Patent Application
20180274110
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2017-057954, filed on Mar. 23, 2017; the entire contents of which are incorporated herein by reference.
Embodiments described herein relate to a laminated electrolyte membrane, a membrane electrode assembly, a water electrolysis cell, a stack, and a water electrolysis apparatus.
Currently, fuel cells are attracting attention and being developed as a clean power generation system that can reduce environmental load. In particular, the fuel cells are beginning to be used in various fields such as home use power supply fuel cells (Enefarm™), on-vehicle fuel cells, buses, and trains. On the other hand, it is essential to reduce CO2 emissions as measures to prevent global warming, and renewable energy such as solar batteries and wind power generators is actively utilized as clean energy that does not emit CO2. Producible energy of these types of renewable energy is greatly influenced by weather. Therefore, such renewable energy is considered as a stable power supply system such as a power storage by a secondary battery or return to chemical energy by compound synthesis.
In recent years, a “hydrogen society” has been proposed in a clean energy supply system that produces hydrogen from renewable energy and generates power by using a fuel cell. From these facts, hydrogen is attracting attention for returning from electric energy to a compound (chemical energy), and examples of a method for producing hydrogen include alkaline water electrolysis, solid polymer electrolyte (PEM) type water electrolysis, and solid oxide type water electrolysis (SOEC). Recently, PEM type water electrolysis has been extensively studied as highly efficient water electrolysis.
For example, in a PEM type water electrolysis apparatus, a platinum group metal is bonded to both sides of a solid polymer electrolyte membrane (fluororesin based cation exchange membrane) so as to be integrated with a membrane, one side is an anode, and the other side is a cathode. When a DC voltage is applied between the electrodes while supplying water to the anode side, oxygen gas is generated from the anode, and hydrogen gas is generated from the cathode. The polymer electrolyte membrane functions as a diaphragm, and the generated hydrogen gas and oxygen gas can be taken out separately.
In order to improve the performance of PEM type water electrolysis, it is necessary to reduce membrane resistance by improving proton conductivity of the electrolyte membrane. However, although thinning the electrolyte membrane improves the conductivity, in addition to a problem that crossover of oxygen from the anode to the cathode and crossover of hydrogen from the cathode to the anode greatly increase, a reduction in mechanical strength is a problem.
In the polymer electrolyte membrane, a fluorine-based electrolyte membrane being used at present is reducing the resistance by thinning. However, the reduction in mechanical strength and an increase in gas permeability are major problems. As an electrolyte membrane used for a water electric field, a hydrocarbon-based electrolyte membrane is known besides a fluorine-based electrolyte membrane. In the hydrocarbon-based electrolyte membrane, gas permeability is about several minutes or less that is less than that of the fluorine-based electrolyte membrane. However, the hydrocarbon-based electrolyte membrane has radical resistance significantly lower than that of the fluorine-based electrolyte membrane and has low durability. In such a current situation, a water electrolysis electrolyte membrane having high performance and durability and a membrane electrode assembly using the same are required for further improvement in performance.
A laminated electrolyte membrane of an embodiment includes: a hydrocarbon-based electrolyte membrane; and a composite electrolyte membrane laminated with the hydrocarbon-based electrolyte, the composite electrolyte membrane containing a perfluorosulfonic acid-based electrolyte and a superstrong acid metal oxide having an acid function (H0) of −12 or less.
Hereinafter, embodiments will be described in detail with reference to the drawings. In the following description, same members are denoted by same reference signs, and description of such as members once described is omitted as appropriate.
A laminated electrolyte membrane according to a first embodiment includes a hydrocarbon-based electrolyte membrane and a composite electrolyte membrane. The composite electrolyte membrane is laminated with the hydrocarbon-based electrolyte and contains a perfluorosulfonic acid-based electrolyte and a superstrong acid metal oxide having an acid function (H0) of −12 or less. When the laminated electrolyte membrane according to the embodiment is used as a water electrolysis electrolyte membrane, it is preferable in view of low membrane resistance of the electrolyte membrane, low crossover, and low resistance.
The thickness of the laminated electrolyte membranes 100 and 101 is preferably 20 μm or more and 400 μm or less. It is not preferable that the thickness of the laminated electrolyte membranes 100 and 101 is less than 20 μm, because the mechanical strength and durability are deteriorated due to the thin membrane. Further, it is not preferable that the thickness of the laminated electrolyte membranes 100 and 101 is thicker than 400 μm, because membrane resistance becomes high, and the efficiency of water electrolysis is lowered. For the above-described reasons, the thickness of the laminated electrolyte membranes 100 and 101 is more preferably 30 μm or more and 150 μm or less, and even more preferably 35 μm or more and 53 μm or less.
In the hydrocarbon-based electrolyte membrane 1, gas permeability per unit membrane thickness is preferably smaller than nafion (trademark) of a fluorine-based electrolyte membrane. The hydrocarbon-based electrolyte membrane 1 is an electrolyte membrane using a hydrocarbon-based polymer electrolyte which does not contain fluorine as a main chain skeleton and has a heat-resistant main chain skeleton. The thickness of the hydrocarbon-based electrolyte membrane 1 is preferably 10 μm or more and 150 μm or less, and more preferably 13 μm or more and 40 μm or less.
The hydrocarbon-based polymer electrolyte is preferably a solid polymer electrolyte having a heat-resistant main chain skeleton. For the hydrocarbon-based polymer electrolyte, a polymer having a functional group such as a sulfonic acid group, a carboxylic acid group, a phosphonic acid group, a phosphinic acid group, a sulfonylimide group, and a phenolic hydroxyl group is used. Specific examples of the hydrocarbon-based polymer electrolyte include polyarylene-based, polyetheretherketone-based, polyether sulfone-based, polyphenylene sulfide-based, polyimide-based, and polybenzazole-based polymers in which main chain aromatic rings are sulfonated.
Furthermore, in order to increase the mechanical strength of these electrolyte membranes, the hydrocarbon-based electrolyte membrane 1 reinforced with a porous membrane may be used. Examples of specific porous membranes include, but are not limited to, polytetrafluoroethylene (PTFE), polyetheretherketone (PEEK), and polypropylene (PP). Further, a membrane to which additives are added can also be used to increase chemical durability. Examples of the additives include a radical scavenger and a radical decomposer. For example, an organic phosphorus compound, an aromatic amine-based compound, a phenol-based compound, a thioether-based compound, CeO2, and MnO2 can be used as additives. The radical scavenger or hydrogen peroxide decomposer is contained in the hydrocarbon-based electrolyte membrane 1 at a ratio of 0 mass % or more and 10 mass % or less.
The composite electrolyte membrane 2 is a membrane of a mixture containing a perfluorosulfonic acid-based electrolyte and a superstrong acid metal oxide having an acid function (HO) of −12 or less. The composite electrolyte membrane 2 has excellent adhesiveness with the hydrocarbon-based electrolyte membrane 1 and imparts chemical resistance to an electrolyte membrane of a laminated electrolyte membrane. It is preferable that the superstrong acid metal oxide having an acid function (H0) of −12 or less in the composite electrolyte membrane is 20 mass % or more and 80 mass % or less. If the superstrong acid metal oxide is less than 20 mass %, the composite electrolyte membrane 2 laminated with the hydrocarbon-based electrolyte membrane 1 tends to peel off in water. Therefore, it becomes difficult to use as a water electrolysis electrolyte. It is not preferable that the hydrocarbon-based electrolyte membrane 1 and the composite electrolyte membrane 2 are peeled off in water, because an electrolysis voltage rises. On the other hand, it is not preferable that the superstrong acid metal oxide exceeds 80 mass %, because membrane resistance increases, and it becomes difficult to maintain a membrane structure. The thickness of the composite electrolyte membrane 2 is preferably 10 μm or more and 200 μm or less, and more preferably 11 μm or more and 23 μm or less.
In water electrolysis, hydrogen peroxide, hydroxy radicals and the like are generated during electrolysis, and a membrane is likely to be easily destructed chemically. Therefore, if the hydrocarbon-based electrolyte membrane 1 is used alone, there is a problem in durability. An electrolyte membrane using a perfluorosulfonic acid-based electrolyte is excellent in chemical resistance. However, when laminated with the hydrocarbon-based electrolyte membrane 1, the electrolyte membrane is easily peeled off in water. Therefore, although there is not much problem for use in a fuel cell, it cannot be used for a water electrolysis electrolyte membrane. The composite electrolyte membrane 2 containing a perfluorosulfonic acid based electrolyte and a superstrong acid metal oxide having an acid function (H0) of −12 or less is excellent in chemical resistance and also excellent in adhesion to the hydrocarbon-based electrolyte membrane 1. Therefore, the laminated electrolyte membranes 100 and 101 according to the embodiment are suitable as a water electrolysis electrolyte membrane.
The superstrong acid metal oxide is oxide particles in which an oxide of an element Y containing at least one selected from the group consisting of B, S, W, Mo, and V is supported on an oxide of an element X containing at least one selected from the group consisting of Ti, Zr, Si, Sn, and Al. The primary particle diameter of the oxide particle is preferably 1 nm or more and 1,000 nm or less, and the average primary particle diameter of the oxide particle is more preferably 4 nm or more and 200 nm or less.
The oxide of the element Y supported on the oxide of the element X in the superstrong acid metal oxide is preferably 2 mass % or more and 20 mass % or less. It is not preferable that the supported amount is less than 2 mass % because proton conductivity is lowered. On the other hand, it is not preferable that the supported amount exceeds 20 mass % because the oxide component of the supported element Y tends to dissolve.
Specific examples of the oxides of the element X include, but are not limited to, at least one oxide selected from the group consisting of TiO2, SiO2, ZrO2, SnO2, SiAlxOy (0<x≤2, 2<y≤5), SiO—Al2O3, and TiWαOβ (0<α≤1, 2<β≤5).
Specific examples of the oxides of the element Y include, but are not limited to, at least one oxide selected from the group consisting of SO4, BO3, WO3, VOY, (1≤γ≤2.5), and MoO3.
Element distribution in the superstrong acid metal oxide is observed and analyzed by analyzing contained elements and contents by an inductively coupled plasma mass spectrometry (ICP-MS) and by mapping them by a scanning electron microscope/energy dispersive X-ray spectroscopy (SEM-EDX). In addition, it is preferable to use an X-ray diffractometer for specifying the oxide.
The radical scavenger or the hydrogen peroxide decomposer described in the hydrocarbon-based electrolyte membrane 1 is contained in the composite electrolyte membrane 2 at a ratio of 0 mass % or more and 10 mass % or less.
The perfluorosulfonic acid-based electrolyte is preferably a polymer having an acidic group such as sulfonic acid group or sulfonamide group in a fluorine-containing main chain skeleton. The perfluorosulfonic acid-based electrolyte imparts chemical resistance to the composite electrolyte membrane 2 and structural strength to the composite electrolyte membrane 2. Examples of the perfluorosulfonic acid based electrolyte include Nafion (TM, Du Pont), Aquivion (TM, SOLVAY), Flemion (TM, Asahi Kasei Corp.), and Aciplex (TM, Asahi Glass Co., Ltd.).
For preparing a composite membrane including a perfluorosulfonic acid based electrolyte and a superstrong acid metal oxide, a material obtained by dispersing a superstrong acid metal oxide in a perfluorosulfonic acid-based electrolyte dispersion solution is used. A solvent to be used for the dispersion may be any one as long as the perfluorosulfonic acid-based electrolyte and the superstrong acid metal oxide are dispersed in a solvent, and a concentration of the solvent may be any concentration as long as coating is possible. Examples of the solvent include, but are not limited to, water; alcohol solvents such as methanol, ethanol, isopropanol, 1-propanol and ethylene glycol; ether solvents such as tetrahydrofuran and dimethoxyethylene; and aprotic polar solvents such as N, N-dimethylformamide, and N-methylpyrrolidone. As a dispersion solvent, a mixed solvent of various solvents may be used.
As a method for dispersing the superstrong acid oxide in the perfluorosulfonic acid-based electrolyte dispersion solution, an existing method can be used. Examples of the methods include, but are not limited to, a pane shaker, a ball mill, and an ultrasonic dispersion device.
Next, the laminated electrolyte membrane 100 is prepared in which the composite electrolyte membrane 2 is formed on the hydrocarbon-based electrolyte membrane 1 by coating and drying the superstrong acid oxide on the hydrocarbon-based electrolyte membrane 1 by using the dispersed perfluorosulfonic acid electrolyte dispersion. Regarding a coating method, any method can be used as long as coating on an electrolyte membrane is possible, and examples of the method include, but are not limited to, a spin coating method, a blade coating method, an inkjet method, a gravure method, and a spray coating method.
The coated membrane is dried by heating drying, and a temperature thereof is preferably 60° C. or more and less than 250° C. A drying time can be adjusted according to a used solvent and the membrane thickness of an electrolyte. If the temperature is less than 60° C., the solvent is not sufficiently volatilized, and if the temperature is 250° C. or higher, the electrolyte membrane may be decomposed. In addition, to further improve adhesion of the membrane, it may be pressurized during heating drying. For example, preferably, in the case of hot pressing, a pressure is in the range where membrane deterioration does not occur, specifically, the pressure is preferably less than 50 kg/cm2. When the pressure is 50 kg/cm2 or more, a decrease in mechanical strength may occur. In addition, a roll method can be applied as a pressurized heating drying method.
A membrane electrode assembly (MEA) according to a second embodiment includes a first electrode, a second electrode, a hydrocarbon-based electrolyte membrane, and a composite electrolyte membrane. The composite electrolyte membrane is laminated with the hydrocarbon-based electrolyte and contains a perfluorosulfonic acid-based electrolyte and a superstrong acid metal oxide having an acid function (H0) of −12 or less. The membrane electrode assembly using a laminated electrolyte membrane according to the embodiment is preferable in that, when it is used for water electrolysis, membrane resistance of the electrolyte membrane is low, crossover is low, and resistance is low.
The first electrode 3 is a cathode. The first electrode 3 includes a catalyst layer in contact with the laminated electrolyte membrane 100 and a support for supporting the catalyst layer. The second electrode 4 is an anode. The first electrode 3 includes a catalyst layer in contact with the laminated electrolyte membrane 100 and a support for supporting the catalyst layer.
The catalyst layer according to the embodiment is preferably a carrierless porous catalyst layer. To obtain high cell characteristics, a catalyst layer to be used generally includes a supported catalyst in which a catalyst is supported on a surface thereof by using a material such as carbon or a conductive oxide as a support. It has been reported that, although the material of the support hardly contributes to main electrocatalytic reaction, a catalyst material can be controlled for improvement of a reaction area of the catalyst material, and also a pore structure, electric conductivity, ion conductivity and the like can be improved by an electrochemical cell. Carrierless means that a carrier is not used for a catalyst included in a catalyst layer. This catalyst layer includes a catalyst unit having a porous structure or a laminated structure including a gap layer. In the case of using a noble metal catalyst, it is possible to maintain high characteristics and high durability of an electrochemical cell even when a small amount of a noble metal catalyst is used.
The predetermined catalyst material used for the carrierless catalyst layer according to the embodiment contains at least one selected from the group consisting of noble metal elements such as Pt, Ru, Rh, Os, Ir, Pd, and Au. Such the catalyst material is excellent in catalytic activity, conductivity, and stability. The above-described metal may be used as an oxide and may be a composite oxide or mixed oxide containing two or more kinds of metals.
An optimum noble metal element can be appropriately selected in accordance with a reaction in which the MEA is used.
For example, when a hydrogen production reaction is needed as a water electrolysis cathode, a catalyst having a composition represented by PtuM1-u is desirable. Here, u is 0<u≤1, and an element M is at least one selected from the group consisting of Co, Ni, Fe, Mn, Ta, W, Hf, Si, Mo, Ti, Zr, Nb, V, Cr, Al, and Sn. This catalyst contains Pt of more than 0 atomic % and 90 atomic % or less and the element M of 10 atomic % or more and less than 100 atomic %.
On the other hand, when an oxidation reaction of water (oxygen evolution reaction) is required as a water electrolysis anode, an oxide catalyst containing at least Ir, an oxide catalyst containing at least one of Pt, Ru, and Ir, a metal catalyst containing any one of Pt, Ru, and Ir, or an alloy catalyst containing any one of Pt, Ru, and Ir is desirable. The oxide catalyst is, for example, a catalyst having a composition represented by IrzM1-xO. Here, z is 0.5<z, and the element M is at least selected from the group consisting of Co, Ni, Fe, Mn, Ta, W, Hf, Si, Mo, Ti, Zr, Nb, V, Cr, Sr, and Sn. This oxide catalyst contains the element M of 50 atomic % or more or 0 atomic % or more and less than 50 atomic % in the case of considering only a metal component element. Specific examples of an oxide catalyst include an oxide catalyst including metal of at least one selected from the group consisting of Pt, Ru, and Ir of at least one selected from the group consisting of IrO2, RuO2, IrRuxOy, IrNixOy, IrSrxOy, and IrRuxNiyOz and arbitrary one or more elements M. However, an anode catalyst of the MEA in which the laminated electrolyte membrane 100 according to the embodiment is used is not limited to the above.
A method for manufacturing a carrierless porous catalyst layer according to the embodiment will be briefly described.
First, in the case of manufacturing a catalyst layer having a catalyst unit, a catalyst layer precursor is formed on a support by sputtering or evaporating a catalyst material and a pore-forming agent material at the same time. Next, the pore forming agent is removed to obtain an electrode. In the case of manufacturing a catalyst layer having a unit having a laminate structure including a gap layer, a catalyst layer precursor is formed on a support by alternately sputtering or evaporating a material containing a catalyst material and a pore-forming agent material. Next, the pore forming agent is removed to obtain an electrode.
The MEA according to the embodiment is prepared by combining an electrolyte membrane by using the above-described catalyst layer as at least either of the first electrode 3 or the second electrode 4. In general, the catalyst layer and the electrolyte membrane are bonded by heating and pressurizing. In this case, in the case where a forming support of the catalyst layer is a gas diffusion layer, the electrolyte membrane 100 is sandwiched with a support containing the catalyst layer and laminated as indicated in
Further, in the case where the forming support of the catalyst layer is a transfer substrate, first, the catalyst layer is transferred from the transfer substrate to the electrolyte membrane 100, the catalyst layer is transferred to the electrolyte membrane 100, and the membrane catalyst layer assembly (catalyst coated membrane (CCM)) is prepared. Then, the CCM is laminated as indicated in
A water electrolysis cell according to a third embodiment includes a membrane electrode assembly, a cathode feed conductor, a separator, a gasket (seal), an anode feed conductor, a separator, and a gasket (seal). The membrane electrode assembly includes a first electrode, a second electrode, a hydrocarbon-based electrolyte membrane, and a composite electrolyte membrane. The composite electrolyte membrane is laminated with the hydrocarbon-based electrolyte membrane and contains a perfluorosulfonic acid-based electrolyte and a superstrong acid metal oxide having an acid function (H0) of −12 or less. Since highly efficient water electrolysis can be performed, the water electrolysis cell using a laminated electrolyte membrane according to the embodiment is preferable in that, when it is used for water electrolysis, membrane resistance of the electrolyte membrane is low, crossover is low, and resistance is low.
In the water electrolysis cell 300 illustrated in
The laminated electrolyte membrane 100 according to the embodiment is difficult to separate in water and therefore excellent in durability. In addition, the laminated electrolyte membrane 100 according to the embodiment is excellent in chemical resistance and has low membrane resistance, and therefore has low crossover and is excellent in decomposition efficiency.
A plurality of membrane electrode assemblies 200 or a plurality of water electrolysis cells is connected in series in a stack 400 according to a fourth embodiment illustrated in
A fifth embodiment relates to a water electrolysis apparatus. For the water electrolysis apparatus, a stack 400 according to the embodiment is used. The water electrolysis apparatus will be described with reference to a schematic diagram in
Hereinafter, the above embodiments will be described in detail in examples.
A coating solution for a composite membrane is adjusted by adding 20 g of ethanol to a predetermined amount of a fluorine-based electrolyte dispersion (20% nafion dispersion solution, Du Pont) in a polyhot, adding a superstrong acid oxide and a predetermined amount thereof, and adding 40 zirconia balls (diameter 5 mm), and dispersing them for 10 minutes by using Rentaro (Thinky Corporation). Compositions of the prepared dispersion in examples 1 to 11 and comparative examples 1 to 4 are summarized in Table 1. In example 7, 8 and comparative example 2, decomposer (hydrogen peroxide decomposer) is used for preparing dispersion.
Synthesis of MoO3/TiO2
An aqueous solution is adjusted in which hexammonium heptamolybdate tetrahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) (NH4)6Mo7O24, 4H2O is dissolved in water. The aqueous solution is mixed with a dispersion (containing 2 mL of concentrated HCl) in which titanium oxide (Super Titania F-6 and F-4, made by Showa Denko K.K.) TiO2 is dispersed in water. The mixture is evaporated to dryness at 80° C. to support ammonium molybdate on TiO2. The obtained precursor is dried at 100° C. for 6H and then calcined at 600° C. for 4H, and ammonium molybdate is thermally decomposed to obtain MoO3/TiO2. The composition of MoO3/TiO2 is 5/95 by a weight ratio.
Synthesis of WO3/TiO2
An aqueous solution is adjusted in which tungsten oxide (Wako Pure Chemical Industries, Ltd.) WO3 is dissolved in heated condensed ammonia aqueous solution (made by Wako Pure Chemical Industries, Ltd., 15% aqueous solution). This aqueous solution is mixed with a dispersion in which titanium oxide (Super Titania F-6 Showa Denko K.K.) TiO2 is dispersed in water. This aqueous solution is evaporated to dryness at 80° C. to support ammonium tungstate on TiO2. The obtained precursor is dried at 100° C. for 6H and then calcined at 700° C. for 4H, and ammonium tungstate is thermally decomposed to obtain WO3/TiO2.
Two kinds of compositions of WO3/TiO2 at a weight ratio of 5/95 and 10/90 are prepared.
Synthesis of VO3/TiO2
An aqueous solution is adjusted in which ammonium metavanadate (Wako Pure Chemical Industries, Ltd.) (NH4)VO3 is dissolved in hot water. The aqueous solution is mixed with a dispersion (containing 2 mL of concentrated HCl) in which titanium oxide (Super Titania F-6 and F-4, Showa Denko K.K.) TiO2 is dispersed in water. The mixture was evaporated to dryness at 80° C. to support ammonium metavanadate on TiO2. The obtained precursor was dried at 100° C. for 6H and then calcined at 600° C. for 4H, and ammonium metavanadate is thermally decomposed to obtain VO3/TiO2. The composition of MoO3/TiO2 is 5/95 by a weight ratio.
Synthesis of WO3/ZrO2
An aqueous solution is adjusted in which tungsten oxide (Wako Pure Chemical Industries, Ltd.) WO3 is dissolved in heated condensed ammonia aqueous solution (Wako Pure Chemical Industries, 15% aqueous solution). This aqueous solution is mixed with a dispersion in which zirconium oxide (Wako Pure Chemical Industries, Ltd.) ZrO2 is dispersed in water. This aqueous solution is evaporated to dryness at 80° C. to support ammonium tungstate on TiO2. The obtained precursor is dried at 100° C. for 6H and then calcined at 700° C. for 4H, and ammonium tungstate is thermally decomposed to obtain WO3/TiO2.
Two kinds of compositions of WO3/TiO2 at a weight ratio of 5/95 and 20/90 are prepared.
Synthesis of SO4/TiO2
A dispersion of titanium oxide is adjusted by mixing 9.500 g of titanium oxide (TiO2, Tayca, AMT-100) and 300 mL of water in a 1,000 mL beaker. Evaporation to dryness is performed by mixing 0.521 g of concentrated sulfuric acid (96%) with this dispersion, further adding water to make the total volume 400 mL, and stirring the solution by a hot stirrer set at 140° C. A precursor is pulverized and passed through a 106 μm sieve, placed on a baking dish, and fired at 600° C. for 3 hours to obtain sulfuric acid-supported titanium oxide SO4/TiO2. Composition analysis by ICP analysis reveals that S is 0.64% (1.92% in terms of SO4), TiO2 is 95.0%, and the rest is moisture. Therefore, the SO4 supporting amount is 2.0% in a state where moisture is removed.
Synthesis of SO4/ZrO2
A dispersion of titanium oxide is adjusted by mixing 9.500 g of zirconium oxide (made by Wako Pure Chemical Industries, Ltd.) and 300 mL of water in a 1000 mL beaker. Evaporation to dryness is performed by mixing 1.01 g of concentrated sulfuric acid (96%) with this dispersion, further adding water to make the total volume 400 mL, and stirring the solution by a hot stirrer set at 140° C. A precursor is pulverized and passed through a 106 μm sieve, placed on a baking dish, and fired at 600° C. for 3 hours to obtain sulfuric acid-supported titanium oxide SO4/TiO2. Composition analysis by ICP analysis reveals that S is 0.96% (2.88% in terms of SO4), TiO2 is 96.0%, and the rest is moisture. Therefore, the SO4 supporting amount is 3.0% in a state where moisture is removed.
WO3/SnO2
SO4/TiO2
A composite laminated membrane is prepared by spraying the above-described adjusted dispersion for a composite membrane on various membrane thickness aromatic hydrocarbon-based electrolyte membranes (EW□400), drying the membranes at 60° C. for 10 minutes, drying at 130° C. for 10 minutes, and further drying at 180° C. for 10 minutes while pressurizing at 10 kg/cm2. Table 2 indicates the prepared various membranes in examples 12 to 25 and comparative examples 5 to 10.
A three-layered laminated membrane (comparative example 11) is prepared by stacking a nafion HP membrane, a 13 μm membrane of the aromatic hydrocarbon-based electrolyte membrane, and a nafion HP membrane in this order and heating and compressing them at 180° C. for 10 minutes while pressurizing to 10 kg/cm2.
Ion exchanged water is sufficiently poured in a beaker, and an immersion test is performed in which the above-described prepared composite laminated membrane is immersed for 5 minutes at room temperature. In Table 2, the case where the membrane is peeled off at an interface of the laminated membrane is marked with x, and the case where the membrane is not peeled off is marked with ∘.
An anode electrode is prepared by sputtering IrNixOy and a gap agent by reactive sputtering on a 200 μm-thick titanium porous body, and etching, heating, and drying after acid treatment. An IrNixOy catalyst layer is an Ir amount of 0.15 mg/cm2 (22 layers).
A cathode electrode is prepared by etching with acid and heating and drying after washing with water after sputtering on a Carpon Paper with a cathode electrode MPL (microporous layer) . A PtCo alloy catalyst is a platinum amount of 0.18 mg/cm2 (28 layers).
Each of the anode electrode and the cathode electrode are cut to 20 mm square each. The anode electrode, a laminated electrolyte membrane, and the cathode electrode are sequentially stacked and pressure-bonded by hot pressing (50 kg, 165° C., 4 minutes), and then cooled to room temperature to prepare an MEA. The process is summarized in Table 3. However, when the composite laminated membrane has two layers, an aromatic hydrocarbon-based electrolyte membrane side is prepared as a cathode electrode side.
An MEA (comparative example 12) is prepared by using nafion 115 as a membrane in the same manner as preparation conditions for the above-described MEA.
In a titanium water electrolysis cell, as a feed conductor (integrated with a separator) of an anode and a cathode, a flow channel plate of titanium is used, and a single cell (anode & cathode; straight channel) having an electrode area of 4 cm2 is used. The cell temperature is 80° C. at atmospheric pressure, and the temperature is maintained by heating by a heater, and ion-exchanged water is used by circulating, to the anode, several times the amount of water necessary for water decomposition. Water electrolysis is performed at a cell temperature of 80° C. by using an electronic load device manufactured by Kikusui Corporation at a current density of 2 A/cm2. Decomposition voltages of water and AC impedance resistance at 1 KHz in such a case are summarized in Table 3.
Water decomposition is carried out at a constant current of the above-described water electrolysis conditions, gas coming out from the anode side is separated by water and repaired for 30 minutes, and a hydrogen concentration is measured by GC-MS. Measurement results are indicated in Table 3.
As indicated in the comparative examples 7 and 11 in Table 2, interface peeling occurred in a laminated membrane in which a fluorine-based electrolyte membrane is simply laminated on an aromatic hydrocarbon-based electrolyte membrane. On the other hand, in the composite laminated membrane, peeling is not observed in an immersion test. As indicated in Table 3, it is revealed that when the aromatic hydrocarbon-based electrolyte membrane is used alone, durability is not sufficient in water electrolysis characteristics. However, it is revealed that durability of the composite laminated membrane is improved without problems after 50 h. In addition, in any case, the MEA using the composite membrane is highly efficient because crossover is low, membrane resistance is low, and a voltage is low in comparison with the comparative example 12 in which nafion 115, standard used in PEM type water electrolysis, is used.
Here, some elements are expressed only by element symbols thereof.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-057954 | Mar 2017 | JP | national |
