Hydrogen generating catalyst, composition for activation of hydrogen generating catalyst, hydrogen generating deice and activation method for hydrogen generating catalyst

Abstract

To provide novel means for enhancing the HER activity of a hydrogen generating catalyst.SOLUTION: A heterocyclic aromatic compound containing at least a portion of its surface with tertiary nitrogen or aromatic ring nitrogen, its salts or hydrates, or their heat-treated products is used. (provided that the case where the aforementioned heterocyclic aromatic compound is caffeine is excluded if the aforementioned catalyst is platinum or the aforementioned catalyst is platinum-supported carbon that has not undergone oxidation treatment.)SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a hydrogen generating catalyst, a composition for activating the hydrogen generating catalyst, a hydrogen generating apparatus, and a method for activating the hydrogen generating catalyst. [Background technology]

[0002] Hydrogen is used as a fuel for fuel cells and does not emit carbon dioxide during the energy extraction process. For this reason, hydrogen is attracting attention as a new energy carrier toward achieving carbon neutrality. One method of producing hydrogen that has a small environmental impact and does not emit carbon dioxide is water electrolysis (also known as electrolysis) using renewable energy.

[0003] The currently most widely used water electrolysis method is solid polymer water electrolysis, which has a high current density and high activity of the hydrogen evolution reaction (HER) under acidic conditions when cation exchange membranes are used. However, under acidic conditions, a large amount of precious metals such as platinum (Pt) is required for the electrodes, and since Pt is rare and expensive, the high cost of the electrodes is a disadvantage. Therefore, in recent years, water electrolysis using anion exchange membranes has attracted attention (Non-Patent Document 1). In solid polymer water electrolysis using anion exchange membranes, the hydrogen evolution reaction (HER: 2H2O + 2e - →H2+OH - ), and oxygen evolution reaction (OER: 2OH) at the anode. - →1 / 2O2+H2O+2e - ) progresses.

[0004] By using an anion exchange membrane, the reaction takes place under alkaline conditions, which makes it less corrosive than when a cation exchange membrane is used. This allows the use of not only precious metals such as Pt, but also base precious metals such as manganese and cobalt for the electrodes, which reduces the amount of platinum used and the cost of the electrodes. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Roby Soni et al.,ACS Applied Energy Materials 4(2021)1053-1058 Summary of the Invention

[0006] However, the HER activity under alkaline conditions is lower than that under acidic conditions, resulting in a smaller current density. Therefore, there is a need to improve the HER activity of hydrogen generation catalysts in water electrolysis.

[0007] As a result of intensive research, the present inventors have found that the HER activity of a hydrogen generating catalyst can be improved even under alkaline conditions by modifying the catalyst with a specific nitrogen-containing structure such as a purine base compound. The present invention is based on this finding.

[0008] Therefore, the present invention provides a technical means for improving the HER activity of hydrogen generation catalysts.

[0009] According to one embodiment of the present invention, there is provided a hydrogen generation catalyst, at least a portion of whose surface is modified or coated with a heterocyclic aromatic compound containing tertiary nitrogen or aromatic ring nitrogen, a salt or hydrate thereof, or a heat-treated product thereof (however, when the catalyst is platinum or platinum-supported carbon and has not been subjected to oxidation treatment, the heterocyclic aromatic compound is caffeine, except for the case where the heterocyclic aromatic compound is caffeine).

[0010] According to a preferred embodiment of the present invention, the heterocyclic aromatic compound is a compound represented by formula (I). [ka] (In the formula, R1, R2, R3, and R4 each independently represent a hydrogen atom, an alkyl group optionally substituted with a hydroxyl group, a carbamoyloxy group, or a carboxyl group, or are absent, and the dotted line between the 4-position carbon atom and the 5-position carbon atom represents a bond; R2 may be taken together with the carbon atom at position 4 to form an alkyl chain optionally substituted with a hydroxyl group, wherein there is no dotted line between the carbon atoms at positions 4 and 5; X1, X2 and X3 each independently represent a hydrogen atom, an amino group, an oxygen atom or NH2 + represents a group, However, X1 or X2 is an oxygen atom or NH2 + When representing a group, the dotted line between X1 or X2 and the carbon atom to which it is bonded represents a bond, and there is no dotted line between the carbon atom to which X1 or X2 is bonded and the nitrogen atom, X3 is an oxygen atom or NH2 + When X represents a group, the dotted line between X and the carbon atom to which it is bonded represents a bond, and there are no dotted lines between the carbon atom to which X is bonded and the nitrogen atoms at positions 7 and 8; When the dotted line between the carbon atom to which X1, X2 or X3 is bonded and the nitrogen atom represents a bond, R1, R2, R3 and R4 bonded to the nitrogen atom do not exist, (Except that when the catalyst is platinum or when the catalyst is supported on a carbon support and has not been subjected to an oxidation treatment, the compound represented by formula (I) is caffeine)

[0011] According to one embodiment of the present invention, there is provided a hydrogen generation electrode comprising the above-mentioned hydrogen generation catalyst.

[0012] Furthermore, according to one embodiment of the present invention, there is provided a composition for activating a hydrogen generation catalyst, comprising a heterocyclic aromatic compound containing tertiary nitrogen or aromatic ring nitrogen, its salt or hydrate, or a heat-treated product thereof (however, when the catalyst is platinum or the catalyst is platinum-supported carbon and has not been oxidized, the heterocyclic aromatic compound is excluding caffeine).

[0013] Furthermore, according to one embodiment of the present invention, there is provided a composition containing a heterocyclic aromatic compound containing tertiary nitrogen or aromatic ring nitrogen, a salt or hydrate thereof, or a heat-treated product thereof, in which an electrolyte for water electrolysis is dissolved (however, when the catalyst is platinum or the catalyst is platinum-supported carbon and has not been subjected to oxidation treatment, the heterocyclic aromatic compound is caffeine, excluding the case where the heterocyclic aromatic compound is caffeine).

[0014] Furthermore, according to one embodiment of the present invention, there is provided a hydrogen generating device including the above electrode or the above composition.

[0015] Furthermore, according to one embodiment of the present invention, there is provided a method for activating a hydrogen generating catalyst, which comprises a step of modifying or coating at least a part of the surface of the hydrogen generating catalyst with a heterocyclic aromatic compound containing tertiary nitrogen or aromatic ring nitrogen, a salt or hydrate thereof, or a heat-treated product thereof (however, when the catalyst is platinum or platinum-supported carbon and has not been oxidized, the heterocyclic aromatic compound is caffeine, excluding the case where the heterocyclic aromatic compound is caffeine).

[0016] According to the present invention, the HER activity of a hydrogen generation catalyst can be improved by using the above-mentioned heterocyclic aromatic compound containing tertiary nitrogen or aromatic ring nitrogen, or a salt or hydrate thereof. Furthermore, the heterocyclic aromatic compound containing tertiary nitrogen or aromatic ring nitrogen, or a salt or hydrate thereof, is relatively inexpensive and can be advantageously used in industrial production. [Brief explanation of the drawings]

[0017] [Figure 1] This graph compares the HER activity at −0.1 V measured by LSV on Pt surfaces with (111), (553), (331), or (110) structures for caffeine- or theophylline-modified Pt single crystal electrodes using electrolytes containing caffeine or theophylline, and for unmodified Pt single crystal electrodes. [Figure 2]1 is a graph comparing the HER activity at −0.1 V measured by LSV on a Pt surface having a (110) structure for a caffeine-, purine-, xanthine-, or hypoxanthine-modified Pt single crystal electrode and an unmodified Pt single crystal electrode using an electrolyte containing caffeine, purine, xanthine, or hypoxanthine. [Figure 3] 1 is a graph comparing the HER activity at −0.1 V measured by LSV on a caffeine- or purine-modified platinum-supported carbon oxidized product electrode and an unmodified platinum-supported carbon oxidized product electrode using an electrolyte containing caffeine or purine. [Figure 4] 1 is a graph comparing the HER activity at −0.1 V measured by LSV on a caffeine- or purine-modified platinum-on-carbon electrode and an unmodified platinum-on-carbon electrode using an electrolyte containing caffeine or purine. [Figure 5] 1 is a graph comparing the HER activity at −0.1 V measured by LSV for a platinum-loaded carbon electrode and an electrode carrying platinum-loaded carbon oxidized with aqueous hydrogen peroxide and heat. [Figure 6] This graph shows the ORR activity at a platinum-on-carbon electrode coated (modified) with indolizino[6,5,4,3-ija]quinoline (IQ) by heating (coated surface area 0, 10, or 20%: IQ-0, 10, or 20-Pt / C) or a platinum-on-carbon electrode coated (modified) with 1,7-phenanthroline (1,7-phen) (coated surface area 20%: 1,7-phen-20-Pt / C). [Figure 7] 1 is a graph showing ORR activity at a platinum-loaded carbon electrode coated (modified) with IQ (coated surface area 0, 10, or 20%: IQ-0, 10, or 20-Pt / C) or a platinum-loaded carbon electrode coated (modified) with 1,7-phen (coated surface area 20%: 1,7-phen-20-Pt / C). [Figure 8]1 is a graph showing the HER activity at an untreated platinum-loaded carbon electrode (untreated Pt / C) or at an IQ-coated (modified) platinum-loaded carbon electrode (0, 10, or 20% surface area: IQ-0, 10, or 20-Pt / C). [Figure 9] Raman spectra are shown for platinum-on-carbon electrodes coated (modified) with IQ (coated surface area 0, 10, 20, or 30%: IQ-0, 10, 20, or 30-Pt / C) and platinum-on-carbon electrodes coated (modified) with 1,7-phen (coated surface area 100%: 1,7-phen-100-Pt / C). [Figure 10] A shows the XPS spectrum (N1s) of a platinum-on-carbon electrode coated (modified) with IQ (coated surface area: 10, 20, or 30%; IQ-0, 10, 20, or 30-Pt / C). B shows the XPS spectrum (Pt4f) of a platinum-on-carbon electrode coated (modified) with IQ (coated surface area: 10, 20, or 30%; IQ-0, 10, 20, or 30-Pt / C). [Figure 11] 1 shows an XPS spectrum (N1s) of a platinum-supported carbon electrode coated (modified) with 1,7-phen (coated surface area 100%: 1,7-phen-100-Pt / C). [Figure 12] 1 is a graph comparing the HER at −0.1 V (RHE) of Pt / C and IQ20% modified Pt / C in 0.1 M LiOH. DETAILED DESCRIPTION OF THE INVENTION

[0018] <Definition> The following describes terms and expressions used in this specification. The following definitions apply throughout this specification unless otherwise specified.

[0019] In this specification, for example, "C1 to C6" means having 1 to 6 carbon atoms.

[0020] The term "alkyl group" refers to a monovalent functional group formed by removing one hydrogen atom from an alkane. The alkyl group may be linear, cyclic, or a combination thereof. A cyclic alkyl group is synonymous with a "cycloalkyl group." The linear group may be either straight-chain or branched-chain. The alkyl group is preferably straight-chain or branched-chain.

[0021] "Alkyl chain" means a monovalent functional group formed by removing two hydrogen atoms from an alkane. The alkyl chain may be linear, cyclic, or a combination thereof.

[0022] The expression "optionally substituted" in relation to a functional group means that one or more hydrogen atoms of the functional group may each independently be replaced with another atom or atomic group, and is synonymous with the term "optionally having a substituent or being unsubstituted."

[0023] When the alkyl group has 1 to 4 carbon atoms, the number of substituents that the alkyl group may have is usually 1 to 3, preferably 1 or 2, and more preferably 1. When the alkyl group has 5 to 9 carbon atoms, the number of substituents that the alkyl group may have is usually 1 to 6, preferably 1 to 5, more preferably 1 to 4, and even more preferably 1 or 2. When the alkyl group has 10 or more carbon atoms, the number of substituents that the alkyl group may have is usually 1 to 9, preferably 1 to 5, more preferably 1 to 4, and even more preferably 1 or 2.

[0024] <Heteroaromatic compounds containing tertiary nitrogen or aromatic ring nitrogen> According to one embodiment of the present invention, at least a portion of the surface of a hydrogen generating catalyst is modified or coated with a heterocyclic aromatic compound containing tertiary nitrogen or aromatic ring nitrogen, its salt, hydrate, or a heat-treated product thereof (however, when the catalyst is platinum or platinum-on-carbon and has not been oxidized, the heterocyclic aromatic compound is caffeine, except for the case where the heterocyclic aromatic compound is caffeine). It is surprising that the hydrogen generating activity of a hydrogen generating catalyst can be significantly improved by using a heterocyclic aromatic compound containing tertiary nitrogen or aromatic ring nitrogen. Here, "heterocyclic aromatic compound containing tertiary nitrogen" refers to a heterocyclic aromatic compound in which a nitrogen atom, all three of whose bonds are bonded to carbon atoms, is present in a ring structure. Furthermore, "heterocyclic aromatic compound containing aromatic ring nitrogen" refers to a heterocyclic aromatic compound containing a nitrogen atom present in an aromatic ring structure, and preferably, all of the bonds of the nitrogen atom are bonded to adjacent carbon atoms. The activity-improving effect of a heterocyclic aromatic compound containing tertiary nitrogen or aromatic ring nitrogen on a hydrogen generation catalyst can be determined by comparing the activity with that in the absence of a heterocyclic aromatic compound containing tertiary nitrogen or aromatic ring nitrogen, using a method similar to that described in the test examples below.

[0025] The number of tertiary nitrogens contained in the heterocyclic aromatic compound is not particularly limited as long as it can act as a hydrogen generating catalyst, but may be, for example, 1 to 6, preferably 1 to 4. The number of aromatic ring nitrogens contained in the heterocyclic aromatic compound is not particularly limited as long as it can act as a hydrogen generating catalyst, but may be, for example, 1 to 6, preferably 1 to 4.

[0026] The number of rings contained in the heterocyclic aromatic compound is not particularly limited as long as it can act as a hydrogen generating catalyst, and may be, for example, a 1- to 7-ring compound, preferably a 1- to 4-ring compound.

[0027] The ring structure of the heterocyclic aromatic compound may be, for example, a combination of 1- to 6-membered rings, but preferably contains a 5-membered ring, a 6-membered ring, or a combination thereof.

[0028] According to a preferred embodiment of the present invention, the heterocyclic aromatic compound is a mono- to tetra-cyclic compound having 1 to 4 tertiary nitrogen atoms, which may be substituted with one or more substituents, The ring constituting the heterocyclic aromatic compound is a 5-membered ring, a 6-membered ring, or a combination thereof. Specific examples of the ring structure of the heterocyclic aromatic compound include a pyridine skeleton, a pyrrole skeleton, a purine skeleton, and a triazine skeleton.

[0029] Examples of the substituent that the heterocyclic aromatic compound may have include a hydroxyl group, an alkyl group optionally substituted with a carbamoyloxy group or a carboxyl group, an amino group, an oxo group, or an imino group, and preferably a hydroxyl group, a halogen atom, a methyl group, an ethyl group, a methoxy group, an ethoxy group, an amino group, an oxo group, or an imino group, and more preferably a methyl group, an amino group, an oxo group, or an imino group.

[0030] According to a preferred embodiment of the present invention, the heterocyclic aromatic compound containing a tertiary or aromatic ring nitrogen is a compound represented by the following formula (I). Therefore, according to one embodiment of the present invention, at least a part of the surface of a hydrogen generating catalyst is modified with a compound represented by formula (I) or a salt or hydrate thereof. It is a surprising fact that the hydrogen generating activity of a hydrogen generating catalyst can be significantly improved by using a compound represented by formula (I) (hereinafter simply referred to as "compound of formula (I)"). The activity improving effect of the compound of formula (I) on the hydrogen generating catalyst can be determined by comparing it with the case where the compound of formula (I) is not used, using a method similar to that of the test example described later.

[0031] [ka]

[0032] According to one embodiment of the present invention, in formula (I), R1, R2, R3, and R4 each independently represent a hydrogen atom, an alkyl group optionally substituted with a hydroxyl group, a carbamoyloxy group, or a carboxyl group, or are absent, and the dotted line between the 4-position carbon atom and the 5-position carbon atom represents a bond; R2 may be taken together with the carbon atom at position 4 to form an alkyl chain optionally substituted with a hydroxyl group, wherein there is no dotted line between the carbon atoms at positions 4 and 5; X1, X2 and X3 each independently represent a hydrogen atom, an amino group, an oxygen atom or NH2 + represents a group, However, X1 or X2 is an oxygen atom or NH2 + When X1 or X2 represents a group, the dotted line between X1 or X2 and the carbon atom to which it is bonded represents a bond, and there is no dotted line between the carbon atom to which X1 or X2 is bonded and the nitrogen atom, and X3 represents an oxygen atom or NH2 + When X represents a group, the dotted line between X and the carbon atom to which it is bonded represents a bond, and there are no dotted lines between the carbon atom to which X is bonded and the nitrogen atoms at positions 7 and 8; When the dotted line between the carbon atom to which X1, X2, or X3 is bonded and the nitrogen atom represents a bond, R1, R2, R3, and R4 bonded to the nitrogen atom do not exist (excluding the case where the catalyst is platinum or the catalyst is platinum-supported carbon and has not been oxidized, in which case the compound represented by formula (I) is caffeine).

[0033] In formula (I), the dotted line represents a bond (single bond) or is absent. When the dotted line represents a bond, it represents a double bond together with the solid line.

[0034] Furthermore, in formula (I), when the dotted line between the carbon atom to which X1, X2, or X3 is bonded and the nitrogen atom represents a bond, the absence of R1, R2, R3, and R4 bonded to the nitrogen atom specifically means that when the dotted line between the carbon atom to which X1 is bonded and the nitrogen atom represents a bond, there is no R1 bonded to the nitrogen atom; when the dotted line between the carbon atom to which X2 is bonded and the nitrogen atom represents a bond, there is no R2 bonded to the nitrogen atom; when the dotted line between the carbon atom to which X3 is bonded and the nitrogen atom at position 7 represents a bond, there is no R3 bonded to the nitrogen atom; or when the dotted line between the carbon atom to which X3 is bonded and the nitrogen atom at position 9 represents a bond, there is no R4 bonded to the nitrogen atom.

[0035] According to one embodiment of the present invention, R1, R2, and R3 each independently represent an alkyl group which may be substituted with a hydroxyl group, a carbamoyloxy group, or a carboxyl group, and R4 is absent. According to another embodiment of the present invention, R1, R2, and R3 are absent, and R4 is a hydrogen atom. According to another embodiment of the present invention, R1 and R2 each independently represent an alkyl group which may be substituted with a hydroxyl group, a carbamoyloxy group, or a carboxyl group, R3 is a hydrogen atom, and R4 is absent. According to another embodiment of the present invention, R1, R2, and R3 are hydrogen atoms, and R4 is absent. According to another embodiment of the present invention, R2 and R3 are hydrogen atoms, and R1 and R4 are absent. According to another embodiment of the present invention, R2 and R4 are hydrogen atoms, and R1 and R4 are absent. According to another embodiment of the present invention, R2 and R4 are hydrogen atoms, and R1 and R3 are absent. According to another embodiment of the present invention, R1 and R3 each independently represent an alkyl group optionally substituted with a hydroxyl group, a carbamoyloxy group, or a carboxyl group, R2 represents a hydrogen atom, and R4 does not exist.

[0036] According to a preferred embodiment of the present invention, at least one of R1, R2 and R3 represents a hydrogen atom or is absent, more preferably at least two of R1, R2 and R3 represent a hydrogen atom or are absent, and even more preferably all of R1, R2 and R3 represent a hydrogen atom or are absent.

[0037] According to another preferred embodiment of the present invention, at least one of R1, R2 and R3 is absent, more preferably at least two of R1, R2 and R3 are absent, and even more preferably all of R1, R2 and R3 are absent.

[0038] According to another embodiment of the present invention, R1 and R2 represent an alkyl group optionally substituted with a hydroxyl group, a carbamoyloxy group or a carboxyl group.

[0039] In addition, in any of the above embodiments, the alkyl group represented by R1, R2, R3 or R4 may be substituted with a hydroxyl group, a carbamoyloxy group or a carboxyl group, but is preferably unsubstituted.

[0040] In any of the above embodiments, the alkyl group represented by R1, R2, R3 or R4 is typically a C1-C 20 , preferably C1 to C 10 , more preferably C1 to C8, even more preferably C1 to C6, and even more preferably C1 to C3.

[0041] Specific examples of the alkyl group include C1 to C6 alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, isobutyl, pentyl, and hexyl groups; heptyl, 1-methylhexyl, 5-methylhexyl, 1,1-dimethylpentyl, 2,2-dimethylpentyl, 4,4-dimethylpentyl, 1-ethylpentyl, 2-ethylpentyl, 1,1,3-trimethylbutyl, 1,2,2-trimethylbutyl, 1,3,3-trimethylbutyl, 2,2,3-trimethylbutyl, 2,3,3-trimethylbutyl, 1-propylbutyl, 1,1,2,2- Examples of groups that can be mentioned include tetramethylpropyl, octyl, 1-methylheptyl, 3-methylheptyl, 6-methylheptyl, 2-ethylhexyl, 5,5-dimethylhexyl, 2,4,4-trimethylpentyl, 1-ethyl-1-methylpentyl, nonyl, 1-methyloctyl, 2-methyloctyl, 3-methyloctyl, 7-methyloctyl, 1-ethylheptyl, 1,1-dimethylheptyl, 6,6-dimethylheptyl, decyl, 1-methylnonyl, 2-methylnonyl, 6-methylnonyl, 1-ethyloctyl, and 1-propylheptyl, with a methyl group being preferred.

[0042] In any of the above embodiments, X1, X2, or X3 may be NH2 + The group may be uncharged depending on the pH of the surrounding environment and may take the form of an NH group. Thus, in any of the above embodiments, the NH2 + The group is an NH group.

[0043] In any of the above embodiments, X1, X2 and X3 are all oxygen atoms or NH2 + In any of the above embodiments, it is preferable that two of X1, X2, and X3 represent an oxygen atom or an NH2 group. + In any of the above embodiments, X1 and X2 each represent an oxygen atom or an NH2 group, and one group preferably represents a hydrogen atom or an amino group. +Preferably, X1 and X2 represent an oxygen atom or an amino group, and X3 represents a hydrogen atom or an amino group. In any of the above embodiments, it is preferred that X1 and X2 represent an oxygen atom or an amino group, and X3 represents a hydrogen atom. In any of the above embodiments, it is preferred that X1 and X3 represent a hydrogen atom, and X2 represents an oxygen atom or an amino group. In any of the above embodiments, it is preferred that X1, X2, and X3 all represent a hydrogen atom.

[0044] According to a preferred embodiment of the present invention, at least one of X1, X2 and X3 represents a hydrogen atom, more preferably at least two of X1, X2 and X3 represent a hydrogen atom, and even more preferably all of X1, X2 and X3 represent a hydrogen atom.

[0045] According to another preferred embodiment of the present invention, at least one of X1, X2 and X3 represents an oxygen atom, more preferably one of X1, X2 and X3 represents an oxygen atom, and even more preferably X2 represents an oxygen atom.

[0046] According to one embodiment of the present invention, R1, R2, R3, and R4 each independently represent a hydrogen atom, an alkyl group, or are absent; X1, X2, and X3 each independently represent a hydrogen atom or an oxygen atom; When X1, X2, or X3 represents an oxygen atom, the dotted line between the carbon atom to which X1, X2, or X3 is bonded represents a bond, and there is no dotted line between the carbon atom to which X1, X2, or X3 is bonded and the nitrogen atom.

[0047] According to one embodiment of the present invention, R1, R2 and R3 each independently represent a hydrogen atom or an alkyl group, R4 represents a hydrogen atom or is absent, X1 and X2 each independently represent a hydrogen atom or an oxygen atom, and X3 represents a hydrogen atom.

[0048] According to one embodiment of the present invention, R1, R2 and R3 are absent, R4 represents a hydrogen atom or is absent, and X1, X2 and X3 all represent a hydrogen atom.

[0049] According to one embodiment of the present invention, R1 and R2 each independently represent a hydrogen atom or an alkyl group, R3 and R4 each independently represent a hydrogen atom or are absent, X1 and X2 each independently represent a hydrogen atom or an oxygen atom, and X3 represents a hydrogen atom.

[0050] According to one embodiment of the present invention, R1, R2 and R3 each independently represent a hydrogen atom or an alkyl group, R4 represents a hydrogen atom or is absent, X1 and X2 each independently represent a hydrogen atom or an oxygen atom, and X3 represents a hydrogen atom.

[0051] According to one embodiment of the present invention, R1 and R3 represent a hydrogen atom or are absent, R2 and R4 represent a hydrogen atom or an alkyl group, X1 and X3 represent a hydrogen atom or an oxygen atom, and X2 represents a hydrogen atom.

[0052] According to one embodiment of the present invention, R1 and R3 each independently represent a hydrogen atom or an alkyl group, R2 and R4 each independently represent a hydrogen atom or are absent, X1 and X2 represent a hydrogen atom or an oxygen atom, and X3 represents a hydrogen atom.

[0053] The compound of formula (I) is not particularly limited as long as it has the effect of improving the activity of the hydrogen generating catalyst. Specific examples include caffeine, xanthine, paraxanthine, theophylline, theobromine, purine, hypoxanthine, 1-methylxanthine, 3-methylxanthine, adenine, guanine, isoguanine, uric acid, saxitocine, and eritadenine, and preferred are caffeine, theophylline, xanthine, hypoxanthine, and purine, and more preferred are hypoxanthine and purine.

[0054] Caffeine is a compound in which, in formula (I), R1, R2, and R3 all represent methyl groups, R4 is absent, X1 and X2 represent oxygen atoms, and X3 represents a hydrogen atom, and is represented by the following formula.

[0055] [ka]

[0056] Purine is a compound in which R1, R2, and R3 are absent in formula (I), and R4, X1, X2, and X3 all represent hydrogen atoms, and is represented by the following formula:

[0057] [ka]

[0058] Theophylline is a compound of formula (I) in which R1 and R2 all represent methyl groups, R4 is absent, X1 and X2 all represent oxygen atoms, and R3 and X3 all represent hydrogen atoms, and is represented by the following formula:

[0059] [ka]

[0060] Xanthine is a compound in which R4 is absent, X1 and X2 represent oxygen atoms, and R1, R2, R3 and X3 represent hydrogen atoms in formula (I), and is represented by the following formula:

[0061] [ka]

[0062] Hypoxanthine is a compound of formula (I) in which R1 and R3 are absent, X2 represents an oxygen atom, and R2, R4, X1, and X3 all represent hydrogen atoms, and is represented by the following formula:

[0063] [ka]

[0064] Theobromine is a compound in which, in formula (I), R1 and R3 all represent methyl groups, R4 is absent, X1 and X2 all represent oxygen atoms, R2 and X3 all represent hydrogen atoms, and R4 is absent, and is represented by the following formula.

[0065] [ka]

[0066] According to another preferred embodiment of the present invention, the heterocyclic aromatic compound is a mono- to tetra-cyclic compound having one to three tertiary nitrogen atoms, which may be substituted with an amino group, The rings constituting the heterocyclic aromatic compound are 5-membered rings, 6-membered rings, or a combination thereof. Furthermore, among the heterocyclic aromatic compounds, those containing aromatic ring nitrogen are advantageous in terms of activating the hydrogen generation catalyst if they generate a tertiary nitrogen structure upon heat treatment, as described below. According to another more preferred embodiment of the present invention, the heterocyclic aromatic compound containing tertiary nitrogen or aromatic ring nitrogen is selected from the following compounds: [ka]

[0067] The salt of the compound of formula (I) is not particularly limited and may be an inorganic acid salt or an organic acid salt. Examples of inorganic acid salts include hydrochloride, sulfate, and perchlorate. Examples of organic acid salts include benzoate.

[0068] The heterocyclic aromatic compound may be an anhydrate or a hydrate. The amount of water of hydration in the hydrate of the compound of formula (I) is not particularly limited, and may be, for example, a monohydrate.

[0069] The heterocyclic aromatic compound, its salt or hydrate may be used as a heat-treated product obtained by heat treatment to activate the hydrogen generating catalyst. The heat-treated product is preferably heated at a heating temperature in the modification or coating method described below.

[0070] In addition, the hydrogen generating catalyst can be activated by modifying or coating the surface of the hydrogen generating catalyst with the above heterocyclic aromatic compound, its salt or hydrate, or a heat-treated product thereof (hereinafter also referred to as "heterocyclic aromatic compound, etc.").

[0071] In one embodiment of the present invention, it is preferable that the heterocyclic aromatic compound or the like is adsorbed on at least a portion of the surface of the hydrogen generation catalyst with its molecular plane perpendicular or inclined to the crystal plane. Without being bound by theory, it is believed that the adsorption of the heterocyclic aromatic compound or the like on the electrode surface changes the hydration structure around the heterocyclic aromatic compound or the like, resulting in a structure that makes it easier for hydrogen in the reactant water to approach the platinum surface, thereby activating HER. In order to form a structure that makes it easier for hydrogen to approach the platinum surface, it is believed that it is preferable that the heterocyclic aromatic compound or the like contains tertiary nitrogen or generates tertiary nitrogen by heating.

[0072] The heterocyclic aromatic compound or the like may coat the hydrogen generating catalyst. The coverage of the hydrogen generating catalyst with the heterocyclic aromatic compound or the like (surface area of ​​the hydrogen generating catalyst coated with the heterocyclic aromatic compound or the like / total surface area of ​​the hydrogen generating catalyst) may be, for example, 0.2 to 0.8, preferably 0.4 to 0.8. The coverage may be appropriately changed depending on the materials of the heterocyclic aromatic compound or the like and the electrodes. Therefore, the coverage of the hydrogen generating catalyst with the heterocyclic aromatic compound or the like (%: (surface area of ​​the hydrogen generating catalyst coated with the heterocyclic aromatic compound or the like / total surface area of ​​the hydrogen generating catalyst) × 100) may be, for example, 1 to 90%, preferably 5 to 40%. The coverage may be calculated using the amount of adsorbed and desorbed hydrogen.

[0073] The hydrogen generation catalyst modified or coated with the heterocyclic aromatic compound or the like is preferably used as a constituent material for an electrode (anode or cathode, preferably cathode) having electrical conductivity and catalytic function, and more preferably a material containing a metal. Such metals include noble metals, base metals, and alloys thereof. Examples of noble metals include platinum, palladium, rhodium, iridium, ruthenium, etc., with platinum being preferred. Base metals are metals other than noble metals, such as nickel, cobalt, manganese, tungsten, etc., with nickel being preferred. Examples of alloys include platinum-palladium alloys, platinum-cobalt alloys, platinum-nickel alloys, platinum-tungsten alloys, and nickel-cobalt alloys, with platinum-nickel alloys being preferred.

[0074] According to one embodiment of the present invention, from the viewpoint of reducing the amount of expensive metals such as platinum used, the hydrogen generation catalyst is preferably a metal-supported carrier. Examples of such carriers include carbon carriers and ceramic carriers, and carbon carriers are preferred.

[0075] According to a preferred embodiment of the present invention, the hydrogen generation catalyst may be platinum single crystal, platinum powder, platinum-supported carbon, platinum-palladium alloy-supported carbon, platinum-cobalt alloy-supported carbon, platinum-nickel alloy-supported carbon, platinum-tungsten alloy-supported carbon, or the like, and is preferably platinum single crystal, platinum-supported carbon, or platinum-nickel alloy-supported carbon.

[0076] Platinum single crystals can be prepared by flame fusion to form spherical single crystals on the tip of a platinum wire, followed by mechanical polishing to achieve the desired crystal plane orientation. The crystal plane orientation can be determined by irradiating a He-Ne laser and observing the angle of the reflected light. Examples of plane orientations for platinum single crystals include (111), (553), (331), and (110). Among these, (553) and (331) are known as high-index planes and are composed of flat terraces and single-atom steps. Figure 1 shows an example of the (553) structure, with the terrace atomic arrangement (n) being 5. From the perspective of improving HER activity, the plane orientation is preferably a high-index plane or (110), more preferably (553), (331), or (110), and even more preferably (110). Without being bound by theory, it is believed that in the present invention, the heterocyclic aromatic compound is stabilized with an appropriate terrace width, and hydrogen atoms in the hydrated water around the heterocyclic aromatic compound are more easily accessible to the platinum surface, thereby improving the HER activity.

[0077] According to one embodiment of the present invention, the HER activity of a platinum single crystal can be controlled by adjusting the crystal plane orientation. The HER activity can be measured, for example, according to the method described in the Test Examples below.

[0078] According to a preferred embodiment of the present invention, the hydrogen generation catalyst is an oxidation-treated catalyst, i.e., an oxidation-treated product. More preferably, the catalyst is an oxidation-treated metal-supported support, i.e., an oxidation-treated product of a metal-supported support, such as an oxidation-treated platinum-supported carbon. Examples of oxidation treatments include, but are not limited to, heat treatment (e.g., heating at 200 to 400°C), hydrogen peroxide (H2O2) treatment, and electrochemical application of a high potential. Without being bound by theory, in the present invention, a portion of the platinum on the surface of a metal-supported support, such as platinum-supported carbon, forms platinum oxide through oxidation treatment. At an electrode potential at which HER occurs, the platinum oxide is reduced, and at this time, a portion of the platinum oxide is eluted. It is believed that the partial elution of surface platinum atoms results in a structure similar to the Pt(110) structure, thereby improving HER activity.

[0079] According to a preferred embodiment of the combination of the hydrogen generation catalyst of the present invention and the heterocyclic aromatic compound, etc., there is mentioned a combination of platinum single crystal, platinum-supported carbon, platinum-nickel alloy-supported carbon, or an oxidation product thereof with caffeine, theophylline, xanthine, hypoxanthine, purine, or theobromine, more preferably a combination of platinum single crystal, platinum-supported carbon, platinum-nickel alloy-supported carbon, or an oxidation product thereof with theophylline, xanthine, hypoxanthine, purine, or theobromine, or a combination of an oxidation product of platinum-supported carbon or an oxidation product of platinum-nickel alloy-supported carbon with caffeine, and even more preferably a combination of platinum single crystal, platinum-supported carbon, platinum-nickel alloy-supported carbon, or an oxidation product thereof with hypoxanthine or purine.

[0080] The HER activity of a platinum single crystal with a (553) plane orientation modified or coated with the above heterocyclic aromatic compound or the like is, for example, −25.0 to −4.0 (mA / cm ) as a current density in a hydrogen evolution reaction at −0.1 V. -2 ), preferably -20.0 to -12.0 (mA / cm -2 The HER activity of a platinum single crystal with a (331) plane orientation modified with the compound of formula (I) is, for example, −20.0 to −4.0 (mA / cm) as a current density in a hydrogen evolution reaction at −0.1 V. -2 ), preferably -15.0 to -8.0 (mA / cm -2 The HER activity of a platinum single crystal with a (110) plane orientation modified or coated with the above heterocyclic aromatic compound or the like is, for example, −30.0 to −5.0 (mA / cm) as a current density in a hydrogen evolution reaction at −0.1 V. -2 ), preferably -25.0 to -9.0 (mA / cm -2 The HER activity of the platinum-supported carbon modified or coated with the heterocyclic aromatic compound or the like is, for example, -10.0 to -2.0 (mA / cm) as a current density in a hydrogen evolution reaction at -0.1 V. -2 ), preferably -7.0 to -3.0 (mA / cm -2), and more preferably -6.5 to -4.0 (mA / cm -2 The HER activity of the oxidized platinum-supported carbon modified or coated with the heterocyclic aromatic compound or the like is, for example, −20.0 to −7.0 (mA / cm) as a current density in a hydrogen generation reaction at −0.1 V. -2 ), preferably -18.0 to -12.0 (mA / cm -2 The current density may be evaluated by previously performing iR correction (voltage correction based on the product of the current value and the DC resistance value) using the DC resistance value obtained from the impedance.

[0081] Furthermore, as described above, the hydrogen generating catalyst modified or coated with the heterocyclic aromatic compound etc. can be used as a constituent material of a water electrolysis electrode (preferably a hydrogen generating electrode). Thus, one embodiment of the present invention provides a hydrogen generating electrode comprising a water electrolysis electrode (preferably a hydrogen generating electrode) the surface of which is partially modified or coated with the heterocyclic aromatic compound etc.

[0082] The water electrolysis electrode can be manufactured by a known method for manufacturing a water electrolysis electrode, except that the hydrogen generation catalyst is modified or coated with the heterocyclic aromatic compound or the like. Examples of methods for modifying or coating with the heterocyclic aromatic compound include a method (addition method) in which an electrolyte composition (electrolyte solution) containing a predetermined concentration of the heterocyclic aromatic compound is used in a hydrogen generation device, and a method (immersion method) in which an electrode composed of a hydrogen generation catalyst is immersed in an aqueous solution containing the heterocyclic aromatic compound, and then excess heterocyclic aromatic compound is removed with ultrapure water. When heating is required in the modification or coating method, the heating temperature can be adjusted appropriately depending on the properties of the raw materials, etc., but is preferably 473 to 1573 K, more preferably 573 to 873 K.

[0083] According to one embodiment of the present invention, a composition for activating a hydrogen generation catalyst comprises the heterocyclic aromatic compound or a salt or hydrate thereof as an active ingredient (however, when the catalyst is platinum or the catalyst is platinum-supported carbon and has not been oxidized, the heterocyclic aromatic compound is caffeine, except in the case where the heterocyclic aromatic compound is caffeine).

[0084] According to one embodiment of the present invention, the concentration of the heterocyclic aromatic compound in the composition for activating the hydrogen generation catalyst is, for example, 1x10 -7 ~1x10 -2 mol / L, but from the viewpoint of improving hydrogen generation activity, it is preferably 1x10 -4 ~1x10 -2 It is expressed in mol / L.

[0085] According to a preferred embodiment of the present invention, the composition for activating the hydrogen generation catalyst is preferably alkaline, and the pH of the composition can be, for example, greater than 7 and less than or equal to 14, but from the viewpoint of improving the hydrogen generation activity, it is preferably 13 to 14.

[0086] In a hydrogen generating device using a hydrogen generating catalyst, from the viewpoint of more efficiently improving hydrogen generation activity, it is preferable to use as the electrolyte a composition (also referred to as an electrolyte composition) containing a predetermined concentration of the heterocyclic aromatic compound (however, when the catalyst is platinum or platinum-supported carbon and has not been oxidized, the heterocyclic aromatic compound is caffeine, excluding the case where the heterocyclic aromatic compound is caffeine) and a dissolved electrolyte for water electrolysis. According to one embodiment of the present invention, a composition for activating a hydrogen generating catalyst, which contains the heterocyclic aromatic compound, is provided as an electrolyte composition for hydrogen generation or water electrolysis. The electrolyte composition for hydrogen generation can be prepared in a solid form (electrolyte membrane, electrolyte layer) or a liquid form (electrolyte solution), but from the viewpoint of adjusting the concentration of the heterocyclic aromatic compound, a liquid form is preferred. The electrolyte solution to which the heterocyclic aromatic compound is added may be an electrolyte solution commonly used in hydrogen generating devices, such as an aqueous solution containing lithium hydroxide, potassium hydroxide, or the like.

[0087] Furthermore, according to one embodiment of the present invention, there is provided a hydrogen generation device including an electrode modified with the heterocyclic aromatic compound or an electrolyte composition containing the compound of formula (I) (however, when the catalyst is platinum or the catalyst is platinum-supported carbon and has not been oxidized, the heterocyclic aromatic compound is caffeine, excluding the case where the heterocyclic aromatic compound is caffeine).

[0088] According to one embodiment of the present invention, a hydrogen generation device (water electrolysis device) includes an electrolyte membrane (ion exchange membrane) and an anode and a cathode separated from each other by the electrolyte membrane. The hydrogen generation device electrolyzes water (water electrolysis) to generate oxygen gas at the anode and hydrogen gas at the cathode. Examples of the hydrogen generation device (water electrolysis device) include a solid polymer water electrolysis device. In the solid polymer water electrolysis device, the above-described activated composition (specifically, a hydrogen generating electrolyte composition) containing the heterocyclic aromatic compound can be used as a solid electrolyte. Specifically, the electrolyte membrane in the device can include a layer of a mixture of fine particles of the hydrogen generation catalyst modified with the heterocyclic aromatic compound and a solid polymer polymer (e.g., QPAF-4) disposed on at least one surface of the electrolyte membrane (e.g., an anion exchange membrane such as QPAF-4) described below. The preferred surface of the electrolyte membrane is the cathode side, and the layer of the mixture of the fine particles of the hydrogen generation catalyst and the solid polymer polymer may be referred to as a cathode catalyst layer. The method for producing the electrolyte membrane includes a step of mixing a hydrogen generating electrolyte composition containing fine particles of a hydrogen generating catalyst and the heterocyclic aromatic compound with a suspension of a solid polymer to obtain an ink, and a step of applying the obtained ink to an electrolyte membrane. In the step of obtaining the ink, the activating composition containing the heterocyclic aromatic compound modifies at least a part of the surface of the catalyst.

[0089] According to one embodiment of the present invention, the electrolyte membrane is, for example, an anion exchange membrane. That is, the electrolyte membrane is an anion exchange membrane. -An example of this type of electrolyte membrane is a hydrocarbon-based solid polymer membrane (e.g., polystyrene or a modified product thereof) having an anion exchange group (e.g., a quaternary ammonium group or a pyridinium group), preferably QPAF-4 or QPAF-4(EM) (manufactured by Takahata Precision Japan).

[0090] According to one embodiment of the present invention, a portion of the surface of at least one or both of a pair of electrodes can be modified with the above-mentioned heterocyclic aromatic compound. However, from the viewpoint of improving the activity of the hydrogen generation reaction at the hydrogen generation electrode of the hydrogen generation device, it is preferable to modify the hydrogen generation electrode with the above-mentioned heterocyclic aromatic compound.

[0091] According to another embodiment of the present invention, there is provided a method for activating a hydrogen generating catalyst, comprising the step of modifying at least a part of the surface of the hydrogen generating catalyst with the heterocyclic aromatic compound or its salt or hydrate (however, when the catalyst is platinum or platinum-on-carbon and has not been oxidized, the heterocyclic aromatic compound is caffeine). The step of modifying at least a part of the surface of the hydrogen generating catalyst can be carried out by the immersion method or addition method as described above.

[0092] Furthermore, according to one embodiment of the present invention, the following is provided. [1] A hydrogen generation catalyst in which at least a portion of the surface is modified or coated with a heterocyclic aromatic compound containing tertiary nitrogen or aromatic ring nitrogen, or a salt or hydrate thereof, or a heat-treated product thereof (excluding cases where the catalyst is platinum or the catalyst is platinum-supported carbon and has not been oxidized, and where the heterocyclic aromatic compound containing tertiary nitrogen is caffeine). [2] The heterocyclic aromatic compound is a mono- to tetracyclic compound having 1 to 4 tertiary nitrogen atoms, which may be substituted with one or more substituents; The hydrogen generation catalyst according to [1], wherein the ring constituting the heterocyclic aromatic compound is a 5-membered ring, a 6-membered ring, or a combination thereof. [3] The hydrogen generation catalyst according to [2], wherein the substituent is at least one selected from a hydroxyl group, a carbamoyloxy group, an alkyl group which may be substituted with a carboxyl group, an amino group, an oxo group, or an imino group. [4] The hydrogen generation catalyst according to any one of [1] to [3], wherein the heterocyclic aromatic compound is a compound represented by formula (I): [ka] (In the formula, R1, R2, R3, and R4 each independently represent a hydrogen atom, an alkyl group optionally substituted with a hydroxyl group, a carbamoyloxy group, or a carboxyl group, or are absent, and the dotted line between the 4-position carbon atom and the 5-position carbon atom represents a bond; R2 may be taken together with the carbon atom at position 4 to form an alkyl chain optionally substituted with a hydroxyl group, wherein there is no dotted line between the carbon atoms at positions 4 and 5; X1, X2 and X3 each independently represent a hydrogen atom, an amino group, an oxygen atom or NH2 + represents a group, However, X1 or X2 is an oxygen atom or NH2 + When representing a group, the dotted line between X1 or X2 and the carbon atom to which it is bonded represents a bond, and there is no dotted line between the carbon atom to which X1 or X2 is bonded and the nitrogen atom, X3 is an oxygen atom or NH2 + When X represents a group, the dotted line between X and the carbon atom to which it is bonded represents a bond, and there are no dotted lines between the carbon atom to which X is bonded and the nitrogen atoms at positions 7 and 8; When the dotted line between the carbon atom to which X1, X2 or X3 is bonded and the nitrogen atom represents a bond, R1, R2, R3 and R4 bonded to the nitrogen atom do not exist, When the catalyst is platinum or when the catalyst is platinum on carbon and is not oxidized, the compound represented by formula (I) is caffeine. [5] R1, R2, R3 and R4 each independently represent a hydrogen atom, an alkyl group, or are absent; X1, X2, and X3 each independently represent a hydrogen atom or an oxygen atom; When X1, X2, or X3 represents an oxygen atom, the dotted line between the carbon atom to which X1, X2, or X3 is bonded represents a bond, and no dotted line exists between the carbon atom to which X1, X2, or X3 is bonded and the nitrogen atom. The hydrogen generation catalyst according to [4]. [6] The hydrogen generating catalyst according to [4] or [5], wherein the compound represented by formula (I) is selected from the group consisting of caffeine, theophylline, xanthine, hypoxanthine, purine, and theobromine. [7] The hydrogen generation catalyst according to any one of [4] to [6], wherein the compound represented by formula (I) is selected from the group consisting of hypoxanthine and purine. [8] The heterocyclic aromatic compound is a mono- to tetra-cyclic compound having 1 to 3 tertiary nitrogen atoms or aromatic ring nitrogen atoms, which may be substituted with an amino group; The hydrogen generation catalyst according to [1], wherein the ring constituting the heterocyclic aromatic compound is a 5-membered ring, a 6-membered ring, or a combination thereof. [9] The hydrogen generation catalyst according to [8], wherein the heterocyclic aromatic compound is selected from the following compounds: [ka]

[10] The hydrogen generating catalyst according to any one of [1] to [9], which comprises a metal, a metal-supported carrier, or an oxidation-treated product thereof.

[11] The hydrogen generation catalyst according to

[10] , wherein the metal comprises platinum (Pt).

[12] The hydrogen generating catalyst according to any one of [1] to

[11] , which is a constituent material of a hydrogen generating electrode.

[13] A hydrogen generating electrode comprising the hydrogen generating catalyst according to any one of [1] to

[12] .

[14] A composition for activating a hydrogen generation catalyst, comprising a heterocyclic aromatic compound containing tertiary nitrogen or aromatic ring nitrogen, its salt or hydrate, or a heat-treated product thereof (however, when the catalyst is platinum or the catalyst is platinum-supported carbon and has not been oxidized, the heterocyclic aromatic compound containing tertiary nitrogen is caffeine, except for the case where the heterocyclic aromatic compound containing tertiary nitrogen is caffeine).

[15] The composition according to

[14] , wherein the composition contains a dissolved electrolyte for water electrolysis.

[16] The composition according to any one of

[14] to

[15] , wherein the composition is alkaline.

[17] The concentration of the compound represented by formula (I) or its salt or hydrate is 1x10 -5 ~1x10 -2 The composition according to any one of

[14] to

[16] , wherein the concentration is 1000 ppm or more.

[18] A hydrogen generating device comprising the composition according to

[13] .

[19] A hydrogen generating device comprising the composition according to any one of

[14] to

[17] .

[20] A method for activating a hydrogen generating catalyst, comprising a step of modifying or coating at least a part of the surface of the hydrogen generating catalyst with a heterocyclic aromatic compound containing tertiary nitrogen, its salt or hydrate, or a heat-treated product thereof (however, when the catalyst is platinum or platinum-supported carbon and has not been oxidized, the heterocyclic aromatic compound containing tertiary nitrogen or aromatic ring nitrogen is caffeine). [Example]

[0093] The present invention will be described in detail below with reference to test examples, but the present invention is not limited to these test examples. In this specification, unless otherwise specified, units and measurement methods are in accordance with the JIS (Japanese Industrial Standards).

[0094] The water and electrodes used in the following test examples were prepared as follows.

[0095] Water purification Tap water was passed through a prefilter to remove residual chlorine and fine particles. It was then passed through a reverse osmosis membrane to remove organic and inorganic matter. An EDI module was used to remove remaining ions. Microorganisms were then removed using a UV lamp to obtain RO water. The obtained RO water was then treated using the MILLI Q ADVANTAGE A10 SYSTEM (Nihon Millipore) to obtain ultrapure water.

[0096] Electrode preparation Preparation of working electrode (Pt single crystal electrode) As platinum (Pt), platinum single crystal having a (110), (111), (331), or (553) plane was used. The tip of a 1.0 mm diameter Pt wire was melted in a hydrogen-oxygen flame to produce a 3.0 mm diameter spherical single crystal (flame fusion method). A He-Ne laser was irradiated onto the facets consisting of the (111) and (100) planes that appeared on the surface of the spherical single crystal, and the crystal plane orientation was determined from the angle of the reflected light. The surface was mechanically polished to the above crystal plane orientation. Before testing, the working electrode was annealed at 1200°C in a hydrogen-oxygen flame and cooled in an Ar atmosphere.

[0097] Preparation of working electrode (Platinum-supported carbon (Pt / C) supported GC electrode) 22 mL of ultrapure water and 3 mL of 1-propanol were added to 8.9 mg of Pt / C (TEC10E50E; platinum loading 50 mass%, Tanaka Kikinzoku Kogyo Co., Ltd.) to form a suspension. Separately from the above, a 0.5 mass% solution of QPAF-4 (manufactured by Takahata Precision Japan Co., Ltd.) was prepared. Specifically, a part of QPAF-4, a film-like polymer, was cut out and subjected to ultrasonic cleaning in ultrapure water for 3 minutes three times. The washed polymer was immersed in 1.0 M KOH (80°C) for 48 hours to convert the counter ion to OH. - After ion exchange with HCl, the polymer was ultrasonically washed in ultrapure water for 3 minutes three times, and then dissolved in methanol to obtain a 0.5% by mass solution. 1 mL of the resulting QPAF-4 solution (0.5% by mass) was added to the above suspension as a binder to obtain a Pt / C catalyst ink. The Pt / C catalyst ink was cooled to below 10°C to prevent aggregation, and then ultrasonically stirred for 30 minutes. 7.28 μL of the ink was then dropped onto a cleaned GC (glassy carbon) electrode. The ink was then vacuum dried to form a working electrode.

[0098] LSV measurement HER (Hydrogen Evolution Reaction) Linear Sweep Voltammetry (LSV) was performed using a Pt single crystal electrode, a Pt / C-supported GC electrode, or a Pt / C oxidized GC electrode (described below) as the working electrode, a GC electrode as the counter electrode, and a reversible hydrogen electrode (RHE) as the reference electrode. The electrochemical measurement cell was used, and the electrolyte was 0.1 M LiOH. The measurement was performed under alkaline conditions (pH 13). The potential scan rate was 10 mV / sec, and the current-potential curve was measured. The gas atmosphere during the measurement was Ar. Dissolved oxygen was removed by bubbling Ar into the electrolyte for approximately 30 minutes before the measurement. The gas phase was kept under Ar atmosphere during the measurement. The electrode was then placed on a rotating disk electrode (RDE), and the electrode surface was brought into contact with the electrolyte while the potential was maintained in the electric double layer region (0.45 V). After confirming that the current value was constant, the electrode was rotated at 1600 rpm, and negative scans were performed from 0.05 V to -0.2 V for the Pt-supported GC electrode and from 0.4 V to -0.1 V for the Pt / C-supported GC electrode, followed by LSV measurements. HER activity was evaluated using the current density at -0.1 V in the LSV measurements. Note that iR correction was performed in Test Examples 1 and 2. Specifically, the iR-corrected values ​​between the working electrode and the reference electrode were measured by electrochemical impedance spectroscopy (i, current; R, resistance). The electrode potential after iR correction was rescaled to the reference electrode (RHE). In Test Examples 3 and 4, iR correction was not performed.

[0099] Calculating coverage The coverage was calculated using the amount of electricity absorbed and desorbed by hydrogen, which was determined by cyclic voltammetry (CV). First, CV measurements were performed under alkaline conditions using a Pt single crystal electrode or a Pt / C oxidized GC electrode (described below) as the working electrode, a GC electrode as the counter electrode, a reversible hydrogen electrode (RHE) as the reference electrode, and a 0.1 M LiOH electrolyte. In the test examples described below, the compound of formula (I) was added to the electrolyte. Measurements were performed at a potential scan rate of 50 mV / sec. The gas atmosphere during measurements was Ar. Before measurement, Ar was bubbled into the electrolyte for approximately 30 minutes to remove dissolved oxygen. After placing the electrode in the RDE, the potential was maintained in the electric double layer region (0.45 V). After confirming that the current value was constant, when using a Pt / C oxidized GC electrode, the potential was first held at 0.4 V for 10 minutes, followed by 100 cycles in the potential range from 0 V to 1.0 V for activation. When using a Pt single crystal electrode, the potential was maintained at 0.05 V to 1.2 V for 50 cycles for activation. After measuring the cyclic voltammogram, the hydrogen desorption charge was determined in the range of 0.05 to 0.45 V (RHE), which is the hydrogen adsorption / desorption region. The coverage was calculated using the obtained charge of adsorbed and desorbed hydrogen. Specifically, the coverage θ was calculated as θ = 1 - Q' / Q, where Q is the charge of adsorbed and desorbed hydrogen on an electrode not modified with the compound of formula (I) (i.e., unmodified), and Q' is the charge of adsorbed and desorbed hydrogen on an electrode modified with the compound of formula (I).

[0100] Test example 1: LSV measurement using Pt Test section 1-1: LSV measurements using a Pt single crystal electrode modified with caffeine or theophylline The Pt single crystal electrode used had a (111), (553), (331) or (110) plane. The Pt single crystal electrode was modified with caffeine or theophylline. The modification method was an addition method. First, 2.5x10 of caffeine or theophylline was added. -3 Next, the concentration of the electrolyte in the electrochemical measurement cell was adjusted to 1x10 -4A caffeine or theophylline aqueous solution was dropped into the electrochemical measurement cell to achieve a concentration of 1000 mol / L, and a Pt single crystal electrode was modified with caffeine or theophylline to prepare a caffeine or theophylline-modified Pt single crystal electrode sample. An unmodified Pt single crystal electrode was also prepared as an unmodified Pt single crystal electrode sample. One sample of each type was prepared. Then, LSV was measured using the method described above. The same sample was measured three times (measurement count: 3).

[0101] The results are shown in Figure 1. The current density of each sample in Figure 1 shows the average, and the error bars show the standard error. n indicates the number of terrace atoms in each plane orientation. The HER activity of the caffeine- or theophylline-modified Pt single crystal electrodes was improved for all Pt surface orientations, and the HER activity of the theophylline-modified Pt single crystal electrode was higher than that of the caffeine-modified Pt single crystal electrode. Furthermore, the HER activity of the unmodified Pt single crystal electrode was most improved on the (110) surface.

[0102] Test section 1-2: LSV measurements using Pt single crystal electrodes modified with caffeine, purine, xanthine, or hypoxanthine The Pt electrode used was a Pt single crystal electrode having a (110) plane. Caffeine, purine, xanthine, or hypoxanthine was used as the activation composition for the hydrogen generation catalyst to modify the Pt single crystal electrode. The modification of the Pt single crystal electrode in Test Area 1-2 was carried out in the same manner as in Test Area 1-1, except that caffeine, purine, xanthine, or hypoxanthine was used to prepare Pt single crystal electrode samples modified with caffeine, purine, xanthine, or hypoxanthine. Thereafter, LSV was measured using the method described above (measurements were performed three times).

[0103] The results are shown in Figure 2. The current density of each sample in Figure 2 shows the average, and the error bars show the standard error. The HER activity was improved when using caffeine-, purine-, xanthine-, or hypoxanthine-modified Pt single crystal electrodes. Compared to the HER activity of the caffeine-modified Pt single crystal electrode, the HER activity of the purine-, xanthine-, or hypoxanthine-modified Pt single crystal electrodes was improved, and the HER activity of the purine-modified Pt single crystal electrode was the most improved. The purine coverage θ was 0.7.

[0104] Test Example 2: LSV measurement using oxidized Pt / C Test section 2-1: LSV measurement using a Pt / C-loaded GC electrode In the above-mentioned HER LSV method, an unmodified Pt / C-supported GC electrode was used as the working electrode, and the results obtained are shown in Figure 3.

[0105] Test section 2-2: LSV measurement using a GC electrode carrying Pt / C oxidized material (oxidized material by heating) Using a tubular furnace, the Pt / C powder before preparing the Pt / C catalyst ink was placed in a quartz tube and heated in dry air to oxidize it, yielding an oxidized product. The heating temperature was 573 K (300 °C), and the heating time was 1 hour. The resulting oxidized Pt / C was used to prepare a Pt / C oxidized product catalyst ink in the same manner as in the "Preparation of a Working Electrode (Pt / C-Supported GC Electrode)" section above, and a Pt / C oxidized product-supported GC electrode sample was fabricated. LSV measurements were performed in the same manner as in Test 2-1, except that a Pt / C oxidized product (heat-oxidized product)-supported GC electrode sample was used. The results are shown in Figure 3.

[0106] Test Section 2-3: LSV measurement using a caffeine-modified Pt / C oxidized product-supported GC electrode Test Section 2-4: LSV method using a purine-modified Pt / C oxidized product-supported GC electrode The addition method was used to modify the Pt / C oxidized product-supported GC electrode with caffeine or purine. -3 The concentration of the electrolyte in the electrochemical measurement cell was 1x10 -4 A caffeine or purine aqueous solution was dropped into the electrochemical measurement cell to obtain a concentration of 0.01 mol / L, and the Pt / C oxidized product-supported GC electrode was modified with caffeine or purine to prepare a Pt / C oxidized product-supported GC electrode sample modified with caffeine or purine. LSV measurements were performed in the same manner as in Test 2-2, except that the obtained caffeine- or purine-modified Pt / C oxidized product-supported GC electrode samples were used. The results are shown in Figure 3. The coverage ratio θ of caffeine on the Pt / C oxidized product-supported GC electrode was 0.4, and the coverage ratio θ of purine was 0.7.

[0107] Test example 3: LSV measurement using Pt / C Test section 3-1: LSV measurement using a Pt / C-loaded GC electrode In the above-mentioned HER LSV method, an unmodified Pt / C-supported GC electrode was used as the working electrode, and the results obtained are shown in Figure 4.

[0108] Test Section 3-2: LSV measurement using a caffeine-modified Pt / C-supported GC electrode Test Section 3-3: LSV method using a purine-modified Pt / C-supported GC electrode The Pt / C-supported GC electrode was modified with caffeine or purine by the addition method. -3 The concentration of the electrolyte in the electrochemical measurement cell was 1x10 -4 A caffeine or purine aqueous solution was dropped into the electrochemical measurement cell so that the concentration became mol / L, and the Pt / C-supported GC electrode was modified with caffeine or purine to prepare a Pt / C-supported GC electrode sample modified with caffeine or purine. LSV measurements were carried out in the same manner as in Test 3-1, except that the obtained caffeine- or purine-modified Pt / C-supported GC electrode samples were used. The results are shown in Figure 4.

[0109] Test Example 4: LSV measurement using oxidized Pt / C Test section 4-1: LSV measurement using a Pt / C-loaded GC electrode In the above-mentioned HER LSV method, an unmodified Pt / C-supported GC electrode was used as the working electrode, and the results obtained are shown in Figure 5.

[0110] Test section 4-2: LSV measurement using a GC electrode loaded with Pt / C oxidized material (oxidized material by hydrogen peroxide solution and heating) Before preparing the Pt / C catalyst ink, 10 mg of Pt / C powder was added to 1 mL of a 3% by mass aqueous solution of hydrogen peroxide and dried under vacuum. The resulting dried powder was placed in a quartz tube in a tubular furnace and heated in dry air to oxidize it. The heating temperature was 573 K (300 °C), and the heating time was 1 hour. 1 mL of 3% by mass aqueous hydrogen peroxide was added to 10 mg of the heated Pt / C powder, and the mixture was dried under vacuum to obtain a Pt / C oxidized product (oxidized by hydrogen peroxide and heating). The resulting Pt / C oxidized product was used to prepare a Pt / C oxide catalyst ink in the same manner as in the "Preparation of a Working Electrode (Pt / C-Supported GC Electrode)" section above, and a Pt / C oxidized product-supported GC electrode sample was fabricated. LSV measurements were performed in the same manner as in Test 2-1, except that a Pt / C oxidized product (oxidized by hydrogen peroxide and heating)-supported GC electrode sample was used. The results are shown in Figure 5.

[0111] Test Example 5 5-1 Indolizino[6,5,4,3- ija ]quinoline (hereinafter also referred to as "IQ") was used to prepare an IQ-THF solution with a concentration of 0.038 wt %.

[0112] In a glass tube washed with hot concentrated sulfuric acid, 0.050 g of Pt / C (platinum loading 50 mass%, carbon black (Ketjen EC300J)) was placed on a plate with a platinum surface area (80 m 2 The IQ-THF solution (0.47, 0.95, 1.41 g) corresponding to 10, 20, and 30% of the Pt / C (g-Pt) was added, and the mixture was vacuum dried at 45°C for 2 hours to remove the solvent. Next, 0.050 g of Pt / C was placed in a glass tube, connected to a vacuum line, and heated at 40°C under reduced pressure for 1 hour. The glass tube was then sealed to prepare an ampoule, which was then heated at 400°C for 1 hour under a nitrogen atmosphere. After heating, the ampoule was opened in a glove box, and unreacted raw materials were removed at 300°C to obtain the final product. In the following examples, the prepared sample is also referred to as "(reagent name)-(coverage)-Pt / C."

[0113] 5-2 A 0.142 wt% 1,7-phenanthroline (hereinafter referred to as "1,7-phen") solution in 1,7-phen-THF was prepared as a nitrogen-containing carbonaceous material. The same process as in 5-1 was then carried out. A 1,7-phen-THF solution equivalent to 20% of the platinum surface area (0.044 g) was placed in a glass tube for 0.010 g of Pt / C. The solvent was removed, heated under reduced pressure, and heated at 400°C under a nitrogen atmosphere. The raw materials were removed at 300°C, and the final product was obtained.

[0114] Test Example 4 To analyze the carbonization of IQ on platinum in more detail, a platinum plate with dimensions of 7 mm x 7 mm and a thickness of 0.025 mm was prepared with IQ supported on it. Specifically, 4.7 mg of a 0.0023 wt% IQ-THF solution was placed in a glass tube washed with hot concentrated sulfuric acid, and the solvent was removed by vacuum drying. The platinum plate was then reduced under a hydrogen atmosphere at 80°C for 1 hour and placed in the glass tube. Next, as with the other samples, the plate was heated under reduced pressure, heated to 400°C under a nitrogen atmosphere, and then the raw materials were removed at 300°C to obtain the final product. Hereinafter, the sample obtained in Test Example 4 will also be referred to as "IQ-100-Pt foil."

[0115] The ORR and HER activities of materials coated by reacting the Pt / C surface with IQ (0 mass%, 10 mass%, 20 mass%) or 1,7-phen (20 mass%) were measured. The results are shown in Figure 6 (ORR activity) and Figure 7 (HER activity). Regarding ORR activity, there was no significant difference in the onset potential, so it is unlikely that ORR activity improved. It is thought that as the coverage of IQ increased, the active sites for ORR on the Pt surface were covered, resulting in a decrease in ORR activity.

[0116] We also measured the HER activity of untreated Pt / C and materials coated with IQ (0 mass%, 10 mass%, and 20 mass%) on the Pt / C surface. As a result, as shown in Figure 8, the HER activity of samples coated with about 10% IQ was almost the same as that of untreated Pt / C, but the highest HER activity was observed at a coating rate of 20%.

[0117] Test Example 6 The Raman spectra (NRS-4500, JASCO Corp., excitation wavelength 532 nm) of the IQ-0~30-Pt / C (a sample in which IQ was reacted on Pt / C) obtained in Test Example 3 and the IQ-100-Pt foil (a sample in which IQ was reacted on a Pt plate) obtained in Test Example 4 were measured.

[0118] The results are shown in FIG. In the Pt / C spectrum, the generation of the G band (derived from graphite) and the D band (derived from defects (disordered band)) was unclear due to the influence of the CB peak. However, the Raman spectrum of the IQ-100-Pt foil showed the generation of the G band and D band, confirming that a carbon material was generated on the Pt plate.

[0119] Test Example 7 The IQ-0 to 30-Pt / C obtained in Test Example 3 or the IQ-100-Pt foil obtained in Test Example 4 was subjected to XPS spectrum measurement (JPS-9030, JEOL Ltd., radiation source: MgKα).

[0120] The XPS spectrum of IQ-0-30-Pt / C was as shown in (A) and (B) of FIG. (A) is related to N1s, and the presence of the spectrum was not confirmed in any of the samples. However, the Pt / C ratio of Pt4f showed that the Pt / C ratio decreased as the IQ coverage increased, confirming that the raw material was coated on Pt.

[0121] The XPS spectrum of the IQ-100-Pt foil is shown in Figure 10. The peaks derived from nitrogen were confirmed, and the results of the Raman spectrum confirmed that a carbon material had been formed on the Pt plate.

[0122] Test Example 7 The HER activity at −0.1 V (RHE) of Pt / C and IQ20%-modified Pt / C in 0.1 M LiOH was compared according to the description in the above test example. The results are shown in Figure 12. The IQ20%-modified Pt / C maintained a high HER activity and showed high durability compared to untreated Pt / C.

Claims

1. A hydrogen generation catalyst, at least a portion of whose surface is modified or coated with a heterocyclic aromatic compound containing tertiary nitrogen or aromatic ring nitrogen, or a salt or hydrate thereof, or a heat-treated product thereof (however, when the catalyst is platinum or platinum-supported carbon and has not been oxidized, the heterocyclic aromatic compound is caffeine, excluding the case where the heterocyclic aromatic compound is caffeine).

2. the heterocyclic aromatic compound is a mono- to tetracyclic compound having 1 to 4 tertiary nitrogen atoms or aromatic ring nitrogen atoms, which may be substituted with one or more substituents; The hydrogen generation catalyst according to claim 1 , wherein the ring constituting the heterocyclic aromatic compound is a five-membered ring, a six-membered ring, or a combination thereof.

3. 3. The hydrogen generation catalyst according to claim 2, wherein the substituent is at least one selected from the group consisting of a hydroxyl group, a carbamoyloxy group, an alkyl group optionally substituted with a carboxyl group, an amino group, an oxo group, and an imino group.

4. The hydrogen generation catalyst according to claim 1 , wherein the heterocyclic aromatic compound is a compound represented by formula (I): 【Chemical 1】 (In the formula, R １ , R ２ , R ３ and R ４ each independently represents a hydrogen atom, an alkyl group which may be substituted with a hydroxyl group, a carbamoyloxy group or a carboxyl group, or is absent, and the dotted line between the 4-position carbon atom and the 5-position carbon atom represents a bond; R ２ may be combined with the carbon atom at position 4 to form an alkyl chain which may be substituted with a hydroxyl group, and there is no dotted line between the carbon atom at position 4 and the carbon atom at position 5; X １ , X ２ and X ３ are each independently a hydrogen atom, an amino group, an oxygen atom, or NH ２ ＋ represents a group, However, X １ or X ２ is an oxygen atom or NH ２ ＋ When representing a group, X １ or X ２ and the carbon atom to which it is bonded represent a bond, and X １ or X ２ There is no dotted line between the carbon atom and the nitrogen atom to which X ３ is an oxygen atom or NH ２ ＋ When representing a group, X ３ and the carbon atom to which it is bonded represent a bond, and X ３ There are no dotted lines between the carbon atom to which is bonded and the nitrogen atoms at positions 7 and 8. X １ , X ２ or X ３ When the dotted line between the carbon atom to which R is bonded and the nitrogen atom represents a bond, R bonded to the nitrogen atom １ , R ２ , R ３ and R ４ does not exist, When the catalyst is platinum or the catalyst is platinum-supported carbon and has not been subjected to oxidation treatment, the case where the compound represented by formula (I) is caffeine is excluded.

5. R １ , R ２ , R ３ and R ４ each independently represents a hydrogen atom, an alkyl group, or is absent; X １ , X ２ and X ３ each independently represents a hydrogen atom or an oxygen atom, X １ , X ２ or X ３ When represents an oxygen atom, X １ , X ２ or X ３ The dotted line between the carbon atom to which X is bonded represents a bond, and １ , X ２ or X ３ The hydrogen generation catalyst of claim 4 , wherein there is no dotted line between the carbon atom to which is bonded and the nitrogen atom.

6. The hydrogen generating catalyst according to claim 4 or 5, wherein the compound represented by formula (I) is selected from the group consisting of caffeine, theophylline, xanthine, hypoxanthine, purine and theobromine.

7. The hydrogen generation catalyst according to claim 4 or 5, wherein the compound represented by formula (I) is selected from the group consisting of hypoxanthine and purine.

8. the heterocyclic aromatic compound is a mono- to tetracyclic compound having one to three tertiary nitrogen atoms or aromatic ring nitrogen atoms, which may be substituted with an amino group; The hydrogen generation catalyst according to claim 1 , wherein the ring constituting the heterocyclic aromatic compound is a five-membered ring, a six-membered ring, or a combination thereof.

9. 9. The hydrogen generation catalyst of claim 8, wherein the heterocyclic aromatic compound is selected from the following compounds: 【Chemistry 2】

10. The hydrogen generation catalyst according to claim 1 or 2, which comprises a metal, a metal-supported carrier, or an oxidized product thereof.

11. The hydrogen generation catalyst of claim 10, wherein the metal comprises platinum (Pt).

12. The hydrogen generating catalyst according to claim 1 or 2, which is a constituent material of a hydrogen generating electrode.

13. A hydrogen generation electrode comprising the hydrogen generation catalyst according to claim 1 or 2.

14. A composition for activating a hydrogen generation catalyst, comprising a heterocyclic aromatic compound containing tertiary nitrogen or aromatic ring nitrogen, its salt or hydrate, or a heat-treated product thereof (however, when the catalyst is platinum or the catalyst is platinum-supported carbon and has not been oxidized, the heterocyclic aromatic compound is caffeine, except for the case where the heterocyclic aromatic compound is caffeine).

15. The composition according to claim 14, wherein the composition contains a dissolved electrolyte for water electrolysis.

16. 16. The composition of claim 14 or 15, wherein the composition is alkaline.

17. The concentration of the compound represented by formula (I) or its salt or hydrate is 1x10 －５ ~1x10 －２ mol / L.

18. A hydrogen generating device comprising the electrode according to claim 13.

19. A hydrogen generating device comprising the composition of claim 14.

20. A method for activating a hydrogen generating catalyst, comprising a step of modifying or coating at least a part of the surface of the hydrogen generating catalyst with a heterocyclic aromatic compound containing tertiary nitrogen or aromatic ring nitrogen, a salt or hydrate thereof, or a heat-treated product thereof (however, when the catalyst is platinum or platinum-supported carbon and has not been oxidized, the heterocyclic aromatic compound is caffeine).

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