KR102580930B1 - Catalyst for oxygen evolution comprising transition metal oxide and nickel oxide, preparation method thereof, and batterfy for water electrolysis using the same - Google Patents

Abstract

The present invention relates to a catalyst for oxygen evolution reaction containing a transition metal oxide and nickel oxide, a method for manufacturing the same, and a water electrolysis cell using the same. The catalyst for oxygen evolution reaction is prepared by mixing a nickel precursor and a transition metal oxide in a solid phase. By manufacturing by heat treatment, the particle size of the catalyst is reduced due to the template effect, and the activity of the catalyst for the oxygen evolution reaction can be increased by having a larger specific surface area. When manufacturing the catalyst for the oxygen evolution reaction, the catalyst can be adjusted according to the heat treatment temperature. stability can be improved.

Description

Catalyst for oxygen evolution reaction comprising transition metal oxide and nickel oxide, preparation method thereof, and water electrolysis battery using the same

The present invention relates to a catalyst for oxygen evolution reaction containing transition metal oxide and nickel oxide and excellent catalytic activity and stability, and a method for producing the same.

Hydrogen is a clean energy source that overcomes serious environmental problems and is attracting attention as it will become a source of future energy. Most hydrogen is still supplied through reforming and by-product hydrogen, so carbon compounds are emitted, but the water electrolysis method has the advantage of producing green hydrogen and producing no by-products. If electricity generated by renewable energy is stored as hydrogen through water electrolysis, clean and high-purity hydrogen can be obtained without generating carbon. However, it still has the disadvantage of low economic feasibility due to the high production cost. This can be overcome by reducing overvoltage and lowering production costs. The electrolysis reaction of water consists of an oxygen evolution reaction and a hydrogen evolution reaction, and at this time, the standard reduction potential difference of 1.23 V vs. 1.23 V vs. The value minus RHE is called overvoltage. To increase the efficiency of hydrogen generation, it is necessary to increase the activity of the oxygen generation reaction because the overvoltage required for the oxygen generation reaction is more than 15 times greater than the hydrogen generation reaction. Transition metal oxides, a representative oxygen evolution reaction catalyst, are inexpensive, but have high overvoltage and low stability. On the other hand, precious metal oxides have excellent activity and stability, but their price is very high, which increases the production cost.

Republic of Korea Patent Publication No. 10-2007-00032358 (published on March 21, 2007)

The purpose of the present invention is to provide a catalyst for oxygen evolution reaction that exhibits excellent catalytic activity and high stability while reducing the amount of transition metal oxide used, a method for manufacturing the same, and a water electrolysis battery using the same.

In order to achieve the above object, the present invention includes the steps of mixing a nickel precursor and a transition metal oxide in a solid phase to prepare a mixture; And heat-treating the prepared mixture in an oxygen atmosphere in a furnace at a temperature of 250°C to 700°C for 2 to 10 hours, wherein the nickel precursor is at least one of nickel hydroxide, nickel chloride, nickel nitrate and acetate nitrate. A method for producing a catalyst for oxygen evolution reaction comprising one or more catalysts is provided.

In addition, the present invention includes nickel oxide and a transition metal oxide, the nickel oxide and transition metal oxide have a porous surface, the average particle size of the transition metal oxide is 1 to 4.5 nm, and the average particle size of the nickel oxide is 1 to 4.5 nm. A catalyst for oxygen evolution reaction having a particle size of 10 to 25 nm is provided.

In addition, the present invention includes an electrode containing the catalyst for the oxygen generation reaction described above; and a reference electrode.

The catalyst for the oxygen evolution reaction according to the present invention is manufactured by mixing a nickel precursor and a transition metal oxide in a solid phase and then heat treating it, thereby reducing the particle size of the catalyst due to the template effect and having a larger specific surface area, making it a catalyst for the oxygen evolution reaction. can increase the activity of.

In addition, the catalyst for oxygen generation reaction according to the present invention can improve the stability of the catalyst depending on the heat treatment temperature during production.

Figure 1 is an image schematically illustrating a method for manufacturing a catalyst for oxygen generation reaction according to the present invention.
Figure 2 is a transmission electron microscope (TEM) image of the catalyst for oxygen generation reaction according to the present invention and the catalyst of the comparative example.
Figure 3 shows the results of BET (Brunauer-Emmett-Teller) analysis of the catalyst for oxygen generation reaction according to the present invention and the catalyst of the comparative example.
Figure 4 shows a graph (a) of the results of analyzing the catalyst for the oxygen evolution reaction according to the present invention and the catalyst of the comparative example by linear sweep voltammetry (LSV) and a graph (a) of the results of analysis by chronopotentiometry ( b).
Figure 5 is a graph showing the active area of the catalyst through slope as analyzed by cyclic voltammetry (CV) for the catalyst for oxygen generation reaction according to the present invention and the catalyst of the comparative example.
Figure 6 is a graph showing the results of analyzing the catalyst for oxygen generation reaction according to the present invention using linear sweep voltammetry (LSV), showing different types of precursors for catalyst production.
Figure 7 is a graph showing the results of analyzing the catalyst for oxygen generation reaction according to the present invention by linear sweep voltammetry (LSV), with different ratios of nickel precursor and transition metal oxide for catalyst production.

Hereinafter, in order to explain the present invention in more detail, preferred embodiments according to the present invention will be described in more detail with reference to the attached drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms.

The present invention includes the steps of mixing a nickel precursor and a transition metal oxide in a solid phase to prepare a mixture; and heat-treating the prepared mixture in an oxygen atmosphere in a furnace at a temperature of 250°C to 700°C for 2 to 10 hours.

The nickel precursor includes at least one of nickel hydroxide, nickel chloride, nickel nitrate, and nitrate acetate. Specifically, the nickel precursor may be nickel hydroxide, nickel chloride, nickel nitrate, or nitrate acetate, and more specifically, the nickel precursor may be nickel hydroxide. By using the above nickel precursor, excellent catalytic activity can be exhibited.

The transition metal oxides include iridium (Ir), niobium (Nb), cobalt (Co), titanium (Ti), vanadium (V), manganese (Mn), zirconium (Zr), rhodium (Rh), tungsten (W), It contains at least one oxide of tantalum (Ta), osmium (Os), rhenium (Re), and molybdenum (Mo). Specifically, the transition metal oxide may include at least one oxide of iridium (Ir), niobium (Nb), cobalt (Co), titanium (Ti), vanadium (V), manganese (Mn), and zirconium (Zr). Can be, and more specifically, the transition metal oxide can be iridium oxide.

In preparing the mixture, the nickel precursor and the transition metal oxide may be mixed at a molar ratio of 1:1 to 7:1. The nickel oxide and the transition metal oxide may be mixed at a molar ratio of 1:1 to 3:1 or 1:1 to 1.5:1.

The heat treatment step is to heat the prepared mixture in a furnace at a temperature of 250°C to 700°C, and the heat treatment step is to heat the mixture in a furnace at a temperature of 350°C to 700°C or 500°C to 650°C for 2 to 10 hours. It can be performed by heat treatment under an oxygen atmosphere.

By mixing nickel oxide and transition metal oxide in the same ratio as above and heat-treating, the different compounds interfere with each other's particle growth due to the template effect, thereby reducing the size of the particles, thereby producing oxygen by producing a catalyst with a high non-porous area. The reaction catalyst may have improved oxygen reduction reaction activity.

Additionally, the present invention provides a catalyst for oxygen evolution reaction containing nickel oxide and transition metal oxide.

The catalyst for oxygen evolution reaction of the present invention may be manufactured using the method for producing the catalyst for oxygen evolution reaction described above.

Specifically, in the catalyst for oxygen generation reaction according to the present invention, the nickel oxide and the transition metal oxide are each provided in the form of particles, and the particles of the nickel oxide and the transition metal oxide may independently have a surface with a porous structure. .

The average particle size of the transition metal oxide may be 1 to 4.5 nm, and the average particle size of the nickel oxide may be 10 to 25 nm. Specifically, the average particle size of the transition metal oxide may be 2 to 4.5 nm, 2.5 to 4.5 nm, or 3 to 4 nm, and the average particle size of the nickel oxide may be 10 to 23 nm, 12 to 20 nm, or 12 to 18 nm. The average particle size of the oxide is much smaller than that in the case of heat treatment of a single material under the same temperature conditions, and by including a transition metal oxide and nickel oxide having the same particle size, the catalyst for the oxygen generation reaction of the present invention has a high active surface area and can exhibit excellent catalytic activity.

The transition metal oxides include iridium (Ir), niobium (Nb), cobalt (Co), titanium (Ti), vanadium (V), manganese (Mn), zirconium (Zr), rhodium (Rh), tungsten (W), It contains at least one oxide of tantalum (Ta), osmium (Os), rhenium (Re), and molybdenum (Mo). Specifically, the transition metal oxide may include at least one oxide of iridium (Ir), niobium (Nb), cobalt (Co), titanium (Ti), vanadium (V), manganese (Mn), and zirconium (Zr). Can be, and more specifically, the transition metal oxide can be iridium oxide.

By including the transition metal oxide as described above, the oxygen reduction reaction activity and durability of the catalyst for oxygen generation reaction of the present invention can be improved.

In the catalyst for the oxygen evolution reaction, the nickel oxide and transition metal oxide may be included in a molar ratio of 1:1 to 7:1. The nickel oxide and transition metal oxide may be included in a molar ratio of 1:1 to 3:1 or 1:1 to 1.5:1. By including nickel oxide and transition metal oxide in the above ratio, improved oxygen reduction reaction activity can be exhibited.

The catalyst for oxygen evolution reaction of the present invention may have a BET specific surface area of 20 to 80 m ² /g. Specifically, the catalyst for the oxygen generation reaction may have a BET specific surface area of 20 to 80 m ² /g or 20 to 80 m ² /g.

In addition, the catalyst for the generation reaction of the present invention was measured at 10 mA/cm ² at 1.25 ~ 1.65 V and measured at 1.23 V vs. When measuring overvoltage by subtracting RHE, the overvoltage increase rate can be 3% to 10% compared to the initial overvoltage. Specifically, the overvoltage increase rate of the catalyst for the generation reaction may be 3% to 9.5%, 3% to 7%, or 3% to 5% compared to the initial overvoltage.

In addition, the catalyst for the generation reaction of the present invention is 0.8 - 1.0 V vs. The active area can be 0.004 to 0.01 F or 0.005 to 0.0099 F by measuring double-layer capacitance (Cdl) through cyclic voltammetry at various scan rates in RHE. Through this, it can be seen that the catalyst for generation reaction according to the present invention has a large active area.

In addition, the present invention provides a water electrolysis cell including an electrode containing the catalyst for oxygen generation reaction described above and a reference electrode.

The water electrolysis cell not only increases the activity of the oxygen reduction reaction in the fuel cell by including the catalyst for the oxygen generation reaction of the present invention in the electrode, but also reduces the performance of the fuel cell from deterioration compared to the initial stage even when charging and discharging are repeated several times. The ratio can be significantly reduced.

The water electrolysis cell includes an anion exchange membrane, electrodes (cathode and anode), a separator, a gasket, a current collector, and a reference electrode.

In a water electrolysis electrode, the electrode is where the actual electrochemical reaction occurs, and a voltage-dependent reaction occurs to produce oxygen and hydrogen. The anion exchange membrane serves to allow the reaction to occur through the movement of ions when a water electrolysis reaction occurs and to block electricity so that it does not directly pass from one electrode to another. The separator plate makes an electrical connection to the electrode and at the same time has a flow path that allows the reactant water to flow easily, thereby reducing material resistance. The gasket fixes the electrode and supports it so that the electrode can receive appropriate pressure. The current collector serves to allow electricity to pass through the electrical conductors and the separator plate. Lastly, the reference electrode was introduced because it is difficult to know the actual voltage at each electrode because there are only two electrodes in existing electrochemical cells, and is used to measure the absolute voltage of each electrode.

Hereinafter, the present invention will be described in detail through examples to aid understanding. However, the following examples only illustrate the content of the present invention and the scope of the present invention is not limited to the following examples. Examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

< Example 1> high law using heat treatment NiO / IrO ₂ -350 Catalyst Manufacturing

First, nickel precursors, nickel hydroxide (Ni(OH) ₂ ) and iridium oxide (IrO ₂ ) were mixed at a molar ratio of 1:1 and mixed in solid phase for 30 minutes, in an oxygen (O ₂ ) atmosphere. The catalyst was prepared by heat treatment in a furnace at a temperature of 350°C for 6 hours.

< Example 2> NiO / IrO ₂ -400 Catalyst Manufacturing

A catalyst for oxygen evolution reaction was prepared in the same manner as in Example 1, except that the heat treatment temperature in the furnace was set to 400°C.

< Example 3> NiO / IrO ₂ -450 Catalyst Manufacturing

A catalyst for oxygen evolution reaction was prepared in the same manner as in Example 1, except that the heat treatment temperature in the furnace was set to 450°C.

< Example 4> NiO / IrO ₂ -500 catalyst manufacturing

A catalyst for oxygen evolution reaction was prepared in the same manner as in Example 1, except that the heat treatment temperature in the furnace was set to 500°C.

< Comparative example 1> IrO ₂ catalyst

IrO ₂ catalyst was purchased commercially.

< Comparative example 2> IrO ₂ -400 catalyst

The IrO ₂ catalyst was heat-treated in a furnace at a temperature of 400° C. for 6 hours.

< Comparative example 3> NiO -400 catalyst

Nickel hydroxide (Ni(OH) ₂ was heat treated in a furnace at a temperature of 400°C for 6 hours.

< Experiment example 1> Structural analysis

In order to confirm the structure of the catalyst for the oxygen evolution reaction according to the present invention, the catalysts for the oxygen evolution reaction of Examples 1 to 4 were photographed with a transmission electron microscope (TEM), and Brunauer-Emmett-Teeler (BET) analysis was performed. This was performed, and the results are shown in Figures 2, 3, and Table 1.

Average IrO ₂ particle size (nm) Average NiO particle size (nm) Comparative Example 1 1.7 - Comparative Example 2 4.8 - Comparative Example 3 - 18.1 Example 1 3.2 12.6 Example 2 3.4 15.5 Example 3 3.6 19.8 Example 4 3.6 22.8

Figure 2 is an image taken with a transmission electron microscope of the catalyst for oxygen generation reaction prepared in Examples 1 to 4, and Table 1 is a table showing the size of particles measured through transmission electron microscope analysis.

Looking at Figure 2 and Table 1, it can be seen that the size of the primary particles increases as the temperature increases. In the case of heat treatment of a single material (Comparative Examples 2 and 3), it can be seen that the particle size is much larger compared to the case of manufacturing a mixed catalyst under the same temperature conditions.

Figure 3 is a graph showing the results of Brunauer-Emmett-Teeler (BET) analysis on the catalysts for oxygen evolution reaction prepared in Examples 1 to 4. Looking at Figure 3, the nitrogen adsorption/desorption isotherm was analyzed as type IV and H3-type hysteresis, confirming that it was a meso or micro pore material. As the temperature increases, the hysteresis of the isothermal adsorption and desorption curve decreases, and it appears that the pores gradually disappear. The total pore volume was 0.189 cm ² /g for the catalyst of Example 1 (350°C), 0.173 cm 2 /g for the catalyst of Example 2 (400°C), and 0.173 cm ² /g for the catalyst of Example 3 (450°C). was measured to be 0.139 cm ² /g, and the catalyst of Example 4 (500°C) was measured to be 0.014 cm ² /g, and as shown in the above results, it can be seen that the total area of pores is reduced, confirming that the pores disappear. In the case of specific surface area, the catalyst of Example 1 (350°C) was 64.4 m ² /g, the catalyst of Example 2 (400°C) was 60.37 m ² /g, and the catalyst of Example 3 (450°C) was 41.26 m ^{2 .} /g, the catalyst of Example 4 (500°C) is 25.34 m ² /g. It can be seen that as the temperature increases, the particle size increases and the pores disappear, so the specific surface area decreases.

< Experiment example 2> Electrochemical analysis

In order to confirm the electrochemical properties of the catalyst for oxygen generation reaction according to the present invention, the catalyst activity of Examples 1 to 4 and Comparative Example 1 was evaluated at 1.25 V vs. 1.65 V vs. A Linear Sweep Voltammetry (LSV) experiment was conducted at RHE, and a Chronopotentiometry (CP) experiment was conducted to evaluate the stability of the catalyst. The results are shown in Figures 4, 5, and Table 2. shown in

matter Comparative Example 1 Example 1 Example 2 Example 3 C _dl (F) 0.02745 0.0095 0.0056 0.0051

Figure 4 shows a graph (a) of the results of analyzing the catalyst for oxygen generation reaction according to the present invention and the catalyst of the comparative example by linear sweep voltammetry (LSV) and a graph (a) of the results of analysis by chronopotentiometry ( b). Figure 5 is a graph showing the active area of the catalyst through slope as analyzed by cyclic voltammetry (CV) for the catalyst for oxygen generation reaction according to the present invention and the catalyst of the comparative example. Looking at Figures 4 and 5, it was confirmed that the catalyst for oxygen generation reaction of the present invention maintained the OER activity of the catalyst even though the amount of noble metal catalyst used was reduced.

1.65 V vs. 1.25 V to evaluate the activity of the catalyst. Linear Sweep Voltammetry (LSV) analysis was performed at RHE. LSV is a method of recording changes in current by scanning the potential of the working electrode in one direction from the initial potential to the final potential at a constant scanning speed, measuring the voltage at 10 mA/cm² and measuring 1.23 V vs. The activity of the catalyst was evaluated by subtracting RHE and expressing it as overvoltage.

As a result of measuring LSV, among the catalysts synthesized with commercial iridium, the overpotential values of the catalysts of Example 1 (350°C) and Example 2 (400°C) were similar, so even though the amount of noble metal catalyst used was reduced, the OER activity was high. It can be seen that it has been maintained.

Referring to Figure 4 (b), Chronopotentiometry (CP) is a measurement method that can evaluate the stability of a catalyst, and is a method of measuring the overvoltage observed over time at a constant current density (10 mA/cm²). am. As a result of CP measurement of a catalyst synthesized with commercial iridium oxide, it can be seen that the overvoltage increases with time in the case of a commercial iridium oxide catalyst or a catalyst heat-treated at a temperature of 350°C, but Example 2 (400°C), Example The catalysts of Example 3 (450°C) and Example 4 (500°C) were shown to be relatively stable. As a result of the LSV after the stability test, the overvoltage increased by 7.9% for the commercial iridium oxide and by 3.51% for the Example 2 (400°C) catalyst, showing that it is very stable.

Table 2 shows the non-Faraday voltage range of 0.8 - 1.0 V vs. This is the result of calculating the active area by measuring double-layer capacitance (Cdl) through cyclic voltammetry at various scanning speeds in RHE. Looking at Table 2, as a result of experiments under various temperature conditions, it was confirmed that, except for commercial iridium oxide, the active area of the catalysts in Examples 1 to 3 increased as the heat treatment temperature increased, which was the same as the specific surface area size of BET. It can be seen that there is a tendency.

<Experimental Example 3> Activity according to precursor type

In order to confirm the activity of the catalyst according to the type used as a precursor for the catalyst for oxygen generation reaction according to the present invention, a catalyst was prepared under the same conditions as in Example 2, but the type of nickel precursor used in catalyst preparation was Nickel Chloride. Catalysts for oxygen evolution reactions were manufactured using a variety of substances such as Chloride, Nickel Nitrate, Nickel Acetate, and Nickel Hydroxide. Then, at 1.25 V vs. 1.65 V to evaluate the activity of the catalyst. LSV analysis was performed in RHE, and the results are shown in Figure 6.

Specifically, using a solid phase method, iridium oxide (IrO ₂ ) and a nickel precursor were simply mixed into a solid state and heat treated to form an IrO ₂ /NiO composite, and the types of nickel precursors were different to form 400 Heat treated at ℃.

Figure 6 is a graph showing the results of analysis of catalysts for oxygen generation reaction according to the type of nickel precursor using linear sweep voltammetry (LSV). Looking at Figure 6, 1.65 V vs. 1.25 V. As a result of measuring LSV in RHE, the overvoltages of nickel chloride, nickel nitrate, nickel acetate, and nickel hydroxide at 10 mA/cm² were 376 mV, 386 mV, 375 mV, and 314 mV, respectively. was measured. Through this, it was confirmed that nickel hydroxide showed the lowest overvoltage at 10 mA/cm², and although a different nickel precursor was used, catalytic activity was still observed.

Therefore, the catalyst for oxygen generation reaction according to the present invention uses a simple solid phase method, but the activity of the catalyst can be controlled by varying the precursor.

<Experimental Example 4> Activity according to molar ratio of nickel precursor

In order to confirm the activity of the catalyst according to the molar ratio of the nickel precursor and transition metal oxide for producing the catalyst for oxygen evolution reaction according to the present invention, the catalyst was prepared under the same conditions as in Example 2, but the catalyst used in preparing the catalyst was A catalyst for oxygen generation reaction was prepared by using various molar ratios of nickel precursor (Nickel Hydroxide) and transition metal oxide (iridium oxide) of 1:1, 2:1, 3:1, 5:1, and 7:1. . Then, to evaluate the activity of the catalyst, LSV analysis was performed at 1.25 V vs. 1.65 V vs. RHE, and the results are shown in Figure 7.

Specifically, using a solid phase method, iridium oxide (IrO ₂ ) and a nickel precursor were simply mixed into a solid state and heat treated to form an IrO ₂ /NiO complex, and the molar ratio of the nickel precursor was varied. Heat treatment was performed at 400°C.

Referring to FIG. 7, samples containing nickel precursor and IrO ₂ mixed at various ratios were synthesized and oxygen generation reaction activity was evaluated. The Ni-IrOx-400 sample synthesized at a 1:1 ratio showed the best activity, and it was confirmed that the activity decreased as the NiO ratio increased.

As the specific parts of the present invention have been described in detail above, it is clear to those skilled in the art that these specific techniques are merely preferred embodiments and do not limit the scope of the present invention. do. That is, the practical scope of the present invention is defined by the appended claims and their equivalents.

Claims (9)

Preparing a mixture by mixing a nickel precursor and a transition metal oxide in a solid phase; and
Heat-treating the prepared mixture in an oxygen atmosphere in a furnace at a temperature of 350°C to 500°C for 2 to 10 hours,
The nickel precursor includes at least one of nickel hydroxide, nickel chloride, nickel nitrate, and nitrate acetate,
In the step of preparing the mixture, the nickel precursor and the transition metal oxide are mixed at a molar ratio of 1:1 to 3:1. According to claim 1,
The transition metal oxides include iridium (Ir), niobium (Nb), cobalt (Co), titanium (Ti), vanadium (V), manganese (Mn), zirconium (Zr), rhodium (Rh), tungsten (W), A method for producing a catalyst for oxygen generation reaction containing at least one oxide of tantalum (Ta), osmium (Os), rhenium (Re), and molybdenum (Mo). delete According to claim 1,
A method of producing a catalyst for oxygen evolution reaction, characterized in that the heat treatment step reduces the particle size of the oxide formed due to a template effect. Contains nickel oxide and transition metal oxide,
The nickel oxide and the transition metal oxide are in the form of particles having a porous surface,
The average particle size of the transition metal oxide is 1 to 4.5 nm,
A catalyst for oxygen evolution reaction in which the average particle size of the nickel oxide is 10 to 25 nm,
The catalyst for the oxygen evolution reaction has a BET specific surface area of 20 to 80 m ² /g,
The catalyst for the oxygen evolution reaction is characterized in that the molar ratio of nickel oxide and transition metal oxide is 1:1 to 3:1. delete delete According to claim 5,
The catalyst for oxygen generation reaction was measured at 10mA/cm ² at 1.25~1.65 V and measured at 1.23 V vs. When measuring overvoltage by subtracting RHE, the overvoltage increase rate is 3% to 10% compared to the initial overvoltage;
A catalyst for oxygen generation reaction, characterized in that the overvoltage increase rate is the rate of increase of the overvoltage measured after 20,000 seconds compared to the overvoltage measured at 0 seconds. An electrode containing the catalyst for oxygen generation reaction according to claim 5; and a water electrolytic cell including a reference electrode.