Accelerated evaluation method for anodes

Abstract

An accelerated evaluation method for anodes is provided, which can simulate highly variable power output, such as from renewable energy sources, and accurately evaluate the durability of anodes powered by such highly variable power output in a shorter time. The accelerated evaluation method for anodes involves electrochemical operations in an aqueous electrolyte to accelerate the evaluation of anode durability. The method includes the following steps: J e Steps, with duration T e Anode loading of 0.1 A / cm 2 The above oxidation current; and E min Steps, with duration T min To maintain the anode at a fixed potential lower than the open circuit potential, J e Steps and E min Repeat each step more than 100 times.

Description

Technical Field

[0001] This invention relates to an accelerated evaluation method for, for example, an anode used in water electrolysis. Background Technology

[0002] Hydrogen is a secondary energy source suitable for storage and transportation with a low environmental impact, making hydrogen energy systems, which utilize hydrogen as an energy carrier, a focus of attention. Currently, hydrogen is mainly produced through methods such as steam modification of fossil fuels. However, from the perspective of the global greenhouse effect and the depletion of fossil fuels, it is also important to produce hydrogen through water electrolysis using renewable energy sources such as solar and wind power. Water electrolysis is low-cost and suitable for large-scale production, making it a promising technology for hydrogen production.

[0003] Currently, practical water electrolysis can be broadly categorized into two types. One is alkaline water electrolysis, which uses a highly concentrated alkaline solution as the electrolyte. The other is solid polymer water electrolysis, which uses a solid polymer membrane (SPE) as the electrolyte. It is generally believed that, for large-scale hydrogen production via water electrolysis, alkaline water electrolysis using inexpensive materials such as nickel-based metals is more suitable than solid polymer water electrolysis, which employs electrodes made from large quantities of expensive precious metals. Recently, the development of water electrolysis using anion exchange membranes is also underway. In water electrolysis using anion exchange membranes, the same electrode materials as in alkaline water electrolysis can be used.

[0004] High-concentration alkaline solutions exhibit increased conductivity with rising temperature, but also increased corrosivity. Therefore, the upper limit of the operating temperature is limited to approximately 80–90°C. Through the development of materials for electrolytic cells resistant to high temperatures and high concentrations of alkaline solutions, the development of various piping materials, low-barrier membranes, and electrodes with increased surface area and catalyst composition, electrolysis performance has been improved at current densities of 0.3–0.4 A·cm⁻¹. -2 The voltage is increased to around 1.7–1.9V (efficiency of 78–87%).

[0005] As anodes for alkaline water electrolysis, nickel-based materials, which are stable in high-concentration alkaline solutions, are used. It is known that nickel-based anodes have a lifespan of several decades when using a stable power source for alkaline water electrolysis. However, when renewable energy sources are used as power sources, the conditions become more severe, such as rapid start-up and shutdown, and load fluctuations, leading to performance degradation of nickel-based anodes.

[0006] The formation and reduction of nickel oxides both occur on the metal surface. Therefore, the detachment of the electrode catalyst formed on the metal surface is promoted along with these reactions. When the power for electrolysis is no longer supplied, electrolysis ceases, and the nickel-based anode is maintained at a potential lower than the oxygen generation potential (1.23 V vs. RHE) and higher than the hydrogen generation cathode (0.00 V vs. RHE) serving as the counter electrode. Electromotive forces based on various chemical species are generated within the electrolytic cell; due to the advancement of the cell reactions, the anode potential is maintained at a low level, and the reduction of nickel oxides is promoted.

[0007] For example, in an electrolytic reactor that combines multiple cells such as an anode chamber and a cathode chamber, the current generated by the cell reaction leaks through the piping connecting the cells. As a countermeasure to prevent such current leakage, methods include continuously flowing a small current when the reactor is shut down. However, continuously flowing a small current when the reactor is shut down requires special power control and continuously produces oxygen and hydrogen, thus incurring excessive management overhead. Furthermore, to intentionally avoid reverse current, liquid can be immediately extracted after shutdown to prevent cell reaction, but this is not a suitable solution when considering operation under conditions of highly variable power output, such as from renewable energy sources.

[0008] Previously, platinum group metals, platinum group metal oxides, valve metal oxides, iron group oxides, and lanthanum group metal oxides were used as catalysts for oxygen generation in alkaline water electrolysis (anodine catalysts). Other known anode catalysts include nickel-based alloys such as Ni-Co and Ni-Fe; nickel with expanded surface area; conductive oxides (ceramic materials) such as spinel-based Co3O4 and NiCo2O4, and perovskite-based LaCoO3 and LaNiO3; noble metal oxides; and oxides formed from lanthanum group metals and noble metals.

[0009] As anodes for oxygen generation in high-concentration alkaline water electrolysis, anodes with a lithium-containing nickel oxide layer pre-formed on the surface of a nickel substrate are known (Patent Documents 1 and 2). Furthermore, anodes for alkaline water electrolysis with a lithium-containing nickel oxide catalyst layer containing lithium and nickel in a specified molar ratio formed on the surface of a nickel substrate have been proposed (Patent Document 3), and anodes for alkaline water electrolysis with a catalyst layer containing nickel-cobalt oxides and either iridium oxide or ruthenium oxide formed on the surface of a nickel substrate have been proposed (Patent Document 4). However, even the anodes proposed in Patent Documents 1-4 tend to degrade in performance when powered by electricity with large output fluctuations, such as from renewable energy sources, making long-term stable use difficult. Therefore, it is desirable to develop an anode that can be used more stably for longer periods, even when powered by electricity with large output fluctuations.

[0010] Furthermore, the service life of electrodes is 5 to 10 years, so it is practically impossible to spend that much time on electrode development and evaluation. Therefore, methods to accelerate the evaluation of anodes and anode catalysts by simulating actual electrolysis conditions such as alkaline water electrolysis and reproducing actual degradation in a shorter time are also very important for the development and quality management of anodes and anode catalysts.

[0011] To date, methods for evaluating the durability of anode catalysts have included repeated use of cyclic voltammetry, cyclic current methods (Non-Patent Documents 1 and 2), and methods involving investigation using varying currents such as sinusoidal waves (Non-Patent Document 3). Furthermore, a test method has been proposed that involves repeated operation at appropriate potentials to select non-precious metal catalysts (Patent Document 5). Moreover, an accelerated test involving the continuous flow of very large currents has been proposed (Patent Document 6).

[0012] On the other hand, the following was reported: when the potential becomes negative compared to the open circuit potential after the water electrolysis reaction is completed, an anodic electrochemical reduction reaction occurs on the surface of the anode, and the catalyst dissolution and stripping are accelerated by repeated switching between reducing and oxidizing conditions (Non-Patent Literature 4 and 5).

[0013] Existing technical documents

[0014] Patent documents

[0015] Patent Document 1: Description of UK Patent Application Publication No. 864457

[0016] Patent Document 2: US Patent No. 2,928,783

[0017] Patent Document 3: Japanese Patent Application Publication No. 2015-86420

[0018] Patent Document 4: Japanese Patent Application Publication No. 2017-190476

[0019] Patent Document 5: U.S. Patent Application Publication No. 2016 / 199821

[0020] Patent Document 6: US Patent No. 4,498,962

[0021] Non-patent literature

[0022] Non-patent literature 1: D. Delgado, F. Bizzotto, A. Zana, and M. Arenz, Chem. Phys. Chem., 2, 3147-3153 (2019)

[0023] Non-patent literature 2: Tsukada, Yudai; Kuroda, Yoshiyuki; Niiro, Hideaki; Fujii, Yuichi; Fujimoto, Norikazu; Mitsushima, Shigenori; Electrochimica Acta (20200901), 353, pp.136544

[0024] Non-patent literature 3: Z. Dobo and AB Palotas, Int. J. Hydrogen Energy, 42, 5649-5656 (2017)

[0025] Non-patent literature 4: M. Bernt et al., Chemie Ing. Tech., 92, 31-39 (2020)

[0026] Non-patent literature 5: A. Weis et al., J. Electrochem. Soc., 166, F487-F497 (2019) Summary of the Invention

[0027] The problem the invention aims to solve

[0028] However, current evaluation methods are insufficient as a means to accelerate the evaluation of the durability of anodes powered by highly variable electricity, such as from renewable energy sources. In other words, the current situation is that no practical method has yet been found to accelerate the evaluation of the lifespan of anodes used in water electrolysis and similar applications by simulating the intermittent characteristics of highly variable output from renewable energy sources.

[0029] The present invention was made in view of the problems of the prior art, and its objective is to provide an accelerated evaluation method for an anode that can simulate electricity with large output fluctuations, such as renewable energy, and accurately evaluate the durability of an anode powered by such electricity with large output fluctuations in a shorter time.

[0030] Solution for solving the problem

[0031] In order to solve the above-mentioned problems, the inventors conducted in-depth research and found that by repeatedly performing the steps of applying a current of a fixed density and maintaining it at a fixed potential, the above-mentioned problems can be solved, thus completing the present invention.

[0032] That is, according to the present invention, an accelerated evaluation method for the anode is provided as shown below.

[0033] [1] An accelerated evaluation method for an anode, which accelerates the evaluation of the anode's durability by performing an electrochemical operation in an aqueous electrolyte, the accelerated evaluation method for the anode comprising the following steps: J e Steps, with duration T e The anode is loaded with 0.1 A / cm 2 The above oxidation current; and E min Steps, with duration T min Maintain the anode at a fixed potential lower than the open circuit potential, and set the J... e Steps and the E min Repeat each step more than 100 times.

[0034] [2] According to the accelerated evaluation method for the anode described in [1], wherein,

[0035] The duration T e and the duration T min Each is less than 120 seconds.

[0036] [3] According to the accelerated evaluation method for the anode described in [1] or [2], wherein,

[0037] In the J e Steps and the E min The steps also include an LSV step, in which the anode is subjected to a process from the J... e The linear scan voltammetry method begins with a low potential at the end of the step, wherein the scan rate SR of the linear scan voltammetry method is in the range of 50 to 500 mV / s.

[0038] [4] According to the accelerated evaluation method for the anode described in [3], wherein,

[0039] In the J e The step between the LSV step and the LSV step also includes an OCP step, in which the anode is kept at an open circuit potential for a period of 10 to 60 seconds.

[0040] [5] An accelerated evaluation method for the anode as described in any one of [1] to [4], wherein,

[0041] In the E min In this step, the anode is maintained at a potential 0.6 to 1.0 V lower than the open circuit potential.

[0042] [6] An accelerated evaluation method for the anode as described in any one of [1] to [5], wherein,

[0043] The anode is an oxygen generating electrode.

[0044] The effects of the invention

[0045] According to the present invention, an accelerated evaluation method for anodes can be provided, which can simulate electricity with large output fluctuations, such as renewable energy, and accurately evaluate the durability of anodes powered by such electricity with large output fluctuations in a shorter time. Attached Figure Description

[0046] Figure 1 This is a diagram illustrating one embodiment of the accelerated evaluation method for the anode of the present invention.

[0047] Figure 2 These are diagrams illustrating other embodiments of the accelerated evaluation method for the anode of the present invention.

[0048] Figure 3 In Example 1, an oxidation current of 0.1 A / cm was described corresponding to the cycle number. 2 A graph of electrode potentials at different times.

[0049] Figure 4 The graph shows the polarization curves at a holding potential of 0.5V vs. RHE ((a)) and a holding potential of 0.7V vs. RHE ((b)) in Example 1.

[0050] Figure 5 In Example 1, an oxidation current of 0.1 A / cm was described corresponding to the cycle number. 2 A graph of electrode potentials at different times.

[0051] Figure 6 In Example 2, an oxidation current of 0.1 A / cm was described corresponding to the cycle number. 2 A graph of electrode potentials at different times.

[0052] Figure 7 This shows the duration T in Example 2. min A graph showing the polarization curves at 10s and 60s.

[0053] Figure 8 In Example 2, an oxidation current of 0.1 A / cm was described corresponding to the cycle number. 2 A graph of electrode potentials at different times.

[0054] Figure 9 In Example 3, an oxidation current of 0.1 A / cm was described corresponding to the cycle number. 2 A graph of electrode potentials at different times.

[0055] Figure 10 In Example 3, an oxidation current of 0.1 A / cm was described corresponding to the cycle number. 2A graph of electrode potentials at different times.

[0056] Figure 11 In Example 4, an oxidation current of 0.1 A / cm was described corresponding to the cycle number. 2 A graph of electrode potentials at different times.

[0057] Figure 12 This shows the duration T in Example 4. min A graph showing the polarization curves at 10s and 60s.

[0058] Figure 13 In Example 4, an oxidation current of 0.1 A / cm was described corresponding to the cycle number. 2 A graph of electrode potentials at different times. Detailed Implementation

[0059] The accelerated evaluation method for the anode of the present invention (hereinafter also referred to as the "evaluation method") is, for example, a method for accelerating the evaluation of the durability of anodes such as anodes (oxygen generating electrodes) used in alkaline water electrolysis by performing electrochemical operations in an aqueous electrolyte. This method includes the following steps: J e Steps, with duration T e Anode loading of 0.1 A / cm 2 The above oxidation current; and E min Steps, with duration T min The anode is maintained at a fixed potential lower than the open-circuit potential. Furthermore, J... e Steps and E min Each step is repeated more than 100 times. Details of the evaluation method of this invention are described below.

[0060] The evaluation method of the present invention is a method for accelerating the evaluation of the durability of an anode powered by electricity whose output varies in complex ways, such as renewable energy sources. It mainly consists of the operation of the steady state under oxidation current and the low potential control achieved when no power is supplied. Figure 1 This is a diagram illustrating one embodiment of the accelerated evaluation method for the anode of the present invention. Figure 1 In the evaluation method of the illustrated embodiment, the evaluation cycle is carried out in an alkaline aqueous solution at room temperature to 100°C for a duration of T. e Anode loading of 0.6 A / cm 2 J, the oxidation current used for water electrolysis e The next step is to implement the procedure for duration T. min Maintaining the anode at a fixed potential E that is lower than the open circuit potential min Steps. And, these J... e Steps and E min Repeat each step more than 100 times.

[0061] Duration T e and duration T min Preferably, the evaluation time is set to 120 seconds (2 minutes) or less, more preferably 90 seconds or less, particularly preferably 60 seconds or less, and most preferably 45 seconds or less. When the time exceeds 120 seconds, the evaluation time becomes excessively long, and even when it exceeds 120 seconds, an increase in the rate of anode degradation cannot be expected. In E... min In this process, it is preferable to maintain the anode at a potential 0.6 to 1.0 V lower than the open-circuit potential. Maintaining the anode at a potential higher than this range tends to decrease the degradation rate. On the other hand, maintaining the anode at a potential lower than the aforementioned range can sometimes lead to excessive reduction of the catalyst or the generation of hydrogen. Therefore, the degradation behavior may sometimes differ slightly from that observed in actual operation.

[0062] like Figure 1 As shown, it is preferred to be in J e Steps and E min The steps also include an LSV step, in which the implementation is performed from the ratio J. e The linear sweep voltammetry (LSV) method starts from a low potential at the end of the step. This allows for a more suitable simulation of the actual fluctuations in power output, such as those from renewable energy sources. Furthermore, the LSV typically starts from a potential near the open-circuit potential (in... Figure 1 The LSV (Low Voltage Sampling) starts at "1.5V". The LSV scan rate SR is preferably set to a range of 50–500 mV / s. When the scan rate SR is too slow, although degradation is accelerated, the overall evaluation time sometimes increases, and it is prone to power fluctuations that are unlikely to occur in practice. On the other hand, when the scan rate SR is too fast, it can sometimes undermine the purpose of setting the LSV step.

[0063] Figure 2 These are diagrams illustrating other embodiments of the accelerated evaluation method for the anode of the present invention. For example... Figure 2 As shown, it is preferred to be in J e Between the LSV step and the OCP step, there is an OCP step, in which the anode is maintained at an open-circuit potential. By further configuring the OCP step, it is possible to more appropriately simulate the actual fluctuations in power output, such as those from renewable energy sources. In the OCP step, the holding time at the open-circuit potential is preferably set to 10–60 seconds. If the holding time is too short, it may be difficult to achieve the desired effect of maintaining the open-circuit potential. On the other hand, if the holding time is too long, it may sometimes negate the purpose of including the OCP step.

[0064] J e Steps and E minThe number of repetitions (number of cycles) of each step also depends on the type of anode being evaluated, etc., and is 100 or more, preferably 10,000 or less. In addition, it is preferable to set the time of each step so that the total time required for evaluation is about several hours to several hundred hours.

[0065] (Anode)

[0066] Next, taking the anode for alkaline water electrolysis as an example of the anode being evaluated. The anode for alkaline water electrolysis (hereinafter also simply referred to as "anode") includes, for example, a conductive substrate, an intermediate layer optionally formed on the surface of the conductive substrate, and a catalyst layer formed on the surface of the intermediate layer.

[0067] The conductive substrate is a conductor for conducting electricity for electrolysis and is a component having the function of serving as a carrier for the intermediate layer and the catalyst layer. At least the surface (the surface on which the intermediate layer and the catalyst layer are formed) of the conductive substrate is formed of nickel or a nickel-based alloy. That is, the conductive substrate may be entirely formed of nickel or a nickel-based alloy, or only the surface may be formed of nickel or a nickel-based alloy. Specifically, the conductive substrate may be a substrate having a coating of nickel or a nickel-based alloy formed on the surface of a metal material such as iron, stainless steel, aluminum, or titanium by plating or the like.

[0068] The thickness of the conductive substrate is preferably 0.05 to 5 mm. The shape of the conductive substrate is preferably a shape having an opening for removing bubbles such as oxygen, hydrogen, etc. generated. For example, an expanded mesh or a porous expanded mesh can be used as the conductive substrate. When the conductive substrate is in a shape having an opening, the opening ratio of the conductive substrate is preferably 10 to 95%.

[0069] The catalyst layer is a layer having catalytic ability formed on the surface of the conductive substrate or the surface of the intermediate layer. By inserting the intermediate layer, the catalyst layer is more firmly fixed to the conductive substrate. The type of catalyst contained in the catalyst layer is not particularly limited, and a catalyst having catalytic ability corresponding to the purpose can be selected for use. Specific examples of the catalyst include nickel cobalt spinel oxide (NiCo2O4), lanthanum-based nickel cobalt perovskite oxide, iridium oxide, ruthenium oxide, and lithium nickel cobalt oxide. The lanthanum-based nickel cobalt perovskite oxide is represented by the structural formula: XNi a Co 1-a O3 (X represents at least any one of lanthanum, cerium, and praseodymium metals, 0 < a < 1).

[0070] The catalyst layer can be formed from a single catalyst or from multiple catalysts. When using multiple catalysts, they can be mixed to form a single catalyst layer. Alternatively, multiple catalyst layers can be stacked to form a stacked catalyst layer. In the case of a stacked catalyst layer, each layer can be formed from a single catalyst or from multiple catalysts. For example, a first layer of lithium nickel oxide or nickel cobalt spinel oxide can be formed on an intermediate layer, followed by a second layer of iridium oxide. There are no particular limitations on the thickness, density, etc., of the catalyst layer; they can be appropriately set according to the intended use of the anode.

[0071] An anode can be manufactured by forming an intermediate layer on the surface of a conductive substrate as needed, followed by the formation of a catalyst layer. The catalyst layer can be formed, for example, by thermal decomposition, electroplating, sputtering, ion plating, plasma spraying, etc. The following description uses the method of forming the catalyst layer by thermal decomposition as an example to illustrate the anode manufacturing method.

[0072] Before forming the catalyst layer, it is preferable to pre-treat the conductive substrate with chemical etching to remove contaminant particles such as metals and organic matter from the surface. The amount of conductive substrate consumed during chemical etching is preferably set at 30 g / m². 2 Above and 400g / m 2 Below, left and right. Furthermore, to improve adhesion with the intermediate layer and catalyst layer, it is preferable to pre-roughen the surface of the conductive substrate. Examples of roughening methods include sandblasting with blowing powder, etching with an acid soluble in the substrate, and plasma spraying.

[0073] An aqueous precursor solution containing the desired metal ions is coated onto the surface of a conductive substrate that has undergone chemical etching. Examples of coating methods include brush coating, roller coating, spin coating, and electrostatic coating. Next, the conductive substrate coated with the aqueous solution is dried as needed. The drying temperature is preferably set to a temperature that avoids vigorous solvent evaporation (e.g., around 60–80°C).

[0074] Next, the conductive substrate coated with the precursor aqueous solution is heat-treated. This allows a catalyst layer to form on the surface of the conductive substrate. The heat treatment temperature can be appropriately set. Considering the decomposition temperature of the precursor and production costs, the heat treatment temperature is preferably set to 450–600°C, more preferably 450–550°C. For example, the decomposition temperature of lithium nitrate is around 430°C, and the decomposition temperature of nickel acetate is around 373°C. Setting the heat treatment temperature above 450°C allows for more reliable decomposition of the components. When the heat treatment temperature exceeds 600°C, oxidation of the conductive substrate is easily promoted, sometimes leading to increased electrode resistance and thus increased voltage loss. The heat treatment time can be appropriately set considering factors such as reaction rate, productivity, and the oxidation resistance of the catalyst layer surface.

[0075] By appropriately setting the number of coating cycles of the aforementioned precursor aqueous solution, the thickness of the formed catalyst layer can be controlled. Furthermore, the aqueous solution coating and drying process can be repeated for each layer, followed by heat treatment of the entire layer after the top layer is formed; alternatively, the aqueous solution coating and heat treatment (pretreatment) can be repeated for each layer, followed by heat treatment of the entire layer after the top layer is formed. The pretreatment temperature can be the same as or different from the overall heat treatment temperature. Additionally, it is preferable that the pretreatment time is shorter than the overall heat treatment time.

[0076] Example

[0077] The present invention will now be specifically described based on embodiments, but the invention is not limited to these embodiments. In the following embodiments, an electrochemical cell (volume: 5L) made of polytetrafluoroethylene (PTFE) was used. This electrochemical cell has three electrodes: an evaluation object (anode) as the working electrode, RHE as the reference electrode, and a spiral nickel wire as the counter electrode. The surface area of ​​the working electrode is 1.0 cm². 2 The electrode was connected to a Ni wire shielded with heat-shrink tubing. The distance between the working electrode and the reference electrode's Luggin capillary was fixed to within approximately 1 cm. The counter electrode was housed within a cylindrical neutral diaphragm to primarily prevent the generated hydrogen from diffusing into the electrolyte within the tank. The electrolyte was a 7.0 mol / L KOH aqueous solution. The electrolyte temperature was maintained at 80 °C during pretreatment (electrochemical activation) and at 25 °C during accelerated evaluation. A Bio-Logic SAS potentiostat (model: VSP-300) controlled by dedicated software (EC-Lab V11.30) was used for electrochemical operation. As electrochemical pretreatment, the anode being evaluated was activated at 80 °C with an A / cm² flow rate of 1.0 A / cm². 2 Water electrolysis was performed for 2 hours using a constant current.

[0078] (Manufacturing of anodes for alkaline water electrolysis)

[0079] Nickel nitrate and cobalt nitrate were dissolved in pure water to obtain a coating solution with a nickel (Ni):cobalt (Co) molar ratio of Ni:Co = 33.3:66.7. The obtained coating solution was then used to coat metal at a rate of 1 g / m² per application. 2 After being coated onto the surface of a surface-treated nickel substrate, the coating solution was dried at room temperature for 10 minutes, and then dried again at 60°C for 10 minutes. Next, it was subjected to thermal decomposition at 350°C for 15 minutes in an air-circulating electric furnace. This process from coating to thermal decomposition was repeated four times to obtain alkaline electrolysis anodes (n=1 and 2) with a catalyst layer (composition: NiCo2O4) formed on the surface of the nickel substrate. The metal content of the formed catalyst layer was 4 g / m³. 2 .

[0080] (Example 1)

[0081] E min The impact of the steps:

[0082] like Figure 1 As shown, in order to simulate the actual fluctuations in electricity from renewable energy sources, in J e Steps and E min An LSV step is set between the steps. In the LSV step, J is... e The potential at the end of the step is maintained at 1.5V vs. RHE, and LSV is performed from this potential at a scan rate SR of 500mV / s. E is set relative to RHE. min =0.3, 0.5 and 0.7V, and the duration T of this step. min Set it to 60 seconds, and then implement it. Figure 3 The figure shows an oxidation current of 0.1 A / cm corresponding to the cycle number. 2 A graph of electrode potentials at different times. Figure 3 The value of the electrode potential in is based on Figure 4 The polarization curve shown is used to calculate the value (scanning speed: 5mV / s).

[0083] like Figure 3 As shown, in E min At 0.3V and 0.5V, the change (deterioration) of the electrode potential is roughly the same. On the other hand, at E min When the voltage is 0.7V, the degradation slows down, indicating that E min The higher the value, the less stress is applied to the anode. For example... Figure 5 As shown, based on J eThe anode potential and electrode degradation behavior during the process can be divided into three main regions: region A, region B, and region C. In region A, the electrode exhibits stable catalytic performance; in region B, the electrode degrades rapidly; and in region C, the catalyst performance decreases to the level of the nickel matrix. Furthermore, SEM-based surface observation confirmed catalyst consumption at the anode in region C.

[0084] (Example 2)

[0085] E min Duration T of the step min Impact:

[0086] like Figure 1 As shown, E min The holding potential (E) in the step min The voltage is fixed at 0.5V, and only the duration T is changed. min An evaluation was conducted. Figure 6 The figure shows an oxidation current of 0.1 A / cm corresponding to the cycle number. 2 A graph of electrode potentials at different times. Figure 6 The value of the electrode potential in is based on Figure 7 The polarization curve shown is used to calculate the value (scanning speed: 5mV / s).

[0087] like Figure 6 As shown, it was observed that when the duration T min When set to 60 seconds, the duration T is... min The degradation progresses faster when the timer is set to 10 seconds. For example... Figure 8 As shown, when the duration T min With a time limit of 10 s, region A significantly expanded, maintaining stable activity over more cycles. It is speculated that after the water electrolysis reaction ends, when the potential becomes negative compared to the open-circuit potential, an electrochemical reduction reaction is initiated at the anode surface, causing degradation reactions of the electrode catalyst such as dissolution and detachment. This degradation reaction is known to depend not only on E... min The hold potential of the step also strongly depends on the duration T. min .

[0088] (Example 3)

[0089] The effect of scan rate SR in the LSV step:

[0090] like Figure 1 As shown, E min The holding potential (E) in the step min The voltage is fixed at 0.5V, and the duration T is... min The evaluation was conducted by fixing the scan rate at 60 seconds and varying only the scan rate SR of the LSV step. Figure 9 and Figure 10 The figure shows an oxidation current of 0.1 A / cm corresponding to the cycle number. 2 A graph showing the electrode potential at different scan rates (SR). At scan rates SR of 50 mV / s and 500 mV / s, the electrode exhibits better durability at 500 mV / s. Additionally, as... Figure 10 As shown, at a scan rate SR of 50 mV / s, region B appears from a relatively small number of cycles. This clarifies that slowing down the scan rate SR accelerates the degradation reaction on the anode surface.

[0091] Based on the results of Examples 1 and 2, degradation of the electrode catalyst, such as dissolution and detachment, was observed, according to J. e Steps and E min The phenomenon of acceleration due to the number of cycles in the LSV step was observed. Furthermore, based on the results of Example 3, it was found that slowing down the scan rate SR of the LSV step facilitated the degradation reaction of the electrode catalyst, leading to a significant decrease in durability. That is, the scan rate SR of the LSV step was confirmed to be an effective factor in accelerating the evaluation.

[0092] (Example 4)

[0093] The impact of the OCP step:

[0094] like Figure 2 As shown, in J e The evaluation was further performed by setting an OCP step between the step and the LSV step, which maintained the anode at an open-circuit potential. Additionally, E... min The holding potential for this step is fixed at 0.5V, and the duration T is... min The evaluation was conducted by fixing the hold time at 60 seconds and varying only the hold time of the OCP step within the range of 10–60 seconds. Figure 11 The figure shows an oxidation current of 0.1 A / cm corresponding to the cycle number. 2 A graph of electrode potentials at different times. Figure 11 The value of the electrode potential in is based on Figure 12 The polarization curve shown is used to calculate the value (scanning speed: 5mV / s).

[0095] like Figure 11 As shown, the interval between OCP steps has a significant impact on improving electrode durability. Furthermore, as... Figure 13 As shown, the range of stable catalytic activity at the anode (region A) is significantly expanded, while the propagation rate in the subsequent region (region B) decreases significantly due to the presence of the OCP step. In Example 4, a phenomenon was observed where the durability of the electrode catalyst was greatly improved by incorporating the OCP step. Although the reason may not be clear, it can be speculated that by maintaining an open circuit, the J...e The structural changes in the catalyst layer produced in the step are mitigated and restored, and the subsequent E min The degradation process during the step is suppressed. This phenomenon can also occur in real-world testing; therefore, by setting the OCP step, an accelerated durability evaluation method that more closely corresponds to real-world testing can be established.

[0096] Industrial availability

[0097] The accelerated evaluation method of the anode of the present invention is useful, for example, as a method for accelerating the evaluation of anodes used in alkaline water electrolysis, such as oxygen generating electrodes powered by electricity with large output fluctuations, such as renewable energy sources.

Claims

1. An accelerated evaluation method for an anode, comprising an electrochemical operation in an aqueous electrolyte to accelerate the evaluation of the anode's durability, the accelerated evaluation method for the anode comprising the following steps: J e Steps, with duration T e The anode is loaded with 0.1 A / cm 2 The above-mentioned fixed density of oxidation current; and E min Steps, with duration T min Maintain the anode at a fixed potential lower than the open circuit potential, and set the J... e Steps and the E min Repeat each step more than 100 times.

2. The accelerated evaluation method for the anode according to claim 1, wherein, The duration T e and the duration T min Each is less than 120 seconds.

3. The accelerated evaluation method for the anode according to claim 1 or 2, wherein, In the J e Steps and the E min The steps also include an LSV step, in which the anode is subjected to a process from the J... e Linear sweep voltammetry, starting from a low potential at the end of the step. The scanning rate SR of the linear scanning voltammetry is in the range of 50 to 500 mV / s.

4. The accelerated evaluation method for the anode according to claim 3, wherein, In the J e The step between this step and the LSV step also includes an OCP step, in which the anode is maintained at an open-circuit potential. The holding time at the open circuit potential is 10 to 60 seconds.

5. The accelerated evaluation method for an anode according to any one of claims 1, 2, or 4, wherein, In the E min In this step, the anode is maintained at a potential 0.6 to 1.0 V lower than the open circuit potential.

6. The accelerated evaluation method for an anode according to any one of claims 1, 2, or 4, wherein, The anode is an oxygen generating electrode.

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