Mesh oxygen electrode with square macropores for anion-exchange membrane unitized regenerative fuel cell and anion-exchange membrane unitized regenerative fuel celle including the same

Abstract

The present invention relates to an oxygen electrode for an anion exchange membrane integrated fuel cell and an anion exchange membrane integrated fuel cell comprising the same, wherein the carbon nanotube structure comprises two or more layers of carbon nanotube layers each comprising a plurality of carbon nanotubes arranged in parallel and a catalyst layer formed on the carbon nanotube structure, wherein the plurality of carbon nanotubes arranged in parallel included in any carbon nanotube layer of the carbon nanotube structure comprises square macropores formed orthogonally to the plurality of carbon nanotubes arranged in parallel included in a carbon nanotube layer adjacent to the upper or lower side.

Description

Technology Field

[0001] The present invention relates to an oxygen electrode for an anion exchange membrane integrated fuel cell and an anion exchange membrane integrated fuel cell including the same. Background Technology

[0002] As interest in green hydrogen, an eco-friendly energy source that does not generate carbon dioxide, intensifies, research is actively underway on water electrolysis technology, a method for producing green hydrogen, and fuel cell technology, which generates electricity using green hydrogen; however, technologies for storing and converting excess energy have limitations.

[0003] To address this, research on anion-exchange membrane unitized regenerative fuel cells capable of operating in both water electrolysis mode and fuel cell mode as a single system is attracting attention.

[0004] This device offers the potential for cost reduction by using an alkaline electrolyte to replace expensive precious metal catalysts with non-precious metal catalysts, and is advantageous for long-cycle energy conversion as it can regenerate and utilize hydrogen.

[0005] However, because the oxygen reduction (ORR) and oxygen evolution (OER) reactions occurring at the oxygen electrode of anion exchange membrane-integrated fuel cells exhibit high overpotentials, resulting in a low round-trip efficiency of approximately 45%, it is necessary to develop an oxygen electrode with high efficiency and durability in both directions. Furthermore, conventional oxygen electrodes require a high catalyst loading amount because the catalyst particles are densely packed, resulting in limited surface exposure of the catalyst and consequently low catalyst utilization. Prior art literature

[0006] Korean Published Patent No. 10-2022-0003709 (Publication Date: January 11, 2022) The problem to be solved

[0007] The technical problem that the present invention aims to solve is to provide an oxygen electrode for an anion exchange membrane integrated fuel cell having a structure with developed macropores necessary to improve the disadvantages of conventional oxygen electrodes, and an anion exchange membrane integrated fuel cell including the same. means of solving the problem

[0008] The present invention relates to a structure having square macropores in a mesh form obtained by stacking carbon nanotubes as a structure with developed macropores necessary to improve the disadvantages of conventional oxygen electrodes, and to an oxygen electrode having square macropores in a three-dimensional mesh form formed by supporting catalyst particles on said structure.

[0009] The oxygen electrode for an anion exchange membrane integrated fuel cell according to the present invention comprises a carbon nanotube structure having a mesh-shaped square macropore formed by stacking two or more carbon nanotube layers each comprising a plurality of carbon nanotubes arranged in parallel, and a catalyst layer formed on the carbon nanotube structure.

[0010] At this time, the square macropores included in the carbon nanotube structure are formed such that a plurality of parallel carbon nanotubes included in any carbon nanotube layer constituting the structure are orthogonal to a plurality of parallel carbon nanotubes included in a carbon nanotube layer adjacent to the upper and / or lower part of the carbon nanotube layer.

[0011] Each carbon nanotube layer constituting the above carbon nanotube structure can be obtained by separating a plurality of parallel carbon nanotubes from a vertically aligned carbon nanotube (VACNT) forest composed of vertically aligned carbon nanotubes.

[0012] The catalyst layer formed on the carbon nanotube structure includes a catalyst active in the oxygen reduction reaction (ORR) and a catalyst active in the oxygen evolution reaction (OER), thereby inducing an oxygen reduction reaction at the oxygen electrode when the anion exchange membrane integrated fuel cell is operated in fuel cell mode and promoting an oxygen evolution reaction at the oxygen electrode when it is operated in water electrolysis mode.

[0013] The catalyst active in the oxygen reduction reaction included in the catalyst layer above may be one or more selected from platinum (Pt), carbon-supported platinum (Pt / C), carbon nanotube-supported platinum (Pt / CNT), platinum alloys (platinum-cobalt (PtCo), platinum-ruthenium (PtRu), platinum-iridium (PtIr), platinum-nickel (PtNi), platinum-yttrium (PtY), etc.), carbon-supported platinum alloys (PtCo / C, PtRu / C, PtIr / C, PtNi / C, PtY / C), carbon nanotube-supported platinum alloys (PtCo / CNT, PtRu / CNT, PtIr / CNT, PtNi / CNT, PtY / CNT), etc., but is not necessarily limited to these.

[0014] In addition, the catalyst active in the oxygen evolution reaction included in the catalyst layer may be composed of a metal selected from cobalt (Co), nickel (Ni), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), copper (Cu), and zinc (Zn), an alloy thereof, or a compound containing said metal, but is not necessarily limited to these.

[0015] For example, the alloy may be a nickel-iron alloy (NiFe), and the compound may be a metal layered double hydroxide (LDH), such as NiFe LDH, NiCo LDH, CoFe LDH, NiCoFe LDH, NiMn LDH, or CoMn LDH.

[0016] For example, the oxygen electrode for an anion exchange membrane integrated fuel cell according to the present invention may comprise a carbon nanotube structure having a mesh-shaped square macropore comprising 10 layers of carbon nanotubes, and a catalyst layer formed on the carbon nanotube structure comprising platinum black (Pt-black) as an oxygen reduction reaction catalyst and nickel-iron alloy (NiFe) as an oxygen evolution reaction catalyst.

[0017] In addition, in another aspect of the invention, the present invention proposes a single-cell unit cell as an anion exchange membrane integrated fuel cell comprising an oxygen electrode having square macropores in the shape of a mesh, wherein a membrane-electrode assembly is coupled to both sides of an anion exchange membrane containing an electrolyte, wherein the oxygen electrode, the hydrogen electrode, and the gas diffusion layer according to the present invention are coupled in sequence. Effects of the invention

[0018] The oxygen electrode for an anion exchange membrane integrated fuel cell according to the present invention includes a carbon nanotube structure having mesh-shaped square macropores, thereby providing high performance by increasing the surface area of ​​the electrode and providing a smooth pathway for reactants and products, compared to conventional oxygen electrodes that have a compressed structure without a pore structure in which catalyst nanoparticles are densely supported, so that catalyst nanoparticles are supported without clumping.

[0019] In addition, the high electrical conductivity of the carbon nanotubes constituting the above structure can lower the electrical resistance of the anion exchange membrane integrated fuel cell, and the high degree of graphitization of the carbon nanotubes contributes to the high stability and reciprocating efficiency of the oxygen electrode for the anion exchange membrane integrated fuel cell.

[0020] The carbon nanotube structure included in the oxygen electrode according to the present invention can be applied as a core component of a hydrogen electrode as well as an oxygen electrode for anion exchange membrane integrated fuel cell, and furthermore, can be utilized in water electrolysis, fuel cells, and metal-air batteries. Brief explanation of the drawing

[0021] Figure 1(a) is a schematic diagram of an oxygen electrode having mesh-shaped square macropores applied to an anion exchange membrane integrated fuel cell. Figure 1(b) is a schematic diagram of an oxygen electrode having mesh-shaped square macropores, and Figure 1(c) is a schematic diagram of a conventional electrode compressed without a pore structure. Figure 1(d) is a scanning electron microscope (SEM) image of a mesh-shaped macropore structure. Figure 1(f) is an SEM of an oxygen electrode with Pt catalyst and NiFe alloy catalyst supported on a mesh-shaped macropore structure. Figure 1(h) is an SEM of a conventional oxygen electrode compressed without a pore structure, with Pt catalyst and NiFe alloy catalyst densely supported without a structure. Figure 1(e) is a transmission electron microscope (TEM) image of a mesh-shaped macropore structure, and Figure 1(g) is a TEM of an oxygen electrode with Pt catalyst and NiFe alloy catalyst supported on a mesh-shaped macropore structure. Figure 1(i) is a TEM image of a conventional oxygen electrode compressed without a pore structure. Figures 1(f) and 1(g) show that the catalyst is well dispersed and supported without agglomeration in the oxygen electrode having mesh-shaped square macropores. On the other hand, Figures 1(h) and 1(i) show that the catalyst particles are densely supported in the conventional oxygen electrode. Figures 2(a) to 2(f) show the analysis results regarding the physicochemical properties of an oxygen electrode having mesh-shaped square macropores and a conventional oxygen electrode. Figure 2(a) revealed that NiFe alloy nanoparticles and Pt nanoparticles were well loaded onto the two electrodes through X-ray diffraction of the two electrodes. Figure 2(b) showed that the oxygen electrode having mesh-shaped square macropores is composed of carbon with a high degree of blackening through Raman analysis, indicating that CNTs are configured within the mesh-shaped square macropore structure. Figure 2(c) confirmed that the oxygen electrode having mesh-shaped square macropores possesses macropores using mercury porosity data. Figures 2(d) to 2(f) show the X-ray absorption near-field edge structure results of Fe K-edge, Ni K-edge, and Pt L3-edge, which show that the oxidation numbers of each constituent element constituting the two electrodes are nearly similar, indicating that the introduction of a mesh-shaped square macropore structure does not cause changes to the oxidation number of the metal or the atomic environment. Figures 3(a) to 3(f) show half-cell test data in an alkaline atmosphere for an oxygen electrode having mesh-shaped square macropores and a conventional compressed oxygen electrode without a pore structure. Figure 3(a) is the LSV curve of the oxygen reduction reaction of the two electrodes, Figure 3(b) is a Tafel plot according to the oxygen reduction reaction of the two electrodes, Figure 3(c) is the LSV curve of the oxygen evolution reaction of the two electrodes, Figure 3(d) is a Tafel plot according to the oxygen evolution reaction of the two electrodes, Figure 3(e) is the constant voltage curve of the two electrodes with a voltage of 0.8 V applied, and Figure 3(f) is the 10 mA cm² of the two electrodes -2 This is the constant current curve when a current is applied. Figures 4(a) through 4(e) show single-cell test data in an alkaline atmosphere for an oxygen electrode having mesh-shaped square macropores and a conventional oxygen electrode. Figure 4(a) shows the LSV curves of the two electrodes in fuel cell mode and water electrolysis mode, and Figure 4(b) shows the reciprocating efficiencies of the two electrodes. Figure 4(c) is a comparison table of the anion exchange membrane water electrolysis performance including the oxygen electrode having mesh-shaped square macropores and previously reported performance, showing that the oxygen electrode having mesh-shaped square macropores has the highest value among previously reported reciprocating efficiencies. Figure 4(d) shows the results of a durability test running 5 cycles for 1 hour each, demonstrating the high stability of the oxygen electrode having mesh-shaped square macropores. Figure 4(e) shows -20 mA cm⁻¹ -2 Fuel cell mode operation results and 20 mA cm -2 The long-term stability of an oxygen electrode having mesh-shaped square macropores is shown as a result of water electrolysis mode operation. Specific details for implementing the invention

[0022] In describing the present invention, if it is determined that a detailed description of related known functions or configurations could unnecessarily obscure the essence of the invention, such detailed description will be omitted.

[0023] Since embodiments according to the concept of the present invention may be subject to various modifications and may take various forms, specific embodiments are illustrated in the drawings and described in detail in this specification or application. However, this is not intended to limit embodiments according to the concept of the present invention to specific disclosed forms, and it should be understood that they include all modifications, equivalents, and substitutions that fall within the spirit and scope of the present invention.

[0024] The terms used herein are merely for describing specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “comprising” or “having” are intended to specify the existence of the described features, numbers, steps, actions, components, parts, or combinations thereof, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0025] The present invention will be described in more detail below with reference to examples.

[0026] The embodiments according to this specification may be modified in various different forms, and the scope of this specification is not to be interpreted as being limited to the embodiments described below. The embodiments of this specification are provided to more fully explain this specification to those with average knowledge in the art.

[0027] <Example> Preparation of an oxygen electrode for an anion exchange membrane integrated fuel cell applying a mesh-shaped square macropore structure

[0028] As an example, an oxygen electrode with a mesh-shaped square macropore structure was prepared. The electrode (5 cm 2To fabricate the structure, a carbon nanotube forest (VACNT forest) composed of vertically aligned carbon nanotubes was utilized. A mesh-shaped square macropore structure (mesh-type CNT framework) was formed by stacking 10 single-layer carbon nanotube structures extracted from this forest in a grid pattern on a carbon paper substrate. Subsequently, nickel-iron alloy (NiFe, Sigma Aldrich Co., USA) nanoparticles and platinum black (Pt-black, Alfa Aesar Co., USA) nanoparticles were dispersed in an ethanol solvent at a mass ratio of 1:1 without an ionomer within the mesh-shaped square macropore structure. The oxygen electrode was then fabricated using a drop-wise method with the dispersion. The dispersion used consisted of 10 wt.% catalyst dispersed in 3 ml of ethanol, with a catalyst loading content of 2.0 mg cm⁻¹. -2 It is produced as.

[0029] The membrane electrode assembly (MEA) of the anion exchange membrane integrated fuel cell was fabricated using the catalyst-coated substrate (CCS) method. FAA-5-30 (Fumatech Co., Germany) was used as the anion exchange membrane, and two types of oxygen electrodes (an oxygen electrode with mesh-shaped square macropores and a conventional compressed electrode without a pore structure) and a hydrogen electrode were used. The hydrogen electrode was fabricated by spraying an ink containing 40 wt.% Pt / C catalyst and FAA-3-Br ionomer (Fumatech Co., Germany) dispersed in an isopropanol solvent onto a carbon paper substrate. By bonding the anion exchange membrane, oxygen electrode, and hydrogen electrode fabricated as described above, an anion exchange membrane integrated fuel cell containing a mesh-shaped oxygen electrode with a square macropore structure was obtained.

[0030] <Comparative Example> Conventional oxygen electrode having a dense catalyst particle structure

[0031] As a comparative example, a method of spraying ink dispersed with nickel-iron alloy particles and platinum particles was used to fabricate a conventional compressed oxygen electrode without a pore structure. Ink in which the two catalyst particles were dispersed in a dispersion solution at a mass ratio of 1:1 was loaded using a spray method. 2.0 mg cm⁻¹ -2 An oxygen electrode was formed with a loading content. The dispersion contains FAA-3 ionomer (Fumatech Co., Germany), water, and a catalyst in an isopropanol solvent. The ionomer content is 10 wt.% of the catalyst content.

[0032] <Experimental Example>

[0033] Figure 1(a) is a diagram of an anion exchange membrane integrated fuel cell with an oxygen electrode having a mesh-shaped square macropore structure. Figure 1(b) is a schematic diagram of the oxygen electrode having a mesh-shaped square macropore structure, and Figure 1(c) is a schematic diagram of a conventional electrode compressed without a pore structure. In the oxygen electrode with a mesh-shaped square macropore structure, it can be observed that nanoparticles are loaded in small sizes without clumping due to the macropores (Figures 1(f, g)). On the other hand, in the conventional electrode, it can be observed that nanoparticles are densely clumped together (Figures 1(h, i)).

[0034] X-ray diffraction (XRD) results confirm that nickel-iron alloy nanoparticles and platinum nanoparticles are well loaded onto each oxygen electrode (Fig. 2(a)). Raman analysis results indicate that the structure constituting the oxygen electrode with a mesh-shaped square macropore structure is composed of carbon nanotubes with high blackness, suggesting excellent long-term stability in fuel cell mode and water electrolysis mode (Fig. 2(b)). In addition, from the mercury porosity results, it can be confirmed that macropores are formed only in the oxygen electrode with a mesh-shaped square macropore structure (Fig. 2(c). From the X-ray absorption near-edge structure (XANES) results of Fe K-edge, Ni K-edge, and Pt L3-edge in Fig. 2(df), it can be seen that the oxidation states of Fe, Ni, and Pt constituting the two electrodes are almost similar to the Fe, Ni, and Pt metallic states, and that the introduction of the mesh-shaped square macropore structure does not affect the oxidation states of the metal atoms and the surrounding electronic environment.

[0035] Figure 3 shows the half-cell test results of an oxygen electrode having a mesh-shaped square macropore structure and a conventional oxygen electrode. According to the half-cell results (Figure 3(ad)), the oxygen electrode having a mesh-shaped square macropore structure exhibits superior oxygen reduction and oxygen evolution activity compared to the conventional oxygen electrode. Furthermore, as shown in Figure 3(e), stable oxygen reduction performance was maintained for 24 hours as a result of a constant voltage test at 0.8 V, and as shown in Figure 3(f), 10 mA cm⁻¹ -2 It was confirmed that the oxygen evolution reaction performance was maintained stably for 100 hours, confirming that the oxygen electrode having a mesh-shaped square macropore structure has long-term stability comparable to that of conventional oxygen electrodes.

[0036] 20 mA cm² based on single cell test results -2 It was confirmed that a high round-trip efficiency of approximately 55% was exhibited at current densities, which is the highest value among currently reported literature. In addition, at 50, 100, and 150 mA cm⁻¹ -2 It was confirmed that the oxygen electrode having a mesh-shaped square macropore structure maintains a high reciprocating efficiency of about 50% at a high current density, thereby confirming that it has high reciprocating efficiency even in the high current range. In addition, it was confirmed that it exhibits high stability compared to the conventional electrode in a long-term stability experiment (Fig. 4(d)) in which 5 cycles were operated for 1 hour each in fuel cell mode and water electrolysis mode.

[0037] In conclusion, when an oxygen electrode having mesh-shaped square macropores was applied to an anion exchange membrane integrated fuel cell, it was confirmed to exhibit high activity, reciprocating efficiency, and durability in both fuel cell mode and water electrolysis mode.

[0038] In the half-cell results evaluating only catalytic activity, the oxygen electrode having a mesh-shaped square macropore structure exhibited superior oxygen reduction and oxygen evolution activities compared to the conventional oxygen electrode. Furthermore, a constant voltage test at 0.8 V showed that stable oxygen reduction performance was maintained for 24 hours, and 10 mA cm⁻¹ -2 It was confirmed that the oxygen evolution reaction performance remained stable for 100 hours, thereby confirming that the oxygen electrode having a mesh-shaped square macropore structure has long-term stability comparable to that of conventional oxygen electrodes.

[0039] 20 mA cm² based on single cell test results -2 It was confirmed that a high round-trip efficiency of approximately 55% was exhibited at current densities, which is the highest value among currently reported literature. In addition, at 50, 100, and 150 mA cm⁻¹ -2It was confirmed that the oxygen electrode having a mesh-shaped square macropore structure maintains a high reciprocating efficiency of about 50% at a high current density, thereby confirming that it has high reciprocating efficiency even in the high current range.

[0040] In addition, in a long-term stability experiment in which fuel cell mode and water electrolysis mode were operated for 5 cycles of 1 hour each, it was confirmed that the electrode exhibited high stability compared to the conventional electrode. The factors contributing to this performance increase were identified as the increased active surface area of ​​the catalyst and the provision of a smooth reaction pathway for reactants and products due to the mesh-shaped square macropore structure, as well as the reduction in resistance due to the high conductivity of carbon nanotubes.

[0041] The present invention is not limited to the above embodiments and can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without changing the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

Claim 1 An oxygen electrode for an anion exchange membrane integrated fuel cell, comprising: a carbon nanotube structure formed by stacking two or more carbon nanotube layers each containing a plurality of parallel carbon nanotubes; and a catalyst layer formed on the carbon nanotube structure; wherein a plurality of parallel carbon nanotubes included in any carbon nanotube layer included in the carbon nanotube structure include a rectangular macropore formed orthogonally to a plurality of parallel carbon nanotubes included in an upper and lower adjacent carbon nanotube layer, and wherein the catalyst layer includes a catalyst active in an oxygen reduction reaction (ORR) and a catalyst active in an oxygen evolution reaction (OER). Claim 2 An oxygen electrode for an anion exchange membrane integrated fuel cell, wherein, in claim 1, the carbon nanotube layer is obtained by separating a plurality of parallel carbon nanotubes from a vertically aligned carbon nanotube (VACNT) forest composed of vertically aligned carbon nanotubes. Claim 3 delete Claim 4 An oxygen electrode for an anion exchange membrane integrated fuel cell, characterized in that, in claim 1, it comprises: a carbon nanotube structure having 10 layers of carbon nanotubes and mesh-shaped square macropores; and a catalyst layer formed on the carbon nanotube structure, comprising platinum black (Pt-black) as an oxygen reduction reaction catalyst and nickel-iron alloy (NiFe) as an oxygen evolution reaction catalyst. Claim 5 An anion exchange membrane integrated fuel cell comprising an oxygen electrode described in any one of claims 1, 2 and 4.

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