KR102088661B1 - Method for preparation Lead(II) chromate via electrolysis - Google Patents

Abstract

The present invention relates to a method for manufacturing lead chromate through electroplating, and more specifically, to a method for manufacturing lead chromate, which manufactures lead chromate micro-rod particles in an operation electrode by immersing a ternary electrode system including the operation electrode, a counter electrode and a reference electrode in electrolyte in which lead salt, chrome salt and potassium salt are mixed. In particular, in the present method, the lead salt contained in the electrolyte has a concentration range of 2-7 mM, the electrolyte uses distilled water as a solvent, and the mole fraction of the lead salt, the chrome salt and the potassium salt is in the range of 1:1-15:15-25. Furthermore, an oxidation potential is applied on the operation electrode.

Description

Method for preparation of lead chromate via electroplating {Method for preparation Lead (II) chromate via electrolysis}

The present invention relates to a method for producing lead chromate through electroplating, and to a method for manufacturing a micro rod of lead chromate (PbCrO ₄ ) having excellent optical and electrochemical properties, having a rod-shaped single crystal by applying a voltage from the electrolyte. will be.

In general, titanium dioxide (TiO ₂ ), which is widely used as a photocatalyst, has excellent properties in decomposing organic matter and water, and has a limitation that it can induce a photocatalytic reaction only in the ultraviolet region containing about 4% of sunlight. Recently, semiconducting metal oxides have been spotlighted as an environmentally friendly decontamination material that exhibits air pollution purification, water pollution purification, and antibacterial functions through photocatalytic reaction and does not cause secondary pollution even after decomposing harmful substances.

The semiconducting metal oxide physically has two energy levels, that is, a valence band (VB) and a conduction band (CB), similarly to a single element semiconductor, and VB is generated by photons having energy above the band gap. Refers to a substance in which electrons are excited to move to CB and holes are generated in VB from which electrons escape. The CB electrons and VB holes thus generated function to reduce and oxidize harmful substances such as volatile organic compounds on the surface of the metal oxide, thereby catalyzing the decomposition of harmful substances.

BiVO ₄ having a band gap energy of 2.4eV is known as a typical transition metal oxide photocatalyst as a narrow bandgap and a material having high visible light reactivity of a photocatalyst, and has been studied a lot in photoelectrochemical water decomposition applications, but is not commercialized due to its low efficiency. Did not.

Lead chromate, which is used as a yellow pigment, is a monoclinic crystal in which Pb ²⁺ cations form a tetrahedron with Cr as the center, and it is known that it can exhibit high-efficiency photocatalytic properties as an n-type semiconductor. Lead chromate, which has excellent photoelectrochemical properties, has not been developed.

1. Republic of Korea Patent Publication No. 10-2014-0098601 (2014. 08. 08. published) 2. Republic of Korea Patent Publication No. 10-2007-0082760 (published on August 22, 2007)

The present invention is to provide a method for producing lead chromate having excellent photoelectrochemical properties and lead chromate microrod particles prepared accordingly.

More specifically, lead chromate is PbCrO ₄ and provides a micro rod having a rod shape having a diameter of 1 μm, thereby providing a method for producing lead chromate having excellent photoelectrochemical properties even in visible light, and providing lead chromate prepared accordingly. have.

The method for producing lead chromate of the present invention is immersed in a ternary electrode system including a working electrode, a counter electrode, and a reference electrode in an electrolyte in which lead salt, chromium salt and potassium salt are mixed, and then leads lead chromate to the working electrode surface through electroplating. It is characterized by manufacturing.

The lead salt contained in the electrolyte has a concentration range of 2 to 7 mM, the electrolyte has distilled water as a solvent, and the molar ratio of lead salt, chromium salt, and potassium salt has a range of 1: 1 to 15: 15 to 25, and the electrolytic plating works It is preferably performed by applying an oxidation potential on the electrode.

The lead chromate has a chemical formula of PbCrO ₄ phosphorus, and is characterized in that it is a rod-shaped micro rod particle having a diameter of 1 µm or more.

The lead salt is at least one selected from lead nitrate (Pb (NO ₃ ) ₂ ), lead acetate (Pb (CH ₃ COO) ₂ ), lead chloride (PbCl ₂ ), and lead sulfate (PbSO ₄ ), and the chromium salt is nitric acid One or more of chromium (Cr (NO ₃ ) ₃ ), chromium acetate (Cr (CH ₃ COO) ₃ ), chromium chloride (CrCl ₃ ), and chromium sulfate (Cr ₂ (SO ₄ ) ₃ ) is selected, and the potassium salt Silver may be selected from one or more of potassium nitrate (KNO ₃ ), potassium acetate (CH ₃ COOK), potassium chloride (KCl), potassium sulfate (K ₂ SO ₄ ).

As the working electrode, any one of Fluorine Doped Tin Oxide (FTO), Aluminum doped Zinc Oxide (AZO), Aluminum doped Tin Oxide (ATO), and Indium Tin Oxide (ITO) may be selected.

In the method of manufacturing lead chromate, the working electrode is characterized in that a lead oxide (PbO ₂ ) layer is formed in advance, and the lead oxide layer may be formed through electroplating in an electrolyte mixed with lead salt and potassium salt. .

When forming the lead oxide layer, the lead salt is characterized in that the molar ratio of lead salt and potassium salt in the range of 2-7 mM concentration is 1: 15 ~ 25, and electrolytic plating is performed by applying an oxidation potential on the working electrode.

The manufacturing method according to the present invention can provide a rod-shaped lead chromate microrod single crystal having a diameter of 1 µm or more through simple electroplating or electroplating.

The lead chromate single crystal absorbs visible light and has excellent photoelectrochemical properties, so that not only water decomposition but also decomposition of harmful substances such as volatile organic compounds can be effectively made.

In addition, the lead chromate microrod single crystal of the present invention can be applied to a wide range of antibacterial products, self-cleaning products, super-hydrophilic products, air pollution purifiers, water pollution purifiers and the like to effectively and effectively solve environmental pollution.

FIG. 1 shows the results of (a) XRD pattern and (b) photocurrent-voltage curve of chromic acid electroplated according to various potentials, and all thin films were heat treated at 550 ° C. for 1 hour after electroplating.
2 is a SEM image of lead chromate formed according to the electrodeposition time at 1.3V.
Figure 3 shows the results of (a) XRD pattern, (b) SEM image, (c) EDS and (d) TEM image of lead chromate after 1.3V and 1 hour electroplating.
4 is (a) Tauc plot (insertion degree) related to UV-Vis absorption spectrum of electrodeposited lead chromate microrods, (b) 0.1 M Na while chopping UV-visible light (full xenon lamp, 100 mW / cm ² ) Linear sweep voltammograms (scan rate: 20 mV / s) of lead chromate measured in ₂ SO ₃ / 0.1M Na ₂ SO ₄ aqueous solution and changes with electrodeposition time and (c) per lead oxide microrod and nanorod area in sulfite oxidation This graph shows the amount of lead chromate and the change in photocurrent.
5 shows (a) XRD pattern and SEM image of lead chromate nanorod on FTO substrate and (b) photoelectrochemical oxidation of sulfite measured while applying 100 mW / cm ² light (using xenon lamp) to lead chromate nanorod It is a result showing the current-voltage curve.
Figure 6 (a) UV-Visible light (xenon full lamp, 100 mW / cm ²⁾ a pH 6.8 phosphate buffer solution, while ^{_{chopping (0.1 M HPO 4 2- /0.1}} MH 2 PO 4 -) in, immediately after deposition, and Co -This graph shows the linear sweep voltammograms (scan rate: 20 mV / s) of lead-decorated lead chromate microrods.
7 is a graph showing Incident photon to current conversion efficiency (IPCE) of Co-Pi decorated lead chromate microrod in photoelectrochemical water oxidation. Photo current is 0.62 V while applying a (vs. Ag / AgCl) pH 6.8 phosphate buffer (HPO 4 2-: H 2 PO 4 - = 1: 1) was determined in an aqueous solution.
Figure 8 (a) Chronoamperograms of lead chromate microrods (electrodeposited in 1.2V vs. Ag / AgCl for 15000 seconds) in pH 6.8 phosphate buffer solution while irradiating UV-visible light (full xenon lamp, 100 mW / cm ² ) ( b) Pb 4f and Cr 2p spectra with and without Co-Pi decoration (c) When lead-chromate microrods are irradiated with UV-visible light (full xenon lamp, 100 mW / cm ² ) and photoelectrochemical water oxidation occurs. This is a schematic diagram showing the calculated Faraday efficiency and photoelectrochemical water oxidation in a Chronocoulomertic plot (d) Co-Pi decorated lead chromate microrod.

The terms or words used in the specification and claims should not be interpreted as being limited to a conventional or dictionary meaning, and the inventor can appropriately define the concept of terms in order to explain his or her invention in the best way. Based on the principle that it should be interpreted as meanings and concepts consistent with the technical spirit of the present invention.

The method for producing lead chromate of the present invention is immersed in a ternary electrode system including a working electrode, a counter electrode, and a reference electrode in an electrolyte in which lead salt, chromium salt and potassium salt are mixed, and then leads lead chromate to the working electrode surface through electroplating. As a method of manufacturing, the working electrode may be selected from any of Fluorine Doped Tin Oxide (FTO), Aluminum doped Zinc Oxide (AZO), Aluminum doped Tin Oxide (ATO), and Indium Tin Oxide (ITO).

The counter electrode may be a platinum wire (Pt wire), the reference electrode may include Ag / AgCl.

The lead salt included in the electroplating has a concentration range of 2 to 7 mM, the electrolyte has distilled water as a solvent, and the molar ratio of lead salt, chromium salt, and potassium salt has a law of 1: 1 to 15: 15 to 25, and the above limitation When the concentration range and the molar ratio are out of range, the rod-shaped lead chromate microrod particles having a diameter of 1 µm or more are not uniformly formed, and thus the range of the concentration and molar ratio defined above is preferable.

Electrolytic plating of the working electrode is preferably performed by applying an oxidation potential on the working electrode. If it is less than 1.2V, it is not formed on lead chromate having phosphorus of the formula PbCrO ₄ on the working electrode, and when it exceeds 1.4V, since the formula Pb ₂ CrO ₅ is formed, it is not formed on lead chromate having excellent photoelectrochemical properties. Causes

The lead salt is at least one selected from lead nitrate (Pb (NO ₃ ) ₂ ), lead acetate (Pb (CH ₃ COO) ₂ ), lead chloride (PbCl ₂ ), and lead sulfate (PbSO ₄ ), and the chromium salt is nitric acid One or more of chromium (Cr (NO ₃ ) ₃ ), chromium acetate (Cr (CH ₃ COO) ₃ ), chromium chloride (CrCl ₃ ), and chromium sulfate (Cr ₂ (SO ₄ ) ₃ ) is selected, and the potassium salt Silver may be selected from one or more of potassium nitrate (KNO ₃ ), potassium acetate (CH ₃ COOK), potassium chloride (KCl), potassium sulfate (K ₂ SO ₄ ), but is not limited thereto.

In the method for producing lead chromate, in order to more effectively form rod-shaped lead chromate microrod particles having a diameter of 1 μm or more, it is preferable to further form a lead oxide (PbO ₂ ) layer on the working electrode, and lead oxide The layer may be formed through electroplating in an electrolyte mixed with lead salt and potassium salt.

PbO ₂ on the working electrode ?? The layer is a lead oxide having a size of 100 to 200 nm, and the lead oxide formed in the working electrode serves to induce electrodeposition to be better than electrolytic plating of chromate.

When forming the lead oxide layer, the lead salt is characterized in that the molar ratio of lead salt and potassium salt is in the range of 2 to 7 mM in a range of 1: 15 to 25, and electrolytic plating is performed by applying an oxidation potential on the working electrode.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art to which the present invention pertains can easily practice. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

<Raw material>

Pb (NO ₃ ) ₂ (> 99%, Sigma-Aldrich), Cr (NO ₃ ) ₃ ㅇ 9H ₂ O (> 99%, Sigma-Aldrich), KNO ₃ (> 99%, Sigma-Aldrich, St.Louis ), Na ₂ SO ₃ (> 98%, Sigma-Aldrich), Na ₂ SO ₄ (> 99%, Acros Chemicals, NewJersey) were used, and Milli-Q deionized (DI) in the process of preparing an aqueous solution in an electrochemical experiment ) water was used. F-doped tin oxide (FTO) coated glass (<14 Ω, 10 mm ㅧ 15 mm, TEC 15, WY-GMS) was used as the substrate.

<Characteristic analysis method>

For X-ray diffraction (XRD) measurement, a SWXD diffractometer (Rigaku Co., Japan) equipped with a CuKα radiation source was used, and PbCrO ₄ was microscopy-energy dispersive spectroscopy (FESEM-EDS, JSM-6500F, JEOL, Japan), transmission Electron microscopy (TEM, JEM 2100, JEOL, Japan), X-ray photoelectron spectroscopy (K-Alpha, ThermoFisher, monochromatic Al X-ray source) were used. In TEM analysis, the PbCrO ₄ ?? thin film was separated from the FTO by sonication of an FTO substrate on which PbCrO ₄ was electrodeposited in DI water, and then dispersed on DI water, and the PbCrO ₄ dispersion solution was analyzed by dropping it on a TEM grid. The UV-visible absorption spectrum was measured at a wavelength of 300-800 nm using a UV-visspectrophotometer (Cary 60 UV-Vis, Aglient Technologies, Santa Clara, CA, USA).

<Preparation of lead chromate microrod particles through electroplating>

5 mM Pb (NO _{3) 2} was added to a 0.1M KNO ₃ electrolyte 1.5V (vs. Ag / AgCl) for 20 seconds, including (18mC / cm ²⁾ FTO substrate using the pt wire (1mm) with the counter electrode Thin PbO ₂ on the phosphorus working electrode ?? A layer was formed. This gives a small nucleus of porous PbO ₂ (100-200nm).

Next, an electrolyte was prepared with 5 mM Pb (NO ₃ ) ₂ , 60mM Cr (NO ₃ ) ₃ ㅇ 9H ₂ O, 0.1M KNO ₃ , and various potentials (1.1 ~ 1.7V) were added to the Ag / AgCl reference electrode at room temperature. Electrolytic plating was performed on the working electrode in which the PbO ₂ layer was formed on the FTO substrate (0.26 cm ² ) according to time. If necessary, the thin film formed with lead chromate was heat treated at 550 ° C. for 1 hour.

<Preparation of lead chromate nanorod particles through a wet method>

Pb (NO ₃ ) ₂ , Na ₂ Cr ₂ O ₇ ?? 2H ₂ O was dissolved in primary distilled water to adjust the raw material solution concentration, and NaOH was added to Na ₂ Cr ₂ O ₇ ?? 2H ₂ O solution to add chromium The pH of the acid lead synthetic solution was adjusted. Fill a 1 L reactor with 500 mL of distilled water and reactant Pb (NO ₃ ) ₂ , Na ₂ Cr ₂ O ₇ ? With a micropump (EYELA MP-3, Rikakikai, Japan) at a reaction temperature of 25 ° C and a stirring speed of 300 rpm. Chromic acid nanorod particles were prepared while supplying 120 mL each of the 2H ₂ O solution at a flow rate of 2 mL / min, and a thin film was prepared on a substrate through a sping coating method.

<Photoelectrochemical Characterization>

The photoactivity of electrodeposited lead chromate is measured in a photoelectrochemical cell. The prepared films (0.26 cm ² ) are used as working electrodes and exposed to electrolyte and light. All measurements were performed in a borosilicate glass cell with Pt counter electrode and Ag / AgCl reference electrode. The UV-vis light was irradiated with Xe lamp (Oriel, Darmstadt, Germany), and the intensity of the irradiated light was about 100 mW / cm ² . Incident photon to current conversion efficiency (IPCE) analysis includes monochromator (Cornerstone 130, Oriel, Darmstadt, Germany), photodiodedetector (918D-UV-OD3R, Newport, Irvine, CA), optical meter (1918-R, Newport, Irvine, CA ). The electrolyte is _{0.1 M Na 2 SO 3 / 0.1M} Na 2 SO 4 or 0.2M phosphate buffer solution (pH 6.8, HPO 4 2-: H 2 PO 4 - = 1: 1) a. For Co-Pi decoration, lead chromate was immersed in a phosphate-buffer solution containing 0.05 mM Co ²⁺ and tested while changing the potential from 0.2 V to 1.0 V (vs. Ag / AgCl) while applying UV-vis light. .

Oxygen generated due to water oxidation in lead chromate was observed through the substrate generation-tip collection mode (SG-TC) mode of scanning electrochemical microscopy (SECM). Pt ultramicroelectrode (UME, dia. 10 ?? ㎛) was used as a tip electrode to capture the generated oxygen. To prepare Pt UME, a platinum wire (Goodfellow, 99.99% purity) with a diameter of 10 μm is wrapped in a borosilicate glass tube (inner diameter: 0.75 mm / outer diameter: 1 mm) in a vacuum. One end is polished with a 600 mesh sandpaper until the metal disk is exposed and flattened with a sandpaper of 1200 mesh abrasive and alumina suspensions of 50 nm or less contained in water. During SECM measurement, the tip position is controlled by an xyz-stepper motor (T-LA28A, Zaber Technologies Inc., Vancouver, Canada). The substrate electrode was electrodeposited with PbCrO ?? in a Teflon cell (exposure area: 0.16 cm2). The tip contacted the substrate weakly to make the initial contact using a stepper motor, and the distance between the tip and the substrate was about 5 μm.

The oxygen reduction reaction (ORR) is -0.3 V (vs. Ag / AgCl) in 0.2 M sodium phosphate buffer solution at the tip, and the substrate potential for the oxygen evolution reaction (OER) is 0.62 V ( vs. Ag / AgCl = 1.23V vs RHE). The tip potential was applied to a sufficient negative potential to ensure the capture of diffused oxygen without ancillary reactions such as a hydrogen evolution reaction (HER). The photoelectrode was irradiated with UV-vis light from the rear side through a hole in the bottom of the Teflon cell.

<Analysis of evaluation results>

The pre-electrodeposited lead oxide shows a noticeable difference in current at a low potential (<1.3 V vs. Ag / AgCl), although the current difference is very small at a high potential at which the lead oxide layer is electrodeposited at the same time. When performing at less than 1.1 V, lead chromate electrodeposited on the working electrode surface was not observed. In the case of electrolytic plating of lead chromate, it is formed at 1.2 V or higher. When the potential is high, it can be confirmed from FIG. 1 that lead chromate is electrodeposited from PbCrO ₄ to Pb ₂ CrO ₅ .

Referring to the XRD pattern of (a) of FIG. 1, it can be confirmed that lead chromate having the formula PbCrO ₄ is formed at a voltage of 1.2 to 1.4 V, whereas Pb ₂ CrO ₅ is formed at 1.5 _V. That is, at 1.5V, electrodeposition was completely converted to Pb ₂ CrO ₅ and at higher potentials, conversion to PbO occurred. The change to Pb ₂ CrO ₅ causes a color change (yellow to orange, inset in Fig. 1 (b)) and is narrower than the band gap of PbCrO ₄ (2.1eV), resulting in a red shift of the absorption band in the UV-vis spectrum. When compared to PbCrO ₄ , Pb ₂ CrO ₅ absorbs light more strongly, but photoactivity is lower than PbCrO ₄ , which may be due to the low conductivity of Pb ₂ CrO ₅ .

2 is a SEM image of lead chromate formed according to the electrodeposition time at 1.2V, and it can be seen that as the electrodeposition time increased, the lead chromate microrod increased significantly. Through the electroplating process, the size of the membrane was grown to a maximum of 21 ㅁ 0.3 µm, and it can be seen that the deposition coverage was significantly increased according to the electrodeposition time.

3 is an analysis result of lead chromate microd formed after electroplating at 1.2V for 1 hour. It can be seen that lead chromate is a single structure of PbCrO ₄ in XRD pattern, and SEM image shows that electrodeposited lead chromate has a polyhedron having a rectangular cross section. Can be confirmed. Through the electroplating process, the size of the membrane grew to a maximum of 21 ㅁ 0.3 µm, and the deposition coverage increased with the electrodeposition time. Through the EDS analysis, the ratio of Pb and Cr is confirmed at a 1: 1 atomic ratio (FIG. 3 (c)), and the selected-area electron diffraction (SAED) of the TEM image confirms that lead chromate is a single crystal (FIG. 3 (d)) )can do. It can be seen that single crystal microrods can be produced through electroplating without heat treatment.

Electroplated semiconductors through self-organization have good physical properties without additional recrystallization steps, so electrodeposited lead chromate microrods have an electrical band structure and high light absorption and photoactivity. Referring to FIG. 4, the starting point of light absorption in the UV-vis spectrum was shown near the wavelength of 550 nm (FIG. 4 (a)), and the band gap of lead chromate in the Tauc plot was the same as the value reported as 2.3 eV (FIG. 4). (a) Insert picture). Lead chromate electroplated on FTO ?? The photoactivity of the microrods was measured in a photoelectrochemical cell, and the oxidation reaction of sulfite (SO ₃ ^2- ) induced by light was observed by irradiation of full Xenon lamp light (FIG. 4 (b)). As the amount of electrodeposited lead chromate increased, the coverage and thickness increased, so the photocurrent (j _ph ) increased, and 0.6mA / cm ?? It can be confirmed that it has reached ² (FIG. 4 (c)). Compared with lead chromate nanorods, it is clear that microrods have better photoreactivity, which is 6 times higher than lead chromate nanorods. In contrast to microrods, the photoreactivity of nanorods did not change positively, which means that the separation and transfer of charge in lead chromate rather than absorption of light limits photoactivity. Since the photoelectrode film made of nanocrystals exhibits greater resistance due to the barrier due to internal particle charge transfer, the high photoactivity of electroplated lead chromate enhances charge transfer, which increases the diffusion length of the minority carrier in the self-organized crystal structure. Is caused by an increase.

6 (a) is a linear sweep voltammograms of electrodeposited lead chromate microrods when UV-vis is incident in 0.2M sodium phosphate buffer (PH 7), and the generation of photooxidation currents participating in water oxidation was found in lead chromate microrod. The increase of the photocurrent and the co-pi decoration of the lead chromate microrod are understood to be similar to the effect of Co-Pi on Fe ₂ O ₃ ?? and BiVO ₄ ??. The photoelectrochemical water oxidation in PbCrO ₄ microrods can confirm the generation of oxygen through SECM, and the properties of the water oxidation reaction in the photoelectrode are successfully confirmed as shown in FIG. 6 (b). Oxygen generation in lead chromate microrods was irradiated with light toward the back of the FTO. At this time, it diffused into a pt disk UME 5 ?? μm above the lead chromate substrate and oxygen was reduced in the UME charged with reduction. When an oxidation current is generated by applying light with a lead chromate microrod, a reduction current is observed in Pt UME. Unlike the oxidizing current, it is produced and dissipated slowly, which can be considered to be related to the diffusion of oxygen to the pt surface.

When applying short wavelength light from Co-Pi decorated lead chromate microrod 0.62V vs. IPCE can be determined by measuring the steady-state photocurrent of photoelectrochemical water oxidation in Ag / AgCl (= 1.23V vs RHE). Referring to the IPCE spectrum of FIG. 7, the photoreactivity appears at 550 nm corresponding to the 2.3eV band gap, and it can be seen that FIG. 4 (a) is consistent with the optical band gap result.

Referring to Figure 8, 1.23V vs. When RHE causes continuous water oxidation in the lead chromate microrod, a gradual decrease in photocurrent is observed, indicating instability, while the Co-Pi decorated lead chromate microrod shows a relatively stable photocurrent as well as an increase in current. In the CV of lead chromate when no light is applied, the surface-related peak is generally observed in the range of 1.0 to 1.3 V (vs.Ag/AgCl), which is the redox peak of Pb ⁴⁺ / Pb ²⁺ in lead oxide. Is similar to Therefore, Pb ²⁺ ?? of lead chromate is photoelectrochemically oxidized with high oxidation water (Pb ⁴⁺ of PbO ₂ ) at the same time as water oxidation. When a high reduction current is applied after blocking the light, a reverse reaction occurs that is reduced back to Pb ²⁺ ??. On the other hand, it can be seen from FIG. 8 (a) that the reduction current of the Co-Pi decorated lead chromate microrod is very small. In the XPS analysis result of lead chromate in FIG. 8 (b), the Pb 4f peak shifted to lower binding energy after water oxidation, which was changed from PbO ₂ to Pb 4f, and the disappearance of Cr 2p peak after water oxidation was chromium. It means photolysis from acid lead to PbO ₂ . On the other hand, Cr in the Co-Pi decorated lead chromate microrod decreased in intensity but was still measured. Fig. 8 (c) shows the water oxidation charge of the lead chromate microrod and the measured Faraday efficiency. Since stability has been improved with Co-Pi decoration, Faraday efficiency continues to increase as opposed to conventional lead chromate. After blocking the light, the reduction current estimated the amount of photo-oxidized Pb, and assuming Faraday efficiency assuming that there was no reaction other than oxidation of Pb ²⁺ and water in Co-Pi decorated lead chromate microrods, Because of the decrease, it showed a Faraday efficiency of almost 100%.

Fig. 8 (d) shows a schematic diagram of photoelectrochemical water oxidation in Co-Pi decorated lead chromate microrods. The photogenerated hole contributes to Pb ²⁺ oxidation in lead chromate (Path 1), and the increased water oxidation rate with Co-Pi decoration increases rapidly for oxygen generation (Path 2). Nevertheless, the photocurrent of the Co-Pi decorated lead chromate microrods slightly decreased, and the Faraday efficiency decreased by 0.04% after 1500 seconds (Fig. 8 (c)), so Co-Pi decoration did not completely reduce the photolysis of lead chromate microrods. It can be seen that lead chromate microrods increase the stability of photooxidation.

In conclusion, the lead chromate microrod of the present invention showed photoelectrochemical activity as a noticeable photocurrent and conversion efficiency in water oxidation although light corrosion was observed, and Co-Pi decoration was able to increase stability as well as photoactivity.

Claims (16)

A method for producing lead chromate, characterized in that lead chromate is prepared on the surface of the working electrode by electroplating by immersing the working electrode in an electrolyte mixed with lead salt, chromium salt and potassium salt. According to claim 1,
The electrolytic plating is a method of manufacturing lead chromate, characterized in that the ternary electrode system comprising a counter electrode and a reference electrode According to claim 1,
The lead salt is a method of producing lead chromate, characterized in that 2 to 7 mM concentration According to claim 1,
Method for producing lead chromate, characterized in that the molar ratio of the lead salt, the chromium salt and the potassium salt is 1: 1 to 15: 15 to 25. According to claim 1,
The electroplating is a method of manufacturing lead chromate, characterized in that is performed by applying an oxidation potential on the working electrode According to claim 1,
The lead chromate is a method for producing lead chromate, characterized in that PbCrO ₄ The method of claim 6,
The lead chromate is a method for producing lead chromate, characterized in that the rod-shaped micro-rod particles having a diameter of 1㎛ According to claim 1,
The lead salt is selected from lead nitrate (Pb (NO ₃ ) ₂ ), lead acetate (Pb (CH ₃ COO) ₂ ), lead chloride (PbCl ₂ ), and lead sulfate (PbSO ₄ ). Manufacturing method According to claim 1,
The chromium is selected from one or more of chromium nitrate (Cr (NO ₃ ) ₃ ), chromium acetate (Cr (CH ₃ COO) ₃ ), chromium chloride (CrCl ₃ ), and chromium sulfate (Cr ₂ (SO ₄ ) ₃ ). Method for producing lead chromate, characterized in that According to claim 1,
The potassium salt is a method for producing lead chromate, characterized in that at least one selected from potassium nitrate (KNO ₃ ), potassium acetate (CH ₃ COOK), potassium chloride (KCl), and potassium sulfate (K ₂ SO ₄ ) is selected. According to claim 1,
The working electrode is a method of manufacturing lead chromate, characterized in that any one selected from Fluorine Doped Tin Oxide (FTO), Aluminum doped Zinc Oxide (AZO), Aluminum doped Tin Oxide (ATO) and Indium Tin Oxide (ITO) is selected. According to claim 1,
A method for producing lead chromate, characterized in that a lead oxide (PbO ₂ ) layer is formed on the working electrode. The method of claim 12,
The lead oxide layer is a method of manufacturing lead chromate, characterized in that formed by electroplating in an electrolyte mixed with lead salt and potassium salt The method of claim 13,
The lead salt is a method of producing lead chromate, characterized in that 2 to 7 mM concentration The method of claim 13,
The lead salt and potassium salt molar ratio of 1: 15 to 25, characterized in that the method for producing lead chromate The method of claim 12,
Electrolytic plating of the lead oxide layer is performed by applying an oxidation potential on the working electrode, the method of manufacturing lead chromate

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