Porous amorphous metal oxide-based catalyst for oxygen evolution reaction and water splitting system using the catalyst

Abstract

To provide an electrochemical catalyst capable of decreasing an overvoltage of oxygen evolution reaction while using inexpensive metals instead of conventional noble metal catalysts in water splitting reactions, and to provide a water splitting system using the same.SOLUTION: A catalyst for an oxygen evolution reaction electrode in a water splitting reaction comprises: a porous amorphous cobalt oxide; and 0.5 to 3 atom% of at least one P-blocking element as a dopant.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a porous amorphous metal oxide-based catalyst for oxygen evolution reaction and a water splitting system using the same. More specifically, the present disclosure relates to an electrochemical catalyst that can reduce the overpotential of the oxygen evolution reaction (OER) during water splitting, even while using an inexpensive metal (specifically, a base metal) instead of conventional precious metal catalysts, which are complex and require high overpotentials in water splitting reactions, and a water splitting system using the same. [Background technology]

[0002] Water splitting (electrolysis of water), i.e., the splitting or dissociation of water into oxygen gas and hydrogen gas, is an important reaction not only for the production of oxygen gas and / or hydrogen gas but also for energy storage. In particular, as interest in alternative energy sources has increased recently due to environmental pollution issues and the depletion of fossil fuels, hydrogen energy produced by water splitting has attracted much attention as an efficient alternative energy source with abundant raw materials and no environmental pollution issues.

[0003] A water splitting reaction is a process in which compounds that do not naturally separate into anions and cations in an aqueous solution are separated into anions and cations by the application of an electric current. Devices used in water splitting reactions generally include an external power source, an anode, and a cathode. The external power source provides the electrical force necessary to separate the electrolysis target into anions and cations, while the cathode and anode transfer the electrical force to the electrolysis target and provide attachment sites for the anions or cations, respectively. In the case of the hydrogen evolution and oxygen evolution reactions in water splitting, the reaction rates are slow and act as the rate-determining step, so an electrochemical catalyst is required to increase the oxygen evolution rate or oxygen reduction rate.

[0004] Specifically, energy is consumed in the reaction of splitting water into hydrogen gas and oxygen gas, while energy is released when hydrogen gas and oxygen gas recombine to form water molecules. The overall reaction mechanism of the water splitting process can be represented by the following reaction equation 1:

[0005] [Reaction Scheme 1] Anode (oxidation reaction): HO → 2H + +2e - +1 / 2O2 Cathode (reduction reaction): 2H + +2e - →H2 Overall reaction: H2O → H2 + 1 / 2O2

[0006] In particular, the half-cell and overall reactions in acidic and alkaline media, respectively, can be represented as follows in Equations 2 and 3:

[0007] [Reaction Scheme 2] Anode (oxidation reaction): 2H2O(l) → O2(g) + 4H + +4e - Cathode (reduction reaction): 4H + +4e - →2H2 Overall reaction: H2O(l) → H2(g) + 1 / 2O2(g)

[0008] [Reaction Scheme 3] Anode (oxidation reaction): 4OH - →O2(g) + 2H2O + 4e - Cathode (reduction reaction): 4H2O + 4e - →2H2(g)+4OH - Overall reaction: H2O(l) → H2(g) + 1 / 2 O2(g)

[0009] The water splitting reaction described above produces oxygen gas and hydrogen gas in a molar ratio of 1:2, and these product gases can be used as a pollution-free energy source or fuel.

[0010] For water splitting technology to be commercially competitive, catalysts must meet the following requirements: (i) high conversion efficiency to hydrogen or oxygen, (ii) excellent durability, (iii) low voltage operation, and (iv) price competitiveness. In particular, electrochemically driven water splitting catalysts are preferred that are pH insensitive and generate hydrogen or oxygen at low voltage.

[0011] However, the slow reaction rate of the water splitting reaction has been a problem, and the applicability of various electrochemical catalysts has been studied. In this regard, precious metal catalysts for water splitting reactions are widely known. That is, platinum-based catalysts are typically used for the hydrogen production reaction, and iridium oxide (IrO3) or ruthenium oxide (RuO3) catalysts are widely used for the oxygen production reaction.

[0012] Electrochemical electrodes used in existing water splitting systems have demonstrated a certain level of catalytic activity in the hydrogen evolution reaction (HER), but when used as an oxygen evolution electrode (anode or positive electrode), there are limitations to achieving good oxygen evolution reaction activity. In particular, the oxygen evolution reaction, one of the two half-reactions in a water splitting system, has a slow reaction rate and requires a high overvoltage, which is recognized as a technical barrier. Furthermore, iridium oxide, which is mainly used as a catalyst for the oxygen evolution reaction at the anode (oxidizing electrode), has recently been pointed out as making its commercialization more difficult due to its higher price compared to other precious metals (e.g., platinum, ruthenium, etc.).

[0013] In addition, examples of electrochemical electrodes for water splitting have been reported in which base metal catalyst components such as manganese dioxide, tungsten, and iron chalcogenide are supported on a metal (e.g., copper, nickel, etc.) plate, foil, or foam-type structure as the anode substrate for water splitting. However, the high catalyst manufacturing costs compared to performance make them unsuitable for commercialization. Furthermore, when cheaper base metal catalysts are used instead of precious metal catalysts, they are corroded by acid or must be operated at high voltages, leaving room for improvement in performance compared to precious metal catalyst components.

[0014] Therefore, there is a need for a method that can realize good water splitting reaction activity, especially oxygen evolution reaction activity, while using inexpensive metals instead of expensive precious metals. Summary of the Invention [Problem to be solved by the invention]

[0015] In one embodiment of the present disclosure, an inexpensive base metal catalyst that can exhibit performance equal to or better than that of noble metal catalysts such as iridium oxide, which have been primarily used as catalysts for electrodes for oxygen evolution reactions, and an electrochemical electrode using the same are provided.

[0016] Another embodiment of the present disclosure is directed to a water splitting system in which the aforementioned base metal-based catalyst is applied to the anode. [Means for solving the problem]

[0017] According to the first aspect of the present disclosure, An electrode catalyst for an oxygen evolution reaction in a water decomposition reaction, a porous amorphous cobalt oxide; 0.5 to 3 atomic percent of at least one P-block element as a dopant; A catalyst for the oxygen evolution reaction of a water splitting reaction comprising:

[0018] According to a second aspect of the disclosure: A method for producing an electrode catalyst for an oxygen evolution reaction in a water decomposition reaction, comprising: a) converting a cobalt precursor into cobalt hydroxide by a solvothermal synthesis reaction; b) heat-treating the solvothermal synthesis product in an oxygen-containing atmosphere at a first heat-treatment temperature to form a porous amorphous cobalt oxide; c) introducing a precursor of at least one P-block element into the porous amorphous cobalt oxide and heat-treating the porous amorphous cobalt oxide in an inert atmosphere at a second heat-treatment temperature; Including, A method for producing a catalyst is provided in which a porous amorphous cobalt oxide is doped with at least one element selected from P-block elements in an amount of 0.5 to 3 atomic % based on the catalyst.

[0019] According to an exemplary embodiment, the solvent of the cobalt precursor solution may be a mixed solvent including a polyglycol and a polyol.

[0020] According to an exemplary embodiment, the volume ratio of polyglycol:polyol in the solvent can be adjusted in the range of 10-50:1.

[0021] According to an exemplary embodiment, the polyglycol may be at least one selected from the group consisting of triethylene glycol, diethylene glycol, dipropylene glycol, and tetraethylene glycol.

[0022] According to an exemplary embodiment, the polyol may be at least one selected from the group consisting of glycerol, trimethylolpropane, glycerol propoxylate, glycerol ethoxylate, and glycerol trihexanoate.

[0023] According to an exemplary embodiment, in step a), the concentration of the cobalt precursor in the solvent may be adjusted to a range of 50 to 200 mM.

[0024] According to an exemplary embodiment, step a) may be carried out at a temperature controlled in the range of 150 to 250°C.

[0025] According to an illustrative example, the first heat treatment temperature and the second heat treatment temperature may be adjusted to a range of 300 to 500°C, respectively.

[0026] According to an exemplary embodiment, in step c), the precursor of at least one P-block element is added in the form of a solution, the concentration of which may be determined in the range of 10 to 150 mM.

[0027] According to an exemplary embodiment, the at least one P-block element may be lead (Pb).

[0028] According to an exemplary embodiment, the specific surface area (BET) of the cobalt oxide is 40 to 90 m 2 / g range.

[0029] According to an exemplary embodiment, the specific surface area (BET) of the catalyst is 35 to 85 m 2 / g range.

[0030] According to an exemplary embodiment, the porous amorphous cobalt oxide in the catalyst is CoO x where x can range from 1 to 4.

[0031] According to an exemplary embodiment, the inert atmosphere may be formed by at least one gas selected from the group consisting of argon, nitrogen and helium.

[0032] According to the third aspect of this disclosure: An oxygen evolution reaction electrode for a water splitting reaction, comprising: an electrode substrate; and a porous amorphous cobalt oxide-based catalyst loaded on the electrode substrate, The porous amorphous cobalt oxide-based catalyst comprises: a porous amorphous cobalt oxide; 0.5 to 3 atomic percent of at least one P-block element as a dopant; An electrode for an oxygen evolution reaction is provided, comprising:

[0033] According to an exemplary embodiment, the electrode has a current of 10 mA / cm 2 Reference current density, scan rate 10mVs -1 It can exhibit an overpotential of 0.4 V (vs. RHE) or less in a 0.1 M KOH solution (pH 13).

[0034] According to an exemplary embodiment, the catalyst loading in the electrode is 0.02 to 0.2 mg / cm 2 The range may be:

[0035] According to the fourth aspect of this disclosure: A water splitting system comprising an anode and a cathode as electrochemical electrodes electrically connected to an external power source, and an aqueous medium containing an electrolyte, When a voltage is applied from the external power supply, oxygen is generated on the anode side, while hydrogen is generated on the cathode side; The anode comprises a porous amorphous cobalt oxide-based catalyst loaded on an electrode substrate; The porous amorphous cobalt oxide-based catalyst includes (i) a porous amorphous cobalt oxide, and (ii) 0.5 to 3 atomic % of at least one P-block element as a dopant, and provides a water splitting system. [Effects of the Invention]

[0036] The porous amorphous cobalt oxide-based catalyst according to an embodiment of the present disclosure can improve the oxygen evolution reaction activity of base metal catalysts, which has been a technical barrier in existing water splitting systems, to levels equal to or higher than those of expensive noble metal catalysts, thereby improving economic efficiency. The catalyst thus prepared can be used as an electrode for the oxygen evolution reaction, offering the advantage of creating high added value suitable for the commercialization of the entire water splitting system. Therefore, a wide range of applications is expected in the future. [Brief explanation of the drawings]

[0037] [Figure 1] 1A-1C are schematic diagrams illustrating a process for preparing a porous amorphous cobalt oxide-based catalyst according to an exemplary embodiment. [Figure 2] 1 shows the results of SEM and EDX (Energy Dispersive X-ray Spectroscopy) mapping analysis of a lead-doped CoOx porous sheet catalyst (Pb-CoOx-PS) and a non-porous CoOx (CoOx) catalyst, respectively. [Figure 3] FIG. 1 shows XRD patterns of a lead-doped CoOx porous sheet catalyst (Pb-CoOx-PS), a CoOx porous sheet (CoOx-PS) catalyst, and a non-porous CoOx (CoOx) catalyst. [Figure 4] 1 is a graph showing the results of adsorption experiments for the specific surface area (BET) analysis of a lead-doped CoOx porous sheet catalyst (Pb-CoOx-PS), a CoOx porous sheet (CoOx-PS) catalyst, and a non-porous CoOx (CoOx) catalyst. [Figure 5] FIG. 1 shows the results of X-ray photoelectron spectroscopy (XPS) analysis of a lead-doped CoOx porous sheet catalyst (Pb-CoOx-PS), a CoOx porous sheet (CoOx-PS) catalyst, and a non-porous CoOx (CoOx) catalyst. [Figure 6] 1 is a graph showing current density versus voltage curves for a commercial iridium oxide (IrO) catalyst, a lead-doped CoO porous sheet catalyst (Pb-CoO-PS), a CoO porous sheet (CoO-PS) catalyst, and a non-porous CoO (CoO) catalyst. [Figure 7] 1 is a graph showing applied voltage versus log current density curves for a commercial iridium oxide (IrO) catalyst, a lead-doped CoO porous sheet catalyst (Pb-CoO-PS), a CoO porous sheet (CoO-PS) catalyst, and a non-porous CoO (CoO) catalyst. DETAILED DESCRIPTION OF THE INVENTION

[0038] The present invention can be fully achieved by the following description. It should be understood that the following description describes preferred embodiments of the present invention, but the present invention is not necessarily limited thereto. In addition, the accompanying drawings are for the purpose of aiding understanding, and the present invention is not limited thereto. Details of individual configurations can be properly understood by referring to the specific meaning of the related description below.

[0039] As used herein, the term "catalyst" may refer to a component that increases the rate of an electrochemical decomposition reaction, participates in the electrolysis reaction itself, but is not consumed by the reaction itself, and can participate in the electrochemical reaction. In a narrower sense, the term may refer to a component that promotes the reaction mechanism of donating or accepting electrons in the hydrogen generation reaction and / or oxygen generation reaction by water decomposition.

[0040] "Solvothermal synthesis" can refer to a chemical reaction that occurs in a solvent in a sealed vessel at a temperature above the boiling point of the solvent. When the solvent is water, it is called "hydrothermal synthesis."

[0041] "Water splitting" may refer to a reaction in which water is separated into oxygen gas and hydrogen gas using externally supplied electrical energy.

[0042] As used herein, the term "electrode" refers to a conductive structure that is electrically connected to an external power source in a water splitting system and is typically externally separated from the external power source, and can refer to a cathode where a reduction reaction occurs and an anode where an oxidation reaction occurs upon application of a voltage from the external power source.

[0043] A "catalytic electrode" may refer to a current collector loaded with a catalyst that is absorbed on or otherwise electrically connected to the current collector. Here, the catalyst may be understood to be capable of associating with the current collector through a change in oxidation state and / or dynamic equilibrium with the aqueous medium when exposed to an aqueous medium (e.g., an aqueous electrolyte solution).

[0044] "Electrochemical electrode" may refer to an electrode structure in which a catalytic component that promotes the water splitting reaction is incorporated into or attached to the substrate of the electrode (cathode and / or anode).

[0045] "Overpotential" can refer to a voltage other than the thermodynamic reduction or oxidation voltage required to achieve a desired catalytic activity. As used herein, it can refer to the voltage that must be applied to an electrode to cause a water-splitting reaction minus the thermodynamic voltage required for that reaction.

[0046] Terms such as "above" or "upper" and "below" or "below" can be understood to describe the relative positional relationship between components or members, and the terms "located above" or "located below" can be understood to express the relative positional relationship not only in a state of contact with a specific object but also in a state of not contacting with the object.

[0047] In this specification, when a numerical range is specified by a lower limit and / or an upper limit, it can be understood that any subcombination within that numerical range is also disclosed. For example, when it is stated as "1 to 5," it includes 1, 2, 3, 4, and 5, as well as any subcombination therebetween.

[0048] In this specification, when a component or member is described as being "connected" to another component or member, unless otherwise specified, this can be understood to include not only when the component or member is directly connected to the other component or member, but also when the component or member is connected via another component or member.

[0049] Similarly, the term "contact" can be understood to include not only direct contact but also contact via another component or member.

[0050] When a term "comprises" a certain element, this means that it may further comprise other elements, unless otherwise specified.

[0051] Catalyst and method for producing the same The process for preparing a porous amorphous cobalt oxide-based catalyst according to an exemplary embodiment is shown schematically in FIG.

[0052] Referring to the figure, to prepare a catalyst applicable to an electrochemical electrode in a water splitting system, specifically an electrode (anode) for an oxygen evolution reaction, a porous amorphous cobalt oxide is first prepared using a cobalt precursor by solvothermal synthesis and subsequent heat treatment.

[0053] Referring to FIG. 1, first, a cobalt precursor (cobalt source) is prepared. The cobalt precursor may be in the form of a salt, specifically a salt having an oxidation value of 2+. For example, the cobalt precursor may be at least one selected from halides (specifically, chlorides), sulfates, nitrates, phosphates, carbonates, acetates, etc., or may be a hydrate of any of the above compounds. More specifically, the cobalt precursor may be a nitrate (or a hydrate thereof). Nitrates have good solubility in polyols and polyglycols, which is advantageous for efficient reaction during the solvothermal synthesis reaction.

[0054] According to the illustrated embodiment, the cobalt precursor described above is added to a solvent, specifically an organic solvent, more specifically an alcohol-based solvent, to produce a cobalt precursor solution as a reactant for solvothermal synthesis.

[0055] According to an illustrative example, a solvent usable in the solvothermal synthesis reaction can be a type that can suppress aggregation of the synthesized cobalt oxide. Such a solvent can be at least one selected from polyglycols, polyols, and the like, specifically a mixed solvent containing a combination of polyglycols and polyols. For example, the solvent can have a relatively high boiling point, for example, at least about 200°C, specifically about 230-350°C, more specifically about 250-320°C, and particularly about 270-300°C. Such a high-boiling-point solvent, specifically a combination of solvents, can effectively suppress aggregation during the solvothermal synthesis of cobalt hydroxide.

[0056] According to an exemplary embodiment, polyglycol may refer to a dihydroxy ether formed by the dehydration reaction of two or more glycol molecules represented by the general formula 1 below:

[0057] [General formula 1] [ka]

[0058] In the formula, each of R1 to R4 can be hydrogen or an alkyl group having 1 to 6 carbon atoms.

[0059] In this embodiment, polyglycol can function as a surfactant and provide reducing power, which is advantageous for producing nanostructured cobalt hydroxide, the product of solvothermal synthesis. In an exemplary embodiment, the polyglycol can be selected from at least one of triethylene glycol, diethylene glycol, dipropylene glycol, tetraethylene glycol, etc., and more specifically, triethylene glycol (TEG) can be used. In this regard, triethylene glycol is advantageous in that it not only has high solubility for the cobalt precursor, but also has good reducing power even at relatively low temperatures.

[0060] On the other hand, the polyol can be an alcohol containing at least three hydroxyl groups, more specifically, an alcohol containing three hydroxyl groups. Here, the polyol can function as a strong surfactant and can control the nanostructure of the cobalt hydroxide product of the solvothermal synthesis. In an exemplary embodiment, the polyol can be selected from at least one of glycerol, trimethylolpropane, glycerol propoxylate, glycerol ethoxylate, glycerol trihexanoate, etc., more specifically, glycerol can be used, which is advantageous because it allows for easy control of the nanostructure even in small amounts.

[0061] According to an illustrative embodiment, the volume ratio of polyglycol to polyol in the mixed solvent can be adjusted to, for example, about 10 to 50:1, specifically about 15 to 40:1, and more specifically about 20 to 30:1. In this regard, if the relative amount of polyglycol is too high or too low, the product may aggregate or the yield may decrease, so it is advantageous to adjust it to the above range. However, the above range can be changed depending on the type of polyglycol and / or polyol, and this embodiment is not limited thereto.

[0062] According to an illustrative embodiment, the concentration of the cobalt precursor in the solution can be determined taking into consideration the degree of particle formation, and can be, for example, in the range of about 50 to 200 mM, specifically about 70 to 150 mM, and more specifically about 90 to 120 mM.

[0063] According to this embodiment, the cobalt precursor in the precursor solution can be converted to cobalt hydroxide by solvothermal synthesis. In this regard, polyglycol (e.g., triethylene glycol) contains hydroxyl groups and functions as a weak reducing agent and surfactant, leading to heterogeneous nucleation during the reaction. The fine particles generated in the initial stage of the reaction continue to grow and aggregate, resulting in an increase in particle size. Here, polyol (e.g., glycerol) can act as a co-surfactant to control particle size.

[0064] According to an illustrative example, the reaction temperature during the solvothermal synthesis can be adjusted, for example, to a range of about 150 to 250° C., specifically about 160 to 220° C., and more specifically about 170 to 200° C. The reaction pressure is not particularly limited, but is typically at least about 15 kg / cm. 2 , more typically about 10-20 kg / cm 2 The reaction time can be adjusted to within a range of 1 to 4 hours. Alternatively, the reaction time can be adjusted to, for example, at least about 1 hour, specifically about 2 to 5 hours, and more specifically about 3 to 4 hours, but this can be understood as an example. Once the solvothermal synthesis is completed, the product can be obtained by, for example, washing the product at least once (using at least one solvent selected from water, acetone, and alcohols having 1 to 4 carbon atoms (specifically, methanol, ethanol, and / or propanol)) and / or drying the product.

[0065] In the illustrated example, the product of the solvothermal synthesis reaction can be converted into porous amorphous cobalt oxide by heat treatment (first heat treatment). The heat treatment can be performed in an oxygen-containing atmosphere, specifically, in an air atmosphere. The heat treatment temperature (first heat treatment temperature) can be adjusted, for example, to about 300 to 500°C, specifically, about 350 to 450°C, and more specifically, about 380 to 420°C. The heat treatment time is not particularly limited as long as it converts substantially all of the product of the hydrothermal synthesis into an oxide form, but can be adjusted, for example, to at least about 2 hours, specifically, about 2 to 6 hours, and more specifically, about 3 to 5 hours.

[0066] Thus, the product formed by heat treatment has the formula CoO x where x can be in the range of about 1 to 4, specifically about 1.5 to 3.5, and more specifically about 2 to 3. Such amorphous properties contain a large number of oxygen vacancies (vacancies or defects), which are the intermediates of the oxygen evolution reaction (OER), and thus can be used to form OH - Since it can effectively adsorb ions, it is advantageous for improving OER performance.

[0067] It is noteworthy that the cobalt oxide prepared by the above method has a sheet-like nanostructure with developed pores, particularly a sponge-like structure with significantly increased porosity compared to conventional cobalt oxide. Furthermore, the cobalt oxide particles constituting the sheet may have morphological characteristics such as spherical, elliptical, linear, etc.

[0068] In this regard, porous cobalt oxide (CoO x The average pore size of the pores can be measured by nitrogen adsorption (N2 sorption) and can be, for example, in the range of about 0.1 to 3 nm, specifically about 0.5 to 2 nm, and more specifically about 1 to 1.5 nm.

[0069] According to an exemplary embodiment, the specific surface area (BET) of the cobalt oxide is, for example, about 40 to 90 m 2 / g, specifically about 50 to 80 m 2 / g, more specifically, about 60-70m 2 The pore volume can be, for example, about 0.05 to 0.3 cm. 3 / g, specifically, approximately 0.8 to 0.2 cm 3 / g, more specifically, approximately 0.1 to 0.15 cm 3 / g range. This developed porosity not only increases the reaction active sites but also induces efficient mass transfer of reactants / products.

[0070] According to one embodiment of the present disclosure, after the porous amorphous cobalt oxide is prepared, a step of doping with a P-block element (which may refer to an element whose last electron occupies the p-orbital (e.g., an element in Groups 13 to 18 of the periodic table)), specifically a Group 14 element (especially a metal) of the periodic table, is carried out. In this embodiment, the P-block element suitable as the dopant may be, for example, a type having an electronegativity (Pauling scale) of about 1.6 to 2, specifically about 1.7 to 1.9, more specifically about 1.9. Exemplarily, the P-block element may be at least one selected from lead (Pb), indium (In), antimony (Sb), tin (Sn), etc.

[0071] In a specific embodiment, the P block element can be lead (Pb), which has excellent pseudocapacitive properties and a high electronegativity (1.9), and is therefore advantageous in that it can promote charge transfer in cobalt oxide and easily control its electrical properties, thereby maximizing catalytic performance.

[0072] According to an exemplary embodiment, the dopant can be introduced in the form of a precursor, specifically, added to the cobalt oxide in the form of a precursor solution. Usable media or solvents include water, ethanol, methanol, and propanol, and can be used alone or in a mixture. More specifically, the media or solvent can be water (e.g., deionized water).

[0073] In a specific example, when the dopant is lead (Pb), the lead precursor is not particularly limited as long as it has the property of being ionized in the medium or solvent, and may be at least one selected from, for example, lead nitrate (Pb(NO3)2), lead chloride (PbCl2), lead sulfate (PbSO4), lead acetylacetonate (Pb(C5H7O2)2), etc. According to an exemplary example, the concentration of the dopant precursor solution may be, for example, in the range of about 10 to 150 mM, specifically about 20 to 100 mM, and more specifically about 30 to 70 mM. If the concentration of the dopant precursor solution is too high or too low, undesired oxides of the dopant precursor may be formed or the doping effect may be reduced, so it is advantageous to appropriately adjust the concentration within the aforementioned range. However, the aforementioned concentration ranges should be understood as exemplary.

[0074] According to an exemplary embodiment, a step of adding or contacting a dopant precursor solution to the previously prepared porous amorphous cobalt oxide may be performed.

[0075] The ratio of dopant precursor to cobalt oxide in the added solution can be determined depending on the final catalyst composition. For example, the dopant precursor solution can be used so that the molar ratio of cobalt oxide to dopant precursor is, for example, about 20 to 2:1, specifically about 15 to 4:1, and more specifically about 10 to 6:1, but this is for illustrative purposes only. The dopant precursor solution can also be added dropwise to the cobalt oxide.

[0076] After adding the dopant precursor as described above, the dopant precursor and impurities remaining without being mixed into the porous cobalt oxide can be removed by washing, for example, at least once. Simultaneously or alternatively, a drying process (for example, at a drying temperature of about 60 to 120°C, specifically about 80 to 100°C) can be carried out.

[0077] The cobalt oxide doped with the dopant precursor is then subjected to a heat treatment (second heat treatment) to prepare an electrochemical catalyst. The heat treatment can be performed in an inert atmosphere. For example, it can be performed in an atmosphere of at least one gas selected from argon, nitrogen, helium, etc., more specifically, a nitrogen atmosphere. The heat treatment temperature (second heat treatment temperature) can be adjusted to, for example, about 300 to 500°C, specifically about 350 to 450°C, more specifically about 380 to 420°C. The heat treatment time is not particularly limited, but can be adjusted to, for example, at least about 2 hours, specifically about 2 to 5 hours, more specifically about 3 to 4 hours. By performing the heat treatment in an inert atmosphere, the P-block element can be doped into the cobalt oxide and converted into a partially oxidized form.

[0078] According to this embodiment, in the case of a cobalt oxide-based electrochemical catalyst, nanosized cobalt oxide particles form a porous sheet structure, where the size (or diameter) of the cobalt oxide particles as measured by SEM can be, for example, in the range of about 20 to 100 nm, specifically about 30 to 80 nm, and more specifically about 40 to 70 nm.

[0079] The width of the porous cobalt oxide sheet formed by the association of cobalt oxide particles can be, for example, in the range of about 1 to 100 μm, specifically about 5 to 80 μm, and more specifically about 10 to 50 μm.

[0080] In addition, dopants, which are P-block elements, can be incorporated into the host component cobalt oxide to effectively control the electronic structure of the cobalt oxide and improve charge transport. In this case, they can be incorporated in the form of a single atom.

[0081] According to illustrative embodiments, the porous amorphous cobalt oxide may contain a P block element as a dopant component in an amount of, for example, about 0.5 to 3 atomic %, specifically about 0.6 to 2.5 atomic %, and more specifically about 0.7 to 2 atomic %, based on the catalyst. According to specific embodiments, the P block element may be contained in an amount of, for example, about 0.8 to 1.5 atomic %, specifically about 0.9 to 1.2 atomic %, based on the catalyst. If the dopant content is too low or too high, the doping effect may be low or oxide may be formed, so it is advantageous to appropriately adjust the dopant content within the aforementioned range.

[0082] In addition, the cobalt oxide-based catalyst according to this embodiment may have a slightly reduced specific surface area compared to the porous cobalt oxide before doping due to the incorporation or doping of the P-blocking element, but still maintains the high porosity of the cobalt oxide. In this regard, the doped cobalt oxide-based catalyst according to this embodiment may have a specific surface area of, for example, about 35 to 85 m 2 / g, specifically about 40 to 75 m 2 / g, more specifically, about 50-70m 2 / g, where the decrease in the specific surface area (BET) compared to before doping can be, for example, about 8% or less, specifically about 6% or less, and more specifically about 4% or less.

[0083] Thus, in the case of the electrochemical catalyst according to this embodiment, the increased specific surface area of ​​the cobalt oxide increases the catalytic active sites, allowing for effective transport of reactants / products, and performance can be maximized by introducing a P-block element, particularly lead (Pb), as a dopant. Furthermore, the electrochemical catalyst according to this embodiment exhibits electrochemical activity, particularly oxygen evolution reaction activity, comparable to or superior to existing iridium oxide catalysts, which is advantageous in terms of economy and commercialization.

[0084] Although the present disclosure is not limited to a particular theory, the reason why base metals exhibit good oxygen evolution reaction (OER) activity can be explained as being due to the synergistic effect of the nanostructure effect, electronic structure control, and the amorphous structure that allows oxygen vacancies to be abundant and effectively distributed on the catalyst surface.

[0085] Oxygen evolution reaction electrode (catalytic electrode) and water splitting system According to another embodiment of the present disclosure, a porous amorphous cobalt oxide catalyst doped with a P-block element can be loaded onto an electrochemical electrode and used to construct a water splitting system. In particular, the catalyst-loaded electrode can be used as the anode where the oxygen evolution reaction occurs in the water splitting system.

[0086] According to an illustrative embodiment, when manufacturing an electrode, a catalyst may be loaded onto a conductive substrate. However, the loading method is not particularly limited, and methods known in the art, such as loading using a slurry, deposition, spray coating, etc., may be applied.

[0087] For example, in the case of the slurry loading method, a slurry of the previously produced catalyst (the dispersion medium can be at least one selected from the group consisting of alcohols having 1 to 4 carbon atoms (e.g., methanol, ethanol, propanol, etc.) and water (e.g., distilled water)) can be produced. Here, the concentration of the catalyst slurry can be adjusted to, for example, about 5 to 30 wt %, specifically, about 10 to 20 wt %. Next, the slurry can be applied to an electrode substrate (e.g., a conductive substrate) and then dried to produce a catalyst electrode.

[0088] Alternatively, a deposition method may be used, in which case the catalyst layer to be loaded may be adjusted by adjusting the deposition rate, drying temperature, etc., and cleaning may be performed after deposition.

[0089] According to illustrative embodiments, the substrate on which the catalyst is loaded may have various shapes, such as a plate, rod, mesh, disk, or wire. The conductive substrate may be made of a material that maintains conductivity even when exposed to an oxidizing atmosphere. For example, the conductive substrate may be made of at least one material (including alloys) selected from valve metals (e.g., titanium, aluminum, chromium, etc.), stainless steel, etc., or carbon.

[0090] In an exemplary embodiment, the amount of catalyst loaded is, for example, about 0.02 to 0.2 mg / cm based on the electrode. 2 , specifically about 0.04 to 0.15 mg / cm 2 , more specifically about 0.08 to 0.12 mg / cm 2 , but this can be understood as an exemplary purpose.

[0091] According to one embodiment of the present disclosure, a water splitting system can be realized in which water is split using the electrochemical electrode described above as an anode to generate hydrogen at the cathode and oxygen at the anode. The water splitting system basically includes a pair of opposing electrodes (i.e., an anode and a cathode), each of which is electrically connected to an external power source (e.g., a potentiostat, a battery, etc.). In addition, in the case of a three-electrode system, a reference electrode can also be included. Such a reference electrode can be selected from the group consisting of Ag / AgCl, a saturated calomel electrode (SCE), Hg / HgO, and Hg / Hg2SO4, and specifically, Ag / AgCl (3M NaCl) can be used.

[0092] According to an exemplary embodiment, the water splitting system uses one of a pair of electrodes, an electrochemical electrode containing or having the above-described catalyst attached thereto, as the anode, and the remaining electrode, the cathode, can be of any type known in the art. In this regard, the cathode can also be made of a conductive material. For example, conductive materials applicable to the cathode can be selected from materials that exhibit particularly low overvoltage while easily generating hydrogen and not decomposing upon contact with an aqueous solution. For example, the material can be at least one selected from platinum, nickel, cobalt, iron, etc. (including alloys). In a water splitting system according to a specific embodiment, each of the cathode and anode can be operated in contact with or immersed in an electrolyte-containing aqueous solution. For example, the pair of electrodes can be operated with at least about 20%, specifically at least about 50%, more specifically at least 80%, and particularly substantially the entire surface of the electrode immersed in the electrolyte-containing aqueous solution.

[0093] Meanwhile, according to an illustrative embodiment, an aqueous medium (water) can be supplied to the water splitting system. More specifically, an aqueous electrolyte solution (which can be acidic or alkaline) in which an electrolyte is dissolved in the aqueous medium can be supplied. Here, the alkaline medium (or electrolyte) can be at least one selected from potassium hydroxide, potassium bicarbonate, potassium bicarbonate, sodium bicarbonate, sodium hydroxide, lithium hydroxide, etc. For example, the concentration of the alkaline medium can be, for example, about 0.05 to 3 M, specifically about 0.08 to 2 M, and more specifically about 0.1 to 1.5 M. Furthermore, the pH of the alkaline medium (specifically, the electrolyte-containing aqueous solution) can be adjusted to a basic range. For example, it can be adjusted to about 9 to 14, specifically about 11 to 14, and more specifically about 12 to 13.

[0094] Meanwhile, according to an illustrative example, the acidic medium (or electrolyte) can be at least one selected from sulfuric acid, nitric acid, phosphoric acid, perchloric acid, hydrochloric acid, etc. Illustratively, the concentration of the acidic medium can be determined in the range of, for example, about 1 to 5 M, specifically about 1 to 4 M, more specifically about 1 to 2 M. Furthermore, the pH of the acidic medium can be adjusted to, for example, about 4 or less, specifically about 1 to 3, more specifically about 1 to 2.

[0095] According to an exemplary embodiment, the water splitting system can perform hydrogen and / or oxygen production reactions using a water splitting tank based on an aqueous solution containing an alkaline or acidic electrolyte.

[0096] Alternatively, a water splitting system can be constructed using a polymer electrolyte membrane as a separator. Such a separator is typically located between the cathode and the anode and serves to form a barrier to prevent oxygen produced at the anode from mixing with hydrogen produced at the cathode to reconstitute water. In this regard, the separator material can be selected from porous ceramic membranes (e.g., zirconia-based membranes), porous polymer membranes (e.g., polyolefin-based, more specifically, polypropylene-based membranes), solid polymer electrolyte membranes (ion-exchange membranes made of perfluorosulfonic acid polymer materials, such as Nafion®), and the like.

[0097] Generally, the thermodynamic decomposition voltage for a water splitting reaction is 1.23 V at 25°C and atmospheric pressure. However, in actual water splitting systems, various resistance factors exist, reducing the reaction rate and preventing water splitting. Therefore, the water splitting reaction typically only occurs when an overvoltage is applied. That is, when the absolute values ​​of the oxidation current generated at the anode and the reduction current at the cathode are equal, i.e., when the amount of electrons flowing at the anode and cathode are equal, a circuit is formed and the water splitting reaction can occur. The potentials for currents of the same intensity to flow at such a pair of opposing electrodes are different at each electrode, and the resulting voltage corresponds to the overvoltage at each electrode.

[0098] In a water splitting system including an electrochemical electrode using the composite catalyst according to this embodiment, the water splitting reaction can be carried out at a low overvoltage. For example, when oxygen (or oxygen gas) is produced from the anode by the water splitting reaction, the system can operate at a low overvoltage. In addition, the water splitting reaction can be carried out at a temperature of, for example, about 15 to 40°C, specifically about 20 to 30°C, and more specifically, room temperature.

[0099] According to this embodiment, when an electrochemical electrode loaded with a porous amorphous cobalt oxide catalyst doped with a P-block element is used as the anode, the OER performance is 10 mA / cm.2 Reference current density, scan rate 10mVs -1 and under the condition of 0.1 M KOH solution (pH 13), the Tafel slope may be, for example, about 0.4 V or less, specifically about 0.38 V or less, more specifically about 0.36 V or less, and particularly about 0.34 V or less. The Tafel slope may be, for example, about 100 mV / dec or less, specifically about 80 mV / dec or less, and more specifically about 70 mV / dec or less.

[0100] On the other hand, when the electrochemical electrode according to this embodiment is applied to a water splitting reaction, oxygen and hydrogen can be recovered from the anode and cathode, respectively. In particular, the purity of oxygen generated from the anode can be, for example, at least about 98% (specifically, at least about 99%, more specifically, at least about 99.9%), and can be substantially 100%. In addition, the purity of hydrogen generated from the cathode can be, for example, at least about 98% (specifically, at least about 99%, more specifically, at least about 99.9%).

[0101] Preferred examples are presented below to aid in understanding the present invention. However, the following examples are provided only to facilitate understanding of the present invention, and the present invention is not limited thereto.

[0102] Example Details of the materials used in this example, catalyst analysis and electrochemical performance tests are as follows:

[0103] A. Substance Cobalt(II) nitrate hexahydrate (Co(NO3)26H2O, 98.5%), lead nitrate hydrate (Pb(NO3)2xH2O, 99.9%), triethylene glycol, glycerol, and potassium hydroxide (KOH, 1.0 M) were purchased from Sigma-Aldrich.

[0104] All materials were used as purchased without further purification, and deionized water was used in the examples.

[0105] B. Catalyst analysis The metal crystal planes were confirmed using X-ray diffraction (XRD; PANalytical) analysis, where measurements were taken using CuKα radiation at 40 kV and 100 mA over a range of 10–80° at a scan rate of 6° per minute with an interval of 0.01°.

[0106] The oxidation state of the transition metals was analyzed using X-ray photoelectron spectroscopy (XPS; ESCALAB 250Xi). All XPS results were corrected based on the carbon 1s binding energy of 284.6 eV.

[0107] The surface structure of the catalyst was analyzed using a scanning electron microscope (SEM; SU8230), and elemental mapping was performed using an EDS detector attached to the scanning electron microscope.

[0108] C. Electrochemical Performance (OER) Evaluation Experiment Lead-doped CoO x Porous sheet (Pb-CoOx-PS) catalyst, CoO x Porous sheet (CoOx-PS) catalyst, non-porous CoO x The (CoOx) catalyst and the commercial catalyst IrO2 were each deposited onto a glassy carbon electrode (a rotating disk electrode) using a micropipette, and then the working electrode was set (loading amount: 0.1 mg / cm). 2 ).

[0109] The polarization of the oxygen evolution reaction (OER) was measured in 0.1 M KOH solution (pH 13) at room temperature and a scan rate of 10 mV / s. Hg / HgO (sat. 1 M NaOH) and Pt wire were used as the reference and counter electrodes, respectively.

[0110] In addition, the potential measured during the electrochemical test was converted from Hg / HgO to a reversible hydrogen electrode (RHE) using the following mathematical formula 1, and all measurements were displayed as "vs RHE (reversible hydrogen electrode)".

[0111] [Mathematical formula 1] E(RHE)=E(Hg / HgO)+0.8676

[0112] Additionally, to measure the water splitting efficiency, LSV (Linear Sweep Voltammetry) was measured and the Tafel slope was calculated based on this.

[0113] Example 1 Lead-doped CoO x Fabrication of porous sheet (Pb-CoOx-PS) catalyst 5 mmol of cobalt nitrate hexahydrate was added to a mixed solvent of 48 mL of triethylene glycol and 2 mL of glycerol, and the mixture was sonicated and stirred until the cobalt precursor was completely dissolved. After that, the mixture was reacted at 170°C for 3 hours using hydrothermal synthesis. After that, the sample was washed with acetone and distilled water, and then heat-treated at 400°C in an air atmosphere to produce cobalt oxide.

[0114] A 0.05 mmol / mL Pb precursor solution was added dropwise to the prepared cobalt oxide using a pipette, dried at 80°C, and then heat-treated at 400°C in a nitrogen atmosphere to obtain a Pb-CoOx-PS catalyst, where the Pb doping amount in the catalyst was 1.0 atomic %.

[0115] Comparative Example 1 CoO x Fabrication of porous sheet (CoOx-PS) catalyst An undoped CoOx-PS catalyst was prepared in the same manner as in Example 1, except that no lead (Pb) solution was added during the catalyst preparation process.

[0116] Comparative Example 2 non-porous CoO x (CoOx) catalyst production A CoOx catalyst was prepared by solvothermal synthesis of a cobalt precursor and heat treatment in the same manner as in Example 1, except that 50 mL of ethylene glycol (Sigma-Aldrich) was used instead of the combination of triethylene glycol and glycerol, and the reaction was carried out at 200 °C for 3 hours.

[0117] Comparative Example 3 A commercial oxide electrode catalyst, IrO2 black (100% by weight, Alfa Aesar), was used.

[0118] Results and Discussion A. Characterization SEM analysis Lead-doped CoO x Porous sheet catalyst (Pb-CoOx-PS) and non-porous CoO x The SEM and EDX (Energy Dispersive X-ray Spectroscopy) mapping analysis results of the (CoOx) catalyst are shown in Figure 2a and Figure 2b, respectively.

[0119] Referring to the figure, it was confirmed that the Pb-CoOx-PS catalyst had a porous sheet structure composed of cobalt oxide particles with an average size of 50 nm. On the other hand, the CoOx catalyst prepared using ethylene glycol in the solvothermal synthesis reaction had a non-porous structure with no structural peculiarities.

[0120] XRD analysis Lead-doped CoO xPorous sheet (Pb-CoOx-PS) catalyst, CoO x Porous sheet (CoOx-PS) catalyst and non-porous CoO x The XRD patterns of each of the (CoOx) catalysts are shown in Figure 3.

[0121] Referring to the figure, no crystalline peaks were observed in any of the three samples analyzed, indicating their amorphous nature.

[0122] Specific surface area (BET) analysis Lead-doped CoO x Porous sheet (Pb-CoOx-PS) catalyst, CoO x Porous sheet (CoOx-PS) catalyst and non-porous CoO x The results of the adsorption experiments for the specific surface area (BET) analysis of each of the (CoOx) catalysts are shown in Table 1 below and FIG.

[0123] [Table 1]

[0124] Referring to the table and figure, it was confirmed that the BET specific surface area of ​​the CoOx-PS catalyst and Pb-CoOx-PS catalyst, which have a porous sheet structure, is approximately two times larger than that of the non-porous CoOx catalyst.

[0125] XPS analysis Lead-doped CoO x Porous sheet (Pb-CoOx-PS) catalyst, CoO x Porous sheet (CoOx-PS) catalyst and non-porous CoO x The XPS analysis results for each of the (CoOx) catalysts are shown in Figure 5.

[0126] Referring to the figure, the XPS analysis results confirmed that CoOx with a predominant CoO structure was synthesized, and in the case of Pb-CoOx-PS, it was confirmed that Pb atoms were successfully doped. In particular, when Pb, a P-blocking element, was doped, a peak shift was observed in the main Co 2p peak, indicating a change in the electronic structure.

[0127] B. Electrochemical Performance Analysis Commercial iridium oxide (IrO2) catalyst, lead-doped CoOx porous sheet (Pb-CoOx-PS) catalyst, CoOx porous sheet (CoOx-PS) catalyst, and non-porous CoO x The overpotential measurement results and current density vs. voltage curves for each of the (CoOx) catalysts are shown in Table 2 below and FIG.

[0128] [Table 2] 1 :iR-corrected data

[0129] According to the table and figure, the oxygen evolution reaction performance was evaluated in the order of IrO2 ≥ Pb-CoOx-PS > CoOx-PS > CoOx. Specifically, the Pb-CoOx-PS catalyst was 10 mA / cm 2 An overpotential of 0.34 V was required to obtain a current density value equivalent to this, which is approximately 40 mV and 120 mV lower than those of the CoOx-PS and CoOx catalysts, respectively. In particular, despite the small catalyst loading, the performance of the Pb-CoOx-PS catalyst is at or above the level of the noble metal IrO2.

[0130] Commercial iridium oxide (IrO2) catalyst, lead-doped CoO x Porous sheet (Pb-CoOx-PS) catalyst, CoO xThe OER kinetics can be evaluated by measuring the slope of the Tafel plot from the applied voltage vs. log current density curves for the porous sheet (CoOx-PS) catalyst and the non-porous CoOx (CoOx) catalyst, respectively, and the results are shown in Figure 7.

[0131] As shown in the figure, the gradient of the Pb-CoOx-PS catalyst (69.5 mV / dec) was similar to that of IrO2 (70.0 mV / dec) and lower than that of CoOx-PS (85.5 mV / dec) and CoOx (108.4 mV / dec).The above results confirm that the Pb-CoOx-PS catalyst promotes the oxygen evolution reaction through a more efficient catalytic reaction pathway.

[0132] The above results are believed to be due to the porous amorphous sheet structure with a large specific surface area, which maximizes the active sites and effectively transports reactants / products.Furthermore, in the case of the Pb-CoOx-PS catalyst, it was confirmed that the electrochemical activity, i.e., oxygen evolution reaction performance, was improved by adjusting the electronic structure through lead (Pb) doping.

[0133] Simple variations and modifications of the present invention can be easily made by those skilled in the art, and all such variations and modifications can be considered to be within the scope of the present invention.

Claims

1. An electrode catalyst for an oxygen evolution reaction in a water decomposition reaction, a porous amorphous cobalt oxide; 0.5 to 3 atomic % of at least one P-block element as a dopant; 1. A catalyst for an electrode for an oxygen evolution reaction in a water splitting reaction, wherein the at least one P block element is lead (Pb).

2. The specific surface area (BET) of the catalyst is 35 to 85 m ２ The electrode catalyst for oxygen evolution reaction in water decomposition reaction according to claim 1, wherein the surface area of ​​the electrode catalyst is in the range of 1 / g.

3. The porous amorphous cobalt oxide in the catalyst is CoO ｘ 2. The electrode catalyst for oxygen evolution reaction in water splitting reaction according to claim 1, wherein x is in the range of 1 to 4.

4. a) converting a cobalt precursor into cobalt hydroxide by a solvothermal synthesis reaction; b) heat-treating the product of the solvothermal synthesis reaction in an oxygen-containing atmosphere at a first heat-treatment temperature to form a porous amorphous cobalt oxide; c) introducing a precursor of at least one P-block element into the porous amorphous cobalt oxide and heat-treating the porous amorphous cobalt oxide in an inert atmosphere at a second heat-treatment temperature; the porous amorphous cobalt oxide is doped with at least one element selected from the P block elements in an amount of 0.5 to 3 atomic % based on the catalyst; 10. The method for preparing a catalyst, wherein in step c), the precursor of the at least one P block element is a lead (Pb) precursor.

5. The method for producing a catalyst according to claim 4, wherein the solvent of the cobalt precursor solution in the solvothermal synthesis reaction is a mixed solvent containing polyglycol and polyol.

6. The method for preparing a catalyst according to claim 5, wherein the volume ratio of polyglycol to polyol in the solvent is adjusted to a range of 10 to 50:

1.

7. 6. The method for producing a catalyst according to claim 5, wherein the polyglycol is at least one selected from the group consisting of triethylene glycol, diethylene glycol, dipropylene glycol, and tetraethylene glycol.

8. 6. The method for producing a catalyst according to claim 5, wherein the polyol is at least one selected from the group consisting of glycerol, trimethylolpropane, glycerol propoxylate, glycerol ethoxylate, and glycerol trihexanoate.

9. 5. The method for preparing a catalyst according to claim 4, wherein in step a), the concentration of the cobalt precursor in the solvent is adjusted to a range of 50 to 200 mM.

10. 5. The method for preparing a catalyst according to claim 4, wherein step a) is carried out at a temperature controlled in the range of 150 to 250°C.

11. 5. The method of claim 4, wherein the first heat treatment temperature and the second heat treatment temperature are adjusted to a range of 300 to 500°C.

12. 5. The method of claim 4, wherein in step c), the precursor of the P block element is added in the form of a solution, and the concentration thereof is determined to be in the range of 10 to 150 mM.

13. The specific surface area (BET) of the cobalt oxide formed in step b) is 40 to 90 m ２ The method for producing a catalyst according to claim 4, wherein the molar ratio is in the range of / g.

14. 5. The method for producing a catalyst according to claim 4, wherein the inert atmosphere is formed by at least one gas selected from the group consisting of argon, nitrogen, and helium.

15. An oxygen evolution reaction electrode for a water splitting reaction, comprising: an electrode substrate; and a porous amorphous cobalt oxide-based catalyst loaded on the electrode substrate, The porous amorphous cobalt oxide-based catalyst comprises: a porous amorphous cobalt oxide; 0.5 to 3 atomic percent of at least one P-block element as a dopant; Including, 10. An electrode for an oxygen evolution reaction, wherein the at least one P-block element is lead (Pb).

16. The electrode is 10 mA / cm ２ Reference current density, scan rate 10 mVs －１ 16. The electrode for oxygen evolution reaction according to claim 15, which exhibits an overvoltage of 0.4 V (vs. RHE) or less under the conditions of 0.1 M KOH solution (pH 13).

17. The catalyst loading in the electrode is 0.02 to 0.2 mg / cm ２ The electrode for oxygen evolution reaction according to claim 15, wherein the range is:

18. A water splitting system comprising an anode and a cathode as electrochemical electrodes electrically connected to an external power source, and an aqueous medium containing an electrolyte, When a voltage is applied from the external power supply, oxygen is generated on the anode side, while hydrogen is generated on the cathode side; The anode comprises a porous amorphous cobalt oxide-based catalyst loaded on an electrode substrate; The porous amorphous cobalt oxide-based catalyst comprises (i) a porous amorphous cobalt oxide, and (ii) 0.5 to 3 atomic % of at least one P-block element as a dopant; 10. A water splitting system, wherein the at least one P-block element is lead (Pb).

19. The water splitting system according to claim 18, wherein the aqueous medium containing the electrolyte is an alkaline medium or an acidic medium.

20. an anode comprising an electrode substrate; a cathode including a conductive material; an aqueous solution containing an electrolyte; a power source; A porous amorphous cobalt oxide-based catalyst is loaded onto the electrode substrate; The porous amorphous cobalt oxide-based catalyst comprises: a porous amorphous cobalt oxide; The porous amorphous cobalt oxide-based catalyst comprises at least one P-block element in an atomic percentage of 0.5 to 3%; 10. A water splitting system, wherein the at least one P-block element is lead (Pb).

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