JP2016169138A - Mixed conductive graphene oxide sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen selective permeable membrane consisting of single component material capable of being manufactured simply at low cost, operating at ambient pressure without needs for large pressure difference, operating in a wide temperature range from room temperature to high temperature about 200°C without needs for high temperature and permeating hydrogen only without permeating helium, oxygen, nitrogen and carbon dioxide or the like other than hydrogen.SOLUTION: There is provided a manufacturing method of a mixed conductive graphene oxide sheet for heat reduction of a part of graphene oxide at a temperature of 80 to 150°C after forming a graphene oxide dispersion to sheet-like or optical reduction of a part of graphene oxide by irradiating ultraviolet light of 100 to 500 W for 1 to 90 minutes. There is provided the mixed conductive graphene oxide sheet exhibiting equivalent values of proton conductivity and electron conductivity at 25°C of 10to 10Scmat relative humidity 90% and 10to 10Scmat relative humidity 40%.SELECTED DRAWING: None

Description

  The present invention relates to a mixed conductive graphene oxide sheet that exhibits both proton conductivity and electrical conductivity at room temperature (about 25 ° C.), a method for producing the graphene oxide sheet, and hydrogen selective permeation using the graphene oxide sheet. Relates to the membrane.

  As a clean energy supply source, a fuel cell using hydrogen has been developed. A stable supply of hydrogen is indispensable for the spread of fuel cells, and there is an urgent need to establish an economical hydrogen production method. As a method for producing hydrogen, a method of purifying by a cryogenic separation method, a pressure fluctuation adsorption method (PSA method) or the like after steam reforming or partial oxidation of hydrocarbons is well known. When hydrogen is produced using hydrocarbon as a raw material, it is necessary to separate and extract only hydrogen because nitrogen, oxygen, carbon monoxide and the like coexist. Therefore, the production cost of hydrogen can be reduced by improving the efficiency of the hydrogen separation / purification process.

  A membrane separation method has been proposed as a method for easily separating and purifying hydrogen at a low cost. Examples of hydrogen separation membranes include porous membranes such as silica, silica-based composite oxides, Ni nanoparticle-dispersed silica, carbon membranes, non-oxides, metals such as Pd and Pd-Ag, and polymers such as polyimide. Non-porous membranes have been proposed. The porous membrane mainly uses the molecular sieve function, and the non-porous membrane mainly uses the selective dissolution diffusivity of hydrogen. The metal-based non-porous membrane is excellent in terms of hydrogen permselectivity and water vapor resistance, but the silica-based porous membrane is excellent in terms of acid resistance, coking resistance, and heat resistance. In addition, the hydrogen permselectivity is temperature-dependent, and conventional hydrogen separation membranes operate at high temperatures, but often do not operate at room temperature, and the operating temperature range is narrow.

  For example, a porous support in a state where water is impregnated in pores is immersed in an organic solvent at a predetermined temperature in which metal alkoxide is dissolved, and the metal alkoxide in the organic solvent is placed on the outermost layer of the porous support. The porous layer is made of ceramic fine particles only on the outermost layer surface of the porous support, and the openings formed between the outermost ceramic particles A hydrogen separation membrane for sealing has been proposed (Patent Document 1). This hydrogen separation membrane is a hydrogen separation membrane utilizing the molecular sieve effect, and pressure loss can be reduced by forming a porous layer made of ceramic fine particles only on the outermost layer. However, there is a problem that it easily permeates carbon dioxide, oxygen, nitrogen, and the like.

  Alternatively, a hydrogen separation membrane in which a Pd—Ag alloy thin film is deposited on the outer surface of a porous ceramic hollow fiber has been proposed (Patent Document 2). This hydrogen separation membrane utilizes the hydrogen selective permeability of Pd and has temperature dependence, so that a high temperature of 300 ° C. or higher is required for operation. Further, Pd is expensive and the transmission speed is not improved unless the film thickness is reduced. In order to prepare a thin film, a high technique such as a CVD method is required, and there is a problem that durability is lowered by thinning the film.

Alternatively, a hydrogen separation membrane made of a porous ceramic membrane in which silica (SiO ₂ ) is supported in pores has been proposed (Patent Document 3). This hydrogen separation membrane utilizes the hydrogen permselectivity of the SiO ₂ membrane and the molecular sieve effect due to the porous body, and because it has temperature dependence, it operates at a high temperature of 150 to 500 ° C., and has an inlet side and an outlet side. It is necessary to provide a pressure difference between the two. In addition, carbon dioxide, oxygen, nitrogen and the like are permeated, resulting in poor hydrogen selectivity.

As a material exhibiting electrochemical hydrogen permeability, a ceramic mixed conductor film in which BeCeO ₃ is doped with a different element has been proposed. However, the operating temperature is as high as 300 ° C. or more, and there is a problem that it reacts with carbon dioxide in the atmosphere and deteriorates. In addition, the workability of the film is extremely poor. In addition, a mixed conductor membrane in which a proton exchange membrane represented by Nafion (registered trademark) and an electronic conductor such as carbon are combined has been proposed and widely used. However, since the mixed conductor film is a heterogeneous bonding material, the hydrogen permeation region is limited only to the interface, and the amount of permeation cannot be increased essentially, making thinning and densification difficult and increasing mechanical strength. Is also inferior.

  On the other hand, ultra-thin hydrogen separation membranes using graphene or graphene oxide, which are single component materials, have also been reported (Non-patent Documents 1 and 2). However, these utilize the molecular sieve function due to the micropores present in graphene and graphene oxide, and helium, carbon dioxide, nitrogen and oxygen also permeate, and there is a problem that they do not function as a hydrogen selective permeable membrane. . Furthermore, these are ultra-thin films of about 100 nm, are inferior in strength, and require a porous support to be used as a hydrogen selective permeable membrane.

JP 2007-229562 A JP-A-6-254361

Science, 342, 91 (2013) Science, 342, 95 (2013)

  The present invention solves the problems of conventionally proposed hydrogen separation membranes, can be manufactured easily and inexpensively, can operate at atmospheric pressure without introducing a large pressure difference, and requires high temperatures. It is possible to operate in a wide temperature range from room temperature to a high temperature of about 200 ° C., and can transmit only hydrogen without transmitting helium, oxygen, nitrogen, carbon dioxide, etc. other than hydrogen. It aims at providing the hydrogen permselective membrane which consists of component materials.

  The present invention also provides a mixed conductive graphene oxide capable of providing a hydrogen permselective membrane made of a single component material and capable of exhibiting the same degree of proton conductivity and electron conductivity at room temperature, and a method for producing the same. The purpose is to do.

  The present inventors paid attention to a graphene oxide membrane having both proton conductivity and electron conductivity as a hydrogen separation membrane made of a single component material. Multilayer graphene oxide has high proton conductivity because it can move protons through epoxy groups through nanofluidic channels. Similarly, it is attracting attention as an excellent proton conductive material in that it is inexpensive and easy to manufacture as compared with Nafion (registered trademark) showing high proton conductivity. However, the proton conductivity of graphene oxide greatly depends on the film thickness, and thus there is a problem that the application is limited. Further, since the proton conductivity of graphene oxide is expressed by an epoxy group, the epoxy group is easily reductively decomposed in a reducing atmosphere, and there is a problem that the proton conductivity is not expressed. On the other hand, reduced graphene oxide has high in-plane electron conductivity. Therefore, as a result of earnest research on a method for producing mixed-conducting graphene oxide that combines proton conductivity and electronic conductivity at the same level, we have learned how to produce partially reduced graphene oxide that can optimally control the degree of reduction. Thus, the present invention has been completed.

Specific embodiments of the present invention are as follows.
[1] A mixed conductive graphene oxide sheet in which both proton conductivity and electron conductivity measured at a temperature of 25 ° C. are equivalent.
[2] Both the proton conductivity and the electronic conductivity are in the range of 10 ⁻¹ to 10 ⁻⁵ Scm ⁻¹ at 90% relative humidity, and 10 ⁻¹ to 10 ⁻⁸ Scm ⁻ at 40% relative humidity. ¹ is a mixed conductive graphene oxide sheet according to [1].
[3] Both the proton conductivity and the electronic conductivity are in the range of 10 ⁻¹ to 10 ⁻⁶ Scm ⁻¹ at 90% relative humidity, and 10 ⁻¹ to 10 ⁻⁶ Scm ⁻ at 40% relative humidity. ¹ is a mixed conductive graphene oxide sheet according to [1].
[4] After the graphene oxide dispersion is formed into a sheet, a part of the graphene oxide is thermally reduced at a reduction temperature of 40 to 150 ° C., according to [1] or [2] A method for producing a mixed conductive graphene oxide sheet.
[5] The graphene oxide dispersion is formed into a sheet and then irradiated with 100 to 500 watts of ultraviolet light for 1 to 90 minutes to photoreduce a part of the graphene oxide. [1] The method for producing a mixed conductive graphene oxide sheet according to [3].
[6] The mixing according to [4] or [5], wherein sulfate ions are added to the graphene oxide dispersion and then formed into a sheet shape, or sulfate ions are added after the graphene oxide is formed A method for producing a conductive graphene oxide sheet.
[7] The mixed conductive graphene oxide sheet according to [6], wherein the addition amount of sulfate ion is in the range of 0.05 to 0.5 as the atomic ratio of sulfur to carbon (S / C) Manufacturing method.
[8] A graphene oxide hydrogen permselective membrane comprising the mixed conductive graphene oxide sheet according to any one of [1] to [3].
[9] A graphene oxide hydrogen permselective membrane comprising a carbon film carrying a platinum group metal or an alloy thereof on both surfaces of the mixed conductive graphene oxide sheet according to any one of [1] to [3] .

  According to the present invention, there is provided a method for producing mixed conductive graphene oxide exhibiting proton conductivity and electron conductivity at the same level at room temperature (about 25 ° C.). The mixed conductive graphene oxide manufactured by the mixed conductive graphene oxide manufacturing method of the present invention is useful as a hydrogen selective permeable membrane made of a single component material.

  The hydrogen permselective membrane of the present invention can be produced easily and inexpensively because the membrane can be produced by a chemical process such as taking out a basic colloidal material from graphite and applying it.

  The hydrogen permselective membrane of the present invention can selectively permeate and separate hydrogen at room temperature under atmospheric pressure.

2 is a photograph of a graphene oxide film obtained in Example 1. In the photoreduction method in Example 1, (a) XPS chart showing changes in functional group of graphene oxide with respect to irradiation time, (b) concentration of oxidized functional group calculated from XPS peak, (c) non-calculated from XPS peak It is a graph which shows the interlayer distance of the density | concentration of an oxidation functional group, and the graphene oxide computed from (d) XRD diffraction peak. In the thermal reduction method in Example 1, (a) XPS chart showing the change of the functional group of graphene oxide with respect to the reduction temperature, (b) concentration of the oxidized functional group calculated from the XPS peak, (c) non-oxidized calculated from the XPS peak It is a graph which shows the interlayer distance of the density | concentration of a functional group, and the graphene oxide computed from (d) XRD diffraction peak. It is a graph which shows the humidity dependence of the proton conductivity of the partially reduced graphene oxide by the photoreduction and thermal reduction in Example 1. It is a graph which shows the relationship between the proton conductivity of the partially reduced graphene oxide by the photoreduction in Example 1, and thermal reduction, and epoxy group content. (A) is a graph which shows the relationship between the irradiation time in the photoreduction in the case of relative humidity 40% and 90% in Example 1, and proton conductivity and electronic conductivity, (b) is the relative humidity in Example 1. It is a graph which shows the relationship between the reduction temperature in proton reduction in the case of 40% and 90%, proton conductivity, and electronic conductivity. (A) is a graph which shows the relationship between the oxygen content in the graphene oxide in Example 1, and the partial graphene oxide, proton conductivity, and electronic conductivity, (b) is the interlayer distance of the partially reduced graphene oxide in Example 1. It is a graph which shows the relationship between (d) and proton conductivity, (c) is a graph which shows the difference between the reduction | restoration methods of thermal reduction and photoreduction, and the relationship between oxygen content and interlayer distance. 4 is an XPS chart of partially reduced graphene oxide (S / C = 1.32) obtained by thermal reduction in Example 2. (A) shows the relationship between the reduction temperature obtained from the XPS chart of the product (S / C = 1.32) in Example 2 and the non-oxidizing functional groups (C—C, C—H defect, C = C). It is a graph, (b) shows the relationship between the reduction temperature obtained from the XPS chart of the product in Example 2 and the oxidation functional groups (C—O—C, C═O, C—OH, O═C—O). It is a graph to show. It is a graph which shows the relationship between the thermal reduction temperature of the product (S / C = 1.32) in Example 2, and the sulfur content (atomic%) in partially reduced graphene oxide. It is an XRD chart of the product (S / C = 1.32) in Example 2 (thermal reduction). It is a graph which shows the relationship between the reduction temperature of the product in Example 2 (thermal reduction), and interlayer distance (d (nm)). It is a graph which shows the influence of reduction temperature and relative humidity with respect to the proton conductivity of the product (S / C = 1.32) in Example 2. It is a graph which shows the relationship of the proton conductivity and electronic conductivity, and reduction | restoration temperature in 40% and 90% of relative humidity of the product (S / C = 1.32) in Example 2. It is a graph which shows the relationship between the thermal reduction temperature at the time of changing the sulfuric acid addition amount in Example 2 to become S / C = 0.06, and proton conductivity and electronic conductivity in relative humidity 40% and 90%. . It is an XRD chart of the product (S / C = 1.32) in Example 2 (photoreduction). It is a graph which shows the relationship between the irradiation time of the product and interlayer distance (d (nm)) in Example 2 (photoreduction). It is a graph which shows the influence of the light irradiation time and relative humidity with respect to the proton conductivity of the product (S / C = 1.32) in Example 2. It is a graph which shows the relationship between 40% of relative humidity of the product (S / C = 1.32) in Example 2, and the proton conductivity and electronic conductivity in 90%, and irradiation time.

Preferred embodiment

  Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

  The present invention relates to a partially reduced graphene oxide film (hereinafter also referred to as “mixed conductive graphene oxide”) in which graphene oxide is partially reduced to develop the same proton conductivity and electron conductivity, and mixed conductive graphene oxide. The present invention relates to a hydrogen selective permeable membrane made of a manufacturing method and mixed conductive graphene oxide.

  Graphene oxide is a nanosheet material obtained by partial oxidation of graphite and then delamination, and has functional groups such as a carboxyl group, a carbonyl group, a hydroxyl group, and an epoxy group as functional groups (Chemical Formula 1).

  The mixed conductive graphene oxide used in the present invention is obtained by partially reducing the graphene oxide while leaving an epoxy group to develop the same degree of proton conductivity and electron conductivity.

  A simplified schematic diagram for explaining the relationship between the degree of reduction of graphene oxide, proton conductivity, and electron conductivity is shown (Chemical Formula 2).

  Graphene oxide (hereinafter also referred to as “GO”) has high proton conductivity (Proton conductivity), while reduced graphene oxide (hereinafter also referred to as “rGO”) has high electron conductivity. By adjusting the degree of reduction of graphene oxide, it is possible to obtain a single component material having mixed conduction having both equivalent proton conductivity and electron conductivity. This partially reduced graphene oxide having mixed conductivity can be used as a hydrogen selective permeable membrane made of a single component material.

  Mixed conductive graphene oxide is obtained by partially reducing a stack of graphene oxide nanosheets prepared from graphite. For ease of understanding, as schematically shown in the upper part of the chemical formula 2 graph, electrons move through the stacked graphene oxide nanosheets, and the surface functional groups between the layers of the stacked reduced graphene oxide nanosheets are protonated. Move.

  A state where the mixed conductive graphene oxide of the present invention has both electronic conductivity and proton conductivity is schematically shown (Chemical Formula 3).

  As shown in Chemical Formula 3, mixed conductive graphene oxide (lower) does not completely reduce graphene oxide nanosheets (upper), and proton conductivity is due to some surface functional groups (epoxy groups) remaining. Is maintained. Reduction of the surface functional group causes CH defects and C═Cπ covalent bond, and the C═Cπ covalent bond exhibits electronic conductivity. C = Cπ covalent bonds provide a narrow interlayer distance and electronic conductivity, while CH defects provide a relatively large interlayer distance. This relatively large interlayer distance gives freedom to the movement of water molecules attached to the epoxy group and enhances proton conductivity. The laminate of mixed conductive graphene oxide nanosheets has a portion where the interlayer distance is not uniform and the interlayer distance is wide due to CH defects and the portion where the interlayer distance is narrow due to C = Cπ covalent bond, and protons that pass protons respectively. An electron nano-passage that allows passage of electrons through a nano-passage is provided.

The mixed conductive graphene oxide of the present invention has similar proton conductivity and electron conductivity at room temperature. Proton conductivity is affected by relative humidity, and proton conductivity decreases as humidity decreases. The proton conductivity and electronic conductivity expressed by the mixed conductive graphene oxide of the present invention are in the range of 10 ⁻¹ to 10 ⁻⁶ Scm ⁻¹ , more preferably 10 ⁻² to 10 ⁻ at 25 ° C. and 90% relative humidity. ³ Scm ^{−1, and} a range of 10 ⁻¹ to 10 ⁻⁸ Scm ⁻¹ at 25 ° C. and a relative humidity of 40%, more preferably 10 ⁻¹ to 10 ⁻⁵ Scm ⁻¹ , and even more preferably 10 ^−1. in the range of to 10 ^-3 Scm ^-1.

The mixed conductive graphene oxide of the present invention can be produced by partially reducing graphene oxide. As the reduction method, photoreduction or thermal reduction can be used. The range in which the proton conductivity and the electron conductivity coincide with each other depending on the partial reduction method. In the mixed conductive graphene oxide sheet obtained by thermal reduction, the range of 10 ⁻¹ to 10 ⁻⁵ Scm ⁻¹ at 90% relative humidity. The proton conductivity and the electron conductivity agree with each other in the range of 10 ⁻¹ to 10 ⁻⁸ Scm ⁻¹ at a relative humidity of 40%. In the mixed conductive graphene oxide sheet obtained by photoreduction, the range of 10 ⁻¹ to 10 ⁻⁶ Scm ⁻¹ at 90% relative humidity and the range of 10 ⁻¹ to 10 ⁻⁶ Scm ⁻¹ at 40% relative humidity. The proton conductivity and the electron conductivity agree with each other.

  The thermal reduction preferably partially reduces graphene oxide in the range of 40 to 150 ° C., more preferably in the range of 50 to 80 ° C., depending on the desired ranges of proton conductivity and electronic conductivity. be able to. The heat reducing atmosphere may be in the air.

  Photoreduction is preferably partially reduced by irradiating the graphene oxide with ultraviolet light of 100 to 500 watts in an irradiation time range of 1 minute to 200 minutes, more preferably in the range of 10 minutes to 90 minutes. It can be varied depending on the desired range of proton conductivity and electronic conductivity.

  In any method of thermal reduction and photoreduction, sulfuric acid may be added to the graphene oxide dispersion or graphene oxide film before reduction. By adding sulfuric acid, high proton conductivity can be realized. The amount of sulfuric acid added is preferably in the range of 0.05 to 0.5 as the atomic ratio of sulfur to carbon (S / C), and particularly preferably 0.1 to 0.2 in order to achieve high proton conductivity.

  A hydrogen permeation mechanism of a hydrogen selective permeable membrane composed of a partially reduced graphene oxide membrane of the present invention is schematically shown (Chemical Formula 4).

  When hydrogen contacts the surface of the partially reduced graphene oxide film, the hydrogen is separated into hydrogen ions and electrons by anodic oxidation (Step 1 surface reaction), and each moves through the proton nanochannel and the electron nanochannel of the partially reduced graphene oxide film. Then (Step 2 bulk diffusion), cathode reduction is performed on the opposite surface, and hydrogen ions and electrons are combined to form hydrogen molecules (Step 3 surface reaction). The partially reduced graphene oxide membrane constituting the hydrogen selective permeable membrane of the present invention has proton conductivity and electron conductivity, but does not have conductivity of other ions, so that only hydrogen is selectively separated. Can do.

  In the hydrogen selective permeable membrane of the present invention, a hydrogen separation catalyst may be supported on the surface of the partially reduced graphene oxide membrane in order to promote hydrogen separation on the membrane surface. The hydrogen separation catalyst is not particularly limited as long as it does not affect the hydrogen permeability of the partially reduced graphene oxide membrane, and preferred examples include white metal metals such as platinum, palladium, ruthenium, and alloys thereof.

  Further, the graphene oxide hydrogen permselective membrane may have a laminated structure having a carbon film carrying a platinum group metal or an alloy thereof on both surfaces of the mixed conductive graphene oxide sheet of the present invention. The graphene oxide hydrogen permselective membrane can be produced by dropping a platinum group-supported carbon alcohol solution onto both sides of a mixed conductive graphene oxide sheet and drying at room temperature. The metal content of the platinum group-supported carbon film is preferably 5 to 50 wt% with respect to 100 wt% of carbon.

  The present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

[Example 1]
According to the procedure of the modified Hummer method shown below (Chemical Formula 5), a graphene oxide dispersion liquid having a concentration of 0.8 mg / mL was prepared, and the graphene oxide dispersion liquid was subjected to suction filtration with a membrane filter to obtain a graphene oxide film ( FIG. 1).

<Photoreduction>
The obtained graphene oxide film was irradiated with ultraviolet light in air using a 500 W high-pressure ultraviolet lamp to prepare a partially reduced graphene oxide film.

<Thermal reduction>
The obtained graphene oxide film is put in an incubator (ESPEC, SH-221) and heated in air at 70 to 150 ° C. and 100% relative humidity for 1 hour to prepare a partially reduced graphene oxide film did.

<Analysis sample preparation>
Sample for AC and DC measurement: A graphene oxide dispersion was dropped onto a comb-shaped electrode (width 2 μm, interval 2 μm, 65 pairs) and dried to prepare a comb-shaped electrode sample.
Samples for X-ray photoelectron analysis (XPS), Fourier transform infrared analysis (FT-IR) and X-ray diffraction analysis (XRD): A graphene oxide film was prepared by dropping a graphene oxide dispersion onto a glass substrate and drying it. .
-Sample for ¹³ C solid state nuclear magnetic resonance analysis (SSNMR): prepared by subjecting a graphene oxide dispersion to filtration using a membrane filter (pore size 0.4 μm) to prepare a graphene oxide film, followed by photoreduction or thermal reduction did.

<Analysis items>
-Shape and thickness of comb-shaped electrode sample: observed with an atomic force microscope.
Interlayer distance of analytical sample on glass substrate: observed by XRD using CuKα (λ = 0.154 nm) radiation at 3 ° -20 ° scan.
Oxidized functional groups (C—O—C, C═O, C—OH, —COOH), non-oxidized functional groups (C sp ³ C—C, C—H defects) on graphene oxide films and partially reduced graphene oxide films ^{, C sp 2 C = C)} : XPS, FT-IR, was observed with SSNMR.
Electronic conductivity: AC impedance measured using a comb-shaped electrode sample using an impedance / gain analyzer (perturbation amplitude voltage 50 mV, frequency range 1 MHz to 1 Hz), or DC resistance R measured using a two-probe DC method, The film width L corresponding to the distance between the two electrodes (2 × 10 ⁻⁴ cm), the film thickness T obtained from the AFM height profile, and the film length D between the two electrodes obtained from the CCD camera are represented by the formula:
σ = L / (R × T × D)
Included in the calculation.
_-Proton conductivity σ _proton : Total conductivity σ _total obtained from AC measurement, and electron conductivity σ _electron obtained from DC measurement are _expressed as follows:
σ _proton = σ _total −σ _electron
Included in the calculation.

<Photoreduction>
FIG. 2 shows the photoreduction effect of the graphene oxide film in air.
(A) is a graphene oxide functional group (C—O—C, C═O, C—OH, —COOH, Csp ³ C—C, C—H defect, Csp ² C═C with respect to irradiation time. It is an XPS chart which shows the transition of).
(B) is an oxidation functional group (C—O—C, C═O, C—OH, —COOH) and oxygen atom% (O / (C + O) with respect to the irradiation time calculated from the XPS peak of (a). )) Concentration change.
(C) shows the concentration change of the non-oxidizing functional groups (C sp ³ C—C, C—H defect, C sp ² C═C) with respect to the irradiation time calculated from the XPS peak of (a).
(D) shows the fluctuation | variation of the interlayer distance d of a graphene oxide with respect to the irradiation time (Irradiation time) computed from the XRD diffraction peak.

  From FIG. 2 (b), as the irradiation time becomes longer, the contents of oxygen atom% (O / (C + O)) and epoxy group (C—O—C) are remarkably decreased, and the hydroxyl group (C—OH) and carboxyl group are reduced. It can be seen that (-COOH) slightly increases.

  From FIG. 2 (c), as the irradiation time becomes longer, CH defects (corresponding to CH bonds at the edge of the pore and CH bonds on the graphene-like main surface) rapidly increase. It can be seen that the C—C bond and the C═C bond are slightly increased.

  FIG. 2D shows that the interlayer distance d decreases as the irradiation time increases. The decrease in the interlayer distance is considered to be due to a decrease in oxygen atomic%. The XRD diffraction pattern after photoreduction is broad, suggesting that the interlayer distance is non-uniform.

  From the above, it can be said that the composition of the graphene oxide film, in particular, the amount of C—O—C groups and O═C—O groups and C—H defects, the distance between layers, and the form can be controlled by the irradiation time.

<Thermal reduction>
FIG. 3 shows the effect of thermal reduction of the graphene oxide film.
(A) is a graphene oxide functional group (C—O—C, C═O, C—OH, —COOH, Csp ³ C—C, C—H defect, Csp ² C═C with respect to the reduction temperature. It is an XPS chart which shows the transition of).
(B) is an oxidation functional group (C—O—C, C═O, C—OH, —COOH) and oxygen atom% (O / (C + O) with respect to the reduction temperature calculated from the XPS peak of (a). )) Concentration change.
(C) shows the concentration change of the non-oxidizing functional group (C sp ³ C—C, C—H defect, Csp ² C = C) with respect to the reduction temperature calculated from the XPS peak of (a).
(D) shows the interlayer distance d of graphene oxide with respect to the reduction temperature calculated from the XRD diffraction peak of (a).

  FIG. 3B shows that when the reduction temperature is low, there are many epoxy groups (C—O—C) and oxygen atom% (O / (C + O)), and the reduction temperature is high. It can be seen that -O-C) and oxygen atom% (O / (C + O)) decrease sharply, but other oxidizing functional groups are less affected by the reduction temperature.

  From FIG. 3 (c), when the reduction temperature exceeds 100 ° C., the C═C bond increases rapidly, the C—C bond decreases, and the C—H defect increases from 100 ° C. to 120 ° C. It can be seen that the number starts to decrease when exceeding.

  FIG. 3D shows that the interlayer distance d decreases as the reduction temperature increases. The sharp XRD diffraction pattern after thermal reduction suggests that the interlayer distance d is uniform.

  From the above, it can be said that the composition of the graphene oxide film, in particular, the amount of C—O—C groups and O═C—O groups and C—H defects, the interlayer distance, and the form can be controlled by the reduction temperature.

  Furthermore, the partially reduced graphene oxide film obtained by photoreduction has many C—H defects and the interlayer distance d is nonuniform, and the partially reduced graphene oxide film obtained by thermal reduction has many C═Cπ bonds and the interlayer distance d is low. By selecting a reduction method so as to be uniform, an optimal partially reduced graphene oxide film can be manufactured according to the application.

<Relationship between humidity and proton conductivity>
As shown in FIGS. 4 (a) and 4 (b), the proton conductivity (measurement temperature 25 ° C.) of partially reduced graphene oxide is dependent on humidity regardless of whether it is photoreduction or thermal reduction. Proton conductivity is high.

  Further, as shown in FIGS. 5A and 5B, the proton conductivity increases as the content of the epoxy group of the partially reduced graphene oxide increases, whether it is photoreduction or thermal reduction. Therefore, the reason why the proton conductivity of the partially reduced graphene oxide decreases is considered to be that the number of proton transfer sites (epoxy groups in the intermediate layer) in the partially reduced graphene oxide decreases.

<Proton conductivity and electronic conductivity>
FIG. 6 (a) shows the relationship between irradiation time (Irradiation time), proton conductivity (Proton conduction), and electron conductivity (Electron conduction) in photoreduction when the relative humidity is 40% and 90%. The electron conductivity is not affected by the relative humidity, and the electron conductivity increases as the irradiation time increases. When the relative humidity was 90%, the irradiation time was about 8800 seconds, the proton conductivity and the electron conductivity were 6 × 10 ⁻⁵ Scm ⁻¹ , and mixed conductive graphene oxide was obtained. When the relative humidity was 40%, the irradiation time was about 4000 seconds, the proton conductivity and the electron conductivity were 2 × 10 ⁻⁶ Scm ⁻¹ , and mixed conductive graphene oxide was obtained.

FIG. 6B shows the relationship between the reduction temperature, the proton conductivity, and the electron conductivity in thermal reduction when the relative humidity is 40% and 90%. The electron conductivity is not affected by the relative humidity, and the electron conductivity increases as the reduction temperature increases. When the relative humidity is 90%, the proton conductivity and the electron conductivity of partially reduced graphene oxide reduced at about 140 ° C. coincide with each other at 5 × 10 ⁻⁵ Scm ^−1. Obtained. When the relative humidity was 40%, the reduction temperature was about 120 ° C., the proton conductivity and the electron conductivity were 9 × 10 ⁻⁸ Scm ⁻¹ , and mixed conductive graphene oxide was obtained.

  FIG. 7A shows the relationship between oxygen content (O / (C + O)), proton conductivity (Proton), and electron conductivity (Electron) in graphene oxide and partially graphene oxide. Plotting the logarithm of electronic conductivity against oxygen content (%) showed good linearity regardless of thermal reduction method or photoreduction method. Therefore, it can be said that both the C—H defect generated by the photoreduction method and the C═C bond generated by the thermal reduction method affect the electron conductivity equally and greatly. Contrary to the fact that conventionally only C = Cπ covalent bonds were thought to promote electronic conduction, this is a surprising result. On the other hand, the proton conductivity of partially graphene oxide was always higher in the photoreduction method than in the thermal reduction method.

  FIG. 7B shows the relationship between the interlayer distance (d) of partially reduced graphene oxide and the proton conductivity. Plotting the logarithm of proton conductivity against the interlayer distance (nm) showed good linearity regardless of thermal reduction method or photoreduction method. Therefore, it can be said that the interlayer distance and the epoxy group content strongly influence the proton conductivity.

  FIG. 7C shows the relationship between the interlayer distance (d) of partially reduced graphene oxide and the oxygen content. The interlayer distance was always higher in the photoreduction method than in the thermal reduction method. C = C π bonds are formed between graphene oxide layers during thermal reduction, and the interlayer distance is shortened by strong π bonds, while C—H defects are formed between graphene oxide layers during photoreduction, resulting in an interlayer distance of This is thought to be due to the lengthening. The large interlayer distance obtained by photoreduction gives freedom to the movement of water molecules attached to the epoxy group, resulting in higher proton conductivity, mixed conductivity with high electron conductivity and high proton conductivity. Graphene oxide is formed.

  The mixed conductive graphene oxide of the present invention is a novel material in that it can exhibit both equivalent electronic conductivity and proton conductivity at room temperature while being a single component material.

[Example 2]
After adding 0.18 mol / L sulfuric acid to the graphene oxide dispersion prepared in the same manner as in Example 1, a graphene oxide film is prepared in the same manner as in Example 1, and the film is subjected to photoreduction and thermal reduction. A partially reduced graphene oxide film was prepared. Various analyzes were performed in the same manner as in Example 1 to confirm the effect of adding sulfuric acid (S / C = 0.13).

<Thermal reduction>
An XPS chart of partially reduced graphene oxide obtained by thermal reduction is shown in FIG. The reduction temperature obtained from the XPS chart of FIG. 8 and non-oxidizing functional groups (C—C, C—H defect, C═C) and oxidizing functional groups (C—O—C, C═O, C—OH, O═ The relationship of (C−O) is shown in FIGS. Comparing FIG. 9A and FIG. 3C, the content of non-oxidizing functional groups (Csp ³ C—C, C—H defect, Csp ² C═C) is increased by adding sulfuric acid. I understand that On the other hand, the content of the oxidized functional group was almost the same and did not vary. Table 1 and FIG. 10 show the relationship between the thermal reduction temperature and the sulfur content (atomic%) in the partially reduced graphene oxide. FIG. 11A shows an XRD chart, and FIG. 11B shows the relationship between the reduction temperature and the interlayer distance (d (nm)). When sulfuric acid is added, sulfate ions remain between the layers, and this is considered to be because the interlayer distance does not decrease even when thermal reduction is performed.

FIG. 12 shows the influence of the reduction temperature and relative humidity on the proton conductivity. By thermal reduction, the proton conductivity decreases, and in particular, as the relative humidity decreases, the decrease rate increases and decreases rapidly at a relative humidity of 55% or less. However, in contrast to Example 1 in which sulfuric acid was not added (FIG. 4 (b)), by adding sulfuric acid, the proton conductivity was about two orders of magnitude higher, and even if the relative humidity was 40%, 10 ⁻⁵ to 10 −10. ^{It was -4} Scm ^-1 order. Further, the higher the reduction temperature, the greater the degree of decrease in proton conductivity.

FIG. 13 shows the relationship between proton conductivity, electron conductivity, and reduction temperature at relative humidity of 40% and 90%. When the relative humidity is 90%, the proton conductivity and the electron conductivity agree with 10 ⁻² Scm ⁻¹ , and when the relative humidity is 40%, the proton conductivity and the electron conductivity agree with 10 ⁻⁵ Scm ^−1. Compared with FIG. 6B, it can be seen that the conductivity at which the proton conductivity and the electron conductivity coincide with each other is increased by about two orders of magnitude by the addition of sulfuric acid.

  FIG. 14 shows the relationship between the thermal reduction temperature and proton conductivity and electron conductivity at 40% and 90% relative humidity when the amount of sulfuric acid added is changed to S / C = 0.06. Compared with FIG. 13 (sulfuric acid addition amount S / C = 0.13), it can be said that the electron conductivity is slightly lowered when the sulfuric acid addition amount is small, but the proton conductivity is not significantly affected.

<Photoreduction>
FIG. 15 shows the relationship between the photoreduction irradiation time and the interlayer distance (d (nm)). The interlayer distance was constant regardless of the irradiation time.

  FIG. 16 shows the influence of light irradiation time and relative humidity on proton conductivity. Similar to the effect of the thermal reduction temperature shown in FIG. 12, the temperature rapidly decreases at a relative humidity of 55% or less, and the degree of decrease increases as the irradiation time increases. Comparing the irradiation time of 600 seconds and the irradiation time of 3600 seconds without addition of sulfuric acid in FIG. 4A, it can be seen that addition of sulfuric acid improves the proton conductivity by about 0.5 to 1 digit.

FIG. 17 shows the relationship between proton conductivity and electron conductivity at a relative humidity of 40% and 90%, and the reduction temperature. When the relative humidity is 90%, the proton conductivity and the electron conductivity are 10 ⁻² Scm ⁻¹ , and when the relative humidity is 40%, the proton conductivity and the electron conductivity are 10 ⁻⁵ Scm ⁻¹ , and Example 1 (FIG. 6 (a Compared with)), it can be seen that the conductivity at which the proton conductivity and the electron conductivity coincide with each other is increased by an order of magnitude when sulfuric acid is added. However, when the relative humidity was 90%, the proton conductivity and the electron conductivity did not match. In this example, since sulfuric acid is added to the graphene oxide film and photoreduction is performed, the interlayer distance is increased and the proton conductivity is increased by the addition of sulfuric acid. It is considered that the electron conductivity was not increased.

[Example 3]
Graphene oxide hydrogen permselective permeation is performed by dropping a platinum (50 wt%)-supported carbon isopropanol solution (5 w%) onto both sides of the mixed conductive graphene oxide film produced by the thermal reduction method of Example 1 and drying at room temperature. A membrane was prepared.

Using this hydrogen permselective membrane, the hydrogen permeability at 25 ° C. was measured. 5% hydrogen gas diluted with Ar was circulated at 50 mL / min on one side of the membrane, and Ar was circulated at 30 mL / min on the other side. When hydrogen permeated to the Ar side was quantified by gas chromatography, hydrogen permeation was confirmed, and the permeation amount was 0.049 mL / min · cm ² . The gas component that permeated through the membrane was confirmed to function as a good hydrogen selective permeation membrane because oxygen alone could not be confirmed through hydrogen.

Claims (9)

  A mixed conductive graphene oxide sheet in which the proton conductivity and the electronic conductivity measured at a temperature of 25 ° C. exhibit the same value. The proton conductivity and the electronic conductivity are both in the range of 10 ⁻¹ to 10 ⁻⁵ Scm ⁻¹ at 90% relative humidity, and in the range of 10 ⁻¹ to 10 ⁻⁸ Scm ⁻¹ at 40% relative humidity. The mixed conductive graphene oxide sheet according to claim 1. Both the proton conductivity and the electron conductivity are in the range of 10 ⁻¹ to 10 ⁻⁶ Scm ⁻¹ at 90% relative humidity and in the range of 10 ⁻¹ to 10 ⁻⁶ Scm ⁻¹ at 40% relative humidity. The mixed conductive graphene oxide sheet according to claim 1.   3. The mixed conductive graphene oxide according to claim 1, wherein a part of the graphene oxide is thermally reduced at a reduction temperature of 40 to 150 ° C. after the graphene oxide dispersion is formed into a sheet shape. 4. Sheet manufacturing method.   A part of the graphene oxide is photoreduced by irradiating 100 to 500 watts of ultraviolet light for 1 to 90 minutes after the graphene oxide dispersion is formed into a sheet. 4. A method for producing a mixed conductive graphene oxide sheet according to 3.   6. The mixed conductive graphene oxide sheet according to claim 4, wherein sulfate ions are added to the graphene oxide dispersion and then formed into a sheet shape, or sulfate ions are added after the graphene oxide is formed. Manufacturing method.   The method for producing a mixed conductive graphene oxide sheet according to claim 6, wherein the addition amount of sulfate ion is in a range of 0.05 to 0.5 as an atomic ratio of sulfur to carbon (S / C). .   A graphene oxide hydrogen permselective membrane comprising the mixed conductive graphene oxide sheet according to claim 1.   A graphene oxide hydrogen permselective membrane comprising a carbon film carrying a platinum group metal or an alloy thereof on both sides of the mixed conductive graphene oxide sheet according to claim 1.