WO2024005549A1

WO2024005549A1 - Chloride ion adsorbent and method of producing hydrogen directly from seawater using same adsorbent

Info

Publication number: WO2024005549A1
Application number: PCT/KR2023/009057
Authority: WO
Inventors: Kyung Su Na; Yu Yeol CHOI; Ji Woong Lee; Marco MILIA
Original assignee: Industry Foundation Of Chonnam National University; University Of Copenhagen
Priority date: 2022-07-01
Filing date: 2023-06-28
Publication date: 2024-01-04
Also published as: KR20240003491A

Abstract

The present invention relates to a hydrogen production technology, and more particularly, to a chloride ion adsorbent, method for manufacturing the adsorbent, and method for direct hydrogen production from seawater using the adsorbent. The present invention which makes it possible to solve the problem of using non-desalinized seawater. That is, a feed of the chloride ion adsorbent to a reactor containing seawater for electrolysis can increase the overall efficiency of the electrolysis and will prevent the lifetimes of the electrode and structural components of the reactor from being shortened due to corrosion and contamination since the generation of chlorine gas (Cl₂) is inhibited by the chloride ion adsorbent while producing hydrogen without treating seawater to freshwater. In the absence of the chloride ion adsorbent, otherwise, a large amount of chloride ions (Cl-) will be oxidized during electrolysis due to NaCl dissolved in a large amount in seawater.

Description

CHLORIDE ION ADSORBENT AND METHOD OF PRODUCING HYDROGEN DIRECTLY FROM SEAWATER USING SAME ADSORBENT

The present invention relates to a hydrogen production technology and, more particularly, to a chloride ion adsorbent, a method for manufacturing the adsorbent, and a method for direct hydrogen production from seawater using the adsorbent, which make it possible to solve the problem of using non-desalinized seawater. That is, when hydrogen is produced directly from seawater which has not undergone desalination, a high concentration of chloride ions (Cl^-)is oxidized instead of oxygen during electrolysis due to the presence of a large amount of NaCl dissolved in the seawater, resulting in generation of chlorine gas (Cl₂) which pollutes the aqueous solution and shortens the service life of the electrode, thereby reducing the water electrolysis efficiency.

Hydrogen energy is one of energy sources available on the earth and has a very high gravimetric energy density which is 4 to 5 times higher than that of petroleum-based gasoline or diesel.

In order to utilize hydrogen energy, three major technologies must be developed complementary to each other. The first is a hydrogen production technology, the second is a technology for storing and transporting the produced hydrogen, and the third is a technology for utilizing hydrogen as an energy source.

Hydrogen production through water electrolysis using a renewable energy source is a very important hydrogen energy production technology in that such hydrogen production technology is required for completion of carbon-zero technology and is required to economically produce valueadded hydrogen. Research on hydrogen production through electrolysis of water has been conducted for a long time, and the hydrogen production through electrolysis of water is thus a technically matured practical technology.

However, in general, water for electrolysis must have very high purity. To produce hydrogen from an aqueous solution such as seawater containing various materials, such a solution must be first desalinated to become highpurity water, and the purified water is electrolyzed to produce hydrogen. When seawater is directly electrolyzed as it is, chloride ions (Cl-) generated from a large amount of NaCl contained in seawater are oxidized in the electrolysis process, resulting in generation of a large amount of chlorine gas (Cl2). This chlorine gas, which is a watersoluble gas, is dissolved in the aqueous solution, thereby causing various problems such as corrosion of electrolysis electrodes, contamination of the aqueous solution, shortening the service life of the electrodes, and reducing water electrolysis efficiency.

Therefore, to save energy and process costs for seawater desalination, a material capable of reducing the amount of chlorine gas generated during seawater electrolysis needs to be developed so that direct seawater electrolysis without desalination of seawater can be performed.

Through numerous studies and experiments, the inventors have developed a chloride ion adsorbent that can reduce the amount of chlorine gas generated when the absorbent is added to a seawater electrolysis solution and thus have completed the present invention.

An objective of the present invention is to provide a chloride ion absorbent having a characteristic of adsorbing chloride ions and desorbing chloride ions under specific conditions so as to reduce the amount of chlorine gas (Cl₂) generated due to the presence of a large amount of NaCl dissolved in seawater during electrolysis to produce hydrogen, so that seawater can be directly used without undergoing desalination, for electrolysis to produce hydrogen.

Another objective of the present invention is to provide a hydrogen production method capable of improving water electrolysis efficiency by preventing seawater contamination and maintaining durability of electrodes by electrolyzing seawater after adding the chloride ion adsorbent to the seawater.

The objective of the present invention is not limited to the objectives mentioned above. Even though not explicitly mentioned, the objectives that can be recognized by those of ordinary skill in the art from the description of the detailed description given below are also regarded as the objectives of the present invention.

To achieve the above objectives, the present invention provides a chloride ion adsorbent comprising porous silica functionalized with an amino group.

In a preferred embodiment, the functionalization may be made by covalent bonding of aminosilane to porous silica.

In a preferred embodiment, the aminosilane may be an organosilane compound containing at least one of a primary amino group and a secondary amino group.

In a preferred embodiment, the functionalization may be performed by introducing a second organic compound having an amino group to a first organic compound after the first organic compound is covalently bonded to the porous silica.

In a preferred embodiment, the second organic compound may be one or more compounds selected from the group consisting of N',N'-dimethylpropane-1,3-diamine (DMAPA), ammonia(NH3),ethylamine, butylamine, N-dodecyl-N’,N’-dimethylpropane-1,3-diamine (C12-DMAPA), hexylamine, octylamine, decylamine, dodecylamine, detradecylamine,hexadecylamine,octadecylamine, ethylenediamine (NH₂CH₂CH₂NH₂), tetramethylenediamine(NH₂(CH₂)4NH₂), hexamethylene diamine (NH₂(CH₂)6NH₂), N-ethylethylenediamine (NH₂CH₂CH₂NHCH₂CH₃), N,N'-dimethylethylene diamine(NH₂CH₂CH₂N(CH₃)₂), N,N'-diethylethylenediamine(NH₂CH₂CH₂N(CH₂CH₃)₂), diethylenetriamine(NH₂CH₂CH₂NHCH₂CH₂NH₂),triethylenetetraamine(NH₂CH₂CH₂NHCH₂CH₂NHCH₂CH₂NH₂), and polyethyleneimine.

In a preferred embodiment, the amino group may be contained in a concentration of 0.3 mmol/g or more.

In a preferred embodiment, the porous silica is silica gel.

In a preferred embodiment, the chloride ion adsorbent may be included in a seawater electrolysis solution to inhibit the generation of chlorine gas and to reduce corrosion of electrodes.

In addition, the present invention provides a chloride ion absorbent preparation method comprising the steps of: heat-treating porous silica; adding the heated porous silica to a solvent; and dropwise adding an aminosilane compound solution to the solvent to which the porous silica is present to functionalize the porous silica with an amino group.

In addition, the present invention provides a chloride ion absorbent preparation method comprising the steps of: heat-treating porous silica; adding the heated porous silica to a solvent; dropwise adding a first organic compound solution containing a first organic compound to the solvent to which the porous silica has been added, to functionalize the porous silica with the first organic compound; washing and drying the porous silica functionalized with the first organic compound; adding the dried porous silica functionalized with the first organic compound to a solvent; and dropwise adding a second organic compound solution containing a second organic compound having an amino group to the solvent to which the dried porous silica functionalized with the first organic compound has been added, to bind the second organic compound to the first organic compound, thereby functionalizing the porous silica with the amino group.

In a preferred embodiment, the aminosilane compound solution or the second organic compound solution containing the second organic compound having an amino group is added so that the concentration of the amino group becomes 0.3 mmol/g or more.

In a preferred embodiment, the step of heat-treating the porous silica may be performed by raising the temperature of the porous silica to a range of 250°C to 600°C for a duration of 90 to 300 minutes and then maintaining the raised temperature for a duration of 180 to 360 minutes.

In a preferred embodiment, the porous silica may be silica gel, and the solvent may be at least one selected from the group consisting of toluene and acetone.

In addition, the present invention provides a method of producing hydrogen directly from seawater, the method comprising the steps of: injecting any one of the above-mentioned chloride ion adsorbents into a reactor containing seawater for electrolysis; electrolyzing the seawater by applying a current to an anodic electrode and a cathodic electrode installed in the reactor; and allowing the chloride ion absorbent to selectively adsorb chloride ions generated during the seawater electrolysis.

In a preferred embodiment, the chloride ion adsorbent may be added in an amount of 50 g to 500 g per 1 L of the seawater.

In a preferred embodiment, the chloride ions adsorbed to the chloride ion adsorbent may be desorbed from the chloride ion adsorbent by diffusion occurring due to a difference in concentration when no current is applied to the anodic electrode and the cathodic electrode.

In a preferred embodiment, since the generation of chlorine gas at the anodic electrode is inhibited, corrosion of the anodic electrode by chlorine gas may be prevented.

In addition, the present invention provides a chloride ion adsorbent comprising an organic compound functionalized with at least one amino group.

In a preferred embodiment, the amino group may comprise at least one of a primary amino group and a secondary amino group.

In a preferred embodiment, the organic compound may be at least one selected from the group consisting of N',N'-dimethylpropane-1,3-diamine (DMAPA), ammonia(NH₃), ethylamine, butylamine, N-dodecyl-N’,N’-dimethylpropane-1,3-diamine (C12-DMAPA), hexylamine, octylamine, decylamine, dodecylamine,detradecylamine, hexadecylamine, octadecylamine, ethylenediamine (NH₂CH₂CH₂NH₂), tetramethylenediamine(NH₂(CH₂)4NH₂), hexamethylenediamine (NH₂(CH₂) 6NH₂), N-ethylethylenediamine(NH₂CH₂CH₂NHCH₂CH₃), N,N'-dimethylethylene diamine(NH₂CH₂CH₂N(CH₃)₂), N,N'-diethylethylenediamine(NH₂CH₂CH₂N(CH₂CH₃)₂), diethylenetriamine(NH₂CH₂CH₂NHCH₂CH₂NH₂),triethylenetetraamine(NH₂CH₂CH₂NHCH₂CH₂NH CH₂CH₂NH₂), and polyethyleneimine.

In a preferred embodiment, the chloride ion adsorbent may be included in the seawater solution for electrolysis for the purpose of suppressing the generation of chlorine gas and reducing the corrosion of electrodes and other structural components of the reactor.

In addition, the present invention provides electrolysis seawater containing any one of the above-mentioned chloride ion adsorbents.

In addition, the present invention provides a method of producing hydrogen directly from seawater, the method comprising the steps of: injecting any one of the above-mentioned chloride ion adsorbents into a reactor containing seawater for electrolysis; electrolyzing the seawater by applying a current to an anodic electrode and a cathodic electrode installed in the reactor; and allowing the chloride ion absorbent to selectively adsorb chloride ions generated during electrolysis of the seawater.

In a preferred embodiment, the chloride ion absorbent is added in an amount of 0.05 to 5 mol per L of the seawater.

In a preferred embodiment, the generation of chlorine gas may be inhibited at the anodic electrode so that corrosion of the electrodes and corrosion of other structural components by the chlorine gas are prevented.

In a preferred embodiment, the generation of chlorine gas may be inhibited at the anodic electrode, thereby inhibiting toxicity at an anodic electrode gas outlet and improving safety.

The chloride ion adsorbent of the present invention described above has a characteristic of adsorbing chloride ions and desorbing the adsorbed chloride ions under specific conditions. Since the chloride ion absorbent absorbs chloride ions derived from a large amount of NaCl dissolved in seawater when the chloride ion absorbent is added to seawater at the time of producing hydrogen directly from seawater without performing desalination of seawater, it is possible to inhibit the generation of chlorine gas (Cl₂). In addition, since the adsorbed chloride ions can be desorbed under specific conditions, the chloride ion absorbent can be easily recovered and reused like catalysts.

In addition, the hydrogen production method of the present invention not only enables hydrogen production directly from seawater without desalination of seawater by adding the chloride ion adsorbent to seawater and then electrolyzing the seawater. In addition, it is possible to prevent seawater contamination and maintain the durability of electrodes, thereby improving water electrolysis efficiency. This makes hydrogen production more economical.

The technical effects of the present invention are not limited to the effects mentioned above. Even though not explicitly mentioned, other effects that can be recognized by those of ordinary skill in the art from the description of the detailed description given below are also regarded as the effects of the present invention.

FIG. 1 includes photographs of a commercial silica gel (SG) which is not functionalized with an amino group, a first chloride ion absorbent 1 (Diamine_SG) which is a silica gel functionalized with an amino group by using an aminosilane according to Example 1 of the present invention, and a first chloride ion absorbent 2 (PEI_SG) functionalized with an amino group by using a second organic compound including a first organic compound and an amino group according to Example 2.

FIG. 2 shows the results of TGA analysis of the first chloride ion adsorbents according to various embodiments of the present invention, and specifically shows a result of analysis of the amount of the functionalized organic material in the Diamine_SG and PEI_SG.

FIG. 3 shows the nitrogen adsorption isotherm results of the first chloride ion adsorbents according to various embodiments of the present invention.

FIG. 4 is a schematic diagram (left) and a photograph (right) of a test device for seawater electrolysis experiments using an H-cell, in which the first chloride ion adsorbents according to various embodiments of the present invention are added to respective oxidizing electrodes (anodic electrodes).

FIG. 5 is a photograph showing a result of comparison between the solutions around the respective oxidizing electrodes (anodic electrodes) after performing electrolysis for 24 hours, using the configuration shown in FIG. 4.

FIG. 6 is a graph showing changes in the amount of chlorine ions remaining in the solution over time after the electrolysis is performed with the configuration illustrated in FIG. 4.

FIG. 7 is a schematic diagram (left) and a photograph (right) of a test device for seawater electrolysis experiments for analyzing the concentration of chloride ions remaining in an aqueous solution after the electrolysis of seawater to which the first chloride ion absorbents according to various embodiments of the present invention are added.

FIG. 8 is a graph showing changes in the amount of the remaining chlorine ions after the electrolysis is performed with the configuration illustrated in FIG. 7.

FIG. 9 is a reaction schematic diagram showing the mechanism of the seawater electrolysis process for inhibiting the oxidation of chlorine ions by adding the first chloride ion adsorbents according to various embodiments of the present invention.

FIG. 10 is a photograph showing a device for experimental electrolysis of seawater by using an H-cell and adding an organic compound, which is one of second chloride ion adsorbents according to various embodiments of the present invention.

FIGS. 11a to 11c are graphs showing the results of analysis of the amount of chloride ions remaining in the solution after 16 hours of electrolysis with an amino compound added, using the test device having the configuration illustrated in FIG. 10, to select an organic compound serving as second chloride ion absorbents according to various embodiments of the present invention, and the amounts of chloride ions are measured through mass spectrometry, Benchtop NMR, and Mohr titration, respectively.

FIGS. 12a and 12b are graphs showing the results of analysis of the amount of chlorine ions remaining in the solution after 16 hours of electrolysis in which the amounts of C12-DMAPA and DMAPA selected as organic compounds suitable for the second chloride ion adsorbent are varied.

FIGS. 13a to 13c are electron microscope images of the surface of an anodic electrode on which a reaction of converting chloride ions into chlorine gas, in which FIG. 13a is an image taken before the reaction, FIG. 13b is an image taken after the reaction in which C12-DMAPA is not used, and FIG. 13c is an image taken after the reaction in which C12-DMAPA is used.

FIG. 14a is a graph showing the results of measurement of the chlorine ion concentration in seawater before and after an electrolysis reaction of seawater to which DMAPA serving as the second chloride ion adsorbent is added and before and after an electrolysis reaction of seawater to which the DMAPA is not added, and FIG. 14b is a photograph of a reactor used for the electrolysis reaction of FIG. 14a. FIGS. 14c and 14d show voltage changes with time during the electrolysis reaction when the DMAPA is not added and when the DMAPA is added, respectively.

FIGS. 15a and 15b are graphs of the results of a cyclic amperometric method performed while changing the voltage applied to the electrode after adding C12-DMAPA serving as the second chloride ion adsorbent to a pH-controlled 3M KCl solution, and FIGS. 15a and 15b are illustrated in different scales. FIG. 15c is a photograph of a three-electrode cell for cyclic voltammetry, in which glassy carbon is used for a working electrode, silver chloride-silver is used for a reference electrode, and platinum is used for a counter electrode.

FIGS. 16a and 16b are graphs of the results of measurement of the amount of chlorine ions included in seawater before and after the electrolysis reaction for each of seawater (Øresund seawater), seawater + KOH 0.1 eq added, and seawater + C12-DMAPA 0.1 eq added, in which the result of FIG. 16a is obtained through benchtop NMR and the result of FIG. 16b is obtained through Mohr titration (Agentometry).

FIG. 17a is a photograph of an H-cell (electrolyzer) used for seawater electrolysis for a kinetic experiment, and FIG. 17b is a graph showing the hydrogen generation rate according to time during the electrolysis performed with the device illustrated in FIG. 17a. The linear regression coefficients for Øresund seawater (dotted line), Øresund seawater + KOH 1 eq (dashed line), and Øresund seawater + C12-DMAPA 1 eq (solid line) correspond to the hydrogen generation rates.

FIG. 18 is a graph showing the voltage stability in an electrolysis system during a kinetic experiment. Øresund seawater (dashed line), Øresund seawater + KOH 0.1 eq (gray solid line), and Øresund seawater + C12-DMAPA 0.1 eq (black solid line).

FIGS. 19a and 19b are NMR spectra resulting from the material structure analysis of C12-DMAPA, in which FIG. 19a shows a spectrum (3) of pure C12-DMAPA, a spectrum (2) of C12-DMAPA extracted from NaCl 0.6 M, and a spectrum (1) of C12-DMAPA extracted after 6 hours of electrolysis of NaCl 0.6 M at 100 mA in order from top to bottom. FIG. 19b shows a spectrum of distilled pure C12-DMAPA at the top and a spectrum of C12-DMAPA extracted from Øresund seawater after 6 hours of electrolysis at 100 mA at the bottom.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well unless the context clearly indicates otherwise. It will be further understood that the terms “comprise”, “include”, or “have” when used in this specification specify the presence of stated features, regions, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components and/or combinations thereof.

Terms “first”, “second”, etc. can be used to discriminate one component from another component, but the order or priority of the elements are not limited by the terms unless specifically stated. These terms are used only for the purpose of distinguishing a component from another component. For example, a first component may be referred to as a second component, and the second component may be also referred to as the first component.

In addition, unless otherwise defined, all terms including technical and scientific terms used herein have the same meaning as commonly understood by those who are ordinarily skilled in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

In interpreting components, it is interpreted as including an error range even though there is no explicit description. In particular, when the terms “about”, “substantially”, etc. indicating degree are used, when inherent tolerances for manufacturing and material are presented, the terms may be interpreted as being used as a meaning close to or at the presented numerical value.

In the case of a description of a temporal relationship, for example, when temporal precedence is described like “after”, “subsequent to”, “next”, “before”', etc., the temporal relationship includes a case where the described events non-consecutively occur as well as a case where the described events consecutively occur unless the word “immediately” or “directly” is used.

Hereinafter, the technical configuration of the present invention will be described in detail with reference to the preferred embodiments and the accompanying drawings.

However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Throughout the following description, like reference numbers refer to like elements.

The present invention technically features a chloride ion adsorbent having a characteristic of adsorbing chloride ions and desorbing the adsorbed chloride ions under specific conditions and a hydrogen production method using the chloride ion absorbent. Since the chloride ion absorbent absorbs chloride ions derived from a large amount of NaCl dissolved in seawater when the chloride ion absorbent is added to the seawater at the time of producing hydrogen directly from seawater without performing desalination of seawater, it is possible to inhibit the generation of chlorine gas (Cl₂) as illustrated in FIG. 9. In addition, since the adsorbed chloride ions can be desorbed from the chloride ion absorbent under specific conditions, the chloride ion absorbent can be easily recovered and reused like catalysts.

As a seawater electrolysis process, which is usually called a chlor-alkali process, an ion exchange membrane method is most widely used. In the ion exchange membrane method, an ion exchange membrane is installed in an electrolytic cell to divide the cell into a cation zone and an anion zone,

and seawater is used as electrolyte to obtain chlorine gas from the anodic electrode and hydrogen and caustic soda from the cathodic electrode. However, the ion exchange membrane method had problems in that the cost was excessive and the electrolysis efficiency was low because an ion exchange membrane was essentially used and a precious metal anodic electrode used to prevent overvoltage at the anodic electrode at which chlorine gas is generated was corroded by chlorine gas generated.

However, when the chloride ion adsorbent of the present invention is used for seawater electrolysis, since an ion exchange membrane is not required and chlorine gas generation is inhibited, not only the overvoltage of the anodic electrode but also the corrosion of the anodic electrode can be prevented, resulting in increase in electrolysis efficiency. Therefore, hydrogen can be economically produced.

A chloride ion adsorbent according to a first aspect of the present invention includes porous silica functionalized with an amino group.

Here, the porous silica is a solid phase made of silicon dioxide (SiO₂) and having a large number of micropores. Any known porous silica material can be used as the porous silica. In examples described below, silica gel is used as the porous silica. In one embodiment, the porous silica is in the form of a spherical powder having a particle size of 0.2 μm to 5 mm. The porous silica has a large number of pores, so that the porous silica preferably has a surface area of 0.1 m²/g to 700 m²/g.

For the porous silica functionalized with an amino group, any known method can be used as long as an amino group can be introduced into the porous silica. In the present invention, the functionalization is performed in a manner described below such that the amino group introduced into the porous silica can be stably bonded to the porous silica.

In a first functionalization method, aminosilane is covalently bonded to porous silica. That is, aminosilane can form a covalent bond with the hydroxyl group of the porous silica and thus can be stably bond to the porous silica. Since the aminosilane contains an amino group, when the aminosilane is combined with the porous silica, the porous silica can be naturally functionalized with the amino group. In the present invention, the aminosilane may be any known organosilane compound containing an amino group. In particular, the aminosilane is preferably an organosilane containing at least one of a primary amino group and a secondary amino group.

In a second functionalization method, a first organic compound is covalently bonded to porous silica, and then a second organic compound having an amino group is introduced into the first organic compound. That is, as the first organic compound is covalently and stably bonded to the hydroxyl group of the porous silica, that the first organic compound is used as an anchor material. Thus, the second organic compound having an amino group can be bonded to the first organic compound. Here, the first organic compound may be any one selected from the group consisting of (n-Chloroalkyl)trimethoxysilanes, and the second organic compound may be or more compounds selected from the group consisting of N',N'-dimethylpropane-1,3-diamine (DMAPA), ammonia(NH₃), ethylamine, butylamine, N-dodecyl-N’,N’-dimethylpropane-1,3-diamine (C₁₂-DMAPA), hexylamine, octylamine, decylamine, dodecylamine, detradecylamine, hexadecylamine, octadecylamine, ethylenediamine (NH₂CH₂CH₂NH₂), tetramethylene diamine (NH₂(CH₂)4NH₂), hexamethylene diamine (NH₂(CH₂) 6NH₂), N-ethylethylenediamine (NH₂CH₂CH₂NHCH₂CH₃), N,N'-dimethylethylene diamine (NH₂CH₂CH₂N(CH₃)₂), N,N'-diethylethylenediamine (NH₂CH₂CH₂N(CH₂CH₃)₂), diethylenetriamine (NH₂CH₂CH₂NHCH₂CH₂NH₂), triethylenetetraamine (NH₂CH₂CH₂NHCH₂CH₂NHCH₂CH₂NH₂), and polyethyleneimine.

In the porous silica functionalized with an amino group, the amino group may be included in a concentration of 0.3 mmol/g or more. When the amino group concentration is lower than 0.3 mmol/g, there is a problem in that the chloride ion adsorption efficiency is low. The chloride ion adsorption efficiency increases as the amino group concentration increases. However, when the amino group concentration exceeds 1.5 mmol/g, there is no significant difference in adsorption efficiency. Therefore, the functionalization is preferably performed in a condition in which the amino group concentration is 1 mmol/g or less in terms of economic feasibility.

Next, a chloride ion adsorbent according to a second aspect of the present invention includes an organic compound functionalized with one or more amino groups. The amino group may include at least one of a primary amino group and a second amino group.

Any organic compound can be used without particular limitation if the organic compound is functionalized with one or more amino groups. In one embodiment, such a functionalized organic compound may include one or more compounds selected from the group consisting of triethyleneamine (TEA), N',N'-dimethylpropane-1,3-diamine (DMAPA), ammonia(NH₃), ethylamine, butylamine, N-dodecyl-N’,N’-dimethylpropane-1,3-diamine (C₁₂-DMAPA), hexylamine, octylamine, decylamine, dodecylamine, detradecylamine, hexadecylamine, octadecylamine, ethylenediamine (NH₂CH₂CH₂NH₂), tetramethylene diamine (NH₂(CH₂)4NH₂), hexamethylene diamine (NH₂(CH₂) 6NH₂), N-ethylethylenediamine (NH₂CH₂CH₂NHCH₂CH₃), N,N'-dimethylethylene diamine (NH₂CH₂CH₂N(CH₃)₂), N,N'-diethylethylenediamine (NH₂CH₂CH₂N(CH₂CH₃)₂), diethylenetriamine (NH₂CH₂CH₂NHCH₂CH₂NH₂), triethylenetetraamine (NH₂CH₂CH₂NHCH₂CH₂NHCH₂CH₂NH₂), and polyethyleneimine.

When the chloride ion adsorbent according to at least one of the first and second aspects of the present invention having the configuration described above is contained in seawater for electrolysis, and chloride ions generated during electrolysis of seawater are adsorbed by the chloride ion absorbent, the adsorbed chloride ions can be easily desorbed from the chloride ion absorbent by washing or diffusion which occurs due to a difference in concentration of chloride ions between the absorbent and the electrolyte. Therefore, the chloride ion absorbent can be reused like catalysts. In particular, the chloride ion adsorbent according to the first aspect is reusable in all cases, and the chloride ion adsorbent according to the second aspect is reusable depending on the characteristics of the organic compound.

In addition, a method of producing a chloride ion adsorbent according to a first aspect of the present invention includes the steps of: heat-treating porous silica; adding the heated porous silica to a solvent; and functionalizing the porous silica with an amino group by dropwise adding an aminosilane compound solution to the solvent to which the porous silica has been added. Alternatively, the method may include the steps of: heat-treating porous silica; adding the heated porous silica to a solvent; dropwise adding a first organic compound solution containing a first organic compound to the solvent to which the porous silica has been added, to functionalize the porous silica with the first organic compound; washing and drying the porous silica functionalized with the first organic compound; adding the dried porous silica functionalized with the first organic compound to a solvent; and dropwise adding a second organic compound solution containing a second organic compound having an amino group to the solvent to which the dried porous silica functionalized with the first organic compound has been added, to bind the second organic compound to the first organic compound, thereby functionalizing the porous silica with the amino group. Here, a first preparation method uses the first functionalization method described above, and a second preparation method uses the second functionalization method described above. In the aminosilane compound solution or the second organic compound solution containing the second organic compound having an amino group, the concentration of the amino group is 0.3 mmol/g or more. If necessary, in both the first and second preparation methods, the step of washing and drying the porous silica functionalized with an amino group may be further performed.

In particular, the step of heat-treating the porous silica is to remove moisture and foreign materials contained in the porous silica. In the step, the temperature of the porous silica is increased to a range of 250°C to 600°C for 90 to 300 minutes in air or nitrogen atmosphere, and then the raised temperature is maintained for 180 to 360 minutes.

The porous silica may be any known porous silica material as described above, but it is preferable to use commercially available silica gel in terms of economic feasibility. The solvent to which the heat-treated porous silica is added is not limited as long as it is an organic solvent that can dissolve aminosilane, the first organic compound, and the second organic compound, but preferably one or more compounds selected from the group consisting of toluene and acetone is used as the solvent.

Next, the seawater for electrolysis used in the present invention is seawater to which any one of the above-mentioned chloride ion adsorbents is added. When the seawater to which the chloride ion adsorbent according to the first or second aspect having the above-described configuration is added is used for electrolysis, the generation of chlorine gas is inhibited, and thus corrosion of the electrodes and other structural components can be reduced.

Next, a method of producing hydrogen directly from seawater, using the chloride ion adsorbent according to the first and/or second aspect of the present invention, includes the steps of: injecting any one of the above-mentioned chloride ion adsorbents into a reactor containing seawater for electrolysis; electrolyzing the seawater by applying a current across an anodic electrode and a cathodic electrode installed in the reactor; and allowing the chloride ion absorbent to selectively adsorb chloride ions generated during the electrolysis of the seawater.

Here, the chloride ion adsorbent according to the first aspect may be added in an amount of 50 g to 500 g per 1 L of seawater. When the chloride ion adsorbent is added in an amount of less than 50 g per 1 L of seawater, there is a problem in that the ion adsorption efficiency decreases due to an insufficient amount of amino groups. On the other hand, when the amount of the added chloride ion absorbent exceeds 500 g per 1 L of seawater, there is a problem in that the resistance increases and the hydrogen production efficiency decreases. The chloride ions adsorbed to the chloride ion adsorbent according to the first aspect can be separated from the chloride ion adsorbent by the diffusion of chloride ions due to a difference in concentration of the chloride ions between the adsorbent and the aqueous solution when no current or voltage is applied between the anodic electrode and the cathodic electrode.

Here, the chloride ion adsorbent according to the second aspect may be added in an amount of 0.05 mol to 5 mol per 1 L of seawater. When the chloride ion adsorbent is added in an amount of less than 0.05 mol per 1 L of seawater, there is a problem in that the ion adsorption efficiency decreases due to an insufficient amount of amino groups. On the other hand, when the amount of the added chloride ion absorbent exceeds 5 mol per 1 L of seawater, there is a problem in that the resistance increases and the hydrogen production efficiency decreases.

If necessary, the chloride ion adsorbent according to the first aspect and the chloride ion adsorbent according to the second aspect may be used in combination. The effect of the combined use is the same as the effect of increasing the amount of the chloride ion adsorbent according to the first or increasing the amount of the chloride ion absorbent according to the second aspect. Therefore, in the case of the combined use, the amount of chloride ions adsorbed may increase.

In the step of electrolyzing seawater, hydrogen is generated at the cathodic electrode, and chloride ions are adsorbed to the chloride ion adsorbent at the anodic electrode, which inhibits the generation of chlorine gas, thereby preventing the electrodes and other structural components in the reactor from being corroded. In addition, since the generation of chlorine gas at the anodic electrode is suppressed, it is possible to prevent an anodic electrode gas outlet from entering a toxic state. That is, safety of the reactor is improved.

Example 1

The chloride ion adsorbent according to the first aspect was prepared using the first functionalization method in a manner described below.

1. Heat treatment of silica gel

Silica gel was heated to 300°C under N₂ conditions for 2 hours and was then retained at the raised temperature for 4 hours so that the silica gel was calcined. Through the process, the hot silica gel from which moisture is sufficiently removed is produced. This is porous silica.

2. Addition of heat-treated silica gel to solvent

After preparing 300 ml of a toluene solution, 20 g of the hot silica gel was quickly transferred to the toluene solution to prevent adsorption of moisture.

3. Functionalization of porous silica with amino group

10 ml of a solution of [3-(2-aminoethylamino)propyl]trimethoxysilane (Sigma-Aldrich) was added dropwise to the toluene solvent to which the heat-treated silica gel had been added, and then the mixed solution was heated to 100°C for 24 hours under stirring for functionalization. That is, the surface of the porous silica was functionalized to produce the porous silica functionalized with an amino group (Diamine_SG).

4. Washing and drying of porous silica functionalized with amino groups

The prepared Diamine_SG was washed with toluene and acetone and then dried in an oven at 110°C. FIG. 1(B) is a photograph of the Diamine_SG thus obtained.

Example 2

The chloride ion adsorbent according to the second aspect was prepared using the second functionalization method in a manner described below.

1. Heat treatment of silica gel

2. Addition of heat-treated silica gel to solvent

3. Functionalization of first organic compound

5 ml of a solution of (3-Chloropropyl) triethoxysilane (Sigma-Aldrich) was added dropwise to the toluene solvent to which the heat-treated silica gel had been added, and then the mixed solution was heated to 100°C for 24 hours under stirring for functionalization. That is, the surface of the porous silica was functionalized to produce the porous silica functionalized with a chloropropyl group.

4. Washing and drying of porous silica functionalized with first organic compound

The prepared porous silica functionalized with a chloropropyl group was washed with toluene and acetone and then dried in an oven at 110°C.

5. Functionalization of porous silica with amino group by binding first organic compound and second organic compound

The dried chloropropyl-functionalized porous silica was transferred to a toluene solvent, 0.5 g of polyethylenimine (PEI, branched (Sigma-Aldrich)) was added, and the mixture was heated and stirred at 100° C for 24 hours so that the surface of the silica gel was functionalized with PEI groups. Thus, amino group-functionalized porous silica (PEI_SG) was prepared.

6. Washing and drying of porous silica functionalized with amino groups

The prepared PEI_SG was washed with toluene and acetone and then dried in an oven at 110°C. FIG. 1(C) is a photograph of the PEI_SG thus obtained.

Example 3

N-dodecyl-N',N'-dimethylpropane-1,3-diamine (C12-DMAPA) was prepared as a chloride ion adsorbent according to the second embodiment in a manner described below.

1. A solution mixture was prepared by dissolving an appropriate amount of a material having an amino group, such as polyethyleneimine (PEI) or DMAPA, in a tetrahydrofuran (THF) solution.

2. In a state in which the reaction temperature is maintained at room temperature, an alkyl halide (C_nH_2n+1X) (X = Cl, Br, I, etc.) was added dropwise to the mixture while the mixture was vigorously stirred.

3. After 18 hours of the reaction, the reaction product was washed with an organic solvent and water, and the remaining gel-like polymer was used as a chloride ion adsorbent without further purification.

The structural formula of C12-DMAPA thus obtained is shown below.

Comparative Example 1

Silica gel was calcined to remove moisture and all organic materials contained in the silica gel by heating under air conditions to 550°C for 4 hours and retaining at 550°C for 4 hours. Thus, porous silica (PS) of Comparative Example was prepared. FIG. 1(A) is a photograph of the silica gel thus obtained.

Experimental Example 1

The Diamine_SG and PEI_SG obtained in Examples 1 and 2 and the SG obtained in Comparative Example were ground into fine particles using a pestle and mortar. Next, about 10 mg of each of the powders was heated at a rate of 10°C/min, and TGA analysis was performed on the heated powders in the presence of air. The results are shown in FIG. 2.

It is confirmed from FIG. 2 that the Diamine_SG and the PEI_SG, unlike the SG, start experiencing a weight reduction at about 250°C at which the organic material starts being decomposed due to the introduction of amino groups thereto, and thus the Diamine_SG and the PEI_SG, unlike the SG, contain the organic material.

Experimental Example 2

In order to check the surface area change attributable to the functionalization of the organic material, the nitrogen adsorption isotherm was obtained from 0.1 g of the PEI_SG, the Diamine_SG, and the SG with an adsorption analyzer (Micrometritics ASAP 2020 Adsorption Analyzer). The results are shown in FIG. 3.

It was confirmed from FIG. 3 that the PEI_SG and the Diamine_SG, unlike the SG, experienced a larger reduction in surface area than the SG because the amino group covered the surface thereof. It was confirmed that the decrease in surface area is the largest in the case of the PEI_SG containing PEI, which is an amine group in the form of a polymer. Through this experiment, it can be confirmed that the amine group functionalization has occurred.

Experimental Example 3

The content of the amine organic group was derived from the TGA results (FIG. 2) obtained in Experimental Examples 1 and 2, and the specific surface area (BET Surface area) was calculated from the nitrogen adsorption isotherm result (FIG. 3). The results are shown in Table 1.

	Content of organic material (%)	Specific surface area (BET surface area) (m²/g)
Silica gel (SG)	less than 5%	558
Diamine_SG	10%	395
PEI_SG	17%	11

From Table 1, it can be seen that when the porous silica is functionalized with amino groups, the content of organic materials increases but the specific surface area decreases. When considering the fact that the surface area decreases with increase in the content of organic materials, it is confirmed that the surface area decreases according to the amount of functionalized amino group. From this fact, it is seen that the porous silica was functionalized, and the amount of functionalized amino group differs for each porous silica.

Experimental Example 4

In a H-cell reactor having the structure as shown in FIG. 4, 2g of the Diamine_SG was put on the anodic electrode side, and each electrode side was supplied with 200ml of 1g/L NaCl solution. Next, electrolysis was performed for 24 hours in a state in which 0.01 A of current was supplied in constant current (CC) mode using a power supply. The color of the solution observed after 24 hours of the reaction on the anodic electrode side with the Diamine-SG supplied is shown in C of FIG. 5. The color of the solution after 24 hours of the reaction on the anodic electrode without the Diamine-SG supplied is shown in B of FIG. 5. In addition, the concentration of chlorine ions over time was measured in the experiment, and the results are shown in FIG. 6.

From FIG. 5, it is seen that the color of the solution on the anodic electrode side for the case of C (the case of the presence of the Diamine-SG) is darker than the color for the case of B (the case of the absence of the Diamine-SG). These results indicate that, when the chloride ion adsorbent of the present invention was not added, chloride ions dissolved in seawater were not adsorbed, and thus chloride ions were oxidized, resulting in generation of a larger amount of chlorine gas. This means that the electrode was more corroded and thus the color was more darkened.

In addition, FIG. 6 indicates that the amount of chlorine ions decreases more rapidly over time in the case where electrolysis is performed in the state where nothing is added than the case where electrolysis is performed in the state where the Diamine_SG is added. From this result, it is seen that when the chloride ion absorbent according to the first aspect of the present invention is not added, chloride ions are oxidized and thus chlorine gas is generated more quickly. In other words, the result shows that the concentration of chloride ions in the solution decreases slowly when electrolysis is performed after the Diamine_SG is added. This means that the chloride ion absorbent according to the first aspect of the present invention prevents oxidation of chloride ions.

Therefore, when the chloride ion adsorbent according to the first aspect of the present invention is added to the seawater electrolysis solution, it is expected that the chloride ion absorbent will be able to help prevent the corrosion of the electrode by reducing the generation of chlorine gas.

Experimental Example 5

In order to analyze the concentration of chlorine ions remaining in the aqueous solution after electrolysis of seawater, a device shown in FIG. 7 was constructed, then 2 g of each of the Diamine_SG and PEI_SG obtained in Examples 1 and 2 and the SG obtained in Comparative Example was placed on the anodic electrode side. After that, electrolysis was performed for 4 hours in each device in 0.01 A constant current (CC) mode. Here, a salt bridge used in FIG. 7 was prepared by a method described below.

5 g of Potassium nitrate (KNO₃, 99%, DAEJUNG) was added to 50 ml of distilled water, and the solution was heat while stirring at 80°C in a water bath. When KNO₃ was sufficiently dissolved, 1 g of agar (DAEJUNG) was added, and the solution was stirred until becoming transparent. When the solution becomes transparent, a 6-mm tube was carefully filled with the solution, using a syringe so as not to create air bubbles in the tube. The tube filled with the solution was immersed in a 1M KNO₃ solution.

In addition, after performing electrolysis for 4 hours, the solution in the tube on the cathodic electrode side was analyzed through titration in a manner described below. The results are shown in FIG. 8.

2 ml of the solution around the cathodic electrode of each of Examples 2-1 and 2-2 recovered after completion of the reaction, 58 ml of distilled water, and 200 μl of 5 wt% K₂CrO₄ were added to and stirred in a 250-ml beaker. Titration was performed by slowly dropwise adding a 0.02 N AgNO₃ solution, using a burette, and the point at which the solution turned from yellow to red was used as the endpoint. The titration was performed at least three times, and the average value was used as the result value.

FIG. 8 shows the amount of chlorine ions remaining after time has elapsed. The amount of current flowing under the reaction conditions of the device shown in FIG. 7 is the same, and the more chlorine gas is generated, the more chloride ions move from the cathodic electrode side to the anodic electrode side through the tube. Therefore, it is seen that the more chloride ions remaining in the solution, the less chlorine gas is generated.

Referring to FIG. 8, when the amount of chloride ions remaining in the solution was represented by 100% before the reaction was performed, when the Diamine_SG and the PEI_SG was added, 90% of the chloride ions remain compared to the case where the Diamine_SG and the PEI_SG was not added. When the reaction was performed with only the SG added, there was no significant difference in the amount of the remaining chloride ions compared to the case where nothing is added (No SG).

In addition, when the Diamine_SG was increased from 2g to 8g, more chloride ions were found to remain, indicating that the effect achieved by an increase in the amount of catalyst also exists. These experimental results mean that chlorine gas generation is reduced by the amine functional group included in the chloride ion adsorbent according to the first aspect of the present invention.

Experimental Example 6

In order to select an organic compound functionalized with an amino group, which is suitable as the chloride ion adsorbent according to the second aspect of the present invention, a 0.6 M NaCl solution was put into a test device shown in FIG. 10. The C12-DMAPA obtained in Example 3, DMAPA which was purchased from Sigma-Aldrich, triethylene amine (TEA, Sigma-Aldrich), and ammonia (NH₃) were respectively added to the devices, and electrolysis was performed for 16 hours under conditions of a voltage of 3.5 to 3.8 V and a current of 20 to 30 mA. The amounts of chlorine ions remaining in the solution before and after the electrolysis were analyzed using a mass spectrometer, a Benchtop NMR spectrometer, and a Mohr titration method, and the respective results are shown in FIGS. 11a to 11c. At this time, 0.1 M (0.1 eq) of each of the organic compounds was added per 1L of the 0.6 M NaCl solution.

As shown in FIGS. 11a to 11c, when a black portion indicating the amount of chlorine ions present before the electrolysis reaction and a gray portion indicating the amount of chlorine ions present after the electrolysis reaction are compared, it is confirmed that a larger amount of chlorine ions is present in the solution in the case where the electrolysis reaction is performed with the amino group-functionalized organic compound added than the case where the electrolysis reaction is performed without the amino group-functionalized organic compound added.

Experimental Example 7

Through Experimental Example 6, electrolysis experiments were performed under the same condition as in Experimental Example 6 while the amount of each of the C12-DMAPA and DMAPA, which were selected as organic compounds suitable for the chloride ion adsorbent according to the second aspect of the present invention, was changed. Thereafter, the amounts of chlorine ions present in the solution before and after electrolysis were analyzed by the Benchtop NMR, and the results are shown in FIGS. 12a and 12b. An electrolysis reaction was also performed on a 0.1 M KCl solution to which nothing was added, and the remaining chlorine ions were analyzed before and after the reaction.

From FIGS. 12a and 12b, it is confirmed that when the C12-DMAPA or DMAPA is added in an amount of more than 0.05 mol (0.05 eq), a reduction rate in the chlorine ion content in the solution between after the reaction and before the reaction is 4 or more times lower when the C12-DMAPA is used and is 2.5 or more times lower when the DMAPA is used compared to the case where nothing is added.

Experimental Example 8

Using the test device shown in FIG. 10, an electrolysis experiment was performed under the same conditions as in Experimental Example 6, on a 0.6 M NaCl solution and a 0.6 M NaCl solution + 0.06M C12-DMAPA. After that, the anodic electrode before the electrolysis reaction, the anodic electrode used in the electrolysis reaction of the 0.6 M NaCl solution, and the anodic electrode used in the electrolysis reaction of the 0.6 M NaCl solution + 0.06M C12-DMAPA were observed with an electron microscope, and the observation result images are shown in FIGS. 13a to 13c, respectively.

FIG. 13a is a photograph showing an electrode not used in the reaction, FIGS. 13b and 13c are photographs showing the dried electrodes after used for the electrolysis reaction of the 0.6 M NaCl solution and used for the electrolysis reaction of the 0.6 M NaCl solution + 0.06 M C12-DMAPA, respectively. In the point in that it can be confirmed from FIG. 13b that salt crystals are formed on the electrode surface after the drying, and it cannot be confirmed from FIG. 13c that salt crystals are formed after the drying, it is possible to confirm that generation of chlorine gas on the electrode surface is inhibited due to the chloride ion adsorption effect during the electrolysis reaction.

Experimental Example 9

Using the test device shown in FIG. 14B, electrolysis was performed on seawater (RSW) from the Red Sea for 6 hours under conditions of 10 V/100 mA (CC) with or without the addition of the 0.6 M of DMAPA. Thereafter, the amounts of chlorine ions present in the seawater before and after electrolysis were analyzed by the Benchtop NMR, and the results are shown in FIG. 14a. In addition, the voltage change according to the electrolysis reaction time was measured, and the results are shown in FIGS. 14c and 14d.

FIG. 14a is a result of an electrolysis reaction actually using seawater from the Red Sea. Electrolysis was performed in the presence of the DMAPA added, which is the second chloride ion adsorbent of the present invention, and then electrolysis was performed without the DMAPA, the concentration of chlorine ions in the seawater was measured for each case, and the results were compared. The result of the comparison reveals that the DMAPA adsorbs chloride ions and thus prevents the formation of chlorine gas during the electrolysis of seawater.

As shown in FIG. 14c, when a lot of chlorine ions are generated during the electrolysis reaction of seawater, as time goes by, the number of chlorine ions decreases and the total number of ions in the solution decreases, so voltage stability may be deteriorated. Similarly, as shown in FIG. 14d, it is seen that when the second chloride ion adsorbent of the present invention, i.e., DMAPA, is added to seawater, the rate at which chloride ions are reduced is lowered, so that voltage stability is restored.

Experimental Example 10

After adding 3 mM of the C12-DMAPA was to each of the 3M KCl solutions respectively adjusted to pH3 and pH7, the voltage applied to the electrode was changed using the device shown in FIG. 15c and a cyclic amperometric method was used. The results are shown in FIGS. 15a and 15b illustrated in different scales.

FIGS. 15a and 15b are graphs showing the results of the cyclic amperometric methods for checking at what voltage the oxidation/reduction reaction occurs on the surface of the electrode while the voltage applied to the electrode is changed. When viewing changing the shape of the graphs, it is seen that the redox occurring in the electrolysis reaction is affected by pH. On the basis of these results, it is possible to determine whether the reaction can proceed with less energy under certain conditions even in the case of a reaction in which the same amount of chlorine gas is produced.

Experimental Example 11

With the test device shown in FIG. 10, for each of seawater (Øresund seawater), seawater + KOH 0.1 eq added, and seawater + C12-DMAPA 0.1 eq added, an electrolysis reaction was performed for 6 hours under the conditions of 100 mA (CC). After that, the concentrations of chlorine ions contained in seawater before and after the electrolysis reaction were measured by the benchtop NMR and the Mohr titration (Agentometry). Graphs showing the results are illustrated in FIGS. 16a and 16b.

FIGS. 16a and 16b show how much chlorine ions are present before and after the electrolysis reaction. The concentrations of chlorine ions before and after the reaction are displayed in black and gray, respectively. It can be seen that the formation of chlorine gas was suppressed when C12-DMAPA, which is the second chloride ion adsorbent of the present invention, was used.

Experimental Example 12

For a kinetic experiment, for each of seawater (Øresund seawater), seawater + KOH 0.1 eq added, and seawater + C12-DMAPA 0.1 eq added, an electrolysis reaction was performed for 20 minutes under the same condition as in Experimental Example 11, using an H-cell (electrolyzer) shown in FIG. 17a, and the hydrogen generation rate was measured. The results are shown in FIG. 17b. In addition, voltage over time was measured during the kinetic experiment, and the results are shown in FIG. 18.

FIG. 17b shows the hydrogen generation rate over time. When the C12-DMAPA was used, the graph slope is gentler than that of the case where the actual seawater (Øresund seawater) was used. This result shows that the hydrogen generation rate is slightly reduced due to the influence of the chloride ion adsorbent according to the second aspect of the present invention.

FIG. 18 is a graph showing the voltage stability of an electrolysis system during the kinetic experiment, and it is confirmed that the voltage stability can be maintained when the C12-DMAPA is added.

Experimental Example 13

For each of the material structure of the C12-DMAPA (i.e., the state (pure C12-DMAPA) obtained in Example 3), C12-DMAPA extracted from NaCl 0.6 M, and C12-DMAPA extracted after electrolysis of NaCl 0.6 M for 6 hours under the condition of a current of 100 mA, the NMR spectrum analysis was performed, and the results are shown in FIGS. 19a and 19b.

FIG. 19a shows a spectrum (3) of pure C12-DMAPA, a spectrum (2) of C12-DMAPA extracted from NaCl 0.6 M, and a spectrum (1) of C12-DMAPA extracted after 6 hours of electrolysis of NaCl 0.6 M at 100 mA in this order from top to bottom. FIG. 19b shows a spectrum of distilled pure C12-DMAPA at the top and a spectrum of C12-DMAPA extracted from Øresund sweater after 6 hours of electrolysis at 100 mA at the bottom.

FIGS. 19a and 19b show that there is no structural change of C12-DMAPA when comparing the NMR data before and after the electrolysis reaction. Therefore, it is seen that the organic compound used as the chloride ion adsorbent according to the second aspect of the present invention also exhibits structural stability in the electrolysis reaction and can be used as a catalyst.

From the above experimental results, it is seen that the chloride ion adsorbents according to the first and second aspects according to the present invention prevent a high concentration of chlorine ions (Cl^-) from being oxidized instead of oxygen during the electrolysis when producing hydrogen directly from seawater that has not undergone desalination, thereby solving the problem that the water electrolysis efficiency is reduced. Therefore, when the present invention is applied to direct hydrogen production from natural seawater, economic benefits can be obtained.

Although the present invention has been described with reference to the preferred example, the ordinarily skilled in the art will appreciate that the present invention is not limited to the example described above and can be diversely changed and modified without departing from the scope of the spirit of the present invention.

Claims

A chloride ion adsorbent comprising porous silica functionalized with an amino group.
The chloride ion adsorbent according to claim 1, wherein the functionalization is made by covalent bonding of aminosilane to porous silica.
The chloride ion adsorbent according to claim 2, wherein the aminosilane is an organosilane compound containing at least one of a primary amino group and a secondary amino group.
The chloride ion adsorbent according to claim 1, wherein the functionalization is performed by introducing a second organic compound having an amino group to a first organic compound after the first organic compound is covalently bonded to the porous silica.
The chloride ion adsorbent according to claim 4, wherein the second organic compound is at least one selected from the group consisting of N',N'-dimethylpropane-1,3-diamine (DMAPA), ammonia(NH₃), ethylamine, butylamine, N-dodecyl-N’,N’-dimethylpropane-1,3-diamine (C12-DMAPA), hexylamine, octylamine, decylamine, dodecylamine, detradecylamine,hexadecylamine,octadecylamine, ethylenediamine (NH₂CH₂CH₂NH₂), tetramethylenediamine(NH₂(CH₂)4NH₂), hexamethylene diamine (NH₂(CH₂)6NH₂), N-ethylethylenediamine (NH₂CH₂CH₂NHCH₂CH₃), N,N'-dimethylethylene diamine(NH₂CH₂CH₂N(CH₃)₂), N,N'-diethylethylenediamine(NH₂CH₂CH₂N(CH₂CH₃)₂), diethylenetriamine(NH₂CH₂CH₂NHCH₂CH₂NH₂),triethylenetetraamine(NH₂CH₂CH₂NHCH₂CH₂NHCH₂CH₂NH₂), and polyethyleneimine.
The chloride ion adsorbent according to claim 1, wherein the amino group is contained in a concentration of 0.3 mmol/g or more.
The chloride ion adsorbent according to claim 1, wherein the porous silica is silica gel.
The chloride ion adsorbent according to any one of claims 1 to 7, wherein the chloride ion adsorbent is included in an electrolysis solution for electrolysis of seawater to inhibit chlorine gas from being generated and electrodes from being corroded.
A method of preparing a chloride ion adsorbent, the method comprising the step(s) of:

heat-treating porous silica;

adding the heated porous silica to a solvent; and

dropwise adding an aminosilane compound solution to the solvent to which the porous silica has been added, to functionalize the porous silica with an amino group.
A method of preparing a chloride ion adsorbent, the method comprising the step(s):

heat-treating porous silica;

adding the heated porous silica to a solvent;

functionalizing the porous silica with a first organic compound by dropwise adding a first solution containing a first organic compound to the solvent to which the porous silica has been added;

washing and drying the porous silica functionalized with the first organic compound;

adding the dried porous silica functionalized with the first organic compound to the solvent; and

dropwise adding a second solution containing a second organic compound having an amino group to the solvent to which the dried porous silica functionalized with the first organic compound has been added, thereby binding the second organic compound to the first organic compound to functionalize the porous silica with an amino group.
The method according to claim 9 or 10, wherein the aminosilane compound solution or the second solution containing the second organic compound having an amino group is added to adjust the concentration of the amino group to 0.3 mmol/g or more.
The method according to claim 9 or 10, wherein the step of heat-treating the porous silica is performed by raising the temperature to 250°C to 600°C for a duration of 90 to 300 minutes and then maintaining the temperature for a duration of 180 to 360 minutes.
The method according to claim 12, wherein the porous silica is silica gel, and the solvent is at least one selected from the group consisting of toluene and acetone.
A method of producing hydrogen directly from seawater, the method comprising the step(s) of:

adding the chloride ion adsorbent of any one of claims 1 to 7 to a reactor containing seawater for electrolysis;

electrolyzing the seawater by applying an electric current to an anodic electrode and a cathodic electrode installed in the reactor; and

causing the chloride ion adsorbent to selectively adsorb chloride ions generated during the electrolysis of the seawater.
The method according to claim 14, wherein the chloride ion adsorbent is added in an amount of 50 g to 500 g per 1 L of the seawater.
The method according to claim 14, wherein the chloride ions adsorbed to the chloride ion adsorbent are desorbed from the chloride ion adsorbent by diffusion due to a difference in concentration when no current is applied to the anodic electrode and the cathodic electrode.
The method according to claim 14, wherein the electrode is not corroded by chlorine gas because the generation of chlorine gas is inhibited at the anodic electrode.
A chloride ion adsorbent comprising an organic compound functionalized with one or more amino groups.
The chloride ion adsorbent according to claim 18, wherein the amino group comprises at least one of a primary amino group and a secondary amino group.
The chloride ion adsorbent according to claim 19, wherein the organic compound is at least one selected from the group consisting of N',N'-dimethylpropane-1,3-diamine (DMAPA), ammonia(NH₃), ethylamine, butylamine, N-dodecyl-N’,N’-dimethylpropane-1,3-diamine (C12-DMAPA), hexylamine, octylamine, decylamine, dodecylamine, detradecylamine,hexadecylamine,octadecylamine, ethylenediamine (NH₂CH₂CH₂NH₂), tetramethylenediamine(NH₂(CH₂)4NH₂), hexamethylene diamine (NH₂(CH₂)6NH₂), N-ethylethylenediamine (NH₂CH₂CH₂NHCH₂CH₃), N,N'-dimethylethylene diamine(NH₂CH₂CH₂N(CH₃)₂), N,N'-diethylethylenediamine(NH₂CH₂CH₂N(CH₂CH₃)₂), diethylenetriamine(NH₂CH₂CH₂NHCH₂CH₂NH₂),triethylenetetraamine(NH₂CH₂CH₂NHCH₂CH₂NHCH₂CH₂NH₂), and polyethyleneimine.
The chloride ion adsorbent according to any one of claims 18 to 20, wherein the chloride ion adsorbent is added to a seawater solution to be electrolyzed for the purpose of inhibiting chlorine gas from being generated and reducing the corrosion of an electrode and other structural components of a reactor.
Seawater for electrolysis to which the chloride ion adsorbent according to any one of claims 1 to 7 or the chloride ion adsorbent according to any one of claims 18 to 20 is added.
A method of producing hydrogen directly from seawater, the method comprising the step(s) of:

adding the chloride ion adsorbent of any one of claims 18 to 21 to a reactor containing seawater for electrolysis;

electrolyzing the seawater by applying a voltage between an anodic electrode and a cathodic electrode installed in the reactor; and

causing the chloride ion absorbent to selectively adsorb chloride ions generated during the electrolysis of the seawater.
The method according to claim 23, wherein the chloride ion adsorbent is added in an amount of 0.05 mol/L to 5 mol/L of seawater.
The method according to claim 24, wherein the electrode corrosion as well as corrosion of other structural components due to chlorine gas is prevented because generation of chlorine gas is inhibited at the anodic electrode.
The method according to claim 24, wherein safety is improved because a solution present around an anodic gas outlet is not toxic because generation of chlorine gas is inhibited at the anodic electrode.