Metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode and method of preparing the same and method of preparing adiponitrile using metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode

Abstract

A method of preparing a metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode is disclosed. The method comprises steps of: preparing a plating solution containing 0.25 M ammonium chloride, 0.067 M to 0.133 M nickel chloride, 0.067 M to 0.133 M ferrous sulfate, and 0.04 M to 2 M sodium hypophosphite; placing a copper iodide-bismuth composite electrode in the plating solution for electrodepositing metallic nickel / nickel-iron hydroxide catalytic layer onto the copper iodide-bismuth composite electrode to obtain the metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode, CuI—Bi / Ni—NiFe(OH)x(r), wherein r is a molar ratio of nickel chloride to ferrous sulfate. A metallic nickel / nickel-iron hydroxide catalytic layer modified copper iodide-bismuth composite electrode and a method of preparing adiponitrile using the metallic nickel / nickel-iron hydroxide catalytic layer modified copper iodide-bismuth composite electrode are further disclosed.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a Paris Convention, which claims the benefit of priority of Taiwan Patent Application No. 113138555 filed on Oct. 9, 2024. The contents of the above application is all incorporated by reference as if fully set forth herein in its entirety.FIELD OF INVENTION

[0002] The present disclosure relates to a method of preparing modified electrodes, and in particular to a method of preparing a metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode. The present disclosure further relates to a modified electrode, and in particular to a metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode. The present disclosure further relates to a method of synthesizing adiponitrile, and in particular to a method of synthesizing adiponitrile through hydrodimerization of acrylonitrile using a metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode.BACKGROUND OF INVENTION

[0003] Nylon 6,6, a polyamide made from hexamethylenediamine and adipic acid via polycondensation, has been extensively used in the textile, plastics and automotive industries. The industrial production of hexamethylenediamine involves the use of adiponitrile as the feedstock.

[0004] Current methods for producing adiponitrile include hydrocyanation of butadiene, dehydrative amination of adipic acid, and electrohydrodimerization of acrylonitrile. The synthesis of adiponitrile via the hydrocyanation of butadiene involves the use of a large amount of highly-toxic hydrogen cyanide and high-pressure operation conditions, which poses threat to our environment and public security. The synthesis of adiponitrile via the dehydrative ammonization of adipic acid involves the use of high-temperature conditions and suffers diverse competing side reactions, thereby affecting the quality and recovery rate of adiponitrile. The electrohydrodimerization of acrylonitrile requires the use of highly toxic heavy metals (e.g., lead and cadmium) as the cathode materials. The leaching of these heavy metal ions during the operation would result in secondary pollution and thus pose a threat to the environment.

[0005] Accordingly, it is highly important to develop highly efficient and environmentally friendly production processes for the synthesis of nylon 6,6 precursors.SUMMARY OF INVENTIONTechnical Problems

[0006] A main purpose of the present disclosure is to provide a method for preparing a metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode. Furthermore, another purpose of the present disclosure is to provide a method for synthesizing adiponitrile by using a metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode prepared by the method, enabling the efficient, safe, and environmentally friendly synthesis of Nylon 6,6 precursors.Technical Solutions

[0007] In order to achieve the foregoing purposes of the present disclosure, the present disclosure provides a method of method of preparing a metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode, comprising steps of: preparing a plating solution containing 0.25 M ammonium chloride, 0.067 M to 0.133 M nickel chloride, 0.067 M to 0.133 M ferrous sulfate, and 0.04 M to 2 M of sodium hypophosphite; placing a copper iodide-bismuth composite electrode in the plating solution for electrodepositing a metallic nickel / nickel-iron hydroxide catalytic layer onto the copper iodide-bismuth composite electrode to obtain the metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode, CuI—Bi / Ni—NiFe(OH)x(r), wherein r is a molar ratio of nickel chloride to ferrous sulfate.

[0008] In one embodiment of the present disclosure, the metallic nickel / nickel-iron hydroxide catalytic layer is electrodeposited onto the copper iodide-bismuth composite electrode at a constant current density of −10 mA cm−2.

[0009] In one embodiment of the present disclosure, duration of electrodeposition ranges from 10 seconds to 60 seconds.

[0010] In order to achieve the foregoing purposes of the present disclosure, the present disclosure further provides a metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode, CuI—Bi / Ni—NiFe(OH)x(r), prepared by the method as mentioned above, wherein r is a molar ratio of nickel chloride to ferrous sulfate.

[0011] In order to achieve the objectives of the present disclosure, the present disclosure further provides a method of synthesizing adiponitrile using the metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode as mentioned above, comprising a step of electrolyzing acrylonitrile in a phosphate buffer solution containing 0.6 M to 0.8 M acrylonitrile using the metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode at constant current densities of −100 mA cm−2 to −400 mA cm−2.

[0012] In one embodiment of the present disclosure, the metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode is modified by electrodepositing a metallic nickel / nickel-iron hydroxide catalytic layer with charge passages of 0.1 C cm−2˜0.6 C cm−2.

[0013] In one embodiment of the present disclosure, the concentration, pH, and the working volume of the phosphate buffer are 0.5 M, pH 8, and 36 mL˜250 mL, respectively.

[0014] In one embodiment of the present disclosure, the phosphate buffer further contains 20 mM to 40 mM of quaternary ammonium salt, and the quaternary ammonium salt is represented by formula (I):wherein R1 to R4 are independently a C2-5 hydrocarbon group, and X− is ClO4−, H2PO4−, or Br−.In one embodiment of the present disclosure, electrolysis of acrylonitrile is carried out in a H-type electrochemical cell or a flow-type electrolyzer.

[0016] In one embodiment of the present disclosure, a flow rate of the electrolyte solution used for the flow-type electrolyzer is 722 sccm.Beneficial Effects

[0017] The metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode prepared by the method of preparing a metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode of the present disclosure can be used to synthesize adiponitrile through the electrohydrodimerization of acrylonitrile. Therefore, the developed electrode materials address the issue in existing methods of requiring toxic lead- or cadmium-based materials. Additionally, it offers high stability and reduced energy consumption during electrolysis, making it suitable for the integration into the flow-type electrolyzer. This advancement holds potential for the large-scale production of adiponitrile.DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the above contents of the present disclosure, the following is a detailed description of the preferred embodiments with reference to the accompanying drawings:

[0019] FIG. 1 is a scheme for the preparation of the CuI—Bi electrode.

[0020] FIG. 2 is a scheme for the preparation of the CuI—Bi / Ni—NiFe(OH)x(r) electrode.

[0021] FIG. 3a shows potential transients recorded during the 2-h electrolysis using the CuI—Bi electrode (i), the CuI—Bi / Ni—NiFe(OH)x(r=∞) electrode (ii), the CuI—Bi / Ni—NiFe(OH)x(r=2) electrode (iii), the CuI—Bi / Ni—NiFe(OH)x(r=1) electrode (iv), the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode (v), and the CuI—Bi / Ni—NiFe(OH)x(r=0) electrode (vi) in the H-type electrochemical cell containing a 0.5 M phosphate buffer (pH 8, 36 mL) containing 0.6 M acrylonitrile and 30 mM tetrabutylammonium phosphate (TBAP) at an applied current density of −100 mA cm−2. FIG. 3b, FIG. 3c, and FIG. 3d, respectively, show the current efficiencies of the products, product selectivity, and production rate (R) of products generated from the 2-h electrolysis at −100 mA cm−2.

[0022] FIG. 4a to FIG. 4e show the SEM images of the CuI—Bi / Ni—NiFe(OH)x(r=∞) electrode (FIG. 4a), CuI—Bi / Ni—NiFe(OH)x(r=2) electrode (FIG. 4b), CuI—Bi / Ni—NiFe(OH)x(r=1) electrode (FIG. 4c), CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode (FIG. 4d), and CuI—Bi / Ni—NiFe(OH)x(r=0) electrode (FIG. 4e).

[0023] FIG. 5a to FIG. 5c show the XPS spectra of the CuI—Bi / Ni—NiFe(OH)x(r) electrodes with various Ni2+ / Fe2+ molar ratios (r), wherein FIG. 5a is Ni 2p3 / 2 region, FIG. 5b is Fe 2p3 / 2 region, and FIG. 5c is O 1s region, respectively.

[0024] FIG. 6a shows potential transients recorded during the 2-h electrolysis using a CuI—Bi electrode and the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode prepared with various charge passages (i: CuI—Bi; ii: 0.1; iii: 0.2; iv: 0.3; v: 0.4; vi: 0.5; and vii: 0.6 C cm−2) in the H-type electrochemical cell containing a 0.5 M phosphate buffer (pH 8, 36 mL) containing 0.6 M acrylonitrile and 30 mM tetrabutylammonium phosphate (TBAP) at an applied current density of −100 mA cm−2. FIG. 6b, FIG. 6c, and FIG. 6d, respectively, show the current efficiencies of the products, product selectivity, and production rate (R) of products generated from the 2-h electrolysis at −100 mA cm−2.

[0025] FIG. 7a to FIG. 7f shows the SEM images of the CuI—Bi electrode (FIG. 7a), and the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes prepared with charge passages of 0.1 C cm−2 (FIG. 7b), 0.2 C cm−2 (FIG. 7c), 0.3 C cm−2 (FIG. 7d), 0.4 C cm−2 (FIG. 7e), and 0.6 C cm−2 (FIG. 7f).

[0026] FIG. 8a to FIG. 8c show the XPS spectra of the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes prepared with various charge passages (i: 0.1 C cm−2; ii: 0.2 C cm−2; iii: 0.3 C cm−2; iv: 0.4 C cm−2; v: 0.5 C cm−2; and v: 0.6 C cm−2), wherein FIG. 8a is Ni 2p3 / 2 region, FIG. 8b is Fe2p3 / 2 region, and FIG. 8c is O 1s region, respectively.

[0027] FIG. 9a shows potential transients recorded during the 2-h electrolysis using the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes prepared with various hypophosphate concentrations (i: CH2PO2−=0 M; ii: CH2PO2−=0.04 M; iii: CH2PO2−=1 M; iv: CH2PO2−=2 M) and a charge passage of 0.1 C cm−2 in the H-type electrochemical cell comprising a 0.5 M of phosphate buffer (pH 8, 36 mL) containing 0.6 M acrylonitrile and 30 mM tetrabutylammonium phosphate (TBAP) at an applied current density of −100 mA cm−2. FIG. 9b, FIG. 9c, and FIG. 9d, respectively, show the current efficiencies of the products, product selectivity, and production rate of products generated from the 2-h electrolysis at −100 mA cm−2.

[0028] FIG. 10a to FIG. 10c show potential transients recorded during the 2-h electrolysis using (i) the CuI—Bi electrode and (ii) the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode in the H-type electrochemical cell comprising a 0.5 M phosphate buffer (pH 8, 36 mL) containing 0.6 M acrylonitrile and 30 mM tetrabutylammonium phosphate (TBAP) at various applied current densities (FIG. 10a: −100 mA cm−2; FIG. 10b: −200 mA cm−2; FIG. 10c: −400 mA cm−2). FIG. 10d, FIG. 10e, and FIG. 10f, respectively, show the current efficiencies of the products, product selectivity, and production rate (R) of products generated from the 2-h electrolysis at various applied current densities.

[0029] FIG. 11a shows potential transients recorded during the 2-h electrolysis using the CuI—Bi electrode (i.e., 0.0 C cm−2; i) and the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes prepared with various charge passages (ii: 0.1 C cm−2; iii: 0.4 C cm−2; iv: 0.6 C cm−2) in the flow-type electrolyzer comprising a 0.5 M phosphate buffer (pH 8, 60 mL) containing 0.8 M acrylonitrile and 30 mM tetrabutylammonium phosphate (TBAP) at an applied current density of −200 mA cm−2. FIG. 11b, FIG. 11c, and FIG. 11d, respectively, show the current efficiencies of the products, product selectivity, and production rate (R) of products generated from the 2-h electrolysis at an applied current density of −200 mA cm−2.

[0030] FIG. 12a shows potential transients recorded during the 2-h electrolysis using the CuI—Bi electrode in the flow-type electrolyzer comprising a 0.5 M phosphate buffer (pH 8, 60 mL) containing 0.8 M acrylonitrile and 30 mM of various ammonium salts (QAS: tetrabutylammonium phosphate, TBAP; tetrapentylammonium bromide, TPAB; tetraethylammonium perchlorate, TEAP; tributylmethylammonium phosphate, MBAP) at an applied current density of −200 mA cm−2. FIG. 12b, FIG. 12c, and FIG. 12d, respectively, show the current efficiencies of the products, product selectivity, and production rate (R) of products generated from the 2-h electrolysis at an applied current density of −200 mA cm−2.

[0031] FIG. 13a shows potential transients recorded during the 2-h electrolysis using the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode, prepared with a charge passage of 0.1 C cm−2, in the flow-type electrolyzer comprising a 0.5 M phosphate buffer (pH 8, 60 mL) containing 0.8 M acrylonitrile and 30 mM of various ammonium salts (QAS: tetrabutylammonium phosphate, TBAP; tetrapentylammonium bromide, TPAB; tetraethylammonium perchlorate, TEAP; tributylmethylammonium phosphate, MBAP) at an applied current density of −200 mA cm−2. FIG. 13b, FIG. 13c, and FIG. 13d, respectively, show the current efficiencies of the products, product selectivity, and production rate (R) of products generated from the 2-h electrolysis at an applied current density of −200 mA cm−2.

[0032] FIG. 14a shows potential transients recorded during the 2-h electrolysis using the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode, prepared with a charge passage of 0.1 C cm−2, in the flow-type electrolyzer comprising a 0.5 M phosphate buffer (pH 8, 60 mL) containing 0.8 M acrylonitrile and tetrabutylammonium phosphate (TBAP) of various concentration (i: CTBAP: 0 mM; ii: CTBAP: 20 mM; iii: CTBAP: 30 mM; iv: CTBAP: 40 mM) at an applied current density of −200 mA cm−2. FIG. 14b, FIG. 14c, and FIG. 14d, respectively, show the current efficiencies of the products, product selectivity, and production rate (R) of products generated from the 2-h electrolysis at an applied current density of −200 mA cm−2.

[0033] FIG. 15a shows potential transients recorded during the 8-h electrolysis using the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode in the flow-type electrolyzer comprising a 0.5 M phosphate buffer (pH 8, 250 mL) containing 0.8 M acrylonitrile and 30 mM tetrabutylammonium phosphate (TBAP) at an applied current density of −200 mA cm−2. FIG. 15b, FIG. 15c, and FIG. 15d, respectively, show the current efficiencies of the products, product selectivity, and production rate (R) of products generated from the 2-h electrolysis at an applied current density of −200 mA cm−2.DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0034] In order to describe the technical solutions of the present disclosure more clearly, numerous specific details are provided in the following specific embodiments. Apparently, the present disclosure can be practiced without certain specific details.

[0035] A method of preparing a metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode according to an embodiment of the present disclosure comprises steps of: preparing a electroplating solution containing 0.25 M ammonium chloride, 0.067 M to 0.133 M (e.g., 0.067, 0.068, 0.069, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.131, 0.132, or 0.133 M) of nickel chloride, 0.067 M to 0.133 M (e.g., 0.067, 0.068, 0.069, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.131, 0.132, or 0.133 M) of ferrous sulfate, and 0.04 M to 2 M (e.g., 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, or 2 M) of sodium hypophosphite; placing a copper iodide-bismuth composite electrode in the plating solution for the electrodeposition of the metallic nickel / nickel-iron hydroxide catalytic layer onto the copper iodide-bismuth composite electrode, so as to obtain the metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode, CuI—Bi / Ni—NiFe(OH)x(r), wherein r is the nickel chloride / ferrous sulfate molar ratio.

[0036] Optionally, the metallic nickel / nickel-iron hydroxide catalytic layer is electrodeposited onto the copper iodide-bismuth composite electrode at a constant current density of −10 mA cm−2, and electrodepositing duration may be range from 10 seconds to 60 seconds, such as 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, or 60 seconds.

[0037] A method of preparing adiponitrile using the metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode as mentioned above according to another embodiment of the present disclosure comprises a step of electrolyzing acrylonitrile in a phosphate buffer containing 0.6 M to 0.8 M acrylonitrile using the metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode as mentioned above at a constant current density of −100 mA cm−2 to −400 mA cm−2. For example, the current density may be −100 mA cm−2, −150 mA cm−2, −200 mA cm−2, −250 mA cm−2, −300 mA cm−2, −350 mA cm−2, or −400 mA cm−2.

[0038] Optionally, the metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode may be obtained by electrodepositing a metallic nickel / nickel iron hydroxide catalytic layer with a charge passage of 0.1 C cm−2 to 0.6 C cm−2 onto the copper iodide-bismuth composite electrode. The charge passage may be 0.1 C cm−2, 0.2 C cm−2, 0.3 C cm−2, 0.4 C cm−2, or 0.6 C cm−2. Preferably, the metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode may be obtained by electrodepositing a metallic nickel / nickel iron hydroxide catalytic layer with a charge passage of 0.1 C cm−2 on the copper iodide-bismuth composite electrode.

[0039] Optionally, the concentration and pH of the phosphate buffer are 0.5 M and pH 8, respectively.

[0040] Optionally, the phosphate buffer further contains 20 mM to 40 mM quaternary ammonium salt, and the quaternary ammonium salt is represented by formula (I):

[0041] wherein R1 to R4 are each independently a C2-5 hydrocarbon group, and X− is ClO4−, H2PO4−, or Br−.

[0042] In addition, the method of preparing adiponitrile using the aforementioned metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode can be implemented in both the H-type electrochemical cell and the flow-type electrolyzer (i.e., performing in a continuous flow process). Using a flow-type electrolyzer electrochemical with a flow rate of electrolyte solution of 722 sccm increases the mass transfer rate of acrylonitrile.

[0043] As used herein and in the appended claims, singular articles such as “a” and “an” and “the” and similar referents in the context of describing the elements (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. As used herein and in the appended claims, the term “or” is to be construed to cover the term “and / or”, unless otherwise indicated herein.

[0044] The preparation of the copper iodide-bismuth composite-modified electrode (CuI—Bi):

[0045] Prior to the preparation of the CuI—Bi electrode, a copper foil was cleaned with diluted HCl aqueous solution (5 v / v %) for 10 min under sonication. As illustrated from FIG. 1, the preparation of the CuI—Bi electrode was performed by immersing the cleaned Cu sheet in the solution (pH 1.75) containing 0.4 M potassium iodide (KI) and 0.04 M bismuth nitrate (bismuth (III) nitrate pentahydrate, Bi(NO3)3·5H2O) for 8 minutes at ambient conditions. The obtained electrode was rinsed with deionized water (DIW) and dried at room temperature before its usage.

[0046] The preparation of the metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode (CuI—Bi / Ni—NiFe(OH)x(r)):

[0047] As revealed in FIG. 2, the preparation of the CuI—Bi / Ni—NiFe(OH)x(r) electrode was performed by subjecting the CuI—Bi electrode to the electrodeposition process at an applied current density of −10 mA cm−2 for the specific duration in the plating solution containing 0.25 M ammonium chloride, 0.067 M to 0.133 M nickel chloride, 0.067 M to 0.133 M ferrous sulfate, and 0.04 M to 2 M sodium hypophosphite under nitrogen purge.

[0048] Effects of Ni2+ / Fe2+ molar ratio (r ratio) on the electrocatalytic performance of the CuI—Bi / Ni—NiFe(OH)x(r) electrode:

[0049] The composition of the metallic nickel / nickel-iron hydroxide catalytic layer (Ni—NiFe(OH)x(r)) was tailored by adjusting the nickel chloride / ferrous sulfate molar ratio (r) while the overall metal concentration was maintained at 0.2 M. The electrocatalytic performance of the CuI—Bi / Ni—NiFe(OH)x(r) electrodes towards the electrohydrodimerization of acrylonitrile (EHD-AN) was then examined by performing a series of 2-h electrolysis experiments using the H-type electrochemical cell with a 0.5 M of phosphate buffer (pH8, 36 mL) containing 0.6 M acrylonitrile and 30 mM tetrabutylammonium phosphate (TBAP) at an applied current density (japp) of −100 mA cm−2.

[0050] FIG. 3a shows potential transients of the CuI—Bi electrode and the CuI—Bi / Ni—NiFe(OH)x(r) electrode obtained during the 2-h electrolysis at japp=−100 mA cm−2. The results show that the potential of the CuI—Bi electrode to maintain japp=−100 mA cm−2 significantly increased by approximately 0.3 V within 2 hours. In contrast, the potentials of the CuI—Bi / Ni—NiFe(OH)x(r) electrode remained stable at ˜−1.0 V vs. RHE.

[0051] FIG. 3b-FIG. 3d show the product distributions obtained from 2-h electrolysis. As revealed, the current efficiency for the production of adiponitrile (CEADN), propionitrile (CEPN), and 1,3,6-tricyanohexane (CETrimer) from the 2-h electrolysis using the CuI—Bi electrode were 72.4±2.1%, 11.8±1.4%, and 5.8±0.3%, respectively. This finding indicates that the CuI—Bi electrode has high selectivity for the production of ADN (SADN: 80.4±1.4%). In addition, when the CuI—Bi electrode was modified with Ni—NiFe(OH)x layer with the charge passage of 0.2 C cm−2, the obtained CuI—Bi / Ni—NiFe(OH)x(r) electrodes showed comparable or even better EHD-AN performance as compared to the CuI—Bi electrode. Notably, the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode exhibited enhanced EHD-AN performance as compared to the CuI—Bi electrode. Specifically, the CEADN and SADN of the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode were 78.5±4.5% and 84.6±14.3%, respectively. Furthermore, the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode also exhibited an ADN production rate (RADN) of 1.5±0.1 mmole cm−2 h−1, which is higher than the CuI—Bi electrode (RADN: 1.3±0.0 mmole cm−2 h−1). The RADN of the CuI—Bi / Ni—NiFe(OH)x(r=0), CuI—Bi / Ni—NiFe(OH)x(r=1), CuI—Bi / Ni—NiFe(OH)x(r=2), CuI—Bi / Ni—NiFe(OH)x(r=0) electrodes were 1.3±0.0 mmole cm−2 h−1, 1.2±0.0 mmole cm−2 h−1, 1.3±0.0 mmole cm−2 h−1, and 1.4±0.0 mmole cm−2 h−1, respectively. It is interesting to note that the CuI—Bi / Ni—NiFe(OH)x(r) electrode also exhibited noticeable activity towards hydrogen evolution reaction. For instance, the current efficiencies of the CuI—Bi / Ni—NiFe(OH)x(r=0) and CuI—Bi / Ni—NiFe(OH)x(r=) electrodes towards hydrogen generation were 14.7±0.0% and 12.2±1.0%, respectively.

[0052] In summary, the CuI—Bi / Ni—NiFe(OH)x(r) electrodes not only require less potential (i.e., energy consumption) to maintain japp=−100 mA cm−2 than the CuI—Bi electrode, but also exhibited comparable or even better EHD-AN performance, in terms of CEADN, SADN, and RADN, as compared to the CuI—Bi electrode, confirming the beneficial role of Ni—NiFe(OH)x catalytic layer in improving the EHD-AN performance.

[0053] The surface morphology of the CuI—Bi / Ni—NiFe(OH)x(r) electrodes with various Ni2+ / Fe2+ molar ratios (i.e., r values) were investigated. The test method comprises measurement with a scanning electron microscope (SEM). As revealed in FIG. 4, the CuI—Bi / Ni—NiFe(OH)x(r) electrodes with r value of ≥1 had the surface covered with spherical particles, whereas the CuI—Bi / Ni—NiFe(OH)x(r) electrodes with r value of <1 had wrinkle-structured surface.

[0054] Characterization of the valence state of metal species on the CuI—Bi / Ni—NiFe(OH)x(r) electrodes:

[0055] A purpose of the present disclosure is to understand the valence state of metal species of the CuI—Bi / Ni—NiFe(OH)x(r) electrodes. The test method comprises a step of measuring spectra of Ni 2p3 / 2, Fe 2p3 / 2, and O 1s using X-ray photoelectron spectroscopy (XPS).

[0056] As revealed in FIG. 5a-FIG. 5c, the CuI—Bi / Ni—NiFe(OH)x(r) electrodes with r>0 contained metallic nickel and nickel hydroxide. In addition, the CuI—Bi / Ni—NiFe(OH)x(r) electrodes with r≥0.5, the CuI—Bi / Ni—NiFe(OH)x(r) electrode also contained iron hydroxide.

[0057] Effects of the amount of Ni—NiFe(OH)x on the EHD-AN performance of the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode:

[0058] The deposition amount of Ni—NiFe(OH)x(r=0.5) on the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode was controlled by adjusting the charge passages (0.1 C cm−2, 0.2 C cm−2, 0.3 C cm−2, 0.4 C cm−2, and 0.6 C cm−2) during the electrodeposition. The effects of the amount of Ni—NiFe(OH)x on the EHD-AN performance of the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode were investigated by performing a series of 2-h electrolysis in 0.5 M of phosphate buffer (pH 8, 36 mL) containing 0.6 M acrylonitrile and tetrabutylammonium phosphate (TBAP) at japp=−100 mA cm−2.

[0059] FIG. 6a shows potential transients of the CuI—Bi electrode and the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes prepared with various charge passages ranging from 0.1 to 0.6 C cm−2. As compared to the CuI—Bi electrode, all the prepared CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes require lower potential to maintain japp=−100 mA cm−2. In addition, among the prepared CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes, the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode prepared with the charge passage of 0.1 C cm−2 required lowest potential (˜−0.99 V vs. RHE) to maintain japp=−100 mA cm−2.

[0060] As revealed in FIG. 6b-FIG. 6d, the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode, prepared with the charge passage of 0.1 C cm−2, shows improved EHD-AN performance, in terms of high CEADN (85.0±2.4%), SADN (88.3±0.5%), and RADN (1.6±0.0 mmole cm−2 h−1). However, the CEADN, SADN and RADN of the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes decreased as the charge passage used for the preparation of the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes was increased. In addition, the EHD-AN performance of the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode was found to be inferior to that of the CuI—Bi electrode when the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode was prepared with the charge passage of ≥0.4 C cm−2, which could be attributed to the competing hydrogen evolution reaction.

[0061] In summary, the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode prepared with a charge passage of 0.1 C cm−2 has the optimal EHD-AN performance, in terms of high CEADN (85.0±2.4%), SADN (88.3±0.5%), and RADN (1.6±0.0 mmole cm−2 h−1 at the expense of lower operation potential. Additionally, the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode remains stable during the electrolysis experiments at the high applied current density.

[0062] FIG. 7a to FIG. 7f shows the SEM images of the CuI—Bi and CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes prepared with different charge passages. As revealed, the CuI—Bi electrode exhibited a dendritic structure. In addition, the deposition of the Ni—NiFe(OH)x(r=0.5) catalytic layer modified the surface morphology of the resulted CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes.

[0063] Characterization of the valence state of metal species on the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes:

[0064] In order to understand the valence state of metal species on the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes prepared with different charge passages (0.1 C cm−2, 0.2 C cm−2, 0.3 C cm−2, 0.4 C cm−2, and 0.6 C cm−2). The test method comprises a step of measuring spectra of Ni 2p3 / 2, Fe 2p3 / 2, and O 1s using X-ray photoelectron spectroscopy (XPS).

[0065] As shown in FIG. 8a to FIG. 8c, all of the prepared CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes contained nickel hydroxide and iron hydroxide. In addition, the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode prepared with the charge passages ranging from 0.1 C cm−2 to 0.3 C cm−2 also contained metallic nickel, a species with stronger hydrogen absorption capacity than bismuth. The presence of metallic nickel in the Ni—NiFe(OH)x modified layer helps adjust the distribution of the adsorbed hydrogen atoms on the catalyst surface, enabling hydrogen atoms to adsorb on nickel rather than bismuth. This adjustment is beneficial in reducing the reaction potential of the overall EHD-AN. Furthermore, the redistribution of hydrogen absorption further prevents the deactivation of CuI—Bi due to the formation of bismuth hydride. As a result, the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode demonstrates improved electrocatalytic stability for the electrohydrodimerization of acrylonitrile compared to the CuI—Bi electrode. The CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode, prepared with a charge passage of 0.1 C cm−2, was selected for subsequent experiments.

[0066] Effects of the hypophosphate concentration (CH2PO2−) on the EHD-AN performance of the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode:

[0067] Furthermore, various concentrations of sodium hypophosphite (CH2PO2−) were added to the electroplating solution to further regulate the EDH-AN performance of the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode. For this purpose, the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes were prepared in the plating solutions containing 0 M to 2 M of sodium hypophosphite, and the EDH-AN performance of the electrodes was investigated by performing a series of 2-h electrolysis in a 0.5 M phosphate buffer (pH 8, 36 mL) containing 0.6 M acrylonitrile and 30 mM tetrabutylammonium phosphate (TBAP) at japp=−100 mA cm−2.

[0068] FIG. 9a shows potential transients of CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes prepared in the electroplating solution containing 0 M to 2 M sodium hypophosphite at an operating current density of −100 mA cm−2. The results show that the potential required for the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes, prepared with different CH2PO2−, to maintain japp=−100 mA cm−2 was about-0.99 V vs. RHE. In addition, all the prepared CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes exhibited excellent stability in the 2-h electrolysis at japp=−100 mA cm−2.

[0069] As revealed in FIG. 9b-FIG. 9d, the CEADN and SADN of the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes prepared with different CH2PO2− were within a range of 78.5%-85.0% and 85.2%-89.4%, respectively. The result shows that regardless of the phosphorus content, the prepared CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes exhibited excellent EHD-AN performance, which confirms the beneficial role of metallic nickel in regulating the hydrogen adsorption capacity of the electrode surface. By facilitating hydrogen adsorption hydrogen on the nickel rather than bismuth, it successfully prevents the formation of the unstable bismuth hydride. As a result, the prepared CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes required less potential to maintain japp=−100 mA cm−2 and exhibited enhanced stability.

[0070] Effects of the applied current density for electrolysis (japp) on the EHD-AN performance of the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode:

[0071] Effects of japp were investigated using the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode prepared with 1 M sodium phosphate and a charge passage of 0.1 C cm−2. The effects of japp on the EDH-AN performance of the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode was analyzed by performing a series of electrolysis experiments in a 0.5 M phosphate buffer (pH 8, 36 mL) containing 0.6 M acrylonitrile and 30 mM tetrabutylammonium phosphate (TBAP) at various japp ranging from −100 mA cm−2 to −400 mA cm−2.

[0072] FIG. 10a-FIG. 10c show the potential transients recorded during the electrolysis experiments at various japp. In order to prevent the changes in the product distribution induced by the excessive consumption of acrylonitrile at high japp, the electrolysis at japp=−400 mA cm−2 was performed only for 1 hour. As revealed in FIG. 10a to FIG. 10c, regardless of japp, the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode exhibited enhanced stability and required less potential to maintain the specific applied current density as compared to the CuI—Bi electrode. As revealed in FIG. 10d-FIG. 10f, both CuI—Bi and CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes exhibited lower CEADN and SADN when the electrolysis experiments were performed at higher japp, which could be attributed to mass-transfer limitation induced by the rapid consumption of acrylonitrile at high japp. Nonetheless, the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode still exhibited better EDH-AN performance, in terms of CEADN, SADN, and RADN, than the CuI—Bi electrode regardless of japp, highlighting the beneficial role of Ni—NiFe(OH)x(r=0.5) catalytic layer in enhancing the EDH-AN performance.

[0073] The set-up of flow-type electrolyzer:

[0074] In order to mitigate the lower EDH-AN performance resulted from the mass-transfer limitation induced by the rapid consumption of acrylonitrile at high japp, a flow-type electrolyzer was subsequently established for the electrosynthesis of adiponitrile. As compared to the amount of acrylonitrile used for the electrosynthesis of adiponitrile using the H-type electrochemical cell, the amount of acrylonitrile used for the electrosynthesis of adiponitrile using the established flow-type electrolyzer was significantly increased by increasing the working volume of electrolyte solution to 60 mL or 250 mL, and increasing acrylonitrile concentration to 0.8 M. The anodic and cathodic compartments of the flow-type electrolyzer were separated with a Neosepta ASE anion exchange membrane (ASTOM Corporation, Tokyo, Japan). The CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes, prepared with 1 M sodium hypophosphite and charge passages ranging from 0.1 C cm−2 to 0.6 C cm−2, were used as the working electrode and placed with Ag / AgCl (sat'd KCl) reference electrode in the cathodic compartment, whereas the nickel foam was used as the counter electrode and placed in the anodic compartment. The flow rates of anolyte and catholyte solutions were controlled by diaphragm pumps.

[0075] FIG. 11a shows the potential transient recorded during the 2-h electrolysis at a japp=−200 mA cm−2 using the developed flow-type electrolyzer. As revealed, all the prepared CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrodes required lower potential to maintain japp=−200 mA cm−2 then the CuI—Bi electrode, which is in agreement with the results obtained using the H-type electrochemical cell. Moreover, the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode prepared with a charge passage of 0.1 C cm−2 required least potential to maintain japp=−200 mA cm−2, demonstrating its applicability for the electrosynthesis of adiponitrile in the flow-type electrolyzer.

[0076] As revealed in FIG. 11b-FIG. 11d, both the Cu—Bi electrode and the CuI—Bi / Ni NiFe(OH)x(r=0.5) electrode, prepared with a charge passage of 0.1 C cm−2, exhibited enhanced EDH-AN performance when the electrolysis experiments were performed in the flow-type electrolyzer. For example, CEADN and SADN of the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode, prepared with a charge passage of 0.1 C cm−2, were 68.5±2.2% and 74.6±3.0%, respectively, when the electrolysis experiments were performed using the flow-type electrolyzer, whereas those obtained were only 63.6±4.6% and 72.3±5.5% when the electrolysis experiments were performed using the H-type electrochemical cell. Additionally, the current efficiency (CEPN) and selectivity (SPN) for the production of propionitrile were reduced from 22.8±6.2% and 25.7±0.5% to 17.0±3.5% and 22.6±2.9%, respectively. These findings confirm the benefits of the use of flow-type electrolyzer and high EDH-AN performance of the CuI—Bi / Ni—NiFe (OH)x(r=0.5) electrode prepared with a charge passage of 0.1 C cm−2.

[0077] Effect of quaternary ammonium salts (QASs) on the EHD-AN performance of the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode:

[0078] Optionally, QASs may be selected from the group consisting of Tetrabutylammonium phosphate (TBAP), tetrapentylammonium bromide (TPAB), tetraethylammonium perchlorate (TEAP), and tributylmethylammonium (MBAP). In order to further confirm whether the beneficial role of the Ni—NiFe(OH)x catalytic layer in enhancing the EHD-AN performance of the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode is still applicable in different QASs, the EDH-AN performance of CuI—Bi and CuI—Bi / Ni—NiFe(OH)x (r=0.5) electrodes were analyzed by performing a series of electrolysis experiments in 0.5 M of phosphate buffer (pH 8, 60 mL) containing 0.8 M acrylonitrile and various types of QAS (30 mM) at japp=−200 mA cm−2.

[0079] As revealed in FIG. 12a, the potentials required for the CuI—Bi electrode to maintain japp=−200 mA cm−2 were around 1.2 V vs. RHE regardless of QAS used for the electrolysis. In addition, significant increases in the potential required for CuI—Bi electrode to maintain japp=−200 mA cm−2 were observed in the prolonged electrolysis in the electrolyte solution containing MBAP, TBAP, or TPAB, which suggests the CuI—Bi electrodes were not stable when electrolysis experiments were performed in the presence of MBAP, TBAP, or TPAB. As revealed in FIG. 12b-FIG. 12d, the CuI—Bi electrode exhibited lower CEADN and SADN when the electrolysis experiments were performed in the electrolyte solution containing TEAP or TPAB. TEAP is a QAS with a 2-carbon branched chain and thus lacks hydrophobicity, which allows water to easily approach the electrode surface and form adsorbed hydrogen, leading to the generation of the propionitrile by-product. TPAB, on the other hand, is a QAS with a 5-carbon branched chain, which is more hydrophobic. This results in a higher acrylonitrile concentration on the electrode surface, making it easier to form oligomers and thus leading to the generation of trimer by-product. The results show that the presence of QAS failed to help reduce the potential for the CuI—Bi electrode to maintain japp=−200 mA cm−2. Besides, the CuI—Bi electrode still suffered instability during the electrolysis.

[0080] As revealed in FIG. 13a, the potential required for the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode to maintain japp=−200 mA cm−2 was smallest when the electrolysis experiments were performed in the electrolyte solution containing TBAP. In addition, as revealed in FIG. 13b-FIG. 13d, the CEADN and SADN of the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode correlated with the hydrophobicity of QAS used for the electrolysis experiments. The increases in the CEADN and SADN in the presence of QASs with high hydrophobicity could be attributed to the fact that QAS can adsorb preferentially and form a hydrophobic layer on the electrode surface, which increases acrylonitrile concentration nearby the electrode surface and thus minimizes the access of electrode to water molecules and subsequent formation of adsorbed hydrogen atoms (Hads) and formation of propionitrile by-product. However, when the hydrophobicity of QAS was further increased (i.e., TPAB), the electrode surface would have significantly high acrylonitrile concentration, making it easier to form oligomers and thus leading to the generation of trimer by-product. As mentioned above, optimal CEADN and SADN can be obtained when electrolysis experiments were performed in the presence of TBAP.

[0081] In summary, compared to the CuI—Bi electrode, the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode has a lower operating potential, enhanced CEADN and SADN, and improved stability, further highlighting the importance of the Ni—NiFe(OH)x(r=0.5) catalytic layer.

[0082] Effect of TBAP concentration on the EHD-AN performance of the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode:

[0083] As revealed in FIG. 14a, the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode has the lowest operating potential in an electrolyte containing 30 mM of TBAP. In addition, a proper addition of TBAP (20 mM-40 mM) promoted improvements of CEADN, SADN, and RADN.

[0084] Long-term stability of the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode:

[0085] In order to demonstrate the feasibility and stability of the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode for industrial EHD-AN process, the EHD-AN performance of the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode was analyzed by performing a series of 8-h electrolysis experiments using the developed flow-type electrolyzer comprising 0.5 M of phosphate buffer (pH 8; 250 mL) containing 0.8 M acrylonitrile and 30 mM of TBAP at japp=−200 mA cm−2.

[0086] FIG. 15a shows EHD-AN potential transients recorded during the electrolysis at japp=−200 mA cm−2. It can be found that the potential required for the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode to maintain japp=−200 mA cm−2 increased from −0.96 V vs. RHE to −1.4 V vs. RHE. As revealed in FIG. 15b-FIG. 15d, the production of propionitrile became pronounced in the prolonged electrolysis. These findings would be attributed to the significant increase in electrolyte pH from 8 to 12 and consumption of acrylonitrile in the prolonged 8-h electrolysis. Nevertheless, the CuI—Bi / Ni—NiFe(OH)x(r=0.5) electrode still exhibited high CEADN (75.1±5.0%) and SADN (78.4±0.5%) after 8-h electrolysis.

[0087] In summary, the metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode prepared by the method of preparing a metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode can be used to synthesize adiponitrile through electrocatalytic hydrodimerization of acrylonitrile. Therefore, the problem of using toxic lead and cadmium electrode materials in the existing technologies could be addressed. Additionally, the stability of the electrolysis process is improved, and the energy consumption is further reduced. Moreover, the metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode can be applied to flow systems, thereby showing its applicability for the large-scale production of adiponitrile.

[0088] While the preferred embodiments of the present disclosure have been described above, it will be recognized and understood that various changes and modifications can be made, and the appended claims are intended to cover all such changes and modifications which may fall within the spirit and scope of the present disclosure.

Claims

1. A method of preparing a metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode, comprising steps of:preparing a plating solution containing 0.25 M ammonium chloride, 0.067 M to 0.133 M nickel chloride, 0.067 M to 0.133 M ferrous sulfate, and 0.04 M to 2 M sodium hypophosphite; placing a copper iodide-bismuth composite electrode in the electroplating solution to deposit metallic nickel / nickel-iron hydroxide catalytic layer onto the copper iodide-bismuth composite electrode, resulting in a metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode, CuI—Bi / Ni—NiFe(OH)x(r), wherein r is a molar ratio of nickel chloride to ferrous sulfate.

2. The method as claimed in claim 1, wherein the metallic nickel / nickel-iron hydroxide catalytic layer is electroplated onto the copper iodide-bismuth composite electrode at a constant current density of −10 mA cm−2.

3. The method as claimed in claim 1, wherein a time of depositing the metallic nickel / nickel-iron hydroxide catalytic layer onto the copper iodide-bismuth composite electrode ranges from 10 seconds to 60 seconds.

4. A metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode, CuI—Bi / Ni—NiFe(OH)x(r), prepared by the method as claimed in claim 1, wherein r is a molar ratio of nickel chloride to ferrous sulfate.

5. A method of preparing adiponitrile using the metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode as claimed in claim 4, comprising a step of: electrolyzing acrylonitrile at a constant current density of −100 mA cm−2 to −400 mA cm−2 in a phosphate buffer containing 0.6 M to 0.8 M acrylonitrile, using the metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode as claimed in claim 4, to synthesize adiponitrile.

6. The method as claimed in claim 5, wherein the metallic nickel / nickel-iron hydroxide catalytic layer-modified copper iodide-bismuth composite electrode is modified by electrodepositing a metallic nickel / nickel iron hydroxide catalytic layer with a charge passage ranging from 0.1 C cm−2 to 0.6 C cm−2.

7. The method as claimed in claim 5, wherein a concentration of the phosphate buffer is 0.5 M and a pH of the phosphate buffer is 8.

8. The method as claimed in claim 5, wherein the phosphate buffer further contains 20 mM to 40 mM quaternary ammonium salt, and the quaternary ammonium salt is represented by formula (I):wherein R1 to R4 are each independently a C2-5 hydrocarbon group, and X− is ClO4−, H2PO4−, or Br−.

9. The method as claimed in claim 5, wherein electrolysis of acrylonitrile is carried out in a H-type electrochemical cell or a flow-type electrolyzer.

10. The method as claimed in claim 9, wherein a flow rate in the flow electrolysis system is 722 sccm.

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