KR102510362B1 - Photoelectrodes for water decomposition with carbon nanodot and a method of manufacturing the same - Google Patents

Abstract

An embodiment of the present invention provides a photoelectrode for water decomposition with carbon nanodots and a manufacturing method thereof. According to an embodiment of the present invention, the photoelectrode for water decomposition comprises: a substrate; a compound semiconductor layer located on the substrate; and a carbon nanodot layer located on the compound semiconductor layer and including a plurality of carbon nanodots.

Description

Photoelectrodes for water decomposition with carbon nanodot and a method of manufacturing the same}

The present invention relates to a photoelectrode for water splitting and a method for manufacturing the same, and more particularly, to a photoelectrode for water splitting having carbon nano dots and a method for manufacturing the same.

The photoelectrochemical water splitting method consists of a semiconducting electrode, a counter electrode, and an electrolyte, and is a method of decomposing water by exciting a photoelectrode with light in a photoelectrochemical system and using electron-hole pairs generated thereby.

At this time, when the photoelectrode receives light having energy equal to or greater than the bandgap energy, it excites electrons from a valence band to a conduction band to form electrons in the conduction band and holes in the valence band.

In addition, in the case of an n-type semiconductor, excited electrons move to the counter electrode through an internal and external circuit of the semiconductor material and participate in a reduction reaction, and holes oxidize the material included in the electrolyte toward the outside.

As a result, separation of electrons and holes occurs efficiently, and electrons generated at the photoelectrode are introduced to the counter electrode through the conducting wire to generate hydrogen.

GaN is a group III-V compound semiconductor and is a material actively used in light emitting diodes and electronic devices. Since the GaN is grown on a sapphire substrate and can form an alloy with InN, AlN, etc., the band gap can theoretically be changed in a large range from 0.7 eV to 6.1 eV.

In addition, GaN has very good chemical stability, so it does not etch or corrode in all acidic and basic solutions. In fact, GaN is very similar to nitrides such as SiNx and AlN when looking only at its chemical properties, and easily creates an alloy with oxides such as ZnO.

However, in practice, the stability of GaN is showing limitations in practical applications. In order to solve this drawback, introducing stable materials to the photoelectrode surface has been widely studied, and such a protective layer not only allows current flow through the interface, but also electrolyte must be chemically stable.

Materials such as platinum, ruthenium, and titanium oxide, which have been previously used as photocatalysts, have disadvantages such as limited reserves, high cost, environmental pollution due to toxicity, inability to disperse in aqueous phase, and instability.

As an alternative to solving this problem, a carbon-based structure, which is the most abundant element on earth, can be used. As the carbon-based structure, for example, carbon-based photocatalysts such as graphene or graphitic carbon nitride have been studied. However, it has the disadvantage that it is difficult to control the properties and does not dissolve well in water.

Republic of Korea Patent Publication No. 10-2006-0058774

The technical problem to be achieved by the present invention is to solve the above-mentioned problems of the prior art, and is provided with carbon nanodot (C-dot) to improve reaction efficiency and increase stability, which can be used universally. It is to provide a photoelectrode and a manufacturing method thereof.

The technical problem to be achieved by the present invention is not limited to the above-mentioned technical problem, and other technical problems not mentioned can be clearly understood by those skilled in the art from the description below. There will be.

In order to achieve the above technical problem, one embodiment of the present invention provides a photoelectrode for water splitting.

In one embodiment of the present invention, the method for manufacturing a photoelectrode for water splitting includes a substrate; a compound semiconductor layer positioned on the substrate; and a carbon nano-dot layer positioned on the compound semiconductor layer and including a plurality of carbon nano-dots.

In one embodiment of the present invention, the compound semiconductor layer may include at least one compound selected from GaN, GaAs, ZnO, InP, and SiC as an n-type semiconductor.

In one embodiment of the present invention, the thickness of the compound semiconductor layer may be 1 μm to 20 μm.

In one embodiment of the present invention, the carbon nanodots may be formed in a hemispherical structure.

In one embodiment of the present invention, the carbon nanodots may have an average diameter of 1 nm to 100 nm.

In order to achieve the above technical problem, another embodiment of the present invention provides a method for manufacturing a photoelectrode for water splitting.

In one embodiment of the present invention, a method for manufacturing a photoelectrode for water splitting includes forming a compound semiconductor layer on a substrate; The method may include forming an organic polymer compound layer on the compound semiconductor layer; and carbonizing the organic polymer compound layer to form a carbon nano dot layer including a plurality of carbon nano dots.

In one embodiment of the present invention, in the step of forming the compound semiconductor layer on the substrate, the compound semiconductor layer may include at least one compound selected from GaN, GaAs, ZnO, InP, and SiC as an n-type semiconductor material. can

In one embodiment of the present invention, in the step of forming the compound semiconductor layer on the substrate, the thickness of the compound semiconductor layer may be 1 μm to 20 μm.

In one embodiment of the present invention, in the step of forming the organic polymer compound layer, the organic polymer compound layer is polyacrylonitrile (PAN), pitch, cellulose, poly(vinyl alcohol) (PVA), polyimide (PI), poly (amic acid) (PAA), and at least one selected from polybenzimidazole (PBI).

In one embodiment of the present invention, in the step of forming the organic polymer compound layer, the organic polymer compound layer is prepared by injecting the organic polymer compound into dimethylformamide (DMF), the organic polymer mixture solution prepared by the compound semiconductor It can be formed by spin coating on a layer.

In one embodiment of the present invention, in the step of forming the organic polymer compound layer, the organic polymer mixture solution may contain 0.01wt% to 0.03wt% of the organic polymer compound.

In one embodiment of the present invention, in the step of forming the carbon nanodot layer, the organic polymer mixture layer is oxidized to induce a cyclization reaction, and then heat treatment is performed using a chemical vapor deposition (CVD) equipment to form the organic polymer mixture layer. A high molecular compound may be carbonized into carbon nanopoints.

In one embodiment of the present invention, in the step of forming the carbon nano dot layer, the oxidation may be heat treatment at a temperature of 150 °C to 300 °C.

In one embodiment of the present invention, in the step of forming the carbon nanodot layer, the carbonization may be heat treated at a temperature of 600 °C to 1000 °C.

According to an embodiment of the present invention, since GaN has excellent stability in an electrolyte and band gap energy that spans the redox potential of water, water can be stably separated without external deflection during the water splitting process.

In addition, the photoelectrode for water splitting according to an embodiment of the present invention includes carbon nanodots (C-dots) having properties similar to those of graphene or graphite carbon nitride, and has morphological properties. and electrical properties can be easily controlled.

The effects of the present invention are not limited to the above effects, and should be understood to include all effects that can be inferred from the detailed description of the present invention or the configuration of the invention described in the claims.

1 is a schematic diagram showing a photoelectrode for water splitting having carbon nanodots according to an embodiment of the present invention.
2 is a flowchart illustrating a method of manufacturing a photoelectrode for water splitting having carbon nanodots according to an embodiment of the present invention.
3 is an image of an X-ray diffraction analysis result for each carbon nano-dot content of a photoelectrode for water splitting having carbon nano-dots according to an embodiment of the present invention.
4 is a result of the size and distribution of the carbon nanopoint content of a photoelectrode for water splitting having carbon nanodots according to an embodiment of the present invention.
5 is a SEM image of a photoelectrode for water splitting having carbon nanodots according to the content of carbon nanodots according to an embodiment of the present invention.
6 is a TEM image of a photoelectrode for water splitting having carbon nanodots according to the content of carbon nanodots according to an embodiment of the present invention.
7 is a Raman spectrum image for each carbon nanopoint content of a photoelectrode for water splitting having carbon nanodots according to an embodiment of the present invention.
8 is a result of measuring the photocurrent density according to the voltage of the photoelectrode for water splitting having carbon nanodots according to an embodiment of the present invention for each carbon nanodot content.
9 is a result of measuring the photocurrent density over time of the photoelectrode for water splitting having carbon nanodots according to an embodiment of the present invention for each carbon nanodot content.

Hereinafter, the present invention will be described with reference to the accompanying drawings. However, the present invention may be embodied in many different forms and, therefore, is not limited to the embodiments described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

Throughout the specification, when a part is said to be "connected (connected, contacted, combined)" with another part, this is not only "directly connected", but also "indirectly connected" with another member in between. "Including cases where In addition, when a part "includes" a certain component, it means that it may further include other components without excluding other components unless otherwise stated.

Terms used in this specification are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as "include" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that the presence or addition of numbers, steps, operations, components, parts, or combinations thereof is not precluded.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

A photoelectrode for water splitting having a carbon nanodot layer will be described with reference to FIG. 1 .

1 is a schematic diagram showing a photoelectrode for water splitting having carbon nanodots according to an embodiment of the present invention.

A photoelectrode for water splitting having carbon nanodots according to an embodiment of the present invention includes a substrate 10; a compound semiconductor layer 20 positioned on the substrate; and a carbon nano-dot layer 30 disposed on the compound semiconductor layer and including a plurality of carbon nano-dots.

A photoelectrode for water splitting having carbon nanodots according to an embodiment of the present invention may include a substrate 10 .

The substrate 10 may be composed of one or more substrates selected from Al ₂ O ₃ , Quartz, Si, and GaN, and may be used if it is a general substrate that can be used as a deposition substrate for compound semiconductors without being limited to the above-mentioned materials. do.

Next, the photoelectrode for water splitting having carbon nano dots according to an embodiment of the present invention may include a compound semiconductor layer 20 .

Specifically, the compound semiconductor layer may be composed of an n-type semiconductor.

In this case, the n-type semiconductor that can be applied in the present invention is a III-V group compound semiconductor and may include one or more compounds selected from GaN, GaAs, ZnO, InP, and SiC.

At this time, in the n-type semiconductor, the excited electrons move to the counter electrode through the inside of the semiconductor material and the external circuit to participate in the reduction reaction, and the holes go outward to oxidize the material included in the electrolyte.

As a result, separation of electrons and holes occurs efficiently, and electrons generated at the photoelectrode are introduced to the counter electrode through the conducting wire to generate hydrogen.

At this time, GaN selected as the n-type semiconductor according to an embodiment of the present invention has a band gap of 0.7eV to 6.1eV and very good chemical stability, so it can have characteristics that are not etched or corroded in any acidic or basic solution. there is.

In this case, the compound semiconductor layer 20 may be formed by performing a chemical vapor deposition (CVD) method, and is not limited thereto as long as it is obvious in the art of the present invention.

Also, the compound semiconductor layer 20 may be formed to a thickness of 1 μm to 20 μm.

Next, the photoelectrode for water splitting having carbon nanodots according to an embodiment of the present invention may include a carbon nanodot layer 30 disposed on the compound semiconductor layer but including a plurality of carbon nanodots. .

The carbon nano dots 30 may be formed in a hemispherical structure.

The hemispherical carbon nano-dots 30 may have an average diameter of 1 nm to 100 nm.

At this time, the method of forming the carbon nano-dot layer 30 is as follows.

First, forming an organic polymer compound layer on a partial region of the compound semiconductor layer 20; and carbonizing the organic polymer compound layer to form a carbon nano-dot layer 30 including a plurality of carbon nano-dots. It can be formed by performing

Specifically, in order for the carbon nanopoints to have a hemispherical structure, the organic polymer mixture layer is oxidized to induce a cyclization reaction, and then heat treatment is performed using chemical vapor deposition (CVD) equipment to convert the organic polymer compound into carbon nanodots. can be carbonized.

That is, when the organic polymer compound layer formed to cover the compound semiconductor layer 20 is carbonized, the organic polymer compound may be aggregated to a certain size to form hemispherical carbon nano dots 30 .

The principle of forming the carbon nanodots is as follows.

The cyclization reaction is performed by a reaction between the polymer chain of the polyacrylonitrile (PAN) precursor and an adjacent -C≡N functional group, and a conversion reaction into a -C=N- bond occurs.

Dehydrogenation (oxidation), one of the stabilization steps of the reaction, is a reaction in which double bonds are formed to stabilize the polymer chain. At this time, the formed double bond increases thermal stability and reduces the breakage of the polymer chain during carbonization.

In the carbonization step conducted under an inert atmosphere, aromatic rings grow at high temperature and polymerization proceeds, and in this process, the mass content of carbon is converted to 90% or more. In this process, cohesion may occur due to the mutual van der Waals force.

The photoelectrode having the carbon nanodots can improve water decomposition efficiency by the photoelectrode due to the material properties of the carbon nanodot material itself having excellent mechanical strength, high electrical conductivity, and chemical stability.

In this case, an experimental example of a specific photocurrent density efficiency of the photoelectrode including the carbon nanodots will be described later.

At this time, the average diameter of the carbon nano dots 30 may be adjusted according to the content of the organic polymer compound.

The organic polymer compound layer may be formed by spin-coating an organic polymer mixture solution prepared by adding an organic polymer compound to dimethylformamide (DMF) on the compound semiconductor layer.

At this time, the organic polymer mixed solution may contain 0.01wt% to 0.03wt% of the organic polymer compound.

At this time, as the content of the organic polymer compound increases, the size of the carbon nano-dots 30 may increase, and detailed experimental examples will be described later.

Therefore, the photocatalyst for water splitting can have excellent mechanical strength and electrical conductivity of the material itself, including carbon nanopoints, and can stably separate water without external deflection in the water splitting process because of its excellent stability. .

Referring to FIG. 2, a method of manufacturing a photoelectrode for water splitting having a carbon nanodot layer will be described.

2 is a flowchart illustrating a method of manufacturing a photoelectrode for water splitting having carbon nano dots according to an embodiment of the present invention.

The manufacturing method of the photoelectrode for water splitting having the carbon nanodots includes forming a compound semiconductor layer on a substrate (S100); Forming an organic polymer compound layer on the compound semiconductor layer (S200); and carbonizing the organic polymer compound layer to form a carbon nanodot layer including a plurality of carbon nanodots (S300). there is.

In the first step, according to an embodiment of the present invention, a step of forming a compound semiconductor layer on a substrate may be included. (S100)

At this time, the substrate may be composed of one or more substrates selected from Al ₂ O ₃ , Quartz, Si and GaN, and it is not limited to the above-mentioned materials and can be used if it is a general substrate that can be used as a deposition substrate for compound semiconductors. .

In addition, the compound semiconductor layer may include at least one compound selected from GaN, GaAs, ZnO, InP, and SiC as an n-type semiconductor material.

At this time, a compound semiconductor layer may be formed on the substrate by performing a chemical vapor deposition (CVD) method.

In addition, the thickness of the compound semiconductor layer may be 1 μm to 20 μm.

In the second step, according to an embodiment of the present invention, a step of forming an organic polymer compound layer on the compound semiconductor layer may be included. (S200)

At this time, the organic polymer compound layer is at least one selected from polyacrylonitrile (PAN), pitch, cellulose, poly (vinyl alcohol) (PVA), polyimide (PI), poly (amic acid) (PAA), and polybenzimidazole (PBI) can include

At this time, at least one material selected from polyacryloniacryl (PAN), pitch, cellulose, poly(vinyl alcohol) (PVA), polyimide (PI), poly(amic acid) (PAA) and polybenzimidazole (PBI) is common. It is a carbon precursor material.

In this case, the organic polymer compound layer may be formed by spin-coating an organic polymer mixture solution prepared by adding an organic polymer compound to dimethylformamide (DMF) on the compound semiconductor layer.

The organic polymer mixed solution may contain 0.01wt% to 0.03wt% of the organic polymer compound.

In the third step, according to an embodiment of the present invention, a step of carbonizing the organic polymer compound layer to form a carbon nano-dot layer including a plurality of carbon nano-dots may be included. (S300)

In the step of carbonizing the organic polymer compound layer to form a carbon nano-dot layer including a plurality of carbon nano-dots, after inducing a cyclization reaction by oxidizing the organic polymer mixture layer, chemical vapor deposition (CVD) equipment is used. Heat treatment may be performed to carbonize the organic polymer compound into carbon nanopoints.

That is, when the organic polymer compound layer formed to cover the compound semiconductor layer is carbonized, the organic polymer compound may be aggregated to a certain size to form carbon nano dots.

The cyclization reaction is performed by a reaction between the polymer chain of the polyacrylonitrile (PAN) precursor and an adjacent -C≡N functional group, and a conversion reaction into a -C=N- bond occurs.

Dehydrogenation (oxidation), one of the stabilization steps of the reaction, is a reaction in which double bonds are formed to stabilize the polymer chain. At this time, the formed double bond increases thermal stability and reduces the breakage of the polymer chain during carbonization.

In the carbonization step conducted under an inert atmosphere, aromatic rings grow at high temperature and polymerization proceeds, and in this process, the mass content of carbon is converted to 90% or more. In this process, they can be cohesive due to the mutual van der Waals forces.

In this case, the oxidation may be heat treated at a temperature of 150 °C to 300 °C.

The reason why the oxidation is performed at a temperature of 150 °C to 300 °C is that in the stabilization step in an oxidizing atmosphere, a cyclization reaction and a dehydrogenation reaction proceed to form a ladder structure having heat resistance, and through this, a high temperature This is because it can prevent the melting of carbon nanopoints in After this stabilization step, the carbon nano dots of the white polyacrylonitrile (PAN) polymer turn brown.

In addition, the carbonization may be heat treated at a temperature of 600 °C to 1000 °C.

The reason why the carbonization is performed at a temperature of 600 ° C to 1000 ° C is that in the carbonization step, which is performed under an inert atmosphere, aromatic rings grow at high temperatures, polymerization proceeds, and in this process, the mass content of carbon can be converted to 90% or more. Because.

At this time, if you look closely at the carbonization process, it can be divided into two steps. The first step is the thermal decomposition process, which is the reaction zone up to 600 °C. In this region, the polymeric ring is unstable and the rate of material transport is slow.

In the second step, in the range of 600 °C to the final carbonization temperature, the polymer ring is structurally stabilized to form final high-purity carbon. In addition, when heated to a temperature of 800 °C or higher, N ₂ and HCN gas increase and CH ₄ , CO, and CO ₂ gas are generated to increase the number of carbon rings, thereby producing high-strength carbon nanodots.

In order to analyze the physical or chemical properties of the photoelectrode for water splitting having the above-described carbon nanodots, after carbonizing the organic polymer compound layer to form a carbon nanodot layer including a plurality of carbon nanodots, the After generating carbon nano dots (C-dots) on the compound semiconductor layer, forming an ohmic junction with a Cu wire using indium solder; Additional insulation of all samples with epoxy resin to prevent leakage current generated when injected into the electrolyte; and curing the epoxy resin by drying at room temperature for one day to analyze the characteristics of the photovoltaic cell (PEC). can do.

Since the photoelectrode for water splitting having carbon nanodots according to an embodiment of the present invention includes an electrolyte that spans the redox potential of water and a compound semiconductor layer having excellent stability in band gap energy, there is no external deflection in the water splitting process. water can be separated reliably.

In addition, the photoelectrode for water splitting according to an embodiment of the present invention includes carbon nanodots (C-dots) having properties similar to those of graphene or graphite carbon nitride, and has morphological properties. and electrical characteristics can be easily controlled.

According to an embodiment of the present invention, the stability of water splitting can be improved due to the development of a carbon nano-dot photocatalyst that is manufactured at low cost and whose properties can be easily controlled.

Example

A method for manufacturing a photoelectrode for water splitting having carbon nanodots according to an embodiment of the present invention will be described.

First, a 2-inch Al ₂ O ₃ substrate is prepared.

Next, an MOCVD method is performed on the Al ₂ O ₃ substrate to form a compound semiconductor layer made of GaN.

Next, an organic polymer mixed solution is prepared by adding polyacrylonitrile (PAN) to dimethylformamide (DMF).

At this time, the content of the polyacrylonicryl (PAN) is 0.03 wt%.

Next, spin coating is performed to form the organic polymer mixed solution in a partial region on the compound semiconductor layer to a thickness of 10 nm.

Next, the spin-coated polyacrylonicryl (PAN) layer is heated at 270° C. for 2 hours in a box furnace to be oxidized.

Next, the substrate on which the oxidized polyacrylonitrile (PAN) layer is formed is put into a chemical vapor deposition (CVD) equipment, and then heat treated at 800°C at a rate of 5°C/min in a hydrogen/argon mixed gas atmosphere. carbonize

Next, an ohmic junction is formed with a copper (Cu) wire using indium solder.

Next, it is further insulated with epoxy resin.

Next, the epoxy resin is cured by drying at room temperature for one day.

Thus, a photoelectrode for water splitting having carbon nanodots was manufactured.

Experimental example

In order to investigate the photoelectrochemical performance, Ag / AgCl / KCl in NaOH electrolyte 1M as a reference electrode (Reference Electrode), Pt wire as a counter electrode (Count Electrode), and for water decomposition having carbon nano dots according to an embodiment of the present invention Photoelectrochemical properties were evaluated using an AM 1.5G solar simulator by configuring three electrodes as a working electrode.

Among the photoelectrodes for water splitting prepared in the above example, each sample carbonized by adjusting the content of polyacryloniacryl (PAN) to 0.01wt%, 0.02wt% or 0.03wt% was prepared with C-dot 0.01 wt%, Abbreviated as C-dot 0.02 wt% or C-dot 0.03 wt%.

3 is an image of an X-ray diffraction analysis result for each carbon nano-dot content of a photoelectrode for water splitting having carbon nano-dots according to an embodiment of the present invention.

3 is an X-ray diffraction analysis result of a photoelectrode containing 0.01wt% C-dot, 0.02wt% C-dot, and 0.03wt% C-dot and the surface of GaN after the carbonization process.

Referring to FIG. 3, when the peaks of the photoelectrode containing 0.01 wt% of C-dot, 0.02 wt% of C-dot, and 0.03 wt% of C-dot are compared with GaN, the peaks of the photoelectrode in which the carbon nano dots are generated It is possible that the X-ray diffraction peak did not shift.

Thus, it can be confirmed that the compound semiconductor layer made of GaN is formed in the photoelectrode having carbon nano dots according to an embodiment of the present invention.

4 is a result of the size and distribution of the carbon nanopoint content of a photoelectrode for water splitting having carbon nanodots according to an embodiment of the present invention.

4 shows that the average size of the carbon nano dots of the photoelectrode containing 0.01 wt% of C-dot is 5.62 nm, and the average size of the photoelectrode containing 0.02 wt% of C-dot is 6.82 nm and 0.03 wt% of C-dot. The average size of the containing photoelectrodes is 11.97 nm.

Referring to Figure 4, it can be seen that the average size of the diameter of the carbon nano-dots (C-Dot) increases as the content of polyacrylonitrile (PAN) increases. Easy to control.

5 is a SEM image of a photoelectrode for water splitting having carbon nanodots according to the content of carbon nanodots according to an embodiment of the present invention.

Figure 5 (a) shows the surface of GaN on which carbon nano dots are not formed, Figure 5 (b) shows the surface of carbon nano dots with a C-dot content of 0.01 wt%, and Figure 5 (c) shows a surface with a C-dot content of 0.02 wt %. The surface of phosphorus carbon nanodots, FIG. 5(d) may show the surface of carbon nanodots having a C-dot content of 0.03 wt%.

Referring to FIG. 5, as the content of polyacrylonitrile (PAN) on the surface of GaN increases, the number of C-Dots applied increases and the size of the C-Dots increases. can do.

6 is a TEM image of a photoelectrode for water splitting having carbon nanodots according to the content of carbon nanodots according to an embodiment of the present invention.

In addition, in order to perform TEM analysis of the photoelectrode for water splitting having the carbon nanodots, a platinum (Pt) layer was formed on the carbon nanodots.

Referring to FIG. 6, as an image showing a cross section of carbon nano dots (C-Dot) formed on the GaN surface, it can be confirmed that the carbon nano dot (C-Dot) maintains a dot shape on the GaN surface. there is.

7 is a Raman spectrum image for each carbon nanopoint content of a photoelectrode for water splitting having carbon nanodots according to an embodiment of the present invention.

7 shows the intensity and lost energy of inelastically scattered light observed in graphene and graphite.

Referring to FIG. 7, the peak labeled G near 1580 cm ^-1 is generated by an in-plane phonon mode with zero momentum, which is a common peak in graphite-related materials. It is marked with G, the first letter of Graphite.

The peak near 1350 cm ^-1 labeled D appears when inelastic scattering by phonons having 1350 cm ^-1 energy and elastic scattering around the defect/substitution point occur consecutively regardless of order, and the defect and substitution occur The larger the number of structures, the greater the intensity of the peak.

In addition, since the peak marked with 2D near 2700 cm ^-1 appears when inelastic scattering by phonons having energy of 1350 cm ^-1 occurs twice in succession, the corresponding peak appears around 2700 cm ^-1 which is twice as large as 1350 cm ^-1 . .

Therefore, looking at the graph of FIG. 7, the photoelectrode for water splitting according to an embodiment of the present invention has peaks appearing in the D band (1363 cm ^-1 ), the G band (1577 cm ^-1 ) and the 2D band (2816 cm ^-1 ). Since there is, it can be confirmed that materials with graphene or carbon properties are included.

At this time, since the same peaks are shown according to the content of carbon nano-dots (C-Dots) carbonized on GaN in the method according to an embodiment of the present invention described above, it can be confirmed that there is almost no difference in quality by content.

8 is a result of measuring the photocurrent density according to the voltage of the photoelectrode for water splitting having carbon nanodots according to an embodiment of the present invention for each carbon nanodot content.

Compared to the water splitting photocurrent density of conventional GaN, it was confirmed that the photocurrent density efficiency was improved in all samples with carbon nano dots (C-Dot), and in particular, the highest photocurrent density was obtained at 0.01 wt% of C-Dot. can do.

At this time, it was confirmed that the photocurrent density of the photoelectrode containing 0.02 wt% of C-Dot and 0.03 wt% of C-Dot was reduced compared to the photocurrent density of the photoelectrode containing 0.01 wt% of C-Dot. This may be due to the increased defect density when the C-Dot) content is increased.

9 is a result of measuring the photocurrent density over time of the photoelectrode for water splitting having carbon nanodots according to an embodiment of the present invention for each carbon nanodot content.

9 is a graph confirming the water decomposition reliability of the photoelectrode including carbon nano-dots (C-Dot).

Referring to FIG. 9 , when carbon nano dots (C-Dots) were formed, the stability of all samples was improved, but it could be confirmed that the C-Dot 0.03 wt% sample showed the lowest reliability.

However, it can be confirmed that the C-Dot 0.03 wt% sample shows higher stability than the conventional GaN.

The carbon nano-dots (C-Dot) according to an embodiment of the present invention can improve the stability of GaN by preventing photoholes from accumulating on the electrode surface as well as increasing photocurrent due to fast charge transfer. there is.

The above description of the present invention is for illustrative purposes, and those skilled in the art can understand that it can be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. will be. Therefore, the embodiments described above should be understood as illustrative in all respects and not limiting. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form.

The scope of the present invention is indicated by the following claims, and all changes or modifications derived from the meaning and scope of the claims and equivalent concepts thereof should be construed as being included in the scope of the present invention.

10: substrate
20: compound semiconductor layer
30: organic high molecular compound layer

Claims (14)

Board;
a compound semiconductor layer positioned on the substrate; and
A carbon nano-dot layer positioned on the compound semiconductor layer and including a plurality of carbon nano-dots,
The carbon nano-dots are photoelectrode for water splitting, characterized in that formed in a hemispherical structure. According to claim 1,
The compound semiconductor layer is an n-type semiconductor photoelectrode for water splitting, characterized in that it contains at least one compound selected from GaN, GaAs, ZnO, InP and SiC. According to claim 1,
A photoelectrode for water splitting, characterized in that the thickness of the compound semiconductor layer is 1 μm to 20 μm. delete According to claim 1,
The carbon nanodots have an average diameter of 1 nm to 100 nm, characterized in that the photoelectrode for water splitting. forming a compound semiconductor layer on the substrate;
forming an organic polymer compound layer on the compound semiconductor layer; and
Carbonizing the organic polymer compound layer to form a carbon nanodot layer including a plurality of carbon nanodots,
After oxidizing the organic polymer mixture layer to induce a cyclization reaction, heat treatment using a chemical vapor deposition (CVD) equipment is performed to carbonize the organic polymer compound into carbon nanodots, and the carbon nanodots are formed in a hemispherical structure. Method for manufacturing a photoelectrode for water splitting, characterized in that. According to claim 6,
In the step of forming a compound semiconductor layer on the substrate,
Wherein the compound semiconductor layer comprises at least one compound selected from GaN, GaAs, ZnO, InP and SiC as an n-type semiconductor material. According to claim 6,
In the step of forming a compound semiconductor layer on the substrate,
The method of manufacturing a photoelectrode for water splitting, characterized in that the thickness of the compound semiconductor layer is 1 ㎛ to 20 ㎛. According to claim 6,
In the step of forming the organic polymer compound layer,
The organic polymer compound layer includes at least one selected from polyacrylonitrile (PAN), pitch, cellulose, poly(vinyl alcohol) (PVA), polyimide (PI), poly(amic acid) (PAA), and polybenzimidazole (PBI) Method for manufacturing a photoelectrode for water splitting, characterized in that. According to claim 6,
In the step of forming the organic polymer compound layer,
The organic polymer compound layer is formed by spin-coating an organic polymer mixture solution prepared by adding an organic polymer compound to dimethylformamide (DMF) on the compound semiconductor layer. According to claim 10,
In the step of forming the organic polymer compound layer,
The method of manufacturing a photoelectrode for water splitting, characterized in that the organic polymer mixed solution contains 0.01wt% to 0.03wt% of the organic polymer compound. delete According to claim 6,
In the step of forming the carbon nano-dot layer,
The oxidation is a method for manufacturing a photoelectrode for water splitting, characterized in that heat treatment at a temperature of 150 ° C to 300 ° C. According to claim 6,
In the step of forming the carbon nano-dot layer,
The carbonization is a method for manufacturing a photoelectrode for water decomposition, characterized in that heat treatment at a temperature of 600 ° C to 1000 ° C.

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