Oxygen generating electrode

Abstract

An electrode suitable for carrying out an oxygen evolution reaction in the electrolysis of water under alkaline conditions. The electrode is made of a ceramic material having a stability factor (SF) calculated by formula (II) in the range of 1.67≦SF≦2.8. [0010] TIFF2025512572000014.tif19150, where r O is an oxide ion (O 2- ) ionic radius, r B,av is the weighted average ionic radius of the transition metal, n A,Av is the weighted average oxidation state of the rare earth metal or alkaline earth metal, r A,av is the weighted average ionic radius of the rare earth metal or alkaline earth metal. The invention further relates to an alkaline electrolysis stack comprising at least one such electrode and a method for electrolysis of water under alkaline conditions using this alkaline electrolysis stack.

Description

[Technical Field]

[0001] The present invention relates to electrodes used in electrolysis, and more particularly to electrodes suitable for use in the electrolysis of water under alkaline conditions and exhibiting a low overpotential for the oxygen evolution reaction. The present invention further relates to an alkaline electrolytic stack comprising at least one such electrode, and to a method for electrolysis of water under alkaline conditions using this alkaline electrolytic stack. [Background technology]

[0002] In alkaline water electrolysis, water is electrochemically converted into hydrogen and oxygen under alkaline conditions: H2O = H2 + 0.5O2. An electrolytic cell has two electrodes: an anode and a cathode. During operation, a potential is applied between the two electrodes, resulting in an electrolytic current flowing through the electrolytic cell. During operation, a hydrogen evolution reaction (HER): 2H2O + 2e - =H2+2OH - Hydrogen is generated according to this process, and at the anode, the oxygen evolution reaction (OER): 2OH - = 0.5O2 + H2O + 2e - Oxygen is generated accordingly. The alkaline electrolytic cell also contains an electrolyte, which comprises a liquid alkaline medium such as an aqueous solution of hydroxide and / or carbonate. The electrolytic cell further comprises a porous separator and / or an ion exchange membrane capable of conducting hydroxide ions.

[0003] In alkaline water electrolysis, it is desirable to minimize both the investment cost and energy consumption of the electrolytic cell simultaneously. All other things being equal, the lower the investment cost and energy consumption of the cell, the lower the cost of producing hydrogen by electrolysis. The investment cost of the electrolytic cell is minimized when low-cost materials are used in the electrolytic cell and such cells are manufactured using low-cost manufacturing methods. The energy consumption of the electrolytic cell is minimized when the required applied potential (voltage) is minimized at a constant operating current or a constant operating current density.

[0004] The required applied potential is the sum of several contributions, including 1) the theoretical potential required for the electrochemical reaction, 2) the potential due to the porous separator and / or ion exchange membrane, 3) the overvoltage due to the anode, 4) the overvoltage due to the cathode, and 5) the potential depending on the distance between the anode and the cathode in the electrolytic cell. Here, the term "overvoltage" means the difference between the theoretical applied potential and the actual applied potential to each electrode, including potential contributions such as bubble formation. It is known to those skilled in the art that the overvoltage of the anode (i.e., OER) is generally higher than that of the cathode (i.e., HER). Therefore, the improvement of the oxygen generation electrode is very important. In particular, such an electrode needs to be composed of low-cost materials and manufactured using a low-cost manufacturing method while showing a lower overvoltage for OER than the electrodes of the state-of-the-art technology.

[0005] In industrial alkaline electrolytic cells, the OER electrode is based on nickel or noble metals. Nickel-based electrodes are relatively low-cost but have the characteristic of high overvoltage, resulting in increased energy consumption of the cell and thus higher hydrogen production costs. In contrast, electrodes based on noble metals or their compounds (such as IrO2, RuO2, Pt, etc.) have low overvoltage but very high investment costs and high hydrogen production costs. A third class of alkaline electrolytic OER electrode materials has been discovered and shown to exhibit both low overvoltage and low cost. Specifically, ceramic materials with a specific crystal structure such as the perovskite structure have been shown to be particularly attractive alternatives to both nickel- and noble metal-based OER electrodes.

[0006] Examples of such ceramic materials are described in WO2013 / 012965, MASSACHUSETTS INST TECHNOLOGY [US], 24.01.2013. Formula A x A’ 1-x B y B’ 1-y O 3±δAn OER catalyst is provided having A and A' independently being a rare earth metal or an alkaline earth metal, x being in the range of 0 to 1, B and B' independently being a transition metal, y being in the range of 0 to 1, and δ being in the range of 0 to 1. Examples of materials described in the reference application are LaCrO3, LaMnO3, LaFeO3, LaCoO3, LaNiO3, LaNi 0.5 Mn 0.5 O3, LaCu 0.5 Mn 0.5 O3, La 0.5 Ca 0.5 MnO 3-δ La 0.5 Ca 0.5 FeO 3-δ La 0.75 Ca 0.25 FeO 3-δ La 0.5 Ca 0.5 OO 3-δ , LaMnO 3-δ Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ This includes. The number of materials that can be explained using the above formula is actually infinite, and A x A' 1-x B y B' 1-y O 3±δ Despite having a composition described as such, some materials are less suitable for use in alkaline electrolytic cells than other materials. Formula A x A' 1-x B y B' 1-y O 3±δ The entirety of is claimed, but e of B, B', or each of the symmetric families of B and B' g It has been claimed that materials in which the occupancy of the sigma bond orbitals is within a certain range exhibit high OER activity. Specifically, Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ However, in 0.1 MKOH, the OER current at an electrode overvoltage of 0.4 V is 100 mA / cm². 2Therefore, under the same conditions, IrO2 was 18 mA / cm². 2 , RuO2 5mA / cm 2 It was found to exhibit particularly high OER activity compared to others.

[0007] The main problem with the approach proposed in publication WO2013 / 012965 is the insufficient stability of the materials claimed under the conditions used in industrial alkaline water electrolysis cells. The authors of WO2013 / 012965 subsequently tested the most electrocatalytically active of the proposed materials, particularly Ba, under OER in a 0.1 MKOH aqueous solution. 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ and SrCo 0.8 Fe 0.2 O 3-δ While one material lost its crystalline structure, several other materials, particularly LaCoO3, did not (Risch et al., J. Phys. Chem. C, 117 (2013) 8628). Generally, the loss of crystalline structure or the selective leaching of elements from a material correlates with a decrease in OER activity (i.e., an increase in overpotential).

[0008] US Publication No. 2016 / 0289850, DE NORA TECH INC [US], 6.10.2016, describes the conditions used in industrial alkaline water electrolysis cells: an alkaline electrolyte of 5-30 wt% KOH or NaOH (e.g., 25 wt% KOH), preheated to 80°C. Thus, industrial conditions are far more difficult in terms of material stability compared to a 1 wt% KOH aqueous solution at room temperature. To lower the required applied potential, it is desirable to operate industrial alkaline water electrolysis cells at high temperatures (e.g., 80°C) and use concentrated alkaline solutions (e.g., 25 wt% KOH). The use of high temperatures and high alkaline concentrations positively affects not only the anode potential but also the potential due to the porous separator and / or ion exchange membrane (increasing the conductivity of the separator and / or membrane), the overpotential due to the cathode, and the potential dependent on the distance between the anode and cathode (increasing the conductivity of the electrolyte, and consequently decreasing the ohmic drop). Therefore, as described in Publication WO2013 / 012965, while operation at lower temperatures and lower concentrations of alkaline solutions is desirable from an anode standpoint for stability reasons, the enhanced anode performance generally does not compensate for the performance penalties that lower temperatures and lower alkali concentrations impose on other components of the electrolytic cell.

[0009] Therefore, there is still a need to identify new ceramic materials that are low-cost, have low OER overpotential, and are stable under industrially appropriate conditions (high temperature, high-concentration alkaline solutions, etc.). [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] WO2013 / 012965 publication [Patent Document 2] US2016 / 0289850 publication [Overview of the project]

[0011] The inventors had a desire to produce low-cost hydrogen by alkaline water electrolysis, but found that the ceramic material-based anodes described in the prior art still had drawbacks. More specifically, Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ Anodes that initially exhibit the lowest OER overpotential, such as those composed of [material name], quickly deactivate under industrially appropriate electrolysis conditions due to insufficient phase stability. On the other hand, anodes that do not deactivate under industrially appropriate electrolysis conditions generally exhibit extremely high OER overpotentials. Currently, the search for negative electrode materials that do not deactivate and exhibit low OER overpotentials is based primarily on intuitive and trial-and-error approaches.

[0012] The inventors have found that a parameter referred to herein as the "stability coefficient," abbreviated as SF, can effectively predict the phase stability of ceramic materials suitable for the anode of an alkaline electrolytic device. More specifically, based on the SF value, the stability of a particular ceramic material in a strongly alkaline solution and its activity with respect to OER (activity is inversely proportional to overpotential) can be estimated. This makes it possible to distinguish between a) active but phase-instable materials, b) phase-stable but inert materials, and c) materials that are both active and phase-stable. Active but phase-instable materials exhibit relatively high SF values, while phase-stable but inert materials exhibit relatively low SF values. Materials with intermediate SF values ​​exhibit sufficient electrochemical activity (i.e., low electrode overpotential with respect to OER) and sufficient phase stability simultaneously.

[0013] According to one aspect of the present invention, an electrode is provided for carrying out an oxygen evolution reaction in the electrolysis of water under alkaline conditions, wherein the electrode is made of a ceramic material [(A x )A' (1-x) ] y B z B' (1-z) O 3-δThe material contains, where A and A' are independently rare earth metals or alkaline earth metals, x is in the range of 0 to 1, y is the A site occupancy rate in the range of 0.5 to 0.99, B and B' are independently transition metals, z is in the range of 0 to 1, O is oxygen, δ is the oxygen unstoichiometric ratio in the range of -1 to 1, and the SF of the ceramic material is between 1.67 and 2.8.

[0014] In the context of this invention, "stability coefficient" or "SF" refers to the parameter defined in the following equation 1.

[0015]

number

[0016] The terms "phase stability" and "phase stable" mean the property of a material to retain its crystal phase when exposed to industrially appropriate alkaline water electrolysis conditions. One method of evaluating the phase stability of a material, or of evaluating whether a material is phase stable, is to obtain X-ray diffraction patterns of the material before and after exposure to industrially appropriate alkaline water electrolysis conditions. Phase stability is confirmed when there is no significant difference in the corresponding X-ray diffraction patterns, i.e., when no phase change has occurred in the bulk of the material. In the context of the present invention, "industrially appropriate alkaline water electrolysis conditions" refers to exposure to an aqueous potassium hydroxide solution containing 20 wt% or more of KOH (20 wt% KOH) at a temperature of 75 to 85 °C, and the application of an electrolytic current may or may not be present. To confirm phase stability, the exposure time to the aforementioned conditions should be at least 24 hours, preferably at least 100 hours. Another method for determining phase stability also exists, but it is important to note that highly surface-sensitive methods such as X-ray photoelectron spectroscopy and low-energy ion scattering spectroscopy are not suitable methods for determining phase stability in the context of the present invention because they cannot examine the bulk of the material.

[0017] The term "A-site occupancy", denoted as "y" in the formulas and equations of the present invention, means the number of A-site cations relative to the number of B-site cations in a ceramic material. For example, Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (This can also be written as [Ba 0.5 Sr 0.5 1.0 Co 0.8 Fe 0.2 O 3-δ ), y = 1.0. In La 0.95 CoO3 ([La 1.0 0.95 CoO3), which is equivalent), y = 0.95. It should be noted that in order to estimate the occupancy of the A-site, the occupancy of the B-site is considered to be equal to 1. For example, LaCo 1.05 O 3.16 ​​To calculate the A-site occupancy, the subscript number of the B-site cation (i.e., Co) is made equal to 1, and as a result, La 0.95 CoO3 is expressed with the material composition, and the result is y = 0.95.

[0018] The terms "A-site" and "B-site" mean energetically different sites in the crystal lattice of a ceramic material. However, the formula [(A x )A’ (1-x) y B z B’ (1-z) O 3-δ generally refers to materials having a perovskite structure (ABO3) or a double perovskite structure (A2B2O5). However, in the context of the present invention, it should be noted that the terms "A-site" and "B-site" are used more broadly and are independent of the crystal structure of the ceramic material.

[0019] The term "oxygen non-stoichiometry" denoted as "δ" in the formulas and equations of the present invention means the number of oxygen vacancies relative to the number of cations at the B-site in a ceramic material. For example, in the case of La 0.90 Ni 0.6 Fe 0.4 O 2.85 (equivalent to La 0.90 Ni 0.6 Fe 0.4 O 3-0.15 ), δ = 0.15. In the case of an oxygen-rich compound, δ has a negative value. For example, in La 0.3 Sr 0.7 TiO 3.15 (equivalent to La 0.3 Sr 0.7 TiO 3+0.15 ), δ = -0.15. The double perovskite A2B2O 5+δ’ can be represented as ABO 3-δ by recognizing δ’ = 1 - 2δ. The oxygen non-stoichiometry depends on temperature, oxygen partial pressure, applied voltage, etc.

[0020] ​The term "ionic radius" refers to the Shannon ionic radius as defined in RD Shannon, Acta Crystallogr. A, 32 (1976) 751-767. For example, the oxide anion O with coordination number 2. 2- The ionic radius of is 1.35 Å. In the context of this invention, the formula [(A x )A' (1-x) ] y B z B' (1-z) O 3-δ The term "weighted average ionic radius of A and A'" for a ceramic material having the above properties refers to the weighted average of the Shannon ionic radii of cation A and cation A', where the weights are x for the ionic radius of A and (1-x) for the ionic radius of A', and the resulting radius is multiplied by the A site occupancy rate y. In other words, it can be expressed by the following formula. r A,Av =[x·r A +(1-x)·r A’ ]·y Here, r A r is the ionic radius of A. A’ is the ionic radius of A'. By analogy, the following equation is obtained. r B,Av =z·r B +(1-z)·r B’

[0021] Formula [(A x )A' (1-x) ] y B z B' (1-z) O 3-δ The term "weighted average oxidation state of A and A'" for a ceramic material having the above properties refers to the weighted average of the oxidation states of cation A and cation A', where the weights are x for the oxidation state of A and (1-x) for the oxidation state of A', multiplied by the A site occupancy rate y. In other words, it can be expressed by the following formula. n A,Av =[x·n A +(1-x)·n A’ ]·y Here, n A n is the oxidation state of A. A’ This is the oxidation state of A'.

[0022] The term "alkaline electrolytic stack" refers to a device containing multiple alkaline electrolytic cells electrically connected in series. The more cells in the stack, the more hydrogen and oxygen can be produced per unit time. Similarly, the larger the surface area (footprint) of each cell in the stack, the more hydrogen and oxygen can be produced. The electrodes of the electrolytic cells in an electrolytic stack are separated by a porous separator (such as zirphon) and / or an ion-exchange membrane capable of conducting hydroxide ions.

[0023] The above embodiments of the present invention offer several significant advantages compared to state-of-the-art technologies. First, the electrodes of the present invention are characterized by sufficient phase stability, meaning that electrodes do not need to be frequently replaced during operation. Second, the electrodes of the present invention are highly active, enabling low overpotential, sufficient efficiency, and consequently, lower hydrogen production costs. Third, since the electrodes of the present invention do not use precious metals such as iridium, platinum, and ruthenium, problems related to the availability of electrode materials are alleviated, and the cost of electrode raw materials is significantly reduced. Fourth, the electrodes of the present invention exhibit lower overpotential for the oxygen evolution reaction than conventional nickel-based electrodes. Since electricity costs are a major factor determining the production cost of hydrogen produced by electrolysis, the electrodes of the present invention enable hydrogen production at a lower cost (OPEX) than conventional nickel-based electrodes.

[0024] EP3587622, ​​Asahi Kasei Corporation [JP], 01.01.2020, describes an anode for water electrolysis comprising a porous substrate and a metal oxide layer containing at least a perovskite-structured metal oxide on part or all of the surface of the porous nickel substrate, wherein the content of the perovskite-structured metal oxide in the crystalline components of the metal oxide layer is 90% or more and 100% or less. EP3587622 further states that the perovskite-structured metal oxide is A x A' (1-x) Ni y B' (1-y) O 3-zThe anode described is a metal oxide having the composition represented by , where A and A' are each alkaline earth metals or rare earth elements, B' is one of Cr, Mn, Fe, Co, and Cu, x satisfies 0 ≤ x ≤ 1, y satisfies 0 ≤ y ≤ 1, and z satisfies 0 ≤ z ≤ 1. EP3587622 describes a 100-hour or 6 kA / m² test. 2 The overvoltage values ​​after total operation are reported, and compared to LaNiO3, Ba 0.5 Sr 0.5 Co 0.8 We have confirmed that FeO3 has inferior performance (likely due to poor phase stability). 0.5 Sr 0.5 Co 0.8 The SF value of FeO3 is 3.91, while the SF value of LaNiO3 is 1.62. In other words, Ba 0.5 Sr 0.5 Co 0.8 FeO3 is insufficiently phase-stable for long-term stability under industrially appropriate conditions, while LaNiO3 is too inert to OER. For example, incorporating an A-site occupancy of 0.5 ≤ y ≤ 0.99 can further favorably reduce the associated overpotential. Furthermore, the method of coating perovskite onto a nickel substrate surface is very laborious, requiring 13 coating and drying cycles followed by a firing cycle.

[0025] The paper by Ma et al., published in Journal of Alloy and Compounds, 854 (2021) 157154, describes a series of perovskite oxides: La 0.95 FeO3, La 0.95 Fe 0.9 Co 0.1 O3, La 0.95 Fe 0.8 Co 0.2 O3, La 0.95 Fe 0.7 Co 0.3 O3, andLa 0.95 Fe 0.6 Co 0.4 O3 is disclosed. Of these five substances, La 0.95 FeO3 and La 0.95 Fe0.6 Co 0.4 Ma et al. ignored O3 without further explanation, and the remaining three substances: La 0.95 Fe 0.9 Co 0.1 O3, La 0.95 Fe 0.8 Co 0.2 O3, La 0.95 Fe 0.7 Co 0.3 The focus is on O3. The authors then subjected three materials to reduction treatment to induce exsolution of Co or Co / Fe nanoparticles and evaluated the OER performance of the resulting materials. Importantly, the composition of the original material inevitably changes during the reduction treatment. For example, La 0.95 Fe 0.9 Co 0.1 O3 is LaFe 0.9 Co 0.1 O3(La 0.95 Fe 0.9 Co 0.1 (0.95 moles of O3 per mole) and Fe 0.9 Co 0.1 (La 0.95 Fe 0.9 Co 0.1 The mixture consists of 0.05 moles of O3 per 1 mole. In all cases, the resulting material no longer has A-site defects. LaFe 0.9 Co 0.1 O3, La 0.95 Fe 0.8 Co 0.2 O3 and La 0.95 Fe 0.7 Co 0.3 The stability coefficients of O3 are calculated to be 1.65, 1.65, and 1.66, respectively. In this invention, no reduction treatment that alters the A-site defects of the material is performed, and therefore this invention differs from this document.

[0026] The paper by Poznyak et al., published in Journal of Solid State Electrochemistry 12 (2008) 15-30, particularly discusses a series of perovskite materials: La 0.3 Sr 0.7 OO 2.924 La 0.3Sr 0.7 Co 0.8 Al 0.2 O 2.85 , (La 0.3 Sr 0.7 ) 0.97 OO 2.896 La 0.5 Sr 0.5 CoO3, La 0.55 Sr 0.45 CoO3, La 0.65 Sr 0.35 CoO3, La 0.7 Sr 0.3 CoO3, La2NiO 4.15 , La2Ni 0.9 Co 0.1 O 4.169 , La2Ni 0.8 Cu 0.2 O 4.124 The following materials are disclosed. Some of these materials have a perovskite structure, one material has an A-site occupancy of less than 1, and some materials have an SF of less than 2.8, but none of the materials in this paper satisfy all three conditions simultaneously. Therefore, the present invention is distinguishable from the prior art.

[0027] According to one aspect of the present invention, the electrode also includes a second material, which is metallic Ni, a metal alloy of Fe and Ni, or a hydroxide of Ni and Fe. The advantage of combining a ceramic material with a second, rather conventional, electrode material is that the second material can provide part of the electrochemical activity of the combined electrode. This is particularly important in situations where the electrode is partially contaminated with impurities. When an electrode is made of multiple materials, the affinities of these materials to different types of impurities differ, i.e., they are affected to different degrees by impurity adsorption. As a result, electrodes made of multiple materials are generally more stable and robust than electrodes made of a single material. It should be noted that the composition of the second material can refer to either the composition of the material before or after exposure to operating conditions. For example, it is well known that Fe impurities in the electrolyte accumulate on the electrode during operation.

[0028] EP3444383B1, Denora Permelec Co., Ltd. [JP], on February 20, 2019, describes an anode for alkaline water electrolysis comprising a conductive substrate having a surface made of at least nickel or a nickel-based alloy, and an electrode catalyst layer formed on the surface of the conductive substrate. The catalyst component constituting the electrode catalyst layer is nickel-cobalt spinel oxide represented by the structural formula NiCo2O4, or structural formula XNi a Co 1-a O3 (where X represents at least one metal selected from lanthanides including lanthanum, cerium, and praseodymium, and 0 < a < 1), a first catalyst component having a lanthanide-nickel-cobalt perovskite oxide, and a second catalyst component having at least one of iridium oxide and ruthenium oxide. The amount of the second catalyst component calculated as the amount of component metals is at least 0.2 g / m 2 . EP3444383B1 describes that the perovskite materials generally exhibit very low SF values. For example, in all compositions of LaNi a Co 1-a O3, SF < 1.67. For example, LaNi 0.1 Co 0.9 O3 (SF = 1.66), LaNi 0.5 Co 0.5 O3 (SF = 1.64), LaNi 0.9 Co 0.1 O3 (SF = 1.63). In other words, the materials selected here are not optimal for OER, they are "too stable", and by introducing an A-site occupancy within the range of, for example, 0.5 to 0.99, more active materials may be obtained. Furthermore, the electrodes described in EP3444383B1 still contain a significant amount of iridium oxide and ruthenium oxide to achieve the required activity level. The use of iridium and ruthenium is problematic because not only are the costs of these elements high, but the available amounts of these elements in the earth's crust are very limited.

[0029] In embodiments of the present invention, the ceramic material is uniformly dispersed on the surface of the second material. The phrase "uniformly dispersed on the surface of Y" means that, given a sufficiently large inspection area, the concentration of X particles on the surface of Y is the same regardless of which part of the surface of Y is inspected. "X" refers to, for example, the ceramic material, and "Y" refers to, for example, the second material. In the context of the present invention, an inspection area is considered sufficiently large if it contains at least 500 X particles when identified, for example, by electron microscopy. The advantage of dispersing the ceramic material on the surface of the second material is that an electrode with uniform electrochemical activity is obtained. Furthermore, since electrochemical reactions on the surface of electrode materials involve large reaction enthalpies, uniform dispersion of the ceramic material helps to avoid "hot spots" (localized temperature gradients) within the electrode that could damage the electrode structure or separator / film.

[0030] According to one aspect of the present invention, ceramic material particles are immobilized and partially encapsulated by a second material. In the context of the present invention, the term "X is immobilized" means that the particles of X cannot be detached or moved during operation of the electrolytic device. Furthermore, the term "X is partially encapsulated by Y" means that the particles of X are in contact with Y from multiple sides (partial encapsulation), but not in contact with Y from all sides (complete encapsulation). The advantage of this aspect of the present invention is that the ceramic material is firmly fixed in place during operation, thereby avoiding situations such as ceramic particles falling to the bottom of the electrolytic stack due to gravity, causing uneven electrode activity or mechanical problems. Partial encapsulation is a particularly effective method for dispersing ceramic material on the surface of a second material because it ensures that the ceramic material adheres firmly to the surface of the second material while still being exposed to the electrolyte and remaining electrochemically active.

[0031] According to one aspect of the present invention, A is an element selected from the following element list: La (lanthanum), Ce (cerium), Gd (gadolinium), Pr (praseodymium), Ba (barium); A' is an element selected from the following element list: Sr (strontium), Ca (calcium), Ba (barium), Ce (cerium); and B or B' is an element independently selected from the following element list: Mn (manganese), Ni (nickel), Fe (iron), Co (cobalt), Ti (titanium), Cr (chromium). The advantage of using La, Ce, Gd, Pr, or Ba as A is that the La in the perovskite lattice 3+ Ce 3+ , Gd 3+ , Pr 3+ Ba 2+ This relates to the suitable combination of cation sizes and the availability (price) of these elements. For example, Dy 3+ or Eu 3+ While suitable from the standpoint of ionic radius, it is too expensive for widespread use. The advantage of using Sr, Ca, Ba, or Ce as A' is that these elements generally increase the electrical conductivity and oxygen vacancy concentration of ceramic materials. There are two advantages to using Mn, Ni, Fe, Co, Ti, or Cr as B or B'. Firstly, using transition metals improves the electronic conductivity of the material due to the many possible oxidation states of the metal, enabling, for example, polaron hopping conduction mechanisms. Secondly, using Mn, Ni, Fe, Co, Ti, or Cr as B or B' is advantageous because they are less expensive than metals such as Ru or Ir.

[0032] In the embodiment of the present invention, the A-site occupancy rate, denoted as y, is in the range of 0.6 to 0.98, preferably in the range of 0.75 to 0.98. A value of less than 1 (e.g., 0.9) for the A-site occupancy rate is advantageous because the A-site cations are more strongly bonded to the crystal structure. However, if the value of the A-site occupancy rate is too low (e.g., less than 0.6), some of the B-site cations will not be incorporated into the structure of the ceramic material, and as a result, there is a risk that some of the B-cations will form a secondary oxide phase. The best results are obtained when the A-site occupancy rate is within a predetermined range, for example, between 0.6 and 0.98, preferably between 0.75 and 0.98.

[0033] In embodiments of the present invention, the average particle size of the ceramic material is 10 nm to 300 nm, preferably 20 nm to 200 nm. Generally, as the specific surface area of ​​a material increases, its electrochemical activity and catalytic activity increase. Therefore, it is desirable to maximize the surface area of ​​the ceramic material, i.e., to reduce the average particle size of the material. However, if the particle size becomes too small (for example, less than 20 nm), the proportion of material atoms occupying the edge and corner sites within the particles increases, causing the material properties to begin to change. This latter phenomenon not only affects the electrochemical activity of the material but also affects the stability of the material, generally leading to a decrease in stability. Therefore, it is desirable that the average particle size of the ceramic material be within an optimal range, such as between 10 nm and 300 nm, or between 20 nm and 200 nm.

[0034] According to one aspect of the present invention, the ceramic material has a perovskite crystal structure. The perovskite structure is advantageous because it is a very versatile class of materials and is generally more stable than the corresponding ruddrudden-popper phase (for example, less susceptible to A-site cation leaching). Perovskites are generally more electrochemically active than the corresponding spinel phase.

[0035] In an embodiment of the present invention, when an oxygen evolution reaction is carried out using a rotating disk electrode with a rotation speed of 1500 rpm in 20-35% KOH at a temperature of 75-85°C, the overpotential of the electrode for the oxygen evolution reaction is 1 mA / cm². 2 The current density is 400 millivolts or less. The electrode of the present invention is optimized for use under industrial alkaline electrolysis conditions, i.e., in 20-35% KOH and within a temperature range of 75°C-85°C. It is desirable to minimize the overpotential of the electrode for the oxygen evolution reaction, which is 1 mA / cm². 2 To achieve performance at least equivalent to that of state-of-the-art iridium electrodes at the given electrolytic current density, the overpotential should be kept below 400 mV. In a typical rotating disk electrode experiment, a ceramic material is deposited on the surface of the electrode (e.g., a glassy carbon electrode) and immersed in a KOH solution. To investigate the effects of the kinetic transport vs. mass transport limitation, the electrode performance (overpotential at different current densities) can be evaluated within a range of electrode rotation speeds. Furthermore, ohmic drop can be corrected by performing additional electrochemical impedance spectroscopy measurements.

[0036] In embodiments of the present invention, the ceramic material is phase-stable for 100 hours in 6MKOH at 80°C. The typical lifespan of an alkaline electrolytic cell stack is approximately 10 years, and all materials used in such stacks must withstand exposure to operating conditions throughout the stack's entire lifespan. However, for the purpose of screening materials for use in alkaline electrolytic cells, a 100-hour exposure period in 6MKOH at 80°C is often sufficient to evaluate the phase stability of the material. Materials that are not phase-stable after 100 hours of exposure in 6MKOH at 80°C are unsuitable for use as electrode materials. [Brief explanation of the drawing]

[0037] [Figure 1] Figure 1 shows the stability and activity of ceramic materials as a function of the stability coefficient.

[0038] (Detailed explanation of the drawing) Figure 1a shows the qualitative relationship (in arbitrary units) between phase stability on the left vertical axis labeled "stability (au)" and the stability coefficient ("SF") on the horizontal axis. More specifically, when the SF value is low, the equation [(A x )A' (1-x) ] y B z B' (1-z) O 3-δ The phase stability of ceramic materials increases, meaning that decomposition and phase changes are less likely to occur when exposed to electrolytic conditions. As the SF value increases, the phase stability of such materials decreases, and when SF > 2.8, the material is no longer phase stable under industrially appropriate electrolytic conditions. Therefore, materials with SF > 2.8 are not particularly suitable for use as oxygen electrodes in alkaline electrolytic cells.

[0039] Furthermore, Figure 1a also shows the qualitative relationship (in arbitrary units) between the electrochemical activity on the right vertical axis labeled "Activity (au)" and the stability coefficient ("SF") on the horizontal axis. More specifically, when the SF value is high, the equation [(A x )A' (1-x) ] y B z B' (1-z) O 3-δ The electrochemical activity of ceramic materials increases, meaning that the overpotential to OER decreases when these materials are exposed to electrolytic conditions. As the SF value decreases, the activity of such materials decreases, and at SF < 1.67, the material no longer exhibits sufficient activity under industrially appropriate electrolytic conditions. Therefore, materials with SF < 1.67 are not particularly suitable for use as oxygen electrodes in alkaline electrolytic cells.

[0040] Figure 1b shows the parameter "stability × activity" (arbitrary unit) on the vertical axis, the stability coefficient ("SF") on the horizontal axis, and the qualitative relationship between them. The optimal material properties, i.e., the combination of high stability and high activity, are obtained when 1.67 ≤ SF ≤ 2.8. [Modes for carrying out the invention]

[0041] This method will be described in more detail in the following non-limiting embodiments. [Examples]

[0042] Example 1 (Comparative Example) Table 1 shows various barium-strontium-cobalt-iron based ceramic materials, along with their relevant material properties and SF values. (Ba with coordination number 12) 2+ The Shannon ion radius is 1.61 Å, and Sr has a coordination number of 9. 2+ The ionic radius of is 1.31 Å, and r A,av = 1.46 Å. Co with a coordination number of 6 3+ The Shannon ion radius is 0.545 Å, and Fe has a coordination number of 6. 3+ The radius of the Shannon ion is 0.55 Å. As a result, r B,av The values ​​are shown in Table 1. (Ba for y=1) 0.5 Sr 0.5 ) 1.0 Co z Fe 1-z O 2.5 In materials, the SF value is almost constant regardless of the Co:Fe ratio. For example, Ba with y=1 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 2.5 The SF value is 3.50, Ba 0.5 Sr 0.5 Co 0.2 Fe 0.8 O 2.5 The SF value is 3.49. In other words, (Ba 0.5 Sr 0.5 ) 1.0 Co z Fe 1-z O 2.5 Regardless of the choice of Co:Fe ratio, this material is predicted to be phase-stable under conditions suitable for industrial alkaline electrolysis. This prediction is in good agreement with Ba. 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ It was shown that it is not stable in 0.1 MKOH.

[0043] The materials listed in Table 1 can be synthesized by mixing metal precursors in desired proportions and processing the resulting mixture to optionally form the correct crystalline phase, using methods such as solid synthesis, coprecipitation, hydrothermal synthesis, sol-gel synthesis, chemical vapor deposition, spray pyrolysis, and atmospheric plasma deposition (but not limited to these). The same methods can also be applied to the synthesis of materials described in the examples below.

[0044] [Table 1]

[0045] Example 2 (Comparative Example) Table 2 shows various barium-strontium-cobalt-iron based ceramic materials, along with their relevant material properties and SF values. In Table 2, (Ba 0.5 Sr 0.5 ) y Co 0.8 Fe 0.2 O 3-δ The A-site occupancy rate of the material is systematically varied within the range of 0.7 ≤ y ≤ 1. As the value of y decreases, the SF value increases, meaning the material becomes phase-unstable. (Ba 0.5 Sr 0.5 ) y Co 0.8 Fe 0.2 O 3-δ Regardless of the value of y, this material is predicted to be phase-stable under conditions suitable for industrial alkaline electrolysis.

[0046] [Table 2]

[0047] Example 3 (Comparative Example) Table 3 shows various barium-strontium-cobalt-iron based ceramic materials, along with their relevant material properties and SF values. In Table 3, (Ba x Sr 1-x ) 1.0 Co 0.8 Fe 0.2 O 2.5The Ba:Sr ratio x of the material is systematically varied within the range of 0.1 ≤ x ≤ 0.9. (Ba x Sr 1-x ) 1.0 Co 0.8 Fe 0.2 O 2.5 Regardless of the value of x, this material is predicted to be phase-stable under conditions suitable for industrial alkaline electrolysis.

[0048] [Table 3]

[0049] Example 4 (Comparative Example) Table 4 contains (A 0.5 Sr 0.5 ) 1.0 Co 0.8 Fe 0.2 Various O3-based ceramic materials are shown along with their relevant material properties and SF values. In Table 4, (A 0.5 Sr 0.5 ) 1.0 Co 0.8 Fe 0.2 O 3-δ A, one of the A-site cations, is Ba 2+ Ce 3+ , Gd 3+ , Pr 3+ La 3+ Select from the options and systematically change A. Ba has a coordination number of 12. 2+ The Shannon ion radius is 1.61 Å, and Sr has a coordination number of 9. 2+ Since the ionic radius of is 1.31 Å, (A 0.5 Sr 0.5 ) 1.0 Co 0.8 Fe 0.2 O 2.5 r A,av = 1.46 Å. La with a coordination number of 12 3+ The Shannon ion radius of is 1.36 Å, (La 0.5 Sr 0.5 ) 1.0 Co 0.8 Fe 0.2 O 2.75 r A,av= 1.335 Å. 3+ (12 coordination), Pr 3+ (9-coordinate), Gd 3+ The radii of the (8-coordinate) Shannon ions are 1.34 Å, 1.18 Å, and 1.05 Å, respectively. (Gd 0.5 Sr 0.5 ) 1.0 Co 0.8 Fe 0.2 O 2.75 , (Pr 0.5 Sr 0.5 ) 1.0 Co 0.8 Fe 0.2 O 2.75 , (La 0.5 Sr 0.5 ) 1.0 Co 0.8 Fe 0.2 O 2.75 , and (Ce 0.5 Sr 0.5 ) 1.0 Co 0.8 Fe 0.2 O 2.75 All of the SF values ​​are less than 3.1, (Ba 0.5 Sr 0.5 ) 1.0 Co 0.8 Fe 0.2 O 2.5 . has SF = 3.5. Therefore, (A 0.5 Sr 0.5 ) 1.0 Co 0.8 Fe 0.2 O 3-δ Although materials with A=Ce, Gd, Pr, and La are expected to be more phase-stable than materials with A=Ba, none of them are phase-stable enough to be used in industrial alkaline electrolysis equipment.

[0050] [Table 4]

[0051] Example 5 Table 5 shows various gadolinium-strontium-cobalt-iron based ceramic materials, along with their relevant material properties and SF values. In Table 5, (Gd x Sr1-x ) 0.97 Co 0.8 Fe 0.2 O 3-δ The Gd:Sr ratio x of the material is systematically varied within the range of 0.1 ≤ x ≤ 0.9. In contrast to the comparative example in Example 3, the two A-site cations have different positive charges (Gd 3+ ,Sr 2+ As a result, phase stability at high Gd content is improved. Materials with 1-x < 0.2 have an SF value of 2.8 or less and are therefore predicted to be phase stable under conditions suitable for industrial alkaline electrolysis. Materials with 0.2 ≤ 1-x ≤ 1 in Table 5 are not phase stable.

[0052] [Table 5]

[0053] Example 6 Table 6 shows (La 0.6 A' 0.4 ) 0.99 Co 0.8 Fe 0.2 O 3-δ Various ceramic materials of the system are shown along with their relevant material properties and SF values. Ca with coordination number 12 2+ The Shannon ion radius is 1.34 Å, and Sr has a coordination number of 9. 2+ The ionic radius of is 1.31 Å. Ba with coordination number 12 2+ The ionic radius of is 1.61 Å, and Ce has a coordination number of 12. 3+ The ionic radius of is 1.34 Å. In Table 6, (La 0.6 A' 0.4 ) 0.99 Co 0.8 Fe 0.2 A', one of the A-site cations of O3, is Sr 2+ Ca 2+ Ba 2+ Ce 3+ A' is systematically varied by selecting from the options. All materials in Table 6 have SF values ​​within the range of 1.67 ≤ SF ≤ 2.8, but none are within the range of 1.9 ≤ SF ≤ 2.6.

[0054] [Table 6]

[0055] Example 7 Table 7 shows (La 0.9 Sr 0.1 ) 0.97 BO 3-δ Various ceramic materials of the system are shown along with their relevant material properties and SF values. In Table 7, (La 0.9 Sr 0.1 ) 0.97 BO 3-δ The B-site cation B is selected from Mn, Ni, Fe, Co, Ti, and Cr, and B is systematically varied. The average oxidation state of Mn, Ni, Fe, Co, and Cr ions is assumed to be 3.1. The exception is Ti, which has an ionic radius of 0.605 Å. 4+ It exists as a (6-coordinate) structure, and δ = -0.455. 3+ Co 4+ Fe 3+ Fe 4+ Mn 3+ Mn 4+ Ni 3+ Ni 4+ , Cr 3+ , Cr 4+ The ionic radii (all with coordination number 6) are 0.545 Å, 0.53 Å, 0.55 Å, 0.585 Å, 0.58 Å, 0.53 Å, 0.56 Å, 0.48 Å, 0.615 Å, and 0.55 Å. For all materials in Table 7, 1.67 ≤ SF ≤ 2.8.

[0056] [Table 7]

[0057] Example 8 Table 8 shows (La 0.9 Sr 0.1 ) y BO 3±δ Various ceramic materials of the system are shown along with their relevant material properties and SF values. In Table 8, (La 0.9 Sr 0.1 ) y BO3±δ The B-site cation B is selected from Mn, Ni, Fe, Co, Ti, and Cr, and B is systematically varied so that 0.65 ≤ y ≤ 0.95. The average charge of the Mn, Ni, Fe, Co, and Cr ions is assumed to be 3.1, and Ti is Ti 4+ Let us assume that it exists as such. Comparing the SF values ​​in Table 8 with the SF values ​​in Table 7, we can see that the SF value systematically increases when the A-site occupancy of the ceramic material is reduced, that is, the activity and phase stability of the material can be matched by changing y. (La 0.9 Sr 0.1 ) 0.90 TiO 3.31 , (La 0.9 Sr 0.1 ) 0.8 TiO 3.16、 (La 0.9 Sr 0.1 ) 0.65 TiO 2.94 , and (La 0.9 Sr 0.1 ) 0.90 CrO 2.86 Some materials, like this one, become too unstable (SF > 2.8), while others maintain phase stability (1.67 ≤ SF ≤ 2.8).

[0058] [Table 8]

[0059] Example 9 Table 9 shows various lanthanum-nickel-iron ceramic materials, along with their relevant material properties and SF values. For example, LaNi y=1 0.6 Fe 0.4 The SF value of O3 is 1.63, and La = 0.95 0.95 Ni 0.6 Fe 0.4 O 2.925 The SF value is 2.10. 0.90 Ni 0.6 Fe 0.4 O 2.85 The SF value of is 2.55, and the SF values ​​of materials with y ≤ 0.85 in Table 9 are greater than 2.8. LaNi 0.6 Fe 0.4O3 (y=1) is phase-stable when exposed to 6MKOH at 80°C, but materials with y≦0.85 in Table 9 are not phase-stable. In more extreme cases, for example, La 0.5 Ni 0.6 Fe 0.4 O 2.25 Therefore, ceramic materials do not form a perovskite structure, and multiphase and multicomponent materials exist even before exposure to industrial alkaline electrolysis conditions. Another extreme example is y=LaNi, which has an SF value of 1.63. 0.6 Fe 0.4 O3 does not exhibit sufficient activity for oxygen evolution reactions because its SF value is very low.

[0060] [Table 9]

[0061] Example 10 La 0.95 OO 2.925 , Pr 0.95 OO 2.925 , Gd 0.95 OO 2.925 , (La 0.9 Sr 0.1 ) 0.95 OO 2.878 La 0.95 NiO 2.925 , LaFeO3, La 0.95 Ni 0.6 Co 0.4 O 2.925 , and La 0.95 Ni 0.6 Fe 0.4 O 2.925 The material was synthesized using an improved sol-gel synthesis route. The obtained material was calcined at 800°C for 3 hours, and an oxide catalyst material with a perovskite structure, as confirmed by X-ray diffraction, was obtained. The material properties and SF values ​​are summarized in Table 10.

[0062] [Table 10]

[0063] The calcined materials were electrochemically characterized using a rotating disk electrode (RDE) setup. For these measurements, each perovskite material was mixed with Nafion solution, isopropanol, and ultrapure water to obtain a slurry. This slurry was then measured at 0.2 mg / cm³. 2 The glassy carbon electrodes were coated with the specified load. The electrodes were tested in a three-electrode setup in 0.1 MKOH saturated with argon. OER kinetics were evaluated by applying a linearly changing potential to the electrodes and measuring the resulting current. The potential was swept from 1.3V to 1.9V relative to RHE and back to 1.3V. The electrodes were rotated at 1500 rpm, and measurements were performed at room temperature.

[0064] Furthermore, to evaluate phase stability, the materials were subjected to strong alkali treatment. Each material was treated in 6MKOH at a temperature of 80°C for 100-120 hours. After treatment, the materials were thoroughly washed with distilled water, dried, and their crystal structure was examined by X-ray diffraction (XRD).

[0065] Specifically, fired Gd 0.95 OO 2.925 The material was found to be mainly composed of perovskite material, and the main XRD peaks (in order of decreasing intensity) were 33.86°, 34.36°, and 33.20° (2θ). The calcined material was electrochemically highly active, at 10 mA / cm². 2 The potential required to reach the OER current was 1.67V. As expected from the high SF value (SF>2.8), this material proved to be phase-stable after treatment with 6MKOH. The main XRD peaks (in decreasing order of intensity) changed to 28.19°, 50.70°, 41.25°, and 29.52°(2θ), indicating that the original perovskite material decomposed. The KOH-treated material was found to be significantly less active in RDE measurements (OER current of 10mA / cm²). 2 (Reaching 1.73V). Gd 0.95 OO 2.925 This is an example of a material that is initially highly electrochemically active but has insufficient phase stability under industrially suitable alkaline electrolysis conditions.

[0066] fired La 0.95 Ni 0.6 Fe 0.4 O 2.925 The material was found to be mainly composed of perovskite material. The main XRD peaks (in order of decreasing intensity) were 32.56°, 32.84°, and 46.94° (2θ). The calcined material was electrochemically active: 10 mA / cm². 2 The potential required to reach the OER current was 1.66V. As expected from the SF value (1.67 ≤ SF ≤ 2.8), the material was proven to be phase-stable after treatment with 6MKOH. The main XRD peaks (in decreasing order of intensity) were 32.60°, 32.80°, and 46.98° (2θ), and the fact that they did not change indicates that the original perovskite material was stable even under the treatment conditions. The KOH-treated material was found to have slightly lower activity in RDE measurements, but the activity was within an acceptable range (OER current of 10 mA / cm²). 2 (It reaches 1.72V). La 0.95 Ni 0.6 Fe 0.4 O 2.925 This is an example of a material that offers a good compromise between electrochemical activity and sufficient phase stability under industrially suitable alkaline electrolysis conditions.

[0067] The sintered LaFeO3 material was found to be mainly composed of perovskite material. The main XRD peaks (in order of decreasing intensity) were 33.16°, 57.40°, and 46.16° (2θ). The sintered material was electrochemically very inert. Even when the potential was raised to 1.9V, the OER current was 10mA / cm². 2 It never reaches that level, and the current density at 1.9V is only 3.5mA / cm². 2 As expected from the low SF value (SF<1.67), the material proved to be phase-stable after treatment with 6MKOH. The main XRD peak remained unchanged, indicating that the original perovskite material did not decompose. LaFeO3 is an example of a material that is highly stable but insufficiently active for OER under industrially suitable alkaline electrolysis conditions.

[0068] An electrode suitable for carrying out the oxygen evolution reaction in the electrolysis of water under alkaline conditions can be designed according to the following procedure.

[0069] (1) Formula [(A x )A' (1-x) ] y B z B' (1-z) O 3-δ For example, LaNi 0.6 Fe 0.4 A ceramic material containing O3 is selected in advance.

[0070] (2) The SF value is estimated based on the ionic radius, oxidation state value, A-site occupancy (y), oxygen unstoichiometric ratio (δ), and doping levels of the A-site and B-site (x and z, respectively), and using the SF calculation formula. For example, LaNi 0.6 Fe 0.4 The SF value of O3 is 1.63.

[0071] (3) If SF is within an appropriate range (1.67 ≤ SF ≤ 2.8), synthesize the material according to the method described in Example 1 (but not limited to these), and select a ceramic material for further testing, such as by exposing the material to 6MKOH at 80°C for 100 hours to confirm phase stability. For example, LaNi 0.6 Fe 0.4 O3 will not be selected for further testing because its SF < 1.67.

[0072] (4) If SF is outside the appropriate range, change the SF value by varying the value of y within the range of 0.5 to 0.99, preferably within the range of 0.6 to 0.98. For example, the value of y is from 1.0 to 0.95 (LaNi 0.6 Fe 0.4 O3 to La 0.95 Ni 0.6 Fe 0.4 O 2.925 By changing it to ), the SF value can be increased to 2.1, satisfying the condition 1.67 ≤ SF ≤ 2.8.

[0073] (5) Instead of step 4, change the SF value by changing the values ​​of x and / or z. For example, change the value of z from 0.6 to 0.1 (LaNi 0.6 Fe 0.4 O3 to LaNit 0.1 Fe 0.9 By switching to O3, the SF value can be increased from 1.63 to 1.65.

[0074] (6) Instead of step 4 or 5, the SF value can also be changed by changing the elemental composition of the ceramic material. For example, by replacing Fe with Co, i.e., changing the composition of the material to LaNi 0.6 Fe 0.4 O3 to LaNit 0.6 Co 0.4 By switching to O3, the SF value can be increased from 1.63 to 1.64.

[0075] (7) Steps 4, 5, and 6 can be combined advantageously. For example, LaNi 0.6 Co 0.4 The SF value of O3 is obtained by decreasing y from 1 to 0.95, i.e., La 0.95 Ni 0.6 Co 0.4 O 2.85 By doing so, the value can be increased from 1.64 to 2.04, which satisfies the condition 1.67 ≤ SF ≤ 2.8.

Claims

1. An electrode suitable for carrying out the oxygen evolution reaction in the electrolysis of water under alkaline conditions, [(A ｘ ) A' （１－ｘ） ] ｙ B ｚ B' （１－ｚ） O ３－δ The ceramic material of formula (I) is provided, Each of A and A' is independently a rare earth metal or an alkaline earth metal, x is in the range of 0 to 1, y is the A site occupancy rate in the range of 0.5 to 0.99, each of B and B' is independently a transition metal, z is in the range of 0 to 1, O is oxygen, δ is the oxygen unstoichiometric ratio in the range of -1 to 1, and The stability coefficient (SF) of ceramic materials is defined by equation (II), [Math 1] r Ｏ is the ionic radius of oxide ions (O ２－ ), r Ｂ，ａv is the weighted average ionic radius of B and B' defined by formula (III), r Ｂ,Ａv =z・r Ｂ +(1-z)・r Ｂ’・・・ (III) r Ｂ r is the ionic radius of B. Ｂ’ n is the ionic radius of B'. Ａ,Ａv is the weighted average oxidation state of A and A' defined by equation (IV), n Ａ,Ａv =[x・n Ａ +(1-x)・n Ａ’ ]・y、 ・・・ (IV) n Ａ n is the oxidation state of A. Ａ’ This is the oxidation state of A', r Ａ，ａv This is the weighted average ionic radius of A and A' defined by equation (V), r Ａ,Ａv =[x・r Ａ +(1-x)・r Ａ’ ]・y、 ・・・ (V) r Ａ r is the ionic radius of A. Ａ’ This is the ionic radius of A', The aforementioned ceramic material has a SF ratio of 1.67 ≤ 2.

8. The electrode further comprises a second material, the second material being a metal alloy of metals Ni, Fe, and Ni, or a hydroxide of Ni and Fe.

2. The electrode according to claim 1, wherein the ceramic material of formula (I) is uniformly dispersed on the surface of the second material.

3. The electrode according to claim 1 or 2, wherein the particles of the ceramic material are immobilized by the second material and partially encapsulated by the second material.

4. A is an element selected from the element list La, Ce, Gd, Pr, Ba, A' is an element selected from the element list Sr, Ca, Ba, Ce. The electrode according to claim 1, wherein B or B' is an element independently selected from the element list Mn, Ni, Fe, Co, Ti, Cr.

5. The electrode according to claim 1 or 4, wherein y is in the range of 0.6 to 0.

98.

6. The electrode according to claim 1, wherein the average particle size of the ceramic material of formula (I) is 10 nm to 300 nm.

7. The electrode according to claim 1, wherein the ceramic material has a perovskite crystal structure.

8. When an oxygen evolution reaction is carried out using a rotating disk electrode with a rotation speed of 1500 rpm in 20-35 wt% KOH at a temperature of 75-85°C, the electrode overpotential for the oxygen evolution reaction is 1 mA / cm². ２ The electrode according to claim 1 or 4, wherein the voltage is 400 millivolts or less.

9. The electrode according to claim 1, wherein the ceramic material of formula (I) is phase-stable for 100 hours in 6MKOH at 80°C.

10. The electrode according to claim 1, wherein 1.9 ≤ SF ≤ 2.

6.

11. An alkaline electrolytic stack comprising at least one electrode as described in claim 1.

12. A method for electrolyzing water under alkaline conditions using the alkaline electrolytic stack described in claim 11.

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