Photoelectrochemical cell used for conversion of carbon dioxide to formate and carbon dioxide conversion method using same

Abstract

The present disclosure relates to a photoelectrochemical cell used for the conversion of carbon dioxide to formate, and a method for converting carbon dioxide using same.

Description

Photoelectrochemical cell used for converting carbon dioxide into formate and method for converting carbon dioxide using the same

[0001] The present invention relates to a photoelectrochemical cell used for converting carbon dioxide into formate and a method for converting carbon dioxide using the same.

[0002] The photoelectrochemical conversion of carbon dioxide (CO2) into high-value chemicals is a promising strategy for mitigating the greenhouse effect and achieving carbon neutrality. Photoelectrocatalysis (PEC) systems combine the advantages of electrocatalysis and photocatalysis. The bias applied to a PEC system promotes the directional transfer of photogenerated electrons, thereby enhancing the separation efficiency of photogenerated carriers. Light energy, meanwhile, serves as a direct energy source, contributing to energy savings. For efficient CO2 conversion, the cathode material used in PEC systems is crucial. Among the various CO2 reaction products, formate is an important hydrogen storage material and chemical fuel. Furthermore, formate is a stable liquid or solid product, making it easy to store and transport, offering significant economic and practical benefits. Furthermore, formic acid is widely used in the chemical industry as a reducing agent, acid, and carbon source.

[0003] An attractive approach to harnessing the power of efficient molecular catalysts and sunlight is to integrate the catalyst into a photoelectrochemical system. However, this approach requires large amounts of catalyst, as most catalysts do not actively participate in the reaction and are inefficient at absorbing and transferring light energy.

[0004] Many molecular catalysts relying on noble metal centers have been developed for CO2 photoconversion. However, most of these catalysts either provide CO as the primary product or a mixture of byproducts (e.g., formate and H2). Recently, the present inventors reported a molecular Ni complex as an efficient and selective catalyst for visible-light-driven CO2 photoconversion.

[0005] Meanwhile, the use of metal oxides, particularly TiO2, to protect unstable photoelectrode materials such as Cu2O has recently attracted significant attention in solar fuel research. These metal oxide overlayers provide ideal substrates for covalent molecular bonding via molecular linkers such as carboxylates and phosphonates, a key approach for realizing efficient dye-sensitized solar cells. However, to date, no case of binding a molecular catalyst to the photoelectrode surface has been reported. For CO2 reduction in PEC systems, most reports on immobilized catalysts have focused on dye-catalyst composites and polymer films.

[0006] [Prior Art Literature]

[0007] [Non-patent literature]

[0008] Wu, D.; Hao, J.; Song, Z.; Fu, X.-Z.; Luo, J.-L. “All roads lead to Rome: An energy-saving integrated electrocatalytic CO2 reduction system for concurrent value-added formate production” Chem. Eng. J. 2021, 412, 127893.

[0009] The present invention aims to provide a photoelectrochemical cell used for converting carbon dioxide into formate and a method for converting carbon dioxide using the same.

[0010] However, the problems that the present invention seeks to solve are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0011] The first aspect of the present invention provides a photoelectrochemical cell comprising: a cathode; a nickel molecular catalyst bonded to the surface of the cathode; a counter electrode electrically connected to the cathode; and an electrolyte solution, wherein the cathode comprises a substrate, a first transparent electrode layer, a photoactive layer, a second transparent electrode layer, and a metal oxide layer, and the nickel molecular catalyst is represented by the following chemical formula 1:

[0012] [Chemical Formula 1]

[0013] .

[0014] The second aspect of the present invention provides a method for converting carbon dioxide into formate using a photoelectrochemical cell according to the first aspect.

[0015] The photoelectrochemical cell and carbon dioxide conversion method using the same according to the embodiments of the present invention have a high conversion rate of 22,000 TON (turnover number) or more for 24 hours and a carbon dioxide conversion rate of 64 μmol / cm 2 ·It exhibits a high reaction rate of more than h, and has superior efficiency and cell performance compared to conventional carbon dioxide formic acid conversion photovoltaic cells.

[0016] The photoelectrochemical cell and the carbon dioxide conversion method using the same according to the embodiments of the present invention can reduce the amount of catalyst used to an amount that actively participates in the reaction by directly bonding a molecular catalyst to the surface of the photoelectrode and thereby heterogeneizing the homogeneous catalyst, and can significantly improve the catalyst yield in electrocatalytic and photocatalytic systems.

[0017] The photoelectrochemical cell and carbon dioxide conversion method using the same according to the embodiments of the present invention have the characteristic that only formic acid is produced as a product from carbon dioxide.

[0018] Figure 1 is a diagram illustrating a CO2 reduction catalyst 1 (Ni(pyS)2(bpy(PO3)) in one embodiment of the present invention. - )2)) is a schematic diagram of a Cu2O / AZO / TiO2 photocathode covalently bonded with the photocathode.

[0019] FIG. 2 shows, in one embodiment of the present invention, (a) a photoanode image of a SrTiO3 film coated on FTO glass; (b) a photoanode image of a Cu2O / AZO / TiO2 film on FTO glass; and (c) a photocathode image of a Cu2O / AZO / TiO2 film fixed with catalyst 1 for 24 hours.

[0020] Figure 3 shows the results of cyclic voltammetry measurements of catalyst 1 bonded to a Cu2O / AZO / TiO2 film (photocathode) on FTO in one embodiment of the present invention.

[0021] Figure 4 is a schematic diagram of a photoelectrochemical cell in one embodiment of the present invention.

[0022] FIG. 5 shows the reaction rate of formate photogeneration by a Cu2O / AZO / TiO2 film modified with polarized catalyst 1 at -1.70 V vs Ag / AgCl in the presence or absence of erythrosin-B in a CO2-saturated state in one embodiment of the present invention.

[0023] Hereinafter, with reference to the attached drawings, implementation examples and embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the present invention. However, the present invention may be implemented in various different forms and is not limited to the implementation examples and embodiments described herein. In addition, in the drawings, parts irrelevant to the description have been omitted to clearly explain the present invention, and similar parts have been designated with similar drawing reference numerals throughout the specification.

[0024] Throughout this specification, when a part is said to be "connected" to another part, this includes not only cases where it is "directly connected" but also cases where it is "electrically connected" with another element in between.

[0025] Throughout this specification, when it is said that an element is "on" another element, this includes not only cases where the element is in contact with the other element, but also cases where another element exists between the two elements.

[0026] Throughout this specification, whenever a part is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0027] The terms "about," "substantially," and the like used in this specification are used in a meaning that is at or close to the numerical value when manufacturing and material tolerances inherent in the meanings mentioned are presented, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosure in which exact or absolute values ​​are mentioned to aid understanding of the present application.

[0028] The terms “step of ~” or “step of ~” as used throughout this specification do not mean “step for ~.”

[0029] Throughout this specification, the term "combination(s) thereof" included in the expressions in the Makushi format means one or more mixtures or combinations selected from the group consisting of the components described in the expressions in the Makushi format, and means including one or more selected from the group consisting of said components.

[0030] Throughout this specification, references to “A and / or B” mean “A or B, or A and B.”

[0031] Below, the implementation examples of the present invention are described in detail, but the present invention may not be limited thereto.

[0032] The first aspect of the present invention provides a photoelectrochemical cell comprising: a cathode; a nickel molecular catalyst bonded to the surface of the cathode; a counter electrode electrically connected to the cathode; and an electrolyte solution, wherein the cathode comprises a substrate, a first transparent electrode layer, a photoactive layer, a second transparent electrode layer, and a metal oxide layer, and the nickel molecular catalyst is represented by the following chemical formula 1:

[0033] [Chemical Formula 1]

[0034] .

[0035] In one embodiment of the present invention, the photoelectrochemical cell may be included in a photoelectrochemical system for carbon dioxide conversion, which converts carbon dioxide into formate with high selectivity and excellent efficiency.

[0036] In one embodiment of the present invention, the substrate may be any transparent substrate that can be typically used as a substrate for an electrode of a photoelectrochemical cell, and may be, without limitation, glass, polyethylene terephthalate, polyethylene naphthalate, or colorless polyimide as non-limiting examples.

[0037] In one embodiment of the present invention, the nickel molecular catalyst may be covalently bonded to the metal oxide layer via a phosphonate group. In one embodiment of the present invention, due to the covalent bond, the nickel molecular catalyst is very strongly bonded to the surface of the metal oxide layer, and thus charge transfer from the cathode to the nickel molecular catalyst may be excellent.

[0038] In one embodiment of the present invention, the nickel molecular catalyst may be physically bonded to the metal oxide layer.

[0039] In one embodiment of the present invention, the nickel molecular catalyst may stably maintain catalytic activity by covalently bonding and / or physically bonding to the metal oxide layer.

[0040] In one embodiment of the present invention, the nickel molecular catalyst may be a heterogeneous catalyst densely present on the surface of the cathode.

[0041] In one embodiment of the present invention, the photoactive layer may include one or more selected from Cu2O, CuO, Si, Fe2O3, Fe3O4, BiVO4, Bi2WO4, TiO2, SrTiO3, ZnO, NiO, SnO2, CoO, In2O3, WO3, MgO, CaO, La2O3, Nd2O3, Y2O3, CeO2, PbO, ZrO2, Co3O4, and Al2O3, but may not be limited thereto.

[0042] In one embodiment of the present invention, the thickness of the photoactive layer is about 100 nm to about 1000 nm, about 100 nm to about 900 nm, about 100 nm to about 800 nm, about 100 nm to about 700 nm, about 100 nm to about 650 nm, about 100 nm to about 600 nm, about 100 nm to about 550 nm, about 100 nm to about 500 nm, about 200 nm to about 1000 nm, about 200 nm to about 900 nm, about 200 nm to about 800 nm, about 200 nm to about 700 nm, about 200 nm to about 650 nm, about 200 nm to about 600 nm, about 200 nm to about 550 nm, about 200 nm to about 500 nm, about 300 nm to about 1000 nm, about 300 nm to about 900 nm, about 300 nm to about 800 nm, about 300 nm to about 700 nm, about 300 nm to about 650 nm, about 300 nm to about 600 nm, about 300 nm to about 550 nm, about 300 nm to about 500 nm, about 400 nm to about 1000 nm, about 400 nm to about 900 nm, about 400 nm to about 800 nm, about 400 nm to about 700 nm, about 400 nm to about 650 nm, about 400 nm to about 600 nm, about 400 nm to about 550 nm, about 400 nm to about 500 nm, about 450 nm to about 1000 nm, about 450 nm about 900 nm, about 450 nm to about 800 nm, about 450 nm to about 700 nm, about 450 nm to about 650 nm, about 450 nm to about 600 nm, about 450 nm to about 550 nm, about 450 nm to about 500 nm, about 500 nm to about 1000 nm, about 500 nm to about 900 nm, about 500 nm to about 800 nm,It may be, but is not limited to, about 500 nm to about 700 nm, about 500 nm to about 650 nm, about 500 nm to about 600 nm, or about 500 nm to about 550 nm.

[0043] In one embodiment of the present invention, the metal oxide layer may include one or more selected from TiO2, Fe3O4, Fe2O3, ZnO, WO3, BiVO4, ZrO2, SrTiO3, BiSe3-Bi2O3, CuGaO2, and KTaO3, but may not be limited thereto.

[0044] In one embodiment of the present invention, the thickness of the metal oxide layer is from about 10 nm to about 500 nm, from about 10 nm to about 300 nm, from about 10 nm to about 250 nm, from about 10 nm to about 200 nm, from about 10 nm to about 150 nm, from about 10 nm to about 100 nm, from about 50 nm to about 500 nm, from about 50 nm to about 300 nm, from about 50 nm to about 250 nm, from about 50 nm to about 200 nm, from about 50 nm to about 150 nm, from about 50 nm to about 100 nm, from about 70 nm to about 500 nm, from about 70 nm to about 300 nm, from about 70 nm to about 250 nm, from about 70 nm to about 200 nm, from about 70 nm to about 150 nm, from about 70 nm to about It may be, but is not limited to, 100 nm, about 90 nm to about 500 nm, about 90 nm to about 300 nm, about 90 nm to about 250 nm, about 90 nm to about 200 nm, about 90 nm to about 150 nm, or about 90 nm to about 100 nm.

[0045] In one embodiment of the present invention, the metal oxide layer may be a mesoporous material.

[0046] In one embodiment of the present invention, the cathode may be formed by supporting the nickel molecular catalyst in the mesopores of the metal oxide.

[0047] In one embodiment of the present invention, the first transparent electrode layer and the second transparent electrode layer may each independently include at least one selected from indium tin oxide (ITO), indium zinc oxide (IZO), indium zinc tin oxide (IZTO), aluminum zinc oxide (AZO), gallium zinc oxide (GZO), fluorine tin oxide (FTO), indium tin oxide-silver-indium tin oxide (ITO-Ag-ITO), indium zinc oxide-silver-indium zinc oxide (IZO-Ag-IZO), indium zinc tin oxide-silver-indium zinc oxide (IZTO-Ag-IZTO), and aluminum zinc oxide-silver-aluminum zinc oxide (AZO-Ag-AZO), but may not be limited thereto.

[0048] In one embodiment of the present invention, the thickness of the first transparent electrode layer and the second transparent electrode layer may be, but is not limited to, about 10 nm to about 100 nm, about 10 nm to about 50 nm, about 10 nm to about 30 nm, or about 10 nm to about 20 nm, respectively.

[0049] In one embodiment of the present invention, the metal oxide layer and the second transparent electrode layer may serve to protect the light absorption layer.

[0050] In one embodiment of the present invention, the metal oxide layer may protect the light absorption layer and allow the nickel molecular catalyst to covalently bond thereto, thereby improving the efficiency and performance of the photoelectrochemical cell.

[0051] In one embodiment of the present invention, the cathode may include FTO as the first transparent electrode layer, CuO2 as the photoactive layer, AZO as the second transparent electrode layer, and TiO2 as the metal oxide layer, but may not be limited thereto.

[0052] In one embodiment of the present invention, the electrolyte solution may include at least one selected from a NaHCO3 aqueous solution, a Na2SO4 aqueous solution, and a KHCO3 aqueous solution, but may not be limited thereto.

[0053] In one embodiment of the present invention, the electrolyte solution may further include one or more organic solvents selected from CH3CN, H2SO4, triethanolamine, acetone, methanol, ethanol, N-methylpyrrolidone, and propylene glycol, but may not be limited thereto.

[0054] In one embodiment of the present invention, the electrolyte solution may further include one or more electrolyte salts selected from Et4NBF4 and 1-butyl-3-methylimidazolium triflate (1-butyl-3-methylimidazolium triflate; [BMIM][TfO]), but may not be limited thereto.

[0055] In one embodiment of the present invention, the electrolyte solution may further include erythrosin-B (Er-B).

[0056] In one embodiment of the present invention, the counter electrode may include a substrate and an electrode layer, but may not be limited thereto.

[0057] In one embodiment of the present invention, the electrode layer of the counter electrode may include one or more selected from SrTiO3, Cu2O, CuO, Si, Fe2O3, Fe3O4, BiVO4, Bi2WO4, TiO2, ZnO, NiO, SnO2, CoO, In2O3, WO3, MgO, CaO, La2O3, Nd2O3, Y2O3, CeO2, PbO, ZrO2, Co3O4 and Al2O3, but may not be limited thereto.

[0058] In one embodiment of the present invention, the photoelectrochemical cell may further include a reference electrode. In one embodiment of the present invention, the photoelectrochemical cell may be configured as a three-electrode system including the cathode, the counter electrode, and the reference electrode.

[0059] In one embodiment of the present invention, the photoelectrochemical cell may include a cathode section including the cathode and a counter electrode section including the counter electrode and the reference electrode, but may not be limited thereto.

[0060] In one embodiment of the present invention, the cathode portion may include, but is not limited to, an electrolyte solution including an aqueous solution of NaHCO3; an organic solvent including CH3CN and triethanolamine; an electrolyte salt including Et4NBF4; and erythrosin-B (Er-B).

[0061] In one embodiment of the present invention, the cathode and the counter electrode may be connected to an electrolyte membrane, but may not be limited thereto.

[0062] In one embodiment of the present invention, the electrolyte membrane may be a Nafion film, but may not be limited thereto.

[0063] In one embodiment of the present invention, the photoelectrochemical cell has excellent charge mobility between the cathode and the nickel molecular catalyst, and thus can exhibit continuous and high catalytic activity.

[0064] The second aspect of the present invention provides a method for converting carbon dioxide into formate using a photoelectrochemical cell according to the first aspect.

[0065] Detailed explanations of parts that overlap with the first aspect of the present application have been omitted, but the contents described in the first aspect of the present application may be equally applied even if the explanation is omitted in the second aspect of the present application.

[0066] In one embodiment of the present invention, the carbon dioxide conversion method may be performed by irradiating the cathode with a light source and supplying carbon dioxide (for example, under conditions of about 1 atm).

[0067] In one embodiment of the present invention, the light source may have a wavelength range of about 400 nm to about 800 nm.

[0068] In one embodiment of the present invention, the light source may be supplied by a xenon lamp or a solar artificial irradiation device, but may not be limited thereto.

[0069] In one embodiment of the present invention, the selectivity of the formate may be about 99% or more or 100%.

[0070] The conversion of carbon dioxide into formate using a photoelectrochemical cell and a carbon dioxide conversion method according to the embodiments of the present invention can exhibit very excellent selectivity without generating carbon products including CO and other side products such as H2 in addition to formate.

[0071] In one embodiment of the present invention, the turnover number (TON) for the conversion of carbon dioxide to formate of the photoelectrochemical cell may be about 20,000 TON or more, about 21,000 TON or more, about 22,000 TON or more, or about 23,000 TON or more for about 24 hours.

[0072] In one embodiment of the present invention, the photocurrent density measured in the carbon dioxide conversion method is about 2.3 mA cm at -2.4 V vs Ag / AgCl. -2 It could be strange.

[0073] In one embodiment of the present invention, the amount of formate produced in the carbon dioxide conversion method is about 64 μmol / cm per hour. 2 It could be strange.

[0074] Hereinafter, the present invention will be described in more detail using examples. However, the following examples are provided only to help understand the present invention, and the contents of the present invention are not limited to the following examples.

[0075] [Example]

[0076] 1. Experiment

[0077] [Materials and Equipment]

[0078] All reagents were purchased from Aldrich and used without further purification unless otherwise specified. Water was purified using a Milli-Q purification system. The 2-(2-pyridyl)benzimidazole (pbi) ligand was purchased from Aldrich.

[0079] UV-visible spectra were recorded on a Hewlett Packard 8453 spectrophotometer. Emission spectra were collected on a Perkin-Elmer LS 55 luminescence spectrophotometer. Nuclear magnetic resonance (NMR) spectra were measured at room temperature on a Bruker 300 MHz spectrometer. Hydrogen production was measured using a DS6200 gas chromatograph (Donam Instruments, Korea) equipped with a Carbosphere 80 / 100 mesh, 6 ft × 1 / 8" OD SS column (Oltech, part number 5682PC) and a thermal conductivity detector (TCD). Formic acid was monitored by HPLC (model YL 9100, Youngin Scientific, Korea) on a column (Inertsil ODS-3V, 5 μm, 4.6 × 150 mm) using H3PO4 solution (0.15%) as the eluent and a UV detector (λ = 210 nm). Electrospray ionization mass spectra (ESI-MS) were acquired on a Thermo Finnigan (San Jose, CA, USA) LCQTM Advantage MAX quadrupole ion trap instrument by directly injecting the sample into the source at a rate of 25 μL / min with a syringe pump. Spray The voltage was set to 4.7 kV and the capillary temperature was set to 220°C.

[0080] [FTO / Pretreatment of Glass Substrates]

[0081] FTO glass substrates were cut into 1 cm × 1 cm pieces. Before use, the FTO / glass slides were ultrasonically cleaned for 30 min using acetone, absolute ethanol, and deionized water. The FTO / glass surfaces were then dried at 60°C.

[0082] [Manufacturing of SrTiO3 photoelectrodes]

[0083] First, strontium chloride (SrCl2, 0.2 M) and titanium n-butoxide (0.1 M) were dissolved in 50 mL of distilled water and ethylene glycol. The solution was stirred for 30 minutes, adjusted to pH 12 with ammonia solution, and placed in a Teflon-lined autoclave. The vessel was heated in an oven at 120°C for 12 hours and then cooled to room temperature. The material was collected and washed with distilled water and ethanol. The material was dried at 100°C for 12 hours. The dried product was placed in an oven and calcined at 900°C for 12 hours.

[0084] [Manufacture of aluminum-doped zinc oxide (AZO)]

[0085] Polyethylene glycol (PEG) (5.0 g) was dissolved in 100 mL of distilled water. Then, 100 mL of zinc nitrate and aluminum nitrate solutions were mixed, and 100 mL of PEG preparation was slowly added to balance the mixture. Then, 100 mL of 0.8 M NaOH solution was added dropwise to the mixture. Finally, a white precipitate was obtained from the mixture, and the solution was stirred at room temperature for 1 hour. The solution was heated with stirring at 60°C for 4 hours, then stirred at room temperature for 6 hours. The solution was washed several times with distilled water and then with ethanol. The resulting product was lightly ground with a mortar and pestle. Finally, the sample was placed in an oven and calcined at 600°C for 4 hours.

[0086] [Photocathode manufacturing]

[0087] To prepare a material for electrochemical testing, 4 mg of complex 1 (referring to a nickel molecular catalyst according to chemical formula 1) was mixed with 120 μL of deionized water and 40 μL of a 5 wt% Nafion solution, and sonicated for 2 h to form a uniform suspension. The solution was evenly distributed on FTO glass (1 cm × 1 cm). The working electrode was dried and stored before use.

[0088] [Photoelectrochemical CO2 reduction and hydrogen production using Cu2O / AZO / TiO2 / complex 1]

[0089] Photoelectrochemical CO2 reduction was performed in CH3CN / erythrosin-B (Er-B) (2 mM) / triethanolamine (400 mM) (1:0.25:0.25, v / v, mL) containing Et4NBF4 (0.1 M). Here, electron transfer from the ground state to the excited state of Er-B plays an important role in the photocatalytic process, which causes the molecular structure to change color transfer from the enol type to the ketone type upon visible light irradiation. In this case, the excited electrons transfer to the photocatalyst and the color returns to the ground state, and accordingly, the ketone-type dye molecule performs color recycling by taking electrons from the electron donor and returning to the enol form.

[0090] Photoelectrochemical CO2 reduction was performed using a Pyrex H-shaped cell with two parts separated by a Nafion membrane. Each part had a volume of 60 mL, and 30 mL of a 50 mM NaHCO3 aqueous solution was added to each part. Cu2O / AZO / TiO2 / 1 was placed in the cathode chamber, and Ag / AgCl and a counter electrode were placed in the anode chamber. A three-electrode configuration with a potentiostat was used for the entire photocatalytic reaction process. CO2 was supplied to the cathode chamber for 45 min before the reaction. The Cu2O / AZO / TiO2 / 1 electrode was illuminated by a 300 W Xe lamp with a cut-off filter at λ ex Illumination was performed at >420 nm. Analysis of formate and H2 gas was performed using HPLC and GC equipment, respectively.

[0091] 2. Results

[0092] In the present invention, efficient catalytic turnover was achieved using a Ni catalyst electrostatically linked to the electrode surface. This method not only enables sequential charge transfer between the photoelectrode and the CO2 reduction catalyst, but also significantly reduces the required amount of catalyst and minimizes informal absorption. The Ni-based complex exhibited excellent performance and high product selectivity when used as a homogeneous photocatalyst for the conversion of CO2 to formate in H2O / EtOH. In addition, the TiO2-protected Cu2O photoelectrode exhibited excellent performance as a low-cost p-type light harvester for water splitting. The bipyridyl ligand of the original complex was modified with a phosphonate linkage to enable covalent bonding to the TiO2 surface protecting the Cu2O photoanode, resulting in catalyst 1(Ni(pyS)2(bpy(PO3) -)2)) was formed. A methylene bridge was inserted between the phosphonate and bipyridyl moieties to minimize the electronic structure modification of the catalyst.

[0093] As described above, the Cu2O photoanode was fabricated by atomic layer deposition of Al-doped ZnO (AZO) and TiO2 after electrodeposition of a Cu2O layer. The thickness of the Cu2O layer was approximately 500 nm, the thickness of the AZO layer was approximately 20 nm, and the thickness of the TiO2 layer was approximately 100 nm. The Cu2O / AZO / TiO2 sample was heated to 150°C under vacuum to remove moisture, and the substrate was immersed in a 1 mM to 2 mM solution of Catalyst 1 for 24 h to coat the Catalyst 1 on the surface of the mesoporous TiO2. The sample was then thoroughly rinsed with MeCN to remove unbound species (Fig. 1).

[0094] Figure 2 is a photograph of a photoanode (a) manufactured from a SrTiO3 film on FTO glass; a Cu2O / AZO / TiO2 film on FTO glass (b); and a photocathode (c) manufactured from a Cu2O / AZO / TiO2 film with complex 1 fixed on FTO glass.

[0095] Potential tests at -1.6 V vs Ag / AgCl under shatter light illumination showed sustained catalytic activity toward CO2 reduction (Fig. 3), during which a gradual decrease in photocurrent was observed.

[0096] The catalytic activity of a Ni complex-loaded photocathode for CO2 conversion was confirmed. The AlZnO2 / Cu2O-supported catalyst on FTO was continuously investigated, and the reaction solution was quantified by high-performance liquid chromatography. Samples reached a formate yield of up to 15,000 TON (turnover number) with the Ni catalyst, whereas negligible formate was observed in the absence of the catalyst (Fig. 5). Furthermore, no formate formation was observed in an Ar-saturated solution (Fig. 5). Considering the observed high TON, a molecular catalyst is indeed required for CO2 conversion.

[0097] Cyclic voltammetry measurements of catalyst 1 bound to Cu2O / AZO / TiO2 films showed a catalytic current for the electroreduction of CO2, which was 2.3 mA cm at -2.4 V vs Ag / AgCl in the presence of CO2. -2 It exhibits a current density exceeding . The current onset is observed at approximately -1.3 V (Fig. 3).

[0098] The entire photoelectrochemical cell was assembled with a photoanode and a photocathode, along with a top light source (Fig. 4). A Nafion film was placed between the two electrodes to facilitate proton transport.

[0099] Potentiostatic tests at -1.7 V vs Ag / AgCl under illumination with a 420 nm cutoff filter showed sustained catalytic activity for CO2 reduction (Fig. 3), during which a gradual decrease in the photocurrent was observed. To confirm the catalytic activity for CO2 conversion, the reaction solution was quantified by liquid chromatography during constant polarization of the TiO2-supported catalyst 1 on FTO. The sample reached 23,000 TON (turnover number) for formate in 24 h, whereas no formate was observed in the absence of catalyst 1 (Fig. 5). The ratio was 64 μmol / cm 2·h, which was the highest compared to previous reports. Gas chromatography of the gas evolved from the photoreaction using the 1-modified Cu2O / AZO / TiO2 cathode revealed that no other carbon products, such as CO, were observed, and even H2 was not observed. Furthermore, no formate formation was observed when polarized under inert helium (Fig. 5). Taken together with the observed high TON, these results indicate that the observed formate originated from the catalytic reaction of CO2 and that the molecular catalyst 1 is indeed required for the conversion of CO2.

[0100] 3. Conclusion

[0101] In this invention, we demonstrate photo-driven carbon dioxide conversion using a covalently immobilized molecular catalyst on a Cu2O photoanode modified with mesoporous TiO2. The observed photocurrent is significantly improved over that previously demonstrated using a molecular catalyst uniformly dissolved in an electrolyte solution. Furthermore, the observed photocurrent and high TON are superior to previous reports of CO2 reduction using photoelectrode-immobilized catalysts, not only based on the immobilization of an earth-abundant metal catalyst on the photoelectrode. Furthermore, high selectivity toward formate was achieved using a Ni complex in the photoelectrochemical reaction. This improvement may be due to the use of a nanostructured photoelectrode surface, which has been shown to be necessary for achieving high photocurrents using covalently bonded catalysts. The present invention demonstrates a method for immobilizing a photoelectrode surface using a molecular Ni catalyst derivatized with a phosphonate linkage. This invention may pave the way for the development of PEC electrodes immobilized with molecular fuel-generating electrocatalysts for efficient CO2 conversion. Therefore, the present invention provides an energy-efficient HCOO using earth-abundant elements in a process of converting environmental pollutants into more useful organic compounds. - It will provide an adjustable path to creation.

[0102] The above description of the present invention is for illustrative purposes only, and those skilled in the art will readily appreciate that the present invention can be readily modified into other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single entity may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined manner.

[0103] The scope of the present invention is indicated by the claims described below rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention.

Claims

1. A cathode; a nickel molecular catalyst bonded to the surface of the cathode; a counter electrode electrically connected to the cathode; and an electrolyte solution. A photoelectrochemical cell comprising: The above cathode comprises a substrate, a first transparent electrode layer, a photoactive layer, a second transparent electrode layer, and a metal oxide layer, The above nickel molecular catalyst is represented by the following chemical formula 1, a photoelectrochemical cell: [Chemical Formula 1] .

2. In paragraph 1, A photoelectrochemical cell, wherein the nickel molecular catalyst is covalently bonded to the metal oxide layer through a phosphonate group.

3. In paragraph 1, The above photoactive layer is Cu 2 O, CuO, Si, Fe 2 O 3 , Fe 3 O 4 , BiVO 4 , Bi 2 WO 4 , TiO 2 , SrTiO 3 , ZnO, NiO, SnO 2 , CoO, In 2 O 3 , WO 3 , MgO, CaO, La 2 O 3 , Nd 2 O 3 , Y 2 O 3 , CeO 2 , PbO, ZrO 2 , Co 3 O 4 , and Al 2 O 3 A photoelectrochemical cell comprising one or more selected from:

4. In paragraph 1, The above metal oxide layer is TiO 2 , Fe 3 O 4 , Fe 2 O 3 , ZnO, WO 3 , BiVO 4 , ZrO 2 , SrTiO 3 , BiSe 3 -Bi 2 O 3 , CuGaO 2 , and KTaO 3 A photoelectrochemical cell comprising one or more selected from:

5. In paragraph 1, A photoelectrochemical cell, wherein the first transparent electrode layer and the second transparent electrode layer each independently include at least one selected from indium tin oxide (ITO), indium zinc oxide (IZO), indium zinc tin oxide (IZTO), aluminum zinc oxide (AZO), gallium zinc oxide (GZO), fluorine tin oxide (FTO), indium tin oxide-silver-indium tin oxide (ITO-Ag-ITO), indium zinc oxide-silver-indium zinc oxide (IZO-Ag-IZO), indium zinc tin oxide-silver-indium zinc oxide (IZTO-Ag-IZTO), and aluminum zinc oxide-silver-aluminum zinc oxide (AZO-Ag-AZO).

6. In paragraph 1, The above electrolyte solution is NaHCO 3 Aqueous solution, Na 2 SO 4 Aqueous solution, and KHCO 3 A photoelectrochemical cell comprising one or more selected from an aqueous solution.

7. In paragraph 6, The above electrolyte solution is CH 3 CN, H 2 SO 4 A photoelectrochemical cell further comprising one or more organic solvents selected from triethanolamine, acetone, methanol, ethanol, N-methylpyrrolidone, and propylene glycol.

8. In paragraph 6, The above electrolyte solution is Et 4 NBF 4 A photoelectrochemical cell further comprising one or more electrolyte salts selected from 1-butyl-3-methylimidazolium triflate.

9. In paragraph 1, A photoelectrochemical cell, wherein the photoelectrochemical cell comprises a cathode section including the cathode and a counter electrode section including the counter electrode and the reference electrode.

10. In paragraph 1, A photoelectrochemical cell, wherein the cathode and the counter electrode are connected to an electrolyte membrane.

11. A method for converting carbon dioxide into formate using a photoelectrochemical cell according to Article 1.

12. In paragraph 11, A method for converting carbon dioxide, which is performed by irradiating a light source to the above cathode and supplying carbon dioxide.

13. In paragraph 11, A method for converting carbon dioxide, wherein the selectivity of the formate is 99% or more.

14. In paragraph 11, The amount of formate produced was 64 μmol / cm per hour. 2 A method for converting carbon dioxide.

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