KR102631072B1 - Method of manufacturing eletrocatalyst for oxygen evolution or oxygen reduction and eletrocatalyst manufactured thereby - Google Patents

Abstract

The present invention relates to a method for producing an electrocatalyst for oxygen generation or oxygen reduction, and to an electrocatalyst prepared therefrom. The present invention relates to an electrocatalyst produced therefrom, whereby the loading amount of the transition metal is improved by electrodepositing a transition metal oxide on the surface of a conductive nanoparticle support, and the transition metal oxide is deposited on the surface of a conductive nanoparticle support. By doping nitrogen into a metal oxide, an electrocatalyst that has excellent conductivity and stability and is highly active in both the oxygen generation reaction and the oxygen reduction reaction in an alkaline electrolyte can be manufactured.

Description

Method for producing an electrocatalyst for oxygen generation or oxygen reduction and an electrocatalyst manufactured therefrom

The present invention relates to a method for producing an electrocatalyst for oxygen generation or oxygen reduction and an electrocatalyst prepared therefrom.

Novel electrocatalysts for oxygen reduction reactions (ORR) and oxygen evolution reactions (OER) have been studied over the past decades for various energy conversion and storage systems, such as regenerative fuel cells, water electrolysis, and metal-air electricity. Globally, environmental regulations due to climate change, along with the depletion of fossil fuels and increased energy consumption, are accelerating the search for potential oxygen electrocatalysts. These promising electrocatalysts must overcome a four-electron path to drive ORR or OER, which is strongly affected by slow chemical kinetics resulting in high overpotentials. The use of a catalyst at the anode is necessary to reduce the overvoltage between the oxygen reduction reaction and the oxygen generation reaction, but since precious metals such as platinum (Pt) are mainly used, the manufacturing cost is high, making commercialization difficult.

Additionally, the durability of the materials under the operating conditions of the energy system must be required for efficient and long-term performance. With this background, many potential candidates, including metal oxides and carbon materials, have been studied for ORR and OER electrocatalysts. However, these oxygen electrocatalysts were all rare metals, which increased production costs and limited activity for OER reactions.

Accordingly, there is an urgent need to develop low-cost new catalysts with high activity and high stability.

Korean Patent No. 2298551

The purpose of the present invention is to provide a method for producing an electrocatalyst for oxygen generation or oxygen reduction.

The present invention aims to provide an electrocatalyst.

The purpose of the present invention is to provide a metal-air battery.

The purpose of the present invention is to provide a water electrolyzer-fuel cell.

1. Electrodepositing a transition metal oxide on the surface of a conductive nanoparticle support; and doping nitrogen into the transition metal oxide electrodeposited on the surface of the conductive nanoparticle support.

2. The method of 1 above, wherein the electrodeposition is performed by applying voltage to a non-aqueous solution containing a transition metal precursor and a conductive nanoparticle support.

3. The method of producing an electrocatalyst for oxygen generation or reduction according to 1 above, wherein the electrodeposition is performed at 20 ℃ to 40 ℃.

4. In 1 above, the conductive nanoparticle support is carbon black, Ketjen black (KB), acetylene black, Denka black, activated carbon, mesoporous carbon, graphite, graphene, carbon nanotubes, and fluorine-doped tin oxide. oxygen-generating nanoparticles of fluorine-doped tin oxide, indium tin oxide and aluminum-doped zinc oxide, titanium nitride (TiN) or titanium carbide (TiC). Or a method for producing an electrocatalyst for reduction.

5. In 1 above, the transition metal is niobium (Nb), tantalum (Ta), vanadium (V), dubium (Db), titanium (Ti), zirconium (Zr), hafnium (Hf), or rutherfordium. (Rf) Method for producing an electrocatalyst for oxygen generation or reduction.

6. The method of 1 above, wherein the doping is performed for 30 minutes to 3 hours at 100°C to 1000°C in a gas atmosphere containing nitrogen.

7. Conductive nanoparticle support; and a plurality of nitrogen-doped transition metal oxide nanoparticles distributed on the surface of the conductive nanoparticle support.

8. The electrocatalyst of item 7 above, wherein the electrocatalyst contains 10% to 50% by weight of transition metal relative to the weight of the conductive nanoparticle support.

9. In item 7 above, the conductive nanoparticle support is carbon black, Ketjen black (KB), acetylene black, Denka black, activated carbon, mesoporous carbon, graphite, graphene, carbon nanotubes, and fluorine-doped tin oxide. Electrocatalysts are nanoparticles of fluorine-doped tin oxide, indium tin oxide and aluminum-doped zinc oxide, titanium nitride (TiN) or titanium carbide (TiC). .

10. In item 7 above, the transition metal is niobium (Nb), tantalum (Ta), vanadium (V), dubium (Db), titanium (Ti), zirconium (Zr), hafnium (Hf), or rutherfordium. (Rf) Phosphorus, electrocatalyst.

11. The electrocatalyst of item 7 above, wherein the particle size of the conductive nanoparticle support is 30 nm to 80 nm.

12. The electrocatalyst of 7 above, wherein the transition metal oxide nanoparticles have a size of 1 nm to 10 nm.

13. A metal-air battery containing the electrocatalyst of any one of items 7 to 11 above.

14 Water electrolysis-fuel cell comprising the electrocatalyst of any one of items 7 to 11 above.

The present invention relates to a method for producing an electrocatalyst for oxygen generation or oxygen reduction, and to an electrocatalyst prepared therefrom. The present invention relates to an electrocatalyst produced therefrom, whereby the loading amount of the transition metal is improved by electrodepositing a transition metal oxide on the surface of a conductive nanoparticle support, and the transition metal oxide is deposited on the surface of a conductive nanoparticle support. By doping nitrogen into a metal oxide, an electrocatalyst that has excellent conductivity and stability and is highly active in both the oxygen generation reaction and the oxygen reduction reaction in an alkaline electrolyte can be manufactured.

Figure 1 shows the XRD analysis results of NbO _x /CB nanoparticles, NbO _x /CB nanoparticles annealed in an Ar gas atmosphere, and N-doped NbO _x /CB nanoparticles annealed in an NH ₃ gas atmosphere.
Figure 2 is a STEM and TEM image of N-doped NbO _x /CB nanoparticles.
Figure 3 is an enlarged TEM image of Figure 2D.
Figure 4 shows the XPS analysis results of NbO _x /CB nanoparticles, NbO _x /CB nanoparticles annealed in an Ar gas atmosphere, and N-doped NbO _x /CB nanoparticles annealed in an NH ₃ gas atmosphere.
Figure 5A is the N2 adsorption-desorption isotherm of CB powder and N-doped NbO _x /CB nanoparticles, and Figure 3B compares the pore size distribution of CB powder and N-doped NbO _x /CB nanoparticles.
Figure 6 compares the ORR and OER properties of N-doped NbO _x /CB nanoparticles, Pt/CB, and Ir/CB catalysts.
Figure 7 shows (a) glassy carbon, (b) deposited NbO _x /CB, (c) CB (d) NbO _x /CB (annealed in Ar), (e) N-doped NbO _x /CB in alkaline solution. The OER and ORR activities of CB were compared.
Figure 8 shows the ORR dynamics established by measuring the hydrodynamic voltammogram of N-doped NbO _x /CB nanoparticles using RDE at different rotation speeds from 100 to 2500 rpm.

Hereinafter, the present invention will be described in detail.

The present invention provides a method for producing an electrocatalyst for oxygen generation or reduction.

The present invention includes electrodepositing a transition metal oxide on the surface of a conductive nanoparticle support.

The conductive nanoparticle support is a conductive nano-sized particle, and is not particularly limited as long as it can electrodeposit a transition metal oxide on the surface. For example, carbon black, Ketjen black (KB), acetylene black, Denka black, Activated carbon, mesoporous carbon, graphite, carbon-based nanoparticles such as graphene and carbon nanotubes, fluorine-doped tin oxide, indium tin oxide, and aluminum-doped zinc oxide. It may be a conductive oxide such as aluminum-doped zinc oxide, or nanoparticles of titanium nitride (TiN) or titanium carbide (TiC).

The transition metal is not particularly limited as long as it is a metal with one or more valences, but for example, niobium (Nb), tantalum (Ta), vanadium (V), dubium (Db), titanium (Ti), and zirconium (Zr). ), hafnium (Hf), or rutherpodium (Rf).

The electrodeposition may be performed using known methods and conditions known in the art. For example, it may be performed by applying a voltage to a non-aqueous solution containing a transition metal precursor and a conductive nanoparticle support.

Specifically, the conductive nanoparticle support is located between carbon sheets fixed in an electrodeposition cell, and when voltage is applied, the non-aqueous solution containing the transition metal precursor rotates through a stirrer and is deposited on the surface of the conductive nanoparticle support. Transition metal oxide may be electrodeposited.

Electrodeposition may be performed at 20°C to 40°C or 25°C to 30°C. The present invention includes ammonium salt as an electrolyte in the non-aqueous solution, so that the transition metal in the non-aqueous solution is not oxidized and maintained in ionic form during the electrodeposition process, so the stability of the non-aqueous solution is high and electrodeposition can be performed at room temperature. there is. Since electrodeposition is performed at room temperature in the present invention, it has the effect of reducing costs.

The ammonium salt in non-aqueous solution may be, for example, but is not limited to ammonium chloride (NH ₄ Cl), ammonium fluoride (NH ₄ F), or ammonium bromide (NH ₄ Br).

The transition metal precursor may be in the form of various salts of the transition metal, for example, if the transition metal is niobium (Nb), the transition metal precursor may be niobium chloride (NbCl ₅ ), niobium fluoride (NbF ₅ ) and niobium bromide ( It may be a niobium halide such as NbBr ₅ ) or a niobium alkoxide such as niobium ethoxide, but is not limited thereto.

Since the present invention involves electrodepositing a transition metal oxide on the surface of a conductive nanoparticle support, more transition metal oxide can be electrodeposited compared to electrodepositing the transition metal oxide on one surface of an electrode. Therefore, the reactivity is excellent due to the high transition metal content.

The present invention includes the step of doping nitrogen to the transition metal oxide electrodeposited on the surface of the conductive nanoparticle support.

The doping may be performed using known methods and conditions known in the art. For example, the transition metal oxide electrodeposited on the surface of the conductive nanoparticle support may be heat treated in a gas atmosphere containing nitrogen.

For example, the heat treatment may be performed in an ammonia gas atmosphere at 100°C to 1000°C or 300°C to 800°C for 30 minutes to 3 hours or 50 minutes to 1.5 hours, but is not limited thereto.

The present invention can improve the conductivity of the transition metal oxide by doping the transition metal oxide with nitrogen.

The present invention may further include the step of washing the conductive nanoparticle support on which the transition metal oxide is electrodeposited before the doping step.

The washing may be performed, for example, with absolute ethanol, but is not limited thereto. The washing removes the remaining transition metal precursor, thereby increasing the efficiency of nitrogen doping and producing a high-purity electrocatalyst.

The present invention provides a conductive nanoparticle support; and a plurality of nitrogen-doped transition metal oxide nanoparticles distributed on the surface of the conductive nanoparticle support.

The electrocatalyst of the present invention has excellent effects on oxygen generation or oxygen reduction reactions in alkaline electrolytes.

The conductive nanoparticle support is a conductive nano-sized particle, and is not particularly limited as long as it can electrodeposit a transition metal oxide on the surface. For example, carbon black, Ketjen black (KB), acetylene black, Denka black, Activated carbon, mesoporous carbon, graphite, carbon-based nanoparticles such as graphene and carbon nanotubes, fluorine-doped tin oxide, indium tin oxide, and aluminum-doped zinc oxide. It may be a conductive oxide such as aluminum-doped zinc oxide, or nanoparticles of titanium nitride (TiN) or titanium carbide (TiC).

The transition metal is not particularly limited as long as it is a metal with one or more valences, but for example, niobium (Nb), tantalum (Ta), vanadium (V), dubium (Db), titanium (Ti), and zirconium (Zr). ), hafnium (Hf), or rutherpodium (Rf).

The nitrogen-doped transition metal oxide may have some of the oxygen in the lattice of the transition metal oxide replaced with a small amount of nitrogen or nitrogen may be included in the empty space in the lattice of the transition metal oxide.

For example, the plurality of nitrogen-doped transition metal oxide nanoparticles may be distributed on the surface of the conductive nanoparticle support in 2 or more, 3 or more, 4 or more, and the upper limit is not particularly limited, but the conductive nano particle It can be determined depending on the particle size of the particle support and the size of the nitrogen-doped transition metal oxide nanoparticles. For example, it may be distributed as 80 or less, 70 or less, and 60 or less. More specifically, the transition metal may be included in an amount of 10% to 50% by weight or 15% to 40% by weight relative to the weight of the conductive nanoparticle support.

The nitrogen-doped transition metal oxide nanoparticles may be distributed in the pores of the conductive nanoparticle support. The larger the number of pores of the conductive nanoparticle support, the more nitrogen-doped transition metal oxide nanoparticles can be distributed, thereby improving reactivity.

The particle size of the conductive nanoparticle support may be 30 nm to 80 nm or 40 nm to 70 nm, but is not limited thereto. The smaller the particle size, the larger the surface area, allowing more transition metal oxide nanoparticles to be deposited, increasing the catalytic activity. However, if the size is too small, the transition metal oxide nanoparticles are buried in the micropores of the conductive nanoparticle support and react as a catalyst. Since it is difficult to participate in the above range, the above range is desirable.

The transition metal oxide nanoparticles may have a size of 1 nm to 10 nm or 2 nm to 6 nm, but are not limited thereto. When the transition metal oxide is in the bulk form, the conductivity is very low (close to an insulator), so it is preferable that the transition metal oxide is in the form of nanoparticles. When the particle size is within the above range, the electrodeposition and catalytic efficiency on the conductive nanoparticle support are reduced. It can be improved.

The present invention provides a metal-air battery or water electrolysis-fuel cell including the electrocatalyst.

The electrocatalyst is as described above.

Metal-air batteries and water electrolyzer-fuel cells may have structures and configurations known in the art.

Water electrolysis-fuel cell is a fusion of a water electrolyzer and a fuel cell, in which an oxygen generation reaction occurs in the water electrolyzer and an oxygen reduction reaction occurs in the fuel cell.

The battery of the present invention may include the electrocatalyst in a catalyst layer, and more specifically, may include the electrocatalyst in the catalyst layer of the air electrode (anode).

The battery of the present invention has a high content of transition metal oxide and the transition metal oxide nanoparticles are doped with nitrogen, so it has excellent activity against oxygen reduction reaction as well as oxygen generation reaction due to the bond between nitrogen and transition metal oxide, and has excellent stability. high.

Hereinafter, the present invention will be described in detail with reference to examples.

Experiment method

1. Preparation of N-doped NbOx/CB powder catalyst

Potentiostatic electrodeposition was performed in a non-aqueous Nb-based solution for loading of NbO _x species on the CB powder surface. 10 mg of CB powder (Ketjen black EC-600JD, Akzo Nobel Functional Chemicals) was sandwiched between two carbon paper sheets (AvCarb MGL190, AvCarb Material Solutions). The sandwich-type CB assembly was fixed using a homemade electrodeposition cell. A cell as a working electrode was mounted on a typical three-electrode system using a potentiostat (CHI700E, CH Instruments, Inc.). Carbon rods and Ag/Ag ⁺ were used as counter and reference electrodes, respectively. The non-aqueous Nb-based solution consisted of 10mM NbCl ₅ (99.9%, Sigma-Aldrich), 10mM NH ₄ Cl (99%, Kanto Chemical) as a supporting electrolyte, and absolute ethanol solvent. _{To electrodeposit NbO _} The electrodeposited CB powder was washed with absolute ethanol to remove the remaining Nb precursor and then completely dried at 298 K. The resulting powder was then annealed in a flow of pure NH ₃ (grade 5N ^{) or Ar (grade 5N) at 200 ml min -1 at} 873 K for 1 hour with a ramp rate of 10 K min -1 .

2. Electrochemical measurements

Catalyst slurries were prepared for ORR and OER electrochemical measurements. 2 mg of the prepared N-doped _NbO This mixture was repeatedly placed in an ultrasonic bath and magnetic stirrer to increase dispersion. 2.5 μl of catalyst slurry was dropped onto a glassy carbon rotating disk electrode (RDE; diameter 4 mm) and air-dried. The loading amount of catalyst was about 128 ㎍ cm ^-2 . For comparison, commercial 20 wt% Pt/CB (Pt from Premetek Co., Vulcan XC-72) and 20 wt% Ir/CB (Ir from Premetek Co., Vulcan XC-72) catalyst slurries were also cast in RDE in the same manner.

Electrochemical measurements were performed using an RDE system consisting of a Hg/HgO reference and carbon rod counter electrode at 298 K. Cyclic and linear sweep voltammograms (CV and LSV) were scanned over a potential range of 2.0 to 0.10 V _RHE at a scan rate of 10 mV s ^-1 in Ar- or O ² -saturated 0.1 M aqueous KOH solution. The potential scale referenced by the Hg/HgO electrode was calibrated with a reversible hydrogen electrode (RHE).

3. Surface and physical characterization

The crystal structure of the prepared N-doped NbO _x /CB catalyst was investigated by X-ray diffraction (XRD; MiniFlex 600, Rigaku) using Cu Kα radiation at 40 kV and 15 mA. The surface morphology of N-doped NbO _x /CB nanoparticles was characterized by field emission transmission electron microscopy (FE-TEM; JEM-2200FS, JEOL). The loading of Nb in N-doped NbO _x /CB was determined by inductively coupled plasma optical emission spectroscopy (ICP-OES; PerkinElmer, Avio 500). The Brunauer-Emmett-Teller (BET) surface area of the prepared catalyst was determined using the BET (ASAP2020, Micromeritics Instrument Corp.) adsorption method based on the adsorption of N ₂ gas at 77 K. The pore size distribution was obtained by the Barrett-Joyner-Halenda (BJH) method using the desorption branch of the isotherm. The chemical states of Nb, O and N species on the N-doped NbO _x /CB surface were determined by high-performance X-ray photoelectron spectroscopy (HP-XPS; K-Alpha+, Thermo Scientific).

Experiment result

_{NbO _} The resulting particles were annealed in NH ₃ flow at 873 K for 1 h to modify the surface properties. For comparison, they were placed in an Ar atmosphere at the same temperature. The crystal structure of the as-deposited and annealed particles was determined by XRD analysis (Figure 1). The XRD pattern of the electrodeposited particles did not show any peaks distinct from those of the non-electrodeposited CB powder. After annealing in Ar, the particles showed some crystallinity with a weak peak at 26° and could almost be assigned to β-NbO ₂ (220) (ICSD #35181). In contrast, particles annealed in NH ₃ showed no diffraction peaks, indicating that the particles may be very fine or amorphous. The surface morphology of the particles was investigated by (S)TEM measurements. Figure 2 shows STEM and TEM images of particles annealed in NH ₃ . In the STEM image of Figure 2A, bright spots made of relatively heavy elements were well dispersed in the ball-shaped support. As cross-confirmed with the TEM image in Figure 2B, the support showed the typical surface morphology of Ketjen Black as CB composed of primary particles smaller than 50 nm in size. Microparticles with a size of approximately 3 nm well dispersed in the CB shown in Figures 2C and 2D were considered to be Nb-based species. The nanoparticles inserted in Figure 2D had a lattice pattern, indicating the crystallinity of the material. Crystalline particles were observed, but the crystal structure was unclear at this stage (Figure 3). Therefore, catalyst synthesis by electrodeposition in NH ₃ and subsequent annealing produced well-dispersed crystalline Nb-based nanoparticles.

The chemical state and composition of Nb-based species were determined by XPS analysis. Figure 4 shows narrow-scan Nb 3d, O 1s, and N 1s XPS spectra for nanoparticles and annealed derivatives deposited in Ar and NH ₃ atmospheres. The Nb 3d spectra for all samples broadened and deviated from the double split peak corresponding to fully oxidized Nb ₂ O ₅ (Nb ⁵⁺ ), indicating a chemical shift to lower valence states. Therefore, the broad Nb 3d spectrum was deconvoluted into different oxidation states of Nb ⁵⁺ and Nb ⁴⁺ . The surface composition ratios of Nb species resulting from the best fit are summarized in Table 1. The convolution clearly showed that the electrodeposited Nb species consisted of two oxidation states. The surface concentration of Nb ⁵⁺ increased after annealing, but the presence of multivalent Nb species still remained unchanged. However, according to the O 1s spectrum, the concentration of oxygen species, including OH ^- /H ₂ O groups adsorbed on the catalyst surface, decreased during annealing in Ar. Annealing of Nb-based nanoparticles in reducing NH ₃ accelerated the reduction of oxygen levels while promoting the insertion of relatively low nitrogen contents. For comparison, when only CB was annealed in NH ₃ , nitrogen concentration was not detected. These results indicate that the prepared catalyst was confirmed to be nitrogen-doped NbO _x nanoparticles, and is hereafter named N-doped NbO x /CB.

The amount of Nb in the catalyst prepared by electrodeposition at -0.4 V _Ag/Ag+ for 30 seconds was determined by ICP-OES analysis. 20.1 wt% Nb was deposited on the CB surface in an electrodeposition system. The high loading of Nb was significant. Additionally, the surface area and pore size distribution of the prepared N-doped NbO _x /CB were estimated using the BET adsorption method. Figure 5(A) shows the N ₂ adsorption-desorption isotherm for the N-doped NbO _x /CB catalyst, which was compared with that of CB powder alone. Ketjen Black was used as the CB support for NbO _x nanoparticles because it is known to be a conducting mesoporous carbon with a large BET surface area. The hysteresis loop for CB represented a type IV adsorption isotherm according to the IUPAC classification. The pore size distribution shown in Figure 5(B) also characterizes mesoporous materials with pore diameters of 2-50 nm. After deposition of _NbO The BET surface areas of N-doped NbO _x /CB and CB were measured to be 1158 and 1251 m ² g ^-1 , respectively. As can be seen from the pore size distribution, the coverage of NbO _x particles above 20 wt% significantly reduced the pore volume of CB to the range of 10–50 nm. Nevertheless, the surface area of the prepared catalyst is large due to the loading of NbO _x fine particles in the catalyst. Therefore, by applying CB with a large surface area, the loading amount and uniform distribution of NbO _x nanoparticles were improved.

The catalytic activities of N-doped NbO _x /CB nanoparticles for ORR and OER are shown in Figure 6(A). CVs were shown in Ar- and O ₂ -purged 0.1 M KOH electrolyte at a scan rate of 10 mV s ^-1 . ORR was significantly catalyzed in the nanoparticles as judged by the high cathodic current in the O ₂ atmosphere compared to almost no current in the Ar atmosphere. It can be seen that reactant O ₂ was used in ORR. High anodic currents in response to OER were observed for nanoparticles regardless of the gas atmosphere. These results demonstrate that N-doped NbO _x /CB nanoparticles are active for both oxygen reactions in alkaline medium. The noble metal Pt/CB is a representative ORR electrocatalyst, and Ir/CB is well known as a notable OER electrocatalyst. For comparison, commercial 20 wt% Pt/CB and Ir/CB catalysts were measured for ORR and OER in O ₂ saturated 0.1 M KOH electrolyte, and the results are shown in Figure 6(B). N _- ^doped _NbO Additionally, the nanoparticles were clearly more active for OER than Pt/CB and 100 mV less active than Ir/CB at an anodic current density of 10 mV cm ^-2 , which represents the OER benchmark. To show the overall oxygen activity of the bifunctional catalysts, the potential difference (ΔE) between the ORR and OER activities for each catalyst is summarized in Table 2. The potential difference of N-doped NbO _x /CB nanoparticles was 1.09 V, which was similar to that of the noble metal catalyst. This indicates that the bifunctional activity of the nanoparticles is remarkable. Therefore, N-doped NbO _x /CB nanoparticles synthesized by electrodeposition and subsequent annealing have the potential to be ideal reversible oxygen electrocatalysts.

To characterize the bifunctional oxygen activity on N-doped NbO _x /CB catalysts, a systematic study on ORR and OER was performed using nanoparticles made with different compositions. The catalytic activities of CB and glassy carbon were evaluated for comparison. Figure 7(A) shows the LSV versus ORR of N-doped NbO _x /CB, NbO _x /CB (annealed in Ar), deposited NbO _x /CB, CB, and glassy carbon in 0.1 M KOH solution. Current density relative to ORR, i ORR was calculated from the difference in cathodic current density between O ₂ - and Ar - saturated atmospheres. CB used as a support showed little activity against ORR compared to glassy carbon. It is known that the ORR of CB occurs to some extent in alkaline solutions, while it is almost negligible in acidic solutions. As-deposited NbO _x /CB showed less activity toward ORR than CB. However, annealing of catalysts deposited in different gas atmospheres greatly improved ORR activity, and NH ₃ atmosphere was a particularly excellent condition. The _onset potential ^of N-doped _NbO The annealed catalyst produced a higher ORR current with a more positive onset potential, demonstrating that the NbO _x nanoparticles were activated as ORR electrocatalysts. The ORR activity of NbO _x nanoparticles in 0.1MH ₂ SO ₄ electrolyte was reported in a previous publication. Ultimately, it is clear that NbO _x /CB nanoparticles can drive ORR in both acidic and alkaline media. Ar annealing was _found to modify ^{the catalyst} surface according to the Oxygen loss was accelerated in the reducing NH ₃ flow. Additionally, a small amount of nitrogen was doped with NbO _x nanoparticles in NH ₃ atmosphere. Therefore, the greatly enhanced ORR activity is due to the more concentrated Nb and nitrogen doping of NbO _x .

Tafel plots of all samples at low overpotentials versus the thermodynamic potential of 1.23 V obtained in Figure 7(A) are shown in Figure 7(B). The Tafel plot of 20 wt% Pt/CB was also compared. The Tafel slope for NbO _x /CB in the deposited state was about 60mV dec ^-1 . However, it became slightly smaller after annealing treatment in Ar and NH ₃ atmospheres, indicating that the rate-determining step for ORR was changed. The Tafel slope was determined to be 48 mV dec ^-1 for N-doped NbO _x /CB, which is similar to 45 mV dec ^-1 for Pt/CB. The Tafel slope of 120 mV dec ⁻¹ suggests that, in general, the single electron transfer reaction is the rate-determining step of ORR and that the surface site of the catalyst is stable under the measurement conditions. In acidic media, the surface of metallic Pt was oxidized to PtO, and a smaller slope of 60 mV dec-1 for ORR was observed in the low overpotential range. Similar electrochemical behavior was also reported in alkaline media. The deposited NbO _x /CB was found to have a Tafel slope of 60 mV dec ^-1, the same as CB. This may explain that NbO _x nanoparticles were not used for ORR because the ORR current was much lower than that of CB. After annealing, the surface oxygen concentration of the catalyst decreases, leading to active NbO _x surface sites for ORR and thus a decrease in Tafel slope at low overpotentials. There have been theoretical studies showing that different surface coverages, such as MOO, MOO-, and MOOH (M=metal), lead to different Tafel slopes during ORR. Therefore, the small slope for the annealed NbO _x /CB nanoparticles may result from the different surface states of non-stoichiometric _NbO Additionally, the hydrodynamic voltammograms of N-doped NbO _x /CB nanoparticles were measured using RDE at different rotation speeds from 100 to 2500 rpm to establish ORR dynamics ( Figure 8 ). The ORR current at low potentials increased with increasing rotation speed, indicating that diffusion-limited currents were dominant. The Koutecky-Levich plot for nanoparticles |i| It represents the linear relationship between ^-1 and ω ^-1/2 and the slope at a given potential approximately parallel to the four electron beams. This indicates that the ORR process for N-doped NbO _x /CB nanoparticles is dominated by four electron transfer paths in the mass transfer region.

_Figure 7(C) _shows the ^OER of N- _doped NbO Shows the LSV for LSV was recorded in the cathodic sweep direction to avoid self-oxidation of the catalyst, as shown in Figure 5(A). The OER activity of as-deposited NbO _x /CB was significantly low, far from the OER benchmark value of 10 mA cm ^-2 at a final potential of 2.0 V _RHE . It was also lower than CB. The anode current increased after Ar annealing and increased significantly with NH ₃ annealing. The activity trend of OER was similar to that of ORR. In the Tafel plot shown in Figure 7(D), the slope ^{of the} N ^- doped _NbO The slope changed little from that of as-deposited NbO _x /CB. However, it was clearly different from the 72 mV dec ^-1 of the Ir/CB catalyst. This may mean that N-doped NbO _x is electrochemically stable at the oxidation potential, while metallic Ir is oxidized. As a result, almost one electron transfer reaction was the rate-determining step during the OER process at low overpotential for the prepared nanoparticles.

Figures 7(E) and 7(F) show the CA curves of N-doped NbO _x /CB catalyst during ORR and OER in O ² -purged 0.1 M KOH electrolyte. For comparison, 20wt% Ir/CB was also evaluated using the same method. The ORR activity ^of N- _{doped NbO} It decreased significantly on CB catalyst. It is noteworthy that the nanoparticles were stable for long-term ORR in alkaline media. Ta-based oxide nanoparticles were also durable against ORR in acidic electrolytes in previous results. Therefore, it can be said that ORR consistently catalyzes oxide nanoparticles regardless of the pH level of the electrolyte. Additionally, the long-term OER activity of the nanoparticles was measured at a benchmark potential of 1.74V _RHE for 10mA cm ^-2 . However, O ₂ generation was so active that the catalyst was separated from the RDE and catalyst stability could not be measured. Therefore, OER activity was evaluated at a potential of 1.61 V _RHE , which is lower than the benchmark potential for 10 mA cm ^-2 for 1 hour. As shown in Figure 7(f), the anode current was relatively stable compared to the Ir/CB catalyst. Therefore, these results demonstrate that N-doped NbO _x /CB nanoparticles are stable in both ORR and OER atmospheres of alkaline media.

Claims (14)

Electrodepositing a transition metal oxide on the surface of a conductive nanoparticle support; and
Doping nitrogen into the transition metal oxide electrodeposited on the surface of the conductive nanoparticle support,
The transition metal is niobium (Nb), tantalum (Ta), vanadium (V), dubium (Db), titanium (Ti), zirconium (Zr), hafnium (Hf), or rutherpodium (Rf).
Method for producing an electrocatalyst for oxygen generation or oxygen reduction.
The method of claim 1, wherein the electrodeposition is performed by applying voltage to a non-aqueous solution containing a transition metal precursor and a conductive nanoparticle support.
The method of claim 1, wherein the electrodeposition is performed at 20°C to 40°C.
The method of claim 1, wherein the conductive nanoparticle support is carbon black, Ketjen black (KB), acetylene black, Denka black, activated carbon, mesoporous carbon, graphite, graphene, carbon nanotubes, and fluorine-doped tin oxide (Fluorine). Oxygen generation or oxygen generation, which are nanoparticles of -doped tin oxide, indium tin oxide and aluminum-doped zinc oxide, titanium nitride (TiN) or titanium carbide (TiC) Method for producing electrocatalyst for reduction.
delete The method of claim 1, wherein the doping is performed at 100°C to 1000°C for 30 minutes to 3 hours in a gas atmosphere containing nitrogen.
Conductive nanoparticle support; and
It includes a plurality of nitrogen-doped transition metal oxide nanoparticles distributed on the surface of the conductive nanoparticle support;
The transition metal is niobium (Nb), tantalum (Ta), vanadium (V), dubium (Db), titanium (Ti), zirconium (Zr), hafnium (Hf), or rutherpodium (Rf).
electrocatalyst.
The electrocatalyst according to claim 7, wherein the electrocatalyst contains 10% to 50% by weight of transition metal relative to the weight of the conductive nanoparticle support.
The method of claim 7, wherein the conductive nanoparticle support is carbon black, Ketjen black (KB), acetylene black, Denka black, activated carbon, mesoporous carbon, graphite, graphene, carbon nanotubes, and fluorine-doped tin oxide (Fluorine). Electrocatalysts, which are nanoparticles of -doped tin oxide, indium tin oxide and aluminum-doped zinc oxide, titanium nitride (TiN) or titanium carbide (TiC).
delete The electrocatalyst according to claim 7, wherein the particle size of the conductive nanoparticle support is 30 nm to 80 nm.
The electrocatalyst of claim 7, wherein the transition metal oxide nanoparticles have a size of 1 nm to 10 nm.
A metal-air battery comprising the electrocatalyst of any one of claims 7 to 9 and 11.
A water electrolysis-fuel cell comprising the electrocatalyst of any one of claims 7 to 9 and 11.