Apparatus and method for producing hydrogen and / or ammonia

Abstract

To provide a manufacturing apparatus and a manufacturing method for hydrogen and / or ammonia that can produce hydrogen and / or ammonia from urea and water.SOLUTION: A manufacturing apparatus for hydrogen and / or ammonia 1 comprises an electrochemical cell 4 having an electrode body 2 and an electrolyte 3. The electrode body 2 comprises a laminate in which a cathode pole 21, a barrier membrane 22, and an anode pole 23 are laminated in order. At least the anode pole 23 is in contact with urea. The electrolyte 3 is composed of alkaline aqueous solution. At least one of the anode pole 23 and the cathode pole 21 is in contact with the electrolyte 3. The barrier membrane 22 is composed of an ion-exchange membrane. Preferably, the ion-exchange membrane is an anionic exchange membrane.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an apparatus for producing hydrogen and / or ammonia from urea and water, and a method for producing hydrogen and / or ammonia.

Background Art

[0002] Hydrogen is useful as a fuel for fuel cells and a raw material for e-fuels, etc. Ammonia is a hydrogen carrier and a raw material for chemical fertilizers, and is useful for removing harmful substances such as NOx by selective catalytic reduction (i.e., SCR). On the other hand, urea has a high energy density, can be safely transported and stored, and can also be easily obtained from industrial and domestic wastewater, etc., and thus has attracted attention as a raw material for producing hydrogen and ammonia.

[0003] For example, in Patent Document 1, a method of causing electrolytic hydrolysis of urea by using a Teflon (registered trademark) membrane or a polypyromethylene membrane as a separator (in other words, a diaphragm or a separator) has been proposed. By this method, ammonia can be produced from urea.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, the generation efficiency of electricity (specifically, the energy conversion efficiency) such as solar power generation has been increasing, and an expansion of the use of renewable energy is expected. Therefore, the development of new production methods and production apparatuses for ammonia and hydrogen, for example, at low energy using electricity (specifically, an electrolysis reaction) is desired.

[0006] The present invention has been made in view of such problems, and aims to provide an apparatus and a method for producing hydrogen and / or ammonia that can electrochemically generate hydrogen and / or ammonia from urea and water.

Means for Solving the Problems

[0007] One aspect of the present invention is a production apparatus (1) for hydrogen and / or ammonia, which is composed of an electrochemical cell (4) having an electrode body (2) and an electrolytic solution (3), wherein the electrode body is composed of a laminate in which a cathode electrode (21), a diaphragm (22), and an anode electrode (23) are sequentially laminated, at least the anode electrode is in contact with urea, the electrolytic solution is composed of an alkaline aqueous solution, and at least one of the anode electrode and the cathode electrode is in contact with the electrolytic solution, and the diaphragm is composed of an ion exchange membrane, in the hydrogen / ammonia production apparatus.

[0008] Another aspect of the present invention is a method for producing hydrogen and / or ammonia, wherein an electrode body (2) is formed by sequentially laminating a cathode electrode (21), a diaphragm (22) composed of an ion exchange membrane, and an anode electrode (23), the anode electrode of the electrode body is brought into contact with urea, and at least one of the anode electrode and the cathode electrode is brought into contact with an electrolytic solution composed of an alkaline aqueous solution, re and a voltage is applied between the cathode electrode and the anode electrode to generate hydrogen and / or ammonia, in the hydrogen / ammonia production method.

Advantages of the Invention

[0009] The production apparatus has the above configuration, and the diaphragm is composed of an ion exchange membrane. Therefore, reaction factors can be directly sent from the cathode electrode to the anode electrode or from the anode electrode to the cathode electrode through the ion exchange membrane. Specifically, the reaction factors are OH、H​+ That is, hydrogen is generated at the cathode, and ammonia is generated at the anode. In this way, hydrogen and / or ammonia can be efficiently generated.

[0010] In the above manufacturing method, the anode of the electrode body is brought into contact with urea, and at least one of the anode and the cathode of the electrode body is brought into contact with an electrolytic solution composed of an alkaline aqueous solution. re Then, a voltage is applied between the cathode and the anode. By applying the voltage, the reaction factor can be directly sent from the cathode to the anode or from the anode to the cathode. As a result, hydrogen is generated at the cathode, and ammonia is generated at the anode. In this way, hydrogen and / or ammonia can be efficiently generated.

[0011] As described above, according to the above aspect, it is possible to provide a hydrogen / ammonia production apparatus and a hydrogen / ammonia production method capable of generating hydrogen and / or ammonia from urea and water. Note that the reference numerals in parentheses described in the claims and the means for solving the problems indicate the correspondence with the specific means described in the embodiments described later, and do not limit the technical scope of the present invention.

Brief Description of Drawings

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Mode for Carrying Out the Invention

[0013] (Embodiment 1) Embodiments related to an apparatus and a method for producing hydrogen and / or ammonia will be described with reference to FIGS. 1 to 3. As illustrated in FIGS. 1 to 3, the hydrogen / ammonia production apparatus 1 is composed of an electrochemical cell 4. The electrochemical cell 4 has an electrode body 2 and an electrolyte 3.

[0014] The electrode body 2 is composed of a laminate in which a cathode electrode 21, a separator 22, and an anode electrode 23 are sequentially laminated. In the electrode body 2, the cathode electrode 21, the separator 22, and the anode electrode 23 are integrally formed. Another layer may be formed between the cathode electrode 21 and the separator 22 and between the anode electrode 23 and the separator 22.

[0015] In the hydrogen / ammonia production apparatus 1, the anode electrode 23 is in contact with urea. Further, at least one of the anode electrode 23 and the cathode electrode 21 is in contact with the electrolyte 3. That is, the electrolyte 3 may be brought into contact with the anode electrode 23, the electrolyte 3 may be brought into contact with the cathode electrode 21, or the electrolyte 3 may be brought into contact with both the cathode electrode 21 and the anode electrode 23. The electrolyte 3 is composed of an alkaline aqueous solution. The separator 22 is composed of an ion exchange membrane, and the ion exchange membrane is a cation exchange membrane or an anion exchange membrane. Thus, in the hydrogen / ammonia production apparatus 1, there are variations in the combination of the type of ion exchange membrane and the electrode with which the electrolyte is brought into contact.

[0016] Urea may be supplied as a solid or as an aqueous solution (i.e., aqueous urea). In the hydrogen / ammonia production apparatus 1, urea is supplied to the anode electrode 23 side. When supplying solid urea, since the anode electrode 23 side can be made into a dry environment (see Fig. 2), it becomes easier to recover the ammonia generated on the anode electrode 23 side. As shown in Fig. 2, when making the anode electrode 23 side into a dry environment, an electrochemical cell 4 is formed by bringing the electrolyte 3 into contact with the cathode electrode 21. The contact between the cathode electrode 21 and the electrolyte 3 is realized, for example, by immersing the cathode electrode 21 in the electrolyte 3. Note that the dry environment means an environment in which no liquid such as the electrolyte 3 or aqueous urea exists, but it is allowed to contain moisture contained in the atmosphere, for example.

[0017] Preferably, the cathode electrode 21 may be in contact with the electrolyte 3 composed of an alkaline aqueous solution (see Figs. 2 and 3). In this case, hydrogen is generated from the water of the alkaline aqueous solution.

[0018] Also, when supplying an aqueous solution of urea to the anode electrode 23 side, an electrolyte 3 containing urea can be supplied to the anode electrode 23 side (see Figs. 1 and 3). In this case, as shown in Fig. 1, the cathode electrode 21 side can also be made into a dry environment. Thereby, it becomes easier to recover the hydrogen generated on the cathode electrode 21 side. Also, an effect of preventing the generated hydrogen gas from becoming bubbles in the liquid and covering the electrode surface to inhibit the reaction can be expected. Also, this is because hydrogen can be easily taken out to the outside from the dry environment on the cathode electrode 21 side by introducing an inert gas such as Ar gas from the outside.

[0019] Also, both the anode electrode 23 and the cathode electrode 21 may be brought into contact with the electrolyte 3 containing urea (see Fig. 3). That is, the anode electrode 23 and the cathode electrode 21 may be immersed in the electrolyte 3 containing urea.

[0020] For the electrolytic solution 3, an alkaline aqueous solution (that is, a basic aqueous solution) is used. As the electrolytic solution 3, an aqueous solution of a hydroxide of an alkali metal and / or a hydroxide of an alkaline earth metal can be used. From the viewpoint of being able to make the pH 14 or higher, the alkaline aqueous solution is preferably an aqueous KOH solution. The higher the pH of the alkaline aqueous solution, the more the oxidation of urea is promoted, the current density increases, and the hydrogen generation rate also improves. In addition, when the anode electrode 23 is brought into contact with the electrolytic solution 3, as described above, an alkaline aqueous solution containing urea can be used.

[0021] The pH of the electrolytic solution 3 at 25°C is preferably 8 or higher. In this case, the oxidation of urea is sufficiently promoted, the current density increases, and the hydrogen generation rate also improves. From the viewpoint of further improving this effect, the pH of the electrolytic solution 3 at 25°C is more preferably 12 or higher, and even more preferably 14 or higher.

[0022] As the anode electrode 23, at least one metal selected from the group consisting of Fe, Co, Ru, Rh, Ni, Ir, Pt, and Cu can be used. As the cathode electrode 21, at least one metal selected from the group consisting of Pt, Ir, Pd, Ru, and Ni can be used. By changing the type of metal constituting the anode electrode 23, variations can be caused in the products generated by the electrolysis of urea or urea water to generate products other than ammonia, or the amount of ammonia generated can be increased. Also, from the viewpoints of increasing the amount of ammonia generated and increasing the amount of hydrogen generated, the anode electrode 23 is preferably an electrode composed of a titanium mesh and a deposit of the above metal formed on this titanium mesh. Also, from the viewpoint of facilitating hydrogen generation, the cathode electrode 21 is preferably a composite of a conductive agent composed of a carbon material such as Ketjen black and the above metal.

[0023] From the viewpoint of further improving the production amount of ammonia from the anode electrode 23, it is preferable to use Ru and / or Ni as the anode electrode 23, and it is more preferable to use Ni. Further, from the viewpoint of sufficiently generating hydrogen from the cathode electrode 21, as the anode electrode 23, it is preferable to use at least one selected from the group consisting of Rh, Co, and Fe, it is more preferable to use Co and / or Fe, and it is even more preferable to use Fe.

[0024] The anode electrode 23 preferably contains a base metal. In this case, the anode electrode 23 can be formed without using a noble metal, and the manufacturing cost can be reduced. And in the hydrogen / ammonia production apparatus 1, hydrogen can be generated at the anode electrode 23 even without using a noble metal for the anode electrode 23. Further, when the anode electrode 23 contains a base metal, the manufacturing cost can be reduced. Also, in this case, the type and production amount of the product can be controlled by selecting the base metal species.

[0025] The diaphragm 22 is composed of an ion exchange membrane. As the ion exchange membrane, a cation exchange membrane or an anion exchange membrane can be used.

[0026] As shown in FIG. 1, when the diaphragm 22 is composed of a cation exchange membrane, when a voltage is applied between the anode electrode 23 and the cathode electrode 21, H of the reaction factor is sent from the anode electrode 23 to the cathode electrode 21 through the cation exchange membrane. At this time, on the anode electrode 23 side, the reactions of the following formulas <2.1>, <2.2>, <2.3>, <2.4> occur. That is, by the co-electrolysis of urea and water, NH such as ammonia + is sent from the anode electrode 23 to the cathode electrode 21. At this time, on the anode electrode 23 side, the reactions of the following formulas <2.1>, <2.2>, <2.3>, <2.4> occur. That is, by the co-electrolysis of urea and water, NH such as ammonia xSpecies such as NCO species, N2, and CO2 are generated. The generation reaction proceeds triggered by the reaction of urea and water to generate hydrogen ions (i.e., protons) as shown in Equation <2.1>. Therefore, it is important that the reaction of Equation <2.1> starts. When a cation exchange membrane is used as the ion exchange membrane, hydrogen ions, which are reaction factors, are sent from the anode electrode 23 to the cathode electrode 21 by the cation exchange membrane, and thus the trigger reaction proceeds. In this way, it is considered that the subsequent ammonia generation reaction and hydrogen generation reaction proceed. Further, on the anode electrode 23 side, oxygen is generated by the reaction of Equation <2.5>. And on the anode electrode 23 side, electrons and protons are generated. The electrons move to the cathode electrode 21 side through the external circuit, and the protons move to the cathode electrode 21 side through the cation exchange membrane. At the cathode electrode 21, as shown in Equation <2.6>, electrons and protons react to generate hydrogen. In Equations <2.1> to <2.6>, SHE represents the standard hydrogen electrode, and the electrode potential E 0 represents the converted value at the standard hydrogen electrode.

[0027]

Chemical formula

[0028] As shown in FIG. 2, when the diaphragm 22 is composed of an anion exchange membrane, when a voltage is applied between the anode electrode 23 and the cathode electrode 21, OH, which is a reaction factor, is sent from the cathode electrode 21 to the anode electrode 23 through the anion exchange membrane. At this time, on the anode electrode 23 side, the reactions of the following Equations <3.1>, <3.2>, and <3.3> occur. The reaction of <3.3> further causes the reactions of <3.3.1> to <3.3.4>. That is, on the anode electrode 23 side, OH - is sent from the cathode electrode 21 to the anode electrode 23. -Through the reaction with urea, nitrogen, carbon dioxide, etc. are generated, and ammonia is generated from urea. As shown in Equation <3.1>, the generation reaction proceeds with the reaction between urea and hydroxide ions as a trigger. Therefore, it is important that the reaction of Equation <3.1> starts. When using an anion exchange membrane as the ion exchange membrane, hydroxide ions, which are reaction factors, are sent from the cathode electrode 21 to the anode electrode 23 by the anion exchange membrane, so the trigger reaction proceeds. In this way, it is considered that the subsequent ammonia generation reaction and hydrogen generation reaction proceed. Also, on the anode electrode 23 side, electrons are generated. The electrons move to the cathode electrode 21 side through the external circuit. Then, at the cathode electrode 21, as shown in Equation <3.4>, water and electrons react to generate hydrogen. In Equations <3.1> to <3.4>, SHE represents the standard hydrogen electrode, and the electrode potential E 0 represents the converted value at the standard hydrogen electrode.

[0029] [Chemical formula]

[0030] As shown in the above reaction formula, in the hydrogen / ammonia production apparatus 1, hydrogen is generated on the cathode electrode 21 side, and ammonia is generated on the anode electrode 23 side. In the above production apparatus 1, it is preferable that the anode electrode 23 side and the cathode electrode 21 side are separated by the electrode body 2. In this case, it is possible to prevent the hydrogen generated on the cathode electrode 21 side from being mixed with the ammonia generated on the anode electrode 23 side. Therefore, it becomes easier to separately recover hydrogen and ammonia.

[0031] Specifically, in the hydrogen / ammonia production apparatus 1, a cathode reaction chamber can be formed on the cathode electrode 21 side of the electrode body 2, an anode reaction chamber can be formed on the anode electrode 23 side, and the cathode reaction chamber and the anode reaction chamber can be separated by the electrode body 2. Thereby, the hydrogen generated in the cathode reaction chamber and the ammonia generated in the anode reaction chamber can be separately recovered.

[0032] The ion exchange membrane is preferably an anion exchange membrane. When the ion exchange membrane is a cation exchange membrane, ammonium ions generated from the electrolysis reaction of urea water are ion-exchanged in the cation exchange membrane, increasing the electrical resistance of the cation exchange membrane. As a result, the cation exchange membrane is damaged and loses its function over time. Therefore, ammonia and hydrogen cannot be sufficiently generated. In contrast, when the ion exchange membrane is an anion exchange membrane, ammonium ions are not ion-exchanged, and no increase in electrical resistance occurs. Therefore, ammonia and hydrogen can be continuously generated, thereby increasing the production amount.

[0033] The anion exchange membrane is preferably composed of a polymer containing at least one ligand selected from the group consisting of an imidazolium ligand, a pyridinium ligand, and a phosphonium ligand. More specifically, the anion exchange membrane is composed of a polymer having a ligand part and a backbone part chemically bonded to the ligand part, and the ligand part is preferably composed of at least one functional group selected from the group consisting of an imidazolium group, a pyridinium group, and a phosphonium group or a salt thereof. From the viewpoints of the stability of the functional group and the base strength, the ligand is preferably an imidazolium ligand. In other words, the ligand part is preferably composed of an imidazolium group or a salt thereof. The backbone part is composed of, for example, a styrene-based resin such as polystyrene or a styrene divinylbenzene copolymer; an acrylic-based resin such as polyhydroxy methacrylate; polyvinyl alcohol, etc.

[0034] In the hydrogen / ammonia production apparatus 1 of this embodiment, the diaphragm 22 is composed of an ion exchange membrane. Therefore, reaction factors can be directly sent from the cathode electrode 21 to the anode electrode 23 or from the anode electrode 23 to the cathode electrode 21 through the ion exchange membrane. Thereby, it becomes possible to control the local pH of the reaction point of the electrode. Specifically, due to the reactions of the above formulas <2.1> and <3.1>, an increase in the local proton concentration at the cathode electrode 21 and a local OH at the anode electrode 23 -It is possible to induce an increase in concentration. Therefore, it becomes possible to cause a reaction that does not depend on the pH of the electrolytic solution. More specifically, for example, when an anion exchange membrane is used as the ion exchange membrane, OH - is generated at the anode electrode 23, so that an environment with a locally increased pH is formed on the surface of the anode electrode 23. Therefore, even if the pH of the electrolytic solution is near neutral (for example, pH is 8 to 12), the production reactions of ammonia and hydrogen proceed, and the production of hydrogen and ammonia becomes possible. Thus, according to the hydrogen / ammonia production apparatus 1 of this embodiment, hydrogen is generated at the cathode electrode 21 and ammonia is generated at the anode electrode 23. In this way, at least one or both of hydrogen and ammonia can be efficiently generated.

[0035] Next, a method for producing hydrogen and / or ammonia will be described. This method can be easily realized by the above production apparatus, but the production method of the present disclosure is not limited to the method using the above production apparatus. The method for producing hydrogen / ammonia is performed by an electrode formation step, an assembly step, and an application step.

[0036] In the electrode formation step, the cathode electrode 21, the separator 22, and the anode electrode 23 are sequentially laminated. Thereby, the electrode body 2 composed of a laminate of the cathode electrode 21, the separator 22, and the anode electrode 23 is formed. The cathode electrode 21, the separator 22, and the anode electrode 23 are as described above.

[0037] In the assembly step, the anode electrode 23 of the electrode body 2 is brought into contact with urea, and at least one of the anode electrode 23 and the cathode electrode 21 is brought into contact with the electrolytic solution 3 composed of an alkaline aqueous solution. re Thereby, the electrochemical cell 4 is constructed by the electrode body 2 and the electrolytic solution 3. Urea and the electrolytic solution 3 are as described above.

[0038] In the application step, a voltage is applied between the cathode electrode 21 and the anode electrode 23. Thereby, hydrogen is generated from the cathode electrode 21 and ammonia is generated from the anode electrode 23.

[0039] In the manufacturing method of this embodiment, the anode electrode 23 of the electrode body 2 is brought into contact with urea, and at least one of the anode electrode 23 and the cathode electrode 21 of the electrode body 2 is brought into contact with an electrolytic solution 3 composed of an alkaline aqueous solution. re Then, a voltage is applied between the cathode electrode 21 and the anode electrode 23. By applying the voltage, reaction factors can be directly sent from the cathode electrode 21 to the anode electrode 23 or from the anode electrode 23 to the cathode electrode 21. As a result, it becomes possible to control the local pH of the reaction point of the electrode. In this way, the same effects as those of the above manufacturing apparatus can be exhibited. Then, hydrogen is generated at the cathode electrode 21, and ammonia is generated at the anode electrode 23. In this way, at least one or both of hydrogen and ammonia can be efficiently generated.

[0040] (Experimental Example 1) This example is an example of generating hydrogen and ammonia by the hydrogen / ammonia production apparatus 1 using an anion exchange membrane. In this example, the influence is examined while changing the material of the anode electrode 23 in the hydrogen / ammonia production apparatus 1. Among the reference numerals used after Experimental Example 1, those the same as the reference numerals used in the previous embodiments represent the same components and the like as those in the previous embodiments unless otherwise specified.

[0041] In this example, as shown in FIG. 4, the hydrogen / ammonia production apparatus 1 was constructed. Specifically, first, AdBlue (a registered trademark of the German Automobile Industry Association (i.e., VDA) 5BIB), which is urea water manufactured by Mitsui Chemicals, was prepared. The urea concentration of this urea water is 32.5 wt%. 1 M equivalent of KOH was dissolved in this urea water to prepare an alkaline aqueous solution containing urea (i.e., the electrolytic solution 3). The pH of the alkaline aqueous solution is 14 or more. Next, 30 mL of the electrolytic solution 3 was placed in a one-chamber container 40, and the electrode body 2 in which the anode electrode 23, the diaphragm 22, and the cathode electrode 21 were integrally formed was immersed in the electrolytic solution 3.

[0042] As the cathode electrode 21, an electrode composed of a mixture of Ketjen black and Pt was used. As the anode electrode 23, an electrode in which Fe, Co, Ru, Rh, or Ni was deposited on a titanium mesh was used respectively. That is, as the anode electrode 23, an Fe / Ti catalyst, a Co / Ti catalyst, a Ru / Ti catalyst, a Rh / Ti catalyst, and a Ni / Ti catalyst were used. As the diaphragm 22, Sustainion (registered trademark) X-37, an anion exchange membrane manufactured by Dioxide Materials, was used. In the hydrogen / ammonia production apparatus 1 of this example, an electrochemical cell 4 is constructed from an electrode body 2 and an electrolytic solution 3 that immerses it.

[0043] The cathode electrode 21 and the anode electrode 23 are electrically connected to an electrochemical measurement device 5 (specifically, a potentiostat / galvanostat). Specifically, the anode electrode 23 is connected to the electrochemical measurement device 5 as a sample electrode (the sample electrode is also called a working electrode), and the cathode electrode 21 is connected to the electrochemical measurement device 5 as a counter electrode.

[0044] As shown in FIG. 4, a tube 611 made of polytetrafluoroethylene (that is, PTFE) is inserted into the electrolytic solution 3 in the container 40, and this tube is connected to a gas inlet 61 formed at the upper part of the container 40 in the vertical direction. Further, a gas outlet 62 is formed at the upper part of the container 40, and the gas outlet 62 is connected to a sample measurement part of gas chromatography. "GC" in FIG. 4 represents gas chromatography.

[0045] Next, while stirring the electrolytic solution 3 using a magnetic stirrer, He was blown into the container 40 from the gas inlet 61 to replace the air in the container 40 with He. The blowing conditions of He are 0.1 MPa and 20 mL / min.

[0046] While continuously performing gas replacement with He for 60 minutes or more, the open-circuit voltage was measured. Next, the applied voltage between the anode electrode 23 and the cathode electrode 21 was controlled to 2.0 V, and constant voltage electrolysis was performed for 2 hours to evaluate the urea water electrolysis activity. The evaluation was carried out by measuring the average current density, the Faraday efficiency of oxygen (i.e., FE(O2)), and the oxygen generation rate (i.e., r(O2)). The results are shown in FIGS. 5 to 7. Note that FIG. 7 shows the change over time of the current density and the current efficiency of hydrogen when an electrode with Ni deposited on a titanium mesh is used as the anode electrode 23.

[0047] In the hydrogen / ammonia production apparatus 1 of this example, it is considered that the reactions of the above formulas <3.1> to <3.4> occur. That is, at the anode electrode 23, N2 and CO2 are generated by the co-electrolysis of urea and water according to formula <3.1>. Also, according to formula <3.2>, the oxygen generation reaction proceeds by water electrolysis. Then, the electrons generated at the anode electrode 23 move to the cathode electrode 21 through the external circuit of the electrochemical cell 4, and according to formula <3.4>, water and electrons react at the cathode electrode 21 and the H2 generation reaction proceeds. The electrolysis was carried out at a constant voltage as described above. For example, when Pt / KB is used as the cathode electrode 21, it is generally known that it shows high activity in the H2 generation reaction and has a small overvoltage even in the high current density region. Therefore, in this example, the experiment was carried out considering the voltage between the two electrodes as the anode potential.

[0048] In this example, as described above, the electrode catalyst activity was evaluated by the average current density, the generation rate of products such as O2, and the selectivity of the products (specifically, the Faraday efficiency). Assuming that the N2 generation reaction proceeds entirely according to formula <3.1>, and assuming the Faraday efficiency as a 6-electron reaction, the Faraday efficiency FE was calculated based on formula (I). In formula (I), Y represents the product yield (unit: mol), n represents the number of reaction electrons (unit: -), and Q represents the charged amount of electricity (unit: C). FE(%) = 100×Y×n×F / Q ···(I)

[0049] If the electrolysis reaction of urea water proceeds as shown in the above formula <3.1>, N2 and CO2 equivalent to urea (i.e., (NH2)2CO) should be generated. However, in this example, since a strongly basic electrolyte 3 is used, CO2 dissolves in the aqueous solution (i.e., electrolyte 3). Therefore, the CO2 detected by gas chromatography is a part of the generated CO2. Thus, the selectivity of the N2 generation reaction was regarded as the selectivity of the urea water electrolysis reaction, and the catalytic activity was evaluated by comparing it with the selectivity of the O2 generation reaction by water electrolysis. That is, as shown in FIG. 6, by examining the generation rate and selectivity of O2, the generation rate of hydrogen, the generation rate of ammonia, the selectivity of hydrogen, and the selectivity of ammonia can be evaluated.

[0050] As can be understood from FIGS. 5 and 6, when the Fe / Ti catalyst was used for the anode electrode 23, it showed a current density close to 50 A / cm². -2 Also, in this case, since the Faraday efficiency of O2 exceeded 80% and the generation rate was close to 700 μmol / h, hydrogen generation can mainly proceed by electrolysis. On the other hand, ammonia generation can be suppressed. That is, when the Fe / Ti catalyst is used, hydrogen can be preferentially generated. The Co / Ti catalyst and the Rh / Ti catalyst are similar to this. -1

[0051] As can be understood from FIGS. 5 and 6, when the Ni / Ti catalyst was used for the anode electrode 23, it showed a current density close to 150 A / cm². On the other hand, the Faraday efficiency of O2 was 0 and no O2 was generated. Ammonia generation can proceed together with hydrogen generation by electrolysis. The Ru / Ti catalyst is similar to this. -2

[0052] As can be understood from FIG. 7, when the Ni / Ti catalyst was used for the anode electrode 23, it showed a high current density exceeding 100 mA / cm² even after 2 hours. Also, hydrogen was generated on the cathode electrode 21 side at a generation rate of 5 mmol / h with a current efficiency of 100%, and high-efficiency hydrogen generation by urea water electrolysis proceeded. -2 -1 In addition, by gas chromatographic analysis, generation of N2 and a small amount of CO2 were observed in the gas phase on the anode electrode 23 side. Note that most of the generated CO2 as described above is considered to have dissolved in the alkaline aqueous solution (that is, the electrolyte solution 3). Further, when the outlet gas was analyzed by gas chromatographic analysis, almost no harmful compounds such as NO2 and NO were observed.

[0053] In addition, as the anode electrode 23, Ir / KB, Ru / KB, Rh / KB, Pt / KB, Ni / KB, Co / KB, Fe / KB, Fe / Ti, Pt / Ti, Ru / Ti, Rh / Ti, Ni / Ti, Ti-mesh were used, and an experiment similar to the above was conducted except that the applied voltage between the anode electrode 23 and the cathode electrode 21 was set to 1.5V. The measurement results of the average current density when electrolyzing urea water are shown in Fig. 8. Note that Ir / KB means an electrode in which iridium is deposited on Ketjen black, and Fe / Ti means an electrode in which iron is deposited on a titanium mesh. The same applies to other electrodes.

[0054] As can be understood from Fig. 8, when various transition metals and noble metals were used for the anode electrode 23, the Ni / Ti catalyst showed extremely high activity in the electrolytic reforming reaction of urea water. Therefore, it can be said that it is preferable to use a Ni / Ti electrode for the anode electrode 23 in order to produce ammonia and hydrogen from urea.

[0055] (Experimental Example 2) In this example, the influence of the KOH concentration in the electrolyte solution on the urea conversion rate was investigated. First, a hydrogen / ammonia production apparatus 1 similar to that in Experimental Example 1 was fabricated. As the anode electrode 23, Ni / Ti was used. Under the condition of room temperature (25°C), the KOH concentration in the electrolyte solution was set to 0, 1M, or 3M, and the urea conversion rate was measured and calculated when a voltage of 1.5V, 1.8V, or 2V was applied between the cathode electrode and the anode electrode for 2 hours. The results are shown in Fig. 9.

[0056] Note that the urea conversion rate was calculated based on the following formula (I). Urea conversion rate = amount of substance of urea used in the reaction / total amount of substance of urea ··· (I) The total amount of urea is calculated from the urea concentration of the aqueous urea solution (in this example, 32.5 wt%). The "amount of urea used in the reaction" is calculated by the following formula (II) from the amount of electricity passed and the Faraday efficiency of O2 (i.e., FE). Amount of urea used = Amount of electricity passed / 96485 × (1 - FE of O2) / 6 This urea conversion rate is an apparent conversion rate obtained on the assumption that all the remaining amount of electricity after subtracting the amount of electricity for oxygen generation from the amount of electricity passed is used for the electrolysis of urea, that is, the 6-electron reaction in the above formula <3.1> proceeds.

[0057] As can be understood from FIG. 9, in the hydrogen / ammonia production apparatus 1 of this example, it can be seen that the urea aqueous solution electrolysis reaction proceeds sufficiently even with an electrolytic solution having a low KOH concentration of 1M. That is, even with a low-concentration KOH aqueous solution, ammonia is generated from the anode electrode 23 and hydrogen is generated from the cathode electrode 21 by the urea aqueous solution electrolysis reaction. This is considered to be because, by using an anion exchange membrane as the diaphragm 22, even when the KOH concentration is low, the pH locally increases and the urea aqueous solution electrolysis reaction is promoted.

[0058] (Experimental Example 3) This example is an example of producing hydrogen and ammonia by the hydrogen / ammonia production apparatus 1 using a cation exchange membrane. In this example, the hydrogen / ammonia production apparatus 1 shown in FIG. 10 was constructed.

[0059] First, an alkaline aqueous solution containing urea (i.e., electrolyte 3) was prepared in the same manner as in Experimental Example 1. Next, an electrode body 2 in which an anode electrode 23, a diaphragm 22, and a cathode electrode 21 were integrally formed was fabricated. The electrode body 2 was inserted into a container 40 (specifically, the first container 40), and the space within the container 40 was divided into two. More specifically, the diaphragm 22 of the electrode body 2 divided the interior of the container 40. The anode electrode 23 is composed of Pt-Black, and the cathode electrode 21 is composed of Pt. Note that Pt-Black refers to black powder of platinum. Also, as the diaphragm 22, Nafion (registered trademark) 117, a cation exchange membrane manufactured by Chemours, was used.

[0060] The electrolyte 3 (specifically, the first electrolyte 3) was injected into the anode electrode 23 side within the container 40. On the other hand, the cathode electrode 21 within the container 40 was exposed to a dry environment. A tube 611 made of polytetrafluoroethylene (i.e., PTFE) was inserted into the electrolyte 3, and this tube 611 was connected to a gas inlet 61 (specifically, the first gas inlet 61) formed at the upper part of the container 40 in the vertical direction.

[0061] Also, a first gas outlet 621 was formed at the upper part of the container 40 on the anode electrode 23 side, and the first gas outlet 621 was connected to the sample measurement unit of a gas chromatograph. On the other hand, a second gas inlet 63 was provided on the cathode electrode 21 side within the container 40. In the hydrogen / ammonia production apparatus 1 of this example, Ar gas is introduced from the second gas inlet 63 in order to send out the hydrogen generated on the cathode electrode 21 side.

[0062] Also, a second gas outlet 622 was formed at the upper part of the container 40 on the cathode electrode 21 side, and the second gas outlet 622 was connected to the sample measurement unit of a gas chromatograph. Note that in FIG. 10, the illustration of the gas chromatograph is omitted.

[0063] As shown in FIG. 10, the diaphragm 22 extends outside the container 40 from the lower part in the vertical direction V, and the diaphragm 22 is immersed in the second electrolyte 39 in the second container 49 provided outside the container 40. The second electrolyte 39 is a 1N aqueous H2SO4 solution. Further, an Ag / AgCl electrode 25 as a reference electrode is inserted into this aqueous H2SO4 solution.

[0064] The cathode electrode 21, the anode electrode 23, and the Ag / AgCl electrode 25 are electrically connected to an electrochemical measurement device 5 (that is, a potentiostat / galvanostat). Specifically, the anode electrode 23 is connected to the electrochemical measurement device 5 as a sample electrode (the sample electrode is also called a working electrode), the cathode electrode 21 is connected to the electrochemical measurement device 5 as a counter electrode, and the Ag / AgCl electrode 25 is connected to the electrochemical measurement device 5 as a reference electrode. In the hydrogen / ammonia production apparatus 1 of this example, a three-electrode electrochemical cell 4 is constructed.

[0065] Next, while stirring the electrolyte 3 using a magnetic stirrer, He was blown into the container 40 from the first gas inlet 61 to replace the air in the container 40 with He. The blowing conditions of He are the same as those in Experimental Example 1.

[0066] While continuously performing gas replacement with He for 60 minutes or more, the open circuit voltage was measured. Next, the applied voltage between the anode electrode 23 and the cathode electrode 21 was controlled to 1.4 V, and constant voltage electrolysis was performed for 2 hours to advance the urea water electrolysis reaction. At this time, the impedance was measured by the electrochemical measurement device 5. The change in impedance over time is shown in FIG. 11.

[0067] In this example, it was confirmed that HNCO was generated on the anode electrode 23 side by the urea water electrolysis reaction at room temperature by the SPE electrolysis method. Further, according to Equation <3.3>, it can be said that ammonia is generated at the anode electrode 23 by the urea water electrolysis reaction. Furthermore, according to Equation <2.5>, it can be said that hydrogen is generated at the cathode electrode 21 by the urea water electrolysis reaction.

[0068] Also, as can be understood from FIG. 11, in this example, the electrical resistance increases over time. This is considered to be because NH4 in the aqueous urea solution + is trapped in the cation exchange membrane by ion exchange. That is, when a cation exchange membrane is used for the diaphragm 22, the membrane may deteriorate over time. Therefore, as the diaphragm 22, an anion exchange membrane is preferable.

[0069] (Experimental Example 4) This example is an example in which the concentration of ammonia generated from the hydrogen / ammonia production apparatus 1 is directly detected. First, as the anode electrode 23, an electrode in which Ni was deposited on a titanium mesh was used to construct a hydrogen / ammonia production apparatus 1 similar to that in Experimental Example 1 (see FIG. 4).

[0070] Using this hydrogen / ammonia production apparatus 1, urea electrolysis was carried out by performing constant voltage electrolysis for 2 hours. The method and conditions of urea electrolysis were the same as those in Experimental Example 1 except that the applied voltage between the electrodes was 1.8 V and the KOH concentration of the electrolyte was 3 M.

[0071] After 2 hours of constant voltage electrolysis, 30 mL of the electrolyte was collected as a measurement sample, and the ammonia concentration in the measurement sample was measured using an ammonia electrode "Ti9001" manufactured by Dongxing Chemical Co., Ltd. The concentration measurement was performed using a calibration curve with an ammonia standard solution. The results of the average current density and the results of the ammonia concentration in this example are shown in FIG. 12.

[0072] As can be understood from FIG. 12, in this example, the current density was high, the urea electrolysis proceeded efficiently, and furthermore, ammonia was sufficiently generated. Therefore, it can be seen that ammonia is generated with high efficiency. Thus, in this example, the generation of ammonia was confirmed by the ammonia electrode.

[0073] (Experimental Example 5) This example is an example of evaluating the dependence of the urea water electrolysis reaction on the applied voltage. First, as the anode electrode 23, an electrode with Ni deposited on a titanium mesh was used to construct a hydrogen / ammonia production apparatus 1 similar to that in Experimental Example 1 (see Figure 4).

[0074] Using this hydrogen / ammonia production apparatus 1, urea water electrolysis was carried out in the same manner as in Experimental Example 1. The method and conditions of urea water electrolysis were the same as those in Example 1 except that the applied voltage between the electrodes was changed. Specifically, in this example, the voltage was increased by 0.1 V from 1.3 V to 1.6 V every 30 minutes. That is, after performing urea water electrolysis at 1.3 V for 30 minutes, the voltage was increased to 1.6 V in increments of 0.1 V, and urea water electrolysis was carried out for 30 minutes at each voltage. The relationship between the elapsed time, current density, and applied voltage in this experiment is shown in Figure 13. As shown in Figure 13, a 5-minute non-application time of voltage was provided between urea water electrolyses at each voltage. The relationship between the applied voltage and current density in this example is shown as a solid line graph in Figure 14.

[0075] Also, for comparison of the above-mentioned urea water electrolysis, a similar experiment (specifically, electrolysis of water) was carried out using an electrolyte solution without added urea. The result (that is, the relationship between the applied voltage and current density) is shown as a dashed line graph in Figure 14.

[0076] As can be seen from Figure 14, in the electrolyte solution with added urea compared to the electrolyte solution without added urea, the current density becomes higher at a lower potential, and electrolysis is occurring. That is, since urea water electrolysis occurs at a low potential, ammonia and hydrogen can be produced with low energy by using urea water as a raw material.

[0077] (Experimental Example 6) This example is an example of producing hydrogen and ammonia using a hydrogen / ammonia production apparatus 1 in which an anion exchange membrane is used as the diaphragm 22 and one of the electrodes is exposed to a dry environment. The production of hydrogen and ammonia was carried out by evaluating the decomposition activity of urea.

[0078] In this example, a hydrogen / ammonia production apparatus 1 shown in FIG. 15 was constructed. Specifically, first, an alkaline aqueous solution containing urea (i.e., the electrolyte solution 3) was prepared in the same manner as in Experimental Example 1. Also, an electrode body 2 in which an anode electrode 23, a diaphragm 22, and a cathode electrode 21 were integrally formed was inserted into a container 40 whose outer wall was made of PTFE, and the space inside the container 40 was divided into two. That is, the inside of the container 40 was divided by the diaphragm 22 of the electrode body 2. The same anion exchange membrane as in Experimental Example 1 was used as the diaphragm 22. The anode electrode 23 is composed of Ni / Ti, and the cathode electrode 21 is composed of Pt / KB. The anode electrode 23 and the cathode electrode 21 are electrically connected to a power supply 55, respectively.

[0079] As shown in FIG. 15, the electrolyte solution 3 was injected into the anode electrode 23 side inside the container 40, and the cathode electrode 21 inside the container 40 was exposed to a dry environment. The same electrolyte solution as in Experimental Example 1 was used as the electrolyte solution 3. In the following description, the side facing the anode electrode 23 and filled with the electrolyte solution 3 inside the container 40 is referred to as the anode chamber 231 (i.e., the left chamber in FIG. 15), and the side facing the cathode electrode 21 and exposed to a dry environment is referred to as the cathode chamber 211 (i.e., the right chamber in FIG. 15).

[0080] A tube 611 was inserted into the anode chamber 231, and He was circulated through the electrolyte solution 3 through the tube 611. Also, a first gas outlet 621 was formed in the anode chamber 231, and a multi-way valve (specifically, a six-way valve) and a membrane flow meter, which are connected to a gas chromatograph although the configuration is not shown, were sequentially connected to the first gas outlet 621. On the other hand, a second gas inlet 63 and a second gas outlet 622 were provided in the cathode chamber 211, and an inert gas (specifically, Ar) was circulated into the cathode chamber 211 through the second gas inlet 63 and the second gas outlet 622.

[0081] The anode electrode 23 is electrically connected to the working electrode terminal and the potential measurement terminal of the electrochemical measurement device (specifically, a potentiostat / galvanostat) by a gold wire, and the cathode electrode 21 is electrically connected to the counter electrode terminal and the reference electrode terminal of the electrochemical measurement device by a gold wire. Note that in FIG. 15, the illustration of the electrochemical measurement device is omitted.

[0082] After sufficiently blowing an inert gas into the cathode chamber 211 to replace the air with the inert gas, the applied voltage was controlled to 2.0 V, and constant voltage electrolysis was performed for 2 hours in the same manner as in Experimental Example 1 to evaluate the urea water electrolysis activity. The evaluation was performed by measuring the Faraday efficiencies of hydrogen, nitrogen, and oxygen (that is, FE(H2), FE(N2), FE(O2)) and the production rates of hydrogen, nitrogen, and oxygen (that is, r(H2) r(N2) r(O2)). The results are shown in FIGS. 17 to 19. Also, the change in current density over time in this example is shown in FIG. 16.

[0083] As known from FIG. 17, the Faraday efficiency FE(H2) of hydrogen at the cathode electrode 21 is 100%, and the production rate r(H2) of hydrogen is also high. From this, it can be seen that in the hydrogen / ammonia production apparatus 1 of this example, hydrogen is sufficiently produced from the cathode electrode 21 with high efficiency. Also, as can be understood from FIG. 18, the current efficiency of nitrogen generation is as low as about 30%, indicating that nitrogen compounds other than nitrogen and ammonia are generated in the reaction solution. Also, as can be understood from FIG. 19, the current efficiency of oxygen generation is as low as about 6%, indicating that urea is efficiently oxidized.

[0084] Thus, it can be seen that even when an anion exchange membrane is used as the ion exchange membrane and the cathode electrode side is in a dry environment, hydrogen and ammonia can be produced by urea water electrolysis.

[0085] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments without departing from the gist thereof.

Explanation of Reference Numerals

[0086] 1 Hydrogen / Ammonia Production Apparatus 2 Electrode Body 21 Cathode Electrode 22 Diaphragm 23 Anode Electrode 3 Electrolyte 4 Electrochemical Cell

Claims

1. A hydrogen and / or ammonia production apparatus (1) composed of an electrochemical cell (4) having an electrode body (2) and an electrolytic solution (3), wherein the electrode body is composed of a laminate in which a cathode electrode (21), a diaphragm (22), and an anode electrode (23) are sequentially laminated, at least the anode electrode is in contact with urea, the electrolytic solution is composed of an alkaline aqueous solution, and at least one of the anode electrode and the cathode electrode is in contact with the electrolytic solution, and the diaphragm is composed of an ion exchange membrane. A hydrogen / ammonia production apparatus.

2. The hydrogen / ammonia production apparatus according to claim 1, wherein the ion exchange membrane is an anion exchange membrane.

3. The hydrogen / ammonia production apparatus according to claim 1 or 2, wherein the anode electrode side and the cathode electrode side in the electrochemical cell are separated by the electrode body.

4. The hydrogen / ammonia production apparatus according to any one of claims 1 to 3, wherein the electrode body is immersed in the electrolytic solution containing the urea.

5. The hydrogen / ammonia production apparatus according to any one of claims 1 to 3, wherein among the anode electrode and the cathode electrode of the electrode body, the electrode not in contact with the electrolytic solution is exposed to a dry environment where no liquid exists.

6. The hydrogen / ammonia production apparatus according to any one of claims 1 to 5, wherein the anode electrode contains a base metal.

7. A method for producing hydrogen and / or ammonia, wherein an electrode body (2) is formed by sequentially laminating a cathode electrode (21), a diaphragm (22) composed of an ion exchange membrane, and an anode electrode (23), the anode electrode of the electrode body is brought into contact with urea, and at least one of the anode electrode and the cathode electrode is brought into contact with an electrolytic solution composed of an alkaline aqueous solution, and hydrogen and / or ammonia is generated by applying a voltage between the cathode electrode and the anode electrode. A method for producing hydrogen / ammonia.

8. The method for producing hydrogen / ammonia according to claim 7, wherein the ion exchange membrane is an anion exchange membrane.

9. The method for producing hydrogen / ammonia according to claim 7 or 8, wherein the electrode body is immersed in the electrolytic solution containing the urea.

10. The method for producing hydrogen / ammonia according to claim 7 or 8, wherein, among the anode electrode and the cathode electrode of the electrode body, the electrode not in contact with the electrolytic solution is exposed to a dry environment where no liquid is present.

11. The method for producing hydrogen / ammonia according to any one of claims 7 to 10, wherein the anode electrode contains a base metal.

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