ELECTROCATALYST FOR POLYMER ELECTROLYTE MEMBRANE (PEM) WATER ELECTROLYSIS, METHOD OF PREPARING SAME, PEM WATER ELECTROLYSIS ELECTRODE INCLUDING SAME, AND PEM WATER ELECTROLYSIS CELL INCLUDING SAME

Description

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No. 10-2024-0109213 and 10-2024-0154627, filed Aug. 14, 2024 and Nov. 4, 2024 respectively, the entire contents of which are incorporated herein for all purposes by this reference.

BACKGROUND

1. Technical Field

The present disclosure relates to an electrocatalyst for polymer electrolyte membrane (PEM) water electrolysis, a method of preparing the same, a PEM water electrolysis electrode including the same, and a PEM water electrolysis cell including the same.

Two Korean national projects supported by the Korean government associated with this invention are described below.

• • Project Unique Number 1415186363
  • Project Serial Number 20020437
  • Government Department Ministry of Trade, Industry and Energy (MOTIE)
  • Specialized Institution for Project Management Korea Planning & Evaluation of Industrial Technology (KEIT)
  • Title of Research Business Nano-Fusion Innovative Product Technology Development
  • Title of Project Development of Fuel Cell Module Technology for Hydrogen Electric Vehicle Based on Production of Platinum Alloy Nanocatalyst with Platinum Loading of 0.2 g/kW or Less in membrane electrode assembly (MEA)
  • Supervising Institute THE CARBON STUDIO INC.
  • Research Period Jan. 1, 2023, to Dec. 31, 2025
  • Project Unique Number 1415185115
  • Project Ser. No. 20022451
  • Government Department MOTIE
  • Specialized Institution for Project Management KEIT
  • Title of Research Business Material Component and Technology Development—Package Type
  • Title of Project Development of Production Technology for Electrolyte Membrane and Catalyst for PEM Water Electrolysis
  • Supervising Institute CHEMTROS CO., LTD.
  • Research Period Jan. 1, 2023, to Dec. 31, 2025

2. Description of the Related Art

Research and development are actively and newly undertaken in the area of energy, in which electrical energy generated from renewable energy sources, such as solar power, wind power, and tidal power, is used to produce and store hydrogen from water through electrolysis and, when needed, such stored hydrogen is supplied to a fuel cell for use as electrical energy.

Water electrolysis technology, one of the various methods of producing hydrogen, can be divided into alkaline, solid oxide, or PEM water electrolysis. Of all these, PEM water electrolysis technology is characterized by operating at relatively low temperatures and using pure water without involving any corrosive solution, thereby achieving higher hydrogen production efficiency than those in the case of other water electrolysis methods and enabling the production of high-purity hydrogen, which provides economic advantages.

In PEM water electrolysis, there is a need for the development of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts to cause reactions in membrane electrode assembly (MEA), one of the crucial components. In particular, in water electrolysis reactions, oxygen overpotential significantly causes a reduction in efficiency, so the development of novel catalysts capable of reducing the overpotential of OER catalysts is essential for commercialization.

Currently available iridium oxide (IrO₂), a representative OER catalyst, differs in activity and durability depending on oxygen arrangement. Amorphous iridium oxide with irregular oxygen arrangement exhibits excellent catalytic performance, but operates in an acidic atmosphere due to the characteristics of PEM water electrolysis. For this reason, some iridium dissolves in water, and the durability of such a catalyst thus becomes poor. In addition, crystalline iridium oxide exhibits poor dispersion on a carrier due to being prepared at high temperatures, resulting in low catalytic activity, but the durability of such a catalyst is excellent. To achieve both high catalytic activity and durability, IrO₂ needs to be developed into a novel catalyst structure having high dispersion on a carrier, a reduced particle size, and high crystallinity.

In addition, technologies to meet both factors, one being size reduction of physical particles and the other being improved crystallinity of iridium oxide through alloying, have not yet been developed. As a result, existing known catalysts have failed to achieve satisfactory levels of activity and durability, meaning that improvements are required.

SUMMARY

The present disclosure aims to provide a novel electrocatalyst for PEM water electrolysis, the electrocatalyst exhibiting improved OER activity and durability.

In addition, the present disclosure aims to provide a method of preparing the aforementioned electrocatalyst for PEM water electrolysis.

Furthermore, the present disclosure aims to provide a PEM water electrolysis electrode including the aforementioned electrocatalyst for PEM water electrolysis, and a PEM water electrolysis cell including the same.

To achieve the objectives described above, an electrocatalyst for PEM water electrolysis, the electrocatalyst including an iridium-based catalyst, is provided, wherein the iridium-based catalyst is a core-shell particle, the core contains iridium metal, and the shell contains an iridium tin composite oxide.

To achieve another objective, a method of preparing the aforementioned electrocatalyst for PEM water electrolysis is provided, the method including the following steps: dispersing a carrier in a polyol to prepare a carrier dispersion; mixing an iridium precursor and a tin precursor with a polyol to obtain a precursor mixture; mixing the carrier dispersion and the precursor mixture to prepare a first mixture; performing a first heat treatment on the first mixture to prepare a catalyst precursor including iridium metal and tin oxide particles; and performing a second heat treatment in an oxidizing gas atmosphere after washing and drying the catalyst precursor, wherein the iridium precursor and the tin precursor are mixed at a molar ratio in the range of 1:0.33 to 0.50.

The first heat treatment is performed at a temperature in the range of 200° C. to 550° C. In addition, the oxidizing gas atmosphere is, for example, an air atmosphere, an oxygen gas atmosphere, or a combination thereof. The second heat treatment is performed at a higher temperature than the first heat treatment and may be performed at a temperature in the range of 350° C. to 600° C.

To achieve a further objective, a PEM water electrolysis electrode including the aforementioned electrocatalyst for PEM water electrolysis is provided.

To achieve yet another objective, a PEM water electrolysis cell including a PEM and a PEM water electrolysis electrode being positioned on one surface of the PEM, the PEM water electrolysis electrode including the aforementioned electrocatalyst for PEM water electrolysis, is provided.

The electrode may include an anode.

An electrocatalyst for PEM water electrolysis, according to the present disclosure, exhibits improved dispersibility and durability. A PEM water electrolysis electrode, including such an electrocatalyst, exhibits improved OER activity. When using such a water electrolysis electrode, a PEM water electrolysis cell exhibiting improved cell performance can be manufactured.

However, effects of the present disclosure are not limited to those described above and may include other effects that are expected from the technical features of the present disclosure, even if not explicitly described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view schematically illustrating a core-shell structure of an electrocatalyst for PEM water electrolysis according to the present disclosure;

FIG. 2 is a flowchart describing a method of preparing an electrocatalyst for PEM water electrolysis according to the present disclosure;

FIG. 3 shows X-ray diffraction (XRD) spectrum for catalysts according to Examples 1 and 2 and Comparative Examples 1 and 2;

FIGS. 4A, 4B, 4C, 4D, 5A, 5B, 5C and 5D show transmission electron microscopy (TEM) images of catalysts according to Examples 1 and 2 and Comparative Examples 1 and 2, in which FIGS. 4A and 4B are TEM images showing states before and after performing a second heat treatment during an electrocatalyst preparation process in Example 1, respectively, FIGS. 4C and 4D are TEM images showing states before and after performing a second heat treatment during an electrocatalyst preparation process in Example 2, respectively, FIGS. 5A and 5B are TEM images showing states before and after performing a second heat treatment during an electrocatalyst preparation process in Comparative Example 1, respectively, and FIGS. 5C and 5D are TEM images showing states before and after performing a second heat treatment during an electrocatalyst preparation process in Comparative Example 2, respectively;

FIG. 6 is a graph showing changes in voltage as a function of current density in PEM water electrolysis cells provided with electrodes including respective electrocatalysts according to Examples 1 and 2 and Comparative Examples 1 and 2; and

FIG. 7 schematically illustrates a structure of a water electrolysis cell having an MEA for PEM water electrolysis according to the present disclosure.

DETAILED DESCRIPTION

Hereinafter, an electrocatalyst for PEM water electrolysis according to one embodiment, a method of preparing the same, a PEM water electrolysis electrode including the same, and a PEM water electrolysis cell including the same are to be described.

However, the present disclosure may be embodied in many different forms and, therefore, is not limited to the embodiments set forth herein.

In the present disclosure, the median particle diameter refers to “D50”, which denotes the particle diameter at which 50% of the total number of particles is accumulated, with the total number defined as 100%, in a cumulative distribution curve in which the particles are arranged from the smallest to the largest. D50 may be measured by methods widely known to those skilled in the art and may be measured, for example, using a particle size analyzer or through TEM or scanning electron microscopy (SEM) images. As one example of another method of measuring the median particle diameter, the median particle diameter may be easily obtained through calculation by using a measurement device based on dynamic light scattering for measurement and then performing data analysis to count the number of particles for each size range.

In addition, the median particle diameter in the present disclosure may be measured using a scanning electron microscope or a transmission electron microscope.

An electrocatalyst for PEM water electrolysis, according to the present disclosure, may include an iridium-based catalyst, wherein the iridium-based catalyst is a core-shell particle, the core contains iridium metal, and the shell contains an iridium tin composite oxide.

PEM water electrolysis produces hydrogen and oxygen through oxidation and reduction using electrical energy, as shown in Reaction Formulas 1 and 2 below.

Cathode: 4H⁺+4e⁻→2H₂  <Reaction Formula 1>

Anode: 2H₂O→O₂+4H⁺+4e⁻  <Reaction Formula 2>

According to Reaction Formula 1, H⁺ ions produced at the anode move to the cathode through a PEM.

The electrocatalyst for PEM water electrolysis, according to the present disclosure, is an OER catalyst in PEM water electrolysis, wherein the core contains iridium metal, and the shell contains an iridium tin composite oxide. The iridium tin composite oxide may be called an iridium oxide-tin oxide (IrSnO₂) alloy.

The electrocatalyst for PEM water electrolysis may further include a carrier. As the carrier, any material having a structure on which the iridium-based catalyst can be supported is usable.

According to one embodiment, the carrier may include a ceramic support.

Examples of such a ceramic support may include an antimony-doped tin oxide (Sb-doped tin oxide, ATO), alumina (Al₂O₃), titania (TiO₂), zirconia (ZnO₂), or combinations thereof. The carrier, according to one embodiment, is an ATO.

The iridium-based catalyst in the electrocatalyst for PEM water electrolysis may be contained in an amount in the range of 10 to 90 parts by weight, 20 to 90 parts by weight, 20 to 85 parts by weight, 30 to 85 parts by weight, 30 to 80 parts by weight, or 30 to 70 parts by weight, based on 100 parts by weight of the carrier. When the amount of the iridium-based catalyst in the electrocatalyst falls within the aforementioned range, the particle size of the iridium-based catalyst is uniform. In addition, the iridium-based catalyst uniformly exists on the carrier without aggregation and, therefore, exhibits excellent dispersibility and improved durability. Furthermore, the OER activity of the electrocatalyst is improved, and a PEM water electrolysis electrode and cell exhibiting improved durability may be manufactured on this basis.

The carrier has a specific surface area, for example, in the range of 5 to 1000 m²/g, 10 to 800 m²/g, or 20 to 600 m²/g.

The electrocatalyst of the present disclosure forms the core containing iridium metal thereinside to minimize the aggregation of the particles of the iridium-based catalyst within the carrier and improve the dispersibility of the carrier. In addition, a tin oxide (SnO_x) formed on the core is alloyed to increase the crystallinity of the oxide when iridium is oxidized to an iridium oxide (IrO_x), thus obtaining core-shell particles exhibiting improved performance and durability.

The iridium metal may be contained in the core of the electrocatalyst for PEM water electrolysis, according to one embodiment, in an amount in the range of 60 to 76 parts by weight, 62 to 76 parts by weight, 63 to 75 parts by weight, or 65 to 75 parts by weight, based on 100 parts by weight of the entire electrocatalyst for PEM water electrolysis. The iridium tin composite oxide may be contained in the shell in an amount in the range of 24 to 40 parts by weight, 25 to 38 parts by weight, 25 to 37 parts by weight, or 25 to 35 parts by weight, based on 100 parts by weight of the entire electrocatalyst for PEM water electrolysis. When the amount of the iridium metal exceeds the above range, the particle size of the iridium-based catalyst decreases, but the amount of the iridium oxide existing in the shell may be relatively small, resulting in reduced OER activity. In addition, when the amount of the iridium tin oxide in the shell exceeds the above range, the OER activity of the iridium oxide increases, but the dispersion of the particles may become poor, resulting in reduced activity and durability.

The iridium tin composite oxide of the shell, which is the outermost layer of the electrocatalyst, is a composite containing an iridium oxide and a tin oxide, and tin may be contained in the iridium tin composite oxide in an amount in the range of 33 to 50 moles, 34 to 48 moles, 35 to 45 moles, 37 to 45 moles, or 39 to 45 moles, based on 100 moles of iridium. When the amount of the tin falls below the aforementioned range, the crystallinity of the iridium oxide may decrease, resulting in reduced OER activity of the electrocatalyst. In addition, when the amount of the tin exceeds the aforementioned range, the amount of the iridium oxide, showing activity on the surface, may be small, resulting in reduced OER activity of the electrocatalyst.

The iridium tin composite oxide of the shell, according to one embodiment, is the composite containing the iridium oxide and the tin oxide, and the tin oxide is contained in the composite in an amount in the range of 33 to 50 parts by weight, 34 to 48 parts by weight, 35 to 45 parts by weight, 37 to 45 parts by weight, or 39 to 45 parts by weight, based on 100 parts by weight of the iridium oxide. When the amount of the tin oxide falls the within range, the above electrocatalyst for PEM water electrolysis exhibits improved OER activity and durability.

According to another embodiment, the iridium tin oxide existing in the shell may further contain a metal dopant. Examples of such a dopant include Sb, Nb, Ta, Bi, W, In, or combinations thereof. The metal dopant may be contained in an amount of 10 parts by weight or less, of 5 parts by weight or less, or in the range of 0.01 to 5 parts by weight, based on 100 parts by weight of the iridium tin oxide. By including this metal dopant, the electrocatalyst may exhibit improved electrical conductivity.

The catalyst for PEM water electrolysis, according to the present disclosure, may improve the dispersibility of the particles of the catalyst having a core-shell structure within the carrier by the iridium metal existing thereinside and thus physically increase the catalytic activity by reducing the particle size. In addition, the iridium tin composite oxide catalyst existing on the surface may significantly increase the crystallinity of the iridium oxide, the chemical activity of which is excellent. Therefore, when using the electrocatalyst according to the present disclosure, both catalytic activity and durability may be achieved at the same time.

The iridium-based catalyst having the core-shell structure may have a median particle diameter in the range of 1 nm to 20 nm. In this case, the median particle diameter of the core particle may be in the range of 0.5 nm to 10 nm or 1 nm to 10 nm. When the median particle diameter of the iridium-based catalyst and the median particle diameter of the core particle fall within the above respective ranges, an electrocatalyst exhibiting improved OER activity and durability may be prepared.

FIG. 1 schematically illustrates the structure of the electrocatalyst for PEM water electrolysis according to one embodiment.

The electrocatalyst 10 has a structure including a core 11 and a shell 12 positioned on the core 11. The core 11 may contain iridium metal, and the shell 12 may contain an iridium tin composite oxide. The electrocatalyst may have a structure as illustrated in FIG. 1, but the median particle diameter of the core and the thickness of the shell are not limited to those illustrated in FIG. 1.

The electrocatalyst of the present disclosure may include, for example, a compound represented by Chemical Formula 1 below.

In Chemical Formula 1, 0.67≤x≤0.75.

In the compound of Chemical Formula 1, iridium exists as a tetravalent cation, and tin also exists as a tetravalent cation.

Examples of the compound of Chemical Formula 1 may include Ir_0.67Sn_0.33O₂, Ir_0.75S_0.25O₂, or a combination thereof. In the XRD spectrum for the electrocatalyst for PEM water electrolysis according to the present disclosure, a multiplet peak (first peak) appears at a diffraction angle 2θ in the range of 26.6° to 28°, and a singlet peak (second peak) appears at a diffraction angle 2θ in the range of 40.5° to 40.9°, in the range of 40.6° to 40.8°, or of 40.7°. In the present disclosure, the first peak is a peak related to the iridium tin composite oxide (IrSnO_x), while the second peak is a peak related to iridium in the core.

According to another embodiment of the present disclosure, a method of preparing an electrocatalyst for PEM water electrolysis, the electrocatalyst including an iridium-based catalyst, is provided.

This method includes the following steps: dispersing a carrier in a polyol to prepare a carrier dispersion; mixing an iridium precursor and a tin precursor with a polyol to obtain a precursor mixture; mixing the carrier dispersion and the precursor mixture to prepare a first mixture; performing a first heat treatment on the first mixture to prepare a catalyst precursor including iridium metal and tin oxide particles; and performing a second heat treatment in an oxidizing gas atmosphere after washing and drying the catalyst precursor.

Hereinafter, the method of preparing the electrocatalyst for PEM water electrolysis, according to the present disclosure, is to be described in more detail with reference to FIG. 2.

First, a carrier is dispersed in a polyol to prepare a carrier dispersion.

In this case, the polyol may be contained in an amount in the range of 100 to 1,000 parts by weight or 200 to 400 parts by weight, with respect to 1 part by weight of the carrier. When the amount of the polyol falls within the above range, the carrier may be dispersed uniformly in the polyol, thus carrier dispersion exhibiting excellent obtaining a dispersibility. Such a dispersion process may be performed through physical methods using homogenizers, ultrasonic devices, and the like. When the amount of ceramic is large without falling within the above range or when the amount of the polyol is small, ceramic particles, serving as a support, are likely to form a lump and aggregate. In addition, when the amount of ceramic in the carrier is small or when the amount of the polyol is large, the reaction processability rather deteriorates, making it difficult to demonstrate the intended effect of the present disclosure.

The polyol may, for example, be one or more selected from the group consisting of ethylene glycol (EG), propylene glycol, diethylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, 2,4-diethyl-1,5-pentanediol, 1,2-hexanediol, and glycerol. For example, EG, which is inexpensive, is easily oxidized to glycolaldehyde at high temperatures, and has strong reducing power, may be used as the polyol.

Separately, a step of mixing an iridium precursor and a tin precursor with a polyol to obtain a precursor mixture is performed.

The iridium precursor and the tin precursor are mixed at a molar ratio in the range of 1:0.33 to 1:0.50, 1:0.35 to 1:0.48, or 1:0.37 to 1:0.45. When the iridium precursor and the tin precursor are mixed at a molar ratio that falls within the above range, an electrocatalyst having a core-shell structure while exhibiting improved activity may be prepared. When the iridium precursor and the tin precursor are mixed at a molar ratio that does not fall within the above range, an Ir-SnO₂ or IrSnO₂ composite may be formed, making it impossible to prepare the desired catalyst having a core-shell structure.

When preparing the precursor mixture, the polyol used may be contained in an amount, for example, in the range of 10 to 1000 parts by weight or 200 to 400 parts by weight of the polyol, based on 1 part by weight of the total weight of the iridium and tin precursors. In the step of obtaining the precursor mixture, physical methods may be performed using homogenizers, ultrasonic devices, and the like to obtain a precursor mixture having a uniform composition.

Examples of the iridium precursor used may include iridium nitrate, iridium sulfate, iridium chloride, and hexachloroiridic acid (Cl₆H₁₄IrO₆; H₂IrCl₆·6H₂O), and examples of the tin precursor used may include tin chloride and tin sulfate.

The carrier dispersion and the precursor mixture, obtained by the above processes, are mixed to prepare a first mixture. In this case, the carrier dispersion and the precursor mixture may be stoichiometrically controlled to obtain the desired composition of the electrocatalyst.

Subsequently, a first heat treatment is performed on the first mixture obtained by the above process to prepare Catalyst precursor A including iridium metal and tin oxide particles.

The first heat treatment is performed at a temperature in the range of 200° C. to 550° C., 230° C. to 500° C., or 250° C. to 400° C. When the first heat treatment is performed at a temperature below 200° C. or above 550° C., the formation of the desired Catalyst precursor A is difficult.

After washing and drying Catalyst precursor A above, a second heat treatment may be performed to obtain the electrocatalyst of the present disclosure.

The second heat treatment is performed at a higher temperature than the first heat treatment.

The second heat treatment is performed in an oxidizing gas atmosphere and may be performed at a temperature in the range of 350° C. to 600° C., 350° C. to 550° C., or 350° C. to 450° C. When the temperature of the second heat treatment is below 350° C., the Ir—SnO₂ composite may exist, resulting in reduced activity. In addition, when the temperature exceeds 600° C., the electrocatalyst made of the IrSnO₂ composite, other than the electrocatalyst structure having the core-shell structure of the present disclosure, may be formed, resulting in performance degradation of a PEM water electrolysis electrode when using this catalyst.

Examples of the oxidizing gas atmosphere may include an oxygen atmosphere or an air atmosphere. When the second heat treatment is performed in an inert gas atmosphere other than the oxidizing gas atmosphere, the electrocatalyst made of the IrSnO₂ composite, other than the electrocatalyst structure having the core-shell structure of the present disclosure, may resulting in performance degradation of the be formed, electrocatalyst.

The polyol used in the method of preparing the electrocatalyst for PEM water electrolysis serves as both a solvent and a reducing agent and may reduce the metal precursors.

According to a further embodiment, a PEM water electrolysis electrode including an anode including the electrocatalyst of the present disclosure is provided. In this case, the water electrolysis electrode may be, for example, the anode.

According to yet another embodiment, a water electrolysis cell including a PEM and a PEM water electrolysis electrode including the electrocatalyst of the present disclosure is provided.

The water electrolysis cell may include an MEA.

The PEM water electrolysis cell, according to the present disclosure, includes one or more MEAs, and the MEA may have a structure as illustrated in FIG. 7.

Referring to FIG. 7, the MEA for PEM water electrolysis has a structure in which a cathode 100 and an anode 200 are positioned on two opposing surfaces of a PEM 300, respectively.

The anode 200 may include the electrocatalyst of the present disclosure as an electrocatalyst. This electrocatalyst is an OER-promoting material.

The cathode 100 includes a cathode catalyst, which is an HER-promoting material in the PEM water electrolysis cell. As the cathode catalyst, one, or a mixture of two or more selected from the group consisting of platinum, ruthenium, iridium, osmium, palladium, a platinum-ruthenium alloy, a platinum-osmium alloy, a platinum-palladium alloy, and oxides thereof may be used. As the cathode catalyst, platinum-coated carbon powder (Pt/C) may be, for example, used.

The cathode 100 and the anode 200 may each independently contain an ionomer. Examples of the ionomer, which is a polymer with proton conductivity, may include polytetrafluoroethylene (PTFE), a polymer represented by Chemical Formula 2, a polymer represented by Chemical Formula 3, a polymer represented by Chemical Formula 4, or combinations thereof.

In Chemical Formula 2, m is a natural number.

In Chemical Formula 3, p is a natural number.

In Chemical Formula 4, n is a natural number.

The polymer represented by Chemical Formula 2 is a polymer composed of a PTFE backbone as a main chain and perfluoropolyether pendant side chains having sulfonic acid groups at the termini. The equivalent weight (EW) (mass of polymer required to supply 1 mole of protons) of this polymer is not limited but is, for example, in the range of 900 to 1200 g/mol. In Chemical Formula 2, m has each range that is calculatable from the EW.

Examples of ion-conducting polymers of Chemical Formula 2 used may include Nafion (EW: 1100 g/mol, the average of m in Chemical Formula 2 is 6.6).

The polymer represented by Chemical Formula 2 or 3 is a polymer composed of a PTFE backbone in a main chain and perfluoropolyether pendant side chains having sulfonic acid groups at the termini. The EW (mass of polymer required to supply 1 mole of protons) of this polymer is not limited but is, for example, in the range of 700 to 9500 g/mol. In Chemical Formula 3 or 4, p and n have each range that is calculatable from the EW.

Examples of ion-conducting polymers of Chemical Formula 3 or 4 may include 3M ionomers purchased from 3M Corporation.

The PEM 300 refers to a membrane formed of a polymer having a cation exchange group capable of delivering hydrogen ions. The PEM 300, a material positioned between the anode and the cathode in the PEM water electrolysis cell, acts as a passage through which hydrogen ions move and may include a fluorine-based polymer or a hydrocarbon-based polymer. Examples of the hydrocarbon-based polymer may include sulfonated polysulfone, sulfonated polyethersulfone, sulfonated polyetherketone, sulfonated polyetheretherketone, sulfonated polyaryleneetheretherketone, sulfonated polyaryleneethersulfone, sulfonated polyaryletherbenzimidazole, and mixtures thereof. In addition, examples of the fluorine-based polymer may include polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), PTFE, fluorinated ethylene-propylene (FEP), or mixtures thereof.

As the PEM, Nafion (DuPont, United States), a representative fluorine-based polymer, may be used.

A method of manufacturing the MEA for PEM water electrolysis, according to the present disclosure, is to be described.

First, a composition for anode formation is prepared by mixing the electrocatalyst for PEM water electrolysis of the present disclosure, serving as an anode catalyst, ionomers, and a solvent. Then, a substrate is coated with the composition and then dried to manufacture an anode.

Separately, composition for cathode formation is prepared using a cathode catalyst, ionomers, and a solvent. Then, a substrate is coated with the composition and then dried to manufacture a cathode.

When manufacturing the cathode and the anode, coating of each of the compositions for cathode formation and anode formation may be performed by one method selected from the group consisting of spray coating, screen printing, tape casting, brushing, printing, and slot die casting.

The cathode and the anode are stacked on two opposing surfaces of a PEM, respectively, to manufacture the MEA. By stacking one or more MEAs, the PEM water electrolysis cell may be manufactured.

Hereinafter, the present disclosure is to be described in detail through examples. However, the following examples are disclosed only to illustrate the present disclosure, and the content of the present disclosure is not limited thereto.

(Preparation of Electrocatalyst)

Example 1

A carrier dispersion was prepared by ultrasonically mixing 0.75 g of ATO (47.2 m²/g, purchased from Sigma-Aldrich) with 350 g of EG at high speed for 30 minutes.

A catalyst particle precursor solution was prepared by mixing 20.60 g of an aqueous iridium precursor solution (5 wt % of H₂IrCl₆·xH₂O, purchased from TMI Chem. Co.) and 1.88 g of a tin precursor solution (20 wt % of SnCl₂·2H₂O in EG, Sigma-Aldrich). The molar ratio at which the iridium precursor and the tin precursor were mixed was 1:0.33

The carrier dispersion and the catalyst particle precursor solution were mixed. Then, the resulting mixture was placed in an autoclave reactor equipped with a stirrer, followed by raising the reactor temperature to approximately 250° C., thereby conducting a first heat treatment to perform a reduction reaction. Upon completion of the reduction reaction, filtration and washing processes were repeatedly performed to obtain a slurry, which was then freeze-dried to prepare a catalyst precursor.

A second heat treatment was performed on the catalyst precursor in a furnace at a temperature of 450° C. in an air gas atmosphere for 6 hours to obtain an electrocatalyst (Ir@IrSnO₂-1).

The total composition, including both the core and shell, is represented by Ir_0.75Sn_0.25O₂.

Example 2

An electrocatalyst (Ir@IrSnO₂-2) was prepared by performing the same method as in Example 1, except for mixing 18.98 g of the aqueous iridium precursor solution (5 wt % of H₂IrCl₆·xH₂O, purchased from TMI Chem. Co.) and 2.60 g of the tin precursor solution (20 wt % of SnCl₂·2H₂O in EG, purchased from Sigma-Aldrich). The molar ratio at which the iridium precursor and the tin precursor were mixed was 1:0.5. The total composition, including both the core and shell, is represented by Ir_0.67Sn_0.33O₂.

Example 3

An electrocatalyst (Ir@IrSnO₂-3) was obtained by performing the same method as in Example 1, except for changing the molar ratio at which the iridium precursor and the tin precursor were mixed to 1:0.4.

Example 4

An electrocatalyst (Ir@IrSnO₂-4) was obtained by performing the same method as in Example 1, except for changing the molar ratio at which the iridium precursor and the tin precursor were mixed to 1:0.45.

Comparative Example 1

An electrocatalyst (IrO₂) was prepared by performing the same method as in Example 1, except for adding 24.85 g of the aqueous iridium precursor solution (5 wt % of H₂IrCl₆·xH₂O, purchased from TMI Chem. Co.) without the tin precursor solution. The molar ratio at which the iridium precursor and the tin precursor were mixed was 1:0.

Comparative Example 2

An electrocatalyst (IrSnO₂) was prepared by performing the same method as in Example 1, except for mixing 15.36 g of the aqueous iridium precursor solution (5 wt % of H₂IrCl₆·xH₂O, purchased from TMI Chem. Co.) and 4.21 g of the tin precursor solution (20 wt % of SnCl₂·2H₂O in EG, purchased from Sigma-Aldrich). The molar ratio at which the iridium precursor and the tin precursor were mixed was 1:1.

Comparative Example 3

An electrocatalyst (Ir—SnO₂ composite) was obtained by performing the same method as in Example 1, except for performing the second heat treatment on the catalyst precursor in a nitrogen gas atmosphere.

Such a prepared electrocatalyst obtained the Ir—SnO₂ composite by performing the method according to Comparative Example 3. This composite did not have a core-shell structure but was in the form of a compound having a single composition.

The molar ratios at which the iridium precursor and the 5 tin precursor, used when preparing the electrocatalysts of Examples 1 and 2 and Comparative Examples 1 and 2, were mixed, and the compositions of the ultimately obtained electrocatalysts are as shown in Table 1 below.

TABLE 1
	Molar ratio at which
	iridium precursor
	and tin precursor
Classification	are mixed	Composition
Example 1	1:0.333	Amount of iridium in
(Ir@IrSnO2-1)		core: 76 parts by weight
		Amount of IrSnOX in shell:
		24 parts by weight
		Weight ratio of iridium
		oxide to tin oxide in
		IrSnOX = 1:0.333
		Amount of iridium-based
		catalyst: 67 parts by
		weight based 100 parts by
		weight of carrier
Example 2	1:0.5	Amount of iridium in core:
(Ir@IrSnO2-2)		60 parts by weight
		Amount of IrSnOX in shell:
		40 parts by weight
		Weight ratio of iridium
		oxide to tin oxide in
		IrSnOX = 1:0.5
		Amount of iridium-based
		catalyst: 63 parts by
		weight based 100 parts by
		weight of carrier
Comparative	1:0	Amount of iridium in
Example 1		core: 0 parts by weight
(IrO2)		Amount of amorphous IrO2
		in shell: 100 parts by
		weight
		Amount of iridium-based
		catalyst: 68 parts by
		weight based 100 parts by
		weight of carrier
Comparative	1:1	Weight ratio of iridium
Example 2		oxide to tin oxide = 1:1
(IrSnO2)		Amount of iridium-based
		catalyst: 65 parts by
		weight based 100 parts by
		weight of carrier

(Manufacture of PEM Water Electrolysis Cell)

Manufacture Example 1

A slurry in which 0.5 g of the electrocatalyst (Ir@IrSnO₂-1) of Example 1, 2.2 g of water, 2.2 g of dipropylene glycol, and 0.27 g of a 20% Nafion dispersion were mixed was prepared. Then, a PTFE film was coated with the slurry and dried, thereby manufacturing an anode as an electrode layer.

In addition, a cathode was manufactured as an electrode layer in the same manner as the anode, serving as the electrode layer, by preparing a slurry using 20 wt % of Pt/C, followed by coating a PTFE film with the slurry and then drying.

A cation exchange membrane (Nafion 115) was stacked on the upper portion of the cathode, and the anode (OER electrode) was stacked on the cation exchange membrane to make the catalyst surface of the anode contact therewith. Then, an MEA was manufactured by performing heat fusion under the following conditions: a temperature of 165° C., a pressure of 20 bar, and a duration of 10 minutes. The MEA was placed in a unit cell having a flow field, and a titanium porous transport layer (Ti-PTL) was stacked on the anode side to manufacture the final MEA, which was then coupled to manufacture a PEM water electrolysis unit cell.

Manufacture Examples 2 to 4

MEAs and water PEM electrolysis unit cells were manufactured by performing the same method as in Manufacture Example 1, except for using the respective electrocatalysts of Examples 2 to 4 instead of the electrocatalyst of Example 1.

Comparative Manufacture Example 1

An MEA and a PEM water electrolysis unit cell were manufactured by performing the same method as in Manufacture Example 1, except for using the electrocatalysts of Comparative Example 1 instead of the electrocatalyst of Example 1.

Comparative Manufacture Example 2

An MEA and a PEM water electrolysis unit cell were manufactured by performing the same method as in Manufacture Example 1, except for using the electrocatalysts of Comparative Example 2 instead of the electrocatalyst of Example 1.

Evaluation Example 1: XRD Analysis

To confirm the crystallographic information of the electrocatalyst for PEM water electrolysis in Examples 1 and 2 and Comparative Examples 1 and 2, XRD analysis (Rigaku DMAX-33) was performed using Cu Kα radiation at a diffraction angle 2θ in the range of 10° to 80°. The analysis results thereof are shown in FIG. 3.

According to FIG. 3, the catalysts of Examples 1 and 2 show diffraction peaks corresponding to Ir metal, IrSnO₂, and the ATO carrier, and in particular, IrSnO₂ shows excellent crystallinity.

In the XRD spectrum for the electrocatalysts, a multiplet peak appeared at a diffraction angle 2θ in the range of 26.6° to 28°, and a singlet peak appeared at a diffraction angle 2θ in the range of 40.5° to 40.9°. The multiplet peak is a peak related to the IrSnO_x composite, while the singlet peak is a peak related to iridium in the core of the electrocatalyst.

On the other hand, in the case of the catalyst (IrO₂) of Comparative Example 1, free of tin, the iridium oxide (IrO_x) was not crystalline, and no Ir metal peaks were observed. In addition, in the case of the catalyst (IrSnO₂) of Comparative Example 2, the amount of Sn was large, and it was seen that the core of the catalyst had an Ir metal-free IrSnO₂ (crystalline) composite structure.

Evaluation Example 2: TEM Analysis

TEM analysis was performed on the electrocatalysts according to Examples 1 and 2 and Comparative Examples 1 and 2. The TEM analysis results are shown in FIGS. 4A, 4B, 4C, 4D, 5A, 5B, 5C, and 5D. In this case, FIGS. 4A, 4C, 5A, and 5C are TEM images showing the states before the second heat treatment in Example 1, Example 2, Comparative Example 1, and Comparative Example 2, respectively. In addition, FIGS. 4B, 4D, 5B, and 5D are TEM images showing the states after the second heat treatment in Example 1, Example 2, Comparative Example 1, and Comparative Example 2, respectively.

Referring to FIGS. 4A, 4B, 4C, 4D, 5A, 5B, 5C and 5D, the electrocatalysts of Examples 1 and 2 exhibited improved dispersion compared to the electrocatalysts of Comparative Examples 1 and 2.

Evaluation Example 3: Water Electrolysis Performance Evaluation

The PEM water electrolysis electrodes were manufactured using the electrocatalysts of Examples 1 and 2 and Comparative Examples 1 and 2, which were then used to manufacture the PEM water electrolysis MEAs of Manufacture Examples 1 and 2 and Comparative Manufacture Examples 1 and 2, and the PEM water electrolysis cells including the respective PEM water electrolysis MEAs. The cell voltage as a function of current density, demonstrating the electrochemical effect of such PEM water electrolysis cells, was measured to evaluate water electrolysis performance.

A graph showing the voltage (V) and current (A) measured through the evaluation is shown in FIG. 6, the results of which are shown in Table 2 below.

	TABLE 2
		Current density (mA/cm2)
	Classification	at 1.7 V and 80° C.

	Example 1	1.71
	Example 2	2.01
	Comparative Example 1	0.78
	Comparative Example 2	0.81

Referring to Table 1 and FIG. 6, it is confirmed that the water electrolysis cells having the PEM water electrolysis electrodes using the catalysts of Examples 1 and 2 at 1.7 V exhibit improved current density, compared to the water electrolysis cells having the electrodes using the electrocatalysts of Comparative Examples 1 and 2 at the same voltage.

In addition, the PEM water electrolysis electrodes were manufactured using the electrocatalysts of Examples 3 and 4, which were then used to manufacture the PEM water electrolysis MEAs of Manufacture Examples 3 and 4, and the PEM water electrolysis cells including the respective PEM water electrolysis MEAs. The water electrolysis performance of such PEM water electrolysis cells was evaluated by the same method as the water electrolysis cell of the Manufacture Example 1.

The evaluation results confirmed that the water electrolysis cells of Manufacture Examples 3 and 4 achieved water electrolysis performance comparable to that of the water electrolysis cell of Manufacture Example 1.

Although the preferred embodiments of the present disclosure have been described in detail hereinabove, the scope of the present disclosure is not limited thereto. That is, various modifications and alternatives made by those skilled in the art using a basic concept of the present disclosure as defined in the appended claims fall within the scope of the present disclosure.