KR20200001725A - Highly efficient water-oxidation catalysts, its manufacturing method and photoelectrode - Google Patents

Abstract

The present invention relates to a high efficiency water oxidation catalyst, a method for manufacturing the same, and a photoelectrode. More specifically, the present invention relates to: a catalyst comprising a cobalt-substituted polyoxometalates-derived CoWO_4 phase; a method for manufacturing the same; and a photoelectrode comprising the same. The present invention can provide the photoelectrode with improved electrochemical and photoelectrochemical water oxidation efficiency.

Description

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

The present invention relates to a high efficiency 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 takes electrons from water abundant on the earth and synthesizes various chemicals (hydrogen, formate, methanol, etc.), which are photoelectrochemical or electrochemical It can be synthesized from carbon dioxide using electrons generated from water reduction reaction and water oxidation.

Photoelectrochemical hydrolysis is the process of making water into oxygen using visible light and electricity. The electrons generated during the hydrolysis process are ultimately used for carbon dioxide reduction and hydrogen production. Photoelectrochemical hydrolysis requires a variety of materials. For example, (1) a semiconductor material that can receive electrons and holes by receiving light, (2) an electron transport material that can transfer electrons received from water well, and (3) water that can decompose water into oxygen. Decomposition catalysts such as water oxidation catalyst (WOC) materials.

Photoelectrochemical hydrolysis has an indispensable catalyst because it has a complex mechanism of four electrons required for the reaction. Conventional catalysts include organometallic compounds including precious metals such as Ru and Ir, transition metal oxides and perovskite nanoparticles, layered double hydroxides, and the like. Existing catalysts have inherent problems such as high cost, low stability, low catalyst performance, and the like, and have a problem in that 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 applications, catalyst efficiency And improvement in stability as well as simplification of the method for immobilization on the desired electrode surface.

The present invention provides a novel catalyst which can be improved in efficiency by using a water decomposition catalyst having inexpensive cobalt ions as a reaction center and can be fixed in a simple manner to a desired substrate.

This invention provides the photoelectrode containing the catalyst by this invention.

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

This invention provides the manufacturing method of the catalyst by this invention.

This invention provides the manufacturing method of the photoelectrode by this invention.

In accordance with one embodiment of the present invention, CoWO ₄ derived from cobalt-substituted polyoxometalates It relates to a catalyst comprising a phase.

CoWO ₄ according to an embodiment of the present invention Phase includes amorphous, crystalline or both, the CoWO ₄ The phase may be a nanoparticle.

According to an embodiment of the present invention, the CoWO ₄ The phase may be cobalt-substituted polyoxometalate; Or cobalt-substituted polyoxometallate and a polymer electrolyte.

According to an embodiment of the present invention, the cobalt-substituted polyoxometallate is selected from [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 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 polyethyleneimine (PEI), branched-poly (ethylene imine) b-PEI, linear-poly (ethylene imine) l-PEI, poly (allylamine hydrochloride) PAH, poly (PAH) allylamine hydrochloride), PDDA (poly (diallyldimethylammonium chloride), PLL (poly (lysine)), PDADMA (poly (diallyldimethylammonium)), PAMPDDA (Poly (acrylamide-co-diallyldimethylammonium), and PDADMAC (polydiallyldimethylammonium chloride) Including one or more selected,

The anionic polymer electrolyte, Polystyrene sulfonate (PSS), Polyacrylic acid (PAA), poly methacrylic acid (PMA), poly styrene sulfonate (PSS) and may comprise one or more selected from the group consisting of HA (hyaluronic acid).

According to one 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 comprises a-CoWO ₄ and c-CoWO ₄ nanoparticles or both, wherein the CoWO ₄ Phase has catalytic activity in the pH 6-8 region, the CoWO ₄ The phase may be to provide a water oxidation reaction by an Eley-Rideal mechanism, a Langmuir-Hinshelwood mechanism, or both.

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

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

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

According to an embodiment of the present invention, the catalyst layer may include a single or multiple layers of catalyst material, or a multilayer film in which a (polymer electrolyte layer / catalyst material layer) is repeatedly laminated 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 the photoelectrode according to the invention.

According to one embodiment of the invention, the step of heat-treating cobalt-substituted polyoxometallate; It relates to a method for producing a catalyst comprising a.

According to one embodiment of the invention, the step of heat treatment may be performed at a temperature of 100 ℃ to 700 ℃.

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

According to one embodiment of the 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 heat treatment after forming the cobalt-substituted polyoxometallate layer.

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

The present invention, CoWO ₄ excellent in catalytic activity through a simple heat treatment of the polyoxometallate catalyst It is possible to provide a novel catalyst comprising a phase and adsorbing a polyoxometallate catalyst on a desired substrate, for example an electrode layer, followed by heat treatment, thereby providing the CoWO ₄ It is possible to provide a photoelectrode having a stable deposition of a catalyst including a phase and improved electrochemical and photoelectrochemical water oxidation efficiency.

The present invention, CoWO ₄ Catalysts comprising a phase can be applied to improve the overall performance of electrochemical and photoelectrochemical cells.

1 is, according to Example 1 of the present invention, (a) the structural change of POM according to the manufacturing process and annealing of POM-derived CoWO _4- based water-oxidation catalysts (WOCs), (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- based WOCs nanoparticles obtained by annealing at 400 ° C. (D) TEM image of POM-derived CoWO _4- based WOCs nanoparticles obtained by annealing at 500 ° C., (e) POM (POM400 and POM500) and POM annealed at 400 ° C. and 500 ° C., respectively. Shows the XRD pattern and (f) Raman spectrum.
FIG. 2 shows, according to Example 1 of the present invention, (a) cyclic voltammograms (CV) graphs and tafel plots for evaluating catalyst activity and (b) POM400 performance prepared in Examples Illustrate the concept of two mechanisms of oxygen evolution reaction.
Figure 3, according to the second embodiment of the present invention, (a) manufacturing process of the photoelectrode formed POM400 WOCs on the carbon felt (CF) electrode, (d, e) SEM image of the photoelectrode, (f) POM400 WOCs The CV graphs of the carbon felt electrodes of (d) and (e) before and after the deposition are shown, and the embedded image in the SEM image is a high magnification SEM.
4 is a cross-sectional view of a photoelectrode in which POM400 WOCs are formed on a hematite (Fe ₂ O ₃ ) electrode, and (b, c) before and after deposition of POM400, according to Example 3 of the present invention. -sectional TEM images (inserted EDS spectra for elemental analysis in TEM images), (d) photocurrent density and initiation potentials, and (e) linear sweep voltammetry related to (d), (f ) Electrochemical impedance spectra of the photoelectrode before and after the deposition of POM400 and (g) transfer efficiencies. The inset image is an equivalent circuit model for fitting and magnified impedance spectra of the photoelectrode on which POM400 WOCs are deposited.

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

The terminology used herein is for the purpose of description and should not be construed as limiting. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as "comprise" or "have" are intended to indicate that there is a feature, number, step, action, component, part, or combination thereof described on the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

In addition, in the description with reference to the accompanying drawings, the same components regardless of reference numerals will be given the same reference numerals and duplicate description thereof will be omitted. In the following description of the embodiment, when it is determined that the detailed description of the related known technology may unnecessarily obscure the gist of the embodiment, the detailed description thereof will be omitted.

Although the embodiments have been described with reference to the accompanying drawings, those skilled in the art may apply various technical modifications and variations based on the above. For example, the techniques described may be performed in a different order than the described method, and / or the components described may be combined or combined in a different form than the described method, or replaced or substituted by other components or equivalents. Appropriate results can be achieved.

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

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

According to one embodiment of the invention, the Co-POM derived catalyst, cobalt-substituted polyoxo metalate; Or cobalt-substituted polyoxometalate and a polymer electrolyte; and at least a part or all of the heat treatment products produced by heat treatment.

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

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

CoWO ₄ The phase shows good catalytic activity compared to the unheated cobalt-substituted polyoxometalate, for example the CoWO ₄ The prize is,

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

The cobalt-substituted polyoxometalate is a catalyst having a structure similar to that of a water decomposition catalyst existing in nature and having a solubility in water having a cobalt (Co) transition metal as a reaction center instead of manganese (Mn). Cobalt substituted may be applied without limitation, 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 both.

CoWO ₄ Apply cobalt and transition metals (except cobalt) -substituted polyoxometalates, transition metals (except cobalt) -substituted polyoxometalates or both in the heat treatment of cobalt-substituted polyoxometalates for the production of phases 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 application of nickel (Ni) and manganese (Mn). The function of can be added.

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

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

The mixing ratio (mass ratio) of the polymer electrolyte to the cobalt-substituted polyoxometalate prior to the heat treatment is more than 0 and less than 1; 0.01 to 0.8; Alternatively 0.1 to 0.3; Or 0.1 to 0.2. When included in the above range, it is possible to provide a deposition layer of a uniform and conformal Co-POM-derived catalyst on the electrode layer, to facilitate the formation of a multilayer film by the LBL to improve the performance of the photoelectrode.

According to one embodiment of the invention, the Co-POM derived catalyst is deposited on a desired substrate, such as a carrier, or an electrode after catalyst formation or on a desired substrate, such as a carrier, or an electrode. After deposition of the 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, and according to an embodiment of the present invention, the photoelectrode includes: an electrode layer; And a catalyst layer comprising a Co-POM derived catalyst according to the present invention formed on at least a portion of the electrode layer.

The electrode layer may include an electrode for electrochemical water decomposition, and may include a semiconductor material, a carbon-based material, or both. The electrode layer may include a semiconductor material and a carbon-based material alone, or a layer including a semiconductor material, a carbon-based material, or 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 one or more selected from the group consisting of metal oxides including at least one of them. For example, nickel foam (Ni foam); 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 , wherein the metal oxide may be doped with the aforementioned 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 hundred μm, for example, 1 nm or more; 1 nm to 900 m; Or 1 nm to 300 μm. The size may mean diameter, length, or the like, depending on the shape of the particles. When included within the size range, it may provide an efficient electron migration path and may aid in the integration of the functional material deposited on the semiconductor material layer.

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

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

The semiconductor material and the carbon-based material may be formed to a thickness of several nm to several hundred μm, for example, 1 nm or more; 1 nm to less than 1000 μm; 10 nm to 900 μm; Or a thickness of 30 nm to 500 μm. When included within the thickness range, an efficient electron migration path may be provided to facilitate the process of electrochemical or photoelectrochemical hydrolysis.

The catalyst layer may include a single or multiple layers of catalyst material or may include 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 including the Co-POM-derived catalyst according to the present invention by the polymer electrolyte layer, and reduces the accumulation amount of the catalyst layer by a layer-by-layer assembly. By increasing, high efficiency can be provided.

The polymer electrolyte layer is to fix the catalyst material layer by electrostatic adsorption to the desired substrate, for example, to improve the surface roughness of the semiconductor material layer, the electrostatic adsorption of the catalyst material layer It is easy to accumulate and / or fix and increase the amount of functional material constituting the catalytic material layer.

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

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

The present invention relates to a method for preparing a catalyst according to the present invention. According to one embodiment of the present invention, the method includes: heat treating a cobalt-substituted polyoxometalate; It may include.

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

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

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

The heat treatment step, the heat treatment in the atmosphere containing air, inert gas or both, at least 1 minute; At least 10 minutes; At least 30 minutes; For 1 hour; Or heat treated for 1 to 10 hours.

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

The depositing step may form a single or multiple layers of cobalt-substituted polyoxometallate, wherein the multiple layers may comprise the same or different components. Alternatively, the depositing step may form a multilayer film of a polymer electrolyte and a cobalt-substituted polyoxometalate crosslinked one or more times (polymer electrolyte layer / cobalt-substituted polyoxometallate layer).

The deposition may be performed by spin coating, dip coating, printing method, spray coating or roll coating.

The heat treatment may be heat treatment at the above-mentioned temperature.

The present invention relates to a method for manufacturing a photoelectrode according to the present invention, in accordance with an embodiment of the present invention, preparing an electrode layer; And forming a catalyst layer on the electrode layer. It may include.

The preparing of the electrode layer may include forming a semiconductor material layer on a substrate or preparing a semiconductor material in the form of a sheet, film, or wafer. Alternatively, electrodes such as the above-described carbon felt, carbon paper and the like can be prepared.

The semiconductor material is, as mentioned above, physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), vacuum deposition spin coating, sputtering, spin coating, dip The coating, printing method, spraying coating, and rolling coating may be used to form a semiconductor material layer on the substrate or the semiconductor material may be grown by physical and / or chemical treatment (or a synthetic process).

The substrate is a transparent substrate, for example, glass, sapphire, transparent polymer substrate, the transparent polymer substrate, polystyrene, polycarbonate, poly methyl 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 The substrate may be one or more conductive substrates, such as FTO and 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 treatment; It may include. That is, by depositing a cobalt-substituted polyoxometalate on the electrode layer, for example, on the surface of the semiconductor material layer or the carbon felt, the thermal treatment is performed to thereby stably deposit the Co-POM derived catalyst according to the present invention on the electrode. The performance of the electrode can be improved.

Forming a cobalt-substituted polyoxometalate layer on the electrode layer, cobalt-substituted polyoxometalate; Or mixtures of cobalt-substituted polyoxometalates and polymer electrolytes; Can be formed. Application of the polymer electrolyte can improve the adsorption of cobalt-substituted polyoxometallate on the electrode layer.

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

According to another embodiment of the present invention, the step of forming a cobalt-substituted polyoxometallate layer on the electrode layer, forming a polymer electrolyte layer on the electrode layer; And forming a polyoxometallate layer on the polymer electrolyte layer. And repeating the above-mentioned step one or more times to form a multilayer film in which (polymer electrolyte layer / cobalt-substituted polyoxometallate layer) is repeatedly laminated one or more times. In the multilayer film, the polymer electrolyte layer and the cobalt-substituted polyoxometallate layer may be single or plural layers, respectively, and may be spin coating, dip coating, printing method, spray coating, roll coating, or the like.

That is, by stacking a polymer electrolyte layer having a different charge and a cobalt-substituted polyoxometallate layer through a layer by layer assembly (LBL) method, the cobalt-substituted polyoxometallate layer is electrostatically interacted. It is possible to provide an electrode having a high efficiency by depositing a catalyst having an increased efficiency by depositing stably on the electrode layer using a) and heat treatment.

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

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

The present invention relates to a photoelectrochemical water decomposition method, according to an embodiment of the present invention, it is possible to improve the water decomposition efficiency using the photoelectrode according to the present invention.

According to one embodiment of the invention, the photoelectrochemical water decomposition method, the step of contacting water with a photoelectrode according to the present invention; Irradiating sunlight after or simultaneously with the contacting step to decompose water electrochemically or photoelectrochemically by a photoelectrode; And collecting and treating the water decomposition products 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 may be utilized in various fields such as hydrogen energy and a fuel cell.

 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 adjusted to pH 7.0 using 1 M HCl. . The resulting precursor solution was then refluxed at 100 ° C. for 2 h and supersaturated with NaCl. The supersaturated solution was filtered to remove NaCl and unreacted material and crystallized to obtain pristine POM (hereinafter POM).

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

α-Fe ₂ O ₃ The photoanode includes single crystal α-Fe ₂ O ₃ (hematite) grown hydrothermally on an FTO glass substrate, and described in 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 allow the FeOOH film to grow. 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) are the reference electrodes of Ag / AgCl filled with "WMPG1000 multichannel potentiostat / galvanostat" and 1M KCl; Pt wire, counter electrode; And “1260A electrochemical impedance spectroscopy (EIS) (Solartron, UK)” in three electrodes including electrodes treated with water-oxidation catalysts (WOCs) and working electrodes.

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

Example 1 Synthesis of POM-Derived CoWO ₄ -Based WOCs

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

In FIG. 1, POM is pristine POMs, and POM400 and POM500 mean POMs annealed at 400 ° C. and 500 ° C., respectively.

In (a) of FIG. 1 (a), POM-derived CoWO _4- based WOCs according to annealing of POM in an air atmosphere have a structure and catalyst properties depending on temperature, 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 Figure 1 (b). 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 a significant difference in solubility in water, which means that POM before annealing is highly soluble in water, while POM400 is almost insoluble in water.

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

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

CVs were measured and compared in the neutral zone to evaluate the catalytic activity for water oxidation. Cyclic voltammetry (CV) plots of POM400 and POM500 prepared in Example 1 and POM were precipitated (H. Jia, J. Stark, LQ Zhou, C. Ling, T. Sekito, Z. Markin, RSC Adv. 2012, 2, 10874-10881.) Is shown in FIG. 2 as compared to a-CoWO ₄ .

In (a) of FIG. 2, POM represents a starting potential of 1.63 V vs. reversible hydrogen electrode (RHE) and a Tafel slope of 144 mV dec ⁻¹ , and POM400 and POM500 prepared in Example 1 are It shows a drastic change in the catalytic activity as well as the crystal structure. POM400 treated at 400 ° C. showed increased catalytic activity and POM500 treated at 500 ° C. showed lower catalytic activity. In addition, it can be confirmed that a-CoWO ₄ prepared by the precipitation method has a low catalytic activity. POM400 with a-CoWO ₄ has a starting potential of 1.41 V to RHE and a Tafel slope of 80 mV dec ⁻¹ , thus providing better performance compared to a-CoWO ₄ prepared by POM500 and 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. Can provide.

Referring to Figure 2 (b), the performance of POM400, can be described in different oxidation mechanism that depends on the distance between the Co ^{2 +} ions _{(Co2 +} D _{+ -Co2)} that closely adjacent. The water oxidation reaction occurs according to the Langmuir-Hinshelwood (LH) mechanism where D _{Co2 + -Co2 +} is similar to the bond length of the oxygen molecule, and the oxygen molecule reacts between oxygen species absorbed on two neighboring active sites. Is formed. Lots of the presence of Co ^{2 + 2 +} -Co pair follows the LH mechanism for POM400 to contain a cluster of Co ^{2 +} ions of the material, POM POM400 having a 3.18 Å to the nearest neighbor distance (neighbor distance).

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

Example 2 Preparation of Photoelectrode CE / POM400

The cationic polymer PEI (poly (ethyleneimine)) was added to 137 mM NaCl and 10 mM phosphate buffer (pH 5.0) at 3 mM (in terms of monomer concentration) to prepare a polymer electrolyte solution. Silver was added to the buffer solution at 1 mM to prepare an anionic POMs solution. Spin coating the polymer electrolyte solution and anionic POMs solution on the carbon felt electrode for 5 minutes each to form one cycle of LbL layer-by-layer assembly and repeat n times to achieve electrostatic interactions. Photoelectrode (PEI / POMs) n adsorbed was prepared on the surface of the carbon felt electrode, and heated at 10 C min ⁻¹ temperature rate to anneal the photoelectrode at 400 ° C. for 1 hour. 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 (a) of FIG. 3, POM-derived CoWO ₄ -based WOCs are deposited on the surface of the porous carbon-felt electrode and the polymer electrolyte is removed. In addition, nanoparticles of POM-derived CoWO _4- based WOCs (hereinafter POM400) can be uniformly coated and provide excellent performance for water oxidation at pH 8.0.

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

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

The cationic polymer PEI (poly (ethyleneimine)) was added to 137 mM NaCl and 10 mM phosphate buffer (pH 5.0) at 3 mM (in terms of monomer concentration) to prepare a polymer electrolyte solution. Silver was added to the buffer solution at 1 mM to prepare an anionic POMs solution. α-Fe ₂ O ₃ Spin coating the polymer electrolyte solution and anionic POMs solution on the substrate (hematite photoanode) for 5 minutes each to form one cycle of layer-by-layer assembly and repeat n times electrostatic interactions. (PEI / POMs) ₃ , (PEI / POMs) ₅ , (PEI / POMs) ₁₀ , (PEI / POMs) ₁₅ and (PEI / POMs) _{20 on} the α-Fe ₂ O ₃ electrode using an adsorption process. This adsorbed photoelectrode was prepared, and the photoelectrode was annealed at 400 ° C. for 1 hour by heating at a temperature increase rate of 10 C min ⁻¹ . 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 and the performance of photoelectrochemical water oxidation of the prepared photoelectrode 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 (b) cross-sectional TEM and energy-dispersive X- rayspectroscopy) shows that the POM400 cocatalyst layer is uniform and a conformal coating is 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, the α-Fe ₂ O ₃ It hardly affects the absorbance of the photoanode. Deposition of POM400 can significantly improve the performance of the α-Fe ₂ O ₃ photoanode for visible-water oxidation.

In (d) of FIG. 4, α-Fe ₂ O ₃ photoanode on which the POM400 cocatalyst is deposited exhibits a starting potential of 0.64 V vs RHE and a photocurrent density of 1.36 mA cm ⁻² at 1.23 V vs RHE under the following conditions: Shown: low ionic strength (80 mM phosphate buffer) and near neutral pH (pH of 8.0). The amount of POM400 cocatalyst deposited can be easily controlled by varying the number of adsorption processes prior to annealing. The photocurrent density rapidly increases after the adsorption process increases up to 10 times and then saturates.

Electrochemical impedance spectroscopy in FIG. 4 (f) demonstrates that the improved photoelectrochemical performance is due to the reduction of catalytic charge transfer resistance at the electrode / electrolyte interface (R2) upon deposition of POM400. Looking at (g) of Figure 4, it can be seen that the charge transfer efficiency (charge transfer efficiency) at the interface is significantly 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 having improved catalytic performance compared to Co-POM before annealing by such an annealing process. It is possible to provide a catalyst to. The catalyst comprising the CoWO ₄ nanoparticles is characterized by the catalytic activity for water oxidation and their structure depending on the annealing temperature, especially when the annealing temperature is 400 ° C., the shortest closest distance of (D _{Co 2 + —Co 2 + )} Provides a CoWO ₄ nanoparticle catalyst having a high amorphous number of Co ^{2 +} -ions having a), which causes a water oxidation reaction according to the Langmuir-Hinshelwood mechanism and can provide significantly improved catalytic performance. . In addition, the present invention, after the deposition of Co-POM on the desired electrode by electrostatic adsorption (electrostatic adsorption), can be annealed to provide a high efficiency photoelectrode and photovoltaic cell for electrochemical and photoelectrochemical water oxidation in a simple manner. .

Although the embodiments have been described with reference to the accompanying drawings, those skilled in the art may apply various technical modifications and variations based on the above. For example, the described techniques may be performed in a different order than the described method, and / or components of the described systems, structures, devices, circuits, etc. may be combined or combined in a different form than the described method, or other components. Or even if replaced or substituted by equivalents, an appropriate result can be achieved.

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

Claims (20)

CoWO ₄ from cobalt-substituted polyoxometalates A catalyst comprising a phase.
The method of claim 1,
CoWO ₄ The phase comprises amorphous, crystalline or both,
CoWO ₄ Phase is a catalyst, which is a nanoparticle.
The method of claim 1,
CoWO ₄ The phase may be cobalt-substituted polyoxometalate; Or a heat treatment product of cobalt-substituted polyoxometallate and a polymer electrolyte.
The method of claim 1,
The cobalt-substituted polyoxometalate 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 3,
The polymer electrolyte includes a cationic polymer electrolyte, an anionic polymer electrolyte, or both,
The cationic polymer electrolyte is polyethyleneimine (PEI), branched-poly (ethylene imine) b-PEI, linear-poly (ethylene imine) l-PEI, poly (allylamine hydrochloride) PAH, poly (PAH) allylamine hydrochloride), PDDA (poly (diallyldimethylammonium chloride), PLL (poly (lysine)), PDADMA (poly (diallyldimethylammonium)), PAMPDDA (Poly (acrylamide-co-diallyldimethylammonium), and PDADMAC (polydiallyldimethylammonium chloride) Including one or more selected,
The anionic polymer electrolyte, Polystyrene sulfonate (PSS), A 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).
The method of claim 3,
The mixing ratio (mass ratio) of the polymer electrolyte to the cobalt-substituted polyoxometalate is more than 0 and less than 1, the catalyst.
The method of claim 1,
CoWO ₄ The phase comprises a-CoWO ₄ and c-CoWO ₄ nanoparticles or both,
CoWO ₄ The phase has catalytic activity in the pH 6-8 region,
CoWO ₄ The phase is a catalyst which provides water oxidation reaction by the ER mechanism (Eley-Rideal mechanism), the Langmuir-Hinshelwood mechanism or both.
The method of claim 1,
The catalyst is an electrochemical or photoelectrochemical water oxidation catalyst, the catalyst.
An electrode layer; And
A catalyst layer comprising the catalyst of claim 1 formed on at least a portion of said electrode layer;
Including,
Photoelectrode.
The method of claim 9,
The electrode layer, a semiconductor material, a carbon-based material or two, the photoelectrode.
The method of claim 9,
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 At least one selected from the group consisting of Cs, La, V, Si, Al, Sr, and metal oxides including at least one of these,
The carbon-based material may be carbon powder, carbon paper, carbon fiber, carbon cloth, carbon felt, glassy carbon, carbon nanotube (CNT). , CNT paper and graphene, including one or more selected from the group consisting of photoelectrodes.
The method of claim 9,
The catalyst layer is a photoelectrode comprising a single or multiple layers of a catalyst material layer or a multilayered film (polymer electrolyte layer / catalyst material layer) repeatedly stacked one or more times.
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,
Method for preparing a catalyst.
The method of claim 15,
The heat treatment step is carried out at a temperature of 100 ℃ to 700 ℃, the production method of the catalyst.
The method of claim 15,
The heat treatment step is carried out in an atmosphere containing air, inert gas or both, a method for producing a catalyst.
Preparing an electrode layer; And
Forming a catalyst layer on the electrode layer;
Including,
Method for producing a photoelectrode.
The method of claim 18,
Forming the catalyst layer,
Forming a cobalt-substituted polyoxometallate layer on the electrode layer; And
Heat treatment after forming the cobalt-substituted polyoxometallate layer; It will include, the manufacturing method of the photoelectrode.
The method of claim 18,
Forming the catalyst layer,
Forming a multilayer film in which (polymer electrolyte layer / cobalt-substituted polyoxometallate layer) is repeatedly laminated one or more times on the electrode layer; And
Heat treating after forming the multilayer film; It will include, the manufacturing method of the photoelectrode.

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