Catalyst and method for producing hydrogen through proton reduction

Abstract

The present invention relates to a catalyst comprising a divalent nickel complex, said complex comprising a 2, 2 '-thiophene-derived bis (thio-hemicarbazone) ligand, said divalent nickel complex being in accordance with the general formula [Chem 6]: [Chem 6] wherein R1 and R2 each independently represent phenyl, optionally have one or several identical or different substituents R3, optionally have one or several identical or different substituents R2, optionally have one or several identical or different substituents R3, optionally have one or several identical or different substituents R3, optionally have one or several identical or different substituents R4, optionally have one or several identical or different substituents R3, optionally have one or several identical or different substituents R4, optionally have one or several identical or different substituents R4, optionally have and R3 is selected from the group consisting of halogen, hydroxyl, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 sulfanyl, C1-C4 dialkylamino, cyano, a CF3 group and an O-CF3 group.

Description

Technical Field

[0001] This invention relates to a catalyst containing a divalent nickel complex containing a 2,2'-thiophene-derived bis(thiohexacarbazone) ligand, and its application in a proton reduction hydrogen production process.

[0002] This invention relates to the technical field of electrochemical hydrogen production. Background Technology

[0003] Faced with the depletion of fossil fuels (oil, coal, natural gas, etc.), environmental pollution, and climate anomalies primarily caused by human activities (such as greenhouse gas emissions like carbon dioxide and methane), the energy transition aimed at achieving carbon neutrality and gradually reducing dependence on fossil fuels has become a major issue of collective concern. In this context, hydrogen (more accurately, dihydrogen, H2) is expected to play a significant role in the global energy transition, namely, shifting towards economical energy sources, reducing dependence on fossil fuels, diversifying the energy structure, and achieving the goals of greenhouse gas emission reduction and climate protection.

[0004] Hydrogen is a gas with significant energy value due to its chemical properties. It has the highest energy density of all fuels (three times that of petroleum and 4.5 times that of coal). The energy contained in hydrogen can be harvested in two ways: by burning it or by converting it into electricity using fuel cells. In both cases, using hydrogen produces only water and no greenhouse gases. Furthermore, hydrogen can be stored, transported, and used after production.

[0005] Water electrolysis is a common method for producing hydrogen. It is an electrolytic reaction that uses an electric current to decompose water into its chemical components: hydrogen (H2) and oxygen (O2). The overall reaction formula [Chem 1] is shown below. Of course, no CO2 is emitted in this process.

[0006] [Chem 1]

[0007]

[0008] Furthermore, if the electricity comes from renewable energy sources, it can completely replace fossil fuels. Note that water is also a final product of the reaction between hydrogen (H2) and oxygen (O2), in which the energy of these fuels is released.

[0009] In an electrolysis system, the electrolysis of water proceeds through two half-reactions: a hydrogen release (H2) reaction at the cathode and an oxygen release (O2) reaction at the anode. The hydrogen and oxygen release reactions are dominant, according to equations [Chem 2] and [Chem 3] in acidic environments and [Chem 4] and [Chem 5] in alkaline environments.

[0010] [Chem 2]

[0011]

[0012] [Chem 3]

[0013]

[0014] [Chem 4]

[0015]

[0016] [Chem 5]

[0017]

[0018] In hydrogen production scenarios, water electrolysis requires the use of a catalyst to minimize the overvoltage required to activate the hydrogen release reaction (also known as the proton reduction reaction).

[0019] Different metals have been studied as catalysts for hydrogen release reactions. To date, the most effective catalysts are based on precious metals, such as platinum. However, the global scarcity and high cost of precious metals make them unsuitable for industrial use, especially for large-scale hydrogen production.

[0020] Recently, catalysts based on non-noble metal transition metals (such as cobalt, copper, iron, manganese, and nickel) have also been investigated as feasible alternatives for activating hydrogen release reactions due to their abundance in nature and low cost. Specifically, a large number of transition metal complexes with various ligand structures have been studied and tested as catalysts, exhibiting varying efficiencies.

[0021] Thiosemicarbazones are a highly attractive class of metal chelating ligands due to their coordination diversity. According to a 2017 article by Straistari T. et al., a divalent nickel complex with ligand 1,2-dimethyl-1,2-ethylenedione-1,2-di[(4-methoxyphenyl)hexacarbazone] (hereinafter referred to as the "NiTSC-OCH3 reference complex") can catalyze hydrogen release reactions, more specifically proton (H+) reactions. + The reaction involves the reduction of hydrogen to hydrogen gas. However, this nickel complex (NiTSC-OCH3) has been found to exhibit low catalytic activity in the hydrogen release reaction (hereinafter referred to as the "proton reduction reaction"). Therefore, it is desirable to improve the catalytic activity of the NiTSC-OCH3 reference complex to make it suitable for economical industrial-scale applications.

[0022] Therefore, it is still necessary to seek new proton reduction reaction catalysts that are effective and do not have the aforementioned defects.

[0023] One object of the present invention is to provide novel metal complexes suitable as catalysts for hydrogen release reactions. Another object of the present invention is to propose novel catalysts exhibiting good catalytic activity in hydrogen release reactions. A further object of the present invention is to provide such metal complexes and such catalysts that are stable and can be produced in a simple and low-cost manner. Summary of the Invention

[0024] Surprisingly, through in-depth research, the inventors of this invention discovered that at least one of the aforementioned objectives can be achieved using a divalent nickel complex containing a 2,2'-thiophene-derived bis(thiohexacarbazone) ligand (also known as bis(thiophene-2-yl)ethane-1,2-dione). In fact, this divalent nickel complex has been shown to exhibit very promising catalytic activity for the electrochemical reduction of protons to hydrogen, exhibiting low overpotential, high Faradaic efficiency, and good performance stability. Furthermore, its synthesis is simple and inexpensive.

[0025] Therefore, the divalent nickel complex proposed in this invention has great potential.

[0026] Therefore, according to a first aspect of the invention, a catalyst containing a divalent nickel complex comprising a 2,2'-thiophene-derived bis(thiohexacarbazone) ligand, said divalent nickel complex conforming to the following general formula [Chem 6]:

[0027] [Chem 6]

[0028]

[0029] Among them, R 1 and R 2 Each of these groups independently represents a phenyl group and may optionally have one or more identical or different substituents R. 3 ,

[0030] R 3 It is selected from halogens, C1-C4 alkyl groups, C1-C4 alkoxy groups, C1-C4 thioalkyl groups, C1-C4 alkylamino groups, C1-C4 dialkylamino groups, cyano groups, CF3 groups, and O-CF3 groups.

[0031] Preferably, when the phenyl group is replaced by one or more identical or different substituents R 3 When substituted, this or these substituents R 3 It can be selected from methyl, methoxy, methylthio, and dimethylamino.

[0032] Specifically, the R 1 and R 2 The functional groups are the same.

[0033] Preferably, the nickel complex is selected from nickel complexes conforming to the following formulas [Chem 7] to [Chem 11]:

[0034] [Chem 7]

[0035]

[0036] [Chem 8]

[0037]

[0038] [Chem 9]

[0039]

[0040] [Chem 10]

[0041]

[0042] [Chem 11]

[0043]

[0044] Advantageously, the catalyst of the present invention is suitable for catalytic reduction of protons to hydrogen.

[0045] According to another aspect, the present invention also relates to the use of the catalyst of the present invention for the catalytic reduction of protons to hydrogen.

[0046] According to another aspect, the present invention also proposes a method for producing hydrogen, comprising contacting a proton source with the catalyst of the present invention in an electrochemical cell and applying a potential to the electrochemical cell, thereby reducing these protons to hydrogen.

[0047] According to another aspect, the present invention also relates to divalent nickel complexes conforming to the aforementioned general formula [Chem 6]. Attached Figure Description

[0049] Other advantages and features of the invention will be better understood by reading the following description of preferred embodiments and by referring to the accompanying drawings, which are given as indicative and non-limiting examples, wherein:

[0050] Figure 1 This diagram illustrates the overall synthesis of 2,2'-thiophene-derived bis(thiohexacarbazone) ligands, whose structure is asymmetric (R... 1 ≠ R 2 ).

[0051] Figure 2 A schematic diagram of the overall synthesis of 2,2'-thiophene-derived bis(thiohexacarbazone) ligands is shown, with a symmetrical structure.

[0052] Figure 3 A schematic diagram of the overall synthesis of the divalent nickel complex of the present invention is shown (where R 1 = R 2 or R 1 ≠ R 2 ).

[0053] Figure 4 A graphical overview of the UV-Vis spectrum of the divalent nickel complex (hereinafter referred to as Ni(thenil)TSC-OCH3 complex) prepared in Example 1a in a 0.05 M DMF solution is shown.

[0054] Figure 5 An ORTEP (Oak Ridge Thermal Ellipsoid) plot of the divalent nickel complex prepared in Example 1a is shown, based on X-ray crystallographic analysis. The ellipsoids are represented with a probability of 50%. Hydrogen atoms have been removed for clarity.

[0055] Figure 6 The graph shows Ni(thenil)TSC-OCH3 (1.0 mmol·L⁻¹) -1 The complex in n-Bu4NPF6 (0.1 mol·L⁻¹) -1 In a DMF solution, a fixed glassy carbon electrode with a diameter of 1 mm was used at a rate of 0.1 Vs⁻¹ to 2 Vs. -1 Cyclic voltammetry plots recorded at different scan rates.

[0056] Figure 7 The figure shows the Ni(thenil)TSC-OCH3 complex (1.0 mmol·L⁻¹). -1 In the presence of trifluoroacetic acid {(A) 0 mmol.L} -1 (B) 20 mmol.L -1 (C) 40 mmol.L -1 (D) 60 mmol.L -1 (E) 80 mmol.L -1 (F) 100 mmol.L -1} or only ((G) 100.0 mmol.L) -1 In the case of n-Bu4NPF6 (0.1 mol·L⁻¹), -1 In a DMF solution, a fixed glassy carbon electrode with a diameter of 1 mm was used at a voltage of 0.5 V / s. -1 The rate was recorded in the cyclic voltammogram.

[0057] Figure 8The figure shows the Ni(thenil)TSC-OCH3 complex (1.0 mmol·L⁻¹). -1 In the presence of trifluoroacetic acid {(A) 0 mmol.L} -1 (B) 20 mmol.L -1 (C) 40 mmol.L -1 (D) 60 mmol.L -1 (E) 80 mmol.L -1 (F) 100 mmol.L -1 In the case of n-Bu4NPF6 (0.1 mol·L⁻¹), -1 In a DMF solution, using a glassy carbon electrode, at a voltage of 0.5 Vs -1 The rate was recorded in the cyclic voltammogram.

[0058] Figure 9 The graph shows the time taken in 0.5 seconds. -1 The cyclic voltammogram was recorded using a glassy carbon electrode, which was used for cyclic voltammetry measurements of the Ni(thenil)TSC-OCH3 complex, followed by fresh n-Bu4NPF6 (0.1 mol·L⁻¹). -1 Washed with DMF solution, then in the presence of trifluoroacetic acid {(A) 0 mmol.L -1 (B) 100 mmol·L -1 In the case of}, it is immersed in the fresh solution.

[0059] Figure 10 The graph shows the (thenil)TSC-OCH3 complex (1.0 mmol·L⁻¹). -1 In the presence and absence of trifluoroacetic acid {(A) 100 mmol·L -1 (B) 0 mmol.L -1 In the case of n-Bu4NPF6 (0.1 mol·L⁻¹), -1 In 8 ml of DMF solution, using a mercury electrode, at -1.70 Vs -1 The rate was recorded in the coulomb measurement curve.

[0060] Figure 11 The (thenil)TSC-OCH3 complex (0.05 mmole L) was shown. -1 DMF solution in the presence and absence of trifluoroacetic acid {(A) 0 mmol.L} -1 (B) 2.5 mmol.L -1 (C) 5 mmol.L -1 The ultraviolet-visible spectrum under the condition of}. Detailed Implementation

[0061] This specification is non-limiting, and each feature set forth in only one embodiment can be extended to other embodiments described herein or the foregoing summary of the invention. Similarly, one or more features set forth in only one embodiment can be combined with one or more other features set forth in another embodiment. It should now be noted that the drawings are highly simplified, and therefore the elements shown therein or between different drawings are not necessarily drawn to scale.

[0062] This invention is based on the accidental discovery that divalent nickel complexes with 2,2'-thiophene-derived bis(thiohexacarbazone) ligands exhibit enhanced electrocatalytic activity in the reduction of protons to hydrogen.

[0063] In fact, divalent nickel complexes can catalyze proton (H) + They are reduced to hydrogen (H2), especially with an increase in overvoltage (η), switching frequency (TOF), and Faraday efficiency (FY). They are also very stable under acidic conditions.

[0064] This invention first relates to a catalyst containing a divalent nickel complex, specifically having a 2,2'-thiophene-derived bis(thiohexacarbazone) ligand. This divalent nickel complex conforms to the general formula [Chem 6]:

[0065] [Chem 6]

[0066]

[0067] Among them, R 1 and R 2 Each of these groups independently represents a phenyl group and may optionally have one or more identical or different substituents R. 3 ,

[0068] R 3 It is selected from halogens, hydroxyl groups, C1-C4 alkyl groups, C1-C4 alkoxy groups, C1-C4 thioalkyl groups, C1-C4 dialkylamino groups, cyano groups, CF3 groups, and O-CF3 groups.

[0069] Throughout this specification, the following expressions may be used indiscriminately and equivalently: “nickel complex”, “divalent nickel complex”, “divalent Ni complex” and “the complex of the present invention”.

[0070] In this invention, the term "halogen" refers to an atom selected from fluorine, chlorine, bromine, and iodine atoms.

[0071] In this invention, the term "hydroxyl group" refers to the -OH group.

[0072] In this invention, the term "C1-C4 alkyl" refers to a straight-chain or branched saturated aliphatic substituent containing 1-4 carbon atoms. Examples include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, and tert-butyl groups.

[0073] In this invention, the term "C1-C4 alkoxy" refers to a straight-chain or branched saturated alkane with 1-4 carbon atoms (as described above) bonded by an oxygen atom, that is, for example, any one of methoxy, ethoxy, n-propoxy, isopropoxy (or 1-methylethoxy), n-butoxy, isobutoxy (or 1-methylpropoxy), tert-butoxy (or 2-methylpropoxy or 1,1-dimethylethoxy) radicals.

[0074] The term "C1-C4 alkylamino" in this invention refers to a (-NH2) group, wherein the nitrogen atom is replaced by a C1-C4 alkyl group. The term "C1-C4 alkyl" is as described above. Examples of C1-C4 alkylamino groups include methylamino, ethylamino, n-propylamino, isopropylamino, n-butylamino, or tert-butylamino.

[0075] The term "C1-C4 dialkylamino" in this invention refers to a (-NH2) group, wherein nitrogen is replaced by two identical or different C1-C4 alkyl groups. The term "C1-C4 alkyl" is as described above. Examples of C1-C4 dialkylamino groups include dimethylamino, diethylamino, ethylmethylamino, methyl(n-propyl)amino, ethyl(n-propyl)amino, di(n-propyl)amino, methyl(n-butyl)amino, ethyl(n-butyl)amino, di(n-butyl)amino, or methyl(tert-butyl)amino.

[0076] In this invention, the term "C1-C4 thioalkyl" refers to a straight-chain or branched saturated alkyl group having 1-4 carbon atoms (as described above) bonded by sulfur atoms, that is, for example, any one of methylthio, ethylthio, n-propylthio, isopropylthio (or 1-methylethylthio), n-butylthio, isobutylthio (or 1-methylpropylthio), tert-butylthio (or 2-methylpropylthio or 1,1-dimethylethylthio) radicals.

[0077] Specifically, R 1 and R 2 One or more optional substituents R of the phenyl group 3 The group is selected indiscriminately from hydroxyl, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 thioalkyl, C1-C4 dialkylamino, CF3 group and O-CF3 group.

[0078] As R 1 and R 2Specific examples of functional groups include the following: phenyl, 4-methylphenyl, 4-(trifluoromethyl)phenyl, 2-methylphenyl, 2,4-dimethylphenyl, 3,4-dimethylphenyl, 4-ethylphenyl, 4-isopropylphenyl, 4-tert-butylphenyl, 4-hydroxyphenyl, 4-methoxyphenyl, 2,4-dimethoxyphenyl, 3,4-dimethoxyphenyl, 4-(trifluoromethoxy)phenyl, 4-chlorophenyl, 4-fluorophenyl, 4-(methylthio)phenyl, 4-(N,N-dimethylamino)phenyl, and 4-cyanophenyl.

[0079] Preferably, R 1 and R 2 One or more optional substituents R of the phenyl group 3 The group is selected indiscriminately from hydroxyl, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 thioalkyl, and C1-C4 dialkylamino, specifically from methyl, methoxy, methylthio, and dimethylamino.

[0080] Preferably, R in the complex conforming to the general formula [Chem 6] 1 and R 2 The functional groups are the same.

[0081] In the divalent nickel complex of general formula I, where R 1 and R 2 The functional groups are identical, and in particular, complexes conforming to the following general formulas [Chem 7] to [Chem 11] can be listed:

[0082] [Chem 7]

[0083]

[0084] [Chem 8]

[0085]

[0086] [Chem 9]

[0087]

[0088] [Chem 10]

[0089]

[0090] [Chem 11]

[0091]

[0092] Synthesis method:

[0093] This invention also relates to the preparation of divalent nickel complexes of the general formula [Chem 6] and their corresponding ligands.

[0094] The nickel complexes and their corresponding ligands of the present invention can be synthesized by any suitable method, including but not limited to the methods described herein.

[0095] General formula [Chem 6] (where R) 1 and R 2 Examples of methods for synthesizing different nickel complex ligands are shown in Figure 1.

[0096] General formula [Chem 6] (where R) 1 and R 2 Another example of a method for synthesizing nickel complex ligands (of the same nature) is as follows: Figure 2 As shown.

[0097] Examples of methods for synthesizing nickel complexes of general formula [Chem 6] are as follows: Figure 3 As shown:

[0098] Reference Figure 1 The synthesis of ligands for the complexes of the present invention, wherein R 1 and R 2 The differences include the following steps:

[0099] i) React 2,2'-thiophene (1) with one molar equivalent of aminothiourea of ​​formula (5), wherein R 1 As defined by general formula [Chem 6], the intermediate product of formula (2) is obtained, where R 1 As defined by general formula [Chem 6];

[0100] ii) React the product of formula (2) with one molar equivalent of aminothiourea of ​​formula (5), wherein R 2 As defined by general formula [Chem 6], the ligands of formula (3), where R １ and R 2 As defined by general formula [Chem 6] (where R... 1 ≠ R 2 ).

[0101] The intermediates of formula (2) and the ligands of formula (3) obtained in steps (i) and (ii), respectively, can be purified according to any conventional purification method known to those skilled in the art, for example, by recrystallization in one or more suitable solvents, or by chromatography, particularly silica gel column chromatography. They can also be used immediately after their respective steps (i) and (ii) without purification.

[0102] Reference Figure 2 Synthesis of complex ligands of general formula [Chem 6], wherein R 1 and R 2 The same applies, including the following steps:

[0103] i') React 2,2'-thiophene (1) with at least two molar equivalents of aminothiourea of ​​formula (5), wherein R 1 As defined by general formula [Chem 6], the ligands of formula (4), where R 1 As defined by general formula [Chem 6].

[0104] Similarly, the ligand of formula (4) obtained in step (i') above can be purified according to any conventional purification method known to those skilled in the art, for example, by recrystallization in one or more suitable solvents, or by chromatography, particularly silica gel column chromatography. It can also be used immediately after step (i') without purification.

[0105] Figure 1 (Steps (i) and (ii)) and Figure 2 The reaction shown in step (i') is typically carried out using an organic solvent, such as ethanol, methanol or toluene, at a temperature typically between 15°C and 150°C, for example under ethanol reflux conditions.

[0106] If necessary, these reactions can be carried out in the presence of an acidic catalyst, such as hydrochloric acid, acetic acid, trifluoroacetic acid, or other suitable acidic catalysts.

[0107] The aminothioureas of formulas (5) and (6) used are generally available on the market, for example from Sigma-Aldrich or Merck, or can be obtained by reacting, for example, hydrazine (NH2-NH2) with the corresponding general formula R 1 -N=C=S or R 2 The reaction of -N=C=S isothiocyanates is prepared, wherein R 1 and R 2 As defined by general formula [Chem 6]. The general formula is R. 1 -N=C=S(or R) 2 Isothiocyanate reagents (-N=C=S) are commercially available or obtained by methods described in the literature, or can be prepared according to methods described in the literature or methods known to those skilled in the art (e.g., see the article by Srivastava K. 2020).

[0108] Reference Figure 3 The synthesis of the nickel complex in this invention includes the following steps:

[0109] iii) React the ligands of formula (3) or (4) obtained above with nickel salts to generate nickel complexes of general formula [Chem 6] (R , R ... 1 ≠R 2 or R 1 =R2 ).

[0110] The reaction in step (iii) above is typically carried out in an organic solvent, such as ethanol, methanol, or toluene, at a temperature between 15°C and 150°C (e.g., under reflux of ethanol). Nickel chloride hexahydrate, nickel nitrate hexahydrate, or nickel acetate tetrahydrate can be used as the nickel salt.

[0111] The nickel complex obtained in step (iii) above can be purified according to any conventional purification method known to those skilled in the art, for example, by recrystallization in one or more suitable solvents, or by chromatography, particularly neutral aluminum (Al2O3) column chromatography.

[0112] In summary, the present invention relates to a method for preparing divalent nickel complexes of the general formula [Chem 6], comprising the following steps:

[0113] (a) Provide ligands of formula (3) or (4),

[0114] (b) Reacting the ligand of formula (3) or (4) with a nickel salt to obtain the desired divalent nickel complex (R3 or R4 respectively). 1 ≠ R 2 or R 1 = R 2 ).

[0115] Catalytic applications:

[0116] The nickel complexes of this invention exhibit significant electrocatalytic efficiency in the catalytic reduction of protons. This fully demonstrates their usefulness as catalysts, and more specifically as electrocatalysts in the electrochemical reaction of proton reduction to hydrogen (molecular hydrogen (H2)).

[0117] Furthermore, this invention also relates to the use of the nickel complexes described above as catalysts for promoting the electrochemical reaction of proton reduction. Such catalysts can be homogeneous or heterogeneous.

[0118] In this invention, the term "homogeneous catalyst" refers to a catalyst that exists in the same liquid phase (or electrolyte solution) as the proton source during the electrochemical reaction of proton reduction. Specifically, a homogeneous catalyst is a catalyst that is at least partially soluble in the solvent (or electrolyte solution) in which the proton reduction electrochemical reaction takes place.

[0119] In this invention, the term "heterogeneous catalyst" refers to a catalyst that exists in a different phase (or electrolyte solution) from the proton source during the electrochemical reaction of proton reduction. Specifically, a heterogeneous catalyst is a catalyst deposited, adsorbed, or printed on the electrode surface, or adsorbed onto a substrate (polymer material (e.g., Nafion®), metal, or ceramic) deposited on the electrode surface.

[0120] The term "electrode" refers to a current conductor used to establish contact with a non-metallic part of a circuit (such as an electrolytic solution). An electrode can also refer to an anode (or negative electrode) or a cathode (or positive electrode). Current conductors can be made of metallic materials (e.g., aluminum, copper, titanium, and the like), carbon materials (e.g., one or more allotropes of carbon, such as glassy carbon, graphene, graphite, amorphous carbon, activated carbon, carbon nanotubes, and carbon fibers, and the like), (semi)conductive polymers (e.g., polyacetylene, polyphenylene, and polypyrrole), and combinations thereof.

[0121] Conventional modified electrode manufacturing methods can be used, such as preparing catalysts by deposition, adsorption or printing (e.g. printing or depositing inks based on carbon materials such as graphite and catalysts on the electrode) (see references: WO2009098403A2; WO2005088657A2).

[0122] Immobilizing (or depositing, printing, adsorbing, etc.) catalysts on the electrode surface has many advantages, including:

[0123] - Optimize the use of catalysts to reduce costs and minimize catalyst loss;

[0124] - Improved exposure of catalytic sites: Due to direct connection to the electrode, the catalyst is optimally exposed, thereby promoting the desired chemical reaction.

[0125] - Improved diffusion kinetics: Immobilizing the catalyst on the electrode surface facilitates the diffusion of reactants (such as protons) to the catalytic site, which accelerates the electrochemical reaction.

[0126] - Overcoming solubility challenges: Organic catalysts are poorly soluble or insoluble in water. Heterogeneous systems allow these catalysts to overcome these challenges, enabling their use in proton-rich aqueous solutions.

[0127] - Easier to determine catalyst lifetime: By monitoring the performance of a stationary catalyst over time, its durability can be more easily assessed.

[0128] - The electrode properties exhibit good repeatability: The electrode with integrated catalyst exhibits repeatable properties, thus ensuring the consistency of experimental results.

[0129] The present invention also relates to a method for producing hydrogen (H2), comprising using a proton source (H2) in an electrochemical cell. + () is contacted with the catalyst of the present invention, and a potential is applied to the electrochemical cell, thereby causing these protons (H) to be in contact with the catalyst of the present invention and to be subjected to a potential ... applied to the electrochemical cell. + It is reduced to hydrogen gas (H2).

[0130] Typically, an electrochemical cell includes a working electrode, a counter electrode, and, if necessary, a reference electrode, all of which are immersed in an electrolyte solution that allows ions to be transferred from the working electrode to the counter electrode.

[0131] Electrochemical cells can be designed in two main ways: they can be membrane-free cells or cells divided into at least two independent compartments. In the latter case, one compartment contains the working electrode, while the other contains the counter electrode. These compartments are separated by a membrane, which can take the form of a membrane permeable to ions in an electrolyte carrier, for example. Generally, membrane-free electrochemical cells are preferred. Electrochemical cells and methods for their manufacture are known to those skilled in the art.

[0132] In this invention, the term "working electrode" refers to the electrode of an electrochemical cell on which relevant electrochemical reactions, such as the reduction of protons to hydrogen, occur.

[0133] The term "counter electrode" refers to the auxiliary electrode in an electrochemical cell, which completes the electrochemical circuit and allows current to flow through the cell. Typically, a potential is applied between the working electrode and the counter electrode to allow relevant electrochemical reactions (such as the reduction of protons to hydrogen) to occur.

[0134] The term "electrolytic solution" in this invention refers to a solution containing an electrolyte and a solvent. The electrolyte is an ion (e.g., H+). + OH - Li + (C4H9)4N + OH - BF4 - PF6 - CF3-SO3 - (CF3-SO2)2N - These ions, such as cations and anions, facilitate the flow of electric current in the electrolyte solution. Specifically, the term "electrolyte" applies to ions that actively participate in the transport of electric current. Therefore, the electrolyte solution is conductive. Electrolytes can be obtained, for example, by dissolving the salts corresponding to the combinations of cations and anions in the electrolyte solution.

[0135] Typically, at room temperature (about 25°C), the divalent nickel complexes of the present invention exhibit good solubility (≥0.5 M) in a variety of organic solvents and various water-organic solvent mixtures. Suitable organic solvents for the electrochemical reaction of proton reduction include aprotic solvents, selected from amides, carbonates, ketones, aromatic compounds, esters, ethers, nitriles, halogenated solvents, sulfoxides, and mixtures thereof. Examples of amides include, but are not limited to, N,N-dimethylformamide (DMF) and N-methyl-2-pyrrolidone (NMP). Examples of suitable carbonates include, but are not limited to, propylene carbonate, ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate. Examples of ketones include, but are not limited to, acetone, butanone, diethyl ketone, and cyclohexanone. Examples of aromatic compounds include, but are not limited to, benzene, toluene, xylene, chlorobenzene, and nitrobenzene. Examples of esters include, but are not limited to, ethyl acetate and methyl acetate. Examples of suitable ethers include, but are not limited to, diethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, and 1,4-dioxane. Examples of suitable nitriles include, but are not limited to, acetonitrile and propionitrile. Examples of suitable halogenated solvents include, but are not limited to, dichloromethane, trichloromethane, and tetrachloromethane. Examples of suitable sulfoxides include, but are not limited to, dimethyl sulfoxide (DMSO).

[0136] Therefore, when using the divalent nickel complex of the present invention as a homogeneous catalyst, one or more alternatives to the above-mentioned aprotic solvents can be used as solvents in the electrolyte solution.

[0137] As the electrolyte, a salt that is at least partially soluble in the electrolyte solution is preferred, particularly a solvent soluble in the electrolyte. Non-limiting examples of electrolytes include tetrabutylammonium hexafluorophosphate (n-Bu4NPF6 or NBu4PF6), tetrabutylammonium tetrafluoroborate (n-Bu4NBF4), lithium hexafluorophosphate (LiPF6), and lithium bis(trifluoromethanesulfonyl)imide. In practical operation, the electrolyte concentration in the electrolyte solution is 0.01-5.00 mol / L, preferably 0.05-3.00 mol / L, specifically 0.10-1.00 mol / L.

[0138] The method of the present invention includes making a proton source (H + The catalyst (homogeneous or heterogeneous) of the present invention is in contact with the catalyst. The term "proton source" in this invention refers to a source capable of providing at least one proton (H+) in the reaction of proton reduction to hydrogen. +Compounds, compositions, or materials thereof. Suitable proton sources include organic acids, including carboxylic acids such as acetic acid, propionic acid, trifluoroacetic acid (TFA), and citric acid; organic sulfonic acids such as methanesulfonic acid, ethanesulfonic acid, and p-toluenesulfonic acid; organic phosphonic acids such as methylphosphonic acid, ethylphosphonic acid, phenylphosphonic acid, nitrophenylphosphonic acid, and chlorophenylphosphonic acid; bis(sulfonyl)imides such as bis(trifluoromethanesulfonyl)imide; organic ammonium salts such as triethyltetrafluoroborate ammonium, benzyldiethyltetrafluoroborate ammonium, benzyldiethylammonium chloride, and hexadecyldimethylammonium chloride; phenols such as phenol; inorganic acids such as sulfuric acid and hydrochloric acid; and combinations of at least two of these proton sources.

[0139] In practice, the proton source (H+) is added to the electrolyte solution to make the proton source (H+) + ( ) in contact with the catalyst. The concentration of the proton source in the electrolyte solution can be 10 -2 Between 10 mol / L and 5 mol / L, for example, at 10 mol / L -2 Between 10 mol / L and 2 mol / L, more specifically between 10 mol / L and 2 mol / L. -2 mol / L to 10 -1 Between mol / L.

[0140] In one embodiment of the invention, the divalent nickel complex of the invention is used as a homogeneous catalyst. In this case, it is at least partially present in the electrolyte solution, preferably completely dissolved. Its concentration in the electrolyte solution can be 10... - 4 Between 10 mol / L and 2 mol / L, for example, at 10 mol / L -4 Between mol / L and 1 mol / L, more specifically in the range of 10 mol / L -4 mol / L to 10 -1 Between mol / L.

[0141] The reaction that reduces protons to hydrogen is accomplished by applying a voltage to the terminals of the working and counter electrodes of an electrochemical cell, in order to reduce protons (H+) to hydrogen gas. + It is reduced to hydrogen gas (H2).

[0142] Typically, the electrochemical cells used consist of multiple components, including a working electrode (modified or unmodified), a counter electrode, and a reference electrode.

[0143] A "reference electrode" is an electrode that provides a stable and constant potential, regardless of the type or concentration of substances present in the electrolyte solution in which the reference electrode is located. Therefore, a significant change in the potential of the working electrode combined with the reference electrode can be detected. These significant changes can be detected by comparing the change in the constant potential of the working electrode relative to the reference electrode. Non-limiting examples of reference electrodes include a silver electrode with a silver / silver chloride pair (hereinafter referred to as Ag / AgCl), a standard hydrogen electrode (EHS), a calomel standard electrode (ECS), and a reversible hydrogen electrode (EHR).

[0144] Electrochemical cells can also be equipped with potentiostats (such as the Origaflex OGF01A potentiostat), which allow a voltage to be applied between the working electrode and the counter electrode of the electrochemical cell and the generated current to be measured.

[0145] Potential is typically measured (or applied) using a potentiostat-like device with reference to a reference electrode. In practice, ferrocene or similar internal standards such as cobalt cadmium are used to calibrate the potential of the reference electrode (e.g., an Ag / AgCl electrode). The use of internal standards such as ferrocene ions / ferrocene (Fc+ / Fc+) is known. 0 ) or (Fc + / 0 A redox pair, suitable for electrolysis experiments in non-aqueous media. Fc + / 0 Redox pairs relative to Ag / Ag + The electrode potential is 0.5 ± 0.2 V.

[0146] Advantageously, the potential applied to the working electrode is below 0 V (e.g., relative to Fc). + / 0 Especially below -0.5 V (e.g., relative to Fc) + / 0 Specifically, below -1.0 V (e.g., relative to Fc). + / 0 More specifically, the applied potential is between -2.5 and -1.0 V (e.g., relative to Fc). + / 0 More specifically, between -2.0 V and -1.5 V (e.g., relative to Fc). + / 0 ).

[0147] The hydrogen production method of the present invention can be carried out under a wide range of operating temperatures or pressures; it is particularly preferred to operate at temperatures between room temperature and 100°C and pressures between atmospheric pressure and 30 bar.

[0148] The proton reduction of the present invention can be carried out for more than 1 minute, especially between 1 minute and 30 hours, specifically between 2 hours and 20 hours.

[0149] This invention has a wide range of industrial applications, particularly for hydrogen production, for use in clean energy production, chemical manufacturing, and other fields that require hydrogen sources.

[0150] In the following descriptions and examples, the range of values ​​given in the form of "between..." includes the specified upper and lower limits.

[0151] Furthermore, all reference numerals in parentheses in the claims shall not be construed as limiting the claims. Additionally, the use of the verbs “having,” “comprising,” or “including,” and variations thereof, does not exclude elements or steps other than those listed in the claims.

[0152] Other features and advantages of the invention will be better presented through the following examples, which are exemplary and not limiting. The scope of the invention should in no way be limited to these examples.

[0153] Example:

[0154] Example 1: Preparation, characterization, and electrochemical behavior study of the divalent nickel complex of the present invention.

[0155] The following description refers primarily to the preparation and use of the divalent nickel complex “Ni(thenil)TSC-OCH3”, namely 2,3-bis(4-(methoxyphenyl-thiohexacarbazone)-2,2'-(but-1,3-diene-2,3-diyl)dithiophene nickel (II). However, it is obvious that this description also applies to all divalent nickel complexes of formula (I) in this invention, provided that necessary adjustments are made to the methods and means of implementation, which can be easily implemented by those skilled in the art.

[0156] Example 1a: 2,3-Di(4-(methoxyphenyl-thiohexacarbazone)-2,2'-(but-1,3-diene-2,3-diyl) Synthesis of Ni(thenil)TSC-OCH3

[0157]

[0158] The Ni(thenil)TSC-OCH3 complex is based on Figure 4 The method and with Figure 5 The method was combined to synthesize the product, but the intermediate product of dithiohexacarbazone ligand was not isolated.

[0159] 2,2'-Thiophene (100 mg, 0.450 mmol) and N-(4-methoxyphenyl)-hydrazine thiocarbamate (222 mg, 1.124 mmol) and a few drops of acetic acid were added to 10 mL of ethanol. The mixture was then refluxed with ethanol and stirred for 6 hours. After the reflux, the mixture was cooled to room temperature to obtain a solution containing a dithiohexacarbazone ligand intermediate. Nickel acetate tetrahydrate “Ni(CH3COO)2,4H2O” (168 mg, 0.675 mmol) was added to this solution. The mixture was then refluxed with ethanol and stirred for 4 hours. After the reflux, the solution was cooled to room temperature. Triethylamine (1 mL) and water (80 mL) were added to the cooled solution. The solution was then filtered to obtain a crude solid containing the Ni(thenil)TSC-OCH3 complex. The crude solid was washed with water and ethanol and then filtered. The remaining solid was dissolved in tetrahydrofuran (THF), filtered, and concentrated under reduced pressure to obtain a solid. The solid was purified by neutral alumina (Al₂O₃) column chromatography (7 / 3 dichloromethane / cyclohexane) to give a dark brown solid Ni(thenil)TSC-OCH₃ complex (47 mg, 16%). 1 H (500 MHz, DMSO-d6, TMS): δ:10.23 (s, 2H), 7.89 (dd, J1= 1.08, J2= 5.03 Hz, 2H), 7.49 (d, J= 8.40 Hz, 4H), 7.04 (t, J= 3.85Hz, 2H), 6.86-6.84 (m, 6H), 3.73 (s, 6H) ppm.RMN 13 C (125 MHz, DMSO-d6, TMS): δ: 173.28 (N=CS), 156.68 (OC=C), 133.91 (NC=C), 132.90 (CC=N), 132.60 (SC=C), 131.33 (C=CC), 127.08 (C=CC), 123.10 (oCC=C), 120.80 (CC=C), 114.59 (mC=CC), 56.15 (COC) ppm. HRMS ESI m / z:[MH] - C 26 H 21 N6O2S4Ni - Calculated value: 634.9968, confirmed value: 634.9967.

[0160] Ultraviolet-Visible Light:

[0161] The electronic structure of the Ni(thenil)TSC-OCH3 complex was characterized by ultraviolet-visible spectroscopy.

[0162] The UV-Vis spectrum of the Ni(thenil)TSC-OCH3 complex of Example 1a was recorded at room temperature in 0.05 M DMF. See Figure 4 The obtained UV-Vis spectrum indicates three electronic absorption bands located at: 273 nm (ε = 41963 M). -1 cm -1 ), 353 nm (ε=16592 M) -1 cm -1 ) and 516 nm (ε=16600 M) -1 cm -1 ).

[0163] Crystal structure:

[0164] Crystals of the Ni(thenil)TSC-OCH3 complex in Example 1a were obtained by slow evaporation of a 50 / 50 (V / V) mixture solution of dichloromethane and cyclohexane of this complex.

[0165] The crystal structure was determined by X-ray diffraction.

[0166] Figure 5 The ORTEP diagram of the formed complex is shown, with atom numbers. Hydrogen atoms have been removed for clarity. Ellipsoids are represented with a probability of 50%.

[0167] Table 1 below lists the crystallographic data, diffraction intensity collection conditions, and processing methods for the Ni(thenil)TSC-OCH3 complex of Example 1a:

[0168] [Table 1]

[0169]

[0170]

[0171] Table 1 shows that the Ni(thenil)TSC-OCH3 complex crystallizes in the monoclinic system (space group P21).

[0172] ORTEP diagram ( Figure 5 This shows that nickel ions exhibit a distorted planar tetragonal coordination geometry commonly found in neutral mononuclear divalent nickel complexes.

[0173] The key geometric parameters determined based on the crystal structure of the Ni(thenil)TSC-OCH3 complex in Example 1a are shown in Table 2 below.

[0174] [Table 2]

[0175]

[0176] Electrochemical research:

[0177] The electrochemical properties of the Ni(thenil)TSC-OCH3 complex were investigated using cyclic voltammetry (CV) and controlled-potential coulometric analysis (also known as controlled-potential electrolysis (large-scale) method).

[0178] Cyclic voltammetry:

[0179] The electrochemical behavior of the Ni(thenil)TSC-OCH3 complex (1 mM) in DMF was investigated, with 0.1 M tetrabutylammonium hexafluorophosphate (NBu4PF6) as the carrier electrolyte and trifluoroacetic acid (TFA) as the proton donor when necessary.

[0180] Cyclic voltammetry (CV) measurements were performed using an Origaflex OGF01A potentiometer. Measurements were conducted at room temperature, using a degassed solution, under a nitrogen atmosphere.

[0181] The CV measurements used a conventional three-electrode system (electrochemical cell), comprising a glassy carbon fixed electrode (1 mm in diameter) as the working electrode, a counter electrode made of platinum wire, and a silver chloride reference electrode (AgCl) using a silver / silver chloride (Ag / AgCl) pair. The capacity of the electrochemical cell in this system was approximately 10 mL.

[0182] In these electrochemical studies, redox effects on Fc + / 0 (The abbreviation for ferrocene) is used as an internal standard to calibrate the potential recorded on the glassy carbon (GC) working electrode in DMF. Note that E is relative to Ag / AgCl. 0 (Fc + / 0 = 0.52 V. Now all the measured potential values ​​will be listed relative to this redox pair.

[0183] The inventors conducted the first set of CV measurements on the Ni(thenil)TSC-OCH3 complex (1 mM) in DMF, with 0.1 M NBu4PF6 present during the measurements, using different potential scan rates (0.1-2 Vs). -1 The cyclic voltammogram recorded on the GC electrode is shown below. Figure 6As shown. These cyclic voltammograms indicate that the Ni(thenil)TSC-OCH3 complex exhibits quasi-irreversible electrochemical behavior during the cathode region scan from 0 to -2.65 V. Figure 6 As shown, two quasi-reversible peaks were observed at each potential scan rate, with the first cathode peak at approximately -2.0 V and the second cathode peak at approximately -1.34 V. These two observed quasi-reversible waves can be attributed to [Ni...] II (thenil)TSC-OCH3] •– and [Ni I (thenil)TSC-OCH3] 2- The formation of these compounds has been confirmed through quantum chemical modeling and is consistent with relevant observations of the NiTSC-OCH3 reference complex (see Straistari, T. et al., 2017).

[0184] in addition, Figure 6 The cyclic voltammogram shown also exhibits the first set of anodic peaks, approximately -1.9 V, and the second set of anodic peaks, approximately -1.3 V.

[0185] Therefore, the results of this first set of CV measurements indicate that [Ni] generated during the reduction process II (thenil)TSC-OCH3] •– and [Ni I (thenil)TSC-OCH3] 2- The product is stable during cyclic voltammetry. This indicates that Ni II The bis(thiohexacarbazone) ligand of the (thenil)TSC-OCH3 complex is able to avoid demetallization during the reduction of divalent nickel ions.

[0186] Subsequently, the inventors evaluated the performance of the Ni(thenil)TSC-OCH3 complex of Example 1a as a catalyst for the catalytic hydrogen release reaction (HER). The inventors recorded cyclic voltammograms of the Ni(thenil)TSC-OCH3 complex (1 mM) in DMF, with 0.1 M NBu4PF6 present during the measurements, using TFA (0-100 mM) as the proton source at a scan rate of 0.5 Vs. -1 Note that in DMF, the pK of TFA... a It is 6.00 ± 0.03.

[0187] The recorded cyclic voltammetry diagram is as follows: Figure 7 and 8 As shown.

[0188] Cyclic voltammetry (CVT) Figure 7This indicates that the addition of TFA to the Ni(thenil)TSC-OCH3 complex solution generates a catalytic current, and two proton-dependent peaks appear when scanning towards the cathode, relative to Fc. + / 0 The first peak is approximately -1.60 V, and the second peak is approximately -1.95 V. When TFA is continuously added, the second peak slowly shifts towards increasingly negative potential values. Figure 7 The inventors also observed that the catalytic current response of this type of peak-shaped wave is proportional to the proton concentration in the Ni(thenil)TSC-OCH3 complex solution.

[0189] In addition, the inventors studied the process that occurred in the first wave, relative to Fc. + / 0 The potential is approximately -1.60 V. The inventors observed that the potential value remained almost unchanged as TFA was gradually added. Figure 8 ]).

[0190] Subsequently, the inventors recorded the cyclic voltammogram of TEA (100 mM) in the DMF, which showed the presence of 0.1 MNBu4PF6 but not the Ni(thenil)TSC-OCH3 complex. Figure 7 The results shown (dashed curve G) demonstrate that the observed enhancement of the catalytic current is indeed due to the presence of the Ni(thenil)TSC-OCH3 complex.

[0191] To verify that the observed catalytic current was not due to substances adsorbed on the surface of the working electrode, the inventors performed immersion and rinsing tests. After CV measurements of the Ni(thenil)TSC-OCH3 complex, the working electrode was removed from the solution and then immersed in a new DMF solution containing NBu4PF6 (0.1 M). Figure 9 As shown in curve A, only the background current was recorded during the potential scan from 0 to -2.75. During the addition of 100 mM TFA, the potential scan only provided the electrochemical response of the TFA (curve B). Figure 9 These impregnation and rinsing tests confirmed that no material was adsorbed onto the glassy carbon working electrode during the CV measurements. The tests also demonstrated that the resulting catalytic current was indeed induced by the dissolved Ni(thenil)TSC-OCH3 complex, and confirmed that the studied electrolysis system indeed corresponds to a homogeneous catalyst.

[0192] Study using controlled potential coulometric method:

[0193] To confirm Figure 7 and Figure 8The recorded electrochemical response corresponds to hydrogen production, and the inventors conducted controlled potential coulometric analysis (CPC) experiments.

[0194] Controlled potential coulometric analysis, also known as electrolytic analysis, allows the measurement of the charge (usually in coulombs (C)) of the electrodes used at a fixed potential over a time t.

[0195] The coulometric analysis experiment is combined with gas detection and quantification using gas chromatography (CPG) with a flame ionization detector (DIF). This allows us to ensure that the only gas produced is hydrogen and to quantify the gas production during the experiment.

[0196] The coulometric analysis also incorporated gas detection and quantification using gas chromatography (CPG). This method allows for ensuring that the only gas produced is hydrogen, while also enabling the quantification of gas production throughout the electrocatalytic process.

[0197] The experiment was conducted in 8 ml of DMF solution containing 1 mM Ni(thénil)TSC-OCH3 complex, 0.1 M NBu4PF6, and 100 mM TFA, relative to Fc + / 0 The electrocatalytic reaction for hydrogen production (H2) was monitored for approximately 960 minutes (16 hours) at a fixed potential of -1.7 V, while the generated gas was continuously analyzed in-line (GPC) to ensure its homogeneity. A mercury-based working electrode was used to ensure that all generated nanoparticles were absorbed by mercury, thus maintaining the homogeneous nature of the electrolysis system under study.

[0198] The following performance parameters can be obtained through these experiments:

[0199] - The number of moles of hydrogen gas produced.

[0200] - The total charge passing through during the electrolysis experiment (Q; unit: coulomb "C").

[0201] - Faraday efficiency or Faraday yield (FY, an abbreviation for Faradaic Yield). FY gives the percentage of electrons used for proton reduction. A 100% Faraday efficiency allows evaluation of whether all electrons offered to the catalyst are used for hydrogen production. When this yield is not quantifiable, it means that some electrons are used for other electrochemical reactions (e.g., due to solvents, TFAs, or other electroactive substances present in the reaction medium) or simply because the catalyst degrades during electrolysis.

[0202] - The Turnover Number (TON) is the number of catalytic cycles a catalyst can complete. The TON number is calculated based on the ratio of the number of moles of hydrogen produced to the number of moles of the complex under study, and its value is n. H2测量= 3.3610 - 4 moles,

[0203] - The TOF number (TurnOver Frequency) is the number of cycles a catalyst completes within a given time. In practice, the unit for the TOF number is seconds (s). -1 The higher the TOF number, the faster the catalyst can complete its work per unit time (s). -1 The more products formed inside, the better.

[0204] - Overpotential (also known as overvoltage). Its unit is V or mV.

[0205] The above parameters are easy for technicians in the field of electrochemistry to understand.

[0206] CPG (Gas Chromatography) analysis confirmed that the gas produced in the coulometric analysis was indeed hydrogen. The number of hydrogen moles produced and quantified by CPG (or GC) within 960 minutes (16 hours) was 3.36 x 10⁻⁶. -4 Moore.

[0207] The graph showing the change of total charge (Q, in coulombs) over time (t, in units) is shown below. Figure 10 As shown in the figure. This figure indicates that, within 960 minutes (16 hours), for a solution containing only TFA, the total charge passing through the working electrode is negligible (curve b). Figure 10 Additionally, for solutions containing both TFA and Ni(thenil)TSC-OCH3 complexes, relatively high total charges (Q) were recorded (curve A, Figure 10 This indicates an improved catalytic activity. For the Ni(thenil)TSC-OCH3 complex, a total charge (Q) of 65.53 C passes through the working electrode, corresponding to a theoretical hydrogen production (n). th 3.40 x 10 -4 The number of moles and the number of TONs is 42.

[0208] Table 3 below provides a comparison of the catalytic activity of the Ni(thenil)TSC-OCH3 complex and the NiTSC-OCH3 reference complex (prior art) of Example 1a:

[0209] [Table 3]

[0210]

[0211] Table 3 clearly shows that the Ni(thenil)TSC-OCH3 complex of Example 1a exhibits increased catalytic activity, with a precisely quantifiable Faraday efficiency (= 99%), compared to 80% for the reference complex, and a TON index (= 42) twice that of the reference complex (= 21).

[0212] The TOF value can be calculated based on data obtained from large-scale electrolysis experiments, following the schemes in the aforementioned literature (see the following articles: Roy, S. et al. 2017, and Queyriaux, N. et al. 2020).

[0213] The heterogeneous decomposition process uses the following formulas [Math 1], [Math 2], and [Math 3]:

[0214] [Math 1]

[0215]

[0216] In the formula [Math 1]:

[0217] F is the Faraday constant (F = 96500 C.mol) -1 ),

[0218] A is the surface area of ​​the working electrode based on mercury (A ~ 0.47 cm²). 2 ),

[0219] D cat It is the diffusion coefficient (unit: cm). 2 .s -1 ),

[0220] [Cat] is the concentration of the catalyst ([Cat] = 1 mM).

[0221] E appl It is the potential (E) applied during the electrolysis process. appl =-1.70 V, relative to Fc + / 0 electrode),

[0222] E 1 / 2 It is the half-wave potential of the catalytic wave.

[0223] i el This represents the current density generated during large-scale electrolysis.

[0224] Current density (i) el It can be calculated according to the following formula [Math 2].

[0225] [Math 2]

[0226]

[0227] In the formula [Math 2]:

[0228] Q el It is the charge that passes through during the electrolysis process.

[0229] FY stands for Faraday yield (or Faraday efficiency).

[0230] t is the electrolysis duration.

[0231] The maximum time-of-flight (TOF) of the divalent nickel complex was then evaluated using the following equation [Math 3]. max )

[0232] [Math 3]

[0233]

[0234] Table 4 below is a comparison table of the parameters determined for the Ni(thenil)TSC-OCH3 complex of Example 1a with the parameters of the NiTSC-OCH3 reference complex.

[0235] [Table 4]

[0236]

[0237] As can be deduced from Table 4, the Ni(thenil)TSC-OCH3 complex of Example 1a exhibits superior catalytic performance. This significant improvement in catalytic performance is attributed to the presence of a phenylthio group at the 2,2' position of the bis(thiohexacarbazone) ligand.

[0238] The overpotential value (Ni(thenil)TSC-OCH3 complex in Example 1a) was determined according to the scheme mentioned in the aforementioned literature (e.g., see: Fourmond, V. et al., 2010). This value was calculated using the following formula [Math 4]:

[0239] [Math 4]

[0240]

[0241] In the formula [Math 4]:

[0242] E cat 1 / 2 It is a half-wave catalytic potential.

[0243] E T 1 / 2 It is the half-wave theoretical potential.

[0244] Table 5 below is a comparison table of the overpotentials determined for the Ni(thenil)TSC-OCH3 complex of Example 1a and the overpotentials of the NiTSC-OCH3 reference complex.

[0245] [Table 5]

[0246]

[0247] As shown in Table 5, the overpotential of the Ni(thenil)TSC-OCH3 complex in Example 1a is significantly lower than that of the NiTSC-OCH3 reference complex. These results suggest that the introduction of two phenylthio groups at the 2,2' position of the dithiohexacarbazone ligand leads to a decrease in the overpotential of the proton reduction reaction (HER reaction).

[0248] Finally, in order to investigate the sequence of events occurring during hydrogen production using the Ni(thenil)TSC-OCH3 complex of Example 1a, the inventors recorded the UV-Vis spectra with and without TFA. The results are as follows: Figure 11 As shown in the figure, the main absorption band of the spectrum did not shift when up to 100 equivalents of TFA were added. These experiments rule out the possibility that a chemical event (protonation) is the first step in the catalytic process.

[0249] References :

[0250] Fourmond, V., Jacques, P.-A., Fontecave, M. & Artero, V. H2Evolution and Molecular Electrocatalysts: Determination of Overpotentials and Effect of Homoconjugation. Inorg. Chem. 49, 10338–10347 (2010).

[0251] Queyriaux N., Sun D., Fize J., Pécaut J., Field M.J., Chavarot-Kerlidou M., Artero V., Electrocatalytic Hydrogen Evolution with a CobaltComplex Bearing Pendant Proton Relays:Acid Strength and Applied PotentialGovern Mechanism and Stability.J. Am.Chem.Soc.142, 274-282 (2020)。

[0252] Roy S., Sharma B, Pécaut J., Simon P., Fontecave M., Tran P.D., DeratE., Artero V., Molecular Cobalt Complexes with Pendant Amines for SelectiveElectrocatalytic Reduction of Carbon Dioxide to Formic Acid.J. Am.Chem.Soc.139, 3685-3696 (2017)。

[0253] Srivastava K., Bhatt A., Singh N., Khare R., Shukla R., ChaturvediD., Kant R. “Synthesis of Isothiocyanates:A Review” Chemistry&BiologyInterface, 2020, 10, 2, 34-50。

[0254] Straistari T., Fize J., Shova S., Réglier M., Artero V., Orio M., AThiosemicarbazone-Nickel(II) Complex as Efficient Electrocatalyst forHydrogen Evolution.ChemCatChem 9, 2262–2268 (2017)。

Claims

1. A catalyst containing a divalent nickel complex, comprising a 2,2'-thiophene-derived bis(thiohexacarbazone) ligand, said divalent nickel complex conforming to the following general formula [Chem 6]: [Chem 6] in, R 1 and R 2 Each of these groups independently represents a phenyl group and may optionally have one or more identical or different substituents R. 3 , The R 3 It is selected from halogens, hydroxyl groups, C1-C4 alkyl groups, C1-C4 alkoxy groups, C1-C4 thioalkyl groups, C1-C4 dialkylamino groups, cyano groups, CF3 groups, and O-CF3 groups.

2. The catalyst according to claim 1, characterized in that, When the phenyl group is substituted by one or more identical or different substituents R 3 When substituted, this or these substituents R 3 It can be selected from methyl, methoxy, methylthio, and dimethylamino.

3. The catalyst according to claim 1 or 2, characterized in that, The R 1 and R 2 The functional groups are the same.

4. The catalyst according to any one of claims 1 to 3, characterized in that, The complex is selected from nickel complexes conforming to the following general formulas [Chem 7] to [Chem 11]: [Chem 7] [Chem 8] [Chem 9] [Chem 10] [Chem 11] 。 5. Use of the catalyst according to any one of claims 1 to 3 for catalytic reduction of protons to hydrogen (H2).

6. A method for producing hydrogen (H2), comprising using a proton source (H2) in an electrochemical cell. + The protons (H) are contacted with the catalyst according to any one of claims 1 to 3, and a potential is applied to the electrochemical cell, thereby causing the protons (H) to be released. + It is reduced to hydrogen gas (H2).

7. The method according to claim 6, wherein: - The electrochemical cell includes a working electrode, a counter electrode, and, if necessary, a reference electrode, all of which are immersed in an electrolyte solution containing an electrolyte, a solvent, and the catalyst; - The proton source (H + Contacting the catalyst with the proton source (H) includes contacting the proton source (H) with the catalyst. + Add to a non-aqueous solution; and Applying a potential to the electrochemical cell includes applying a voltage to the terminals of the working electrode and the counter electrode to convert the protons (H+) into electrons. + It is reduced to hydrogen gas (H2).

8. The hydrogen (H2) production method according to claim 6 or 7, wherein the solvent of the electrolyte solution is an aprotic solvent selected from amides, carbonates, ketones, aromatic compounds, esters, ethers, nitriles, halogenated solvents, sulfoxides, and mixtures thereof.

9. A divalent nickel complex containing a 2,2'-thiophene-derived bis(thiohexacarbazone) ligand, said divalent nickel complex conforming to the following general formula [Chem 6]: [Chem 6] in, R 1 and R 2 Each of these groups independently represents a phenyl group and may optionally have one or more identical or different substituents R. 3 , The R 3 It is selected from halogens, hydroxyl groups, C1-C4 alkyl groups, C1-C4 alkoxy groups, C1-C4 thioalkyl groups, C1-C4 dialkylamino groups, cyano groups, CF3 groups, and O-CF3 groups.

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