KR20180022606A - Photoelectrochemical cell and manufacturing method thereof, water electrolysis system and manufacturing method thereof - Google Patents

Abstract

Disclosed is a photoelectrochemical cell which comprises: a plurality of optical electrodes dipped in an electrolyte; and a counter electrode dipped in the electrolyte. The plurality of optical electrodes are electrically connected to the counter electrode.

Description

TECHNICAL FIELD [0001] The present invention relates to a photovoltaic cell, a photovoltaic cell, a manufacturing method thereof, a water electrolysis system, and a method of manufacturing the same. BACKGROUND ART [

A photovoltaic cell using a metal oxide semiconductor, and a water electrolysis system.

The advantages of metal oxide semiconductors are in solution-based processes, which are generally good stability in aqueous solutions, low cost and easy scale-up, and most metal oxides are composed of earth-abundant elements.

The metal oxide semiconductor is a promising photoelectrode material for decomposing sunlight due to its robustness and low cost in an aqueous solution. However, the electrical properties of metal oxides are not as high as solar-to-hydrogen conversion efficiencies (η _STH ) in photoelectrochemical (PEC) water separation.

Recent research on BiVO ₄ shows significantly higher photon-to-current efficiencies (IPCE) of up to 90%, but only uses photons at wavelengths below 510 nm due to rather large band gaps.

Conversely, Fe ₂ O ₃ has a nearly ideal small bandgap of less than 2.0 eV and can utilize long wavelength photons up to 620 nm. However, η _STH of Fe ₂ O ₃ exists in a low state due to its poor electrical properties. Thus, by combining these two semiconductors, different parts of the solar spectrum can be utilized.

The most common way to utilize different bandgaps for efficient light absorption is to form heterojunctions, where BiVO ₄ (upper layer) and Fe ₂ O ₃ (lower layer) are combined to form a bilayer type heterojunction , The double layer type photoelectrode exhibits PEC water oxidation performance inferior to that of a single photo electrode.

This is because BiVO ₄ / Fe ₂ O ₃ junctions have straddling (Type I) band alignment instead of the preferred staggering (Type II) band gap of BiVO ₄ / WO ₃ junctions. These band alignments prevent holes generated in Fe ₂ O ₃ from being transferred to BiVO ₄ and are therefore not suitable for effective charge separation. In addition, the photoelectron generated in the BiVO ₄ is through the Fe ₂ O ₃ having a poor electrical properties and reaches the F-doped SnO ₂ glass (F-doped SnO ₂ glass, FTO).

A new method for increasing η _STH of metal oxides is provided, namely, a photoalogical cell and a water electrolysis system of natural seaweed-simulated in which a plurality of photoelectrodes having different band gaps are connected in parallel for extended light harvesting do.

A photoelectrochemical cell according to the present invention includes: a plurality of photoelectrodes immersed in an electrolyte; And a counter electrode immersed in the electrolyte, wherein the plurality of photoelectrodes are electrically connected in parallel with the counter electrode.

The plurality of photoelectrons may include a semiconductor and may be arranged in the order of the photoelectrode having a bandgap energy of the semiconductor from the front side with respect to a direction in which the light is irradiated.

The plurality of photoelectrodes may each include a semiconductor, and may be a combination of n type semiconductors or a combination of both p type semiconductors.

The optical electrode includes a first optical electrode; And a second photoelectrode that absorbs light having a wavelength longer than that of the first photoelectrode. Light emitted from the counter electrode may be sequentially absorbed by the first photoelectrode and the second photoelectrode.

The first optical electrode includes a first conductive substrate; And the first light-absorbing layer disposed on the first conductive substrate, said first light absorption layer, and includes _{silver, SiO 2, TiO 2, WO} 3, Fe 2 O 3, SnO 2, ZnO, ZrO 2, In 2 O ₃ , MoS ₂ , BiVO ₄ , SrTiO ₃ , CaTiO ₃ and KTaO ₃ .

The first conductive substrate may be made of FTO, and the first light absorbing layer may include BiVO ₄ .

The BiVO ₄ may be doped with Mo and doped with Mo such that the atomic ratio of Bi: (V + MO) is 1: 0.8 to 1: 1.2.

The first photoelectrode further includes a first coenzyme layer positioned on the first light absorbing layer, and the first coenzyme layer may include FeOOH and NiOOH.

Wherein the second optical electrode comprises: a second conductive substrate; The second light absorption layer disposed on the second conductive substrate, said second light absorption layer, and includes silver, SiO _2, TiO _2, WO _3, Fe ₂ O _3, SnO _2, ZnO, ZrO _2, In ₂ O ₃ , MoS ₂ , BiVO ₄ , SrTiO ₃ , CaTiO ₃ and KTaO ₃ .

The second conductive substrate may be made of FTO, and the second light absorbing layer may include Fe ₂ O ₃ .

The Fe ₂ O ₃ may be doped with Ti such that the atomic ratio of Fe: Ti is 1: 0.003 to 1: 0.007.

The second light electrode may further include a surface treatment layer located on the second light absorption layer and including TiO ₂ .

Wherein the second photoelectrode further comprises a second coenzyme layer positioned on the surface treatment layer and the second coenzyme layer comprises at least one compound selected from NiFeO _x , Ni ₂ FeO _x and Ni ₃ FeO _x .

The electrolyte may be a potassium bicarbonate aqueous solution having a pH of 9 to 10.

According to another aspect of the present invention, there is provided a method of manufacturing a photoelectrochemical cell, comprising: preparing a plurality of photoelectrodes; Preparing a counter electrode; And immersing the plurality of photoelectrodes and the counter electrode in an electrolyte, and electrically connecting the plurality of photoelectrons to the counter electrode electrically in parallel.

Preparing the plurality of photoelectrodes includes: preparing a first photoelectrode by positioning a first photoabsorption layer on a first conductive substrate; And preparing a second optical electrode by positioning a second light absorbing layer on the second conductive substrate.

The step of preparing the first photoelectrode includes the steps of: preparing a first precursor solution by mixing a bismuth raw material, a vanadium raw material, a molybdenum raw material, and a first solvent; And dropping the first precursor solution on the first conductive substrate composed of FTO, and drying and heat-treating the first precursor solution to form a first light absorbing layer.

In the process of forming the first light absorbing layer, the volume of the first precursor solution dropped on the first conductive substrate may be more than 10 쨉 l and less than 80 쨉 l.

After the step of forming the first light absorbing layer, a process of reducing the first light absorbing layer using a borohydride decomposition method may be further included.

And a step of forming a first coenzyme layer containing FeOOH and NiOOH by depositing a solution of a ferrous iron oxide solution and a solution of nickel sulfate in the first light absorbing layer after forming the first light absorbing layer have.

Preparing the second photoelectrode comprises: preparing a second precursor solution by mixing an iron source material, a titanium source material, a polymer binder, and a second solvent; And dropping the second precursor solution onto the second conductive substrate formed of FTO, and drying and heat-treating the second precursor solution to form a second light absorbing layer.

After the step of forming the second light absorbing layer, a process of reducing the second light absorbing layer using a borohydride decomposition method may be further included.

After the process of forming the second light absorbing layer, a process of preparing a coating liquid by mixing a titanium oxide raw material and a third solvent; And coating the coating solution on the second light absorption layer and forming a surface treatment layer by heat treatment.

After the process of forming the surface treatment layer, a process of preparing a mixed solution by mixing nickel nitrate, nitrate oxide and a fourth solvent; And a step of dripping the mixed solution onto the surface treatment layer, followed by drying and heat treatment to form a second coenzyme layer.

A water electrolysis system according to the present invention includes: a plurality of photoelectrodes immersed in an electrolyte; A counter electrode immersed in the electrolyte; And a solar cell, wherein the plurality of photoelectrodes are electrically connected in parallel with the first electrode of the solar cell, and the counter electrode is electrically connected to the second electrode of the solar cell.

The plurality of photoelectrodes may be arranged in the order of increasing band gap energy from the front with reference to the direction in which the light is irradiated.

The plurality of photoelectrodes may include a first photoelectrode; And a second optical electrode that absorbs light having a wavelength longer than that of the first optical electrode, wherein the first optical electrode is insulated on one surface of the second optical electrode, The second pole of the battery can be insulated.

The solar cell may be selected from a silicon solar cell, a dye-sensitized solar cell, a compound semiconductor solar cell, and a laminated solar cell.

A method of manufacturing a water electrolysis system according to the present invention includes: preparing a plurality of photoelectrodes; Preparing a counter electrode; And a step of immersing the plurality of photoelectrodes and the counter electrode in an electrolyte, electrically connecting the plurality of photoelectrons to the first electrode of the solar cell in parallel, and electrically connecting the counter electrode to the second electrode of the solar cell Step.

Preparing the plurality of photoelectrodes includes: preparing a first photoelectrode by positioning a first photoabsorption layer on a first conductive substrate; And preparing a second optical electrode by positioning a second light absorbing layer on the second conductive substrate.

And inserting the first conductive substrate and the second light absorbing layer in an insulating state and insulating the second conductive substrate and the second electrode after the step of preparing the second optical electrode .

The photochemical cell according to the present invention can obtain a water oxidation photocurrent density of 7.0 ± 0.2 mA / cm ² at 1.23 V _RHE by using a plurality of photoelectrodes electrically connected in parallel with the counter electrode.

The water electrolysis system according to the present invention can use η _STH of 7.7% by using a plurality of photoelectrodes connected in parallel with a solar cell and a solar cell.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing IV curves of a double layer type heterojunction photocathode. FIG.
(a) 1% Mo: BiVO 4 ( _{top) /0.5% Ti: Fe 2 O 3} , (b) 1% Mo: BiVO 4 (top) / WO 3 as the hetero-junction Gwangyang pole broken line are measured as rear lights IV (1.5 G filtering or 100 mW / cm ² , 0.5 M KPi + 0.5 M Na ₂ SO ₃ , injection rate: 20 mV / sec, forward scanning). (c) WO ₃ , Fe ₂ O ₃ and BiVO ₄ band alignment.
2 is a scanning electron microscope photograph.
(a) 1% Mo-doped BiVO ₄ (1% Mo: BiVO ₄ ) and (b) 1% Mo: BiVO ₄ (H, 1% Mo: BiVO ₄ ) hydrotreated. (c) NiOOH / FeOOH / H , 1% Mo: and _{BiVO 4, (d) H,} 1% Mo on the FTO: BiVO ₄ It is a cross-sectional image of Gwangyang pole. The average film thickness is about 300 nm and all scale bars are 500 nm.
3 is a scanning electron micrograph.
(a, b) 0.5% Ti-doped Fe ₂ O _{3 (0.5% Ti: Fe 2 O} 3), (c, d) of hydrotreating _{0.5% Ti: Fe 2 O 3} (H, 0.5% Ti: Fe 2 O 3), (e, f) H, TiO 2 / 0.5% Ti: the _{Fe 2 O 3: Fe 2 O} 3, (g, h) N i2 FeO x / H, TiO 2 /0.5% Ti.
the scale bar of (a, c, e, g) is 200 nm and the scale bar of (b, d, f, h) is 100 nm. (e) is a cross-sectional image of H, TiO ₂ /0.5% Ti: Fe ₂ O ₃ on FTO having a thickness of about 400-500 nm.
4 shows an XRD pattern.
(a) BiVO ₄ -based Kwangyang pole, (bc) Fe ₂ O ₃ -based Kwangyang pole, and T indicates FTO pattern (F-doped tin oxide).
Figure 5 shows an X-ray photoelectron spectra (XPS).
(a) Bi 4f, (b ) V 2p, (c) 1% Mo: the _{BiVO 4 Mo 3d, (d)} Fe 3d, (e) 0.5% Ti:: BiVO 4 and H, 1% Mo Fe ₂ O _{3, H, 0.5% Ti:} Fe 2 O 3, TiO 2 /0.5% Ti: Fe 2 O 3 and H, TiO 2 /0.5% Ti: the _{Fe 2 O 3 Ti 2p, (} f) Fe 3d, (g ) O 2s of Ni 2p, (h, i) Ni ₂ FeO _x / H, TiO ₂ /0.5% Ti: Fe ₂ O ₃ and NiOOH / FeOOH / H, 1% Mo: BiVO ₄ (all peak intensities are normalized have).
Fig. 6 is an IV curve of a gwangyang pole in a sulfite sacrificial reagent.
is the bulk separation efficiency calculated by the J _abs value of (a) BiVO ₄ -based Kwangyang pole, (b) Fe ₂ O ₃ -based Kwangyang pole, and (c, d) Measurement conditions: AM 1.5 G (100 mW / cm ² ), 0.5 M KPi + 0.5 M Na ₂ SO ₃ , pH 7.0, scanning rate of 20 mV / sec, and F and B beside the material show front and back illumination, respectively.
FIG. 7 is a graph showing the relationship between (a) the steady-state current-potential (IV) behavior at the Fe ₂ O ₃ photocathode, (b) the incident light- (0.5 M KPi and 0.5 M Na ₂ SO ₃ , pH = 7.0) of bare Fe ₂ O ₃ , 0.5% Ti: Fe ₂ O ₃ and H, and 0.5% Ti: Fe ₂ O ₃ , respectively.
Fig. 8 shows the IV curves (a, b) and Mott-Schottky plot of the copper-free gwangyang pole, (c, d) BiVO ₄ system gwangyang pole, (e, f) Fe ₂ O ₃ system gwangyang pole, 1.0 MKCi pH 9.2) (frequency: 1000 Hz, scanning rate: 20 mV / sec).
Figure 9 is a natural tandem cell (wavelength-selective solar absorption by natural seaweed) and an artificial heterogeneous double light electrode.
(a) It depends on the depth of seawater that absorbs different parts of the solar spectrum, algae distribution, algae (algae), algae (brown algae), red flora (red algae) and solar spectrum. (b) a hetero-type dual light electrode (HDP) made of different bandgap materials.
10 is a sacrificial sulfite BiVO ₄ and Fe ₂ O ₃ in the two kinds of solution-type double electrode optical _{(HDP, BiVO 4 || Fe 2} O 3) (a) a polar Gwangyang HDP BiVO ₄ || Photograph of the electrode manufactured showing schematic operation principle (b) a good transparency of the photoelectric cell having a Fe ₂ O _3, (e) the incident photon-current efficiency (IPCE), (f) the AM 1.5G spectrum due to the different photon currents, (c) the steady-state IV behavior, (d) the optimization of BiVO ₄ and Fe ₂ O ₃ for best photocurrent generation, Analysis was carried out in 0.5M KPi and 0.5M Na ₂ SO ₃ at pH 7.0 as the application of light.
11 shows the photocurrent generation and applied bias photon-to-current efficiency (ABPE) in PEC water separation using various coenzyme: (a, c) H, 1% Mo: BiVO ₄ , , d) H, TiO ₂ /0.5% Ti: Fe ₂ O ₃ (electrolyte: 1.0 M KCi, pH = 9.2).
Fig. 12 shows the effect of surface passivation by the over layer and electrolyte pH in the Fe ₂ O ₃ -based glow-poles.
(b) 1.0 M KPi, pH 7.0, (c) 1.0 M KCi, pH 9.2, (d) 1.0 M KOH, pH 13.6, (e) The IV curves of Ni ₂ FeO _x catalyzed and non-catalyzed H, TiO ₂ /0.5% Ti: Fe ₂ O ₃ . The vertical line of vertical line of red (1.0M KOH), blue (1.0M KCi), and black (1.0M KPi) represents the position of 1.23V _RHE with the transition of the potential scale.
Figure 13 shows the effect of electrolyte pH on Ni ₂ FeO _x , FeO _x and NiO _x electrocatalysts on FTO.
(a) 1.0 M KOH (pH 13.6) and (b) 1.0 M KCi (pH 9.2).
A similar process was used for electrocatalyst deposition. Thus, Ni, Fe and Ni ₂ Fe precursors (0.2 M, 3 μl each) were dropped onto FTO glass (0.5 cm ² ) and dried in a soot hood for 30 seconds. Then, prior to analysis, the sample was washed gently with 1.0 M KOH for 10 seconds. Samples were directly used for electrochemical analysis (injection rate: 20 mV / sec)
Figure 14 (a) BiVO ₄ and Fe ₂ O ₃ light-harvesting efficiency (light harvesting efficiency, LHE), Fe ₂ O ₃ the absorbance, (b) AM 1.5G significant to the spectrum from the transmitted light through a transmission (T) and BiVO ₄ LHE absorption photocurrent (J _abs ): BiVO ₄ (5.08 mA / cm ² , <516 nm), Fe ₂ O ₃ (10.81 mA / cm ² , <620 nm), Fe ₂ O ₃ behind BiVO ₄ (4.69 mA / cm ² , <620nm) and _{HDP (BiVO 4 || Fe 2 O} 3) (5.08 mA / cm 2, <516nm + 4.69mA / cm 2, at ^{<620nm = 9.77mA / cm 2)} BiVO 4 and Fe ₂ O ₃ in the 2.4eV and 2.0eV light utilization thresholds. The samples used for the analysis were H, 1% Mo: BiVO ₄ and H, TiO ₂ /0.5% Ti: Fe- ₂ O ₃ , respectively. Note that the absorption of BiVO ₄ at 516 nm is not calculated to be available for HDP.
15 is different from the loading amount (the amount of precursor in the BiVO _4, Fe ₂ O ₃ in the In from _{(a) BiVO 4, (b} ) Fe 2 O 3 picture, (c), BiVO _4, and (d) Fe ₂ O ₃ optical properties, (e) BiVO ₄ composed of different precursors both of the number of layers) IV behavior (sulfur oxide, on the left) and under the front light absorber (shown on the right, filtered), the corresponding IV curve of Fe ₂ O ₃ Gwangyang electrode, (f), different from Fe ₂ O ₃ of Gwangyang pole IV curve in the load number (inserted The graph is the Jabs current calculated in (d)). In BiVO ₄ , the indication-H, 1% Mo: BiVO ₄ and Fe ₂ O ₃ -H and 0.5% Ti: Fe ₂ O ₃ were used. 0.5 M Na ₂ SO ₃ + 0.5 M KPi, pH 7.0 at AM 1.5G illumination (100 mW / cm ² ).
Figure 16 shows (a) normalized LHE of BiVO ₄ and (b) normalized LHE of Fe ₂ O ₃ with different deposition amounts. The dotted line is drawn at the point of curvature intersection. Instruction - H in BiVO ₄ , 1% Mo: BiVO ₄ and Fe ₂ O ₃ - H, and 0.5% Ti: Fe ₂ O ₃ were used.
Figure 17 relates to an assisted solar water separation HDP-PV tandem cell.
(a) a schematic view of a tandem cell with HDP (BiVO ₄ Fe Fe ₂ O ₃ ) and a parallel-connected Si solar cell (2p c-Si), (b) Artificial leaves (monolithic tandem cell), (c) BiVO ₄ , Fe ₂ O ₃ and BiVO ₄ || Electrode AM 1.5 IV curve in a 2p c-Si solar cell after the Fe ₂ O ₃ photocathode and each photo-electrode, (d) the stability of the separation of the non-deflected material (0.0V, counter electrode) (During the induction time in the tandem cell). Photoelectrode is NiOOH / FeOOH / H, 1% Mo: was Fe ₂ O _3: BiVO ₄ and _{Ni 2 FeO x / H, TiO} 2 /0.5% Ti. All data were collected in an electrolyte of 1.0 M KCi, pH 9.2.
Figure 18 shows a water electrolysis system in the form of a monolithic tandem cell in operation under simulated 1 sun conditions. HDP BiVO _4, Fe ₂ O ₃ , and 2p c-Si solar cells. The measurement conditions are AM 1.5G (100 mW / cm ² ), 1.0 M KCi (pH 9.2), active area: 5.0 cm ² , and counter electrode area: 1.0 cm ² .
19 shows solar water separation in a non-deflecting photoelectrochemical cell.
(a) steady state IV behavior, (b) IPCE at 1.23V _RHE , (c) stability test, and (d) gas evolution from PEC water separation of the Gwangyang Pole at 1.15V _RHE , Lt; / RTI > (e) The action spectrum of BiVO ₄ (all data were obtained with an electrolyte of 1.0 M KCi at pH 9.2 under 1 sun illumination).
20 is an IV curve using chopped illumination.
(a) NiOOH / FeOOH / H , 1% Mo: BiVO 4, (b) Ni 2 FeO x / H, TiO 2 /0.5% Ti: Fe 2 O 3, (c) HDP (NiOOH / FeOOH / H, 1 % Mo: BiVO ₄ Ni ₂ FeO _x / H, TiO ₂ /0.5% Ti: Fe ₂ O ₃ ), (d) the best results for each photoelectrode (electrolyte: 1.0M KCi, pH 9.2) the photoelectrode is BiVO ₄ used in the 4.5 to _{^{5.0mA / cm 2, Fe 2 O}} 3 3.3 to about 4.1mA / cm ² and the HDP was 6.5 to 7.0 mA / cm ² at 1.23V _RHE.
Figure 21 is a light-absorbing layer under 1 sun BiVO _{(AM 1.5G) 4, Fe 2} O 3 and Fe ₂ O ₃ having || ₄ BiVO a 2p c-Si 2p c-Si solar not provided with the solar cell and the light absorbing layer The IV curve of the cell. The insertion table includes performance data of a 2p c-Si solar cell having an active area of 0.25 cm &lt; ^{2 &} gt ;.
22 is an IV curve of the gwangyang pole.
(a) a three-electrode configuration for measurement, and (b) a two-electrode configuration for measurement.
Metal oxide film / 2 c-Si solar cells of the IV curve of the actual tandem cell, the photo-electrode (c) consisting of NiOOH / FeOOH / H, 1% Mo: BiVO 4, (d) Ni 2 FeO x / H, TiO 2 were compared with _{Fe 2 O 3, (e)} HDP (BiVO 4 || Fe 2 O 3): /0.5% Ti. The measurement conditions were AM 1.5G (100mW / cm ² ), 1.0M KCi (pH 9.2), post scan (20mV / sec), counter electrode Pt mesh and active area (0.24cm ² ).
23 is a photocurrent report of a metal oxide photocathode (BiVO ₄ , Fe ₂ O ₃ , WO ₃ and BiVO ₄ / WO ₃ heterojunction). HDP represents the BiVO ₄ || Fe ₂ O ₃ heterogeneous double electrode, and the blank sign indicates that the photocurrent value was measured at a potential different from the standard 1.23 V _RHE .
24 is a schematic diagram of a water electrolysis system according to an embodiment of the present invention.

Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

In order to clearly illustrate the present invention, parts not related to the description are omitted, and the same or similar components are denoted by the same reference numerals throughout the specification.

In addition, since the sizes and thicknesses of the respective components shown in the drawings are arbitrarily shown for convenience of explanation, the present invention is not necessarily limited to those shown in the drawings. In the drawings, the thickness is enlarged to clearly represent the layers and regions. In the drawings, for the convenience of explanation, the thicknesses of some layers and regions are exaggerated.

Also, when a portion such as a layer, a film, an area, a plate, etc. is referred to as being "on" or "on" another portion, this includes not only the case where the other portion is "directly on" . Conversely, when a part is "directly over" another part, it means that there is no other part in the middle. Also, to be "on" or "on" the reference portion is located above or below the reference portion and does not necessarily mean "above" or "above" toward the opposite direction of gravity .

Also, throughout the specification, when an element is referred to as "including" an element, it is understood that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise.

Photoelectric chemistry  Cell

A photoelectrochemical cell according to the present invention includes a plurality of photoelectrodes immersed in an electrolyte and a counter electrode immersed in an electrolyte, wherein the plurality of photoelectrodes are electrically connected in parallel with the counter electrode.

Here, the parallel connection means that a plurality of optical electrodes are independent from each other, and each optical electrode is connected to the counter electrode.

Conventional heterojunction photoelectrodes are made by combining single liquid-semiconductor junctions and solid-solid junctions with a single photoelectrode.

Alternatively, the plurality of photoelectrodes according to the present invention comprise a plurality of independent liquid-semiconductor junctions. Thus, each photoelectrode can be independently optimized, and the performance of the photoelectrochemical cell is a sum of a plurality of individual performances.

That is, considering that the light absorption and the light utilization ability differ depending on the kind of material, and the urgent problem in the photoelectrochemical cell is the photocurrent value, not the light voltage, it is possible to increase the photocurrent by using a plurality of photoelectrodes in parallel connection.

The plurality of photoelectrodes and the counter electrode are all immersed in the electrolyte and can be divided into a region in which a plurality of photoelectrodes are immersed through a membrane and a region in which a counter electrode is immersed.

When a plurality of photoelectrodes are irradiated with light, electrons and holes (hydrogen ions) are generated in the photoelectrode, and oxygen is generated. Since the plurality of photoelectrodes are electrically connected in parallel with the counter electrode, electrons generated in each photoelectrode are transferred to the counter electrode, and hydrogen ions are reduced from the counter electrode.

The counter electrode may include Pt, and may be prepared by coating 0.5 M H ₂ PtCl ₆ * 6H ₂ O diluted in ethanol on the FTO and then heat-treating.

Each of the plurality of photoelectrons may include a semiconductor and may be arranged in the order of the photoelectrode having a bandgap energy of the semiconductor from the front side with respect to a direction in which the light is irradiated.

When using semiconductors that convert photons to electrons, the most important requirement is the proper bandgap. Photons with energy lower than the bandgap are not absorbed by the semiconductor (unabsorbed loss), while electrons with energies above the bandgap pass through phonons (lattice vibration, heat) during absorption (thermal neutronization loss) To lose some energy.

For efficient utilization of solar energy, these two fundamental losses must be minimized, and among the methods of minimizing such losses, multiple joining methods are already proven methods.

Thus, a large bandgap semiconductor first absorbs high energy photons, and a small bandgap semiconductor behind it absorbs low energy photons. As a result, the theoretical efficiency of the multi-junction solar cell can reach 68%.

For example, the plurality of photoelectrodes each include a semiconductor, and the semiconductor has different band gap energies. The plurality of photoelectrodes are connected in parallel with the counter electrode, and arranged in the order of increasing band gap energy from the front with reference to the direction in which the light is irradiated.

Accordingly, the light irradiated from the front passes through the photoelectrode including the largest bandgap semiconductor to absorb the high energy photons, and the relatively low energy photons are absorbed through the photoelectrode including the bandgap semiconductor.

By absorbing the high-energy photons sequentially from the photoelectrode, it is possible to minimize the loss of solar energy and utilize it efficiently.

The plurality of photoelectrodes each include a semiconductor, and may be a combination of n type semiconductors or a combination of both p type semiconductors.

In order to add a photocurrent, a plurality of semiconductors, which are light absorbing materials, must be polarized in the same direction. Therefore, only semiconductor combinations of n type / n type or p type / p type can be used.

The photoelectrode includes a first photoelectrode and a second photoelectrode that absorbs light of a longer wavelength than the first photoelectrode. Light emitted from the counter electrode may be sequentially absorbed by the first photoelectrode and the second photoelectrode. have.

First optical electrode of claim 1 including a first light absorption layer disposed on the conductive substrate and the first conductive substrate, a first light-absorbing layer is _{SiO 2, TiO 2, WO 3} , Fe 2 O 3, SnO 2, and ZnO, _{ZrO 2, in 2 O 3,} MoS 2, BiVO 4, SrTiO 3, may include one or more semiconductors selected from the group consisting of CaTiO ₃ and KTaO _3.

Specifically, the first conductive substrate may be comprised of FTO and the first light absorbing layer may comprise BiVO ₄ . Also, BiVO ₄ can be doped with Mo such that the atomic ratio of Bi: (V + MO) is 1: 0.8 to 1: 1.2.

The first photoelectrode further comprises a first coenzyme layer located on the first light absorbing layer, wherein the first coenzyme layer may comprise FeOOH and NiOOH.

Second optical electrode comprising a second light absorption layer disposed on the second conductive substrate, the second conductive substrate, the second light absorbing layer is SiO _2, TiO _2, WO _3, Fe ₂ O _3, SnO _2, ZnO, ZrO _{2, in 2 O 3, MoS} 2, BiVO 4, SrTiO 3, may include one or more semiconductors selected from the group consisting of CaTiO ₃ and KTaO _3.

The second conductive substrate may be comprised of FTO and the second light absorbing layer may comprise Fe ₂ O ₃ . Also, Fe ₂ O ₃ may be doped with Ti such that the atomic ratio of Fe: Ti is 1: 0.003 to 1: 0.007, which is doped with Ti.

On the other hand, the second optical electrode is located on the second light absorption layer and may further include a surface treatment layer containing TiO ₂ .

The second photoelectrode further comprises a second coenzyme layer positioned on the surface treatment layer and the second coenzyme layer may comprise one or more compounds selected from NiFeO _x , Ni ₂ FeO _x and Ni ₃ FeO _x .

The advantages of metal oxide semiconductors are in solution-based processes, which are generally good stability in aqueous solutions, low cost and easy scale-up, and most metal oxides are composed of earth-abundant elements.

However, the electrical properties of metal oxides show normal η _STH values in photoelectrochemical (PEC) water separation. Recent research on BiVO ₄ shows significantly higher photon-to-current efficiencies (IPCE) of up to 90%, but only uses photons at wavelengths below 510 nm due to rather large band gaps.

Conversely, Fe ₂ O ₃ has an almost ideal small bandgap of less than 2.0 eV and can utilize long wavelength photons up to 620 nm. However, η _STH of Fe ₂ O ₃ exists in a low state due to its poor electrical properties. Thus, by combining these two semiconductors, different parts of the solar spectrum can be utilized.

The most common way to utilize different band gaps for efficient light absorption is to form a heterojunction. As shown in Fig. 1, BiVO ₄ (upper layer) and Fe ₂ O ₃ (lower layer) When a junction is formed, the double layer type photo electrode exhibits PEC water oxidation performance inferior to that of a single photo electrode. This is because BiVO ₄ / Fe ₂ O ₃ junctions have straddling (Type I) band alignment instead of the preferred staggering (Type II) band gap of BiVO ₄ / WO ₃ junctions. This band alignment prevents holes generated in Fe ₂ O ₃ from being transferred to BiVO ₄ , which is not suitable for effective charge separation.

In addition, the photoelectron generated in the BiVO ₄ is through the Fe ₂ O ₃ having a poor electrical properties and reaches the F-doped SnO ₂ glass (F-doped SnO ₂ glass, FTO).

In order to study efficient light absorption methods for water separation using two semiconductors with different bandgaps, natural algae have been shown to vary in color depending on the depth of their seas. A photon with a short wavelength of 420 nm or less can pass through the depths of the ocean where a photon with a wavelength longer than 600 nm can not reach it. Algae adapt to different wavelength photons, and their color changes to green (green algae), yellow (brown algae) and red (red algae) as they penetrate deep into the sea, developing selective light harvesting ability for photosynthesis.

The photochemical electric cell according to the present invention introduces a hetero-type dual photoelectrode (HDP) in consideration of this simple and effective natural example.

Each of the photoelectrodes can be independently optimized by using the first photoelectrode including BiVO ₄ electrically connected in parallel with the counter electrode and the second photoelectrode including Fe ₂ O ₃ , It is the sum of individual performance.

BiVO ₄ is used for the absorption of high energy photons through the arrangement of the first and second photoelectrodes and when the Fe ₂ O ₃ is used for absorption of low energy photons, both the non-absorption loss and the thermal neutronization loss are minimized can do.

It is necessary to individually optimize the first optical electrode and the second optical electrode for an efficient HDP system to extract the best performance as a single optical electrode.

Specifically, it is necessary to minimize the scattering by the first optical electrode in front and to cause the transmitted light to reach the second photodetector in the rear side. To this end, bulk and surface modification of the first light absorbing layer and the second light absorbing layer are performed. More specifically, doping of BiVO ₄ and Fe ₂ O ₃ and coarse loading were used to improve charge separation on the bulk and surface, respectively.

A first photoelectrode containing basic BiVO ₄ was prepared by a metal-organic deposition (MOD) method. Followed by doping and reduction treatment with 1 at% Mo to increase bulk charge separation efficiency. The reduction treatment with the borohydride decomposition method induced a Vo defect which effectively increased the charge carrier density in the BiVO ₄ lattice.

A second photoelectrode containing basic Fe ₂ O ₃ was prepared by the nitrate decomposition method. Subsequently, doping and reduction treatment with 0.5 at% Ti was performed to increase the bulk charge separation efficiency. Similarly, the reduction treatment with the borohydride decomposition method induced a Vo defect which effectively increased the charge carrier density in the Fe ₂ O ₃ lattice.

Accordingly, the n type conductivity is improved by doping and reducing the first and second photoelectrodes.

On the other hand, the first co-enzyme layer containing NiOOH / FeOOH was deposited on the surface of BiVO ₄ to improve charge carrier injection efficiency for the electrolyte.

In addition, the second coarse layer containing Ni ₂ FeO _x was deposited on the surface of Fe ₂ O ₃ having a thin TiO ₂ surface treatment layer to improve charge carrier injection efficiency for the electrolyte.

As can be seen in the SEM images of FIGS. 2 and 3, BiVO ₄ and Fe ₂ O ₃ are nanoporous and well connected anisotropic forms with sizes of about 50 nm and about 10 nm, respectively. The SEM images of FIGS. 2 and 3 show that the coenzyme nanoparticles are well dispersed on each semiconductor surface.

As can be found in 4, the first light absorbing layer 2 and the XRD crystal structure of the light absorbing layer is a standard monoclinic BiVO ₄ and hematite α-Fe ₂ O _3.

As can be seen from FIG. 5, the XPS spectrum shows the binding energy at the predicted position in BiVO ₄ and Fe ₂ O ₃ .

The bulk-reforming film was tested as a photoelectrode for PEC oxidation of a sacrificial sulfite (SO ₃ ^2- ) solution in a photoelectrochemical cell according to the present invention to evaluate light absorption capacity and bulk separation efficiency (η _bulk ).

As can be seen in Fig. 6, the Mo (or Ti) doping and reduction treatment significantly increased photocurrent and eta _bulk . The decrease in the 1% Mo BiVO _4: BiVO ₄ represents more than 90% in _bulk η 1.23V _RHE. Doping and partial reduction processes also reduce the photocurrent gap between front and back illumination and improve bulk electron transport. In addition, the highest η _bulk at 1.23 V _RHE was only 41%, but the same tendency was observed in Fe ₂ O ₃ .

As can be found at 7, 400nm or more IPCE value in the order of hematite is relatively low, because due to the inefficient indirect dd transition of Fe ^{+ 3.} However, Ti doping and reduction processes are particularly effective at increasing the IPCE of indirect transitions near the absorption edge.

As can be seen from the Mott-Schottky graph of FIG. 8, the major effect of the doping and reduction process is to increase the charge carrier density of BiVO ₄ and Fe ₂ O ₃ to improve bulk charge transport properties.

As can be seen from FIGS. 9 (b) and 10 (a), BiVO ₄ (H, HV) is applied from the front based on the direction in which the light is irradiated by using two optical electrodes optimized in the water electrolysis system of the present invention. 1% Mo: the first optical electrode, a back comprising a _{BiVO 4) Fe 2 O 3 (} H, TiO 2 /0.5% Ti: by placing a second optical electrode comprising an Fe ₂ O ₃₎ BiVO ₄ || HDP represented by Fe ₂ O ₃ was prepared.

As is found in 10 (b), a single photo-electrode, Fe single optical electrode including the ₂ O ₃ and Fe ₂ O ₃ BiVO ₄ || HDP is highly transparent both together comprising a single BiVO ₄ containing BiVO ₄ The photoelectrode has a transmittance of 75% at 550 nm, a single light electrode containing Fe ₂ O ₃ at 70% at 650 nm, and a transmittance of 50% at 650 nm for HDP.

In the photoelectrochemical cell according to the present invention, the electrolyte may be a potassium bicarbonate aqueous solution having a pH of 9 to 10.

The single electrode including BiVO ₄ is optimal for pH 7 in terms of activity and stability, and the single electrode containing Fe ₂ O ₃ is optimal for electrolyte with pH 12 or higher in terms of activity and stability. Therefore, the first and most important task of applying HDP is to use BiVO ₄ And Fe ₂ O ₃ .

As can be seen in the screening test of Figures 11-13, a 1.0 M bicarbonate KCi solution of pH 9.2 is a good compromise for both semiconductors and selected coenzyme. It can be seen that NiOOH / FeOOH as BiO ₄ as the oxygen generating coenzyme and Ni ₂ FeO _x / TiO ₂ as Fe ₂ O ₃ are the most excellent.

In particular, the surface treatment layer comprising the thin TiO ₂ deposited on the second light-absorbing layer comprising Fe ₂ O ₃ has an undesirable electron-hole recombination in the Helmholtz layer and a Fe ₂ Passivates the surface state of O ₃ . Thus, the process not only improves photocurrent generation, but also produces a voice transfer of the initiation potential and a larger photovoltaic output from the electrode.

Photoelectric chemical cell  Manufacturing method

A method of manufacturing an opto-electrochemical cell according to the present invention includes the steps of preparing a plurality of photoelectrodes, preparing a counter electrode, immersing a plurality of photoelectrodes and a counter electrode in an electrolyte, electrically connecting a plurality of photoelectrons .

Preparing the plurality of photoelectrodes includes the steps of preparing a first photoelectrode by placing a first photoabsorption layer on a first conductive substrate, preparing a second photoabsorption layer by placing a second photoabsorption layer on the second conductive substrate, .

Specifically, the step of preparing the first photoelectrode includes a step of preparing a first precursor solution by mixing a bismuth raw material, a vanadium raw material, a molybdenum raw material and a first solvent, and a step of mixing the first precursor solution with a first precursor solution Forming a first light absorbing layer by dripping onto a conductive substrate, followed by drying and heat treatment.

After the step of forming the first light absorbing layer, the first light absorbing layer may be reduced using a borohydride decomposition method.

After the step of forming the first light absorbing layer, a step of forming a first coenzyme layer containing FeOOH and NiOOH by depositing a solution of iron oxide iron and a solution of nickel sulfide onto the first light absorbing layer may be further included.

[Production example of first optical electrode]

A first photoelectrode containing BiVO ₄ was prepared by a metal-organic decomposition (MOD) method.

A vanadium raw material dissolved in acetic acid (99.7%; Kanto Chemicals) dissolved in bismuth raw material 0.2M Bi (NO ₃ ) * 5H ₂ O (99.8%; Kanto Chemicals) and acetylacetone (99.0% A first precursor solution was prepared by mixing 0.03 M VO (acac) ₂ (98.0%; Sigma Aldrich) and 0.03 M MoO ₂ (acac) ₂ (98.0%; Sigma Aldrich), a raw material of molybdenum, in a stoichiometric amount. The first solvent may be a mixture of acetic acid and acetylacetone.

Mo was doped so as to satisfy the Bi: (V + Mo) = 1: 1 atomic ratio to form a first light absorbing layer containing 1% Mo: BiVO ₄ . 60 占 퐇 of the first precursor solution was dropped onto FTO glass (2 cm x 2.5 cm) and dried in an Ar atmosphere for 15 minutes. Depending on the synthesis conditions, 10 to 80 [mu] l of the first precursor solution may be used.

The first conductive substrate, FTO glass (TEC 8; Pilkington), was washed with KOH (0.1 M) + ethanol mixed at a mass ratio of 1: 5, washed with an abundant amount of deionized water, and finally stored in acetone before use .

Green transparent precursor film was calcined at 550 DEG C for 25 minutes to form a yellow first light absorbing layer. After the annealing process, a 2 cm x 2.5 cm BiVO ₄ / FTO was separated to obtain a photoelectrode having a net irradiation area of 0.24 cm ² sealed by an epoxy resin, which was connected by silver paste and copper wiring.

A first co-enzyme layer containing NiOOH / FeOOH was deposited using photo-assisted electrodeposition (PED) under AM 1.5G illumination.

0.25 V in Ar, FeOOH was deposited from 0.1 M Fe (SO ₄ ) ₂ 7H ₂ O (99%; Sigma Aldrich) solution pre-purged for 15 minutes in Ag / AgCl.

NiOOH was then deposited from a 0.1 M Ni (SO ₄ ) ₂ 6 H ₂ O (99%; Sigma Aldrich) solution at 0.11 V, Ag / AgCl at pH 7.0 or higher (with 0.1 M KOH).

The optimum deposition times of FeOOH and NiOOH were 15 min and 6 min, respectively. Prior to the PED process for FeOOH, the electrode was agitated vigorously for 5 minutes on an idle to minimize bubble attachment during the deposition process. After the PED process for both coenzymes, the constant current mode (0.03 mA / cm ² , potential record of 1.3 V, Ag / AgCl and potential gradually decreased) was used in the dark for 2 minutes to completely cover the surface of the electrode , Available pinhole covers).

Specifically, the step of preparing the second photoelectrode includes the steps of preparing the second precursor solution by mixing the iron source material, the titanium raw material, the polymer and the second solvent, and the second precursor solution by mixing the second precursor solution with the second conductive substrate And then drying and heat-treating the second light absorbing layer to form a second light absorbing layer.

After the process of forming the second light absorbing layer, the second light absorbing layer may be reduced using a borohydride decomposition method.

After the process of forming the second light absorbing layer, a process of preparing a coating liquid by mixing titanium oxide raw material and a third solvent, and a process of coating a coating liquid on the second light absorbing layer and forming a surface treatment layer by heat treatment .

After the process of forming the surface treatment layer, a process of preparing a mixed solution by mixing nickel nitrate, nitrate oxide and a fourth solvent and a process of dropping the mixed solution onto the surface treatment layer, drying and heat treatment to form a second coenzyme layer .

[Production example of second optical electrode]

A second photoelectrode containing Fe ₂ O ₃ was prepared using a polymer-assisted nitrate decomposition method. Therefore, the iron raw material _{0.5M Fe (NO 3) 2 *} 3H 2 O; a (99.0% Kanto Chemicals) 2- methyl-methanol (98.0%; Kanto Chemicals); was dissolved in (Kanto Chemicals 99.0%) and acetylacetone. The volume ratio of 2-methylmethanol and acetylacetone was 7: 3.

Then, 500 mg of polyethyleneglycol (PEG) 8000 (polymer mass) (99.0%; Sigma Aldrich) was added to 10 ml of polymer binder. The prepared solution was sonicated for 1 hour to prepare a homogeneous, opaque red solution.

Then, a second precursor solution was prepared by adding a solution in which 0.5 M Ti (IV) propoxide (99%; Sigma Aldrich), a titanium raw material, was dissolved in 2-methylmethanol (98.0%; Kanto Chemicals). At this time, for the 0.5% Ti concentration, the Fe: Ti atomic ratio was adjusted to be 0.995: 0.005 (1: 0.005025). The second solvent may be a mixture of 2-methylmethanol (98.0%; Kanto Chemicals) and acetylacetone (99.0%; Kanto Chemicals).

6 mL of the second precursor solution was dropped onto FTO glass (2 cm x 2.5 cm) and dried in an Ar atmosphere for 15 minutes. The precursor film was preheated at 80 DEG C for 10 minutes in an Ar atmosphere until the color of the film became light purple, and heat-treated at 500 DEG C for 10 minutes in a furnace.

The above process was repeated three times to obtain the desired second light absorbing layer, and finally annealed at 500 DEG C for 75 minutes.

(90%; Sigma Aldrich), which is a raw material of titanium oxide, was dissolved in a third solvent, 2-methylmethanol (98.0%; Kanto Chemicals), to form a surface treatment layer containing TiO ₂ Coating solution was used.

The coating liquid was coated on the second light absorbing layer by spin coating (1000 rpm, 20 seconds, 2 times) and heated at 500 캜 for 10 minutes.

Next, a single solution method was used according to Berlinguette et al. To deposit a second coarse layer containing Ni ₂ FeO _x , Ni ₃ FeO _x and NiFeO _x on the surface treatment layer. Precursor solutions of Ni (NO ₃ ) ₂ * 3H ₂ O (99.0%; Sigma Aldrich) and Fe (NO ₃ ) ₂ * 3H ₂ O (99.0%; Kanto Chemicals) ; Kanto Chemicals), and a suitable ratio of Ni: Fe mixture was prepared.

The mixed solution was diluted to a concentration of 0.01M. For the deposition of the electrocatalyst, 1 mL of a mixed solution was dropped on the surface treatment layer, dried in air, and then rinsed with 0.1 M KOH for 10 seconds.

Alternatively, 0.3 mM Co of _{pH 7 (NO 3) 2 *} 6H 2 O (≥98%; Aldrich) and 100ml of 0.5 M potassium phosphate (KHPO ₄₎ lit from 0.4V (Ag / AgCl) in the (100mW / cm &lt; ² &gt;) was deposited on the second co-enzyme layer by photo-assisted electrodeposition (PED). Very little deposition photocurrent was observed during deposition (15 uA / cm ² ) and deposition was performed for 120 seconds. Under the same conditions used in BiVO ₄ , only FeOOH was deposited by PED at a higher potential of 0.45 V (Ag / AgCl).

On the other hand, in the process of forming the first light absorbing layer, the volume of the first precursor solution dropped onto the first conductive substrate may be more than 10 μl and less than 80 μl.

For optimization of BiVO ₄ and Fe ₂ O ₃ , the light harvesting amount of two layers was measured. The lower the amount of metal oxide, the larger the light transmission but the lower the light harvesting efficiency (LHE). As shown in FIG. 10 (e), when the volume of the first precursor solution used is 80 μl or more, the light transmittance is not good. When the volume of the first precursor solution is 10 μl or less, LHE is poor.

As is found in 15, the first precursor solution used for the material prepared in the 80㎕ BiVO ₄ is the transmittance was rapidly reduced and visual turbidity. On the other hand, while the highest photocurrent (5.40 mA / cm ² at 1.23 V _RHE ) greatly suppressed the photocurrent in Fe ₂ O ₃ , the photocurrent was shown to be a precise balance in achieving effective HDP with photon absorption and transmission .

As can be seen from the normal curve of FIG. 16, a larger photocurrent was observed in Fe ₂ O ₃ using BiVO _{4 which} was sufficiently transparent, resulting in a blue shift of BiVO ₄ . This will too would come from the small amount of BiVO _4, although a large amount shows the amount of water absorption in the active region of BiVO ₄ shifted even more to limit the effective area of BiVO ₄ to 500nm or less (as compared to the optimal level in the case 60㎕) .

Water electrolysis system

A water electrolysis system according to the present invention includes a plurality of photoelectrodes immersed in an electrolyte, a counter electrode immersed in an electrolyte, and a solar cell, wherein the plurality of photoelectrodes are electrically connected in parallel with the first electrode of the solar cell, The electrode is electrically connected to the second electrode of the solar cell.

The presence of the solar cell in which the first electrode is electrically connected to the plurality of photoelectrons and the second electrode is electrically connected to the counter electrode is necessary to generate a sufficient bias light voltage to spontaneously separate the water.

When a plurality of photoelectrodes are irradiated with light, electrons and holes (hydrogen ions) are generated in the photoelectrode, and oxygen is generated. The plurality of photoelectrodes are electrically connected in parallel with the first electrode of the solar cell, which is the hole transferring side, so that the electrons generated in the respective photoelectrodes are transferred to the first electrode of the solar cell. The electrons are transferred from the second electrode of the solar cell, which is the electron transfer side, to the counter electrode, and the hydrogen ions are reduced from the counter electrode to generate hydrogen.

The plurality of photoelectrodes may be arranged in the order of increasing band gap energy from the front with reference to the direction in which the light is irradiated.

The plurality of photoelectrodes include a first photoelectrode and a second photoelectrode that absorbs light of a longer wavelength than the first photoelectrode. The first photoelectrode is insulated on one surface of the second photoelectrode, And the second electrode of the solar cell may be insulated on the other surface.

The solar cell can be selected from a silicon solar cell, a dye-sensitized solar cell, a compound semiconductor solar cell, and a laminated solar cell.

A monolithic tandem cell in which the first optical electrode, the second optical electrode and the solar cell are attached to each other can be manufactured. In the case of solar cells, c-Si solar cells can be used, and two small c-Si solar cells connected in series can be used. The first electrode of the c-Si solar cell may include Al, and the second electrode may be composed of ITO.

The first optical electrode may be insulated from one side of the second optical electrode through a glue. The second electrode of the solar cell can be insulated from the other surface of the second optical electrode through the glue.

Specifically, the first coarse substrate of the first optical electrode and the second coarse layer of the second optical electrode can be insulated through the glue. In addition, the second conductive substrate of the second electrode and the second electrode of the solar cell may be insulated through the glue.

Each of the first and second photoelectrodes may be electrically connected to the first electrode of the solar cell through a copper sheet or copper wiring, and the counter electrode may be electrically connected to the second electrode of the solar cell.

Light radiated from the front is absorbed by the first optical electrode, and light passing through the first optical electrode is absorbed in turn into the second optical electrode and the solar electrode.

As shown in FIGS. 9 (b) and 10 (a), by using two optical electrodes optimized in the water electrolysis system of the present invention, BiVO ₄ (H, 1 % Mo: first optical electrode comprising BiVO _4), the rear _{Fe 2 O 3 (H, TiO} 2 /0.5% Ti: by placing a second optical electrode comprising an _{Fe 2 O 3) BiVO 4 ||} Fe ₂ O ₃ .

As is found in 10 (b), a single photo-electrode, Fe single optical electrode including the ₂ O ₃ and Fe ₂ O ₃ BiVO ₄ || HDP is highly transparent both together comprising a single BiVO ₄ containing BiVO ₄ The photoelectrode has a transmittance of 75% at 550 nm, a single light electrode containing Fe ₂ O ₃ at 70% at 650 nm, and a transmittance of 50% at 650 nm for HDP.

Thus, more than 50% of the incident light can be used in solar cells (dual c-Si) located behind the HDP, which generates a sufficient bias photovoltage to spontaneously separate the water.

HDP must be successfully applied to a water electrolysis system using actual solar light. Therefore, as shown in FIG. 17 (a), a thin film c-Si solar cell is manufactured by integrating a HDP BiVO ₄ || Fe ₂ O ₃ optical electrode It has been proven by a tandem cell type non-biased solar water electrolysis system.

In addition, as shown in Fig. 17 (b) and Fig. 18, a water electrolysis system in the form of a monolithic tandem cell was manufactured. Monolithic devices have simplicity and flexibility in small or mobile applications. By using two parallel c-Si solar cells with a photovoltage of about 1.2 V as the ultimate absorber, this system can be used in a "Q6" system, ie a quadruple absorber requiring six photons for the production of H ₂ molecules .

Manufacturing method of water electrolysis system

A method of manufacturing a water electrolysis system according to the present invention includes the steps of preparing a plurality of photoelectrodes, preparing a counter electrode, dipping a plurality of photoelectrodes and a counter electrode in an electrolyte, And electrically connecting the counter electrode to the second electrode of the solar cell.

Preparing the plurality of photoelectrodes includes the steps of preparing a first photoelectrode by placing a first photoabsorption layer on a first conductive substrate, preparing a second photoabsorption layer by placing a second photoabsorption layer on the second conductive substrate, .

Meanwhile, after the step of preparing the second optical electrode for manufacturing the monolithic tandem cell, the first conductive substrate and the second light absorbing layer are insulated from each other, and the second conductive substrate and the second electrode are insulated from each other As shown in FIG.

[Production Example of Water Electrolysis System]

HDP and c-Si solar cells. The first optical electrode and the second optical electrode constituting the HDP are prepared in accordance with the production example of the first optical electrode and the production example of the second optical electrode described above.

The counter electrode was prepared by spin coating (1000 rpm, 10 seconds) 0.5 mM H ₂ PtCl ₆ * 6H ₂ O (99%; Aldrich) diluted in ethanol on FTO and annealing at 450 ° C. for 30 minutes to obtain Pt / FTO cm &lt; ² &gt;).

In the case of solar cells, c-Si solar cells are cut into small pieces and electrically connected. Two pieces of c-Si having a first electrode (hole transfer side) and a second electrode (electron transfer side) composed of ITO were connected using an Ag paste containing Al. The area of the two pieces was 0.30 cm ² (0.5 cm x 0.6 cm).

Next, the first optical electrode, the second optical electrode, and the solar cell are attached through a glue to form an integral body. The first optical electrode is insulated from one side of the second optical electrode through a glue, and the distance between the first optical electrode and the second optical electrode can be adjusted to 0.3 cm using a glue. The second electrode of the solar cell can be insulated from the other surface of the second optical electrode through the glue.

Specifically, one surface of the second light electrode may be a second light absorbing layer, and may be attached to the first conductive substrate of the first light electrode. The other surface of the second optical electrode may be a second conductive substrate and may be attached to the second active electrode of the solar cell.

Then, the first and second photoelectrodes are electrically connected in parallel with the first electrode of the solar cell using a copper wiring, and the counter electrode is electrically connected to the second electrode of the solar cell.

Hereinafter, specific examples of the present invention will be described. However, the following examples are only a concrete example of the present invention, and the present invention is not limited to the following examples.

Example  And Comparative Example

[Preparation of photoelectrochemical cell containing sacrificial agent]

The counter electrode was prepared by spin-coating (1000 rpm, 10 seconds) 0.5 mM H ₂ PtCl ₆ * 6H ₂ O (99%; Aldrich) diluted in ethanol on FTO and Pt / FTO annealed at 450 ° C. for 30 minutes cm &lt; ² &gt;) was used. The electrolyte was an aqueous solution containing a sacrificial agent (0.5M KPi + 0.5M Na ₂ SO ₃ ).

A single optical electrode including BiVO ₄ , a single optical electrode including Fe ₂ O _3, and a single optical electrode including BiVO ₄ disposed in front in accordance with the above-described [first production example of optical electrode] and [production example of second optical electrode] A single photoelectrode containing Fe ₂ O ₃ and BiVO ₄ Fe Fe ₂ O ₃ HDP were prepared to fabricate each photochemical cell.

[Performance evaluation]

The hole injection efficiency (η _surface ) is essentially 100% since it is easy to photo-oxidize the sulfite. Therefore, it is possible to compare the bulk photocathode of the photocathode while avoiding any problem of hole injection at the semiconductor-electrolyte interface.

10 (c), BiVO ₄ was photocurrent of 5.0 ± 0.2 mA / cm ² at 1.23 V _RHE , Fe ₂ O ₃ photocurrent of 4.5 ± 0.2 mA / cm ² at 1.23 V _RHE , BiVO ₄ the rear Fe ₂ O ₃ is the photoelectric current of 2.2 ± 0.1mA / cm ² at 1.23V _RHE, BiVO ₄ || Fe ₂ O ₃ was followed to obtain a photocurrent of 7.1 ± 0.2mA / cm ² at 1.23V _RHE respectively.

Overall, HDP exhibits a photocurrent of about 29.3% greater than the photocurrent of a single BiVO ₄ photoelectrode. BiVO ₄ And BiVO ₄ Is nearly equal to the sum of the photocurrents generated by the rear Fe ₂ O ₃ , indicating that the HDP concept is definitely working.

Also, the starting potential of BiVO ₄ Fe Fe ₂ O ₃ is 0.2 V _RHE , which is a single BiVO ₄ And is much lower than a single Fe ₂ O ₃ photoelectrode (0.4 V _RHE ).

In FIG. 10 (e), the IPCE of the single BiVO ₄ photoelectrode is higher than the IPCE of the single Fe ₂ O ₃ photoelectrode in the range of 300 to 450 nm, which indicates that BiVO ₄ is suitable as the first photoabsorber layer. BiVO ₄ || Fe ₂ O ₃ The IPCE of the HDP increases to 95% due to the additional photocurrent generated by the transmission of the transmitted light passing through the first optical electrode containing BiVO ₄ through the second optical electrode containing Fe ₂ O ₃ .

The IPCE of a single BiVO ₄ photoelectrode drops sharply due to the reduced light harvesting efficiency (LHE) and indirect band transfer (direct: 2.7 eV, indirect: 2.4 eV) properties in the 450 to 510 nm range. This is a single BiVO ₄ theoretical maximum photocurrent of the light absorber ^{_{BiVO 4 (7.5 mA / cm 2}} ) is an important reason is difficult to achieve.

However, Fe ₂ O ₃ is an additional light absorber and can effectively utilize transmitted light in this region. In the 510 to 610 nm region, only Fe ₂ O ₃ contributes to the overall performance of the HDP. This effect is very important because even though the IPCE value in this region is much lower than at 510 nm (less than 20%), more than 50% of the solar energy available by the photoelectrode is in this region. The theoretical maximum photocurrent of Fe ₂ O ₃ is about 13.6 mA / cm ² , and almost half of it comes from photons in the 500 to 620 nm range. Therefore, this area should be used to further improve the performance of the HDP.

[Manufacture of non-deflecting photovoltaic cell]

The counter electrode was prepared by spin-coating (1000 rpm, 10 seconds) 0.5 mM H ₂ PtCl ₆ * 6H ₂ O (99%; Aldrich) diluted in ethanol on FTO and Pt / FTO annealed at 450 ° C. for 30 minutes cm &lt; ² &gt;) was used. The electrolyte was a 1.0M bicarbonate KCi solution of pH 9.2.

A single optical electrode including BiVO ₄ , a single optical electrode including Fe ₂ O _3, and a single optical electrode including BiVO ₄ disposed in front in accordance with the above-described [first production example of optical electrode] and [production example of second optical electrode] A single photoelectrode containing Fe ₂ O ₃ and BiVO ₄ Fe Fe ₂ O ₃ HDP were prepared to fabricate each photochemical cell.

[Performance evaluation]

As shown in FIG. 19 (a), BiVO ₄ was photocurrent of 5.0 ± 0.1 mA / cm ² at 1.23 V _RHE , Fe ₂ O ₃ photocurrent of 4.0 ± 0.2 mA / cm ² at 1.23 V _RHE , BiVO ₄ to 2.0 ± photoelectric current of 0.1mA / cm ² in the rear Fe ₂ O ₃ is 1.23V _RHE, BiVO ₄ || Fe ₂ O ₃ is the photoelectric current of 7.0 ± 0.2mA / cm ² at 1.23V _RHE, from 1.5V _RHE 8.0 +/- 0.2 mA / cm &lt; ² &gt;, respectively.

This PED performance is the highest recorded on the stable metal oxide photoelectrode. As can be seen in FIG. 19 (d) and FIG. 20, the performance was highly reproducible, and most of the photocurrent was observed in 2H ₂ + O ₂ gas, with almost complete Faraday efficiency). HDP utilizes visible light up to 610 nm in water separation as shown by the action spectra of Figures 19 (e) -19 (g).

In water separation, photocurrent and IPCE show values similar to those in FIG. 10 using sacrificial sulfurous acid oxidation, with surface charge separation efficiency (eta _surface ) _ranging from 89 to 100%.

[Preparation of tandem cell type water electrolysis system]

A single BiVO ₄ light electrode, a counter electrode, and a c-Si solar cell were connected in accordance with the above-mentioned [first production example of optical electrode], [production example of second optical electrode] An electrolysis system, a water electrolysis system in which a single Fe ₂ O ₃ optical electrode, a counter electrode and a c-Si solar cell are connected, and a BiVO ₄ || Fe ₂ O ₃ HDP, a counter electrode, and a water electrolysis system to which a c-Si solar cell was connected, respectively.

[Performance evaluation]

As Figure 17 (c) to determine the intersection of the performance curve of the photo-electrode and the solar cell, a single BiVO ₄ water electrolysis system is connected photoelectrode is 4.5mA / cm ^2, Fe ₂ O ₃ single photo-electrode is connected to electric water The decomposition system was 3.2 mA / cm ² , BiVO ₄ || Fe ₂ O ₃ The water electrolysis system to which HDP is connected produces a predicted working photocurrent of 6.3 mA / cm ² .

This corresponds to the solar-to-hydrogen conversion efficiency (? _STH ) of 5.6%, 3.9% and 7.7%, respectively, as shown in Figs. 17 (c), 21 and 22, respectively. The actual water electrolysis system reproduces this predicted value, which represents the highest η _STH obtained in a non-deflected solar water electrolysis system using a stable metal oxide photoelectrode.

There was no signal of a decline during the continuous running of the water electrolysis system, indicating complete isolation of the solar cell components from the electrolyte, as can be seen in Figure 17 (d).

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims and their equivalents. It will be understood that the invention may be embodied in other specific forms without departing from the spirit or scope of the invention. It is therefore to be understood that the embodiments and / or the examples described above are illustrative in all aspects and not restrictive.

Claims (31)

A plurality of photoelectrodes immersed in an electrolyte; And
And a counter electrode immersed in the electrolyte,
Wherein the plurality of photoelectrodes are electrically connected in parallel to the counter electrode. The method according to claim 1,
Wherein the plurality of photoelectrodes comprise:
Each including a semiconductor,
A photoelectrochemical cell arranged in the order of photoelectrodes having a bandgap energy of the semiconductor from the front side with respect to a direction in which light is irradiated. The method according to claim 1,
Wherein the plurality of photoelectrodes comprise:
Each including a semiconductor,
A photoelectrochemical cell comprising a combination of both n-type semiconductors or a combination of both p-type semiconductors. The method according to claim 1,
The photo-
A first optical electrode; And
And a second optical electrode that absorbs light of a longer wavelength than the first optical electrode,
Wherein light irradiated from the counter electrode direction is sequentially absorbed by the first photo-electrode and the second photo-electrode. The method of claim 3,
The first photoelectrode includes a first electrode,
A first conductive substrate; And
And a first light absorbing layer disposed on the first conductive substrate,
Wherein the first light absorbing layer
_{SiO 2, TiO 2, WO 3} , Fe 2 O 3, SnO 2, ZnO, ZrO 2, In 2 O 3, MoS 2, BiVO 4, SrTiO 3, comprising at least one semiconductor selected from the group consisting of CaTiO ₃ and KTaO ₃ Optoelectrochemical cell. 6. The method of claim 5,
Wherein the first conductive substrate is made of FTO,
The first light-absorbing layer including a photoelectric cell of BiVO _4. The method according to claim 6,
The BiVO ₄ is doped with Mo,
Mo: Mo-doped so that the atomic ratio of Bi: (V + MO) is 1: 0.8 to 1: 1.2. 6. The method of claim 5,
The first photoelectrode includes a first electrode,
And a first coenzyme layer disposed on the first light absorbing layer,
Wherein the first coenzyme layer comprises:
A photoelectrochemical cell comprising FeOOH and NiOOH. The method of claim 3,
The second photo-
A second conductive substrate;
And a second light absorbing layer disposed on the second conductive substrate,
Wherein the second light absorbing layer
_{SiO 2, TiO 2, WO 3} , Fe 2 O 3, SnO 2, ZnO, ZrO 2, In 2 O 3, MoS 2, BiVO 4, SrTiO 3, comprising at least one semiconductor selected from the group consisting of CaTiO ₃ and KTaO ₃ Optoelectrochemical cell. 10. The method of claim 9,
The second conductive substrate is made of FTO,
Wherein the second light absorbing layer comprises Fe ₂ O ₃ . 11. The method of claim 10,
Wherein the Fe ₂ O ₃ is doped with Ti,
Ti: doped such that the atomic ratio of Fe: Ti is 1: 0.003 to 1: 0.007. 10. The method of claim 9,
The second photo-
And a surface treatment layer located on the second light absorbing layer and comprising TiO ₂ . 13. The method of claim 12,
The second photo-
And a second coenzyme layer positioned on the surface treatment layer,
Wherein the second coenzyme layer comprises:
NiFeO _x , Ni ₂ FeO _x, and Ni ₃ FeO _x . The method according to claim 1,
Wherein the electrolyte is a potassium bicarbonate solution having a pH of from 9 to 10. Preparing a plurality of photoelectrodes;
Preparing a counter electrode; And
And immersing the plurality of photoelectrodes and the counter electrode in an electrolyte, and electrically connecting the plurality of photoelectrons to the counter electrode electrically in parallel. 16. The method of claim 15,
Wherein the step of preparing the plurality of photoelectrodes comprises:
Placing a first light absorbing layer on a first conductive substrate to prepare a first photoelectrode; And
And preparing a second photoelectrode by positioning a second photoabsorption layer on a second conductive substrate. 17. The method of claim 16,
The step of preparing the first photo-
Preparing a first precursor solution by mixing a bismuth raw material, a vanadium raw material, a molybdenum raw material, and a first solvent; And
And dipping the first precursor solution on the first conductive substrate made of FTO, and drying and heat-treating the first precursor solution to form a first photoabsorption layer. 18. The method of claim 17,
In the process of forming the first light absorbing layer,
Wherein the volume of the first precursor solution dropped onto the first conductive substrate is greater than 10 袖 l and less than 80 袖 l. 18. The method of claim 17,
After the process of forming the first light absorbing layer,
And reducing the first light absorbing layer using a borohydride decomposition method. 18. The method of claim 17,
After the process of forming the first light absorbing layer,
And forming a first coenzyme layer containing FeOOH and NiOOH by depositing a solution of sulfur iron oxide and a solution of nickel sulfide on the first light absorbing layer. 17. The method of claim 16,
The step of preparing the second photo-
Preparing a second precursor solution by mixing an iron raw material, a titanium raw material, a polymer binder, and a second solvent; And
And dipping the second precursor solution on the second conductive substrate, which is made of FTO, followed by drying and heat treatment to form a second light absorbing layer. 22. The method of claim 21,
After the process of forming the second light absorbing layer,
And reducing the second light absorbing layer using a borohydride decomposition method. 22. The method of claim 21,
After the process of forming the second light absorbing layer,
A titanium oxide raw material and a third solvent to prepare a coating solution; And
Coating the coating liquid on the second light absorbing layer, and heat treating the coating liquid to form a surface treatment layer. 24. The method of claim 23,
After the process of forming the surface treatment layer,
A process for preparing a mixed solution by mixing nickel nitrate, nitric oxide and a fourth solvent; And
And dropping the mixed solution onto the surface treatment layer, followed by drying and heat treatment to form a second coenzyme layer. A plurality of photoelectrodes immersed in an electrolyte;
A counter electrode immersed in the electrolyte; And
A solar cell,
Wherein the plurality of photoelectrodes are electrically connected in parallel to the first electrode of the solar cell,
And the counter electrode is electrically connected to the second electrode of the solar cell. 26. The method of claim 25,
Wherein the plurality of photoelectrodes comprise:
A water electrolysis system in which the band gap energy is arranged in order from the front, with respect to the direction in which the light is irradiated. 26. The method of claim 25,
Wherein the plurality of photoelectrodes comprise:
A first optical electrode; And
And a second optical electrode that absorbs light of a longer wavelength than the first optical electrode,
The first optical electrode is insulated on one surface of the second optical electrode,
And a second electrode of the solar cell is attached to the other surface of the second optical electrode. 26. The method of claim 25,
In the solar cell,
A water electrolysis system selected from silicon solar cells, dye-sensitized solar cells, compound semiconductor solar cells, and laminated solar cells. Preparing a plurality of photoelectrodes;
Preparing a counter electrode; And
The method comprising the steps of: immersing the plurality of photoelectrodes and the counter electrode in an electrolyte; electrically connecting the plurality of photoelectrodes to the first electrode of the solar cell in parallel; and electrically connecting the counter electrode to the second electrode of the solar cell &Lt; / RTI &gt; 30. The method of claim 29,
Wherein the step of preparing the plurality of photoelectrodes comprises:
Placing a first light absorbing layer on a first conductive substrate to prepare a first photoelectrode; And
And preparing a second photoelectrode by placing a second light absorbing layer on the second conductive substrate. 31. The method of claim 30,
After the step of preparing the second optical electrode,
Inserting the first conductive substrate and the second light absorbing layer in an insulating state, and insulating the second conductive substrate and the second electrode.

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