Electrode for gas evolution in an electrolytic process

Abstract

The present invention relates to an electrode for gas evolution in an electrolytic process and to a method for producing such an electrode, which electrode comprises a metal substrate and a coating formed on the substrate, wherein the coating comprises at least a highly porous catalytic outer layer containing nickel oxide and nickel hydroxide, the porous outer layer having a surface area (BET) of at least 40 m 2 / g. The catalytic layer is produced from a Ni oxide / V oxide initial coating with subsequent leaching of V.

Description

Technical Field

[0001] This invention relates to an electrode for gas evolution during electrolysis, comprising a nickel substrate and a nickel-based catalytic coating. Such an electrode can be particularly used as an anode in an electrochemical cell, for example as an oxygen evolution anode in alkaline water electrolysis. Background Technology

[0002] Alkaline water electrolysis is typically carried out in an electrochemical cell where the anode and cathode compartments are separated by a suitable separator, such as a diaphragm or membrane. An alkaline aqueous solution, such as KOH aqueous solution, with a pH higher than 7, is supplied to the cell, and a current flows between the electrodes in the cathode and anode compartments, i.e., between the cathode and anode, with a potential difference (cell voltage) typically ranging from 1.8 to 2.4 V. Under these conditions, water is decomposed into its components, resulting in the evolution of gaseous hydrogen at the cathode and gaseous oxygen at the anode. Removal of the gaseous products from the cell allows for continuous operation. The anode oxygen evolution reaction can be summarized as follows:

[0003] 4OH - →O2 + 2H2O + 4e -

[0004] Alkaline water electrolysis is typically carried out in a temperature range of 40–90°C. Alkaline water electrolysis is a promising technology in the field of energy storage, especially for storing energy from fluctuating renewable energy sources such as solar and wind power.

[0005] In this regard, it is particularly important to reduce technology costs in terms of less expensive equipment, such as less expensive electrodes, and in terms of overall process efficiency. An important aspect of cell efficiency involves the required cell voltage for efficient water electrolysis. The overall cell voltage is essentially controlled by: the reversible voltage, i.e., its thermodynamic contribution to the overall reaction; the voltage loss due to ohmic resistance in the system; the hydrogen overpotential related to the kinetics of the hydrogen evolution reaction at the cathode; and the oxygen overpotential related to the kinetics of the oxygen evolution reaction at the anode.

[0006] The oxygen evolution reaction has slow kinetics, which is the reason for the high overpotential at the anode. This results in increased operating cell voltage and difficulties in the large-scale commercialization of this technology.

[0007] Another key feature of the electrodes is their resistance to unprotected shutdowns. In fact, during typical operation of an electrolysis unit consisting of a cluster of individual electrochemical cells, maintenance due to technical issues often requires power outages, causing harmful polarity reversals of the electrodes. Such reversals are typically avoided using an external polarization system (or polarizer) that maintains current flow in the desired direction. This auxiliary component mitigates potential electrode degradation caused by metal dissolution or electrode corrosion but increases the system's initial investment cost.

[0008] In the prior art, preferred anode / anode catalysts for alkaline water electrolysis include bare nickel (Ni) electrodes, Raney nickel (Ni+Al) electrodes, and electrodes with an iridium oxide (Ir)-based catalytic coating.

[0009] The bare nickel electrode is formed solely from a nickel substrate, such as a Ni mesh, which can be easily manufactured at low cost but exhibits a high oxygen overpotential that results in slow kinetics.

[0010] Raney nickel electrodes are manufactured via plasma spraying, which involves the deposition of a thin film of Ni+Al catalytic powder. At the industrial level, plasma spraying is not commonly used for catalytic coatings due to its high production costs and associated health and safety hazards such as noise, explosions, intense flames exceeding 3000°C, and fumes. Furthermore, Raney nickel manufacturing methods include activation processes, which involve extracting aluminum from the catalytic coating, leaving nearly pure nickel on the surface, and significantly increasing the surface area. During the Al dissolution reaction, H2 is generated, which poses a problem during the manufacturing process due to the sudden exothermic reaction. Another technical problem with Raney nickel deposited via plasma spraying is the rather jagged morphology of the coating. Sharp jagged surfaces in the zero-gap grooves where the electrode contacts the film can cause damage to the film.

[0011] Electrodes with iridium-based catalytic coatings are produced by thermal decomposition, a well-established technique offering less harm. However, iridium, used in these electrodes, is one of the least abundant precious metals in the Earth's crust, leading not only to high prices but also to difficulties in procuring large quantities for industrial-scale manufacturing methods (e.g., gold is 40 times more abundant than iridium and platinum is 10 times more abundant). Furthermore, iridium-based coatings are typically multilayered, resulting in expensive manufacturing processes. Multilayered catalytic coatings comprise, for example, an intermediate layer applied directly to a Ni substrate, an active layer applied to the intermediate layer, and an outer layer of iridium oxide. These multilayer compositions typically exhibit low tolerance to unprotected shutdown because Ir and other non-Ni metals present in their formulations, such as Co, can dissolve into the electrolyte solution during polarity reversal.

[0012] CN 110394180 A describes an electrode having a nickel substrate and a surface comprising nickel hydroxide and nickel oxide, which can be used as an anode in alkaline water electrolysis. CN 110863211 A, CN 109972158 A, CN 110438528 A and CN110952111 A describe foamed nickel electrodes having an outer surface layer comprising nickel hydroxide and nickel oxide.

[0013] Therefore, the object of this invention is to provide an improved electrode that exhibits low oxygen overpotential in alkaline water electrolysis applications and can be manufactured more safely and cost-effectively than prior art electrodes. Furthermore, it is desirable for the new electrode to exhibit improved resistance to unprotected shutdowns. Summary of the Invention

[0014] The invention is based on the concept of an electrochemically active thin film for oxygen evolution exhibiting a very high surface area. The high surface area of ​​the coating allows a large number of electrolytes to contact the catalyst and its active sites, thereby enhancing electrochemical performance, for example, for the production of gaseous oxygen (O2). By combining, modulating, and designing techniques from different fields such as sol-gel synthesis and metallurgy, stable, highly porous nickel oxide coatings particularly suitable for oxygen evolution reactions can be produced.

[0015] The invention is described in the appended claims.

[0016] This invention relates to an electrode for gas evolution during electrolysis, comprising a metallic substrate and a coating formed on said substrate, wherein the coating comprises at least a catalytically porous nickel oxide outer layer exhibiting high porosity, wherein the porous outer layer has a porosity of at least 40 μm as measured by BET (Brunauer, Emmett, Teller). 2 / g surface area. Due to the characteristics of the highly porous nickel oxide outer layer forming the electrode of the invention (which will be explained in more detail below), two different nickel oxide phases (i.e., different oxidation states of nickel) exist in the outer layer, namely nickel oxide (NiO) and nickel hydroxide (Ni(OH)2). The inventors have surprisingly discovered that the highly porous nickel oxide / nickel hydroxide catalyst layer on the metal substrate exhibits a low oxygen overpotential value, making it possible to produce a very efficient electrolyzer for alkaline water electrolysis using such an electrode. Naturally, the electrode of the present invention can be advantageously used in any other application that benefits from low oxygen overpotential.

[0017] The metallic substrate of the electrode of the present invention is preferably selected from the following substrates: nickel-based substrates, titanium-based substrates, and iron-based substrates. Nickel-based substrates include nickel substrates, nickel alloy substrates (particularly NiFe alloys and NiCO alloys and combinations thereof), and nickel oxide substrates. Iron-based substrates include iron alloys such as stainless steel. In the context of the present invention, metallic nickel substrates are particularly preferred. Like a bare nickel electrode, the electrode of the present invention benefits from the catalytic properties of nickel but does not exhibit the slow kinetics of a bare nickel electrode and does not require additional noble metals or other metals to improve reaction kinetics. Therefore, the coating of the present invention is substantially free of noble metals such as iridium or other transition metals such as cobalt. "Substantially free" means that the corresponding metal is typically outside any detectable range when using, for example, typical laboratory X-ray diffraction (XRD) techniques. However, the coating may contain trace amounts of vanadium (V) produced by the preferred manufacturing techniques described below, although in a preferred embodiment, the electrode is also substantially free of vanadium.

[0018] In one embodiment, the outer catalytic layer consists only of nickel oxide (NiO) and nickel hydroxide (Ni(OH)2). Therefore, the catalyst does not contain any rare and expensive metals.

[0019] Preferably, the surface area of ​​the porous outer layer is at least 60, more preferably at least 80 m². 2 / g(BET). In some embodiments, the surface area of ​​the porous outer layer is between 40 and 120, between 60 and 110, or between 80 and 100 m². 2 The electrode of the invention has a catalytic layer with a highly porous nickel-based catalytic outer layer, which translates to a significantly higher surface area than, for example, typically less than 10 m². 2 / g range of commercially available iridium-based catalytic coating surface area.

[0020] According to a preferred embodiment of the invention, a porous outer layer is obtained by leaching vanadium oxide from a heat-treated gel-like precursor coating containing nickel and vanadium salts. Thus, the invention combines two techniques for obtaining a porous nickel oxide catalytic coating: sol-gel synthesis combined with thermally formed nickel oxide (NiO) and vanadium oxide (VO). Furthermore, the removal of vanadium oxide using the concept of selective metallization to remove sacrificial metals results in a further increase in surface area. Therefore, the oxide coating is produced by thermal decomposition, a well-developed method readily adaptable to large-scale production. Moreover, the thermal decomposition technique can be readily adapted to a wide variety of nickel substrates, regardless of the substrate geometry or size. Additionally, a highly porous nickel oxide coating is obtained solely from nickel and vanadium (i.e., metals highly abundant in the Earth's crust and significantly less expensive than precious metals such as iridium). Due to their high abundance, large-scale purchases required for industrial-scale production are readily achievable. Furthermore, the leaching steps required to remove vanadium oxide from the coating are less challenging than those for Raney nickel production because vanadium leaching does not generate hydrogen gas during its dissolution, thus avoiding associated health and safety hazards. Finally, the coating produced by the method according to the invention has a substantially flat morphology, thereby avoiding damage to the film in a zero-gap electrolytic cell.

[0021] In a preferred embodiment, the coating comprises a nickel-based interlayer deposited between a nickel substrate and a catalytic porous outer layer. Preferably, the nickel-based interlayer consists of metallic nickel or a combination of metallic nickel and nickel oxide. The nickel / nickel oxide interlayer preferably has a thickness of less than about 1 μm. 2 / g porosity. Surprisingly, it was found that the catalytic coating, when applied to the nickel / nickel oxide interlayer described above, could withstand unprotected shutdowns imposed by the operation and maintenance of the electrolysis unit without requiring additional expensive polarization equipment.

[0022] The nickel interlayer has a content of 100-3000 g / m² (based on metallic elements). 2The preferred nickel loading within the range, or even more preferably 200-800 g / m³, is preferred. 2 .

[0023] The intermediate layer is usually denser than the outer catalyst layer.

[0024] In one embodiment, the intermediate layer has a double-layer capacitance in the range of about 1.0 to about 10.0 mF / g.

[0025] Various techniques, such as thermal spraying, laser cladding, or electroplating, can be used to obtain the intermediate layer. In a preferred embodiment, the thermal spraying technique is selected from the following: wire-arc spraying and plasma spraying.

[0026] In one embodiment, the porous outer layer has a thickness in the range of 5 to 40 micrometers (μm), preferably in the range of 10 to 20 μm. The porous outer layer has a thickness of 5-50 g / m³ based on metal elements. 2 Preferred nickel loading levels within the specified range. When applied directly to a nickel substrate, the catalytic coating is particularly suitable for low current density applications (e.g., at 1 kA / m²). 2 Or at most a few kA / m 2 (within the range). For these applications, the preferred nickel loading is typically 6-15 g / m³. 2 Within this range. If a porous outer layer is applied to the nickel intermediate layer, these implementations can be used for high current density applications (e.g., at 10 kA / m²). 2 (and larger), making it typically preferred at 15-25 g / m³ 2 And higher nickel loading over a wider range.

[0027] The coating, consisting of a porous outer layer and an intermediate layer, has a thickness in the range of 30-300 μm, preferably about 50 μm.

[0028] The coating, consisting of a porous outer layer and an optional intermediate layer, can be applied to one or both sides of the metal substrate of the electrode, as is common in the art, and depends on the trench construction and the electrode arrangement within the trench.

[0029] Preferably, the metal substrate is nickel-based, and even more preferably nickel mesh, which can be used in various configurations with respect to mesh thickness and mesh geometry. A preferred mesh thickness is in the range of 0.2 to 1 mm, more preferably about 0.5 mm. A typical mesh opening is a diamond-shaped opening with a long width in the range of 2 to 10 mm and a short width in the range of 1 to 5 mm.

[0030] Due to its low oxygen overvoltage value, the electrode of the present invention is preferably used as an anode for oxygen evolution, particularly as an anode in an electrolyzer for alkaline water electrolysis. Therefore, the present invention also relates to an electrolyzer for electrochemical processes, particularly for alkaline water electrolysis, comprising an anode and a cathode for oxygen evolution, wherein the anode is the electrode as defined above.

[0031] The present invention also relates to a method for producing electrodes as defined above, wherein the method comprises the following steps:

[0032] a) Applying a coating solution containing nickel salts, vanadium salts, and a gelling agent to a metal substrate.

[0033] b) Subsequently, drying is carried out at a temperature in the range of 80-150°C, preferably for 20-40 minutes, typically for 30 minutes.

[0034] c) Then calcining at a temperature in the range of 300-500°C, typically at 400°C, preferably for 5 to 15 minutes, typically for 10 minutes, to oxidize the metal salt into a metal oxide.

[0035] d) Repeat steps a) to c) until a coating with the desired nickel specific load is obtained (it should be understood that if the desired load is achieved in a single performance of steps a) to c), it is not necessary to repeat the process);

[0036] e) The final heat treatment (second calcination) is preferably carried out at a temperature in the range of 300-500°C, typically at 400°C, for 1 to 4 hours, typically for 2 hours;

[0037] f) Vanadium is extracted from the coating in an alkaline bath to produce a highly porous catalytic outer layer comprising nickel oxide and nickel hydroxide.

[0038] According to the present invention, an external catalytic layer of nickel oxide / nickel hydroxide can be generated in a series of layers to precisely adjust the desired nickel loading. Because only one coating composition is used, the fabrication of the coated electrode is faster, simpler, and therefore cheaper than prior art methods. Furthermore, the oxide coating is produced by thermal decomposition, a well-developed method for large-scale coating production.

[0039] The application of the coating solution to the substrate in step a) is preferably accomplished by brushing or spraying, and the coating solution is preferably water-based.

[0040] The combination of organic and inorganic chemical precursors in the coating solution produces a macroporous gel structure in which metal salts are embedded. In a drying step, the solvent is dried off. During a subsequent heat treatment at a temperature capable of calcining the precursor metal salts, the dissolved metal becomes an oxide, while other components evaporate or burn off, leaving behind a porous metal oxide structure. The coating solution preferably contains a solvent made of water and / or alcohols such as ethanol and acids such as hydrochloric acid. Suitable additives acting as gelling agents include ethylene glycol and citric acid. In one embodiment, the solvent and gelling agent used in the sol-gel method comprise ethanol or water or an ethanol / water mixture and hydrochloric acid as solvents, ethylene glycol, and citric acid (i.e., solvent: ethylene glycol: citric acid) in a molar ratio of 14:4, 5:1. As a complement to its role in sol-gel synthesis, ethylene glycol, after vaporization during heat treatment, produces a “dry sludge” form: heating ethylene glycol above its decomposition temperature and burning it off as CO2 leaves a particularly open structure compared to conventional pure inorganic coating solutions used for the manufacture of size-stabilized anodes.

[0041] The nickel salt is preferably a nickel halide, such as nickel chloride, and the vanadium salt is preferably a vanadium halide, such as vanadium chloride.

[0042] After application to a metal substrate, the coating consists of two separate crystalline phases: nickel oxide (NiO) and vanadium oxide (VO). The vanadium oxide is removed by leaching with an alkaline solution (e.g., 6M KOH at 80°C) to obtain an activated microporous Ni oxide structure (a mixed phase of NiO and Ni(OH)₂). Therefore, step f) is preferably carried out in an aqueous alkaline hydroxide solution, such as 6M NaOH or 6M KOH solution, at a temperature between 60 and 100°C, typically at 80°C, for a period ranging from 12 to 36 hours, typically for 24 hours.

[0043] It has been discovered that the nickel oxide / nickel hydroxide ratio can be adjusted by selecting a suitable niobium / vanadium ratio in the coating solution. Preferably, the atomic ratio of Ni / V in the coating solution is approximately 100 / 100, resulting in an atomic percentage of approximately 25-15 atomic% NiO and approximately 75-85 atomic% Ni(OH)₂ in the final outer catalyst layer. Typically, the atomic percentage of Ni(OH)₂ in the catalyst coating decreases as the V content in the coating solution decreases.

[0044] In the context of this invention, the catalytically highly porous (HP) nickel oxide outer layer obtained by thermal decomposition of a dried gel-like coating comprising nickel and vanadium salts, followed by vanadium oxide extraction, is referred to as HP-NiO. x .

[0045] In a preferred embodiment, an intermediate step a0) is performed before step a), wherein, prior to step a), a nickel or nickel / nickel oxide interlayer is preferably applied to the metal substrate by thermal spraying, laser cladding, or electroplating, such that the interlayer exhibits an appearance of less than about 1 μm. 2 The porosity (BET) is 1 / g. This results in electrodes with higher resistance to unprotected shutdowns, especially at high current densities.

[0046] Preferably, step a0) includes plasma spraying nickel powder onto a metal substrate in ambient air. In one embodiment, the nickel powder plasma sprayed onto the substrate has an average particle size of about 10 μm to about 150 μm, preferably about 45 μm to about 90 μm. Attached Figure Description

[0047] The invention will now be described in more detail, together with some preferred embodiments and corresponding drawings.

[0048] In the attached diagram,

[0049] Figure 1 SEM images of the surface of the electrode in Example 2 without a nickel interlayer and cross-sectional images of the catalytic outer layer are shown.

[0050] Figure 2 The results of BET surface area measurement of the outer surface of the electrode in Example 2 are described.

[0051] Figure 3 Describe the diffraction pattern of the electrode in Example 2;

[0052] Figure 4 The results of accelerated life testing of the electrode in Example 2 are shown compared to prior art electrodes;

[0053] Figure 5 SEM images of the surface of the electrode of Example 3 with a nickel interlayer and cross-sectional images of the catalytic outer layer are shown.

[0054] Figure 6 The results of the shutdown test of the electrode in Example 3 are shown compared to the exposed nickel electrode of the prior art; and

[0055] Figure 7 The results of the shutdown test of the electrode of Example 3 are shown compared with those of the prior art iridium-based electrodes. Detailed Implementation

[0056] Example 1: Preparation of coating solution

[0057] To prepare a 1-liter (1) coating solution, 0.41 g of softened water, 0.41 g of ethylene glycol, and 0.21 g of 37% hydrochloric acid were mixed in a flask and stirred for 10 minutes. 300 g of VCl3 was added to the solution and dissolved under stirring for 30 minutes. Subsequently, 450 g of NiCl2·6H2O was added to the solution and dissolved under stirring for 30 minutes. 300 g of citric acid was added to the solution and dissolved under continuous stirring for 45 minutes.

[0058] Example 2: Coated HP-NiO without intermediate layer x Preparation of nickel mesh electrodes

[0059] In order to prepare 1m 2 The coated mesh was sandblasted with a 0.5 mm thick nickel diamond mesh and etched in a hydrochloric acid solution. 4 ml of the coating solution from Example 1 was deposited by brushing it onto each side of the mesh, dried at 130°C for 30 minutes, and calcined at 400°C for 10 minutes, resulting in 1 g / m² for one cycle. 2 Nickel loading per projected area. A total of 10 cycles of repeated deposition, drying, and calcination were performed to obtain 10 g / m². 2 The final nickel loading of the projected area was determined. The coated electrode was then post-baked at 400°C for 2 hours. Finally, the electrode was immersed in an alkaline NaOH bath at 80°C for a total time of 24 hours for vanadium removal.

[0060] Example 3: HP-NiO coating with a nickel interlayer x Preparation of nickel mesh electrode

[0061] A 0.5 mm thick nickel rhombic mesh (Fe<0.5, O<0.4, C<0.02, S<0.01) was plasma-sprayed using 99.9% pure nickel powder with a particle size of 45±10 μm. The surface area on both sides was 4.8±0.5 g / dm² in ambient air. 2 (And with a target thickness of 50 μm on each side). Subsequently, the sprayed mesh was heated in an oven at 350°C in air for 15 minutes. The plasma-sprayed woven mesh was cooled and then coated with the precursor composition using a brush in a series of coating, heating, and cooling steps. To prepare a 1m... 2 A coated mesh with a nickel interlayer was provided, and 14 ml of the coating solution of Example 1 was deposited by brushing it onto each side of the mesh, dried at 130°C for 30 minutes and calcined at 400°C for 10 minutes, resulting in 3 g / m² for one cycle. 2 Nickel loading per projected area. A total of 7 cycles of repeated deposition, drying, and calcination were performed to obtain 21 g / m². 2 The final nickel loading of the projected area was determined. The coated electrode was then post-baked at 400°C for 2 hours. Finally, the electrode was immersed in an alkaline NaOH bath for vanadium removal at 80°C for a total time of 24 hours.

[0062] Counterexample 4

[0063] The precursor solution is obtained by sequentially applying each corresponding precursor solution to the mesh substrate (or its respective underlying layer) via brushing and thermal decomposition, thereby obtaining a substrate comprising LiNiO, NiCoO, and other components. x Intermediate layer and IrO x The top layer is a three-layer coated nickel diamond mesh with a thickness of 0.5 mm.

[0064] Counterexample 5

[0065] The precursor solution is obtained by sequentially applying each corresponding precursor solution to the mesh substrate (or the layer preceding it) by brushing and thermally decomposing it, thereby obtaining a substrate consisting of LiNiO, LiNiIrO, and LiNiO. x The top layer is made of a two-layer coated nickel diamond mesh with a thickness of 0.5 mm.

[0066] The electrodes of Embodiments 2 and 3 according to the present invention were characterized using different techniques and compared with counterexamples 4 and 5.

[0067] A. Electrode characterizing Example 2 (with HP-NiO) x (Electrode with a catalyst layer but no nickel interlayer)

[0068] A.1 Scanning electron microscopy (SEM) was used to evaluate the morphology of the coatings on the surface and cross-section, respectively. Analysis was performed on both fresh and used samples to qualitatively evaluate coating properties such as stability, adhesion, and wear. Figure 1 SEM images showing a surface view (a) and a cross-sectional view (b) of the electrode of the present invention prepared according to Example 2. Morphological surface analysis shows HPNiO x The coating exhibits a flat, "dry mud" morphology, while the cross-section reveals its porosity. Furthermore, phase homogeneity is visible in the cross-section. The image, particularly the cross-sectional view (b), shows that the host nickel substrate 10 exhibits some toughness after sandblasting and etching, which is beneficial for the adhesion / fixation of the catalytic porous outer layer 11 to the substrate. However, the outer surface of the catalytic outer layer 11 applied according to the method of the invention is smooth, thus preventing damage to the fragile membrane when assembled in the electrolytic cell.

[0069] A.2 Compared with existing anodes used in alkaline water electrolysis, the electrochemical performance of the invented electrode was characterized using a modified impedance single electrode potential (CISEP) test. To determine the oxygen overvoltage of the electrode of the present invention, it was tested as the anode in a three-electrode beaker. The test conditions are summarized in Table 1.

[0070] Table 1

[0071] electrolytes <![CDATA[25 wt% KOH (1.5 l) in ultrapure H2O]]> temperature 80℃ cathode <![CDATA[Nickel mesh (projected area 12 cm 2 )]]> Working anode electrolysis area <![CDATA[1cm 2 Projected area Reference electrode Saturated calomel electrode (SCE)

[0072] Initially, the sample underwent 2 hours of 10 kA / m 2Pre-electrolysis (conditioning) was performed to stabilize the oxygen overvoltage (OOV). Then, several chronopotential steps were applied to the sample. The final output of the CISEP test was 10 kA / m. 2 The average value of the three steps is corrected for the resistance of the electrolyte.

[0073] Table 2 summarizes the results of the bare nickel anode (Base Ni), the iridium-based anode (CEx 4) of Counterexample 4, the Raney nickel anode (Ni Raney), and the electrode of Example 2 (HP-NiO). x Comparison between:

[0074] Table 2

[0075] <![CDATA[10kA / m 2 OOV vs NHE[mV]<!-- 6 --> ]]> Bare Ni 340 CEx 4 260 Ni Raney 240 <![CDATA[HP-NiO x ]]> 200

[0076] The energy savings (140mV lower than Bare Ni) achieved with the anode of this invention solve the problem of high operating costs caused by the slow kinetics of the anode reaction of uncoated nickel mesh that does not include expensive precious metals or harmful manufacturing methods.

[0077] A.3 BET measurements were performed to determine the surface area of ​​the electrode of Example 2, compared with the electrode (CEx 5) of Counterexample 5, which is also suitable for alkaline water electrolysis. Figure 2 The results shown indicate that the electrode of Example 2 has a significantly larger surface area than that of prior art electrodes.

[0078] A.4 X-ray diffraction (XRD) techniques were used to evaluate the types of oxides formed and their crystal structures. Figure 3 The typical diffraction pattern generated by the electrode according to Example 2 is shown in the figure. The x-axis represents the diffraction angle 2θ and the y-axis represents the diffraction intensity in arbitrary units (e.g., in count / scan). Strong peaks (1), (2), and (3) correspond to the Ni substrate of crystallographic planes (111), (200), and (220), respectively. Weaker peaks (4), (5), and (6) correspond to the NiO phase of the highly porous outer catalytic layer of crystallographic planes (111), (200), and (220), respectively. Even weaker peaks (7), (8), (9), and (10) correspond to the Ni(OH)2 phase of the highly porous outer catalytic coating of crystallographic planes (001), (100), (101), and (110), respectively. Therefore, it was determined that the catalytic coating is composed of nickel oxide (NiO) and nickel hydroxide (Ni(OH)2). Furthermore, as can be seen from Figure 3 The diffraction patterns clearly show that the highly porous catalytic coating of this invention does not contain any iridium or other rare / expensive metals. Therefore, the electrodes of this invention can be used to avoid the cost and supply problems associated with prior art electrodes.

[0079] A.5 Accelerated Life Testing (ALT) is used to evaluate the lifetime of the catalytic coating. The test consists of long-term electrolysis in a beaker bath with a two-electrode setup and a continuous electrolytic current applied directly to them. The applied conditions are more stringent than those of the CISEP test and exceed typical operating conditions in order to accelerate the wear process. The conditions required for accelerated life testing are summarized in Table 3 below:

[0080] Table 3

[0081] electrolytes <![CDATA[30 wt% KOH in ultrapure H2O]]> Current density <![CDATA[20-40kA / m 2 ]]> temperature 88℃ counter electrode Nickel mesh Working electrode electrolysis area <![CDATA[1cm 2 Projected area

[0082] exist Figure 4 The ALT data are displayed in the figure. The x-axis represents the duration of the test in hours and the y-axis represents the cell voltage in volts. Data point (1) shows the results for the uncoated Ni substrate, showing that the cell voltage increased from 2.5V to 2.7V after only a few hours of operation. The cell voltage remained stable at 2.7V, indicating that no further deterioration occurred. Data point (2) shows the electrode of Example 2, which maintained a lower cell voltage of 2.5V for approximately 250 hours until the cell voltage increased and subsequent electrode failure occurred. This indicates that the electrode of Example 2, with its highly porous external catalytic nickel oxide layer (without an intermediate layer), has superior performance in terms of cell voltage compared to the bare nickel substrate, but is not suitable for long-term operation under the harsh conditions of ALT. As shown above, the electrode of Example 2 is particularly suitable for operation at lower current densities. Data points (3) and (4) will be described in detail along with the electrodes characterizing Example 3 below.

[0083] B) Characterizing the electrode of Example 3 (with HPNiO) x (Electrode with catalyst layer and nickel interlayer)

[0084] B.1 Again, scanning electron microscopy (SEM) was used to evaluate the coating morphology on the surface and cross-section, respectively. Analysis was also performed on both fresh and used samples to qualitatively evaluate coating properties such as stability, adhesion, and wear. Figure 5 SEM images showing the surface (a) and cross-section (b) of the electrode of the present invention prepared according to Example 3 (note) Figure 5 The image is in comparison Figure 1 (The image was obtained at a lower resolution / magnification). Again, especially the cross-sectional view (b), shows that although the main nickel substrate 10 exhibits some toughness after sandblasting and etching, the application of the nickel intermediate layer 12 by plasma spraying and the application of the catalytic outer layer 11 using the method of the present invention result in a smooth surface.

[0085] B.2 The accelerated lifetime test (ALT) described in Section A.5 above was also performed using the electrode of Example 3. The corresponding results are also described in Table 4. Data point (3) indicates that the NiO with plasma spraying x The intermediate layer is a nickel substrate, i.e., without additional HP-NiO. xCatalytic outer layer. Only the intermediate layer electrode exhibited a lower cell voltage than the bare nickel substrate, but still at least 100 mV higher than the electrode of Example 2, with further continuous increases throughout the electrode lifetime. Data point (4) shows the electrode of Example 3, i.e., the nickel substrate with a plasma-sprayed nickel intermediate layer and a highly porous catalytic outer layer. Electrode 3 showed the best performance in accelerated lifetime testing, with a similarly low starting cell voltage of 2.5 V, with very slow continuous increases over a nearly 1,500-hour operating lifetime.

[0086] B.3 To evaluate the polarity reversal resistance of the electrode of Example 3 and to assess its resistance to simulated device shutdown, a shutdown test was conducted under the operating conditions summarized in Table 4 below:

[0087] Table 4

[0088] temperature 80℃ electrolytes <![CDATA[30 wt% KOH in ultrapure H2O]]> Current density <![CDATA[10kA / m 2 ]]>

[0089] The following test protocol was implemented: After a 48-hour grate-in period, a 6-hour shutdown was simulated by keeping the electrolyzer open with the pump and allowing the temperature to drop to room temperature. After shutdown, electrolysis continued for 6 hours under the operating conditions in Table 4. The shutdown cycle was repeated until the electrodes failed.

[0090] Figure 6 The results for the electrode of Example 3 (data point (1)) and the bare nickel electrode (data point (2)) are shown. The number of shutdowns is described on the x-axis, while the cell voltage is shown on the y-axis. The results show that the bare nickel electrode, although operating at a higher cell voltage, could only withstand 40 shutdowns, while the electrode of Example 3 maintained its low cell voltage for up to 55 shutdowns.

[0091] exist Figure 7 The image shows a comparison between the electrode (data point (1)) of Example 3 and the electrode (data point (2)) of Counterexample 4. The x-axis describes the number of shutdowns, while the y-axis shows the deviation from the standardized cell voltage to evaluate the construction of the cathode and separator. (See also...) Figure 7 As observed, the highly porous nickel oxide outer catalyst layer on the plasma-sprayed nickel intermediate layer can withstand more than 50 shutdowns without increasing the cell voltage. In contrast, the cell voltage of the electrode in Counterexample 4 began to increase after 20 shutdowns.

[0092] The preceding description is not intended to limit the invention, which can be used in various embodiments without departing from its purpose, and the scope of the invention is uniquely defined by the appended claims.

[0093] In the specification and claims of this application, the terms “comprising,” “including,” and “containing” are not intended to exclude the presence of other additional elements, components, or method steps.

[0094] Discussions of literature, terminology, materials, devices, articles, etc., are included in this specification only to provide background information for the invention. It is not recommended or implied that any or all of these subjects constitute part of the prior art or general knowledge in the field related to this invention prior to the priority date of each claim of this application.

Claims

1. A method for producing electrodes, The electrode is used for gas evolution during the electrolysis process. The electrode comprises a metal substrate and a coating formed on the substrate. The coating comprises at least a catalytic porous outer layer containing nickel oxide and nickel hydroxide, the porous outer layer having a diameter of at least 40 μm. 2 / g BET surface area, and said method includes the following steps: a) Applying a coating solution containing nickel salts, vanadium salts and a gelling agent to a metal substrate; b) Dry at a temperature ranging from 80 to 150°C; c) Calcination at a temperature ranging from 300 to 500°C; d) Repeat steps a) to c) until a coating with the desired nickel specific load is obtained; e) Final heat treatment at a temperature in the range of 300-500℃; f) Vanadium is extracted from the coating in an alkaline bath.

2. The method according to claim 1, wherein the coating solution comprises a solvent, the solvent comprising water and / or alcohol, and an acid.

3. The method according to claim 2, wherein the alcohol is ethanol and the acid is hydrochloric acid.

4. The method according to any one of claims 1 to 3, wherein the gelling agent comprises ethylene glycol and citric acid.

5. The method according to any one of claims 1 to 3, wherein the nickel salt is a nickel halide and the vanadium salt is a vanadium halide.

6. The method according to any one of claims 1 to 3, wherein step f) is carried out in an alkaline hydroxide aqueous solution at a temperature in the range of 60-100°C for a period of time between 12 and 36 hours.

7. The method according to any one of claims 1 to 3, comprising an intermediate step a0) prior to step a), wherein step a0) comprises forming an intermediate layer of nickel and / or nickel oxide on a metal substrate by thermal spraying, laser cladding, or electroplating, the intermediate layer having a thickness of less than 1 μm. 2 Porosity of / g BET.

8. The method of claim 7, wherein the intermediate layer in step a0) is formed by electro-thermal spraying of nickel powder onto a metal substrate in ambient air or by plasma spraying.

9. The method of claim 8, wherein the nickel powder is plasma-sprayed onto a metal substrate and has an average particle size of 10 µm-150 µm.

10. The method of claim 9, wherein the nickel powder is plasma-sprayed onto a metal substrate and has an average particle size of 45 µm-90 µm.

11. The method according to any one of claims 1 to 3, wherein the metal substrate is selected from the following substrates: nickel-based substrates, titanium-based substrates, and iron-based substrates.

12. The method according to any one of claims 1 to 3, wherein the porous outer layer is composed of nickel oxide and nickel hydroxide.

13. The method according to any one of claims 1 to 3, wherein the porous outer layer has 40 and 120 μm 2 The surface area of ​​BET between / g.

14. The method of claim 7, wherein the intermediate layer is deposited between the metal substrate and the catalytic porous outer layer, the intermediate layer comprising nickel and / or nickel oxide.

15. The method according to any one of claims 1 to 3, wherein the porous outer layer has a thickness in the range of 5-40 µm.

16. The method according to any one of claims 1 to 3, wherein the porous outer layer has a content of 5-50 g / m³ based on metallic elements. 2 Nickel loading within the range.

17. The method of claim 7, wherein the intermediate layer has a content of 100-3000 g / m³ in terms of metallic elements. 2 Nickel loading within the range.

18. The method of claim 7, wherein the intermediate layer has a double-layer capacitance normalized by metal loading in the range of 1.0-10.0 mF / g.

19. The method of claim 7, wherein the coating consisting of a porous outer layer and an intermediate layer has a total thickness in the range of 30-300 µm.

20. The method according to claim 7, wherein the thermal spraying is wire arc spraying or plasma spraying.

21. The method according to any one of claims 1 to 3, wherein the substrate is a nickel mesh.

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