KR102144409B1 - Highly efficient water-oxidation catalysts, its manufacturing method and photoelectrode - Google Patents

Abstract

The present invention relates to a highly efficient water oxidation catalyst, a method for preparing the same, and a photoelectrode, and more specifically, to CoWO ₄ derived from cobalt-substituted polyoxometalates. It relates to a catalyst including a phase, a method for preparing the same, and a photoelectrode including the same.

Description

High-efficiency water oxidation catalyst, its manufacturing method and photoelectrode {HIGHLY EFFICIENT WATER-OXIDATION CATALYSTS, ITS MANUFACTURING METHOD AND PHOTOELECTRODE}

The present invention relates to a highly efficient water oxidation catalyst, a method for preparing the same, and a photoelectrode including the same.

Photoelectrochemical water splitting is a photoelectrochemical or electrochemical reaction that synthesizes various chemical substances (hydrogen, formate, methanol, etc.) by obtaining electrons from abundant water on the earth. These are photoelectrochemical or electrochemical reactions. It can be synthesized from carbon dioxide using electrons generated from water reduction reactions and water oxidation.

Photoelectrochemical water decomposition is a method of converting water into oxygen using visible light and electricity. The electrons generated in the water decomposition process are ultimately used for carbon dioxide reduction and hydrogen generation. Various substances are required for photoelectrochemical water decomposition. For example, (1) a semiconductor material that can generate electrons and holes by receiving light, (2) an electron transport material that can transfer electrons from water, and (3) water that can decompose water into oxygen. Decomposition catalysts, such as water oxidation catalyst (WOC) materials.

Photoelectrochemical water decomposition requires a catalyst indispensably because it has a complex mechanism with four electrons required for reaction. As conventional catalysts, organometallic compounds including noble metals such as Ru and Ir, transition metal oxides and perovskite nanoparticles, and layered double hydroxides have been developed. Existing catalysts have inherent problems such as high cost, low stability, and low catalytic performance, and the synthesis method is complex and adversely affects the environment.

Recently, polyoxometalate (POM) containing oxo-bridged transition metal clusters has been applied as a water oxidation catalyst, which has advantages in terms of catalytic activity, low cost and durability, but for practical application, catalyst efficiency And there is a need for improved stability, as well as a simplification of the method for fixing on the desired electrode surface.

The present invention is to provide a novel catalyst that improves efficiency by using a water decomposition catalyst having an inexpensive cobalt ion as a reaction center and can be fixed to a desired substrate in a simple manner.

The present invention is to provide a photoelectrode comprising the catalyst according to the present invention.

The present invention is to provide a photovoltaic cell comprising the photoelectrode according to the present invention.

The present invention is to provide a method for producing a catalyst according to the present invention.

The present invention is to provide a method for manufacturing a photoelectrode according to the present invention.

According to an embodiment of the present invention, CoWO ₄ derived from cobalt-substituted polyoxometalates It relates to a catalyst, comprising a phase.

According to an embodiment of the present invention, the CoWO ₄ The phase is amorphous, crystalline or includes both, and the CoWO ₄ The phase may be nanoparticles.

According to an embodiment of the present invention, the CoWO ₄ Phase is cobalt-substituted polyoxometalate; Or cobalt-substituted polyoxometallate and a polymer electrolyte; may be a heat treatment product.

According to an embodiment of the present invention, the cobalt-substituted polyoxometallate is [Co ₄ (H ₂ O) (VW ₉ O ₃₄ ) ₂ ] ^10- , [Co ₄ (H ₂ O) ₂ (α -PW ₉ O ₃₄ ) ₂ ] ^10- or may include both.

According to an embodiment of the present invention, the polymer electrolyte includes a cationic polymer electrolyte, an anionic polymer electrolyte, or both,

The cationic polymer electrolyte is PEI (polyethyleneimine), b-PEI (branched-poly(ethylene imine)), l-PEI (linear-poly(ethylene imine)), PAH (poly(allylamine hydrochloride)), PAH (poly( allylamine hydrochloride)), PDDA (poly(diallyldimethylammonium chloride), PLL (poly(lysine)), PDADMA (poly(diallyldimethylammonium))), PAMPDDA (poly(acrylamide-co-diallyldimethylammonium)), and PDADMAC (polydiallyldimethylammonium chloride). Including at least one selected,

The anionic polymer electrolyte, PSS (polystyrene sulfonate), It may include at least one selected from the group consisting of polyacrylic acid (PAA), poly methacrylic acid (PMA), poly styrene sulfonate (PSS), and hyaluronic acid (HA).

According to an embodiment of the present invention, the mixing ratio (mass ratio) of the polymer electrolyte to the cobalt-substituted polyoxometallate may be greater than 0 and less than 1.

According to an embodiment of the present invention, the CoWO ₄ The phase includes a-CoWO ₄ and c-CoWO ₄ nanoparticles or both, and the CoWO ₄ The phase has catalytic activity in the range of pH 6 to 8, and the CoWO ₄ The phase may be to provide a water oxidation reaction by an ER mechanism (Eley-Rideal mechanism), a Langmuir-Hinshelwood mechanism (LH mechanism), or both.

According to an embodiment of the present invention, the catalyst may be an electrochemical or photoelectrochemical water oxidation catalyst.

According to an embodiment of the present invention, an electrode layer; And a catalyst layer comprising the catalyst of claim 1 formed on at least a portion of the electrode layer. It relates to a photoelectrode comprising a.

According to an embodiment of the present invention, the electrode layer may include a semiconductor material, a carbon-based material, or both.

According to an embodiment of the present invention, the semiconductor material is Ti, Sn, Zn, Mn, Mg, Ni, W, Co, Fe, Ba, In, Zr, Cu, Al, Bi, Pb, Ag, Cd, Y, Mo, Rh, Pd, Sb, Cs, La, V, Si, Al, Sr, and at least one selected from the group consisting of metal oxides containing at least one of them,

The carbon-based material is carbon powder, carbon paper, carbon fiber, carbon cloth, carbon felt, glassy carbon, CNT (carbon nanotube) , CNT paper and graphene may include one or more selected from the group consisting of.

According to an embodiment of the present invention, the catalyst layer may include a single or multiple layers of a catalyst material layer, or a multilayer membrane in which (polymer electrolyte layer/catalyst material layer) is repeatedly stacked one or more times.

According to an embodiment of the present invention, the electrode layer may be an anode, a cathode, or both.

According to one embodiment of the invention, it relates to a photovoltaic cell, comprising a photoelectrode according to the invention.

In accordance with an embodiment of the present invention, the steps of heat-treating the cobalt-substituted polyoxometallate; It relates to a method for producing a catalyst comprising a.

According to an embodiment of the present invention, the step of heat-treating may be performed at a temperature of 100° C. to 700° C.

According to an embodiment of the present invention, the heat treatment may be performed in an atmosphere including air, an inert gas, or both.

According to an embodiment of the present invention, the present invention comprises the steps of preparing an electrode layer; And forming a catalyst layer on the electrode layer. It relates to a method of manufacturing a photoelectrode comprising a.

According to an embodiment of the present invention, the forming of the catalyst layer may include forming a cobalt-substituted polyoxometallate layer on the electrode layer; And performing heat treatment after the step of forming the cobalt-substituted polyoxometallate layer.

According to an embodiment of the present invention, the step of forming the catalyst layer may include forming a multilayer film in which (polymer electrolyte layer/cobalt-substituted polyoxometallate layer) is repeatedly stacked one or more times on the electrode layer; And performing heat treatment after the step of forming the multilayer film. It may be to include.

The present invention is CoWO ₄ excellent in catalytic activity through a simple heat treatment of a polyoxometallate catalyst. A novel catalyst including a phase can be provided, and after adsorbing a polyoxometallate catalyst on a desired substrate, for example, an electrode layer, heat treatment is performed, and the CoWO ₄ It is possible to stably deposit a catalyst including a phase and provide a photoelectrode with improved electrochemical and photoelectrochemical water oxidation efficiency.

The present invention, the CoWO ₄ By applying a catalyst including a phase, the overall performance of electrochemical and photoelectrochemical cells can be improved.

1 is, according to Example 1 of the present invention, (a) POM-derived CoWO _4- based WOCs (water-oxidation catalysts) manufacturing process and the structural change of POM according to annealing, (b) POM and 400 ℃ and 500 Diffuse reflectance spectra of each POM annealed at °C, (c) TEM (transmission electron microscopy) images of POM-derived CoWO ₄ series WOCs nanoparticles obtained by annealing at 400 °C Diffraction patterns are shown.), (d) TEM images of POM-derived CoWO ₄ based WOCs nanoparticles obtained by annealing at 500°C, (e) POMs (POM400 and POM500) and POM annealed at 400°C and 500°C, respectively It shows the XRD pattern and (f) Raman spectrum of.
Figure 2 is, according to Example 1 of the present invention, (a) CV (cyclic voltammograms) graph and Tafel plots for evaluating catalytic activity and (b) for explaining the POM400 performance prepared in Example The concept of the two mechanisms of oxygen evolution reaction is illustrated by way of example.
3 is, according to Example 2 of the present invention, (a) manufacturing process of a photoelectrode in which POM400 WOCs are formed on a carbon felt (CF) electrode, (d, e) SEM images of the photoelectrode, (f) POM400 WOCs CV graphs of the carbon felt electrodes of (d) and (e) before and after the deposition of are shown, and the embedded image in the SEM image is a high magnification SEM.
Figure 4 is, according to Example 3 of the present invention, (a) a manufacturing process of a photoelectrode in which POM400 WOCs are formed on a hematite (Fe ₂ O ₃ ) electrode, (b, c) Cross of the photoelectrode before and after deposition of POM400 -sectional TEM image (the EDS spectrum for elemental analysis was inserted in the TEM image), (d) photocurrent density and starting potential, and (e) linear sweep voltammetry related to (d), (f) ) It shows the electrochemical impedance spectra and (g) transfer efficiencies of the photoelectrode before and after the deposition of POM400. The inserted image is the magnified impedance spectra of the photoelectrode on which POM400 WOCs are deposited and an equivalent circuit model for fitting.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. However, various changes may be made to the embodiments, and thus the scope of the patent application is not limited or limited by these embodiments. It should be understood that all changes, equivalents, or substitutes to the embodiments are included in the scope of the rights.

The terms used in the examples are used for illustrative purposes only and should not be interpreted as limiting. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present specification, terms such as "comprise" or "have" are intended to designate the presence of features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, but one or more other features. It is to be understood that the presence or addition of elements or numbers, steps, actions, components, parts, or combinations thereof does not preclude in advance.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiment belongs. Terms as defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and should not be interpreted as an ideal or excessively formal meaning unless explicitly defined in this application. Does not.

In addition, in the description with reference to the accompanying drawings, the same reference numerals are assigned to the same components regardless of the reference numerals, and redundant descriptions thereof will be omitted. In describing the embodiments, if it is determined that a detailed description of related known technologies may unnecessarily obscure the subject matter of the embodiments, the detailed description thereof will be omitted.

As described above, although the embodiments have been described by the limited drawings, a person of ordinary skill in the art can apply various technical modifications and variations based on the above. For example, even if the described techniques are performed in a different order from the described method, and/or the described components are combined or combined in a form different from the described method, or are replaced or substituted by other components or equivalents. Appropriate results can be achieved.

Therefore, other implementations, other embodiments, and claims and equivalents fall within the scope of the following claims.

The present invention relates to a catalyst, and according to an embodiment of the present invention, CoWO ₄ derived from cobalt-substituted polyoxometalates (Cobalt Polyoxometalates, or Co-POM) It relates to a catalyst comprising a phase (hereinafter, a catalyst derived from Co-POM), and has a catalytic activity for an electrochemical or photoelectrochemical water decomposition catalyst, and is, for example, a water oxidation catalyst.

According to an embodiment of the present invention, the Co-POM-derived catalyst includes a cobalt-substituted polyoxometallate; Alternatively, a cobalt-substituted polyoxometallate and a polymer electrolyte; may include at least a part or all of a heat treatment product generated by heat treatment.

The CoWO ₄ Phase is cobalt-substituted polyoxometalate; Or cobalt-substituted polyoxometallate (POM) and a polymer electrolyte; may be at least part or all of the heat treatment products generated by heat treatment. The CoWO ₄ The phase has catalytic activity for electrochemical or photoelectrochemical water decomposition catalysts, and is, for example, a water oxidation catalyst. The CoWO ₄ The phase may be applied alone or as a cocatalyst to provide improved electrochemical and photoelectrochemical water oxidation efficiency.

The CoWO ₄ The phase includes amorphous, crystalline or both, and may be nanoparticles. Preferably, it is amorphous or a mixture of amorphous and crystalline, and may include, for example, a-CoWO ₄ and c-CoWO ₄ nanoparticles or both. The CoWO ₄ The phase is, in order to form a uniform, conformal coating layer upon deposition on the electrode layer, and to provide excellent photoelectrode or photovoltaic performance, 0.01 nm or more; 0.1 nm or more; 1 nm or more; 1 nm to 50 nm; Alternatively, it may be a nanoparticle having a size of 1 nm to 10 nm.

The CoWO ₄ The phase exhibits excellent catalytic activity compared to the unheated cobalt-substituted polyoxometallate, for example, the CoWO ₄ Sangeun,

The ER mechanism (Eley-Rideal mechanism), the LH mechanism (Langmuir-Hinshelwood mechanism) or a water oxidation reaction according to the two provides oxygen, and is preferably a Langmuir-Hinshelwood (LH) mechanism. In addition, the CoWO ₄ The phase has a catalytic activity in the entire range of pH, and can provide excellent catalytic activity, for example, in the range of pH 6 to 8.

The cobalt-substituted polyoxometallate is a material having a structure similar to a water decomposition catalyst existing in nature, and is a catalyst having solubility in water having a transition metal of cobalt (Co) as a reaction center instead of manganese (Mn), If it is cobalt substituted, it may be applied without limitation, and preferably [Co ₄ (H ₂ O) ₂ (VW ₉ O ₃₄ ) ₂ ] ^10- , [Co ₄ (H ₂ O) ₂ (α-PW ₉ O ₃₄ ) ₂ ] ^10- or may include both.

The CoWO ₄ In the heat treatment of cobalt-substituted polyoxometallate for phase formation, cobalt and transition metal (excluding cobalt)-substituted polyoxometallate, transition metal (excluding cobalt)-substituted polyoxometallate, or both are further applied. can do. For example, the transition metal is at least one selected from the group consisting of ruthenium (Ru), nickel (Ni) and manganese (Mn), and in particular, a hydrogen generation catalyst by the application of nickel (Ni) and manganese (Mn) The function of can be added.

The polymer electrolyte includes an ionic polymer electrolyte, the polymer electrolyte includes a liquid polymer electrolyte, a gel polymer electrolyte, or both, and the polymer electrolyte includes a cationic polymer electrolyte, an anionic polymer electrolyte, or both. Can include.

The cationic polymer electrolyte is PEI (polyethyleneimine), b-PEI (branched-poly(ethylene imine)), l-PEI (linear-poly(ethylene imine)), PAH (poly(allylamine hydrochloride)), PAH (poly( allylamine hydrochloride), PDDA (poly(diallyldimethylammonium chloride)), PLL (poly(lysine)), PDADMA (poly(diallyldimethylammonium)), PAMPDDA (poly(acrylamide-co-diallyldimethylammonium)), and PDADMAC (polydiallyldimethylammonium chloride). Including at least one selected, the anionic polymer electrolyte, PSS (polystyrene sulfonate), It may include at least one selected from the group consisting of polyacrylic acid (PAA), poly methacrylic acid (PMA), poly styrene sulfonate (PSS), and hyaluronic acid (HA).

The mixing ratio (mass ratio) of the polymer electrolyte to the cobalt-substituted polyoxometallate before the heat treatment is greater than 0 and less than 1; 0.01 to 0.8; Alternatively 0.1 to 0.3; Or 0.1 to 0.2. If it is within the above range, a uniform and conformal deposition layer of a Co-POM-derived catalyst may be provided on the electrode layer, and the multilayer film may be easily formed by LBL, thereby improving the performance of the photoelectrode.

According to an embodiment of the present invention, the Co-POM-derived catalyst is deposited on a desired substrate, for example, a carrier, or an electrode, or on a desired substrate, for example, a carrier, or an electrode, after formation of the catalyst. After deposition of cobalt-substituted polyoxometallate, it may be heat-treated to form a deposition layer on the carrier or electrode.

The present invention relates to a photoelectrode. According to an embodiment of the present invention, the photoelectrode comprises: an electrode layer; And a catalyst layer including a catalyst derived from Co-POM according to the present invention formed on at least a portion of the electrode layer.

The electrode layer includes an electrode for electrochemical water decomposition, and may include a semiconductor material, a carbon-based material, or both. The electrode layer may include the semiconductor material and the carbon-based material alone, or a semiconductor material, a carbon-based material, or a layer including both formed on a substrate or a transparent electrode. The electrode layer may be an anode, a cathode, or both. The semiconductor material and/or carbon-based material may form a porous electrode layer.

The semiconductor material is Ti, Sn, Zn, Mn, Mg, Ni, W, Co, Fe, Ba, In, Zr, Cu, Al, Bi, Pb, Ag, Cd, Y, Mo, Rh, Pd, Sb , Cs, La, V, Si, Al, Sr, and may include at least one selected from the group consisting of metal oxides including at least one of them. Ni foam, for example; BaTiO ₃ , BaSnO ₃ , Bi ₂ O ₃ , V ₂ O ₅ , VO ₂ , Fe ₂ O ₃ (or α-Fe ₂ O ₃ ), Fe ₃ O ₄ , BiVO ₄ , Bi ₂ WO ₄ , TiO ₂ , SrTiO ₃ , ZnO, CuO , Cu ₂ O, NiO, SnO ₂ , CoO, In ₂ O ₃ , WO ₃ , MgO, CaO, La ₂ O ₃ , Nd ₂ O ₃ , Nb ₂ O _{5 ,} Y ₂ O ₃ , CeO ₂ , PbO, ZrO _{2 ,} Co ₃ O ₄ And at least one metal oxide selected from the group consisting of Al ₂ O ₃ , and the metal oxide may be doped with the above-mentioned elements, for example, Sn- doped α-Fe ₂ O ₃ , Ti- Doped α-Fe ₂ O ₃ , S-doped TiO ₂ , C-doped TiO ₂ , Mo-BiVO ₄ , W-doped BiVO ₄ , and the like.

The semiconductor material includes particles having a size of several nm to several hundreds of µm, for example, 1 nm or more; 1 nm to 900 μm; Alternatively, it may have a size of 1 nm to 300 μm. The size may mean diameter, length, etc., depending on the shape of the particle. If included within the size range, an efficient electron movement path may be provided, and it may be helpful to integrate a functional material stacked on the semiconductor material layer.

The semiconductor material is in the group consisting of a sphere type, a plate type, a flake type, a rod type, a tube type, a wire type, and a needle type. It may include particles having one or more selected shapes.

The carbon-based material is carbon powder, carbon paper, carbon fiber, carbon cloth, carbon felt, glassy carbon, CNT (carbon nanotube) , CNT paper and graphene may include one or more selected from the group consisting of.

The semiconductor material and the carbon-based material may be formed to a thickness of several nm to several hundreds of μm, for example, 1 nm or more; 1 nm to less than 1000 μm; 10 nm to 900 μm; Alternatively, it may have a thickness of 30 nm to 500 μm. When included within the above thickness range, an efficient electron movement path may be provided to smoothly proceed the electrochemical or photoelectrochemical water decomposition process.

The catalyst layer may include a single or multiple layers of a catalyst material layer, or a multilayer membrane in which (polymer electrolyte layer/catalyst material layer) is repeatedly stacked one or more times. That is, the photoelectrode stably fixes the catalyst layer containing the Co-POM-derived catalyst according to the present invention by the polymer electrolyte layer, and the accumulation amount of the catalyst layer is controlled by a layer-by-layer assembly method. By increasing it, high efficiency can be provided.

The polymer electrolyte layer is to fix the catalyst material layer by electrostatic adsorption to a desired substrate, for example, to improve the surface roughness of the semiconductor material layer, and to improve the surface roughness of the catalyst material layer by electrostatic adsorption. It is possible to facilitate integration and/or fixation, and to increase the amount of functional materials constituting the catalyst material layer.

In the multilayer membrane, the polymer electrolyte layer and the catalyst material layer may be composed of single or multiple layers, respectively. In the plurality of layers, each layer may have the same or different components, configurations, and/or charge characteristics.

The present invention relates to a photovoltaic cell comprising the photoelectrode according to the present invention, wherein the photovoltaic cell comprises an anode, a cathode or both as the photoelectrode comprising the catalyst derived from Co-POM according to the present invention, and the photovoltaic cell Is applied to the field using electrochemical or photoelectrochemical properties, and for example, electrochemical or photoelectrochemical water decomposition and carbon dioxide reduction/recycling can be used.

The present invention relates to a method for preparing a catalyst according to the present invention, and according to an embodiment of the present invention, the method comprises: heat-treating cobalt-substituted polyoxometallate; It may include.

The manufacturing method can provide a Co-POM-derived catalyst having significantly improved catalytic activity compared to the conventional cobalt-substituted polyoxometallate by a simple heat treatment. In addition, a desired substrate, for example, a cobalt-substituted polyoxometallate on an electrode layer may be subjected to simple heat treatment after deposition to form a uniform and conformal Co-POM-derived catalyst coating layer.

The heat treatment may include cobalt-substituted polyoxometallate; Alternatively, a mixture of a cobalt-substituted polyoxometallate and a polymer electrolyte may be heat treated, and at least 50°C; 100 ℃ to 700 ℃ temperature; 200 ℃ to 600 ℃; Alternatively, the cobalt-substituted polyoxometallate may be heat treated at 300°C to 500°C.

The heat treatment may include powder of cobalt-substituted polyoxometallate, a solution (or gel, sol, or dispersion) containing cobalt-substituted polyoxometallate, or droplets of the solution by ultrasonic spraying. It can be heat treated in the state of.

The step of heat-treating may be heat-treated in an atmosphere containing air, an inert gas, or both, for 1 minute or more; More than 10 minutes; More than 30 minutes; For 1 hour; Alternatively, it may be heat treated for 1 hour to 10 hours.

According to another embodiment of the present invention, the manufacturing method includes the steps of depositing a cobalt-substituted polyoxometallate on a substrate; And thermally treating after the depositing step. The deposition is performed by adsorbing cobalt-substituted polyoxometallate on a substrate, forming a coating layer or film, and heat treatment to form CoWO ₄ derived from cobalt-substituted polyoxometallate. A catalyst (layer) including a phase may be formed on the substrate.

The depositing step may form a single or multiple layers of cobalt-substituted polyoxometallate, and the multiple layers may include the same or different components. Alternatively, the depositing step may form a multilayer film of (polymer electrolyte layer/cobalt-substituted polyoxometallate layer) in which a polymer electrolyte and cobalt-substituted polyoxometallate are cross-stacked one or more times.

The depositing step may be performed by spin coating, dip coating, printing, spraying, coating, and roll coating.

The step of heat-treating may be heat-treated at the above-mentioned temperature.

The present invention relates to a method of manufacturing a photoelectrode according to the present invention, comprising the steps of: preparing an electrode layer according to an embodiment of the present invention; And forming a catalyst layer on the electrode layer. It may include.

In the preparing of the electrode layer, a semiconductor material layer may be formed on a substrate, or a semiconductor material in the form of a sheet, film, or wafer may be prepared. Alternatively, an electrode such as carbon felt, carbon paper or the like mentioned above may be prepared.

The semiconductor material is as mentioned above, and physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD, Atomic Layer Deposition), vacuum deposition spin coating, sputtering, spin coating, dip A semiconductor material layer may be formed on the substrate using a coating, printing method, spray 　 coating 　 and roll 　 coating, or the semiconductor material may be grown by physical and/or chemical treatment (or synthesis process).

The substrate is a transparent substrate, for example, glass, sapphire, a transparent polymer substrate, and the transparent polymer substrate is polystyrene, polycarbonate, polymethyl methacrylate, polyethylene Terephthalate (polyetheylene terephtalate), polyethylene naphthalate (poly(ethylenenaphthalate) polyphthalate carbonate (polyphthalate carbonate), polyurethane (polyurethane), poly (ether sulfone)) and polyimide (polyimide) selected from the group consisting of In addition, the substrate may be a conductive substrate such as FTO or ITO.

According to an embodiment of the present invention, the forming of the catalyst layer may include forming a cobalt-substituted polyoxometallate layer on the electrode layer; And heat-treating; It may include. That is, by depositing cobalt-substituted polyoxometallate on the electrode layer, for example, on the surface of a semiconductor material layer or carbon felt, and then heat treatment, the Co-POM-derived catalyst according to the present invention is stably deposited on the electrode. And, the performance of the electrode can be improved.

Forming a cobalt-substituted polyoxometallate layer on the electrode layer may include: cobalt-substituted polyoxometallate; Or a mixture of cobalt-substituted polyoxometallate and a polymer electrolyte; Can be formed. The application of the polymer electrolyte can improve adsorption of cobalt-substituted polyoxometallate on the electrode layer.

In the heat treatment step, heat treatment after the step of forming the cobalt-substituted polyoxometallate layer may be performed to provide an electrode layer, for example, a Co-POM-derived catalyst layer uniformly and conformally formed on the semiconductor metal layer. have. The heat treatment step may be carried out under the above-mentioned conditions.

According to another embodiment of the present invention, forming a cobalt-substituted polyoxometallate layer on the electrode layer may include forming a polymer electrolyte layer on the electrode layer; And forming a polyoxometallate layer on the polymer electrolyte layer. Including, and repeating the above-mentioned step one or more times, (polymer electrolyte layer/cobalt-substituted polyoxometallate layer) may be repeatedly stacked one or more times to form a multilayer film. In the multilayer film, the polymer electrolyte layer and the cobalt-substituted polyoxometallate layer may be single or multiple layers, respectively, and spin coating, dip coating, printing method, spraying coating and roll coating may be used.

That is, by laminating a polymer electrolyte layer having different charges and a cobalt-substituted polyoxometallate layer through the LBL (Layer by Layer assembly) method, the cobalt-substituted polyoxometallate layer is subjected to electrostatic interactions. ) To stably deposit on the electrode layer, and heat treatment to deposit a catalyst with increased efficiency, thereby providing an electrode having high efficiency.

The multilayer film of the (polymer electrolyte layer/cobalt-substituted polyoxometallate layer) may be heat treated each time each layer is formed or may be heat treated after the entire layer is formed.

According to another embodiment of the present invention, the step of forming the catalyst layer may include forming a catalyst material layer by coating the catalyst derived from Co-POM according to the present invention on the electrode layer; Or forming a multilayer film in which the (polymer electrolyte layer/catalyst material layer) is repeatedly stacked one or more times. The multilayer film may be formed by laminating a polymer electrolyte and a catalyst derived from Co-POM according to the present invention.

The present invention relates to a photoelectrochemical water decomposition method, and according to an embodiment of the present invention, water decomposition efficiency can be improved by using the photoelectrode according to the present invention.

According to an embodiment of the present invention, the photoelectrochemical water decomposition method includes the steps of contacting water with a photoelectrode according to the present invention; Decomposing water electrochemically or photoelectrochemically by photoelectrode by irradiating sunlight after the contacting step or simultaneously; And collecting and treating a water decomposition product obtained in the step of decomposing the water. It may include. The photoelectrode provides a water oxidation reaction, and the water decomposition product is hydrogen and/or oxygen, and can be used in various fields such as hydrogen energy and fuel cells.

1. Manufacturing example

(1) Co-POM: [Co ₄ (H ₂ O) ₂ (PW ₉ O ₃₄ ) ₂ ] ^10-

"Q. Yin, JM Tan, C. Besson, Y. V Geletii, DG Musaev, AE Kuznetsov, Z. Luo, KI Hardcastle, CL Hill, Science 2010, 328, 342." It was prepared with reference to.

That is, 1.08 M Na ₂ WO ₄₂ H ₂ O, 0.12 M Na ₂ HPO ₄ and 0.24 M Co(NO ₃ ) ₂₆ H ₂ O were mixed in 250 mL of water, and the pH was adjusted to 7.0 using 1 M HCl. . Next, the resulting precursor solution was refluxed at 100° C. for 2 h, and supersaturated with NaCl. The supersaturated solution was filtered to remove NaCl and unreacted substances, and crystallized to obtain pristine POM (hereinafter, POM).

(2) Electrode layer: FTO/α-Fe ₂ O ₃ (hematite)

α-Fe₂O₃ The photoanode is a single crystal α-Fe grown by hydrothermal synthesis on an FTO glass substrate.₂O₃(hematite), "J.-W. Jang, C. Du, Y. Ye, Y. Lin, X. Yao, J. Thorne, E. Liu, G. McMahon, J. Zhu, A. Javey , J. Guo, D. Wang, Nat. Commun. 2015, 6, 7447."

Specifically, the FTO substrate was injected into a 50 mL Teflon-lined stainless steel autoclave containing 10 mL of 0.15 M FeCl ₃ and 1.0 M NaNO ₃ aqueous solution, and treated at 100° C. for 1 h to grow the FeOOH film. Tin-doped hematite film was prepared by annealing a FeOOH film on FTO at 800° C. in an air atmosphere for 5 min.

2. Evaluation of electrochemical and photoelectrochemical properties

Linear sweep voltammetry (LSV) and cyclic voltammetry (CV) include “WMPG1000 multichannel potentiostat/galvanostat” and a reference electrode of Ag/AgCl filled with 1M KCl; Pt wire, counter electrode; And it was measured using "1260A electrochemical impedance spectroscopy (EIS) (Solartron, UK)" in three electrodes including an electrode and a working electrode treated with water-oxidation catalysts (WOCs).

As for the photoelectrochemical characteristics, a 300W Xe lamp equipped with a "400nm cut-on filter (100 mW cm ^-2 )" and a water infrared filter as a light source were used. The charge transfer efficiency was calculated by comparing the LSV curves in 80 mM phosphate buffer with or without the addition of 0.1MH ₂ O ₂ according to the following equation.

Example 1: Synthesis of POM-derived CoWO _4- based WOCs

According to the manufacturing process of Fig. 1 (a), the Co-POM of the preparation example was heated at a temperature increase rate of 10 C min ^-1 and annealed for 1 hour at each temperature (400° C. and 500° C.) to POM-derived CoWO ₄ system. WOCs were synthesized. Diffuse reflectance spectra, TEM, XRD patterns, and Raman spectra of the products prepared according to each temperature were measured and shown in FIG. 1.

In Fig. 1, POM is pristine POMs, and POM400 and POM500 refer to POMs annealed at 400°C and 500°C, respectively.

In Figure 1 (a), POM-derived CoWO ₄ based WOCs according to the annealing of POM in an air atmosphere depend on temperature in structure and catalyst properties, which are powder colors such as cobalt blue of POM400 and dark green of POM500, It can be seen from the continuous change in the diffuse reflection spectrum of the POM according to the annealing temperature shown in FIG. 1B. That is, the absorption peak of the POM in the 560 nm region is shifted to the red region by the heat treatment. In addition, POM and POM-derived CoWO ₄ based WOCs nanoparticles have significant differences in solubility in water, which is that POM before annealing has high solubility in water, but POM400 is almost insoluble in water.

In Figure 1 (c) and (d), it can be seen that nanoparticles having a diameter of several nm were obtained by annealing POM having a diameter of 2 nm or less, respectively, in the electron diffraction analysis of POM400 and POM500, amorphous and crystalline phase It can be confirmed that this was formed. In the XRD pattern shown in Figure 1 (e), POM400 did not have a peak, but in POM500 monoclinic CoWO ₄ (ICDD 01-072-0479) and orthorhombic Na ₂ W ₂ O ₇ (ICDD 01-073-0554) The peak characteristics of were confirmed, and two types of crystalline substances were mixed.

In addition, the Raman spectrum in FIG. 1(f) shows that the Raman peak related to WO ₄ is compared with the crystalline POM500, and the amorphous POM400 is shifted to the blue region. This movement occurs frequently in the presence of compressive stress, and POM400 with a-CoWO ₄ has a more compact structure compared to POM500 and POM with c-CoWO ₄ . Similarly, the shift to the red region of the Raman spectrum can be indicated by the formation of c-CoWO ₄ in a-CoWO ₄ . Therefore, it can be confirmed that a- and c-CoWO ₄ nanoparticles are formed from POM by simple heat treatment.

In order to evaluate the catalytic activity for water oxidation, CV was measured and compared in the neutral region. CV (cyclic voltammetry) plots of POM400 and POM500 and POM prepared in Example 1 were calculated by precipitation method (H. Jia, J. Stark, LQ Zhou, C. Ling, T. Sekito, Z. Markin, RSC Adv. 2012, 2, 10874-10881.) is shown in FIG. 2 in comparison with a-CoWO ₄ .

In Figure 2 (a), POM represents an initiation potential of 1.63 V versus a reversible hydrogen electrode (RHE) and a Tafel slope of 144 mV dec ^-1 , and POM400 and POM500 prepared in Example 1 are, It shows rapid changes in catalytic activity as well as crystal structure. POM400 treated at 400° C. increased catalytic activity, and POM500 treated at 500° C. showed a tendency to decrease catalytic activity. In addition, it can be seen that a-CoWO ₄ prepared by the precipitation method also has low catalytic activity. POM400 with a-CoWO ₄ has an onset potential of 1.41 V versus RHE and a Tafel slope of 80 mV dec ^-1 , thus providing better performance compared to POM500 and a-CoWO ₄ prepared by the precipitation method. At a current density of 100 mA cm ^-2 for POM, the overpotential is 0.498, 0.385 and 0.55 V for POM, POM400 and POM500, respectively, and POM400 exhibits significantly higher catalytic activity compared to a-CoWO ₄ prepared by precipitation method. Can provide.

Referring to (b) of FIG. 2, the performance of _POM400 can be described as various water oxidation mechanisms depending on the distance between adjacent Co ^{2 +} ions (D _Co2+-Co2+ ). The water oxidation reaction occurs according to the Langmuir-Hinshelwood (LH) mechanism when D _{Co2 +- Co2 +} is similar to the bond length of the oxygen molecule, and the oxygen molecule reacts between the oxygen species absorbed on two neighboring active sites. Is formed by There are many Co ^{2 +} -Co ^{2 +} pairs, and POM, the material of POM400, follows the LH mechanism for POM400 because it contains clusters of Co ^{2 +} ions having 3.18 Å as the nearest neighbor distance.

In addition, when D _{Co2 +- Co2 +} is longer than the binding length of the oxygen molecule, the ER (Eley-Rideal) mechanism is that the oxygen molecule is formed from a single active site. The ER mechanism requires a higher overpotential than the LH mechanism, and POM400 with a-CoWO ₄ and POM500 with c-CoWO ₄ follow the LH and ER mechanisms, respectively, and POM400 is a-CoWO ₄ by precipitation method. It provides higher catalyst performance.

Example 2: Preparation of photoelectrode (CE/POM400)

Cationic polymer PEI (poly(ethyleneimine)) was added to 3 mM (in terms of monomer concentration) in a buffer solution (pH 5.0) of 137 mM NaCl and 10 mM phosphate buffer to prepare a polymer electrolyte solution, and anionic POMs Was added to the buffer solution at 1 mM to prepare an anionic POMs solution. The polymer electrolyte solution and the anionic POMs solution were spin-coated on the carbon felt electrode for 5 minutes each to form 1 cycle of LbL assembly (Layer-by-layer assembly), and then repeated n times to prevent electrostatic interactions. A photoelectrode to which (PEI/POMs) n was adsorbed on the surface of a carbon felt electrode was prepared, and the photoelectrode was annealed at 400° C. for 1 hour by heating at a heating rate of 10 C min ⁻¹ . A photoelectrode (CE/POM400) treated with POM-derived CoWO4-based WOCs was prepared on the surface of the electrode. The SEM image of the prepared photoelectrode and the performance of photoelectrochemical water oxidation were evaluated and shown in FIG. 3.

In Figure 3 (a), it can be seen that POM-derived CoWO _4- based WOCs were deposited on the surface of the porous carbon-felt electrode and the polymer electrolyte was removed. In addition, nanoparticles of POM-derived CoWO _4- based WOCs (hereinafter, POM400) are uniformly coated, and excellent performance against water oxidation at pH 8.0 can be provided.

In (c) of FIG. 3, the overpotentials at 10 and 100 mA cm ^-2 current densities are 0.392 and 0.72 V, respectively, and it can be seen that these values are significantly higher than those measured in the neutral pH region.

Example 3: Preparation of photoelectrode (FTO/α-Fe ₂ O ₃ /POM400)

Cationic polymer PEI (poly(ethyleneimine)) was added to 3 mM (in terms of monomer concentration) in a buffer solution (pH 5.0) of 137 mM NaCl and 10 mM phosphate buffer to prepare a polymer electrolyte solution, and anionic POMs Was added to the buffer solution at 1 mM to prepare an anionic POMs solution. α-Fe ₂ O ₃ A polymer electrolyte solution and an anionic POMs solution were spin-coated on a substrate (hematite photoanode) for 5 minutes each to form 1 cycle of LbL assembly (Layer-by-layer assembly), and then repeated n times to form electrostatic interactions. ) On the α-Fe ₂ O ₃ electrode using an adsorption process (PEI/POMs) ₃ , (PEI/POMs) ₅ , (PEI/POMs) ₁₀ , (PEI/POMs) ₁₅ and (PEI/POMs) ₂₀ The adsorbed photoelectrode was prepared, heated at a temperature increase rate of 10 C min ^−1, and annealed at 400° C. for 1 hour. A photoelectrode (FTO/α-Fe ₂ O ₃ /POM400) treated with POM-derived CoWO ₄ based WOCs was prepared on the surface of the electrode. The TME image of the prepared photoelectrode and the performance of photoelectrochemical water oxidation were evaluated and shown in FIG. 4.

In (a) of FIG. 4, POM400 may be deposited on the photoanode of α-Fe ₂ O ₃ through high-temperature annealing after adsorption of POM, and cross-sectional TEM and EDS (energy-dispersive X-) of (b) rayspectroscopy) confirmed that the POM400 cocatalyst layer was uniform and conformal coating was formed on the rough α-Fe ₂ O ₃ particle surface. In addition, since the formation of the POM400 layer is coated in a relatively small amount, α-Fe ₂ O _{3 in the} dotted line It hardly affects the absorbance of the photoanode. The deposition of POM400 can significantly improve the performance of the α-Fe ₂ O ₃ photoanode for visible light-water oxidation.

In (d) of Figure 4, the α-Fe ₂ O ₃ photoanode on which the POM400 cocatalyst is deposited has a photocurrent density of 1.36 mA cm ^-2 in 0.64 V vs. RHE and 1.23 V vs. RHE under the following conditions. It is shown: low ionic strength (80 mM phosphate buffer) and near neutral pH (pH of 8.0). The amount of deposited POM400 cocatalyst can be easily controlled by changing the number of adsorption processes before annealing. As for the photocurrent density, when the adsorption process is increased up to 10 times, the amount of POM400 cocatalyst increases rapidly and then becomes saturated.

The electrochemical impedance spectroscopy in FIG. 4(f) proves that the improved photoelectrochemical performance is due to a decrease in catalytic charge transfer resistance at the electrode/electrolyte interface (R2) following the deposition of POM400. Looking at (g) of FIG. 4, it can be seen that the charge transfer efficiency at the interface is remarkably improved.

The present invention provides a catalyst comprising CoWO ₄ nanoparticles produced by annealing Co-POM in an air atmosphere, and includes CoWO ₄ nanoparticles with improved catalytic performance compared to Co-POM before annealing by this annealing process. It can provide a catalyst. The catalyst comprising the CoWO ₄ nanoparticles, the catalytic activity for water oxidation and their structure depend on the annealing temperature, especially when the annealing temperature is 400 °C, the shortest close distance (D _{Co2 +- Co2 + )} To provide a CoWO ₄ nanoparticle catalyst having an amorphous property with a high number of Co ^{2 +-} ions, which can cause a water oxidation reaction according to the Langmuir-Hinshelwood mechanism and provide remarkably improved catalytic performance. . In addition, the present invention can provide a high-efficiency photoelectrode and photovoltaic cell for electrochemical and photoelectrochemical water oxidation by annealing after depositing Co-POM on a desired electrode by electrostatic adsorption. .

As described above, although the embodiments have been described by the limited drawings, a person of ordinary skill in the art can apply various technical modifications and variations based on the above. For example, the described techniques are performed in an order different from the described method, and/or components such as a system, structure, device, circuit, etc. described are combined or combined in a form different from the described method, or other components Alternatively, even if substituted or substituted by an equivalent, an appropriate result can be achieved.

Therefore, other implementations, other embodiments, and claims and equivalents fall within the scope of the following claims.

Claims (20)

Including a CoWO ₄ phase derived from cobalt-substituted polyoxometalates,
The CoWO ₄ phase, cobalt-substituted polyoxometallate; Or cobalt-substituted polyoxometalate and a polymer electrolyte; Is a heat treatment product of,
The CoWO ₄ phase is a nanoparticle having a size of 0.01 nm to 50 nm,
The CoWO ₄ phase has catalytic activity in the range of pH 6 to 8,
The catalyst that is an electrochemical or photoelectrochemical water oxidation catalyst.
The method of claim 1,
The CoWO ₄ The phase includes amorphous, crystalline or both,
The CoWO ₄ The phase, which is a nanoparticle, the catalyst.
delete The method of claim 1,
The cobalt-substituted polyoxometallate is [Co ₄ (H ₂ O)(VW ₉ O ₃₄ ) ₂ ] ^10- , [Co ₄ (H ₂ O) ₂ (α-PW ₉ O ₃₄ ) ₂ ] ^{10 -} or would that includes both a catalyst.
The method of claim 1,
The polymer electrolyte includes a cationic polymer electrolyte, an anionic polymer electrolyte, or both,
The cationic polymer electrolyte is PEI (polyethyleneimine), b-PEI (branched-poly(ethylene imine)), l-PEI (linear-poly(ethylene imine)), PAH (poly(allylamine hydrochloride)), PAH (poly( allylamine hydrochloride), PDDA (poly(diallyldimethylammonium chloride)), PLL (poly(lysine)), PDADMA (poly(diallyldimethylammonium)), PAMPDDA (poly(acrylamide-co-diallyldimethylammonium)), and PDADMAC (polydiallyldimethylammonium chloride). Including at least one selected,
The anionic polymer electrolyte, PSS (polystyrene sulfonate), The catalyst comprising at least one selected from the group consisting of polyacrylic acid (PAA), poly methacrylic acid (PMA), poly styrene sulfonate (PSS), and hyaluronic acid (HA).
According to claim 1
The mixing ratio (mass ratio) of the polymer electrolyte to the cobalt-substituted polyoxometallate is greater than 0 and less than 1, the catalyst.
The method of claim 1,
The CoWO ₄ phase includes a-CoWO ₄ , c-CoWO ₄ nanoparticles or both,
The CoWO ₄ phase, the ER mechanism (Eley-Rideal mechanism), LH mechanism (Langmuir-Hinshelwood mechanism), or to provide a water oxidation reaction by both, catalyst.
The method of claim 1,
The catalyst is an electrochemical or photoelectrochemical water oxidation catalyst.
Electrode layer; And
A catalyst layer including a catalyst formed on at least a portion of the electrode layer;
Including,
The catalyst includes a CoWO ₄ phase derived from cobalt-substituted polyoxometalates,
The CoWO ₄ phase, cobalt-substituted polyoxometallate; Or cobalt-substituted polyoxometalate and a polymer electrolyte; Is a heat treatment product of,
The CoWO ₄ phase is a nanoparticle having a size of 0.01 nm to 50 nm,
The CoWO ₄ phase, which has a catalytic activity in the range of pH 6 to 8,
Photoelectrode.
The method of claim 9,
The electrode layer is a photoelectrode comprising a semiconductor material, a carbon-based material, or both.
The method of claim 10,
The semiconductor material is Ti, Sn, Zn, Mn, Mg, Ni, W, Co, Fe, Ba, In, Zr, Cu, Al, Bi, Pb, Ag, Cd, Y, Mo, Rh, Pd, Sb , Cs, La, V, Si, Al, Sr, and at least one selected from the group consisting of metal oxides containing at least one of them,
The carbon-based material is carbon powder, carbon paper, carbon fiber, carbon cloth, carbon felt, glassy carbon, CNT (carbon nanotube) The photoelectrode comprising at least one selected from the group consisting of, CNT paper and graphene.
The method of claim 9,
The catalyst layer, a single or a plurality of layers of the catalyst material layer, or (polymer electrolyte layer / catalyst material layer) is to include a multi-layered film is repeatedly stacked one or more times, the photoelectrode.
The method of claim 9,
The electrode layer is an anode, a cathode, or both, the photoelectrode.
A photovoltaic cell comprising the photoelectrode of claim 9.
Heat-treating the cobalt-substituted polyoxometallate;
Including,
Including a CoWO ₄ phase derived from cobalt-substituted polyoxometalates, which is an electrochemical or photoelectrochemical water oxidation catalyst,
Method for producing a catalyst.
The method of claim 15,
The step of heat treatment is to be carried out at a temperature of 100 ℃ to 700 ℃, the method of producing a catalyst.
The method of claim 15,
The step of heat-treating is carried out in an atmosphere containing air, an inert gas, or both.
Preparing an electrode layer; And
Forming a catalyst layer on the electrode layer;
Including,
The step of forming the catalyst layer,
Forming a cobalt-substituted polyoxometallate layer on the electrode layer; And
Heat treatment after the step of forming the cobalt-substituted polyoxometallate layer; Including,
The step of forming the catalyst layer is to form a catalyst comprising a CoWO ₄ phase derived from cobalt-substituted polyoxometalates,
Method of manufacturing a photoelectrode.
delete The method of claim 18,
The step of forming the catalyst layer,
Forming a multilayer film in which (polymer electrolyte layer/cobalt-substituted polyoxometallate layer) is repeatedly stacked one or more times on the electrode layer; And
Performing heat treatment after the step of forming the multilayer film; Including a method of manufacturing a photoelectrode.

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