KR20190083511A - Photoanode comprising Ti:B co-doped hematite and preparing method thereof - Google Patents

Abstract

The present invention relates to a photoanode including hematite heterogeneously doped with titanium and boron, and a manufacturing method thereof. More specifically, the hematite photoanode heterogeneously doped with titanium and boron reduces the number of Ti^(4+) and Sn^(4 +) ions causing an electronic-hole pair (EHP) recombination on a surface of hematite, and generates an inner electric field to facilitate hole extraction such that a maximum length (500 to 600 nm) of the well-known hematite with the most excellent photoelectrochemical (PEC) performance is increased up to 890 nm. Accordingly, a chronic short hole diffusion length problem causing a high electronic-hole recombination speed can be removed and thus, the hematite photoanode heterogeneously doped with titanium and boron can be usefully applied as a photoanode for a hydrolysis PEC cell.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a photoanode comprising hematite heterodoped with titanium and boron and a method of manufacturing the same.

The present invention relates to a photodeode comprising hematite heterogeneously doped with titanium and boron and a method of making the same, and more particularly to a photodeode comprising hematite heterogeneously doped with titanium and boron, The present invention relates to a photoanode and a method for manufacturing the same, which can be very useful as a water-decomposable PEC battery because it can solve the problem of short-length short hole diffusion length which causes a high speed.

As energy consumption increases, environmental problems are also increasing. The development of clean, low-cost, and renewable energy sources is one of the important challenges to meet both energy and environmental aspects.

Solar, biomass, and geothermal energy are presented as clean, renewable sources of energy that can meet both energy and environmental aspects. Water decomposition is a reaction mechanism that generates hydrogen gas by solar energy in photoelectrochemical (PEC) cells.

The PEC cell is composed of two parts, a photoanode and a counter electrode. The photoanode generates an oxygen evolution reaction (OER ', 2H ₂ O + 4h ⁺ ? O ₂ + 4H ⁺ ) And a hydrogen evolution reaction (hereinafter referred to as 'HER', 4H ⁺ + 4e ^- ? 2H ₂ ) occurs in the counter electrode.

The performance improvement of PEC cell for water decomposition, in which hydrogen and oxygen gas are generated by sunlight, is becoming an important problem in energy and environment field, and there is strong demand for cheap and clean energy. Metal-oxide semiconductors such as TiO ₂ , ZnO, BiVO ₄ and α-Fe ₂ O ₃ have been extensively studied as photoanodes suitable for PEC water decomposition systems.

Hematite (α-Fe ₂ O ₃ ) has the theoretical solar-to-hydrogen (STH) efficiency (16.8%), low cost, suitable bandgap for visible light absorption (1.8-2.2 eV) And are ideal oxidation-metal photodiodes for PEC systems due to their excellent chemical stability in neutral electrolytes. However, the realization of the theoretical STH efficiency of hematite is still limited, because the hematite has a high electron-hole recombination rate resulting in short hole-diffusion length (2-4 nm), poor conductivity and surface defects. It further reduces the PEC performance of the hematite due to its low absorption coefficient, low OER activity, and slow charge mobility kinetics.

To overcome these shortcomings, various strategies such as doping, synthesis of nanostructures and OER catalyst deposition have been introduced. Among them, the use of dopants in hematite has been widely used to improve the conductivity and improve the PEC performance of? -Fe ₂ O ₃ . The elemental doping is performed by doping a metal ion dopant (n type dopants: Ti ^{4 +} , Sn ^{4 +} , Pt ^{4 +} , and Zr ^{4 +} and p type dopants: Mg ^{2 +} , Zn ^{2 +} , Ag ⁺ and Cu ^{2 +} And a non-metal dopant such as P is used. The n-type dopant of α-Fe ₂ O ₃ generally reduces the Fe ^{3 +} to Fe ^{2 +} by introducing electrons into the nearby Fe ^{3 +} region and increases the probability of polaron hopping by lattice transformation, Thereby enhancing the electrical conductivity. It also improves charge transfer by increasing the donor concentration and reducing the effective mass of electrons.

The p-type dopant creates an additional state on the balance band of the hematite and forms a pn junction at the surface. The pn junction effectively reduces charge recombination by providing a complementary charge-coupled driving force due to the increased internal potential. Similarly, nn ⁺ homo-junctions, which cause the interface between lightly doped semiconductors and heavily doped semiconductors, have been used to reduce the contact resistance between semiconductor and metal contacts by inducing slight bending of the energy band.

So far, only Si and P have been reported as nonmetal dopants for hematite. The electron conductivity of the non-metal doped hematite is difficult to capture electrons in the free radial orbit of Si-O and PO due to the high electron carrier potentials of Si and P, so that the electron conductivity of the nonmetallically doped hematite is less than that of metal doped hematite ≪ / RTI > Thus, non-metallic dopants do not interfere with charge transport through the original polarophone hopping mechanism in the? -Fe ₂ O ₃ lattice and enhance the PEC performance of the hematite.

On the other hand, there is still a need for research and development on a photoanode for a water-decomposable PEC battery which can solve the problem of chronic short hole diffusion length leading to a high electron-hole recombination speed.

Korean Patent No. 1520260

It is an object of the present invention to provide a photoanode for a water-decomposable PEC battery and a method of manufacturing the same, which can solve the problem of short, short-hole-diffusion length leading to a high electron-hole recombination speed.

In order to achieve the above object, the present invention provides a transparent electrode substrate, And a photodiode comprising titanium and boron-doped hematite in a rod shape on the transparent electrode substrate.

The present invention also provides a photoelectrochemical cell (PEC cell) for decomposing water containing the photoanode.

The present invention also relates to a method for preparing a solution, comprising: preparing a solution by mixing a titanium source and an iron source; Immersing the transparent electrode substrate in the solution to grow FeOOH (Ti-FeOOH) doped with titanium on the transparent electrode substrate through hydrothermal growth; Synthesizing _{a: (B-Fe 2 O 3} Ti); the Ti-FeOOH the growth was the transparent electrode substrate is immersed in acid solution after heat treatment to a titanium and boron-doped hematite And wherein the Ti: B-Fe ₂ O ₃ cleaning, and provides a method for producing the photo-node containing a heterologous doped Hema Tate by including the step of drying, the titanium and boron.

The titanium and boric acid heterodoped hematite photoanode according to the present invention is a technique to solve the problem of chronic short hole diffusion length resulting in a high electron-hole recombination rate and accordingly the critical length limitation of hematite. In the case of EHP recombination as well as to reduce the number of Ti ^{4 +} and Sn ^{4 +} ions to cause, easy to generate the internal electric field by allowing the hole extraction known in the art the best PEC performance hematite maximum length (500 nm to having 600 nm ) Can be increased to 890 nm. In particular, with a diameter of length and 70 nm of 890 nm of titanium and boron two kinds of doped hematite converts incident photons in a much less recombinant EHP ^{and, 1.92 mA / cm 2, 1.50} V RHE at 2.83 mA at 1.23 V _RHE / cm < ^{2 &} gt ;.

1, Ti: B-Fe ₂ O ₃ produced a schematic view _{(a), Fe 2 O 3} , Ti-Fe 2 O 3, and Ti of: B-Fe ₂ O for ₃ XRD data _{(b), Ti-Fe 2} O 3, And (c, d, e) of XPS analysis of Ti: B-Fe ₂ O ₃ ,
FIG. 2 is a schematic diagram (a: Ti-Fe ₂ O ₃ , b: Ti: B-Fe ₂ O ₃ ) of the energy band diagram and charge transfer process (r _b means recombination)
3 is _{Fe 2 O 3, Ti-Fe} 2 O 3, and Ti: photoelectric current density according to the growth period of the _{B-Fe 2 O 3 (a} ), Fe 2 O 3, Ti-Fe 2 O 3, and Ti: B-Fe ₂ O ₃ of the IV curve (b), 1.50 V _RHE a _{Fe 2 O 3, Ti-Fe} 2 O 3, and Ti measured at: IPCE (c) of the _{B-Fe 2 O 3, 1.50} V RHE, (D) of Fe ₂ O ₃ , Ti-Fe ₂ O ₃ , and Ti: B-Fe ₂ O ₃ measured under illumination,
4 is a _{FeOOH-Ti: B-Fe 2} O 3 -3 of a TEM image (a), Ti: B- Fe 2 O 3 -3 and _{FeOOH-Ti: B-Fe 2} O 3 -3 of the IV curve (b ),
5 shows SEM images of Fe ₂ O ₃ -1, Ti-Fe ₂ O ₃ -1, B-Fe ₂ O ₃ -1 and Ti: B-Fe ₂ O ₃ -1,
Figure 6 shows a TEM image of Ti-Fe ₂ O ₃ (a) and Ti: B-Fe ₂ O ₃ (b)
FIG. 7 is a graph showing the relationship between Fe ₂ O ₃ , Ti-Fe ₂ O ₃ , B-Fe ₂ O ₃ And Ti: B-Fe ₂ O ₃ , respectively.
8 is a Ti: SEM image of a _{B-Fe 2 O 3 -1 (} a, e, i), Ti: B-Fe 2 O 3 -2 of the SEM images (b, f, j), Ti: B-Fe ₂ O ₃ in the SEM image -3 (c, g, k) , Ti: will showing a B-Fe ₂ O ₃ -4 of the SEM images (d, h, l),
9 is a _{Ti-Fe 2 O 3 (1.71} eV) , and Ti: 2.10 for the _{B-Fe 2 O 3: B} -Fe 2 O 3 VBM of (1.35 eV) (a), Ti-Fe 2 O 3 and Ti eV and a Tauc plot (b) as a photon energy function providing an optimum band gap (Eg) of 2.14 eV,
FIG. 10 is a graph showing the relationship between Fe ₂ O ₃ , Ti-Fe ₂ O ₃ , B-Fe ₂ O ₃ And Ti: B-Fe ₂ O ₃ ,
11 is under AM 1.5 solar simulator in 1M NaOH electrolyte at 1.23 V _RHE for 18 hours Ti: will shown the stability data of the B-Fe ₂ O _3,
FIG. 12 is a graph showing the relationship between Fe ₂ O ₃ , Ti-Fe ₂ O ₃ , B-Fe ₂ O ₃ And Ti: B-Fe ₂ O ₃ .

Hereinafter, the present invention will be described in more detail.

The present invention relates to a transparent electrode substrate; And a photodiode comprising titanium and boron-doped hematite in a rod shape on the transparent electrode substrate.

The transparent electrode substrate may be any one selected from the group consisting of FTO, ZnO, ITO, AZO, GZO, IZO, and IGZO, but is not limited thereto.

The titanium and boron doped hematite preferably have an average length of 300 nm to 890 nm and an average diameter of 50 nm to 100 nm.

The node in the port may further comprise a FeOOH thin layer.

The present invention also provides a photoelectrochemical cell (PEC cell) for decomposing water containing the photoanode.

The present invention also relates to a method for preparing a solution, comprising: preparing a solution by mixing a titanium source and an iron source; Immersing the transparent electrode substrate in the solution to grow FeOOH (Ti-FeOOH) doped with titanium on the transparent electrode substrate through hydrothermal growth; Synthesizing _{a: (B-Fe 2 O 3} Ti); the Ti-FeOOH the growth was the transparent electrode substrate is immersed in acid solution after heat treatment to a titanium and boron-doped hematite And wherein the Ti: B-Fe ₂ O ₃ cleaning, and provides a method for producing the photo-node containing a heterologous doped hematite by including the step of drying, the titanium and boron.

Node production method in the picture is, the Ti: may further comprise the step of depositing a thin layer on the FeOOH B-Fe ₂ O ₃ surface.

The titanium source, titanium chloride (TiCl _3), titanium dioxide (TiO _2), a hydrogenated titanium (TiH _2), titanium tetrachloride (TiCl _4), titanium nitride (TiN), and titanium isopropoxide (C ₁₂ H ₂₈ O ₄ Ti), but the present invention is not limited thereto.

The iron source is ferric chloride, hexahydrate _{(FeCl 3 · 6H 2 O)} , fluorine hwacheol hydrate _{(FeF 2 · xH 2 O)} , iron sulfide hydrate _{(FeSO 4 · xH 2 O)} , iron acetate (Fe (CO ₂ CH ₃ ) ₂ ) and iron nitride hydrate (Fe (NO ₃ ) ₃ xH ₂ O), but the present invention is not limited thereto.

The transparent electrode substrate may be any one selected from the group consisting of FTO, ZnO, ITO, AZO, GZO, IZO, and IGZO, but is not limited thereto.

The step of growing titanium-doped FeOOH (Ti-FeOOH) on the transparent electrode substrate is performed by immersing the transparent electrode substrate in the solution and then performing heat treatment from 30 ° C to 100 ° C for 1 to 3 hours, And can be maintained for 2 to 4 hours.

The step of synthesizing the titanium and boron-doped hematite may be performed by immersing the Ti-FeOOH-grown transparent electrode substrate in a boric acid solution for 10 minutes to 1 hour, and then heat-treating at 700 to 900 ° C for 15 to 30 minutes .

The Ti: depositing a thin layer on the FeOOH B-Fe ₂ O ₃ surface, the Ti through hydrothermal growth: it is possible to deposit a thin layer of FeOOH in the B-Fe ₂ O ₃ surface.

More specifically, according to an embodiment of the present invention, metal ions (Ti ^{4 +} ) and nonmetal (B) are doped by in-situ and ex-situ methods for improving the performance of hematite-based PEC water- And a? -Fe ₂ O ₃ (Ti: B-Fe ₂ O ₃ ) PEC water-decomposing cell. Ti: Ti- doped iron oxide to produce a B-Fe ₂ O _3, by hydrothermal processes using TiCl ₃ solution (III) - hydroxide (β-FeOOH) and then synthesizing the nano-rods, and boric acid solution (H ₃ BO ₃ ) and then subjected to a high-temperature heat treatment (at 800 ° C for 20 minutes). Ti: B-Fe ₂ O ₃ has exhibited a photoelectric current density of 1.92 mA at 1.23 V _RHE, which means a 225% improvement in PEC activity than the α-Fe ₂ O _3.

In the present invention, the synergistic effect of the reduction of recombination due to the decrease of the metal ion concentration of the hematite lattice and the additional charge separation driving force for hole extraction by the formation of the nn ⁺ junction at the Ti: B-Fe ₂ O ₃ surface is great, B-Fe ₂ O _3, insert the cheap OER catalyst (FeOOH) to the surface, FeOOH / Ti: B-Fe 2 O photoelectric current density of ₃ is reached 2.35 mA / cm ² eseo 1.23 V _RHE the nn ⁺ junction and OER catalyst Lt; / RTI >

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the present invention is not limited by these examples.

Example 1 Preparation of Hematite Photoanode Heterologically Doped with Titanium and Boron

1. Fe ₂ O ₃  And Ti-doped Fe ₂ O ₃  Photo anode manufacturing

The hematite (α-Fe ₂ O ₃ ) photoanode was grown on a fluorine doped tin oxide (FTO) glass substrate through a previously known water-soluble chemical growth method followed by a high temperature heat treatment process . The experiment was carried out in an aqueous solution containing 100 mL of 150 mM ferric chloride hexahydrate (FeCl ₃ 6H ₂ O). The solution was placed in a cap-sealed glass vial containing two successive slips of FTO glass leaning against the inner wall. The glass vials were placed in a forced convection oven with a programmed temperature controller. The mixture was heated from 30 ° C to 100 ° C for 2 hours, and then maintained for 3 hours to synthesize a β-FeOOH rod on the FTO substrate. It was then thoroughly rinsed with deionized water and dried with N ₂ gas. The β-FeOOH formed on the FTO substrate was placed in a furnace tube at 800 ° C. for 20 minutes and taken out under ambient conditions. For this experiment, solution-derived β-FeOOH rod growth was repeated four times. Each label is represented by Fe ₂ O ₃ -1, Fe ₂ O ₃ -2, Fe ₂ O ₃ -3 and Fe ₂ O ₃ -4. Ti doped Fe ₂ O ₃ photoanode was prepared by adding 7 μl TiCl ₃ solution to 100 ml of 150 mM ferric chloride hexahydrate (FeCl ₃ 6H ₂ O). Ti-doped Fe ₂ O ₃ photo process for producing the anode was also repeated four times, each cover-Fe ₂ O ₃ -1 Ti, Ti-Fe ₂ O ₃ -2, Ti-Fe ₂ O ₃ and Ti-Fe ₂ O ₃ -4.

2. Boron doping Fe ₂ O ₃ (B-Fe ₂ O ₃ ) And Ti: B heterodoped Fe ₂ O ₃ (Ti: B-Fe ₂ O ₃ ) Photo anode manufacturing

The β-FeOOH bar or Ti-doped β-FeOOH formed on the FTO substrate was immersed in 10 mM boric acid (H ₃ BO ₃ ) solution for 30 minutes, then thoroughly rinsed with deionized water and dried with N ₂ gas. Each sample was placed in a furnace tube at 800 ° C for 20 minutes and taken out under ambient conditions. Boron doped _{Fe 2 O 3 (B-Fe} 2 O 3) a _{B-Fe 2 O 3 -1,} B-Fe 2 O 3 -2, B-Fe 2 O 3 -3 and B-Fe ₂ O ₃ -4 exhibited by, Ti: B doping two kinds of _{Fe 2 O 3 (Ti: B} -Fe 2 O 3) a _{Ti: B-Fe 2 O 3} -1, Ti: B-Fe 2 O 3 -2, Ti: B- Fe ₂ O ₃ -3 and Ti: B-Fe ₂ O ₃ -4.

FIG. 1 (a) shows a schematic diagram of a process for producing Ti: B-Fe ₂ O _{3. After} the boron ions are diffused to the surface of Ti-Fe ₂ O ₃ during the heat treatment process, Ti-Fe _2-x B _x O ₃ compound was synthesized. The presence of the outer Fe _2-x B _x O ₃ layer with an increase in the bandgap of Ti: B-Fe ₂ O ₃ was confirmed by UV-vis spectroscopy and Tauc plot as previously reported (Figs. 7 and 9) .

≪ Example 2 > Performance evaluation of hematite photodiodes heterogeneously doped with titanium and boron

5 shows SEM images of Fe ₂ O ₃ , Ti-Fe ₂ O ₃ , and Ti: B-Fe ₂ O ₃ . Ti: The diameter of B-Fe ₂ O ₃ is caused in the boric acid solution with a small erosion of the Ti-FeOOH even slightly less than the Ti-Fe ₂ O ₃ Ti: B-Fe ₂ O ₃ Fe ₂ O ₃ and the original Ti- Fe ₂ O ₃ . As shown in the XRD data (Fig. 1 (b)), the (110) plane, which plays an important role in electron transfer in the lattice of the hematite, was not degraded by the heterodoping of Ti and B.

X-ray photoelectron spectroscopy (XPS) was carried out as shown in FIG. 1 (c) in order to reveal the surface characteristics of Ti: B-Fe ₂ O ₃ . The XPS spectrum of the B1s region was separated into three peaks centered at 188.8, 190.3 and 192.0 eV corresponding to the binding energy (BE) of Ti-B, Fe-BO and Ti-BO, respectively. The oxygen binding of Fe-B and Fe ₂ -B with binding energy of 187.9 eV and 188.3 eV decreased the B1s electron density and the BE of Fe-BO increased from Fe-B of 190.7 eV to 190.3 eV. The XPS signal at 192.0 eV corresponds to the BE of Ti-BO, which implies the gap doping of B in the hematite. BE of B ₂ O ₃ was detected at 192.0 eV at the XPS peak, but Fe ₂ O ₃ The external B ₂ O ₃ layer on the substrate was not observed in the TEM image (FIG. 6) due to the weak chemical stability in the highly alkaline solution (1 M NaOH).

In Figure 1. As shown in (d), Ti-Fe ₂ O ₃ in the case _{459.0 eV (Ti 2P 3/2} ) and have two peaks at _{465.0 eV (Ti 2P 1/2} ), which Fe ₂ O ₃ Ti ^{4 +} is present. After adding B ions to the surface of Ti-Fe ₂ O ₃ , the downward shifted XPS peak of Ti 2 P _3/2 appeared at 458.3 eV, which is due to the formation of Ti ^{3 +} species. The overall XPS peaks of Ti 2P _3/2 and Ti 2P _1/2 were reduced, which means that the Ti ions substituted in the lattice of the hematite were replaced by boron ions. B ³⁺ is due to provide electrons to Ti ^{+ 4} via the charge compensation mechanism Ti: Fe ₂ O ₃ is in the-B Ti ^{+ 3} was produced.

Figure 1 (e) As shown in the Ti-Fe ₂ O ₃ and Ti: B-Fe ₂ O ₃ are all respectively Sn 3d _5/2, and Sn 3d _{3 /} at 486.4 and 494.4 eV corresponding to the BE of ₂ Sn 3d Peak. This is because the Sn ^{4 +} ions are known to diffuse from the FTO substrate to the hematite lattice during the high temperature conversion process (from Ti: B-FeOOH / FTO to Ti: B-Fe ₂ O ₃ / FTO at 20O 0 C for 20 minutes). The peak intensity of Sn ^{4 +} ion in Ti: B-Fe ₂ O ₃ was lower than that of Ti-Fe ₂ O ₃ as shown in FIG. 1 (e). This means that the same valence B (+3) as Fe (+3) facilitates the doping of hematite more easily than Sn (+4) by treatment with H ₃ BO ₃ .

< Example  3> Heterogeneous to titanium and boron Doped Hematite Photo anode  Review effects

Hereinafter, the positive effects of heterodoping of Ti and B of hematite on the formation of nn ⁺ homo-junction and charge transfer in Ti: B-Fe ₂ O ₃ will be described.

The maximum valence band (VBM) of Ti: B-Fe ₂ O ₃ is located at a high level (1.35 eV) as compared with 1.71 eV of Ti-Fe ₂ O ₃ (FIG. 9A) . As shown in the Tauc plot (FIG. 9B), the optical bandgaps of Ti-Fe ₂ O ₃ and Ti: B-Fe ₂ O ₃ were 2.10 eV and 2.14 eV, respectively. As shown in FIG. 2, an energy band gap diagram of an n-type semiconductor (Ti-Fe ₂ O ₃ ) having an nn ⁺ homojunction in an electrolyte was formed by combining a VBM and a photonic bandgap.

As shown in FIG. 2 (a, I), the electron-hole pairs (EHPs) generated in the recombined bulk region due to the absence of the special driving force for the charge extraction, Only holes were released to the electrolyte from Ti-F ₂ O ₃ .

It is also reported that substituted Ti ^{4 +} and Sn ^{4 +} ions improve the conductivity of the hematite, but Ti ^{4 +} and Sn ^{4 +} ions near the Ti-F ₂ O ₃ surface become recombination sites and α-Fe ₂ O ₃ due to structural changes generated by metal doping in the lattice near the conduction band minimum (CBM), which impedes the charge transfer between the hematite and the electrolyte, thereby degrading the PEC performance. On the other _{hand, Ti: B-Fe 2 O} 3 Fe ₂ O ₃ of the bulk-Ti The holes from the region were easily released into the electrolyte due to the internal electric field induced by the Ti-Fe _{2 - x} B _x O ₃ layer, which significantly reduced the recombination as in Figure 2b (II).

In addition,, Ti as it demonstrated in the XPS data: Structure of the grating on the surface of B-Fe ₂ O ₃ is a Ti: minimized because of the Ti ^{4 +,} and Sn ^{4 +} ions reduced at the surface of the B-Fe ₂ O ₃ And the Ti ^{4 +} and Sn ^{4 +} ions in the bulk region remained the same due to the short diffusion length of boron ions during the ex-situ B-doping process (II). Therefore, the in situ and ex-situ co-doping methods according to the present invention not only reduced recombination at the edges of hematite but also increased the conductivity inside the hematite, thereby improving the overall PEC performance.

FIG. 3A shows photocurrent density of Fe ₂ O ₃ , Ti-Fe ₂ O ₃ and Ti: B-Fe ₂ O ₃ at 1.23 V _RHE in a 1M NaOH solution under an AM 1.5 solar simulator according to the length of the sample. The length of each sample was set at 300 nm, 630 nm, 890 nm and 1.45 μm, and the growth period was increased from 1 to 4 times (FIG. 5).

As shown in Fig. 8, the domain size of the hematite lump also increased from 200 nm to 0.62 mu m, 1.54 mu m, and 3.92 mu m as the growth period increased. The photoanode of the hematite is composed of Fe ₂ O ₃ -1 (300 nm), Fe ₂ O ₃ -2 (630 nm), Fe ₂ O ₃ -3 (890 nm) and Fe ₂ O ₃ -4 ㎛) and other samples were named in the same way. The IV curves of each photoanode are summarized in FIG.

Overall, the photocurrent density of Ti: B-Fe ₂ O ₃ was higher than that of Ti-Fe ₂ O ₃ and much higher than that of Fe ₂ O ₃ . The photocurrent density of Fe ₂ O ₃ -2 using 630 nm high nanorods (Fe ₂ O ₃ -2) was higher than that of 300 nm Fe ₂ O ₃ -1 due to the wide SCR (black) without metal ions. Because of the band bending between the hematite and the electrolyte, more EHP was extracted by the electric field in the wider SCR, the EHP of Fe ₂ O ₃ -2 overcomes the short hole-diffusion length problem of hematite and the photocurrent density Was higher than that of Fe ₂ O ₃ -1. However, when the length is 870 nm, it is difficult to extract EHP as in other reports. The photocurrent density of Ti-Fe ₂ O ₃ decreased as the growth period increased. However, it was larger than Fe ₂ O ₃ of the same length due to the improved conductivity achieved by Ti doping. Indeed, the highest photocurrent density of Fe ₂ O ₃ -2 (0.85 mA / cm ² ) was still lower than that of Ti-Fe ₂ O ₃ -2 (0.96 mA / cm ² ). The photocurrent density of the Ti-Fe ₂ O ₃ -2, due to increased recombination due to the extension of the movement path of the inner tighter Hema hole photocurrent density was lower than the Ti-Fe ₂ O ₃ -1. Recombination has been reported to be dominant in hematite with high electrical resistivity when the length of the hematite is greater than ~ 500 nm. Thus, in most recent studies (in any case less than 700 nm) in which recombination and EHP production are most balanced, the optimal hematite length was set at about 500 nm. However, nn ⁺ homo - Ti having a junction: in B-Fe ₂ O ₃ photo current density is due to the desired electric field by the high conductivity and the nn ⁺ junction due to recombinant reduced by the metal dopant, the third growth period (of 890 nm in length Sample, blue).

The high photocurrent density of Ti: B-Fe ₂ O ₃ -3 (1.92 mA / cm ² at 1.23 V _RHE ) increases the light absorption from the thick hematite as shown in the UV-Vis spectroscopy (FIG. 7) to be. In order to compare the overall performance of different prepared samples (hereinafter Fe ₂ O ₃ -2, Ti-Fe ₂ O ₃ -1 and Ti: B-Fe ₂ O ₃ -3 are simply Fe ₂ O ₃ , Ti-Fe ₂ O ₃ and Ti: B-Fe ₂ O ₃ ) were selected as representative samples. The IV curves of Fe ₂ O ₃ , Ti-Fe ₂ O ₃ and Ti: B-Fe ₂ O _{3 in} a 1M NaOH solution under an AM 1.5 solar simulator with Ag / AgCl reference electrode are shown in FIG. Ti-Fe ₂ O ₃ is 1.50 in the V _RHE has a photoelectric current density and 0.91 V _RHE start potential of ^{1.68 mA / cm 2, Ti:} B-Fe photoelectric current density of ₂ O ₃ is 1.50 V _RHE at 2.83 mA / cm ² And the initiation potential was 0.92 V _RHE . This clearly shows that the synergy of reduced recombination due to the reduction of the Ti ^{4 +} and Sn ^{4 +} ions at the surface and the generation of the internal electric field by the nn ⁺ junction overcomes the length limitation of the hematite (~500 nm) And improved the PEC performance in the water decomposition reaction.

The IPCE data of FIG. 3c shows that the ratio of Ti: B-Fe ₂ O ₃ compared to Fe ₂ O ₃ and Ti-Fe ₂ O ₃ ranges from 300 nm to 550 nm at 1.23 V _RHE using 1 M NaOH solution, The photocurrent density was higher. The Fe _{2 - x} B _x O ₃ layer slightly increased the band gap of Ti: B - Fe ₂ O ₃ as shown in FIG. 9, but the graph of IPCE values of all the samples showed a very similar tendency, and Fe _{2 - x} B _x O ₃ film very lightly on the photoreaction in the range of 550 nm to 600 nm. Ti: B-Fe ₂ O ₃ exhibited very stable performance in 1M NaOH solution for 18 hours as shown in FIG.

Electrochemical impedance spectroscopy (EIS) was measured as shown in Fig. 3 (d) to reveal the charge transfer mechanism at the interface between the bulk hematite region and the electrolyte and the surface of the hematite. The equivalent circuit model was used to analyze Nyquist plots of Fe ₂ O ₃ , Ti-Fe ₂ O ₃ and Ti: B-Fe ₂ O ₃ as shown in the inset of FIG. 3 (d). Equivalent circuit is the resistance inside the bulk hematite, R ₁ , the space charge capacity at the interface of the bulk hematite, C ₁ , the charge transfer resistance between the electrolyte and the surface of the hematite, R ₂ , the interface between the electrolyte and the hematite surface C ₂ , and the sheet resistance of the hematite / FTO, R _s .

As shown in Figure 12, the charge transfer resistance (R ₂ ) between the bulk / hematite electrolyte / surface of the bulk hematite resistor (R ₁ ) and Ti-Fe ₂ O ₃ increases when the length is greater than 630 nm, Charge transfer between the electrolyte / surface of hematite with high recombination due to short band banding region with narrow SCR of metal ion doped hematite for extracting photoexcited holes and insufficient charge transfer characteristics in the hematite region .

As shown in Figure 3 (d), Ti: R 1 and R ₂ of the B-Fe ₂ O ₃ is was lower than Fe ₂ O ₃ and Ti-Fe ₂ O ₃ bulk due to the electrostatic potential from the nn ⁺ junction Showed excellent charge transfer at the interface between the hematite as well as the electrolyte / hematite surface. This suggests that a combination of internal n-type doping and an external p-type (boron) doping method may help increase the UV-Vis absorbance by increasing the thickness of the hematite, ie, length, and successfully overcoming the length limitation of the hematite .

In order to further improve the PEC performance of Ti: B-Fe ₂ O ₃ -3, as shown in FIG. 4 (a), a FeOOH thin layer 1-2 nm which is a cheaper oxygen generating reaction (OER) : B-Fe ₂ O ₃ -3. _{FeOOH-Ti: B-Fe 2} O 3 -3 was 1.23 V in the _RHE as shown in 0.835 V _RHE starting potential and the fourth degree expressed photocurrent density of 2.35 mA / cm ² (b) of Ti: B-Fe ₂ PEC performance was 1.2 times higher than that of O ₃ -3 (initiation potential: 0.920 V _RHE , photocurrent density 1.23 V _RHE : 1.92 mA / cm ² ). This was due to the passivation effect of the surface state of the recombination site and the improved water oxidation kinetics of the hematite surface.

In conclusion, the present invention has developed co-doped hematites with Ti and B having nn ⁺ junctions produced by in-situ and ex-situ methods to produce high-performance PEC photoanodes. Simultaneous doping of Ti and B in hematite not only reduced the number of Ti ^{4 +} and Sn ^{4 +} ions associated with EHP recombination at the hematite surface, but also generated an internal electric field for easy hole extraction. 890 nm length of the Ti: B-Fe ₂ O ₃ exhibited a high photocurrent density of ^{1.92 mA / cm 2, 1.50 V} RHE at 2.83 mA / cm ² at 1.23 V _RHE was the recombinant reduced so small. Accordingly, the present invention is the first invention to propose a method for solving the problem of the length limitation of hematite having a short hole diffusion length which reduces recombination of EHP and potentially improves PEC water decomposition performance.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It is to be understood that various modifications and changes may be made without departing from the scope of the appended claims.

Claims (13)

A transparent electrode substrate; And
And a rod-shaped titanium and boron-doped hematite on the transparent electrode substrate. The method according to claim 1,
Wherein the transparent electrode substrate comprises:
FTO, ZnO, ITO, AZO, GZO, IZO, and IGZO. The method according to claim 1,
The titanium and boron doped hematite may be,
An average length of 300 nm to 890 nm and an average diameter of 50 nm to 100 nm. The method according to claim 1,
The photo-
RTI ID = 0.0 &gt; FeOOH &lt; / RTI &gt; thin layer. A photoelectrochemical cell (PEC cell) for decomposing water comprising a photoanode according to any one of claims 1 to 4. Preparing a solution by mixing a titanium source and an iron source;
Immersing the transparent electrode substrate in the solution to grow FeOOH (Ti-FeOOH) doped with titanium on the transparent electrode substrate through hydrothermal growth;
Synthesizing _{a: (B-Fe 2 O 3} Ti); the Ti-FeOOH the growth was the transparent electrode substrate is immersed in acid solution after heat treatment to a titanium and boron-doped hematite And
Wherein the Ti: B-Fe ₂ O ₃ cleaning, and the method comprising a heterologous picture doped hematite by including the step of drying, the titanium and boron anode manufacture. The method of claim 6,
The photoanode fabrication method includes:
Wherein the Ti: B-Fe ₂ O ₃ on the surface of the picture containing the heterologous doped hematite depositing a thin layer as FeOOH, characterized in that it further comprises, titanium and boron anode method. The method according to claim 6 or 7,
The titanium source may comprise,
(C ₁₂ H ₂₈ O ₄ Ti) with titanium chloride (TiCl ₃ ), titanium dioxide (TiO ₂ ), titanium hydride (TiH ₂ ), titanium tetrachloride (TiCl ₄ ), titanium nitride (TiN), and titanium isopropoxide Wherein the dopant is one selected from the group consisting of titanium and boron doped hematite. The method according to claim 6 or 7,
The iron source,
(FeCl ₃ .6H ₂ O), iron fluoride · hydrate (FeF ₂ · xH ₂ O), iron sulfate · hydrate (FeSO ₄ · xH ₂ O), iron acetate (Fe (CO ₂ CH ₃ ) ₂ ) And iron nitride hydrate (Fe (NO ₃ ) ₃ .xH ₂ O). _{2. The method} of claim 1, wherein the molten iron is at least one selected from the group consisting of titanium oxide and boron nitride. The method according to claim 6 or 7,
Wherein the transparent electrode substrate comprises:
Wherein the dopant is any one selected from the group consisting of FTO, ZnO, ITO, AZO, GZO, IZO, and IGZO. The method according to claim 6 or 7,
The step of growing titanium-doped FeOOH (Ti-FeOOH) on the transparent electrode substrate includes:
Characterized in that the transparent electrode substrate is immersed in the solution and then heat-treated at 30 ° C to 100 ° C for 1 to 3 hours and maintained at 100 ° C for 2 to 4 hours. &Lt; / RTI &gt; The method according to claim 6 or 7,
The step of synthesizing the titanium and boron doped hematite comprises:
Wherein the Ti-FeOOH-grown transparent electrode substrate is immersed in a boric acid solution for 10 minutes to 1 hour and then heat-treated at 700 to 900 ° C for 15 to 30 minutes. &Lt; / RTI &gt; The method of claim 7,
The Ti: depositing a thin layer on the FeOOH B-Fe ₂ O ₃ surface,
B-Fe ₂ O ₃ on a surface, comprising a step of depositing a thin layer of FeOOH, picture containing a heterologous doped hematite in titanium and boron anode method: the Ti through hydrothermal growth.

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