Method for producing electrocatalyst for alkaline water electrolysis

Abstract

The present invention provides a method for producing an electrocatalyst for alkaline water electrolysis, comprising the following steps: (i) producing an aqueous electrolyte comprising suspended graphene and graphite nanoplatelet structures less than 100 nm thick in an electrochemical cell, wherein the cell comprises: (a) a negative electrode comprising graphite; (b) a positive electrode comprising graphite; and (c) an aqueous electrolyte comprising ions in a solvent, the ions comprising cations and anions, the anions comprising sulfate anions; and applying a current to the cell to obtain an amount of exfoliated graphene and graphite nanoplatelet structures in the aqueous electrolyte greater than 5 g / L; (ii) forming an electroplating bath containing suspended graphene and graphite nanoplatelet structures in an amount greater than 2 g / L, wherein the electroplating bath comprises an aqueous solution of nickel sulfate and the aqueous electrolyte of step (i) containing the suspended sub-100 nm graphene and graphite nanoplatelet structures in an amount greater than 5 g / L; (iii) electroplating a composite layer of Ni or Ni alloy and graphene and graphite particles onto a support from the electroplating bath to form an electrocatalyst. The present invention relates to the method comprising the steps of:

Description

[Technical Field] 【0001】 The present invention relates to a method for producing an electrocatalyst for alkaline water electrolysis. The present invention also relates to an electroplating bath for use in the method. Furthermore, the present invention relates to an alkaline water electrolysis apparatus incorporating the electrocatalyst obtained by the method. [Background technology] 【0002】 The production of hydrogen and oxygen from water by water electrolysis is a globally established technological process. Three related processes for water electrolysis are distinguished by the electrolyte used: alkaline electrolysis, which uses a liquid alkaline electrolyte; acidic PEM electrolysis, which uses a proton-conducting polymer electrolyte membrane; and high-temperature electrolysis, which uses a solid oxide electrolyte. 【0003】 The most commonly used water electrolysis technology is alkaline electrolysis, characterized by high efficiency and low cost. The purity of hydrogen obtained by electrolysis using this type of device is very high, ranging from approximately 99.0% to 99.7%. A typical electrolysis device of this type consists of two electrodes immersed in an electrolyte and separated by a membrane. The role of the solution is to maximize ionic conductivity. The solution contains primarily KOH. The operating temperature of the process ranges from approximately 40°C to 90°C. Solutions of NaCl or NaOH can also be used as electrolytes, but are less common. In this type of device, water containing the electrolyte is placed on both sides of the electrodes. The cathode and anode are separated by a thin polymer membrane. OH, which is produced as a result of the reaction occurring at the cathode, is then introduced into the anode. - Ions permeate the membrane: hydrogen is obtained from the cathode, and water, along with a small amount of oxygen, is obtained from the anode. 【0004】 Electrocatalysis for alkaline electrolysis is a well-developed technology. In recent years, the rise of nanotechnology has spurred new research trends to further develop electrocatalysts. Theoretically, platinum is the best available electrocatalyst, but its prohibitive cost makes it a poor candidate for industrial-scale water electrolysis. Traditionally, nickel and its alloys have been the most widely used electrode materials for alkaline electrolysis due to their stability and favorable activity in the alkaline range. However, a major problem is the formation of nickel-hydrogen complexes on the surface due to the high hydrogen concentration on the cathode side, deactivating the catalyst over time. Recent research has focused on stabilizing nickel catalysts against deactivation using multicatalyst systems with tailored chemical and physical properties. Recently, with support from new nanotechnology developments, a new concept of nanostructured electrocatalysts has emerged. The main objectives are to increase the surface area and provide unique catalytic properties for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). 【0005】 HERs on Ni using graphene or graphene oxide have been investigated for use in alkaline solutions. Studies have shown that the electrocatalytic activity of these composites is significantly improved compared to Ni alone. The improved electrocatalytic activity of these composites is explained by their good electrical conductivity, large specific surface area, and high activity in hydrogen adsorption / desorption. 【0006】 Graphene can be produced from carbon sources by mechanical exfoliation, molecular assembly, chemical vapor deposition (CVD), and electrochemical methods. Graphene produced using electrochemical methods can be of relatively high quality due to minimized hole defects and tunable oxidation levels. In the art, graphene or graphite nanoplatelet structures produced by electrochemical exfoliation are typically separated from the electrolyte by several separation techniques, including filtration, centrifugal force to precipitate the graphene or graphite nanoplatelet structures, recovery of the graphene or graphite nanoplatelet structures at the interface of two immiscible solvents, and sedimentation. Electrochemically exfoliated graphene or graphite nanoplatelet structures may be further processed after exfoliation. For example, ultrasonic energy and other techniques known to those skilled in the art can be used to further exfoliate the material and reduce the flake size and number of graphene layers. At present, the commercial availability of large quantities of graphene is limited and the cost is very high, with a typical price range of around 200-400 euros for one gram of commercial-grade pure 3 nm filtered graphene nanopowder. 【0007】 There remains an inherent challenge to increase the throughput of these advanced materials for large-scale and cost-effective (e.g., ideally using only abundant materials) electrode construction. Summary of the Invention 【0008】 It is therefore an object of the present invention to provide a cost-effective method for producing an electrocatalyst for alkaline water electrolysis. 【0009】 This object, other objects and further advantages are achieved or exceeded by the present invention, which provides a method according to claim 1, an electroplating bath according to claim 12 and an alkaline water electrolysis apparatus according to claim 14 as well as preferred embodiments of the dependent claims. [Brief explanation of the drawings] 【0010】 [Figure 1A] FIG. 1A shows the results of applying electroplating solution 2 according to the present invention to a bare Ni-plated substrate and platinum. [Figure 1B] FIG. 1B shows the results of applying Comparative Baths 1, 2 and 3 to platinum. DETAILED DESCRIPTION OF THE INVENTION 【0011】 To achieve this object, in a first aspect, the present invention provides a method for producing an electrocatalyst for alkaline water electrolysis, comprising the following steps: (i) producing in an electrochemical cell an aqueous electrolyte (1) comprising suspended graphene and graphite nanoplatelet structures having a thickness of <100 nm, preferably <50 nm, wherein the cell comprises: (a) a negative electrode which is graphitic, (b) a positive electrode which is graphitic, and (c) an aqueous electrolyte comprising ions in a solvent, the ions comprising cations and anions, and the anions comprising sulfate anions; and applying a current to the cell to obtain exfoliated graphene and graphite nanoplatelet structures in an amount greater than 5 g / L, preferably greater than 10 g / L, in the aqueous electrolyte; (ii) forming an electroplating bath (2) containing suspended graphene and graphite nanoplatelet structures having a thickness of less than 100 nm in an amount greater than 2 g / L, preferably greater than 5 g / L, and more preferably greater than 10 g / L, wherein the electroplating bath (2) comprises an aqueous solution of nickel sulfate (3) and the aqueous electrolyte (1) of step (i) containing the suspended graphene and graphite nanoplatelet structures having a thickness of less than 100 nm in an amount greater than 5 g / L, preferably greater than 10 g / L; (iii) electroplating a combined layer of Ni or Ni alloy and graphene and graphite particles onto a support from the electroplating bath (2) to form an electrocatalyst for alkaline water electrolysis. The method includes: 【0012】 In the electrochemical exfoliation of step (i), as the intercalation of sulfate proceeds, the graphite transforms into graphene and graphite nanoplatelet structures having a thickness of less than 100 nm, preferably less than 50 nm, more preferably less than 20 nm. 【0013】 The term "nanoplatelet" is intended to mean a substantially flat particle of graphene or graphite having a thickness (z) on the order of nanometers, typically less than 100 nm, preferably less than 50 nm, more preferably less than 20 nm, and a lateral dimension (x, y) greater than the thickness. 【0014】 A key feature of the present invention is that both the anode and cathode used in electrochemical exfoliation are graphitic, resulting in high product yields of graphene and graphite nanoplatelet structures. The scalability of the present method allows for large-scale production of graphene and graphite nanoplatelet structures. The elimination of the need for complex electrolytes to establish exfoliation eliminates the need for organic ions, Li ions, Mg ions, etc., which increase the component complexity of the electrochemical exfoliation process, the corresponding safety requirements, costs, and disposal of process waste and by-products. 【0015】 Another important feature of the present invention is that the aqueous electrolyte (1) and the aqueous solution (3) each contain sulfate as one of their main components, and both aqueous solutions (1) and (3) are compatible and easily mixable without technical or chemical difficulties, thereby enabling the production of a Ni or Ni alloy electroplating bath (2), preferably an acidic electroplating bath, containing suspended graphene and graphite nanoplatelet structures with a thickness of less than 100 nm in an amount greater than 2 g / L, preferably greater than 5 g / L, and more preferably greater than 10 g / L. This eliminates the need for intermediate separation of the graphene and graphite nanoplatelet structures from the aqueous electrolyte (1), significantly reducing costs and processing time. The aqueous electrolyte (1) may be used directly as a raw material for forming the electroplating bath (2). 【0016】 The process of the present invention is a simple process that uses readily available components already accepted for use in the chemical and metallurgical industries. The process of the present invention is scalable to industrial scale and can be operated continuously. The resulting electrocatalyst can be produced on a large scale, on the scale of several square meters or more. The resulting electrocatalyst can be produced in large quantities at a fairly low cost. 【0017】 The inventor has 2We found that the hydrogen evolution reaction (HER) of electrodeposited layers of Ni combined with graphene or graphite particles using their effective geometric surface area after three voltammetric cycles in 1 M KOH is very close to that of platinum, making the resulting electrocatalyst suitable for alkaline water electrolysis, even for industrial-scale alkaline water electrolysis. Ni is a much more abundant material than rare earth metals and other metals (e.g., platinum, cobalt, iridium, and molybdenum) used for their catalytic capacity. 【0018】 While the catalytic capacity or efficiency may be slightly lower compared to very small scale scientifically or academically produced electrocatalysts, the low cost and mass production makes the resulting electrocatalysts highly suitable and economically attractive for use in industrial scale alkaline water electrolysis. 【0019】 In one embodiment, electrochemical stripping is carried out using an aqueous electrolyte (1) comprising an inorganic salt selected from the group consisting of Na2SO4, K2SO4, and (NH4)2SO4 as the primary source of sulfate anions. While the use of sulfate anions provides efficient stripping, the use of, for example, NH4Cl or NaNO3 results in significantly poorer stripping and very low product yields. 【0020】 In one embodiment, electrochemical stripping is carried out using an aqueous electrolyte (1) having a sulfate ion concentration in the range of 0.4 to 3M, preferably in the range of 0.4 to 1.3M. 【0021】 In a preferred embodiment, electrochemical stripping is performed using an aqueous electrolyte (1) based on sodium sulfate (NaSO). Sodium sulfate is a commonly accepted component in the chemical industry and is readily available at an affordable price. Sodium sulfate is also compatible with subsequently constructed electroplating baths for the co-deposition of Ni or Ni alloys, transforming the graphite into graphene and graphite nanoplatelet structures less than 100 nm thick, preferably less than 50 nm thick. Preferably, sodium sulfate is present at a concentration in the range of 0.4-3 M, more preferably in the range of 0.4-1.3 M, and most preferably in the range of 0.5-1 M. 【0022】 The operating parameters of the electrochemical cell for the electrochemical exfoliation of graphene and graphite nanoplatelets are: an operating cell temperature in the range of about 10 to 90°C, preferably about 20 to 70°C, more preferably about 40 to 65°C; a pH in the range of about 1 to 5, preferably about 2 to 4; Approximately 30 to 100 A / dm 2 , preferably 60 to 90 A / dm 2 current density; Voltage of 10 to 40 V, preferably 15 to 40 V Good results can be obtained when the composition contains one or more of the following: 【0023】 The operating potential of the cell is at least that of the standard potential for reductive intercalation. An overpotential may be used to increase the reaction rate and drive cations into the graphite galleries of the negative electrode. An overpotential of about 1 mV to 10 V, more preferably about 1 mV to 5 V, relative to a suitable reference known to those skilled in the art is preferably used. In cells with only two terminals and no reference, a larger potential may be applied between the electrodes, but a significant amount of potential will be dropped across the cell resistance rather than acting as an overpotential at the electrodes. In these cases, the applied potential may be up to about 20 V or up to about 40 V. 【0024】 The voltage applied between the electrodes may be cycled or swept. In one embodiment, both electrodes comprise graphite and the potential is swept to change the electrodes from positive to negative or vice versa. In this embodiment, cation exfoliation occurs at both electrodes depending on the polarity of the electrodes during the voltage cycle. In some embodiments, an alternating current can be used to enable both fast intercalation and deintercalation. 【0025】 The current density at the negative electrode is controlled by a combination of the surface area of the electrode and the overpotential used. The method of the present invention can also be carried out under current control. 【0026】 A key feature of the present invention is that both the anode and cathode used in electrochemical exfoliation contain graphite, resulting in a high product yield of graphene and graphite nanoplatelet structures. A wide range of carbon materials can be used, including natural graphite flakes, artificial graphite, highly ordered pyrolytic graphite (HOPG), pitch-based graphite, carbon rods, amorphous carbon, and the sources disclosed in patent document US2018 / 0179648A1 published June 28, 2018, which is incorporated herein by reference. 【0027】 In one embodiment, graphene and graphite nanoplatelet structures less than 100 nm thick, preferably less than 50 nm thick, more preferably less than 20 nm thick, suspended in electrolyte (1) are subjected to high shear mixing as known in the art to obtain a homogenous suspension, which may achieve some degree of further exfoliation. 【0028】 In one embodiment, the graphene and graphite nanoplatelet structures having a thickness of less than 100 nm, preferably less than 50 nm, and more preferably less than 20 nm, suspended in the electrolyte (1) are further exfoliated by ultrasonic treatment. Preferably, the ultrasonic treatment is carried out at an energy level of 10 to 200 Wh per gram of exfoliated graphene and graphite obtained in step (i). More preferably, the ultrasonic treatment is carried out at an energy level of 10 to 100 Wh per gram. The ultrasonic treatment is carried out using equipment such as a commercially available ultrasonic generator for liquid processing, where a sonotrode immersed in the liquid is used to transfer acoustic energy into the system by cavitation (i.e., the formation and implosion of gas bubbles) at a wave frequency of about 24 kHz and a power as defined above. 【0029】 The electroplating bath (2) for codepositing a composite layer of Ni or Ni alloy with graphene and graphite particles on a support is composed of (a) an aqueous electrolyte (1) containing sulfate anions and containing suspended graphene and graphite nanoplatelet structures, and (b) an aqueous solution of nickel sulfate (3) suitable for electrodepositing Ni or Ni alloy particles on a substrate or support. Because the aqueous electrolyte (1) and the aqueous solution (3) each contain sulfate as one of their main components, both aqueous solutions (1) and (3) are compatible and can be mixed to form the electroplating bath (2) unless technical difficulties or inconveniences arise. 【0030】 The aqueous mixture (3) containing nickel sulfate serves as the primary source for electroplating a composite layer of Ni or Ni alloy with graphene and graphite particles onto a carrier or substrate. 【0031】 In a preferred embodiment, the aqueous solution (3) contains nickel sulfate, nickel chloride, and preferably boric acid. In a more preferred embodiment, the aqueous solution (3) contains 10 to 400 g / L of nickel sulfate (NaSO), 10 to 150 g / L of nickel chloride (NiCl), and 5 to 100 g / L of boric acid (HBO). Such an aqueous solution (3), also known in the art as a Watts bath, is highly scalable and is used to electroplating a Ni or Ni alloy layer on a metal substrate on an industrial scale, for example, for Ni-plated battery cases. The Watts bath is used not only in batch processes but also on a continuous industrial scale. 【0032】 In one embodiment, aqueous solution (3) contains nickel sulfate, nickel chloride, and citrate-gluconate. In a more preferred embodiment, aqueous solution (3) contains 100-300 g / L of nickel sulfate, 10-80 g / L of nickel chloride, 10-70 g / L of ammonium sulfate ((NH4)2SO4), 50-200 g / L of sodium citrate, and 10-50 g / L of sodium gluconate. The sodium citrate prevents the formation of solid compounds (nickel salts) in the bath and functions as a pH buffer. While this aqueous solution (3) is usable, it is less preferred because it is chemically more complex than a Watts bath. 【0033】 Electroplating of the composite layer of Ni or Ni alloy with graphene and graphite on a support or substrate to form an electrocatalyst is carried out in an electroplating bath (2) that contains nickel sulfate as one of its main components. 【0034】 In an electroplating process for deposition, the operating parameters are: a bath temperature in the range of about 20-70°C, preferably in the range of about 40-65°C; a pH in the range of 1 to 5, preferably in the range of 2 to 5, more preferably in the range of 2 to 4; ·About 0.2~10.0A / dm 2 , preferably about 0.5 to 5.0 A / dm 2 current density; a plating time of 1 to 400 seconds, preferably 20 to 200 seconds, more preferably 20 to 150 seconds; Contains: 10-400 g / L nickel sulfate, preferably 200-300 g / L nickel sulfate; 10-150 g / L of nickel chloride, preferably 30-60 g / L of nickel chloride; optionally, 5 to 100 g / L of boric acid, preferably 20 to 50 g / L of boric acid; and at least 2 g / L, preferably at least 5 g / L, more preferably at least 10 g / L of graphene and graphite nanoplatelet structures with a thickness of less than 100 nm, preferably less than 50 nm, more preferably less than 20 nm, derived from the aqueous electrolyte (1) obtained from step (i); a composition of a plating bath (2) comprising: Good results can be obtained when the composition contains one or more of the following: 【0035】 Some mild agitation may be applied to the bath to keep the nanoplatelet structures suspended. The bath composition may also include a low concentration of a reagent to prevent coagulation of the suspended graphene and graphite nanoplatelet structures. Suitable reagents are methylpyrrolidone, dimethyl sulfoxide, anthraquinodiazonium salts, or cationic surfactants. Aside from the presence of graphene and graphite nanoplatelet structures less than 100 nm thick, such an electroplating process using these operating parameters is sometimes referred to in the art as a Watt process. 【0036】 These operating parameters result in electrocatalysts suitable for alkaline water electrolysis. The plating process uses readily available chemical components that are well known and accepted in the chemical and metallurgical industries. The plating process can be carried out as a batch process. However, an additional advantage is that it can be operated as a continuous process, allowing for the production of large quantities of electrocatalyst materials suitable for alkaline water electrolysis, both in terms of number and surface area. 【0037】 In one embodiment, the thickness of the composite layer of Ni or Ni alloy and graphene and graphite particles electroplated onto the support from the electroplating bath (2) to form the electrocatalyst is at least about 0.1 μm, preferably at least about 0.5 μm. 【0038】 In the present invention, the support or deposition substrate is not limited and can be any material used in the art as an anode material in alkaline water electrolysis, such as nickel sheet, cold-rolled carbon steel (e.g., any of the grades DC01 to DC07), or stainless steel (e.g., 904L or 905L), preferably a metal substrate provided with a thin nickel layer. 【0039】 In a further aspect, the invention is embodied in an electroplating bath (2) comprising step (ii) of the method of the invention as described and claimed herein. The plating bath (2) comprises graphene and graphite nanoplatelet structures less than 100 nm thick, preferably less than 50 nm thick, and more preferably less than 20 nm thick. The graphene and graphite nanoplatelet structures are present in an amount greater than 2 g / L, preferably greater than 5 g / L, and more preferably greater than 10 g / L. 【0040】 Such electroplating baths (2) comprising graphene and graphite nanoplatelet structures of defined size and concentration constructed in accordance with the present invention may be advantageously commercialized process-independently. 【0041】 In one embodiment, the electroplating bath (2) contains nickel sulfate as one of its main components. 【0042】 In one embodiment, the pH of the electroplating bath (2) is in the range of 1 to 5, preferably in the range of 2 to 5, and more preferably in the range of 2 to 4. 【0043】 In one embodiment, the electroplating bath (2) comprises: 10 to 400 g / L of nickel sulfate, preferably 200 to 300 g / L of nickel sulfate; and 10 to 150 g / L of nickel chloride, preferably 30 to 60 g / L of nickel chloride; and Optionally, 5 to 100 g / L of boric acid, preferably 20 to 50 g / L of boric acid Includes: 【0044】 In another embodiment, the electroplating bath (2) contains 100 to 300 g / L of nickel sulfate, 10 to 80 g / L of nickel chloride, 10 to 70 g / L of ammonium sulfate ((NH4)2SO4), 50 to 200 g / L of sodium citrate, and 10 to 50 g / L of sodium gluconate. 【0045】 In a further aspect, the present invention is also embodied in an alkaline water electrolysis apparatus comprising at least one electrocatalyst obtained by the method of the present invention. In one embodiment, the alkaline water electrolysis apparatus comprises six or more electrocatalyst plates, preferably ten or more electrocatalyst plates. Typically, the electrocatalyst plates are spaced apart from each other by about 1 to 5 cm. In one embodiment, each electrocatalyst plate in the alkaline water electrolysis apparatus is spaced apart from each other by at least about 0.5 m. 2 (e.g., plate dimensions of 10 x 50 cm or 20 x 50 cm), preferably at least about 1.5 m 2 It has a surface area of [Example] 【0046】 The present invention will now be described in detail with reference to non-limiting comparative examples and examples of the present invention. 【0047】 In accordance with the present invention, two suspensions of exfoliated graphene and graphite nanoplatelets were prepared using electrochemical cells in which both the positive and negative electrode materials were graphite SGL plates (Sigraflex) or both materials were solid graphite rods (Atotech). The electrochemical cell conditions were: volume: 3000 mL, sodium sulfate: 0.75 M, current density: 45 A / dm 2 The conditions were: voltage: 31 V, temperature: 50-55°C, and treatment time: 4 hours. As a result, two solutions were obtained: one containing graphene and graphite nanoplatelets less than 100 nm thick at approximately 8.4 g / L based on a graphite SGL plate Sigraflex electrode, and the other containing graphene and graphite nanoplatelets less than 100 nm thick at approximately 14.7 g / L based on a solid graphite rod electrode. 【0048】 Based on these two suspensions, two acidic electroplating baths were constructed in accordance with the present invention. 【0049】 Electroplating Solution 1 Graphite SGL Plate: A 1000 mL suspension containing approximately 8.4 g / L of graphene and graphite nanoplatelets less than 100 nm thick based on Sigraflex electrodes, to which 250 g of nickel sulfate hexahydrate, 50 g of nickel chloride hexahydrate, and 30 g of boric acid were added. 【0050】 Electroplating Solution 2 : A 1000 mL suspension containing graphene and graphite nanoplatelets less than 100 nm thick based on a solid graphite rod electrode at approximately 14.7 g / L, to which 250 g of nickel sulfate hexahydrate, 50 g of nickel chloride hexahydrate, and 30 g of boric acid were added. 【0051】 Based on these two electroplating baths according to the present invention, a composite layer of nickel and graphene and graphite nanoplatelet structures was deposited on a Ni-plated carbon steel support having a dimension of 100 × 100 mm, which had been pretreated by degreasing and desmutting as known in the art. Both baths were plated under the same conditions, i.e., 50 °C, current density 5 A / dm 2 A plating time of 120 seconds was used, resulting in a complete coverage of the support surface and a layer thickness of 2 μm. 【0052】 The presence of nano-sized multilayer graphene flakes was demonstrated by Raman spectroscopy, which showed them to be a mixture of graphene and graphene oxide. 【0053】 Additionally, three comparative acidic electroplating baths or solutions were prepared for electroplating composite layers of Ni and other nano-sized particles onto supports. These comparative baths were based on literature references suggesting high catalytic activity. These baths were based on commercially available powders, with intentional additions of graphite powder, SiC powder, and MoS powder, respectively. The compositions of the three plating baths were as follows: 【0054】 Comparison bath 1 A mixture of: 1000 mL of demineralized water, 250 g of nickel sulfate hexahydrate, 50 g of nickel chloride hexahydrate, 30 g of boric acid, and 20 g of pure graphite powder (natural, microcrystalline grade, APS2-15 micron, 99.9995% (metal basis), UCP-1-M grade, ultra "F" purity, lot: 61200828, ThermoFischer (Kandel) GmbH). The suspension was mixed in a high-shear mixer for 2 hours. 【0055】 Comparison bath 2 1000 mL of demineralized water, 250 g of nickel sulfate hexahydrate, 50 g of nickel chloride hexahydrate, 30 g of boric acid, and 20 g of silicon carbide (SiC) powder (beta phase, nanopowder, 45-45 nm APS powder, SA 70-90 m 2 / g, lot: R21E078, ThermoFischer (Kandel) GmbH). The suspension was mixed in a high shear mixer for 2 hours. 【0056】 Comparison bath 3 The suspension was mixed in a high shear mixer for 2 hours: 1000 mL of demineralized water, 250 g of nickel sulfate hexahydrate, 50 g of nickel chloride hexahydrate, 30 g of boric acid, and 20 g of molybdenum disulfide (MoS2) powder (98%, 325 mesh powder). 【0057】 Based on these three baths, composite layers of nickel and C, SiC, or MoS particles were deposited on Ni-plated carbon steel supports with dimensions of 100 × 100 mm, which had been pretreated by degreasing and desmutting methods well known in the art. All three electroplating baths were used under the same plating conditions, i.e., 50 °C, current density 5 A / dm 2 A plating time of 120 seconds was used, resulting in a complete coverage of the support surface and a layer thickness of 2 μm. 【0058】 The hydrogen evolution reaction (HER) of the electrodeposited materials from electroplating solution 2 and comparative baths 1 to 3 was 1.0 cm 2 The effective geometric surface area was evaluated after three voltammetric cycles in a 1.0 M KOH solution. Samples were tested against bare Ni-plated substrate material and against platinum sheets. The results are shown in Figures 1A and 1B. 【0059】 Figure 1A shows the results of applying electroplating solution 2 according to the present invention to a bare Ni-plated substrate and platinum, and Figure 1B shows the results of applying comparative baths 1, 2 and 3 to platinum. 【0060】 1A and 1B, it can be seen that the graphene curve of electroplating solution 2 according to the present invention exhibits significantly higher HER activity compared to comparative bath 2 containing pure graphite powder. Furthermore, the shape of the graphene curve (produced according to the present invention) was found to be nearly identical to that of platinum, and therefore, the catalytic activity of the graphene-coated sample is expected to be nearly equivalent to that of platinum. 【0061】 Therefore, although electrocatalysts produced according to the present invention may have slightly lower catalytic capacity or efficiency compared to platinum, the resulting electrocatalysts can be mass-produced at low cost, making them highly suitable and economically attractive for use in industrial-scale alkaline water electrolysis. 【0062】 While the present invention has been fully described above, it will be apparent to those skilled in the art that many changes and modifications can be made without departing from the spirit or scope of the invention as set forth herein.

Claims

[Claim 1] A method for producing an electrolytic catalyst for alkaline water electrolysis, comprising the following steps: (i) A step of producing an aqueous electrolyte (1) containing suspended nanoplatelet structures of graphene and graphite less than 100 nm thick in an electrochemical cell, wherein the cell contains (a) a negative electrode containing graphite, (b) a positive electrode containing graphite, and (c) an aqueous electrolyte containing ions in a solvent, wherein the ions include cations and anions, and the anions include sulfate anions, and the method includes passing an electric current through the cell to obtain an amount of exfoliated nanoplatelet structures of graphene and graphite in the aqueous electrolyte in an amount exceeding 5 g / L, preferably at least 10 g / L; (ii) A step of constructing an electroplating bath (2) containing a suspended graphene and graphite nanoplatelet structure less than 100 nm thick in an amount greater than 2 g / L, wherein the electroplating bath (2) comprises an aqueous solution of nickel sulfate (3) and the aqueous electrolyte (1) of step (i), which contains the suspended graphene and graphite nanoplatelet structure less than 100 nm thick in an amount greater than 5 g / L, preferably at least 10 g / L; (iii) A step of electroplating a composite layer of Ni or Ni alloy and graphene and graphite particles from the electroplating bath (2) onto a support to form an electrolytic catalyst, preferably an electrolytic catalyst for alkaline water electrolysis. The method, including the method described above. [Claim 2] The aqueous electrolyte (1) is Na ２ SO ４ _K ２ SO ４ and (NH ４ ) ２ SO ４ The method according to claim 1, comprising a sulfate anion derived from an inorganic salt selected from the group consisting of the following. [Claim 3] The method according to claim 1, wherein the aqueous electrolyte (1) contains sulfate anions in a range of 0.4 to 3 M, preferably in a range of 0.4 to 1.3 M. [Claim 4] The method according to claim 1, wherein the aqueous electrolyte (1) contains sulfate anions derived from sodium sulfate, preferably in the range of 0.4 to 3 M, and preferably in the range of 0.4 to 1.3 M. [Claim 5] The method according to claim 1, wherein the aqueous solution (3) contains nickel sulfate and nickel chloride. [Claim 6] The method according to claim 1, wherein the aqueous solution (3) comprises nickel sulfate, nickel chloride, and boric acid. [Claim 7] The method according to claim 1, wherein the aqueous solution (3) comprises 10 to 400 g / L of nickel sulfate, 10 to 150 g / L of nickel chloride, and optionally 5 to 100 g / L of boric acid. [Claim 8] The method according to claim 1, wherein the electroplating bath (2) comprises the aqueous solution (3) containing nickel sulfate and the aqueous electrolyte (1) containing the suspended graphene and graphite nanoplatelet structure with a thickness of less than 100 nm in an amount of more than 5 g / L, preferably more than 10 g / L. [Claim 9] The method according to claim 1, wherein the electroplating bath (2) comprises 10 to 400 g / L of nickel sulfate, 10 to 150 g / L of nickel chloride, optionally 5 to 100 g / L of boric acid, and a nanoplatelet structure of graphene and graphite with a thickness of less than 100 nm in an amount exceeding 2 g / L, preferably exceeding 5 g / L. [Claim 10] The electroplating from the aforementioned electroplating bath (2) is performed using the following operating parameters: Bath temperature in the range of 20 to 70°C, preferably in the range of 40 to 65°C; pH in the range of 1 to 5, preferably in the range of 2 to 5; 0.2 to 10.0 A / dm ２ , preferably 0.5 to 5.0 A / dm ２ of current density; Plating time: 1 to 400 seconds, preferably 20 to 200 seconds. The method according to claim 1, comprising one or more of the following. [Claim 11] The method according to claim 1, wherein the thickness of the composite layer of Ni or Ni alloy and graphene and graphene particles on the carrier electrodeposited in step (iii) is at least 0.1 μm, preferably at least 0.5 μm. [Claim 12] An electroplating bath (2) comprising the process (ii) described in any one of claims 1 to 9, It contains suspended nanoplatelet structures of graphene and graphite with a thickness of less than 100 nm in an amount exceeding 2 g / L. (a) an aqueous solution of nickel sulfate (3) and (b) the aqueous electrolyte (1) containing more than 5 g / L, preferably at least 10 g / L, of the suspended graphene and graphite nanoplatelet structures with a thickness of less than 100 nm obtained in step (i). [Claim 13] Nickel sulfate in a concentration of 10 to 400 g / L, preferably 200 to 300 g / L: Nickel chloride in a concentration of 10 to 150 g / L, preferably 30 to 60 g / L; and Optionally, 5 to 100 g / L of boric acid, preferably 20 to 50 g / L of boric acid. The electroplating bath according to claim 12, including the following: [Claim 14] An alkaline water electrolysis apparatus comprising an electrolytic catalyst obtained by the method of any one of claims 1 to 11. [Claim 15] It is equipped with at least six electrolytic catalyst plates, Preferably, the surface area of ​​each electrolytic catalyst plate is at least 0.5 m². ２ Preferably at least 1.5 m ２ The alkaline water electrolysis apparatus according to claim 14.

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