Electrochemical system and method for manufacturing the oxygen electrode of the electrochemical system

Abstract

This system provides an electrochemical system with an oxygen electrode that exhibits good OER performance. [Solution] An electrochemical system having a cathode electrode and an anode electrode, wherein either the cathode electrode or the anode electrode is an oxygen electrode, and the oxygen electrode is provided with a Ti substrate, a Ta2O5 layer, a ZrN layer and a zirconium oxide layer in that order.

Description

[Technical Field]

[0001] This invention relates to an electrochemical system and a method for manufacturing an oxygen electrode for an electrochemical system. [Background technology]

[0002] Electrochemical systems such as alkaline water electrolyzers and alkaline fuel cells are equipped with an oxygen electrode, which serves as either an anode electrode for generating oxygen or a cathode electrode for reducing oxygen.

[0003] In electrochemical systems such as alkaline water electrolyzers and alkaline fuel cells, metal materials such as Ni and Fe, as well as pevrosite-based materials, have been used, evaluated, and studied for oxygen evolution reactions in alkaline solutions. While these materials exhibit activity and durability, there are challenges regarding their stability, particularly in the impact on reverse current in high-concentration alkaline environments and when operating with fluctuating power sources such as renewable energy sources. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] A. Aracena et al., “Trans. Nonferrous Met. Soc. China, 28, 177(2018).” [Non-Patent Document 2] Matsuzawa et al., Mater. Sci Eng. B, 267, 115112 (2021) [Non-Patent Document 3] Matsuzawa et al., ECS Trans, 111(4), 39(2023) [Overview of the project] [Problems that the invention aims to solve]

[0005] In contrast, zirconium oxides, such as zirconium itself, are extremely stable even in high-concentration alkalis (Non-Patent Document 1). However, from the perspective of electron conductivity, although oxygen evolution reactions (OERs) do occur, their activity is extremely low (Non-Patent Documents 2 and 3).

[0006] To solve these problems, the present invention aims to provide an electrochemical system equipped with an oxygen electrode having good OER capacity. [Means for solving the problem]

[0007] The above problems are solved by the present invention, which is defined as follows. (1) An electrochemical system having a cathode electrode and an anode electrode, Either the cathode electrode or the anode electrode is an oxygen electrode. The oxygen electrode is an electrochemical system in which a Ti substrate, a Ta2O5 layer, a ZrN layer, and a zirconium oxide layer are provided in this order. (2) The electrochemical system is an alkaline water electrolysis device, The electrochemical system according to (1), wherein the oxygen electrode is the anode electrode of the alkaline water electrolysis apparatus. (3) The electrochemical system is an alkaline fuel cell, The electrochemical system according to (1), wherein the oxygen electrode is the cathode electrode of the alkaline fuel cell. (4) A step of forming a Ta2O5 layer on the surface of a Ti substrate by high-frequency magnetron sputtering, The process involves forming a ZrN layer on the surface of the Ta2O5 layer using ammonia by atomic layer deposition, A step of forming a zirconium oxide layer on the surface of the ZrN layer by electrolytic oxidation, A method for manufacturing an oxygen electrode in an electrochemical system according to any one of (1) to (3) above, wherein the oxygen electrode is manufactured by the method described above. [Effects of the Invention]

[0008] According to the present invention, an electrochemical system having an oxygen electrode with good OER performance can be provided.

Brief Description of the Drawings

[0009] [Figure 1] It is a schematic diagram of an oxygen electrode according to an embodiment of the present invention. [Figure 2] It is a schematic diagram of an alkaline water electrolysis device according to an embodiment of the present invention. [Figure 3] It is a schematic diagram of an alkaline fuel cell according to an embodiment of the present invention. [Figure 4] FIG. 4(A) is a photoelectron spectrum of Sample 1, and FIG. 4(B) is a photoelectron spectrum of Sample 2. [Figure 5] It is a graph showing current-potential curves according to Example 1 and Comparative Example 1.

Modes for Carrying Out the Invention

[0010] Next, modes for carrying out the present invention will be described in detail with reference to the drawings. It should be understood that the present invention is not limited to the following embodiments, and modifications and improvements in design can be appropriately made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

[0011] <Electrochemical System> The electrochemical system according to an embodiment of the present invention is an electrochemical system having a cathode electrode and an anode electrode, and either the cathode electrode or the anode electrode is an oxygen electrode. As shown in FIG. 1, the oxygen electrode 10 is composed of a Ti substrate 11, a Ta2O5 layer 12, a ZrN layer 13, and a zirconium oxide layer 14 provided in this order.

[0012] The thickness of the Ti substrate 11 is not particularly limited, but is preferably 2 to 12 μm, and more preferably 7 to 10 μm.

[0013] The Ta2O5 layer 12 is provided as an intermediate layer between the Ti substrate 11 and the ZrN layer 13. The surface of the Ti substrate 11 has irregularities. Even if the surface of the Ti substrate 11 is mirror-polished in advance, irregularities exist at the micro level. Due to these irregularities, when a catalyst layer (Zr layer) is placed on the Ti substrate 11, many gaps exist at the interface. Due to these gaps, an oxide (Ti oxide) is likely to occur on the surface of the Ti substrate 11. This Ti oxide may prevent the flow of current at the oxygen electrode. Regarding such a problem, in the oxygen electrode according to the embodiment of the present invention, as described above, the Ta2O5 layer 12 is provided as an intermediate layer between the Ti substrate 11 and the ZrN layer 13. It is presumed that the Ta2O5 layer 12 has good adhesion to the Ti substrate 11, and due to this property, gaps are unlikely to occur at the interface with the Ti substrate 11. As a result, the generation of Ti oxide can be suppressed well. Therefore, the flow of current at the oxygen electrode becomes good, and the OER performance of the oxygen electrode is improved. The thickness of the Ta2O5 layer 12 is preferably 1 to 5 nm, more preferably 2 to 4 nm.

[0014] The thickness of the ZrN layer 13 is not particularly limited, but is preferably 4 to 20 nm, more preferably 5 to 14 nm.

[0015] The zirconium oxide layer 14 is a layer of an oxide of Zr that is formed on the surface of the ZrN layer 13 by electrolytic oxidation as described later. The zirconium oxide layer 14 is gradually oxidized from the ZrN layer 13 side, and is completely oxidized (ZrO2) on the outermost surface of the zirconium oxide layer 14. Therefore, the chemical formula of the zirconium oxide layer 14 can be represented by ZrO x (where 0 < x ≦ 2). The thickness of the zirconium oxide layer 14 is not particularly limited, but is preferably 3 to 8 nm, more preferably 5 to 7 nm.

[0016] Examples of the electrochemical system include an alkaline water electrolysis device and an alkaline fuel cell, etc., and specific embodiments thereof will be described in detail below.

[0017] <Alkaline water electrolysis device> Figure 2 is a schematic diagram of an alkaline water electrolysis apparatus 20 according to an embodiment of the present invention. The alkaline water electrolysis apparatus 20 has an anode chamber 22 provided with an anode electrode 24, a cathode chamber 21 provided with a cathode electrode 23, and a diaphragm 25 that separates the anode chamber 22 and the cathode chamber 21.

[0018] In the alkaline water electrolysis apparatus 20, the following reactions occur as the cathode reaction, anode reaction, and electrolysis apparatus reaction, as shown in the following reaction equations. Cathode reaction: 2H2O + 2e - → H2 + 2OH - Anodic reaction: 2OH - + H2O → 1 / 2O2 + 2e - Electrolytic reaction: H2O → H2+ 1 / 2O2

[0019] The cathode electrode 23 and diaphragm 25 of the alkaline water electrolysis apparatus 20 according to the embodiment of the present invention can be of a configuration known in the technical field related to alkaline water electrolysis apparatuses. Specifically, the cathode electrode 23 can be made of a known material, for example, an iron-based material, a nickel-based material, etc. The diaphragm 25 can be made of a known material, for example, an asbestos, polymer-reinforced asbestos, PTFE-bound potassium titanate, PTFE-bound zirconia, polysulfone-bound polyantimonate / antimony oxide, sintered nickel, ceramics / nickel oxide-coated nickel, polysulfone, etc.

[0020] In the alkaline water electrolysis apparatus 20 according to an embodiment of the present invention, the alkaline water 26 to be electrolyzed can be an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, or the like, and in particular, an aqueous potassium hydroxide solution of 20 to 30% by mass can be used.

[0021] As the anode electrode 24 of the alkaline water electrolysis device 20 according to an embodiment of the present invention, the oxygen electrode (oxygen electrode 10 in FIG. 1) of the electrochemical system according to an embodiment of the present invention is used. According to such a configuration, the OER ability of the oxygen electrode in the electrochemical system becomes good.

[0022] <Alkaline fuel cell> FIG. 3 is a schematic diagram of an alkaline fuel cell 30 according to an embodiment of the present invention. The alkaline fuel cell 30 is provided with a cathode electrode 33 and an anode electrode 34 so as to sandwich an electrolyte solution 31.

[0023] In the alkaline fuel cell 30, the anode electrode 34 serves as a hydrogen electrode, and the cathode electrode 33 functions as an oxygen electrode. An electrolyte solution 31 through which hydroxide ions can pass is sandwiched between the anode electrode 34 and the cathode electrode 33 and used as an electrolyte. When hydrogen gas as fuel is supplied to the anode electrode 34 and oxygen gas is supplied to the cathode electrode 33, the cathode reaction and anode reaction shown in the following reaction formulas proceed at the respective electrodes, and a battery reaction occurs due to these. The hydroxide ions generated by the cathode reaction pass through the electrolyte solution 31 and move to the anode electrode 34. At the anode electrode 34, a reaction to generate water proceeds.

[0024] Cathode reaction: 1 / 2O2 + H2O + 2e - → 2OH - Anode reaction: H2 + 2OH - → 2H2O + 2e - Battery reaction: H2 + 1 / 2O2 → H2O

[0025] For the electrolyte solution 31 and the anode electrode 34 of the alkaline fuel cell 30 according to an embodiment of the present invention, those having known configurations can be used respectively. Specifically, for the anode electrode 34, known materials can be used, and for example, it can be composed of an iron-based material, a nickel-based material, or the like.

[0026] As the cathode electrode 33 of the alkaline fuel cell 30 according to the embodiment of the present invention, the oxygen electrode of the electrochemical system according to the embodiment of the present invention (oxygen electrode 10 in Figure 1) is used. With this configuration, the OER capacity of the oxygen electrode in the electrochemical system is improved.

[0027] <Manufacturing method for oxygen electrodes in electrochemical systems> Next, a method for manufacturing the oxygen electrode of an electrochemical system according to an embodiment of the present invention will be described in detail. First, a Ta2O5 layer is formed on the surface of the Ti substrate by radio frequency (RF) magnetron sputtering. RF magnetron sputtering allows for efficient formation of an insulating film by using a high-frequency power supply. Furthermore, it is preferable to embed the Ti substrate in resin, then mirror polish it, and then form the Ta2O5 layer on the polished surface of the mirror-polished Ti substrate by the aforementioned RF magnetron sputtering.

[0028] Next, a ZrN layer is formed on the surface of the Ta2O5 layer using atomic layer deposition (ALD) with ammonia. Ammonia is used to form nitrides. ALD is a technique that uses vacuum to form thin films at the atomic layer level on a substrate. Because the film is deposited one atomic layer at a time, it offers precise control over film thickness. Furthermore, because it utilizes self-limiting surface reactions, it is possible to deposit films with very few pinholes or foreign particles.

[0029] Next, a zirconium oxide layer is formed on the surface of the ZrN layer by electrolytic oxidation. Electrolytic oxidation is a method of electrochemically oxidizing a substance by utilizing the oxidation reaction at the anode of electrolysis without adding an oxidizing agent, thereby generating an electrolytic oxide film (zirconium oxide layer).

[0030] Electrolytic oxidation is preferable because good catalytic activity can be obtained when oxidation occurs in a high-potential state under high-concentration alkali. When conventional oxidation is performed, the thickness of the zirconium oxide layer formed on the surface of the ZrN layer is unknown, but by using electrolytic oxidation as in the embodiment of the present invention, the thickness of the zirconium oxide layer can be controlled. As described above, an oxygen electrode for an electrochemical system according to an embodiment of the present invention is obtained. [Examples]

[0031] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0032] (Example 1) A disc-shaped Ti substrate with a height of 9 mm and a diameter of 5 mm was prepared, and its surface was mirror-polished. Next, a 2nm thick Ta2O5 layer was formed on the surface of the Ti substrate by RF magnetron sputtering. The RF magnetron sputtering conditions are shown below. • Equipment used: RF magnetron sputtering system manufactured by ULVAC, Inc. • Target: Ta metal disc (manufactured by Furuuchi Chemical Co., Ltd., purity 99.9%) • Spattering time: 1 hour Output: 150W Oxygen partial pressure: 0.15 Pa Argon partial pressure: 0.23 Pa ·Substrate heating temperature: 300℃

[0033] Next, a 12.5 nm thick ZrN layer was formed on the surface of the Ta2O5 layer using atomic layer deposition with ammonia under the following conditions. • Equipment used: Atomic layer deposition system manufactured by Anric Technologies (USA) • Precursor: Tetrakisdimethylamido-zirconium • Nitride agent: Ammonia gas ·Substrate heating temperature: 175℃ • Deposition cycle: 150 cycles (0.083 nm / cycle)

[0034] Next, SSV (Surface Stabilization Variation) was performed on the sample with the ZrN layer formed as described above under the following conditions, and the electrochemical properties related to the oxygen evolution reaction were evaluated. During the evaluation of these electrochemical properties, the surface of the ZrN layer was electrolytically oxidized. As a result, a zirconium oxide layer was formed on the surface of the ZrN layer, and an oxygen electrode was obtained. (SSV: Slow Scan Volumetric) • Electrochemical system: Three-electrode cell • Reference electrode: Reversible hydrogen electrode (RHE) • Opposite: Glassy Carbon Plate • Working electrode: Oxygen electrode prepared in Example 1 ·Electrolyte: 7.0M KOH • Nitrogen atmosphere: Nitrogen flow rate 20 sccm bubbling Bathtub temperature: 30℃±0.5℃ • Voltage range: 1.2~2.0V vs. RHE • Scanning speed: 5mVs -1

[0035] (Comparative Example 1) A Zr substrate (99.2% purity) with dimensions of 10mm x 20mm and a thickness of 0.5mm was prepared. Next, plasma deposition was performed on the Zr substrate under the following conditions to form a ZrO2 film with a thickness of 30 nm. This yielded the oxygen electrode according to Comparative Example 1. • Equipment used: Arc plasma deposition system manufactured by Advance Engineering Co., Ltd. • Target: Zr ·Temperature: Room temperature • Ambient: Ar-based with O2 (flow rate: 100 ccm) • Operating voltage: 100V • Film deposition cycle: 650 shots

[0036] For the oxygen electrode obtained in Comparative Example 1, electrochemical measurements were performed using SSV in the same manner as in Example 1, followed by surface analysis of the oxygen electrode surface using X-ray photoelectron spectroscopy (XPS).

[0037] <XPS Surface Analysis> In Example 1, for Sample 1 immediately after forming the ZrN layer on the surface of the Ta2O5 layer and Sample 2 of the oxygen electrode after the above-described electrochemical measurement, as an X-ray photoelectron spectrometer, XPS Quantera SXM manufactured by ULVAC-PHI, Inc. was used to perform surface analysis by X-ray photoelectron spectroscopy (XPS) under the following conditions. · X-ray source: Monochromatic Al (1486.6 eV) · Detection area: 100 μmφ · Detection depth: Approximately 4 - 5 nm (Take-out angle 45°)

[0038] The photoelectron spectrum of Sample 1 is shown in Fig. 4(A), and the photoelectron spectrum of Sample 2 is shown in Fig. 4(B). From these results, it can be seen that during the electrochemical measurement, the surface of the ZrN layer was electrolytically oxidized, and a zirconium oxide layer was formed on the surface of the ZrN layer.

[0039] <Electrochemical Measurement Results> From the results of SSV, the current-potential curve is shown in Fig. 5. In Example 1, it can be seen that compared with Comparative Example 1, the increase in current density is remarkable, and an electrochemical system equipped with an oxygen electrode having good OER performance is obtained.

Explanation of Reference Signs

[0040] 10 Oxygen electrode 11 Ti substrate 12 Ta2O5 layer 13 ZrN layer 14 Zirconium oxide layer 20 Alkaline water electrolyzer 21 Cathode chamber 22 Anode chamber 23 Cathode electrode 24 Anode electrode (oxygen electrode) 25 Membrane 26 Alkaline water 30 Alkaline fuel cell 31 Electrolyte solution 33 Cathode electrode (oxygen electrode) 34 Anode electrode (hydrogen electrode)

Claims

1. An electrochemical system having a cathode electrode and an anode electrode, Either the cathode electrode or the anode electrode is an oxygen electrode. The oxygen electrode is a Ti substrate, Ta 2 O 5 An electrochemical system in which a layer, a ZrN layer, and a zirconium oxide layer are arranged in this order.

2. The aforementioned electrochemical system is an alkaline water electrolysis device. The electrochemical system according to claim 1, wherein the oxygen electrode is the anode electrode of the alkaline water electrolysis apparatus.

3. The electrochemical system is an alkaline fuel cell. The electrochemical system according to claim 1, wherein the oxygen electrode is the cathode electrode of the alkaline fuel cell.

4. Ta is applied to the surface of the Ti substrate by high-frequency magnetron sputtering. 2 O 5 The process of forming layers, The Ta 2 O 5 A process of forming a ZrN layer on the surface of the layer using ammonia by atomic layer deposition, A step of forming a zirconium oxide layer on the surface of the ZrN layer by electrolytic oxidation, A method for manufacturing an oxygen electrode for an electrochemical system according to any one of claims 1 to 3, wherein the oxygen electrode is manufactured by the method described above.

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