Method for preparing nickel-based transition metal composite catalytic electrode by utilizing one-step electrodeposition method and desalting combined catalytic electrode device

Abstract

The present invention provides a desalination combined catalytic electrode device comprising an anode chamber / BPM / [AEM / CEM] n / BPM / cathode chamber, in which a Ni / 3d transition metal composite catalytic electrode is contained in the anode chamber, the 3d transition metal fraction of the electrode is 0.3 or less, AEM and CEM are alternately provided so that n is a natural number of 1 to 5, and the 50% desalination time ([tau] 1 / 2) of the electrolytic cell is 2.2 to 6.4 hours at J = 10 mA cm <-2 >. The specific energy consumption (SEC) is 1.79 to 7.03 kWh m <-3 >. In addition, the invention provides a method for preparing a nickel-based transition metal composite catalytic electrode by utilizing a one-step electrodeposition method, which comprises the following steps of: forming a mixed solution from a Ni hydrate and a 3d transition metal hydrate according to a ratio of 1: 3 to 3: 1; after a Ni substrate is soaked in the solution, cathode bias electro-deposition is carried out for 10-180 seconds; and carrying out anodic oxidation on the deposited Ni / 3d transition metal double compound composite catalytic electrode, and washing and drying the Ni / 3d transition metal double compound composite catalytic electrode.

Description

Technical Field

[0001] The present invention relates to a method for preparing a nickel-based transition metal composite catalytic electrode by a one-step electrodeposition method and a desalination combined catalytic electrode device. Specifically, it relates to a method for preparing a nickel-based transition metal composite catalytic electrode by a one-step electrodeposition method using a method of cathodic electrodeposition in a nickel foam substrate and a desalination combined catalytic electrode device. Background Art

[0002] Seawater has attracted much attention as a freshwater supply source to solve the global water shortage caused by the climate crisis. In particular, electro-deionization has the characteristic of directly applying electric energy to seawater desalination, so it has technical application value in non-traditional and decentralized freshwater supply markets such as in linkage with renewable energy.

[0003] Moreover, the carbon contained in seawater in the form of bicarbonate ions is about 140 times that of the same volume of the atmosphere. Therefore, the electro-deionization process can have an effect of capturing carbon by concentrating bicarbonate ions, and as a negative emission technology for carbon, it can contribute to carbon neutrality in the seawater desalination market.

[0004] However, since the catalysts frequently used in electro-deionization water electrolysis are limited to noble metals such as platinum, iridium, and ruthenium, there are limitations in terms of process scale expansion and market economy. Therefore, this research aims to develop a catalytic electrode made of transition metals such as nickel and manganese that can replace noble metal catalysts, thereby realizing a low-cost and high-efficiency electro-deionization device.

[0005] (Korean Patent Publication) No. 10-2022-0136038 Summary of the Invention

[0006] Technical Problem In order to solve the above problems, an object of the present invention is to provide a desalination combined catalytic electrode device.

[0007] In addition, an object of the present invention is to provide a method for preparing a nickel-based transition metal composite catalytic electrode by a one-step electrodeposition method.

[0008] Technical Solution In order to achieve the above object, the present invention provides a desalination combined catalytic electrode device, as an electrolytic cell composed of an anode chamber / bipolar membrane (BPM) / [anion exchange membrane (AEM) / cation exchange membrane (CEM)]n / bipolar membrane (BPM) / cathode chamber, the anode chamber contains a Ni / 3d transition metal composite catalytic electrode, and the 3d transition metal fraction of the electrode is 0.3 or less, AEM and CEM are alternately arranged with n being a natural number from 1 to 5, The electrolytic cell is at J=10mA / cm -2 Under 50% desalination time (τ 1 / 2 ) is 2.2 to 6.4 hours, and the specific energy consumption (SEC) is 1.79 to 7.03 kWhm -3 .

[0009] In order to achieve the other object, the present invention provides a method for preparing a nickel-based transition metal composite catalytic electrode by a one-step electrodeposition method, comprising the following steps: Forming a mixed solution containing Ni hydrate and 3d transition metal hydrate in a ratio of 1:3 to 3:1; After immersing the Ni substrate in the solution, performing cathode bias electrodeposition for 10 to 180 seconds; and The deposited Ni / 3d transition metal double hydrate composite catalytic electrode is anodized, washed and dried.

[0010] Technical Effects The preparation method of the catalytic electrode of the present invention can reduce the cost of water electrolysis and electrical desalination processes by introducing low-cost and high-efficiency electrodes, and can prepare electrodes with high electrical efficiency under alkaline electrolyte conditions. In addition, the desalination combined catalytic electrode device using the composite electrode catalyst according to the preparation method of the present invention can achieve negative carbon emissions by linking with the seawater dissolved carbon capture process. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 Schematic diagram showing an electrolytic cell designed to be composed of a NiFe-LDH anode and a NiMo cathode according to an embodiment of the present invention.

[0012] Figure 2 is a diagram showing the surface characterization of NiFe-LDH samples as-deposited (AD) and after anodization (PA) according to an embodiment of the present invention.

[0013] Figure 3 is a diagram showing the surface characterization of a NiFe-LDH sample after anodization according to an embodiment of the present invention.

[0014] Figure 4 1 is a diagram showing a voltammogram, a Tafel curve, and an O 2 generation rate graph according to an embodiment of the present invention.

[0015] Figure 5 is a diagram showing the surface characterization of a NiMo catalyst synthesized according to one embodiment of the present invention.

[0016] Figure 6 Shows the voltammogram, Tafel curve, and H2 generation rate chart according to an embodiment of the present invention.

[0017] Figure 7 Shows the electrochemical behavior of the NiFe-LDH anode and NiMo cathode pair in a two-chamber cell device according to an embodiment of the present invention.

[0018] Figure 8 Shows the E of the desalination combined electrocatalytic unit device according to an embodiment of the present invention 装置 and ionic conductivity (σ), desalination ions (Cl - and Na + ), concentration changes of acidic chamber, alkaline chamber and electrolyte solution, and pH value changes of acidic chamber, alkaline chamber and electrolyte solution.

[0019] Figure 9 Shows the E of the desalination combined electrocatalytic stack device according to an embodiment of the present invention 装置 and ionic conductivity (σ), desalination ions (Cl - and Na + ), concentration changes of acidic chamber, alkaline chamber and electrolyte solution, and pH value changes of acidic chamber, alkaline chamber and electrolyte solution. Detailed Description of the Invention

[0020] Hereinafter, the present invention will be described in more detail.

[0021] According to an aspect of the present invention, there is provided a desalination combined catalytic electrode device, which is an electrolytic cell composed of an anode chamber (cell) / bipolar membrane (BPM) / [anion exchange membrane (AEM) / cation exchange membrane (CEM)]n / bipolar membrane (BPM) / cathode chamber (cell). The anode chamber contains a Ni / 3d transition metal composite catalytic electrode, and the 3d transition metal fraction of the electrode is 0.3 or less. The anion exchange membrane (AEM) and the cation exchange membrane (CEM) are alternately arranged with n being a natural number from 1 to 5. The electrolytic cell has a 50% desalination time (τ -2 (or mA / cm 2 )) of 2.2 to 6.4 hours and a specific energy consumption (SEC) of 1.79 to 7.03 kWhm 1 / 2 (or kWh / m -3 (or kWh / m 3 ) at J = 10 mA / cm

[0022] The desalination combined catalytic electrode device of the present invention is composed of an anode chamber, a bipolar membrane (BPM: bipolar membrane), an acidic chamber, an anion exchange membrane (AEM: Anion Exchange Membrane), a desalination chamber, a cation exchange membrane (CEM: Cation Exchange Membrane), a basic chamber, a bipolar membrane (BPM), and a cathode chamber. According to requirements, AEM and CEM can be alternately inserted between the acidic chamber and the basic chamber, and 1 to 5 AEM and CEM can be stacked in the present invention. When the same energy is provided to the device, the 50% desalination time (τ 1 / 2 ) of 5 stacked layers is shorter than the 50% desalination time (τ 1 / 2 ) of 1 stacked layer.

[0023] The anode chamber of the present invention contains a double hydroxide (Ni / 3d transition metal-LDH) composite catalytic electrode of Ni and a 3d transition metal layer. In a mixed solution of Ni hydroxide and 3d transition metal hydroxide, when the molar ratio of Ni:3d transition metal is 1:1, the molar fraction of the 3d transition metal in the synthesized catalytic electrode (3d transition metal / (Ni + 3d transition metal)) is 0.3 or less. The formed composite catalytic electrode is in the form of an aggregate composed of fine particles with a size of about 50 nm covering a porous Ni substrate, and the Ni / 3d transition metal particles have a layered nanostructure. In addition, the composite catalytic electrode of the present invention is based on 3d-transition metal (oxy) hydroxide, and the available 3d-transition metals are Ni, Co, Fe, and Mn, and preferably Fe. The activities of these transition metals are similar to those of catalytic electrodes prepared using noble metals (for example, IrO2 and RuO2). Ni / 3d transition metal-LDH is characterized by having abundant active sites for OH adsorption and an optimal binding energy for M-OH.

[0024] The cathode chamber of the present invention contains a NiMo catalytic electrode, and the particle size of the synthesized catalyst is about 2 μm. In addition, the Mo molar fraction in the NiMo catalytic electrode is 0.1 or less. If NiMo is used in a HER active electrode, the surface area is enlarged, the activity and durability of the electrode catalyst are improved, and hydrogen adsorption energy and hydrogen evolution are caused by inducing electron synergy.

[0025] The desalination combined catalytic electrode device of the present invention can enable oxygen generation, hydrogen generation, and desalination to occur simultaneously, and an oxygen evolution reaction (OER) is carried out on the anode chamber side, and a hydrogen evolution reaction (HER) is carried out on the cathode chamber side. If the water for on-site desalination is electrolyzed, an electrochemical deviation will be generated for the anode chamber and the cathode chamber, and this deviation causes Cl - and Na +It is unidirectionally transported to the acidic chamber and the alkaline chamber through AEM and CEM. In addition, the deviation further dissociates the water absorbed by BPM (H2O → H + +OH - ), and provides OH - to the oxidation electrode solution, provides H + to the acidic chamber, provides OH - to the alkaline chamber, and provides H + to the reduction electrode solution. Since the device of the present invention continuously receives OH - , H + from BPM, the pH of the oxidation electrode solution is maintained at about 0.5, and the pH of the reduction electrode solution is maintained at about 14. The pH difference of about 13.5 can reduce the overpotential of OER.

[0026] In the device of the present invention, when the number of desalination chambers is 1 to 5, at J = 10 mA cm -2 to 100 mA cm -2 , the 50% desalination time (τ 1 / 2 ) is 0.5 to 7 hours, the specific energy consumption (SEC) is 1.8 to 16 kWh m -3 , and the ion transport efficiency (ITE) is 75% to 450%. At J = 10 mA cm -2 , the 50% desalination time (τ 1 / 2 ) is 2.2 to 6.4 hours, the specific energy consumption (SEC) is 1.79 to 7.03 hours, and the ion transport efficiency (ITE) is 80% to 360%.

[0027] The preferred device is composed of five desalination chambers. At J = 10 mA cm -2 , the 50% desalination time (τ 1 / 2 ) is 2 to 2.5 hours, preferably 2 to 2.3 hours, the SEC is 1.5 to 2.0 kWh m -3 , preferably 1.5 to 1.8 kWh m -3 , and most preferably 1.8 kWh m -3 of specific energy, the ITE is 80% to 85%, preferably 83% to 85%. At this time, in the case of introducing a carbon capture system, about 3.5 mM of carbon is concentrated and captured in the desalination energy consumption.

[0028] In addition, when the device of the present invention performs long-term bulk electrolysis, it has a Faraday efficiency (FE) value of >95% within 20 hours, and the initial pH values of the oxidation electrode solution and the reduction electrode solution remain unchanged.

[0029] According to another aspect of the present invention, there is provided a method for preparing a nickel-based transition metal composite catalytic electrode by a one-step electrodeposition method, comprising the following steps: forming a mixed solution of Ni and a 3d transition metal hydrate in a ratio of 1:3 to 3:1; after immersing a Ni substrate in the solution, performing cathodic bias electrodeposition for 10 seconds to 180 seconds; and anodizing the deposited Ni / 3d transition metal double hydrate composite catalytic electrode, and performing washing and drying.

[0030] The most common method for preparing a nickel-based transition metal hydrate catalytic electrode is the hydrothermal method. Although the hydrothermal method easily forms a stable structure, the preparation time is more than 10 hours and the heating condition is about 200 °C, etc., so it cannot be carried out under general normal temperature and pressure conditions. In addition, in order to form a crystallized catalytic structure into a catalytic electrode, an additional process of mixing and coating a liquid binder such as perfluorosulfonic acid polymer (Nafion) on a conductive support such as glassy carbon is required. In contrast, the electrodeposition method only performs the step of electrodepositing a conductive support (Ni substrate) immersed in an aqueous solution of nickel-transition metal hydrate, so it is more economical.

[0031] The method for preparing a nickel-based transition metal composite catalytic electrode by the one-step electrodeposition method of the present invention is as follows. First, an aqueous solution formed by mixing a nickel hydrate and a 3d transition metal hydrate is formed, wherein the ratio of Ni to the 3d transition metal is 1:3 to 3:1, preferably 1:2 to 2:1, and most preferably 1:1. In the present invention, the transition metal is a 3d-transition metal, and the available transition metals are Ni, Co, Fe, and Mn, and preferably Fe.

[0032] The nickel hydrate of the present invention can use one or more of nickel(II) bromide trihydrate (NiBr₂·3H₂O), nickel(II) nitrate hexahydrate (Ni(NO₃)₂·6H₂O), nickel(II) sulfate hexahydrate (NiSO₄·6H₂O), and nickel(II) chloride hexahydrate (NiCl₂·6H₂O), and is preferably nickel(II) chloride hexahydrate. In addition, the transition metal hydrate of the present invention is preferably an iron hydrate, which can be iron(III) perchlorate hydrate (Fe(ClO₄)₃·H₂O), iron(III) chloride hexahydrate (FeCl₃·6H₂O), iron(III) phosphate dihydrate (FePO₄·2H₂O), and iron(III) nitrate nonahydrate (Fe(NO₃)₃·9H₂O), and is preferably iron(III) nitrate nonahydrate.

[0033] Next, the Ni substrate is immersed in the mixed solution, and cathodic bias electrodeposition is performed for 10 to 180 seconds, preferably 100 to 180 seconds, more preferably 120 to 180 seconds.

[0034] Then, the electrode catalyst after electrodeposition is immersed in an alkaline solution for electrooxidation for 60 to 600 seconds, preferably 100 to 400 seconds, most preferably 300 seconds, and an anodic oxidation treatment is performed, followed by washing with pure water and ethanol, and then air-drying at 40°C to 70°C, most preferably 60°C for more than 10 minutes, preferably 10 to 30 minutes.

[0035] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, the configurations that are easily understood by those skilled in the art, as well as the illustrations and detailed descriptions of their functions and effects, will be briefly or omitted, and the description will be centered on the parts related to the present invention.

[0036] <Example> Example 1 - Synthesis of Electrode Catalyst The nickel (Ni) foam (1×1 cm) connected by a nickel wire (99.5%, diameter 0.5 mm, Alfa Aesar) 2, >99.99%, thickness 1.6 mm, Korea MTI Co., Ltd.) was ultrasonically treated with HCl (1 M, Daejung Co., Ltd.) for 10 minutes, washed with deionized water (18 MΩ·cm, Human Corp. Co., Ltd.) and ethanol, and then dried at about 60 °C for 10 minutes. The prepared Ni substrate (for working electrode) for electrodepositing NiFe-LDH was immersed in an aqueous solution mixed with nickel(II) chloride hexahydrate (NiCl2·6H2O, 23-26% Ni basis, Sigma-Aldrich) and / or iron(III) nitrate nonahydrate (Fe(NO3)3 9H2O, ≥98%, Sigma-Aldrich) at various molar ratios of Ni / Fe (1 / 0, 0.75 / 0.25, 0.5 / 0.5, 0.25 / 0.75, and 0 / 1). Then, it was cathodically biased at J = -100 mA cm -2 for 10 to 180 seconds. A saturated calomel electrode (SCE) and a platinum (Pt) foil were used as the reference electrode and the counter electrode, respectively. The deposited NiFe-LDH was anodically oxidized in an aqueous KOH solution (1 M, pH about 13.7, Daejung) at J = 10 mA cm -2 for 5 minutes. Unless otherwise specified, in this study, NiFe-LDH refers to the sample synthesized by depositing for 120 seconds under the condition of a Ni / Fe ratio of 0.5 / 0.5.

[0037] For the electrosynthesis of NiMo, it was immersed in a mixed aqueous solution containing NiCl2·6H2O (120 mM, 23-26% Ni basis, Sigma-Aldrich), sodium molybdate dihydrate (80 mM, Na2MoO4·2H2O, ≥99.5%, Sigma-Aldrich), and trisodium citrate dihydrate (120 mM, HOC(COONa)(CH2COONa)2·2H2O, ≥99.0%, Sigma-Aldrich) at J = -120 mA cm -2 for 20 minutes. The solution pH was adjusted to 10.5 using ammonium hydroxide (NH4OH, ≥25% NH3 in H2O, Sigma-Aldrich). Finally, the as-synthesized original NiFe-LDH and NiMo were washed with deionized water and air-dried.

[0038] Example 2 - Surface Characterization The morphology and elemental composition of the synthesized samples were investigated using an energy-dispersive spectrometer (EDS) at an accelerating voltage of 5 kV with a field-emission scanning electron microscope (FE-SEM, S-4800, Hitachi). The morphology and crystal structure of the synthesized samples were characterized using a field-emission transmission electron microscope (FE-TEM, 200 kV, Titan G2 with ChemiSTEM CsProbe, FEI Company) equipped with a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM), selected-area electron diffraction (SAED), and high-resolution transmission electron microscopy (HR-TEM). To further investigate the elemental binding state and crystal structure, the samples were characterized by X-ray photoelectron spectroscopy (XPS, NEXSA, Thermo Fisher) and X-ray diffraction (XRD, EMPYREAN, PANalytical), respectively. The surface area and average pore size of the samples were evaluated using a BET analyzer (BET: Brunauer-Emmett-Teller) with N2 adsorption-desorption (Quantachrome) and a BJH analyzer (BJH: Barrett-Joyner-Halenda), respectively.

[0039] Example 3 - Electrochemical Reaction and Analysis Linear sweep voltammograms (LSVs) of the as-synthesized NiFe-LDH and NiMo electrodes (working electrodes) were obtained in 1 M KOH (Daejung) and 1 M H2SO4 (Daejung) aqueous solutions using an electrochemical device (Ivium) with an SCE (reference electrode) and a Pt foil (counter electrode). In NiFe-LDH, the potential was scanned at a scan rate of 1 mV s 1 from 0.6 V to 0.1 V versus SCE, and in NiMo, from -0.1 V to -0.7 V versus SCE. Tafel plots were obtained from the LSV data. The electrochemical double-layer capacitance (C dl : electrochemical double-layer capacitance) values were obtained by measuring the cyclic voltammograms (CVs: cyclic voltammograms) of each sample at various scan rates (5 - 30 mV s -1 ) in the non-Faradaic region of a 0.1 V-potential window. Bulk electrolysis was performed in a custom-made single-chamber Teflon reactor using OER with 1 M KOH or HER with 1 M H2SO4 at J = 10 mA cm -2 .

[0040] Before starting electrolysis, the electrolyte was purged with N2 gas (>99.99%) for 30 minutes. The gas released from the electrolyte during the electrochemical reaction was periodically sampled and quantified using a gas chromatograph (GC, Agilent 7820A). To maintain the initial pH values of the anolyte (1M KOH) and catholyte (1M H2SO4), the electrocatalytic activities and stabilities of NiFe-LDH and NiMo cathode pairs were tested in a two-chamber Teflon reactor separated by BPM (Fumasep FBM, FuMA-Tech). Figure 1 a).

[0041] A desalination combined electrochemical cell device was designed. The device includes: an anodic chamber with NiFe-LDH / BPM / acidic chamber / AEM (AMI-7001S, Membrane International) / desalination chamber / CEM (CMI-7000S, Membrane International) / alkaline chamber / BPM / cathodic chamber with NiMo Figure 1 b). When necessary, five desalination chambers were stacked by alternately inserting AEM and CEM between the acidic chamber and the alkaline chamber (NiFe-LDH / BPM / [AEM / CEM]n / BPM / NiMo; n = 5). Figure 1 c).

[0042] The chambers located between adjacent desalination cells were labeled as concentration cells. The anolyte of 1M KOH (20 mL) and the catholyte of 1M H2SO4 (20 mL) were of the batch type (non-circulating). As a control, the solutions in the acidic chamber (20 mL) and the alkaline chamber (20 mL) were circulated at a flow rate of 10 mL / min using a peristaltic pump (Reglo ICC, ISMATEC). -1 The flow rate was

[0043] The desalination chamber (40 mL, 0.171M NaCl or 10 g·L -1 ) and the concentration chamber (40 mL, 0.171M NaCl) were also circulated at a flow rate of 10 mL / min -1 When necessary, artificial seawater (Instant Ocean Sea Salt, salinity 36 g·L -1 ) was used as the brine. The stack with a NiFe-LDH anode and a NiMo cathode was used in the electrochemical device at J = 10 mA cm -2 or 100 mA cm -2In the desalination chamber during the following operation, the ionic conductivity of the brine and the pH values of the acidic chamber solution and the alkaline chamber solution were recorded by using a pH conductivity meter (Seven Compact™ S213, METTLER TOLEDO™). When necessary, the solutions in the acidic chamber and the alkaline chamber were periodically sampled and analyzed using an ion chromatograph (IC, Thermo Scientific, DIONEX ICS-1100) to identify and quantify the transported ions. When the ionic conductivity of the brine reached approximately 500 μS cm -1 the entire process was ended.

[0044] The Faradaic efficiency (FE), specific energy consumption (SEC), and ion transport efficiency (ITE) of the released O2 and H2 gases were calculated using the following equations:

Mathematical formula 1

Mathematical formula 2

Mathematical formula 3

[0045]

Results and Evaluation

[0046] Referring to Figure 2 a of [], the results of observing the NiFe sample composed of two parts in the as-deposited state and the post-anodized state by XRD are shown. Both samples exhibit the same diffraction pattern corresponding to the NiFe-LDH structure (2θ = 34.4° (012), 39.0° (015), and 61.3° (113); International Center for Diffraction Data (ICDD) No. 00-040-0215).

[0047] Referring to Figure 2 b of [], the XPS spectra of Ni 2p and Fe 2p are shown. The analysis results show that Ni 0 (852.9 eV) and Ni 2+ (the 2p3 / 2 and 2p1 / 2 correspond to 856.4 eV and 874.1 eV respectively) states are mixed in the deposited sample. The Ni 0 state is attributed to the reduction of Ni 2+ during the cathodic deposition process. However, after anodization, the Ni 0 state is not observed in the sample, and the Ni 2+ state dominates. On the contrary, the Fe 3+ state is observed in both samples.

[0048] Referring to Figure 2 c of [], the XPS spectrum of O 1s is shown. The O 1s spectrum also shows the coexistence of oxygen atoms combined with metal (M-O 28.7%), adsorbed hydroxyl groups (M-OH 38.4%), and H2O (32.8%) in the deposited sample. Except for the relatively large fraction of MO (58.7%) due to the partial conversion of Ni 0 and Ni(OH)2 to NiOOH and the partial conversion of Fe(OH)3 to FeOOH, the same oxygen pattern is found in the sample after anodization. The post-anodization process shifts the binding energies of Ni, Fe, and O towards lower energy, indicating a structural rearrangement of the deposited NiFe-LDH.

[0049] Referring to Figure 2 d of [], the influence of the scan rate on the capacitive J in the non-Faradaic region is shown. The C dl value of NiFe-LDH after anodization treatment is speculated to be 20 times larger than the C dl value in the deposited state (0.79 mF·cm -2 vs. 0.037 mF·cm -2 ). Considering C dlRegarding the proportional relationship with the electrochemically active surface area, anodic oxidation should effectively improve the electrode / solution interface area. Although the BET area slightly decreases after anodic oxidation, the pore diameter increases.

[0050] Figure 3 is a figure showing the surface characterization of the NiFe-LDH sample after anodic oxidation according to an embodiment of the present invention.

[0051] Referring to Figure 3 a and b of, FE-SEM images of the sample are shown, confirming that the porous Ni substrate is covered with aggregates composed of fine particles of about 50 nm in size. Referring to Figure 3 c and d of, TEM images of the sample and HAADF-STEM images of the rectangular region of c are shown respectively, and it can be seen that the NiFe particles collected from the Ni substrate have a layered nanostructure.

[0052] Referring to Figure 3 e and g of, EDS elemental mappings of the rectangular region of c are shown, and it can be confirmed that Ni, Fe, and O are uniformly distributed, and the Fe fraction of the sample synthesized at an Fe fraction of 0.5 (i.e., Fe / (Ni + Fe)) is estimated to be about 0.3.

[0053] Referring to Figure 3 h of, SAED patterns of the sample are shown, presenting the presence of the (012), (015), and (113) planes related to amorphous NiFe-LDH. Referring to Figure 3 i of, HR-TEM images of the plane are shown, confirming that the plane has a lattice spacing of 0.20 nm.

[0054] Figure 4 is a figure showing the voltammogram, Tafel curve, and O2 generation rate chart according to an embodiment of the present invention. Referring to Figure 4 a to c of, voltammograms of the NiFe-LDH electrode according to the Ni / Fe ratio and deposition time are shown. For the voltammogram, after the electrode was held at 1.64 V for 20 seconds, in order to separate the OER from the redox reaction of Ni and accurately estimate η OER a cathodic scan was performed. When the Ni / Fe ratio is 1 / 0 (i.e., only Ni), a cathodic peak is observed at about 1.25 V, and this peak slightly shifts to a lower potential as the deposition time increases. In addition, the same peak is also observed when the Ni / Fe ratio is 1 / 1. However, the peak intensity and the degree of peak shift are not obvious. Therefore, it is confirmed that the cathodic peak should be generated only by reducing the oxidized Ni species (such as Ni 3+ →Ni 2+ ). At J = 10 mA cm - ² and J = 100 mA cm -² (η and η respectively 10 and η 100 ), η varies significantly according to the synthesis conditions. At a deposition time of > 120 s, the lowest η is obtained when the Ni / Fe ratio is 1 / 1 OER and η (about 200 mV and about 280 mV respectively). This value is significantly lower than the values obtained from Ni substrates and platinum (Pt), and is similar to the values reported in the literature 10 and η 100 .

[0055] Refer to Figure 4 d, showing the Tafel curves obtained using NiFe-LDH electrodes (only Ni, only Fe, and Ni / Fe ratio of 1 / 1). The Tafel curves further show that among the electrodes tested, the lowest slope is in NiFe-LDH with a Ni / Fe ratio of 1 / 1 (39.9 mV dec -1 ). The lowest slope means that the charge transfer of the electrode catalyst occurs most effectively on the (oxy)hydroxide surface of NiFe-LDH. The numbers on the graph represent the Tafel slope (mV dec -1 ).

[0056] Refer to Figure 4 e, showing the O2 production rate obtained through NiFe-LDH electrodes and Faraday efficiency (FE) for OER at J = 10 mA cm -2 . Also, to study OER in 1 M KOH solution, bulk electrolysis using optimized NiFe-LDH was also performed

[0057] Figure 5 shows the surface characterization of the NiMo catalyst synthesized according to an embodiment of the present invention. Refer to Figure 5 a, which is an FE-SEM image. The synthesized NiMo sample shows a subdivided surface with a particle size of about 2 μm

[0058] Figure 5 b to d show the XRD spectra. b shows the typical pattern of the intermetallic alloy NiMo (Ni 0.88 Mo 0.12 ; 2θ = 43.7°(111), 51.0°(200), and 75.0°(220); ICDD number 04-023-7853) with overlapping peaks generated in the Ni substrate. In addition, according to SEM-EDS elemental analysis, a Mo fraction of about 0.1 was measured, which is consistent with the pattern in XRD. As can be seen in c and d, the Ni 2p spectrum is composed of Ni 0 and Ni 2+ , and the Mo 3d spectrum is composed of Mo0 and Mo 6 + It is composed of. Thus, the NiMo deposited as the cathode is only partially oxidized in the atmosphere before XPS analysis, and the Ni / Mo ratio in the XPS spectrum is 0.82 / 0.18, which is consistent with the ratio based on the SEM-EDS analysis and the crystal structure of XRD.

[0059] The electrocatalytic activity of the synthesized NiMo electrode was examined and compared with that of the porous Ni substrate and Pt in 1 M aqueous H2SO4 solution. Figure 6 Figure 9 shows the voltammogram, Tafel curve, and H2 generation rate according to an embodiment of the present invention. In addition, Figure 6 The inset of (a) is an enlarged voltammogram near the E on region, Figure 6 The inset of (c) is a graph of the extrinsic change of E over time.

[0060] Referring to Figure 6 of (a), through the linear sweep voltammograms of the NiMo, Ni, and Pt electrodes, the onset potentials (E on s) of the Ni substrate and NiMo were measured to be -0.006 V and 0.060 V, respectively. In particular, the η 10 and η 100 of the Ni substrate were measured to be -198 mV and -331 mV, respectively, while the η 10 and η 100 of the NiMo substrate were -59 mV and -200 mV, respectively. For comparison, the η 10 and η 100 of the Pt electrode were -24 mV and -116 mV, respectively, and E on was 0.05 V.

[0061] Referring to Figure 6 of (b), the Tafel curves obtained using the NiMo, Ni, and Pt electrodes are shown. The Tafel slopes of the Ni substrate and the NiMo electrode were measured to be approximately 123 mV -1 and approximately 85 mV dec -1 . Thus, it was confirmed that NiMo exhibits faster electrocatalytic reaction kinetics.

[0062] Referring to Figure 6 of (c), it relates to the NiMo electrode for HER and the H2 generation rate under FE conditions at J = -10 mA cm -2 . The H2 gas is linearly generated over time, the FE of HER is 80 - 90%, and E 10 is maintained between -0.04 V and -0.05 V.

[0063] Combination of NiFe-LDH and NiMo via BPM Figure 7 Shows the electrochemical behavior of the NiFe-LDH anode and NiMo cathode pair in a two-chamber device according to an embodiment of the present invention. A two-chamber device divided by a BPM with 1 M KOH as the anolyte and 1 M H2SO4 as the catholyte was used.

[0064] Referring to Figure 7 a of 装置 shows the J-E 装置 curves. The paired J-E on curves indicate that the E 装置 values of approximately 1.3 V, approximately 1.5 V, and approximately 2.1 V are observed at J = 10 mA cm -2 and 100 mA cm -2 conditions, respectively. Referring to Figure 7 b of -2 shows the respective variations of O2 and H2 over time in the anolyte and catholyte, and the FE values at J = 100 mA cm -2 Using the long-term bulk electrolysis of the NiFe-LDH and NiMo pair, O2 and H2 are generated in the anolyte and catholyte, respectively, at a stoichiometric ratio with a FE value of >95% within 20 hours. On the graph, the dashed lines represent 100% FE of O2 and H2 generation. Referring to Figure 7 c of 装置 relates to the variations of electrolyte pH and E 装置 over time at J = 100 mA cm + During electrolysis, E + remains stably at approximately 2.12 V, although H on is generated through OER in the anolyte and H 装置 is consumed in the catholyte through HER, the initial pH values of various electrolytes are maintained for more than 20 hours.

[0065] A pair of Pt anodes and Pt cathodes was also studied. The Pt-Pt pair exhibits larger E -2 values (>1.6 V) and E -2 values (approximately 1.7 V and approximately 2.43 V at J = 10 mA cm Figure 7For a), the excellent performance of NiFe-LDH and NiMo pairs relative to the Pt-Pt pair can be attributed to the much higher activity of the NiFe-LDH anode than that of the Pt anode. The Ni-Ni pair was also tested and showed lower activity. Despite the above behavior of the Pt-Pt pair and Ni-Ni pair, when the two electrolytes were separated by the BPM, the pH values of the anolyte and catholyte did not change within 20 h. Other types of ion exchange membranes (AEM, CEM, and PEM) were used instead of the BPM, and the bulk electrolysis was investigated with NiFe-LDH and NiMo pairs at J = 100 mA / cm 2 2.

[0066] In all three membranes, E 装置 gradually increased and then suddenly increased to >3 V. The pH of the anolyte (1 M KOH) gradually decreased and suddenly dropped to <3, but the pH of the catholyte (1 M H2SO4) remained relatively unchanged due to the high proton concentration. The same-time variations of E 装置 and the anolyte pH gave the following insights: the decrease in the anolyte pH caused the dissolution and deactivation of the NiFe-LDH anode, resulting in a sharp increase in E 装置 . The change in the anolyte pH was attributed to the consumption of hydroxide due to OER (4OH → O2 + 2H2O + 4e - ). To maintain charge balance during electrolysis, different types of ions passed through the membrane and were transported between the anolyte and catholyte. Referring to Figure 7 d, for AEM, about 0.3 M SO4 2- was found in the anolyte after 4 h, but no K + was found in the catholyte. For CEM and PEM, 0.7 - 0.8 M of K + was transferred to the catholyte, while the transfer of SO4 2- was effectively retarded. As a control, the transport of K + and SO4 2- through the BPM was significantly suppressed. This is because charge balance was maintained by continuously supplying OH - and H + during electrolysis, resulting in the stability of the NiFe-LDH anode.

[0067] Desalination Combined Electrode Catalyst The electrode catalyst using the NiFe-LDH anode and NiMo cathode pair was combined with the desalination of brine by designing a desalination chamber (0.171 NaCl) between the anolyte (1 M KOH) and catholyte (1 M H2SO4) (refer to Figure 1For b) of , in order to further use the desalted ions, individual acidic chambers (0.1 M NaCl, pH approximately 6) and alkaline chambers (0.1 M NaCl, pH approximately 6) are arranged between the desalination chamber and the electrode chambers.

[0068] Figure 8 shows the E of a desalination combined electrocatalysis unit device according to an embodiment of the present invention 装置 and the ionic conductivity (σ), the concentration changes of desalinated ions (Cl - and Na + ), and the pH value changes of the acidic chamber, alkaline chamber and electrolyte solution.

[0069] Referring to Figure 8 a of , shows the E of brine according to the electrolysis time 装置 and the change of ionic conductivity (σ). At J = 10 mA cm -2 , the E of approximately 2.4 V in the initial stage gradually increases within 10 hours, while in the desalination chamber, the ionic conductivity (σ) of the brine linearly decreases with time. The decrease in σ may be because Cl 装置 and Na - are transferred from the brine to the respective acidic chamber and alkaline chamber respectively, resulting in an increase in the overall resistivity of the device. + respectively from the brine to the respective acidic chamber and alkaline chamber, resulting in an increase in the overall resistivity of the device.

[0070] Referring to Figure 8 b of , regarding the concentration changes of desalinated ions (Cl - and Na + ), in each of the acidic chamber and alkaline chamber, the countercurrent of each ion is confirmed by the gradual increase in the concentration of Cl - and Na + . Referring to Figure 8 c of , shows the pH value changes of the acidic chamber, alkaline chamber and electrolyte solution. At the same time, by continuously supplying H + and OH - from the BPM (BPM-a) beside the acidic chamber and the BPM (BPM-b) beside the alkaline chamber respectively, the pH values of the acidic chamber and alkaline chamber become approximately 1 and 12.5 respectively. This shows that the acidic chamber and alkaline chamber are rich in HCl and NaOH respectively. However, due to the supply of OH - and H +, so the pH values of the anolyte and catholyte remain unchanged. The observed concentration changes in the desalinated ions are significantly similar to the theoretical values predicted based on J. Due to the incomplete functionality of the commercially available ion exchange membranes used, there are slight deviations. If ideal ion transport is assumed, when the brine is completely desalinated, the pH values of the acidic and alkaline chambers should become approximately 0.77 and 13.2, respectively. Nevertheless, according to Case Study I in Table 1 below, the overall ITE is 85%. The SEC is estimated to be 6.58 kWh m -3 , which is approximately 35% lower than the previous report. If this lower SEC is considered in the system used for the simultaneous production of more value-added chemicals (H2, HCl, and NaOH), it is ideal.

[0071]

Table 1

[0072] According to Case Study II, the increase in the initial NaCl concentration (from 0.1 M to 0.2 M) in the acidic and alkaline chambers has a negligible effect on the desalination behavior. For example, the 50% desalination time (τ 1 / 2 ) is 5.6 hours, and the ITE is 82%. The SEC increases slightly to approximately 7 kWh m -3 . In addition, according to Case Study III, when HCl (0.1 M) and NaOH (0.1 M) are used in the acidic and alkaline chambers instead of NaCl (0.1 M), respectively, the overall device performance remains unchanged, with an ITE similar to approximately 85% and an SEC of 6.62 kWhm -3 . The initial pH value of 1.75 in the acidic chamber gradually decreases during electrolysis and reaches 0.70 at 100% desalination, showing further acidification caused by HCl (or alkalization caused by NaOH). In contrast, referring to Case Study IV, if J is increased by 10 times (100 mA cm -2 ), the desalination process kinetics increase by 10 times, and it is completed within 1 hour (τ 1 / 2 approximately 0.6 h). This gives the implication that the overall desalination kinetics only depend on J. However, although the total charge (J×τ 1 / 2 ) is similar to that in Case Study III, the SEC increases by 2.4 times (15.8 kWh m -3 ). To reduce the SEC while enhancing the desalination kinetics, five desalination chambers are arranged between the acidic and alkaline chambers by alternately arranging AEM and CEM ( Figure 1 of c). As Figure 9 shown, from the use of the desalination chamber unit device ( Figure 1b) Several different behaviors were observed. First, at J = 10 mA cm -2 −2, the initial E 装置 value (about 3.0 V) increased slightly due to the increase in the element resistance caused by the membranes with a maximum membrane resistance of about 40 Ω / sq for each membrane. Second, according to Case Study V, although the volume of the brine was tripled, the desalination kinetics were significantly improved. The desalination was completed within 4 hours with a τ 1 / 2 of about 2 hours. This improved kinetics was attributed to the enlarged ion-exchange membrane area in contact with the saline solution, resulting in an ITE as high as 417%. However, the ITE normalized by the number of desalination chambers (417% / 5 chambers = 83.4% / chamber) was similar to the ITE obtained using a unit device (85%). The observed ITE value being less than 100% was particularly attributed to the slow ion transfer through the membranes used at high J values (see Case Study IV). In particular, a rather low SEC value (1.79 kWh m -3 −3) was obtained, which was equivalent to 27% of the SEC value obtained using a unit device (Case Study I), and it could be compared with the state-of-the-art processes in the literature. Finally, in Case Study VI, a multi-desalination chamber array device was tested for the desalination of seawater (36 g L -1 −1). The initial E 装置 value was similar to that of brackish water (0.171 M NaCl). However, the salinity of seawater was almost three times higher than that of brackish water, so a τ 1 / 2 three times longer (6.4 h) was required. If only Na + and Cl - transfer was considered, the ITE was estimated to be about 360%. When other ions present in seawater (e.g., SO4 2- 2−, Mg 2+ 2+, Ca 2+ 2+ and K + +) were included, the ITE increased to about 400%. The pH values of the acidic and alkaline chambers became <1 and >12, respectively. All the results indicate that although the former matrix is more complex, the overall device performance using seawater is similar to that using brackish water.

Claims

1. A desalination combined catalytic electrode device, which is an electrolytic cell composed of an anode chamber / bipolar membrane / [anion exchange membrane / cation exchange membrane]n / bipolar membrane / cathode chamber, characterized in that, The anode chamber contains a Ni / 3d transition metal composite catalytic electrode, and the 3d transition metal fraction of the electrode is 0.3 or less. The anion exchange membrane and the cation exchange membrane are alternately arranged with n being a natural number from 1 to 5. The electrolytic cell has a 50% desalination time (τ -2 ), at J = 10 mA / cm 1 / 2 ), of 2.2 to 6.4 hours, and a specific energy consumption (SEC) of 1.79 to 7.03 kWh m -3 .

2. The desalination combined catalytic electrode device according to claim 1, characterized in that, The composite catalytic electrode is formed by electrodeposition.

3. The desalination combined catalytic electrode device according to claim 1, characterized in that, The composite catalytic electrode is a 3d-transition metal-based (oxy)hydroxide.

4. A method for preparing a nickel-based transition metal composite catalytic electrode by a one-step electrodeposition method, characterized in that, It includes the following steps: Form a mixed solution by mixing a hydrate containing Ni and a hydrate of a 3d transition metal in a ratio of 1:3 to 3:1; After immersing a Ni substrate in the solution, perform cathodic bias electrodeposition for 10 seconds to 180 seconds; And Anodize the deposited Ni / 3d transition metal double hydrate composite catalytic electrode, and perform washing and drying.

5. The method for preparing a nickel-based transition metal composite catalytic electrode by a one-step electrodeposition method according to claim 4, characterized in that, The composite catalytic electrode is a 3d-transition metal-based (oxy)hydroxide.

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