Hydrogen isotope enrichment equipment

Abstract

To inexpensively obtain gaseous deuterium from mixed gas of hydrogen and deuterium.SOLUTION: A first unit U1 formed mainly from an MEA M1 on an upper side functions as a fuel cell by generating a first reaction, and a D composition of input gas supplied to an anode side gas chamber 31 in the MEA M1 is concentrated. First discharge gas having an enhanced D / H composition ratio in the first input gas is discharged from a first gas chamber 31 of the MEA M1. A second unit U2 functions so as to further enhance D concentration of the first discharge gas. The first electrode 11 in an MEA M2 is electrically connected to the first electrode 11 in the MEA M1, and the second electrode 12 in the MEA M2 is electrically connected to the second electrode 12 in the MEA M1. The second discharge gas having further enhanced the D / H composition ratio in the first discharge gas is discharged as final output gas from the anode side gas chamber 31 of the MEA M2.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present invention relates to a method for producing hydrogen ( 1 This paper deals with a hydrogen isotope enrichment device that selectively enriches deuterium in a mixture of hydrogen (H) and deuterium. [Background technology]

[0002] A stable isotope of hydrogen that exists in nature, such as water and hydrogen gas, has a mass number of 1 (the nucleus is made up of only one proton). 1 H (hereafter referred to as H) and deuterium, which has a mass number of 2 (the nucleus is made up of one proton and one neutron). 2 There is H (hereafter referred to as D), and the abundance ratio of D is overwhelmingly smaller than that of H. H and D have almost the same chemical properties, but D is known to be particularly effective in applications in the nuclear and semiconductor manufacturing fields. For this reason, there is a demand for technology to selectively extract (separate) D in particular from water or hydrogen gas in which H and D are mixed. However, since it is practically impossible to completely separate H and D instantly, in reality, in order to separate substances in which they are mixed (water, hydrogen gas, etc.), treatment is carried out to increase the concentration of one of them (especially D).

[0003] Since the chemical properties of H and D are almost the same, they are generally not easily separated by chemical methods, and there are known techniques for separating them using their properties, such as differences in boiling point and vapor pressure. However, such techniques require high or extremely low temperatures, complex processes, and expensive chemicals, making it difficult to obtain D at low cost. There are also known techniques for separating H and D using the differences in zero-point vibrational energy and atomic size, but these also require an extremely low-temperature environment, making it similarly difficult to obtain D at low cost.

[0004] On the other hand, as described in Non-Patent Document 1, a technique is also known in which the diffusion coefficients of H and D in a metal (such as Pd) that allows hydrogen to permeate are different, and these are used to separate them. This method can be easily realized with a simple configuration compared to the above-mentioned chemical methods, but there is a problem that the metal used is embrittled by hydrogen. In order to reduce the effect of embrittlement, for example, it is effective to make the metal (such as Pd) thick, and the thickness is, for example, several hundred nm to several tens of μm. It is also effective to use this metal as an alloy with another metal (such as Ag). However, in these cases, there are problems such as the metal material being expensive or the separation efficiency being reduced. It is also effective to perform this treatment at a high temperature, but this makes the device configuration complicated. Furthermore, in order to allow hydrogen to permeate through this metal, it is also necessary to provide a pressure difference between the upstream side and the downstream side of the metal.

[0005] In contrast, Patent Document 1 describes a technology for separating H and D using a fuel cell structure. Here, a proton conductor is sandwiched between electrodes (anode, cathode), and hydrogen gas containing H and D is supplied to the anode side, and oxygen gas (air) is supplied to the cathode side. In this case, positive H ions or D ions supplied from the anode side and passing through the proton conductor react with oxygen on the cathode side to generate water, and a voltage is generated between the anode and cathode, which is the opposite action to the electrolysis of water. Nafion (registered trademark) and the like are used as proton conductors. Here, to be precise, H2, HD, and D2 exist in the hydrogen gas supplied to the anode side, and to be precise, the water generated on the cathode side is a mixture of H2O, HDO, and the like. At this time, due to the difference in the conduction state and reaction rate in the proton conductor of H ions and D ions, HDO containing D is more likely to be generated on the cathode side than H2O, so the D component increases more on the cathode side than on the anode side. In this technology, the D component is concentrated while generating electricity by functioning as a fuel cell, so the amount of electricity required for concentration can be particularly reduced.

[0006] Here, an oxidation reaction occurs on the anode side, and a reduction reaction occurs on the cathode side, and the materials constituting the anode and cathode are made of materials that function as catalysts to promote these reactions. As such materials, precious metals such as platinum (Pt) and ruthenium (Ru) are used. However, in a fuel cell, it is more efficient to disperse Pt fine particles in the electrode than to densely construct the entire electrode with Pt, because the surface area of ​​Pt used in the catalytic reaction can be increased and H ions and D ions can be easily transported in the proton conductor. For this reason, as described in Non-Patent Document 2 and the like, Pt / C electrodes in which Pt fine particles are dispersed in a carbon (C) sheet are used as the anode and cathode in this case. This technology makes it possible to increase (concentrate) the D component on the cathode side more than on the anode side. With this device, deuterium can be concentrated more cheaply than when the device described in Non-Patent Document 1 is used. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Yasuo Suzuki, Takashi Kimura, "Study on separation of hydrogen isotopes including tritium using palladium alloy membranes," Seisan Kenkyu, Vol. 36, No. 6, p. 293 (June 1983) [Non-Patent Document 2] Hiroshi Fukazawa, Takeshi Ume, Naotoshi Suzuki, "Platinum-reducing Technology for Fuel Cell Catalyst Layers," Toshiba Review, Vol. 68, No. 4, p. 54 (2013) [Patent documents]

[0008] [Patent Document 1] International Publication No. 2018 / 049343 Summary of the Invention [Problem to be solved by the invention]

[0009] In the techniques described in Patent Document 1 and Non-Patent Document 2, what is obtained by concentration (separation) is liquid such as HDO, and it is difficult to obtain D in a gaseous state (HD, D2, etc.). Furthermore, in the techniques described in Non-Patent Document 1 and Patent Document 1, the separation efficiency of H and D is low, so a technique that can obtain D at a lower cost is desired.

[0010] For this reason, a technology was needed to inexpensively obtain gaseous deuterium from a mixture of hydrogen (H) and deuterium.

[0011] The present invention has been made in consideration of the above problems, and an object of the present invention is to provide an invention that solves the above problems. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention has the following configuration. The hydrogen isotope enrichment device of the present invention is a hydrogen ( 1a first unit that receives the input gas and functions as a fuel cell to generate a DC voltage, and a second unit that outputs the output gas by applying the DC voltage, wherein each of the first unit and the second unit is made of a proton conductor that conducts positive hydrogen ions, and includes a membrane electrode assembly having a proton conducting layer having two opposing main surfaces, a first electrode formed on one main surface of the proton conducting layer, and a second electrode formed on the other main surface of the proton conducting layer, wherein the first electrode in the first unit and the second electrode in the second unit, and the second electrode in the first unit and the first electrode in the second unit are electrically connected to each other, and the first electrode in the second unit is selected from the group consisting of palladium (Pd), vanadium (V), tungsten (Ti), ... a first reaction occurs in which oxygen is introduced into the space in contact with the second electrode, causing the hydrogen and the hydrogen isotopes in the input gas to move toward the second electrode, generating water on the second electrode side, and generating an electromotive force that is negative on the first electrode side and positive on the second electrode side; a first exhaust gas, which is the input gas after the hydrogen and the hydrogen isotopes are consumed by the first reaction, is discharged; and a second reaction occurs in which the hydrogen and the hydrogen isotopes in the first exhaust gas move toward the second electrode side, generating a product gas on the second electrode side; a second exhaust gas, which is the first exhaust gas after the hydrogen and the hydrogen isotopes are consumed by the second reaction, is discharged; and The hydrogen isotope enrichment device of the present invention is characterized in that, in the second unit, the second electrode contains platinum (Pt) particles, and the hydrogen permeable metal in the first electrode has a denser structure than the platinum in the second electrode. The hydrogen isotope enrichment apparatus of the present invention is characterized in that in the second unit, the second electrode is made of a thin film of the hydrogen permeable metal. Hydrogen isotope enrichment device of the present invention In the second unit, the first electrode is a vapor-deposited film of the hydrogen-permeable metal. The hydrogen isotope enrichment device of the present invention is characterized in that the first electrode and the proton conducting layer are in contact with each other via monolayer graphene. The hydrogen isotope enrichment device of the present invention is characterized in that the proton conductive layer, the first electrode, and the second electrode in the first unit, and the proton conductive layer, the first electrode, and the second electrode in the second unit are each made of the same material. The hydrogen isotope enrichment device of the present invention is characterized in that a membrane electrode assembly base material is used that includes the first electrode, the second electrode, and the proton conductive layer, and the membrane electrode assemblies in the first unit and the second unit are formed as different regions within a surface of the single membrane electrode assembly base material. The hydrogen isotope enrichment apparatus of the present invention is characterized in that multiple enrichment units, which are the hydrogen isotope enrichment apparatus, are used in stages, and the output gas from the enrichment unit in the preceding stage is used as the input gas for the adjacent enrichment unit in the subsequent stage. The hydrogen isotope enrichment apparatus of the present invention is characterized in that the product gas in one of the enrichment units is used as the input gas for the enrichment unit in a stage upstream of the one of the enrichment units. In the hydrogen isotope enrichment device of the present invention, the hydrogen isotope is deuterium ( 2 H or D), or tritium ( 3 H or T). Effect of the Invention

[0013] Since the present invention is configured as described above, gaseous deuterium can be obtained inexpensively from a mixture of hydrogen (H) and deuterium gas. In this case, no power is required for operation, or only low power is required. [Brief description of the drawings]

[0014] [Figure 1] 1 is a diagram showing a configuration of a membrane electrode assembly (MEA) and its periphery used in a hydrogen isotope enrichment device according to an embodiment of the present invention. [Diagram 2] FIG. 13 is a diagram showing a configuration when measurements were carried out on an MEA of Reference Example 1 etc., in which a first electrode is an anode and a second electrode is a cathode. [Diagram 3] 1 shows the results of measuring the time change in ion current corresponding to H, D, and HD in the generated gas in Reference Example 1(a) and Comparative Example 1(b). [Figure 4] 1 shows the results of measuring the composition ratio of the generated gas in Reference Example 1 and Comparative Examples 1 and 2. [Diagram 5] 1 shows the results of calculating the D concentration ratio in the exhaust gas from Reference Example 1 and Comparative Examples 1 and 2. [Figure 6] The graph shows the results of measuring the D concentration rate for Reference Example 1, Comparative Example 1, and Comparative Example 2 while changing the applied voltage. [Figure 7] 1 shows the results of measuring the composition of exhaust gas in Reference Example 1 and Comparative Example 2. [Figure 8] 1 shows the results of measuring the power generation characteristics of an MEA according to Reference Example 1 of the present invention when it is made to function as a fuel cell. [Figure 9] 1 shows the results of measuring the D concentration rate of exhaust gas by changing the reaction efficiency when the MEA of Reference Example 1 etc. of the present invention is functioned as a fuel cell. [Figure 10] 1 is a diagram showing a configuration of a hydrogen isotope enrichment device according to an embodiment of the present invention. [Figure 11] FIG. 2 is a diagram showing a configuration of a first modified example of a hydrogen isotope enrichment apparatus according to an embodiment of the present invention. [Figure 12] FIG. 4 is a diagram showing a configuration of a second modified example of a hydrogen isotope enrichment apparatus according to an embodiment of the present invention. [Figure 13] FIG. 13 is a diagram showing the configuration when measurements were carried out on an MEA of Reference Example 2 etc. in which a first electrode is a cathode and a second electrode is an anode. [Figure 14]1 shows the results of calculating the D enrichment ratios in the produced gases of Reference Examples 2 to 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] An isotope separation device according to an embodiment of the present invention will be described below. In this isotope separation device, two membrane electrode assemblies (MEA) are combined to output an output gas in which the D component in an input gas containing a mixture of hydrogen gas (H2) and deuterium gas (D2) is concentrated. One of the MEAs functions as a fuel cell, and the other MEA is supplied with a voltage obtained by the MEA functioning as a fuel cell, thereby increasing the D concentration in the input gas and outputting it as an output gas. Therefore, no power supply (voltage application) is required from outside to concentrate the D component in this way.

[0016] These two MEAs have common features. FIG. 1 shows the configuration of this MEA M and its periphery, and the two MEAs are similar within the scope described herein. In this configuration, two electrodes (a first electrode 11 and a second electrode 12) and a proton conductive layer 20 sandwiched between them are used. When this MEA M performs one of the above functions (functions as a fuel cell), hydrogen H and deuterium D move from the first electrode 11 side to the second electrode 12 side and combine with oxygen to generate water on the second electrode 12 side, and a first reaction occurs in which a negative potential is generated on the first electrode 11 and a positive potential is generated on the second electrode 12 side. On the other hand, when this MEA M performs the other function (outputs an output gas with an increased D concentration by supplying a voltage), hydrogen H and deuterium D move from the first electrode 11 side to the second electrode 12 side and combine again on the second electrode 12 side, and a second reaction occurs in which a product gas containing a mixture of H2, D2, etc. is generated again on the second electrode 12 side.

[0017] In the following, first, a case where this MEA M is used to cause the second reaction will be described. In this case, a DC voltage is applied between the first electrode 11 (terminal A) and the second electrode 12 (terminal B), and the first electrode 11 is set as the positive side. The atmosphere on the first electrode 11 side (the left side of the first electrode 11 in FIG. 1) and the atmosphere on the second electrode 12 side (the right side of the second electrode 12 in FIG. 1) are both gaseous.

[0018] In FIG. 1, a gas containing hydrogen H and deuterium D (a mixed gas of H2 and D2) is input from the upper side of the figure to the space where the surface of the first electrode 11, which is the anode, is located (the space on the left side of the figure: the anode-side gas chamber 31), and this gas is called the input gas. H2 and D2 in this input gas are dissociated on the surface of the first electrode 11 (anode), and the H component and the D component react and are consumed as described below. Meanwhile, the H component (H ion) and the D component (D ion) move through the proton conducting layer 20 to the right side of the figure, and combine on the surface of the second electrode 12 (cathode), thereby forming H2 and D2 again in the space where the surface of the second electrode 12 is located (the space on the right side of the figure: the cathode-side gas chamber 32). The gas generated on the cathode side in this way is called the generated gas.

[0019] The first electrode 11 is an electrode made of a metal (hydrogen-permeable metal) that allows hydrogen (H component, D component) to pass therethrough, and as described later, this hydrogen-permeable metal is, for example, Pd. The H (positive) ions and D (positive) ions that have passed through the first electrode 11 flow through the proton conducting layer 20 to the second electrode 12 side. Of the input gas, a portion of H2 and D2 flows from the anode to the cathode in this way, where they are consumed and become exhaust gas. When the first electrode 11 contains Pd in ​​this way, Pd undergoes catalytic reactions according to the following formulas (1) and (2), converting H + , D + are generated and flow through the proton conducting layer 20 to the right in the figure.

[0020]

number

[0021] The material constituting the proton conducting layer 20 may be a conductor of H ions and D ions (proton conductor), such as Nafion (registered trademark) as described in Patent Document 1. These ions flow through the proton conducting layer 20 from the left to the right in the figure, and an oxidation reaction occurs again at the second electrode 12, whereby H2, D2, etc., which are the same as the input gas, are generated as product gases on the second electrode 12 side.

[0022] 1, when the first electrode 11 is used as an anode and the second electrode 12 is used as a cathode, H ions and D ions flow from the left side to the right side in the proton conducting layer 20. In this case, if the hydrogen (H) component in the input gas flows more easily into the atmosphere on the cathode side (right side in the figure) than the deuterium (D) component, the H / D composition ratio in the generated gas becomes higher than the H / D composition ratio in the input gas. For this reason, more H2 is consumed in the input gas than D2, and the D component is concentrated in the exhaust gas discharged after the H and D components of the input gas are thus consumed, so that this exhaust gas can be made into an output gas with an increased concentration of the D component.

[0023] Here, in the fuel cell described in Patent Document 1, the same material (platinum (Pt), etc.) is used for the anode and cathode, and in particular, a Pt / C catalyst in which catalytic Pt is combined with carbon particles in the form of fine particles is often used as the electrode material. In this case, the surface area of ​​Pt is increased by using the fine particles, which strengthens the catalytic action, and hydrogen can easily permeate this electrode. Meanwhile, a thin film of a hydrogen-permeable metal, which is any one of palladium (Pd), vanadium (V), tantalum (Ta), and titanium (Ti), is used as the first electrode 11 in this MEA M. Here, this thin film has a denser structure than Pt in the Pt / C catalyst, and is a thin film formed by, for example, vacuum deposition. Even though the hydrogen-permeable metal used here has such a dense structure, hydrogen can sufficiently permeate this thin film.

[0024] The experimental results on this point are explained below. Here, Nafion with a thickness of 52 μm was used as the proton conductive layer 20, and the first electrode 11 was the anode and the second electrode 12 was the cathode in FIG. 1. Pt / C was used as the second electrode 12, and various materials were used as the first electrode 11. Here, Pt / C is an electrode in which a Pt / C catalyst is supported on a carbon sheet, similar to that of a fuel cell. A Pt / C catalyst is a carbon particle with an average particle size of about 10 to 50 nm, on which a large number of Pt particles with an average particle size of several nm are supported. This Pt / C electrode is generally used as an electrode for a fuel cell, and in this case, the carbon sheet mainly functions as the electrode, and the Pt particles mainly function as the catalyst.

[0025] Here, three types of materials were used for the first electrode 11: Pt / C, which is the same as the second electrode 12 (Comparative Example 1); Pd / C, in which the Pt fine particles in Pt / C are replaced with Pd fine particles (Comparative Example 2); and a Pd thin film formed by vapor deposition (Reference Example 1). Comparative Example 1 corresponds to a structure similar to that of the fuel cell described in Patent Document 1 and the like. Both Reference Example 1 and Comparative Example 2 use Pd, but in different ways. The thickness of the Pd thin film (Reference Example 1) was set to 6 nm. The Pd in ​​the Pd thin film in Reference Example 1 has a denser structure than the Pd in ​​the Pd / C in Comparative Example 2 or the Pt in the Pt / C in Comparative Example 1. That is, the Pd in ​​Reference Example 1 and Comparative Example 2 differ greatly in their denseness.

[0026] The D concentration rate was measured when these three types were used. FIG. 2 shows a schematic diagram of the device configuration when this measurement was performed. Here, as the actual input gas on the first electrode 11 side, a mixed gas of Ar, H2, and D2, the flow rates of which were controlled by mass flow controllers (MFC) 101, 102, and 103, was used. Here, Ar was used as a carrier gas. In addition, since a water (H2O) component is necessary for conduction in the proton conductive layer 20 (Nafion), Ar was also flowed on the second electrode 12 (product gas) side after Ar, the flow rate of which was adjusted by the mass flow controller 104, was bubbled with H2O in the bubbler 105. In FIG. 2, the atmospheres on both the first electrode 11 side and the second electrode 12 side were both at atmospheric pressure, and the proton conductive layer 20 and the like were at room temperature. The H and D composition analysis of the generated gas on the second electrode 12 side was performed by a Q-mass (quadrupole mass spectrometer) 120 after the generated gas was evacuated by a vacuum exhaust system 110 (a combination of a turbo molecular pump and a dry pump). The H and D composition of the input gas was set by the MFCs 102 and 103.

[0027] In this case, since the H / D composition ratio in the generated gas in Reference Example 1 is increased as described later, the exhaust gas in Figures 1 and 2 can be used as the output gas as described above. In this case, the D / H composition ratio (molar ratio) in the input gas initially introduced is in and D / H, which is the D / H composition ratio in the exhaust gas in which H and D are consumed and discharged as described above. out We compared (D / H in ) / (D / H out ) can be used as the D enrichment factor. When this D enrichment factor is 1, there is no selectivity between H and D in the configuration of Figure 1, and when this D enrichment factor exceeds 1, it means that there is an effect of selectively removing H in the input gas as described above. However, the composition ratio of H and D was actually measured here in the input gas (composition D / H in ) and the product gas generated on the cathode side. outcan be calculated assuming that the amount of H and D in the input gas multiplied by the reaction efficiency has undergone the above reaction to produce the composition of the product gas. Here, the D enrichment rate was calculated assuming that the reaction efficiency is 50%.

[0028] 3 shows the results of measurements of the time change in ion current corresponding to the H2, HD, and D2 compositions separated and recognized according to mass in Q-mass 120 for Reference Example 1(a) and Comparative Example 1(b) when a voltage was applied between first electrode 11 and second electrode 12 so that the current flowing was 0.025 A (in this case, the voltage was about 0.01 to 0.1 V). In both cases, it is clear that the above reaction progresses, and H ions and D ions flow to the cathode side, causing H2 and D2 to be gradually generated on the cathode side, and HD is also generated, and after about 45 minutes, each composition becomes constant (saturates).

[0029] The composition ratios when the saturation value of the composition of the generated gas is set to each composition of the generated gas are shown in Fig. 4 for each of the three materials of the first electrode 11 (anode). In addition, in this case, when the reaction efficiency on the anode side is set to 50% as described above, the D concentration rate in the output gas (exhaust gas) is shown in Fig. 5 for each material. From these results, it is possible to selectively generate a large amount of H component in the generated gas as shown in Fig. 4, and consume more H component in the input gas, and it is possible to increase the D composition in the output gas (exhaust gas) (make the D concentration rate larger than 1) as shown in Fig. 5, particularly in Reference Example 1 in which a Pd thin film was used in the anode.

[0030] 5, when Pd / C (Comparative Example 2) and Pt / C (Comparative Example 1) were used as the anode, the D enrichment ratio was close to 1.0, which means that in these cases, the selectivity between H and D was not significant. On the other hand, only when the Pd thin film (Reference Example 1) was used, the D enrichment ratio was 3.0, and the D concentration in the exhaust gas could be increased.

[0031] FIG. 6 shows the results of measuring the D enrichment rate for Reference Example 1, Comparative Example 1, and Comparative Example 2 by changing the applied voltage. Here, since the current flowing between the electrodes and the reaction efficiency correspond one-to-one, the horizontal axis represents the reaction efficiency converted from the current corresponding to the applied voltage. From this result, regardless of the voltage between the first electrode 11 and the second electrode 12, the D composition cannot be enriched in Comparative Example 1 in which Pt / C is used, and the D composition is enriched in Reference Example 1 and Comparative Example 2 in which Pd is used. However, this effect is particularly remarkable in Reference Example 1 in which a Pd thin film is used, and is small in Comparative Example 2 in which Pd / C is used. Note that the absolute value of the D enrichment rate here is slightly different from that in FIG. 5 due to the difference in the measurement mode from that in FIG. 5.

[0032] Since the surface area of ​​Pd is larger in Comparative Example 2 than in Reference Example 1, the efficiency of the reaction (oxidation reaction) in which hydrogen molecules (H2, D2) dissociate on the anode 11 is higher in Comparative Example 2. Therefore, the above result means that the high D concentration rate is not due to this oxidation reaction, but rather due to other reactions, such as the subsequent absorption and diffusion of H ions and D ions into the anode. In addition, as described above, in Reference Example 1, the thickness of Pd is 6 nm, which is thinner than the case where it is used as an independent hydrogen permeable membrane as described in Non-Patent Document 1, so that this anode can be made inexpensive. Even if Pd is thin like this, the main part of the structure in FIG. 1 is the thick proton conductive layer 20, so problems caused by Pd being embrittled by hydrogen are unlikely to occur. In addition, since thin Pd is used, it is clear that the above configuration can be obtained inexpensively.

[0033] The results of detailed composition analysis of the output gas (exhaust gas in Figures 1 and 2) in Reference Example 1 (when the anode is Pd) were compared with those of Comparative Example 2, in which Pd was also used. Here, the compositions of H2, D2, and HD in the output gas when the same input gas was used were measured. Figure 7 shows the measurement results for Reference Example 1 and Comparative Example 2. It is clear from these results that the presence of HD in the output gas is prominent in Comparative Example 2, whereas the HD component is extremely small in Reference Example 1.

[0034] In the configuration of Fig. 2, HD does not exist in the input gas originally, and HD is generated by the combination of H and D dissociated by the catalytic action of Pd. For this reason, as in the case of the generated gas shown in Fig. 4, it is considered that a particularly large amount of HD was generated on the anode side in Comparative Example 2, in which Pd / C, which has a large Pd surface area and strong catalytic action, was used as the anode. What is particularly required as gaseous deuterium is not HD in which D is combined with H, but D2, which consists only of D and does not contain H. From this point of view, Reference Example 1, in which a Pd thin film (evaporated film) was used, is preferable as a deuterium concentrator.

[0035] The above results are the results when the MEA M in FIG. 1 is not used as a fuel cell, but a DC voltage is applied between terminals A and B in FIG. 1 to cause the second reaction. Next, the results when the same MEA M is used as a fuel cell and the first reaction is caused will be described. Here, O2 is introduced into the cathode gas chamber 32, and water (H2O, etc.) is generated there. As is well known, a DC voltage is generated between terminals A and B at this time. As is well known, in this case, a positive voltage is generated at B in FIG. 1, and a negative voltage is generated at A. For convenience, the side where the input gas flows as in FIG. 1 is defined as the anode gas chamber 31, and the side where the generated gas is generated is defined as the cathode gas chamber 32. FIG. 8 shows the results of measuring the power generation characteristics (relationship between the electromotive voltage between terminals A and B and the current density) in this case for structures similar to those of Reference Example 1, Comparative Example 1, and Comparative Example 2. From these results, by introducing O2 into the cathode gas chamber 32, all of Reference Example 1, Comparative Example 1, and Comparative Example 2 function as fuel cells. However, among these, Comparative Example 1 has the best power generation characteristics (high electromotive force and large current density), and this fuel cell is similar to the one described in Patent Document 1. However, Reference Example 1 and Comparative Example 2, in which Pd was used, also function as fuel cells, and there is no significant difference in their power generation characteristics.

[0036] Next, the D enrichment rate in the exhaust gas in this case was measured using a configuration similar to that shown in Figure 2. Figure 9 shows the results. Here, an external resistor was connected between terminals A and B, and the current density was adjusted by this resistance value. The reaction efficiency was calculated from this current density.

[0037] From this result, the D concentration ratio in Comparative Example 1 is smaller than 1. This means that in Comparative Example 1 (when Pt / C is used for the anode), D contributes more to power generation than H. On the other hand, in Reference Example 1 and Comparative Example 2 in which Pd was used, a D concentration ratio larger than 1 was obtained, similar to the result in FIG. 6 (when not used as a fuel cell). That is, the MEA M of Reference Example 1 in which a Pd thin film was used for the first electrode 11 can concentrate the D composition in the input gas to obtain an output gas (exhaust gas) both when it is not used as a fuel cell and a voltage is applied between terminals A and B as described above, and when it is used as a fuel cell that generates an electromotive force between terminals A and B.

[0038] As described above, a highly efficient hydrogen isotope enrichment device can be obtained by combining a structure in which the above MEA M in which a Pd thin film is used for the first electrode 11 is used as a fuel cell with another similar MEA M to which a voltage obtained from this MEA M is applied. FIG. 10 is a diagram showing a schematic configuration of this hydrogen isotope enrichment device 1. Here, two MEAs (M1, M2) of the same configuration are used, aligned vertically (in-plane direction). In both cases, the above Pd thin film is used as the first electrode 11, the above Pt / C is used as the second electrode 12, and the above Nafion is used as the proton conductive layer 20.

[0039] Here, the first unit U1 formed mainly of the upper MEA M1 functions as a fuel cell by the first reaction, and the D composition of the input gas (first input gas) supplied to the anode side gas chamber 31 of the MEA M1 is concentrated. Since O2 is supplied from the outside to the cathode side gas chamber 32 of the MEA M1, H ions and D ions that move from the first electrode 11 side to the second electrode 12 side generate water (H2O, D2O, HDO) as a product (first product) on the second electrode 12 side. At this time, an electromotive force is generated between the first electrode 11 and the second electrode 12, with the first electrode 11 side being negative and the second electrode 12 side being positive. At this time, as shown in FIG. 9, the H component in the first input gas selectively flows to the second electrode 12 side, and a first exhaust gas with an increased D / H composition ratio in the first input gas is discharged from the first gas chamber 31 of the MEA M1.

[0040] The second unit U2 mainly composed of MEA M2 at the bottom of the figure functions to further increase the D concentration of this first exhaust gas. The first electrode 11 in MEA M2 is electrically connected to the second electrode 12 in MEA M1, and the second electrode 12 in MEA M2 is electrically connected to the first electrode 11 in MEA M1. Therefore, in MEA M2, a voltage is applied between the first electrode 11 and the second electrode 12 in the same manner as in the case shown in Figure 2. Note that, in reality, Ar is introduced into the atmosphere on the second electrode 12 side to supply H2O to the proton conductive layer 20 as shown in Figure 2, but its description is omitted here.

[0041] Further, the first exhaust gas with an increased D / H composition ratio is directly supplied as an input gas (second input gas) to the anode-side gas chamber 31 of the MEA M2. As a result, gaseous hydrogen gas (H2, D2, HD) is generated as a product (second product: generated gas) on the second electrode 12 side. At this time, as shown in FIG. 4 and the like, the H component in the second input gas flows selectively to the second electrode 12 side, so that the second exhaust gas with a further increased D / H composition ratio in the second input gas (first exhaust gas) is discharged from the anode-side gas chamber 31 of the MEA M2 as a final output gas. At this time, as described above, the catalytic effect of the Pd thin film (Reference Example 1) is smaller than that of Pt / C (Comparative Example 1) and Pd / C (Comparative Example 2), so that the D2 component is generated in the first output gas and the second exhaust gas, while the HD component is hardly generated.

[0042] Therefore, in this hydrogen isotope enrichment apparatus 1, the D component in the input gas can be enriched in two stages with high efficiency using the first unit U1 and the second unit U2 without using an external power supply. Note that, as shown in Fig. 2, an MFC is actually used to control the flow rate of the input gas, etc., but the power generated by the first unit U1 can also be used to control components other than the second unit U2, such as the MFC, without supplying all of it to the second unit U2.

[0043] In addition, in FIG. 10, the MEA M1 and the MEA M2 are described as being separate and electrically connected, but it is also possible to use MEAs in which the materials and thicknesses of the layers are the same. In this case, the MEAs M1 and M2 can actually be provided as different regions on the surface of a single large MEA (membrane electrode assembly base material). That is, the configuration of FIG. 10 can be easily realized by separating the first electrode 11 and the second electrode 12 into regions, forming the anode side gas chamber 31 and the cathode side gas chamber 32 in two different regions, and electrically connecting them as shown in FIG. 10. Such a configuration can be particularly easily realized because the D concentration action described above is performed in a gaseous state at room temperature.

[0044] On the other hand, as long as the first unit U1 functions as a fuel cell, discharges a first exhaust gas with an increased D concentration, and outputs a second exhaust gas with an increased D concentration of the first exhaust gas by applying a voltage to the second unit U2, the MEA M1 and the MEA M2 do not need to have the same configuration. For example, as shown in Figs. 8 and 9, there is no significant difference in the power generation characteristics and D concentration ratios of fuel cells using a Pd thin film (Reference Example 1) and Pd / C (Comparative Example 2) as the first electrode 11, so that either a Pd thin film or Pd / C can be preferably used as the first electrode 11 of the MEA M1. On the other hand, as shown in Fig. 5, as the MEA M2, the characteristics of Pd / C (Comparative Example 2) are not significantly different from those of Pt / C (Comparative Example 1), and the Pd thin film (Reference Example 1) has better characteristics than these. Therefore, for example, Pd / C can be used as the first electrode 11 of MEA M1, and a Pd thin film can be used as the first electrode 11 of MEA M2. In this case, MEAs M1 and MEA M2 are manufactured separately, and after forming the anode side gas chamber 31 and the cathode side gas chamber 32 in each MEA, gas piping can be formed as shown in Figure 10.

[0045] As an example, measurements were actually performed on the hydrogen isotope enrichment apparatus 1 having the configuration of FIG. 10, in which the first electrode 11 in the first unit U1 was made of Pd / C similar to the comparative example 2, the first electrode 11 in the second unit U2 was made of Pd similar to the reference example 1, and the second electrode 12 was made of Pt / C similar to the above. As shown in FIG. 10, the power (voltage) supply to the second unit U2 was only performed by the first unit U1. In this case, when the reaction efficiency in the first unit U1 and the second unit U2 was both set to 50%, the D enrichment rate in the case of such two-stage enrichment was 2.0, and when the reaction efficiency in the first unit U1 and the second unit U2 was both set to 20%, the D enrichment rate in the case of such two-stage enrichment was 1.4. That is, the D concentration in the input gas was increased in this way and output as the output gas without external power supply.

[0046] In the example of FIG. 10, the hydrogen isotope enrichment apparatus 1 is formed by combining the first unit U1 (MEA M1) and the second unit U2 (MEA M2), but this hydrogen isotope enrichment apparatus 1 can be combined in multiple stages to obtain a more efficient hydrogen isotope enrichment apparatus. FIG. 11 is a diagram showing the configuration of a hydrogen isotope enrichment apparatus 2 which is such a first modified example. Here, each of the three enrichment units 1A to 1C has the same configuration as the hydrogen isotope enrichment apparatus 1 of FIG. 10. That is, the enrichment unit 1A has an MEA M1 and an anode side gas chamber 31 and a cathode side gas chamber 32 associated therewith, and a 2MEA M2 and an anode side gas chamber 31 and a cathode side gas chamber 32 associated therewith. Therefore, as shown in FIG. 10, for example, a first input gas is input to the enrichment unit 1A as an input gas of the first stage, and a second exhaust gas is output as an output gas with an increased D concentration. Here, such input gas in enrichment unit 1A is referred to as the first enrichment unit input gas, its output gas as the first enrichment unit output gas, such input gas in enrichment unit 1B is referred to as the second enrichment unit input gas, its output gas as the second enrichment unit output gas, such input gas in enrichment unit 1C is referred to as the third enrichment unit input gas, and its output gas as the third enrichment unit output gas.

[0047] In Fig. 11, the output gas of the first enrichment unit is used as the input gas of the second enrichment unit, and the output gas of the second enrichment unit is used as the input gas of the third enrichment unit. That is, the output gas of the enrichment unit at the front stage is used as the input gas for the enrichment unit at the rear stage. Therefore, when the input gas for the entire hydrogen isotope enrichment apparatus 2 is the input gas of the first enrichment unit, and the output gas of the third enrichment unit is used as the overall output gas, the D component can be enriched with high efficiency. In the example of Fig. 11, enrichment units are used in three stages, but more enrichment units can be used in the same manner.

[0048] 12 shows the configuration of a hydrogen isotope enrichment apparatus 3, which is a further modified example (second modified example) of the above-mentioned hydrogen isotope enrichment apparatus 2. Here, four enrichment units 1A-1D each having the same configuration as the above-mentioned hydrogen isotope enrichment apparatus 1 are used. Here, as in the configuration of FIG. 11, the output gas of the first enrichment unit is used as the input gas of the second enrichment unit, the output gas of the second enrichment unit is used as the input gas of the third enrichment unit, and the output gas of the third enrichment unit is used as the input gas of the fourth enrichment unit. In other words, the output gas of the enrichment unit on the front stage is used as the input gas for the enrichment unit on the rear stage.

[0049] In this way, when the concentration units are connected in series and the D concentration is increased stepwise, the D concentration of the input gas and output gas of each concentration unit increases toward the downstream (lower side in the figure). Therefore, the D concentration of the product gas in each concentration unit also inevitably increases toward the downstream. In this case, as described above, the D concentration of the product gas is lower than the D concentration of the input gas and exhaust gas (output gas) for one concentration unit, but the D concentration of the product gas in the downstream stage may be higher than the D concentration of the exhaust gas (output gas) of the previous stage. In the configuration of FIG. 12, if the D concentration of the product gas of the third concentration unit 1C, which is the product gas of the third concentration unit 1C, is higher than the D concentration of the output gas of the first concentration unit, the D concentration of the input gas of the second concentration unit can be further increased by merging the product gas of the third concentration unit with the output gas of the first concentration unit to form the input gas of the second concentration unit, and this can further increase the D concentration of the output gas of the second concentration unit 1B (output gas of the second concentration unit). Similarly, the product gas (product gas of the fourth concentration unit) of the concentration unit 1D and the output gas (output gas of the second concentration unit) of the second concentration unit 1B can be combined to form the input gas (input gas of the third concentration unit) of the third concentration unit 1C.

[0050] The configurations shown in Figures 11 and 12 can be particularly easily realized because they use the above-mentioned MEA and because not only the substance used as the input (input gas), but also the exhaust gas discharged from the anode side gas chamber 31 and the generated gas discharged from the cathode side gas chamber 32 are all gases.

[0051] In the example of Fig. 12, the product gases (third product gas, fourth product gas) of the third concentrating unit 1C and fourth concentrating unit 1D are used as part of the input gases (second concentrating unit input gas, third concentrating unit input gas) of the second concentrating unit 1B and third concentrating unit 1C, which are located one stage before them. However, when more concentrating units are used, the product gas may be used as part of the input gas two or more stages before the concentrating unit that generated the product gas. This setting can be made according to the D concentrations of the input gas, output gas, and product gas in each concentrating unit.

[0052] As described above, in the hydrogen isotope enrichment apparatus 1 of Fig. 10, the MEA M1 and MEA M2 used can be formed on a common membrane electrode assembly base material. In the hydrogen isotope enrichment apparatuses 2 and 3 described above, all of the MEAs in all of the enrichment units used therein can be similarly formed on a common membrane electrode assembly base material. This configuration can be particularly easily realized because the D enrichment action described above is performed in a gaseous state and at room temperature.

[0053] Next, a case will be described in which a material other than Pd is used as the first electrode 11. However, for the convenience of the experiment, contrary to the above, this MEA was used not as a fuel cell (the above MEA M2), and, contrary to the above, the first electrode 11 was used as the cathode and the second electrode 12 was used as the anode. At this time, the case in which the Pd thin film in the above Reference Example 1 was used as the cathode was also investigated, and the effectiveness of materials other than Pd was indirectly investigated.

[0054] The apparatus configuration when this measurement was performed is shown in FIG. 13, which corresponds to FIG. 2. Contrary to the case of FIG. 2, the anode side gas chamber 31 is in contact with the second electrode 12, and the cathode side gas chamber 32 is in contact with the first electrode 11. The gas input to the anode side gas chamber 31 is the input gas, the gas discharged from the anode side gas chamber 31 is the discharge gas, and the gas generated in the cathode side gas chamber 32 is the generated gas. In this case, since the D / H ratio in the generated gas in the reference example was higher than that of the input gas, the generated gas on the cathode side was used as the output gas as described above. In this case, the composition of the output gas (generated gas) was measured by the Q-mass 120 in the configuration of FIG. 13.

[0055] Here, the first electrode 11 is used as the cathode and the second electrode 12 is used as the anode as described above, and the second electrode 12 is made of Pt / C as described above, the first electrode 11 is made of Pd, and the cathode 12 is made of vanadium (V), tantalum (Ta), or titanium (Ti), which is a metal that is permeable to hydrogen like Pd, as materials for the cathode 12. These are referred to as Reference Examples 2 to 5, and the D concentration ratio was measured by carrying out the same measurement. In this case, too, the input gas is configured to contact the surface on the anode (second electrode 12) side, and H ions and D ions flow through the proton conducting layer 20 from the anode side toward the cathode (first electrode 11) side. The measurement result of the D concentration ratio in this case is shown in FIG. 14. Here, for the convenience of handling the MEA, metal foils of Pd, V, Ta, and Ti with a thickness of 50 μm were used as the first electrode 11 in Reference Examples 2 to 5. However, even when the evaporated film that became the first electrode in Example 1 was thickened to 20 nm, the results were not significantly different from those in Example 1. Therefore, there is no essential difference between this metal foil and the evaporated film, and it is believed that, at least within these film thickness ranges, there is no difference due to the film thickness.

[0056] From this result, in Reference Examples 2 to 5, a D concentration rate sufficiently larger than 1 was obtained. That is, by using these metals having a dense structure as the cathode (first electrode 11), it is possible to obtain an output gas (produced gas) in which D in the input gas is concentrated. In this case, V, Ta, and Ti can be used in addition to Pd. As described above, these hydrogen permeable metals are metals that allow H ions and D ions to pass through, and it is preferable to use such hydrogen permeable metals formed into a dense structure as the first electrode 11. Note that, as in Reference Example 2, when the materials in Comparative Example 2 (anode: Pd / C, cathode: Pt / C) were reversed between the anode and cathode (anode: Pt / C, cathode: Comparative Example 3), the D concentration rate was 1.

[0057] In addition, when the first electrode 11 and the second electrode 12 were both Pd thin films (Reference Example 6), the D concentration ratio was also large at about 2.9. From the above results, it is estimated that the above-mentioned effect of D concentration is brought about particularly by the characteristics of the first electrode 11 or the interface between the first electrode 11 and the proton conductive layer 20, and is basically independent of the polarity or the second electrode 12. In addition, in either polarity, the input gas is input so as to contact the anode side, and the output gas with an increased D concentration is taken out from the first electrode 11 side (the anode side in FIG. 2, and the cathode side in FIG. 8). At this time, a Pd thin film was used in Reference Examples 1, 2, and 6, but it can be estimated from the results of Reference Examples 3 to 5 that similar results can be obtained even when a V, Ta, or Ti thin film is used.

[0058] Next, the results when a thin layer composed of a material other than a hydrogen-permeable metal is added to the first electrode 11 will be described. Here, as such a layer, graphene was used, which can permeate hydrogen like Pd, as described in S. Hu, M. Lozada-Hidalgo, FC Wang, A. Mishchenko, F. Schedin, R. R. Nair, E. W. Hill, D. W. Boukhvalov, M. I. Katsnelson, RAW Dryfe, I. V. Grigorieva, H. A. Wu and AK Geim, "Proton Transport Through One-Atom-Thick Crystals", Nature, Vol. 516, pp. 227-230 (2014). H ions and D ions permeate the hexagonal crystal structure of graphene.

[0059] Here, as such a reference example (Reference Example 7), before Pd with a thickness of 6 nm is formed as the anode by vapor deposition as in Reference Example 1, monolayer graphene is formed on the surface of the proton conducting layer 20 (the electrode material of the anode in this case is referred to as Pd / Gr hereinafter). As the cathode, Pt / C, which is the second electrode 12 similar to Reference Example 1, was used. The D concentration rate in this case was 6.7, which is higher than that of Reference Example 1. That is, by interposing monolayer graphene between Pd (first electrode 11) and the ion conducting layer 20, the D concentration rate is further improved.

[0060] This is believed to be because the difference in zero-point vibrational energy between H ions and D ions in the proton conducting layer 20 on the first electrode 11 side becomes larger when graphene is present than when graphene is not present. That is, the difference in zero-point vibrational energy between H ions and D ions can be increased in this way, and the D concentration can be particularly increased by interposing a substance that can permeate hydrogen (H ions, D ions) between the hydrogen permeable metal and the proton conducting layer 20. Even when the polarity of Reference Example 7 was reversed (when the first electrode 11 and graphene were on the cathode side: Reference Example 8), a D concentration rate greater than 1 was obtained. However, the D concentration rate in this case was about 2.1, which was smaller than that of Reference Example 7. That is, the configuration in which graphene is combined with the first electrode 11 is particularly effective when these are on the anode side.

[0061] The D enrichment rates measured in the above-mentioned Reference Examples and Comparative Examples are shown in Table 1. The results show that a particularly high D enrichment rate can be obtained when the above-mentioned hydrogen-permeable metal thin film is used as an electrode in the above-mentioned MEA M2. Similar electrodes can also be used in the above-mentioned MEA M1.

[0062] [Table 1]

[0063] In the above example, deuterium ( 2 H, D) is hydrogen ( 1 It has been shown that deuterium can be selectively enriched from a gas mixture of tritium ( 3 It is clear that hydrogen isotopes (H, T) can be enriched in the same way. The same is true for other hydrogen isotopes. [Explanation of symbols]

[0064] 1~3 Hydrogen isotope enrichment device 1A~1D Concentration Unit 11 1st electrode 12 Second electrode 20 Proton Conducting Layer 31 Anode gas chamber 32 Cathode gas chamber 101~104 Mass flow controller (MFC) 105 Bubbler 110 Vacuum Exhaust System 120 Q-mass (quadrupole mass spectrometer) M, M1, M2 Membrane Electrode Assembly (MEA) U1 1st Unit U2 2nd Unit

Claims

1. hydrogen( １ A hydrogen isotope enrichment apparatus for outputting an output gas in which an input gas containing a mixture of hydrogen isotopes, the hydrogen isotopes being an isotope of the hydrogen, and hydrogen isotopes are mixed, the output gas being increased in concentration of the hydrogen isotopes relative to the hydrogen, a first unit that receives the input gas and functions as a fuel cell to generate a DC voltage, and a second unit that outputs the output gas by applying the DC voltage to the first unit, Each of the first unit and the second unit is a proton conducting layer made of a proton conductor that conducts positive hydrogen ions and having two opposing main surfaces; a first electrode formed on one main surface of the proton conducting layer; a second electrode formed on the other main surface of the proton conducting layer; A membrane electrode assembly having the first electrode in the first unit and the second electrode in the second unit, and the second electrode in the first unit and the first electrode in the second unit are electrically connected to each other, the first electrode in the second unit is made of a thin film of a hydrogen-permeable metal selected from the group consisting of palladium (Pd), vanadium (V), tantalum (Ta), and titanium (Ti); On the first unit side, the input gas is caused to flow into a space in contact with the first electrode, and oxygen is introduced into a space in contact with the second electrode, whereby the hydrogen and the hydrogen isotopes in the input gas move toward the second electrode, producing water on the second electrode side and causing a first reaction in which an electromotive force is generated that is negative on the first electrode side and positive on the second electrode side, and a first exhaust gas, which is the input gas after the hydrogen and the hydrogen isotopes are consumed by the first reaction, is exhausted, On the second unit side, the first exhaust gas is caused to flow into a space in contact with the first electrode, a second reaction occurs in which the hydrogen and the hydrogen isotopes in the first exhaust gas move toward the second electrode side and a product gas is generated on the second electrode side, and a second exhaust gas, which is the first exhaust gas after the hydrogen and the hydrogen isotopes are consumed by the second reaction, is discharged; The hydrogen isotope enrichment apparatus is characterized in that the second exhaust gas is the output gas.

2. In the second unit, the second electrode includes platinum (Pt) particles; 2. The hydrogen isotope enrichment device according to claim 1, wherein the hydrogen permeable metal in the first electrode has a denser structure than platinum in the second electrode.

3. In the second unit, 2. The hydrogen isotope enrichment device according to claim 1, wherein the second electrode is made of a thin film of the hydrogen permeable metal.

4. A hydrogen isotope enrichment device described in any one of claims 1 to 3, characterized in that the first electrode in the second unit is a vapor-deposited film of the hydrogen-permeable metal.

5. 5. The hydrogen isotope enrichment device according to claim 1, wherein the first electrode and the proton conductive layer are in contact with each other via a monolayer graphene.

6. 6. The hydrogen isotope enrichment device according to claim 1, wherein the proton conductive layer, the first electrode, and the second electrode in the first unit, and the proton conductive layer, the first electrode, and the second electrode in the second unit are each made of the same material.

7. 7. The hydrogen isotope enrichment device according to claim 6, wherein a membrane electrode assembly base material is used that includes the first electrode, the second electrode, and the proton conductive layer, and the membrane electrode assemblies in the first unit and the second unit are formed as different regions within a plane of a single membrane electrode assembly base material.

8. A plurality of enrichment units, which are the hydrogen isotope enrichment apparatus according to any one of claims 1 to 7, are used in stages, 1. A hydrogen isotope enrichment apparatus, wherein the output gas from the enrichment unit in a preceding stage is used as the input gas for the enrichment unit in an adjacent subsequent stage.

9. 9. The hydrogen isotope enrichment apparatus according to claim 8, wherein the product gas in one of the enrichment units is used as the input gas for the enrichment unit in a stage preceding the one of the enrichment units.

10. The hydrogen isotope is deuterium ( ２ H or D), or tritium ( ３ 10. The hydrogen isotope enrichment device according to claim 1, wherein the hydrogen isotope enrichment element is a hydrogen isotope enrichment element.

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