative Example 3 through a photoconductive atomic force microscope (AFM) according to light conditions;
12 is a graph showing the results of electrochemical impedance spectroscopy (EIS) analysis of the photoelectrodes prepared in Example 3 and Comparative Example 3;
13 (a) is a schematic view showing a photoelectrode for a conventional photoelectric chemical cell, and FIG. 13 (b) is a schematic diagram schematically showing a photoelectrode for a photoelectrochemical cell according to the present invention.

Hereinafter, the present invention will be described in detail.

According to the present invention,

Board;

A transparent electrode provided on the substrate;

A buffer layer provided on the transparent electrode and including graphitic carbon connected with a plurality of fullerenes; And

And a semiconductor oxide layer provided on the buffer layer.

Hereinafter, a photoelectrode for a photoelectrochemical cell according to the present invention will be described in detail.

Generally, a photoelectric chemical cell is composed of a photoelectrode where a semiconductor oxide absorbs sunlight to form an exciton of an electron-hole, and a counter electrode connected to the photoelectrode by an external circuit. These two electrodes are in contact with an aqueous electrolyte And the oxidation and reduction reactions of water occur at the two electrodes, respectively, to produce oxygen and hydrogen.

In general, a photoacid decomposition cell can be fabricated using an inorganic semiconductor having a band gap of 1.23 eV or more. However _, in the case of a cell made of a single-layer inorganic material such as TiO _{2 and} WO ₃ , an ultraviolet (UV) wavelength , The solar-to-hydrogen conversion efficiency is as low as less than 1%. SrTiO ₃ , TiO ₂ , and WO _{3 with a} bandgap of 2.5 eV or more are mainly used. However, materials having a band gap of 2.5 eV or more absorb ultraviolet light, which occupies less than 4% of the sunlight, Therefore, the solar-to-hydrogen energy conversion efficiency is very low, which is not economical. Also, the generated electron / hole pairs are rapidly recombined, the reverse reaction easily occurs, and the activation of the inorganic semiconductor by visible light is low.

Accordingly, in order to improve the solar-to-hydrogen energy conversion efficiency, the present invention provides a photoelectrode for a photoelectrochemical cell having a buffer layer comprising graphite carbon connected between a semiconductor oxide layer and a conductive transparent electrode by a plurality of fullerenes, The charge generated in the photoelectrode can be selectively separated / moved due to the electron affinity of the hole transporting layer and the block characteristic of the hole transport, and in particular, the recombination of the charges generated inside the photoelectrode bulk is prevented, Efficiency can be obtained.

At this time, the substrate may be made of glass, titanium, nickel, molybdenum, or the like, and the transparent electrode provided on the substrate may be made of aluminum-zinc oxide (AZO) indium tin oxide (ITO; indium-tin oxide) , zinc oxide (ZnO), zinc sulfide (ZnS), aluminum tin oxide (ATO; Aluminium-tin oxide; SnO 2: Al) and fluorine-containing tin oxide (FTO: Fluorine- doped tin oxide) may be used, but the present invention is not limited thereto.

In addition, the semiconductor oxide provided on the buffer layer may be a metal oxide. Examples of the oxide include TiO ₂ , Ga ₂ O ₃ , In ₂ O ₃ , ZnO, Nb ₂ O ₅ , WO ₃ , SnO, SnO ₂ , MgO, or the like may be used, but the present invention is not limited thereto.

Further, according to the present invention,

Coating a mixed solution of fullerene and an organic solvent on the upper portion of the transparent electrode, and then heat-treating the mixed solution to form a buffer layer (Step 1); And

And coating a semiconductor oxide solution on the buffer layer, followed by heat treatment (step 2).

Hereinafter, a method of manufacturing a photoelectrode for an electrochemical cell according to the present invention will be described in detail.

In the step 1, a mixed solution of a fullerene derivative and an organic solvent is coated on an upper portion of the transparent electrode, followed by heat treatment to form a buffer layer. The concentration of fullerene in the mixed solution is preferably 10 to 30 mg / mL.

When the concentration of fullerene is less than 10 mg / ml, or when the concentration of fullerene is more than 30 mg / ml, a uniform mixture solution can be prepared due to the limited solubility. And a uniformly coated buffer layer can not be formed. That is, the photocurrent density may be significantly reduced.

The organic solvent used in the mixed solution may be dichlorobenzene, dichloromethane, chloroform, N, N-dimethylformamide (DMF), tetrahydrofuran (THF) and ethyl acetate , But is not limited thereto.

On the other hand, the mixed solution in which the fullerene is dissolved is coated on the transparent electrode by spin coating, spin casting, roll coating, dip coating or the like, followed by heat treatment at 80 to 120 ° C for about 1 minute to form a buffer layer .

Next, in the method for manufacturing a photoelectrode for photoelectrochemical cells according to the present invention, the step 2 is a step of coating a semiconductor oxide solution on the buffer layer and then performing a heat treatment, thereby forming a semiconductor layer.

The semiconductor oxide of step 2 may be TiO ₂ , Ga ₂ O ₃ , In ₂ O ₃ , ZnO, Nb ₂ O ₅ , WO ₃ , SnO, SnO ₂ and MgO. After mixing with the solvent, dissolve until the color of the semiconductor oxide disappears. When the solution becomes transparent, it may be coated on the buffer layer by spin coating, spin casting, roll coating, dip coating or the like, followed by heat treatment.

The heat treatment may be performed at a temperature of 80 to 120 ° C for about 1 minute, and then a heat treatment may be performed at 450 to 550 ° C for 1 to 3 hours to form a semiconductor layer.

If the temperature of the heat treatment is out of the above range, the crystal of the conductive transparent electrode, for example FTO, may be deformed or deformed to a substrate such as glass. Also, when performed at the temperature within the above range, a semiconductor layer having monolithic crystallinity can be formed.

On the other hand, the buffer layer containing fullerene formed in step 1 may be graphitic carbon connected to a plurality of fullerenes by breaking the structure of fullerene after heat treatment at 450 to 550 ° C for 1 to 3 hours in step 2, 13 (b).

13 (a) is a schematic view showing a photoelectrode for a conventional photoelectric chemical cell, and FIG. 13 (b) is a schematic diagram schematically showing a photoelectrode for a photoelectrochemical cell according to the present invention.

As shown in FIG. 13 (b), a buffer layer containing fullerene may be provided between the transparent electrode (FTO electrode) and the semiconductor layer WO ₃ , and the buffer layer may be graphitic carbon connected with a plurality of fullerenes. Also, by providing the buffer layer on the photoelectrode, the charges excited in the semiconductor layer can be effectively moved quickly, which can solve the problems of recombination of charge-hole pairs and slow charge transfer in the conventional photoelectrode.

In addition, the manufacturing method of the photoelectrode for the photoelectrochemical cell according to the present invention can be easily manufactured compared to the carbon based material (CNT, Graphene) reported in the past, and is particularly easy to make a uniform large-area film.

Further, according to the present invention,

An optical electrode according to the present invention; A reference electrode; A counter electrode; And an electrolyte,

And the photoelectrode and the counter electrode are electrically connected to each other.

For example, the reference electrode may be an aqueous solution reference electrode such as a hydrogen electrode (Pt / H ₂ ), a calomel electrode (Hg / HgCl ₂ ), a silver-silver chloride electrode (Ag / AgCl) , A mercury-mercury-sulfuric acid mercury electrode (Hg / HgSO ₄ ), and a mercury-mercury-mercury electrode (Hg / HgO) can be used.

The counter electrode may be at least one metal selected from the group consisting of platinum (Pt), iridium (Ir), lead (Pd), and tantalum (Ta), or an alloy thereof. Can be used.

On the other hand, the photoelectrode and the counter electrode are in contact with the aqueous electrolyte, and the oxidation and reduction reactions of water occur at the two electrodes, respectively, to produce oxygen and hydrogen.

In addition, the photoelectrochemical cell has a characteristic of rapidly separating / transferring charges generated in the photoelectrode due to the electron affinity and blocking characteristic of hole transport of the buffer layer including graphite carbon connected by a plurality of fullerenes As a result, it is possible to prevent the recombination of electrons and holes generated in the inside of the photo-electrode (bulk), thereby achieving an improved solar-hydrogen efficiency.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following embodiments are only examples of the present invention, but the present invention is not limited thereto.

PREPARATION EXAMPLE 1 Preparation of tungsten oxide (WO ₃ ) solution

To prepare a tungsten oxide (WO ₃ ) solution, 1.14 g of a tungsten-based compound dark-blue tungsten chloride (WCl ₆ ) was dissolved in 20 ml of ethanol.

The solution was dissolved in an inert atmosphere for 24 hours until the deep blue color disappeared to produce a clear solution.

≪ Example 1 >

Step 1: 12 mg of fullerene (C ₇₀ ) was dissolved in 1 ml of 1,2-dichlorobenzene. The mixed solution was spin-coated on the transparent electrode (glass coated with FTO) at a speed of 2000 rpm for 40 seconds, and then heat-treated for 1 minute on a hot plate at 100 ° C.

Step 2: The tungsten oxide solution prepared in Preparation Example 1 was spin-coated on the buffer layer formed in the step 1 for 30 seconds at a speed of 600 rpm and then heat-treated for 1 minute on a hot plate at 100 ° C .

Step 3: After performing the heat treatment in the step 2, the photoelectrode for a photoelectrochemical cell was prepared by heat treatment in an oven at 500 ° C for 2 hours.

≪ Example 2 >

A photoelectrode for a photoelectrochemical cell was prepared in the same manner as in Example 1, except that the step 2 was performed twice.

≪ Example 3 >

A photoelectrode for a photoelectrochemical cell was prepared in the same manner as in Example 1, except that the process of Step 2 was repeated three times.

<Example 4>

A photoelectrode for a photoelectrochemical cell was prepared in the same manner as in Example 1, except that the step 2 was repeated five times.

&Lt; Example 5 >

A photoelectrode for a photoelectrochemical cell was prepared in the same manner as in Example 1, except that the process of the step 2 was repeated seven times.

&Lt; Example 6 >

A photoelectrode for a photoelectrochemical cell was prepared in the same manner as in Example 1 except that 20 mg of fullerene was used in the step 1 in Example 1.

&Lt; Example 7 >

A photoelectrode for a photoelectrochemical cell was produced in the same manner as in Example 1, except that 30 mg of fullerene was used in the step 1 in Example 1.

&Lt; Comparative Example 1 &

Step 1: The tungsten oxide solution prepared in Preparation Example 1 was spin-coated on the transparent electrode (glass coated with FTO) at a speed of 600 rpm for 30 seconds, and then coated on a hot plate at 100 ° C for 1 minute Lt; / RTI &gt;

Step 2: After the heat treatment in the step 1, the photoelectrode for a photoelectrochemical cell was manufactured by performing heat treatment in an oven at 500 ° C for 2 hours.

&Lt; Comparative Example 2 &

In Comparative Example 1, a photoelectrode for a photoelectrochemical cell was prepared in the same manner as in Comparative Example 1 except that the process of Step 1 was performed twice.

&Lt; Comparative Example 3 &

In Comparative Example 1, a photoelectrode for a photoelectrochemical cell was prepared in the same manner as in Comparative Example 1, except that the process of Step 1 was repeated three times.

&Lt; Comparative Example 4 &

A photoelectrode for a photoelectrochemical cell was prepared in the same manner as in Comparative Example 1, except that the process of Step 1 was repeated five times in Comparative Example 1.

&Lt; Comparative Example 5 &

In Comparative Example 1, a photoelectrode for a photoelectrochemical cell was manufactured in the same manner as in Comparative Example 1, except that the process of Step 1 was repeated seven times.

&Lt; Comparative Example 6 >

A photoelectrode for a photoelectrochemical cell was produced in the same manner as in Example 1 except that 40 mg of fullerene was used in the step 1 in Example 1.

&Lt; Comparative Example 7 &

A photoelectrode for a photoelectrochemical cell was prepared in the same manner as in Example 1 except that 50 mg of fullerene was used in the step 1 in Example 1.

Experimental Example 1 X-ray diffraction analysis

X-ray diffraction (XRD) was performed to analyze crystals of the photo-electrode prepared in Example 3 and Comparative Example 3. The results are shown in FIG.

As shown in FIG. 1, it was confirmed that tungsten oxide (WO ₃ ) exhibited three separate distinct peaks between 23 ° and 24.5 ° and had a monoclinic phase crystal structure. In the case of Example 3 including a buffer layer, a structure with a low crystallinity was formed, and it was found that the buffer layer containing fullerene did not affect the morphology of tungsten oxide.

The results of X-ray diffraction analysis of the buffer layer containing fullerene according to the present invention before and after the firing at 500 ° C are shown in FIG. 2. The peak of the fullerene fired through the XRD pattern is not clearly shown .

<Experimental Example 2> High resolution transmission electron microscope and scanning electron microscopic analysis

FIG. 3 shows a photograph of the surface of the photoelectrode prepared in Comparative Examples 3 and 3 and the structure of the buffer layer through a high-resolution transmission electron microscopy (HR-STEM) , And a heat-treated fullerene which is a spot having a side size of 10 to 20 nm. Therefore, it can be confirmed that the fullerene after firing is partially dispersed in the tungsten oxide layer.

FIG. 4 shows a photograph of a cross section of the photoelectrode prepared in Comparative Example 3 through a field emission scanning electron microscope (FE-SEM), and it was confirmed that a tungsten oxide layer with a thickness of about 300 nm was formed .

&Lt; Experimental Example 3 > Raman spectroscopy (Raman spectroscopy)

FIG. 5 shows Raman spectra of the photoelectrodes prepared in Comparative Examples 3 and 3 in order to examine the structure of the buffer layer containing fullerene according to the present invention.

As can be seen from FIG. 5 (a), the high crystallinity of the tungsten oxide layer can be confirmed at 1000 cm ^-1 or less, and particularly the WOW Raman peak can be confirmed at around 710 to 805 cm ^-1 .

On the other hand, as shown in FIG. 5 (b), which is an enlarged view of FIG. 5 (a), in the case of the photoelectrode of Example 3, two peaks were observed in the region of 1300 to 1700 cm ^-1 , Each representing disordered carbon and graphitic carbon.

Therefore, it can be seen from the above results that the buffer layer containing fullerene has a structure in which fullerene does not remain and is at least partially broken after firing at 500 ° C. In addition, it can be seen that the high firing temperature is necessary for the tungsten oxide to form high crystallinity and is an important factor for obtaining high light-harvesting efficiency.

On the other hand, the Raman spectrum before and after firing the fullerene at 500 ° C is shown in Fig. 6, and it can be seen that the fullerene is graphitic carbon after firing.

<Experimental Example 4> Measurement of photocurrent density

To understand the photoelectrochemical properties of the photoelectrode according to the present invention, a photoelectrochemical cell including the photoelectrode was prepared.

A schematic diagram of the structure of the photoelectrochemical cell including the photoelectrode according to the present invention is shown in Fig. 7, a platinum wire was used as a counter electrode, silver / silver chloride (Ag / AgCl) electrode was used as a reference electrode, and a photoelectrode according to the present invention having an area of 2.54 cm ² The photoelectrochemical cell was prepared by supporting the photoelectrode and the counter electrode in an electrolyte aqueous solution containing 0.1 M of sodium sulfate (Na ₂ S) (pH ~ 4.0).

Photocurrents were measured with a solar simulator under the conditions of AM 1.5 (1sun, 100 mW / cm ² ) and 1.23 V using the photoelectrochemical cell including the photoelectrode manufactured in Examples 1 to 5 and Comparative Examples 1 to 5 And the results are shown in Fig.

8 (a) is a graph showing the photocurrent density (mA / cm ² ) of the photo-electrochemical cell manufactured under the photo-conversion condition. At this time, the photoelectrodes prepared in Examples 1 to 5 and Comparative Examples 1 to 5, in which the tungsten oxide solution was spin-coated 1, 2, 3, 5 and 7 times, are shown on the graph as t1, t2, t3, t5 and t7 Respectively.

As the number of times of the tungsten oxide spin coating was increased, the thickness of the tungsten oxide layer was increased by about 100 nm, and the tungsten oxide layer included in the photo electrode was formed to a thickness of 100 to 700 nm.

8 (a), the dotted lines show the photocurrent density of the photoelectrode manufactured in Comparative Examples 1 to 5, and the solid line in the graph of FIG. 8 (a) On the graph of the photocurrent density, the X-axis represents the number of times of spin coating in the WO ₃ layer deposition as a tungsten oxide layer (WO ₃ layer).

As shown in FIG. 8, as the thickness of the tungsten oxide layer is increased, the light absorption is improved and the photocurrent density is also increased. In the photoelectrode having the buffer layer according to the present invention, Can be confirmed to have higher photocurrent density than the optical electrodes of Comparative Examples 1 to 5 in which no buffer layer is provided.

Therefore, it can be seen that the buffer layer including the fired fullerene is provided between the transparent electrode and the semiconductor layer, so that the charge transfer at the interface is excellent.

9 (b) shows the photoelectrochemical cell including the photoelectrode prepared in Examples 1, 6 and 7 and Comparative Examples 6 and 7 in order to examine the effects of the change in the concentration of fullerene, Fig. 9 (b) shows the result of photocurrent measurement under the condition of AM 1.5 (1sun, 100 mW / cm ² ) using a solar simulator.

As shown in FIG. 9 (a), the photocurrent density of Examples 1, 6, and 7 using the mixed solution having the fullerene concentration of 12, 20, and 30 mg / mL was increased as the concentration of fullerene increased. However, in Comparative Examples 6 and 7 using a mixed solution having a concentration of fullerene of more than 30 mg / mL, a uniform solution was not formed due to the limited solubility, and an uneven coating film was formed as shown in FIG. 9 (b) The photocurrent density value was decreased.

Therefore, it can be seen that the concentration of fullerene used in the production of the buffer layer according to the present invention is preferably 10 to 30 mg / mL or less.

<Experimental Example 5> Photoluminescence analysis

Photoluminescence and time-resolved photoluminescence of the photoelectrode prepared in Example 3 and Comparative Example 3 were analyzed to know the charge transfer characteristics of the photoelectrode provided with the buffer layer according to the present invention 10.

As shown in Fig. 10 (a), it is confirmed that the light emission is suppressed by the buffer layer containing fullerene.

In addition, the photoelectrode prepared in Example 3 (WO ₃ / C ₇₀ / FTO electrode) and Comparative Example 3 (WO ₃ / FTO electrode) and the photo electrode (R-WO ₃ / FTO) is shown in FIG. 10 (b), and the average lifetime of the electron-hole pairs estimated from the curve of FIG. 10 (b) .

As shown in FIG. 10 (c), the optical electrode manufactured in Example 3 including the buffer layer exhibited an average lifetime of 0.8 nanoseconds (ns) and 0.8 nanoseconds (ns) in Comparative Example 3 not including the buffer layer . In the case of the photoelectrode deposited with fullerene on the tungsten oxide layer, the lifetime of the electron-hole pair was 0.7 nanoseconds (ns).

From the result of the low quantum yield of the photoluminescence as described above, it can be predicted that the photoelectrode having the buffer layer according to the present invention is selectively excited in the tungsten oxide and the charge moves effectively to the buffer layer.

 <Experimental Example 6> Photoconductive atomic force microscopy

The photoelectrodes prepared in Example 3 (WO ₃ / C ₇₀ / FTO) and Comparative Example 3 (WO ₃ / FTO) were subjected to photoconductive atomic force microscopy Photoconductive-AFM), a current mapping map and a current graph are shown in FIG. 11, and the average current values thereof are shown in Table 1.

11 shows that the bright portion of the AFM photograph shows high conductivity and that the photoelectrode of Example 3 has higher conductivity than the photoelectrode of Comparative Example 3 from the AFM photograph.

Photoelectrode Average current (㎂) Light off Light on Comparative Example 3 0.33 0.38 Example 3 0.78 3.88

As shown in Table 1, in the light off condition, the average current value of the photoelectrode of Comparative Example 3 was 0.33 占,, and the average current value of the photoelectrode of Example 3 was 0.78 占..

In the light condition, the average current value of the optical electrode of Comparative Example 3 was 0.78, and the average current value of the optical electrode of Example 3 was 3.68 占..

From the results of FIG. 11 and Table 1, it can be seen that the current of the photoelectrode including the buffer layer according to the light condition has a current value about 2 to 10 times higher than that of the photoelectrode not including the buffer layer.

Experimental Example 7 Electrochemical Impedance Spectroscopy

Electrochemical impedance spectroscopy (EIS) was performed to investigate the charge transfer resistance (R _ct ) of the photoelectrode-electrolyte interface of the photoelectrochemical cell having the photoelectrode of Example 3 and Comparative Example 3. The electrochemical impedance spectroscopy And the results are shown in FIG. 12 and Table 2.

As shown in FIG. 12, the impedance analysis results of the photoelectrode-electrolyte interface according to the applied potentials (0.6 V, 0.8 V, and 1.0 V) are shown by Nyquist plots. From the measured data, The charge transfer resistance (R _ct ) was calculated from the analysis and is shown in Table 2.

The magnitude of the arc in the impedance spectrum indicates the charge transfer resistance (R _ct ) of the tungsten oxide layer-electrolyte interface. The smaller the arc size, the faster the charge transfer. Charge transport is also influenced by recombinaiton at the interface with the material, which is generally known.

Therefore, as shown in FIG. 12, it can be seen that the charge transfer resistance (R _ct ) of the photoelectrode provided with the buffer layer according to the present invention is the lowest. As a result, The recombination rate of the recombinant DNA is also slow.

Potential Photoelectrode Surface resistance
R _s / Ω Charge transfer resistance R _ct / Ω Constant Phase Element CPE (Constant Phase Element) / ㎌ Time constant
τ / s 0.6 Comparative Example 3 41 1.795 92 0.85 Example 3 37 1.542 69 0.56 0.8
Comparative Example 3 42 1.390 100 0.69 Example 3 37 1.303 78 0.45 1.0
Comparative Example 3 39 1.073 118 0.56 Example 3 38 991 94 0.37

As shown in Table 2, the charge transfer resistance (R _ct ) and the time constant (τ) of the photoelectrode prepared in Comparative Examples 3 and 3 tended to decrease with increasing potential. In addition, in the case of Example 3 having a buffer layer, a short time constant was shown, and it can be seen that hole transport is rapidly performed in the place where water is oxidized due to easy transport of holes which are not recombined.

As can be seen from Table 2, the difference (? Rct) in charge transfer resistance between the photoelectrode-electrolyte interfaces of Comparative Example 3 and Example 3 tended to decrease as the dislocation increased, and the fired fullerene It can be seen that the effect of the buffer layer containing graphitic carbon in which a plurality of fullerenes are connected is more effective in a low potential region.

Claims (15)

Board;
A transparent electrode provided on the substrate;
A buffer layer formed on the transparent electrode and including graphitic carbon connected with a plurality of fullerenes; And
And a semiconductor layer provided on the buffer layer.
The method of claim 1, wherein the transparent electrode is formed of a material selected from the group consisting of aluminum-doped zinc oxide (AZO), indium-tin oxide (ITO), zinc oxide (ZnO) (ZnS), aluminum tin oxide (ATO; Aluminium-tin oxide; SnO 2: Al) and fluorine-containing tin oxide (FTO: fluorine-doped tin oxide ) , characterized in that it comprises at least one element selected from the group consisting of Photoelectrode for photoelectrochemical cell.
The photoelectrode for a photoelectrochemical cell according to claim 1, wherein the substrate is one selected from the group consisting of glass, titanium, nickel, and molybdenum.
The semiconductor according to claim 1, wherein the semiconductor is at least one selected from the group consisting of TiO ₂ , Ga ₂ O ₃ , In ₂ O ₃ , ZnO, Nb ₂ O ₅ , WO ₃ , SnO, SnO ₂ , Photoelectrochemical cell.
Coating a mixed solution of fullerene and an organic solvent on the upper portion of the transparent electrode, and then heat-treating the mixed solution to form a buffer layer (Step 1); And
And forming a semiconductor layer (step 2) by coating a semiconductor oxide solution on the buffer layer and then performing heat treatment.
6. The method of claim 5, wherein the concentration of fullerene in the mixed solution in step 1 is 10 to 30 mg / mL.
6. The method according to claim 5, wherein the organic solvent in step 1 is dichloromethane, dichloromethane, chloroform, N, N-dimethylformamide (DMF), tetrahydrofuran (THF) Wherein the photoelectrochemical cell comprises at least one selected from the group consisting of a metal oxide and a metal oxide.
[6] The method of claim 5, wherein the mixed solution of step 1 is coated on top of the first electrode by spin coating, spin casting, roll coating, or dip coating.
[6] The method of claim 5, wherein the heat treatment in step 1 is performed at 80 to 120 [deg.] C.
[6] The method of claim 5, wherein the heat treatment in step 2 is performed at 450 to 550 [deg.] C for 1 to 3 hours after preheating at 80 to 120 [deg.] C.
The method of claim 5, wherein the semiconductor oxide of the step 2 is one member selected from the group consisting of TiO _2, Ga ₂ O _3, In ₂ O _3, ZnO, Nb ₂ O _5, WO _3, Sn0, SnO ₂ and MgO By weight based on the total weight of the photoelectrochemical cell.
6. The method of claim 5, wherein the semiconductor oxide solution of step 2 is coated on the buffer layer formed in step 1 by one of spin coating, spin casting, roll coating and dip coating. Gt;
An optical electrode according to claim 1; A reference electrode; A counter electrode; And an electrolyte,
And the photoelectrode and the counter electrode are electrically connected to each other.
14. The method of claim 13, wherein the reference electrode (reference electrode) is a hydrogen electrode (Pt / H _2), calomel electrodes (Hg / HgCl _2), silver-silver chloride electrode (Ag / AgCl), mercury-sulphate mercury electrode (Hg / HgSO ₄ ), and a mercury-mercury-silver electrode (Hg / HgO).
The method of claim 13, wherein the counter electrode comprises at least one metal selected from the group consisting of platinum (Pt), iridium (Ir), palladium (Pd), and tantalum (Ta) Characterized by a photoelectrochemical cell.

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